Subpulse drifting, nulling, and mode changing in PSR J1822-2256

NASA Astrophysics Data System (ADS)

Basu, Rahul; Mitra, Dipanjan

2018-05-01

We report a detailed observational study of the single pulses from the pulsar J1822-2256. The pulsar shows the presence of subpulse drifting, nulling as well as multiple emission modes. During these observations the pulsar existed primarily in two modes; mode A with prominent drift bands and mode B which was more disorderly without any clear subpulse drifting. A third mode C was also seen for a short duration with a different drifting periodicity compared to mode A. The nulls were present throughout the observations but were more frequent during the disorderly B mode. The nulling also exhibited periodicity with a clear peak in the fluctuation spectra. Before the transition from mode A to nulling the pulsar switched to a third drifting state with periodicity different from both mode A and C. The diversity seen in the single pulse behaviour from the pulsar J1822-2256 provides an unique window into the emission physics.

Generation of Multiple Vortex Beams with Specified Vortex Number from Lasers with Controlled Ince-Gaussian Modes

NASA Astrophysics Data System (ADS)

Chu, Shu-Chun

2008-07-01

This study proposes a systematic method of selecting excitations of part of Ince-Gaussian modes (IGMs) and a three-lens configuration for generating multiple vortex beams with forced IGMs in the model of laser-diode (LD)-pumped solid-state lasers. Simply changing the lateral off-axis position of the tight pump beam focus on the laser crystal can produce the desired multiple optical vortex beam from the laser in a well-controlled manner using a proposed astigmatic mode converter assembled into one body with the laser cavity.

Giant moving vortex mass in thick magnetic nanodots

PubMed Central

Guslienko, K. Y.; Kakazei, G. N.; Ding, J.; Liu, X. M.; Adeyeye, A. O.

2015-01-01

Magnetic vortex is one of the simplest topologically non-trivial textures in condensed matter physics. It is the ground state of submicron magnetic elements (dots) of different shapes: cylindrical, square etc. So far, the vast majority of the vortex dynamics studies were focused on thin dots with thickness 5–50 nm and only uniform across the thickness vortex excitation modes were observed. Here we explore the fundamental vortex mode in relatively thick (50–100 nm) dots using broadband ferromagnetic resonance and show that dimensionality increase leads to qualitatively new excitation spectra. We demonstrate that the fundamental mode frequency cannot be explained without introducing a giant vortex mass, which is a result of the vortex distortion due to interaction with spin waves. The vortex mass depends on the system geometry and is non-local because of important role of the dipolar interaction. The mass is rather small for thin dots. However, its importance increases drastically with the dot thickness increasing. PMID:26355430

Giant moving vortex mass in thick magnetic nanodots.

PubMed

Guslienko, K Y; Kakazei, G N; Ding, J; Liu, X M; Adeyeye, A O

2015-09-10

Magnetic vortex is one of the simplest topologically non-trivial textures in condensed matter physics. It is the ground state of submicron magnetic elements (dots) of different shapes: cylindrical, square etc. So far, the vast majority of the vortex dynamics studies were focused on thin dots with thickness 5-50 nm and only uniform across the thickness vortex excitation modes were observed. Here we explore the fundamental vortex mode in relatively thick (50-100 nm) dots using broadband ferromagnetic resonance and show that dimensionality increase leads to qualitatively new excitation spectra. We demonstrate that the fundamental mode frequency cannot be explained without introducing a giant vortex mass, which is a result of the vortex distortion due to interaction with spin waves. The vortex mass depends on the system geometry and is non-local because of important role of the dipolar interaction. The mass is rather small for thin dots. However, its importance increases drastically with the dot thickness increasing.

Vortices in Saturn’s Northern Hemisphere (2008–2015) Observed by Cassini ISS

PubMed Central

Trammell, Harold Justin; Li, Liming; Jiang, Xun; Pan, Yefeng; Smith, Mark A.; Bering, Edgar A.; Hörst, Sarah M.; Vasavada, Ashwin R.; Ingersoll, Andrew P.; Janssen, Michael A.; West, Robert A.; Porco, Carolyn C.; Li, Cheng; Simon, Amy A.; Baines, Kevin H.

2018-01-01

We use observations from the Imaging Science Subsystem on Cassini to create maps of Saturn’s Northern Hemisphere (NH) from 2008 to 2015, a time period including a seasonal transition (i.e., Spring Equinox in 2009) and the 2010 giant storm. The processed maps are used to investigate vortices in the NH during the period of 2008–2015. All recorded vortices have diameters (east-west) smaller than 6000 km except for the largest vortex that developed from the 2010 giant storm. The largest vortex decreased its diameter from ~11000 km in 2011 to ~5000 km in 2015, and its average diameter is ~6500 km during the period of 2011–2015. The largest vortex lasts at least 4 years, which is much longer than the lifetimes of most vortices (less than 1 year). The largest vortex drifts to north, which can be explained by the beta drift effect. The number of vortices displays varying behaviors in the meridional direction, in which the 2010 giant storm significantly affects the generation and development of vortices in the middle latitudes (25–45°N). In the higher latitudes (45–90°N), the number of vortices also displays strong temporal variations. The solar flux and the internal heat do not directly contribute to the vortex activities, leaving the temporal variations of vortices in the higher latitudes (45–90°N) unexplained. PMID:29629249

Optical vortex generation from a diode-pumped alexandrite laser

NASA Astrophysics Data System (ADS)

Thomas, G. M.; Minassian, A.; Damzen, M. J.

2018-04-01

We present the demonstration of an optical vortex mode directly generated from a diode-pumped alexandrite slab laser, operating in the bounce geometry. This is the first demonstration of an optical vortex mode generated from an alexandrite laser or from any other vibronic laser. An output power of 2 W for a vortex mode with a ‘topological charge’ of 1 was achieved and the laser was made to oscillate with both left- and right-handed vorticity. The laser operated at two distinct wavelengths simultaneously, 755 and 759 nm, due to birefringent filtering in the alexandrite gain medium. The result offers the prospect of broadly wavelength tunable vortex generation directly from a laser.

Experiments on tip vortices interacting with downstream wings

NASA Astrophysics Data System (ADS)

Chen, C.; Wang, Z.; Gursul, I.

2018-05-01

The interaction of meandering tip vortices shed from a leading wing with a downstream wing was investigated experimentally in a water tunnel using flow visualization, particle image velocimetry measurements, and volumetric velocity measurements. Counter-rotating upstream vortices may exhibit sudden variations of the vortex core location when the wing-tip separation is within approximately twice the vortex core radius. This is caused by the formation of vortex dipoles near the wing tip. In contrast, co-rotating upstream vortices do not exhibit such sensitivity. Large spanwise displacement of the trajectory due to the image vortex is possible when the incident vortex is further inboard. For both co-rotating and counter-rotating vortices, as long as there is no direct impingement upon the wing, there is a little change in the structure of the time-averaged vortex past the wing, even though the tip vortex shed from the downstream wing may be substantially weakened or strengthened. In the absence of the downstream wing, as well as for weak interactions, the most energetic unsteady modes represent the first helical mode | m| = 1, which is estimated from the three-dimensional Proper Orthogonal Decomposition modes and has a very large wavelength, on the order of 102 times the vortex core radius, λ/ a = O(102). Instantaneous vorticity measurements as well as flow visualization suggest the existence of a smaller wavelength, λ/ a = 5-6, which is not among the most energetic modes. These two-orders of magnitude different wavelengths are in agreement with the previous measurements of tip vortices and also exhibit qualitative agreement with the transient energy growth analysis. The very long wavelength mode in the upstream vortex may persist during the interaction, and reveal coupling with the trailing vortex as well as increased meandering.

On the secondary instability of the most dangerous Goertler vortex

NASA Technical Reports Server (NTRS)

Otto, S. R.; Denier, James P.

1993-01-01

Recent studies have demonstrated the most unstable Goertler vortex mode is found in flows, both two and three-dimensional, with regions of (moderately) large body curvature and these modes reside within a thin layer situated at the base of the conventional boundary layer. Further work concerning the nonlinear development of the most dangerous mode demonstrates that the flow results in a self induced flow reversal. However, prior to the point at which flow reversal is encountered, the total streamwise velocity profile is found to be highly inflectional in nature. Previous work then suggests that the nonlinear vortex state will become unstable to secondary, inviscid, Rayleigh wave instabilities prior to the point of flow reversal. Our concern is with the secondary instability of the nonlinear vortex states, which result from the streamwise evolution of the most unstable Goertler vortex mode, with the aim of determining whether such modes can induce a transition to a fully turbulent state before separation is encountered.

Normal modes and mode transformation of pure electron vortex beams

PubMed Central

Thirunavukkarasu, G.; Mousley, M.; Babiker, M.

2017-01-01

Electron vortex beams constitute the first class of matter vortex beams which are currently routinely produced in the laboratory. Here, we briefly review the progress of this nascent field and put forward a natural quantum basis set which we show is suitable for the description of electron vortex beams. The normal modes are truncated Bessel beams (TBBs) defined in the aperture plane or the Fourier transform of the transverse structure of the TBBs (FT-TBBs) in the focal plane of a lens with the said aperture. As these modes are eigenfunctions of the axial orbital angular momentum operator, they can provide a complete description of the two-dimensional transverse distribution of the wave function of any electron vortex beam in such a system, in analogy with the prominent role Laguerre–Gaussian (LG) beams played in the description of optical vortex beams. The characteristics of the normal modes of TBBs and FT-TBBs are described, including the quantized orbital angular momentum (in terms of the winding number l) and the radial index p>0. We present the experimental realization of such beams using computer-generated holograms. The mode analysis can be carried out using astigmatic transformation optics, demonstrating close analogy with the astigmatic mode transformation between LG and Hermite–Gaussian beams. This article is part of the themed issue ‘Optical orbital angular momentum’. PMID:28069769

Normal modes and mode transformation of pure electron vortex beams.

PubMed

Thirunavukkarasu, G; Mousley, M; Babiker, M; Yuan, J

2017-02-28

Electron vortex beams constitute the first class of matter vortex beams which are currently routinely produced in the laboratory. Here, we briefly review the progress of this nascent field and put forward a natural quantum basis set which we show is suitable for the description of electron vortex beams. The normal modes are truncated Bessel beams (TBBs) defined in the aperture plane or the Fourier transform of the transverse structure of the TBBs (FT-TBBs) in the focal plane of a lens with the said aperture. As these modes are eigenfunctions of the axial orbital angular momentum operator, they can provide a complete description of the two-dimensional transverse distribution of the wave function of any electron vortex beam in such a system, in analogy with the prominent role Laguerre-Gaussian (LG) beams played in the description of optical vortex beams. The characteristics of the normal modes of TBBs and FT-TBBs are described, including the quantized orbital angular momentum (in terms of the winding number l) and the radial index p>0. We present the experimental realization of such beams using computer-generated holograms. The mode analysis can be carried out using astigmatic transformation optics, demonstrating close analogy with the astigmatic mode transformation between LG and Hermite-Gaussian beams.This article is part of the themed issue 'Optical orbital angular momentum'. © 2017 The Author(s).

The Craik-Leibovich Vortex Force as a Skin Effect

NASA Astrophysics Data System (ADS)

Malecha, Ziemowit; Chini, Gregory; Julien, Keith

2013-11-01

The Craik-Leibovich (CL) equations are a surface-wave filtered version of the instantaneous Navier-Stokes equations in which the rectified effects of the surface waves are captured through a so-called ``vortex force'' term: the cross-product of the Stokes, or Lagrangian, mass drift associated with the filtered surface waves and the filtered vorticity vector. For locally generated wind waves, the Stokes drift is very strongly surface confined. In this scenario, the induced body force may be represented as a surface, or skin, effect. Using matched asymptotic analysis in this limit, we derive effective boundary conditions (BCs) for the flow beneath the Stokes drift layer (i.e. in the bulk of the mixed layer). We establish the regime of validity of the resulting formulation by performing linear stability analyses and numerical simulations of both the asymptotic model and the full CL equations for a variety of vertical Stokes drift profiles. The effective BC formulation offers both theoretical and computational advantages, and should be particularly useful for LES of Langmuir turbulence for which the need to resolve very small scale near-surface flow structures imposes severe computational constraints. GPC would like to acknowledge funding from the NSF award 0934827, administered by the Physical Oceanography Program.

Neptune's New Dark Vortex: Imaging with HST/WFC3

NASA Astrophysics Data System (ADS)

Wong, M. H.; Tollefson, J.; De Pater, I.; de Kleer, K.; Hammel, H. B.; Luszcz-Cook, S.; Hueso, R.; Sanchez-Lavega, A.; Simon, A. A.; Delcroix, M.; Sromovsky, L. A.; Fry, P. M.; Orton, G. S.; Baranec, C.

2016-12-01

A bright, unusually long-lived outburst of cloud activity on Neptune was observed in 2015 (Hueso et al. 2015, DPS 400.02). This led to speculation about whether the clouds were convective in nature, or bright companions to an unseen dark vortex (similar to the Great Dark Spot studied in detail by Voyager 2: Smith et al. 1989, Science 246, 1422). HST OPAL images at blue wavelengths finally answered this question by discovering a new dark vortex at 45 deg S. We call this feature SDS-2015, for "southern dark spot discovered in 2015" (Wong et al. 2016, CBET 4278). Dark vortices on Neptune are rare; SDS-2015 is only the fifth ever seen. All five were diverse in terms of size and shape, the distribution of bright companion clouds, and horizontal motions (oscillations and drifts). The drift of these vortices is highly sensitive to horizontal and vertical wind shear, making them valuable probes into the structure of Neptune's atmospheric jets. We will present imaging observations of SDS-2015 obtained with the WFC3/UVIS camera on the Hubble Space Telescope, covering the discovery of the vortex in September 2015 and follow-up observations in May 2016. No significant latitudinal drift was seen over this time span. We will compare size estimates, which are complicated by the continual presence of companion clouds, and by the low contrast between the vortex and its surroundings. The 2015 observations included 7 filters spanning 467-845 nm, weighted toward longer wavelengths to study general cloud motions and vertical distributions. The 2016 observations included 7 filters spanning 336-763 nm, weighted toward shorter wavelengths where the dark spot itself can be detected. A companion abstract (Tollefson et al., this meeting) will present results from radiative transfer modeling of the multispectral data. [This conference abstract is based on observations made with the NASA/ESA Hubble Space Telescope, associated with programs GO-13937 ("OPAL") and GO-14492.

Numerical study of the properties of optical vortex array laser tweezers.

PubMed

Kuo, Chun-Fu; Chu, Shu-Chun

2013-11-04

Chu et al. constructed a kind of Ince-Gaussian modes (IGM)-based vortex array laser beams consisting of p x p embedded optical vortexes from Ince-Gaussian modes, IG(e)(p,p) modes [Opt. Express 16, 19934 (2008)]. Such an IGM-based vortex array laser beams maintains its vortex array profile during both propagation and focusing, and is applicable to optical tweezers. This study uses the discrete dipole approximation (DDA) method to study the properties of the IGM-based vortex array laser tweezers while it traps dielectric particles. This study calculates the resultant force exerted on the spherical dielectric particles of different sizes situated at the IGM-based vortex array laser beam waist. Numerical results show that the number of trapping spots of a structure light (i.e. IGM-based vortex laser beam), is depended on the relation between the trapped particle size and the structure light beam size. While the trapped particle is small comparing to the beam size of the IGM-based vortex array laser beams, the IGM-based vortex array laser beams tweezers are suitable for multiple traps. Conversely, the tweezers is suitable for single traps. The results of this study is useful to the future development of the vortex array laser tweezers applications.

Multiplexing of adjacent vortex modes with the forked grating coupler

NASA Astrophysics Data System (ADS)

Nadovich, Christopher T.; Kosciolek, Derek J.; Crouse, David T.; Jemison, William D.

2017-08-01

For vortex fiber multiplexing to reach practical commercial viability, simple silicon photonic interfaces with vortex fiber will be required. These interfaces must support multiplexing. Toward this goal, an efficient singlefed multimode Forked Grating Coupler (FGC) for coupling two different optical vortex OAM charges to or from the TE0 and TE1 rectangular waveguide modes has been developed. A simple, apodized device implemented with e-beam lithography and a conventional dual-etch processing on SOI wafer exhibits low crosstalk and reasonable mode match. Advanced designs using this concept are expected to further improve performance.

The physics of transverse mode instability-induced nonlinear phase distortions in large area optical fiber amplifiers and their mitigation with applications in scaling of pulsed and continuous wave high-energy lasers

DTIC Science & Technology

2016-12-13

plate and novel all-fiber fused coupler. Such work has laid the platform to demonstrate the mitigation of thermal mode instability through vortex beam...at IIT Madras to experimentally validate the above results as well as to explore the generation of vortex modes through a spiral phase plate and...modes through spiral phase plates and novel all-fiber fused couplers. We have demonstrated the excitation of a vortex mode with charge 1 through a

Majorana Kramers pair in a nematic vortex

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

Wu, Fengcheng; Martin, Ivar

A time-reversal (TR) invariant topological superconductor is characterized by a Kramers pair of Majorana zero-energy modes on boundaries and in a core of a TR invariant vortex. A vortex defect that preserves TR symmetry has remained primarily of theoretical interest, since typically a magnetic field, which explicitly breaks TR, needs to be applied to create vortices in superconductors. In this paper, we show that an odd-parity topological superconductor with a nematic pairing order parameter can host a nematic vortex that preserves TR symmetry and binds a Majorana Kramers pair. Such a nematic superconductor could be realized in metal-doped Bi 2Semore » 3, as suggested by recent experiments. We provide an analytic solution for the zero modes in a continuous nematic vortex. In lattice, crystalline anisotropy can pin the two-component order parameter along high-symmetry directions. We show that a discrete nematic vortex, which forms when three nematic domains meet, also supports a TR pair of Majorana modes. Lastly, we discuss possible experiments to probe the zero modes.« less

Majorana Kramers pair in a nematic vortex

DOE PAGES

Wu, Fengcheng; Martin, Ivar

2017-06-05

A time-reversal (TR) invariant topological superconductor is characterized by a Kramers pair of Majorana zero-energy modes on boundaries and in a core of a TR invariant vortex. A vortex defect that preserves TR symmetry has remained primarily of theoretical interest, since typically a magnetic field, which explicitly breaks TR, needs to be applied to create vortices in superconductors. In this paper, we show that an odd-parity topological superconductor with a nematic pairing order parameter can host a nematic vortex that preserves TR symmetry and binds a Majorana Kramers pair. Such a nematic superconductor could be realized in metal-doped Bi 2Semore » 3, as suggested by recent experiments. We provide an analytic solution for the zero modes in a continuous nematic vortex. In lattice, crystalline anisotropy can pin the two-component order parameter along high-symmetry directions. We show that a discrete nematic vortex, which forms when three nematic domains meet, also supports a TR pair of Majorana modes. Lastly, we discuss possible experiments to probe the zero modes.« less

Decay of homogeneous two-dimensional quantum turbulence

NASA Astrophysics Data System (ADS)

Baggaley, Andrew W.; Barenghi, Carlo F.

2018-03-01

We numerically simulate the free decay of two-dimensional quantum turbulence in a large, homogeneous Bose-Einstein condensate. The large number of vortices, the uniformity of the density profile, and the absence of boundaries (where vortices can drift out of the condensate) isolate the annihilation of vortex-antivortex pairs as the only mechanism which reduces the number of vortices, Nv, during the turbulence decay. The results clearly reveal that vortex annihilation is a four-vortex process, confirming the decay law Nv˜t-1 /3 where t is time, which was inferred from experiments with relatively few vortices in small harmonically trapped condensates.

Combined action of transverse oscillations and uniform cross-flow on vortex formation and pattern of a circular cylinder

NASA Astrophysics Data System (ADS)

Lam, K. M.; Liu, P.; Hu, J. C.

2010-07-01

This paper attempts to study the roles of lateral cylinder oscillations and a uniform cross-flow in the vortex formation and wake modes of an oscillating circular cylinder. A circular cylinder is given lateral oscillations of varying amplitudes (between 0.28 and 1.42 cylinder-diameters) in a slow uniform flow stream (Reynolds number=284) to produce the 2S, 2P and P+S wake modes. Detailed flow information is obtained with time-resolved particle-image velocimetry and the phase-locked averaging techniques. In the 2S and 2P mode, the flow speeds relative to the cylinder movement are less than the uniform flow velocity and it is found that initial formation of a vortex is caused by shear-layer separation of the uniform flow on the cylinder. Subsequent development of the shear-layer vortices is affected by the lateral cylinder movement. At small cylinder oscillation amplitudes, vortices are shed in synchronization with the cylinder movement, resulting in the 2S mode. The 2P mode occurs at larger cylinder oscillation amplitudes at which each shear-layer vortex is found to undergo intense stretching and eventual bifurcation into two separate vortices. The P+S mode occurs when the cylinder moving speeds are, for most of the time, higher than the speed of the uniform flow. These situations are found at fast and large-amplitude cylinder oscillations in which the flow relative to the cylinder movement takes over the uniform flow in governing the initial vortex formation. The formation stages of vortices from the cylinder are found to bear close resemblance to those of a vortex street pattern of a cylinder oscillating in an otherwise quiescent fluid at Keulegan-Carpenter numbers around 16. Vortices in the inclined vortex street pattern so formed are then convected downstream by the uniform flow as the vortex pairs in the 2P mode.

Direct emission of chirality controllable femtosecond LG01 vortex beam

NASA Astrophysics Data System (ADS)

Wang, S.; Zhang, S.; Yang, H.; Xie, J.; Jiang, S.; Feng, G.; Zhou, S.

2018-05-01

Direct emission of a chirality controllable ultrafast LG01 mode vortex optical beam from a conventional z-type cavity design SESAM (SEmiconductor Saturable Absorber Mirror) mode locked LD pumped Yb:Phosphate laser has been demonstrated. A clean 360 fs vortex beam of ˜45.7 mW output power has been achieved. A radial shear interferometer has been built to determine the phase singularity and the wavefront helicity of the ultrafast output laser. Theoretically, it is found that the LG01 vortex beam is obtained via the combination effect of diagonal HG10 mode generation by off-axis pumping and the controllable Gouy phase difference between HG10 and HG01 modes in the sagittal and tangential planes. The chirality of the LG01 mode can be manipulated by the pump position to the original point of the laser cavity optical axis.

Wake Vortex and Groundwind Meteorological Measurements

DOT National Transportation Integrated Search

1976-05-01

Wake vortex groundwind and meteorological measurements obtained by DOT-TSC at John F. Kennedy (JKF) International Airport have been reduced, analyzed, and correlated with a theoretical vortex transport model. The predictive Wake Vortex Transport Mode...

On the effects of viscosity on the stability of a trailing-line vortex

NASA Technical Reports Server (NTRS)

Duck, Peter W.; Khorrami, Mehdi R.

1991-01-01

The linear stability of the Batchelor (1964) vortex is investigated. Particular emphasis is placed on modes found recently in a numerical study by Khorrami (1991). These modes have a number of features very distinct from those found previously for this vortex, including exhibiting small growth rates at large Reynolds numbers and susceptibility to destabilization by viscosity. These modes are described using asymptotic techniques, producing results which compare favorably with fully numerical results at large Reynolds numbers.

Stable donutlike vortex beam generation from lasers with controlled Ince-Gaussian modes

NASA Astrophysics Data System (ADS)

Chu, Shu-Chun; Otsuka, Kenju

2007-11-01

This study proposes a three-lens configuration for generating a stable donutlike vortex laser beam with controlled Ince-Gaussian mode (IGM) operation in the model of laser-diode (LD)-pumped solid-state lasers. Simply controlling the lateral off-axis position of the pump beam's focus on the laser crystal can generate a desired donutlike vortex beam from the proposed simple and easily made three-lens configuration, a proposed astigmatic mode converter assembled into one body with a concave-convex laser cavity.

Analysis of turbulent synthetic jet by dynamic mode decomposition

NASA Astrophysics Data System (ADS)

Hyhlík, Tomáš; Netřebská, Hana; Devera, Jakub; Kalinay, Radomír

The article deals with the analysis of CFD results of the turbulent synthetic jet. The numerical simulation of Large Eddy Simulation (LES) using commercial solver ANSYS CFX has been performed. The unsteady flow field is studied from the point of view of identification of the moving vortex ring, which has been identified both on the snapshots of flow field using swirling-strength criterion and using the Dynamic Mode Decomposition (DMD) of five periods. It is shown that travelling vortex ring vanishes due to interaction with vortex structures in the synthesised turbulent jet. DMD modes with multiple of the basic frequency of synthetic jet, which are connected with travelling vortex structure, have largest DMD amplitudes.

Dual-polarization and dual-mode orbital angular momentum radio vortex beam generated by using reflective metasurface

NASA Astrophysics Data System (ADS)

Yu, Shixing; Li, Long; Shi, Guangming

2016-08-01

A metasurface, which is composed of printed cross-dipole elements with different arm lengths, is designed, fabricated, and experimentally demonstrated to generate orbital angular momentum (OAM) vortex waves of dual polarizations and dual modes in the radio frequency domain simultaneously. The prototype of a practical metasurface is fabricated and measured to validate the results of theoretical analysis and design at 5.8 GHz. Numerical and experimental results verify that vortex waves with dual OAM modes and dual polarizations can be flexibly generated by using a reflective metasurface. The proposed method paves a way to generate diverse OAM vortex waves for radio frequency and microwave wireless communication applications.

Intracavity vortex beam generation

NASA Astrophysics Data System (ADS)

Naidoo, Darryl; Aït-Ameur, Kamel; Forbes, Andrew

2011-10-01

In this paper we explore vortex beams and in particular the generation of single LG0l modes and superpositions thereof. Vortex beams carry orbital angular momentum (OAM) and this intrinsic property makes them prevalent in transferring this OAM to matter and to be used in quantum information processing. We explore an extra-cavity and intra-cavity approach in LG0l mode generation respectively. The outputs of a Porro-prism resonator are represented by "petals" and we show that through a full modal decomposition, the "petal" fields are a superposition of two LG0l modes.

Spiral Transformation for High-Resolution and Efficient Sorting of Optical Vortex Modes.

PubMed

Wen, Yuanhui; Chremmos, Ioannis; Chen, Yujie; Zhu, Jiangbo; Zhang, Yanfeng; Yu, Siyuan

2018-05-11

Mode sorting is an essential function for optical multiplexing systems that exploit the orthogonality of the orbital angular momentum mode space. The familiar log-polar optical transformation provides a simple yet efficient approach whose resolution is, however, restricted by a considerable overlap between adjacent modes resulting from the limited excursion of the phase along a complete circle around the optical vortex axis. We propose and experimentally verify a new optical transformation that maps spirals (instead of concentric circles) to parallel lines. As the phase excursion along a spiral in the wave front of an optical vortex is theoretically unlimited, this new optical transformation can separate orbital angular momentum modes with superior resolution while maintaining unity efficiency.

Spiral Transformation for High-Resolution and Efficient Sorting of Optical Vortex Modes

NASA Astrophysics Data System (ADS)

Wen, Yuanhui; Chremmos, Ioannis; Chen, Yujie; Zhu, Jiangbo; Zhang, Yanfeng; Yu, Siyuan

2018-05-01

Mode sorting is an essential function for optical multiplexing systems that exploit the orthogonality of the orbital angular momentum mode space. The familiar log-polar optical transformation provides a simple yet efficient approach whose resolution is, however, restricted by a considerable overlap between adjacent modes resulting from the limited excursion of the phase along a complete circle around the optical vortex axis. We propose and experimentally verify a new optical transformation that maps spirals (instead of concentric circles) to parallel lines. As the phase excursion along a spiral in the wave front of an optical vortex is theoretically unlimited, this new optical transformation can separate orbital angular momentum modes with superior resolution while maintaining unity efficiency.

Nonlinear dynamics of drift structures in a magnetized dissipative plasma

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

Aburjania, G. D.; Rogava, D. L.; Kharshiladze, O. A.

2011-06-15

A study is made of the nonlinear dynamics of solitary vortex structures in an inhomogeneous magnetized dissipative plasma. A nonlinear transport equation for long-wavelength drift wave structures is derived with allowance for the nonuniformity of the plasma density and temperature equilibria, as well as the magnetic and collisional viscosity of the medium and its friction. The dynamic equation describes two types of nonlinearity: scalar (due to the temperature inhomogeneity) and vector (due to the convectively polarized motion of the particles of the medium). The equation is fourth order in the spatial derivatives, in contrast to the second-order Hasegawa-Mima equations. Anmore » analytic steady solution to the nonlinear equation is obtained that describes a new type of solitary dipole vortex. The nonlinear dynamic equation is integrated numerically. A new algorithm and a new finite difference scheme for solving the equation are proposed, and it is proved that the solution so obtained is unique. The equation is used to investigate how the initially steady dipole vortex constructed here behaves unsteadily under the action of the factors just mentioned. Numerical simulations revealed that the role of the vector nonlinearity is twofold: it helps the dispersion or the scalar nonlinearity (depending on their magnitude) to ensure the mutual equilibrium and, thereby, promote self-organization of the vortical structures. It is shown that dispersion breaks the initial dipole vortex into a set of tightly packed, smaller scale, less intense monopole vortices-alternating cyclones and anticyclones. When the dispersion of the evolving initial dipole vortex is weak, the scalar nonlinearity symmetrically breaks a cyclone-anticyclone pair into a cyclone and an anticyclone, which are independent of one another and have essentially the same intensity, shape, and size. The stronger the dispersion, the more anisotropic the process whereby the structures break: the anticyclone is more intense and localized, while the cyclone is less intense and has a larger size. In the course of further evolution, the cyclone persists for a relatively longer time, while the anticyclone breaks into small-scale vortices and dissipation hastens this process. It is found that the relaxation of the vortex by viscous dissipation differs in character from that by the frictional force. The time scale on which the vortex is damped depends strongly on its typical size: larger scale vortices are longer lived structures. It is shown that, as the instability develops, the initial vortex is amplified and the lifetime of the dipole pair components-cyclone and anticyclone-becomes longer. As time elapses, small-scale noise is generated in the system, and the spatial structure of the perturbation potential becomes irregular. The pattern of interaction of solitary vortex structures among themselves and with the medium shows that they can take part in strong drift turbulence and anomalous transport of heat and matter in an inhomogeneous magnetized plasma.« less

Wake Vortex Transport and Decay in Ground Effect: Vortex Linking with the Ground

NASA Technical Reports Server (NTRS)

Proctor, Fred H.; Hamilton, David W.; Han, Jongil

2000-01-01

Numerical simulations are carried out with a three-dimensional Large-Eddy Simulation (LES) model to explore the sensitivity of vortex decay and transport in ground effect (IGE). The vortex decay rates are found to be strongly enhanced following maximum descent into ground effect. The nondimensional decay rate is found to be insensitive to the initial values of circulation, height, and vortex separation. The information gained from these simulations is used to construct a simple decay relationship. This relationship compares well with observed data from an IGE case study. Similarly, a relationship for lateral drift due to ground effect is constructed from the LES data. In the second part of this paper, vortex linking with the ground is investigated. Our numerical simulations of wake vortices for IGE show that a vortex may link with its image beneath the ground, if the intensity of the ambient turbulence is moderate to high. This linking with the ground (which is observed in real cases)gives the appearance of a vortex tube that bends to become vertically oriented and which terminates at the ground. From the simulations conducted, the linking time for vortices in the free atmosphere; i.e., a function of ambient turbulence intensity.

Nonlinear frequency doubling characteristics of asymmetric vortices of tunable, broad orbital angular momentum spectrum

NASA Astrophysics Data System (ADS)

Alam, Sabir Ul; Rao, A. Srinivasa; Ghosh, Anirban; Vaity, Pravin; Samanta, G. K.

2018-04-01

We report on a simple experimental scheme to generate and control the orbital angular momentum (OAM) spectrum of the asymmetric vortex beams in a nonlinear frequency conversion process. Using a spiral phase plate (SPP) and adjusting the transverse shift of the SPP with respect to the incident Gaussian beam axis, we have transformed the symmetric (intensity distribution) optical vortex of order l into an asymmetric vortex beam of measured broad spectrum of OAM modes of orders l, l - 1, l - 2, …, 0 (Gaussian mode). While the position of the SPP determines the distribution of the OAM modes, we have also observed that the modal distribution of the vortex beam changes with the shift of the SPP of all orders and finally results in a Gaussian beam (l = 0). Using single-pass frequency doubling of the asymmetric vortices, we have transferred the pump OAM spectra, l, l - 1, l - 2, …, 0, into the broad spectra of higher order OAM modes, 2l, 2l - 1, 2l - 2, …, 0 at green wavelength, owing to OAM conservation in nonlinear processes. We also observed an increase in single-pass conversion efficiency with the increase in asymmetry of the pump vortices producing a higher power vortex beam of mixed OAM modes at a new wavelength than that of the pure OAM mode.

Impact of Cross-field Drifts on Detachment in DIII-D

NASA Astrophysics Data System (ADS)

Jaervinen, A. E.; Allen, S. L.; McLean, A. G.; Rognlien, T. D.; Samuell, C. M.; Porter, G. D.; Groth, M.; Hill, D. N.; Leonard, A. W.

2017-10-01

Simulations of DIII-D plasmas have revealed the strong role of E ×B-drifts in the low field side (LFS) detachment structure. High confinement modes (H-mode) with the ∇B-drift towards the X-point (fwd BT) enter detachment at 20% higher upstream density, ne,sep, than plasmas with the ∇B-drift away from the X-point (rev BT). In contrast, low confinement modes (L-mode) enter detachment at 10% lower ne,sep in fwd BT. Despite this, both L- and H-modes detached plasmas show strong target flux, JSAT, reduction with increasing ne,sep in fwd BT, while only a modest reduction occurs in rev BT. In fwd BT H-mode, a step-wise transition from attached to strongly detached conditions is observed with increasing ne,sep. UEDGE simulations indicate that the strong poloidal E ×B-drift in the private flux region in H-mode drives the difference for the detachment onset relative to L-mode. In fwd BT, the dependence of this poloidal E ×B-drift on the divertor conditions can reinforce the plasma into either attached or strongly detached state. In rev BT, radial E ×B-drift depletes strike-line ne, limiting the degree of detachment. Work supported by the US DOE under DE-FC02-04ER54698, DE-AC52-07NA27344, and LLNL LDRD project 17-ERD-020.

Excitation of high density surface plasmon polariton vortex array

NASA Astrophysics Data System (ADS)

Kuo, Chun-Fu; Chu, Shu-Chun

2018-06-01

This study proposes a method to excite surface plasmon polariton (SPP) vortex array of high spatial density on metal/air interface. A doughnut vector beam was incident at four rectangularly arranged slits to excite SPP vortex array. The doughnut vector beam used in this study has the same field intensity distribution as the regular doughnut laser mode, TEM01* mode, but a different polarization distribution. The SPP vortex array is achieved through the matching of both polarization state and phase state of the incident doughnut vector beam with the four slits. The SPP field distribution excited in this study contains stable array-distributed time-varying optical vortices. Theoretical derivation, analytical calculation and numerical simulation were used to discuss the characteristics of the induced SPP vortex array. The period of the SPP vortex array induced by the proposed method had only half SPPs wavelength. In addition, the vortex number in an excited SPP vortex array can be increased by enlarging the structure.

Development of test methods for scale model simulation of aerial applications in the NASA Langley Vortex Research Facility. [agricultural aircraft

NASA Technical Reports Server (NTRS)

Jordan, F. L., Jr.

1980-01-01

As part of basic research to improve aerial applications technology, methods were developed at the Langley Vortex Research Facility to simulate and measure deposition patterns of aerially-applied sprays and granular materials by means of tests with small-scale models of agricultural aircraft and dynamically-scaled test particles. Interactions between the aircraft wake and the dispersed particles are being studied with the objective of modifying wake characteristics and dispersal techniques to increase swath width, improve deposition pattern uniformity, and minimize drift. The particle scaling analysis, test methods for particle dispersal from the model aircraft, visualization of particle trajectories, and measurement and computer analysis of test deposition patterns are described. An experimental validation of the scaling analysis and test results that indicate improved control of chemical drift by use of winglets are presented to demonstrate test methods.

Observation of orbital angular momentum transfer between acoustic and optical vortices in optical fiber.

PubMed

Dashti, Pedram Z; Alhassen, Fares; Lee, Henry P

2006-02-03

Acousto-optic interaction in optical fiber is examined from the perspective of copropagating optical and acoustic vortex modes. Calculation of the acousto-optic coupling coefficient between different optical modes leads to independent conservation of spin and orbital angular momentum of the interacting photons and phonons. We show that the orbital angular momentum of the acoustic vortex can be transferred to a circularly polarized fundamental optical mode to form a stable optical vortex in the fiber carrying orbital angular momentum. The technique provides a useful way of generating stable optical vortices in the fiber medium.

Shock/vortex interaction and vortex-breakdown modes

NASA Technical Reports Server (NTRS)

Kandil, Osama A.; Kandil, H. A.; Liu, C. H.

1992-01-01

Computational simulation and study of shock/vortex interaction and vortex-breakdown modes are considered for bound (internal) and unbound (external) flow domains. The problem is formulated using the unsteady, compressible, full Navier-Stokes (NS) equations which are solved using an implicit, flux-difference splitting, finite-volume scheme. For the bound flow domain, a supersonic swirling flow is considered in a configured circular duct and the problem is solved for quasi-axisymmetric and three-dimensional flows. For the unbound domain, a supersonic swirling flow issued from a nozzle into a uniform supersonic flow of lower Mach number is considered for quasi-axisymmetric and three-dimensional flows. The results show several modes of breakdown; e.g., no-breakdown, transient single-bubble breakdown, transient multi-bubble breakdown, periodic multi-bubble multi-frequency breakdown and helical breakdown.

An experimental investigation of bending wave instability modes in a generic four-vortex wake

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

Babie, Brian M.; Nelson, Robert C.

2010-07-15

An experimental study of a planar wake consisting of four vortices that simulate the trailing vortex wakes generated by transport airplanes in either takeoff or landing configurations is presented. The objective of this study was to examine naturally occurring wake instabilities. Specifically, the focus of the study was centered on bending wave instabilities of which the Crow instability represents a particular case. A unique method of generating a four-vortex wake was developed for this study. The four-vortex wake generating device permitted direct variation of the spacing between vortices as well as control over the vortex circulation strength. Two quantitative flowmore » visualization experiments were instrumental in identifying wake configurations that were conducive to the rapid growth of bending wave modes and in the identification of the long-wavelength mode. Detailed experiments were also conducted to examine the flow structure in the near-field or roll-up region using a four sensor, hot-wire probe that could measure all three velocity components in the wake simultaneously. The results of both the flow visualization and hot-wire experiments indicate that the long-wavelength mode and the first short-wavelength mode likely dominate the far-field wake physics and may potentially be utilized in a wake control strategy.« less

Cascade conical refraction for annular pumping of a vortex Nd:YAG laser and selective excitation of low- and high-order Laguerre–Gaussian modes

NASA Astrophysics Data System (ADS)

Wu, Yongxiao; Wang, Zhongyang; Chen, Sanbin; Shirakwa, Akira; Ueda, Ken-ichi; Li, Jianlang

2018-05-01

We proposed an efficient and vortex Nd:YAG laser for selective lasing of low- and high-order vortex modes, in which multiple-ring pump light was originated from cascaded conical refraction of multiple biaxial crystals. In our proof of concept demonstration, we used two-crystal cascade conical refraction to generate two-ring pump light; the mutual intensity ratio and relative separation of the inner ring and outer ring were controlled by rotating the second biaxial crystal and by moving the imaging lens, respectively. As a result, we obtained selective excitation of Laguerre–Gaussian (LG01 and LG03) vortex modes in the end-pump Nd:YAG laser. For LG01-mode output, the laser power reached 439 mW with 52.5% slope efficiency; for LG03-mode output, the laser power reached 160 mW with 41.3% slope efficiency. Our results revealed that the multiple-ring pumping technique based on cascaded conical refraction would pave the way for realization of the efficient and switchable excitation of low- and high-order LG modes in an end-pumped solid-state laser.

Wavelength-tunable Hermite-Gaussian modes and an orbital-angular-momentum-tunable vortex beam in a dual-off-axis pumped Yb:CALGO laser.

PubMed

Shen, Yijie; Meng, Yuan; Fu, Xing; Gong, Mali

2018-01-15

A dual-off-axis pumping scheme is presented to generate wavelength-tunable high-order Hermite-Gaussian (HG) modes in Yb:CaGdAlO 4 lasers. The mode and wavelength can be actively controlled by the off-axis displacements and pump power. The purities of the output HG modes are quantified by intensity distributions and the measured M 2 values. The highest order reaches m=15 for stable HG m,0 mode, and wavelength-tunable width is about 10 nm. Moreover, through externally converting the HG m,0 modes, the vortex beams carrying orbital angular momentum (OAM) with a large OAM-tunable range from ±1ℏ to ±15ℏ are produced. This work is effective for largely scaling the spectral and OAM tunable ranges of optical vortex beams.

Size dependence of vortex-type spin torque oscillation in a Co2Fe0.4Mn0.6Si Heusler alloy disk

NASA Astrophysics Data System (ADS)

Seki, T.; Kubota, T.; Yamamoto, T.; Takanashi, K.

2018-02-01

This paper reports the systematic investigation of vortex-type spin torque oscillation in circular disks of highly spin-polarized Co2Fe0.4Mn0.6Si (CFMS) Heusler alloys. We fabricated the current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices with various disk diameters (D) using the layer stack of CFMS/Ag3Mg/CFMS. The gyrotropic motion of the vortex core was successfully excited for the CFMS circular disks with 0.2 µm  ⩽  D  ⩽  0.3 µm. The CPP-GMR device with D  =  0.2 µm exhibited the Q factor of more than 5000 and the large output power of 0.4 nW owing to the high coherency of vortex dynamics and the high spin-polarization of CFMS. However, the Q factor was remarkably decreased as D was reduced from 0.2 µm to 0.14 µm. The comparison with the calculated resonance frequencies suggested that this degradation of the Q factor was due to the transition of the oscillation mode from the vortex mode to other modes such as the low-coherent out-of-plane precession mode. The present experimental results also suggest that there exists an adequate disk size for the enhanced Q factor of the vortex-type spin torque oscillation.

Featured Image: A New Dark Vortex on Neptune

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2018-03-01

This remarkable series of images by the Hubble Space Telescope (click for the full view) track a dark vortex only the fifth ever observed on Neptune as it evolves in Neptunes atmosphere. These Hubble images, presented in a recent study led by Michael Wong (University of California, Berkeley), were taken in 2015 September, 2016 May, 2016 October, and 2017 October; the observations have monitored the evolution of the vortex as it has gradually weakened and drifted polewards. Confirmation of the vortex solved a puzzle that arose in 2015, when astronomers spotted an unexplained outburst of cloud activity on Neptune. This outburst was likely a group of bright companion clouds that form as air flows over high-pressure dark vortices, causing gases to freeze into methane ice crystals. To learn more about what the authors have since learned by studying this vortex, check out the paper below.CitationMichael H. Wong et al 2018 AJ 155 117. doi:10.3847/1538-3881/aaa6d6

Vortex shedding experiment with flat and curved bluff plates in water

NASA Technical Reports Server (NTRS)

Reed, D.; Nesman, T.; Howard, P.

1988-01-01

Vortex shedding experiments were conducted in a water flow facility in order to simulate the strong discrete 4000-Hz vibration detected in the Space Shuttle Main Engine (SSME) which is thought to be associated with the SSME LOX inlet tee splitter vanes on the Main Injector. For the case of a flat vane with a blunt trailing edge excited by flow induced vortex shedding, lock-in with the first bending mode of the plate was observed. A curved vane displayed similar behavior, with the lock-in being a more discrete higher amplitude response. Aluminum vanes were employed to decouple the first vane bending mode from the vortex shedding mode. The application of an asymmetric 30-deg trailing edge bevel to both the flat and curved vanes was found to greatly reduce the strength of the shed vortices.

Generation of high-order Hermite-Gaussian modes in end-pumped solid-state lasers for square vortex array laser beam generation.

PubMed

Chu, Shu-Chun; Chen, Yun-Ting; Tsai, Ko-Fan; Otsuka, Kenju

2012-03-26

This study reports the first systematic approach to the excitation of all high-order Hermite-Gaussian modes (HGMs) in end-pumped solid-state lasers. This study uses a metal-wire-inserted laser resonator accompanied with the "off axis pumping" approach. This study presents numerical analysis of the excitation of HGMs in end-pumped solid-state lasers and experimentally generated HGM patterns. This study also experimentally demonstrates the generation of an square vortex array laser beams by passing specific high-order HGMs (HGn,n + 1 or HGn + 1,n modes) through a Dove prism-embedded unbalanced Mach-Zehnder interferometer [Optics Express 16, 19934-19949]. The resulting square vortex array laser beams with embedded vortexes aligned in a square array can be applied to multi-spot dark optical traps in the future.

Generation of intense high-order vortex harmonics.

PubMed

Zhang, Xiaomei; Shen, Baifei; Shi, Yin; Wang, Xiaofeng; Zhang, Lingang; Wang, Wenpeng; Xu, Jiancai; Yi, Longqiong; Xu, Zhizhan

2015-05-01

This Letter presents for the first time a scheme to generate intense high-order optical vortices that carry orbital angular momentum in the extreme ultraviolet region based on relativistic harmonics from the surface of a solid target. In the three-dimensional particle-in-cell simulation, the high-order harmonics of the high-order vortex mode is generated in both reflected and transmitted light beams when a linearly polarized Laguerre-Gaussian laser pulse impinges on a solid foil. The azimuthal mode of the harmonics scales with its order. The intensity of the high-order vortex harmonics is close to the relativistic region, with the pulse duration down to attosecond scale. The obtained intense vortex beam possesses the combined properties of fine transversal structure due to the high-order mode and the fine longitudinal structure due to the short wavelength of the high-order harmonics. In addition to the application in high-resolution detection in both spatial and temporal scales, it also presents new opportunities in the intense vortex required fields, such as the inner shell ionization process and high energy twisted photons generation by Thomson scattering of such an intense vortex beam off relativistic electrons.

A note on the effects of viscosity on the stability of a trailing-line vortex

NASA Technical Reports Server (NTRS)

Duck, Peter W.; Khorrami, Mehdi R.

1992-01-01

The linear stability of the Batchelor (1964) vortex is examined with emphasis on new viscous modes recently found numerically by Khorrami (1991). Unlike the previously reported inviscid modes of instability, these modes are destabilized by viscosity and exhibit small growth rates at large Reynolds numbers. The analysis presented here uses a combination of asymptotic and numerical techniques. The results confirm the existence of the additional modes of instability due to viscosity.

Nonlinear ELM simulations based on a nonideal peeling–ballooning model using the BOUT++ code

DOE PAGES

Xu, X. Q.; Dudson, B. D.; Snyder, P. B.; ...

2011-09-23

A minimum set of equations based on the peeling–ballooning (P–B) model with nonideal physics effects (diamagnetic drift, E × B drift, resistivity and anomalous electron viscosity) is found to simulate pedestal collapse when using the BOUT++ simulation code, developed in part from the original fluid edge code BOUT. Linear simulations of P–B modes find good agreement in growth rate and mode structure with ELITE calculations. The influence of the E × B drift, diamagnetic drift, resistivity, anomalous electron viscosity, ion viscosity and parallel thermal diffusivity on P–B modes is being studied; we find that (1) the diamagnetic drift and Emore » × B drift stabilize the P–B mode in a manner consistent with theoretical expectations; (2) resistivity destabilizes the P–B mode, leading to resistive P–B mode; (3) anomalous electron and parallel ion viscosities destabilize the P–B mode, leading to a viscous P–B mode; (4) perpendicular ion viscosity and parallel thermal diffusivity stabilize the P–B mode. With addition of the anomalous electron viscosity under the assumption that the anomalous kinematic electron viscosity is comparable to the anomalous electron perpendicular thermal diffusivity, or the Prandtl number is close to unity, it is found from nonlinear simulations using a realistic high Lundquist number that the pedestal collapse is limited to the edge region and the ELM size is about 5–10% of the pedestal stored energy. Furthermore, this is consistent with many observations of large ELMs. The estimated island size is consistent with the size of fast pedestal pressure collapse. In the stable α-zones of ideal P–B modes, nonlinear simulations of viscous ballooning modes or current-diffusive ballooning mode (CDBM) for ITER H-mode scenarios are presented.« less

Generation of Hermite-Gaussian modes and vortex arrays based on two-dimensional gain distribution controlled microchip laser.

PubMed

Kong, Weipeng; Sugita, Atsushi; Taira, Takunori

2012-07-01

We have demonstrated high-order Hermite-Gaussian (HG) mode generation based on 2D gain distribution control edge-pumped, composite all-ceramic Yb:YAG/YAG microchip lasers using a V-type cavity. Several hundred milliwatts to several watts HG(mn) modes are achieved. We also generated different kinds of vortex arrays directly from the oscillator with the same power level. In addition, a more than 7 W doughnut-shape mode can be generated in the same cavity.

Drift and geodesic effects on the ion sound eigenmode in tokamak plasmas

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

Elfimov, A. G., E-mail: elfimov@if.usp.br; Smolyakov, A. I., E-mail: andrei.smolyakov@usask.ca; Melnikov, A. V.

A kinetic treatment of geodesic acoustic modes (GAMs), taking into account ion parallel dynamics, drift and the second poloidal harmonic effects is presented. It is shown that first and second harmonics of the ion sound modes, which have respectively positive and negative radial dispersion, can be coupled due to the geodesic and drift effects. This coupling results in the drift geodesic ion sound eigenmode with a frequency below the standard GAM continuum frequency. Such eigenmode may be able to explain the split modes observed in some experiments.

Unloading Characteristics of Sand-drift in Wind-shallow Areas along Railway and the Effect of Sand Removal by Force of Wind

PubMed Central

Cheng, Jian-jun; Xin, Guo-Wei; Zhi, Ling-yan; Jiang, Fu-qiang

2017-01-01

Wind-shield walls decrease the velocity of wind-drift sand flow in transit. This results in sand accumulating in the wind-shadow zone of both windshield wall and track line, causing severe sand sediment hazard. This study reveals the characteristics of sand accumulation and the laws of wind-blown sand removal in the wind-shadow areas of three different types of windshield walls, utilizing three-dimensional numerical simulations and wind tunnel experiments and on-site sand sediment tests. The results revealed the formation of apparent vortex and acceleration zones on the leeward side of solid windshield walls. For uniform openings, the vortex area moved back and narrowed. When bottom-opening windshield walls were adopted, the track-supporting layer at the step became a conflux acceleration zone, forming a low velocity vortex zone near the track line. At high wind speeds, windshield walls with bottom-openings achieved improved sand dredging. Considering hydrodynamic mechanisms, the flow field structure on the leeward side of different types of windshield structures is a result of convergence and diffusion of fluids caused by an obstacle. This convergence and diffusion effect of air fluid is more apparent at high wind velocities, but not obvious at low wind velocities. PMID:28120915

Experimental detection of a Majorana mode in the core of a magnetic vortex inside a topological insulator-superconductor Bi(2)Te(3)/NbSe(2) heterostructure.

PubMed

Xu, Jin-Peng; Wang, Mei-Xiao; Liu, Zhi Long; Ge, Jian-Feng; Yang, Xiaojun; Liu, Canhua; Xu, Zhu An; Guan, Dandan; Gao, Chun Lei; Qian, Dong; Liu, Ying; Wang, Qiang-Hua; Zhang, Fu-Chun; Xue, Qi-Kun; Jia, Jin-Feng

2015-01-09

Majorana fermions have been intensively studied in recent years for their importance to both fundamental science and potential applications in topological quantum computing. They are predicted to exist in a vortex core of superconducting topological insulators. However, it is extremely difficult to distinguish them experimentally from other quasiparticle states for the tiny energy difference between Majorana fermions and these states, which is beyond the energy resolution of most available techniques. Here, we circumvent the problem by systematically investigating the spatial profile of the Majorana mode and the bound quasiparticle states within a vortex in Bi(2)Te(3) films grown on a superconductor NbSe(2). While the zero bias peak in local conductance splits right off the vortex center in conventional superconductors, it splits off at a finite distance ∼20  nm away from the vortex center in Bi(2)Te(3). This unusual splitting behavior has never been observed before and could be possibly due to the Majorana fermion zero mode. While the Majorana mode is destroyed by the interaction between vortices, the zero bias peak splits as a conventional superconductor again. This work provides self-consistent evidences of Majorana fermions and also suggests a possible route to manipulating them.

Robust vortex lines, vortex rings, and hopfions in three-dimensional Bose-Einstein condensates

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

Bisset, R. N.; Wang, Wenlong; Ticknor, Christopher

Performing a systematic Bogoliubov–de Gennes spectral analysis, we illustrate that stationary vortex lines, vortex rings, and more exotic states, such as hopfions, are robust in three-dimensional atomic Bose-Einstein condensates, for large parameter intervals. Importantly, we find that the hopfion can be stabilized in a simple parabolic trap, without the need for trap rotation or inhomogeneous interactions. We supplement our spectral analysis by studying the dynamics of such stationary states; we find them to be robust against significant perturbations of the initial state. In the unstable regimes, we not only identify the unstable mode, such as a quadrupolar or hexapolar mode,more » but we also observe the corresponding instability dynamics. Moreover, deep in the Thomas-Fermi regime, we investigate the particlelike behavior of vortex rings and hopfions.« less

Robust vortex lines, vortex rings, and hopfions in three-dimensional Bose-Einstein condensates

DOE PAGES

Bisset, R. N.; Wang, Wenlong; Ticknor, Christopher; ...

2015-12-07

Performing a systematic Bogoliubov–de Gennes spectral analysis, we illustrate that stationary vortex lines, vortex rings, and more exotic states, such as hopfions, are robust in three-dimensional atomic Bose-Einstein condensates, for large parameter intervals. Importantly, we find that the hopfion can be stabilized in a simple parabolic trap, without the need for trap rotation or inhomogeneous interactions. We supplement our spectral analysis by studying the dynamics of such stationary states; we find them to be robust against significant perturbations of the initial state. In the unstable regimes, we not only identify the unstable mode, such as a quadrupolar or hexapolar mode,more » but we also observe the corresponding instability dynamics. Moreover, deep in the Thomas-Fermi regime, we investigate the particlelike behavior of vortex rings and hopfions.« less

The initial value problem in Lagrangian drift kinetic theory

NASA Astrophysics Data System (ADS)

Burby, J. W.

2016-06-01

> Existing high-order variational drift kinetic theories contain unphysical rapidly varying modes that are not seen at low orders. These unphysical modes, which may be rapidly oscillating, damped or growing, are ushered in by a failure of conventional high-order drift kinetic theory to preserve the structure of its parent model's initial value problem. In short, the (infinite dimensional) system phase space is unphysically enlarged in conventional high-order variational drift kinetic theory. I present an alternative, `renormalized' variational approach to drift kinetic theory that manifestly respects the parent model's initial value problem. The basic philosophy underlying this alternate approach is that high-order drift kinetic theory ought to be derived by truncating the all-orders system phase-space Lagrangian instead of the usual `field particle' Lagrangian. For the sake of clarity, this story is told first through the lens of a finite-dimensional toy model of high-order variational drift kinetics; the analogous full-on drift kinetic story is discussed subsequently. The renormalized drift kinetic system, while variational and just as formally accurate as conventional formulations, does not support the troublesome rapidly varying modes.

Two-dimensional complex source point solutions: application to propagationally invariant beams, optical fiber modes, planar waveguides, and plasmonic devices.

PubMed

Sheppard, Colin J R; Kou, Shan S; Lin, Jiao

2014-12-01

Highly convergent beam modes in two dimensions are considered based on rigorous solutions of the scalar wave (Helmholtz) equation, using the complex source point formalism. The modes are applicable to planar waveguide or surface plasmonic structures and nearly concentric microcavity resonator modes in two dimensions. A novel solution is that of a vortex beam, where the direction of propagation is in the plane of the vortex. The modes also can be used as a basis for the cross section of propagationally invariant beams in three dimensions and bow-tie-shaped optical fiber modes.

Negative velocity fluctuations and non-equilibrium fluctuation relation for a driven high critical current vortex state.

PubMed

Bag, Biplab; Shaw, Gorky; Banerjee, S S; Majumdar, Sayantan; Sood, A K; Grover, A K

2017-07-17

Under the influence of a constant drive the moving vortex state in 2H-NbS 2 superconductor exhibits a negative differential resistance (NDR) transition from a steady flow to an immobile state. This state possesses a high depinning current threshold ([Formula: see text]) with unconventional depinning characteristics. At currents well above [Formula: see text], the moving vortex state exhibits a multimodal velocity distribution which is characteristic of vortex flow instabilities in the NDR regime. However at lower currents which are just above [Formula: see text], the velocity distribution is non-Gaussian with a tail extending to significant negative velocity values. These unusual negative velocity events correspond to vortices drifting opposite to the driving force direction. We show that this distribution obeys the Gallavotti-Cohen Non-Equilibrium Fluctuation Relation (GC-NEFR). Just above [Formula: see text], we also find a high vortex density fluctuating driven state not obeying the conventional GC-NEFR. The GC-NEFR analysis provides a measure of an effective energy scale (E eff ) associated with the driven vortex state. The E eff corresponds to the average energy dissipated by the fluctuating vortex state above [Formula: see text]. We propose the high E eff value corresponds to the onset of high energy dynamic instabilities in this driven vortex state just above [Formula: see text].

A Small Postmidnight Substorm During IMF Bz+ and By+ Conditions -- Joint Optical, Radar, Magnetic and Satellite Observations

NASA Astrophysics Data System (ADS)

Liang, J.; Sofko, G.; Donovan, E.; Greenwald, R.

2002-12-01

Multi-instrument observations of a small postmidnight substorm event during a period of IMF dominated by Bz+ and By+ conditions on October 9, 2000, showed the substorm structure with high time resolution. Three optical intensifications and Pi2 bursts occurred. The last and strongest Pi2 burst was associated with an expansive phase (EP) onset, characterized by a 100 nT magnetic bay at Fort Churchill and an auroral breakup in which the 630 nm emissions moved poleward about 2.5 degrees. About 11 minutes after the first EP onset, a second stage of auroral brightening occurred. For each of the three initial optical intensifications, there was an eastward-moving discrete azimuthal structure. SuperDARN HF radar line-of-sight velocity measurements revealed eastward electric fields within each Pi2 wave train. The observations are interpreted as resulting from the drift-Alfven-ballooning (DAB) mode instability at near-geosynchronous orbit (NGO) locations. Within the NGO drift waves, regions of charge separation led to electric fields and field-aligned currents (FACs) of alternating direction. The ionospheric reflection of Alfven wave energy likely generated the Pi2 pulsations observed on the ground. The multi-instrument ground observations agree quite well with the substorm onset scenario based upon CRRES satellite observations by Erickson et al. [2000]. There was a single, relatively confined (~4 hour in MLT) counterclockwise convection cell during the growth phase and EP onset. A clearly defined vortex at its center defined the center of the downward FAC. This vortex, initially northward of the optical aurora, moved eastward and then suddenly southward just prior to the EP onset. At that time, the FAC structure was typical of the substorm current wedge (SCW). Reasons for the convection cell motion and SCW development are discussed. Erickson, G. M., N. C. Maynard, W. J. Burke, G. R. Wilson, and M. A. Heinemann, Electromagnetics of substorm onsets in the near-geosynchronous plasma sheet, J. Geophys. Res., 105, 25265, 2000.

Generation of 2 µm Laguerre-Gaussian mode in a Tm:LuYAG solid-state laser

NASA Astrophysics Data System (ADS)

Liu, Qiyao; Ding, Manman; Zhao, Yongguang; Zhou, Wei; Shen, Deyuan

2018-04-01

In this article, we discuss the first vortex laser in the 2 µm spectral range directly generated from a Tm:LuYAG oscillator, in which a pump beam with annular intensity distribution is employed in line with Laguerre-Gaussian modes. Laser thresholds of different-order Laguerre-Gaussian modes are theoretically analyzed and discussed. Vortex lasers with orbital angular momentum of ħ and  -ħ were experimentally produced with corresponding output powers of 1.75 W and 1.64 W, respectively. This directly emitted vortex laser generated in the ~2 µm region from a compact and robust Tm:LuYAG oscillator has potential applications in the areas of molecular spectroscopy and organic material processing amongst others.

Dynamics of the aircraft in a vortex wake

NASA Astrophysics Data System (ADS)

Gaifullin, A. M.; Sviridenko, Yu N.

2018-03-01

This paper considers the aerodynamics and the dynamics of an aircraft on various modes when the aircraft enters a strongly swirling flow. This is the case when an aircraft purposefully enters the jet-vortex wake of another aircraft in the course of in-flight refuelling, when an aircraft is flying in the trail of an aircraft carrier during landing, or when an aircraft accidentally enters other aircrafts’ vortex wakes. These situations, according to pilots’ evaluation, are the most dangerous and the most difficult modes for piloting. That is why their real time modelling on flight simulators has taken on particular importance. This article provides the algorithms and methodology of mathematical modelling of aerodynamic forces and moments which act upon an aircraft in vortex wakes.

Generation of cylindrically polarized vector vortex beams with digital micromirror device

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

Gong, Lei; Liu, Weiwei; Wang, Meng

We propose a novel technique to directly transform a linearly polarized Gaussian beam into vector-vortex beams with various spatial patterns. Full high-quality control of amplitude and phase is implemented via a Digital Micro-mirror Device (DMD) binary holography for generating Laguerre-Gaussian, Bessel-Gaussian, and helical Mathieu–Gaussian modes, while a radial polarization converter (S-waveplate) is employed to effectively convert the optical vortices into cylindrically polarized vortex beams. Additionally, the generated vector-vortex beams maintain their polarization symmetry after arbitrary polarization manipulation. Due to the high frame rates of DMD, rapid switching among a series of vector modes carrying different orbital angular momenta paves themore » way for optical microscopy, trapping, and communication.« less

Generation of vortex array laser beams with Dove prism embedded unbalanced Mach-Zehnder interferometer

NASA Astrophysics Data System (ADS)

Chu, Shu-Chun

2009-02-01

This paper introduces a scheme for generation of vortex laser beams from a solid-state laser with off-axis laser-diode pumping. The proposed system consists of a Dove prism embedded in an unbalanced Mach-Zehnder interferometer configuration. This configuration allows controlled construction of p × p vortex array beams from Ince-Gaussian modes, IGep,p modes. An incident IGe p,p laser beam of variety order p can easily be generated from an end-pumped solid-state laser with an off-axis pumping mechanism. This study simulates this type of vortex array laser beam generation and discusses beam propagation effects. The formation of ordered transverse emission patterns have applications in a variety of areas such as optical data storage, distribution, and processing that exploit the robustness of soliton and vortex fields and optical manipulations of small particles and atoms in the featured intensity distribution.

Estimation of perspective errors in 2D2C-PIV measurements for 3D concentrated vortices

NASA Astrophysics Data System (ADS)

Ma, Bao-Feng; Jiang, Hong-Gang

2018-06-01

Two-dimensional planar PIV (2D2C) is still extensively employed in flow measurement owing to its availability and reliability, although more advanced PIVs have been developed. It has long been recognized that there exist perspective errors in velocity fields when employing the 2D2C PIV to measure three-dimensional (3D) flows, the magnitude of which depends on out-of-plane velocity and geometric layouts of the PIV. For a variety of vortex flows, however, the results are commonly represented by vorticity fields, instead of velocity fields. The present study indicates that the perspective error in vorticity fields relies on gradients of the out-of-plane velocity along a measurement plane, instead of the out-of-plane velocity itself. More importantly, an estimation approach to the perspective error in 3D vortex measurements was proposed based on a theoretical vortex model and an analysis on physical characteristics of the vortices, in which the gradient of out-of-plane velocity is uniquely determined by the ratio of the maximum out-of-plane velocity to maximum swirling velocity of the vortex; meanwhile, the ratio has upper limits for naturally formed vortices. Therefore, if the ratio is imposed with the upper limits, the perspective error will only rely on the geometric layouts of PIV that are known in practical measurements. Using this approach, the upper limits of perspective errors of a concentrated vortex can be estimated for vorticity and other characteristic quantities of the vortex. In addition, the study indicates that the perspective errors in vortex location, vortex strength, and vortex radius can be all zero for axisymmetric vortices if they are calculated by proper methods. The dynamic mode decomposition on an oscillatory vortex indicates that the perspective errors of each DMD mode are also only dependent on the gradient of out-of-plane velocity if the modes are represented by vorticity.

Saturation of the lower-hybrid-drift instability by mode coupling

NASA Technical Reports Server (NTRS)

Drake, J. F.; Guzdar, P. N.; Huba, J. D.

1983-01-01

A nonlinear mode-coupling theory of the lower-hybrid-drift instability is presented. It is found that the instability saturates by transferring energy from the growing, long wavelength modes to the damped, short wavelength modes. The saturation energy, mean square of the potential fluctuations, and diffusion coefficient are calculated self-consistently.

Flow structure of vortex-wing interaction

NASA Astrophysics Data System (ADS)

McKenna, Christopher K.

Impingement of a streamwise-oriented vortex upon a fin, tail, blade or wing represents a fundamental class of flow-structure interaction that extends across a range of applications. This interaction can give rise to time-averaged loading, as well as unsteady loading known as buffeting. The loading is sensitive to parameters of the incident vortex as well as the location of vortex impingement on the downstream aerodynamic surface, generically designated as a wing. Particle image velocimetry is employed to determine patterns of velocity, vorticity, swirl ratio, and streamlines on successive cross-flow planes upstream of and along the wing, which lead to volume representations and thereby characterization of the interaction. At locations upstream of the leading edge of the wing, the evolution of the incident vortex is affected by the presence of the wing, and is highly dependent on the spanwise location of vortex impingement. Even at spanwise locations of impingement well outboard of the wing tip, a substantial influence on the structure of the incident vortex at locations significantly upstream of the leading edge of the wing was observed. For spanwise locations close to or intersecting the vortex core, the effects of upstream influence of the wing on the vortex are to: decrease the swirl ratio; increase the streamwise velocity deficit; decrease the streamwise vorticity; increase the azimuthal vorticity; increase the upwash; decrease the downwash; and increase the root-mean-square fluctuations of both streamwise velocity and vorticity. The interrelationship between these effects is addressed, including the rapid attenuation of axial vorticity in presence of an enhanced defect of axial velocity in the central region of the vortex. Moreover, when the incident vortex is aligned with, or inboard of, the tip of the wing, the swirl ratio decreases to values associated with instability of the vortex, giving rise to enhanced values of azimuthal vorticity relative to the streamwise (axial) vorticity, as well as relatively large root-mean-square values of streamwise velocity and vorticity. Along the chord of the wing, the vortex interaction gives rise to distinct modes, which may involve either enhancement or suppression of the vortex generated at the tip of the wing. These modes are classified and interpreted in conjunction with computed modes at the Air Force Research Laboratory. Occurrence of a given mode of interaction is predominantly determined by the dimensionless location of the incident vortex relative to the tip of the wing and is generally insensitive to the Reynolds number and dimensionless circulation of the incident vortex. The genesis of the basic modes of interaction is clarified using streamline topology with associated critical points. Whereas formation of an enhanced tip vortex involves a region of large upwash in conjunction with localized flow separation, complete suppression of the tip vortex is associated with a small-scale separation-attachment bubble bounded by downwash at the wing tip. Oscillation of the wing at an amplitude and velocity nearly two orders of magnitude smaller than the wing chord and free stream velocity respectively can give rise to distinctive patterns of upwash, downwash, and shed vorticity, which are dependent on the outboard displacement of the incident vortex relative to the wing tip. Moreover, these patterns are a strong function of the phase of the wing motion during its oscillation cycle. At a given value of phase, the wing oscillation induces upwash that is reinforced by the upwash of the incident vortex, giving a maximum value of net upwash. Conversely, when these two origins of upwash counteract, rather than reinforce, one another during the oscillation cycle, the net upwash has its minimum value. Analogous interpretations hold for regions of maximum and minimum net downwash located outboard of the regions of upwash. During the oscillation cycle of the wing, the magnitude and scale of the vorticity shed from the tip of the wing are directly correlated with the net upwash, which takes different forms related to the outboard displacement of the incident vortex. As the location of the incident vortex is displaced towards the wing tip, both the maximum upwash and the maximum vorticity of the tip vortex initially increase, then decrease. For the limiting case where the incident vortex impinges directly upon the tip of the wing, there is no tip vortex or induced region of upwash. Furthermore, at small values of vortex displacement from the wing tip, the position of the incident vortex varies significantly from its nominal position during the oscillation cycle. For all locations of the incident vortex, it is shown that, despite the small amplitude of the wing motion, the flow topology is fundamentally different at maximum positive and negative values of the wing velocity, that is, they are not symmetric.

Viscous instabilities in the q-vortex at large swirl numbers

NASA Astrophysics Data System (ADS)

Fabre, David; Jacquin, Laurent

2002-11-01

This comunication deals with the temporal stability of the q-vortex trailing line vortex model. We describe a family of viscous instabilities existing in a range of parameters which is usually assumed to be stable, namely large swirl parameters (q>1.5) and large Reynolds numbers. These instabilities affect negative azimuthal wavenumbers (m < 0) and take the form of centre-modes (i.e. with a structure concentrated along the vortex centerline). They are related to a family of viscous modes described by Stewartson, Ng & Brown (1988) in swirling Poiseuille flow, and are the temporal counterparts of weakly amplified spatial modes recently computed by Olendraru & Sellier (2002). These instabilities are studied numerically using an original and highly accurate Chebyshev collocation method, which allows a mapping of the unstable regions up to Rey 10^6 and q 7. Our results indicate that in the limit of very large Reynolds numbers, trailing vortices are affected by this kind of instabilities whatever the value of the swirl number.

Chiral Modes at Exceptional Points in Exciton-Polariton Quantum Fluids

NASA Astrophysics Data System (ADS)

Gao, T.; Li, G.; Estrecho, E.; Liew, T. C. H.; Comber-Todd, D.; Nalitov, A.; Steger, M.; West, K.; Pfeiffer, L.; Snoke, D. W.; Kavokin, A. V.; Truscott, A. G.; Ostrovskaya, E. A.

2018-02-01

We demonstrate the generation of chiral modes-vortex flows with fixed handedness in exciton-polariton quantum fluids. The chiral modes arise in the vicinity of exceptional points (non-Hermitian spectral degeneracies) in an optically induced resonator for exciton polaritons. In particular, a vortex is generated by driving two dipole modes of the non-Hermitian ring resonator into degeneracy. Transition through the exceptional point in the space of the system's parameters is enabled by precise manipulation of real and imaginary parts of the closed-wall potential forming the resonator. As the system is driven to the vicinity of the exceptional point, we observe the formation of a vortex state with a fixed orbital angular momentum (topological charge). This method can be extended to generate higher-order orbital angular momentum states through coalescence of multiple non-Hermitian spectral degeneracies. Our Letter demonstrates the possibility of exploiting nontrivial and counterintuitive properties of waves near exceptional points in macroscopic quantum systems.

Commissioning and first light results of an L'-band vortex coronagraph with the Keck II adaptive optics NIRC2 science instrument

NASA Astrophysics Data System (ADS)

Femenía Castellá, Bruno; Serabyn, Eugene; Mawet, Dimitri; Absil, Olivier; Wizinowich, Peter; Matthews, Keith; Huby, Elsa; Bottom, Michael; Campbell, Randy; Chan, Dwight; Carlomagno, Brunella; Cetre, Sylvain; Defrère, Denis; Delacroix, Christian; Gomez Gonzalez, Carlos; Jolivet, Aïssa; Karlsson, Mikael; Lanclos, Kyle; Lilley, Scott; Milner, Steven; Ngo, Henry; Reggiani, Maddalena; Simmons, Julia; Tran, Hien; Vargas Catalan, Ernesto; Wertz, Olivier

2016-07-01

On March 2015 an L'-band vortex coronagraph based on an Annular Groove Phase Mask made up of a diamond sub-wavelength grating was installed on NIRC2 as a demonstration project. This vortex coronagraph operates in the L' band not only in order to take advantage from the favorable star/planet contrast ratio when observing beyond the K band, but also to exploit the fact that the Keck II Adaptive Optics (AO) system delivers nearly extreme adaptive optics image quality (Strehl ratios values near 90%) at 3.7μm. We describe the hardware installation of the vortex phase mask during a routine NIRC2 service mission. The success of the project depends on extensive software development which has allowed the achievement of exquisite real-time pointing control as well as further contrast improvements by using speckle nulling to mitigate the effect of static speckles. First light of the new coronagraphic mode was on June 2015 with already very good initial results. Subsequent commissioning nights were interlaced with science nights by members of the VORTEX team with their respective scientific programs. The new capability and excellent results so far have motivated the VORTEX team and the Keck Science Steering Committee (KSSC) to offer the new mode in shared risk mode for 2016B.

Three-dimensional boundary layer stability and transition

NASA Technical Reports Server (NTRS)

Malik, M. R.; Li, F.

1992-01-01

Nonparallel and nonlinear stability of a three-dimensional boundary layer, subject to crossflow instability, is investigated using parabolized stability equations (PSEs). Both traveling and stationary disturbances are considered and nonparallel effect on crossflow instability is found to be destabilizing. Our linear PSE results for stationary disturbances agree well with the results from direct solution of Navier-Stokes equations obtained by Spalart (1989). Nonlinear calculations have been carried out for stationary vortices and the computed wall vorticity pattern results in streamwise streaks which resemble remarkably well with the surface oil-flow visualizations in swept-wing experiments. Other features of the stationary vortex development (half-mushroom structure, inflected velocity profiles, vortex doubling, etc.) are also captured in our nonlinear calculations. Nonlinear interaction of the stationary amplitude of the stationary vortex is large as compared to the traveling mode, and the stationary vortex dominates most of the downstream development. When the two modes have the same initial amplitude, the traveling mode dominates the downstream development owing to its higher growth rate, and there is a tendency for the stationary mode to be suppressed. The effect of nonlinear wave development on the skin-friction coefficient is also computed.

Vortex based information storage in Bose-Einstein condensates

NASA Astrophysics Data System (ADS)

Dutton, Zachary; Ruostekoski, Janne

2004-05-01

Recent demonstrations of coherent optical storage in atomic clouds [1,2] have opened up new possibilities for both classical and quantum information storage. In parallel, there have been advances in the generation of Laguerre-Gaussian (LG) modes with angular momentum (optical vortices)[3] and applications of these modes to quantum information architectures based on a alphabets larger than the traditional two-state systems. Here we theoretically consider the storage of such LG modes in atomic Rb-87 Bose-Einstein condensates (BECs). An LG mode writes its vortex phase pattern into a two-component BEC vortex state. The angular momentum information can then be stored in the BEC and then efficiently read back onto the optical field by switching a control field on. We study the fidelity of the writing, storage, and read-out processes. We also consider applying this method to to the transfer of more complicated states, such as two-component vortex lattices, between two spatially distinct BECs. 1. C. Liu, Z. Dutton, C.H. Behroozi, and L.V. Hau, Nature 409, 490 (2001). 2. D.F. Phillips, A. Fleischhauer, A. Mair, R.L. Walsworth, and M.D. Lukin, Phys. Rev. Lett. 86, 783 (2001). 3. A. Vaziri, Gregor Weihs, and A. Zeilinger, cond-mat/0111033.

Tunable magnetic vortex resonance in a potential well

NASA Astrophysics Data System (ADS)

Warnicke, P.; Wohlhüter, P.; Suszka, A. K.; Stevenson, S. E.; Heyderman, L. J.; Raabe, J.

2017-11-01

We use frequency-resolved x-ray microscopy to fully characterize the potential well of a magnetic vortex in a soft ferromagnetic permalloy square. The vortex core is excited with magnetic broadband pulses and simultaneously displaced with a static magnetic field. We observe a frequency increase (blueshift) in the gyrotropic mode of the vortex core with increasing bias field. Supported by micromagnetic simulations, we show that this frequency increase is accompanied by internal deformation of the vortex core. The ability to modify the inner structure of the vortex core provides a mechanism to control the dynamics of magnetic vortices.

Comparison between firing tests and numerical simulation of vortex shedding in a 2-D test solid motor

NASA Astrophysics Data System (ADS)

Lupoglazoff, N.; Vuillot, F.

Some comparisons between firing tests and numerical simulations of vortex shedding via a simple test case called 'C1experimental' are presented. These experiments are performed to validate further numerical simulations, as well as to serve as a tool for facilitating interpretation. At ignition time, spectra of pressure are more complex: it is the effect of vortex pairings. For 6.5-mm burnt, the second longitudinal mode dominates. For 8-mm burnt, the first longitudinal mode dominates. For 11.5-mm burnt, there is only the first longitudinal mode, with a slight shift of the frequency value. Tables are presented which give the pressure oscillation amplitudes of 'C1experimental' with operating pressures, and these amplitudes relative to the corresponding operating pressure.

A parametric study of the drift-tearing mode using an extended-magnetohydrodynamic model

DOE PAGES

King, Jacob R.; Kruger, S. E.

2014-10-24

The linear, collisional, constant-ψ drift-tearing mode is analyzed for different regimes of the plasma-β, ion-skin-depth parameter space with an unreduced, extended-magnetohydrodynamic model. Here, new dispersion relations are found at moderate plasma β and previous drift-tearing results are classified as applicable at small plasma β.

Efficient creation of electron vortex beams for high resolution STEM imaging.

PubMed

Béché, A; Juchtmans, R; Verbeeck, J

2017-07-01

The recent discovery of electron vortex beams carrying quantised angular momentum in the TEM has led to an active field of research, exploring a variety of potential applications including the possibility of mapping magnetic states at the atomic scale. A prerequisite for this is the availability of atomic sized electron vortex beams at high beam current and mode purity. In this paper we present recent progress showing that by making use of the Aharonov-Bohm effect near the tip of a long single domain ferromagnetic Nickel needle, a very efficient aperture for the production of electron vortex beams can be realised. The aperture transmits more than 99% of all electrons and provides a vortex mode purity of up to 92%. Placing this aperture in the condenser plane of a state of the art Cs corrected microscope allows us to demonstrate atomic resolution HAADF STEM images with spatial resolution better than 1 Angström, in agreement with theoretical expectations and only slightly inferior to the performance of a non-vortex probe on the same instrument. Copyright © 2016 Elsevier B.V. All rights reserved.

Diamagnetic drift effects on the low-n magnetohydrodynamic modes at the high mode pedestal with plasma rotation

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

Zheng, L. J.; Kotschenreuther, M. T.; Valanju, P.

2014-06-15

The diamagnetic drift effects on the low-n magnetohydrodynamic instabilities at the high-mode (H-mode) pedestal are investigated in this paper with the inclusion of bootstrap current for equilibrium and rotation effects for stability, where n is the toroidal mode number. The AEGIS (Adaptive EiGenfunction Independent Solutions) code [L. J. Zheng and M. T. Kotschenreuther, J. Comp. Phys. 211 (2006)] is extended to include the diamagnetic drift effects. This can be viewed as the lowest order approximation of the finite Larmor radius effects in consideration of the pressure gradient steepness at the pedestal. The H-mode discharges at Jointed European Torus is reconstructedmore » numerically using the VMEC code [P. Hirshman and J. C. Whitson, Phys. Fluids 26, 3553 (1983)], with bootstrap current taken into account. Generally speaking, the diamagnetic drift effects are stabilizing. Our results show that the effectiveness of diamagnetic stabilization depends sensitively on the safe factor value (q{sub s}) at the safety-factor reversal or plateau region. The diamagnetic stabilization are weaker, when q{sub s} is larger than an integer; while stronger, when q{sub s} is smaller or less larger than an integer. We also find that the diamagnetic drift effects also depend sensitively on the rotation direction. The diamagnetic stabilization in the co-rotation case is stronger than in the counter rotation case with respect to the ion diamagnetic drift direction.« less

Recurrent noise-induced phase singularities in drifting patterns.

PubMed

Clerc, M G; Coulibaly, S; del Campo, F; Garcia-Nustes, M A; Louvergneaux, E; Wilson, M

2015-11-01

We show that the key ingredients for creating recurrent traveling spatial phase defects in drifting patterns are a noise-sustained structure regime together with the vicinity of a phase transition, that is, a spatial region where the control parameter lies close to the threshold for pattern formation. They both generate specific favorable initial conditions for local spatial gradients, phase, and/or amplitude. Predictions from the stochastic convective Ginzburg-Landau equation with real coefficients agree quite well with experiments carried out on a Kerr medium submitted to shifted optical feedback that evidence noise-induced traveling phase slips and vortex phase-singularities.

Nonlinear mode coupling theory of the lower-hybrid-drift instability

NASA Technical Reports Server (NTRS)

Drake, J. F.; Guzdar, P. N.; Hassam, A. B.; Huba, J. D.

1984-01-01

A nonlinear mode coupling theory of the lower-hybrid-drift instability is presented. A two-dimensional nonlinear wave equation is derived which describes lower-hybrid drift wave turbulence in the plane transverse to B (k.B = 0), and which is valid for finite beta, collisional and collisionless plasmas. The instability saturates by transferring energy from growing, long wavelength modes to damped, short wavelength modes. Detailed numerical results are presented which compare favorably to both recent computer simulations and experimental observations. Applications of this theory to space plasmas, the earth's magnetotail and the equatorial F region ionosphere, are discussed. Previously announced in STAR as N84-17734

Acoustic Resonance and Vortex Shedding from Tube Banks of Boiler Plant

NASA Astrophysics Data System (ADS)

Hamakawa, Hiromitsu; Matsue, Hiroto; Nishida, Eiichi; Fukano, Tohru

This paper focuses on the relationship between acoustic resonance and vortex shedding from the tube banks of a boiler plant. We have built a model similar to the actual boiler plant to clarify the characteristics of acoustic resonance phenomena and vortex shedding. The model used in-line tube banks with a small tube pitch ratio. We examined the relationship between the acoustic resonance of the actual plant and that of the model, and measured the sound pressure level, acoustic pressure mode shape, spectrum of velocity fluctuation, and gap velocity. Gap velocity was defined as the mean velocity in the smallest gaps between two neighboring tubes in the transverse direction. As a result, the resonant frequencies and mode shapes of the acoustic resonances in the actual boiler plant agreed well with those in the similar model. We found many peak frequencies in the sound pressure level spectrum when acoustic resonances occurred. The typical Strouhal numbers at the onset velocity of acoustic resonances were about 0.19, 0.26 and 0.52. Periodic velocity fluctuation caused by vortex shedding was observed inside the tube banks without acoustic resonance. The Strouhal number measured for vortex shedding was 0.15. Acoustic resonances of higher-order modes were generated in this plant.

Dynamics of circular arrangements of vorticity in two dimensions

NASA Astrophysics Data System (ADS)

Swaminathan, Rohith V.; Ravichandran, S.; Perlekar, Prasad; Govindarajan, Rama

2016-07-01

The merger of two like-signed vortices is a well-studied problem, but in a turbulent flow, we may often have more than two like-signed vortices interacting. We study the merger of three or more identical corotating vortices initially arranged on the vertices of a regular polygon. At low to moderate Reynolds numbers, we find an additional stage in the merger process, absent in the merger of two vortices, where an annular vortical structure is formed and is long lived. Vortex merger is slowed down significantly due to this. Such annular vortices are known at far higher Reynolds numbers in studies of tropical cyclones, which have been noticed to a break down into individual vortices. In the preannular stage, vortical structures in a viscous flow are found here to tilt and realign in a manner similar to the inviscid case, but the pronounced filaments visible in the latter are practically absent in the former. Five or fewer vortices initially elongate radially, and then reorient their long axis closer to the azimuthal direction so as to form an annulus. With six or more vortices, the initial alignment is already azimuthal. Interestingly at higher Reynolds numbers, the merger of an odd number of vortices is found to proceed very differently from that of an even number. The former process is rapid and chaotic whereas the latter proceeds more slowly via pairing events. The annular vortex takes the form of a generalized Lamb-Oseen vortex (GLO), and diffuses inward until it forms a standard Lamb-Oseen vortex. For lower Reynolds number, the numerical (fully nonlinear) evolution of the GLO vortex follows exactly the analytical evolution until merger. At higher Reynolds numbers, the annulus goes through instabilities whose nonlinear stages show a pronounced difference between even and odd mode disturbances. Here again, the odd mode causes an early collapse of the annulus via decaying turbulence into a single central vortex, whereas the even mode disturbance causes a more orderly progression into a single vortex. Results from linear stability analysis agree with the nonlinear simulations, and predict the frequencies of the most unstable modes better than they predict the growth rates. It is hoped that the present findings, that multiple vortex merger is qualitatively different from the merger of two vortices, will motivate studies on how multiple vortex interactions affect the inverse cascade in two-dimensional turbulence.

Measuring mode indices of a partially coherent vortex beam with Hanbury Brown and Twiss type experiment

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

Liu, Ruifeng; Wang, Feiran; Chen, Dongxu

2016-02-01

It is known that the cross-correlation function (CCF) of a partially coherent vortex (PCV) beam shows a robust link with the radial and azimuthal mode indices. However, the previous proposals are difficult to measure the CCF in practical systems, especially in the case of astronomical objects. In this letter, we demonstrate experimentally that the Hanbury Brown and Twiss effect can be used to measure the mode indices of the original vortex beam and investigate the relationship between the spatial coherent width and the characterization of CCF of the PCV beam. The technique we exploit is quite efficient and robust, andmore » it may be useful in the field of free space communication and astronomy which are related to the photon's orbital angular momentum.« less

High-Order Dielectric Metasurfaces for High-Efficiency Polarization Beam Splitters and Optical Vortex Generators

NASA Astrophysics Data System (ADS)

Guo, Zhongyi; Zhu, Lie; Guo, Kai; Shen, Fei; Yin, Zhiping

2017-08-01

In this paper, a high-order dielectric metasurface based on silicon nanobrick array is proposed and investigated. By controlling the length and width of the nanobricks, the metasurfaces could supply two different incremental transmission phases for the X-linear-polarized (XLP) and Y-linear-polarized (YLP) light with extremely high efficiency over 88%. Based on the designed metasurface, two polarization beam splitters working in high-order diffraction modes have been designed successfully, which demonstrated a high transmitted efficiency. In addition, we have also designed two vortex-beam generators working in high-order diffraction modes to create vortex beams with the topological charges of 2 and 3. The employment of dielectric metasurfaces operating in high-order diffraction modes could pave the way for a variety of new ultra-efficient optical devices.

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.

Drift Wave Simulation in Toroidal Geometry.

NASA Astrophysics Data System (ADS)

Lebrun, Maurice Joseph, III

1988-12-01

The drift wave, a general category of plasma behavior arising from a plasma inhomogeneity, is studied using the particle simulation method. In slab geometry, the drift wave (or universal mode) is stabilized by any finite amount of magnetic shear. In toroidal geometry, however, the coupling of the poloidal harmonics gives rise to a new branch of drift wave eigenmodes called the toroidicity -induced mode, which is predicted to be unstable in some regimes. The drift wave in a toroidal system is intrinsically three-dimensional, and is sensitive to the handling of the parallel electron dynamics, the (nearly) perpendicular wave dynamics, and the radial variation of magnetic field vector (shear). A simulation study must therefore be kinetic in nature, motivating the extension of particle simulation techniques to complex geometries. From this effort a three dimensional particle code in a toroidal coordinate system has been developed and applied to the toroidal drift wave problem. The code uses an (r,theta,phi) -type coordinate system, and a nonuniform radial grid that increases resolution near the mode-rational surfaces. Full ion dynamics and electron guiding center dynamics are employed. Further, the algorithm incorporates a straightforward limiting process to cylindrical geometry and slab geometry, enabling comparison to the theoretical results in these regimes. Simulations of the density-driven modes in toroidal geometry retain a single toroidal mode number (n = 9). In this regime, the poloidal harmonics are expected to be strongly coupled, giving rise to the marginally unstable toroidicity-induced drift mode. Analysis of the simulation data reveals a strong, low-frequency response that peaks near each mode rational surface. Further, the characteristic oscillation frequencies persist from one mode rational surface to the next, which identifies them as multiple harmonics of the toroidicity-induced mode. The lowest harmonic occurs at a frequency of omega/ omega^{*} ~ 0.26, which is reasonably close to the prediction of linear theory. Interferogram analysis of these modes indicates a "ballooning" structure toward the outside of the torus. The amplitude of the potential is observed to grow exponentially for the m = 8 through m = 10 poloidal mode numbers, with a growth rate of approximately gamma/omega ^{*} ~ 0.075. Saturation occurs at time t ~ 1000 Omega_sp{i}{-1}, and may be caused by quasilinear flattening of the density profile.

Characterization of Ventilatory Modes in Dragonfly Nymph

NASA Astrophysics Data System (ADS)

Roh, Chris; Saxton-Fox, Theresa; Gharib, Morteza

2013-11-01

A dragonfly nymph's highly modified hindgut has multiple ventilatory modes: hyperventilation (i.e. jet propulsion), gulping ventilation (extended expiratory phase) and normal ventilation. Each mode involves dynamic manipulation of the exit diameter and pressure. To study the different fluid dynamics associated with the three modes, Anisopteran larvae of the family Aeshnidae were tethered onto a rod for flow visualization. The result showed distinct flow structures. The hyperventilation showed a highly turbulent and powerful jet that occurred at high frequency. The gulping ventilation produced a single vortex at a moderate frequency. The normal ventilation showed two distinct vortices, a low-Reynolds number vortex, followed by a high-Reynolds number vortex. Furthermore, a correlation of the formation of the vortices with the movement of the sternum showed that the dragonfly is actively controlling the timing and the speed of the vortices to have them at equal distance from the jet exit at the onset of inspiration. This behavior prevents inspiration of the oxygen deficient expirated water, resulting in the maximization of the oxygen intake. Supported by NSF GRFP.

Non-equilibrium effects of diatomic and polyatomic gases on the shock-vortex interaction based on the second-order constitutive model of the Boltzmann-Curtiss equation

NASA Astrophysics Data System (ADS)

Singh, S.; Karchani, A.; Myong, R. S.

2018-01-01

The rotational mode of molecules plays a critical role in the behavior of diatomic and polyatomic gases away from equilibrium. In order to investigate the essence of the non-equilibrium effects, the shock-vortex interaction problem was investigated by employing an explicit modal discontinuous Galerkin method. In particular, the first- and second-order constitutive models for diatomic and polyatomic gases derived rigorously from the Boltzmann-Curtiss kinetic equation were solved in conjunction with the physical conservation laws. As compared with a monatomic gas, the non-equilibrium effects result in a substantial change in flow fields in both macroscale and microscale shock-vortex interactions. Specifically, the computational results showed three major effects of diatomic and polyatomic gases on the shock-vortex interaction: (i) the generation of the third sound waves and additional reflected shock waves with strong and enlarged expansion, (ii) the dominance of viscous vorticity generation, and (iii) an increase in enstrophy with increasing bulk viscosity, related to the rotational mode of gas molecules. Moreover, it was shown that there is a significant discrepancy in flow fields between the microscale and macroscale shock-vortex interactions in diatomic and polyatomic gases. The quadrupolar acoustic wave source structures, which are typically observed in macroscale shock-vortex interactions, were not found in any microscale shock-vortex interactions. The physics of the shock-vortex interaction was also investigated in detail to examine vortex deformation and evolution dynamics over an incident shock wave. A comparative study of first- and second-order constitutive models was also conducted for the enstrophy and dissipation rate. Finally, the study was extended to the shock-vortex pair interaction case to examine the effects of pair interaction on vortex deformation and evolution dynamics.

A Study of Dean Vortex Development and Structure in a Curved Rectangular Channel with Aspect Ratio of 40 at Dean Numbers up to 430

NASA Technical Reports Server (NTRS)

Ligrani, Phillip M.

1994-01-01

Flow in a curved channel with mild curvature, an aspect ratio of 40 to 1, and an inner to outer radius ratio of 0.979 is studied at Dean numbers De ranging from 35 to 430. For positions from the start of curvature ranging from 85 to 145 degrees, the sequence of transition events begins with curved channel Poiseuille flow at De less than 40-64. As the Dean number increases, observations show initial development of Dean vortex pairs, followed by symmetric vortex pairs which, when viewed in spanwise/radial planes, cover the entire channel height (De=90-100). At De from 40 to 125-130, the vortex pairs often develop intermittent waviness in the form of vortex undulations. Splitting and merging of vortex pairs is also observed over the same experimental conditions as well as at higher De. When Dean numbers range from 130 to 185-200, the undulating wavy mode is replaced by a twisting mode with higher amplitudes of oscillation and shorter wavelengths. The twisting wavy mode results in the development of regions where turbulence intensity is locally augmented at Dean numbers from 150 to 185-200, principally in the upwash regions between the two individual vortices which make up each vortex pair. These turbulent regions eventually increase in intensity and spatial extent as the Dean number increases further, until individual regions merge together so that the entire cross section of the channel contains chaotic turbulent motions. When Dean numbers then reach 400-435, spectra of velocity fluctuations then evidence fully turbulent flow.

Radial plasma drifts deduced from VLF whistler mode signals - A modelling study

NASA Astrophysics Data System (ADS)

Poulter, E. M.; Andrews, M. K.; Bailey, G. J.; Moffett, R. J.

1984-05-01

VLF whistler mode signals have previously been used to infer radial plasma drifts in the equatorial plane of the plasmasphere and the field-aligned ionosphere-protonosphere coupling fluxes. Physical models of the plasmasphere consisting of O(+) adn H(+) ions along dipole magnetic field lines, and including radial E x B drifts, are applied to a mid-latitude flux tube appropriate to whistler mode signals received at Wellington, New Zealand, from the fixed frequency VLF transmitter NLK (18.6 kHz) in Seattle, U.S.A. These models are first shown to provide a good representation of the recorded Doppler shift and group delay data. They are then used to simulate the process of deducing the drifts and fluxes from the recorded data. Provided the initial whistler mode duct latitude and the ionospheric contributions are known, the drifts at the equatorial plane can be estimated to about + or - 20 m/s (approximately 10-15 percent), and the two hemisphere ionosphere-protonosphere coupling fluxes to about + or - 10 to the 12th/sq m-sec (approximately 40 percent).

Shear-flow driven dissipative instability and investigation of nonlinear drift-vortex modes in dusty plasmas with non-thermal ion population

NASA Astrophysics Data System (ADS)

Gul-e-Ali, Masood, W.; Mirza, Arshad M.

2017-12-01

The shear flow in dust dynamics driven waves in combination with the dust-neutral drag is studied in a plasma comprising of ions, electrons, and dust. Non-thermal population of ions is considered, which has been observed by many satellite missions. It is found that the dissipative instability produced by dust sheared flow and dust-neutral drag gets modified by the presence of nonthermal ions. It is found that the dissipative instability enhances for the Cairns distribution, whereas the kappa distribution arrests the growth of this instability. In the nonlinear regime, the formation of vortices in the system is studied. It is found that the nonthermal population of ions significantly alters these structures in comparison with their Maxwellian counterpart. The results obtained in this paper may have relevance in the planetary magnetospheres where the dust particles are present and non-Maxwellian distribution of particles have been observed by Freja and Viking satellites.

Dynamic mode decomposition of separated flow over a finite blunt plate: time-resolved particle image velocimetry measurements

NASA Astrophysics Data System (ADS)

Liu, Yingzheng; Zhang, Qingshan

2015-07-01

Dynamic mode decomposition (DMD) analysis was performed on a large number of realizations of the separated flow around a finite blunt plate, which were determined by using planar time-resolved particle image velocimetry (TR-PIV). Three plates with different chord-to-thickness ratios corresponding to globally different flow patterns were particularly selected for comparison: L/D = 3.0, 6.0 and 9.0. The main attention was placed on dynamic variations in the dominant events and their interactive influences on the global fluid flow in terms of the DMD analysis. Toward this end, a real-time data transfer from the high-speed camera to the arrayed disks was built to enable continuous sampling of the spatiotemporally varying flows at the frequency of 250 Hz for a long run. The spectra of the wall-normal velocity fluctuation, the energy spectra of the DMD modes, and their spatial patterns convincingly determined the energetic unsteady events, i.e., St = 0.051 (Karman vortex street), 0.109 (harmonic event of Karman vortex street) and 0.197 (leading-edge vortex) in the shortest system L/D = 3.0, St = 0.159 (Karman vortex street) and 0.242 (leading-edge vortex) in the system L/D = 6.0, and St = 0.156 (Karman vortex street) and 0.241 (leading-edge vortex) in the longest system L/D = 9.0. In the shortest system L/D = 3.0, the first DMD mode pattern demonstrated intensified entrainment of the massive fluid above and below the whole plate by the Karman vortex street. The phase-dependent variation in the low-order flow field elucidated that this motion was sustained by the consecutive mechanisms of the convective leading-edge vortices near the upper and lower trailing edges, and the large-scale vortical structures occurring immediately behind the trailing edge, whereas the leading-edge vortices were entrained and decayed into the near wake. For the system L/D = 6.0, the closely approximated energy spectra at St = 0.159 and 0.242 indicated the balanced dominance of dual unsteady events in the measurement region. The Karman vortex street was found to induce considerable localized movement of the fluid near the trailing edges of the plate. However, the leading-edge vortices near the trailing edge were found to detach away from the plate and fully decay around 0.5 D behind the trailing edge, where a well-ordered origination of the downstream large-scale vortical structures (the Karman vortex street) was established and might be locally energized by the decayed leading-edge vortex. In the longest system L/D = 9.0, the phase-dependent variations in the low-order flow disclosed a rapid decay of the leading-edge vortices beyond the reattachment zone, reaching the fully diffused state near the trailing edges. Accordingly, no clear signature of the interaction between the Karman vortex street and the leading-edge vortex could be found in the dynamic process of the leading-edge vortex.

Coupled-cavity drift-tube linac

DOEpatents

Billen, James H.

1996-01-01

A coupled-cavity drift-tube linac (CCDTL) combines features of the Alvarez drift-tube linac (DTL) and the .pi.-mode coupled-cavity linac (CCL). In one embodiment, each accelerating cavity is a two-cell, 0-mode DTL. The center-to-center distance between accelerating gaps is .beta..lambda., where .lambda. is the free-space wavelength of the resonant mode. Adjacent accelerating cavities have oppositely directed electric fields, alternating in phase by 180 degrees. The chain of cavities operates in a .pi./2 structure mode so the coupling cavities are nominally unexcited. The CCDTL configuration provides an rf structure with high shunt impedance for intermediate velocity charged particles, i.e., particles with energies in the 20-200 MeV range.

Coupled-cavity drift-tube linac

DOEpatents

Billen, J.H.

1996-11-26

A coupled-cavity drift-tube linac (CCDTL) combines features of the Alvarez drift-tube linac (DTL) and the {pi}-mode coupled-cavity linac (CCL). In one embodiment, each accelerating cavity is a two-cell, 0-mode DTL. The center-to-center distance between accelerating gaps is {beta}{lambda}, where {lambda} is the free-space wavelength of the resonant mode. Adjacent accelerating cavities have oppositely directed electric fields, alternating in phase by 180 degrees. The chain of cavities operates in a {pi}/2 structure mode so the coupling cavities are nominally unexcited. The CCDTL configuration provides an rf structure with high shunt impedance for intermediate velocity charged particles, i.e., particles with energies in the 20-200 MeV range. 5 figs.

A planetary-scale disturbance in a long living three vortex coupled system in Saturn's atmosphere

NASA Astrophysics Data System (ADS)

del Río-Gaztelurrutia, T.; Sánchez-Lavega, A.; Antuñano, A.; Legarreta, J.; García-Melendo, E.; Sayanagi, K. M.; Hueso, R.; Wong, M. H.; Pérez-Hoyos, S.; Rojas, J. F.; Simon, A. A.; de Pater, I.; Blalock, J.; Barry, T.

2018-03-01

The zonal wind profile of Saturn has a unique structure at 60°N with a double-peaked jet that reaches maximum zonal velocities close to 100 ms-1. In this region, a singular group of vortices consisting of a cyclone surrounded by two anticyclones was active since 2012 until the time of this report. Our observation demonstrates that vortices in Saturn can be long-lived. The three-vortex system drifts at u = 69.0 ± 1.6 ms-1, similar to the speed of the local wind. Local motions reveal that the relative vorticity of the vortices comprising the system is ∼2-3 times the ambient zonal vorticity. In May 2015, a disturbance developed at the location of the triple vortex system, and expanded eastwards covering in two months a third of the latitudinal circle, but leaving the vortices essentially unchanged. At the time of the onset of the disturbance, a fourth vortex was present at 55°N, south of the three vortices and the evolution of the disturbance proved to be linked to the motion of this vortex. Measurements of local motions of the disturbed region show that cloud features moved essentially at the local wind speeds, suggesting that the disturbance consisted of passively advecting clouds generated by the interaction of the triple vortex system with the fourth vortex to the south. Nonlinear simulations are able to reproduce the stability and longevity of the triple vortex system under low vertical wind shear and high static stability in the upper troposphere of Saturn.

Evolution of an electron plasma vortex in a strain flow

NASA Astrophysics Data System (ADS)

Danielson, J. R.

2016-10-01

Coherent vortex structures are ubiquitous in fluids and plasmas and are examples of self-organized structures in nonlinear dynamical systems. The fate of these structures in strain and shear flows is an important issue in many physical systems, including geophysical fluids and shear suppression of turbulence in plasmas. In two-dimensions, an inviscid, incompressible, ideal fluid can be modeled with the Euler equations, which is perhaps the simplest system that supports vortices. The Drift-Poisson equations for pure electron plasmas in a strong, uniform magnetic field are isomorphic to the Euler equations, and so electron plasmas are an excellent test bed for the study of 2D vortex dynamics. This talk will describe results from a new experiment using pure electron plasmas in a specially designed Penning-Malmberg (PM) trap to study the evolution of an initially axisymmetric 2D vortex subject to externally imposed strains. Complementary vortex-in-cell simulations are conducted to validate the 2D nature of the experimental results and to extend the parameter range of these studies. Data for vortex destruction using both instantaneously applied and time dependent strains with flat (constant vorticity) and extended radial profiles will be presented. The role of vortex self-organization will be discussed. A simple 2D model works well for flat vorticity profiles. However, extended profiles exhibit more complicated behavior, such as filamentation and stripping; and these effects and their consequences will be discussed. Work done in collaboration with N. C. Hurst, D. H. E. Dubin, and C. M. Surko.

Vortex-slip transitions in superconducting a-NbGe mesoscopic channels

NASA Astrophysics Data System (ADS)

Kokubo, N.; Sorop, T. G.; Besseling, R.; Kes, P. H.

2006-06-01

Intriguing and novel physical aspects related to the vortex flow dynamics have been recently observed in mesoscopic channel devices of a-NbGe with NbN channel edges. In this work we have systematically studied the flow properties of vortices confined in such mesoscopic channels as a function of the magnetic field history, using dc-transport and mode-locking (ML) measurements. As opposed to the field-down situation, in the field-up case a kink anomaly in the dc I-V curves is detected. The mode-locking measurements reveal that this anomaly is, in fact, a flow induced vortex slip transition: by increasing the external drive (either dc or ac) a sudden change occurs from n to n+2 moving vortex rows in the channel. The observed features can be explained in terms of an interplay between field focusing due to screening currents and a change in the predominant pinning mechanism.

Mechanically Reconfigurable Single-Arm Spiral Antenna Array for Generation of Broadband Circularly Polarized Orbital Angular Momentum Vortex Waves.

PubMed

Li, Long; Zhou, Xiaoxiao

2018-03-23

In this paper, a mechanically reconfigurable circular array with single-arm spiral antennas (SASAs) is designed, fabricated, and experimentally demonstrated to generate broadband circularly polarized orbital angular momentum (OAM) vortex waves in radio frequency domain. With the symmetrical and broadband properties of single-arm spiral antennas, the vortex waves with different OAM modes can be mechanically reconfigurable generated in a wide band from 3.4 GHz to 4.7 GHz. The prototype of the circular array is proposed, conducted, and fabricated to validate the theoretical analysis. The simulated and experimental results verify that different OAM modes can be effectively generated by rotating the spiral arms of single-arm spiral antennas with corresponding degrees, which greatly simplify the feeding network. The proposed method paves a reconfigurable way to generate multiple OAM vortex waves with spin angular momentum (SAM) in radio and microwave satellite communication applications.

Anomalous matching effect and attractive vortex interaction in 7.5-/μm triangular microhole lattice on Pb film

NASA Astrophysics Data System (ADS)

Ishida, Takekazu; Yoshida, Masaaki; Nakata, Shin'ichiro; Koyama, Tomio

2002-10-01

It is considerably exciting to explore the novel vortex physics in multiply connected superconductors. We prepare triangular microhole lattice on Pb film (TriMHoLP) by evaporation of a type-I superconductor Pb upon a capillary plate (6-μm hole and 7.5-μm pitch) in vacuum. We measure the magnetization of TriMHoLP in the RSO mode under low fields (| H|⩽4.7 G). The polarity of magnetization peaks is identical against the field reversal. The magnetization curves as a function of temperature taken in a field-cooling mode of RSO are always positive irrelevant to the field polarity. We show that a vortex-vortex interaction is not always repulsive in a low- κ superconductor. We consider that a spontaneous magnetization and an anomalous matching effect near Tc are relevant to the attractive interaction between vortices.

The stability of a trailing-line vortex in compressible flow

NASA Technical Reports Server (NTRS)

Stott, Jillian A. K.; Duck, Peter W.

1992-01-01

We consider the inviscid stability of the Batchelor (1964) vortex in a compressible flow. The problem is tackled numerically and also asymptotically, in the limit of large (aximuthal and streamwise) wavenumbers, together with large Mach numbers. The nature of the solution passes through different regimes as the Mach number increases, relative to the wavenumbers. At very high wavenumbers and Mach numbers, the mode which is present in the incompressible case ceases to be unstable, while new 'center mode' forms, whose stability characteristics, are determined primarily by conditions close to the vortex axis. We find that generally the flow becomes less unstable as the Mach number increases, and that the regime of instability appears generally confined to disturbances in a direction counter to the direction of the rotation of the swirl of the vortex. Throughout the paper, comparison is made between our numerical results and results obtained from the various asymptotic theories.

Helical vortices: linear stability analysis and nonlinear dynamics

NASA Astrophysics Data System (ADS)

Selçuk, C.; Delbende, I.; Rossi, M.

2018-02-01

We numerically investigate, within the context of helical symmetry, the dynamics of a regular array of two or three helical vortices with or without a straight central hub vortex. The Navier-Stokes equations are linearised to study the instabilities of such basic states. For vortices with low pitches, an unstable mode is extracted which corresponds to a displacement mode and growth rates are found to compare well with results valid for an infinite row of point vortices or an infinite alley of vortex rings. For larger pitches, the system is stable with respect to helically symmetric perturbations. In the nonlinear regime, we follow the time-evolution of the above basic states when initially perturbed by the dominant instability mode. For two vortices, sequences of overtaking events, leapfrogging and eventually merging are observed. The transition between such behaviours occurs at a critical ratio involving the core size and the vortex-separation distance. Cases with three helical vortices are also presented.

On the Vortex Waves in Nonadiabatic Flows

NASA Astrophysics Data System (ADS)

Ibáñez S., Miguel H.; Núñez, Luis A.

2018-03-01

Linear disturbances superposed on steady flows in nonadiabatic plasmas are analyzed. In addition to the potential modes resulting (two sound waves and a thermal mode) that are Doppler shifted, a rotational mode appears identified as an entropy-vortex wave (evw) which is carried along by the gas flow. In adiabatic flows, as well as in nonadiabatic flows, the evw always shows a null pressure disturbance. But in the second case, the wave number of the evw disturbance is fixed for the particular thermal conditions of the gas. The above holds for optically thin gases, as well as for radiating flows, if the dynamical effects of the radiation field are neglected in a first approximation. The above results allow us to calculate the dimensions of the vortex elements that are expected to be formed in nonadiabatic gas flows, particularly in hot ionized plasmas of interest in astrophysics.

A new reversal mode in exchange coupled antiferromagnetic/ferromagnetic disks: distorted viscous vortex

DOE PAGES

Gilbert, Dustin A.; Ye, Li; Varea, Aïda; ...

2015-04-28

Magnetic vortices have generated intense interest in recent years due to their unique reversal mechanisms, fascinating topological properties, and exciting potential applications. In addition, the exchange coupling of magnetic vortices to antiferromagnets has also been shown to lead to a range of novel phenomena and functionalities. Here we report a new magnetization reversal mode of magnetic vortices in exchange coupled Ir 20Mn 80/Fe 20Ni 80 microdots: distorted viscous vortex reversal. In contrast to the previously known or proposed reversal modes, the vortex is distorted close to the interface and viscously dragged due to the uncompensated spins of a thin antiferromagnet,more » which leads to unexpected asymmetries in the annihilation and nucleation fields. Lastly, these results provide a deeper understanding of the physics of exchange coupled vortices and may also have important implications for applications involving exchange coupled nanostructures.« less

The effects of viscosity on the stability of a trailing-line vortex in compressible flow

NASA Technical Reports Server (NTRS)

Stott, Jillian A. K.; Duck, Peter W.

1994-01-01

We consider the effects of viscosity on the inviscid stability of the Batchelor vortex in a compressible flow. The problem is tackled asymptotically, in the limit of large (streamwise and azimuthal) wavenumbers, together with large Mach numbers. Previous studies, with viscous effects neglected, found that the nature of the solution passes through different regimes as the Mach number increases, relative to the wavenumber. This structure persists when viscous effects are included in the analysis. In the present study the mode present in the incompressible case ceases to be unstable at high Mach numbers and a center mode forms, whose stability characteristics are determined primarily by conditions close to the vortex axis. We find generally that viscosity has a stabilizing influence on the flow, while in the case of center modes, viscous effects become important at much larger Reynolds numbers than for the first class of disturbance.

Langmuir Turbulence

DTIC Science & Technology

2015-09-30

1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Langmuir Turbulence Eric A. D’Asaro, Ramsey Harcourt...definitive experimental tests of the hypothesis that Langmuir Turbulence , specifically the equations of motion with the addition of the Craik-Leibovich...vortex force and advection by the surface wave Stokes drift, can accurately describe turbulence in the upper ocean boundary layer under conditions of

Electromagnetic drift waves dispersion for arbitrarily collisional plasmas

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

Lee, Wonjae, E-mail: wol023@ucsd.edu; Krasheninnikov, Sergei I., E-mail: skrash@mae.ucsd.edu; Angus, J. R.

2015-07-15

The impacts of the electromagnetic effects on resistive and collisionless drift waves are studied. A local linear analysis on an electromagnetic drift-kinetic equation with Bhatnagar-Gross-Krook-like collision operator demonstrates that the model is valid for describing linear growth rates of drift wave instabilities in a wide range of plasma parameters showing convergence to reference models for limiting cases. The wave-particle interactions drive collisionless drift-Alfvén wave instability in low collisionality and high beta plasma regime. The Landau resonance effects not only excite collisionless drift wave modes but also suppress high frequency electron inertia modes observed from an electromagnetic fluid model in collisionlessmore » and low beta regime. Considering ion temperature effects, it is found that the impact of finite Larmor radius effects significantly reduces the growth rate of the drift-Alfvén wave instability with synergistic effects of high beta stabilization and Landau resonance.« less

Kinematics, hydrodynamics and energetic advantages of burst-and-coast swimming of koi carps (Cyprinus carpio koi).

PubMed

Wu, Guanhao; Yang, Yan; Zeng, Lijiang

2007-06-01

Koi carps frequently swim in burst-and-coast style, which consists of a burst phase and a coast phase. We quantify the swimming kinematics and the flow patterns generated by the carps in burst-and-coast swimming. In the burst phase, the carps burst in two modes: in the first, the tail beats for at least one cycle (multiple tail-beat mode); in the second, the tail beats for only a half-cycle (half tail-beat mode). The carp generates a vortex ring in each half-cycle beat. The vortex rings generated during bursting in multiple tail-beat mode form a linked chain, but only one vortex ring is generated in half tail-beat mode. The wake morphologies, such as momentum angle and jet angle, also show much difference between the two modes. In the burst phase, the kinematic data and the impulse obtained from the wake are linked to obtain the drag coefficient (C(d,burst) approximately 0.242). In the coast phase, drag coefficient (C(d,coast) approximately 0.060) is estimated from swimming speed deceleration. Our estimation suggests that nearly 45% of energy is saved when burst-and-coast swimming is used by the koi carps compared with steady swimming at the same mean speed.

Coherent Structures in Magnetic Confinement Systems

NASA Astrophysics Data System (ADS)

Horton, W.

2006-04-01

Coherent structures are long-lived, nonlinear localized solutions of the selfconsistient plasma-electromagnetic field equations. They contain appreciable energy density and control various transport and magnetic reconnection processes in plasmas. These structures are self-binding from the nonlinearity balancing, or overcoming, the wave dispersion of energy in smaller amplitude structures. The structures evolve out of the nonlinear interactions in various instabilities or external driving fields. The theoretical basis for these structures are reviewed giving examples from various plasma instabilities and their reduced descriptions from the appropriate partial differential equations. A classic example from drift waves is the formation of monopole, dipole and tripolar vortex structures which have been created in both laboratory and simulation experiments. For vortices, the long life-time and nonlinear interactions of the structures can be understood with conservation laws of angular momentum given by the vorticity field associated with dynamics. Other morphologies include mushrooms, Kelvin-Helmholtz vorticity roll-up, streamers and blobs. We show simulation movies of various examples drawn from ETG modes in NSTX, H-mode like shear flow layers in LAPD and the vortices measured with soft x-ray tomography in the GAMMA 10 tandem mirror. Coherent current-sheet structures form in driven magnetic reconnection layers and control the rate of transformation of magnetic energy to flow and thermal energy.

FAST TRACK COMMUNICATION: Gyration mode splitting in magnetostatically coupled magnetic vortices in an array

NASA Astrophysics Data System (ADS)

Barman, Anjan; Barman, Saswati; Kimura, T.; Fukuma, Y.; Otani, Y.

2010-10-01

We present the experimental observation of gyration mode splitting by the time-resolved magneto-optical Kerr effect in an array consisting of magnetostatically coupled Ni81Fe19 discs of 1 µm diameter, 50 nm thickness and inter-disc separations varying between 150 and 270 nm. A splitting of the vortex core gyration mode is observed when the inter-disc separation is 200 nm or less and the splitting is controllable by a bias magnetic field. The observed mode splitting is interpreted by micromagnetic simulations as the normal modes of the vortex cores analogous to the coupled classical oscillators. The splitting depends upon the strength of the inter-disc magnetostatic coupling mediated by magnetic side charges, which depends strongly on the magnetic ground states of the samples.

Investigation of propagation dynamics of truncated vector vortex beams.

PubMed

Srinivas, P; Perumangatt, C; Lal, Nijil; Singh, R P; Srinivasan, B

2018-06-01

In this Letter, we experimentally investigate the propagation dynamics of truncated vector vortex beams generated using a Sagnac interferometer. Upon focusing, the truncated vector vortex beam is found to regain its original intensity structure within the Rayleigh range. In order to explain such behavior, the propagation dynamics of a truncated vector vortex beam is simulated by decomposing it into the sum of integral charge beams with associated complex weights. We also show that the polarization of the truncated composite vector vortex beam is preserved all along the propagation axis. The experimental observations are consistent with theoretical predictions based on previous literature and are in good agreement with our simulation results. The results hold importance as vector vortex modes are eigenmodes of the optical fiber.

Drift mode accelerometry for spaceborne gravity measurements

NASA Astrophysics Data System (ADS)

Conklin, John W.

2015-11-01

A drift mode accelerometer is a precision instrument for spacecraft that overcomes much of the acceleration noise and readout dynamic range limitations of traditional electrostatic accelerometers. It has the potential of achieving acceleration noise performance similar to that of drag-free systems over a restricted frequency band without the need for external drag-free control or continuous spacecraft propulsion. Like traditional accelerometers, the drift mode accelerometer contains a high-density test mass surrounded by an electrode housing, which can control and sense all six degrees of freedom of the test mass. Unlike traditional accelerometers, the suspension system is operated with a low duty cycle so that the limiting suspension force noise only acts over brief, known time intervals, which can be neglected in the data analysis. The readout is performed using a laser interferometer which is immune to the dynamic range limitations of even the best voltage references typically used to determine the inertial acceleration of electrostatic accelerometers. The drift mode accelerometer is a novel offshoot of the like-named operational mode of the LISA Pathfinder spacecraft, in which its test mass suspension system is cycled on and off to estimate the acceleration noise associated with the front-end electronics. This paper presents the concept of a drift mode accelerometer, describes the operation of such a device, develops models for its performance with respect to non-drag-free satellite geodesy and gravitational wave missions, and discusses plans for testing the performance of a prototype sensor in the laboratory using torsion pendula.

Oblique and Parallel Modes of Vortex Shedding in the Wake of a Circular Cylinder at Low Reynolds Numbers

DTIC Science & Technology

1989-12-01

differences in the shedding angles between experiments. It might then be j,. Vortex shedding in the wake of a circular cylinder 583 suggested that these...sandwiched between cels of frequency fL. In I " :. - Vortex shedding in the wake of a circular cylinder 593 (a) (b) Fioru’ 6. Visualization of the different ...Iparticularly’ suitable (heck, because the water tank is at oistinctl ’ different facility from the wind tunnel. The vortex frequencies in the wakes

Mapping of all polarization-singularity C-point morphologies

NASA Astrophysics Data System (ADS)

Galvez, E. J.; Rojec, B. L.; Beach, K.

2014-02-01

We present theoretical descriptions and measurements of optical beams carrying isolated polarization-singularity C-points. Our analysis covers all types of C-points, including asymmetric lemons, stars and monstars. They are formed by the superposition of a circularly polarized mode carrying an optical vortex and a fundamental Gaussian mode in the opposite state of polarization. The type of C-point can be controlled experimentally by varying two parameters controlling the asymmetry of the optical vortex. This was implemented via a superposition of modes with singly charged optical vortices of opposite sign, and varying the relative amplitude and phase. The results are in excellent agreement with the predictions.

Investigation on flow oscillation modes and aero-acoustics generation mechanism in cavity

NASA Astrophysics Data System (ADS)

Yang, Dang-Guo; Lu, Bo; Cai, Jin-Sheng; Wu, Jun-Qiang; Qu, Kun; Liu, Jun

2018-05-01

Unsteady flow and multi-scale vortex transformation inside a cavity of L/D = 6 (ratio of length to depth) at Ma = 0.9 and 1.5 were studied using the numerical simulation method of modified delayed detached eddy simulation (DDES) in this paper. Aero-acoustic characteristics for the cavity at same flow conditions were obtained by the numerical method and 0.6 m by 0.6 m transonic and supersonic wind-tunnel experiments. The analysis on the computational and experimental results indicates that some vortex generates from flow separation in shear-layer over the cavity, and the vortex moves from forward to downward of the cavity at some velocity, and impingement of the vortex and the rear-wall of the cavity occurs. Some sound waves spread abroad to the cavity fore-wall, which induces some new vortex generation, and the vortex sheds, moves and impinges on the cavity rear-wall. New sound waves occur. The research results indicate that sound wave feedback created by the impingement of the shedding-vortices and rear cavity face leads to flow oscillations and noise generation inside the cavity. Analysis on aero-acoustic characteristics inside the cavity is feasible. The simulated self-sustained flow-oscillation modes and peak sound pressure on typical frequencies inside the cavity agree well with Rossiter’s and Heller’s predicated results. Moreover, the peak sound pressure occurs in the first and second flow-oscillation modes and most of sound energy focuses on the low-frequency region. Compared with subsonic speed (Ma = 0.9), aerodynamic noise is more intense at Ma = 1.5, which is induced by compression wave or shock wave in near region of fore and rear cavity face.

Gradient-Type Magnetoelectric Current Sensor with Strong Multisource Noise Suppression.

PubMed

Zhang, Mingji; Or, Siu Wing

2018-02-14

A novel gradient-type magnetoelectric (ME) current sensor operating in magnetic field gradient (MFG) detection and conversion mode is developed based on a pair of ME composites that have a back-to-back capacitor configuration under a baseline separation and a magnetic biasing in an electrically-shielded and mechanically-enclosed housing. The physics behind the current sensing process is the product effect of the current-induced MFG effect associated with vortex magnetic fields of current-carrying cables (i.e., MFG detection) and the MFG-induced ME effect in the ME composite pair (i.e., MFG conversion). The sensor output voltage is directly obtained from the gradient ME voltage of the ME composite pair and is calibrated against cable current to give the current sensitivity. The current sensing performance of the sensor is evaluated, both theoretically and experimentally, under multisource noises of electric fields, magnetic fields, vibrations, and thermals. The sensor combines the merits of small nonlinearity in the current-induced MFG effect with those of high sensitivity and high common-mode noise rejection rate in the MFG-induced ME effect to achieve a high current sensitivity of 0.65-12.55 mV/A in the frequency range of 10 Hz-170 kHz, a small input-output nonlinearity of <500 ppm, a small thermal drift of <0.2%/℃ in the current range of 0-20 A, and a high common-mode noise rejection rate of 17-28 dB from multisource noises.

Gradient-Type Magnetoelectric Current Sensor with Strong Multisource Noise Suppression

PubMed Central

2018-01-01

A novel gradient-type magnetoelectric (ME) current sensor operating in magnetic field gradient (MFG) detection and conversion mode is developed based on a pair of ME composites that have a back-to-back capacitor configuration under a baseline separation and a magnetic biasing in an electrically-shielded and mechanically-enclosed housing. The physics behind the current sensing process is the product effect of the current-induced MFG effect associated with vortex magnetic fields of current-carrying cables (i.e., MFG detection) and the MFG-induced ME effect in the ME composite pair (i.e., MFG conversion). The sensor output voltage is directly obtained from the gradient ME voltage of the ME composite pair and is calibrated against cable current to give the current sensitivity. The current sensing performance of the sensor is evaluated, both theoretically and experimentally, under multisource noises of electric fields, magnetic fields, vibrations, and thermals. The sensor combines the merits of small nonlinearity in the current-induced MFG effect with those of high sensitivity and high common-mode noise rejection rate in the MFG-induced ME effect to achieve a high current sensitivity of 0.65–12.55 mV/A in the frequency range of 10 Hz–170 kHz, a small input-output nonlinearity of <500 ppm, a small thermal drift of <0.2%/℃ in the current range of 0–20 A, and a high common-mode noise rejection rate of 17–28 dB from multisource noises. PMID:29443920

The Fine Transverse Structure of a Vortex Flow Beyond the Edge of a Disc Rotating in a Stratified Fluid

NASA Astrophysics Data System (ADS)

Chashechkin, Yu. D.; Bardakov, R. N.

2018-02-01

By the methods of schlieren visualization, the evolution of elements of the fine structure of transverse vortex loops formed in the circular vortex behind the edge of a disk rotating in a continuously stratified fluid is traced for the first time. An inhomogeneous distribution of the density of a table-salt solution in a basin was formed by the continuous-squeezing method. The development of periodic perturbations at the outer boundary of the circular vortex and their transformation at the vortex-loop vertex are traced. A slow change in the angular size of the structural elements in the supercritical-flow mode is noted.

Design, fabrication, and measurement of reflective metasurface for orbital angular momentum vortex wave in radio frequency domain

NASA Astrophysics Data System (ADS)

Yu, Shixing; Li, Long; Shi, Guangming; Zhu, Cheng; Zhou, Xiaoxiao; Shi, Yan

2016-03-01

In this paper, a reflective metasurface is designed, fabricated, and experimentally demonstrated to generate an orbital angular momentum (OAM) vortex wave in radio frequency domain. Theoretical formula of phase-shift distribution is deduced and used to design the metasurface producing vortex radio waves. The prototype of a practical configuration is designed, fabricated, and measured to validate the theoretical analysis at 5.8 GHz. The simulated and experimental results verify that the vortex waves with different OAM mode numbers can be flexibly generated by using sub-wavelength reflective metasurfaces. The proposed method and metasurface pave a way to generate the OAM vortex waves for radio and microwave wireless communication applications.

Novel x-ray silicon detector for 2D imaging and high-resolution spectroscopy

NASA Astrophysics Data System (ADS)

Castoldi, Andrea; Gatti, Emilio; Guazzoni, Chiara; Longoni, Antonio; Rehak, Pavel; Strueder, Lothar

1999-10-01

A novel x-ray silicon detector for 2D imaging has been recently proposed. The detector, called Controlled-Drift Detector, is operated in integrate-readout mode. Its basic feature is the fast transport of the integrated charge to the output electrode by means of a uniform drift field. The drift time of the charge packet identifies the pixel of incidence. A new architecture to implement the Controlled- Drift Detector concept will be presented. The potential wells for the integration of the signal charge are obtained by means of a suitable pattern of deep n-implants and deep p-implants. During the readout mode the signal electrons are transferred in the drift channel that flanks each column of potential wells where they drift towards the collecting electrode at constant velocity. The first experimental measurements demonstrate the successful integration, transfer and drift of the signal electrons. The low output capacitance of the readout electrode together with the on- chip front-end electronics allows high resolution spectroscopy of the detected photons.

Vortex operation in Er:LuYAG crystal laser at ∼1.6 μm

NASA Astrophysics Data System (ADS)

Liu, Qiyao; Zhao, Yongguang; Zhou, Wei; Shen, Deyuan

2017-09-01

An Er3+-doped Lu1.5Y1.5Al5O12 (Er:LuYAG) solid-state laser with direct generation of optical vortex is reported. The vortex laser operation was realized through being pumped by an annular beam at 1532 nm, which was reformatted by a specially fabricated optical mirror. With two different laser output couplers of 10% and 20% transmissions, pure LG01 mode lasers with right-handedness at 1647.7 nm and 1619.5 nm were yielded from a simple two-mirror cavity, respectively, without any helicity control optical element. Furthermore, stable pulse trains at 1647.7 nm have been achieved via employing an acousto-optic Q-switch, and ∼0.66 mJ pulsed energy and ∼65 ns pulse duration were finally obtained at 1 kHz repetition rate, corresponding to a peak power of ∼10.2 kW. The generated pulse vortex maintained LG01 mode with well-determined right-handedness, as in the case of cw laser operation.

Filtered Rayleigh scattering mixing measurements of merging and non-merging streamwise vortex interactions in supersonic flow

NASA Astrophysics Data System (ADS)

Ground, Cody R.; Gopal, Vijay; Maddalena, Luca

2018-04-01

By introducing large-scale streamwise vortices into a supersonic flow it is possible to enhance the rate of mixing between two fluid streams. However, increased vorticity content alone does not explicitly serve as a predictor of mixing enhancement. Additional factors, particularly the mutual interactions occurring between neighboring vortical structures, affect the underlying fundamental physics that influence the rate at which the fluids mix. As part of a larger systematic study on supersonic streamwise vortex interactions, this work experimentally quantifies the average rate of mixing of helium and air in the presence of two separate modes of vortex interaction, the merging and non-merging of a pair of co-rotating vortices. In these experiments vortex-generating expansion ramps are placed on a strut injector. The freestream Mach number is set at 2.5 and helium is injected as a passive scalar. Average injectant mole fractions at selected flow planes downstream of the injector are measured utilizing the filtered Rayleigh scattering technique. The filtered Rayleigh scattering measurements reveal that, in the domain surveyed, the merging vortex interaction strongly displaces the plume from its initial horizontal orientation while the non-merging vortex interaction more rapidly mixes the helium and air. The results of the current experiments are consistent with associated knowledge derived from previous analyses of the two studied configurations which have included the detailed experimental characterization of entrainment, turbulent kinetic energy, and vorticity of both modes of vortex interaction.

Analytical and numerical treatment of resistive drift instability in a plasma slab

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

Mirnov, V. V., E-mail: vvmirnov@wisc.edu; Sauppe, J. P.; Hegna, C. C.

An analytic approach combining the effect of equilibrium diamagnetic flows and the finite ionsound gyroradius associated with electron−ion decoupling and kinetic Alfvén wave dispersion is derived to study resistive drift instabilities in a plasma slab. Linear numerical computations using the NIMROD code are performed with cold ions and hot electrons in a plasma slab with a doubly periodic box bounded by two perfectly conducting walls. A linearly unstable resistive drift mode is observed in computations with a growth rate that is consistent with the analytic dispersion relation. The resistive drift mode is expected to be suppressed by magnetic shear inmore » unbounded domains, but the mode is observed in numerical computations with and without magnetic shear. In the slab model, the finite slab thickness and the perfectly conducting boundary conditions are likely to account for the lack of suppression.« less

Long-wavelength asymptotics of unstable crossflow modes, including the effect of surface curvature

NASA Technical Reports Server (NTRS)

Choudhari, Meelan

1994-01-01

Stationary vortex instabilities with wavelengths significantly larger than the thickness of the underlying three-dimensional boundary layer are studied with asymptotic methods. The long-wavelength Rayleigh modes are locally neutral and are aligned with the direction of the local inviscid streamline. For a spanwise wave number Beta much less than 1, the spatial growth rate of these vortices is O(Beta(exp 3/2)). When Beta becomes O(R(exp -1/7)), the viscous correction associated with a thin sublayer near the surface modifies the inviscid growth rate to the leading order. As Beta is further decreased through this regime, viscous effects assume greater significance and dominate the growth-rate behavior. The spatial growth rate becomes comparable to the real part of the wave number when Beta = O(R(exp -1/4)). At this stage, the disturbance structure becomes fully viscous-inviscid interactive and is described by the triple-deck theory. For even smaller values of Beta, the vortex modes become nearly neutral again and align themselves with the direction of the wall-shear stress. Thus, the study explains the progression of the crossflow-vortex structure from the inflectional upper branch mode to nearly neutral long-wavelength modes that are aligned with the wall-shear direction.

Characterizing the propagation evolution of wave patterns and vortex structures in astigmatic transformations of Hermite-Gaussian beams

NASA Astrophysics Data System (ADS)

Chen, Y. F.; Chang, C. C.; Lee, C. Y.; Tung, J. C.; Liang, H. C.; Huang, K. F.

2018-01-01

Theoretical wave functions are analytically derived to characterize the propagation evolution of the Hermite-Gaussian (HG) beams transformed by a single-lens astigmatic mode converter with arbitrary angle. The derived wave functions are related to the combination of the rotation transform and the antisymmetric fractional Fourier transform. The derived formula is systematically validated by using an off-axis diode-pumped solid-state laser to generate various high-order HG beams for mode conversions. In addition to validation, the creation and evolution of vortex structures in the transformed HG beams are numerically manifested. The present theoretical analyses can be used not only to characterize the evolution of the transformed beams but to design the optical vortex beams with various forms.

Chladni solitons and the onset of the snaking instability for dark solitons in confined superfluids.

PubMed

Muñoz Mateo, A; Brand, J

2014-12-19

Complex solitary waves composed of intersecting vortex lines are predicted in a channeled superfluid. Their shapes in a cylindrical trap include a cross, spoke wheels, and Greek Φ, and trace the nodal lines of unstable vibration modes of a planar dark soliton in analogy to Chladni's figures of membrane vibrations. The stationary solitary waves extend a family of solutions that include the previously known solitonic vortex and vortex rings. Their bifurcation points from the dark soliton indicating the onset of new unstable modes of the snaking instability are predicted from scale separation for Bose-Einstein condensates (BECs) and superfluid Fermi gases across the BEC-BCS crossover, and confirmed by full numerical calculations. Chladni solitons could be observed in ultracold gas experiments by seeded decay of dark solitons.

Chladni Solitons and the Onset of the Snaking Instability for Dark Solitons in Confined Superfluids

NASA Astrophysics Data System (ADS)

Muñoz Mateo, A.; Brand, J.

2014-12-01

Complex solitary waves composed of intersecting vortex lines are predicted in a channeled superfluid. Their shapes in a cylindrical trap include a cross, spoke wheels, and Greek Φ , and trace the nodal lines of unstable vibration modes of a planar dark soliton in analogy to Chladni's figures of membrane vibrations. The stationary solitary waves extend a family of solutions that include the previously known solitonic vortex and vortex rings. Their bifurcation points from the dark soliton indicating the onset of new unstable modes of the snaking instability are predicted from scale separation for Bose-Einstein condensates (BECs) and superfluid Fermi gases across the BEC-BCS crossover, and confirmed by full numerical calculations. Chladni solitons could be observed in ultracold gas experiments by seeded decay of dark solitons.

The effect of vortex merging and non-merging on the transfer of modal turbulent kinetic energy content

NASA Astrophysics Data System (ADS)

Ground, Cody; Vergine, Fabrizio; Maddalena, Luca

2016-08-01

A defining feature of the turbulent free shear layer is that its growth is hindered by compressibility effects, thus limiting its potential to sufficiently mix the injected fuel and surrounding airstream at the supersonic Mach numbers intrinsic to the combustor of air-breathing hypersonic vehicles. The introduction of streamwise vorticity is often proposed in an attempt to counteract these undesired effects. This fact makes the strategy of introducing multiple streamwise vortices and imposing upon them certain modes of mutual interaction in order to potentially enhance mixing an intriguing concept. However, many underlying fundamental characteristics of the flowfields in the presence such interactions are not yet well understood; therefore, the fundamental physics of these flowfields should be independently investigated before the explicit mixing performance is characterized. In this work, experimental measurements are taken with the stereoscopic particle image velocimetry technique on two specifically targeted modes of vortex interaction—the merging and non-merging of two corotating vortices. The fluctuating velocity fields are analyzed utilizing the proper orthogonal decomposition (POD) in order to identify the content, organization, and distribution of the modal turbulent kinetic energy content of the fluctuating velocity eigenmodes. The effects of the two modes of vortex interaction are revealed by the POD analysis which shows distinct differences in the modal features of the two cases. When comparing the low-order eigenmodes of the two cases, the size of the structures contained within the first ten modes is seen to increase as the flow progresses downstream for the merging case, whereas the opposite is true for the non-merging case. Additionally, the relative modal energy contribution of the first ten eigenmodes increases as the vortices evolve downstream for the merging case, whereas in the non-merging case the relative modal energy contribution decreases. The POD results show that the vortex merging process reorients and redistributes the relative turbulent kinetic energy content toward the larger-scale structures within the low-order POD eigenmodes. This result suggests that by specifically designing the vortex generation system to impose preselected modes of vortex interaction upon the flow it is possible to exert some form of control over the downstream evolution and distribution of the global and modal turbulent kinetic energy content.

Stability of drift-cyclotron loss-cone waves in H-mode plasmas

DOE PAGES

Farmer, W. A.; Morales, G. J.

2016-05-24

The drift-cyclotron loss-cone mode was first studied in mirror machines. In such devices, particles with small pitch angles are not confined, creating a hole in the velocity distribution function that is a source of free energy and leads to micro-instabilities in the cyclotron-range of frequencies. In the edge region of tokamak devices operating under H-mode conditions, ion loss also occurs. In this case, gradient drift carries ions moving opposite to the plasma current preferentially into the divertor, creating a one-sided loss cone. A simple analysis shows that for the quiescent H-mode plasmas in DIII-D the critical gradient for instability ismore » exceeded within 2 cm of the separatrix, and the maximum growth rate at the separatrix is 3×10 7 s -1.« less

Study of Transition Mechanism in a Wake Behind an Airfoil with a Small Angle of Attack by Using a Towing Wind Tunnel

NASA Astrophysics Data System (ADS)

Morita, Toshiyuki; Maekawa, Hiroshi

This paper describes an experimental investigation of the transitional mechanism of a wake generated behind a thin airfoil with a small angle of attack in a towing wind tunnel. A linear stability analysis shows that the wake is characterized by a region of absolute instability in the near wake (x=30mm) and one of convective instability further downstream. When the airfoil starts to run in the tunnel, boundary layers develop on the upper/lower airfoil surfaces with different thickness. Since the asymmetric wake is generated, starting vortices of a single row are observed first in the wake, which is different from the Karman vortex street. The experimental results show that time-harmonic fluctuations of the starting vortex sustain in the natural transition process due to a self sustained resonance in the absolutely unstable region behind the trailing edge. The wake profile in the saturation steady state yields the vortex street structure, where the fluctuation frequency defined as the fundamental unstable mode is found in the final saturation steady state. The growth of the fundamental unstable mode in the convectively unstable region suppresses the high frequency fluctuations associated with the starting vortex generation. On the other hand, low-frequency fluctuations in the quasi-steady state sustaining in the saturation state grow gradually during the vortex street formation, which lead to the vortex deformation downstream.

Direct generation of an optical vortex beam in a single-frequency Nd:YVO4 laser.

PubMed

Kim, D J; Kim, J W

2015-02-01

A simple method for generating a Laguerre-Gaussian (LG) mode optical vortex beam with well-determined handedness in a single-frequency solid state laser end-pumped by a ring-shaped pump beam is reported. After investigating the intensity profile and the wavefront helicity of each longitudinal mode output to understand generation of the LG mode in a Nd:YVO4 laser resonator, selection of the wavefront handedness has been achieved simply by inserting and tilting an etalon in the resonator, which breaks the propagation symmetry of the Poynting vectors with opposite helicity. Simple calculation and the experimental results are discussed for supporting this selection mechanism.

Resonant-spin-ordering of vortex cores in interacting mesomagnets

NASA Astrophysics Data System (ADS)

Jain, Shikha

2013-03-01

The magnetic system of interacting vortex-state elements have a dynamically reconfigurable ground state characterized by different relative polarities and chiralities of the individual disks; and have a corresponding dynamically controlled spectrum of collective excitation modes that determine the microwave absorption of the crystal. The development of effective methods for dynamic control of the ground state in this vortex-type magnonic crystal is of interest both from fundamental and technological viewpoints. Control of vortex chirality has been demonstrated previously using various techniques; however, control and manipulation of vortex polarities remain challenging. In this work, we present a robust and efficient way of selecting the ground state configuration of interacting magnetic elements using resonant-spin-ordering approach. This is achieved by driving the system from the linear regime of constant vortex gyrations to the non-linear regime of vortex-core reversals at a fixed excitation frequency of one of the coupled modes. Subsequently reducing the excitation field to the linear regime stabilizes the system to a polarity combination whose resonant frequency is decoupled from the initialization frequency. We have utilized the resonant approach to transition between the two polarity combinations (parallel or antiparallel) in a model system of connected dot-pairs which may form the building blocks of vortex-based magnonic crystals. Taking a step further, we have extended the technique by studying many-particle system for its potential as spin-torque oscillators or logic devices. Work at Argonne was supported by the U. S. DOE, Office of BES, under Contract No. DE-AC02-06CH11357. This work was in part supported by grant DMR-1015175 from the U. S. National Science Foundation, by a Contract from the U.S. Army TARDEC and RDECOM.

Time-resolved orbital angular momentum spectroscopy

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

Noyan, Mehmet A.; Kikkawa, James M.

We introduce pump-probe magneto-orbital spectroscopy, wherein Laguerre-Gauss optical pump pulses impart orbital angular momentum to the electronic states of a material and subsequent dynamics are studied with 100 fs time resolution. The excitation uses vortex modes that distribute angular momentum over a macroscopic area determined by the spot size, and the optical probe studies the chiral imbalance of vortex modes reflected off the sample. First observations in bulk GaAs yield transients that evolve on time scales distinctly different from population and spin relaxation, as expected, but with surprisingly large lifetimes.

Aeroacoustic Duster

NASA Technical Reports Server (NTRS)

Marshall, Jeffrey S. (Inventor); Chen, Di (Inventor); Vachon, Nicholas Mario (Inventor); Hitt, Darren (Inventor); Wu, Junru (Inventor)

2014-01-01

The aero-acoustic duster invention disclosed herein provides for high particle removal rate from surfaces with low energy expenditure relative to competing vacuum-based devices. The device removes particulate matter from a surface using a two-step process: 1. Acoustic radiation is used to break the adhesive bonds between dust and the surface, forcing particles into a mode where they continuously bounce up and down on the surface; and, 2. A bounded vortex is generated over the surface, with suction in the vortex center and jets for blowing air along the periphery. The jets are tilted in the tangential direction to induce vortex motion within the suction region. The vortex is said to be bounded because streamlines originating in the downward jets are entrained back into the central vortex.

Dynamic control of metastable remanent states in mesoscale magnetic elements

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

Ding, J.; Jain, S.; Pearson, J. E.

2015-05-07

The formation of the vortex-antivortex-vortex (v-av-v) metastable remanent states in elongated magnetic elements have been systematically investigated using micromagnetic modeling. It is demonstrated that the v-av-v magnetization pattern can be effectively stabilized by exciting the single vortex state with an external RF field. Furthermore, we show that a set of different polarity combinations of the vortex cores can be achieved by adjusting the frequency and amplitude of the excitation field. The corresponding dynamic response in time- and frequency-domain has also been presented. Owing to the diversity of the collective modes with different vortex-antivortex combinations, this system may open promising perspectivesmore » in the area of spin transfer torque oscillators.« less

Generating multiple orbital angular momentum vortex beams using a metasurface in radio frequency domain

NASA Astrophysics Data System (ADS)

Yu, Shixing; Li, Long; Shi, Guangming; Zhu, Cheng; Shi, Yan

2016-06-01

In this paper, an electromagnetic metasurface is designed, fabricated, and experimentally demonstrated to generate multiple orbital angular momentum (OAM) vortex beams in radio frequency domain. Theoretical formula of compensated phase-shift distribution is deduced and used to design the metasurface to produce multiple vortex radio waves in different directions with different OAM modes. The prototype of a practical configuration of square-patch metasurface is designed, fabricated, and measured to validate the theoretical analysis at 5.8 GHz. The simulated and experimental results verify that multiple OAM vortex waves can be simultaneously generated by using a single electromagnetic metasurface. The proposed method paves an effective way to generate multiple OAM vortex waves in radio and microwave wireless communication applications.

Discovery of multiple, ionization-created CS{sub 2} anions and a new mode of operation for drift chambers

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

Snowden-Ifft, Daniel P.

2014-01-15

This paper focuses on the surprising discovery of multiple species of ionization-created CS{sub 2} anions in gas mixtures containing electronegative CS{sub 2} and O{sub 2}, identified by their slightly different drift velocities. Data are presented to understand the formation mechanism and identity of these new anions. Regardless of the micro-physics, however, this discovery offers a new, trigger-less mode of operation for the drift chambers. A demonstration of trigger-less operation is presented.

Rossby and drift wave turbulence and zonal flows: The Charney-Hasegawa-Mima model and its extensions

NASA Astrophysics Data System (ADS)

Connaughton, Colm; Nazarenko, Sergey; Quinn, Brenda

2015-12-01

A detailed study of the Charney-Hasegawa-Mima model and its extensions is presented. These simple nonlinear partial differential equations suggested for both Rossby waves in the atmosphere and drift waves in a magnetically-confined plasma, exhibit some remarkable and nontrivial properties, which in their qualitative form, survive in more realistic and complicated models. As such, they form a conceptual basis for understanding the turbulence and zonal flow dynamics in real plasma and geophysical systems. Two idealised scenarios of generation of zonal flows by small-scale turbulence are explored: a modulational instability and turbulent cascades. A detailed study of the generation of zonal flows by the modulational instability reveals that the dynamics of this zonal flow generation mechanism differ widely depending on the initial degree of nonlinearity. The jets in the strongly nonlinear case further roll up into vortex streets and saturate, while for the weaker nonlinearities, the growth of the unstable mode reverses and the system oscillates between a dominant jet, which is slightly inclined to the zonal direction, and a dominant primary wave. A numerical proof is provided for the extra invariant in Rossby and drift wave turbulence-zonostrophy. While the theoretical derivations of this invariant stem from the wave kinetic equation which assumes weak wave amplitudes, it is shown to be relatively well-conserved for higher nonlinearities also. Together with the energy and enstrophy, these three invariants cascade into anisotropic sectors in the k-space as predicted by the Fjørtoft argument. The cascades are characterised by the zonostrophy pushing the energy to the zonal scales. A small scale instability forcing applied to the model has demonstrated the well-known drift wave-zonal flow feedback loop. The drift wave turbulence is generated from this primary instability. The zonal flows are then excited by either one of the generation mechanisms, extracting energy from the drift waves as they grow. Eventually the turbulence is completely suppressed and the zonal flows saturate. The turbulence spectrum is shown to diffuse in a manner which has been mathematically predicted. The insights gained from this simple model could provide a basis for equivalent studies in more sophisticated plasma and geophysical fluid dynamics models in an effort to fully understand the zonal flow generation, the turbulent transport suppression and the zonal flow saturation processes in both the plasma and geophysical contexts as well as other wave and turbulence systems where order evolves from chaos.

Point vortex modelling of the wake dynamics behind asymmetric vortex generator arrays

NASA Astrophysics Data System (ADS)

Baldacchino, D.; Ferreira, C.; Ragni, D.; van Bussel, G. J. W.

2016-09-01

In this work, we present a simple inviscid point vortex model to study the dynamics of asymmetric vortex rows, as might appear behind misaligned vortex generator vanes. Starting from the existing solution of the infinite vortex cascade, a numerical model of four base-vortices is chosen to represent two primary counter-rotating vortex pairs and their mirror plane images, introducing the vortex strength ratio as a free parameter. The resulting system of equations is also defined in terms of the vortex row separation and the qualitative features of the ensuing motion are mapped. A translating and orbiting regime are identified for different cascade separations. The latter occurs for all unequal strength vortex pairs. Thus, the motion is further classified by studying the cyclic behaviour of the orbiting regime and it is shown that for small mismatches in vortex strength, the orbiting length and time scales are sufficiently large as to appear, in the near wake, as translational (non-orbiting). However, for larger mismatches in vortex strength, the orbiting motion approaches the order of the starting height of the vortex. Comparisons between experimental data and the potential flow model show qualitative agreement whilst viscous effects account for the major discrepancies. Despite this, the model captures the orbital mode observed in the measurements and provides an impetus for considering the impact of these complex interactions on vortex generator designs.

Feeding modes in stream salmonid population models: Is drift feeding the whole story?

Treesearch

Bret Harvey; Steve Railsback

2014-01-01

Drift-feeding models are essential components of broader models that link stream habitat to salmonid populations and community dynamics. But is an additional feeding mode needed for understanding and predicting salmonid population responses to streamflow and other environmental factors? We addressed this question by applying two versions of the individual-based model...

Fluctuations and discrete particle noise in gyrokinetic simulation of drift waves

NASA Astrophysics Data System (ADS)

Jenkins, Thomas G.; Lee, W. W.

2007-03-01

The relevance of the gyrokinetic fluctuation-dissipation theorem (FDT) to thermal equilibrium and nonequilibrium states of the gyrokinetic plasma is explored, with particular focus being given to the contribution of weakly damped normal modes to the fluctuation spectrum. It is found that the fluctuation energy carried in the normal modes exhibits the proper scaling with particle count (as predicted by the FDT in thermal equilibrium) even in the presence of drift waves, which grow linearly and attain a nonlinearly saturated steady state. This favorable scaling is preserved, and the saturation amplitude of the drift wave unaffected, for parameter regimes in which the normal modes become strongly damped and introduce a broad spectrum of discreteness-induced background noise in frequency space.

Experimental investigation of starting characteristics and wave propagation from a shallow open cavity and its acoustic emission at supersonic speed

NASA Astrophysics Data System (ADS)

Pandian, S.; Desikan, S. L. N.; Niranjan, Sahoo

2018-01-01

Experiments were carried out on a shallow open cavity (L/D = 5) at a supersonic Mach number (M = 1.8) to understand its transient starting characteristics, wave propagation (inside and outside the cavity) during one vortex shedding cycle, and acoustic emission. Starting characteristics and wave propagation were visualized through time resolved schlieren images, while acoustic emissions were captured through unsteady pressure measurements. Results showed a complex shock system during the starting process which includes characteristics of the bifurcated shock system, shock train, flow separation, and shock wave boundary layer interaction. In one vortex shedding cycle, vortex convection from cavity leading edge to cavity trailing edge was observed. Flow features outside the cavity demonstrated the formation and downstream movement of a λ-shock due to the interaction of shock from the cavity leading edge and shock due to vortex and generation of waves on account of shear layer impingement at the cavity trailing edge. On the other hand, interesting wave structures and its propagation were monitored inside the cavity. In one vortex shedding cycle, two waves such as a reflected compression wave from a cavity leading edge in the previous vortex shedding cycle and a compression wave due to the reflection of Mach wave at the cavity trailing edge corner in the current vortex shedding cycle were visualized. The acoustic emission from the cavity indicated that the 2nd to 4th modes/tones are dominant, whereas the 1st mode contains broadband spectrum. In the present studies, the cavity feedback mechanism was demonstrated through a derived parameter coherence coefficient.

Acoustic response of vortex breakdown modes in a coaxial isothermal unconfined swirling jet

NASA Astrophysics Data System (ADS)

Santhosh, R.; Basu, Saptarshi

2015-03-01

The present experimental work is concerned with the study of amplitude dependent acoustic response of an isothermal coaxial swirling jet. The excitation amplitude is increased in five distinct steps at the burner's Helmholtz resonator mode (i.e., 100 Hz). Two flow states are compared, namely, sub-critical and super-critical vortex breakdown (VB) that occur before and after the critical conical sheet breakdown, respectively. The geometric swirl number is varied in the range 2.14-4.03. Under the influence of external pulsing, global response characteristics are studied based on the topological changes observed in time-averaged 2D flow field. These are obtained from high resolution 2D PIV (particle image velocimetry) in the longitudinal-mid plane. PIV results also illustrate the changes in the normalized vortex core coordinates (rvcc/(rvcc)0 Hz, yvcc/(yvcc)0 Hz) of internal recirculation zone (IRZ). A strong forced response is observed at 100 Hz (excitation frequency) in the convectively unstable region which get amplified based on the magnitude of external forcing. The radial extent of this forced response region at a given excitation amplitude is represented by the acoustic response region (b). The topological placement of the responsive convectively unstable region is a function of both the intensity of imparted swirl (characterized by swirl number) and forcing amplitude. It is observed that for sub-critical VB mode, an increase in the excitation amplitude till a critical value shifts the vortex core centre (particularly, the vortex core moves downstream and radially outwards) leading to drastic fanning-out/widening of the IRZ. This is accompanied by ˜30% reduction in the recirculation velocity of the IRZ. It is also observed that b < R (R: radial distance from central axis to outer shear layer-OSL). At super-critical amplitudes, the sub-critical IRZ topology transits back (the vortex core retracts upstream and radially inwards) and finally undergoes a transverse shrinkage ((4vcc)/(rvcc) 0 Hz decreases by ˜20%) when b ≥ R. In contrast, the vortex core of super-critical breakdown mode consistently spreads radially outwards and is displaced further downstream. Finally, the IRZ fans-out at the threshold excitation amplitude. However, the acoustic response region b is still less than R. This is explained based on the characteristic geometric swirl number (SG) of the flow regimes. The super-critical flow mode with higher SG (hence, higher radial pressure drop due to rotational effect which scales as ΔP ˜ ρuθ2 and acts inwards towards the center line) compared to sub-critical state imposes a greater resistance to the radial outward spread of b. As a result, the acoustic energy supplied to the super-critical flow mode increases the degree of acoustic response at the pulsing frequency and energizes its harmonics (evident from power spectra). As a disturbance amplifier, the stronger convective instability mode within the flow structure of super-critical VB causes the topology to widen/fan-out severely at threshold excitation amplitude.

Decoding algorithm for vortex communications receiver

NASA Astrophysics Data System (ADS)

Kupferman, Judy; Arnon, Shlomi

2018-01-01

Vortex light beams can provide a tremendous alphabet for encoding information. We derive a symbol decoding algorithm for a direct detection matrix detector vortex beam receiver using Laguerre Gauss (LG) modes, and develop a mathematical model of symbol error rate (SER) for this receiver. We compare SER as a function of signal to noise ratio (SNR) for our algorithm and for the Pearson correlation algorithm. To our knowledge, this is the first comprehensive treatment of a decoding algorithm of a matrix detector for an LG receiver.

A computational study of the topology of vortex breakdown

NASA Technical Reports Server (NTRS)

Spall, Robert E.; Gatski, Thomas B.

1991-01-01

A fully three-dimensional numerical simulation of vortex breakdown using the unsteady, incompressible Navier-Stokes equations has been performed. Solutions to four distinct types of breakdown are identified and compared with experimental results. The computed solutions include weak helical, double helix, spiral, and bubble-type breakdowns. The topological structure of the various breakdowns as well as their interrelationship are studied. The data reveal that the asymmetric modes of breakdown may be subject to additional breakdowns as the vortex core evolves in the streamwise direction. The solutions also show that the freestream axial velocity distribution has a significant effect on the position and type of vortex breakdown.

Calculation of the force acting on a micro-sized particle with optical vortex array laser beam tweezers

NASA Astrophysics Data System (ADS)

Kuo, Chun-Fu; Chu, Shu-Chun

2013-03-01

Optical vortices possess several special properties, including carrying optical angular momentum (OAM) and exhibiting zero intensity. Vortex array laser beams have attracts many interests due to its special mesh field distributions, which show great potential in the application of multiple optical traps and dark optical traps. Previously study developed an Ince-Gaussian Mode (IGM)-based vortex array laser beam1. This study develops a simulation model based on the discrete dipole approximation (DDA) method for calculating the resultant force acting on a micro-sized spherical dielectric particle that situated at the beam waist of the IGM-based vortex array laser beams1.

Flow-excited acoustic resonance of a Helmholtz resonator: Discrete vortex model compared to experiments

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

Dai, Xiwen; Jing, Xiaodong, E-mail: jingxd@buaa.edu.cn; Sun, Xiaofeng

The acoustic resonance in a Helmholtz resonator excited by a low Mach number grazing flow is studied theoretically. The nonlinear numerical model is established by coupling the vortical motion at the cavity opening with the cavity acoustic mode through an explicit force balancing relation between the two sides of the opening. The vortical motion is modeled in the potential flow framework, in which the oscillating motion of the thin shear layer is described by an array of convected point vortices, and the unsteady vortex shedding is determined by the Kutta condition. The cavity acoustic mode is obtained from the one-dimensionalmore » acoustic propagation model, the time-domain equivalent of which is given by means of a broadband time-domain impedance model. The acoustic resistances due to radiation and viscous loss at the opening are also taken into account. The physical processes of the self-excited oscillations, at both resonance and off-resonance states, are simulated directly in the time domain. Results show that the shear layer exhibits a weak flapping motion at the off-resonance state, whereas it rolls up into large-scale vortex cores when resonances occur. Single and dual-vortex patterns are observed corresponding to the first and second hydrodynamic modes. The simulation also reveals different trajectories of the two vortices across the opening when the first and second hydrodynamic modes co-exist. The strong modulation of the shed vorticity by the acoustic feedback at the resonance state is demonstrated. The model overestimates the pressure pulsation amplitude by a factor 2, which is expected to be due to the turbulence of the flow which is not taken into account. The model neglects vortex shedding at the downstream and side edges of the cavity. This will also result in an overestimation of the pulsation amplitude.« less

Investigation of the n  =  1 resistive wall modes in the ITER high-mode confinement

NASA Astrophysics Data System (ADS)

Zheng, L. J.; Kotschenreuther, M. T.; Valanju, P.

2017-06-01

The n  =  1 resistive wall mode (RWM) stability of ITER high-mode confinement is investigated with bootstrap current included for equilibrium, together with the rotation and diamagnetic drift effects for stability. Here, n is the toroidal mode number. We use the CORSICA code for computing the free boundary equilibrium and AEGIS code for stability. We find that the inclusion of bootstrap current for equilibrium is critical. It can reduce the local magnetic shear in the pedestal, so that the infernal mode branches can develop. Consequently, the n  =  1 modes become unstable without a stabilizing wall at a considerably lower beta limit, driven by the steep pressure gradient in the pedestal. Typical values of the wall position stabilize the ideal mode, but give rise to the ‘pedestal’ resistive wall modes. We find that the rotation can contribute a stabilizing effect on RWMs and the diamagnetic drift effects can further improve the stability in the co-current rotation case. But, generally speaking, the rotation stabilization effects are not as effective as the case without including the bootstrap current effects on equilibrium. We also find that the diamagnetic drift effects are actually destabilizing when there is a counter-current rotation.

A New Dark Vortex on Neptune

NASA Astrophysics Data System (ADS)

Wong, Michael H.; Tollefson, Joshua; Hsu, Andrew I.; de Pater, Imke; Simon, Amy A.; Hueso, Ricardo; Sánchez-Lavega, Agustín; Sromovsky, Lawrence; Fry, Patrick; Luszcz-Cook, Statia; Hammel, Heidi; Delcroix, Marc; de Kleer, Katherine; Orton, Glenn S.; Baranec, Christoph

2018-03-01

An outburst of cloud activity on Neptune in 2015 led to speculation about whether the clouds were convective in nature, a wave phenomenon, or bright companions to an unseen dark vortex (similar to the Great Dark Spot studied in detail by Voyager 2). The Hubble Space Telescope (HST) finally answered this question by discovering a new dark vortex at 45 degrees south planetographic latitude, named SDS-2015 for “southern dark spot discovered in 2015.” SDS-2015 is only the fifth dark vortex ever seen on Neptune. In this paper, we report on imaging of SDS-2015 using HST’s Wide Field Camera 3 across four epochs: 2015 September, 2016 May, 2016 October, and 2017 October. We find that the size of SDS-2015 did not exceed 20 degrees of longitude, more than a factor of two smaller than the Voyager dark spots, but only slightly smaller than previous northern-hemisphere dark spots. A slow (1.7–2.5 deg/year) poleward drift was observed for the vortex. Properties of SDS-2015 and its surroundings suggest that the meridional wind shear may be twice as strong at the deep level of the vortex as it is at the level of cloud-tracked winds. Over the 2015–2017 period, the dark spot’s contrast weakened from about -7 % to about -3 % , while companion clouds shifted from offset to centered, a similar evolution to some historical dark spots. The properties and evolution of SDS-2015 highlight the diversity of Neptune’s dark spots and the need for faster cadence dark spot observations in the future.

Spontaneous generation of vortex and coherent vector beams from a thin-slice c-cut Nd:GdVO4 laser with wide-aperture laser-diode end pumping: application to highly sensitive rotational and translational Doppler velocimetry

NASA Astrophysics Data System (ADS)

Otsuka, Kenju; Chu, Shu-Chun

2017-07-01

Selective excitation of Laguerre-Gauss modes (optical vortices: helical LG0,2 and LG0,1), reflecting their weak transverse cross-saturation of population inversions against a preceding higher-order Ince-Gauss (IG0,2) or Hermite-Gauss (HG2,1) mode, was observed in a thin-slice c-cut Nd:GdVO4 laser with wide-aperture laser-diode end pumping. Single-frequency coherent vector beams were generated through the transverse mode locking of a pair of orthogonally polarized IG2,0 and LG0,2 or HG2,1 and LG0,1 modes. Highly sensitive self-mixing rotational and translational Doppler velocimetry is demonstrated by using vortex and coherent vector beams.

Fully nonlinear development of the most unstable goertler vortex in a three dimensional boundary layer

NASA Technical Reports Server (NTRS)

Otto, S. R.; Bassom, Andrew P.

1992-01-01

The nonlinear development is studied of the most unstable Gortler mode within a general 3-D boundary layer upon a suitably concave surface. The structure of this mode was first identified by Denier, Hall and Seddougui (1991) who demonstrated that the growth rate of this instability is O(G sup 3/5) where G is the Gortler number (taken to be large here), which is effectively a measure of the curvature of the surface. Previous researchers have described the fate of the most unstable mode within a 2-D boundary layer. Denier and Hall (1992) discussed the fully nonlinear development of the vortex in this case and showed that the nonlinearity causes a breakdown of the flow structure. The effect of crossflow and unsteadiness upon an infinitesimal unstable mode was elucidated by Bassom and Hall (1991). They demonstrated that crossflow tends to stabilize the most unstable Gortler mode, and for certain crossflow/frequency combinations the Gortler mode may be made neutrally stable. These vortex configurations naturally lend themselves to a weakly nonlinear stability analysis; work which is described in a previous article by the present author. Here we extend the ideas of Denier and Hall (1992) to the three-dimensional boundary layer problem. It is found that the numerical solution of the fully nonlinear equations is best conducted using a method which is essentially an adaption of that utilized by Denier and Hall (1992). The influence of crossflow and unsteadiness upon the breakdown of the flow is described.

New Insights on Insect's Silent Flight. Part I: Vortex Dynamics and Wing Morphing

NASA Astrophysics Data System (ADS)

Ren, Yan; Liu, Geng; Dong, Haibo; Geng, Biao; Zheng, Xudong; Xue, Qian

2016-11-01

Insects are capable of conducting silent flights. This is attributed to its specially designed wing material properties for the control of vibration and surface morphing during the flapping flight. In current work, we focus on the roles of dynamic wing morphing on the unsteady vortex dynamics of a cicada in steady flight. A 3D image-based surface reconstruction method is used to obtain kinematical and morphological data of cicada wings from high-quality high-speed videos. The observed morphing wing kinematics is highly complex and a singular value decomposition method is used to decompose the wing motion to several dominant modes with distinct motion features. A high-fidelity immersed-boundary-based flow solver is then used to study the vortex dynamics in details. The results show that vortical structures closely relate to the morphing mode, which plays key role in the development and attachment of leading-edge vortex (LEV), thus helps the silent flapping of the cicada wings. This work is supported by AFOSR FA9550-12-1-0071 and NSF CBET-1313217.

Generation of singular optical beams from fundamental Gaussian beam using Sagnac interferometer

NASA Astrophysics Data System (ADS)

Naik, Dinesh N.; Viswanathan, Nirmal K.

2016-09-01

We propose a simple free-space optics recipe for the controlled generation of optical vortex beams with a vortex dipole or a single charge vortex, using an inherently stable Sagnac interferometer. We investigate the role played by the amplitude and phase differences in generating higher-order Gaussian beams from the fundamental Gaussian mode. Our simulation results reveal how important the control of both the amplitude and the phase difference between superposing beams is to achieving optical vortex beams. The creation of a vortex dipole from null interference is unveiled through the introduction of a lateral shear and a radial phase difference between two out-of-phase Gaussian beams. A stable and high quality optical vortex beam, equivalent to the first-order Laguerre-Gaussian beam, is synthesized by coupling lateral shear with linear phase difference, introduced orthogonal to the shear between two out-of-phase Gaussian beams.

Magnetic vortex core reversal by excitation of spin waves.

PubMed

Kammerer, Matthias; Weigand, Markus; Curcic, Michael; Noske, Matthias; Sproll, Markus; Vansteenkiste, Arne; Van Waeyenberge, Bartel; Stoll, Hermann; Woltersdorf, Georg; Back, Christian H; Schuetz, Gisela

2011-01-01

Micron-sized magnetic platelets in the flux-closed vortex state are characterized by an in-plane curling magnetization and a nanometer-sized perpendicularly magnetized vortex core. Having the simplest non-trivial configuration, these objects are of general interest to micromagnetics and may offer new routes for spintronics applications. Essential progress in the understanding of nonlinear vortex dynamics was achieved when low-field core toggling by excitation of the gyrotropic eigenmode at sub-GHz frequencies was established. At frequencies more than an order of magnitude higher vortex state structures possess spin wave eigenmodes arising from the magneto-static interaction. Here we demonstrate experimentally that the unidirectional vortex core reversal process also occurs when such azimuthal modes are excited. These results are confirmed by micromagnetic simulations, which clearly show the selection rules for this novel reversal mechanism. Our analysis reveals that for spin-wave excitation the concept of a critical velocity as the switching condition has to be modified.

The collisional drift mode in a partially ionized plasma. [in the F region

NASA Technical Reports Server (NTRS)

Hudson, M. K.; Kennel, C. F.

1974-01-01

The structure of the drift instability was examined in several density regimes. Let sub e be the total electron mean free path, k sub z the wave-vector component along the magnetic field, and the ratio of perpendicular ion diffusion to parallel electron streaming rates. At low densities (k sub z lambda 1) the drift mode is isothermal and should be treated kineticly. In the finite heat conduction regime square root of m/M k sub z Lambda sub 1) the drift instability threshold is reduced at low densities and increased at high densities as compared to the isothermal threshold. Finally, in the energy transfer limit (k sub z kambda sub e square root of m/M) the drift instability behaves adiabatically in a fully ionized plasma and isothermally in a partially ionized plasma for an ion-neutral to Coulomb collision frequency ratio.

Dust acoustic and drift waves in a non-Maxwellian dusty plasma with dust charge fluctuation

NASA Astrophysics Data System (ADS)

Zakir, U.; Haque, Q.; Imtiaz, N.; Qamar, A.

2015-12-01

> ) on the wave dispersion and instability are presented. It is found that the presence of the non-thermal electron and ion populations reduce the growth rate of the instability which arises due to the dust charging effect. In addition, the nonlinear vortex solutions are also obtained. For illustration, the results are analysed by using the dusty plasma parameters of Saturn's magnetosphere.

Magnetic vortex nucleation modes in static magnetic fields

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

Vanatka, Marek; Urbanek, Michal; Jira, Roman

The magnetic vortex nucleation process in nanometer- and micrometer-sized magnetic disks undergoes several phases with distinct spin configurations called the nucleation states. Before formation of the final vortex state, small submicron disks typically proceed through the so-called C-state while the larger micron-sized disks proceed through the more complicated vortex-pair state or the buckling state. This work classifies the nucleation states using micromagnetic simulations and provides evidence for the stability of vortex-pair and buckling states in static magnetic fields using magnetic imaging techniques and electrical transport measurements. Lorentz Transmission Electron Microscopy and Magnetic Transmission X-ray Microscopy are employed to reveal themore » details of spin configuration in each of the nucleation states. We further show that it is possible to unambiguously identify these states by electrical measurements via the anisotropic magnetoresistance effect. Combination of the electrical transport and magnetic imaging techniques confirms stability of a vortex-antivortex-vortex spin configuration which emerges from the buckling state in static magnetic fields.« less

Magnetic vortex nucleation modes in static magnetic fields

DOE PAGES

Vanatka, Marek; Urbanek, Michal; Jira, Roman; ...

2017-10-03

The magnetic vortex nucleation process in nanometer- and micrometer-sized magnetic disks undergoes several phases with distinct spin configurations called the nucleation states. Before formation of the final vortex state, small submicron disks typically proceed through the so-called C-state while the larger micron-sized disks proceed through the more complicated vortex-pair state or the buckling state. This work classifies the nucleation states using micromagnetic simulations and provides evidence for the stability of vortex-pair and buckling states in static magnetic fields using magnetic imaging techniques and electrical transport measurements. Lorentz Transmission Electron Microscopy and Magnetic Transmission X-ray Microscopy are employed to reveal themore » details of spin configuration in each of the nucleation states. We further show that it is possible to unambiguously identify these states by electrical measurements via the anisotropic magnetoresistance effect. Combination of the electrical transport and magnetic imaging techniques confirms stability of a vortex-antivortex-vortex spin configuration which emerges from the buckling state in static magnetic fields.« less

Inner Core Rotation from Geomagnetic Westward Drift and a Stationary Spherical Vortex in Earth's Core

NASA Technical Reports Server (NTRS)

Voorhies, Coerte V.

1998-01-01

The idea that geomagnetic westward drift indicates convective leveling of the planetary momentum gradient within Earth's core is pursued in search of a differentially rotating mean state, upon which various oscillations and secular effects might be superimposed. The desired state conforms to roughly spherical boundary conditions, minimizes dissipative interference with convective cooling in the bulk of the core, yet may aid core cooling by depositing heat in the uppermost core and lower mantle. The variational calculus of stationary dissipation applied to a spherical vortex within the core yields an interesting differential rotation profile, akin to spherical Couette flow bounded by thin Hartmann layers. Four boundary conditions are required. To concentrate shear induced dissipation near the core-mantle boundary, these are taken to be: (i) no-slip at the core-mantle interface; (ii) geomagnetically estimated bulk westward flow at the base of the core-mantle boundary layer; (iii) no-slip at the inner-outer core interface; and, to describe magnetic locking of the inner core to the deep outer core; (iv) hydrodynamically stress-free at the inner-outer core boundary. By boldly assuming the axial core angular momentum anomaly to be zero, the super-rotation of the inner core relative to the mantle is calculated to be at most 1.5 deg./yr.

Inner Core Rotation from Geomagnetic Westward Drift and a Stationary Spherical Vortex in Earth's Core

NASA Technical Reports Server (NTRS)

Voorhies, C. V.

1999-01-01

The idea that geomagnetic westward drift indicates convective leveling of the planetary momentum gradient within Earth's core is pursued in search of a differentially rotating mean state, upon which various oscillations and secular effects might be superimposed. The desired state conforms to roughly spherical boundary conditions, minimizes dissipative interference with convective cooling in the bulk of the core, yet may aide core cooling by depositing heat in the uppermost core and lower mantle. The variational calculus of stationary dissipation applied to a spherical vortex within the core yields an interesting differential rotation profile akin to spherical Couette flow bounded by thin Hartmann layers. Four boundary conditions are required. To concentrate shear induced dissipation near the core-mantle boundary, these are taken to be: (i) no-slip at the core-mantle interface; (ii) geomagnetically estimated bulk westward flow at the base of the core-mantle boundary layer; (iii) no-slip at the inner-outer core interface; and, to describe magnetic locking of the inner core to the deep outer core, (iv) hydrodynamically stress-free at the inner-outer core boundary. By boldly assuming the axial core angular momentum anomaly to be zero, the super-rotation of the inner core is calculated to be at most 1.5 degrees per year.

Chaotic neoclassical separatrix dissipation in parametric drift-wave decay.

PubMed

Kabantsev, A A; Tsidulko, Yu A; Driscoll, C F

2014-02-07

Experiments and theory characterize a parametric decay instability between plasma drift waves when the nonlinear coupling is modified by an electrostatic barrier. Novel mode coupling terms representing enhanced dissipation and mode phase shifts are caused by chaotic separatrix crossings on the wave-ruffled separatrix. Experimental determination of these coupling terms is in broad agreement with new chaotic neoclassical transport analyses.

Drift Mode Accelerometry for Spaceborne Gravity Measurements

NASA Astrophysics Data System (ADS)

Conklin, J. W.; Shelley, R.; Chilton, A.; Olatunde, T.; Ciani, G.; Mueller, G.

2014-12-01

A drift mode accelerometer is a precision instrument for spacecraft that overcomes much of the acceleration noise and readout dynamic range limitations of traditional electrostatic accelerometers. It has the potential of achieving acceleration noise performance similar to that of drag-free systems over a restricted frequency band without the need for external drag-free control or continuous spacecraft propulsion. Like traditional accelerometers, the drift mode accelerometer contains a high-density test mass surrounded by an electrode housing, which can control and sense all six degrees of freedom of the test mass. Unlike traditional accelerometers, the suspension system is operated with a low duty cycle so that the limiting suspension force noise only acts over brief, known time intervals, which can be accounted for in the data analysis. The readout is performed using a laser interferometer which is immune to the dynamic range limitations of even the best voltage references typically used to determine the inertial acceleration of electrostatic accelerometers. This presentation describes operation and performance modeling for such a device with respect to a low Earth orbiting satellite geodesy mission. Methods for testing the drift mode accelerometer with the University of Florida precision torsion pendulum will also be discussed.

Generating multiple orbital angular momentum vortex beams using a metasurface in radio frequency domain

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

Yu, Shixing; Li, Long, E-mail: lilong@mail.xidian.edu.cn, E-mail: gmshi@xidian.edu.cn; Shi, Guangming, E-mail: lilong@mail.xidian.edu.cn, E-mail: gmshi@xidian.edu.cn

In this paper, an electromagnetic metasurface is designed, fabricated, and experimentally demonstrated to generate multiple orbital angular momentum (OAM) vortex beams in radio frequency domain. Theoretical formula of compensated phase-shift distribution is deduced and used to design the metasurface to produce multiple vortex radio waves in different directions with different OAM modes. The prototype of a practical configuration of square-patch metasurface is designed, fabricated, and measured to validate the theoretical analysis at 5.8 GHz. The simulated and experimental results verify that multiple OAM vortex waves can be simultaneously generated by using a single electromagnetic metasurface. The proposed method paves an effectivemore » way to generate multiple OAM vortex waves in radio and microwave wireless communication applications.« less

On multiple manifestations of the second response branch in streamwise vortex-induced vibrations

NASA Astrophysics Data System (ADS)

Cagney, N.; Balabani, S.

2013-07-01

The structural motion and velocity field in the wake of a cylinder exhibiting vortex-induced vibration (VIV) in the streamwise direction were measured using Particle-Image Velocimetry. The effect of hysteresis on the amplitude response of the cylinder and the existence of multiple wake modes in the region of the second response branch were examined. As the reduced velocity was decreased, there was a reduction in the lock-in range; outside this range the amplitude response was found to be negligible and the A-II mode (which is similar to the von Kármán vortex street) was observed in the wake. When the reduced velocity was increased the second branch could be manifested in two forms, depending on whether the wake exhibited the SA or the A-IV mode (in which two and four vortices are shed per wake cycle, respectively). The A-IV mode has been observed in studies in which a cylinder was forced to oscillate in the streamwise direction; however, this represents the first time that it has been recorded in the wake of a freely oscillating body, and it was not previously known that the A-IV mode was capable of exciting self-sustaining vibrations. Both the SA and A-IV modes were stable and no intermittent mode-switching was observed; however, it was found to be unpredictable which mode would dominate as the reduced velocity was varied and the cylinder entered the second response branch. Analysis of the cylinder displacement signals measured while each mode was dominant indicated that the SA mode excited larger amplitude vibrations than the A-IV mode. A reduced velocity near the second response branch was identified at which the wake could exhibit either the SA, A-IV, or A-II modes, with the latter occurring as the reduced velocity was decreased. Although bi-modal behaviour is well established in VIV studies, as far as the authors are aware, this represents the first time that a point has been observed in the response regime of a freely oscillating structure in which three stable states have been observed, each corresponding to a different wake mode and vibration amplitude, for the same structural parameters, reduced velocity, and Reynolds number. This suggests that the mechanism determining which wake mode dominates and the fluid-structure interaction in the case of streamwise VIV may be more complex than has previously been thought. Finally, the vortex-formation and shedding processes associated with the A-II, SA, and A-IV modes were described using phase-averaged vorticity fields, and the differences between the SA and A-IV modes were discussed.

Stabilization of lower hybrid drift modes by finite parallel wavenumber and electron temperature gradients in field-reversed configurations

NASA Astrophysics Data System (ADS)

Farengo, R.; Guzdar, P. N.; Lee, Y. C.

1989-08-01

The effect of finite parallel wavenumber and electron temperature gradients on the lower hybrid drift instability is studied in the parameter regime corresponding to the TRX-2 device [Fusion Technol. 9, 48 (1986)]. Perturbations in the electrostatic potential and all three components of the vector potential are considered and finite beta electron orbit modifications are included. The electron temperature gradient decreases the growth rate of the instability but, for kz=0, unstable modes exist for ηe(=T'en0/Ten0)>6. Since finite kz effects completely stabilize the mode at small values of kz/ky(≂5×10-3), magnetic shear could be responsible for stabilizing the lower hybrid drift instability in field-reversed configurations.

Influence of the properties of soft collective spin wave modes on the magnetization reversal in finite arrays of dipolarly coupled magnetic dots

NASA Astrophysics Data System (ADS)

Stebliy, Maxim; Ognev, Alexey; Samardak, Alexander; Chebotkevich, Ludmila; Verba, Roman; Melkov, Gennadiy; Tiberkevich, Vasil; Slavin, Andrei

2015-06-01

Magnetization reversal in finite chains and square arrays of closely packed cylindrical magnetic dots, having vortex ground state in the absence of the external bias field, has been studied experimentally by measuring static hysteresis loops, and also analyzed theoretically. It has been shown that the field Bn of a vortex nucleation in a dot as a function of the finite number N of dots in the array's side may exhibit a monotonic or an oscillatory behavior depending on the array geometry and the direction of the external bias magnetic field. The oscillations in the dependence Bn(N) are shown to be caused by the quantization of the collective soft spin wave mode, which corresponds to the vortex nucleation in a finite array of dots. These oscillations are directly related to the form and symmetry of the dispersion law of the soft SW mode: the oscillation could appear only if the minimum of the soft mode spectrum is not located at any of the symmetric points inside the first Brillouin zone of the array's lattice. Thus, the purely static measurements of the hysteresis loops in finite arrays of coupled magnetic dots can yield important information about the properties of the collective spin wave excitations in these arrays.

Experimental verification of position-dependent angular-momentum selection rules for absorption of twisted light by a bound electron

NASA Astrophysics Data System (ADS)

Afanasev, Andrei; Carlson, Carl E.; Schmiegelow, Christian T.; Schulz, Jonas; Schmidt-Kaler, Ferdinand; Solyanik, Maria

2018-02-01

We analyze the multipole excitation of atoms with twisted light, i.e, by a vortex light field that carries orbital angular momentum. A single trapped 40Ca+ ion serves as a localized and positioned probe of the exciting field. We drive the {S}1/2\\to {D}5/2 transition and observe the relative strengths of different transitions, depending on the ion's transversal position with respect to the center of the vortex light field. On the other hand, transition amplitudes are calculated for a twisted light field in form of a Bessel beam, a Bessel-Gauss and a Laguerre-Gauss mode. Analyzing experimental obtained transition amplitudes we find agreement with the theoretical predictions at a level of better than 3%. Finally, we propose measurement schemes with two-ion crystals to enhance the sensing accuracy of vortex modes in future experiments.

Freely Drifting Swallow Float Array: August 1988 Trip Report

DTIC Science & Technology

1989-01-01

situ meas- urements of the floats’ clock drifts were obtained; the absolute drifts were on the order of / one part in 105 and the relative clock...Finally, in situ meas- urements of the floats’ clock drifts were obtained, the absolute drifts were on the order of one part in W05 and the relative...FSK mode). That is, the pseudo-random noise generator (PRNG) created a string of ones and zeros ; a zero caused a 12 kHz tone to be broadcast from

ADVANTG Shielding Analysis for Closure Operations in an Open-Mode Repository

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

Bevill, Aaron M; Radulescu, Georgeta; Scaglione, John M

2013-01-01

en-mode repository concepts could require worker entry into access drifts after placement of fuel casks in order to perform activities related to backfill, plug emplacement, routine maintenance, or performance confirmation. An ideal emplacement-drift shielding configuration would minimize dose to workers while maximizing airflow through the emplacement drifts. This paper presents a preliminary investigation of the feasibility and effectiveness of radiation shielding concepts that could be employed to facilitate worker operations in an open-mode repository. The repository model for this study includes pressurized-water reactor fuel assemblies (60 GWd/MTU burnup, 40 year post-irradiation cooldown) in packages of 32 assemblies. The closest fuelmore » packages are 5 meters from dosimetry voxels in the access drift. The unshielded dose to workers in the access drift is 73.7 rem/hour. Prior work suggests that open-mode repository concepts similar to this one would require 15 m3/s of ventilation airflow. Shielding concepts considered here include partial concrete plugs, labyrinthine shields, and stainless steel photon attenuator grids. Maximum dose to workers in the access drift was estimated for each shielding concept using MCNP5 with variance reduction parameters generated by ADVANTG. Because airflow through the shielding is important for open-mode repositories, a semi-empirical estimate of the head loss due to each shielding configuration was also calculated. Airflow and shielding performance vary widely among the proposed shielding configurations. Although the partial plug configuration had the best airflow performance, it allowed dose rates 1500 greater than the specified target. Labyrinthine shielding concepts yield doses on the order of 1 mrem/hour with configurations that impose 3 to 11 J/kg head loss. Adding 1 cm lead lining to the airflow channels of labyrinthine designs further reduces the worker dose by 65% to 95%. Photon-attenuator concepts may reduce worker dose to as low as 29 mrem/hour with head loss on the order of 1.9 J/kg.« less

Simulations of Jovian Vortices: Sensitivity to Vertical Shear below the Cloud Tops.

NASA Astrophysics Data System (ADS)

Morales-Juberías, R.; Dowling, T. E.; Palotai, Cs. J.

2003-05-01

We have multiple, detailed observations of individual spots drifting with different velocities at different latitudes within a given shear zone. We also have indications from modeling Jupiter's White Ovals that the drift rates of anticyclones and cyclones are influenced by the structure of the atmosphere below the cloud tops. Therefore, it should be possible to combine such observations with modeling to learn about the abyssal circulation. We are investigating the influence the vertical wind shear has on jovian vortices with two versions of the EPIC atmospheric model, the original pure-isentropic-coordinate model and the new hybrid-coordinate model that transitions smoothly to a pressure-based coordinate where the atmosphere becomes nearly neutrally stratified and the potential temperature ceases to be a useful coordinate. The hybrid model allows us to achieve significantly greater depth and vertical resolution, and so gain more sensitivity to the baroclinic effects of the vertical shear of the zonal wind. There are technical issues that arise with the hybrid, in particular it is more challenging to introduce a balanced vortex since there is no simple streamfunction like the Montgomery streamfunction used in the isentropic-coordinate case. Our scientific goal is to reproduce the observed interactions of cyclones with anticyclones. For example, previous to the final merger of White Ovals BE and FA, the cyclonic vortex between them, which appeared to act as a merger inhibitor---a common occurrance when two White Ovals drifted close to each other---was pulled out of the triple system by the nearby transit of the Great Red Spot, thereby leaving a free path for BE and FA to merge. We will present our latest results on anticyclone-cyclone interactions and the influence of the abyssal circulation. This research is funded by NASA's Planetary Atmospheres and EPSCoR programs.

Parametric Simulations of the Great Dark Spots of Neptune

NASA Astrophysics Data System (ADS)

Deng, Xiaolong; Le Beau, R.

2006-09-01

Observations by Voyager II and the Hubble Space Telescope of the Great Dark Spots (GDS) of Neptune suggest that large vortices with lifespans of years are not uncommon occurrences in the atmosphere of Neptune. The variability of these features over time, in particular the complex motions of GDS-89, make them challenging candidates to simulate in atmospheric models. Previously, using the Explicit Planetary Isentropic-Coordinate (EPIC) General Circulation Model, LeBeau and Dowling (1998) simulated the GDS-like vortex features. Qualitatively, the drift, oscillation, and tail-like features of GDS-89 were recreated, although precise numerical matches were only achieved for the meridional drift rate. In 2001, Stratman et al. applied EPIC to simulate the formation of bright companion clouds to the Great Dark Spots. In 2006, Dowling et al. presented a new version of EPIC, which includes hybrid vertical coordinate, cloud physics, advanced chemistry, and new turbulence models. With the new version of EPIC, more observation results, and more powerful computers, it is the time to revisit CFD simulations of the Neptune's atmosphere and do more detailed work on GDS-like vortices. In this presentation, we apply the new version of EPIC to simulate GDS-89. We test the influences of different parameters in the EPIC model: potential vorticity gradient, wind profile, initial latitude, vortex shape, and vertical structure. The observed motions, especially the latitudinal drift and oscillations in orientation angle and aspect ratio, are used as diagnostics of these unobserved atmospheric conditions. Increased computing power allows for more refined and longer simulations and greater coverage of the parameter space than previous efforts. Improved quantitative results have been achieved, including voritices with near eight-day oscillations and comparable variations in shape to GDS-89. This research has been supported by Kentucky NASA EPSCoR.

Self-focusing of ultraintense femtosecond optical vortices in air.

PubMed

Polynkin, P; Ament, C; Moloney, J V

2013-07-12

Our experiments show that the critical power for self-focusing collapse of femtosecond vortex beams in air is significantly higher than that of a flattop beam and grows approximately linearly with the vortex order. With less than 10% of initial transverse intensity modulation of the beam profiles, the dominant mode of self-focusing collapse is the azimuthal breakup of the vortex rings into individual filaments, the number of which grows with the input beam power. The generated bottlelike distributions of plasma filaments rotate on propagation in the direction determined by the sense of vorticity.

Zero modes of the non-relativistic self-dual Chern-Simons vortices on the Toda backgrounds

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

Yoon, Yongsung

The two-dimensional self-dual equations are the governing equations of the static zero-energy vortex solutions for the non-relativistic, non-Abelian Chern-Simons models. The zero modes of the non-relativistic vortices are examined by index calculation for the self-dual equations. The index for the self-dual equations is zero for non-Abelian groups, but a non-zero index is obtained by the Toda Ansatz which reduces the self-dual equations to the Toda equations. The number of zero modes for the non-relativistic Toda vortices is 2 {Sigma}{sub {alpha},{beta}}{sup r}K{sub {alpha}{beta}}Q{sup {beta}} which is twice the total number of isolated zeros of the vortex functions. For the affine Todamore » system, there are additional adjoint zero modes which give a zero index for the SU(N) group.« less

The effect of a dominant initial single mode on the Kelvin–Helmholtz instability evolution: New insights on previous experimental results

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

Shimony, Assaf; Shvarts, Dov; Malamud, Guy

2016-04-12

This paper brings new insights on an experiment, measuring the Kelvin–Helmholtz (KH) instability evolution, performed on the OMEGA-60 laser facility. Experimental radiographs show that the initial seed perturbations in the experiment are of multimode spectrum with a dominant single-mode of 16 μm wavelength. In single-mode-dominated KH instability flows, the mixing zone (MZ) width saturates to a constant value comparable to the wavelength. However, the experimental MZ width at late times has exceeded 100 μm, an order of magnitude larger. In this work, we use numerical simulations and a statistical model in order to investigate the vortex dynamics of the KHmore » instability for the experimental initial spectrum. Here, we conclude that the KH instability evolution in the experiment is dominated by multimode, vortex-merger dynamics, overcoming the dominant initial mode.« less

Transverse ac-driven and geometric ratchet effects for vortices in conformal crystal pinning arrays

DOE PAGES

Reichhardt, Charles; Reichhardt, Cynthia Jane Olsen

2016-02-11

A conformal pinning array is created by taking a conformal transformation of a uniform hexagonal lattice to create a structure in which the sixfold ordering of the original lattice is preserved but which has a spatial gradient in the pinning site density. With a series of conformal arrays it is possible to create asymmetric substrates, and it was previously shown that when an ac drive is applied parallel to the asymmetry direction, a pronounced ratchet effect occurs with a net dc flow of vortices in the same direction as the ac drive. Here, in this article, we show that whenmore » the ac drive is applied perpendicular to the substrate asymmetry direction, it is possible to realize a transverse ratchet effect where a net dc flow of vortices is generated perpendicular to the ac drive. The conformal transverse ratchet effect is distinct from previous versions of transverse ratchets in that it occurs due to the generation of non-Gaussian transverse vortex velocity fluctuations by the plastic motion of vortices, so that the system behaves as a noise correlation ratchet. The transverse ratchet effect is much more pronounced in the conformal arrays than in random gradient arrays and is absent in square gradient arrays due the different nature of the vortex flow in each geometry. We show that a series of reversals can occur in the transverse ratchet effect due to changes in the vortex flow across the pinning gradient as a function of vortex filling, pinning strength, and ac amplitude. We also consider the case where a dc drive applied perpendicular to the substrate asymmetry direction generates a net flow of vortices perpendicular to the dc drive, producing what is known as a geometric or drift ratchet that again arises due to non-Gaussian dynamically generated fluctuations. The drift ratchet is more efficient than the ac driven ratchet and also exhibits a series of reversals for varied parameters. Lastly, our results should be general to a wide class of systems undergoing nonequilibrium dynamics on conformal substrates, such as colloidal particles on optical traps.« less

Controlling the numerical Cerenkov instability in PIC simulations using a customized finite difference Maxwell solver and a local FFT based current correction

DOE PAGES

Li, Fei; Yu, Peicheng; Xu, Xinlu; ...

2017-01-12

In this study we present a customized finite-difference-time-domain (FDTD) Maxwell solver for the particle-in-cell (PIC) algorithm. The solver is customized to effectively eliminate the numerical Cerenkov instability (NCI) which arises when a plasma (neutral or non-neutral) relativistically drifts on a grid when using the PIC algorithm. We control the EM dispersion curve in the direction of the plasma drift of a FDTD Maxwell solver by using a customized higher order finite difference operator for the spatial derivative along the direction of the drift (1ˆ direction). We show that this eliminates the main NCI modes with moderate |k 1|, while keepsmore » additional main NCI modes well outside the range of physical interest with higher |k 1|. These main NCI modes can be easily filtered out along with first spatial aliasing NCI modes which are also at the edge of the fundamental Brillouin zone. The customized solver has the possible advantage of improved parallel scalability because it can be easily partitioned along 1ˆ which typically has many more cells than other directions for the problems of interest. We show that FFTs can be performed locally to current on each partition to filter out the main and first spatial aliasing NCI modes, and to correct the current so that it satisfies the continuity equation for the customized spatial derivative. This ensures that Gauss’ Law is satisfied. Lastly, we present simulation examples of one relativistically drifting plasma, of two colliding relativistically drifting plasmas, and of nonlinear laser wakefield acceleration (LWFA) in a Lorentz boosted frame that show no evidence of the NCI can be observed when using this customized Maxwell solver together with its NCI elimination scheme.« less

Controlling the numerical Cerenkov instability in PIC simulations using a customized finite difference Maxwell solver and a local FFT based current correction

NASA Astrophysics Data System (ADS)

Li, Fei; Yu, Peicheng; Xu, Xinlu; Fiuza, Frederico; Decyk, Viktor K.; Dalichaouch, Thamine; Davidson, Asher; Tableman, Adam; An, Weiming; Tsung, Frank S.; Fonseca, Ricardo A.; Lu, Wei; Mori, Warren B.

2017-05-01

In this paper we present a customized finite-difference-time-domain (FDTD) Maxwell solver for the particle-in-cell (PIC) algorithm. The solver is customized to effectively eliminate the numerical Cerenkov instability (NCI) which arises when a plasma (neutral or non-neutral) relativistically drifts on a grid when using the PIC algorithm. We control the EM dispersion curve in the direction of the plasma drift of a FDTD Maxwell solver by using a customized higher order finite difference operator for the spatial derivative along the direction of the drift (1 ˆ direction). We show that this eliminates the main NCI modes with moderate |k1 | , while keeps additional main NCI modes well outside the range of physical interest with higher |k1 | . These main NCI modes can be easily filtered out along with first spatial aliasing NCI modes which are also at the edge of the fundamental Brillouin zone. The customized solver has the possible advantage of improved parallel scalability because it can be easily partitioned along 1 ˆ which typically has many more cells than other directions for the problems of interest. We show that FFTs can be performed locally to current on each partition to filter out the main and first spatial aliasing NCI modes, and to correct the current so that it satisfies the continuity equation for the customized spatial derivative. This ensures that Gauss' Law is satisfied. We present simulation examples of one relativistically drifting plasma, of two colliding relativistically drifting plasmas, and of nonlinear laser wakefield acceleration (LWFA) in a Lorentz boosted frame that show no evidence of the NCI can be observed when using this customized Maxwell solver together with its NCI elimination scheme.

Controlling the numerical Cerenkov instability in PIC simulations using a customized finite difference Maxwell solver and a local FFT based current correction

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

Li, Fei; Yu, Peicheng; Xu, Xinlu

In this study we present a customized finite-difference-time-domain (FDTD) Maxwell solver for the particle-in-cell (PIC) algorithm. The solver is customized to effectively eliminate the numerical Cerenkov instability (NCI) which arises when a plasma (neutral or non-neutral) relativistically drifts on a grid when using the PIC algorithm. We control the EM dispersion curve in the direction of the plasma drift of a FDTD Maxwell solver by using a customized higher order finite difference operator for the spatial derivative along the direction of the drift (1ˆ direction). We show that this eliminates the main NCI modes with moderate |k 1|, while keepsmore » additional main NCI modes well outside the range of physical interest with higher |k 1|. These main NCI modes can be easily filtered out along with first spatial aliasing NCI modes which are also at the edge of the fundamental Brillouin zone. The customized solver has the possible advantage of improved parallel scalability because it can be easily partitioned along 1ˆ which typically has many more cells than other directions for the problems of interest. We show that FFTs can be performed locally to current on each partition to filter out the main and first spatial aliasing NCI modes, and to correct the current so that it satisfies the continuity equation for the customized spatial derivative. This ensures that Gauss’ Law is satisfied. Lastly, we present simulation examples of one relativistically drifting plasma, of two colliding relativistically drifting plasmas, and of nonlinear laser wakefield acceleration (LWFA) in a Lorentz boosted frame that show no evidence of the NCI can be observed when using this customized Maxwell solver together with its NCI elimination scheme.« less

Dynamics of vortex domain walls in ferromagnetic nanowires - A possible method for chirality manipulation

NASA Astrophysics Data System (ADS)

Li, Y.; Lu, Z.; Chen, C.; Cheng, M.; Yin, H.; Wang, W.; Li, C.; Liu, Y.; Xiong, R.; Shi, J.

2018-06-01

The dynamic behaviors of vortex domain walls (VDWs) in ferromagnetic nanowires driven by a magnetic field above Walker breakdown field (Hw) were investigated using micromagnetic simulation. It was found when nanowire has proper geometrical dimensions, the VDW may oscillate in a chirality invariant mode or a chirality switching mode depending on applied field and damping constant. At fixed damping constant, the oscillation mode can be controlled by applied field - with the increase of applied field, the oscillation of VDW change from a chirality invariant mode to a variant one. As the oscillation of VDW changes from chirality invariant regime to chirality switching regime, the oscillation frequency and amplification will undergo an abnormal change, which may offer a fingerprint for the switch of oscillation mode. Our finding proposes a simple way to control the chirality of a VDW by properly manipulating nanowire geometry and applied field, which may have important applications in VDW-based devices.

A dual-polarized and reconfigurable reflectarray for generation of vortex radio waves

NASA Astrophysics Data System (ADS)

Li, Chen-Chen; Wu, Lin-Sheng; Yin, Wen-Yan

2018-05-01

Electromagnetic (EM) waves with orbital angular momentum (OAM) provide a new degree of freedom for channel multiplexing to improve the capacity of wireless communication. For OAM-based systems, it is important to design specific configurations to generate vortex radios. In this paper, a reconfigurable reflectarray antenna is proposed with independent control of dual polarizations. A reflective cell is proposed by properly assigning the variable capacitances of four varactors, which are placed between metal square rings of each unit. The varactors of each unit are divided into two groups and the capacitance value of each group controls the reflection phase for a single linear polarization. By using the equivalent circuit model, the reflective units and array can be designed efficiently. Smooth phase variation and good reflection efficiency are achieved. Then, the reflectarray is set into sectors and a simple phase-shifting surface model is used to generate vortex beam. Each sector is realized with reflective units satisfying desired reflection phases for different modes. This kind of OAM-generating method can reduce the required variation range of reflection phase and provide more choices for a specific OAM mode combination with dual polarization, which is helpful to reduce mutual coupling between the two linear polarizations. Finally, full-wave simulations show that the 0, ±1, ±2 modes of vortex beam are successfully generated at 3.5 GHz with arbitrary combination in dual-polarization, which is also supported by OAM modes purity and reflection efficiency analysis. Therefore, in our design, the reconfigurable OAM and spin angular momentum (SAM), related with polarization, can be utilized simultaneously and independently for high-capacity wireless communication.

High fidelity phase locked PIV measurements analysing the flow fields surrounding an oscillating piezoelectric fan

NASA Astrophysics Data System (ADS)

Jeffers, Nicholas; Nolan, Kevin; Stafford, Jason; Donnelly, Brian

2014-07-01

Piezoelectric fans have been studied extensively and are seen as a promising technology for thermal management due to their ability to provide quiet, reliable cooling with low power consumption. The fluid mechanics of an unconfined piezoelectric fan are complex which is why the majority of the literature to date confines the fan in an attempt to simplify the flow field. This paper investigates the fluid mechanics of an unconfined fan operating in its first vibration frequency mode. The piezoelectric fan used in this study measures 12.7mm × 70mm and resonates at 92.5Hz in air. A custom built experimental facility was developed to capture the fan's flow field using phase locked Particle Image Velocimetry (PIV). The phase locked PIV results are presented in terms of vorticity and show the formation of a horse shoe vortex. A three dimensional A2 criterion constructed from interpolated PIV measurements was used to identify the vortex core in the vicinity of the fan. This analysis was used to clearly identify the formation of a horse shoe vortex that turns into a hairpin vortex before it breaks up due to a combination of vortex shedding and flow along the fan blade. The results presented in this paper contribute to both the fluid dynamics and heat transfer literature concerning first mode fan oscillation.

Acoustic far-field of shroud-lip-scattered instability modes of supersonic co-flowing jets

NASA Astrophysics Data System (ADS)

Samanta, Arnab; Freund, Jonathan B.

2013-11-01

We consider the acoustic radiation of instability modes in dual-stream jets, with the inner nozzle buried within the outer shroud, particularly the upstream scattering into acoustic modes that occurs at the shroud lip. For supersonic core jets, several families of instability waves are possible, beyond the regular Kelvin-Helmholtz (K-H) mode, with very different modal shapes and propagation characteristics, which are candidates for changing the sound character of very high-speed jets. The co-axial shear layers are modeled as vortex sheets, with the Wiener-Hopf method used to compute these modes coupled with an asymptotic solution for the far-field radiation. A broadband mode spectra as well as single propagating modes are considered as incident and scattered waves. The resulting far-field directivity patterns are quantified, to show the efficiency of some of these radiation mechanisms, particularly in the upstream direction, which is not directly affected by the Mach-wave-like sound that is radiated from these modes irrespective of any scattering surface. A full Kutta condition, which provides the usual boundary condition at the shroud lip, is altered to examine how vortex shedding, perhaps controllable at the lip, affects the radiated sound.

Dynamics of vortices in complex wakes: Modeling, analysis, and experiments

NASA Astrophysics Data System (ADS)

Basu, Saikat

The thesis develops singly-periodic mathematical models for complex laminar wakes which are formed behind vortex-shedding bluff bodies. These wake structures exhibit a variety of patterns as the bodies oscillate or are in close proximity of one another. The most well-known formation comprises two counter-rotating vortices in each shedding cycle and is popularly known as the von Karman vortex street. Of the more complex configurations, as a specific example, this thesis investigates one of the most commonly occurring wake arrangements, which consists of two pairs of vortices in each shedding period. The paired vortices are, in general, counter-rotating and belong to a more general definition of the 2P mode, which involves periodic release of four vortices into the flow. The 2P arrangement can, primarily, be sub-classed into two types: one with a symmetric orientation of the two vortex pairs about the streamwise direction in a periodic domain and the other in which the two vortex pairs per period are placed in a staggered geometry about the wake centerline. The thesis explores the governing dynamics of such wakes and characterizes the corresponding relative vortex motion. In general, for both the symmetric as well as the staggered four vortex periodic arrangements, the thesis develops two-dimensional potential flow models (consisting of an integrable Hamiltonian system of point vortices) that consider spatially periodic arrays of four vortices with their strengths being +/-Gamma1 and +/-Gamma2. Vortex formations observed in the experiments inspire the assumed spatial symmetry. The models demonstrate a number of dynamic modes that are classified using a bifurcation analysis of the phase space topology, consisting of level curves of the Hamiltonian. Despite the vortex strengths in each pair being unequal in magnitude, some initial conditions lead to relative equilibrium when the vortex configuration moves with invariant size and shape. The scaled comparisons of the model results with experiments conducted in a owing soap film with an airfoil, which was imparted with forced oscillations, are satisfactory and validate the reduced order modeling framework. The experiments have been performed by a collaborator group at the Department of Physics and Fluid Dynamics at the Technical University of Denmark (DTU), led by Dr. Anders Andersen. Similar experiments have also been run at Virginia Tech as part of this dissertation and the preliminary results are included in this treatise. The thesis also employs the same dynamical systems techniques, which have been applied to study the 2P regime dynamics, to develop a mathematical model for the P+S mode vortex wakes, with three vortices present in each shedding cycle. The model results have also been compared favorably with an experiment and the predictions regarding the vortex circulation data match well with the previous results from literature. Finally, the thesis introduces a novel concept of clean and renewable energy extraction from vortex-induced vibrations of bluff bodies. The slow-moving currents in the off-shore marine environments and riverine flows are beyond the operational capabilities of the more established hydrokinetic energy converters and the discussed technology promises to be a significant tool to generate useful power from these copiously available but previously untapped sources.

The Influence of Atmospheric Stability on Wind Drift from Ultra-Low-volume Aerial Forest Spray Applications.

NASA Astrophysics Data System (ADS)

Crabbe, R. S.; McCooeye, M.; Mickle, R. E.

1994-04-01

Measurements of drift cloud mass from 11 cases selected from a study of wind-borne droplet drift from ultra low-volume aerial spray applications over northern Ontario forests are presented as a function of atmospheric stability. Six swaths were overlaid onto a flight line in 30 min to obtain ensemble-averaged data from rotary atomizer emissions from an agricultural spray plane flying at about 21 and 26 m above ground level. The estimated volume median diameters of the spray were 100 µm for the 21-m height and 70 µm for the 26-m height. The mass of spray material in the drift cloud was measured at 400, 1200, and 2200 m downwind of the (crosswind) flight line using Rotorods' suspended from tethered blimps. Wind speed at aircraft height varied from 2 to 5 m s1 and meteorological conditions varied from moderately stable to moderately unstable.Analysis of the data revealed that 35% more drift occurred in stable than in unstable conditions. The lowest drift was measured when the aircraft was flown in the morning mixing layer beneath a low capping inversion. Under thee conditions, only 18% of the emission drifted put 400 m downwind and 10% past 1200 m. The highest drift occurred in moderately stable flow, 71% past 400 m and 50% past 2200 m in 3 m s1 wind speeds and, in slightly stable flow, 77% past 400 m and 27% past 2200 m in 5 m s1 wind speeds.Within experimental error, little difference was observed between wind drift of the 100-µm-diameter droplets and the 70-µm-diameter droplets past 400 m downwind although farther downwind, drift from the larger-droplet emission was less. This difference is discussed in terms of the descent rate of the aircraft vortex wake in stable conditions.

Transfer of Orbital and Spin angular momentum from non-paraxial optical vortex to atomic BEC

NASA Astrophysics Data System (ADS)

Bhowmik, Anal; Mondal, Pradip Kumar; Majumder, Sonjoy; Deb, Bimalendu

2017-04-01

Allen and co-workers first brought up the realization that optical vortex can carry well defined orbital angular momentum (OAM) associated with its spatial mode. Spin angular momentum (SAM) of the light, associated with the polarization, interacts with the internal electronic motion of the atom. The exchange of orbital angular momentum (OAM) between optical vortex and the center-of-mass (CM) motion of an atom or molecule is well known in paraxial approximation. We show that, how the total angular momentum (TAM) of non-paraxial optical vortex is shared with atom, in terms of OAM and SAM. Both the angular momenta are now possible to be transferred to the internal electronic and external CM motion of atom. Here we have studied how the Rabi frequencies of the excitations of two-photon Raman transitions with respect to focusing angles. Also, we investigate the properties of the vortex superposed state for a Bose-Einstein condensate condensate by a single non-paraxial vortex beam. The density distribution of the vortex-antivortex superposed state has a petal structure which is determined by the quantum circulations and proportion of the vortex and antivortex.

Crossflow-Vortex Breakdown on Swept Wings: Correlation of Nonlinear Physics

NASA Technical Reports Server (NTRS)

Joslin, R. D.; Streett, C. L.

1994-01-01

The spatial evolution of cross flow-vortex packets in a laminar boundary layer on a swept wing are computed by the direct numerical simulation of the incompressible Navier- Stokes equations. A wall-normal velocity distribution of steady suction and blowing at the wing surface is used to generate a strip of equally spaced and periodic disturbances along the span. Three simulations are conducted to study the effect of initial amplitude on the disturbance evolution, to determine the role of traveling cross ow modes in transition, and to devise a correlation function to guide theories of transition prediction. In each simulation, the vortex packets first enter a chordwise region of linear independent growth, then, the individual packets coalesce downstream and interact with adjacent packets, and, finally, the vortex packets nonlinearly interact to generate inflectional velocity profiles. As the initial amplitude of the disturbance is increased, the length of the evolution to breakdown decreases. For this pressure gradient, stationary modes dominate the disturbance evolution. A two-coeffcient function was devised to correlate the simulation results. The coefficients, combined with a single simulation result, provide sufficient information to generate the evolution pattern for disturbances of any initial amplitude.

Near-body vorticity dynamics of a square cylinder subjected to an inline pulsatile free stream flow

NASA Astrophysics Data System (ADS)

Krishnan, Hrisheekesh; Agrawal, Amit; Sharma, Atul; Sheridan, John

2016-09-01

In the present work, the effect of an inflow sinusoidal excitation that is superimposed over the mean flow on the vortex-shedding characteristics of a square cylinder is studied. The frequency of pulsation is varied around the natural vortex-shedding frequency, and the amplitude of pulsation is varied moderately in comparison to the cylinder diameter, at a fixed Reynolds number (=100). A flow regime map is prepared and compared with the experimental results, which are available for a circular cylinder that is subjected to inline excitation. We correlate the spectra to the corresponding flow regime. Visualization of the vorticity contours reveals that the significant interaction of the base-region vorticities with the main shear layer vorticities is important in the mechanism of formation of the several vortex-shedding modes. The strength and sign of base region vorticity with respect to the shear layers has a fundamental role to play in the mechanism of formation. It is hypothesized that the similarity in vortex-shedding modes across different excitation types, bluff body geometry, and for different parameters is due to the similarity in the underlying vorticity dynamics.

Controlling abruptly autofocusing vortex beams to mitigate crosstalk and vortex splitting in free-space optical communication.

PubMed

Yan, Xu; Guo, Lixin; Cheng, Mingjian; Li, Jiangting

2018-05-14

Orbital angular momentum (OAM) mode crosstalk induced by atmospheric turbulence is a challenging phenomenon commonly occurring in OAM-based free-space optical (FSO) communication. Recent advances have facilitated new practicable methods using abruptly autofocusing light beams for weakening the turbulence effect on the FSO link. In this work, we show that a circular phase-locked Airy vortex beam array (AVBA) with sufficient elements has the inherent ability to form an abruptly autofocusing light beam carrying OAM, and its focusing properties can be controlled on demand by adjusting the topological charge values and locations of these vortices embedded in the array elements. The performance of a tailored Airy vortex beam array (TAVBA) through atmospheric turbulence is numerically studied. In a comparison with the ring Airy vortex beam (RAVB), the results indicate that TAVBA can be a superior light source for effectively reducing the intermodal crosstalk and vortex splitting, thus leading to improvement in the FSO system performance.

NASA Agricultural Aircraft Research Program in the Langley Vortex Research Facility and the Langley Full Scale Wind Tunnel

NASA Technical Reports Server (NTRS)

Jordan, F. L., Jr.; Mclemore, H. C.; Bragg, M. B.

1978-01-01

The current status of aerial applications technology research at the Langley's Vortex Research Facility and Full-Scale Wind Tunnel is reviewed. Efforts have been directed mainly toward developing and validating the required experimental and theoretical research tools. A capability to simulate aerial dispersal of materials from agricultural airplanes with small-scale airplane models, numerical methods, and dynamically scaled test particles was demonstrated. Tests on wake modification concepts have proved the feasibility of tailoring wake properties aerodynamically to produce favorable changes in deposition and to provide drift control. An aerodynamic evaluation of the Thrush Commander 800 agricultural airplane with various dispersal systems installed is described. A number of modifications intended to provide system improvement to both airplane and dispersal system are examined, and a technique for documenting near-field spray characteristics is evaluated.

Front propagation in a regular vortex lattice: Dependence on the vortex structure.

PubMed

Beauvier, E; Bodea, S; Pocheau, A

2017-11-01

We investigate the dependence on the vortex structure of the propagation of fronts in stirred flows. For this, we consider a regular set of vortices whose structure is changed by varying both their boundary conditions and their aspect ratios. These configurations are investigated experimentally in autocatalytic solutions stirred by electroconvective flows and numerically from kinematic simulations based on the determination of the dominant Fourier mode of the vortex stream function in each of them. For free lateral boundary conditions, i.e., in an extended vortex lattice, it is found that both the flow structure and the front propagation negligibly depend on vortex aspect ratios. For rigid lateral boundary conditions, i.e., in a vortex chain, vortices involve a slight dependence on their aspect ratios which surprisingly yields a noticeable decrease of the enhancement of front velocity by flow advection. These different behaviors reveal a sensitivity of the mean front velocity on the flow subscales. It emphasizes the intrinsic multiscale nature of front propagation in stirred flows and the need to take into account not only the intensity of vortex flows but also their inner structure to determine front propagation at a large scale. Differences between experiments and simulations suggest the occurrence of secondary flows in vortex chains at large velocity and large aspect ratios.

Spacecraft Interactions Studies with a 1 Kw Class Closed-Drift Hall Thruster

DTIC Science & Technology

1998-01-31

Closed Drift Hall thruster plume with spacecraft surfaces and systems. Two basic interaction modes were investigated: (1) the influence of the plume...Spectrometer (MBMS) capable of discerning both the mass and energy of Hall thruster plume species, and the ion acoustic wave probe to measure the drift velocity of the plume plasma.

Generation of high-order Bessel vortex beam carrying orbital angular momentum using multilayer amplitude-phase-modulated surfaces in radiofrequency domain

NASA Astrophysics Data System (ADS)

Kou, Na; Yu, Shixing; Li, Long

2017-01-01

A high-order Bessel vortex beam carrying orbital angular momentum (OAM) is generated by using multilayer amplitude-phase-modulated surfaces (APMSs) at 10 GHz. The APMS transmitarray is composed of four-layer conformal square-loop (FCSL) surfaces with both amplitude and phase modulation. The APMS can transform a quasi-spherical wave emitted from the feeding source into a pseudo non-diffractive high-order Bessel vortex beam with OAM. The APMS for a second-order Bessel beam carrying OAM in the n = 2 mode is designed, fabricated, and measured. Full-wave simulation and measurement results confirm that Bessel vortex beams with OAM can be effectively generated using the proposed APMS transmitarray.

Ancrage des vortex dans les supraconducteurs Description phénoménologique de la réponse linéaire d'un de vortex ancré

NASA Astrophysics Data System (ADS)

Lütke-Entrup, N.; Plaçais, B.; Mathieu, P.; Simon, Y.

Vortices pinning in supraconductors In this article we report on the investigation of the dynamics of vortices based on the high frequency linear response. We present a serie of measurements of the complex penetration depth in the mixed state in a variety of samples, including conventional materials (Nb, V, PbIn), the non-conventional heavy fermion UPt3, and the high-T_c cuprate YBaCuO. We have explored a large frequency range (1 kHz 10 MHz) so as to cover the cross-over from the quasi-static response, which is dominated by elastic interactions between vortices and sample defects, to the high-frequency regime, which is governed by viscous damping due to vortex friction against the host crystal. For a quantitative description of the frequency spectrum we start from a phenomenological theory which makes a rigorous distinction between vortex lines, along a vortex field omega, and magnetic field lines B. It predicts a second electrodynamical mode, which is linked to the vortex line tension and has a rather short range. We show that, in the limit of small vortex oscillations, amplitude and phase of the linear response are governed by an additional boundary condition for the vortex lattice at the sample surface ; it takes the form of a slipping condition with a characteristic length that depends on the surface roughness. The frequency spectrum deduced from this mechanism is clearly different from the Campbell spectrum, which is the common signature of all bulk pinning mechanisms. Our results on samples of PbIn, Nb, V, and YBaCuO entirely confirm our model, including some non-intuitive size effects which appear at low frequency when the sample becomes transparent to the flux flow mode. However, our measurements in the B and C phases of UPt3 reveal and important contribution of the bulk to the vortex pinning. Ce travail porte sur l'étude de l'ancrage des vortex par la réponse linéaire haute fréquence. Nous présentons une série de mesures de la profondeur de pénétration complexe dans l'état mixte sur une variété d'échantillons qui va des supraconducteurs classiques (Nb, V, PbIn), aux composés de fermions lourds non-conventionnels (UPt3), en passant par les cuprates à haute température critique (YBaCuO). La large gamme des fréquences explorées (1 kHz 10 MHz) permet de couvrir le changement de régime entre la réponse quasistatique dominée par l'interaction élastique des vortex avec les défauts, et la réponse haute fréquence amortie par la friction visqueuse du réseau de vortex au cristal ionique. Pour décrire quantitativement le spectre de fréquence, nous nous appuyons sur une théorie phénoménologique qui fait une distinction explicite et rigoureuse entre lignes de vortex, décrites par un champ omega, et lignes de champ magnétique B. On prédit ainsi l'existence d'un second mode électrodynamique, évanescent et de courte portée, lié à la tension de ligne des vortex. On montre que la réponse aux petits mouvements, amplitude et phase, est réglée par une condition limite supplémentaire sur le réseau de vortex à la surface ; elle prend la forme d'une condition de glissement avec une longueur phénoménologique contrôlée par la rugosité de l'échantillon. Le spectre de fréquence associé à ce mécanisme se distingue nettement du spectre de Campbell, générique des modèles d'ancrage en volume. Nos mesures sur des échantillons PbIn, Nb, V et YBaCuO confirment entièrement notre modèle, y compris des effets de taille peu intuitifs qui se produisent à basse fréquence quand l'échantillon devient transparent au mode flux flow. En revanche, l'étude des vortex dans les phases B et C d'UPt3 montre une contribution importante du volume à l'ancrage des vortex.

Hub vortex instability within wind turbine wakes: Effects of wind turbulence, loading conditions, and blade aerodynamics

NASA Astrophysics Data System (ADS)

Ashton, Ryan; Viola, Francesco; Camarri, Simone; Gallaire, Francois; Iungo, Giacomo Valerio

2016-11-01

The near wake of wind turbines is characterized by the presence of the hub vortex, which is a coherent vorticity structure generated from the interaction between the root vortices and the boundary layer evolving over the turbine nacelle. By moving downstream, the hub vortex undergoes an instability with growth rate, azimuthal and axial wavenumbers determined by the characteristics of the incoming wind and turbine aerodynamics. Thus, a large variability of the hub vortex instability is expected for wind energy applications with consequent effects on wake downstream evolution, wake interactions within a wind farm, power production, and fatigue loads on turbines invested by wakes generated upstream. In order to predict characteristics of the hub vortex instability for different operating conditions, linear stability analysis is carried out by considering different statistics of the incoming wind turbulence, thrust coefficient, tip speed ratio, and blade lift distribution of a wind turbine. Axial and azimuthal wake velocity fields are modeled through Carton-McWilliams velocity profiles by mimicking the presence of the hub vortex, helicoidal tip vortices, and matching the wind turbine thrust coefficient predicted through the actuator disk model. The linear stability analysis shows that hub vortex instability is strongly affected by the wind turbine loading conditions, and specifically it is promoted by a larger thrust coefficient. A higher load of the wind turbines produces an enhanced axial velocity deficit and, in turn, higher shear in the radial direction of the streamwise velocity. The axial velocity shear within the turbine wake is also the main physical mechanism promoting the hub vortex instability when varying the lift distribution over the blade span for a specific loading condition. Cases with a larger velocity deficit in proximity of the wake center and less aerodynamic load towards the blade tip result to be more unstable. Moreover, wake swirl promotes hub vortex instability, and it can also affect the azimuthal wave number of the most unstable mode. Finally, higher Reynolds stresses and turbulent eddy viscosity decrease both growth rate and azimuthal wave number of the most unstable mode.

On random pressure pulses in the turbine draft tube

NASA Astrophysics Data System (ADS)

Kuibin, P. A.; Shtork, S. I.; Skripkin, S. G.; Tsoy, M. A.

2017-04-01

The flow in the conical part of the hydroturbine draft tube undergoes various instabilities due to deceleration and flow swirling at off-design operation points. In particular, the precessing vortex rope develops at part-load regimes in the draft tube. This rope induces periodical low-frequency pressure oscillations in the draft tube. Interaction of rotational (asynchronous) mode of disturbances with the elbow can bring to strong oscillations in the whole hydrodynamical system. Recent researches on flow structure in the discharge cone in a regime of free runner had revealed that helical-like vortex rope can be unstable itself. Some coils of helix close to each other and reconnection appears with generation of a vortex ring. The vortex ring moves toward the draft tube wall and downstream. The present research is focused on interaction of vortex ring with wall and generation of pressure pulses.

Selective equal spin Andreev reflection at vortex core center in magnetic semiconductor-superconductor heterostructure.

PubMed

Li, Chuang; Hu, Lun-Hui; Zhou, Yi; Zhang, Fu-Chun

2018-05-18

Sau, Lutchyn, Tewari and Das Sarma (SLTD) proposed a heterostructure consisting of a semiconducting thin film sandwiched between an s-wave superconductor and a magnetic insulator and showed possible Majorana zero mode. Here we study spin polarization of the vortex core states and spin selective Andreev reflection at the vortex center of the SLTD model. In the topological phase, the differential conductance at the vortex center contributed from the Andreev reflection, is spin selective and has a quantized value [Formula: see text] at zero bias. In the topological trivial phase, [Formula: see text] at the lowest quasiparticle energy of the vortex core is spin selective due to the spin-orbit coupling (SOC). Unlike in the topological phase, [Formula: see text] is suppressed in the Giaever limit and vanishes exactly at zero bias due to the quantum destruction interference.

ProFile Vortex and Vortex Blue Nickel-Titanium Rotary Instruments after Clinical Use.

PubMed

Shen, Ya; Zhou, Huimin; Coil, Jeffrey M; Aljazaeri, Bassim; Buttar, Rene; Wang, Zhejun; Zheng, Yu-feng; Haapasalo, Markus

2015-06-01

The aim of this study was to analyze the incidence and mode of ProFile Vortex and Vortex Blue instrument defects after clinical use in a graduate endodontic program and to examine the impact of clinical use on the instruments' metallurgical properties. A total of 330 ProFile Vortex and 1136 Vortex Blue instruments from the graduate program were collected after each had been used in 3 teeth. The incidence and type of instrument defects were analyzed. The lateral surfaces and fracture surfaces of the fractured files were examined by using scanning electron microscopy. Unused and used instruments were examined by full and partial differential scanning calorimetry. No fractures were observed in the 330 ProFile Vortex instruments, whereas 20 (6.1%) revealed bent or blunt defects. Only 2 of the 1136 Vortex Blue files fractured during clinical use. The cause of fracture was shear stress. The fractures occurred at the tip end of the spirals. Only 1.8% (21 of 1136) of the Vortex Blue files had blunt tips. Austenite-finish temperatures were very similar for unused and used ProFile Vortex files and were all greater than 50°C. The austenite-finish temperatures of used and unused Vortex Blue files (38.5°C) were lower than those in ProFile Vortex instruments (P < .001). However, the transformation behavior of Vortex Blue files had an obvious 2-stage transformation, martensite-to-R phase and R-to-austenite phase. The trends of differential scanning calorimetry plots of unused Vortex Blue instruments and clinically used instruments were very similar. The risk of ProFile Vortex and Vortex Blue instrument fracture is very low when instruments are discarded after clinical use in the graduate endodontic program. The Vortex Blue files have metallurgical behavior different from ProFile Vortex instruments. Copyright © 2015 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Model experiments to evaluate vortex dissipation devices proposed for installation on or near aircraft runways

NASA Technical Reports Server (NTRS)

Kohl, R. E.

1973-01-01

The effectiveness of various vortex dissipation devices proposed for installation on or near aircraft runways is evaluated on basis of results of experiments conducted with a 0.03-scale model of a Boeing 747 transport aircraft in conjunction with a simulated runway. The test variables included type of vortex dissipation device, mode of operation of the powered devices, and altitude, lift coefficient and speed of the generating aircraft. A total of fifteen devices was investigated. The evaluation is based on time sequence photographs taken in the vertical and horizontal planes during each run.

Blobs and drift wave dynamics

DOE PAGES

Zhang, Yanzeng; Krasheninnikov, S. I.

2017-09-29

The modified Hasegawa-Mima equation retaining all nonlinearities is investigated from the point of view of the formation of blobs. The linear analysis shows that the amplitude of the drift wave packet propagating in the direction of decreasing background plasma density increases and eventually saturates due to nonlinear effects. Nonlinear modification of the time averaged plasma density profile results in the formation of large amplitude modes locked in the radial direction, but still propagating in the poloidal direction, which resembles the experimentally observed chain of blobs propagating in the poloidal direction. Such specific density profiles, causing the locking of drift waves,more » could form naturally at the edge of tokamak due to a neutral ionization source. Thus, locked modes can grow in situ due to plasma instabilities, e.g., caused by finite resistivity. Furthermore, the modulation instability (in the poloidal direction) of these locked modes can result in a blob-like burst of plasma density.« less

Fishbone Oscillations in the Experimental Advanced Superconductivity Tokamak

NASA Astrophysics Data System (ADS)

Xu, Li-Qing; Hu, Li-Qun; Yuan, Yi; Li, Ying-Ying; Zhong, Guo-Qiang; Liu, Hai-Qing; Chen, Kai-Yun; Shi, Tong-Hui; Duan, Yan-Min

2018-03-01

A fishbone oscillation was observed in the neutral beam injection plasma at Experimental Advanced Superconductivity Tokamak (EAST). This m = 1/n = 1 ( m, n: poloidal, toroidal mode numbers, respectively) typical internal kink mode travels in the ion-diamagnetism direction in the poloidal section with a rotation speed close to the ion diamagnetic drift frequency. A high thermal plasma beta and high amounts of energetic ions are necessary for the mode to develop. Fishbone oscillations can expel heavy impurities in the core, which favors sustaining a high-performance plasma. The born frequency of the fishbone oscillation is the ion diamagnetic drift frequency and the chirping down of the frequency during the initial growth phase is the result of a drop in iondiamagnetic drift frequency. The excitation energy is thought to be due to the thermal plasma pressure gradient; however, the development of a fishbone oscillation is related to energetic ions.

A numerical simulation of the dispersal of aerial sprays

NASA Technical Reports Server (NTRS)

Bragg, M. B.

1981-01-01

A computer program was developed to predict the trajectory, ground deposition, and drift of liquid sprays injected into the wake of an agricultural aircraft in ground effect. The program uses a horseshoe vortex wake model and includes the effects of liquid droplet evaporation, crosswind, the propeller slipstream, ground effect, and tunnel walls on small scale models. This user's guide includes several case examples demonstrating user options. A complete listing of the FORTRAN program is provided.

Poincare oscillations and geostrophic adjustment in a rotating paraboloid

NASA Astrophysics Data System (ADS)

Kalashnik, M.; Kakhiani, V.; Patarashvili, K.; Tsakadze, S.

2009-10-01

Free liquid oscillations (Poincare oscillations) in a rotating paraboloid are investigated theoretically and experimentally. Within the framework of shallow-water theory, with account for the centrifugal force, expressions for the free oscillation frequencies are obtained and corrections to the frequencies related with the finiteness of the liquid depth are found. It is shown that in the rotating liquid, apart from the wave modes of free oscillations, a stationary vortex mode is also generated, that is, a process of geostrophic adjustment takes place. Solutions of the shallow-water equations which describe the wave dynamics of the adjustment process are presented. In the experiments performed the wave and vortex modes were excited by removing a previously immersed hemisphere from the central part of the paraboloid. Good agreement between theory and experiment was obtained. Address: alex_gaina@yahoo.com Database: phy

Plasma-resistivity-induced strong damping of the kinetic resistive wall mode.

PubMed

He, Yuling; Liu, Yueqiang; Liu, Yue; Hao, Guangzhou; Wang, Aike

2014-10-24

An energy-principle-based dispersion relation is derived for the resistive wall mode, which incorporates both the drift kinetic resonance between the mode and energetic particles and the resistive layer physics. The equivalence between the energy-principle approach and the resistive layer matching approach is first demonstrated for the resistive plasma resistive wall mode. As a key new result, it is found that the resistive wall mode, coupled to the favorable average curvature stabilization inside the resistive layer (as well as the toroidal plasma flow), can be substantially more stable than that predicted by drift kinetic theory with fast ion stabilization, but with the ideal fluid assumption. Since the layer stabilization becomes stronger with decreasing plasma resistivity, this regime is favorable for reactor scale, high-temperature fusion devices.

Toward single mode, atomic size electron vortex beams.

PubMed

Krivanek, Ondrej L; Rusz, Jan; Idrobo, Juan-Carlos; Lovejoy, Tracy J; Dellby, Niklas

2014-06-01

We propose a practical method of producing a single mode electron vortex beam suitable for use in a scanning transmission electron microscope (STEM). The method involves using a holographic "fork" aperture to produce a row of beams of different orbital angular momenta, as is now well established, magnifying the row so that neighboring beams are separated by about 1 µm, selecting the desired beam with a narrow slit, and demagnifying the selected beam down to 1-2 Å in size. We show that the method can be implemented by adding two condenser lenses plus a selection slit to a straight-column cold-field emission STEM. It can also be carried out in an existing instrument, the monochromated Nion high-energy-resolution monochromated electron energy-loss spectroscopy-STEM, by using its monochromator in a novel way. We estimate that atom-sized vortex beams with ≥ 20 pA of current should be attainable at 100-200 keV in either instrument.

Particle-in-cell simulations of the lower-hybrid instability driven by an ion-ring distribution

NASA Astrophysics Data System (ADS)

Swanekamp, Stephen; Richardson, Steve; Mithaiwala, Manish; Crabtree, Chris

2013-10-01

Fully electromagnetic particle-in-cell simulations of the excitation of the lower-hybrid mode in a plasma driven by an ion-ring distribution using the Lsp code are presented. At early times the simulations agree with linear theory. The resulting wave evolution and non-linear plasma and ring-ion heating are compared with theoretical models [Mithaiwala et al. 2010; Crabtree et al., this meeting] and previous simulation results [Winske and Daughton, 2012]. 2D simulations show that when the magnetic field is perpendicular to the wave vector, k, the electrostatic potential fluctuations work in conjunction with the applied magnetic field causing a circular electron E ×B drift around a positively charged center. Similar phenomena are observed in 2D simulations of magnetic-field penetration into a spatially inhomogeneous unmagnetized plasma [Richardson et al., this meeting] where circular paramagnetic vortices are formed. These vortices are altered by the addition of a small, in-plane, component of magnetic field which allows electrons to stream along field lines effectively shorting out one component of the electric field. In this case, the vortex structures are no longer circular but elongated along the direction of the in-plane magnetic field component.

On the interaction of stationary crossflow vortices and Tollmien-Schlichting waves in the boundary layer on a rotating disc

NASA Technical Reports Server (NTRS)

Bassom, Andrew P.; Hall, Philip

1989-01-01

There are many fluid flows where the onset of transition can be caused by different instability mechanisms which compete among themselves. The interaction is considered of two types of instability mode (at an asymptotically large Reynolds number) which can occur in the flow above a rotating disc. In particular, the interaction is examined between lower branch Tollmien-Schlichting (TS) waves and the upper branch, stationary, inviscid crossflow vortex whose asymptotic structure has been described by Hall (1986). This problem is studied in the context of investigating the effect of the vortex on the stability characteristics of a small TS wave. Essentially, it is found that the primary effect is felt through the modification to the mean flow induced by the presence of the vortex. Initially, the TS wave is taken to be linear in character and it is shown (for the cases of both a linear and a nonlinear stationary vortex) that the vortex can exhibit both stabilizing and destabilizing effects on the TS wave and the nature of this influence is wholly dependent upon the orientation of this latter instability. Further, the problem is examined with a larger TS wave, whose size is chosen so as to ensure that this mode is nonlinear in its own right. An amplitude equation for the evolution of the TS wave is derived which admits solutions corresponding to finite amplitude, stable, traveling waves.

Studies of the generation mechanisms of steady vortex formations in the channels of nuclear-power installations for purposes of improving the reliability and safety of their work

NASA Astrophysics Data System (ADS)

Mitrofanova, O.

2017-01-01

The analysis of the results of experimental researches on revealing the mechanisms of vortex formation in channels of complex geometry in the neutral and conductive media is carried out. The directions of researches related to the study of mechanisms of vortex generation and accumulation of energy by large-scale vortex structures are considered for the possibility of predictions of the man-made accidents and catastrophic natural phenomena. The main goal of ongoing investigations is the solution of the task aimed at improving the safety of nuclear power installations and, in particular, of the fast neutron reactors with liquid-metal coolants, and the prevention of emergency modes arising from acoustic, magnetic and hydrodynamic resonance effects.

Collisionless kinetic theory of oblique tearing instabilities

DOE PAGES

Baalrud, S. D.; Bhattacharjee, A.; Daughton, W.

2018-02-15

The linear dispersion relation for collisionless kinetic tearing instabilities is calculated for the Harris equilibrium. In contrast to the conventional 2D geometry, which considers only modes at the center of the current sheet, modes can span the current sheet in 3D. Modes at each resonant surface have a unique angle with respect to the guide field direction. Both kinetic simulations and numerical eigenmode solutions of the linearized Vlasov-Maxwell equations have recently revealed that standard analytic theories vastly overestimate the growth rate of oblique modes. In this paper, we find that this stabilization is associated with the density-gradient-driven diamagnetic drift. Themore » analytic theories miss this drift stabilization because the inner tearing layer broadens at oblique angles sufficiently far that the assumption of scale separation between the inner and outer regions of boundary-layer theory breaks down. The dispersion relation obtained by numerically solving a single second order differential equation is found to approximately capture the drift stabilization predicted by solutions of the full integro-differential eigenvalue problem. Finally, a simple analytic estimate for the stability criterion is provided.« less

Collisionless kinetic theory of oblique tearing instabilities

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

Baalrud, S. D.; Bhattacharjee, A.; Daughton, W.

The linear dispersion relation for collisionless kinetic tearing instabilities is calculated for the Harris equilibrium. In contrast to the conventional 2D geometry, which considers only modes at the center of the current sheet, modes can span the current sheet in 3D. Modes at each resonant surface have a unique angle with respect to the guide field direction. Both kinetic simulations and numerical eigenmode solutions of the linearized Vlasov-Maxwell equations have recently revealed that standard analytic theories vastly overestimate the growth rate of oblique modes. In this paper, we find that this stabilization is associated with the density-gradient-driven diamagnetic drift. Themore » analytic theories miss this drift stabilization because the inner tearing layer broadens at oblique angles sufficiently far that the assumption of scale separation between the inner and outer regions of boundary-layer theory breaks down. The dispersion relation obtained by numerically solving a single second order differential equation is found to approximately capture the drift stabilization predicted by solutions of the full integro-differential eigenvalue problem. Finally, a simple analytic estimate for the stability criterion is provided.« less

Collisionless kinetic theory of oblique tearing instabilities

NASA Astrophysics Data System (ADS)

Baalrud, S. D.; Bhattacharjee, A.; Daughton, W.

2018-02-01

The linear dispersion relation for collisionless kinetic tearing instabilities is calculated for the Harris equilibrium. In contrast to the conventional 2D geometry, which considers only modes at the center of the current sheet, modes can span the current sheet in 3D. Modes at each resonant surface have a unique angle with respect to the guide field direction. Both kinetic simulations and numerical eigenmode solutions of the linearized Vlasov-Maxwell equations have recently revealed that standard analytic theories vastly overestimate the growth rate of oblique modes. We find that this stabilization is associated with the density-gradient-driven diamagnetic drift. The analytic theories miss this drift stabilization because the inner tearing layer broadens at oblique angles sufficiently far that the assumption of scale separation between the inner and outer regions of boundary-layer theory breaks down. The dispersion relation obtained by numerically solving a single second order differential equation is found to approximately capture the drift stabilization predicted by solutions of the full integro-differential eigenvalue problem. A simple analytic estimate for the stability criterion is provided.

Frequency-feature based antistrong-disturbance signal processing method and system for vortex flowmeter with single sensor

NASA Astrophysics Data System (ADS)

Xu, Ke-Jun; Luo, Qing-Lin; Wang, Gang; Liu, San-Shan; Kang, Yi-Bo

2010-07-01

Digital signal processing methods have been applied to vortex flowmeter for extracting the useful information from noisy output of the vortex flow sensor. But these approaches are unavailable when the power of the mechanical vibration noise is larger than that of the vortex flow signal. In order to solve this problem, an antistrong-disturbance signal processing method is proposed based on frequency features of the vortex flow signal and mechanical vibration noise for the vortex flowmeter with single sensor. The frequency bandwidth of the vortex flow signal is different from that of the mechanical vibration noise. The autocorrelation function can represent bandwidth features of the signal and noise. The output of the vortex flow sensor is processed by the spectrum analysis, filtered by bandpass filters, and calculated by autocorrelation function at the fixed delaying time and at τ =0 to obtain ratios. The frequency corresponding to the minimal ratio is regarded as the vortex flow frequency. With an ultralow-power microcontroller, a digital signal processing system is developed to implement the antistrong-disturbance algorithm, and at the same time to ensure low-power and two-wire mode for meeting the requirement of process instrumentation. The water flow-rate calibration and vibration test experiments are conducted, and the experimental results show that both the algorithm and system are effective.

Frequency-feature based antistrong-disturbance signal processing method and system for vortex flowmeter with single sensor.

PubMed

Xu, Ke-Jun; Luo, Qing-Lin; Wang, Gang; Liu, San-Shan; Kang, Yi-Bo

2010-07-01

Digital signal processing methods have been applied to vortex flowmeter for extracting the useful information from noisy output of the vortex flow sensor. But these approaches are unavailable when the power of the mechanical vibration noise is larger than that of the vortex flow signal. In order to solve this problem, an antistrong-disturbance signal processing method is proposed based on frequency features of the vortex flow signal and mechanical vibration noise for the vortex flowmeter with single sensor. The frequency bandwidth of the vortex flow signal is different from that of the mechanical vibration noise. The autocorrelation function can represent bandwidth features of the signal and noise. The output of the vortex flow sensor is processed by the spectrum analysis, filtered by bandpass filters, and calculated by autocorrelation function at the fixed delaying time and at tau=0 to obtain ratios. The frequency corresponding to the minimal ratio is regarded as the vortex flow frequency. With an ultralow-power microcontroller, a digital signal processing system is developed to implement the antistrong-disturbance algorithm, and at the same time to ensure low-power and two-wire mode for meeting the requirement of process instrumentation. The water flow-rate calibration and vibration test experiments are conducted, and the experimental results show that both the algorithm and system are effective.

Instability of vortex pair leapfrogging

NASA Astrophysics Data System (ADS)

Tophøj, Laust; Aref, Hassan

2013-01-01

Leapfrogging is a periodic solution of the four-vortex problem with two positive and two negative point vortices all of the same absolute circulation arranged as co-axial vortex pairs. The set of co-axial motions can be parameterized by the ratio 0 < α < 1 of vortex pair sizes at the time when one pair passes through the other. Leapfrogging occurs for α > σ2, where σ = sqrt{2}-1 is the silver ratio. The motion is known in full analytical detail since the 1877 thesis of Gröbli and a well known 1894 paper by Love. Acheson ["Instability of vortex leapfrogging," Eur. J. Phys. 21, 269-273 (2000)], 10.1088/0143-0807/21/3/310 determined by numerical experiments that leapfrogging is linearly unstable for σ2 < α < 0.382, but apparently stable for larger α. Here we derive a linear system of equations governing small perturbations of the leapfrogging motion. We show that symmetry-breaking perturbations are essentially governed by a 2D linear system with time-periodic coefficients and perform a Floquet analysis. We find transition from linearly unstable to stable leapfrogging at α = ϕ2 ≈ 0.381966, where φ = 1/2(sqrt{5}-1) is the golden ratio. Acheson also suggested that there was a sharp transition between a "disintegration" instability mode, where two pairs fly off to infinity, and a "walkabout" mode, where the vortices depart from leapfrogging but still remain within a finite distance of one another. We show numerically that this transition is more gradual, a result that we relate to earlier investigations of chaotic scattering of vortex pairs [L. Tophøj and H. Aref, "Chaotic scattering of two identical point vortex pairs revisited," Phys. Fluids 20, 093605 (2008)], 10.1063/1.2974830. Both leapfrogging and "walkabout" motions can appear as intermediate states in chaotic scattering at the same values of linear impulse and energy.

Photonic simulation of topological superconductor edge state and zero-energy mode at a vortex

PubMed Central

Tan, Wei; Chen, Liang; Ji, Xia; Lin, Hai-Qing

2014-01-01

Photonic simulations of quantum Hall edge states and topological insulators have inspired considerable interest in recent years. Interestingly, there are theoretical predictions for another type of topological states in topological superconductors, but debates over their experimental observations still remain. Here we investigate the photonic analogue of the px + ipy model of topological superconductor. Two essential characteristics of topological superconductor, particle-hole symmetry and px + ipy pairing potentials, are well emulated in photonic systems. Its topological features are presented by chiral edge state and zero-energy mode at a vortex. This work may fertilize the study of photonic topological states, and open up the possibility for emulating wave behaviors in superconductors. PMID:25488408

Dual mode ion mobility spectrometer and method for ion mobility spectrometry

DOEpatents

Scott, Jill R [Idaho Falls, ID; Dahl, David A [Idaho Falls, ID; Miller, Carla J [Idaho Falls, ID; Tremblay, Paul L [Idaho Falls, ID; McJunkin, Timothy R [Idaho Falls, ID

2007-08-21

Ion mobility spectrometer apparatus may include an ion interface that is operable to hold positive and negative ions and to simultaneously release positive and negative ions through respective positive and negative ion ports. A first drift chamber is operatively associated with the positive ion port of the ion interface and encloses an electric field therein. A first ion detector operatively associated with the first drift chamber detects positive ions from the first drift chamber. A second drift chamber is operatively associated with the negative ion port of the ion interface and encloses an electric field therein. A second ion detector operatively associated with the second drift chamber detects negative ions from said second drift chamber.

Tempest in a glass tube: A helical vortex formation in a complex plasma

NASA Astrophysics Data System (ADS)

Saitou, Yoshifumi; Ishihara, Osamu; Ishihara

2014-12-01

A collective behavior of dust particles in a complex plasma with a magnetic field (up to 4 kG) is investigated. Dust particles form a dust disk which is rotating in a horizontal plane pushed by ions rotating with the E × B drift as a trigger force. The thickness of the disk is determined by controlling the experimental conditions. The disk rotates in a horizontal plane and forms a two-dimensional thin structure when the pressure pAr is relatively high. The dust particles are ejected from near the disk center and form a rotation in the vertical plane and, hence, forms a helical vortex when the disk is thick for relatively low pAr . The reason the dust disk has the different thickness is due to the neutral pressure. Under a higher (lower) neutral gas pressure, the disk becomes two (three) dimensional due to the influence of the neutral drag force.

Clog Retard of a Vortex Throttle Joule-Thomson Cryocooler: Further Experimental Verification

NASA Astrophysics Data System (ADS)

Maytal, B.-Z.

2010-04-01

The demand of high purity gas supply for Joule-Thomson cryocoolers and liquefiers is crucial in order to avoid plug formation at the delicate throttling device. A throttle which would tolerate higher level of contamination is greatly desirable for more reliable operation. The vortex throttle has such a potential. A series of vortex throttles were applied to a miniature Joule-Thomson cryocooler and tested with precisely contaminated coolant. The instantaneous flow rate and the mode of its decay indicate the rate and nature of plug formation. Each experiment was a simultaneous run of two cryocoolers in parallel at similar conditions: one with a traditional throttle of short hole, and the other one with the vortex throttle. The clog retard behavior of the vortex throttle was verified. It runs about 2.5 times longer than the traditional one, while being fed by water vapor contaminated nitrogen at the levels of 5 and 17 PPM. The contamination level by carbon dioxide was 80 PPM and exhibited a different behavior of clog formation. Its effect on the cryocooler temperature stability with the vortex throttle was quite minor.

Fundamental Processes in Plasmas

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

Driscoll, Charles Fred

This Final Technical Report gives brief summaries of the plasma physics results developed under DOE grant DE-SC0002451; and provides reference to the published journal articles giving full scientific descriptions. General topics include 1) cyclotron modes; 2) damping and decay of Langmuir modes; 3) 2D vortex dynamics and diocotron modes; 4) separatrix-induced transport and damping; and 5) long-range collisional velocity slowing.

Final report: Mapping Interactions in Hybrid Systems with Active Scanning Probes

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

Berezovsky, Jesse

2017-09-29

This project aimed to study and map interactions between components of hybrid nanodevices using a novel scanning probe approach. To enable this work, we initially constructed a flexible experimental apparatus allowing for simultaneous scanning probe and confocal optical microscopy measurements. This setup was first used for all-optical measurements of nanostructures, with the focus then shifting to hybrid devices in which single coherent electron spins are coupled to micron-scale ferromagnetic elements, which may prove useful for addressing single spins, enhanced sensing, or spin-wave-mediated coupling of spins for quantum information applications. A significant breakthrough was the realization that it is not necessarymore » to fabricate a magnetic structure on a scanning probe – instead a ferromagnetic vortex core can act as an integrated, solid state, scanning probe. The core of the vortex produces a very strong, localized fringe field which can be used analogously to an MFM tip. Unlike a traditional MFM tip, however, the vortex core is scanned within an integrated device (eliminating drift), and can be moved on vastly faster timescales. This approach allows the detailed investigation of interactions between single spins and complex driven ferromagnetic dynamics.« less

Single-mode 140 nm swept light source realized by using SSG-DBR lasers

NASA Astrophysics Data System (ADS)

Fujiwara, N.; Yoshimura, R.; Kato, K.; Ishii, H.; Kano, F.; Kawaguchi, Y.; Kondo, Y.; Ohbayashi, K.; Oohashi, H.

2008-02-01

We demonstrate a single-mode and fast wavelength swept light source by using Superestrucuture grating distributed Bragg reflector (SSG-DBR) lasers for use in optical frequency-domain reflectometry optical coherence tomography. The SSG-DBR lasers provide single-mode operation resulting in high coherency. Response of the wavelength tuning is very fast; several nanoseconds, but there was an unintentional wavelength drift resulting from a thermal drift due to injecting tuning current. The dri1ft unfortunately requires long time to converge; more than a few milliseconds. For suppressing the wavelength drift, we introduced Thermal Drift Compensation mesa (TDC) parallel to the laser mesa with the spacing of 20 μm. By controlling TDC current to satisfy the total electric power injected into both the laser mesa and the TDC mesa, the thermal drift can be suppressed. In the present work, we fabricated 4 wavelength's kinds of SSG-DBR laser, which covers respective wavelength band; S-band (1496-1529 nm), C-band (1529-1564 nm), L --band (1564-1601 nm), and L +-band (1601-1639). We set the frequency channel of each laser with the spacing 6.25 GHz and 700 channels. The total frequency channel number is 2800 channels (700 ch × 4 lasers). We simultaneously operated the 4 lasers with a time interval of 500 ns/channel. A wavelength tuning range of more than 140 nm was achieved within 350 μs. The output power was controlled to be 10 mW for all channels. A single-mode, accurate, wide, and fast wavelength sweep was demonstrated with the SSG-DBR lasers having TDC mesa structure for the first time.

Transmission characteristics of Bessel-Gaussian vortex beams propagating along both longitudinal and transverse directions in a subway tunnel

NASA Astrophysics Data System (ADS)

Wang, Xiaohui; Song, Yingxiong

2018-02-01

By exploiting the non-Kolmogorov model and Rytov approximation theory, a propagation model of Bessel-Gaussian vortex beams (BGVB) propagating in a subway tunnel is derived. Based on the propagation model, a model of orbital angular momentum (OAM) mode probability distribution is established to evaluate the propagation performance when the beam propagates along both longitudinal and transverse directions in the subway tunnel. By numerical simulations and experimental verifications, the influences of the various parameters of BGVB and turbulence on the OAM mode probability distribution are evaluated, and the results of simulations are consistent with the experimental statistics. The results verify that the middle area of turbulence is more beneficial for the vortex beam propagation than the edge; when the BGVB propagates along the longitudinal direction in the subway tunnel, the effects of turbulence on the OAM mode probability distribution can be decreased by selecting a larger anisotropy parameter, smaller coherence length, larger non-Kolmogorov power spectrum coefficient, smaller topological charge number, deeper subway tunnel, lower train speed, and longer wavelength. When the BGVB propagates along the transverse direction, the influences can be also mitigated by adopting a larger topological charge number, less non-Kolmogorov power spectrum coefficient, smaller refractive structure index, shorter wavelength, and shorter propagation distance.

Crossbar H-mode drift-tube linac design with alternative phase focusing for muon linac

NASA Astrophysics Data System (ADS)

Otani, M.; Futatsukawa, K.; Hasegawa, K.; Kitamura, R.; Kondo, Y.; Kurennoy, S.

2017-07-01

We have developed a Crossbar H-mode (CH) drift-tube linac (DTL) design with an alternative phase focusing (APF) scheme for a muon linac, in order to measure the anomalous magnetic moment and electric dipole moment (EDM) of muons at the Japan Proton Accelerator Research Complex (J-PARC). The CH-DTL accelerates muons from β = v/c = 0.08 to 0.28 at an operational frequency of 324 MHz. The design and results are described in this paper.

Vortex shedding from obstacles: theoretical frequency prediction

NASA Astrophysics Data System (ADS)

Pier, Benoît

2001-11-01

The existence of self-sustained oscillations in spatially developing systems is closely related to the presence of a locally absolutely unstable region. A recent investigation of a ``synthetic wake'' (a wake with no solid obstacle and no reverse flow region) has proved [Pier and Huerre, J. Fluid Mech. 435, 145 (2001)] that the observed Kármán vortex street is a nonlinear elephant global mode. The same criterion is now shown to hold for real obstacles. Local properties are derived from the unperturbed basic flow computed by enforcing a symmetry condition on the central line. Application of the theoretical criterion then yields the expected Strouhal vortex shedding frequency. The thus predicted frequency is in excellent agreement with direct numerical simulations of the complete flow. The use of the frequency selection mechanism to control the vortex shedding will also be discussed.

Transport of light, trace impurities in Alcator C-Mod

NASA Astrophysics Data System (ADS)

Rowan, W. L.; Bespamyatnov, I. O.; Liao, K. T.; Horton, W.; Fu, X. R.; Hughes, J. W.

2012-10-01

Light impurity profiles for boron were measured in ITB, H-mode, L-mode, and I-mode discharges in Alcator C-Mod. Within this wide range of modes, the profiles varied from peaked to hollow to flat. Specifically, hollow profiles are often observed in H-mode, while ITBs produce strong peaking, and L-mode produces moderate peaking. I-mode discharges are characterized by flat impurity profiles. For the study reported here, the profiles were measured with charge exchange recombination spectroscopy. The dependences of Rv/D were sought on dimensionless quantities including ion density scale length, effective charge, collisionality, and temperature scale length. We find that neoclassical transport consistently underestimates the measured transport. The excess measured transport is assumed to be turbulent. The strongest dependence of Rv/D is with temperature scale length. In addition, the measured transport was compared with the prediction of an analytical theory of drift wave turbulence that identifies transport implications for drift waves driven by ion and impurity density gradients.

Student-Teacher-Researcher Collaboration through NOAA's Adopt A Drifter Program

NASA Astrophysics Data System (ADS)

Stanitski, D.; Cronin, M. F.; Malan, N.; Ansorge, I. J.; Beal, L. M.; Hermes, J. C.; Lumpkin, R.; Dolk, S.

2016-02-01

NOAA scientists and students in South Africa and the USA performed oceanographic experiments by deploying two surface drifting buoys in the Agulhas Current east of South Africa with the intent to determine the direction and path of each drifter's movement. The drifters were provided by the Global Drifter Program and the education component supported by the NOAA Adopt A Drifter Program (ADP). In a "surface dispersion" experiment, students in the classes that co-adopted the pair of surface drifters developed hypotheses about the drifters' paths, including whether they might drift into the Atlantic, Indian, Southern, or Pacific Oceans. They hypothesized why, when, and where the two drifters would separate. As part of the ADP, the collaborating schools tracked the drifters together via the internet. Several months after the drifters were deployed, a NOAA researcher discussed the surprising results with the collaborating students and teachers, including K-12 school children in George, Western Cape and Mossel Bay, South Africa and Bethesda, Maryland USA. One drifter pair had an interesting path. Although deployed in the center of the Agulhas Current, the pair became entrained in a submesoscale cyclonic vortex that formed as the jet flowed across the continental shelf break. The submesoscale vortex (with the drifter pair) then separated from the jet and leaked into the Atlantic Ocean. The eddy was visible in high-resolution satellite images of the sea surface temperature, but was not resolved in satellite altimetry fields. As discussed in a paper led by University of Cape Town graduate student Neil Malan currently under review, this implies that estimates of Agulhas leakage may be underestimated as they do not include this new pathway provided by submesoscale cyclonic vortices. Data from the adopted drifting buoys contribute to the Global Drifter Program, a component of the Global Ocean Observing System, and can be viewed from the NOAA Adopt a Drifter Program tracking page.

Interaction of N-vortex structures in a continuum, including atmosphere, hydrosphere and plasma

NASA Astrophysics Data System (ADS)

Belashov, Vasily Yu.

2017-10-01

The results of analysis and numerical simulation of evolution and interaction of the N-vortex structures of various configuration and different vorticities in the continuum including atmosphere, hydrosphere and plasma are presented. It is found that in dependence on initial conditions the regimes of weak interaction with quasi-stationary evolution and active interaction with the "phase intermixing", when the evolution can lead to formation of complex forms of vorticity regions, are realized in the N-vortex systems. For the 2-vortex interaction the generalized critical parameter determining qualitative character of interaction of vortices is introduced. It is shown that for given initial conditions its value divides modes of active interaction and quasi-stationary evolution. The results of simulation of evolution and interaction of the two-dimensional and three-dimensional vortex structures, including such phenomena as dynamics of the atmospheric synoptic vortices of cyclonic types and tornado, hydrodynamic 4-vortex interaction and also interaction in the systems of a type of "hydrodynamic vortex - dust particles" are presented. The applications of undertaken approach to the problems of such plasma systems as streams of charged particles in a uniform magnetic field B and plasma clouds in the ionosphere are considered. It is shown that the results obtained have obvious applications in studies of the dynamics of the vortex structures dynamics in atmosphere, hydrosphere and plasma.

On sharp vorticity gradients in elongating baroclinic eddies and their stabilization with a solid-body rotation

NASA Astrophysics Data System (ADS)

Sutyrin, Georgi G.

2016-06-01

Wide compensated vortices are not able to remain circular in idealized two-layer models unless the ocean depth is assumed to be unrealistically large. Small perturbations on both cyclonic and anticyclonic eddies grow slower if a middle layer with uniform potential vorticity (PV) is added, owing to a weakening of the vertical coupling between the upper and lower layers and a reduction of the PV gradient in the deep layer. Numerical simulations show that the nonlinear development of the most unstable elliptical mode causes self-elongation of the upper vortex core and splitting of the deep PV anomaly into two corotating parts. The emerging tripolar flow pattern in the lower layer results in self-intensification of the fluid rotation in the water column around the vortex center. Further vortex evolution depends on the model parameters and initial conditions, which limits predictability owing to multiple equilibrium attractors existing in the dynamical system. The vortex core strips thin filaments, which roll up into submesoscale vortices to result in substantial mixing at the vortex periphery. Stirring and damping of vorticity by bottom friction are found to be essential for subsequent vortex stabilization. The development of sharp PV gradients leads to nearly solid-body rotation inside the vortex core and formation of transport barriers at the vortex periphery. These processes have important implications for understanding the longevity of real-ocean eddies.

Dynamics of Isolated Tip Vortex Cavitation

NASA Astrophysics Data System (ADS)

Pennings, Pepijn; Bosschers, Johan; van Terwisga, Tom

2014-11-01

Performance of ship propellers and comfort levels in the surroundings are limited by various forms of cavitation. Amongst these forms tip vortex cavitation is one of the first appearing forms and is expected to be mainly responsible for the emission of broadband pressure fluctuations typically occurring between the 4th to the 7th blade passing frequency (approx. 40--70 Hz). These radiated pressure pulses are likely to excite parts of the hull structure resulting in a design compromise between efficiency and comfort. Insight is needed in the mechanism of acoustic emission from the oscillations by a tip vortex cavity. In the current experimental study the tip vortex cavity from a blade with an elliptic planform and sections based on NACA 662 - 415 with meanline a = 0 . 8 is observed using high speed shadowgraphy in combination with blade force and acoustic measurements. An analytic model describing three main cavity deformation modes is verified and used to explain the origin of a cavity eigenfrequency or ``vortex singing'' phenomenon observed by Maines and Arndt (1997) on the tip vortex cavity originating from the same blade. As no hydrodynamic sound originating from the tip vortex cavity was observed it is posed that a tip flow instability is essential for ``vortex singing.'' This research was funded by the Lloyd's Register Foundation as part of the International Institute for Cavitation Research.

Dynamics of the vortex wakes of flying and swimming vertebrates.

PubMed

Rayner, J M

1995-01-01

The vortex wakes of flying and swimming animals provide evidence of the history of aero- and hydrodynamic force generation during the locomotor cycle. Vortex-induced momentum flux in the wake is the reaction of forces the animal imposes on its environment, which must be in equilibrium with inertial and external forces. In flying birds and bats, the flapping wings generate lift both to provide thrust and to support the weight. Distinct wingbeat and wake movement patterns can be identified as gaits. In flow visualization experiments, only two wake patterns have been identified: a vortex ring gait with inactive upstroke, and a continuous vortex gait with active upstroke. These gaits may be modelled theoretically by free vortex and lifting line theory to predict mechanical energy consumption, aerodynamic forces and muscle activity. Longer-winged birds undergo a distinct gait change with speed, but shorter-winged species use the vortex ring gait at all speeds. In swimming fish, the situation is more complex: the wake vortices form a reversed von Kármán vortex street, but little is known about the mechanism of generation of the wake, or about how it varies with speed and acceleration or with body form and swimming mode. An unresolved complicating factor is the interaction between the drag wake of the flapping fish body and the thrusting wake from the tail.

Experimental Study of the Richtmyer-Meshkov Instability of Incompressible Fluids

NASA Technical Reports Server (NTRS)

Niederhaus, Charles; Jacobs, Jeffrey W.

2002-01-01

The Richtmyer-Meshkov instability of a low Atwood number, miscible, two-liquid system is investigated experimentally. The initially stratified fluids are contained within a rectangular tank mounted to a sled that rides on a vertical set of rails. The instability is generated by dropping the sled onto a coil spring, producing a nearly impulsive upward acceleration. The subsequent freefall that occurs as the container travels upward and then downward on the rails allows the instability to evolve in the absence of gravity. The interface separating the two liquids initially has a well-defined, sinusoidal perturbation that quickly inverts and then grows in amplitude after undergoing the impulsive acceleration. Disturbance amplitudes are measured and compared to theoretical predictions. Linear stability theory gives excellent agreement with the measured initial growth rate, a(sub 0), for single-mode perturbations with the predicted amplitudes differing by less than 10% from experimental measurements up to a nondimensional time ka(sub 0)t = 0.7, where k is the wavenumber. Linear stability theory also provides excellent agreement for the individual mode amplitudes of multi-mode initial perturbations up until the interface becomes multi-valued. Comparison with previously published weakly nonlinear single-mode models shows good agreement up to ka(sub 0)t = 3, while published nonlinear single-mode models provide good agreement up to ka(sub 0)t = 30. The effects of Reynolds number on the vortex core evolution and overall growth rate of the interface are also investigated. Measurements of the overall amplitude are found to be unaffected by the Reynolds number for the range of values studied here. However, experiments carried out at lower values of Reynolds numbers were found to have decreased vortex core rotation rates. In addition, an instability in the vortex cores is observed.

Experiments on two- and three-dimensional vortex flows in lid-driven cavities

NASA Astrophysics Data System (ADS)

Siegmann-Hegerfeld, Tanja; Albensoeder, Stefan; Kuhlmann, Hendrik C.

2009-11-01

Vortex flows in one-sided lid-driven cavities with different cross-sectional aspect ratios (γ = 0.26 up to γ = 6.3) are investigated experimentally. In all cases the spanwise aspect ratio λ>>γ is very large and much larger than most previous experiments. Flow-structure visualizations will be presented together with quantitative LDA and PIV measurements. The experimental results are in good agreement with the critical data from numerical stability analyses and with nonlinear simulations. Experimentally, we find four different three-dimensional instabilities. Particular attention is paid to the so-called C4 mode which arises at large cross-sectional aspect ratios. When the spanwise aspect ratio is small the first bifurcation of the C4 mode is strongly imperfect.

Probing the Cold Dust Emission in the AB Aur Disk: A Dust Trap in a Decaying Vortex?

PubMed

Fuente, Asunción; Baruteau, Clément; Neri, Roberto; Carmona, Andrés; Agúndez, Marcelino; Goicoechea, Javier R; Bachiller, Rafael; Cernicharo, José; Berné, Olivier

2017-09-01

One serious challenge for planet formation is the rapid inward drift of pebble-sized dust particles in protoplanetary disks. Dust trapping at local maxima in the disk gas pressure has received much theoretical attention but still lacks observational support. The cold dust emission in the AB Aur disk forms an asymmetric ring at a radius of about 120 au, which is suggestive of dust trapping in a gas vortex. We present high spatial resolution (0".58×0".78 ≈ 80×110 au) NOEMA observations of the 1.12 mm and 2.22 mm dust continuum emission from the AB Aur disk. Significant azimuthal variations of the flux ratio at both wavelengths indicate a size segregation of the large dust particles along the ring. Our continuum images also show that the intensity variations along the ring are smaller at 2.22 mm than at 1.12 mm, contrary to what dust trapping models with a gas vortex have predicted. Our two-fluid (gas+dust) hydrodynamical simulations demonstrate that this feature is well explained if the gas vortex has started to decay due to turbulent diffusion, and dust particles are thus losing the azimuthal trapping on different timescales depending on their size. The comparison between our observations and simulations allows us to constrain the size distribution and the total mass of solid particles in the ring, which we find to be of the order of 30 Earth masses, enough to form future rocky planets.

Interpretations of the impact of cross-field drifts on divertor flows in DIII-D with UEDGE

DOE PAGES

Jaervinen, Aaro E.; Allen, Steve L.; Groth, Mathias; ...

2017-01-27

Simulations using the multi-fluid code UEDGE indicates that, in low confinement (Lmode) plasmas in DIII-D, recycling driven flows dominate poloidal particle flows in the divertor, whereas E×B drift flows dominate the radial particle flows. In contrast, in high confinement (H-mode) conditions E×B drift flows dominate both poloidal and radial particle flows in the divertor. UEDGE indicates that the toroidal C 2+ flow velocities in the divertor plasma are entrained within 30% to the background deuterium flow in both Land H-mode plasmas in the plasma region where the CIII 465 nm emission is measured. Therefore, UEDGE indicates that the Carbon Dopplermore » Coherence Imaging System (CIS), measuring the toroidal velocity of the C 2+ ions, can provide insight to the deuterium flows in the divertor. Parallel-to-B velocity dominates the toroidal divertor flow; direct drift impact being less than 1%. Toroidal divertor flow is predicted to reverse when the magnetic field is reversed. This is explained by the parallel-B flow towards the nearest divertor plate corresponding to opposite toroidal directions in opposite toroidal field configurations. Due to strong poloidal E×B flows in H-mode, net poloidal particle transport can be in opposite direction than the poloidal component of the parallel-B plasma flow.« less

Real fuel effects on flame extinction and re-ignition

NASA Astrophysics Data System (ADS)

Zhao, Xinyu; Wu, Bifen; Xu, Chao; Lu, Tianfeng; Chen, Jacqueline H.

2016-11-01

Flame-vortex interactions have significant implications in studying combustion in practical aeronautical engines, and can be used to facilitate the model development in capturing local extinction and re-ignition. To study the interactions between the complex fuel and the intense turbulence that are commonly encountered in engines, direct numerical simulations of the interactions between a flame and a vortex pair are carried out using a recently-developed 24-species reduced chemistry for n-dodecane. Both non-premixed and premixed flames with different initial and inlet thermochemical conditions are studied. Parametric studies of different vortex strengths and orientations are carried out to induce maximum local extinction and re-ignition. Chemical-explosive-mode-analysis based flame diagnostic tools are used to identify different modes of combustion, including auto-ignition and extinction. Results obtained from the reduced chemistry are compared with those obtained from one-step chemistry to quantify the effect of fuel pyrolysis on the extinction limit. Effects of flame curvature, heat loss and unsteadiness on flame extinction are also explored. Finally, the validity of current turbulent combustion models to capture the local extinction and re-ignition will be discussed.

Glassy vortex behavior in superconducting SrPd2Ge2 single crystals

NASA Astrophysics Data System (ADS)

Sung, N. H.; Jo, Y. J.; Cho, B. K.

2012-07-01

In this study we report the vortex-glass behavior of superconducting ternary germanide SrPd2Ge2 single crystals with a ThCr2Si2-type structure. We observed flux trapping and its nonexponential decay with time after the magnetic field was turned off at T = 2 K. In addition, we found that the diamagnetism in the zero field cooling (ZFC) mode below Tc was irreversible, depending on the temperature and field history, whereas the diamagnetism in the field-cooled warming (FCW) mode was reversible if the applied magnetic field was parallel to the c-axis. An irreversibility line Tr(H) was determined by the ZFC and FCW measurements at various magnetic fields, and the temperature dependence of Tr(H) was found to agree with the de Almeida-Thouless relation, H = H0[1-Tr(H)/Tc(0)]γ, where γ = 3/2. Including these vortex-glass behaviors, we discuss the critical current density, Jc(T), determined from isothermal magnetization measurements at various temperatures, and the pinning potential, determined from the slope of an Arrhenius plot, lnR(T,B) versus 1/T.

Transverse angular momentum in topological photonic crystals

NASA Astrophysics Data System (ADS)

Deng, Wei-Min; Chen, Xiao-Dong; Zhao, Fu-Li; Dong, Jian-Wen

2018-01-01

Engineering local angular momentum of structured light fields in real space enables applications in many fields, in particular, the realization of unidirectional robust transport in topological photonic crystals with a non-trivial Berry vortex in momentum space. Here, we show transverse angular momentum modes in silicon topological photonic crystals when considering transverse electric polarization. Excited by a chiral external source with either transverse spin angular momentum or transverse phase vortex, robust light flow propagating along opposite directions is observed in several kinds of sharp-turn interfaces between two topologically-distinct silicon photonic crystals. A transverse orbital angular momentum mode with alternating phase vortex exists at the boundary of two such photonic crystals. In addition, unidirectional transport is robust to the working frequency even when the ring size or location of the pseudo-spin source varies in a certain range, leading to the superiority of the broadband photonic device. These findings enable one to make use of transverse angular momentum, a kind of degree of freedom, to achieve unidirectional robust transport in the telecom region and other potential applications in integrated photonic circuits, such as on-chip robust delay lines.

Electromigration-Induced Surface Drift and Slit Propagation in Polycrystalline Interconnects: Insights from Phase-Field Simulations

NASA Astrophysics Data System (ADS)

Mukherjee, Arnab; Ankit, Kumar; Selzer, Michael; Nestler, Britta

2018-04-01

We employ the phase-field method to assess electromigration (EM) damage in wide polycrystalline interconnects due to grain-boundary grooving. An interplay of surface and grain-boundary diffusion is shown to drastically influence the mode of progressive EM damage. Rapid atomic transport along the surface leads to shape-preserving surface drift reminiscent of Blech drift-velocity experiments. On the other hand, a comparatively faster grain-boundary transport localizes the damage, resulting in the proliferation of intergranular slits with a shape-preserving tip. At steady state, the two regimes exhibit exponents of 1 and 3 /2 , respectively, in Black's law. While surface drift obeys an inverse scaling with grain size, slits exhibit a direct relationship at small sizes, with the dependence becoming weaker at larger ones. Furthermore, we explain the influence of curvature- or EM-mediated healing fluxes running along the surface on groove replenishment. Insights derived from phase-field simulations of EM in bicrystals are extended to investigate the multiphysics of mixed-mode damage of a polycrystalline interconnect line that is characterized by a drift of small grain surfaces, slit propagation, and coarsening. The triple and quadruple junctions are identified as prominent sites of failure.

Theoretical study of the effect of pump wavelength drift on mode instability in a high-power fiber amplifier

NASA Astrophysics Data System (ADS)

Liu, Yakun; Tao, Rumao; Su, Rongtao; Wang, Xiaolin; Ma, Pengfei; Zhang, Hanwei; Zhou, Pu; Si, Lei

2018-04-01

This paper presents an investigation of the effect of pump wavelength drift on the threshold of mode instability (MI) in high-power ytterbium-doped fiber lasers. By using a semi-analytical model, we study the effects of pump wavelength drift with a central pump wavelength around 976 nm and 915 nm, respectively. The influences of the pump absorption coefficient and total pump absorption are considered simultaneously. The results indicate that the effect of pump wavelength drift around 976 nm is stronger than that around 915 nm. For more efficient suppression of MI by shifting the pump wavelength, efficient absorption of pump power is required. The MI thresholds for fibers with different total pump absorptions and cladding diameters are compared. When the total pump absorption is increased, the gain saturation is enhanced, which results in the MI being mitigated more effectively and being more sensitive to pump wavelength drift. The MI threshold in gain fibers with larger inner cladding diameter is higher but more dependent upon pump wavelength. The results of this work can help in optimizing the pump wavelength and fiber parameters and suppressing MI in high-power fiber lasers.

Generating and Separating Twisted Light by gradient-rotation Split-Ring Antenna Metasurfaces.

PubMed

Zeng, Jinwei; Li, Ling; Yang, Xiaodong; Gao, Jie

2016-05-11

Nanoscale compact optical vortex generators promise substantially significant prospects in modern optics and photonics, leading to many advances in sensing, imaging, quantum communication, and optical manipulation. However, conventional vortex generators often suffer from bulky size, low vortex mode purity in the converted beam, or limited operation bandwidth. Here, we design and demonstrate gradient-rotation split-ring antenna metasurfaces as unique spin-to-orbital angular momentum beam converters to simultaneously generate and separate pure optical vortices in a broad wavelength range. Our proposed design has the potential for realizing miniaturized on-chip OAM-multiplexers, as well as enabling new types of metasurface devices for the manipulation of complex structured light beams.

Temporal genetic structure in a poecilogonous polychaete: the interplay of developmental mode and environmental stochasticity

PubMed Central

2014-01-01

Background Temporal variation in the genetic structure of populations can be caused by multiple factors, including natural selection, stochastic environmental variation, migration, or genetic drift. In benthic marine species, the developmental mode of larvae may indicate a possibility for temporal genetic variation: species with dispersive planktonic larvae are expected to be more likely to show temporal genetic variation than species with benthic or brooded non-dispersive larvae, due to differences in larval mortality and dispersal ability. We examined temporal genetic structure in populations of Pygospio elegans, a poecilogonous polychaete with within-species variation in developmental mode. P. elegans produces either planktonic, benthic, or intermediate larvae, varying both among and within populations, providing a within-species test of the generality of a relationship between temporal genetic variation and larval developmental mode. Results In contrast to our expectations, our microsatellite analyses of P. elegans revealed temporal genetic stability in the UK population with planktonic larvae, whereas there was variation indicative of drift in temporal samples of the populations from the Baltic Sea, which have predominantly benthic and intermediate larvae. We also detected temporal variation in relatedness within these populations. A large temporal shift in genetic structure was detected in a population from the Netherlands, having multiple developmental modes. This shift could have been caused by local extiction due to extreme environmental conditions and (re)colonization by planktonic larvae from neighboring populations. Conclusions In our study of P. elegans, temporal genetic variation appears to be due to not only larval developmental mode, but also the stochastic environment of adults. Large temporal genetic shifts may be more likely in marine intertidal habitats (e.g. North Sea and Wadden Sea) which are more prone to environmental stochasticity than the sub-tidal Baltic habitats. Sub-tidal and/or brackish (less saline) habitats may support smaller P. elegans populations and these may be more susceptible to the effects of random genetic drift. Moreover, higher frequencies of asexual reproduction and the benthic larval developmental mode in these populations leads to higher relatedness and contributes to drift. Our results indicate that a general relationship between larval developmental mode and temporal genetic variation may not exist. PMID:24447386

Temporal genetic structure in a poecilogonous polychaete: the interplay of developmental mode and environmental stochasticity.

PubMed

Kesäniemi, Jenni E; Mustonen, Marina; Boström, Christoffer; Hansen, Benni W; Knott, K Emily

2014-01-22

Temporal variation in the genetic structure of populations can be caused by multiple factors, including natural selection, stochastic environmental variation, migration, or genetic drift. In benthic marine species, the developmental mode of larvae may indicate a possibility for temporal genetic variation: species with dispersive planktonic larvae are expected to be more likely to show temporal genetic variation than species with benthic or brooded non-dispersive larvae, due to differences in larval mortality and dispersal ability. We examined temporal genetic structure in populations of Pygospio elegans, a poecilogonous polychaete with within-species variation in developmental mode. P. elegans produces either planktonic, benthic, or intermediate larvae, varying both among and within populations, providing a within-species test of the generality of a relationship between temporal genetic variation and larval developmental mode. In contrast to our expectations, our microsatellite analyses of P. elegans revealed temporal genetic stability in the UK population with planktonic larvae, whereas there was variation indicative of drift in temporal samples of the populations from the Baltic Sea, which have predominantly benthic and intermediate larvae. We also detected temporal variation in relatedness within these populations. A large temporal shift in genetic structure was detected in a population from the Netherlands, having multiple developmental modes. This shift could have been caused by local extiction due to extreme environmental conditions and (re)colonization by planktonic larvae from neighboring populations. In our study of P. elegans, temporal genetic variation appears to be due to not only larval developmental mode, but also the stochastic environment of adults. Large temporal genetic shifts may be more likely in marine intertidal habitats (e.g. North Sea and Wadden Sea) which are more prone to environmental stochasticity than the sub-tidal Baltic habitats. Sub-tidal and/or brackish (less saline) habitats may support smaller P. elegans populations and these may be more susceptible to the effects of random genetic drift. Moreover, higher frequencies of asexual reproduction and the benthic larval developmental mode in these populations leads to higher relatedness and contributes to drift. Our results indicate that a general relationship between larval developmental mode and temporal genetic variation may not exist.

Tunable orbital angular momentum mode filter based on optical geometric transformation.

PubMed

Huang, Hao; Ren, Yongxiong; Xie, Guodong; Yan, Yan; Yue, Yang; Ahmed, Nisar; Lavery, Martin P J; Padgett, Miles J; Dolinar, Sam; Tur, Moshe; Willner, Alan E

2014-03-15

We present a tunable mode filter for spatially multiplexed laser beams carrying orbital angular momentum (OAM). The filter comprises an optical geometric transformation-based OAM mode sorter and a spatial light modulator (SLM). The programmable SLM can selectively control the passing/blocking of each input OAM beam. We experimentally demonstrate tunable filtering of one or multiple OAM modes from four multiplexed input OAM modes with vortex charge of ℓ=-9, -4, +4, and +9. The measured output power suppression ratio of the propagated modes to the blocked modes exceeds 14.5 dB.

Flow Control

DTIC Science & Technology

2013-04-08

fined as p( xs , t), to the flow state which is modeled by the time coefficients of a POD truncation (a fj (t) in equation 17) (Note: the f superscript...spatially to desired flow features (e.g. vortex shedding, vortex pairing, boundary layer growth, separation points, etc.) are chosen and defined as ( xs ...within the numeric simulation. A surface POD analysis, p( xs , t)≃ k ∑ p=1 asp(t)ϕsp( xs ), (30) yields surface POD modes φ sp( xs ). The resulting

Tripolar vortex formation in dense quantum plasma with ion-temperature-gradients

NASA Astrophysics Data System (ADS)

Qamar, Anisa; Ata-ur-Rahman, Mirza, Arshad M.

2012-05-01

We have derived system of nonlinear equations governing the dynamics of low-frequency electrostatic toroidal ion-temperature-gradient mode for dense quantum magnetoplasma. For some specific profiles of the equilibrium density, temperature, and ion velocity gradients, the nonlinear equations admit a stationary solution in the form of a tripolar vortex. These results are relevant to understand nonlinear structure formation in dense quantum plasmas in the presence of equilibrium ion-temperature and density gradients.

Burst-mode manipulation of magnonic vortex crystals

NASA Astrophysics Data System (ADS)

Hänze, Max; Adolff, Christian F.; Weigand, Markus; Meier, Guido

2015-03-01

The manipulation of polarization states in 4 ×4 vortex crystals using sinusoidal magnetic field bursts is investigated by means of a broadband ferromagnetic-resonance setup. Magnetic field excitation with the proper amplitude and frequency allows tuning different polarization states, which are observed in the measured absorption spectra. The variation of the sinusoidal burst width consecutively identifies the time scale of the underlying process. A memorylike polarization state writing process is demonstrated on the submicrosecond time scale.

Mesoscale spiral vortex embedded within a Lake Michigan snow squall band - High resolution satellite observations and numerical model simulations

NASA Technical Reports Server (NTRS)

Lyons, Walter A.; Keen, Cecil S.; Hjelmfelt, Mark; Pease, Steven R.

1988-01-01

It is known that Great Lakes snow squall convection occurs in a variety of different modes depending on various factors such as air-water temperature contrast, boundary-layer wind shear, and geostrophic wind direction. An exceptional and often neglected source of data for mesoscale cloud studies is the ultrahigh resolution multispectral data produced by Landsat satellites. On October 19, 1972, a clearly defined spiral vortex was noted in a Landsat-1 image near the southern end of Lake Michigan during an exceptionally early cold air outbreak over a still very warm lake. In a numerical simulation using a three-dimensional Eulerian hydrostatic primitive equation mesoscale model with an initially uniform wind field, a definite analog to the observed vortex was generated. This suggests that intense surface heating can be a principal cause in the development of a low-level mesoscale vortex.

Experimental study of the velocity field on a delta wing

NASA Technical Reports Server (NTRS)

Payne, F. M.; Ng, T. T.; Nelson, R. C.

1987-01-01

An experimental study of the leading edge vortices on delta wings at large angles of incidence is presented. A combination of flow visualization, seven-hole pressure probe surveys and laser velocimeter measurements were used to study the leading edge vortex formation and breakdown for a set of delta wings. The delta wing models were thin flat plates with sharp leading edges having sweep angles of 70, 75, 80, and 85 degrees. The flow structure was examined for angles of incidence from 10 to 40 degrees and chord Reynolds numbers from 85,000 to 640,000. Vortex breakdown was observed on all the wings tested. Both bubble and spiral modes of breakdown were observed. The visualization and wake survey data shows that when vortex breakdown occurs the core flow transforms abruptly from a jet-like flow to a wake-like flow. The result also revealed that probe induced vortex breakdown was more steady than the natural breakdown.

Generation of topologically diverse acoustic vortex beams using a compact metamaterial aperture

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

Naify, Christina J., E-mail: christina.naify@nrl.navy.mil; Rohde, Charles A.; Martin, Theodore P.

2016-05-30

Here, we present a class of metamaterial-based acoustic vortex generators which are both geometrically simple and broadly tunable. The aperture overcomes the significant limitations of both active phasing systems and existing passive coded apertures. The metamaterial approach generates topologically diverse acoustic vortex waves motivated by recent advances in leaky wave antennas by wrapping the antenna back upon itself to produce an acoustic vortex wave antenna. We demonstrate both experimentally and analytically that this single analog structure is capable of creating multiple orthogonal orbital angular momentum modes using only a single transducer. The metamaterial design makes the aperture compact, with amore » diameter nearly equal to the excitation wavelength and can thus be easily integrated into high-density systems. Applications range from acoustic communications for high bit-rate multiplexing to biomedical devices such as microfluidic mixers.« less

Vortex knots in tangled quantum eigenfunctions

PubMed Central

Taylor, Alexander J.; Dennis, Mark R.

2016-01-01

Tangles of string typically become knotted, from macroscopic twine down to long-chain macromolecules such as DNA. Here, we demonstrate that knotting also occurs in quantum wavefunctions, where the tangled filaments are vortices (nodal lines/phase singularities). The probability that a vortex loop is knotted is found to increase with its length, and a wide gamut of knots from standard tabulations occur. The results follow from computer simulations of random superpositions of degenerate eigenstates of three simple quantum systems: a cube with periodic boundaries, the isotropic three-dimensional harmonic oscillator and the 3-sphere. In the latter two cases, vortex knots occur frequently, even in random eigenfunctions at relatively low energy, and are constrained by the spatial symmetries of the modes. The results suggest that knotted vortex structures are generic in complex three-dimensional wave systems, establishing a topological commonality between wave chaos, polymers and turbulent Bose–Einstein condensates. PMID:27468801

Linear instability regimes in L-mode edges using reduced MHD models in BOUT + +

NASA Astrophysics Data System (ADS)

Bass, Eric; Holland, Chris; Cohen, Bruce; Umansky, Maxim

2016-10-01

We compare linear instabilities in the edge of two DIII-D L-mode discharges using reduced two-fluid MHD models implemented in BOUT + +. Discharge 119919, a case used in a previous BOUT + + validation study, has a cold edge and is dominated by resistive ballooning modes (RBMs). Hotter discharge 128913, an L-mode shortfall benchmark case, is drift-wave (DW) dominant. The model captures essential drift wave physics through the electron pressure parallel gradient drive term in the A| | evolution. At relevant toroidal mode numbers (50-200), the leading DWs in 128913 are flutelike with high kr and require about an order of magnitude greater radial resolution than the leading RBMs in 119919. We quantify when such high kr modes must be resolved in practice. To aid eigenfunction confirmation, and to identify potential subdominant DWs, a companion eigenvalue solver for the BOUT + + models is under development. Prepared by UCSD under Contract Number DE-FG02-06ER54871.

Spectral transfers and zonal flow dynamics in the generalized Charney-Hasegawa-Mima model

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

Lashmore-Davies, C.N.; Thyagaraja, A.; McCarthy, D.R.

2005-12-15

The mechanism of four nonlinearly interacting drift or Rossby waves is used as the basic process underlying the turbulent evolution of both the Charney-Hasegawa-Mima-equation (CHME) and its generalized modification (GCHME). Hasegawa and Kodama's concept of equivalent action (or quanta) is applied to the four-wave system and shown to control the distribution of energy and enstrophy between the modes. A numerical study of the GCHME is described in which the initial state contains a single finite-amplitude drift wave (the pump wave), and all the modulationally unstable modes are present at the same low level (10{sup -6} times the pump amplitude). Themore » simulation shows that at first the fastest-growing modulationally unstable modes dominate but reveals that at a later time, before pump depletion occurs, long- and short-wavelength modes, driven by pairs of fast-growing modes, grow at 2{gamma}{sub max}. The numerical simulation illustrates the development of a spectrum of turbulent modes from a finite-amplitude pump wave.« less

Benchmark studies of the gyro-Landau-fluid code and gyro-kinetic codes on kinetic ballooning modes

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

Tang, T. F.; Lawrence Livermore National Laboratory, Livermore, California 94550; Xu, X. Q.

2016-03-15

A Gyro-Landau-Fluid (GLF) 3 + 1 model has been recently implemented in BOUT++ framework, which contains full Finite-Larmor-Radius effects, Landau damping, and toroidal resonance [Ma et al., Phys. Plasmas 22, 055903 (2015)]. A linear global beta scan has been conducted using the JET-like circular equilibria (cbm18 series), showing that the unstable modes are kinetic ballooning modes (KBMs). In this work, we use the GYRO code, which is a gyrokinetic continuum code widely used for simulation of the plasma microturbulence, to benchmark with GLF 3 + 1 code on KBMs. To verify our code on the KBM case, we first perform the beta scan basedmore » on “Cyclone base case parameter set.” We find that the growth rate is almost the same for two codes, and the KBM mode is further destabilized as beta increases. For JET-like global circular equilibria, as the modes localize in peak pressure gradient region, a linear local beta scan using the same set of equilibria has been performed at this position for comparison. With the drift kinetic electron module in the GYRO code by including small electron-electron collision to damp electron modes, GYRO generated mode structures and parity suggest that they are kinetic ballooning modes, and the growth rate is comparable to the GLF results. However, a radial scan of the pedestal for a particular set of cbm18 equilibria, using GYRO code, shows different trends for the low-n and high-n modes. The low-n modes show that the linear growth rate peaks at peak pressure gradient position as GLF results. However, for high-n modes, the growth rate of the most unstable mode shifts outward to the bottom of pedestal and the real frequency of what was originally the KBMs in ion diamagnetic drift direction steadily approaches and crosses over to the electron diamagnetic drift direction.« less

Vortex instabilities in 3D boundary layers: The relationship between Goertler and crossflow vortices

NASA Technical Reports Server (NTRS)

Bassom, Andrew; Hall, Philip

1990-01-01

The inviscid and viscous stability problems are addressed for a boundary layer which can support both Goertler and crossflow vortices. The change in structure of Goertler vortices is found when the parameter representing the degree of three-dimensionality of the basic boundary layer flow under consideration is increased. It is shown that crossflow vortices emerge naturally as this parameter is increased and ultimately become the only possible vortex instability of the flow. It is shown conclusively that at sufficiently large values of the crossflow there are no unstable Goertler vortices present in a boundary layer which, in the zero crossflow case, is centrifugally unstable. The results suggest that in many practical applications Goertler vortices cannot be a cause of transition because they are destroyed by the 3-D nature of the basic state. In swept wing flows the Goertler mechanism is probably not present for typical angles of sweep of about 20 degrees. Some discussion of the receptivity problem for vortex instabilities in weakly 3-D boundary layers is given; it is shown that inviscid modes have a coupling coefficient marginally smaller than those of the fastest growing viscous modes discussed recently by Denier, Hall, and Seddougui (1990). However the fact that the growth rates of the inviscid modes are the largest in most situations means that they are probably the most likely source of transition.

Effect of density gradients in confined supersonic shear layers. Part 2: 3-D modes

NASA Astrophysics Data System (ADS)

Peroomian, Oshin; Kelly, R. E.

1994-11-01

The effect of basic flow density gradients on the supersonic wall modes were investigated in Part 1 of this analysis. In that investigation only the 2-D modes were studied. Tam and Hu investigated the 3-D modes in a confined vortex sheet and reported that the first 2-D Class A mode (A01) had the highest growth rate compared to all other 2-D and 3-D modes present in the vortex sheet for that particular set of flow patterns. They also showed that this result also held true for finite thickness shear layers with delta(sub w) less than 0.125. For free shear layers, Sandham and Reynolds showed that the 3-D K-H mode became the dominant mode for M(sub c) greater than 0.6. Jackson and Grosch investigated the effect of crossflow and obliqueness on the slow and fast odes present in a M(sub c) greater than 1 environment and showed that for certain combination of crossflow and wave angles the growth rates could be increased by up to a factor of 2 with respect to the 2-D case. The case studied here is a confined shear layer shown in Part 1. All solution procedures and basic low profiles are the same as in Part 1. The effect of density gradients on the 3-D modes present in the density ratios considered in Part 1 are investigated.

Theory based scaling of edge turbulence and implications for the scrape-off layer width

NASA Astrophysics Data System (ADS)

Myra, J. R.; Russell, D. A.; Zweben, S. J.

2016-11-01

Turbulence and plasma parameter data from the National Spherical Torus Experiment (NSTX) [Ono et al., Nucl. Fusion 40, 557 (2000)] is examined and interpreted based on various theoretical estimates. In particular, quantities of interest for assessing the role of turbulent transport on the midplane scrape-off layer heat flux width are assessed. Because most turbulence quantities exhibit large scatter and little scaling within a given operation mode, this paper focuses on length and time scales and dimensionless parameters between operational modes including Ohmic, low (L), and high (H) modes using a large NSTX edge turbulence database [Zweben et al., Nucl. Fusion 55, 093035 (2015)]. These are compared with theoretical estimates for drift and interchange rates, profile modification saturation levels, a resistive ballooning condition, and dimensionless parameters characterizing L and H mode conditions. It is argued that the underlying instability physics governing edge turbulence in different operational modes is, in fact, similar, and is consistent with curvature-driven drift ballooning. Saturation physics, however, is dependent on the operational mode. Five dimensionless parameters for drift-interchange turbulence are obtained and employed to assess the importance of turbulence in setting the scrape-off layer heat flux width λq and its scaling. An explicit proportionality of the width λq to the safety factor and major radius (qR) is obtained under these conditions. Quantitative estimates and reduced model numerical simulations suggest that the turbulence mechanism is not negligible in determining λq in NSTX, at least for high plasma current discharges.

Imaging of Nuclear Weapon Trainers

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

Schwellenbach, David

2017-12-06

The Configurable Muon Tracker (CMT) is an adaptation of the existing drift tube detector commercially available from Decision Sciences International Corporation (DSIC). NSTec engineered the CMT around commercially available drift tube assemblies to make a detector that is more versatile than previous drift tube assemblies. The CMT became operational in February 2013. Traditionally, cosmic-ray muon trackers rely on near-vertical trajectory muons for imaging. Since there are scenarios where imaging using vertical trajectory muons is not practical, NSTec designed the CMT specifically for quick configurability to track muons from any trajectory. The CMT was originally designed to be changed from verticalmore » imaging mode to horizontal imaging mode in a few hours with access to a crane or other lifting equipment. In FY14, locations for imaging weapon trainers and SNM were identified and it was determined that lifting equipment would not typically be available in experimental areas. The CMT was further modified and a portable lifting system was developed to allow reconfiguration of the CMT without access to lifting equipment at the facility. This system was first deployed at Los Alamos National Laboratory’s W-division, where several trainers were imaged in both horizontal and vertical modes. Real-time images have been compared in both modes showing that imaging can be done in both modes with the expected longer integration time for horizontal mode. Further imaging and post processing of the data is expected to continue into early FY15.« less

Theory based scaling of edge turbulence and implications for the scrape-off layer width

DOE PAGES

Myra, J. R.; Russell, D. A.; Zweben, S. J.

2016-11-01

Turbulence and plasma parameter data from the National Spherical Torus Experiment (NSTX) is examined and interpreted based on various theoretical estimates. In particular, quantities of interest for assessing the role of turbulent transport on the midplane scrape-off layer heat flux width are assessed. Because most turbulence quantities exhibit large scatter and little scaling within a given operation mode, this paper focuses on length and time scales and dimensionless parameters between operational modes including Ohmic, low (L), and high (H) modes using a large NSTX edge turbulence database. These are compared with theoretical estimates for drift and interchange rates, profile modificationmore » saturation levels, a resistive ballooning condition, and dimensionless parameters characterizing L and H mode conditions. It is argued that the underlying instability physics governing edge turbulence in different operational modes is, in fact, similar, and is consistent with curvature-driven drift ballooning. Saturation physics, however, is dependent on the operational mode. Five dimensionless parameters for drift-interchange turbulence are obtained and employed to assess the importance of turbulence in setting the scrape-off layer heat flux width λ q and its scaling. An explicit proportionality of the width λ q to the safety factor and major radius (qR) is obtained under these conditions. Lastly, quantitative estimates and reduced model numerical simulations suggest that the turbulence mechanism is not negligible in determining λ q in NSTX, at least for high plasma current discharges.« less

Drift-insensitive distributed calibration of probe microscope scanner in nanometer range: Virtual mode

NASA Astrophysics Data System (ADS)

Lapshin, Rostislav V.

2016-08-01

A method of distributed calibration of a probe microscope scanner is suggested. The main idea consists in a search for a net of local calibration coefficients (LCCs) in the process of automatic measurement of a standard surface, whereby each point of the movement space of the scanner can be characterized by a unique set of scale factors. Feature-oriented scanning (FOS) methodology is used as a basis for implementation of the distributed calibration permitting to exclude in situ the negative influence of thermal drift, creep and hysteresis on the obtained results. Possessing the calibration database enables correcting in one procedure all the spatial systematic distortions caused by nonlinearity, nonorthogonality and spurious crosstalk couplings of the microscope scanner piezomanipulators. To provide high precision of spatial measurements in nanometer range, the calibration is carried out using natural standards - constants of crystal lattice. One of the useful modes of the developed calibration method is a virtual mode. In the virtual mode, instead of measurement of a real surface of the standard, the calibration program makes a surface image ;measurement; of the standard, which was obtained earlier using conventional raster scanning. The application of the virtual mode permits simulation of the calibration process and detail analysis of raster distortions occurring in both conventional and counter surface scanning. Moreover, the mode allows to estimate the thermal drift and the creep velocities acting while surface scanning. Virtual calibration makes possible automatic characterization of a surface by the method of scanning probe microscopy (SPM).

Experimental investigations of on-demand vortex generators

NASA Astrophysics Data System (ADS)

Saddoughi, Seyed G.

1994-12-01

Conventional vortex generators as found on many civil aircrafts are mainly for off-design conditions - e.g. suppression of separation or loss of aileron power when the Mach number accidentally rises above the design (cruise) value. In normal conditions they perform no useful function and exert a significant drag penalty. Recently there have been advances in new designs for passive vortex generators and boundary layer control. While traditionally the generators heights were of the order of the boundary layer thickness (delta), recent advances have been made where generators of the order of delta/4 have been shown to be effective. The advancement of MIcro-Electro-Mechanical (MEM) devices has prompted several efforts in exploring the possibility of using such devices in turbulence control. These new devices offer the possibility of boundary layer manipulation through the production of vortices, momentum jets, or other features in the flow. However, the energy output of each device is low in general, but they can be used in large numbers. Therefore, the possibility of moving from passive vortex generators to active (on-demand) devices becomes of interest. Replacement of fixed rectangular or delta-wing generators by devices that could be activated when needed would produce substantial economies. Our proposed application is not strictly 'active' control: the vortex generators would simply be switched on, all together, when needed (e.g. when the aircraft Mach number exceeded a certain limit). To this extent our scheme is simpler; however, to promote mixing and suppress separation we desire to deposit longitudinal vortices into the outer layer of the boundary layer as in conventional vortex generators. This requires a larger device although an alternative might be an array of smaller devices, for example, a longitudinal row with phase differences in the modulation signals so that the periodic vortices join up. The vortex pair with common flow up has the advantage that it will naturally drift away from the surface, but the disadvantage is that the net vorticity is zero so that the pair is eventually obliterated by turbulent mixing, rather than simply being diffused as in the case of a single vortex. It should be possible to devise alternative shapes of cavity wall so that the jet emerges obliquely and produces net longitudinal vorticity.

Experimental investigations of on-demand vortex generators

NASA Technical Reports Server (NTRS)

Saddoughi, Seyed G.

1994-01-01

Conventional vortex generators as found on many civil aircrafts are mainly for off-design conditions - e.g. suppression of separation or loss of aileron power when the Mach number accidentally rises above the design (cruise) value. In normal conditions they perform no useful function and exert a significant drag penalty. Recently there have been advances in new designs for passive vortex generators and boundary layer control. While traditionally the generators heights were of the order of the boundary layer thickness (delta), recent advances have been made where generators of the order of delta/4 have been shown to be effective. The advancement of MIcro-Electro-Mechanical (MEM) devices has prompted several efforts in exploring the possibility of using such devices in turbulence control. These new devices offer the possibility of boundary layer manipulation through the production of vortices, momentum jets, or other features in the flow. However, the energy output of each device is low in general, but they can be used in large numbers. Therefore, the possibility of moving from passive vortex generators to active (on-demand) devices becomes of interest. Replacement of fixed rectangular or delta-wing generators by devices that could be activated when needed would produce substantial economies. Our proposed application is not strictly 'active' control: the vortex generators would simply be switched on, all together, when needed (e.g. when the aircraft Mach number exceeded a certain limit). To this extent our scheme is simpler; however, to promote mixing and suppress separation we desire to deposit longitudinal vortices into the outer layer of the boundary layer as in conventional vortex generators. This requires a larger device although an alternative might be an array of smaller devices, for example, a longitudinal row with phase differences in the modulation signals so that the periodic vortices join up. The vortex pair with common flow up has the advantage that it will naturally drift away from the surface, but the disadvantage is that the net vorticity is zero so that the pair is eventually obliterated by turbulent mixing, rather than simply being diffused as in the case of a single vortex. It should be possible to devise alternative shapes of cavity wall so that the jet emerges obliquely and produces net longitudinal vorticity.

Superburst oscillations: ocean and crustal modes excited by carbon-triggered type I X-ray bursts

NASA Astrophysics Data System (ADS)

Chambers, F. R. N.; Watts, A. L.; Cavecchi, Y.; Garcia, F.; Keek, L.

2018-07-01

Accreting neutron stars (NS) can exhibit high frequency modulations in their light curves during thermonuclear X-ray bursts, known as burst oscillations. The frequencies can be offset from the spin frequency of the NS by several Hz, and can drift by 1-3 Hz. One possible explanation is a mode in the bursting ocean, the frequency of which would decrease (in the rotating frame) as the burst cools, hence explaining the drifts. Most burst oscillations have been observed during the H/He-triggered bursts; however there has been one observation of oscillations during a superburst; hours long Type I X-ray bursts caused by unstable carbon burning deeper in the ocean. This paper calculates the frequency evolution of an oceanic r mode during a superburst. The rotating frame frequency varies during the burst from 4-14 Hz and is sensitive to the background parameters, in particular the temperature of the ocean and ignition depth. This calculation is compared to the superburst oscillations observed on 4U-1636-536. The predicted mode frequencies (˜10 Hz) would require a spin frequency of ˜592 Hz to match observations; 6 Hz higher than the spin inferred from an oceanic r-mode model for the H/He-triggered burst oscillations. This model also overpredicts the frequency drift during the superburst by 90 per cent.

Superburst oscillations: ocean and crustal modes excited by Carbon-triggered Type I X-ray bursts

NASA Astrophysics Data System (ADS)

Chambers, F. R. N.; Watts, A. L.; Cavecchi, Y.; Garcia, F.; Keek, L.

2018-04-01

Accreting neutron stars (NS) can exhibit high frequency modulations in their lightcurves during thermonuclear X-ray bursts, known as burst oscillations. The frequencies can be offset from the spin frequency of the NS by several Hz, and can drift by 1-3 Hz. One possible explanation is a mode in the bursting ocean, the frequency of which would decrease (in the rotating frame) as the burst cools, hence explaining the drifts. Most burst oscillations have been observed during H/He triggered bursts, however there has been one observation of oscillations during a superburst; hours' long Type I X-ray bursts caused by unstable carbon burning deeper in the ocean. This paper calculates the frequency evolution of an oceanic r-mode during a superburst. The rotating frame frequency varies during the burst from 4 - 14 Hz, and is sensitive to the background parameters, in particular the temperature of the ocean and ignition depth. This calculation is compared to the superburst oscillations observed on 4U-1636-536. The predicted mode frequencies (˜10 Hz) would require a spin frequency of ˜592 Hz to match observations; 6 Hz higher than the spin inferred from an oceanic r-mode model for the H/He triggered burst oscillations. This model also over-predicts the frequency drift during the superburst by 90%.

Observation of dual-mode, Kelvin-Helmholtz instability vortex merger in a compressible flow

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

Wan, W. C.; Malamud, Guy; Shimony, A.

Here, we report the first observations of Kelvin-Helmholtz vortices evolving from well-characterized, dual-mode initial conditions in a steady, supersonic flow. The results provide the first measurements of the instability's vortex merger rate and supplement data on the inhibition of the instability's growth rate in a compressible flow. These experimental data were obtained by sustaining a shockwave over a foam-plastic interface with a precision-machined seed perturbation. This technique produced a strong shear layer between two plasmas at high-energy-density conditions. The system was diagnosed using x-ray radiography and was well-reproduced using hydrodynamic simulations. Experimental measurements imply that we observed the anticipated vortexmore » merger rate and growth inhibition for supersonic shear flow.« less

Observation of dual-mode, Kelvin-Helmholtz instability vortex merger in a compressible flow

DOE PAGES

Wan, W. C.; Malamud, Guy; Shimony, A.; ...

2017-04-25

Here, we report the first observations of Kelvin-Helmholtz vortices evolving from well-characterized, dual-mode initial conditions in a steady, supersonic flow. The results provide the first measurements of the instability's vortex merger rate and supplement data on the inhibition of the instability's growth rate in a compressible flow. These experimental data were obtained by sustaining a shockwave over a foam-plastic interface with a precision-machined seed perturbation. This technique produced a strong shear layer between two plasmas at high-energy-density conditions. The system was diagnosed using x-ray radiography and was well-reproduced using hydrodynamic simulations. Experimental measurements imply that we observed the anticipated vortexmore » merger rate and growth inhibition for supersonic shear flow.« less

Generalized banana-drift transport

NASA Astrophysics Data System (ADS)

Mynick, H. E.

1985-10-01

The theory of tokamak ripple transport in the banana-drift and ripple-plateau is extended in a number of directions. The theory is valid for small values of the toroidal periodicity number n of the perturbation, as well as for the moderate values (n approx. 10 - 20) previously assumed. It is shown that low-n perturbations can produce much greater transport than the larger-n perturbations usually studied. In addition, the ripple perturbation is allowed arbitrary values of poloidal mode number m and frequency omega, making it applicable to the transport induced by MHD modes. Bounce averaging is avoided, so the theory includes the contributions to transport from all harmonics of the bounce frequency, providing a continuous description of the transition from the banana drift to the ripple-plateau regime. The implications of the theory for toroidal rotation in tokamaks are considered.

High helicity vortex conversion in a rubidium vapor

NASA Astrophysics Data System (ADS)

Chopinaud, Aurélien; Jacquey, Marion; Viaris de Lesegno, Bruno; Pruvost, Laurence

2018-06-01

The orbital angular momentum (OAM) of light is a quantity explored for communication and quantum technology, its key strength being a wide set of values offering a large basis for quantum working. In this context we have studied the vortex conversion from a red optical vortex to a blue one, for OAMs ranging -30 to +30 . The conversion is realized in a rubidium vapor, via the 5 S1 /2-5 D5 /285Rb two-photon transition done with a Gaussian beam at 780 nm plus a Laguerre-Gaussian beam at 776 nm with the OAM ℓ , producing a radiation at 420 nm . With copropagating input beams, we demonstrate a conversion from red to blue for high-ℓ input vortices. We show that the output blue vortex respects the azimuthal phase matching, has a size determined by the product of the input beams, and a power decreasing with ℓ , in agreement with their overlap. Its propagation indicates that the generated blue wave is a nearly pure Laguerre-Gaussian mode. The vortex converter thus permits a correct OAM transmission.

Disruption of current filaments and isotropization of magnetic field in counter-streaming plasmas

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

Fiuza, Frederico

We study the stability of current filaments produced by the Weibel, or current filamentation, instability in weakly magnetized counter-streaming plasmas. It is shown that a resonance exists between the current-carrying ions and a longitudinal drift-kink mode that strongly deforms and eventually breaks the current filaments. Analytical estimates of the wavelength, growth rate and saturation level of the resonant mode are derived and validated by three-dimensional particle-in-cell simulations. Furthermore, self-consistent simulations of counter-streaming plasmas indicate that this drift-kink mode is dominant in the slow down of the flows and in the isotropization of the magnetic field, playing an important role inmore » the formation of collision less shocks.« less

Thermal chiral vortical and magnetic waves: New excitation modes in chiral fluids

DOE PAGES

Kalaydzhyan, Tigran; Murchikova, Elena

2017-03-24

In certain circumstances, chiral (parity-violating) medium can be described hydrodynamically as a chiral fluid with microscopic quantum anomalies. Possible examples of such systems include strongly coupled quark–gluon plasma, liquid helium 3He-A, neutron stars and the Early Universe. Here, we study first-order hy-drodynamics of a chiral fluid on a vortex background and in an external magnetic field. We show that there are two previously undiscovered modes describing heat waves propagating along the vortex and magnetic field. We call them the Thermal Chiral Vortical Wave and Thermal Chiral Magnetic Wave. We also identify known gapless excitations of density (chiral vortical and chiralmore » magnetic waves) and transverse velocity (chiral Alfvén wave). We also demonstrate that the velocity of the chiral vortical wave is zero, when the full hydrodynamic framework is applied, and hence the wave is absent and the excitation reduces to the charge diffusion mode. We also comment on the frame-dependent contributions to the obtained propagation velocities.« less

Decision algorithm for data center vortex beam receiver

NASA Astrophysics Data System (ADS)

Kupferman, Judy; Arnon, Shlomi

2017-12-01

We present a new scheme for a vortex beam communications system which exploits the radial component p of Laguerre-Gauss modes in addition to the azimuthal component l generally used. We derive a new encoding algorithm which makes use of the spatial distribution of intensity to create an alphabet dictionary for communication. We suggest an application of the scheme as part of an optical wireless link for intra data center communication. We investigate the probability of error in decoding, for several detector options.

Generating A Strobed Laser Light Sheet

NASA Technical Reports Server (NTRS)

Leighty, Bradley D.; Franke, John M.; Rhodes, David B.; Jones, Stephen B.

1994-01-01

An optoelectronic system generating synchronous, strobed sheet of laser light developed for use in making visible flow of air about model helicopter rotor. Used in wind-tunnel tests to determine actual locations of vortices for comparison with locations predicted by mathematical models to validate models. Each blade tip produces vortex. By establishing successive vortex locations, researcher determines trajectory of vortex pattern. Light-sheet strobe circuits provide selection of blade positions, strobe-pulse durations, and multiple pulses per revolution for rotors having two to nine blades. To make flow visible, vaporizing propylene glycol injected upstream of model. System also provides calibrated trigger delay of strobe pulses, adjustable strobe-pulse durations, selectable number of blades, and slip-sync mode to make flow visible as though in slow motion.

Geometric stabilization of the electrostatic ion-temperature-gradient driven instability. I. Nearly axisymmetric systems

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

Zocco, A.; Plunk, G. G.; Xanthopoulos, P.

The effects of a non-axisymmetric (3D) equilibrium magnetic field on the linear ion-temperature-gradient (ITG) driven mode are investigated. We consider the strongly driven, toroidal branch of the instability in a global (on the magnetic surface) setting. Previous studies have focused on particular features of non-axisymmetric systems, such as strong local shear or magnetic ripple, that introduce inhomogeneity in the coordinate along the magnetic field. In contrast, here we include non-axisymmetry explicitly via the dependence of the magnetic drift on the field line label α, i.e., across the magnetic field, but within the magnetic flux surface. We consider the limit wheremore » this variation occurs on a scale much larger than that of the ITG mode, and also the case where these scales are similar. Close to axisymmetry, we find that an averaging effect of the magnetic drift on the flux surface causes global (on the surface) stabilization, as compared to the most unstable local mode. In the absence of scale separation, we find destabilization is also possible, but only if a particular resonance occurs between the magnetic drift and the mode, and finite Larmor radius effects are neglected. We discuss the relative importance of surface global effects and known radially global effects.« less

Atomic physics effects on tokamak edge drift-tearing modes

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

Hahm, T.S.

1993-03-01

The effects of ionization and charge exchange on the linear stability of drift-tearing modes are analytically investigated. In particular, the linear instability threshold {Delta}{sup Th}, produced by ion sound wave coupling is modified. In the strongly collisional regime, the ionization breaks up the near cancellation of the perturbed electric field and the pressure gradient along the magnetic field, and increases the threshold. In the semi-collisional regime, both ionization and charge exchange act as drag on the ion parallel velocity, and consequently decrease the threshold by reducing the effectiveness of ion sound wave propagation.

Atomic physics effects on tokamak edge drift-tearing modes

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

Hahm, T.S.

1993-03-01

The effects of ionization and charge exchange on the linear stability of drift-tearing modes are analytically investigated. In particular, the linear instability threshold [Delta][sup Th], produced by ion sound wave coupling is modified. In the strongly collisional regime, the ionization breaks up the near cancellation of the perturbed electric field and the pressure gradient along the magnetic field, and increases the threshold. In the semi-collisional regime, both ionization and charge exchange act as drag on the ion parallel velocity, and consequently decrease the threshold by reducing the effectiveness of ion sound wave propagation.

Dynamic characteristics of 4H-SiC drift step recovery diodes

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

Ivanov, P. A., E-mail: Pavel.Ivanov@mail.ioffe.ru; Kon’kov, O. I.; Samsonova, T. P.

The dynamic characteristics of 4H-SiC p{sup +}–p–n{sub 0}–n{sup +} diodes are experimentally studied in the pulsed modes characteristic of the operation of drift step recovery diodes (DSRD-mode). The effect of the subnanosecond termination of the reverse current maintained by electron-hole plasma preliminarily pumped by a forward current pulse is analyzed in detail. The influence exerted on the DSRD effect by the amplitude of reverse-voltage pulses, the amplitude and duration of forward-current pulses, and the time delay between the forward and reverse pulses is demonstrated and accounted for.

Direct Observations of ULF and Whistler-Mode Chorus Modulation of 500eV EDI Electrons by MMS

NASA Astrophysics Data System (ADS)

Paulson, K. W.; Argall, M. R.; Ahmadi, N.; Torbert, R. B.; Le Contel, O.; Ergun, R.; Khotyaintsev, Y. V.; Strangeway, R. J.; Magnes, W.; Russell, C. T.

2016-12-01

We present here direct observations of chorus-wave modulated field-aligned 500 eV electrons using the Electron Drift Instrument (EDI) on board the Magnetospheric Multiscale mission. These periods of wave activity were additionally observed to be modulated by Pc5-frequency magnetic perturbations, some of which have been identified as drifting mirror-mode structures. The spacecraft encountered these mirror-mode structures just inside of the duskside magnetopause. Using the high sampling rate provided by EDI in burst sampling mode, we are able to observe the individual count fluctuations of field-aligned electrons in this region up to 512 Hz. We use the multiple look directions of EDI to generate both pitch angle and gyrophase plots of the fluctuating counts. Our observations often show unidirectional flow of these modulated electrons along the background field, and in some cases demonstrate gyrophase bunching in the wave region.

Nonlinear simulations of peeling-ballooning modes with anomalous electron viscosity and their role in edge localized mode crashes

DOE PAGES

Xu, X. Q.; Dudson, B.; Snyder, P. B.; ...

2010-10-22

A minimum set of equations based on the peeling-ballooning (P-B) model with nonideal physics effects (diamagnetic drift, E×B drift, resistivity, and anomalous electron viscosity) is found to simulate pedestal collapse when using the new BOUT++ simulation code, developed in part from the original fluid edge code BOUT. Nonlinear simulations of P-B modes demonstrate that the P-B modes trigger magnetic reconnection, which leads to the pedestal collapse. With the addition of a model of the anomalous electron viscosity under the assumption that the electron viscosity is comparable to the anomalous electron thermal diffusivity, it is found from simulations using a realisticmore » high-Lundquist number that the pedestal collapse is limited to the edge region and the edge localized mode (ELM) size is about 5–10% of the pedestal stored energy. Furthermore, this is consistent with many observations of large ELMs.« less

Probing the Cold Dust Emission in the AB Aur Disk: A Dust Trap in a Decaying Vortex?

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

Fuente, Asunción; Bachiller, Rafael; Baruteau, Clément

One serious challenge for planet formation is the rapid inward drift of pebble-sized dust particles in protoplanetary disks. Dust trapping at local maxima in the disk gas pressure has received much theoretical attention but still lacks observational support. The cold dust emission in the AB Aur disk forms an asymmetric ring at a radius of about 120 au, which is suggestive of dust trapping in a gas vortex. We present high spatial resolution (0.″58 × 0.″78 ≈ 80 × 110 au) NOEMA observations of the 1.12 mm and 2.22 mm dust continuum emission from the AB Aur disk. Significant azimuthalmore » variations of the flux ratio at both wavelengths indicate a size segregation of the large dust particles along the ring. Our continuum images also show that the intensity variations along the ring are smaller at 2.22 mm than at 1.12 mm, contrary to what dust trapping models with a gas vortex have predicted. Our two-fluid (gas+dust) hydrodynamical simulations demonstrate that this feature is well explained if the gas vortex has started to decay due to turbulent diffusion, and dust particles are thus losing the azimuthal trapping on different timescales depending on their size. The comparison between our observations and simulations allows us to constrain the size distribution and the total mass of solid particles in the ring, which we find to be of the order of 30 Earth masses, enough to form future rocky planets.« less

Parameter-Space Survey of Linear G-mode and Interchange in Extended Magnetohydrodynamics

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

Howell, E. C.; Sovinec, C. R.

The extended magnetohydrodynamic stability of interchange modes is studied in two configurations. In slab geometry, a local dispersion relation for the gravitational interchange mode (g-mode) with three different extensions of the MHD model [P. Zhu, et al., Phys. Rev. Lett. 101, 085005 (2008)] is analyzed. Our results delineate where drifts stablize the g-mode with gyroviscosity alone and with a two-fluid Ohm’s law alone. Including the two-fluid Ohm’s law produces an ion drift wave that interacts with the g-mode. This interaction then gives rise to a second instability at finite k y. A second instability is also observed in numerical extended MHD computations of linear interchange in cylindrical screw-pinch equilibria, the second configuration. Particularly with incomplete models, this mode limits the regions of stability for physically realistic conditions. But, applying a consistent two-temperature extended MHD model that includes the diamagnetic heat flux density (more » $$\\vec{q}$$ *) makes the onset of the second mode occur at larger Hall parameter. For conditions relevant to the SSPX experiment [E.B. Hooper, Plasma Phys. Controlled Fusion 54, 113001 (2012)], significant stabilization is observed for Suydam parameters as large as unity (D s≲1).« less

Parameter-Space Survey of Linear G-mode and Interchange in Extended Magnetohydrodynamics

DOE PAGES

Howell, E. C.; Sovinec, C. R.

2017-09-11

The extended magnetohydrodynamic stability of interchange modes is studied in two configurations. In slab geometry, a local dispersion relation for the gravitational interchange mode (g-mode) with three different extensions of the MHD model [P. Zhu, et al., Phys. Rev. Lett. 101, 085005 (2008)] is analyzed. Our results delineate where drifts stablize the g-mode with gyroviscosity alone and with a two-fluid Ohm’s law alone. Including the two-fluid Ohm’s law produces an ion drift wave that interacts with the g-mode. This interaction then gives rise to a second instability at finite k y. A second instability is also observed in numerical extended MHD computations of linear interchange in cylindrical screw-pinch equilibria, the second configuration. Particularly with incomplete models, this mode limits the regions of stability for physically realistic conditions. But, applying a consistent two-temperature extended MHD model that includes the diamagnetic heat flux density (more » $$\\vec{q}$$ *) makes the onset of the second mode occur at larger Hall parameter. For conditions relevant to the SSPX experiment [E.B. Hooper, Plasma Phys. Controlled Fusion 54, 113001 (2012)], significant stabilization is observed for Suydam parameters as large as unity (D s≲1).« less

Cloud morphology and dynamics in Saturn's northern polar region

NASA Astrophysics Data System (ADS)

Antuñano, Arrate; del Río-Gaztelurrutia, Teresa; Sánchez-Lavega, Agustín; Rodríguez-Aseguinolaza, Javier

2018-01-01

We present a study of the cloud morphology and motions in the north polar region of Saturn, from latitude ∼ 70°N to the pole based on Cassini ISS images obtained between January 2009 and November 2014. This region shows a variety of dynamical structures: the permanent hexagon wave and its intense eastward jet, a large field of permanent ;puffy; clouds with scales from 10 - 500 km, probably of convective origin, local cyclone and anticyclones vortices with sizes of ∼1,000 km embedded in this field, and finally the intense cyclonic polar vortex. We report changes in the albedo of the clouds that delineate rings of circulation around the polar vortex and the presence of ;plume-like; activity in the hexagon jet, in both cases not accompanied with significant variations in the corresponding jets. No meridional migration is observed in the clouds forming and merging in the field of puffy clouds, suggesting that their mergers do not contribute to the maintenance of the polar vortex. Finally, we analyze the dominant growing modes for barotropic and baroclinic instabilities in the hexagon jet, showing that a mode 6 barotropic instability is dominant at the latitude of the hexagon.

Force Generation by Flapping Foils

NASA Astrophysics Data System (ADS)

Bandyopadhyay, P. R.; Donnelly, M.

1996-11-01

Aquatic animals like fish use flapping caudal fins to produce axial and cross-stream forces. During WW2, German scientists had built and tested an underwater vehicle powered by similar flapping foils. We have examined the forces produced by a pair of flapping foils. We have examined the forced produced by a pair of flapping foils attached to the tail end of a small axisymmetric cylinder. The foils operate in-phase (called waving), or in anti-phase (called clapping). In a low-speed water tunnel, we have undertaken time-dependent measurements of axial and cross-stream forces and moments that are exerted by the vortex shedding process over the entire body. Phase-matched LDV measurements of vorticity-velocity vectors, as well as limited flow visualization of the periodic vortex shedding process have also been carried out. The direction of the induced velocity within a pair of shed vortices determines the nature of the forces produced, viz., thrust or drag or cross-stream forces. The clapping mode produces a widely dispersed symmetric array of vortices which results in axial forces only (thrust and rag). On the other hand, the vortex array is staggered in the waving mode and cross-stream (maneuvering) forces are then generated.

Simulation of Vortex Structure in Supersonic Free Shear Layer Using Pse Method

NASA Astrophysics Data System (ADS)

Guo, Xin; Wang, Qiang

The method of parabolized stability equations (PSE) are applied in the analysis of nonlinear stability and the simulation of flow structure in supersonic free shear layer. High accuracy numerical techniques including self-similar basic flow, high order differential method, appropriate transformation and decomposition of nonlinear terms are adopted and developed to solve the PSE effectively for free shear layer. The spatial evolving unstable waves which dominate the flow structure are investigated through nonlinear coupling spatial marching methods. The nonlinear interactions between harmonic waves are further analyzed and instantaneous flow field are obtained by adding the harmonic waves into basic flow. Relevant data agree well with that of DNS. The results demonstrate that T-S wave does not keeping growing exponential as the linear evolution, the energy transfer to high order harmonic modes and finally all harmonic modes get saturation due to the nonlinear interaction; Mean flow distortion is produced by the nonlinear interaction between the harmonic and its conjugate harmonic, makes great change to the average flow and increases the thickness of shear layer; PSE methods can well capture the large scale nonlinear flow structure in the supersonic free shear layer such as vortex roll-up, vortex pairing and nonlinear saturation.

Neoclassical quasilinear theory in the superbanana plateau regime and banana kinetics in tokamaks

NASA Astrophysics Data System (ADS)

Shaing, K. C.

2017-12-01

Neoclassical quasilinear transport theory, which is part of a more general theory that unifies neoclassical and quasilinear theories, is extended to the superbanana plateau regime for low frequency (of the order of the drift frequency) electrostatic fluctuations. The physics mechanism that is responsible for the transport losses in this regime is the superbanana plateau resonance. Besides the usual magnetic drifts, Doppler shifted mode frequency also contributes to the resonance condition. Because the characteristic frequency involved in the resonance is of the order of the drift frequency, which is lower than either the bounce or the transit frequency of the particles, the transport losses are higher than the losses calculated in the conventional quasilinear theory. The important effects of the finite banana width, i.e., banana kinetics, are included and are found to reduce the transport losses for short wavelength modes. The implications on the energetic alpha particle energy loss are discussed.

Gyrokinetic particle simulations of the effects of compressional magnetic perturbations on drift-Alfvenic instabilities in tokamaks

DOE PAGES

Dong, Ge; Bao, Jian; Bhattacharjee, Amitava; ...

2017-08-10

The compressional component of magnetic perturbation δB- || to can play an important role in drift-Alfvenic instabilities in tokamaks, especially as the plasma β increases (β is the ratio of kinetic pressure to magnetic pressure). In this work, we have formulated a gyrokinetic particle simulation model incorporating δB- ||, and verified the model in kinetic Alfven wave simulations using the Gyrokinetic Toroidal Code in slab geometry. Simulations of drift-Alfvenic instabilities in tokamak geometry shows that the kinetic ballooning mode (KBM) growth rate decreases more than 20% when δB- || is neglected for β e = 0.02, and that δB- ||more » to has stabilizing effects on the ion temperature gradient instability, but negligible effects on the collisionless trapped electron mode. Lastly, the KBM growth rate decreases about 15% when equilibrium current is neglected.« less

Subharmonic mechanism of the mode C instability

NASA Astrophysics Data System (ADS)

Sheard, G. J.; Thompson, M. C.; Hourigan, K.

2005-11-01

The perturbation field of the recently discovered subharmonic mode C instability in the wake behind a ring is compared via a side-by-side comparison to the perturbation fields of the modes A and B instabilities familiar from past studies of the vortex street behind a circular cylinder. Snapshots of the wake are presented over a full shedding cycle, along with evidence from a linear stability analysis, to verify and better understand how the subharmonic instability is sustained.

Helicon modes in uniform plasmas. I. Low m modes

NASA Astrophysics Data System (ADS)

Urrutia, J. M.; Stenzel, R. L.

2015-09-01

Helicons are whistler modes with azimuthal wave numbers. They arise in bounded gaseous and solid state plasmas, but the present work shows that very similar modes also exist in unbounded uniform plasmas. The antenna properties determine the mode structure. A simple antenna is a magnetic loop with dipole moment aligned either along or across the ambient background magnetic field B0. For such configurations, the wave magnetic field has been measured in space and time in a large and uniform laboratory plasma. The observed wave topology for a dipole along B0 is similar to that of an m = 0 helicon mode. It consists of a sequence of alternating whistler vortices. For a dipole across B0, an m = 1 mode is excited which can be considered as a transverse vortex which rotates around B0. In m = 0 modes, the field lines are confined to each half-wavelength vortex while for m = 1 modes they pass through the entire wave train. A subset of m = 1 field lines forms two nested helices which rotate in space and time like corkscrews. Depending on the type of the antenna, both m = + 1 and m = -1 modes can be excited. Helicons in unbounded plasmas also propagate transverse to B0. The transverse and parallel wave numbers are about equal and form oblique phase fronts as in whistler Gendrin modes. By superimposing small amplitude fields of several loop antennas, various antenna combinations have been created. These include rotating field antennas, helical antennas, and directional antennas. The radiation efficiency is quantified by the radiation resistance. Since helicons exist in unbounded laboratory plasmas, they can also arise in space plasmas.

Vortex nucleation in a dissipative variant of the nonlinear Schrödinger equation under rotation

DOE PAGES

Carretero-González, R.; Kevrekidis, P. G.; Kolokolnikov, T.

2016-03-01

In this work, we motivate and explore the dynamics of a dissipative variant of the nonlinear Schrödinger equation under the impact of external rotation. As in the well established Hamiltonian case, the rotation gives rise to the formation of vortices. We show, however, that the most unstable mode leading to this instability scales with an appropriate power of the chemical potential μ of the system, increasing proportionally to μ 2/3. The precise form of the relevant formula, obtained through our asymptotic analysis, provides the most unstable mode as a function of the atomic density and the trap strength. We showmore » how these unstable modes typically nucleate a large number of vortices in the periphery of the atomic cloud. However, through a pattern selection mechanism, prompted by symmetry-breaking, only few isolated vortices are pulled in sequentially from the periphery towards the bulk of the cloud resulting in highly symmetric stable vortex configurations with far fewer vortices than the original unstable mode. We conclude that these results may be of relevance to the experimentally tractable realm of finite temperature atomic condensates.« less

Balloon-borne measurements of aerosol, condensation nuclei, and cloud particles in the stratosphere at McMurdo Station, Antarctica, during the spring of 1987

NASA Technical Reports Server (NTRS)

Hofmann, D. J.; Rosen, J. M.; Harder, J. W.; Hereford, J. V.

1989-01-01

Measurements of the vertical profile of particles with condensation nuclei counters and eight channel aerosol detectors at McMurdo Station, Antarctica, in 1987 verified observations made in 1986 concerning the absence of upwelling in the polar vortex and the presence of a condensation nuclei layer in conjunction with the ozone hole region. New observations of a bimodal aerosol size distribution, consisting of a large-particle mode mixed in with the small-particle sulfate mode, at temperatures below -79 C are consistent with the presence of nitric acid-water particles at low concentrations. Higher concentrations of large particles were observed in association with nacreous clouds. An unusual particle layer which contained enhanced concentrations of both the small-particle (sulfate) mode and the large-particle (nitric acid) mode was detected at temperatures below -85 C, suggesting simultaneous nucleation and growth phenomena. The vortex condensation nuclei layer was observed to form at the same time as the ozone hole, indicating that formation of the layer is triggered by photochemical processes and may be important in controlling ozone depletion above 22 km.

Vector mode conversion based on tilted fiber Bragg grating in ring-core fibers

NASA Astrophysics Data System (ADS)

Mi, Yuean; Ren, Guobin; Gao, Yixiao; Li, Haisu; Zhu, Bofeng; Liu, Yu

2018-03-01

We propose a vector mode conversion approach based on tilted fiber Bragg grating (TFBG) written in ring-core fiber with effective separation of eigenmodes. The mode coupling properties of TFBG are numerically investigated. It is shown that under the constraint of phase matching, the conversion of high-order vector modes could be achieved at specific wavelengths. Moreover, the polarization of incident light and tilt angle of TFBG play critical roles in mode coupling process. The proposed TFBG provides an efficient method to realize high-order vector mode conversion, and it shows great potential for fibers based OAM beam generation and fiber lasers with vortex beams output.

Coherent structures in bypass transition induced by a cylinder wake

NASA Astrophysics Data System (ADS)

Pan, Chong; Wang, Jin Jun; Zhang, Pan Feng; Feng, Li Hao

Flat-plate boundary layer transition induced by the wake vortex of a two-dimensional circular cylinder is experimentally investigated. Combined visualization and velocity measurements show a different transition route from the Klebanoff mode in free-stream turbulence-induced transition. This transition scenario is mainly characterized as: (i) generation of secondary transverse vortical structures near the flat plate surface in response to the von Kn vortex street of the cylinder; (ii) formation of hairpin vortices due to the secondary instability of secondary vortical structures; (iii) growth of hairpins which is accelerated by wake-vortex induction; (iv) formation of hairpin packets and the associated streaky structures. Detailed investigation shows that during transition the evolution dynamics and self-sustaining mechanisms of hairpins, hairpin packets and streaks are consistent with those in a turbulent boundary layer. The wake vortex mainly plays the role of generating and destabilizing secondary transverse vortices. After that, the internal mechanisms become dominant and lead to the setting up of a self-sustained turbulent boundary layer.

Elliptic jets, part 2. Dynamics of coherent structures: Pairing

NASA Technical Reports Server (NTRS)

Husain, Hyder S.; Hussain, Fazle

1992-01-01

The dynamics of the jet column mode of vortex pairing in the near field of an elliptic jet was investigated. Hot-wire measurements and flow visualization were used to examine the details of the pairing mechanism of nonplanar vortical elliptic structures and its effect on such turbulence measures as coherent velocities, incoherent turbulence intensities, incoherent and coherent Reynolds, stresses, turbulence production, and mass entrainment. It was found that pairing of elliptic vortices in the jet column does not occur uniformly around the entire perimeter, unlike in a circular jet. Merger occurs only in the initial major-axis plane. In the initial minor-axis plane, the trailing vortex rushes through the leading vortex without pairing and then breaks down violently, producing considerably greater entrainment and mixing than in circular or plane jets.

Crossflow Stability and Transition Experiments in Swept-Wing Flow

NASA Technical Reports Server (NTRS)

Dagenhart, J. Ray; Saric, William S.

1999-01-01

An experimental examination of crossflow instability and transition on a 45deg swept wing was conducted in the Arizona State University Unsteady Wind Tunnel. The stationary-vortex pattern and transition location are visualized by using both sublimating chemical and liquid-crystal coatings. Extensive hot-wire measurements were obtained at several measurement stations across a single vortex track. The mean and travelling wave disturbances were measured simultaneously. Stationary crossflow disturbance profiles were determined by subtracting either a reference or a span-averaged velocity profile from the mean velocity data. Mean, stationary crossflow, and traveling wave velocity data were presented as local boundary layer profiles and contour plots across a single stationary crossflow vortex track. Disturbance mode profiles and growth rates were determined. The experimental data are compared with predictions from linear stability theory.

Relativistic electron motion in cylindrical waveguide with strong guiding magnetic field and high power microwave

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

Wu, Ping; Science and Technology on High Power Microwave Laboratory, Northwest Institute of Nuclear Technology, Xi'an 710024; Sun, Jun

2015-06-15

In O-type high power microwave (HPM) devices, the annular relativistic electron beam is constrained by a strong guiding magnetic field and propagates through an interaction region to generate HPM. Some papers believe that the E × B drift of electrons may lead to beam breakup. This paper simplifies the interaction region with a smooth cylindrical waveguide to research the radial motion of electrons under conditions of strong guiding magnetic field and TM{sub 01} mode HPM. The single-particle trajectory shows that the radial electron motion presents the characteristic of radial guiding-center drift carrying cyclotron motion. The radial guiding-center drift is spatiallymore » periodic and is dominated by the polarization drift, not the E × B drift. Furthermore, the self fields of the beam space charge can provide a radial force which may pull electrons outward to some extent but will not affect the radial polarization drift. Despite the radial drift, the strong guiding magnetic field limits the drift amplitude to a small value and prevents beam breakup from happening due to this cause.« less

Mathematical modeling of vortex induced vibrations of an elastic rod under air flow influence

NASA Astrophysics Data System (ADS)

Pogudalina, S. V.; Fedorova, N. N.

2018-03-01

The results of simulations of the oscillations of an elastic rod placed normally to the external air flow and rigidly fixed on a substrate are presented. The computations were carried out in ANSYS using the technology of two-way fluid-structure interaction (2FSI). Calculations of the problem were performed for various flow velocities, geometric parameters and properties of the rod material. The frequencies, amplitudes and shapes of vortex induced vibration were studied including those that are close to the lock-in mode.

Hub vortex helical instability as the origin of wake meandering in the lee of a model wind-turbine

NASA Astrophysics Data System (ADS)

Viola, Francesco; Iungo, Giacomo Valerio; Camarri, Simone; Porte-Agel, Fernando; Gallaire, Francois

2012-11-01

Wind tunnel measurements were performed for the wake produced by a three-bladed wind turbine immersed in uniform flow. These tests show the presence of a vorticity structure in the near wake region mainly oriented along the streamwise direction, which is denoted as hub vortex. The hub vortex is characterized by oscillations with frequencies lower than the one connected to the rotational velocity of the rotor, which are ascribed to wake meandering by previous works. This phenomenon consists in transversal oscillations of the wind turbine wake, which are excited by the shedding of vorticity structures from the rotor disc acting as a bluff body. In this work temporal and spatial linear stability analyses of a wind turbine wake are performed on a base flow obtained through time-averaged wind tunnel velocity measurements. This study shows that the low frequency spectral component detected experimentally is the result of a convective instability of the hub vortex, which is characterized by a counter-winding single-helix structure. Simultaneous hot-wire measurements confirm the presence of a helicoidal unstable mode of the hub vortex with a streamwise wavenumber roughly equal to the one predicted from the linear instability analysis.

On the role of the lower hybrid drift instability in substorm dynamics

NASA Technical Reports Server (NTRS)

Huba, J. D.; Gladd, N. T.; Drake, J. F.

1981-01-01

Recent studies of the lower hybrid drift instability have shed new light on the role of this mode in field-reversed plasmas. For substorm magnetotail conditions it is found that the lower hybrid drift instability can penetrate to the neutral line and can dissipate magnetic energy at a rate of approximately 4 x 10 to the 17th erg/s. Thus this instability is capable of playing a major role in the onset of substorms and providing resistivity for reconnection processes in the context of the neutral line substorm model.

Three-dimensional transition after wake deflection behind a flapping foil.

PubMed

Deng, Jian; Caulfield, C P

2015-04-01

We report the inherently three-dimensional linear instabilities of a propulsive wake, produced by a flapping foil, mimicking the caudal fin of a fish or the wing of a flying animal. For the base flow, three sequential wake patterns appear as we increase the flapping amplitude: Bénard-von Kármán (BvK) vortex streets; reverse BvK vortex streets; and deflected wakes. Imposing a three-dimensional spanwise periodic perturbation, we find that the resulting Floquet multiplier |μ| indicates an unstable "short wavelength" mode at wave number β=30, or wavelength λ=0.21 (nondimensionalized by the chord length) at sufficiently high flow Reynolds number Re=Uc/ν≃600, where U is the upstream flow velocity, c is the chord length, and ν is the kinematic viscosity of the fluid. Another, "long wavelength" mode at β=6 (λ=1.05) becomes critical at somewhat higher Reynolds number, although we do not expect that this mode would be observed physically because its growth rate is always less than the short wavelength mode, at least for the parameters we have considered. The long wavelength mode has certain similarities with the so-called mode A in the drag wake of a fixed bluff body, while the short wavelength mode appears to have a period of the order of twice that of the base flow, in that its structure seems to repeat approximately only every second cycle of the base flow. Whether it is appropriate to classify this mode as a truly subharmonic mode or as a quasiperiodic mode is still an open question however, worthy of a detailed parametric study with various flapping amplitudes and frequencies.

Three-dimensional transition after wake deflection behind a flapping foil

NASA Astrophysics Data System (ADS)

Deng, Jian; Caulfield, C. P.

2015-04-01

We report the inherently three-dimensional linear instabilities of a propulsive wake, produced by a flapping foil, mimicking the caudal fin of a fish or the wing of a flying animal. For the base flow, three sequential wake patterns appear as we increase the flapping amplitude: Bénard-von Kármán (BvK) vortex streets; reverse BvK vortex streets; and deflected wakes. Imposing a three-dimensional spanwise periodic perturbation, we find that the resulting Floquet multiplier |μ | indicates an unstable "short wavelength" mode at wave number β =30 , or wavelength λ =0.21 (nondimensionalized by the chord length) at sufficiently high flow Reynolds number Re=U c /ν ≃600 , where U is the upstream flow velocity, c is the chord length, and ν is the kinematic viscosity of the fluid. Another, "long wavelength" mode at β =6 (λ =1.05 ) becomes critical at somewhat higher Reynolds number, although we do not expect that this mode would be observed physically because its growth rate is always less than the short wavelength mode, at least for the parameters we have considered. The long wavelength mode has certain similarities with the so-called mode A in the drag wake of a fixed bluff body, while the short wavelength mode appears to have a period of the order of twice that of the base flow, in that its structure seems to repeat approximately only every second cycle of the base flow. Whether it is appropriate to classify this mode as a truly subharmonic mode or as a quasiperiodic mode is still an open question however, worthy of a detailed parametric study with various flapping amplitudes and frequencies.

A field-assisted moderator for low-energy positron beams

NASA Astrophysics Data System (ADS)

Beling, C. D.; Simpson, R. I.; Charlton, M.; Jacobsen, F. M.; Griffith, T. C.; Moriarty, P.; Fung, S.

1987-01-01

A new positron field-assisted (FA) moderator based on the drift of positrons across a cooled silicon crystal is proposed. Using estimates for both the β + implantation profile and attainable drift velocities, the efficiency of drift to a slow e+ emitting surface is calculated using a diffusion equation which incorporates terms describing positron drift and annihilation. It is conjectured that efficiencies of up to 10% can be achieved. The use of epitaxially grown metallic suicide contacts to facilitate the application of the electric field is described and the consequences of using such contacts are fully discussed. Applications of the FA transmission mode moderator described here to produce timed brightness enhanced beams are briefly discussed.

Magnetic zero-modes, vortices and Cartan geometry

NASA Astrophysics Data System (ADS)

Ross, Calum; Schroers, Bernd J.

2018-04-01

We exhibit a close relation between vortex configurations on the 2-sphere and magnetic zero-modes of the Dirac operator on R^3 which obey an additional nonlinear equation. We show that both are best understood in terms of the geometry induced on the 3-sphere via pull-back of the round geometry with bundle maps of the Hopf fibration. We use this viewpoint to deduce a manifestly smooth formula for square-integrable magnetic zero-modes in terms of two homogeneous polynomials in two complex variables.

Genetic sex determination and extinction.

PubMed

Hedrick, Philip W; Gadau, Jürgen; Page, Robert E

2006-02-01

Genetic factors can affect the probability of extinction either by increasing the effect of detrimental variants or by decreasing the potential for future adaptive responses. In a recent paper, Zayed and Packer demonstrate that low variation at a specific locus, the complementary sex determination (csd) locus in Hymenoptera (ants, bees and wasps), can result in a sharply increased probability of extinction. Their findings illustrate situations in which there is a feedback process between decreased genetic variation at the csd locus owing to genetic drift and decreased population growth, resulting in an extreme type of extinction vortex for these ecologically important organisms.

Comparison of ionospheric plasma drifts obtained by different techniques

NASA Astrophysics Data System (ADS)

Kouba, Daniel; Arikan, Feza; Arikan, Orhan; Toker, Cenk; Mosna, Zbysek; Gok, Gokhan; Rejfek, Lubos; Ari, Gizem

2016-07-01

Ionospheric observatory in Pruhonice (Czech Republic, 50N, 14.9E) provides regular ionospheric sounding using Digisonde DPS-4D. The paper is focused on F-region vertical drift data. Vertical component of the drift velocity vector can be estimated by several methods. Digisonde DPS-4D allows sounding in drift mode with direct output represented by drift velocity vector. The Digisonde located in Pruhonice provides direct drift measurement routinely once per 15 minutes. However, also other different techniques can be found in the literature, for example the indirect estimation based on the temporal evolution of measured ionospheric characteristics is often used for calculation of the vertical drift component. The vertical velocity is thus estimated according to the change of characteristics scaled from the classical quarter-hour ionograms. In present paper direct drift measurement is compared with technique based on measuring of the virtual height at fixed frequency from the F-layer trace on ionogram, technique based on variation of h`F and hmF. This comparison shows possibility of using different methods for calculating vertical drift velocity and their relationship to the direct measurement used by Digisonde. This study is supported by the Joint TUBITAK 114E092 and AS CR 14/001 projects.

Energetic-particle-induced geodesic acoustic mode.

PubMed

Fu, G Y

2008-10-31

A new energetic particle-induced geodesic acoustic mode (EGAM) is shown to exist. The mode frequency and mode structure are determined nonperturbatively by energetic particle kinetic effects. In particular the EGAM frequency is found to be substantially lower than the standard GAM frequency. The radial mode width is determined by the energetic particle drift orbit width and can be fairly large for high energetic particle pressure and large safety factor. These results are consistent with the recent experimental observation of the beam-driven n=0 mode in DIII-D.

Non-perturbative modelling of energetic particle effects on resistive wall mode: Anisotropy and finite orbit width

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

Liu, Yueqiang, E-mail: yueqiang.liu@ccfe.ac.uk; Chapman, I. T.; Graves, J. P.

2014-05-15

A non-perturbative magnetohydrodynamic-kinetic hybrid formulation is developed and implemented into the MARS-K code [Liu et al., Phys. Plasmas 15, 112503 (2008)] that takes into account the anisotropy and asymmetry [Graves et al., Nature Commun. 3, 624 (2012)] of the equilibrium distribution of energetic particles (EPs) in particle pitch angle space, as well as first order finite orbit width (FOW) corrections for both passing and trapped EPs. Anisotropic models, which affect both the adiabatic and non-adiabatic drift kinetic energy contributions, are implemented for both neutral beam injection and ion cyclotron resonant heating induced EPs. The first order FOW correction does notmore » contribute to the precessional drift resonance of trapped particles, but generally remains finite for the bounce and transit resonance contributions, as well as for the adiabatic contributions from asymmetrically distributed passing particles. Numerical results for a 9MA steady state ITER plasma suggest that (i) both the anisotropy and FOW effects can be important for the resistive wall mode stability in ITER plasmas; and (ii) the non-perturbative approach predicts less kinetic stabilization of the mode, than the perturbative approach, in the presence of anisotropy and FOW effects for the EPs. The latter may partially be related to the modification of the eigenfunction of the mode by the drift kinetic effects.« less

Energization of Radiation Belt Electrons by High and Low Azimuthal Mode Number Poloidal Mode ULF Waves

NASA Astrophysics Data System (ADS)

Hudson, M. K.; Brito, T.; Elkington, S. R.; Kress, B. T.; Liang, Y.

2011-12-01

CME-shock and CIR-driven geomagnetic storms are characterized by enhanced ULF wave activity in the magnetosphere. This enhanced ULF wave power produces both coherent and diffusive transport and energization, as well as pitch angle modification of radiation belt electrons in drift resonance with azimuthally propagating ULF waves. Recent observations of two CME-driven storms1,2 have suggested that poloidal mode waves with both low and high azimuthal mode number may be efficient at accelerating radiation belt electrons. We extend up to m = 50 the analysis of Ozeke and Mann3 who examined drift resonance for poloidal modes up to m = 40. We calculate radial diffusion coefficients for source population electrons in the 50 -500 keV range, and continued resonance with lower m-numbers at higher energies for ULF waves in the Pc 5, 0.4 - 10 mHz range. We use an analytic model for ULF waves superimposed on a compressed dipole, developed for equatorial plane studies by Elkington et al.4 and extended to 3D by Perry et al.4 Assuming a power spectrum which varies as ω-2, consistent with earlier observations, we find greater efficiency for radial transport and acceleration at lower m number where there is greater power for drift resonance at a given frequency. This assumption is consistent with 3D global MHD simulations using the Lyon-Fedder-Mobarry code which we have carried out for realistic solar wind driving conditions during storms. Coherent interaction with ULF waves can also occur at a rate which exceeds nominal radial diffusion estimates but is slower than prompt injection on a drift time scale. Depending on initial electron drift phase, some electrons are accelerated due to the westward azimuthal electric field Eφ, while others are decelerated by eastward Eφ, decreasing their pitch angle. A subset of trapped electrons are seen to precipitate to the atmosphere in 3D LFM simulations, showing modulation at the coherent poloidal mode ULF wave frequency in both simulations and MINIS balloon observations for the January 21, 2005 CME-driven storm. Thus Pc 5 poloidal mode ULF waves cause competing increase and decrease in relativistic electron flux. The relative efficiencies of both coherent and diffusive processes will be examined. 1Zong et al., JGR, doi:10.1029/2009JA014393, 2009. 2Tan et al., JGR, doi:10.1029/2010JA016226, 2011. 3Ozeke and Mann, JGR, doi:10.1029/2007JA012468, 2008. 4Elkington et al., doi:10.1029/2001JA009202, 2003, 2003. 5Perry et al., doi:10.1029/2004JA010760, 2005.

Resonant Formation and Control of m-Fold Symmetric V-States

NASA Astrophysics Data System (ADS)

Friedland, Lazar; Shagalov, Arkadi

2000-10-01

Magnetized, pure electron plasmas trapped in a Malmberg-Penning trap can be modeled (in the drift approximation) by two-dimensional Euler equations of ideal fluids. The plasma density in this approximation is analogous to vorticity, while the radial electric field potential to the stream function of the fluid velocity field. For instance, electron plasma cylinder aligned with the magnetic field is analogous to a circular vortex patch solution of an ideal fluid. We shall show that by starting in such a circular equilibrium one can drive an m-fold symmetric interface (vortex) waves in two dimensions (V-states, discovered by Deem and Zabusky [1] nearly 20 years ago)into a highly nonlinear excitation by applying a weak external oscillating potential of appropriate symmetry and slowly varying the frequency of these oscillations. The phenomenon is due to autoresonance [2,3] in the system as the excited plasma (vortex) boundary preserves its functional form despite the drive, but self-adjusts the aspect ratio to synchronize with the driving potential oscillations. A similar approach can be used in controlling interface dynamics subject to global constraints in many other fields of physics. Work supported by Israel Science Foundation grant 607-97 and INTAS grant 99-1068. [1] G. Deem and N. Zabusky, Phys. Rev. Lett. 40, 859 (1978). [2] L. Friedland, Phys. Rev. E, 4106 (1999). [3] J. Fajans, E. Gilson, and L. Friedland, Phys. Rev. Lett. 82, 4444 (1999).

The effect of crossflow on Taylor vortices: A model problem

NASA Technical Reports Server (NTRS)

Otto, S. R.; Bassom, Andrew P.

1993-01-01

A number of practically relevant problems involving the impulsive motion or the rapid rotation of bodies immersed in fluid are susceptible to vortex-like instability modes. Depending upon the configuration of any particular problem the stability properties of any high-wavenumber vortices can take on one of two distinct forms. One of these is akin to the structure of Gortler vortices in boundary layer flows while the other is similar to the situation for classical Taylor vortices. Both the Gortler and Taylor problems have been extensively studied when crossflow effects are excluded from the underlying base flows. Recently, studies were made concerning the influence of crossflow on Gortler modes and a linearized stability analysis is used to examine crossflow properties for the Taylor mode. This work allows us to identify the most unstable vortex as the crossflow component increases and it is shown how, like the Gortler case, only a very small crossflow component is required in order to completely stabilize the flow. Our investigation forms the basis for an extension to the nonlinear problem and is of potential applicability to a range of pertinent flows.

Analysis of Poiseuille Flow Property in Two-Dimensional Mi-cro Channels of Microfluidic Pneumatic Micro-Valve

NASA Astrophysics Data System (ADS)

Yang, Shaohua; Long, Wei; Chen, Yajun

2018-03-01

In this paper, the control mechanism and mathematical description of the microfluidic flow in the microfluidic process of the PDMS membrane type pneumatic micro-valve were studied. The velocity and pressure variation law of the velocity field inside micro valve was analyzed by numerical simulation method. The influence of the two kinds of inlet drive modes on the working effect and the pressure flow characteristics of the pneumatic micro-valve was studied. The structure of the elastic solid valve diaphragm under the dual action of the airway and the liquid channel was analyzed. Deformation and stress distribution. The results show that the gas flow in the gas flow channel under the diaphragm by the vacuum part of the role of the formation of a suction gas vortex, pressure-driven mode was easier under the diaphragm to produce a strong gas vortex, resulting in internal and external pressure to promote diaphragm cut-off liquid channel; In the pressure pneumatic mode, the stress at both ends of the diaphragm was smaller, the membrane was not easy to tear failure.

Vortex dynamics and heat transfer behind self-oscillating inverted flags of various lengths in channel flow

NASA Astrophysics Data System (ADS)

Yu, Yuelong; Liu, Yingzheng; Chen, Yujia

2018-04-01

The influence of an inverted flag's length-to-channel-width ratio (C* = L/W) on its oscillating behavior in a channel flow and the resultant vortex dynamics and heat transfer are determined experimentally. Three systems with C* values of 0.125, 0.250, and 0.375 were chosen for comparison. The interaction of highly unsteady flow with the inverted flag is measured with time-resolved particle image velocimetry. Variations in the underlying flow physics are discussed in terms of the statistical flow quantities, flag displacement, phase-averaged flow field, and vortex dynamics. The results show that the increase in C* shifts the occurrence of the flapping regime at high dimensionless bending stiffness. With the flag in the flapping region, three distinct vortex dynamics—the von Kármán vortex street, the G mode, and the singular mode—are identified at C* values of 0.375, 0.250, and 0.125, respectively. Finally, the heat transfer enhancement from the self-oscillating inverted flag is measured to serve as complementary information to quantify the cause-and-effect relationship between vortex dynamics and wall heat transfer. The increase in C* strongly promotes wall heat removal because disruption of the boundary layer by the energetic vortices is substantially intensified. Among all systems, wall heat transfer removal is most efficient at the intermediate C* value of 0.250.

Two improvements on numerical simulation of 2-DOF vortex-induced vibration with low mass ratio

NASA Astrophysics Data System (ADS)

Kang, Zhuang; Ni, Wen-chi; Zhang, Xu; Sun, Li-ping

2017-12-01

Till now, there have been lots of researches on numerical simulation of vortex-induced vibration. Acceptable results have been obtained for fixed cylinders with low Reynolds number. However, for responses of 2-DOF vortex-induced vibration with low mass ratio, the accuracy is not satisfactory, especially for the maximum amplitudes. In Jauvtis and Williamson's work, the maximum amplitude of the cylinder with low mass ratio m*=2.6 can reach as large as 1.5 D to be called as the "super-upper branch", but from current literatures, few simulation results can achieve such value, even fail to capture the upper branch. Besides, it is found that the amplitude decays too fast in the lower branch with the RANS-based turbulence model. The reason is likely to be the defects of the turbulence model itself in the prediction of unsteady separated flows as well as the unreasonable setting of the numerical simulation parameters. Aiming at above issues, a modified turbulence model is proposed in this paper, and the effect of the acceleration of flow field on the response of vortex-induced vibration is studied based on OpenFOAM. By analyzing the responses of amplitude, phase and trajectory, frequency and vortex mode, it is proved that the vortex-induced vibration can be predicted accurately with the modified turbulence model under appropriate flow field acceleration.

Localized tearing modes in the magnetotail driven by curvature effects

NASA Technical Reports Server (NTRS)

Sundaram, A. K.; Fairfield, D. H.

1995-01-01

The stability of collisionless tearing modes is examined in the presence of curvature drift resonances and the trapped particle effects. A kinetic description for both electrons and ions is employed to investigate the stability of a two-dimensional equilibrium model. The main features of the study are to treat the ion dynamics properly by incorporating effects associated with particle trajectories in the tail fields and to include the linear coupling of trapped particle modes. Generalized dispersion relations are derived in several parameter regimes by considering two important sublayers of the reconnecting region. For a typical choice of parameters appropriate to the current sheet region, we demonstrate that localized tearing modes driven by ion curvature drift resonance effects are excited in the current sheet region with growth time of the order of a few seconds. Also, we examine nonlocal characteristics of tearing modes driven by curvature effects and show that modes growing in a fraction of a second arise when mode widths are larger than the current sheet width. Further, we show that trapped particle effects, in an interesting frequency regime, significantly enhance the growth rate of the tearing mode. The relevance of this theory for substorm onset phase and other features of the substorms is briefly discussed.

Vortex dynamics of in-line twin synthetic jets in a laminar boundary layer

NASA Astrophysics Data System (ADS)

Wen, Xin; Tang, Hui; Duan, Fei

2015-08-01

An experimental investigation is conducted on the vortices induced by twin synthetic jets (SJs) in line with a laminar boundary layer flow over a flat plate. The twin SJs operating at four different phase differences, i.e., Δϕ = 0°, 90°, 180°, and 270°, are visualized using a stereoscopic color dye visualization system and measured using a two-dimensional particle image velocimetry (PIV) system. It is found that depending on the phase difference of twin SJs, three types of vortex structures are produced. At Δϕ = 90°, the two hairpin vortices interact in a very constructive way in terms of the vortex size, strength, and celerity, forming one combined vortex. At Δϕ = 270°, the two individual hairpin vortices do not have much interaction, forming two completely separated hairpin vortices that behave like doubling the frequency of the single SJ case. At Δϕ = 0° and 180°, the two hairpin vortices produced by the twin SJ actuators are close enough, with the head of one hairpin vortex coupled with the legs of the other, forming partially interacting vortex structures. Quantitative analysis of the twin SJs is conducted, including the time histories of vortex circulation in the mid-span plane as well as a selected spanwise-wall-normal plane, and the influence of the twin SJs on the boundary layer flow filed. In addition, dynamic mode decomposition analysis of the PIV data is conducted to extract representative coherent structures. Through this study, a better understanding in the vortex dynamics associated with the interaction of in-line twin SJs in laminar boundary layers is achieved, which provides useful information for future SJ-array applications.

Cavitating vortices in the guide vanes region related to the pump-turbine pumping mode rotating stall

NASA Astrophysics Data System (ADS)

Ješe, U.; Skotak, A.; Mikulašek, J.

2017-04-01

Reversible pump-turbines used in Pumped Storage Power Plants are among the most cost-efficient solutions for storing and recovering large amount of energy in short time. Presented paper is focused on the pump-turbine pumping mode part-load instabilities, among them the rotating stall and the cavitating vortex in the distributor region. Rotating stall can be described as a periodic occurrence and decay of the recirculation zones in the distributor with its own rotational characteristics frequency. Unstable behaviour can result in high radial forces, high pressure fluctuations and local velocity fluctuations that can in some cases lead into the occurrence of the cavitating vortex in the distributor region, even though the distributor is located in the high pressure region. Computationally demanding calculations have been performed using commercial CFD code. Analysed results have been compared to the experimental data obtained in the ČKD Blansko Engineering hydraulic laboratory.

Orszag Tang vortex - Kinetic study of a turbulent plasma

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

Parashar, T. N.; Servidio, S.; Shay, M. A.

Kinetic evolution of the Orszag-Tang vortex is studied using collisionless hybrid simulations based on particle in cell ions and fluid electrons. In magnetohydrodynamics (MHD) this configuration leads rapidly to broadband turbulence. An earlier study estimated the dissipation in the system. A comparison of MHD and hybrid simulations showed similar behavior at large scales but substantial differences at small scales. The hybrid magnetic energy spectrum shows a break at the scale where Hall term in the Ohm's law becomes important. The protons heat perpendicularly and most of the energy is dissipated through magnetic interactions. Here, the space time structure of themore » system is studied using frequency-wavenumber (k-omega) decomposition. No clear resonances appear, ruling out the cyclotron resonances as a likely candidate for the perpendicular heating. The only distinguishable wave modes present, which constitute a small percentage of total energy, are magnetosonic modes.« less

Effects of homogeneous condensation in compressible flows: Ludwieg-tube experiments and simulations

NASA Astrophysics Data System (ADS)

Luo, Xisheng; Lamanna, Grazia; Holten, A. P. C.; van Dongen, M. E. H.

Effects of homogeneous nucleation and subsequent droplet growth in compressible flows in humid nitrogen are investigated numerically and experimentally. A Ludwieg tube is employed to produce expansion flows. Corresponding to different configurations, three types of experiment are carried out in such a tube. First, the phase transition in a strong unsteady expansion wave is investigated to demonstrate the mutual interaction between the unsteady flow and the condensation process and also the formation of condensation-induced shock waves. The role of condensation-induced shocks in the gradual transition from a frozen initial structure to an equilibrium structure is explained. Second, the condensing flow in a slender supersonic nozzle G2 is considered. Particular attention is given to condensation-induced oscillations and to the transition from symmetrical mode-1 oscillations to asymmetrical mode-2 oscillations in a starting nozzle flow, as first observed by Adam & Schnerr. The transition is also found numerically, but the amplitude, frequency and transition time are not yet well predicted. Third, a sharp-edged obstacle is placed in the tube to generate a starting vortex. Condensation in the vortex is found. Owing to the release of latent heat of condensation, an increase in the pressure and temperature in the vortex core is observed. Condensation-induced shock waves are found, for a sufficiently high initial saturation ratio, which interact with the starting vortex, resulting in a very complex flow. As time proceeds, a subsonic or transonic free jet is formed downstream of the sharp-edged obstacle, which becomes oscillatory for a relatively high main-flow velocity and for a sufficiently high humidity.

Linear instability in the wake of an elliptic wing

NASA Astrophysics Data System (ADS)

He, Wei; Tendero, Juan Ángel; Paredes, Pedro; Theofilis, Vassilis

2017-12-01

Linear global instability analysis has been performed in the wake of a low aspect ratio three-dimensional wing of elliptic cross section, constructed with appropriately scaled Eppler E387 airfoils. The flow field over the airfoil and in its wake has been computed by full three-dimensional direct numerical simulation at a chord Reynolds number of Rec=1750 and two angles of attack, {AoA}=0° and 5°. Point-vortex methods have been employed to predict the inviscid counterpart of this flow. The spatial BiGlobal eigenvalue problem governing linear small-amplitude perturbations superposed upon the viscous three-dimensional wake has been solved at several axial locations, and results were used to initialize linear PSE-3D analyses without any simplifying assumptions regarding the form of the trailing vortex system, other than weak dependence of all flow quantities on the axial spatial direction. Two classes of linearly unstable perturbations were identified, namely stronger-amplified symmetric modes and weaker-amplified antisymmetric disturbances, both peaking at the vortex sheet which connects the trailing vortices. The amplitude functions of both classes of modes were documented, and their characteristics were compared with those delivered by local linear stability analysis in the wake near the symmetry plane and in the vicinity of the vortex core. While all linear instability analysis approaches employed have delivered qualitatively consistent predictions, only PSE-3D is free from assumptions regarding the underlying base flow and should thus be employed to obtain quantitative information on amplification rates and amplitude functions in this class of configurations.

Flux-driven algebraic damping of m = 1 diocotron mode

NASA Astrophysics Data System (ADS)

Chim, Chi Yung; O'Neil, Thomas M.

2016-07-01

Recent experiments with pure electron plasmas in a Malmberg-Penning trap have observed the algebraic damping of m = 1 diocotron modes. Transport due to small field asymmetries produces a low density halo of electrons moving radially outward from the plasma core, and the mode damping begins when the halo reaches the resonant radius r = Rw at the wall of the trap. The damping rate is proportional to the flux of halo particles through the resonant layer. The damping is related to, but distinct from, spatial Landau damping, in which a linear wave-particle resonance produces exponential damping. This paper explains with analytic theory the new algebraic damping due to particle transport by both mobility and diffusion. As electrons are swept around the "cat's eye" orbits of the resonant wave-particle interaction, they form a dipole (m = 1) density distribution. From this distribution, the electric field component perpendicular to the core displacement produces E × B-drift of the core back to the axis, that is, damps the m = 1 mode. The parallel component produces drift in the azimuthal direction, that is, causes a shift in the mode frequency.

Entangled singularity patterns of photons in Ince-Gauss modes

NASA Astrophysics Data System (ADS)

Krenn, Mario; Fickler, Robert; Huber, Marcus; Lapkiewicz, Radek; Plick, William; Ramelow, Sven; Zeilinger, Anton

2013-01-01

Photons with complex spatial mode structures open up possibilities for new fundamental high-dimensional quantum experiments and for novel quantum information tasks. Here we show entanglement of photons with complex vortex and singularity patterns called Ince-Gauss modes. In these modes, the position and number of singularities vary depending on the mode parameters. We verify two-dimensional and three-dimensional entanglement of Ince-Gauss modes. By measuring one photon and thereby defining its singularity pattern, we nonlocally steer the singularity structure of its entangled partner, while the initial singularity structure of the photons is undefined. In addition we measure an Ince-Gauss specific quantum-correlation function with possible use in future quantum communication protocols.

A Long-lived Cyclone In Saturn's Atmosphere: Observations And Models

NASA Astrophysics Data System (ADS)

Del Rio Gaztelurrutia, Teresa; Legarreta, J.; Hueso, R.; Pérez-Hoyos, S.; Sánchez-Lavega, A.

2009-09-01

The atmospheres of the Giant Planets Jupiter and Saturn possess large numbers of atmospheric vortices. On Jupiter, anticyclones are generally long-lived structures while cyclones survive a much shorter time. A long term survey of images of Saturn atmosphere obtained by the Cassini ISS camera has revealed the presence of a long-lived cyclone in Saturn's southern hemisphere during at least four years, making this vortex the longest lived cyclone on either Jupiter or Saturn. We find that the vortex drifts following the wind profile, with changes in velocity following changes of latitude. During the four years of our survey its size remained essentially constant, and there was no other structure of comparable size at its latitude. Internal circulation is cyclonic, with a maximum velocity of 20±5 m/s and an average vorticity of 4·10-5 s-1, an order of magnitude lower than planetary vorticity, but only slightly higher than the ambient vorticity. Photometric analysis shows that the vortex is located at a slightly lower altitude than its surroundings, at an average of 10-20 mbar below adjacent clouds. Finally, EPIC simulations of the vortex that reproduce its behavior imply a Rossby deformation radius of 2000 km in the weather layer (1 - 10 bar), consistent with the size of the cyclone. The long-lifetime of this cyclonic spot is surprising in view of its low tangential velocity and it suggests that low dissipation conditions prevail at mid-latitudes in Saturn's upper troposphere. Acknowledgements This work has been funded by Spanish MEC AYA2006-07735 with FEDER support and Grupos Gobierno Vasco IT-464-07. RH acknowledges a "Ramón y Cajal” contract from MEC.

A femtosecond Yb-doped fiber laser with generalized vector vortex beams output (Conference Presentation)

NASA Astrophysics Data System (ADS)

Huo, Tiancheng; Qi, Li; Zhang, Buyun; Chen, Zhongping

2017-03-01

Light carries both spin and orbital angular momentum (OAM) and the superpositions of these two dynamical properties have found many applications. Many techniques exist to create such light sources but none allow their creation at the femtosecond fiber laser. Here we report on a novel mode-locked Ytterbium-doped fiber laser that generates femtosecond pulses with generalized vector vortex states. The controlled generation of such pulses such as azimuthally and radially polarized light with definite orbital angular momentum modes are demonstrated. A unidirectional ring cavity constructed with the Yb-doped fiber placed at the end of the fiber section to reduces unnecessary nonlinear effects is employed for self-starting operation. Pairs of diffraction gratings are used for compensating the normal group velocity dispersion of the fiber and other elements. Mode-locked operation is achieved based on nonlinear polarization evolution, which is mainly implemented with the single mode fiber, the bulk wave plates and the variable spiral plates (q-plate with topological charge q=0.5). The conversion from spin angular momentum to the OAM and reverse inside the laser cavity are realized by means of a quarter-wave plate and a q-plate so that the polarization control was mapped to OAM mode control. The fiber laser is diode pumped by a wavelength-division multiplexing coupler, which leads to excellent stability and portability.

Topological defects in the Georgi-Machacek model

NASA Astrophysics Data System (ADS)

Chatterjee, Chandrasekar; Kurachi, Masafumi; Nitta, Muneto

2018-06-01

We study topological defects in the Georgi-Machacek model in a hierarchical symmetry breaking in which extra triplets acquire vacuum expectation values before the doublet. We find a possibility of topologically stable non-Abelian domain walls and non-Abelian flux tubes (vortices or cosmic strings) in this model. In the limit of the vanishing U (1 )Y gauge coupling in which the custodial symmetry becomes exact, the presence of a vortex spontaneously breaks the custodial symmetry, giving rise to S2 Nambu-Goldstone (NG) modes localized around the vortex corresponding to non-Abelian fluxes. Vortices are continuously degenerated by these degrees of freedom, thereby called non-Abelian. By taking into account the U (1 )Y gauge coupling, the custodial symmetry is explicitly broken, the NG modes are lifted to become pseudo-NG modes, and all non-Abelian vortices fall into a topologically stable Z string. This is in contrast to the standard model in which Z strings are nontopological and are unstable in the realistic parameter region. Non-Abelian domain walls also break the custodial symmetry and are accompanied by localized S2 NG modes. Finally, we discuss the existence of domain wall solutions bounded by flux tubes, where their S2 NG modes match. The domain walls may quantum mechanically decay by creating a hole bounded by a flux tube loop, and would be cosmologically safe. Gravitational waves produced from unstable domain walls could be detected by future experiments.

Crossflow Stability and Transition Experiments in a Swept-Wing Flow. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Dagenhart, John Ray

1992-01-01

An experimental examination of crossflow instability and transition on a 45 degree swept wing is conducted in the Arizona State University Unsteady Wind Tunnel. The stationary-vortex pattern and transition location are visualized using both sublimating-chemical and liquid-crystal coatings. Extensive hot-wire measurements are conducted at several measurement stations across a single vortex track. The mean and travelling-wave disturbances are measured simultaneously. Stationary-crossflow disturbance profiles are determined by subtracting either a reference or a span-averaged velocity profile from the mean-velocity data. Mean, stationary-crossflow, and travelling-wave velocity data are presented as local boundary-layer profiles and as contour plots across a single stationary-crossflow vortex track. Disturbance-mode profiles and growth rates are determined. The experimental data are compared to predictions from linear stability theory.

Numerical study of spherical Taylor-Couette flow

NASA Technical Reports Server (NTRS)

Yang, R.-J.

1989-01-01

A new technique to simulate Taylor vortices in a spherical gap between a rotating inner sphere and a stationary outer one has been developed and tested. Paths leading to zero-, one-, and two-vortex flows are designed heuristically. Fictitious symmetric boundaries near the equator are imposed, and the choice of the location of the fictitious boundaries is determined by either one- or two-vortex flow being stimulated. The imposition of one or two fictitious boundaries during the initial calculation generates the state suitable for one-or two-vortex flow to exist. After removing the fictitious boundaries, the flow settles down into its own attractor. Using this method, the three steady flow modes can be simulated by using a half domain. The technique can converge to desired flows very fast, and its results show excellent agreement with experimental ones.

Drift waves control using emissive cathodes in the laboratory

NASA Astrophysics Data System (ADS)

Plihon, N.; Desangles, V.; De Giorgio, E.; Bousselin, G.; Marino, R.; Pustelnik, N.; Poye, A.

2017-12-01

Low frequency plasma fluctuations are known to be the cause of strong transport perpendicular to magnetic guiding field line. These low frequency drift waves have been studied in linear devices in the laboratory over the last two decades. Their excitation or mitigation have been addressed using different drives, such as ring biasing or electromagnetic low frequency fields. Here we present an experimental characterization of the behavior of drift waves when the profile of the background plasma rotation is controlled using hot emissive cathodes. We show that electron emission from the cathodes modify the plasma potential, which in turn controls the rotation profile. Mitigation or enhancement of drift waves (on the amplitude or azimuthal mode number) is observed depending on the plasma rotation profile.

Ion-mobility study of two functionalized pentacene structural isomers using a modified electrospray/triple quadrupole mass spectrometer

NASA Astrophysics Data System (ADS)

Prada, Svitlana V.; Bohme, Diethard K.; Baranov, Vladimir I.

2007-03-01

We report ion-mobility measurements with a modified triple quadrupole mass spectrometer fitted with an ion molecule reactor (IMR) designed to investigate ion molecule reactivity in organic mass spectrometry. Functionalized pentacene ions, which are generally unreactive were chosen for study to decouple drift/diffusion effects from reactivity (including clustering). The IMR is equipped with a variable axial electrostatic drift field (ADF) and is able to trap ions. These capabilities were successfully employed in the measurement of ion mobilities in different modes of IMR operation. Theoretical modeling of the drift dynamics and the special localization of the large ion packet was successfully implemented. The contribution of the quadrupole RF field to the drift dynamics also was taken into consideration.

Optical-vortex pair creation and annihilation and helical astigmatism of a nonplanar ring resonator

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

Heckenberg, N.R.; Vaupel, M.; Malos, J.T.

1996-09-01

The creation and annihilation of pairs of optical vortices have been studied in transitions between patterns produced in a photorefractive oscillator. Smooth metamorphosis between stable patterns occurs through pair creation or annihilation but can be modeled using superposition of modes taking into account lifting of degeneracy of helical modes by helical astigmatism of the resonator. {copyright} {ital 1996 The American Physical Society.}

Center Frequency Stabilization in Planar Dual-Mode Resonators during Mode-Splitting Control

NASA Astrophysics Data System (ADS)

Naji, Adham; Soliman, Mina H.

2017-03-01

Shape symmetry in dual-mode planar electromagnetic resonators results in their ability to host two degenerate resonant modes. As the designer enforces a controllable break in the symmetry, the degeneracy is removed and the two modes couple, exchanging energy and elevating the resonator into its desirable second-order resonance operation. The amount of coupling is controlled by the degree of asymmetry introduced. However, this mode coupling (or splitting) usually comes at a price. The centre frequency of the perturbed resonator is inadvertently drifted from its original value prior to coupling. Maintaining centre frequency stability during mode splitting is a nontrivial geometric design problem. In this paper, we analyse the problem and propose a novel method to compensate for this frequency drift, based on field analysis and perturbation theory, and we validate the solution through a practical design example and measurements. The analytical method used works accurately within the perturbational limit. It may also be used as a starting point for further numerical optimization algorithms, reducing the required computational time during design, when larger perturbations are made to the resonator. In addition to enabling the novel design example presented, it is hoped that the findings will inspire akin designs for other resonator shapes, in different disciplines and applications.

Effects of in-plane magnetic field on the transport of 2D electron vortices in non-uniform plasmas

NASA Astrophysics Data System (ADS)

Angus, Justin; Richardson, Andrew; Schumer, Joseph; Pulsed Power Team

2015-11-01

The formation of electron vortices in current-carrying plasmas is observed in 2D particle-in-cell (PIC) simulations of the plasma-opening switch. In the presence of a background density gradient in Cartesian systems, vortices drift in the direction found by crossing the magnetic field with the background density gradient as a result of the Hall effect. However, most of the 2D simulations where electron vortices are seen and studied only allow for in-plane currents and thus only an out-of-plane magnetic field. Here we present results of numerical simulations of 2D, seeded electron vortices in an inhomogeneous background using the generalized 2D electron-magneto-hydrodynamic model that additionally allows for in-plane components of the magnetic field. By seeding vortices with a varying axial component of the velocity field, so that the vortex becomes a corkscrew, it is found that a pitch angle of around 20 degrees is sufficient to completely prevent the vortex from propagating due to the Hall effect for typical plasma parameters. This work is supported by the NRL Base Program.

NUMERICAL SIMULATIONS OF KELVIN–HELMHOLTZ INSTABILITY: A TWO-DIMENSIONAL PARAMETRIC STUDY

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

Tian, Chunlin; Chen, Yao, E-mail: chunlin.tian@sdu.edu.cn

2016-06-10

Using two-dimensional simulations, we numerically explore the dependences of Kelvin–Helmholtz (KH) instability upon various physical parameters, including viscosity, the width of the sheared layer, flow speed, and magnetic field strength. In most cases, a multi-vortex phase exists between the initial growth phase and the final single-vortex phase. The parametric study shows that the evolutionary properties, such as phase duration and vortex dynamics, are generally sensitive to these parameters, except in certain regimes. An interesting result is that for supersonic flows, the phase durations and saturation of velocity growth approach constant values asymptotically as the sonic Mach number increases. We confirmmore » that the linear coupling between magnetic field and KH modes is negligible if the magnetic field is weak enough. The morphological behavior suggests that the multi-vortex coalescence might be driven by the underlying wave–wave interaction. Based on these results, we present a preliminary discussion of several events observed in the solar corona. The numerical models need to be further improved to perform a practical diagnostic of the coronal plasma properties.« less

Highly Efficient Broadband Multiplexed Millimeter-Wave Vortices from Metasurface-Enabled Transmit-Arrays of Subwavelength Thickness

NASA Astrophysics Data System (ADS)

Jiang, Zhi Hao; Kang, Lei; Hong, Wei; Werner, Douglas H.

2018-06-01

Structured electromagnetic waves carrying nonvanishing orbital angular momentum (OAM) have recently opened up alternative frontiers in the field of wave physics, holding great promise for a wide range of potential applications. By leveraging geometric phases originating from spin-to-orbital interactions, spin-dependent wave phenomena can be created, leading to a more versatile realm of dispersionless wave-front manipulation. However, the currently available transmissive vortex-beam generators suffer from a narrow bandwidth, require an optically thick device profile, or are limited by a low efficiency, severely restricting their integration into systems and/or widespread usage for practical applications. We present the design methodology and a physical analysis and complete experimental characterization of a class of millimeter-wave Pancharatnam-Berry transmit-arrays with a thickness of about λ0/3 , which enables highly efficient generation and separation of spin-controlled vortex beams over a broad bandwidth, achieving an unprecedented peak efficiency of 88% for a single vortex beam and 71% for dual vortex beams. The proposed transmit-array, which is capable of providing two-dimensional OAM multiplexing and demultiplexing without normal-mode background interference, overcomes all previous roadblocks and paves the way for high-efficiency electromagnetic vortex-beam generation as well as other wave-front-shaping devices from microwave frequencies to optical wavelengths.

Radiation from a space charge dominated linear electron beam

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

Biswas, Debabrata

2008-01-15

It is commonly known that radiation loss in linear beam transport is largely unimportant. For a space charge dominated linear beam, however, radiation power loss can be an appreciable fraction of the injected beam power [Biswas, Kumar, and Puri, Phys. Plasmas 14, 094702 (2007)]. Exploring this further, the electromagnetic nature of radiation due to the passage of a space charge dominated electron beam in a 'closed' drift tube is explicitly demonstrated by identifying the cavity modes where none existed prior to beam injection. It is further shown that even in an 'open' drift tube from which radiation may leak, themore » modes that escape contribute to the time variation of the electric and magnetic fields in the transient phase. As the window opening increases, the oscillatory transient phase disappears altogether. However, the 'bouncing ball' modes survive and can be observed between the injection and collection plates.« less

Triggered emissions close to the proton gyrofrequency seen by Cluster

NASA Astrophysics Data System (ADS)

Grison, Benjamin; Pickett, Jolene; Omura, Yoshiharu; Santolik, Ondrej; Decreau, Pierrette; Masson, Arnaud; Engebretson, Mark; Cornilleau-Wehrlin, Nicole; Robert, Patrick; Dandouras, Iannis

Electromagnetic ion cyclotron (EMIC) triggered emissions have been recently observed onboard the Cluster spacecraft close to the plasmapause in the equatorial region of the magnetosphere. These waves appear as "risers": electromagnetic structures that have a positive frequency drift with time, i.e., the EMIC analogue of rising frequency whistler mode triggered emissions and chorus waves. In our first results concerning the emission process based on a single event, these risers have the following properties: they propagate away from the direction of the magnetic equator, they have elliptical left-handed polarization corresponding to the transverse Alfven mode, and frequency drifts of about 30 mHz/s. These risers are not common in the Cluster data set. Nevertheless a few other events were found with similar properties. Another interesting preliminary result is the existence of risers with a polarization opposite that of the EMIC triggered emissions and which correspond to the fast magnetosonic mode.

Advection modes by optimal mass transfer

NASA Astrophysics Data System (ADS)

Iollo, Angelo; Lombardi, Damiano

2014-02-01

Classical model reduction techniques approximate the solution of a physical model by a limited number of global modes. These modes are usually determined by variants of principal component analysis. Global modes can lead to reduced models that perform well in terms of stability and accuracy. However, when the physics of the model is mainly characterized by advection, the nonlocal representation of the solution by global modes essentially reduces to a Fourier expansion. In this paper we describe a method to determine a low-order representation of advection. This method is based on the solution of Monge-Kantorovich mass transfer problems. Examples of application to point vortex scattering, Korteweg-de Vries equation, and hurricane Dean advection are discussed.

Stability of Mars' annular polar vortex

NASA Astrophysics Data System (ADS)

Seviour, W.; Waugh, D.; Scott, R.

2016-12-01

In common with the Earth and several other planetary bodies, the martian atmosphere exhibits regions of high potential vorticity (PV) near the winter pole, known as polar vortices. On Earth, PV increases monotonically from the equator to pole, however, on Mars there is a local minimum at the pole, with an annulus of high PV encircling it. Recently produced reanalyses of the martian atmospheric circulation have confirmed that this annular vortex is a persistent feature, forming in autumn and lasting until spring. This finding is surprising since an isolated band of PV is barotropically unstable, a result going back to Rayleigh. Here we investigate the stability of an annular vortex using numerical integrations of the rotating shallow water equations. We show that the mode of instability and its growth rate strongly depends upon the latitude and width of the annulus. By introducing thermal relaxation with a time scale similar to that of the instability we are able to simulate a persistent annular vortex with similar characteristics as that observed in the martian atmosphere. This time scale, typically 1-2 sols, is similar to thermal relaxation timescales which have been estimated for the martian atmosphere. We also demonstrate that the persistence of an annular vortex is robust to topographic forcing, as long as it is below a certain amplitude. We hence propose that the persistence of this barotropically unstable annular vortex is permitted due to the combination of short radiative relaxation time scales and relatively weak topographic forcing in the martian polar atmosphere.

Anomalous transport in the H-mode pedestal of Alcator C-Mod discharges

NASA Astrophysics Data System (ADS)

Pankin, A. Y.; Hughes, J. W.; Greenwald, M. J.; Kritz, A. H.; Rafiq, T.

2017-02-01

Anomalous transport in the H-mode pedestal region of five Alcator C-Mod discharges, representing a collisionality scan is analyzed. The understanding of anomalous transport in the pedestal region is important for the development of a comprehensive model for the H-mode pedestal slope. In this research, a possible role of the drift resistive inertial ballooning modes (Rafiq et al 2010 Phys. Plasmas 17 082511) in the edge of Alcator C-Mod discharges is analyzed. The stability analysis, carried out using the TRANSP code, indicates that the DRIBM modes are strongly unstable in Alcator C-Mod discharges with large electron collisionality. An improved interpretive analysis of H-mode pedestal experimental data is carried out utilizing the additive flux minimization technique (Pankin et al 2013 Phys. Plasmas 20 102501) together with the guiding-center neoclassical kinetic XGC0 code. The neoclassical and neutral physics are simulated in the XGC0 code and the anomalous fluxes are computed using the additive flux minimization technique. The anomalous fluxes are reconstructed and compared with each other for the collisionality scan Alcator C-Mod discharges. It is found that the electron thermal anomalous diffusivities at the pedestal top increase with the electron collisionality. This dependence can also point to the drift resistive inertial ballooning modes as the modes that drive the anomalous transport in the plasma edge of highly collisional discharges.

Experimental study on parasitic mode suppression using FeSiAl in relativistic klystron amplifier

NASA Astrophysics Data System (ADS)

Zhang, Zehai

2015-03-01

Experimental study of parasitic mode suppression using electromagnetic attenuate material FeSiAl in an S-band Relativistic Klystron Amplifier (RKA) is presented in this paper. The FeSiAl powder is coated and sintered onto the inner surface of a drift tube which locates between the input and the middle cavity of the RKA. Cold tests show that the attenuate rate of the tube against parasitic mode TE11 is about 50%. Experiments carried out on the Torch-01 accelerator present that the tube is effective in suppressing the parasitic mode. Two typical outputs are obtained. When the diode voltage is on a moderate level, the RKA operates well and the parasitic mode is totally suppressed. The pulse length of the High Power Microwave (HPM) almost equals the electron beam pulse length and the HPM average output power is about 300 MW, with a power efficiency of 10%. When the diode voltage is on a higher level, the output power and efficiency rise but the parasitic mode oscillation occurred and the pulse length is shortened. By contrast, the parasitic mode oscillation is too strong for the RKA to operate normally with un-sintered drift tube. The experimental study implies that FeSiAl is effective in suppressing the parasitic mode oscillation in a certain extent. However, total suppression needs a deeper attenuate rate and further investigation.

Experimental study on parasitic mode suppression using FeSiAl in Relativistic Klystron Amplifier.

PubMed

Zhang, Zehai

2015-03-01

Experimental study of parasitic mode suppression using electromagnetic attenuate material FeSiAl in an S-band Relativistic Klystron Amplifier (RKA) is presented in this paper. The FeSiAl powder is coated and sintered onto the inner surface of a drift tube which locates between the input and the middle cavity of the RKA. Cold tests show that the attenuate rate of the tube against parasitic mode TE11 is about 50%. Experiments carried out on the Torch-01 accelerator present that the tube is effective in suppressing the parasitic mode. Two typical outputs are obtained. When the diode voltage is on a moderate level, the RKA operates well and the parasitic mode is totally suppressed. The pulse length of the High Power Microwave (HPM) almost equals the electron beam pulse length and the HPM average output power is about 300 MW, with a power efficiency of 10%. When the diode voltage is on a higher level, the output power and efficiency rise but the parasitic mode oscillation occurred and the pulse length is shortened. By contrast, the parasitic mode oscillation is too strong for the RKA to operate normally with un-sintered drift tube. The experimental study implies that FeSiAl is effective in suppressing the parasitic mode oscillation in a certain extent. However, total suppression needs a deeper attenuate rate and further investigation.

BOUT++ simulations of edge turbulence in Alcator C-Mod's EDA H-mode

NASA Astrophysics Data System (ADS)

Davis, E. M.; Porkolab, M.; Hughes, J. W.; Labombard, B.; Snyder, P. B.; Xu, X. Q.; MIT PSFC Team; Atomics Team, General; LLNL Team

2013-10-01

Energy confinement in tokamaks is believed to be strongly controlled by plasma transport in the pedestal. The pedestal of Alcator C-Mod's Enhanced Dα (EDA) H-mode (ν* > 1) is regulated by a quasi-coherent mode (QCM), an edge fluctuation believed to reduce particle confinement and allow steady-state H-mode operation. ELITE calculations indicate that EDA H-modes sit well below the ideal peeling-ballooning instability threshold, in contrast with ELMy H-modes. Here, we use a 3-field reduced MHD model in BOUT++ to study the effects of nonideal and nonlinear physics on EDA H-modes. In particular, incorporation of realistic pedestal resistivity is found to drive resistive ballooning modes (RBMs) and increase linear growth rates above the corresponding ideal rates. These RBMs may ultimately be responsible for constraining the EDA pedestal gradient. However, recent high-fidelity mirror Langmuir probe measurements indicate that the QCM is an electron drift-Alfvén wave - not a RBM. Inclusion of the parallel pressure gradient term in the 3-field reduced MHD Ohm's law and various higher field fluid models are implemented in an effort to capture this drift wave-like response. This work was performed under the auspices of the USDoE under awards DE-FG02-94-ER54235, DE-AC52-07NA27344, DE-AC52-07NA27344, and NNSA SSGF.

BOUT++ Simulations of Edge Turbulence in Alcator C-Mod's EDA H-Mode

NASA Astrophysics Data System (ADS)

Davis, E. M.; Porkolab, M.; Hughes, J. W.; Labombard, B.; Snyder, P. B.; Xu, X. Q.

2013-10-01

Energy confinement in tokamaks is believed to be strongly controlled by plasma transport in the pedestal. The pedestal of Alcator C-Mod's Enhanced Dα (EDA) H-mode (ν* > 1) is regulated by a quasi-coherent mode (QCM), an edge fluctuation believed to reduce particle confinement and allow steady-state H-mode operation. ELITE calculations indicate that EDA H-modes sit well below the ideal peeling-ballooning instability threshold, in contrast with ELMy H-modes. Here, we use a 3-field reduced MHD model in BOUT++ to study the effects of nonideal and nonlinear physics on EDA H-modes. In particular, incorporation of realistic pedestal resistivity is found to drive resistive ballooning modes (RBMs) and increase linear growth rates above the corresponding ideal rates. These RBMs may ultimately be responsible for constraining the EDA pedestal gradient. However, recent high-fidelity mirror Langmuir probe measurements indicate that the QCM is an electron drift-Alfvén wave - not a RBM. Inclusion of the parallel pressure gradient term in the 3-field reduced MHD Ohm's law and various higher field fluid models are implemented in an effort to capture this drift wave-like response. This work was performed under the auspices of the USDoE under awards DE-FG02-94-ER54235, DE-AC52-07NA27344, DE-AC52-07NA27344, and NNSA SSGF.

Parallel and perpendicular velocity sheared flows driven tripolar vortices in an inhomogeneous electron-ion quantum magnetoplasma

NASA Astrophysics Data System (ADS)

Mirza, Arshad M.; Masood, W.

2011-12-01

Nonlinear equations governing the dynamics of finite amplitude drift-ion acoustic-waves are derived by taking into account sheared ion flows parallel and perpendicular to the ambient magnetic field in a quantum magnetoplasma comprised of electrons and ions. It is shown that stationary solution of the nonlinear equations can be represented in the form of a tripolar vortex for specific profiles of the equilibrium sheared flows. The tripolar vortices are, however, observed to form on very short scales in dense quantum plasmas. The relevance of the present investigation with regard to dense astrophysical environments is also pointed out.

Fundamental mode of ultra-low frequency electrostatic dust-cyclotron surface waves in a magnetized complex plasma with drifting ions

NASA Astrophysics Data System (ADS)

Lee, Seungjun; Lee, Myoung-Jae

2012-10-01

The electrostatic dust-cyclotron (EDC) waves in a magnetized dusty plasma was reported that they could be excited by gravity in a collisional plasma [1]. Rosenberg suggested that EDC waves could be excited by ions drifting along the magnetic field in a collisional plasma containing dust grains with large thermal speeds [2]. The existing investigations, however, focus on EDC volume waves in which the boundary effects are not considered. In this work, we attempt to obtain some physical results concerning the fundamental mode of EDC surface wave and the stability of wave by utilizing a kinetic method. The EDC surface wave is assumed to propagate along an external magnetic field at the interface between the plasma and the vacuum. The plasma is comprised of drifting ions flowing along an external magnetic field. To derive the growth rate of surface waves, we employ the specular reflection boundary conditions. The EDC surface wave is found to be unstable when the ion drift velocity is larger than the phase velocity of the wave. In addition, the wave becomes to be more unstable if dust particles carry more negative charges.[4pt] [1] N. D'Angelo, Phys. Lett. A 323, 445 (2004).[0pt] [2] M. Rosenberg, Phys. Scr. 82, 035505 (2010).

Strings, vortex rings, and modes of instability

DOE PAGES

Gubser, Steven S.; Nayar, Revant; Parikh, Sarthak

2015-01-12

We treat string propagation and interaction in the presence of a background Neveu–Schwarz three-form field strength, suitable for describing vortex rings in a superfluid or low-viscosity normal fluid. A circular vortex ring exhibits instabilities which have been recognized for many years, but whose precise boundaries we determine for the first time analytically in the small core limit. Two circular vortices colliding head-on exhibit stronger instabilities which cause splitting into many small vortices at late times. We provide an approximate analytic treatment of these instabilities and show that the most unstable wavelength is parametrically larger than a dynamically generated length scalemore » which in many hydrodynamic systems is close to the cutoff. We also summarize how the string construction we discuss can be derived from the Gross–Pitaevskii Lagrangian, and also how it compares to the action for giant gravitons.« less

The W. M. Keck Observatory Infrared Vortex Coronagraph and a First Image of HIP 79124 B

NASA Astrophysics Data System (ADS)

Serabyn, E.; Huby, E.; Matthews, K.; Mawet, D.; Absil, O.; Femenia, B.; Wizinowich, P.; Karlsson, M.; Bottom, M.; Campbell, R.; Carlomagno, B.; Defrère, D.; Delacroix, C.; Forsberg, P.; Gomez Gonzalez, C.; Habraken, S.; Jolivet, A.; Liewer, K.; Lilley, S.; Piron, P.; Reggiani, M.; Surdej, J.; Tran, H.; Vargas Catalán, E.; Wertz, O.

2017-01-01

An optical vortex coronagraph has been implemented within the NIRC2 camera on the Keck II telescope and used to carry out on-sky tests and observations. The development of this new L‧-band observational mode is described, and an initial demonstration of the new capability is presented: a resolved image of the low-mass companion to HIP 79124, which had previously been detected by means of interferometry. With HIP 79124 B at a projected separation of 186.5 mas, both the small inner working angle of the vortex coronagraph and the related imaging improvements were crucial in imaging this close companion directly. Due to higher Strehl ratios and more relaxed contrasts in L‧ band versus H band, this new coronagraphic capability will enable high-contrast, small-angle observations of nearby young exoplanets and disks on a par with those of shorter-wavelength extreme adaptive optics coronagraphs.

Determination of the mode composition of long-wave disturbances in a supersonic flow in a hotshot wind tunnel

NASA Astrophysics Data System (ADS)

Tsyryulnikov, I. S.; Kirilovskiy, S. V.; Poplavskaya, T. V.

2016-10-01

In this paper, we describe a new method of mode decomposition of disturbances on the basis of specific features of interaction of long-wave free-stream disturbances with the shock wave and knowing the trends of changing of the conversion factors of various disturbance modes due to variations of the shock wave incidence angle. The range of admissible root-mean-square amplitudes of oscillations of vortex, entropy, and acoustic modes in the free stream generated in IT-302M was obtained by using the pressure fluctuations measured on the model surface and the calculated conversion factors.

Fluid-structure-interaction of a flag in a channel flow

NASA Astrophysics Data System (ADS)

Liu, Yingzheng; Yu, Yuelong; Zhou, Wenwu; Wang, Weizhe

2017-11-01

The unsteady flow field and flapping dynamics of an inverted flag in water channel are investigated using time resolved particle image velocimetry (TR-PIV) measurements. The dynamically deformed profiles of the inverted flag are determined by a novel algorithm that combines morphological image processing and principle component analysis. Instantaneous flow field, phase averaged vorticity, time-mean flow field and turbulent kinematic energy are addressed for the flow. Four modes are discovered as the dimensionless bending stiffness decreases, i.e., the straight mode, the biased mode, the flapping mode and the deflected mode. Among all modes, the flapping mode is characterized by large flapping amplitude and the reverse von Kármán vortex street wake, which is potential to enhance heat transfer remarkably. National Natural Science Foundation of China.

Density-Gradient-Driven trapped-electron-modes in improved-confinement RFP plasmas

NASA Astrophysics Data System (ADS)

Duff, James

2016-10-01

Short wavelength density fluctuations in improved-confinement MST plasmas exhibit multiple features characteristic of the trapped-electron-mode (TEM), strong evidence that drift wave turbulence emerges in RFP plasmas when transport associated with MHD tearing is reduced. Core transport in the RFP is normally governed by magnetic stochasticity stemming from long wavelength tearing modes that arise from current profile peaking. Using inductive control, the tearing modes are reduced and global confinement is increased to values expected for a comparable tokamak plasma. The improved confinement is associated with a large increase in the pressure gradient that can destabilize drift waves. The measured density fluctuations have frequencies >50 kHz, wavenumbers k_phi*rho_s<0.14, and propagate in the electron drift direction. Their spectral emergence coincides with a sharp decrease in fluctuations associated with global tearing modes. Their amplitude increases with the local density gradient, and they exhibit a density-gradient threshold at R/L_n 15, higher than in tokamak plasmas by R/a. the GENE code, modified for RFP equilibria, predicts the onset of microinstability for these strong-gradient plasma conditions. The density-gradient-driven TEM is the dominant instability in the region where the measured density fluctuations are largest, and the experimental threshold-gradient is close to the predicted critical gradient for linear stability. While nonlinear analysis shows a large Dimits shift associated with predicted strong zonal flows, the inclusion of residual magnetic fluctuations causes a collapse of the zonal flows and an increase in the predicted transport to a level close to the experimentally measured heat flux. Similar circumstances could occur in the edge region of tokamak plasmas when resonant magnetic perturbations are applied for the control of ELMs. Work supported by US DOE.

Research of the high performance low temperature vortex street flowmeter

NASA Astrophysics Data System (ADS)

Gao, Feng; Chen, Yang; Zhang, Zhen-peng; Geng, Wei-guo

2007-07-01

Flow measurement is the key method for R&D and operation monitoring of liquid rocket engine. Therefore, it is important to measure flux of low temperature liquid propellants for the liquid hydrogen/liquid oxygen or the liquid oxygen/kerosene rocket engine. Presently in China, the level meter and the turbine flowmeter are usually used in the experimentation of the liquid hydrogen/liquid oxygen rocket engine. The level meter can only scale average flux and the precision of the turbine flowmeter (the measuring wild point is 1.5%) can not be ensured due to the reason which there is not devices of low temperature real-time demarcation in China. Therefore, it is required to research the high performance low temperature flow measurement equipment and the vortex street flowmeter is selected because of its advantages. In the paper, some key techniques of low temperature vortex street flowmeter are researched from the design aspect. Firstly, the basic theoretical research of vortex street flowmeter includes signal detection method, shape of vortex producer and effects of dimension of vertex producer to vortex quality. Secondly, low temperature vortex street flowmeter adopts the method of piezoelectric components stress mode. As for the weakness of phase-change, lattice change and fragility for many piezoelectric materials in low temperature, it can not be fulfilled piezoelectric signal and mechanism performance under this condition. Some piezoelectric materials which can be used in low temperature are illustrated in the paper by lots of research in order for the farther research. The article places emphasis upon low temperature trait of piezoelectric materials, and the structure designs of signal detector and calculation of stress, electric charge quantity and heat transfer.

Development and Breakdown of Goertler Vortices in High Speed Boundary Layers

NASA Technical Reports Server (NTRS)

Li, Fei; Choudhari, Meelan; Chang, Chau-Lyan; Wu, Minwei; Greene, Ptrick T.

2010-01-01

The nonlinear development of G rtler instability over a concave surface gives rise to a highly distorted stationary flow in the boundary layer that has strong velocity gradients in both spanwise and wall-normal directions. This distorted flow is susceptible to strong, high frequency secondary instability that leads to the onset of transition. For high Mach number flows, the boundary layer is also subject to the second mode instability. The nonlinear development of G rtler vortices and the ensuing growth and breakdown of secondary instability, the G rtler vortex interactions with second mode instabilities as well as oblique second mode interactions are examined in the context of both internal and external hypersonic configurations using nonlinear parabolized stability equations, 2-D eigenvalue analysis and direct numerical simulation. For G rtler vortex development inside the Purdue Mach 6 Ludwieg tube wind tunnel, multiple families of unstable secondary eigenmodes are identified and their linear and nonlinear evolution is examined. The computation of secondary instability is continued past the onset of transition to elucidate the physical mechanisms underlying the laminar breakdown process. Nonlinear breakdown scenarios associated with transition over a Mach 6 compression cone configuration are also explored.

Flow-structure interaction effects on a jet emanating from a flexible nozzle

PubMed Central

Murugappan, S.; Gutmark, E. J.; Lakhamraju, R. R.; Khosla, S.

2008-01-01

In recent years, a wide variety of applications have been found for the use of pulsed jets in the area of flow control. The goal of the current study was to identify the flow field and mixing characteristics associated with an incompressible elongated jet emitted from a flexible nozzle. The shape of the nozzle was that of a high aspect ratio jet deforming from a fully opened to a completely closed configuration. The jet was characterized by a pulsatile flow that was self-excited by the motion of the flexible tube. The frequency of excitation was found to be between 150 and 175 Hz and the Strouhal number (nondimensional frequency) varied from 0.17 to 0.45. The jet flow was dominated by vortices that were shed from the nozzle with an axis parallel to the major axis. The vortices in the near field were quasi-two-dimensional so that measurements performed at the center plane represented the dynamics of the entire vortex. The nozzle excited two different modes depending on the tension applied to the flexible nozzle and the volumetric flow through it. The first was a flapping mode, which was associated with alternate shedding of vortices. This caused strong steering of the jet to one side or the other. The second mode was a symmetric mode that was associated with the formation of counter-rotating vortex pairs. Turbulence and jet spread in the measured planes were much larger in the first mode than the second one. PMID:19547723

Reversal modes in FeCoNi nanowire arrays: Correlation between magnetostatic interactions and nanowires length

NASA Astrophysics Data System (ADS)

Samanifar, S.; Almasi Kashi, M.; Ramazani, A.; Alikhani, M.

2015-03-01

FeCoNi nanowire arrays (175 nm in diameter and lengths ranging from 5 to 40 μm) were fabricated into nanopores of hard-anodized aluminum oxide templates using pulsed ac electrodeposition technique. Increasing the length had no considerable effect on the composition and crystalline characteristics of Fe47Co38Ni15 nanowires (NWs). By eliminating the dendrites formed at the bottom of the pores, we report a careful investigation on the effect of magnetostatic interactions on magnetic properties and the effect of nanowire length on reversal modes. Hysteresis loop measurements indicated that increasing the length decreases coercivity and squareness values. On the other hand, first-order reversal curve measurements show a linear correlation between the magnetostatic interactions and length of NWs. Comparing reversal modes of the NWs both experimentally and theoretically using angular dependence of coercivity, we find that when L≤22 μm, a vortex domain wall mode is only occurred. When L>22 μm, a non-monotonic behavior indicates a transition from the vortex to transverse domain wall propagation. As a result, a critical length was found above which the transition between the reversal modes is occurred due the enhanced interactions. The transition angle also shifts toward a lower angle as the length increases. Moreover, with increasing length from 22 to 31 μm, the single domain structure of NWs changes to a pseudo single domain state. A multidomain-like behavior is also found for the longest NWs length.

Laser dissection sampling modes for direct mass spectral analysis [using a hybrid optical microscopy/laser ablation liquid vortex capture/electrospray ionization system

DOE PAGES

Cahill, John F.; Kertesz, Vilmos; Van Berkel, Gary J.

2016-02-01

Here, laser microdissection coupled directly with mass spectrometry provides the capability of on-line analysis of substrates with high spatial resolution, high collection efficiency, and freedom on shape and size of the sampling area. Establishing the merits and capabilities of the different sampling modes that the system provides is necessary in order to select the best sampling mode for characterizing analytically challenging samples. The capabilities of laser ablation spot sampling, laser ablation raster sampling, and laser 'cut and drop' sampling modes of a hybrid optical microscopy/laser ablation liquid vortex capture electrospray ionization mass spectrometry system were compared for the analysis ofmore » single cells and tissue. Single Chlamydomonas reinhardtii cells were monitored for their monogalactosyldiacylglycerol (MGDG) and diacylglyceryltrimethylhomo-Ser (DGTS) lipid content using the laser spot sampling mode, which was capable of ablating individual cells (4-15 m) even when agglomerated together. Turbid Allium Cepa cells (150 m) having unique shapes difficult to precisely measure using the other sampling modes could be ablated in their entirety using laser raster sampling. Intact microdissections of specific regions of a cocaine-dosed mouse brain tissue were compared using laser 'cut and drop' sampling. Since in laser 'cut and drop' sampling whole and otherwise unmodified sections are captured into the probe, 100% collection efficiencies were achieved. Laser ablation spot sampling has the highest spatial resolution of any sampling mode, while laser ablation raster sampling has the highest sampling area adaptability of the sampling modes. In conclusion, laser ablation spot sampling has the highest spatial resolution of any sampling mode, useful in this case for the analysis of single cells. Laser ablation raster sampling was best for sampling regions with unique shapes that are difficult to measure using other sampling modes. Laser 'cut and drop' sampling can be used for cases where the highest sensitivity is needed, for example, monitoring drugs present in trace amounts in tissue.« less

Laser dissection sampling modes for direct mass spectral analysis [using a hybrid optical microscopy/laser ablation liquid vortex capture/electrospray ionization system

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

Cahill, John F.; Kertesz, Vilmos; Van Berkel, Gary J.

Here, laser microdissection coupled directly with mass spectrometry provides the capability of on-line analysis of substrates with high spatial resolution, high collection efficiency, and freedom on shape and size of the sampling area. Establishing the merits and capabilities of the different sampling modes that the system provides is necessary in order to select the best sampling mode for characterizing analytically challenging samples. The capabilities of laser ablation spot sampling, laser ablation raster sampling, and laser 'cut and drop' sampling modes of a hybrid optical microscopy/laser ablation liquid vortex capture electrospray ionization mass spectrometry system were compared for the analysis ofmore » single cells and tissue. Single Chlamydomonas reinhardtii cells were monitored for their monogalactosyldiacylglycerol (MGDG) and diacylglyceryltrimethylhomo-Ser (DGTS) lipid content using the laser spot sampling mode, which was capable of ablating individual cells (4-15 m) even when agglomerated together. Turbid Allium Cepa cells (150 m) having unique shapes difficult to precisely measure using the other sampling modes could be ablated in their entirety using laser raster sampling. Intact microdissections of specific regions of a cocaine-dosed mouse brain tissue were compared using laser 'cut and drop' sampling. Since in laser 'cut and drop' sampling whole and otherwise unmodified sections are captured into the probe, 100% collection efficiencies were achieved. Laser ablation spot sampling has the highest spatial resolution of any sampling mode, while laser ablation raster sampling has the highest sampling area adaptability of the sampling modes. In conclusion, laser ablation spot sampling has the highest spatial resolution of any sampling mode, useful in this case for the analysis of single cells. Laser ablation raster sampling was best for sampling regions with unique shapes that are difficult to measure using other sampling modes. Laser 'cut and drop' sampling can be used for cases where the highest sensitivity is needed, for example, monitoring drugs present in trace amounts in tissue.« less

Verification of long wavelength electromagnetic modes with a gyrokinetic-fluid hybrid model in the XGC code

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

Hager, Robert; Lang, Jianying; Chang, C. S.

As an alternative option to kinetic electrons, the gyrokinetic total-f particle-in-cell (PIC) code XGC1 has been extended to the MHD/fluid type electromagnetic regime by combining gyrokinetic PIC ions with massless drift-fluid electrons. Here, two representative long wavelength modes, shear Alfven waves and resistive tearing modes, are verified in cylindrical and toroidal magnetic field geometries.

Verification of long wavelength electromagnetic modes with a gyrokinetic-fluid hybrid model in the XGC code

DOE PAGES

Hager, Robert; Lang, Jianying; Chang, C. S.; ...

2017-05-24

As an alternative option to kinetic electrons, the gyrokinetic total-f particle-in-cell (PIC) code XGC1 has been extended to the MHD/fluid type electromagnetic regime by combining gyrokinetic PIC ions with massless drift-fluid electrons. Here, two representative long wavelength modes, shear Alfven waves and resistive tearing modes, are verified in cylindrical and toroidal magnetic field geometries.

Resolving Structural Isomers of Monosaccharide Methyl Glycosides Using Drift Tube and Traveling Wave Ion Mobility Mass Spectrometry

PubMed Central

Li, Hongli; Giles, Kevin; Bendiak, Brad; Kaplan, Kimberly; Siems, William F.; Hill, Herbert H.

2013-01-01

Monosaccharide structural isomers including sixteen methyl-D-glycopyranosides and four methyl-N-acetylhexosamines were subjected to ion mobility measurements by electrospray ion mobility mass spectrometry. Two ion mobility-MS systems were employed: atmospheric pressure drift tube ion mobility time-of-flight mass spectrometry and a Synapt G2 HDMS system which incorporates a low pressure traveling wave ion mobility separator. All the compounds were investigated as [M+Na]+ ions in the positive mode. A majority of the monosaccharide structural isomers exhibited different mobility drift times in either system, depending on differences in their anomeric and stereochemical configurations. In general, drift time patterns (relative drift times of isomers) matched between the two instruments. Higher resolving power was observed using the atmospheric pressure drift tube. Collision cross section values of monosaccharide structural isomers were directly calculated from the atmospheric pressure ion mobility experiments and a collision cross section calibration curve was made for the traveling wave ion mobility instrument. Overall, it was demonstrated that ion mobility-mass spectrometry using either drift tube or traveling wave ion mobility is a valuable technique for resolving subtle variations in stereochemistry among the sodium adducts of monosaccharide methyl glycosides. PMID:22339760

Comparison of higher order modes damping techniques for 800 MHz single cell superconducting cavities

NASA Astrophysics Data System (ADS)

Shashkov, Ya. V.; Sobenin, N. P.; Petrushina, I. I.; Zobov, M. M.

2014-12-01

At present, applications of 800 MHz harmonic cavities in both bunch lengthening and shortening regimes are under consideration and discussion in the framework of the High Luminosity LHC project. In this paper we study electromagnetic characteristics of high order modes (HOMs) for a single cell 800 MHz superconducting cavity and arrays of such cavities connected by drifts tubes. Different techniques for the HOMs damping such as beam pipe grooves, coaxial-notch loads, fluted beam pipes etc. are investigated and compared. The influence of the sizes and geometry of the drift tubes on the HOMs damping is analyzed. The problems of a multipacting discharge in the considered structures are discussed and the operating frequency detuning due to the Lorentz force is evaluated.

Measurement of electrodynamics characteristics of higher order modes for harmonic cavity at 2400 MHz

NASA Astrophysics Data System (ADS)

Shashkov, Ya V.; Sobenin, N. P.; Gusarova, M. A.; Lalayan, M. V.; Bazyl, D. S.; Donetskiy, R. V.; Orlov, A. I.; Zobov, M. M.; Zavadtsev, A. A.

2016-09-01

In the frameworks of the High Luminosity Large Hadron Collider (HL-LHC) upgrade program an application of additional superconducting harmonic cavities operating at 800 MHz is currently under discussion. As a possible candidate, an assembly of two cavities with grooved beam pipes connected by a drift tube and housed in a common cryomodule, was proposed. In this article we discuss measurements of loaded Q-factors of higher order modes (HOM) performed on a scaled aluminium single cell cavity prototype with the fundamental frequency of 2400 MHz and on an array of two such cavities connected by a narrow beam pipe. The measurements were performed for the system with and without the matching load in the drift tube..

The electromagnetic interchange mode in a partially ionized collisional plasma. [spread F region

NASA Technical Reports Server (NTRS)

Hudson, M. K.; Kennel, C. F.

1974-01-01

A collisional electromagnetic dispersion relation is derived from two-fluid theory for the interchange mode coupled to the Alfven, acoustic, drift and entropy modes in a partially ionized plasma. The fundamental electromagnetic nature of the interchange model is noted; coupling to the intermediate Alfven mode is strongly stabilizing for finite k sub z. Both ion viscous and ion-neutral stabilization are included, and it was found that collisions destroy the ion finite Larmor radius cutoff at short perpendicular wavelengths.

A Multi Water Bag model of drift kinetic electron plasmaa

NASA Astrophysics Data System (ADS)

Morel, Pierre; Ghiro, Florent Dreydemy; Berionni, Vincent; Coulette, David; Besse, Nicolas; Gürcan, Özgür D.

2014-08-01

A Multi Water Bag model is proposed for describing drift kinetic plasmas in a magnetized cylindrical geometry, relevant for various experimental devices, solar wind modeling... The Multi Water Bag (MWB) model is adapted to the description of a plasma with kinetic electrons as well as an arbitrary number of kinetic ions. This allows to describe the kinetic dynamics of the electrons, making possible the study of electron temperature gradient (ETG) modes, in addition to the effects of non adiabatic electrons on the ion temperature gradient (ITG) modes, that are of prime importance in the magnetized plasmas micro-turbulence [X. Garbet, Y. Idomura, L. Villard, T.H. Watanabe, Nucl. Fusion 50, 043002 (2010); J.A. Krommes, Ann. Rev. Fluid Mech. 44, 175 (2012)]. The MWB model is shown to link kinetic and fluid descriptions, depending on the number of bags considered. Linear stability of the ETG modes is presented and compared to the existing results regarding cylindrical ITG modes [P. Morel, E. Gravier, N. Besse, R. Klein, A. Ghizzo, P. Bertrand, W. Garbet, Ph. Ghendrih, V. Grandgirard, Y. Sarazin, Phys. Plasmas 14, 112109 (2007)].

Progress towards modeling tokamak boundary plasma turbulence and understanding its role in setting divertor heat flux widths

NASA Astrophysics Data System (ADS)

Chen, Bin

2017-10-01

QCMs (quasi-coherent modes) are well characterized in the edge of Alcator C-Mod, when operating in the Enhanced Dα (EDA) H-mode, a promising alternative regime for ELM (edge localized modes) suppressed operation. To improve the understanding of the physics behind the QCMs, three typical C-Mod EDA H-Mode discharges are simulated by BOUT + + using a six-field two-fluid model (based on the Braginskii equations). The simulated characteristics of the frequency versus wave number spectra of the modes is in reasonable agreement with phase contrast imaging data. The key simulation results are: 1) Linear spectrum analysis and the nonlinear phase relationship indicate the dominance of resistive-ballooning modes and drift-Alfven wave instabilities; 2) QCMs originate inside the separatrix; (3) magnetic flutter causes the mode spreading into the SOL; 4) the boundary electric field Er changes the turbulent characteristics of the QCMs and controls edge transport and the divertor heat flux width; 5) the magnitude of the divertor heat flux depends on the physics models, such as sources and sinks, sheath boundary conditions, and parallel heat flux limiting coefficient. The BOUT + + simulations have also been performed for inter-ELM periods of DIII-D and EAST discharges, and similar quasi-coherent modes have been found. The parallel electron heat fluxes projected onto the target from these BOUT + + simulations follow the experimental heat flux width scaling, in particular the inverse dependence of the width on the poloidal magnetic field with an outlier. Further turbulence statistics analysis shows that the blobs are generated near the pedestal peak gradient region inside the separatrix and contribute to the transport of the particle and heat in the SOL region. To understand the Goldston heuristic drift-based model, results will also be presented from self-consistent transport simulations with the electric and magnetic drifts in BOUT + + and with the sheath potential included in the SOL. Work supported by LLNL under Contract DE-AC52-07NA27344. This work was also supported by US DOE Grant DE-FC02-99ER54512, using Alcator C-Mod, a DOE Office of Science User Facility, and under the auspices of the CSC (No. 201506340019).

The Role of the Upper Atmosphere for Dawn-Dusk and Interhemispheric Differences in the Coupled Magnetosphere-Ionosphere-Thermosphere System

NASA Astrophysics Data System (ADS)

Foerster, M.; Doornbos, E.; Haaland, S.

2016-12-01

Solar wind and IMF interaction with the geomagnetic field sets up a large-scale plasma circulation in the Earth's magnetosphere and the magnetically tightly connected ionosphere. The ionospheric ExB ion drift at polar latitudes accelerates the neutral gas as a nondivergent momentum source primarily in force balance with pressure gradients, while the neutral upper thermosphere circulation is essentially modified by apparent forces due to Earth's rotation (Coriolis and centrifugal forces) as well as advection and viscous forces. The apparent forces affect the dawn and dusk side asymmetrically, favouring a large dusk-side neutral wind vortex, while the non-dipolar portions of the Earth's magnetic field constitute significant hemispheric differences in magnetic flux and field configurations that lead to essential interhemispheric differences of the ion-neutral interaction. We present statistical studies of both the high-latitude ionospheric convection and the upper thermospheric circulation patterns based on measurements of the electron drift instrument (EDI) on board the Cluster satellites and by the accelerometer on board the CHAMP, GOCE, and Swarm spacecraft, respectively.

Variational principles for stochastic fluid dynamics

PubMed Central

Holm, Darryl D.

2015-01-01

This paper derives stochastic partial differential equations (SPDEs) for fluid dynamics from a stochastic variational principle (SVP). The paper proceeds by taking variations in the SVP to derive stochastic Stratonovich fluid equations; writing their Itô representation; and then investigating the properties of these stochastic fluid models in comparison with each other, and with the corresponding deterministic fluid models. The circulation properties of the stochastic Stratonovich fluid equations are found to closely mimic those of the deterministic ideal fluid models. As with deterministic ideal flows, motion along the stochastic Stratonovich paths also preserves the helicity of the vortex field lines in incompressible stochastic flows. However, these Stratonovich properties are not apparent in the equivalent Itô representation, because they are disguised by the quadratic covariation drift term arising in the Stratonovich to Itô transformation. This term is a geometric generalization of the quadratic covariation drift term already found for scalar densities in Stratonovich's famous 1966 paper. The paper also derives motion equations for two examples of stochastic geophysical fluid dynamics; namely, the Euler–Boussinesq and quasi-geostropic approximations. PMID:27547083

Nonequilibrium dynamic phases in driven vortex lattices with periodic pinning

NASA Astrophysics Data System (ADS)

Reichhardt, Charles Michael

1998-12-01

We present the results of an extensive series of simulations of flux-gradient and current driven vortices interacting with either random or periodically arranged pinning sites. First, we consider flux-gradient-driven simulations of superconducting vortices interacting with strong randomly-distributed columnar pinning defects, as an external field H(t) is quasi-statically swept from zero through a matching field Bsb{phi}. Here, we find significant changes in the behavior of the local flux density B(x, y, H(t)), magnetization M(H(t)), critical current Jsb{c}(B(t)), and the individual vortex flow paths, as the local flux density crosses Bsb{phi}. Further, we find that for a given pin density, Jsb{c}(B) can be enhanced by maximizing the distance between the pins for B < Bsb{phi}. For the case of periodic pinning sites as a function of applied field, we find a rich variety of ordered and partially-ordered vortex lattice configurations. We present formulas that predict the matching fields at which commensurate vortex configurations occur and the vortex lattice orientation with respect to the pinning lattice. Our results are in excellent agreement with recent imaging experiments on square pinning arrays (K. Harada et al., Science 274, 1167 (1996)). For current driven simulations with periodic pinning we find a remarkable number of dynamical plastic flow phases. Signatures of the transitions between these different dynamical phases include sudden jumps in the current-voltage curves, hysteresis, as well as marked changes in the vortex trajectories and vortex lattice order. These phases are outlined in a series of dynamic phase diagrams. We show that several of these phases and their phase-boundaries can be understood in terms of analytical arguments. Finally, when the vortex lattice is driven at varying angles with respect to the underlying periodic pinning array, the transverse voltage-current V(I) curves show a series of mode-locked plateaus with the overall V(I) forming a devil's staircase structure.

Tones Encountered with a Coannular Nozzle and a Method for Their Suppression

NASA Technical Reports Server (NTRS)

Zaman, Khairul Bmq; Bridges, James E.; Fagan, Amy Florence; Miller, Christopher J.

2017-01-01

With multi-stream coannular nozzles, sometimes tones occur that may cause the nozzle to fail noise regulation standards. A two-stream nozzle was studied experimentally and numerically in an attempt to identify the sources of such tones and explore remedies. For the given nozzle configuration, sharp tones occurred in a range of low jet Mach numbers. The tones apparently occurred due to a coupling between vortex shedding from the struts, which held the nozzles and the center-body together, with various duct acoustic modes. A leading edge treatment of the struts is shown to eliminate the tones via disruption of the vortex shedding.

Shaping perfect optical vortex with amplitude modulated using a digital micro-mirror device

NASA Astrophysics Data System (ADS)

Zhang, Chonglei; Min, Changjun; Yuan, X.-C.

2016-12-01

We propose a technique to generate of perfect optical vortex (POV) via Fourier transformation of Bessel-Gauss (BG) beams through encoding of the amplitude of the optical field with binary amplitude digital micro-mirrors device (DMD). Furthermore, we confirm the correct phase patterns of the POV with the method of Mach-Zehnder interferometer. Our approach to generate the POV has the advantages that rapidly switch among the different modes, wide spectral regions and high energy tolerance. Since the POV possess propagation properties that not shape-invariant, we therefore suppose that our proposed approach will find potential applications in optical microscopy, optical fabrication, and optical communication.

Protein Folding Using a Vortex Fluidic Device.

PubMed

Britton, Joshua; Smith, Joshua N; Raston, Colin L; Weiss, Gregory A

2017-01-01

Essentially all biochemistry and most molecular biology experiments require recombinant proteins. However, large, hydrophobic proteins typically aggregate into insoluble and misfolded species, and are directed into inclusion bodies. Current techniques to fold proteins recovered from inclusion bodies rely on denaturation followed by dialysis or rapid dilution. Such approaches can be time consuming, wasteful, and inefficient. Here, we describe rapid protein folding using a vortex fluidic device (VFD). This process uses mechanical energy introduced into thin films to rapidly and efficiently fold proteins. With the VFD in continuous flow mode, large volumes of protein solution can be processed per day with 100-fold reductions in both folding times and buffer volumes.

Tones Encountered with a Coannular Nozzle and a Method for their Suppression

NASA Technical Reports Server (NTRS)

Zaman, Khairul; Bridges, James; Fagan, Amy; Miller, Chris

2017-01-01

With multi-stream coannular nozzles, sometimes tones are generated that make the nozzle fail noise regulation criteria. A two-stream nozzle was studied experimentally in an attempt to identify the sources of such tones and explore remedies. With the given nozzle configuration, sharp tones occurred in a range of low jet Mach numbers (M (sub j)). The tones could be traced to a coupling of vortex shedding from the struts, that hold the nozzles and the center-body together, and various acoustic resonance modes of the ducts. A leading edge treatment of the struts is shown to suppress the vortex shedding and eliminate the tones.

Tones Encountered with a Coannular Nozzle and a Method for their Suppression

NASA Technical Reports Server (NTRS)

Zaman, K. B. M. Q.; Bridges, J. E.; Fagan, A. F.; Miller, C. J.

2017-01-01

With multi-stream coannular nozzles, sometimes tones occur that may cause the nozzle to fail noise regulation standards. A two-stream nozzle was studied experimentally and numerically in an at-tempt to identify the sources of such tones and explore remedies. For the given nozzle configuration, sharp tones occurred in a range of low jet Mach numbers. The tones apparently occurred due to a coupling between vortex shedding from the struts, which held the nozzles and the center-body together, with various duct acoustic modes. A leading edge treatment of the struts is shown to eliminate the tones via disruption of the vortex shedding.

Flow-around modes for a rhomboid wing with a stall vortex in the shock layer

NASA Astrophysics Data System (ADS)

Zubin, M. A.; Maximov, F. A.; Ostapenko, N. A.

2017-12-01

The results of theoretical and experimental investigation of an asymmetrical hypersonic flow around a V-shaped wing with the opening angle larger than π on the modes with attached shockwaves on forward edges, when the stall flow is implemented on the leeward wing cantilever behind the kink point of the cross contour. In this case, a vortex of nonviscous nature is formed in which the velocities on the sphere exceeding the speed of sound and resulting in the occurrence of pressure shocks with an intensity sufficient for the separation of the turbulent boundary layer take place in the reverse flow according to the calculations within the framework of the ideal gas. It is experimentally established that a separation boundary layer can exist in the reverse flow, and its structure is subject to the laws inherent to the reverse flow in the separation region of the turbulent boundary layer arising in the supersonic conic flow under the action of a shockwave incident to the boundary layer.

Active control of jet flowfields

NASA Astrophysics Data System (ADS)

Kibens, Valdis; Wlezien, Richard W.

1987-06-01

Passive and active control of jet shear layer development were investigated as mechanisms for modifying the global characteristics of jet flowfields. Slanted and stepped indeterminate origin (I.O.) nozzles were used as passive, geometry-based control devices which modified the flow origins. Active control techniques were also investigated, in which periodic acoustic excitation signals were injected into the I.O. nozzle shear layers. Flow visualization techniques based on a pulsed copper-vapor laser were used in a phase-conditioned image acquisition mode to assemble optically averaged sets of images acquired at known times throughout the repetition cycle of the basic flow oscillation period. Hot wire data were used to verify the effect of the control techniques on the mean and fluctuating flow properties. The flow visualization images were digitally enhanced and processed to show locations of prominent vorticity concentrations. Three-dimensional vortex interaction patterns were assembled in a format suitable for movie mode on a graphic display workstation, showing the evolution of three-dimensional vortex system in time.

A comparison of the structureborne and airborne paths for propfan interior noise

NASA Technical Reports Server (NTRS)

Eversman, W.; Koval, L. R.; Ramakrishnan, J. V.

1986-01-01

A comparison is made between the relative levels of aircraft interior noise related to structureborne and airborne paths for the same propeller source. A simple, but physically meaningful, model of the structure treats the fuselage interior as a rectangular cavity with five rigid walls. The sixth wall, the fuselage sidewall, is a stiffened panel. The wing is modeled as a simple beam carried into the fuselage by a large discrete stiffener representing the carry-through structure. The fuselage interior is represented by analytically-derived acoustic cavity modes and the entire structure is represented by structural modes derived from a finite element model. The noise source for structureborne noise is the unsteady lift generation on the wing due to the rotating trailing vortex system of the propeller. The airborne noise source is the acoustic field created by a propeller model consistent with the vortex representation. Comparisons are made on the basis of interior noise over a range of propeller rotational frequencies at a fixed thrust.

Controlled Growth of Gigantic Swirls in a Laboratory Magnetosphere

NASA Astrophysics Data System (ADS)

Worstell, M. W.; Mauel, M. E.; Roberts, T. M.

2012-10-01

Space and laboratory plasma confined by a strong magnetic field have remarkable properties. Low frequency mixing of the plasma occurs through the interchange of long plasma-filled tubes aligned with the magnetic field. The plasma dynamics becomes two-dimensional because these tubes can only move radially or circulate around the poles of the magnetic dipole. Studies of turbulent interchange dynamics made using the Collisionless Terella Experiment (CTX) show that turbulence appears as chaotic time-varying modes with broad global mode structures that interact nonlinearly and form an inverse cascade.footnotetextB.A. Grierson, M.W. Worstell, M.E. Mauel, Phys. Plasmas 16 055902 (2009) When we drive vortex mixing through the application of electrostatic bias to multiple probes, we break the rotational symmetry of the plasma and small vortex tubes are seen to drive larger ``gigantic'' swirls. Statistical analysis of the time-evolving spectra and measurement of the bicoherence of the turbulence show an increase of three wave coupling during non-axisymmetric electrostatic drive of the probe array.

Hydrodynamic aspects of thrust generation in gymnotiform swimming

NASA Astrophysics Data System (ADS)

Shirgaonkar, Anup A.; Curet, Oscar M.; Patankar, Neelesh A.; Maciver, Malcolm A.

2008-11-01

The primary propulsor in gymnotiform swimmers is a fin running along most of the ventral midline of the fish. The fish propagates traveling waves along this ribbon fin to generate thrust. This unique mode of thrust generation gives these weakly electric fish great maneuverability cluttered spaces. To understand the mechanical basis of gymnotiform propulsion, we investigated the hydrodynamics of a model ribbon-fin of an adult black ghost knifefish using high-resolution numerical experiments. We found that the principal mechanism of thrust generation is a central jet imparting momentum to the fluid with associated vortex rings near the free edge of the fin. The high-fidelity simulations also reveal secondary vortex rings potentially useful in rapid sideways maneuvers. We obtained the scaling of thrust with respect to the traveling wave kinematic parameters. Using a fin-plate model for a fish, we also discuss improvements to Lighthill's inviscid theory for gymnotiform and balistiform modes in terms of thrust magnitude, viscous drag on the body, and momentum enhancement.

On the nonlinear development of the most unstable Goertler vortex mode

NASA Technical Reports Server (NTRS)

Denier, James P.; Hall, Philip

1991-01-01

The nonlinear development of the most unstable Gortler vortex mode in boundary layer flows over curved walls is investigated. The most unstable Gortler mode is confined to a viscous wall layer of thickness O(G -1/5) and has spanwise wavelength O(G 11/5); it is, of course, most relevant to flow situations where the Gortler number G is much greater than 1. The nonlinear equations covering the evolution of this mode over an O(G -3/5) streamwise lengthscale are derived and are found to be of a fully nonparallel nature. The solution of these equations is achieved by making use of the numerical scheme used by Hall (1988) for the numerical solution of the nonlinear Gortler equations valid for O(1) Gortler numbers. Thus, the spanwise dependence of the flow is described by a Fourier expansion, whereas the streamwise and normal variations of the flow are dealt with by employing a suitable finite difference discretization of the governing equations. Our calculations demonstrate that, given a suitable initial disturbance, after a brief interval of decay, the energy in all the higher harmonics grows until a singularity is encountered at some downstream position. The structure of the flowfield as this singularity is approached suggests that the singularity is responsible for the vortices, which are initially confined to the thin viscous wall layer, moving away from the wall and into the core of the boundary layer.

Two-dimensional Nonlinear Simulations of Temperature-anisotropy Instabilities with a Proton-alpha Drift

NASA Astrophysics Data System (ADS)

Markovskii, S. A.; Chandran, Benjamin D. G.; Vasquez, Bernard J.

2018-04-01

We present two-dimensional hybrid simulations of proton-cyclotron and mirror instabilities in a proton-alpha plasma with particle-in-cell ions and a neutralizing electron fluid. The instabilities are driven by the protons with temperature perpendicular to the background magnetic field larger than the parallel temperature. The alpha particles with initially isotropic temperature have a nonzero drift speed with respect to the protons. The minor ions are known to influence the relative effect of the proton-cyclotron and mirror instabilities. In this paper, we show that the mirror mode can dominate the power spectrum at the nonlinear stage even if its linear growth rate is significantly lower than that of the proton-cyclotron mode. The proton-cyclotron instability combined with the alpha-proton drift is a possible cause of the nonzero magnetic helicity observed in the solar wind for fluctuations propagating nearly parallel to the magnetic field. Our simulations generally confirm this concept but reveal a complex helicity spectrum that is not anticipated from the linear theory of the instability.

Heat flux modeling using ion drift effects in DIII-D H-mode plasmas with resonant magnetic perturbations

DOE PAGES

Wingen, Andreas; Schmitz, Oliver; Evans, Todd E.; ...

2014-01-01

The heat flux patterns measured in low-collisionality DIII-D H-mode plasmas strongly deviate from simultaneously measured CII emission patterns, used as indicator of particle flux, during applied resonant magnetic perturbations. While the CII emission clearly shows typical striations, which are similar to magnetic footprint patterns obtained from vacuum field line tracing, the heat flux is usually dominated by one large peak at the strike point position. The vacuum approximation, which only considers applied magnetic fields and neglects plasma response and plasma effects, cannot explain the shape of the observed heat flux pattern. One possible explanation is the effect of particle drifts.more » This is included in the field line equations and the results are discussed with reference to the measurement. Electrons and ions show di fferent drift motions at thermal energy levels in a guiding center approximation. While electrons hardly deviate from the field lines, ions can drift several centimetres away from field line flux surfaces. A model is presented in which an ion heat flux, based on the ion drift motion from various kinetic energies as they contribute to a thermal Maxwellian distribution, is calculated. The simulated heat flux is directly compared to measurements with a varying edge safety factor q95. This analysis provides evidence for the dominate e ect of high-energy ions in carrying heat from the plasma inside the separatrix to the target. High-energy ions are deposited close to the unperturbed strike line while low-energy ions can travel into the striated magnetic topology.« less

On the evolution of vortices in massive protoplanetary discs

NASA Astrophysics Data System (ADS)

Pierens, Arnaud; Lin, Min-Kai

2018-05-01

It is expected that a pressure bump can be formed at the inner edge of a dead-zone, and where vortices can develop through the Rossby Wave Instability (RWI). It has been suggested that self-gravity can significantly affect the evolution of such vortices. We present the results of 2D hydrodynamical simulations of the evolution of vortices forming at a pressure bump in self-gravitating discs with Toomre parameter in the range 4 - 30. We consider isothermal plus non-isothermal disc models that employ either the classical β prescription or a more realistic treatment for cooling. The main aim is to investigate whether the condensating effect of self-gravity can stabilize vortices in sufficiently massive discs. We confirm that in isothermal disc models with Q ≳ 15, vortex decay occurs due to the vortex self-gravitational torque. For discs with 3≲ Q ≲ 7, the vortex develops gravitational instabilities within its core and undergoes gravitational collapse, whereas more massive discs give rise to the formation of global eccentric modes. In non-isothermal discs with β cooling, the vortex maintains a turbulent core prior to undergoing gravitational collapse for β ≲ 0.1, whereas it decays if β ≥ 1. In models that incorpore both self-gravity and a better treatment for cooling, however, a stable vortex is formed with aspect ratio χ ˜ 3 - 4. Our results indicate that self-gravity significantly impacts the evolution of vortices forming in protoplanetary discs, although the thermodynamical structure of the vortex is equally important for determining its long-term dynamics.

Vortex Laser based on III-V semiconductor metasurface: direct generation of coherent Laguerre-Gauss modes carrying controlled orbital angular momentum

PubMed Central

Seghilani, Mohamed S.; Myara, Mikhael; Sellahi, Mohamed; Legratiet, Luc; Sagnes, Isabelle; Beaudoin, Grégoire; Lalanne, Philippe; Garnache, Arnaud

2016-01-01

The generation of a coherent state, supporting a large photon number, with controlled orbital-angular-momentum L = ħl (of charge l per photon) presents both fundamental and technological challenges: we demonstrate a surface-emitting laser, based on III-V semiconductor technology with an integrated metasurface, generating vortex-like coherent state in the Laguerre-Gauss basis. We use a first order phase perturbation to lift orbital degeneracy of wavefunctions, by introducing a weak anisotropy called here “orbital birefringence”, based on a dielectric metasurface. The azimuthal symmetry breakdown and non-linear laser dynamics create “orbital gain dichroism” allowing selecting vortex handedness. This coherent photonic device was characterized and studied, experimentally and theoretically. It exhibits a low divergence (<1°) diffraction limited beam, emitting 49 mW output power in the near-IR at λ ≃ 1 μm, a charge l = ±1, … ±4 (>50 dB vortex purity), and single frequency operation in a stable low noise regime (0.1% rms). Such high performance laser opens the path to widespread new photonic applications. PMID:27917885

Some experiments in swirling flows: Detailed velocity measurements of a vortex breakdown using a laser Doppler anemometer. Ph.D. Thesis - Cornell Univ. Final Report

NASA Technical Reports Server (NTRS)

Faler, J. H.

1976-01-01

The results of an experimental study of spiraling flows in a slightly diverging, circular duct are reported. Seven types of flow disturbances were observed. In addition to the spiral and axisymmetric vortex breakdowns and the double helix mode, four other forms were identified and are reported. The type and axial location of the disturbance depended on the Reynolds and circulation numbers of the flow. Detailed velocity measurements were made by using a laser Doppler anemometer. Measurements made far upstream of any disturbance showed that the introduction of swirl resulted in the formation of a high axial velocity jet centered around the vortex center. A mapping of the velocity field of a so-called axisymmetric breakdown, formed at a Reynolds number of 2560, revealed that the recirculation zone is a two-celled structure, with four stagnation points on the vortex axis marking the axial extremes of the concentric cells. The dominant feature of the flow inside the bubble was the strong, periodic velocity fluctuations. Existing theoretical models do not predict the two-celled structure and the temporal velocity fluctuations that were observed.

Experimental study on parasitic mode suppression using FeSiAl in relativistic klystron amplifier

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

Zhang, Zehai

2015-03-15

Experimental study of parasitic mode suppression using electromagnetic attenuate material FeSiAl in an S-band Relativistic Klystron Amplifier (RKA) is presented in this paper. The FeSiAl powder is coated and sintered onto the inner surface of a drift tube which locates between the input and the middle cavity of the RKA. Cold tests show that the attenuate rate of the tube against parasitic mode TE{sub 11} is about 50%. Experiments carried out on the Torch-01 accelerator present that the tube is effective in suppressing the parasitic mode. Two typical outputs are obtained. When the diode voltage is on a moderate level,more » the RKA operates well and the parasitic mode is totally suppressed. The pulse length of the High Power Microwave (HPM) almost equals the electron beam pulse length and the HPM average output power is about 300 MW, with a power efficiency of 10%. When the diode voltage is on a higher level, the output power and efficiency rise but the parasitic mode oscillation occurred and the pulse length is shortened. By contrast, the parasitic mode oscillation is too strong for the RKA to operate normally with un-sintered drift tube. The experimental study implies that FeSiAl is effective in suppressing the parasitic mode oscillation in a certain extent. However, total suppression needs a deeper attenuate rate and further investigation.« less

Spray particle drift mitigation using field corn (Zea mays L.) as a drift barrier.

PubMed

Vieira, Bruno C; Butts, Thomas R; Rodrigues, Andre O; Golus, Jeffrey A; Schroeder, Kasey; Kruger, Greg R

2018-04-24

Herbicide particle drift reduces application efficacy and can cause severe impacts on nearby vegetation depending on the herbicide mode-of-action, exposure level, and tolerance to the herbicide. A particle drift mitigation effort placing windbreaks or barriers on the field boundaries to reduce off-target movement of spray particles has been utilized in the past. The objective of this research was to evaluate the effectiveness of field corn (Zea mays L.) at different heights as a particle drift barrier. Applications with a non-air inclusion flat fan nozzle (ER11004) resulted in greater particle drift when compared to an air inclusion nozzle (TTI11004). Eight rows of corn were used as barriers (0.91, 1.22, and 1.98 m height) which reduced the particle drift for both nozzles, especially at shorter downwind distances. Applications with the ER11004 nozzle without corn barriers had 1% of the applied rate (D 99 ) predicted to deposit at 14.8 m downwind, whereas this distance was reduced (up to 7-fold) when applications were performed with corn barriers. The combination of corn drift barriers and nozzle selection (TTI11004) provided satisfactory particle drift reduction when the D 99 estimates were compared to applications with the ER11004 nozzle without corn barriers (up to 10-fold difference). The corn drift barriers were effective in reducing particle drift from applications with the ER11004 and the TTI11004 nozzles (Fine and Ultra Coarse spray classifications, respectively). The corn drift barrier had appropriate porosity and width as the airborne spray was captured within its canopy instead of deflecting up and over it. This article is protected by copyright. All rights reserved.

A comparative numerical analysis of linear and nonlinear aerodynamic sound generation by vortex disturbances in homentropic constant shear flows

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

Hau, Jan-Niklas, E-mail: hau@fdy.tu-darmstadt.de; Oberlack, Martin; GSC CE, Technische Universität Darmstadt, Dolivostraße 15, 64293 Darmstadt

2015-12-15

Aerodynamic sound generation in shear flows is investigated in the light of the breakthrough in hydrodynamics stability theory in the 1990s, where generic phenomena of non-normal shear flow systems were understood. By applying the thereby emerged short-time/non-modal approach, the sole linear mechanism of wave generation by vortices in shear flows was captured [G. D. Chagelishvili, A. Tevzadze, G. Bodo, and S. S. Moiseev, “Linear mechanism of wave emergence from vortices in smooth shear flows,” Phys. Rev. Lett. 79, 3178-3181 (1997); B. F. Farrell and P. J. Ioannou, “Transient and asymptotic growth of two-dimensional perturbations in viscous compressible shear flow,” Phys.more » Fluids 12, 3021-3028 (2000); N. A. Bakas, “Mechanism underlying transient growth of planar perturbations in unbounded compressible shear flow,” J. Fluid Mech. 639, 479-507 (2009); and G. Favraud and V. Pagneux, “Superadiabatic evolution of acoustic and vorticity perturbations in Couette flow,” Phys. Rev. E 89, 033012 (2014)]. Its source is the non-normality induced linear mode-coupling, which becomes efficient at moderate Mach numbers that is defined for each perturbation harmonic as the ratio of the shear rate to its characteristic frequency. Based on the results by the non-modal approach, we investigate a two-dimensional homentropic constant shear flow and focus on the dynamical characteristics in the wavenumber plane. This allows to separate from each other the participants of the dynamical processes — vortex and wave modes — and to estimate the efficacy of the process of linear wave-generation. This process is analyzed and visualized on the example of a packet of vortex modes, localized in both, spectral and physical, planes. Further, by employing direct numerical simulations, the wave generation by chaotically distributed vortex modes is analyzed and the involved linear and nonlinear processes are identified. The generated acoustic field is anisotropic in the wavenumber plane, which results in highly directional linear sound radiation, whereas the nonlinearly generated waves are almost omni-directional. As part of this analysis, we compare the effectiveness of the linear and nonlinear mechanisms of wave generation within the range of validity of the rapid distortion theory and show the dominance of the linear aerodynamic sound generation. Finally, topological differences between the linear source term of the acoustic analogy equation and of the anisotropic non-normality induced linear mechanism of wave generation are found.« less

Observation of Quasi-Two-Dimensional Nonlinear Interactions in a Drift-Wave Streamer

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

Yamada, T.; Nagashima, Y.; Itoh, S.-I.

2010-11-26

A streamer, which is a bunching of drift-wave fluctuations, and its mediator, which generates the streamer by coupling with other fluctuations, have been observed in a cylindrical magnetized plasma. Their radial structures were investigated in detail by using the biphase analysis. Their quasi-two-dimensional structures were revealed to be equivalent with a pair of fast and slow modes predicted by a nonlinear Schroedinger equation based on the Hasegawa-Mima model.

Gyrokinetic theory of slab universal modes and the non-existence of the gradient drift coupling (GDC) instability

NASA Astrophysics Data System (ADS)

Rogers, Barrett N.; Zhu, Ben; Francisquez, Manaure

2018-05-01

A gyrokinetic linear stability analysis of a collisionless slab geometry in the local approximation is presented. We focus on k∥=0 universal (or entropy) modes driven by plasma gradients at small and large plasma β. These are small scale non-MHD instabilities with growth rates that typically peak near k⊥ρi˜1 and vanish in the long wavelength k⊥→0 limit. This work also discusses a mode known as the Gradient Drift Coupling (GDC) instability previously reported in the gyrokinetic literature, which has a finite growth rate γ=√{β/[2 (1 +β)] }Cs/|Lp| with Cs2=p0/ρ0 for k⊥→0 and is universally unstable for 1 /Lp≠0 . We show that the GDC instability is a spurious, unphysical artifact that erroneously arises due to the failure to respect the total equilibrium pressure balance p0+B02/(8 π)=constant , which renders the assumption B0'=0 inconsistent if p0'≠0 .

Shock drift acceleration in the presence of waves

NASA Technical Reports Server (NTRS)

Decker, R. B.; Vlahos, L.

1985-01-01

Attention is given to the initial results of a model designed to study the modification of the scatter-free, shock drift acceleration of energetic test particles by wave activity in the vicinity of a quasi-perpendicular, fast-mode MHD shock. It is emphasized that the concept of magnetic moment conservation is a valid approximation only in the perpendicular and nearly perpendicular regimes, when the angle theta-Bn between the shock normal and the upstream magnetic field vector is in the range from 70 deg to 90 deg. The present investigation is concerned with one step in a program which is being developed to combine the shock drift and diffusive processes at a shock of arbitrary theta-Bn.

Unusual characteristics of electromagnetic waves excited by cometary newborn ions with large perpendicular energies

NASA Technical Reports Server (NTRS)

Brinca, A. L.; Tsurutani, B. T.

1987-01-01

The characteristics of electromagnetic waves excited by cometary newborn ions with large perpendicular energies are examined using a model of solar wind permeated by dilute drifting ring distributions of electrons and oxygen ions with finite thermal spreads. The model has parameters compatible with the ICE observations at the Giacobini-Zinner comet. It is shown that cometary newborn ions with large perpendicular energies can excite a wave mode with rest frame frequencies in the order of the heavy ion cyclotron frequency, Omega(i), and unusual propagation characteristics at small obliquity angles. For parallel propagation, the mode is left-hand circularly polarized, might be unstable in a frequency range containing Omega(i), and moves in the direction of the newborn ion drift along the static magnetic field.

Rotation and kinetic modifications of the tokamak ideal-wall pressure limit.

PubMed

Menard, J E; Wang, Z; Liu, Y; Bell, R E; Kaye, S M; Park, J-K; Tritz, K

2014-12-19

The impact of toroidal rotation, energetic ions, and drift-kinetic effects on the tokamak ideal wall mode stability limit is considered theoretically and compared to experiment for the first time. It is shown that high toroidal rotation can be an important destabilizing mechanism primarily through the angular velocity shear; non-Maxwellian fast ions can also be destabilizing, and drift-kinetic damping can potentially offset these destabilization mechanisms. These results are obtained using the unique parameter regime accessible in the spherical torus NSTX of high toroidal rotation speed relative to the thermal and Alfvén speeds and high kinetic pressure relative to the magnetic pressure. Inclusion of rotation and kinetic effects significantly improves agreement between measured and predicted ideal stability characteristics and may provide new insight into tearing mode triggering.

Generation of spirally polarized propagation-invariant beam using fiber microaxicon.

PubMed

Philip, Geo M; Viswanathan, Nirmal K

2011-10-01

We present here a fiber microaxicon (MA)based method to generate spirally polarized propagation-invariant optical beam. MA chemically etched in the tip of a two-mode fiber efficiently converts the generic cylindrically polarized vortex fiber mode into a spirally polarized propagation-invariant (Bessel-type) beam via radial dependence of polarization rotation angle. The combined roles of helico-conical phase and nonparaxial propagation in the generation and characteristics of the output beam from the fiber MA are discussed. © 2011 Optical Society of America

Tight focusing of higher orders Laguerre-Gaussian modes

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

Savelyev, Dmitry A., E-mail: dmitrey.savelyev@yandex.ru; Khonina, Svetlana N.; Samara State Aerospace University, 34 Moskovskoye Shosse, Samara 443086

2016-04-13

The spatial redistribution of the contribution of different electric field components provides a decrease in the size of the central focal spot for higher orders Laguerre-Gaussian modes. It was shown that when sharply focusing laser beams with vortex or special binary phase plate, a sub-wavelength light localization of separate vector field components is possible for any polarization type. This fact should be considered for the interaction of laser radiation with materials selectively sensitive to lateral and longitudinal components of the electromagnetic field.

Tomographic reconstruction of heat release rate perturbations induced by helical modes in turbulent swirl flames

NASA Astrophysics Data System (ADS)

Moeck, Jonas P.; Bourgouin, Jean-François; Durox, Daniel; Schuller, Thierry; Candel, Sébastien

2013-04-01

Swirl flows with vortex breakdown are widely used in industrial combustion systems for flame stabilization. This type of flow is known to sustain a hydrodynamic instability with a rotating helical structure, one common manifestation of it being the precessing vortex core. The role of this unsteady flow mode in combustion is not well understood, and its interaction with combustion instabilities and flame stabilization remains unclear. It is therefore important to assess the structure of the perturbation in the flame that is induced by this helical mode. Based on principles of tomographic reconstruction, a method is presented to determine the 3-D distribution of the heat release rate perturbation associated with the helical mode. Since this flow instability is rotating, a phase-resolved sequence of projection images of light emitted from the flame is identical to the Radon transform of the light intensity distribution in the combustor volume and thus can be used for tomographic reconstruction. This is achieved with one stationary camera only, a vast reduction in experimental and hardware requirements compared to a multi-camera setup or camera repositioning, which is typically required for tomographic reconstruction. Different approaches to extract the coherent part of the oscillation from the images are discussed. Two novel tomographic reconstruction algorithms specifically tailored to the structure of the heat release rate perturbations related to the helical mode are derived. The reconstruction techniques are first applied to an artificial field to illustrate the accuracy. High-speed imaging data acquired in a turbulent swirl-stabilized combustor setup with strong helical mode oscillations are then used to reconstruct the 3-D structure of the associated perturbation in the flame.

New insights on boundary plasma turbulence and the Quasi-Coherent Mode in Alcator C-Mod using a Mirror Langmuir Probe

NASA Astrophysics Data System (ADS)

Labombard, Brian

2013-10-01

A ``Mirror Langmuir Probe'' (MLP) diagnostic has been used to interrogate edge plasma profiles and turbulence in Alcator C-Mod with unprecedented detail, yielding fundamental insights on the Quasi-Coherent Mode (QCM) - a mode that regulates plasma density and impurities in EDA H-modes without ELMs. The MLP employs a fast-switching, self-adapting bias scheme, recording density, electron temperature and plasma potential simultaneously at high bandwidth (~1 MHz) on each of four separate electrodes on a scanning probe. Temporal dynamics are followed in detail; wavenumber-frequency spectra and phase relationships are readily deduced. Poloidal field fluctuations are recorded separately with a two-coil, scanning probe. Results from ohmic L-mode and H-mode plasmas are reported, including key observations of the QCM: The QCM lives in a region of positive radial electric field, with a mode width (~3 mm) that spans open and closed field line regions. Remarkably large amplitude (~30%), sinusoidal bursts in density, electron temperature and plasma potential fluctuations are observed that are in phase; potential lags density by at most 10 degrees. Propagation velocity of the mode corresponds to the sum of local E × B and electron diamagnetic drift velocities - quantities that are deduced directly from time-averaged profiles. Poloidal magnetic field fluctuations project to parallel current densities of ~5 amps/cm2 in the mode layer, with significant parallel electromagnetic induction. Electron force balance is examined, unambiguously identifying the mode type. It is found that fluctuations in parallel electron pressure gradient are roughly balanced by the sum of electrostatic and electromotive forces. Thus the primary mode structure of the QCM is that of a drift-Alfven wave. Work supported by US DoE award DE-FC02-99ER54512.

Holocene history of drift ice in the northern North Atlantic: Evidence for different spatial and temporal modes

USGS Publications Warehouse

Moros, M.; Andrews, John T.; Eberl, D.D.; Jansen, E.

2006-01-01

We present new high-resolution proxy data for the Holocene history of drift ice off Iceland based on the mineralogy of the <2-mm sediment fraction using quantitative X-ray diffraction. These new data, bolstered by a comparison with published proxy records, point to a long-term increasing trend in drift ice input into the North Atlantic from 6 to 5 ka toward the present day at sites influenced by the cold east Greenland Current. This feature reflects the late Holocene Neoglacial or cooling period recorded in ice cores and further terrestrial archives on Greenland. In contrast, a decrease in drift ice during the same period is recorded at sites underlying the North Atlantic Drift, which may reflect a warming of this region. The results document that Holocene changes in iceberg rafting and sea ice advection did not occur uniformly across the North Atlantic. Centennial-scale climate variability in the North Atlantic region over the last ???4 kyr is linked to the observed changes in drift ice input. Increased drift ice may have played a role in the increase of cold intervals during the late Holocene, e.g., the Little Ice Age cooling. Copyright 2006 by the American Geophysical Union.

Targeting specific azimuthal modes using wall changes in turbulent pipe flow

NASA Astrophysics Data System (ADS)

van Buren, Tyler; Hellström, Leo; Marusic, Ivan; Smits, Alexander

2017-11-01

We experimentally study turbulent pipe flow at Re =3486 using stereoscopic particle image velocimetry. Using pipe inserts with non-circular geometry to perturb the flow upstream of the measurement location, we excite specific naturally occurring energetic modes. We consider inserts that directly manipulate the flow momentum (vortex generators), and/or induce secondary flows through Reynolds stresses (sinusoidally varying wall shape). These inserts substantially change the mean flow, and produce distinct regions of low and high momentum corresponding to the mode being excited. The inserts add energy in the targeted modes while simultaneously reducing the energy in the non-excited azimuthal modes. In addition, inserts designed to excite two modes simultaneously exhibit non-linear interactions. Supported under ONR Grant N00014-15-1-2402, Program Manager/Director Thomas Fu and the Australian Research Council.

Interchange mode excited by trapped energetic ions

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

Nishimura, Seiya, E-mail: n-seiya@kobe-kosen.ac.jp

2015-07-15

The kinetic energy principle describing the interaction between ideal magnetohydrodynamic (MHD) modes with trapped energetic ions is revised. A model is proposed on the basis of the reduced ideal MHD equations for background plasmas and the bounce-averaged drift-kinetic equation for trapped energetic ions. The model is applicable to large-aspect-ratio toroidal devices. Specifically, the effect of trapped energetic ions on the interchange mode in helical systems is analyzed. Results show that the interchange mode is excited by trapped energetic ions, even if the equilibrium states are stable to the ideal interchange mode. The energetic-ion-induced branch of the interchange mode might bemore » associated with the fishbone mode in helical systems.« less

Drift effects on the tokamak power scrape-off width

NASA Astrophysics Data System (ADS)

Meier, E. T.; Goldston, R. J.; Kaveeva, E. G.; Mordijck, S.; Rozhansky, V. A.; Senichenkov, I. Yu.; Voskoboynikov, S. P.

2015-11-01

Recent experimental analysis suggests that the scrape-off layer (SOL) heat flux width (λq) for ITER will be near 1 mm, sharply narrowing the planned operating window. In this work, motivated by the heuristic drift (HD) model, which predicts the observed inverse plasma current scaling, SOLPS-ITER is used to explore drift effects on λq. Modeling focuses on an H-mode DIII-D discharge. In initial results, target recycling is set to 90%, resulting in sheath-limited SOL conditions. SOL particle diffusivity (DSOL) is varied from 0.1 to 1 m2/s. When drifts are included, λq is insensitive to DSOL, consistent with the HD model, with λq near 3 mm; in no-drift cases, λq varies from 2 to 5 mm. Drift effects depress near-separatrix potential, generating a channel of strong electron heat convection that is insensitive to DSOL. Sensitivities to thermal diffusivities, plasma current, toroidal magnetic field, and device size are also assessed. These initial results will be discussed in detail, and progress toward modeling experimentally relevant high-recycling conditions will be reported. Supported by U.S. DOE Contract DE-SC0010434.

Assimilation of the seabird and ship drift data in the north-eastern sea of Japan into an operational ocean nowcast/forecast system

PubMed Central

Miyazawa, Yasumasa; Guo, Xinyu; Varlamov, Sergey M.; Miyama, Toru; Yoda, Ken; Sato, Katsufumi; Kano, Toshiyuki; Sato, Keiji

2015-01-01

At the present time, ocean current is being operationally monitored mainly by combined use of numerical ocean nowcast/forecast models and satellite remote sensing data. Improvement in the accuracy of the ocean current nowcast/forecast requires additional measurements with higher spatial and temporal resolution as expected from the current observation network. Here we show feasibility of assimilating high-resolution seabird and ship drift data into an operational ocean forecast system. Data assimilation of geostrophic current contained in the observed drift leads to refinement in the gyre mode events of the Tsugaru warm current in the north-eastern sea of Japan represented by the model. Fitting the observed drift to the model depends on ability of the drift representing geostrophic current compared to that representing directly wind driven components. A preferable horizontal scale of 50 km indicated for the seabird drift data assimilation implies their capability of capturing eddies with smaller horizontal scale than the minimum scale of 100 km resolved by the satellite altimetry. The present study actually demonstrates that transdisciplinary approaches combining bio-/ship- logging and numerical modeling could be effective for enhancement in monitoring the ocean current. PMID:26633309

A study of the temporal stability of multiple cell vortices

NASA Technical Reports Server (NTRS)

Khorrami, Mehdi R.

1989-01-01

The effect of initial mean velocity field on the stability characteristics of longitudinal vortices is documented in detail. The temporal stability of isolated multiple cell vortices is considered. The types of vortices studied include single cell as well as two and three cell vortices. It is shown that cell multiplicity in the vortex core has drastic effects on the stability characteristics. On the basis of numerical calculations, it is concluded that the growth rates of instabilities in multiple cell vortices are substantially larger (two to threefold increases are observed) than those of a single cell vortex. It is also determined that there is a substantial increase in the effective range of axial and azimuthal wavenumbers where instabilities are present. But most importantly, there is the appearance of a variety of viscous modes of instability. In the case of vortices, these latter instabilities which highlight the importance of viscous forces have never been reported before. These effects are discussed in detail for the case of a two cell vortex.

Nonlinear Evolution of Azimuthally Compact Crossflow-Vortex Packet over a Yawed Cone

NASA Astrophysics Data System (ADS)

Choudhari, Meelan; Li, Fei; Paredes, Pedro; Duan, Lian; NASA Langley Research Center Team; Missouri Univ of Sci; Tech Team

2017-11-01

Hypersonic boundary-layer flows over a circular cone at moderate incidence angle can support strong crossflow instability and, therefore, a likely scenario for laminar-turbulent transition in such flows corresponds to rapid amplification of high-frequency secondary instabilities sustained by finite amplitude stationary crossflow vortices. Direct numerical simulations (DNS) are used to investigate the nonlinear evolution of azimuthally compact crossflow vortex packets over a 7-degree half-angle, yawed circular cone in a Mach 6 free stream. Simulation results indicate that the azimuthal distribution of forcing has a strong influence on the stationary crossflow amplitudes; however, the vortex trajectories are nearly the same for both periodic and localized roughness height distributions. The frequency range, mode shapes, and amplification characteristics of strongly amplified secondary instabilities in the DNS are found to overlap with the predictions of secondary instability theory. The DNS computations also provide valuable insights toward the application of planar, partial-differential-equation based eigenvalue analysis to spanwise inhomogeneous, fully three-dimensional, crossflow-dominated flow configurations.

Investigation of corner shock boundary layer interactions to understand inlet unstart

NASA Astrophysics Data System (ADS)

Funderburk, Morgan

2015-11-01

Inlet unstart is a detrimental phenomenon in dual-mode ramjet/scramjet engines that causes severe loss of thrust, large transient structural load, and potentially a loss of the aircraft. In order to analyze the effects that the corner shock boundary layer interaction (SBLI) has on initiating and perpetuating inlet unstart, a qualitative and quantitative investigation into mean and dynamic features of corner SBLI at various Mach numbers is made. Surface streakline visualization showed that the corner SBLI is highly three-dimensional with a dominant presence of corner separation vortex. Further, the peak r.m.s. pressure was located at the periphery of corner separation vortex, suggesting that the unsteady loading is caused by the corner vortex. Power spectral densities of wall-pressure fluctuations in the peak r.m.s. location were analyzed in order to characterize the dominant frequencies of oscillation of the flow structures and to unravel the dynamic interactions between them in order to expand the operating margin of future hypersonic air breathing vehicles.

Compound hydraulic shear-modulated vortex amplifiers

NASA Technical Reports Server (NTRS)

Goldschmied, F. R.

1977-01-01

A novel two-stage shear-modulated hydraulic vortex amplifier (U.S. patent 3,520,317) has been fabricated and put through preliminary steady-state testing at the 1000 psi supply pressure level with flows up to 15 gpm. The invention comprises a conventional fluidic vortex power stage and a shear-modulated pilot stage. In the absence of any mechanical moving parts, water may be used as the hydraulic medium thus opening the way to many underseas applications. At blocked load, a control input from 0 to 150 psi was required to achieve an output from 0 to 900 psi; at wide-open load, a control input of 0 to 120 psi was needed to achieve an output from 0 to 15 gpm. The power stage has been found unsuitable for the proportional control mode because of its nonlinear performance in the intermediate load range and because of strong pressure fluctuations (plus or minus 150 psi) in the intermediate control range. The addition of the shear-modulated pilot stage improves intermediate load linearity.

Integrated Physics-based Modeling and Experiments for Improved Prediction of Combustion Dynamics in Low-Emission Systems

NASA Technical Reports Server (NTRS)

Anderson, William E.; Lucht, Robert P.; Mongia, Hukam

2015-01-01

Concurrent simulation and experiment was undertaken to assess the ability of a hybrid RANS-LES model to predict combustion dynamics in a single-element lean direct-inject (LDI) combustor showing self-excited instabilities. High frequency pressure modes produced by Fourier and modal decomposition analysis were compared quantitatively, and trends with equivalence ratio and inlet temperature were compared qualitatively. High frequency OH PLIF and PIV measurements were also taken. Submodels for chemical kinetics and primary and secondary atomization were also tested against the measured behavior. For a point-wise comparison, the amplitudes matched within a factor of two. The dependence on equivalence ratio was matched. Preliminary results from simulation using an 18-reaction kinetics model indicated instability amplitudes closer to measurement. Analysis of the simulations suggested a band of modes around 1400 Hz were due to a vortex bubble breakdown and a band of modes around 6 kHz were due to a precessing vortex core hydrodynamic instability. The primary needs are directly coupled and validated ab initio models of the atomizer free surface flow and the primary atomization processes, and more detailed study of the coupling between the 3D swirling flow and the local thermoacoustics in the diverging venturi section.

Light bullets in coupled nonlinear Schrödinger equations with variable coefficients and a trapping potential.

PubMed

Xu, Si-Liu; Zhao, Guo-Peng; Belić, Milivoj R; He, Jun-Rong; Xue, Li

2017-04-17

We analyze three-dimensional (3D) vector solitary waves in a system of coupled nonlinear Schrödinger equations with spatially modulated diffraction and nonlinearity, under action of a composite self-consistent trapping potential. Exact vector solitary waves, or light bullets (LBs), are found using the self-similarity method. The stability of vortex 3D LB pairs is examined by direct numerical simulations; the results show that only low-order vortex soliton pairs with the mode parameter values n ≤ 1, l ≤ 1 and m = 0 can be supported by the spatially modulated interaction in the composite trap. Higher-order LBs are found unstable over prolonged distances.

SOL effects on the pedestal structure in DIII-D discharges

DOE PAGES

Sontag, Aaron C.; Chen, Xi; Canik, John; ...

2017-05-24

SOLPS analysis explains the differences in pedestal structure associated with different ion ∇B drift directions in DIII-D. Core transport models predict that fusion power scales roughly as the square of the pressure at the top of the pedestal, so understanding the effects that determine pedestal structure in steady-state operational scenarios is important to projecting scenarios developed in DIII-D to ITER and other devices. Both experiments and modeling indicate that scrape off layer (SOL) conditions are important in optimizing the pedestal structure for high-beta steady-state scenarios. The SOLPS code is used to provide interpretive analysis of the pedestal and SOL tomore » examine the nature of flows and fueling on the pedestal structure including the effects of drifts in the fluid model. This analysis shows that flows driven by the ion ∇B drift are outward when this drift is toward the x-point in a single-null divertor configuration (favorable ∇B direction for reduced H-mode power threshold), and inward when the drift is away from the x-point (unfavorable ∇B direction). It is hypothesized that these flows decrease the density gradient in the pedestal in the favorable direction, thereby stabilizing the kinetic ballooning mode (KBM) and increasing the pedestal width. Comparisons of pedestal structures in similarly shaped DIII-D steady-state plasmas confirm this change, showing increased density pedestal width and lower peak density and lower separatrix density with the favorable drift direction. The pedestal temperature is higher in the lower density case, resulting in an increased pedestal pressure, which indicates that the increased particle flux does not significantly degrade energy confinement. Modeling of cases with constant ∇B drift direction but changing between the more open lower divertor and more closed upper divertor show that there is increased fueling inside the pedestal with the more open geometry. As a result, the pedestal fueling rate for both attached and detached cases is always lower with more closed divertor geometry than in any cases with more open geometry.« less

SOL effects on the pedestal structure in DIII-D discharges

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

Sontag, Aaron C.; Chen, Xi; Canik, John

SOLPS analysis explains the differences in pedestal structure associated with different ion ∇B drift directions in DIII-D. Core transport models predict that fusion power scales roughly as the square of the pressure at the top of the pedestal, so understanding the effects that determine pedestal structure in steady-state operational scenarios is important to projecting scenarios developed in DIII-D to ITER and other devices. Both experiments and modeling indicate that scrape off layer (SOL) conditions are important in optimizing the pedestal structure for high-beta steady-state scenarios. The SOLPS code is used to provide interpretive analysis of the pedestal and SOL tomore » examine the nature of flows and fueling on the pedestal structure including the effects of drifts in the fluid model. This analysis shows that flows driven by the ion ∇B drift are outward when this drift is toward the x-point in a single-null divertor configuration (favorable ∇B direction for reduced H-mode power threshold), and inward when the drift is away from the x-point (unfavorable ∇B direction). It is hypothesized that these flows decrease the density gradient in the pedestal in the favorable direction, thereby stabilizing the kinetic ballooning mode (KBM) and increasing the pedestal width. Comparisons of pedestal structures in similarly shaped DIII-D steady-state plasmas confirm this change, showing increased density pedestal width and lower peak density and lower separatrix density with the favorable drift direction. The pedestal temperature is higher in the lower density case, resulting in an increased pedestal pressure, which indicates that the increased particle flux does not significantly degrade energy confinement. Modeling of cases with constant ∇B drift direction but changing between the more open lower divertor and more closed upper divertor show that there is increased fueling inside the pedestal with the more open geometry. As a result, the pedestal fueling rate for both attached and detached cases is always lower with more closed divertor geometry than in any cases with more open geometry.« less

Drift chamber readout system of the DIRAC experiment

NASA Astrophysics Data System (ADS)

Afanasyev, L.; Karpukhin, V.

2002-10-01

A drift chamber readout system of the DIRAC experiment at CERN is presented. The system is intended to read out the signals from planar chambers operating in a high current mode. The sense wire signals are digitized in the 16-channel time-to-digital converter boards which are plugged in the signal plane connectors. This design results in a reduced number of modules, a small number of cables and high noise immunity. The system has been successfully operating in the experiment since 1999.

Wake Vortex Tracking Using a 35 GHz Pulsed Doppler Radar

NASA Technical Reports Server (NTRS)

Neece, Robert T.; Britt, Charles L.; White, Joseph H.; Mudukutore, Ashok; Nguyen, Chi; Hooper, Bill

2005-01-01

A 35 GHz, pulsed-Doppler radar system has been designed and assembled for wake vortex detection and tracking in low visibility conditions. Aircraft wake vortices continue to be an important factor in determining safe following distances or spacings for aircraft in the terminal area. Currently, under instrument meteorological conditions (IMC), aircraft adhere to conservative, fixed following-distance guidelines based primarily on aircraft weight classifications. When ambient conditions are such that vortices will either drift or dissipate, leaving the flight corridor clear, the prescribed spacings are unnecessarily long and result in decreased airport throughput. There is a potential for significant airport efficiency improvement, if a system can be employed to aid regulators and pilots in setting safe and efficient following distances based on airport conditions. The National Aeronautics and Space Administration (NASA), the Federal Aviation Agency, and Volpe National Transportation Systems Center have promoted and worked to develop systems that would increase airport capacity and provide for safe reductions in aircraft separation. The NASA Aircraft Vortex Spacing System (AVOSS), a wake vortex spacing system that can provide dynamic adjustment of spacings based on real-time airport weather conditions, has demonstrated that Lidar systems can be successfully used to detect and track vortices in clear air conditions. To fill the need for detection capability in low-visibility conditions, a 35 GHz, pulsed-Doppler radar system is being investigated for use as a complimentary, low-visibility sensor for wake vortices. The radar sensor provides spatial and temporal information similar to that provided by Lidar, but under weather conditions that a Lidar cannot penetrate. Currently, we are analyzing the radar design based upon the data and experience gained during the wake vortex Lidar deployment with AVOSS at Dallas/Fort Worth International Airport. As part of this study, two numerical models were utilized in system simulations. The results of this study improve our understanding of the method of detection, resolution requirements for range and azimuth, pulse compression, and performance prediction. Simulations applying pulse compression techniques show that detection is good in heavy fog to greater than 2000 m. Both compressed and uncompressed short pulses show the vortex structure. To explore operational challenges, siting and scanning strategies were also analyzed. Simulation results indicate that excellent wake vortex detection, tracking and classification is possible in drizzle (+15 dBZ) and heavy fog (- 13 dBZ) using short pulse techniques (<99ns) at ranges on the order of 900 m, with a modest power of 500 W output. At 1600 m, detection can be expected at reflectivities as low as -13 dBZ (heavy fog). The radar system, as designed and built, has the potential to support field studies of a wake vortex spacing system in low-visibility conditions ranging from heavy fog to rain, when sited within 2000m of the flight path.

A static predictor of seismic demand on frames based on a post-elastic deflected shape

USGS Publications Warehouse

Mori, Y.; Yamanaka, T.; Luco, N.; Cornell, C.A.

2006-01-01

Predictors of seismic structural demands (such as inter-storey drift angles) that are less time-consuming than nonlinear dynamic analysis have proven useful for structural performance assessment and for design. Luco and Cornell previously proposed a simple predictor that extends the idea of modal superposition (of the first two modes) with the square-root-of-sum-of-squares (SRSS) rule by taking a first-mode inelastic spectral displacement into account. This predictor achieved a significant improvement over simply using the response of an elastic oscillator; however, it cannot capture well large displacements caused by local yielding. A possible improvement of Luco's predictor is discussed in this paper, where it is proposed to consider three enhancements: (i) a post-elastic first-mode shape approximated by the deflected shape from a nonlinear static pushover analysis (NSPA) at the step corresponding to the maximum drift of an equivalent inelastic single-degree-of-freedom (SDOF) system, (ii) a trilinear backbone curve for the SDOF system, and (iii) the elastic third-mode response for long-period buildings. Numerical examples demonstrate that the proposed predictor is less biased and results in less dispersion than Luco's original predictor. Copyright ?? 2006 John Wiley & Sons, Ltd.

Density-Gradient-Driven trapped-electron-modes in improved-confinement RFP plasmas

NASA Astrophysics Data System (ADS)

Duff, James; Sarff, John; Ding, Weixing; Brower, David; Parke, Eli; Chapman, Brett; Terry, Paul; Pueschel, M. J.; Williams, Zach

2017-10-01

Short wavelength density fluctuations in improved-confinement MST plasmas exhibit multiple features characteristic of the trapped-electron-mode (TEM). Core transport in the RFP is normally governed by magnetic stochasticity stemming from long wavelength tearing modes that arise from current profile peaking, which are suppressed via inductive control for this work. The improved confinement is associated with an increase in the pressure gradient that can destabilize drift waves. The measured density fluctuations have f 50 kHz, kϕρs < 0.14 , and propagate in the electron drift direction. Their spectral emergence coincides with a sharp decrease in global tearing mode associated fluctuations, their amplitude increases with local density gradient, and they exhibit a density-gradient threshold at R /Ln 15 . The GENE code, modified for the RFP, predicts the onset of density-gradient-driven TEM for these strong-gradient plasma conditions. While nonlinear analysis shows a large Dimits shift associated with predicted strong zonal flows, the inclusion of residual magnetic fluctuations, comparable to experimental magnetic fluctuations, causes a collapse of the zonal flows and an increase in the predicted transport to a level close to the experimentally measured heat flux. Work supported by US DOE.

Off-equilibrium infrared structure of self-interacting scalar fields: Universal scaling, vortex-antivortex superfluid dynamics, and Bose-Einstein condensation

NASA Astrophysics Data System (ADS)

Deng, Jian; Schlichting, Soeren; Venugopalan, Raju; Wang, Qun

2018-05-01

We map the infrared dynamics of a relativistic single-component (N =1 ) interacting scalar field theory to that of nonrelativistic complex scalar fields. The Gross-Pitaevskii (GP) equation, describing the real-time dynamics of single-component ultracold Bose gases, is obtained at first nontrivial order in an expansion proportional to the powers of λ ϕ2/m2 where λ , ϕ , and m are the coupling constant, the scalar field, and the particle mass respectively. Our analytical studies are corroborated by numerical simulations of the spatial and momentum structure of overoccupied scalar fields in (2+1)-dimensions. Universal scaling of infrared modes, vortex-antivortex superfluid dynamics, and the off-equilibrium formation of a Bose-Einstein condensate are observed. Our results for the universal scaling exponents are in agreement with those extracted in the numerical simulations of the GP equation. As in these simulations, we observe coarsening phase kinetics in the Bose superfluid with strongly anomalous scaling exponents relative to that of vertex resummed kinetic theory. Our relativistic field theory framework further allows one to study more closely the coupling between superfluid and normal fluid modes, specifically the turbulent momentum and spatial structure of the coupling between a quasiparticle cascade to the infrared and an energy cascade to the ultraviolet. We outline possible applications of the formalism to the dynamics of vortex-antivortex formation and to the off-equilibrium dynamics of the strongly interacting matter formed in heavy-ion collisions.

Flow Separation Control Over a Ramp Using Sweeping Jet Actuators

NASA Technical Reports Server (NTRS)

Koklu, Mehti; Owens, Lewis R.

2014-01-01

Flow separation control on an adverse-pressure-gradient ramp model was investigated using various flow-control methods in the NASA Langley 15-Inch Wind Tunnel. The primary flow-control method studied used a sweeping jet actuator system to compare with more classic flow-control techniques such as micro-vortex generators, steady blowing, and steady- and unsteady-vortex generating jets. Surface pressure measurements and a new oilflow visualization technique were used to characterize the effects of these flow-control actuators. The sweeping jet actuators were run in three different modes to produce steady-straight, steady-angled, and unsteady-oscillating jets. It was observed that all of these flow-control methods are effective in controlling the separated flows on the ramp model. The steady-straight jet energizes the boundary layer by momentum addition and was found to be the least effective method for a fixed momentum coefficient. The steady-angled jets achieved better performance than the steady-straight jets because they generate streamwise vortices that energize the boundary layer by mixing high-momentum fluid with near wall low-momentum fluid. The unsteady-oscillating jets achieved the best performance by increasing the pressure recovery and reducing the downstream flow separation. Surface flow visualizations indicated that two out-of-phase counter-rotating vortices are generated per sweeping jet actuator, while one vortex is generated per vortex-generating jets. The extra vortex resulted in increased coverage, more pressure recovery, and reduced flow separation.

Targeted energy transfer in laminar vortex-induced vibration of a sprung cylinder with a nonlinear dissipative rotator

NASA Astrophysics Data System (ADS)

Blanchard, Antoine; Bergman, Lawrence A.; Vakakis, Alexander F.

2017-07-01

We computationally investigate the dynamics of a linearly-sprung circular cylinder immersed in an incompressible flow and undergoing transverse vortex-induced vibration (VIV), to which is attached a rotational nonlinear energy sink (NES) consisting of a mass that freely rotates at constant radius about the cylinder axis, and whose motion is restrained by a rotational linear viscous damper. The inertial coupling between the rotational motion of the attached mass and the rectilinear motion of the cylinder is ;essentially nonlinear;, which, in conjunction with dissipation, allows for one-way, nearly irreversible targeted energy transfer (TET) from the oscillating cylinder to the nonlinear dissipative attachment. At the intermediate Reynolds number Re = 100, the NES-equipped sprung cylinder undergoes repetitive cycles of slowly decaying oscillations punctuated by intervals of chaotic instabilities. During the slowly decaying portion of each cycle, the dynamics of the cylinder is regular and, for large enough values of the ratio ε of the NES mass to the total mass (i.e., NES mass plus cylinder mass), can lead to significant vortex street elongation with partial stabilization of the wake. As ε approaches zero, no such vortex elongation is observed and the wake patterns appear similar to that for a sprung cylinder with no NES. We apply proper orthogonal decomposition (POD) to the velocity flow field during a slowly decaying portion of the solution and show that, in situations where vortex elongation occurs, the NES, though not in direct contact with the surrounding fluid, has a drastic effect on the underlying flow structures, imparting significant and continuous passive redistribution of energy among POD modes. We construct a POD-based reduced-order model for the lift coefficient to characterize energy transactions between the fluid and the cylinder throughout the slowly decaying cycle. We introduce a quantitative signed measure of the work done by the fluid on the cylinder over one quasi-period of the slowly decaying response and find that vortex elongation is associated with a sign change of that measure, indicating that a reversal of the direction of energy transfer, with the cylinder ;leaking energy back; to the flow, is responsible for partial stabilization and elongation of the wake. We interpret these findings in terms of the spatial structure and energy distribution of the POD modes, and relate them to the mechanism of transient resonance capture into a slow invariant manifold of the fluid-structure interaction dynamics.

draco: Analysis and simulation of drift scan radio data

NASA Astrophysics Data System (ADS)

Shaw, J. Richard

2017-12-01

draco analyzes transit radio data with the m-mode formalism. It is telescope agnostic, and is used as part of the analysis and simulation pipeline for the CHIME (Canadian Hydrogen Intensity Mapping Experiment) telescope. It can simulate time stream data from maps of the sky (using the m-mode formalism) and add gain fluctuations and correctly correlated instrumental noise (i.e. Wishart distributed). Further, it can perform various cuts on the data and make maps of the sky from data using the m-mode formalism.

Verification of long wavelength electromagnetic modes with a gyrokinetic-fluid hybrid model in the XGC code

PubMed Central

Lang, Jianying; Ku, S.; Chen, Y.; Parker, S. E.; Adams, M. F.

2017-01-01

As an alternative option to kinetic electrons, the gyrokinetic total-f particle-in-cell (PIC) code XGC1 has been extended to the MHD/fluid type electromagnetic regime by combining gyrokinetic PIC ions with massless drift-fluid electrons analogous to Chen and Parker [Phys. Plasmas 8, 441 (2001)]. Two representative long wavelength modes, shear Alfvén waves and resistive tearing modes, are verified in cylindrical and toroidal magnetic field geometries. PMID:29104419

Magnetic field shift due to mechanical vibration in functional magnetic resonance imaging.

PubMed

Foerster, Bernd U; Tomasi, Dardo; Caparelli, Elisabeth C

2005-11-01

Mechanical vibrations of the gradient coil system during readout in echo-planar imaging (EPI) can increase the temperature of the gradient system and alter the magnetic field distribution during functional magnetic resonance imaging (fMRI). This effect is enhanced by resonant modes of vibrations and results in apparent motion along the phase encoding direction in fMRI studies. The magnetic field drift was quantified during EPI by monitoring the resonance frequency interleaved with the EPI acquisition, and a novel method is proposed to correct the apparent motion. The knowledge on the frequency drift over time was used to correct the phase of the k-space EPI dataset. Since the resonance frequency changes very slowly over time, two measurements of the resonance frequency, immediately before and after the EPI acquisition, are sufficient to remove the field drift effects from fMRI time series. The frequency drift correction method was tested "in vivo" and compared to the standard image realignment method. The proposed method efficiently corrects spurious motion due to magnetic field drifts during fMRI. (c) 2005 Wiley-Liss, Inc.

Exercise science: research to sustain and enhance performance

NASA Astrophysics Data System (ADS)

Wingo, Jonathan E.

2013-05-01

Cardiovascular adjustments accompanying exercise in high ambient temperatures are likely responsible for diminished aerobic capacity and performance in such conditions. These adjustments include a phenomenon known as cardiovascular drift in which heart rate rises and stroke volume declines progressively over time during constant-rate exercise. A variety of factors modulate the magnitude of cardiovascular drift, e.g., elevated core and skin temperatures, dehydration, and exercise intensity. Regardless of the mode of manipulation, decreases in stroke volume associated with cardiovascular drift result in directionally and proportionally similar decreases in maximal aerobic capacity. Maximal aerobic capacity is determined by maximal heart rate, maximal tissue oxygen extraction, and maximal stroke volume. Because maximal heart rate and maximal tissue oxygen extraction are unaffected during exercise in the heat, decreased stroke volume associated with cardiovascular drift likely persists during maximal efforts and explains the decrease in maximal aerobic capacity. Decreased maximal aerobic capacity results in a greater perceptual and physiological strain accompanying any given level of work. Therefore, sustaining and enhancing performance involves sophisticated monitoring of physiological strain combined with development of countermeasures that mitigate the magnitude of deleterious phenomena like cardiovascular drift.

Drift mobility of holes in phenanthrene single crystals

NASA Technical Reports Server (NTRS)

Sonnonstine, T. J.; Hermann, A. M.

1974-01-01

The temperature dependence of drift mobilities of holes in single crystals of phenanthrene was measured in the range from 203 to 353 K in three crystallographic directions. Below the anomaly temperature of 72 C, the mobility temperature dependences are consistent with the Munn and Siebrand slow-phonon hopping process in the b direction and the Munn and Siebrand slow-phonon coherent mode in the a and c prime directions. The drift mobility temperature dependences in crystals that have been cooled through the anomaly temperature in the presence of illumination and an electric field are consistent with the model of Spielberg et al. (1971), in which the hindered vibration of the 4,5 hydrogens introduces a new degree of freedom above 72 C.

Multidimensional Separation of Natural Products Using Liquid Chromatography Coupled to Hadamard Transform Ion Mobility Mass Spectrometry

NASA Astrophysics Data System (ADS)

Liu, Wenjie; Zhang, Xing; Knochenmuss, Richard; Siems, William F.; Hill, Herbert H.

2016-05-01

A high performance liquid chromatograph (HPLC)was interfaced to an atmospheric drift tube ion mobility time of flight mass spectrometry. The power of multidimensional separation was demonstrated using chili pepper extracts. The ambient pressure drift tube ion mobility provided high resolving powers up to 166 for the HPLC eluent. With implementation of Hadamard transform (HT), the duty cycle for the ion mobility drift tube was increased from less than 1% to 50%, and the ion transmission efficiency was improved by over 200 times compared with pulsed mode, improving signal to noise ratio 10 times. HT ion mobility and TOF mass spectrometry provide an additional dimension of separation for complex samples without increasing the analysis time compared with conventional HPLC.

Electromagnetic nonlinear gyrokinetics with polarization drift

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

Duthoit, F.-X.; Hahm, T. S., E-mail: tshahm@snu.ac.kr; Wang, Lu

2014-08-15

A set of new nonlinear electromagnetic gyrokinetic Vlasov equation with polarization drift and gyrokinetic Maxwell equations is systematically derived by using the Lie-transform perturbation method in toroidal geometry. For the first time, we recover the drift-kinetic expression for parallel acceleration [R. M. Kulsrud, in Basic Plasma Physics, edited by A. A. Galeev and R. N. Sudan (North-Holland, Amsterdam, 1983)] from the nonlinear gyrokinetic equations, thereby bridging a gap between the two formulations. This formalism should be useful in addressing nonlinear ion Compton scattering of intermediate-mode-number toroidal Alfvén eigenmodes for which the polarization current nonlinearity [T. S. Hahm and L. Chen,more » Phys. Rev. Lett. 74, 266 (1995)] and the usual finite Larmor radius effects should compete.« less

Electromagnetic nonlinear gyrokinetics with polarization drift

NASA Astrophysics Data System (ADS)

Duthoit, F.-X.; Hahm, T. S.; Wang, Lu

2014-08-01

A set of new nonlinear electromagnetic gyrokinetic Vlasov equation with polarization drift and gyrokinetic Maxwell equations is systematically derived by using the Lie-transform perturbation method in toroidal geometry. For the first time, we recover the drift-kinetic expression for parallel acceleration [R. M. Kulsrud, in Basic Plasma Physics, edited by A. A. Galeev and R. N. Sudan (North-Holland, Amsterdam, 1983)] from the nonlinear gyrokinetic equations, thereby bridging a gap between the two formulations. This formalism should be useful in addressing nonlinear ion Compton scattering of intermediate-mode-number toroidal Alfvén eigenmodes for which the polarization current nonlinearity [T. S. Hahm and L. Chen, Phys. Rev. Lett. 74, 266 (1995)] and the usual finite Larmor radius effects should compete.

Numerical simulations of vortex-induced vibrations of a flexible riser with different aspect ratiosin uniform and shear currents

NASA Astrophysics Data System (ADS)

Duanmu, Yu; Zou, Lu; Wan, De-cheng

2017-12-01

This paper aimed at describing numerical simulations of vortex-induced vibrations (VIVs) of a long flexible riser with different length-to-diameter ratio (aspect ratio) in uniform and shear currents. Three aspect ratios were simulated: L/D = 500, 750 and 1 000. The simulation was carried out by the in-house computational fluid dynamics (CFD) solver viv-FOAM-SJTU developed by the authors, which was coupled with the strip method and developed on the OpenFOAM platform. Moreover, the radial basis function (RBF) dynamic grid technique is applied to the viv-FOAM-SJTU solver to simulate the VIV in both in-line (IL) and cross-flow (CF) directions of flexible riser with high aspect ratio. The validation of the benchmark case has been completed. With the same parameters, the aspect ratio shows a significant influence on VIV of a long flexible riser. The increase of aspect ratio exerted a strong effect on the IL equilibrium position of the riser while producing little effect on the curvature of riser. With the aspect ratio rose from 500 to 1 000, the maximum IL mean displacement increased from 3 times the diameter to 8 times the diameter. On the other hand, the vibration mode of the riser would increase with the increase of aspect ratio. When the aspect ratio was 500, the CF vibration was shown as a standing wave with a 3rd order single mode. When the aspect ratio was 1 000, the modal weights of the 5th and 6th modes are high, serving as the dominant modes. The effect of the flow profile on the oscillating mode becomes more and more apparent when the aspect ratio is high, and the dominant mode of riser in shear flow is usually higher than that in uniform flow. When the aspect ratio was 750, the CF oscillations in both uniform flow and shear flow showed multi-mode vibration of the 4th and 5th mode. While, the dominant mode in uniform flow is the 4th order, and the dominant mode in shear flow is the 5th order.

Graphene, a material for high temperature devices – intrinsic carrier density, carrier drift velocity, and lattice energy

PubMed Central

Yin, Yan; Cheng, Zengguang; Wang, Li; Jin, Kuijuan; Wang, Wenzhong

2014-01-01

Heat has always been a killing matter for traditional semiconductor machines. The underlining physical reason is that the intrinsic carrier density of a device made from a traditional semiconductor material increases very fast with a rising temperature. Once reaching a temperature, the density surpasses the chemical doping or gating effect, any p-n junction or transistor made from the semiconductor will fail to function. Here, we measure the intrinsic Fermi level (|EF| = 2.93 kBT) or intrinsic carrier density (nin = 3.87 × 106 cm−2K−2·T2), carrier drift velocity, and G mode phonon energy of graphene devices and their temperature dependencies up to 2400 K. Our results show intrinsic carrier density of graphene is an order of magnitude less sensitive to temperature than those of Si or Ge, and reveal the great potentials of graphene as a material for high temperature devices. We also observe a linear decline of saturation drift velocity with increasing temperature, and identify the temperature coefficients of the intrinsic G mode phonon energy. Above knowledge is vital in understanding the physical phenomena of graphene under high power or high temperature. PMID:25044003

Hard x-ray response of a CdZnTe ring-drift detector

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

Owens, A.; Hartog, R. den; Quarati, F.

We present the results of an experimental study of a special type of CdZnTe detector of hard x and {gamma} rays--A-drift detector. The device consists of a double ring electrode structure surrounding a central point anode with a guard plane surrounding the outer anode ring. The detector can be operated in two distinctively different modes of charge collection--pseudohemispherical and pseudodrift. We study the detector response profiles obtained by scanning the focused x-ray beam over the whole detector area, specifically the variations in count rate, peak position, and energy resolution for x rays from 10 to 100 keV. In addition, atmore » 662 keV the energy resolution was shown to be 4.8 keV, more than a factor of 2 better than for CdZnTe coplanar grid detectors. To interpret the experimental data, we derive an analytical expression for the spatial distribution of the electric field inside the detector and neglecting carrier diffusion, and identify carrier collection patterns for both modes of operation within the drift model approximation. We show that this model provides a good understanding of measured profiles.« less

Bowhead whale localization using asynchronous hydrophones in the Chukchi Sea.

PubMed

Warner, Graham A; Dosso, Stan E; Hannay, David E; Dettmer, Jan

2016-07-01

This paper estimates bowhead whale locations and uncertainties using non-linear Bayesian inversion of their modally-dispersed calls recorded on asynchronous recorders in the Chukchi Sea, Alaska. Bowhead calls were recorded on a cluster of 7 asynchronous ocean-bottom hydrophones that were separated by 0.5-9.2 km. A warping time-frequency analysis is used to extract relative mode arrival times as a function of frequency for nine frequency-modulated whale calls that dispersed in the shallow water environment. Each call was recorded on multiple hydrophones and the mode arrival times are inverted for: the whale location in the horizontal plane, source instantaneous frequency (IF), water sound-speed profile, seabed geoacoustic parameters, relative recorder clock drifts, and residual error standard deviations, all with estimated uncertainties. A simulation study shows that accurate prior environmental knowledge is not required for accurate localization as long as the inversion treats the environment as unknown. Joint inversion of multiple recorded calls is shown to substantially reduce uncertainties in location, source IF, and relative clock drift. Whale location uncertainties are estimated to be 30-160 m and relative clock drift uncertainties are 3-26 ms.

Reynolds stress of localized toroidal modes

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

Zhang, Y.Z.; Mahajan, S.M.

1995-02-01

An investigation of the 2D toroidal eigenmode problem reveals the possibility of a new consistent 2D structure, the dissipative BM-II mode. In contrast to the conventional ballooning mode, the new mode is poloidally localized at {pi}/2 (or -{pi}/2), and possesses significant radial asymmetry. The radial asymmetry, in turn, allows the dissipative BM-II to generate considerably larger Reynolds stress as compared to the standard slab drift type modes. It is also shown that a wide class of localized dissipative toroidal modes are likely to be of the dissipative BM-II nature, suggesting that at the tokamak edge, the fluctuation generated Reynolds stressmore » (a possible source of poloidal flow) can be significant.« less

A uniform doping ultra-thin SOI LDMOS with accumulation-mode extended gate and back-side etching technology

NASA Astrophysics Data System (ADS)

Yan-Hui, Zhang; Jie, Wei; Chao, Yin; Qiao, Tan; Jian-Ping, Liu; Peng-Cheng, Li; Xiao-Rong, Luo

2016-02-01

A uniform doping ultra-thin silicon-on-insulator (SOI) lateral-double-diffused metal-oxide-semiconductor (LDMOS) with low specific on-resistance (Ron,sp) and high breakdown voltage (BV) is proposed and its mechanism is investigated. The proposed LDMOS features an accumulation-mode extended gate (AG) and back-side etching (BE). The extended gate consists of a P- region and two diodes in series. In the on-state with VGD > 0, an electron accumulation layer is formed along the drift region surface under the AG. It provides an ultra-low resistance current path along the whole drift region surface and thus the novel device obtains a low temperature distribution. The Ron,sp is nearly independent of the doping concentration of the drift region. In the off-state, the AG not only modulates the surface electric field distribution and improves the BV, but also brings in a charge compensation effect to further reduce the Ron,sp. Moreover, the BE avoids vertical premature breakdown to obtain high BV and allows a uniform doping in the drift region, which avoids the variable lateral doping (VLD) and the “hot-spot” caused by the VLD. Compared with the VLD SOI LDMOS, the proposed device simultaneously reduces the Ron,sp by 70.2% and increases the BV from 776 V to 818 V. Project supported by the National Natural Science Foundation of China (Grant Nos. 61176069 and 61376079).

Optical vortex knots – one photon at a time

PubMed Central

Tempone-Wiltshire, Sebastien J.; Johnstone, Shaun P.; Helmerson, Kristian

2016-01-01

Feynman described the double slit experiment as “a phenomenon which is impossible, absolutely impossible, to explain in any classical way and which has in it the heart of quantum mechanics”. The double-slit experiment, performed one photon at a time, dramatically demonstrates the particle-wave duality of quantum objects by generating a fringe pattern corresponding to the interference of light (a wave phenomenon) from two slits, even when there is only one photon (a particle) at a time passing through the apparatus. The particle-wave duality of light should also apply to complex three dimensional optical fields formed by multi-path interference, however, this has not been demonstrated. Here we observe particle-wave duality of a three dimensional field by generating a trefoil optical vortex knot – one photon at a time. This result demonstrates a fundamental physical principle, that particle-wave duality implies interference in both space (between spatially distinct modes) and time (through the complex evolution of the superposition of modes), and has implications for topologically entangled single photon states, orbital angular momentum multiplexing and topological quantum computing. PMID:27087642

Ground state, collective mode, phase soliton and vortex in multiband superconductors.

PubMed

Lin, Shi-Zeng

2014-12-10

This article reviews theoretical and experimental work on the novel physics in multiband superconductors. Multiband superconductors are characterized by multiple superconducting energy gaps in different bands with interaction between Cooper pairs in these bands. The discovery of prominent multiband superconductors MgB2 and later iron-based superconductors, has triggered enormous interest in multiband superconductors. The most recently discovered superconductors exhibit multiband features. The multiband superconductors possess novel properties that are not shared with their single-band counterpart. Examples include: the time-reversal symmetry broken state in multiband superconductors with frustrated interband couplings; the collective oscillation of number of Cooper pairs between different bands, known as the Leggett mode; and the phase soliton and fractional vortex, which are the main focus of this review. This review presents a survey of a wide range of theoretical exploratory and experimental investigations of novel physics in multiband superconductors. A vast amount of information derived from these studies is shown to highlight unusual and unique properties of multiband superconductors and to reveal the challenges and opportunities in the research on the multiband superconductivity.

Two-component vector solitons in defocusing Kerr-type media with spatially modulated nonlinearity

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

Zhong, Wei-Ping, E-mail: zhongwp6@126.com; Texas A and M University at Qatar, P.O. Box 23874 Doha; Belić, Milivoj

2014-12-15

We present a class of exact solutions to the coupled (2+1)-dimensional nonlinear Schrödinger equation with spatially modulated nonlinearity and a special external potential, which describe the evolution of two-component vector solitons in defocusing Kerr-type media. We find a robust soliton solution, constructed with the help of Whittaker functions. For specific choices of the topological charge, the radial mode number and the modulation depth, the solitons may exist in various forms, such as the half-moon, necklace-ring, and sawtooth vortex-ring patterns. Our results show that the profile of such solitons can be effectively controlled by the topological charge, the radial mode number,more » and the modulation depth. - Highlights: • Two-component vector soliton clusters in defocusing Kerr-type media are reported. • These soliton clusters are constructed with the help of Whittaker functions. • The half-moon, necklace-ring and vortex-ring patterns are found. • The profile of these solitons can be effectively controlled by three soliton parameters.« less

Vortex-induced vibrations of two cylinders in tandem arrangement in the proximity–wake interference region

PubMed Central

BORAZJANI, IMAN; SOTIROPOULOS, FOTIS

2009-01-01

We investigate numerically vortex-induced vibrations (VIV) of two identical two-dimensional elastically mounted cylinders in tandem in the proximity–wake interference regime at Reynolds number Re = 200 for systems having both one (transverse vibrations) and two (transverse and in-line) degrees of freedom (1-DOF and 2-DOF, respectively). For the 1-DOF system the computed results are in good qualitative agreement with available experiments at higher Reynolds numbers. Similar to these experiments our simulations reveal: (1) larger amplitudes of motion and a wider lock-in region for the tandem arrangement when compared with an isolated cylinder; (2) that at low reduced velocities the vibration amplitude of the front cylinder exceeds that of the rear cylinder; and (3) that above a threshold reduced velocity, large-amplitude VIV are excited for the rear cylinder with amplitudes significantly larger than those of the front cylinder. By analysing the simulated flow patterns we identify the VIV excitation mechanisms that lead to such complex responses and elucidate the near-wake vorticity dynamics and vortex-shedding modes excited in each case. We show that at low reduced velocities vortex shedding provides the initial excitation mechanism, which gives rise to a vertical separation between the two cylinders. When this vertical separation exceeds one cylinder diameter, however, a significant portion of the incoming flow is able to pass through the gap between the two cylinders and the gap-flow mechanism starts to dominate the VIV dynamics. The gap flow is able to periodically force either the top or the bottom shear layer of the front cylinder into the gap region, setting off a series of very complex vortex-to-vortex and vortex-to-cylinder interactions, which induces pressure gradients that result in a large oscillatory force in phase with the vortex shedding and lead to the experimentally observed larger vibration amplitudes. When the vortex shedding is the dominant mechanism the front cylinder vibration amplitude is larger than that of the rear cylinder. The reversing of this trend above a threshold reduced velocity is associated with the onset of the gap flow. The important role of the gap flow is further illustrated via a series of simulations for the 2-DOF system. We show that when the gap-flow mechanism is triggered, the 2-DOF system can develop and sustain large VIV amplitudes comparable to those observed in the corresponding (same reduced velocity) 1-DOF system. For sufficiently high reduced velocities, however, the two cylinders in the 2-DOF system approach each other, thus significantly reducing the size of the gap region. In such cases the gap flow is entirely eliminated, and the two cylinders vibrate together as a single body with vibration amplitudes up to 50% lower than the amplitudes of the corresponding 1-DOF in which the gap flow is active. Three-dimensional simulations are also carried out to examine the adequacy of two-dimensional simulations for describing the dynamic response of the tandem system at Re = 200. It is shown that even though the wake transitions to a weakly three-dimensional state when the gap flow is active, the three-dimensional modes are too weak to affect the dynamic response of the system, which is found to be identical to that obtained from the two-dimensional computations. PMID:19693281

On the stability of the internal kink mode in the banana regime

NASA Astrophysics Data System (ADS)

Fogaccia, G.; Romanelli, F.

1995-01-01

The stability of the internal kink mode is investigated taking into account the kinetic response associated to the trapped thermal ions. Ion-ion collisions and diamagnetic effects in the layer are also considered. A significant stabilizing contribution is obtained, even at low-β values, on the mode, which might be stable, on present experiments, even though predicted unstable according to the Bussac criterion [Bussac et al., Phys. Rev. Lett. 35, 1638 (1975)]. In addition, a trapped-ion instability is found, characterized by mode frequency of the order of the trapped-ion bounce-averaged magnetic drift frequency.

The resonance of twin supersonic jets

NASA Technical Reports Server (NTRS)

Morris, Philip J.

1989-01-01

This paper presents an analytical study of the resonant interaction between twin supersonic jets. An instability wave model is used to describe the large scale coherent structures in the jet mixing layers. A linearized shock cell model is also given for the jets when operating off design. The problem's geometry admits four types of normal modes associated with each azimuthal mode number in the single jet. The stability of these modes is examined for both a vortex sheet model of the jet and a jet flow represented by realistic profiles. The growth rates of each mode number and type are found to vary with jet separation and mixing layer thickness and Strouhal number. Contours of equal pressure level are obtained for each mode. The region close to the symmetry axis is found to have the greatest pressure fluctuation amplitude.

Pressure Oscillations and Structural Vibrations in Space Shuttle RSRM and ETM-3 Motors

NASA Technical Reports Server (NTRS)

Mason, D. R.; Morstadt, R. A.; Cannon, S. M.; Gross, E. G.; Nielsen, D. B.

2004-01-01

The complex interactions between internal motor pressure oscillations resulting from vortex shedding, the motor's internal acoustic modes, and the motor's structural vibration modes were assessed for the Space Shuttle four-segment booster Reusable Solid Rocket Motor and for the five-segment engineering test motor ETM-3. Two approaches were applied 1) a predictive procedure based on numerically solving modal representations of a solid rocket motor s acoustic equations of motion and 2) a computational fluid dynamics two-dimensional axi-symmetric large eddy simulation at discrete motor burn times.

Nonlinear Diamagnetic Stabilization of Double Tearing Modes in Cylindrical MHD Simulations

NASA Astrophysics Data System (ADS)

Abbott, Stephen; Germaschewski, Kai

2014-10-01

Double tearing modes (DTMs) may occur in reversed-shear tokamak configurations if two nearby rational surfaces couple and begin reconnecting. During the DTM's nonlinear evolution it can enter an ``explosive'' growth phase leading to complete reconnection, making it a possible driver for off-axis sawtooth crashes. Motivated by similarities between this behavior and that of the m = 1 kink-tearing mode in conventional tokamaks we investigate diamagnetic drifts as a possible DTM stabilization mechanism. We extend our previous linear studies of an m = 2 , n = 1 DTM in cylindrical geometry to the fully nonlinear regime using the MHD code MRC-3D. A pressure gradient similar to observed ITB profiles is used, together with Hall physics, to introduce ω* effects. We find the diamagnetic drifts can have a stabilizing effect on the nonlinear DTM through a combination of large scale differential rotation and mechanisms local to the reconnection layer. MRC-3D is an extended MHD code based on the libMRC computational framework. It supports nonuniform grids in curvilinear coordinates with parallel implicit and explicit time integration.

Observation of Drifting Icebergs and Sea Ice from Space by TerraSAR-X and TanDEM-X

NASA Astrophysics Data System (ADS)

Won, Joong-Sun

2017-04-01

Detection and monitoring drifting icebergs and sea ice is of interest across wide range of Arctic and Antarctic coastal studies such as security of navigation, climatic impact, geological impact, etc. It is not easy to discriminate drifting ices from stationary ones, and to measure their drifting speeds. There is a potential to use space-borne SAR for this purpose, but it is difficult to precisely measure because the drift velocity is usually very slow. In this study, we investigate two approaches for discriminating drifting ices on the sea from surrounding static ones and for measuring their range velocity. The first method is to utilize the quad-pol TerraSAR-X which adopts dual receive antenna (DRA), and the second one is to examine the potential use of TanDEM-X bistatic along-track interferometry (ATI). To utilize DRA mode quad-pol SAR as ATI, it is necessary to remove the phase difference of scattering centers between transmitted H- and V-pol signals. By assume that the individual scattering center of returned signal does not change for a few inter-pulse periods, it is possible to measure the Doppler frequency induced by motion through measuring slow-time (or azimuth time) Doppler phase derivative of co-pol or cross-pol pairs. Results applied to TerraSAR-X quad-pol data over the Cape Columbia in the Arctic Ocean are to be presented and discussed. It was successful to detect and measure drift sea ice that was flowing away from the antenna with a velocity of about 0.37 m/s (or 1.4 km/h) to 0.67 m/s (or 2.4 km/h) while neighboring ones were static. A more sophisticated approach would be a bistatic ATI which exploits a long along-track baseline for observation of slowly moving ground objects. TanDEM-X bistatic ATI pairs are examined, which were acquired at an Antarctic coast. The ATI interferograms show an innovative capability of TanDEM-X/TerraSAR-X constellation. An along-track baseline of a few hundred meters is superior to a few meter baseline of DRA mode ATI system. However, topographic phase is inevitably mixed with Doppler phase associated with target motion because of a non-zero perpendicular baseline (or effective baseline). Thus it is necessary to separate target motion components from topographic components that are unknown for icebergs. Here we examine characteristics of the topographic phase of drift sea ice in the bistatic ATI interferograms, and discuss a detouring approach to quick detection of drifting icebergs by TanDEM-X bistatic ATI. The results demonstrate that it would be efficient to detect drifting icebergs and sea ice from space by utilizing high resolution SAR systems while the precise measurement of the drifting speeds requires further studies.

Q-switched Nd:YAG optical vortex lasers.

PubMed

Kim, D J; Kim, J W; Clarkson, W A

2013-12-02

Q-switched operation of a high-quality Nd:YAG optical vortex laser with the first order Laguerre-Gaussian mode and well-determined helical wavefronts using a fiber-based pump beam conditioning scheme is reported. A simple two-mirror resonator incorporating an acousto-optic Q-switch was employed, along with an etalon and a Brewster plate to enforce the particular helicity of the output. The laser yielded Q-switched pulses with ~250 μJ pulse energy and ~33 ns pulse duration (FWHM) at a 0.1 kHz repetition rate for 5.1 W of absorbed pump power. The handedness of the helical wavefronts was preserved regardless of the repetition rates. The prospects of further power scaling and improved laser performance are discussed.

Thermo-aerodynamic efficiency of non-circular ducts with vortex enhancement of heat exchange in different types of compact heat exchangers

NASA Astrophysics Data System (ADS)

Vasilev, V. Ya; Nikiforova, S. A.

2018-03-01

Experimental studies of thermo-aerodynamic characteristics of non-circular ducts with discrete turbulators on walls and interrupted channels have confirmed the rational enhancement of convective heat transfer, in which the growth of heat transfer outstrips or equals the growth of aerodynamic losses. Determining the regularities of rational (energy-saving) enhancement of heat transfer and the proposed method for comparing the characteristics of smooth-channel (without enhancement) heat exchangers with effective analogs provide new results, confirming the high efficiency of vortex enhancement of convective heat transfer in non-circular ducts of plate-finned heat exchange surfaces. This allows creating heat exchangers with much smaller mass and volume for operation in energy-saving modes.

Purity of Vector Vortex Beams through a Birefringent Amplifier

NASA Astrophysics Data System (ADS)

Sroor, Hend; Lisa, Nyameko; Naidoo, Darryl; Litvin, Igor; Forbes, Andrew

2018-04-01

Creating high-quality vector vortex (VV) beams is possible with a myriad of techniques at low power, and while a few studies have produced such beams at high power, none have considered the impact of amplification on the vector purity. Here we employ tools to study the amplification of VV beams and, in particular, the purity of such modes. We outline a versatile toolbox for such investigations and demonstrate its use in the general case of VV beams through a birefringent gain medium. Intriguingly, we show that it is possible to enhance the purity of such beams during amplification, paving the way for high-brightness VV beams, a requirement for their use in high-power applications such as optical communication and laser-enabled manufacturing.

Fluids and vortex from constrained fluctuations around C-metric black holes

NASA Astrophysics Data System (ADS)

Hao, Xin; Wu, Bin; Zhao, Liu

2017-08-01

By foliating the four-dimensional C-metric black hole spacetime, we consider a kind of initial-value-like formulation of the vacuum Einstein's equation, the holographic initial data is a double consisting of the induced metric and the Brown-York energy momentum tensor on an arbitrary initial hypersurface. Then by perturbing the initial data that generates the background spacetime, it is shown that, in an appropriate limit, the fluctuation modes are governed by the continuity equation and the compressible Navier-Stokes equation which describe the momentum transport in non-relativistic viscous fluid on a flat Newtonian space. It turns out that the flat space fluid behaves as a pure vortex and the viscosity to entropy ratio is subjected to the black hole acceleration.

Engineering of many-body Majorana states in a topological insulator/s-wave superconductor heterostructure.

PubMed

Hung, Hsiang-Hsuan; Wu, Jiansheng; Sun, Kuei; Chiu, Ching-Kai

2017-06-14

We study a vortex chain in a thin film of a topological insulator with proximity-induced superconductivity-a promising platform to realize Majorana zero modes (MZMs)-by modeling it as a two-leg Majorana ladder. While each pair of MZMs hybridizes through vortex tunneling, we hereby show that MZMs can be stabilized on the ends of the ladder with the presence of tilted external magnetic field and four-Majorana interaction. Furthermore, a fruitful phase diagram is obtained by controlling the direction of magnetic field and the thickness of the sample. We reveal many-body Majorana states and interaction-induced topological phase transitions and also identify trivial-superconducting and commensurate/incommensurate charge-density-wave states in the phase diagram.

Shear flow driven tripolar vortices in a nonuniform electron-ion magnetoplasma with non-Maxwellian electrons

NASA Astrophysics Data System (ADS)

Masood, W.; Mirza, Arshad M.

2014-04-01

A set of nonlinear equations governing the dynamics of finite amplitude drift-ion acoustic-waves is derived for sheared ion flows parallel and perpendicular to the ambient magnetic field in the presence of Cairns and Kappa distributed electrons. It is shown that stationary solution of the nonlinear equations can be represented in the form of a tripolar vortex for specific profiles of the equilibrium sheared flows. The tripolar vortices are, however, observed to form on a scale of the order of ion Larmor radius ρ i which is calculated to be around a Kilometer for the plasma parameters found in the Saturn's E-ring. The relevance of the present investigation in planetary environments is also pointed out.

Dusty waves and vortices in rf magnetron discharge plasma

NASA Astrophysics Data System (ADS)

Filippov, A. V.; Pal, A. F.; Ryabinkin, A. N.; Serov, A. O.; Shugaev, F. V.

2018-01-01

The appearance and subsequent growth of metallic particles in plasma of planar rf magnetron sputter were observed. The origin of the particles is sputtering of the rf electrode by ion flux from the plasma. In some regions of formed dust cloud the particles were involved in the horizontal or vertical circular movement. The horizontal rotation along the sputtered track in the cyclotron drift direction was observed close to the main magnetron plasma. The torus-shaped dust vortex ring engirdled the secondary plasma of the discharge at height of a few centimeters over the electrode. Close to this region particle density waves propagated through the cloud. The possible role of discharge plasma azimuthal inhomogeneity and gas dynamics effects in the forming the observed structures was considered.

Plasma heating, electric fields and plasma flow by electron beam ionospheric injection

NASA Technical Reports Server (NTRS)

Winckler, J. R.; Erickson, K. N.

1990-01-01

The electric fields and the floating potentials of a Plasma Diagnostics Payload (PDP) located near a powerful electron beam injected from a large sounding rocket into the auroral zone ionosphere have been studied. As the PDP drifted away from the beam laterally, it surveyed a region of hot plasma extending nearly to 60 m radius. Large polarization electric fields transverse to B were imbedded in this hot plasma, which displayed large ELF wave variations and also an average pattern which has led to a model of the plasma flow about the negative line potential of the beam resembling a hydrodynamic vortex in a uniform flow field. Most of the present results are derived from the ECHO 6 sounding rocket mission.

Suppression of phase mixing in drift-kinetic plasma turbulence

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

Parker, J. T., E-mail: joseph.parker@stfc.ac.uk; OCIAM, Mathematical Institute, University of Oxford, Andrew Wiles Building, Radcliffe Observatory Quarter, Woodstock Road, Oxford OX2 6GG; Brasenose College, Radcliffe Square, Oxford OX1 4AJ

2016-07-15

Transfer of free energy from large to small velocity-space scales by phase mixing leads to Landau damping in a linear plasma. In a turbulent drift-kinetic plasma, this transfer is statistically nearly canceled by an inverse transfer from small to large velocity-space scales due to “anti-phase-mixing” modes excited by a stochastic form of plasma echo. Fluid moments (density, velocity, and temperature) are thus approximately energetically isolated from the higher moments of the distribution function, so phase mixing is ineffective as a dissipation mechanism when the plasma collisionality is small.

Drift dust acoustic soliton in the presence of field-aligned sheared flow and nonextensivity effects

NASA Astrophysics Data System (ADS)

Shah, AttaUllah; Mushtaq, A.; Farooq, M.; Khan, Aurangzeb; Aman-ur-Rehman

2018-05-01

Low frequency electrostatic dust drift acoustic (DDA) waves are studied in an inhomogeneous dust magnetoplasma comprised of dust components of opposite polarity, Boltzmannian ions, and nonextensive distributed electrons. The magnetic-field-aligned dust sheared flow drives the electrostatic drift waves in the presence of ions and electrons. The sheared flow decreases or increases the frequency of the DDA wave, mostly depending on its polarity. The conditions of instability for this mode, with nonextensivity and dust streaming effects, are discussed. The nonlinear dynamics is then investigated for the DDA wave by deriving the Koeteweg-deVries (KdV) nonlinear equation. The KdV equation yields an electrostatic structure in the form of a DDA soliton. The relevancy of the work to laboratory four component dusty plasmas is illustrated.

Gyrokinetic-water-bag modeling of low-frequency instabilities in a laboratory magnetized plasma column

NASA Astrophysics Data System (ADS)

Gravier, E.; Klein, R.; Morel, P.; Besse, N.; Bertrand, P.

2008-12-01

A new model is presented, named collisional-gyro-water-bag (CGWB), which describes the collisional drift waves and ion-temperature-gradient (ITG) instabilities in a plasma column. This model is based on the kinetic gyro-water-bag approach recently developed [P. Morel et al., Phys. Plasmas 14, 112109 (2007)] to investigate ion-temperature-gradient modes. In CGWB electron-neutral collisions have been introduced and are now taken into account. The model has been validated by comparing CGWB linear analysis with other models previously proposed and experimental results as well. Kinetic effects on collisional drift waves are investigated, resulting in a less effective growth rate, and the transition from collisional drift waves to ITG instability depending on the ion temperature gradient is studied.

Monte Carlo criticality source convergence in a loosely coupled fuel storage system.

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

Blomquist, R. N.; Gelbard, E. M.

2003-06-10

The fission source convergence of a very loosely coupled array of 36 fuel subassemblies with slightly non-symmetric reflection is studied. The fission source converges very slowly from a uniform guess to the fundamental mode in which about 40% of the fissions occur in one corner subassembly. Eigenvalue and fission source estimates are analyzed using a set of statistical tests similar to those used in MCNP, including the ''drift-in-mean'' test and a new drift-in-mean test using a linear fit to the cumulative estimate drift, the Shapiro-Wilk test for normality, the relative error test, and the ''1/N'' test. The normality test doesmore » not detect a drifting eigenvalue or fission source. Applied to eigenvalue estimates, the other tests generally fail to detect an unconverged solution, but they are sometimes effective when evaluating fission source distributions. None of the test provides completely reliable indication of convergence, although they can detect nonconvergence.« less

Magnetic field diffusion and dissipation in reversed-field plasmas

NASA Technical Reports Server (NTRS)

Drake, J. F.; Gladd, N. T.; Huba, J. D.

1981-01-01

A diffusion equation is derived which describes the evolution of a magnetic field in a plasma of arbitrary beta and resistivity. The equation is valid for a one-dimensional slab geometry, assumes the plasma remains in quasi-equilibrium throughout its evolution and does not include thermal transport. Scaling laws governing the rate of change of the magnetic energy, particle drift energy, and magnetic flux are calculated. It is found that the magnetic free energy can be substantially larger than the particle drift energy and can be an important energy reservoir in driving plasma instabilities (e.g., the lower-hybrid-drift instability). In addition, the effect of a spatially varying resistivity on the evolution of a reversed-field plasma is studied. The resistivity model used is based upon the anomalous transport properties associated with the nonlocal mode structure of the lower-hybrid-drift instability. The relevance of this research to laboratory plasmas (e.g., theta pinches, reversed-field theta pinches) and space plasmas (e.g., the earth's magnetotail) is discussed.

Amplifier improvement circuit

NASA Technical Reports Server (NTRS)

Sturman, J.

1968-01-01

Stable input stage was designed for the use with a integrated circuit operational amplifier to provide improved performance as an instrumentation-type amplifier. The circuit provides high input impedance, stable gain, good common mode rejection, very low drift, and low output impedance.

Nonlinear Mode Coupling Theory of the Lower-Hybrid-Drift Instability.

DTIC Science & Technology

1983-11-25

University of lows Iowa City, Iowa 52242 Tenerin, Michael Space Science Lab. University of California Berkeley, California 94720 Vlahos, Loukas Dept. of fysics University of Maryland College Park, Maryland 20742 44 FILMED 1=84 DTIC

Equilibrium energy spectrum of point vortex motion with remarks on ensemble choice and ergodicity

NASA Astrophysics Data System (ADS)

Esler, J. G.

2017-01-01

The dynamics and statistical mechanics of N chaotically evolving point vortices in the doubly periodic domain are revisited. The selection of the correct microcanonical ensemble for the system is first investigated. The numerical results of Weiss and McWilliams [Phys. Fluids A 3, 835 (1991), 10.1063/1.858014], who argued that the point vortex system with N =6 is nonergodic because of an apparent discrepancy between ensemble averages and dynamical time averages, are shown to be due to an incorrect ensemble definition. When the correct microcanonical ensemble is sampled, accounting for the vortex momentum constraint, time averages obtained from direct numerical simulation agree with ensemble averages within the sampling error of each calculation, i.e., there is no numerical evidence for nonergodicity. Further, in the N →∞ limit it is shown that the vortex momentum no longer constrains the long-time dynamics and therefore that the correct microcanonical ensemble for statistical mechanics is that associated with the entire constant energy hypersurface in phase space. Next, a recently developed technique is used to generate an explicit formula for the density of states function for the system, including for arbitrary distributions of vortex circulations. Exact formulas for the equilibrium energy spectrum, and for the probability density function of the energy in each Fourier mode, are then obtained. Results are compared with a series of direct numerical simulations with N =50 and excellent agreement is found, confirming the relevance of the results for interpretation of quantum and classical two-dimensional turbulence.

Suppression of Higher Order Modes in an Array of Cavities Using Waveguides

NASA Astrophysics Data System (ADS)

Shashkov, Ya. V.; Sobenin, N. P.; Bazyl, D. S.; Kaminskiy, V. I.; Mitrofanov, A. A.; Zobov, M. M.

An application of additional harmonic cavities operating at multiplies of the main RF system frequency of 400 MHz is currently under discussionin the framework of the High Luminosity LHC upgrade program [1,2]. A structure consisting of two 800 MHz single cell superconducting cavities with grooved beam pipes coupled by drift tubes has been suggested for implementation. However, it is desirable to increase the number of single cells installed in one cryomodule in order to decrease the number of transitions between "warm" and "cold" parts of the collider vacuum chamber. Unfortunately, it can lead to the appearance of higher order modes (HOM) trapped between the cavities. In order to solve this problem the methods of HOM damping with rectangular waveguides connected to the drift tubes were investigated and compared. We describe the results obtained for arrays of 2, 4 and 8 cavitiesin this paper.

Combined effects of trapped energetic ions and resistive layer damping on the stability of the resistive wall mode

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

He, Yuling; Liu, Yue, E-mail: Yueqiang.Liu@ccfe.ac.uk, E-mail: liuyue@dlut.edu.cn; Liu, Chao

2016-01-15

A dispersion relation is derived for the stability of the resistive wall mode (RWM), which includes both the resistive layer damping physics and the toroidal precession drift resonance damping from energetic ions in tokamak plasmas. The dispersion relation is numerically solved for a model plasma, for the purpose of systematic investigation of the RWM stability in multi-dimensional plasma parameter space including the plasma resistivity, the radial location of the resistive wall, as well as the toroidal flow velocity. It is found that the toroidal favorable average curvature in the resistive layer contributes a significant stabilization of the RWM. This stabilizationmore » is further enhanced by adding the drift kinetic contribution from energetic ions. Furthermore, two traditionally assumed inner layer models are considered and compared in the dispersion relation, resulting in different predictions for the stability of the RWM.« less

Modulated electron cyclotron drift instability in a high-power pulsed magnetron discharge.

PubMed

Tsikata, Sedina; Minea, Tiberiu

2015-05-08

The electron cyclotron drift instability, implicated in electron heating and anomalous transport, is detected in the plasma of a planar magnetron. Electron density fluctuations associated with the mode are identified via an adapted coherent Thomson scattering diagnostic, under direct current and high-power pulsed magnetron operation. Time-resolved analysis of the mode amplitude reveals that the instability, found at MHz frequencies and millimeter scales, also exhibits a kHz-scale modulation consistent with the observation of larger-scale plasma density nonuniformities, such as the rotating spoke. Sharply collimated axial fluctuations observed at the magnetron axis are consistent with the presence of escaping electrons in a region where the magnetic and electric fields are antiparallel. These results distinguish aspects of magnetron physics from other plasma sources of similar geometry, such as the Hall thruster, and broaden the scope of instabilities which may be considered to dictate magnetron plasma features.

Transport and discrete particle noise in gyrokinetic simulations

NASA Astrophysics Data System (ADS)

Jenkins, Thomas; Lee, W. W.

2006-10-01

We present results from our recent investigations regarding the effects of discrete particle noise on the long-time behavior and transport properties of gyrokinetic particle-in-cell simulations. It is found that the amplitude of nonlinearly saturated drift waves is unaffected by discreteness-induced noise in plasmas whose behavior is dominated by a single mode in the saturated state. We further show that the scaling of this noise amplitude with particle count is correctly predicted by the fluctuation-dissipation theorem, even though the drift waves have driven the plasma from thermal equilibrium. As well, we find that the long-term behavior of the saturated system is unaffected by discreteness-induced noise even when multiple modes are included. Additional work utilizing a code with both total-f and δf capabilities is also presented, as part of our efforts to better understand the long- time balance between entropy production, collisional dissipation, and particle/heat flux in gyrokinetic plasmas.

The Rubber Hand Illusion: Feeling of Ownership and Proprioceptive Drift Do Not Go Hand in Hand

PubMed Central

Rohde, Marieke; Di Luca, Massimiliano; Ernst, Marc O.

2011-01-01

In the Rubber Hand Illusion, the feeling of ownership of a rubber hand displaced from a participant's real occluded hand is evoked by synchronously stroking both hands with paintbrushes. A change of perceived finger location towards the rubber hand (proprioceptive drift) has been reported to correlate with this illusion. To measure the time course of proprioceptive drift during the Rubber Hand Illusion, we regularly interrupted stroking (performed by robot arms) to measure perceived finger location. Measurements were made by projecting a probe dot into the field of view (using a semi-transparent mirror) and asking participants if the dot is to the left or to the right of their invisible hand (Experiment 1) or to adjust the position of the dot to that of their invisible hand (Experiment 2). We varied both the measurement frequency (every 10 s, 40 s, 120 s) and the mode of stroking (synchronous, asynchronous, just vision). Surprisingly, with frequent measurements, proprioceptive drift occurs not only in the synchronous stroking condition but also in the two control conditions (asynchronous stroking, just vision). Proprioceptive drift in the synchronous stroking condition is never higher than in the just vision condition. Only continuous exposure to asynchronous stroking prevents proprioceptive drift and thus replicates the differences in drift reported in the literature. By contrast, complementary subjective ratings (questionnaire) show that the feeling of ownership requires synchronous stroking and is not present in the asynchronous stroking condition. Thus, subjective ratings and drift are dissociated. We conclude that different mechanisms of multisensory integration are responsible for proprioceptive drift and the feeling of ownership. Proprioceptive drift relies on visuoproprioceptive integration alone, a process that is inhibited by asynchronous stroking, the most common control condition in Rubber Hand Illusion experiments. This dissociation implies that conclusions about feelings of ownership cannot be drawn from measuring proprioceptive drift alone. PMID:21738756

Explosive magnetic reconnection caused by an X-shaped current-vortex layer in a collisionless plasma

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

Hirota, M.; Hattori, Y.; Morrison, P. J.

2015-05-15

A mechanism for explosive magnetic reconnection is investigated by analyzing the nonlinear evolution of a collisionless tearing mode in a two-fluid model that includes the effects of electron inertia and temperature. These effects cooperatively enable a fast reconnection by forming an X-shaped current-vortex layer centered at the reconnection point. A high-resolution simulation of this model for an unprecedentedly small electron skin depth d{sub e} and ion-sound gyroradius ρ{sub s}, satisfying d{sub e}=ρ{sub s}, shows an explosive tendency for nonlinear growth of the tearing mode, where it is newly found that the explosive widening of the X-shaped layer occurs locally aroundmore » the reconnection point with the length of the X shape being shorter than the domain length and the wavelength of the linear tearing mode. The reason for the onset of this locally enhanced reconnection is explained theoretically by developing a novel nonlinear and nonequilibrium inner solution that models the local X-shaped layer, and then matching it to an outer solution that is approximated by a linear tearing eigenmode with a shorter wavelength than the domain length. This theoretical model proves that the local reconnection can release the magnetic energy more efficiently than the global one and the estimated scaling of the explosive growth rate agrees well with the simulation results.« less

Computational Analysis of Intra-Ventricular Flow Pattern Under Partial and Full Support of BJUT-II VAD.

PubMed

Zhang, Qi; Gao, Bin; Chang, Yu

2017-02-27

BACKGROUND Partial support, as a novel support mode, has been widely applied in clinical practice and widely studied. However, the precise mechanism of partial support of LVAD in the intra-ventricular flow pattern is unclear. MATERIAL AND METHODS In this study, a patient-specific left ventricular geometric model was reconstructed based on CT data. The intra-ventricular flow pattern under 3 simulated conditions - "heart failure", "partial support", and "full support" - were simulated by using fluid-structure interaction (FSI). The blood flow pattern, wall shear stress (WSS), time-average wall shear stress (TAWSS), oscillatory shear index (OSI), and relative residence time (RRT) were calculated to evaluate the hemodynamic effects. RESULTS The results demonstrate that the intra-ventricular flow pattern is significantly changed by the support level of BJUT-II VAD. The intra-ventricular vortex was enhanced under partial support and was eliminated under full support, and the high OSI and RRT regions changed from the septum wall to the cardiac apex. CONCLUSIONS In brief, the support level of the BJUT-II VAD has significant effects on the intra-ventricular flow pattern. The partial support mode of BJUT-II VAD can enhance the intra-ventricular vortex, while the distribution of high OSI and RRT moved from the septum wall to the cardiac apex. Hence, the partial support mode of BJUT-II VAD can provide more benefit for intra-ventricular flow pattern.

Invited Article: Generation of one-million-mode continuous-variable cluster state by unlimited time-domain multiplexing

NASA Astrophysics Data System (ADS)

Yoshikawa, Jun-ichi; Yokoyama, Shota; Kaji, Toshiyuki; Sornphiphatphong, Chanond; Shiozawa, Yu; Makino, Kenzo; Furusawa, Akira

2016-09-01

In recent quantum optical continuous-variable experiments, the number of fully inseparable light modes has drastically increased by introducing a multiplexing scheme either in the time domain or in the frequency domain. Here, modifying the time-domain multiplexing experiment reported in the work of Yokoyama et al. [Nat. Photonics 7, 982 (2013)], we demonstrate the successive generation of fully inseparable light modes for more than one million modes. The resulting multi-mode state is useful as a dual-rail continuous variable cluster state. We circumvent the previous problem of optical phase drifts, which has limited the number of fully inseparable light modes to around ten thousands, by continuous feedback control of the optical system.

Instability of rectangular jets

NASA Technical Reports Server (NTRS)

Tam, Christopher K. W.; Thies, Andrew T.

1993-01-01

The instability of rectangular jets is investigated using a vortex-sheet model. It is shown that such jets support four linearly independent families of instability waves. Within each family there are infinitely many modes. A way to classify these modes according to the characteristics of their mode shapes or eigenfunctions is proposed. It is demonstrated that the boundary element method can be used to calculate the dispersion relations and eigenfunctions of these instability wave modes. The method is robust and efficient. A parametric study of the instability wave characteristics has been carried out. A sample of the numerical results is reported here. It is found that the first and third modes of each instability wave family are corner modes. The pressure fluctuations associated with these instability waves are localized near the corners of the jet. The second mode, however, is a center mode with maximum fluctuations concentrated in the central portion of the jet flow. The center mode has the largest spatial growth rate. It is anticipated that as the instability waves propagate downstream the center mode would emerge as the dominant instability of the jet.

Hydrological and dynamical characterization of Meddies in the Azores region: A paradigm for baroclinic vortex dynamics

NASA Astrophysics Data System (ADS)

Tychensky, A.; Carton, X.

1998-10-01

The Structure des Echanges Mer-Atmosphere, Proprietes des Heterogeneites Oceaniques: Recherche Expérimentale (SEMAPHORE) oceanographic experiment surveyed a 500 × 500 km2 domain south of the Azores from June to November 1993 and collected hydrological data, float trajectories, and current meter recordings. This data exhibited three intrathermocline eddies of Mediterranean water (Meddies), two of them being repeatedly sampled. Their hydrological and dynamical properties are quantified here by an isopycnic analysis. For the three Meddies, intense temperature and salinity anomalies (up to 4°C and 1.1 practical salinity units (psu)) are observed extending vertically over up to 1000 m and centered around 1000 m. Horizontally, these anomalies spread out to radii of 50-60 km, while the maximum azimuthal velocities (30 cm s-1, as computed by geostrophy) lie only at 35-40 km from the central axis. These Meddies followed curved trajectories, with drift velocities up to 7.5 cm s-1, under the influence of the neighboring mesoscale features (cyclonic vortices or Azores Current meanders). The three-dimensional structure of potential vorticity in and around these features evidences their complex interactions. Northwest of the domain, a Meddy was coupled to a subsurface anticyclone, forming an "aligned" vortex. It later interacted with the Azores Current, creating a large-amplitude northward meander by vertical alignment of vorticity. In the southeastern part of the domain, another Meddy was vertically aligned with an anticyclonic meander of the Azores Current and horizontally coupled with a cyclone of large vertical extent. These two features, as well as a small warm and salty fragment in their vicinity, seem to result from the southward crossing of the Meddy under the Azores Current. These observations illustrate previous theoretical studies of baroclinic vortex dynamics.

A numerical study of three-dimensional vortex breakdown

NASA Technical Reports Server (NTRS)

Spall, Robert E.; Ash, Robert L.

1987-01-01

A numerical simulation of bubble-type vortex breakdown using a unique discrete form of the full 3-D, unsteady incompressible Navier-Stokes equations was performed. The Navier-Stokes equations were written in a vorticity-velocity form and the physical problem was not restricted to axisymmetric flow. The problem was parametized on a Rossby- Reynolds-number basis. Utilization of this parameter duo was shown to dictate the form of the free-field boundary condition specification and allowed control of axial breakdown location within the computational domain. The structure of the breakdown bubble was studied through time evolution plots of planar projected velocity vectors as well as through plots of particle traces and vortex lines. These results compared favorably with previous experimental studies. In addition, profiles of all three velocity components are presented at various axial stations and a Fourier analysis was performed to identify the dominant circumferential modes. The dynamics of the breakdown process were studied through plots of axial variation of rate of change of integrated total energy and rate of change of integrated enstrophy, as well as through contour plots of velocity, vorticity and pressure.

Evolution of the Orszag-Tang vortex system in a compressible medium. II - Supersonic flow

NASA Technical Reports Server (NTRS)

Picone, J. Michael; Dahlburg, Russell B.

1991-01-01

A study is presented on the effect of embedded supersonic flows and the resulting emerging shock waves on phenomena associated with MHD turbulence, including reconnection, the formation of current sheets and vortex structures, and the evolution of spatial and temporal correlations among physical variables. A two-dimensional model problem, the Orszag-Tang (1979) vortex system, is chosen, which involves decay from nonrandom initial conditions. The system is doubly periodic, and the initial conditions consist of single-mode solenoidal velocity and magnetic fields, each containing X points and O points. The initial mass density is flat, and the initial pressure fluctuations are incompressible, balancing the local forces for a magnetofluid of unit mass density. Results on the evolution of the local structure of the flow field, the global properties of the system, and spectral correlations are presented. The important dynamical properties and observational consequences of embedded supersonic regions and emerging shocks in the Orszag-Tang model of an MHD system undergoing reconnection are discussed. Conclusions are drawn regarding the effects of local supersonic regions on MHD turbulence.

Modulation of the Polar Vortex by Energetic Particle Precipitation and Quasi-Biennial Oscillation via Ozone Loss

NASA Astrophysics Data System (ADS)

Asikainen, T.; Salminen, A.; Maliniemi, V.; Mursula, K.

2017-12-01

Energetic particle precipitation (EPP) has been shown to cause ozone loss in the stratosphere during polar winter. This has been suggested to enhance polar vortex with the effect propagating even to ground level, where it is observed as a more positive phase of the Northern Annular Mode (NAM), the dominant ground circulation pattern in the winter time at high latitudes. Recent research has also shown that the quasi-biennial oscillation (QBO) modulates the relationship between the ground NAM and EPP so that the positive correlation between the two is more clearly seen in the easterly phase of QBO measured at 30 hPa height especially during the late winter season. Here we elaborate the QBO modulated connection between EPP and NAM by studying how the EPP affects the stratospheric polar vortex in the two phases of the QBO. Since the EPP presumably affects the polar stratosphere via indirect ozone loss we will study how the EPP modulates the amount of ozone, the stratospheric temperatures and zonal winds in the two QBO phases.

Separated Flow Control with Actuated Membrane Wings

NASA Astrophysics Data System (ADS)

Bohnker, Jillian; Breuer, Kenneth

2017-11-01

By perturbing shear layer instabilities, some level of control over highly separated flows can be established, as has been demonstrated on rigid wings using synthetic jet actuators or acoustic excitation. Here, we demonstrate similar phenomena using sinusoidal actuation of a dielectric membrane wing. The effect of actuation on lift is examined as a function of freestream velocity (5-25 m/s), angle of attack (10°-40°), and actuation frequency (0.1

Vortex creep and the internal temperature of neutron stars - Linear and nonlinear response to a glitch

NASA Technical Reports Server (NTRS)

Alpar, M. A.; Cheng, K. S.; Pines, D.

1989-01-01

The dynamics of pinned superfluid in neutron stars is determined by the thermal 'creep' of vortices. Vortex creep can respond to changes in the rotation rate of the neutron star crust and provide the observed types of dynamical relaxation following pulsar glitches. It also gives rise to energy dissipation, which determines the thermal evolution of pulsars once the initial heat content has been radiated away. The different possible regimes of vortex creep are explored, and it is shown that the nature of the dynamical response of the pinned superfluid evolves with a pulsar's age. Younger pulsars display a linear regime, where the response is linear in the initial perturbation and is a simple exponential relaxation as a function of time. A nonliner response, with a characteristic nonlinear dependence on the initial perturbation, is responsible for energy dissipation and becomes the predominant mode of response as the pulsar ages. The transition from the linear to the nonlinear regime depends sensitively on the temperature of the neutron star interior. A preliminary review of existing postglitch observations is given within this general evolutionary framework.

Modulation of the polar vortex by energetic particle precipitation and Quasi-Biennial Oscillation via ozone loss

NASA Astrophysics Data System (ADS)

Salminen, Antti; Asikainen, Timo; Maliniemi, Ville; Mursula, Kalevi

2017-04-01

Energetic particle precipitation (EPP) has been shown to cause ozone loss in the stratosphere during polar winter. This has been suggested to enhance polar vortex with the effect propagating even to ground level, where it is observed as a more positive phase of the Northern Annular Mode (NAM), the dominant ground circulation pattern in the winter time at high latitudes. Recent research has also shown that the quasi-biennial oscillation (QBO) modulates the relationship between the ground NAM and EPP so that the positive correlation between the two is more clearly seen in the easterly phase of QBO measured at 30 hPa height especially during the late winter season. Here we elaborate the QBO modulated connection between EPP and NAM by studying how the EPP affects the stratospheric polar vortex in the two phases of the QBO. Since the EPP presumably affects the polar stratosphere via indirect ozone loss we will study how the EPP modulates the amount of ozone, the stratospheric temperatures and zonal winds in the two QBO phases.

Swirl ratio effects on tornado-like vortices

NASA Astrophysics Data System (ADS)

Hashemi-Tari, Pooyan; Gurka, Roi; Hangen, Horia

2007-11-01

The effect of swirl ratio on the flow field for a tornado-like vortex simulator (TVS) is investigated. Different swirl ratios are obtained by changing the geometry and tangential velocity which determine the vortex evolution. Flow visualizations, surface pressure and Particle Image Velocimetry (PIV) measurements are performed in a small TVS for swirl ratios S between 0 and 1. The PIV data was acquired for two orthogonal planes: normal and parallel to the solid boundary at several height locations. The ratio between the angular momentum and the radial momentum which characterize the swirl ratio is investigated. Statistical analysis to the turbulent field is performed by mean and rms profiles of the velocity, stresses and vorticity are presented. A Proper Orthogonal Decomposition (POD) is performed on the vorticity field. The results are used to: (i) provide a relation between these 3 sets of qualitative and quantitative measurements and the swirl ratio in an attempt to relate the fluid dynamics parameters to the forensic, Fujita scale, and (ii) understand the spatio-temporal distribution of the most energetic POD modes in a tornado-like vortex.

Control of 3-D Modes in a Boundary Layer Undergoing Subharmonic Transition.

NASA Astrophysics Data System (ADS)

Corke, T. C.; Peto, J.; Speer, A.; Paroozan, P.; Sciammarella, C.

1997-11-01

The effect of alternating standing patterns of wall displacements in the transition region of a Falkner-Skan boundary layer with an adverse pressure gradient is investigated. Transition is controlled by introducing disturbances to excite a pair of oblique modes along with a plane TS mode. The oblique modes are at the TS subharmonic frequency in order to promote subharmonic resonance. Measurements consist of a spanwise rake of hot-wire sensors placed near the wall below the critical layer, and a 2-D (15 x 15) array of optical pressure sensors. The space-time data series are processed using 2-D Fourier analysis to determine the spanwise wave number content of the flow. Of particular interest is the streamwise vortex mode which results from a difference interaction of the subharmonic oblique modes. We examine the effect of different patterns and amplitudes of upstream wall displacements on the development of the travelling and stationary modes in this case leading to transition. Supported by ARO Grant No. DAAH04-93-G-0212

Fluid transport by dipolar vortices

NASA Astrophysics Data System (ADS)

I, Eames; J.-B, Flór

1998-08-01

The transport properties of dipolar vortices propagating on an f-plane are studied experimentally by examining the distortion of a series of material surfaces. The observations are compared with a model based on characterising the flow around the dipole as irrotational flow past a rigid cylinder of volume V. Measurements made of the volume of fluid permanently displaced forward by the vortices, agree to within 20% of that predicted by the proposition of Darwin [Darwin, C., 1953. A note on hydrodynamics. Proc. Cambridge Philos. Soc., 49, 342-354], namely that the vortex will displace a volume CMV forward, where CM=1 for a Lamb's dipole. The results are applied to examine fluid transport by dipolar vortices propagating on the β-plane, where the ambient potential vorticity field causes easterly propagating dipolar vortices to meander sinusoidally between the North and South. We demonstrate that as the vortex moves between the North and South, it exchanges a volume CMV sin α by the drift effect (where α is the angle between the velocity of the dipole and the material surface), which is generally larger than that attributed to other mechanisms such as lobe shedding. The results are applied to give new insight to the effect of vortices in enhancing diffusion, and the secondary flow generated by the transport of ambient potential vorticity.

Application of CCD drift-scan photoelectric technique on monitoring GEO satellites

NASA Astrophysics Data System (ADS)

Yu, Yong; Zhao, Xiao-Fen; Luo, Hao; Mao, Yin-Dun; Tang, Zheng-Hong

2018-05-01

Geosynchronous Earth Orbit (GEO) satellites are widely used because of their unique characteristics of high-orbit and remaining permanently in the same area of the sky. Precise monitoring of GEO satellites can provide a key reference for the judgment of satellite operation status, the capture and identification of targets, and the analysis of collision warning. The observation using ground-based optical telescopes plays an important role in the field of monitoring GEO targets. Different from distant celestial bodies, there is a relative movement between the GEO target and the background reference stars, which makes the conventional observation method limited for long focal length telescopes. CCD drift-scan photoelectric technique is applied on monitoring GEO targets. In the case of parking the telescope, the good round images of the background reference stars and the GEO target at the same sky region can be obtained through the alternating observation of CCD drift-scan mode and CCD stare mode, so as to improve the precision of celestial positioning for the GEO target. Observation experiments of GEO targets were carried out with 1.56-meter telescope of Shanghai Astronomical Observatory. The results show that the application of CCD drift-scan photoelectric technique makes the precision of observing the GEO target reach the level of 0.2″, which gives full play to the advantage of the long focal length of the telescope. The effect of orbit improvement based on multi-pass of observations is obvious and the prediction precision of extrapolating to 72-h is in the order of several arc seconds in azimuth and elevation.

L-H transitions driven by ion heating in scrape-off layer turbulence (SOLT) model simulations

NASA Astrophysics Data System (ADS)

Russell, D. A.; D'Ippolito, D. A.; Myra, J. R.

2015-11-01

The original SOLT model now includes the evolution of ion pressure consistent with drift-ordering. It is a two-dimensional, electrostatic reduced model wherein closure relations, obtained by integrating the equations along the B-field, model parallel physics that includes sheath-mediated current and heat flux in the scrape-off-layer and electron drift waves inside the separatrix. Low (L) and high (H) confinement regimes are observed in SOLT simulations, depending on the strength of an ion pressure (i.e., ion heating) source localized inside the separatrix: With increasing heating, particle and energy confinement times at first decrease in the L-mode then rise in the H-mode. The L-H transition is marked by distinct changes in sheared-flow profiles. The addition of ion pressure dynamics enables modeling the self-consistent interaction between the ion diamagnetic drift and the radial electric field (mean and zonal flows). The roles of these sheared flows in mediating the L-H transition are explored. A new diagnostic, based on the density correlation function, is applied to study blob velocities in different regimes. Work supported by the U.S. Department of Energy Office of Science, Office of Fusion Energy Sciences, under Award Number DE-FG02-97ER54392.

Pitch Angle Dependence of Drift Resonant Ions Observed by the Van Allen Probes

NASA Astrophysics Data System (ADS)

Rankin, R.; Wang, C.; Wang, Y.; Zong, Q. G.; Zhou, X.

2017-12-01

Acceleration and modulation of ring current ions by poloidal mode ULF waves is investigated. A simplified MHD model of ULF waves in a dipole magnetic field is presented that includes phase mixing to perpendicular scales determined by the ionospheric Pedersen conductivity. The wave model is combined with a full Lorentz force test particle code to study drift and drift bounce resonance wave-particle interactions. Ion trajectories are traced backward-in-time to an assumed form of the distribution function, and Liouville's method is used to reconstruct the phase space density response (PSD) poloidal mode waves observed by the Van Allen Probes. In spite of its apparent simplicity, simulations using the wave and test particle models are able to explain the acceleration of ions and energy dispersion observed by the Van Allen Probes. The paper focuses on the pitch angle evolution of the initial PSD as it responds to the action of ULF waves. An interesting aspect of the study is the formation of butterfly ion distributions as ions make periodic radial oscillations across L. Ions become trapped in an effective potential well across a limited range of L and follow trajectories that cause them to surf along constant phase fronts. The impications of this new trapping mechanism for both ions and electrons is discussed.

Combined effects of drift waves and neoclassical transport on density profiles in tokamaks

NASA Astrophysics Data System (ADS)

Houlberg, W. A.; Strand, P.

2005-10-01

The relative importance of neoclassical and anomalous particle transport depends on the charge number of the species being studied. The detailed particle balance including the EDWM [1] drift wave model for anomalous transport that includes ITG, TEM and in some cases ETG modes, and the neoclassical model NCLASS [2], are illustrated by simulations with the DEA particle transport code. DEA models the evolution of all ion species, and can be run in a mode to evaluate dynamic responses to perturbations or to conditions far from equilibrium by perturbing the profiles from the experimental measurements. The perturbations allow the fluxes to be decomposed into diffusive and convective (pinch) terms. The different scaling with charge number between drift wave and neoclassical models favors a stronger component of neoclassical transport for higher Z impurities through the effective pinch term. Although trace impurities illustrate a simple Ficks Law form, the main ions as well as higher concentrations of intrinsic impurities exhibit non-linear responses to the density gradients as well as off-diagonal gradient dependencies, leading to a more complicated response for the particle fluxes.[1] H. Nordman, et al., Plasma Phys. Control. Fusion 47 (2005) L11. [2] W.A. Houlberg, et al., Phys. Plasmas 4 (1997) 3230.

A low-drift, low-noise, multichannel dc voltage source for segmented-electrode Paul traps

NASA Astrophysics Data System (ADS)

Beev, Nikolai; Fenske, Julia-Aileen; Hannig, Stephan; Schmidt, Piet O.

2017-05-01

We present the design, construction, and characterization of a multichannel, low-drift, low-noise dc voltage source specially designed for biasing the electrodes of segmented linear Paul traps. The system produces 20 output voltage pairs having a common-mode range of 0 to +120 V with 3.7 mV/LSB (least significant bit) resolution and differential ranges of ±5 V with 150 μV/LSB or ±16 V with 610 μV/LSB resolution. All common-mode and differential voltages are independently controllable, and all pairs share the same ground reference. The measured drift of the voltages after warm-up is lower than 1 LSB peak-to-peak on the time scale of 2 h. The noise of an output voltage measured with respect to ground is <10 μVRMS within 10 Hz-100 kHz, with spectral density lower than 3 nV Hz-1/2 above 50 kHz. The performance of the system is limited by the external commercial multichannel DAC unit NI 9264, and in principle, it is possible to achieve higher stability and lower noise with the same voltage ranges. The system has a compact, modular, and scalable architecture, having all parts except for the DAC chassis housed within a single 19″ 3HE rack.

An H-band Vector Vortex Coronagraph for the Subaru Coronagraphic Extreme-adaptive Optics System

NASA Astrophysics Data System (ADS)

Kühn, J.; Serabyn, E.; Lozi, J.; Jovanovic, N.; Currie, T.; Guyon, O.; Kudo, T.; Martinache, F.; Liewer, K.; Singh, G.; Tamura, M.; Mawet, D.; Hagelberg, J.; Defrere, D.

2018-03-01

The vector vortex is a coronagraphic imaging mode of the recently commissioned Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) platform on the 8 m Subaru Telescope. This multi-purpose high-contrast visible and near-infrared (R- to K-band) instrument is not only intended to serve as a VLT-class “planet-imager” instrument in the northern hemisphere, but also to operate as a technology demonstration testbed ahead of the ELTs-era, with a particular emphasis on small inner-working angle (IWA) coronagraphic capabilities. The given priority to small-IWA imaging led to the early design choice to incorporate focal-plane phase-mask coronagraphs. In this context, a test H-band vector vortex liquid crystal polymer waveplate was provided to SCExAO, to allow a one-to-one comparison of different small-IWA techniques on the same telescope instrument, before considering further steps. Here we present a detailed overview of the vector vortex coronagraph, from its installation and performances on the SCExAO optical bench, to the on-sky results in the extreme AO regime, as of late 2016/early 2017. To this purpose, we also provide a few recent on-sky imaging examples, notably high-contrast ADI detection of the planetary-mass companion κ Andromedae b, with a signal-to-noise ratio above 100 reached in less than 10 mn exposure time.

Simulation of density fluctuations before the L-H transition for Hydrogen and Deuterium plasmas in the DIII-D tokamak using the BOUT++ code

NASA Astrophysics Data System (ADS)

Wang, Y. M.; Xu, X. Q.; Yan, Z.; Mckee, G. R.; Grierson, B. A.; Xia, T. Y.; Gao, X.

2018-02-01

A six-field two-fluid model has been used to simulate density fluctuations. The equilibrium is generated by experimental measurements for both Deuterium (D) and Hydrogen (H) plasmas at the lowest densities of DIII-D low to high confinement (L-H) transition experiments. In linear simulations, the unstable modes are found to be resistive ballooning modes with the most unstable mode number n  =  30 or k_θρ_i˜0.12 . The ion diamagnetic drift and E× B convection flow are balanced when the radial electric field (E r ) is calculated from the pressure profile without net flow. The curvature drift plays an important role in this stage. Two poloidally counter propagating modes are found in the nonlinear simulation of the D plasma at electron density n_e˜1.5×1019 m-3 near the separatrix while a single ion mode is found in the H plasma at the similar lower density, which are consistent with the experimental results measured by the beam emission spectroscopy (BES) diagnostic on the DIII-D tokamak. The frequency of the electron modes and the ion modes are about 40 kHz and 10 kHz respectively. The poloidal wave number k_θ is about 0.2 cm -1 (k_θρ_i˜0.05 ) for both ion and electron modes. The particle flux, ion and electron heat fluxes are  ˜3.5-6 times larger for the H plasma than the D plasma, which makes it harder to achieve H-mode for the same heating power. The change of the atomic mass number A from 2 to 1 using D plasma equilibrium make little difference on the flux. Increase the electric field will suppress the density fluctuation. The electric field scan and ion mass scan results show that the dual-mode results primarily from differences in the profiles rather than the ion mass.

Reduction of timing fluctuations in a mode-locked Nd:YAG laser by electronic feedback

NASA Astrophysics Data System (ADS)

Rodwell, M. J. W.; Weingarten, K. J.; Bloom, D. M.; Baer, T.; Kolner, B. H.

1986-10-01

The timing fluctuations of a mode-locked Nd:YAG laser are reduced by electronic feedback. Timing fluctuations at rates of 50 to 250 Hz are reduced by more than 20 dB, the total timing fluctuations are reduced from 2.9 to 0.9 psec rms, and long-term drift is reduced to 0.5 psec/min. Applications include time-resolved probing experiments and synchronization of lasers.

Long-wave instabilities of two interlaced helical vortices

NASA Astrophysics Data System (ADS)

Quaranta, H. U.; Brynjell-Rahkola, M.; Leweke, T.; Henningson, D. S.

2016-09-01

We present a comparison between experimental observations and theoretical predictions concerning long-wave displacement instabilities of the helical vortices in the wake of a two-bladed rotor. Experiments are performed with a small-scale rotor in a water channel, using a set-up that allows the individual triggering of various instability modes at different azimuthal wave numbers, leading to local or global pairing of successive vortex loops. The initial development of the instability and the measured growth rates are in good agreement with the predictions from linear stability theory, based on an approach where the helical vortex system is represented by filaments. At later times, local pairing develops into large-scale distortions of the vortices, whereas for global pairing the non-linear evolution returns the system almost to its initial geometry.

Mechanism of instabilities in turbulent combustion leading to flashback

NASA Astrophysics Data System (ADS)

Keller, J. O.; Vaneveld, L.; Ghoniem, A. F.; Daily, J. W.; Oppenheim, A. K.; Korschelt, D.; Hubbard, G. L.

1981-01-01

High-speed schlieren cinematography, combined with synchronized pressure transducer records, was used to investigate the mechanism of combustion instabilities leading to flashback. The combustion chamber had an oblong rectangular cross-section to model the essential features of planar flow, and was provided with a rearward facing step acting as a flameholder. As the rich limit was approached, three instability modes were observed: (1) humming - a significant increase in the amplitude of the vortex pattern; (2) buzzing - a large-scale oscillation of the flame; and (3) chucking - a cyclic reformation of the flame, which results in flashback. The mechanism of these phenomena is ascribed to the action of vortices in the recirculation zone and their interactions with the trailing vortex pattern of the turbulent mixing layer behind the step.

Analysis of helicopter blade vortex structure by laser velocimetry

NASA Astrophysics Data System (ADS)

Boutier, A.; Lefèvre, J.; Micheli, F.

1996-05-01

In descent flight, helicopter external noise is mainly generated by the Blade Vortex Interaction (BVI). To under-stand the dynamics of this phenomenon, the vortex must be characterized before its interaction with the blade, which means that its viscous core radius, its strength and its distance to the blade have to be determined by non-intrusive measurement techniques. As part of the HART program (Higher Harmonic Control Aeroacoustic Rotor Test, jointly conducted by US Army, NASA, DLR, DNW and ONERA), a series of tests have been made in the German Dutch Wind Tunnel (DNW) on a helicopter rotor with 2 m long blades, rotating at 1040 rpm; several flight configurations, with an advance ratio of 0.15 and a shaft angle of 5.3°, have been studied with different higher harmonic blade pitch angles superposed on the conventional one (corresponding to the baseline case). The flow on the retreating side has been analyzed with an especially designed 3D laser velocimeter, and, simultaneously, the blade tip attitude has been determined in order to get the blade-vortex miss distance, which is a crucial parameter in the noise reduction. A 3D laser velocimeter, in backscatter mode with a working distance of 5 m, was installed on a platform 9 m high, and flow seeding with submicron incense smoke was achieved in the settling chamber using a remotely controlled displacement device. Acquisition of instantaneous velocity vectors by an IFA 750 yielded mean velocity and turbulence maps across the vortex as well as the vortex position, intensity and viscous radius. The blade tip attitude (altitude, jitter, angle of incidence) was recorded by the TART method (Target Attitude in Real Time) which makes use of a CCD camera on which is formed the image of two retroreflecting targets attached to the blade tip and lighted by a flash lamp. In addition to the mean values of the aforementioned quantities, spectra of their fluctuations have been established up to 8 Hz.

Data Assimilation Cycling for Weather Analysis

NASA Technical Reports Server (NTRS)

Tran, Nam; Li, Yongzuo; Fitzpatrick, Patrick

2008-01-01

This software package runs the atmospheric model MM5 in data assimilation cycling mode to produce an optimized weather analysis, including the ability to insert or adjust a hurricane vortex. The program runs MM5 through a cycle of short forecasts every three hours where the vortex is adjusted to match the observed hurricane location and storm intensity. This technique adjusts the surrounding environment so that the proper steering current and environmental shear are achieved. MM5cycle uses a Cressman analysis to blend observation into model fields to get a more accurate weather analysis. Quality control of observations is also done in every cycle to remove bad data that may contaminate the analysis. This technique can assimilate and propagate data in time from intermittent and infrequent observations while maintaining the atmospheric field in a dynamically balanced state. The software consists of a C-shell script (MM5cycle.driver) and three FORTRAN programs (splitMM5files.F, comRegrid.F, and insert_vortex.F), and are contained in the pre-processor component of MM5 called "Regridder." The model is first initialized with data from a global model such as the Global Forecast System (GFS), which also provides lateral boundary conditions. These data are separated into single-time files using splitMM5.F. The hurricane vortex is then bogussed in the correct location and with the correct wind field using insert_vortex.F. The modified initial and boundary conditions are then recombined into the model fields using comRegrid.F. The model then makes a three-hour forecast. The three-hour forecast data from MM5 now become the analysis for the next short forecast run, where the vortex will again be adjusted. The process repeats itself until the desired time of analysis is achieved. This code can also assimilate observations if desired.

Coherent motion in excited free shear flows

NASA Technical Reports Server (NTRS)

Wygnanski, Israel J.; Petersen, Robert A.

1987-01-01

The application of the inviscid instability approach to externally excited turbulent free shear flows at high Reynolds numbers is explored. Attention is given to the cases of a small-deficit plane turbulent wake, a plane turbulent jet, an axisymmetric jet, the nonlinear evolution of instabilities in free shear flows, the concept of the 'preferred mode', vortex pairing in turbulent mixing layers, and experimental results for the control of free turbulent shear layers. The special features often attributed to pairing or to the preferred mode are found to be difficult to comprehend; the concept of feedback requires further substantiation in the case of incompressible flow.

d +i d chiral superconductivity in a triangular lattice from trigonal bipyramidal complexes

NASA Astrophysics Data System (ADS)

Lu, Chen; Zhang, Li-Da; Wu, Xianxin; Yang, Fan; Hu, Jiangping

2018-04-01

We model the newly predicted high-Tc superconducting candidates constructed by corner-shared trigonal bipyramidal complexes with an effective three-orbital tight-binding Hamiltonian and investigate the pairing symmetry of their superconducting states driven by electron-electron interactions. Our combined weak- and strong-coupling-based calculations consistently identify the chiral d +i d superconductivity as the leading pairing symmetry in a wide doping range with realistic interaction parameters. This pairing state has a nontrivial topological Chern number and can host gapless chiral edge modes, and the vortex cores under magnetic field can carry Majorana zero modes.

Microdefects and self-interstitial diffusion in crystalline silicon

NASA Astrophysics Data System (ADS)

Knowlton, William Barthelemy

In this thesis, a study is presented of D-defects and self-interstitial diffusion in silicon using Li ion (Lisp+) drifting in an electric field and transmission electron microscopy (TEM). Obstruction of Lisp+ drifting has been found in wafers from certain but not all FZ p-type Si. Incomplete Lisp+ drifting always occurs in the central region of the wafers. This work established that interstitial oxygen is not responsible for hindering Lisp+ drifting. The Osb i concentration was measured ({˜}2× 10sp{15}\\ cmsp{-3}) by local vibrational mode Fourier transform infrared spectroscopy and did not vary radially across the wafer. TEM was performed on a samples from the partially Lisp+ drifted area and compared to regions without D-defects. Precipitates were found only in the region containing D-defects that had partially Lisp+ drifted. This result indicates D-defects are responsible for the precipitation that halts the Lisp+ drift process. The precipitates were characterized using selected area diffraction (SAD) and image contrast analysis. The results suggested that the precipitates may cause stacking faults and their identity may be lithium silicides such as Lisb{21}Sisb5\\ and\\ Lisb{13}Sisb4. TEM revealed a decreasing distribution of Li precipitates as a function of Lisp+ drift depth along the growth direction. A preliminary model is presented that simulates Lisp+ drifting. The objective of the model is to incorporate the Li precipitate density distribution and Lisp+ drift depth to extract the size and capture cross-section of the D-defects. Nitrogen (N) doping has been shown to eliminate D-defects as measured by conventional techniques. However, Lisp+ drifting has shown that D-defects are indeed still present. Lisp+ drifting is able to detect D-defects at concentrations lower than conventional techniques. Lisp+ drifting and D-defects provide a useful means to study Si self-interstitial diffusion. The process modeling program SUPREM-IV was used to simulate the results of Si self-interstitial diffusion obtained from Lisp+ drifting experiments. Anomalous results from the Si self-interstitial diffusion experiments forced a re-examination of the possibility of thermal dissociation of D-defects. Thermal annealing experiments that were performed support this possibility. A review of the current literature illustrates the need for more research on the effects of thermal processing on FZ Si to understand the dissolution kinetics of D-defects.

Effect of pectoral fin kinematics on manta ray propulsion

NASA Astrophysics Data System (ADS)

Lu, Hao; Yeo, Khoon Seng; Chew, Chee-Meng

2018-05-01

Recent advancement of bio-inspired underwater vehicles has led to a growing interest in understanding the fluid mechanics of fish locomotion, which involves complex interaction between the deforming structure and its surrounding fluid. Unlike most natural swimmers that undulate their body and caudal fin, manta rays employ an oscillatory mode by flapping their large, flattened pectoral fins to swim forward. Such a lift-based mode can achieve a substantially high propulsive efficiency, which is beneficial to long-distance swimming. In this study, numerical simulations are carried out on a realistic manta ray model to investigate the effect of pectoral fin kinematics on the propulsive performance and flow structure. A traveling wave model, which relates a local deflection angle to radial and azimuthal wavelengths, is applied to generate the motion of the pectoral fins. Hydrodynamic forces and propulsive efficiency are reported for systematically varying kinematic parameters such as wave amplitude and wavelengths. Key flow features, including a leading edge vortex (LEV) that forms close to the tip of each pectoral fin, and a wake consisting of interconnected vortex rings, are identified. In addition, how different fin motions alter the LEV behavior and hence affect the thrust and efficiency is illustrated.