Is interstellar archeology possible?

NASA Astrophysics Data System (ADS)

Carrigan, Richard A.

2012-09-01

Searching for signatures of cosmic-scale archeological artifacts such as Dyson spheres is an interesting alternative to conventional radio SETI. Uncovering such an artifact does not require the intentional transmission of a signal on the part of the original civilization. This type of search is called interstellar archeology or sometimes cosmic archeology. A variety of interstellar archeology signatures is discussed including non-natural planetary atmospheric constituents, stellar doping, Dyson spheres, as well as signatures of stellar, and galactic-scale engineering. The concept of a Fermi bubble due to interstellar migration is reviewed in the discussion of galactic signatures. These potential interstellar archeological signatures are classified using the Kardashev scale. A modified Drake equation is introduced. With few exceptions interstellar archeological signatures are clouded and beyond current technological capabilities. However SETI for so-called cultural transmissions and planetary atmosphere signatures are within reach.

Feedback by massive stars and the emergence of superbubbles. I. Energy efficiency and Vishniac instabilities

NASA Astrophysics Data System (ADS)

Krause, M.; Fierlinger, K.; Diehl, R.; Burkert, A.; Voss, R.; Ziegler, U.

2013-02-01

Context. Massive stars influence their environment through stellar winds, ionising radiation, and supernova explosions. This is signified by observed interstellar bubbles. Such feedback is an important factor for galaxy evolution theory and galactic wind models. The efficiency of the energy injection into the interstellar medium (ISM) via bubbles and superbubbles is uncertain, and is usually treated as a free parameter for galaxy scale effects. In particular, since many stars are born in groups, it is interesting to study the dependence of the effective energy injection on the concentration of the stars. Aims: We aim to reproduce observations of superbubbles, their relation to the energy injection of the parent stars, and to understand their effective energy input into the ISM, as a function of the spatial configuration of the group of parent stars. Methods: We study the evolution of isolated and merging interstellar bubbles of three stars (25, 32, and 60 M⊙) in a homogeneous background medium with a density of 10mp cm-3 via 3D-hydrodynamic simulations with standard ISM thermodynamics (optically thin radiative cooling and photo-electric heating) and time-dependent energy and mass input according to stellar evolutionary tracks. We vary the position of the three stars relative to each other to compare the energy response for cases of isolated, merging and initially cospatial bubbles. Results: Mainly due to the Vishniac instability, our simulated bubbles develop thick shells and filamentary internal structures in column density. The shell widths reach tens of per cent of the outer bubble radius, which compares favourably to observations. More energy is retained in the ISM for more closely packed groups, by up to a factor of three and typically a factor of two for intermediate times after the first supernova. Once the superbubble is established, different positions of the contained stars make only a minor difference to the energy tracks. For our case of three massive stars, the energy deposition varies only very little for distances up to about 30 pc between the stars. Energy injected by supernovae is entirely dissipated in a superbubble on a timescale of about 1 Myr, which increases slightly with the superbubble size at the time of the explosion. Conclusions: The Vishniac instability may be responsible for the broadening of the shells of interstellar bubbles. Massive star winds are significant energetically due to their - in the long run - more efficient, steady energy injection and because they evacuate the space around the massive stars. For larger scale simulations, the feedback effect of close groups of stars or clusters may be subsumed into one effective energy input with insignificant loss of energy accuracy. The movie associated to Fig. 3 is available at http://www.aanda.org

Interstellar heliospheric probe/heliospheric boundary explorer mission—a mission to the outermost boundaries of the solar system

NASA Astrophysics Data System (ADS)

Wimmer-Schweingruber, Robert F.; McNutt, Ralph; Schwadron, Nathan A.; Frisch, Priscilla C.; Gruntman, Mike; Wurz, Peter; Valtonen, Eino

2009-05-01

The Sun, driving a supersonic solar wind, cuts out of the local interstellar medium a giant plasma bubble, the heliosphere. ESA, jointly with NASA, has had an important role in the development of our current understanding of the Suns immediate neighborhood. Ulysses is the only spacecraft exploring the third, out-of-ecliptic dimension, while SOHO has allowed us to better understand the influence of the Sun and to image the glow of interstellar matter in the heliosphere. Voyager 1 has recently encountered the innermost boundary of this plasma bubble, the termination shock, and is returning exciting yet puzzling data of this remote region. The next logical step is to leave the heliosphere and to thereby map out in unprecedented detail the structure of the outer heliosphere and its boundaries, the termination shock, the heliosheath, the heliopause, and, after leaving the heliosphere, to discover the true nature of the hydrogen wall, the bow shock, and the local interstellar medium beyond. This will greatly advance our understanding of the heliosphere that is the best-known example for astrospheres as found around other stars. Thus, IHP/HEX will allow us to discover, explore, and understand fundamental astrophysical processes in the largest accessible plasma laboratory, the heliosphere.

JET TRAILS AND MACH CONES: THE INTERACTION OF MICROQUASARS WITH THE INTERSTELLAR MEDIUM

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

Yoon, D.; Morsony, B.; Heinz, S.

2011-11-20

A subset of microquasars exhibits high peculiar velocity with respect to the local standard of rest due to the kicks they receive when being born in supernovae. The interaction between the radio plasma released by microquasar jets from such high-velocity binaries with the interstellar medium must lead to the production of trails and bow shocks similar to what is observed in narrow-angle tailed radio galaxies and pulsar wind nebulae. We present a set of numerical simulations of this interaction that illuminate the long-term dynamical evolution and the observational properties of these microquasar bow-shock nebulae and trails. We find that thismore » interaction always produces a structure that consists of a bow shock, a trailing neck, and an expanding bubble. Using our simulations to model emission, we predict that the shock surrounding the bubble and the neck should be visible in H{sub {alpha}} emission, the interior of the bubble should be visible in synchrotron radio emission, and only the bow shock is likely to be detectable in X-ray emission. We construct an analytic model for the evolution of the neck and bubble shape and compare this model with observations of the X-ray binary SAX J1712.6-3739.« less

A large bubble around the Crab Nebula

NASA Technical Reports Server (NTRS)

Romani, Roger W.; Reach, William T.; Koo, Bon Chul; Heiles, Carl

1990-01-01

IRAS and 21 cm observations of the interstellar medium around the Crab nebula show evidence of a large bubble surrounded by a partial shell. If located at the canonical 2 kpc distance of the Crab pulsar, the shell is estimated to have a radius of about 90 pc and to contain about 50,000 solar masses of swept-up gas. The way in which interior conditions of this bubble can have important implications for observations of the Crab are described, and the fashion in which presupernova evolution of the pulsar progenitor has affected its local environment is described.

Supernova remnant evolution in wind bubbles: A closer look at Kes 27

NASA Astrophysics Data System (ADS)

Dwarkadas, V. V.; Dewey, D.

2013-03-01

Massive Stars (>8M⊙) lose mass in the form of strong winds. These winds accumulate around the star, forming wind-blown bubbles. When the star explodes as a supernova (SN), the resulting shock wave expands within this wind-blown bubble, rather than the interstellar medium. The properties of the resulting remnant, its dynamics and kinematics, the morphology, and the resulting evolution, are shaped by the structure and properties of the wind-blown bubble. In this article we focus on Kes 27, a supernova remnant (SNR) that has been proposed by [1] to be evolving in a wind-blown bubble, explore its properties, and investigate whether the X-Ray properties could be ascribed to evolution of a SNR in a wind-blown bubble. Our initial model does not support the scenario proposed by [1], due to the fact that the reflected shock is expanding into much lower densities.

Wind bubbles within H ii regions around slowly moving stars

NASA Astrophysics Data System (ADS)

Mackey, Jonathan; Gvaramadze, Vasilii V.; Mohamed, Shazrene; Langer, Norbert

2015-01-01

Interstellar bubbles around O stars are driven by a combination of the star's wind and ionizing radiation output. The wind contribution is uncertain because the boundary between the wind and interstellar medium is difficult to observe. Mid-infrared observations (e.g., of the H ii region RCW 120) show arcs of dust emission around O stars, contained well within the H ii region bubble. These arcs could indicate the edge of an asymmetric stellar wind bubble, distorted by density gradients and/or stellar motion. We present two-dimensional, radiation-hydrodynamics simulations investigating the evolution of wind bubbles and H ii regions around massive stars moving through a dense (nH = 3000 cm-3), uniform medium with velocities ranging from 4 to 16 km s-1. The H ii region morphology is strongly affected by stellar motion, as expected, but the wind bubble is also very aspherical from birth, even for the lowest space velocity considered. Wind bubbles do not fill their H ii regions (we find filling factors of 10-20 per cent), at least for a main sequence star with mass M⋆ ~ 30 M⊙. Furthermore, even for supersonic velocities the wind bow shock does not significantly trap the ionization front. X-ray emission from the wind bubble is soft, faint, and comes mainly from the turbulent mixing layer between the wind bubble and the H ii region. The wind bubble radiates <1 per cent of its energy in X-rays; it loses most of its energy by turbulent mixing with cooler photoionized gas. Comparison of the simulations with the H ii region RCW 120 shows that its dynamical age is ≲0.4 Myr and that stellar motion ≲4 km s-1 is allowed, implying that the ionizing source is unlikely to be a runaway star but more likely formed in situ. The region's youth, and apparent isolation from other O or B stars, makes it very interesting for studies of massive star formation and of initial mass functions. Movies are available in electronic form at http://www.aanda.org

Streams of Charged Particles

NASA Image and Video Library

2011-04-28

This graphic shows the different streams of charged particles inside the bubble around our sun and outside, in the unexplored territory of interstellar space. The heliosheath, where NASA two Voyager spacecraft are now traveling, is shown in red.

Massive stars: Their lives in the interstellar medium; Proceedings of the Symposium, ASP Annual Meeting, 104th, Univ. of Wisconsin, Madison, June 23-25, 1992

NASA Astrophysics Data System (ADS)

Cassinelli, Joseph P.; Churchwell, Edward B.

1993-01-01

Various papers on massive stars and their relationship to the interstellar medium are presented. Individual topics addressed include: observations of newly formed massive stars, star formation with nonthermal motions, embedded stellar clusters in H II regions, a Milky Way concordance, NH3 and H2O masers, PIGs in the Trapezium, star formation in photoevaporating molecular clouds, massive star evolution, mass loss from cool supergiant stars, massive runaway stars, CNO abundances in three A-supergiants, mass loss from late-type supergiants, OBN stars and blue supergiant supernovae, the most evolved W-R stars, X-ray variability in V444 Cygni, highly polarized stars in Cassiopeia, H I bubbles around O stars, interstellar H I LY-alpha absorption, shocked ionized gas in 30 Doradus, wind mass and energy deposition. Also discussed are: stellar wind bow shocks, O stars giant bubbles in M33, Eridanus soft X-ray enhancement, wind-blown bubbles in ejecta medium, nebulae around W-R stars, highly ionized gas in the LMC, cold ionized gas around hot H II regions, initial mass function in the outer Galaxy, late stages in SNR evolution, possible LBV in NGC 1313, old SN-pulsar association, cold bright matter near SN1987A, starbursts in the nearby universe, giant H II regions, powering the superwind in NGC 253, obscuration effects in starburst Galactic nuclei, starburst propagation in dwarf galaxies, 30 Doradus, W-R content of NGC 595 and NGC 604, Cubic Cosmic X-ray Background Experiment.

Starry Messages - Searching for Signatures of Interstellar Archaeology

NASA Astrophysics Data System (ADS)

Carrigan, R. A., Jr.

Searching for signatures of cosmic-scale archaeological artefacts such as Dyson spheres or Kardashev civilizations is an interesting alternative to conventional SETI. Uncovering such an artifact does not require the intentional transmission of a signal on the part of the originating civilization. This type of search is called interstellar archaeology or sometimes cosmic archaeology . The detection of intelligence elsewhere in the Universe with interstellar archaeology or SETI would have broad implications for science. For example, the constraints of the anthropic principle would have to be loosened if a different type of intelligence was discovered elsewhere. A variety of interstellar archaeology signatures are discussed including non-natural planetary atmospheric constituents, stellar doping with isotopes of nuclear wastes, Dyson spheres, as well as signatures of stellar and galactic-scale engineering. The concept of a Fermi bubble due to interstellar migration is introduced in the discussion of galactic signatures. These potential interstellar archaeological signatures are classified using the Kardashev scale. A modified Drake equation is used to evaluate the relative challenges of finding various sources. With few exceptions interstellar archaeological signatures are clouded and beyond current technological capabilities. However SETI for so-called cultural transmissions and planetary atmosphere signatures are within reach.

Starry messages: Searching for signatures of interstellar archaeology

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

Carrigan, Richard A., Jr.; /Fermilab

2009-12-01

Searching for signatures of cosmic-scale archaeological artifacts such as Dyson spheres or Kardashev civilizations is an interesting alternative to conventional SETI. Uncovering such an artifact does not require the intentional transmission of a signal on the part of the original civilization. This type of search is called interstellar archaeology or sometimes cosmic archaeology. The detection of intelligence elsewhere in the Universe with interstellar archaeology or SETI would have broad implications for science. For example, the constraints of the anthropic principle would have to be loosened if a different type of intelligence was discovered elsewhere. A variety of interstellar archaeology signaturesmore » are discussed including non-natural planetary atmospheric constituents, stellar doping with isotopes of nuclear wastes, Dyson spheres, as well as signatures of stellar and galactic-scale engineering. The concept of a Fermi bubble due to interstellar migration is introduced in the discussion of galactic signatures. These potential interstellar archaeological signatures are classified using the Kardashev scale. A modified Drake equation is used to evaluate the relative challenges of finding various sources. With few exceptions interstellar archaeological signatures are clouded and beyond current technological capabilities. However SETI for so-called cultural transmissions and planetary atmosphere signatures are within reach.« less

A Tale of Two Comets: Encke

NASA Image and Video Library

2013-11-25

How did scientists know that NASA Voyager spacecraft entered interstellar space? Increase in the density of charged particles was the key piece of evidence. Our sun sits in a bubble, called the heliosphere, carved out by wind emitted from the hot sun.

The Wolf-Rayet nebula NGC 3199 - an interstellar snow plough?

NASA Astrophysics Data System (ADS)

Dyson, J. E.; Ghanbari, J.

1989-12-01

The Wolf-Rayet nebula NGC 3199 has a highly asymmetric morphology, with a very bright hemisphere near the exciting star HD 89358 and a much fainter and more extended other hemisphere. This nebula is modeled in terms of the distorted bubble produced by a moving star blowing a strong stellar wind into a surrounding uniform interstellar medium; this model is fitted to the morphology and observed kinematic data. The exciting star appears to be moving at about 60 km/s into local interstellar gas of density of about 10/cu cm, and has a mass-loss rate of about 0.000027 solar mass/yr. This latter mass-loss rate is in excellent agreement with observed mass-loss rates from Wolf-Rayet stars.

The Origin of the Local 1/4-KeV X-Ray Flux in Both Charge Exhange and a Hot Bubble

NASA Technical Reports Server (NTRS)

Galeazzi, M.; Chiao, M.; Collier, M. R.; Cravens, T.; Koutroumpa, D.; Kuntz, K. D.; Lallement, R.; Lepri, S. T.; McCammon, D.; Morgan, K.;

The origin of the local 1/4-keV X-ray flux in both charge exchange and a hot bubble.

PubMed

Galeazzi, M; Chiao, M; Collier, M R; Cravens, T; Koutroumpa, D; Kuntz, K D; Lallement, R; Lepri, S T; McCammon, D; Morgan, K; Porter, F S; Robertson, I P; Snowden, S L; Thomas, N E; Uprety, Y; Ursino, E; Walsh, B M

2014-08-14

The solar neighbourhood is the closest and most easily studied sample of the Galactic interstellar medium, an understanding of which is essential for models of star formation and galaxy evolution. Observations of an unexpectedly intense diffuse flux of easily absorbed 1/4-kiloelectronvolt X-rays, coupled with the discovery that interstellar space within about a hundred parsecs of the Sun is almost completely devoid of cool absorbing gas, led to a picture of a 'local cavity' filled with X-ray-emitting hot gas, dubbed the local hot bubble. This model was recently challenged by suggestions that the emission could instead be readily produced within the Solar System by heavy solar-wind ions exchanging electrons with neutral H and He in interplanetary space, potentially removing the major piece of evidence for the local existence of million-degree gas within the Galactic disk. Here we report observations showing that the total solar-wind charge-exchange contribution is approximately 40 per cent of the 1/4-keV flux in the Galactic plane. The fact that the measured flux is not dominated by charge exchange supports the notion of a million-degree hot bubble extending about a hundred parsecs from the Sun.

Beyond Pluto: The Search for the Edge of the Solar System

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

Funsten, Herb

In July, we finally visited the last major body of our solar system, Pluto. But what lies beyond? The stellar wind from our Sun forms an enormous bubble in interstellar space. This “sphere of our Sun,” or heliosphere, extends far beyond Pluto and forms a protective cocoon that shields us from cosmic radiation. In this talk, we will travel to the edge of the solar system, peer into the structure and dynamics of the outer heliosphere as it interacts with the interstellar medium and anticipate the future of the solar system as it moves through our galactic neighborhood.

THE MILKY WAY PROJECT: LEVERAGING CITIZEN SCIENCE AND MACHINE LEARNING TO DETECT INTERSTELLAR BUBBLES

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

Beaumont, Christopher N.; Williams, Jonathan P.; Goodman, Alyssa A.

We present Brut, an algorithm to identify bubbles in infrared images of the Galactic midplane. Brut is based on the Random Forest algorithm, and uses bubbles identified by >35,000 citizen scientists from the Milky Way Project to discover the identifying characteristics of bubbles in images from the Spitzer Space Telescope. We demonstrate that Brut's ability to identify bubbles is comparable to expert astronomers. We use Brut to re-assess the bubbles in the Milky Way Project catalog, and find that 10%-30% of the objects in this catalog are non-bubble interlopers. Relative to these interlopers, high-reliability bubbles are more confined to themore » mid-plane, and display a stronger excess of young stellar objects along and within bubble rims. Furthermore, Brut is able to discover bubbles missed by previous searches—particularly bubbles near bright sources which have low contrast relative to their surroundings. Brut demonstrates the synergies that exist between citizen scientists, professional scientists, and machine learning techniques. In cases where ''untrained' citizens can identify patterns that machines cannot detect without training, machine learning algorithms like Brut can use the output of citizen science projects as input training sets, offering tremendous opportunities to speed the pace of scientific discovery. A hybrid model of machine learning combined with crowdsourced training data from citizen scientists can not only classify large quantities of data, but also address the weakness of each approach if deployed alone.« less

Beyond Pluto: The Search for the Edge of the Solar System

ScienceCinema

Funsten, Herb

2018-01-16

In July, we finally visited the last major body of our solar system, Pluto. But what lies beyond? The stellar wind from our Sun forms an enormous bubble in interstellar space. This “sphere of our Sun,” or heliosphere, extends far beyond Pluto and forms a protective cocoon that shields us from cosmic radiation. In this talk, we will travel to the edge of the solar system, peer into the structure and dynamics of the outer heliosphere as it interacts with the interstellar medium and anticipate the future of the solar system as it moves through our galactic neighborhood.

Improvement of ore recovery efficiency in a flotation column cell using ultra-sonic enhanced bubbles

NASA Astrophysics Data System (ADS)

Filippov, L. O.; Royer, J. J.; Filippova, I. V.

2017-07-01

The ore process flotation technique is enhanced by using external ultra-sonic waves. Compared to the classical flotation method, the application of ultrasounds to flotation fluids generates micro-bubbles by hydrodynamic cavitation. Flotation performances increase was modelled as a result of increased probabilities of the particle-bubble attachment and reduced detachment probability under sonication. A simplified analytical Navier-Stokes model is used to predict the effect of ultrasonic waves on bubble behavior. If the theory is verified by experimentation, it predicts that the ultrasonic waves would create cavitation micro-bubbles, smaller than the flotation bubble added by the gas sparger. This effect leads to increasing the number of small bubbles in the liquid which promote particle-bubble attachment through coalescence between bubbles and micro-bubbles. The decrease in the radius of the flotation bubbles under external vibration forces has an additional effect by enhancing the bubble-particle collision. Preliminary results performed on a potash ore seem to confirm the theory.

Self-organization of cosmic radiation pressure instability. II - One-dimensional simulations

NASA Technical Reports Server (NTRS)

Hogan, Craig J.; Woods, Jorden

1992-01-01

The clustering of statistically uniform discrete absorbing particles moving solely under the influence of radiation pressure from uniformly distributed emitters is studied in a simple one-dimensional model. Radiation pressure tends to amplify statistical clustering in the absorbers; the absorbing material is swept into empty bubbles, the biggest bubbles grow bigger almost as they would in a uniform medium, and the smaller ones get crushed and disappear. Numerical simulations of a one-dimensional system are used to support the conjecture that the system is self-organizing. Simple statistics indicate that a wide range of initial conditions produce structure approaching the same self-similar statistical distribution, whose scaling properties follow those of the attractor solution for an isolated bubble. The importance of the process for large-scale structuring of the interstellar medium is briefly discussed.

A review of the theory of interstellar communication

NASA Technical Reports Server (NTRS)

Billingham, J.; Wolfe, J. H.; Oliver, B. M.

1975-01-01

The probability is analyzed that intelligent civilizations capable of interstellar communication exist in the galaxy. Drake's (1960) equation for the prevalence of communicative civilization is used in the calculations, and attempts are made to place limits on the search range that must be covered to contact other civilizations, the longevity of the communicative phase of such civilizations, and the possible number of two-way exchanges between civilizations in contact with each other. The minimum estimates indicate that some 100,000 civilizations probably coexist within several tens of astronomical units of each other and that some 1,000,000 probably coexist within 10 light years of each other. Attempts to detect coherent signals characteristic of intelligent life are briefly noted, including Projects Ozma and Cyclops as well as some Soviet attempts. Recently proposed American and Soviet programs for interstellar communication are outlined.

Stardust@home: A Massively Distributed Public Search for Interstellar Dust in the Stardust Interstellar Dust Collector

NASA Technical Reports Server (NTRS)

Westphal, Andrew J.; Butterworth, Anna L.; Snead, Christopher J.; Craig, Nahide; Anderson, David; Jones, Steven M.; Brownlee, Donald E.; Farnsworth, Richard; Zolensky, Michael E.

2005-01-01

In January 2006, the Stardust mission will return the first samples from a solid solar system body beyond the Moon. Stardust was in the news in January 2004, when it encountered comet Wild2 and captured a sample of cometary dust. But Stardust carries an equally important payload: the first samples of contemporary interstellar dust ever collected. Although it is known that interstellar (IS) dust penetrates into the inner solar system [2, 3], to date not even a single contemporary interstellar dust particle has been captured and analyzed in the laboratory. Stardust uses aerogel collectors to capture dust samples. Identification of interstellar dust impacts in the Stardust Interstellar Dust Collector probably cannot be automated, but will require the expertise of the human eye. However, the labor required for visual scanning of the entire collector would exceed the resources of any reasonably-sized research group. We are developing a project to recruit the public in the search for interstellar dust, based in part on the wildly popular SETI@home project, which has five million subscribers. We call the project Stardust@home. Using sophisticated chemical separation techniques, certain types of refractory ancient IS particles (so-called presolar grains) have been isolated from primitive meteorites (e.g., [4] ). Recently, presolar grains have been identified in Interplanetary Dust Particles[6]. Because these grains are not isolated chemically, but are recognized only by their unusual isotopic compositions, they are probably less biased than presolar grains isolated from meteorites. However, it is entirely possible that the typical interstellar dust particle is isotopically solar in composition. The Stardust collection of interstellar dust will be the first truly unbiased one.

A General Method for Assessing the Origin of Interstellar Small Bodies: The Case of 1I/2017 U1 (‘Oumuamua)

NASA Astrophysics Data System (ADS)

Zuluaga, Jorge I.; Sánchez-Hernández, Oscar; Sucerquia, Mario; Ferrín, Ignacio

2018-06-01

With the advent of more and deeper sky surveys, the discovery of interstellar small objects entering into the solar system has been finally possible. In 2017 October 19, using observations of the Pan-STARRS survey, a fast moving object, now officially named 1I/2017 U1 (‘Oumuamua), was discovered in a heliocentric unbound trajectory, suggesting an interstellar origin. Assessing the provenance of interstellar small objects is key for understanding their distribution, spatial density, and the processes responsible for their ejection from planetary systems. However, their peculiar trajectories place a limit on the number of observations available to determine a precise orbit. As a result, when its position is propagated ∼105–106 years backward in time, small errors in orbital elements become large uncertainties in position in the interstellar space. In this paper we present a general method for assigning probabilities to nearby stars of being the parent system of an observed interstellar object. We describe the method in detail and apply it for assessing the origin of ‘Oumuamua. A preliminary list of potential progenitors and their corresponding probabilities is provided. In the future, when further information about the object and/or the nearby stars be refined, the probabilities computed with our method can be updated. We provide all the data and codes we developed for this purpose in the form of an open source C/C++/Python package, iWander, which is publicly available at http://github.com/seap-udea/iWander.

The Fermi paradox: An approach based on percolation theory

NASA Technical Reports Server (NTRS)

Landis, Geoffrey A.

1993-01-01

If even a very small fraction of the hundred billion stars in the galaxy are home to technological civilizations which colonize over interstellar distances, the entire galaxy could be completely colonized in a few million years. The absence of such extraterrestrial civilizations visiting Earth is the Fermi paradox. A model for interstellar colonization is proposed using the assumption that there is a maximum distance over which direct interstellar colonization is feasible. Due to the time lag involved in interstellar communications, it is assumed that an interstellar colony will rapidly develop a culture independent of the civilization that originally settled it. Any given colony will have a probability P of developing a colonizing civilization, and a probability (1-P) that it will develop a non-colonizing civilization. These assumptions lead to the colonization of the galaxy occuring as a percolation problem. In a percolation problem, there will be a critical value of percolation probability, P(sub c). For P less than P(sub c), colonization will always terminate after a finite number of colonies. Growth will occur in 'clusters', with the outside of each cluster consisting of non-colonizing civilizations. For P greater than P(sub c), small uncolonized voids will exist, bounded by non-colonizing civilizations. For P approximately = to P(sub c), arbitrarily large filled regions exist, and also arbitrarily large empty regions.

Abundances of Deuterium, Oxygen and Nitrogen in the Local Interstellar Medium: Overview of First Results from the Far Ultraviolet Spectroscopic Explorer Mission

NASA Technical Reports Server (NTRS)

Moos, H. W.; Sembach, K. R.; Vidal-Madjar, A.; York, D. G.; Friedman, S. D.; Hebrard, G.; Kruk, J. W.; Lehner, N.; Lemoine, M.; Sonneborn, G.;

Hubble peers inside a celestial geode

NASA Astrophysics Data System (ADS)

2004-08-01

celestial geode hi-res Size hi-res: 148 Kb Credits: ESA/NASA, Yäel Nazé (University of Liège, Belgium) and You-Hua Chu (University of Illinois, Urbana, USA) Hubble peers inside a celestial geode In this unusual image, the NASA/ESA Hubble Space Telescope captures a rare view of the celestial equivalent of a geode - a gas cavity carved by the stellar wind and intense ultraviolet radiation from a young hot star. Real geodes are handball-sized, hollow rocks that start out as bubbles in volcanic or sedimentary rock. Only when these inconspicuous round rocks are split in half by a geologist, do we get a chance to appreciate the inside of the rock cavity that is lined with crystals. In the case of Hubble's 35 light-year diameter ‘celestial geode’ the transparency of its bubble-like cavity of interstellar gas and dust reveals the treasures of its interior. Low resolution version (JPG format) 148 Kb High resolution version (TIFF format) 1929 Kb Acknowledgment: This image was created with the help of the ESA/ESO/NASA Photoshop FITS Liberator. Real geodes are handball-sized, hollow rocks that start out as bubbles in volcanic or sedimentary rock. Only when these inconspicuous round rocks are split in half by a geologist, do we get a chance to appreciate the inside of the rock cavity that is lined with crystals. In the case of Hubble's 35 light-year diameter ‘celestial geode’ the transparency of its bubble-like cavity of interstellar gas and dust reveals the treasures of its interior. The object, called N44F, is being inflated by a torrent of fast-moving particles (what astronomers call a 'stellar wind') from an exceptionally hot star (the bright star just below the centre of the bubble) once buried inside a cold dense cloud. Compared with our Sun (which is losing mass through the so-called 'solar wind'), the central star in N44F is ejecting more than a 100 million times more mass per second and the hurricane of particles moves much faster at 7 million km per hour (as opposed to less than 1.5 million km per hour for our Sun). Because the bright central star does not exist in empty space but is surrounded by an envelope of gas, the stellar wind collides with this gas, pushing it out, like a snow plough. This forms a bubble, whose striking structure is clearly visible in the crisp Hubble image. The nebula N44F is one of a handful of known interstellar bubbles. Bubbles like these have been seen around evolved massive stars (called 'Wolf-Rayet stars'), and also around clusters of stars (where they are called 'super-bubbles'). But they have rarely been viewed around isolated stars, as is the case here. On closer inspection N44F harbours additional surprises. The interior wall of its gaseous cavity is lined with several four to eight light-year high finger-like columns of cool dust and gas. (The structure of these 'columns' is similar to the Eagle Nebula’s iconic 'Pillars of Creation' photographed by Hubble a decade ago, and is seen in a few other nebulae as well). The fingers are created by a blistering ultraviolet radiation from the central star. Like wind socks caught in a gale, they point in the direction of the energy flow. These pillars look small in this image only because they are much farther away from us then the Eagle Nebula’s pillars. N44F is located about 160 000 light-years in the neighbouring dwarf galaxy the Large Magellanic Cloud, in the direction of the southern constellation Dorado. N44F is part of the larger N44 complex, which contains a large super-bubble, blown out by the combined action of stellar winds and multiple supernova explosions. N44 itself is roughly 1000 light-years across. Several compact star-forming regions, including N44F, are found along the rim of the central super-bubble. This image was taken with Hubble's Wide Field Planetary Camera 2, using filters that isolate light emitted by sulphur (shown in blue, a 1200-second exposure) and hydrogen gas (shown in red, a 1000-second exposure).

Searching for extraterrestrial civilizations

NASA Technical Reports Server (NTRS)

Kuiper, T. B. H.; Morris, M.

1977-01-01

Three interrelated assumptions are critically examined in an attempt to outline a productive strategy for a search for extraterrestrial intelligence. Questions concerning the feasibility of interstellar travel are investigated. It is concluded that the probability of interstellar travel is high enough that, given a modest number of advanced civilizations, at least one of them will engage in interstellar voyages and colonize the galaxy. Assuming, however, that technological civilizations are rare the galaxy would be essentially unpopulated. Attention is given to the present lack of contact with extraterrestrial beings and frequencies for interstellar beacons.

Newly detected molecules in dense interstellar clouds

NASA Astrophysics Data System (ADS)

Irvine, William M.; Avery, L. W.; Friberg, P.; Matthews, H. E.; Ziurys, L. M.

Several new interstellar molecules have been identified including C2S, C3S, C5H, C6H and (probably) HC2CHO in the cold, dark cloud TMC-1; and the discovery of the first interstellar phosphorus-containing molecule, PN, in the Orion "plateau" source. Further results include the observations of 13C3H2 and C3HD, and the first detection of HCOOH (formic acid) in a cold cloud.

Cavitation bubble nucleation induced by shock-bubble interaction in a gelatin gel

NASA Astrophysics Data System (ADS)

Oguri, Ryota; Ando, Keita

2018-05-01

An optical visualization technique is developed to study cavitation bubble nucleation that results from interaction between a laser-induced shock and a preexisting gas bubble in a 10 wt. % gelatin gel; images of the nucleated cavitation bubbles are captured and the cavitation inception pressure is determined based on Euler flow simulation. A spherical gas cavity is generated by focusing an infrared laser pulse into a gas-supersaturated gel and the size of the laser-generated bubble in mechanical equilibrium is tuned via mass transfer of the dissolved gas into the bubble. A spherical shock is then generated, through rapid expansion of plasma induced by the laser focusing, in the vicinity of the gas bubble. The shock-bubble interaction is recorded by a CCD camera with flash illumination of a nanosecond green laser pulse. The observation captures cavitation inception in the gel under tension that results from acoustic impedance mismatching at the bubble interface interacting with the shock. We measure the probability of cavitation inception from a series of the repeated experiments, by varying the bubble radius and the standoff distance. The threshold pressure is defined at the cavitation inception probability equal to one half and is calculated, through comparisons to Euler flow simulation, at -24.4 MPa. This threshold value is similar to that from shock-bubble interaction experiments using water, meaning that viscoelasticity of the 10 wt. % gelatin gel has a limited impact on bubble nucleation dynamics.

Single-bubble dynamics in pool boiling of one-component fluids.

PubMed

Xu, Xinpeng; Qian, Tiezheng

2014-06-01

We numerically investigate the pool boiling of one-component fluids with a focus on the effects of surface wettability on the single-bubble dynamics. We employed the dynamic van der Waals theory [Phys. Rev. E 75, 036304 (2007)], a diffuse-interface model for liquid-vapor flows involving liquid-vapor transition in nonuniform temperature fields. We first perform simulations for bubbles on homogeneous surfaces. We find that an increase in either the contact angle or the surface superheating can enhance the bubble spreading over the heating surface and increase the bubble departure diameter as well and therefore facilitate the transition into film boiling. We then examine the dynamics of bubbles on patterned surfaces, which incorporate the advantages of both hydrophobic and hydrophilic surfaces. The central hydrophobic region increases the thermodynamic probability of bubble nucleation while the surrounding hydrophilic region hinders the continuous bubble spreading by pinning the contact line at the hydrophobic-hydrophilic intersection. This leads to a small bubble departure diameter and therefore prevents the transition from nucleate boiling into film boiling. With the bubble nucleation probability increased and the bubble departure facilitated, the efficiency of heat transfer on such patterned surfaces is highly enhanced, as observed experimentally [Int. J. Heat Mass Transfer 57, 733 (2013)]. In addition, the stick-slip motion of contact line on patterned surfaces is demonstrated in one-component fluids, with the effect weakened by surface superheating.

Term Projects on Interstellar Comets

ERIC Educational Resources Information Center

Mack, John E.

1975-01-01

Presents two calculations of the probability of detection of an interstellar comet, under the hypothesis that such comets would escape from comet clouds similar to that believed to surround the sun. Proposes three problems, each of which would be a reasonable term project for a motivated undergraduate. (Author/MLH)

Maximum number of habitable planets at the time of Earth's origin: new hints for panspermia?

PubMed

von Bloh, Werner; Franck, Siegfried; Bounama, Christine; Schellnhuber, Hans-Joachim

2003-04-01

New discoveries have fuelled the ongoing discussion of panspermia, i.e. the transport of life from one planet to another within the solar system (interplanetary panspermia) or even between different planetary systems (interstellar panspermia). The main factor for the probability of interstellar panspermia is the average density of stellar systems containing habitable planets. The combination of recent results for the formation rate of Earth-like planets with our estimations of extrasolar habitable zones allows us to determine the number of habitable planets in the Milky Way over cosmological time scales. We find that there was a maximum number of habitable planets around the time of Earth's origin. If at all, interstellar panspermia was most probable at that time and may have kick-started life on our planet.

Freeze/Thaw-Induced Embolism: Probability of Critical Bubble Formation Depends on Speed of Ice Formation

DOE PAGES

Sevanto, Sanna; Holbrook, N. Michele; Ball, Marilyn C.

2012-06-06

Bubble formation in the conduits of woody plants sets a challenge for uninterrupted water transportation from the soil up to the canopy. Freezing and thawing of stems has been shown to increase the number of air-filled (embolized) conduits, especially in trees with large conduit diameters. Despite numerous experimental studies, the mechanisms leading to bubble formation during freezing have not been addressed theoretically. We used classical nucleation theory and fluid mechanics to show which mechanisms are most likely to be responsible for bubble formation during freezing and what parameters determine the likelihood of the process. Our results confirm the common assumptionmore » that bubble formation during freezing is most likely due to gas segregation by ice. If xylem conduit walls are not permeable to the salts expelled by ice during the freezing process, osmotic pressures high enough for air seeding could be created. The build-up rate of segregated solutes in front of the ice-water interface depends equally on conduit diameter and freezing velocity. Therefore, bubble formation probability depends on these variables. The dependence of bubble formation probability on freezing velocity means that the experimental results obtained for cavitation threshold conduit diameters during freeze/thaw cycles depend on the experimental setup; namely sample size and cooling rate. The velocity dependence also suggests that to avoid bubble formation during freezing trees should have narrow conduits where freezing is likely to be fast (e.g., branches or outermost layer of the xylem). Avoidance of bubble formation during freezing could thus be one piece of the explanation why xylem conduit size of temperate and boreal zone trees varies quite systematically.« less

Freeze/Thaw-induced embolism: probability of critical bubble formation depends on speed of ice formation.

PubMed

Sevanto, Sanna; Holbrook, N Michele; Ball, Marilyn C

2012-01-01

Bubble formation in the conduits of woody plants sets a challenge for uninterrupted water transportation from the soil up to the canopy. Freezing and thawing of stems has been shown to increase the number of air-filled (embolized) conduits, especially in trees with large conduit diameters. Despite numerous experimental studies, the mechanisms leading to bubble formation during freezing have not been addressed theoretically. We used classical nucleation theory and fluid mechanics to show which mechanisms are most likely to be responsible for bubble formation during freezing and what parameters determine the likelihood of the process. Our results confirm the common assumption that bubble formation during freezing is most likely due to gas segregation by ice. If xylem conduit walls are not permeable to the salts expelled by ice during the freezing process, osmotic pressures high enough for air seeding could be created. The build-up rate of segregated solutes in front of the ice-water interface depends equally on conduit diameter and freezing velocity. Therefore, bubble formation probability depends on these variables. The dependence of bubble formation probability on freezing velocity means that the experimental results obtained for cavitation threshold conduit diameters during freeze/thaw cycles depend on the experimental setup; namely sample size and cooling rate. The velocity dependence also suggests that to avoid bubble formation during freezing trees should have narrow conduits where freezing is likely to be fast (e.g., branches or outermost layer of the xylem). Avoidance of bubble formation during freezing could thus be one piece of the explanation why xylem conduit size of temperate and boreal zone trees varies quite systematically.

Dynamics of supernova driven superbubbles

NASA Astrophysics Data System (ADS)

Yadav, Naveen; Mukherjee, Dipanjan; Sharma, Prateek; Nath, Biman

2015-08-01

Energy injection by supernovae is believed to be one of the primary sources which powers the expansion of supershells. There is a qualitative difference between isolated supernovae (SNe) and overlapping SNe. For typical interstellar medium (ISM) conditions an isolated supernova loses most of the injected mechanical energy by 1 Myr. In contrast, for SNe going off in bubbles the radiative losses are much smaller. While the outer shock going off in the dense ISM (~1 cm-3) becomes radiative well before 1 Myr, there is a strong non-radiative termination shock that keeps the bubble over-pressured till the lifetime of the OB association (10s of Myr; Sharma et al. 2014). This has relevance for supernova feedback in galaxy formation simulations. In our previous 1-D treatment all the SNe were assumed to occur at the same location in space. It was found that a steady wind inside the bubble (Chevalier & Clegg 1985) can occur only if the number of SNe is large (>~104) and a supernova going off inside the bubble can thermalize within the termination shock. In the present work we study the effect of SNe separated in both space and time using 3-D hydrodynamic simulations with radiative cooling. If the separation between SNe is larger than the remnant’s radius at the time it becomes radiative, SNe are in the isolated regime. The explosion energy is deposited as thermal energy in a uniform, static interstellar medium (ISM) with temperature 104 K, corresponding to the warm neutral medium. The key parameters of our idealized setup are the ISM density (ngas), the number of SNe (N★) and the spatial separation between SNe (Rcl). The shock radius when it becomes radiative depends on the ISM density and number of SNe. We obtain the critical values of the key parameters (ngas, N★, Rcl) which lead to the formation of a superbubble. e.g., at least 103 SNe are required to maintain an over-pressured bubble at 20 Myr in an ISM with 1 cm-3 similarly 102 SNe going off within a region of 100 pc in an ISM with 1 cm-3 are effectively in the isolated regime. We also compare our simulation results with observational data on superbubbles.

Cluster membership probability: polarimetric approach

NASA Astrophysics Data System (ADS)

Medhi, Biman J.; Tamura, Motohide

2013-04-01

Interstellar polarimetric data of the six open clusters Hogg 15, NGC 6611, NGC 5606, NGC 6231, NGC 5749 and NGC 6250 have been used to estimate the membership probability for the stars within them. For proper-motion member stars, the membership probability estimated using the polarimetric data is in good agreement with the proper-motion cluster membership probability. However, for proper-motion non-member stars, the membership probability estimated by the polarimetric method is in total disagreement with the proper-motion cluster membership probability. The inconsistencies in the determined memberships may be because of the fundamental differences between the two methods of determination: one is based on stellar proper motion in space and the other is based on selective extinction of the stellar output by the asymmetric aligned dust grains present in the interstellar medium. The results and analysis suggest that the scatter of the Stokes vectors q (per cent) and u (per cent) for the proper-motion member stars depends on the interstellar and intracluster differential reddening in the open cluster. It is found that this method could be used to estimate the cluster membership probability if we have additional polarimetric and photometric information for a star to identify it as a probable member/non-member of a particular cluster, such as the maximum wavelength value (λmax), the unit weight error of the fit (σ1), the dispersion in the polarimetric position angles (overline{ɛ }), reddening (E(B - V)) or the differential intracluster reddening (ΔE(B - V)). This method could also be used to estimate the membership probability of known member stars having no membership probability as well as to resolve disagreements about membership among different proper-motion surveys.

Single-bubble dynamics in pool boiling of one-component fluids

NASA Astrophysics Data System (ADS)

Xu, Xinpeng; Qian, Tiezheng

2014-06-01

We numerically investigate the pool boiling of one-component fluids with a focus on the effects of surface wettability on the single-bubble dynamics. We employed the dynamic van der Waals theory [Phys. Rev. E 75, 036304 (2007), 10.1103/PhysRevE.75.036304], a diffuse-interface model for liquid-vapor flows involving liquid-vapor transition in nonuniform temperature fields. We first perform simulations for bubbles on homogeneous surfaces. We find that an increase in either the contact angle or the surface superheating can enhance the bubble spreading over the heating surface and increase the bubble departure diameter as well and therefore facilitate the transition into film boiling. We then examine the dynamics of bubbles on patterned surfaces, which incorporate the advantages of both hydrophobic and hydrophilic surfaces. The central hydrophobic region increases the thermodynamic probability of bubble nucleation while the surrounding hydrophilic region hinders the continuous bubble spreading by pinning the contact line at the hydrophobic-hydrophilic intersection. This leads to a small bubble departure diameter and therefore prevents the transition from nucleate boiling into film boiling. With the bubble nucleation probability increased and the bubble departure facilitated, the efficiency of heat transfer on such patterned surfaces is highly enhanced, as observed experimentally [Int. J. Heat Mass Transfer 57, 733 (2013), 10.1016/j.ijheatmasstransfer.2012.10.080]. In addition, the stick-slip motion of contact line on patterned surfaces is demonstrated in one-component fluids, with the effect weakened by surface superheating.

Morphological diagnostics of star formation in molecular clouds

NASA Astrophysics Data System (ADS)

Beaumont, Christopher Norris

Molecular clouds are the birth sites of all star formation in the present-day universe. They represent the initial conditions of star formation, and are the primary medium by which stars transfer energy and momentum back to parsec scales. Yet, the physical evolution of molecular clouds remains poorly understood. This is not due to a lack of observational data, nor is it due to an inability to simulate the conditions inside molecular clouds. Instead, the physics and structure of the interstellar medium are sufficiently complex that interpreting molecular cloud data is very difficult. This dissertation mitigates this problem, by developing more sophisticated ways to interpret morphological information in molecular cloud observations and simulations. In particular, I have focused on leveraging machine learning techniques to identify physically meaningful substructures in the interstellar medium, as well as techniques to inter-compare molecular cloud simulations to observations. These contributions make it easier to understand the interplay between molecular clouds and star formation. Specific contributions include: new insight about the sheet-like geometry of molecular clouds based on observations of stellar bubbles; a new algorithm to disambiguate overlapping yet morphologically distinct cloud structures; a new perspective on the relationship between molecular cloud column density distributions and the sizes of cloud substructures; a quantitative analysis of how projection effects affect measurements of cloud properties; and an automatically generated, statistically-calibrated catalog of bubbles identified from their infrared morphologies.

T he Analysis of the seasonal variations of equatorial plasma bubble, occurrence observed from Oukaimeden Observatory, Morroco

NASA Astrophysics Data System (ADS)

Amine, Lagheryeb; Zouhair, Benkhaldoun; Jonathan, Makela; Mohamed, Kaab; Aziza, Bounhir; Brian, Hardin; Dan, Fisher; Tmuthy, Duly

2016-04-01

T he Analysis of the seasonal variations of equatorial plasma bubble, occurrence using the 630.0 nm airglow images collected by the PICASSO imager deployed at the Oukkaimden observatory in Morocco. Data have been taken since November 2013 to december 2015. We show the monthly average of appearance of EPBs. A maximum probability for bubble development is seen in the data in January and between late February and early March. We also observe that there are a maximum period of appearance where the plasma is observed (3-5 nights successivies) and we will discuss its connection with the solar activity in storm time. Future analysis will compare the probability of bubble occurrence in our site with the data raised in other observation sites.

What Will Colleges Do when the Bubble Bursts?

ERIC Educational Resources Information Center

Shaw, Jane S.

2011-01-01

The problem facing American colleges and universities is larger than even the term "bubble" implies. A bursting bubble would force change on the more than four thousand postsecondary institutions in the United States, but something even more destructive is going to hit higher education, probably at the same time. The major sign that a…

Extraterrestrials - Where are they?

NASA Astrophysics Data System (ADS)

Hart, M. H.; Zuckerman, B.

Explanations for the absence of evidence for extraterrestrial beings are discussed, together with the probabilities of other habitable planets in the universe, programs to detect radio signals from other civilizations, and the processes that can lead to the appearance of life. Probability estimates are presented for the appearance of life, the occurrence of interstellar colonization, and the times involved in interstellar colonization. It is suggested that the first civilization to begin interstellar colonization will be the civilization that colonizes the Galaxy, and calculations are presented for the propulsion methods, techniques for terraforming planets, and the incidence of habitable planets in the Galaxy. Primordial organic chemistry is reviewed, together with nucleosynthesis and evolution in the Galaxy, and consideration is devoted to the rate of formation of DNA strands and other substances by which life forms could exist in the infinite universe. For individual items see A83-41502 to A83-41515

Problems of Interplanetary and Interstellar Trade

NASA Astrophysics Data System (ADS)

Hickman, John

2008-01-01

If and when interplanetary and interstellar trade develops, it will be novel in two respects. First, the distances and time spans involved will reduce all or nearly all trade to the exchange of intangible goods. That threatens the possibility of conducting business in a genuinely common currency and of enforcing debt agreements, especially those involving sovereign debt. Second, interstellar trade suggests trade between humans and aliens. Cultural distance is a probable obstacle to initiating and sustaining such trade. Such exchange also threatens the release of new and potentially toxic memes.

Dust evolution, a global view I. Nanoparticles, nascence, nitrogen and natural selection … joining the dots

NASA Astrophysics Data System (ADS)

Jones, A. P.

2016-12-01

The role and importance of nanoparticles for interstellar chemistry and beyond is explored within the framework of The Heterogeneous dust Evolution Model for Interstellar Solids (THEMIS), focusing on their active surface chemistry, the effects of nitrogen doping and the natural selection of interesting nanoparticle sub-structures. Nanoparticle-driven chemistry, and in particular the role of intrinsic epoxide-type structures, could provide a viable route to the observed gas phase OH in tenuous interstellar clouds en route to becoming molecular clouds. The aromatic-rich moieties present in asphaltenes probably provide a viable model for the structures present within aromatic-rich interstellar carbonaceous grains. The observed doping of such nanoparticle structures with nitrogen, if also prevalent in interstellar dust, could perhaps have important and observable consequences for surface chemistry and the formation of precursor pre-biotic species.

A Radio Study of the Seyfert Galaxy Markarian 6: Implications for Seyfert Life Cycles

NASA Astrophysics Data System (ADS)

Kharb, P.; O'Dea, C. P.; Baum, S. A.; Colbert, E. J. M.; Xu, C.

2006-11-01

We have carried out an extensive radio study with the Very Large Array on the Seyfert 1.5 galaxy Mrk 6 and imaged a spectacular radio structure in the source. The radio emission occurs on three different spatial scales: ~7.5 kpc bubbles, ~1.5 kpc bubbles lying nearly orthogonal to them, and a ~1 kpc radio jet lying orthogonal to the kiloparsec-scale bubble. To explain the complex morphology, we first consider a scenario in which the radio structures are the result of superwinds ejected by a nuclear starburst. However, recent Spitzer observations of Mrk 6 provide an upper limit to the star formation rate (SFR) of ~5.5 Msolar yr-1, an estimate much lower than the SFR of ~33 Msolar yr-1 derived assuming that the bubbles are a result of starburst winds energized by supernova explosions. Thus, a starburst alone cannot meet the energy requirements for the creation of the bubbles in Mrk 6. We then present an energetically plausible model wherein the bubbles are a result of energy deposited by the kiloparsec-scale jet as it plows into the interstellar medium. Finally, we consider a model in which the complex radio structure is a result of an episodically powered precessing jet that changes its orientation. This model is the most attractive as it can naturally explain the complex radio morphology and is consistent with the energetics, the spectral index, and the polarization structure. Radio emission in this scenario is a short-lived phenomenon in the lifetime of a Seyfert galaxy, which results from an accretion event.

Modeling the Variable Heliopause Location

NASA Astrophysics Data System (ADS)

Hensley, Kerry

2018-03-01

In 2012, Voyager 1 zipped across the heliopause. Five and a half years later, Voyager 2 still hasnt followed its twin into interstellar space. Can models of the heliopause location help determine why?How Far to the Heliopause?Artists conception of the heliosphere with the important structures and boundaries labeled. [NASA/Goddard/Walt Feimer]As our solar system travels through the galaxy, the solar outflow pushes against the surrounding interstellar medium, forming a bubble called the heliosphere. The edge of this bubble, the heliopause, is the outermost boundary of our solar system, where the solar wind and the interstellar medium meet. Since the solar outflow is highly variable, the heliopause is constantly moving with the motion driven by changes inthe Sun.NASAs twin Voyager spacecraft were poisedto cross the heliopause after completingtheir tour of the outer planets in the 1980s. In 2012, Voyager 1 registered a sharp increase in the density of interstellar particles, indicating that the spacecraft had passed out of the heliosphere and into the interstellar medium. The slower-moving Voyager 2 was set to pierce the heliopause along a different trajectory, but so far no measurements have shown that the spacecraft has bid farewell to oursolar system.In a recent study, ateam of scientists led by Haruichi Washimi (Kyushu University, Japan and CSPAR, University of Alabama-Huntsville) argues that models of the heliosphere can help explain this behavior. Because the heliopause location is controlled by factors that vary on many spatial and temporal scales, Washimiand collaborators turn to three-dimensional, time-dependent magnetohydrodynamics simulations of the heliosphere. In particular, they investigate how the position of the heliopause along the trajectories of Voyager 1 and Voyager 2 changes over time.Modeled location of the heliopause along the paths of Voyagers 1 (blue) and 2 (orange). Click for a closer look. The red star indicates the location at which Voyager 1 crossed the heliopause. The current location of Voyager 2 is marked with a red circle. [Washimi et al. 2017]A Time-Varying BarrierThe authorsconsider the impact that solar flares, coronal mass ejections, and other disturbances in the solar outflow have on the heliopause distance. These solar disturbances intermingle as they travel outward to form what the authors call global merged interaction regions.Using their hydrodynamical simulations, Washimi and collaborators capture the complex behavior of the global merged interaction regions as they propagate through the termination shock and collide with the heliopause. Part of the shock is transmitted into the local interstellar medium, while part of it is reflected back toward and collides with the termination shock, which is pushed toward the Sun. This complex interplay of transmitted and reflected shocks combined with the nonuniformity of the local interstellar medium causes the heliopause location to vary dramatically in time as well as space.What Does this Mean for Voyager 2?Washimi and collaborators find that the location of the heliopause along the trajectories of Voyagers 1 and 2 has changed considerably over the past decade. In particular, they find that the heliopause has been pushed outward over the past few years due to an increase in the solar wind ram pressure. According to their simulations, Voyager 2 is currently traveling outward faster than the heliopause is advancing, which means that the spacecraft should soon cross the boundary perhaps even thisyear to become Earths second interstellar messenger.CitationHaruichi Washimi et al 2017 ApJL 846 L9. doi:10.3847/2041-8213/aa8556

A Multi-Wavelength Study of the Hot Component of the Interstellar Medium

NASA Technical Reports Server (NTRS)

Nichols, Joy; Oliversen, Ronald K. (Technical Monitor)

2002-01-01

The goals of this research are as follows: (1) Using the large number of lines of sight available in the ME database, identify the lines of sight with high-velocity components in interstellar lines, from neutral species through Si VI, C IV, and N V; (2) Compare the column density of the main components (i.e. low velocity components) of the interstellar lines with distance, galactic longitude and latitude, and galactic radial position. Derive statistics on the distribution of components in space (e.g. mean free path, mean column density of a component). Compare with model predictions for the column densities in the walls of old SNR bubbles and superbubbles, in evaporating cloud boundaries and in turbulent mixing layers; (3) For the lines of sight associated with multiple high velocity, high ionization components, model the shock parameters for the associated superbubble and SNR to provide more accurate energy input information for hot phase models and galactic halo models. Thus far 49 lines of sight with at least one high velocity component to the C IV lines have been identified; and (4) Obtain higher resolution data for the lines of sight with high velocity components (and a few without) to further refine these models.

Unveiling Vela: time variability of interstellar lines in the direction of the Vela supernova remnant - II. Na D and Ca II

NASA Astrophysics Data System (ADS)

Kameswara Rao, N.; Lambert, David L.; Reddy, Arumalla B. S.; Gupta, Ranjan; Muneer, S.; Singh, Harinder P.

2017-05-01

In a survey conducted between 2011 and 2012 of interstellar Na I D line profiles in the direction of the Vela supernova remnant (SNR), a few lines of sight showed dramatic changes in low-velocity absorption components with respect to profiles from 1993 to 1994 reported by Cha & Sembach. Three stars - HD 63578, HD 68217 and HD 76161 - showed large decrease in strength over the 1993-2012 interval. HD 68217 and HD 76161 are associated with the Vela SNR whereas HD 63578 is associated with γ2 Velorum wind bubble. Here, we present high spectral resolution observations of Ca II K lines obtained with the Southern African Large Telescope towards these three stars along with simultaneous observations of Na I D lines. These new spectra confirm that the Na D interstellar absorption weakened drastically between 1993-1994 and 2011-2012 but show for the first time that the Ca II K line is unchanged between 1993-1994 and 2015. This remarkable contrast between the behaviour of Na D and Ca II K absorption lines is a puzzle concerning gas presumably affected by the outflow from the SNR and the wind from γ2 Velorum.

Some Thoughts on the Implications of Faster-Than-Light Interstellar Space Travel

NASA Astrophysics Data System (ADS)

Crawford, I. A.

1995-09-01

There are reasons for believing that faster-than-light (FTL) interstellar space travel may be consistent with the laws of physics, and a brief review of various FTL travel concepts is presented. It is argued that FTL travel would revolutionise the scientific exploration of the Universe, but would only significantly shorten the Galactic colonisation timescale from the 106 years estimated on the assumption of sub-light interstellar travel if the mass-production of FTL space vehicles proves to be practical. FTL travel would permit the development of interstellar social and political institutions which would probably be impossible otherwise, and may therefore strengthen the 'zoo hypothesis' as an explanation for the apparent absence of extraterrestrial beings in the Solar System.

Flow of foams in two-dimensional disordered porous media

NASA Astrophysics Data System (ADS)

Dollet, Benjamin; Geraud, Baudouin; Jones, Sian A.; Meheust, Yves; Cantat, Isabelle; Institut de Physique de Rennes Team; Geosciences Rennes Team

2015-11-01

Liquid foams are a yield stress fluid with elastic properties. When a foam flow is confined by solid walls, viscous dissipation arises from the contact zones between soap films and walls, giving very peculiar friction laws. In particular, foams potentially invade narrow pores much more efficiently than Newtonian fluids, which is of great importance for enhanced oil recovery. To quantify this effect, we study experimentally flows of foam in a model two-dimensional porous medium, consisting of an assembly of circular obstacles placed randomly in a Hele-Shaw cell, and use image analysis to quantify foam flow at the local scale. We show that bubbles split as they flow through the porous medium, by a mechanism of film pinching during contact with an obstacle, yielding two daughter bubbles per split bubble. We quantify the evolution of the bubble size distribution as a function of the distance along the porous medium, the splitting probability as a function of bubble size, and the probability distribution function of the daughter bubbles. We propose an evolution equation to model this splitting phenomenon and compare it successfully to the experiments, showing how at long distance, the porous medium itself dictates the size distribution of the foam.

Sonar gas flux estimation by bubble insonification: application to methane bubble flux from seep areas in the outer Laptev Sea

NASA Astrophysics Data System (ADS)

Leifer, Ira; Chernykh, Denis; Shakhova, Natalia; Semiletov, Igor

2017-06-01

Sonar surveys provide an effective mechanism for mapping seabed methane flux emissions, with Arctic submerged permafrost seepage having great potential to significantly affect climate. We created in situ engineered bubble plumes from 40 m depth with fluxes spanning 0.019 to 1.1 L s-1 to derive the in situ calibration curve (Q(σ)). These nonlinear curves related flux (Q) to sonar return (σ) for a multibeam echosounder (MBES) and a single-beam echosounder (SBES) for a range of depths. The analysis demonstrated significant multiple bubble acoustic scattering - precluding the use of a theoretical approach to derive Q(σ) from the product of the bubble σ(r) and the bubble size distribution where r is bubble radius. The bubble plume σ occurrence probability distribution function (Ψ(σ)) with respect to Q found Ψ(σ) for weak σ well described by a power law that likely correlated with small-bubble dispersion and was strongly depth dependent. Ψ(σ) for strong σ was largely depth independent, consistent with bubble plume behavior where large bubbles in a plume remain in a focused core. Ψ(σ) was bimodal for all but the weakest plumes. Q(σ) was applied to sonar observations of natural arctic Laptev Sea seepage after accounting for volumetric change with numerical bubble plume simulations. Simulations addressed different depths and gases between calibration and seep plumes. Total mass fluxes (Qm) were 5.56, 42.73, and 4.88 mmol s-1 for MBES data with good to reasonable agreement (4-37 %) between the SBES and MBES systems. The seepage flux occurrence probability distribution function (Ψ(Q)) was bimodal, with weak Ψ(Q) in each seep area well described by a power law, suggesting primarily minor bubble plumes. The seepage-mapped spatial patterns suggested subsurface geologic control attributing methane fluxes to the current state of subsea permafrost.

H2 formation on interstellar dust grains: The viewpoints of theory, experiments, models and observations

NASA Astrophysics Data System (ADS)

Wakelam, Valentine; Bron, Emeric; Cazaux, Stephanie; Dulieu, Francois; Gry, Cécile; Guillard, Pierre; Habart, Emilie; Hornekær, Liv; Morisset, Sabine; Nyman, Gunnar; Pirronello, Valerio; Price, Stephen D.; Valdivia, Valeska; Vidali, Gianfranco; Watanabe, Naoki

2017-12-01

Molecular hydrogen is the most abundant molecule in the universe. It is the first one to form and survive photo-dissociation in tenuous environments. Its formation involves catalytic reactions on the surface of interstellar grains. The micro-physics of the formation process has been investigated intensively in the last 20 years, in parallel of new astrophysical observational and modeling progresses. In the perspectives of the probable revolution brought by the future satellite JWST, this article has been written to present what we think we know about the H2 formation in a variety of interstellar environments.

Unorthodox bubbles when boiling in cold water.

PubMed

Parker, Scott; Granick, Steve

2014-01-01

High-speed movies are taken when bubbles grow at gold surfaces heated spotwise with a near-infrared laser beam heating water below the boiling point (60-70 °C) with heating powers spanning the range from very low to so high that water fails to rewet the surface after bubbles detach. Roughly half the bubbles are conventional: They grow symmetrically through evaporation until buoyancy lifts them away. Others have unorthodox shapes and appear to contribute disproportionately to heat transfer efficiency: mushroom cloud shapes, violently explosive bubbles, and cavitation events, probably stimulated by a combination of superheating, convection, turbulence, and surface dewetting during the initial bubble growth. Moreover, bubbles often follow one another in complex sequences, often beginning with an unorthodox bubble that stirs the water, followed by several conventional bubbles. This large dataset is analyzed and discussed with emphasis on how explosive phenomena such as cavitation induce discrepancies from classical expectations about boiling.

Upper limits on the probability of an interstellar civilization arising in the local Solar neighbourhood

NASA Astrophysics Data System (ADS)

Cartin, Daniel

2015-10-01

At this point in time, there is very little empirical evidence on the likelihood of a space-faring species originating in the biosphere of a habitable world. However, there is a tension between the expectation that such a probability is relatively high (given our own origins on Earth), and the lack of any basis for believing the Solar System has ever been visited by an extraterrestrial colonization effort. From the latter observational fact, this paper seeks to place upper limits on the probability of an interstellar civilization arising on a habitable planet in its stellar system, using a percolation model to simulate the progress of such a hypothetical civilization's colonization efforts in the local Solar neighbourhood. To be as realistic as possible, the actual physical positions and characteristics of all stars within 40 parsecs of the Solar System are used as possible colony sites in the percolation process. If an interstellar civilization is very likely to have such colonization programmes, and they can travel over large distances, then the upper bound on the likelihood of such a species arising per habitable world is of the order of 10-3 on the other hand, if civilizations are not prone to colonize their neighbours, or do not travel very far, then the upper limiting probability is much larger, even of order one.

Interstellar Deuterium, Nitrogen and Oxygen Abundances Toward BD+28(deg) 4211: Results from the Far Ultraviolet Spectroscopic Explorer

NASA Technical Reports Server (NTRS)

Sonneborn, George; Andre, Martial; Oliveira, Cristina; Hebrard, Guillaume; Howk, J. Christopher; Tripp, Todd M.; Chayer, Pierre; Friedman, Scott D.; Kruk, Jeffery W.; Jenkins, Edward B.;

Absorption Reveals and Hydrogen Addition Explains New Interstellar Aldehydes: Propenal and Propanal

NASA Technical Reports Server (NTRS)

Hollis, J. M.; Jewell, P. R.; Lovas, F. J.; Remijan, A.; Mollendal, H.

2004-01-01

New interstellar molecules propenal (CH2CHCHO) and propanal (CH3CH2CHO) have been detected largely in absorption toward the star-forming region Sagittarius B2(N) by means of rotational transitions observed with the 100-m Green Bank Telescope (GBT) operating in the range of 18 GHz (lambda approximately 1.7 cm) to 26 GHz (lambda approximately 1.2 cm). The GBT was also used to observe the previously reported interstellar aldehyde propynal (HC2CHO) in Sagittarius B2(N) which is known for large molecules believed to form on interstellar grains. The presence of these three interstellar aldehydes toward Sagittarius B2(N) strongly suggests that simple hydrogen addition on interstellar grains accounts for successively larger molecular species: from propynal to propenal and from propenal to propanal. Energy sources within Sagittarius B2(N) likely permit the hydrogen addition reactions on grain surfaces to proceed. This work demonstrates that successive hydrogen addition is probably an important chemistry route in the formation of a number of complex interstellar molecules. We also searched for but did not detect the three-carbon sugar glyceraldehyde (CH2OHCHOHCHO).

Synthesis and chirality of amino acids under interstellar conditions.

PubMed

Giri, Chaitanya; Goesmann, Fred; Meinert, Cornelia; Evans, Amanda C; Meierhenrich, Uwe J

2013-01-01

Amino acids are the fundamental building blocks of proteins, the biomolecules that provide cellular structure and function in all living organisms. A majority of amino acids utilized within living systems possess pre-specified orientation geometry (chirality); however the original source for this specific orientation remains uncertain. In order to trace the chemical evolution of life, an appreciation of the synthetic and evolutional origins of the first chiral amino acids must first be gained. Given that the amino acids in our universe are likely to have been synthesized in molecular clouds in interstellar space, it is necessary to understand where and how the first synthesis might have occurred. The asymmetry of the original amino acid synthesis was probably the result of exposure to chiral photons in the form of circularly polarized light (CPL), which has been detected in interstellar molecular clouds. This chirality transfer event, from photons to amino acids, has been successfully recreated experimentally and is likely a combination of both asymmetric synthesis and enantioselective photolysis. A series of innovative studies have reported successful simulation of these environments and afforded production of chiral amino acids under realistic circumstellar and interstellar conditions: irradiation of interstellar ice analogues (CO, CO2, NH3, CH3OH, and H2O) with circularly polarized ultraviolet photons at low temperatures does result in enantiomer enriched amino acid structures (up to 1.3% ee). This topical review summarizes current knowledge and recent discoveries about the simulated interstellar environments within which amino acids were probably formed. A synopsis of the COSAC experiment onboard the ESA cometary mission ROSETTA concludes this review: the ROSETTA mission will soft-land on the nucleus of the comet 67P/Churyumov-Gerasimenko in November 2014, anticipating the first in situ detection of asymmetric organic molecules in cometary ices.

Hubble's Blue Bubble

NASA Image and Video Library

2017-12-08

A large blue bubble with a bright star in the center on a black background filled with stars Sparkling at the center of this beautiful NASA/ESA Hubble Space Telescope image is a Wolf–Rayet star known as WR 31a, located about 30,000 light-years away in the constellation of Carina (The Keel). The distinctive blue bubble appearing to encircle WR 31a is a Wolf–Rayet nebula — an interstellar cloud of dust, hydrogen, helium and other gases. Created when speedy stellar winds interact with the outer layers of hydrogen ejected by Wolf–Rayet stars, these nebulae are frequently ring-shaped or spherical. The bubble — estimated to have formed around 20,000 years ago — is expanding at a rate of around 220,000 kilometers (136,700 miles) per hour! Unfortunately, the lifecycle of a Wolf–Rayet star is only a few hundred thousand years — the blink of an eye in cosmic terms. Despite beginning life with a mass at least 20 times that of the sun, Wolf–Rayet stars typically lose half their mass in less than 100,000 years. And WR 31a is no exception to this case. It will, therefore, eventually end its life as a spectacular supernova, and the stellar material expelled from its explosion will later nourish a new generation of stars and planets. Image credi: ESA/Hubble & NASA, Acknowledgement: Judy Schmidt

Extraterrestrial organic matter: a review

NASA Technical Reports Server (NTRS)

Irvine, W. M.

1998-01-01

We review the nature of the widespread organic material present in the Milky Way Galaxy and in the Solar System. Attention is given to the links between these environments and between primitive Solar System objects and the early Earth, indicating the preservation of organic material as an interstellar cloud collapsed to form the Solar System and as the Earth accreted such material from asteroids, comets and interplanetary dust particles. In the interstellar medium of the Milky Way Galaxy more than 100 molecular species, the bulk of them organic, have been securely identified, primarily through spectroscopy at the highest radio frequencies. There is considerable evidence for significantly heavier organic molecules, particularly polycyclic aromatics, although precise identification of individual species has not yet been obtained. The so-called diffuse interstellar bands are probably important in this context. The low temperature kinetics in interstellar clouds leads to very large isotopic fractionation, particularly for hydrogen, and this signature is present in organic components preserved in carbonaceous chondritic meteorites. Outer belt asteroids are the probable parent bodies of the carbonaceous chondrites, which may contain as much as 5% organic material, including a rich variety of amino acids, purines, pyrimidines, and other species of potential prebiotic interest. Richer in volatiles and hence less thermally processed are the comets, whose organic matter is abundant and poorly characterized. Cometary volatiles, observed after sublimation into the coma, include many species also present in the interstellar medium. There is evidence that most of the Earth's volatiles may have been supplied by a 'late' bombardment of comets and carbonaceous meteorites, scattered into the inner Solar System following the formation of the giant planets. How much in the way of intact organic molecules of potential prebiotic interest survived delivery to the Earth has become an increasingly debated topic over the last several years. The principal source for such intact organics was probably accretion of interplanetary dust particles of cometary origin.

Agitation, Mixing, and Transfers Induced by Bubbles

NASA Astrophysics Data System (ADS)

Risso, Frédéric

2018-01-01

Bubbly flows involve bubbles randomly distributed within a liquid. At large Reynolds number, they experience an agitation that can combine shear-induced turbulence (SIT), large-scale buoyancy-driven flows, and bubble-induced agitation (BIA). The properties of BIA strongly differ from those of SIT. They have been determined from studies of homogeneous swarms of rising bubbles. Regarding the bubbles, agitation is mainly caused by the wake-induced path instability. Regarding the liquid, two contributions must be distinguished. The first one corresponds to the anisotropic flow disturbances generated near the bubbles, principally in the vertical direction. The second one is the almost isotropic turbulence induced by the flow instability through a population of bubbles, which turns out to be the main cause of horizontal fluctuations. Both contributions generate a k-3 spectral subrange and exponential probability density functions. The subsequent issue will be to understand how BIA interacts with SIT.

Blue bubble in Carina

NASA Image and Video Library

2016-02-22

Sparkling at the centre of this beautiful NASA/ESA Hubble Space Telescope image is a Wolf–Rayet star known as WR 31a, located about 30 000 light-years away in the constellation of Carina (The Keel). The distinctive blue bubble appearing to encircle WR 31a, and its uncatalogued stellar sidekick, is a Wolf–Rayet nebula — an interstellar cloud of dust, hydrogen, helium and other gases. Created when speedy stellar winds interact with the outer layers of hydrogen ejected by Wolf–Rayet stars, these nebulae are frequently ring-shaped or spherical. The bubble — estimated to have formed around 20 000 years ago — is expanding at a rate of around 220 000 kilometres per hour! Unfortunately, the lifecycle of a Wolf–Rayet star is only a few hundred thousand years — the blink of an eye in cosmic terms. Despite beginning life with a mass at least 20 times that of the Sun, Wolf–Rayet stars typically lose half their mass in less than 100 000 years. And WR 31a is no exception to this case. It will, therefore, eventually end its life as a spectacular supernova, and the stellar material expelled from its explosion will later nourish a new generation of stars and planets.

Movement of fine particles on an air bubble surface studied using high-speed video microscopy.

PubMed

Nguyen, Anh V; Evans, Geoffrey M

2004-05-01

A CCD high-speed video microscopy system operating at 1000 frames per second was used to obtain direct quantitative measurements of the trajectories of fine glass spheres on the surface of air bubbles. The glass spheres were rendered hydrophobic by a methylation process. Rupture of the intervening water film between a hydrophobic particle and an air bubble with the consequent formation of a three-phase contact was observed. The bubble-particle sliding attachment interaction is not satisfactorily described by the available theories. Surface forces had little effect on the particle sliding with a water film, which ruptured probably due to the submicrometer-sized gas bubbles existing at the hydrophobic particle-water interface.

Ultraviolet gas absorption and dust extinction toward M8

NASA Technical Reports Server (NTRS)

Boggs, Don; Bohm-Vitense, Erika

1990-01-01

Interstellar absorption lines are analyzed using high-resolution IUE spectra of 11 stars in the young cluster NGC 6530 located in the M8 region. High-velocity clouds at -35 km/s and -60 km/s are seen toward all cluster stars. The components arise in gases that are part of large interstellar bubbles centered on the cluster and driven by stellar winds of the most luminous members. Absorption lines of species of different ionization states are separated in velocity. The velocity stratification is best explained as a 'champagne' flow of ionized gas away from the cluster. The C IV/Si IV ratios toward the hotter cluster members are consistent with simple photoionization models if the gas-phase C/Si ratio is increased by preferential accretion onto dust grains. High ion column densities in the central cluster decline with distance from W93, suggesting that radiation from a hot source near W93 has photoionized gas in the central cluster.

Odds of observing the multiverse

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

Dahlen, A.

2010-03-15

Eternal inflation predicts that our observable universe lies within a bubble (or pocket universe) embedded in a volume of inflating space. The interior of the bubble undergoes inflation and standard cosmology, while the bubble walls expand outward and collide with other neighboring bubbles. The collisions provide either an opportunity to make a direct observation of the multiverse or, if they produce unacceptable anisotropy, a threat to inflationary theory. The probability of an observer in our bubble detecting the effects of collisions has an absolute upper bound set by the odds of being in the part of our bubble that liesmore » in the forward light cone of a collision; in the case of collisions with bubbles of identical vacua, this bound is given by the bubble nucleation rate times (H{sub O}/H{sub I}){sup 2}, where H{sub O} is the Hubble scale outside the bubbles and H{sub I} is the scale of the second round of inflation that occurs inside our bubble. Similar results were obtained by Freigovel et al. using a different method for the case of collisions with bubbles of much larger cosmological constant; here, it is shown to hold in the case of collisions with identical bubbles as well.« less

Observing Interstellar and Intergalactic Magnetic Fields

NASA Astrophysics Data System (ADS)

Han, J. L.

2017-08-01

Observational results of interstellar and intergalactic magnetic fields are reviewed, including the fields in supernova remnants and loops, interstellar filaments and clouds, Hii regions and bubbles, the Milky Way and nearby galaxies, galaxy clusters, and the cosmic web. A variety of approaches are used to investigate these fields. The orientations of magnetic fields in interstellar filaments and molecular clouds are traced by polarized thermal dust emission and starlight polarization. The field strengths and directions along the line of sight in dense clouds and cores are measured by Zeeman splitting of emission or absorption lines. The large-scale magnetic fields in the Milky Way have been best probed by Faraday rotation measures of a large number of pulsars and extragalactic radio sources. The coherent Galactic magnetic fields are found to follow the spiral arms and have their direction reversals in arms and interarm regions in the disk. The azimuthal fields in the halo reverse their directions below and above the Galactic plane. The orientations of organized magnetic fields in nearby galaxies have been observed through polarized synchrotron emission. Magnetic fields in the intracluster medium have been indicated by diffuse radio halos, polarized radio relics, and Faraday rotations of embedded radio galaxies and background sources. Sparse evidence for very weak magnetic fields in the cosmic web is the detection of the faint radio bridge between the Coma cluster and A1367. Future observations should aim at the 3D tomography of the large-scale coherent magnetic fields in our Galaxy and nearby galaxies, a better description of intracluster field properties, and firm detections of intergalactic magnetic fields in the cosmic web.

Voyager in-situ and Cassini Remote Measurements Suggest a Bubble-like Shape for the Global Heliosphere

NASA Astrophysics Data System (ADS)

Dialynas, K.; Krimigis, S. M.; Mitchell, D. G.; Decker, R. B.; Roelof, E. C.

2017-12-01

The Low Energy Charged Particle (LECP) in situ measurements from Voyager 1 and Voyager 2 (V1, V2) have revealed the reservoir of ions and electrons that constitute the heliosheath after crossing the termination shock 35 deg north and 32 deg south of the ecliptic plane at 94 and 84 astronomical units (1 AU=1.5x108 km), respectively. In August 2012, at 121.6 AU, V1 crossed the heliopause to enter the interstellar space, while V2 remains in the heliosheath since 2007. The advent of Energetic Neutral Atom (ENA, produced through charge exchange between ions and neutral particles flowing through the heliosphere) imaging, has revealed the global nature of the heliosheath at both high (5.2-55 keV, Cassini/Ion and Neutral Camera-INCA, from 10 AU) and low (<6 keV, Interstellar Boundary Explorer-IBEX, from 1 AU) energies. The presence of the two Voyagers measuring ions locally in the heliosheath contemporaneously with INCA global imaging through ENA in overlapping energy bands provides a powerful tool for examining the spatial, temporal, and spectral evolution of the source hot plasma ions. Here we report 5.2-55 keV ENA global images of the heliosphere from Cassini/INCA and compare them with V1,2/LECP 28-53 keV ions measured within the heliosheath over a 13-year period (2003-2016). The similarity between the time profiles of ENA and ions establish that the heliosheath ions are the source of ENA. These measurements also demonstrate that the heliosphere responds promptly, within 2-3 years, to outward propagating solar wind changes (manifested in solar sunspot numbers and solar wind energy input) in both the upstream (nose) and downstream (tail) hemispheres. These results, taken together with the V1 measurement of a 0.5 nT interstellar magnetic field and the enhanced ratio between particle pressure and magnetic pressure in the heliosheath, constrain the shape of the global heliosphere: by contrast to the magnetosphere-like heliotail (that past modeling broadly assumed for more than 55 years), a more symmetric, diamagnetic bubble-like heliosphere, with few substantial tail-like features is revealed.

Interaction of the Local Interstellar Medium with the Heliosphere: Role of the Interior and Exterior Magnetic Fields

NASA Technical Reports Server (NTRS)

Barnes, Aaron; DeVincenzi, Donald (Technical Monitor)

2000-01-01

A complete model of the global interaction between the solar wind and the local interstellar medium must take account of interstellar neutral atoms, interstellar ionized gas, solar and galactic magnetic fields, galactic and anomalous cosmic rays. For now, however, in view of the many uncertainties about conditions in the interstellar medium, etc., all models must be regarded as highly idealized and incomplete. In the present review I concentrate on the role of magnetic fields of solar and interstellar origin. The former, the interior field, has negligible influence on the unshocked solar wind; the immediate post-shock solar wind is probably low-beta, so that the interior magnetic field is still unimportant, but this situation changes as the plasma flows through the heliosheath, and a ridge of strong magnetic field may form to separate materials of polar and equatorial origin. The exterior (interstellar) field is likely to play an important role in determining the global morphology of the system outside the termination shock. If the exterior field is strong enough, it can compress the heliosphere (although exterior neutral and/or ionized hydrogen may play the dominant role). Even if the interstellar magnetic field does not provide the dominant pressure, its orientation can substantially affect the configuration of the heliosphere, especially the location and orientation of the heliospheric discontinuities. The configurations can be quite different for the situations in which the field and flow are (a) aligned or (b) transverse. Obliquity of the field produces asymmetry in the geometry of the system; in particular the noses of heliopause and interstellar bow shock are shifted away from the interstellar flow direction, and in opposite directions, due to the asymmetric draping of the magnetic field.

Exploring the Dust Content of Galactic Winds with MIPS

NASA Astrophysics Data System (ADS)

Martin, Crystal; Engelbracht, Charles; Gordon, Karl

2005-06-01

This program explores the dust content of galactic winds. Nearly half of all stars in the universe probably form in a starburst event, where high concentrations of supernova explosions drive galactic-scale gaseous outflows. In nearby starburst galaxies, winds have been mapped at radio, optical, and X-ray frequencies revealing bipolar lobes of hot gas laced with cooler filaments bubbling out of the host galaxy. Most of the outflowing material is entrained interstellar gas, so it will remain quite dusty unless the grains are destroyed. Dusty winds have significant implications for the circulation of heavy elements in galaxies, the dust content of the intergalactic medium, and the acceleration of gaseous outflows. GALEX images of scattered ultraviolet light from galactic winds now provide compelling evidence for the survival of some grains. MIPS photometry of starburst winds at 24, 70, and 160 microns can, in principle, measure the dust temperature providing accurate estimates of the amount of dust (e.g. Engelbracht et al. 2004). To date, however, most MIPS observations of starburst galaxies are far too shallow to detect thermal emission from halo dust. The requested observations would provide the most sensitive observations currently possible for a sample of starburst galaxies, selected to span the full range of starburst luminosity and spatial geometry in the local universe.

The North Galactic Pole Rift and the Local Hot Bubble

NASA Technical Reports Server (NTRS)

Snowden, S. L.; Koutroumpa, D.; Kuntz, K. D.; Lallement, R.; Puspitarini, L.

2015-01-01

The North Galactic Pole Rift (NGPR) is one of the few distinct neutral hydrogen clouds at high Galactic latitudes that have well-defined distances. It is located at the edge of the Local Cavity (LC) and provides an important test case for understanding the Local Hot Bubble (LHB), the presumed location for the hot diffuse plasma responsible for much of the observed 1/4 keV emission originating in the solar neighborhood. Using data from the ROSAT All- Sky Survey and the Planck reddening map, we find the path length within the LC (LHB plus Complex of Local Interstellar Clouds) to be 98 plus or minus 27 pc, in excellent agreement with the distance to the NGPR of 98 +/- 6 pc. In addition, we examine another 14 directions that are distributed over the sky where the LC wall is apparently optically thick at 1/4 keV. We find that the data in these directions are also consistent with the LHB model and a uniform emissivity plasma filling most of the LC.

The hydrogen coverage of interstellar PAHs

NASA Technical Reports Server (NTRS)

Barker, J. R.; Cohen, M.; Tielens, Alexander G. G. M.; Allamandola, Louis J.; Barker, J. R.; Barker, J. R.

1986-01-01

The rate at which the CH bond in interstellar Polycyclic Aromatic Hydrocarbons (PAHs) rupture due to the absorption of a UV photon has been calculated. The results show that small PAHs (less than or equal to 25 carbon atoms) are expected to be partially dehydrogenated in regions with intense UV fields, while large PAHs (greater than or equal to 25 atoms) are expected to be completely hydrogenated in those regions. Because estimate of the carbon content of interstellar PAHs lie in the range of 20 to 25 carbon atoms, dehydrogenation is probably not very important. Because of the absence of other emission features besides the 11.3 micrometer feature in ground-based 8 to 13 micrometer spectra, it has been suggested that interstellar PAHs are partially dehydrogenated. However, IRAS 8 to 22 micrometer spectra of most sources that show strong 7.7 and 11.2 micrometer emission features also show a plateau of emission extending from about 11.3 to 14 micrometer. Like the 11.3 micrometer feature, this new feature is attributed to the CH out of plane bending mode in PAHs. This new feature shows that interstellar PAHs are not as dehydrogenated as estimated from ground-based 8 to 13 micrometer spectra. It also constrains the molecular structure of interstellar PAHs. In particular, it seems that very condensed PAHs, such as coronene and circumcoronene, dominate the interstellar PAH mixture as expected from stability arguments.

How a short double-stranded DNA bends

NASA Astrophysics Data System (ADS)

Shin, Jaeoh; Lee, O.-Chul; Sung, Wokyung

2015-04-01

A recent experiment using fluorescence microscopy showed that double-stranded DNA fragments shorter than 100 base pairs loop with the probabilities higher by the factor of 102-106 than predicted by the worm-like chain (WLC) model [R. Vafabakhsh and T. Ha, Science 337, 1101(2012)]. Furthermore, the looping probabilities were found to be nearly independent of the loop size. The results signify a breakdown of the WLC model for DNA mechanics which works well on long length scales and calls for fundamental understanding for stressed DNA on shorter length scales. We develop an analytical, statistical mechanical model to investigate what emerges to the short DNA under a tight bending. A bending above a critical level initiates nucleation of a thermally induced bubble, which could be trapped for a long time, in contrast to the bubbles in both free and uniformly bent DNAs, which are either transient or unstable. The trapped bubble is none other than the previously hypothesized kink, which releases the bending energy more easily as the contour length decreases. It leads to tremendous enhancement of the cyclization probabilities, in a reasonable agreement with experiment.

In vivo bubble nucleation probability in sheep brain tissue.

PubMed

Gateau, J; Aubry, J-F; Chauvet, D; Boch, A-L; Fink, M; Tanter, M

2011-11-21

Gas nuclei exist naturally in living bodies. Their activation initiates cavitation activity, and is possible using short ultrasonic excitations of high amplitude. However, little is known about the nuclei population in vivo, and therefore about the rarefaction pressure required to form bubbles in tissue. A novel method dedicated to in vivo investigations was used here that combines passive and active cavitation detection with a multi-element linear ultrasound probe (4-7 MHz). Experiments were performed in vivo on the brain of trepanated sheep. Bubble nucleation was induced using a focused single-element transducer (central frequency 660 kHz, f-number = 1) driven by a high power (up to 5 kW) electric burst of two cycles. Successive passive recording and ultrafast active imaging were shown to allow detection of a single nucleation event in brain tissue in vivo. Experiments carried out on eight sheep allowed statistical studies of the bubble nucleation process. The nucleation probability was evaluated as a function of the peak negative pressure. No nucleation event could be detected with a peak negative pressure weaker than -12.7 MPa, i.e. one order of magnitude higher than the recommendations based on the mechanical index. Below this threshold, bubble nucleation in vivo in brain tissues is a random phenomenon.

Composition, structure, and chemistry of interstellar dust

NASA Technical Reports Server (NTRS)

Tielens, A. G. G. M.; Allamandola, L. J.

1987-01-01

Different dust components present in the interstellar medium (IM) such as amorphous carbon, polycyclic aromatic hydrocarbons, and those IM components which are organic refractory grains and icy grain mantles are discussed as well as their relative importance. The physical properties of grain surface chemistry are discussed with attention given to the surface structure of materials, the adsorption energy and residence time of species on a grain surface, and the sticking probability. Consideration is also given to the contribution of grains to the gas-phase composition of molecular clouds.

A COMPREHENSIVE SEARCH FOR STELLAR BOWSHOCK NEBULAE IN THE MILKY WAY: A CATALOG OF 709 MID-INFRARED SELECTED CANDIDATES

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

Kobulnicky, Henry A.; Chick, William T.; Schurhammer, Danielle P.

2016-12-01

We identify 709 arc-shaped mid-infrared nebula in 24 μ m Spitzer Space Telescope or 22 μ m Wide Field Infrared Explorer surveys of the Galactic Plane as probable dusty interstellar bowshocks powered by early-type stars. About 20% are visible at 8 μ m or at shorter mid-infrared wavelengths. The vast majority (660) have no previous identification in the literature. These extended infrared sources are strongly concentrated near the Galactic mid-plane, with an angular scale height of ∼0.°6. All host a symmetrically placed star implicated as the source of a stellar wind sweeping up interstellar material. These are candidate “runaway” starsmore » potentially having high velocities in the reference frame of the local medium. Among the 286 objects with measured proper motions, we find an unambiguous excess with velocity vectors aligned with the infrared morphology—kinematic evidence that many of these are “runaway” stars with large peculiar motions responsible for the bowshock signature. We discuss a population of “in situ” bowshocks (∼103 objects) that face giant H ii regions where the relative motions between the star and ISM may be caused by bulk outflows from an overpressured bubble. We also identify ∼58 objects that face 8 μ m bright-rimmed clouds and apparently constitute a sub-class of in situ bowshocks where the stellar wind interacts with a photoevaporative flow (PEF) from an eroding molecular cloud interface (i.e., “PEF bowshocks”). Orientations of the arcuate nebulae exhibit a correlation over small angular scales, indicating that external influences such as H ii regions are responsible for producing some bowshock nebulae. However, the vast majority of the nebulae in this sample appear to be isolated (499 objects) from obvious external influences.« less

Revised Depletions and New Constraints on Interstellar Dust Composition

NASA Technical Reports Server (NTRS)

Snow, Theodore P.; Witt, Adolf N.

1996-01-01

We have reviewed the literature on composition of young stars, both hot and cool, as well as older solar-type stars. We find that all these classes of stars have lower abundances of the heavy elements (specifically C, N, O, Mg, Si, and Fe) than the sun. Therefore studies of interstellar depletions in which the solar composition is used as the reference standard are probably in error, tending to overestimate the total quantities of these elements, hence the depletions. We have revised the depletion estimates, using stellar abundances as the reference standard and making use of recent IS gas-phase abundance measurements. As a result of our revised depletions, we can place new and stringent constraints on several published models for the interstellar dust.

Heliosphere Responds to a Large Solar Wind Intensification: Decisive Observations from IBEX

NASA Astrophysics Data System (ADS)

McComas, D. J.; Dayeh, M. A.; Funsten, H. O.; Heerikhuisen, J.; Janzen, P. H.; Reisenfeld, D. B.; Schwadron, N. A.; Szalay, J. R.; Zirnstein, E. J.

2018-03-01

Our heliosphere—the bubble in the local interstellar medium produced by the Sun’s outflowing solar wind—has finally responded to a large increase in solar wind output and pressure in the second half of 2014. NASA’s Interstellar Boundary Explorer (IBEX) mission remotely monitors the outer heliosphere by observing energetic neutral atoms (ENAs) returning from the heliosheath, the region between the termination shock and heliopause. IBEX observed a significant enhancement in higher energy ENAs starting in late 2016. While IBEX observations over the previous decade reflected a general reduction of ENA intensities, indicative of a deflating heliosphere, new observations show that the large (∼50%), persistent increase in the solar wind dynamic pressure has modified the heliosheath, producing enhanced ENA emissions. The combination of these new observations with simulation results indicate that this pressure is re-expanding our heliosphere, with the termination shock and heliopause already driven outward in the locations closest to the Sun. The timing between the IBEX observations, a large transient pressure enhancement seen by Voyager 2, and the simulations indicates that the pressure increase propagated through the heliosheath, reflected off the heliopause, and the enhanced density of the solar wind filled the heliosheath behind it before generating significantly enhanced ENA emissions. The coming years should see significant changes in anomalous cosmic rays, galactic cosmic radiation, and the filtration of interstellar neutral atoms into the inner heliosphere.

Evaluation of Gas Phase Dispersion in Flotation under Predetermined Hydrodynamic Conditions

NASA Astrophysics Data System (ADS)

Młynarczykowska, Anna; Oleksik, Konrad; Tupek-Murowany, Klaudia

2018-03-01

Results of various investigations shows the relationship between the flotation parameters and gas distribution in a flotation cell. The size of gas bubbles is a random variable with a specific distribution. The analysis of this distribution is useful to make mathematical description of the flotation process. The flotation process depends on many variable factors. These are mainly occurrences like collision of single particle with gas bubble, adhesion of particle to the surface of bubble and detachment process. These factors are characterized by randomness. Because of that it is only possible to talk about the probability of occurence of one of these events which directly affects the speed of the process, thus a constant speed of flotation process. Probability of the bubble-particle collision in the flotation chamber with mechanical pulp agitation depends on the surface tension of the solution, air consumption, degree of pul aeration, energy dissipation and average feed particle size. Appropriate identification and description of the parameters of the dispersion of gas bubbles helps to complete the analysis of the flotation process in a specific physicochemical conditions and hydrodynamic for any raw material. The article presents the results of measurements and analysis of the gas phase dispersion by the size distribution of air bubbles in a flotation chamber under fixed hydrodynamic conditions. The tests were carried out in the Laboratory of Instrumental Methods in Department of Environmental Engineering and Mineral Processing, Faculty of Mining and Geoengineerin, AGH Univeristy of Science and Technology in Krakow.

Dust evolution, a global view: II. Top-down branching, nanoparticle fragmentation and the mystery of the diffuse interstellar band carriers

PubMed Central

2016-01-01

The origin of the diffuse interstellar bands (DIBs), one of the longest-standing mysteries of the interstellar medium (ISM), is explored within the framework of The Heterogeneous dust Evolution Model for Interstellar Solids (THEMIS). The likely nature of the DIB carriers and their evolution is here explored within the framework of the structures and sub-structures inherent to doped hydrogenated amorphous carbon grains in the ISM. Based on the natural aromatic-rich moieties (asphaltenes) recovered from coal and oil, the likely structure of their interstellar analogues is investigated within the context of the diffuse band problem. It is here proposed that the top-down evolution of interstellar carbonaceous grains, and, in particular, a-C(:H) nanoparticles, is at the heart of the formation and evolution of the DIB carriers and their associations with small molecules and radicals, such as C2, C3, CH and CN. It is most probable that the DIBs are carried by dehydrogenated, ionized, hetero-cyclic, olefinic and aromatic-rich moieties that form an integral part of the contiguous structure of hetero-atom-doped hydrogenated amorphous carbon nanoparticles and their daughter fragmentation products. Within this framework, it is proposed that polyene structures in all their variants could be viable DIB carrier candidates. PMID:28083089

Dust evolution, a global view: II. Top-down branching, nanoparticle fragmentation and the mystery of the diffuse interstellar band carriers

NASA Astrophysics Data System (ADS)

Jones, A. P.

2016-12-01

The origin of the diffuse interstellar bands (DIBs), one of the longest-standing mysteries of the interstellar medium (ISM), is explored within the framework of The Heterogeneous dust Evolution Model for Interstellar Solids (THEMIS). The likely nature of the DIB carriers and their evolution is here explored within the framework of the structures and sub-structures inherent to doped hydrogenated amorphous carbon grains in the ISM. Based on the natural aromatic-rich moieties (asphaltenes) recovered from coal and oil, the likely structure of their interstellar analogues is investigated within the context of the diffuse band problem. It is here proposed that the top-down evolution of interstellar carbonaceous grains, and, in particular, a-C(:H) nanoparticles, is at the heart of the formation and evolution of the DIB carriers and their associations with small molecules and radicals, such as C2, C3, CH and CN. It is most probable that the DIBs are carried by dehydrogenated, ionized, hetero-cyclic, olefinic and aromatic-rich moieties that form an integral part of the contiguous structure of hetero-atom-doped hydrogenated amorphous carbon nanoparticles and their daughter fragmentation products. Within this framework, it is proposed that polyene structures in all their variants could be viable DIB carrier candidates.

Eternal inflation, bubble collisions, and the disintegration of the persistence of memory

NASA Astrophysics Data System (ADS)

Freivogel, Ben; Kleban, Matthew; Nicolis, Alberto; Sigurdson, Kris

2009-08-01

We compute the probability distribution for bubble collisions in an inflating false vacuum which decays by bubble nucleation. Our analysis generalizes previous work of Guth, Garriga, and Vilenkin to the case of general cosmological evolution inside the bubble, and takes into account the dynamics of the domain walls that form between the colliding bubbles. We find that incorporating these effects changes the results dramatically: the total expected number of bubble collisions in the past lightcone of a typical observer is N ~ γ Vf/Vi , where γ is the fastest decay rate of the false vacuum, Vf is its vacuum energy, and Vi is the vacuum energy during inflation inside the bubble. This number can be large in realistic models without tuning. In addition, we calculate the angular position and size distribution of the collisions on the cosmic microwave background sky, and demonstrate that the number of bubbles of observable angular size is NLS ~ (Ωk)1/2N, where Ωk is the curvature contribution to the total density at the time of observation. The distribution is almost exactly isotropic.

Bubbles in live-stranded dolphins.

PubMed

Dennison, S; Moore, M J; Fahlman, A; Moore, K; Sharp, S; Harry, C T; Hoppe, J; Niemeyer, M; Lentell, B; Wells, R S

2012-04-07

Bubbles in supersaturated tissues and blood occur in beaked whales stranded near sonar exercises, and post-mortem in dolphins bycaught at depth and then hauled to the surface. To evaluate live dolphins for bubbles, liver, kidneys, eyes and blubber-muscle interface of live-stranded and capture-release dolphins were scanned with B-mode ultrasound. Gas was identified in kidneys of 21 of 22 live-stranded dolphins and in the hepatic portal vasculature of 2 of 22. Nine then died or were euthanized and bubble presence corroborated by computer tomography and necropsy, 13 were released of which all but two did not re-strand. Bubbles were not detected in 20 live wild dolphins examined during health assessments in shallow water. Off-gassing of supersaturated blood and tissues was the most probable origin for the gas bubbles. In contrast to marine mammals repeatedly diving in the wild, stranded animals are unable to recompress by diving, and thus may retain bubbles. Since the majority of beached dolphins released did not re-strand it also suggests that minor bubble formation is tolerated and will not lead to clinically significant decompression sickness.

Preliminary Examination of the Interstellar Collector of Stardust

NASA Technical Reports Server (NTRS)

Westphal, A. J.; Allen, C.; Bastien, R.; Borg, J.; Brenker, F.; Bridges, J.; Brownlee, D. E.; Butterworth, A. L.; Floss, C.; Flynn, G.;

Is there a real-estate bubble in the US?

NASA Astrophysics Data System (ADS)

Zhou, Wei-Xing; Sornette, Didier

2006-02-01

Using a methodology developed in previous papers, we analyze the quarterly average sale prices of new houses sold in the USA as a whole, in the Northeast, Midwest, South, and West of the USA, in each of the 50 states and the District of Columbia of the USA, to determine whether they have grown at a faster-than-exponential rate which we take as the diagnostic of a bubble. We find that 22 states (mostly Northeast and West) exhibit clear-cut signatures of a fast-growing bubble. From the analysis of the S&P 500 Home Index, we conclude that the turning point of the bubble will probably occur around mid-2006.

Photolysis products of CO, NH3 aND H2O and their significance to reactions on interstellar grains

NASA Technical Reports Server (NTRS)

Ferris, J. P.

1986-01-01

With the increase in evidence that interstellar grains are the basic building blocks of comets and with the realization that comet collisions with the earth have probably occured at a much higher frequency than earlier assumed it may be presumed that interstellar dust chemistry played an important role in the early chemistry of the earth. As a part of the study of the photochemical processes taking place on interstellar grains the photolysis of mixtures of CO, NH3 and H2O was performed at 10 K, 77K and 298K. The reaction products were determined by GC/MS and HPLC analysis to be lactic acid, glycolic acid, hydroxyacetamide, urea, biuret, oxamic acid, oxamide, glyceric acid and glyceramide. Ethylene glycol and glycerol were also detected but is is not clear at present whether these are true photoproducts or contaminants. The mechanism of formation of these molecules are discussed as well as their possible significance to the origins of life.

Formation of cyanoallene (buta-2, 3-dienenitrile) in the interstellar medium: a quantum chemical and spectroscopic study

NASA Astrophysics Data System (ADS)

Singh, Amresh; Shivani; Misra, Alka; Tandon, Poonam

2014-03-01

The interstellar medium, filling the vast space between stars, is a rich reservoir of molecular material ranging from simple diatomic molecules to more complex, astrobiologically important molecules such as vinylcyanide, methylcyanodiaccetylene, cyanoallene, etc. Interstellar molecular cyanoallene is one of the most stable isomers of methylcynoacetylene. An attempt has been made to explore the possibility of forming cyanoallene in interstellar space by radical-radical and radical-molecule interaction schemes in the gaseous phase. The formation of cyanoallene starting from some simple, neutral interstellar molecules and radicals has been studied using density functional theory. The reaction energies and structures of the reactants and products show that the formation of cyanoallene is possible in the gaseous phase. Both of the considered reaction paths are totally exothermic and barrierless, thus giving rise to a high probability of occurrence. Rate constants for each step in the formation process of cyanoallene in both the reaction paths are estimated. A full vibrational analysis has been attempted for cyanoallene in the harmonic and anharmonic approximations. Anharmonic spectroscopic parameters such as rotational constants, rotation-vibration coupling constants and centrifugal distortion constants have been calculated.

Optical observations of nearby interstellar gas

NASA Astrophysics Data System (ADS)

Frisch, P. C.; York, D. G.

1984-11-01

Observations indicated that a cloud with a heliocentric velocity of approximately -28 km/s and a hydrogen column density that possibly could be on the order of, or greater than, 5 x 10 to the 19 power/square cm is located within the nearest 50 to 80 parsecs in the direction of Ophiuchus. This is a surprisingly large column density of material for this distance range. The patchy nature of the absorption from the cloud indicates that it may not be a feature with uniform properties, but rather one with small scale structure which includes local enhancements in the column density. This cloud is probably associated with the interstellar cloud at about the same velocity in front of the 20 parsec distant star alpha Oph (Frisch 1981, Crutcher 1982), and the weak interstellar polarization found in stars as near as 35 parsecs in this general region (Tinbergen 1982). These data also indicate that some portion of the -14 km/s cloud also must lie within the 100 parsec region. Similar observations of both Na1 and Ca2 interstellar absorption features were performed in other lines of sight. Similar interstellar absorption features were found in a dozen stars between 20 and 100 parsecs of the Sun.

Optical Observations of Nearby Interstellar Gas

NASA Technical Reports Server (NTRS)

Frisch, P. C.; York, D. G.

1984-01-01

Observations indicated that a cloud with a heliocentric velocity of approximately -28 km/s and a hydrogen column density that possibly could be on the order of, or greater than, 5 x 10 to the 19 power/square cm is located within the nearest 50 to 80 parsecs in the direction of Ophiuchus. This is a surprisingly large column density of material for this distance range. The patchy nature of the absorption from the cloud indicates that it may not be a feature with uniform properties, but rather one with small scale structure which includes local enhancements in the column density. This cloud is probably associated with the interstellar cloud at about the same velocity in front of the 20 parsec distant star alpha Oph (Frisch 1981, Crutcher 1982), and the weak interstellar polarization found in stars as near as 35 parsecs in this general region (Tinbergen 1982). These data also indicate that some portion of the -14 km/s cloud also must lie within the 100 parsec region. Similar observations of both Na1 and Ca2 interstellar absorption features were performed in other lines of sight. Similar interstellar absorption features were found in a dozen stars between 20 and 100 parsecs of the Sun.

Final Reports of the Stardust ISPE: Seven Probable Interstellar Dust Particles

NASA Technical Reports Server (NTRS)

Allen, Carlton; Sans Tresseras, Juan-Angel; Westphal, Andrew J.; Stroud, Rhonda M.; Bechtel, Hans A.; Brenker, Frank E.; Butterworth, Anna L.; Flynn, George J.; Frank, David R.; Gainsforth, Zack;

Interstellar Travel and Galactic Colonization: Insights from Percolation Theory and the Yule Process

NASA Astrophysics Data System (ADS)

Lingam, Manasvi

2016-06-01

In this paper, percolation theory is employed to place tentative bounds on the probability p of interstellar travel and the emergence of a civilization (or panspermia) that colonizes the entire Galaxy. The ensuing ramifications with regard to the Fermi paradox are also explored. In particular, it is suggested that the correlation function of inhabited exoplanets can be used to observationally constrain p in the near future. It is shown, by using a mathematical evolution model known as the Yule process, that the probability distribution for civilizations with a given number of colonized worlds is likely to exhibit a power-law tail. Some of the dynamical aspects of this issue, including the question of timescales and generalizing percolation theory, were also studied. The limitations of these models, and other avenues for future inquiry, are also outlined.

Bayes to the Rescue: Continuous Positive Airway Pressure Has Less Mortality Than High-Flow Oxygen.

PubMed

Modesto I Alapont, Vicent; Khemani, Robinder G; Medina, Alberto; Del Villar Guerra, Pablo; Molina Cambra, Alfred

2017-02-01

The merits of high-flow nasal cannula oxygen versus bubble continuous positive airway pressure are debated in children with pneumonia, with suggestions that randomized controlled trials are needed. In light of a previous randomized controlled trial showing a trend for lower mortality with bubble continuous positive airway pressure, we sought to determine the probability that a new randomized controlled trial would find high-flow nasal cannula oxygen superior to bubble continuous positive airway pressure through a "robust" Bayesian analysis. Sample data were extracted from the trial by Chisti et al, and requisite to "robust" Bayesian analysis, we specified three prior distributions to represent clinically meaningful assumptions. These priors (reference, pessimistic, and optimistic) were used to generate three scenarios to represent the range of possible hypotheses. 1) "Reference": we believe bubble continuous positive airway pressure and high-flow nasal cannula oxygen are equally effective with the same uninformative reference priors; 2) "Sceptic on high-flow nasal cannula oxygen": we believe that bubble continuous positive airway pressure is better than high-flow nasal cannula oxygen (bubble continuous positive airway pressure has an optimistic prior and high-flow nasal cannula oxygen has a pessimistic prior); and 3) "Enthusiastic on high-flow nasal cannula oxygen": we believe that high-flow nasal cannula oxygen is better than bubble continuous positive airway pressure (high-flow nasal cannula oxygen has an optimistic prior and bubble continuous positive airway pressure has a pessimistic prior). Finally, posterior empiric Bayesian distributions were obtained through 100,000 Markov Chain Monte Carlo simulations. In all three scenarios, there was a high probability for more death from high-flow nasal cannula oxygen compared with bubble continuous positive airway pressure (reference, 0.98; sceptic on high-flow nasal cannula oxygen, 0.982; enthusiastic on high-flow nasal cannula oxygen, 0.742). The posterior 95% credible interval on the difference in mortality identified a future randomized controlled trial would be extremely unlikely to find a mortality benefit for high-flow nasal cannula oxygen over bubble continuous positive airway pressure, regardless of the scenario. Interpreting these findings using the "range of practical equivalence" framework would recommend rejecting the hypothesis that high-flow nasal cannula oxygen is superior to bubble continuous positive airway pressure for these children. For children younger than 5 years with pneumonia, high-flow nasal cannula oxygen has higher mortality than bubble continuous positive airway pressure. A future randomized controlled trial in this population is unlikely to find high-flow nasal cannula oxygen superior to bubble continuous positive airway pressure.

Extreme conditions in a dissolving air nanobubble

NASA Astrophysics Data System (ADS)

Yasui, Kyuichi; Tuziuti, Toru; Kanematsu, Wataru

2016-07-01

Numerical simulations of the dissolution of an air nanobubble in water have been performed taking into account the effect of bubble dynamics (inertia of the surrounding liquid). The presence of stable bulk nanobubbles is not assumed in the present study because the bubble radius inevitably passes the nanoscale in the complete dissolution of a bubble. The bubble surface is assumed to be clean because attachment of hydrophobic materials on the bubble surface could considerably change the gas diffusion rate. The speed of the bubble collapse (the bubble wall speed) increases to about 90 m/s or less. The shape of a bubble is kept nearly spherical because the amplitude of the nonspherical component of the bubble shape is negligible compared to the instantaneous bubble radius. In other words, a bubble never disintegrates into daughter bubbles during the dissolution. At the final moment of the dissolution, the temperature inside a bubble increases to about 3000 K due to the quasiadiabatic compression. The bubble temperature is higher than 1000 K only for the final 19 ps. However, the Knudsen number is more than 0.2 for this moment, and the error associated with the continuum model should be considerable. In the final 2.3 ns, only nitrogen molecules are present inside a bubble as the solubility of nitrogen is the lowest among the gas species. The radical formation inside a bubble is negligible because the probability of nitrogen dissociation is only on the order of 10-15. The pressure inside a bubble, as well as the liquid pressure at the bubble wall, increases to about 5 GPa at the final moment of dissolution. The pressure is higher than 1 GPa for the final 0.7 ns inside a bubble and for the final 0.6 ns in the liquid at the bubble wall. The liquid temperature at the bubble wall increases to about 360 K from 293 K at the final stage of the complete dissolution.

Infrared emission from hydrogenated amorphous carbon and amorphous carbon grains in the interstellar medium

NASA Technical Reports Server (NTRS)

Duley, W. W.; Jones, A. P.; Taylor, S. D.; Williams, D. A.

1993-01-01

The correlations deduced by Boulanger et al. (1990) from IRAS maps of the Chamaeleon, Taurus and Ursa Major molecular cloud complexes are interpreted in terms of the evolutionary hydrogenated amorphous carbon model of interstellar dust. In particular, regions of relatively strong 12-micron emission may be regions where recently accreted carbon is being converted by ambient UV to small PAHs in situ. Regions of weak 12-micron emission are probably quiescent regions where carbon has been annealed to amorphous carbon. Observational consequences of these inferences are briefly described.

Calculations concerning the HCO(+)/HOC(+) abundance ratio in dense interstellar clouds

NASA Technical Reports Server (NTRS)

Defrees, D. J.; Mclean, A. D.; Herbst, E.

1984-01-01

Calculations have been performed to determine the rate coefficients of several reactions involved in both the formation and depletion of interstellar HCO(+) and HOC(+). The abundance of HOC(+) deduced from these calculations is consistent with the tentative identification of HOC(+) in Sgr B2 by Woods et al. (1983). The large HCO(+)/HOC(+) abundance ratio observed by Woods et al. is due at least in part to a more rapid formation rate for HCO(+) and probably due as well to a more rapid depletion rate for HOC(+).

Modelling chemical reactions in dc plasma inside oxygen bubbles in water

NASA Astrophysics Data System (ADS)

Takeuchi, N.; Ishii, Y.; Yasuoka, K.

2012-02-01

Plasmas generated inside oxygen bubbles in water have been developed for water purification. Zero-dimensional numerical simulations were used to investigate the chemical reactions in plasmas driven by dc voltage. The numerical and experimental results of the concentrations of hydrogen peroxide and ozone in the solution were compared with a discharge current between 1 and 7 mA. Upon increasing the water vapour concentration inside bubbles, we saw from the numerical results that the concentration of hydrogen peroxide increased with discharge current, whereas the concentration of ozone decreased. This finding agreed with the experimental results. With an increase in the discharge current, the heat flux from the plasma to the solution increased, and a large amount of water was probably vaporized into the bubbles.

Plants in Space

NASA Astrophysics Data System (ADS)

Tomic, A. T.

2018-04-01

I do not believe that humans in current form are able to reach any interstellar distances. Probably genetic and cyber biology will come up with the solutions, but until then we still can try to grow plants in space.

Observations of O VI Emission from the Diffuse Interstellar Medium

NASA Technical Reports Server (NTRS)

Shelton, R. L.; Kruk, J. W.; Murphy, E. M.; Andersson, B. G.; Blair, W. P.; Dixon, W. V.; Edelstein, J.; Fullerton, A. W.; Gry, C.; Howk, J. C.;

Interstellar Travel and Galactic Colonization: Insights from Percolation Theory and the Yule Process.

PubMed

Lingam, Manasvi

2016-06-01

In this paper, percolation theory is employed to place tentative bounds on the probability p of interstellar travel and the emergence of a civilization (or panspermia) that colonizes the entire Galaxy. The ensuing ramifications with regard to the Fermi paradox are also explored. In particular, it is suggested that the correlation function of inhabited exoplanets can be used to observationally constrain p in the near future. It is shown, by using a mathematical evolution model known as the Yule process, that the probability distribution for civilizations with a given number of colonized worlds is likely to exhibit a power-law tail. Some of the dynamical aspects of this issue, including the question of timescales and generalizing percolation theory, were also studied. The limitations of these models, and other avenues for future inquiry, are also outlined. Complex life-Extraterrestrial life-Panspermia-Life detection-SETI. Astrobiology 16, 418-426.

Statistics of equivalent width data and new oscillator strengths for Si II, Fe II, and Mn II. [in interstellar medium

NASA Technical Reports Server (NTRS)

Van Buren, Dave

1986-01-01

Equivalent width data from Copernicus and IUE appear to have an exponential, rather than a Gaussian distribution of errors. This is probably because there is one dominant source of error: the assignment of the background continuum shape. The maximum likelihood method of parameter estimation is presented for the case of exponential statistics, in enough generality for application to many problems. The method is applied to global fitting of Si II, Fe II, and Mn II oscillator strengths and interstellar gas parameters along many lines of sight. The new values agree in general with previous determinations but are usually much more tightly constrained. Finally, it is shown that care must be taken in deriving acceptable regions of parameter space because the probability contours are not generally ellipses whose axes are parallel to the coordinate axes.

Numerical studies on the link between radioisotopic signatures on Earth and the formation of the Local Bubble. I. 60Fe transport to the solar system by turbulent mixing of ejecta from nearby supernovae into a locally homogeneous interstellar medium

NASA Astrophysics Data System (ADS)

Schulreich, M. M.; Breitschwerdt, D.; Feige, J.; Dettbarn, C.

2017-08-01

Context. The discovery of radionuclides like 60Fe with half-lives of million years in deep-sea crusts and sediments offers the unique possibility to date and locate nearby supernovae. Aims: We want to quantitatively establish that the 60Fe enhancement is the result of several supernovae which are also responsible for the formation of the Local Bubble, our Galactic habitat. Methods: We performed three-dimensional hydrodynamic adaptive mesh refinement simulations (with resolutions down to subparsec scale) of the Local Bubble and the neighbouring Loop I superbubble in different homogeneous, self-gravitating environments. For setting up the Local and Loop I superbubble, we took into account the time sequence and locations of the generating core-collapse supernova explosions, which were derived from the mass spectrum of the perished members of certain stellar moving groups. The release of 60Fe and its subsequent turbulent mixing process inside the superbubble cavities was followed via passive scalars, where the yields of the decaying radioisotope were adjusted according to recent stellar evolution calculations. Results: The models are able to reproduce both the timing and the intensity of the 60Fe excess observed with rather high precision, provided that the external density does not exceed 0.3 cm-3 on average. Thus the two best-fit models presented here were obtained with background media mimicking the classical warm ionised and warm neutral medium. We also found that 60Fe (which is condensed onto dust grains) can be delivered to Earth via two physical mechanisms: either through individual fast-paced supernova blast waves, which cross the Earth's orbit sometimes even twice as a result of reflection from the Local Bubble's outer shell, or, alternatively, through the supershell of the Local Bubble itself, injecting the 60Fe content of all previous supernovae at once, but over a longer time range.

Observational Evidence For The Comet-Like Heliosphere

NASA Astrophysics Data System (ADS)

Bzowski, M.; Czechowski, A.; Funsten, H. O.; Grygorczuk, J.; Heerikhuisen, J.; Kubiak, M. A.; Moebius, E.; McComas, D. J.; Schwadron, N.; Sokol, J. M.; Swaczyna, P.; Zirnstein, E.

2017-12-01

The shape of the heliosphere is a subject of ongoing debate. The traditional comet-like image has recently been challenged by ideas of croissant- or bubble-like forms. Here we seek to resolve this debate by confronting available observational evidence with global modeling. Several MHD models of a comet-like heliosphere were used to simulate the radius and center of the IBEX Ribbon to fit the direction and intensity of the interstellar magnetic field (ISMF). These models assumed the secondary ENA emission mechanism, which was recently strengthened due to direct measurement of the distance to the Ribbon source most likely just beyond the heliopause. The same mechanism explains the dependence of the Ribbon center position on energy due to the latitudinal structure of solar wind. The obtained ISMF vector agrees among these models and is consistent with the draped IMF measured by Voyager. Independently, we have shown by modeling that the Warm Breeze discovered by IBEX is naturally created in the outer heliosheath due to charge-exchange between interstellar He+ ions and He atoms. Now we simulate the Warm Breeze for various directions and intensities of the local IMF and we find that the simulation results are in best agreement with IBEX observations for the IMF vector obtained from the above-mentioned Ribbon analyses and Voyager measurements. These arguments, along with the co-planarity of the inflow directions of interstellar neutral H, He, O, and the Warm Breeze, directions of the Ribbon center and ISMF, as well as measurements of the plasma flow directions in the IHS by Voyager 2 indicate the existence of a common plane of approximate mirror symmetry of the heliosphere, defined by the directions of ISMF and the Sun's motion through the local interstellar medium. This suggests that the global structure of the outer heliosphere mostly results from the conditions in the local interstellar medium and the Sun's velocity. This evidence, obtained from very different spacecraft and measurement techniques, supports a homogeneous and consistent picture of the heliosphere with a comet-like shape and organized by the plane of approximate mirror symmetry.

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

Wood, Brian E.; Müller, Hans-Reinhard; Bzowski, Maciej

We explore the possibility that interstellar O and Ne may be contributing to the particle signal from the GAS instrument on Ulysses, which is generally assumed to be entirely He. Motivating this study is the recognition that an interstellar temperature higher than any previously estimated from Ulysses data could potentially resolve a discrepancy between Ulysses He measurements and those from the Interstellar Boundary Explorer (IBEX). Contamination by O and Ne could lead to Ulysses temperature measurements that are too low. We estimate the degree of O and Ne contamination necessary to increase the inferred Ulysses temperature to 8500 K, whichmore » would be consistent with both the Ulysses and IBEX data given the same interstellar flow speed. We find that producing the desired effect requires a heavy element contamination level of ∼9% of the total Ulysses/GAS signal. However, this degree of heavy element contribution is about an order of magnitude higher than expected based on our best estimates of detection efficiencies, ISM abundances, and heliospheric survival probabilities, making it unlikely that heavy element contamination is significantly affecting temperatures derived from Ulysses data.« less

Radical formation, chemical processing, and explosion of interstellar grains

NASA Technical Reports Server (NTRS)

Greenberg, J. M.

1976-01-01

The ultraviolet radiation in interstellar space is shown to create a sufficient steady-state density of free radicals in the grain mantle material consisting of oxygen, carbon, nitrogen, and hydrogen to satisfy the critical condition for initiation of chain reactions. The criterion for minimum critical particle size for maintaining the chain reaction is of the order of the larger grain sizes in a distribution satisfying the average extinction and polarization measures. The triggering of the explosion of interstellar grains leading to the ejection of complex interstellar molecules is shown to be most probable where the grains are largest and where radiation is suddenly introduced; i.e., in regions of new star formation. Similar conditions prevail at the boundaries between very dark clouds and H II regions. When the energy released by the chemical activity of the free radicals is inadequate to explode the grain, the resulting mantle material must consist of extremely large organic molecules which are much more resistant to the hostile environment of H II regions than the classical dirty-ice mantles made up of water, methane, and ammonia.

DESPOTIC - a new software library to Derive the Energetics and SPectra of Optically Thick Interstellar Clouds

NASA Astrophysics Data System (ADS)

Krumholz, Mark R.

2014-01-01

I describe DESPOTIC, a code to Derive the Energetics and SPectra of Optically Thick Interstellar Clouds. DESPOTIC represents such clouds using a one-zone model, and can calculate line luminosities, line cooling rates, and in restricted cases line profiles using an escape probability formalism. It also includes approximate treatments of the dominant heating, cooling and chemical processes for the cold interstellar medium, including cosmic ray and X-ray heating, grain photoelectric heating, heating of the dust by infrared and ultraviolet radiation, thermal cooling of the dust, collisional energy exchange between dust and gas, and a simple network for carbon chemistry. Based on these heating, cooling and chemical rates, DESPOTIC can calculate clouds' equilibrium gas and dust temperatures, equilibrium carbon chemical state and time-dependent thermal and chemical evolution. The software is intended to allow rapid and interactive calculation of clouds' characteristic temperatures, identification of their dominant heating and cooling mechanisms and prediction of their observable spectra across a wide range of interstellar environments. DESPOTIC is implemented as a PYTHON package, and is released under the GNU General Public License.

H2-rich interstellar grain mantles: An equilibrium description

NASA Technical Reports Server (NTRS)

Dissly, Richard W.; Allen, Mark; Anicich, Vincent G.

1994-01-01

Experiments simulating the codeposition of molecular hydrogen and water ice on interstellar grains demonstrate that amorphous water ice at 12 K can incorporate a substantial amount of H2, up to a mole ratio of H2/H2O = 0.53. We find that the physical behavior of approximately 80% of the hydrogen can be explained satisfactorily in terms of an equilibrium population, thermodynamically governed by a wide distribution of binding site energies. Such a description predicts that gas phase accretion could lead to mole fractions of H2 in interstellar grain mantles of nearly 0.3; for the probable conditions of WL5 in the rho Ophiuchi cloud, an H2 mole fraction of between 0.05 and 0.3 is predicted, in possible agreement with the observed abundance reported by Sandford, Allamandola, & Geballe. Accretion of gas phase H2 onto grain mantles, rather than photochemical production of H2 within the ice, could be a general explanation for frozen H2 in interstellar ices. We speculate on the implications of such a composition for grain mantle chemistry and physics.

The variance of dispersion measure of high-redshift transient objects as a probe of ionized bubble size during reionization

NASA Astrophysics Data System (ADS)

Yoshiura, Shintaro; Takahashi, Keitaro

2018-01-01

The dispersion measure (DM) of high-redshift (z ≳ 6) transient objects such as fast radio bursts can be a powerful tool to probe the intergalactic medium during the Epoch of Reionization. In this paper, we study the variance of the DMs of objects with the same redshift as a potential probe of the size distribution of ionized bubbles. We calculate the DM variance with a simple model with randomly distributed spherical bubbles. It is found that the DM variance reflects the characteristics of the probability distribution of the bubble size. We find that the variance can be measured precisely enough to obtain the information on the typical size with a few hundred sources at a single redshift.

On The Origin Of Two-Shell Supernova Remnants

NASA Astrophysics Data System (ADS)

Gvaramadze, V. V.

2006-08-01

It is known that proper motion of massive stars causes them to explode far from the geometric centers of their wind-driven bubbles and thereby affects the symmetry of the resulting diffuse supernova remnants (SNRs). We use this fact to explain the origin of SNRs consisting of two partially overlapping shells (e.g. 3C 400.2, Cygnus Loop, Kes32, etc.), whose unusual morphology is usually treated in terms of the collision (or superposition) of two separate SNRs or breakout phenomena in a region with a density discontinuity. We propose that a SNR of this type is a natural consequence of an off-centered cavity supernova (SN) explosion of a moving massive star, which ended its evolution near the edge of the main-sequence (MS) wind-driven bubble. Our proposal implies that one of the shells is the former MS bubble reenergized by the SN blast wave. The second shell, however, could originate in two somewhat different ways, depending on the initial mass of the SN progenitor star. It could be a shell swept-up by the SN blast wave expanding through the unperturbed ambient interstellar medium if the massive star ends its evolution as a red supergiant (RSG). Or it could be the remainder of a pre-existing shell (adjacent to the MS bubble) swept-up by the fast progenitor's wind during the late evolutionary phases if after the RSG phase the star evolves through the Wolf-Rayet phase. In both cases the resulting (two-shell) SNR should be associated only with one (young) neutron star (thus one can somewhat improve the statistics of neutron star/SNR associations since the two-shell SNRs are quite numerous). We discuss several criteria to discern the SNRs formed by SN explosion after the RSG or WR phase.

Direct spectroscopic evidence for ionized polycyclic aromatic hydrocarbons in the interstellar medium.

PubMed

Sloan, G C; Hayward, T L; Allamandola, L J; Bregman, J D; DeVito, B; Hudgins, D M

1999-03-01

Long-slit 8-13 micrometers spectroscopy of the nebula around NGC 1333 SVS 3 reveals spatial variations in the strength and shape of emission features that are probably produced by polycyclic aromatic hydrocarbons (PAHs). Close to SVS 3, the 11.2 micrometers feature develops an excess at approximately 10.8-11.0 micrometers and a feature appears at approximately 10 micrometers. These features disappear with increasing distance from the central source, and they show striking similarities to recent laboratory data of PAH cations, providing the first identification of emission features arising specifically from ionized PAHs in the interstellar medium.

Life beyond the solar system.

NASA Technical Reports Server (NTRS)

Sagan, C.

1972-01-01

Review of some of the highlights and more recent developments in the search for extraterrestrial intelligence. The first major problem is one of the generality of the formation of planetary systems. Observations of the nearest stars which are not members of binary or multiple stars indicates that fully half have companions of planetary mass. The presence of organic compounds in meteorites, probably in Jovian planets, in comets, in the interstellar medium, and in cool stars implies that the production of organic compounds essential for the origin of life should be pervasive throughout the universe. Possibilities of interstellar communication are discussed.

Segregating gas from melt: an experimental study of the Ostwald ripening of vapor bubbles in magmas

USGS Publications Warehouse

Lautze, Nicole C.; Sisson, Thomas W.; Mangan, Margaret T.; Grove, Timothy L.

2011-01-01

Diffusive coarsening (Ostwald ripening) of H2O and H2O-CO2 bubbles in rhyolite and basaltic andesite melts was studied with elevated temperature–pressure experiments to investigate the rates and time spans over which vapor bubbles may enlarge and attain sufficient buoyancy to segregate in magmatic systems. Bubble growth and segregation are also considered in terms of classical steady-state and transient (non-steady-state) ripening theory. Experimental results are consistent with diffusive coarsening as the dominant mechanism of bubble growth. Ripening is faster in experiments saturated with pure H2O than in those with a CO2-rich mixed vapor probably due to faster diffusion of H2O than CO2 through the melt. None of the experimental series followed the time1/3 increase in mean bubble radius and time-1 decrease in bubble number density predicted by classical steady-state ripening theory. Instead, products are interpreted as resulting from transient regime ripening. Application of transient regime theory suggests that bubbly magmas may require from days to 100 years to reach steady-state ripening conditions. Experimental results, as well as theory for steady-state ripening of bubbles that are immobile or undergoing buoyant ascent, indicate that diffusive coarsening efficiently eliminates micron-sized bubbles and would produce mm-sized bubbles in 102–104 years in crustal magma bodies. Once bubbles attain mm-sizes, their calculated ascent rates are sufficient that they could transit multiple kilometers over hundreds to thousands of years through mafic and silicic melt, respectively. These results show that diffusive coarsening can facilitate transfer of volatiles through, and from, magmatic systems by creating bubbles sufficiently large for rapid ascent.

Effect of Slotted Anode on Gas Bubble Behaviors in Aluminum Reduction Cell

NASA Astrophysics Data System (ADS)

Sun, Meijia; Li, Baokuan; Li, Linmin; Wang, Qiang; Peng, Jianping; Wang, Yaowu; Cheung, Sherman C. P.

2017-12-01

In the aluminum reduction cells, gas bubbles are generated at the bottom of the anode which eventually reduces the effective current contact area and the system efficiency. To encourage the removal of gas bubbles, slotted anode has been proposed and increasingly adopted by some industrial aluminum reduction cells. Nonetheless, the exact gas bubble removal mechanisms are yet to be fully understood. A three-dimensional (3D) transient, multiphase flow mathematical model coupled with magnetohydrodynamics has been developed to investigate the effect of slotted anode on the gas bubble movement. The Eulerian volume of fluid approach is applied to track the electrolyte (bath)-molten aluminum (metal) interface. Meanwhile, the Lagrangian discrete particle model is employed to handle the dynamics of gas bubbles with considerations of the buoyancy force, drag force, virtual mass force, and pressure gradient force. The gas bubble coalescence process is also taken into account based on the O'Rourke's algorithm. The two-way coupling between discrete bubbles and fluids is achieved by the inter-phase momentum exchange. Numerical predictions are validated against the anode current variation in an industrial test. Comparing the results using slotted anode with the traditional one, the time-averaged gas bubble removal rate increases from 36 to 63 pct; confirming that the slotted anode provides more escaping ways and shortens the trajectories for gas bubbles. Furthermore, the slotted anode also reduces gas bubble's residence time and the probability of coalescence. Moreover, the bubble layer thickness in aluminum cell with slotted anode is reduced about 3.5 mm (17.4 pct), so the resistance can be cut down for the sake of energy saving and the metal surface fluctuation amplitude is significantly reduced for the stable operation due to the slighter perturbation with smaller bubbles.

Reheating-volume measure in the string theory landscape

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

Winitzki, Sergei

2008-12-15

I recently proposed the ''reheating-volume'' (RV) prescription as a possible solution to the measure problem in ''multiverse'' cosmology. The goal of this work is to extend the RV measure to scenarios involving bubble nucleation, such as the string theory landscape. In the spirit of the RV prescription, I propose to calculate the distribution of observable quantities in a landscape that is conditioned in probability to nucleate a finite total number of bubbles to the future of an initial bubble. A general formula for the relative number of bubbles of different types can be derived. I show that the RV measuremore » is well defined and independent of the choice of the initial bubble type, as long as that type supports further bubble nucleation. Applying the RV measure to a generic landscape, I find that the abundance of Boltzmann brains is always negligibly small compared with the abundance of ordinary observers in the bubbles of the same type. As an illustration, I present explicit results for a toy landscape containing four vacuum states, and for landscapes with a single high-energy vacuum and a large number of low-energy vacua.« less

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

Liang, Linyun; Mei, Zhi-Gang; Yacout, Abdellatif M.

We have developed a mesoscale phase-field model for studying the effect of recrystallization on the gas-bubble-driven swelling in irradiated U-Mo alloy fuel. The model can simulate the microstructural evolution of the intergranular gas bubbles on the grain boundaries as well as the recrystallization process. Our simulation results show that the intergranular gas-bubble-induced fuel swelling exhibits two stages: slow swelling kinetics before recrystallization and rapid swelling kinetics with recrystallization. We observe that the recrystallization can significantly expedite the formation and growth of gas bubbles at high fission densities. The reason is that the recrystallization process increases the nucleation probability of gasmore » bubbles and reduces the diffusion time of fission gases from grain interior to grain boundaries by increasing the grain boundary area and decreasing the diffusion distance. The simulated gas bubble shape, size distribution, and density on the grain boundaries are consistent with experimental measurements. We investigate the effect of the recrystallization on the gas-bubble-driven fuel swelling in UMo through varying the initial grain size and grain aspect ratio. We conclude that the initial microstructure of fuel, such as grain size and grain aspect ratio, can be used to effectively control the recrystallization and therefore reduce the swelling in U-Mo fuel.« less

Gas-Liquid Separation Strategies in Microgravity Environment

NASA Technical Reports Server (NTRS)

Antar, Basil N.; Reiss, Donald A.; Lehman, Daniel

2006-01-01

Bubble entrainment in liquids represents a serious problem in the microgravity environment. Whenever bubbles are entrained in a liquid,they tend to remain stationary in the liquid bulk in the absence of any external forcing. This is due to the reduction or complete absence of the buoyancy force in the microgravity environment, Thus the buoyancy force can not the be exploited to place the bubbles at the top of the liquid volume as in Ig(sub o) conditions. This situation represents a serious drawback in many space based engineering and scientific applications. We have demonstrated in a series of low gravity experiments conducted during parabolic flight on board aircraft that bubbles can be controlled in such a manner as to increase,the probability of their expulsion from a liquid bulk. In these tests the liquid'bulk was made either to be contained within, or to flow through specially designed containers using capillary force alone. Such containers appear to facilitate bubble removal, from the liquid bulk. Different successful liquid flow configurations will be discussed and the efficacy of the resulting bubble expulsion mechanisms will be demonstrated.

An X-ray image of the violent interstellar medium in 30 Doradus

NASA Technical Reports Server (NTRS)

Wang, Q.; Helfand, D. J.

1991-01-01

A detailed analysis of the X-ray emission from the largest H II region complex in the Local Group, 30 Dor, is presented. Applying a new maximum entropy deconvolution algorithm to the Einstein Observatory data, reveals striking correlations among the X-ray, radio, and optical morphologies of the region, with X-ray-emitting bubbles filling cavities surrounded by H-alpha shells and coextensive diffuse X-ray and radio continuum emission from throughout the region. The total X-ray luminosity in the 0.16-3.5 keV band from an area within 160 pc of the central cluster R136 is about 2 x 10 to the 37th ergs/sec.

Structural and chemical alteration of crystalline olivine under low energy He+ irradiation

NASA Astrophysics Data System (ADS)

Demyk, K.; Carrez, Ph.; Leroux, H.; Cordier, P.; Jones, A. P.; Borg, J.; Quirico, E.; Raynal, P. I.; d'Hendecourt, L.

2001-03-01

We present the results of irradiation experiments on crystalline olivine with He+ ions at energies of 4 and 10 keV and fluences varying from 5 1016 to 1018 ions/cm2. The aim of these experiments is to simulate ion implantation into interstellar grains in shocks in the ISM. Irradiated samples were analysed by transmission electron microscopy (TEM). The irradiation causes the amorphization of the olivine, at all He+ fluences considered. The thickness of the amorphized region is 40 +/- 15 nm and 90 +/- 10 nm for the 4 keV and 10 keV experiments, respectively. The amorphization of the olivine occurs in conjunction with an increase in the porosity of the material due to the formation of bubbles. In addition, the amorphized layer is deficient in oxygen and magnesium. We find that the O/Si and Mg/Si ratios decrease as the He+ fluence increases. These experiments show that the irradiation of dust in supernova shocks can efficiently alter the dust structure and composition. Our result are consistent with the lack of crystalline silicates in the interstellar medium and also with the compositional evolution observed from olivine-type silicates around evolved stars to pyroxene-type silicates around protostars.

Formation and processing of organics in the early solar system.

PubMed

Kerridge, J F

1999-01-01

Until pristine samples can be returned from cometary nuclei, primitive meteorites represent our best source of information about organic chemistry in the early solar system. However, this material has been affected by secondary processing on asteroidal parent bodies which probably did not affect the material now present in cometary nuclei. Production of meteoritic organic matter apparently involved the following sequence of events: Molecule formation by a variety of reaction pathways in dense interstellar clouds; Condensation of those molecules onto refractory interstellar grains; Irradiation of organic-rich interstellar-grain mantles producing a range of molecular fragments and free radicals; Inclusion of those interstellar grains into the protosolar nebula with probable heating of at least some grain mantles during passage through the shock wave bounding the solar accretion disc; Agglomeration of residual interstellar grains and locally produced nebular condensates into asteroid-sized planetesimals; Heating of planetesimals by decay of extinct radionuclides; Melting of ice to produce liquid water within asteroidal bodies; Reaction of interstellar molecules, fragments and radicals with each other and with the aqueous environment, possibly catalysed by mineral grains; Loss of water and other volatiles to space yielding a partially hydrated lithology containing a complex suite of organic molecules; Heating of some of this organic matter to generate a kerogen-like complex; Mixing of heated and unheated material to yield the meteoritic material now observed. Properties of meteoritic organic matter believed to be consistent with this scenario include: Systematic decrease of abundance with increasing C number in homologous series of characterisable molecules; Complete structural diversity within homologous series; Predominance of branched-chain isomers; Considerable isotopic variability among characterisable molecules and within kerogen-like material; Substantial deuterium enrichment in all organic fractions; Some fractions significantly enriched in nitrogen-15; Modest excesses of L-enantiomers in some racemisation-resistant molecules but no general enantiomeric preference. Despite much speculation about the possible role of Fischer-Tropsch catalytic hydrogenation of CO in production of organic molecules in the solar nebula, no convincing evidence for such material has been found in meteorites. A similarity between some meteoritic organics and those produced by Miller-Urey discharge synthesis may reflect involvement of common intermediates rather than the operation of electric discharges in the early solar system. Meteoritic organic matter constitutes a useful, but not exact, guide to what we shall find with in situ analytical and sample-return missions to cometary nuclei.

Trajectories and distribution of interstellar dust grains in the heliosphere

DOE PAGES

Slavin, Jonathan D.; Frisch, Priscilla C.; Müller, Hans-Reinhard; ...

2012-11-01

The solar wind carves a bubble in the surrounding interstellar medium (ISM) known as the heliosphere. Charged interstellar dust grains (ISDG) encountering the heliosphere may be diverted around the heliopause or penetrate it depending on their charge-to-mass ratio. Here, we present new calculations of trajectories of ISDG in the heliosphere, and the dust density distributions that result. We include up-to-date grain charging calculations using a realistic UV radiation field and full three-dimensional magnetohydrodynamic fluid + kinetic models for the heliosphere. Models with two different (constant) polarities for the solar wind magnetic field (SWMF) are used, with the grain trajectory calculationsmore » done separately for each polarity. Small grains a gr ≲ 0.01 μm are completely excluded from the inner heliosphere. Large grains, a gr ≳ 1.0 μm, pass into the inner solar system and are concentrated near the Sun by its gravity. Trajectories of intermediate size grains depend strongly on the SWMF polarity. When the field has magnetic north pointing to ecliptic north, the field de-focuses the grains resulting in low densities in the inner heliosphere, while for the opposite polarity the dust is focused near the Sun. The ISDG density outside the heliosphere inferred from applying the model results to in situ dust measurements is inconsistent with local ISM depletion data for both SWMF polarities but is bracketed by them. Our result points to the need to include the time variation in the SWMF polarity during grain propagation. This provides valuable insights for interpretation of the in situ dust observations from Ulysses.« less

THE INTERSTELLAR MEDIUM IN THE KEPLER SEARCH VOLUME

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

Johnson, Marshall C.; Redfield, Seth; Jensen, Adam G., E-mail: mjohnson@astro.as.utexas.edu

2015-07-10

The properties of the interstellar medium (ISM) surrounding a planetary system can impact planetary climate through a number of mechanisms, including changing the size of the astrosphere (one of the major shields for cosmic rays) as well as direct deposition of material into planetary atmospheres. In order to constrain the ambient ISM conditions for exoplanetary systems, we present observations of interstellar Na i and K i absorption toward seventeen early type stars in the Kepler prime mission field of view (FOV). We identify 39 Na i and 8 K i velocity components, and attribute these to 11 ISM clouds. Sixmore » of these are detected toward more than one star, and for these clouds we put limits on the cloud properties, including distance and hydrogen number density. We identify one cloud with significant (≳1.5 cm{sup −3}) hydrogen number density located within the nominal ∼100 pc boundary of the Local Bubble. We identify systems with confirmed planets within the Kepler FOV that could lie within these ISM clouds, and estimate upper limits on the astrosphere sizes of these systems under the assumption that they do lie within these clouds. Under this condition, the Kepler-20, 42, and 445 multiplanet systems could have compressed astrospheres much smaller than the present-day heliosphere. Among the known habitable zone planet hosts, Kepler-186 could have an astrosphere somewhat smaller than the heliosphere, while Kepler-437 and KOI-4427 could have astrospheres much larger than the heliosphere. The thick disk star Kepler-444 may have an astrosphere just a few AU in radius.« less

A Polarimetric Investigation on Interstellar Dust Within 50-PARSECS from the Sun

NASA Astrophysics Data System (ADS)

Leroy, J. L.

1993-07-01

We have analyzed the polarization catalogue, for 1000 stars closer than 50 Pc, which has been presented in a companion paper. Although the accuracy of the measurements is generally very good (better than 0.02% for more than 700 stars), the catalogue contains essentially unpolarized stars, which is to be related to the well known depletion of dust in the Sun's vicinity. However, setting apart some stars which are known to display intrinsic polarization (e.g. several Ap magnetic variables), we have been able to select 25 stars whose polarization is indisputable. But, looking in more detail at the (presently available) data on the distance of this sample reveals that, in almost all the cases, the distances have been under-estimated. While this result will require a confirmation with the help of the Hipparcos parallaxes, we can already say that we fully confirm the main result of the preceding investigation on this topic by Tinbergen (1982), namely the complete depletion of dust within 35 pc from the Sun. Actually, we find that the dust signature begins at 40-50 pc in a few cases, but more much frequently at 70 to 100 pc, which seems to be the boundary of the local Bubble, as far as dust is concerned. We cannot confirm the previous detection by Tinbergen of a faint, near-by dusty region around l = 0°, b = -20°. Altogether, the picture given by the polarization analysis is consistent (although more sensitive) with the data derived from reddening measurements, and, to a lesser extent, with the investigations based on the measurements of interstellar absorption lines. Extending the polarization measurements to the 50-100 pc zone would provide a very precise picture of the location of those dust clouds which appear, here and there, as one gets out from the local Bubble.

A discrete trinomial model for the birth and death of stock financial bubbles

NASA Astrophysics Data System (ADS)

Di Persio, Luca; Guida, Francesco

2017-11-01

The present work proposes a novel way to model the dynamic of financial bubbles. In particular we exploit the so called trinomial tree technique, which is mainly inspired by the typical market order book (MOB) structure. According to the typical MOB rules, we exploit a bottom-up approach to derive the relevant generator process for the financial quantities characterizing the market we are considering. Our proposal pays attention in considering the real world changes in probability levels characterizing the bid-ask preferences, focusing the attention on the market movements. In particular, we show that financial bubbles are originated by these movements which also act amplify their growth.

Implications for Planetary System Formation from Interstellar Object 1I/2017 U1 (‘Oumuamua)

NASA Astrophysics Data System (ADS)

Trilling, David E.; Robinson, Tyler; Roegge, Alissa; Chandler, Colin Orion; Smith, Nathan; Loeffler, Mark; Trujillo, Chad; Navarro-Meza, Samuel; Glaspie, Lori M.

2017-12-01

The recently discovered minor body 1I/2017 U1 (‘Oumuamua) is the first known object in our solar system that is not bound by the Sun’s gravity. Its hyperbolic orbit (eccentricity greater than unity) strongly suggests that it originated outside our solar system; its red color is consistent with substantial space weathering experienced over a long interstellar journey. We carry out a simple calculation of the probability of detecting such an object. We find that the observed detection rate of 1I-like objects can be satisfied if the average mass of ejected material from nearby stars during the process of planetary formation is ˜20 Earth masses, similar to the expected value for our solar system. The current detection rate of such interstellar interlopers is estimated to be 0.2 yr-1, and the expected number of detections over the past few years is almost exactly one. When the Large Synoptic Survey Telescope begins its wide, fast, deep all-sky survey, the detection rate will increase to 1 yr-1. Those expected detections will provide further constraints on nearby planetary system formation through a better estimate of the number and properties of interstellar objects.

Radiative Cooling of Warm Molecular Gas

NASA Technical Reports Server (NTRS)

Neufeld, David A.; Kaufman, Michael J.

1993-01-01

We consider the radiative cooling of warm (T >= 100 K), fully molecular astrophysical gas by rotational and vibrational transitions of the molecules H2O, CO, and H2. Using an escape probability method to solve for the molecular level populations, we have obtained the cooling rate for each molecule as a function of temperature, density, and an optical depth parameter. A four-parameter expression proves useful in fitting the run of cooling rate with density for any fixed values of the temperature and optical depth parameter. We identify the various cooling mechanisms which are dominant in different regions of the astrophysically relevant parameter space. Given the assumption that water is very abundant in warm regions of the interstellar medium, H2O rotational transitions are found to dominate the cooling of warm interstellar gas over a wide portion of the parameter space considered. While chemical models for the interstellar medium make the strong prediction that water will be produced copiously at temperatures above a few hundred degrees, our assumption of a high water abundance has yet to be tested observationally. The Infrared Space Observatory and the Submillimeter Wave Astronomy Satellite will prove ideal instruments for testing whether water is indeed an important coolant of interstellar and circumstellar gas.

Interstellar and Solar Nebula Materials in Cometary Dust

NASA Technical Reports Server (NTRS)

Messenger, Scott; Nakamura-Messenger, Keiko; Keller, Lindsay; Nguyen, Ann; Clemett, Simon

2017-01-01

Laboratory studies of cometary dust collected in the stratosphere and returned from comet 81P/Wild 2 by the Stardust spacecraft have revealed ancient interstellar grains and molecular cloud organic matter that record a range of astrophysical processes and the first steps of planetary formation. Presolar materials are rarer meteorites owing to high temperature processing in the solar nebula and hydrothermal alteration on their asteroidal parent bodies. The greater preservation of presolar materials in comets is attributed to their low accretion temperatures and limited planetary processing. Yet, comets also contain a large complement of high temperature materials from the inner Solar System. Owing to the limited and biased sampling of comets to date, the proportions of interstellar and Solar System materials within them remains highly uncertain. Interstellar materials are identified by coordinated isotopic, mineralogical, and chemical measurements at the scale of individual grains. Chondritic porous interplanetary dust particles (CP IDPs) that likely derive from comets are made up of 0.1 - 10 micron-sized silicates, Fe-Ni-sulfides, oxides, and other phases bound by organic material. As much as 1% of the silicates are interstellar grains that have exotic isotopic compositions imparted by nucleosynthetic processes in their parent stars. Crystalline silicates in CP IDPs dominantly have normal isotopic compositions and probably formed in the Solar System. 81P samples include isotopically normal refractory minerals that resemble Ca-Al rich inclusions and chondrules common in meteorites. The origins of sub-micron amorphous silicates in IDPs are not certain, but at least a few % of them are interstellar grains. The remainder have isotopic compositions consistent with Solar System origins and elemental compositions that are inconsistent with interstellar grain properties, thus favoring formation in the solar nebula [4]. The organic component in comets and primitive meteorites has large enrichments in D/H and N-15/N-14 relative to terrestrial materials. These isotopic signatures are probably due to low temperature chemical processes in cold molecular clouds or the outermost reaches of the protoplanetary disk. The greatest isotopic anomalies are found in sub-micron organic nanoglobules that show chemical signatures of interstellar chemistry. The observation that cometary dust is mostly composed of isotopically normal minerals within isotopically anomalous organic matter is difficult to reconcile with the formation models of each component. The mineral component likely formed in high temperature processes in the inner Solar System, while the organic fraction shows isotopic and chemical signatures of formation near 10 K. Studying more primitive remnants of the Solar System starting materials would help in resolving this paradox. Comets formed across a vast expanse of the outer disk under differing thermal and collisional regimes, and some are likely to be better preserved than others. Finding truly pristine aggregates of presolar materials may require return of a pristine sample of comet nucleus material.

Rotation measure synthesis at the 2 m wavelength of the FAN region: unveiling screens and bubbles

NASA Astrophysics Data System (ADS)

Iacobelli, M.; Haverkorn, M.; Katgert, P.

2013-01-01

Context. Rotation measure synthesis of the Westerbork Synthesis Radio Telescope (WSRT) observations at λ ~ 2 m of the FAN region at l = 137°, b = +7° shows the morphology of structures in the ionized interstellar medium. Aims: We interpret the diffuse polarized synchrotron emission in terms of coherent structures in the interstellar medium and the properties of the interstellar magnetic field. Methods: We performed statistical analysis of the polarization data cube obtained through rotation measure synthesis. For the first time, cross-correlation is applied to identify and characterize polarized structures in Faraday depth space. Complementary information about the medium are derived from Hα emission, properties of nearby pulsars, and optical polarized starlight measurements. Results: We find an overall asymmetric Faraday dispersion function in a Faraday depth range of [-13, +5] rad m-2, which is peaked around -1 rad m-2. Three morphological patterns are recognized, showing structures on scales from degrees down to the beam size. The first structure is a nearby synchrotron emission component with low Faraday depth, filling the entire field of view. The second pattern is a circular polarization structure with enhanced (negative) Faraday depth, which has the same morphology as a low-emission region within the third component. This third component is interpreted as the background in which the circular structure is embedded. At low Faraday depth values, a low gradient across the imaged field is detected, almost aligned with the Galactic plane. Power spectra of polarized structures in Faraday depth space provide evidence of turbulence. Conclusions: A sign reversal in Faraday depth from the nearby component to the circular component indicates a reversal of the magnetic field component along the line of sight, from towards the observer and nearby to away from the observer at large distances. The distance to the nearby, extended component is estimated as ≲100 pc, which suggests that this structure corresponds to the Local Bubble wall. For the circular component, various physical interpretations are discussed. The most likely explanation is that the circular component seems to be the presence of a nearby (~200 pc away) relic Strömgren sphere, associated with an old unidentified white dwarf star and expanding in a low-density environment. Faraday rotation datacubes are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/549/A56

TERRESTRIAL EFFECTS OF NEARBY SUPERNOVAE IN THE EARLY PLEISTOCENE

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

Thomas, B. C.; Engler, E. E.; Kachelrieß, M.

Recent results have strongly confirmed that multiple supernovae happened at distances of ∼100 pc, consisting of two main events: one at 1.7–3.2 million years ago, and the other at 6.5–8.7 million years ago. These events are said to be responsible for excavating the Local Bubble in the interstellar medium and depositing {sup 60}Fe on Earth and the Moon. Other events are indicated by effects in the local cosmic ray (CR) spectrum. Given this updated and refined picture, we ask whether such supernovae are expected to have had substantial effects on the terrestrial atmosphere and biota. In a first look atmore » the most probable cases, combining photon and CR effects, we find that a supernova at 100 pc can have only a small effect on terrestrial organisms from visible light and that chemical changes such as ozone depletion are weak. However, tropospheric ionization right down to the ground, due to the penetration of ≥TeV CRs, will increase by nearly an order of magnitude for thousands of years, and irradiation by muons on the ground and in the upper ocean will increase twentyfold, which will approximately triple the overall radiation load on terrestrial organisms. Such irradiation has been linked to possible changes in climate and increased cancer and mutation rates. This may be related to a minor mass extinction around the Pliocene-Pleistocene boundary, and further research on the effects is needed.« less

Terrestrial Effects of Nearby Supernovae in the Early Pleistocene

NASA Astrophysics Data System (ADS)

Thomas, B. C.; Engler, E. E.; Kachelrieß, M.; Melott, A. L.; Overholt, A. C.; Semikoz, D. V.

2016-07-01

Recent results have strongly confirmed that multiple supernovae happened at distances of ˜100 pc, consisting of two main events: one at 1.7-3.2 million years ago, and the other at 6.5-8.7 million years ago. These events are said to be responsible for excavating the Local Bubble in the interstellar medium and depositing 60Fe on Earth and the Moon. Other events are indicated by effects in the local cosmic ray (CR) spectrum. Given this updated and refined picture, we ask whether such supernovae are expected to have had substantial effects on the terrestrial atmosphere and biota. In a first look at the most probable cases, combining photon and CR effects, we find that a supernova at 100 pc can have only a small effect on terrestrial organisms from visible light and that chemical changes such as ozone depletion are weak. However, tropospheric ionization right down to the ground, due to the penetration of ≥TeV CRs, will increase by nearly an order of magnitude for thousands of years, and irradiation by muons on the ground and in the upper ocean will increase twentyfold, which will approximately triple the overall radiation load on terrestrial organisms. Such irradiation has been linked to possible changes in climate and increased cancer and mutation rates. This may be related to a minor mass extinction around the Pliocene-Pleistocene boundary, and further research on the effects is needed.

The many sides of RCW 86: a Type Ia supernova remnant evolving in its progenitor's wind bubble

NASA Astrophysics Data System (ADS)

Broersen, Sjors; Chiotellis, Alexandros; Vink, Jacco; Bamba, Aya

2014-07-01

We present the results of a detailed investigation of the Galactic supernova remnant RCW 86 using the XMM-Newton X-ray telescope. RCW 86 is the probable remnant of SN 185 A.D., a supernova that likely exploded inside a wind-blown cavity. We use the XMM-Newton Reflection Grating Spectrometer to derive precise temperatures and ionization ages of the plasma, which are an indication of the interaction history of the remnant with the presumed cavity. We find that the spectra are well fitted by two non-equilibrium ionization models, which enables us to constrain the properties of the ejecta and interstellar matter plasma. Furthermore, we performed a principal component analysis on EPIC MOS and pn data to find regions with particular spectral properties. We present evidence that the shocked ejecta, emitting Fe K and Si line emission, are confined to a shell of approximately 2 pc width with an oblate spheroidal morphology. Using detailed hydrodynamical simulations, we show that general dynamical and emission properties at different portions of the remnant can be well reproduced by a Type Ia supernova that exploded in a non-spherically symmetric wind-blown cavity. We also show that this cavity can be created using general wind properties for a single degenerate system. Our data and simulations provide further evidence that RCW 86 is indeed the remnant of SN 185, and is the likely result of a Type Ia explosion of single degenerate origin.

Black Widow Nebula Hiding in the Dust

NASA Technical Reports Server (NTRS)

2005-01-01

In this Spitzer image, the two opposing bubbles are being formed in opposite directions by the powerful outflows from massive groups of forming stars. The baby stars can be seen as specks of yellow where the two bubbles overlap.

When individual stars form from molecular clouds of gas and dust they produce intense radiation and very strong particle winds. Both the radiation and the stellar winds blow the dust outward from the star creating a cavity or, bubble.

In the case of the Black Widow Nebula, astronomers suspect that a large cloud of gas and dust condensed to create multiple clusters of massive star formation. The combined winds from these groups of large stars probably blew out bubbles into the direction of least resistance, forming a double bubble.

The infrared image was captured by the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) Legacy project. The Spitzer picture is a four-channel false-color composite, showing emission from wavelengths of 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange) and 8.0 microns (red).

Use of ultrasound in altitude decompression modeling

NASA Technical Reports Server (NTRS)

Olson, Robert M.; Pilmanis, Andrew A.

1993-01-01

A model that predicts the probability of developing decompression sickness (DCS) with various denitrogenation schedules is being developed by the Armstrong Laboratory, using human data from previous exposures. It was noted that refinements are needed to improve the accuracy and scope of the model. A commercially developed ultrasonic echo imaging system is being used in this model development. Using this technique, bubbles images from a subject at altitude can be seen in the gall bladder, hepatic veins, vena cava, and chambers of the heart. As judged by their motion and appearance in the vena cava, venous bubbles near the heart range in size from 30 to 300 M. The larger bubbles skim along the top, whereas the smaller ones appear as faint images near the bottom of the vessel. Images from growing bubbles in a model altitude chamber indicate that they grow rapidly, going from 20 to 100 M in 3 sec near 30,000 ft altitude. Information such as this is valuable in verifying those aspects of the DCS model dealing with bubble size, their growth rate, and their site of origin.

Near-Local Interstellar Medium (LISM): What we know from the Voyagers and ENA and what an Interstellar Probe (ISP) can do

NASA Astrophysics Data System (ADS)

Krimigis, S. M.

2017-12-01

In situ measurements by the two Voyagers over the past 13 years have revealed the presence of the long-predicted termination shock (TS) and heliopause (HP), albeit not where theory had placed them. Further, the advent of energetic neutral atom (ENA) imaging by Cassini/INCA since 2003 and IBEX since 2009 have provided images of the global heliosphere that have challenged our long-held views of its shape and the processes that are dominant in its formation (Krimigis et al, and McComas et al, 2009; Dialynas et al, 2017). In addition, continuing measurements from Voyager 1 beyond the HP, now at 140 AU (1 AU=1.5x108 km, the Sun-Earth distance), have shown that the influence of the Sun extends well beyond the HP (at 122 AU). This influence is manifested through the occasional appearance of anisotropies in the galactic cosmic rays (GCR) where none were predicted, that last as long as a year and are accompanied by electron plasma oscillations in the vicinity of the spacecraft. Thus, an ISP mission with a fast ( 15 AU per year compared to Voyager's 3.6) trajectory would traverse a dynamic region near and beyond the TS and HP, and enable imaging the shape of the heliosphere from beyond its boundaries through ENA. In situ measurements should include the ISM magnetic field (ISMF), plasma density and distribution function, plasma waves, and neutral atom density and composition, as a minimum. All of these measurements would be new information with modern instrumentation that would place the very limited Voyager measurements into the proper context. References: Krimigis, S. M., D. G. Mitchell, E. C. Roelof, K. C. Hsieh and D. J. McComas, Imaging the Interaction of the Heliosphere with the Interstellar Medium from Saturn with Cassini, Science, 326, 5955, p. 971, doi: 10.1126/science.1181079, 2009 McComas, D. J., et al, Global Observations of the Interstellar Interaction from the Interstellar Boundary Explorer (IBEX), Science, 326, 5955, pp. 959, doi: 10.1126/science.1180906, 2009. Dialynas, K., S. M. Krimigis, D. G. Mitchell, R. B. Decker, and E. C. Roelof, Voyager and Cassini measurements suggest a "bubble-like" shape of the global heliosphere, Nature Astronomy, 1, 0115 (2017) | DOI: 10.1038/s41550-017-0115

Black Holes Are The Rhythm at The Heart of Galaxies

NASA Astrophysics Data System (ADS)

2008-11-01

The powerful black holes at the center of massive galaxies and galaxy clusters act as hearts to the systems, pumping energy out at regular intervals to regulate the growth of the black holes themselves, as well as star formation, according to new data from NASA's Chandra X-Ray Observatory. People Who Read This Also Read... Milky Way’s Giant Black Hole Awoke from Slumber 300 Years Ago A New Way To Weigh Giant Black Holes Discovery of Most Recent Supernova in Our Galaxy NASA Unveils Cosmic Images Book in Braille for Blind Readers Scientists from the University of Michigan, the Max-Planck Institute for Extraterrestrial Physics in Germany, the University of Maryland, Baltimore County (UMBC), the Harvard-Smithsonian Center for Astrophysics and Jacobs University in Germany contributed to the results. The gravitational pull of black holes is so strong that not even light can escape from them. Supermassive black holes with masses of more than a billion suns have been detected at the center of large galaxies. The material falling on the black holes causes sporadic or isolated bursts of energy, by which black holes are capable of influencing the fate of their host galaxies. The insight gained by this new research shows that black holes can pump energy in a gentler and rhythmic fashion, rather then violently. The scientists observed and simulated how the black hole at the center of elliptical galaxy M84 dependably sends bubbles of hot plasma into space, heating up interstellar space. This heat is believed to slow both the formation of new stars and the growth of the black hole itself, helping the galaxy remain stable. Interstellar gases only coalesce into new stars when the gas is cool enough. The heating is more efficient at the sites where it is most needed, the scientists say. Alexis Finoguenov, of UMBC and the Max-Planck Institute for Extraterrestrial Physics in Germany, compares the central black hole to a heart muscle. "Just like our hearts periodically pump our circulatory systems to keep us alive, black holes give galaxies a vital warm component. They are a careful creation of nature, allowing a galaxy to maintain a fragile equilibrium," Finoguenov said. X-rayChandra X-ray Image This finding helps to explain a decades-long paradox of the existence of large amounts of warm gas around certain galaxies, making them appear bright to the Chandra X-ray telescope. "For decades astronomers were puzzled by the presence of the warm gas around these objects. The gas was expected to cool down and form a lot of stars," said Mateusz Ruszkowski, an assistant professor in the University of Michigan Department of Astronomy. "Now, we see clear and direct evidence that the heating mechanism of black holes is persistent, producing enough heat to significantly suppress star formation. These plasma bubbles are caused by bursts of energy that happen one after another rather than occasionally, and the direct evidence for such periodic behavior is difficult to find." The bubbles form one inside to another, for a sort of Russian doll effect that has not been seen before, Ruszkowski said. One of the bubbles of hot plasma appears to be bursting and its contents spilling out, further contributing to the heating of the interstellar gas. "Disturbed gas in old galaxies is seen in many images that NASA's Chandra observatory obtained, but seeing multiple events is a really impressive evidence for persistent black hole activity," says Christine Jones, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics. A paper on the research called "In-depth Chandra study of the AGN feedback in Virgo Elliptical Galaxy M84" has been published in Astrophysical Journal.

DIBS independent of accretion in T Tauri stars

NASA Technical Reports Server (NTRS)

Ghandour, Louma; Jenniskens, Peter; Hartigan, P.

1994-01-01

The examination of high resolution spectra (5200 - 7000 Angstroms) of 36 T Tauri stars ranging in accretion rates was performed. Only the lambda lambda 5780, 5797, and 6613 bands were found detectable to within an equivalent width of 10 micro Angstroms. They are strongest in DG Tau, DR Tau, Dl Tau, and AS 353A. DR Tau was monitored over the course of four years; during this time, the accretion rate varied by a factor of five, but the equivalent widths of the DIB's (Diffuse Interstellar Bands) remained constant. The lack of correlation of the strength of the bands with the accretion rates implies that the bands are not directly produced by UV radiation from the accretion process. The bands have line strengths and ratios characteristic of the diffuse interstellar medium, from which we conclude that the diffuse interstellar bands seen in the spectra of T Tauri stars do not originate in the stars' immediate environment. Instead, they are part of a foreground extinction, probably due to the parent molecular cloud.

Isotopic composition of carbonaceous-chondrite kerogen Evidence for an interstellar origin of organic matter in meteorites

NASA Technical Reports Server (NTRS)

Kerridge, J. F.

1983-01-01

Stepwise combustion has revealed systematic patterns of isotopic heterogeneity for C, H and N in the insoluble organic fraction (m-kerogen) from the Orgueil and Murray carbonaceous chondrites. Those patterns are essentially identical for both meteorites, indicating a common source of m-kerogen. The data cannot be reconciled with a single mass-fractionation process acting upon a single precursor composition. This indicates either a multi-path history of mass-dependent processing or a significant nucleogenetic contribution, or both. If mass-fractionation were the dominant process, the magnitude of the observed isotopic variability strongly suggests that ion-molecule reactions at very low temperatures, probably in interstellar clouds, were responsible. In any case, an interstellar, rather than solar nebular, origin for at least some of the meteoritic organic matter is indicated. This has interesting implications for the origin of prebiotic molecules, temperatures in the early solar system, and the isotopic compositions of volatiles accreted by the terrestrial planets.

Primary gamma rays. [resulting from cosmic ray interaction with interstellar matter

NASA Technical Reports Server (NTRS)

Fichtel, C. E.

1974-01-01

Within this galaxy, cosmic rays reveal their presence in interstellar space and probably in source regions by their interactions with interstellar matter which lead to gamma rays with a very characteristic energy spectrum. From the study of the intensity of the high energy gamma radiation as a function of galactic longitude, it is already clear that cosmic rays are almost certainly not uniformly distributed in the galaxy and are not concentrated in the center of the galaxy. The galactic cosmic rays appear to be tied to galactic structural features, presumably by the galactic magnetic fields which are in turn held by the matter in the arm segments and the clouds. On the extragalactic scale, it is now possible to say that cosmic rays are not universal at the density seen near the earth. The diffuse celestial gamma ray spectrum that is observed presents the interesting possibility of cosmological studies and possible evidence for a residual universal cosmic ray density, which is much lower than the present galactic cosmic ray density.

Electronic and rovibrational quantum chemical analysis of C3P-: the next interstellar anion?

NASA Astrophysics Data System (ADS)

Fortenberry, Ryan C.; Lukemire, Joseph A.

2015-11-01

C3P- is analogous to the known interstellar anion C3N- with phosphorus replacing nitrogen in a simple step down the periodic table. In this work, it is shown that C3P- is likely to possess a dipole-bound excited state. It has been hypothesized and observationally supported that dipole-bound excited states are an avenue through which anions could be formed in the interstellar medium. Additionally, C3P- has a valence excited state that may lead to further stabilization of this molecule, and C3P- has a larger dipole moment than neutral C3P (˜6 D versus ˜4 D). As such, C3P- is probably a more detectable astromolecule than even its corresponding neutral radical. Highly accurate quantum chemical quartic force fields are also applied to C3P- and its singly 13C substituted isotopologues in order to provide structures, vibrational frequencies, and spectroscopic constants that may aid in its detection.

In-situ observations of bubble growth in basaltic, andesitic and rhyodacitic melts

NASA Astrophysics Data System (ADS)

Masotta, M.; Ni, H.; Keppler, H.

2013-12-01

Bubble growth strongly affects the physical properties of degassing magmas and their eruption dynamics. Natural samples and products from quench experiments provide only a snapshot of the final state of volatile exsolution, leaving the processes occurring during its early stages unconstrained. In order to fill this gap, we present in-situ high-temperature observations of bubble growth in magmas of different compositions (basalt, andesite and rhyodacite) at 1100 to 1240 °C and 1 bar, obtained using a moissanite cell apparatus. The data show that nucleation occurs at very small degrees of supersaturaturation (<20 MPa in basalt and andesite, ca. 100 MPa in rhyodacite), probably due to heterogeneous nucleation of bubbles occurring simultaneously with the nucleation of crystals. During the early stages of exsolution, melt degassing is the driving mechanism of bubble growth, with coalescence becoming increasingly important as exsolution progresses. Ostwald ripening occurs only at the end of the process and only in basaltic melt. The average bubble growth rate (GR) ranges from 3.4*10-6 to 5.2*10-7 mm/s, with basalt and andesite showing faster growth rates than rhyodacite. The bubble number density (NB) at nucleation ranges from 1.8*108 to 7.9*107 cm-3 and decreases exponentially over time. While the rhyodacite melt maintained a well-sorted bubble-size distribution (BSD) through time, the BSD's of basalt and andesite are much more inhomogeneous. Our experimental observations demonstrate that bubble growth cannot be ascribed to a single mechanism but is rather a combination of many processes, which depend on the physical properties of the melt. Depending on coalescence rate, annealing of bubbles following a single nucleation event can produce complex bubble size distributions. In natural samples, such BSD's may be misinterpreted as resulting from several separate nucleation events. Incipient crystallization upon cooling of a magma may allow bubble nucleation already at very small degrees of supersaturation and could therefore be an important trigger for volatile release and explosive eruptions.

Some new reaction pathways for the formation of cytosine in interstellar space - A quantum chemical study

NASA Astrophysics Data System (ADS)

Gupta, V. P.; Tandon, Poonam; Mishra, Priti

2013-03-01

The detection of nucleic acid bases in carbonaceous meteorites suggests that their formation and survival is possible outside of the Earth. Small N-heterocycles, including pyrimidine, purines and nucleobases, have been extensively sought in the interstellar medium. It has been suggested theoretically that reactions between some interstellar molecules may lead to the formation of cytosine, uracil and thymine though these processes involve significantly high potential barriers. We attempted therefore to use quantum chemical techniques to explore if cytosine can possibly form in the interstellar space by radical-radical and radical-molecule interaction schemes, both in the gas phase and in the grains, through barrier-less or low barrier pathways. Results of DFT calculations for the formation of cytosine starting from some of the simple molecules and radicals detected in the interstellar space are being reported. Global and local descriptors such as molecular hardness, softness and electrophilicity, and condensed Fukui functions and local philicity indices were used to understand the mechanistic aspects of chemical reaction. The presence and nature of weak bonds in the molecules and transition states formed during the reaction process have been ascertained using Bader's quantum theory of atoms in molecules (QTAIMs). Two exothermic reaction pathways starting from propynylidyne (CCCH) and cyanoacetylene (HCCCN), respectively, have been identified. While the first reaction path is found to be totally exothermic, it involves a barrier of 12.5 kcal/mol in the gas phase against the lowest value of about 32 kcal/mol reported in the literature. The second path is both exothermic and barrier-less. The later has, therefore, a greater probability of occurrence in the cold interstellar clouds (10-50 K).

Technical Civilizations in the Galaxy

NASA Technical Reports Server (NTRS)

Jones, Harry

2005-01-01

Are there other technical civilizations in the galaxy? Past analyses come to different conclusions. Cocconi and Morrison demonstrated in 1959 that interstellar radio communication was possible and Drake conducted the first search for beacons in 1960. The Drake equation estimates the number of galactic civilizations that are transmitting beacons as the product of the rate of star formation in the galaxy, the fraction of stars with planets, their average number of earthlike planets, the fraction with intelligent life and interstellar communication, and the average lifetime of a technical civilization. The Drake model of the galaxy contains many technical civilizations with communication but no interstellar travel. Michael Hart in 1975 strongly challenged this model. Starting with the fact that no extraterrestrials have been observed on Earth, and assuming that interstellar colonization is possible, he concluded that it was very likely that we are the first civilization in our galaxy and that searching or beacons is probably a waste of time and money. The Fermi paradox similarly reasons that if extraterrestrials exist: they should be here, and asks, Where are they? The Hart/Fermi model of the galaxy contains only our civilization and suggests we may colonize the galaxy. A third galactic model is that we are alone but will never develop interstellar travel. The fourth alternate model has many technical civilizations, with interstellar travel and colonization. The possibilities are clear and momentous. Either we are the only technical civilization in the galaxy or there are others. Technical civilizations will colonize the galaxy or not. We have four cosmic conjectures - one or many, colonization or not - but however unlikely they seem based on our limited evidence, one of these four models must be collect.

Interstellar fullerene compounds and diffuse interstellar bands

NASA Astrophysics Data System (ADS)

Omont, Alain

2016-05-01

Recently, the presence of fullerenes in the interstellar medium (ISM) has been confirmed and new findings suggest that these fullerenes may possibly form from polycyclic aromatic hydrocarbons (PAHs) in the ISM. Moreover, the first confirmed identification of two strong diffuse interstellar bands (DIBs) with the fullerene, C60+, connects the long standing suggestion that various fullerenes could be DIB carriers. These new discoveries justify reassessing the overall importance of interstellar fullerene compounds, including fullerenes of various sizes with endohedral or exohedral inclusions and heterofullerenes (EEHFs). The phenomenology of fullerene compounds is complex. In addition to fullerene formation in grain shattering, fullerene formation from fully dehydrogenated PAHs in diffuse interstellar clouds could perhaps transform a significant percentage of the tail of low-mass PAH distribution into fullerenes including EEHFs. But many uncertain processes make it extremely difficult to assess their expected abundance, composition and size distribution, except for the substantial abundance measured for C60+. EEHFs share many properties with pure fullerenes, such as C60, as regards stability, formation/destruction and chemical processes, as well as many basic spectral features. Because DIBs are ubiquitous in all lines of sight in the ISM, we address several questions about the interstellar importance of various EEHFs, especially as possible carriers of diffuse interstellar bands. Specifically, we discuss basic interstellar properties and the likely contributions of fullerenes of various sizes and their charged counterparts such as C60+, and then in turn: 1) metallofullerenes; 2) heterofullerenes; 3) fulleranes; 4) fullerene-PAH compounds; 5) H2@C60. From this reassessment of the literature and from combining it with known DIB line identifications, we conclude that the general landscape of interstellar fullerene compounds is probably much richer than heretofore realized. EEHFs, together with pure fullerenes of various sizes, have many properties necessary to be suitably carriers of DIBs: carbonaceous nature; stability and resilience in the harsh conditions of the ISM; existing with various heteroatoms and ionization states; relatively easy formation; few stable isomers; spectral lines in the right spectral range; various and complex energy internal conversion; rich Jahn-Teller fine structure. This is supported by the first identification of a DIB carrier as C60+. Unfortunately, the lack of any precise information about the complex optical spectra of EEHFs and most pure fullerenes other than C60 and about their interstellar abundances still precludes definitive assessment of the importance of fullerene compounds as DIB carriers. Their compounds could significantly contribute to DIBs, but it still seems difficult that they are the only important DIB carriers. Regardless, DIBs appear as the most promising way of tracing the interstellar abundances of various fullerene compounds if the breakthrough in identifying C60+ as a DIB carrier can be extended to more spectral features through systematic studies of their laboratory gas-phase spectroscopy.

Possible high sonic velocity due to the inclusion of gas bubbles in water

NASA Astrophysics Data System (ADS)

Banno, T.; Mikada, H.; Goto, T.; Takekawa, J.

2010-12-01

If formation water becomes multi-phase by inclusion of gas bubbles, sonic velocities would be strongly influenced. In general, sonic velocities are knocked down due to low bulk moduli of the gas bubbles. However, sonic velocities may increase depending on the size of gas bubbles, when the bubbles in water or other media oscillate due to incoming sonic waves. Sonic waves are scattered by the bubbles and the superposition of the incoming and the scattered waves result in resonant-frequency-dependent behavior. The phase velocity of sonic waves propagating in fluids containing bubbles, therefore, probably depends on their frequencies. This is a typical phenomenon called “wave dispersion.” So far we have studied about the bubble impact on sonic velocity in bubbly media, such as the formation that contains gas bubbles. As a result, it is shown that the bubble resonance effect is a key to analyze the sonic phase velocity increase. Therefore to evaluate the resonance frequency of bubbles is important to solve the frequency response of sonic velocity in formations having bubbly fluids. There are several analytical solutions of the resonance frequency of bubbles in water. Takahira et al. (1994) derived a equation that gives us the resonance frequency considering bubble - bubble interactions. We have used this theory to calculate resonance frequency of bubbles at the previous work. However, the analytical solution of the Takahira’s equation is based on several assumptions. Therefore we used a numerical approach to calculate the bubble resonance effect more precisely in the present study. We used the boundary element method (BEM) to reproduce a bubble oscillation in incompressible liquid. There are several reasons to apply the BEM. Firstly, it arrows us to model arbitrarily sets and shapes of bubbles. Secondly, it is easy to use the BEM to reproduce a boundary-surface between liquid and gas. The velocity potential of liquid surrounding a bubble satisfies the Laplace equation when the liquid is supposed to be incompressible. We got the boundary integral equation from the Laplace equation and solved the boundary integral equation by the BEM. Then, we got the gradient of the velocity potential from the BEM. We used this gradient to get time derivative of the velocity potential from the Bernouii’s equation. And we used the second order Adams-Bashforth method to execute time integration of the velocity potential. We conducted this scheme iteratively to calculate a bubble oscillation. At each time step, we input a pressure change as a sinusoidal wave. As a result, we observed a bubble oscillation following the pressure frequency. We also evaluated the resonance frequency of a bubble by changing the pressure frequency. It showed a good agreement with the analytical solution described above. Our future work is to extend the calculation into plural bubbles condition. We expect that interaction between bubbles becomes strong and resonance frequency of bubbles becomes small when distance between bubbles becomes small.

Searching for extra-terrestrial civilizations

NASA Technical Reports Server (NTRS)

Gindilis, L. M.

1974-01-01

The probability of radio interchange with extraterrestrial civilizations is discussed. Difficulties constitute absorption, scattering, and dispersion of signals by the rarified interstellar medium as well as the deciphering of received signals and convergence of semantic concept. A cybernetic approach considers searching for signals that develop from astroengineering activities of extraterrestrial civilizations.

Modelling injection rates of PUIs from photoionization using kinetic simulations of interstellar neutrals traversing the heliosphere

NASA Astrophysics Data System (ADS)

Keilbach, D.; Drews, C.; Taut, A.; Wimmer-Schweingruber, R. F.

2016-12-01

Recent studies of the inflow direction of the local insterstellar medium from PUI density distributions have shown that the extrema of the longitudinal distribution of PUI velocities (with respect to the solar wind speed) can be attributed to the radial velocity of the interstellar neutral seed population and is symmetric around the inflow direction of the local interstellar medium. This work is aimed to model pickup ion injection rates from photoionization (which is the main process of interstellar PUI production) throughout the heliosphere. To that end a seed population of interstellar neutrals is injected into a model heliosphere at 60 AU distance from the sun, whereas each particle's initial speed is given by a maxwellian distribution at a temperature of 1 eV and an inflow speed of 22 km/s. Then the density of the interstellar neutrals is integrated over the model heliosphere, while the movement of the neutrals is simulated using timestep methods. To model the focusing of the interstellar neutral trajectories from the sun's gravitational potential the model heliosphere contains a central gravitational potential.Each neutral test particle can be ionized via photoionization with a per-timestep probability antiproportional to the neutral's distance to the sun squared. By tracking the ionization rate location-dependently, PUI injection rates have been determined. Therefore using these simulations the density distributions of different species of interstellar neutrals have been calculated. In addition location-dependent injection rates of different species of PUIs have been calculated, which show an increased rate of PUI production in the focusing cone region (e.g. for He+ PUIs), but also in the crescent region (e.g. for O+ PUIs).Furthermore the longitudinal distribution of the neutrals' velocity at 1 AU is calculated from the simulation's results in order to estimate the PUI cut-off as a function of ecliptic longitude. Figure: Simulated He neutral density (left) and simulated He PUI production rates from photoionization (right). The sun is located at 0 AU at both x-and y-axes.

Infrared Photometric Properties of 709 Candidate Stellar Bowshock Nebulae

NASA Astrophysics Data System (ADS)

Kobulnicky, Henry A.; Schurhammer, Danielle P.; Baldwin, Daniel J.; Chick, William T.; Dixon, Don M.; Lee, Daniel; Povich, Matthew S.

2017-11-01

Arcuate infrared nebulae are ubiquitous throughout the Galactic Plane and are candidates for partial shells, bubbles, or bowshocks produced by massive runaway stars. We tabulate infrared photometry for 709 such objects using images from the Spitzer Space Telescope, the Wide-field Infrared Explorer, and the Herschel Space Observatory (HSO). Of the 709 objects identified at 24 or 22 μm, 422 are detected at the HSO 70 μm bandpass. Of these, only 39 are detected at HSO 160 μm. The 70 μm peak surface brightnesses are 0.5-2.5 Jy arcmin-2. Color temperatures calculated from the 24 to 70 μm ratios range from 80 to 400 K. Color temperatures from 70 to 160 μm ratios are systematically lower, 40-200 K. Both of these temperature are, on average, 75% higher than the nominal temperatures derived by assuming that dust is in steady-state radiative equilibrium. This may be evidence of stellar wind bowshocks sweeping up and heating—possibly fragmenting but not destroying—interstellar dust. Infrared luminosity correlates with standoff distance, R 0, as predicted by published hydrodynamical models. Infrared spectral energy distributions are consistent with interstellar dust exposed to either single radiant energy density, U={10}3{--}{10}5 (in more than half of the objects) or a range of radiant energy densities U min = 25 to U max = 103-105 times the mean interstellar value for the remainder. Hence, the central OB stars dominate the energetics, making these enticing laboratories for testing dust models in constrained radiation environments. The spectral energy densities are consistent with polycyclic aromatic hydrocarbon fractions {q}{PAH}≲ 1 % in most objects.

Voyager Approaches Final Frontier Artist Concept

NASA Image and Video Library

2003-12-12

An artist's concept illustrates the positions of the Voyager spacecraft in relation to structures formed around our Sun by the solar wind. Also illustrated is the termination shock, a violent region the spacecraft must pass through before reaching the outer limits of the solar system. At the termination shock, the supersonic solar wind abruptly slows from an average speed of 400 kilometers per second to less than 100 kilometer per second (900,000 to less than 225,000 miles per hour). Beyond the termination shock is the solar system's final frontier, the heliosheath, a vast region where the turbulent and hot solar wind is compressed as it presses outward against the interstellar wind that is beyond the heliopause. A bow shock likely forms as the interstellar wind approaches and is deflected around the heliosphere, forcing it into a teardrop-shaped structure with a long, comet-like tail. The exact location of the termination shock is unknown, and it originally was thought to be closer to the Sun than Voyager 1 currently is. As Voyager 1 cruised ever farther from the Sun, it confirmed that all the planets are inside an immense bubble blown by the solar wind and the termination shock was much more distant. http://photojournal.jpl.nasa.gov/catalog/PIA04927

The high velocity symbiotic star AG Draconis after its 1980 outburst

NASA Technical Reports Server (NTRS)

Viotti, R.; Altamore, A.; Baratta, G. B.; Cassatella, A.; Friedjung, M.; Giangrande, A.; Ponz, D.; Ricciardi, O.

1982-01-01

High and low resolution spectra of AG Dra taken in 1981 are analyzed. The UV spectrum of AG Dra is characterized by prominent high ionization emission lines superimposed on a strong continuum. At high resolution, several intense absorption lines of interstellar origin are seen, in spite of the low interstellar extinction. A similar situation is displayed by the high galactic latitude sd0 stars. The radial velocity difference between the emission lines and the i.s. lines is about -105 Km/sec in agreement with the optical observations. The He II 1640 A line appears much stronger than in other symbiotic stars and suggests the presence of a hot source which is variable according to the activity of the star. The line also exhibits broad emission wings which could be formed in a rotating disk. The NV resonance doublet displays a P Cygni profile and is probably formed in a warm wind. Two components in the UV continuum are identified: a steep component dominating the far UV probably associated with the hot source, and a flatter continuum in the near UV which cannot be accounted for by f-f and f-b emission alone, but which is probably emitted by an optically thick region or disk.

The Evolution of the Interstellar Medium in the Mildly Disturbed Spiral Galaxy NGC 4647

NASA Astrophysics Data System (ADS)

Young, L. M.; Rosolowsky, E.; van Gorkom, J. H.; Lamb, S. A.

2006-10-01

We present matched-resolution maps of H I and CO emission in the Virgo Cluster spiral NGC 4647. The galaxy shows a mild kinematic disturbance in which one side of the rotation curve flattens but the other side continues to rise. This kinematic asymmetry is coupled with a dramatic asymmetry in the molecular gas distribution but not in the atomic gas. An analysis of the gas column densities and the interstellar pressure suggests that the H2/H I surface density ratio on the east side of the galaxy is 3 times higher than expected from the hydrostatic pressure contributed by the mass of the stellar disk. We discuss the probable effects of ram pressure, gravitational interactions, and asymmetric potentials on the interstellar medium and suggest it is likely that a m=1 perturbation in the gravitational potential could be responsible for all of the galaxy's features. Kinematic disturbances of the type seen here are common, but the curious thing about NGC 4647 is that the molecular distribution appears more disturbed than the H I distribution. Thus, it is the combination of the two gas phases that provides such interesting insight into the galaxy's history and into models of the interstellar medium.

Turbulent water flow in a channel at Reτ = 400 laden with 0.25 mm diameter air-bubbles clustered near the wall

NASA Astrophysics Data System (ADS)

Lakehal, D.; Métrailler, D.; Reboux, S.

2017-06-01

This paper presents Direct Numerical Simulation (DNS) results of a turbulent water flow in a channel at Reτ = 400 laden with 0.25 mm diameter air bubbles clustered near the wall (maximum void fraction of α = 8% at y+ ˜ 20). The bubbles were fully resolved using the level set approach built within the CFD/CMFD code TransAT. The fluid properties (air and water) were kept real, including density, viscosity, and surface tension coefficient. The aim of this work is to understand the effects of the bubbles on near-wall turbulence, paving the way towards convective wall-boiling flow studies. The interactions between the gas bubbles and the water stream were studied through an in-depth analysis of the turbulence statistics. The near-wall flow is overall affected by the bubbles, which act like roughness elements during the early phase, prior to their departure from the wall. The average profiles are clearly altered by the bubbles dynamics near the wall, which somewhat contrasts with the findings from similar studies [J. Lu and G. Tryggvason, "Dynamics of nearly spherical bubbles in a turbulent channel upflow," J. Fluid Mech. 732, 166 (2013)], most probably because the bubbles were introduced uniformly in the flow and not concentrated at the wall. The shape of the bubbles measured as the apparent to initial diameter ratio is found to change by a factor of at least two, in particular at the later stages when the bubbles burst out from the boundary layer. The clustering of the bubbles seems to be primarily localized in the zone populated by high-speed streaks and independent of their size. More importantly, the bubbly flow seems to differ from the single-phase flow in terms of turbulent stress distribution and energy exchange, in which all the stress components seem to be increased in the region very close to the wall, by up to 40%. The decay in the energy spectra near the wall was found to be significantly slower for the bubbly flow than for a single-phase flow, which confirms that the bubbles increase the energy at smaller scales. The coherent structures in the boundary layer are broken by the bubbles, which disrupts the formation of long structures, reducing the streamwise integral length scale.

MOPRA CO OBSERVATIONS OF THE BUBBLE H II REGION RCW 120

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

Anderson, L. D.; Deharveng, L.; Zavagno, A.

2015-02-20

We use the Mopra radio telescope to test for expansion of the molecular gas associated with the bubble H II region RCW 120. A ring, or bubble, morphology is common for Galactic H II regions, but the three-dimensional geometry of such objects is still unclear. Detected near- and far-side expansion of the associated molecular material would be consistent with a three-dimensional spherical object. We map the J = 1 → 0 transitions of {sup 12}CO, {sup 13}CO, C{sup 18}O, and C{sup 17}O, and detect emission from all isotopologues. We do not detect the 0{sub 0} → 1{sub –1} E masingmore » lines of CH{sub 3}OH at 108.8939 GHz. The strongest CO emission is from the photo-dissociation region (PDR), and there is a deficit of emission toward the bubble interior. We find no evidence for expansion of the molecular material associated with RCW 120 and therefore can make no claims about its geometry. The lack of detected expansion is roughly in agreement with models for the time-evolution of an H II region like RCW 120, and is consistent with an expansion speed of ≲ 1.5 km s{sup –1}. Single-position CO spectra show signatures of expansion, which underscores the importance of mapped spectra for such work. Dust temperature enhancements outside the PDR of RCW 120 coincide with a deficit of emission in CO, confirming that these temperature enhancements are due to holes in the RCW 120 PDR. H-alpha emission shows that RCW 120 is leaking ∼5% of the ionizing photons into the interstellar medium (ISM) through PDR holes at the locations of the temperature enhancements. Hα emission also shows a diffuse 'halo' from leaked photons not associated with discrete holes in the PDR. Overall ∼25% ± 10% of all ionizing photons are leaking into the nearby ISM.« less

Testing Fundamental Properties of Ionic Liquids for Colloid Microthruster Applications

NASA Technical Reports Server (NTRS)

Anderson, John R.; Plett, Gary; Anderson, Mark; Ziemer, John

2006-01-01

NASA's New Millennium Program is scheduled to test a Disturbance Reduction System (DRS) on Space Technology 7 (ST7) as part of the European Space Agency's (ESA's) LISA Pathfinder Mission in late 2009. Colloid Micronewton Thrusters (CMNTs) will be used to counteract forces, mainly solar photon pressure, that could disturb gravitational reference sensors as part of the DRS. The micronewton thrusters use an ionic liquid, a room temperature molten salt, as propellant. The ionic liquid has a number of unusual properties that have a direct impact on thruster design. One of the most important issues is bubble formation before and during operation, especially during rapid pressure transitions from atmospheric to vacuum conditions. Bubbles have been observed in the feed system causing variations in propellant flow rate that can adversely affect thruster control. Bubbles in the feed system can also increase the likelihood that propellant will spray onto surfaces that can eventually lead to shorting high voltage electrodes. Two approaches, reducing the probability of bubble formation and removing bubbles with a new bubble eliminator device in the flow system, were investigated at Busek Co., Inc. and the Jet Propulsion Laboratory (JPL) to determine the effectiveness of both approaches. Results show that bubble formation is mainly caused by operation at low pressure and volatile contaminants in the propellant coming out of solution. A specification for the maximum tolerable level of contamination has been developed, and procedures for providing system cleanliness have been tested and implemented. The bubble eliminator device has also been tested successfully and has been implemented in recent thruster designs at Busek. This paper focuses on the propellant testing work at JPL, including testing of a breadboard level bubble eliminator device.

Modeling of a bubble-memory organization with self-checking translators to achieve high reliability.

NASA Technical Reports Server (NTRS)

Bouricius, W. G.; Carter, W. C.; Hsieh, E. P.; Wadia, A. B.; Jessep, D. C., Jr.

1973-01-01

Study of the design and modeling of a highly reliable bubble-memory system that has the capabilities of: (1) correcting a single 16-adjacent bit-group error resulting from failures in a single basic storage module (BSM), and (2) detecting with a probability greater than 0.99 any double errors resulting from failures in BSM's. The results of the study justify the design philosophy adopted of employing memory data encoding and a translator to correct single group errors and detect double group errors to enhance the overall system reliability.

Prevalence of patent foramen ovale with right-to-left shunting in dogs with pulmonic stenosis.

PubMed

Fujii, Y; Nishimoto, Y; Sunahara, H; Takano, H; Aoki, T

2012-01-01

Right-to-left (R-L) shunt caused by patent foramen ovale (PFO) concurrent with pulmonic stenosis (PS) is considered common, although there is a lack of published evidence. To investigate the prevalence of R-L shunt caused by a PFO in dogs with PS. Thirty-one client-owned dogs with PS, without obvious extracardiac disease detected on the clinical examinations. Case control study: R-L shunt probably caused by PFO was diagnosed when IV injected microbubbles appeared at the left atrial level with an intact atrial septum on echocardiography (bubble-positive dogs). The severity of PS concurrent tricuspid regurgitation (TR), relative thickness of the right ventricle, and relative right atrial area were compared between bubble-positive and bubble-negative dogs. The prevalence of R-L shunts caused by PFO was 39% (12 of 31 cases). The instantaneous pressure gradient (PG) across the pulmonic valve and relative thickness of the right ventricle were significantly increased in bubble-positive compared with those in bubble-negative dogs. None of the dogs with mild or moderate PS (pressure gradient < 80 mm Hg, n = 2) demonstrated R-L shunt. The prevalence of TR in bubble-positive dogs was significantly higher than that in bubble-negative dogs. DISCUSSION AND CLINICAL RELEVANCE: Patent foramen ovale PFO with R-L shunt was more common in dogs with very severe PS and absent in dogs with mild PS. Copyright © 2011 by the American College of Veterinary Internal Medicine.

Age-Defying Star

NASA Image and Video Library

2016-08-29

An age-defying star called IRAS 19312+1950 exhibits features characteristic of a very young star and a very old star. The object stands out as extremely bright inside a large, chemically rich cloud of material, as shown in this image from NASA's Spitzer Space Telescope. IRAS 19312+1950 is the bright red star in the center of this image. A NASA-led team of scientists thinks the star -- which is about 10 times as massive as our sun and emits about 20,000 times as much energy -- is a newly forming protostar. That was a big surprise, because the region had not been known as a stellar nursery before. But the presence of a nearby interstellar bubble, which indicates the presence of a recently formed massive star, also supports this idea. http://photojournal.jpl.nasa.gov/catalog/PIA20914

Copernicus spectra and infrared photometry of 42 Orionis

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

Johnson, H.M.; Snow, T.P. Jr.; Gehrz, R.D.

1977-04-01

The Orion sword star 42 Ori is embedded in a nebula north of and separated from the Orion nebula. The B1 V star is probably normal. Other members of the multiple remain poorly defined, and the nebula may exhibit some peculiarities that may depend on them. Copernicus ultraviolet spectra of the star are described here, especially in the form of tables of wavelength identifications. The properties of the interstellar material in the line of sight are also discussed. We present infrared photometry which suggests that 3 less than or equal to R less than or equal to 3.5 for themore » interstellar matter in the direction of 42 Ori. The IR photometry provides no evidence for companion stellar or circumstellar components.« less

Copernicus spectra and infrared photometry of 42 Orionis

NASA Technical Reports Server (NTRS)

Johnson, H. M.; Snow, T. P., Jr.; Gehrz, R. D.; Hackwell, J. A.

1977-01-01

The Orion sword star 42 Ori is embedded in a nebula north of and separated from the Orion nebula. The B1 V star is probably normal. Other members of the multiple remain poorly defined, and the nebula may exhibit some peculiarities that may depend on them. Copernicus ultraviolet spectra of the star are described here, especially in the form of tables of wavelength identifications. The properties of the interstellar material in the line of sight are also discussed. Infrared photometry is presented which suggests that the ratio of total to selective extinction ranges from 3 to 3.5 for the interstellar matter in the direction of 42 Ori. The IR photometry provides no evidence for companion stellar or circumstellar components.

Detection of the aromatic molecule benzonitrile (c-C6H5CN) in the interstellar medium

NASA Astrophysics Data System (ADS)

McGuire, Brett A.; Burkhardt, Andrew M.; Kalenskii, Sergei; Shingledecker, Christopher N.; Remijan, Anthony J.; Herbst, Eric; McCarthy, Michael C.

2018-01-01

Polycyclic aromatic hydrocarbons and polycyclic aromatic nitrogen heterocycles are thought to be widespread throughout the universe, because these classes of molecules are probably responsible for the unidentified infrared bands, a set of emission features seen in numerous Galactic and extragalactic sources. Despite their expected ubiquity, astronomical identification of specific aromatic molecules has proven elusive. We present the discovery of benzonitrile (c-C6H5CN), one of the simplest nitrogen-bearing aromatic molecules, in the interstellar medium. We observed hyperfine-resolved transitions of benzonitrile in emission from the molecular cloud TMC-1. Simple aromatic molecules such as benzonitrile may be precursors for polycyclic aromatic hydrocarbon formation, providing a chemical link to the carriers of the unidentified infrared bands.

In situ observations of bubble growth in basaltic, andesitic and rhyodacitic melts

NASA Astrophysics Data System (ADS)

Masotta, M.; Ni, H.; Keppler, H.

2014-02-01

Bubble growth strongly affects the physical properties of degassing magmas and their eruption dynamics. Natural samples and products from quench experiments provide only a snapshot of the final state of volatile exsolution, leaving the processes occurring during its early stages unconstrained. In order to fill this gap, we present in situ high-temperature observations of bubble growth in magmas of different compositions (basalt, andesite and rhyodacite) at 1,100 to 1,240 °C and 0.1 MPa (1 bar), obtained using a moissanite cell apparatus. The data show that nucleation occurs at very small degrees of supersaturaturation (<60 MPa in basalt and andesite, 200 MPa in rhyodacite), probably due to heterogeneous nucleation of bubbles occurring simultaneously with the nucleation of crystals. During the early stages of exsolution, melt degassing is the driving mechanism of bubble growth, with coalescence becoming increasingly important as exsolution progresses. Ostwald ripening occurs only at the end of the process and only in basaltic melt. The average bubble growth rate ( G R) ranges from 3.4 × 10-6 to 5.2 × 10-7 mm/s, with basalt and andesite showing faster growth rates than rhyodacite. The bubble number density ( N B) at nucleation ranges from 7.9 × 104 mm-3 to 1.8 × 105 mm-3 and decreases exponentially over time. While the rhyodacite melt maintained a well-sorted bubble size distribution (BSD) through time, the BSDs of basalt and andesite are much more inhomogeneous. Our experimental observations demonstrate that bubble growth cannot be ascribed to a single mechanism but is rather a combination of many processes, which depend on the physical properties of the melt. Depending on coalescence rate, annealing of bubbles following a single nucleation event can produce complex bubble size distributions. In natural samples, such BSDs may be misinterpreted as resulting from several separate nucleation events. Incipient crystallization upon cooling of a magma may allow bubble nucleation already at very small degrees of supersaturation and could therefore be an important trigger for volatile release and explosive eruptions.

Vela X: A plerion or part of a shell?

NASA Astrophysics Data System (ADS)

Gvaramadze, V. V.

1998-03-01

An analysis of the radio, optical, and X-ray observations of the supernova remnant (SNR) in Vela has led us to conclude that the radio source Vela X is part of the SNR shell. The high brightness of this radio source is assumed to be a result of the interaction of dome-shaped deformations (bubbles) on the SNR shell, which gives rise to bright radio filaments. The deformations could be produced by Richtmaier-Meshkov's instability, which develops during the impulsive acceleration of a shell of gas (swept up from the interstellar medium by the wind from a presupernova) by a shock wave (generated by a supernova explosion). The brightest radio filament and the X-ray jet extending along it are shown to be located in the region of interaction of two prominent bubbles on the SNR shell. We conclude that the X-ray jet, like Vela X, is part of the shell, and that it has its origin in the Mach reflection of two semispherical shock waves. Our estimate of the plasma temperature behind the front of the Mach wave matches the jet temperature. We also show that the large spread in the estimates of the spectral index for Vela X could be caused by the instrumental effect which arises during observations of extended radio sources with a nonuniform surface-brightness distribution.

Foam Flow Through a 2D Porous Medium: Evolution of the Bubble Size Distribution

NASA Astrophysics Data System (ADS)

Meheust, Y.; Géraud, B.; Cantat, I.; Dollet, B.

2017-12-01

Foams have been used for decades as displacing fluids for EOR and aquifer remediation, and more recently as carriers of chemical amendments for remediation of the vadose zone. Bulk foams are shear-thinning fluids; but for foams with bubbles of order at least the typical pore size of the porous medium, the rheology cannot be described at the continuum scale, as viscous dissipation occurs mostly at the contact between soap films and solid walls. We have investigated the flow of an initially monodisperse foam through a transparent 2D porous medium[1]. The resulting complex flow phenomenology has been characterized quantitatively from optical measurements of the bubble dynamics. In addition to preferential flow path and local flow intermittency, we observe an irreversible evolution of the probability density function (PDF) for bubbles size as bubbles travel along the porous medium. This evolution is due to bubble fragmentation by lamella division, which is by far the dominant mechanism of film creation/destruction. We measure and characterize this evolution of the PDF as a function of the experimental parameters, and model it numerically based on a fragmentation equation, with excellent agreement. The model uses two ingredients obtained from the experimental data, namely the statistics of the bubble fragmentation rate and of the fragment size distributions[2]. It predicts a nearly-universal scaling of all PDFs as a function of the bubble area normalized by the initial mean bubble area. All the PDFs measured in various experiments, with different mean flow velocities, initial bubble sizes and foam qualities, collapse on a master distribution which is only dependent on the geometry of the medium.References:[1] B. Géraud, S. A. Jones, I. Cantat, B. Dollet & Y. Méheust (2016), WRR 52(2), 773-790. [2] B. Géraud, Y. Méheust, I. Cantat & B. Dollet (2017), Lamella division in a foam flowing through a two-dimensional porous medium: A model fragmentation process, PRL 118, 098003.

The spectral energy distribution of Zeta Puppis and HD 50896

NASA Technical Reports Server (NTRS)

Holm, A. V.; Cassinelli, J. P.

1977-01-01

The ultraviolet spectral energy distribution of the O5f star Zeta Pup and the WN5 star HD 50896 are derived from OAO-2 observations with the calibration of Bless, Code, and Fairchild (1976). An estimate of the interstellar reddening (0.12 magnitude) of the Wolf-Rayet star is determined from the size of the characteristic interstellar extinction bump at 4.6 inverse microns. After correction for extinction, both stars show a flat energy distribution in the ultraviolet. The distribution of HD 50896 from 1100 A to 2 microns is in good agreement with results of extended model atmospheres, but some uncertainty remains because of the interstellar-extinction correction. The absolute energy distribution of Zeta Pup is fitted by a 42,000-K plane-parallel model if the model's flux is adjusted for the effects of electron scattering in the stellar wind and for UV line blanketing that was determined empirically from high-resolution Copernicus satellite observations. To achieve this fit, it is necessary to push both the spectroscopically determined temperature and the ultraviolet calibration to the limits of their probable errors.

Chemistry and Evolution of Interstellar Clouds

NASA Technical Reports Server (NTRS)

Wooden, D. H.; Charnley, S. B.; Ehrenfreund, P.

2003-01-01

In this chapter we describe how elements have been and are still being formed in the galaxy and how they are transformed into the reservoir of materials present at the time of formation of our protosolar nebula. We discuss the global cycle of matter, beginning at its formation site in stars, where it is ejected through winds and explosions into the diffuse interstellar medium. In the next stage of the global cycle occurs in cold, dense molecular clouds, where the complexity of molecules and ices increases relative to the diffuse ISM.. When a protostar forms in a dense core within a molecular cloud, it heats the surrounding infalling matter warms and releases molecules from the solid phase into the gas phase in a warm, dense core, sponsoring a rich gas-phase chemistry. Some material from the cold and warm regions within molecular clouds probably survives as interstellar matter in the protostellar disk. For the diffuse ISM, for cold, dense clouds, and for dense-warm cores, the physio-chemical processes that occur within the gas and solid phases are discussed in detail.

Interstellar X-Ray Absorption Spectroscopy of the Crab Pulsar with the LETGS

NASA Technical Reports Server (NTRS)

Paerels, Frits; Weisskopf, Martin C.; Tennant, Allyn F.; ODell, Stephen L.; Swartz, Douglas A.; Kahn, Steven M.; Behar, Ehud; Becker, Werner; Whitaker, Ann F. (Technical Monitor)

2001-01-01

We study the interstellar X-ray absorption along the line of sight to the Crab Pulsar. The Crab was observed with the Low Energy Transmission Grating Spectrometer on the Chandra X-ray Observatory, and the pulsar, a point source, produces a full resolution spectrum. The continuum spectrum appears smooth, and we compare its parameters with other measurements of the pulsar spectrum. The spectrum clearly shows absorption edges due to interstellar Ne, Fe, and O. The O edge shows spectral structure that is probably due to O bound in molecules or dust. We search for near-edge structure (EXAFS) in the O absorption spectrum. The Fe L absorption spectrum is largely due to a set of unresolved discrete n=2-3 transitions in neutral or near-neutral Fe, and we analyze it using a new set of dedicated atomic structure calculations, which provide absolute cross sections. In addition to being interesting in its own right, the ISM absorption needs to be understood in quantitative detail in order to derive spectroscopic constraints on possible soft thermal radiation from the pulsar.

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

Park, J.; Kucharek, H.; Möbius, E.

In this paper we report on a two-year study to estimate the Ne/O abundance ratio in the gas phase of the local interstellar cloud (LIC). Based on the first two years of observations with the Interstellar Boundary Explorer, we determined the fluxes of interstellar neutral (ISN) O and Ne atoms at the Earth's orbit in spring 2009 and 2010. A temporal variation of the Ne/O abundance ratio at the Earth's orbit could be expected due to solar cycle-related effects such as changes of ionization. However, this study shows that there is no significant change in the Ne/O ratio at themore » Earths orbit from 2009 to 2010. We used time-dependent survival probabilities of the ISNs to calculate the Ne/O abundance ratio at the termination shock. Then we estimated the Ne/O abundance ratio in the gas phase of the LIC with the use of filtration factors and the ionization fractions. From our analysis, the Ne/O abundance ratio in the LIC is 0.33 ± 0.07, which is in agreement with the abundance ratio inferred from pickup-ion measurements.« less

Global Distribution of Density Irregularities in the Equatorial Ionosphere

NASA Technical Reports Server (NTRS)

Kil, Hyosub; Heelis, R. A.

1998-01-01

We analyzed measurements of ion number density made by the retarding potential analyzer aboard the Atmosphere Explorer-E (AE-E) satellite, which was in an approximately circular orbit at an altitude near 300 km in 1977 and later at an altitude near 400 km. Large-scale (greater than 60 km) density measurements in the high-altitude regions show large depletions of bubble-like structures which are confined to narrow local time longitude, and magnetic latitude ranges, while those in the low-altitude regions show relatively small depletions which are broadly distributed,in space. For this reason we considered the altitude regions below 300 km and above 350 km and investigated the global distribution of irregularities using the rms deviation delta N/N over a path length of 18 km as an indicator of overall irregularity intensity. Seasonal variations of irregularity occurrence probability are significant in the Pacific regions, while the occurrence probability is always high in die Atlantic-African regions and is always low in die Indian regions. We find that the high occurrence probability in the Pacific regions is associated with isolated bubble structures, while that near 0 deg longitude is produced by large depictions with bubble structures which are superimposed on a large-scale wave-like background. Considerations of longitude variations due to seeding mechanisms and due to F region winds and drifts are necessary to adequately explain the observations at low and high altitudes. Seeding effects are most obvious near 0 deg longitude, while the most easily observed effect of the F region is the suppression of irregularity growth by interhemispheric neutral winds.

Lyα-emitting galaxies as a probe of reionization: large-scale bubble morphology and small-scale absorbers

NASA Astrophysics Data System (ADS)

Kakiichi, Koki; Dijkstra, Mark; Ciardi, Benedetta; Graziani, Luca

2016-12-01

The visibility of Lyα-emitting galaxies during the Epoch of Reionization is controlled by both diffuse H I patches in large-scale bubble morphology and small-scale absorbers. To investigate their impacts on Lyα transfer, we apply a novel combination of analytic modelling and cosmological hydrodynamical, radiative transfer simulations to three reionization models: (I) the `bubble' model, where only diffuse H I outside ionized bubbles is present; (II) the `web' model, where H I exists only in overdense self-shielded gas; and (III) the hybrid `web-bubble' model. The three models can explain the observed Lyα luminosity function equally well, but with very different H I fractions. This confirms a degeneracy between the ionization topology of the intergalactic medium (IGM) and the H I fraction inferred from Lyα surveys. We highlight the importance of the clustering of small-scale absorbers around galaxies. A combined analysis of the Lyα luminosity function and the Lyα fraction can break this degeneracy and provide constraints on the reionization history and its topology. Constraints can be improved by analysing the full MUV-dependent redshift evolution of the Lyα fraction of Lyman break galaxies. We find that the IGM-transmission probability distribution function is unimodal for bubble models and bimodal in web models. Comparing our models to observations, we infer that the neutral fraction at z ˜ 7 is likely to be of the order of tens of per cent when interpreted with bubble or web-bubble models, with a conservative lower limit ˜1 per cent when interpreted with web models.

OVII and Temperature Limits on the Local Hot Bubble

NASA Astrophysics Data System (ADS)

Pirtle, Robert; Petre, N.; McCammon, D.; Morgan, K.; Sauter, P.; Clavadetscher, K.; Fujimoto, R.; Hagihara, T.; Masui, K.; Mitsuda, K.; Takei, Y.; Wang, Q. D.; Yamasaki, N. Y.; Yao, Y.; Yoshino, T.

2013-01-01

The observed ¼-keV (ROSAT R12 band) X-ray background originates largely in a region of hot ionized gas roughly 100 pc in extent surrounding the Sun known as the Local Hot Bubble (LHB). The observed flux is quite uniform at low latitudes (|b| < 30°), but there a several large areas at intermediate and high latitudes that are enhanced by factors of 2 - 3. Charge exchange between highly charged ions in the Solar wind and interstellar neutral H and He moving through interplanetary space might provide a very roughly isotropic contribution about equal to the low- latitude flux (Koutroumpa et al. 2008), but cannot produce the enhancements. Correlations with the interstellar absorbing column show that some of these bright regions are apparently due to clumps of hot gas in the Galactic halo, while many of them show no correlation and must be due to extensions of the LHB (Kuntz & Snowden 2000, Bellm & Vaillancourt 2005). Global fits of simple plasma emission spectra give temperatures near 1.0 x 106 K for both LHB and halo emission, but the possibility of a substantial contamination by charge exchange could distort this result in unknown ways. Thermal excitation of O VII is strongly temperature dependent in this range, so we have tried to correlate O VII fluxes measured with Suzaku with variations in ¼-keV intensity from the ROSAT R12 band map to determine the temperature. We take eleven O VII intensity measurements from Yoshino et al. (2009), one from Masui et al. (2009), and an additional eighteen from archival Suzaku pointings and correlate these with the R12 band local and halo intensities as separated by Kunzt & Snowden (2000). The lack of detectable correlation in both cases strongly limits any O VII production by the material producing the enhancements, and upper limits to the temperatures are set. This work was supported in part by the National Science Foundation's REU program through NSF Award AST-1004881 and by NASA grant NNX09AF09G. *present address: Department of Physics, Lewis & Clark College, Portland, OR. This work was supported in part by the National Science Foundation's REU program through NSF Award AST-1004881.

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

Curtis, Jason Lee, E-mail: jasoncurtis.astro@gmail.com

The solar analogs of M67 let us glimpse the probable behavior of the Sun on timescales surpassing the duration of human civilization. M67 can serve as a solar proxy because its stars share a similar age and composition with the Sun. Previous surveys of M67 observed that 15% of its Sun-like stars exhibited chromospheric activity levels below solar minimum, which suggest that these stars might be in activity-minimum states analogous to the Maunder Minimum. The activity diagnostic used, the HK index (relative intensities of the Ca ii H and K lines integrated over 1 Å bandpasses), was measured from low-resolution spectramore » ( R ≈ 5000), as is traditional and suitable for nearby, bright stars. However, for stars beyond the Local Bubble, the interstellar medium (ISM) imprints absorption lines in spectra at Ca ii H and K, which negatively bias activity measurements when these lines fall within the HK index bandpass. I model the ISM clouds in the M67 foreground with high-resolution spectra of blue stragglers and solar analogs. I demonstrate that ISM absorption varies across the cluster and must be accounted for on a star-by-star basis. I then apply the ISM model to a solar spectrum and broaden it to the lower spectral resolution employed by prior surveys. Comparing HK indices measured from ISM-free and ISM-contaminated spectra, I find that all stars observed below solar minimum can be explained by this ISM bias. I conclude that there is no compelling evidence for Maunder Minimum candidates in M67 at this time.« less

Nebular and Interstellar Materials in a Giant Cluster IDP of Probable Cometary Origin

NASA Technical Reports Server (NTRS)

Messenger, S.; Brownlee, D. E.; Joswiak, D. J.; Nguyen, A. N.

2015-01-01

Comets contain a complex mixture of materials with presolar and Solar System origins. Chondritic porous interplanetary dust particles (CP-IDPs) are associated with comets by their fragile nature, unequilibrated anhydrous mineralogy and high abundances of circumstellar grains and isotopically anomalous organic materials. Comet 81P/Wild 2 samples returned by the Stardust spacecraft contain presolar materials as well as refractory 16O-rich Ca-Al-rich inclusion- (CAI), chondrule-, and AOA-like materials. We are conducting coordinated chemical, mineralogical, and isotopic studies of a giant cluster CP-IDP (U2-20-GCA) to determine the proportions of inner Solar System and interstellar materials. We previously found that this IDP contains abundant presolar silicates (approx. 1,800 ppm) and 15N-rich hotspots [6].

The abundance of boron in three halo stars

NASA Technical Reports Server (NTRS)

Duncan, Douglas K.; Lambert, David L.; Lemke, Michael

1992-01-01

B abundances for three halo stars: HD 140283, HD 19445, and HD 201891 are presented. Using recent determinations of the Be abundance in HD 140283, B/Be of 10 +5/-4 is found for this star, and similar ratios are inferred for HD 19445 and HD 201891. This ratio is equal to the minimum value of 10 expected from a synthesis of B and Be by high-energy cosmic-ray spallation reactions in the interstellar medium. It is shown that the accompanying synthesis of Li by alpha on alpha fusion reactions is probably a minor contributor to the observed 'primordial' Li of halo stars. The observed constant ratios of B/O and Be/O are expected if the principal channel of synthesis involves cosmic-ray CNO nuclei from the supernovae colliding with interstellar protons.

The planetary and interstellar components of meteorites - A review

NASA Technical Reports Server (NTRS)

Marvin, Ursula B.

1987-01-01

Recent analyses show that, although most meteorites are collisional debris of asteroids, three meteorites collected on the Antarctic ice sheet were projected to earth from the highlands of the moon, and eight meteorites have chemical and isotopic compositions suggestive of derivation from Mars. Although meteorites are primarily of interest to planetary scientists for the abundance of clues they hold to the materials and processes that formed the solar system, they have begun to engage the attention of astrochemists because of isotopic and mineralogical indications that they contain interstellar components. Although each individual observation to this effect is inconclusive, the body of evidence is becoming ever more persuasive. This paper reviews the main classes of meteorites and their probable sources, with special emphasis on components that appear to be exotic to the solar system.

Massive Stars and the Energy Balance of the Interstellar Medium. 1; The Impact of an Isolated 60 M. Star

NASA Technical Reports Server (NTRS)

Freyer, Tim; Hensler, Gerhard; Yorke, Harold W.

2003-01-01

We present results of numerical simulations carried out with a two-dimensional radiation hydrodynamics code in order to study the impact of massive stars on their surrounding interstellar medium. This first paper deals with the evolution of the circumstellar gas around an isolated 60 M. star. The interaction of the photo- ionized H II region with the stellar wind bubble forms a variety of interesting structures like shells, clouds, fingers, and spokes. These results demonstrate that complex structures found in H II regions are not necessarily relics from the time before the gas became ionized but may result from dynamical processes during the course of the H II region evolution. We have also analyzed the transfer and deposit of the stellar wind and radiation energy into the circumstellar medium until the star explodes as a supernova. Although the total mechanical wind energy supplied by the star is negligible compared to the accumulated energy of the Lyman continuum photons, the kinetic energy imparted to the circumstellar gas over the star s lifetime is 4 times higher than for a comparable windless simulation. Furthermore, the thermal energy of warm photoionized gas is lower by some 55%). Our results document the necessity to consider both ionizing radiation and stellar winds for an appropriate description of the interaction of OB stars with their circumstellar environment.

Hubble Sees a Star ‘Inflating’ a Giant Bubble

NASA Image and Video Library

2017-12-08

For the 26th birthday of NASA’s Hubble Space Telescope, astronomers are highlighting a Hubble image of an enormous bubble being blown into space by a super-hot, massive star. The Hubble image of the Bubble Nebula, or NGC 7635, was chosen to mark the 26th anniversary of the launch of Hubble into Earth orbit by the STS-31 space shuttle crew on April 24, 1990 “As Hubble makes its 26th revolution around our home star, the sun, we celebrate the event with a spectacular image of a dynamic and exciting interaction of a young star with its environment. The view of the Bubble Nebula, crafted from WFC-3 images, reminds us that Hubble gives us a front row seat to the awe inspiring universe we live in,” said John Grunsfeld, Hubble astronaut and associate administrator of NASA’s Science Mission Directorate at NASA Headquarters, in Washington, D.C. The Bubble Nebula is seven light-years across—about one-and-a-half times the distance from our sun to its nearest stellar neighbor, Alpha Centauri, and resides 7,100 light-years from Earth in the constellation Cassiopeia. The seething star forming this nebula is 45 times more massive than our sun. Gas on the star gets so hot that it escapes away into space as a “stellar wind” moving at over four million miles per hour. This outflow sweeps up the cold, interstellar gas in front of it, forming the outer edge of the bubble much like a snowplow piles up snow in front of it as it moves forward. As the surface of the bubble's shell expands outward, it slams into dense regions of cold gas on one side of the bubble. This asymmetry makes the star appear dramatically off-center from the bubble, with its location in the 10 o’clock position in the Hubble view. Dense pillars of cool hydrogen gas laced with dust appear at the upper left of the picture, and more “fingers” can be seen nearly face-on, behind the translucent bubble. The gases heated to varying temperatures emit different colors: oxygen is hot enough to emit blue light in the bubble near the star, while the cooler pillars are yellow from the combined light of hydrogen and nitrogen. The pillars are similar to the iconic columns in the “Pillars of Creation” Eagle Nebula. As seen with the structures in the Eagle Nebula, the Bubble Nebula pillars are being illuminated by the strong ultraviolet radiation from the brilliant star inside the bubble. The Bubble Nebula was discovered in 1787 by William Herschel, a prominent British astronomer. It is being formed by a proto-typical Wolf-Rayet star, BD +60º2522, an extremely bright, massive, and short-lived star that has lost most of its outer hydrogen and is now fusing helium into heavier elements. The star is about four million years old, and in 10 million to 20 million years, it will likely detonate as a supernova. Hubble’s Wide Field Camera-3 imaged the nebula in visible light with unprecedented clarity in February 2016. The colors correspond to blue for oxygen, green for hydrogen, and red for nitrogen. This information will help astronomers understand the geometry and dynamics of this complex system. The Bubble Nebula is one of only a handful of astronomical objects that have been observed with several different instruments onboard Hubble. Hubble also imaged it with the Wide Field Planetary Camera (WFPC) in September 1992, and with Wide Field Planetary Camera-2 (WFPC2) in April 1999. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

Synthetic Observations of 21 cm H I Line Profiles from Inhomogeneous Turbulent Interstellar H I Gas with Magnetic Fields

NASA Astrophysics Data System (ADS)

Fukui, Yasuo; Hayakawa, Takahiro; Inoue, Tsuyoshi; Torii, Kazufumi; Okamoto, Ryuji; Tachihara, Kengo; Onishi, Toshikazu; Hayashi, Katsuhiro

2018-06-01

We carried out synthetic observations of interstellar atomic hydrogen at 21 cm wavelength by utilizing the magnetohydrodynamic numerical simulations of the inhomogeneous turbulent interstellar medium. The cold neutral medium (CNM) shows a significantly clumpy distribution with a small volume filling factor of 3.5%, whereas the warm neutral medium (WNM) has a distinctly different and smooth distribution with a large filling factor of 96.5%. In projection on the sky, the CNM exhibits a highly filamentary distribution with a subparsec width, whereas the WNM shows a smooth, extended distribution. In the H I optical depth, the CNM is dominant and the contribution of the WNM is negligibly small. The CNM has an area covering factor of 30% in projection, while the WNM has a covering factor of 70%. This means that the emission–absorption measurements toward radio continuum compact sources tend to sample the WNM with a probability of 70%, yielding a smaller H I optical depth and a smaller H I column density than those of the bulk H I gas. The emission–absorption measurements, which are significantly affected by the small-scale large fluctuations of the CNM properties, are not suitable for characterizing the bulk H I gas. Larger-beam emission measurements that are able to fully sample the H I gas will provide a better tool for that purpose, if a reliable proxy for hydrogen column density, possibly dust optical depth and gamma rays, is available. The present results provide a step toward precise measurements of the interstellar hydrogen with ∼10% accuracy. This will be crucial in interstellar physics, including identification of the proton–proton interaction in gamma-ray supernova remnants.

The Wait Calculation: The Broader Consequences of the Minimum Time from Now to Interstellar Destinations and its Significance to the Space Economy

NASA Astrophysics Data System (ADS)

Kennedy, A.

This paper summarises the wait calculation [1] of interstellar voyagers which finds the minimum time to destination given exponential growth in the rate of travel available to a civilisation. The minimum time obliges stellar system colonisers to consider departure times a significant risk factor in their voyages since a departure then to a destination will beat a departure made at any other time before or after. Generalised conclusions will be drawn about the significant impact that departures to interstellar destinations before, at, or after the minimum time will have on the economic potential of missions and on the inevitability of competition between them. There will be no international law operating in interstellar space and an ability to escape predatory actions en route, or at the destination, can only be done by precise calculations of departure times. Social and economic forces affecting the factors in the growth equation are discussed with reference to the probability of accelerating growth reaching the technological Singularity and strengthening the growth incentive trap. Islamic banking practices are discussed as a credible alternative to compounding interest bearing paper for funding the space economy in the long term and for supporting stakeholder investment in such long term mission development. The paper considers the essential free productivity of the Earth's biosphere and the capital accumulations made possible by land productivity are essential components to a viable long term space economy and that research into re-creating the costless productivity of the biosphere at a destination will determine both the mission's ultimate success and provide means of returns for stakeholders during the long build up. Conclusions of these arguments suggest that the Icarus project should ignore a robotic interstellar mission concept and develop a manned colonising mission from now.

Broken bridges: a counter-example of the ER=EPR conjecture

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

Chen, Pisin; Wu, Chih-Hung; Yeom, Dong-han, E-mail: pisinchen@phys.ntu.edu.tw, E-mail: b02202007@ntu.edu.tw, E-mail: innocent.yeom@gmail.com

In this paper, we provide a counter-example to the ER=EPR conjecture. In an anti-de Sitter space, we construct a pair of maximally entangled but separated black holes. Due to the vacuum decay of the anti-de Sitter background toward a deeper vacuum, these two parts can be trapped by bubbles. If these bubbles are reasonably large, then within the scrambling time, there should appear an Einstein-Rosen bridge between the two black holes. Now by tracing more details on the bubble dynamics, one can identify parameters such that one of the two bubbles either monotonically shrinks or expands. Because of the changemore » of vacuum energy, one side of the black hole would evaporate completely. Due to the shrinking of the apparent horizon, a signal of one side of the Einstein-Rosen bridge can be viewed from the opposite side. We analytically and numerically demonstrate that within a reasonable semi-classical parameter regime, such process can happen. Bubbles are a non-perturbative effect, which is the crucial reason that allows the transmission of information between the two black holes through the Einstein-Rosen bridge, even though the probability is highly suppressed. Therefore, the ER=EPR conjecture cannot be generic in its present form and its validity maybe restricted.« less

Astronomers puzzle over a peculiar age-defying massive star

NASA Image and Video Library

2017-12-08

An age-defying star designated as IRAS 19312+1950 exhibits features characteristic of a very young star and a very old star. The object stands out as extremely bright inside a large, chemically rich cloud of material, as shown in this image from NASA’s Spitzer Space Telescope. A NASA-led team of scientists thinks the star – which is about 10 times as massive as our sun and emits about 20,000 times as much energy – is a newly forming protostar. That was a big surprise because the region had not been known as a stellar nursery before. But the presence of a nearby interstellar bubble, which indicates the presence of a recently formed massive star, also supports this idea. Read more: go.nasa.gov/2bMza9d Image Credit: NASA/JPL-Caltech

A HIRES analysis of the FIR emission of supernova remnants

NASA Technical Reports Server (NTRS)

Wang, Zhong

1994-01-01

The high resolution (HiRes) algorithm has been used to analyze the far infrared emission of shocked gas and dust in supernova remnants. In the case of supernova remnant IC 443, we find a very good match between the resolved features in the deconvolved images and the emissions of shocked gas mapped in other wavelengths (lines of H2, CO, HCO+, and HI). Dust emission is also found to be surrounding hot bubbles of supernova remnants which are seen in soft X-ray maps. Optical spectroscopy on the emission of the shocked gas suggests a close correlation between the FIR color and local shock speed, which is a strong function of the ambient (preshock) gas density. These provide a potentially effective way to identify regions of strong shock interaction, and thus facilitate studies of kinematics and energetics in the interstellar medium.

INTERACTIONS OF THE INFRARED BUBBLE N4 WITH ITS SURROUNDINGS

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

Liu, Hong-Li; Li, Jin-Zeng; Yuan, Jing-Hua

The physical mechanisms that induce the transformation of a certain mass of gas in new stars are far from being well understood. Infrared bubbles associated with H ii regions have been considered to be good samples for investigating triggered star formation. In this paper we report on the investigation of the dust properties of the infrared bubble N4 around the H ii region G11.898+0.747, analyzing its interaction with its surroundings and star formation histories therein, with the aim of determining the possibility of star formation triggered by the expansion of the bubble. Using Herschel PACS and SPIRE images with a widemore » wavelength coverage, we reveal the dust properties over the entire bubble. Meanwhile, we are able to identify six dust clumps surrounding the bubble, with a mean size of 0.50 pc, temperature of about 22 K, mean column density of 1.7 × 10{sup 22} cm{sup −2}, mean volume density of about 4.4 × 10{sup 4} cm{sup −3}, and a mean mass of 320 M{sub ⊙}. In addition, from PAH emission seen at 8 μm, free–free emission detected at 20 cm, and a probability density function in special regions, we could identify clear signatures of the influence of the H ii region on the surroundings. There are hints of star formation, though further investigation is required to demonstrate that N4 is the triggering source.« less

Shear Stress induced Stretching of Red Blood Cells by Oscillating Bubbles within a Narrow Gap

NASA Astrophysics Data System (ADS)

Li, Fenfang; Mohammadzadeh, Milad; Ohl, Claus-Dieter; Claus-Dieter Ohl Team

2013-11-01

The flow pattern, especially the boundary layer caused by the expanding/contracting bubble in a narrow gap (15 μm) and the resultant stretching of red blood cells is investigated in this work. High speed recordings show that a red blood cell (biconcave shape, thickness of 1-2 μm) can be elongated to five times its original length by a laser-induced cavitation bubble within the narrow gap. However, flexible cancer cells in suspension (RKO, spherical shape, diameter of 10-15 μm) are hardly elongated under the same experimental condition. We hypothesize that the shear stress at the boundary layer is crucial for this elongation to occur. Therefore, in order to resolve the related fluid dynamics, we conducted numerical simulations using the finite element method (Fluent). The rapidly expanding/contracting vapor bubble is successfully modeled by employing viscosity and surface tension. The transient pressure inside the bubble and the velocity profile of the flow is obtained. We observe strong shear near the upper and lower boundary during the bubble oscillation. The flow fields are compared with analytical solutions to transient and pulsating flows in 2D. In the experiment the red blood cells sit within the lower boundary layer, thus are probably elongated by this strong shear flow. In contrast, the spherical cancer cells are of comparable size to the gap height so that they are lesser affected by this boundary layer flow.

Quasiopen inflation

NASA Astrophysics Data System (ADS)

García-Bellido, Juan; Garriga, Jaume; Montes, Xavier

1998-04-01

We show that a large class of two-field models of single-bubble open inflation does not lead to infinite open universes, as was previously thought, but to an ensemble of very large but finite inflating ``islands.'' The reason is that the quantum tunneling responsible for the nucleation of the bubble does not occur simultaneously along both field directions and equal-time hypersurfaces in the open universe are not synchronized with equal-density or fixed-field hypersurfaces. The most probable tunneling trajectory corresponds to a zero value of the inflaton field; large values, necessary for the second period of inflation inside the bubble, only arise as localized fluctuations. The interior of each nucleated bubble will contain an infinite number of such inflating regions of comoving size of order γ-1, where γ is the supercurvature eigenvalue, which depends on the parameters of the model. Each one of these islands will be a quasi-open universe. Since the volume of the hyperboloid is infinite, inflating islands with all possible values of the field at their center will be realized inside of a single bubble. We may happen to live in one of those patches of comoving size d<~γ-1, where the universe appears to be open. In particular, we consider the ``supernatural'' model proposed by Linde and Mezhlumian. There, an approximate U(1) symmetry is broken by a tunneling field in a first order phase transition, and slow-roll inflation inside the nucleated bubble is driven by the pseudo Goldstone field. We find that the excitations of the pseudo Goldstone field produced by the nucleation and subsequent expansion of the bubble place severe constraints on this model. We also discuss the coupled and uncoupled two-field models.

Analysis of bubbles and crashes in the TRY/USD, TRY/EUR, TRY/JPY and TRY/CHF exchange rate within the scope of econophysics

NASA Astrophysics Data System (ADS)

Deviren, Bayram; Kocakaplan, Yusuf; Keskin, Mustafa; Balcılar, Mehmet; Özdemir, Zeynel Abidin; Ersoy, Ersan

2014-09-01

In this study, we analyze the Turkish Lira/US Dollar (TRY/USD), Turkish Lira/Euro (TRY/EUR), Turkish Lira/Japanese Yen (TRY/JPY) and Turkish Lira/Swiss Franc (TRY/CHF) exchange rates in the global financial crisis period to detect the bubbles and crashes in the TRY by using a mathematical methodology developed by Watanabe et al. (2007). The methodology defines the bubbles and crashes in financial market price fluctuations by considering an exponential fitting of the associated data. This methodology is applied to detect the bubbles and crashes in the TRY/USD, TRY/EUR, TRY/JPY and TRY/CHF exchange rates from January, 1, 2005 to December, 20, 2013. In this mathematical methodology, the whole period of bubbles and crashes can be determined purely from past data, and the start of bubbles and crashes can be identified even before its bursts. In this way, the periods of bubbles and crashes in the TRY/USD, TRY/EUR, TRY/JPY and TRY/CHF are determined, and the beginning and end points of these periods are detected. The results show that the crashes in the TRY/CHF exchange rate are commonly finished earlier than in the other exchange rates; hence it is probable that the crashes in the other exchange rates would be finished soon when the crashes in the TRY/CHF exchange rate ended. We also find that the periods of crashes in the TRY/EUR exchange rate take longer time than in the other exchange rates. This information can be used in risk management and/or speculative gain. The crashes' periods in the TRY/EUR and TRY/USD exchange rates are observed to be relatively longer than in the other exchange rates.

Near-infrared spectroscopy of the proto-planetary nebula CRL 618 and the origin of the hydrocarbon dust component in the interstellar medium.

PubMed

Chiar, J E; Pendleton, Y J; Geballe, T R; Tielens, A G

1998-11-01

A new 2.8-3.8 micrometers spectrum of the carbon-rich protoplanetary nebula CRL 618 confirms the previous detection of a circumstellar 3.4 micrometers absorption feature in this object (Lequeux & Jourdain de Muizon). The high resolution and high signal-to-noise ratio of our spectrum allow us to derive the detailed profile of this absorption feature, which is very similar to that observed in the spectrum of the Galactic center and also resembles the strong 3.4 micrometers emission feature in some post-asymptotic giant branch stars. A weak 3.3 micrometers unidentified infrared band, marginally detected in the CRL 618 spectrum of Lequeux & Jourdain de Muizon, is present in our spectrum. The existence of the 3.4 micrometers feature implies the presence of relatively short-chained, aliphatic hydrocarbon materials (-CH2-/-CH3 approximately = 2-2.5) in the circumstellar environment around CRL 618. It also implies that the carriers of the interstellar 3.4 micrometers feature are produced at least in part in circumstellar material, and it calls into question whether any are produced by the processing of interstellar ices in dense interstellar clouds, as has been previously proposed. Other features in the spectrum are recombination lines of hydrogen, rotational and vibration-rotation lines of molecular hydrogen, and a broad absorption probably due to a blend of HCN and C2H2 bands.

Near-infrared spectroscopy of the proto-planetary nebula CRL 618 and the origin of the hydrocarbon dust component in the interstellar medium

NASA Technical Reports Server (NTRS)

Chiar, J. E.; Pendleton, Y. J.; Geballe, T. R.; Tielens, A. G.

1998-01-01

A new 2.8-3.8 micrometers spectrum of the carbon-rich protoplanetary nebula CRL 618 confirms the previous detection of a circumstellar 3.4 micrometers absorption feature in this object (Lequeux & Jourdain de Muizon). The high resolution and high signal-to-noise ratio of our spectrum allow us to derive the detailed profile of this absorption feature, which is very similar to that observed in the spectrum of the Galactic center and also resembles the strong 3.4 micrometers emission feature in some post-asymptotic giant branch stars. A weak 3.3 micrometers unidentified infrared band, marginally detected in the CRL 618 spectrum of Lequeux & Jourdain de Muizon, is present in our spectrum. The existence of the 3.4 micrometers feature implies the presence of relatively short-chained, aliphatic hydrocarbon materials (-CH2-/-CH3 approximately = 2-2.5) in the circumstellar environment around CRL 618. It also implies that the carriers of the interstellar 3.4 micrometers feature are produced at least in part in circumstellar material, and it calls into question whether any are produced by the processing of interstellar ices in dense interstellar clouds, as has been previously proposed. Other features in the spectrum are recombination lines of hydrogen, rotational and vibration-rotation lines of molecular hydrogen, and a broad absorption probably due to a blend of HCN and C2H2 bands.

On the Detectability of Interstellar Objects Like 1I/'Oumuamua

NASA Astrophysics Data System (ADS)

Ragozzine, Darin

2018-04-01

Almost since Oort's 1950 hypothesis of a tenuously bound cloud of comets, planetary formation theorists have realized that the process of planet formation must have ejected very large numbers of planetesimals into interstellar space. Unforunately, these objects are distributed over galactic volumes, while they are only likely to be detectable if they pass within a few AU of Earth, resulting in an incredibly sparse detectable population. Furthermore, hypotheses for the formation and distribution of these bodies allows for uncertainties of orders of magnitude in the expected detection rate: our analysis suggested LSST would discover 0.01-100 objects during its lifetime (Cook et al. 2016). The discovery of 1I/'Oumuamua by a survey less powerful that LSST indicates either a low probability event and/or that properties of this population are on the more favorable end of the spectrum. We revisit the detailed detection analysis of Cook et al. 2016 in light of the detection of 1I/'Oumuamua. We use these results to better understand 1I/'Oumuamua and to update our assessment of future detections of interstellar objects. We highlight some key questions that can be answered only by additional discoveries.

BURST OF STAR FORMATION DRIVES BUBBLE IN GALAXY'S CORE

NASA Technical Reports Server (NTRS)

2002-01-01

These NASA Hubble Space Telescope snapshots reveal dramatic activities within the core of the galaxy NGC 3079, where a lumpy bubble of hot gas is rising from a cauldron of glowing matter. The picture at left shows the bubble in the center of the galaxy's disk. The structure is more than 3,000 light-years wide and rises 3,500 light-years above the galaxy's disk. The smaller photo at right is a close-up view of the bubble. Astronomers suspect that the bubble is being blown by 'winds' (high-speed streams of particles) released during a burst of star formation. Gaseous filaments at the top of the bubble are whirling around in a vortex and are being expelled into space. Eventually, this gas will rain down upon the galaxy's disk where it may collide with gas clouds, compress them, and form a new generation of stars. The two white dots just above the bubble are probably stars in the galaxy. The close-up reveals that the bubble's surface is lumpy, consisting of four columns of gaseous filaments that tower above the galaxy's disk. The filaments disperse at a height of 2,000 light-years. Each filament is about 75 light-years wide. Velocity measurements taken by the Canada-France-Hawaii Telescope in Hawaii show that the gaseous filaments are ascending at more than 4 million miles an hour (6 million kilometers an hour). According to theoretical models, the bubble formed when ongoing winds from hot stars mixed with small bubbles of very hot gas from supernova explosions. Observations of the core's structure by radio telescopes indicate that those processes are still active. The models suggest that this outflow began about a million years ago. They occur about every 10 million years. Eventually, the hot stars will die, and the bubble's energy source will fade away. Astronomers have seen evidence of previous outbursts from radio and X-ray observations. Those studies show rings of dust and gas and long plumes of material, all of which are larger than the bubble. NGC 3079 is 50 million light-years from Earth in the constellation Ursa Major. The colors in this image accentuate important details in the bubble. Glowing gas is red and starlight is blue/green. Hubble's Wide Field and Planetary Camera 2 snapped this picture in 1998. The results appear in the July 1, 2001 issue of the Astrophysical Journal. Credits: NASA, Gerald Cecil (University of North Carolina), Sylvain Veilleux (University of Maryland), Joss Bland-Hawthorn (Anglo-Australian Observatory), and Alex Filippenko (University of California at Berkeley).

The Ultra-Soft X-ray Background: A Probe of the Hot Interstellar Medium and the Local Bubble - ADP-99

NASA Technical Reports Server (NTRS)

Smith, Randall

2003-01-01

The Ultra-Soft X-ray Telescope (UXT) was a sounding rocket mission flown three times in 1984 - 1986. At the beginning of the project, the data existed solely in form of raw telemetry data stored on 9 track tapes. The primary goal of this proposal has been to extract event files from the raw telemetry stream and to create instrument response models and calibrated spectra from it. We have completed this project, and the data will soon be available to all via the HEASARC archive of high-energy data at Goddard Space Flight Center. We are in the process of combining the results with the ALEXIS and DXS observations of the Local Bubble in modelling the 72 eV iron line (recently observed by the X-ray Quantum Calorimeter) and the carbon emission lines that are uniquely visible in this dataset. Our results agree with the XQC observation which predicts a maximum emission in the 72 eV iron lines that is below the limit observable with UXT. However, this leaves an open question as to what lines were responsible for the observed Be-band emission. The answer to this question will likely require more observations of soft X-rays with the Chandra LETGS and new atomic data models of potentially emitting ions.

A search for diffuse band profile variations in the rho Ophiuchi cloud

NASA Technical Reports Server (NTRS)

Snow, T. P.; Timothy, J. G.; Sear, S.

1982-01-01

High signal-to-noise profiles of the broad diffuse interstellar band at 4430 A were obtained on the 2.2-m telescope at the Mauna Kea Observatory, using the newly-developed pulse-counting multi-anode microchannel array detector system in an effort to determine whether the band profile varies with mean grain size as expected if the band is produced by absorbers embedded in grain lattices. The lack of profile variability over several lines of sight where independent evidence indicates that the mean grain size varies shows that lambda 4430 is probably not formed by the same grains that are responsible for interstellar extinction at visible wavelengths. The possibility that this band is created by a population of very small ( approximately 100 A) grains is still viable, as is the hypothesis that it has a molecular origin.

Transition Dipole Moments and Transition Probabilities of the CN Radical

NASA Astrophysics Data System (ADS)

Yin, Yuan; Shi, Deheng; Sun, Jinfeng; Zhu, Zunlue

2018-04-01

This paper studies the transition probabilities of electric dipole transitions between 10 low-lying states of the CN radical. These states are X2Σ+, A2Π, B2Σ+, a4Σ+, b4Π, 14Σ‑, 24Π, 14Δ, 16Σ+, and 16Π. The potential energy curves are calculated using the CASSCF method, which is followed by the icMRCI approach with the Davidson correction. The transition dipole moments between different states are calculated. To improve the accuracy of potential energy curves, core–valence correlation and scalar relativistic corrections, as well as the extrapolation of potential energies to the complete basis set limit are included. The Franck–Condon factors and Einstein coefficients of emissions are calculated. The radiative lifetimes are determined for the vibrational levels of the A2Π, B2Σ+, b4Π, 14Σ‑, 24Π, 14Δ, and 16Π states. According to the transition probabilities and radiative lifetimes, some guidelines for detecting these states spectroscopically are proposed. The spin–orbit coupling effect on the spectroscopic and vibrational properties is evaluated. The splitting energy in the A2Π state is determined to be 50.99 cm‑1, which compares well with the experimental ones. The potential energy curves, transition dipole moments, spectroscopic parameters, and transition probabilities reported in this paper can be considered to be very reliable. The results obtained here can be used as guidelines for detecting these transitions, in particular those that have not been measured in previous experiments or have not been observed in the Sun, comets, stellar atmospheres, dark interstellar clouds, and diffuse interstellar clouds.

Bubble-driven mixer integrated with a microfluidic bead-based ELISA for rapid bladder cancer biomarker detection.

PubMed

Lin, Yen-Heng; Wang, Chia-Chu; Lei, Kin Fong

2014-04-01

In this study, fine bubbles were successfully generated and used as a simple, low-cost driving force for mixing fluids in an integrated microfluidic bead-based enzyme-linked immunosorbent assay (ELISA) to rapidly and quantitatively detect apolipoprotein A1 (APOA1), a biomarker highly correlated with bladder cancer. A wooden gas diffuser was embedded underneath a microfluidic chip to refine injected air and generate bubbles of less than 0.3 mm. The rising bubbles caused disturbances and convection in the fluid, increasing the probability of analyte interaction. This setup not only simplifies the micromixer design but also achieves rapid mixing with a small airflow as a force. We used this bubble-driven micromixer in a bead-based ELISA that targeted APOA1. The results indicate that this micromixer reduced the time for each incubation from 60 min in the conventional assay to 8 min with the chip, resulting in a reduction of total ELISA reaction time from 3-4 h to 30-40 min. Furthermore, the concentration detection limit was 9.16 ng/mL, which was lower than the detection cut-off value (11.16 ng/mL) for bladder cancer diagnosis reported in the literature. Therefore, this chip can be used to achieve rapid low-cost bladder cancer detection and may be used in point-of-care cancer monitoring.

Interaction dynamics of temporal and spatial separated cavitation bubbles in water

NASA Astrophysics Data System (ADS)

Tinne, N.; Ripken, T.; Lubatschowski, H.

2010-02-01

The LASIK procedure is a well established laser based treatment in ophthalmology. Nowadays it includes a cutting of the corneal tissue bases on ultra short pulses which are focused below the tissue surface to create an optical breakdown and hence a dissection of the tissue. The energy of the laser pulse is absorbed by non-linear processes that result in an expansion of a cavitation bubble and rupturing of the tissue. Due to a reduction of the duration of treatment the current development of ultra short laser systems points to higher repetition rates. This in turn results in a probable interaction between different cavitation bubbles of adjacent optical breakdowns. While the interaction of one single laser pulse with biological tissue is analyzed reasonably well experimentally and theoretically, the interaction of several spatial and temporal following pulses is scarcely determined yet. We present a high-speed photography analysis of cavitation bubble interaction for two spatial separated laser-induced optical breakdowns varying the laser pulse energy as well as the spatial distance. Depending on a change of these parameters different kinds of interactions such as a flattening and deformation of bubble shape, asymmetric water streams and jet formation were observed. The results of this research can be used to comprehend and optimize the cutting effect of ultra short pulse laser systems with high repetition rates (> 1 MHz).

Impact sensitivity test of liquid energetic materials

NASA Astrophysics Data System (ADS)

Tiutiaev, A.; Dolzhikov, A.; Zvereva, I.

2017-10-01

This paper presents new experimental method for sensitivity evaluation at the impact. A large number of researches shown that the probability of explosion initiating of liquid explosives by impact depends on the chemical nature and the various external characteristics. But the sensitivity of liquid explosive in the presence of gas bubbles increases many times as compared with the liquid without gas bubbles. In this case local chemical reaction focus are formed as a result of compression and heating of the gas inside the bubbles. In the liquid as a result of convection, wave motion, shock, etc. gas bubbles are easily generated, it is necessary to develop methods for determining sensitivity of liquid explosives to impact and to research the explosives ignition with bubbles. For the experimental investigation, the well-known impact machine and the so-called appliance 1 were used. Instead of the metal cup in the standard method in this paper polyurethane foam cylindrical container with liquid explosive was used. Polyurethane foam cylindrical container is easily deforms by impact. A large number of tests with different liquid explosives were made. It was found that the test liquid explosive to impact in appliance 1 with polyurethane foam to a large extent reflect the real mechanical sensitivity due to the small loss of impact energy on the deformation of the metal cup, as well as the best differentiation liquid explosive sensitivity due to the higher resolution method.

Patent Foramen Ovale as a Risk Factor for Altitude Decompression Illness

DTIC Science & Technology

2001-06-01

TTE ). In 48 volunteers at DCIEM screened for the PRP studies with a TTE , 14 (29%) were found to have an echo-probable PFO. In 29 altitude-exposed...subjects who had a TTE , there were 5 echo-probable PFOs. None of these 5 subjects experienced DCI. Two of these subjects had a high bubble load with grade...16% incidence (by TTE ) of PFO amongst 24 cases of Type II altitude DCI using trans- esophogeal echocardiography (TEE), suggesting that there was no

Temperature impact on the micro structure of tungsten exposed to He irradiation in LHD

NASA Astrophysics Data System (ADS)

Bernard, Elodie; Sakamoto, Ryuichi; Tokitani, Masayuki; Masuzaki, Suguru; Hayashi, Hiromi; Yamada, Hiroshi; Yoshida, Naoaki

2017-02-01

A new temperature controlled material probe was designed for the exposure of tungsten samples to helium plasma in the LHD. Samples were exposed to estimated fluences of ∼1023 m-2 and temperatures ranging from 65 to 600 °C. Transmission Electron Microscopy analysis allowed the study of the impact of He irradiation under high temperatures on tungsten micro structure for the first time in real-plasma exposure conditions. Both dislocation loops and bubbles appeared from low to medium temperatures and saw an impressive increase of size (factor 4 to 6) most probably by coalescence as the temperature reaches 600 °C, with 500 °C appearing as a threshold for bubble growth. Annealing of the samples up to 800 C highlighted the stability of the dislocation damages formed by helium irradiation at high surface temperature, as bubbles and dislocation loops seem to conserve their characteristics. Additional studies on cross-sections showed that bubbles were formed much deeper (70-100 nm) than the heavily damaged surface layer (10-20 nm), raising concern about the impact on the material mechanical properties conservation and potential additional trapping of hydrogen isotopes.

The interaction of the halo around the butterfly planetary nebula NGC 650-1 with the interstellar medium

NASA Astrophysics Data System (ADS)

Ramos-Larios, G.; Guerrero, M. A.; Nigoche-Netro, A.; Olguín, L.; Gómez-Muñoz, M. A.; Sabin, L.; Vázquez, R.; Akras, S.; Ramírez Vélez, J. C.; Chávez, M.

2018-03-01

With its bright and wide equatorial waist seen almost edge-on (`the butterfly body') and the faint and broad bipolar extensions (`the butterfly wings'), NGC 650-1 is the archetypical example of bipolar planetary nebula (PN) with butterfly morphology. We present here deep high-resolution broad- and narrow-band optical images that expose the rich and intricate fine structure of this bipolar PN, with small-scale bubble-like features and collimated outflows. A SHAPE spatio-kinematic model indicates that NGC 650-1 has a broad central torus with an inclination angle of 75° with respect to the line of sight, whereas that of the bipolar lobes, which are clearly seen in the position-velocity maps, is 85°. Large field of view deep images show, for first time, an arc-like diffuse envelope in low- and high-excitation emission lines located up to 180 arcsec towards the east-south-east of the central star, well outside the main nebula. This morphological component is confirmed by Spitzer MIPS and WISE infrared imaging, as well as by long-slit low- and high-dispersion optical spectroscopic observations. Hubble Space Telescope images of NGC 650-1 obtained at two different epochs ˜14 yr apart reveal the proper motion of the central star along this direction. We propose that this motion of the star through the interstellar medium compresses the remnant material of a slow asymptotic giant branch wind, producing this bow-shock-like feature.

Stardust Interstellar Preliminary Examination

NASA Astrophysics Data System (ADS)

Westphal, A.; Stardust Interstellar Preliminary Examation Team: http://www. ssl. berkeley. edu/~westphal/ISPE/

2011-12-01

A. J. Westphal, C. Allen, A. Ansari, S. Bajt, R. S. Bastien, H. A. Bechtel, J. Borg, F. E. Brenker, J. Bridges, D. E. Brownlee, M. Burchell, M. Burghammer, A. L. Butterworth, A. M. Davis, P. Cloetens, C. Floss, G. Flynn, D. Frank, Z. Gainsforth, E. Grün, P. R. Heck, J. K. Hillier, P. Hoppe, G. Huss, J. Huth, B. Hvide, A. Kearsley, A. J. King, B. Lai, J. Leitner, L. Lemelle, H. Leroux, R. Lettieri, W. Marchant, L. R. Nittler, R. Ogliore, F. Postberg, M. C. Price, S. A. Sandford, J.-A. Sans Tresseras, T. Schoonjans, S. Schmitz, G. Silversmit, A. Simionovici, V. A. Solé, R. Srama, T. Stephan, V. Sterken, J. Stodolna, R. M. Stroud, S. Sutton, M. Trieloff, P. Tsou, A. Tsuchiyama, T. Tyliszczak, B. Vekemans, L. Vincze, D. Zevin, M. E. Zolensky, >29,000 Stardust@home dusters ISPE author affiliations are at http://www.ssl.berkeley.edu/~westphal/ISPE/. In 2000 and 2002, a ~0.1m2 array of aerogel tiles and alumi-num foils onboard the Stardust spacecraft was exposed to the interstellar dust (ISD) stream for an integrated time of 200 days. The exposure took place in interplanetary space, beyond the orbit of Mars, and thus was free of the ubiquitous orbital debris in low-earth orbit that precludes effective searches for interstellar dust there. Despite the long exposure of the Stardust collector, <<100 ISD particles are expected to have been captured. The particles are thought to be ~1μm or less in size, and the total ISD collection is probably <10-6 by mass of the collection of cometary dust parti-cles captured in the Stardust cometary dust collector from the coma of the Jupiter-family comet Wild 2. Thus, although the first solid sample from the local interstellar medium is clearly of high interest, the diminutive size of the particles and the low numbers of particles present daunting challenges. Nevertheless, six recent developments have made a Preliminary Examination (PE) of this sample practical: (1) rapid automated digital optical scanning microscopy for three-dimensional imaging of the aerogel collector; (2) rapid automated digital scanning electron microscopy for imaging of the aluminum foils; (3) an effective, massively-distributed search by citizen scientists through the Internet; (4) extraction and sample preparation tech-niques for μm-sized particles in aerogel; (5) advances in capabili-ties of synchrotron infrared and X-ray microprobes that enable non-destructive analyses of sub-μm particles in situ in aerogel; and (6) the development of focused-ion beam (FIB) milling tech-niques for sample preparation. The Stardust Interstellar PE consists of six related projects: the identification of tracks through automated scanning microscopy and distributed searching by volunteers (Stardust@home); the extraction of tracks from aerogel in "picokeystones"; the analysis of tracks using synchrotron microprobes; the identifica-tion and analysis of impacts in aluminum foils; laboratory investigations of ISD analogs using an electrostatic dust accelerator; and modeling of ISD propagation in the heliosphere. To date we have identified four impacts in the aerogel collector and one on the foils of probable interstellar origin. We will report on our analyses and implications for the solid component of the local interstellar medium.

Pure iron grains are rare in the universe.

PubMed

Kimura, Yuki; Tanaka, Kyoko K; Nozawa, Takaya; Takeuchi, Shinsuke; Inatomi, Yuko

2017-01-01

The abundant forms in which the major elements in the universe exist have been determined from numerous astronomical observations and meteoritic analyses. Iron (Fe) is an exception, in that only depletion of gaseous Fe has been detected in the interstellar medium, suggesting that Fe is condensed into a solid, possibly the astronomically invisible metal. To determine the primary form of Fe, we replicated the formation of Fe grains in gaseous ejecta of evolved stars by means of microgravity experiments. We found that the sticking probability for the formation of Fe grains is extremely small; only a few atoms will stick per hundred thousand collisions so that homogeneous nucleation of metallic Fe grains is highly ineffective, even in the Fe-rich ejecta of type Ia supernovae. This implies that most Fe is locked up as grains of Fe compounds or as impurities accreted onto other grains in the interstellar medium.

Pure iron grains are rare in the universe

PubMed Central

Kimura, Yuki; Tanaka, Kyoko K.; Nozawa, Takaya; Takeuchi, Shinsuke; Inatomi, Yuko

2017-01-01

The abundant forms in which the major elements in the universe exist have been determined from numerous astronomical observations and meteoritic analyses. Iron (Fe) is an exception, in that only depletion of gaseous Fe has been detected in the interstellar medium, suggesting that Fe is condensed into a solid, possibly the astronomically invisible metal. To determine the primary form of Fe, we replicated the formation of Fe grains in gaseous ejecta of evolved stars by means of microgravity experiments. We found that the sticking probability for the formation of Fe grains is extremely small; only a few atoms will stick per hundred thousand collisions so that homogeneous nucleation of metallic Fe grains is highly ineffective, even in the Fe-rich ejecta of type Ia supernovae. This implies that most Fe is locked up as grains of Fe compounds or as impurities accreted onto other grains in the interstellar medium. PMID:28116359

Measurements of the Activation Energies for Atomic Hydrogen Diffusion on Pure Solid CO

NASA Astrophysics Data System (ADS)

Kimura, Y.; Tsuge, M.; Pirronello, V.; Kouchi, A.; Watanabe, N.

2018-05-01

The diffusion of hydrogen atoms on dust grains is a key process in the formation of interstellar H2 and some hydrogenated molecules such as formaldehyde and methanol. We investigate the adsorption and diffusion of H atoms on pure solid CO as an analog of dust surfaces observed toward some cold interstellar regions. Using a combination of photostimulated desorption and resonance-enhanced multiphoton ionization methods to detect H atoms directly, the relative adsorption probabilities and diffusion coefficients of the H atoms are measured on pure solid CO at 8, 12, and 15 K. There is little difference between the diffusion coefficients of the hydrogen and deuterium atoms, indicating that the diffusion is limited by thermal hopping. The activation energies controlling the H-atom diffusion depend on the surface temperature, and values of 22, 30, and ∼37 meV were obtained for 8, 12, and 15 K, respectively.

Statistical time-dependent model for the interstellar gas

NASA Technical Reports Server (NTRS)

Gerola, H.; Kafatos, M.; Mccray, R.

1974-01-01

We present models for temperature and ionization structure of low, uniform-density (approximately 0.3 per cu cm) interstellar gas in a galactic disk which is exposed to soft X rays from supernova outbursts occurring randomly in space and time. The structure was calculated by computing the time record of temperature and ionization at a given point by Monte Carlo simulation. The calculation yields probability distribution functions for ionized fraction, temperature, and their various observable moments. These time-dependent models predict a bimodal temperature distribution of the gas that agrees with various observations. Cold regions in the low-density gas may have the appearance of clouds in 21-cm absorption. The time-dependent model, in contrast to the steady-state model, predicts large fluctuations in ionization rate and the existence of cold (approximately 30 K), ionized (ionized fraction equal to about 0.1) regions.

The interstellar redding law in the ultraviolet deduced from filter photometry obtained by the OAO-2 satellite

NASA Technical Reports Server (NTRS)

Laget, M.

1972-01-01

Filter photometry has been obtained of 16 BO stars at ten effective wavelengths in the range 4250-1430 A. The wavelength dependence of the interstellar reddening law, deduced from a least squares fit of the observed values to the reddening line at each band, is found in satisfactory agreement with that derived by Bless and Savage (1972). Toward the shorter wavelengths the increase of the computed probable error of the slope of the mean reddening line suggests that large fluctuations in the law may occur from star to star. Similar computations, separating main-sequence stars and supergiants, indicate that the large fluctuations of the law appear to be well related to the luminosity of the stars; the supergiants show systematically less extinction, this deficiency becoming large toward the far UV. The small number in the sample however, does not allow a general conclusion to be drawn.

ALMA Detection of Interstellar Methoxymethanol (CH3OCH2OH)

NASA Astrophysics Data System (ADS)

McGuire, Brett A.; Shingledecker, Christopher N.; Willis, Eric R.; Burkhardt, Andrew M.; El-Abd, Samer; Motiyenko, Roman A.; Brogan, Crystal L.; Hunter, Todd R.; Margulès, Laurent; Guillemin, Jean-Claude; Garrod, Robin T.; Herbst, Eric; Remijan, Anthony J.

2017-12-01

We report the detection of interstellar methoxymethanol (CH3OCH2OH) in Atacama Large Millimeter/submillimeter Array (ALMA) Bands 6 and 7 toward the MM1 core in the high-mass star-forming region NGC 6334I at ∼0.″1–1″ spatial resolution. A column density of 4(2) × 1018 cm‑2 at T ex = 200 K is derived toward MM1, ∼34 times less abundant than methanol (CH3OH), and significantly higher than predicted by astrochemical models. Probable formation and destruction pathways are discussed, primarily through the reaction of the CH3OH photodissociation products, the methoxy (CH3O) and hydroxymethyl (CH2OH) radicals. Finally, we comment on the implications of these mechanisms on gas-phase versus grain-surface routes operative in the region, and the possibility of electron-induced dissociation of CH3OH rather than photodissociation.

Investigating the dynamical history of the interstellar object 'Oumuamua

NASA Astrophysics Data System (ADS)

Dybczyński, Piotr A.; Królikowska, Małgorzata

2018-02-01

Here we try to find the origin of 1I/2017 U1 'Oumuamua, the first interstellar object recorded inside the solar system. To this aim, we searched for close encounters between 'Oumuamua and all nearby stars with known kinematic data during their past motion. We had checked over 200 thousand stars and found just a handful of candidates. If we limit our investigation to within a 60 pc sphere surrounding the Sun, then the most probable candidate for the 'Oumuamua parent stellar habitat is the star UCAC4 535-065571. However GJ 876 is also a favourable candidate. However, the origin of 'Oumuamua from a much more distant source is still an open question. Additionally, we found that the quality of the original orbit of 'Oumuamua is accurate enough for such a study and that none of the checked stars had perturbed its motion significantly. All numerical results of this research are available in the appendix.

Spin-forbidden and spin-allowed cyclopropenone (c-H{sub 2}C{sub 3}O) formation in interstellar medium

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

Ahmadvand, Seyedsaeid; Zaari, Ryan R.; Varganov, Sergey A., E-mail: svarganov@unr.edu

2014-11-10

Three proposed mechanisms of cyclopropenone (c-H{sub 2}C{sub 3}O) formation from neutral species are studied using high-level electronic structure methods in combination with nonadiabatic transition state and collision theories to deduce the likelihood of each reaction mechanism under interstellar conditions. The spin-forbidden reaction involving the singlet electronic state of cyclopenylidene (c-C{sub 3}H{sub 2}) and the triplet state of atomic oxygen is studied using nonadiabatic transition state theory to predict the rate constant for c-H{sub 2}C{sub 3}O formation. The spin-allowed reactions of c-C{sub 3}H{sub 2} with molecular oxygen and acetylene with carbon monoxide were also investigated. The reaction involving the ground electronicmore » states of acetylene and carbon monoxide has a very large reaction barrier and is unlikely to contribute to c-H{sub 2}C{sub 3}O formation in interstellar medium. The spin-forbidden reaction of c-C{sub 3}H{sub 2} with atomic oxygen, despite the high probability of nonadiabatic transition between the triplet and singlet states, was found to have a very small rate constant due to the presence of a small (3.8 kcal mol{sup –1}) reaction barrier. In contrast, the spin-allowed reaction between c-C{sub 3}H{sub 2} and molecular oxygen is found to be barrierless, and therefore can be an important path to the formation of c-H{sub 2}C{sub 3}O molecule in interstellar environment.« less

Evolution of Interstellar Ices

NASA Astrophysics Data System (ADS)

Allamandola, Louis J.; Bernstein, Max P.; Sandford, Scott A.; Walker, Robert L.

1999-10-01

Infrared observations, combined with realistic laboratory simulations, have revolutionized our understanding of interstellar ice and dust, the building blocks of comets. Ices in molecular clouds are dominated by the very simple molecules H2O, CH3OH, NH3, CO, CO2, and probably H2CO and H2. More complex species including nitriles, ketones, and esters are also present, but at lower concentrations. The evidence for these, as well as the abundant, carbon-rich, interstellar, polycyclic aromatic hydrocarbons (PAHs) is reviewed. Other possible contributors to the interstellar/pre-cometary ice composition include accretion of gas-phase molecules and in situ photochemical processing. By virtue of their low abundance, accretion of simple gas-phase species is shown to be the least important of the processes considered in determining ice composition. On the other hand, photochemical processing does play an important role in driving dust evolution and the composition of minor species. Ultraviolet photolysis of realistic laboratory analogs readily produces H2, H2CO, CO2, CO, CH4, HCO, and the moderately complex organic molecules: CH3CH2OH (ethanol), HC(=O)NH2 (formamide), CH3C(=O)NH2 (acetamide), R-CN (nitriles), and hexamethylenetetramine (HMT, C6H12N4), as well as more complex species including amides, ketones, and polyoxymethylenes (POMs). Inclusion of PAHs in the ices produces many species similar to those found in meteorites including aromatic alcohols, quinones and ethers. Photon assisted PAH-ice deuterium exchange also occurs. All of these species are readily formed and are therefore likely cometary constituents.

Pickup protons and pressure-balanced structures: Voyager 2 observations in merged interaction regions near 35 AU

NASA Astrophysics Data System (ADS)

Burlaga, L. F.; Ness, N. F.; Belcher, J. W.; Szabo, A.; Isenberg, P. A.; Lee, M. A.

1994-11-01

Five pressure-balanced structures, each with a scale of the order of a few hundredths of an astonomical unit (AU), were identified in two merged interaction regions (MIRs) near 35 AU in the Voyager 2 plasma and magnetic field data. They include a tangential discontinuity, simple and complex magnetic holes, slow correlated variations among the plasma and magnetic field parameters, and complex uncorrelated variations among the parameters. The changes in the magnetic pressure in these events are balanced by changes in the pressure of interstellar pickup protons. Thus the pickup protons probably play a major role in the dynamics of the MIRs. The solar wind proton and electron pressures are relatively unimportant in the MIRs at 35 AU and beyond. The region near 35 AU is transition region: the Sun is the source of the magnetic field, but the interstellar medium in source of pickups protons. Relative to the solar wind proton guyroadius, the thicknesses of the discontinuities and simple magnetic holes observed near 35 AU are at least an order of magnitude greater than those observed at 1 AU. However, the thicknesses of the tangential discontinuity and simple magnetic holes observed near 35 AU (in units of the pickup proton Larmor radius) are comparable to those observed at 1 AU (in units of the solar wind proton gyroradius). Thus the gyroradius of interstellar pickup protons controls the thickness of current sheets near 35 AU. We determine the interstellar pickup proton pressure in the PBSs. Using a model for the pickup proton temperature, we estimate that the average interstellar pickup proton pressure, temperature, and density in the MIRs at 35 AU are (0.53 +/- 0.14) x 10-12 erg/cu cm, (5.8 +/- 0.4) x 106 K and (7 +/- 2) x 10-4/cu cm.

THE INTERSTELLAR MAGNETIC FIELD CLOSE TO THE SUN. II

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

Frisch, P. C.; Andersson, B-G; Berdyugin, A.

2012-12-01

The magnetic field in the local interstellar medium (ISM) provides a key indicator of the galactic environment of the Sun and influences the shape of the heliosphere. We have studied the interstellar magnetic field (ISMF) in the solar vicinity using polarized starlight for stars within 40 pc of the Sun and 90 Degree-Sign of the heliosphere nose. In Frisch et al. (Paper I), we developed a method for determining the local ISMF direction by finding the best match to a group of interstellar polarization position angles obtained toward nearby stars, based on the assumption that the polarization is parallel tomore » the ISMF. In this paper, we extend the analysis by utilizing weighted fits to the position angles and by including new observations acquired for this study. We find that the local ISMF is pointed toward the galactic coordinates l, b =47 Degree-Sign {+-} 20 Degree-Sign , 25 Degree-Sign {+-} 20 Degree-Sign . This direction is close to the direction of the ISMF that shapes the heliosphere, l, b =33 Degree-Sign {+-} 4 Degree-Sign , 55 Degree-Sign {+-} 4 Degree-Sign , as traced by the center of the 'Ribbon' of energetic neutral atoms discovered by the Interstellar Boundary Explorer (IBEX) mission. Both the magnetic field direction and the kinematics of the local ISM are consistent with a scenario where the local ISM is a fragment of the Loop I superbubble. A nearby ordered component of the local ISMF has been identified in the region l Almost-Equal-To 0 Degree-Sign {yields} 80 Degree-Sign and b Almost-Equal-To 0 Degree-Sign {yields} 30 Degree-Sign , where PlanetPol data show a distance-dependent increase of polarization strength. The ordered component extends to within 8 pc of the Sun and implies a weak curvature in the nearby ISMF of {approx}0.{sup 0}25 pc{sup -1}. This conclusion is conditioned on the small sample of stars available for defining this rotation. Variations from the ordered component suggest a turbulent component of {approx}23 Degree-Sign . The ordered component and standard relations between polarization, color excess, and H{sup o} column density predict a reasonable increase of N(H) with distance in the local ISM. The similarity of the ISMF directions traced by the polarizations, the IBEX Ribbon, and pulsars inside the Local Bubble in the third galactic quadrant suggest that the ISMF is relatively uniform over spatial scales of 8-200 pc and is more similar to interarm than spiral-arm magnetic fields. The ISMF direction from the polarization data is also consistent with small-scale spatial asymmetries detected in GeV-TeV cosmic rays with a galactic origin. The peculiar geometrical relation found earlier between the cosmic microwave background dipole moment, the heliosphere nose, and the ISMF direction is supported by this study. The interstellar radiation field at {approx}975 A does not appear to play a role in grain alignment for the low-density ISM studied here.« less

Disintegration of Dust Aggregates in Interstellar Shocks and the Lifetime of Dust Grains in the ISM

NASA Technical Reports Server (NTRS)

Dominik, C.; Jones, A. P.; Tielens, A. G. G. M.; Cuzzi, Jeff (Technical Monitor)

1994-01-01

Interstellar grains are destroyed by shock waves moving through the ISM. In fact, the destruction of grains may be so effective that it is difficult to explain the observed abundance of dust in the ISM as a steady state between input of grains from stellar sources and destruction of grains in shocks. This is especially a problem for the larger grains. Therefore, the dust grains must be protected in some way. Jones et al. have already considered coatings and the increased post-shock drag effects for low density grains. In molecular clouds and dense clouds, coagulation of grains is an important process, and the largest interstellar grains may indeed be aggregates of smaller grains rather than homogeneous particles. This may provide a means to protect the larger grains, in that, in moderate velocity grain-grain collisions in a shock the aggregates may disintegrate rather than be vaporized. The released small particles are more resilient to shock destruction (except in fast shocks) and may reform larger grains later, recovering the observed size distribution. We have developed a model for the binding forces in grain aggregates and apply this model to the collisions between an aggregate and fast small grains. We discuss the results in the light of statistical collision probabilities and grain life times.

Dynamic and interaction of fs-laser induced cavitation bubbles for analyzing the cutting effect

NASA Astrophysics Data System (ADS)

Tinne, N.; Schumacher, S.; Nuzzo, V.; Ripken, T.; Lubatschowski, H.

2009-07-01

A prominent laser based treatment in ophthalmology is the LASIK procedure which nowadays includes a cutting of the corneal tissue based on ultra short pulses. Focusing an ultra short laser pulse below the surface of biological tissue an optical breakdown is caused and hence a dissection is obtained. The laser energy of the laser pulses is absorbed by nonlinear processes. As a result a cavitation bubble expands and ruptures the tissue. Hence positioning of several optical breakdowns side by side generates an incision. Due to a reduction of the duration of the treatment the current development of ultra short laser systems points to higher repetition rates in the range of hundreds of KHz or even MHz instead of tens of kHz. This in turn results in a probable occurrence of interaction between different optical breakdowns and respectively cavitation bubbles of adjacent optical breakdowns. While the interaction of one single laser pulse with biological tissue is analyzed reasonably well experimentally and theoretically, the interaction of several spatial and temporal following pulses is scarcely determined yet. Thus the aim of this study is to analyse the dynamic and interaction of two cavitation bubbles by using high speed photography. The applied laser pulse energy, the energy ratio and the spot distance between different cavitation bubbles were varied. Depending on a change of these parameters different kinds of interactions such as a flattening and deformation of bubble shape or jet formation are observed. Based on these results a further research seems to be inevitable to comprehend and optimize the cutting effect of ultra short pulse laser systems with high (> 1 MHz) repetition rates.

On the origin of the system PSR B 1757-24/SNR G 5.4-1.2

NASA Astrophysics Data System (ADS)

Gvaramadze, V. V.

2004-03-01

A scenario for the origin of the system PSR B 1757-24/supernova remnant (SNR) G 5.4-1.2 is proposed. It is suggested that both objects are the remnants of a supernova (SN) that exploded within a pre-existing bubble blown-up by a runaway massive star (the SN progenitor) during the final (Wolf-Rayet) phase of its evolution. This suggestion implies that (a) the SN blast centre was significantly offset from the geometric centre of the wind-blown bubble (i.e. from the centre of the future SNR), (b) the bubble was surrounded by a massive wind-driven shell, and (c) the SN blast wave was drastically decelerated by the interaction with the shell. Therefore, one can understand how the relatively young and low-velocity pulsar PSR B 1757-24 was able to escape from the associated SNR G 5.4-1.2 and why the inferred vector of pulsar transverse velocity does not point away from the geometric centre of the SNR. A possible origin of the radio source G 5.27-0.9 (located between PSR B 1757-24 and the SNR G 5.4-1.2) is proposed. It is suggested that G 5.27-0.9 is a lobe of a low Mach number (≃1.7) jet of gas outflowing from the interior of G 5.4-1.2 through the hole bored in the SNR's shell by the escaping pulsar. It is also suggested that the non-thermal emission of the comet-shaped pulsar wind nebula originates in the vicinity of the termination shock and in the cylindric region of subsonically moving shocked pulsar wind. The role of magnetized wind-driven shells (swept-up during the Wolf-Rayet phase from the ambient interstellar medium with the regular magnetic field) in formation of elongated axisymmetric SNRs is discussed.

A Radio-Polarisation and Rotation Measure Study of the Gum Nebula and Its Environment

NASA Astrophysics Data System (ADS)

Purcell, C. R.; Gaensler, B. M.; Sun, X. H.; Carretti, E.; Bernardi, G.; Haverkorn, M.; Kesteven, M. J.; Poppi, S.; Schnitzeler, D. H. F. M.; Staveley-Smith, L.

2015-05-01

The Gum Nebula is 36°-wide shell-like emission nebula at a distance of only ˜450 pc. It has been hypothesized to be an old supernova remnant, fossil H ii region, wind-blown bubble, or combination of multiple objects. Here we investigate the magneto-ionic properties of the nebula using data from recent surveys: radio-continuum data from the NRAO VLA and S-band Parkes All Sky Surveys, and H α data from the Southern H-Alpha Sky Survey Atlas. We model the upper part of the nebula as a spherical shell of ionized gas expanding into the ambient medium. We perform a maximum-likelihood Markov chain Monte Carlo fit to the NVSS rotation measure data, using the H α data to constrain average electron density in the shell ne. Assuming a latitudinal background gradient in rotation measure, we find {{n}e}=1.3-0.4+0.4 c{{m}-3}, angular radius {{φ }outer}=22\\buildrel{\\circ}\\over{.} 7-0.1+0.1, shell thickness dr=18.5-1.4+1.5 pc, ambient magnetic field strength {{B}0}=3.9-2.2+4.9 μ G, and warm gas filling factor f=0.3-0.1+0.3. We constrain the local, small-scale (˜260 pc) pitch-angle of the ordered Galactic magnetic field to +7{}^\\circ ≲ \\wp ≲ +44{}^\\circ , which represents a significant deviation from the median field orientation on kiloparsec scales (˜-7.°2). The moderate compression factor X=6.0-2.5+5.1 at the edge of the H α shell implies that the “old supernova remnant” origin is unlikely. Our results support a model of the nebula as a H ii region around a wind-blown bubble. Analysis of depolarization in 2.3 GHz S-PASS data is consistent with this hypothesis and our best-fitting values agree well with previous studies of interstellar bubbles.

The physiological kinetics of nitrogen and the prevention of decompression sickness.

PubMed

Doolette, D J; Mitchell, S J

2001-01-01

Decompression sickness (DCS) is a potentially crippling disease caused by intracorporeal bubble formation during or after decompression from a compressed gas underwater dive. Bubbles most commonly evolve from dissolved inert gas accumulated during the exposure to increased ambient pressure. Most diving is performed breathing air, and the inert gas of interest is nitrogen. Divers use algorithms based on nitrogen kinetic models to plan the duration and degree of exposure to increased ambient pressure and to control their ascent rate. However, even correct execution of dives planned using such algorithms often results in bubble formation and may result in DCS. This reflects the importance of idiosyncratic host factors that are difficult to model, and deficiencies in current nitrogen kinetic models. Models describing the exchange of nitrogen between tissues and blood may be based on distributed capillary units or lumped compartments, either of which may be perfusion- or diffusion-limited. However, such simplistic models are usually poor predictors of experimental nitrogen kinetics at the organ or tissue level, probably because they fail to account for factors such as heterogeneity in both tissue composition and blood perfusion and non-capillary exchange mechanisms. The modelling of safe decompression procedures is further complicated by incomplete understanding of the processes that determine bubble formation. Moreover, any formation of bubbles during decompression alters subsequent nitrogen kinetics. Although these factors mandate complex resolutions to account for the interaction between dissolved nitrogen kinetics and bubble formation and growth, most decompression schedules are based on relatively simple perfusion-limited lumped compartment models of blood: tissue nitrogen exchange. Not surprisingly, all models inevitably require empirical adjustment based on outcomes in the field. Improvements in the predictive power of decompression calculations are being achieved using probabilistic bubble models, but divers will always be subject to the possibility of developing DCS despite adherence to prescribed limits.

Optical pulse characteristics of sonoluminescence at low acoustic drive levels.

PubMed

Arakeri, V H; Giri, A

2001-06-01

From a nonaqueous alkali-metal salt solution, it is possible to observe sonoluminescence (SL) at low acoustic drive levels with the ratio of the acoustic pressure amplitude to the ambient pressure being about 1. In this case, the emission has a narrowband spectral content and consists of a few flashes of light from a levitated gas bubble going through an unstable motion. A systematic statistical study of the optical pulse characteristics of this form of SL is reported here. The results support our earlier findings [Phys. Rev. E 58, R2713 (1998)], but in addition we have clearly established a variation in the optical pulse duration with certain physical parameters such as the gas thermal conductivity. Quantitatively, the SL optical pulse width is observed to vary from 10 ns to 165 ns with the most probable value being 82 ns, for experiments with krypton-saturated sodium salt ethylene glycol solution. With argon, the variation is similar to that of krypton but the most probable value is reduced to 62 ns. The range is significantly smaller with helium, being from 22 ns to 65 ns with the most probable value also being reduced to 42 ns. The observed large variation, for example with krypton, under otherwise fixed controllable experimental parameters indicates that it is an inherent property of the observed SL process, which is transient in nature. It is this feature that necessitated our statistical study. Numerical simulations of the SL process using the bubble dynamics approach of Kamath, Prosperetti, and Egolfopoulos [J. Acoust. Soc. Am. 94, 248 (1993)] suggest that a key uncontrolled parameter, namely the initial bubble radius, may be responsible for the observations. In spite of the fact that certain parameters in the numerical computations have to be fixed from a best fit to one set of experimental data, the observed overall experimental trends of optical pulse characteristics are predicted reasonably well.

Optical pulse characteristics of sonoluminescence at low acoustic drive levels

NASA Astrophysics Data System (ADS)

Arakeri, Vijay H.; Giri, Asis

2001-06-01

From a nonaqueous alkali-metal salt solution, it is possible to observe sonoluminescence (SL) at low acoustic drive levels with the ratio of the acoustic pressure amplitude to the ambient pressure being about 1. In this case, the emission has a narrowband spectral content and consists of a few flashes of light from a levitated gas bubble going through an unstable motion. A systematic statistical study of the optical pulse characteristics of this form of SL is reported here. The results support our earlier findings [Phys. Rev. E 58, R2713 (1998)], but in addition we have clearly established a variation in the optical pulse duration with certain physical parameters such as the gas thermal conductivity. Quantitatively, the SL optical pulse width is observed to vary from 10 ns to 165 ns with the most probable value being 82 ns, for experiments with krypton-saturated sodium salt ethylene glycol solution. With argon, the variation is similar to that of krypton but the most probable value is reduced to 62 ns. The range is significantly smaller with helium, being from 22 ns to 65 ns with the most probable value also being reduced to 42 ns. The observed large variation, for example with krypton, under otherwise fixed controllable experimental parameters indicates that it is an inherent property of the observed SL process, which is transient in nature. It is this feature that necessitated our statistical study. Numerical simulations of the SL process using the bubble dynamics approach of Kamath, Prosperetti, and Egolfopoulos [J. Acoust. Soc. Am. 94, 248 (1993)] suggest that a key uncontrolled parameter, namely the initial bubble radius, may be responsible for the observations. In spite of the fact that certain parameters in the numerical computations have to be fixed from a best fit to one set of experimental data, the observed overall experimental trends of optical pulse characteristics are predicted reasonably well.

Extreme scattering events towards two young pulsars

NASA Astrophysics Data System (ADS)

Kerr, M.; Coles, W. A.; Ward, C. A.; Johnston, S.; Tuntsov, A. V.; Shannon, R. M.

2018-03-01

We have measured the scintillation properties of 151 young, energetic pulsars with the Parkes radio telescope and have identified two extreme scattering events (ESEs). Towards PSR J1057-5226, we discovered a 3 yr span of strengthened scattering during which the variability in flux density and the scintillation bandwidth decreased markedly. The transverse size of the scattering region is ˜23 au, and strong flux density enhancement before and after the ESE may arise from refractive focusing. Long observations reveal scintillation arcs characteristic of interference between rays scattered at large angles, and the clearest arcs appear during the ESE. The arcs suggest scattering by a screen 100-200 pc from the Earth, perhaps ionized filamentary structure associated with the boundary of the local bubble(s). Towards PSR J1740-3015, we observed a `double dip' in the measured flux density similar to ESEs observed towards compact extragalactic radio sources. The observed shape is consistent with that produced by a many-au scale diverging plasma lens with electron density ˜500 cm-3. The continuing ESE is at least 1500 d long, making it the longest detected event to date. These detections, with materially different observational signatures, indicate that well-calibrated pulsar monitoring is a keen tool for ESE detection and interstellar medium (ISM) diagnostics. They illustrate the strong role au-scale non-Kolmogorov density fluctuations and the local ISM structure play in such events and are key to understanding both their intrinsic physics and their impact on other phenomena, particularly fast radio bursts.

A Look at Six Years of IBEX

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2015-10-01

The objective of the Interstellar Boundary Explorer, or IBEX, is to study the interaction between the solar wind and the interstellar medium (ISM) at the outer boundary of our solar system. In a special issue of the Astrophysical Journal Supplement Series, a set of 14 papers presents some of the most recent scientific results to come from the first six years of IBEX data.The Heliosphere and IBEXThe IBEX spacecraft, launched in October 2008. [NASA]As the solar wind streams outward, it blows a bubble into the ISM known as the heliosphere. The outer boundary of the heliosphere, where the solar wind is no longer able to push the ISM out of the way, marks the edge of our solar system. Wed like to understand the composition and properties of both the heliosphere and the local interstellar environment, as well as the processes at work in the interstellar space around our Sun.How do we learn about these things? One approach is to send spacecraft to the edge of the heliosphere to make measurements, such as Voyagers 1 and 2. But these spacecraft are only able to measure properties at their specific locations and since the heliosphere doesnt appear to be symmetric, this is a major limitation. This is where IBEX comes in.IBEXs orbit around the Earth, at various stages in the Earths orbit around the Sun. IBEX makes its observations while outside of the Earths magnetosphere (purple shaded region). [SwRI/IBEX Team]IBEX is a spacecraft on a highly elliptical orbit around Earth. Its orbit takes it outside of the Earths magnetosphere, where its able to detect neutral atoms of varying energies that have traveled from the outer edges of our solar system. IBEXs observations are therefore of particles rather than light; the spacecraft detects the directions and energies of roughly 600 particles per day. This data has provided us with a full 3D view of the outer boundary of the heliosphere.IBEXs detections rely on two types of particles: 1) energetic neutral atoms, which are produced by charge exchange at the solar system boundary when the solar wind ions and the neutral ISM gas interact, and 2) various species of interstellar neutral atoms themselves that pass through the heliosphere and stream toward Earth. Detections of the latter type are the focus of the papers in this special issue of ApJS.Latest ResultsIn the overview paper of this ApJS issue, PI David McComas (Southwest Research Institute) and coauthors outline the recent science results of IBEX. The major outcomes include:Resolution of the differences between IBEXs and Ulyssess measurements of helium atoms in the ISMThe space mission Ulysses, which gathered data while orbiting the Sun until 2009, measured a different temperature and direction for the interstellar flow of helium atoms than IBEX did. These two studies have now been reconciled and confirm that the local interstellar wind is significantly hotter than originally measured by Ulysses.Determination of where the pristine ISM startsUnderstanding the properties of the ISM outside of our solar system requires knowing how far out we need to look to observe ISM that hasnt been mixed with atoms from our solar system. The studies presented here find that the distance to the pristine ISM is 1000 AU (thats more than 30 times the distance to Neptune!). The temperature, speed, and direction of the ISM flow at that location are also presented.Measurement of other interstellar neutral atomsIBEX has gathered neutral hydrogen, oxygen, and neon particles, helping to identify the flows of these interstellar neutral atoms and the composition of the local region surrounding the heliosphere.These results are the latest in a long stream of important scientific findings from IBEX and as the mission has been extended through at least 2017, it seems likely that there will be many more!CitationD. J. McComas et al 2015 ApJS 220 22. doi:10.1088/0067-0049/220/2/22The entire ApJS issue can be found here: http://iopscience.iop.org/0067-0049/220/2

Getting the gas out - developing gas networks in magmatic systems

NASA Astrophysics Data System (ADS)

Cashman, Katharine; Rust, Alison; Oppenheimer, Julie; Belien, Isolde

2015-04-01

Volcanic eruption style, and explosive potential, are strongly controlled by the pre-eruptive history of the magmatic volatiles: specifically, the more efficient the gas loss prior to eruption, the lower the likelihood of primary (magmatic) explosive activity. Commonly considered gas loss mechanisms include separated flow, where individual bubbles (or bubble clouds) travel at a rate that is faster than the host magma, and permeable flow, where gas escapes through permeable (connected) pathways developed within a (relatively) static matrix. Importantly, gas loss via separated flow is episodic, while gas loss via permeable flow is likely to be continuous. Analogue experiments and numerical models on three phase (solid-liquid-gas) systems also suggest a third mechanism of gas loss that involves the opening and closing of 'pseudo fractures'. Pseudo fractures form at a critical crystallinity that is close to the maximum particle packing. Fractures form by local rearrangement of solid particles and liquid to form a through-going gas fracture; gas escape is episodic, and modulated by the available gas volume and the rate of return flow of interstitial liquid back into the fracture. In all of the gas escape scenarios described above, a fundamental control on gas behaviour is the melt viscosity, which affects the rate of individual bubble rise, the rate of bubble expansion, the rate of film thinning (required for bubble coalescence), and the rate of melt flow into gas-generated fractures. From the perspective of magma degassing, rates of gas expansion and film thinning are key to the formation of an interconnected (permeable) gas pathway. Experiments with both analogue and natural materials show that bubble coalescence is relatively slow, and, in particle-poor melts, does not necessarily create permeable gas networks. As a result, degassing efficiency is modulated by the time scales required either (1) to produce large individual bubbles or bubble clouds (in low viscosity melts) or (2) to develop sufficient porosity for full connectivity of a bubble network (in high viscosity melts). In contrast, our experiments suggest that the presence of solid particles may greatly enhance gas escape. On the one hand, the addition of solid particles increases the bulk viscosity of the mixture, which reduces the migration rate of large single bubbles. On the other hand, the strength of networks created by touching crystals inhibits bulk magma deformation and forces smaller bubbles to deform to occupy the spaces between particles, thereby increasing both the bubble shape anisotropy and, correspondingly, the probability of bubble coalescence. Gas pathways created in this way take advantage of inhomogeneities in the spatial distribution of crystals and allow large-scale gas release at relatively low vesicularities. This mechanism of gas escape is likely to be important not only in mafic arc volcanoes, where shallow conduits are likely to be highly crystalline, but also for degassing of crystal-mush-dominated magmatic systems.

Probability of cavitation for single ultrasound pulses applied to tissues and tissue-mimicking materials

PubMed Central

Maxwell, Adam D.; Cain, Charles A.; Hall, Timothy L.; Fowlkes, J. Brian; Xu, Zhen

2012-01-01

In this article, the negative pressure values at which inertial cavitation consistently occurs in response to a single, 2-cycle, focused ultrasound pulse were measured in several media relevant to cavitation-based ultrasound therapy. The pulse was focused into a chamber containing one of the media, which included liquids, tissue-mimicking materials, and ex-vivo canine tissue. Focal waveforms were measured by two separate techniques using a fiber-optic hydrophone. Inertial cavitation was identified by high-speed photography in optically transparent media and an acoustic passive cavitation detector. The probability of cavitation (Pcav) for a single pulse as a function of peak negative pressure (p−) followed a sigmoid curve, with the probability approaching 1 when the pressure amplitude was sufficient. The statistical threshold (defined as Pcav = 0.5) was between p− = 26.0–30.0 MPa in all samples with a high water content, but varied between p− = 13.7 to > 36 MPa for other media. A model for radial cavitation bubble dynamics was employed to evaluate the behavior of cavitation nuclei at these pressure levels. A single bubble nucleus with an inertial cavitation threshold of p− = 28.2 MPa was estimated to have a 2.5 nm radius in distilled water. These data may be valuable for cavitation-based ultrasound therapy to predict the likelihood of cavitation at different pressure levels and dimensions of cavitation-induced lesions in tissue. PMID:23380152

The surface reactivity of acrylonitrile with oxygen atoms on an analogue of interstellar dust grains

NASA Astrophysics Data System (ADS)

Kimber, Helen J.; Toscano, Jutta; Price, Stephen D.

2018-06-01

Experiments designed to reveal the low-temperature reactivity on the surfaces of interstellar dust grains are used to probe the heterogeneous reaction between oxygen atoms and acrylonitrile (C2H3CN, H2C=CH-CN). The reaction is studied at a series of fixed surface temperatures between 14 and 100 K. After dosing the reactants on to the surface, temperature-programmed desorption, coupled with time-of-flight mass spectrometry, reveals the formation of a product with the molecular formula C3H3NO. This product results from the addition of a single oxygen atom to the acrylonitrile reactant. The oxygen atom attack appears to occur exclusively at the C=C double bond, rather than involving the cyano(-CN) group. The absence of reactivity at the cyano site hints that full saturation of organic molecules on dust grains may not always occur in the interstellar medium. Modelling the experimental data provides a reaction probability of 0.007 ± 0.003 for a Langmuir-Hinshelwood style (diffusive) reaction mechanism. Desorption energies for acrylonitrile, oxygen atoms, and molecular oxygen, from the multilayer mixed ice their deposition forms, are also extracted from the kinetic model and are 22.7 ± 1.0 kJ mol-1 (2730 ± 120 K), 14.2 ± 1.0 kJ mol-1 (1710 ± 120 K), and 8.5 ± 0.8 kJ mol-1 (1020 ± 100 K), respectively. The kinetic parameters we extract from our experiments indicate that the reaction between atomic oxygen and acrylonitrile could occur on interstellar dust grains on an astrophysical time-scale.

IRAS 08572+3915: constraining the aromatic versus aliphatic content of interstellar HACs

NASA Astrophysics Data System (ADS)

Dartois, E.; Geballe, T. R.; Pino, T.; Cao, A.-T.; Jones, A.; Deboffle, D.; Guerrini, V.; Bréchignac, Ph.; D'Hendecourt, L.

2007-02-01

We analyze dust features present in the mid-infrared (Spitzer) and recently published L-band (UKIRT) spectra of the infrared galaxy IRAS 08572+3915. The line of sight toward the AGN nucleus crosses a high column density of carbonaceous dust whose characteristic absorption features appear clearly. They provide a real insight into the chemical environment of the diffuse interstellar medium. Thanks to the moderate redshift of IRAS 08572+3915, the wavelength of the aromatic CH stretching mode is free of major telluric lines, and a strong observational constraint of Hsp2 /Hsp3 ≤ 0.08 has been determined. This limit clearly shows that the bonding of hydrogen atoms in interstellar hydrogenated amorphous carbon is highly aliphatic. The presence of a broad absorption feature centered at 6.2 μm, probably arising from olefinic/aromatic structures, corresponds to the backbone of this carbonaceous material, which is the major carbon-containing component of the interstellar medium along this line of sight. Based on observations made with the Spitzer Space Telescope (GO-3336 program), which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. Based on data obtained at the United Kingdom Infrared Telescope, which is operated by the Joint Astronomy Center on behalf of the UK Particle Physics and Astronomy Research Council. Part of this work has been financed by the french CNRS program "Physique et Chimie du Milieu Interstellaire" (PCMI-CNRS). TRG's esearch is supported by the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., on behalf of the international Gemini partnership of Argentina, Australia, Brazil, Canada, Chile, the United Kingdom, and the United States of America.

Multiple generations of grain aggregation in different environments preceded solar system body formation.

PubMed

Ishii, Hope A; Bradley, John P; Bechtel, Hans A; Brownlee, Donald E; Bustillo, Karen C; Ciston, James; Cuzzi, Jeffrey N; Floss, Christine; Joswiak, David J

2018-06-26

The solar system formed from interstellar dust and gas in a molecular cloud. Astronomical observations show that typical interstellar dust consists of amorphous ( a -) silicate and organic carbon. Bona fide physical samples for laboratory studies would yield unprecedented insight about solar system formation, but they were largely destroyed. The most likely repositories of surviving presolar dust are the least altered extraterrestrial materials, interplanetary dust particles (IDPs) with probable cometary origins. Cometary IDPs contain abundant submicron a- silicate grains called GEMS (glass with embedded metal and sulfides), believed to be carbon-free. Some have detectable isotopically anomalous a- silicate components from other stars, proving they are preserved dust inherited from the interstellar medium. However, it is debated whether the majority of GEMS predate the solar system or formed in the solar nebula by condensation of high-temperature (>1,300 K) gas. Here, we map IDP compositions with single nanometer-scale resolution and find that GEMS contain organic carbon. Mapping reveals two generations of grain aggregation, the key process in growth from dust grains to planetesimals, mediated by carbon. GEMS grains, some with a- silicate subgrains mantled by organic carbon, comprise the earliest generation of aggregates. These aggregates (and other grains) are encapsulated in lower-density organic carbon matrix, indicating a second generation of aggregation. Since this organic carbon thermally decomposes above ∼450 K, GEMS cannot have accreted in the hot solar nebula, and formed, instead, in the cold presolar molecular cloud and/or outer protoplanetary disk. We suggest that GEMS are consistent with surviving interstellar dust, condensed in situ, and cycled through multiple molecular clouds. Copyright © 2018 the Author(s). Published by PNAS.

Recent Advances in Organic Cosmochemistry

NASA Technical Reports Server (NTRS)

Sandford, Scott A.; Witteborn, Fred C. (Technical Monitor)

1994-01-01

The Astrochemistry Laboratory at NASA's Ames Research Center pursues a variety of activities, most of which center around the use of spectroscopy (ultraviolet to far-infrared) for the interpretation of astronomical and meteoritic data. One of our key activities is the study of the chemical and physical properties of cometary, interstellar, and planetary ice analogs and matrix-isolated molecules of astrophysical interest. As a result of these studies it is now known that a significant fraction of the carbon in the interstellar medium (ISM) is in reasonably complex forms, some of which are clearly of interest for exobiology. Examples of compounds known or suspected to be present in space include polycyclic aromatic hydrocarbons (PAHs), microdiamonds, an aliphatic-rich component found in the diffuse interstellar medium, and a variety of molecular species produced by the irradiation of mixed molecular ices in dense clouds. A number of the species produced by irradiation contain nitrogen and appear to offer an additional means of producing some of the amino acids found in meteorites. I will review these complex carbonaceous materials and discuss how they are connected with each other and the organic materials that ultimately ended up as part of our own Solar System. Specific points that will probably be covered include: (1) the composition of the ices in interstellar dense molecular clouds; (2) the more complex organic compounds produced when these ices are irradiated and/or warmed; (3) the detection of microdiamonds in space; (4) the discovery that aliphatic materials may constitute as much as 15% of all the carbon in the diffuse ISM, appears to be present everywhere in the galaxy, and yet seems to be present everywhere in the galaxy, and yet seems to be significantly concentrated towards the center of the galaxy.

Carbonaceous Components in the Comet Halley Dust

NASA Technical Reports Server (NTRS)

Fomenkova, M. N.; Chang, S.; Mukhin, L. M.

1994-01-01

Cometary grains containing large amounts of carbon and/or organic matter (CHON) were discovered by in situ measurements of comet Halley dust composition during VEGA and GIOTTO flyby missions. In this paper, we report the classification of these cometary, grains by means of cluster analysis, discuss the resulting compositional groups, and compare them with substances observed or hypothesized in meteorites, interplanetary dust particles, and the interstellar medium. Grains dominated by carbon and/or organic matter (CHON grains) represent approx. 22% of the total population of measured cometary dust particles. They, usually contain a minor abundance of rock-forming elements as well. Grains having organic material are relatively more abundant in the vicinity of the nucleus than in the outer regions of the coma, which suggests decomposition of the organics in the coma environment. The majority of comet Halley organic particles are multicomponent mixtures of carbon phases and organic compounds. Possibly, the cometary CHON grains may be related to kerogen material of an interstellar origin in carbonaceous meteorites. Pure carbon grains, hydrocarbons and polymers of cyanopolyynes, and multi-carbon monoxides are present in cometary dust as compositionally simple and distinctive components among a variety of others. There is no clear evidence of significant presence of pure formaldehyde or HCN polymers in Halley dust particles. The diversity of types of cometary organic compounds is consistent with the inter-stellar dust model of comets and probably reflects differences in composition of precursor dust. Preservation of this heterogeneity among submicron particles suggest the gentle formation of cometary, nucleus by aggregation of interstellar dust in the protosolar nebula without complete mixing or chemical homogenization at the submicron level.

Preliminary Examination of Impact Craters on Al Foil from the Stardust Interstellar Dust Collector

NASA Astrophysics Data System (ADS)

Stroud, R.; Stardust Interstellar Preliminary Examination Team; 29,000 Stardust@home Dusters

2011-12-01

The Interstellar Dust Collector from the NASA Stardust mission provides an unprecedented opportunity for direct laboratory study of particles from the contemporary interstellar dust (ISD) stream in order to obtain such information as grain composition and microstructure. The collector is comprised of two collection media: silica aerogel tiles and Al foil strips. Preliminary examination (PE) of particles captured in each medium is on-going. To-date, four grains analyzed in situ in aerogel with synchrotron X-ray techniques show track trajectories and elemental composition that indicate a probable interstellar origin. In addition, we report here the discovery of one crater on an Al foil for which the residue elemental composition and crater shape are consistent with the impact of a grain of interstellar origin, although an interplanetary origin has not been ruled out. Automated mapping by SEM is the primary tool for identifi-cation of craters on the Al foils. A complete map of each foil requires collection of several thousand images at a resolution of ~ 50 nm/px. Automated software has been developed to identify crater candidates, but so far it has not replaced manual efforts. Identified candidates are then re-imaged at ~ 15 nm/px, for confirmation as impact craters. Fifteen foils have been imaged; crater identification is complete for eight, yielding 32 craters. The average areal density of craters is 9.7 cm-2, which extrapolates to ~1500 craters on the total foil collection area. Initial elemental analysis of residues in six craters has been performed with a combination of Auger spectroscopy, conventional, off-axis energy dispersive X-ray spectroscopy (EDX), on-axis, silicon drift-detector EDX. Additional analysis by TEM of the residue composition and crater morphology was obtained on FIB cross-sections of four of the craters. All craters contained detectable levels of Si and O. One crater was found to contain Mg, Si, O, Fe, Ni, S, Ca and Cr, indicative of an interstellar or interplanetary origin. The shape of this crater is consistent with the impact of a fluffy aggregate grain at < 10 km/s, similar to three of the four ISD candidates identified in the aerogel, and slower than expected for an interplanetary dust grain. In three cases the impacting grain was determined by detection of additional Ce, Zn, Ti, K, or Na to be a fragment of the solar cell cover glass.

The VLT-FLAMES Tarantula Survey. IX. The interstellar medium seen through diffuse interstellar bands and neutral sodium&

NASA Astrophysics Data System (ADS)

van Loon, J. Th.; Bailey, M.; Tatton, B. L.; Maíz Apellániz, J.; Crowther, P. A.; de Koter, A.; Evans, C. J.; Hénault-Brunet, V.; Howarth, I. D.; Richter, P.; Sana, H.; Simón-Díaz, S.; Taylor, W.; Walborn, N. R.

2013-02-01

Context. The Tarantula Nebula (a.k.a. 30 Dor) is a spectacular star-forming region in the Large Magellanic Cloud (LMC), seen through gas in the Galactic disc and halo. Diffuse interstellar bands (DIBs) offer a unique probe of the diffuse, cool-warm gas in these regions. Aims: The aim is to use DIBs as diagnostics of the local interstellar conditions, whilst at the same time deriving properties of the yet-unknown carriers of these enigmatic spectral features. Methods: Spectra of over 800 early-type stars from the Very Large Telescope Flames Tarantula Survey (VFTS) were analysed. Maps were created, separately, for the Galactic and LMC absorption in the DIBs at 4428 and 6614 Å and - in a smaller region near the central cluster R 136 - neutral sodium (the Na i D doublet); we also measured the DIBs at 5780 and 5797 Å. Results: The maps show strong 4428 and 6614 Å DIBs in the quiescent cloud complex to the south of 30 Dor but weak absorption in the harsher environments to the north (bubbles) and near the OB associations. The Na maps show at least five kinematic components in the LMC and a shell-like structure surrounding R 136, and small-scale structure in the Milky Way. The strengths of the 4428, 5780, 5797 and 6614 Å DIBs are correlated, also with Na absorption and visual extinction. The strong 4428 Å DIB is present already at low Na column density but the 6614, 5780 and 5797 Å DIBs start to be detectable at subsequently larger Na column densities. Conclusions: The carriers of the 4428, 6614, 5780 and 5797 Å DIBs are increasingly prone to removal from irradiated gas. The relative strength of the 5780 and 5797 Å DIBs clearly confirm the Tarantula Nebula as well as Galactic high-latitude gas to represent a harsh radiation environment. The resilience of the 4428 Å DIB suggests its carrier is large, compact and neutral. Structure is detected in the distribution of cool-warm gas on scales between one and >100 pc in the LMC and as little as 0.01 pc in the Sun's vicinity. Stellar winds from the central cluster R 136 have created an expanding shell; some infalling gas is also detected, reminiscent of a galactic "fountain". Full Tables A.2-A.4 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/550/A108

Membrane-Based Gas Traps for Ammonia, Freon-21, and Water Systems to Simplify Ground Processing

NASA Technical Reports Server (NTRS)

Ritchie, Stephen M. C.

2003-01-01

Gas traps are critical for the smooth operation of coolant loops because gas bubbles can cause loss of centrifugal pump prime, interference with sensor readings, inhibition of heat transfer, and blockage of passages to remote systems. Coolant loops are ubiquitous in space flight hardware, and thus there is a great need for this technology. Conventional gas traps will not function in micro-gravity due to the absence of buoyancy forces. Therefore, clever designs that make use of adhesion and momentum are required for adequate separation, preferable in a single pass. The gas traps currently used in water coolant loops on the International Space Station are composed of membrane tube sets in a shell. Each tube set is composed of a hydrophilic membrane (used for water transport and capture of bubbles) and a hydrophobic membrane (used for venting of air bubbles). For the hydrophilic membrane, there are two critical pressures, the pressure drop and the bubble pressure. The pressure drop is the decrease in system pressure across the gas trap. The bubble pressure is the pressure required for air bubbles to pass across the water filled membrane. A significant difference between these pressures is needed to ensure complete capture of air bubbles in a single pass. Bubbles trapped by the device adsorb on the hydrophobic membrane in the interior of the hydrophilic membrane tube. After adsorption, the air is vented due to a pressure drop of approximately 1 atmosphere across the membrane. For water systems, the air is vented to the ambient (cabin). Because water vapor can also transport across the hydrophobic membrane, it is critical that a minimum surface area is used to avoid excessive water loss (would like to have a closed loop for the coolant). The currently used gas traps only provide a difference in pressure drop and bubble pressure of 3-4 psid. This makes the gas traps susceptible to failure at high bubble loading and if gas venting is impaired. One mechanism for the latter is when particles adhere to the hydrophobic membrane, promoting formation of a water layer about it that can blind the membrane for gas transport (Figure 1). This mechanism is the most probable cause for observed failures with the existing design. The objective of this project was to devise a strategy for choosing new membrane materials (database development and procedure), redesign of the gas trap to mitigate blinding effects, and to develop a design that can be used in ammonia and Freon-21 coolant loops.

Measures for a multidimensional multiverse

NASA Astrophysics Data System (ADS)

Chung, Hyeyoun

2015-04-01

We explore the phenomenological implications of generalizing the causal patch and fat geodesic measures to a multidimensional multiverse, where the vacua can have differing numbers of large dimensions. We consider a simple model in which the vacua are nucleated from a D -dimensional parent spacetime through dynamical compactification of the extra dimensions, and compute the geometric contribution to the probability distribution of observations within the multiverse for each measure. We then study how the shape of this probability distribution depends on the time scales for the existence of observers, for vacuum domination, and for curvature domination (tobs,tΛ , and tc, respectively.) In this work we restrict ourselves to bubbles with positive cosmological constant, Λ . We find that in the case of the causal patch cutoff, when the bubble universes have p +1 large spatial dimensions with p ≥2 , the shape of the probability distribution is such that we obtain the coincidence of time scales tobs˜tΛ˜tc . Moreover, the size of the cosmological constant is related to the size of the landscape. However, the exact shape of the probability distribution is different in the case p =2 , compared to p ≥3 . In the case of the fat geodesic measure, the result is even more robust: the shape of the probability distribution is the same for all p ≥2 , and we once again obtain the coincidence tobs˜tΛ˜tc . These results require only very mild conditions on the prior probability of the distribution of vacua in the landscape. Our work shows that the observed double coincidence of time scales is a robust prediction even when the multiverse is generalized to be multidimensional; that this coincidence is not a consequence of our particular Universe being (3 +1 )-dimensional; and that this observable cannot be used to preferentially select one measure over another in a multidimensional multiverse.

A NEW ELECTRON-DENSITY MODEL FOR ESTIMATION OF PULSAR AND FRB DISTANCES

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

Yao, J. M.; Wang, N.; Manchester, R. N.

2017-01-20

We present a new model for the distribution of free electrons in the Galaxy, the Magellanic Clouds, and the intergalactic medium (IGM) that can be used to estimate distances to real or simulated pulsars and fast radio bursts (FRBs) based on their dispersion measure (DM). The Galactic model has an extended thick disk representing the so-called warm interstellar medium, a thin disk representing the Galactic molecular ring, spiral arms based on a recent fit to Galactic H ii regions, a Galactic Center disk, and seven local features including the Gum Nebula, Galactic Loop I, and the Local Bubble. An offsetmore » of the Sun from the Galactic plane and a warp of the outer Galactic disk are included in the model. Parameters of the Galactic model are determined by fitting to 189 pulsars with independently determined distances and DMs. Simple models are used for the Magellanic Clouds and the IGM. Galactic model distances are within the uncertainty range for 86 of the 189 independently determined distances and within 20% of the nearest limit for a further 38 pulsars. We estimate that 95% of predicted Galactic pulsar distances will have a relative error of less than a factor of 0.9. The predictions of YMW16 are compared to those of the TC93 and NE2001 models showing that YMW16 performs significantly better on all measures. Timescales for pulse broadening due to interstellar scattering are estimated for (real or simulated) Galactic and Magellanic Cloud pulsars and FRBs.« less

Molecular spectroscopy and collisional excitation. [in astrophysics

NASA Technical Reports Server (NTRS)

Green, S.

1975-01-01

The paper examines the basic principles underlying the molecular transitions responsible for interstellar molecular spectra. The energy levels of molecules are discussed in detail with special attention given to the Born-Oppenheimer approximation, the electronic Hamiltonian, and the parameters of vibrational and rotational energy. The probabilities for radiative and collisional transitions are calculated. A brief review of techniques for molecular spectroscopy is presented along with methods used to determine collision cross sections on both an experimental and a theoretical basis.

Experimental investigation on the phenomena around the onset nucleate boiling during the impacting of a droplet on the hot surface

NASA Astrophysics Data System (ADS)

Mitrakusuma, Windy H.; Deendarlianto, Kamal, Samsul; Indarto, Nuriyadi, M.

2016-06-01

Onset of nucleate boiling of a droplet when impacted onto hot surface was investigated. Three kinds of surfaces, normal stainless steel (NSS), stainless steel with TiO2 coating (UVN), and stainless steel with TiO2 coating and radiated by ultraviolet ray were employed to examine the effect of wettability. The droplet size was 2.4 mm diameter, and dropped under different We number. The image is generated by high speed camera with the frame speed of 1000 fps. The boiling conditions are identified as natural convection, nucleate boiling, critical heat flux, transition, and film boiling. In the present report, the discussion will be focused on the beginning of nucleate boiling on the droplet. Nucleate boiling occurs when bubbles are generated. These bubbles are probably caused by nucleation on the impurities within the liquid rather than at nucleation sites on the heated surface because the bubbles appear to be in the bulk of the liquid instead of at the liquid-solid interface. In addition, the smaller the contact angle, the fastest the boiling.

Effects of pH on nano-bubble stability and transport in saturated porous media

NASA Astrophysics Data System (ADS)

Hamamoto, Shoichiro; Takemura, Takato; Suzuki, Kenichiro; Nishimura, Taku

2018-01-01

An understanding of nano-scale bubble (NB) transport in porous media is important for potential application of NBs in soil/groundwater remediation. It is expected that the solution chemistry of NB water highly influences the surface characteristics of NBs and porous media and the interaction between them, thus affecting the stability and transport characteristics of NB. In this study, in addition to stability experiments, one-dimensional column transport experiments using glass beads were conducted to investigate the effects of pH on the NB transport behavior. The results showed that the NBs were more stable under higher pH. Column transport experiments revealed that entrapment of NBs, especially larger ones, was enhanced in lower-pH water, likely suggesting pH-dependent NB attachment and physical straining, both of which are also probably influenced by bubble size. Although relatively smaller NBs were released after switching the eluting fluid to one with lower ionic strength, most of the NBs in lower-pH water were still retained in the porous media even altering the chemical condition.

Compositional Discrimination of Decompression and Decomposition Gas Bubbles in Bycaught Seals and Dolphins

PubMed Central

Bernaldo de Quirós, Yara; Seewald, Jeffrey S.; Sylva, Sean P.; Greer, Bill; Niemeyer, Misty; Bogomolni, Andrea L.; Moore, Michael J.

2013-01-01

Gas bubbles in marine mammals entangled and drowned in gillnets have been previously described by computed tomography, gross examination and histopathology. The absence of bacteria or autolytic changes in the tissues of those animals suggested that the gas was produced peri- or post-mortem by a fast decompression, probably by quickly hauling animals entangled in the net at depth to the surface. Gas composition analysis and gas scoring are two new diagnostic tools available to distinguish gas embolisms from putrefaction gases. With this goal, these methods have been successfully applied to pathological studies of marine mammals. In this study, we characterized the flux and composition of the gas bubbles from bycaught marine mammals in anchored sink gillnets and bottom otter trawls. We compared these data with marine mammals stranded on Cape Cod, MA, USA. Fresh animals or with moderate decomposition (decomposition scores of 2 and 3) were prioritized. Results showed that bycaught animals presented with significantly higher gas scores than stranded animals. Gas composition analyses indicate that gas was formed by decompression, confirming the decompression hypothesis. PMID:24367623

Microbial community evolution of black and stinking rivers during in situ remediation through micro-nano bubble and submerged resin floating bed technology.

PubMed

Sun, Yanmei; Wang, Shiwei; Niu, Junfeng

2018-06-01

Microbes play important roles during river remediation and the interaction mechanism illustration between microorganisms and sewage is of great significance to improve restoration technology. In this study, micro-nano bubble and submerged resin floating bed composite technology (MBSR) was firstly used to restore two black and stinking urban rivers. After restoration, the water pollution indices such as dissolved oxygen (DO), ammonia nitrogen (NH 4 + -N), total phosphorous (TP), chemical oxygen demand (COD Cr ), water clarity, and the number of facial coliform were significantly improved. Microbial community composition and relative abundance both varied and more aerobic microbes emerged after remediation. The microbial changes showed correlation with DO, NH 4 + -N, TP and COD Cr of the rivers. In summary, the MBSR treatment improved the physiochemical properties of the two black and stinking urban rivers probably through oxygen enrichment of micro-nano bubble and adsorption of submerged resin floating bed, which thereby stimulated functional microbes to degrade pollutants. Copyright © 2018 Elsevier Ltd. All rights reserved.

Effects of pH on nano-bubble stability and transport in saturated porous media.

PubMed

Hamamoto, Shoichiro; Takemura, Takato; Suzuki, Kenichiro; Nishimura, Taku

2018-01-01

An understanding of nano-scale bubble (NB) transport in porous media is important for potential application of NBs in soil/groundwater remediation. It is expected that the solution chemistry of NB water highly influences the surface characteristics of NBs and porous media and the interaction between them, thus affecting the stability and transport characteristics of NB. In this study, in addition to stability experiments, one-dimensional column transport experiments using glass beads were conducted to investigate the effects of pH on the NB transport behavior. The results showed that the NBs were more stable under higher pH. Column transport experiments revealed that entrapment of NBs, especially larger ones, was enhanced in lower-pH water, likely suggesting pH-dependent NB attachment and physical straining, both of which are also probably influenced by bubble size. Although relatively smaller NBs were released after switching the eluting fluid to one with lower ionic strength, most of the NBs in lower-pH water were still retained in the porous media even altering the chemical condition. Copyright © 2017 Elsevier B.V. All rights reserved.

Learning about the very local interstellar medium from the Voyagers

NASA Astrophysics Data System (ADS)

Florinski, V. A.; Guo, X.; Burlaga, L. F.

2017-12-01

The outer heliosheath is the region in front of the heliopause affected by the interaction between the solar wind and the flow of interstellar gas. Voyager 1 has been exploring this region for over five years uncovering a number of remarkable phenomena not present elsewhere in space directly accessible by spacecraft. The very local interstellar medium (VLISM) is characterized by remarkably low levels of magnetic fluctuation intensities presenting a nearly scatter free environment for energetic particle propagation. The fluctuations have power law spectra and probably belong to the inertial range of a turbulent cascade fed by a variety of sources, including large and kinetic scale instabilities and the inner heliosheath structures transmitted across the heliopause. While the fluxes of galactic cosmic rays are, on average, very steady in the VLISM, in agreement with theoretical expectations, they also show episodic depletions at the 90 degree pitch angle. These anisotropy events may be associated with the passage of weak compressive magnetic structures resembling shock waves, but with ramp widths orders of magnitude broader than the relevant kinetic plasma scales. The key to understanding the VLISM lies in recognizing the interconnections between the magnetic field data, which has a "local" character, the highly mobile cosmic rays that sample vast regions of space along magnetic field lines, and neutral atom populations measured by IBEX that can reveal kinetic scale physics of energetic ions produced in charge exchange events.

The mean intensity of radiation at 2 microns in the solar neighborhood

NASA Technical Reports Server (NTRS)

Jura, M.

1979-01-01

Consideration is given to the value of the mean intensity at 2 microns in the solar neighborhood, and it is found that it is likely to be a factor of four greater than previously estimated on theoretical grounds. It is noted however, that the estimate does agree with a reasonable extrapolation of the results of the survey of the Galactic plane by the Japanese group. It is concluded that the mean intensity in the solar neighborhood therefore probably peaks somewhat longward of 1 micron, and that this result is important for understanding the temperature of interstellar dust and the intensity of the far infrared background. This means specifically that dark clouds probably emit significantly more far infrared radiation than previously predicted.

Depriming of arterial heat pipes: An investigation of CTS thermal excursions

NASA Technical Reports Server (NTRS)

Antoniuk, D.; Edwards, D. K.

1980-01-01

Four thermal excursions of the Transmitter Experiment Package (TEP) were the result of the depriming of the arteries in all three heat pipes in the Variable Conductance Heat Pipe System which cooled the TEP. The determined cause of the depriming of the heat pipes was the formation of bubbles of the nitrogen/helium control gas mixture in the arteries during the thaw portion of a freeze/thaw cycle of the inactive region of the condenser section of the heat pipe. Conditions such as suction freezeout or heat pipe turn-on, which moved these bubbles into the active region of the heat pipe, contributed to the depriming mechanism. Methods for precluding, or reducing the probability of, this type of failure mechanism in future applications of arterial heat pipes are included.

Black Hole Blows Big Bubble

NASA Astrophysics Data System (ADS)

2010-07-01

Combining observations made with ESO's Very Large Telescope and NASA's Chandra X-ray telescope, astronomers have uncovered the most powerful pair of jets ever seen from a stellar black hole. This object, also known as a microquasar, blows a huge bubble of hot gas, 1000 light-years across, twice as large and tens of times more powerful than other known microquasars. The discovery is reported this week in the journal Nature. "We have been astonished by how much energy is injected into the gas by the black hole," says lead author Manfred Pakull. "This black hole is just a few solar masses, but is a real miniature version of the most powerful quasars and radio galaxies, which contain black holes with masses of a few million times that of the Sun." Black holes are known to release a prodigious amount of energy when they swallow matter. It was thought that most of the energy came out in the form of radiation, predominantly X-rays. However, the new findings show that some black holes can release at least as much energy, and perhaps much more, in the form of collimated jets of fast moving particles. The fast jets slam into the surrounding interstellar gas, heating it and triggering an expansion. The inflating bubble contains a mixture of hot gas and ultra-fast particles at different temperatures. Observations in several energy bands (optical, radio, X-rays) help astronomers calculate the total rate at which the black hole is heating its surroundings. The astronomers could observe the spots where the jets smash into the interstellar gas located around the black hole, and reveal that the bubble of hot gas is inflating at a speed of almost one million kilometres per hour. "The length of the jets in NGC 7793 is amazing, compared to the size of the black hole from which they are launched," says co-author Robert Soria [1]. "If the black hole were shrunk to the size of a soccer ball, each jet would extend from the Earth to beyond the orbit of Pluto." This research will help astronomers understand the similarity between small black holes formed from exploded stars and the supermassive black holes at the centres of galaxies. Very powerful jets have been seen from supermassive black holes, but are thought to be less frequent in the smaller microquasar variety. The new discovery suggests that many of them may simply have gone unnoticed so far. The gas-blowing black hole is located 12 million light-years away, in the outskirts of the spiral galaxy NGC 7793 (eso0914b). From the size and expansion velocity of the bubble the astronomers have found that the jet activity must have been ongoing for at least 200 000 years. Note: [1] Astronomers do not have yet any means of measuring the size of the black hole itself. The smallest stellar black hole discovered so far has a radius of about 15 km. An average stellar black hole of about 10 solar masses has a radius of about 30 km, while a "big" stellar black hole may have a radius of up to 300 km. This is still much smaller than the jets, which extend out to 1000 light-years, or about 9000 million million km! More Information: This result appears in a paper published in this week's issue of the journal Nature (A 300 parsec long jet-inflated bubble around a powerful microquasar in the galaxy NGC 7793, by Manfred W. Pakull, Roberto Soria and Christian Motch). ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world's most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world's most advanced visible-light astronomical observatory and VISTA, the world's largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become "the world's biggest eye on the sky".

Black Hole Blows Big Bubble

NASA Astrophysics Data System (ADS)

2010-07-01

Combining observations made with ESO's Very Large Telescope and NASA's Chandra X-ray telescope, astronomers have uncovered the most powerful pair of jets ever seen from a stellar black hole. This object, also known as a microquasar, blows a huge bubble of hot gas, 1000 light-years across, twice as large and tens of times more powerful than other known microquasars. The discovery is reported this week in the journal Nature. "We have been astonished by how much energy is injected into the gas by the black hole," says lead author Manfred Pakull. "This black hole is just a few solar masses, but is a real miniature version of the most powerful quasars and radio galaxies, which contain black holes with masses of a few million times that of the Sun." Black holes are known to release a prodigious amount of energy when they swallow matter. It was thought that most of the energy came out in the form of radiation, predominantly X-rays. However, the new findings show that some black holes can release at least as much energy, and perhaps much more, in the form of collimated jets of fast moving particles. The fast jets slam into the surrounding interstellar gas, heating it and triggering an expansion. The inflating bubble contains a mixture of hot gas and ultra-fast particles at different temperatures. Observations in several energy bands (optical, radio, X-rays) help astronomers calculate the total rate at which the black hole is heating its surroundings. The astronomers could observe the spots where the jets smash into the interstellar gas located around the black hole, and reveal that the bubble of hot gas is inflating at a speed of almost one million kilometres per hour. "The length of the jets in NGC 7793 is amazing, compared to the size of the black hole from which they are launched," says co-author Robert Soria [1]. "If the black hole were shrunk to the size of a soccer ball, each jet would extend from the Earth to beyond the orbit of Pluto." This research will help astronomers understand the similarity between small black holes formed from exploded stars and the supermassive black holes at the centres of galaxies. Very powerful jets have been seen from supermassive black holes, but are thought to be less frequent in the smaller microquasar variety. The new discovery suggests that many of them may simply have gone unnoticed so far. The gas-blowing black hole is located 12 million light-years away, in the outskirts of the spiral galaxy NGC 7793 (eso0914b). From the size and expansion velocity of the bubble the astronomers have found that the jet activity must have been ongoing for at least 200 000 years. Notes [1] Astronomers do not have yet any means of measuring the size of the black hole itself. The smallest stellar black hole discovered so far has a radius of about 15 km. An average stellar black hole of about 10 solar masses has a radius of about 30 km, while a "big" stellar black hole may have a radius of up to 300 km. This is still much smaller than the jets, which extend out to several hundreds light years on each side of the black hole, or about several thousand million million km! More information This result appears in a paper published in this week's issue of the journal Nature (A 300 parsec long jet-inflated bubble around a powerful microquasar in the galaxy NGC 7793, by Manfred W. Pakull, Roberto Soria and Christian Motch). ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world's most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world's most advanced visible-light astronomical observatory and VISTA, the world's largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become "the world's biggest eye on the sky".

Mass extinctions and missing matter

NASA Technical Reports Server (NTRS)

Stothers, R. B.

1984-01-01

The possible influence of 'invisible matter' on the solar system's comet halo, and therefore on quasi-periodic cometary bombardment of the earth and consequent mass extinctions, is briefly addressed. Invisible matter consisting of small or cold interstellar molecular clouds could significantly modulate the comet background flux, while invisible matter consisting of a large population of old, dead stars with a relatively small galactic concentration probably could not. It is also shown that the downward force exerted by the Galaxy will perturb the halo, but will not produce any periodicity.

Interaction dynamics of fs-laser induced cavitation bubbles and their impact on the laser-tissue-interaction of modern ophthalmic laser systems

NASA Astrophysics Data System (ADS)

Tinne, N.; Ripken, T.; Lubatschowski, H.; Heisterkamp, A.

2011-07-01

A today well-known laser based treatment in ophthalmology is the LASIK procedure which nowadays includes cutting of the corneal tissue with ultra-short laser pulses. Instead of disposing a microkeratome for cutting a corneal flap, a focused ultra-short laser pulse is scanned below the surface of biological tissue causing the effect of an optical breakdown and hence obtaining a dissection. Inside the tissue, the energy of the laser pulses is absorbed by non-linear processes; as a result a cavitation bubble expands and ruptures the tissue. Hence, positioning of several optical breakdowns side by side generates an incision. Due to a reduction of the amount of laser energy, with a moderate duration of treatment at the same time, the current development of ultra-short pulse laser systems points to higher repetition rates in the range of even Megahertz instead of tens or hundreds of Kilohertz. In turn, this results in a pulse overlap and therefor a probable occurrence of interaction between different optical breakdowns and respectively cavitation bubbles of adjacent optical breakdowns. While the interaction of one single laser pulse with biological tissue is analyzed reasonably well experimentally and theoretically, the interaction of several spatial and temporal following pulses is scarcely determined yet. Thus, the aim of this study is to analyse the dynamic and interaction of two cavitation bubbles by using high speed photography. The applied laser pulse energy, the energy ratio and the spot distance between different cavitation bubbles were varied. Depending on a change of these parameters different kinds of interactions such as a flattening and deformation of bubble shape or jet formation are observed. The effects will be discussed regarding the medical ophthalmic application of fs-lasers. Based on these results a further research seems to be inevitable to comprehend and optimize the cutting effect of ultra-short pulse laser systems with high (> 500 kHz) repetition rates.

Simulating Gamma-Ray Emission in Star-forming Galaxies

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

Pfrommer, Christoph; Pakmor, Rüdiger; Simpson, Christine M.

Star-forming galaxies emit GeV and TeV gamma-rays that are thought to originate from hadronic interactions of cosmic-ray (CR) nuclei with the interstellar medium. To understand the emission, we have used the moving-mesh code Arepo to perform magnetohydrodynamical galaxy formation simulations with self-consistent CR physics. Our galaxy models exhibit a first burst of star formation that injects CRs at supernovae. Once CRs have sufficiently accumulated in our Milky Way–like galaxy, their buoyancy force overcomes the magnetic tension of the toroidal disk field. As field lines open up, they enable anisotropically diffusing CRs to escape into the halo and to accelerate amore » bubble-like, CR-dominated outflow. However, these bubbles are invisible in our simulated gamma-ray maps of hadronic pion-decay and secondary inverse-Compton emission because of low gas density in the outflows. By adopting a phenomenological relation between star formation rate (SFR) and far-infrared emission and assuming that gamma-rays mainly originate from decaying pions, our simulated galaxies can reproduce the observed tight relation between far-infrared and gamma-ray emission, independent of whether we account for anisotropic CR diffusion. This demonstrates that uncertainties in modeling active CR transport processes only play a minor role in predicting gamma-ray emission from galaxies. We find that in starbursts, most of the CR energy is “calorimetrically” lost to hadronic interactions. In contrast, the gamma-ray emission deviates from this calorimetric property at low SFRs due to adiabatic losses, which cannot be identified in traditional one-zone models.« less

Simulating Gamma-Ray Emission in Star-forming Galaxies

NASA Astrophysics Data System (ADS)

Pfrommer, Christoph; Pakmor, Rüdiger; Simpson, Christine M.; Springel, Volker

2017-10-01

Star-forming galaxies emit GeV and TeV gamma-rays that are thought to originate from hadronic interactions of cosmic-ray (CR) nuclei with the interstellar medium. To understand the emission, we have used the moving-mesh code Arepo to perform magnetohydrodynamical galaxy formation simulations with self-consistent CR physics. Our galaxy models exhibit a first burst of star formation that injects CRs at supernovae. Once CRs have sufficiently accumulated in our Milky Way-like galaxy, their buoyancy force overcomes the magnetic tension of the toroidal disk field. As field lines open up, they enable anisotropically diffusing CRs to escape into the halo and to accelerate a bubble-like, CR-dominated outflow. However, these bubbles are invisible in our simulated gamma-ray maps of hadronic pion-decay and secondary inverse-Compton emission because of low gas density in the outflows. By adopting a phenomenological relation between star formation rate (SFR) and far-infrared emission and assuming that gamma-rays mainly originate from decaying pions, our simulated galaxies can reproduce the observed tight relation between far-infrared and gamma-ray emission, independent of whether we account for anisotropic CR diffusion. This demonstrates that uncertainties in modeling active CR transport processes only play a minor role in predicting gamma-ray emission from galaxies. We find that in starbursts, most of the CR energy is “calorimetrically” lost to hadronic interactions. In contrast, the gamma-ray emission deviates from this calorimetric property at low SFRs due to adiabatic losses, which cannot be identified in traditional one-zone models.

The unsteady end to a powerful Plinian eruption: insights from a Vulcanian block apron from the 1912 eruption of Novarupta, Alaska

NASA Astrophysics Data System (ADS)

Isgett, S. J.; Houghton, B. F.; Burgisser, A.; Arbaret, L.

2016-12-01

Current models propose a static conduit architecture prior to Vulcanian eruptions where a dense, outgassed dome/plug overlies an orderly, texturally horizontally layered conduit. Blocks from a Vulcanian phase (Episode IV) during the 1912 eruption of Novarupta provide special insight to the state of the magma within a complex shallow conduit prior to fragmentation. Extreme conduit heterogeneity is seen in a diverse range of dacitic block types, including pumiceous, dense, flow-banded, and variably welded breccia clasts, all with a range of surface-breadcrusting. Diverse 2D and 3D textures suggest a variety of degassing states, with ranges of vesicle textures (e.g. bubble number, shape, and size) in each of the block types. The nonbreadcrusted pumice exhibit textures similar to preceding Plinian phases, reflecting bubble nucleation, growth, and coalescence followed by fragmentation. Breadcrusted rind and dense dacite textures are the result of bubble collapse with the dense dacites progressing furthest along the outgassing pathway. Residual water contents within the quenched glass are all less than 0.5 wt% and indicate that the melt came from the upper 100 m of the conduit. There is no correlation between water content and vesicularity. Overall, the evidence indicates 1) the mingling of variably degassed and outgassed melts in varying states of chemical disequilibrium over a narrow depth range close to the surface and 2) fragmentation was probably driven by the melt forming the non-breadcrusted pumices which we consider was probably newly arrived in the shallow conduit at the time of fragmentation. We therefore propose a revised, dynamic model applicable to Vulcanian explosions in the context of downscaling Plinian eruptions that involves vigorous mingling of melts that are all actively degassing and outgassing to varying degrees within the shallow conduit.

Limited role for thermal erosion by turbulent lava in proximal Athabasca Valles, Mars

PubMed Central

Cataldo, Vincenzo; Williams, David A.; Dundas, Colin M.; Keszthelyi, Laszlo P.

2017-01-01

The Athabasca Valles flood lava is among the most recent (<50 Ma) and best preserved effusive lava flows on Mars and was probably emplaced turbulently. The Williams et al. [2005] model of thermal erosion by lava has been applied to what we term “proximal Athabasca,” the 75 km long upstream portion of Athabasca Valles. For emplacement volumes of 5000 and 7500 km3 and average flow thicknesses of 20 and 30 m, the duration of the eruption varies between ~11 and ~37 days. The erosion of the lava flow substrate is investigated for three eruption temperatures (1270°C, 1260°C, and 1250°C), and volatile contents equivalent to 0–65 vol% bubbles. The largest erosion depths of ~3.8–7.5 m are at the lava source, for 20 m thick and bubble-free flows that erupted at their liquidus temperature (1270°C). A substrate containing 25 vol% ice leads to maximum erosion. A lava temperature 20°C below liquidus reduces erosion depths by a factor of ~2.2. If flow viscosity increases with increasing bubble content in the lava, the presence of 30–50 vol % bubbles leads to erosion depths lower than those relative to bubble-free lava by a factor of ~2.4. The presence of 25 vol % ice in the substrate increases erosion depths by a factor of 1.3. Nevertheless, modeled erosion depths, consistent with the emplacement volume and flow duration constraints, are far less than the depth of the channel (~35–100 m). We conclude that thermal erosion does not appear to have had a major role in excavating Athabasca Valles. PMID:29082120

Limited role for thermal erosion by turbulent lava in proximal Athabasca Valles, Mars

USGS Publications Warehouse

Cataldo, Vincenzo; Williams, David A.; Dundas, Colin M.; Kestay, Laszlo P.

2015-01-01

The Athabasca Valles flood lava is among the most recent (<50 Ma) and best preserved effusive lava flows on Mars and was probably emplaced turbulently. The Williams et al. (2005) model of thermal erosion by lava has been applied to what we term “proximal Athabasca,” the 75 km long upstream portion of Athabasca Valles. For emplacement volumes of 5000 and 7500 km3and average flow thicknesses of 20 and 30 m, the duration of the eruption varies between ~11 and ~37 days. The erosion of the lava flow substrate is investigated for three eruption temperatures (1270°C, 1260°C, and 1250°C), and volatile contents equivalent to 0–65 vol % bubbles. The largest erosion depths of ~3.8–7.5 m are at the lava source, for 20 m thick and bubble-free flows that erupted at their liquidus temperature (1270°C). A substrate containing 25 vol % ice leads to maximum erosion. A lava temperature 20°C below liquidus reduces erosion depths by a factor of ~2.2. If flow viscosity increases with increasing bubble content in the lava, the presence of 30–50 vol % bubbles leads to erosion depths lower than those relative to bubble-free lava by a factor of ~2.4. The presence of 25 vol % ice in the substrate increases erosion depths by a factor of 1.3. Nevertheless, modeled erosion depths, consistent with the emplacement volume and flow duration constraints, are far less than the depth of the channel (~35–100 m). We conclude that thermal erosion does not appear to have had a major role in excavating Athabasca Valles.

Simulating the universe(s): from cosmic bubble collisions to cosmological observables with numerical relativity

NASA Astrophysics Data System (ADS)

Wainwright, Carroll L.; Johnson, Matthew C.; Peiris, Hiranya V.; Aguirre, Anthony; Lehner, Luis; Liebling, Steven L.

2014-03-01

The theory of eternal inflation in an inflaton potential with multiple vacua predicts that our universe is one of many bubble universes nucleating and growing inside an ever-expanding false vacuum. The collision of our bubble with another could provide an important observational signature to test this scenario. We develop and implement an algorithm for accurately computing the cosmological observables arising from bubble collisions directly from the Lagrangian of a single scalar field. We first simulate the collision spacetime by solving Einstein's equations, starting from nucleation and ending at reheating. Taking advantage of the collision's hyperbolic symmetry, the simulations are performed with a 1+1-dimensional fully relativistic code that uses adaptive mesh refinement. We then calculate the comoving curvature perturbation in an open Friedmann-Robertson-Walker universe, which is used to determine the temperature anisotropies of the cosmic microwave background radiation. For a fiducial Lagrangian, the anisotropies are well described by a power law in the cosine of the angular distance from the center of the collision signature. For a given form of the Lagrangian, the resulting observational predictions are inherently statistical due to stochastic elements of the bubble nucleation process. Further uncertainties arise due to our imperfect knowledge about inflationary and pre-recombination physics. We characterize observational predictions by computing the probability distributions over four phenomenological parameters which capture these intrinsic and model uncertainties. This represents the first fully-relativistic set of predictions from an ensemble of scalar field models giving rise to eternal inflation, yielding significant differences from previous non-relativistic approximations. Thus, our results provide a basis for a rigorous confrontation of these theories with cosmological data.

Vapor nucleation paths in lyophobic nanopores.

PubMed

Tinti, Antonio; Giacomello, Alberto; Casciola, Carlo Massimo

2018-04-19

In recent years, technologies revolving around the use of lyophobic nanopores gained considerable attention in both fundamental and applied research. Owing to the enormous internal surface area, heterogeneous lyophobic systems (HLS), constituted by a nanoporous lyophobic material and a non-wetting liquid, are promising candidates for the efficient storage or dissipation of mechanical energy. These diverse applications both rely on the forced intrusion and extrusion of the non-wetting liquid inside the pores; the behavior of HLS for storage or dissipation depends on the hysteresis between these two processes, which, in turn, are determined by the microscopic details of the system. It is easy to understand that molecular simulations provide an unmatched tool for understanding phenomena at these scales. In this contribution we use advanced atomistic simulation techniques in order to study the nucleation of vapor bubbles inside lyophobic mesopores. The use of the string method in collective variables allows us to overcome the computational challenges associated with the activated nature of the phenomenon, rendering a detailed picture of nucleation in confinement. In particular, this rare event method efficiently searches for the most probable nucleation path(s) in otherwise intractable, high-dimensional free-energy landscapes. Results reveal the existence of several independent nucleation paths associated with different free-energy barriers. In particular, there is a family of asymmetric transition paths, in which a bubble forms at one of the walls; the other family involves the formation of axisymmetric bubbles with an annulus shape. The computed free-energy profiles reveal that the asymmetric path is significantly more probable than the symmetric one, while the exact position where the asymmetric bubble forms is less relevant for the free energetics of the process. A comparison of the atomistic results with continuum models is also presented, showing how, for simple liquids in mesoporous materials of characteristic size of ca. 4nm, the nanoscale effects reported for smaller pores have a minor role. The atomistic estimates for the nucleation free-energy barrier are in qualitative accord with those that can be obtained using a macroscopic, capillary-based nucleation theory.

Status of the Stardust ISPE and the Origin of Four Interstellar Dust Candidates

NASA Technical Reports Server (NTRS)

Westphal, A. J.; Allen, C.; Ansari, A.; Bajt, S.; Bastien, R. S.; Bassim, N.; Bechtel, H. A.; Borg, J.; Brenker, F. E.; Bridges, J.;

Primitive Liquid Water of the Solar System in an Aqueous Altered Carbonaceous Chondrite

NASA Technical Reports Server (NTRS)

Tsuchiyama, A.; Miyake, A.; Kitayama, A.; Matsuno, J.; Takeuchi, A.; Uesugi, K.; Suzuki, Y.; Nakano, T.; Zolensky, M. E.

2016-01-01

Non-destructive 3D observations of the aqueous altered CM chondrite Sutter's Mill using scanning imaging x-ray microscopy (SIXM) showed that some of calcite and enstatite grains contain two-phase inclusion, which is most probably composed of liquid water and bubbles. This water should be primitive water responsible for aqueous alteration in an asteroid in the early solar system.

Hydrocarbons on Saturns Satellites: Relationship to Interstellar Dust and the Solar Nebula

NASA Technical Reports Server (NTRS)

Cruikshank, D. P.

2012-01-01

To understand the origin and evolution of our Solar System, and the basic components that led to life on Earth, we study interstellar and planetary spectroscopic signatures. The possible relationship of organic material detected in carbonaceous meteorites, interplanetary dust particles (IDPs), comets and the interstellar medium have been the source of speculation over the years as the composition and processes that governed the early solar nebula have been explored to understand the extent to which primitive material survived or became processed. The Cassini VIMS has provided new data relevant to this problem. Three of Saturn's satellites, Phoebe, Iapetus, and Hyperion, are found to have aromatic and aliphatic hydrocarbons on their surfaces. The aromatic hydrocarbon signature (C-H stretching mode at 3.28 micrometers) is proportionally significantly stronger (relative to the aliphatic bands) than that seen in other Solar System bodies (e.g., comets) and materials (Stardust samples, IDPs, meteorites) and the distinctive sub-features of the 3.4 micrometer aliphatic band (CH2 and CH3 groups) are reminiscent of those widely detected throughout the diffuse ISM. Phoebe may be a captured object that originated in the region beyond the present orbit of Neptune, where the solar nebula contained a large fraction of original interstellar ice and dust that was less processed than material closer to the Sun. Debris from Phoebe now resident on Iapetus and Hyperion, as well as o Phoebe itself, thus presents a unique blend of hydrocarbons, amenable to comparisons with interstellar hydrocarbons and other Solar System materials. The dust ring surrounding Saturn, in which Phoebe is embedded, probably originated from a collision with Phoebe. Dust ring particles are the likely source of the organic-bearing materials, and perhaps the recently identified small particles of Fe detected on Saturn's satellites. Lab measurements of the absolute band strengths of representative aliphatic and aromatic molecules, together with measurements from the VIMS data, allow us to calculate the number of C atoms to find the relative abundances of C atoms in the two kinds of organic molecules. The strength of the prominent aromatic C-H stretch band relative to the aliphatic band complex in Phoebe and Iapetus indicates that the relative abundance of aromatic to aliphatic carbon is very large (greater than 200). In contract, the aromatic band is nearly imperceptible in spectra of interplanetary dust particles (IDP), returned samples from comet 91P/Wild 2, insoluable carbonaceous material in most meteorites, and the diffuse interstellar dust (DISM) (although aromatics are known in all these materials-here we consider only the spectroscopic signature)

Unstable density distribution associated with equatorial plasma bubble

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

Kherani, E. A., E-mail: esfhan.kherani@inpe.br; Meneses, F. Carlos de; Bharuthram, R.

2016-04-15

In this work, we present a simulation study of equatorial plasma bubble (EPB) in the evening time ionosphere. The fluid simulation is performed with a high grid resolution, enabling us to probe the steepened updrafting density structures inside EPB. Inside the density depletion that eventually evolves as EPB, both density and updraft are functions of space from which the density as implicit function of updraft velocity or the density distribution function is constructed. In the present study, this distribution function and the corresponding probability distribution function are found to evolve from Maxwellian to non-Maxwellian as the initial small depletion growsmore » to EPB. This non-Maxwellian distribution is of a gentle-bump type, in confirmation with the recently reported distribution within EPB from space-borne measurements that offer favorable condition for small scale kinetic instabilities.« less

Interstellar and Solar System Organic Matter Preserved in Interplanetary Dust

NASA Technical Reports Server (NTRS)

Messenger, Scott; Nakamura-Messenger, Keiko

2015-01-01

Interplanetary dust particles (IDPs) collected in the Earth's stratosphere derive from collisions among asteroids and by the disruption and outgassing of short-period comets. Chondritic porous (CP) IDPs are among the most primitive Solar System materials. CP-IDPs have been linked to cometary parent bodies by their mineralogy, textures, C-content, and dynamical histories. CP-IDPs are fragile, fine-grained (less than um) assemblages of anhydrous amorphous and crystalline silicates, oxides and sulfides bound together by abundant carbonaceous material. Ancient silicate, oxide, and SiC stardust grains exhibiting highly anomalous isotopic compositions are abundant in CP-IDPs, constituting 0.01 - 1 % of the mass of the particles. The organic matter in CP-IDPs is isotopically anomalous, with enrichments in D/H reaching 50x the terrestrial SMOW value and 15N/14N ratios up to 3x terrestrial standard compositions. These anomalies are indicative of low T (10-100 K) mass fractionation in cold molecular cloud or the outermost reaches of the protosolar disk. The organic matter shows distinct morphologies, including sub-um globules, bubbly textures, featureless, and with mineral inclusions. Infrared spectroscopy and mass spectrometry studies of organic matter in IDPs reveals diverse species including aliphatic and aromatic compounds. The organic matter with the highest isotopic anomalies appears to be richer in aliphatic compounds. These materials also bear similarities and differences with primitive, isotopically anomalous organic matter in carbonaceous chondrite meteorites. The diversity of the organic chemistry, morphology, and isotopic properties in IDPs and meteorites reflects variable preservation of interstellar/primordial components and Solar System processing. One unifying feature is the presence of sub-um isotopically anomalous organic globules among all primitive materials, including IDPs, meteorites, and comet Wild-2 samples returned by the Stardust mission.

First exploration of a single thermal interface between the two dominant phases of the interstellar medium

NASA Astrophysics Data System (ADS)

Gry, Cecile

2017-08-01

Two phases of the interstellar medium, the Warm Neutral Medium (WNM) and the Hot Ionized Medium (HIM) occupy most the volume of space in the plane of our Galaxy. Because the boundaries between these phases are important sources of energy loss for the hot gas, they are supposed to play an important role in the thermal structure and evolution of the ISM and of galaxies.Many theorists have created descriptions of the nature of such boundaries and have derived two fundamental concepts: (1) a conductive interface and (2) a turbulent mixing layer.We have yet to observe in detail either kind of boundary. This is achieved by using UV absorption lines of moderately high ionization stages of heavy elements. Yet, over most lines of sight the diagnostics are blurred out by the superposition of different regions with vastly different physical conditions, making them difficult to interpret. To characterize the nature of the physical processes at a boundary one must observe along a sight line that penetrates just one such region. The simplest configuration is the outer boundary of the Local Cloud, the WNM ((T 7000 K) that surrounds the Sun and which is embedded in a very low density, soft X-ray emitting hot medium ( 10^6 K) that fills a cavity ( 200 pc in diameter) called the Local Bubble.We propose to observe an ideal target: a nearby, bright B9V star (i.e. hot enough to provide a high-SNR continuum, but not enough to contaminate it with absorptions from circumstellar high-ionization species), located in a direction where the relative orientation of the magnetic field and the cloud boundary does not quench thermal conduction and thus favors a full extent of the interface.

Inner-ear decompression sickness: 'hubble-bubble' without brain trouble?

PubMed

Tremolizzo, Lucio; Malpieri, Massimo; Ferrarese, Carlo; Appollonio, Ildebrando

2015-06-01

Inner-ear decompression sickness (DCS) is an incompletely understood and increasingly recognized condition in compressed-air divers. Previous reports show a high association of inner-ear DCS with persistent foramen ovale (PFO), suggesting that a moderate-to-severe right-to-left shunt might represent a major predisposing factor, and more properly defining it as an event from arterial gas embolism (AGE). However, other conditions characterized by bubbles entering the arterial circulation, such as open-chamber cardiac surgery, do not produce inner-ear involvement, while sometimes damaging the brain extensively. Moreover, in other sites, such as the spinal cord, the prevailing mechanism for DCS is not AGE, but more likely local bubble formation with subsequent compression of venules and capillaries. Thus, AGE might be, more properly, a predisposing condition, neither sufficient, nor possibly even strictly necessary for inner-ear DCS. A 'two-hit hypothesis' has been proposed, implying a locally selective vulnerability of the inner ear to AGE. Modelled kinetics for gas removal are slower in the inner ear compared to the brain, leading to a supersaturated environment which allows bubbles to grow until they eventually obstruct the labyrinthine artery. Since this artery is relatively small, there is a low probability for a bubble to enter it; this might explain the disproportion between the high prevalence of PFO in the general population (25-30%) and the very low incidence of inner-ear DCS in compressed-air diving (approximately 0.005%). Furthermore, given that the labyrinthine artery usually originates either from the anterior inferior cerebellar artery, or directly from the basilar artery, shunting bubbles will more frequently swarm through the entire brain. In this case, however, the brain's much faster gas removal kinetics might allow for them to be reabsorbed without damaging brain tissue. In line with this scenario is the low probability (approx. 15%) of inner-ear DCS presenting with concomitant symptoms suggestive of brain involvement. Interestingly, PFO is a putative risk factor not only for DCS but also for ischaemic stroke, and it has been hypothesized that a predominantly silent ischaemic cerebral burden might represent a meaningful surrogate of end-organ damage in divers with PFO, with implications for stroke or cognitive decline. Here we report the case of a 44-year-old diving instructor (> 350 dives) who suffered from inner-ear DCS about 10 min after a routine dive (5 min/40 metres' fresh water (mfw), ascent 7.5 mfw·min⁻¹, stop 10 min/5 mfw), resulting in severe left cochlear/vestibular impairment (complete deafness and marked vertigo, only the latter slowly receding after a few hours). The patient was not recompressed. A few months later, transcranial Doppler ultrasonography demonstrated a moderate-to-severe shunt (> 30 bubbles), presumably due to a PFO (he refused confirmatory echocardiography), while a brain MRI (1.5 T) was reported as negative for both recent and remote lacunar infarcts (Figure 1). We believe this may be evidence that inner-ear DCS could occur while the brain is completely spared, not only clinically, but also at neuroimaging. This would support either of two hypotheses: (a) that the brain is indeed relatively protected from arterial bubbles that preferentially harm the inner ear where, however, they only rarely infiltrate, or (b) that direct bubble formation within the inner ear cannot be completely discarded, and that the elevated PFO-inner-ear DCS association might be, in this latter case, merely circumstantial. We favour the hypothesis that inner-ear DCS might be related to AGE in an anatomically vulnerable region. More precise data regarding the exact incidence of inner-ear involvement, isolating those subjects with moderate-to-severe shunt, should be obtained before exploring the risk-to-benefit ratio given by transcatheter occlusion of a PFO for prevention of inner-ear DCS; odds that could end up to be sensibly different with respect to other types of DCS presentation.

Experimental investigation on the phenomena around the onset nucleate boiling during the impacting of a droplet on the hot surface

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

Mitrakusuma, Windy H., E-mail: windyhm@polban.ac.id; Refrigeration and Airconditioning Department, Politeknik Negeri Bandung, Jl. Gegerkalong Hilir, Ds. Ciwaruga Kotak Pos 1234 Bandung; Deendarlianto,

2016-06-03

Onset of nucleate boiling of a droplet when impacted onto hot surface was investigated. Three kinds of surfaces, normal stainless steel (NSS), stainless steel with TiO{sub 2} coating (UVN), and stainless steel with TiO{sub 2} coating and radiated by ultraviolet ray were employed to examine the effect of wettability. The droplet size was 2.4 mm diameter, and dropped under different We number. The image is generated by high speed camera with the frame speed of 1000 fps. The boiling conditions are identified as natural convection, nucleate boiling, critical heat flux, transition, and film boiling. In the present report, the discussionmore » will be focused on the beginning of nucleate boiling on the droplet. Nucleate boiling occurs when bubbles are generated. These bubbles are probably caused by nucleation on the impurities within the liquid rather than at nucleation sites on the heated surface because the bubbles appear to be in the bulk of the liquid instead of at the liquid-solid interface. In addition, the smaller the contact angle, the fastest the boiling.« less

We are alone in our Galaxy

NASA Astrophysics Data System (ADS)

Tipler, F. J.

1982-10-01

An assessment is presented of the probability of the existence of intelligent extraterrestrial life in view of biological evolutionary constraints, in order to furnish some perspective for the hopes and claims of search of extraterrestrial intelligence (SETI) enthusiasts. Attention is given to a hypothetical extraterrestrial civilization's exploration/colonization of interstellar space by means of von Neumann machine-like, endlessly self-replicating space probes which would eventually reach the planetary systems of all stars in the Galaxy. These probes would be able to replicate the biology of their creator species, upon reaching a hospitable planet. It is suggested that the fundamental technological feasibility of such schemes, and their geometrically progressive comprehension of the Galaxy, would make actual colonization of the earth by extraterrestrials so probable as to destroy the hopes of SETI backers for occasional contact.

1I/‘Oumuamua as a Tidal Disruption Fragment from a Binary Star System

NASA Astrophysics Data System (ADS)

Ćuk, Matija

2018-01-01

1I/‘Oumuamua is the first known interstellar small body, probably being only about 100 m in size. Against expectations based on comets, ‘Oumuamua does not show any activity and has a very elongated figure, and it also exhibits undamped rotational tumbling. In contrast, ‘Oumuamua’s trajectory indicates that it was moving with the local stars, as expected from a low-velocity ejection from a relatively nearby system. Here, I assume that ‘Oumuamua is typical of 100 m interstellar objects and speculate on its origins. I find that giant planets are relatively inefficient at ejecting small bodies from inner solar systems of main-sequence stars, and that binary systems offer a much better opportunity for ejections of non-volatile bodies. I also conclude that ‘Oumuamua is not a member of a collisional population, which could explain its dramatic difference from small asteroids. I observe that 100 m small bodies are expected to carry little mass in realistic collisional populations and that occasional events, when whole planets are disrupted in catastrophic encounters, may dominate the interstellar population of 100 m fragments. Unlike the Sun or Jupiter, red dwarf stars are very dense and are capable of thoroughly tidally disrupting terrestrial planets. I conclude that ‘Oumuamua may have originated as a fragment from a planet that was tidally disrupted and then ejected by a dense member of a binary system, which could explain its peculiarities.

ENERGETIC NEUTRAL HYDROGEN OBSERVATIONS DEMONSTRATE THAT VOYAGER 1 IS NOT OBSERVING THE EXTRAORDINARILY STRONG INTERSTELLAR MAGNETIC FIELD

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

Gloeckler, G.; Fisk, L. A., E-mail: gglo@umich.edu

It is generally believed that Voyager 1 ( V1 ) is now in interstellar space, having crossed the heliopause at a heliocentric distance of 121.58 au in late August of 2012. Here we use recently published spectra of energetic neutral hydrogen, and the magnetic field and energetic particles directly measured by V1 to find the average pressure in the inner heliosheath (termination shock to 122 au). This pressure turns out to be surprisingly large, (3.57 ± 0.71) × 10{sup −12} dyn cm{sup −2}, and is completely dominated by pressures of pickup ions (PUIs), created in the inner heliosheath, and their suprathermal tails (43%), andmore » PUIs and their tails that are produced upstream of the termination shock and enter the heliosheath (46%). We compute the total particle pressure in the outer heliosheath near the heliopause from distribution functions of the interstellar plasma and locally created PUIs using profiles of proton density, proton temperature, and neutral hydrogen density from model 2 in Zank et al., and find it to be at most 7.7 × 10{sup −13} dyn cm{sup −2}. Balancing pressure across the heliopause, thus requires an unusually large magnetic pressure (2.8 × 10{sup −12} dyn cm{sup −2}). The resulting strength and 1 σ uncertainty of the draped magnetic field in the outer heliosheath near the heliopause is 0.839 ± 0.106 nT. The 3 σ lower limit field strength (0.52 nT) is greater than the field of ∼0.43 ± 0.02 nT measured by V1 , implying that there is less than 1% probability that V1 is measuring the interstellar draped field.« less

THE SIZE AND EXTENT OF THE INTERSTELLAR GAS CLOUD SURROUNDING THE SUN

NASA Technical Reports Server (NTRS)

2002-01-01

Two astronomical observatories in orbit around the Earth, the Hubble Space Telescope and the Extreme Ultraviolet Explorer, have been used to investigate the structure of the interstellar gas cloud in which the Sun resides. A compilation and interpretation of the results of these studies is being presented today at the American Astronomical Society meeting in Madison, WI by Drs. Jeffrey L. Linsky, Nikolai Piskunov, and Brian E. Wood of JILA and the University of Colorado. Measuring the properties of the local interstellar medium (LISM) is important for understanding how the LISM interacts with the solar wind and for investigating the possibility that changes in the LISM in the immediate vicinity of the Sun could have an effect on the Earth's atmosphere and climate. When astronomers observe the ultraviolet light emitted by nearby stars, it is always found that some of the light is absorbed by atoms and ions in the LISM. The properties of the LISM can therefore be investigated by measuring the amount of absorption observed. Using ultraviolet spectra taken by the Hubble Space Telescope and the Extreme Ultraviolet Explorer, the total amount of local interstellar matter has been measured for many lines of sight through the LISM. These studies suggest that the interstellar gas surrounding the Sun has a temperature of about 7000 K (about 12,000 degrees Fahrenheit) and has a velocity of about 16 miles per second relative to the Sun. Measurements made for very short (less than 10 light years) lines of sight toward very nearby stars suggest an average density of about 0.1 hydrogen atoms per cubic centimeter for the local interstellar gas, hydrogen being by far the most abundant atom in the LISM. Measurements made for lines of sight toward more distant stars suggest lower average densities. This suggests that parts of the lines of sight to these more distant stars are in regions of space with extremely low densities. We believe this means that these stars lie outside the local gas cloud. We can estimate a distance from the Sun to the edge of the local cloud for each line of sight to a star that lies outside the cloud. Combining these measurements, we can then crudely map out the shape of the local cloud. The results are shown as orange ellipsoids in the accompanying illustration. According to this model, the cloud is about 60 light years across along its largest axis, and the Sun is only about 4 light years from the edge. Note that we have very little data toward the Galactic Center. Other data not presented here suggest that the cloud actually extends further in that direction than our crude model suggests. The space outside the local gas cloud is not completely empty, but is instead believed to be occupied by extremely hot (about 1,000,000 K) gas with very low densities (about 0.001 particles per cubic centimeter). The local cloud is in fact thought to reside in a region of space called the 'Local Bubble', in which most of the volume of the bubble consists of this very hot gas. The Local Bubble, which is roughly 300 light years in diameter, may have been created by a supernova explosion. The gas cloud surrounding the Sun is not completely uniform. Different parts of the cloud, which we can perhaps call 'cloudlets', are moving at slightly different speeds and in slightly different directions. The purple ellipsoids in the accompanying illustration indicate our estimate for the size and shape of the cloudlet in which the Sun resides. The crudeness of these models is indicated by the fact that part of the purple ellipsoid actually lies outside the yellow ellipsoid. The purple cloudlet in the illustration is about 30 light years across along its largest axis and the Sun is only about 0.1 light years from the edge of the cloudlet. Furthermore, the Sun's velocity relative to this cloudlet should carry the Sun outside the cloudlet in a few thousand years. Another example of the inhomogeneity of the local cloud is that we have found that the abundance of magnesium varies greatly within the cloud. For one line of sight we find that the abundance of magnesium is consistent with the magnesium abundance found in the Sun (about 39 magnesium atoms per million hydrogen atoms), but for other lines of sight the magnesium abundance is as much as 40 times lower than the solar abundance. For these lines of sight, perhaps most of the magnesium is locked up in dust grains and is therefore undetectable. This work is supported by grants from NASA. For further information, contact: Dr. Jeffrey L. Linsky (303) 492-7838 jlinsky@jila.colorado.edu Dr. Nikolai Piskunov +46-18-51-4490 piskunov@astro.uu.se Brian E. Wood (303) 492-5122 woodb@marmot.colorado.edu FIGURE CAPTION: A model of the gas cloud surrounding the Sun (orange ellipsoid), as seen from three different viewpoints: from the Galactic Center (GC), from the North Galactic Pole (NGP), and from a Galactic longitude of 270 degrees. This model is based on estimates of the location of the edge of the cloud (blue asterisks) made for 15 lines-of-sight to nearby stars. The yellow asterisks mark the locations of 3 very nearby stars that we believe lie inside the local cloud. The Sun's location is indicated by a small black circle. The names of the 18 stars used to probe the shape of the local cloud are given in the figure. The sizes of the asterisks indicate their distances from the point-of-view, with the larger asterisks being in the foreground and the smaller asterisks being in the background. Different parts of the cloud, which we can perhaps call 'cloudlets', are moving at slightly different speeds and in slightly different directions. The purple ellipsoid indicates our estimate for the size and shape of the cloudlet in which the Sun resides.

Some properties of the filamentary nebula at 1723 - 46

NASA Technical Reports Server (NTRS)

Bedford, D. K.; Elliott, K. H.; Ramsey, B.; Meaburn, J.

1984-01-01

High resolution spectra of the interstellar NaI D2 absorption line have been obtained for seven B-type stars aligned with an extensive filamentary nebula. Very fine filaments have now been found on a high contrast print of a deep H-alpha and forbidden N II plate, making identification as a fossilized remnant probable but uncertain. The inferred age is about 20,000 yr, the distance less than 200 pc, the diameter less than 17.5 pec, but the initial energy is only about 2 x 10 to the 47th erg.

Secondary Interstellar Oxygen in the Heliosphere: Numerical Modeling and Comparison with IBEX-Lo Data

NASA Astrophysics Data System (ADS)

Baliukin, I. I.; Izmodenov, V. V.; Möbius, E.; Alexashov, D. B.; Katushkina, O. A.; Kucharek, H.

2017-12-01

Quantitative analysis of the interstellar heavy (oxygen and neon) atom fluxes obtained by the Interstellar Boundary Explorer (IBEX) suggests the existence of the secondary interstellar oxygen component. This component is formed near the heliopause due to charge exchange of interstellar oxygen ions with hydrogen atoms, as was predicted theoretically. A detailed quantitative analysis of the fluxes of interstellar heavy atoms is only possible with a model that takes into account both the filtration of primary and the production of secondary interstellar oxygen in the boundary region of the heliosphere as well as a detailed simulation of the motion of interstellar atoms inside the heliosphere. This simulation must take into account photoionization, charge exchange with the protons of the solar wind and solar gravitational attraction. This paper presents the results of modeling interstellar oxygen and neon atoms through the heliospheric interface and inside the heliosphere based on a three-dimensional kinetic-MHD model of the solar wind interaction with the local interstellar medium and a comparison of these results with the data obtained on the IBEX spacecraft.

Gas exsolution and bubbles nucleation from the 1669 lava flow of Mount Etna (Italy): evidences from phase-contrast synchrotron X-ray microtomography

NASA Astrophysics Data System (ADS)

Lanzafame, Gabriele; Ferlito, Carmelo; Mancini, Lucia

2017-04-01

Bubbles are usually present in lavas, often showing an increase in their size and number from bottom to the top of vertical profile of the flows. Their presence is commonly interpreted as the final phase of the degassing processes starting and massively occurring at depth, before the eruption. In this work we present the results of a detailed study of size, shape and volumetric distribution of bubbles in lavas from the 1669 eruption of Mount Etna (Italy), one of the most voluminous and destructive historic events of this volcano. The lava field produced during this event extends up to 18 km from the craters, and the massive presence of bubbles in lavas sampled many kilometres away from the emission point is in contrast with the models predicting their almost total exsolution from the magma before the eruption, at depth of several kilometres beneath the volcano edifice. Sampling of the 1669 lava field has been performed along the longitudinal profile of the field at increasing distance from the vent. Collected rocks have been analysed by X-ray fluorescence and phase-contrast synchrotron X-ray computed microtomography in order to extract three-dimensional (3D) qualitative and quantitative information on the bubbles network. The use of synchrotron light permitted to investigate small portions of the samples at high spatial and contrast resolution and allowed us to obtain the 3D morphology and distribution of the micro-bubbles present in the lava, avoiding the limitations of the traditional two-dimensional analysis on thin sections. Results indicate that bubbles in lavas are present in various abundance, constituting up to 18% of the rocks volume, and are randomly distributed, with no regards for the distance from the vent. Their casual abundance, morphological characteristics and spatial distribution indicate large nucleation from syn- to post-eruptive stage, during the lava flowing and probably after it halted its run. These observations are in contrast with the general view that considers the magma completely (or largely) degassed and the volcanic gas species (mostly H2O, CO2, SO2) as largely exsolved when magma reaches the surface. On the contrary, results indicate that the exsolution of bubble-forming volcanic gases can occur far from the emission vent and right before the complete solidification of the lava. Finally, this process could easily explain, for the case of 1669 eruption, the impressive fluidity of the lavas, which display pahoehoe morphology 16 km away from the emission vent.

Interstellar C2, CH, and CN in translucent molecular clouds

NASA Technical Reports Server (NTRS)

Black, John H.; Van Dishoeck, Ewine F.

1989-01-01

Optical absorption-line techniques have been applied to the study of a number of translucent molecular clouds in which the total column densities are large enough that substantial molecular abundances can be maintained. Results are presented for a survey of absorption lines of interstellar C2, CH, and CN. Detections of CN through the A 2Pi-X 2Sigma(+) (1,O) and (2,O) bands of the red system are reported and compared with observations of the violet system for one line of sight. The population distributions in C2 provide diagnostic information on temperature and density. The measured column densities of the three species can be used to test details of the theory of molecule formation in clouds where photoprocesses still play a significant role. The C2 and CH column densities are strongly correlated with each other and probably also with the H2 column density. In contrast, the CN column densities are found to vary greatly from cloud to cloud. The observations are discussed with reference to detailed theoretical models.

Ultraviolet photometry from the Orbiting Astronomical Observatory. XX - The ultraviolet extinction bump

NASA Technical Reports Server (NTRS)

Savage, B. D.

1975-01-01

Ultraviolet extinction bumps are investigated in the interstellar extinction curves between 1800 and 3600 A for 36 stars which have (B-V) excesses ranging from 0.03 to 0.55 and are mostly confined to the brighter OB associations distributed along the galactic plane. Each extinction curve is found to have a broad bump which peaks near 2175 A and whose position and profile appear to be constant among all the stars. It is shown that the bump is probably interstellar in origin and that the constancy of its position and shape places such severe restrictions on grain geometrical parameters that classical scattering theory cannot be used to explain the feature unless the dust grains in widely separated regions of space and with very different physical conditions are assumed to have nearly identical size and shape distributions. Three extinction curves which extend to 1100 A are examined and found to have the same general characteristics as the others. Several extinction curves are analyzed for fine structure, but no convincing evidence is found in the present interval. Some processes are discussed which may be responsible for the bumps.

Analysis of Spectral-type A/B Stars in Five Open Clusters

NASA Astrophysics Data System (ADS)

Wilhelm, Ronald J.; Rafuil Islam, M.

2014-01-01

We have obtained low resolution (R = 1000) spectroscopy of N=68, spectral-type A/B stars in five nearby open star clusters using the McDonald Observatory, 2.1m telescope. The sample of blue stars in various clusters were selected to test our new technique for determining interstellar reddening and distances in areas where interstellar reddening is high. We use a Bayesian approach to find the posterior distribution for Teff, Logg and [Fe/H] from a combination of reddened, photometric colors and spectroscopic line strengths. We will present calibration results for this technique using open cluster star data with known reddening and distances. Preliminary results suggest our technique can produce both reddening and distance determinations to within 10% of cluster values. Our technique opens the possibility of determining distances for blue stars at low Galactic latitudes where extinction can be large and differential. We will also compare our stellar parameter determinations to previously reported MK spectral classifications and discuss the probability that some of our stars are not members of their reported clusters.

The interstellar C-H stretching band near 3.4 microns - Constraints on the composition of organic material in the diffuse interstellar medium

NASA Technical Reports Server (NTRS)

Sandford, S. A.; Allamandola, L. J.; Tielens, A. G. G. M.; Pendleton, Y.; Sellgren, K.

1991-01-01

The composition and history of dust in the diffuse ISM was studied using 3600-2700/cm absorption spectra of objects which have widely varying amounts of visual extinctions along different lines of sight. The 3300/cm and 2950/cm features are attributed to O-H and C-H stretching vibrations, respectively. The O-H feature in OH 32.8-0.3 is suggestive of circumstellar water ice and is probably not due to material in the diffuse ISM. The features in the 3100-2700/cm region are attributed either to C-H vibrations or to M stars. The spectra of the latter show a series of narrow features in this region that are identified with photospheric OH. Objects in which these bands are seen include OH 01-477, T629-5, and the Galactic center source IRS 7. The C-H stretch feature of diffuse ISM dust has subpeaks which fall within 5/cm of C-H stretching vibrations in the -CH2- and -CH3 groups of saturated aliphatic hydrocarbons.

Comets: Cosmic connections with carbonaceous meteorites, interstellar molecules and the origin of life

NASA Technical Reports Server (NTRS)

Chang, S.

1979-01-01

The ions, radicals, and molecules observed in comets may be derived intact or by partial decomposition from parent compounds of the sort found either in the interstellar medium or in carbonaceous meteorites. The early loss of highly reducing primitive atmosphere and its replacement by a secondary atmosphere dominated by H2O, CO2, and N2, as depicted in current models of the earth's evolution, pose a dilemma for the origin of life: the synthesis of organic compounds necessary for life from components of the secondary atmosphere appears to be difficult, and plausible mechanisms have not been evaluated. Both comets and carbonaceous meteorites are implicated as sources for the earth's atmophilic and organogenic elements. A mass balance argument involving the estimated ratios of hydrogen to carbon in carbonaceous meteorites, comets, and the crust and upper mantle suggests that comets supplied the earth with a large fraction of its volatiles. The probability that comets contributed significantly to the earth's volatile inventory suggests a chemical evolutionary link between comets, prebiotic organic synthesis, and the origin of life.

Analysis of interstellar cloud structure based on IRAS images

NASA Technical Reports Server (NTRS)

Scalo, John M.

1992-01-01

The goal of this project was to develop new tools for the analysis of the structure of densely sampled maps of interstellar star-forming regions. A particular emphasis was on the recognition and characterization of nested hierarchical structure and fractal irregularity, and their relation to the level of star formation activity. The panoramic IRAS images provided data with the required range in spatial scale, greater than a factor of 100, and in column density, greater than a factor of 50. In order to construct densely sampled column density maps of star-forming clouds, column density images of four nearby cloud complexes were constructed from IRAS data. The regions have various degrees of star formation activity, and most of them have probably not been affected much by the disruptive effects of young massive stars. The largest region, the Scorpius-Ophiuchus cloud complex, covers about 1000 square degrees (it was subdivided into a few smaller regions for analysis). Much of the work during the early part of the project focused on an 80 square degree region in the core of the Taurus complex, a well-studied region of low-mass star formation.

Outbursts in Symbiotic Binaries

NASA Technical Reports Server (NTRS)

Sonneborn, George (Technical Monitor); Kenyon, Scott J.

2004-01-01

Two models have been proposed for the outbursts of symbiotic stars. In the thermonuclear model, outbursts begin when the hydrogen burning shell of a hot white dwarf reaches a critical mass. After a rapid increase in the luminosity and effective temperature, the white dwarf evolves at constant luminosity to lower effective temperatures, remains at optical maximum for several years, and then returns to quiescence along a white dwarf cooling curve. In disk instability models, the brightness rises when the accretion rate from the disk onto the central white dwarf abruptly increases by factors of 5-20. After a few month to several year period at maximum, both the luminosity and the effective temperature of the disk decline as the system returns to quiescence. If most symbiotic stars undergo thermonuclear eruptions, then symbiotics are probably poor candidates for type I supernovae. However, they can then provide approx. 10% of the material which stars recycle back into the interstellar medium. If disk instabilities are the dominant eruption mechanism, symbiotics are promising type Ia candidates but recycle less material into the interstellar medium.

Probability of cavitation for single ultrasound pulses applied to tissues and tissue-mimicking materials.

PubMed

Maxwell, Adam D; Cain, Charles A; Hall, Timothy L; Fowlkes, J Brian; Xu, Zhen

2013-03-01

In this study, the negative pressure values at which inertial cavitation consistently occurs in response to a single, two-cycle, focused ultrasound pulse were measured in several media relevant to cavitation-based ultrasound therapy. The pulse was focused into a chamber containing one of the media, which included liquids, tissue-mimicking materials, and ex vivo canine tissue. Focal waveforms were measured by two separate techniques using a fiber-optic hydrophone. Inertial cavitation was identified by high-speed photography in optically transparent media and an acoustic passive cavitation detector. The probability of cavitation (P(cav)) for a single pulse as a function of peak negative pressure (p(-)) followed a sigmoid curve, with the probability approaching one when the pressure amplitude was sufficient. The statistical threshold (defined as P(cav) = 0.5) was between p(-) = 26 and 30 MPa in all samples with high water content but varied between p(-) = 13.7 and >36 MPa in other media. A model for radial cavitation bubble dynamics was employed to evaluate the behavior of cavitation nuclei at these pressure levels. A single bubble nucleus with an inertial cavitation threshold of p(-) = 28.2 megapascals was estimated to have a 2.5 nm radius in distilled water. These data may be valuable for cavitation-based ultrasound therapy to predict the likelihood of cavitation at various pressure levels and dimensions of cavitation-induced lesions in tissue. Copyright © 2013 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Summer School on Interstellar Processes: Abstracts of contributed papers

NASA Technical Reports Server (NTRS)

Hollenbach, D. J. (Editor); Thronson, H. A., Jr. (Editor)

1986-01-01

The Summer School on Interstellar Processes was held to discuss the current understanding of the interstellar medium and to analyze the basic physical processes underlying interstellar phenomena. Extended abstracts of the contributed papers given at the meeting are presented. Many of the papers concerned the local structure and kinematics of the interstellar medium and focused on such objects as star formation regions, molecular clouds, HII regions, reflection nebulae, planetary nebulae, supernova remnants, and shock waves. Other papers studied the galactic-scale structure of the interstellar medium either in the Milky Way or other galaxies. Some emphasis was given to observations of interstellar grains and

Interstellar Dust: Contributed Papers

NASA Technical Reports Server (NTRS)

Tielens, Alexander G. G. M. (Editor); Allamandola, Louis J. (Editor)

1989-01-01

A coherent picture of the dust composition and its physical characteristics in the various phases of the interstellar medium was the central theme. Topics addressed included: dust in diffuse interstellar medium; overidentified infrared emission features; dust in dense clouds; dust in galaxies; optical properties of dust grains; interstellar dust models; interstellar dust and the solar system; dust formation and destruction; UV, visible, and IR observations of interstellar extinction; and quantum-statistical calculations of IR emission from highly vibrationally excited polycyclic aromatic hydrocarbon (PAH) molecules.

Radical routes to interstellar glycolaldehyde. The possibility of stereoselectivity in gas-phase polymerization reactions involving CH(2)O and ˙CH(2)OH.

PubMed

Wang, Tianfang; Bowie, John H

2010-10-21

A previous report that the interstellar molecule glycolaldehyde (HOCH(2)CHO) can be made from hydroxymethylene (HOCH:) and formaldehyde has been revisited at the CCSD(T)/6-311++G(3df,2p)//MP2/6-311++G(3df,2p) level of theory. This reaction competes with the formation of acetic acid and methylformate, molecules which have also been detected in interstellar clouds. Other possible modes of formation of glycolaldehyde by radical/radical reactions have been shown to be viable theoretically as follows: HO˙+˙CH2CHO -->HOCH2CHO [ΔG(Γ)(298K)=-303kJ mol⁻¹] HOCH2˙+˙CHO-->HOCH2CHO (-259kJ mol⁻¹). The species in these two processes are known interstellar molecules. Key radicals ˙CH(2)CHO and ˙CH(2)OH in these sequences have been shown to be stable for the microsecond duration of neutralization/reionization experiments in the dual collision cells of a VG ZAB 2HF mass spectrometer. The polymerization reaction HOCH(2)CH˙OH + nCH(2)O → HOCH(2)[CH(OH)](n)˙CHOH (n = 1 to 3) has been studied theoretically and shown to be energetically feasible, as is the cyclization reaction of HOCH(2)[(CH(2)OH)(4)]˙CHOH (in the presence of one molecule of water at the reacting centre) to form glucose. The probability of such a reaction sequence is small even if polymerization were to occur in interstellar ice containing a significant concentration of CH(2)O. The large number of stereoisomers produced by such a reaction sequence makes the formation of a particular sugar, again for example glucose, an inefficient synthesis. The possibility of stereoselectivity occurring during the polymerization was investigated for two diastereoisomers of HOCH(2)[(CHOH)](2)˙CHOH. No significant difference was found in the transition state energies for addition of CH(2)O to these two diastereoisomers, but a barrier difference of 12 kJ mol(-1) was found for the H transfer reactions ˙OCH(2)[(CHOH)](2)CH(2)OH → HOCH(2)[(CHOH)(2)˙CHOH of the two diastereoisomers.

Interstellar hydrogen bonding

NASA Astrophysics Data System (ADS)

Etim, Emmanuel E.; Gorai, Prasanta; Das, Ankan; Chakrabarti, Sandip K.; Arunan, Elangannan

2018-06-01

This paper reports the first extensive study of the existence and effects of interstellar hydrogen bonding. The reactions that occur on the surface of the interstellar dust grains are the dominant processes by which interstellar molecules are formed. Water molecules constitute about 70% of the interstellar ice. These water molecules serve as the platform for hydrogen bonding. High level quantum chemical simulations for the hydrogen bond interaction between 20 interstellar molecules (known and possible) and water are carried out using different ab-intio methods. It is evident that if the formation of these species is mainly governed by the ice phase reactions, there is a direct correlation between the binding energies of these complexes and the gas phase abundances of these interstellar molecules. Interstellar hydrogen bonding may cause lower gas abundance of the complex organic molecules (COMs) at the low temperature. From these results, ketenes whose less stable isomers that are more strongly bonded to the surface of the interstellar dust grains have been observed are proposed as suitable candidates for astronomical observations.

Hubble Space Telescope STIS Observations of the Wolf-Rayet Star HD 5980 in the Small Magellanic Cloud. II. The Interstellar Medium Components

NASA Astrophysics Data System (ADS)

Koenigsberger, Gloria; Georgiev, Leonid; Peimbert, Manuel; Walborn, Nolan R.; Barbá, Rodolfo; Niemela, Virpi S.; Morrell, Nidia; Tsvetanov, Zlatan; Schulte-Ladbeck, Regina

2001-01-01

Observations of the interstellar and circumstellar absorption components obtained with the Hubble Space Telescope Space Telescope Imaging Spectrograph (STIS) along the line of sight toward the Wolf-Rayet-luminous blue variable (LBV) system HD 5980 in the Small Magellanic Cloud are analyzed. Velocity components from C I, C I*, C II, C II*, C IV, N I, N V, O I, Mg II, Al II, Si II, Si II*, Si III, Si IV, S II, S III, Fe II, Ni II, Be I, Cl I, and CO are identified, and column densities estimated. The principal velocity systems in our data are (1) interstellar medium (ISM) components in the Galactic disk and halo (Vhel=1.1+/-3, 9+/-2 km s-1) (2) ISM components in the SMC (Vhel=+87+/-6, +110+/-6, +132+/-6, +158+/-8, +203+/-15 km s-1) (3) SMC supernova remnant SNR 0057-7226 components (Vhel=+312+/-3, +343+/-3, +33, +64 km s-1) (4) circumstellar (CS) velocity systems (Vhel=-1020, -840, -630, -530, -300 km s-1) and (5) a possible system at -53+/-5 km s-1 (seen only in some of the Si II lines and marginally in Fe II) of uncertain origin. The supernova remnant SNR 0057-7226 has a systemic velocity of +188 km s-1, suggesting that its progenitor was a member of the NGC 346 cluster. Our data allow estimates to be made of Te~40,000 K, ne~100 cm-3, N(H)~(4-12)×1018 cm-2 and a total mass between 400 and 1000 Msolar for the supernova remnant (SNR) shell. We detect C I absorption lines primarily in the +132 and +158 km s-1 SMC velocity systems. As a result of the LBV-type eruptions in HD 5980, a fast-wind/slow-wind circumstellar interaction region has appeared, constituting the earliest formation stages of a windblown H II bubble surrounding this system. Variations over a timescale of 1 year in this circumstellar structure are detected. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Four Interstellar Dust Candidates from the Stardust Interstellar Dust Collector

NASA Astrophysics Data System (ADS)

Westphal, A. J.; Allen, C.; Bajt, S.; Bechtel, H. A.; Borg, J.; Brenker, F.; Bridges, J.; Brownlee, D. E.; Burchell, M.; Burghammer, M.; Butterworth, A. L.; Cloetens, P.; Davis, A. M.; Floss, C.; Flynn, G. J.; Fougeray, P.; Frank, D.; Gainsforth, Z.; Grün, E.; Heck, P. R.; Hillier, J. K.; Hoppe, P.; Howard, L.; Hudson, B.; Huss, G. R.; Huth, J.; Kearsley, A.; King, A. J.; Lai, B.; Leitner, J.; Lemelle, L.; Leroux, H.; Lettieri, R.; Marchant, W.; Nittler, L. R.; Ogliore, R. C.; Postberg, F.; Price, M. C.; Sandford, S. A.; Sans Tresseras, J. A.; Schmitz, S.; Schoonjans, T.; Silversmit, G.; Simionovici, A.; Srama, R.; Stadermann, F. J.; Stephan, T.; Stodolna, J.; Stroud, R. M.; Sutton, S. R.; Toucoulou, R.; Trieloff, M.; Tsou, P.; Tsuchiyama, A.; Tyliczszak, T.; Vekemans, B.; Vincze, L.; Wordsworth, N.; Zevin, D.; Zolensky, M. E.; 29,000 Stardust@Home Dusters

2011-03-01

We report the discovery of two new interstellar dust candidates in the aerogel collectors of the Stardust Interstellar Dust Collector, and the analyses of these and two previously identified candidates.

Coupled LBM-DEM Three-phase Simulation on Seepage of CO2 Stored under the Seabed.

NASA Astrophysics Data System (ADS)

Kano, Y.; Sato, T.

2017-12-01

Concerning the seepage of CO2 stored in a subsea formation, CO2 bubble/droplet rises to the sea-surface dissolving into the seawater, and the acidification of local seawater will be a problem. Previous research indicated that seepage rate and bubble size significantly affect its behaviour (Kano et al., 2009; Dewar et al., 2013). On the other hand, Kawada's experiments (2014) indicated that grain size affects formation of gas channels and bubbles through granular media. CO2 seepage through marine sediments probably shows similar behaviour. Additionally, such mobilisation and displacement of sand grains by gas migration may also cause capillary fracturing of CO2 in the reservoir and seal. To predict these phenomena, it is necessary to reveal three-phase behaviour of gas-water-sediment grains. We built gas-liquid-solid three-phase flow 3D simulator by coupling LBM-DEM program, and simulation results showed that the mobilisation of sand grain forms gas channels and affects bubble formation compared with that through solid porous media (Kano and Sato, 2017). In this presentation, we will report simulation results on effects of porosity, grain size and gas flow rate on the formation of gas channels and bubble and their comparison with laboratory experimental data. The results indicate that porosity and grain size of sand gravels affect the width of formed gas channels and resulting formed bubble size on the order of supposed seepage rate in the CO2 storage and that in most of experiment's conditions. References: Abe, S., Place, D., Mora, P., 2004. Pure. Appl. Geophys., 161, 2265-2277. (accessed Aug 01, 2017). Dewar, M., Wei, W., McNeil, D., Chen, B., 2013. Marine Pollution Bulletin 73(2), 504-515. Kano, Y., Sato, T., Kita, J., Hirabayashi, S., Tabeta, S., 2009. Int. J. Greenhouse Gas Control, Vol. 3(5), 617-625. Kano, Y. and Sato, T., 2017. In Proceeding of GHGT-13, Lausanne, Switzerland, Nov. 14-18, 2016. Kawada, R. 2014. Graduation thesis. Faculty of Engineering, The University of Tokyo. (in Japanese).

Evidence of fueling of the 2000 new economy bubble by foreign capital inflow: implications for the future of the US economy and its stock market

NASA Astrophysics Data System (ADS)

Sornette, Didier; Zhou, Wei-Xing

2004-02-01

Previous analyses of a large ensemble of stock markets have demonstrated that a log-periodic power law (LPPL) behavior of the prices constitutes a qualifying signature of speculative bubbles that often land with a crash. We detect such a LPPL signature in the foreign capital inflow during the bubble on the US markets culminating in March 2000. We detect a weak synchronization and lag with the NASDAQ LPPL pattern. We propose to rationalize these observations by the existence of positive feedback loops between market-appreciation/increased-spending/increased-deficit-of-balance-of-payment/larger-foreign-surplus/increased-foreign-capital-inflows and so on. Our analysis suggests that foreign capital inflow has been following rather than causing the bubble. We then combine a macroeconomic analysis of feedback processes occurring between the economy and the stock market with a technical analysis of more than 200 years of the DJIA to investigate possible scenarios for the future, three years after the end of the bubble and deep into a bearish regime. We conclude that the low interest rates and depreciating dollar are the indispensable ingredients for a lower sustainable burden of the global US debt structure and for allowing the slow rebuilding of an internationally competitive economy. This will probably be accompanied by a weak stock market on the medium term as the growing Federal deficit is consuming a large part of the foreign surplus dollars and the stock market is remaining a very risky and unattractive investment. Notwithstanding strong surge of liquidity in recent months orchestrated by the Federal Reserve, this macroeconomic analysis which incorporates an element of collective behavior is in line with our recent analyses of the bearish market that started in 2000 in terms of a LPPL “anti-bubble”. We project this LPPL anti-bubble to continue at least for another year. On the short term, increased availability of liquidity (M1) and self-fulfilling bullish anticipations may hold the stock market for a while.

Organic chemistry and biology of the interstellar medium

NASA Technical Reports Server (NTRS)

Sagan, C.

1973-01-01

Interstellar organic chemistry is discussed as the field of study emerging from the discovery of microwave lines of formaldehyde and of hydrogen cyanide in the interstellar medium. The reliability of molecular identifications and comparisons of interstellar and cometary compounds are considered, along with the degradational origin of simple organics. It is pointed out that the contribution of interstellar organic chemistry to problems in biology is not substantive but analogical. The interstellar medium reveals the operation of chemical processes which, on earth and perhaps on vast numbers of planets throughout the universe, led to the origin of life, but the actual molecules of the interstellar medium are unlikely to play any significant biological role.

Volume-weighted measure for eternal inflation

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

Winitzki, Sergei

2008-08-15

I propose a new volume-weighted probability measure for cosmological 'multiverse' scenarios involving eternal inflation. The 'reheating-volume (RV) cutoff' calculates the distribution of observable quantities on a portion of the reheating hypersurface that is conditioned to be finite. The RV measure is gauge-invariant, does not suffer from the 'youngness paradox', and is independent of initial conditions at the beginning of inflation. In slow-roll inflationary models with a scalar inflaton, the RV-regulated probability distributions can be obtained by solving nonlinear diffusion equations. I discuss possible applications of the new measure to 'landscape' scenarios with bubble nucleation. As an illustration, I compute themore » predictions of the RV measure in a simple toy landscape.« less

Time-dependent interstellar chemistry

NASA Technical Reports Server (NTRS)

Glassgold, A. E.

1985-01-01

Some current problems in interstellar chemistry are considered in the context of time-dependent calculations. The limitations of steady-state models of interstellar gas-phase chemistry are discussed, and attempts to chemically date interstellar clouds are reviewed. The importance of studying the physical and chemical properties of interstellar dust is emphasized. Finally, the results of a series of studies of collapsing clouds are described.

Processing Mechanisms for Interstellar Ices: Connections to the Solar System

NASA Technical Reports Server (NTRS)

Pendleton, Y. J.; Cuzzi, Jeffrey N. (Technical Monitor)

1995-01-01

The organic component of the interstellar medium, which has revealed itself through the ubiquitous 3.4 micrometers hydrocarbon absorption feature, is widespread throughout the disk of our galaxy and has been attributed to dust grains residing in the diffuse interstellar medium. The absorption band positions near 3.4 micrometers are characteristic of C-H stretching vibrations in the -CH3 and -CH2- groups of saturated aliphatic hydrocarbons associated with perturbing chemical groups. The production of complex molecules is thought to occur within dense molecular clouds when ice-mantled grains are processed by various energetic mechanisms. Studies of the processing of interstellar ices and the subsequent production of organic residues have relevance to studies of ices in the solar system, because primitive, icy solar system bodies such as those in the Kuiper belt are likely reservoirs of organic material, either preserved from the interstellar medium or produced in situ. Connections between the interstellar medium and the early solar nebula have long been a source of interest. A comparison of the interstellar organics and the Murchison meteorite illustrates the importance of probing the interstellar connection to the solar system, because although the carbonaceous meteorites are undoubtedly highly processed, they do retain specific interstellar signatures (such as diamonds, SiC grains, graphite and enriched D/H). The organic component, while not proven interstellar, has a remarkable similarity to the interstellar organics observed in over a dozen sightlines through our galaxy. This paper compares spectra from laboratory organics produced through the processing of interstellar ice analog materials with the high resolution infrared observations of the interstellar medium in order to investigate the mechanisms (such as ion bombardment, plasma processing, and UV photolysis) that may be producing the organics in the ISM.

Properties of interstellar wind leading to shape morphology of the dust surrounding HD 61005

NASA Astrophysics Data System (ADS)

Pástor, P.

2017-08-01

Aims: A structure formed by dust particles ejected from the debris ring around HD 61005 is observed in the scattered light. The main aim here is to constrain interstellar wind parameters that lead to shape morphology in the vicinity of HD 61005 using currently available observational data for the debris ring. Methods: Equation of motion of 2 × 105 dust particles ejected from the debris ring under the action of the electromagnetic radiation, stellar wind, and interstellar wind is solved. A two-dimensional (2D) grid is placed in a given direction for accumulation of the light scattered on the dust particles in order to determine the shape morphology. The interaction of the interstellar wind and the stellar wind is considered. Results: Groups of unknown properties of the interstellar wind that create the observed morphology are determined. A relation between number densities of gas components in the interstellar wind and its relative velocity is found. Variations of the shape morphology caused by the interaction with the interstellar clouds of various temperatures are studied. When the interstellar wind velocity is tilted from debris ring axis a simple relation between the properties of the interstellar wind and an angle between the line of sight and the interstellar wind velocity exists. Dust particles that are most significantly influenced by stellar radiation move on the boundary of observed structure. Conclusions: Observed structure at HD 61005 can be explained as a result of dust particles moving under the action of the interstellar wind. Required number densities or velocities of the interstellar wind are much higher than that of the interstellar wind entering the solar system.

Interstellar matter research with the Copernicus satellite

NASA Technical Reports Server (NTRS)

Spitzer, L., Jr.

1976-01-01

The use of the Copernicus satellite in an investigation of interstellar matter makes it possible to study absorption lines in the ultraviolet range which cannot be observed on the ground because of atmospheric absorption effects. A brief description is given of the satellite and the instrument used in the reported studies of interstellar matter. The results of the studies are discussed, giving attention to interstellar molecular hydrogen, the chemical composition of the interstellar gas, the coronal gas between the stars, and the interstellar abundance ratio of deuterium to hydrogen.

Titanium carbide and titania phases on Antarctic ice particles of probable extraterrrestrial origin

NASA Technical Reports Server (NTRS)

Zolensky, M. E.; Pun, A.; Thomas, K. L.

1989-01-01

Two unique titania-rich particles, found within ancient Antarctic ice have been discovered and characterized, and are believed to be of extraterrestrial origin. Both particles contain abundant submicron-sized crystals of Magneli phases (Ti(n)O(2n-1). In addition, one particle contains a core of TiC. Whereas the Magneli phases would have been stable in the early solar nebula, and so probably formed there, the TiC is more likely to have condensed in the cool, dusty, carbon-rich outer shell of a red giant star. It is suggested that both particles are interplanetary dust particles whose Magneli phases carry a record of the PO2-T conditions of the early solar nebula. It is further suggested that the TiC grain in particle 705 is remnant interstellar dust.

Manipulation of double-stranded DNA melting by force

NASA Astrophysics Data System (ADS)

Singh, Amit Raj; Granek, Rony

2017-09-01

By integrating elasticity—as described by the Gaussian network model—with bond binding energies that distinguish between different base-pair identities and stacking configurations, we study the force induced melting of a double-stranded DNA (dsDNA). Our approach is a generalization of our previous study of thermal dsDNA denaturation [J. Chem. Phys. 145, 144101 (2016), 10.1063/1.4964285] to that induced by force at finite temperatures. It allows us to obtain semimicroscopic information about the opening of the chain, such as whether the dsDNA opens from one of the ends or from the interior, forming an internal bubble. We study different types of force manipulation: (i) "end unzipping," with force acting at a single end base pair perpendicular to the helix, (ii) "midunzipping," with force acting at a middle base pair perpendicular to the helix, and (iii) "end shearing," where the force acts at opposite ends along the helix. By monitoring the free-energy landscape and probability distribution of intermediate denaturation states, we show that different dominant intermediate states are stabilized depending on the type of force manipulation used. In particular, the bubble state of the sequence L60B36, which we have previously found to be a stable state during thermal denaturation, is absent for end unzipping and end shearing, whereas very similar bubbles are stabilized by midunzipping, or when the force location is near the middle of the chain. Ours results offer a simple tool for stabilizing bubbles and loops using force manipulations at different temperatures, and may implicate on the mechanism in which DNA enzymes or motors open regions of the chain.

Measuring systolic arterial blood pressure. Possible errors from extension tubes or disposable transducer domes.

PubMed

Rothe, C F; Kim, K C

1980-11-01

The purpose of this study was to evaluate the magnitude of possible error in the measurement of systolic blood pressure if disposable, built-in diaphragm, transducer domes or long extension tubes between the patient and pressure transducer are used. Sinusoidal or arterial pressure patterns were generated with specially designed equipment. With a long extension tube or trapped air bubbles, the resonant frequency of the catheter system was reduced so that the arterial pulse was amplified as it acted on the transducer and, thus, gave an erroneously high systolic pressure measurement. The authors found this error to be as much as 20 mm Hg. Trapped air bubbles, not stopcocks or connections, per se, lead to poor fidelity. The utility of a continuous catheter flush system (Sorenson, Intraflow) to estimate the resonant frequency and degree of damping of a catheter-transducer system is described, as are possibly erroneous conclusions. Given a rough estimate of the resonant frequency of a catheter-transducer system and the magnitude of overshoot in response to a pulse, the authors present a table to predict the magnitude of probable error. These studies confirm the variability and unreliability of static calibration that may occur using some safety diaphragm domes and show that the system frequency response is decreased if air bubbles are trapped between the diaphragms. The authors conclude that regular procedures should be established to evaluate the accuracy of the pressure measuring systems in use, the transducer should be placed as close to the patient as possible, the air bubbles should be assiduously eliminated from the system.

Electronic Spectroscopy of Organic Cations in Gas-Phase at 6 K:IDENTIFICATION of C60/^+ in the Interstellar Medium

NASA Astrophysics Data System (ADS)

Maier, John P.

2016-06-01

After the discovery of C60, the question of its relevance to the diffuse interstellar bands was raised. In 1987 H. W. Kroto wrote: ``The present observations indicate that C60 might survive in the general interstellar medium (probably as the ion C60/^+)''. In 1994 two diffuse interstellar bands (DIBs) at 9632 and 9577 Å/ were detected and proposed to be the absorption features of C60/^+. This was based on the proximity of these wavelengths to the two prominent absorption bands of C60/^+ measured by us in a neon matrix in 1993. Confirmation of the assignment required the gas phase spectrum of C60/^+ and has taken 20 years. The approach which succeeded confines C60/^+ ions in a radiofrequency trap, cools them by collisions with high density helium allowing formation of the weakly bound C60/^+--He complexes below 10 K. The photofragmentation spectrum of this mass-selected complex is then recorded using a cw laser. In order to infer the position of the absorption features of the bare C60/^+ ion, measurements on C60/^+--He_2 were also made. The spectra show that the presence of a helium atom shifts the absorptions by less than 0.2 Å, much less than the accuracy of the astronomical measurements. The two absorption features in the laboratory have band maxima at 9632.7(1) and 9577.5(1) Å, exactly the DIB wavelengths, and the widths and relative intensities agree. This leads to the first definite identification of now five bands among the five hundred or so DIBs known and proves the presence of gaseous C60/^+ in the interstellar medium. The absorption of cold C70/^+ has also been obtained by this approach. In addition the electronic spectra of a number of cations of astrophysical interest ranging from those of carbon chains including oxygen to larger polycyclic aromatic hydrocarbon could be measured in the gas phase at around 10 K in the ion trap but using an excitation-dissociation approach. The implications of these laboratory spectra in relation to the diffuse interstellar band absorptions can be discussed. H. W. Kroto, J. R. Heath, S. C. O'Brian, R. E. Curl & R. E. Smalley, Nature, 318, 162, 1985 H. W. Kroto in ``Polycyclic aromatic hydrocarbons and astrophysics'', eds. A. Leger, L. B. d'Hendecourt & N. Boccara, Reidel, Dordrecht, 1987, p.197 B. H. Foing & P. Ehrenfreund, Nature, 369, L296, 1994 J. Fulara, M. Jakobi & J. P. Maier, Chem. Phys. Lett., 211, 227, 1993 E. K. Campbell, M. Holz, D. Gerlich & J. P. Maier, Nature, 523, 323, 2015 G. A. H. Walker, D. A. Bohlender, J. P. Maier & E. Campbell, Astrophys. J. Lett., 812, L8, 2015

New Large Interstellar Molecules Detected with the GBT

NASA Technical Reports Server (NTRS)

Hollis, Jan M.

2005-01-01

At present, more than 135 different molecules have been identified in interstellar clouds. The newest instrument in the interstellar molecule search arsenal is the recently commissioned Green Bank Telescope (GBT). In 2004, the large aldehydes propenal (CH2CHCHO) and propanal (CH3CH2CHO) were the first new interstellar molecules discovered with the GBT. At the same time, the GBT was used to observe interstellar glycolaldehyde (CH2OHCHO), which is the simplest possible aldehyde sugar; interstellar ethylene glycol (HOCH2CH2OH), which is the sugar alcohol of glycolaldehyde; and interstellar methylcyanodiacetylene (CH3C5N). These new GBT observations suggest that successive atomic addition reactions are common in the formation of larger related species. The observations will be presented and discussed.

GLOBULAR CLUSTERS AS CRADLES OF LIFE AND ADVANCED CIVILIZATIONS

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

Stefano, R. Di; Ray, A., E-mail: rdistefano@cfa.harvard.edu, E-mail: akr@tifr.res.in

2016-08-10

Globular clusters are ancient stellar populations in compact dense ellipsoids. There is no star formation and there are no core-collapse supernovae, but several lines of evidence suggest that globular clusters are rich in planets. If so, and if advanced civilizations can develop there, then the distances between these civilizations and other stars would be far smaller than typical distances between stars in the Galactic disk, facilitating interstellar communication and travel. The potent combination of long-term stability and high stellar densities provides a globular cluster opportunity. Yet the very proximity that promotes interstellar travel also brings danger, as stellar interactions canmore » destroy planetary systems. We find, however, that large portions of many globular clusters are “sweet spots,” where habitable-zone planetary orbits are stable for long times. Globular clusters in our own and other galaxies are, therefore, among the best targets for searches for extraterrestrial intelligence (SETI). We use the Drake equation to compare the likelihood of advanced civilizations in globular clusters to that in the Galactic disk. We also consider free-floating planets, since wide-orbit planets can be ejected to travel through the cluster. Civilizations spawned in globular clusters may be able to establish self-sustaining outposts, reducing the probability that a single catastrophic event will destroy the civilization. Although individual civilizations may follow different evolutionary paths, or even be destroyed, the cluster may continue to host advanced civilizations once a small number have jumped across interstellar space. Civilizations residing in globular clusters could therefore, in a sense, be immortal.« less

Globular Clusters as Cradles of Life and Advanced Civilizations

NASA Astrophysics Data System (ADS)

Di Stefano, R.; Ray, A.

2016-08-01

Globular clusters are ancient stellar populations in compact dense ellipsoids. There is no star formation and there are no core-collapse supernovae, but several lines of evidence suggest that globular clusters are rich in planets. If so, and if advanced civilizations can develop there, then the distances between these civilizations and other stars would be far smaller than typical distances between stars in the Galactic disk, facilitating interstellar communication and travel. The potent combination of long-term stability and high stellar densities provides a globular cluster opportunity. Yet the very proximity that promotes interstellar travel also brings danger, as stellar interactions can destroy planetary systems. We find, however, that large portions of many globular clusters are “sweet spots,” where habitable-zone planetary orbits are stable for long times. Globular clusters in our own and other galaxies are, therefore, among the best targets for searches for extraterrestrial intelligence (SETI). We use the Drake equation to compare the likelihood of advanced civilizations in globular clusters to that in the Galactic disk. We also consider free-floating planets, since wide-orbit planets can be ejected to travel through the cluster. Civilizations spawned in globular clusters may be able to establish self-sustaining outposts, reducing the probability that a single catastrophic event will destroy the civilization. Although individual civilizations may follow different evolutionary paths, or even be destroyed, the cluster may continue to host advanced civilizations once a small number have jumped across interstellar space. Civilizations residing in globular clusters could therefore, in a sense, be immortal.

Radiation response of ODS ferritic steels with different oxide particles under ion-irradiation at 550 °C

NASA Astrophysics Data System (ADS)

Song, Peng; Morrall, Daniel; Zhang, Zhexian; Yabuuchi, Kiyohiro; Kimura, Akihiko

2018-04-01

In order to investigate the effects of oxide particles on radiation response such as hardness change and microstructural evolution, three types of oxide dispersion strengthened (ODS) ferritic steels (named Y-Ti-ODS, Y-Al-ODS and Y-Al-Zr-ODS), mostly strengthened by Y-Ti-O, Y-Al-O and Y-Zr-O dispersoids, respectively, were simultaneously irradiated with iron and helium ions at 550 °C up to a damage of 30 dpa and a corresponding helium (He) concentration of ∼3500 appm to a depth of 1000-1300 nm. A single iron ion beam irradiation was also performed for reference. Transmission electron microscopy revealed that after the dual ion irradiation helium bubbles of 2.8, 6.6 and 4.5 nm in mean diameter with the corresponding number densities of 1.1 × 1023, 2.7 × 1022 and 3.6 × 1022 m-3 were observed in Y-Ti-ODS, Y-Al-ODS and Y-Al-Zr-ODS, respectively, while no such bubbles were observed after single ion irradiation. About 80% of intragranular He bubbles were adjacent to oxide particles in the ODS ferritic steels. Although the high number density He bubbles were observed in the ODS steels, the void swelling in Y-Ti-ODS, Y-Al-ODS and Y-Al-Zr-ODS was still small and estimated to be 0.13%, 0.53% and 0.20%, respectively. The excellent swelling resistance is dominantly attributed to the high sink strength of oxide particles that depends on the morphology of particle dispersion rather than the crystal structure of the particles. In contrast, no dislocation loops were produced in any of the irradiated steels. Nanoindentation measurements showed that no irradiation hardening but softening was found in the ODS ferritic steels, which was probably due to irradiation induced dislocation recovery. The helium bubbles in high number density never contributed to the irradiation hardening of the ODS steels at these irradiation conditions.

Contrasting patterns of vesiculation in low, intermediate, and high Hawaiian fountains: A case study of the 1969 Mauna Ulu eruption

USGS Publications Warehouse

Parcheta, Carolyn E.; Houghton, Bruce F.; Swanson, Donald A.

2013-01-01

Hawaiian-style eruptions, or Hawaiian fountains, typically occur at basaltic volcanoes and are sustained, weakly explosive jets of gas and dominantly coarse, juvenile ejecta (dense spatter to delicate reticulite). Almost the entire range of styles and mass eruption rates within Hawaiian fountaining occurred during twelve fountaining episodes recorded at Mauna Ulu, Kīlauea between May and December 1969. Such diversity in intensity and style is controlled during magma ascent by many processes that can be constrained by the size and shape of vesicles in the 1969 pyroclasts. This paper describes pyroclast vesicularity from high, intermediate, and low fountaining episodes with eruption rates from 0.05 to 1.3 × 106 m3 h− 1. As each eruptive episode progressed, magma ascent slowed in and around the vent system, offering extended time for bubbles to grow and coalesce. Late ejected pyroclasts are thus characterized by populations of fewer and larger vesicles with relaxed shapes. This progression continued in the intervals between episodes after termination of fountain activity. The time scale for this process of shallow growth, coalescence and relaxation of bubbles is typically tens of hours. Rims and cores of pumiceous pyroclasts from moderate to high fountaining episodes record a second post-fragmentation form of vesicle maturation. Partially thermally insulated pyroclasts can have internal bubble populations evolve more dynamically with continued growth and coalescence, on a time scale of only minutes, during transport in the fountains. Reticulite, which formed in a short-lived fountain 540 m in height, underwent late, short-lived bubble nucleation followed by rapid growth of a uniform bubble population in a thermally insulated fountain, and quenched at the onset of permeability before significant coalescence. These contrasting patterns of shallow degassing and outgassing were the dominant controls in determining both the form and duration of fountaining episodes at Mauna Ulu, and probably for many other Hawaiian-style eruptions.

The Diffuse Interstellar Bands: Solving a Century Old Problem

NASA Technical Reports Server (NTRS)

Salama, Farid

2017-01-01

The Diffuse Interstellar Bands (DIBs) are a set of apporoximately 500 absorption bands that are seen in the spectra of reddened stars (i.e., stars obscured by the presence of interstellar clouds in their line of sight). The first DIBs were detected in the visible over a century ago. Diffuse Interstellar Bands are now detected from the near ultraviolet to the near infrared in the spectra of reddened stars spanning a variety of interstellar environments in our local, and in other galaxies. Although DIB carriers are a significant part of the interstellar chemical inventory as they account for a noticeable fraction of the interstellar extinction, the nature of their carriers is still unknown over a century after the detection of the first bands. DIB carriers are stable and ubiquitous in a broad variety of interstellar environments and play a unique role in interstellar physics and chemistry. It has long been realized that the solving of the DIB problem requires a strong synergy between astronomical observations, laboratory astrophysics and astrochemistry, quantum chemistry calculations and astrophysical modeling of line-of-sights. In this review, we'll present and discuss the current state of this perplexing problem. We'll review the progress and the failures that have been encountered in the long quest for the identification of the carriers of these ubiquitous interstellar bands.

iWander: Dynamics of interstellar wanderers

NASA Astrophysics Data System (ADS)

Zuluaga, Jorge I.; Sanchez-Hernandez, Oscar; Sucerquia, Mario; Ferrin, Ignacio

2018-01-01

iWander assesses the origin of interstellar small bodies such as asteroids and comets. It includes a series of databases and tools that can be used in general for studying the dynamics of an interstellar vagabond object (small‑body, interstellar spaceship and even stars).

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

Bzowski, M.; Kubiak, M. A.; Sokol, J. M.

Because of its high ionization potential and weak interaction with hydrogen, neutral interstellar helium (NISHe) is almost unaffected at the heliospheric interface with the interstellar medium and freely enters the solar system. This second most abundant species provides some of the best information on the characteristics of the interstellar gas in the local interstellar cloud. The Interstellar Boundary Explorer (IBEX) is the second mission to directly detect NISHe. We present a comparison between recent IBEX NISHe observations and simulations carried out using a well-tested quantitative simulation code. Simulation and observation results compare well for times when measured fluxes are dominatedmore » by NISHe (and contributions from other species are small). Differences between simulations and observations indicate a previously undetected secondary population of neutral helium, likely produced by interaction of interstellar helium with plasma in the outer heliosheath. Interstellar neutral parameters are statistically different from previous in situ results obtained mostly from the GAS/Ulysses experiment, but they do agree with the local interstellar flow vector obtained from studies of interstellar absorption: the newly established flow direction is ecliptic longitude 79.{sup 0}2, latitude -5.{sup 0}1, the velocity is {approx}22.8 km s{sup -1}, and the temperature is 6200 K. These new results imply a markedly lower absolute velocity of the gas and thus significantly lower dynamic pressure on the boundaries of the heliosphere and different orientation of the Hydrogen Deflection Plane compared to prior results from Ulysses. A different orientation of this plane also suggests a new geometry of the interstellar magnetic field, and the lower dynamic pressure calls for a compensation by other components of the pressure balance, most likely a higher density of interstellar plasma and strength of interstellar magnetic field.« less

LOCAL INTERSTELLAR MEDIUM: SIX YEARS OF DIRECT SAMPLING BY IBEX

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

McComas, D. J.; Fuselier, S. A.; Schwadron, N. A., E-mail: dmccomas@swri.edu, E-mail: sfuselier@swri.edu, E-mail: Nathan.schwadron@unh.edu

2015-10-15

The Interstellar Boundary Explorer (IBEX) has been directly observing neutral atoms from the local interstellar medium for the last six years (2009–2014). This paper ties together the 14 studies in this Astrophysical Journal Supplement Series Special Issue, which collectively describe the IBEX interstellar neutral results from this epoch and provide a number of other relevant theoretical and observational results. Interstellar neutrals interact with each other and with the ionized portion of the interstellar population in the “pristine” interstellar medium ahead of the heliosphere. Then, in the heliosphere's close vicinity, the interstellar medium begins to interact with escaping heliospheric neutrals. Inmore » this study, we compare the results from two major analysis approaches led by IBEX groups in New Hampshire and Warsaw. We also directly address the question of the distance upstream to the pristine interstellar medium and adjust both sets of results to a common distance of ∼1000 AU. The two analysis approaches are quite different, but yield fully consistent measurements of the interstellar He flow properties, further validating our findings. While detailed error bars are given for both approaches, we recommend that for most purposes, the community use “working values” of ∼25.4 km s{sup −1}, ∼75.°7 ecliptic inflow longitude, ∼ −5.°1 ecliptic inflow latitude, and ∼7500 K temperature at ∼1000 AU upstream. Finally, we briefly address future opportunities for even better interstellar neutral observations to be provided by the Interstellar Mapping and Acceleration Probe mission, which was recommended as the next major Heliophysics mission by the NRC's 2013 Decadal Survey.« less

Observational aspects of polycyclic aromatic hydrocarbon charging in the Interstellar Medium

NASA Technical Reports Server (NTRS)

Bakes, E. L. O.; Tielens, Alexander G. G. M.

1995-01-01

We have investigated the charging processes which affect small carbonaceous dust grains and polycyclic aromatic hydrocarbons (PAH's). Because of their high abundance, interstellar PAH molecules can dominate the charge balance of the interstellar medium (ISM), which controls the heating and cooling interstellar gas and interstellar chemistry. We present the results of our model, which compare well with observations and suggest further applications to both laboratory measurements and data obtainable from the KAO.

Local ISM 3D Distribution and Soft X-ray Background Inferences for Nearby Hot Gas

NASA Technical Reports Server (NTRS)

Puspitarini, L.; Lallement, R.; Snowden, Steven L.; Vergely, J.-L.; Snowden, S.

2014-01-01

Three-dimensional (3D) interstellar medium (ISM) maps can be used to locate not only interstellar (IS) clouds, but also IS bubbles between the clouds that are blown by stellar winds and supernovae, and are filled by hot gas. To demonstrate this, and to derive a clearer picture of the local ISM, we compare our recent 3D IS dust distribution maps to the ROSAT diffuse Xray background maps after removal of heliospheric emission. In the Galactic plane, there is a good correspondence between the locations and extents of the mapped nearby cavities and the soft (0.25 keV) background emission distribution, showing that most of these nearby cavities contribute to this soft X-ray emission. Assuming a constant dust to gas ratio and homogeneous 106 K hot gas filling the cavities, we modeled in a simple way the 0.25 keV surface brightness along the Galactic plane as seen from the Sun, taking into account the absorption by the mapped clouds. The data-model comparison favors the existence of hot gas in the solar neighborhood, the so-called Local Bubble (LB). The inferred mean pressure in the local cavities is found to be approx.9,400/cu cm K, in agreement with previous studies, providing a validation test for the method. On the other hand, the model overestimates the emission from the huge cavities located in the third quadrant. Using CaII absorption data, we show that the dust to CaII ratio is very small in those regions, implying the presence of a large quantity of lower temperature (non-X-ray emitting) ionized gas and as a consequence a reduction of the volume filled by hot gas, explaining at least part of the discrepancy. In the meridian plane, the two main brightness enhancements coincide well with the LB's most elongated parts and chimneys connecting the LB to the halo, but no particular nearby cavity is found towards the enhancement in the direction of the bright North Polar Spur (NPS) at high latitude. We searched in the 3D maps for the source regions of the higher energy (0.75 keV) enhancements in the fourth and first quadrants. Tunnels and cavities are found to coincide with the main bright areas, however no tunnel nor cavity is found to match the low-latitude b > or approx. 8deg, brightest part of the NPS. In addition, the comparison between the 3D maps and published spectral data favors a NPS central source region location beyond 230 pc, i.e. at larger distance than usually considered. Those examples illustrate the potential use of more detailed 3D distributions of the nearby ISM for the interpretation of the diffuse soft X-ray background.

The violent interstellar medium

NASA Technical Reports Server (NTRS)

Mccray, R.; Snow, T. P., Jr.

1979-01-01

Observational evidence for high-velocity and high-temperature interstellar gas is reviewed. The physical processes that characterize this gas are described, including the ionization and emissivity of coronal gas, the behavior and appearance of high-velocity shocks, and interfaces between coronal gas and cooler interstellar gas. Hydrodynamical models for the action of supernova explosions and stellar winds on the interstellar medium are examined, and recent attempts to synthesize all the processes considered into a global model for the interstellar medium are discussed.

The interstellar depletion mystery, or where have all those atoms gone. [cosmic abundance as grain model evidence

NASA Technical Reports Server (NTRS)

Greenberg, J. M.

1974-01-01

The observed depletion of intermediate-weight elements O, C, and N from the interstellar medium is shown to be significantly greater than can be accounted for by accretion on interstellar dust. A number of possible explanations are presented, ranging from the existence in interstellar space of many 'snowballs' intermediate in size between dust grains and comets to the existence of many far more complicated interstellar molecules than have been detected.

PHYSIOLOGICAL DYNAMICS OF SIPHONOPHORES FROM DEEP SCATTERING LAYERS.

DTIC Science & Technology

Effects of siphonophores on sound propagation in the sea were studied by determining the size of gas bubbles they contain and produce, and the times...volumes, and rates involved in these processes. Major findings were: (1) gases contained in fresh siphonophore floats are generally close to...constants for siphonophore floats are close to those for chitin; (4) calculated energy requirements for countering hydrostatic pressures indicate that float refilling times are probably no more than a few hours. (Author)

Dust coagulation in ISM

NASA Technical Reports Server (NTRS)

Chokshi, Arati; Tielens, Alexander G. G. M.; Hollenbach, David

1989-01-01

Coagulation is an important mechanism in the growth of interstellar and interplanetary dust particles. The microphysics of the coagulation process was theoretically analyzed as a function of the physical properties of the coagulating grains, i.e., their size, relative velocities, temperature, elastic properties, and the van der Waal interaction. Numerical calculations of collisions between linear chains provide the wave energy in individual particles and the spectrum of the mechanical vibrations set up in colliding particles. Sticking probabilities are then calculated using simple estimates for elastic deformation energies and for the attenuation of the wave energy due to absorption and scattering processes.

High energy gamma ray results from the second small astronomy satellite

NASA Technical Reports Server (NTRS)

Fichtel, C. E.; Hartman, R. C.; Kniffen, D. A.; Thompson, D. J.; Bignami, G. F.; Oegelman, H.; Oezel, M. F.; Tuemer, T.

1974-01-01

A high energy (35 MeV) gamma ray telescope employing a thirty-two level magnetic core spark chamber system was flown on SAS 2. The high energy galactic gamma radiation is observed to dominate over the general diffuse radiation along the entire galactic plane, and when examined in detail, the longitudinal and latitudinal distribution seem generally correlated with galactic structural features, particularly with arm segments. The general high energy gamma radiation from the galactic plane, explained on the basis of its angular distribution and magnitude, probably results primarily from cosmic ray interactions with interstellar matter.

Evidence for interstellar SiC in the Murray carbonaceous meteorite

NASA Technical Reports Server (NTRS)

Bernatowicz, Thomas; Wopenka, Brigitte; Fraundorf, Gail; Ming, Tang; Anders, Edward

1987-01-01

Silicon carbide has been identified in two separates from the Murray carbonaceous chondrite that are enriched 20,000-fold in isotopically anomalous neon and xenon. The SiC is present in the form of crystalline grains 0.1-1 micron in size. Cubic and 111-plane-twinned cubic are the most common ordered polytypes observed so far. The anomalous isotopic composition of its carbon, nitrogen, and silicon indicates a presolar origin, probably in the atmospheres of red giants. An additional silicon- and oxygen-rich phase shows large isotropic anomalies in nitrogen and silicon, also associated with a presolar origin.

Origin and Evolution of Prebiotic Organic Matter as Inferred from the Tagish Lake Meteorite

NASA Technical Reports Server (NTRS)

Herd, Christopher D.; Blinova, Alexandra; Simkus, Danielle N.; Huang, Yongsong; Tarozo, Rafael; Alexander, Conel M.; Gyngard, Frank; Nittler, Larry R.; Cody, George D.; Fogel, Marilyn L.;

Interstellar molecules and dense clouds.

NASA Technical Reports Server (NTRS)

Rank, D. M.; Townes, C. H.; Welch, W. J.

1971-01-01

Current knowledge of the interstellar medium is discussed on the basis of recent published studies. The subjects considered include optical identification of interstellar molecules, radio molecular lines, interstellar clouds, isotopic abundances, formation and disappearance of interstellar molecules, and interstellar probing techniques. Diagrams are plotted for the distribution of galactic sources exhibiting molecular lines, for hydrogen molecule, hydrogen atom and electron abundances due to ionization, for the densities, velocities and temperature of NH3 in the direction of Sagitarius B2, for the lower rotational energy levels of H2CO, and for temporal spectral variations in masing H2O clouds of the radio source W49. Future applications of the maser and of molecular microscopy in this field are visualized.

Analysis of "Midnight" Tracks in the Stardust Interstellar Dust Collector: Possible Discovery of a Contemporary Interstellar Dust Grain

NASA Technical Reports Server (NTRS)

Westphal, A. J.; Allen, C.; Bajit, S.; Bastien, R.; Bechtel, H.; Bleuet, P.; Borg, J.; Brenker, F.; Bridges, J.; Brownlee, D. E.;

The interstellar N2 abundance towards HD 124314 from far-ultraviolet observations.

PubMed

Knauth, David C; Andersson, B-G; McCandliss, Stephan R; Moos, H Warren

2004-06-10

The abundance of interstellar molecular nitrogen (N2) is of considerable importance: models of steady-state gas-phase interstellar chemistry, together with millimetre-wavelength observations of interstellar N2H+ in dense molecular clouds predict that N2 should be the most abundant nitrogen-bearing molecule in the interstellar medium. Previous attempts to detect N2 absorption in the far-ultraviolet or infrared (ice features) have hitherto been unsuccessful. Here we report the detection of interstellar N2 at far-ultraviolet wavelengths towards the moderately reddened star HD 124314 in the constellation of Centaurus. The N2 column density is larger than expected from models of diffuse clouds and significantly smaller than expected for dense molecular clouds. Moreover, the N2 abundance does not explain the observed variations in the abundance of atomic nitrogen (N I) towards high-column-density sightlines, implying that the models of nitrogen chemistry in the interstellar medium are incomplete.

Copernicus observations of interstellar matter in the direction of HR 1099

NASA Technical Reports Server (NTRS)

Anderson, R. C.; Weiler, E. J.

1978-01-01

Results are reported for high-resolution Copernicus U1 and V2 scans of the bright RS CVn spectroscopic binary HR 1099. The observations reveal strong UV emission lines at L-alpha and Mg II h and k from the stars as well as interstellar H I and D I L-alpha absorption lines and interstellar Mg II h and k absorption in the direction of the binary system. Column densities, bulk velocities, and temperatures are derived for the interstellar features. A comparison of the derived number density of interstellar H I with data for the nearby star Epsilon Eri indicates an inhomogeneous distribution of interstellar hydrogen along the line of sight. The range of values obtained for the D/H ratio is shown to be consistent with results of other studies. A depletion factor of at least 5 with respect to the solar abundance is estimated for the interstellar magnesium.

Excess depletion of Al, Ca, Ti from interstellar gas

NASA Technical Reports Server (NTRS)

Clayton, D. D.

1986-01-01

Thermal condensation, cold sticking, and sputtering by interstellar shock are combined with a chemical memory of the condensation sequence to account for depletion of aluminum, calcium, and titanium in interstellar gas. The extra depletion of aluminum and calcium becomes an indicator of the structural history of the refractory parts of interstellar grains.

Where is the Most Likely Location Where the Secondary Interstellar Oxygen Atoms Are Created Around the Heliosheath?

NASA Astrophysics Data System (ADS)

Park, J.; Kucharek, H.; Szabo, A.; Paschalidis, N.; Grocer, A.; Jones, S.

2017-12-01

The secondary component of the interstellar neutral gas flow is originated from charge exchange between the undisturbed primary interstellar neutrals and the ions that have been deflected as they approach the heliopause. The secondary neutrals that are emitted from the interstellar ion flow through charge exchange carry information on the diverted flow and a fraction of them can travel to the Sun. Therefore, the secondary component of the interstellar neutrals is an excellent diagnostic tool to provide important information to constrain the shape of the heliopause. The presence of the secondary neutrals was predicted in the global heliospheric models and they are observed by Interstellar Boundary Explorer (IBEX) at Earth's orbit. Using the IBEX observations of neutral helium atoms, Kubiak et al. (2016, ApJS, 223, 25) approximated the parent distribution of the secondary interstellar He atoms (so-called Warm Breeze) with a homogeneous Maxwellian distribution function. Park et al. (2016, ApJ, 833, 130) analyzed IBEX observations of secondary interstellar helium and oxygen distributions at Earth's orbit. Lee et al. (2012, ApJS, 198, 10) constructed the heliospheric phase-space distribution function of an interstellar gas species in the Earth frame as a function of solar longitude. In this distribution, the authors assume that the distribution is a drifting Maxwellian at large distances from the Sun. In this study, we assume that a fraction of the secondary neutral atoms has a velocity vector toward the Sun and they can be described as a flow with a drifting Maxwellian distribution near the heliopause. Unlike the primary interstellar gas flow, the distribution of the secondary neutrals is expected to have a wide width and their bulk speeds are slower than the bulk speed of the primary interstellar gas flow. We compare Lee's distribution and IBEX observations of neutral oxygen atoms and then estimate the most likely direction where the secondary interstellar oxygen atoms are created near the heliopause.

Polycyclic aromatic hydrocarbons and the unidentified infrared emission bands - Auto exhaust along the Milky Way

NASA Technical Reports Server (NTRS)

Allamandola, L. J.; Tielens, A. G. G. M.; Barker, J. R.

1985-01-01

The unidentified infrared emission features (UIR bands) are attributed to a collection of partially hydrogenated, positively charged polycyclic aromatic hydrocarbons (PAHs). This assignment is based on a spectroscopic analysis of the UIR bands. Comparison of the observed interstellar 6.2 and 7.7-micron bands with the laboratory measured Raman spectrum of a collection of carbon-based particulates (auto exhaust) shows a very good agreement, supporting this identification. The infrared emission is due to relaxation from highly vibrationally and electronically excited states. The excitation is probably caused by UV photon absorption. The infrared fluorescence of one particular, highly vibrationally excited PAH (chrysene) is modeled. In this analysis the species is treated as a molecule rather than bulk material and the non-thermodynamic equilibrium nature of the emission is fully taken into account. From a comparison of the observed ratio of the 3.3 to 11.3-micron UIR bands with the model calculations, the average number of carbon atoms per molecule is estimated to be about 20. The abundance of interstellar PAHs is calculated to be about 2 x 10 to the -7th with respect to hydrogen.

A Broad 22 Micron Emission Feature in the Carina Nebula H ii Region.

PubMed

Chan; Onaka

2000-04-10

We report the detection of a broad 22 µm emission feature in the Carina Nebula H ii region by the Infrared Space Observatory (ISO) short-wavelength spectrometer. The feature shape is similar to that of the 22 µm emission feature of newly synthesized dust observed in the Cassiopeia A supernova remnant. This finding suggests that both of the features are arising from the same carrier and that supernovae are probably the dominant production sources of this new interstellar grain. A similar broad emission dust feature is also found in the spectra of two starburst galaxies from the ISO archival data. This new dust grain could be an abundant component of interstellar grains and can be used to trace the supernova rate or star formation rate in external galaxies. The existence of the broad 22 µm emission feature complicates the dust model for starburst galaxies and must be taken into account correctly in the derivation of dust color temperature. Mg protosilicate has been suggested as the carrier of the 22 µm emission dust feature observed in Cassiopeia A. The present results provide useful information in studies on the chemical composition and emission mechanism of the carrier.

High-Accuracy Quartic Force Field Calculations for the Spectroscopic Constants and Vibrational Frequencies of 1(exp 1)A' l-C3H(-): A Possible Link to Lines Observed in the Horsehead Nebula PDR

NASA Technical Reports Server (NTRS)

Fortenberry, Ryan C.; Huang, Xinchuan; Crawford, T. Daniel; Lee, Timothy J.

2013-01-01

It has been shown that rotational lines observed in the Horsehead nebula photon-dominated-region (PDR) are probably not caused by l-C3H+, as was originally suggested. In the search for viable alternative candidate carriers, quartic force fields are employed here to provide highly accurate rotational constants, as well as fundamental vibrational frequencies, for another candidate carrier: 1 (sup 1)A' C3H(-). The ab initio computed spectroscopic constants provided in this work are, compared to those necessary to define the observed lines, as accurate as the computed spectroscopic constants for many of the known interstellar anions. Additionally, the computed D-eff for C3H(-) is three times closer to the D deduced from the observed Horsehead nebula lines relative to l-C3H(+). As a result, 1 (sup 1)A' C3H(-). is a more viable candidate for these observed rotational transitions and would be the seventh confirmed interstellar anion detected within the past decade and the first C(sub n)H(-) molecular anion with an odd n.

Interstellar gamma-ray emission from cosmic rays in star-forming galaxies

NASA Astrophysics Data System (ADS)

Martin, P.

2014-04-01

Context. Fermi/LAT observations of star-forming galaxies in the ~0.1-100 GeV range have made possible a first population study. Evidence was found for a correlation between γ-ray luminosity and tracers of the star formation activity. Studying galactic cosmic rays (CRs) in various global conditions can yield information about their origin and transport in the interstellar medium (ISM). Aims: This work addresses the question of the scaling laws that can be expected for the interstellar γ-ray emission as a function of global galactic properties, with the goal of establishing whether the current experimental data in the GeV range can be constraining. Methods: I developed a 2D model for the non-thermal emissions from steady-state CR populations interacting with the ISM in star-forming galaxies. Most CR-related parameters were taken from Milky Way studies, and a large number of galaxies were then simulated with sizes from 4 to 40 kpc, several gas distributions, and star formation rates (SFRs) covering six orders of magnitude. Results: The evolution of the γ-ray luminosity over the 100 keV-100 TeV range is presented, with emphasis on the contribution of the different emission processes and particle populations, and on the transition between transport regimes. The model can reproduce the normalisation and trend inferred from the Fermi/LAT population study over most of the SFR range. This is obtained with a plain diffusion scheme, a single diffusion coefficient, and the assumption that CRs experience large-scale volume-averaged interstellar conditions. There is, however, no universal relation between high-energy γ-ray luminosity and star formation activity, as illustrated by the scatter introduced by different galactic global properties and the downturn in γ-ray emission at the low end. Conclusions: The current Fermi/LAT population study does not call for major modifications of the transport scheme for CRs in the Milky Way when extrapolated to other systems, probably because the uncertainties are still too large. Additional constraints may be expected from doubling the Fermi/LAT exposure time and later from observing at TeV energies with the Cherenkov Telescope Array.

Experimental interstellar organic chemistry - Preliminary findings

NASA Technical Reports Server (NTRS)

Khare, B. N.; Sagan, C.

1973-01-01

Review of the results of some explicit experimental simulation of interstellar organic chemistry consisting in low-temperature high-vacuum UV irradiation of condensed simple gases known or suspected to be present in the interstellar medium. The results include the finding that acetonitrile may be present in the interstellar medium. The implication of this and other findings are discussed.

Comets, carbonaceous chondrites, and interstellar clouds: Condensation of carbon

NASA Technical Reports Server (NTRS)

Field, G. B.

1979-01-01

Comets, carbonaceous chondrites, and interstellar clouds are discussed in relation to information on interstellar dust. The formation and presence of carbon in stars, comets, and meteorites is investigated. The existence of graphite in the interstellar medium, though it is predicted from thermodynamic calculations, is questioned and the form of carbon contained in comets is considered.

Four Interstellar Dust Candidates from the Stardust Interstellar Dust Collector

NASA Technical Reports Server (NTRS)

Westphal, A. J.; Allen, C.; Bajt, S.; Bechtel, H. A.; Borg, J.; Brenker, F.; Bridges, J.; Brownlee, D. E.; Burchell, M.; Burghammer, M.;

Counteracting negative venous line pressures to avoid arterial air bubbles: an experimental study comparing two different types of miniaturized extracorporeal perfusion systems.

PubMed

Aboud, Anas; Mederos-Dahms, Hendrikje; Liebing, Kai; Zittermann, Armin; Schubert, Harald; Murray, Edward; Renner, Andre; Gummert, Jan; Börgermann, Jochen

2015-05-29

Because of its low rate of clinical complications, miniaturized extracorporeal perfusion systems (MEPS) are frequently used in heart centers worldwide. However, many recent studies refer to the higher probability of gaseous microemboli formation by MEPS, caused by subzero pressure values. This is the main reason why various de-airing devices were developed for today's perfusion systems. In the present study, we investigated the potential benefits of a simple one-way-valve connected to a volume replacement reservoir (OVR) for volume and pressure compensation. In an experimental study on 26 pigs, we compared MEPS (n = 13) with MEPS plus OVR (n = 13). Except OVR, perfusion equipment was identical in both groups. Primary endpoints were pressure values in the venous line and the right atrium as well as the number and volume of air bubbles. Secondary endpoints were biochemical parameters of systemic inflammatory response, ischemia, hemodilution and hemolysis. One animal was lost in the MEPS + OVR group. In the MEPS + OVR group no pressure values below -150 mmHg in the venous line and no values under -100 mmHg in right atrium were noticed. On the contrary, nearly 20% of venous pressure values in the MEPS group were below -150 and approximately 10% of right atrial pressure values were below -100 mmHg. Compared with the MEPS group, the bubble counter device showed lower numbers of arterial air bubbles in the MEPS + OVR group (mean ± SD: 13444 ± 5709 vs. 1 ± 2, respectively; p < 0.001). In addition, bubble volume was significantly lower in the MEPS + OVR group than in the MEPS group (mean ± SD: 1522 ± 654 μl vs. 4 ± 6 μl, respectively; p < 0.001). The proinflammatory cytokine interleukin-6 and biochemical indices of cardiac ischemia (creatine kinase, and troponin I) were comparable between both groups. The use of a miniaturized perfusion system with a volume replacement reservoir is able to counteract excessive negative venous line pressures and to reduce the number and volume of arterial air bubbles. This approach may lead to a lower rate of neurological complications.

Dark clouds in the vicinity of the emission nebula Sh2-205: interstellar extinction and distances

NASA Astrophysics Data System (ADS)

Straižys, V.; Čepas, V.; Boyle, R. P.; Zdanavičius, J.; Maskoliūnas, M.; Kazlauskas, A.; Zdanavičius, K.; Černis, K.

2016-05-01

Results of CCD photometry in the seven-colour Vilnius system for 922 stars down to V = 16-17 mag and for 302 stars down to 19.5 mag are used to investigate the interstellar extinction in an area of 1.5 square degrees in the direction of the P7 and P8 clumps of the dark cloud TGU H942, which lies in the vicinity of the emission nebula Sh2-205. In addition, we used 662 red clump giants that were identified by combining the 2MASS and WISE infrared surveys. The resulting plots of extinction versus distance were compared with previous results of the distribution and radial velocities of CO clouds and with dust maps in different passbands of the IRAS and WISE orbiting observatories. A possible distance of the front edge of the nearest cloud layer at 130 ± 10 pc was found. This dust layer probably covers all the investigated area, which results in extinction of up to 1.8 mag in some directions. A second rise of the extinction seems to be present at 500-600 pc. Within this layer, the clumps P7 and P8 of the dust cloud TGU H942, the Sh2-205 emission nebula, and the infrared cluster FSR 655 are probably located. In the direction of these clouds, we identified 88 young stellar objects and a new infrared cluster. Full Tables 1 and 2 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/590/A21

Surface chemistry in photodissociation regions

NASA Astrophysics Data System (ADS)

Esplugues, G. B.; Cazaux, S.; Meijerink, R.; Spaans, M.; Caselli, P.

2016-06-01

Context. The presence of dust can strongly affect the chemical composition of the interstellar medium. We model the chemistry in photodissociation regions (PDRs) using both gas-phase and dust-phase chemical reactions. Aims: Our aim is to determine the chemical compositions of the interstellar medium (gas/dust/ice) in regions with distinct (molecular) gas densities that are exposed to radiation fields with different intensities. Methods: We have significantly improved the Meijerink PDR code by including 3050 new gas-phase chemical reactions and also by implementing surface chemistry. In particular, we have included 117 chemical reactions occurring on grain surfaces covering different processes, such as adsorption, thermal desorption, chemical desorption, two-body reactions, photo processes, and cosmic-ray processes on dust grains. Results: We obtain abundances for different gas and solid species as a function of visual extinction, depending on the density and radiation field. We also analyse the rates of the formation of CO2 and H2O ices in different environments. In addition, we study how chemistry is affected by the presence/absence of ice mantles (bare dust or icy dust) and the impact of considering different desorption probabilities. Conclusions: The type of substrate (bare dust or icy dust) and the probability of desorption can significantly alter the chemistry occurring on grain surfaces, leading to differences of several orders of magnitude in the abundances of gas-phase species, such as CO, H2CO, and CH3OH. The type of substrate, together with the density and intensity of the radiation field, also determine the threshold extinction to form ices of CO2 and H2O. We also conclude that H2CO and CH3OH are mainly released into the gas phase of low, far-ultraviolet illuminated PDRs through chemical desorption upon two-body surface reactions, rather than through photodesorption.

Energy Dissipation and Nonthermal Diffusion on Interstellar Ice Grains

NASA Astrophysics Data System (ADS)

Fredon, A.; Lamberts, T.; Cuppen, H. M.

2017-11-01

Interstellar dust grains are known to facilitate chemical reactions by acting as a meeting place and adsorbing energy. This process strongly depends on the ability of the reactive species to effectively diffuse over the surface. The cold temperatures around 10 K strongly hamper this for species other than H and H2. However, complex organic molecules have been observed in the gas phase at these cold conditions, indicating that their formation, as well as their return to the gas phase, should be effective. Here, we show how the energy released following surface reactions can be employed to solve both problems by inducing desorption or diffusion. To this purpose, we have performed thousands of Molecular Dynamics simulations to quantify the outcome of an energy dissipation process. Admolecules on top of a crystalline water surface have been given translational energy between 0.5 and 5 eV. Three different surface species are considered (CO2, H2O, and CH4), spanning a range in binding energies, number of internal degrees of freedom, and molecular weights. The admolecules are found to be able to travel up to several hundreds of angstroms before coming to a stand still, allowing for follow-up reactions en route. The probability of travel beyond any particular radius, as determined by our simulations, shows the same r dependence for all three admolecule species. Furthermore, we have been able to quantify the desorption probability, which depends on the binding energy of the species and the translational excitation. We provide expressions that can be incorporated in astrochemical models to predict grain surface formation and return into the gas phase of these products.

Sub-micron particles in northwest Atlantic shelf water

NASA Astrophysics Data System (ADS)

Longhurst, A. R.; Koike, I.; Li, W. K. W.; Rodriguez, J.; Dickie, P.; Kepay, P.; Partensky, F.; Bautista, B.; Ruiz, J.; Wells, M.; Bird, D. F.

1992-01-01

The existence of numerous (1.0 × 10 7 ml -1) sub-micron particles has been confirmed in northwest Atlantic shelf water. These particles were counted independently by two different resistive-pulse instruments, and their existence confirmed by our ability to reduce their numbers by ultracentrifugation, serial dilution and surface coagulation in a bubbling column. There are important implications for the dynamics of DOM in seawater if, as seems probable, these particles represent a fraction of "dissolved" organic material in seawater.

Ground-Based Centimeter, Millimeter, and Submillimeter Observations of Recent Comets

NASA Technical Reports Server (NTRS)

Milam, S. N.; Chuang, Y.-L.; Charnley, S. B.; Kuan, Y. -J.; Villanueva, G. L.; Coulson, I. M.; Remijan. A. R.

2012-01-01

Comets provide important clues to the physical and chemical processes that occurred during the formation and early evolution of the Solar System, and could also have been important for initiating prebiotic chemistry on the early Earth [I]. Comets are comprised of molecular ices, that may be pristine interstellar remnants of Solar System formation, along with high-temperature crystalline silicate dust that is indicative of a more thermally varied history in the protosolar nebula [2]. Comparing abundances of cometary parent volatiles, and isotopic fractionation ratios, to those found in the interstellar medium, in disks around young stars, and between cometary families, is vital to understanding planetary system formation and the processing history experienced by organic matter in the so-called interstellar-comet connection [3]. In the classical picture, the long-period comets probably formed in the nebular disk across the giant planet formation region (5-40 AU) with the majority of them originating from the Uranus-Neptune region. They were subsequently scattered out to the Oort Cloud (OC) by Jupiter. The short-period comets (also known as ecliptic or Jupiter Family Comets - JFC) reside mainly in the Edgeworth-Kuiper belt where they were formed. Given the gradient in physical conditions expected across this region of the nebula, chemical diversity in this comet population is to be expected [4,5]. We have conducted observations of comets I 03P/Hartley 2 (JFC) and C/2009 PI (Garradd) (OC), at primarily millimeter and submillimeter wavelengths, to determine important cosmogonic quantities, such as the ortho:para ratio and isotope ratios, as well as probe the origin of cometary organics and if they vary between the two dynamic reservoirs.

The abundance of interstellar sulphur and zinc in high density sight-lines

NASA Technical Reports Server (NTRS)

Harris, A. W.; Mashesse, J. M.

1986-01-01

On the basis of early absorption line studies of individual lines of sight with the Copernicus satellite, chlorine, sulphur and zinc were classed together as elements which showed little or no depletion, relative to hydrogen, in the interstellar medium. The abundances of other less volatile elements, such as Fe and Mg were found to vary widely from one sight-line to another with gas-phase abundances in some cases being orders of magnitude below their solar counterparts. Detailed studies are reported of the depletion/density behavior of two other volatile elements which were previously considered to be virtually undepleted, S and Zn, using equivalent width data from both Copernicus and IUE observations. The results provide further evidence that the established dependence of depletion on n bar (H) extends to volatile elements and show that their use as tracers of metallicity, or for estimating hydrogen column densities, may lead to large errors in sight-lines through dense regions. It now appears that such elements may take part in the surface chemistry of grains and be important constituents of grain mantle material, although they probably do not contribute significantly to the bulk mass of grains. Due to the very similar atomic masses and ionization potentials of sulphur and phosphorous, the thermal velocity distributions of the singly ionized species of these elements in interstellar clouds should be very similar. However, a comparison of Doppler widths (b-values) derived for SIT and PIT in the same sight-lines from the Bohlin et al Copernicus equivalent width measurements has revealed an unexpected systematic discrepancy of a factor of approx. 1.7. This Discrepancy indicates that the normally adopted oscillators strengths of the PII lambda lambda 1153 and 1302 A lines may require revision.

Searching for extraterrestrial civilizations.

PubMed

Kuiper, T B; Morris, M

1977-05-06

We have argued that planning for a search for extraterrestrial intelligence should involve a minimum number of assumptions. In view of the feasibility (at our present level of understanding) of using nuclear fusion to effect interstellar travel at a speed of 0.1c, it appears unwarranted (at this time) to assume that it would not occur for at least some technologically advanced civilizations. One cannot even conclude that humans would not attempt this within the next few centuries. On the contrary, the most likely future situation, given the maintenance of technological growth and the absence of extraterrestrial interference, is that our civilization will explore and colonize our galactic neighborhood. A comparison of the time scales of galactic evolution and interstellar travel leads to the conclusion that the galaxy is either essentially empty with respect to technological civilizations or extensively colonized. In the former instance, a SETI would be unproductive. In the latter, a SETI could be fruitful if a signal has been deliberately directed at the earth or at an alien outpost, probe, or communication relay station in our solar system. In the former case, an existing antenna would probably be sufficient to detect the signal. In the latter case, success would depend on the way in which the communications were coded. Failure to detect a signal could permit any of the following conclusions: (i) the galaxy is devoid of technological civilizations, advanced beyond our own, (ii) such civilizations exist, but cannot (for some reason which is presently beyond our ken) engage in interstellar colonization, or (iii) such civilizations are not attempting overt contact with terrestrial civilizations and their intercommunications, if present, are not coded in a simple way. To plan at this time for a high-cost, large-array SETI based on the last two possibilities appears to be rather premature.

A study of the neutral hydrogen in direction to the GUM nebula

NASA Astrophysics Data System (ADS)

Dubner, G.; Giacani, E.; Cappa de Nicolau, C.; Reynoso, E.

1992-12-01

This paper presents 44 gray-scale maps at constant velocity of the distribution of H I in the direction of the Gum nebula. It is shown that there is no H I shell with a size comparable to the 36 deg diameter optical nebulosities and that there is a thick H I shell, about 7 deg in radius, shifted from the center of the optical nebula by more than 10 deg. The observations are consistent with a model in which the Gum nebula is the remnant of a supernova explosion that occurred about 2.6 million yr ago. The presence of two new H I bubbles associated with SWR 12 and 14, plus a possible one around WR 13, are disclosed from analysis of the H I gas distribution around the four WR star located beyond the Gum nebula. These H I bubbles have characteristics similar to those previously observed. Three shell-like objects probably related to OB stars and H II regions are also described.

Direct Observations of Interstellar H, He, and O by the Interstellar Boundary Explorer (Invited)

NASA Astrophysics Data System (ADS)

Moebius, E.; Bochsler, P. A.; Bzowski, M.; Crew, G. B.; Funsten, H. O.; Fuselier, S. A.; Ghielmetti, A.; Heirtzler, D.; Izmodenov, V.; Kubiak, M.; Kucharek, H.; Lee, M. A.; Leonard, T.; McComas, D. J.; Petersen, L.; Saul, L. A.; Scheer, J.; Schwadron, N. A.; Witte, M.; Wurz, P.

2009-12-01

Due to the motion of the Sun relative to its neighborhood, the neutral gas of the local in-terstellar medium (LISM) flows through the inner heliosphere where it is subject to ioni-zation, the Sun’s gravity, and radiation pressure. Observing the resulting spatial distribu-tion and flow pattern of several interstellar gas species with UV backscatter, pickup ion, and neutral atom imaging techniques allows us to unravel the physical conditions of the LISM and its interaction with the heliosphere. Imaging of the neutral gas flow directly with energetic neutral atom (ENA) cameras yields the most accurate account of the ki-netic parameters of the interstellar gas, but so far this has been carried out only for He using Ulysses GAS. IBEX, which was launched in October 2008, provides the capability for simultaneous flow observations of several interstellar species with its triple-time-of-flight IBEX-Lo sensor. Because H and O are strongly affected by the heliospheric inter-face while He is not, a direct comparison between these species enables an independent assessment of the slowdown and heating processes in the outer heliosheath. Likewise, IBEX observations will constrain models of the heliospheric interaction and provide a test of the heliospheric asymmetry - recently inferred from Voyager and SOHO SWAN observations - that is seen as an indicator for the interstellar magnetic field direction. During the first half year of its mission IBEX has observed the interstellar He, O, and H flow. We will present an overview and preliminary analysis of these first interstellar mul-tispecies scans of the interstellar gas flow in spring and fall 2009.

Aliphatic Hydrocarbon Content of Interstellar Dust

NASA Astrophysics Data System (ADS)

Günay, B.; Schmidt, T. W.; Burton, M. G.; Afşar, M.; Krechkivska, O.; Nauta, K.; Kable, S. H.; Rawal, A.

2018-06-01

There is considerable uncertainty as to the amount of carbon incorporated in interstellar dust. The aliphatic component of the carbonaceous dust is of particular interest because it produces a significant 3.4 μm absorption feature when viewed against a background radiation source. The optical depth of the 3.4 μm absorption feature is related to the number of aliphatic carbon C-H bonds along the line of sight. It is possible to estimate the column density of carbon locked up in the aliphatic hydrocarbon component of interstellar dust from quantitative analysis of the 3.4 μm interstellar absorption feature providing that the absorption coefficient of aliphatic hydrocarbons incorporated in the interstellar dust is known. We report laboratory analogues of interstellar dust by experimentally mimicking interstellar/circumstellar conditions. The resultant spectra of these dust analogues closely match those from astronomical observations. Measurements of the absorption coefficient of aliphatic hydrocarbons incorporated in the analogues were carried out by a procedure combining FTIR and 13C NMR spectroscopies. The absorption coefficients obtained for both interstellar analogues were found to be in close agreement (4.76(8) × 10-18 cm group-1 and 4.69(14) × 10-18 cm group-1), less than half those obtained in studies using small aliphatic molecules. The results thus obtained permit direct calibration of the astronomical observations, providing rigorous estimates of the amount of aliphatic carbon in the interstellar medium.

Kramers-Kronig relations for interstellar polarization

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

Martin, P.G.

1975-12-01

The difficulties encountered in using the Kramers-Kronig relations to predict the behavior of interstellar polarization are pointed out, while at the same time their value in an interpretive role is acknowledged. Observations of interstellar circular polarization lead to restrictions on the interstellar grain composition, and additional constraints should be possible through measurement of linear polarization in the infrared and the ultraviolet. (AIP)

Gas Phase Spectroscopy of Cold PAH Ions: Contribution to the Interstellar Extinction and the Diffuse Interstellar Bands

NASA Technical Reports Server (NTRS)

Biennier, L.; Salama, F.; Allamandola, L. J.; Scherer, J. J.; OKeefe, A.

2002-01-01

Polycyclic Aromatic Hydrocarbon molecules (PAHs) are ubiquitous in the interstellar medium (ISM) and constitute the building blocks of interstellar dust grains. Despite their inferred important role in mediating the energetic and chemical processes in thc ISM, their exact contribution to the interstellar extinction, and in particular to the diffuse interstellar bands (DIBs) remains unclear. The DIBs are spectral absorption features observed in the line of sight of stars that are obscured by diffuse interstellar clouds. More than 200 bands have been reported to date spanning from the near UV to the near IR with bandwidths ranging from 0.4 to 40 Angstroms (Tielens & Snow 1995). The present consensus is that the DIBs arise from free flying, gas-phase, organic molecules and/or ions that are abundant under the typical conditions reigning in the diffuse ISM. PAHs have been proposed as possible carriers (Allamandola et al. 1985; Leger & DHendecourt 1985). The PAH hypothesis is consistent with the cosmic abundance of Carbon and Hydrogen and with the required photostability of the DIB carriers against the strong VUV radiation field in the diffuse interstellar clouds. A significant fraction of PAHs is expected to be ionized in the diffuse ISM.

Characterization of novel pin-hole based plasma source for generation of discharge in liquids supplied by DC non-pulsing voltage

NASA Astrophysics Data System (ADS)

Krčma, F.; Kozáková, Z.; Mazánková, V.; Horák, J.; Dostál, L.; Obradović, B.; Nikiforov, A.; Belmonte, T.

2018-06-01

A recently presented novel plasma source generating discharge in liquids based on the pin-hole discharge configuration is characterized in detail. The system is supplied by DC non-pulsing high voltage of both polarities in NaCl water solutions at a conductivity range of 100–15 000 μS/cm. The discharge itself shows self-pulsing operation. The discharge ignition is observed in micro bubbles by transient discharge followed by a glow discharge in positive polarity at lower conductivities propagating inside the bubbles. At high conductivities, the glow regime is particularly replaced by a more energetic sequence of transient discharges followed by a shorter glow mode operation. The transient regime probability and its intensity are higher in the negative discharge polarity. The transient discharge produces acoustic waves and shock waves, which are observed at the moment of the bubble cavitation. The average gas temperature of 700–1500 K was calculated from the lowest OH (A-X) 0-0 band transitions. The average electron concentrations of 1020–1023 m‑3 were calculated from H α and H β line profiles. Finally, the production of a chemically active species is determined by hydrogen peroxide energy yields related to the energy consumption of the whole interelectrode system. All these quantities are dependent on the solution conductivity, the discharge polarity, and the applied power.

The ESO Diffuse Interstellar Band Large Exploration Survey (EDIBLES)

NASA Astrophysics Data System (ADS)

Cami, J.; Cox, N. L.; Farhang, A.; Smoker, J.; Elyajouri, M.; Lallement, R.; Bacalla, X.; Bhatt, N. H.; Bron, E.; Cordiner, M. A.; de Koter, A..; Ehrenfreund, P.; Evans, C.; Foing, B. H.; Javadi, A.; Joblin, C.; Kaper, L.; Khosroshahi, H. G.; Laverick, M.; Le Petit, F..; Linnartz, H.; Marshall, C. C.; Monreal-Ibero, A.; Mulas, G.; Roueff, E.; Royer, P.; Salama, F.; Sarre, P. J.; Smith, K. T.; Spaans, M.; van Loon, J. T..; Wade, G.

2018-03-01

The ESO Diffuse Interstellar Band Large Exploration Survey (EDIBLES) is a Large Programme that is collecting high-signal-to-noise (S/N) spectra with UVES of a large sample of O and B-type stars covering a large spectral range. The goal of the programme is to extract a unique sample of high-quality interstellar spectra from these data, representing different physical and chemical environments, and to characterise these environments in great detail. An important component of interstellar spectra is the diffuse interstellar bands (DIBs), a set of hundreds of unidentified interstellar absorption lines. With the detailed line-of-sight information and the high-quality spectra, EDIBLES will derive strong constraints on the potential DIB carrier molecules. EDIBLES will thus guide the laboratory experiments necessary to identify these interstellar “mystery molecules”, and turn DIBs into powerful diagnostics of their environments in our Milky Way Galaxy and beyond. We present some preliminary results showing the unique capabilities of the EDIBLES programme.

Stardust Interstellar Preliminary Examination II: Curating the Interstellar Dust Collector, Picokeystones, and Sources of Impact Tracks

NASA Technical Reports Server (NTRS)

Frank, David R.; Westphal, Andrew J.; Zolensky, Michael E.; Gainsforth, Zack; Butterworth, Anna L.; Bastien, Ronald K.; Allen, Carlton; Anderson, David; Bechtel, Hans A.; Sandford, Scott A.

2013-01-01

We discuss the inherent difficulties that arise during "ground truth" characterization of the Stardust interstellar dust collector. The challenge of identifying contemporary interstellar dust impact tracks in aerogel is described within the context of background spacecraft secondaries and possible interplanetary dust particles and beta-meteoroids. In addition, the extraction of microscopic dust embedded in aerogel is technically challenging. Specifically, we provide a detailed description of the sample preparation techniques developed to address the unique goals and restrictions of the Interstellar Preliminary Exam. These sample preparation requirements and the scarcity of candidate interstellar impact tracks exacerbate the difficulties. We also illustrate the role of initial optical imaging with critically important examples, and summarize the overall processing of the collection to date.

Thermodynamics and Charging of Interstellar Iron Nanoparticles

NASA Astrophysics Data System (ADS)

Hensley, Brandon S.; Draine, B. T.

2017-01-01

Interstellar iron in the form of metallic iron nanoparticles may constitute a component of the interstellar dust. We compute the stability of iron nanoparticles to sublimation in the interstellar radiation field, finding that iron clusters can persist down to a radius of ≃4.5 Å, and perhaps smaller. We employ laboratory data on small iron clusters to compute the photoelectric yields as a function of grain size and the resulting grain charge distribution in various interstellar environments, finding that iron nanoparticles can acquire negative charges, particularly in regions with high gas temperatures and ionization fractions. If ≳10% of the interstellar iron is in the form of ultrasmall iron clusters, the photoelectric heating rate from dust may be increased by up to tens of percent relative to dust models with only carbonaceous and silicate grains.

Decades-long changes of the interstellar wind through our solar system.

PubMed

Frisch, P C; Bzowski, M; Livadiotis, G; McComas, D J; Moebius, E; Mueller, H-R; Pryor, W R; Schwadron, N A; Sokół, J M; Vallerga, J V; Ajello, J M

2013-09-06

The journey of the Sun through the dynamically active local interstellar medium creates an evolving heliosphere environment. This motion drives a wind of interstellar material through the heliosphere that has been measured with Earth-orbiting and interplanetary spacecraft for 40 years. Recent results obtained by NASA's Interstellar Boundary Explorer mission during 2009-2010 suggest that neutral interstellar atoms flow into the solar system from a different direction than found previously. These prior measurements represent data collected from Ulysses and other spacecraft during 1992-2002 and a variety of older measurements acquired during 1972-1978. Consideration of all data types and their published results and uncertainties, over the three epochs of observations, indicates that the trend for the interstellar flow ecliptic longitude to increase linearly with time is statistically significant.

Aluminum Foils of the Stardust Interstellar Collector: The Challenge of Recognizing Micrometer-sized Impact Craters made by Interstellar Grains

NASA Technical Reports Server (NTRS)

Kearsley, A. T.; Westphal, A. J.; Burchell, M. J.; Zolensky, Michael E.

2008-01-01

Preliminary Examination (PE) of the Stardust cometary collector revealed material embedded in aerogel and on aluminium (Al) foil. Large numbers of sub-micrometer impact craters gave size, structural and compositional information. With experience of finding and analyzing the picogram to nanogram mass remains of cometary particles, are we now ready for PE of the Interstellar (IS) collector? Possible interstellar particle (ISP) tracks in the aerogel are being identified by the stardust@home team. We are now assessing challenges facing PE of Al foils from the interstellar collector.

The Destructive Birth of Massive Stars and Massive Star Clusters

NASA Astrophysics Data System (ADS)

Rosen, Anna; Krumholz, Mark; McKee, Christopher F.; Klein, Richard I.; Ramirez-Ruiz, Enrico

2017-01-01

Massive stars play an essential role in the Universe. They are rare, yet the energy and momentum they inject into the interstellar medium with their intense radiation fields dwarfs the contribution by their vastly more numerous low-mass cousins. Previous theoretical and observational studies have concluded that the feedback associated with massive stars' radiation fields is the dominant mechanism regulating massive star and massive star cluster (MSC) formation. Therefore detailed simulation of the formation of massive stars and MSCs, which host hundreds to thousands of massive stars, requires an accurate treatment of radiation. For this purpose, we have developed a new, highly accurate hybrid radiation algorithm that properly treats the absorption of the direct radiation field from stars and the re-emission and processing by interstellar dust. We use our new tool to perform a suite of three-dimensional radiation-hydrodynamic simulations of the formation of massive stars and MSCs. For individual massive stellar systems, we simulate the collapse of massive pre-stellar cores with laminar and turbulent initial conditions and properly resolve regions where we expect instabilities to grow. We find that mass is channeled to the massive stellar system via gravitational and Rayleigh-Taylor (RT) instabilities. For laminar initial conditions, proper treatment of the direct radiation field produces later onset of RT instability, but does not suppress it entirely provided the edges of the radiation-dominated bubbles are adequately resolved. RT instabilities arise immediately for turbulent pre-stellar cores because the initial turbulence seeds the instabilities. To model MSC formation, we simulate the collapse of a dense, turbulent, magnetized Mcl = 106 M⊙ molecular cloud. We find that the influence of the magnetic pressure and radiative feedback slows down star formation. Furthermore, we find that star formation is suppressed along dense filaments where the magnetic field is amplified. Our results suggest that the combined effect of turbulence, magnetic pressure, and radiative feedback from massive stars is responsible for the low star formation efficiencies observed in molecular clouds.

Coordinated Microanalyses of Seven Particles of Probable Interstellar Origin from the Stardust Mission

NASA Technical Reports Server (NTRS)

Westphal, Andrew J.; Stroud, Rhonda M.; Bechtel, Hans A.; Brenker, Frank E.; Butterworth, Anna L.; Flynn, George J.; Frank, David R.; Gainsforth, Zack; Hillier, Jon K.; Postberg, Frank;

Stardust Interstellar Preliminary Examination VII: Synchrotron X-Ray Fluorescence Analysis of Six Stardust Interstellar Candidates Measured with the Advanced Photon Source 2-ID-D Microprobe

NASA Technical Reports Server (NTRS)

Allen, Carlton C.; Anderson, David; Bastien, Ron K.; Brenker, Frank E.; Flynn, George J.; Frank, David; Gainsforth, Zack; Sandford, Scott A.; Simionovici, Alexandre S.; Zolensky, Michael E.

2014-01-01

The NASA Stardust spacecraft exposed an aerogel collector to the interstellar dust passing through the solar system. We performed X-ray fluorescence element mapping and abundance measurements, for elements 19 < or = Z < or = 30, on six "interstellar candidates," potential interstellar impacts identified by Stardust@Home and extracted for analyses in picokeystones. One, I1044,3,33, showed no element hot-spots within the designated search area. However, we identified a nearby surface feature, consistent with the impact of a weak, high-speed particle having an approximately chondritic (CI) element abundance pattern, except for factor-of-ten enrichments in K and Zn and an S depletion. This hot-spot, containing approximately 10 fg of Fe, corresponds to an approximately 350 nm chondritic particle, small enough to be missed by Stardust@Home, indicating that other techniques may be necessary to identify all interstellar candidates. Only one interstellar candidate, I1004,1,2, showed a track. The terminal particle has large enrichments in S, Ti, Cr, Mn, Ni, Cu, and Zn relative to Fe-normalized CI values. It has high Al/Fe, but does not match the Ni/Fe range measured for samples of Al-deck material from the Stardust sample return capsule, which was within the field-of-view of the interstellar collector. A third interstellar candidate, I1075,1,25, showed an Al-rich surface feature that has a composition generally consistent with the Al-deck material, suggesting that it is a secondary particle. The other three interstellar candidates, I1001,1,16, I1001,2,17, and I1044,2,32, showed no impact features or tracks, but allowed assessment of submicron contamination in this aerogel, including Fe hot-spots having CI-like Ni/Fe ratios, complicating the search for CI-like interstellar/interplanetary dust.

Stardust Interstellar Preliminary Examination VII: Synchrotron X-ray fluorescence analysis of six Stardust interstellar candidates measured with the Advanced Photon Source 2-ID-D microprobe

NASA Astrophysics Data System (ADS)

Flynn, George J.; Sutton, Steven R.; Lai, Barry; Wirick, Sue; Allen, Carlton; Anderson, David; Ansari, Asna; Bajt, SašA.; Bastien, Ron K.; Bassim, Nabil; Bechtel, Hans A.; Borg, Janet; Brenker, Frank E.; Bridges, John; Brownlee, Donald E.; Burchell, Mark; Burghammer, Manfred; Butterworth, Anna L.; Changela, Hitesh; Cloetens, Peter; Davis, Andrew M.; Doll, Ryan; Floss, Christine; Frank, David; Gainsforth, Zack; Grün, Eberhard; Heck, Philipp R.; Hillier, Jon K.; Hoppe, Peter; Hudson, Bruce; Huth, Joachim; Hvide, Brit; Kearsley, Anton; King, Ashley J.; Leitner, Jan; Lemelle, Laurence; Leroux, Hugues; Leonard, Ariel; Lettieri, Robert; Marchant, William; Nittler, Larry R.; Ogliore, Ryan; Ong, Wei Ja; Postberg, Frank; Price, Mark C.; Sandford, Scott A.; Tresseras, Juan-Angel Sans; Schmitz, Sylvia; Schoonjans, Tom; Silversmit, Geert; Simionovici, Alexandre; Sol, Vicente A.; Srama, Ralf; Stadermann, Frank J.; Stephan, Thomas; Sterken, Veerle; Stodolna, Julien; Stroud, Rhonda M.; Trieloff, Mario; Tsou, Peter; Tsuchiyama, Akira; Tyliszczak, Tolek; Vekemans, Bart; Vincze, Laszlo; von Korff, Joshua; Westphal, Andrew J.; Wordsworth, Naomi; Zevin, Daniel; Zolensky, Michael E.

2014-09-01

The NASA Stardust spacecraft exposed an aerogel collector to the interstellar dust passing through the solar system. We performed X-ray fluorescence element mapping and abundance measurements, for elements 19 ≤ Z ≤ 30, on six "interstellar candidates," potential interstellar impacts identified by Stardust@Home and extracted for analyses in picokeystones. One, I1044,3,33, showed no element hot-spots within the designated search area. However, we identified a nearby surface feature, consistent with the impact of a weak, high-speed particle having an approximately chondritic (CI) element abundance pattern, except for factor-of-ten enrichments in K and Zn and an S depletion. This hot-spot, containing approximately 10 fg of Fe, corresponds to an approximately 350 nm chondritic particle, small enough to be missed by Stardust@Home, indicating that other techniques may be necessary to identify all interstellar candidates. Only one interstellar candidate, I1004,1,2, showed a track. The terminal particle has large enrichments in S, Ti, Cr, Mn, Ni, Cu, and Zn relative to Fe-normalized CI values. It has high Al/Fe, but does not match the Ni/Fe range measured for samples of Al-deck material from the Stardust sample return capsule, which was within the field-of-view of the interstellar collector. A third interstellar candidate, I1075,1,25, showed an Al-rich surface feature that has a composition generally consistent with the Al-deck material, suggesting that it is a secondary particle. The other three interstellar candidates, I1001,1,16, I1001,2,17, and I1044,2,32, showed no impact features or tracks, but allowed assessment of submicron contamination in this aerogel, including Fe hot-spots having CI-like Ni/Fe ratios, complicating the search for CI-like interstellar/interplanetary dust.

Interstellar Probe: First Step to the Stars

NASA Astrophysics Data System (ADS)

McNutt, R. L., Jr.

2017-12-01

The idea of an "Interstellar Probe," a robotic spacecraft traveling into the nearby interstellar medium for the purpose of scientific investigation, dates to the mid-1960s. The Voyager Interstellar Mission (VIM), an "accidental" 40-year-old by-product of the Grand Tour of the solar system, has provided initial answers to the problem of the global heliospheric configuration and the details of its interface with interstellar space. But the twin Voyager spacecraft have, at most, only another decade of lifetime, and only Voyager 1 has emerged from the heliosheath interaction region. To understand the nature of the interaction, a near-term mission to the "near-by" interstellar medium with modern and focused instrumentation remains a compelling priority. Imaging of energetic neutral atoms (ENAs) by the Ion Neutral CAmera (INCA) on Cassini and from the Interstellar Boundary Explorer (IBEX) in Earth orbit have provided significant new insights into the global interaction region but point to discrepancies with our current understanding. Exploring "as far as possible" into "pristine" interstellar space can resolve these. Hence, reaching large heliocentric distances rapidly is a driver for an Interstellar Probe. Such a mission is timely; understanding the interstellar context of exoplanet systems - and perhaps the context for the emergence of life both here and there - hinges upon what we can discover within our own stellar neighborhood. With current spacecraft technology and high-capability launch vehicles, such as the Space Launch System (SLS), a small, but extremely capable spacecraft, could be dispatched to the near-by interstellar medium with at least twice the speed of the Voyagers. Challenges remain with payload mass and power constraints for optimized science measurements. Mission longevity, as experienced by, but not designed into, the Voyagers, communications capability, and radioisotope power system performance and lifetime are solvable engineering challenges. Such a robotic craft can be built, and could be built and launched soon - to enable our first deliberate step to the stars.

Diagnosing the Neutral Interstellar Gas Flow at 1 AU with IBEX-Lo

NASA Astrophysics Data System (ADS)

Möbius, E.; Kucharek, H.; Clark, G.; O'Neill, M.; Petersen, L.; Bzowski, M.; Saul, L.; Wurz, P.; Fuselier, S. A.; Izmodenov, V. V.; McComas, D. J.; Müller, H. R.; Alexashov, D. B.

2009-08-01

Every year in fall and spring the Interstellar Boundary Explorer (IBEX) will observe directly the interstellar gas flow at 1 AU over periods of several months. The IBEX-Lo sensor employs a powerful triple time-of-flight mass spectrometer. It can distinguish and image the O and He flow distributions in the northern fall and spring, making use of sensor viewing perpendicular to the Sun-pointing spin axis. To effectively image the narrow flow distributions IBEX-Lo has a high angular resolution quadrant in its collimator. This quadrant is employed selectively for the interstellar gas flow viewing in the spring by electrostatically shutting off the remainder of the aperture. The operational scenarios, the expected data, and the necessary modeling to extract the interstellar parameters and the conditions in the heliospheric boundary are described. The combination of two key interstellar species will facilitate a direct comparison of the pristine interstellar flow, represented by He, which has not been altered in the heliospheric boundary region, with a flow that is processed in the outer heliosheath, represented by O. The O flow distribution consists of a depleted pristine component and decelerated and heated neutrals. Extracting the latter so-called secondary component of interstellar neutrals will provide quantitative constraints for several important parameters of the heliosheath interaction in current global heliospheric models. Finding the fraction and width of the secondary component yields an independent value for the global filtration factor of species, such as O and H. Thus far filtration can only be inferred, barring observations in the local interstellar cloud proper. The direction of the secondary component will provide independent information on the interstellar magnetic field strength and orientation, which has been inferred from SOHO SWAN Ly- α backscattering observations and the two Voyager crossings of the termination shock.

From Interstellar Polycyclic Aromatic Hydrocarbons and Ice to the Origin of Life

NASA Technical Reports Server (NTRS)

Allamandola, Louis

2004-01-01

Tremendous strides have been made in our understanding of interstellar material over the past twenty years thanks to significant, parallel developments in observational astronomy and laboratory astrophysics. Twenty years ago the composition of interstellar dust was largely guessed at, the concept of ices in dense molecular clouds ignored, and the notion of large, abundant, gas phase, carbon rich molecules widespread throughout the interstellar medium (ISM) considered impossible. Today the composition of dust in the diffuse ISM is reasonably well constrained to cold refractory materials comprised of amorphous and crystalline silicates mixed with an amorphous carbonaceous material containing aromatic structural units and short, branched aliphatic chains. In the dense ISM, the birthplace of stars and planets, these cold dust particles are coated with mixed molecular ices whose composition is very well constrained. Lastly, the signature of carbon-rich polycyclic aromatic hydrocarbons (PAHs), shockingly large molecules by early interstellar chemistry standards, is widespread throughout the Universe. The first part of this talk will describe how infrared studies of interstellar space, combined with laboratory simulations, have revealed the composition of interstellar ices (the building blocks of comets) and the high abundance and nature of interstellar PAHs. The laboratory database has now enabled us to gain insight into the identities, abundances, and physical state of many interstellar materials. Within a dense molecular cloud, and especially in the presolar nebula, the materials frozen into the interstellar/precometary ices are photoprocessed by ultraviolet light and produce more complex molecules. The remainder of the presentation will focus on the photochemical evolution of these materials and the possible role of these compounds on the to the carbonaceous components of micrometeorites, they are likely to have been important sources of complex materials on the early Earth and their composition may be related to the origin of life.

Researchers Use NRAO Telescope to Study Formation Of Chemical Precursors to Life

NASA Astrophysics Data System (ADS)

2006-08-01

In just two years of work, an international research team has discovered eight new complex, biologically-significant molecules in interstellar space using the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT) in West Virginia. "This is a feat unprecedented in the 35-year history of searching for complex molecules in space and suggests that a universal prebiotic chemistry is at work," said Jan M. Hollis of the NASA Goddard Space Flight Center, leader of the research team. Chemistry Cycle The Cosmic Chemistry Cycle CREDIT: Bill Saxton, NRAO/AUI/NSF Full Size Image Files Interactive Graphic With "Mouseover" Text Blocks Chemical Cycle Graphic (above image, JPEG, 129K) Graphic With Text Blocks (JPEG, 165K) High-Res TIFF (44.2M) High-Res TIFF With Text Blocks (44.2M) Green Bank Telescope and Molecule Diagrams (JPEG, 58K) Green Bank Telescope and Molecule Diagrams (TIFF, 21M) New Molecules: Chemical Diagrams (PDF, 64K) The new discoveries are helping scientists unlock the secrets of how the molecular precursors to life can form in the giant clouds of gas and dust in which stars and planets are born. "The first of the many chemical processes that ultimately led to life on Earth probably took place even before our planet was formed. The GBT has taken the leading role in exploring the origin of biomolecules in interstellar clouds," said Phil Jewell of the National Radio Astronomy Observatory (NRAO). The eight new molecules discovered with the GBT bring the total to 141 different molecular species found in interstellar space. About 90 percent of those interstellar molecules contain carbon, which is required for a molecule to be classified as organic. The newly-discovered molecules all contain carbon and are composed of 6 to 11 atoms each. These results suggest, the scientists say, that chemical evolution occurs routinely in the gas and dust from which stars and planets eventually are born. The mass of an interstellar cloud is 99 percent gas and one percent dust. The GBT discoveries have been made in just two prototypical interstellar clouds. The molecules acetamide (CH3CONH2), cyclopropenone (H2C3O), propenal (CH2CHCHO), propanal (CH3CH2CHO), and ketenimine (CH2CNH) were found in a cloud called Sagittarius B2(N), which is near the center of our Milky Way Galaxy some 26,000 light years from Earth. This star-forming region is the largest repository of complex interstellar molecules known. The molecules methyl-cyano-diacetylene (CH3C5N), methyl-triacetylene (CH3C6H), and cyanoallene (CH2CCHCN) were found in the Taurus Molecular Cloud (TMC-1), which is relatively nearby at a distance of 450 light years. The starless TMC-1 cloud is dark and cold with a temperature of only 10 degrees above absolute zero and may eventually evolve into a star-forming region. "The discovery of these large organic molecules in the coldest regions of the interstellar medium has certainly changed the belief that large organic molecules would only have their origins in hot molecular cores. It has forced us to rethink the paradigms of interstellar chemistry," said Anthony Remijan of the NRAO. These large molecules found with the GBT are built up from smaller ones, the scientists say, by two principal mechanisms. In the first, simple chemical reactions add an atom to a molecular structure residing on the surface of a dust grain. As an example of this process, the researchers cite a molecule called cyclopropenylidene (c-C3H2, where "c-" means cyclic), which contains three carbon atoms in a ring. Cyclopropenylidene was discovered in interstellar space in 1987, and is known to be highly reactive. In 2005, using the GBT, scientists discovered another molecule, cyclopropenone (c-H2C3O), which can be produced by adding an oxygen atom to cyclopropenylidene. The second method for constructing larger molecules from smaller ones involves neutral-radical reactions that can occur within the gas in an interstellar cloud. For example, in 2006, the scientists discovered acetamide (CH3CONH2), which can be formed when a previously-discovered neutral molecule called formamide (HCONH2) combines with radicals such as CH2 and CH3, also previously discovered. Acetamide is particularly interesting because it contains a peptide bond which is the means for linking amino acids together to form proteins. Once interstellar molecules are ejected from dust grains into the gas phase, presumably by shock waves, they are free to rotate end-over-end. As gas molecules change their rotational modes, they can emit or absorb radiation at precise radio frequencies, called transitions, that are unique to each type of molecule. By detecting several rotational transitions, astronomers can unambiguously identify a specific interstellar molecule. "It is important to note that likely interstellar molecule candidates are first studied in gas-phase laboratory experiments so that transition frequencies are known in advance of an interstellar experiment," said Frank Lovas of the National Institute of Standards and Technology. Along the line of sight from the interstellar cloud to the telescope, thousands of billions of molecules undergo the exact same transition, producing a signal strong enough to be detected by sensitive equipment. For this type of work, the GBT is the world's most sensitive tool that can be accurately pointed and track astronomical objects. In addition to Hollis, Jewell, Remijan, and Lovas, the research team included Lewis Snyder of the University of Illinois; Harald Mollendal of the University of Oslo, Norway; Vadim Ilyushin of the Institute of Radio Astronomy of the National Academy of Sciences of the Ukraine; and Isabell Kleiner of the Universite Paris, France. The astronomers' reports on their results appeared in 8 separate editions of the Astrophysical Journal. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Interrelationships between interstellar and interplanetary grains

NASA Technical Reports Server (NTRS)

Clayton, D. D.

1986-01-01

The relationship between solar system dust (SSD) and interstellar dust particles (ISMD) is being reconsidered because of the discovery of isotopic anomalies in meteorites. Meteoritic, circumstellar/meteoritic, interstellar/meteoritic, planetary, and cometary data are reviewed.

Chaotic bubbling and nonstagnant foams.

PubMed

Tufaile, Alberto; Sartorelli, José Carlos; Jeandet, Philippe; Liger-Belair, Gerard

2007-06-01

We present an experimental investigation of the agglomeration of bubbles obtained from a nozzle working in different bubbling regimes. This experiment consists of a continuous production of bubbles from a nozzle at the bottom of a liquid column, and these bubbles create a two-dimensional (2D) foam (or a bubble raft) at the top of this column. The bubbles can assemble in various dynamically stable arrangement, forming different kinds of foams in a liquid mixture of water and glycerol, with the effect that the bubble formation regimes influence the foam obtained from this agglomeration of bubbles. The average number of bubbles in the foam is related to the bubble formation frequency and the bubble mean lifetime. The periodic bubbling can generate regular or irregular foam, while a chaotic bubbling only generates irregular foam.

Interstellar Travel

NASA Astrophysics Data System (ADS)

Rabayda, Adam; Keller, Luke

Interstellar space travel is a topic that is often dismissed as highly unlikely due to the vast distances involved and to considerable engineering and socioeconomic challenges. Some are left believing that it may be far from possible for us, as a species, to go anywhere beyond our solar system. We demonstrate not only the possibility of covering interstellar distances in decades or less, but also that interstellar travel is possible (in principle) with existing technology. For example: Using only special relativity and calculus, we calculated that an interstellar spacecraft could reach the Andromeda Galaxy (2.5 Million light-years from Earth) in just over 28 years at an acceleration of 9 . 81m/s , which would emulate Earth gravity. We also calculated that the energy required for interstellar space travel, often deemed impossible with current technology, is, in fact, possible through certain methods such as nuclear fusion.

THERMODYNAMICS AND CHARGING OF INTERSTELLAR IRON NANOPARTICLES

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

Hensley, Brandon S.; Draine, B. T., E-mail: brandon.s.hensley@jpl.nasa.gov

Interstellar iron in the form of metallic iron nanoparticles may constitute a component of the interstellar dust. We compute the stability of iron nanoparticles to sublimation in the interstellar radiation field, finding that iron clusters can persist down to a radius of ≃4.5 Å, and perhaps smaller. We employ laboratory data on small iron clusters to compute the photoelectric yields as a function of grain size and the resulting grain charge distribution in various interstellar environments, finding that iron nanoparticles can acquire negative charges, particularly in regions with high gas temperatures and ionization fractions. If ≳10% of the interstellar ironmore » is in the form of ultrasmall iron clusters, the photoelectric heating rate from dust may be increased by up to tens of percent relative to dust models with only carbonaceous and silicate grains.« less

Intense gas bubble emissions in the Kerch seep area - A newly discovered high-flux seep site in the Black Sea

NASA Astrophysics Data System (ADS)

Römer, M.; Sahling, H.; Pape, T.; Bahr, A.; Feseker, T.; Wintersteller, P.; Bohrmann, G.

2012-04-01

More than 500 bubble-induced hydroacoustic anomalies (flares) were found in the water column above the seafloor in the study area comprising about 430 km2 at the Don-Kuban paleo-fan (Eastern Black Sea) by using ship mounted single beam and multibeam echosounders. Almost all flares originated from the seafloor above the gas hydrate stability zone (GHSZ), which in that region is located below ~700 m water depth. This observation confirms the sealing mechanism of gas hydrate, which impedes migration of free gas through the GHSZ and subsequent bubble emission from the seafloor. However, an intense seep site, called the "Kerch seep area" was discovered as an exception at 890 m water depth well within the GHSZ. In situ temperature measurements in shallow sediments indicate locally elevated temperatures probably caused by enhanced upward fluid flow. The base of the GHSZ in this region is generally situated at about 150 m below the seafloor. However, the local thermal anomalies result in a thinning of the gas hydrate occurrence zone to only a few meters below the seafloor and allow free gas to reach the seafloor. At sites where gas migrated into near-surface deposits, shallow gas hydrate deposits evolved and up-doming of overlying sediments led to the formation of mounds rising several meters from the surrounding seafloor. Further gas bubbles ascending from greater depth are accumulated below the gas hydrate layer at the base of the mound structures and migrate horizontally to their rims. At the mound edges gas bubbles either might form fresh gas hydrates and increase the extent of the mound structures by pushing up overlying sediments or escape at several sites into the water column. Two mounds were mapped in ultra-high resolution during dives with the autonomous underwater vehicle 'AUV MARUM SEAL 5000'. Several individual flares were detected in the Kerch seep area using hydroacoustic systems. Repeated surveys in that area conducted during three cruises within four years suggested that gas discharge varied spatially and temporally while the total number of flares remained rather constant. During seafloor inspections with MARUḾs remotely operated vehicle 'ROV QUEST 4000 m' gas bubble emission sites were investigated in detail. Gas bubbles collected during the ROV dives mainly consisted of methane predominantly of microbial origin. By analyzing the high-definition video material the gas flux from several bubble emission sites was calculated. In combination with the hydroacoustic results (flare distributions) it is estimated that about 2.2 - 87 × 106 mol CH4/yr are emitted from the seafloor at the Kerch seep area. Despite this high mass of methane injected into the hydrosphere, the peak of the highest flares at ~350 m water depth as revealed by echosounder recording suggest that the ascending methane completely dissolves in the water column and does not pass the sea-atmosphere boundary.

Terrestrial record of the solar system's oscillation about the galactic plane

NASA Technical Reports Server (NTRS)

Stothers, R. B.

1985-01-01

A new study is presented of the observational evidence pertaining to the theory which attributes the episodic component of the earth's impact cratering record over the past 600 Myr to gravitational encounters between the solar system and interstellar clouds that cause comets to fall into the solar system and impact the earth. Contrary to a claim by Thaddeus and Chanan (1985), the vertical scale height of the clouds seems to be sufficently small and the sun's vertical trajectory sufficiently large for the modulating effect of the sun's galactovertical motion to be detectable in the terrestrial record of impact cratering with at least a 50 percent a priori probability.

Laboratory experiments on interstellar ice analogs: The sticking and desorption of small physisorbed molecules

NASA Technical Reports Server (NTRS)

Fuchs, G. W.; Acharyya, K.; Bisschop, S. E.; Oberg, K. I.; vanBroekhuizen, F. A.; Fraser, H. J.; Schlemmer, S.; vanDishoeck, E. F.; Linnartz, H.

2006-01-01

Molecular oxygen and nitrogen are difficult to observe since they are infrared inactive and radio quiet. The low O2 abundances found so far combined with general considerations of dense cloud conditions suggest molecular oxygen is frozen out at low temperatures (< 20 K) in the shielded inner regions of cloud cores. In solid form O2 and N2 can only be observed as adjuncts within other ice constituents, like CO. In this work we focus on fundamental properties of N2 and O2 in CO ice-gas systems, e.g. desorption characteristics and sticking probabilities at low temperatures for different ice morphologies.

Recent observations of traveling ionospheric disturbances and plasma bubbles using Optical Mesosphere Thermosphere Imagers in Asian and African sectors

NASA Astrophysics Data System (ADS)

Shiokawa, K.; Otsuka, Y.; Tsuchiya, S.; Moral, A. C.; Okoh, D.

2017-12-01

We review recent observational results of medium-scale traveling ionospheric disturbances (MSTIDs) and equatorial plasma bubbles obtained by using airglow imagers and Fabry-Perot interferometers of the Optical Mesosphere Thermosphere Imagers (OMTIs) at Asian and African sectors. The OMTIs contains 20 airglow imagers and 5 Fabry-Perot interferometers (FPIs) at Canada, USA (Alaska), Russia, Finland, Norway, Iceland, Japan, Thailand, Indonesia, Australia, and Nigeria (http://stdb2.isee.nagoya-u.ac.jp/omti/). The 3-dimentional Fast Fourier Transformation of airglow images makes it possible to analyze 16-year airglow images obtained at Shigaraki (34.8N) and Rikubetsu (43.5N), Japan, to obtain phase velocity spectra of gravity waves and MSTIDs. The MSTIDs spectra show clear southwestward preference of propagation and minor northeastward propagation over Japan. We also found clear negative correlation between MSTID power and solar F10.7 flux, indicating that MSTIDs becomes more active during solar quiet time. This fact suggest the control of ionospheric Perkins and E-F coupling instabilities by solar activities. Three TIDs in airglow images over Indonesia, including midnight brightness waves (MBWs), were compared with CHAMP-satellite overpass to investigate neutral density variations in the thermosphere associated with the TIDs. We found clear correspondence in variations between the airglow intensities and neutral densities, suggesting that the observed TIDs over the equatorial region is caused by gravity waves. We also compare average thermospheric temperatures measured by the four FPIs for 3-4 years with the MSIS90E and GAIA models. The comparison shows that GAIA generally shows better fitting than the MSIS90E, but at the equatorial stations, GAIA tends to fail to reproduce the FPI temperature, probably due to ambiguity of location of the midnight temperature maximum. We also made statistics of plasma bubble occurrence using airglow imager and GNSS receiver at Abuja (9.0N), Nigeria near the geomagnetic equator based on 1.6 year observations. The bubble occurrence is high at equinoxes. There are 33 % of events for which bubble detection by airglow image and GNSS ROTI is different. We discuss possible cause of these differences in the presentation.

Approaching behavior of a pair of spherical bubbles in quiescent liquids

NASA Astrophysics Data System (ADS)

Sanada, Toshiyuki; Kusuno, Hiroaki

2015-11-01

Some unique motions related bubble-bubble interaction, such as equilibrium distance, wake induced lift force, have been proposed by theoretical analysis or numerical simulations. These motions are different from the solid spheres like DKT model (Drafting, Kissing and Tumbling). However, there is a lack of the experimental verification. In this study, we experimentally investigated the motion of a pair of bubbles initially positioned in-line configuration in ultrapure water or an aqueous surfactant solution. The bubble motion were observed by two high speed video cameras. The bubbles Reynolds number was ranged from 50 to 300 and bubbles hold the spherical shape in this range. In ultrapure water, initially the trailing bubble deviated from the vertical line on the leading bubble owing to the wake of the leading bubble. And then, the slight difference of the bubble radius changed the relative motion. When the trailing bubble slightly larger than the leading bubble, the trailing bubble approached to the leading bubble due to it's buoyancy difference. The bubbles attracted and collided only when the bubbles rising approximately side by side configuration. In addition, we will also discuss the motion of bubbles rising in an aqueous surfactant solution.

The heliosphere's interstellar interaction: no bow shock.

PubMed

McComas, D J; Alexashov, D; Bzowski, M; Fahr, H; Heerikhuisen, J; Izmodenov, V; Lee, M A; Möbius, E; Pogorelov, N; Schwadron, N A; Zank, G P

2012-06-08

As the Sun moves through the local interstellar medium, its supersonic, ionized solar wind carves out a cavity called the heliosphere. Recent observations from the Interstellar Boundary Explorer (IBEX) spacecraft show that the relative motion of the Sun with respect to the interstellar medium is slower and in a somewhat different direction than previously thought. Here, we provide combined consensus values for this velocity vector and show that they have important implications for the global interstellar interaction. In particular, the velocity is almost certainly slower than the fast magnetosonic speed, with no bow shock forming ahead of the heliosphere, as was widely expected in the past.

Observations of interstellar zinc

NASA Technical Reports Server (NTRS)

Jura, M.; York, D.

1981-01-01

The International Ultraviolet Explorer observations of interstellar zinc toward 10 stars are examined. It is found that zinc is at most only slightly depleted in the interstellar medium; its abundance may serve as a tracer of the true metallicity in the gas. The local interstellar medium has abundances that apparently are homogeneous to within a factor of two, when integrated over paths of about 500 pc, and this result is important for understanding the history of nucleosynthesis in the solar neighborhood. The intrinsic errors in detecting weak interstellar lines are analyzed and suggestions are made as to how this error limit may be lowered to 5 mA per target observation.

Deflection of the Interstellar Neutral Hydrogen Flow Across the Heliospheric Interface: an Interstellar Magnetic Compass

NASA Astrophysics Data System (ADS)

Lallement, R.; Eric, Q.; Jean-Loup, B.; Dimitra, K.; Risto, P.

2005-05-01

Analyses of SOHO-SWAN observations show that the interstellar neutral H flow direction differs by about 4 degrees from the neutral He flow direction recently derived with an unprecedented accuracy using combined data sets (Mobius et al, 2004). The most likely explanation is a distortion of the heliospheric interface under the action of an inclined interstellar magnetic field, with imprints of the distorsion on the neutral H flow due to charge-transfer reactions between H atoms and ions. The direction of the ambient interstellar magnetic field and the heliospheric shape can be derived from the observed deviation. Implications for Voyager trajectories are discussed.

Voyager 1 Entering Interstellar Space Artist Concept

NASA Image and Video Library

2013-09-12

This artist concept depicts NASA Voyager 1 spacecraft entering interstellar space. Interstellar space is dominated by the plasma, or ionized gas, that was ejected by the death of nearby giant stars millions of years ago.

Interstellar Polycyclic Aromatic Compounds and Astrophysics

NASA Technical Reports Server (NTRS)

Hodgins, Douglas M.; DeVincenzi, Donald (Technical Monitor)

1999-01-01

Polycyclic aromatic compounds (PACs), a class of organic molecules whose structures are characterized by the presence of two or more fused aromatic rings, have been the subject of astrophysical interest for nearly two decades. Large by interstellar standards (from as few as 20 to perhaps as many as several hundred atoms), it has been suggested that these species are among the most abundant interstellar molecules impacting a wide range of astrophysical phenomena including: the ubiquitous family of infrared emission bands observed in an ever-increasing assortment of astronomical objects; the subtle but rich array of discrete visible/near-infrared interstellar molecular absorption features known as the diffuse interstellar bands (DIBs); the broad near-infrared quasi-continuum observed in a number of nebulae known as excess red emission (ERE); the interstellar ultraviolet extinction curve and broad '2200 Angstrom bump'; the heating/cooling mechanisms of interstellar clouds. Nevertheless, until recently a lack of good-quality laboratory spectroscopic data on PACs under astrophysically relevant conditions (i.e. isolated, ionized molecules; ionized molecular clusters, etc.) has hindered critical evaluation and extension of this model

Matrix isolation as a tool for studying interstellar chemical reactions

NASA Technical Reports Server (NTRS)

Ball, David W.; Ortman, Bryan J.; Hauge, Robert H.; Margrave, John L.

1989-01-01

Since the identification of the OH radical as an interstellar species, over 50 molecular species were identified as interstellar denizens. While identification of new species appears straightforward, an explanation for their mechanisms of formation is not. Most astronomers concede that large bodies like interstellar dust grains are necessary for adsorption of molecules and their energies of reactions, but many of the mechanistic steps are unknown and speculative. It is proposed that data from matrix isolation experiments involving the reactions of refractory materials (especially C, Si, and Fe atoms and clusters) with small molecules (mainly H2, H2O, CO, CO2) are particularly applicable to explaining mechanistic details of likely interstellar chemical reactions. In many cases, matrix isolation techniques are the sole method of studying such reactions; also in many cases, complexations and bond rearrangements yield molecules never before observed. The study of these reactions thus provides a logical basis for the mechanisms of interstellar reactions. A list of reactions is presented that would simulate interstellar chemical reactions. These reactions were studied using FTIR-matrix isolation techniques.

Ultrafast Outflows: Galaxy-scale Active Galactic Nucleus Feedback

NASA Astrophysics Data System (ADS)

Wagner, A. Y.; Umemura, M.; Bicknell, G. V.

2013-01-01

We show, using global three-dimensional grid-based hydrodynamical simulations, that ultrafast outflows (UFOs) from active galactic nuclei (AGNs) result in considerable feedback of energy and momentum into the interstellar medium (ISM) of the host galaxy. The AGN wind interacts strongly with the inhomogeneous, two-phase ISM consisting of dense clouds embedded in a tenuous, hot, hydrostatic medium. The outflow floods through the intercloud channels, sweeps up the hot ISM, and ablates and disperses the dense clouds. The momentum of the UFO is primarily transferred to the dense clouds via the ram pressure in the channel flow, and the wind-blown bubble evolves in the energy-driven regime. Any dependence on UFO opening angle disappears after the first interaction with obstructing clouds. On kpc scales, therefore, feedback by UFOs operates similarly to feedback by relativistic AGN jets. Negative feedback is significantly stronger if clouds are distributed spherically rather than in a disk. In the latter case, the turbulent backflow of the wind drives mass inflow toward the central black hole. Considering the common occurrence of UFOs in AGNs, they are likely to be important in the cosmological feedback cycles of galaxy formation.

ULTRAFAST OUTFLOWS: GALAXY-SCALE ACTIVE GALACTIC NUCLEUS FEEDBACK

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

Wagner, A. Y.; Umemura, M.; Bicknell, G. V., E-mail: ayw@ccs.tsukuba.ac.jp

We show, using global three-dimensional grid-based hydrodynamical simulations, that ultrafast outflows (UFOs) from active galactic nuclei (AGNs) result in considerable feedback of energy and momentum into the interstellar medium (ISM) of the host galaxy. The AGN wind interacts strongly with the inhomogeneous, two-phase ISM consisting of dense clouds embedded in a tenuous, hot, hydrostatic medium. The outflow floods through the intercloud channels, sweeps up the hot ISM, and ablates and disperses the dense clouds. The momentum of the UFO is primarily transferred to the dense clouds via the ram pressure in the channel flow, and the wind-blown bubble evolves inmore » the energy-driven regime. Any dependence on UFO opening angle disappears after the first interaction with obstructing clouds. On kpc scales, therefore, feedback by UFOs operates similarly to feedback by relativistic AGN jets. Negative feedback is significantly stronger if clouds are distributed spherically rather than in a disk. In the latter case, the turbulent backflow of the wind drives mass inflow toward the central black hole. Considering the common occurrence of UFOs in AGNs, they are likely to be important in the cosmological feedback cycles of galaxy formation.« less

A CHANDRA OBSERVATION OF SNR 0540 - 697

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

Seward, F. D.; Williams, R. M.; Chu, Y.-H.

2010-07-15

This paper describes a Chandra observation of SNR 0540 - 697 within the H II complex N159 in the Large Magellanic Cloud (LMC). Scattering from the nearby bright source LMC X-1, which obscures the western edge of the remnant, has been removed. Larger than previously believed, the 2.'0 x 2.'8 remnant is defined by optical filaments and two lobes of X-ray emission. A band of intervening material absorbs X-rays from the central part of the remnant. The N Lobe of the remnant is relatively bright and well defined, while emission from the S Lobe is much weaker. There is structuremore » within the N Lobe but no clear X-ray emission from an outer shell indicating a shock in the interstellar medium. The X-ray spectrum is thermal with emission lines from Fe, Mg, and Si. The observed temperature and luminosity of the hot gas are 0.6 keV and 6 x 10{sup 35} erg s{sup -1}, respectively. These are consistent with characteristics expected for older remnants. There is also diffuse thermal X-ray emission north of N159 extending into N160, evidence for a larger remnant or bubble.« less

The Fermi Galactic Center GeV excess and implications for dark matter

DOE PAGES

Ackermann, M.; Ajello, M.; Albert, A.; ...

2017-05-04

Here, the region around the Galactic Center (GC) is now well established to be brighter at energies of a few GeV than what is expected from conventional models of diffuse gamma-ray emission and catalogs of known gamma-ray sources. We study the GeV excess using 6.5 yr of data from the Fermi Large Area Telescope. We characterize the uncertainty of the GC excess spectrum and morphology due to uncertainties in cosmic-ray source distributions and propagation, uncertainties in the distribution of interstellar gas in the Milky Way, and uncertainties due to a potential contribution from the Fermi bubbles. We also evaluate uncertaintiesmore » in the excess properties due to resolved point sources of gamma rays. The GC is of particular interest, as it would be expected to have the brightest signal from annihilation of weakly interacting massive dark matter (DM) particles. However, control regions along the Galactic plane, where a DM signal is not expected, show excesses of similar amplitude relative to the local background. Furthermore, based on the magnitude of the systematic uncertainties, we conservatively report upper limits for the annihilation cross-section as a function of particle mass and annihilation channel.« less

The Fermi Galactic Center GeV Excess and Implications for Dark Matter

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

Ackermann, M.; Buehler, R.; Ajello, M.

2017-05-01

The region around the Galactic Center (GC) is now well established to be brighter at energies of a few GeV than what is expected from conventional models of diffuse gamma-ray emission and catalogs of known gamma-ray sources. We study the GeV excess using 6.5 yr of data from the Fermi Large Area Telescope. We characterize the uncertainty of the GC excess spectrum and morphology due to uncertainties in cosmic-ray source distributions and propagation, uncertainties in the distribution of interstellar gas in the Milky Way, and uncertainties due to a potential contribution from the Fermi bubbles. We also evaluate uncertainties inmore » the excess properties due to resolved point sources of gamma rays. The GC is of particular interest, as it would be expected to have the brightest signal from annihilation of weakly interacting massive dark matter (DM) particles. However, control regions along the Galactic plane, where a DM signal is not expected, show excesses of similar amplitude relative to the local background. Based on the magnitude of the systematic uncertainties, we conservatively report upper limits for the annihilation cross-section as a function of particle mass and annihilation channel.« less

Boundary conditions for the paleoenvironment: Chemical and Physical Processes in dense interstellar clouds

NASA Technical Reports Server (NTRS)

Irvine, W. M.; Schloerb, F. P.; Ziurys, L. M.

1986-01-01

The present research includes searches for important new interstellar constituents; observations relevant to differentiating between different models for the chemical processes that are important in the interstellar environment; and coordinated studies of the chemistry, physics, and dynamics of molecular clouds which are the sites or possible future sites of star formation. Recent research has included the detection and study of four new interstellar molecules; searches which have placed upper limits on the abundance of several other potential constituents of interstellar clouds; quantitative studies of comparative molecular abundances in different types of interstellar clouds; investigation of reaction pathways for astrochemistry from a comparison of theory and the observed abundance of related species such as isomers and isotopic variants; studies of possible tracers of energenic events related to star formation, including silicon and sulfur containing molecules; and mapping of physical, chemical, and dynamical properties over extended regions of nearby cold molecular clouds.

The effect of catastrophic collisional fragmentation and diffuse medium accretion on a computational interstellar dust system

NASA Technical Reports Server (NTRS)

Liffman, Kurt

1990-01-01

The effects of catastrophic collisional fragmentation and diffuse medium accretion on a the interstellar dust system are computed using a Monte Carlo computer model. The Monte Carlo code has as its basis an analytic solution of the bulk chemical evolution of a two-phase interstellar medium, described by Liffman and Clayton (1989). The model is subjected to numerous different interstellar processes as it transfers from one interstellar phase to another. Collisional fragmentation was found to be the dominant physical process that shapes the size spectrum of interstellar dust. It was found that, in the diffuse cloud phase, 90 percent of the refractory material is locked up in the dust grains, primarily due to accretion in the molecular medium. This result is consistent with the observed depletions of silicon. Depletions were found to be affected only slightly by diffuse cloud accretion.

CAN IBEX DETECT INTERSTELLAR NEUTRAL HELIUM OR OXYGEN FROM ANTI-RAM DIRECTIONS?

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

Galli, A.; Wurz, P.; Park, J.

To better constrain the parameters of the interstellar neutral flow, we searched the Interstellar Boundary EXplorer (IBEX)-Lo database for helium and oxygen from the interstellar medium in the anti-ram direction in the three years (2009–2011) with the lowest background rates. We found that IBEX-Lo cannot observe interstellar helium from the anti-ram direction because the helium energy is too low for indirect detection by sputtering off the IBEX-Lo conversion surface. Our results show that this sputtering process has a low energy threshold between 25 and 30 eV, whereas the energy of the incident helium is only 10 eV for these observations.more » Interstellar oxygen, on the other hand, could in principle be detected in the anti-ram hemisphere, but the expected magnitude of the signal is close to the detection limit imposed by counting statistics and by the magnetospheric foreground.« less

Global Anisotropies in TeV Cosmic Rays Related to the Sun's Local Galactic Environment from IBEX

NASA Technical Reports Server (NTRS)

Schwadron, N. A.; Adams, F. C.; Christian, E. R.; Desiati, P.; Frisch, P.; Funsten, H. O.; Jokipii, J. R.; McComas, D. J.; Moebius, E.; Zank, G. P.

2014-01-01

Observations with the Interstellar Boundary Explorer (IBEX) have shown enhanced energetic neutral atom (ENA) emission from a narrow, circular ribbon likely centered on the direction of the local interstellar medium (LISM) magnetic field. Here, we show that recent determinations of the local interstellar velocity, based on interstellar atom measurements with IBEX, are consistent with the interstellar modulation of high-energy (tera-electron volts, TeV) cosmic rays and diffusive propagation from supernova sources revealed in global anisotropy maps of ground-based high-energy cosmic-ray observatories (Milagro, Asg, and IceCube). Establishing a consistent local interstellar magnetic field direction using IBEX ENAs at hundreds to thousands of eV and galactic cosmic rays at tens of TeV has wide-ranging implications for the structure of our heliosphere and its interactions with the LISM, which is particularly important at the time when the Voyager spacecraft are leaving our heliosphere.

Ultraviolet observations of cool stars. VII - Local interstellar hydrogen and deuterium Lyman-alpha

NASA Technical Reports Server (NTRS)

Mcclintock, W.; Henry, R. C.; Linsky, J. L.; Moos, H. W.

1978-01-01

High-resolution Copernicus spectra of Epsilon Eri and Epsilon Ind containing interstellar hydrogen and deuterium L-alpha absorption lines are presented, reduced, and analyzed. Parameters of the interstellar hydrogen and deuterium toward these two stars are derived independently, without any assumptions concerning the D/H ratio. Copernicus spectra of Alpha Aur and Alpha Cen A are reanalyzed, and limits on the D/H number-density ratio consistent with the data for all four stars are considered. A comparison of the present estimates for the parameters of the local interstellar medium with those obtained by other techniques shows that there is no compelling evidence for significant variations in the hydrogen density and D/H ratio in the local interstellar medium. On this basis the hypothesis of an approaching local interstellar cloud proposed by Vidal-Madjar et al. (1978) is rejected

Global anisotropies in TeV cosmic rays related to the Sun's local galactic environment from IBEX.

PubMed

Schwadron, N A; Adams, F C; Christian, E R; Desiati, P; Frisch, P; Funsten, H O; Jokipii, J R; McComas, D J; Moebius, E; Zank, G P

2014-02-28

Observations with the Interstellar Boundary Explorer (IBEX) have shown enhanced energetic neutral atom (ENA) emission from a narrow, circular ribbon likely centered on the direction of the local interstellar medium (LISM) magnetic field. Here, we show that recent determinations of the local interstellar velocity, based on interstellar atom measurements with IBEX, are consistent with the interstellar modulation of high-energy (tera-electron volts, TeV) cosmic rays and diffusive propagation from supernova sources revealed in global anisotropy maps of ground-based high-energy cosmic-ray observatories (Milagro, Asγ, and IceCube). Establishing a consistent local interstellar magnetic field direction using IBEX ENAs at hundreds to thousands of eV and galactic cosmic rays at tens of TeV has wide-ranging implications for the structure of our heliosphere and its interactions with the LISM, which is particularly important at the time when the Voyager spacecraft are leaving our heliosphere.

Interaction mechanism of double bubbles in hydrodynamic cavitation

NASA Astrophysics Data System (ADS)

Li, Fengchao; Cai, Jun; Huai, Xiulan; Liu, Bin

2013-06-01

Bubble-bubble interaction is an important factor in cavitation bubble dynamics. In this paper, the dynamic behaviors of double cavitation bubbles driven by varying pressure field downstream of an orifice plate in hydrodynamic cavitation reactor are examined. The bubble-bubble interaction between two bubbles with different radii is considered. We have shown the different dynamic behaviors between double cavitation bubbles and a single bubble by solving two coupling nonlinear equations using the Runge-Kutta fourth order method with adaptive step size control. The simulation results indicate that, when considering the role of the neighbor smaller bubble, the oscillation of the bigger bubble gradually exhibits a lag in comparison with the single-bubble case, and the extent of the lag becomes much more obvious as time goes by. This phenomenon is more easily observed with the increase of the initial radius of the smaller bubble. In comparison with the single-bubble case, the oscillation of the bigger bubble is enhanced by the neighbor smaller bubble. Especially, the pressure pulse of the bigger bubble rises intensely when the sizes of two bubbles approach, and a series of peak values for different initial radii are acquired when the initial radius ratio of two bubbles is in the range of 0.9˜1.0. Although the increase of the center distance between two bubbles can weaken the mutual interaction, it has no significant influence on the enhancement trend. On the one hand, the interaction between two bubbles with different radii can suppress the growth of the smaller bubble; on the other hand, it also can enhance the growth of the bigger one at the same time. The significant enhancement effect due to the interaction of multi-bubbles should be paid more attention because it can be used to reinforce the cavitation intensity for various potential applications in future.

Recommended Rest Frequencies for Observed Interstellar Molecular Microwave Transitions - 2002 Revision

National Institute of Standards and Technology Data Gateway

SRD 116 NIST Recommended Rest Frequencies for Observed Interstellar Molecular Microwave Transitions - 2002 Revision (Web, free access)   Critically evaluated transition frequencies for the molecular transitions detected in interstellar and circumstellar clouds are presented.

Interstellar Travel. (Latest citations from the Aerospace Database)

NASA Technical Reports Server (NTRS)

1996-01-01

The bibliography contains citations concerning travel between the stars. Topics include cost considerations, hyperspace navigation, exploration, and propulsion systems for vehicles to be used in interstellar travel. Human factor issues and social aspects of interstellar travel are also discussed.

A Multi-ionic Kinematic Investigation of NGC 595, a Giant Extragalactic H II Region in M33

NASA Astrophysics Data System (ADS)

Lagrois, Dominic; Joncas, Gilles

2009-08-01

Spectro-interferometric observations of the Hα, [O III], and [S II] optical emission lines are combined with radio observations of the 21 cm line in order to obtain a reliable kinematic image of NGC 595, the second largest giant extragalactic H II region in M33. The Hα and [O III] observations reveal that the nebula is exposed to two distinct kinematical regimes. While symmetric, broad velocity profiles dominate a sizeable fraction of the ionized extent, evidence for line splitting is detected in a small region near the most massive stars of the star cluster. A quantitative investigation proposes that two expanding wind-blown bubbles could be held responsible for the observed line splitting. The kinematics of the ionized material presenting one-component velocity profiles likely indicates that Champagne flows are present at the periphery of the molecular component leading to accelerated ionized material in the ambient interstellar medium. In areas not dominated by the photoionization of the molecular clouds, the H+ and S+ material shows a kinematical behavior roughly in agreement with the atomic gas. Mean nonthermal line widths show relatively large, supersonic values especially in [O III]. Models of structure functions indicate that the Hα and [O III] components could be exposed to different turbulent motions which could explain the broadening excess observed for the latter ion. On the full ionized extent of the nebula, the S+ material shows narrower line widths than the two other ions. Combined with the absence of line splitting, these peculiar characteristics indicate that the [S II] component is likely located at the periphery of the nebula and probably does not coexist with Hα and [O III]. The shape of the [S II] structure function is in agreement with a relatively low number of large-scale velocity gradients which partially explains the narrower profiles observed. The mean electron density in the nebula is estimated at 162 ± 106(1σ) cm-3, in agreement with previous studies of similar extragalactic H II regions. We provide the first bidimensional electron density map ever presented for a giant extragalactic nebula.

Diamonds in dense molecular clouds - A challenge to the standard interstellar medium paradigm

NASA Technical Reports Server (NTRS)

Allamandola, L. J.; Sandford, S. A.; Tielens, A. G. G. M.; Herbst, T. M.

1993-01-01

Observations of a newly discovered infrared C-H stretching band indicate that interstellar diamond-like material appears to be characteristic of dense clouds. In sharp contrast, the spectral signature of dust in the diffuse interstellar medium is dominated by -CH2- and -CH3 groups. This dichotomy in the aliphatic organic component between the dense and diffuse media challenges standard assumptions about the processes occurring in, and interactions between, these two media. The ubiquity of this interstellar diamond-like material rules out models for meteoritic diamond formation in unusual circumstellar environments and implies that the formation of the diamond-like material is associated with common interstellar processes or stellar types.

Deuterium Abundance in the Local Interstellar Medium

NASA Technical Reports Server (NTRS)

Ferlet, R.; Gry, C.; Vidal-Madjar, A.

1984-01-01

The present situation of deuterium abundance evaluation in interstellar space is discussed, and it is shown that it should be or = .00001 by studying in more detail lambda the Sco line of sight and by observing two NaI interstellar components toward that star, it can be shown that the D/H evaluation made toward lambda Sco is in fact related to the local interstellar medium (less than 10 pc from the Sun). Because this evaluation is also or = .00001 it is in striking contrast with the one made toward alpha Aur (D/H or = .000018 confirming the fact that the deuterium abundance in the local interstellar medium varies by at least a factor of two over few parsecs.

Squeezed between shells? The origin of the Lupus I molecular cloud. APEX/LABOCA, Herschel, and Planck observations

NASA Astrophysics Data System (ADS)

Gaczkowski, B.; Preibisch, T.; Stanke, T.; Krause, M. G. H.; Burkert, A.; Diehl, R.; Fierlinger, K.; Kroell, D.; Ngoumou, J.; Roccatagliata, V.

2015-12-01

Context. The Lupus I cloud is found between the Upper Scorpius (USco) and the Upper Centaurus-Lupus (UCL) subgroups of the Scorpius-Centaurus OB association, where the expanding USco H I shell appears to interact with a bubble currently driven by the winds of the remaining B-stars of UCL. Aims: We want to study how collisions of large-scale interstellar gas flows form and influence new dense clouds in the ISM. Methods: We performed LABOCA continuum sub-mm observations of Lupus I that provide for the first time a direct view of the densest, coldest cloud clumps and cores at high angular resolution. We complemented these data with Herschel and Planck data from which we constructed column density and temperature maps. From the Herschel and LABOCA column density maps we calculated probability density functions (PDFs) to characterize the density structure of the cloud. Results: The northern part of Lupus I is found to have, on average, lower densities, higher temperatures, and no active star formation. The center-south part harbors dozens of pre-stellar cores where density and temperature reach their maximum and minimum, respectively. Our analysis of the column density PDFs from the Herschel data show double-peak profiles for all parts of the cloud, which we attribute to an external compression. In those parts with active star formation, the PDF shows a power-law tail at high densities. The PDFs we calculated from our LABOCA data trace the denser parts of the cloud showing one peak and a power-law tail. With LABOCA we find 15 cores with masses between 0.07 and 1.71 M⊙ and a total mass of ≈8 M⊙. The total gas and dust mass of the cloud is ≈164 M⊙ and hence ~5% of the mass is in cores. From the Herschel and Planck data we find a total mass of ≈174 M⊙ and ≈171 M⊙, respectively. Conclusions: The position, orientation, and elongated shape of Lupus I, the double-peak PDFs and the population of pre-stellar and protostellar cores could be explained by the large-scale compression from the advancing USco H I shell and the UCL wind bubble. The Atacama Pathfinder Experiment (APEX) is a collaboration between the Max-Planck-Institut für Radioastronomie (MPIfR), the European Southern Observatory (ESO), and the Onsala Space Observatory (OSO).Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Final APEX cube and Herschel N and T maps as FITS files are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/584/A36

Interstellar Gas Flow Vector and Temperature Determination over 5 Years of IBEX Observations

NASA Astrophysics Data System (ADS)

Möbius, E.; Bzowski, M.; Fuselier, S. A.; Heirtzler, D.; Kubiak, M. A.; Kucharek, H.; Lee, M. A.; Leonard, T.; McComas, D. J.; Schwadron, N.; Sokół, J. M.; Wurz, P.

2015-01-01

The Interstellar Boundary Explorer (IBEX) observes the interstellar neutral gas flow trajectories at their perihelion in Earth's orbit every year from December through early April, when the Earth's orbital motion is into the oncoming flow. These observations have defined a narrow region of possible, but very tightly coupled interstellar neutral flow parameters, with inflow speed, latitude, and temperature as well-defined functions of inflow longitude. The best- fit flow vector is different by ≈ 3° and lower by ≈ 3 km/s than obtained previously with Ulysses GAS, but the temperature is comparable. The possible coupled parameter space reaches to the previous flow vector, but only for a substantially higher temperature (by ≈ 2000 K). Along with recent pickup ion observations and including historical observations of the interstellar gas, these findings have led to a discussion, whether the interstellar gas flow into the solar system has been stable or variable over time. These intriguing possibilities call for more detailed analysis and a longer database. IBEX has accumulated observations over six interstellar flow seasons. We review key observations and refinements in the analysis, in particular, towards narrowing the uncertainties in the temperature determination. We also address ongoing attempts to optimize the flow vector determination through varying the IBEX spacecraft pointing and discuss related implications for the local interstellar cloud and its interaction with the heliosphere.

Visualization of airflow growing soap bubbles

NASA Astrophysics Data System (ADS)

Al Rahbi, Hamood; Bock, Matthew; Ryu, Sangjin

2016-11-01

Visualizing airflow inside growing soap bubbles can answer questions regarding the fluid dynamics of soap bubble blowing, which is a model system for flows with a gas-liquid-gas interface. Also, understanding the soap bubble blowing process is practical because it can contribute to controlling industrial processes similar to soap bubble blowing. In this study, we visualized airflow which grows soap bubbles using the smoke wire technique to understand how airflow blows soap bubbles. The soap bubble blower setup was built to mimic the human blowing process of soap bubbles, which consists of a blower, a nozzle and a bubble ring. The smoke wire was placed between the nozzle and the bubble ring, and smoke-visualized airflow was captured using a high speed camera. Our visualization shows how air jet flows into the growing soap bubble on the ring and how the airflow interacts with the soap film of growing bubble.

Double bubble with the big-bubble technique during deep anterior lamellar keratoplasty.

PubMed

Wise, Stephanie; Dubord, Paul; Yeung, Sonia N

2017-04-28

To report a case of intraoperative double bubble that formed during big-bubble DALK surgery in a patient with corneal scarring secondary to herpetic stromal keratitis. Case report. A 22 year old woman presented with a large corneal scar, likely secondary to previous herpetic stromal keratitis. She underwent big-bubble DALK surgery for visual rehabilitation. Intraoperatively, a mixed bubble with persistent type 2 bubble postoperatively was noted. The second bubble resorbed with clearance of the graft and good visual outcome after 6 weeks. This case report describes the unusual development of a mixed bubble during big-bubble DALK surgery. This graft cleared with resolution of the second bubble postoperatively without further surgical intervention.

FTIR Analysis of Aerogel Keystones from the Stardust Interstellar Dust Collector: Assessment of Terrestrial Organic Contamination and X-Ray Microprobe Beam Damage

NASA Astrophysics Data System (ADS)

Bechtel, H. A.; Allen, C.; Bajt, S.; Borg, J.; Brenker, F.; Bridges, J.; Brownlee, D. E.; Burchell, M.; Burghammer, M.; Butterworth, A. L.; Cloetens, P.; Davis, A. M.; Floss, C.; Flynn, G. J.; Frank, D.; Gainsforth, Z.; Grun, E.; Heck, P. R.; Hillier, J. K.; Hoppe, P.; Howard, L.; Huss, G. R.; Huth, J.; Kearsley, A.; King, A. J.; Lai, B.; Leitner, J.; Lemelle, L.; Leroux, H.; Nittler, L. R.; Ogliore, R. C.; Postberg, F.; Price, M. C.; Sandford, S. A.; Sans Tresseras, J. A.; Schmitz, S.; Schoonjans, T.; Silversmit, G.; Simionovici, A.; Srama, R.; Stadermann, F. J.; Stephan, T.; Stodolna, J.; Stroud, R. M.; Sutton, S. R.; Toucoulou, R.; Trieloff, M.; Tsou, P.; Tsuchiyama, A.; Tyliczszak, T.; Vekemans, B.; Vincze, L.; Westphal, A. J.; Zolensky, M. E.; 29,000 Stardust@Home Dusters

2011-03-01

More than 20 aerogel keystones, many of which contained candidates for interstellar dust, were extracted from the Stardust interstellar dust collector and examined with synchrotron FTIR spectromicroscopy.

Towards Probablistic Assessment of Hypobaric Decompression Sickness Treatment

NASA Technical Reports Server (NTRS)

Conkin, J.; Abercromby, A. F.; Feiveson, A. H.; Gernhardt, M. L.; Norcross, J. R.; Ploutz-Snyder, R.; Wessel, J. H., III

2013-01-01

INTRODUCTION: Pressure, oxygen (O2), and time are the pillars to effective treatment of decompression sickness (DCS). The NASA DCS Treatment Model links a decrease in computed bubble volume to the resolution of a symptom. The decrease in volume is realized in two stages: a) during the Boyle's Law compression and b) during subsequent dissolution of the gas phase by the O2 window. METHODS: The cumulative distribution of 154 symptoms that resolved during repressurization was described with a log-logistic density function of pressure difference (deltaP as psid) associated with symptom resolution and two other explanatory variables. The 154 symptoms originated from 119 cases of DCS during 969 exposures in 47 different altitude tests. RESULTS: The probability of symptom resolution [P(symptom resolution)] = 1 / (1+exp(- (ln(deltaP) - 1.682 + 1.089×AMB - 0.00395×SYMPTOM TIME) / 0.633)), where AMB is 1 when the subject ambulated as part of the altitude exposure or else 0 and SYMPTOM TIME is the elapsed time in min from start of the altitude exposure to recognition of a DCS symptom. The P(symptom resolution) was estimated from computed deltaP from the Tissue Bubble Dynamics Model based on the "effective" Boyle's Law change: P2 - P1 (deltaP, psid) = P1×V1/V2 - P1, where V1 is the computed volume of a spherical bubble in a unit volume of tissue at low pressure P1 and V2 is computed volume after a change to a higher pressure P2. V2 continues to decrease through time at P2, at a faster rate if 100% ground level O2 was breathed. The computed deltaP is the effective treatment pressure at any point in time as if the entire ?deltaP was just from Boyle's Law compression. DISCUSSION: Given the low probability of DCS during extravehicular activity and the prompt treatment of a symptom with options through the model it is likely that the symptom and gas phase will resolve with minimum resources and minimal impact on astronaut health, safety, and productivity.

Turbulent aerosol fluxes over the Arctic Ocean: 2. Wind-driven sources from the sea

NASA Astrophysics Data System (ADS)

Nilsson, E. D.; Rannik, Ü.; Swietlicki, E.; Leck, C.; Aalto, P. P.; Zhou, J.; Norman, M.

2001-12-01

An eddy-covariance flux system was successfully applied over open sea, leads and ice floes during the Arctic Ocean Expedition in July-August 1996. Wind-driven upward aerosol number fluxes were observed over open sea and leads in the pack ice. These particles must originate from droplets ejected into the air at the bursting of small air bubbles at the water surface. The source flux F (in 106 m-2 s-1) had a strong dependency on wind speed, log>(F>)=0.20U¯-1.71 and 0.11U¯-1.93, over the open sea and leads, respectively (where U¯ is the local wind speed at about 10 m height). Over the open sea the wind-driven aerosol source flux consisted of a film drop mode centered at ˜100 nm diameter and a jet drop mode centered at ˜1 μm diameter. Over the leads in the pack ice, a jet drop mode at ˜2 μm diameter dominated. The jet drop mode consisted of sea-salt, but oxalate indicated an organic contribution, and bacterias and other biogenic particles were identified by single particle analysis. Particles with diameters less than -100 nm appear to have contributed to the flux, but their chemical composition is unknown. Whitecaps were probably the bubble source at open sea and on the leads at high wind speed, but a different bubble source is needed in the leads owing to their small fetch. Melting of ice in the leads is probably the best candidate. The flux over the open sea was of such a magnitude that it could give a significant contribution to the condensation nuclei (CCN) population. Although the flux from the leads were roughly an order of magnitude smaller and the leads cover only a small fraction of the pack ice, the local source may till be important for the CCN population in Arctic fogs. The primary marine aerosol source will increase both with increased wind speed and with decreased ice fraction and extent. The local CCN production may therefore increase and influence cloud or fog albedo and lifetime in response to greenhouse warming in the Arctic Ocean region.

Challenges in the determination of the interstellar flow longitude from the pickup ion cutoff

NASA Astrophysics Data System (ADS)

Taut, A.; Berger, L.; Möbius, E.; Drews, C.; Heidrich-Meisner, V.; Keilbach, D.; Lee, M. A.; Wimmer-Schweingruber, R. F.

2018-03-01

Context. The interstellar flow longitude corresponds to the Sun's direction of movement relative to the local interstellar medium. Thus, it constitutes a fundamental parameter for our understanding of the heliosphere and, in particular, its interaction with its surroundings, which is currently investigated by the Interstellar Boundary EXplorer (IBEX). One possibility to derive this parameter is based on pickup ions (PUIs) that are former neutral ions that have been ionized in the inner heliosphere. The neutrals enter the heliosphere as an interstellar wind from the direction of the Sun's movement against the partially ionized interstellar medium. PUIs carry information about the spatial variation of their neutral parent population (density and flow vector field) in their velocity distribution function. From the symmetry of the longitudinal flow velocity distribution, the interstellar flow longitude can be derived. Aim. The aim of this paper is to identify and eliminate systematic errors that are connected to this approach of measuring the interstellar flow longitude; we want to minimize any systematic influences on the result of this analysis and give a reasonable estimate for the uncertainty. Methods: We use He+ data measured by the PLAsma and SupraThermal Ion Composition (PLASTIC) sensor on the Solar TErrestrial RElations Observatory Ahead (STEREO A) spacecraft. We analyze a recent approach, identify sources of systematic errors, and propose solutions to eliminate them. Furthermore, a method is introduced to estimate the error associated with this approach. Additionally, we investigate how the selection of interplanetary magnetic field angles, which is closely connected to the pickup ion velocity distribution function, affects the result for the interstellar flow longitude. Results: We find that the revised analysis used to address part of the expected systematic effects obtains significantly different results than presented in the previous study. In particular, the derived uncertainties are considerably larger. Furthermore, an unexpected systematic trend of the resulting interstellar flow longitude with the selection of interplanetary magnetic field orientation is uncovered.

From Interstellar PAHs and Ices to the Origin of Life

NASA Technical Reports Server (NTRS)

Allamandola, Louis J.; DeVincenzi, Donald L. (Technical Monitor)

2000-01-01

Tremendous strides have been made in our understanding of interstellar material over the past twenty years thanks to significant, parallel developments in observational astronomy and laboratory astrophysics. Twenty years ago the composition of interstellar dust was largely guessed at, the concept of ices in dense molecular clouds ignored, and the notion of large, abundant, gas phase, carbon rich molecules widespread throughout the interstellar medium (ISM) considered impossible. Today the composition of dust in the diffuse ISM is reasonably well constrained to micron-sized cold refractory materials comprised of amorphous and crystalline silicates mixed with an amorphous carbonaceous material containing aromatic structural units and short, branched aliphatic chains. In dense molecular clouds, the birthplace of stars and planets, these cold dust particles are coated with mixed molecular ices whose composition is very well constrained. Lastly, the signature of carbon-rich polycyclic aromatic hydrocarbons (PAHs), shockingly large molecules by earlier interstellar chemistry standards, is widespread throughout the Universe. The first part of this lecture will describe how infrared studies of interstellar space, combined with laboratory simulations, have revealed the composition of interstellar ices (the building blocks of comets) and the high abundance and nature of interstellar PAHs. The laboratory database has now enabled us to gain insight into the identities, concentrations, and physical state of many interstellar materials. Within a dense molecular cloud, and especially in the solar nebula during the star and planet formation stage, the materials frozen into interstellar/precometary ices are photoprocessed by ultraviolet light, producing more complex molecules. The remainder of the presentation will focus on the photochemical evolution of these materials and the possible role of these compounds on the early Earth. As these materials are thought to be the building blocks of comets and related to the carbonaceous components of micrometeorites, they are likely to have been important sources of complex organic materials on the early Earth and their composition may be related to the origin of life.

Experimental study on bubble dynamics and wall heat transfer arising from a single nucleation site at subcooled flow boiling conditions – Part 2: Data analysis on sliding bubble characteristics and associated wall heat transfer

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

Yooa, Junsoo; Estrada-Perez, Carlos E.; Hassan, Yassin A.

In this second of two companion papers presents an analysis of sliding bubble and wall heat transfer parameters measured during subcooled boiling in a square, vertical, upward flow channel. Bubbles were generated only from a single nucleation site for better observation of both the sliding bubbles’ characteristics and their impact on wall heat transfer through optical measurement techniques. Specific interests include: (i) bubbles departure and subsequent growth while sliding, (ii) bubbles release frequency, (iii) coalescence of sliding bubbles, (iv) sliding bubbles velocity, (v) bubbles size distribution and (vi) wall heat transfer influenced by sliding bubbles. Our results showed that slidingmore » bubbles involve two distinct growth behaviors: (i) at low mass fluxes, sliding bubbles grew fast near the nucleation site, subsequently shrank, and then grew again, (ii) as mass flux increased, however, sliding bubbles grew more steadily. The bubbles originating from the single nucleation site coalesced frequently while sliding, which showed close relation with bubbles release frequency. The sliding bubble velocity near the nucleation site consistently decreased by increasing mass flux, while the observation often became reversed as the bubbles slid downstream due to the effect of interfacial drag. The sliding bubbles moved faster than the local liquid (i.e., ur<0) at low mass flux conditions, but it became reversed as the mass flux increased. The size distribution of sliding bubbles followed Gaussian distribution well both near and far from the nucleation site. The standard deviation of bubble size varied insignificantly through sliding compared to the changes in mean bubble size. Lastly, the sliding bubbles enhanced the wall heat transfer and the effect became more noticeable as inlet subcooling/mass flux decreased or wall heat flux increased. Particularly, the sliding bubble characteristics such as bubble growth behavior observed near the nucleation site played a dominant role in determining the ultimate level of wall heat transfer enhancement within the test channel.« less

Experimental study on bubble dynamics and wall heat transfer arising from a single nucleation site at subcooled flow boiling conditions – Part 2: Data analysis on sliding bubble characteristics and associated wall heat transfer

DOE PAGES

Yooa, Junsoo; Estrada-Perez, Carlos E.; Hassan, Yassin A.

2016-04-28

In this second of two companion papers presents an analysis of sliding bubble and wall heat transfer parameters measured during subcooled boiling in a square, vertical, upward flow channel. Bubbles were generated only from a single nucleation site for better observation of both the sliding bubbles’ characteristics and their impact on wall heat transfer through optical measurement techniques. Specific interests include: (i) bubbles departure and subsequent growth while sliding, (ii) bubbles release frequency, (iii) coalescence of sliding bubbles, (iv) sliding bubbles velocity, (v) bubbles size distribution and (vi) wall heat transfer influenced by sliding bubbles. Our results showed that slidingmore » bubbles involve two distinct growth behaviors: (i) at low mass fluxes, sliding bubbles grew fast near the nucleation site, subsequently shrank, and then grew again, (ii) as mass flux increased, however, sliding bubbles grew more steadily. The bubbles originating from the single nucleation site coalesced frequently while sliding, which showed close relation with bubbles release frequency. The sliding bubble velocity near the nucleation site consistently decreased by increasing mass flux, while the observation often became reversed as the bubbles slid downstream due to the effect of interfacial drag. The sliding bubbles moved faster than the local liquid (i.e., ur<0) at low mass flux conditions, but it became reversed as the mass flux increased. The size distribution of sliding bubbles followed Gaussian distribution well both near and far from the nucleation site. The standard deviation of bubble size varied insignificantly through sliding compared to the changes in mean bubble size. Lastly, the sliding bubbles enhanced the wall heat transfer and the effect became more noticeable as inlet subcooling/mass flux decreased or wall heat flux increased. Particularly, the sliding bubble characteristics such as bubble growth behavior observed near the nucleation site played a dominant role in determining the ultimate level of wall heat transfer enhancement within the test channel.« less

A Heliosphere Buffeted by Interstellar Turbulence?

NASA Astrophysics Data System (ADS)

Jokipii, J. R.; Giacalone, J.

2014-12-01

Recent observations from IBEX combined with previous measurements from other sources suggest new, local, effects of interstellar turbulence. Observations of various interstellar parameters such as the magnetic field, fluid velocity and electron density, over large spatial scales, have revealed a broadband Kolmogorov spectrum of interstellar turbulence which pervades most of interstellar space. The outer scale (or coherence scale of this turbulence) is found to be approximately 10^19 cm and the inner cutoff scale is less than 1000 km. The root-mean-square relative fluctuation in the fluid and the magnetic-field parameters is of order unity. If this turbulence exists at the heliosphere, the root-mean-square relative fluctuations at 100 (heliospheric) AU scales is approximately 0.1. The recently published value for the change In observed velocity direction for the interstellar flow relative to the heliosphere (Frisch, etal, 2014)is consistent with this. Similarly, interpreting the width of the IBEX ribbon in terms of a fluctuating magnetic field also is in agreement with this picture. Observations of TeV cosmic rays can also be explained. Potential effects of these fluctuations in the interstellar medium on the heliosphere will be discussed. Reference: Frisch, etal, Science, 341, 480

The detection of interstellar C I in the immediate vicinity of the sun

NASA Technical Reports Server (NTRS)

Bruhweiler, F. C.; Kondo, Y.

1982-01-01

Multiple stacked IUE spectra reveal the presence of interstellar C I 1657 in the trough of a corresponding photospheric feature in the nearby star, Alpha PsA (d = 7 pc). This represents the first detection of this neutral atom in the interstellar medium within the immediate vicinity of the sun. It is suggested that C I may be a much better diagnostic tool in studying the local interstellar medium than the neutral species K I and Na I, which are observable at visual wavelengths. Variations in C I column density, coupled with b-values deduced from the Mg II doublet ratio, may prove to be an important means to unravel density and temperature fluctuations in the very local interstellar medium. Comparison of the line of sight toward Alpha PsA with previous Copernicus interstellar Mg II results for that of Alpha Leo tentatively indicates that the distribution of Mg II in the local cloud is not homogeneous about the sun. Rough constraints on the ionization fraction of hydrogen toward Alpha PsA do not conflict with previous data, implying that the very local interstellar medium is significantly ionized.

The demography of extraterrestrial civilizations

NASA Technical Reports Server (NTRS)

Billingham, J.

1981-01-01

Studies carried out within the last ten years on the nature and distribution of extraterrestrial intelligent life are reviewed. Arguments for the absence of intelligent life in the Galaxy based on the assumption that at least some of these would have engaged in colonization and for the presence of colonies of extraterrestrials in some undiscovered location in the solar system are presented, and it is noted that both these views rest on the notion that interstellar travel can be achieved at high velocities in very large vehicles, which has been questioned. Alternative suggestions concerning interstellar exploration by automated probes and the possible extended time scale and motivation for galactic colonization are pointed out. Attention is then given to arguments for the extreme smallness of one of the factors in the Drake equation used to estimate the number of communicative extraterrestrial civilizations in the Galaxy, including the frequency of single stars, the likelihood that planets with the correct initial composition and conditions for life are at the proper distance from their stars, the probability of the formation of DNA and the origin of life, and the time for the evolution of intelligence. It is concluded that it seems likely that other civilizations exist in the Galaxy, although the number and distribution of such civilizations may only be determined by the detection of one or more examples.

Black hole feedback in a multiphase interstellar medium

NASA Astrophysics Data System (ADS)

Bourne, Martin A.; Nayakshin, Sergei; Hobbs, Alexander

2014-07-01

Ultrafast outflows (UFOs) from supermassive black holes (SMBHs) are thought to regulate the growth of SMBHs and host galaxies, resulting in a number of observational correlations. We present high-resolution numerical simulations of the impact of a thermalized UFO on the ambient gas in the inner part of the host galaxy. Our results depend strongly on whether the gas is homogeneous or clumpy. In the former case all of the ambient gas is driven outward rapidly as expected based on commonly used energy budget arguments, while in the latter the flows of mass and energy de-couple. Carrying most of the energy, the shocked UFO escapes from the bulge via paths of least resistance, taking with it only the low-density phase of the host. Most of the mass is however in the high-density phase, and is affected by the UFO much less strongly, and may even continue to flow inwards. We suggest that the UFO energy leakage through the pores in the multiphase interstellar medium (ISM) may explain why observed SMBHs are so massive despite their overwhelmingly large energy production rates. The multiphase ISM effects reported here are probably under-resolved in cosmological simulations but may be included in prescriptions for active galactic nuclei feedback in future simulations and in semi-analytical models.

INTERSTELLAR SONIC AND ALFVENIC MACH NUMBERS AND THE TSALLIS DISTRIBUTION

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

Tofflemire, Benjamin M.; Burkhart, Blakesley; Lazarian, A.

2011-07-20

In an effort to characterize the Mach numbers of interstellar medium (ISM) magnetohydrodynamic (MHD) turbulence, we study the probability distribution functions (PDFs) of spatial increments of density, velocity, and magnetic field for 14 ideal isothermal MHD simulations at a resolution of 512{sup 3}. In particular, we fit the PDFs using the Tsallis function and study the dependency of the fit parameters on the compressibility and magnetization of the gas. We find that the Tsallis function fits PDFs of MHD turbulence well, with fit parameters showing sensitivities to the sonic and Alfven Mach numbers. For three-dimensional density, column density, and Position-Position-Velocitymore » data, we find that the amplitude and width of the PDFs show a dependency on the sonic Mach number. We also find that the width of the PDF is sensitive to the global Alfvenic Mach number especially in cases where the sonic number is high. These dependencies are also found for mock observational cases, where cloud-like boundary conditions, smoothing, and noise are introduced. The ability of Tsallis statistics to characterize the sonic and Alfvenic Mach numbers of simulated ISM turbulence points to it being a useful tool in the analysis of the observed ISM, especially when used simultaneously with other statistical techniques.« less

Passage of a ''Nemesis''-like object through the planetary system

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

Hills, J.G.

1985-09-01

The probability that passing stars could have perturbed the hypothetical stellar companion, Nemesis, into an orbit that penetrates the planetary system is about 15%. The planetary orbits crossed by Nemesis would become highly eccentric, and some would even become hyperbolic. If Nemesis ejects Jupiter from the solar system, the semimajor axis of the orbit of Nemesis would shrink down to a few hundred AU. The probability of any object in the inner edge of the Oort cloud at a semimajor axis of 2 x 10/sup 4/ AU having passed inside the orbit of Saturn is about 80%. The apparent lackmore » of damage to the planetary orbits implies a low probability of there being any objects more massive than 0.02 M/sub sun/ in the inner edge of the Oort comet cloud. However, several objects less massive than 0.01 M/sub sun/ or 10 Jupiter masses could pass through the planetary system from the Oort cloud without causing any significant damage to the planetary orbits. The lack of damage to the planetary system also requires that no black dwarf more massive than 0.05 M/sub sun/ has entered the planetary system from interstellar space.« less

Siphonophores and the Deep Scattering Layer.

PubMed

Barham, E G

1963-05-17

Bathyscaphe dives in the San Diego Trough have revealed a close spatial relation between siphonophores and the deep scattering layer as recorded by precision depth recording echo-sounders. Measurements of gas bubbles within the flotation structures of Nanomia bijuga captured in a closing net in an ascended scattering layer indicate that these are very close to the resonant size for 12-kcy/sec sound. Because such organisms are capable of making prolonged vertical migrations, and are widespread geographically, they are very probably the major cause of stratified zones of scattering throughout the oceans of the world.

Interstellar reddening information system

NASA Astrophysics Data System (ADS)

Burnashev, V. I.; Grigorieva, E. A.; Malkov, O. Yu.

2013-10-01

We describe an electronic bibliographic information system, based on a card catalog, containing some 2500 references (publications of 1930-2009) on interstellar extinction. We have classified the articles according to their content. We present here a list of articles devoted to two categories: maps of total extinction and variation of interstellar extinction with the distance to the object. The catalog is tested using published data on open clusters, and conclusions on the applicability of different maps of interstellar extinctions for various distances are made.

Flow of neutral interstellar helium into the heliosphere as inferred from IBEX-Lo observations and simulations

NASA Astrophysics Data System (ADS)

Bzowski, M.; Kubiak, M. A.; Hlond, M.; Moebius, E.; Leonard, T.; Heirtzler, D.; Kucharek, H.; Bochsler, P. A.; Schwadron, N. A.; Crew, G. B.; McComas, D. J.; Fuselier, S. A.

2010-12-01

Previously, a team coordinated through the International Space Science Institute (ISSI) examined direct neutral gas, pickup ion, and UV backscatter observations to produce consensus values for the inflow direction (λ, β), speed v, and temperature T of neutral interstellar helium from the Local Interstellar Cloud (LIC) with relatively small uncertainties. Since then, NASA’s Interstellar Boundary Explorer (IBEX) has started to provide new observations of the interstellar He flow in Earth orbit, with data currently available from the spring seasons of 2009 and 2010. Using a test-particle simulation to compute the spin-phase distributions that IBEX observes during each orbit, we optimize input LIC parameters to best fit the observations. The simulations take into account actual ionization rates as derived from solar EUV observations by SOHO CELIAS SEM, the OMNI solar wind data set, the positions and velocity vectors of the Earth during the actual integration intervals for each orbit, and the IBEX-Lo field-of-view. The simulations were performed on a grid of bulk flow vectors and temperatures, starting with the ISSI team consensus values based most heavily on Ulysses GAS observations (v = 26.4 km/s, T = 6318 K, and λ = 255.4o, β = -5.31o in J2000 coordinates). The Mach number of the flow derived from the IBEX observations is generally lower than derived from Ulysses measurements, which would be consistent with a higher temperature (up to 10 000 K) and/or a lower flow speed (down to ≈22.5 km/s) of the LIC. Based on these findings, the possible LIC parameter sets most probably lie within a narrow range between (λ = 255.4°, β = 5.3°, v = 26.4 km/s, M = 4.5 or T = 10,000 K) and (λ = 261.2°, β = 4.9, v = 23.05 km/s, M = 4.9, or T = 6300 K). At one end of the acceptable range, the parameters agree with the previous values except for the temperature, and at the other end, the temperatures agree, but the direction is different by almost 6° and the velocity is lower by ≈4 km/s. The simulations appear to agree with the IBEX observations slightly better for the different inflow direction. The results obtained separately from the two passes through the He flow (in 2009 and 2010) are identical within observational uncertainties. Potential reasons for the differences from previous results will be discussed. Any modifications in these critical inflow parameters will require modification of current global heliosphere models. In particular, a reduced flow speed and thus reduced ram pressure would require an increase in the total LIC density and/or the magnetic field strength to maintain pressure balance at the heliopause.

Bubble dynamics and bubble-induced turbulence of a single-bubble chain

NASA Astrophysics Data System (ADS)

Lee, Joohyoung; Park, Hyungmin

2016-11-01

In the present study, the bubble dynamics and liquid-phase turbulence induced by a chain of bubbles injected from a single nozzle have been experimentally investigated. Using a high-speed two-phase particle image velociemtry, measurements on the bubbles and liquid-phase velocity field are conducted in a transparent tank filled with water, while varying the bubble release frequency from 0.1 to 35 Hz. The tested bubble size ranges between 2.0-3.2 mm, and the corresponding bubble Reynolds number is 590-1100, indicating that it belongs to the regime of path instability. As the release frequency increases, it is found that the global shape of bubble dispersion can be classified into two regimes: from asymmetric (regular) to axisymmetric (irregular). In particular, at higher frequency, the wake vortices of leading bubbles cause an irregular behaviour of the following bubble. For the liquid phase, it is found that a specific trend on the bubble-induced turbulence appears in a strong relation to the above bubble dynamics. Considering this, we try to provide a theoretical model to estimate the liquid-phase turbulence induced by a chain of bubbles. Supported by a Grant funded by Samsung Electronics, Korea.

Hubble Supernova Bubble Resembles Holiday Ornament

NASA Image and Video Library

2017-12-08

NASA image release December 14, 2010 A delicate sphere of gas, photographed by NASA's Hubble Space Telescope, floats serenely in the depths of space. The pristine shell, or bubble, is the result of gas that is being shocked by the expanding blast wave from a supernova. Called SNR 0509-67.5 (or SNR 0509 for short), the bubble is the visible remnant of a powerful stellar explosion in the Large Magellanic Cloud (LMC), a small galaxy about 160,000 light-years from Earth. Ripples in the shell's surface may be caused by either subtle variations in the density of the ambient interstellar gas, or possibly driven from the interior by pieces of the ejecta. The bubble-shaped shroud of gas is 23 light-years across and is expanding at more than 11 million miles per hour (5,000 kilometers per second). Astronomers have concluded that the explosion was one of an especially energetic and bright variety of supernovae. Known as Type Ia, such supernova events are thought to result from a white dwarf star in a binary system that robs its partner of material, takes on much more mass than it is able to handle, and eventually explodes. Hubble's Advanced Camera for Surveys observed the supernova remnant on Oct. 28, 2006 with a filter that isolates light from glowing hydrogen seen in the expanding shell. These observations were then combined with visible-light images of the surrounding star field that were imaged with Hubble's Wide Field Camera 3 on Nov. 4, 2010. With an age of about 400 years as seen from Earth, the supernova might have been visible to southern hemisphere observers around the year 1600, however, there are no known records of a "new star" in the direction of the LMC near that time. A more recent supernova in the LMC, SN 1987A, did catch the eye of Earth viewers and continues to be studied with ground- and space-based telescopes, including Hubble. For images and more information about SNR 0509, visit: hubblesite.org/news/2010/27 heritage.stsci.edu/2010/27 www.nasa.gov/hubble The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI) conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA) Acknowledgment: J. Hughes (Rutgers University) NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Join us on Facebook

Atmospheric H2O2 measurement: comparison of cold trap method with impinger bubbling method

NASA Technical Reports Server (NTRS)

Sakugawa, H.; Kaplan, I. R.

1987-01-01

Collection of atmospheric H2O2 was performed by a cold trap method using dry ice-acetone as the refrigerant. The air was drawn by a pump into a glass gas trap immersed in the dry ice-acetone slush in a dewar flask at a flow rate of 2.5 l min-1 for approximately 2 h. Collection efficiency was > 99% and negligible interferences by O3, SO2 or organic matter with the collected H2O2 in the trap were observed. This method was compared with the air impinger bubbling method which has been previously described (Kok et al., 1978a, b, Envir. Sci. Technol. 12, 1072-1080). The measured total peroxide (H2O2 + organic peroxide) values in a series of aim samples collected by the impinger bubbling method (0.06-3.7 ppb) were always higher than those obtained by the cold trap method (0.02-1.2 ppb). Laboratory experiments suggest that the difference in values between the two methods probably results from the aqueous phase generation of H2O2 and organic peroxide in the impinger solution by a reaction of atmospheric O3 with olefinic and aromatic compounds. If these O3-organic compound reactions which occur in the impinger also occur in aqueous droplets in the atmosphere, the process could be very important for aqueous phase generation of H2O2 in clouds and rainwater.

Evaluation of safety of hypobaric decompressions and EVA from positions of probabilistic theory

NASA Astrophysics Data System (ADS)

Nikolaev, V. P.

Formation and subsequent evolution of gas bubbles in blood and tissues of subjects exposed to decompression are casual processes in their nature. Such character of bubbling processes in a body predetermines probabilistic character of decompression sickness (DCS) incidence in divers, aviators and astronauts. Our original probabilistic theory of decompression safety is based on stochastic models of these processes and on the concept of critical volume of a free gas phase in body tissues. From positions of this theory, the probability of DCS incidence during single-stage decompressions and during hypobaric decompressions under EVA in particular, is defined by the distribution of possible values of nucleation efficiency in "pain" tissues and by its critical significance depended on the parameters of a concrete decompression. In the present study the following is shown: 1) the dimensionless index of critical nucleation efficiency for "pain" body tissues is a more adequate index of decompression stress in comparison with Tissue Ratio, TR; 2) a priory the decompression under EVA performed according to the Russian protocol is more safe than decompression under EVA performed in accordance with the U.S. protocol; 3) the Russian space suit operated at a higher pressure and having a higher "rigidity" induces a stronger inhibition of mechanisms of cavitation and gas bubbles formation in tissues of a subject located in it, and by that provides a more considerable reduction of the DCS risk during real EVA performance.

Mixing on the Heard Island Plateau during HEOBI

NASA Astrophysics Data System (ADS)

Robertson, R.

2016-12-01

On the plateau near Heard and McDonald Islands, the water column was nearly always well mixed. Typically, temperature differences between the surface and the bottom, 100-200 m, were less than 0.2oC and often less that 0.1oC. Surface stratification developed through insolation and deep primarily through a combination of upwelling from canyons and over the edge of the plateau and tidal advection. This stratification was primarily removed by a combination of wind and tidal mixing. Persistent winds of 30 knots mixed the upper 20-50 m. Strong wind events, 40-60 knots, mixed the water column to 100-200 m depth, which over the plateau, was often the entire water column. Benthic tidal friction mixed the bottom 30-50 m. Although the water column was unstratified at the two plume sites intensively investigated, tidal velocities were baroclinic, probably due to topographic controls. Tidal advection changed the bottom temperatures by 0.5oC within 8 hours, more than doubling the prior stratification. Wind mixing quickly homogenized the water column, resulting in the surface often showing the deeper upwelling and advective events. Although acoustic plumes with bubbles were observed in the water column, there was no evidence of geothermal vents or geothermal influence on temperatures. Mixing by bubbles rising in the water column was indistinguishable from the wind and tidal mixing, although the strongest upward vertical velocities were observed at the sites of these acoustic/bubble plumes.

Far Ultraviolet Spectroscopy of the Intergalactic and Interstellar Absorption Toward 3C 273

NASA Technical Reports Server (NTRS)

Sembach, Kenneth R.; Howk, J. Christopher; Savage, Blair D.; Shull, J. Michael; Oegerle, William R.; Fisher, Richard R. (Technical Monitor)

2001-01-01

We present Far Ultraviolet Spectroscopic Explorer observations of the molecular, neutral atomic, weakly ionized, and highly ionized components of the interstellar and intergalactic material toward the quasar 3C273. We identify Ly-beta absorption in eight of the known intergalactic Ly-alpha absorbers along the sight line with the rest-frame equivalent widths W(sub r)(Ly-alpha) > 50 micro-angstroms. Refined estimates of the H(I) column densities and Doppler parameters (b) of the clouds are presented. We find a range of b = 16-46 km/s. We detect multiple H(I) lines (Ly-beta - Ly-theta) in the 1590 km/s Virgo absorber and estimate logN(H(I)) = 15.85 +/- 0.10, ten times more H(I) than all of the other absorbers along the sight line combined. The Doppler width of this absorber, b = 16 km/s, implies T < 15,000 K. We detect O(VI) absorption at 1015 km/s at the 2-3(sigma) level that may be associated with hot, X-ray emitting gas in the Virgo Cluster. We detect weak C(III) and O(VI) absorption in the IGM at z=0.12007; this absorber is predominantly ionized and has N(H+)/N(H(I)) > 4000/Z, where Z is the metallicity. Strong Galactic interstellar O(VI) is present between -100 and +100 km/s with an additional high-velocity wing containing about 13% of the total O(VI) between +100 and +240 km/s. The Galactic O(VI), N(V), and C(IV) lines have similar shapes, with roughly constant ratios across the -100 to +100 km/s velocity range. The high velocity O(VI) wing is not detected in other species. Much of the interstellar high ion absorption probably occurs within a highly fragmented medium within the Loop IV remnant or in the outer cavity walls of the remnant. Multiple hot gas production mechanisms are required. The broad O(VI) absorption wing likely traces the expulsion of hot gas out of the Galactic disk into the halo. A flux limit of 5.4 x 10(epx -16) erg/sq cm/s on the amount of diffuse O(VI) emission present = 3.5' off the 3C273 sight line combined with the observed O(VI) column density toward 3C273, logN O(VI) = 14.73 +/- 0.04, implies n(sub e) < 0.02/cubic cm and P/k < 11,500/cubic cm for an assumed temperature of 3 x 10(exp 5) K. The elemental abundances in the neutral and weakly-ionized interstellar clouds are similar to those found for other halo clouds. The warm neutral and warm ionized clouds along the sight line have similar dust-phase abundances, implying that the properties of the dust grains in the two types of clouds are similar. Interstellar H2 absorption is present at positive velocities at a level of logN(H2) = 15.71, but is very weak at the velocities of the main column density concentration along the sight line observed in H(I) 21 cm emission.

Gas Bubble Migration and Trapping in Porous Media: Pore-Scale Simulation

NASA Astrophysics Data System (ADS)

Mahabadi, Nariman; Zheng, Xianglei; Yun, Tae Sup; van Paassen, Leon; Jang, Jaewon

2018-02-01

Gas bubbles can be naturally generated or intentionally introduced in sediments. Gas bubble migration and trapping affect the rate of gas emission into the atmosphere or modify the sediment properties such as hydraulic and mechanical properties. In this study, the migration and trapping of gas bubbles are simulated using the pore-network model extracted from the 3D X-ray image of in situ sediment. Two types of bubble size distribution (mono-sized and distributed-sized cases) are used in the simulation. The spatial and statistical bubble size distribution, residual gas saturation, and hydraulic conductivity reduction due to the bubble trapping are investigated. The results show that the bubble size distribution becomes wider during the gas bubble migration due to bubble coalescence for both mono-sized and distributed-sized cases. And the trapped bubble fraction and the residual gas saturation increase as the bubble size increases. The hydraulic conductivity is reduced as a result of the gas bubble trapping. The reduction in hydraulic conductivity is apparently observed as bubble size and the number of nucleation points increase.

Nonspherical laser-induced cavitation bubbles

NASA Astrophysics Data System (ADS)

Lim, Kang Yuan; Quinto-Su, Pedro A.; Klaseboer, Evert; Khoo, Boo Cheong; Venugopalan, Vasan; Ohl, Claus-Dieter

2010-01-01

The generation of arbitrarily shaped nonspherical laser-induced cavitation bubbles is demonstrated with a optical technique. The nonspherical bubbles are formed using laser intensity patterns shaped by a spatial light modulator using linear absorption inside a liquid gap with a thickness of 40μm . In particular we demonstrate the dynamics of elliptic, toroidal, square, and V-shaped bubbles. The bubble dynamics is recorded with a high-speed camera at framing rates of up to 300000 frames per second. The observed bubble evolution is compared to predictions from an axisymmetric boundary element simulation which provides good qualitative agreement. Interesting dynamic features that are observed in both the experiment and simulation include the inversion of the major and minor axis for elliptical bubbles, the rotation of the shape for square bubbles, and the formation of a unidirectional jet for V-shaped bubbles. Further we demonstrate that specific bubble shapes can either be formed directly through the intensity distribution of a single laser focus, or indirectly using secondary bubbles that either confine the central bubble or coalesce with the main bubble. The former approach provides the ability to generate in principle any complex bubble geometry.

Aspherical bubble dynamics and oscillation times

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

Godwin, R.P.; Chapyak, E.J.; Noack, J.

1999-03-01

The cavitation bubbles common in laser medicine are rarely perfectly spherical and are often located near tissue boundaries, in vessels, etc., which introduce aspherical dynamics. Here, novel features of aspherical bubble dynamics are explored. Time-resolved experimental photographs and simulations of large aspect ratio (length:diameter {approximately}20) cylindrical bubble dynamics are presented. The experiments and calculations exhibit similar dynamics. A small high-pressure cylindrical bubble initially expands radially with hardly any axial motion. Then, after reaching its maximum volume, a cylindrical bubble collapses along its long axis with relatively little radial motion. The growth-collapse period of these very aspherical bubbles differs only sightlymore » from twice the Rayleigh collapse time for a spherical bubble with an equivalent maximum volume. This fact justifies using the temporal interval between the acoustic signals emitted upon bubble creation and collapse to estimate the maximum bubble volume. As a result, hydrophone measurements can provide an estimate of the bubble energy even for aspherical bubbles. The prolongation of the oscillation period of bubbles near solid boundaries relative to that of isolated spherical bubbles is also discussed.« less

Density probability distribution functions of diffuse gas in the Milky Way

NASA Astrophysics Data System (ADS)

Berkhuijsen, E. M.; Fletcher, A.

2008-10-01

In a search for the signature of turbulence in the diffuse interstellar medium (ISM) in gas density distributions, we determined the probability distribution functions (PDFs) of the average volume densities of the diffuse gas. The densities were derived from dispersion measures and HI column densities towards pulsars and stars at known distances. The PDFs of the average densities of the diffuse ionized gas (DIG) and the diffuse atomic gas are close to lognormal, especially when lines of sight at |b| < 5° and |b| >= 5° are considered separately. The PDF of at high |b| is twice as wide as that at low |b|. The width of the PDF of the DIG is about 30 per cent smaller than that of the warm HI at the same latitudes. The results reported here provide strong support for the existence of a lognormal density PDF in the diffuse ISM, consistent with a turbulent origin of density structure in the diffuse gas.

The difficulty of ultraviolet emssion from supernovae

NASA Technical Reports Server (NTRS)

Colgate, S. A.

1971-01-01

There are certain conceptual difficulties in the theory of the generation of ultraviolet radiation which is presumed for the creation of the optical fluorescence mechanism of supernova light emission and ionization of a nebula as large as the Gum nebula. Requirements concerning the energy distribution of the ultraviolet photons are: 1) The energy of the greater part of the photons must be sufficient to cause both helium fluorescence and hydrogen ionization. 2) If the photons are emitted in an approximate black body spectrum, the fraction of energy emitted in the optical must be no more than what is already observed. Ultraviolet black body emission depends primarily on the energy source. The probability that the wide mixture of elements present in the interstellar medium and supernova ejecta results in an emission localized in a limited region with less than 0.001 emission in the visible, for either ionization or fluorescence ultraviolet, is remote. Therefore transparent emission must be excluded as unlikely, and black body or at least quasi-black-body emission is more probable.

Mechanisms for the inversion of chirality: global reaction route mapping of stereochemical pathways in a probable chiral extraterrestrial molecule, 2-aminopropionitrile.

PubMed

Kaur, Ramanpreet; Vikas

2015-02-21

2-Aminopropionitrile (APN), a probable candidate as a chiral astrophysical molecule, is a precursor to amino-acid alanine. Stereochemical pathways in 2-APN are explored using Global Reaction Route Mapping (GRRM) method employing high-level quantum-mechanical computations. Besides predicting the conventional mechanism for chiral inversion that proceeds through an achiral intermediate, a counterintuitive flipping mechanism is revealed for 2-APN through chiral intermediates explored using the GRRM. The feasibility of the proposed stereochemical pathways, in terms of the Gibbs free-energy change, is analyzed at the temperature conditions akin to the interstellar medium. Notably, the stereoinversion in 2-APN is observed to be more feasible than the dissociation of 2-APN and intermediates involved along the stereochemical pathways, and the flipping barrier is observed to be as low as 3.68 kJ/mol along one of the pathways. The pathways proposed for the inversion of chirality in 2-APN may provide significant insight into the extraterrestrial origin of life.

Composition, structure and chemistry of interstellar dust

NASA Technical Reports Server (NTRS)

Tielens, Alexander G. G. M.; Allamandola, Louis J.

1986-01-01

The observational constraints on the composition of the interstellar dust are analyzed. The dust in the diffuse interstellar medium consists of a mixture of stardust (amorphous silicates, amorphous carbon, polycyclic aromatic hydrocarbons, and graphite) and interstellar medium dust (organic refractory material). Stardust seems to dominate in the local diffuse interstellar medium. Inside molecular clouds, however, icy grain mantles are also important. The structural differences between crystalline and amorphous materials, which lead to differences in the optical properties, are discussed. The astrophysical consequences are briefly examined. The physical principles of grain surface chemistry are discussed and applied to the formation of molecular hydrogen and icy grain mantles inside dense molecular clouds. Transformation of these icy grain mantles into the organic refractory dust component observed in the diffuse interstellar medium requires ultraviolet sources inside molecular clouds as well as radical diffusion promoted by transient heating of the mantle. The latter process also returns a considerable fraction of the molecules in the grain mantle to the gas phase.

Analysis of ultraviolet spectrophotometric data from Copernicus

NASA Technical Reports Server (NTRS)

Snow, T. P., Jr.

1979-01-01

Ultraviolet spectral data from the OAO 3 satellite are being used to study interstellar absorption lines and stellar and circumstellar lines in hot stars. The interstellar data are beneficial in analyzing the depletions of heavy elements from the gas phase and in elucidating how these depletions depend on physical conditions. Abundances in separate velocity components were determined from line profiles. Observations were carried out for interstellar abundances, both atomic and molecular, towards a number of stars. The better quality data are being analyzed for profile information and the lesser data are being used in curve-of-growth analyses. Molecular observations were carried out as well, N2 was sought; interstellar C2 was detected and its rotational excitation utilized to establish limits in interstellar cloud temperatures. An extensive search for H2O resulted in a tentative identification which will produce new information on chemical reaction rates. Interstellar depletions and grain properties in the rho Ophiuchi cloud, stellar wind variability, and circumstellar lines are also under study.

The dynamics of histotripsy bubbles

NASA Astrophysics Data System (ADS)

Kreider, Wayne; Bailey, Michael R.; Sapozhnikov, Oleg A.; Khokhlova, Vera A.; Crum, Lawrence A.

2011-09-01

Histotripsy describes treatments in which high-amplitude acoustic pulses are used to excite bubbles and erode tissue. Though tissue erosion can be directly attributed to bubble activity, the genesis and dynamics of bubbles remain unclear. Histotripsy lesions that show no signs of thermal coagulative damage have been generated with two different acoustic protocols: relatively long acoustic pulses that produce local boiling within milliseconds and relatively short pulses that are higher in amplitude but likely do not produce boiling. While these two approaches are often distinguished as `boiling' versus `cavitation', such labels can obscure similarities. In both cases, a bubble undergoes large changes in radius and vapor is transported into and out of the bubble as it oscillates. Moreover, observations from both approaches suggest that bubbles grow to a size at which they cease to collapse violently. In order to better understand the dynamics of histotripsy bubbles, a single-bubble model has been developed that couples acoustically excited bubble motions to the thermodynamic state of the surrounding liquid. Using this model for bubbles exposed to histotripsy sound fields, simulations suggest that two mechanisms can act separately or in concert to lead to the typically observed bubble growth. First, nonlinear acoustic propagation leads to the evolution of shocks and an asymmetry in the positive and negative pressures that drive bubble motion. This asymmetry can have a rectifying effect on bubble oscillations whereby the bubble grows on average during each acoustic cycle. Second, vapor transport to/from the bubble tends to produce larger bubbles, especially at elevated temperatures. Vapor transport by itself can lead to rectified bubble growth when the ambient temperature exceeds 100 °C (`boiling') or local heating in the vicinity of the bubble leads to a superheated boundary layer.

Effects of Ultrasound Frequency and Tissue Stiffness on the Histotripsy Intrinsic Threshold for Cavitation

PubMed Central

Vlaisavljevich, Eli; Lin, Kuang-Wei; Maxwell, Adam; Warnez, Matthew; Mancia, Lauren; Singh, Rahul; Putnam, Andrew J.; Fowlkes, Brian; Johnsen, Eric; Cain, Charles; Xu, Zhen

2015-01-01

Histotripsy is an ultrasound ablation method that depends on the initiation of a cavitation bubble cloud to fractionate soft tissue. Previous work has demonstrated a cavitation cloud can be formed by a single pulse with one high amplitude negative cycle, when the negative pressure amplitude directly exceeds a pressure threshold intrinsic to the medium. We hypothesize that the intrinsic threshold in water-based tissues is determined by the properties of the water inside the tissue and changes in tissue stiffness or ultrasound frequency will have a minimal impact on the histotripsy intrinsic threshold. To test this hypothesis, the histotripsy intrinsic threshold was investigated both experimentally and theoretically. The probability of cavitation was measured by subjecting tissue phantoms with adjustable mechanical properties and ex vivo tissues to a histotripsy pulse of 1–2 cycles produced by 345 kHz, 500 kHz, 1.5 MHz, and 3 MHz histotripsy transducers. Cavitation was detected and characterized by passive cavitation detection and high-speed photography, from which the probability of cavitation was measured vs. pressure amplitude. The results demonstrated that the intrinsic threshold (the negative pressure at which probability=0.5) is independent of stiffness for Young’s moduli (E) < 1 MPa with only a small increase (~2–3 MPa) in the intrinsic threshold for tendon (E=380 MPa). Additionally, results for all samples showed only a small increase of ~2–3 MPa when the frequency was increased from 345 kHz to 3 MHz. The intrinsic threshold was measured to be between 24.7–30.6 MPa for all samples and frequencies tested in this study. Overall, the results of this study indicate that the intrinsic threshold to initiate a histotripsy bubble cloud is not significantly impacted by tissue stiffness or ultrasound frequency in hundreds of kHz to MHz range. PMID:25766571

Effects of ultrasound frequency and tissue stiffness on the histotripsy intrinsic threshold for cavitation.

PubMed

Vlaisavljevich, Eli; Lin, Kuang-Wei; Maxwell, Adam; Warnez, Matthew T; Mancia, Lauren; Singh, Rahul; Putnam, Andrew J; Fowlkes, Brian; Johnsen, Eric; Cain, Charles; Xu, Zhen

2015-06-01

Histotripsy is an ultrasound ablation method that depends on the initiation of a cavitation bubble cloud to fractionate soft tissue. Previous work has indicated that a cavitation cloud can be formed by a single pulse with one high-amplitude negative cycle, when the negative pressure amplitude directly exceeds a pressure threshold intrinsic to the medium. We hypothesize that the intrinsic threshold in water-based tissues is determined by the properties of the water inside the tissue, and changes in tissue stiffness or ultrasound frequency will have a minimal impact on the histotripsy intrinsic threshold. To test this hypothesis, the histotripsy intrinsic threshold was investigated both experimentally and theoretically. The probability of cavitation was measured by subjecting tissue phantoms with adjustable mechanical properties and ex vivo tissues to a histotripsy pulse of 1-2 cycles produced by 345-kHz, 500-kHz, 1.5-MHz and 3-MHz histotripsy transducers. Cavitation was detected and characterized by passive cavitation detection and high-speed photography, from which the probability of cavitation was measured versus pressure amplitude. The results revealed that the intrinsic threshold (the negative pressure at which probability = 0.5) is independent of stiffness for Young's moduli (E) <1 MPa, with only a small increase (∼2-3 MPa) in the intrinsic threshold for tendon (E = 380 MPa). Additionally, results for all samples revealed only a small increase of ∼2-3 MPa when the frequency was increased from 345 kHz to 3 MHz. The intrinsic threshold was measured to be between 24.7 and 30.6 MPa for all samples and frequencies tested in this study. Overall, the results of this study indicate that the intrinsic threshold to initiate a histotripsy bubble cloud is not significantly affected by tissue stiffness or ultrasound frequency in the hundreds of kilohertz to megahertz range. Copyright © 2015 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Size distribution of dust grains: A problem of self-similarity

NASA Technical Reports Server (NTRS)

Henning, TH.; Dorschner, J.; Guertler, J.

1989-01-01

Distribution functions describing the results of natural processes frequently show the shape of power laws, e.g., mass functions of stars and molecular clouds, velocity spectrum of turbulence, size distributions of asteroids, micrometeorites and also interstellar dust grains. It is an open question whether this behavior is a result simply coming about by the chosen mathematical representation of the observational data or reflects a deep-seated principle of nature. The authors suppose the latter being the case. Using a dust model consisting of silicate and graphite grains Mathis et al. (1977) showed that the interstellar extinction curve can be represented by taking a grain radii distribution of power law type n(a) varies as a(exp -p) with 3.3 less than or equal to p less than or equal to 3.6 (example 1) as a basis. A different approach to understanding power laws like that in example 1 becomes possible by the theory of self-similar processes (scale invariance). The beta model of turbulence (Frisch et al., 1978) leads in an elementary way to the concept of the self-similarity dimension D, a special case of Mandelbrot's (1977) fractal dimension. In the frame of this beta model, it is supposed that on each stage of a cascade the system decays to N clumps and that only the portion beta N remains active further on. An important feature of this model is that the active eddies become less and less space-filling. In the following, the authors assume that grain-grain collisions are such a scale-invarient process and that the remaining grains are the inactive (frozen) clumps of the cascade. In this way, a size distribution n(a) da varies as a(exp -(D+1))da (example 2) results. It seems to be highly probable that the power law character of the size distribution of interstellar dust grains is the result of a self-similarity process. We can, however, not exclude that the process leading to the interstellar grain size distribution is not fragmentation at all. It could be, e.g., diffusion-limited growth discussed by Sander (1986), who applied the theory of fractal geometry to the classification of non-equilibrium growth processes. He received D=2.4 for diffusion-limited aggregation in 3d-space.

Vapor Bubbles

NASA Astrophysics Data System (ADS)

Prosperetti, Andrea

2017-01-01

This article reviews the fundamental physics of vapor bubbles in liquids. Work on bubble growth and condensation for stationary and translating bubbles is summarized and the differences with bubbles containing a permanent gas stressed. In particular, it is shown that the natural frequency of a vapor bubble is proportional not to the inverse radius, as for a gas bubble, but to the inverse radius raised to the power 2/3. Permanent gas dissolved in the liquid diffuses into the bubble with strong effects on its dynamics. The effects of the diffusion of heat and mass on the propagation of pressure waves in a vaporous bubbly liquid are discussed. Other topics briefly touched on include thermocapillary flow, plasmonic nanobubbles, and vapor bubbles in an immiscible liquid.

Anti-Bubbles

NASA Astrophysics Data System (ADS)

Tufaile, Alberto; Sartorelli, José Carlos

2003-08-01

An anti-bubble is a striking kind of bubble in liquid that seemingly does not comply the buoyancy, and after few minutes it disappears suddenly inside the liquid. Different from a simple air bubble that rises directly to the liquid surface, an anti-bubble wanders around in the fluid due to its slightly lesser density than the surrounding liquid. In spite of this odd behavior, an anti-bubble can be understood as the opposite of a conventional soap bubble in air, which is a shell of liquid surrounding air, and an anti-bubble is a shell of air surrounding a drop of the liquid inside the liquid. Two-phase flow has been a subject of interest due to its relevance to process equipment for contacting gases and liquids applied in industry. A chain of bubbles rising in a liquid formed from a nozzle is a two-phase flow, and there are certain conditions in which spherical air shells, called anti-bubbles, are produced. The purpose of this work is mainly to note the existence of anti-bubbling regime as a sequel of a bubbling system. We initially have presented the experimental apparatus. After this we have described the evolution of the bubbling regimes, and emulated the effect of bubbling coalescence with simple maps. Then is shown the inverted dripping as a consequence of the bubble coalescence, and finally the conditions for anti-bubble formation.

Boundary conditions for the paleoenvironment: Chemical and physical processes in the pre-solar nebula. [molecular clouds, interstellar matter, and abundance

NASA Technical Reports Server (NTRS)

Irvine, W. M.; Schloerb, F. P.

1985-01-01

Two additional hyperfine components of the interstellar radical C3H were detected. In addition, methanol was discovered in interstellar clouds. The abundance of HCCN and various chemical isomers in molecular clouds was investigated.

Monte Carlo simulation of spectral reflectance and BRDF of the bubble layer in the upper ocean.

PubMed

Ma, Lanxin; Wang, Fuqiang; Wang, Chengan; Wang, Chengchao; Tan, Jianyu

2015-09-21

The presence of bubbles can significantly change the radiative properties of seawater and these changes will affect remote sensing and underwater target detection. In this work, the spectral reflectance and bidirectional reflectance characteristics of the bubble layer in the upper ocean are investigated using the Monte Carlo method. The Hall-Novarini (HN) bubble population model, which considers the effect of wind speed and depth on the bubble size distribution, is used. The scattering coefficients and the scattering phase functions of bubbles in seawater are calculated using Mie theory, and the inherent optical properties of seawater for wavelengths between 300 nm and 800 nm are related to chlorophyll concentration (Chl). The effects of bubble coating, Chl, and bubble number density on the spectral reflectance of the bubble layer are studied. The bidirectional reflectance distribution function (BRDF) of the bubble layer for both normal and oblique incidence is also investigated. The results show that bubble populations in clear waters under high wind speed conditions significantly influence the reflection characteristics of the bubble layer. Furthermore, the contribution of bubble populations to the reflection characteristics is mainly due to the strong backscattering of bubbles that are coated with an organic film.

A multiwavelength study of the Eridanus soft X-ray enhancement

NASA Technical Reports Server (NTRS)

Burrows, D. N.; Singh, K. P.; Nousek, J. A.; Garmire, G. P.; Good, J.

1993-01-01

We present soft X-ray, N(H), and IR maps of the Eridanus soft X-ray enhancement. Soft X-ray maps from the HEAO 1 A-2 LED experiment, processed with a maximum entropy method (MEM) algorithm, show that the enhancement consists of two distinct components: a large hook-shaped component and a small circular component at different temperatures. Both of these are located in 'holes' in the IR emission, and they correspond to N(H) features at very different velocities. The dust surrounding the X-ray enhancements appears to be associated with several high-latitude molecular clouds, which allow us to obtain a probable distance of about 130 pc to the near edge of the main enhancement. The total power emitted by the hot gas is then about 10 exp 35 to 10 exp 36 ergs/s. We consider alternative interpretations of these objects as adiabatic supernova remnants or as stellar wind bubbles and conclude that they are more likely to be stellar wind bubbles, possibly reheated by a SN explosion in the case of the main, hook-shaped object.

Influence of liquid medium on the activity of a low-alpha Fischer-Tropsch catalyst

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

Gormley, R.J.; Zarochak, M.F.; Deffenbaugh, P.W.

1995-12-31

The purpose of this research was to measure activity, selectivity, and the maintenance of these properties in slurry autoclave experiments with a Fischer-Tropsch (FT) catalyst that was used in the {open_quotes}FT II{close_quotes} bubble-column test, conducted at the Alternative Fuels Development Unit (AFDU) at LaPorte, Texas during May 1994. The catalyst contained iron, copper, and potassium and was formulated to produce mainly hydrocarbons in the gasoline range with lesser production of diesel-range products and wax. The probability of chain growth was thus deliberately kept low. Principal goals of the autoclave work have been to find the true activity of this catalystmore » in a stirred tank reactor, unhindered by heat or mass transfer effects, and to obtain a steady conversion and selectivity over the approximately 15 days of each test. Slurry autoclave testing of the catalyst in heavier waxes also allows insight into operation of larger slurry bubble column reactors. The stability of reactor operation in these experiments, particularly at loadings exceeding 20 weight %, suggests the likely stability of operations on a larger scale.« less

Compatible atmospheres for a space suit, Space Station, and Shuttle based on physiological principles

NASA Technical Reports Server (NTRS)

Hills, B. A.

1985-01-01

Fundamental physiological principles have been invoked to design compatible environments for a space suit, Space Station and the spacecraft used to transport the astronauts from earth. These principles include the long-term memory of tissues for a bubble-provoking decompression, the intermittent nature of blood flow in the tight connective tissue(s) responsible for the bends whose incidence in aviators has been shown to be related to bubble volume by the Weibull distribution. In the overall design an astronaut breathing a mixture of 30 percent O2 in N2 for 4-5 h in a spacecraft at 11.9 psia can transfer to a Space Station filled with the same mix at 8.7 psia and, after a further 4-5 h, go EVA at any time without any oxygen prebreathing at any stage. The probable incidence of decompression sickness has been estimated as less than 0.5 percent using the present suit operating at 4.3 psia but the risk could be reduced to zero if the suit pressure were increased to 6.5 psia.

Sonoluminescence in an Acoustically Levitated Water Filled Shell

NASA Astrophysics Data System (ADS)

Rivera, P. J.; Stephens, R. B.; Jones, J. P.

1998-11-01

The possibility of using shells levitated by acoustic waves to improve the conditions to study sonoluminescence was conducted. Single bubble sonoluminescence (SBSL) was generated using a 2 mm diameter water filled plastic shell, supported in air with 1 MHz sound waves. The bubble was generated and compressed with a separate transducer emitting pulsed 5 MHz acoustic waves which were focussed on the center of the suspended shell. This approach is considerably different from the typical generation technique of SBSL in that the acoustic power is coupled through the air rather than by a solid bond to the container. With this configuration, the water container can be substantially reduced in size and the luminescence pulse rate is probably not connected with cavity resonances. As a result, optical access to the spark is improved, water attenuation is reduced (water thickness ~1 mm), and repetition rate can be considerably higher. This geometry presents problems and opportunities in controlling the gas content and temperature of the water. It might also be sensitive to the perfection of the enclosing plastic shell, so success is erratic. Details will be discussed.

The Einstein objective grating spectrometer survey of galactic binary X-ray sources

NASA Technical Reports Server (NTRS)

Vrtilek, S. D.; Mcclintock, J. E.; Seward, F. D.; Kahn, S. M.; Wargelin, B. J.

1991-01-01

The results of observations of 22 bright Galactic X-ray point sources are presented, and the most reliable measurements to date of X-ray column densities to these sources are derived. The results are consistent with the idea that some of the objects have a component of column density intrinsic to the source in addition to an interstellar component. The K-edge absorption due to oxygen is clearly detected in 10 of the sources and the Fe L and Ne K edges are detected in a few. The spectra probably reflect emission originating in a collisionally excited region combined with emission from a photoionized region excited directly by the central source.

Strong stellar winds.

PubMed

Conti, P S; McCray, R

1980-04-04

The hottest and most luminous stars lose a substantial fraction of their mass in strong stellar winds. These winds not only affect the evolution of the star, they also carve huge expanding cavities in the surrounding interstellar medium, possibly affecting star formation. The winds are probably driven by radiation pressure, but uncertainties persist in their theoretical description. Strong x-ray sources associated with a few of these hot stars may be used to probe the stellar winds. The nature of the weak x-ray sources recently observed to be associated with many of these stars is uncertain. It is suggested that roughly 10 percent of the luminous hot stars may have as companions neutron stars or black holes orbiting within the stellar winds.

Bursting star formation and the overabundance of Wolf-Rayet stars

NASA Technical Reports Server (NTRS)

Bodigfee, G.; Deloore, C.

1985-01-01

The ratio of the number of WR-stars to their OB progenitors appears to be significantly higher in some extragalactic systems than in our Galaxy. This overabundance of Wolf-Rayet-stars can be explained as a consequence of a recent burst of star formation. It is suggested that this burst is the manifestation of a long period nonlinear oscillation in the star formation process, produced by positive feedback effects between young stars and the interstellar medium. Star burst galaxies with large numbers of WR-stars must generate gamma - fluxes but due to the distance, all of them are beyond the reach of present-day ray detectors, except probably 30 Dor.

The Effect of Hawking Radation on Fermion Re-Inflation of a Schwartszchild Kugelblitz

NASA Astrophysics Data System (ADS)

Lee, J. S.

The implementation of laser-created subatomic black holes (Schwarzschild Kugelblitzes or SKs) as propulsive and power sources for interstellar starships has been presented in the literature [l]. SKs with life expectancies of only several years resulting from petawatt Hawking Radiation suggest the appeal of a mechanism to "re-inflate" the SK. This paper calculates the absorption cross-sections and absorption probabilities of attometer Schwarzschild Kugelblitzes, and demonstrates the need for incoming inflating particles to have an energy in the TeV-PeV range. The interaction between collimated re-inflating fermions and the instantaneous spectrum of Hawking radiation, and the challenges associated with subnuclear-scale beam collimation are examined.

Voyager 1: Three "Tsunami Waves" in Interstellar Space

NASA Image and Video Library

2017-03-22

Voyager 1: Three "Tsunami Waves" in Interstellar Space. The Voyager 1 spacecraft has experienced three "tsunami waves" in interstellar space. Listen to how these waves cause surrounding ionized matter to ring. More details on this sound can be found here: www.nasa.gov/jpl/nasa-voyager-t…nterstellar-space/

Instellar grains within interstellar grains

NASA Technical Reports Server (NTRS)

Bernatowicz, Thomas J.; Amari, Sachiko; Zinner, Ernst K.; Lewis, Roy S.

1991-01-01

The discovery of crystals of titanium carbide in an interstellar graphite spherule is reported. The new species is particularly interesting in that it came in a protective wrapping (the graphite spherule) which eliminated the possibility of chemical alteration during its residence in the interstellar medium and in the meteorite in which it was discovered.

Correlation properties of interstellar dust: Diffuse interstellar bands

NASA Technical Reports Server (NTRS)

Somerville, W. B.

1989-01-01

Results are presented from a research program in which an attempt was made to establish the physical nature of the interstellar grains, and the carriers of the diffuse interstellar bands, by comparing relations between different observed properties; the properties used include the extinction in the optical and ultraviolet (including wavelength 2200 and the far-UV rise), cloud density, atomic depletions, and strengths of the diffuse bands. Observations and also data from literature were used, selecting particularly sight-lines where some observed property was found to have anomalous behavior.

Chemical abundances in cold, dark interstellar clouds

NASA Technical Reports Server (NTRS)

Irvine, William M.; Kaifu, Norio; Ohishi, Masatoshi

1991-01-01

Current tabulations are presented of the entire range of known interstellar molecules, giving attention to that subset which has been identified in the cold, dark interstellar clouds out of which the sun has been suggested to have formed. The molecular abundances of two such clouds, Taurus Molecular Cloud 1 and Lynd's 134N, exhibit prepossessing chemical differences despite considerable physical similarities. This discrepancy may be accounted for by the two clouds' differing evolutionary stages. Two novel classes of interstellar molecules are noted: sulfur-terminated carbon chains and silicon-terminated ones.

Cometary and interstellar dust grains - Analysis by ion microprobe mass spectrometry and other techniques

NASA Technical Reports Server (NTRS)

Zinner, Ernst

1991-01-01

A survey of microanalytical measurements on interplanetary dust particles (IDPs) and interstellar dust grains from primitive meteorites is presented. Ion-microprobe mass spectrometry with its capability to determine isotopic compositions of many elements on a micron spatial scale has played a special role. Examples are measurements of H, N, and O isotopes and refractory trace elements in IDPs; C, N, Mg, and Si isotopes in interstellar SiC grains; and C and N isotopes and H, N, Al, and Si concentrations in interstellar graphite grains.

Radioastronomical Searches for Instellar Biomolecules

NASA Technical Reports Server (NTRS)

Kuan, Y.-J.; Huang, H.-C.; Charnley, S. B.; Markwick, A.; Botta, O.; Ehrenfreund, P.; Kisiel, Z.; Butner, H. M.

2003-01-01

Impacts of comets and asteroids could have delivered large amounts of organic matter to the early Earth. to retain a significant interstellar signature; observations of recent bright comets indicate that they have a molecular inventory consistent with their ices being largely unmodified interstellar material. Many simple organic molecules with biochemical significance observed in circumstellar envelopes and in molecular clouds, similar to that from which the Solar System formed, may have acted as the precursors of the more complex organics found in meteorites. Therefore, there is potentially a strong link between interstellar organics and prebiotic chemical evolution. Radioastronomical observations, particularly at millimeter wavelengths, allow us to determine the chemical composition and characteristics of the molecular inventory in interstellar space. Here we report some of our recent results from extensive astronomical searches for astrobiologically-important interstellar organics.

The Laboratory Production of Complex Organic Molecules in Simulated Interstellar Ices

NASA Technical Reports Server (NTRS)

Dworkin, J. P.; Sandford, S. A.; Bernstein, M. P.; Allamandola, L. J.

2002-01-01

Much of the volatiles in interstellar dense clouds exist in ices surrounding dust grains. Their low temperatures preclude most chemical reactions, but ionizing radiation can drive reactions that produce a suite of new species, many of which are complex organics. The Astrochemistry Lab at NASA Ames studies the UV radiation processing of interstellar ice analogs to better identify the resulting products and establish links between interstellar chemistry, the organics in meteorites, and the origin of life on Earth. Once identified, the spectral properties of the products can be quantified to assist with the search for these species in space. Of particular interest are findings that UV irradiation of interstellar ice analogs produces molecules of importance in current living organisms, including quinones, amphiphiles, and amino acids.

Experimental interstellar organic chemistry: Preliminary findings

NASA Technical Reports Server (NTRS)

Khare, B. N.; Sagan, C.

1971-01-01

In a simulation of interstellar organic chemistry in dense interstellar clouds or on grain surfaces, formaldehyde, water vapor, ammonia and ethane are deposited on a quartz cold finger and ultraviolet-irradiated in high vacuum at 77K. The HCHO photolytic pathway which produces an aldehyde radical and a superthermal hydrogen atom initiates solid phase chain reactions leading to a range of new compounds, including methanol, ethanol, acetaldehyde, acetonitrile, acetone, methyl formate, and possibly formic acid. Higher nitriles are anticipated. Genetic relations among these interstellar organic molecules (e.g., the Cannizzaro and Tischenko reactions) must exist. Some of them, rather than being synthesized from smaller molecules, may be degradation products of larger organic molecules, such as hexamethylene tetramine, which are candidate consitituents of the interstellar grains. The experiments reported here may also be relevant to cometary chemistry.

The Evolution of Dust in the Multiphase Interstellar Medium

NASA Technical Reports Server (NTRS)

Oliversen, Ronald J. (Technical Monitor); Slavin, Jonathan

2003-01-01

Interstellar dust has a profound effect on the structure and evolution of the interstellar medium (ISM) and on the processes by which stars form from it. Dust obscures regions of star formation from view, and the uncertain quantities of elements in dust makes it difficult to measure accurately the abundances of the elements in low density regions. Despite the central importance of dust in astrophysics, we cannot answer some of the most basic questions about it: Why is it that most of the refractory elements are in dust grains? What determines the sizes of interstellar grains? It has been the goal of our proposed theoretical investigations to address these questions by studying the destruction of interstellar grains, and to develop observational diagnostics that can test the models we develop.

Instellar Gas Experiment (IGE): Testing interstellar gas particles to provide information on the processes of nucleosynthesis in the big bang stars and supernova

NASA Technical Reports Server (NTRS)

Lind, Don

1985-01-01

The Interstellar Gas Experiment (IGE) is designed to collect particles of the interstellar gas - a wind of interstellar media particles moving in the vicinity of the solar system. These particles will be returned to earth where the isotopic ratios of the noble gases among these particles will be measured. IGE was designed and programmed to expose 7 sets of six copper-beryllium metallic collecting foils to the flux of neutral interstellar gas particles which penetrate the heliosphere to the vicinity of the earth's orbit. These particles are trapped in the collecting foils and will be returned to earth for mass-spectrographic analysis when Long Duration Exposure Facility (LDEF) on which IGE was launched, is recovered.

Vibrational Spectroscopy after OSU - From C2- to Interstellar Polycyclic Aromatic Hydrocarbons

NASA Technical Reports Server (NTRS)

Allamandola, Louis J.

2006-01-01

The composition of interstellar ice and dust provides insight into the chemical history of the interstellar medium and early solar system. It is now possible to probe this unique and unusual chemistry and determine the composition of these microscopic interstellar particles which are hundreds to many thousands of light years away thanks to substantial progress in two areas: astronomical spectroscopic techniques in the middle-infrared, the spectral region most diagnostic of chemical composition, and laboratory simulations which realistically reproduce the critical conditions in various interstellar environments. High quality infrared spectra of many different astronomical sources, some associated with giant, dark molecular clouds -the birthplace of stars and planets- and others in more tenuous, UV radiation rich regions are now available. The fundamentals of IR spectroscopy and what comparisons of astronomical IR spectra with laboratory spectra of materials prepared under realistic simulated interstellar conditions tell us about the components of these materials is the subject of this talk. These observations have shown that mixed molecular ices comprised of H2O, CH3OH, CO, NH3 and H2CO contain most of the molecular material in molecular clouds and that gas phase, ionized polycyclic aromatic hydrocarbons (PAHs) are widespread and surprisingly abundant throughout most of the interstellar medium.

Complex Organics from Laboratory Simulated Interstellar Ices

NASA Technical Reports Server (NTRS)

Dworkin, J. P.

2003-01-01

Many of the volatiles in interstellar dense clouds exist in ices surrounding dust grains. The low temperatures of these ices (T < 50 K) preclude most chemical reactions, but photolysis can drive reactions that produce a suite of new species, many of which are complex organics. We study the UV and proton radiation processing of interstellar ice analogs to explore links between interstellar chemistry, the organics in comets and meteorites, and the origin of life on Earth. The high D/H ratios in some interstellar species, and the knowledge that many of the organics in primitive meteorites are D-enriched, suggest that such links are plausible. Once identified, these species may serve as markers of interstellar heritage of cometary dust and meteorites. Of particular interest are our findings that UV photolysis of interstellar ice analogs produce molecules of importance in current living organisms, including quinones, amphiphiles, and amino acids. Quinones are essential in vital metabolic roles such as electron transport. Studies show that quinones should be made wherever polycyclic aromatic hydrocarbons are photolyzed in interstellar ices. In the case of anthracene-containing ices, we have observed the production of 9-anthrone and 9,10 anthraquinone, both of which have been observed in the Murchison meteorite. Amphiphiles are also made when mixed molecular ices are photolyzed. These amphiphiles self-assemble into fluorescent vesicles when placed in liquid water, as do Murchison extracts. Both have the ability to trap an ionic dye. Photolysis of plausible ices can also produce alanine, serine, and glycine as well as a number of small alcohols and amines. Flash heating of the room temperature residue generated by such experiments generates mass spectral distributions similar to those of IDPs. The detection of high D/H ratios in some interstellar molecular species, and the knowledge that many of the organics, such as hydroxy and amino acids, in primitive meteorites are D-enriched provides evidence for a connection between intact organic material in the interstellar medium and in meteorites. Thus, some of the oxidized aromatics, amphiphiles, amino acids, hydroxy acids, and other compounds found in meteorites may have had an interstellar ancestry and not solely a product of parent body aqueous alteration. Such compounds should also be targeted for searches of organics in cometary dust.

Bubbles in an acoustic field: an overview.

PubMed

Ashokkumar, Muthupandian; Lee, Judy; Kentish, Sandra; Grieser, Franz

2007-04-01

Acoustic cavitation is the fundamental process responsible for the initiation of most of the sonochemical reactions in liquids. Acoustic cavitation originates from the interaction between sound waves and bubbles. In an acoustic field, bubbles can undergo growth by rectified diffusion, bubble-bubble coalescence, bubble dissolution or bubble collapse leading to the generation of primary radicals and other secondary chemical reactions. Surface active solutes have been used in association with a number of experimental techniques in order to isolate and understand these activities. A strobe technique has been used for monitoring the growth of a single bubble by rectified diffusion. Multibubble sonoluminescence has been used for monitoring the growth of the bubbles as well as coalescence between bubbles. The extent of bubble coalescence has also been monitored using a newly developed capillary technique. An overview of the various experimental results has been presented in order to highlight the complexities involved in acoustic cavitation processes, which on the other hand arise from a simple, mechanical interaction between sound waves and bubbles.

Bubbles with shock waves and ultrasound: a review.

PubMed

Ohl, Siew-Wan; Klaseboer, Evert; Khoo, Boo Cheong

2015-10-06

The study of the interaction of bubbles with shock waves and ultrasound is sometimes termed 'acoustic cavitation'. It is of importance in many biomedical applications where sound waves are applied. The use of shock waves and ultrasound in medical treatments is appealing because of their non-invasiveness. In this review, we present a variety of acoustics-bubble interactions, with a focus on shock wave-bubble interaction and bubble cloud phenomena. The dynamics of a single spherically oscillating bubble is rather well understood. However, when there is a nearby surface, the bubble often collapses non-spherically with a high-speed jet. The direction of the jet depends on the 'resistance' of the boundary: the bubble jets towards a rigid boundary, splits up near an elastic boundary, and jets away from a free surface. The presence of a shock wave complicates the bubble dynamics further. We shall discuss both experimental studies using high-speed photography and numerical simulations involving shock wave-bubble interaction. In biomedical applications, instead of a single bubble, often clouds of bubbles appear (consisting of many individual bubbles). The dynamics of such a bubble cloud is even more complex. We shall show some of the phenomena observed in a high-intensity focused ultrasound (HIFU) field. The nonlinear nature of the sound field and the complex inter-bubble interaction in a cloud present challenges to a comprehensive understanding of the physics of the bubble cloud in HIFU. We conclude the article with some comments on the challenges ahead.

Bubbles with shock waves and ultrasound: a review

PubMed Central

Ohl, Siew-Wan; Klaseboer, Evert; Khoo, Boo Cheong

2015-01-01

The study of the interaction of bubbles with shock waves and ultrasound is sometimes termed ‘acoustic cavitation'. It is of importance in many biomedical applications where sound waves are applied. The use of shock waves and ultrasound in medical treatments is appealing because of their non-invasiveness. In this review, we present a variety of acoustics–bubble interactions, with a focus on shock wave–bubble interaction and bubble cloud phenomena. The dynamics of a single spherically oscillating bubble is rather well understood. However, when there is a nearby surface, the bubble often collapses non-spherically with a high-speed jet. The direction of the jet depends on the ‘resistance' of the boundary: the bubble jets towards a rigid boundary, splits up near an elastic boundary, and jets away from a free surface. The presence of a shock wave complicates the bubble dynamics further. We shall discuss both experimental studies using high-speed photography and numerical simulations involving shock wave–bubble interaction. In biomedical applications, instead of a single bubble, often clouds of bubbles appear (consisting of many individual bubbles). The dynamics of such a bubble cloud is even more complex. We shall show some of the phenomena observed in a high-intensity focused ultrasound (HIFU) field. The nonlinear nature of the sound field and the complex inter-bubble interaction in a cloud present challenges to a comprehensive understanding of the physics of the bubble cloud in HIFU. We conclude the article with some comments on the challenges ahead. PMID:26442143

Bubble dynamics in a standing sound field: the bubble habitat.

PubMed

Koch, P; Kurz, T; Parlitz, U; Lauterborn, W

2011-11-01

Bubble dynamics is investigated numerically with special emphasis on the static pressure and the positional stability of the bubble in a standing sound field. The bubble habitat, made up of not dissolving, positionally and spherically stable bubbles, is calculated in the parameter space of the bubble radius at rest and sound pressure amplitude for different sound field frequencies, static pressures, and gas concentrations of the liquid. The bubble habitat grows with static pressure and shrinks with sound field frequency. The range of diffusionally stable bubble oscillations, found at positive slopes of the habitat-diffusion border, can be increased substantially with static pressure.

How many bubbles in your glass of bubbly?

PubMed

Liger-Belair, Gérard

2014-03-20

The issue about how many carbon dioxide bubbles are likely to nucleate in a glass of champagne (or bubbly) is of concern for sommeliers, wine journalists, experienced tasters, and any open minded physical chemist wondering about complex phenomena at play in a glass of bubbly. The whole number of bubbles likely to form in a single glass is the result of the fine interplay between dissolved CO2, tiny gas pockets trapped within particles acting as bubble nucleation sites, and ascending bubble dynamics. Based on theoretical models combining ascending bubble dynamics and mass transfer equations, the falsely naı̈ve question of how many bubbles are likely to form per glass is discussed in the present work. A theoretical relationship is derived, which provides the whole number of bubbles likely to form per glass, depending on various parameters of both the wine and the glass itself.

Venous gas embolism after an open-water air dive and identical repetitive dive.

PubMed

Schellart, N A M; Sterk, W

2012-01-01

Decompression tables indicate that a repetitive dive to the same depth as a first dive should be shortened to obtain the same probability of occurrence of decompression sickness (pDCS). Repetition protocols are based on small numbers, a reason for re-examination. Since venous gas embolism (VGE) and pDCS are related, one would expect a higher bubble grade (BG) of VGE after the repetitive dive without reducing bottom time. BGs were determined in 28 divers after a first and an identical repetitive air dive of 40 minutes to 20 meters of sea water. Doppler BG scores were transformed to log number of bubbles/cm2 (logB) to allow numerical analysis. With a previously published model (Model2), pDCS was calculated for the first dive and for both dives together. From pDCS, theoretical logBs were estimated with a pDCS-to-logB model constructed from literature data. However, pDCS the second dive was provided using conditional probability. This was achieved in Model2 and indirectly via tissue saturations. The combination of both models shows a significant increase of logB after the second dive, whereas the measurements showed an unexpected lower logB. These differences between measurements and model expectations are significant (p-values < 0.01). A reason for this discrepancy is uncertain. The most likely speculation would be that the divers, who were relatively old, did not perform physical activity for some days before the first dive. Our data suggest that, wisely, the first dive after a period of no exercise should be performed conservatively, particularly for older divers.

Using a Novel Optical Sensor to Characterize Methane Ebullition Processes

NASA Astrophysics Data System (ADS)

Delwiche, K.; Hemond, H.; Senft-Grupp, S.

2015-12-01

We have built a novel bubble size sensor that is rugged, economical to build, and capable of accurately measuring methane bubble sizes in aquatic environments over long deployment periods. Accurate knowledge of methane bubble size is important to calculating atmospheric methane emissions from in-land waters. By routing bubbles past pairs of optical detectors, the sensor accurately measures bubbles sizes for bubbles between 0.01 mL and 1 mL, with slightly reduced accuracy for bubbles from 1 mL to 1.5 mL. The sensor can handle flow rates up to approximately 3 bubbles per second. Optional sensor attachments include a gas collection chamber for methane sampling and volume verification, and a detachable extension funnel to customize the quantity of intercepted bubbles. Additional features include a data-cable running from the deployed sensor to a custom surface buoy, allowing us to download data without disturbing on-going bubble measurements. We have successfully deployed numerous sensors in Upper Mystic Lake at depths down to 18 m, 1 m above the sediment. The resulting data gives us bubble size distributions and the precise timing of bubbling events over a period of several months. In addition to allowing us to characterize typical bubble size distributions, this data allows us to draw important conclusions about temporal variations in bubble sizes, as well as bubble dissolution rates within the water column.

Soap bubbles in analytical chemistry. Conductometric determination of sub-parts per million levels of sulfur dioxide with a soap bubble.

PubMed

Kanyanee, Tinakorn; Borst, Walter L; Jakmunee, Jaroon; Grudpan, Kate; Li, Jianzhong; Dasgupta, Purnendu K

2006-04-15

Soap bubbles provide a fascinating tool that is little used analytically. With a very low liquid volume to surface area ratio, a soap bubble can potentially provide a very useful interface for preconcentration where mass transfer to an interfacial surface is important. Here we use an automated system to create bubbles of uniform size and film thickness. We utilize purified Triton-X 100, a nonionic surfactant, to make soap bubbles. We use such bubbles as a gas-sampling interface. Incorporating hydrogen peroxide into the bubble provides a system where electrical conductance increases as the bubble is exposed to low concentrations of sulfur dioxide gas. We theoretically derive the conductance of a hollow conducting spherical thin film with spherical cap electrodes. We measure the film thickness by incorporating a dye in the bubble making solution and laser transmission photometry and find that it agrees well with the geometrically computed thickness. With the conductance of the bubble-making soap solution being measured by conventional methods, we show that the measured values of the bubble conductance with known bubble and electrode dimensions closely correspond to the theoretically computed value. Finally, we demonstrate that sub-ppm levels of SO(2) can readily be detected by the conductivity change of a hydrogen peroxide-doped soap bubble, measured in situ, when the gas flows around the bubble.

Use of a "small-bubble technique" to increase the success of Anwar's "big-bubble technique" for deep lamellar keratoplasty with complete baring of Descemet's membrane.

PubMed

Parthasarathy, Anand; Por, Yong Ming; Tan, Donald T H

2007-10-01

To describe a quick and simple "small-bubble" technique to immediately determine the success of attaining complete Descemet's membrane (DM) separation from corneal stroma through Anwar's "big-bubble" technique of deep anterior lamellar keratoplasty (DALK) for complete stromal removal. A partial trephination was followed by a lamellar dissection of the anterior stroma. Deep stromal air injection was then attempted to achieve the big bubble to help separate the stroma from the DM. To confirm that a big bubble had been achieved, a small air bubble was injected into the anterior chamber (AC) through a limbal paracentesis. If the small bubble is then seen at the corneal periphery, it confirms that the big-bubble separation of DM was successful because the convex nature of the bubble will cause it to protrude posteriorly, forcing the small AC bubble to the periphery. If the small AC bubble is not seen in the corneal periphery, this means that it is present in the centre, beneath the opaque corneal stroma, and therefore the big bubble has not been achieved. We used the small-bubble technique to confirm the presence of the big bubble in three (one keratoconus, one interstitial keratitis and one dense corneal scar) out of 41 patients who underwent DALK. The small-bubble technique confirmed that the big bubble was achieved in the eye of all three patients. Complete stromal removal with baring of the DM was achieved, and postoperatively all three eyes achieved best corrected vision of 6/6. The small-bubble technique can be a useful surgical tool for corneal surgeons attempting lamellar keratoplasty using the big-bubble technique. It helps in confirming the separation of DM from the deep stroma, which is important in achieving total stromal replacement. It will help to make the transition to lamellar keratoplasty smoother, enhance corneal graft success and improve visual outcomes in patients.

Photodissociation Regions in the Interstellar Medium of Galaxies

NASA Technical Reports Server (NTRS)

Hollenbach, David J.; Tielens, A. G. G. M.; DeVincenzi, Donald L. (Technical Monitor)

1999-01-01

The interstellar medium of galaxies is the reservoir out of which stars are born and into which stars inject newly created elements as they age. The physical properties of the interstellar medium are governed in part by the radiation emitted by these stars. Far-ultraviolet (6 eV less than h(nu) less than 13.6 eV) photons from massive stars dominate the heating and influence the chemistry of the neutral atomic gas and much of the molecular gas in galaxies. Predominantly neutral regions of the interstellar medium in which the heating and chemistry are regulated by far ultraviolet photons are termed Photo-Dissociation Regions (PDRs). These regions are the origin of most of the non-stellar infrared (IR) and the millimeter and submillimeter CO emission from galaxies. The importance of PDRs has become increasingly apparent with advances in IR and submillimeter astronomy. The IR emission from PDRs includes fine structure lines of C, C+, and O; rovibrational lines of H2, rotational lines of CO; broad middle features of polycyclic aromatic hydrocarbons; and a luminous underlying IR continuum from interstellar dust. The transition of H to H2 and C+ to CO occurs within PDRs. Comparison of observations with theoretical models of PDRs enables one to determine the density and temperature structure, the elemental abundances, the level of ionization, and the radiation field. PDR models have been applied to interstellar clouds near massive stars, planetary nebulae, red giant outflows, photoevaporating planetary disks around newly formed stars, diffuse clouds, the neutral intercloud medium, and molecular clouds in the interstellar radiation field-in summary, much of the interstellar medium in galaxies. Theoretical PDR models explain the observed correlations of the [CII] 158 microns with the COJ = 1-0 emission, the COJ = 1-0 luminosity with the interstellar molecular mass, and the [CII] 158 microns plus [OI] 63 microns luminosity with the IR continuum luminosity. On a more global scale, MR models predict the existence of two stable neutral phases of the interstellar medium, elucidate the formation and destruction of star-forming molecular clouds, and suggest radiation-induced feedback mechanisms that may regulate star formation rates and the column density of gas through giant molecular clouds.

Acoustic bubble removal method

NASA Technical Reports Server (NTRS)

Trinh, E. H.; Elleman, D. D.; Wang, T. G. (Inventor)

1983-01-01

A method is described for removing bubbles from a liquid bath such as a bath of molten glass to be used for optical elements. Larger bubbles are first removed by applying acoustic energy resonant to a bath dimension to drive the larger bubbles toward a pressure well where the bubbles can coalesce and then be more easily removed. Thereafter, submillimeter bubbles are removed by applying acoustic energy of frequencies resonant to the small bubbles to oscillate them and thereby stir liquid immediately about the bubbles to facilitate their breakup and absorption into the liquid.

Rise characteristics of gas bubbles in a 2D rectangular column: VOF simulations vs experiments

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

Krishna, R.; Baten, J.M. van

About five centuries ago, Leonardo da Vinci described the sinuous motion of gas bubbles rising in water. The authors have attempted to simulate the rise trajectories of bubbles of 4, 5, 7, 8, 9, 12, and 20 mm in diameter rising in a 2D rectangular column filled with water. The simulations were carried out using the volume-of-fluid (VOF) technique developed by Hirt and Nichols (J. Computational Physics, 39, 201--225 (1981)). To solve the Navier-Stokes equations of motion the authors used a commercial solver, CFX 4.1c of AEA Technology, UK. They developed their own bubble-tracking algorithm to capture sinuous bubble motions.more » The 4 and 5 mm bubbles show large lateral motions observed by Da Vinci. The 7, 8 and 9 mm bubble behave like jellyfish. The 12 mm bubble flaps its wings like a bird. The extent of lateral motion of the bubbles decreases with increasing bubble size. Bubbles larger than 20 mm in size assume a spherical cap form and simulations of the rise characteristics match experiments exactly. VOF simulations are powerful tools for a priori determination of the morphology and rise characteristics of bubbles rising in a liquid. Bubble-bubble interactions are also properly modeled by the VOF technique.« less

Star Formation in the DR21 Region (B)

NASA Technical Reports Server (NTRS)

2004-01-01

[figure removed for brevity, see original site] Annotated mosaic

Hidden behind a shroud of dust in the constellation Cygnus is an exceptionally bright source of radio emission called DR21. Visible light images reveal no trace of what is happening in this region because of heavy dust obscuration. In fact, visible light is attenuated in DR21 by a factor of more than 10,000,000,000,000,000,000,000,000,000,000,000,000,000 (ten thousand trillion heptillion).

New images from NASA's Spitzer Space Telescope allow us to peek behind the cosmic veil and pinpoint one of the most massive natal stars yet seen in our Milky Way galaxy. The never-before-seen star is 100,000 times as bright as the Sun. Also revealed for the first time is a powerful outflow of hot gas emanating from this star and bursting through a giant molecular cloud.

The upper image is a large-scale mosaic assembled from individual photographs obtained with the InfraRed Array Camera (IRAC) aboard Spitzer. The image covers an area about two times that of a full moon. The mosaic is a composite of images obtained at mid-infrared wavelengths of 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange) and 8 microns (red). The brightest infrared cloud near the top center corresponds to DR21, which presumably contains a cluster of newly forming stars at a distance of 10,000 light-years.

Protruding out from DR21 toward the bottom left of the image is a gaseous outflow (green), containing both carbon monoxide and molecular hydrogen. Data from the Spitzer spectrograph, which breaks light into its constituent individual wavelengths, indicate the presence of hot steam formed as the outflow heats the surrounding molecular gas. Outflows are physical signatures of processes that create supersonic beams, or jets, of gas. They are usually accompanied by discs of material around the new star, which likely contain the materials from which future planetary systems are formed. Additional newborn stars, depicted in green, can be seen surrounding the DR21 region.

The red filaments stretching across this image denote the presence of polycyclic aromatic hydrocarbons. These organic molecules, comprised of carbon and hydrogen, are excited by surrounding interstellar radiation and become luminescent at wavelengths near 8.0 microns. The complex pattern of filaments is caused by an intricate combination of radiation pressure, gravity and magnetic fields. The result is a tapestry in which winds, outflows and turbulence move and shape the interstellar medium.

To the lower left of the mosaic is a large bubble of gas and dust, which may represent the remnants of a past generation of stars.

The lower panel shows a 24-micron image mosaic, obtained with the Multiband Imaging Photometer aboard Spitzer (MIPS). This image maps the cooler infrared emission from interstellar dust found throughout the interstellar medium. The DR21 complex is clearly seen near the center of the strip, which covers about twice the area of the IRAC image.

Perhaps the most fascinating feature in this image is a long and shadowy linear filament extending towards the 10 o'clock position of DR21. This jet of cold and dense gas, nearly 50 light-years in extent, appears in silhouette against a warmer background. This filament is too long and massive to be a stellar jet and may have formed from a pre-existing molecular cloud core sculpted by DR21's strong winds. Regardless of its true nature, this jet and the numerous other arcs and wisps of cool dust signify the interstellar turbulence normally unseen by the human eye.

Where Do Messy Planetary Nebulae Come From?

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-03-01

If you examined images of planetary nebulae, you would find that many of them have an appearance that is too messy to be accounted for in the standard model of how planetary nebulae form. So what causes these structures?Examples of planetary nebulae that have a low probability of having beenshaped by a triple stellar system. They are mostly symmetric, with only slight departures (labeled) that can be explained by instabilities, interactions with the interstellar medium, etc. [Bear and Soker 2017]A Range of LooksAt the end of a stars lifetime, in the red-giant phase, strong stellar winds can expel the outer layers of the star. The hot, luminous core then radiates in ultraviolet, ionizing the gas of the ejected stellar layers and causing them to shine as a brightly colored planetary nebula for a few tens of thousands of years.Planetary nebulae come in a wide variety of morphologies. Some are approximately spherical, but others can be elliptical, bipolar, quadrupolar, or even more complex.Its been suggested that non-spherical planetary nebulae might be shaped by the presence of a second star in a binary system with the source of the nebula but even this scenario should still produce a structure with axial or mirror symmetry.A pair of scientists from Technion Israel Institute of Technology, Ealeal Bear and Noam Soker, argue that planetary nebulae with especially messy morphologies those without clear axial or point symmetries may have been shaped by an interacting triple stellar system instead.Examples of planetary nebulae that might have been shaped by a triple stellar system. They have some deviations from symmetry but also show signs of interacting with the interstellar medium. [Bear and Soker 2017]Departures from SymmetryTo examine this possibility more closely, Bear and Soker look at a sample of thousands planetary nebulae and qualitatively classify each of them into one of four categories, based on the degree to which they show signs of having been shaped by a triple stellar progenitor. The primary signs the authors look for are:SymmetriesIf a planetary nebula has a strong axisymmetric or point-symmetric structure (i.e., its bipolar, elliptical, spherical, etc.), it was likely not shaped by a triple progenitor. If clear symmetries are missing, however, or if there is a departure from symmetry in specific regions, the morphology of the planetary nebula may have been shaped by the presence of stars in a close triple system.Interaction with the interstellar mediumSome asymmetries, especially local ones, can be explained by interaction of the planetary nebula with the interstellar medium. The authors look for signs of such an interaction, which decreases the likelihood that a triple stellar system need be involved to produce the morphology we observe.Examples of planetary nebulae that are extremely likely to have been shaped by a triple stellar system. They have strong departures from symmetry and dont show signs of interacting with the interstellar medium. [Bear and Soker 2017]Influential TriosFrom the images in two planetary nebulae catalogs the Planetary Nebula Image Catelog and the HASH catalog Bear and Soker find that 275 and 372 planetary nebulae are categorizable, respectively. By assigning crude probabilities to their categories, the authors estimate that the total fraction of planetary nebulae shaped by three stars in a close system is around 1321%.The authors argue that in some cases, all three stars might survive. This means that we may be able to find direct evidence of these triple stellar systems lying in the hearts of especially messy planetary nebulae.CitationEaleal Bear and Noam Soker 2017 ApJL 837 L10. doi:10.3847/2041-8213/aa611c

Experimental study on wake structure of single rising clean bubble

NASA Astrophysics Data System (ADS)

Sato, Ayaka; Takedomi, Yuta; Shirota, Minori; Sanada, Toshiyuki; Watanabe, Masao

2007-11-01

Wake structure of clean bubble rising in quiescent silicone oil solution of photochromic dye is experimentally studied. A single bubble is generated, immediately after UV sheet light illuminates the part of the liquid just above the bubble generation nozzle in order to activate photochromic dye. Once the bubble passes across the colored part of the liquid, the bubble is accompanied by some portion of activated dye tracers; hence the flow structure in the rear of the single rising bubble is visualized. We capture stereo images of both wake structure and bubble motion. We study how wake structure changes with the increase in bubble size. We observe the stable axisymmetric wake structure, which is called `standing eddy' when bubble size is relatively small, and then wake structure becomes unstable and starts to oscillate with the increase in bubble size. With further increase in bubble size, a pair of streamwise vortices, which is called `double thread', is observed. We discuss in detail this transition from the steady wake to unsteady wake structure, especially double thread wake development and hairpin vortices shedding, in relation to the transition from rectilinear to spiral or zigzag bubble motions.

Bubble Departure from Metal-Graphite Composite Surfaces and Its Effects on Pool Boiling Heat Transfer

NASA Technical Reports Server (NTRS)

Chao, David F.; Sankovic, John M.; Motil, Brian J.; Yang, W-J.; Zhang, Nengli

2010-01-01

The formation and growth processes of a bubble in the vicinity of graphite micro-fiber tips on metal-graphite composite boiling surfaces and their effects on boiling behavior are investigated. It is discovered that a large number of micro bubbles are formed first at the micro scratches and cavities on the metal matrix in pool boiling. By virtue of the non-wetting property of graphite, once the growing micro bubbles touch the graphite tips, the micro bubbles are sucked by the tips and merged into larger micro bubbles sitting on the end of the tips. The micro bubbles grow rapidly and coalesce to form macro bubbles, each spanning several tips. The necking process of a detaching macro bubble is analyzed. It is revealed that a liquid jet is produced by sudden break-off of the bubble throat. The composite surfaces not only have higher temperatures in micro- and macrolayers but also make higher frequency of the bubble departure, which increase the average heat fluxes in both the bubble growth stage and in the bubble departure period. Based on these analyses, the enhancement mechanism of pool boiling heat transfer on composite surfaces is clearly revealed.

Review-Physicochemical hydrodynamics of gas bubbles in two phase electrochemical systems.

PubMed

Taqieddin, Amir; Nazari, Roya; Rajic, Ljiljana; Alshawabkeh, Akram

2017-01-01

Electrochemical systems suffer from poor management of evolving gas bubbles. Improved understanding of bubbles behavior helps to reduce overpotential, save energy and enhance the mass transfer during chemical reactions. This work investigates and reviews the gas bubbles hydrodynamics, behavior, and management in electrochemical cells. Although the rate of bubble growth over the electrode surface is well understood, there is no reliable prediction of bubbles break-off diameter from the electrode surface because of the complexity of bubbles motion near the electrode surface. Particle Image Velocimetry (PIV) and Laser Doppler Anemometry (LDA) are the most common experimental techniques to measure bubble dynamics. Although the PIV is faster than LDA, both techniques are considered expensive and time-consuming. This encourages adapting Computational Fluid Dynamics (CFD) methods as an alternative to study bubbles behavior. However, further development of CFD methods is required to include coalescence and break-up of bubbles for better understanding and accuracy. The disadvantages of CFD methods can be overcome by using hybrid methods. The behavior of bubbles in electrochemical systems is still a complex challenging topic which requires a better understanding of the gas bubbles hydrodynamics and their interactions with the electrode surface and bulk liquid, as well as between the bubbles itself.

Dynamics of Single Hydrogen Bubbles at a Platinum Microelectrode.

PubMed

Yang, Xuegeng; Karnbach, Franziska; Uhlemann, Margitta; Odenbach, Stefan; Eckert, Kerstin

2015-07-28

Bubble dynamics, including the formation, growth, and detachment, of single H2 bubbles was studied at a platinum microelectrode during the electrolysis of 1 M H2SO4 electrolyte. The bubbles were visualized through a microscope by a high-speed camera. Electrochemical measurements were conducted in parallel to measure the transient current. The periodic current oscillations, resulting from the periodic formation and detachment of single bubbles, allow the bubble lifetime and size to be predicted from the transient current. A comparison of the bubble volume calculated from the current and from the recorded bubble image shows a gas evolution efficiency increasing continuously with the growth of the bubble until it reaches 100%. Two different substrates, glass and epoxy, were used to embed the Pt wire. While nearly no difference was found with respect to the growth law for the bubble radius, the contact angle differs strongly for the two types of cell. Data provided for the contact point evolution further complete the image of single hydrogen bubble growth. Finally, the velocity field driven by the detached bubble was measured by means of PIV, and the effects of the convection on the subsequent bubble were evaluated.

Molecular diagnostics of interstellar shocks

NASA Technical Reports Server (NTRS)

Hartquist, T. W.; Dalgarno, A.; Oppenheimer, M.

1980-01-01

The chemistry of molecules in shocked regions of the interstellar gas is considered and calculations are carried out for a region subjected to a shock at a velocity of 8 km/sec. Substantial enhancements are predicted in the concentrations of the molecules H2S, SO, and SiO compared to those anticipated in cold interstellar clouds.

The Submillimeter-wave Rotational Spectra of Interstellar Molecules

NASA Technical Reports Server (NTRS)

Herbst, Eric; DeLucia, Frank C.; Butler, R. A. H.; Winnewisser, M.; Winnewisser, G.; Fuchs, U.; Groner, P.; Sastry, K. V. L. N.

2002-01-01

We discuss past and recent progress in our long-term laboratory program concerning the submillimeter-wave rotational spectroscopy of known and likely interstellar molecules, especially those associated with regions of high-mass star formation. Our program on the use of spectroscopy to study rotationally inelastic collisions of interstellar interest is also briefly mentioned.

Molecular diagnostics of interstellar shocks

NASA Astrophysics Data System (ADS)

Hartquist, T. W.; Dalgarno, A.; Oppenheimer, M.

1980-02-01

The chemistry of molecules in shocked regions of the interstellar gas is considered and calculations are carried out for a region subjected to a shock at a velocity of 8 km/sec. Substantial enhancements are predicted in the concentrations of the molecules H2S, SO, and SiO compared to those anticipated in cold interstellar clouds.

Observations of Interstellar HI Toward Nearby Late-type Stars

NASA Technical Reports Server (NTRS)

Landsman, W. B.; Henry, R. C.; Moos, H. W.; Linsky, J. L.

1984-01-01

High-disperson Copernicus and IUE observations of chromospheric Ly alpha emission are used to study the distribution of HI in the local interstellar medium. Interstellar parameters are derived toward 3 stars within 5 pc of the Sun, and upper limits are given for the Ly alpha flux from 9 other stars within 10 pc.

Bubble Proliferation in Shock Wave Lithotripsy Occurs during Inertial Collapse

NASA Astrophysics Data System (ADS)

Pishchalnikov, Yuri A.; McAteer, James A.; Pishchalnikova, Irina V.; Williams, James C.; Bailey, Michael R.; Sapozhnikov, Oleg A.

2008-06-01

In shock wave lithotripsy (SWL), firing shock pulses at slow pulse repetition frequency (0.5 Hz) is more effective at breaking kidney stones than firing shock waves (SWs) at fast rate (2 Hz). Since at fast rate the number of cavitation bubbles increases, it appears that bubble proliferation reduces the efficiency of SWL. The goal of this work was to determine the basis for bubble proliferation when SWs are delivered at fast rate. Bubbles were studied using a high-speed camera (Imacon 200). Experiments were conducted in a test tank filled with nondegassed tap water at room temperature. Acoustic pulses were generated with an electromagnetic lithotripter (DoLi-50). In the focus of the lithotripter the pulses consisted of a ˜60 MPa positive-pressure spike followed by up to -8 MPa negative-pressure tail, all with a total duration of about 7 μs. Nonlinear propagation steepened the shock front of the pulses to become sufficiently thin (˜0.03 μm) to impose differential pressure across even microscopic bubbles. High-speed camera movies showed that the SWs forced preexisting microbubbles to collapse, jet, and break up into daughter bubbles, which then grew rapidly under the negative-pressure phase of the pulse, but later coalesced to re-form a single bubble. Subsequent bubble growth was followed by inertial collapse and, usually, rebound. Most, if not all, cavitation bubbles emitted micro-jets during their first inertial collapse and re-growth. After jetting, these rebounding bubbles could regain a spherical shape before undergoing a second inertial collapse. However, either upon this second inertial collapse, or sometimes upon the first inertial collapse, the rebounding bubble emerged from the collapse as a cloud of smaller bubbles rather than a single bubble. These daughter bubbles could continue to rebound and collapse for a few cycles, but did not coalesce. These observations show that the positive-pressure phase of SWs fragments preexisting bubbles but this initial fragmentation does not yield bubble proliferation, as the daughter bubbles coalesce to reform a single bubble. Instead, bubble proliferation is the product of the subsequent inertial collapses.

Interstellar Propulsion Research Within NASA

NASA Technical Reports Server (NTRS)

Johnson, Les; Cook, Stephen (Technical Monitor)

2001-01-01

NASA is actively conducting advanced propulsion research and technology development in various in-space transportation technologies with potential application to interstellar missions and precursors. Within the last few years, interest in the scientific community in interstellar missions as well as outer heliospheric missions, which could function as interstellar precursor missions, has increased. A mission definition team was charted by NASA to define such a precursor, The Interstellar Probe, which resulted in a prioritization of relatively near-term transportation technologies to support its potential implementation. In addition, the goal of finding and ultimately imaging extra solar planets has raised the issue of our complete inability to mount an expedition to such as planet, should one be found. Even contemplating such a mission with today's technology is a stretch of the imagination. However, there are several propulsion concepts, based on known physics, that have promise to enable interstellar exploration in the future. NASA is making small, incremental investments in some key advanced propulsion technologies in an effort to advance their state-of-the-art in support potential future mission needs. These technologies, and their relative maturity, are described.

Analysis of ultraviolet spectrophotometric data from Copernicus. Final report

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

Snow, T.P. Jr

1979-04-17

Ultraviolet spectral data from the OAO 3 satellite are being used to study interstellar absorption lines and stellar and circumstellar lines in hot stars. The interstellar data are beneficial in analyzing the depletions of heavy elements from the gas phase and in elucidating how these depletions depend on physical conditions. Abundances in separate velocity components were determined from line profiles. Observations were carried out for interstellar abundances, both atomic and molecular, towards a number of stars. The better quality data are being analyzed for profile information and the lesser data are being used in curve-of-growth analyses. Molecular observations were carriedmore » out as well; N/sup 2/ was sought, interstellar C/sup 2/ was detected and its rotational excitation utilized to establish limits in interstellar cloud temperatures. An extensive search for H/sup 2/O resulted in a tentative identification which will produce new information on chemical reaction rates. Interstellar depletions and grain properties in the rho Ophiuchi cloud, stellar wind variability, and circumstellar lines are also under study.« less

Behavior of Rapidly Sheared Bubble Suspensions

NASA Technical Reports Server (NTRS)

Sangani, A. S.; Kushch, V. I.; Hoffmann, M.; Nahra, H.; Koch, D. L.; Tsang, Y.

2002-01-01

An experiment to be carried out aboard the International Space Station is described. A suspension consisting of millimeter-sized bubbles in water containing some dissolved salt, which prevents bubbles from coalescing, will be sheared in a Couette cylindrical cell. Rotation of the outer cylinder will produce centrifugal force which will tend to accumulate the bubbles near the inner wall. The shearing will enhance collisions among bubbles creating thereby bubble phase pressure that will resist the tendency of the bubbles to accumulate near the inner wall. The bubble volume fraction and velocity profiles will be measured and compared with the theoretical predictions. Ground-based research on measurement of bubble phase properties and flow in vertical channel are described.

Cavitation inception by the backscattering of pressure waves from a bubble interface

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

Takahira, Hiroyuki, E-mail: takahira@me.osakafu-u.ac.jp; Ogasawara, Toshiyuki, E-mail: oga@me.osakafu-u.ac.jp; Mori, Naoto, E-mail: su101064@edu.osakafu-u.ac.jp

2015-10-28

The secondary cavitation that occurs by the backscattering of focused ultrasound from a primary cavitation bubble caused by the negative pressure part of the ultrasound (Maxwell, et al., 2011) might be useful for the energy exchange due to bubble oscillations in High Intensity Focused Ultrasound (HIFU). The present study is concerned with the cavitation inception by the backscattering of ultrasound from a bubble. In the present experiment, a laser-induced bubble which is generated by a pulsed focused laser beam with high intensity is utilized as a primary cavitation bubble. After generating the bubble, focused ultrasound is emitted to the bubble.more » The acoustic field and the bubble motion are observed with a high-speed video camera. It is confirmed that the secondary cavitation bubble clouds are generated by the backscattering from the laser-induced bubble. The growth of cavitation bubble clouds is analyzed with the image processing method. The experimental results show that the height and width of the bubble clouds grow in stepwise during their evolution. The direct numerical simulations are also conducted for the backscattering of incident pressure waves from a bubble in order to evaluate a pressure field near the bubble. It is shown that the ratio of a bubble collapse time t{sub 0} to a characteristic time of wave propagation t{sub S}, η = t{sub 0}/t{sub s}, is an important determinant for generating negative pressure region by backscattering. The minimum pressure location by the backscattering in simulations is in good agreement with the experiment.« less

Electromagnetic Forces on a Relativistic Spacecraft in the Interstellar Medium

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

Hoang, Thiem; Loeb, Abraham, E-mail: thiemhoang@kasi.re.kr, E-mail: aloeb@cfa.harvard.edu

2017-10-10

A relativistic spacecraft of the type envisioned by the Breakthrough Starshot initiative will inevitably become charged through collisions with interstellar particles and UV photons. Interstellar magnetic fields would therefore deflect the trajectory of the spacecraft. We calculate the expected deflection for typical interstellar conditions. We also find that the charge distribution of the spacecraft is asymmetric, producing an electric dipole moment. The interaction between the moving electric dipole and the interstellar magnetic field is found to produce a large torque, which can result in fast oscillation of the spacecraft around the axis perpendicular to the direction of motion, with amore » period of ∼0.5 hr. We then study the spacecraft rotation arising from impulsive torques by dust bombardment. Finally, we discuss the effect of the spacecraft rotation and suggest several methods to mitigate it.« less

The Interstellar Medium in External Galaxies: Summaries of contributed papers

NASA Technical Reports Server (NTRS)

Hollenbach, David J. (Editor); Thronson, Harley A., Jr. (Editor)

1990-01-01

The Second Wyoming Conference entitled, The Interstellar Medium in External Galaxies, was held on July 3 to 7, 1989, to discuss the current understanding of the interstellar medium in external galaxies and to analyze the basic physical processes underlying interstellar phenomena. The papers covered a broad range of research on the gas and dust in external galaxies and focused on such topics as the distribution and morphology of the atomic, molecular, and dust components; the dynamics of the gas and the role of the magnetic field in the dynamics; elemental abundances and gas depletions in the atomic and ionized components; cooling flows; star formation; the correlation of the nonthermal radio continuum with the cool component of the interstellar medium; the origin and effect of hot galactic halos; the absorption line systems seen in distant quasars; and the effect of galactic collisions.

Theoretical Modeling of Interstellar Chemistry

NASA Technical Reports Server (NTRS)

Charnley, Steven

2009-01-01

The chemistry of complex interstellar organic molecules will be described. Gas phase processes that may build large carbon-chain species in cold molecular clouds will be summarized. Catalytic reactions on grain surfaces can lead to a large variety of organic species, and models of molecule formation by atom additions to multiply-bonded molecules will be presented. The subsequent desorption of these mixed molecular ices can initiate a distinctive organic chemistry in hot molecular cores. The general ion-molecule pathways leading to even larger organics will be outlined. The predictions of this theory will be compared with observations to show how possible organic formation pathways in the interstellar medium may be constrained. In particular, the success of the theory in explaining trends in the known interstellar organics, in predicting recently-detected interstellar molecules, and, just as importantly, non-detections, will be discussed.

A detailed investigation of proposed gas-phase syntheses of ammonia in dense interstellar clouds

NASA Technical Reports Server (NTRS)

Herbst, Eric; Defrees, D. J.; Mclean, A. D.

1987-01-01

The initial reactions of the Herbst and Klemperer (1973) and the Dalgarno (1974) schemes (I and II, respectively) for the gas-phase synthesis of ammonia in dense interstellar clouds were investigated. The rate of the slightly endothermic reaction between N(+) and H2 to yield NH(+) and H (scheme I) under interstellar conditions was reinvestigated under thermal and nonthermal conditions based on laboratory data. It was found that the relative importance of this reaction in synthesizing ammonia is determined by how the laboratory data at low temperature are interpreted. On the other hand, the exothermic reaction between N and H3(+) to form NH2(+) + H (scheme II) was calculated to possess significant activation energy and, therefore, to have a negligible rate coefficient under interstellar conditions. Consequently, this reaction cannot take place appreciably in interstellar clouds.

Electromagnetic Forces on a Relativistic Spacecraft in the Interstellar Medium

NASA Astrophysics Data System (ADS)

Hoang, Thiem; Loeb, Abraham

2017-10-01

A relativistic spacecraft of the type envisioned by the Breakthrough Starshot initiative will inevitably become charged through collisions with interstellar particles and UV photons. Interstellar magnetic fields would therefore deflect the trajectory of the spacecraft. We calculate the expected deflection for typical interstellar conditions. We also find that the charge distribution of the spacecraft is asymmetric, producing an electric dipole moment. The interaction between the moving electric dipole and the interstellar magnetic field is found to produce a large torque, which can result in fast oscillation of the spacecraft around the axis perpendicular to the direction of motion, with a period of ˜0.5 hr. We then study the spacecraft rotation arising from impulsive torques by dust bombardment. Finally, we discuss the effect of the spacecraft rotation and suggest several methods to mitigate it.

Laboratory Investigations into the Spectra and Origin of Propylene Oxide: A Chiral Interstellar Molecule

NASA Technical Reports Server (NTRS)

Hudson, R. L.; Loeffler, M. J.; Yocum, K. M.

2017-01-01

Propylene oxide was recently identified in the interstellar medium, but few laboratory results are available for this molecule to guide current and future investigations. To address this situation, here we report infrared spectra, absorption coefficients, and band strengths of solid propylene oxide along with the first measurement of its refractive index and a calculation of its density, all for the amorphous solid form of the compound. We present the first experimental results showing a low-temperature formation pathway for propylene oxide near 10 K in interstellar ice analogs. Connections are drawn between our new results and the interstellar molecules propanal and acetone, and predictions are made about several as yet unobserved vinyl alcohols and methylketene. Comparisons are given to earlier laboratory work and a few applications to interstellar and solar system astrochemistry are described.

Laboratory Investigations into the Spectra and Origin of Propylene Oxide: A Chiral Interstellar Molecule

NASA Astrophysics Data System (ADS)

Hudson, R. L.; Loeffler, M. J.; Yocum, K. M.

2017-02-01

Propylene oxide was recently identified in the interstellar medium, but few laboratory results are available for this molecule to guide current and future investigations. To address this situation, here we report infrared spectra, absorption coefficients, and band strengths of solid propylene oxide along with the first measurement of its refractive index and a calculation of its density, all for the amorphous solid form of the compound. We present the first experimental results showing a low-temperature formation pathway for propylene oxide near 10 K in interstellar ice analogs. Connections are drawn between our new results and the interstellar molecules propanal and acetone, and predictions are made about several as yet unobserved vinyl alcohols and methylketene. Comparisons are given to earlier laboratory work and a few applications to interstellar and solar system astrochemistry are described.

Spontaneous and Directional Bubble Transport on Porous Copper Wires with Complex Shapes in Aqueous Media.

PubMed

Li, Wenjing; Zhang, Jingjing; Xue, Zhongxin; Wang, Jingming; Jiang, Lei

2018-01-24

Manipulation of gas bubble behaviors is crucial for gas bubble-related applications. Generally, the manipulation of gas bubble behaviors generally takes advantage of their buoyancy force. It is very difficult to control the transportation of gas bubbles in a specific direction. Several approaches have been developed to collect and transport bubbles in aqueous media; however, most reliable and effective manipulation of gas bubbles in aqueous media occurs on the interfaces with simple shapes (i.e., cylinder and cone shapes). Reliable strategies for spontaneous and directional transport of gas bubbles on interfaces with complex shapes remain enormously challenging. Herein, a type of 3D gradient porous network was constructed on copper wire interfaces, with rectangle, wave, and helix shapes. The superhydrophobic copper wires were immersed in water, and continuous and stable gas films then formed on the interfaces. With the assistance of the Laplace pressure gradient between two bubbles, gas bubbles (including microscopic gas bubbles) in the aqueous media were subsequently transported, continuously and directionally, on the copper wires with complex shapes. The small gas bubbles always moved to the larger ones.

Predawn plasma bubble cluster observed in Southeast Asia

NASA Astrophysics Data System (ADS)

Watthanasangmechai, Kornyanat; Yamamoto, Mamoru; Saito, Akinori; Tsunoda, Roland; Yokoyama, Tatsuhiro; Supnithi, Pornchai; Ishii, Mamoru; Yatini, Clara

2016-06-01

Predawn plasma bubble was detected as deep plasma depletion by GNU Radio Beacon Receiver (GRBR) network and in situ measurement onboard Defense Meteorological Satellite Program F15 (DMSPF15) satellite and was confirmed by sparse GPS network in Southeast Asia. In addition to the deep depletion, the GPS network revealed the coexisting submesoscale irregularities. A deep depletion is regarded as a primary bubble. Submesoscale irregularities are regarded as secondary bubbles. Primary bubble and secondary bubbles appeared together as a cluster with zonal wavelength of 50 km. An altitude of secondary bubbles happened to be lower than that of the primary bubble in the same cluster. The observed pattern of plasma bubble cluster is consistent with the simulation result of the recent high-resolution bubble (HIRB) model. This event is only a single event out of 76 satellite passes at nighttime during 3-25 March 2012 that significantly shows plasma depletion at plasma bubble wall. The inside structure of the primary bubble was clearly revealed from the in situ density data of DMSPF15 satellite and the ground-based GRBR total electron content.

IBEX-Lo Observations of Secondary Interstellar Helium and Oxygen Distributions

NASA Astrophysics Data System (ADS)

Park, J.; Kucharek, H.; Moebius, E.; Kubiak, M. A.; Bzowski, M.; Galli, A.; McComas, D. J.

2015-12-01

Observations of the Interstellar Boundary EXplorer (IBEX) show, among other features, the pristine interstellar neutral gas flow and additional populations associated with neutral helium and oxygen. Kubiak et al. (2014, ApJS, 213, 29) discovered the "Warm Breeze", or additional He component, which is slower and warmer than the primary interstellar He population and its flow direction differs by about 19° from the interstellar neutral (ISN) flow. Park et al. (2015, ApJS, In Press) studied the combined count rate maps of heavy neutral atoms with three statistical analysis methods and found an extended tail of the ISN O flow, centered around 190° in ecliptic longitude and +15° in ecliptic latitude, or approximately 38° from the ISN O and Ne flow peak. The most likely sources for the Warm Breeze and the extended O tail may be secondary populations of interstellar He and O, created by charge exchange between ISN atoms and interstellar ions in the outer heliosheath. The charge exchange between interstellar He atoms and He+ ions is the most important reaction to generate the secondary neutral He in the outer heliosheath, with a reaction rate of 1.7×10-10 s-1 and a mean free path of ~950 AU. For O+, the charge exchange with interstellar H atoms with a rate ~1.0×10-9 s-1 and a mean free path of ~100 AU is most important. Because the differences in the reaction rates and atomic masses for He and O result in different velocity distributions in the outer heliosheath, the directional distributions of these populations at Earth orbit are not identical. In this study, we use the IBEX flux maps of the observed helium and oxygen atoms to compare their directional distributions. These observed distributions may provide constraints and information to improve our current understanding of the interactions in the outer heliosheath.

Science From Beyond: NASA's Pioneer Plaque and the History of Interstellar Communication, 1957- 1972

NASA Astrophysics Data System (ADS)

Macauley, William

2012-05-01

In the late twentieth century, science and technology facilitated exploration beyond the Solar System and extended human knowledge through messages comprised of pictures and mathematical symbols, transmitted from radio telescopes and inscribed on material artifacts attached to spacecraft. ‘Interstellar communication' refers to collective efforts by scientists and co-workers to detect and transmit intelligible messages between humans and supposed extraterrestrial intelligence in remote star systems. Interstellar messages are designed to communicate universal knowledge without recourse to text, human linguistic systems or anthropomorphic content because it is assumed that recipients have no prior knowledge of humankind or the planet we inhabit. Scientists must therefore imagine how extraterrestrials will relate to human knowledge and culture. The production and transmission of interstellar messages became interdisciplinary design problems that involved collaboration and exchange of ideas between scientists, visual artists, and others. My proposed paper will review sociocultural aspects of interstellar communication since the late 1950s and focus on key issues regarding conception, design and production of a specific interstellar message launched into space during the early 1970s - NASA's Pioneer plaque. The paper will explore how research on the history of interstellar communication relates to previous historical and sociological studies on rhetorical aspects of visual representation and mathematics in scientific practice. In particular, I will explain how the notion of ‘inscription' is an appropriate conceptual tool for analyzing how scientists have used pictures to articulate and validate knowledge claims and scientific facts. I argue that scientific knowledge carried on interstellar messages such as the Pioneer plaque is constituted in material practices and inscription technologies that translate natural objects, agency and culture into legible forms. Graphical techniques for creating pictorial interstellar messages are enmeshed with contemporaneous methods for creating displays and images in routine scientific work, in fields such as radio astronomy and planetary science.

Centrosymmetric molecules as possible carriers of diffuse interstellar bands

NASA Astrophysics Data System (ADS)

Kaźmierczak, M.; Schmidt, M. R.; Galazutdinov, G. A.; Musaev, F. A.; Betelesky, Y.; Krełowski, J.

2010-11-01

In this paper, we present new data with interstellar C2 (Phillips bands A 1 Πu-X1 Σ+g), from observations made with the Ultraviolet-Visual Echelle Spectrograph of the European Southern Observatory. We have determined the interstellar column densities and excitation temperatures of C2 for nine Galactic lines. For seven of these, C2 has never been observed before, so in this case the still small sample of interstellar clouds (26 lines of sight), where a detailed analysis of C2 excitation has been made, has increased significantly. This paper is a continuation of previous works where interstellar molecules (C2 and diffuse interstellar bands) have been analysed. Because the sample of interstellar clouds with C2 has increased, we can show that the width and shape of the profiles of some diffuse interstellar bands (6196 and 5797 Å) apparently depend on the gas kinetic and rotational temperatures of C2; the profiles are broader because of the higher values of the gas kinetic and rotational temperatures of C2. There are also diffuse interstellar bands (4964 and 5850 Å) for which this effect does not exist. Based on observations made with ESO telescopes at the Paranal Observatory under programme IDs 266.D-5655(A), 67.C-0281(A), 71.C-0513(C), 67.D-0439(A) and 082.C-0566(A) and at La Silla under programme IDs 078.C-0403(A), 076.C-0164(A) and 073.C-0337(A). Also based on observations made with the 1.8-m telescope in South Korea and the 2-m telescope at the International Centre for Astronomical and Medico-Ecological Research, Terskol, Russia. E-mail: kazmierczak@astri.uni.torun.pl (MK); schmidt@ncac.torun.pl (MRS); runizag@gmail.com (GAG); ybialets@eso.org (YB); jacek@astri.uni.torun.pl (JK)

Bubble migration in a compacting crystal-liquid mush

NASA Astrophysics Data System (ADS)

Boudreau, Alan

2016-04-01

Recent theoretical models have suggested that bubbles are unlikely to undergo significant migration in a compaction crystal mush by capillary invasion while the system remains partly molten. To test this, experiments of bubble migration during compaction in a crystal-liquid mush were modeled using deformable foam crystals in corn syrup in a volumetric burette, compacted with rods of varying weights. A bubble source was provided by sodium bicarbonate (Alka-Seltzer®). Large bubbles (>several crystal sizes) are pinched by the compacting matrix and become overpressured and deformed as the bubbles experience a load change from hydrostatic to lithostatic. Once they begin to move, they move much faster than the compaction-driven liquid. Bubbles that are about the same size as the crystals but larger than the narrower pore throats move by deformation or breaking into smaller bubbles as they are forced through pore restrictions. Bubbles that are less than the typical pore diameter generally move with the liquid: The liquid + bubble mixture behaves as a single phase with a lower density than the bubble-free liquid, and as a consequence it rises faster than bubble-free liquid and allows for faster compaction. The overpressure required to force a bubble through the matrix (max grain size = 5 mm) is modest, about 5 %, and it is estimated that for a grain size of 1 mm, the required overpressure would be about 25 %. Using apatite distribution in a Stillwater olivine gabbro as an analog for bubble nucleation and growth, it is suggested that relatively large bubbles initially nucleate and grow in liquid-rich channels that develop late in the compaction history. Overpressure from compaction allows bubbles to rise higher into hotter parts of the crystal pile, where they redissolve and increase the volatile content of the liquid over what it would have without the bubble migration, leading to progressively earlier vapor saturation during crystallization of the interstitial liquid. Bubbles can also move rapidly by `surfing' on porosity waves that can develop in a compacting mush.

Study on the bubble transport mechanism in an acoustic standing wave field.

PubMed

Xi, Xiaoyu; Cegla, Frederic B; Lowe, Michael; Thiemann, Andrea; Nowak, Till; Mettin, Robert; Holsteyns, Frank; Lippert, Alexander

2011-12-01

The use of bubbles in applications such as surface chemistry, drug delivery, and ultrasonic cleaning etc. has been enormously popular in the past two decades. It has been recognized that acoustically-driven bubbles can be used to disturb the flow field near a boundary in order to accelerate physical or chemical reactions on the surface. The interactions between bubbles and a surface have been studied experimentally and analytically. However, most of the investigations focused on violently oscillating bubbles (also known as cavitation bubble), less attention has been given to understand the interactions between moderately oscillating bubbles and a boundary. Moreover, cavitation bubbles were normally generated in situ by a high intensity laser beam, little experimental work has been carried out to study the translational trajectory of a moderately oscillating bubble in an acoustic field and subsequent interactions with the surface. This paper describes the design of an ultrasonic test cell and explores the mechanism of bubble manipulation within the test cell. The test cell consists of a transducer, a liquid medium and a glass backing plate. The acoustic field within the multi-layered stack was designed in such a way that it was effectively one dimensional. This was then successfully simulated by a one dimensional network model. The model can accurately predict the impedance of the test cell as well as the mode shape (distribution of particle velocity and stress/pressure field) within the whole assembly. The mode shape of the stack was designed so that bubbles can be pushed from their injection point onto a backing glass plate. Bubble radial oscillation was simulated by a modified Keller-Miksis equation and bubble translational motion was derived from an equation obtained by applying Newton's second law to a bubble in a liquid medium. Results indicated that the bubble trajectory depends on the acoustic pressure amplitude and initial bubble size: an increase of pressure amplitude or a decrease of bubble size forces bubbles larger than their resonant size to arrive at the target plate at lower heights, while the trajectories of smaller bubbles are less influenced by these factors. The test cell is also suitable for testing the effects of drag force on the bubble motion and for studying the bubble behavior near a surface. Copyright © 2011 Elsevier B.V. All rights reserved.

Wetting of soap bubbles on hydrophilic, hydrophobic, and superhydrophobic surfaces

NASA Astrophysics Data System (ADS)

Arscott, Steve

2013-06-01

Wetting of sessile bubbles on various wetting surfaces (solid and liquid) has been studied. A model is presented for the apparent contact angle of a sessile bubble based on a modified Young's equation--the experimental results agree with the model. Wetting a hydrophilic surface results in a bubble contact angle of 90° whereas using a superhydrophobic surface one observes 134°. For hydrophilic surfaces, the bubble angle diminishes with bubble radius whereas on a superhydrophobic surface, the bubble angle increases. The size of the plateau borders governs the bubble contact angle, depending on the wetting of the surface.