Singular behavior of jet substructure observables

DOE PAGES

Larkoski, Andrew J.; Moult, Ian

2016-01-20

Jet substructure observables play a central role at the Large Hadron Collider for identifying the boosted hadronic decay products of electroweak scale resonances. The complete description of these observables requires understanding both the limit in which hard substructure is resolved, as well as the limit of a jet with a single hard core. In this paper we study in detail the perturbative structure of two prominent jet substructure observables, N-subjettiness and the energy correlation functions, as measured on background QCD jets. In particular, we focus on the distinction between the limits in which two-prong structure is resolved or unresolved. Dependingmore » on the choice of subjet axes, we demonstrate that at fixed order, N-subjettiness can manifest myriad behaviors in the unresolved region: smooth tails, end-point singularities, or singularities in the physical region. The energy correlation functions, by contrast, only have non-singular perturbative tails extending to the end point. We discuss the effect of hadronization on the various observables with Monte Carlo simulation and demonstrate that the modeling of these effects with non-perturbative shape functions is highly dependent on the N-subjettiness axes definitions. Lastly, our study illustrates those regions of phase space that must be controlled for high-precision jet substructure calculations, and emphasizes how such calculations can be facilitated by designing substructure observables with simple singular structures.« less

Investigation of supersonic jets shock-wave structure

NASA Astrophysics Data System (ADS)

Zapryagaev, V. I.; Gubanov, D. A.; Kavun, I. N.; Kiselev, N. P.; Kundasev, S. G.; Pivovarov, A. A.

2017-10-01

The paper presents an experimental studies overview of the free supersonic jet flow structure Ma = 1.0, Npr = 5, exhausting from a convergent profiled nozzle into a ambient space. Also was observed the jets in the presence of artificial streamwise vortices created by chevrons and microjets located on the nozzle exit. The technique of experimental investigation, schlieren-photographs and schemes of supersonic jets, and Pitot pressure distributions, are presented. A significant effect of vortex generators on the shock-wave structure of the flow is shown.

Analysis of noise produced by an orderly structure of turbulent jets

NASA Technical Reports Server (NTRS)

Hardin, J. C.

1973-01-01

The orderly structure which has been observed recently by numerous researchers within the transition region of subsonic turbulent jets is analyzed to reveal its noise-producing potential. For a circular jet, this structure is molded as a train of toroidal vortex rings which are formed near the jet exit and propagate downstream. The noise produced by the model is evaluated from a reformulation of Lighthill's expression for the far-field acoustic density, which emphasizes the importance of the vorticity within the turbulent flow field. It is shown that the noise production occurs mainly close to the jet exit and depends primarily upon temporal changes in the toroidal radii. The analysis suggests that the process of formation of this regular structure may also be an important contribution of the high-frequency jet noise. These results may be helpful in the understanding of jet-noise generation and in new approaches to jet-noise suppression.

FAST TRACK COMMUNICATION: Modelling of streamer propagation in atmospheric-pressure helium plasma jets

NASA Astrophysics Data System (ADS)

Naidis, G. V.

2010-10-01

The results of a two-dimensional numerical simulation of positive streamer propagation in atmospheric-pressure helium jets injected into ambient air are presented. It is shown that depending on the jet width and the initial radial distribution of electron number density streamer structures of two types can be formed: one with maxima of electric field and electron density at the jet axis and another with maxima of these parameters near the boundary between the jet and surrounding air. The latter structure is similar to the observed ring-shaped structures of plasma bullets.

The Shock Dynamics of Heterogeneous YSO Jets: 3D Simulations Meet Multi-epoch Observations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hansen, E. C.; Frank, A.; Hartigan, P.

High-resolution observations of young stellar object (YSO) jets show them to be composed of many small-scale knots or clumps. In this paper, we report results of 3D numerical simulations designed to study how such clumps interact and create morphologies and kinematic patterns seen in emission line observations. Our simulations focus on clump scale dynamics by imposing velocity differences between spherical, over-dense regions, which then lead to the formation of bow shocks as faster clumps overtake slower material. We show that much of the spatial structure apparent in emission line images of jets arises from the dynamics and interactions of thesemore » bow shocks. Our simulations show a variety of time-dependent features, including bright knots associated with Mach stems where the shocks intersect, a “frothy” emission structure that arises from the presence of the Nonlinear Thin Shell Instability along the surfaces of the bow shocks, and the merging and fragmentation of clumps. Our simulations use a new non-equilibrium cooling method to produce synthetic emission maps in H α and [S ii]. These are directly compared to multi-epoch Hubble Space Telescope observations of Herbig–Haro jets. We find excellent agreement between features seen in the simulations and the observations in terms of both proper motion and morphologies. Thus we conclude that YSO jets may be dominated by heterogeneous structures and that interactions between these structures and the shocks they produce can account for many details of YSO jet evolution.« less

Determination of temperature maps of EUV coronal hole jets

NASA Astrophysics Data System (ADS)

Nisticò, Giuseppe; Patsourakos, Spiros; Bothmer, Volker; Zimbardo, Gaetano

2011-11-01

Coronal hole jets are fast ejections of plasma occurring within coronal holes, observed at Extreme-UltraViolet (EUV) and X-ray wavelengths. Recent observations of jets by the STEREO and Hinode missions show that they are transient phenomena which occur at much higher rates than large-scale impulsive phenomena like flares and Coronal Mass Ejections (CMEs). In this paper we describe some typical characteristics of coronal jets observed by the SECCHI instruments of STEREO spacecraft. We show an example of 3D reconstruction of the helical structure for a south pole jet, and present how the angular distribution of the jet position angles changes from the Extreme-UltraViolet-Imager (EUVI) field of view to the CORonagraph1 (COR1) (height ∼2.0 R⊙ heliocentric distance) field of view. Then we discuss a preliminary temperature determination for the jet plasma by using the filter ratio method at 171 and 195 Å and applying a technique for subtracting the EUV background radiation. The results show that jets are characterized by electron temperatures ranging between 0.8 and 1.3 MK. We present the thermal structure of the jet as temperature maps and we describe its thermal evolution.

Structure of gamma-ray burst jets: intrinsic versus apparent properties

NASA Astrophysics Data System (ADS)

Salafia, O. S.; Ghisellini, G.; Pescalli, A.; Ghirlanda, G.; Nappo, F.

2015-07-01

With this paper we introduce the concept of apparent structure of a gamma-ray burst (GRB) jet, as opposed to its intrinsic structure. The latter is customarily defined specifying the functions ɛ(θ) (the energy emitted per jet unit solid angle) and Γ(θ) (the Lorentz factor of the emitting material); the apparent structure is instead defined by us as the isotropic equivalent energy Eiso(θv) as a function of the viewing angle θv. We show how to predict the apparent structure of a jet given its intrinsic structure. We find that a Gaussian intrinsic structure yields a power-law apparent structure: this opens a new viewpoint on the Gaussian (which can be understood as a proxy for a realistic narrow, well-collimated jet structure) as a possible candidate for a quasi-universal GRB jet structure. We show that such a model (a) is consistent with recent constraints on the observed luminosity function of GRBs; (b) implies fewer orphan afterglows with respect to the standard uniform model; (c) can break out the progenitor star (in the collapsar scenario) without wasting an unreasonable amount of energy; (d) is compatible with the explanation of the Amati correlation as a viewing angle effect; (e) can be very standard in energy content, and still yield a very wide range of observed isotropic equivalent energies.

Limb-brightened jet of 3C 84 revealed by the 43 GHz very-long-baseline-array observation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nagai, H.; Hada, K.; Haga, T.

2014-04-10

We present a study of the sub-parsec scale radio structure of the radio galaxy 3C 84/NGC 1275 based on the Very Long Baseline Array data at 43 GHz. We discover a limb brightening in the 'restarted' jet that is associated with the 2005 radio outburst. In the 1990s, the jet structure was ridge brightening rather than limb brightening, despite the observations being done with similar angular resolutions. This indicates that the transverse jet structure has recently changed. This change in the morphology reveals an interesting agreement with the γ-ray flux increase, i.e., the γ-ray flux in the 1990s was atmore » least seven times lower than the current one. One plausible explanation for the limb brightening is that the velocity structure of the jet is in the context of the stratified jet, which is a successful scenario that explains the γ-ray emission in some active galactic nuclei. If this is the case, then the change in apparent transverse structure might be caused by the change in the transverse velocity structure. We argue that the transition from ridge brightening to limb brightening is related to the γ-ray time variability on the timescale of decades. We also discuss the collimation profile of the jet.« less

MMS observations of guide field reconnection at the interface between colliding reconnection jets inside flux rope-like structures at the magnetopause

NASA Astrophysics Data System (ADS)

Oieroset, M.; Phan, T.; Haggerty, C. C.; Shay, M.; Eastwood, J. P.; Gershman, D. J.; Drake, J. F.; Fujimoto, M.; Ergun, R.; Mozer, F.; Oka, M.; Torbert, R. B.; Burch, J. L.; Wang, S.; Chen, L. J.; Swisdak, M.; Pollock, C. J.; Dorelli, J.; Fuselier, S. A.; Lavraud, B.; Kacem, I.; Giles, B. L.; Moore, T. E.; Saito, Y.; Avanov, L. A.; Paterson, W. R.; Strangeway, R. J.; Schwartz, S. J.; Khotyaintsev, Y. V.; Lindqvist, P. A.; Malakit, K.

2017-12-01

The formation and evolution of magnetic flux ropes is of critical importance for a number of collisionless plasma phenomena. At the dayside magnetopause flux rope-like structures can form between two X-lines. The two X-lines produce converging plasma jets. At the interface between the colliding jets a compressed current sheet can form, which in turn can undergo reconnection. We present MMS observations of the exhaust and diffusion region of such reconnection.

Towards an understanding of the correlations in jet substructure

DOE PAGES

Adams, D.; Arce, A.; Asquith, L.; ...

2015-09-09

Over the past decade, a large number of jet substructure observables have been proposed in the literature, and explored at the LHC experiments. Such observables attempt to utilize the internal structure of jets in order to distinguish those initiated by quarks, gluons, or by boosted heavy objects, such as top quarks and W bosons. This report, originating from and motivated by the BOOST2013 workshop, presents original particle-level studies that aim to improve our understanding of the relationships between jet substructure observables, their complementarity, and their dependence on the underlying jet properties, particularly the jet radius and jet transverse momentum. Thismore » is explored in the context of quark/gluon discrimination, boosted W boson tagging and boosted top quark tagging.« less

CUSP-SHAPED STRUCTURE OF A JET OBSERVED BY IRIS AND SDO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yuzong; Zhang, Jun, E-mail: yuzong@nao.cas.cn, E-mail: zjun@nao.cas.cn

2017-01-01

On 2014 August 29, the trigger and evolution of a cusp-shaped jet were captured in detail at 1330 Å by the Interface Region Imaging Spectrograph . At first, two neighboring mini-prominences arose in turn from the low solar atmosphere and collided with a loop-like system over them. The collisions between the loop-like system and the mini-prominences lead to the blowout, and then a cusp-shaped jet formed with a spire and an arch-base. In the spire, many brightening blobs originating from the junction between the spire and the arch-base moved upward in a rotating manner and then in a straight line inmore » the late phase of the jet. In the arch-base, dark and bright material simultaneously tracked in a fan-like structure, and the majority of the material moved along the fan's threads. At the later phase of the jet's evolution, bidirectional flows emptied the arch-base, while downflows emptied the spire, thus making the jet entirely vanish. The extremely detailed observations in this study shed new light on how magnetic reconnection alters the inner topological structure of a jet and provides a beneficial complement for understanding current jet models.« less

Intrinsic physical conditions and structure of relativistic jets in active galactic nuclei

NASA Astrophysics Data System (ADS)

Nokhrina, E. E.; Beskin, V. S.; Kovalev, Y. Y.; Zheltoukhov, A. A.

2015-03-01

The analysis of the frequency dependence of the observed shift of the cores of relativistic jets in active galactic nuclei (AGNs) allows us to evaluate the number density of the outflowing plasma ne and, hence, the multiplicity parameter λ = ne/nGJ, where nGJ is the Goldreich-Julian number density. We have obtained the median value for λmed = 3 × 1013 and the median value for the Michel magnetization parameter σM, med = 8 from an analysis of 97 sources. Since the magnetization parameter can be interpreted as the maximum possible Lorentz factor Γ of the bulk motion which can be obtained for relativistic magnetohydrodynamic (MHD) flow, this estimate is in agreement with the observed superluminal motion of bright features in AGN jets. Moreover, knowing these key parameters, one can determine the transverse structure of the flow. We show that the poloidal magnetic field and particle number density are much larger in the centre of the jet than near the jet boundary. The MHD model can also explain the typical observed level of jet acceleration. Finally, casual connectivity of strongly collimated jets is discussed.

Numerical models of jet disruption in cluster cooling flows

NASA Technical Reports Server (NTRS)

Loken, Chris; Burns, Jack O.; Roettiger, Kurt; Norman, Mike

1993-01-01

We present a coherent picture for the formation of the observed diverse radio morphological structures in dominant cluster galaxies based on the jet Mach number. Realistic, supersonic, steady-state cooling flow atmospheres are evolved numerically and then used as the ambient medium through which jets of various properties are propagated. Low Mach number jets effectively stagnate due to the ram pressure of the cooling flow atmosphere while medium Mach number jets become unstable and disrupt in the cooling flow to form amorphous structures. High Mach number jets manage to avoid disruption and are able to propagate through the cooling flow.

On the internal structure of relativistic jets collimated by ambient gas pressure

NASA Astrophysics Data System (ADS)

Beskin, V. S.; Chernoglazov, A. V.; Kiselev, A. M.; Nokhrina, E. E.

2017-12-01

Recent progress in very long baseline interferometry (VLBI) observations of relativistic jets outflowing from active galactic nuclei gives us direct information about jet width rjet(l) dependence on the distance l from the 'central engine'. Being the missing link in previous works, this relation opens the possibility of determining the internal structure of a jet. In this article, we consider a relativistic jet submerged in an external medium with finite gas pressure Pext. Neither an external magnetic field nor an infinitely thin current sheet will be assumed. This approach allows us to construct a reasonable solution in which both the magnetic field and the flow velocity vanish at the jet boundary r = rjet. In particular, the connection between external gas pressure and internal structure of a relativistic jet is determined.

Angular structure of jet quenching within a hybrid strong/weak coupling model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Casalderrey-Solana, Jorge; Gulhan, Doga Can; Milhano, José Guilherme

Within the context of a hybrid strong/weak coupling model of jet quenching, we study the modification of the angular distribution of the energy within jets in heavy ion collisions, as partons within jet showers lose energy and get kicked as they traverse the strongly coupled plasma produced in the collision. To describe the dynamics transverse to the jet axis, we add the effects of transverse momentum broadening into our hybrid construction, introducing a parameter K≡qˆ/T3K≡q^/T3 that governs its magnitude. We show that, because of the quenching of the energy of partons within a jet, even when K ≠ 0 themore » jets that survive with some specified energy in the final state are narrower than jets with that energy in proton-proton collisions. For this reason, many standard observables are rather insensitive to K. We also propose a new differential jet shape ratio observable in which the effects of transverse momentum broadening are apparent. We also analyze the response of the medium to the passage of the jet through it, noting that the momentum lost by the jet appears as the momentum of a wake in the medium. After freezeout this wake becomes soft particles with a broad angular distribution but with net momentum in the jet direction, meaning that the wake contributes to what is reconstructed as a jet. Thus, this effect must be included in any description of the angular structure of the soft component of a jet. We show that the particles coming from the response of the medium to the momentum and energy deposited in it leads to a correlation between the momentum of soft particles well separated from the jet in angle with the direction of the jet momentum, and find qualitative but not quantitative agreement with experimental data on observables designed to extract such a correlation. Generally, by confronting the results that we obtain upon introducing transverse momentum broadening and the response of the medium to the jet with available jet data, we highlight the importance of these processes for understanding the internal, soft, angular structure of high energy jets.« less

Angular structure of jet quenching within a hybrid strong/weak coupling model

DOE PAGES

Casalderrey-Solana, Jorge; Gulhan, Doga Can; Milhano, José Guilherme; ...

2017-03-27

Within the context of a hybrid strong/weak coupling model of jet quenching, we study the modification of the angular distribution of the energy within jets in heavy ion collisions, as partons within jet showers lose energy and get kicked as they traverse the strongly coupled plasma produced in the collision. To describe the dynamics transverse to the jet axis, we add the effects of transverse momentum broadening into our hybrid construction, introducing a parameter K≡qˆ/T3K≡q^/T3 that governs its magnitude. We show that, because of the quenching of the energy of partons within a jet, even when K ≠ 0 themore » jets that survive with some specified energy in the final state are narrower than jets with that energy in proton-proton collisions. For this reason, many standard observables are rather insensitive to K. We also propose a new differential jet shape ratio observable in which the effects of transverse momentum broadening are apparent. We also analyze the response of the medium to the passage of the jet through it, noting that the momentum lost by the jet appears as the momentum of a wake in the medium. After freezeout this wake becomes soft particles with a broad angular distribution but with net momentum in the jet direction, meaning that the wake contributes to what is reconstructed as a jet. Thus, this effect must be included in any description of the angular structure of the soft component of a jet. We show that the particles coming from the response of the medium to the momentum and energy deposited in it leads to a correlation between the momentum of soft particles well separated from the jet in angle with the direction of the jet momentum, and find qualitative but not quantitative agreement with experimental data on observables designed to extract such a correlation. Generally, by confronting the results that we obtain upon introducing transverse momentum broadening and the response of the medium to the jet with available jet data, we highlight the importance of these processes for understanding the internal, soft, angular structure of high energy jets.« less

`Orphan' afterglows in the Universal structured jet model for γ-ray bursts

NASA Astrophysics Data System (ADS)

Rossi, Elena M.; Perna, Rosalba; Daigne, Frédéric

2008-10-01

The paucity of reliable achromatic breaks in γ-ray burst afterglow light curves motivates independent measurements of the jet aperture. Serendipitous searches of afterglows, especially at radio wavelengths, have long been the classic alternative. These survey data have been interpreted assuming a uniformly emitting jet with sharp edges (`top-hat' jet), in that case the ratio of weakly relativistically beamed afterglows to GRBs scales with the jet solid angle. In this paper, we consider, instead, a very wide outflow with a luminosity that decreases across the emitting surface. In particular, we adopt the universal structured jet (USJ) model, which is an alternative to the top-hat model for the structure of the jet. However, the interpretation of the survey data is very different: in the USJ model, we only observe the emission within the jet aperture and the observed ratio of prompt emission rate to afterglow rate should solely depend on selection effects. We compute the number and rate of afterglows expected in all-sky snapshot observations as a function of the survey sensitivity. We find that the current (negative) results for OA searches are in agreement with our expectations. In radio and X-ray bands, this was mainly due to the low sensitivity of the surveys, while in the optical band the sky coverage was not sufficient. In general, we find that X-ray surveys are poor tools for OA searches, if the jet is structured. On the other hand, the Faint Images of the Radio Sky at Twenty-cm radio survey and future instruments like the Allen Telescope Array (in the radio band) and especially GAIA, Panoramic Survey Telescope and Rapid Response System and Large Synoptic Survey Telescope (in the optical band) will have chances to detect afterglows.

Rapid variability of the arcsec-scale X-ray jets of SS 433

NASA Astrophysics Data System (ADS)

Migliari, S.; Fender, R. P.; Blundell, K. M.; Méndez, M.; van der Klis, M.

2005-04-01

We present X-ray images of all the available Chandra observations of the galactic jet source SS 433. We have studied the morphology of the X-ray images and inspected the evolution of the arcsec X-ray jets, recently found to be manifestations of in situ reheating of the relativistic gas downstream in the jets. The Chandra images reveal that the arcsec X-ray jets are not steady long-term structures; the structure varies, indicating that the reheating processes have no preference for a particular precession phase or distance from the binary core. Three observations made within about five days in 2001 May, and a 60-ks observation made in 2003 July, show that the variability of the jets can be very rapid, from time-scales of days to (possibly) hours. The three 2001 May images show two resolved knots in the east jet getting brighter one after the other, suggesting that a common phenomenon might be at the origin of the sequential reheatings of the knots. We discuss possible scenarios and propose a model to interpret these brightenings in terms of a propagating shock wave, revealing a second, faster outflow in the jet.

Solar Coronal Jets Extending to High Altitudes Observed during the 2017 August 21 Total Eclipse

NASA Astrophysics Data System (ADS)

Hanaoka, Yoichiro; Hasuo, Ryuichi; Hirose, Tsukasa; Ikeda, Akiko C.; Ishibashi, Tsutomu; Manago, Norihiro; Masuda, Yukio; Morita, Sakuhiro; Nakazawa, Jun; Ohgoe, Osamu; Sakai, Yoshiaki; Sasaki, Kazuhiro; Takahashi, Koichi; Toi, Toshiyuki

2018-06-01

Coronal jets, which extend from the solar surface to beyond 2 R ⊙, were observed in the polar coronal hole regions during the total solar eclipse on 2017 August 21. In a time-series of white-light images of the corona spanning 70 minutes taken with our multi-site observations of this eclipse, six jets were found as narrow structures upwardly ejected with an apparent speed of about 450 km s‑1 in polar plumes. On the other hand, extreme-ultraviolet (EUV) images taken with the Atmospheric Image Assembly of the Solar Dynamics Observatory show that all of the eclipse jets were preceded by EUV jets. Conversely, all the EUV jets whose brightnesses are comparable to ordinary soft X-ray jets and that occurred in the polar regions near the eclipse period, were observed as eclipse jets. These results suggest that ordinary polar jets generally reach high altitudes and escape from the Sun as part of the solar wind.

Newly Uncovered Large-Scale Component of the Northern Jet in R Aqr

NASA Astrophysics Data System (ADS)

Montez, Rodolfo; Karovska, Margarita; Nichols, Joy S.; Kashyap, Vinay

2017-06-01

R Aqr is a symbiotic system comprised a compact white dwarf and Mira giant star. The interaction of these stars is responsible for the presence of a two-sided jet structure that is seen across the electromagnetic spectrum. X-ray emission from the jet was first discovered in 2000 with an observation by the Chandra X-ray Observatory. Since then follow-up observations have traced the evolution of the X-ray emission from the jet and a central compact source. In X-rays, the NE jet is brighter than the SW jet, but the full extent of the SW jet was larger - before it began fading below the detection threshold. However, we have uncovered evidence for large-scale emission associated with the NE jet that matches the extent of the SW jet. The emission has escaped previous identification because it is near the detection threshold, but it has been present since the first 2000 observation and clearly evolves in subsequent observations. We present our study of the emission from this component of the NE jet, its relationship to multiwavelength observations, and how it impacts our interpretation of the jet-phenomenon in R Aqr.

Rich phenomenology encountered when two jets collide in microgravity

NASA Astrophysics Data System (ADS)

Suñol, Francesc; Gonzalez-Cinca, Ricard

The collision between two impinging liquid jets has been experimentally studied in the low gravity environment provided by the ZARM drop tower. The effects of impact angle and liquid flow rate on the collision between like-doublet jets have been considered. Tests were carried out with distilled water injected through nozzles with an internal diameter of 0.7 mm into a test cell. Impact angle varied between 10(°) and 180(°) (frontal collision), while the liquid flow rate ranged between 20 ml/min and 80 ml/min for each nozzle. Such a large parameter range allowed us to observe different phenomena resulting from the jets collision: oscillating droplets attached to the nozzles, a non-uniform spatial distribution of bouncing droplets, coalescing droplets generating a single central droplet, coalescing jets, bouncing jets, liquid chains and liquid sheets. A map of the different patterns observed has been obtained. We present results on the structure of the jets after collision, the breakup length and the size of the generated droplet. The resulting structure of impinging jets highly depends on the Reynolds and Weber numbers, and the proper alignment of the colliding jets.

Casimir meets Poisson: improved quark/gluon discrimination with counting observables

DOE PAGES

Frye, Christopher; Larkoski, Andrew J.; Thaler, Jesse; ...

2017-09-19

Charged track multiplicity is among the most powerful observables for discriminating quark- from gluon-initiated jets. Despite its utility, it is not infrared and collinear (IRC) safe, so perturbative calculations are limited to studying the energy evolution of multiplicity moments. While IRC-safe observables, like jet mass, are perturbatively calculable, their distributions often exhibit Casimir scaling, such that their quark/gluon discrimination power is limited by the ratio of quark to gluon color factors. In this paper, we introduce new IRC-safe counting observables whose discrimination performance exceeds that of jet mass and approaches that of track multiplicity. The key observation is that trackmore » multiplicity is approximately Poisson distributed, with more suppressed tails than the Sudakov peak structure from jet mass. By using an iterated version of the soft drop jet grooming algorithm, we can define a “soft drop multiplicity” which is Poisson distributed at leading-logarithmic accuracy. In addition, we calculate the next-to-leading-logarithmic corrections to this Poisson structure. If we allow the soft drop groomer to proceed to the end of the jet branching history, we can define a collinear-unsafe (but still infrared-safe) counting observable. Exploiting the universality of the collinear limit, we define generalized fragmentation functions to study the perturbative energy evolution of collinear-unsafe multiplicity.« less

Casimir meets Poisson: improved quark/gluon discrimination with counting observables

DOE Office of Scientific and Technical Information (OSTI.GOV)

Frye, Christopher; Larkoski, Andrew J.; Thaler, Jesse

Charged track multiplicity is among the most powerful observables for discriminating quark- from gluon-initiated jets. Despite its utility, it is not infrared and collinear (IRC) safe, so perturbative calculations are limited to studying the energy evolution of multiplicity moments. While IRC-safe observables, like jet mass, are perturbatively calculable, their distributions often exhibit Casimir scaling, such that their quark/gluon discrimination power is limited by the ratio of quark to gluon color factors. In this paper, we introduce new IRC-safe counting observables whose discrimination performance exceeds that of jet mass and approaches that of track multiplicity. The key observation is that trackmore » multiplicity is approximately Poisson distributed, with more suppressed tails than the Sudakov peak structure from jet mass. By using an iterated version of the soft drop jet grooming algorithm, we can define a “soft drop multiplicity” which is Poisson distributed at leading-logarithmic accuracy. In addition, we calculate the next-to-leading-logarithmic corrections to this Poisson structure. If we allow the soft drop groomer to proceed to the end of the jet branching history, we can define a collinear-unsafe (but still infrared-safe) counting observable. Exploiting the universality of the collinear limit, we define generalized fragmentation functions to study the perturbative energy evolution of collinear-unsafe multiplicity.« less

The [N II] Kinematics of R Aquarii

NASA Technical Reports Server (NTRS)

Hollis, J. M.; Vogel, S. N.; VanBuren, D.; Strong, J. P.; Lyon, R. G.; Dorband, J. E.

1998-01-01

We report a kinematic study of the symbiotic star system R Aqr derived from [N H]lambda 6584 emission observations with a Fabry-Perot imaging spectrometer. The [N II] spatial structure of the R Aqr jet, first observed circa 1977, and surrounding hourglass-shaped nebulosity, due to an explosion approximately 660 years ago, are derived from 41 velocity planes spaced at approximately 12 km/s intervals. Fabry-Perot imagery shows the elliptical nebulosity comprising the waist of the hourglass shell is consistent with a circular ring expanding radially at 55 km/s as seen at an inclination angle, i approximately 70 deg. Fabry-Perot imagery shows the two-sided R Aqr jet is collimated flow in opposite directions. The intensity-velocity structure of the strong NE jet component is shown in contrast to the amorphous SW jet component. We offer a idealized schematic model for the R Aqr jet motion which results in a small-scale helical structure forming around a larger-scale helical path. The implications of such a jet model are discussed. We present a movie showing a side-by-side comparison of the spatial structure of the model and the data as a function of the 41 velocity planes.

Experimental and Theoretical Studies of Axisymmetric Free Jets

NASA Technical Reports Server (NTRS)

Love, Eugene S.; Grigsby, Carl E.; Lee, Louise P.; Woodling, Mildred J.

1959-01-01

Some experimental and theoretical studies have been made of axisymmetric free jets exhausting from sonic and supersonic nozzles into still air and into supersonic streams with a view toward problems associated with propulsive jets and the investigation of these problems. For jets exhausting into still air, consideration is given to the effects of jet Mach number, nozzle divergence angle, and jet static pressure ratio upon jet structure, jet wavelength, and the shape and curvature of the jet boundary. Studies of the effects of the ratio of specific heats of the jets are included are observations pertaining to jet noise and jet simulation. For jets exhausting into supersonic streams, an attempt has been made to present primarily theoretical certain jet interference effects and in formulating experimental studies. The primary variables considered are jet Mach number, free stream Mach number, jet static pressure ratio, ratio of specific heats of the jet, nozzle exit angle, and boattail angle. The simulation problem and the case of a hypothetical hypersonic vehicle are examined, A few experimental observations are included.

Faint Object Camera observations of M87 - The jet and nucleus

NASA Technical Reports Server (NTRS)

Boksenberg, A.; Macchetto, F.; Albrecht, R.; Barbieri, C.; Blades, J. C.; Crane, P.; Deharveng, J. M.; Disney, M. J.; Jakobsen, P.; Kamperman, T. M.

1992-01-01

UV and optical images of the central region and jet of the nearby elliptical galaxy M87 have been obtained with about 0.1 arcsec resolution in several spectral bands with the Faint Object Camera (FOC) on the HST, including polarization images. Deconvolution enhances the contrast of the complex structure and filamentary patterns in the jet already evident in the aberrated images. Morphologically there is close similarity between the FOC images of the extended jet and the best 2-cm radio maps obtained at similar resolution, and the magnetic field vectors from the UV and radio polarimetric data also correspond well. We observe structure in the inner jet within a few tenths arcsec of the nucleus which also has been well studied at radio wavelengths. Our UV and optical photometry of regions along the jet shows little variation in spectral index from the value 1.0 between markedly different regions and no trend to a steepening spectrum with distance along the jet.

Jet-torus connection in radio galaxies. Relativistic hydrodynamics and synthetic emission

NASA Astrophysics Data System (ADS)

Fromm, C. M.; Perucho, M.; Porth, O.; Younsi, Z.; Ros, E.; Mizuno, Y.; Zensus, J. A.; Rezzolla, L.

2018-01-01

Context. High resolution very long baseline interferometry observations of active galactic nuclei have revealed asymmetric structures in the jets of radio galaxies. These asymmetric structures may be due to internal asymmetries in the jets or they may be induced by the different conditions in the surrounding ambient medium, including the obscuring torus, or a combination of the two. Aims: In this paper we investigate the influence of the ambient medium, including the obscuring torus, on the observed properties of jets from radio galaxies. Methods: We performed special-relativistic hydrodynamic (SRHD) simulations of over-pressured and pressure-matched jets using the special-relativistic hydrodynamics code Ratpenat, which is based on a second-order accurate finite-volume method and an approximate Riemann solver. Using a newly developed radiative transfer code to compute the electromagnetic radiation, we modelled several jets embedded in various ambient medium and torus configurations and subsequently computed the non-thermal emission produced by the jet and thermal absorption from the torus. To better compare the emission simulations with observations we produced synthetic radio maps, taking into account the properties of the observatory. Results: The detailed analysis of our simulations shows that the observed properties such as core shift could be used to distinguish between over-pressured and pressure matched jets. In addition to the properties of the jets, insights into the extent and density of the obscuring torus can be obtained from analyses of the single-dish spectrum and spectral index maps.

ELLERMAN BOMBS WITH JETS: CAUSE AND EFFECT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reid, A.; Mathioudakis, M.; Scullion, E.

2015-05-20

Ellerman Bombs (EBs) are thought to arise as a result of photospheric magnetic reconnection. We use data from the Swedish 1 m Solar Telescope to study EB events on the solar disk and at the limb. Both data sets show that EBs are connected to the foot points of forming chromospheric jets. The limb observations show that a bright structure in the Hα blue wing connects to the EB initially fueling it, leading to the ejection of material upwards. The material moves along a loop structure where a newly formed jet is subsequently observed in the red wing of Hα.more » In the disk data set, an EB initiates a jet which propagates away from the apparent reconnection site within the EB flame. The EB then splits into two, with associated brightenings in the inter-granular lanes. Micro-jets are then observed, extending to 500 km with a lifetime of a few minutes. Observed velocities of the micro-jets are approximately 5–10 km s{sup −1}, while their chromospheric counterparts range from 50 to 80 km s{sup −1}. MURaM simulations of quiet Sun reconnection show that micro-jets with properties similar to those of the observations follow the line of reconnection in the photosphere, with associated Hα brightening at the location of increased temperature.« less

Multi-Epoch 8.4GHz VLBI Observations of the Nucleus of Centaurus A

NASA Technical Reports Server (NTRS)

Meier, David L.

1992-01-01

We present the results of several 8.4 GHz VLBI observations of the nucleus of Centaurus A. We fing that the source possesses a classical core-jet structure with the inner portion of the jet expanding at a proper motion of 4.o mas yr or an apparet velocity of 0.26c along the jet.

Flame deformation and entrainment associated with an isothermal transverse fuel jet

NASA Technical Reports Server (NTRS)

Jenkins, D. W.; Karagozian, A. R.

1992-01-01

This paper describes an analytical model of an incompressible, isothermal reacting jet in crossflow. The model represents the flow in the jet cross-section by a counter rotating vortex pair, a flow structure that has been observed to dominate the jet behavior. The reaction surface surrounding the fuel jet is represented as a composite of strained diffusion flames that are stretched and deformed by the vortex pair flow. The results shed new light on the interaction between the vortex pair circulation and flame structure evolution and their relation to the concept of entrainment.

The Interior Structure, Dynamics, and Heliospheric Impact of Reconnection-Driven Solar Coronal Hole Jets

NASA Astrophysics Data System (ADS)

Roberts, Merrill Alan

From bright loop structures and polar plumes to solar flares and coronal mass ejections (CMEs), our Sun has shown itself to be a highly dynamic star over a multitude of spatial and temporal scales. In fact, as the resolutions of our observations have improved, it has become clear that even coronal holes, the Sun's so called dark and quiet regions, are full of activity. Coronal hole (CH) jets are one example of this activity, a solar transient that occurs ubiquitously in coronal hole regions and which may contribute significant mass and energy to the corona and the solar wind. CH jets have been shown to share many properties with their larger and more energetic cousins, flares and CMEs, thereby providing an opportunity to understand these more complex and infrequent solar features. CH jets may also provide a source for microstreams and torsional Alfven waves found in the solar wind and interplanetary medium, as well as insight into basic processes for driving the fast solar wind and heating the corona. The purpose of this work is to deepen our understanding of CH jets by examining state-of-the-art fully 3D MHD simulations of CH jet eruptions. First, we investigate the internal structure and turbulent flows inside a model CH jet through an analysis of the simulation described by Karpen et al. (2017). An analysis of the radial variability within the simulated jet is performed, as well as a multi-scale turbulence analysis. We confirm the occurrence of multi-scale MHD turbulence within the model jet, and show that the resulting jet wake can be divided into three radially stratified regions based on its internal structure. Second, the 3D model space is extended to 60 solar radii and simulated encounters of the soon-to-be-launched Parker Solar Probe (PSP, Fox et al., 2016) mission with our model jet are produced and analyzed in order to identify signatures that may be seen in the eventual PSP observations. Our results suggest that PSP should encounter CH jets in situ, and that each of the three jet regions found have unique, identifiable signatures that could be detected by PSP. These findings suggest that CH jets are internally complex, with multi-scale, radially stratified internal structure which evolves as the jet progresses through the heliosphere. PSP will have a unique opportunity to observe this newly predicted and previously unobserved fine structure when it descends into the corona in the 2020s, and our results will serve to interpret the PSP data, as well as provide a means to test the validity of our model by comparison with them.

Characteristics of polar coronal hole jets

NASA Astrophysics Data System (ADS)

Chandrashekhar, K.; Bemporad, A.; Banerjee, D.; Gupta, G. R.; Teriaca, L.

2014-01-01

Context. High spatial- and temporal-resolution images of coronal hole regions show a dynamical environment where mass flows and jets are frequently observed. These jets are believed to be important for the coronal heating and the acceleration of the fast solar wind. Aims: We studied the dynamics of two jets seen in a polar coronal hole with a combination of imaging from EIS and XRT onboard Hinode. We observed drift motions related to the evolution and formation of these small-scale jets, which we tried to model as well. Methods: Stack plots were used to find the drift and flow speeds of the jets. A toymodel was developed by assuming that the observed jet is generated by a sequence of single reconnection events where single unresolved blobs of plasma are ejected along open field lines, then expand and fall back along the same path, following a simple ballistic motion. Results: We found observational evidence that supports the idea that polar jets are very likely produced by multiple small-scale reconnections occurring at different times in different locations. These eject plasma blobs that flow up and down with a motion very similar to a simple ballistic motion. The associated drift speed of the first jet is estimated to be ≈27 km s-1. The average outward speed of the first jet is ≈171 km s-1, well below the escape speed, hence if simple ballistic motion is considered, the plasma will not escape the Sun. The second jet was observed in the south polar coronal hole with three XRT filters, namely, C-poly, Al-poly, and Al-mesh filters. Many small-scale (≈3″-5″) fast (≈200-300 km s-1) ejections of plasma were observed on the same day; they propagated outwards. We observed that the stronger jet drifted at all altitudes along the jet with the same drift speed of ≃7 km s-1. We also observed that the bright point associated with the first jet is a part of sigmoid structure. The time of appearance of the sigmoid and that of the ejection of plasma from the bright point suggest that the sigmoid is the progenitor of the jet. Conclusions: The enhancement in the light curves of low-temperature EIS lines in the later phase of the jet lifetime and the shape of the jet's stack plots suggests that the jet material falls back, and most likely cools down. To further support this conclusion, the observed drifts were interpreted within a scenario where reconnection progressively shifts along a magnetic structure, leading to the sequential appearance of jets of about the same size and physical characteristics. On this basis, we also propose a simple qualitative model that mimics the observations. Movies 1-3 are available in electronic form at http://www.aanda.org Warning, no authors found for 2014A&A...561A..97.

Characteristics of EUV Coronal Jets Observed with STEREO/SECCHI

NASA Astrophysics Data System (ADS)

Nisticò, G.; Bothmer, V.; Patsourakos, S.; Zimbardo, G.

2009-10-01

In this paper we present the first comprehensive statistical study of EUV coronal jets observed with the SECCHI (Sun Earth Connection Coronal and Heliospheric Investigation) imaging suites of the two STEREO spacecraft. A catalogue of 79 polar jets is presented, identified from simultaneous EUV and white-light coronagraph observations, taken during the time period March 2007 to April 2008, when solar activity was at a minimum. The twin spacecraft angular separation increased during this time interval from 2 to 48 degrees. The appearances of the coronal jets were always correlated with underlying small-scale chromospheric bright points. A basic characterization of the morphology and identification of the presence of helical structure were established with respect to recently proposed models for their origin and temporal evolution. Though each jet appeared morphologically similar in the coronagraph field of view, in the sense of a narrow collimated outward flow of matter, at the source region in the low corona the jet showed different characteristics, which may correspond to different magnetic structures. A classification of the events with respect to previous jet studies shows that amongst the 79 events there were 37 Eiffel tower-type jet events, commonly interpreted as a small-scale (˜35 arc sec) magnetic bipole reconnecting with the ambient unipolar open coronal magnetic fields at its loop tops, and 12 lambda-type jet events commonly interpreted as reconnection with the ambient field happening at the bipole footpoints. Five events were termed micro-CME-type jet events because they resembled the classical coronal mass ejections (CMEs) but on much smaller scales. The remaining 25 cases could not be uniquely classified. Thirty-one of the total number of events exhibited a helical magnetic field structure, indicative for a torsional motion of the jet around its axis of propagation. A few jets are also found in equatorial coronal holes. In this study we present sample events for each of the jet types using both, STEREO A and STEREO B, perspectives. The typical lifetimes in the SECCHI/EUVI ( Extreme UltraViolet Imager) field of view between 1.0 to 1.7 R ⊙ and in SECCHI/COR1 field of view between 1.4 to 4 R ⊙ are obtained, and the derived speeds are roughly estimated. In summary, the observations support the assumption of continuous small-scale reconnection as an intrinsic feature of the solar corona, with its role for the heating of the corona, particle acceleration, structuring and acceleration of the solar wind remaining to be explored in more detail in further studies.

BROADBAND JET EMISSION IN YOUNG AND POWERFUL RADIO SOURCES: THE CASE OF THE COMPACT STEEP SPECTRUM QUASAR 3C 186

DOE Office of Scientific and Technical Information (OSTI.GOV)

Migliori, Giulia; Siemiginowska, Aneta; Celotti, Annalisa, E-mail: migliori@cfa.harvard.edu

2012-04-20

We present the X-ray analysis of a deep ({approx}200 ks) Chandra observation of the compact steep spectrum radio-loud quasar 3C 186 (z = 1.06) and investigate the contribution of the unresolved radio jet to the total X-ray emission. The spectral analysis is not conclusive on the origin of the bulk of the X-ray emission. In order to examine the jet contribution to the X-ray flux, we model the quasar spectral energy distribution, adopting several scenarios for the jet emission. For the values of the main physical parameters favored by the observables, a dominant role of the jet emission in themore » X-ray band is ruled out when a single-zone (leptonic) scenario is adopted, even including the contribution of the external photon fields as seed photons for inverse Compton emission. We then consider a structured jet, with the blazar component that-although not directly visible in the X-ray band-provides an intense field of seed synchrotron photons Compton-scattered by electrons in a mildly relativistic knot. In this case, the whole X-ray emission can be accounted for if we assume a blazar luminosity within the range observed from flat spectrum radio quasars. The X-ray radiative efficiency of such a (structured) jet is intimately related to the presence of a complex velocity structure. The jet emission can provide a significant contribution in X-rays if it decelerates within the host galaxy on kiloparsec scales. We discuss the implications of this model in terms of jet dynamics and interaction with the ambient medium.« less

Transition mixing study empirical model report

NASA Technical Reports Server (NTRS)

Srinivasan, R.; White, C.

1988-01-01

The empirical model developed in the NASA Dilution Jet Mixing Program has been extended to include the curvature effects of transition liners. This extension is based on the results of a 3-D numerical model generated under this contract. The empirical model results agree well with the numerical model results for all tests cases evaluated. The empirical model shows faster mixing rates compared to the numerical model. Both models show drift of jets toward the inner wall of a turning duct. The structure of the jets from the inner wall does not exhibit the familiar kidney-shaped structures observed for the outer wall jets or for jets injected in rectangular ducts.

Magnetic Untwisting in Jets that Go into the Outer Solar Corona in Polar Coronal Holes

NASA Astrophysics Data System (ADS)

Moore, Ronald L.; Sterling, Alphonse C.; Falconer, David

2014-06-01

We present results from a study of 14 jets that were observed in SDO/AIA EUV movies to erupt in the Sun’s polar coronal holes. These jets were similar to the many other jets that erupt in coronal holes, but reached higher than the vast majority, high enough to be observed in the outer corona beyond 2 solar radii from Sun center by the SOHO/LASCO/C2 coronagraph. We illustrate the characteristic structure and motion of these high-reaching jets by showing observations of two representative jets. We find that (1) the speed of the jet front from the base of the corona out to 2-3 solar radii is typically several times the sound speed in jets in coronal holes, (2) each high-reaching jet displays unusually large rotation about its axis (spin) as it erupts, and (3) in the outer corona, many jets display lateral swaying and bending of the jet axis with an amplitude of a few degrees and a period of order 1 hour. From these observations we infer that these jets are magnetically driven, propose that the driver is a magnetic-untwisting wave that is basically a large-amplitude (non-linear) torsional Alfven wave that is put into the open magnetic field in the jet by interchange reconnection as the jet erupts, and estimate that the magnetic-untwisting wave loses most of its energy before reaching the outer corona. These observations of high-reaching coronal jets suggest that the torsional magnetic waves observed in Type-II spicules can similarly dissipate in the corona and thereby power much of the coronal heating in coronal holes and quiet regions. This work is funded by the NASA/SMD Heliophysics Division’s Living With a Star Targeted Research & Technology Program.

Investigation of acoustic and gas dynamic characteristics of strongly swirled turbulent jets

NASA Astrophysics Data System (ADS)

Krasheninnikov, S. Yu; Maslov, VP; Mironov, AK; Toktaliev, PD

2018-03-01

Generalization of the series of experimental and numerical results for properties and characteristics of swirling jets with high swirling intensity W0>1 is considered. These jets are typically used in gas turbine aviation engines for intensification of mixing process and combustion process stabilization. Flow structures in swirling jets and in the near-field are analyzed. It is shown, that, in the main, the flow structure behind the swirling device can be determined by swirling intensity W 0 and acoustic fluctuations field formed far from the jet boundaries. Experimental measurements and numerical simulation of the noise levels of the highly swirling jet are performed using Ffowcs-Williams-Hawkins analogy. Maximum levels of noise axis are observed at angles of 50°-70° from the jet.

Three-Dimensional Simulations of Tearing and Intermittency in Coronal Jets

NASA Technical Reports Server (NTRS)

Wyper, P. F.; DeVore, C. R.; Karpen, J. T.; Lynch, B. J.

2016-01-01

Observations of coronal jets increasingly suggest that local fragmentation and intermittency play an important role in the dynamics of these events. In this work we investigate this fragmentation in high-resolution simulations of jets in the closed-field corona. We study two realizations of the embedded-bipole model, whereby impulsive helical out flows are driven by reconnection between twisted and untwisted field across the domed fan plane of a magnetic null. We find that the reconnection region fragments following the onset of a tearing-like instability, producing multiple magnetic null points and flux-rope structures within the current layer. The flux ropes formed within the weak- field region in the center of the current layer are associated with \\blobs" of density enhancement that become filamentary threads as the flux ropes are ejected from the layer, whereupon new flux ropes form behind them. This repeated formation and ejection of flux ropes provides a natural explanation for the intermittent out flows, bright blobs of emission, and filamentary structure observed in some jets. Additional observational signatures of this process are discussed. Essentially all jet models invoke reconnection between regions of locally closed and locally open field as the jet-generation mechanism. Therefore, we suggest that this repeated tearing process should occur at the separatrix surface between the two flux systems in all jets. A schematic picture of tearing-mediated jet reconnection in three dimensions is outlined.

THREE-DIMENSIONAL SIMULATIONS OF TEARING AND INTERMITTENCY IN CORONAL JETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wyper, P. F.; DeVore, C. R.; Karpen, J. T.

Observations of coronal jets increasingly suggest that local fragmentation and intermittency play an important role in the dynamics of these events. In this work, we investigate this fragmentation in high-resolution simulations of jets in the closed-field corona. We study two realizations of the embedded-bipole model, whereby impulsive helical outflows are driven by reconnection between twisted and untwisted field across the domed fan plane of a magnetic null. We find that the reconnection region fragments following the onset of a tearing-like instability, producing multiple magnetic null points and flux-rope structures within the current layer. The flux ropes formed within the weak-fieldmore » region in the center of the current layer are associated with “blobs” of density enhancement that become filamentary threads as the flux ropes are ejected from the layer, whereupon new flux ropes form behind them. This repeated formation and ejection of flux ropes provides a natural explanation for the intermittent outflows, bright blobs of emission, and filamentary structure observed in some jets. Additional observational signatures of this process are discussed. Essentially all jet models invoke reconnection between regions of locally closed and locally open field as the jet-generation mechanism. Therefore, we suggest that this repeated tearing process should occur at the separatrix surface between the two flux systems in all jets. A schematic picture of tearing-mediated jet reconnection in three dimensions is outlined.« less

Experimental characterization of a transition from collisionless to collisional interaction between head-on-merging supersonic plasma jets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moser, Auna L., E-mail: mosera@fusion.gat.com; Hsu, Scott C., E-mail: scotthsu@lanl.gov

We present results from experiments on the head-on merging of two supersonic plasma jets in an initially collisionless regime for the counter-streaming ions. The plasma jets are of either an argon/impurity or hydrogen/impurity mixture and are produced by pulsed-power-driven railguns. Based on time- and space-resolved fast-imaging, multi-chord interferometry, and survey-spectroscopy measurements of the overlapping region between the merging jets, we observe that the jets initially interpenetrate, consistent with calculated inter-jet ion collision lengths, which are long. As the jets interpenetrate, a rising mean-charge state causes a rapid decrease in the inter-jet ion collision length. Finally, the interaction becomes collisional andmore » the jets stagnate, eventually producing structures consistent with collisional shocks. These experimental observations can aid in the validation of plasma collisionality and ionization models for plasmas with complex equations of state.« less

Parsec-scale Faraday rotation and polarization of 20 active galactic nuclei jets

NASA Astrophysics Data System (ADS)

Kravchenko, E. V.; Kovalev, Y. Y.; Sokolovsky, K. V.

2017-05-01

We perform polarimetry analysis of 20 active galactic nuclei jets using the very long baseline array at 1.4, 1.6, 2.2, 2.4, 4.6, 5.0, 8.1, 8.4 and 15.4 GHz. The study allowed us to investigate linearly polarized properties of the jets at parsec scales: distribution of the Faraday rotation measure (RM) and fractional polarization along the jets, Faraday effects and structure of Faraday-corrected polarization images. Wavelength dependence of the fractional polarization and polarization angle is consistent with external Faraday rotation, while some sources show internal rotation. The RM changes along the jets, systematically increasing its value towards synchrotron self-absorbed cores at shorter wavelengths. The highest core RM reaches 16 900 rad m-2 in the source rest frame for the quasar 0952+179, suggesting the presence of highly magnetized, dense media in these regions. The typical RM of transparent jet regions has values of an order of a hundred rad m-2. Significant transverse RM gradients are observed in seven sources. The magnetic field in the Faraday screen has no preferred orientation, and is observed to be random or regular from source to source. Half of the sources show evidence for the helical magnetic fields in their rotating magneto-ionic media. At the same time jets themselves contain large-scale, ordered magnetic fields and tend to align its direction with the jet flow. The observed variety of polarized signatures can be explained by a model of spine-sheath jet structure.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Liping; He, Jiansen; Tu, Chuanyi

Observations with the space-based solar observatory Hinode show that small-scale magnetic structures in the photosphere are found to be associated with a particular class of jets of plasma in the chromosphere called anemone jets. The goal of our study is to conduct a numerical experiment of such chromospheric anemone jets related to the moving magnetic features (MMFs). We construct a 2.5 dimensional numerical MHD model to describe the process of magnetic reconnection between the MMFs and the pre-existing ambient magnetic field, which is driven by the horizontal motion of the magnetic structure in the photosphere. We include thermal conduction parallelmore » to the magnetic field and optically thin radiative losses in the corona to account for a self-consistent description of the evaporation process during the heating of the plasma due to the reconnection process. The motion of the MMFs leads to the expected jet and our numerical results can reproduce many observed characteristics of chromospheric anemone jets, topologically and quantitatively. As a result of the tearing instability, plasmoids are generated in the reconnection process that are consistent with the observed bright moving blobs in the anemone jets. An increase in the thermal pressure at the base of the jet is also driven by the reconnection, which induces a train of slow-mode shocks propagating upward. These shocks are a secondary effect, and only modulate the outflow of the anemone jet. The jet itself is driven by the energy input due to the reconnection of the MMFs and the ambient magnetic field.« less

Convolved substructure: analytically decorrelating jet substructure observables

NASA Astrophysics Data System (ADS)

Moult, Ian; Nachman, Benjamin; Neill, Duff

2018-05-01

A number of recent applications of jet substructure, in particular searches for light new particles, require substructure observables that are decorrelated with the jet mass. In this paper we introduce the Convolved SubStructure (CSS) approach, which uses a theoretical understanding of the observable to decorrelate the complete shape of its distribution. This decorrelation is performed by convolution with a shape function whose parameters and mass dependence are derived analytically. We consider in detail the case of the D 2 observable and perform an illustrative case study using a search for a light hadronically decaying Z'. We find that the CSS approach completely decorrelates the D 2 observable over a wide range of masses. Our approach highlights the importance of improving the theoretical understanding of jet substructure observables to exploit increasingly subtle features for performance.

Noise produced by the large-scale transition region structure of turbulent jets

NASA Technical Reports Server (NTRS)

Hardin, J. C.

1974-01-01

The 'orderly' structure which has been observed recently by numerous researchers within the transition region of subsonic turbulent jets is analyzed to reveal its noise-producing potential. For the case of a circular jet, this structure is modeled as a train of toroidal vortex rings which are formed near the jet exit and propagate downstream. The noise produced by the model is evaluated from a reformulation of Lighthill's expression for the far-field acoustic density which emphasizes the importance of the vorticity within the turbulent flow field. It is shown that the noise production occurs mainly close to the jet exit and depends primarily upon temporal changes in the toroidal radii. These results suggest a new approach to noise suppression which has been substantiated experimentally.

Numerical Simulations of Chromospheric Anemone Jets Associated with Moving Magnetic Features

NASA Astrophysics Data System (ADS)

Yang, Liping; He, Jiansen; Peter, Hardi; Tu, Chuanyi; Zhang, Lei; Feng, Xueshang; Zhang, Shaohua

2013-11-01

Observations with the space-based solar observatory Hinode show that small-scale magnetic structures in the photosphere are found to be associated with a particular class of jets of plasma in the chromosphere called anemone jets. The goal of our study is to conduct a numerical experiment of such chromospheric anemone jets related to the moving magnetic features (MMFs). We construct a 2.5 dimensional numerical MHD model to describe the process of magnetic reconnection between the MMFs and the pre-existing ambient magnetic field, which is driven by the horizontal motion of the magnetic structure in the photosphere. We include thermal conduction parallel to the magnetic field and optically thin radiative losses in the corona to account for a self-consistent description of the evaporation process during the heating of the plasma due to the reconnection process. The motion of the MMFs leads to the expected jet and our numerical results can reproduce many observed characteristics of chromospheric anemone jets, topologically and quantitatively. As a result of the tearing instability, plasmoids are generated in the reconnection process that are consistent with the observed bright moving blobs in the anemone jets. An increase in the thermal pressure at the base of the jet is also driven by the reconnection, which induces a train of slow-mode shocks propagating upward. These shocks are a secondary effect, and only modulate the outflow of the anemone jet. The jet itself is driven by the energy input due to the reconnection of the MMFs and the ambient magnetic field.

GRB 170817A: a short GRB seen off-axis

NASA Astrophysics Data System (ADS)

He, Xin-Bo; Tam, Pak-Hin Thomas; Shen, Rong-Feng

2018-04-01

The angular distribution of gamma-ray burst (GRB) jets is not yet clear. The observed luminosity of GRB 170817A is the lowest among all known short GRBs, which is best explained by the fact that our line of sight is outside of the jet opening angle, θ obs > θ j , where θ obs is the angle between our line of sight and the jet axis. As inferred by gravitational wave observations, as well as radio and X-ray afterglow modeling of GRB 170817A, it is likely that θ obs ∼ 20° – 28°. In this work, we quantitatively consider two scenarios of angular energy distribution of GRB ejecta: a top-hat jet and a structured jet with a power law index s. For the top-hat jet model, we get a large θ j (e.g., θ j > 10°), a rather high local (i.e., z < 0.01) short GRB rate ∼8–15×103, Gpc‑3, yr‑1 (estimated to be 90∼1850 Gpc‑3, yr‑1 in Fong et al.) and an extremely high E peak,0 (on-axis, rest-frame) > 7.5 × 104, keV (∼500, keV for a typical short GRB). For the structured jet model, we use θ obs to give limits on s and θj for typical on-axis luminosity of a short GRB (e.g., 1049 erg s‑1 ∼ 1051 erg s‑1), and a low on-axis luminosity case (e.g., 1049 erg s‑1) gives more reasonable values of s. The structured jet model is more feasible for GRB 170817A than the top-hat jet model due to the rather high local short GRB rate, and the extremely high on-axis E peak,0 almost rules out the top-hat jet model. GRB 170817A is likely a low on-axis luminosity GRB (1049 erg s‑1) with a structured jet.

Evidence for the Magnetic Breakout Model in AN Equatorial Coronal-Hole Jet

NASA Astrophysics Data System (ADS)

Kumar, P.; Karpen, J.; Antiochos, S. K.; Wyper, P. F.; DeVore, C. R.; DeForest, C. E.

2017-12-01

We analyzed an equatorial coronal-hole jet observed by Solar Dynamic Observatory (SDO)/AtmosphericImaging Assembly (AIA). The source-region magnetic field structure is consistent withthe embedded-bipole topology that we identified and modeled previously as a source of coronal jets. Theinitial brightening was observed below a sigmoid structure about 25 min before the onset of an untwisting jet.A circular magnetic flux rope with a mini-filament rose slowly at the speed of ˜15 km/s , then accelerated(˜126 km/s) during the onset of explosive breakout reconnection. Multiple plasmoids, propagating upward(˜135 km/s) and downward (˜55 km/s ), were detected behind the rising flux rope shortly before andduring explosive breakout reconnection. The jet was triggered when the rising flux rope interacted with theoverlying magnetic structures near the outer spine. This event shows a clear evidence of reconnection not onlybelow the flux rope but also a breakout reconnection above the flux rope. During the breakout reconnection,we observed heating of the flux rope, deflection of loops near the spine, and formation of multiple ribbons.The explosive breakout reconnection destroyed the flux rope that produced an untwisting jet with a speed of˜380 km/s . HMI magnetograms reveal the shear motion at theeruption site, but do not show any significant flux emergence or cancellation during or 2 hours before theeruption. Therefore, the free energy powering this jet most likely originated in magnetic shear concentratedat the polarity inversion line within the embedded bipole-a mini-filament channel-possibly created by helicitycondensation. The result of of a statistical study of multiple jets will also be discussed.

Probing the collimation of pristine post-AGB jets with STIS

NASA Astrophysics Data System (ADS)

Sanchez Contreras, Carmen

2009-07-01

The shaping of planetary and protoplanetary nebulae {PNe and PPNe} is probably the most exciting yet least understood problem in the late evolution of 1-8 solar mass stars. An increasing number of astronomers believe that fast jet-like winds ejected in the PPN phase are responsible for carving out the diverse shapes in the dense envelopes of the Asymptotic Giant Branch {AGB} stars. To date, the properties of these post-AGB jets have not been characterized and, indeed, their launching/collimation mechanism is still subject to controversial debate. This is due to the lack of the direct observations probing the spatio-kinematic structure of post-AGB winds in the stellar vicinity { 10e16cm}, which is only possible with HST+STIS. Recently, STIS observations have allowed us for the first time the DIRECT study of the structure and kinematics of the elusive post-AGB winds in one PPN, He3-1475 {Sanchez Contreras & Sahai 2001}. Those winds have been discovered through H-alpha blue-shifted absorption features in the inner 0.3"-0.7" of the nebula. These STIS observations have revealed an ultra-fast collimated outflow relatively unaffected by the interaction with the AGB wind that is totally hidden in ground-based spectroscopic observations and HST images. The discovery of the pristine ultra-fast { 2300km/s} jet in He3-1475 is the first observational confirmation of the presence of collimated outflows as close as 10e16cm from the central star. Most importantly, the spatio-kinematic structure of the ultra-fast jet clearly rules out hydrodynamical collimation alone and favors magnetic wind collimation. Therefore, STIS observations provide a unique method of probing the structure, kinematics, and collimation mechanism of the elusive post-AGB winds. We now propose similar observations for a sample of bipolar PPNe with ongoing post-AGB ejections in order to investigate the frequency of jets like those in He3-1475 in other PPNe and elucidate their nature and collimation mechanism. The observational characterization of these winds is indispensable for understanding this violent and important phase of post-AGB evolution.

Improved Phased Array Imaging of a Model Jet

NASA Technical Reports Server (NTRS)

Dougherty, Robert P.; Podboy, Gary G.

2010-01-01

An advanced phased array system, OptiNav Array 48, and a new deconvolution algorithm, TIDY, have been used to make octave band images of supersonic and subsonic jet noise produced by the NASA Glenn Small Hot Jet Acoustic Rig (SHJAR). The results are much more detailed than previous jet noise images. Shock cell structures and the production of screech in an underexpanded supersonic jet are observed directly. Some trends are similar to observations using spherical and elliptic mirrors that partially informed the two-source model of jet noise, but the radial distribution of high frequency noise near the nozzle appears to differ from expectations of this model. The beamforming approach has been validated by agreement between the integrated image results and the conventional microphone data.

A Study of Vehicle Structural Layouts in Post-WWII Aircraft

NASA Technical Reports Server (NTRS)

Sensmeier, Mark D.; Samareh, Jamshid A.

2004-01-01

In this paper, results of a study of structural layouts of post-WWII aircraft are presented. This study was undertaken to provide the background information necessary to determine typical layouts, design practices, and industry trends in aircraft structural design. Design decisions are often predicated not on performance-related criteria, but rather on such factors as manufacturability, maintenance access, and of course cost. For this reason, a thorough understanding of current best practices in the industry is required as an input for the design optimization process. To determine these best practices and industry trends, a large number of aircraft structural cutaway illustrations were analyzed for five different aircraft categories (commercial transport jets, business jets, combat jet aircraft, single engine propeller aircraft, and twin-engine propeller aircraft). Several aspects of wing design and fuselage design characteristics are presented here for the commercial transport and combat aircraft categories. A great deal of commonality was observed for transport structure designs over a range of eras and manufacturers. A much higher degree of variability in structural designs was observed for the combat aircraft, though some discernable trends were observed as well.

High Temperature Supersonic Jet Noise - Fundamental Studies and Control using Advanced Actuation Methods

DTIC Science & Technology

2016-08-24

the manifestations of the initial shear layer instabilities that originate at the nozzle exit. Crow and Champagne 1 and Moore 2 were among the first...structures ( or instability waves/wave packets) , first clearly observed by Crow and Champagne 1 and Moore 2 in axisymmetric jets, are generally...grant, is continuing under an NSF grant. Bibliography 1. Crow, S. and Champagne , F. H., “Orderly structure in jet turbulence,” Journal of Fluid

Numerical studies of solar chromospheric jets

NASA Astrophysics Data System (ADS)

Iijima, Haruhisa

2016-03-01

The solar chromospheric jet is one of the most characteristic structures near the solar surface. The quantitative understanding of chromospheric jets is of substantial importance for not only the partially ionized phenomena in the chromosphere but also the energy input and dissipation processes in the corona. In this dissertation, the formation and dynamics of chromospheric jets are investigated using the radiation magnetohydrodynamic simulations. We newly develop a numerical code for the radiation magnetohydrodynamic simulations of the comprehensive modeling of solar atmosphere. Because the solar chromosphere is highly nonlinear, magnetic pressure dominated, and turbulent, a robust and high-resolution numerical scheme is required. In Chapter 2, we propose a new algorithm for the simulation of magnetohydrodynamics. Through the test problems and accuracy analyses, the proposed scheme is proved to satisfy the requirements. In Chapter 3, the effect of the non-local radiation energy transport, Spitzer-type thermal conduction, latent heat of partial ionization and molecule formation, and gravity are implemented to the magnetohydrodynamic code. The numerical schemes for the radiation transport and thermal conduction is carefully chosen in a view of the efficiency and compatibility with the parallel computation. Based on the developed radiation magnetohydrodynamic code, the formation and dynamics of chromospheric jets are investigated. In Chapter 4, we investigate the dependence of chromospheric jets on the coronal temperature in the two-dimensional simulations. Various scale of chromospheric jets with the parabolic trajectory are found with the maximum height of 2-8 Mm, lifetime of 2-7 min, maximum upward velocity of 10- 50 km/s, and deceleration of 100-350 m/s2. We find that chromospheric jets are more elongated under the cool corona and shorter under the hot corona. We also find that the pressure gradient force caused by the periodic shock waves accelerates some of the short chromospheric jets. The taller jets tend to follow ballistic trajectory. The contribution of the coronal conditions are quantitatively modeled in the form of a power law based on the amplification of shock waves under the density stratified medium. In Chapter 5, the role of the magnetic field is investigated using the two-dimensional simulations. We distinguish the contribution of the corona and magnetic field using the power law. The average magnetic field strength produces only a small effect on the scale of chromospheric jets. The observed regional difference is mainly explained by the difference of the coronal conditions, which is caused by the different magnetic field structure. We also find shorter chromospheric jets above the strong magnetic flux tube. This is in contrast to the observational studies. In Chapter 6, a three-dimensional simulation is presented to investigate the effect of three-dimensionality on the scale of chromospheric jets and the dependence on the photospheric magnetic field structure. The tall chromospheric jets with the maximum height of 10-11 Mm and lifetime of 8-10 min are formed. These tall jets are located above the strong magnetic field concentration. This result is different from the two-dimensional study and consistent with the observational reports. The strongly entangled chromospheric magnetic field drives these tall chromospheric jets through the Lorentz force. We also find that the produced chromospheric jets form a cluster with the diameter of several Mm with finer strands. In Chapter 7, we summarize and discuss our new findings and their implications for the solar chromospheric jets. The regional difference of chromospheric jets is explained through the coronal temperature and density, which is produced by the heating process with the different strength and structure of the magnetic field. The observational relation between the magnetic network and chromospheric jets are interpreted through the magii netic energy release in the complex photospheric magnetic field with mixed-polarity. The formation of the horizontal structure like the multi-threaded nature of solar spicules and the possible driver of observed chromospheric jets are also discussed. The comprehensive numerical model developed in this dissertation allows various future applications for the dynamics on the sun. The most important new results in this dissertation are (1) the reproduction of tall (> 6 Mm) chromospheric jets using the simulation with realistic physical processes, (2) the quantification of the effect of the coronal condition and magnetic field on the scale of jets, and (3) the reproduction of the cluster of jets with fine-scale internal structure. We conclude that the solar chromospheric jets reflect the information of not only the magnetic field but also the corona and fine-scale motion in the lower atmosphere.

On the dynamical nature of Saturn's North Polar hexagon

NASA Astrophysics Data System (ADS)

Rostami, Masoud; Zeitlin, Vladimir; Spiga, Aymeric

2017-11-01

An explanation of long-lived Saturn's North Polar hexagonal circumpolar jet in terms of instability of the coupled system polar vortex - circumpolar jet is proposed in the framework of the rotating shallow water model, where scarcely known vertical structure of the Saturn's atmosphere is averaged out. The absence of a hexagonal structure at Saturn's South Pole is explained similarly. By using the latest state-of-the-art observed winds in Saturn's polar regions a detailed linear stability analysis of the circumpolar jet is performed (i) excluding (;jet-only; configuration), and (2) including (;jet + vortex; configuration) the north polar vortex in the system. A domain of parameters: latitude of the circumpolar jet and curvature of its azimuthal velocity profile, where the most unstable mode of the system has azimuthal wavenumber 6, is identified. Fully nonlinear simulations are then performed, initialized either with the most unstable mode of small amplitude, or with the random combination of unstable modes. It is shown that developing barotropic instability of the ;jet+vortex; system produces a long-living structure akin to the observed hexagon, which is not the case of the ;jet-only; system, which was studied in this context in a number of papers in literature. The north polar vortex, thus, plays a decisive dynamical role. The influence of moist convection, which was recently suggested to be at the origin of Saturn's North Polar vortex system in the literature, is investigated in the framework of the model and does not alter the conclusions.

On the dynamical nature of Saturn's North Polar hexagon

NASA Astrophysics Data System (ADS)

Rostami, Masoud; Zeitlin, Vladimir; Spiga, Aymeric

2017-04-01

An explanation of long-lived Saturn's North Pole hexagonal circumpolar jet in terms of instability of the coupled system polar vortex - circumpolar jet is proposed in the framework of the rotating shallow water model, where scarcely known vertical structure of the Saturn's atmosphere is averaged out. The absence of a hexagonal structure at the Saturn's South Pole is explained along the same lines. By using the latest state-of-the-art observed winds in Saturn's polar regions a detailed linear stability analysis of the circumpolar jet is performed (i) excluding (``jet-only" configuration), and (2) including (``jet+vortex" configuration) the north polar vortex in the system. A domain of parameters: latitude of the circumpolar jet and curvature of its azimuthal velocity profile, where the most unstable mode of the system has azimuthal wavenumber 6, is identified. Fully nonlinear simulations are then performed, initialized either with the most unstable mode of small amplitude, or with the random combination of unstable modes. It is shown that developing barotropic instability of the ``jet+vortex" system produces a long-living structure akin to the observed hexagon, which is not the case of the ``jet-only" system, which was studied in this context in a number of papers in literature. The north polar vortex, thus, plays a decisive dynamical role. The influence of moist convection, which was recently suggested to be at the origin of Saturn's north polar vortex system in the literature, is investigated in the framework of the model and does not alter the conclusions.

Modeling the Morphology of Comet LINEAR (2001 A2)

NASA Astrophysics Data System (ADS)

Woodney, L. M.; Barkume, K. M.; Schleicher, D. G.

2002-09-01

Imaging of Comet LINEAR (2001 A2) obtained at the Lowell Observatory June 29 - 30, 2001 revealed CN arcs symmetrical about p.a. 250o. Three successive arcs separated by approximately 12 000 km were observed on each side; outward motion of the arcs was detected. Simlar arcs are seen in C2 and C3, but no jets were observed in the dust continuum. No jet structure was apparent by our next set of observations on July 8. We will present results from Monte Carlo modeling of these gas jets.

OBSERVATIONS OF A SERIES OF FLARES AND ASSOCIATED JET-LIKE ERUPTIONS DRIVEN BY THE EMERGENCE OF TWISTED MAGNETIC FIELDS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lim, Eun-Kyung; Yurchyshyn, Vasyl; Kim, Sujin

We studied temporal changes of morphological and magnetic properties of a succession of four confined flares followed by an eruptive flare using the high-resolution New Solar Telescope (NST) operating at the Big Bear Solar Observatory (BBSO) and Helioseismic and Magnetic Imager (HMI) magnetograms and Atmospheric Image Assembly (AIA) EUV images provided by the Solar Dynamics Observatory (SDO). From the NST/Hα and the SDO/AIA 304 Å observations we found that each flare developed a jet structure that evolved in a manner similar to evolution of the blowout jet: (1) an inverted-Y-shaped jet appeared and drifted away from its initial position; (2) jets formed amore » curtain-like structure that consisted of many fine threads accompanied by subsequent brightenings near the footpoints of the fine threads; and finally, (3) the jet showed a twisted structure visible near the flare maximum. Analysis of the HMI data showed that both the negative magnetic flux and the magnetic helicity have been gradually increasing in the positive-polarity region, indicating the continuous injection of magnetic twist before and during the series of flares. Based on these results, we suggest that the continuous emergence of twisted magnetic flux played an important role in producing successive flares and developing a series of blowout jets.« less

Flaring radio lanterns along the ridge line: long-term oscillatory motion in the jet of S5 1803+784

NASA Astrophysics Data System (ADS)

Kun, E.; Karouzos, M.; Gabányi, K. É.; Britzen, S.; Kurtanidze, O. M.; Gergely, L. Á.

2018-07-01

We present a detailed analysis of 30 very long baseline interferometric (VLBI) observations of the BL Lac object S5 1803+784 (z= 0.679), obtained between mean observational time 1994.67 and 2012.91 at observational frequency 15 GHz. The long-term behaviour of the jet ridge line reveals the jet experiences an oscillatory motion superposed on its helical jet kinematics on a time-scale of about 6 yr. The excess variance of the positional variability indicates the jet components being farther from the VLBI core have larger amplitude in their position variations. The fractional variability amplitude shows slight changes in 3 yrbins of the component's position. The temporal variability in the Doppler boosting of the ridge line results in jet regions behaving as flaring `radio lanterns'. We offer a qualitative scenario leading to the oscillation of the jet ridge line that utilizes the orbital motion of the jet emitter black hole due to a binary black hole companion. A correlation analysis implies composite origin of the flux variability of the jet components, emerging due to possibly both the evolving jet structure and its intrinsic variability.

A gigantic coronal jet ejected from a compact active region in a coronal hole

NASA Technical Reports Server (NTRS)

Shibata, K.; Nitta, N.; Strong, K. T.; Matsumoto, R.; Yokoyama, T.; Hirayama, T.; Hudson, H.; Ogawara, Y.

1994-01-01

A gigantic coronal jet greater than 3 x 10(exp 5) km long (nearly half the solar radius) has been found with the soft X-ray telescope (SXT) on board the solar X-ray satellite, Yohkoh. The jet was ejected on 1992 January 11 from an 'anemone-type' active region (AR) appearing in a coronal hole and is one of the largest coronal X-ray jets observed so far by SXT. This gigantic jet is the best observed example of many other smaller X-ray jets, because the spatial structures of both the jet and the AR located at its base are more easily resolved. The range of apparent translational velocities of the bulk of the jet was between 90 and 240 km s(exp -1), with the corresponding kinetic energy estimated to be of order of 10(exp 28) ergs. A detailed analysis reveals that the jet was associated with a loop brightening (a small flare) that occurred in the active region. Several features of this observation suggest and are consistent with a magnetic reconnection mechanism for the production of such a 'jet-loop-brightening' event.

Flaring radio lanterns along the ridge line: long-term oscillatory motion in the jet of S5 1803+784

NASA Astrophysics Data System (ADS)

Kun, E.; Karouzos, M.; Gabányi, K. É.; Britzen, S.; Kurtanidze, O. M.; Gergely, L. Á.

2018-04-01

We present a detailed analysis of 30 very long baseline interferometric observations of the BL Lac object S5 1803+784 (z = 0.679), obtained between mean observational time 1994.67 and 2012.91 at observational frequency 15 GHz. The long-term behaviour of the jet ridge line reveals the jet experiences an oscillatory motion superposed on its helical jet kinematics on a time-scale of about 6 years. The excess variance of the positional variability indicates the jet components being farther from the VLBI core have larger amplitude in their position variations. The fractional variability amplitude shows slight changes in 3-year bins of the component's position. The temporal variability in the Doppler boosting of the ridge line results in jet regions behaving as flaring "radio lanterns". We offer a qualitative scenario leading to the oscillation of the jet ridge line, that utilizes the orbital motion of the jet emitter black hole due to a binary black hole companion. A correlation analysis implies composite origin of the flux variability of the jet components, emerging due to possibly both the evolving jet-structure and its intrinsic variability.

Jet activity in the symbiotic variable R Aquarii

NASA Technical Reports Server (NTRS)

Michalitsianos, A. G.; Hollis, J. M.; Kafatos, M.

1986-01-01

Low-resolution ultraviolet spectra of the R Aquarii jet have been obtained with the International Ultraviolet Explorer (IUE). The most recent IUE observations indicate the ionization state of the jet is increasing. Subarcsecond, Very Large Array observations of R Aquarii have resolved the radio-continuum structure into discrete parcels of emission that are extended and nearly collinear. R Aquarii provides evidence that indicates stellar jet activity is not unique to objects associated with high-energy emission processes alone. Rather, the nature of the aligned radio-optical features that comprise the R Aquarii jet indicate that directional mass expulsion, in the form of discrete-collimated ejecta, probably reflect a general, underlying, physical process associated with a wide variety of peculiar stellar objects. As such, the R Aquarii jet constitutes a prototype for jet activity in composite or peculiar emission stars.

Observation of hard scattering in photoproduction events with a large rapidity gap at HERA

NASA Astrophysics Data System (ADS)

Derrick, M.; Krakauer, D.; Magill, S.; Musgrave, B.; Repond, J.; Schlereth, J.; Stanek, R.; Talaga, R. L.; Thron, J.; Arzarello, F.; Ayad, R.; Bari, G.; Basile, M.; Bellagamba, L.; Boscherini, D.; Bruni, A.; Bruni, G.; Bruni, P.; Cara Romeo, G.; Castellini, G.; Chiarini, M.; Cifarelli, L.; Cindolo, F.; Ciralli, F.; Contin, A.; D'Auria, S.; Frasconi, F.; Gialas, I.; Giusti, P.; Iacobucci, G.; Laurenti, G.; Levi, G.; Margotti, A.; Massam, T.; Nania, R.; Nemoz, C.; Palmonari, F.; Polini, A.; Sartorelli, G.; Timellini, R.; Zamora Garcia, Y.; Zichichi, A.; Bargende, A.; Crittenden, J.; Desch, K.; Diekmann, B.; Doeker, T.; Eckert, M.; Feld, L.; Frey, A.; Geerts, M.; Geitz, G.; Grothe, M.; Hartmann, H.; Haun, D.; Heinloth, K.; Hilger, E.; Jakob, H.-P.; Katz, U. F.; Mari, S. M.; Mass, A.; Mengel, S.; Mollen, J.; Paul, E.; Rembser, Ch.; Schattevoy, R.; Schramm, D.; Stamm, J.; Wedemeyer, R.; Campbell-Robson, S.; Cassidy, A.; Dyce, N.; Foster, B.; George, S.; Gilmore, R.; Heath, G. P.; Heath, H. F.; Llewellyn, T. J.; Morgado, C. J. S.; Norman, D. J. P.; O'Mara, J. A.; Tapper, R. J.; Wilson, S. S.; Yoshida, R.; Rau, R. R.; Arneodo, M.; Iannotti, L.; Schioppa, M.; Susinno, G.; Bernstein, A.; Caldwell, A.; Parsons, J. A.; Ritz, S.; Sciulli, F.; Straub, P. B.; Wai, L.; Yang, S.; Zhu, Q.; Borzemski, P.; Chwastowski, J.; Eskreys, A.; Piotrzkowski, K.; Zachara, M.; Zawiejski, L.; Adamczyk, L.; Bednarek, B.; Eskreys, K.; Jeleń, K.; Kisielewska, D.; Kowalski, T.; Rulikowska-Zarȩbska, E.; Suszycki, L.; Zajaç, J.; Kotański, A.; Przybycień, M.; Bauerdick, L. A. T.; Behrens, U.; Bienlein, J. K.; Böttcher, S.; Coldewey, C.; Drews, G.; Flasiński, M.; Gilkinson, D. J.; Göttlicher, P.; Gutjahr, B.; Haas, T.; Hain, W.; Hasell, D.; Heßling, H.; Hultschig, H.; Iga, Y.; Joos, P.; Kasemann, M.; Klanner, R.; Koch, W.; Köpke, L.; Kötz, U.; Kowalski, H.; Kröger, W.; Krüger, J.; Labs, J.; Ladage, A.; Löhr, B.; Löwe, M.; Lüke, D.; Mańczak, O.; Ng, J. S. T.; Nickel, S.; Notz, D.; Ohrenberg, K.; Roco, M.; Rohde, M.; Roldán, J.; Schneekloth, U.; Schulz, W.; Selonke, F.; Stiliaris, E.; Voß, T.; Westphal, D.; Wolf, G.; Youngman, C.; Grabosch, H. J.; Leich, A.; Meyer, A.; Rethfeldt, C.; Schlenstedt, S.; Barbagli, G.; Pelfer, P.; Anzivino, G.; Maccarrone, G.; De Pasquale, S.; Qian, S.; Votano, L.; Bamberger, A.; Freidhof, A.; Poser, T.; Söldner-Rembold, S.; Schroeder, J.; Theisen, G.; Trefzger, T.; Brook, N. H.; Bussey, P. J.; Doyle, A. T.; Fleck, I.; Jamieson, V. A.; Saxon, D. H.; Utley, M. L.; Wilson, A. S.; Dannemann, A.; Holm, U.; Horstmann, D.; Kammerlocher, H.; Krebs, B.; Neumann, T.; Sinkus, R.; Wick, K.; Badura, E.; Burow, B. D.; Fürtjes, A.; Hagge, L.; Lohrmann, E.; Mainusch, J.; Milewski, J.; Nakahata, M.; Pavel, N.; Poelz, G.; Schott, W.; Terron, J.; Zetsche, F.; Bacon, T. C.; Beuselinck, R.; Butterworth, I.; Gallo, E.; Harris, V. L.; Hung, B. H.; Long, K. R.; Miller, D. B.; Morawitz, P. P. O.; Prinias, A.; Sedgbeer, J. K.; Whitfield, A. F.; Mallik, U.; McCliment, E.; Wang, M. Z.; Wang, S. M.; Wu, J. T.; Zhang, Y.; Cloth, P.; Filges, D.; An, S. H.; Hong, S. M.; Nam, S. W.; Park, S. K.; Suh, M. H.; Yon, S. H.; Imlay, R.; Kartik, S.; Kim, H.-J.; McNeil, R. R.; Metcalf, W.; Nadendla, V. K.; Barreiro, F.; Cases, G.; Graciani, R.; Hernández, J. M.; Hervás, L.; Labarga, L.; del Peso, J.; Puga, J.; de Trocóniz, J. F.; Smith, G. R.; Corriveau, F.; Hanna, D. S.; Hartmann, J.; Hung, L. W.; Lim, J. N.; Matthews, C. G.; Patel, P. M.; Sinclair, L. E.; Stairs, D. G.; Laurent, M. St.; Ullmann, R.; Zacek, G.; Bashkirov, V.; Dolgoshein, B. A.; Stifutkin, A.; Bashindzhagyan, G. L.; Ermolov, P. F.; Gladilin, L. K.; Golubkov, Y. A.; Kobrin, V. D.; Kuzmin, V. A.; Proskuryakov, A. S.; Savin, A. A.; Shcheglova, L. M.; Solomin, A. N.; Zotov, N. P.; Bentvelsen, S.; Botje, M.; Chlebana, F.; Dake, A.; Engelen, J.; de Jong, P.; de Kamps, M.; Kooijman, P.; Kruse, A.; O'Dell, V.; Tenner, A.; Tiecke, H.; Verkerke, W.; Vreeswijk, M.; Wiggers, L.; de Wolf, E.; van Woudenberg, R.; Acosta, D.; Bylsma, B.; Durkin, L. S.; Honscheid, K.; Li, C.; Ling, T. Y.; McLean, K. W.; Murray, W. N.; Park, I. H.; Romanowski, T. A.; Seidlein, R.; Bailey, D. S.; Blair, G. A.; Byrne, A.; Cashmore, R. J.; Cooper-Sarkar, A. M.; Daniels, D.; Devenish, R. C. E.; Harnew, N.; Lancaster, M.; Luffman, P. E.; Lindemann, L.; McFall, J.; Nath, C.; Quadt, A.; Uijterwaal, H.; Walczak, R.; Wilson, F. F.; Yip, T.; Abbiendi, G.; Bertolin, A.; Brugnera, R.; Carlin, R.; Dal Corso, F.; De Giorgi, M.; Dosselli, U.; Limentani, S.; Morandin, M.; Posocco, M.; Stanco, L.; Stroili, R.; Voci, C.; Bulmahn, J.; Butterworth, J. M.; Feild, R. G.; Oh, B. Y.; Whitmore, J. J.; D'Agostini, G.; Iori, M.; Marini, G.; Mattioli, M.; Nigro, A.; Tassi, E.; Hart, J. C.; McCubbin, N. A.; Prytz, K.; Shah, T. P.; Short, T. L.; Barberis, E.; Cartiglia, N.; Dubbs, T.; Heusch, C.; Van Hook, M.; Hubbard, B.; Lockman, W.; Rahn, J. T.; Sadrozinski, H. F.-W.; Seiden, A.; Biltzinger, J.; Seifert, R. J.; Walenta, A. H.; Zech, G.; Abramowicz, H.; Briskin, G.; Dagan, S.; Levy, A.; Hasegawa, T.; Hazumi, M.; Ishii, T.; Kuze, M.; Mine, S.; Nagasawa, Y.; Nagira, T.; Nakao, M.; Suzuki, I.; Tokushuku, K.; Yamada, S.; Yamazaki, Y.; Chiba, M.; Hamatsu, R.; Hirose, T.; Homma, K.; Kitamura, S.; Nagayama, S.; Nakamitsu, Y.; Cirio, R.; Costa, M.; Ferrero, M. I.; Lamberti, L.; Maselli, S.; Peroni, C.; Sacchi, R.; Solano, A.; Staiano, A.; Dardo, M.; Bailey, D. C.; Bandyopadhyay, D.; Benard, F.; Brkic, M.; Crombie, M. B.; Gingrich, D. M.; Hartner, G. F.; Joo, K. K.; Levman, G. M.; Martin, J. F.; Orr, R. S.; Sampson, C. R.; Teuscher, R. J.; Catterall, C. D.; Jones, T. W.; Kaziewicz, P. B.; Lane, J. B.; Saunders, R. L.; Shulman, J.; Blankenship, K.; Kochocki, J.; Lu, B.; Mo, L. W.; Bogusz, W.; Charchuła, K.; Ciborowski, J.; Gajewski, J.; Grzelak, G.; Kasprzak, M.; Krzyżanowski, M.; Muchorowski, K.; Nowak, R. J.; Pawlak, J. M.; Tymieniecka, T.; Wróblewski, A. K.; Zakrzewski, J. A.; Żarnecki, A. F.; Adamus, M.; Eisenberg, Y.; Glasman, C.; Karshon, U.; Revel, D.; Shapira, A.; Ali, I.; Behrens, B.; Dasu, S.; Fordham, C.; Foudas, C.; Goussiou, A.; Loveless, R. J.; Reeder, D. D.; Silverstein, S.; Smith, W. H.; Tsurugai, T.; Bhadra, S.; Frisken, W. R.; Furutani, K. M.; ZEUS Collaboration

1995-02-01

Events with a large rapidity gap and total transverse energy greater than 5 GeV have been observed in quasi-real photoproduction at HERA with the ZEUS detector. The distribution of these events as a function of the γp centre of mass energy is consistent with diffractive scattering. For total transverse energies above 12 GeV, the hadronic final states show predominantly a two-jet structure with each jet having a transverse energy greater than 4 GeV. For the two-jet events, little energy flow is found outside the jets. This observation is consistent with the hard scattering of a quasi-real photon with a colourless object in the proton.

Classification and Physical parameters EUV coronal jets with STEREO/SECCHI.

NASA Astrophysics Data System (ADS)

Nistico, Giuseppe; Bothmer, Volker; Patsourakos, Spiro; Zimbardo, Gaetano

In this work we present observations of EUV coronal jets, detected with the SECCHI (Sun Earth Connection Coronal and Heliospheric Investigation) imaging suites of the two STEREO spacecraft. Starting from catalogues of polar and equatorial coronal hole jets (Nistico' et al., Solar Phys., 259, 87, 2009; Ann. Geophys. in press), identified from simultaneous EUV and white-light coronagraph observations, taken during the time period March 2007 to April 2008 when solar activity was at minimum, we perfom a detailed study of some events. A basic char-acterisation of the magnetic morphology and identification of the presence of helical structure were established with respect to recently proposed models for their origin and temporal evo-lution. A classification of the events with respect to previous jet studies shows that amongst the 79 events, identified into polar coronal holes, there were 37 Eiffel tower -type jet events commonly interpreted as a small-scale ( 35 arcsec) magnetic bipole reconnecting with the ambi-ent unipolar open coronal magnetic fields at its looptops, 12 lambda-type jet events commonly interpreted as reconnection with the ambient field happening at the bipoles footpoints. Five events were termed micro-CME type jet events because they resembled classical three-part structured coronal mass ejections (CMEs) but on much smaller scales. The remainig 25 cases could not be uniquely classified. Thirty-one of the total number of events exhibited a helical magnetic field structure, indicative for a torsional motion of the jet around its axis of propaga-tion. The jet events are found to be also present in equatorial coronal holes. We also present the 3-D reconstruction, temperature, velocity, and density measurements of a number of jets during their evolution.

Gravitational Effects on Flow Instability and Transition in Low Density Jets

NASA Technical Reports Server (NTRS)

Agrawal, Ajay K.; Parthasarathy, Ramkumar

2004-01-01

Experiments were conducted in Earth gravity and microgravity to acquire quantitative data on near field flow structure of helium jets injected into air. Microgravity conditions were simulated in the 2.2-second drop tower at NASA Glenn Research Center. The jet flow was observed by quantitative rainbow schlieren deflectometry, a non-intrusive line of sight measurement technique suited for the microgravity environment. The flow structure was characterized by distributions of helium mole fraction obtained from color schlieren images taken at 60 Hz. Results show that the jet in microgravity was up to 70 percent wider than that in Earth gravity. Experiments reveal that the global flow oscillations observed in Earth gravity are absent in microgravity. The report provides quantitative details of flow evolution as the experiment undergoes change in gravity in the drop tower.

The Reel Deal: Interpreting HST Multi-Epoch Movies of YSO Jets.

NASA Astrophysics Data System (ADS)

Frank, Adam

2010-09-01

The goal of this proposal is to bring the theoretical interpretation of Young Stellar Object jets and their environments to a new level of realism. We propose to build on the results of a successful Cycle 16 observing proposal that has obtained 3rd epoch images of HH jets. We will use Adaptive Mesh Refinement MHD simulations {developed by our team} to carry forward a detailed program of modeling and interpretation of the time-dependent behavior revealed in the new, extended multi-epoch data set. Only with the third epoch observations can we explore forces: i.e. accelerations, decelerations and structural changes to develop an accurate understanding of physical processes occurring in hypersonic, magnetized jet flows. Our studies will allow us to characterize the jets and, therefore, make the crucial link with jet central engines. We note an innovative feature of our project is its link with laboratory astrophysical experiments of jets. Our analysis of the observations will be used to determine future laboratory experiments which will explore A?clumpyA? jet propagation issues.

Experimental characterization of a transition from collisionless to collisional interaction between head-on-merging supersonic plasma jets a)

DOE PAGES

Moser, Auna L.; Hsu, Scott C.

2015-05-01

We present results from experiments on the head-on merging of two supersonic plasma jets in an initially collisionless regime for the counter-streaming ions [A. L. Moser & S. C. Hsu, Phys. Plasmas, submitted (2014)]. The plasma jets are of either an argon/impurity or hydrogen/impurity mixture and are produced by pulsed-power-driven railguns. Based on time- and space-resolved fast-imaging, multi-chord interferometry, and survey-spectroscopy measurements of the overlapping region between the merging jets, we observe that the jets initially interpenetrate, consistent with calculated inter-jet ion collision lengths, which are long. As the jets interpenetrate, a rising mean-charge state causes a rapid decrease inmore » the inter-jet ion collision length. Finally, the interaction becomes collisional and the jets stagnate, eventually producing structures consistent with collisional shocks. These experimental observations can aid in the validation of plasma collisionality and ionization models for plasmas with complex equations of state.« less

Experimental characterization of a transition from collisionless to collisional interaction between head-on-merging supersonic plasma jets a)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moser, Auna L.; Hsu, Scott C.

We present results from experiments on the head-on merging of two supersonic plasma jets in an initially collisionless regime for the counter-streaming ions [A. L. Moser & S. C. Hsu, Phys. Plasmas, submitted (2014)]. The plasma jets are of either an argon/impurity or hydrogen/impurity mixture and are produced by pulsed-power-driven railguns. Based on time- and space-resolved fast-imaging, multi-chord interferometry, and survey-spectroscopy measurements of the overlapping region between the merging jets, we observe that the jets initially interpenetrate, consistent with calculated inter-jet ion collision lengths, which are long. As the jets interpenetrate, a rising mean-charge state causes a rapid decrease inmore » the inter-jet ion collision length. Finally, the interaction becomes collisional and the jets stagnate, eventually producing structures consistent with collisional shocks. These experimental observations can aid in the validation of plasma collisionality and ionization models for plasmas with complex equations of state.« less

New angles on energy correlation functions

DOE PAGES

Moult, Ian; Necib, Lina; Thaler, Jesse

2016-12-29

Jet substructure observables, designed to identify specific features within jets, play an essential role at the Large Hadron Collider (LHC), both for searching for signals beyond the Standard Model and for testing QCD in extreme phase space regions. In this paper, we systematically study the structure of infrared and collinear safe substructure observables, defining a generalization of the energy correlation functions to probe n-particle correlations within a jet. These generalized correlators provide a flexible basis for constructing new substructure observables optimized for specific purposes. Focusing on three major targets of the jet substructure community — boosted top tagging, boosted W/Z/Hmore » tagging, and quark/gluon discrimination — we use power-counting techniques to identify three new series of powerful discriminants: M i, N i, and U i. The Mi series is designed for use on groomed jets, providing a novel example of observables with improved discrimination power after the removal of soft radiation. The N i series behave parametrically like the N -subjettiness ratio observables, but are defined without respect to subjet axes, exhibiting improved behavior in the unresolved limit. Finally, the U i series improves quark/gluon discrimination by using higher-point correlators to simultaneously probe multiple emissions within a jet. Taken together, these observables broaden the scope for jet substructure studies at the LHC.« less

New angles on energy correlation functions

NASA Astrophysics Data System (ADS)

Moult, Ian; Necib, Lina; Thaler, Jesse

2016-12-01

Jet substructure observables, designed to identify specific features within jets, play an essential role at the Large Hadron Collider (LHC), both for searching for signals beyond the Standard Model and for testing QCD in extreme phase space regions. In this paper, we systematically study the structure of infrared and collinear safe substructure observables, defining a generalization of the energy correlation functions to probe n-particle correlations within a jet. These generalized correlators provide a flexible basis for constructing new substructure observables optimized for specific purposes. Focusing on three major targets of the jet substructure community — boosted top tagging, boosted W/Z/H tagging, and quark/gluon discrimination — we use power-counting techniques to identify three new series of powerful discriminants: M i , N i , and U i . The M i series is designed for use on groomed jets, providing a novel example of observables with improved discrimination power after the removal of soft radiation. The N i series behave parametrically like the N -subjettiness ratio observables, but are defined without respect to subjet axes, exhibiting improved behavior in the unresolved limit. Finally, the U i series improves quark/gluon discrimination by using higher-point correlators to simultaneously probe multiple emissions within a jet. Taken together, these observables broaden the scope for jet substructure studies at the LHC.

Hubble Space Telescope scale 3D simulations of MHD disc winds: a rotating two-component jet structure

NASA Astrophysics Data System (ADS)

Staff, J. E.; Koning, N.; Ouyed, R.; Thompson, A.; Pudritz, R. E.

2015-02-01

We present the results of large scale, three-dimensional magnetohydrodynamics simulations of disc winds for different initial magnetic field configurations. The jets are followed from the source to 90 au scale, which covers several pixels of Hubble Space Telescope images of nearby protostellar jets. Our simulations show that jets are heated along their length by many shocks. We compute the emission lines that are produced, and find excellent agreement with observations. The jet width is found to be between 20 and 30 au while the maximum velocities perpendicular to the jet are found to be up to above 100 km s-1. The initially less open magnetic field configuration simulations result in a wider, two-component jet; a cylindrically shaped outer jet surrounding a narrow and much faster, inner jet. These simulations preserve the underlying Keplerian rotation profile of the inner jet to large distances from the source. However, for the initially most open magnetic field configuration the kink mode creates a narrow corkscrew-like jet without a clear Keplerian rotation profile and even regions where we observe rotation opposite to the disc (counter-rotating). The RW Aur jet is narrow, indicating that the disc field in that case is very open meaning the jet can contain a counter-rotating component that we suggest explains why observations of rotation in this jet have given confusing results. Thus magnetized disc winds from underlying Keplerian discs can develop rotation profiles far down the jet that is not Keplerian.

Particle Acceleration, Magnetic Field Generation, and Emission in Relativistic Pair Jets

NASA Technical Reports Server (NTRS)

Nishikawa, K. I.; Hardee, P.; Hededal, C. B.; Richardson, G.; Sol, H.; Preece, R.; Fishman, G. J.

2004-01-01

Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman, Weibel and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic jet front propagating into an ambient plasma. We find that the growth times depend on the Lorenz factors of jets. The jets with larger Lorenz factors grow slower. Simulations show that the Weibel instability created in the collisionless shock front accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. The small scale magnetic field structure generated by the Weibel instability is appropriate to the generation of "jitter" radiation from deflected electrons (positrons) as opposed to synchrotron radiation. The jitter radiation resulting from small scale magnetic field structures may be important for understanding the complex time structure and spectral evolution observed in gamma-ray bursts or other astrophysical sources containing relativistic jets and relativistic collisionless shocks.

Observations of Seven Blue/Gigantic Jets above One Storm over the Atlantic Ocean

NASA Astrophysics Data System (ADS)

Liu, N.; Spiva, N.; Dwyer, J. R.; Rassoul, H.; Free, D. L.; Cummer, S. A.

2013-12-01

Blue/gigantic jets are electrical discharges developing from thundercloud tops and propagating to the upper atmosphere [e.g., Pasko et al., Nature, 416, 152, 2002; Su et al., Nature, 423, 973, 2003]. Not just producing an impressive display, gigantic jets establish a direct path of electrical contact between the upper troposphere and the lower ionosphere, capable of transferring a large amount of charge between them [Cummer et al., Nat. Geosci., 2, 617, 2009]. It has been suggested that they may play an important role in the earth's electrical environment [e. g., Pasko, Nature, 423, 927, 2003]. Upward discharges from thunderstorms like blue/gigantic jets are believed to originate from lightning leaders escaping from thunderclouds when the cloud's charges of different polarities are not balanced [Krehbiel et al., Nat. Geosci., 1, 233, 2008; Riousset et al., JGR, 115, A00E10, 2010]. On the evening of August 2, 2013, 4 gigantic jets, 2 blue jets and 1 blue starter were recorded within 26 min above a storm over the Atlantic Ocean by a low light level camera from the campus of Florida Institute of Technology. The events were also captured by two all-sky cameras: one again from the Florida Tech campus and the other from a nearby location. According to the NLDN data, positive intra-cloud flashes preceded all events except one gigantic jet. The distance between the observation site to the locations of the NLDN lightning discharges varies from 77 to 82 km. Optical signatures of intra-cloud discharge activities accompanied the events are clearly visible in the videos. The duration of each jet varies from about 300 ms to 1.2 s, and the 1.2 s duration is probably the longest that has been reported to date for jets. Rebrightening of gigantic jet structures occurs for at least two of the events. The upper terminal altitude of the 4 gigantic jets is greater than 76-81 km, the 2 blue jets reach about 48 and 51 km altitude, respectively, and the blue starter reaches 24 km altitude. The altitude of cloud tops varies from 14 to 20 km. All events exhibit a tree-like structure and develop in an impulsive manner. Similar to other observations of gigantic jets, bright beads appear at the tops of the gigantic jets. The impulsive upward propagation of the jets together with the positive polarity of the preceding intra-cloud discharges suggests that the jets originate from upward propagating negative leaders initiated inside the thundercloud. All events propagate upward from the top of the cloud nearly vertically except for one event that develops in a slanted direction, about twenty three degrees from the vertical. With only a few branches, the three blue jet/starter events display a structure very similar to a cloud-to-ground lightning stroke. Our observations support the unified view of the upward discharges from thunderclouds advanced by Krehbiel et al. [2008] and Riousset et al. [2010]. In this talk, we discuss the video observations of the events and the associated radio signatures in detail.

The inner radio structure of Centaurus A - Clues to the origin of the jet X-ray emission

NASA Technical Reports Server (NTRS)

Burns, J. O.; Feigelson, E. D.; Schreier, E. J.

1983-01-01

VLA observations at 1.4 and 4.9 GHz of the jet and inner lobes of the nearby radio galaxy Centaurus A have been used to construct maps of total intensity and polarization at resolutions of 31 x 10 and 3.6 x 1.1 arcsec. Surface brightness and pressure distributions in the jet, combined with the apparent X-ray emission from the ISM of NGC 5128, indicate that it is thermally confined. A comparison of the radio structure and the optical galaxy shows that the jet in Cen A emerges nearly along the major axis of the elliptical stellar component that is parallel to the angular momentum vector of the dust lane. The outer radio structure bends toward the galaxy minor axis. Evidence is found for a common synchrotron radiation origin of the full spectrum jet emission.

Reconnection Processes in the Chromosphere and Corona

NASA Astrophysics Data System (ADS)

Shibata, Kazunari

2012-07-01

Magnetic reconnection is a fundamental key physical process in magnetized plasmas. Recent space solar observations revealed that magnetic reconnection is ubiquitous in the solar chromospheres and corona. Especially recent Hinode observations has found various types of tiny chromospheric jets, such as chromospheric anemone jets (Shibata et al. 2007), penumbral microjets (Katsukawa et al. 2007), light bridge jets from sunspot umbra (Shimizu et al. 2009), etc. It was also found that the corona is full of tiny X-ray jets (Cirtain et al. 2007). Often they are seen as helical spinning jets (Shimojo et al. 2007, Patsourakos et al. 2008, Pariat et al. 2009, Filippov et al. 2009, Kamio et al. 2010) with Alfvenic waves (Nishizuka et al. 2008, Liu et al. 2009) and there are increasing evidence of magnetic reconnection in these tiny jets. We can now say that as spatial resolution of observations become better and better, smaller and smaller flares and jets have been discovered, which implies that the magnetized solar atmosphere consist of fractal structure and dynamics, i.e., fractal reconnection. Bursty radio and hard X-ray emissions from flares also suggest the fractal reconnection and associated particle acceleration. Since magnetohydrodynamics (MHD) does not contain any characteristic length and time scale, it is natural that MHD structure, dynamics, and reconnection, tend to become fractal in ideal MHD plasmas with large magnetic Reynolds number such as in the solar atmosphere. We would discuss recent observations and theories related to fractal reconnection in the chromospheres and corona, and discuss possible implication to chromospheric and coronal heating.

Axial plasma jet characterization on a microsecond x-pinch

NASA Astrophysics Data System (ADS)

Jaar, G. S.; Appartaim, R. K.

2018-06-01

The jets produced on a microsecond x-pinch (quarter period T1/4 ˜ 1 μs, dI/dt ˜ 0.35 kA/ns) have been studied through light-field schlieren imaging and optical framing photographs across 4 different materials: Al, Ti, Mo, and W. The axial velocity of the jets was measured and exhibited no dependence on atomic number (Z) of the wire material. There may be a dependence on another factor(s), namely, the current rise rate. The average axial jet velocity across all four materials was measured to be 2.9 ± 0.5 × 106 cm/s. The average jet diameter and the average radial jet expansion rate displayed inverse relationships with Z, which may be attributed to radiative cooling and inertia. Asymmetry between the anode and cathode jet behavior was observed and is thought to be caused by electron beam activity. The mean divergence angle of the jet was found to vary with wire material and correlated inversely with the thermal conductivity of the cold wire. Optical images indicated a two-layer structure in Al jets which may be caused by standing shocks and resemble phenomena observed in astrophysical jet formation and collimation. Kinks in the jets have also been observed which may be caused by m = 1 MHD instability modes or by the interaction of the jet with the electrode plasma.

Effect of Swirl on Turbulent Structures in Supersonic Jets

NASA Technical Reports Server (NTRS)

Rao, Ram Mohan; Lundgren, Thomas S.

1998-01-01

Direct Numerical Simulation (DNS) is used to study the mechanism of generation and evolution of turbulence structures in a temporally evolving supersonic swirling round jet and also to examine the resulting acoustic radiations. Fourier spectral expansions are used in the streamwise and azimuthal directions and a 1-D b-spline Galerkin representation is used in the radial direction. Spectral-like accuracy is achieved using this numerical scheme. Direct numerical simulations, using the b-spline spectral method, are carried out starting from mean flow initial conditions which are perturbed by the most unstable linear stability eigenfunctions. It is observed that the initial helical instability waves evolve into helical vortices which eventually breakdown into smaller scales of turbulence. 'Rib' structures similar to those seen in incompressible mixing layer flow of Rogers and Moserl are observed. The jet core breakdown stage exhibits increased acoustic radiations.

Evidence for a nuclear radio jet and its structure down to ≲100 Schwarzschild radii in the center of the Sombrero galaxy (M 104, NGC 4594)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hada, Kazuhiro; Giroletti, Marcello; Giovannini, Gabriele

2013-12-10

The Sombrero galaxy (M 104, NGC 4594) is associated with one of the nearest low-luminosity active galactic nuclei (AGNs). We investigated the detailed radio structure of the Sombrero nucleus using high-resolution, quasi-simultaneous, multi-frequency, phase-referencing Very Long Baseline Array observations. We obtained high-quality images of this nucleus at seven frequencies, where those at 15, 24, and 43 GHz are the first clear very long baseline interferometry detections. At 43 GHz, the nuclear structure was imaged on a linear scale under 0.01 pc or 100 Schwarzschild radii, revealing a compact, high-brightness-temperature (≳ 3 × 10{sup 9} K) radio core. We discovered themore » presence of the extended structure emanating from the core on two sides in the northwest and southeast directions. The nuclear radio spectra show a clear spatial gradient, which is similar to that seen in more luminous AGNs with powerful relativistic jets. Moreover, the size and position of the core tend to be frequency dependent. These findings provide evidence that the central engine of the Sombrero is powering radio jets and the jets are overwhelming the emission from the underlying radiatively inefficient accretion flow over the observed frequencies. Based on these radio characteristics, we constrained the following physical parameters for the M 104 jets: (1) the northern side is approaching, whereas the southern one is receding; (2) the jet viewing angle is relatively close to our line-of-sight (≲ 25°); and (3) the intrinsic jet velocity is highly sub-relativistic (≲ 0.2c). The derived pole-on nature of the M 104 jets is consistent with the previous argument that this nucleus contains a true type II AGN, i.e., the broad line region is actually absent or intrinsically weak if the plane of the circumnuclear torus is perpendicular to the jet axis.« less

A KPC-scale X-ray jet in the BL LAC Source S5 2007+777

NASA Technical Reports Server (NTRS)

Sambruna, Rita; Maraschi, Laura; Tavecchio, Fabrizio

2008-01-01

The BL Lac S3 2007++777, a classical radio-selected BL Lac from the sample of Stirkel et al. exhibiting an extended (19") radio jet. was observed with Chandra revealing an X-ray jet with simi1ar morphology. The hard X-ray spectrum and broad band SED is consistent with an IC/CMB origin for the X-ray emission, implying a highly relativistic flow at small angle to the line of sight with an unusually large deprojected length, 300 kpc. A structured jet consisting of a fast spine and slow wall is consistent with the observations.

Successive Two-sided Loop Jets Caused by Magnetic Reconnection between Two Adjacent Filamentary Threads

NASA Astrophysics Data System (ADS)

Tian, Zhanjun; Liu, Yu; Shen, Yuandeng; Elmhamdi, Abouazza; Su, Jiangtao; Liu, Ying D.; Kordi, Ayman. S.

2017-08-01

We present observational analysis of two successive two-sided loop jets observed by the ground-based New Vacuum Solar Telescope and the space-borne Solar Dynamics Observatory. The two successive two-sided loop jets manifested similar evolution processes and both were associated with the interaction of two small-scale adjacent filamentary threads, magnetic emerging, and cancellation processes at the jet’s source region. High temporal and high spatial resolution observations reveal that the two adjacent ends of the two filamentary threads are rooted in opposite magnetic polarities within the source region. The two threads approached each other, and then an obvious brightening patch is observed at the interaction position. Subsequently, a pair of hot plasma ejections are observed heading in opposite directions along the paths of the two filamentary threads at a typical speed for two-sided loop jets of the order 150 km s-1. Close to the end of the second jet, we report the formation of a bright hot loop structure at the source region, which suggests the formation of new loops during the interaction. Based on the observational results, we propose that the observed two-sided loop jets are caused by magnetic reconnection between the two adjacent filamentary threads, largely different from the previous scenario that a two-sided loop jet is generated by magnetic reconnection between an emerging bipole and the overlying horizontal magnetic fields.

Experimental and Computational Study of Sonic and Supersonic Jet Plumes

NASA Technical Reports Server (NTRS)

Venkatapathy, E.; Naughton, J. W.; Fletcher, D. G.; Edwards, Thomas A. (Technical Monitor)

1994-01-01

Study of sonic and supersonic jet plumes are relevant to understanding such phenomenon as jet-noise, plume signatures, and rocket base-heating and radiation. Jet plumes are simple to simulate and yet, have complex flow structures such as Mach disks, triple points, shear-layers, barrel shocks, shock-shear-layer interaction, etc. Experimental and computational simulation of sonic and supersonic jet plumes have been performed for under- and over-expanded, axisymmetric plume conditions. The computational simulation compare very well with the experimental observations of schlieren pictures. Experimental data such as temperature measurements with hot-wire probes are yet to be measured and will be compared with computed values. Extensive analysis of the computational simulations presents a clear picture of how the complex flow structure develops and the conditions under which self-similar flow structures evolve. From the computations, the plume structure can be further classified into many sub-groups. In the proposed paper, detail results from the experimental and computational simulations for single, axisymmetric, under- and over-expanded, sonic and supersonic plumes will be compared and the fluid dynamic aspects of flow structures will be discussed.

Sonic and Supersonic Jet Plumes

NASA Technical Reports Server (NTRS)

Venkatapathy, E.; Naughton, J. W.; Flethcher, D. G.; Edwards, Thomas A. (Technical Monitor)

1994-01-01

Study of sonic and supersonic jet plumes are relevant to understanding such phenomenon as jet-noise, plume signatures, and rocket base-heating and radiation. Jet plumes are simple to simulate and yet, have complex flow structures such as Mach disks, triple points, shear-layers, barrel shocks, shock- shear- layer interaction, etc. Experimental and computational simulation of sonic and supersonic jet plumes have been performed for under- and over-expanded, axisymmetric plume conditions. The computational simulation compare very well with the experimental observations of schlieren pictures. Experimental data such as temperature measurements with hot-wire probes are yet to be measured and will be compared with computed values. Extensive analysis of the computational simulations presents a clear picture of how the complex flow structure develops and the conditions under which self-similar flow structures evolve. From the computations, the plume structure can be further classified into many sub-groups. In the proposed paper, detail results from the experimental and computational simulations for single, axisymmetric, under- and over-expanded, sonic and supersonic plumes will be compared and the fluid dynamic aspects of flow structures will be discussed.

The stratified two-sided jet of Cygnus A. Acceleration and collimation

NASA Astrophysics Data System (ADS)

Boccardi, B.; Krichbaum, T. P.; Bach, U.; Mertens, F.; Ros, E.; Alef, W.; Zensus, J. A.

2016-01-01

Aims: High-resolution Very-Long-Baseline Interferometry (VLBI) observations of relativistic jets are essential for constraining the fundamental parameters of jet formation models. At a distance of 249 Mpc, Cygnus A is a unique target for such studies, since it is the only Fanaroff-Riley Class II radio galaxy for which a detailed subparsec scale imaging of the base of both jet and counter-jet can be obtained. Observing at millimeter wavelengths unveils those regions that appear self-absorbed at longer wavelengths and enables an extremely sharp view toward the nucleus to be obtained. Methods: We performed 7 mm Global VLBI observations, achieving ultra-high resolution imaging on scales down to 90 μas. This resolution corresponds to a linear scale of only ~400 Schwarzschild radii (for MBH = 2.5 × 109M⊙). We studied the kinematic properties of the main emission features of the two-sided flow and probed its transverse structure through a pixel-based analysis. Results: We suggest that a fast and a slow layer with different acceleration gradients exist in the flow. The extension of the acceleration region is large (~ 104RS), indicating that the jet is magnetically driven. The limb brightening of both jet and counter-jet and their large opening angles (φJ ~ 10°) strongly favour a spine-sheath structure. In the acceleration zone, the flow has a parabolic shape (r ∝ z0.55 ± 0.07). The acceleration gradients and the collimation profile are consistent with the expectations for a jet in "equilibrium", achieved in the presence of a mild gradient of the external pressure (p ∝ z- k,k ≤ 2).

RESOLVING THE ROTATION MEASURE OF THE M87 JET ON KILOPARSEC SCALES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Algaba, J. C.; Asada, K.; Nakamura, M., E-mail: algaba@asiaa.sinica.edu.tw

2016-06-01

We investigate the distribution of Faraday rotation measure (RM) in the M87 jet at arcsecond scales by using archival polarimetric Very Large Array data at 8, 15, 22 and 43 GHz. We resolve the structure of the RM in several knots along the jet for the first time. We derive the power spectrum in the arcsecond-scale jet and find indications that the RM cannot be associated with a turbulent magnetic field with a 3D Kolmogorov spectrum. Our analysis indicates that the RM probed on jet scales has a significant contribution of a Faraday screen associated with the vicinity of themore » jet, in contrast with that on kiloparsec scales, typically assumed to be disconnected from the jet. Comparison with previous RM analyses suggests that the magnetic fields giving rise to the RMs observed in jet scales have different properties and are well less turbulent than those observed in the lobes.« less

The nearest X-ray emitting protostellar jet (HH 154) observed with Hubble

NASA Astrophysics Data System (ADS)

Bonito, R.; Fridlund, C. V. M.; Favata, F.; Micela, G.; Peres, G.; Djupvik, A. A.; Liseau, R.

2008-06-01

Context: The jet coming from the YSO binary L1551 IRS5 is the closest astrophysical jet known. It is therefore a unique laboratory for studies of outflow mechanisms and of the shocks occurring when expanding material hits the ambient medium as well as of how the related processes influence the star- (and planet-) forming process. Aims: The optical data are related to other data covering the spectrum from the optical band to X-rays with goal of understanding the energetics of low-mass star jets, in general, and of this jet in particular. We study the time evolution of the jet, by measuring the proper motions of knots as they progress outwards from the originating source. Methods: The nebulosities associated with the jet(s) from the protostellar binary L1551 IRS5 were imaged in a number of spectral bands using the Hubble Space Telescope. This allows the proper motion to be measured and permits a simple characterization of the physical conditions in different structures. To this end we developed a reproducible method of data analysis, which allows us to define the position and shape of each substructure observed within the protostellar jet. Using this approach, we derive the proper motion of the knots in the jet, as well as their flux variability and shock emission. Results: The time base over which HST observations were carried out is now about ten years. The sub-structures within the jet undergo significant morphological variations: some knots seem to disappear in a few years and collision between different knots, ejected at different epochs and maybe with different speed, may occur. The velocities along the jet vary between ~100 km s-1 and over 400 km s-1, with the highest speed corresponding to the knots at the base of the jet. Conclusions: There are indications that the HH 154 jet has been active relatively recently. Our results suggest the presence of a new shock front at the base of the jet identified with an internal working surface. From the analysis of the terminal and internal working surfaces within the jet, we find that the more likely scenario for the HH 154 jet is that of a jet traveling through a denser ambient medium (a “light jet”). These results are consistent with the Bonito et al. (2007) model predictions. Furthermore, there is strong evidence that the knots at the base of the northern jet correspond to the location where the highest velocity and the highest excitation component are measured along the jet. More important, this is the location where the X-ray source has been discovered. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs #6127, #6411 & #10351.

Flame behavior and thermal structure of combusting plane jets with and without self-excited transverse oscillations

NASA Astrophysics Data System (ADS)

Huang, Rong Fung; Kivindu, Reuben Mwanza; Hsu, Ching Min

2017-12-01

The flame behavior and thermal structure of combusting plane jets with and without self-excited transverse oscillations were investigated experimentally. The transversely-oscillating plane jet was generated by a specially designed fluidic oscillator. Isothermal flow patterns were observed using the laser-assisted smoke flow visualization method. Meanwhile, the flame behaviour was studied using instantaneous and long-exposure photography techniques. Temperature distributions and combustion-product concentrations were measured using a fine-wire type R thermocouple and a gas analyzer, respectively. The results showed that the combusting transversely-oscillating plane jets had distributed turbulent blue flames with plaited-like edges, while the corresponding combusting non-oscillating plane jet had laminar blue-edged flames in the near field. At a high Reynolds number, the transversely-oscillating jet flames were significantly shorter and wider with shorter reaction-dominated zones than those of the non-oscillating plane jet flames. In addition, the transversely-oscillating combusting jets presented larger carbon dioxide and smaller unburned hydrocarbon concentrations, as well as portrayed characteristics of partially premixed flames. The non-oscillating combusting jets presented characteristics of diffusion flames, and the transversely-oscillating jet flame had a combustion performance superior to its non-oscillating plane jet flame counterpart. The high combustion performance of the transversely-oscillating jets was due to the enhanced entrainment, mixing, and lateral spreading of the jet flow, which were induced by the vortical flow structure generated by lateral periodic jet oscillations, as well as the high turbulence created by the breakup of the vortices.

Flame behavior and thermal structure of combusting plane jets with and without self-excited transverse oscillations

NASA Astrophysics Data System (ADS)

Huang, Rong Fung; Kivindu, Reuben Mwanza; Hsu, Ching Min

2018-06-01

The flame behavior and thermal structure of combusting plane jets with and without self-excited transverse oscillations were investigated experimentally. The transversely-oscillating plane jet was generated by a specially designed fluidic oscillator. Isothermal flow patterns were observed using the laser-assisted smoke flow visualization method. Meanwhile, the flame behaviour was studied using instantaneous and long-exposure photography techniques. Temperature distributions and combustion-product concentrations were measured using a fine-wire type R thermocouple and a gas analyzer, respectively. The results showed that the combusting transversely-oscillating plane jets had distributed turbulent blue flames with plaited-like edges, while the corresponding combusting non-oscillating plane jet had laminar blue-edged flames in the near field. At a high Reynolds number, the transversely-oscillating jet flames were significantly shorter and wider with shorter reaction-dominated zones than those of the non-oscillating plane jet flames. In addition, the transversely-oscillating combusting jets presented larger carbon dioxide and smaller unburned hydrocarbon concentrations, as well as portrayed characteristics of partially premixed flames. The non-oscillating combusting jets presented characteristics of diffusion flames, and the transversely-oscillating jet flame had a combustion performance superior to its non-oscillating plane jet flame counterpart. The high combustion performance of the transversely-oscillating jets was due to the enhanced entrainment, mixing, and lateral spreading of the jet flow, which were induced by the vortical flow structure generated by lateral periodic jet oscillations, as well as the high turbulence created by the breakup of the vortices.

Evidence for the Magnetic Breakout Model in an Equatorial Coronal-hole Jet

NASA Astrophysics Data System (ADS)

Kumar, Pankaj; Karpen, Judith T.; Antiochos, Spiro K.; Wyper, Peter F.; DeVore, C. Richard; DeForest, Craig E.

2018-02-01

Small, impulsive jets commonly occur throughout the solar corona, but are especially visible in coronal holes. Evidence is mounting that jets are part of a continuum of eruptions that extends to much larger coronal mass ejections and eruptive flares. Because coronal-hole jets originate in relatively simple magnetic structures, they offer an ideal testbed for theories of energy buildup and release in the full range of solar eruptions. We analyzed an equatorial coronal-hole jet observed by the Solar Dynamics Observatory (SDO)/AIA on 2014 January 9 in which the magnetic-field structure was consistent with the embedded-bipole topology that we identified and modeled previously as an origin of coronal jets. In addition, this event contained a mini-filament, which led to important insights into the energy storage and release mechanisms. SDO/HMI magnetograms revealed footpoint motions in the primary minority-polarity region at the eruption site, but show negligible flux emergence or cancellation for at least 16 hr before the eruption. Therefore, the free energy powering this jet probably came from magnetic shear concentrated at the polarity inversion line within the embedded bipole. We find that the observed activity sequence and its interpretation closely match the predictions of the breakout jet model, strongly supporting the hypothesis that the breakout model can explain solar eruptions on a wide range of scales.

Evidence for the Magnetic Breakout Model in an Equatorial Coronal-Hole Jet

NASA Technical Reports Server (NTRS)

Kumar, Pankaj; Karpen, Judith T.; Antiochos, Spiro K.; Wyper, Peter F.; Devore, C. Richard; DeForest, Craig E.

2018-01-01

Small, impulsive jets commonly occur throughout the solar corona, but are especially visible in coronal holes. Evidence is mounting that jets are part of a continuum of eruptions that extends to much larger coronal mass ejections and eruptive flares. Because coronal-hole jets originate in relatively simple magnetic structures, they offer an ideal testbed for theories of energy buildup and release in the full range of solar eruptions. We analyzed an equatorial coronal-hole jet observed by the Solar Dynamics Observatory (SDO)/AIA (Atmospheric Imaging Assembly)) on 2014 January 9 in which the magnetic-field structure was consistent with the embedded-bipole topology that we identified and modeled previously as an origin of coronal jets. In addition, this event contained a mini-filament, which led to important insights into the energy storage and release mechanisms. SDO/HMI (Solar Dynamics Observatory/Helioseismic and Magnetic Imager) magnetograms revealed footpoint motions in the primary minority-polarity region at the eruption site, but show negligible flux emergence or cancellation for at least 16 hours before the eruption. Therefore, the free energy powering this jet probably came from magnetic shear concentrated at the polarity inversion line within the embedded bipole. We find that the observed activity sequence and its interpretation closely match the predictions of the breakout jet model, strongly supporting the hypothesis that the breakout model can explain solar eruptions on a wide range of scales.

GRB 170817A as a jet counterpart to gravitational wave trigger GW 170817

NASA Astrophysics Data System (ADS)

Lamb, Gavin P.; Kobayashi, Shiho

2018-05-01

Fermi/GBM (Gamma-ray Burst Monitor) and INTEGRAL (the International Gamma-ray Astrophysics Laboratory) reported the detection of the γ-ray counterpart, GRB 170817A, to the LIGO (Light Interferometer Gravitational-wave Observatory)/Virgo gravitational wave detected binary neutron star merger, GW 170817. GRB 170817A is likely to have an internal jet or another origin such as cocoon emission, shock-breakout, or a flare from a viscous disc. In this paper we assume that the γ-ray emission is caused by energy dissipation within a relativistic jet and we model the afterglow synchrotron emission from a reverse- and forward-shock in the outflow. We show the afterglow for a low-luminosity γ-ray burst (GRB) jet with a high Lorentz-factor (Γ); a low-Γ and low-kinetic energy jet; a low-Γ, high kinetic energy jet; structured jets viewed at an inclination within the jet-half-opening angle; and an off-axis `typical' GRB jet. All jet models will produce observable afterglows on various timescales. The late-time afterglow from 10-110 days can be fit by a Gaussian structured jet viewed at a moderate inclination, however the GRB is not directly reproduced by this model. These jet afterglow models can be used for future GW detected NS merger counterparts with a jet afterglow origin.

Fabrication and characterization of anode catalyst layers with structural variations for DMFC

NASA Astrophysics Data System (ADS)

Wang, Dazhi; Shi, Peng; Zhou, Peng; Mao, Qing; Liang, Junsheng; Wang, Suli; Li, Yang; Ren, Tongqun; Sun, Gongquan

2018-04-01

In this work, the electrohydrodynamic jet (E-Jet) Layer-by-Layer (LbL) deposition technique was employed to produce anode catalyst layer (CL) structure for direct methanol fuel cells (DMFC). The CLs with different thickness and porosity were fabricated with the control of the E-Jet deposition parameters. Then, the deposited anode CLs with structural variations were assembled to membrane electrode assemblies (MEAs). The results showed that the anode CL with higher porosity contributed higher dispersed catalyst, which further induced greater electrochemical active surface area (ESA) and higher performance. At optimized working condition the anode CL with high-dispersed catalyst of was produced using the E-Jet LbL deposition technique. It was observed that the peak power density is 72.8 mW cm‑2 for the cell having a porosity of 0.63, which has an increase of about 33% after modification of the CL structure.

A cosmic double helix in the archetypical quasar 3C273.

PubMed

Lobanov, A P; Zensus, J A

2001-10-05

Finding direct evidence for plasma instability in extragalactic jets is crucial for understanding the nature of relativistic outflows from active galactic nuclei. Our radio interferometric observations of the quasar 3C273 made with the orbiting radio telescope, HALCA, and an array of ground telescopes have yielded an image in which the emission across the jet is resolved, revealing two threadlike patterns that form a double helix inside the jet. This double helical structure is consistent with a Kelvin-Helmholtz instability, and at least five different instability modes can be identified and modeled by a light jet with a Lorentz factor of 2 and Mach number of 3.5. The model reproduces in detail the internal structure of the jet on scales of up to 30 milli-arc seconds ( approximately 300 parsecs) and is consistent with the general morphology of the jet on scales of up to 1 kiloparsec.

Collimated Outflow Formation via Binary Stars: Three-Dimensional Simulations of Asymptotic Giant Branch Wind and Disk Wind Interactions

NASA Astrophysics Data System (ADS)

García-Arredondo, F.; Frank, Adam

2004-01-01

We present three-dimensional hydrodynamic simulations of the interaction of a slow wind from an asymptotic giant branch (AGB) star and a jet blown by an orbiting companion. The jet or ``collimated fast wind'' is assumed to originate from an accretion disk that forms via Bondi accretion of the AGB wind or Roche lobe overflow. We present two distinct regimes in the wind-jet interaction determined by the ratio of the AGB wind to jet momentum flux. Our results show that when the wind momentum flux overwhelms the flux in the jet, a more disordered outflow results with the jet assuming a corkscrew pattern and multiple shock structures driven into the AGB wind. In the opposite regime, the jet dominates and will drive a highly collimated, narrow-waisted outflow. We compare our results with scenarios described by Soker & Rappaport and extrapolate to the structures observed in planetary nebulae (PNs) and symbiotic stars.

Small-Scale Activity Above the Penumbra of a Fast-Rotating Sunspot

NASA Astrophysics Data System (ADS)

Bharti, L.; Quintero Noda, C.; Rakesh, S.; Sobha, B.; Pandya, A.; Joshi, C.

2018-03-01

High-resolution observations of small-scale activity above the filamentary structure of a fast-rotating sunspot of NOAA Active Region 10930 are presented. The penumbral filament that intrudes into the umbra shows a central dark core and substructures. It almost approached another end of the umbra, like a light bridge. The chromospheric Ca ii H images show many jet-like structures with a bright leading edge above it. These bright jets move across the filament tips and show coordinated up and down motions. Transition region images also show brightening at the same location above the intrusion. Coronal 195 Å images suggest that one end of the bright coronal loop footpoints resides in this structure. The intrusion has opposite polarity with respect to the umbra. Strong downflows are observed at the edges along the length of the intrusion where the opposite-polarity field is enhanced. We also observe a counter-Evershed flow in the filamentary structure that also displays brightening and energy dissipation in the upper atmosphere. This scenario suggests that the jets and brightenings are caused by low-altitude reconnection driven by opposite-polarity fields and convective downflows above such structures.

Radio observations of a few selected blazars

NASA Technical Reports Server (NTRS)

Saikia, D. J.; Salter, C. J.; Neff, S. G.; Gower, A. C.; Sinha, R. P.

1987-01-01

The paper presents total-intensity and linear-polarization observations of four selected blazars, 0716+714, 0752+258, 1156+295 and 1400+162, with the VLA A-array, and MERLIN and EVN observations of 1400+162. The sources 0752+258 and 1400+162 which have nearly constant optical polarization, have well-defined double-lobed radio structure, with relatively weak radio cores, and are likely to be at large viewing angles. In addition, 0752+258 appears to be a twin-jet blazar. The position angle (PA) of the VLBI jet in 1400+162 is close to that of the arcsec-scale jet near the nucleus, as well as the optical and 2-cm core polarization PAs. The blazars 0716+714 and 1156+295, which exhibit strongly variable optical polarization, have a core-dominated radio structure and perhaps have their jet axes close to the line-of-sight. From polarization observations at 20, 18, 6, and 2 cm, it is found that the rotation measure of the radio core in 0716+714 is about -20 rad/sq m. It is suggested that low values of core rotation measure in core-dominated sources could be consistent with the relativistic beaming models.

A model for straight and helical solar jets: II. Parametric study of the plasma beta.

PubMed

Pariat, E; Dalmasse, K; DeVore, C R; Antiochos, S K; Karpen, J T

2016-12-01

Jets are dynamic, impulsive, well-collimated plasma events that develop at many different scales and in different layers of the solar atmosphere. Jets are believed to be induced by magnetic reconnection, a process central to many astrophysical phenomena. Within the solar atmosphere, jet-like events develop in many different environments, e.g., in the vicinity of active regions as well as in coronal holes, and at various scales, from small photospheric spicules to large coronal jets. In all these events, signatures of helical structure and/or twisting/rotating motions are regularly observed. The present study aims to establish that a single model can generally reproduce the observed properties of these jet-like events. In this study, using our state-of-the-art numerical solver ARMS, we present a parametric study of a numerical tridimensional magnetohydrodynamic (MHD) model of solar jet-like events. Within the MHD paradigm, we study the impact of varying the atmospheric plasma β on the generation and properties of solar-like jets. The parametric study validates our model of jets for plasma β ranging from 10 -3 to 1, typical of the different layers and magnetic environments of the solar atmosphere. Our model of jets can robustly explain the generation of helical solar jet-like events at various β ≤ 1. This study introduces the new original result that the plasma β modifies the morphology of the helical jet, explaining the different observed shapes of jets at different scales and in different layers of the solar atmosphere. Our results allow us to understand the energisation, triggering, and driving processes of jet-like events. Our model allows us to make predictions of the impulsiveness and energetics of jets as determined by the surrounding environment, as well as the morphological properties of the resulting jets.

Solar Tornadoes Triggered by Interaction between Filaments and EUV Jets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Huadong; Zhang, Jun; Ma, Suli

We investigate the formations and evolutions of two successive solar tornadoes in/near AR 12297 during 2015 March 19–20. Recurrent EUV jets close to two filaments were detected along a large-scale coronal loop prior to the appearances of the tornadoes. Under the disturbances from the activities, the filaments continually ascended and finally interacted with the loops tracked by the jets. Subsequently, the structures of the filaments and the loop were merged together, probably via magnetic reconnections, and formed tornado-like structures with a long spiral arm. Our observations suggest that solar tornadoes can be triggered by the interaction between filaments and nearbymore » coronal jets, which has rarely been reported before. At the earlier development phase of the first tornado, about 30 small-scale sub-jets appeared in the tornado’s arm, accompanied by local EUV brightenings. They have an ejection direction approximately vertical to the axis of the arm and a typical maximum speed of ∼280 km s{sup −1}. During the ruinations of the two tornadoes, fast plasma outflows from the strong EUV brightenings inside tornadoes are observed, in company with the untangling or unwinding of the highly twisted tornado structures. These observational features indicate that self reconnections probably occurred between the tangled magnetic fields of the tornadoes and resulted in the rapid disintegrations and disappearances of the tornadoes. According to the reconnection theory, we also derive the field strength of the tornado core to be ∼8 G.« less

Solar Tornadoes Triggered by Interaction between Filaments and EUV Jets

NASA Astrophysics Data System (ADS)

Chen, Huadong; Zhang, Jun; Ma, Suli; Yan, Xiaoli; Xue, Jianchao

2017-05-01

We investigate the formations and evolutions of two successive solar tornadoes in/near AR 12297 during 2015 March 19-20. Recurrent EUV jets close to two filaments were detected along a large-scale coronal loop prior to the appearances of the tornadoes. Under the disturbances from the activities, the filaments continually ascended and finally interacted with the loops tracked by the jets. Subsequently, the structures of the filaments and the loop were merged together, probably via magnetic reconnections, and formed tornado-like structures with a long spiral arm. Our observations suggest that solar tornadoes can be triggered by the interaction between filaments and nearby coronal jets, which has rarely been reported before. At the earlier development phase of the first tornado, about 30 small-scale sub-jets appeared in the tornado’s arm, accompanied by local EUV brightenings. They have an ejection direction approximately vertical to the axis of the arm and a typical maximum speed of ˜280 km s-1. During the ruinations of the two tornadoes, fast plasma outflows from the strong EUV brightenings inside tornadoes are observed, in company with the untangling or unwinding of the highly twisted tornado structures. These observational features indicate that self reconnections probably occurred between the tangled magnetic fields of the tornadoes and resulted in the rapid disintegrations and disappearances of the tornadoes. According to the reconnection theory, we also derive the field strength of the tornado core to be ˜8 G.

The flame structure and vorticity generated by a chemically reacting transverse jet

NASA Technical Reports Server (NTRS)

Karagozian, A. R.

1986-01-01

An analytical model describing the behavior of a turbulent fuel jet injected normally into a cross flow is developed. The model places particular emphasis on the contrarotating vortex pair associated with the jet, and predicts the flame length and shape based on entrainment of the oxidizer by the fuel jet. Effects of buoyancy and density variations in the flame are neglected in order to isolate the effects of large-scale mixing. The results are compared with a simulation of the transverse reacting jet in a liquid (acid-base) system. For a wide range of ratios of the cross flow to jet velocity, the model predicts flame length quite well. In particular, the observed transitional behavior in the flame length between cross-flow velocity to jet velocity of orifice ratios of 0.0 to 0.1, yielding an approximate minimum at the ratio 0.05, is reproduced very clearly by the present model. The transformation in flow structure that accounts for this minimum arises from the differing components of vorticity dominant in the near-field and far-field regions of the jet.

Dual-Frequency VLBI Study of Centaurus A on Sub-Parsec Scales: The Highest-Resolution View of an Extragalactic Jet

NASA Technical Reports Server (NTRS)

Mueller, C.; Kadler, M.; Ojha, R.; Wilms, J.; Boeck, M.; Edwards, P.; Fromm, C. M.; Hase, H.; Horiuchi, S.; Katz, U.;

Real-time evolution of a large-scale relativistic jet

NASA Astrophysics Data System (ADS)

Martí, Josep; Luque-Escamilla, Pedro L.; Romero, Gustavo E.; Sánchez-Sutil, Juan R.; Muñoz-Arjonilla, Álvaro J.

2015-06-01

Context. Astrophysical jets are ubiquitous in the Universe on all scales, but their large-scale dynamics and evolution in time are hard to observe since they usually develop at a very slow pace. Aims: We aim to obtain the first observational proof of the expected large-scale evolution and interaction with the environment in an astrophysical jet. Only jets from microquasars offer a chance to witness the real-time, full-jet evolution within a human lifetime, since they combine a "short", few parsec length with relativistic velocities. Methods: The methodology of this work is based on a systematic recalibraton of interferometric radio observations of microquasars available in public archives. In particular, radio observations of the microquasar GRS 1758-258 over less than two decades have provided the most striking results. Results: Significant morphological variations in the extended jet structure of GRS 1758-258 are reported here that were previously missed. Its northern radio lobe underwent a major morphological variation that rendered the hotspot undetectable in 2001 and reappeared again in the following years. The reported changes confirm the Galactic nature of the source. We tentatively interpret them in terms of the growth of instabilities in the jet flow. There is also evidence of surrounding cocoon. These results can provide a testbed for models accounting for the evolution of jets and their interaction with the environment.

A STUDY OF RADIO POLARIZATION IN PROTOSTELLAR JETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cécere, Mariana; Velázquez, Pablo F.; De Colle, Fabio

2016-01-10

Synchrotron radiation is commonly observed in connection with shocks of different velocities, ranging from relativistic shocks associated with active galactic nuclei, gamma-ray bursts, or microquasars, to weakly or non-relativistic flows such as those observed in supernova remnants. Recent observations of synchrotron emission in protostellar jets are important not only because they extend the range over which the acceleration process works, but also because they allow us to determine the jet and/or interstellar magnetic field structure, thus giving insights into the jet ejection and collimation mechanisms. In this paper, we compute for the first time polarized (synchrotron) and non-polarized (thermal X-ray)more » synthetic emission maps from axisymmetrical simulations of magnetized protostellar jets. We consider models with different jet velocities and variability, as well as a toroidal or helical magnetic field. Our simulations show that variable, low-density jets with velocities of ∼1000 km s{sup −1} and ∼10 times lighter than the environment can produce internal knots with significant synchrotron emission and thermal X-rays in the shocked region of the leading bow shock moving in a dense medium. While models with a purely toroidal magnetic field show a very large degree of polarization, models with a helical magnetic field show lower values and a decrease of the degree of polarization, in agreement with observations of protostellar jets.« less

Glider Surveys of Philippine Archipelago Seas

DTIC Science & Technology

2011-08-03

opening of the system of’ deeper straits connecting the SCS and Sulu Sea. The Sulu glider also completed a track across the Panay Gulf’ mouth -between...Observe diurnal isopycnal displacements and strain. • Examine the spatial structure of the sea’s response to Mindoro’s wind jets. • Contribute...than 1000 m. mean and -variable structure near a large reef, a sea’s response to wind jets and wakes, across-strait structure at the archipelago’s

The Most Compact Bright Radio-loud AGNs. II. VLBA Observations of 10 Sources at 43 and 86 GHz

NASA Astrophysics Data System (ADS)

Cheng, X.-P.; An, T.; Hong, X.-Y.; Yang, J.; Mohan, P.; Kellermann, K. I.; Lister, M. L.; Frey, S.; Zhao, W.; Zhang, Z.-L.; Wu, X.-C.; Li, X.-F.; Zhang, Y.-K.

2018-01-01

Radio-loud active galactic nuclei (AGNs), hosting powerful relativistic jet outflows, provide an excellent laboratory for studying jet physics. Very long baseline interferometry (VLBI) enables high-resolution imaging on milli-arcsecond (mas) and sub-mas scales, making it a powerful tool to explore the inner jet structure, shedding light on the formation, acceleration, and collimation of AGN jets. In this paper, we present Very Long Baseline Array observations of 10 radio-loud AGNs at 43 and 86 GHz that were selected from the Planck catalog of compact sources and are among the brightest in published VLBI images at and below 15 GHz. The image noise levels in our observations are typically 0.3 and 1.5 mJy beam‑1 at 43 and 86 GHz, respectively. Compared with the VLBI data observed at lower frequencies from the literature, our observations with higher resolutions (with the highest resolution being up to 0.07 mas at 86 GHz and 0.18 mas at 43 GHz) and at higher frequencies detected new jet components at sub-parsec scales, offering valuable data for studies of the physical properties of the innermost jets. These include the compactness factor of the radio structure (the ratio of core flux density to total flux density), and core brightness temperature ({T}{{b}}). In all these sources, the compact core accounts for a significant fraction (> 60 % ) of the total flux density. Their correlated flux density at the longest baselines is higher than 0.16 Jy. The compactness of these sources make them good phase calibrators of millimeter-wavelength ground-based and space VLBI.

Scaled laboratory experiments explain the kink behaviour of the Crab Nebula jet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, C. K.; Tzeferacos, P.; Lamb, D.

X-ray images from the Chandra X-ray Observatory show that the South-East jet in the Crab nebula changes direction every few years. This remarkable phenomenon is also observed in jets associated with pulsar wind nebulae and other astrophysical objects, and therefore is a fundamental feature of astrophysical jet evolution that needs to be understood. Theoretical modeling and numerical simulations have suggested that this phenomenon may be a consequence of magnetic fields (B) and current-driven magnetohydrodynamic (MHD) instabilities taking place in the jet, but until now there has been no verification of this process in a controlled laboratory environment. Here we reportmore » the first such experiments, using scaled laboratory plasma jets generated by high-power lasers to model the Crab jet and monoenergetic-proton radiography to provide direct visualization and measurement of magnetic fields and their behavior. The toroidal magnetic field embedded in the supersonic jet triggered plasma instabilities and resulted in considerable deflections throughout the jet propagation, mimicking the kinks in the Crab jet. We also demonstrated that these kinks are stabilized by high jet velocity, consistent with the observation that instabilities alter the jet orientation but do not disrupt the overall jet structure. We successfully modeled these laboratory experiments with a validated three-dimensional (3D) numerical simulation, which in conjunction with the experiments provide compelling evidence that we have an accurate model of the most important physics of magnetic fields and MHD instabilities in the observed, kinked jet in the Crab nebula. The experiments initiate a novel approach in the laboratory for visualizing fields and instabilities associated with jets observed in various astrophysical objects, ranging from stellar to extragalactic systems. We expect that future work along this line will have important impact on the study and understanding of such fundamental astrophysical phenomena.« less

Scaled laboratory experiments explain the kink behaviour of the Crab Nebula jet

DOE PAGES

Li, C. K.; Tzeferacos, P.; Lamb, D.; ...

2016-10-07

X-ray images from the Chandra X-ray Observatory show that the South-East jet in the Crab nebula changes direction every few years. This remarkable phenomenon is also observed in jets associated with pulsar wind nebulae and other astrophysical objects, and therefore is a fundamental feature of astrophysical jet evolution that needs to be understood. Theoretical modeling and numerical simulations have suggested that this phenomenon may be a consequence of magnetic fields (B) and current-driven magnetohydrodynamic (MHD) instabilities taking place in the jet, but until now there has been no verification of this process in a controlled laboratory environment. Here we reportmore » the first such experiments, using scaled laboratory plasma jets generated by high-power lasers to model the Crab jet and monoenergetic-proton radiography to provide direct visualization and measurement of magnetic fields and their behavior. The toroidal magnetic field embedded in the supersonic jet triggered plasma instabilities and resulted in considerable deflections throughout the jet propagation, mimicking the kinks in the Crab jet. We also demonstrated that these kinks are stabilized by high jet velocity, consistent with the observation that instabilities alter the jet orientation but do not disrupt the overall jet structure. We successfully modeled these laboratory experiments with a validated three-dimensional (3D) numerical simulation, which in conjunction with the experiments provide compelling evidence that we have an accurate model of the most important physics of magnetic fields and MHD instabilities in the observed, kinked jet in the Crab nebula. The experiments initiate a novel approach in the laboratory for visualizing fields and instabilities associated with jets observed in various astrophysical objects, ranging from stellar to extragalactic systems. We expect that future work along this line will have important impact on the study and understanding of such fundamental astrophysical phenomena.« less

The Flowfield Characteristics of a Mach 2 Diamond Jet

NASA Technical Reports Server (NTRS)

Washington, Donnell; Alvi, Farrukh S.; Krothapalli, Anjanevulu

1997-01-01

The potential for using a novel diamond-shaped nozzle which may allow for superior mixing characteristics of supersonic jets without significant thrust losses is explored. The results of flow visualization and pressure measurements indicate the presence of distinct structures in the shear layers, not normally observed in shear layers of axisymmetric and rectangular jets. As characteristics of these features suggests that they are a manifestation of significant streamwise vorticity in the shear layers. Despite the distinct nature of the flowfield structure of the present shear layer, the global growth rates of this shear layer were found to be very similar to its two-dimensional and axisymmetric counterparts. These and other observations suggest that the presence of streamwise vorticity may not play a significant role in the global development of a compressible shear layer.

Ordered structures and jet noise

NASA Technical Reports Server (NTRS)

Petersen, R. A.; Kaplan, R. E.; Laufer, J.

1974-01-01

A series of measurements of near field pressures and turbulent velocity fluctuations were made in a jet having a Reynolds number of about 50,000 in order to investigate more quantitatively the character and behavior of the large scale structures, and to ascertain their importance to the jet noise problem. It was found that the process of interaction between vortices can be inhibited by artificially exciting the shear layers with periodic disturbances of certain frequency. The turbulent fluctuation amplitudes measured at four diameters downstream decreased considerably. Finally, it was observed that the passage frequency of the structures decreased with x in a similar manner as the frequency corresponding to the maximum intensity radiation emanating from the same value of x.

Atmospheric-Pressure Plasma Interaction with Soft Materials as Fundamental Processes in Plasma Medicine.

PubMed

Takenaka, Kosuke; Miyazaki, Atsushi; Uchida, Giichiro; Setsuhara, Yuichi

2015-03-01

Molecular-structure variation of organic materials irradiated with atmospheric pressure He plasma jet have been investigated. Optical emission spectrum in the atmospheric-pressure He plasma jet has been measured. The spectrum shows considerable emissions of He lines, and the emission of O and N radicals attributed to air. Variation in molecular structure of Polyethylene terephthalate (PET) film surface irradiated with the atmospheric-pressure He plasma jet has been observed via X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). These results via XPS and FT-IR indicate that the PET surface irradiated with the atmospheric-pressure He plasma jet was oxidized by chemical and/or physical effect due to irradiation of active species.

Expected neutrino fluence from short Gamma-Ray Burst 170817A and off-axis angle constraints

NASA Astrophysics Data System (ADS)

Biehl, D.; Heinze, J.; Winter, W.

2018-05-01

We compute the expected neutrino fluence from SGRB 170817A, associated with the gravitational wave event GW 170817, directly based on Fermi observations in two scenarios: structured jet and off-axis (observed) top-hat jet. While the expected neutrino fluence for the structured jet case is very small, large off-axis angles imply high radiation densities in the jet, which can enhance the neutrino production efficiency. In the most optimistic allowed scenario, the neutrino fluence can reach only 10-4 of the sensitivity of the neutrino telescopes. We furthermore demonstrate that the fact that gamma-rays can escape limits the baryonic loading (energy in protons versus photons) and the off-axis angle for the internal shock scenario. In particular, for a baryonic loading of 10, the off-axis angle is more strongly constrained by the baryonic loading than by the time delay between the gravitational wave event and the onset of the gamma-ray emission.

Investigating the Interaction of a Supersonic Single Expansion Ramp Nozzle and Sonic Wall Jet

NASA Astrophysics Data System (ADS)

Berry, Matthew G.

For nearly 80 years, the jet engine has set the pace for aviation technology around the world. Complexity of design has compounded upon each iteration of nozzle development, while the rate of fundamental fluids knowledge struggles to keep up. The increase in velocities associated with supersonic jets, have exacerbated the need for flow physics research. Supersonic flight remains the standard for military aircraft and is being rediscovered for commercial use. With the addition of multiple streams, complex nozzle geometries, and airframe integration in modern aircraft, the flow physics rapidly become more difficult. As performance capabilities increase, so do the noise producing mechanisms and unsteady dynamics. This has prompted an experimental investigation into the flow field and turbulence quantities of a modern jet nozzle configuration. A rectangular supersonic multi-stream nozzle with aft deck is characterized using time-resolved schlieren imaging, stereo PIV measurements, deck mounted pressure transducers, and far-field microphones. These experiments are performed at the Skytop Turbulence Laboratory at Syracuse University. LES data by The Ohio State University are paired with these experiments and give valuable insight into regions of the flow unable to be probed. By decomposing this complex flow field into two canonical flows, a supersonic rectangular nozzle and a sonic wall jet, a fundamental approach is taken to observe how these two jets interact. Thorough investigations of the highly turbulent flow field are being performed. Current analytical techniques employed are statistical quantities, turbulence properties, and low-dimensional models. Results show a dominant high frequency structure that propagates through the entire field and is observable in all experimental methods. The structures emanate from the interaction point of the supersonic jet and sonic wall jet. Additionally, the propagation paths are directionally dependent. Further, spanwise PIV measurements observe the asymmetric nozzle to be relatively two-dimensional across half of the jet span. An investigation into the effect of the aft deck has shown that the jet plume deflection depended on the aft deck length. This deflection is tied to separation and reattachment caused by reflecting oblique shocks. Additionally, low-dimensional models in the form of POD and DMD observe the most energetic and periodic structures in the turbulent flow field. Finally, these experimental results are paired with LES using data fusion techniques to form a more complete view of the flow. The comprehensive dataset will help validate computational models and create a basis for future SERN and aft deck designs.

Successive Two-sided Loop Jets Caused by Magnetic Reconnection between Two Adjacent Filamentary Threads

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tian, Zhanjun; Liu, Yu; Shen, Yuandeng

We present observational analysis of two successive two-sided loop jets observed by the ground-based New Vacuum Solar Telescope and the space-borne Solar Dynamics Observatory . The two successive two-sided loop jets manifested similar evolution processes and both were associated with the interaction of two small-scale adjacent filamentary threads, magnetic emerging, and cancellation processes at the jet’s source region. High temporal and high spatial resolution observations reveal that the two adjacent ends of the two filamentary threads are rooted in opposite magnetic polarities within the source region. The two threads approached each other, and then an obvious brightening patch is observedmore » at the interaction position. Subsequently, a pair of hot plasma ejections are observed heading in opposite directions along the paths of the two filamentary threads at a typical speed for two-sided loop jets of the order 150 km s{sup −1}. Close to the end of the second jet, we report the formation of a bright hot loop structure at the source region, which suggests the formation of new loops during the interaction. Based on the observational results, we propose that the observed two-sided loop jets are caused by magnetic reconnection between the two adjacent filamentary threads, largely different from the previous scenario that a two-sided loop jet is generated by magnetic reconnection between an emerging bipole and the overlying horizontal magnetic fields.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nishizuka, N.; Nakamura, T.; Kawate, T.

The Solar Optical Telescope on board Hinode has revealed numerous tiny jets in all regions of the chromosphere outside of sunspots. A typical chromospheric anemone jet has a cusp-shaped structure and bright footpoint, similar to the shape of an X-ray anemone jet observed previously with the Soft X-ray Telescope on board Yohkoh. The similarity in the shapes of chromospheric and X-ray anemone jets suggests that chromospheric anemone jets are produced as a result of the magnetic reconnection between a small bipole (perhaps a tiny emerging flux) and a pre-existing uniform magnetic field in the lower chromosphere. We examine various chromosphericmore » anemone jets in the solar active region near the solar limb and study the typical features (e.g., length, width, lifetime, and velocity) of the chromospheric anemone jets. Statistical studies show that chromospheric anemone jets have: (1) a typical length {approx}1.0-4.0 Mm, (2) a width {approx}100-400 km, (3) a lifetime {approx}100-500 s, and (4) a velocity {approx}5-20 km s{sup -1}. The velocity of the chromospheric anemone jets is comparable to the local Alfven speed in the lower solar chromosphere ({approx}10 km s{sup -1}). The histograms of chromospheric anemone jets near the limb and near the disk center show similar averages and shapes of distributions, suggesting that the characteristic behavior of chromospheric anemone jets is independent of whether they are observed on the disk or at the limb. The observed relationship between the velocity and length of chromospheric anemone jets shows that the jets do not follow ballistic motion but are more likely accelerated by some other mechanism. This is consistent with numerical simulations of chromospheric anemone jets.« less

Fuselage Structure Response to Boundary Layer, Tonal Sound, and Jet Noise

NASA Technical Reports Server (NTRS)

Maestrello, L.

2004-01-01

Experiments have been conducted to study the response of curved aluminum and graphite-epoxy fuselage structures to flow and sound loads from turbulent boundary layer, tonal sound, and jet noise. Both structures were the same size. The aluminum structure was reinforced with tear stoppers, while the graphite-epoxy structure was not. The graphite-epoxy structure weighed half as much as the aluminum structure. Spatiotemporal intermittence and chaotic behavior of the structural response was observed, as jet noise and tonal sound interacted with the turbulent boundary layer. The fundamental tone distributed energy to other components via wave interaction with the turbulent boundary layer. The added broadband sound from the jet, with or without a shock, influenced the responses over a wider range of frequencies. Instantaneous spatial correlation indicates small localized spatiotemporal regions of convected waves, while uncorrelated patterns dominate the larger portion of the space. By modifying the geometry of the tear stoppers between panels and frame, the transmitted and reflected waves of the aluminum panels were significantly reduced. The response level of the graphite-epoxy structure was higher, but the noise transmitted was nearly equal to that of the aluminum structure. The fundamental shock mode is between 80 deg and 150 deg and the first harmonic is between 20 deg and 80 deg for the underexpanded supersonic jet impinging on the turbulent boundary layer influencing the structural response. The response of the graphite-epoxy structure due to the fundamental mode of the shock impingement was stabilized by an externally fixed oscillator.

More Macrospicule Jets in On-Disk Coronal Holes

NASA Astrophysics Data System (ADS)

Adams, Mitzi; Sterling, Alphonse; Moore, Ronald

2015-04-01

We examine the magnetic structure and dynamics of multiple jets found in coronal holes close to or at disk center. All data are from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory (SDO). We report on observations of about ten jets in an equatorial coronal hole spanning 2011 February 27 and 28. We show the evolution of these jets in AIA 193 Å, examine the magnetic field configuration and flux changes in the jet area, and discuss the probable trigger mechanism of these events. We reported on another jet in this same coronal hole on 2011 February 27, ~13:04 UT (Adams et al 2014, ApJ, 783: 11). That jet is a previously unrecognized variety of blowout jet, in which the base-edge bright point is a miniature filament-eruption flare arcade made by internal reconnection of the legs of the erupting field. In contrast, in the presently-accepted "standard" picture for blowout jets, the base-edge bright point is made by interchange reconnection of initially-closed erupting jet-base field with ambient open field. This poster presents further evidence of the production of the base-edge bright point in blowout jets by internal reconnection. Our observations suggest that most of the bigger and brighter EUV jets in coronal holes are blowout jets of the new-found variety.

More Macrospicule Jets in On-Disk Coronal Holes

NASA Technical Reports Server (NTRS)

Adams, M. L.; Sterling, A. C.; Moore, R. L.

2015-01-01

We examine the magnetic structure and dynamics of multiple jets found in coronal holes close to or on disk center. All data are from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory (SDO). We report on observations of about ten jets in an equatorial coronal hole spanning 2011 February 27 and 28. We show the evolution of these jets in AIA 193 A, examine the magnetic field configuration and flux changes in the jet area, and discuss the probable trigger mechanism of these events. We reported on another jet in this same coronal hole on 2011 February 27, (is) approximately 13:04 UT (Adams et al 2014, ApJ, 783: 11). That jet is a previously-unrecognized variety of blowout jet, in which the base-edge bright point is a miniature filament-eruption flare arcade made by internal reconnection of the legs of the erupting field. In contrast, in the presently-accepted 'standard' picture for blowout jets, the base-edge bright point is made by interchange reconnection of initially-closed erupting jet-base field with ambient open field. This poster presents further evidence of the production of the base-edge bright point in blowout jets by internal reconnection. Our observations suggest that most of the bigger and brighter EUV jets in coronal holes are blowout jets of the new-found variety.

Numerical modeling of planetary-scale waves on Jupiter

NASA Astrophysics Data System (ADS)

Cosentino, Richard; Morales-Juberias, Raul; Simon, Amy

2014-11-01

The atmosphere of Jupiter has multiple alternating east-wind wind jets with different cloud morphologies some of which can be explained by the presence of atmospheric waves. One jet feature observed by Cassini and HST at 30N, called the Jovian Ribbon for its similarity to Saturn's Ribbon, displays chaotic cloud morphology caused by multiple wave components with dominating planetary scale wave-numbers ranging from 13 to 30. Both the cloud morphology and the dominant wave numbers observed change as a function of time and correlate to changes in the jet's speed. The average speed of the westward jet where this Jovian Ribbon is found is small compared to other notable jets that display wave behavior, namely the high velocity eastward jets at 7N (hot spots) and 7S (chevrons). We present the results of numerical simulations that show how attributes like jet speed, location, vertical shear and other background properties of the atmosphere (e.g. static stability) contribute to the development and evolution of wave structures in jets similar to those observed. Additionally, we explore the effects of local convective events and other atmospheric disturbances such as spots, on the morphology of these jets and waves. This work was supported by NASA PATM grant number NNX14AH47G. Computing resources for this research were provided by NMT and Yellowstone at CISL.

A Model for Solar Polar Jets

NASA Technical Reports Server (NTRS)

Pariat, E.; Antiochos, S. K.; DeVore, C. R.

2008-01-01

We propose a model for the jetting activity that is commonly observed in the Sun's corona, especially in the open-field regions of polar coronal holes. Magnetic reconnection is the process driving the jets and a relevant magnetic configuration is the well-known null point and fan separatrix topology. The primary challenge in explaining the observations is that reconnection must occur in a short-duration energetic burst rather than quasi-continuously as is implied by the observations of long-lived structures in coronal holes, such as polar plumes, for example. The key idea underlying our model for jets is that reconnection is forbidden for an axisymmetric null-point topology. Consequently, by imposing a twisting motion that maintains the axisymmetry, magnetic stress can be built up to large levels until an ideal instability breaks the symmetry and leads to an explosive release of energy via reconnection. Using 3D MHD simulations we demonstrate that this mechanism does produce jets with high speed and mass, driven by nonlinear Alfven waves. We discuss the implications of our results for observations of the solar corona.

The high-resolution structure of the Centaurus A nucleus at 2.3 and 8.4 GHz

NASA Technical Reports Server (NTRS)

Meier, David L.; Preston, Robert A.; Morabito, David D.; Skjerve, Lyle; Slade, Martin A.; Wehrle, Ann E.; Niell, Arthur E.; Jauncey, David L.; Batchelor, Robert; Tzioumis, Anastasios K.

1989-01-01

VLBI observations of the nucleus of Centaurus A have been made at two frequencies with an array of five Australian radio telescopes as part of the Southern Hemisphere VLBI Experiment. Observations were made at 2.3 GHz with all five antennas, while only two were employed at 8.4 GHz. At 2.3 GHz seven tracks in the (u,v) plane with coverage of 6-8 hr each were obtained, yielding significant information on the structure of the nuclear jet. At 8.4 GHz a compact unresolved core was detected as well. It is found that the source consists of the compact self-absorbed core, a jet containing a set of three knots extending from 100 to 160 mas from the core, and a very long, narrow component elongated along the same position angle as the knots. The allowable range for the position angle of the jet is 51 + or - 3 deg, in agreement with that of the radio and X-ray structure on arcsecond and arcminute scales. The jet has brightened at 2.3 GHz by about 4 Jy, a factor of nearly 3, since the early 1970s, 1.8 Jy of which has occurred in the last 2 yr with no discernable changes in structure.

Studies of the pedestal structure and inter-ELM pedestal evolution in JET with the ITER-like wall

NASA Astrophysics Data System (ADS)

Maggi, C. F.; Frassinetti, L.; Horvath, L.; Lunniss, A.; Saarelma, S.; Wilson, H.; Flanagan, J.; Leyland, M.; Lupelli, I.; Pamela, S.; Urano, H.; Garzotti, L.; Lerche, E.; Nunes, I.; Rimini, F.; Contributors, JET

2017-11-01

The pedestal structure of type I ELMy H-modes has been analysed for JET with the ITER-like Wall (JET-ILW). The electron pressure pedestal width is independent of ρ * and increases proportionally to  √β pol,PED. Additional broadening of the width is observed, at constant β pol, PED, with increasing ν * and/or neutral gas injection and the contribution of atomic physics effects in setting the pedestal width cannot as yet be ruled out. Neutral penetration alone does not determine the shape of the edge density profile in JET-ILW. The ratio of electron density to electron temperature scale lengths in the edge transport barrier region, η e, is of order 2-3 within experimental uncertainties. Existing understanding, represented in the stationary linear peeling-ballooning mode stability and the EPED pedestal structure models, is extended to the dynamic evolution between ELM crashes in JET-ILW, in order to test the assumptions underlying these two models. The inter-ELM temporal evolution of the pedestal structure in JET-ILW is not unique, but depends on discharge conditions, such as heating power and gas injection levels. The strong reduction in p e,PED with increasing D 2 gas injection at high power is primarily due to clamping of \

Time-frequency analysis of submerged synthetic jet

NASA Astrophysics Data System (ADS)

Kumar, Abhay; Saha, Arun K.; Panigrahi, P. K.

2017-12-01

The coherent structures transport the finite body of fluid mass through rolling which plays an important role in heat transfer, boundary layer control, mixing, cooling, propulsion and other engineering applications. A synthetic jet in the form of a train of vortex rings having coherent structures of different length scales is expected to be useful in these applications. The propagation and sustainability of these coherent structures (vortex rings) in downstream direction characterize the performance of synthetic jet. In the present study, the velocity signal acquired using the S-type hot-film probe along the synthetic jet centerline has been taken for the spectral analysis. One circular and three rectangular orifices of aspect ratio 1, 2 and 4 actuating at 1, 6 and 18 Hz frequency have been used for creating different synthetic jets. The laser induced fluorescence images are used to study the flow structures qualitatively and help in explaining the velocity signal for detection of coherent structures. The study depicts four regions as vortex rollup and suction region (X/D h ≤ 3), steadily translating region (X/D h ≤ 3-8), vortex breakup region (X/Dh ≤ 4-8) and dissipation of small-scale vortices (X/D h ≤ 8-15). The presence of coherent structures localized in physical and temporal domain is analyzed for the characterization of synthetic jet. Due to pulsatile nature of synthetic jet, analysis of velocity time trace or signal in time, frequency and combined time-frequency domain assist in characterizing the signatures of coherent structures. It has been observed that the maximum energy is in the first harmonic of actuation frequency, which decreases slowly in downstream direction at 6 Hz compared to 1 and 18 Hz of actuation.

A swirling jet in the quasar 1308+326

NASA Astrophysics Data System (ADS)

Britzen, S.; Qian, S.-J.; Steffen, W.; Kun, E.; Karouzos, M.; Gergely, L.; Schmidt, J.; Aller, M.; Aller, H.; Krause, M.; Fendt, C.; Böttcher, M.; Witzel, A.; Eckart, A.; Moser, L.

2017-06-01

Context. Despite numerous and detailed studies of the jets of active galactic nuclei (AGN) on pc-scales, many questions are still debated. The physical nature of the jet components is one of the most prominent unsolved problems, as is the launching mechanism of jets in AGN. The quasar 1308+326 (z = 0.997) allows us to study the overall properties of its jet in detail and to derive a more physical understanding of the nature and origin of jets in general. The long-term data provided by the Monitoring Of Jets in Active galactic nuclei with Very Long Baseline Array (VLBA) experiments (MOJAVE) survey permit us to trace out the structural changes in 1308+326 that we present here. The long-lived jet features in this source can be followed for about two decades. Aims: We investigate the very long baseline interferomety (VLBI) morphology and kinematics of the jet of 1308+326 to understand the physical nature of this jet and jets in general, the role of magnetic fields, and the causal connection between jet features and the launching process. Methods: Fifty VLBA observations performed at 15 GHz from the MOJAVE survey were re-modeled with Gaussian components and re-analyzed (the time covered: 20 Jan. 1995-25 Jan. 2014). The analysis was supplemented by multi-wavelength radio-data (UMRAO, at 4.8, 8.0, and 14.5 GHz) in polarization and total intensity. We fit the apparent motion of the jet features with the help of a model of a precessing nozzle. Results: The jet features seem to be emitted with varying viewing angles and launched into an ejection cone. Tracing the component paths yields evidence for rotational motion. Radio flux-density variability can be explained as a consequence of enhanced Doppler boosting corresponding to the motion of the jet relative to the line of sight. Based on the presented kinematics and other indicators, such as electric-vector polarization position-angle (EVPA) rotation, we conclude that the jet of 1308+326 has a helical structure, meaning that the components are moving along helical trajectories and the trajectories themselves are also experiencing a precessing motion. A model of a precessing nozzle was applied to the data and a subset of the observed jet feature paths can be modeled successfully within this model. The data till 2012 are consistent with a swing period of 16.9 yr. We discuss several scenarios to explain the observed motion phenomena, including a binary black hole model. It seems unlikely that the accretion disk around the primary black hole, which is disturbed by the tidal forces of the secondary black hole, is able to launch a persistent axisymmetric jet. Conclusions: We conclude that we are observing a rotating helix. In particular, the observed EVPA swings can be explained by a shock moving through a straight jet that is pervaded by a helical magnetic field. We compare our results for 1308+326 with other astrophysical scenarios where similar, wound-up filamentary structures are found. They are all related to accretion-driven processes. A helically moving or wound up object is often explained by filamentary features moving along magnetic field lines of magnetic flux tubes. It seems that a "component" comprises plasma tracing the magnetic field, which guides the motion of the radiating radio-band plasma. Further investigations and modeling are in preparation. The reduced Figs. A.1-A.13 (FITS files) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/602/A29 http://www.physics.purdue.edu/astro/MOJAVE/ http://www.physics.purdue.edu/astro/MOJAVE/ http://www.physics.purdue.edu/astro/MOJAVE/animated/1308+326.I.mpg http://www.physics.purdue.edu/MOJAVE/sourcepages/1308+326.shtml

X-ray Jets in the CH Cyg Symbiotic System

NASA Astrophysics Data System (ADS)

Karovska, Margarita; Gaetz, T.; Lee, N.; Raymond, J.; Hack, W.; Carilli, C.

2009-09-01

Symbiotic binaries are interacting systems in which a compact stellar source accretes matter from the wind of the cool evolved companion. There are a few hundred symbiotic systems known today, but jet activity has been detected in only a few of them, including in CH Cyg. CH Cyg is a symbiotic system that has shown significant activity since the mid 1960s. Jets have been detected in optical and radio since 1984, and more recently in 2001 in X-rays using Chandra observations.In 2008 we carried out coordinated multi-wavelength observations of the CH Cyg system with Chandra, HST, and the VLA, in order to study the propagation and interaction with the circumbinary medium of the jet detected in 2001. We report here on the detection of the 2001 SE jet which has expanded in seven years from ˜350AU to ˜1400 AU. The apex of the loop delineating the region of interaction with the circumbinary matter is moving with a speed of ˜700 km/s. Assuming a linear expansion, the jet was launched during the 1999-2000 active phase. We also report on a detection of a powerful new jet in the SW direction, observed in X-ray, optical and radio wavelengths. The new jet has a multi-component structure including an inner jet and counter jet, and a SW component ending in several clumps extending up to a distance of about 750AU.

Spray formation processes of impinging jet injectors

NASA Technical Reports Server (NTRS)

Anderson, W. E.; Ryan, H. M.; Pal, S.; Santoro, R. J.

1993-01-01

A study examining impinging liquid jets has been underway to determine physical mechanisms responsible for combustion instabilities in liquid bi-propellant rocket engines. Primary atomization has been identified as an important process. Measurements of atomization length, wave structure, and drop size and velocity distribution were made under various ambient conditions. Test parameters included geometric effects and flow effects. It was observed that pre-impingement jet conditions, specifically whether they were laminar or turbulent, had the major effect on primary atomization. Comparison of the measurements with results from a two dimensional linear aerodynamic stability model of a thinning, viscous sheet were made. Measured turbulent impinging jet characteristics were contrary to model predictions; the structure of waves generated near the point of jet impingement were dependent primarily on jet diameter and independent of jet velocity. It has been postulated that these impact waves are related to pressure and momentum fluctuations near the impingement region and control the eventual disintegration of the liquid sheet into ligaments. Examination of the temporal characteristics of primary atomization (ligament shedding frequency) strongly suggests that the periodic nature of primary atomization is a key process in combustion instability.

Improvements in Modeling the Collimated Jets of Comet 19P/Borrelly from the Stereo Images of the Deep Space 1 Flyby

NASA Astrophysics Data System (ADS)

Melville, Kenneth J.; Farnham, T.; Hoban, S.

2010-10-01

On September 22, 2001, the spacecraft Deep Space 1 (DS1), which was primarily designed for testing advanced technologies in space, preformed an extended mission flyby of the comet 19P/Borrelly. This encounter provided scientists with the best images taken of a comet. These images from the DS1 Miniature Integrated Camera and Spectrometer (MICAS) instrument show features of comet Borrelly's surface; collimated dust jets escaping the nucleus, and the coma of gas and dust that surrounds the nucleus. Properties of the jet, such as rate and angle of expansion have been measured accurately due to the jet's geometric structure and position on the rotation axis of the comet. These measurements have been taken for several points along the spacecrafts approach, flyby, and from additional McDonald ground based observatory images. A model of the jet with similar geometry has been constructed in order to reproduce the observational data found in the flyby images. Other proposed models are tested as well. Once these models has been adjusted to replicate the data, they can be used to investigate the collimation mechanism below the comets surface producing the jet. Comet 19P/Borrelly is the idea test for this model due to the simple structure of the jet, as well as the wide variety of angles and observation times. Using information from this model, scientists may be able to make new assumptions on the composition and physical structure of other comets. This research was supported by the NASA Planetary Data System: Small Bodies Node, and College Student Investigator Program at UMBC Goddard Earth Sciences & Technology Center.

Deep Chandra observations of Pictor A

NASA Astrophysics Data System (ADS)

Hardcastle, M. J.; Lenc, E.; Birkinshaw, M.; Croston, J. H.; Goodger, J. L.; Marshall, H. L.; Perlman, E. S.; Siemiginowska, A.; Stawarz, Ł.; Worrall, D. M.

2016-02-01

We report on deep Chandra observations of the nearby broad-line radio galaxy Pictor A, which we combine with new Australia Telescope Compact Array (ATCA) observations. The new X-ray data have a factor of 4 more exposure than observations previously presented and span a 15 yr time baseline, allowing a detailed study of the spatial, temporal and spectral properties of the AGN, jet, hotspot and lobes. We present evidence for further time variation of the jet, though the flare that we reported in previous work remains the most significantly detected time-varying feature. We also confirm previous tentative evidence for a faint counterjet. Based on the radio through X-ray spectrum of the jet and its detailed spatial structure, and on the properties of the counterjet, we argue that inverse-Compton models can be conclusively rejected, and propose that the X-ray emission from the jet is synchrotron emission from particles accelerated in the boundary layer of a relativistic jet. For the first time, we find evidence that the bright western hotspot is also time-varying in X-rays, and we connect this to the small-scale structure in the hotspot seen in high-resolution radio observations. The new data allow us to confirm that the spectrum of the lobes is in good agreement with the predictions of an inverse-Compton model and we show that the data favour models in which the filaments seen in the radio images are predominantly the result of spatial variation of magnetic fields in the presence of a relatively uniform electron distribution.

Observations and Numerical Modeling of the Jovian Ribbon

NASA Technical Reports Server (NTRS)

Cosentino, R. G.; Simon, A.; Morales-Juberias, R.; Sayanagi, K. M.

2015-01-01

Multiple wavelength observations made by the Hubble Space Telescope in early 2007 show the presence of a wavy, high-contrast feature in Jupiter's atmosphere near 30 degrees North. The "Jovian Ribbon," best seen at 410 nanometers, irregularly undulates in latitude and is time-variable in appearance. A meridional intensity gradient algorithm was applied to the observations to track the Ribbon's contour. Spectral analysis of the contour revealed that the Ribbon's structure is a combination of several wavenumbers ranging from k equals 8-40. The Ribbon is a dynamic structure that has been observed to have spectral power for dominant wavenumbers which vary over a time period of one month. The presence of the Ribbon correlates with periods when the velocity of the westward jet at the same location is highest. We conducted numerical simulations to investigate the stability of westward jets of varying speed, vertical shear, and background static stability to different perturbations. A Ribbon-like morphology was best reproduced with a 35 per millisecond westward jet that decreases in amplitude for pressures greater than 700 hectopascals and a background static stability of N equals 0.005 per second perturbed by heat pulses constrained to latitudes south of 30 degrees North. Additionally, the simulated feature had wavenumbers that qualitatively matched observations and evolved throughout the simulation reproducing the Jovian Ribbon's dynamic structure.

Hubble Space Telescope images and follow-up spectroscopy of the Orion nebula

NASA Technical Reports Server (NTRS)

O'Dell, C. R.; Wen, Zheng; Hester, J. J.

1991-01-01

Recently published HST images of the Orion nebula reveal elephant-trunk structures, an apparent jet of material, and fine-scale structure in the Herbig-Haro object HH2, which is located at the base of an elephant trunk. High-resolution spectroscopy shows that the apparent jet is actually an ionization front seen edge-on. HH2 shows a complex structure in the several stages of ionization observed. There seem to be two velocity systems characterized by a bright central region and an accompanying shell-like emission. These two systems are most likely to be the result of a bow shock and corresponding Mach disk formed from the interaction of a collimated jet and the ambient gas of the nebula.

A numerical model for the Serpens radio jet

NASA Astrophysics Data System (ADS)

Raga, A. C.; Curiel, S.; Rodríguez, L. F.; Cantó, J.

2000-12-01

The Serpens (``triple source'') radio continuum jet shows a series of aligned knots with ~ 1-2'' angular separations, forming a curved structure circumscribed within a cone of ~ 10o full opening angle. We present a high resolution, 3D numerical simulation of a jet with variable ejection direction and velocity with parameters appropriate for the Serpens jet, from which we obtain predictions of 3.6 cm radio continuum maps. We find that the general morphology of the radio emission, and the time evolution of the successive knots, qualitatively agree with 3.6 cm VLA observations of the Serpens radio jet. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA. Members of the Consortium on the ISOPHOT Serendipity Survey (CISS) are MPIA Heidelberg, ESA ISO SOC Villafranca, AIP Potsdam, IPAC Pasadena, Imperial College London.

The outflow structure of GW170817 from late-time broad-band observations

NASA Astrophysics Data System (ADS)

Troja, E.; Piro, L.; Ryan, G.; van Eerten, H.; Ricci, R.; Wieringa, M. H.; Lotti, S.; Sakamoto, T.; Cenko, S. B.

2018-07-01

We present our broad-band study of GW170817 from radio to hard X-rays, including NuSTAR and Chandra observations up to 165 d after the merger, and a multimessenger analysis including LIGO constraints. The data are compared with predictions from a wide range of models, providing the first detailed comparison between non-trivial cocoon and jet models. Homogeneous and power-law shaped jets, as well as simple cocoon models are ruled out by the data, while both a Gaussian shaped jet and a cocoon with energy injection can describe the current data set for a reasonable range of physical parameters, consistent with the typical values derived from short GRB afterglows. We propose that these models can be unambiguously discriminated by future observations measuring the post-peak behaviour, with Fν ∝ t˜-1.0 for the cocoon and Fν∝ t˜-2.5 for the jet model.

The outflow structure of GW170817 from late time broadband observations

NASA Astrophysics Data System (ADS)

Troja, E.; Piro, L.; Ryan, G.; van Eerten, H.; Ricci, R.; Wieringa, M.; Lotti, S.; Sakamoto, T.; Cenko, S. B.

2018-04-01

We present our broadband study of GW170817 from radio to hard X-rays, including NuSTAR and Chandra observations up to 165 days after the merger, and a multi-messenger analysis including LIGO constraints. The data are compared with predictions from a wide range of models, providing the first detailed comparison between non-trivial cocoon and jet models. Homogeneous and power-law shaped jets, as well as simple cocoon models are ruled out by the data, while both a Gaussian shaped jet and a cocoon with energy injection can describe the current dataset for a reasonable range of physical parameters, consistent with the typical values derived from short GRB afterglows. We propose that these models can be unambiguously discriminated by future observations measuring the post-peak behaviour, with Fν∝t˜-1.0 for the cocoon and Fν∝t˜-2.5 for the jet model.

Large-Scale Flow Structure in Turbulent Nonpremixed Flames under Normal- And Low-Gravity Conditions

NASA Technical Reports Server (NTRS)

Clemens, N. T.; Idicheria, C. A.; Boxx, I. G.

2001-01-01

It is well known that buoyancy has a major influence on the flow structure of turbulent nonpremixed jet flames. Buoyancy acts by inducing baroclinic torques, which generate large-scale vortical structures that can significantly modify the flow field. Furthermore, some suggest that buoyancy can substantially influence the large-scale structure of even nominally momentum-dominated flames, since the low velocity flow outside of the flame will be more susceptible to buoyancy effects. Even subtle buoyancy effects may be important because changes in the large-scale structure affects the local entrainment and fluctuating strain rate, and hence the structure of the flame. Previous studies that have compared the structure of normal- and micro-gravity nonpremixed jet flames note that flames in microgravity are longer and wider than in normal-gravity. This trend was observed for jet flames ranging from laminar to turbulent regimes. Furthermore, imaging of the flames has shown possible evidence of helical instabilities and disturbances starting from the base of the flame in microgravity. In contrast, these characteristics were not observed in normal-gravity. The objective of the present study is to further advance our knowledge of the effects of weak levels of buoyancy on the structure of transitional and turbulent nonpremixed jet flames. In later studies we will utilize the drop tower facilities at NASA Glenn Research Center (GRC), but the preliminary work described in this paper was conducted using the 1.25-second drop tower located at the University of Texas at Austin. A more detailed description of these experiments can be found in Idicheria et al.

A Recollimation Shock in a Stationary Jet Feature with Limb-brightening in the Gamma-Ray-emitting Narrow-line Seyfert 1 Galaxy 1H 0323+342

NASA Astrophysics Data System (ADS)

Doi, Akihiro; Hada, Kazuhiro; Kino, Motoki; Wajima, Kiyoaki; Nakahara, Satomi

2018-04-01

We report the discovery of a local convergence of a jet cross section in the quasi-stationary jet feature in the γ-ray-emitting narrow-line Seyfert 1 galaxy (NLS1) 1H 0323+342. The convergence site is located at ∼7 mas (corresponding to the order of 100 pc in deprojection) from the central engine. We also found limb-brightened jet structures at both the upstream and downstream of the convergence site. We propose that the quasi-stationary feature showing the jet convergence and limb-brightening occurs as a consequence of recollimation shock in the relativistic jets. The quasi-stationary feature is one of the possible γ-ray-emitting sites in this NLS1, in analogy with the HST-1 complex in the M87 jet. Monitoring observations have revealed that superluminal components passed through the convergence site and the peak intensity of the quasi-stationary feature, which showed apparent coincidences with the timing of observed γ-ray activities.

A Model for Straight and Helical Solar Jets: II. Parametric Study of the Plasma Beta

NASA Technical Reports Server (NTRS)

Pariat, E.; Dalmasse, K.; DeVore, C. R.; Antiochos, S. K.; Karpen, J. T.

2016-01-01

Context. Jets are dynamic, impulsive, well-collimated plasma events that develop at many different scales and in different layers of the solar atmosphere. Aims. Jets are believed to be induced by magnetic reconnection, a process central to many astrophysical phenomena. Within the solar atmosphere, jet-like events develop in many different environments, e.g. in the vicinity of active regions as well as in coronal holes, and at various scales, from small photospheric spicules to large coronal jets. In all these events, signatures of helical structure and/or twisting/rotating motions are regularly observed. The present study aims to establish that a single model can generally reproduce the observed properties of these jet-like events. Methods. In this study, using our state-of-the-art numerical solver ARMS, we present a parametric study of a numerical tridimensional magnetohydrodynamic (MHD) model of solar jet-like events. Within the MHD paradigm, we study the impact of varying the atmospheric plasma beta on the generation and properties of solar-like jets. Results. The parametric study validates our model of jets for plasma beta ranging from 10(sup 3) to 1, typical of the different layers and magnetic environments of the solar atmosphere. Our model of jets can robustly explain the generation of helical solar jet-like events at various beta less than or equal to 1. We show that the plasma beta modifies the morphology of the helical jet, explaining the different observed shapes of jets at different scales and in different layers of the solar atmosphere. Conclusions. Our results allow us to understand the energisation, triggering, and driving processes of jet-like events. Our model allows us to make predictions of the impulsiveness and energetics of jets as determined by the surrounding environment, as well as the morphological properties of the resulting jets.

Magnetic field analysis of the bow and terminal shock of the SS 433 jet

NASA Astrophysics Data System (ADS)

Sakemi, Haruka; Machida, Mami; Akahori, Takuya; Nakanishi, Hiroyuki; Akamatsu, Hiroki; Kurahara, Kohei; Farnes, Jamie

2018-03-01

We report a polarization analysis of the eastern region of W 50, observed with the Australia Telescope Compact Array (ATCA) at 1.4-3.0 GHz. In order to study the physical structures in the region where the SS 433 jet and W 50 interact, we obtain an intrinsic magnetic field vector map of that region. We find that the orientation of the intrinsic magnetic field vectors are aligned along the total intensity structures, and that there are characteristic, separate structures related to the jet, the bow shock, and the terminal shock. The Faraday rotation measures (RMs), and the results of Faraday tomography suggest that a high-intensity, filamentary structure in the north-south direction of the eastern-edge region can be separated into at least two parts to the north and south. The results of Faraday tomography also show that there are multiple components along the line of sight and/or within the beam area. In addition, we analyze the X-ray ring-like structure observed with XMM-Newton. While the possibility still remains that this X-ray ring is "real", it seems that the structure is not ring-like at radio wavelengths. Finally, we suggest that the structure is a part of the helical structure that coils the eastern ear of W 50.

Novel Analysis of the Multiwavelength Structure of the Relativistic Jet in Quasar 3C 273

NASA Astrophysics Data System (ADS)

Marchenko, Volodymyr; Harris, D. E.; Ostrowski, Michał; Stawarz, Łukasz; Bohdan, Artem; Jamrozy, Marek; Hnatyk, Bohdan

2017-07-01

We present a detailed analysis of the best-quality multiwavelength data gathered for the large-scale jet in the core-dominated quasar 3C 273. We analyze all the archival observations of the target with the Chandra X-ray Observatory, the far-ultraviolet observations with the Hubble Space Telescope, and the 8.4 GHz map obtained with the Very Large Array. In our study, we focus on investigating the morphology of the outflow at different frequencies, and therefore we apply various techniques for the image deconvolution, paying particular attention to a precise modeling of the Chandra and Hubble point-spread functions. We find that the prominent brightness enhancements in the X-ray and far-ultraviolet jet of 3C 273—the “knots”—are not point-like, and can be resolved transversely as extended features with sizes of about ≃ 0.5 {kpc}. Also, the radio outflow is wider than the deconvolved X-ray/ultraviolet jet. We have also found circumstantial evidence that the intensity peaks of the X-ray knots are located systematically upstream of the corresponding radio intensity peaks, with the projected spatial offsets along the jet ranging from ≲ 0.2 {kpc} up to ≃ 1 {kpc}. We discuss our findings in the wider context of multi-component models for the emission and structure of large-scale quasar jets, and speculate on the physical processes enabling an efficient acceleration of the emitting ultrarelativistic electrons along the entire jet length that exceeds 100 kpc.

Mechanisms of Plasma Acceleration in Coronal Jets

NASA Astrophysics Data System (ADS)

Soto, N.; Reeves, K.; Savcheva, A. S.

2016-12-01

Jets are small explosions that occur frequently in the Sun possibly driven by the local reconfiguration of the magnetic field, or reconnection. There are two types of coronal jets: standard jets and blowout jets. The purpose of this project is to determine which mechanisms accelerate plasma in two different jets, one that occurred in January 17, 2015 at the disk of the sun and another in October 24, 2015 at the limb. Two possible acceleration mechanisms are chromospheric evaporation and magnetic acceleration. Using SDO/AIA, Hinode/XRT and IRIS data, we create height-time plots, and calculate the velocities of each wavelength for both jets. We calculate the potential magnetic field of the jet and the general region around it to gain a more detailed understanding of its structure, and determine if the jet is likely to be either a standard or blowout jet. Finally, we calculate the magnetic field strength for different heights along the jet spire, and use differential emission measures to calculate the plasma density. Once we have these two values, we calculate the Alfven speed. When analyzing our results we are looking for certain patterns in our velocities. If the plasma in a jet is accelerated by chromospheric evaporation, we expect the velocities to increase as function of temperature, which is what we observed in the October 24th jet. The magnetic models for this jet also show the Eiffel Tower shaped structure characteristic of standard jets, which tend to have plasma accelerated by this mechanism. On the other hand, if the acceleration mechanism were magnetic acceleration, we would expect the velocities to be similar regardless of temperature. For the January 17th jet, we saw that along the spire, the velocities where approximately 200 km/s in all wavelengths, but the velocities of hot plasma detected at the base were closer to the Alfven speed, which was estimated to be about 2,000 km/s. These observations suggest that the plasma in the January 17th jet is magnetically accelerated. The magnetic model for this jet needs to be studied further by using a NLFFF magnetic field model and not just the potential magnetic field. This work supported by the NSF-REU solar physics program at SAO, grant number AGS-1560313 and NASA Grant NNX15AF43G

A (likely) X-ray jet from NGC6217 observed by XMM-Newton

NASA Astrophysics Data System (ADS)

Falocco, Serena; Larsson, Josefin; Nandi, Sumana

2017-12-01

NGC6217 is a nearby spiral galaxy with a starburst region near its centre. Evidence for a low-luminosity Active Galactic Nucleus (AGN) in its core has also been found in optical spectra. Intriguingly, X-ray observations by ROSAT revealed three knots aligned with the galaxy centre, resembling a jet structure. This paper presents a study of XMM-Newton observations made to assess the hypothesis of a jet emitted from the centre of NGC6217. The XMM data confirm the knots found with ROSAT and our spectral analysis shows that they have similar spectral properties with a hard photon index Γ ∼ 1.7. The core of NGC6217 is well fitted by a model with an AGN and a starburst component, where the AGN contributes at most 46 per cent of the total flux. The candidate jet has an apparent length ∼15 kpc and a luminosity of ∼5 × 1038 erg s- 1. It stands out by being hosted by a spiral galaxy, since jets are more widely associated with ellipticals. To explain the jet launching mechanism we consider the hypothesis of an advection dominated accretion flow with a low accretion rate. The candidate jet emitted from NGC6217 is intriguing since it represents a challenge to the current knowledge of the connection between AGN, jets and host galaxies.

Exploring Jets from a Supermassive Black Hole

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2018-06-01

What are the feeding and burping habits of the supermassive black holes peppering the universe? In a new study, observations of one such monster reveal more about the behavior of its powerful jets.Beams from BehemothsAcross the universe, supermassive black holes of millions to billions of solar masses lie at the centers of galaxies, gobbling up surrounding material. But not all of the gas and dust that spirals in toward a black hole is ultimately swallowed! A large fraction of it can instead be flung out into space again, in the form of enormous, powerful jets that extend for thousands or even millions of light-years in opposite directions.M87, shown in this Hubble image, is a classic example of a nearby (55 million light-years distant) supermassive black hole with a visible, collimated jet. Its counter-jet isnt seen because relativistic effects make the receding jet appear less bright. [The Hubble Heritage Team (STScI/AURA) and NASA/ESA]What causes these outflows to be tightly beamed collimated in the form of jets, rather than sprayed out in all directions? Does the pressure of the ambient medium the surrounding gas and dust that the jet is injected into play an important role? In what regions do these jets accelerate and decelerate? There are many open questions that scientists hope to understand by studying some of the active black holes with jets that live closest to us.Eyes on a Nearby GiantIn a new study led by Satomi Nakahara (The Graduate University for Advanced Studies in Japan), a team of scientists has used multifrequency Very Long Baseline Array (VLBA) and Very Long Array (VLA) images to explore jets emitted from a galaxy just 100 million light-years away: NGC 4261.This galaxys (relatively) close distance as well as the fact that were viewing it largely from the side, so we can clearly see both of its polar jets allows us to observe in detail the structure and intensity of its jets as a function of their distance from the black hole. Nakahara and collaborators observations span the enormous radial distance of a thousand to a billion times the radius of the black hole, or about 54 light-days to more than a million light-years.Scale for ChangeThe width of the jet as a function of radial distance from the black hole, for NGC 4261 (red) compared to the few other jets from nearby supermassive black holes that weve measured. NGC 4261s jets transition from parabolic to conical at around 10,000 times the radius of the black hole (RS). [Nakahara et al. 2018]The authors observations of NGC 4261s jets indicate that a transition occurs at 10,000 times the radius of the black hole (thats a little over a light-year from the black hole). At this point, the jets structures change from parabolic (becoming more tightly beamed) to conical (expanding freely). Around the same location, Nakahara and collaborators also see the radiation profile of one of the jets change, suggesting the physical conditions in the jets transition here as well.This is the first time weve been able to examine jet width this closely for both of the jets emitted from a supermassive black hole. The fact that the structure changes at the same distance for both jets indicates that the shape of these powerful streams is likely governed by global properties of the environment surrounding the galaxys nucleus, or properties of the jets themselves, rather than by a local condition.The authors next hope to pin down velocities inside NGC 4261s jets to determine where the jets accelerate and decelerate. This nearby powerhouse is clearly going to be a useful laboratory in the future, helping to unveil the secrets of more distant, feeding monsters.BonusCurious what these hungry supermassive black holes look like? Check out this artists imagining of NGC 4261, which shows how it feeds from a large, swirling accretion disk and emits fast-moving, collimated jets. [Original video credit to Dana Berry, Space Telescope Science Institute]CitationSatomi Nakahara et al 2018 ApJ 854 148. doi:10.3847/1538-4357/aaa45e

A wide and collimated radio jet in 3C84 on the scale of a few hundred gravitational radii

NASA Astrophysics Data System (ADS)

Giovannini, G.; Savolainen, T.; Orienti, M.; Nakamura, M.; Nagai, H.; Kino, M.; Giroletti, M.; Hada, K.; Bruni, G.; Kovalev, Y. Y.; Anderson, J. M.; D'Ammando, F.; Hodgson, J.; Honma, M.; Krichbaum, T. P.; Lee, S.-S.; Lico, R.; Lisakov, M. M.; Lobanov, A. P.; Petrov, L.; Sohn, B. W.; Sokolovsky, K. V.; Voitsik, P. A.; Zensus, J. A.; Tingay, S.

2018-06-01

Understanding the formation of relativistic jets in active galactic nuclei remains an elusive problem1. This is partly because observational tests of jet formation models suffer from the limited angular resolution of ground-based very-long-baseline interferometry that has thus far been able to probe the structure of the jet acceleration and collimation region in only two sources2,3. Here, we report observations of 3C84 (NGC 1275)—the central galaxy of the Perseus cluster—made with an interferometric array including the orbiting radio telescope of the RadioAstron4 mission. The data transversely resolve the edge-brightened jet in 3C84 only 30 μas from the core, which is ten times closer to the central engine than was possible in previous ground-based observations5 and allows us to measure the jet collimation profile from 102 to 104 gravitational radii (rg) from the black hole. The previously found5, almost cylindrical jet profile on scales larger than a few thousand rg is seen to continue at least down to a few hundred rg from the black hole, and we find a broad jet with a transverse radius of ≳250 rg at only 350 rg from the core. This implies that either the bright outer jet layer goes through a very rapid lateral expansion on scales ≲102 rg or it is launched from the accretion disk.

A precessing jet in the NGC2264G outflow

NASA Astrophysics Data System (ADS)

McCoey, Carolyn; Teixeira, P. S.; Fich, M.; Lada, C. J.

2007-05-01

We present new infrared imaging of the NGC 2264 G protostellar outflow region, obtained with the Spitzer Space Telescope. A jet in the red (eastern) outflow lobe is clearly detected in all four IRAC bands and, for the first time, is shown to continuously extend over the entire length of the red outflow lobe, as traced by CO observations. The jet also extends to a deeply embedded Class 0 source, VLA2, confirming previous suggestions that it is the driving source of the outflow. The images show that the easternmost part of the jet exhibits what appears to be multiple changes of direction. We consider two possible explanations for the jet morphology: (i) deflection of the jet off the walls of the outflow lobes as proposed by Fich & Lada (1997) and (ii) precession. The jet structure shown in the IRAC images can be largely, although not entirely, explained by a slowly precessing jet (period 8000 yr) that lies mostly on the plane of the sky. In either case it appears that the observed and inferred changes in the jet direction are sufficient to broaden the NGC 2264 G outflow to an extent comparable to that observed in the CO emission. P. S. T. acknowledges support from the scholarship SFRH/BD/13984/2003 awarded by the Fundaçao para a Ciencia e Tecnologia (Portugal). Both M. F. and C. M. are supported by a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant.

A wide and collimated radio jet in 3C84 on the scale of a few hundred gravitational radii

NASA Astrophysics Data System (ADS)

Giovannini, G.; Savolainen, T.; Orienti, M.; Nakamura, M.; Nagai, H.; Kino, M.; Giroletti, M.; Hada, K.; Bruni, G.; Kovalev, Y. Y.; Anderson, J. M.; D'Ammando, F.; Hodgson, J.; Honma, M.; Krichbaum, T. P.; Lee, S.-S.; Lico, R.; Lisakov, M. M.; Lobanov, A. P.; Petrov, L.; Sohn, B. W.; Sokolovsky, K. V.; Voitsik, P. A.; Zensus, J. A.; Tingay, S.

2018-04-01

Understanding the formation of relativistic jets in active galactic nuclei remains an elusive problem1. This is partly because observational tests of jet formation models suffer from the limited angular resolution of ground-based very-long-baseline interferometry that has thus far been able to probe the structure of the jet acceleration and collimation region in only two sources2,3. Here, we report observations of 3C84 (NGC 1275)—the central galaxy of the Perseus cluster—made with an interferometric array including the orbiting radio telescope of the RadioAstron4 mission. The data transversely resolve the edge-brightened jet in 3C84 only 30 μas from the core, which is ten times closer to the central engine than was possible in previous ground-based observations5 and allows us to measure the jet collimation profile from 102 to 104 gravitational radii (rg) from the black hole. The previously found5, almost cylindrical jet profile on scales larger than a few thousand rg is seen to continue at least down to a few hundred rg from the black hole, and we find a broad jet with a transverse radius of ≳250 rg at only 350 rg from the core. This implies that either the bright outer jet layer goes through a very rapid lateral expansion on scales ≲102 rg or it is launched from the accretion disk.

The Structure of High Speed Fluid Jets and Their Use in Cutting Various Soil and Material Types

DTIC Science & Technology

1975-04-30

fluid , a reduction which grows with increase in Reynolds Number (Figure 101) . Franz states that this drag reduction might explain the...176 From photographs Goldin observed that Carbopol, a viscoinelastic fluid which does not give drag reduction , gave a lower jet cohesive...tension and viscoelasticity ), (5) prop- erties of the ambient fluid , (6) the steadiness of the jet flow, and (7) nozzle velocity. In the present study

A Connection Between Corona and Jet

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-03-01

The structure immediately around a supermassive black hole at the heart of an active galaxy can tell us about how material flows in and out of these monsters but this region is hard to observe! A new study provides us with clues of what might be going on in these active and energetic cores of galaxies.In- and OutflowsIn active galactic nuclei (AGN), matter flows both in and out. As material flows toward the black hole via its surrounding accretion disk, much of this gas and dust can then be expelled from the vicinity via highly collimated jets.Top: The fraction of X-rays that is reflected decreases as jet power increases. Bottom: the distance between the corona and the reflecting part of the disk increases as jet power increases. [Adapted from King et al. 2017]To better understand this symbiosis between accretion and outflows, we examine whats known as the corona the hot, X-ray-emitting gas thats located in the closest regions around the black hole. But because the active centers of galaxies are generally obscured by surrounding gas and dust, its difficult for us to learn about the structure of these inner regions near the black hole.Where are the X-rays of the corona produced: in the inner accretion flow, or at the base of the jet? How far away is this corona from the disk? And how does the coronas behavior relate to that of the jet?Reflected ObservationsTo address some of these questions, a group of scientists led by Ashley King (Einstein Fellow at Stanford University) has analyzed X-ray observations from NuSTAR and XMM-Newton of over 40 AGN. The team examined the reflections of the X-rays off of the accretion disk and used two measurements to learn about the structure around the black hole:the fraction of the coronas X-rays that are reflected by the disk, andthe time lag between the original and reflected X-rays, which reveals the distance from the corona to the reflecting part of the disk.A visualization of the authors model for an AGN. The accretion disk is red, corona is green, and jet is blue. The corona shines on the disk, causing the inner regions (colored brighter) to fluoresce, reflecting the radiation. As the accretion rate increases from the top to the bottom panel, the jet power increases and the dominant reflective part of the disk moves outward due to the ionization of the inner region (which puffs up into a torus). [Adapted from King et al. 2017]King and collaborators find two interesting relationships between the corona and the jet: there is an inverse correlation between jet power and reflection fraction, and there is a correlation between jet power and the distance of the corona from the reflecting part of the disk the disk. These observations indicate that there is a relationship between changes in the corona and jet production in AGN.Modeling the CoronaThe authors use these observations to build a self-consistent model of an AGNs corona. In their picture, the corona is located at the base of the jet and movesmildly relativistically away from the disk, propagating into the large-scale jets.As the velocity of the corona increases, more of its radiation is relativistically beamed away from the accretion disk, which decreases the fraction of X-rays that are reflected explaining the inverse correlation between jet power and reflection fraction.At the same time, the increased mass accretion further ionizesthe inner disk region, pushing the dominant reflection region to further out in the disk which explains the correlation between jet power and the distance from corona to reflection region.King and collaborators show that this model is fully consistent with the X-ray observations of the 40 AGN they examined. Future X-ray observations of the strongest radio jet sources will help us to further pin down whats happening at the heart of active galaxies.CitationAshley L. King et al 2017 ApJ 835 226. doi:10.3847/1538-4357/835/2/226

Experiments on free and impinging supersonic microjets

NASA Astrophysics Data System (ADS)

Phalnikar, K. A.; Kumar, R.; Alvi, F. S.

2008-05-01

The fluid dynamics of microflows has recently commanded considerable attention because of their potential applications. Until now, with a few exceptions, most of the studies have been limited to low speed flows. This experimental study examines supersonic microjets of 100-1,000 μm in size with exit velocities in the range of 300-500 m/s. Such microjets are presently being used to actively control larger supersonic impinging jets, which occur in STOVL (short takeoff and vertical landing) aircraft, cavity flows, and flow separation. Flow properties of free as well as impinging supersonic microjets have been experimentally investigated over a range of geometric and flow parameters. The flowfield is visualized using a micro-schlieren system with a high magnification. These schlieren images clearly show the characteristic shock cell structure typically observed in larger supersonic jets. Quantitative measurements of the jet decay and spreading rates as well as shock cell spacing are obtained using micro-pitot probe surveys. In general, the mean flow features of free microjets are similar to larger supersonic jets operating at higher Reynolds numbers. However, some differences are also observed, most likely due to pronounced viscous effects associated with jets at these small scales. Limited studies of impinging microjets were also conducted. They reveal that, similar to the behavior of free microjets, the flow structure of impinging microjets strongly resembles that of larger supersonic impinging jets.

Explaining the morphology of supernova remnant (SNR) 1987A with the jittering jets explosion mechanism

NASA Astrophysics Data System (ADS)

Bear, Ealeal; Soker, Noam

2018-07-01

We find that the remnant of supernova (SN) 1987A shares some morphological features with four supernova remnants (SNRs) that have signatures of shaping by jets, and from that we strengthen the claim that jets played a crucial role in the explosion of SN 1987A. Some of the morphological features appear also in planetary nebulae (PNe) where jets are observed. The clumpy ejecta brings us to support the claim that the jittering jets explosion mechanism can account for the structure of the remnant of SN 1987A, i.e. SNR 1987A. We conduct a preliminary attempt to quantify the fluctuations in the angular momentum of the mass that is accreted on to the newly born neutron star via an accretion disc or belt. The accretion disc/belt launches jets that explode core collapse supernovae (CCSNe). The relaxation time of the accretion disc/belt is comparable to the duration of a typicalfigu jet-launching episode in the jittering jets explosion mechanism, and hence the disc/belt has no time to relax. We suggest that this might explain the two unequal opposite jets that later lead to the unequal sides of the elongated structures in some SNRs of CCSNe. We reiterate our earlier call for a paradigm shift from a neutrino-driven explosion to a jet-driven explosion of CCSNe.

Explaining the morphology of supernova remnant (SNR) 1987A with the jittering jets explosion mechanism

NASA Astrophysics Data System (ADS)

Bear, Ealeal; Soker, Noam

2018-04-01

We find that the remnant of supernova (SN) 1987A shares some morphological features with four supernova remnants (SNRs) that have signatures of shaping by jets, and from that we strengthen the claim that jets played a crucial role in the explosion of SN 1987A. Some of the morphological features appear also in planetary nebulae (PNe) where jets are observed. The clumpy ejecta bring us to support the claim that the jittering jets explosion mechanism can account for the structure of the remnant of SN 1987A, i.e., SNR 1987A. We conduct a preliminary attempt to quantify the fluctuations in the angular momentum of the mass that is accreted on to the newly born neutron star via an accretion disk or belt. The accretion disk/belt launches the jets that explode core collapse supernovae (CCSNe). The relaxation time of the accretion disk/belt is comparable to the duration of a typical jet-launching episode in the jittering jets explosion mechanism, and hence the disk/belt has no time to relax. We suggest that this might explain two unequal opposite jets that later lead to unequal sides of the elongated structures in some SNRs of CCSNe. We reiterate our earlier call for a paradigm shift from neutrino-driven explosion to a jet-driven explosion of CCSNe.

MOJAVE - XIV. Shapes and opening angles of AGN jets

NASA Astrophysics Data System (ADS)

Pushkarev, A. B.; Kovalev, Y. Y.; Lister, M. L.; Savolainen, T.

2017-07-01

We present 15 GHz stacked VLBA images of 373 jets associated with active galactic nuclei (AGNs) having at least five observing epochs within a 20 yr time interval 1994-2015 from the Monitoring Of Jets in Active galactic nuclei with VLBA Experiments (MOJAVE) programme and/or its precursor, the 2-cm VLBA Survey. These data are supplemented by 1.4 GHz single-epoch VLBA observations of 135 MOJAVE AGNs to probe larger scale jet structures. The typical jet geometry is found to be close to conical on scales from hundreds to thousands of parsecs, while a number of galaxies show quasi-parabolic streamlines on smaller scales. A true jet geometry in a considerable fraction of AGNs appears only after stacking epochs over several years. The jets with significant radial accelerated motion undergo more active collimation. We have analysed total intensity jet profiles transverse to the local jet ridgeline and derived both apparent and intrinsic opening angles of the flows, with medians of 21.5° and 1.3°, respectively. The Fermi LAT-detected gamma-ray AGNs in our sample have, on average, wider apparent and narrower intrinsic opening angle, and smaller viewing angle than non-LAT-detected AGNs. We have established a highly significant correlation between the apparent opening angle and gamma-ray luminosity, driven by Doppler beaming and projection effects.

Organized motions in a jet in crossflow

NASA Astrophysics Data System (ADS)

Rivero, A.; Ferré, J. A.; Giralt, Francesc

2001-10-01

An experimental study to identify the structures present in a jet in crossflow has been carried out at a jet-to-crossflow velocity ratio U/Ucf = 3.8 and Reynolds number Re = UcfD/v = 6600. The hot-wire velocity data measured with a rake of eight X-wires at x/D = 5 and 15 and flow visualizations using planar laser-induced fluorescence (PLIF) confirm that the well-established pair of counter-rotating vortices is a feature of the mean field and that the upright, tornado-like or Fric's vortices that are shed to the leeward side of the jet are connected to the jet flow at the core. The counter-rotating vortex pair is strongly modulated by a coherent velocity field that, in fact, is as important as the mean velocity field. Three different structures folded vortex rings, horseshoe vortices and handle-type structures contribute to this coherent field. The new handle-like structures identified in the current study link the boundary layer vorticity with the counter-rotating vortex pair through the upright tornado-like vortices. They are responsible for the modulation and meandering of the counter-rotating vortex pair observed both in video recordings of visualizations and in the instantaneous velocity field. These results corroborate that the genesis of the dominant counter-rotating vortex pair strongly depends on the high pressure gradients that develop in the region near the jet exit, both inside and outside the nozzle.

Probing the Magnetic Field Structure in Sgr A* on Black Hole Horizon Scales with Polarized Radiative Transfer Simulations

NASA Astrophysics Data System (ADS)

Gold, Roman; McKinney, Jonathan C.; Johnson, Michael D.; Doeleman, Sheperd S.

2017-03-01

Magnetic fields are believed to drive accretion and relativistic jets in black hole accretion systems, but the magnetic field structure that controls these phenomena remains uncertain. We perform general relativistic (GR) polarized radiative transfer of time-dependent three-dimensional GR magnetohydrodynamical simulations to model thermal synchrotron emission from the Galactic Center source Sagittarius A* (Sgr A*). We compare our results to new polarimetry measurements by the Event Horizon Telescope (EHT) and show how polarization in the visibility (Fourier) domain distinguishes and constrains accretion flow models with different magnetic field structures. These include models with small-scale fields in disks driven by the magnetorotational instability as well as models with large-scale ordered fields in magnetically arrested disks. We also consider different electron temperature and jet mass-loading prescriptions that control the brightness of the disk, funnel-wall jet, and Blandford-Znajek-driven funnel jet. Our comparisons between the simulations and observations favor models with ordered magnetic fields near the black hole event horizon in Sgr A*, though both disk- and jet-dominated emission can satisfactorily explain most of the current EHT data. We also discuss how the black hole shadow can be filled-in by jet emission or mimicked by the absence of funnel jet emission. We show that stronger model constraints should be possible with upcoming circular polarization and higher frequency (349 GHz) measurements.

Screech tones from free and ducted supersonic jets

NASA Technical Reports Server (NTRS)

Tam, C. K. W.; Ahuja, K. K.; Jones, R. R., III

1994-01-01

It is well known that screech tones from supersonic jets are generated by a feedback loop. The loop consists of three main components. They are the downstream propagating instability wave, the shock cell structure in the jet plume, and the feedback acoustic waves immediately outside the jet. Evidence will be presented to show that the screech frequency is largely controlled by the characteristics of the feedback acoustic waves. The feedback loop is driven by the instability wave of the jet. Thus the tone intensity and its occurrence are dictated by the characteristics of the instability wave. In this paper the dependence of the instability wave spectrum on the azimuthal mode number (axisymmetric or helical/flapping mode, etc.), the jet-to-ambient gas temperature ratio, and the jet Mach number are studied. The results of this study provide an explanation for the observed screech tone mode switch phenomenon (changing from axisymmetric to helical mode as Mach number increases) and the often-cited experimental observation that tone intensity reduces with increase in jet temperature. For ducted supersonic jets screech tones can also be generated by feedback loops formed by the coupling of normal duct modes to instability waves of the jet. The screech frequencies are dictated by the frequencies of the duct modes. Super resonance, resonance involving very large pressure oscillations, can occur when the feedback loop is powered by the most amplified instability wave. It is proposed that the observed large amplitude pressure fluctuations and tone in the test cells of Arnold Engineering Development Center were generated by super resonance. Estimated super-resonance frequency for a Mach 1.3 axisymmetric jet tested in the facility agrees well with measurement.

A new view on the M 87 jet origin: Turbulent loading leading to large-scale episodic wiggling

NASA Astrophysics Data System (ADS)

Britzen, S.; Fendt, C.; Eckart, A.; Karas, V.

2017-05-01

Context. The nearby, giant radio galaxy M 87 hosts a supermassive black hole (BH) and is well-known for a bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large BH mass, M 87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. Many kinematic studies have been performed to determine the proper motions in the jet. Despite M 87 providing all proofs of being an active BH, the apparent jet speed remained puzzling, because proper motion measurements between 15 and 43 GHz for the same region of 1-10 mas core distance provided largely discrepant results. This source is a prime object to be studied in exquisite detail with the upcoming Event Horizon Telescope (EHT) observations because it promises to allow a direct view on the jet launching process itself. Aims: We aim to decipher some of the kinematic puzzles in the pc-scale jet with the analysis we present here. Methods: We re-modeled and re-analyzed 31 VLBA observations at 15 GHz obtained within the MOJAVE program. The data span a time range between Jul. 1995 and May 2011. We performed a detailed investigation of the pc-scale jet kinematics on different timescales, the shortest periods between the observations beeing 10 and 80 days, and in different jet modes, making use of VLBA observations. In addition, we studied the jet ridge line behavior as a function of time. Special care was taken to analyze the region close to the 15 GHz core, and the dynamics and distribution of newly emerging jet features in the jet. Results: We find an indication for apparent superluminal motion in the jet. Moreover, we present evidence for acceleration between 0.5 and 10 mas of core separation. The data suggest that the central part of M 87 at 15 GHz seems to be rotating. Jet components and counter-jet components are ejected in different directions under varying angles, explaining the impression of a broad opening angle. In this paper we present evidence for two different operating modes of the jet of M 87. The jet switches between two phases: I) the jet ridge line is at least double or the jet axis is displaced vertically, and II) an unperturbed phase where the jet ridge line remains almost straight but is smoothly curved and the jet components are aligned along a classical jet axis. The mode change occurs every couple of years. Between the two operating modes, a transition phase is visible. Conclusions: The M 87 jet visible at 15 GHz probes a different physical zone compared to the standard blazar-zone we tend to see in AGN jets. The most likely scenario explaining the observed phenomena is a turbulent mass loading into the jet, most probably due to local, fast reconnection processes driven by turbulence of a tangled magnetic field, which is either generated in the accretion disk or the disk corona. In addition, on large scales, a global magnetic structure is required to channel the turbulent flow into what evolves into a large-scale jet. Large-scale jet instabilities may explain the curved pattern of the observed jet flow.

A Precessing Jet in the CH Cyg Symbiotic System

NASA Astrophysics Data System (ADS)

Karovska, Margarita; Gaetz, Terrance J.; Carilli, Christopher L.; Hack, Warren; Raymond, John C.; Lee, Nicholas P.

2010-02-01

Jets have been detected in only a few symbiotic binaries to date, and CH Cyg is one of them. In 2001, a non-relativistic jet was detected in CH Cyg for the first time in X-rays. We carried out coordinated Chandra, Hubble Space Telescope (HST), and VLA observations in 2008 to study the propagation of this jet and its interaction with the circumbinary medium. We detected the jet with Chandra and HST and determined that the apex has expanded to the south from ~300 AU to ~1400 AU, with the shock front propagating with velocity <100 km s-1. The shock front has significantly slowed down since 2001. Unexpectedly, we also discovered a powerful jet in the NE-SW direction, in the X-ray, optical and radio. This jet has a multi-component structure, including an inner jet and a counterjet at ~170 AU, and a SW component ending in several clumps extending out to ~750 AU. The structure of the jet and the curvature of the outer portion of the SW jet suggest an episodically powered precessing jet or a continuous precessing jet with occasional mass ejections or pulses. We carried out detailed spatial mapping of the X-ray emission and correlation with the optical and radio emission. X-ray spectra were extracted from the central source, inner NE counterjet, and the brightest clump at a distance of ~500 AU from the central source. We discuss the initial results of our analyses, including the multi-component spectral fitting of the jet components and of the central source.

Simulations of Solar Jets

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-02-01

Formation of a coronal jet from twisted field lines that have reconnected with the ambient field. The colors show the radial velocity of the plasma. [Adapted from Szente et al. 2017]How do jets emitted from the Suns surface contribute to its corona and to the solar wind? In a recent study, a team of scientists performed complex three-dimensional simulations of coronal jets to answer these questions.Small ExplosionsCoronal jets are relatively small eruptions from the Suns surface, with heights of roughly 100 to 10,000 km, speeds of 10 to 1,000 km/s, and lifetimes of a few minutes to around ten hours. These jets are constantly present theyre emitted even from the quiet Sun, when activity is otherwise low and weve observed them with a fleet of Sun-watching space telescopes spanning the visible, extreme ultraviolet (EUV), and X-ray wavelength bands.A comparison of simulated observations based on the authors model (left panels) to actual EUV and X-ray observations of jets (right panels). [Szente et al. 2017]Due to their ubiquity, we speculate that these jets might contribute to heating the global solar corona (which is significantly hotter than the surface below it, a curiosity known as the coronal heating problem). We can also wonder what role these jets might play in driving the overall solar wind.Launching a JetLed by Judit Szente (University of Michigan), a team of scientists has explored the impact of coronal jets on the global corona and solar wind with a series of numerical simulations. Szente and collaborators used three-dimensional, magnetohydrodynamic simulations that provide realistic treatment of the solar atmosphere, the solar wind acceleration, and the complexities of heat transfer throughout the corona.In the authors simulations, a jet is initiated as a magnetic dipole rotates at the solar surface, winding up field lines. Magnetic reconnection between the twisted lines and the background field then launches the jet from the dense and hot solar chromosphere, and erupting plasma is released outward into the solar corona.A second comparison of simulated observations based on the authors model (left panels) to actual EUV observations of jets (right panels). [Szente et al. 2017]Global InfluencesAfter demonstrating that their models could successfully lead to jet production and propagation, Szente and collaborators compared their results to actual observations of solar jets. The authors constructed simulated EUV and X-ray observations of their modeled events, and they verified that the behavior and structures in these simulated observations were very similar to real observations of coronal jet events from telescopes like SDO/AIA and Hinode.With this confirmed, the authors then used their models to determine how the jets influence the global solar corona and the solar wind. They found that the large-scale corona is significantly affected by the plasma waves from the jet, which travel across 40 in latitude and out to 24 solar radii. In spite of this, the simulated jets contributed only a few percent to the steady-state solar-wind energy outflow.These simulations represent an important step in realistic modeling of the quiet Sun. Because the models make specific predictions about temperature and density gradients within the corona, we can look forward to testing them with upcoming missions like Solar Probe Plus, which should be able to explore the Sun all the way down to ninesolar radii.CitationJ. Szente et al 2017 ApJ 834 123. doi:10.3847/1538-4357/834/2/123

Buoyancy Effects on Flow Structure and Instability of Low-Density Gas Jets

NASA Technical Reports Server (NTRS)

Pasumarthi, Kasyap Sriramachandra

2004-01-01

A low-density gas jet injected into a high-density ambient gas is known to exhibit self-excited global oscillations accompanied by large vortical structures interacting with the flow field. The primary objective of the proposed research is to study buoyancy effects on the origin and nature of the flow instability and structure in the near-field of low-density gas jets. Quantitative rainbow schlieren deflectometry, Computational fluid dynamics (CFD) and Linear stability analysis were the techniques employed to scale the buoyancy effects. The formation and evolution of vortices and scalar structure of the flow field are investigated in buoyant helium jets discharged from a vertical tube into quiescent air. Oscillations at identical frequency were observed throughout the flow field. The evolving flow structure is described by helium mole percentage contours during an oscillation cycle. Instantaneous, mean, and RMS concentration profiles are presented to describe interactions of the vortex with the jet flow. Oscillations in a narrow wake region near the jet exit are shown to spread through the jet core near the downstream location of the vortex formation. The effects of jet Richardson number on characteristics of vortex and flow field are investigated and discussed. The laminar, axisymmetric, unsteady jet flow of helium injected into air was simulated using CFD. Global oscillations were observed in the flow field. The computed oscillation frequency agreed qualitatively with the experimentally measured frequency. Contours of helium concentration, vorticity and velocity provided information about the evolution and propagation of vortices in the oscillating flow field. Buoyancy effects on the instability mode were evaluated by rainbow schlieren flow visualization and concentration measurements in the near-field of self-excited helium jets undergoing gravitational change in the microgravity environment of 2.2s drop tower at NASA John H. Glenn Research Center. The jet Reynolds number was varied from 200 to 1500 and jet Richardson number was varied from 0.72 to 0.002. Power spectra plots generated from Fast Fourier Transform (FFT) analysis of angular deflection data acquired at a temporal resolution of 1000Hz reveal substantial damping of the oscillation amplitude in microgravity at low Richardson numbers (0.002). Quantitative concentration data in the form of spatial and temporal evolutions of the instability data in Earth gravity and microgravity reveal significant variations in the jet flow structure upon removal of buoyancy forces. Radial variation of the frequency spectra and time traces of helium concentration revealed the importance of gravitational effects in the jet shear layer region. Linear temporal and spatio-temporal stability analyses of a low-density round gas jet injected into a high-density ambient gas were performed by assuming hyper-tan mean velocity and density profiles. The flow was assumed to be non parallel. Viscous and diffusive effects were ignored. The mean flow parameters were represented as the sum of the mean value and a small normal-mode fluctuation. A second order differential equation governing the pressure disturbance amplitude was derived from the basic conservation equations. The effects of the inhomogeneous shear layer and the Froude number (signifying the effects of gravity) on the temporal and spatio-temporal results were delineated. A decrease in the density ratio (ratio of the density of the jet to the density of the ambient gas) resulted in an increase in the temporal amplification rate of the disturbances. The temporal growth rate of the disturbances increased as the Froude number was reduced. The spatio-temporal analysis performed to determine the absolute instability characteristics of the jet yield positive absolute temporal growth rates at all Fr and different axial locations. As buoyancy was removed (Fr . 8), the previously existing absolute instability disappeared at all locations establhing buoyancy as the primary instability mechanism in self-excited low-density jets.

Post-stenotic plug-like jet with a vortex ring demonstrated by 4D flow MRI.

PubMed

Kim, Guk Bae; Ha, Hojin; Kweon, Jihoon; Lee, Sang Joon; Kim, Young-Hak; Yang, Dong Hyun; Kim, Namkug

2016-05-01

To investigate the details of the flow structure of a plug-like jet that had a vortex ring in pulsatile stenotic phantoms using 4D flow MRI. Pulsatile Newtonian flows in two stenotic phantoms with 50% and 75% reductions in area were scanned by 4D flow MRI. Blood analog working fluid was circulated via the stenotic phantom using a pulsatile pump at a constant pulsating frequency of 1Hz. The velocity and vorticity fields of the plug-like jet with a vortex ring were quantitatively analyzed in the spatial and temporal domains. Pulsatile stenotic flow showed a plug-like jet at the specific stenotic degree of 50% in our pulsatile waveform design. This plug-like jet was found at the decelerating period in the post-stenotic region of 26.4mm (1.2 D). It revealed a vortex ring structure with vorticity strength in the range of ±100s(-1). We observed a plug-like jet with a vortex ring in pulsatile stenotic flow by in vitro visualization using 4D flow MRI. In this plug-like jet, the local fastest flow region occurred at the post-systole phase in the post-stenotic region, which was distinguishable from a typical stenotic jet flow at systole phase. Copyright © 2015 Elsevier Inc. All rights reserved.

Structure of a swirling jet with vortex breakdown and combustion

NASA Astrophysics Data System (ADS)

Sharaborin, D. K.; Dulin, V. M.; Markovich, D. M.

2018-03-01

An experimental investigation is performed in order to compare the time-averaged spatial structure of low- and high-swirl turbulent premixed lean flames by using the particle image velocimetry and spontaneous Raman scattering techniques. Distributions of the time-average velocity, density and concentration of the main components of the gas mixture are measured for turbulent premixed swirling propane/air flames at atmospheric pressure for the equivalence ratio Φ = 0.7 and Reynolds number Re = 5000 for low- and high-swirl reacting jets. For the low-swirl jet (S = 0.41), the local minimum of the axial mean velocity is observed within the jet center. The positive value of the mean axial velocity indicates the absence of a permanent recirculation zone, and no clear vortex breakdown could be determined from the average velocity field. For the high-swirl jet (S = 1.0), a pronounced vortex breakdown took place with a bubble-type central recirculation zone. In both cases, the flames are stabilized in the inner mixing layer of the jet around the central wake, containing hot combustion products. O2 and CO2 concentrations in the wake of the low-swirl jet are found to be approximately two times smaller and greater than those in the recirculation zone of the high-swirl jet, respectively.

Coma morphology of comet 67P controlled by insolation over irregular nucleus

NASA Astrophysics Data System (ADS)

Shi, X.; Hu, X.; Mottola, S.; Sierks, H.; Keller, H. U.; Rose, M.; Güttler, C.; Fulle, M.; Fornasier, S.; Agarwal, J.; Pajola, M.; Tubiana, C.; Bodewits, D.; Barbieri, C.; Lamy, P. L.; Rodrigo, R.; Koschny, D.; Barucci, M. A.; Bertaux, J.-L.; Bertini, I.; Boudreault, S.; Cremonese, G.; Da Deppo, V.; Davidsson, B.; Debei, S.; De Cecco, M.; Deller, J.; Groussin, O.; Gutiérrez, P. J.; Hviid, S. F.; Ip, W.-H.; Jorda, L.; Knollenberg, J.; Kovacs, G.; Kramm, J.-R.; Kührt, E.; Küppers, M.; Lara, L. M.; Lazzarin, M.; Lopez-Moreno, J. J.; Marzari, F.; Naletto, G.; Oklay, N.; Toth, I.; Vincent, J.-B.

2018-05-01

While the structural complexity of cometary comae is already recognizable from telescopic observations1, the innermost region, within a few radii of the nucleus, was not resolved until spacecraft exploration became a reality2,3. The dust coma displays jet-like features of enhanced brightness superposed on a diffuse background1,4,5. Some features can be traced to specific areas on the nucleus, and result conceivably from locally enhanced outgassing and/or dust emission6-8. However, diffuse or even uniform activity over topographic concavity can converge to produce jet-like features9,10. Therefore, linking observed coma morphology to the distribution of activity on the nucleus is difficult11,12. Here, we study the emergence of dust activity at sunrise on comet 67P/Churyumov-Gerasimenko using high-resolution, stereo images from the OSIRIS camera onboard the Rosetta spacecraft, where the sources and formation of the jet-like features are resolved. We perform numerical simulations to show that the ambient dust coma is driven by pervasive but non-uniform water outgassing from the homogeneous surface layer. Physical collimations of gas and dust flows occur at local maxima of insolation and also via topographic focusing. Coma structures are projected to exhibit jet-like features that vary with the perspective of the observer. For an irregular comet such as 67P/Churyumov-Gerasimenko, near-nucleus coma structures can be concealed in the shadow of the nucleus, which further complicates the picture.

Superheated liquid carbon dioxide jets: setting up and phenomena

NASA Astrophysics Data System (ADS)

Engelmeier, Lena; Pollak, Stefan; Peters, Franz; Weidner, Eckhard

2018-01-01

We present an experimental investigation on liquid, superheated carbon dioxide jets. Our main goal is to identify the setting up requirements for generating coherent jets because these raise expectations on applications in the cleaning and cutting industry. The study leads us through a number of phenomena, which are described, categorized and explained. The experiments are based on compressed (350 MPa) and cooled carbon dioxide, which expands through a cylindrical nozzle into the atmosphere. The nozzle provokes hydraulic flip by a sharp-edge inlet leading to separation and constriction. Upstream-temperature and pressure are varied and the jet's structure and phase state are monitored by a high-speed camera. We observe coherent, liquid jets far from equilibrium, which demands the solid or gaseous state. Therefore, these jets are superheated. Carbon dioxide jets, like water jets, below certain nozzle diameters are subject to fluid dynamic instabilities resulting in breakup. Above certain diameters flashing jet breakup appears, which is associated with nucleation.

Validation of a reduced-order jet model for subsonic and underexpanded hydrogen jets

DOE PAGES

Li, Xuefang; Hecht, Ethan S.; Christopher, David M.

2016-01-01

Much effort has been made to model hydrogen releases from leaks during potential failures of hydrogen storage systems. A reduced-order jet model can be used to quickly characterize these flows, with low computational cost. Notional nozzle models are often used to avoid modeling the complex shock structures produced by the underexpanded jets by determining an “effective” source to produce the observed downstream trends. In our work, the mean hydrogen concentration fields were measured in a series of subsonic and underexpanded jets using a planar laser Rayleigh scattering system. Furthermore, we compared the experimental data to a reduced order jet modelmore » for subsonic flows and a notional nozzle model coupled to the jet model for underexpanded jets. The values of some key model parameters were determined by comparisons with the experimental data. Finally, the coupled model was also validated against hydrogen concentrations measurements for 100 and 200 bar hydrogen jets with the predictions agreeing well with data in the literature.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aaboud, M.; Aad, G.; Abbott, B.

The distributions of transverse momentum and longitudinal momentum fraction of charged particles in jets are measured in Pb+Pb and pp collisions with the ATLAS detector at the LHC. The distributions are measured as a function of jet transverse momentum and rapidity. The analysis utilises an integrated luminosity of 0.14 nb -1 of Pb+Pb data and 4.0 pb -1 of pp data collected in 2011 and 2013, respectively, at the same centre-of-mass energy of 2.76 TeV per colliding nucleon pair. The distributions measured in pp collisions are used as a reference for those measured in Pb+Pb collisions in order to evaluatemore » the impact on the internal structure of jets from the jet energy loss of fast partons propagating through the hot, dense medium created in heavy-ion collisions. Modest but significant centrality-dependent modifications of fragmentation functions in Pb+Pb collisions with respect to those in pp collisions are seen. Finally, no significant dependence of modifications on jet p T and rapidity selections is observed except for the fragments with the highest transverse momenta for which some reduction of yields is observed for more forward jets.« less

Experimental study of elliptical jet from sub to supercritical conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muthukumaran, C. K.; Vaidyanathan, Aravind, E-mail: aravind7@iist.ac.in

2014-04-15

The jet mixing at supercritical conditions involves fluid dynamics as well as thermodynamic phenomena. All the jet mixing studies at critical conditions to the present date have focused only on axisymmetric jets. When the liquid jet is injected into supercritical environment, the thermodynamic transition could be well understood by considering one of the important fluid properties such as surface tension since it decides the existence of distinct boundary between the liquid and gaseous phase. It is well known that an elliptical liquid jet undergoes axis-switching phenomena under atmospheric conditions due to the presence of surface tension. The experimental investigations weremore » carried out with low speed elliptical jet under supercritical condition. Investigation of the binary component system with fluoroketone jet and N{sub 2} gas as environment shows that the surface tension force dominates for a large downstream distance, indicating delayed thermodynamic transition. The increase in pressure to critical state at supercritical temperature is found to expedite the thermodynamic transition. The ligament like structures has been observed rather than droplets for supercritical pressures. However, for the single component system with fluoroketone jet and fluoroketone environment shows that the jet disintegrates into droplets as it is subjected to the chamber conditions even for the subcritical pressures and no axis switching phenomenon is observed. For a single component system, as the pressure is increased to critical state, the liquid jet exhibits gas-gas like mixing behavior and that too without exhibiting axis-switching behavior.« less

The effect of a metal wall on confinement in JET and ASDEX Upgrade

NASA Astrophysics Data System (ADS)

Beurskens, M. N. A.; Schweinzer, J.; Angioni, C.; Burckhart, A.; Challis, C. D.; Chapman, I.; Fischer, R.; Flanagan, J.; Frassinetti, L.; Giroud, C.; Hobirk, J.; Joffrin, E.; Kallenbach, A.; Kempenaars, M.; Leyland, M.; Lomas, P.; Maddison, G.; Maslov, M.; McDermott, R.; Neu, R.; Nunes, I.; Osborne, T.; Ryter, F.; Saarelma, S.; Schneider, P. A.; Snyder, P.; Tardini, G.; Viezzer, E.; Wolfrum, E.; the ASDEX Upgrade Team; Contributors, JET-EFDA

2013-12-01

In both JET and ASDEX Upgrade (AUG) the plasma energy confinement has been affected by the presence of a metal wall by the requirement of increased gas fuelling to avoid tungsten pollution of the plasma. In JET with a beryllium/tungsten wall the high triangularity baseline H-mode scenario (i.e. similar to the ITER reference scenario) has been the strongest affected and the benefit of high shaping to give good normalized confinement of H98 ˜ 1 at high Greenwald density fraction of fGW ˜ 0.8 has not been recovered to date. In AUG with a full tungsten wall, a good normalized confinement H98 ˜ 1 could be achieved in the high triangularity baseline plasmas, albeit at elevated normalized pressure βN > 2. The confinement lost with respect to the carbon devices can be largely recovered by the seeding of nitrogen in both JET and AUG. This suggests that the absence of carbon in JET and AUG with a metal wall may have affected the achievable confinement. Three mechanisms have been tested that could explain the effect of carbon or nitrogen (and the absence thereof) on the plasma confinement. First it has been seen in experiments and by means of nonlinear gyrokinetic simulations (with the GENE code), that nitrogen seeding does not significantly change the core temperature profile peaking and does not affect the critical ion temperature gradient. Secondly, the dilution of the edge ion density by the injection of nitrogen is not sufficient to explain the plasma temperature and pressure rise. For this latter mechanism to explain the confinement improvement with nitrogen seeding, strongly hollow Zeff profiles would be required which is not supported by experimental observations. The confinement improvement with nitrogen seeding cannot be explained with these two mechanisms. Thirdly, detailed pedestal structure analysis in JET high triangularity baseline plasmas have shown that the fuelling of either deuterium or nitrogen widens the pressure pedestal. However, in JET-ILW this only leads to a confinement benefit in the case of nitrogen seeding where, as the pedestal widens, the obtained pedestal pressure gradient is conserved. In the case of deuterium fuelling in JET-ILW the pressure gradient is strongly degraded in the fuelling scan leading to no net confinement gain due to the pedestal widening. The pedestal code EPED correctly predicts the pedestal pressure of the unseeded plasmas in JET-ILW within ±5%, however it does not capture the complex variation of pedestal width and gradient with fuelling and impurity seeding. Also it does not predict the observed increase of pedestal pressure by nitrogen seeding in JET-ILW. Ideal peeling ballooning MHD stability analysis shows that the widening of the pedestal leads to a down shift of the marginal stability boundary by only 10-20%. However, the variations in the pressure gradient observed in the JET-ILW fuelling experiment is much larger and spans a factor of more than two. As a result the experimental points move from deeply unstable to deeply stable on the stability diagram in a deuterium fuelling scan. In AUG-W nitrogen seeded plasmas, a widening of the pedestal has also been observed, consistent with the JET observations. The absence of carbon can thus affect the pedestal structure, and mainly the achieved pedestal gradient, which can be recovered by seeding nitrogen. The underlying physics mechanism is still under investigation and requires further understanding of the role of impurities on the pedestal stability and pedestal structure formation.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Xuefang; Hecht, Ethan S.; Christopher, David M.

Much effort has been made to model hydrogen releases from leaks during potential failures of hydrogen storage systems. A reduced-order jet model can be used to quickly characterize these flows, with low computational cost. Notional nozzle models are often used to avoid modeling the complex shock structures produced by the underexpanded jets by determining an “effective” source to produce the observed downstream trends. In our work, the mean hydrogen concentration fields were measured in a series of subsonic and underexpanded jets using a planar laser Rayleigh scattering system. Furthermore, we compared the experimental data to a reduced order jet modelmore » for subsonic flows and a notional nozzle model coupled to the jet model for underexpanded jets. The values of some key model parameters were determined by comparisons with the experimental data. Finally, the coupled model was also validated against hydrogen concentrations measurements for 100 and 200 bar hydrogen jets with the predictions agreeing well with data in the literature.« less

Directionally Aligned Amorphous Polymer Chains via Electrohydrodynamic-Jet Printing: Analysis of Morphology and Polymer Field-Effect Transistor Characteristics.

PubMed

Kim, Yebyeol; Bae, Jaehyun; Song, Hyun Woo; An, Tae Kyu; Kim, Se Hyun; Kim, Yun-Hi; Park, Chan Eon

2017-11-15

Electrohydrodynamic-jet (EHD-jet) printing provides an opportunity to directly assembled amorphous polymer chains in the printed pattern. Herein, an EHD-jet printed amorphous polymer was employed as the active layer for fabrication of organic field-effect transistors (OFETs). Under optimized conditions, the field-effect mobility (μ FET ) of the EHD-jet printed OFETs was 5 times higher than the highest μ FET observed in the spin-coated OFETs, and this improvement was achieved without the use of complex surface templating or additional pre- or post-deposition processing. As the chain alignment can be affected by the surface energy of the dielectric layer in EHD-jet printed OFETs, dielectric layers with varying wettability were examined. Near-edge X-ray absorption fine structure measurements were performed to compare the amorphous chain alignment in OFET active layers prepared by EHD-jet printing and spin coating.

Reconnection-Driven Magnetohydrodynamic Turbulence in a Simulated Coronal-Hole Jet

NASA Technical Reports Server (NTRS)

Uritskiy, Vadim M.; Roberts, Merrill A.; DeVore, C. Richard; Karpen, Judith T.

2017-01-01

Extreme-ultraviolet and X-ray jets occur frequently in magnetically open coronal holes on the Sun, especially at high solar latitudes. Some of these jets are observed by white-light coronagraphs as they propagate through the outer corona toward the inner heliosphere, and it has been proposed that they give rise to microstreams and torsional Alfven waves detected in situ in the solar wind. To predict and understand the signatures of coronal-hole jets, we have performed a detailed statistical analysis of such a jet simulated with an adaptively refined magnetohydrodynamics model. The results confirm the generation and persistence of three-dimensional, reconnection-driven magnetic turbulence in the simulation. We calculate the spatial correlations of magnetic fluctuations within the jet and find that they agree best with the Meuller - Biskamp scaling model including intermittent current sheets of various sizes coupled via hydrodynamic turbulent cascade. The anisotropy of the magnetic fluctuations and the spatial orientation of the current sheets are consistent with an ensemble of nonlinear Alfven waves. These properties also reflect the overall collimated jet structure imposed by the geometry of the reconnecting magnetic field. A comparison with Ulysses observations shows that turbulence in the jet wake is in quantitative agreement with that in the fast solar wind.

Reconnection-driven Magnetohydrodynamic Turbulence in a Simulated Coronal-hole Jet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Uritsky, Vadim M.; Roberts, Merrill A.; DeVore, C. Richard

Extreme-ultraviolet and X-ray jets occur frequently in magnetically open coronal holes on the Sun, especially at high solar latitudes. Some of these jets are observed by white-light coronagraphs as they propagate through the outer corona toward the inner heliosphere, and it has been proposed that they give rise to microstreams and torsional Alfvén waves detected in situ in the solar wind. To predict and understand the signatures of coronal-hole jets, we have performed a detailed statistical analysis of such a jet simulated by an adaptively refined magnetohydrodynamics model. The results confirm the generation and persistence of three-dimensional, reconnection-driven magnetic turbulencemore » in the simulation. We calculate the spatial correlations of magnetic fluctuations within the jet and find that they agree best with the Müller–Biskamp scaling model including intermittent current sheets of various sizes coupled via hydrodynamic turbulent cascade. The anisotropy of the magnetic fluctuations and the spatial orientation of the current sheets are consistent with an ensemble of nonlinear Alfvén waves. These properties also reflect the overall collimated jet structure imposed by the geometry of the reconnecting magnetic field. A comparison with Ulysses observations shows that turbulence in the jet wake is in quantitative agreement with that in the fast solar wind.« less

Multiscale Currents Observed by MMS in the Flow Braking Region

NASA Astrophysics Data System (ADS)

Nakamura, Rumi; Varsani, Ali; Genestreti, Kevin J.; Le Contel, Olivier; Nakamura, Takuma; Baumjohann, Wolfgang; Nagai, Tsugunobu; Artemyev, Anton; Birn, Joachim; Sergeev, Victor A.; Apatenkov, Sergey; Ergun, Robert E.; Fuselier, Stephen A.; Gershman, Daniel J.; Giles, Barbara J.; Khotyaintsev, Yuri V.; Lindqvist, Per-Arne; Magnes, Werner; Mauk, Barry; Petrukovich, Anatoli; Russell, Christopher T.; Stawarz, Julia; Strangeway, Robert J.; Anderson, Brian; Burch, James L.; Bromund, Ken R.; Cohen, Ian; Fischer, David; Jaynes, Allison; Kepko, Laurence; Le, Guan; Plaschke, Ferdinand; Reeves, Geoff; Singer, Howard J.; Slavin, James A.; Torbert, Roy B.; Turner, Drew L.

2018-02-01

We present characteristics of current layers in the off-equatorial near-Earth plasma sheet boundary observed with high time-resolution measurements from the Magnetospheric Multiscale mission during an intense substorm associated with multiple dipolarizations. The four Magnetospheric Multiscale spacecraft, separated by distances of about 50 km, were located in the southern hemisphere in the dusk portion of a substorm current wedge. They observed fast flow disturbances (up to about 500 km/s), most intense in the dawn-dusk direction. Field-aligned currents were observed initially within the expanding plasma sheet, where the flow and field disturbances showed the distinct pattern expected in the braking region of localized flows. Subsequently, intense thin field-aligned current layers were detected at the inner boundary of equatorward moving flux tubes together with Earthward streaming hot ions. Intense Hall current layers were found adjacent to the field-aligned currents. In particular, we found a Hall current structure in the vicinity of the Earthward streaming ion jet that consisted of mixed ion components, that is, hot unmagnetized ions, cold E × B drifting ions, and magnetized electrons. Our observations show that both the near-Earth plasma jet diversion and the thin Hall current layers formed around the reconnection jet boundary are the sites where diversion of the perpendicular currents take place that contribute to the observed field-aligned current pattern as predicted by simulations of reconnection jets. Hence, multiscale structure of flow braking is preserved in the field-aligned currents in the off-equatorial plasma sheet and is also translated to ionosphere to become a part of the substorm field-aligned current system.

Background Oriented Schlieren Implementation in a Jet-Surface Interaction Test

NASA Technical Reports Server (NTRS)

Clem, Michelle M.; Brown, Clifford A.; Fagan, Amy

2013-01-01

Many current and future aircraft designs rely on the wing or other aircraft surfaces to shield the engine noise from observers on the ground. However the available data regarding how a planar surface interacts with a jet to shield and/or enhance the jet noise are currently limited. Therefore, the Jet-Surface Interaction Tests supported by NASA's Fundamental Aeronautics Program's Fixed Wing Project were undertaken to supply experimental data covering a wide range of surface geometries and positions interacting with high-speed jet flows in order to support the development of noise prediction methods. Phase 1 of the Test was conducted in the Aero-Acoustic Propulsion Laboratory at NASA Glenn Research Center and consisted of validating noise prediction schemes for a round nozzle interacting with a planar surface. Phased array data and far-field acoustic data were collected for both the shielded and reflected sides of the surface. Phase 1 results showed that the broadband shock noise was greatly reduced by the surface when the jet was operated at the over-expanded condition, however, it was unclear whether this reduction was due a change in the shock cell structure by the surface. In the present study, Background Oriented Schlieren is implemented in Phase 2 of the Jet-Surface Interaction Tests to investigate whether the planar surface interacts with the high-speed jet ow to change the shock cell structure. Background Oriented Schlieren data are acquired for under-expanded, ideally-expanded, and over-expanded ow regimes for multiple axial and radial positions of the surface at three different plate lengths. These data are analyzed with far-field noise measurements to relate the shock cell structure to the broadband shock noise produced by a jet near a surface.

The correlation between the total magnetic flux and the total jet power

NASA Astrophysics Data System (ADS)

Nokhrina, Elena E.

2017-12-01

Magnetic field threading a black hole ergosphere is believed to play the key role in both driving the powerful relativistic jets observed in active galactic nuclei and extracting the rotational energy from a black hole via Blandford-Znajek process. The magnitude of magnetic field and the magnetic flux in the vicinity of a central black hole is predicted by theoretical models. On the other hand, the magnetic field in a jet can be estimated through measurements of either the core shift effect or the brightness temperature. In both cases the obtained magnetic field is in the radiating domain, so its direct application to the calculation of the magnetic flux needs some theoretical assumptions. In this paper we address the issue of estimating the magnetic flux contained in a jet using the measurements of a core shift effect and of a brightness temperature for the jets, directed almost at the observer. The accurate account for the jet transversal structure allow us to express the magnetic flux through the observed values and an unknown rotation rate of magnetic surfaces. If we assume the sources are in a magnetically arrested disk state, the lower limit for the rotation rate can be obtained. On the other hand, the flux estimate may be tested against the total jet power predicted by the electromagnetic energy extraction model. The resultant expression for power depends logarithmically weakly on an unknown rotation rate. We show that the total jet power estimated through the magnetic flux is in good agreement with the observed power. We also obtain the extremely slow rotation rates, which may be an indication that the majority of the sources considered are not in the magnetically arrested disk state.

Geometrical and Kinematic Parameters of the Jet of the Blazar S5 0716+71 in a Helical-Jet Model

NASA Astrophysics Data System (ADS)

Butuzova, M. S.

2018-02-01

Periodic variations of the position angle of the inner jet of the blazar S5 0716+71 suggest a helical structure for the jet. The geometrical parameters of a model helical jet are determined. It is shown that, when the trajectories of the jet components are non-ballistic, the angle between their velocity vectors and the line of sight lies in a broader interval than is the case for ballistic motions of the components, in agreement with available estimates. The contradictory results for the apparent speeds of components in the inner and outer jet at epochs 2004 and 2008-2010 can be explained in such a model. The ratio of the apparent speeds in the inner and outer jet are used to derive a lower limit for the physical speed of the components ( β > 0.999) and to determine the pitch angle of the helical jet ( p = 5.5°). The derived parameters can give rise to the conditions required to observe high speeds (right to 37 c) for individual jet components.

Probing the Magnetic Field Structure in Sgr A* on Black Hole Horizon Scales with Polarized Radiative Transfer Simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gold, Roman; McKinney, Jonathan C.; Johnson, Michael D.

Magnetic fields are believed to drive accretion and relativistic jets in black hole accretion systems, but the magnetic field structure that controls these phenomena remains uncertain. We perform general relativistic (GR) polarized radiative transfer of time-dependent three-dimensional GR magnetohydrodynamical simulations to model thermal synchrotron emission from the Galactic Center source Sagittarius A* (Sgr A*). We compare our results to new polarimetry measurements by the Event Horizon Telescope (EHT) and show how polarization in the visibility (Fourier) domain distinguishes and constrains accretion flow models with different magnetic field structures. These include models with small-scale fields in disks driven by the magnetorotationalmore » instability as well as models with large-scale ordered fields in magnetically arrested disks. We also consider different electron temperature and jet mass-loading prescriptions that control the brightness of the disk, funnel-wall jet, and Blandford–Znajek-driven funnel jet. Our comparisons between the simulations and observations favor models with ordered magnetic fields near the black hole event horizon in Sgr A*, though both disk- and jet-dominated emission can satisfactorily explain most of the current EHT data. We also discuss how the black hole shadow can be filled-in by jet emission or mimicked by the absence of funnel jet emission. We show that stronger model constraints should be possible with upcoming circular polarization and higher frequency (349 GHz) measurements.« less

Subparsec-scale structure and evolution of Centaurus A (NGC5128).

PubMed Central

Jauncey, D L; Tingay, S J; Preston, R A; Reynolds, J E; Lovell, J E; McCulloch, P M; Tzioumis, A K; Costa, M E; Murphy, D W; Meier, D L; Jones, D L; Amy, S W; Biggs, J D; Blair, D G; Clay, R W; Edwards, P G; Ellingsen, S P; Ferris, R H; Gough, R G; Harbison, P; Jones, P A; King, E A; Kemball, A J; Migenes, V; Nicolson, G D; Sinclair, M W; Van Ommen, T; Wark, R M; White, G L

1995-01-01

We present a series of 8.4-GHz very-long-baseline radio interferometry images of the nucleus of Centaurus A (NGC5128) made with a Southern Hemisphere array, representing a 3.3-year monitoring effort. The nuclear radio jet is approximately 50 milliarcseconds in extent, or at the 3.5-megaparsec distance of NGC5128, approximately 1 parsec in length. Subluminal motion is seen and structural changes are observed on time scales shorter than 4 months. High-resolution observations at 4.8 and 8.4 GHz made in November 1992 reveal a complex morphology and allow us to unambiguously identify the self-absorbed core located at the southwestern end of the jet. PMID:11607599

Subparsec-scale structure and evolution of Centaurus A (NGC5128).

PubMed

Jauncey, D L; Tingay, S J; Preston, R A; Reynolds, J E; Lovell, J E; McCulloch, P M; Tzioumis, A K; Costa, M E; Murphy, D W; Meier, D L; Jones, D L; Amy, S W; Biggs, J D; Blair, D G; Clay, R W; Edwards, P G; Ellingsen, S P; Ferris, R H; Gough, R G; Harbison, P; Jones, P A; King, E A; Kemball, A J; Migenes, V; Nicolson, G D; Sinclair, M W; Van Ommen, T; Wark, R M; White, G L

1995-12-05

We present a series of 8.4-GHz very-long-baseline radio interferometry images of the nucleus of Centaurus A (NGC5128) made with a Southern Hemisphere array, representing a 3.3-year monitoring effort. The nuclear radio jet is approximately 50 milliarcseconds in extent, or at the 3.5-megaparsec distance of NGC5128, approximately 1 parsec in length. Subluminal motion is seen and structural changes are observed on time scales shorter than 4 months. High-resolution observations at 4.8 and 8.4 GHz made in November 1992 reveal a complex morphology and allow us to unambiguously identify the self-absorbed core located at the southwestern end of the jet.

Macrospicule Jets in On-Disk Coronal Holes

NASA Technical Reports Server (NTRS)

Adams, M. L.; Sterling, A. C.; Moore, R. L.

2014-01-01

We examine the magnetic structure and dynamics of multiple jets found in coronal holes close to or on disk center. All data are from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory (SDO). We report on observations of six jets in an equatorial coronal hole spanning 2011 February 27 and 28. We show the evolution of these jets in AIA 193 A, examine the magnetic field configuration, and postulate the probable trigger mechanism of these events. We recently reported on another jet in the same coronal hole on 2011 February 27, approximately 13:04 Universal Time (Adams et al 2014, Astrophysical Journal, 783: 11); this jet is a previously-unrecognized variety of blowout jet. In this variety, the reconnection bright point is not made by interchange reconnection of initially-closed erupting field in the base of the jet with ambient open field. Instead, there is a miniature filament-eruption flare arcade made by internal reconnection of the legs of the erupting field.

Formation of a White-Light Jet Within a Quadrupolar Magnetic Configuration

NASA Astrophysics Data System (ADS)

Filippov, Boris; Koutchmy, Serge; Tavabi, Ehsan

2013-08-01

We analyze multi-wavelength and multi-viewpoint observations of a large-scale event viewed on 7 April 2011, originating from an active-region complex. The activity leads to a white-light jet being formed in the outer corona. The topology and evolution of the coronal structures were imaged in high resolution using the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). In addition, large field-of-view images of the corona were obtained using the Sun Watcher using Active Pixel System detector and Image Processing (SWAP) telescope onboard the PRoject for Onboard Autonomy (PROBA2) microsatellite, providing evidence for the connectivity of the coronal structures with outer coronal features that were imaged with the Large Angle Spectrometric Coronagraph (LASCO) C2 on the S olar and Heliospheric Observatory (SOHO). The data sets reveal an Eiffel-tower type jet configuration extending into a narrow jet in the outer corona. The event starts from the growth of a dark area in the central part of the structure. The darkening was also observed in projection on the disk by the Solar TErrestrial RElations Observatory-Ahead (STEREO-A) spacecraft from a different point of view. We assume that the dark volume in the corona descends from a coronal cavity of a flux rope that moved up higher in the corona but still failed to erupt. The quadrupolar magnetic configuration corresponds to a saddle-like shape of the dark volume and provides a possibility for the plasma to escape along the open field lines into the outer corona, forming the white-light jet.

A Million-Second Chandra View of Cassiopeia A

NASA Technical Reports Server (NTRS)

Hwang, Una; Laming, J. Martin; Badenes, Carles; Berendse, Fred; Blondin, John; Cioffi, Denis; DeLaney, Tracey; Dewey, Daniel; Fesen, Robert; Flanagan, Kathryn A.

2004-01-01

We introduce a million-second observation of the supernova remnant Cassiopeia A with the Chandra X-ray Observatory. The bipolar structure of the Si-rich ejecta (NE jet and SW counterpart) is clearly evident in the new images, and their chemical similarity is confirmed by their spectra. These are most likely due to jets of ejecta as opposed to cavities in the circumstellar medium, since we can reject simple models for the latter. The properties of these jets and the Fe-rich ejecta will provide clues to the explosion of Cas A.

Corkscrew Structures and Precessing Jets

NASA Astrophysics Data System (ADS)

Sahai, Raghvendra

2005-07-01

Collimated jets are one of the most intriguing, yet poorly understood phenomena in astrophysics. Jets have been found in a wide variety of object classes which include AGNs, YSOs, massive X-ray binaries {e.g. SS433}, black hole X-ray transients, symbiotic stars, supersoft X-ray sources, and finally, planetary and preplanetary nebulae {PNs & PPNs}. In the case of PNs and PPNs, we have propsoed that wobbling collimated jets are the universal mechanism which can shape the wide variety of bipolar and multipolar morphologies seen in these objects. Most of our knowledge of post-AGB jets is indirectly inferred from their effects on the circumstellar envelopes of the progenitor AGB stars and, for that reason, these jets remain very poorly understood. Thus the mechanism that powers and collimates these jet-like post-AGB outflows remains as one of the most important, unsolved issues in post-AGB evolution. We propose an archival study of two bipolar PPNs, motivated by two recent discoveries which indicate that precessing jets are likely to be operational in them, and that the properties of the jets and the bipolar lobes produced by them, may be directly measured. One of these is IRAS16342-3814 {IRAS1634}, previously imaged with WPFC2, in which new Adaptive Optics {AO} observations at near-IR wavelengths show a remarkable corkscrew-shaped structure, the tell-tale signature of a precessing jet. Inspection of WFPC2 images of another PPN, OH231.8+4.2 in which we have recently discovered a A-type companion to the central mass-losing star, shows a sinuous nebulosity in a broad-band continuum image, resembling a corkscrew structure. We will use the latter to constrain the phsyical properties of the jet {precession period, opening angle, jet beam diameter, temporal history} in OH231.8. Using the multi-wavelength data on both sources, we will build models of the density distribution of the lobes and their interiors. In the case of IRAS1634, these models will be used to investigate the hypothesis that the HST images do not show the corkscrew structure because of opacity effects. Under the assumption that the jets are driven by an accretion disk around the companion, we will use theoretical relationships between disk precession and binary rotation period to estimate the properties of the binary {period, separation}. The results of this study will provide quantitative constraints for jet-driven shaping of PNs and inspire new models for the launching of jets from accretion disks in dying stars with binary companions.

High resolution simulations of a variable HH jet

NASA Astrophysics Data System (ADS)

Raga, A. C.; de Colle, F.; Kajdič, P.; Esquivel, A.; Cantó, J.

2007-04-01

Context: In many papers, the flows in Herbig-Haro (HH) jets have been modeled as collimated outflows with a time-dependent ejection. In particular, a supersonic variability of the ejection velocity leads to the production of "internal working surfaces" which (for appropriate forms of the time-variability) can produce emitting knots that resemble the chains of knots observed along HH jets. Aims: In this paper, we present axisymmetric simulations of an "internal working surface" in a radiative jet (produced by an ejection velocity variability). We concentrate on a given parameter set (i.e., on a jet with a constante ejection density, and a sinusoidal velocity variability with a 20 yr period and a 40 km s-1 half-amplitude), and carry out a study of the behaviour of the solution for increasing numerical resolutions. Methods: In our simulations, we solve the gasdynamic equations together with a 17-species atomic/ionic network, and we are therefore able to compute emission coefficients for different emission lines. Results: We compute 3 adaptive grid simulations, with 20, 163 and 1310 grid points (at the highest grid resolution) across the initial jet radius. From these simulations we see that successively more complex structures are obtained for increasing numerical resolutions. Such an effect is seen in the stratifications of the flow variables as well as in the predicted emission line intensity maps. Conclusions: .We find that while the detailed structure of an internal working surface depends on resolution, the predicted emission line luminosities (integrated over the volume of the working surface) are surprisingly stable. This is definitely good news for the future computation of predictions from radiative jet models for carrying out comparisons with observations of HH objects.

A Strong High Altitude Narrow Jet At Saturn'S Equator From Cassini/ISS Images

NASA Astrophysics Data System (ADS)

Garcia-Melendo, Enrique; Sánchez-Lavega, A.; Legarreta, J.; Pérez-Hoyos, S.; Hueso, R.

2010-10-01

The intense equatorial eastward jets observed at cloud level in Jupiter and Saturn, represent a major challenge for geophysical fluid dynamics. Saturn's equatorial jet is of particular interest in view of its three dimensional structure, suspected large temporal variability, and related stratospheric semiannual oscillation. Here we report the discovery at the upper cloud level of an extremely narrow and strong jet centered in the middle of the broad equatorial jet. Previously published works on Saturn's equatorial winds at cloud level provided only a partial coverage. Automatic correlation of brightness scans and manually tracked cloud features, retrieved from images obtained by the Cassini Imaging Science Subsystem (ISS), show that the jet reaches 430 ms-1 with a peak speed difference of 180 ms-1 relative to nearby latitudes at 60 mbar and 390 ms-1 at depths > 500 mbar. Images were obtained in two filters: MT3, centred at the 889nm strong methane absorption band, and CB3 centred at the near infrared 939nm continuum, which are sensitive to different altitude levels at the upper clouds and hazes. Contrarily to what is observed in other latitudes, its velocity increases with altitude. Our findings helps to extend the view we have of the equatorial stratospheric dynamics of fast rotating planets beyond the best known terrestrial environment, and extract more general consequences of the interaction between waves and mean flow. It remains to be known if this equatorial jet structure, now determined in detail in three dimensions, is permanent or variable with the seasonal solar insolation cycle, including the variable shadow cast by the rings. EGM, ASL, JL, SPH, and RH have been funded by the Spanish MICIIN AYA2009-10701 with FEDER support and ASL, JL, SPH, and RH by Grupos Gobierno Vasco IT-464-07

Flux rope breaking and formation of a rotating blowout jet

NASA Astrophysics Data System (ADS)

Joshi, Navin Chandra; Nishizuka, Naoto; Filippov, Boris; Magara, Tetsuya; Tlatov, Andrey G.

2018-05-01

We analysed a small flux rope eruption converted into a helical blowout jet in a fan-spine configuration using multiwavelength observations taken by Solar Dynamics Observatory, which occurred near the limb on 2016 January 9. In our study, first, we estimated the fan-spine magnetic configuration with the potential-field calculation and found a sinistral small filament inside it. The filament along with the flux rope erupted upwards and interacted with the surrounding fan-spine magnetic configuration, where the flux rope breaks in the middle section. We observed compact brightening, flare ribbons, and post-flare loops underneath the erupting filament. The northern section of the flux rope reconnected with the surrounding positive polarity, while the southern section straightened. Next, we observed the untwisting motion of the southern leg, which was transformed into a rotating helical blowout jet. The sign of the helicity of the mini-filament matches the one of the rotating jets. This is consistent with recent jet models presented by Adams et al. and Sterling et al. We focused on the fine thread structure of the rotating jet and traced three blobs with the speed of 60-120 km s- 1, while the radial speed of the jet is ˜400 km s- 1. The untwisting motion of the jet accelerated plasma upwards along the collimated outer spine field lines, and it finally evolved into a narrow coronal mass ejection at the height of ˜9Rsun. On the basis of detailed analysis, we discussed clear evidence of the scenario of the breaking of the flux rope and the formation of the helical blowout jet in the fan-spine magnetic configuration.

Observational and Model Analysis of a Two-ribbon Flare Possibly Induced by a Neighboring Blowout Jet

NASA Astrophysics Data System (ADS)

Joshi, Bhuwan; Thalmann, Julia K.; Mitra, Prabir K.; Chandra, Ramesh; Veronig, Astrid M.

2017-12-01

In this paper, we present unique observations of a blowout coronal jet that possibly triggered a two-ribbon confined C1.2 flare in bipolar solar active region NOAA 12615 on 2016 December 5. The jet activity initiates at chromospheric/transition region heights with a small brightening that eventually increases in volume, with well-developed standard morphological jet features, viz., base and spire. The spire widens up with a collimated eruption of cool and hot plasma components, observed in the 304 and 94 Å channels of AIA, respectively. The speed of the plasma ejection, which forms the jet’s spire, was higher for the hot component (˜200 km s-1) than the cooler one (˜130 km s-1). The NLFF model of coronal fields at the pre- and post-jet phases successfully reveals openings of previously closed magnetic field lines with a rather inclined/low-lying jet structure. The peak phase of the jet emission is followed by the development of a two-ribbon flare that shows coronal loop emission in HXRs up to ˜25 keV energy. The coronal magnetic fields rooted at the location of EUV flare ribbons, derived from the NLFF model, demonstrate the pre-flare phase to exhibit an “X-type” configuration, while the magnetic fields at the post-flare phase are more or less oriented parallel. Comparisons of multi-wavelength measurements with the magnetic field extrapolations suggest that the jet activity likely triggered the two-ribbon flare by perturbing the field in the interior of the active region.

MULTI-WAVELENGTH POLARIMETRY AND SPECTRAL STUDY OF THE M87 JET DURING 2002–2008

DOE Office of Scientific and Technical Information (OSTI.GOV)

Avachat, Sayali S.; Perlman, Eric S.; Adams, Steven C.

We present a multi-wavelength polarimetric and spectral study of the M87 jet obtained at sub-arcsecond resolution between 2002 and 2008. The observations include multi-band archival VLA polarimetry data sets along with Hubble Space Telescope ( HST ) imaging polarimetry. These observations have better angular resolution than previous work by factors of 2–3 and in addition, allow us to explore the time domain. These observations envelop the huge flare in HST-1 located 0.″86 from the nucleus. The increased resolution enables us to view more structure in each knot, showing several resolved sub-components. We also see apparent helical structure in the polarizationmore » vectors in several knots, with polarization vectors turning either clockwise or counterclockwise near the flux maxima in various places as well as showing filamentary undulations. Some of these characteristics are correlated with flux and polarization maxima while others are not. We also examine the total flux and fractional polarization and look for changes in both radio and optical since the observations of Perlman et al. (1999) and test them against various models based on shocks and instabilities in the jet. Our results are broadly consistent with previous spine-sheath models and recollimation shock models; however, they require additional combinations of features to explain the observed complexity, e.g., shearing of magnetic field lines near the jet surface and compression of the toroidal component near shocks. In particular, in many regions we find apparently helical features both in total flux and polarization. We discuss the physical interpretation of these features.« less

The bipolar jet of the symbiotic star R Aquarii: A study of its morphology using the high-resolution HST WFC3/UVIS camera

NASA Astrophysics Data System (ADS)

Melnikov, Stanislav; Stute, Matthias; Eislöffel, Jochen

2018-04-01

Context. R Aqr is a symbiotic binary system consisting of a Mira variable with a pulsation period of 387 days and a hot companion which is presumably a white dwarf with an accretion disk. This binary system is the source of a prominent bipolar gaseous outflow. Aims: We use high spatial resolution and sensitive images from the Hubble Space Telescope (HST) to identify and investigate the different structural components that form the complex morphology of the R Aqr jet. Methods: We present new high-resolution HST WFC3/UVIS narrow-band images of the R Aqr jet obtained in 2013/14 using the [OIII]λ5007, [OI]λ6300, [NII]λ6583, and Hα emission lines. These images also allow us to produce detailed maps of the jet flow in several line ratios such as [OIII]λ5007/[OI]λ6300 and [NII]λ6583/[OI]λ6300 which are sensitive to the outflow temperature and its hydrogen ionisation fraction. The new emission maps together with archival HST data are used to derive and analyse the proper motion of prominent emitting features which can be traced over 20 years with the HST observations. Results: The images reveal the fine gas structure of the jet out to distances of a few tens of arcseconds from the central region, as well as in the innermost region, within a few arcseconds around the stellar source. They reveal for the first time the straight, highly collimated jet component which can be traced to up to 900 AU in the NE direction. Images in [OIII]λ5007, [OI]λ6300, and [NII]λ6583 clearly show a helical pattern in the jet beams which may derive from the small-scale precession of the jet. The highly collimated jet is accompanied by a wide opening angle outflow which is filled by low excitation gas. The position angles of the jet structures as well as their opening angles are calculated. Our measurements of the proper motions of some prominent emission knots confirm the scenario of gas acceleration during the propagation of the outflow. Finally, we produce several detailed line ratio maps which present a mosaic combined from the large field and the PSF-subtracted inner region. Conclusions: The high signal-to-noise HST WFC3/UVIS images provide powerful tools for the study of the jet morphology and also bring detailed information about the physical jet gas conditions. The simultaneous observations of [OIII], [OI], [NII], and [SII] would allow us to measure basic parameters of the ionised gas in the R Aqr outflow such as electron density, electron temperature and hydrogen ionisation fraction, and compare them with other stellar jets.

A small-scale eruption leading to a blowout macrospicule jet in an on-disk coronal hole

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adams, Mitzi; Sterling, Alphonse C.; Moore, Ronald L.

2014-03-01

We examine the three-dimensional magnetic structure and dynamics of a solar EUV-macrospicule jet that occurred on 2011 February 27 in an on-disk coronal hole. The observations are from the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) and the SDO Helioseismic and Magnetic Imager (HMI). The observations reveal that in this event, closed-field-carrying cool absorbing plasma, as in an erupting mini-filament, erupted and opened, forming a blowout jet. Contrary to some jet models, there was no substantial recently emerged, closed, bipolar-magnetic field in the base of the jet. Instead, over several hours, flux convergence and cancellation at the polarity inversionmore » line inside an evolved arcade in the base apparently destabilized the entire arcade, including its cool-plasma-carrying core field, to undergo a blowout eruption in the manner of many standard-sized, arcade-blowout eruptions that produce a flare and coronal mass ejection. Internal reconnection made bright 'flare' loops over the polarity inversion line inside the blowing-out arcade field, and external reconnection of the blowing-out arcade field with an ambient open field made longer and dimmer EUV loops on the outside of the blowing-out arcade. That the loops made by the external reconnection were much larger than the loops made by the internal reconnection makes this event a new variety of blowout jet, a variety not recognized in previous observations and models of blowout jets.« less

A cosmic ray super high energy multicore family event. 2: Structure and fragmentation characteristics of the jets

NASA Technical Reports Server (NTRS)

1985-01-01

Quarks and gluons are not directly observable, but may be displayed through fragmentation in the form of hadronic jets, the evidence of which was first revealed in cosmic ray interactions before the advent of the modern theory of strong interactions. Experimental results from ISR and SPPS collider rendered the jet phenomena more confident and definite. All the properties of jets observed up to now at ISR and SPPS collider are in agreement with the predictions of QCD. In order to make further test of QCD in still higher energy regions, detailed study of super high energy jet events in cosmic rays is very desirable. The event KO E19 observed in the Mt. Kambala emulsion chamber is an interesting event for such study. The general features of KO E19 is described. Its total visible energy is sigma E sub gamma = 1537 TeV(E sub min = 1.5 TeV) and production height H=(70 + or - 30)m, with a hadron as its primary particle. Besides about forty small clusters, there are five super high energy cores or jets, one lying near the center of the event while the other four surrounding it, having incident directions making small angles with that of the primary particle. Detailed analysis is done on the emulsion plates inserted in the chamber, making full use of their fine granularity, superior in detecting and analyzing jet events, specially their substructures.

Measurement of jet fragmentation in Pb+Pb and pp collisions at $$\\sqrt{s}$$$_ {NN}$$ = 2.76 TeV with the ATLAS detector at the LHC

DOE PAGES

Aaboud, M.; Aad, G.; Abbott, B.; ...

2017-06-08

The distributions of transverse momentum and longitudinal momentum fraction of charged particles in jets are measured in Pb+Pb and pp collisions with the ATLAS detector at the LHC. The distributions are measured as a function of jet transverse momentum and rapidity. The analysis utilises an integrated luminosity of 0.14 nb -1 of Pb+Pb data and 4.0 pb -1 of pp data collected in 2011 and 2013, respectively, at the same centre-of-mass energy of 2.76 TeV per colliding nucleon pair. The distributions measured in pp collisions are used as a reference for those measured in Pb+Pb collisions in order to evaluatemore » the impact on the internal structure of jets from the jet energy loss of fast partons propagating through the hot, dense medium created in heavy-ion collisions. Modest but significant centrality-dependent modifications of fragmentation functions in Pb+Pb collisions with respect to those in pp collisions are seen. Finally, no significant dependence of modifications on jet p T and rapidity selections is observed except for the fragments with the highest transverse momenta for which some reduction of yields is observed for more forward jets.« less

North-South Asymmetry in the Magnetic Deflection of Polar Coronal Jets

NASA Astrophysics Data System (ADS)

Nisticò, Giuseppe; Zimbardo, Gaetano; Bothmer, Volker; Patsourakos, Spiros

Solar jets observed with the Extreme Ultra-Violet Imager (EUVI) and CORonagraphs (COR) instruments aboard the STEREO mission provide a tool to probe and understand the magnetic structure of the corona. Since the corona is an environment where the magnetic pressure is greater than the kinetic pressure, the magnetic field controls the dynamics of plasma and, on average, jets during their propagation trace the magnetic field lines. We discuss the North-South asymmetry of the magnetic field of the Sun as inferred from measurements of the deflection of polar coronal hole jets when they propagate throughout the corona. We measured the position angle at 1 and at 2 solar radii for the 79 jets of the catalogue of Nisticò et al. (2009), based on the STEREO ultraviolet and visible observations, and we found that the propagation is not radial. The average jet deflection is studied both in the plane perpendicular to the line of sight, and, for a reduced number of jets in the three dimensional (3D) space. We find that the magnetic deflection of jets is larger in the North than in the South, with an asymmetry which is consistent with the N-S asymmetry of the heliospheric magnetic field inferred from the Ulysses in situ measurements, and gives clues to the study of the large scale solar magnetic field.

Extracting Near-Field Structures Related to Noise Production in High Speed Jet

NASA Astrophysics Data System (ADS)

Kan, Pinqing; Lewalle, Jacques; Syracuse University Team

2015-11-01

Jet noise research started with Lighthill's seminal work on aerodynamic sound in 1952. The current consensus is that jet noise has two main kinds of sources, the large turbulent structures and the fine-scale turbulence. Coherent structures and the noise they produce are the focus of this paper because they offer better odds for control and they are associated with the most energetic part of the acoustic spectrum. We develop an algorithm using cross-correlation, continuous wavelet and pattern recognition techniques to search for near-field (NF) structures associated with far-field (FF) acoustic noise at aft angles. An experimental data is analyzed which measured a cold circular jet of Mach 0.6 (Low et al. 2013). The events identified are short wave packets in the time-frequency domain, distorted by ambient perturbations. The statistics of the event properties, including intermittency, frequency and magnitude are consistent with observations from other researchers. We investigate the localization and time sequencing of the events and use ensemble average to bring out the distinct structures associated to noise production. The filtered signals including / excluding the events are compared and the results are further tested using synthetic and randomized signals. This work has been funded by Spectral Energies LLC through an Air Force Research Lab SBIR, an AFOSR Grant and Syracuse University.

Collimation, Acceleration, and Recollimation Shock in the Jet of Gamma-Ray Emitting Radio-loud Narrow-line Seyfert 1 Galaxy 1H0323+342

NASA Astrophysics Data System (ADS)

Hada, Kazuhiro; Doi, Akihiro; Wajima, Kiyoaki; D’Ammando, Filippo; Orienti, Monica; Giroletti, Marcello; Giovannini, Gabriele; Nakamura, Masanori; Asada, Keiichi

2018-06-01

We investigated the detailed radio structure of the jet of 1H 0323+342 using high-resolution multifrequency Very Long Baseline Array observations. This source is known as the nearest γ-ray emitting radio-loud narrow-line Seyfert 1 (NLS1) galaxy. We discovered that the morphology of the inner jet is well characterized by a parabolic shape, indicating that the jet is continuously collimated near the jet base. On the other hand, we found that the jet expands more rapidly at larger scales, resulting in a conical shape. The location of the “collimation break” is coincident with a bright quasi-stationary feature at 7 mas from core (corresponding to a deprojected distance on the order of ∼100 pc), where the jet width locally contracts together with highly polarized signals, suggesting a recollimation shock. We found that the collimation region is coincident with the region where the jet speed gradually accelerates, suggesting a coexistence of the jet acceleration and collimation zone, ending up with the recollimation shock, which could be a potential site of high-energy γ-ray flares detected by the Fermi-LAT. Remarkably, these observational features of the 1H 0323+342 jet are overall very similar to those of the nearby radio galaxy M87 and HST-1 as well as some blazars, suggesting that a common jet formation mechanism might be at work. Based on the similarity of the jet profile of the two sources, we also briefly discuss the mass of the central black hole of 1H 0323+342, which is also still highly controversial in this source and NLS1s in general.

Multiscale Currents Observed by MMS in the Flow Braking Region.

PubMed

Nakamura, Rumi; Varsani, Ali; Genestreti, Kevin J; Le Contel, Olivier; Nakamura, Takuma; Baumjohann, Wolfgang; Nagai, Tsugunobu; Artemyev, Anton; Birn, Joachim; Sergeev, Victor A; Apatenkov, Sergey; Ergun, Robert E; Fuselier, Stephen A; Gershman, Daniel J; Giles, Barbara J; Khotyaintsev, Yuri V; Lindqvist, Per-Arne; Magnes, Werner; Mauk, Barry; Petrukovich, Anatoli; Russell, Christopher T; Stawarz, Julia; Strangeway, Robert J; Anderson, Brian; Burch, James L; Bromund, Ken R; Cohen, Ian; Fischer, David; Jaynes, Allison; Kepko, Laurence; Le, Guan; Plaschke, Ferdinand; Reeves, Geoff; Singer, Howard J; Slavin, James A; Torbert, Roy B; Turner, Drew L

2018-02-01

We present characteristics of current layers in the off-equatorial near-Earth plasma sheet boundary observed with high time-resolution measurements from the Magnetospheric Multiscale mission during an intense substorm associated with multiple dipolarizations. The four Magnetospheric Multiscale spacecraft, separated by distances of about 50 km, were located in the southern hemisphere in the dusk portion of a substorm current wedge. They observed fast flow disturbances (up to about 500 km/s), most intense in the dawn-dusk direction. Field-aligned currents were observed initially within the expanding plasma sheet, where the flow and field disturbances showed the distinct pattern expected in the braking region of localized flows. Subsequently, intense thin field-aligned current layers were detected at the inner boundary of equatorward moving flux tubes together with Earthward streaming hot ions. Intense Hall current layers were found adjacent to the field-aligned currents. In particular, we found a Hall current structure in the vicinity of the Earthward streaming ion jet that consisted of mixed ion components, that is, hot unmagnetized ions, cold E × B drifting ions, and magnetized electrons. Our observations show that both the near-Earth plasma jet diversion and the thin Hall current layers formed around the reconnection jet boundary are the sites where diversion of the perpendicular currents take place that contribute to the observed field-aligned current pattern as predicted by simulations of reconnection jets. Hence, multiscale structure of flow braking is preserved in the field-aligned currents in the off-equatorial plasma sheet and is also translated to ionosphere to become a part of the substorm field-aligned current system.

ATMOSPHERIC CIRCULATION OF BROWN DWARFS: JETS, VORTICES, AND TIME VARIABILITY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Xi; Showman, Adam P., E-mail: xiz@lpl.arizona.edu

2014-06-10

A variety of observational evidence demonstrates that brown dwarfs exhibit active atmospheric circulations. In this study we use a shallow-water model to investigate the global atmospheric dynamics in the stratified layer overlying the convective zone on these rapidly rotating objects. We show that the existence and properties of the atmospheric circulation crucially depend on key parameters including the energy injection rate and radiative timescale. Under conditions of strong internal heat flux and weak radiative dissipation, a banded flow pattern comprised of east-west jet streams spontaneously emerges from the interaction of atmospheric turbulence with the planetary rotation. In contrast, when themore » internal heat flux is weak and/or radiative dissipation is strong, turbulence injected into the atmosphere damps before it can self-organize into jets, leading to a flow dominated by transient eddies and isotropic turbulence instead. The simulation results are not very sensitive to the form of the forcing. Based on the location of the transition between jet-dominated and eddy-dominated regimes, we suggest that many brown dwarfs may exhibit atmospheric circulations dominated by eddies and turbulence (rather than jets) due to the strong radiative damping on these worlds, but a jet structure is also possible under some realistic conditions. Our simulated light curves capture important features from observed infrared light curves of brown dwarfs, including amplitude variations of a few percent and shapes that fluctuate between single-peak and multi-peak structures. More broadly, our work shows that the shallow-water system provides a useful tool to illuminate fundamental aspects of the dynamics on these worlds.« less

Luminosity function and jet structure of Gamma-Ray Burst

NASA Astrophysics Data System (ADS)

Pescalli, A.; Ghirlanda, G.; Salafia, O. S.; Ghisellini, G.; Nappo, F.; Salvaterra, R.

2015-02-01

The structure of gamma-ray burst (GRB) jets impacts on their prompt and afterglow emission properties. The jet of GRBs could be uniform, with constant energy per unit solid angle within the jet aperture, or it could be structured, namely with energy and velocity that depend on the angular distance from the axis of the jet. We try to get some insight about the still unknown structure of GRBs by studying their luminosity function. We show that low (1046-48 erg s-1) and high (i.e. with L ≥ 1050 erg s-1) luminosity GRBs can be described by a unique luminosity function, which is also consistent with current lower limits in the intermediate luminosity range (1048-50 erg s-1). We derive analytical expressions for the luminosity function of GRBs in uniform and structured jet models and compare them with the data. Uniform jets can reproduce the entire luminosity function with reasonable values of the free parameters. A structured jet can also fit adequately the current data, provided that the energy within the jet is relatively strongly structured, i.e. E ∝ θ-k with k ≥ 4. The classical E ∝ θ-2 structured jet model is excluded by the current data.

Interaction of Vortex Rings and Steady Jets with Permeable Screens of Varied Porosity

NASA Astrophysics Data System (ADS)

Musta, Mustafa

2013-11-01

Vortex ring and steady jet interaction with a porous matrix formed from several parallel, transparent permeable screens with the same grid geometry for open area ratios (φ) 49.5% - 83.8% was studied previously using digital particle image velocimetry (DPIV) at jet Reynolds number (Re) of 1000-3000. Vortex ring results showed that unlike the experiments with thin screens, a transmitted vortex ring, which has a similar diameter to the primary one, wasn't formed. Instead a centerline vortex ring like structure formed and its diameter, circulation, and dissipation time decreased as φ decreased. However, for the case of screens φ = 55.7% with large screen spacing, reformation of large scale weak vortex rings was observed downstream of the first screen. The present work experimentally investigates the interaction of vortex rings and steady jets with screens of decreasing φ (83.8%-49.5%) in the flow direction. A piston type vortex ring generator was used and measurements were made using DPIV. The vortex ring results show that the size and circulation of the vortex ring like flow structure was changed based on the screen φ within the permeable screen matrix. Similarly, steady jet flow structure and the local turbulent kinetic energy was changed based on the local screen φ.

VLBI Monitoring of the Nucleus of Centaurus A

NASA Technical Reports Server (NTRS)

Preston, Robert

1995-01-01

A series of 8.4 GHz VLBI images of the nucleus of Centaurus A have been made with a Southern Hemisphere array over more than a 3-year time span. The nuclear radio jet is approximately 50 mas in length, or about 1 pc at the 3.5 Mpc distance of Centaurus A. Sub-luminal motion is seen and structural changes observed on time-scales shorter than four months. Observations at both 4.8 and 8.4 GHz at one epoch allow identification of the core at the southwestern end of the jet.

THE ROTATION PERIOD OF C/2014 Q2 (LOVEJOY)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Serra-Ricart, Miquel; Licandro, Javier, E-mail: mserra@iac.es, E-mail: jlicandr@iac.es

2015-11-20

C/2014 Q2 (Lovejoy) was observed around perihelion (2015 January 30) on 15 nights between 2015 January 21 and February 11 using the TADer 0.3-m astrograph telescope at Teide Observatory (IAC, Tenerife, Spain). Two large spiral jet structures were observed over several cometary rotations. A new method of searching for periodicities in the PA of spiral jets in the coma region at a fixed distance (20,624 km) from the cometary optocenter is presented and used to determine a nuclear rotation period of 17.89 ± 0.17 hr.

On the Surface Breakup of a Non-turbulent Round Liquid Jet in Cross-flow

NASA Astrophysics Data System (ADS)

Behzad, Mohsen; Ashgriz, Nasser

2011-11-01

The atomization of a non-turbulent liquid jet injected into a subsonic cross-flow consists of two parts: (1) primary breakup and (2) secondary breakup. Two distinct regimes for the liquid jet primary breakup have been recognized; the so called column breakup and surface breakup. In the column breakup mode, the entire liquid jet undergoes disintegration into large liquid lumps. Quiet differently in the surface breakup regime, liquid fragments with various sizes and shapes are separated from the surface of the jet. Despite many experimental studies the mechanisms of jet surface breakup is not fully understood. Thus this study aims at providing useful observations regarding the underlying physics involving the surface breakup mechanism of a liquid jet in cross-flow, using detailed numerical simulations. The results show that a two-stage mechanism can be responsible for surface breakup. In the first stage, a sheet-like structure extrudes towards the downstream, and in the second stage it disintegrates into ligaments and droplets due to aerodynamic instability.

Flow and acoustic properties of low Reynolds number supersonic underexpanded jets

NASA Technical Reports Server (NTRS)

Hu, T. F.; Mclaughlin, D. K.

1981-01-01

Flow and acoustic measurements are made of cold model jets exhausting from a choked nozzle at pressure conditions corresponding to those of Mach 1.4 and 2.1 jets to investigate noise production properties of underexpanded supersonic jets. Mean flow measurements are made using pitot and static pressure probes, with flow fluctuation measurements made with a hot-wire probe and acoustic measurements made with a transversing microphone. Two convergent nozzles with exit diameters of 7.0 and 7.9 mm are used with an exciter consisting of a 0.8 mm tungsten electrode positioned 2 mm from the exit. Shock structure is observed as having a significant effect on the development of the flow field, while large-scale instabilities have higher growth rates in the shock containing underexpanded jets. The role of the asymmetric n = + or - 1 sinusoidal instability is clarified, and results suggest that the broadband shock associated noise of conventional high Reynolds number jets is not related to large-scale jet instability.

Radiation from Relativistic Jets

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.; Mizuno, Y.; Hardee, P.; Sol, H.; Medvedev, M.; Zhang, B.; Nordlund, A.; Frederiksen, J. T.; Fishman, G. J.; Preece, R.

2008-01-01

Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., gamma-ray bursts (GRBs), active galactic nuclei (AGNs), and Galactic microquasar systems usually have power-law emission spectra. Recent PIC simulations of relativistic electron-ion (electron-positron) jets injected into a stationary medium show that particle acceleration occurs within the downstream jet. In the presence of relativistic jets, instabilities such as the Buneman instability, other two-streaming instability, and the Weibel (filamentation) instability create collisionless shocks, which are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The 'jitter' radiation from deflected electrons in small-scale magnetic fields has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation, a case of diffusive synchrotron radiation, may be important to understand the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.

[Kelvin-Helmholtz instability in protostellar jets

NASA Technical Reports Server (NTRS)

Stone, James; Hardee, Philip

1996-01-01

NASA grant NAG 5 2866, funded by the Astrophysics Theory Program, enabled the study the Kelvin-Helmholtz instability in protostellar jets. In collaboration with co-investigator Philip Hardee, the PI derived the analytic dispersion relation for the instability in including a cooling term in the energy equation which was modeled as one of two different power laws. Numerical solutions to this dispersion relation over a wide range of perturbation frequencies, and for a variety of parameter values characterizing the jet (such as Mach number, and density ratio) were found It was found that the growth rates and wavelengths associated with unstable roots of the dispersion relation in cooling jets are significantly different than those associated with adiabatic jets, which have been studied previously. In collaboration with graduate student Jianjun Xu (funded as a research associate under this grant), hydrodynamical simulations were used to follow the growth of the instability into the nonlinear regime. It was found that asymmetric surface waves lead to large amplitude, sinusoidal distortions of the jet, and ultimately to disruption Asymmetric body waves, on the other hand, result in the formation of shocks in the jet beam in the nonlinear regime. In cooling jets, these shocks lead to the formation of dense knots and filaments of gas within the jet. For sufficiently high perturbation frequencies, however, the jet cannot respond and it remains symmetric. Applying these results to observed systems, such as the Herbig-Haro jets HH34, HH111 and HH47 which have been observed with the Hubble Space Telescope, we predicted that some of the asymmetric structures observed in these systems could be attributed to the K-H modes, but that perturbations on timescales associated with the inner disk (about 1 year) would be too rapid to cause disruption. Moreover, it was discovered that weak shock 'spurs' in the ambient gas produced by ripples in the jet surface due to nonlinear, modes of surface and/or body waves could accelerate the ambient gas to low velocity. This latter effect represents a new mechanism by which supersonic jets can accelerate low velocity outflows.

Formation of X-ray emitting stationary shocks in magnetized protostellar jets

NASA Astrophysics Data System (ADS)

Ustamujic, S.; Orlando, S.; Bonito, R.; Miceli, M.; Gómez de Castro, A. I.; López-Santiago, J.

2016-12-01

Context. X-ray observations of protostellar jets show evidence of strong shocks heating the plasma up to temperatures of a few million degrees. In some cases, the shocked features appear to be stationary. They are interpreted as shock diamonds. Aims: We investigate the physics that guides the formation of X-ray emitting stationary shocks in protostellar jets; the role of the magnetic field in determining the location, stability, and detectability in X-rays of these shocks; and the physical properties of the shocked plasma. Methods: We performed a set of 2.5-dimensional magnetohydrodynamic numerical simulations that modelled supersonic jets ramming into a magnetized medium and explored different configurations of the magnetic field. The model takes into account the most relevant physical effects, namely thermal conduction and radiative losses. We compared the model results with observations, via the emission measure and the X-ray luminosity synthesized from the simulations. Results: Our model explains the formation of X-ray emitting stationary shocks in a natural way. The magnetic field collimates the plasma at the base of the jet and forms a magnetic nozzle there. After an initial transient, the nozzle leads to the formation of a shock diamond at its exit which is stationary over the time covered by the simulations ( 40-60 yr; comparable with timescales of the observations). The shock generates a point-like X-ray source located close to the base of the jet with luminosity comparable with that inferred from X-ray observations of protostellar jets. For the range of parameters explored, the evolution of the post-shock plasma is dominated by the radiative cooling, whereas the thermal conduction slightly affects the structure of the shock. A movie is available at http://www.aanda.org

An experimental study of the structure and acoustic field of a jet in a cross stream. [Ames 7-ft by 10-ft wind tunnel tests

NASA Technical Reports Server (NTRS)

Camelier, I.; Karamcheti, K.

1976-01-01

The plane of symmetry of a high speed circular jet was surveyed to measure the mean and turbulent velocity fields by using constant temperature hot wire anemometry. The intensity of the noise radiated from the jet was determined in the tunnel test section by utilizing the cross-correlation at a particular time delay between the signals of two microphones suitably located along a given direction. Experimental results indicate that the turbulent intensity inside the crossflow jet increases by a factor of (1 + 1/2) as compared to the turbulent intensity of the same jet under free conditions, with r indicating the ratio of the jet velocity by the cross stream velocity. The peak observed in the turbulence spectra obtained inside the potential core of the jet has a frequency that increases by the same factor with respect to the corresponding frequency measured in the case of the free jet. The noise radiated by the jet becomes more intense as the crossflow velocity increases. The measured acoustic intensity of the crossflow jet is higher than the value which would be expected from the increase of the turbulent intensity only.

Observations and Analysis of the GK Persei Nova Shell and its "Jet-like" Feature

NASA Astrophysics Data System (ADS)

Harvey, E.; Redman, M. P.; Boumis, P.; Akras, S.

2015-12-01

GK Persei (1901, the "Firework Nebula") is an old but bright nova remnant that offers a chance to probe the physics and kinematics of nova shells. The kinematics in new and archival longslit optical echelle spectra were analysed using the SHAPE software. New imaging from the Aristarchos telescope continues to track the proper motion, extinction and structural evolution of the knots, which have been observed intermittently over several decades. We present for the first time, kinematical constraints on a large faint "jet" feature, that was previously detected beyond the shell boundary. These observational constraints allow for the generation of models for individual knots, interactions within knot complexes, and the "jet" feature. Put together, and taking into account dwarf-nova accelerated winds emanating from the central source, these data and models give a deeper insight into the GK Per nova remnant as a whole.

Jet-Like Structures and Wake in Mg I (518 nm) Images of 1999 Leonid Storm Meteors

NASA Technical Reports Server (NTRS)

Taylor, M. J.; Murray, I. S.; Jenniskens, P.

2000-01-01

Small meteoric fragments are ejected at significant transverse velocities from some (up to approx. 8%) fast Leonid meteors. We reach this conclusion using low light intensified image measurements obtained during the 1999 Leonid Multi-Instrument Aircraft Campaign. High spatial resolution, narrow band image measurements of the Mg I emission at 518 nm have been used to clearly identify jet-like features in the meteor head that are the same as first observed in white light. We postulate that these unusual structures are caused by tiny meteoroid fragments (containing metallic grains) being rapidly ejected away from the core meteoroid as the constituent glue evaporates. Marked curvature observed in the jet-like filaments suggest that the parent meteoroids are spinning and as the whirling fragments are knocked away by the impinging air molecules, or by grain-grain collisions in the fragment ensemble, they ablate quickly generating an extended area of structured luminosity up to about 1-2 km from the meteoroid center. Fragments with smaller transverse velocity components are thought to be responsible for the associated beading evident in the wake of these unusual Leonid meteors.

Opposed jet diffusion flames of nitrogen-diluted hydrogen vs air - Axial LDA and CARS surveys; fuel/air rates at extinction

NASA Technical Reports Server (NTRS)

Pellett, G. L.; Northam, G. B.; Wilson, L. G.; Jarrett, Olin, Jr.; Antcliff, R. R.

1989-01-01

An experimental study of H-air counterflow diffusion flames (CFDFs) is reported. Coaxial tubular opposed jet burners were used to form dish-shaped CFDFs centered by opposing laminar jets of H2/N2 and air in an argon bath at 1 atm. Jet velocities for extinction and flame restoration limits are shown versus input H2 concentration. LDA velocity data and CARS temperature and absolute N2, O2 density data give detailed flame structure on the air side of the stagnation point. The results show that air jet velocity is a more fundamental and appropriate measure of H2-air CFDF extinction than input H2 mass flux or fuel jet velocity. It is proposed that the observed constancy of air jet velocity for fuel mixtures containing 80 to 100 percent H2 measure a maximum, kinetically controlled rate at which the CFDF can consume oxygen in air. Fuel velocity mainly measures the input jet momentum required to center an H2/N2 versus air CFDF.

Experimental investigation of coaxial-gun-formed plasmas injected into a background transverse magnetic field or plasma

NASA Astrophysics Data System (ADS)

Zhang, Yue; Fisher, Dustin M.; Gilmore, Mark; Hsu, Scott C.; Lynn, Alan G.

2018-05-01

Injection of coaxial-gun-formed magnetized plasmas into a background transverse vacuum magnetic field or into a background magnetized plasma has been studied in the helicon-cathode (HelCat) linear plasma device at the University of New Mexico [M. Gilmore et al., J. Plasma Phys. 81, 345810104 (2015)]. A magnetized plasma jet launched into a background transverse magnetic field shows emergent kink stabilization of the jet due to the formation of a sheared flow in the jet above the kink stabilization threshold 0.1kVA [Y. Zhang et al., Phys. Plasmas 24, 110702 (2017)]. Injection of a spheromak-like plasma into a transverse background magnetic field led to the observation of finger-like structures on the side with a stronger magnetic field null between the spheromak and the background field. The finger-like structures are consistent with magneto-Rayleigh-Taylor instability. Jets or spheromaks launched into a background, low-β magnetized plasma show similar behavior as above, respectively, in both cases.

Highly porous micro-roughened structures developed on aluminum surface using the jet of rotating arc discharges at atmospheric pressure

NASA Astrophysics Data System (ADS)

Asadollahi, Siavash; Farzaneh, Masoud; Stafford, Luc

2018-02-01

Aluminum 6061 samples were exposed to the jet of an atmospheric pressure rotating arc discharge operated in either nitrogen or air. After multiple passes of treatment with an air-based plasma jet at very short source-to-substrate distances, scanning electron microscopy combined with x-ray photoelectron spectroscopy revealed a highly porous micro-roughened alumina-based structure on the surface of aluminum. Based on optical emission spectroscopy and high-speed optical imaging of the jet interacting with aluminum samples, it was found that the process is mainly driven by the energy transfer from the plasma source to the surface through transient plasma-transferred arcs. The occurrence of multiple arc discharges over very short time scales can induce rapid phase transformations of aluminum with characteristics similar to the ones usually observed during laser ablation of materials with femto- to nanosecond laser pulses or during the formation of cathode spots on the surface of metals.

Jet-cooled laser-induced dispersed fluorescence spectroscopy of TaN: Observation of a3Δ and A1Δ states

NASA Astrophysics Data System (ADS)

Mukund, Sheo; Bhattacharyya, Soumen; Nakhate, S. G.

2016-07-01

Laser-induced dispersed fluorescence spectra of TaN molecules, produced in a free-jet apparatus, have been studied. Two spin components of the lowest-lying a3Δ state along with their vibrational structure have been observed. The A1Δ state, which was predicted earlier by ab initio calculation has also been observed. The X1Σ+ ground state vibrational progression up to v = 9 has been recorded. The experimentally determined term energies and vibrational constants at equilibrium for the ground and a3Δ states are in fairly good agreement with the ab initio values reported earlier.

Modification of vortex dynamics and transport properties of transitional axisymmetric jets using zero-net-mass-flux actuation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Önder, Asim; Meyers, Johan, E-mail: johan.meyers@mech.kuleuven.be

2014-07-15

We study the near field of a zero-net-mass-flux (ZNMF) actuated round jet using direct numerical simulations. The Reynolds number of the jet Re{sub D} = 2000 and three ZNMF actuators are used, evenly distributed over a circle, and directed towards the main jet. The actuators are triggered in phase, and have a relatively low momentum coefficient of C{sub μ} = 0.0049 each. We study four different control frequencies with Strouhal numbers ranging from St{sub D} = 0.165 to St{sub D} = 1.32; next to that, also two uncontrolled baseline cases are included in the study. We find that this typemore » of ZNMF actuation leads to strong deformations of the near-field jet region that are very similar to those observed for non-circular jets. At the end of the jet's potential core (x/D = 5), the jet-column cross section is deformed into a hexagram-like geometry that results from strong modifications of the vortex structures. Two mechanisms lead to these modifications, i.e., (i) self-deformation of the jet's primary vortex rings started by distortions in their azimuthal curvature by the actuation, and (ii) production of side jets by the development and subsequent detachment of secondary streamwise vortex pairs. Further downstream (x/D = 10), the jet transforms into a triangular pattern, as the sharp corner regions of the hexagram entrain fluid and spread. We further investigate the global characteristics of the actuated jets. In particular when using the jet preferred frequency, i.e., St{sub D} = 0.33, parameters such as entrainment, centerline decay rate, and mean turbulent kinetic energy are significantly increased. Furthermore, high frequency actuation, i.e., St{sub D} = 1.32, is found to suppress the mechanisms leading to large scale structure growth and turbulent kinetic energy production. The simulations further include a passive scalar equation, and passive scalar mixing is also quantified and visualized.« less

Very Long Baseline Array Imaging of Type-2 Seyferts with Double-peaked Narrow Emission Lines: Searches for Sub-kpc Dual AGNs and Jet-powered Outflows

NASA Astrophysics Data System (ADS)

Liu, Xin; Lazio, T. Joseph W.; Shen, Yue; Strauss, Michael A.

2018-02-01

This paper presents Very Long Baseline Array (VLBA) observations of 13 double-peaked [O III] emission-line type-2 active galactic nuclei (AGNs) at redshifts 0.06 < z < 0.41 (with a median redshift of z ∼ 0.15) identified in the Sloan Digital Sky Survey. Such double-peaked emission-line objects may result from jets or outflows from the central engine or from a dual AGN. The VLBA provides an angular resolution of ≲10 pc at the distance of many of these galaxies, sufficient to resolve the radio emission from extremely close dual AGNs and to contribute to understanding the origin of double-peaked [O III] emission lines. Of the 13 galaxies observed at 3.6 cm (8.4 GHz), we detect six at a 1σ sensitivity level of ∼0.15 mJy beam‑1, two of which show clear jet structures on scales ranging from a few milliarcseconds to tens of milliarcseconds (corresponding to a few pc to tens of pc at a median redshift of 0.15). We suggest that radio-loud, double-peaked emission-line type-2 AGNs may be indicative of jet produced structures, but a larger sample of double-peaked [O III] AGNs with high angular resolution radio observations will be required to confirm this suggestion. Based, in part, on observations made with the Very Long Baseline Array, obtained at the Long Baseline Observatory. The Long Baseline Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Formation of dynamical structures in relativistic jets: the FRI case

NASA Astrophysics Data System (ADS)

Rossi, P.; Mignone, A.; Bodo, G.; Massaglia, S.; Ferrari, A.

2008-09-01

Context: Strong observational evidence indicates that all extragalactic jets associated with AGNs move at relativistic speed up to 100 pc-1 kpc scales from the nucleus. At greater distances, reflecting the Fanaroff-Riley radio source classification, we observe an abrupt deceleration in FR-I jets while relativistic motions persist up to Mpc scale in FR-II. Moreover, VLBI observations of some object such as B2 1144+35, Mrk501 and M87 show limb brightening of the jet radio emission on the parsec scale. This effect is interpreted kinematically as due to the deboosted central spine at high Lorentz factor and of a weakly relativistic external layer. Aims: In this paper we investigate whether these effects can be interpreted by a braking of the collimated flow by external medium entrainment favored by shear instabilities, namely Kelvin-Helmholtz instabilities. We examine in details the physical conditions under which significant deceleration of a relativistic flow is produced. Methods: We investigated the phenomenon by means of high-resolution three-dimensional relativistic hydrodynamic simulations using the PLUTO code for computational astrophysics. Results: We find that the most important parameter in determining the instability evolution and the entrainment properties is the ambient/jet density contrast. We show that lighter jets suffer stronger slowing down in the external layer than in the central part and conserve a central spine with a high Lorentz factor. Conclusions: Our model is verified by constructing synthetic emission maps from the numerical simulations which compare reasonably well with VLBI observations of the inner part of FR-I sources.

AN INTRIGUING CHROMOSPHERIC JET OBSERVED BY HINODE: FINE STRUCTURE KINEMATICS AND EVIDENCE OF UNWINDING TWISTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu Wei; Berger, Thomas E.; Title, Alan M.

2009-12-10

We report a chromospheric jet lasting for more than 1 hr observed by the Hinode Solar Optical Telescope in unprecedented detail. The ejection occurred in three episodes separated by 12-14 minutes, with the amount and velocity of material decreasing with time. The upward velocities range from 438 to 33 km s{sup -1}, while the downward velocities of the material falling back have smaller values (mean: -56km s{sup -1}) and a narrower distribution (standard deviation: 14km s{sup -1}). The average acceleration inferred from parabolic spacetime tracks is 141 m s{sup -2}, a fraction of the solar gravitational acceleration. The jet consistsmore » of fine threads (0.''5-2'' wide), which exhibit coherent, oscillatory transverse motions perpendicular to the jet axis and about a common equilibrium position. These motions propagate upward along the jet, with the maximum phase speed of 744+-11 km s{sup -1}at the leading front of the jet. The transverse oscillation velocities range from 151 to 26 km s{sup -1}, amplitudes from 6.0 to 1.9 Mm, and periods from 250 to 536 s. The oscillations slow down with time and cease when the material starts to fall back. The falling material travels along almost straight lines in the original direction of ascent, showing no transverse motions. These observations are consistent with the scenario that the jet involves untwisting helical threads, which rotate about the axis of a single large cylinder and shed magnetic helicity into the upper atmosphere.« less

KELVIN–HELMHOLTZ INSTABILITY IN SOLAR CHROMOSPHERIC JETS: THEORY AND OBSERVATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuridze, D.; Henriques, V.; Mathioudakis, M.

2016-10-20

Using data obtained by the high-resolution CRisp Imaging SpectroPolarimeter instrument on the Swedish 1 m Solar Telescope, we investigate the dynamics and stability of quiet-Sun chromospheric jets observed at the disk center. Small-scale features, such as rapid redshifted and blueshifted excursions, appearing as high-speed jets in the wings of the H α line, are characterized by short lifetimes and rapid fading without any descending behavior. To study the theoretical aspects of their stability without considering their formation mechanism, we model chromospheric jets as twisted magnetic flux tubes moving along their axis, and use the ideal linear incompressible magnetohydrodynamic approximation tomore » derive the governing dispersion equation. Analytical solutions of the dispersion equation indicate that this type of jet is unstable to Kelvin–Helmholtz instability (KHI), with a very short (few seconds) instability growth time at high upflow speeds. The generated vortices and unresolved turbulent flows associated with the KHI could be observed as a broadening of chromospheric spectral lines. Analysis of the H α line profiles shows that the detected structures have enhanced line widths with respect to the background. We also investigate the stability of a larger-scale H α jet that was ejected along the line of sight. Vortex-like features, rapidly developing around the jet’s boundary, are considered as evidence of the KHI. The analysis of the energy equation in the partially ionized plasma shows that ion–neutral collisions may lead to fast heating of the KH vortices over timescales comparable to the lifetime of chromospheric jets.« less

Scalar Measurements and Analysis of Helium Jets in Earth Gravity and Microgravity using Rainbow Schlieren Deflectometry

NASA Technical Reports Server (NTRS)

Yep, Tze Wing

2001-01-01

Recent experiments have shown that low-density gas jets injected into a high-density gas undergo an instability mode leading to highly periodic oscillations in the flow field. The transition from laminar to turbulent flow in these jets is abrupt, without a gradual change in scales. Although this type of instability at high Richardson numbers has been attributed to buoyancy, direct physical evidence was not acquired through experiments. In this study, several experiments were conducted in Earth gravity and microgravity to acquire qualitative data on near field flow structure of helium jets injected into air. Microgravity conditions were simulated in the 2.2-second drop tower at NASA Glenn Research Center. The operating parameters of this study included the tube inside diameter, the jet Reynolds number, and the jet Richardson number. Tubes with inside diameters of 19.05 mm and 31.75 mm were used in the experiments conducted in the drop tower. The jet flow was analyzed using quantitative rainbow schlieren deflectometry, a non-intrusive line of sight measurement technique for the whole field. The flow structure was characterized by distributions of angular deflection and the resulting helium mole fraction obtained from color schlieren images taken at 60 Hz. Three sets of experimental data with respect to three schlieren fields of view were acquired for each tube. Results show that the jet in microgravity was up to 70 percent wider than that in Earth gravity. The global jet flow oscillations observed in Earth gravity were absent in microgravity, providing direct experimental evidence that the flow instability in the low-density jet was buoyancy-induced. This study provides quantitative details of temporal flow evolution as the experiments undergo change in gravity in the drop tower.

Evidence for the Magnetic Breakout Model in an Equatorial Coronal-Hole Jet

NASA Astrophysics Data System (ADS)

Karpen, Judith T.; Kumar, Pankaj; Antiochos, Spiro K.; Wyper, Peter; DeVore, C. Richard

2017-08-01

We have analyzed an equatorial coronal-hole jet observed by SDO/AIA on 09 January 2014. The source-region magnetic field structure is consistent with the embedded-bipole topology that we identified and modeled previously as a source of coronal jets (Pariat et al. 2009, 2010, 2015, 2016; Karpen et al. 2017; Wyper et al. 2016). Initial brightenings were observed below a small but distinct “mini-filament” about 25 min before jet onset. A bright circular structure, interpreted as magnetic flux rope (MFR), surrounded the mini-filament. The MFR and filament rose together slowly at first, with a speed of ˜15 km s-1. When bright footpoints and loops appeared below, analogous to flare ribbons and arcade, the MFR/mini-filament rose rapidly (˜126 km s-1), and a bright elongated feature interpreted as a current sheet appeared between the MFR and the growing arcade. Multiple plasmoids propagating upward (˜135 km s-1) and downward (˜55 km s-1) were detected in this sheet. The jet was triggered when the rising MFR interacted with the overlying magnetic structure, most likely at a stressed magnetic null distorted into a current sheet. This event thus exhibits clear evidence of “flare” reconnection below the MFR as well as breakout reconnection above it, consistent with the breakout model for a wide range of solar eruptions (Antiochos et al. 1999; Devore & Antiochos 2008; Karpen et al. 2012; Wyper et al. 2017). Breakout reconnection destroyed the MFR and enabled the entrained coronal plasma and mini-filament to escape onto open field lines, producing an untwisting jet. SDO/HMI magnetograms reveal small footpoint motions at the eruption site and its surroundings, but do not show significant flux emergence or cancellation during or 1-2 hours before the eruption. Therefore, the free energy powering this jet most likely originated in magnetic shear concentrated at the polarity inversion line within the embedded bipole - a mini-filament channel - possibly created by helicity condensation (Antiochos 2013; Knizhnik et al. 2015, 2017).This work was supported in part by a grant from the NASA H-SR program and the NASA Postdoctoral Program.

The chromosphere above a δ-sunspot in the presence of fan-shaped jets

NASA Astrophysics Data System (ADS)

Robustini, Carolina; Leenaarts, Jorrit; de la Cruz Rodríguez, Jaime

2018-01-01

Context. Delta-sunspots are known to be favourable locations for fast and energetic events like flares and coronal mass ejections. The photosphere of this sunspot type has been thoroughly investigated in the past three decades. The atmospheric conditions in the chromosphere are not as well known, however. Aims: This study is focused on the chromosphere of a δ-sunspot that harbours a series of fan-shaped jets in its penumbra. The aim of this study is to establish the magnetic field topology and the temperature distribution in the presence of jets in the photosphere and the chromosphere. Methods: We use data from the Swedish 1m Solar Telescope (SST) and the Solar Dynamics Observatory. We invert the spectropolarimetric Fe I 6302 Å and Ca II 8542 Å data from the SST using the non-LTE inversion code NICOLE to estimate the magnetic field configuration, temperature, and velocity structure in the chromosphere. Results: A loop-like magnetic structure is observed to emerge in the penumbra of the sunspot. The jets are launched from this structure. Magnetic reconnection between this emerging field and the pre-existing vertical field is suggested by hot plasma patches on the interface between the two fields. The height at which the reconnection takes place is located between log τ500 = -2 and log τ500 = -3. The magnetic field vector and the atmospheric temperature maps show a stationary configuration during the whole observation. Movies associated to Figs. 3-5 are available at http://www.aanda.org

Pelton turbine Needle erosion prediction based on 3D three- phase flow simulation

NASA Astrophysics Data System (ADS)

Chongji, Z.; Yexiang, X.; Wei, Z.; Yangyang, Y.; Lei, C.; Zhengwei, W.

2014-03-01

Pelton turbine, which applied to the high water head and small flow rate, is widely used in the mountainous area. During the operation period the sediment contained in the water does not only induce the abrasion of the buckets, but also leads to the erosion at the nozzle which may damage the needle structure. The nozzle and needle structure are mainly used to form high quality cylindrical jet and increase the efficiency of energy exchange in the runner to the most. Thus the needle erosion will lead to the deformation of jet, and then may cause the efficiency loss and cavitation. The favourable prediction of abrasion characteristic of needle can effectively guide the optimization design and maintenance of needle structure. This paper simulated the unsteady three-dimensional multi-phase flow in the nozzle and injected jet flow. As the jet containing water and sediment is injected into the free atmosphere air with high velocity, the VOF model was adopted to predict the water and air flow. The sediment is simplified into round solid particle and the discrete particle model (DPM) was employed to predict the needle abrasion characteristic. The sand particle tracks were analyzed to interpret the mechanism of sand erosion on the needle surface. And the numerical result of needle abrasion was obtained and compared with the abrasion field observation. The similarity of abrasion pattern between the numerical results and field observation illustrated the validity of the 3D multi-phase flow simulation method.

Controlling the development of coherent structures in high speed jets and the resultant near field

NASA Astrophysics Data System (ADS)

Speth, Rachelle

This work uses Large-Eddy Simulations to examine the effect of actuator parameters and jet exit properties on the evolution of coherent structures and their impact on the near-acoustic field without and with control. For the controlled cases, Localized Arc Filament Plasma Actuators (LAFPAs) are considered, and modeled with a simple heating approach that successfully reproduces the main observations and trends of experiments. A parametric study is first conducted, using the flapping mode (m = +/-1), to investigate the sensitivity of the results to various actuator parameters including: actuator model temperature, actuator duty cycle, and excitation frequency. It is shown by considering a Mach 1.3 jet at Reynolds number of 1 x 106 that the response of the jet is relatively insensitive to actuator model temperature within the limits of the experimentally measured temperature values. Furthermore, duty cycles in the range of 20%--90% were observed to be effective in reproducing the characteristic coherent structures of the flapping mode. Next, jet flow parameters were explored to determine the control authority under different operating conditions. To begin, the effect of the laminar nozzle exit boundary layer thickness was examined by varying its value from essentially uniform flow to 25% of the diameter. In the absence of control, the distance between the nozzle lip and the initial appearance of breakdown is proportional to the boundary-layer thickness, which is consistent with theory and previous results obtained by other researchers at Mach 0.9. The second flow parameter studied was the effect of Reynolds number on a Mach 1.3 jet controlled by the flapping mode at an excitation Strouhal number of 0.3. The higher Reynolds number (Re=1,100,000) jet exhibited reduced control authority compared to the Re=100,000 jet. Like the effect of increasing the nozzle exit boundary layer thickness, increasing the Reynolds number cause a reduction in spreading on the flapping plane and an increase on the non-flapping plane. Therefore, these thicker layers and higher Reynolds number jets may require actuators with a higher energy input (i.e. higher duty cycle, higher actuator temperature, more actuators) to ensure the excitation of the flow instability. The final parameter studied is the effect of Mach number on the development and decay of large scale structures for no-control and control cases for Mach 0.9 and Mach 1.3 jets. For this exercise, the axisymmetric mode (m=0) was considered at excitation frequencies of St=0.05, 0.15, and 0.25, with emphasis on the evolution of coherent structures and their effects on the resultant near field pressure map. Without control, the two jets have similar shear layer growth until the end of the potential core length of the subsonic case, at which point the subsonic jet spreads at a higher rate. For the controlled cases, relatively larger streamwise hairpin vortices have been noted for the subsonic cases than the supersonic cases resulting in stronger entrainment of the ambient fluid. This increased entrainment in the subsonic cases causes a reduction in the normalized convective velocity resulting in similar normalized values to that of the supersonic cases. As the excitation frequency is increased, more hairpin vortices are present and the normalized convective velocity is reduced for both subsonic and supersonic cases. (Abstract shortened by ProQuest.).

Artificial plasma jet in the ionosphere

NASA Astrophysics Data System (ADS)

Haerendel, G.; Sagdeev, R. Z.

The dynamics of an artificially injected plasma beam in the near-earth space are analyzed in terms of the beam structure, its propagation across the magnetic field, and the resulting wave phenomena (Porcupine Project, flight 4, March 31, 1979). Out of the four ejectable canisters attached to the main payload, two were instrumented by the U.S., one by the USSR (the Xenon plasma beam experiment), and one by West Germany (carrying a barium ion jet experiment). The propagation of the plasma seems to occur in three stages, with high-frequency broad-band oscillations mainly localized in the 'core' of the jet, while low-frequency oscillations were spatially separated from it. The generation region of LF oscillations was found to be much wider than the jet core. As a result of the interaction between the plasma beam and the ambient medium a heating of electrons, up to energies of about 20 eV, associated with LF noise was observed. The behavior of high-energy ions and the observed HF wave phenomena need further analysis.

Coma Morphology Due to an Extended Active Region and Implications for the Spin State of Comet Hale-Bopp

NASA Technical Reports Server (NTRS)

Samarasinha, Nalin H.

2000-01-01

We show that the circular character of continuum structures observed in the coma of comet Hale-Bopp around the perihelion passage is most likely due to a dust jet from a large extended active region on the surface. Coma morphology due to a wide jet is different from that due to a narrow jet. The latter shows foreshortening effects due to observing geometry, wider jet produces more circular features. This circularization effect provides a self-consistent explanation for the evolution of near-perihelion coma morphology. No changes in the direction of the rotational angular momentum vector are required during this period in contrast to the models of Schleicher et al. This circularization effect also enables us to produce near-circular coma features in the S-E quadrant during 1997 late February and therefore questions the basic premise on which Sekanina bases his morphological arguments for a gravitationally bound satellite nucleus.

Minifilament Eruption as the Source of a Blowout Jet, C-class Flare, and Type-III Radio Burst

NASA Astrophysics Data System (ADS)

Hong, Junchao; Jiang, Yunchun; Yang, Jiayan; Li, Haidong; Xu, Zhe

2017-01-01

We report a strong minifilament eruption associated with Geostationary Operational Environmental Satellite C1.6 flare and WIND type-III radio burst. The minifilament, which lies at the periphery of active region 12259, is detected by Hα images from the New Vacuum Solar Telescope. The minifilament undergoes a partial and then a full eruption. Simultaneously, two co-spatial jets are successively observed in extreme ultraviolet images from the Solar Dynamic Observatory. The first jet exhibits a typical fan-spine geometry, suggesting that the co-spatial minifilament is possibly embedded in magnetic fields with a fan-spine structure. However, the second jet displays blowout morphology when the entire minifilament erupts upward, leaving behind a hard X-ray emission source in the base. Differential emission measure analyses show that the eruptive region is heated up to about 4 MK during the fan-spine jet, while up to about 7 MK during the blowout jet. In particular, the blowout jet is accompanied by an interplanetary type-III radio burst observed by WIND/WAVES in the frequency range from above 10 to 0.1 MHz. Hence, the minifilament eruption is correlated with the interplanetary type-III radio burst for the first time. These results not only suggest that coronal jets can result from magnetic reconnection initiated by erupting minifilaments with open fields, but also shed light on the potential influence of minifilament eruption on interplanetary space.

MINIFILAMENT ERUPTION AS THE SOURCE OF A BLOWOUT JET, C-CLASS FLARE, AND TYPE-III RADIO BURST

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, Junchao; Jiang, Yunchun; Yang, Jiayan

We report a strong minifilament eruption associated with Geostationary Operational Environmental Satellite C1.6 flare and WIND type-III radio burst. The minifilament, which lies at the periphery of active region 12259, is detected by H α images from the New Vacuum Solar Telescope. The minifilament undergoes a partial and then a full eruption. Simultaneously, two co-spatial jets are successively observed in extreme ultraviolet images from the Solar Dynamic Observatory . The first jet exhibits a typical fan-spine geometry, suggesting that the co-spatial minifilament is possibly embedded in magnetic fields with a fan-spine structure. However, the second jet displays blowout morphology whenmore » the entire minifilament erupts upward, leaving behind a hard X-ray emission source in the base. Differential emission measure analyses show that the eruptive region is heated up to about 4 MK during the fan-spine jet, while up to about 7 MK during the blowout jet. In particular, the blowout jet is accompanied by an interplanetary type-III radio burst observed by WIND /WAVES in the frequency range from above 10 to 0.1 MHz. Hence, the minifilament eruption is correlated with the interplanetary type-III radio burst for the first time. These results not only suggest that coronal jets can result from magnetic reconnection initiated by erupting minifilaments with open fields, but also shed light on the potential influence of minifilament eruption on interplanetary space.« less

Particle Acceleration, Magnetic Field Generation and Emission from Relativistic Jets

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.; Hardee, P.; Hededal, C.; Mizuno, Yosuke; Fishman, G. Jerry; Hartmann, D. H.

2006-01-01

Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., active galactic nuclei (AGNs), gamma-ray bursts (GRBs), supernova remnants, and Galactic microquasar systems usually have power-law emission spectra. Fermi acceleration is the mechanism usually assumed for the acceleration of particles in astrophysical environments. Recent PIC simulations using injected relativistic electron-ion (electro-positron) jets show that particle acceleration occurs within the downstream jet, rather than by the scattering of particles back and forth across the shock as in Fermi acceleration. Shock acceleration' is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different spectral properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants. We will review recent PIC simulations of relativistic jets and try to make a connection with observations.

Space Shuttle Orbiter Reaction Jet Driver (RJD): Independent Technical Assessment/Inspection (ITA/I) Report, Version 1.0

NASA Technical Reports Server (NTRS)

Gilbrech, Richard J.; Kichak, Robert A.; Davis, Mitchell; Williams, Glenn; Thomas, Walter, III; Slenski, George A.; Hetzel, Mark

2005-01-01

The Space Shuttle Program (SSP) has a zero-fault-tolerant design related to an inadvertent firing of the primary reaction control jets on the Orbiter during mated operations with the International Space Station (ISS). Failure modes identified by the program as a wire-to-wire "smart" short or a Darlington transistor short resulting in a failed-on primary thruster during mated operations with ISS can drive forces that exceed the structural capabilities of the docked Shuttle/ISS structure. The assessment team delivered 17 observations, 6 findings and 15 recommendations to the Space Shuttle Program.

Evidence for Precursors of the Coronal Hole Jets in Solar Bright Points

NASA Astrophysics Data System (ADS)

Bagashvili, Salome R.; Shergelashvili, Bidzina M.; Japaridze, Darejan R.; Kukhianidze, Vasil; Poedts, Stefaan; Zaqarashvili, Teimuraz V.; Khodachenko, Maxim L.; De Causmaecker, Patrick

2018-03-01

A set of 23 observations of coronal jet events that occurred in coronal bright points has been analyzed. The focus was on the temporal evolution of the mean brightness before and during coronal jet events. In the absolute majority of the cases either single or recurrent coronal jets (CJs) were preceded by slight precursor disturbances observed in the mean intensity curves. The key conclusion is that we were able to detect quasi-periodical oscillations with characteristic periods from sub-minute up to 3–4 minute values in the bright point brightness that precedes the jets. Our basic claim is that along with the conventionally accepted scenario of bright-point evolution through new magnetic flux emergence and its reconnection with the initial structure of the bright point and the coronal hole, certain magnetohydrodynamic (MHD) oscillatory and wavelike motions can be excited and these can take an important place in the observed dynamics. These quasi-oscillatory phenomena might play the role of links between different epochs of the coronal jet ignition and evolution. They can be an indication of the MHD wave excitation processes due to the system entropy variations, density variations, or shear flows. It is very likely a sharp outflow velocity transverse gradients at the edges between the open and closed field line regions. We suppose that magnetic reconnections can be the source of MHD waves due to impulsive generation or rapid temperature variations, and shear flow driven nonmodel MHD wave evolution (self-heating and/or overreflection mechanisms).

Modeling Reconnection-Driven Solar Polar Jets with Gravity and Wind

NASA Astrophysics Data System (ADS)

Karpen, Judith T.; DeVore, C. R.; Antiochos, S. K.

2013-07-01

Solar polar jets are dynamic, narrow, radially extended structures observed in EUV emission. They have been found to originate within the open magnetic field of coronal holes in “anemone” regions, which are generally accepted to be intrusions of opposite polarity. The associated embedded-dipole topology consists of a spine line emanating from a null point atop a dome-shaped fan surface. Previous work (Pariat et al. 2009, 2010) has validated the idea that magnetic free energy stored on twisted closed field lines within the fan surface can be released explosively by the onset of fast reconnection between the highly stressed closed field inside the null and the unstressed open field outside (Antiochos 1996). The simulations showed that a dense jet comprising a nonlinear, torsional Alfven wave is ejected into the outer corona on the newly reconnected open field lines. While proving the principle of the basic model, those simulations neglected the important effects of gravity, the solar wind, and an expanding spherical geometry. We introduce those additional physical processes in new simulations of reconnection-driven jets, to determine whether the model remains robust in the resulting more realistic setting, and to begin establishing the signatures of the jets in the inner heliosphere for comparison with observations. Initial results demonstrate explosive energy release and a jet in the low corona very much like that in the earlier Cartesian, gravity-free, static-atmosphere runs. We report our analysis of the results, their comparison with previous work, and their implications for observations. This work was supported by NASA’s LWS TR&T program.Abstract (2,250 Maximum Characters): Solar polar jets are dynamic, narrow, radially extended structures observed in EUV emission. They have been found to originate within the open magnetic field of coronal holes in “anemone” regions, which are generally accepted to be intrusions of opposite polarity. The associated embedded-dipole topology consists of a spine line emanating from a null point atop a dome-shaped fan surface. Previous work (Pariat et al. 2009, 2010) has validated the idea that magnetic free energy stored on twisted closed field lines within the fan surface can be released explosively by the onset of fast reconnection between the highly stressed closed field inside the null and the unstressed open field outside (Antiochos 1996). The simulations showed that a dense jet comprising a nonlinear, torsional Alfven wave is ejected into the outer corona on the newly reconnected open field lines. While proving the principle of the basic model, those simulations neglected the important effects of gravity, the solar wind, and an expanding spherical geometry. We introduce those additional physical processes in new simulations of reconnection-driven jets, to determine whether the model remains robust in the resulting more realistic setting, and to begin establishing the signatures of the jets in the inner heliosphere for comparison with observations. Initial results demonstrate explosive energy release and a jet in the low corona very much like that in the earlier Cartesian, gravity-free, static-atmosphere runs. We report our analysis of the results, their comparison with previous work, and their implications for observations. This work was supported by NASA’s LWS TR&T program.

An accelerating high-latitude jet in Earth's core

NASA Astrophysics Data System (ADS)

Finlay, C. C.; Livermore, P. W.; Hollerbach, R.

2016-12-01

The structure of the core-generated magnetic field, and how it changes in time (its secular variation or SV), supplies an invaluable constraint on the dynamics of the outer core. At high latitude, previous studies have noted distinctive behaviour of secular change, in particular suggesting a polar vortex tied to the dynamics within the tangent cylinder region. Recent high-resolution observational models that include data from the Swarm satellites have refined the structure of observed SV, to a rapidly changing circular daisy-chain configuration centred on the north geographic pole, on or very close to the tangent cylinder itself. Motivated by theoretical considerations of the likely dynamical regime of the core, we demonstrate that this feature can be explained by a localised westwards cylindrical jet of 420 km width centred the tangent cylinder, whose amplitude appears to have increased in strength by a factor of three over the period 2000-2016 to about 40 km/yr. The current accelerating phase may be a short fragment of decadal fluctuations of the jet strength linked to both torsional wave activity and the rotation direction of the inner core.

Microscopic Processes in Relativistic Jets

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.; Hardee, P.; Mizuno, Y.; Medvedev, M.; Zhang, B.; Nordlund, A.; Fredricksen, J.; Sol, H.; Niemiec, J.; Lyubarsky, Y.;

Parallel and Perpendicular Alignment of Anisotropic Particles in Free Liquid Microjets and Emerging Microdroplets.

PubMed

Schlenk, Mathias; Hofmann, Eddie; Seibt, Susanne; Rosenfeldt, Sabine; Schrack, Lukas; Drechsler, Markus; Rothkirch, Andre; Ohm, Wiebke; Breu, Josef; Gekle, Stephan; Förster, Stephan

2018-04-24

Liquid microjets play a key role in fiber spinning, inkjet printing, and coating processes. In all of these applications, the liquid jets carry dispersed particles whose spatial and orientational distributions within the jet critically influence the properties of the fabricated structures. Despite its importance, there is currently no knowledge about the orientational distribution of particles within microjets and droplets. Here, we demonstrate a microfluidic device that allows to determine the local particle distribution and orientation by X-ray scattering. Using this methodology, we discovered unexpected changes in the particle orientation upon exiting the nozzle to form a free jet, and upon jet break-up into droplets, causing an unusual biaxial particle orientation. We show how flow and aspect ratio determine the flow orientation of anisotropic particles. Furthermore, we demonstrate that the observed phenomena are a general characteristic of anisotropic particles. Our findings greatly enhance our understanding of particle orientation in free jets and droplets and provide a rationale for controlling particle alignment in liquid jet-based fabrication methodologies.

Characteristics Of Turbulent Nonpremixed Jet-Flames And Jet-Flames In Crossflow In Normal- And Low-Gravity

NASA Technical Reports Server (NTRS)

Clemens, N. T.; Boxx, I. G.; Idicheria, C. A.

2003-01-01

It is well known that buoyancy has a major influence on the flow structure of turbulent nonpremixed jet flames. For example, previous studies have shown that transitional and turbulent jet flames exhibit flame lengths that are as much as a factor of two longer in microgravity than in normal gravity. The objective of this study is to extend these previous studies by investigating both mean and fluctuating characteristics of turbulent nonpremixed jet flames under three different gravity levels (1 g, 20 mg and 100 micrograms). This work is described in more detail elsewhere. In addition, we have recently initiated a new study into the effects of buoyancy on turbulent nonpremixed jet flames in cross-flow (JFICF). Buoyancy has been observed to play a key role in determining the centerline trajectories of such flames.6 The objective of this study is to use the low gravity environment to study the effects of buoyancy on the turbulent characteristics of JFICF.

Particle Acceleration, Magnetic Field Generation, and Associated Emission in Collisionless Relativistic Jets

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.

2007-01-01

Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., active galactic nuclei (AGNs), gamma-ray bursts (GRBs), and Galactic microquasar systems usually have power-law emission spectra. Recent PIC simulations using injected relativistic electron-ion (electro-positron)jets show that acceleration occurs within the downstream jet. Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.

Particle Acceleration, Magnetic Field Generation and Associated Emission in Collisionless Relativistic Jets

NASA Technical Reports Server (NTRS)

Nishikawa, K. I.; Ramirez-Ruiz, E.; Hardee, P.; Mizuno, Y.; Fishman. G. J.

2007-01-01

Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., active galactic nuclei (AGNs), gamma-ray bursts (GRBs), and Galactic microquasar systems usually have power-law emission spectra. Recent PIC simulations using injected relativistic electron-ion (electro-positron) jets show that acceleration occurs within the downstream jet. Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.

Analysis of the effects of firing Orbiter primary reaction control system jets with an attached truss structure

NASA Technical Reports Server (NTRS)

Kaszubowski, M.; Raney, J. P.

1986-01-01

A study was conducted to determine the dynamic effects of firing the orbiter primary reaction control jets during assembly of protoflight space station structure. Maximum longeron compressive load was calculated as a function of jet pulse time length, number of jet pulses, and total torque imposed by the reaction control jets. The study shows that it is possible to fire selected jets to achieve a pitch maneuver without causing failure of the attached structure.

On the structure and stability of magnetic tower jets

DOE PAGES

Huarte-Espinosa, M.; Frank, A.; Blackman, E. G.; ...

2012-09-05

Modern theoretical models of astrophysical jets combine accretion, rotation, and magnetic fields to launch and collimate supersonic flows from a central source. Near the source, magnetic field strengths must be large enough to collimate the jet requiring that the Poynting flux exceeds the kinetic energy flux. The extent to which the Poynting flux dominates kinetic energy flux at large distances from the engine distinguishes two classes of models. In magneto-centrifugal launch models, magnetic fields dominate only at scales <~ 100 engine radii, after which the jets become hydrodynamically dominated (HD). By contrast, in Poynting flux dominated (PFD) magnetic tower models,more » the field dominates even out to much larger scales. To compare the large distance propagation differences of these two paradigms, we perform three-dimensional ideal magnetohydrodynamic adaptive mesh refinement simulations of both HD and PFD stellar jets formed via the same energy flux. We also compare how thermal energy losses and rotation of the jet base affects the stability in these jets. For the conditions described, we show that PFD and HD exhibit observationally distinguishable features: PFD jets are lighter, slower, and less stable than HD jets. Here, unlike HD jets, PFD jets develop current-driven instabilities that are exacerbated as cooling and rotation increase, resulting in jets that are clumpier than those in the HD limit. Our PFD jet simulations also resemble the magnetic towers that have been recently created in laboratory astrophysical jet experiments.« less

Numerical Investigation of the Hydrogen Jet Flammable Envelope Extent with Account for Unsteady Phenomena

NASA Astrophysics Data System (ADS)

Chernyavsky, Boris; Benard, Pierre

2010-11-01

An important aspect of safety analysis in hydrogen applications is determination of the extent of flammable gas envelope in case of hydrogen jet release. Experimental investigations had shown significant disagreements between the extent of average flammable envelope predicted by steady-state numerical methods, and the region observed to support ignition, with proposed cause being non-steady jet phenomena resulting in significant variations of instantaneous gas concentration and velocity fields in the jet. In order to investigate the influence of these transient phenomena, a numerical investigation of hydrogen jet at low Mach number had been performed using unsteady Large Eddy Simulation. Instantaneous hydrogen concentration and velocity fields were monitored to determine instantaneous flammable envelope. The evolution of the instantaneous fields, including the development of the turbulence structures carrying hydrogen, their extent and frequency, and their relation with averaged fields had been characterized. Simulation had shown significant variability of the flammable envelope, with jet flapping causing shedding of large scale rich and lean gas pockets from the main jet core, which persist for significant times and substantially alter the extent of flammability envelope.

Streamwise Vorticity Generation in Laminar and Turbulent Jets

NASA Technical Reports Server (NTRS)

Demuren, Aodeji O.; Wilson, Robert V.

1999-01-01

Complex streamwise vorticity fields are observed in the evolution of non-circular jets. Generation mechanisms are investigated via Reynolds-averaged (RANS), large-eddy (LES) and direct numerical (DNS) simulations of laminar and turbulent rectangular jets. Complex vortex interactions are found in DNS of laminar jets, but axis-switching is observed only when a single instability mode is present in the incoming mixing layer. With several modes present, the structures are not coherent and no axis-switching occurs, RANS computations also produce no axis-switching. On the other hand, LES of high Reynolds number turbulent jets produce axis-switching even for cases with several instability modes in the mixing layer. Analysis of the source terms of the mean streamwise vorticity equation through post-processing of the instantaneous results shows that, complex interactions of gradients of the normal and shear Reynolds stresses are responsible for the generation of streamwise vorticity which leads to axis-switching. RANS computations confirm these results. k - epsilon turbulence model computations fail to reproduce the phenomenon, whereas algebraic Reynolds stress model (ASM) computations, in which the secondary normal and shear stresses are computed explicitly, succeeded in reproducing the phenomenon accurately.

Transient jet formation and state transitions from large-scale magnetic reconnection in black hole accretion discs

NASA Astrophysics Data System (ADS)

Dexter, Jason; McKinney, Jonathan C.; Markoff, Sera; Tchekhovskoy, Alexander

2014-05-01

Magnetically arrested accretion discs (MADs), where the magnetic pressure in the inner disc is dynamically important, provide an alternative mechanism for regulating accretion to what is commonly assumed in black hole systems. We show that a global magnetic field inversion in the MAD state can destroy the jet, significantly increase the accretion rate, and move the effective inner disc edge in to the marginally stable orbit. Reconnection of the MAD field in the inner radii launches a new type of transient outflow containing hot plasma generated by magnetic dissipation. This transient outflow can be as powerful as the steady magnetically dominated Blandford-Znajek jet in the MAD state. The field inversion qualitatively describes many of the observational features associated with the high-luminosity hard-to-soft state transition in black hole X-ray binaries: the jet line, the transient ballistic jet, and the drop in rms variability. These results demonstrate that the magnetic field configuration can influence the accretion state directly, and hence the magnetic field structure is an important second parameter in explaining observations of accreting black holes across the mass and luminosity scales.

On Unified Mode in Grid Mounted Round Jets

NASA Astrophysics Data System (ADS)

Parimalanathan, Senthil Kumar; T, Sundararajan; v, Raghavan

2015-11-01

The turbulence evolution in a free round jet is strongly affected by its initial conditions. Since the transition to turbulence is moderated by instability modes, the initial conditions seem to play a major role in altering the dynamics of these modes. In the present investigation, grids of different configurations are placed at the jet nozzle exit and the flow field characterization is carried out using a bi-component hot-wire anemometer. The instability modes has been obtained by analyzing the velocity spectral data. Free jets are characterized by the presence of two instability modes, viz., the preferred mode and the shear mode. The preferred mode corresponds to the most amplified oscillations along the jet centerline, while the shear modes are due to the dynamic evolution of vortical structures in the jet shear layer. The presence of grid clearly alters the jet structure, and plays a major role in altering the shear layer mode in particular. In fact, it is observed that close to the nozzle exit, the presence of grids deviate the streamlines inwards around the edge due to the momentum difference between the jet central core and the boundary layer region near the wall. This result in a single unified mode, where there is no distinct preferred or shear mode. This phenomena is more dominant in case of the grids having higher blockage ratio with small grid opening. In the present study, investigation of the physics behind the evolution of unified mode and how the grids affect the overall turbulent flow field evolution has been reported. Experimental Fluid Mechanics.

Observations of diffusion-limited aggregation-like patterns by atmospheric plasma jet

NASA Astrophysics Data System (ADS)

Chiu, Ching-Yang; Chu, Hong-Yu

2017-11-01

We report on the observations of diffusion-limited aggregation-like patterns during the thin film removal process by an atmospheric plasma jet. The fractal patterns are found to have various structures like dense branching and tree-like patterns. The determination of surface morphology reveals that the footprints of discharge bursts are not as random as expected. We propose a diffusion-limited aggregation model with a few extra requirements by analogy with the experimental results, and thereby present the beauty of nature. We show that the model simulates not only the shapes of the patterns similar to the experimental observations, but also the growing sequences of fluctuating, oscillatory, and zigzag traces.

Far Infrared Spectroscopy of H II Regions. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Ward, D. B.

1975-01-01

The far infrared spectra of H II regions are investigated. A liquid helium cooled grating spectrometer designed to make observations from the NASA Lear Jet is described along with tests of the instrument. The observing procedure on the Lear Jet telescope is described and the method of data analysis is discussed. Results are presented from a search for the (O III) 88.16 micron line. An upper limit on the emission in this line is obtained and line detection is described. Results are compared to theoretical predictions, and future applications of fine structure line observations are discussed. Coarse resolution results are given along with calibration problems. The spectra obtained are compared to models for dust emission.

THE JETS OF TeV BLAZARS AT HIGHER RESOLUTION: 43 GHz AND POLARIMETRIC VLBA OBSERVATIONS FROM 2005 TO 2009

DOE Office of Scientific and Technical Information (OSTI.GOV)

Piner, B. Glenn; Pant, Niraj; Edwards, Philip G., E-mail: gpiner@whittier.ed, E-mail: Philip.Edwards@csiro.a

We present 23 new VLBA images of the six established TeV blazars Markarian 421, Markarian 501, H 1426+428, 1ES 1959+650, PKS 2155-304, and 1ES 2344+514, obtained from 2005 to 2009. Most images were obtained at 43 GHz (7 mm), and they reveal the parsec-scale structures of three of these sources (1ES 1959+650, PKS 2155-304, and 1ES 2344+514) at factors of 2-3 higher resolution than has previously been attained. These images reveal new morphological details, including a high degree of jet bending in the inner milliarcsecond in PKS 2155-304. This establishes strong apparent jet bending on VLBI scales as a commonmore » property of TeV blazars, implying viewing angles close to the line of sight. Most of the remaining images map the linear polarization structures at a lower frequency of 22 GHz (1 cm). We discuss the transverse structures of the jets as revealed by the high-frequency and polarimetric imaging. The transverse structures include significant limb brightening in Mrk 421, and 'spine-sheath' structures in the electric vector position angle and fractional polarization distributions in Mrk 421, Mrk 501, and 1ES 1959+650. We use new measured component positions to update measured apparent jet speeds, in many cases significantly reducing the statistical error over previously published results. With the increased resolution at 43 GHz, we detect new components within 0.1-0.2 mas of the core in most of these sources. No motion is apparent in these new components over the time span of our observations, and we place upper limits on the apparent speeds of the components near the core of <2c. From those limits, we conclude that {Gamma}{sub 2} < ({Gamma}{sub 1}){sup 1/2} at {approx}10{sup 5} Schwarzschild radii, where {Gamma}{sub 1} and {Gamma}{sub 2} are the bulk Lorentz factors in the TeV emitting and 43 GHz emitting regions, respectively, assuming that their velocity vectors are aligned.« less

The first science result with the JENSA gas-jet target: Confirmation and study of a strong subthreshold F 18 ( p , α ) O 15 resonance

DOE PAGES

Bardayan, D. W.; Chipps, K. A.; Ahn, S.; ...

2015-11-28

The astrophysical 18F( p,α) 15O rate determines, in large part, the extent to which the observable radioisotope 18F is produced in novae. This rate, however, has been extremely uncertain owing to the unknown properties of a strong subthreshold resonance and its possible interference with higher-lying resonances. In addition, the new Jet Experiments in Nuclear Structure and Astrophysics (JENSA) gas-jet target has been used for the first time to determine the spin of this important resonance and significantly reduce uncertainties in the 18F( p,α) 15O rate.

The first science result with the JENSA gas-jet target: Confirmation and study of a strong subthreshold F 18 ( p , α ) O 15 resonance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bardayan, D. W.; Chipps, K. A.; Ahn, S.

The astrophysical 18F( p,α) 15O rate determines, in large part, the extent to which the observable radioisotope 18F is produced in novae. This rate, however, has been extremely uncertain owing to the unknown properties of a strong subthreshold resonance and its possible interference with higher-lying resonances. In addition, the new Jet Experiments in Nuclear Structure and Astrophysics (JENSA) gas-jet target has been used for the first time to determine the spin of this important resonance and significantly reduce uncertainties in the 18F( p,α) 15O rate.

Magnetic Untwisting in Most Solar X-Ray Jets

NASA Technical Reports Server (NTRS)

Moore, Ronald; Sterling, Alphonse; Falconer, David; Robe, Dominic

2013-01-01

From 54 X-ray jets observed in the polar coronal holes by Hinode's X-Ray Telescope (XRT) during coverage in movies from Solar Dynamic Observatory's Atmospheric Imaging Assembly (AIA) taken in its He II 304 Å band at a cadence of 12 s, we have established a basic characteristic of solar X-ray jets: untwisting motion in the spire. In this presentation, we show the progression of few of these X-ray jets in XRT images and track their untwisting in AIA He II images. From their structure displayed in their XRT movies, 19 jets were evidently standard jets made by interchange reconnection of the magnetic-arcade base with ambient open field, 32 were evidently blowout jets made by blowout eruption of the base arcade, and 3 were of ambiguous form. As was anticipated from the >10,000 km span of the base arcade in most polar X-ray jets and from the disparity of standard jets and blowout jets in their magnetic production, few of the standard X-ray jets (3 of 19) but nearly all of the blowout X-ray jets (29 of 32) carried enough cool (T is approximately 105 K) plasma to be seen in their He II movies. In the 32 X-ray jets that showed a cool component, the He II movies show 10-100 km/s untwisting motions about the axis of the spire in all 3 standard jets and in 26 of the 29 blowout jets. Evidently, the open magnetic field in nearly all blowout X-ray jets and probably in most standard X-ray jets carries transient twist. This twist apparently relaxes by propagating out along the open field as a torsional wave. High-resolution spectrograms and Dopplergrams have shown that most Type-II spicules have torsional motions of 10-30 km/s. Our observation of similar torsional motion in X-ray jets strengthens the case for Type-II spicules being made in the same way as X-ray jets, by blowout eruption of a twisted magnetic arcade in the spicule base and/or by interchange reconnection of the twisted base arcade with the ambient open field. This work was funded by NASA's Heliophysics Division through its LWS TRT Program and its Hinode Project, and by NSF through its Research Experience for Undergraduates Program.

The Detection of Diffuse Extended Structure in 3C 273: Implications for Jet Power

NASA Astrophysics Data System (ADS)

Punsly, Brian; Kharb, Preeti

2016-12-01

We present deep Very Large Array imaging of 3C 273 in order to determine the diffuse, large scale radio structure of this famous radio-loud quasar. Diffuse extended structure (radio lobes) is detected for the first time in these observations as a consequence of high dynamic range in the 327.5 and 1365 MHz images. This emission is used to estimate a time averaged jet power, 7.2 × 1043 erg s-1 < \\overline{Q} < 3.7 × 1044 erg s-1. Brightness temperature arguments indicate consistent values of the time variability Doppler factor and the compactness Doppler factor for the inner jet, δ ≳ 10. Thus, the large apparent broadband bolometric luminosity of the jet, ˜3 × 1046 erg s-1, corresponds to a modest intrinsic luminosity ≳1042 erg s-1, or ˜1% of \\overline{Q}. In summary, we find that 3C 273 is actually a “typical” radio-loud quasar contrary to suggestions in the literature. The modest \\overline{Q} is near the peak of the luminosity distribution for radio-loud quasars and it is consistent with the current rate of dissipation emitted from millimeter wavelengths to gamma rays. The extreme core-jet morphology is an illusion from a near pole-on line of sight to a highly relativistic jet that produces a Doppler enhanced glow that previously swamped the lobe emission. 3C 273 apparently has the intrinsic kpc scale morphology of a classical double radio source, but it is distorted by an extreme Doppler aberration.

Structure of the Mesosphere of Venus from the reanalized Venera 15 IR-spectrometry data

NASA Astrophysics Data System (ADS)

Zasova, L. V.; Moroz, V. I.; Ignatiev, N. I.; Khatountsev, I. V.

1998-09-01

The results of IR-spectromerty on board VENERA-15 have been reanalyzed. The new data concerned temperature, aerosol, water vapor and thermal zonal wind profiles have been obtained and the latitudinal and local time related variations have been investigated. The cyclostrophic zonal wind fields show the presence of mid-latitudinal jet which changes its position with solar time, so that its altitude and wind speed are correlated and indicated the conservation of angular momentum. The connection between altitude of jet and its velocity shows the flux conservation. The wind velocity in the midlatitudinal jet is correlated with temperature inversion in the "cold collar". The low-latitudinal jet (at about 80 km near 20 deg.) is also connected with inversion in temperature profile observed there.

Interaction of a liquid jet with an oncoming gas stream

NASA Astrophysics Data System (ADS)

Koval', M. A.; Shvets, A. I.

1987-06-01

Wind-tunnel tests were carried out to study the interaction between water jets issuing from various types of nozzles (including cylindrical) and subsonic and supersonic air streams with Mach numbers from 0.3 to 3 and Reynolds numbers from 1 x 10 to the 6th to 3 x 10 to the 7th. The following interaction structure was observed: (1) at moderate outflow velocities, the liquid jet has an extended region, which subsequently expands abruptly as a spherical or mushroom-shaped drop; (2) this drop is atomized in the peripheral region and is carried away as a gas-liquid mixture; (3) a shock wave is formed in front of the jet in the oncoming supersonic stream; and (4) a separated flow region is present in the vicinity of the cylindrical nozzle section.

Active Chevrons for Jet Noise Reduction

NASA Technical Reports Server (NTRS)

Depuru-Mohan, N. K.; Doty, M. J.

2017-01-01

Jet noise is often a dominant component of aircraft noise, particularly at takeoff. To meet the stringent noise regulations, the aircraft industry is in a pressing need of advanced noise reduction concepts. In the present study, the potential of piezoelectrically-activated chevrons for jet noise reduction was experimentally investigated. The perturbations near the nozzle exit caused by piezoelectrically-activated chevrons could be used to modify the growth rate of the mixing layer and thereby potentially reduce jet noise. These perturbations are believed to increase the production of small-scale disturbances at the expense of large-scale turbulent structures. These large-scale turbulent structures are responsible for the dominant portion of the jet mixing noise, particularly low-frequency noise. Therefore, by exciting the static chevron geometry through piezoelectric actuators, an additional acoustic benefit could possibly be achieved. To aid in the initial implementation of this concept, several flat-faced faceted nozzles (four, six, and eight facets) were investigated. Among the faceted nozzles, it was found that the eight-faceted nozzle behaves very similarly to the round nozzle. Furthermore, among the faceted nozzles with static chevrons, the four-faceted nozzle with static chevrons was found to be most effective in terms of jet noise reduction. The piezoelectrically-activated chevrons reduced jet noise up to 2 dB compared to the same nozzle geometry without excitation. This benefit was observed over a wide range of excitation frequencies by applying very low voltages to the piezoelectric actuators.

Structure of a Reconnection Layer Poleward of the Cusp Under Extreme Density Asymmetry

NASA Astrophysics Data System (ADS)

Muzamil, F. M.; Farrugia, C. J.; Torbert, R. B.; Mozer, F.; Pritchett, P. L.; Scudder, J. D.; Sandholt, P. E.; Russell, C. T.; Denig, W. F.

2013-12-01

We present in situ observations made by the Polar spacecraft of a reconnection layer poleward of the northern cusp. Interplanetary conditions monitored by Wind showed an ICME with a strong (~ 20 nT ) northward pointing field component (clock angle ~ 200) lasting for ~13 hours. Polar traversed the layer several times from the magnetosphere (MSP) and magnetosheath (MSH). It recorded an event characterized by extreme density (over two orders of magnitude) and temperature (about one order of magnitude) asymmetries between the two regimes. By contrast the magnetic field on either side of the reconnection was practically equal (ratio= 0.85) and sheared by 1530. During each crossing of the layer, Polar intercepted sunward-flowing jets reaching up to 500km/s. Supplementing the Polar data by low-altitude, polar orbiting, DMSP observations, we show continued patterns of reverse convection in the northern hemisphere which lasted for as long as the external field was northward pointing. Here, we examine one Polar crossing in detail. The observations show (1) a prominent density dip region lasting for ~18 seconds is detected at the separatrix on the MSP side. (2) A clear, though much less pronounced, density dip at the separatrix on MSH side was also detected. (3) Intense electric field fluctuations reaching up to 60 mV/m mostly in the normal component to MP (Hall E field). (4) The ion bulk outflow jet was strongly biased towards to the MSP side. (5) The Hall, out-of-plane magnetic field has a unipolar structure. We compare our findings with those from 2D PIC simulations of Tanaka et al. (Ann. Geophys. 26, 2008) who also focused on density asymmetry (NMSH/NMSP=10) with no guide field. We find good agreement. In our case, however we find (1) a more intense EN field and (2) the ion bulk ouflow jet being more strongly biased towards the MSP side. An interesting feature of our observations is the presence of a clear structure in the outflow jet bearing similarities to a micro FTEs but does not have a flux rope structure.

Statistical mechanics explanation for the structure of ocean eddies and currents

NASA Astrophysics Data System (ADS)

Venaille, A.; Bouchet, F.

2010-12-01

The equilibrium statistical mechanics of two dimensional and geostrophic flows predicts the outcome for the large scales of the flow, resulting from the turbulent mixing. This theory has been successfully applied to describe detailed properties of Jupiter's Great Red Spot. We discuss the range of applicability of this theory to ocean dynamics. It is able to reproduce mesoscale structures like ocean rings. It explains, from statistical mechanics, the westward drift of rings at the speed of non dispersive baroclinic waves, and the recently observed (Chelton and col.) slower northward drift of cyclonic eddies and southward drift of anticyclonic eddies. We also uncover relations between strong eastward mid-basin inertial jets, like the Kuroshio extension and the Gulf Stream, and statistical equilibria. We explain under which conditions such strong mid-basin jets can be understood as statistical equilibria. We claim that these results are complementary to the classical Sverdrup-Munk theory: they explain the inertial part basin dynamics, the jets structure and location, using very simple theoretical arguments. References: A. VENAILLE and F. BOUCHET, Ocean rings and jets as statistical equilibrium states, submitted to JPO F. BOUCHET and A. VENAILLE, Statistical mechanics of two-dimensional and geophysical flows, arxiv ...., submitted to Physics Reports P. BERLOFF, A. M. HOGG, W. DEWAR, The Turbulent Oscillator: A Mechanism of Low- Frequency Variability of the Wind-Driven Ocean Gyres, Journal of Physical Oceanography 37 (2007) 2363-+. D. B. CHELTON, M. G. SCHLAX, R. M. SAMELSON, R. A. de SZOEKE, Global observations of large oceanic eddies, Geo. Res. Lett.34 (2007) 15606-+ b) and c) are snapshots of streamfunction and potential vorticity (red: positive values; blue: negative values) in the upper layer of a three layer quasi-geostrophic model of a mid-latitude ocean basin (from Berloff and co.). a) Streamfunction predicted by statistical mechanics. Even in an out-equilibrium situation like this one, equilibrium statistical mechanics predicts remarkably the overall qualitative flow structure. Observation of westward drift of ocean eddies and of slower northward drift of cyclones and southward drift of anticyclones by Chelton and co. We explain these observations from statistical mechanics.

Surface pressure fluctuations due to an impinging underexpanded supersonic jet

NASA Astrophysics Data System (ADS)

Pundir, Binu

The impingement of supersonic jets on surfaces is of interest because of its important application to jet blast deflectors (JBD), and short takeoff and vertical landing aircraft (STOVL) during hover. Typically, on an aircraft carrier deck, the impingement of the jet blast on the deflector generates impingement tones, and structural vibrations, not only on the JBD but also on the ship deck. Therefore, apart from direct transmission of jet noise to the gallery level, there is a component of noise transmitted due to the impingement of the jet on the JBD. The objectives of this work are to study the pressure spectra (i) on a flat plate, and separately on a cone due to axisymmetric impingement of a supersonic underexpanded cold jet issuing from a convergent-divergent nozzle and (ii) on a plane jet impinging on a finite plate and an adjoining ground plane due to the impingement of a planar jet on the plate. The characteristics of the surface pressure fluctuations are numerically investigated using WIND-US 2.0. The time-dependent, compressible Euler equations for perfect gas are employed for the present computations. The impingement distance between the jet nozzle and the deflector plate, and the plate inclination with respect to the incident jet are varied. The impingement zone stagnation bubble and a high-speed radial jet with several embedded structures (shocklets) were identified on the perpendicular plate. Flows involving cones reveal the presence of detached cone shocks, enclosing a recirculation zone. The location and magnitude of the peak pressure on the cone surface are a strong function of the cone apex angle. For the two-dimensional jet impingement on angled plate the peak value of pressure occurs at normal jet impingement. The pressure at the intersection point of the plate and the ground plane is sometimes higher than the peak pressure on the plate. Beyond this point there is a sharp decrease in pressure. As the flow accelerates, an oblique shock is sometimes formed in this grazing flow region. A recirculation region at the lower lip of the nozzle was observed for all the separation distances and plate inclinations.

Reconfinement and loss of stability in jets from active galactic nuclei

NASA Astrophysics Data System (ADS)

Gourgouliatos, Konstantinos N.; Komissarov, Serguei S.

2018-02-01

Jets powered by active galactic nuclei appear impressively stable compared with their terrestrial and laboratory counterparts—they can be traced from their origin to distances exceeding their injection radius by up to a billion times1,2. However, some less energetic jets get disrupted and lose their coherence on the scale of their host galaxy1,3. Quite remarkably, on the same scale, these jets are expected to become confined by the thermal pressure of the intra-galactic gas2. Motivated by these observations, we have started a systematic study of active galactic nuclei jets undergoing reconfinement via computer simulations. Here, we show that in the case of unmagnetized relativistic jets, the reconfinement is accompanied by the development of an instability and transition to a turbulent state. During their initial growth, the perturbations have a highly organized streamwise-oriented structure, indicating that it is not the Kelvin-Helmholtz instability, the instability which has been the main focus of the jet stability studies so far4,5. Instead, it is closely related to the centrifugal instability6. This instability is likely to be behind the division of active galactic nuclei jets into two morphological types in the Fanaroff-Riley classification7.

A Baroclinic Nocturnal Low-Level Jet over the Great Plains

NASA Astrophysics Data System (ADS)

Shapiro, A.; Gebauer, J.; Fedorovich, E.

2016-12-01

The nocturnal low-level jet (LLJ) is a warm-season atmospheric boundary layer phenomenon common to the Great Plains of the United States and other places worldwide. Low-level jets develop around sunset in fair weather conditions conducive to strong radiative cooling and reach peak intensity in the pre-dawn hours. Key precursors to their formation are the establishment of a strongly turbulent dry convective boundary layer during the afternoon and a rapid cessation of the turbulence during the early evening transition. The two main physical mechanisms underpinning the generation of nocturnal low-level jets over the Great Plains are associated with diurnal variations in turbulent mixing (Blackadar mechanism) and in heating/cooling of the gently sloping terrain (Holton mechanism). These two mechanisms were recently combined within a single unified theory (Shapiro et al. 2016) in which analytical solutions of the Boussinesq equations of motion and thermal energy were obtained. In the present study we apply the unified theory to the case where the free-atmosphere geostrophic wind is zero, and there is strong daytime heating of the slope. When appropriately tuned, the analytical model predicts the low elevation (jet nose within 250 m of the ground) and strong wind maximum (> 15 m/s) characteristic of the strongly baroclinic jet observed over northern Kansas on 10 June 2015 during Intensive Observing Period 7 of the Plains Elevated Convection at Night (PECAN) field experiment. Although there is generally good agreement between the tuned model and observations (including soundings and aircraft data), our main interest is in investigating the profound roles of the free-atmosphere stratification, daytime heating, and daytime/nighttime mixing on jet strength and structure.

SPHERE/ZIMPOL observations of the symbiotic system R Aquarii. I. Imaging of the stellar binary and the innermost jet clouds

NASA Astrophysics Data System (ADS)

Schmid, H. M.; Bazzon, A.; Milli, J.; Roelfsema, R.; Engler, N.; Mouillet, D.; Lagadec, E.; Sissa, E.; Sauvage, J.-F.; Ginski, C.; Baruffolo, A.; Beuzit, J. L.; Boccaletti, A.; Bohn, A. J.; Claudi, R.; Costille, A.; Desidera, S.; Dohlen, K.; Dominik, C.; Feldt, M.; Fusco, T.; Gisler, D.; Girard, J. H.; Gratton, R.; Henning, T.; Hubin, N.; Joos, F.; Kasper, M.; Langlois, M.; Pavlov, A.; Pragt, J.; Puget, P.; Quanz, S. P.; Salasnich, B.; Siebenmorgen, R.; Stute, M.; Suarez, M.; Szulágyi, J.; Thalmann, C.; Turatto, M.; Udry, S.; Vigan, A.; Wildi, F.

2017-06-01

Context. R Aqr is a symbiotic binary system consisting of a mira variable, a hot companion with a spectacular jet outflow, and an extended emission line nebula. Because of its proximity to the Sun, this object has been studied in much detail with many types of high resolution imaging and interferometric techniques. We have used R Aqr as test target for the visual camera subsystem ZIMPOL, which is part of the new extreme adaptive optics (AO) instrument SPHERE at the Very Large Telescope (VLT). Aims: We describe SPHERE/ZIMPOL test observations of the R Aqr system taken in Hα and other filters in order to demonstrate the exceptional performance of this high resolution instrument. We compare our observations with data from the Hubble Space Telescope (HST) and illustrate the complementarity of the two instruments. We use our data for a detailed characterization of the inner jet region of R Aqr. Methods: We analyze the high resolution ≈ 25 mas images from SPHERE/ZIMPOL and determine from the Hα emission the position, size, geometric structure, and line fluxes of the jet source and the clouds in the innermost region <2'' (<400 AU) of R Aqr. The data are compared to simultaneous HST line filter observations. The Hα fluxes and the measured sizes of the clouds yield Hα emissivities for many clouds from which one can derive the mean density, mass, recombination time scale, and other cloud parameters. Results: Our Hα data resolve for the first time the R Aqr binary and we measure for the jet source a relative position 45 mas West (position angle -89.5°) of the mira. The central jet source is the strongest Hα component with a flux of about 2.5 × 10-12 erg cm-2 s-1. North east and south west from the central source there are many clouds with very diverse structures. Within 0.5'' (100 AU) we see in the SW a string of bright clouds arranged in a zig-zag pattern and, further out, at 1''-2'', fainter and more extended bubbles. In the N and NE we see a bright, very elongated filamentary structure between 0.2''-0.7'' and faint perpendicular "wisps" further out. Some jet clouds are also detected in the ZIMPOL [O I] and He I filters, as well as in the HST-WFC3 line filters for Hα, [O III], [N II], and [O I]. We determine jet cloud parameters and find a very well defined correlation Ne ∝ r-1.3 between cloud density and distance to the central binary. Densities are very high with typical values of Ne ≈ 3 × 105 cm-3 for the "outer" clouds around 300 AU, Ne ≈ 3 × 106 cm-3 for the "inner" clouds around 50 AU, and even higher for the central jet source. The high Ne of the clouds implies short recombination or variability timescales of a year or shorter. Conclusions: Hα high resolution data provide a lot of diagnostic information for the ionized jet gas in R Aqr. Future Hα observations will provide the orientation of the orbital plane of the binary and allow detailed hydrodynamical investigations of this jet outflow and its interaction with the wind of the red giant companion. The reduced Hα image given in Fig. 6 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/602/A53

Driving Extreme Variability: Measurements of the changing coronae and evidence for jet launching

NASA Astrophysics Data System (ADS)

Wilkins, D.; Gallo, L.; Fabian, A.; Kara, E.

2015-07-01

Through analysis of the X-rays reflected from the accretion disc, it is possible to probe the innermost structures around accreting black holes and to measure the geometry and structure of the corona that produces the intense X-ray continuum. We conducted detailed analysis of the narrow line Seyfert 1 galaxies 1H0707-495 and Markarian 335, over observations with XMM-Newton as well as Suzaku and NuSTAR spanning nearly a decade to measure the underlying changes in the structure of the X-ray emitting corona that gave rise to more than an order of magnitude variation in luminosity. Underlying this long timescale variability lies much more complex patterns of behaviour on short timescales. We are, for the first time, able to measure the changes accompanying transient phenomena including a flare from Markarian 335 seen during a low flux state. This flaring event was found to mark a reconfiguration of the corona while there is evidence that the flare itself was caused by an aborted jet-launching event. This gives us important insight into the processes by which energy is liberated from black hole accretion flows and allows observational constraints to be placed upon models of how jets are launched and how these extreme objects are powered.

Identification of crystalline structures in jet-cooled acetylene large clusters studied by two-dimensional correlation infrared spectroscopy

NASA Astrophysics Data System (ADS)

Matsumoto, Yoshiteru; Yoshiura, Ryuto; Honma, Kenji

2017-07-01

We investigated the crystalline structures of jet-cooled acetylene (C2H2) large clusters by laser spectroscopy and chemometrics. The CH stretching vibrations of the C2H2 large clusters were observed by infrared (IR) cavity ringdown spectroscopy. The IR spectra of C2H2 clusters were measured under the conditions of various concentrations of C2H2/He mixture gas for supersonic jets. Upon increasing the gas concentration from 1% to 10%, we observed a rapid intensity enhancement for a band in the IR spectra. The strong dependence of the intensity on the gas concentration indicates that the band was assigned to CH stretching vibrations of the large clusters. An analysis of the IR spectra by two-dimensional correlation spectroscopy revealed that the IR absorption due to the C2H2 large cluster is decomposed into two CH stretching vibrations. The vibrational frequencies of the two bands are almost equivalent to the IR absorption of the pure- and poly-crystalline orthorhombic structures in the aerosol particles. The characteristic temperature behavior of the IR spectra implies the existence of the other large cluster, which is discussed in terms of the phase transition of a bulk crystal.

Interaction between plasma synthetic jet and subsonic turbulent boundary layer

NASA Astrophysics Data System (ADS)

Zong, Haohua; Kotsonis, Marios

2017-04-01

This paper experimentally investigates the interaction between a plasma synthetic jet (PSJ) and a subsonic turbulent boundary layer (TBL) using a hotwire anemometer and phase-locked particle imaging velocimetry. The PSJ is interacting with a fully developed turbulent boundary layer developing on the flat wall of a square wind tunnel section of 1.7 m length. The Reynolds number based on the freestream velocity (U∞ = 20 m/s) and the boundary layer thickness (δ99 = 34.5 mm) at the location of interaction is 44 400. A large-volume (1696 mm3) three-electrode plasma synthetic jet actuator (PSJA) with a round exit orifice (D = 2 mm) is adopted to produce high-speed (92 m/s) and short-duration (Tjet = 1 ms) pulsed jets. The exit velocity variation of the adopted PSJA in a crossflow is shown to remain almost identical to that in quiescent conditions. However, the flow structures emanating from the interaction between the PSJ and the TBL are significantly different from what were observed in quiescent conditions. In the midspan xy plane (z = 0 mm), the erupted jet body initially follows a wall-normal trajectory accompanied by the formation of a distinctive front vortex ring. After three convective time scales the jet bends to the crossflow, thus limiting the peak penetration depth to approximately 0.58δ99. Comparison of the normalized jet trajectories indicates that the penetration ability of the PSJ is less than steady jets with the same momentum flow velocity. Prior to the jet diminishing, a recirculation region is observed in the leeward side of the jet body, experiencing first an expansion and then a contraction in the area. In the cross-stream yz plane, the signature structure of jets in a crossflow, the counter-rotating vortex pair (CVP), transports high-momentum flow from the outer layer to the near-wall region, leading to a fuller velocity profile and a drop in the boundary layer shape factor (1.3 to 1.2). In contrast to steady jets, the CVP produced by the PSJ exhibits a prominent spatiotemporal behaviour. The residence time of the CVP is estimated as the jet duration time, while the maximum extent of the affected flow in the three coordinate directions (x, y, and z) is approximately 32D, 8.5D, and 10D, respectively. An extremely high level of turbulent kinetic energy production is shown in the jet shear-layer, front vortex ring, and CVP, of which the contribution of the streamwise Reynolds normal stress is dominant. Finally, a conceptual model of the interaction between the PSJ and the TBL is proposed.

Location of γ-ray emission and magnetic field strengths in OJ 287

NASA Astrophysics Data System (ADS)

Hodgson, J. A.; Krichbaum, T. P.; Marscher, A. P.; Jorstad, S. G.; Rani, B.; Marti-Vidal, I.; Bach, U.; Sanchez, S.; Bremer, M.; Lindqvist, M.; Uunila, M.; Kallunki, J.; Vicente, P.; Fuhrmann, L.; Angelakis, E.; Karamanavis, V.; Myserlis, I.; Nestoras, I.; Chidiac, C.; Sievers, A.; Gurwell, M.; Zensus, J. A.

2017-01-01

Context. The γ-ray BL Lac object OJ 287 is known to exhibit inner-parsec "jet-wobbling", high degrees of variability at all wavelengths and quasi-stationary features, including an apparent (≈100°) position-angle change in projection on the sky plane. Aims: Sub-50 micro-arcsecond resolution 86 GHz observations with the global mm-VLBI array (GMVA) supplement ongoing multi-frequency VLBI blazar monitoring at lower frequencies. Using these maps, together with cm/mm total intensity and γ-ray observations from Fermi-LAT from 2008-2014, we aim to determine the location of γ-ray emission and to explain the inner-mas structural changes. Methods: Observations with the GMVA offer approximately double the angular resolution compared with 43 GHz VLBA observations and enable us to observe above the synchrotron self-absorption peak frequency. Fermi-LAT γ-ray data were reduced and analysed. The jet was spectrally decomposed at multiple locations along the jet. From this, we could derive estimates of the magnetic field using equipartition and synchrotron self-absorption arguments. How the field decreases down the jet provided an estimate of the distance to the jet apex and an estimate of the magnetic field strength at the jet apex and in the broad line region. Combined with accurate kinematics, we attempt to locate the site of γ-ray activity, radio flares, and spectral changes. Results: Strong γ-ray flares appeared to originate from either the so-called core region, a downstream stationary feature, or both, with γ-ray activity significantly correlated with radio flaring in the downstream quasi-stationary feature. Magnetic field estimates were determined at multiple locations along the jet, with the magnetic field found to be ≥1.6 G in the core and ≤0.4 G in the downstream quasi-stationary feature. We therefore found upper limits on the location of the VLBI core as ≲6.0 pc from the jet apex and determined an upper limit on the magnetic field near the jet base of the order of thousands of Gauss. The 3 mm GMVA data are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/597/A80

Application of the Nonballistic Model to the Black Hole Candidate XTE J1752-223 and the Quasar NRAO 150

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, T. Y.; Gong, B. P., E-mail: bpgong@mail.hust.edu.cn

2017-02-01

Optical and radio observations of the black hole candidate XTE J1752-223 have exhibited a slightly curved motion of the jet components, which is associated with its radio light curve. In addition, observations of the quasar NRAO 150 have revealed a core–jet structure wobbling with a high angular speed. In this paper, the phenomena displayed in these two different sources are interpreted as the precession of a bent jet. In such a scenario, hot spots reproduced at different separations from the core precess on the same precession cone, in which different components correspond to different propagation times to the observer. Bymore » fitting the kinematics of the components of XTE J1752-223 and its light curve with a curved pattern of precession period 314 days, we find that the propagation time can make an earlier event appear later, and the jet axis can oscillate during its precession. Simulating the quasar NRAO 150 with the same scenario reveals that the knots at larger separation from the core precess at a slower speed than those closer in. A possible mechanism relating to the cooling time of a component is proposed. These three new results are of importance in understanding the physics underlying the curved jet as well as the activity of the central engine of different black hole systems.« less

Enceladus Plume Structure and Time Variability: Comparison of Cassini Observations

PubMed Central

Perry, Mark E.; Hansen, Candice J.; Waite, J. Hunter; Porco, Carolyn C.; Spencer, John R.; Howett, Carly J. A.

2017-01-01

Abstract During three low-altitude (99, 66, 66 km) flybys through the Enceladus plume in 2010 and 2011, Cassini's ion neutral mass spectrometer (INMS) made its first high spatial resolution measurements of the plume's gas density and distribution, detecting in situ the individual gas jets within the broad plume. Since those flybys, more detailed Imaging Science Subsystem (ISS) imaging observations of the plume's icy component have been reported, which constrain the locations and orientations of the numerous gas/grain jets. In the present study, we used these ISS imaging results, together with ultraviolet imaging spectrograph stellar and solar occultation measurements and modeling of the three-dimensional structure of the vapor cloud, to constrain the magnitudes, velocities, and time variability of the plume gas sources from the INMS data. Our results confirm a mixture of both low and high Mach gas emission from Enceladus' surface tiger stripes, with gas accelerated as fast as Mach 10 before escaping the surface. The vapor source fluxes and jet intensities/densities vary dramatically and stochastically, up to a factor 10, both spatially along the tiger stripes and over time between flyby observations. This complex spatial variability and dynamics may result from time-variable tidal stress fields interacting with subsurface fissure geometry and tortuosity beyond detectability, including changing gas pathways to the surface, and fluid flow and boiling in response evolving lithostatic stress conditions. The total plume gas source has 30% uncertainty depending on the contributions assumed for adiabatic and nonadiabatic gas expansion/acceleration to the high Mach emission. The overall vapor plume source rate exhibits stochastic time variability up to a factor ∼5 between observations, reflecting that found in the individual gas sources/jets. Key Words: Cassini at Saturn—Geysers—Enceladus—Gas dynamics—Icy satellites. Astrobiology 17, 926–940. PMID:28872900

Investigating the anatomy of magnetosheath jets - MMS observations

NASA Astrophysics Data System (ADS)

Karlsson, Tomas; Plaschke, Ferdinand; Hietala, Heli; Archer, Martin; Blanco-Cano, Xóchitl; Kajdič, Primož; Lindqvist, Per-Arne; Marklund, Göran; Gershman, Daniel J.

2018-04-01

We use Magnetosphere Multiscale (MMS) mission data to investigate a small number of magnetosheath jets, which are localized and transient increases in dynamic pressure, typically due to a combined increase in plasma velocity and density. For two approximately hour-long intervals in November, 2015 we found six jets, which are of two distinct types. (a) Two of the jets are associated with the magnetic field discontinuities at the boundary between the quasi-parallel and quasi-perpendicular magnetosheath. Straddling the boundary, the leading part of these jets contains an ion population similar to the quasi-parallel magnetosheath, while the trailing part contains ion populations similar to the quasi-perpendicular magnetosheath. Both populations are, however, cooler than the surrounding ion populations. These two jets also have clear increases in plasma density and magnetic field strength, correlated with a velocity increase. (b) Three of the jets are found embedded within the quasi-parallel magnetosheath. They contain ion populations similar to the surrounding quasi-parallel magnetosheath, but with a lower temperature. Out of these three jets, two have a simple structure. For these two jets, the increases in density and magnetic field strength are correlated with the dynamic pressure increases. The other jet has a more complicated structure, and no clear correlations between density, magnetic field strength and dynamic pressure. This jet has likely interacted with the magnetosphere, and contains ions similar to the jets inside the quasi-parallel magnetosheath, but shows signs of adiabatic heating. All jets are associated with emissions of whistler, lower hybrid, and broadband electrostatic waves, as well as approximately 10 s period electromagnetic waves with a compressional component. The latter have a Poynting flux of up to 40 µW m-2 and may be energetically important for the evolution of the jets, depending on the wave excitation mechanism. Only one of the jets is likely to have modified the surrounding magnetic field into a stretched configuration, as has recently been reported in other studies. None of the jets are associated with clear signatures of either magnetic or thermal pressure gradient forces acting on them. The different properties of the two types also point to different generation mechanisms, which are discussed here. Their different properties and origins suggest that the two types of jets need to be separated in future statistical and simulation studies.

Accumulation of electric currents driving jetting events in the solar atmosphere

NASA Astrophysics Data System (ADS)

Vargas Domínguez, S.; Guo, Y.; Demoulin, P.; Schmieder, B.; Ding, M.; Liu, Y.

2013-12-01

The solar atmosphere is populated with a wide variety of structures and phenomena at different spatial and temporal scales. Explosive phenomena are of particular interest due to their contribution to the atmosphere's energy budget and their implications, e.g. coronal heating. Recent instrumental developments have provided important observations and therefore new insights for tracking the dynamic evolution of the solar atmosphere. Jets of plasma are frequently observed in the solar corona and are thought to be a consequence of magnetic reconnection, however, the physics involved is not fully understood. Unprecedented observations (EUV and vector magnetic fields) are used to study solar jetting events, from which we derive the magnetic flux evolution, the photospheric velocity field, and the vertical electric current evolution. The evolution of magnetic parasitic polarities displaying diverging flows are detected to trigger recurrent jets in a solar regionon 17 September 2010. The interaction drive the build up of electric currents. Observed diverging flows are proposed to build continuously such currents. Magnetic reconnection is proposed to occur periodically, in the current layer created between the emerging bipole and the large scale active region field. SDO/AIA EUV composite images. Upper: SDO/AIA 171 Å image overlaid by the line-of-sight magnetic field observed at the same time as that of the 171 Å image. Lower: Map of photospheric transverse velocities derived from LCT analysis with the HMI magnetograms.

Shelf Circulation Induced by an Orographic Wind Jet

NASA Astrophysics Data System (ADS)

Ràfols, Laura; Grifoll, Manel; Jordà, Gabriel; Espino, Manuel; Sairouní, Abdel; Bravo, Manel

2017-10-01

The dynamical response to cross-shelf wind-jet episodes is investigated. The study area is located at the northern margin of the Ebro Shelf, in the Northwestern (NW) Mediterranean Sea, where episodes of strong northwesterly wind occur. In this case, the wind is channeled through the Ebro Valley and intensifies upon reaching the sea, resulting in a wind jet. The wind-jet response in terms of water circulation and vertical density structure is investigated using a numerical model. The numerical outputs agree with water current observations from a high-frequency radar. Additionally, temperature, sea level, and wind measurements are also used for the skill assessment of the model. For the wind-jet episodes, the numerical results show a well-defined two-layer circulation in the cross-shelf direction, with the surface currents in the direction of the wind. This pattern is consistent with sea level set-down due to the wind effect. The comparison of the vertical structure response for different episodes revealed that the increase of stratification leads to an onshore displacement of the transition from inner shelf to mid-shelf. In general, the cross-shelf momentum balance during a wind-jet episode exhibits a balance between the frictional terms and the pressure gradient in shallow waters, shifting to a balance between the Coriolis force and the wind stress terms in deeper waters.

A model for periodic blazars

NASA Astrophysics Data System (ADS)

Sobacchi, Emanuele; Sormani, Mattia C.; Stamerra, Antonio

2017-02-01

We describe a scenario to explain blazar periodicities with time-scales of ˜ few years. The scenario is based on a binary supermassive black hole (SMBH) system in which one of the two SMBHs carries a jet. We discuss the various mechanisms that can cause the jet to precess and produce corkscrew patterns through space with a scale of ˜ few pc. It turns out that the dominant mechanism responsible for the precession is simply the imprint of the jet-carrying SMBH orbital speed on the jet. Gravitational deflection and Lense-Thirring precession (due to the gravitational field of the other SMBH) are second-order effects. We complement the scenario with a kinematical jet model which is inspired to the spine-sheath structure observed in M87. One of the main advantages of such a structure is that it allows the peak of the synchrotron emission to scale with frequency according to νF ∝ νξ as the viewing angle is changed, where ξ is not necessarily 3 or 4 as in the case of jets with uniform velocity, but can be ξ ˜ 1. Finally, we apply the model to the source PG1553+113, which has been recently claimed to show a Tobs = (2.18 ± 0.08) yr periodicity. We are able to reproduce the optical and gamma-ray light curves and multiple synchrotron spectra simultaneously. We also give estimates of the source mass and size.

Mode selection in swirling jet experiments: a linear stability analysis

NASA Astrophysics Data System (ADS)

Gallaire, François; Chomaz, Jean-Marc

2003-11-01

The primary goal of the study is to identify the selection mechanism responsible for the appearance of a double-helix structure in the pre-breakdown stage of so-called screened swirling jets for which the circulation vanishes away from the jet. The family of basic flows under consideration combines the azimuthal velocity profiles of Carton & McWilliams (1989) and the axial velocity profiles of Monkewitz (1988). This model satisfactorily represents the nozzle exit velocity distributions measured in the swirling jet experiment of Billant et al. (1998). Temporal and absolute/convective instability properties are directly retrieved from numerical simulations of the linear impulse response for different swirl parameter settings. A large range of negative helical modes, winding with the basic flow, are destabilized as swirl is increased, and their characteristics for large azimuthal wavenumbers are shown to agree with the asymptotic analysis of Leibovich & Stewartson (1983). However, the temporal study fails to yield a clear selection principle. The absolute/convective instability regions are mapped out in the plane of the external axial flow and swirl parameters. The absolutely unstable domain is enhanced by rotation and it remains open for arbitrarily large swirl. The swirling jet with zero external axial flow is found to first become absolutely unstable to a mode of azimuthal wavenumber m {=} {-}2, winding with the jet. It is suggested that this selection mechanism accounts for the experimental observation of a double-helix structure.

Structure analyses of the explosive extratropical cyclone: A case study over the Northwestern Pacific in March 2007

NASA Astrophysics Data System (ADS)

Wang, Shuai; Fu, Gang; Pang, Huaji

2017-12-01

The synoptic situation and mesoscale structure of an explosive extratropical cyclone over the Northwestern Pacific in March 2007 are investigated through weather station observations and data reanalysis. The cyclone is located beneath the poleward side of the exit of a 200 hPa jet, which is a strong divergent region aloft. At mid-level, the cyclone lies on the downstream side of a well-developed trough, where a strong ascending motion frequently occurs. Cross-section analyses with weather station data show that the cyclone has a warm and moist core. A `nose' of the cold front, which is characterized by a low-level protruding structure in the equivalent potential temperature field, forms when the cyclone moves offshore. This `nose' structure is hypothesized to have been caused by the heating effect of the Kuroshio Current. Two low-level jet streams are also identified on the western and eastern sides of the cold front. The western jet conveys cold and dry air at 800-900 hPa. The wind in the northern part is northeasterly, and the wind in the southern part is northwesterly. By contrast, the eastern jet carries warm and moist air into the cyclone system, ascending northward from 900 hPa to 600-700 hPa. The southern part is dominated by the southerly wind, and the wind in the northern part is southwesterly. The eastern and western jets significantly increase the air temperature and moisture contrast in the vicinity of the cold front. This increase could play an important role in improving the rapid cyclogenesis process.

ON THE ORIGIN OF INNER COMA STRUCTURES OBSERVED BY ROSETTA DURING A DIURNAL ROTATION OF COMET 67P/CHURYUMOV–GERASIMENKO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kramer, Tobias; Noack, Matthias

2016-05-20

The Rosetta probe around comet 67P/Churyumov–Gerasimenko (67P) reveals an anisotropic dust distribution of the inner coma with jet-like structures. The physical processes leading to jet formation are under debate, with most models for cometary activity focusing on localized emission sources, such as cliffs or terraced regions. Here we suggest, by correlating high-resolution simulations of the dust environment around 67P with observations, that the anisotropy and the background dust density of 67P originate from dust released across the entire sunlit surface of the nucleus rather than from few isolated sources. We trace back trajectories from coma regions with high local dustmore » density in space to the non-spherical nucleus and identify two mechanisms of jet formation: areas with local concavity in either two dimensions or only one. Pits and craters are examples of the first case; the neck region of the bi-lobed nucleus of 67P is an example of the latter case. The conjunction of multiple sources, in addition to dust released from all other sunlit areas, results in a high correlation coefficient (∼0.8) of the predictions with observations during a complete diurnal rotation period of 67P.« less

Modeling unsteady sound refraction by coherent structures in a high-speed jet

NASA Astrophysics Data System (ADS)

Kan, Pinqing; Lewalle, Jacques

2011-11-01

We construct a visual model for the unsteady refraction of sound waves from point sources in a Ma = 0.6 jet. The mass and inviscid momentum equations give an equation governing acoustic fluctuations, including anisotropic propagation, attenuation and sources; differences with Lighthill's equation will be discussed. On this basis, the theory of characteristics gives canonical equations for the acoustic paths from any source into the far field. We model a steady mean flow in the near-jet region including the potential core and the mixing region downstream of its collapse, and model the convection of coherent structures as traveling wave perturbations of this mean flow. For a regular distribution of point sources in this region, we present a visual rendition of fluctuating distortion, lensing and deaf spots from the viewpoint of a far-field observer. Supported in part by AFOSR Grant FA-9550-10-1-0536 and by a Syracuse University Graduate Fellowship.

CFD Analyses and Jet-Noise Predictions of Chevron Nozzles with Vortex Stabilization

NASA Technical Reports Server (NTRS)

Dippold, Vance

2008-01-01

The wind computational fluid dynamics code was used to perform a series of analyses on a single-flow plug nozzle with chevrons. Air was injected from tubes tangent to the nozzle outer surface at three different points along the chevron at the nozzle exit: near the chevron notch, at the chevron mid-point, and near the chevron tip. Three injection pressures were used for each injection tube location--10, 30, and 50 psig-giving injection mass flow rates of 0.1, 0.2, and 0.3 percent of the nozzle mass flow. The results showed subtle changes in the jet plume s turbulence and vorticity structure in the region immediately downstream of the nozzle exit. Distinctive patterns in the plume structure emerged from each injection location, and these became more pronounced as the injection pressure was increased. However, no significant changes in centerline velocity decay or turbulent kinetic energy were observed in the jet plume as a result of flow injection. Furthermore, computational acoustics calculations performed with the JeNo code showed no real reduction in jet noise relative to the baseline chevron nozzle.

Fabrication of micro/nano-structures by electrohydrodynamic jet technique

NASA Astrophysics Data System (ADS)

Wang, Dazhi; Zhao, Xiaojun; Lin, Yigao; Ren, Tongqun; Liang, Junsheng; Liu, Chong; Wang, Liding

2017-12-01

Electrohydrodynamic jet (E-Jet) is an approach to the fabrication of micro/nano-structures by the use of electrical forces. In this process, the liquid is subjected to electrical and mechanical forces to form a liquid jet, which is further disintegrated into droplets. The major advantage of the E-Jet technique is that the sizes of the jet formed can be at the nanoscale far smaller than the nozzle size, which can realize high printing resolution with less risk of nozzle blockage. The E-Jet technique, which mainly includes E-Jet deposition and E-Jet printing, has a wide range of applications in the fabrication of micro/nano-structures for micro/nano-electromechanical system devices. This technique is also considered a micro/nano-fabrication method with a great potential for commercial use. This study mainly reviews the E-Jet deposition/printing fundamentals, fabrication process, and applications.

The effects of the stellar wind and orbital motion on the jets of high-mass microquasars

NASA Astrophysics Data System (ADS)

Bosch-Ramon, V.; Barkov, M. V.

2016-05-01

Context. High-mass microquasar jets propagate under the effect of the wind from the companion star, and the orbital motion of the binary system. The stellar wind and the orbit may be dominant factors determining the jet properties beyond the binary scales. Aims: This is an analytical study, performed to characterise the effects of the stellar wind and the orbital motion on the jet properties. Methods: Accounting for the wind thrust transferred to the jet, we derive analytical estimates to characterise the jet evolution under the impact of the stellar wind. We include the Coriolis force effect, induced by orbital motion and enhanced by the wind's presence. Large-scale evolution of the jet is sketched, accounting for wind-to-jet thrust transfer, total energy conservation, and wind-jet flow mixing. Results: If the angle of the wind-induced jet bending is larger than its half-opening angle, the following is expected: (I) a strong recollimation shock; (II) bending against orbital motion, caused by Coriolis forces and enhanced by the wind presence; and (III) non-ballistic helical propagation further away. Even if disrupted, the jet can re-accelerate due to ambient pressure gradients, but wind entrainment can weaken this acceleration. On large scales, the opening angle of the helical structure is determined by the wind-jet thrust relation, and the wind-loaded jet flow can be rather slow. Conclusions: The impact of stellar winds on high-mass microquasar jets can yield non-ballistic helical jet trajectories, jet partial disruption and wind mixing, shocks, and possibly non-thermal emission. Among other observational diagnostics, such as radiation variability at any band, the radio morphology on milliarcsecond scales can be informative on the wind-jet interaction.

[CII] emission from NGC 4258 with SOFIA/FIFI-LS

NASA Astrophysics Data System (ADS)

Fadda, Dario; Appleton, Philip N.; Diaz Santos, Tanio; Togi, Aditya; Ogle, Patrick

2018-06-01

We present the [CII]157.7μm map of the NGC 4258 (M106) galaxy obtained with the FIFI-LS spectrometer onboard SOFIA.M106 contains an active nucleus classified as type 1.9 Seyfert with a warped inner rotating disk of water-vapor masers which allowed for the first high accuracy measurements of the mass of a supermassive black hole in any galaxy. A relativistic jet is thought to be responsible for anomalous radio-continuum spiral arms, which appear several kpc from the center, and extend outwards through the outer disk. These arms do not correlate with the galaxy's underlying stellar spiral structure, and their presence suggest that in the past, the jet has strongly interacted with the galaxy's outer disk , exciting synchrotron radiation. Since that time, a new burst of activity seems to have occurred, creating a compact jet at the core of the galaxy, and two radio hotspots further out associated with optical "bow-shocks". The position angle of this new "active" jet is different from that needed to excited the outer radio arms, presumably because the jet has precessed, perhaps as a result of precession of the axis of the inner warped accretion disk.Our observations reveal three main sources of [CII] emission: two associated with large regions of gas at the ends of the active jet, and a third minor axis filament associated with linear clumps of star formation and dust seen in HST images offset from the nucleus. We combine the SOFIA observations with previous Spitzer mid-IR, Chandra X-ray and VLA radio observations to explore the nature of the detected [CII] emission. In regions along the northern active jet, we see a significant deficiency in the [CII]/FIR ratio, and higher ratios near the ends of the jet. This implies that the jet has changed the conditions of the gas along its length. In several places near the jet, the [CII] emission shows very broad lines, suggestive of enhanced turbulence. Additionally, the minor-axis filament we discovered may represent gas in-falling towards the nucleus perpendicular to the jet. The results provide clues about how radio jets in active galaxies can influence the star formation properties of their host galaxies.

Formation of Relativistic Jets : Magnetohydrodynamics and Synchrotron Radiation

NASA Astrophysics Data System (ADS)

Porth, Oliver J. G.

2011-11-01

In this thesis, the formation of relativistic jets is investigated by means of special relativistic magnetohydrodynamic simulations and synchrotron radiative transfer. Our results show that the magnetohydrodynamic jet self-collimation paradigm can also be applied to the relativistic case. In the first part, jets launched from rotating hot accretion disk coronae are explored, leading to well collimated, but only mildly relativistic flows. Beyond the light-cylinder, the electric charge separation force balances the classical trans-field Lorentz force almost entirely, resulting in a decreased efficiency of acceleration and collimation in comparison to non-relativistic disk winds. In the second part, we examine Poynting dominated flows of various electric current distributions. By following the outflow for over 3000 Schwarzschild radii, highly relativistic jets of Lorentz factor 8 and half-opening angles below 1 degree are obtained, providing dynamical models for the parsec scale jets of active galactic nuclei. Applying the magnetohydrodynamic structure of the quasi-stationary simulation models, we solve the relativistically beamed synchrotron radiation transport. This yields synthetic radiation maps and polarization patterns that can be used to confront high resolution radio and (sub-) mm observations of nearby active galactic nuclei. Relativistic motion together with the helical magnetic fields of the jet formation site imprint a clear signature on the observed polarization and Faraday rotation. In particular, asymmetries in the polarization direction across the jet can disclose the handedness of the magnetic helix and thus the spin direction of the central engine. Finally, we show first results from fully three-dimensional, high resolution adaptive mesh refinement simulations of jet formation from a rotating magnetosphere and examine the jet stability. Relativistic field-line rotation leads to an electric charge separation force that opposes the magnetic Lorentz force, such that we obtain an increased stability of relativistic flows. Accordingly, the non-axisymmetric modes applied to the field-line foot-points saturate quickly, with no signs of enhanced dissipation or disruption near the jet launching site.

Causality and Communication: Relativistic astrophysical jets and the implementation of science communication training in astronomy classes

NASA Astrophysics Data System (ADS)

Kohler, Susanna

Part I: Relativistic jets emitted from the centers of some galaxies (called active galaxies) exhibit many interesting behaviors that are not yet fully understood: acceleration and collimation over vast distances, for instance, and occasional flaring activity. In the first part of my thesis, I examine the possibility of collimation and acceleration of relativistic jets by the pressure of the ambient medium surrounding the jet base. I discuss the differences in predicted jet behavior due to including the effects of a magnetic field threading the jet interior, and I describe the conditions that create some observed jet shapes, such as the "hollow cone" structure seen in M87 and similar jets. I also discuss what happens when the pressure outside of the jet drops so slowly that the jet shocks repeatedly, generating entropy at its boundary. Finally, I examine the spectra of the 40 brightest gamma-ray flares from blazars (active galaxies with jets pointed toward us) recorded by the Fermi Gamma-ray Space Telescope in its first four years of operation. I develop models to describe the observed behavior of these flares and discuss the physical implications of these models. Part II: The ability to clearly communicate scientific concepts to both peers and the lay public is an important component of being a scientist. Few training programs exist, however, for scientists to obtain these skills. In the second part of my thesis, I examine the impact of two different training efforts for very early-career scientists: first, a short science communication workshop for science, technology, engineering and math (STEM) graduate students, and second, science communication training integrated into existing astronomy classes for undergraduate STEM majors and early STEM graduate students. I evaluate whether the students' written communication skills demonstrate measurable improvement after training, and track students' attitudes toward science communication.

Extreme jet ejections from the black hole X-ray binary V404 Cygni

NASA Astrophysics Data System (ADS)

Tetarenko, A. J.; Sivakoff, G. R.; Miller-Jones, J. C. A.; Rosolowsky, E. W.; Petitpas, G.; Gurwell, M.; Wouterloot, J.; Fender, R.; Heinz, S.; Maitra, D.; Markoff, S. B.; Migliari, S.; Rupen, M. P.; Rushton, A. P.; Russell, D. M.; Russell, T. D.; Sarazin, C. L.

2017-08-01

We present simultaneous radio through sub-mm observations of the black hole X-ray binary (BHXB) V404 Cygni during the most active phase of its June 2015 outburst. Our 4 h long set of overlapping observations with the Very Large Array, the Sub-millimeter Array and the James Clerk Maxwell Telescope (SCUBA-2) covers eight different frequency bands (including the first detection of a BHXB jet at 666 GHz/450 μm), providing an unprecedented multifrequency view of the extraordinary flaring activity seen during this period of the outburst. In particular, we detect multiple rapidly evolving flares, which reach Jy-level fluxes across all of our frequency bands. With this rich data set, we performed detailed MCMC modelling of the repeated flaring events. Our custom model adapts the van der Laan synchrotron bubble model to include twin bi-polar ejections, propagating away from the black hole at bulk relativistic velocities, along a jet axis that is inclined to the line of sight. The emission predicted by our model accounts for projection effects, relativistic beaming and the geometric time delay between the approaching and receding ejecta in each ejection event. We find that a total of eight bi-polar, discrete jet ejection events can reproduce the emission that we observe in all of our frequency bands remarkably well. With our best-fitting model, we provide detailed probes of jet speed, structure, energetics and geometry. Our analysis demonstrates the paramount importance of the mm/sub-mm bands, which offer a unique, more detailed view of the jet than can be provided by radio frequencies alone.

Multiple Plasma Ejections and Intermittent Nature of Magnetic Reconnection in Solar Chromospheric Anemone Jets

NASA Astrophysics Data System (ADS)

Singh, K. A. P.; Isobe, H.; Nishizuka, N.; Nishida, K.; Shibata, K.

2012-11-01

The recent discovery of chromospheric anemone jets with the Solar Optical Telescope (SOT) on board Hinode has shown an indirect evidence of magnetic reconnection in the solar chromosphere. However, the basic nature of magnetic reconnection in chromosphere is still unclear. We studied nine chromospheric anemone jets from SOT/Hinode using Ca II H filtergrams, and we found multiple bright, plasma ejections along the jets. In most cases, the major intensity enhancements (larger than 30% relative to the background intensity) of the loop correspond to the timing of the plasma ejections. The typical lifetime and size of the plasma ejecta are about 20-60 s and 0.3-1.5 Mm, respectively. The height-time plot of jet shows many sub-structures (or individual jets) and the typical lifetime of the individual jet is about one to five minutes. Before the onset of the jet activity, a loop appears in Ca II H and gradually increases in size, and after few minutes several jets are launched from the loop. Once the jet activity starts and several individual jets are launched, the loop starts shrinking with a speed of ~4 km s-1. In some events, a downward moving blob with a speed of ~35 km s-1 was observed, associated with the upward moving plasma along one of the legs of the loop hosting the jets. The upward moving plasma gradually developed into jets. Multiple plasma ejections in chromospheric anemone jet show the strongly time-dependent as well as intermittent nature of magnetic reconnection in the solar chromosphere.

A gyrokinetic perspective on the JET-ILW pedestal

NASA Astrophysics Data System (ADS)

Hatch, D. R.; Kotschenreuther, M.; Mahajan, S.; Valanju, P.; Liu, X.

2017-03-01

JET has been unable to recover historical confinement levels when operating with an ITER-like wall (ILW) due largely to the inaccessibility of high pedestal temperatures. Finding a path to overcome this challenge is of utmost importance for both a prospective JET DT campaign and for future ITER operation. Gyrokinetic simulations (using the Gene code) quantitatively capture experimental transport levels for a representative experimental discharge and qualitatively recover the major experimental trends. Microtearing turbulence is a major transport mechanisms for the low-temperature pedestals characteristic of unseeded JET-ILW discharges. At higher temperatures and/or lower {ρ\\ast} , we identify electrostatic ITG transport of a type that is strongly shear-suppressed on smaller machines. Consistent with observations, this transport mechanism is strongly reduced by the presence of a low-Z impurity (e.g. carbon or nitrogen at the level of {{Z}\\text{eff}}∼ 2 ), recovering the accessibility of high pedestal temperatures. Notably, simulations based on dimensionless {ρ\\ast} scans recover historical scaling behavior except in the unique JET-ILW parameter regime where ITG turbulence becomes important. Our simulations also elucidate the observed degradation of confinement caused by gas puffing, emphasizing the important role of the density pedestal structure. This study maps out important regions of parameter space, providing insights that may point to optimal physical regimes that can enable the recovery of high pedestal temperatures on JET.

A Thermodynamic, kinematic and microphysical analysis of a jet and gigantic jet-producing Florida thunderstorm

NASA Astrophysics Data System (ADS)

Lazarus, S. M.; Splitt, M. E.; Brownlee, James; Spiva, Nicholas; Liu, Ningyu

2015-08-01

This paper presents a meteorological analysis of a storm that produced two jets, four gigantic jets (GJ), and a starter, which were observed by two radars as well as the Kennedy Space Center 4-Dimensional Lightning Surveillance System on 3 August 2013 in Central Florida. The work is the first application of dual polarization data to a jet-producing storm and is the fifth case related to a tropical disturbance. The storm environment is consistent with the moist tropical paradigm that characterizes about three quarters of the surface and aircraft observed jet and GJ events. The most unstable (MU) convective available potential energy is not unusual for Florida summer convection and is below the climatological mean for these events. An unusual speed shear layer is located near the storm equilibrium level (EL) and the storm exhibits a tilted structure with CGs displaced upshear. The turbulence, as measured by the eddy dissipation rate, is extreme near the storm top during the event window, consistent with the GJ mixing hypothesis. The individual events are collocated with, and track along, the center axis of the divergent outflow at the EL and occur within the region of the coldest GOES IR temperatures—placing the events within the overshoot. The dual polarization data indicate a deep graupel column, extending above the mixed phase layer, to a 13 km altitude.

Investigation of compound jet electrospray: Particle encapsulation

NASA Astrophysics Data System (ADS)

Mei, Fan; Chen, Da-Ren

2007-10-01

Experiments were performed to investigate the effect of surface tension on the particle encapsulation formation in the compound jet electrospray process. The outer liquid used in this study were olive oil and mineral oil; and inner liquids were ethanol, tri-butyl phosphate, ethylene glycol, and triethylene glycol. It was found that the core-shell structured droplets are formed only when the ratio of charge relaxation lengths of the inner and outer jets [i.e., rO*/rI*, where r *=(Qɛɛ0/K)1/3, in which ɛ is the dielectric constant of liquid] is less than 500, and the ratio of inertial breakup lengths of the inner and outer jets [i.e., RO*/RI*, where R *=(ρQ2/γ)1/3, in which ρ and γ are the density and surface tension of liquid, respectively] is less than 0.015. In this work we further studied the effect of inner and outer liquid flow rates on the size of compound droplets using an Aerosizer (TSI model 3220). The parameters affecting the droplet size distribution were obtained. We also observed that the spray current emitted through the compound jet was merely a linear function of the inner jet flow rate. This observation implies that olive oil and mineral oil, as the outer liquids, serve as an electrically insulated layer during the spray process.

Probing collective effects in hadronisation with the extremes of the underlying event

NASA Astrophysics Data System (ADS)

Martin, T.; Skands, P.; Farrington, S.

2016-05-01

We define a new set of observables to probe the structure of the underlying event in hadron collisions. We use the conventional definition of the "transverse region" in jet events and, for a fixed window in jet p_perp , propose to measure several discriminating quantities as a function of the level of activity in the transverse region. The measurement of these observables in LHC data would reveal whether, e.g., the properties of "low-UE" events are compatible with equivalent measurements in e^+e^- collisions (jet universality), and whether the scaling behaviour towards "high-UE" events exhibits properties of non-trivial soft-QCD dynamics, such as colour reconnections or other collective phenomena. We illustrate at √{s} = 13 {TeV} that significant discriminatory power is obtained in comparisons between MC models with varying treatments of collective effects, including Pythia 8, epos, and Dipsy.

Plasma jets in the near-Earth's magnetotail (Julius Bartels Medal Lecture)

NASA Astrophysics Data System (ADS)

Nakamura, Rumi

2014-05-01

The Earth's magnetosphere is formed as a consequence of the interaction between the magnetized solar wind and the terrestrial magnetic field. While the large-scale and average (>hours) properties of the Earth's magnetotail current sheet can be well described by overall solar wind-magnetosphere interaction, the most dramatic energy conversion process takes place in an explosive manner involving transient (up to several minutes) and localized (up to a few RE) phenomena in the plasma sheet/current sheet regions. One of the most clear observables of such processes are the localized and transient plasma jets called Bursty bulk flows (BBF), embedding velocity peaks of 1-min duration, which are called flow bursts. This talk is a review of the current understanding of these plasma jets by highlighting the results from multi-spacecraft observations by the Cluster and THEMIS spacecraft. The first four-spacecraft mission Cluster crossed the near-Earth plasma sheet with inter-spacecraft distance of about 250 km to 10000 km, ideal for studying local structures of the flow bursts. The five-spacecraft THEMIS mission , separated by larger distances , succeeded to monitor the large-scale evolution of the fast flows from the mid-tail to the inner magnetosphere. Multi-point observations of BBFS have established the importance of measuring local gradients of the fields and the plasma to understand the BBF structures such as the spatial scales and 3D structure of localized Earthward convecting flux tubes. Among others the magnetic field disturbance forming at the front of BBF, called dipolarization front (DF), has been intensively studied. From the propagation properties of DF relative to the flows and by comparing with ionospheric data, the evolution of the fast flows in terms of magnetosphere-ionospheric coupling through field-aligned currents are established. An important aspect of BBF is the interaction of the Earthward plasma jets and the Earth's dipole field. Multi-point observations combined with ground-based observations enabled to resolve how the BBFs are braked , diverted, or bounced back at the high-pressure gradient region. The multi-point capabilities in space enabled to study the BBF structure as well as large-scale evolution of BBFs. These processes are also universal processes in space plasmas and are, for example, associated with the reconnection process during the solar flares or leading to auroral phenomena at different planets.

Depth of a strong jovian jet from a planetary-scale disturbance driven by storms.

PubMed

Sánchez-Lavega, A; Orton, G S; Hueso, R; García-Melendo, E; Pérez-Hoyos, S; Simon-Miller, A; Rojas, J F; Gómez, J M; Yanamandra-Fisher, P; Fletcher, L; Joels, J; Kemerer, J; Hora, J; Karkoschka, E; de Pater, I; Wong, M H; Marcus, P S; Pinilla-Alonso, N; Carvalho, F; Go, C; Parker, D; Salway, M; Valimberti, M; Wesley, A; Pujic, Z

2008-01-24

The atmospheres of the gas giant planets (Jupiter and Saturn) contain jets that dominate the circulation at visible levels. The power source for these jets (solar radiation, internal heat, or both) and their vertical structure below the upper cloud are major open questions in the atmospheric circulation and meteorology of giant planets. Several observations and in situ measurements found intense winds at a depth of 24 bar, and have been interpreted as supporting an internal heat source. This issue remains controversial, in part because of effects from the local meteorology. Here we report observations and modelling of two plumes in Jupiter's atmosphere that erupted at the same latitude as the strongest jet (23 degrees N). The plumes reached a height of 30 km above the surrounding clouds, moved faster than any other feature (169 m s(-1)), and left in their wake a turbulent planetary-scale disturbance containing red aerosols. On the basis of dynamical modelling, we conclude that the data are consistent only with a wind that extends well below the level where solar radiation is deposited.

Linking high-energy cosmic particles by black-hole jets embedded in large-scale structures

NASA Astrophysics Data System (ADS)

Fang, Ke; Murase, Kohta

2018-04-01

The origin of ultrahigh-energy cosmic rays (UHECRs) is a half-century-old enigma1. The mystery has been deepened by an intriguing coincidence: over ten orders of magnitude in energy, the energy generation rates of UHECRs, PeV neutrinos and isotropic sub-TeV γ-rays are comparable, which hints at a grand unified picture2. Here we report that powerful black hole jets in aggregates of galaxies can supply the common origin for all of these phenomena. Once accelerated by a jet, low-energy cosmic rays confined in the radio lobe are adiabatically cooled; higher-energy cosmic rays leaving the source interact with the magnetized cluster environment and produce neutrinos and γ-rays; the highest-energy particles escape from the host cluster and contribute to the observed cosmic rays above 100 PeV. The model is consistent with the spectrum, composition and isotropy of the observed UHECRs, and also explains the IceCube neutrinos and the non-blazar component of the Fermi γ-ray background, assuming a reasonable energy output from black hole jets in clusters.

Mini-filament Eruption as the Initiation of a Jet along Coronal Loops

NASA Astrophysics Data System (ADS)

Hong, Junchao; Jiang, Yunchun; Yang, Jiayan; Yang, Bo; Xu, Zhe; Xiang, Yongyuan

2016-10-01

Minifilament eruptions (MFEs) and coronal jets are different types of solar small-scale explosive events. We report an MFE observed at the New Vacuum Solar Telescope (NVST). As seen in the NVST Hα images, during the rising phase, the minifilament erupts outward orthogonally to its length, accompanied with a flare-like brightening at the bottom. Afterward, dark materials are found to possibly extend along the axis of the expanded filament body. The MFE is analogous to large filament eruptions. However, a simultaneous observation of the Solar Dynamics Observatory shows that a jet is initiated and flows out along nearby coronal loops during the rising phase of the MFE. Meanwhile, small hot loops, which connect the original eruptive site of the minifilament to the footpoints of the coronal loops, are formed successively. A differential emission measure analysis demonstrates that, on the top of the new small loops, a hot cusp structure exists. We conjecture that the magnetic fields of the MFE interact with magnetic fields of the coronal loops. This interaction is interpreted as magnetic reconnection that produces the jet and the small hot loops.

Coronal Jets Simulated with the Global Alfvén Wave Solar Model

NASA Astrophysics Data System (ADS)

Szente, J.; Toth, G.; Manchester, W. B., IV; van der Holst, B.; Landi, E.; Gombosi, T. I.; DeVore, C. R.; Antiochos, S. K.

2017-01-01

This paper describes a numerical modeling study of coronal jets to understand their effects on the global corona and their contribution to the solar wind. We implement jets into a well-established three-dimensional, two-temperature magnetohydrodynamic (MHD) solar corona model employing Alfvén-wave dissipation to produce a realistic solar-wind background. The jets are produced by positioning a compact magnetic dipole under the solar surface and rotating the boundary plasma around the dipole's magnetic axis. The moving plasma drags the magnetic field lines along with it, ultimately leading to a reconnection-driven jet similar to that described by Pariat et al. We compare line-of-sight synthetic images to multiple jet observations at EUV and X-ray bands, and find very close matches in terms of physical structure, dynamics, and emission. Key contributors to this agreement are the greatly enhanced plasma density and temperature in our jets compared to previous models. These enhancements arise from the comprehensive thermodynamic model that we use and, also, our inclusion of a dense chromosphere at the base of our jet-generating regions. We further find that the large-scale corona is affected significantly by the outwardly propagating torsional Alfvén waves generated by our polar jet, across 40° in latitude and out to 24 R⊙. We estimate that polar jets contribute only a few percent to the steady-state solar-wind energy outflow.

Propulsive jet simulation with air and helium in launcher wake flows

NASA Astrophysics Data System (ADS)

Stephan, Sören; Radespiel, Rolf

2017-06-01

The influence on the turbulent wake of a generic space launcher model due to the presence of an under-expanded jet is investigated experimentally. Wake flow phenomena represent a significant source of uncertainties in the design of a space launcher. Especially critical are dynamic loads on the structure. The wake flow is investigated at supersonic (M=2.9) and hypersonic (M=5.9) flow regimes. The jet flow is simulated using air and helium as working gas. Due to the lower molar mass of helium, higher jet velocities are realized, and therefore, velocity ratios similar to space launchers can be simulated. The degree of under-expansion of the jet is moderate for the supersonic case (p_e/p_∞ ≈ 5) and high for the hypersonic case (p_e/p_∞ ≈ 90). The flow topology is described by Schlieren visualization and mean-pressure measurements. Unsteady pressure measurements are performed to describe the dynamic wake flow. The influences of the under-expanded jet and different jet velocities are reported. On the base fluctuations at a Strouhal number, around St_D ≈ 0.25 dominate for supersonic free-stream flows. With air jet, a fluctuation-level increase on the base is observed for Strouhal numbers above St_D ≈ 0.75 in hypersonic flow regime. With helium jet, distinct peaks at higher frequencies are found. This is attributed to the interactions of wake flow and jet.

Observed trends in the global jet stream characteristics during the second half of the 20th century

NASA Astrophysics Data System (ADS)

Pena-Ortiz, Cristina; Gallego, David; Ribera, Pedro; Ordonez, Paulina; Alvarez-Castro, Maria Del Carmen

2013-04-01

In this paper, we propose a new method based on the detection of jet cores with the aim to describe the climatological features of the jet streams and to estimate their trends in latitude, altitude, and velocity in the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) and 20th Century reanalysis data sets. Due to the fact that the detection method uses a single grid point to define the position of jet cores, our results reveal a greater latitudinal definition allowing a more accurate picture of the split flow configurations and double jet structures. To the best of our knowledge, these results provide the first multiseasonal and global trend analysis of jet streams based on a daily-resolution 3-D detection algorithm. Trends have been analyzed over 1958-2008 and during the post-satellite period, 1979-2008. We found that, in general, trends in jet velocities and latitudes have been faster for the Southern Hemisphere jets and especially for the southern polar front jet which has experienced the fastest velocity increase and poleward shift over 1979-2008 during the austral summer and autumn. Results presented here show an acceleration and a poleward shift of the northern and southern winter subtropical jets over 1979-2008 that occur at a faster rate and over larger zonally extended regions during this latter period than during 1958-2008.

Signatures of Relativistic Helical Motion in the Rotation Measures of Active Galactic Nucleus Jets

NASA Astrophysics Data System (ADS)

Broderick, Avery E.; Loeb, Abraham

2009-10-01

Polarization has proven to be an invaluable tool for probing magnetic fields in relativistic jets. Maps of the intrinsic polarization vectors have provided the best evidence to date for uniform, toroidally dominated magnetic fields within jets. More recently, maps of the rotation measure (RM) in jets have for the first time probed the field geometry of the cool, moderately relativistic surrounding material. In most cases, clear signatures of the toroidal magnetic field are detected, corresponding to gradients in RM profiles transverse to the jet. However, in many objects, these profiles also display marked asymmetries that are difficult to explain in simple helical jet models. Furthermore, in some cases, the RM profiles are strongly frequency and/or time dependent. Here we show that these features may be naturally accounted for by including relativistic helical motion in the jet model. In particular, we are able to reproduce bent RM profiles observed in a variety of jets, frequency-dependent RM profile morphologies, and even the time dependence of the RM profiles of knots in 3C 273. Finally, we predict that some sources may show reversals in their RM profiles at sufficiently high frequencies, depending upon the ratio of the components of jet sheath velocity transverse and parallel to the jet. Thus, multi-frequency RM maps promise a novel way in which to probe the velocity structure of relativistic outflows.

Vortex dynamics and wall shear stress behaviour associated with an elliptic jet impinging upon a flat plate

NASA Astrophysics Data System (ADS)

Long, J.; New, T. H.

2016-07-01

Vortical structures and dynamics of a Re h = 2100 elliptic jet impinging upon a flat plate were studied at H/ d h = 1, 2 and 4 jet-to-plate separation distances. Flow investigations were conducted along both its major and minor planes using laser-induced fluorescence and digital particle image velocimetry techniques. Results show that the impingement process along the major plane largely consists of primary jet ring-vortex and wall-separated secondary vortex formations, where they subsequently separate from the flat plate at smaller H/ d h = 1 and 2 separation distances. Key vortex formation locations occur closer to the impingement point as the separation distance increases. Interestingly, braid vortices and rib structures begin to take part in the impingement process at H/ d h = 4 and wave instabilities dominate the flow field. In contrast, significantly more coherent primary and secondary vortices with physically larger vortex core sizes and higher vortex strengths are observed along the minor plane, with no signs of braid vortices and rib structures. Lastly, influences of these different flow dynamics on the major and minor plane instantaneous and mean skin friction coefficient levels are investigated to shed light on the effects of separation distance on the wall shear stress distributions.

Observational Implications of Gamma-Ray Burst Afterglow Jet Simulations and Numerical Light Curve Calculations

NASA Astrophysics Data System (ADS)

van Eerten, Hendrik J.; MacFadyen, Andrew I.

2012-06-01

We discuss jet dynamics for narrow and wide gamma-ray burst (GRB) afterglow jets and the observational implications of numerical simulations of relativistic jets in two dimensions. We confirm earlier numerical results that sideways expansion of relativistic jets during the bulk of the afterglow emission phase is logarithmic in time and find that this also applies to narrow jets with half opening angle of 0.05 rad. As a result, afterglow jets remain highly nonspherical until after they have become nonrelativistic. Although sideways expansion steepens the afterglow light curve after the jet break, the jet edges becoming visible dominates the jet break, which means that the jet break is sensitive to the observer angle even for narrow jets. Failure to take the observer angle into account can lead to an overestimation of the jet energy by up to a factor of four. This weakens the challenge posed to the magneter energy limit by extreme events such as GRB090926A. Late-time radio calorimetry based on a spherical nonrelativistic outflow model remains relevant when the observer is approximately on-axis and where differences of a few in flux level between the model and the simulation are acceptable. However, this does not imply sphericity of the outflow and therefore does not translate to high observer angles relevant to orphan afterglows. For more accurate calorimetry and in order to model significant late-time features such as the rise of the counterjet, detailed jet simulations remain indispensable.

Simulations of Viscous Accretion Flow around Black Holes in a Two-dimensional Cylindrical Geometry

NASA Astrophysics Data System (ADS)

Lee, Seong-Jae; Chattopadhyay, Indranil; Kumar, Rajiv; Hyung, Siek; Ryu, Dongsu

2016-11-01

We simulate shock-free and shocked viscous accretion flows onto a black hole in a two-dimensional cylindrical geometry, where initial conditions were chosen from analytical solutions. The simulation code used the Lagrangian total variation diminishing plus remap routine, which enabled us to attain high accuracy in capturing shocks and to handle the angular momentum distribution correctly. The inviscid shock-free accretion disk solution produced a thick disk structure, while the viscous shock-free solution attained a Bondi-like structure, but in either case, no jet activity nor any quasi-periodic oscillation (QPO)-like activity developed. The steady-state shocked solution in the inviscid as well as in the viscous regime matched theoretical predictions well. However, increasing viscosity renders the accretion shock unstable. Large-amplitude shock oscillation is accompanied by intermittent, transient inner multiple shocks. This oscillation of the inner part of the disk is interpreted as the source of QPO in hard X-rays observed in micro-quasars. Strong shock oscillation induces strong episodic jet emission. The jets also show the existence of shocks, which are produced as one shell hits the preceding one. The periodicities of the jets and shock oscillation are similar; the jets for the higher viscosity parameter appear to be stronger and faster.

SIMULATIONS OF VISCOUS ACCRETION FLOW AROUND BLACK HOLES IN A TWO-DIMENSIONAL CYLINDRICAL GEOMETRY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Seong-Jae; Hyung, Siek; Chattopadhyay, Indranil

2016-11-01

We simulate shock-free and shocked viscous accretion flows onto a black hole in a two-dimensional cylindrical geometry, where initial conditions were chosen from analytical solutions. The simulation code used the Lagrangian total variation diminishing plus remap routine, which enabled us to attain high accuracy in capturing shocks and to handle the angular momentum distribution correctly. The inviscid shock-free accretion disk solution produced a thick disk structure, while the viscous shock-free solution attained a Bondi-like structure, but in either case, no jet activity nor any quasi-periodic oscillation (QPO)-like activity developed. The steady-state shocked solution in the inviscid as well as inmore » the viscous regime matched theoretical predictions well. However, increasing viscosity renders the accretion shock unstable. Large-amplitude shock oscillation is accompanied by intermittent, transient inner multiple shocks. This oscillation of the inner part of the disk is interpreted as the source of QPO in hard X-rays observed in micro-quasars. Strong shock oscillation induces strong episodic jet emission. The jets also show the existence of shocks, which are produced as one shell hits the preceding one. The periodicities of the jets and shock oscillation are similar; the jets for the higher viscosity parameter appear to be stronger and faster.« less

Probing the Hardest Branching within Jets in Heavy-Ion Collisions

NASA Astrophysics Data System (ADS)

Chien, Yang-Ting; Vitev, Ivan

2017-09-01

Heavy ion collisions present exciting opportunities to study the effects of quantum coherence in the formation of subatomic particle showers. We report on the first calculation of the momentum sharing and angular separation distributions between the leading subjets inside a reconstructed jet in such collisions. These observables are directly sensitive to the hardest branching within jets and can probe the early stage of the jet formation. We find that the leading-order medium-induced splitting functions, here obtained in the framework of soft-collinear effective theory with Glauber gluon interactions, capture the essential many-body physics, which is different from proton-proton reactions. Qualitative and in most cases quantitative agreement between theory and preliminary CMS measurements suggests that hard parton branching in strongly interacting matter can be dramatically modified. We also propose a new measurement that will illuminate its angular structure.

Probing the Hardest Branching within Jets in Heavy-Ion Collisions.

PubMed

Chien, Yang-Ting; Vitev, Ivan

2017-09-15

Heavy ion collisions present exciting opportunities to study the effects of quantum coherence in the formation of subatomic particle showers. We report on the first calculation of the momentum sharing and angular separation distributions between the leading subjets inside a reconstructed jet in such collisions. These observables are directly sensitive to the hardest branching within jets and can probe the early stage of the jet formation. We find that the leading-order medium-induced splitting functions, here obtained in the framework of soft-collinear effective theory with Glauber gluon interactions, capture the essential many-body physics, which is different from proton-proton reactions. Qualitative and in most cases quantitative agreement between theory and preliminary CMS measurements suggests that hard parton branching in strongly interacting matter can be dramatically modified. We also propose a new measurement that will illuminate its angular structure.

Measurements of condensation nuclei above the jet stream - Evidence for cross jet transport by waves and new particle formation at high altitudes

NASA Technical Reports Server (NTRS)

Wilson, J. C.; Lai, W. T.; Smith, S. D.

1991-01-01

Condensation nuclei were used as a tracer in midlatitude NASA Stratosphere-Troposphere Exchange Project (STEP) experiments in April and May 1984 in order to study transport in the stratosphere. The very large scale, mean CN distribution was distorted by waves which had the effect of transporting air with anticyclonic properties several degrees to the cyclonic side of the jet and created a strongly layered structure in the CN distribution. Unfiltered CN data revealed short-wavelength oscillations in the CN distribution at the interface between the transported anticyclonic air parcel and the adjacent cyclonic air mass. These oscillations were also seen in the ozone data and increase the potential for mixing along that interface. If the mixing does occur, a wave mechanism for cross-jet transport has been observed.

Simulated In Situ Measurements and Structural Analysis of Reconnection-Driven Solar Polar Jets

NASA Astrophysics Data System (ADS)

Roberts, Merrill A.; Uritsky, Vadim M.; Karpen, Judith T.; DeVore, C. R.

2015-04-01

Solar polar jets are observed to originate in regions within the open field of solar coronal holes. These so called “anemone” regions are associated with an embedded dipole topology, consisting of a fan-separatrix and a spine line emanating from a null point occurring at the top of the dome shaped fan surface (Antiochos 1998). In this study, we analyze simulations using the Adaptively Refined MHD Solver (ARMS) that take into account gravity, solar wind, and spherical geometry to generate polar jets by reconnection between a twisted embedded bipole and the surrounding open field (Karpen et al. 2015). These new simulations confirm and extend previous Cartesian studies of polar jets based on this mechanism (Pariat et al. 2009, 2010, 2015). Focusing on the plasma density, velocity, and magnetic field, we interpolate the adaptively gridded simulation data onto a regular grid, and analyze the signatures that the jet produces as it propagates outward from the solar surface. The trans-Alfvénic nature of the jet front is confirmed by temporally differencing the plasma mass density and comparing the result with the local Alfvén speed. We perform a preliminary analysis of the magnetized plasma turbulence, and examine how the turbulence affects the overall structure of the jet. We also conduct simulated spacecraft fly-throughs of the jet, illustrating the signatures that spacecraft such as Solar Probe Plus may encounter in situ as the jet propagates into the heliosphere. These fly-throughs are performed in several different velocity regimes to better model the changing velocity of Solar Probe Plus relative to the Sun and its jets over the course of the mission.This research was supported by NASA grant NNG11PL10A 670.036 to CUA/IACS (M.A.R. and V.M.U.) and the Living With a Star Targeted Research and Technology (J.T.K. and C.R.D.) program.

Coronal Jets in Closed Magnetic Regions on the Sun

NASA Astrophysics Data System (ADS)

Wyper, Peter Fraser; DeVore, C. R.

2015-04-01

Coronal jets are dynamic, collimated structures observed in solar EUV and X-ray emission. They appear predominantly in the open field of coronal holes, but are also observed in areas of closed field, especially active regions. A common feature of coronal jets is that they originate from the field above a parasitic polarity of opposite sign to the surrounding field. Some process - such as instability onset or flux emergence - induces explosive reconnection between the closed “anemone” field and the surrounding open field that generates the jet. The lesser number of coronal jets in closed-field regions suggests a possible stabilizing effect of the closed configuration with respect to coronal jet formation. If the scale of the jet region is small compared with the background loop length, as in for example type II spicules, the nearby magnetic field may be treated as locally open. As such, one would expect that if a stabilizing effect exists it becomes most apparent as the scale of the anemone region approaches that of the background coronal loops.To investigate if coronal jets are indeed suppressed along shorter coronal loops, we performed a number of simulations of jets driven by a rotation of the parasitic polarity (as in the previous open-jet calculations by Pariat et. al 2009, 2010, 2015) embedded in a large-scale closed bipolar field. The simulations were performed with the state of the art Adaptively Refined Magnetohydrodynamics Solver. We will report here how the magnetic configuration above the anemone region determines the nature of the jet, when it is triggered, and how much of the stored magnetic energy is released. We show that regions in which the background field and the parasitic polarity region are of comparable scale naturally suppress explosive energy release. We will also show how in the post-jet relaxation phase a combination of confined MHD waves and weak current layers are generated by the jet along the background coronal loops, both of which may have implications for coronal heating.This work was supported by an appointment to the NASA Postdoctoral Program (P.F.W.) and by NASA’s Living With a Star Targeted Research and Technology program (C.R.D.).

Analyses of microstructure, composition and retention of hydrogen isotopes in divertor tiles of JET with the ITER-like wall

NASA Astrophysics Data System (ADS)

Masuzaki, S.; Tokitani, M.; Otsuka, T.; Oya, Y.; Hatano, Y.; Miyamoto, M.; Sakamoto, R.; Ashikawa, N.; Sakurada, S.; Uemura, Y.; Azuma, K.; Yumizuru, K.; Oyaizu, M.; Suzuki, T.; Kurotaki, H.; Hamaguchi, D.; Isobe, K.; Asakura, N.; Widdowson, A.; Heinola, K.; Jachmich, S.; Rubel, M.; contributors, JET

2017-12-01

Results of the comprehensive surface analyses of divertor tiles and dusts retrieved from JET after the first ITER-like wall campaign (2011-2012) are presented. The samples cored from the divertor tiles were analyzed. Numerous nano-size bubble-like structures were observed in the deposition layer on the apron of the inner divertor tile, and a beryllium dust with the same structures were found in the matter collected from the inner divertor after the campaign. This suggests that the nano-size bubble-like structures can make the deposition layer to become brittle and may lead to cracking followed by dust generation. X-ray photoelectron spectroscopy analyses of chemical states of species in the deposition layers identified the formation of beryllium-tungsten intermetallic compounds on an inner vertical tile. Different tritium retention profiles along the divertor tiles were observed at the top surfaces and at deeper regions of the tiles by using the imaging plate technique.

Search for X-ray jets from high redshift radio sources.

NASA Astrophysics Data System (ADS)

Schwartz, Daniel A.; Cheung, Teddy; Gobeille, Doug; Marshall, Herman L.; Migliori, Giulia; Siemiginowska, Aneta; Wardle, John F. C.; Worrall, Diana M.; Birkinshaw, Mark

2018-06-01

We are conducting a Chandra "snapshot" survey of 14 radio quasars at redshifts z>3. These are selected to have one sided, arc-sec scale structure, either a jet or lobe, and come from a complete, objectively-defined sample of sources with radio flux density > 70 mJy, and with a spectroscopic redshift from the SDSS. Our objectives are to find X-ray emitting jets, compare the X-ray and radio morphology, and detect X-ray emission arising from inverse Compton scattering of the cosmic microwave background even for those cases where the radio emission is no longer detectable. For this meeting, we expect 5 of the 14 sources to have been observed.

On the Variability of the East Australian Current: Jet Structure, Meandering, and Influence on Shelf Circulation

NASA Astrophysics Data System (ADS)

Archer, Matthew R.; Roughan, Moninya; Keating, Shane R.; Schaeffer, Amandine

2017-11-01

Given the importance of western boundary currents over a wide range of scales in the ocean, it is crucial that we understand their dynamics to accurately predict future changes. For this, we need detailed knowledge of their structure and variability. Here we investigate the jet structure of the East Australian Current (EAC), using observations from HF radars and moorings deployed at 30°S-31°S. Meandering, core velocity, width, and eddy kinetic energy (EKE) are quantified from 4 years of hourly 1.5 km resolution surface current maps (2012-2016), to obtain the most detailed representation of the surface EAC jet to date. The EAC flows predominantly over the ˜1,500 m isobath 50 km offshore but makes large amplitude displacements eastward every 65-100 days—the time scale associated with mesoscale eddy shedding at the EAC separation. Smaller-amplitude, higher-frequency meanders occur every 20-45 days. Using a coordinate frame that follows the jet, we show core velocity and EKE exhibit seasonality in both magnitude and variance, being maximum in summer (1.55 m s-1 mean core velocity), minimum in winter (0.8 m s-1). However, it is the eddy-shedding time scale that dominates jet variability. As the EAC moves shoreward, shelf temperature and along-stream velocity vary linearly with jet movement, within ˜35 km of the core. The EAC is within this range 75% of the time, demonstrating its importance to the shelf circulation. Temperature and velocity fluctuations at the 70 m (100 m) isobath are more influenced by wind (EAC encroachment), with the strongest response occurring when wind and EAC act constructively.

Numerical Analysis of Flow Evolution in a Helium Jet Injected into Ambient Air

NASA Technical Reports Server (NTRS)

Satti, Rajani P.; Agrawal, Ajay K.

2005-01-01

A computational model to study the stability characteristics of an evolving buoyant helium gas jet in ambient air environment is presented. Numerical formulation incorporates a segregated approach to solve for the transport equations of helium mass fraction coupled with the conservation equations of mixture mass and momentum using a staggered grid method. The operating parameters correspond to the Reynolds number varying from 30 to 300 to demarcate the flow dynamics in oscillating and non-oscillating regimes. Computed velocity and concentration fields were used to analyze the flow structure in the evolving jet. For Re=300 case, results showed that an instability mode that sets in during the evolution process in Earth gravity is absent in zero gravity, signifying the importance of buoyancy. Though buoyancy initiates the instability, below a certain jet exit velocity, diffusion dominates the entrainment process to make the jet non-oscillatory as observed for the Re=30 case. Initiation of the instability was found to be dependent on the interaction of buoyancy and momentum forces along the jet shear layer.

Microscopic Processes On Radiation from Accelerated Particles in Relativistic Jets

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.; Hardee, P. E.; Mizuno, Y.; Medvedev, M.; Zhang, B.; Sol, H.; Niemiec, J.; Pohl, M.; Nordlund, A.; Fredriksen, J.;

Breakup phenomena of a coaxial jet in the non-dilute region using real-time X-ray radiography

NASA Astrophysics Data System (ADS)

Cheung, F. B.; Kuo, K. K.; Woodward, R. D.; Garner, K. N.

1990-07-01

An innovative approach to the investigation of liquid jet breakup processes in the near-injector region has been developed to overcome the experimental difficulties associated with optically opaque, dense sprays. Real-time X-ray radiography (RTR) has been employed to observe the inner structure and breakup phenomena of coaxial jets. In the atomizing regime, droplets much smaller than the exit diameter are formed beginning essentially at the injector exit. Through the use of RTR, the instantaneous contour of the liquid core was visualized. Experimental results consist of controlled-exposure digital video images of the liquid jet breakup process. Time-averaged video images have also been recorded for comparison. A digital image processing system is used to analyze the recorded images by creating radiance level distributions of the jet. A rudimentary method for deducing intact-liquid-core length has been suggested. The technique of real-time X-ray radiography has been shown to be a viable approach to the study of the breakup processes of high-speed liquid jets.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, K. A. P.; Nishida, K.; Shibata, K.

The recent discovery of chromospheric anemone jets with the Solar Optical Telescope (SOT) on board Hinode has shown an indirect evidence of magnetic reconnection in the solar chromosphere. However, the basic nature of magnetic reconnection in chromosphere is still unclear. We studied nine chromospheric anemone jets from SOT/Hinode using Ca II H filtergrams, and we found multiple bright, plasma ejections along the jets. In most cases, the major intensity enhancements (larger than 30% relative to the background intensity) of the loop correspond to the timing of the plasma ejections. The typical lifetime and size of the plasma ejecta are aboutmore » 20-60 s and 0.3-1.5 Mm, respectively. The height-time plot of jet shows many sub-structures (or individual jets) and the typical lifetime of the individual jet is about one to five minutes. Before the onset of the jet activity, a loop appears in Ca II H and gradually increases in size, and after few minutes several jets are launched from the loop. Once the jet activity starts and several individual jets are launched, the loop starts shrinking with a speed of {approx}4 km s{sup -1}. In some events, a downward moving blob with a speed of {approx}35 km s{sup -1} was observed, associated with the upward moving plasma along one of the legs of the loop hosting the jets. The upward moving plasma gradually developed into jets. Multiple plasma ejections in chromospheric anemone jet show the strongly time-dependent as well as intermittent nature of magnetic reconnection in the solar chromosphere.« less

The C IV doublet ratio intensity effect in symbiotic stars

NASA Technical Reports Server (NTRS)

Michalitsianos, A. G.; Fahey, M.; Kafatos, M.; Viotti, R.; Cassatella, A.

1988-01-01

High-resolution UV spectra in the 1200-2000 wavelength range of the symbiotic variable R Aqr and its nebular jet were obtained in July 1987 with the IUE. The line profile structure of the C IV 1548, 1550 doublet in the jet indicates multicomponent velocity structure from an optically thin emitting gas. The C IV doublet profiles in the compact H II region engulfing the Mira and hot companion binary also suggest multicomponent structure with radial velocities up to about -100 km/s. The value of the doublet intensity ratio in the R Aqr H II region has been observed in other similar symbiotic stars, such as RX Pup. It is suggested that the anomalous behavior of the C IV doublet intensities may be useful for studying the spatial structure and temporal nature of winds in symbiotic stars.

Bipolar Jets Launched by a Mean-field Accretion Disk Dynamo

NASA Astrophysics Data System (ADS)

Fendt, Christian; Gaßmann, Dennis

2018-03-01

By applying magnetohydrodynamic simulations, we investigate the launching of jets driven by a disk magnetic field generated by a mean-field disk dynamo. Extending our earlier studies, we explore the bipolar evolution of the disk α 2Ω-dynamo and the outflow. We confirm that a negative dynamo-α leads to a dipolar field geometry, whereas positive values generate quadrupolar fields. The latter remain mainly confined to the disk and cannot launch outflows. We investigate a parameter range for the dynamo-α ranging from a critical value below which field generation is negligible, {α }0,{crit}=-0.0005, to α 0 = ‑1.0. For weak | {α }0| ≤slant 0.07, two magnetic loop structures with opposite polarity may arise, which leads to reconnection and disturbs the field evolution and accretion-ejection process. For a strong dynamo-α, a higher poloidal magnetic energy is reached, roughly scaling with {E}mag}∼ | {α }0| , which also leads to higher accretion and ejection rates. The terminal jet speed is governed by the available magnetic energy and increases with the dynamo-α. We find jet velocities on the order of the inner disk Keplerian velocity. For a strong dynamo-α, oscillating dynamo modes may occur that can lead to a pulsed ejection. This is triggered by an oscillating mode in the toroidal field component. The oscillation period is comparable to the Keplerian timescale in the launching region, thus too short to be associated with the knots in observed jets. We find a hemispherically asymmetric evolution for the jet and counter-jet in the mass flux and field structure.

Tickling a high speed round jet

NASA Astrophysics Data System (ADS)

Arakeri, Vijay; Krothapalli, Anjaneyulu; Siddavaram, Vikram; Alkislar, Mehmet

2001-11-01

We have experimentally studied the effect of tickling a Mach 0.9 round jet with a set of microjets.Two dimensional velocity field measurements with PIV show a significant reduction in the turbulent intensities in the developing region of the jet with the activation of the microjets.Quantitatively,the axial and normal turbulence intensities are reduced by about 15respectively;even a larger effect is found on the magnitude of the correlation of axial and normal fluctuation intensities with a reduction of almost 40possible with a mass flow rate of the microjets being only about one percent of the main jet mass flow rate and hence justifying the use of the term `tickling`.The above findings are difficult to explain on the basis of stability considerations since there is very little change in the mean profile.Physically,the observed effect could be due to the alteration of the large eddy structures,which are so natural to a round jet,by the presence of the microjets.Exact nature of this interaction may be clarified with three dimensional PIV studies.It is expected that the tickling of the jet done as presently could have a favourable reflection in the aeroacoustics characteristics of the main jet.

Particle Acceleration, Magnetic Field Generation and Emission from Relativistic Jets and Supernova Remnants

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.; Hartmann, D. H.; Hardee, P.; Hededal, C.; Mizunno, Y.; Fishman, G. J.

2006-01-01

We performed numerical simulations of particle acceleration, magnetic field generation, and emission from shocks in order to understand the observed emission from relativistic jets and supernova remnants. The investigation involves the study of collisionless shocks, where the Weibel instability is responsible for particle acceleration as well as magnetic field generation. A 3-D relativistic particle-in-cell (RPIC) code has been used to investigate the shock processes in electron-positron plasmas. The evolution of theWeibe1 instability and its associated magnetic field generation and particle acceleration are studied with two different jet velocities (0 = 2,5 - slow, fast) corresponding to either outflows in supernova remnants or relativistic jets, such as those found in AGNs and microquasars. Slow jets have intrinsically different structures in both the generated magnetic fields and the accelerated particle spectrum. In particular, the jet head has a very weak magnetic field and the ambient electrons are strongly accelerated and dragged by the jet particles. The simulation results exhibit jitter radiation from inhomogeneous magnetic fields, generated by the Weibel instability, which has different spectral properties than standard synchrotron emission in a homogeneous magnetic field.

X-ray Properties and the Environment of Compact Radio Sources.

NASA Astrophysics Data System (ADS)

Siemiginowska, Aneta; Sobolewska, Malgorzata; Guainazzi, Matteo; Hardcastle, Martin; Migliori, Giulia; Ostorero, Luisa; Stawarz, Lukasz

2018-01-01

Compact extragalactic radio sources provide important insights into the initial stages of radio source evolution and probe states of a black hole activity at the time of the formation of the relativistic outflow. Such outflows propagate out to hundreds kpc distances from the origin and impact environment on many scales, and thus influence evolution of structures in the universe. These compact sources show radio features typically observed in large-scale radio galaxies (jets, lobes, hot spots), but contained within the central 1 kpc region of the host galaxy. Compact Symmetric Objects (CSOs, a subclass of GigaHertz Peaked spectrum radio sources) are symmetric and not affected by beaming. Their linear radio size can be translated into a source age if one measures the expansion velocity of the radio structures. Such ages has been measured for a small sample of CSOs. Using the Chandra X-ray Observatory and XMM-Newton we observed a pilot samples of 16 CSOs in X-rays (6 for the first time). Our results show heterogeneous nature of the CSOs X-ray emission indicating a range of AGN luminosities and a complex environment. In particular, we identified four Compton Thick sources with a dense medium (equivalent column > 1e24 cm^-2) capable of disturbing/slowing down the jet and confining the jet to a small region. Thus for the first time we gain the observational evidence in X-ray domain in favor of the hypothesis that in a sub-population of CSOs the radio jets may be confined by the dense X-ray obscuring medium. As a consequence, the kinematic ages of these CSOs may be underestimated.. We discuss the implications of our results on the emission models of CSOs, the earliest stages of the radio source evolution, jet interactions with the ISM, diversity of the environments in which the jets expand, and jet-galaxy co-evolution.Partial support for this work was provided by the NASA grants GO1-12145X, GO4-15099X, NNX10AO60G, NNX17AC23G and XMM AO15 project 78461. This work supported in part by NASA under contract NAS 8-03060 to the Smithsonian Astrophysical Observatory for operation of the Chandra X-ray Center.

Mid-Infrared Observational and Theoretical Studies of Star Formation and Early Solar Systems

NASA Technical Reports Server (NTRS)

Jones, Barbara

1997-01-01

The first 2 years of this program were used to make mid-IR observations of regions of star formation in the Orion nebula with the UCSD mid-IR camera at the UCSD/University of Minnesota telescope at Mt. Lemmon. These observations attempted to make the first systematic study of an extended region, known to have newly forming stars, and expected to have complex mid-IR emission. We discovered, to our surprise, that most of the thermal emission originated from extended sources rather than from point sources. This interesting observation made the analysis of the data much more complex, since the chop/nod procedures used at these wavelengths produce a differential measurement of the emission in one region compared to that in the adjacent region. Disentangling complex extended emission in such a situation is very difficult. In parallel with this work we were also observing comets in the thermal infrared, the other component of the original proposal. Some spectacular data on the comet Swift-Tuttle was acquired and published. A changing jet structure observed over a 2 week period is described. The rotation period of the comet can be measured at 66 hours. The size of the nucleus can also be estimated (at 30 km) from the observed excess flux from the nucleus. These data have lead to the development of models describing the action of dust particles of differing sizes and composition leaving the nucleus. The spatial distribution of the predicted IR emission has been compared to the observed jet structures, leading to estimates of both particles sizes, relative amounts of silicate vs organic grains, and the amounts of dust emitted in the jets vs isotopic emission.

Comparison of characteristics and downstream uniformity of linear-field and cross-field atmospheric pressure plasma jet array in He

NASA Astrophysics Data System (ADS)

Zhang, Bo; Fang, Zhi; Liu, Feng; Zhou, Renwu; Zhou, Ruoyu

2018-06-01

Using an atmospheric pressure plasma jet array is an effective way for expanding the treatment area of a single jet, and generating arrays with well downstream uniformity is of great interest for its applications. In this paper, a plasma jet array in helium is generated in a linear-field jet array with a ring-ring electrode structure excited by alternating current. The characteristics and downstream uniformity of the array and their dependence on the applied voltage and gas flow rate are investigated through optical, electrical, and Schlieren diagnostics. The results are compared with those of our reported work of a cross-field jet array with a needle-ring electrode structure. The results show that the linear-field jet array can generate relatively large-scale plasma with better uniformity and longer plumes than the cross-field case. The divergences observed in gas channels and the plasma plume trajectories are much less than those of the cross-field one. The deflection angle of lateral plumes is less than 6°, which is independent of the gas flow rate and applied voltage. The maximum downstream plumes of 23 mm can be obtained at 7 kV peak applied voltage and 4 l/min gas flow rate. The better uniformity of linear-field jet arrays is due to the effective suppression of hydrodynamic and electrical interactions among the jets in the arrays with a more uniform electric field distribution. The hydrodynamic interaction induced by the gas heating in the linear-field jet array is less than that of the cross-field one. The more uniform electric field distribution in the linear-field jet arrays can reduce the divergence of the propagation trajectories of the plasma plumes. It will generate less residual charge between the adjacent discharges and thus can reduce the accumulation effect of Coulomb force between the plasma plumes. The reported results can help design controllable and scalable plasma jet arrays with well uniformity for material surface and biomedical treatments.

The role and production of polar/subtropical jet superpositions in two high-impact weather events over North America

NASA Astrophysics Data System (ADS)

Winters, Andrew C.

Careful observational work has demonstrated that the tropopause is typically characterized by a three-step pole-to-equator structure, with each break between steps in the tropopause height associated with a jet stream. While the two jet streams, the polar and subtropical jets, typically occupy different latitude bands, their separation can occasionally vanish, resulting in a vertical superposition of the two jets. A cursory examination of a number of historical and recent high-impact weather events over North America and the North Atlantic indicates that superposed jets can be an important component of their evolution. Consequently, this dissertation examines two recent jet superposition cases, the 18--20 December 2009 Mid-Atlantic Blizzard and the 1--3 May 2010 Nashville Flood, in an effort (1) to determine the specific influence that a superposed jet can have on the development of a high-impact weather event and (2) to illuminate the processes that facilitated the production of a superposition in each case. An examination of these cases from a basic-state variable and PV inversion perspective demonstrates that elements of both the remote and local synoptic environment are important to consider while diagnosing the development of a jet superposition. Specifically, the process of jet superposition begins with the remote production of a cyclonic (anticyclonic) tropopause disturbance at high (low) latitudes. The cyclonic circulation typically originates at polar latitudes, while organized tropical convection can encourage the development of an anticyclonic circulation anomaly within the tropical upper-troposphere. The concurrent advection of both anomalies towards middle latitudes subsequently allows their individual circulations to laterally displace the location of the individual tropopause breaks. Once the two circulation anomalies position the polar and subtropical tropopause breaks in close proximity to one another, elements within the local environment, such as proximate convection or transverse vertical circulations, can work to further deform the tropopause and to aid in the production of the two-step tropopause structure characteristic of a superposed jet. The analysis also demonstrates that the intensified transverse vertical circulation that accompanies a superposed jet serves as the primary mechanism through which it can influence the evolution of a high-impact weather event.

On the structure of pulsed plasma jets

NASA Astrophysics Data System (ADS)

Cavolowsky, John Arthur

A pulsed plasma jet is a turbulent, inhomogeneous fluid mechanical discharge capable of initiating and inhancing combustion. Having shown the ability to ignite lean fuel mixtures, is now offers the potential for real-time control of combustion processes. The fluid mechanical and chemical properties of such jets are explored. The fluid mechanical structure of the jet was examined using two optical diagnostic techniques. Self-light streak photography provided information on the motion of luminous gas particles in its core. The turbulent, thermal evolution of the jet was explored using high speed laser schlieren cinematography. By examine plasma jet generators with both opaque and transparent plasma cavities, detailed information on plasma formation and jet structure, beginning with the electric arc discharge in the cavity, was obtained. Molecular beam mass spectroscopy was used to determine temperature and species concentration in the jet. Both noncombustible and combustible jets were studied. Species measurements in combustible jets revealed significant concentrations of radicals and products of complete as well as incomplete combustion.

Good News from Big Bad Black Holes: Jet-Induced Star Formation in ``Minkowski's Object"

NASA Astrophysics Data System (ADS)

van Breugel, W.; Croft, S.; de Vries, W.; van Gorkom, J. H.; Morganti, R.; Osterloo, T.; Dopita, M.

2004-12-01

We present VLA neutral hydrogen (HI) observations which show that ``Minkowski's Object", a peculiar starburst system, is due to the interaction of a low luminosity (FR-I type) radio jet with the intergalactic medium (IGM) in the cluster of galaxies A194. The transverse size and bimodal structure of the HI cloud, straddling the jet; its location downstream from the star forming region; and kinematic evidence for gas entrainment all are in agreement with previous numerical simulations (Fragile et al 2004) which concluded that FR-I type jets can trigger star formation by driving radiative shocks into the moderately dense, warm gas that is typical of central galaxy cluster regions. We compare the timescales for HI formation with the age of the starburst derived from recent Keck, Lick and HST spectroscopic and imaging data (see poster by Croft et al), which allows us to put constraints on the physical conditions in the radio jet (speed) and its ambient medium (density).

Anomalous transport in Charney-Hasegawa-Mima flows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Leoncini, Xavier; Agullo, Olivier; Benkadda, Sadruddin

2005-08-01

The transport properties of particles evolving in a system governed by the Charney-Hasegawa-Mima equation are investigated. Transport is found to be anomalous with a nonlinear evolution of the second moments with time. The origin of this anomaly is traced back to the presence of chaotic jets within the flow. All characteristic transport exponents have a similar value around {mu}=1.75, which is also the one found for simple point vortex flows in the literature, indicating some kind of universality. Moreover, the law {gamma}={mu}+1 linking the trapping-time exponent within jets to the transport exponent is confirmed, and an accumulation toward zero ofmore » the spectrum of the finite-time Lyapunov exponent is observed. The localization of a jet is performed, and its structure is analyzed. It is clearly shown that despite a regular coarse-grained picture of the jet, the motion within the jet appears as chaotic, but that chaos is bounded on successive small scales.« less

Recent progress on the understanding of the medium-induced jet evolution and energy loss in pQCD

NASA Astrophysics Data System (ADS)

Apolinário, Liliana

2017-03-01

Motivated by the striking modifications of jets observed both at RHIC and the LHC, significant progress towards the understanding of jet dynamics within QGP has occurred over the last few years. In this talk, I review the recent theoretical developments in the study of medium-induced jet evolution and energy loss within a perturbative framework. The main mechanisms of energy loss and broadening will be firstly addressed with focus on leading particle calculations beyond the eikonal approximation. Then, I will provide an overview of the modifications of the interference pattern between the different parton emitters that build up the parton shower when propagating through an extended coloured medium. I will show that the interplay between color coherence/decoherence that arises from such effects is the main mechanism for the modification of the jet core angular structure. Finally, I discuss the possibility of a probabilistic picture of the parton shower evolution in the limit of a very dense or infinite medium.

European VLBI network observations of fourteen GHz-peaked-spectrum radio sources at 5 GHz

NASA Astrophysics Data System (ADS)

Xiang, L.; Reynolds, C.; Strom, R. G.; Dallacasa, D.

2006-08-01

We present the results of EVN polarization observations of fourteen GHz-Peaked-Spectrum (GPS) radio sources at 5 GHz. These sources were selected from bright GPS source samples and we aimed at finding Compact Symmetric Objects (CSOs). We have obtained full polarization 5 GHz VLBI observations of 14 sources providing information on their source structure and spectral indices. The results show that two core-jet sources 1433-040 and DA193, out of 14 GPS sources, exhibit integrated fractional polarizations of 3.6% and 1.0% respectively. The other 12 sources have no clear detection of pc-scale polarization. The results confirm that the GPS sources generally have very low polarization at 5 GHz. The sources 1133+432, 1824+271 and 2121-014 are confirmed as CSOs. Three new CSOs 0914+114, 1518+046 and 2322-040 (tentative) have been classified on the basis of 5 GHz images and spectral indices. The sources 1333+589, 1751+278 and 2323+790 can be classified either as compact doubles, and then they are likely CSO candidates or core-jet sources; further observations are needed for an appropriate classification; 0554-026, 1433-040 and 1509+054 are core-jet sources. In addition, we estimate that a component in the jet of quasar DA193 has superluminal motion of 3.3±0.6 h-1 c in 5.5 years.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mizuta, Akira; Ioka, Kunihito

We investigate the jet propagation and breakout from the stellar progenitor for gamma-ray burst (GRB) collapsars by performing two-dimensional relativistic hydrodynamic simulations and analytical modeling. We find that the jet opening angle is given by θ{sub j} ∼ 1/5Γ{sub 0} and infer the initial Lorentz factor of the jet at the central engine, Γ{sub 0}, is a few for existing observations of θ{sub j}. The jet keeps the Lorentz factor low inside the star by converging cylindrically via collimation shocks under the cocoon pressure and accelerates at jet breakout before the free expansion to a hollow-cone structure. In this newmore » picture, the GRB duration is determined by the sound crossing time of the cocoon, after which the opening angle widens, reducing the apparent luminosity. Some bursts violating the maximum opening angle θ{sub j,{sub max}} ∼ 1/5 ∼ 12° imply the existence of a baryon-rich sheath or a long-acting jet. We can explain the slopes in both Amati and Yonetoku spectral relations using an off-centered photosphere model, if we make only one assumption that the total jet luminosity is proportional to the initial Lorentz factor of the jet. We also numerically calibrate the pre-breakout model (Bromberg et al.) for later use.« less

Cometary jets in interaction with the solar wind: a hybrid simulation study

NASA Astrophysics Data System (ADS)

Wiehle, Stefan; Motschmann, Uwe; Gortsas, Nikolaos; Mueller, Joachim; Kriegel, Hendrik; Koenders, Christoph; Glassmeier, Karl-Heinz

The effect of a cometary jet on the solar wind interaction is studied using comet 67P/Churyumov-Gerasimenko as case study. This comet is the target of the Rosetta-mission which will arrive in 2014. Observations suggest that cometary outgassing is confined to only a few percent of the cometary surface; thus, the measurement of jets is expected. Most former comet simulations did not attend to this fact and used an isotropic outgassing scheme or simplified outgassing patterns. Here, a single sun-facing jet is set to be the only source of cometary gas produc-tion. Using an analytic profile, this outgassing jet was implemented in a hybrid simulation code which treats protons and cometary heavy ions as particles and electrons as massless fluid. In a simulation series, the geometric parameters of the jet were varied to study the effect of different opening angles while the integrated outgassing rate remained constant. It was shown that the resulting solar wind interaction is highly dependent on the geometry of the jet. The plasma-structures like the solar wind pile-up found in the situation with isotropic outgassing are moved more and more sunward as the opening angle of the jet decreases. Furthermore, the cometary ion tail shows some kind of splitting which is not known from isotropic models.

Characteristics of Plasma Synthetic Jet Actuators in Crossflow

NASA Astrophysics Data System (ADS)

Santhanakrishnan, Arvind; Jacob, Jamey

2006-11-01

The plasma synthetic jet actuator (PSJA) consists of two annular electrodes separated by dielectric material that results in a circular region of dielectric barrier discharge plasma. In quiescent conditions, this plasma ring produces a synthetic jet which can be used for active flow control applications. Unsteady pulsing of the actuator results in the formation of multiple primary and secondary vortex rings, the latter remaining fixed or trapped in space. The jet is observed to be formed by the advection and interaction of the primary vortices, resembling a conventional synthetic jet. This presentation examines the operation of the PSJA in a crossflow at three different jet to freestream velocity ratios. PIV measurements in the streamwise and cross-stream planes are used to illustrate the three dimensionality of the jet and associated vortical structures. The strength of the vortex ring is found to vary along its circumference due to interaction with the freestream. The boundary layer characteristics obtained from these experiments suggest that the mechanism of the PSJA in crossflow is similar to an active boundary layer trip. Both the penetration of the jet and effectiveness of the trip action are found to decrease with increase in freestream velocity. The effects of unsteady pulsing and increasing input power on actuator created crossflow vortices will also be presented.

Functional characterization of steam jet-cooked buckwheat flour as a fat replacer in cake-baking.

PubMed

Min, Bockki; Lee, Seung Mi; Yoo, Sang-Ho; Inglett, George E; Lee, Suyong

2010-10-01

With rising consumer awareness of obesity, the food industry has a market-driven impetus to develop low-fat or fat-free foods with acceptable taste and texture. Fancy buckwheat flour was thus subjected to steam jet-cooking and the performance of the resulting product in cake-baking was evaluated as a fat replacer. Steam jet-cooking caused structural breakdown and starch gelatinization of buckwheat flour, thus increasing its water hydration properties. In the pasting measurements, steam jet-cooked buckwheat flour exhibited high initial viscosity, while no peak viscosity was observed. Also, the suspensions of steam jet-cooked buckwheat flour exhibited shear-thinning behaviors, which were well characterized by the power law model. When shortening in cakes was replaced with steam jet-cooked buckwheat gels, the specific gravity of cake batters significantly increased, consequently affecting cake volume after baking. However, shortening replacement with steam jet-cooked buckwheat up to 20% by weight appeared to be effective in producing cakes as soft as the control without volume loss. When buckwheat flour was thermomechanically modified by steam jet-cooking, it was successfully incorporated into cake formulations for shortening up to 20% by weight, producing low-fat cakes with comparable volume and textural properties to the control. Copyright © 2010 Society of Chemical Industry.

Jets Spout Far Closer to Black Hole Than Thought, Scientists Say

NASA Astrophysics Data System (ADS)

2004-01-01

Scientists at the Massachusetts Institute of Technology, taking advantage of multiple unique views of black hole particle jets over the course of a year with NASA's Chandra X-ray Observatory, have assembled a "picture" of the region that has revealed several key discoveries. They have found that the jets may be originating five times closer to the black hole than previously thought; they see in better detail how these jets change with time and distance from the black hole; and they could use this information as a new technique to measure black hole mass. Presented today in a press conference at the meeting of the American Astronomical Society in Atlanta, the observation will ultimately help solve the mystery of the great cosmic contradiction, in which black holes, notorious for pulling matter in, somehow manage to also shoot matter away in particle jets moving close to the speed of light. The observation is of a familiar source named SS 433 -- a binary star system within our Galaxy in the constellation Aquila, the Eagle, about 16,000 light years away. The black hole and its companion are about two-thirds closer to each other than the planet Mercury is to the Sun. The jets shoot off at 175 million miles per hour, 26 percent of light speed. "The high-speed jets in nearby SS 433 may be caused by the same mechanisms as the powerful outflows in the most distant and much more massive black holes, such as quasars," said Laura Lopez, an undergraduate student at MIT and lead author on a paper about the result. "SS 433 provides a nice local laboratory to study the formation of and conditions in relativistic jets." Dr. Herman Marshall, Ms. Lopez's research supervisor, led the investigation. Matter from the companion star pours into the black hole via a swirling accretion disk, much like water down a drain. Black hole particles jets are thought to be produced as some of the matter encounters strong magnetic fields close to the black hole. SS 433 is angled in such a way that one jet is shooting away from us while the other is aimed slightly towards us. The black hole's companion star enters the picture here as it periodically eclipses parts of the jets. Scientists use the eclipse, called an occultation, as a tool to block one part of the jet so that they can study other parts more easily. Using the Chandra High Energy Transmission Grating Spectrometer, the MIT group measured many characteristics of the jets, forming the best view of a jet's structure ever obtained. No image was created, as in other Chandra observations. Rather, the scientists pieced together the scene through spectroscopy, the fingerprint of chemical elements that reveals temperature and velocity of matter in the jets. They determined the length of the X-ray-emitting portion of the jet (over one million miles, about five times the distance from the Earth to the Moon); the temperature range (dropping from about 100 million degrees Celsius to 10 million degrees farther out); the chemical abundances (iron, silicon, and more); and the jet opening angle. In a previous observation they measured the jet's density. With this information, the team could determine that the jet base was five times closer to the black hole than previously observed, with a base diameter of about 1,280 miles. Also, from a bit of geometry along with information on the size of the binary system from optical observations by a team led by Douglas Gies of Georgia State University, the MIT group determined that the size of the companion star that blocked the view of the receding jet is about nine times the size of the Sun. From that, they estimated that the black hole is 16 solar masses. (For many years scientists have speculated whether SS 433 contains a black hole or a neutron star. Today's announcement of a 16-solar-mass object confirms that it is indeed a black hole, too massive to be a neutron star.) "The uniqueness of SS 433 cannot be overstated," said Marshall. "SS 433 provides an excellent opportunity to study the origin, evolution, and long-term behavior of jets because the X rays come from a region very close to the black hole. Of the hundreds of jets observed in the radio and X-ray bands, this is the only one for which we have a solid statement that it contains atomic nuclei and for which we are sure of the internal temperature and density." Supermassive black holes with jets, such as quasars, might display similar behavior, but they are so massive and so distant that changes cannot be observed because time scales are too long. Thus SS 433 serves as a laboratory to study the jet phenomenon "close to home," Marshall said. As such, further Chandra observations are planned. Collaborators on the investigation were Claude Canizares, Julie Kane, and Norbert Schulz, all of MIT. For images, refer to http://space.mit.edu/~hermanm/ss433.html.

Fluid dynamics of stellar jets in real time: Third Epoch Hubble Space Telescope images of HH 1, HH 34, AND HH 47

DOE PAGES

Hartigan, P.; Frank, A.; Foster, J. M.; ...

2011-07-01

We present new, third-epoch Hubble Space Telescope Hα and [S II] images of three Herbig-Haro (HH) jets (HH 1&2, HH 34, and HH 47) and compare the new images with those from previous epochs. The high spatial resolution, coupled with a time series whose cadence is of order both the hydrodynamic and radiative cooling timescales of the flow, allows us to follow the hydrodynamic/magnetohydrodynamic evolution of an astrophysical plasma system in which ionization and radiative cooling play significant roles. Cooling zones behind the shocks are resolved, so it is possible to identify which way material flows through a given shockmore » wave. The images show that heterogeneity is paramount in these jets, with clumps dominating the morphologies of both bow shocks and their Mach disks. This clumpiness exists on scales smaller than the jet widths and determines the behavior of many of the features in the jets. Evidence also exists for considerable shear as jets interact with their surrounding molecular clouds, and in several cases we observe shock waves as they form and fade where material emerges from the source and as it proceeds along the beam of the jet. Fine structure within two extended bow shocks may result from Mach stems that form at the intersection points of oblique shocks within these clumpy objects. Taken altogether, these observations represent the most significant foray thus far into the time domain for stellar jets, and comprise one of the richest data sets in existence for comparing the behavior of a complex astrophysical plasma flow with numerical simulations and laboratory experiments.« less

An Explanation for Saturn's Hexagon

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2015-08-01

For over three decades, weve been gathering observations of the mysterious hexagonal cloud pattern encircling Saturns north pole. Now, researchers believe they have a model that can better explain its formation.Fascinating GeometrySaturns northern Hexagon is a cloud band circling Saturns north pole at 78 N, first observed by the Voyager flybys in 198081. This remarkable pattern has now persisted for more than a Saturn year (29.5 Earth years).Eight frames demonstrating the motion within Saturns Hexagon. Click to watch the animation! The view is from a reference frame rotating with Saturn. [NASA/JPL-Caltech/SSI/Hampton University]Observations by Voyager and, more recently, Cassini have helped to identify many key characteristics of this bizarre structure. Two interesting things weve learned are:The Hexagon is associated with an eastward zonal jet moving at more than 200 mph.The cause of the Hexagon is believed to be a jet stream, similar to the ones that we experience on Earth. The path of the jet itself appears to follow the hexagons outline.The Hexagon rotates at roughly the same rate as Saturns overall rotation.While we observe individual storms and cloud patterns moving at different speeds within the Hexagon, the vertices of the Hexagon move at almost exactly the same rotational speed as that of Saturn itself.Attempts to model the formation of the Hexagon with a jet stream have yet to fully reproduce all of the observed features and behavior. But now, a team led by Ral Morales-Juberas of the New Mexico Institute of Mining and Technology believes they have created a model that better matches what we see.Simulating a Meandering JetThe team ran a series of simulations of an eastward, Gaussian-profile jet around Saturns pole. They introduced small perturbations to the jet and demonstrated that, as a result of the perturbations, the jet can meander into a hexagonal shape. With the initial conditions of the teams model, the meandering jet is able to settle into a stable hexagonal shape that rotates with very nearly the same period as Saturns rotational period.The formation of this hexagon depends on factors such as the initial amplitude and curvature of the jet. The models treatment of the wind profile within Saturns atmosphere is another key component that allowed them to match the observed characteristics of the Hexagon, such as its shape, vorticity behavior, temperature gradient, and seasonal stability.BonusThe gif below shows part of an animation the authors produced of the jet evolution in their model. You can see a hexagon begin to develop at around 230 days into the simulation, and by about 400 days it becomes stable and non-rotating (were looking at it from a reference frame rotating with Saturn). The full animation can be viewed here. [Morales-Juberas et al., 2015]CitationR. Morales-Juberas et al.2015 ApJ 806 L18 doi:10.1088/2041-8205/806/1/L18

Structure of hydrogen-rich transverse jets in a vitiated turbulent flow

DOE PAGES

Lyra, Sgouria; Wilde, Benjamin; Kolla, Hemanth; ...

2014-11-24

Our paper reports the results of a joint experimental and numerical study of the flow characteristics and flame structure of a hydrogen rich jet injected normal to a turbulent, vitiated crossflow of lean methane combustion products. Simultaneous high-speed stereoscopic PIV and OH PLIF measurements were obtained and analyzed alongside three-dimensional direct numerical simulations of inert and reacting JICF with detailed H2/COH2/CO chemistry. Both the experiment and the simulation reveal that, contrary to most previous studies of reacting JICF stabilized in low-to-moderate temperature air crossflow, the present conditions lead to a burner-attached flame that initiates uniformly around the burner edge. Significantmore » asymmetry is observed, however, between the reaction zones located on the windward and leeward sides of the jet, due to the substantially different scalar dissipation rates. The windward reaction zone is much thinner in the near field, while also exhibiting significantly higher local and global heat release than the much broader reaction zone found on the leeward side of the jet. The unsteady dynamics of the windward shear layer, which largely control the important jet/crossflow mixing processes in that region, are explored in order to elucidate the important flow stability implications arising in the inert and reacting JICF. The paper concludes with an analysis of the ignition, flame characteristics, and global structure of the burner-attached flame. FurthermoreChemical explosive mode analysis (CEMA) shows that the entire windward shear layer, and a large region on the leeward side of the jet, are highly explosive prior to ignition and are dominated by non-premixed flame structures after ignition. The predominantly mixing limited nature of the flow after ignition is examined by computing the Takeno flame index, which shows that ~70% of the heat release occurs in non-premixed regions.« less

Magnetic Braids in Eruptions of a Spiral Structure in the Solar Atmosphere

NASA Astrophysics Data System (ADS)

Huang, Zhenghua; Xia, Lidong; Nelson, Chris J.; Liu, Jiajia; Wiegelmann, Thomas; Tian, Hui; Klimchuk, James A.; Chen, Yao; Li, Bo

2018-02-01

We report on high-resolution imaging and spectral observations of eruptions of a spiral structure in the transition region, which were taken with the Interface Region Imaging Spectrograph, and the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). The eruption coincided with the appearance of two series of jets, with velocities comparable to the Alfvén speeds in their footpoints. Several pieces of evidence of magnetic braiding in the eruption are revealed, including localized bright knots, multiple well-separated jet threads, transition region explosive events, and the fact that all three of these are falling into the same locations within the eruptive structures. Through analysis of the extrapolated 3D magnetic field in the region, we found that the eruptive spiral structure corresponded well to locations of twisted magnetic flux tubes with varying curl values along their lengths. The eruption occurred where strong parallel currents, high squashing factors, and large twist numbers were obtained. The electron number density of the eruptive structure is found to be ∼3 × 1012 cm‑3, indicating that a significant amount of mass could be pumped into the corona by the jets. Following the eruption, the extrapolations revealed a set of seemingly relaxed loops, which were visible in the AIA 94 Å channel, indicating temperatures of around 6.3 MK. With these observations, we suggest that magnetic braiding could be part of the mechanisms explaining the formation of solar eruption and the mass and energy supplement to the corona.

Magnetosheath High-Speed Jets: Coupling Bow Shock Processes to the Magnetosphere

NASA Astrophysics Data System (ADS)

Hietala, H.

2016-12-01

Magnetosheath high-speed jets (HSJs) - dynamic pressure enhancements typically of 1 Earth radius in size - are the most common dayside transient. They impact the magnetopause many times per hour, especially during intervals of low interplanetary magnetic field cone-angle. Upon impact they cause large amplitude yet localized magnetopause indentations, and can couple to global dynamics by driving magnetospheric waves that alter radiation belt electron populations, and by affecting subsolar magnetopause reconnection. Previous observational studies have provided considerable insight into properties of the HSJs. Similarly, recent hybrid simulations have demonstrated the formation of jets downstream of the quasi-parallel shock with properties resembling the observed ones. Yet these studies were based on differing definitions of transients, have used varying terminology, methodology, data sets/simulations, and yielded, not unexpectedly, differing results on origin and characteristics of jets. In this talk we will present the first results towards a more unified understanding of these jets from a dedicated International Space Science Institute (ISSI) team. In particular, we compare the three selection criteria used in the recent observational statistical studies: (i) high dynamic pressure in the Sun-Earth direction with respect to the solar wind; (ii) enhancement of the total dynamic pressure with respect to the ambient magnetosheath plasma; (iii) enhancement of density with respect to the ambient plasma. We apply these criteria to global kinetic simulations and compare what structures they pick out. Consequently, we can effectively demonstrate where the different criteria agree and where they disagree.

On the Two Components of Turbulent Mixing Noise from Supersonic Jets

NASA Technical Reports Server (NTRS)

Tam, Christopher K. W.; Golebiowski, Michel; Seiner, J. M.

1996-01-01

It is argued that because of the lack of intrinsic length and time scales in the core part of the jet flow, the radiated noise spectrum of a high-speed jet should exhibit similarity. A careful analysis of all the axisymmetric supersonic jet noise spectra in the data-bank of the Jet Noise Laboratory of the NASA Langley Research Center has been carried out. Two similarity spectra, one for the noise from the large turbulence structures/instability waves of the jet flow, the other for the noise from the fine-scale turbulence, are identified. The two similarity spectra appear to be universal spectra for axisymmetric jets. They fit all the measured data including those from subsonic jets. Experimental evidence are presented showing that regardless of whether a jet is supersonic or subsonic the noise characteristics and generation mechanisms are the same. There is large turbulence structures/instability waves noise from subsonic jets. This noise component can be seen prominently inside the cone of silence of the fine-scale turbulence noise near the jet axis. For imperfectly expanded supersonic jets, a shock cell structure is formed inside the jet plume. Measured spectra are provided to demonstrate that the presence of a shock cell structure has little effect on the radiated turbulent mixing noise. The shape of the noise spectrum as well as the noise intensity remain practically the same as those of a fully expanded jet. However, for jets undergoing strong screeching, there is broadband noise amplification for both turbulent mixing noise components. It is discovered through a pilot study of the noise spectrum of rectangular and elliptic supersonic jets that the turbulent mixing noise of these jets is also made up of the same two noise components found in axisymmetric jets. The spectrum of each individual noise component also fits the corresponding similarity spectrum of axisymmetric jets.

Reprint of: Reaction measurements with the Jet Experiments in Nuclear Structure and Astrophysics (JENSA) gas jet target

NASA Astrophysics Data System (ADS)

Chipps, K. A.

2018-01-01

Explosive stellar environments are sometimes driven by nuclear reactions on short-lived, radioactive nuclei. These reactions often drive the stellar explosion, alter the observable light curves produced, and dictate the final abundances of the isotopes created. Unfortunately, many reaction rates at stellar temperatures cannot be directly measured in the laboratory, due to the physical limitations of ultra-low cross sections and high background rates. An additional complication arises because many of the important reactions involve radioactive nuclei which have lifetimes too short to be made into a target. As such, direct reactions require very intense and pure beams of exotic nuclei. Indirect approaches with both stable and radioactive beams can, however, provide crucial information on the nuclei involved in these astrophysical reactions. A major development toward both direct and indirect studies of nuclear reactions rates is the commissioning of the Jet Experiments in Nuclear Structure and Astrophysics (JENSA) supersonic gas jet target. The JENSA system provides a pure, homogeneous, highly localized, dense, and robust gaseous target for radioactive ion beam studies. Charged-particle reactions measurements made with gas jet targets can be cleaner and display better resolution than with traditional targets. With the availability of pure and localized gas jet targets in combination with developments in exotic radioactive ion beams and next-generation detector systems, the range of reaction studies that are experimentally possible is vastly expanded. Various representative cases will be discussed.

Particle Acceleration and Magnetic Field Generation in Electron-Positron Relativistic Shocks

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.; Hardee, P.; Richardson, G.; Preece, R.; Sol, H.; Fishman, G. J.

2004-01-01

Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman, Weibel and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic electron-positron jet front propagating into an ambient electron-positron plasma with and without initial magnetic fields. We find small differences in the results for no ambient and modest ambient magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. The non-linear fluctuation amplitudes of densities, currents, electric, and magnetic fields in the electron-positron shock are larger than those found in the electron-ion shock studied in a previous paper. This comes from the fact that both electrons and positrons contribute to generation of the Weibel instability. Additionally, we have performed simulations with different electron skin depths. We find that growth times scale inversely with the plasma frequency, and the sizes of structures created by the Weibel instability scale proportional to the electron skin depth. This is the expected result and indicates that the simulations have sufficient grid resolution. While some Fermi acceleration may occur at the jet front, the majority of electron and positron acceleration takes place behind the jet front and cannot be characterized as Fermi acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying nonuniform, small-scale magnetic fields which contribute to the electron's (positron's) transverse deflection behind the jet head. This small scale magnetic field structure is appropriate to the generation of "jitter" radiation from deflected electrons (positrons) as opposed to synchrotron radiation. The jitter radiation has different properties than synchrotron radiation calculated assuming a a uniform magnetic field. The jitter radiation resulting from small scale magnetic field structures may be important for understanding the complex time structure and spectral evolution observed in gamma-ray bursts or other astrophysical sources containing relativistic jets and relativistic collisionless shocks.

Particle Acceleration and Magnetic Field Generation in Electron-Positron Relativistic Shocks

NASA Technical Reports Server (NTRS)

Nishikawa, K.-L.; Hardee, P.; Richardson, G.; Preece, R.; Sol, H.; Fishman, G. J.

2004-01-01

Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman, Weibel and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic electron-positron jet front propagating into an ambient electron-positron plasma with and without initial magnetic fields. We find small differences in the results for no ambient and modest ambient magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. The non-linear fluctuation amplitudes of densities, currents, electric, and magnetic fields in the electron-positron shock are larger than those found in the electron-ion shock studied in a previous paper at the comparable simulation time. This comes from the fact that both electrons and positrons contribute to generation of the Weibel instability. Additionally, we have performed simulations with different electron skin depths. We find that growth times scale inversely with the plasma frequency, and the sizes of structures created by the Weibel instability scale proportional to the electron skin depth. This is the expected result and indicates that the simulations have sufficient grid resolution. While some Fermi acceleration may occur at the jet front, the majority of electron and positron acceleration takes place behind the jet front and cannot be characterized as Fermi acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying nonuniform: small-scale magnetic fields which contribute to the electron's (positron's) transverse deflection behind the jet head. This small scale magnetic field structure is appropriate to the generation of jitter radiation from deflected electrons (positrons) as opposed to synchrotron radiation. The jitter radiation has different properties than synchrotron radiation calculated assuming a a uniform magnetic field. The jitter radiation resulting from small scale magnetic field structures may be important for understanding the complex time structure and spectral evolution observed in gamma-ray bursts or other astrophysical sources containing relativistic jets and relativistic collisionless shocks.

Particle Acceleration and Magnetic Field Generation in Electron-Positron Relativistic Shocks

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.; Hardee, P.; Richardson, G.; Preece, R.; Sol, H.; Fishman, G. J.

2005-01-01

Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman, Weibel, and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a three-dimensional relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic electron-positron jet front propagating into an ambient electron-positron plasma with and without initial magnetic fields. We find small differences in the results for no ambient and modest ambient magnetic fields. New simulations show that the Weibel instability created in the collisionless shock front accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. Furthermore, the nonlinear fluctuation amplitudes of densities, currents, and electric and magnetic fields in the electron-positron shock are larger than those found in the electron-ion shock studied in a previous paper at a comparable simulation time. This comes from the fact that both electrons and positrons contribute to generation of the Weibel instability. In addition, we have performed simulations with different electron skin depths. We find that growth times scale inversely with the plasma frequency, and the sizes of structures created by tine Weibel instability scale proportionally to the electron skin depth. This is the expected result and indicates that the simulations have sufficient grid resolution. While some Fermi acceleration may occur at the jet front, the majority of electron and positron acceleration takes place behind the jet front and cannot be characterized as Fermi acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying nonuniform, small-scale magnetic fields, which contribute to the electron s (positron s) transverse deflection behind the jet head. This small- scale magnetic field structure is appropriate to the generation of "jitter" radiation from deflected electrons (positrons) as opposed to synchrotron radiation. The jitter radiation has different properties than synchrotron radiation calculated assuming a uniform magnetic field. The jitter radiation resulting from small-scale magnetic field structures may be important for understanding the complex time structure and spectral evolution observed in gamma-ray bursts or other astrophysical sources containing relativistic jets and relativistic collisionless shocks.

Response Sensitivity of Typical Aircraft Jet Engine Fan Blade-Like Structures to Bird Impacts.

DTIC Science & Technology

1982-05-01

AIRCRAFT ENGINE BU--ETC F/G 21/5 RESPONSE SENSITIVITY OF TYPICAL AIRCRAFT JET ENGINE FAN BLADE -L...SENSITIVITY OF TYPICAL AIRCRAFT JET ENGINE FAN BLADE -LIKE STRUCTURES TO BIRD IMPACTS David P. Bauer Robert S. Bertke University of Dayton Research...COVERED RESPONSE SENSITIVITY OF TYPICAL AIRCRAFT FINAL REPORT JET ENGINE FAN BLADE -LIKE STRUCTURES Oct. 1977 to Jan. 1979 TO BIRD IMPACTS s.

The Reel Deal In 3D: The Spatio-Temporal Evolution of YSO Jets

NASA Astrophysics Data System (ADS)

Frank, Adam

2014-10-01

Jets are a ubiquitous phenomena in astrophysics, though in most cases their central engines are unresolvable. Thus the structure of the jets often acts as a proxy for understanding the objects creating them. Jets are also of interest in their own right, serving as critical examples of rapidly evolving astrophysical magnetized plasma systems. And while millions of CPU hours {at least} have been spent simulating the kinds of astrophysical plasma dynamics that occur routinely in jets, we rarely have had the chance to study their real-time evolution. In this proposal we seek to use a unique multi-epoch HST dataset of protostellar jets to carry forward an innovative theoretical, numerical and laboratory-based study of magnetized outflows and the plasma processes which determine their evolution. Our work will make direct and detailed contact with these HST data sets and will articulate newly-observed features of jet dynamics that have not been possible to explore before. Using numerical simulations and laboratory plasma studies we seek to articulate the full 3-D nature of new behaviors seen in the HST data. Our collaboration includes the use of scaled laboratory plasma experiments with hypersonic magnetized radiative jets. The MHD experiments have explored how jets break up into clumps via kink-mode instabilities. Therefore such experiments are directly relevant to the initial conditions in our models.

Measurements of jet-related observables at the LHC

NASA Astrophysics Data System (ADS)

Kokkas, P.

2015-11-01

During the first years of the LHC operation a large amount of jet data was recorded by the ATLAS and CMS experiments. In this review several measurements of jet-related observables are presented, such as multi-jet rates and cross sections, ratios of jet cross sections, jet shapes and event shape observables. All results presented here are based on jet data collected at a centre-of-mass energy of 7 TeV. Data are compared to various Monte Carlo generators, as well as to theoretical next-to-leading-order calculations allowing a test of perturbative Quantum Chromodynamics in a previously unexplored energy region.

Eruptions from the Sun

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2015-11-01

The Sun often exhibits outbursts, launching material from its surface in powerful releases of energy. Recent analysis of such an outburst captured on video by several Sun-monitoring spacecraft may help us understand the mechanisms that launch these eruptions.Many OutburstsSolar jets are elongated, transient structures that are thought to regularly release magnetic energy from the Sun, contributing to coronal heating and solar wind acceleration. Coronal mass ejections (CMEs), on the other hand, are enormous blob-like explosions, violently ejecting energy and mass from the Sun at incredible speeds.But could these two types of events actually be related? According to a team of scientists at the University of Science and Technology of China, they may well be. The team, led by Jiajia Liu, has analyzed observations of a coronal jet that they believe prompted the launch of a powerful CME.Observing an ExplosionGif of a movie of the CME, taken by the Solar Dynamics Observatorys Atmospheric Imaging Assembly at a wavelength of 304. The original movie can be found in the article. [Liu et al.]An army of spacecraft was on hand to witness the event on 15 Jan 2013 including the Solar Dynamics Observatory (SDO), the Solar and Heliospheric Observatory (SOHO), and the Solar Terrestrial Relations Observatory (STEREO). The instruments on board these observatories captured the drama on the northern limb of the Sun as, at 19:32 UT, a coronal jet formed. Just eight minutes later, a powerful CME was released from the same active region.The fact that the jet and CME occurred in the same place at roughly the same time suggests theyre related. But did the initial motions of the CME blob trigger the jet? Or did the jet trigger the CME?Tying It All TogetherIn a recently published study, Liu and collaborators analyzed the multi-wavelength observations of this event to find the heights and positions of the jet and CME. From this analysis, they determined that the coronal jet triggered the release of material to form the CME, which then erupted into space with the jet at its core at speeds of over 1000 km/s.Based on observed clues of the magnetic field configurations, the team has put together a theory for how this event unfolded. They believe that sudden magnetic reconnection in an active region accelerated plasma to form a large-scale coronal jet. This burst of energy also provided a push on a blob of gas, threaded with magnetic field lines, that lay above the jet. The blob then rose, and when the field lines broke, it was released as a CME with the jet at its core.CitationJiajia Liu et al 2015 ApJ 813 115. doi:10.1088/0004-637X/813/2/115

Microwave spectroscopy and curious molecular dynamics of ethyl trifluoroacetate

NASA Astrophysics Data System (ADS)

Bohn, Robert K.; Montgomery, John A.; Harvey Michels, H.; Acharte, Christian

2017-05-01

The first ethyl ester whose structure was determined by microwave spectroscopy is ethyl formate. It exists in two conformations. In the 1970s, that study was used as a model to determine the structures of other ethyl esters, ethyl cyanoformate, chloroformate, and trifluoroacetate. They display the same conformations as ethyl formate. But under the experimental conditions used, Stark modulation with a maximum electric field, static low pressure gas, rapid sweeping, and long detector time constants, each of those esters displays bands of an additional third species. A careful, high resolution study of ethyl cyanoformate only observed two conformers. A model has been proposed that the third species derives from a dense array of torsionally excited states with broadened transitions due to short lifetimes. The present study of ethyl trifluoroacetate in a pulsed jet Fourier Transform spectrometer is intended to clarify the earlier results. Two conformers are observed including all their monosubstituted 13C and 18O isotopologs. In a pulsed jet Fourier Transform spectrometer using argon as the carrier gas, only one conformer is observed. Switching to helium as the carrier gas, another, higher energy conformer is also observed.

Swirl effect on flow structure and mixing in a turbulent jet

NASA Astrophysics Data System (ADS)

Kravtsov, Z. D.; Sharaborin, D. K.; Dulin, V. M.

2018-03-01

The paper reports on experimental study of turbulent transport in the initial region of swirling turbulent jets. The particle image velocimetry and planar laser-induced fluorescence techniques are used to investigate the flow structure and passive scalar concentration, respectively, in free air jet with acetone vapor. Three flow cases are considered, viz., non-swirling jets and swirling jets with and without vortex breakdown and central recirculation zone. Without vortex breakdown, the swirl is shown to promote jet mixing with surrounding air and to decrease the jet core length. The vortex core breakdown further enhances mixing as the jet core disintegrates at the nozzle exit.

Jet creation in post-AGB binaries: the circum-companion accretion disk around BD+46°442

NASA Astrophysics Data System (ADS)

Bollen, Dylan; Van Winckel, Hans; Kamath, Devika

2017-11-01

Aims: We aim at describing and understanding binary interaction processes in systems with very evolved companions. Here, we focus on understanding the origin and determining the properties of the high-velocity outflow observed in one such system. Methods: We present a quantitative analysis of BD+46°442, a post-AGB binary that shows active mass transfer that leads to the creation of a disk-driven outflow or jet. We obtained high-resolution optical spectra from the HERMES spectrograph, mounted on the 1.2 m Flemish Mercator Telescope. By performing a time-series analysis of the Hα profile, we identified the different components of the system. We deduced the jet geometry by comparing the orbital phased data with our jet model. In order to image the accretion disk around the companion of BD+46°442, we applied the technique of Doppler tomography. Results: The orbital phase-dependent variations in the Hα profile can be related to an accretion disk around the companion, from which a high-velocity outflow or jet is launched. Our model shows that there is a clear correlation between the inclination angle and the jet opening angle. The latitudinally dependent velocity structure of our jet model shows a good correspondence to the data, with outflow velocities higher than at least 400 km s-1. The intensity peak in the Doppler map might be partly caused by a hot spot in the disk, or by a larger asymmetrical structure in the disk. Conclusions: We show that BD+46°442 is a result of a binary interaction channel. The origin of the fast outflow in this system might be to a gaseous disk around the secondary component, which is most likely a main-sequence star. Our analysis suggests that the outflow has a rather wide opening angle and is not strongly collimated. Our time-resolved spectral monitoring reveals the launching site of the jet in the binary BD+46°442. Similar orbital phase-dependent Hα profiles are commonly observed in post-AGB binaries. Post-AGB binaries provide ideal test beds to study jet formation and launching mechanisms over a wide range of orbital conditions. Based on observations made with the Mercator Telescope, operated on the island of La Palma by the Flemmish Community, at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.The reduced spectra (FITS files) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/607/A60

Evidence of 3-D Reconnection at Null Point from the Observations of Circular Flares and Homologous Jets

NASA Astrophysics Data System (ADS)

Wang, Haimin; Liu, C.

2012-05-01

In recent studies by Pariat, Antiochos and DeVore (2009, 2010), fan-separatrix topology and magnetic reconnection at the null-point were simulated and found to produce homologous jets. This motivates us to search for axisymmetric magnetic structure and associated flaring/jetting activity. Using high-resolution ( 0.15" per pixel) and high-cadence ( 15 s) H-alpha center/offband observations obtained from the recently digitized films of Big Bear Solar Observatory, we were able to identify five large circular flares with associated surges. All the events exhibit a central parasite magnetic field surrounded by opposite polarity, forming a circular polarity inversion line (PIL). Consequently, a compact flare kernel at the center is surrounded by a circular ribbon, and together with the upward ejecting dark surge, these seem to depict a dome-like magnetic structure. Very interestingly, (1) the circular ribbon brightens sequentially rather than simultaneously, (2) the central compact flare kernel shows obvious motion, and (3) a remote elongated, co-temporal flare ribbon at a region with the same polarity as the central parasite site is seen in the series of four homologous events on 1991 March 17 and 18. The remote ribbon is 120" away from the jet location. Moreover, magnetic reconnection across the circular PIL is evident from the magnetic flux cancellation. These rarely observed homologous surges with circular as well as central and remote flare ribbons provide valuable evidence concerning the dynamics of magnetic reconnection in a null-point topology. This study is dedicated to Professor Hal Zirin, the founder of Big Bear Solar Observatory, who passed away on January 3, 2012.

Active Control of High-Speed Free Jets Using High-Frequency Excitation

NASA Astrophysics Data System (ADS)

Upadhyay, Puja

Control of aerodynamic noise generated by high-performance jet engines continues to remain a serious problem for the aviation community. Intense low frequency noise produced by large-scale coherent structures is known to dominate acoustic radiation in the aft angles. A tremendous amount of research effort has been dedicated towards the investigation of many passive and active flow control strategies to attenuate jet noise, while keeping performance penalties to a minimum. Unsteady excitation, an active control technique, seeks to modify acoustic sources in the jet by leveraging the naturally-occurring flow instabilities in the shear layer. While excitation at a lower range of frequencies that scale with the dynamics of large-scale structures, has been attempted by a number of studies, effects at higher excitation frequencies remain severely unexplored. One of the major limitations stems from the lack of appropriate flow control devices that have sufficient dynamic response and/or control authority to be useful in turbulent flows, especially at higher speeds. To this end, the current study seeks to fulfill two main objectives. First, the design and characterization of two high-frequency fluidic actuators (25 and 60 kHz) are undertaken, where the target frequencies are guided by the dynamics of high-speed free jets. Second, the influence of high-frequency forcing on the aeroacoustics of high-speed jets is explored in some detail by implementing the nominally 25 kHz actuator on a Mach 0.9 (Re D = 5 x 105) free jet flow field. Subsequently, these findings are directly compared to the results of steady microjet injection experiments performed in the same rig and to prior jet noise control studies, where available. Finally, limited acoustic measurements were also performed by implementing the nominally 25 kHz actuators on jets at higher Mach numbers, including shock containing jets, and elevated temperatures. Using lumped element modeling as an initial guide, the current work expands on the previous development of low-frequency (2-8 kHz) Resonance Enhanced Micro-actuators (REM) to design actuators that are capable of producing high amplitude pulses at much higher frequencies. Extensive benchtop characterization, using acoustic measurements as well as optical diagnostics using a high resolution micro-schlieren setup, is employed to characterize the flow properties and dynamic response of these actuators. The actuators produced high-amplitude output a range of frequencies, 20.3-27.8 kHz and 54.8-78.2 kHz, respectively. In addition to providing information on the actuator flow physics and performances at various operating conditions, the benchtop study serves to develop relatively easy-to-integrate, high-frequency actuators for active control of high-speed jets for noise reduction. Following actuator characterization studies, the nominally 25 kHz ( StDF ≈ 2.2) actuators are implemented on a Mach 0.9 free jet flow field. Eight actuators are azimuthally distributed at the nozzle exit to excite the initial shear layer at frequencies that are approximately an order of magnitude higher compared to the jet preferred frequency, StP ≈ 0.2-0.3. The influence of control on the mean and turbulent characteristics of the jet, especially the developing shear layer, is examined in great detail using planar and stereoscopic Particle Image Velocimetry (PIV). Examination of cross-stream velocity profiles revealed that actuation leads to strong, spatially coherent streamwise vortex pairs which in turn significantly modify the mean flow field, resulting in a prominently undulated shear layer. These vortices grow as they convect downstream, enhancing local entrainment and significantly thickening the initial shear layer. Azimuthal inhomogeneity introduced in the jet shear layer is also evident in the simultaneous redistribution and reduction of peak turbulent fluctuations in the cross-plane near the nozzle exit. Further downstream, control results in a global suppression of turbulence intensities for all axial locations, also evidenced by a longer potential core and overall reduced jet spreading. The resulting impact on the noise signature is estimated via far-field acoustic measurements. Noise reduction was observed at low to moderate frequencies for all observation angles. Direct comparison of these results with that of steady microjet injection revealed some notable differences in the initial development of streamwise vorticity and the redistribution of peak turbulence in the azimuthal direction. However, despite significant differences in the near nozzle aerodynamics, the downstream evolution of the jet appeared to approach near similar conditions with both high-frequency and steady microjet injection. Moreover, the impact on far-field noise was also comparable between the two injection methods as well as with others reported in the literature. Finally, for jets at higher Mach numbers and elevated temperatures, the effect of control was observed to vary with jet conditions. While the impact of the two control mechanisms were fairly comparable on non-shock containing jets, high-frequency forcing was observed to produce significantly larger reductions in screech and broadband shock-associated noise (BBSN) at select under-expanded jet conditions. The observed variations in control effects at different jet conditions call for further investigation.

Experimental investigation of the noise reduction of supersonic exhaust jets with fluidic inserts

NASA Astrophysics Data System (ADS)

Powers, Russell William Walter

The noise produced by the supersonic, high temperature jets that exhaust from military aircraft is becoming a hazard to naval personnel and a disturbance to communities near military bases. Methods to reduce the noise produced from these jets in a practical full-scale environment are difficult. The development and analysis of distributed nozzle blowing for the reduction of radiated noise from supersonic jets is described. Model scale experiments of jets that simulate the exhaust jets from typical low-bypass ratio military jet aircraft engines during takeoff are performed. Fluidic inserts are created that use distributed blowing in the divergent section of the nozzle to simulate mechanical, hardwall corrugations, while having the advantage of being an active control method. This research focuses on model scale experiments to better understand the fluidic insert noise reduction method. Distributed blowing within the divergent section of the military-style convergent divergent nozzle alters the shock structure of the jet in addition to creating streamwise vorticity for the reduction of mixing noise. Enhancements to the fluidic insert design have been performed along with experiments over a large number of injection parameters and core jet conditions. Primarily military-style round nozzles have been used, with preliminary measurements of hardwall corrugations and fluidic inserts in rectangular nozzle geometries also performed. It has been shown that the noise reduction of the fluidic inserts is most heavily dependent upon the momentum flux ratio between the injector and core jet. Maximum reductions of approximately 5.5 dB OASPL have been observed with practical mass flow rates and injection pressures. The first measurements with fluidic inserts in the presence of a forward flight stream have been performed. Optimal noise reduction occurs at similar injector parameters in the presence of forward flight. Fluidic inserts in the presence of a forward flight stream were observed to reduce the peak mixing noise below the already reduced levels by nearly 4 dB OASP and the broadband shock-associated noise by nearly 3 dB OASP. Unsteady velocity measurements are used to complement acoustic results of jets with fluidic inserts. Measured axial turbulence intensities and mean axial velocity are examined to illuminate the differences in the flow field from jets with fluidic inserts. Comparisons of laser Doppler measurements with RANS CFD simulations are shown with good agreement. Analysis of the effect of spatial turbulence on the measured quantities is performed. Experimental model scale measurements of jets with and without fluidic inserts over a simulated carrier deck are presented. The model carrier environment consists of a ground plane of adjustable distance below the jet, and a simulated jet blast deflector similar to those found in practice. Measurements are performed with far-field microphones, near-field microphones, and unsteady pressure sensors. The constructive and destructive interference that results from the interaction of the direct and reflected sound waves is observed and compared with results from free jets. The noise reduction of fluidic inserts in a realistic carrier deck environment with steering of the "quiet planes" is examined. The overall sound pressure level in heat-simulated jets is reduced by 3-5 dB depending on the specific angle and ground plane height. Jets impinging upon a modeled jet blast deflector are tested in addition to jets solely in the presence of the carrier deck. Observed modifications to the acoustic field from the presence of the jet blast deflector include downstream acoustic shielding and low frequency augmentation. The region of maximum noise radiation for heat-simulated jets from nozzles with fluidic inserts impinging on the jet blast deflector is reduced in overall sound pressure level by 4-7 dB. This region includes areas where aircraft carrier personnel are located. iv.

CORONAL JETS SIMULATED WITH THE GLOBAL ALFVÉN WAVE SOLAR MODEL

DOE Office of Scientific and Technical Information (OSTI.GOV)

Szente, J.; Toth, G.; Manchester IV, W. B.

This paper describes a numerical modeling study of coronal jets to understand their effects on the global corona and their contribution to the solar wind. We implement jets into a well-established three-dimensional, two-temperature magnetohydrodynamic (MHD) solar corona model employing Alfvén-wave dissipation to produce a realistic solar-wind background. The jets are produced by positioning a compact magnetic dipole under the solar surface and rotating the boundary plasma around the dipole's magnetic axis. The moving plasma drags the magnetic field lines along with it, ultimately leading to a reconnection-driven jet similar to that described by Pariat et al. We compare line-of-sight syntheticmore » images to multiple jet observations at EUV and X-ray bands, and find very close matches in terms of physical structure, dynamics, and emission. Key contributors to this agreement are the greatly enhanced plasma density and temperature in our jets compared to previous models. These enhancements arise from the comprehensive thermodynamic model that we use and, also, our inclusion of a dense chromosphere at the base of our jet-generating regions. We further find that the large-scale corona is affected significantly by the outwardly propagating torsional Alfvén waves generated by our polar jet, across 40° in latitude and out to 24 R {sub ⊙}. We estimate that polar jets contribute only a few percent to the steady-state solar-wind energy outflow.« less

Stretched Inertial Jets

NASA Astrophysics Data System (ADS)

Ghabache, Elisabeth; Antkowiak, Arnaud; Seon, Thomas; Villermaux, Emmanuel

2015-11-01

Liquid jets often arise as short-lived bursting liquid flows. Cavitation or impact-driven jets, bursting champagne bubbles, shaped-charge jets, ballistospores or drop-on-demand inkjet printing are a few examples where liquid jets are suddenly released. The trademark of all these discharge jets is the property of being stretched, due to the quenching injection. the present theoretical and experimental investigation, the structure of the jet flow field will be unraveled experimentally for a few emblematic occurrences of discharge jets. Though the injection markedly depends on each flow configuration, the jet velocity field will be shown to be systematically and rapidly attracted to the universal stretching flow z/t. The emergence of this inertial attractor actually only relies on simple kinematic ingredients, and as such is fairly generic. The universality of the jet velocity structure will be discussed.

Evidence for Alfvén Waves in Source Flares of Impulsive Solar Energetic Particle Events

NASA Astrophysics Data System (ADS)

Bucik, R.; Innes, D.; Mason, G. M.; Wiedenbeck, M. E.; Gomez-Herrero, R.; Nitta, N.

2017-12-01

Impulsive solar energetic particle events, characterised by a peculiar elemental composition with the rare elements like 3He and ultra-heavy ions enhanced by factors up to ten thousand above their thermal abundance, have been puzzling for almost 50 years. The solar sources of these events have been commonly associated with coronal jets, believed to be a signature of magnetic reconnection involving field lines open to interplanetary space. Here we present some of the most intense events, highly enriched in both 3He and heavier ions. The corresponding high-resolution, extreme-ultraviolet imaging observations have revealed for the first time a helical structure in the source flare with a jet-like shape. A mini-filament at the base of the jet appears to trigger these events. The events were observed with the two Solar Terrestrial Relations Observatories on the backside of the Sun, during the period of increased solar activity in 2014. During the last decade, it has been established that the helical motions in coronal jets represent propagating Alfvén waves. Revealing such magnetic-untwisting waves in the solar sources of highly enriched events in this study is consistent with a stochastic acceleration mechanism. An examination of jets in previously reported impulsive solar energetic particle events indicates that they tend to be large-scale blowout jets, sometimes cleanly showing a twisted configuration.The work of R. Bucik is supported by the Deutsche Forschungsgemeinschaft grant BU 3115/2-1.

ON THE OBSERVATION AND SIMULATION OF SOLAR CORONAL TWIN JETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Jiajia; Wang, Yuming; Zhang, Quanhao

We present the first observation, analysis, and modeling of solar coronal twin jets, which occurred after a preceding jet. Detailed analysis on the kinetics of the preceding jet reveals its blowout-jet nature, which resembles the one studied in Liu et al. However, the erupting process and kinetics of the twin jets appear to be different from the preceding one. Lacking detailed information on the magnetic fields in the twin jet region, we instead use a numerical simulation using a three-dimensional (3D) MHD model as described in Fang et al., and find that in the simulation a pair of twin jetsmore » form due to reconnection between the ambient open fields and a highly twisted sigmoidal magnetic flux, which is the outcome of the further evolution of the magnetic fields following the preceding blowout jet. Based on the similarity between the synthesized and observed emission, we propose this mechanism as a possible explanation for the observed twin jets. Combining our observation and simulation, we suggest that with continuous energy transport from the subsurface convection zone into the corona, solar coronal twin jets could be generated in the same fashion addressed above.« less

Active zone of the nucleus of the quasar 3C 273

NASA Astrophysics Data System (ADS)

Matveyenko, L. I.; Seleznev, S. V.

2017-04-01

The superfine structure of the quasar 3C 273 has been investigated at wavelengths λ = 2 and 6 cm with angular resolutions up to φ = 20 μas for epochs 2005-2014. We have identified a nozzle and a bipolar outflow: a jet and a counterjet consisting of coaxial high- and low-velocity components. The separation between the nozzles in the plane of the sky is Δ ρ = 0.84 ± 0.16 pc; the flow ejection velocity is v ≤ 0.1 c. The nozzle brightness temperature reaches T b ≈ 45 × 1012 K, φ = 20 μas, λ = 2 cm. The ejected electrons radiatively cool at a distance up to ≤4 pc. However, the jet afterglow is observed at a 8% level at a distance up to ρ ≈ 16 pc; the acceleration compensates for the radiative losses. The reduction in the emission level of the central flow at large distances determines the jet bifurcation. The counterjet shape is a mirror reflection of the initial part of the jet, suggesting a symmetry and identity of the ejected flows. The counterjet and jet nozzles are in the near and remote parts of the active region, respectively. The emission from the nozzles is absorbed by a factor of 2 and 15, respectively. The absorption decreases with increasing distance and the brightness of the jet fragments rises to its maximum at 0.5 pc from the nozzle. Arclike structures, arm fragments, are observed in the region of the nozzles. The relativistic plasma comes to the nozzles and is ejected. The brightness temperature of the arclike structures reaches 10% of the peak value, which is determined by the a smaller optical depth, the visibility in the transverse direction. The central high-velocity flow is surrounded by low-velocity components, hollow tubes being ejected as an excess angular momentum is accumulated. The remainder of the material flows along the arms toward the disk center until the next accumulation of an excess angular momentum and the process is repeated. The diameter of the outer nozzle is Ø = 25 pc and, further out, decreases exponentially; Ø n ≈ 80 exp(-1.15 n) pc. The flow kinematics, collimation, and acceleration have a vortical nature. Ring currents producing magnetic fields, which accelerate and stabilize the processes, are generated in the rotating flows (tubes). The tangential directions of the currents are observed as parallel chains of components.

An experimental study of interacting swirl flows in a model gas turbine combustor

NASA Astrophysics Data System (ADS)

Vishwanath, Rahul B.; Tilak, Paidipati Mallikarjuna; Chaudhuri, Swetaprovo

2018-03-01

In this experimental work, we analyze the flow structures emerging from the mutual interaction between adjacent swirling flows at variable degrees of swirl, issued into a semi-confined chamber, as it could happen in a three cup sector of an annular premixed combustor of a modern gas turbine engine. Stereoscopic particle image velocimetry ( sPIV) is used to characterize both the non-reacting and reacting flow fields in the central diametrical (vertical) plane of the swirlers and the corresponding transverse (horizontal) planes at different heights above the swirlers. A central swirling flow with a fixed swirl vane angle is allowed to interact with its neighboring flows of varied swirl levels, with constant inlet bulk flow velocity through the central port. It is found that the presence of straight jets with zero swirl or co-rotating swirling jets with increasing swirl on both sides of the central swirling jet, significantly alters its structures. As such, an increase in the amount of swirl in the neighboring flows increases the recirculation levels in central swirling flow leading to a bubble-type vortex breakdown, not formed otherwise. It is shown with the aid of Helmholtz decomposition that the transition from conical to bubble-type breakdown is captured well by the radial momentum induced by the azimuthal vorticity. Simultaneous sPIV and OH-planar laser-induced fluorescence (PLIF) are employed to identify the influence of the neighboring jets on the reacting vortex breakdown states. Significant changes in the vortex breakdown size and structure are observed due to variation in swirl levels of the neighboring jets alongside reaction and concomitant flow dilatation.

Initial drop size and velocity distributions for airblast coaxial atomizers

NASA Technical Reports Server (NTRS)

Eroglu, H.; Chigier, N.

1991-01-01

Phase Doppler measurements were used to determine initial drop size and velocity distributions after a complete disintegration of coaxial liquid jets. The Sauter mean diameter (SMD) distribution was found to be strongly affected by the structure and behavior of the preceding liquid intact jet. The axial measurement stations were determined from the photographs of the coaxial liquid jet at very short distances (1-2 mm) downstream of the observed break-up locations. Minimum droplet mean velocities were found at the center, and maximum velocities were near the spray boundary. Size-velocity correlations show that the velocity of larger drops did not change with drop size. Drop rms velocity distributions have double peaks whose radial positions coincide with the maximum mean velocity gradients.

Observational features of equatorial coronal hole jets

NASA Astrophysics Data System (ADS)

Nisticò, G.; Bothmer, V.; Patsourakos, S.; Zimbardo, G.

2010-03-01

Collimated ejections of plasma called "coronal hole jets" are commonly observed in polar coronal holes. However, such coronal jets are not only a specific features of polar coronal holes but they can also be found in coronal holes appearing at lower heliographic latitudes. In this paper we present some observations of "equatorial coronal hole jets" made up with data provided by the STEREO/SECCHI instruments during a period comprising March 2007 and December 2007. The jet events are selected by requiring at least some visibility in both COR1 and EUVI instruments. We report 15 jet events, and we discuss their main features. For one event, the uplift velocity has been determined as about 200 km s-1, while the deceleration rate appears to be about 0.11 km s-2, less than solar gravity. The average jet visibility time is about 30 min, consistent with jet observed in polar regions. On the basis of the present dataset, we provisionally conclude that there are not substantial physical differences between polar and equatorial coronal hole jets.

Catching the radio flare in CTA 102. I. Light curve analysis

NASA Astrophysics Data System (ADS)

Fromm, C. M.; Perucho, M.; Ros, E.; Savolainen, T.; Lobanov, A. P.; Zensus, J. A.; Aller, M. F.; Aller, H. D.; Gurwell, M. A.; Lähteenmäki, A.

2011-07-01

Context. The blazar CTA 102 (z = 1.037) underwent a historical radio outburst in April 2006. This event offered a unique chance to study the physical properties of the jet. Aims: We used multifrequency radio and mm observations to analyze the evolution of the spectral parameters during the flare as a test of the shock-in-jet model under these extreme conditions. Methods: For the analysis of the flare we took into account that the flaring spectrum is superimposed on a quiescent spectrum. We reconstructed the latter from archival data and fitted a synchrotron self-absorbed distribution of emission. The uncertainties of the derived spectral parameters were calculated using Monte Carlo simulations. The spectral evolution is modeled by the shock-in-jet model, and the derived results are discussed in the context of a geometrical model (varying viewing angle) and shock-shock interaction Results: The evolution of the flare in the turnover frequency-turnover flux density (νm - Sm) plane shows a double peak structure. The nature of this evolution is dicussed in the frame of shock-in-jet models. We discard the generation of the double peak structure in the νm - Sm plane purely based on geometrical changes (variation of the Doppler factor). The detailed modeling of the spectral evolution favors a shock-shock interaction as a possible physical mechanism behind the deviations from the standard shock-in-jet model.

Shells in the C2 coma of Comet P/Halley

NASA Technical Reports Server (NTRS)

Schulz, Rita; A'Hearn, Michael F.

1995-01-01

We reanalyzed the CN images of Comet P/Halley, in which jets have been discovered for the first time, in search of shell structures. Shells were actually detected at the outer edges of the frames on those dates for which shells with radii small enough to be covered by the limited field of view of the CCD were predicted. The C2 images of the same data set were subjected to an analogous investigation which led to the discovery of shell structures in C2 as well. The morphology of the CN and the C2 shells is essentially equal on the same observational date. They have the same radii and show almost identical asymmetries which suggests that CN and C2 in the shells originate from the same general source. The comparison of the jets in both species before and after a two-dimensional continuum subtraction supports this supposition. The similar morphology of the jets indicates that both species are produced from the same bulk of precursor material which has been ejected in the form of jets from the same active area. However, similarly located and oriented jets in CN and C2 do not show similar relative intensities in most cases. These differences in the intensity distribution imply that the production rates of CN and C2 follow different laws.

Turbulence structure of the marine stable boundary layer over the Baltic Sea

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smedman, A.S.; Hoegstroem, U.

For more than half of the year the land surfaces surrounding the Baltic Sea is warmer than the sea surface, and the marine boundary layer over the Baltic is stable. Observations, at various sites in the Baltic Sea area during the last decade. also indicate frequent occurrence of low-level jets at the top of the stable boundary layer. In many cases the marine jet can be considered as an analogy in space to the evolution of the nocturnal jet with time. The frictional decoupling occurs when warm air over the land is flowing out over the sea. Data from twomore » areas together with model simulations are used in this study to characterize turbulence structure in the marine boundary layer. The measurements include profiles of wind and temperature on towers situated at two isolated islands, together with turbulence recordings and aircraft measurements. Also wave height and water surface temperature have been measured. The model simulations are performed with a second-order closure model.« less

Application of atmospheric-pressure argon plasma jet for bread mold decontamination

NASA Astrophysics Data System (ADS)

Thonglor, P.; Amnuaycheewa, P.

2017-09-01

Atmospheric-pressure argon plasma (APAP) is a promising non-thermal technology for microbial control and prevention minimally affecting quality of foods. Effect of APAP jet on the growth of bread molds, including two Aspergillus sp., Rhizopus stolonifer, and Penicillium roqueforti, isolated from white bread were investigated. The molds were isolated, verified, cultured to fully grown on potato dextrose agar (PDA), and subsequently treated with APAP jet using plasma generating power at 24 W for 5, 10, and 20 min, respectively. The inhibition of mold growth was investigated by comparing fungal dry weights and the effect on fungal cell structure was observed using compound light microscope. The results indicated that the 20-min treatment time is most effective in retarding the growth of the three bread molds. However, this level of generating power did not lead to destruction of the cellular structures for all the four fungi. Plasma generating power and treatment time are significant parameters determining the success of bread mold decontamination and further investigation on real bread matrix is needed.

Evolution of Fine-scale Penumbral Magnetic Structure and Formation of Penumbral Jets

NASA Astrophysics Data System (ADS)

Tiwari, S. K.; Moore, R. L.; Rempel, M.; Winebarger, A. R.

2015-12-01

Sunspot penumbra consists of spines (more vertical field) and penumbral filaments (interspines). Spines are outward extension of umbra. Penumbral filaments are recently found, both in observations and magnetohydrodynamic (MHD) simulations, to be magnetized stretched granule-like convective cells, with strong upflows near the head that continues along the central axis with weakening strength of the flow. Strong downflows are found at the tails of filaments and weak downflows along the sides of it. These lateral downflows often contain opposite polarity magnetic field to that of spines; most strongly near the heads of filaments. In spite of this advancement in understanding of small-scale structure of sunspot penumbra, how the filaments and spines evolve and interact remains uncertain. Penumbral jets, bright, transient features, seen in the chromosphere, are one of several dynamic events in sunspot penumbra. It has been proposed that these penumbral microjets result from component (acute angle) reconnection of the magnetic field in spines with that in interspines and could contribute to transition-region and coronal heating above sunspots. In a recent investigation, it was proposed that the jets form as a result of reconnection between the opposite polarity field at edges of filaments with spine field, and it was found that these jets do not significantly directly heat the corona above sunspots. We discuss how the proposed formation of penumbral jets is integral to the formation mechanism of penumbral filaments and spines, and may explain why penumbral jets are few and far between. We also point out that the generation of the penumbral jets could indirectly drive coronal heating via generation of MHD waves or braiding of the magnetic field.

A Reconnection Switch to Trigger gamma-Ray Burst Jet Dissipation

DOE Office of Scientific and Technical Information (OSTI.GOV)

McKinney, Jonathan C.; Uzdensky, Dmitri A.

2012-03-14

Prompt gamma-ray burst (GRB) emission requires some mechanism to dissipate an ultrarelativistic jet. Internal shocks or some form of electromagnetic dissipation are candidate mechanisms. Any mechanism needs to answer basic questions, such as what is the origin of variability, what radius does dissipation occur at, and how does efficient prompt emission occur. These mechanisms also need to be consistent with how ultrarelativistic jets form and stay baryon pure despite turbulence and electromagnetic reconnection near the compact object and despite stellar entrainment within the collapsar model. We use the latest magnetohydrodynamical models of ultrarelativistic jets to explore some of these questionsmore » in the context of electromagnetic dissipation due to the slow collisional and fast collisionless reconnection mechanisms, as often associated with Sweet-Parker and Petschek reconnection, respectively. For a highly magnetized ultrarelativistic jet and typical collapsar parameters, we find that significant electromagnetic dissipation may be avoided until it proceeds catastrophically near the jet photosphere at large radii (r {approx} 10{sup 13}-10{sup 14}cm), by which the jet obtains a high Lorentz factor ({gamma} {approx} 100-1000), has a luminosity of L{sub j} {approx} 10{sup 50}-10{sup 51} erg s{sup -1}, has observer variability timescales of order 1s (ranging from 0.001-10s), achieves {gamma}{theta}{sub j} {approx} 10-20 (for opening half-angle {theta}{sub j}) and so is able to produce jet breaks, and has comparable energy available for both prompt and afterglow emission. A range of model parameters are investigated and simplified scaling laws are derived. This reconnection switch mechanism allows for highly efficient conversion of electromagnetic energy into prompt emission and associates the observed prompt GRB pulse temporal structure with dissipation timescales of some number of reconnecting current sheets embedded in the jet. We hope this work helps motivate the development of self-consistent radiative compressible relativistic reconnection models.« less

Experimental studies of the emissions characteristics of nonpremixed gas-air flames of various configurations

NASA Astrophysics Data System (ADS)

Bandaru, Ramarao Venkat

2000-10-01

Flow structure plays an important role in the mixing and chemical reaction processes in turbulent jet diffusion flames, which in turn influence the formation of pollutants. Fundamental studies on pollutant formation have mainly focussed on vertical, straight jet, turbulent flames. However, in many practical combustion systems such as boilers and furnaces, flames of various configurations are used. In the present study, along with vertical straight jet flames, pollutant emissions characteristics of crossflow flames and precessing jet flames are studied. In vertical, straight jet flames, in-flame temperature and NO concentration measurements were made to ascertain the influence of flame radiation on NO x emissions observed in earlier studies. Radiation affects flame temperatures and this is seen in the measured temperature fields in, undiluted and diluted, methane and ethylene flames. Measured NO distribution fields in undiluted methane and ethylene flames inversely correlated with the temperature, and thereby explaining the observed relationship between flame radiation and NO x emissions. Flames in most practical combustion devices have complex mixing characteristics. One such configuration is the crossflow flame, where the flame is subjected to a crossflow stream. The presence of twin counter-rotating vortices in the flames leading to increased entrainment rates and shorter residence times (i.e. shorter flame lengths). The variation of NOx emissions characteristics of crossflow flames from those of straight jet flames depends on the sooting propensity of the fuel used. Additionally, the nearfield region of the flame (i.e., region near the burner exit) has a strong influence on the CO and unburned hydrocarbon emissions, and on the NO2-to-NO x ratios. Another flame configuration used in the present study is the precessing jet flame. In the practical implementation of this unique flame configuration, the fuel jet precesses about the burner axis due to natural fluid mechanical instability occurring inside the burner at a sudden expansion. Studies have shown that these flames emit up to 70% less NOx than straight jet flames. In precessing jet flames, the turbulent mixing scales are several times larger than those of straight jet flames.

Vortex structure and breakup mechanism of gaseous jet in supersonic crossflow with laminar boundary layer

NASA Astrophysics Data System (ADS)

Zhao, Yanhui; Liang, Jianhan; Zhao, Yuxin

2016-11-01

Employing nano-particle planar laser scattering and particle image velocimetry technology, underexpanded jet in supersonic crossflow with laminar boundary layer is experimental investigated in a low noise wind tunnel. Instantaneous flow structures and average velocity distribution of jet plume are captured in experimental images. Horseshoe vortex system is dominated by oscillating and coalescing regime, contributing to vortex generation of jet shear layer. The "tilting-stretching-tearing" mechanism dominating in near field raises average fractal dimension. But vortex structures generated on the windward side of jet plume scatter in jet plume and dissipate gradually, which makes the vortexes break up from outside in near field and break down into small turbulence completely in far field.

MINI-FILAMENT ERUPTION AS THE INITIATION OF A JET ALONG CORONAL LOOPS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, Junchao; Jiang, Yunchun; Yang, Jiayan

Minifilament eruptions (MFEs) and coronal jets are different types of solar small-scale explosive events. We report an MFE observed at the New Vacuum Solar Telescope (NVST). As seen in the NVST H α images, during the rising phase, the minifilament erupts outward orthogonally to its length, accompanied with a flare-like brightening at the bottom. Afterward, dark materials are found to possibly extend along the axis of the expanded filament body. The MFE is analogous to large filament eruptions. However, a simultaneous observation of the Solar Dynamics Observatory shows that a jet is initiated and flows out along nearby coronal loopsmore » during the rising phase of the MFE. Meanwhile, small hot loops, which connect the original eruptive site of the minifilament to the footpoints of the coronal loops, are formed successively. A differential emission measure analysis demonstrates that, on the top of the new small loops, a hot cusp structure exists. We conjecture that the magnetic fields of the MFE interact with magnetic fields of the coronal loops. This interaction is interpreted as magnetic reconnection that produces the jet and the small hot loops.« less

Weak and compact radio emission in early massive star formation regions: an ionized jet toward G11.11–0.12P1

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rosero, V.; Hofner, P.; McCoy, M.

2014-12-01

We report 1.3 cm and 6 cm continuum observations toward the massive proto-stellar candidate G11.11–0.12P1 using the Karl G. Jansky Very Large Array. We detect a string of four unresolved radio continuum sources coincident with the mid-infrared source in G11P1. The continuum sources have positive spectral indices consistent with a thermal (free-free) ionized jet. The most likely origins of the ionized gas are shocks due to the interaction of a stellar wind with the surrounding high-density material. We also present NIR United Kingdom Infrared Telescope (UKIRT) archival data that show an extended structure detected only at K band (2.2 μm),more » which is oriented perpendicular to the jet, and that may be scattered light from a circumstellar disk around the massive protostar. Our observations plus the UKIRT archival data thus provide new evidence that a disk/jet system is present in the massive proto-stellar candidate located in the G11.11–0.12P1 core.« less

Using astrophysical jets for establishing an upper limit for the photon mass

NASA Astrophysics Data System (ADS)

Ryutov, D. D.

2004-11-01

Finite photon mass is compatible with general principles of the relativity theory; how small it (the mass) actually is has to be established experimentally. The presently accepted upper limit [1], E-22 of the electron mass, is established [2] based on the observations of the Solar wind. This estimate corresponds to the photon Compton length of L=3E6 km. I discuss possible ways of improving this estimate based on the properties of those of astrophysical jets where the pinch force is important for establishing the jet structure. It turns out that, if the jet radius is much greater than L, both pinch equilibrium and stability become very different from the massless photon case. In particular, the equilibrium pressure maximum coincides with the maximum of the current density. These new features are often incompatible with the observations, providing a way for improving the estimate of the photon mass by orders of magnitude. Work performed for the U.S. DOE by UC LLNL under contract W-7405-Eng-48. [1] S. Eidelman, and Particle Phys. Group. "Review of Particle Physics," Phys. Lett. B592, p.1, 2004; [2] D.D. Ryutov. Plasma Phys. Contr. Fus., 39, p.A73, 1997.

Impact of red giant/AGB winds on active galactic nucleus jet propagation

NASA Astrophysics Data System (ADS)

Perucho, M.; Bosch-Ramon, V.; Barkov, M. V.

2017-10-01

Context. Dense stellar winds may mass-load the jets of active galactic nuclei, although it is unclear on what time and spatial scales the mixing takes place. Aims: Our aim is to study the first steps of the interaction between jets and stellar winds, and also the scales on which the stellar wind mixes with the jet and mass-loads it. Methods: We present a detailed 2D simulation - including thermal cooling - of a bubble formed by the wind of a star designed to study the initial stages of jet-star interaction. We also study the first interaction of the wind bubble with the jet using a 3D simulation in which the star enters the jet. Stability analysis is carried out for the shocked wind structure to evaluate the distances over which the jet-dragged wind, which forms a tail, can propagate without mixing with the jet flow. Results.The 2D simulations point to quick wind bubble expansion and fragmentation after about one bubble shock crossing time. Three-dimensional simulations and stability analysis point to local mixing in the case of strong perturbations and relatively low density ratios between the jet and the jet dragged-wind, and to a possibly more stable shocked wind structure at the phase of maximum tail mass flux. Analytical estimates also indicate that very early stages of the star jet-penetration time may be also relevant for mass-loading. The combination of these and previous results from the literature suggests highly unstable interaction structures and efficient wind-jet flow mixing on the scale of the jet interaction height. Conclusions: The winds of stars with strong mass loss can efficiently mix with jets from active galactic nuclei. In addition, the initial wind bubble shocked by the jet leads to a transient, large interaction surface. The interaction between jets and stars can produce strong inhomogeneities within the jet. As mixing is expected to be effective on large scales, even individual asymptotic giant branch stars can significantly contribute to the mass-load of the jet and thus affect its dynamics. Shear layer mass-entrainment could be important. The interaction structure can be a source of significant non-thermal emission.

The free jet microwave spectrum of 2-phenylethylamine-water.

PubMed

Melandri, Sonia; Maris, Assimo; Giuliano, Barbara M; Favero, Laura B; Caminati, Walther

2010-09-21

We observed the rotational spectrum of the 1:1 molecular adduct between 2-phenylethylamine and water (normal and H(2)(18)O species) by free jet absorption microwave spectroscopy in the frequency region 60-78 GHz. The dominant spectrum belongs to the structure where the PEA moiety is in the most stable gauche conformation and the water molecule is hydrogen bound to the nitrogen lone pair. The orientation of the water molecule is such that the oxygen atom is almost equidistant (ca. 2.5 A) from the closest methylenic and aromatic hydrogen atoms.

Internal shocks in microquasar jets with a continuous Lorentz factor modulation

NASA Astrophysics Data System (ADS)

Pjanka, Patryk; Stone, James M.

2018-06-01

We perform relativistic hydrodynamic simulations of internal shocks formed in microquasar jets by continuous variation of the bulk Lorentz factor, in order to investigate the internal shock model. We consider one-, two-, and flicker noise 20-mode variability. We observe emergence of a forward-reverse shock structure for each peak of the Lorentz factor modulation. The high pressure in the shocked layer launches powerful outflows perpendicular to the jet beam into the ambient medium. These outflows dominate the details of the jet's kinetic energy thermalization. They are responsible for mixing between the jet and the surrounding medium and generate powerful shocks in the latter. These results do not concur with the popular picture of well-defined internal shells depositing energy as they collide within the confines of the jet, in fact collisions between internal shells themselves are quite rare in our continuous formulation of the problem. For each of our simulations, we calculate the internal energy deposited in the system, the `efficiency' of this deposition (defined as the ratio of internal to total flow energy), and the maximum temperature reached in order to make connections to emission mechanisms. We probe the dependence of these diagnostics on the Lorentz factor variation amplitudes, modulation frequencies, as well as the initial density ratio between the jet and the ambient medium.

3-D RPIC simulations of relativistic jets: Particle acceleration, magnetic field generation, and emission

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.

2006-01-01

Nonthermal radiation observed from astrophysical systems containing (relativistic) jets and shocks, e.g., supernova remnants, active galactic nuclei (AGNs), gamma-ray bursts (GRBs), and Galactic microquasar systems usually have power-law emission spectra. Fermi acceleration is the mechanism usually assumed for the acceleration of particles in astrophysical environments. Recent PIC simulations using injected relativistic electron-ion (electro-positron) jets show that acceleration occurs within the downstream jet, rather than by the scattering of particles back and forth across the shock as in Fermi acceleration. Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel instability) created in the .shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants. We will review recent PIC simulations which show particle acceleration in jets.

Structure of saligenin: microwave, UV and IR spectroscopy studies in a supersonic jet combined with quantum chemistry calculations.

PubMed

Kumar, Sumit; Singh, Santosh K; Calabrese, Camilla; Maris, Assimo; Melandri, Sonia; Das, Aloke

2014-08-28

In this study, we have determined the structure of a medicinally important molecule saligenin (2-hydroxybenzyl alcohol) using UV, IR and microwave absorption spectroscopy in a supersonic jet combined with ab initio calculations. The structure of the only observed conformer of saligenin corresponds to the global minimum on the conformational surface. The observed structure is stabilized by an intramolecular strong O-H···O hydrogen bonding as well as a very weak O-H···π interaction. The hydrogen bond is formed through phenolic OH as the hydrogen bond donor and benzylic OH as the hydrogen bond acceptor while the O-H···π interaction is through benzylic O-H as the hydrogen bond donor and phenyl group as the hydrogen bond acceptor. It has been observed that the benzylic OH stretching frequency in saligenin is more red-shifted compared to that in benzyl alcohol as the strong O-H···O interaction present in saligenin acts on the benzylic O-H group. In fact, there is a subtle interplay among the strong O-H···O hydrogen bond, weak O-H···π interaction, and steric effects arising from the ortho substitution of the OH group in benzyl alcohol. This fine-tuning of multiple interactions very often governs the specific structures of biomolecules and materials.

Determining the Discharge Rate from a Submerged Oil Leaks using ROV Video and CFD study

NASA Astrophysics Data System (ADS)

Saha, Pankaj; Shaffer, Frank; Shahnam, Mehrdad; Savas, Omer; Devites, Dave; Steffeck, Timothy

2016-11-01

The current paper reports a technique to measure the discharge rate by analyzing the video from a Remotely Operated Vehicle (ROV). The technique uses instantaneous images from ROV video to measure the velocity of visible features (turbulent eddies) along the boundary of an oil leak jet and subsequently classical theory of turbulent jets is imposed to determine the discharge rate. The Flow Rate Technical Group (FRTG) Plume Team developed this technique that manually tracked the visible features and produced the first accurate government estimates of the oil discharge rate from the Deepwater Horizon (DWH). For practical application this approach needs automated control. Experiments were conducted at UC Berkeley and OHMSETT that recorded high speed, high resolution video of submerged dye-colored water or oil jets and subsequently, measured the velocity data employing LDA and PIV software. Numerical simulation have been carried out using experimental submerged turbulent oil jets flow conditions employing LES turbulence closure and VOF interface capturing technique in OpenFOAM solver. The CFD results captured jet spreading angle and jet structures in close agreement with the experimental observations. The work was funded by NETL and DOI Bureau of Safety and Environmental Enforcement (BSEE).

A MAGNETOHYDRODYNAMIC MODEL OF THE M87 JET. I. SUPERLUMINAL KNOT EJECTIONS FROM HST-1 AS TRAILS OF QUAD RELATIVISTIC MHD SHOCKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nakamura, Masanori; Garofalo, David; Meier, David L., E-mail: nakamura@stsci.ed, E-mail: david.a.garofalo@jpl.nasa.go, E-mail: david.l.meier@jpl.nasa.go

2010-10-01

This is the first in a series of papers that introduces a new paradigm for understanding the jet in M87: a collimated relativistic flow in which strong magnetic fields play a dominant dynamical role. Here, we focus on the flow downstream of HST-1-an essentially stationary flaring feature that ejects trails of superluminal components. We propose that these components are quad relativistic magnetohydrodynamic shock fronts (forward/reverse fast and slow modes) in a narrow jet with a helically twisted magnetic structure. And we demonstrate the properties of such shocks with simple one-dimensional numerical simulations. Quasi-periodic ejections of similar component trails may bemore » responsible for the M87 jet substructures observed further downstream on 10{sup 2}-10{sup 3} pc scales. This new paradigm requires the assimilation of some new concepts into the astrophysical jet community, particularly the behavior of slow/fast-mode waves/shocks and of current-driven helical kink instabilities. However, the prospects of these ideas applying to a large number of other jet systems may make this worth the effort.« less

Analytical and experimental study of the acoustics and the flow field characteristics of cavitating self-resonating water jets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chahine, G.L.; Genoux, P.F.; Johnson, V.E. Jr.

1984-09-01

Waterjet nozzles (STRATOJETS) have been developed which achieve passive structuring of cavitating submerged jets into discrete ring vortices, and which possess cavitation incipient numbers six times higher than obtained with conventional cavitating jet nozzles. In this study we developed analytical and numerical techniques and conducted experimental work to gain an understanding of the basic phenomena involved. The achievements are: (1) a thorough analysis of the acoustic dynamics of the feed pipe to the nozzle; (2) a theory for bubble ring growth and collapse; (3) a numerical model for jet simulation; (4) an experimental observation and analysis of candidate second-generation low-sigmamore » STRATOJETS. From this study we can conclude that intensification of bubble ring collapse and design of highly resonant feed tubes can lead to improved drilling rates. The models here described are excellent tools to analyze the various parameters needed for STRATOJET optimizations. Further analysis is needed to introduce such important factors as viscosity, nozzle-jet interaction, and ring-target interaction, and to develop the jet simulation model to describe the important fine details of the flow field at the nozzle exit.« less

Aeroacoustics of Turbulent High-Speed Jets

NASA Technical Reports Server (NTRS)

Rao, Ram Mohan; Lundgren, Thomas S.

1996-01-01

Aeroacoustic noise generation in a supersonic round jet is studied to understand in particular the effect of turbulence structure on the noise without numerically compromising the turbulence itself. This means that direct numerical simulations (DNS's) are needed. In order to use DNS at high enough Reynolds numbers to get sufficient turbulence structure we have decided to solve the temporal jet problem, using periodicity in the direction of the jet axis. Physically this means that turbulent structures in the jet are repeated in successive downstream cells instead of being gradually modified downstream into a jet plume. Therefore in order to answer some questions about the turbulence we will partially compromise the overall structure of the jet. The first section of chapter 1 describes some work on the linear stability of a supersonic round jet and the implications of this for the jet noise problem. In the second section we present preliminary work done using a TVD numerical scheme on a CM5. This work is only two-dimensional (plane) but shows very interesting results, including weak shock waves. However this is a nonviscous computation and the method resolves the shocks by adding extra numerical dissipation where the gradients are large. One wonders whether the extra dissipation would influence small turbulent structures like small intense vortices. The second chapter is an extensive discussion of preliminary numerical work using the spectral method to solve the compressible Navier-Stokes equations to study turbulent jet flows. The method uses Fourier expansions in the azimuthal and streamwise direction and a 1-D B-spline basis representation in the radial direction. The B-spline basis is locally supported and this ensures block diagonal matrix equations which are solved in O(N) steps. A very accurate highly resolved DNS of a turbulent jet flow is expected.

Predictions for boson-jet observables and fragmentation function ratios from a hybrid strong/weak coupling model for jet quenching

DOE PAGES

Casalderrey-Solana, Jorge; Gulhan, Doga Can; Milhano, José Guilherme; ...

2016-03-09

We have previously introduced a hybrid strong/weak coupling model for jet quenching in heavy ion collisions in which we describe the production and fragmentation of jets at weak coupling, using Pythia, and describe the rate at which each parton in the jet shower loses energy as it propagates through the strongly coupled plasma, dE/dx, using an expression computed holographically at strong coupling. The model has a single free parameter that we fit to a single experimental measurement. We then confront our model with experimental data on many other jet observables, focusing in this paper on boson-jet observables, finding that itmore » provides a good description of present jet data. Next, we provide the predictions of our hybrid model for many measurements to come, including those for inclusive jet, dijet, photon-jet and Z-jet observables in heavy ion collisions with energy √s = 5 : 02 ATeV coming soon at the LHC. As the statistical uncertainties on near-future measurements of photon-jet observables are expected to be much smaller than those in present data, with about an order of magnitude more photon-jet events expected, predictions for these observables are particularly important. We find that most of our pre- and post-dictions do not depend sensitively on the form we choose for the rate of energy loss dE/dx of the partons in the shower. This gives our predictions considerable robustness. To better discriminate between possible forms for the rate of energy loss, though, we must turn to intrajet observables. Here, we focus on ratios of fragmentation functions. Finally, we close with a suggestion for a particular ratio, between the fragmentation functions of inclusive and associated jets with the same kinematics in the same collisions, which is particularly sensitive to the x- and E-dependence of dE/dx, and hence may be used to learn which mechanism of parton energy loss best describes the quenching of jets.« less

Assessment of Unusual Gigantic Jets observed during the Monsoon season: First observations from Indian Subcontinent.

PubMed

Singh, Rajesh; Maurya, Ajeet K; Chanrion, Olivier; Neubert, Torsten; Cummer, Steven A; Mlynarczyk, Janusz; Cohen, Morris B; Siingh, Devendraa; Kumar, Sushil

2017-11-27

Gigantic Jets are electric discharges from thunderstorm cloud tops to the bottom of ionosphere at ~90 km altitude and electrically connect the troposphere and lower ionosphere. Since their first report in 2002, sporadic observations have been reported from ground and space based observations. Here we report first observations of Gigantic Jets in Indian subcontinent over the Indo-Gangetic plains during the monsoon season. Two storms each produced two jets with characteristics not documented so far. Jets propagated ~37 km up remarkably in ~5 ms with velocity of ~7.4 × 10 6 ms -1 and disappeared within ~40-80 ms, which is faster compared to jets reported earlier. The electromagnetic signatures show that they are of negative polarity, transporting net negative charge of ~17-23 C to the lower ionosphere. One jet had an unusual form observed for the first time, which emerged from the leading edge of a slowly drifting complex convective cloud close to the highest regions at ~17 km altitude. A horizontal displacement of ~10 km developed at ~50 km altitude before connecting to the lower ionosphere. Modeling of these Gigantic jets suggests that Gigantic Jets may bend when initiated at the edge of clouds with misaligned vertical charge distribution.

Ceramic micro-injection molded nozzles for serial femtosecond crystallography sample delivery

NASA Astrophysics Data System (ADS)

Beyerlein, K. R.; Adriano, L.; Heymann, M.; Kirian, R.; Knoška, J.; Wilde, F.; Chapman, H. N.; Bajt, S.

2015-12-01

Serial femtosecond crystallography (SFX) using X-ray Free-Electron Lasers (XFELs) allows for room temperature protein structure determination without evidence of conventional radiation damage. In this method, a liquid suspension of protein microcrystals can be delivered to the X-ray beam in vacuum as a micro-jet, which replenishes the crystals at a rate that exceeds the current XFEL pulse repetition rate. Gas dynamic virtual nozzles produce the required micrometer-sized streams by the focusing action of a coaxial sheath gas and have been shown to be effective for SFX experiments. Here, we describe the design and characterization of such nozzles assembled from ceramic micro-injection molded outer gas-focusing capillaries. Trends of the emitted jet diameter and jet length as a function of supplied liquid and gas flow rates are measured by a fast imaging system. The observed trends are explained by derived relationships considering choked gas flow and liquid flow conservation. Finally, the performance of these nozzles in a SFX experiment is presented, including an analysis of the observed background.

Two-loop beam and soft functions for rapidity-dependent jet vetoes

NASA Astrophysics Data System (ADS)

Gangal, Shireen; Gaunt, Jonathan R.; Stahlhofen, Maximilian; Tackmann, Frank J.

2017-02-01

Jet vetoes play an important role in many analyses at the LHC. Traditionally, jet vetoes have been imposed using a restriction on the transverse momentum p Tj of jets. Alternatively, one can also consider jet observables for which p Tj is weighted by a smooth function of the jet rapidity y j that vanishes as | y j | → ∞. Such observables are useful as they provide a natural way to impose a tight veto on central jets but a looser one at forward rapidities. We consider two such rapidity-dependent jet veto observables, T_{Bj} and {T_{Cj} , and compute the required beam and dijet soft functions for the jet-vetoed color-singlet production cross section at two loops. At this order, clustering effects from the jet algorithm become important. The dominant contributions are computed fully analytically while corrections that are subleading in the limit of small jet radii are expressed in terms of finite numerical integrals. Our results enable the full NNLL' resummation and are an important step towards N3LL resummation for cross sections with a T_{Bj} or T_{Cj} jet veto.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goldstein, Adam; Connaughton, Valerie; Briggs, Michael S.

We present a method to estimate the jet opening angles of long duration gamma-ray bursts (GRBs) using the prompt gamma-ray energetics and an inversion of the Ghirlanda relation, which is a correlation between the time-integrated peak energy of the GRB prompt spectrum and the collimation-corrected energy in gamma-rays. The derived jet opening angles using this method and detailed assumptions match well with the corresponding inferred jet opening angles obtained when a break in the afterglow is observed. Furthermore, using a model of the predicted long GRB redshift probability distribution observable by the Fermi Gamma-ray Burst Monitor (GBM), we estimate themore » probability distributions for the jet opening angle and rest-frame energetics for a large sample of GBM GRBs for which the redshifts have not been observed. Previous studies have only used a handful of GRBs to estimate these properties due to the paucity of observed afterglow jet breaks, spectroscopic redshifts, and comprehensive prompt gamma-ray observations, and we potentially expand the number of GRBs that can be used in this analysis by more than an order of magnitude. In this analysis, we also present an inferred distribution of jet breaks which indicates that a large fraction of jet breaks are not observable with current instrumentation and observing strategies. We present simple parameterizations for the jet angle, energetics, and jet break distributions so that they may be used in future studies.« less

Oscillations in solar jets observed with the SOT of Hinode: viscous effects during reconnection

NASA Astrophysics Data System (ADS)

Tavabi, E.; Koutchmy, S.

2014-07-01

Transverse oscillatory motions and recurrence behavior in the chromospheric jets observed by Hinode/SOT are studied. A comparison is considered with the behavior that was noticed in coronal X-ray jets observed by Hinode/XRT. A jet like bundle observed at the limb in Ca II H line appears to show a magnetic topology that is similar to X-ray jets (i.e., the Eiffel tower shape). The appearance of such magnetic topology is usually assumed to be caused by magnetic reconnection near a null point. Transverse motions of the jet axis are recorded but no clear evidence of twist is appearing from the highly processed movie. The aim is to investigate the dynamical behavior of an incompressible magnetic X-point occurring during the magnetic reconnection in the jet formation region. The viscous effect is specially considered in the closed line-tied magnetic X-shape nulls. We perform the MHD numerical simulation in 2-D by solving the visco-resistive MHD equations with the tracing of velocity and magnetic field. A qualitative agreement with Hinode observations is found for the oscillatory and non-oscillatory behaviors of the observed solar jets in both the chromosphere and the corona. Our results suggest that the viscous effect contributes to the excitation of the magnetic reconnection by generating oscillations that we observed at least inside this Ca II H line cool solar jet bundle.

Jet Stability and the Generation of Superluminal and Stationary Components

NASA Technical Reports Server (NTRS)

Agudo, Ivan; Gomez, Jose-Luis; Marti, Jose-Maria; Ibanez, Jose-Maria; Marscher, Alan P.; Alberdi, Antonio; Aloy, Miguel-Angel; Hardee, Philip E.

2001-01-01

We present a numerical simulation of the response of an expanding relativistic jet to the ejection of a superluminal component. The simulation has been performed with a relativistic time-dependent hydrodynamical code from which simulated radio maps are computed by integrating the transfer equations for synchrotron radiation. The interaction of the superluminal component with the underlying jet results in the formation of multiple conical shocks behind the main perturbation. These trailing components can be easily distinguished because they appear to be released from the primary superluminal component instead of being ejected from the core. Their oblique nature should also result in distinct polarization properties. Those appearing closer to the core show small apparent motions and a very slow secular decrease in brightness and could be identified as stationary components. Those appearing farther downstream are weaker and can reach superluminal apparent motions. The existence of these trailing components indicates that not all observed components necessarily represent major perturbations at the jet inlet; rather, multiple emission components can be generated by a single disturbance in the jet. While the superluminal component associated with the primary perturbation exhibits a rather stable pattern speed, trailing components have velocities that increase with distance from the core but move at less than the jet speed. The trailing components exhibit motion and structure consistent with the triggering of pinch modes by the superluminal component. The increase in velocity of the trailing components is an indirect consequence of the acceleration of the expanding fluid, which is assumed to be relativistically hot; if observed, such accelerations would therefore favor an electron-positron (as opposed to proton rest mass) dominated jet.

Solar Polar Jets Driven by Magnetic Reconnection, Gravity, and Wind

NASA Astrophysics Data System (ADS)

DeVore, C. Richard; Karpen, Judith T.; Antiochos, Spiro K.

2014-06-01

Polar jets are dynamic, narrow, radially extended structures observed in solar EUV emission near the limb. They originate within the open field of coronal holes in “anemone” regions, which are intrusions of opposite magnetic polarity. The key topological feature is a magnetic null point atop a dome-shaped fan surface of field lines. Applied stresses readily distort the null into a current patch, eventually inducing interchange reconnection between the closed and open fields inside and outside the fan surface (Antiochos 1996). Previously, we demonstrated that magnetic free energy stored on twisted closed field lines inside the fan surface is released explosively by the onset of fast reconnection across the current patch (Pariat et al. 2009, 2010). A dense jet comprised of a nonlinear, torsional Alfvén wave is ejected into the outer corona along the newly reconnected open field lines. Now we are extending those exploratory simulations by including the effects of solar gravity, solar wind, and expanding spherical geometry. We find that the model remains robust in the resulting more complex setting, with explosive energy release and dense jet formation occurring in the low corona due to the onset of a kink-like instability, as found in the earlier Cartesian, gravity-free, static-atmosphere cases. The spherical-geometry jet including gravity and wind propagates far more rapidly into the outer corona and inner heliosphere than a comparison jet simulation that excludes those effects. We report detailed analyses of our new results, compare them with previous work, and discuss the implications for understanding remote and in-situ observations of solar polar jets.This work was supported by NASA’s LWS TR&T program.

Simultaneous velocity and concentration field measurements of passive-scalar mixing in a confined rectangular jet

NASA Astrophysics Data System (ADS)

Feng, Hua; Olsen, Michael G.; Hill, James C.; Fox, Rodney O.

2007-06-01

Simultaneous velocity and concentration fields in a confined liquid-phase rectangular jet with a Reynolds number based on the hydraulic diameter of 50,000 (or 10,000 based on the velocity difference between streams and the jet exit dimension) and a Schmidt number of 1,250 were obtained by means of a combined particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) system. Data were collected at the jet exit and six further downstream locations. The velocity and concentration field data were analyzed for flow statistics such as turbulent fluxes, turbulent viscosity and diffusivity, and turbulent Schmidt number ( Sc T ). The streamwise turbulent flux was found to be larger than the transverse turbulent flux, and the mean concentration gradient was not aligned with the turbulent flux vector. The average Sc T was found to vary both in streamwise and in cross stream directions and had a mean value around 0.8, a value consistent with the literature. Spatial correlation fields of turbulent fluxes and concentration were then determined. The R u'ϕ' correlation was elliptical in shape with a major axis tilted downward with respect to the streamwise axis, whereas the R v'ϕ' correlation was an ellipse with a major axis aligned with the cross-stream direction. Negative regions of R u'ϕ' were observed in the outer streams, and these negatively correlated regions decayed with downstream distance and finally disappeared altogether. The R ϕ'ϕ' correlation field was found to be an ellipse with the major axis inclined at about 45° with respect to the streamwise direction. Linear stochastic estimation was used to interpret spatial correlation data and to determine conditional flow structures. It is believed that a vortex street formed near the splitter plate is responsible for the negatively correlated region observed in the R u'ϕ' spatial correlations of turbulent fluxes. A positive concentration fluctuation event was observed to correspond to a finger of nearly uniform concentration fluid reaching out into the outer stream, whereas a negative event corresponds to a pocket of nearly uniform fluid being entrained from the outer stream into the center jet region. Large-scale vortical structures were observed in the conditional velocity fields with an elliptical shape and a streamwise major axis. The growth of the structure size increased linearly initially but then grew more slowly as the flow transitioned toward channel flow.

An elevation of 0.1 light-seconds for the optical jet base in an accreting Galactic black hole system

NASA Astrophysics Data System (ADS)

Gandhi, P.; Bachetti, M.; Dhillon, V. S.; Fender, R. P.; Hardy, L. K.; Harrison, F. A.; Littlefair, S. P.; Malzac, J.; Markoff, S.; Marsh, T. R.; Mooley, K.; Stern, D.; Tomsick, J. A.; Walton, D. J.; Casella, P.; Vincentelli, F.; Altamirano, D.; Casares, J.; Ceccobello, C.; Charles, P. A.; Ferrigno, C.; Hynes, R. I.; Knigge, C.; Kuulkers, E.; Pahari, M.; Rahoui, F.; Russell, D. M.; Shaw, A. W.

2017-12-01

Relativistic plasma jets are observed in many systems that host accreting black holes. According to theory, coiled magnetic fields close to the black hole accelerate and collimate the plasma, leading to a jet being launched1-3. Isolating emission from this acceleration and collimation zone is key to measuring its size and understanding jet formation physics. But this is challenging because emission from the jet base cannot easily be disentangled from other accreting components. Here, we show that rapid optical flux variations from an accreting Galactic black-hole binary are delayed with respect to X-rays radiated from close to the black hole by about 0.1 seconds, and that this delayed signal appears together with a brightening radio jet. The origin of these subsecond optical variations has hitherto been controversial4-8. Not only does our work strongly support a jet origin for the optical variations but it also sets a characteristic elevation of ≲103 Schwarzschild radii for the main inner optical emission zone above the black hole9, constraining both internal shock10 and magnetohydrodynamic11 models. Similarities with blazars12,13 suggest that jet structure and launching physics could potentially be unified under mass-invariant models. Two of the best-studied jetted black-hole binaries show very similar optical lags8,14,15, so this size scale may be a defining feature of such systems.

Spreading Characteristics and Thrust of Jets from Asymmetric Nozzles

NASA Technical Reports Server (NTRS)

Zaman, K. B. M. Q.

1995-01-01

The spreading characteristics of jets from several asymmetric nozzles are studied in comparison to those of an axisymmetric jet, over the Mach number (M(sub J)) range of 0.3 to 1.96. The effect of tabs in two cases, the axisymmetric nozzle fitted with four tabs and a rectangular nozzle fitted with two large tabs, is also included in the comparison. Compared to the axisymmetric jet, the asymmetric jets spread only slightly faster at subsonic conditions, while at supersonic conditions, when screech occurs, they spread much faster. Screech profoundly increases the spreading of all jets. The effect varies in the different stages of screech, and the corresponding unsteady flowfield characteristics are documented via phase-averaged measurement of the fluctuating total pressure. An organization and intensification of the azimuthal vortical structures under the screeching condition is believed to be responsible for the increased spreading. Curiously, the jet from a 'lobed mixer' nozzle spreads much less at supersonic conditions compared to all other cases. This is due to the absence of screech with this nozzle. Jet spreading for the two tab configurations, on the other hand, is significantly more than any of the no-tab cases. This is true in the subsonic regime, as well as in the supersonic regime in spite of the fact that screech is essentially eliminated by the tabs. The dynamics of the streamwise vortex pairs produced by the tabs cause the most efficient jet spreading thus far observed in the study.

Gravitational Effects on Flow Instability and Transition in Low Density Jets

NASA Technical Reports Server (NTRS)

Agrawal A. K.; Parthasarathy, K.; Pasumarthi, K.; Griffin, D. W.

2000-01-01

Recent experiments have shown that low-density gas jets injected into a high-density ambient gas undergo an instability mode, leading to highly-periodic oscillations in the flow-field for certain conditions. The transition from laminar to turbulent flow in these jets is abrupt, without the gradual change in scales. Even the fine scale turbulent structure repeats itself with extreme regularity from cycle to cycle. Similar observations were obtained in buoyancy-dominated and momentum-dominated jets characterized by the Richardson numbers, Ri = [gD(rho(sub a)-rho(sub j))/rho(sub j)U(sub j)(exp 2) ] where g is the gravitational acceleration, D is the jet diameter, rho(sub a) and rho(sub a) are, respectively, the free-stream and jet densities, and U(sub j) is the mean jet exit velocity. At high Richardson numbers, the instability is presumably caused by buoyancy since the flow-oscillation frequency (f) or the Strouhal number, St = [fD/U(sub j)] scales with Ri. In momentum-dominated jets, however, the Strouhal number of the oscillating flow is relatively independent of the Ri. In this case, a local absolute instability is predicted in the potential core of low-density jets with S [= rho(sub j)/rho(sub a)] < 0.7, which agrees qualitatively with experiments. Although the instability in gas jets of high Richardson numbers is attributed to buoyancy, direct physical evidence has not been acquired in experiments. If the instability is indeed caused by buoyancy, the near-field flow structure of the jet will change significantly when the buoyancy is removed, for example, in the microgravity environment. Thus, quantitative data on the spatial and temporal evolutions of the instability, length and time scale of the oscillating mode and its effects on the mean flow and breakdown of the potential core are needed in normal and microgravity to delineate gravitational effects in buoyant jets. In momentum dominated low-density jets, the instability is speculated to originate in the potential core. However, experiments have not succeeded in identifying the direct physical cause of the instability. For example, the theory predicts an oscillating mode for S<0.62 in the limit of zero momentum thickness, which contradicts with the experimental findings of Kyle and Sreenivasan. The analyses of momentum-dominated jets neglect buoyancy effects because of the small Richardson number. Although this assumption is appropriate in the potential core, the gravitational effects are important in the annular region surrounding the jet, where the density and velocity gradients are large. This reasoning provides basis for the hypothesis that the instability in low Richardosn number jets studied by Kyle and Sreenivasan and Monkewitz et al. is caused by buoyancy. The striking similarity in characteristics of the instability and virtually the identical conclusions reached by Subbarao and Cantwell in buoyant (Ri>0.5) helium jets on one hand and by Kyle and Sreenivasan in momentum-dominated (Ri<1x10(exp -3)) helium jets on the other support this hypothesis. However, quantitative experiments in normal and microgravity are necessary to obtain direct physical evidence of buoyancy effects on the flow instability and structure of momentum-dominated low-density jets. The primary objective of this new research project is to quantify how buoyancy affects the flow instability and structure in the near field of low-density jets. The flow will be described by the spatial and temporal evolutions of the instability, length and time scales of the oscillating mode, and the mean and fluctuating concentration fields. To meet this objective, concentration measurements will be obtained across the whole field using quantitative Rainbow Schlieren Deflectometry, providing spatial resolution of 0.1mm and temporal resolution of 0.017s to 1ms. The experimental effort will be supplemented with linear stability analysis of low-density jets by considering buoyancy. The first objective of this research is to investigate the effects of gravity on the flow instability and structure of low-density jets. The flow instability in these jets has been attributed to buoyancy. By removing buoyancy in our experiments, we seek to obtain the direct physical evidence of the instability mechanism. In the absence of the instability, the flow structure will undergo a significant change. We seek to quantify these changes by mapping the flow field (in terms of the concentration profiles) of these jets at non-buoyant conditions. Such information is presently lacking in the existing literature. The second objective of this research is to determine if the instability in momentum-driven, low-density jets is caused by buoyancy. At these conditions, the buoyancy effects are commonly ignored because of the small Richardson based on global parameters. By eliminating buoyancy in our experiments, globally as well as locally, we seek to examine the possibility that the instability mechanism in self-excited, buoyant or momentum-driven jets is the same. To meet this objective, we would quantify the jet flow in normal and microgravity, while systematically decreasing the Richardson number from buoyancy-driven to momentum driven flow regime. The third objective of this research is to perform a linear stability analysis of low-density gas jets by including the gravitational effects. The flow oscillations in these jets are attributed to an absolute instability, whereby the disturbance grows exponentially at the site to ultimately contaminate the entire flow field. We seek to study the characteristics of both convective and absolute instabilities and demarcate the boundary between them.

New Relativistic Particle-In-Cell Simulation Studies of Prompt and Early Afterglows from GRBs

NASA Technical Reports Server (NTRS)

Nishikawa, Ken-ichi; Hardee, P.; Mizuno, Y.; Zhang, B.; Medvedev, M.; Hartmann, D.; Fishman, J. F.; Preece, R.

2008-01-01

Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., gamma-ray bursts (GRBs), active galactic nuclei (AGNs), and Galactic microquasar systems usually have power-law emission spectra. Recent PIC simulations of relativistic electron-ion (electro-positron) jets injected into a stationary medium show that particle acceleration occurs within the downstream jet. In the collisionless relativistic shock particle acceleration is due to plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel (filamentation) instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The 'jitter' radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.

Relativistic jet models for the BL Lacertae object Mrk 421 during three epochs of observation

NASA Technical Reports Server (NTRS)

Mufson, S. L.; Hutter, D. J.; Kondo, Y.; Wisniewski, W. Z.

1988-01-01

Coordinated observation of the nearby BL Lacertae object Mrk 421 obtained during May 1980, January 1984, and March 1984 are described. These observations give a time-frozen picture of the continuous spectrum of Mrk 421 at X-ray, ultraviolet, optical, and radio wavelengths. The observed spectra have been fitted to an inhomogeneous relativistic jet model. In general, the models reproduce the data well. Many of the observed differences during the three epochs can be attributed to variations in the opening angle of the jet and in the angle that the jet makes to the line of sight. The jet models obtained here are compared with the homogeneous, spherically symmetric, synchrotron self-Compton models for this source. The models are also compared with the relativistic jet models obtained for other active galactic nuclei.

Investigation of coherent structures in a superheated jet using decomposition methods

NASA Astrophysics Data System (ADS)

Sinha, Avick; Gopalakrishnan, Shivasubramanian; Balasubramanian, Sridhar

2016-11-01

A superheated turbulent jet, commonly encountered in many engineering flows, is complex two phase mixture of liquid and vapor. The superposition of temporally and spatially evolving coherent vortical motions, known as coherent structures (CS), govern the dynamics of such a jet. Both POD and DMD are employed to analyze such vortical motions. PIV data is used in conjunction with the decomposition methods to analyze the CS in the flow. The experiments were conducted using water emanating into a tank containing homogeneous fluid at ambient condition. Three inlet pressure were employed in the study, all at a fixed inlet temperature. 90% of the total kinetic energy in the mean flow is contained within the first five modes. The scatterplot for any two POD coefficients predominantly showed a circular distribution, representing a strong connection between the two modes. We speculate that the velocity and vorticity contours of spatial POD basis functions show presence of K-H instability in the flow. From DMD, eigenvalues away from the origin is observed for all the cases indicating the presence of a non-oscillatory structure. Spatial structures are also obtained from DMD. The authors are grateful to Confederation of Indian Industry and General Electric India Pvt. Ltd. for partial funding of this project.

Acoustic Efficiency of Azimuthal Modes in Jet Noise Using Chevron Nozzles

NASA Technical Reports Server (NTRS)

Brown, Clifford A.; Bridges, James

2006-01-01

The link between azimuthal modes in jet turbulence and in the acoustic sound field has been examined in cold, round jets. Chevron nozzles, however, impart an azimuthal structure on the jet with a shape dependent on the number, length and penetration angle of the chevrons. Two particular chevron nozzles, with 3 and 4 primary chevrons respectively, and a round baseline nozzle are compared at both cold and hot jet conditions to determine how chevrons impact the modal structure of the flow and how that change relates to the sound field. The results show that, although the chevrons have a large impact on the azimuthal shape of the mean axial velocity, the impact of chevrons on the azimuthal structure of the fluctuating axial velocity is small at the cold jet condition and smaller still at the hot jet condition. This is supported by results in the azimuthal structure of the sound field, which also shows little difference in between the two chevron nozzles and the baseline nozzle in the distribution of energy across the azimuthal modes measured.

Flow structure and unsteadiness in the supersonic wake of a generic space launcher

NASA Astrophysics Data System (ADS)

Schreyer, Anne-Marie; Stephan, Sören; Radespiel, Rolf

2015-11-01

At the junction between the rocket engine and the main body of a classical space launcher, a separation-dominated and highly unstable flow field develops and induces strong wall-pressure oscillations. These can excite structural vibrations detrimental to the launcher. It is desirable to minimize these effects, for which a better understanding of the flow field is required. We study the wake flow of a generic axisymmetric space-launcher model with and without propulsive jet (cold air). Experimental investigations are performed at Mach 2.9 and a Reynolds number ReD = 1 . 3 .106 based on model diameter D. The jet exits the nozzle at Mach 2.5. Velocity measurements by means of Particle Image Velocimetry and mean and unsteady wall-pressure measurements on the main-body base are performed simultaneously. Additionally, we performed hot-wire measurements at selected points in the wake. We can thus observe the evolution of the wake flow along with its spectral content. We describe the mean and turbulent flow topology and evolution of the structures in the wake flow and discuss the origin of characteristic frequencies observed in the pressure signal at the launcher base. The influence of a propulsive jet on the evolution and topology of the wake flow is discussed in detail. The German Research Foundation DFG is gratefully acknowledged for funding this research within the SFB-TR40 ``Technological foundations for the design of thermally and mechanically highly loaded components of future space transportation systems.''

Multiepoch VLBI observations of 4C 39.25 - Superluminal motion amid stationary structure

NASA Technical Reports Server (NTRS)

Shaffer, David B.; Marscher, Alan P.; Marcaide, Jon; Romney, Jonathan D.

1987-01-01

Eight VLBI maps of the quasar 4C 39.25 are presented, covering the time interval November 1979 to July 1985. During this period the compact components at the eastern and western ends of the source remained roughly stationary with respect to each other. A third component emerged from the western component in 1982 and proceeded to move (relative to the other two components) eastward at a rate of 0.16 + or - 0.02 marcsec per year. This corresponds to an average apparent speed between 3.2c and 8.4c for Hubble's constant between 100 and 50 km/s Mpc and q0 between 1 and 0. This superluminal motion contrasts with the stationary structure observed in the 1970s and also still observed between the eastern and western ends of the source. Possible explanations include superluminal feeding of a stationary compact counterpart to a classical radio lobe, an obstacle in a relativistic jet, a relativistic jet which alternatively expands and contracts owing to gradients in the confining pressure, and gravitational lensing of the compact radio emission.

Revealing structure within the coronae of Seyfert galaxies

NASA Astrophysics Data System (ADS)

Wilkins, D.

2017-10-01

Detailed analysis of the reflection and reverberation of X-rays from the innermost regions of AGN accretion discs reveals the structure and processes that produce the intense continuum emission and the extreme variability we see, right down to the innermost stable orbit and event horizon of the black hole. Observations of Seyfert galaxies spanning more than a decade have enabled measurement of the geometry of the corona and how it evolves, leading to orders of magnitude of variability. They reveal processes the corona undergoes during transient events, notably the collimation and ejection of the corona during X-ray flares, reminiscent of the aborted launching of a jet. Recent reverberation studies, including those of the Seyfert galaxy I Zwicky 1 with XMM-Newton, are revealing structures within the corona for the first time. A persistent collimated core is found, akin to the base of a jet embedded in the innermost regions. The evolution of both the collimated and extended portions point to the mechanisms powering the X-ray emission and variability. This gives us important constraints on the processes by which energy is liberated from black hole accretion flows and by which jets are launched, allowing us to understand how these extreme objects are powered.

African Easterly Jet: Structure and Maintenance

NASA Technical Reports Server (NTRS)

Wu, Man-Li C.; Reale, Oreste; Schubert, Siegfried D.; Suarez, Max J.; Koster, Randy D.; Pegion, Philip J.

2009-01-01

This article investigates the African Easterly Jet (AEJ), its structure and the forcings contributing to its maintenance, critically revisiting previous work which attributed the maintenance of the jet to soil moisture gradients over tropical Africa. A state-of-the-art global model in a high-end computer framework is used to produce a 3-member 73-year ensemble run forced by observed SST to represent the Control run. The AEJ as produced by the Control is compared with the representation of the AEJ in the European Center for Medium Range Forecast Reanalyses (ERA-40) and other observational data sets and found very realistic. Five Experiments are then performed, each represented by sets of 3-member 22 year long (1980-2001) ensemble runs. The goal of the Experiments is to investigate the role of meridional soil moisture gradients, different land surface properties and orography. Unlike previous studies, which have suppressed soil moisture gradients within a highly idealized framework (i.e., the so-called bucket model), terrestrial evaporation control is here achieved with a highly sophisticated landsurface treatment and with an extensively tested and complex methodology. The results show that the AEJ is suppressed by a combination of absence of meridional evaporation gradients over Africa and constant vegetation, even if the individual forcings taken separately do not lead to the AEJ disappearance, but only its modification. Moreover, the suppression of orography also leads to a different circulation in which there is no AEJ. This work suggests that it is not just soil moisture gradients, but a unique combination of geographical features present only in northern tropical Africa, which causes and maintains the jet.

Formation of nocturnal low-level jets and structure of the nocturnal boundary layer in the Southern Great Plains

NASA Astrophysics Data System (ADS)

Klein, P. M.; Bonin, T. A.; Newman, J. F.; Wainwright, C. E.; Blumberg, W. G.; Turner, D. D.; Chilson, P. B.; Wharton, S.

2014-12-01

The Lower Atmospheric Boundary Layer Experiment (LABLE) included two measurement campaigns at the Atmospheric Radiation Measurement (ARM) Southern Great Plains site in Oklahoma in 2012 and 2013. Its main objective was to study turbulent phenomena in the lowest 2-km of the atmosphere using a variety of novel atmospheric profiling techniques including a sodar, multiple Doppler wind lidars (DWL), a Raman lidar and an atmospheric emitted radiance interferometer (AERI). Several instruments from the University of Oklahoma and Lawrence Livermore National Laboratory were deployed to augment the suite of in-situ and remote sensing instruments at the ARM site. The complementary nature of the deployed instruments with respect to resolution and height coverage provides for a near-complete picture of the dynamic and thermodynamic structure of the atmospheric boundary layer. LABLE can be considered unique in that it was designed as a multi-phase, low-cost, and multi-agency collaboration. Graduate students served as principal investigators who took the lead in designing and conducting experiments aimed at examining boundary-layer processes. This presentation provides an overview of the LABLE experiments and a summary of important results. One focus area will be the dynamic and thermodynamic structure of the nocturnal boundary layer and the formation of nocturnal low-level jets. Such low-level jets were frequently observed during both LABLE campaigns and often interacted with mesoscale atmospheric disturbances such as frontal passages. The combination of high-resolution AERI temperature profiles with DWL mean wind and turbulence profiles provided new insights about the structure and evolution of low-level jets.

Nuclear Radio Jet from a Low-luminosity Active Galactic Nucleus in NGC 4258

NASA Astrophysics Data System (ADS)

Doi, Akihiro; Kohno, Kotaro; Nakanishi, Kouichiro; Kameno, Seiji; Inoue, Makoto; Hada, Kazuhiro; Sorai, Kazuo

2013-03-01

The nearby low-luminosity active galactic nucleus (LLAGN) NGC 4258 has a weak radio continuum component at the galactic center. We investigate its radio spectral properties on the basis of our new observations using the Nobeyama Millimeter Array at 100 GHz and archival data from the Very Large Array at 1.7-43 GHz and the James Clerk Maxwell telescope at 347 GHz. The NGC 4258 nuclear component exhibits (1) an intra-month variable and complicated spectral feature at 5-22 GHz and (2) a slightly inverted spectrum at 5-100 GHz (α ~ 0.3; F νvpropνα) in time-averaged flux densities, which are also apparent in the closest LLAGN M81. These similarities between NGC 4258 and M81 in radio spectral natures in addition to previously known core shift in their AU-scale jet structures produce evidence that the same mechanism drives their nuclei. We interpret the observed spectral property as the superposition of emission spectra originating at different locations with frequency-dependent opacity along the nuclear jet. Quantitative differences between NGC 4258 and M81 in terms of jet/counter jet ratio, radio loudness, and degree of core shift can be consistently understood by fairly relativistic speeds (Γ >~ 3) of jets and their quite different inclinations. The picture established from the two closest LLAGNs is useful for understanding the physical origin of unresolved and flat/inverted spectrum radio cores that are prevalently found in LLAGNs, including Sgr A*, with starved supermassive black holes in the present-day universe.

Solar Jets as Sources of Outflows, Heating and Waves

NASA Astrophysics Data System (ADS)

Nishizuka, N.

2013-05-01

Recent space solar observations of the Sun, such as Hinode and SDO, have revealed that magnetic reconnection is ubiquitous in the solar atmosphere, ranging from small scale reconnection (observed as nanoflares) to large scale one (observed as long duration flares or giant arcades). Especially recent Hinode observations has found various types of tiny chromospheric jets, such as chromospheric anemone jets, penumbral microjets and light bridge jets from sunspot umbra. It was also found that the corona is full of tiny X-ray jets. Often they are seen as helical spinning jets with Alfvenic waves in the corona. Sometimes they are seen as chromospheric jets with slow-mode magnetoacoustic waves and sometimes as unresolved jet-like events at the footpoint of recurrent outflows and waves at the edge of the active region. There is increasing evidence of magnetic reconnection in these tiny jets and its association with waves. The origin of outflows and waves is one of the issues concerning coronal heating and solar wind acceleration. To answer this question, we had a challenge to reproduce solar jets with laboratory plasma experiment and directly measured outflows and waves. As a result, we could find a propagating wave excited by magnetic reconnection, whose energy flux is 10% of the released magnetic energy. That is enough for solar wind acceleration and locally enough for coronal heating, consistent with numerical MHD simulations of solar jets. Here we would discuss recent observations with Hinode, theories and experimental results related to jets and waves by magnetic reconnection, and discuss possible implication to reconnection physics, coronal heating and solar wind acceleration.

Comparing different Ultraviolet Imaging Spectrograph (UVIS) occultation observations using modeling of water vapor jets

NASA Astrophysics Data System (ADS)

Portyankina, Ganna; Esposito, Larry W.; Hansen, Candice; Aye, Klaus-Michael

2016-10-01

Motivation: On March 11, 2016 the Cassini UVIS observed its 6th star occultation by Enceladus' plume. This observation was aimed to determine variability in the total gas flux from the Enceladus' southern polar region. The analysis of the received data suggests that the total gas flux is moderately increased comparing to the average gas flux observed by UVIS from 2005 to 2011 [1]. However, UVIS detected variability in individual jets. In particular, Baghdad 1 is more collimated in 2016 than in 2005, meaning its gas escapes at higher velocity.Model and fits: We use 3D DSMC model for water vapor jets to compare different UVIS occultation observations from 2005 to 2016. The model traces test articles from jets' sources [2] into space and results in coordinates and velocities for a set of test particles. We convert particle positions into the particle number density and integrate along UVIS line of sight (LoS) for each time step of the UVIS observation using precise observational geometry derived from SPICE [3]. We integrate all jets that are crossed by the LoS and perform constrained least-squares fit of resulting modeled opacities to the observed data to solved for relative strengths of jets. The geometry of each occultation is specific, for example, during solar occultation in 2010 UVIS LoS was almost parallel to tiger stripes, which made it possible to distinguish jets venting from different tiger stripes. In 2011 Eps Orionis occultation LoS was perpendicular to tiger stripes and thus many of the jets were geometrically overlapping. Solar occultation provided us with the largest inventory of active jets - our model fit detects at least 43 non-zero jet contributions. Stellar occultations generally have lower temporal resolution and observe only a sub-set of these jets: 2011 Eps Orionis needs minimum 25 non-zero jets to fit UVIS data. We will discuss different occultations and models fits, including the most recent Epsilon Orionis occultation of 2016.[1] Hansen et al., DPS 48, 2016 [2] Porco et al. 2014 The Astronomical Journal 148, 4 [3] Acton, C.H., 1996 PSS 44, 65-70

Modification of jet-like correlations in Pb-Au collisions at 158A GeV/c

NASA Astrophysics Data System (ADS)

Ceres Collaboration; Adamová, D.; Agakichiev, G.; Antończyk, D.; Appelshäuser, H.; Belaga, V.; Bielčíková, J.; Braun-Munzinger, P.; Busch, O.; Cherlin, A.; Damjanović, S.; Dietel, T.; Dietrich, L.; Drees, A.; Dubitzky, W.; Esumi, S. I.; Filimonov, K.; Fomenko, K.; Fraenkel, Z.; Garabatos, C.; Glässel, P.; Holeczek, J.; Kalisky, M.; Kniege, S.; Kushpil, V.; Maas, A.; Marín, A.; Milošević, J.; Milov, A.; Miśkowiec, D.; Panebrattsev, Yu.; Petchenova, O.; Petráček, V.; Pfeiffer, A.; Płoskoń, M.; Rak, J.; Ravinovich, I.; Rehak, P.; Sako, H.; Schmitz, W.; Schuchmann, S.; Sedykh, S.; Shimansky, S.; Stachel, J.; Šumbera, M.; Tilsner, H.; Tserruya, I.; Wessels, J. P.; Wienold, T.; Wurm, J. P.; Xie, W.; Yurevich, S.; Yurevich, V.

2009-07-01

Results of a two-particle correlation analysis of high-p charged particles in Pb-Au collisions at 158A GeV/c are presented. The data have been recorded by the CERES experiment at the CERN-SPS. The correlations are studied as function of transverse momentum, particle charge and collision centrality. We observe a jet-like structure in the vicinity of a high-p trigger particle and a broad back-to-back distribution. The yields of associated particles per trigger show a strong dependence on the trigger/associate charge combination. A comparison to PYTHIA confirms the jet-like pattern at the near-side but suggests a strong modification at the away-side, implying significant energy transfer of the hard-scattered parton to the medium.

The structure and dynamics of barrier jets along the southeast Alaskan coast

NASA Astrophysics Data System (ADS)

Olson, Joseph Benjamin

Coastal barrier jets along the complex orography of southeastern Alaska were investigated using high resolution observations and model simulations. Barrier jet events were sampled with the Wyoming King-Air research aircraft during the Southeastern Alaskan Regional Jet (SARJET) field experiment in 2004. These observations, combined with simulations of select cases by the Penn State-NCAR Mesoscale Model (MM5), were used to better understand barrier jet structure and dynamics. A suite of idealized simulations were used to put the case studies in perspective with a larger set of atmospheric conditions, while also evaluating previous theoretical and observational results. Two SARJET case studies were investigated along the tall and steep Fairweather Mountains near Juneau, Alaska. The first case (24 September 2004) was a classical barrier jet forced primarily by onshore flow and upslope adiabatic cooling, with maximum winds >30 m s-1 at the coast between 600-800 m ASL and an offshore extent of ˜60 km. In contrast, the hybrid jet (12 October 2004) was influenced by an offshore-directed gap flow at the coast, which produced a warm anomaly over the coast associated with downslope flow and a wind maximum (˜30 m s-1) that was displaced 30-40 km offshore at 500 m ASL. A sensitivity experiment in which the coastal mountain gap was filled led to a ˜40% reduction in the jet width, and the position of the jet maximum shifted ˜40 km to the coast, but the overall jet intensity remained approximately the same. The generality of these SARJET results was tested by generating a set of three-dimensional idealized MM5 simulations by varying wind speeds, wind directions, and static stabilities for the classical jet simulations, while incrementing the magnitude of the inland cold pool (instead of static stability) for hybrid jet simulations. The broad inland terrain was shown to impact the upstream winds by rotating them cyclonically to become more terrain-parallel within 500-1000 km of the coast. This reduced cross-barrier component acted to reduce the local Froude number of the impinging flow, thus enhancing the potential for flow blocking. Thus, the enhancement of the large-scale mountain anticyclone by the inland terrain acts to "precondition" the impinging flow for barrier jet development. The largest simulated wind speed enhancements (˜1.9-2.0) for the classic and hybrid jets occurred for low Froude numbers ( Fr), with a maximum at Fr ˜0.3-0.4. Low ambient wind speeds (10--15 m s-1) and southerly (170-180°) wind directions (˜30-45° from coast-parallel) were also ingredients for the largest wind speed enhancements. The widest barrier jets were found in simulations with ambient winds oriented nearly terrain-parallel (˜160°) with strong static stability (N > 0.01 s-1). Hybrid barrier jets were slightly wider than the classical, with the gap outflows acting to shift the position of the jet maximum further away from the coast. During periods of maximal gap outflow (hrs 6-18), the height of the jet maximums were typically lower than the classical simulations, since the hybrid jet maximum was located at the top of the shallow gap outflow. The jet height was most correlated with total wind speed, Utotal, and negatively correlated with static stability, N, suggesting that the height of the jet maximum approximately scales as U total/N, which is proportional to the vertical wavelength of a mountain wave. Finally, a detailed assessment of the usefulness of the previous linear theory and scale analysis on barrier jets was performed. The high Fr relationship (L = Nhm/ f) performed better than the low Fr relationship (L = Un/f) in determining the offshore extent of the barrier jet. The implementation of the dividing streamline concept of Sheppard's model for determining the proper blocking height (hd) resulted in a modified form (L = Nhd/ f), which improved the predictive skill. For the determination of maximum wind speeds, the high Fr relationship (DeltaV = Nhm) was found to be better correlated with the measured values than the low Fr relationship ( DeltaV = Un) throughout the full range of Fr. Two-dimensional linear theory performed poorly for Fr < 0.5. Modifications were made to these previous relationships to better account for the three dimensional winds, which helped to improve the estimated wind speed enhancements.

Experimental and theoretical study of combustion jet ignition

NASA Technical Reports Server (NTRS)

Chen, D. Y.; Ghoniem, A. F.; Oppenheim, A. K.

1983-01-01

A combustion jet ignition system was developed to generate turbulent jets of combustion products containing free radicals and to discharge them as ignition sources into a combustible medium. In order to understand the ignition and the inflammation processes caused by combustion jets, the studies of the fluid mechanical properties of turbulent jets with and without combustion were conducted theoretically and experimentally. Experiments using a specially designed igniter, with a prechamber to build up and control the stagnation pressure upstream of the orifice, were conducted to investigate the formation processes of turbulent jets of combustion products. The penetration speed of combustion jets has been found to be constant initially and then decreases monotonically as turbulent jets of combustion products travel closer to the wall. This initial penetration speed to combustion jets is proportional to the initial stagnation pressure upstream of the orifice for the same stoichiometric mixture. Computer simulations by Chorin's Random Vortex Method implemented with the flame propagation algorithm for the theoretical model of turbulent jets with and without combustion were performed to study the turbulent jet flow field. In the formation processes of the turbulent jets, the large-scale eddy structure of turbulence, the so-called coherent structure, dominates the entrainment and mixing processes. The large-scale eddy structure of turbulent jets in this study is constructed by a series of vortex pairs, which are organized in the form of a staggered array of vortex clouds generating local recirculation flow patterns.

A Numerical Model of Hercules A by Magnetic Tower

NASA Astrophysics Data System (ADS)

Nakamura, Masanori; Tregillis, I. L.; Li, H.; Li, S.

2009-01-01

We apply magnetohydrodynamic (MHD) modeling to the radio galaxy Hercules A for investigating the jet-driven shock, jet/lobe transition, wiggling, and magnetic field distribution associated with this source. The model consists of magnetic tower jets in a galaxy cluster environment. The profile of underlying ambient gas plays an important role in jet-lobe morphology. The balance between the magnetic pressure generated by axial current and the ambient gas pressure can determine the lobe radius. The jet body is confined jointly by the external pressure and gravity inside the cluster core radius, while outside this radius it expands radially to form fat lobes in a steeply decreasing ambient thermal pressure gradient. The current-carrying jets are responsible for generating a strong, tightly wound helical magnetic field. This magnetic configuration will be unstable against the current-driven kink mode and it visibly grows beyond the cluster core radius where a separation between the jet forward and return currents occurs. The reversed pinch profile of global magnetic field associated with the jet and lobes produces projected magnetic-vector distributions aligned with the jet flow and the lobe edge. AGN-driven shock powered by the expanding magnetic tower jet surrounds the jet/lobe structure and heats the ambient ICM. The lobes expand subsonically; no obvious hot spots are produced at the heads of lobes. Several key features in our MHD modeling may be qualitatively supported by the observations of Hercules A. This work was carried out under the auspices of the National Nuclear Security Administration of the U.S. Department of Energy at Los Alamos National Laboratory under Contract No. DE-AC52-06NA25396. It was supported by the Laboratory Directed Research and Development Program at LANL and by IGPP at LANL.

Selforganized Structure Formation in Organized Microstructuring by Laser-Jet Etching

NASA Astrophysics Data System (ADS)

Rabbow, T. J.; Plath, P. J.; Mora, A.; Haase, M.

Laser-jet induced wet etching of stainless steel in 5M H3PO4 has been investigated. By this method, it is possible to cut and microstructure metals and alloys that form passive layers in strong etchants. Due to the laser heating of the metal and the adjacent layers of the etchant, the passive layer is removed and an active dissolution of the base metal together with the formation of hydrogen is observed. The reactions are limited by the transport of fresh acid and the removal of dissolved metal. A jet of etchant reduces the transport limitations. For definite ranges of the laser power, the feed velocity and the etchant jet velocity, a regime of periodic structure formation of the kerf, often called ripples, has been found. The ripple length depends on all three parameters. The ripple formation can be brought into correlation with a periodic change of the intensity of the reflected light as well as oscillations of the potential workpiece. It could be shown that the periodic structure formation is connected to a spreading of an etching front from the laser activated area, that temporarily moves ahead to the laser. This leads to modulations of the interface for the laser absorption, which results, for example, in oscillations of the intensity of the reflected light. This means the laser induced etching reaction attracts a feedback based on the conditions of absorption for the laser. For those parameters of feed velocity, laser power and etchant jet velocity, without ripple formation the laser induced etching front is of a constant distance to the laser which results in steady conditions at the interface for the absorption of the laser.

On the start up of supersonic underexpanded jets

NASA Astrophysics Data System (ADS)

Lacerda, Nehemias Lima

An impulsively started jet can be formed by a gas confined in a high pressure reservoir that escapes suddenly through an exit orifice, into a controlled atmosphere. Supersonic gas jets of this type are unsteady and differ from the steady jet that develops later by the presence of a bow shock, a jet head and a nonstationary Mach disk. The effects of the pressure ratio between the high pressure gas inside the reservoir and the lower pressure atmospheric gas, as well as the gas combination used, are studied experimentally. The gases used for the jet and the atmosphere were selected from helium, nitrogen and sulfur hexafluoride. The data acquisition consisted of: high resolution flash photography to obtain detail from the pictures; high-speed movie pictures to obtain the time development of selected features; and fast-response pressure transducers located at the reservoir end plate, the tank end plate and the jet exit. The initial development of the jet is highly time dependent. During this phase, the shape that the jet assumes varies with pressure ratio and with the choice of gas. In particular an extremely light gas exhausting into a heavy atmosphere, exhibits an uncommon shape. It develops as a bubble wrapped by the bow shock, that increases its volume with flow time and pressure ratio. As the pressure ratio increases, it becomes more tightly wrapped by the bow shock. At later times the jet assumes conventional linear growth. After the jet starts, a Mach disk is observed close to the jet exit which moves downstream as the exit pressure builds up. The monotonic increase in exit pressure is caused by the slow breaking of the diaphragm. The position of the Mach disk is furthest from the jet exit when the exit pressure is a maximum. After that it oscillates around the location predicted by the steady theory of Ashkenas and Sherman (1966) at a frequency close to one of the resonant frequencies of the reservoir. The features observed for the inner structure of the jet were verified to agree with those obtained for impulsive flow generated by a muzzle blast. The frontal part of the jet forms the jet head, whose shape changes with the flow conditions. The initial evolution of the jet head is linear but after propagating a distance of around ten exit diameters, it reaches asymptotic behavior with an evolution that is approximately proportional to square root of time. The head creates a bow shock ahead of it that propagates downstream and increases the pressure of the atmospheric gas. This bow shock was found to be less attenuated than in spherically symmetric explosions. The asymptotic behavior of the bow shock was reached after about eight exit diameters.

Parsec-Scale Kinematic and Polarization Properties of MOJAVE AGN Jets

NASA Astrophysics Data System (ADS)

Lister, Matthew L.

2013-12-01

We describe the parsec-scale kinematics and statistical polarization properties of 200 AGN jets based on 15 GHz VLBA data obtained between 1994 Aug 31 and 2011 May 1. Nearly all of the 60 most heavily observed jets show significant changes in their innermost position angle over a 12 to 16 year interval, ranging from 10° to 150° on the sky, corresponding to intrinsic variations of ~ 0.5° to ~ 2°. The BL Lac jets show smaller variations than quasars. Roughly half of the heavily observed jets show systematic position angle trends with time, and 20 show indications of oscillatory behavior. The time spans of the data sets are too short compared to the fitted periods (5 to 12 y), however, to reliably establish periodicity. The rapid changes and large jumps in position angle seen in many cases suggest that the superluminal AGN jet features occupy only a portion of the entire jet cross section, and may be energized portions of thin instability structures within the jet. We have derived vector proper motions for 887 moving features in 200 jets having at least five VLBA epochs. For 557 well-sampled features, there are sufficient data to additionally study possible accelerations. The moving features are generally non-ballistic, with 70% of the well-sampled features showing either significant accelerations or non-radial motions. Inward motions are rare (2% of all features), are slow (< 0.1 mas per y), are more prevalent in BL Lac jets, and are typically found within 1 mas of the unresolved core feature. There is a general trend of increasing apparent speed with distance down the jet for both radio galaxies and BL Lac objects. In most jets, the speeds of the features cluster around a characteristic value, yet there is a considerable dispersion in the distribution. Orientation variations within the jet cannot fully account for the dispersion, implying that the features have a range of Lorentz factor and/or pattern speed. Very slow pattern speed features are rare, comprising only 4% of the sample, and are more prevalent in radio galaxy and BL Lac jets. We confirm a previously reported upper envelope to the distribution of speed versus beamed luminosity for moving jet features. Below 1026 W Hz-1 there is a fall-off in maximum speed with decreasing 15 GHz radio luminosity. A preliminary analysis of the multi-epoch jet polarization properties indicates a wide range of behavior in the core electric vector position angles over time, with the latter remaining relatively stable in some jets, and varying rapidly in others. The fractional polarization level generally increases down the jet, and high-synchrotron peaked (HSP) blazars tend to have lower core fractional polarization levels. A general trend of decreasing maximum jet speed for higher synchrotron peaked blazars further suggests lower Doppler factors in the radio-emitting jets of HSP BL Lac objects.

On Three-dimensional Structures in Relativistic Hydrodynamic Jets

NASA Astrophysics Data System (ADS)

Hardee, Philip E.

2000-04-01

The appearance of wavelike helical structures on steady relativistic jets is studied using a normal mode analysis of the linearized fluid equations. Helical structures produced by the normal modes scale relative to the resonant (most unstable) wavelength and not with the absolute wavelength. The resonant wavelength of the normal modes can be less than the jet radius even on highly relativistic jets. High-pressure regions helically twisted around the jet beam may be confined close to the jet surface, penetrate deeply into the jet interior, or be confined to the jet interior. The high-pressure regions range from thin and ribbon-like to thick and tubelike depending on the mode and wavelength. The wave speeds can be significantly different at different wavelengths but are less than the flow speed. The highest wave speed for the jets studied has a Lorentz factor somewhat more than half that of the underlying flow speed. A maximum pressure fluctuation criterion found through comparison between theory and a set of relativistic axisymmetric jet simulations is applied to estimate the maximum amplitudes of the helical, elliptical, and triangular normal modes. Transverse velocity fluctuations for these asymmetric modes are up to twice the amplitude of those associated with the axisymmetric pinch mode. The maximum amplitude of jet distortions and the accompanying velocity fluctuations at, for example, the resonant wavelength decreases as the Lorentz factor increases. Long-wavelength helical surface mode and shorter wavelength helical first body mode generated structures should be the most significant. Emission from high-pressure regions as they twist around the jet beam can vary significantly as a result of angular variation in the flow direction associated with normal mode structures if they are viewed at about the beaming angle θ=1/γ. Variation in the Doppler boost factor can lead to brightness asymmetries by factors up to 6 as long-wavelength helical structure produced by the helical surface mode winds around the jet. Higher order surface modes and first body modes produce less variation. Angular variation in the flow direction associated with the helical mode appears consistent with precessing jet models that have been proposed to explain the variability in 3C 273 and BL Lac object AO 0235+164. In particular, cyclic angular variation in the flow direction produced by the normal modes could produce the activity seen in BL Lac object OJ 287. Jet precession provides a mechanism for triggering the helical modes on multiple length scales, e.g., the galactic superluminal GRO J1655-40.

An X-Ray Imaging Survey of Quasar Jets: The Complete Survey

NASA Astrophysics Data System (ADS)

Marshall, H. L.; Gelbord, J. M.; Worrall, D. M.; Birkinshaw, M.; Schwartz, D. A.; Jauncey, D. L.; Griffiths, G.; Murphy, D. W.; Lovell, J. E. J.; Perlman, E. S.; Godfrey, L.

2018-03-01

We present Chandra X-ray imaging of a flux-limited sample of flat spectrum radio-emitting quasars with jet-like structure. X-rays are detected from 59% of 56 jets. No counter-jets were detected. The core spectra are fitted by power-law spectra with a photon index Γ x , whose distribution is consistent with a normal distribution, with a mean of 1.61+0.04 ‑0.05 and dispersion of 0.15+0.04 ‑0.03. We show that the distribution of α rx , the spectral index between the X-ray and radio band jet fluxes, fits a Gaussian with a mean of 0.974 ± 0.012 and dispersion of 0.077 ± 0.008. We test the model in which kiloparsec-scale X-rays result from inverse Compton scattering of cosmic microwave background photons off the jet’s relativistic electrons (the IC-CMB model). In the IC-CMB model, a quantity Q computed from observed fluxes and the apparent size of the emission region depends on redshift as (1 + z)3+α . We fit Q ∝ (1 + z) a , finding a = 0.88 ± 0.90, and reject at 99.5% confidence the hypothesis that the average α rx depends on redshift in the manner expected in the IC-CMB model. This conclusion is mitigated by a lack of detailed knowledge of the emission region geometry, which requires deeper or higher resolution X-ray observations. Furthermore, if the IC-CMB model is valid for X-ray emission from kiloparsec-scale jets, then the jets must decelerate on average: bulk Lorentz factors should drop from about 15 to 2–3 between parsec and kiloparsec scales. Our results compound the problems that the IC-CMB model has in explaining the X-ray emission of kiloparsec-scale jets.

Plasma flow patterns in and around magnetosheath jets

NASA Astrophysics Data System (ADS)

Plaschke, Ferdinand; Hietala, Heli

2018-05-01

The magnetosheath is commonly permeated by localized high-speed jets downstream of the quasi-parallel bow shock. These jets are much faster than the ambient magnetosheath plasma, thus raising the question of how that latter plasma reacts to incoming jets. We have performed a statistical analysis based on 662 cases of one THEMIS spacecraft observing a jet and another (second) THEMIS spacecraft providing context observations of nearby plasma to uncover the flow patterns in and around jets. The following results are found: along the jet's path, slower plasma is accelerated and pushed aside ahead of the fastest core jet plasma. Behind the jet core, plasma flows into the path to fill the wake. This evasive plasma motion affects the ambient magnetosheath, close to the jet's path. Diverging and converging plasma flows ahead and behind the jet are complemented by plasma flows opposite to the jet's propagation direction, in the vicinity of the jet. This vortical plasma motion results in a deceleration of ambient plasma when a jet passes nearby.

Observational Evidence for the Causes and Consequences of Chromospheric Reconnection

NASA Astrophysics Data System (ADS)

Yan, Limei; He, Jiansen; Xia, Lidong; Jiao, Fangran

2015-05-01

The chromospheric anemone jets with an inverse “Y” shape are ubiquitous, as revealed by the Solar Optical Telescope observations. These jets are considered to be consequences of chromospheric magnetic reconnections. Although these jets have been studied intensively, the dynamics and their driving causes remain unclear observationally. In this work, we report a case of a chromospheric jet showing complete observational evidence for the cause and consequence of chromospheric intermittent reconnection. The intermittent eruption of this jet shows two distinct quasi-periods, 50-60 s and 600-700 s. The short-period eruptions may be related to the plasmoid-induced reconnection, and the long-period ones may be interpreted as sequences of cycles of energy storage and release during magnetic reconnections. The observations also reveal Alfvénic waves with a mean period around 88 s and a maximum transverse displacement around 0.″26. The jet is hosted by a loop moving smoothly with a horizontal speed of ˜0.4 km s-1. Our results provide observational evidence supporting the magnetic reconnection model of the formation of the chromospheric jets with related products, in which the loop advection drives intermittent magnetic reconnections, and the reconnection outflows carrying plasmoids collide further with the ambient field lines and finally excite waves and jets.

MMS Observations of Large Guide Field Symmetric Reconnection Between Colliding Reconnection Jets at the Center of a Magnetic Flux Rope at the Magnetopause

NASA Technical Reports Server (NTRS)

Oieroset, M.; Phan, T. D.; Haggerty, C.; Shay, M. A.; Eastwood, J. P.; Gershman, D. J.; Drake, J. F.; Fujimoto, M.; Ergun, R. E.; Mozer, F. S.;

MMS observations of large guide field symmetric reconnection between colliding reconnection jets at the center of a magnetic flux rope at the magnetopause

NASA Astrophysics Data System (ADS)

Øieroset, M.; Phan, T. D.; Haggerty, C.; Shay, M. A.; Eastwood, J. P.; Gershman, D. J.; Drake, J. F.; Fujimoto, M.; Ergun, R. E.; Mozer, F. S.; Oka, M.; Torbert, R. B.; Burch, J. L.; Wang, S.; Chen, L. J.; Swisdak, M.; Pollock, C.; Dorelli, J. C.; Fuselier, S. A.; Lavraud, B.; Giles, B. L.; Moore, T. E.; Saito, Y.; Avanov, L. A.; Paterson, W.; Strangeway, R. J.; Russell, C. T.; Khotyaintsev, Y.; Lindqvist, P. A.; Malakit, K.

2016-06-01

We report evidence for reconnection between colliding reconnection jets in a compressed current sheet at the center of a magnetic flux rope at Earth's magnetopause. The reconnection involved nearly symmetric inflow boundary conditions with a strong guide field of two. The thin (2.5 ion-skin depth (di) width) current sheet (at ~12 di downstream of the X line) was well resolved by MMS, which revealed large asymmetries in plasma and field structures in the exhaust. Ion perpendicular heating, electron parallel heating, and density compression occurred on one side of the exhaust, while ion parallel heating and density depression were shifted to the other side. The normal electric field and double out-of-plane (bifurcated) currents spanned almost the entire exhaust. These observations are in good agreement with a kinetic simulation for similar boundary conditions, demonstrating in new detail that the structure of large guide field symmetric reconnection is distinctly different from antiparallel reconnection.

MMS observations of large guide field symmetric reconnection between colliding reconnection jets at the center of a magnetic flux rope at the magnetopause

NASA Astrophysics Data System (ADS)

Oieroset, M.; Phan, T.; Haggerty, C. C.; Shay, M. A.; Eastwood, J. P.; Gershman, D. J.; Drake, J. F.; Fujimoto, M.; Ergun, R.; Mozer, F.; Oka, M.; Torbert, R. B.; Burch, J. L.; Wang, S.; Chen, L. J.; Swisdak, M.; Pollock, C.; Dorelli, J.; Fuselier, S. A.; Lavraud, B.; Giles, B. L.; Moore, T. E.; Saito, Y.; Avanov, L. A.; Paterson, W. R.; Strangeway, R. J.; Russell, C. T.; Khotyaintsev, Y. V.; Lindqvist, P. A.; Malakit, K.

2016-12-01

We report evidence for reconnection between colliding reconnection jets in a compressed current sheet at the center of a magnetic flux rope at Earth's magnetopause. The reconnection involved nearly symmetric inflow boundary conditions with a strong guide field of two. The thin (2.5 ion-skin depth (di) width) current sheet (at 12 di downstream of the X line) was well resolved by Magnetospheric Multiscale, which revealed large asymmetries in plasma and field structures in the exhaust. Ion perpendicular heating, electron parallel heating, and density compression occurred on one side of the exhaust, while ion parallel heating and density depression were shifted to the other side. The normal electric field and double out-of-plane (bifurcated) currents spanned almost the entire exhaust. These observations are in good agreement with a kinetic simulation for similar boundary conditions, demonstrating in new detail that the structure of large guide field symmetric reconnection is distinctly different from antiparallel reconnection.

FOUR DUAL AGN CANDIDATES OBSERVED WITH THE VLBA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gabányi, K. É.; Frey, S.; An, T.

According to hierarchical structure formation models, merging galaxies are expected to be seen in different stages of coalescence. However, there are currently no straightforward observational methods to either select or to confirm a large number of dual active galactic nucleus (AGN) candidates. Most attempts involve obtaining a better understanding of double-peaked narrow emission line sources, in order to distinguish the objects for which the emission lines originate from narrow-line kinematics or jet-driven outflows, from those which might harbor dual AGNs. We observed four such candidate sources with the Very Long Baseline Array (VLBA), at 1.5 GHz with a ∼10 masmore » angular resolution, for which the spectral profiles of AGN optical emission suggested the existence of dual AGNs. In SDSS J210449.13–000919.1 and SDSS J23044.82–093345.3 the radio structures are aligned with the optical emission features, thus the double-peaked emission lines might be the results of jet-driven outflows. In the third detected source SDSS J115523.74+150756.9, the radio structure is less extended and is oriented nearly perpendicular to the position angle derived from optical spectroscopy. The fourth source remained undetected with the VLBA, but it was imaged with the Very Large Array at arcsec resolution a few months before our observations, suggesting the existence of an extended radio structure. We did not detect two radio-emitting cores in any of the four sources, a convincing signature of duality.« less

Magnetospheric Multiscale Observations of an Ion Diffusion Region With Large Guide Field at the Magnetopause: Current System, Electron Heating, and Plasma Waves

NASA Astrophysics Data System (ADS)

Zhou, M.; Berchem, J.; Walker, R. J.; El-Alaoui, M.; Goldstein, M. L.; Lapenta, G.; Deng, X.; Li, J.; Le Contel, O.; Graham, D. B.; Lavraud, B.; Paterson, W. R.; Giles, B. L.; Burch, J. L.; Torbert, R. B.; Russell, C. T.; Strangeway, R. J.; Zhao, C.; Ergun, R. E.; Lindqvist, P.-A.; Marklund, G.

2018-03-01

We report Magnetospheric Multiscale (MMS) observations of a reconnecting current sheet in the presence of a weak density asymmetry with large guide field at the dayside magnetopause. An ion diffusion region (IDR) was detected associated with this current sheet. Parallel current dominated over the perpendicular current in the IDR, as found in previous studies of component reconnection. Electrons were preferentially heated parallel to the magnetic field within the IDR. The heating was manifested as a flattop distribution below 400 eV. Two types of electromagnetic electron whistler waves were observed within the regions where electrons were heated. One type of whistler wave was associated with nonlinear structures in E|| with amplitudes up to 20 mV/m. The other type was not associated with any structures in E||. Poynting fluxes of these two types of whistler waves were directed away from the X-line. We suggest that the nonlinear evolution of the oblique whistler waves gave rise to the solitary structures in E||. There was a perpendicular super-Alfvénic outflow jet that was carried by magnetized electrons. Intense electrostatic lower hybrid drift waves were localized in the current sheet center and were probably driven by the super-Alfvénic electron jet, the velocity of which was approximately equal to the diamagnetic drift of demagnetized ions. Our observations suggest that the guide field significantly modified the structures (Hall electromagnetic fields and current system) and wave properties in the IDR.

On the jet of a young star RWAurA and related problems

NASA Astrophysics Data System (ADS)

Berdnikov, L. N.; Burlak, M. A.; Vozyakova, O. V.; Dodin, A. V.; Lamzin, S. A.; Tatarnikov, A. M.

2017-07-01

Having compared images of a jet of the young star RWAurA obtained with an interval of 21.3 yr, we have found that the outermost knots of the jet have emerged approximately 350 years ago. We come up with arguments that the jet itself has appeared at the same time, and intensive accretion onto the star has begun due to rearrangement of its protoplanetary disk structure caused by the tidal effect of the companion RWAur B. More precisely suppose that intensification of accretion is a response to changing conditions in the outer-disk regions which has followed after the sound wave, generated by these changes, has passed the disk in the radial direction. In our opinion difference in the parameters of blue and red lobes of the RWAurA jet is a result of the asymmetric distribution of the circumstellar matter above and below the disk due to companion's passage. It was found from the analysis of the RWAur historical light curve that deep and long-term (Δ t > 150 days) light attenuations of RWAurA observed after 2010 had no precedents in the previous 110 years.We also associate the change in the character of photometric variability of the star with the rearrangement of the structure of inner ( r < 1 AU) regions of its protoplanetary disk, and discuss why these changes have begun only 350 years after the beginning of the active accretion phase.

Proto-jet configurations in RADs orbiting a Kerr SMBH: symmetries and limiting surfaces

NASA Astrophysics Data System (ADS)

Pugliese, D.; Stuchlík, Z.

2018-05-01

Ringed accretion disks (RADs) are agglomerations of perfect-fluid tori orbiting around a single central attractor that could arise during complex matter inflows in active galactic nuclei. We focus our analysis to axi-symmetric accretion tori orbiting in the equatorial plane of a supermassive Kerr black hole; equilibrium configurations, possible instabilities, and evolutionary sequences of RADs were discussed in our previous works. In the present work we discuss special instabilities related to open equipotential surfaces governing the material funnels emerging at various regions of the RADs, being located between two or more individual toroidal configurations of the agglomerate. These open structures could be associated to proto-jets. Boundary limiting surfaces are highlighted, connecting the emergency of the jet-like instabilities with the black hole dimensionless spin. These instabilities are observationally significant for active galactic nuclei, being related to outflows of matter in jets emerging from more than one torus of RADs orbiting around supermassive black holes.

Investigation of Cooling Water Injection into Supersonic Rocket Engine Exhaust

NASA Astrophysics Data System (ADS)

Jones, Hansen; Jeansonne, Christopher; Menon, Shyam

2017-11-01

Water spray cooling of the exhaust plume from a rocket undergoing static testing is critical in preventing thermal wear of the test stand structure, and suppressing the acoustic noise signature. A scaled test facility has been developed that utilizes non-intrusive diagnostic techniques including Focusing Color Schlieren (FCS) and Phase Doppler Particle Anemometry (PDPA) to examine the interaction of a pressure-fed water jet with a supersonic flow of compressed air. FCS is used to visually assess the interaction of the water jet with the strong density gradients in the supersonic air flow. PDPA is used in conjunction to gain statistical information regarding water droplet size and velocity as the jet is broken up. Measurement results, along with numerical simulations and jet penetration models are used to explain the observed phenomena. Following the cold flow testing campaign a scaled hybrid rocket engine will be constructed to continue tests in a combusting flow environment similar to that generated by the rocket engines tested at NASA facilities. LaSPACE.

Jet and Vortex Projectile Flows in Shock/bubble-on-wall Configuration

NASA Astrophysics Data System (ADS)

Peng, Gaozhu; Zabusky, Norman

2001-11-01

We observe intense coaxial upstream and radial flow structures from a shock in air interacting with a SF6 half-bubble placed against an ideally reflecting wall. Our axisymmetric numerical simulations were done with PPM and models a spherical bubble struck symmetrically by two identical approaching shocks . A "dual" vorticity deposition arises at early time and a coaxial upstream moving primary jet and radial vortex ring flow appears. A coherent vortex ring or vortex projectile (VP), with entrained shocklets originates from the vortex layer produced at the Mach stem (which arises from the primary reflected shock). This VP moves ahead of the jet. The original transmitted wave and other trapped waves in the expanding axial jet causes a collapsing and expanding cavity and other instabilities on the complex bubble interface. We present and analyze our results with different diagnostics: vorticity, density, divergence of velocity, and numerical shadowgraph patterns; global quantification of circulation, enstrophy and r-integrated vorticity; etc. We also discuss data projection and filtering for quantifying and validating complex flows.

First observations of Gigantic Jets from Monsoon Thunderstorms over India

NASA Astrophysics Data System (ADS)

Singh, Rajesh; Maurya, Ajeet; Chanrion, Olivier; Neubert, Torsten; Cummer, Steven; Mlynarczyk, Janusz; Bór, József; Siingh, Devendraa; Cohen, Morris; Kumar, Sushil

2016-04-01

Gigantic Jets are electric discharges from thunderstorm cloud tops to the bottom of the ionosphere at ~80 km altitude. After their first discovery in 2001, relatively few observations have been reported. Most of these are from satellites at large distances and a few tens from the ground at higher spatial resolution. Here we report the first Gigantic Jets observed in India from two thunderstorm systems that developed over the land surface from monsoon activity, each storm producing two Gigantic Jets. The jets were recorded by a video camera system at standard video rate (20 ms exposure) at a few hundred km distance. ELF measurements suggest that the jets are of the usual negative polarity and that they develop in less than 40 ms, which is faster than most jets reported in the past. The jets originate from the leading edge of a slowly drifting convective cloud complex close to the highest regions of the clouds and carry ~25 Coulomb of charge to the ionosphere. One jet has a markedly horizontal displacement that we suggest is caused by a combination of close-range cloud electric fields at inception, and longer-range cloud fields at larger distances during full development. The Gigantic Jets are amongst the few that have been observed over land.

Pitched and Yawed Circular Jets in Cross-Flow

NASA Technical Reports Server (NTRS)

Milanovic, Ivana M.; Zaman, K. B. M. Q.; Reddy, D. R. (Technical Monitor)

2002-01-01

Results from an experimental investigation of flow field generated by pitched and yawed jets discharging from a flat plate into a cross-flow are presented. The circular jet was pitched at alpha = 20 degrees and 45 degrees and yawed between beta = 0 degrees and 90 degrees in increments of 15 degrees. The measurements were performed with two X-wires providing all three components of velocity and turbulence intensity. These data were obtained at downstream locations of x = 3, 5, 10 and 20, where the distance x normalized by the jet diameter, is measured from the center of the orifice. Data for all configurations were acquired at a momentum-flux ratio J = 8. Additionally, for selected angles and locations, surveys were conducted for J = 1.5, 4, and 20. As expected, the jet penetration is found to be higher at larger alpha. With increasing beta the jet spreads more. The rate of reduction of peak streamwise vorticity, with the downstream distance is significantly lessened at higher alpha but is found to be practically independent of alpha. Thus, at the farthest measurement station x = 20, omega(sub xmax) is about five times larger for beta = 0 degrees compared to the levels at beta = 0 degrees. Streamwise velocity within the jet-vortex structure is found to depend on the parameter J. At J = 1.5 and 4, 'wake-like' velocity profiles are observed. In comparison, a 'jet-like' overshoot is present at higher J.

Wave Number Selection for Incompressible Parallel Jet Flows Periodic in Space

NASA Technical Reports Server (NTRS)

Miles, Jeffrey Hilton

1997-01-01

The temporal instability of a spatially periodic parallel flow of an incompressible inviscid fluid for various jet velocity profiles is studied numerically using Floquet Analysis. The transition matrix at the end of a period is evaluated by direct numerical integration. For verification, a method based on approximating a continuous function by a series of step functions was used. Unstable solutions were found only over a limited range of wave numbers and have a band type structure. The results obtained are analogous to the behavior observed in systems exhibiting complexity at the edge of order and chaos.

Traveling magnetopause distortion related to a large-scale magnetosheath plasma jet: THEMIS and ground-based observations

NASA Astrophysics Data System (ADS)

Dmitriev, A. V.; Suvorova, A. V.

2012-08-01

Here, we present a case study of THEMIS and ground-based observations of the perturbed dayside magnetopause and the geomagnetic field in relation to the interaction of an interplanetary directional discontinuity (DD) with the magnetosphere on 16 June 2007. The interaction resulted in a large-scale local magnetopause distortion of an "expansion - compression - expansion" (ECE) sequence that lasted for ˜15 min. The compression was caused by a very dense, cold, and fast high-βmagnetosheath plasma flow, a so-called plasma jet, whose kinetic energy was approximately three times higher than the energy of the incident solar wind. The plasma jet resulted in the effective penetration of magnetosheath plasma inside the magnetosphere. A strong distortion of the Chapman-Ferraro current in the ECE sequence generated a tripolar magnetic pulse "decrease - peak- decrease" (DPD) that was observed at low and middle latitudes by some ground-based magnetometers of the INTERMAGNET network. The characteristics of the ECE sequence and the spatial-temporal dynamics of the DPD pulse were found to be very different from any reported patterns of DD interactions with the magnetosphere. The observed features only partially resembled structures such as FTE, hot flow anomalies, and transient density events. Thus, it is difficult to explain them in the context of existing models.

Ultra-High Resolution Observations Of Selected Blazars

NASA Astrophysics Data System (ADS)

Hodgson, Jeffrey A.

2015-01-01

Active Galactic Nuclei are the luminous centres of active galaxies that produce powerful relativistic jets from central super massive black holes (SMBH). When these jets are oriented towards the observer's line-of-sight, they become very bright, very variable and very energetic. These sources are known as blazars and Very Long Baseline Interferometry (VLBI) provides a direct means of observing into the heart of these objects. VLBI performed at 3 mm with the Global mm-VLBI Array (GMVA) and 7 mm VLBI performed with the Very Long Baseline Array (VLBA), allows some of the highest angular resolution images of blazars to be produced. In this thesis, we present the first results of an ongoing monitoring program of blazars known to emit at γ-ray energies. The physical processes that produce these jets and the γ-ray emission are still not well known. The jets are thought to be produced by converting gravitational energy around the black hole into relativistic particles that are accelerated away at near the speed of light. However, the exact mechanisms for this and the role that magnetic fields play is not fully clear. Similarly, γ-rays have been long known to have been emitted from blazars and that their production is often related to the up-scattering of synchrotron radiation from the jet. However, the origin of seed photons for the up-scattering (either from within the jet itself or from an external photon field) and the location of the γ-ray emission regions has remained inconclusive. In this thesis, we aim to describe the likely location of γ-ray emission in jets, the physical structure of blazar jets, the location of the VLBI features relative to the origin of the jet and the nature of the magnetic field, both of the VLBI scale jet and in the region where the jet is produced. We present five sources that have been monitored at 3 mm using the GMVA from 2008 until 2012. These sources have been analysed with near-in-time 7 mm maps from the Very Long Baseline Array (VLBA), γ-ray light curves from the Fermi/LAT space telescope and cm to mm-wave total-intensity light curves. In one source, OJ 287, the source has additionally been analysed with monthly imaging at 7 mm with the VLBA and near-in-time 2 cm VLBI maps. We use these resources to analyse high angular resolution structural and spectral changes and see if they correlate with flaring (both radio and γ-ray) activity and with VLBI component ejections. By spectrally decomposing sources, we can determine the spatially resolved magnetic field structure in the jets at the highest yet performed resolutions and at frequencies that are near or above the turnover frequency for synchrotron self-absorption (SSA). We compute the magnetic field estimates from SSA theory and by assuming equipartition between magnetic fields and relativistic particle energies. All sources analysed exhibit downstream quasi-stationary features which sometimes exhibit higher brightness temperatures and flux density variability than the VLBI "core", which we interpret as being recollimation or oblique shocks. We find that γ-ray flaring, mm-wave radio flaring and changes in opacity from optically thick to optically thin, is in many cases consistent with component ejections past both the VLBI "core" and these quasi-stationary downstream features. We find decreasing apparent brightness temperatures and Doppler factors as a function of increased "core" separation, which is interpreted as consistent with a slowly accelerating jet over the de-projected inner ˜10-20 pc. Assuming equipartition between magnetic energy and relativistic particle energy, the magnetic field strengths within the jets at these scales are, on average, between B ˜ 0.3 - 0.9 G, with the highest strengths found within the VLBI "core". From the observed gradient in magnetic field strengths, we can place the mmwave "core" ˜1-3 pc downstream of the base of the jet. Additionally, we estimate the the magnetic field is Bapex ˜ 3000 - 18000 G at the base of the jet. We computed theoretical estimates based on jet production under magnetically arrested disks (MAD) and find our estimates to be consistent. In the BL Lac source OJ 287, we included monthly 7 mm and near-in-time 2 cm VLBA maps to provide full kinematics and increased spectral coverage. Following a previously reported radical change in inner-jet PA of ˜100° we find unusually discrepant PAs compared with the previous jet direction, that follow very different trajectories. The source exhibits a downstream quasi-stationary feature that at times has higher brightness temperatures than the "core". The source also exhibited a large change in apparent component speeds as compared with previous epochs, which we propose could be due to changes in jet pressure causing changes in the location of downstream recollimation or oblique shocks and hence their line-of-sight viewing angle. The addition of 2 cm VLBA data allows for a comparison of magnetic fields derived from SSA and equipartition. The magnetic field estimates are consistent within 20%, with BSSA ≥ 1.6 G and Bequi ≥ 1.2 G in the "core" and BSSA ≤ 0.4 G and Bequi ≤ 0.3 G in the stationary feature. Gamma-ray emission appears to originate in the "core" and the stationary feature. The decrease in magnetic field strengths places the mmwave "core' downstream of the jet base by ≤6 pc and likely outside of the broad line region (BLR). This, combined with the results in other sources are consistent with γ-rays being produced in the vicinity of the VLBI "core" of in further downstream stationary features, which are likely over a parsec downstream of the central black hole, favouring the scenario of photons being up-scattered within the relativistic jet.

Small-scale filament eruptions as the driver of X-ray jets in solar coronal holes.

PubMed

Sterling, Alphonse C; Moore, Ronald L; Falconer, David A; Adams, Mitzi

2015-07-23

Solar X-ray jets are thought to be made by a burst of reconnection of closed magnetic field at the base of a jet with ambient open field. In the accepted version of the 'emerging-flux' model, such a reconnection occurs at a plasma current sheet between the open field and the emerging closed field, and also forms a localized X-ray brightening that is usually observed at the edge of the jet's base. Here we report high-resolution X-ray and extreme-ultraviolet observations of 20 randomly selected X-ray jets that form in coronal holes at the Sun's poles. In each jet, contrary to the emerging-flux model, a miniature version of the filament eruptions that initiate coronal mass ejections drives the jet-producing reconnection. The X-ray bright point occurs by reconnection of the 'legs' of the minifilament-carrying erupting closed field, analogous to the formation of solar flares in larger-scale eruptions. Previous observations have found that some jets are driven by base-field eruptions, but only one such study, of only one jet, provisionally questioned the emerging-flux model. Our observations support the view that solar filament eruptions are formed by a fundamental explosive magnetic process that occurs on a vast range of scales, from the biggest mass ejections and flare eruptions down to X-ray jets, and perhaps even down to smaller jets that may power coronal heating. A similar scenario has previously been suggested, but was inferred from different observations and based on a different origin of the erupting minifilament.

Probing jets from young embedded sources

NASA Astrophysics Data System (ADS)

Nisini, Brunella

2017-08-01

Jets are intimately related to the process of star formation and disc accretion. Our present knowledge of this key ingredient in protostars mostly relies on observations of optical jets from T Tauri stars, where the original circumstellar envelope has been already cleared out. However, to understand how jets are originally formed and how their properties evolve with time, detailed observations of young accreting protostars, i.e. the class 0/I sources, are mandatory. The study of class0/I jets will be revolutionised by JWST, able to penetrate protostars dusty envelopes with unprecedented sensitivity and resolution. However, complementary information on parameters inferred from lines in different excitation regimes, for at least a representative sample of a few bright sources, is essential for a correct interpretation of the JWST results. Here we propose to observe four prototype bright jets from class0/I sources with the WFC3 in narrow band filters in order to acquire high angular resolution images in the [OI]6300A, [FeII]1.25 and [FeII]1.64um lines. These images will be used to: 1) provide accurate extinction maps of the jets that will be an important archival reference for any future observation on these jets. 2) measure key parameters as the mass flux, the iron abundance and the jet collimation on the hot gas component of the jets. These information will provide an invaluable reference frame for a comparison with similar parameters measured by JWST in a different gas regime. In addition, these observations will allow us to confront the properties of class 0/I jets with those of the more evolved T Tauri stars.

A New Observational Strategy for Monitoring the Tropical Cyclone Outflow Layer and its Relationship to Intensity and Structure Change

DTIC Science & Technology

2013-09-30

vertical structure of outflow layer jets for Hurricanes Leslie and Nadine in 2012 and Invest 97L in 2013 has been conducted using NCAR- EOL /Vaisala mini...generation of dropsonde, the Yankee, Inc HDSS and XDD sonde was intercompared during CIRPAS Twin Otter test flights on 24-25 June, 2011 with NCAR- EOL

On the existence of a luminosity threshold of GRB jets in massive stars

NASA Astrophysics Data System (ADS)

Aloy, M. A.; Cuesta-Martínez, C.; Obergaulinger, M.

2018-05-01

Motivated by the many associations of γ-ray bursts (GRBs) with energetic supernova (SN) explosions, we study the propagation of relativistic jets within the progenitor star in which a SN shock wave may be launched briefly before the jets start to propagate. Based on analytic considerations and verified with an extensive set of 2D axisymmetric relativistic hydrodynamic simulations, we have estimated a threshold intrinsic jet luminosity, L_j^thr, for successfully launching a jet. This threshold depends on the structure of the progenitor and, thus, it is sensitive to its mass and to its metallicity. For a prototype host of cosmological long GRBs, a low-metallicity star of 35 M⊙, it is L_j^thr˜eq 1.35× 10^{49} erg s-1. The observed equivalent isotropic γ-ray luminosity, L_{γ ,iso,BO} ˜eq 4 ɛ _γ L_j θ _BO^{-2}, crucially depends on the jet opening angle after breakout, θBO, and on the efficiency for converting the intrinsic jet luminosity into γ-radiation, ɛγ. Highly energetic jets can produce low-luminosity events if either their opening angle after the breakout is large, which is found in our models, or if the conversion efficiency of kinetic and internal energy into radiation is low enough. Beyond this theoretical analysis, we show how the presence of a SN shock wave may reduce this luminosity threshold by means of numerical simulations. We foresee that the high-energy transients released by jets produced near the luminosity threshold will be more similar to llGRBs or XRFs than to GRBs.

New potentional of high-speed water jet technology for renovating concrete structures

NASA Astrophysics Data System (ADS)

Bodnárová, L.; Sitek, L.; Hela, R.; Foldyna, J.

2011-06-01

The paper discusses the background and results of research focused on the action of a high-speed water jet on concrete with different qualities. The sufficient and careful removal of degraded concrete layers is very important for the renovation of concrete structures. High-speed water jet technology is one of the most common methods used for removing degraded concrete layers. Different types of high-speed water jets were tested in the experimental part. The classical technology of a single continuous water jet generated with one nozzle was tested as well as the technology of revolving water jets generated by multiple nozzles (used mainly for the renovation of larger areas). A continuous flat water jet and pulsating flat water jet were tested the first time, because the connection of a water jet with the acoustic generator of a pulsating jet offers new possibilities for the use of a water jet (see [1] and [2]). A water jet with such a modification is capable of efficient action and can even be used for cutting solid concrete with a relatively low consumption of energy. A flat pulsating water jet which can be newly used for renovation seems to be a promising technology.

Survey of Milliarcsec Structure in Eight Seyfert Galaxies: Results on NGC 1068 and NGC 4151

NASA Astrophysics Data System (ADS)

Roy, A. L.; Ulvestad, J. S.; Colbert, E. J. M.; Wilson, A. S.; Norris, R. P.

We are surveying eight nearby Seyfert galaxies (four Sy1s and four Sy2s) that have compact radio cores, using the VLBA. We are interested in parsec-scale morphology and low-frequency absorption effects, and so are observing four frequencies (1.6, 4.8, 8.4 and 15 GHz) to get spectral-index diagnostics. In this paper, we present results on two galaxies, NGC 1068 and NGC 4151. NGC 4151 shows a curved radio jet on the sub-parsec scale, with the smallest scale structure misaligned by $55^\\circ$ from the jet on scales of parsecs to hundreds of parsecs. NGC 1068 contains several components in the inner tens of parsecs, with those components showing a variety of absorption and resolution effects.

Significant and variable linear polarization during the prompt optical flash of GRB 160625B.

PubMed

Troja, E; Lipunov, V M; Mundell, C G; Butler, N R; Watson, A M; Kobayashi, S; Cenko, S B; Marshall, F E; Ricci, R; Fruchter, A; Wieringa, M H; Gorbovskoy, E S; Kornilov, V; Kutyrev, A; Lee, W H; Toy, V; Tyurina, N V; Budnev, N M; Buckley, D A H; González, J; Gress, O; Horesh, A; Panasyuk, M I; Prochaska, J X; Ramirez-Ruiz, E; Lopez, R Rebolo; Richer, M G; Román-Zúñiga, C; Serra-Ricart, M; Yurkov, V; Gehrels, N

2017-07-26

Newly formed black holes of stellar mass launch collimated outflows (jets) of ionized matter that approach the speed of light. These outflows power prompt, brief and intense flashes of γ-rays known as γ-ray bursts (GRBs), followed by longer-lived afterglow radiation that is detected across the electromagnetic spectrum. Measuring the polarization of the observed GRB radiation provides a direct probe of the magnetic fields in the collimated jets. Rapid-response polarimetric observations of newly discovered bursts have probed the initial afterglow phase, and show that, minutes after the prompt emission has ended, the degree of linear polarization can be as high as 30 per cent-consistent with the idea that a stable, globally ordered magnetic field permeates the jet at large distances from the central source. By contrast, optical and γ-ray observations during the prompt phase have led to discordant and often controversial results, and no definitive conclusions have been reached regarding the origin of the prompt radiation or the configuration of the magnetic field. Here we report the detection of substantial (8.3 ± 0.8 per cent from our most conservative simulation), variable linear polarization of a prompt optical flash that accompanied the extremely energetic and long-lived prompt γ-ray emission from GRB 160625B. Our measurements probe the structure of the magnetic field at an early stage of the jet, closer to its central black hole, and show that the prompt phase is produced via fast-cooling synchrotron radiation in a large-scale magnetic field that is advected from the black hole and distorted by dissipation processes within the jet.

Significant and variable linear polarization during the prompt optical flash of GRB 160625B.

NASA Astrophysics Data System (ADS)

Troja, E.; Lipunov, V. M.; Mundell, C. G.; Butler, N. R.; Watson, A. M.; Kobayashi, S.; Cenko, S. B.; Marshall, F. E.; Ricci, R.; Fruchter, A.; Wieringa, M. H.; Gorbovskoy, E. S.; Kornilov, V.; Kutyrev, A.; Lee, W. H.; Toy, V.; Tyurina, N. V.; Budnev, N. M.; Buckley, D. A. H.; González, J.; Gress, O.; Horesh, A.; Panasyuk, M. I.; Prochaska, J. X.; Ramirez-Ruiz, E.; Rebolo Lopez, R.; Richer, M. G.; Roman-Zuniga, C.; Serra-Ricart, M.; Yurkov, V.; Gehrels, N.

2017-07-01

Newly formed black holes of stellar mass launch collimated outflows (jets) of ionized matter that approach the speed of light. These outflows power prompt, brief and intense flashes of γ-rays known as γ-ray bursts (GRBs), followed by longer-lived afterglow radiation that is detected across the electromagnetic spectrum. Measuring the polarization of the observed GRB radiation provides a direct probe of the magnetic fields in the collimated jets. Rapid-response polarimetric observations of newly discovered bursts have probed the initial afterglow phase, and show that, minutes after the prompt emission has ended, the degree of linear polarization can be as high as 30 per cent - consistent with the idea that a stable, globally ordered magnetic field permeates the jet at large distances from the central source. By contrast, optical and γ-ray observations during the prompt phase have led to discordant and often controversial results, and no definitive conclusions have been reached regarding the origin of the prompt radiation or the configuration of the magnetic field. Here we report the detection of substantial (8.3 ± 0.8 per cent from our most conservative simulation), variable linear polarization of a prompt optical flash that accompanied the extremely energetic and long-lived prompt γ-ray emission from GRB 160625B. Our measurements probe the structure of the magnetic field at an early stage of the jet, closer to its central black hole, and show that the prompt phase is produced via fast-cooling synchrotron radiation in a large-scale magnetic field that is advected from the black hole and distorted by dissipation processes within the jet.

Prediction of Turbulence-Generated Noise in Unheated Jets. Part 2; JeNo Users' Manual (Version 1.0)

NASA Technical Reports Server (NTRS)

Khavaran, Abbas; Wolter, John D.; Koch, L. Danielle

2009-01-01

JeNo (Version 1.0) is a Fortran90 computer code that calculates the far-field sound spectral density produced by axisymmetric, unheated jets at a user specified observer location and frequency range. The user must provide a structured computational grid and a mean flow solution from a Reynolds-Averaged Navier Stokes (RANS) code as input. Turbulence kinetic energy and its dissipation rate from a k-epsilon or k-omega turbulence model must also be provided. JeNo is a research code, and as such, its development is ongoing. The goal is to create a code that is able to accurately compute far-field sound pressure levels for jets at all observer angles and all operating conditions. In order to achieve this goal, current theories must be combined with the best practices in numerical modeling, all of which must be validated by experiment. Since the acoustic predictions from JeNo are based on the mean flow solutions from a RANS code, quality predictions depend on accurate aerodynamic input.This is why acoustic source modeling, turbulence modeling, together with the development of advanced measurement systems are the leading areas of research in jet noise research at NASA Glenn Research Center.

Connection Between X-Ray Dips and Superluminal Ejections in the Radio Galaxy 3C 120

NASA Technical Reports Server (NTRS)

Aller, Margo F.

2005-01-01

This work represents a part of a long-term study of the X-ray flux variability of 3C 120 and its relation to flux and structural changes in the radio jet of this galaxy. The grant included fiinding for the rediiction and analysis of data obt,ained during the time pwiod of Rossi XTE cycle 8 (March 1, 2003-February 29, 2004). Prior RXTE observations, combined with single dish monitoring at centimeter wavelengths and 43 GHz mapping (monthly until February 1999 and bimonthly thereafter) of the inner jet with the VLBA, had identified the presence of X-ray dips in the light curves and X-ray spectral hardening 4 weeks prior to the ejection of new VLBI components in the radio jet. This suggested a picture in which the radio jet was fed by accretion events near the black hole. The specific goals of the cycle 8 observations were to better define the relation between the X-ray dips and the radio events using higher sampling, to include more events in the correlation and hence improve the statistics, to look for a possible optical X-ray connection, and to search for quasi periodicities on timescales of 1-3 days. In cycle 8 this project was awarded time for 4 pointings weekly with RXTE.

Effect of slotted exit orifice on performance of plasma synthetic jet actuator

NASA Astrophysics Data System (ADS)

Zong, Haohua; Kotsonis, Marios

2017-03-01

This study experimentally investigates the influence of exit orifice shape on the performance characteristics of a three-electrode plasma synthetic jet actuator. High-speed Schlieren imaging system and phase-locked two-component PIV measurements are used for flowfield characterisation in quiescent conditions. Two actuator configurations with the same exit area but different exit orifice shape (round orifice and slot orifice) are studied. Results indicate a close correspondence between the shapes of the starting vortex ring with the shapes of the respective exit orifices. For the slot orifice, the elongated starting vortex ring gradually expands during propagation, while its ends become warped. A distinct K-H instability structure is observed, inducing continuous oscillation of the high-speed jet. Compared with the jet from the round orifice, the slot jet has a higher entrainment rate of surrounding air, thus resulting in a lower propagation velocity of the jet front. The exit velocity of PSJA within one period initially shows a rapid increase, then persists at a relatively high level (100-130 m/s), and finally drops with some small-scale oscillations. The oscillation amplitude is less than 10 m/s, and the oscillation period is approximately 600 µs. Under conditions of same exit area, orifice shape has little influence on the variation of the exit velocity.

High order harmonics anomaly of jet screech

NASA Astrophysics Data System (ADS)

Chen, Zhe; Wu, Jiu Hui; Ren, A.-Dan; Chen, Xin

2018-05-01

Imperfectly expanded supersonic jets under strong screech could generate both fundamental screech tones and multiple tones at the harmonics of the fundamental frequency. The paper compares the fundamental frequency of jets from both AR = 3 (Aspect Ratio) and AR = 4 rectangular nozzles, and conducts analysis of harmonics on Sound Pressure Level (SPL) spectrums of jet noise. The research suggests that the fundamental frequency of the first two- or three-order harmonics increases when the Nozzle Pressure Ratio (NPR) decreases, whereas the highest order harmonic decreases when the NPR decreases. Besides, the paper also observes the differences between the highest order harmonics and other harmonics that have never been reported before. Further analysis on flow field schlieren of AR = 3 nozzle indicates that the highest order harmonic is the outcome of interaction between second shock-cell and nonlinear instable wave. The revolution of these high order harmonics can provide guidance for the prevention of small-scale structure fatigue damage. Moreover, the distribution test of the noises is also carried out to verify the high order harmonics anomaly, and indicate that the jet noise spreads mainly towards downstream while screech towards upstream. In addition, the broadband shock-associated noise spreads vertical to the jet flow and exhibits the feature of directivity.

Multiwavelength and parsec-scale properties of extragalactic jets. Doctoral Thesis Award Lecture 2015

NASA Astrophysics Data System (ADS)

Müller, C.

2016-07-01

Extragalactic jets originating from the central supermassive black holes of active galaxies are powerful, highly relativistic plasma outflows, emitting light from the radio up to the γ-ray regime. The details of their formation, composition and emission mechanisms are still not completely clear. The combination of high-resolution observations using very long baseline interferometry (VLBI) and multiwavelength monitoring provides the best insight into these objects. Here, such a combined study of sources of the TANAMI sample is presented, investigating the parsec-scale and high-energy properties. The TANAMI program is a multiwavelength monitoring program of a sample of the radio and γ-ray brightest extragalactic jets in the southern sky, below -30o declination. We obtain the first-ever VLBI images for most of the sources, providing crucial information on the jet kinematics and brightness distribution at milliarcsecond resolution. Two particular sources are discussed in detail: PMN J1603-4904 , which can be classified either as an atypical blazar or a γ-ray loud (young) radio galaxy, and Centaurus A, the nearest radio-loud active galaxy. The VLBI kinematics of the innermost parsec of Centaurus A's jet result in a consistent picture of an accelerated jet flow with a spine-sheath like structure.

On the interaction of jet noise with a nearby flexible structure

NASA Technical Reports Server (NTRS)

Mcgreevy, J. L.; Bayliss, A.; Maestrello, L.

1994-01-01

The model of the interaction of the noise from a spreading subsonic jet with a panel-stringer assembly is studied numerically in two dimensions. The radiation resulting from this flow/acoustic/structure coupling is computed and analyzed in both the time and frequency domains. The jet is initially excited by a pulse-like source inserted into the flow field. The pulse triggers instabilities associated with the inviscid instability of the jet mean flow shear layer. These instabilities in turn generate sound which provides the primary loading for the panels. The resulting structural vibration and radiation depends strongly on their placement relative to the jet/nozzle configuration. Results are obtained for the panel responses as well as the transmitted and incident pressure. The effect of the panels is to act as a narrow filter, converting the relatively broad band forcing, heavily influenced by jet instabilities, into radiation concentrated in narrow spectral bands.

Influence of gas flow and applied voltage on interaction of jets in a cross-field helium plasma jet array

NASA Astrophysics Data System (ADS)

Wan, Meng; Liu, Feng; Fang, Zhi; Zhang, Bo; Wan, Hui

2017-09-01

Atmospheric Pressure Plasma Jet arrays can greatly enhance the treatment area to fulfill the need for large-scale surface processing, while the spatial uniformity of the plasma jet array is closely related to the interactions of the adjacent jets. In this paper, a three-tube one-dimensional (1D) He plasma jet array with a cross-field needle-ring electrode structure is used to investigate the influences of the gas flow rate and applied voltage on the interactions of the adjacent jets through electrical, optical, and fluid measurements. The repulsion of the adjacent plume channels is observed using an intensified charge-coupled device (ICCD) and the influence of the gas flow rate and applied voltage on the electrostatic repulsion force, Coulomb force, is discussed. It is found that electrical coupling, mainly electrostatic repulsion force, exists among the jets in the array, which causes both the divergence of the lateral plumes and the nonlinear changes of the discharge power and the transport charge. The deflection angle of the lateral plumes with respect to the central plume in the optical images increases with the increase of applied voltage and decreases with the increase of gas flow rate. The deflection angle of the lateral plumes in the optical images is obviously larger than that of the lateral gas streams in the Schlieren images under the same experimental conditions, and the unconformity of the deflection angles is mainly attributed to the electrostatic repulsion force in adjacent plasma plume channels. The experimental results can help understand the interaction mechanisms of jets in the array and design controllable and scalable plasma jet arrays.

Coherent structures in axisymmetric jets

NASA Astrophysics Data System (ADS)

Durao, D. F. G.; Nina, M. N. R.; Pita, G.

Laser Doppler anemometry has been used to measure the mean and rms values of the axial and radial velocity components in jets with Reynolds numbers of up to 28,700. It is shown that even in flows that are not excited externally, coherent structures with Strouhal numbers of about 0.33 and 0.55 can be detected. The coherent structures associated with the higher Strouhal number are shown to result from vorticity at the edge of the jet. The oscillation associated with the lower Strouhal number is related to eddy breakdown and to the preferred vibration mode of axisymmetric jets.

Stability of azimuthal-angle observables under higher order corrections in inclusive three-jet production

NASA Astrophysics Data System (ADS)

Caporale, F.; Celiberto, F. G.; Chachamis, G.; Gómez, D. Gordo; Vera, A. Sabio

2017-04-01

Recently, a new family of observables consisting of azimuthal-angle generalized ratios was proposed in a kinematical setup that resembles the usual Mueller-Navelet jets but with an additional tagged jet in the central region of rapidity. Nontagged minijet activity between the three jets can affect significantly the azimuthal angle orientation of the jets and is accounted for by the introduction of two Balitsky-Fadin-Kuraev- Lipatov (BFKL) gluon Green functions. Here, we calculate the, presumably, most relevant higher order corrections to the observables by now convoluting the three leading order jet vertices with two gluon Green functions at next-to-leading logarithmic approximation. The corrections appear to be mostly moderate, giving us confidence that the recently proposed observables are actually an excellent way to probe the BFKL dynamics at the LHC. Furthermore, we allow for the jets to take values in different rapidity bins in various configurations such that a comparison between our predictions and the experimental data is a straightforward task.

Fine Structure of the Core of the Blazar OJ 287-I

NASA Astrophysics Data System (ADS)

Matveyenko, L. I.; Sivakon', S. S.

2017-12-01

The fine structure of the active region, the bulge, of the blazar OJ 287 has been investigated with a resolution of 20 μas (0.1 pc) at a wavelength of 7 mm, the epochs of 2007-2017. The structure and kinematics correspond to a vortex nature. The surrounding matter, the plasma, is transferred to the center along two arms from opposite directions. The emerging excess angular momentum is carried away along the rotation axis by bipolar outflows, rotating coaxial tubes, in a direction X ≈ -120° in the plane of the sky as it is accumulated. The central high-velocity bipolar outflow has a helical shape. The diameters of the low-velocity flows are ø1 ≈ 0.3 and ø2 ≈ 0.65 mas, or 1.4 and 3 pc, respectively. Ring currents whose tangential directions are observed as parallel chains of components are excited in the flow walls. The peak brightness temperature of the nozzle reaches Tb ≈ 1012-1013 K. A "disk" with a diameter ø ≈ 0.5 mas (≈2.2 pc) is observed by the absorption of synchrotron radiation. The disk is inclined to the plane of the sky at an angle of 60° in the jet direction. The fragments are seen from a distance of ˜0.2 mas outside the absorption zone. The jet sizes exceed considerably the counterjet ones. An enhanced supply of plasma from the northern arm gives rise to an independent vortex 0.2 mas away from the central one in the NW direction. As in the first case, the helical central bipolar outflow is surrounded by a low-velocity component ø ≈ 0.28 mas in diameter with built-in ring currents. The jet is ejected in the direction X = -50° in the plane of the sky. The jet orientation changes, X = -130° at a distance of 1 mas. A high activity of the central and two side nozzles spaced 0.22 mas apart in the direction X = -40° is occasionally observed simultaneously. The active region of the blazar is observed through an ionized medium, a screen, whose influence is significant even at a wavelength of 7 mm. The absorption and refraction of the transmitted emission in the screen affect the apparent brightness relative to the positions of the fragments.

Probing Collimated Jets and Dusty Waists in Dying Stars with Keck LGSAO

NASA Astrophysics Data System (ADS)

Sahai, R.; Le Mignant, D.; Sanchez Contreras, C.; Stute, M.; Morris, M.

2005-12-01

The shaping of planetary nebulae (PNs) is probably the most exciting yet least understood problem in the late evolution of intermediate mass stars. PNs evolve from the envelopes of AGB stars via a supposedly short ( ˜1000 yr) pre-planetary nebula (PPN) phase. HST imaging of PPNs and PNs has shown the widespread presence of diverse bipolar and multipolar morphologies. In 1998, in a radical departure from the long-standing theoretical paradigm for PN formation, Sahai & Trauger proposed that as most stars evolve off the AGB, they drive collimated fast winds that sweep up and shock the AGB circumstellar envelope, producing the observed dramatic changes in circumstellar geometry and kinematics from the AGB to the PN phase. The search for these collimated jets has proved to be rather elusive, partly because these are most likely episodic and operate only for a few x 100 years in the early PPN phase. During this phase, much of the circumstellar environment, including the central dusty waist of these nebulae, is optically-thick at visible wavelengths. We are therefore carrying out a program of observing PPNs with the LGSAO system on Keck II at near-infrared (1.1-4.7 micron) wavelengths. Our very first attempt met with remarkable success -- observations of the bipolar young PPN, IRAS16342-3814, revealed a remarkable corkscrew-shaped structure apparently etched into the lobe walls -- direct signature of an underlying precessing jet. Here we present results from new high-resolution (55 mas at 2 micron) observations of a small sample of PPNs with the LGSAO system. As in their HST images, our objects display bipolar/multipolar morphologies, but in addition, the bubble-like ``wind-swept" structure of the lobes is clearly revealed. Furthermore, the dusty waists appear much thinner geometrically than in the HST images, but surprisingly, in some PPNs, the central stars still remain obscured, with important implications for the poorly-known physical structure of the waists. We discuss some preliminary results from our data such as the nature of the illuminating sources, quantitative analysis of the mass and dynamics of different nebular components by combining our AO data with complementary data from our multi-wavelength survey of PPNs, and numerical simulations of precessing jets interacting with AGB winds.

History of Chandra X-Ray Observatory

NASA Image and Video Library

1999-09-01

After barely 2 months in space, the Chandra X-Ray Observatory (CXO) took this sturning image of the Crab Nebula, the spectacular remains of a stellar explosion, revealing something never seen before, a brilliant ring around the nebula's heart. The image shows the central pulsar surrounded by tilted rings of high-energy particles that appear to have been flung outward over a distance of more than a light-year from the pulsar. Perpendicular to the rings, jet-like structures produced by high-energy particles blast away from the pulsar. Hubble Space Telescope images have shown moving knots and wisps around the neutron star, and previous x-ray images have shown the outer parts of the jet and hinted at the ring structure. With CXO's exceptional resolution, the jet can be traced all the way in to the neutron star, and the ring pattern clearly appears. The image was made with CXO's Advanced Charge-Coupled Device (CCD) Imaging Spectrometer (ACIS) and High Energy Transmission Grating. The Crab Nebula, easily the most intensively studied object beyond our solar system, has been observed using virtually every astronomical instrument that could see that part of the sky

Motion and properties of nuclear radio components in Seyfert galaxies seen with VLBI

NASA Astrophysics Data System (ADS)

Middelberg, E.; Roy, A. L.; Nagar, N. M.; Krichbaum, T. P.; Norris, R. P.; Wilson, A. S.; Falcke, H.; Colbert, E. J. M.; Witzel, A.; Fricke, K. J.

2004-04-01

We report EVN, MERLIN and VLBA observations at 18 cm, 6 cm and 3.6 cm of the Seyfert galaxies NGC 7674, NGC 5506, NGC 2110 and Mrk 1210 to study their structure and proper motions on pc scales and to add some constraints on the many possible causes of the radio-quietness of Seyferts. The component configurations in NGC 7674 and NGC 2110 are simple, linear structures, whereas the configurations in NGC 5506 and Mrk 1210 have multiple components with no clear axis of symmetry. We suggest that NGC 7674 is a low-luminosity compact symmetric object. Comparing the images at different epochs, we find a proper motion in NGC 7674 of (0.92±0.07) c between the two central components separated by 282 pc and, in NGC 5506, we find a 3 σ upper limit of 0.50 c for the components separated by 3.8 pc. Our results confirm and extend earlier work showing that the outward motion of radio components in Seyfert galaxies is non-relativistic on pc scales. We briefly discuss whether this non-relativistic motion is intrinsic to the jet-formation process or results from deceleration of an initially relativistic jet by interaction with the pc or sub-pc scale interstellar medium. We combined our sample with a list compiled from the literature of VLBI observations made of Seyfert galaxies, and found that most Seyfert nuclei have at least one flat-spectrum component on the VLBI scale, which was not seen in the spectral indices measured at arcsec resolution. We found also that the bimodal alignment of pc and kpc radio structures displayed by radio galaxies and quasars is not displayed by this sample of Seyferts, which shows a uniform distribution of misalignment between 0° and 90°. The frequent misalignment could result from jet precession or from deflection of the jet by interaction with gas in the interstellar medium.

High-Speed Rainbow Schlieren Visualization of an Oscillating Helium Jet Undergoing Gravitational Change

NASA Technical Reports Server (NTRS)

Leptuch, Peter A.; Agrawal, Ajay K.

2005-01-01

Rainbow schlieren deflectometry combined with high-speed digital imaging was used to study buoyancy effects on flow structure of a helium jet discharged vertically into air. The experimental data were taken using the 2.2-sec drop tower facility at the NASA John H. Glenn Research Center in Cleveland, Ohio. The test conditions pertained to jet Reynolds number of 490 and jet Richardson number of 0.11, for which buoyancy is often considered unimportant. Experimental results show global oscillations at a frequency of 27 Hz in Earth gravity. In microgravity, the jet oscillations vanished and the jet width increased. Results provide a direct physical evidence of the importance of buoyancy on the flow structure of low-density gas jets at a Richardson number considered too small to account for gravity.

Measurement of jet quenching with semi-inclusive hadron-jet distributions in central Pb-Pb collisions at $$\\sqrt{s_{\\mathrm{NN}}}=2.76$$ TeV

DOE PAGES

Adam, J.

2015-09-24

We report the measurement of a new observable of jet quenching in central Pb-Pb collisions at √sNN = 2.76 TeV, based on the semi-inclusive rate of charged jets recoiling from a high transverse momentum (high-p T) charged hadron trigger. Jets are measured using collinear-safe jet reconstruction with infrared cutoff for jet constituents of 0.15 GeV, for jet resolution parameters R = 0.2, 0.4 and 0.5. Underlying event background is corrected at the event-ensemble level, without imposing bias on the jet population. Recoil jet spectra are reported in the range 20 < p T,jet ch < 100 GeV. Reference distributions formore » pp collisions at √s = 2.76TeV are calculated using Monte Carlo and NLO pQCD methods, which are validated by comparing with measurements in pp collisions at √s = 7TeV. The recoil jet yield in central Pb-Pb collisions is found to be suppressed relative to that in pp collisions. No significant medium-induced broadening of the intra-jet energy profile is observed within 0.5 radians relative to the recoil jet axis. The angular distribution of the recoil jet yield relative to the trigger axis is found to be similar in central Pb-Pb and pp collisions, with no significant medium-induced acoplanarity observed. Lastly, large-angle jet deflection, which may provide a direct probe of the nature of the quasi-particles in hot QCD matter, is explored.« less

Measurement of jet quenching with semi-inclusive hadron-jet distributions in central Pb-Pb collisions at √{s_{NN}}=2.76 TeV

NASA Astrophysics Data System (ADS)

Adam, J.; Adamová, D.; Aggarwal, M. M.; Aglieri Rinella, G.; Agnello, M.; Agrawal, N.; Ahammed, Z.; Ahn, S. U.; Aimo, I.; Aiola, S.; Ajaz, M.; Akindinov, A.; Alam, S. N.; Aleksandrov, D.; Alessandro, B.; Alexandre, D.; Alfaro Molina, R.; Alici, A.; Alkin, A.; Almaraz, J. R. M.; Alme, J.; Alt, T.; Altinpinar, S.; Altsybeev, I.; Alves Garcia Prado, C.; Andrei, C.; Andronic, A.; Anguelov, V.; Anielski, J.; Antičić, T.; Antinori, F.; Antonioli, P.; Aphecetche, L.; Appelshäuser, H.; Arcelli, S.; Armesto, N.; Arnaldi, R.; Arsene, I. C.; Arslandok, M.; Audurier, B.; Augustinus, A.; Averbeck, R.; Azmi, M. D.; Bach, M.; Badalà, A.; Baek, Y. W.; Bagnasco, S.; Bailhache, R.; Bala, R.; Baldisseri, A.; Baltasar Dos Santos Pedrosa, F.; Baral, R. C.; Barbano, A. M.; Barbera, R.; Barile, F.; Barnaföldi, G. G.; Barnby, L. S.; Barret, V.; Bartalini, P.; Barth, K.; Bartke, J.; Bartsch, E.; Basile, M.; Bastid, N.; Basu, S.; Bathen, B.; Batigne, G.; Batista Camejo, A.; Batyunya, B.; Batzing, P. C.; Bearden, I. G.; Beck, H.; Bedda, C.; Behera, N. K.; Belikov, I.; Bellini, F.; Bello Martinez, H.; Bellwied, R.; Belmont, R.; Belmont-Moreno, E.; Belyaev, V.; Bencedi, G.; Beole, S.; Berceanu, I.; Bercuci, A.; Berdnikov, Y.; Berenyi, D.; Bertens, R. A.; Berzano, D.; Betev, L.; Bhasin, A.; Bhat, I. R.; Bhati, A. K.; Bhattacharjee, B.; Bhom, J.; Bianchi, L.; Bianchi, N.; Bianchin, C.; Bielčík, J.; Bielčíková, J.; Bilandzic, A.; Biswas, R.; Biswas, S.; Bjelogrlic, S.; Blanco, F.; Blau, D.; Blume, C.; Bock, F.; Bogdanov, A.; Bøggild, H.; Boldizsár, L.; Bombara, M.; Book, J.; Borel, H.; Borissov, A.; Borri, M.; Bossú, F.; Botta, E.; Böttger, S.; Braun-Munzinger, P.; Bregant, M.; Breitner, T.; Broker, T. A.; Browning, T. A.; Broz, M.; Brucken, E. J.; Bruna, E.; Bruno, G. E.; Budnikov, D.; Buesching, H.; Bufalino, S.; Buncic, P.; Busch, O.; Buthelezi, Z.; Butt, J. B.; Buxton, J. T.; Caffarri, D.; Cai, X.; Caines, H.; Calero Diaz, L.; Caliva, A.; Calvo Villar, E.; Camerini, P.; Carena, F.; Carena, W.; Castillo Castellanos, J.; Castro, A. J.; Casula, E. A. R.; Cavicchioli, C.; Ceballos Sanchez, C.; Cepila, J.; Cerello, P.; Cerkala, J.; Chang, B.; Chapeland, S.; Chartier, M.; Charvet, J. L.; Chattopadhyay, S.; Chattopadhyay, S.; Chelnokov, V.; Cherney, M.; Cheshkov, C.; Cheynis, B.; Chibante Barroso, V.; Chinellato, D. D.; Chochula, P.; Choi, K.; Chojnacki, M.; Choudhury, S.; Christakoglou, P.; Christensen, C. H.; Christiansen, P.; Chujo, T.; Chung, S. U.; Chunhui, Z.; Cicalo, C.; Cifarelli, L.; Cindolo, F.; Cleymans, J.; Colamaria, F.; Colella, D.; Collu, A.; Colocci, M.; Conesa Balbastre, G.; Conesa del Valle, Z.; Connors, M. E.; Contreras, J. G.; Cormier, T. M.; Corrales Morales, Y.; Cortés Maldonado, I.; Cortese, P.; Cosentino, M. R.; Costa, F.; Crochet, P.; Cruz Albino, R.; Cuautle, E.; Cunqueiro, L.; Dahms, T.; Dainese, A.; Danu, A.; Das, D.; Das, I.; Das, S.; Dash, A.; Dash, S.; De, S.; De Caro, A.; de Cataldo, G.; de Cuveland, J.; De Falco, A.; De Gruttola, D.; De Marco, N.; De Pasquale, S.; Deisting, A.; Deloff, A.; Dénes, E.; D'Erasmo, G.; Di Bari, D.; Di Mauro, A.; Di Nezza, P.; Diaz Corchero, M. A.; Dietel, T.; Dillenseger, P.; Divià, R.; Djuvsland, Ø.; Dobrin, A.; Dobrowolski, T.; Domenicis Gimenez, D.; Dönigus, B.; Dordic, O.; Dubey, A. K.; Dubla, A.; Ducroux, L.; Dupieux, P.; Ehlers, R. J.; Elia, D.; Engel, H.; Erazmus, B.; Erdemir, I.; Erhardt, F.; Eschweiler, D.; Espagnon, B.; Estienne, M.; Esumi, S.; Eum, J.; Evans, D.; Evdokimov, S.; Eyyubova, G.; Fabbietti, L.; Fabris, D.; Faivre, J.; Fantoni, A.; Fasel, M.; Feldkamp, L.; Felea, D.; Feliciello, A.; Feofilov, G.; Ferencei, J.; Fernández Téllez, A.; Ferreiro, E. G.; Ferretti, A.; Festanti, A.; Feuillard, V. J. G.; Figiel, J.; Figueredo, M. A. S.; Filchagin, S.; Finogeev, D.; Fiore, E. M.; Fleck, M. G.; Floris, M.; Foertsch, S.; Foka, P.; Fokin, S.; Fragiacomo, E.; Francescon, A.; Frankenfeld, U.; Fuchs, U.; Furget, C.; Furs, A.; Fusco Girard, M.; Gaardhøje, J. J.; Gagliardi, M.; Gago, A. M.; Gallio, M.; Gangadharan, D. R.; Ganoti, P.; Gao, C.; Garabatos, C.; Garcia-Solis, E.; Gargiulo, C.; Gasik, P.; Germain, M.; Gheata, A.; Gheata, M.; Ghosh, P.; Ghosh, S. K.; Gianotti, P.; Giubellino, P.; Giubilato, P.; Gladysz-Dziadus, E.; Glässel, P.; Gomez Ramirez, A.; González-Zamora, P.; Gorbunov, S.; Görlich, L.; Gotovac, S.; Grabski, V.; Graczykowski, L. K.; Graham, K. L.; Grelli, A.; Grigoras, A.; Grigoras, C.; Grigoriev, V.; Grigoryan, A.; Grigoryan, S.; Grinyov, B.; Grion, N.; Grosse-Oetringhaus, J. F.; Grossiord, J.-Y.; Grosso, R.; Guber, F.; Guernane, R.; Guerzoni, B.; Gulbrandsen, K.; Gulkanyan, H.; Gunji, T.; Gupta, A.; Gupta, R.; Haake, R.; Haaland, Ø.; Hadjidakis, C.; Haiduc, M.; Hamagaki, H.; Hamar, G.; Hansen, A.; Harris, J. W.; Hartmann, H.; Harton, A.; Hatzifotiadou, D.; Hayashi, S.; Heckel, S. T.; Heide, M.; Helstrup, H.; Herghelegiu, A.; Herrera Corral, G.; Hess, B. A.; Hetland, K. F.; Hilden, T. E.; Hillemanns, H.; Hippolyte, B.; Hosokawa, R.; Hristov, P.; Huang, M.; Humanic, T. J.; Hussain, N.; Hussain, T.; Hutter, D.; Hwang, D. S.; Ilkaev, R.; Ilkiv, I.; Inaba, M.; Ippolitov, M.; Irfan, M.; Ivanov, M.; Ivanov, V.; Izucheev, V.; Jacobs, P. M.; Jadlovska, S.; Jahnke, C.; Jang, H. J.; Janik, M. A.; Jayarathna, P. H. S. Y.; Jena, C.; Jena, S.; Jimenez Bustamante, R. T.; Jones, P. G.; Jung, H.; Jusko, A.; Kalinak, P.; Kalweit, A.; Kamin, J.; Kang, J. H.; Kaplin, V.; Kar, S.; Karasu Uysal, A.; Karavichev, O.; Karavicheva, T.; Karayan, L.; Karpechev, E.; Kebschull, U.; Keidel, R.; Keijdener, D. L. D.; Keil, M.; Khan, K. H.; Khan, M. M.; Khan, P.; Khan, S. A.; Khanzadeev, A.; Kharlov, Y.; Kileng, B.; Kim, B.; Kim, D. W.; Kim, D. J.; Kim, H.; Kim, J. S.; Kim, M.; Kim, M.; Kim, S.; Kim, T.; Kirsch, S.; Kisel, I.; Kiselev, S.; Kisiel, A.; Kiss, G.; Klay, J. L.; Klein, C.; Klein, J.; Klein-Bösing, C.; Kluge, A.; Knichel, M. L.; Knospe, A. G.; Kobayashi, T.; Kobdaj, C.; Kofarago, M.; Kollegger, T.; Kolojvari, A.; Kondratiev, V.; Kondratyeva, N.; Kondratyuk, E.; Konevskikh, A.; Kopcik, M.; Kour, M.; Kouzinopoulos, C.; Kovalenko, O.; Kovalenko, V.; Kowalski, M.; Koyithatta Meethaleveedu, G.; Kral, J.; Králik, I.; Kravčáková, A.; Krelina, M.; Kretz, M.; Krivda, M.; Krizek, F.; Kryshen, E.; Krzewicki, M.; Kubera, A. M.; Kučera, V.; Kugathasan, T.; Kuhn, C.; Kuijer, P. G.; Kulakov, I.; Kumar, A.; Kumar, J.; Kumar, L.; Kurashvili, P.; Kurepin, A.; Kurepin, A. B.; Kuryakin, A.; Kushpil, S.; Kweon, M. J.; Kwon, Y.; La Pointe, S. L.; La Rocca, P.; Lagana Fernandes, C.; Lakomov, I.; Langoy, R.; Lara, C.; Lardeux, A.; Lattuca, A.; Laudi, E.; Lea, R.; Leardini, L.; Lee, G. R.; Lee, S.; Legrand, I.; Lehas, F.; Lemmon, R. C.; Lenti, V.; Leogrande, E.; León Monzón, I.; Leoncino, M.; Lévai, P.; Li, S.; Li, X.; Lien, J.; Lietava, R.; Lindal, S.; Lindenstruth, V.; Lippmann, C.; Lisa, M. A.; Ljunggren, H. M.; Lodato, D. F.; Loenne, P. I.; Loginov, V.; Loizides, C.; Lopez, X.; López Torres, E.; Lowe, A.; Luettig, P.; Lunardon, M.; Luparello, G.; Luz, P. H. F. N. D.; Ma, R.; Maevskaya, A.; Mager, M.; Mahajan, S.; Mahmood, S. M.; Maire, A.; Majka, R. D.; Malaev, M.; Maldonado Cervantes, I.; Malinina, L.; Mal'Kevich, D.; Malzacher, P.; Mamonov, A.; Manko, V.; Manso, F.; Manzari, V.; Marchisone, M.; Mareš, J.; Margagliotti, G. V.; Margotti, A.; Margutti, J.; Marín, A.; Markert, C.; Marquard, M.; Martin, N. A.; Martin Blanco, J.; Martinengo, P.; Martínez, M. I.; Martínez García, G.; Martinez Pedreira, M.; Martynov, Y.; Mas, A.; Masciocchi, S.; Masera, M.; Masoni, A.; Massacrier, L.; Mastroserio, A.; Masui, H.; Matyja, A.; Mayer, C.; Mazer, J.; Mazzoni, M. A.; Mcdonald, D.; Meddi, F.; Melikyan, Y.; Menchaca-Rocha, A.; Meninno, E.; Mercado Pérez, J.; Meres, M.; Miake, Y.; Mieskolainen, M. M.; Mikhaylov, K.; Milano, L.; Milosevic, J.; Minervini, L. M.; Mischke, A.; Mishra, A. N.; Miskowiec, D.; Mitra, J.; Mitu, C. M.; Mohammadi, N.; Mohanty, B.; Molnar, L.; Montaño Zetina, L.; Montes, E.; Morando, M.; Moreira De Godoy, D. A.; Moretto, S.; Morreale, A.; Morsch, A.; Muccifora, V.; Mudnic, E.; Mühlheim, D.; Muhuri, S.; Mukherjee, M.; Mulligan, J. D.; Munhoz, M. G.; Murray, S.; Musa, L.; Musinsky, J.; Nandi, B. K.; Nania, R.; Nappi, E.; Naru, M. U.; Nattrass, C.; Nayak, K.; Nayak, T. K.; Nazarenko, S.; Nedosekin, A.; Nellen, L.; Ng, F.; Nicassio, M.; Niculescu, M.; Niedziela, J.; Nielsen, B. S.; Nikolaev, S.; Nikulin, S.; Nikulin, V.; Noferini, F.; Nomokonov, P.; Nooren, G.; Noris, J. C. C.; Norman, J.; Nyanin, A.; Nystrand, J.; Oeschler, H.; Oh, S.; Oh, S. K.; Ohlson, A.; Okatan, A.; Okubo, T.; Olah, L.; Oleniacz, J.; Oliveira Da Silva, A. C.; Oliver, M. H.; Onderwaater, J.; Oppedisano, C.; Orava, R.; Ortiz Velasquez, A.; Oskarsson, A.; Otwinowski, J.; Oyama, K.; Ozdemir, M.; Pachmayer, Y.; Pagano, P.; Paić, G.; Pajares, C.; Pal, S. K.; Pan, J.; Pandey, A. K.; Pant, D.; Papcun, P.; Papikyan, V.; Pappalardo, G. S.; Pareek, P.; Park, W. J.; Parmar, S.; Passfeld, A.; Paticchio, V.; Patra, R. N.; Paul, B.; Peitzmann, T.; Pereira Da Costa, H.; Pereira De Oliveira Filho, E.; Peresunko, D.; Pérez Lara, C. E.; Perez Lezama, E.; Peskov, V.; Pestov, Y.; Petráček, V.; Petrov, V.; Petrovici, M.; Petta, C.; Piano, S.; Pikna, M.; Pillot, P.; Pinazza, O.; Pinsky, L.; Piyarathna, D. B.; Ploskon, M.; Planinic, M.; Pluta, J.; Pochybova, S.; Podesta-Lerma, P. L. M.; Poghosyan, M. G.; Polichtchouk, B.; Poljak, N.; Poonsawat, W.; Pop, A.; Porteboeuf-Houssais, S.; Porter, J.; Pospisil, J.; Prasad, S. K.; Preghenella, R.; Prino, F.; Pruneau, C. A.; Pshenichnov, I.; Puccio, M.; Puddu, G.; Pujahari, P.; Punin, V.; Putschke, J.; Qvigstad, H.; Rachevski, A.; Raha, S.; Rajput, S.; Rak, J.; Rakotozafindrabe, A.; Ramello, L.; Raniwala, R.; Raniwala, S.; Räsänen, S. S.; Rascanu, B. T.; Rathee, D.; Read, K. F.; Real, J. S.; Redlich, K.; Reed, R. J.; Rehman, A.; Reichelt, P.; Reidt, F.; Ren, X.; Renfordt, R.; Reolon, A. R.; Reshetin, A.; Rettig, F.; Revol, J.-P.; Reygers, K.; Riabov, V.; Ricci, R. A.; Richert, T.; Richter, M.; Riedler, P.; Riegler, W.; Riggi, F.; Ristea, C.; Rivetti, A.; Rocco, E.; Rodríguez Cahuantzi, M.; Rodriguez Manso, A.; Røed, K.; Rogochaya, E.; Rohr, D.; Röhrich, D.; Romita, R.; Ronchetti, F.; Ronflette, L.; Rosnet, P.; Rossi, A.; Roukoutakis, F.; Roy, A.; Roy, C.; Roy, P.; Rubio Montero, A. J.; Rui, R.; Russo, R.; Ryabinkin, E.; Ryabov, Y.; Rybicki, A.; Sadovsky, S.; Šafařík, K.; Sahlmuller, B.; Sahoo, P.; Sahoo, R.; Sahoo, S.; Sahu, P. K.; Saini, J.; Sakai, S.; Saleh, M. A.; Salgado, C. A.; Salzwedel, J.; Sambyal, S.; Samsonov, V.; Sanchez Castro, X.; Šándor, L.; Sandoval, A.; Sano, M.; Sarkar, D.; Scapparone, E.; Scarlassara, F.; Scharenberg, R. P.; Schiaua, C.; Schicker, R.; Schmidt, C.; Schmidt, H. R.; Schuchmann, S.; Schukraft, J.; Schulc, M.; Schuster, T.; Schutz, Y.; Schwarz, K.; Schweda, K.; Scioli, G.; Scomparin, E.; Scott, R.; Seeder, K. S.; Seger, J. E.; Sekiguchi, Y.; Sekihata, D.; Selyuzhenkov, I.; Senosi, K.; Seo, J.; Serradilla, E.; Sevcenco, A.; Shabanov, A.; Shabetai, A.; Shadura, O.; Shahoyan, R.; Shangaraev, A.; Sharma, A.; Sharma, M.; Sharma, M.; Sharma, N.; Shigaki, K.; Shtejer, K.; Sibiriak, Y.; Siddhanta, S.; Sielewicz, K. M.; Siemiarczuk, T.; Silvermyr, D.; Silvestre, C.; Simatovic, G.; Simonetti, G.; Singaraju, R.; Singh, R.; Singha, S.; Singhal, V.; Sinha, B. C.; Sinha, T.; Sitar, B.; Sitta, M.; Skaali, T. B.; Slupecki, M.; Smirnov, N.; Snellings, R. J. M.; Snellman, T. W.; Søgaard, C.; Soltz, R.; Song, J.; Song, M.; Song, Z.; Soramel, F.; Sorensen, S.; Spacek, M.; Spiriti, E.; Sputowska, I.; Spyropoulou-Stassinaki, M.; Srivastava, B. K.; Stachel, J.; Stan, I.; Stefanek, G.; Steinpreis, M.; Stenlund, E.; Steyn, G.; Stiller, J. H.; Stocco, D.; Strmen, P.; Suaide, A. A. P.; Sugitate, T.; Suire, C.; Suleymanov, M.; Sultanov, R.; Šumbera, M.; Symons, T. J. M.; Szabo, A.; Szanto de Toledo, A.; Szarka, I.; Szczepankiewicz, A.; Szymanski, M.; Takahashi, J.; Tanaka, N.; Tangaro, M. A.; Tapia Takaki, J. D.; Tarantola Peloni, A.; Tarhini, M.; Tariq, M.; Tarzila, M. G.; Tauro, A.; Tejeda Muñoz, G.; Telesca, A.; Terasaki, K.; Terrevoli, C.; Teyssier, B.; Thäder, J.; Thomas, D.; Tieulent, R.; Timmins, A. R.; Toia, A.; Trogolo, S.; Trubnikov, V.; Trzaska, W. H.; Tsuji, T.; Tumkin, A.; Turrisi, R.; Tveter, T. S.; Ullaland, K.; Uras, A.; Usai, G. L.; Utrobicic, A.; Vajzer, M.; Vala, M.; Valencia Palomo, L.; Vallero, S.; Van Der Maarel, J.; Van Hoorne, J. W.; van Leeuwen, M.; Vanat, T.; Vande Vyvre, P.; Varga, D.; Vargas, A.; Vargyas, M.; Varma, R.; Vasileiou, M.; Vasiliev, A.; Vauthier, A.; Vechernin, V.; Veen, A. M.; Veldhoen, M.; Velure, A.; Venaruzzo, M.; Vercellin, E.; Vergara Limón, S.; Vernet, R.; Verweij, M.; Vickovic, L.; Viesti, G.; Viinikainen, J.; Vilakazi, Z.; Villalobos Baillie, O.; Vinogradov, A.; Vinogradov, L.; Vinogradov, Y.; Virgili, T.; Vislavicius, V.; Viyogi, Y. P.; Vodopyanov, A.; Völkl, M. A.; Voloshin, K.; Voloshin, S. A.; Volpe, G.; von Haller, B.; Vorobyev, I.; Vranic, D.; Vrláková, J.; Vulpescu, B.; Vyushin, A.; Wagner, B.; Wagner, J.; Wang, H.; Wang, M.; Wang, Y.; Watanabe, D.; Watanabe, Y.; Weber, M.; Weber, S. G.; Wessels, J. P.; Westerhoff, U.; Wiechula, J.; Wikne, J.; Wilde, M.; Wilk, G.; Wilkinson, J.; Williams, M. C. S.; Windelband, B.; Winn, M.; Yaldo, C. G.; Yang, H.; Yang, P.; Yano, S.; Yin, Z.; Yokoyama, H.; Yoo, I.-K.; Yurchenko, V.; Yushmanov, I.; Zaborowska, A.; Zaccolo, V.; Zaman, A.; Zampolli, C.; Zanoli, H. J. C.; Zaporozhets, S.; Zardoshti, N.; Zarochentsev, A.; Závada, P.; Zaviyalov, N.; Zbroszczyk, H.; Zgura, I. S.; Zhalov, M.; Zhang, H.; Zhang, X.; Zhang, Y.; Zhao, C.; Zhigareva, N.; Zhou, D.; Zhou, Y.; Zhou, Z.; Zhu, H.; Zhu, J.; Zhu, X.; Zichichi, A.; Zimmermann, A.; Zimmermann, M. B.; Zinovjev, G.; Zyzak, M.

2015-09-01

We report the measurement of a new observable of jet quenching in central Pb-Pb collisions at √{s_{NN}}=2.76 TeV, based on the semi-inclusive rate of charged jets recoiling from a high transverse momentum (high- p T) charged hadron trigger. Jets are measured using collinear-safe jet reconstruction with infrared cutoff for jet constituents of 0.15 GeV, for jet resolution parameters R = 0 .2, 0 .4 and 0 .5. Underlying event background is corrected at the event-ensemble level, without imposing bias on the jet population. Recoil jet spectra are reported in the range 20 < p T,jet ch < 100 GeV. Reference distributions for pp collisions at √{s}=2.76 TeV are calculated using Monte Carlo and NLO pQCD methods, which are validated by comparing with measurements in pp collisions at √{s}=7 TeV. The recoil jet yield in central Pb-Pb collisions is found to be suppressed relative to that in pp collisions. No significant medium-induced broadening of the intra-jet energy profile is observed within 0.5 radians relative to the recoil jet axis. The angular distribution of the recoil jet yield relative to the trigger axis is found to be similar in central Pb-Pb and pp collisions, with no significant medium-induced acoplanarity observed. Large-angle jet deflection, which may provide a direct probe of the nature of the quasi-particles in hot QCD matter, is explored. [Figure not available: see fulltext.

Faint Object Camera imaging and spectroscopy of NGC 4151

NASA Technical Reports Server (NTRS)

Boksenberg, A.; Catchpole, R. M.; Macchetto, F.; Albrecht, R.; Barbieri, C.; Blades, J. C.; Crane, P.; Deharveng, J. M.; Disney, M. J.; Jakobsen, P.

1995-01-01

We describe ultraviolet and optical imaging and spectroscopy within the central few arcseconds of the Seyfert galaxy NGC 4151, obtained with the Faint Object Camera on the Hubble Space Telescope. A narrowband image including (O III) lambda(5007) shows a bright nucleus centered on a complex biconical structure having apparent opening angle approximately 65 deg and axis at a position angle along 65 deg-245 deg; images in bands including Lyman-alpha and C IV lambda(1550) and in the optical continuum near 5500 A, show only the bright nucleus. In an off-nuclear optical long-slit spectrum we find a high and a low radial velocity component within the narrow emission lines. We identify the low-velocity component with the bright, extended, knotty structure within the cones, and the high-velocity component with more confined diffuse emission. Also present are strong continuum emission and broad Balmer emission line components, which we attribute to the extended point spread function arising from the intense nuclear emission. Adopting the geometry pointed out by Pedlar et al. (1993) to explain the observed misalignment of the radio jets and the main optical structure we model an ionizing radiation bicone, originating within a galactic disk, with apex at the active nucleus and axis centered on the extended radio jets. We confirm that through density bounding the gross spatial structure of the emission line region can be reproduced with a wide opening angle that includes the line of sight, consistent with the presence of a simple opaque torus allowing direct view of the nucleus. In particular, our modelling reproduces the observed decrease in position angle with distance from the nucleus, progressing initially from the direction of the extended radio jet, through our optical structure, and on to the extended narrow-line region. We explore the kinematics of the narrow-line low- and high-velocity components on the basis of our spectroscopy and adopted model structure.

OBSERVATIONAL EVIDENCE FOR THE CAUSES AND CONSEQUENCES OF CHROMOSPHERIC RECONNECTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Limei; Xia, Lidong; Jiao, Fangran

The chromospheric anemone jets with an inverse “Y” shape are ubiquitous, as revealed by the Solar Optical Telescope observations. These jets are considered to be consequences of chromospheric magnetic reconnections. Although these jets have been studied intensively, the dynamics and their driving causes remain unclear observationally. In this work, we report a case of a chromospheric jet showing complete observational evidence for the cause and consequence of chromospheric intermittent reconnection. The intermittent eruption of this jet shows two distinct quasi-periods, 50–60 s and 600–700 s. The short-period eruptions may be related to the plasmoid-induced reconnection, and the long-period ones may bemore » interpreted as sequences of cycles of energy storage and release during magnetic reconnections. The observations also reveal Alfvénic waves with a mean period around 88 s and a maximum transverse displacement around 0.″26. The jet is hosted by a loop moving smoothly with a horizontal speed of ∼0.4 km s{sup −1}. Our results provide observational evidence supporting the magnetic reconnection model of the formation of the chromospheric jets with related products, in which the loop advection drives intermittent magnetic reconnections, and the reconnection outflows carrying plasmoids collide further with the ambient field lines and finally excite waves and jets.« less

Chromospheric Anemone Jets Observed with Hinode/SOT and Hida Ca II Spectroheliograph

NASA Astrophysics Data System (ADS)

Morita, S.; Shibata, K.; Ueno, S.; Ichimoto, K.; Kitai, R.; Otsuji, K.

2012-08-01

We present the first simultaneous observations of chromospheric “anemone” jets in active regions with the Ca II H broadband filetergram on the Hinode/SOT and with the Ca II K spetroheliogram on the Domeless Solar Telescope (DST) at the Hida Observatory. During coordinated observation period, 9 chromospheric anemone jets were simultaneously observed with the two instruments. These observations revealed: (1) the jets are generated in the low chromosphere because these cannot be seen in Ca II K3, (2) these jets are associated with mixed polarity regions which are either small emerging flux regions or moving magnetic features, (3) the Ca II K line often show red or blue asymmetry in K2/K1 component; the footpoint of the jets associated with emerging flux regions often show red asymmetry (2-16 km s-1), while the one with moving magnetic features show blue asymmetry (˜5 km s-1). The magnetic cancellations were observed at the footpoint of the jets. The canceling rates are of order of 1016 Mx s-1, and the resulting magnetic energy release rate (1.1-10)×1024 erg s-1, with the total energy release (1-13)×1026 erg for the duration of the magnetic cancellations, ˜130 s. These are comparable to the estimated total energy, ˜1026 erg, in a single chromospheric anemone jet.

An Experimental Study of Turbulent Nonpremixed Jet Flames in Crossflow Under Low-Gravity Conditions

NASA Astrophysics Data System (ADS)

Boxx, Isaac G.; Idicheria, Cherian A.; Clemens, Noel T.

2002-11-01

We will present results of a study of turbulent nonpremixed jet flames in crossflow under normal and low gravity conditions. This enables us to experimentally separate the competing influences of initial jet-to-crossflow momentum ratio and buoyancy effects on the flame structure. The low gravity conditions (10-30 milli-g) are achieved by dropping a self-contained jet flame rig in the University of Texas 1.25-second drop tower facility. This rig uses a small blow-through wind tunnel to create the crossflow. The jet flames issue from an orifice that is flush with the wall. High-speed CCD imaging of jet flame luminosity is the primary diagnostic. We present results for hydrocarbon jet flames with initial jet-to-crossflow momentum ratios of 10-20. Results such as flame trajectory, flame length, large scale structure and flame tip dynamics will be presented.

Magnetic jets from accretion disks : field structure and X-ray emission

NASA Astrophysics Data System (ADS)

Memola, Elisabetta

2002-06-01

Jets are highly collimated flows of matter. They are present in a large variety of astrophysical sources: young stars, stellar mass black holes (microquasars), galaxies with an active nucleus (AGN) and presumably also intense flashes of gamma-rays. In particular, the jets of microquasars, powered by accretion disks, are probably small-scale versions of the outflows from AGN. Beside observations of astrophysical jet sources, also theoretical considerations have shown that magnetic fields play an important role in jet formation, acceleration and collimation. Collimated jets seem to be systematically associated with the presence of an accretion disk around a star or a collapsed object. If the central object is a black hole, the surrounding accretion disk is the only possible location for a magnetic field generation. We are interested in the formation process of highly relativistic jets as observed from microquasars and AGN. We theoretically investigate the jet collimation region, whose physical dimensions are extremely tiny even compared to radio telescopes spatial resolution. Thus, for most of the jet sources, global theoretical models are, at the moment, the only possibility to gain information about the physical processes in the innermost jet region. For the first time, we determine the global two-dimensional field structure of stationary, axisymmetric, relativistic, strongly magnetized (force-free) jets collimating into an asymptotically cylindrical jet (taken as boundary condition) and anchored into a differentially rotating accretion disk. This approach allows for a direct connection between the accretion disk and the asymptotic collimated jet. Therefore, assuming that the foot points of the field lines are rotating with Keplerian speed, we are able to achieve a direct scaling of the jet magnetosphere in terms of the size of the central object. We find a close compatibility between the results of our model and radio observations of the M87 galaxy innermost jet. We also calculate the X-ray emission in the energy range 0.2--10.1,keV from a microquasar relativistic jet close to its source of 5 solar masses. In order to do it, we apply the jet flow parameters (densities, velocities, temperatures of each volume element along the collimating jet) derived in the literature from the relativistic magnetohydrodynamic equations. We obtain theoretical thermal X-ray spectra of the innermost jet as composition of the spectral contributions of the single volume elements along the jet. Since relativistic effects as Doppler shift and Doppler boosting due to the motion of jets toward us might be important, we investigate how the spectra are affected by them considering different inclinations of the line of sight to the jet axis. Emission lines of highly ionized iron are clearly visible in our spectra, probably also observed in the Galactic microquasars GRS 1915+105 and XTE J1748-288. The Doppler shift of the emission lines is always evident. Due to the chosen geometry of the magnetohydrodynamic jet, the inner X-ray emitting part is not yet collimated. Ergo, depending on the viewing angle, the Doppler boosting does not play a major role in the total spectra. This is the first time that X-ray spectra have been calculated from the numerical solution of a magnetohydrodynamic jet. Astrophysikalische Jets sind stark kollimierte Materieströmungen hoher Geschwindigkeit. Sie stehen im Zusammenhang mit einer Fülle verschiedener astrophysikalischer Objekte wie jungen Sternen, stellaren schwarzen Löchern ('Mikro-Quasare'), Galaxien mit aktivem Kern (AGN) und wahrscheinlich auch mit dem beobachteten intensiven Aufblitzen von Gamma-Strahlung (Gamma Ray Bursts). Insbesondere hat sich gezeigt, dass die Jets der Mikro-Quasare wahrscheinlich als kleinskalige Version der Jets der AGN anzusehen sind. Neben den Beobachtungen haben vor allem auch theoretische Überlegungen gezeigt, dass Magnetfelder bei der Jetentstehung, -beschleunigung und -kollimation eine wichtige Rolle spielen. Weiterhin scheinen Jets systematisch verknüpft zu sein mit dem Vorhandensein einer Akkretionsscheibe um das zentrale Objekt. Insbesondere wenn ein schwarzes Loch den Zentralkörper darstellt, ist die umgebende Akkretionsscheibe der einzig mögliche Ort um Magnetfeld erzeugen zu können. Wir sind speziell interessiert am Entstehungsprozess hoch relativistischer Jets wie sie bei Mikro-Quasaren und AGN beobachtet werden. Insbesondere untersuchen wir die Region, in der der Jet kollimiert, eine Region, deren räumliche Ausdehnung extrem klein ist selbst im Vergleich zur Auflösung der Radioteleskope. Dies ist ein Grund, wieso zum heutigen Zeitpunkt für die meisten Quellen die theoretische Modellierung die einzige Möglichkeit darstellt, um Information über die physikalischen Prozesse in der innersten Region der Jetentstehung zu erhalten. Uns ist es zum ersten Mal gelungen, die globale zwei-dimensionale Magnetfeldstruktur stationärer, axialsymmetrischer, relativistischer und stark magnetisierter (kräfte-freier) Jets zu berechnen, die zum einen asymptotisch in einen zylindrischen Jet kollimieren, zum anderen aber in einer differential rotierenden Akkretionsscheibe verankert sind. Damit erlaubt dieser Ansatz eine physikalische Verkn¨upfung zwischen Akkretionsscheibe und dem asymptotischen Jet. Nimmt man also an, dass die Fupunkte der Magnetfeldlinien mit Keplergeschwindigkeit rotieren, so kann man eine direkte Skalierung der Jetmagnetosphere mit der Gröe des Zentralobjektes erhalten. Unsere Resultate zeigen eine gute Übereinstimmung zwischen unserem Modell und Beobachtungen des Jets von M87. Für das Beispiel eines relativistischen Mikroquasarjets haben wir die Röntgenemission im Bereich von 0.2-10.1 keV berechnet. Dafür haben wir in der Literatur aus den relativistischen magnetohydrodynamischen Gleichungen berechnete Jetgröen (Dichte-, Geschwindigkeits-, und Temperaturprofil) verwendet und das Spektrum für jeden Punkt entlang der Jetströmung abgeleitet. Das theoretische thermische Röntgenspektrum des innersten, heien Teils des Jets erhalten wir zusammengesetzt aus den spektralen Anteilen der einzelnen Volumenelemente entlang des Jets. Um relativistische Effekte wie Dopplerverschiebung und -verstärkung (boosting) aufgrund der Jetbewegung zu untersuchen, haben wir für verschiedene Inklinationswinkel des Jets zur Sichtlinie berechnet, wie die erhaltenen Spektren davon beeinflusst werden. Unsere Spektren zeigen deutlich die hochionisierten Eisen-Emissionslinien, die in den galaktischen Mikroquasaren GRS 1915+105 und XTE J1748-288 andeutungsweise beobachtet wurden. Eine Dopplerverschiebung dieser Linien ist in unseren Spektren deutlichzu sehen. Da die innerste, Röntgenstrahlung emittierende Region des magnetohydrodynamischen Jets allerdings noch unkollimiert ist, spielt Dopplerboosting in unseren Spektren, abhängig vom Sichtwinkel, keine groe Rolle. Mit unseren Resultaten konnte zum ersten Mal ein Röntgenspektrum gewonnen werden, das auf der numerischen Lösung eines magnetohydrodynamischen Jets beruht.

Numerical analysis of exhaust jet secondary combustion in hypersonic flow field

NASA Astrophysics Data System (ADS)

Yang, Tian-Peng; Wang, Jiang-Feng; Zhao, Fa-Ming; Fan, Xiao-Feng; Wang, Yu-Han

2018-05-01

The interaction effect between jet and control surface in supersonic and hypersonic flow is one of the key problems for advanced flight control system. The flow properties of exhaust jet secondary combustion in a hypersonic compression ramp flow field were studied numerically by solving the Navier-Stokes equations with multi-species and combustion reaction effects. The analysis was focused on the flow field structure and the force amplification factor under different jet conditions. Numerical results show that a series of different secondary combustion makes the flow field structure change regularly, and the temperature increases rapidly near the jet exit.

Study of kinematic observables sentitive to the Higgs boson production channel in pp → Hjj process

NASA Astrophysics Data System (ADS)

Belyaev, N.; Konoplich, R.; Prokofiev, K.

2017-12-01

After the Higgs boson discovery at the LHC, a lot of additional measurements should be performed to understand in details the properties of the observed particle. These measurements include cross sections measurements, couplings measurements, studies of the interaction vertex structures etc. One of the most perspective subjects to study is the kinematics of the production jets, associated with the Higgs boson. It is demonstrated, that the kinematic correlations of such jets can be used to distinguish different production channels of Higgs boson: gluon-gluon fusion (ggF) and vector boson fusion (VBF). Such separation plays an important role because possible beyond the Standard Model contributions in ggF and VBF channels lead to different effects, which should be taken into account in searches for BSM physics.

SHAPING POINT- AND MIRROR-SYMMETRIC PROTOPLANETARY NEBULAE BY THE ORBITAL MOTION OF THE CENTRAL BINARY SYSTEM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haro-Corzo, Sinhue A. R.; Velazquez, Pablo F.; Raga, Alejandro C.

We present three-dimensional hydrodynamical simulations of a jet launched from the secondary star of a binary system inside a protoplanetary nebula. The secondary star moves around the primary in a close eccentric orbit. From the gasdynamic simulations we compute synthetic [N II] lambda 6583 emission maps. Different jet axis inclinations with respect to the orbital plane, as well as different orientations of the flow with respect to the observer, are considered. For some parameter combinations, we obtain structures that show point- or mirror-symmetric morphologies depending on the orientation of the flow with respect to the observer. Furthermore, our models canmore » explain some of the emission distribution asymmetries that are summarized in the classification given by Soker and Hadar.« less

ON A CORONAL BLOWOUT JET: THE FIRST OBSERVATION OF A SIMULTANEOUSLY PRODUCED BUBBLE-LIKE CME AND A JET-LIKE CME IN A SOLAR EVENT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shen Yuandeng; Liu Yu; Su Jiangtao

2012-02-01

The coronal blowout jet is a peculiar category among various jet phenomena, in which the sheared base arch, often carrying a small filament, experiences a miniature version of blowout eruption that produces large-scale coronal mass ejection (CME). In this paper, we report such a coronal blowout jet with high-resolution multi-wavelength and multi-angle observations taken from Solar Dynamics Observatory, Solar Terrestrial Relations Observatory, and Big Bear Solar Observatory. For the first time, we find that simultaneous bubble-like and jet-like CMEs were dynamically related to the blowout jet that showed cool and hot components next to each other. Our observational results indicatemore » that (1) the cool component resulted from the eruption of the filament contained within the jet's base arch, and it further caused the bubble-like CME; (2) the jet-like CME was associated with the hot component, which was the outward moving heated plasma generated by the reconnection of the base arch and its ambient open field lines. On the other hand, bifurcation of the jet's cool component was also observed, which resulted from the uncoupling of the erupting filament's two legs that were highly twisted at the very beginning. Based on these results, we propose a model to interpret the coronal blowout jet, in which the external reconnection not only produces the jet-like CME, but also leads to the rising of the filament. Subsequently, internal reconnection starts underneath the rising filament and thereby causes the bubble-like CME.« less

Deformations of free jets

NASA Astrophysics Data System (ADS)

Paruchuri, Srinivas

This thesis studies three different problems. First we demonstrate that a flowing liquid jet can be controllably split into two separate subfilaments through the applications of a sufficiently strong tangential stress to the surface of the jet. In contrast, normal stresses can never split a liquid jet. We apply these results to observations of uncontrolled splitting of jets in electric fields. The experimental realization of controllable jet splitting would provide an entirely novel route for producing small polymeric fibers. In the second chapter we present an analytical model for the bending of liquid jets and sheets from temperature gradients, as recently observed by Chwalek et al. [Phys. Fluids, 14, L37 (2002)]. The bending arises from a local couple caused by Marangoni forces. The dependence of the bending angle on experimental parameters is presented, in qualitative agreement with reported experiments. The methodology gives a simple framework for understanding the mechanisms for jet and sheet bending. In chapter 4 we address the discrepancy between hydrodynamic theory of liquid jets, and the snap-off of narrow liquid jets observed in molecular dynamics (MD) simulations [23]. This has been previously attributed to the significant role of thermal fluctuations in nanofluidic systems. We argue that hydrodynamic description of such systems should include corrections to the Laplace pressure which result from the failure of the sharp interface assumption when the jet diameter becomes small enough. We show that this effect can in principle give rise to jet shapes similar to those observed in MD simulations, even when thermal fluctuations are completely neglected. Finally we summarize an algorithm developed to simulate droplet impact on a smooth surface.

Numerical simulations of negatively buoyant jets in an immiscible fluid using the Particle Finite Element Method

NASA Astrophysics Data System (ADS)

Mier-Torrecilla, Monica; Geyer, Adelina; Phillips, Jeremy C.; Idelsohn, Sergio R.; Oñate, Eugenio

2010-05-01

In this work we investigate numerically the injection of a negatively buoyant jet into a homogenous immiscible ambient fluid using the Particle Finite Element Method (PFEM), a newly developed tool that combines the flexibility of particle-based methods with the accuracy of the finite element discretization. In order to test the applicability of PFEM to the study of negatively buoyant jets, we have compared the two-dimensional numerical results with experiments investigating the injection of a jet of dyed water through a nozzle in the base of a cylindrical tank containing rapeseed oil. In both simulations and experiments, the fountain inlet flow velocity and nozzle diameter were varied to cover a wide range of Reynolds Re and Froude numbers Fr, such that 0.1 < Fr < 30, reproducing both weak and strong fountains in a laminar regime (8 < Re < 1350). Numerical results, together with the experimental observations, allow us to describe three different fountain behaviors that have not been previously reported. Based on the Re and Fr values for the numerical and experimental simulations, we have built a regime map to define how these values may control the occurrence of each of the observed flow types. Whereas the Fr number itself provides a prediction of the maximum penetration height of the jet, its combination with the Re number provides a prediction of the flow behavior for a specific nozzle diameter and injection velocity. Conclusive remarks concerning the dynamics of negatively buoyant jets may be applied later on to several geological situations, e.g. the flow structure of a fully submerged subaqueous eruptive vent discharging magma or the replenishment of magma chambers in the Earth's crust.

Radio Emission from Three-dimensional Relativistic Hydrodynamic Jets: Observational Evidence of Jet Stratification

NASA Astrophysics Data System (ADS)

Aloy, Miguel-Angel; Gómez, José-Luis; Ibáñez, José-María; Martí, José-María; Müller, Ewald

2000-01-01

We present the first radio emission simulations from high-resolution three-dimensional relativistic hydrodynamic jets; these simulations allow us to study the observational implications of the interaction between the jet and the external medium. This interaction gives rise to a stratification of the jet in which a fast spine is surrounded by a slow high-energy shear layer. The stratification (in particular, the large specific internal energy and slow flow in the shear layer) largely determines the emission from the jet. If the magnetic field in the shear layer becomes helical (e.g., resulting from an initial toroidal field and an aligned field component generated by shear), the emission shows a cross section asymmetry, in which either the top or the bottom of the jet dominates the emission. This, as well as limb or spine brightening, is a function of the viewing angle and flow velocity, and the top/bottom jet emission predominance can be reversed if the jet changes direction with respect to the observer or if it presents a change in velocity. The asymmetry is more prominent in the polarized flux because of field cancellation (or amplification) along the line of sight. Recent observations of jet cross section emission asymmetries in the blazar 1055+018 can be explained by assuming the existence of a shear layer with a helical magnetic field.

Electron Scale Structures and Magnetic Reconnection Signatures in the Turbulent Magnetosheath

NASA Technical Reports Server (NTRS)

Yordanova, E.; Voros, Z.; Varsani, A.; Graham, D. B.; Norgren, C.; Khotyaintsev, Yu. V.; Vaivads, A.; Eriksson, E.; Nakamura, R.; Lindqvist, P.-A.;

OFF-AXIS THERMAL AND SYNCHROTRON EMISSION FOR SHORT GAMMA RAY BURST

NASA Astrophysics Data System (ADS)

Xie, Xiaoyi

2018-01-01

We present light curves of photospheric and synchrotron emission from a relativistic jet propagating through the ejecta cloud of a neutron star merger. We use a moving-mesh relativistic hydrodynamics code with adaptive mesh refinement to compute the continuous evolution of jet over 13 orders of magnitude in radius from the scale of the central merger engine all the way through the late afterglow phase. As the jet propagates through the cloud it forms a hot cocoon surrounding the jet core. We find that the photospheric emission released by the hot cocoon is bright for on-axis observers and is detectable for off-axis observers at a wide range of observing angles for sufficiently close sources. As the jet and cocoon drive an external shock into the surrounding medium we compute synchrotron light curves and find bright emission for off-axis observers which differs from top-hat Blandford-McKee jets, especially for lower explosion energies.

JET2 Viewer: a database of predicted multiple, possibly overlapping, protein-protein interaction sites for PDB structures.

PubMed

Ripoche, Hugues; Laine, Elodie; Ceres, Nicoletta; Carbone, Alessandra

2017-01-04

The database JET2 Viewer, openly accessible at http://www.jet2viewer.upmc.fr/, reports putative protein binding sites for all three-dimensional (3D) structures available in the Protein Data Bank (PDB). This knowledge base was generated by applying the computational method JET 2 at large-scale on more than 20 000 chains. JET 2 strategy yields very precise predictions of interacting surfaces and unravels their evolutionary process and complexity. JET2 Viewer provides an online intelligent display, including interactive 3D visualization of the binding sites mapped onto PDB structures and suitable files recording JET 2 analyses. Predictions were evaluated on more than 15 000 experimentally characterized protein interfaces. This is, to our knowledge, the largest evaluation of a protein binding site prediction method. The overall performance of JET 2 on all interfaces are: Sen = 52.52, PPV = 51.24, Spe = 80.05, Acc = 75.89. The data can be used to foster new strategies for protein-protein interactions modulation and interaction surface redesign. © The Author(s) 2016. Published by Oxford University Press on behalf of Nucleic Acids Research.

Jets in Polar Coronal Holes

NASA Astrophysics Data System (ADS)

Scullion, E.; Popescu, M. D.; Banerjee, D.; Doyle, J. G.; Erdélyi, R.

2009-10-01

Here, we explore the nature of small-scale jet-like structures and their possible relation to explosive events and other known transient features, like spicules and macrospicules, using high-resolution spectroscopy obtained with the Solar and Heliospheric Observatory/Solar Ultraviolet Measurements of Emitted Radiation instrument. We present a highly resolved spectroscopic analysis and line parameter study of time-series data for jets occurring on-disk and off-limb in both a northern and a southern coronal hole. The analysis reveals many small-scale transients which rapidly propagate between the mid-transition region (N IV 765 Å line formation: 140,000 K) and the lower corona (Ne VIII 770 Å line formation: 630,000 K). In one example, a strong jet-like event is associated with a cool feature not present in the Ne VIII 770 Å line radiance or Doppler velocity maps. Another similar event is observed, but with a hot component, which could be perceived as a blinker. Our data reveal fast, repetitive plasma outflows with blueshift velocities of ≈145 km s-1 in the lower solar atmosphere. The data suggest a strong role for smaller jets (spicules), as a precursor to macrospicule formation, which may have a common origin with explosive events.

Reduction and degradation of amyloid aggregates by a pulsed radio-frequency cold atmospheric plasma jet

NASA Astrophysics Data System (ADS)

Bayliss, D. L.; Walsh, J. L.; Shama, G.; Iza, F.; Kong, M. G.

2009-11-01

Surface-borne amyloid aggregates with mature fibrils are used as a non-infectious prion model to evaluate cold atmospheric plasmas (CAPs) as a prion inactivation strategy. Using a helium-oxygen CAP jet with pulsed radio-frequency (RF) excitation, amyloid aggregates deposited on freshly cleaved mica discs are reduced substantially leaving only a few spherical fragments of sub-micrometer sizes in areas directly treated by the CAP jet. Outside the light-emitting part of the CAP jet, plasma treatment results in a 'skeleton' of much reduced amyloid stacks with clear evidence of fibril fragmentation. Analysis of possible plasma species and the physical configuration of the jet-sample interaction suggests that the skeleton structures observed are unlikely to have arisen as a result of physical forces of detachment, but instead by progressive diffusion of oxidizing plasma species into porous amyloid aggregates. Composition of chemical bonds of this reduced amyloid sample is very different from that of intact amyloid aggregates. These suggest the possibility of on-site degradation by CAP treatment with little possibility of spreading contamination elsewhere , thus offering a new reaction chemistry route to protein infectivity control with desirable implications for the practical implementation of CAP-based sterilization systems.

The Stability of Radiatively Cooling Jets I. Linear Analysis

NASA Technical Reports Server (NTRS)

Hardee, Philip E.; Stone, James M.

1997-01-01

The results of a spatial stability analysis of a two-dimensional slab jet, in which optically thin radiative cooling is dynamically important, are presented. We study both magnetized and unmagnetized jets at external Mach numbers of 5 and 20. We model the cooling rate by using two different cooling curves: one appropriate to interstellar gas, and the other to photoionized gas of reduced metallicity. Thus, our results will be applicable to both protostellar (Herbig-Haro) jets and optical jets from active galactic nuclei. We present analytical solutions to the dispersion relations in useful limits and solve the dispersion relations numerically over a broad range of perturbation frequencies. We find that the growth rates and wavelengths of the unstable Kelvin-Helmholtz (K-H) modes are significantly different from the adiabatic limit, and that the form of the cooling function strongly affects the results. In particular, if the cooling curve is a steep function of temperature in the neighborhood of the equilibrium state, then the growth of K-H modes is reduced relative to the adiabatic jet. On the other hand, if the cooling curve is a shallow function of temperature, then the growth of K-H modes can be enhanced relative to the adiabatic jet by the increase in cooling relative to heating in overdense regions. Inclusion of a dynamically important magnetic field does not strongly modify the important differences between an adiabatic jet and a cooling jet, provided the jet is highly supermagnetosonic and not magnetic pressure-dominated. In the latter case, the unstable modes behave more like the transmagnetosonic magnetic pressure-dominated adiabatic limit. We also plot fluid displacement surfaces associated with the various waves in a cooling jet in order to predict the structures that might arise in the nonlinear regime. This analysis predicts that low-frequency surface waves and the lowest order body modes will be the most effective at producing observable features in the jet.

The complete set of Cassini's UVIS occultation observations of Enceladus plume: model fits

NASA Astrophysics Data System (ADS)

Portyankina, G.; Esposito, L. W.; Hansen, C. J.

2017-12-01

Since the discovery in 2005, plume of Enceladus was observed by most of the instruments onboard Cassini spacecraft. Ultraviolet Imaging Spectrograph (UVIS) have observed Enceladus plume and collimated jets embedded in it in occultational geometry on 6 different occasions. We have constructed a 3D direct simulation Monte Carlo (DSMC) model for Enceladus jets and apply it to the analysis of the full set of UVIS occultation observations conducted during Cassini's mission from 2005 to 2017. The Monte Carlo model tracks test particles from their source at the surface into space. The initial positions of all test particles for a single jet are fixed to one of 100 jets sources identified by Porco et al. (2014). The initial three-dimensional velocity of each particle contains two components: a velocity Vz which is perpendicular to the surface, and a thermal velocity which is isotropic in the upward hemisphere. The direction and speed of the thermal velocity of each particle is chosen randomly but the ensemble moves isotropically at a speed which satisfies a Boltzmann distribution for a given temperature Tth. A range for reasonable Vz is then determined by requiring that modeled jet widths match the observed ones. Each model run results in a set of coordinates and velocities of a given set of test particles. These are converted to the test particle number densities and then integrated along LoS for each time step of the occultation observation. The geometry of the observation is calculated using SPICE. The overarching result of the simulation run is a test particle number density along LoS for each time point during the occultation observation for each of the jets separately. To fit the model to the data, we integrate all jets that are crossed by the LoS at each point during an observation. The relative strength of the jets must be determined to fit the observed UVIS curves. The results of the fits are sets of active jets for each occultation. Each UVIS occultation observation was done under a unique observational geometry. Consequently, the model fits produce different sets of active jets and different minimum Vz. We discuss and compare the results of fitting all UVIS occultation observations.

Large Scale Turbulent Structures in Supersonic Jets

NASA Technical Reports Server (NTRS)

Rao, Ram Mohan; Lundgren, Thomas S.

1997-01-01

Jet noise is a major concern in the design of commercial aircraft. Studies by various researchers suggest that aerodynamic noise is a major contributor to jet noise. Some of these studies indicate that most of the aerodynamic jet noise due to turbulent mixing occurs when there is a rapid variation in turbulent structure, i.e. rapidly growing or decaying vortices. The objective of this research was to simulate a compressible round jet to study the non-linear evolution of vortices and the resulting acoustic radiations. In particular, to understand the effect of turbulence structure on the noise. An ideal technique to study this problem is Direct Numerical Simulations(DNS), because it provides precise control on the initial and boundary conditions that lead to the turbulent structures studied. It also provides complete 3-dimensional time dependent data. Since the dynamics of a temporally evolving jet are not greatly different from those, of a spatially evolving jet, a temporal jet problem was solved, using periodicity ill the direction of the jet axis. This enables the application of Fourier spectral methods in the streamwise direction. Physically this means that turbulent structures in the jet are repeated in successive downstream cells instead of being gradually modified downstream into a jet plume. The DNS jet simulation helps us understand the various turbulent scales and mechanisms of turbulence generation in the evolution of a compressible round jet. These accurate flow solutions will be used in future research to estimate near-field acoustic radiation by computing the total outward flux across a surface and determine how it is related to the evolution of the turbulent solutions. Furthermore, these simulations allow us to investigate the sensitivity of acoustic radiations to inlet/boundary conditions, with possible application to active noise suppression. In addition, the data generated can be used to compute various turbulence quantities such as mean velocities, turbulent stresses, etc. which will aid in turbulence modeling. This report will be presented in two chapters. The first chapter describes some work on the linear stability of a supersonic round jet and the implications of this for the jet noise problem. The second chapter is an extensive discussion of numerical work using the spectral method which we use to solve the compressible Navier-Stokes equations to study turbulent jet flows. The method uses Fourier expansions in the azimuthal and streamwise direction and a 1-D B-spline basis representation in the radial direction. The B-spline basis is locally supported and this ensures block diagonal matrix equations which can be solved in O(N) steps. This is a modification of a boundary layer code developed by Robert Moser. A very accurate highly resolved Direct Numerical Simulation (DNS) of a turbulent jet flow is produced.

Large Scale Turbulent Structures in Supersonic Jets

NASA Technical Reports Server (NTRS)

Rao, Ram Mohan; Lundgren, Thomas S.

1997-01-01

Jet noise is a major concern in the design of commercial aircraft. Studies by various researchers suggest that aerodynamic noise is a major contributor to jet noise. Some of these studies indicate that most of the aerodynamic jet noise due to turbulent mixing occurs when there is a rapid variation in turbulent structure, i.e. rapidly growing or decaying vortices. The objective of this research was to simulate a compressible round jet to study the non-linear evolution of vortices and the resulting acoustic radiations. In particular, to understand the effect of turbulence structure on the noise. An ideal technique to study this problem is Direct Numerical Simulations (DNS), because it provides precise control on the initial and boundary conditions that lead to the turbulent structures studied. It also provides complete 3-dimensional time dependent data. Since the dynamics of a temporally evolving jet are not greatly different from those of a spatially evolving jet, a temporal jet problem was solved, using periodicity in the direction of the jet axis. This enables the application of Fourier spectral methods in the streamwise direction. Physically this means that turbulent structures in the jet are repeated in successive downstream cells instead of being gradually modified downstream into a jet plume. The DNS jet simulation helps us understand the various turbulent scales and mechanisms of turbulence generation in the evolution of a compressible round jet. These accurate flow solutions will be used in future research to estimate near-field acoustic radiation by computing the total outward flux across a surface and determine how it is related to the evolution of the turbulent solutions. Furthermore, these simulations allow us to investigate the sensitivity of acoustic radiations to inlet/boundary conditions, with possible appli(,a- tion to active noise suppression. In addition, the data generated can be used to compute, various turbulence quantities such as mean velocities, turbulent stresses, etc. which will aid in turbulence modeling. This report will be presented in two chapters. The first chapter describes some work on the linear stability of a supersonic round jet and the implications of this for the jet noise problem. The second chapter is an extensive discussion of numerical work using the spectral method which we use to solve the compressible Navier-Stokes equations to study turbulent jet flows. The method uses Fourier expansions in the azimuthal and streamwise direction and a 1-D B-spline basis representation in the radial direction. The B-spline basis is locally supported and this ensures block diagonal matrix equations which can be solved in O(N) steps. This is a modification of a boundary layer code developed by Robert Moser. A very accurate highly resolved DNS of a turbulent jet flow is produced.

First image of the L1157 molecular jet by the CALYPSO IRAM-PdBI survey

NASA Astrophysics Data System (ADS)

Podio, L.; Codella, C.; Gueth, F.; Cabrit, S.; Maury, A.; Tabone, B.; Lefèvre, C.; Anderl, S.; André, P.; Belloche, A.; Bontemps, S.; Hennebelle, P.; Lefloch, B.; Maret, S.; Testi, L.

2016-09-01

Context. Fast jets are thought to be a crucial ingredient of star formation because they might extract angular momentum from the disk and thus allow mass accretion onto the star. However, it is unclear whether jets are ubiquitous, and likewise, their contribution to mass and angular momentum extraction during protostar formation remains an open question. Aims: Our aim is to investigate the ejection process in the low-mass Class 0 protostar L1157. This source is associated with a spectacular bipolar outflow, and the recent detection of high-velocity SiO suggests the occurrence of a jet. Methods: Observations of CO 2 -1 and SiO 5 - 4 at ~0.8 arcsec resolution were obtained with the IRAM Plateau de Bure Interferometer (PdBI) as part of the CALYPSO large program. The jet and outflow structure were fit with a precession model. We derived the column density of CO and SiO, as well as the jet mass-loss rate and mechanical luminosity. Results: High-velocity CO and SiO emission resolve for the first time the first 200 au of the outflow-driving molecular jet. The jet is strongly asymmetric, with the blue lobe ~0.65 times slower than the red lobe. This suggests that the large-scale asymmetry of the outflow is directly linked to the jet velocity and that the asymmetry in the launching mechanism has been at work for the past 1800 yr. Velocity asymmetries are common in T Tauri stars, which suggests that the jet formation mechanism from Class 0 to Class II stages might be similar. Our model simultaneously fits the properties of the inner jet and of the clumpy 0.2 pc scale outflow by assuming that the jet precesses counter-clockwise on a cone inclined by 73° to the line of sight with an opening angle of 8° on a period of ~1640 yr. The estimated jet mass flux and mechanical luminosity are Ṁjet ~ 7.7 × 10-7M⊙ yr-1 and Ljet ~ 0.9L⊙, indicating that the jet could extract at least 25% of the gravitational energy released by the forming star.

Fatigue of reinforcing bars during hydro-demolition

NASA Astrophysics Data System (ADS)

Hyland, C. W. K.; Ouwejan, A.

2017-05-01

Reinforcing steel fractured during hydro-demolition of a reinforced concrete pier head due to low cycle flexural fatigue from vibration caused by impact of the high pressure water jet on the exposed length of the bars. Research into the fatigue performance of steel reinforcing steel tends to focus on the high cycle axial performance in reinforced concrete members and re-bending behaviour. However with the increasing use of hydro-demolition of concrete structures as part of remediation works care is required to ensure the steel reinforcement exposed to the high pressure jet of water is not going to suffer relatively low cycle flexural damage that may compromise the designed performance of the completed reinforced concrete structure. This paper describes the failure assessment, fatigue analysis, and metallographic examination that was undertaken. It was found that the rib to flank transition radius on the reinforcement steel was small enough to cause a significant stress concentration effect and was the location of fatigue crack growth. A relatively simple analysis using the maximum unrestrained cantilevered bar length and force exerted by the water jet was used to calculate the maximum expected bending moment. This was compared to the bending capacity at initiation of yielding at the rib flank transition accounting for stress concentration effects. This showed that the observed cyclic reversing ductile crack growth and fracture of the H25 bars was consistent with the loading applied. A method is proposed based on these observations to assess suitable limits for unrestrained bar lengths or maximum working offset of the water jet from the point of bar restraint when undertaking hydro-demolition work. The fatigue critical performance requirements of AS/NZS4671 500E bars are also therefore compared with those of BS4449:2005 and PN EN/ISO 15630-1:2011 for comparable 500C bars

3D relativistic MHD numerical simulations of X-shaped radio sources

NASA Astrophysics Data System (ADS)

Rossi, P.; Bodo, G.; Capetti, A.; Massaglia, S.

2017-10-01

Context. A significant fraction of extended radio sources presents a peculiar X-shaped radio morphology: in addition to the classical double lobed structure, radio emission is also observed along a second axis of symmetry in the form of diffuse wings or tails. In a previous investigation we showed the existence of a connection between the radio morphology and the properties of the host galaxies. Motivated by this connection we performed two-dimensional numerical simulations showing that X-shaped radio sources may naturally form as a jet propagates along the major axis a highly elliptical density distribution, because of the fast expansion of the cocoon along the minor axis of the distribution. Aims: We intend to extend our analysis by performing three-dimensional numerical simulations and investigating the role of different parameters in determining the formation of the X-shaped morphology. Methods: The problem is addressed by numerical means, carrying out three-dimensional relativistic magnetohydrodynamic simulations of bidirectional jets propagating in a triaxial density distribution. Results: We show that only jets with power ≲ 1044 erg s-1 can give origin to an X-shaped morphology and that a misalignment of 30° between the jet axis and the major axis of the density distribution is still favourable to the formation of this kind of morphology. In addition we compute synthetic radio emission maps and polarization maps. Conclusions: In our scenario for the formation of X-shaped radio sources only low power FRII can give origin to such kind of morphology. Our synthetic emission maps show that the different observed morphologies of X-shaped sources can be the result of similar structures viewed under different perspectives.

Ceramic micro-injection molded nozzles for serial femtosecond crystallography sample delivery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beyerlein, K. R.; Adriano, L.; Heymann, M.

Serial femtosecond crystallography (SFX) using X-ray Free-Electron Lasers (XFELs) allows for room temperature protein structure determination without evidence of conventional radiation damage. In this method, a liquid suspension of protein microcrystals can be delivered to the X-ray beam in vacuum as a micro-jet, which replenishes the crystals at a rate that exceeds the current XFEL pulse repetition rate. Gas dynamic virtual nozzles produce the required micrometer-sized streams by the focusing action of a coaxial sheath gas and have been shown to be effective for SFX experiments. Here, we describe the design and characterization of such nozzles assembled from ceramic micro-injectionmore » molded outer gas-focusing capillaries. Trends of the emitted jet diameter and jet length as a function of supplied liquid and gas flow rates are measured by a fast imaging system. The observed trends are explained by derived relationships considering choked gas flow and liquidflow conservation. In conclusion, the performance of these nozzles in a SFX experiment is presented, including an analysis of the observed background.« less

Ceramic micro-injection molded nozzles for serial femtosecond crystallography sample delivery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beyerlein, K. R.; Heymann, M.; Kirian, R.

Serial femtosecond crystallography (SFX) using X-ray Free-Electron Lasers (XFELs) allows for room temperature protein structure determination without evidence of conventional radiation damage. In this method, a liquid suspension of protein microcrystals can be delivered to the X-ray beam in vacuum as a micro-jet, which replenishes the crystals at a rate that exceeds the current XFEL pulse repetition rate. Gas dynamic virtual nozzles produce the required micrometer-sized streams by the focusing action of a coaxial sheath gas and have been shown to be effective for SFX experiments. Here, we describe the design and characterization of such nozzles assembled from ceramic micro-injectionmore » molded outer gas-focusing capillaries. Trends of the emitted jet diameter and jet length as a function of supplied liquid and gas flow rates are measured by a fast imaging system. The observed trends are explained by derived relationships considering choked gas flow and liquid flow conservation. Finally, the performance of these nozzles in a SFX experiment is presented, including an analysis of the observed background.« less

Ceramic micro-injection molded nozzles for serial femtosecond crystallography sample delivery

DOE PAGES

Beyerlein, K. R.; Adriano, L.; Heymann, M.; ...

2015-12-08

Serial femtosecond crystallography (SFX) using X-ray Free-Electron Lasers (XFELs) allows for room temperature protein structure determination without evidence of conventional radiation damage. In this method, a liquid suspension of protein microcrystals can be delivered to the X-ray beam in vacuum as a micro-jet, which replenishes the crystals at a rate that exceeds the current XFEL pulse repetition rate. Gas dynamic virtual nozzles produce the required micrometer-sized streams by the focusing action of a coaxial sheath gas and have been shown to be effective for SFX experiments. Here, we describe the design and characterization of such nozzles assembled from ceramic micro-injectionmore » molded outer gas-focusing capillaries. Trends of the emitted jet diameter and jet length as a function of supplied liquid and gas flow rates are measured by a fast imaging system. The observed trends are explained by derived relationships considering choked gas flow and liquidflow conservation. In conclusion, the performance of these nozzles in a SFX experiment is presented, including an analysis of the observed background.« less

Very Large Array Ammonia Observations of the HH 111/HH 121 Protostellar System: A Detection of a New Source with a Peculiar Chemistry

NASA Astrophysics Data System (ADS)

Sewiło, Marta; Wiseman, Jennifer; Indebetouw, Remy; Charnley, Steven B.; Pineda, Jaime E.; Lindberg, Johan E.; Qin, Sheng-Li

2017-11-01

We present the results of Very Large Array NH3 (J,K)=(1,1) and (2,2) observations of the HH 111/HH 121 protostellar system. HH 111, with a spectacular collimated optical jet, is one of the most well-known Herbig-Haro objects. We report the detection of a new source, NH3-S, in the vicinity of HH 111/HH 121 (˜0.03 pc from the HH 111 jet source) in two epochs of the ammonia observations. This constitutes the first detection of this source, in a region that has been thoroughly covered previously by both continuum and spectral line interferometric observations. We study the kinematic and physical properties of HH 111 and the newly discovered NH3-S. We also use HCO+ and HCN (J=4-3) data obtained with the James Clerk Maxwell Telescope and archival Atacama Large Millimeter/submillimeter Array 13CO, 12CO, and C18O (J=2-1), N2D+ (J=3-2), and 13CS (J=5-4) data to gain insight into the nature of NH3-S. The chemical structure of NH3-S shows evidence for “selective freeze-out,” an inherent characteristic of dense cold cores. The inner part of NH3-S shows subsonic nonthermal velocity dispersions indicating a “coherent core,” while they increase in the direction of the jets. Archival near- to far-infrared data show no indication of any embedded source in NH3-S. The properties of NH3-S and its location in the infrared dark cloud suggest that it is a starless core located in a turbulent medium, with the turbulence induced by Herbig-Haro jets and associated outflows. More data are needed to fully understand the physical and chemical properties of NH3-S and if/how its evolution is affected by nearby jets.

Very Large Array Ammonia Observations of the HH 111/HH 121 Protostellar System: A Detection of a New Source with a Peculiar Chemistry

NASA Technical Reports Server (NTRS)

Sewilo, Marta; Wiseman, Jennifer; Indebetouw, Remy; Charnley, Steven B.; Pineda, Jaime E.; Lindberg, Johan E.; Qin, Sheng-Li

2017-01-01

We present the results of Very Large Array NH3 (J, K) = (1, 1) and (2, 2) observations of the HH 111/HH 121 protostellar system. HH 111, with a spectacular collimated optical jet, is one of the most well-known Herbig-Haro objects. We report the detection of a new source, NH3-S, in the vicinity of HH 111/HH 121 (approximately 0.03 parsecs from the HH 111 jet source) in two epochs of the ammonia observations. This constitutes the first detection of this source, in a region that has been thoroughly covered previously by both continuum and spectral line interferometric observations. We study the kinematic and physical properties of HH 111 and the newly discovered NH3-S. We also use HCO plus and HCN (J=4-3) data obtained with the James Clerk Maxwell Telescope and archival Atacama Large Millimeter/submillimeter Array (sup 13) CO, (sup 12) CO, and C (sup 18) O (J=2-1), N2D plus (J=3-2), and (sup 13) CS (J=5-4) data to gain insight into the nature of NH3-S. The chemical structure of NH3-S shows evidence for "selective freeze-out,"� an inherent characteristic of dense cold cores. The inner part of NH3-S shows subsonic nonthermal velocity dispersions indicating a "coherent core,"� while they increase in the direction of the jets. Archival near- to far-infrared data show no indication of any embedded source in NH3-S. The properties of NH3-S and its location in the infrared dark cloud suggest that it is a starless core located in a turbulent medium, with the turbulence induced by Herbig-Haro jets and associated outflows. More data are needed to fully understand the physical and chemical properties of NH3-S and if/how its evolution is affected by nearby jets.

Tracking the global jet streams through objective analysis

NASA Astrophysics Data System (ADS)

Gallego, D.; Peña-Ortiz, C.; Ribera, P.

2009-12-01

Although the tropospheric jet streams are probably the more important single dynamical systems in the troposphere, their study at climatic scale has been usually troubled by the difficulty of characterising their structure. During the last years, a deal of effort has been made in order to construct long-term scale objective climatologies of the jet stream or at least to understand the variability of the westerly flux in the upper troposphere. A main problem with studying the jets is the necessity of using highly derivated fields as the potential vorticity or even the analysis of chemical tracers. Despite their utility, these approaches are very problematic to construct an automatic searching algorithm because of the difficulty of defining criteria for these extremely noisy fields. Some attempts have been addressed trying to use only the wind field to find the jet. This direct approach avoids the use of derivate variables, but it must contain some stringent criteria to filter the large number of tropospheric wind maxima not related to the jet currents. This approach has offered interesting results for the relatively simple structure of the Southern Hemisphere tropospheric jets (Gallego et al. Clim. Dyn, 2005). However, the much more complicated structure of its northern counterpart has resisted the analysis with the same degree of detail by using the wind alone. In this work we present a new methodology able to characterise the position, strength and altitude of the jet stream at global scale on a daily basis. The method is based on the analysis of the 3-D wind field alone and it searches, at each longitude, relative wind maxima in the upper troposphere between the levels of 400 and 100 hPa. An ad-hoc defined density function (dependent on the season and the longitude) of the detection positions is used as criteria to filter spurious wind maxima not related to the jet. The algorithm has been applied to the NCEP/NCAR reanalysis and the results show that the basic problems of a detection algorithm focused on searching the jets are avoided. Thus, a clear separation between the subtropical and polar jets for both hemispheres is found. The meandering of the northern hemisphere polar jet is accurately characterised while the large annual cycle in the strength of the subtropical jet is clearly found. In addition, the algorithm has shown to be able of finding structures for which it was not originally intended, as the tropical easterly jet stream above Southeast Asia, India and Africa. The new method opens some new possibilities to the study of the upper level tropospheric circulation. So the temporal variability of each jet on a daily basis, the single or double jet structures through a seasonal cycle or the trends of multiple jet characteristics (strength, location, height, wavenumber, separation between jets, etc.) can be easily computed to construct a new jet climatology.

Simulations of Jetted Relativistic Blastwaves in Astrophysics

NASA Astrophysics Data System (ADS)

Salmonson, Jay; Fragile, Chris; Anninos, Peter

2005-10-01

We present new 2D relativistic hydrodynamic simulations of jetted blastwaves using the Cosmos++ astrophysics code. In particular, we simulate the asymmetric outflow resulting from the giant flare of December 27, 2004 from SGR 1806-20. We find that the asymmetric radio nebula observed to expand over the months following the flare cannot be explained by a simple ballistic ejection of material during the flare, but requires angular dependence of the energy injection with respect to the jet axis. In addition, we present simulations of jetted blastwaves of the relativistic afterglows resulting from gamma-ray bursts. Evolving these jetted blastwaves from Lorentz factors of order 10, we explore the dependence of observed lightcurves on initial jet opening angle, energy distribution, and observer angle with respect to the jet axis. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.

Determining the structure of Higgs couplings at the CERN LargeHadron Collider.

PubMed

Plehn, Tilman; Rainwater, David; Zeppenfeld, Dieter

2002-02-04

Higgs boson production via weak boson fusion at the CERN Large Hadron Collider has the capability to determine the dominant CP nature of a Higgs boson, via the tensor structure of its coupling to weak bosons. This information is contained in the azimuthal angle distribution of the two outgoing forward tagging jets. The technique is independent of both the Higgs boson mass and the observed decay channel.

3-D Digitization of Stereoscopic Jet-in-Crossflow Vortex Structure Images via Augmented Reality

NASA Astrophysics Data System (ADS)

Sigurdson, Lorenz; Strand, Christopher; Watson, Graeme; Nault, Joshua; Tucker, Ryan

2006-11-01

Stereoscopic images of smoke-laden vortex flows have proven useful for understanding the topology of the embedded 3-D vortex structures. Images from two cameras allow a perception of the 3-D structure via the use of red/blue eye glasses. The human brain has an astonishing capacity to calculate and present to the observer the complex turbulent smoke volume. We have developed a technique whereby a virtual cursor is introduced to the perception, which creates an ``augmented reality.'' The perceived position of this cursor in the 3-D field can be precisely controlled by the observer. It can be brought near a characteristic vortex structure in order to digitally estimate the spatial coordinates of that feature. A calibration procedure accounts for camera positioning. Vortex tubes can be traced and recorded for later or real time supersposition of tube skeleton models. These models can be readily digitally obtained for display in graphics systems to allow complete exploration from any location or perspective. A unique feature of this technology is the use of the human brain to naturally perform the difficult computation of the shape of the translucent smoke volume. Examples are given of application to low velocity ratio and Reynolds number elevated jets-in-crossflow.

Direct Numerical Simulation of a Plane Transitional Wall Jet

NASA Astrophysics Data System (ADS)

Ramesh, O.; Varghese, Joel

2017-11-01

A transitional plane wall jet is studied using direct numerical simulation. The presence of an inflectional point leads to the outer layer rolling up into vortices that interacts with the inner region resulting in a double array of counter rotating vortices before breakdown into turbulence. Past studies have focused on forced wall jet which results in shorter transition region and prominent vortical structures. In the present work, natural transition will be discussed by analysing the coherent structures and scaled frequency spectra. Clear hairpin like structures leaning downstream in the inner region(as in a boundary layer) and leaning upstream in the outerstream (as in a jet) are evident.

The magnetically controlled stellar wind of HD 21699

NASA Technical Reports Server (NTRS)

Brown, D. N.; Shore, S. N.; Sonneborn, G.

1985-01-01

The discovery of a magnetically controlled stellar mass outflow in the helium-weak sn star HD 21699 = HR 1063 is reported. IUE observations show that the C IV resonance doublet is variable on the rotational time scale of about 2.5 days, and that there are no other observable spectrum variations in the UV. The magnetic field reverses sign on the rotational time scale. An interpretation of the observations in terms of magnetically structured jets is presented.

Analysis of Three-Dimensional, Nonlinear Development of Wave-Like Structure in a Compressible Round Jet

NASA Technical Reports Server (NTRS)

Dahl, Milo D.; Mankbadi, Reda R.

2002-01-01

An analysis of the nonlinear development of the large-scale structures or instability waves in compressible round jets was conducted using the integral energy method. The equations of motion were decomposed into two sets of equations; one set governing the mean flow motion and the other set governing the large-scale structure motion. The equations in each set were then combined to derive kinetic energy equations that were integrated in the radial direction across the jet after the boundary-layer approximations were applied. Following the application of further assumptions regarding the radial shape of the mean flow and the large structures, equations were derived that govern the nonlinear, streamwise development of the large structures. Using numerically generated mean flows, calculations show the energy exchanges and the effects of the initial amplitude on the coherent structure development in the jet.

Experimental and computational investigation of supersonic counterflow jet interaction in atmospheric conditions

NASA Astrophysics Data System (ADS)

Ivanchenko, Oleksandr

The flow field generated by the interaction of a converging-diverging nozzle (exit diameter, D=26 mm M=1.5) flow and a choked flow from a minor jet (exit diameter, d=2.6 mm) in a counterflow configuration was investigated. During the tests both the main C-D nozzle and the minor jet stagnation pressures were varied as well as the region of interaction. Investigations were made in the near field, at most about 2D distance, and in the far field, where the repeated patterns of shock waves were eliminated by turbulence. Both nozzles exhausted to the atmospheric pressure conditions. The flow physics was studied using Schlieren imaging techniques, Pitot-tube, conical Mach number probe, Digital Particle Image Velocimetry (DPIV) and acoustic measurement methods. During the experiments in the far field the jets interaction was observed as the minor jet flow penetrates into the main jet flow. The resulting shock structure caused by the minor jet's presence was dependent on the stagnation pressure ratio between the two jets. The penetration length of the minor jet into the main jet was also dependent on the stagnation pressure ratio. In the far field, increasing the minor jet stagnation pressure moved the bow shock forward, towards the main jet exit. In the near field, the minor jet flow penetrates into the main jet flow, and in some cases modified the flow pattern generated by the main jet, revealing a new effect of jet flow interaction that was previously unknown. A correlation function between the flow modes and the jet stagnation pressure ratios was experimentally determined. Additionally the flow interaction between the main and minor jets was simulated numerically using FLUENT. The optimal mesh geometry was found and the k-epsilon turbulence model was defined as the best fit. The results of the experimental and computational studies were used to describe the shock attenuation effect as self-sustain oscillations in supersonic flow. The effects described here can be used in different flow fields to reduce the total pressure losses that occur due to the presence of shock waves. It will result in better designs of ramjet/scramjets combustors, fighter aircraft inlets and as well as in noise reduction of existing aircraft engines. It can also improve performance of rotating machinery; ramjet fuel injectors and aircraft control mechanisms.

The Stability of Radiatively Cooling Jets. 2: Nonlinear Evolution

NASA Technical Reports Server (NTRS)

Stone, James M.; Xu, Jianjun; Hardee, Philip

1997-01-01

We use two-dimensional time-dependent hydrodynamical simulations to follow the growth of the Kelvin-Helmholtz (K-H) instability in cooling jets into the nonlinear regime. We focus primarily on asymmetric modes that give rise to transverse displacements of the jet beam. A variety of Mach numbers and two different cooling curves are studied. The growth rates of waves in the linear regime measured from the numerical simulations are in excellent agreement with the predictions of the linear stability analysis presented in the first paper in this series. In the nonlinear regime, the simulations show that asymmetric modes of the K-H instability can affect the structure and evolution of cooling jets in a number of ways. We find that jets in which the growth rate of the sinusoidal surface wave has a maximum at a so-called resonant frequency can be dominated by large-amplitude sinusoidal oscillations near this frequency. Eventually, growth of this wave can disrupt the jet. On the other hand, nonlinear body waves tend to produce low-amplitude wiggles in the shape of the jet but can result in strong shocks in the jet beam. In cooling jets, these shocks can produce dense knots and filaments of cooling gas within the jet. Ripples in the surface of the jet beam caused by both surface and body waves generate oblique shock "spurs" driven into the ambient gas. Our simulations show these shock "spurs" can accelerate ambient gas at large distances from the jet beam to low velocities, which represents a new mechanism by which low-velocity bipolar outflows may be driven by high-velocity jets. Rapid entrainment and acceleration of ambient gas may also occur if the jet is disrupted. For parameters typical of protostellar jets, the frequency at which K-H growth is a maximum (or highest frequency to which the entire jet can respond dynamically) will be associated with perturbations with a period of - 200 yr. Higher frequency (shorter period) perturbations excite waves associated with body modes that produce internal shocks and only small-amplitude wiggles within the jet. The fact that most observed systems show no evidence for large-amplitude sinusoidal oscillation leading to disruption is indicative that the perturbation frequencies are generally large, consistent with the suggestion that pro- tostellar jets arise from the inner regions (r less than 1 AU) of accretion disks.

The evolution of the X-ray afterglow emission of GW 170817/ GRB 170817A in XMM-Newton observations

NASA Astrophysics Data System (ADS)

D'Avanzo, P.; Campana, S.; Salafia, O. S.; Ghirlanda, G.; Ghisellini, G.; Melandri, A.; Bernardini, M. G.; Branchesi, M.; Chassande-Mottin, E.; Covino, S.; D'Elia, V.; Nava, L.; Salvaterra, R.; Tagliaferri, G.; Vergani, S. D.

2018-05-01

We report our observation of the short gamma-ray burst (GRB) GRB 170817A, associated to the binary neutron star merger gravitational wave (GW) event GW 170817, performed in the X-ray band with XMM-Newton 135 d after the event (on 29 December, 2017). We find evidence for a flattening of the X-ray light curve with respect to the previously observed brightening. This is also supported by a nearly simultaneous optical Hubble Space Telescope observation and successive X-ray Chandra and low-frequency radio observations recently reported in the literature. Since the optical-to-X-ray spectral slope did not change with respect to previous observations, we exclude that the change in the temporal evolution of the light curve is due to the passage of the cooling frequency: its origin must be geometric or dynamical. We interpret all the existing afterglow data with two models: i) a structured jet and ii) a jet-less isotropic fireball with some stratification in its radial velocity structure. Both models fit the data and predict that the radio flux must decrease simultaneously with the optical and X-ray emission, making it difficult to distinguish between them at the present stage. Polarimetric measurements and the rate of short GRB-GW associations in future LIGO/Virgo runs will be key to disentangle these two geometrically different scenarios.