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Sample records for runaway stellar collision

  1. The evolution of runaway stellar collision products

    NARCIS (Netherlands)

    Glebbeek, E.; Gaburov, E.; de Mink, S.E.; Pols, O.R.; Portegies Zwart, S.F.

    2009-01-01

    In the cores of young dense star clusters, repeated stellar collisions involving the same object can occur. It has been suggested that this leads to the formation of an intermediate-mass black hole. To verify this scenario we compute the detailed evolution of the merger remnant of three sequences,

  2. Runaways.

    Science.gov (United States)

    Greenberg, Keith Elliot

    This essay with photographs describes the experiences of two runaways, examining why they left home and how they found help. Although runaways have a reputation for being irresponsible, they usually have good reasons for leaving home. The nun who ran Noah's Ark, where both the runaways featured found shelter and help, estimated that only about two…

  3. Formation of intermediate-mass black holes through runaway collisions in the first star clusters

    Science.gov (United States)

    Sakurai, Yuya; Yoshida, Naoki; Fujii, Michiko S.; Hirano, Shingo

    2017-12-01

    We study the formation of massive black holes in the first star clusters. We first locate star-forming gas clouds in protogalactic haloes of ≳107 M⊙ in cosmological hydrodynamics simulations and use them to generate the initial conditions for star clusters with masses of ˜105 M⊙. We then perform a series of direct-tree hybrid N-body simulations to follow runaway stellar collisions in the dense star clusters. In all the cluster models except one, runaway collisions occur within a few million years, and the mass of the central, most massive star reaches ˜400-1900 M⊙. Such very massive stars collapse to leave intermediate-mass black holes (IMBHs). The diversity of the final masses may be attributed to the differences in a few basic properties of the host haloes such as mass, central gas velocity dispersion and mean gas density of the central core. Finally, we derive the IMBH mass to cluster mass ratios, and compare them with the observed black hole to bulge mass ratios in the present-day Universe.

  4. Baryogenesis and Gravitational Waves from Runaway Bubble Collisions

    CERN Document Server

    Katz, Andrey

    2016-11-07

    We propose a novel mechanism for production of baryonic asymmetry in the early Universe. The mechanism takes advantage of the strong first order phase transition that produces runaway bubbles in the hidden sector that propagate almost without friction with ultra-relativistic velocities. Collisions of such bubbles can non-thermally produce heavy particles that further decay out-of-equilibrium into the SM and produce the observed baryonic asymmetry. This process can proceed at the very low temperatures, providing a new mechanism of post-sphaleron baryogenesis. In this paper we present a fully calculable model which produces the baryonic asymmetry along these lines as well as evades all the existing cosmological constraints. We emphasize that the Gravitational Waves signal from the first order phase transition is completely generic and can potentially be detected by the future eLISA interferometer. We also discuss other potential signals, which are more model dependent, and point out the unresolved theoretical q...

  5. Formation of massive black holes through runaway collisions in dense young star clusters.

    Science.gov (United States)

    Zwart, Simon F Portegies; Baumgardt, Holger; Hut, Piet; Makino, Junichiro; McMillan, Stephen L W

    2004-04-15

    A luminous X-ray source is associated with MGG 11--a cluster of young stars approximately 200 pc from the centre of the starburst galaxy M 82 (refs 1, 2). The properties of this source are best explained by invoking a black hole with a mass of at least 350 solar masses (350 M(o)), which is intermediate between stellar-mass and supermassive black holes. A nearby but somewhat more massive cluster (MGG 9) shows no evidence of such an intermediate-mass black hole, raising the issue of just what physical characteristics of the clusters can account for this difference. Here we report numerical simulations of the evolution and motion of stars within the clusters, where stars are allowed to merge with each other. We find that for MGG 11 dynamical friction leads to the massive stars sinking rapidly to the centre of the cluster, where they participate in a runaway collision. This produces a star of 800-3,000 M(o) which ultimately collapses to a black hole of intermediate mass. No such runaway occurs in the cluster MGG 9, because the larger cluster radius leads to a mass segregation timescale a factor of five longer than for MGG 11.

  6. Baryogenesis and gravitational waves from runaway bubble collisions

    Energy Technology Data Exchange (ETDEWEB)

    Katz, Andrey [Theory Division, CERN,CH-1211 Geneva 23 (Switzerland); Département de Physique Théorique and Center for Astroparticle Physics (CAP),Université de Genève, 24 quai Ansermet, CH-1211 Genève 4 (Switzerland); Riotto, Antonio [Département de Physique Théorique and Center for Astroparticle Physics (CAP),Université de Genève, 24 quai Ansermet, CH-1211 Genève 4 (Switzerland)

    2016-11-07

    We propose a novel mechanism for production of baryonic asymmetry in the early Universe. The mechanism takes advantage of the strong first order phase transition that produces runaway bubbles in the hidden sector that propagate almost without friction with ultra-relativistic velocities. Collisions of such bubbles can non-thermally produce heavy particles that further decay out-of-equilibrium into the SM and produce the observed baryonic asymmetry. This process can proceed at the very low temperatures, providing a new mechanism of post-sphaleron baryogenesis. In this paper we present a fully calculable model which produces the baryonic asymmetry along these lines as well as evades all the existing cosmological constraints. We emphasize that the Gravitational Waves signal from the first order phase transition is completely generic and can potentially be detected by the future eLISA interferometer. We also discuss other potential signals, which are more model dependent, and point out the unresolved theoretical questions related to our proposal.

  7. Early Hydrodynamic Evolution of a Stellar Collision

    Science.gov (United States)

    Kushnir, Doron; Katz, Boaz

    2014-04-01

    The early phase of the hydrodynamic evolution following the collision of two stars is analyzed. Two strong shocks propagate from the contact surface and move toward the center of each star at a velocity that is a small fraction of the velocity of the approaching stars. The shocked region near the contact surface has a planar symmetry and a uniform pressure. The density vanishes at the (Lagrangian) surface of contact, and the speed of sound diverges there. The temperature, however, reaches a finite value, since as the density vanishes, the finite pressure is radiation dominated. For carbon-oxygen white dwarf (CO WD) collisions, this temperature is too low for any appreciable nuclear burning shortly after the collision, which allows for a significant fraction of the mass to be highly compressed to the density required for efficient 56Ni production in the detonation wave that follows. This property is crucial for the viability of collisions of typical CO WD as progenitors of type Ia supernovae, since otherwise only massive (>0.9 M ⊙) CO WDs would have led to such explosions (as required by all other progenitor models). The divergence of the speed of sound limits numerical studies of stellar collisions, as it makes convergence tests exceedingly expensive unless dedicated schemes are used. We provide a new one-dimensional Lagrangian numerical scheme to achieve this. A self-similar planar solution is derived for zero-impact parameter collisions between two identical stars, under some simplifying assumptions (including a power-law density profile), which is the planar version of previous piston problems that were studied in cylindrical and spherical symmetries.

  8. Evolution of stellar collision products in open clusters : II. A grid of low-mass collisions

    NARCIS (Netherlands)

    Glebbeek, E.|info:eu-repo/dai/nl/30483324X; Pols, O.R.|info:eu-repo/dai/nl/111811155

    2008-01-01

    In a companion paper we studied the detailed evolution of stellar collision products that occurred in an N-body simulation of the old open cluster M 67 and compared our detailed models to simple prescriptions. In this paper we extend this work by studying the evolution of the collision products in

  9. Including collisions in gyrokinetic tokamak and stellarator simulations

    Energy Technology Data Exchange (ETDEWEB)

    Kauffmann, Karla

    2012-04-10

    Particle and heat transport in fusion devices often exceed the neoclassical prediction. This anomalous transport is thought to be produced by turbulence caused by microinstabilities such as ion and electron-temperature-gradient (ITG/ETG) and trapped-electron-mode (TEM) instabilities, the latter ones known for being strongly influenced by collisions. Additionally, in stellarators, the neoclassical transport can be important in the core, and therefore investigation of the effects of collisions is an important field of study. Prior to this thesis, however, no gyrokinetic simulations retaining collisions had been performed in stellarator geometry. In this work, collisional effects were added to EUTERPE, a previously collisionless gyrokinetic code which utilizes the {delta}f method. To simulate the collisions, a pitch-angle scattering operator was employed, and its implementation was carried out following the methods proposed in [Takizuka and Abe 1977, Vernay Master's thesis 2008]. To test this implementation, the evolution of the distribution function in a homogeneous plasma was first simulated, where Legendre polynomials constitute eigenfunctions of the collision operator. Also, the solution of the Spitzer problem was reproduced for a cylinder and a tokamak. Both these tests showed that collisions were correctly implemented and that the code is suited for more complex simulations. As a next step, the code was used to calculate the neoclassical radial particle flux by neglecting any turbulent fluctuations in the distribution function and the electric field. Particle fluxes in the neoclassical analytical regimes were simulated for tokamak and stellarator (LHD) configurations. In addition to the comparison with analytical fluxes, a successful benchmark with the DKES code was presented for the tokamak case, which further validates the code for neoclassical simulations. In the final part of the work, the effects of collisions were investigated for slab and toroidal

  10. The growth of massive stars via stellar collisions in ensemble star clusters

    Science.gov (United States)

    Fujii, M. S.; Portegies Zwart, S.

    2013-04-01

    Recent simulations and observations suggest that star clusters form via the assembling of smaller subclusters. Because of their short relaxation time, subclusters experience core collapse much earlier than virialized solo clusters, which have similar properties of the merger remnant of the assembling clusters. As a consequence, it seems that the assembling clusters result in efficient multiple collisions of stars in the cluster core. We performed a series of N-body simulations of ensemble and solitary clusters including stellar collisions and found that the efficiency of multiple collisions between stars is suppressed if subclusters assemble after they experience core collapse individually. In this case, subclusters form their own multiple collision stars which experienced a few collisions, but they fail to collide with each other after their host subclusters assemble. The multiple collision stars scatter each other and escape, and furthermore the central density of the remnant clusters had already been depleted for the stars to experience more collisions. On the other hand, if subclusters assemble before they experience core collapse, the multiple collisions of stars proceed efficiently in the remnant cluster, and the collision products are more massive than virialized solo clusters and comparable in mass to cold solo clusters.

  11. Evolution of stellar collision products in open clusters : I. Blue stragglers in N-body models of M 67

    NARCIS (Netherlands)

    Glebbeek, E.|info:eu-repo/dai/nl/30483324X; Pols, O.R.|info:eu-repo/dai/nl/111811155; Hurley, J.R.

    2008-01-01

    Stellar collisions are an important formation channel for blue straggler stars in globular and old open clusters. Hydrodynamical simulations have shown that the remnants of such collisions are out of thermal equilibrium, are not strongly mixed and can rotate very rapidly. Detailed evolution models

  12. Inelastic aluminium-hydrogen collision data for non-LTE applications in stellar atmospheres

    Science.gov (United States)

    Belyaev, Andrey K.

    2013-12-01

    Aims: Rate coefficients for inelastic Al + H and Al+ + H- collisions are calculated for all transitions between the seven low-lying levels up to and including the ionic state, namely Al(3p,4s,3d,4p,5s,nd)+H(1s) and Al+ + H-. The data are needed for non-LTE applications in stellar atmospheres and are presented for a temperature range of 1000-10 000 K. Methods: The calculations were obtained by means of the recently proposed model approach based on the asymptotic method for electronic molecular structure determination and on the branching probability current method for the nonadiabatic nuclear dynamics. Results: It is shown that the processes with the highest rates are the excitation and de-excitation ones between the Al(3d), Al(4p) and Al(4s) states in collisions with H, as well as the ion-pair formation and the mutual neutralization processes between these states and the ionic state.

  13. Formation and termination of runaway beams in ITER disruptions

    Science.gov (United States)

    Martín-Solís, J. R.; Loarte, A.; Lehnen, M.

    2017-06-01

    A self-consistent analysis of the relevant physics regarding the formation and termination of runaway beams during mitigated disruptions by Ar and Ne injection is presented for selected ITER scenarios with the aim of improving our understanding of the physics underlying the runaway heat loads onto the plasma facing components (PFCs) and identifying open issues for developing and accessing disruption mitigation schemes for ITER. This is carried out by means of simplified models, but still retaining sufficient details of the key physical processes, including: (a) the expected dominant runaway generation mechanisms (avalanche and primary runaway seeds: Dreicer and hot tail runaway generation, tritium decay and Compton scattering of γ rays emitted by the activated wall), (b) effects associated with the plasma and runaway current density profile shape, and (c) corrections to the runaway dynamics to account for the collisions of the runaways with the partially stripped impurity ions, which are found to have strong effects leading to low runaway current generation and low energy conversion during current termination for mitigated disruptions by noble gas injection (particularly for Ne injection) for the shortest current quench times compatible with acceptable forces on the ITER vessel and in-vessel components ({τ\\text{res}}∼ 22~\\text{ms} ). For the case of long current quench times ({τ\\text{res}}∼ 66~\\text{ms} ), runaway beams up to  ∼10 MA can be generated during the disruption current quench and, if the termination of the runaway current is slow enough, the generation of runaways by the avalanche mechanism can play an important role, increasing substantially the energy deposited by the runaways onto the PFCs up to a few hundreds of MJs. Mixed impurity (Ar or Ne) plus deuterium injection proves to be effective in controlling the formation of the runaway current during the current quench, even for the longest current quench times, as well as in decreasing

  14. Kinetic modelling of runaway electrons in dynamic scenarios

    CERN Document Server

    Stahl, A; Papp, G; Landreman, M; Fülöp, T

    2016-01-01

    Improved understanding of runaway-electron formation and decay processes are of prime interest for the safe operation of large tokamaks, and the dynamics of the runaway electrons during dynamical scenarios such as disruptions are of particular concern. In this paper, we present kinetic modelling of scenarios with time-dependent plasma parameters; in particular, we investigate hot-tail runaway generation during a rapid drop in plasma temperature. With the goal of studying runaway-electron generation with a self-consistent electric-field evolution, we also discuss the implementation of a conservative collision operator and demonstrate its properties. An operator for avalanche runaway-electron generation, which takes the energy dependence of the scattering cross section and the runaway distribution into account, is investigated. We show that the simpler avalanche model of Rosenbluth & Putvinskii [Nucl. Fusion 37, 1355 (1997)] can give very inaccurate results for the avalanche growth rate (either lower or hig...

  15. Runaway massive stars as a new class of galactic gamma-ray sources

    Science.gov (United States)

    del Valle, M. V.; Romero, G. E.

    2014-10-01

    Runaway stars have high spatial velocities, V > 30 km s^{-1}, and if the are massive, can produce bowshocks in the surrounding ISM. These bowshocks develop as arc-shaped structures pointing in the same direction as the supersonic stellar velocity. The piled-up shocked matter emits thermal radiation. Additionally, a population of locally accelerated relativistic particles can produce non-thermal emission over a wide range of energies. This has been recently confirmed by a bunch of observations at radio, X-ray and even gamma-ray wavelengths. Runaway early-type stars might be variable gamma-ray sources, with variability time scales depending on the scales of density inhomogeneities in the medium and the stellar velocity. Protons can easily escape from the emitting region without much loss on energy. These protons might diffuse in the surrounding molecular cloud interacting with the matter via p-p inelastic collisions. These yield gamma rays and secondary particles. Molecular clouds illuminated by these relativistic particles might become into diffuse non-thermal sources. We calculate all relevant non-thermal processes related to these stellar objects and discuss the observational prospects.

  16. Hydrogen Atom Collision Processes in Cool Stellar Atmospheres: Effects on Spectral Line Strengths and Measured Chemical Abundances in Old Stars

    Science.gov (United States)

    Barklem, Paul S.

    2012-12-01

    The precise measurement of the chemical composition of stars is a fundamental problem relevant to many areas of astrophysics. State-of-the-art approaches attempt to unite accurate descriptions of microphysics, non-local thermodynamic equilibrium (non-LTE) line formation and 3D hydrodynamical model atmospheres. In this paper I review progress in understanding inelastic collisions of hydrogen atoms with other species and their influence on spectral line formation and derived abundances in stellar atmospheres. These collisions are a major source of uncertainty in non-LTE modelling of spectral lines and abundance determinations, especially for old, metal-poor stars, which are unique tracers of the early evolution of our galaxy. Full quantum scattering calculations of direct excitation processes X(nl) + H leftrightarrow X(n'l') + H and charge transfer processes X(nl) + H leftrightarrow X+ + H- have been done for Li, Na and Mg [1,2,3] based on detailed quantum chemical data, e.g. [4]. Rate coefficients have been calculated and applied to non-LTE modelling of spectral lines in stellar atmospheres [5,6,7,8,9]. In all cases we find that charge transfer processes from the first excited S-state are very important, and the processes affect measured abundances for Li, Na and Mg in some stars by as much as 60%. Effects vary with stellar parameters (e.g. temperature, luminosity, metal content) and so these processes are important not only for accurate absolute abundances, but also for relative abundances among dissimilar stars.

  17. Control of runaway electron secondary generation by changing Z(eff)

    NARCIS (Netherlands)

    Pankratov, I. M.; R. Jaspers,; Finken, K.H.; Entrop, I.; Mank, G.

    1998-01-01

    The effect of Z(eff) on the runaway generation process by close collisions has been studied experimentally in the TEXTOR-94 tokamak in ohmic low density discharges. It is shown that the effective avalanching time increases with increasing Z(eff). This opens the possibility of controlling the runaway

  18. Phase-space dynamics of runaway electrons in magnetic fields

    Science.gov (United States)

    Guo, Zehua; McDevitt, Christopher J.; Tang, Xian-Zhu

    2017-04-01

    Dynamics of runaway electrons in magnetic fields are governed by the competition of three dominant physics: parallel electric field acceleration, Coulomb collision, and synchrotron radiation. Examination of the energy and pitch-angle flows reveals that the presence of local vortex structure and global circulation is crucial to the saturation of primary runaway electrons. Models for the vortex structure, which has an O-point to X-point connection, and the bump of runaway electron distribution in energy space have been developed and compared against the simulation data. Identification of these velocity-space structures opens a new venue to re-examine the conventional understanding of runaway electron dynamics in magnetic fields.

  19. Runaway snakes in TEXTOR-94

    NARCIS (Netherlands)

    Entrop, I.; R. Jaspers,; Cardozo, N. J. L.; Finken, K.H.

    1999-01-01

    Observations of a runaway beam confined in an island-like structure, a so-called runaway snake, are reported. The observations are made in TEXTOR-94 by measurement of synchrotron radiation emitted by these runaways. A full poloidal View allows for the study of the synchrotron pattern of the snake to

  20. Enigma of Runaway Stars Solved

    Science.gov (United States)

    1997-01-01

    bow shocks of compressed matter, which look very much like the bow wave around a boat crossing the ocean. They are of the same physical nature as a bow shock created by a jet-fighter in the air. The explanation is similar: when an OB-runaway star plows through the interstellar medium (a very thin mixture of gas and dust particles) with supersonic velocity [3], interstellar matter is swept up in a bow shock. Stars of low velocity do not create bow shocks. Thus, the detection of a bow shock around a particular OB star indicates that it must have a supersonic velocity, thereby securely identifying it as a runaway star, even if its velocity has not been measured directly. Runaway stars come from stellar groups When a star's direction of motion in space is known, it is possible to reconstruct its previous path and, even more interestingly, to find the place where the star originally came from. It turns out that the paths of many OB-runaways can be traced back to socalled OB-associations , that is groups of 10 to 100 OB-type stars which are located in the spiral arms of our galaxy. About fifty OB-associations are known in the Milky Way. In fact, the majority of all known OB stars are members of an OB-association. Therefore, it is not very surprising that OB-runaway stars should also originate from OB-associations. This is also how they got their name: at some moment, they apparently left the association in which they were formed. The ejection mechanism But why were the OB-runaway stars kicked out of the OB-association and how did they achieve such high speeds? One possibility is that some OB stars in an OB-association are ejected due to strong gravitational effects at the time of close encounters between the members of the group. Complicated computer simulations show that this is in principle possible. Nevertheless, since many years, most astronomers think that a more likely scenario is that of violent supernova explosions, first proposed in 1961 by Adriaan Blaauw. Stellar

  1. Phase-space Dynamics of Runaway Electrons In Tokamaks

    Energy Technology Data Exchange (ETDEWEB)

    Xiaoyin Guan, Hong Qin, and Nathaniel J. Fisch

    2010-08-31

    The phase-space dynamics of runaway electrons is studied, including the influence of loop voltage, radiation damping, and collisions. A theoretical model and a numerical algorithm for the runaway dynamics in phase space are developed. Instead of standard integrators, such as the Runge-Kutta method, a variational symplectic integrator is applied to simulate the long-term dynamics of a runaway electron. The variational symplectic integrator is able to globally bound the numerical error for arbitrary number of time-steps, and thus accurately track the runaway trajectory in phase space. Simulation results show that the circulating orbits of runaway electrons drift outward toward the wall, which is consistent with experimental observations. The physics of the outward drift is analyzed. It is found that the outward drift is caused by the imbalance between the increase of mechanical angular momentum and the input of toroidal angular momentum due to the parallel acceleration. An analytical expression of the outward drift velocity is derived. The knowledge of trajectory of runaway electrons in configuration space sheds light on how the electrons hit the first wall, and thus provides clues for possible remedies.

  2. Runaway electrons and ITER

    Science.gov (United States)

    Boozer, Allen H.

    2017-05-01

    The potential for damage, the magnitude of the extrapolation, and the importance of the atypical—incidents that occur once in a thousand shots—make theory and simulation essential for ensuring that relativistic runaway electrons will not prevent ITER from achieving its mission. Most of the theoretical literature on electron runaway assumes magnetic surfaces exist. ITER planning for the avoidance of halo and runaway currents is focused on massive-gas or shattered-pellet injection of impurities. In simulations of experiments, such injections lead to a rapid large-scale magnetic-surface breakup. Surface breakup, which is a magnetic reconnection, can occur on a quasi-ideal Alfvénic time scale when the resistance is sufficiently small. Nevertheless, the removal of the bulk of the poloidal flux, as in halo-current mitigation, is on a resistive time scale. The acceleration of electrons to relativistic energies requires the confinement of some tubes of magnetic flux within the plasma and a resistive time scale. The interpretation of experiments on existing tokamaks and their extrapolation to ITER should carefully distinguish confined versus unconfined magnetic field lines and quasi-ideal versus resistive evolution. The separation of quasi-ideal from resistive evolution is extremely challenging numerically, but is greatly simplified by constraints of Maxwell’s equations, and in particular those associated with magnetic helicity. The physics of electron runaway along confined magnetic field lines is clarified by relations among the poloidal flux change required for an e-fold in the number of electrons, the energy distribution of the relativistic electrons, and the number of relativistic electron strikes that can be expected in a single disruption event.

  3. Toroidal runaway beams.

    Science.gov (United States)

    Fussmann, G

    2013-01-01

    We investigate the dynamics of a special group of runaway electrons which possibly play an important role in toroidal fusion devices. Starting from the torus center they are accelerated by a toroidal electric field and are hence forced to move across the toroidal magnetic field into regions with rising poloidal field in order to compensate for the centrifugal forces. Can such particles finally form a tight beam of relativistic runaways in the outboard region or is this prevented due to the perpendicular momentum they gain by passing the toroidal field? Since neither the energy nor the magnetic momentum of the particles is conserved this question has been treated by invoking the relativistic equations of motion. It turns out, however, that the problem can be essentially simplified since, apart from the centrifugal forces associated with the toroidal motion, the inertia forces are negligible. The resulting first order equation can be solved analytically. From the solution it is concluded that the formation of narrow runaway beams with diameters in the range of micrometers and very small pitch angles (v(perpendicular)/v(||)<10(-6)) appears feasible. Such electrons would perform low-frequency oscillations about three to four orders of magnitude lower than the gyrofrequency in the toroidal field. When passing the maximum poloidal magnetic field strength they are suddenly lost from the plasma region.

  4. Clues from stellar catastrophes

    NARCIS (Netherlands)

    Rimoldi, Alexander

    2016-01-01

    This thesis uses catastrophic stellar events (supernovae and stellar collisions) to investigate different aspects of their environment. The first part of the thesis examines what happens to supernova remnants near supermassive black holes like the one in the Milky Way Galaxy. To do so, a technique

  5. The phenomenon of runaway electrons in partially ionized non-ideal plasma

    Energy Technology Data Exchange (ETDEWEB)

    Ramazanov, T S; Turekhanova, K M [IETP, Al Farabi Kazakh National University, Tole Bi 96a, 050012 Almaty (Kazakhstan)], E-mail: kunduz@physics.kz

    2009-05-29

    The effect of runaway electrons in partially ionized hydrogen plasma is investigated on the basis of pseudopotential models. The conditions of runaway electrons were determined. Dependences of an electron free path on the plasma density and coupling parameter were obtained. It is shown that if the quantum-mechanical and screening effects in non-ideal partially ionized plasma are taken into consideration, the collision frequency curve for electrons has maxima and free path curves for electrons have minima.

  6. Models of the circumstellar medium of evolving, massive runaway stars moving through the Galactic plane

    NARCIS (Netherlands)

    Meyer, D.M.-A.; Mackey, J.; Langer, N.; Gvaramadze, V.V.; Mignone, A.; Izzard, R.G.; Kaper, L.

    2014-01-01

    At least 5 per cent of the massive stars are moving supersonically through the interstellar medium (ISM) and are expected to produce a stellar wind bow shock. We explore how the mass-loss and space velocity of massive runaway stars affect the morphology of their bow shocks. We run two-dimensional

  7. X-ray study of bow shocks in runaway stars

    Science.gov (United States)

    De Becker, M.; del Valle, M. V.; Romero, G. E.; Peri, C. S.; Benaglia, P.

    2017-11-01

    Massive runaway stars produce bow shocks through the interaction of their winds with the interstellar medium, with the prospect for particle acceleration by the shocks. These objects are consequently candidates for non-thermal emission. Our aim is to investigate the X-ray emission from these sources. We observed with XMM-Newton a sample of five bow shock runaways, which constitutes a significant improvement of the sample of bow shock runaways studied in X-rays so far. A careful analysis of the data did not reveal any X-ray emission related to the bow shocks. However, X-ray emission from the stars is detected, in agreement with the expected thermal emission from stellar winds. On the basis of background measurements we derive conservative upper limits between 0.3 and 10 keV on the bow shocks emission. Using a simple radiation model, these limits together with radio upper limits allow us to constrain some of the main physical quantities involved in the non-thermal emission processes, such as the magnetic field strength and the amount of incident infrared photons. The reasons likely responsible for the non-detection of non-thermal radiation are discussed. Finally, using energy budget arguments, we investigate the detectability of inverse Compton X-rays in a more extended sample of catalogued runaway star bow shocks. From our analysis we conclude that a clear identification of non-thermal X-rays from massive runaway bow shocks requires one order of magnitude (or higher) sensitivity improvement with respect to present observatories.

  8. On the effect of runaway electrons in dense plasma

    Energy Technology Data Exchange (ETDEWEB)

    Ramazanov, T.S.; Turekhanova, K.M. [IETP, Al Farabi Kazakh National University, Tole Bi 96, 480012 Almaty (Kazakhstan)

    2003-10-01

    The effect of runaway electrons has been studied in this work. There were derived the conditions runaway electrons, the influence of electric field on the electron velocity distribution is considered for nonideal classical plasma models. The dependence of friction force on electrons on their velocities,electron-ion collision frequency as a function of the coupling parameter and the strength of critical electric field on particle density and temperature are determined. The results are compared with the asymptotic theory. It has been shown that for the definite density and temperature ranges the difference between critical electric field values is essential for various plasma models. (copyright 2003 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. X-RAY EMISSION FROM STELLAR JETS BY COLLISION AGAINST HIGH-DENSITY MOLECULAR CLOUDS: AN APPLICATION TO HH 248

    Energy Technology Data Exchange (ETDEWEB)

    López-Santiago, J.; Ustamujic, S.; Castro, A. I. Gómez de [S. D. Astronomía y Geodesia, Facultad de Ciencias Matemáticas, Universidad Complutense de Madrid, E-28040 Madrid (Spain); Bonito, R.; Orlando, S. [Dipartimento di Fisica e Chimica, Università di Palermo, Piazza del Parlamento 1, I-90134 Palermo (Italy); Orellana, M. [Sede Andina de la Universidad Nacional de Río Negro (Argentina); Miceli, M. [INAF-Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, I-90134 Palermo (Italy); Albacete-Colombo, J. F. [Sede Atlántica de la Universidad Nacional de Río Negro, Don Bosco y Leloir s/n, 8500 Viedma RN (Argentina); Castro, E. de [Dpto. de Astrofísica y CC. de la Atmósfera, Facultad de Física, Universidad Complutense de Madrid, E-28040 Madrid (Spain)

    2015-06-10

    We investigate the plausibility of detecting X-ray emission from a stellar jet that impacts a dense molecular cloud, a scenario that may be typical for classical T Tauri stars with jets in dense star-forming complexes. We first model the impact of a jet against a dense cloud using two-dimensional axisymmetric hydrodynamic simulations, exploring different configurations of the ambient environment. Then, we compare our results with XMM-Newton observations of the Herbig–Haro object HH 248, where extended X-ray emission aligned with the optical knots is detected at the edge of the nearby IC 434 cloud. Our simulations show that a jet can produce plasma with temperatures up to 10{sup 7} K, consistent with production of X-ray emission, after impacting a dense cloud. We find that jets denser than the ambient medium but less dense than the cloud produce detectable X-ray emission only at impact with the cloud. From an exploration of the model parameter space, we constrain the physical conditions (jet density and velocity and cloud density) that reproduce the intrinsic luminosity and emission measure of the X-ray source possibly associated with HH 248 well. Thus, we suggest that the extended X-ray source close to HH 248 corresponds to a jet impacting a dense cloud.

  10. STELLARATOR INJECTOR

    Science.gov (United States)

    Post, R.F.

    1962-09-01

    A method and means are described for injecting energetic neutral atoms or molecular ions into dense magnetically collimated plasma columns of stellarators and the like in such a manner that the atoms or ions are able to significantly penetrate the column before being ionized by collision with the plasma constituent particles. Penetration of the plasma column by the neutral atoms or molecular ions is facilitated by superposition of two closely spaced magnetic mirrors on the plasma confinement field. The mirrors are moved apart to magnetically sweep plasma from a region between the mirrors and establish a relatively low plasma density therein. By virture of the low density, neutral atoms or molecular ions injected into the region significantly penetrate the plasma column before being ionized. Thereafter, the mirrors are diminished to permit the injected material to admix with the plasma in the remainder of the column. (AEC)

  11. A kinetic model for runaway electrons in the ionosphere

    Directory of Open Access Journals (Sweden)

    G. Garcia

    2006-09-01

    Full Text Available Electrodynamic models and measurements with satellites and incoherent scatter radars predict large field aligned current densities on one side of the auroral arcs. Different authors and different kinds of studies (experimental or modeling agree that the current density can reach up to hundreds of µA/m2. This large current density could be the cause of many phenomena such as tall red rays or triggering of unstable ion acoustic waves. In the present paper, we consider the issue of electrons moving through an ionospheric gas of positive ions and neutrals under the influence of a static electric field. We develop a kinetic model of collisions including electrons/electrons, electrons/ions and electrons/neutrals collisions. We use a Fokker-Planck approach to describe binary collisions between charged particles with a long-range interaction. We present the essential elements of this collision operator: the Langevin equation for electrons/ions and electrons/electrons collisions and the Monte-Carlo and null collision methods for electrons/neutrals collisions. A computational example is given illustrating the approach to equilibrium and the impact of the different terms (electrons/electrons and electrons/ions collisions on the one hand and electrons/neutrals collisions on the other hand. Then, a parallel electric field is applied in a new sample run. In this run, the electrons move in the z direction parallel to the electric field. The first results show that all the electron distribution functions are non-Maxwellian. Furthermore, runaway electrons can carry a significant part of the total current density, up to 20% of the total current density.

  12. Measurement of runaway electron energy distribution function during high-Z gas injection into runaway electron plateaus in DIII-Da)

    Energy Technology Data Exchange (ETDEWEB)

    Hollmann, E. M. [University of California—San Diego, 9500 Gilman Dr., La Jolla, California 92093, USA; Parks, P. B. [General Atomics, PO Box 85608, San Diego, California 92186, USA; Commaux, N. [Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, Tennessee 37831, USA; Eidietis, N. W. [General Atomics, PO Box 85608, San Diego, California 92186, USA; Moyer, R. A. [University of California—San Diego, 9500 Gilman Dr., La Jolla, California 92093, USA; Shiraki, D. [Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, Tennessee 37831, USA; Austin, M. E. [Institute for Fusion Studies, University of Texas—Austin, 2100 San Jacinto Blvd, Austin, Texas 78712, USA; Lasnier, C. J. [Lawrence Livermore National Laboratory, 7000 East Ave, Livermore, California 94550, USA; Paz-Soldan, C. [General Atomics, PO Box 85608, San Diego, California 92186, USA; Rudakov, D. L. [University of California—San Diego, 9500 Gilman Dr., La Jolla, California 92093, USA

    2015-05-01

    The evolution of the runaway electron (RE) energy distribution function fεfε during massive gas injection into centered post-disruption runaway electron plateaus has been reconstructed. Overall, fεfε is found to be much more skewed toward low energy than predicted by avalanche theory. The reconstructions also indicate that the RE pitch angle θ is not uniform, but tends to be large at low energies and small θ ~0.1–0.2 at high energies. Overall power loss from the RE plateau appears to be dominated by collisions with background free and bound electrons, leading to line radiation. However, the drag on the plasma current appears to be dominated by collisions with impurity ions in most cases. Synchrotron emission appears not to be significant for overall RE energy dissipation but may be important for limiting the peak RE energy.

  13. Massive runaway stars in the Large Magellanic Cloud

    Science.gov (United States)

    Gvaramadze, V. V.; Kroupa, P.; Pflamm-Altenburg, J.

    2010-09-01

    The origin of massive field stars in the Large Magellanic Cloud (LMC) has long been an enigma. The recent measurements of large offsets (˜ 100 km s-1) between the heliocentric radial velocities of some very massive (O2-type) field stars and the systemic LMC velocity provides a possible explanation of this enigma and suggests that the field stars are runaway stars ejected from their birthplaces at the very beginning of their parent cluster's dynamical evolution. A straightforward way to prove this explanation is to measure the proper motions of the field stars and to show that they are moving away from one of the nearby star clusters or OB associations. This approach is, however, complicated by the long distance to the LMC, which makes accurate proper motion measurements difficult. We used an alternative approach for solving the problem (first applied for Galactic field stars), based on the search for bow shocks produced by runaway stars. The geometry of detected bow shocks would allow us to infer the direction of stellar motion, thereby determining their possible parent clusters. In this paper we present the results of a search for bow shocks around six massive field stars that have been proposed as candidate runaway stars. Using archival Spitzer Space Telescope data, we found a bow shock associated with one of our programme stars, the O2 V((f*)) star BI 237, which is the first-ever detection of bow shocks in the LMC. Orientation of the bow shock suggests that BI 237 was ejected from the OB association LH 82 (located at ≃ 120 pc in projection from the star). A by-product of our search is the detection of bow shocks generated by four OB stars in the field of the LMC and an arc-like structure attached to the candidate luminous blue variable R81 (HD 269128). The geometry of two of these bow shocks is consistent with the possibility that their associated stars were ejected from the 30 Doradus star-forming complex. We discuss implications of our findings for the

  14. Simulating Thermonuclear Runaway in Novae

    Science.gov (United States)

    Dursi, L. J.; Truran, J.; Zingale, M.; Calder, A. C.; Fryxell, B.; Olson, K.; Ricker, P.; Rosner, R.; Timmes, F. X.; Tufo, H. M.; MacNeice, P.

    2000-12-01

    A nova is a thought to result from a partially degenerate thermonuclear runaway on the surface of a white dwarf. Material from the underlying white dwarf must be dredged up into the atmosphere in order to produce an explosion with the observed energies; the carbon and oxygen serve as catalysts for the hydrogen burning, allowing the much more temperature-sensitive CNO burning to occur. In order to understand this dredge-up problem, we are running two different types of simulations. The first are large-scale simulations with the FLASH code (Fryxell et al., 2000), using a one-dimensional set of initial conditions of a nova about to undergo runaway created by Ami Glasner. These initial conditions have been used in previous multidimensional simulations (Glasner et al. 1997; Kercek et al. 1998), but these simulations have given widely different results because of different mixing behaviors in the two codes. Our set of simulations will shed some light on this discrepancy; since our code has adaptive mesh refinement (MacNeice et al., 2000), we can afford to highly refine the region of the star where the mixing occurs, without the cost of highly refining the entire region. Because these large-scale computations are extremely compute-intensive, they are not appropriate for broad exploration of initial conditions. To do this, we use a One-Dimensional Turbulence (ODT) model which has been used in astrophysical models previously (Niemeyer & Kerstein, 1997). This allows us to use ODT simulations of the nova as experiments to guide us to interesting regimes to study further with multidimensional FLASH code simulations. This work was supported in part by the Department of Energy Grant No. B341495 to the Center for Astrophysical Thermonuclear Flashes at the University of Chicago under the ASCI Strategic Alliances Program and by NASA/Goddard Space Flight Center

  15. Parameters of a runaway electron avalanche

    Science.gov (United States)

    Oreshkin, E. V.; Barengolts, S. A.; Oreshkin, V. I.; Mesyats, G. A.

    2017-10-01

    The features of runaway electron avalanches developing in air at different pressures are investigated using a three-dimensional numerical simulation. The simulation results indicate that an avalanche of this type can be characterized, besides the time and length of its exponential growth, by the propagation velocity and by the average kinetic energy of the runaway electrons. It is shown that these parameters obey the similarity laws applied to gas discharges.

  16. Synchrotron radiation from a runaway electron distribution in tokamaks

    Energy Technology Data Exchange (ETDEWEB)

    Stahl, A.; Fülöp, T. [Department of Applied Physics, Nuclear Engineering, Chalmers University of Technology and Euratom-VR Association, SE-412 96 Göteborg (Sweden); Landreman, M. [Plasma Science and Fusion Center, MIT, Cambridge, Massachusetts 02139 (United States); Papp, G. [Department of Applied Physics, Nuclear Engineering, Chalmers University of Technology and Euratom-VR Association, SE-412 96 Göteborg (Sweden); Department of Nuclear Techniques, Budapest University of Technology and Economics, Association EURATOM, H-1111 Budapest (Hungary); Hollmann, E. [Center for Energy Research, University of California, San Diego, La Jolla, California 92093-0417 (United States)

    2013-09-15

    The synchrotron radiation emitted by runaway electrons in a fusion plasma provides information regarding the particle momenta and pitch-angles of the runaway electron population through the strong dependence of the synchrotron spectrum on these parameters. Information about the runaway density and its spatial distribution, as well as the time evolution of the above quantities, can also be deduced. In this paper, we present the synchrotron radiation spectra for typical avalanching runaway electron distributions. Spectra obtained for a distribution of electrons are compared with the emission of mono-energetic electrons with a prescribed pitch-angle. We also examine the effects of magnetic field curvature and analyse the sensitivity of the resulting spectrum to perturbations to the runaway distribution. The implications for the deduced runaway electron parameters are discussed. We compare our calculations to experimental data from DIII-D and estimate the maximum observed runaway energy.

  17. Runaway breakdown and electrical discharges in thunderstorms

    Science.gov (United States)

    Milikh, Gennady; Roussel-Dupré, Robert

    2010-12-01

    This review considers the precise role played by runaway breakdown (RB) in the initiation and development of lightning discharges. RB remains a fundamental research topic under intense investigation. The question of how lightning is initiated and subsequently evolves in the thunderstorm environment rests in part on a fundamental understanding of RB and cosmic rays and the potential coupling to thermal runaway (as a seed to RB) and conventional breakdown (as a source of thermal runaways). In this paper, we describe the basic mechanism of RB and the conditions required to initiate an observable avalanche. Feedback processes that fundamentally enhance RB are discussed, as are both conventional breakdown and thermal runaway. Observations that provide clear evidence for the presence of energetic particles in thunderstorms/lightning include γ-ray and X-ray flux intensifications over thunderstorms, γ-ray and X-ray bursts in conjunction with stepped leaders, terrestrial γ-ray flashes, and neutron production by lightning. Intense radio impulses termed narrow bipolar pulses (or NBPs) provide indirect evidence for RB particularly when measured in association with cosmic ray showers. Our present understanding of these phenomena and their enduring enigmatic character are touched upon briefly.

  18. Heterosynaptic Plasticity Prevents Runaway Synaptic Dynamics

    Science.gov (United States)

    Chen, Jen-Yung; Lonjers, Peter; Lee, Christopher; Chistiakova, Marina; Volgushev, Maxim

    2013-01-01

    Spike timing-dependent plasticity (STDP) and other conventional Hebbian-type plasticity rules are prone to produce runaway dynamics of synaptic weights. Once potentiated, a synapse would have higher probability to lead to spikes and thus to be further potentiated, but once depressed, a synapse would tend to be further depressed. The runaway synaptic dynamics can be prevented by precisely balancing STDP rules for potentiation and depression; however, experimental evidence shows a great variety of potentiation and depression windows and magnitudes. Here we show that modifications of synapses to layer 2/3 pyramidal neurons from rat visual and auditory cortices in slices can be induced by intracellular tetanization: bursts of postsynaptic spikes without presynaptic stimulation. Induction of these heterosynaptic changes depended on the rise of intracellular calcium, and their direction and magnitude correlated with initial state of release mechanisms. We suggest that this type of plasticity serves as a mechanism that stabilizes the distribution of synaptic weights and prevents their runaway dynamics. To test this hypothesis, we develop a cortical neuron model implementing both homosynaptic (STDP) and heterosynaptic plasticity with properties matching the experimental data. We find that heterosynaptic plasticity effectively prevented runaway dynamics for the tested range of STDP and input parameters. Synaptic weights, although shifted from the original, remained normally distributed and nonsaturated. Our study presents a biophysically constrained model of how the interaction of different forms of plasticity—Hebbian and heterosynaptic—may prevent runaway synaptic dynamics and keep synaptic weights unsaturated and thus capable of further plastic changes and formation of new memories. PMID:24089497

  19. Modeling the gamma-ray emission produced by runaway cosmic rays in the environment of RX J1713.7-3946

    OpenAIRE

    Casanova, S.; Jones, D. I.; Aharonian, F. A.; Fukui, Y.; Gabici, S.; Kawamura, A.; Onishi, T.; Rowell, G.; Sano, H.; Torii, K.; Yamamoto, H.

    2010-01-01

    Diffusive shock acceleration in supernova remnants is the most widely invoked paradigm to explain the Galactic cosmic ray spectrum. Cosmic rays escaping supernova remnants diffuse in the interstellar medium and collide with the ambient atomic and molecular gas. From such collisions gamma-rays are created, which can possibly provide the first evidence of a parent population of runaway cosmic rays. We present model predictions for the GeV to TeV gamma-ray emission produced by the collisions of ...

  20. Stellar formation

    CERN Document Server

    Reddish, V C

    1978-01-01

    Stellar Formation brings together knowledge about the formation of stars. In seeking to determine the conditions necessary for star formation, this book examines questions such as how, where, and why stars form, and at what rate and with what properties. This text also considers whether the formation of a star is an accident or an integral part of the physical properties of matter. This book consists of 13 chapters divided into two sections and begins with an overview of theories that explain star formation as well as the state of knowledge of star formation in comparison to stellar structure

  1. Modeling nonthermal emission from stellar bow shocks

    Science.gov (United States)

    Pereira, V.; López-Santiago, J.; Miceli, M.; Bonito, R.; de Castro, E.

    2016-04-01

    Context. Runaway O- and early B-type stars passing through the interstellar medium at supersonic velocities and characterized by strong stellar winds may produce bow shocks that can serve as particle acceleration sites. Previous theoretical models predict the production of high-energy photons by nonthermal radiative processes, but their efficiency is still debated. Aims: We aim to test and explain the possibility of emission from the bow shocks formed by runaway stars traveling through the interstellar medium by using previous theoretical models. Methods: We applied our model to AE Aurigae, the first reported star with an X-ray detected bow shock, to BD+43 3654, in which the observations failed in detecting high-energy emission, and to the transition phase of a supergiant star in the late stages of its life. Results: From our analysis, we confirm that the X-ray emission from the bow shock produced by AE Aurigae can be explained by inverse Compton processes involving the infrared photons of the heated dust. We also predict low high-energy flux emission from the bow shock produced by BD+43 3654, and the possibility of high-energy emission from the bow shock formed by a supergiant star during the transition phase from blue to red supergiant. Conclusions: Bow shocks formed by different types of runaway stars are revealed as a new possible source of high-energy photons in our neighborhood.

  2. Stellar remnants

    CERN Document Server

    Kawaler, S D; Srinivasan, G

    1997-01-01

    This volume examines the internal structure, origin and evolution of white dwarfs, neutron stars and black holes, all objects at the final stage of stellar evolution. It covers topics such as: pulsation of white dwarfs; millisecond pulsars; and the dynamics around black holes.

  3. Abrupt climate transition of icy worlds from snowball to moist or runaway greenhouse

    Science.gov (United States)

    Yang, Jun; Ding, Feng; Ramirez, Ramses M.; Peltier, W. R.; Hu, Yongyun; Liu, Yonggang

    2017-08-01

    Ongoing and future space missions aim to identify potentially habitable planets in our Solar System and beyond. Planetary habitability is determined not only by a planet's current stellar insolation and atmospheric properties, but also by the evolutionary history of its climate. It has been suggested that icy planets and moons become habitable after their initial ice shield melts as their host stars brighten. Here we show from global climate model simulations that a habitable state is not achieved in the climatic evolution of those icy planets and moons that possess an inactive carbonate-silicate cycle and low concentrations of greenhouse gases. Examples for such planetary bodies are the icy moons Europa and Enceladus, and certain icy exoplanets orbiting G and F stars. We find that the stellar fluxes that are required to overcome a planet's initial snowball state are so large that they lead to significant water loss and preclude a habitable planet. Specifically, they exceed the moist greenhouse limit, at which water vapour accumulates at high altitudes where it can readily escape, or the runaway greenhouse limit, at which the strength of the greenhouse increases until the oceans boil away. We suggest that some icy planetary bodies may transition directly to a moist or runaway greenhouse without passing through a habitable Earth-like state.

  4. Adjoint Fokker-Planck equation and runaway electron dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Chang; Brennan, Dylan P.; Bhattacharjee, Amitava [Princeton University, Princeton, New Jersey 08544 (United States); Boozer, Allen H. [Columbia University, New York, New York 10027 (United States)

    2016-01-15

    The adjoint Fokker-Planck equation method is applied to study the runaway probability function and the expected slowing-down time for highly relativistic runaway electrons, including the loss of energy due to synchrotron radiation. In direct correspondence to Monte Carlo simulation methods, the runaway probability function has a smooth transition across the runaway separatrix, which can be attributed to effect of the pitch angle scattering term in the kinetic equation. However, for the same numerical accuracy, the adjoint method is more efficient than the Monte Carlo method. The expected slowing-down time gives a novel method to estimate the runaway current decay time in experiments. A new result from this work is that the decay rate of high energy electrons is very slow when E is close to the critical electric field. This effect contributes further to a hysteresis previously found in the runaway electron population.

  5. Bump formation in the runaway electron tail

    CERN Document Server

    Decker, J; Fülöp, T

    2015-01-01

    Runaway electrons are generated in a magnetized plasma when the parallel electric field exceeds a critical value. For such electrons with energies typically reaching tens of MeV, the Abraham-Lorentz-Dirac (ALD) radiation force, in reaction to the synchrotron emission, is significant and can be the dominant process limiting the electron acceleration. The effect of the ALD-force on runaway electron dynamics in a homogeneous plasma is investigated using the relativistic finite-difference Fokker-Planck codes LUKE [Decker & Peysson, Report EUR-CEA-FC-1736, Euratom-CEA, (2004)] and CODE [Landreman et al, Comp. Phys. Comm. 185, 847 (2014)]. Under the action of the ALD force, we find that a bump is formed in the tail of the electron distribution function if the electric field is sufficiently large. We also observe that the energy of runaway electrons in the bump increases with the electric field amplitude, while the population increases with the bulk electron temperature. The presence of the bump divides the elec...

  6. Full-orbit and backward Monte Carlo simulation of runaway electrons

    Science.gov (United States)

    Del-Castillo-Negrete, Diego

    2017-10-01

    High-energy relativistic runaway electrons (RE) can be produced during magnetic disruptions due to electric fields generated during the thermal and current quench of the plasma. Understanding this problem is key for the safe operation of ITER because, if not avoided or mitigated, RE can severely damage the plasma facing components. In this presentation we report on RE simulation efforts centered in two complementary approaches: (i) Full orbit (6-D phase space) relativistic numerical simulations in general (integrable or chaotic) 3-D magnetic and electric fields, including radiation damping and collisions, using the recently developed particle-based Kinetic Orbit Runaway electron Code (KORC) and (ii) Backward Monte-Carlo (MC) simulations based on a recently developed efficient backward stochastic differential equations (BSDE) solver. Following a description of the corresponding numerical methods, we present applications to: (i) RE synchrotron radiation (SR) emission using KORC and (ii) Computation of time-dependent runaway probability distributions, RE production rates, and expected slowing-down and runaway times using BSDE. We study the dependence of these statistical observables on the electric and magnetic field, and the ion effective charge. SR is a key energy dissipation mechanism in the high-energy regime, and it is also extensively used as an experimental diagnostic of RE. Using KORC we study full orbit effects on SR and discuss a recently developed SR synthetic diagnostic that incorporates the full angular dependence of SR, and the location and basic optics of the camera. It is shown that oversimplifying the angular dependence of SR and/or ignoring orbit effects can significantly modify the shape and overestimate the amplitude of the spectra. Applications to DIII-D RE experiments are discussed.

  7. Equilibrium, confinement and stability of runaway electrons in tokamaks

    Energy Technology Data Exchange (ETDEWEB)

    Spong, D A

    1976-03-01

    Some of the ramifications of the runaway population in tokamak experiments are investigated. Consideration is given both to the normal operating regime of tokamaks where only a small fraction of high energy runaways are present and to the strong runaway regime where runaways are thought to carry a significant portion of the toroidal current. In particular, the areas to be examined are the modeling of strong runaway discharges, single particle orbit characteristics of runaways, macroscopic beam-plasma equilibria, and stability against kink modes. A simple one-dimensional, time-dependent model has been constructed in relation to strong runaway discharges. Single particle orbits are analyzed in relation to both the strong runaway regime and the weak regime. The effects of vector E x vector B drifts are first considered in strong runaway discharges and are found to lead to a slow inward shrinkage of the beam. Macroscopic beam-plasma equilibria are treated assuming a pressureless relativistic beam with inertia and using an ideal MHD approximation for the plasma. The stability of a toroidal relativistic beam against kink perturbations is examined using several models. (MOW)

  8. Astrospheres and Solar-like Stellar Winds

    Directory of Open Access Journals (Sweden)

    Wood Brian E.

    2004-07-01

    Full Text Available Stellar analogs for the solar wind have proven to be frustratingly difficult to detect directly. However, these stellar winds can be studied indirectly by observing the interaction regions carved out by the collisions between these winds and the interstellar medium (ISM. These interaction regions are called "astrospheres", analogous to the "heliosphere" surrounding the Sun. The heliosphere and astrospheres contain a population of hydrogen heated by charge exchange processes that can produce enough H I Ly alpha absorption to be detectable in UV spectra of nearby stars from the Hubble Space Telescope (HST. The amount of astrospheric absorption is a diagnostic for the strength of the stellar wind, so these observations have provided the first measurements of solar-like stellar winds. Results from these stellar wind studies and their implications for our understanding of the solar wind are reviewed here. Of particular interest are results concerning the past history of the solar wind and its impact on planetary atmospheres.

  9. Stellar evolution

    CERN Document Server

    Meadows, A J

    2013-01-01

    Stellar Evolution, Second Edition covers the significant advances in the understanding of birth, life, and death of stars.This book is divided into nine chapters and begins with a description of the characteristics of stars according to their brightness, distance, size, mass, age, and chemical composition. The next chapters deal with the families, structure, and birth of stars. These topics are followed by discussions of the chemical composition and the evolution of main-sequence stars. A chapter focuses on the unique features of the sun as a star, including its evolution, magnetic fields, act

  10. DOUBLE BOW SHOCKS AROUND YOUNG, RUNAWAY RED SUPERGIANTS: APPLICATION TO BETELGEUSE

    Energy Technology Data Exchange (ETDEWEB)

    Mackey, Jonathan; Mohamed, Shazrene; Neilson, Hilding R.; Langer, Norbert; Meyer, Dominique M.-A., E-mail: jmackey@astro.uni-bonn.de [Argelander-Institut fuer Astronomie, Auf dem Huegel 71, D-53121 Bonn (Germany)

    2012-05-20

    A significant fraction of massive stars are moving supersonically through the interstellar medium (ISM), either due to disruption of a binary system or ejection from their parent star cluster. The interaction of their wind with the ISM produces a bow shock. In late evolutionary stages these stars may undergo rapid transitions from red to blue and vice versa on the Hertzsprung-Russell diagram, with accompanying rapid changes to their stellar winds and bow shocks. Recent three-dimensional simulations of the bow shock produced by the nearby runaway red supergiant (RSG) Betelgeuse, under the assumption of a constant wind, indicate that the bow shock is very young (<30, 000 years old), hence Betelgeuse may have only recently become an RSG. To test this possibility, we have calculated stellar evolution models for single stars which match the observed properties of Betelgeuse in the RSG phase. The resulting evolving stellar wind is incorporated into two-dimensional hydrodynamic simulations in which we model a runaway blue supergiant (BSG) as it undergoes the transition to an RSG near the end of its life. We find that the collapsing BSG wind bubble induces a bow shock-shaped inner shell around the RSG wind that resembles Betelgeuse's bow shock, and has a similar mass. Surrounding this is the larger-scale retreating bow shock generated by the now defunct BSG wind's interaction with the ISM. We suggest that this outer shell could explain the bar feature located (at least in projection) just in front of Betelgeuse's bow shock.

  11. Models of primary runaway electron distribution in the runaway vortex regime

    Science.gov (United States)

    Guo, Zehua; Tang, Xian-Zhu; McDevitt, Christopher J.

    2017-11-01

    A number of recent numerical calculations have shown the formation of a bump in runaway electron (RE) energy distribution by taking into account the synchrontron radiational damping force due to RE's gyromotions. Here, we present a detailed examination on how the bump location changes at different pitch-angles and the characteristics of the RE pitch-angle distribution. Although REs moving along the magnetic field are preferably accelerated and then populate the phase-space of larger pitch-angle mainly through diffusions, an off-axis (i.e., at finite pitch) peak can still form due to the presence of a runaway vortex that accumulates REs at a finite pitch-angle. A simplified Fokker-Planck model and its semi-analytical solutions based on local expansions around the O point are used to illustrate the characteristics of RE distribution around the O point of the runaway vortex in phase-space. The calculated energy location of the O point together with the local energy and pitch-angle distributions agree with the full numerical solution, confirming a previous empirical model for the runaway vortex location and explaining the off-axis peak in the distribution.

  12. A backward Monte Carlo method for efficient computation of runaway probabilities in runaway electron simulation

    Science.gov (United States)

    Zhang, Guannan; Del-Castillo-Negrete, Diego

    2017-10-01

    Kinetic descriptions of RE are usually based on the bounced-averaged Fokker-Planck model that determines the PDFs of RE. Despite of the simplification involved, the Fokker-Planck equation can rarely be solved analytically and direct numerical approaches (e.g., continuum and particle-based Monte Carlo (MC)) can be time consuming specially in the computation of asymptotic-type observable including the runaway probability, the slowing-down and runaway mean times, and the energy limit probability. Here we present a novel backward MC approach to these problems based on backward stochastic differential equations (BSDEs). The BSDE model can simultaneously describe the PDF of RE and the runaway probabilities by means of the well-known Feynman-Kac theory. The key ingredient of the backward MC algorithm is to place all the particles in a runaway state and simulate them backward from the terminal time to the initial time. As such, our approach can provide much faster convergence than the brute-force MC methods, which can significantly reduce the number of particles required to achieve a prescribed accuracy. Moreover, our algorithm can be parallelized as easy as the direct MC code, which paves the way for conducting large-scale RE simulation. This work is supported by DOE FES and ASCR under the Contract Numbers ERKJ320 and ERAT377.

  13. On the origin of high-velocity runaway stars

    NARCIS (Netherlands)

    Gvaramadze, V.V.; Gualandris, A.; Portegies Zwart, S.

    2009-01-01

    We explore the hypothesis that some high-velocity runaway stars attain their peculiar velocities in the course of exchange encounters between hard massive binaries and a very massive star (either an ordinary 50-100 M-circle dot star or a more massive one, formed through runaway mergers of ordinary

  14. Experimental Investigation of Runaway Electron Generation in Textor

    NARCIS (Netherlands)

    R. Jaspers,; Finken, K.H.; Mank, G.; Hoenen, F.; Boedo, J. A.; Cardozo, N. J. L.; Schüller, F. C.

    1993-01-01

    An experimental study of the generation of runaway electrons in TEXTOR has been performed. From the infrared synchrotron radiation emitted by relativistic electrons, the number of runaway electrons can be obtained as a function of time. In low density discharges (n(e)BAR < 1 X 10(19) m-3)

  15. Predictors of Trauma-Related Symptoms among Runaway Adolescents

    Science.gov (United States)

    McCarthy, Michael D.; Thompson, Sanna J.

    2010-01-01

    Little is known about trauma-related symptoms among runaway adolescents. Precocious departure from familial homes often exposes youth to traumatic victimization. This study examined the extent to which runaway adolescents present trauma symptomotology and assessed factors that predict trauma symptoms. Participants (N = 350) were 12-18 years of age…

  16. Runaway generation during disruptions in JET and TEXTOR

    NARCIS (Netherlands)

    Lehnen, M.; Abdullaev, S. S.; Arnoux, G.; Bozhenkov, S. A.; Jakubowski, M. W.; R. Jaspers,; Plyusnin, V. V.; Riccardo, V.; Samm, U.

    2009-01-01

    Runaway electrons generated during ITER disruptions are of concern for the integrity of the plasma facing components. It is expected that a power of up to 8 GW is exposed to ITER PFCs. We present ill this article observations from JET and TEXTOR on the generation of runaways and the heat load

  17. Velocity Distributions of Runaway Stars Produced by Supernovae in ...

    Indian Academy of Sciences (India)

    Using a method of population synthesis, we investigate the runaway stars produced by disrupted binaries via asymmetric core collapse supernova explosions (CC-RASs) and thermonuclear supernova explosions (TN-RASs). We find the velocities of CC-RASs in the range of about 30--100 km s − 1 . The runaway stars ...

  18. Runaway pacemaker: a still existing complication and therapeutic guidelines

    DEFF Research Database (Denmark)

    Mickley, H; Andersen, C; Nielsen, L H

    1989-01-01

    Runaway pacemaker is a rare, but still existing potential lethal complication in permanent pacemakers. Within 4 1/2 years, we saw two cases of runaway pacemaker in patients with multiprogrammable, VVI pacemakers (Siemens-Elema, Model 668). In both cases a pacemaker-induced ventricular tachycardia...

  19. Runaway with Words: Teaching Poetry to At-Risk Teens.

    Science.gov (United States)

    Gardner, Joann

    1993-01-01

    Reports on "Runaway with Words," a poetry workshop for at-risk teens in Florida's runaway shelters. Describes how, through various exercises, oral recitations, and conversations, troubled teens learn basic writing skills that help them gain control over their emotions. (SR)

  20. Nowhere to Run: HIV Prevention for Runaway and Homeless Youth.

    Science.gov (United States)

    Posner, Marc

    This volume is a guide to providing effective Human Immunodeficiency Virus (HIV) and substance abuse prevention services to runaway and homeless youth. The guide is based on current research and the best programs in this field. Chapters 1 and 2 summarize what is known about runaway and homeless youth, the services these youth require if they are…

  1. Thermal Runaways in LHC Interconnections: Experiments

    CERN Document Server

    Willering, G P; Bottura, L; Scheuerlein, C; Verweij, A P

    2011-01-01

    The incident in the LHC in September 2008 occurred in an interconnection between two magnets of the 13 kA dipole circuit. This event was traced to a defect in one of the soldered joints between two superconducting cables stabilized by a copper busbar. Further investigation revealed defective joints of other types. A combination of (1) a poor contact between the superconducting cable and the copper stabilizer and (2) an electrical discontinuity in the stabilizer at the level of the connection can lead to an unprotected quench of the busbar. Once the heating power in the unprotected superconducting cable exceeds the heat removal capacity a thermal run-away occurs, resulting in a fast melt-down of the non-stabilized cable. We have performed a thorough investigation of the conditions upon which a thermal run-away in the defect can occur. To this aim, we have prepared heavily instrumented samples with well-defined and controlled defects. In this paper we describe the experiment, and the analysis of the data, and w...

  2. Local Thermonuclear Runaways in Dwarf Novae?

    Science.gov (United States)

    Shara, Michael

    2012-10-01

    We have no hope of understanding the structure and evolution of a class of astrophysical objects if we cannot identify the dominant energy source of those objects.The Disk Instability Model {DIM} postulates that Dwarf Nova {DN} outbursts are powered by runaway accretion from an accretion disk onto a White Dwarf {WD} in a red dwarf-WD mass transferring binary. Ominously, HST observations {e.g. Sion et al. 2001} of WD surface abundances hint at a significant shortcoming of the DIM. The data from the present proposal will be able to unequivocally demonstrate if the observed highly Carbon-depleted and Nitrogen-enhanced abundances on WD surfaces {NOT predicted by DIM} vary with binary orbital phase, or throughout a DN quiescence cycle, or from cycle to cycle. These same data will test if predicted {but never observed} Local Thermonuclear Runaways {"Nuclear-powered mini-novas"} occur on the WDs of DN. Such events could trigger or even power DN, providing the long-sought physical mechanism of DN eruptions that DIM lacks. As a "free" bonus, the same data may also directly detect the diffusion of accreted metals in a WD atmosphere for the first time, or provide significant limits on the diffusion rate.

  3. Magnetic field threshold for runaway generation in tokamak disruptions

    Science.gov (United States)

    F"Ul"Op, T.; Pokol, G.; Smith, H. M.; Helander, P.

    2009-05-01

    Due to a sudden cooling of the plasma in tokamak disruptions a beam of relativistic runaway electrons is sometimes generated, which may cause damage on plasma facing components. Experimental observations on large tokamaks show that the number of runaway electrons produced in disruptions depends on the magnetic field strength. In this work, two possible reasons for this threshold are studied. The first possible explanation for these observations is that the runaway beam excites whistler waves that scatter the electrons in velocity space and prevents the beam from growing. The growth rates of the most unstable whistler waves are inversely proportional to the magnetic field strength and it is possible to derive a magnetic field threshold below which no runaways are expected. The second possible explanation is the magnetic field dependence of the criterion for substantial runaway production determined by the induced electric field available and by the efficiency of the generation mechanisms. It is shown, that even in rapidly cooling plasmas, where hot-tail generation is expected to give rise to substantial runaway population, the whistler waves can stop the runaway formation below a certain magnetic field unless the post-disruption temperature is very low.

  4. One-Dimensional Modelling of Marine Current Turbine Runaway Behaviour

    Directory of Open Access Journals (Sweden)

    Staffan Lundin

    2016-04-01

    Full Text Available If a turbine loses its electrical load, it will rotate freely and increase speed, eventually achieving that rotational speed which produces zero net torque. This is known as a runaway situation. Unlike many other types of turbine, a marine current turbine will typically overshoot the final runaway speed before slowing down and settling at the runaway speed. Since the hydrodynamic forces acting on the turbine are dependent on rotational speed and acceleration, turbine behaviour during runaway becomes important for load analyses during turbine design. In this article, we consider analytical and numerical models of marine current turbine runaway behaviour in one dimension. The analytical model is found not to capture the overshoot phenomenon, while still providing useful estimates of acceleration at the onset of runaway. The numerical model incorporates turbine wake build-up and predicts a rotational speed overshoot. The predictions of the models are compared against measurements of runaway of a marine current turbine. The models are also used to recreate previously-published results for a tidal turbine and applied to a wind turbine. It is found that both models provide reasonable estimates of maximum accelerations. The numerical model is found to capture the speed overshoot well.

  5. Runaway studies in the ATF (Advanced Toroidal Facility) torsatron

    Energy Technology Data Exchange (ETDEWEB)

    England, A.C.; DeVan, W.R.; Eberle, C.C.; Fowler, R.H.; Gabbard, W.A.; Glowienka, J.C.; Harris, J.H.; Haste, G.R.; Kindsfather, R.R.; Morris, R.N.

    1989-01-01

    Pulsed torsatrons and heliotrons are susceptible to runaway electron formation and confinement resulting from the inherent good containment in the vacuum fields and the high loop voltages during the initiation and termination of the helical and vertical fields (''field ramping''). Because runaway electrons can cause an unacceptable level of hard X rays near the machine, a runaway suppression system was designed and included in the initial operation of the Advanced Toroidal Facility (ATF). The main component of the system is a rotating paddle that is normally left in the vacuum chamber during the field ramps. This device proved to be very effective in reducing the runaway population. Measurements of hard X rays from ATF have shown that the runaways are produced primarily during the field ramping but that usually a small steady-state runaway component is also present during the ''flat-top'' portion of the fields. The paddle is the main source of the hard X rays (thick-target bremsstrahlung), although other objects in the vacuum chamber also serve as targets for the runaways at various times. The maximum X-ray energy found by pulse height analysis is /approximately/12--15 MeV; the mean energy appears to be a few mega-electron-volts. A noticeable forward peaking of the bremsstrahlung from the paddle is evident. The limiters do not appear to be major sources of bremsstrahlung. 17 refs., 14 figs.

  6. Project Runaway: Calibrating the Spectroscopic Distance Scale Using Runaway O and Wolf-Rayet Stars

    Science.gov (United States)

    Hartkopf, William I.; Mason, B. D.

    2009-05-01

    Well-determined O star masses are notoriously difficult to obtain, due to such factors as broad spectral lines, larger and less-reliable average distances, high multiplicity rates, crowded fields, and surrounding nebulosity. Some of these difficulties are reduced for the subset of O stars known as runaways, however. They have escaped some of the nebulosity and crowding, and the event leading to their ejection virtually guarantees that these objects are either single stars or extremely hard spectroscopic binaries. The goal of this project is to increase the sample of known runaway stars, using updated proper motions from the soon-to-be-released UCAC3 catalog, as well as published radial velocities and data from recent duplicity surveys of massive stars using AO and speckle interferometry. Input files include the Galactic O Star Catalog of Maiz-Apellaniz et al. (2004 ApJSS 151, 103) as well as the Seventh Catalogue of Galactic Wolf-Rayet Stars and its more recent Annex (van der Hucht 2001 NewAR 45, 135; 2006 A&A 458, 453). The new runaway star sample will form the basis for a list of SIM targets aimed at improving the distances of Galactic O and WR stars, calibrating the spectroscopic distance scale and leading to more accurate mass estimates for these massive stars.

  7. Mitigating Thermal Runaway Risk in Lithium Ion Batteries

    Science.gov (United States)

    Darcy, Eric; Jeevarajan, Judy; Russell, Samuel

    2014-01-01

    The JSC/NESC team has successfully demonstrated Thermal Runaway (TR) risk reduction in a lithium ion battery for human space flight by developing and implementing verifiable design features which interrupt energy transfer between adjacent electrochemical cells. Conventional lithium ion (li-Ion) batteries can fail catastrophically as a result of a single cell going into thermal runaway. Thermal runaway results when an internal component fails to separate electrode materials leading to localized heating and complete combustion of the lithium ion cell. Previously, the greatest control to minimize the probability of cell failure was individual cell screening. Combining thermal runaway propagation mitigation design features with a comprehensive screening program reduces both the probability, and the severity, of a single cell failure.

  8. Production of runaway electrons by negative streamer discharges

    DEFF Research Database (Denmark)

    Chanrion, Olivier Arnaud; Neubert, Torsten

    2010-01-01

    and the conditions on the electric field for the acceleration of electrons into the runaway regime. We use particle codes to describe the process of stochastic acceleration and introduce a novel technique that improves the statistics of the relatively few electrons that reach high energies. The calculation......In this paper we estimate the probability that cold electrons can be accelerated by an ambient electric field into the runaway regime, and discuss the implications for negative streamer formation. The study is motivated by the discovery of ms duration bursts of γ-rays from the atmosphere above......V. Instead the relativistic runaway electron discharge has been proposed which requires a lower threshold electric field; however, seed electrons must be born with energies in the runaway regime. In this work we study the fundamental problem of electron acceleration in a conventional discharge...

  9. Runaway effects at the plasma boundary in ISTTOK

    Energy Technology Data Exchange (ETDEWEB)

    Plyusnin, V.V. E-mail: vladislav.plyusnin@cfn.ist.utl.pt; Cabral, J.A.C.; Figueiredo, H.; Varandas, C.A.F

    2003-03-01

    Experimental results on minor and major disruption events in discharges with runaway electrons in the small tokamak ISTTOK and corresponding numerical analysis are presented. Using the experimental data from the soft X-ray diagnostic the image of the plasma column in the presence of runaway electron instability and disruptions was reconstructed. The most probable zones of the interaction of energetic electrons with the plasma surrounding surfaces were detected as spots of the soft X-ray emission on the top and bottom parts of the plasma column during the development of the disruptions. Numerical analysis of the runaway instability allowed determining the runaway electrons characteristics, such as energy (W{sub eRA}{<=}30 keV) and density (n{sub RA}{approx}(0.001-0.01)n{sub e}). On the basis of this analysis the level of electrostatic turbulence due to the instability was estimated.

  10. Runaway generation during disruptions in JET and TEXTOR

    Energy Technology Data Exchange (ETDEWEB)

    Lehnen, M., E-mail: m.lehnen@fz-juelich.d [Institute of Energy Research - Plasma Physics, Forschungszentrum Juelich GmbH, Association EURATOM-FZJ, Juelich (Germany); Abdullaev, S.S. [Institute of Energy Research - Plasma Physics, Forschungszentrum Juelich GmbH, Association EURATOM-FZJ, Juelich (Germany); Arnoux, G. [EURATOM/UKAEA Fusion Association, Culham Science Centre, OX14 3DB (United Kingdom); Bozhenkov, S.A. [Institute of Energy Research - Plasma Physics, Forschungszentrum Juelich GmbH, Association EURATOM-FZJ, Juelich (Germany); Jakubowski, M.W. [Max-Planck-Institut fuer Plasmaphysik, IPP-EURATOM Association, Teilinstitut Greifswald, Wendelsteinstr. 1, 17491 Greifswald (Germany); Jaspers, R. [FOM-Rijnhuizen, Association EURATOM-FOM, PO Box 1207, 3430 BE Nieuwegein (Netherlands); Plyusnin, V.V. [Instituto de Plasmas e Fusao Nuclear/IST, Associacao EURATOM-IST, Av. Rovisco Pais, 1049-001 Lisbon (Portugal); Riccardo, V. [EURATOM/UKAEA Fusion Association, Culham Science Centre, OX14 3DB (United Kingdom); Samm, U. [Institute of Energy Research - Plasma Physics, Forschungszentrum Juelich GmbH, Association EURATOM-FZJ, Juelich (Germany)

    2009-06-15

    Runaway electrons generated during ITER disruptions are of concern for the integrity of the plasma facing components. It is expected that a power of up to 8 GW is exposed to ITER PFCs. We present in this article observations from JET and TEXTOR on the generation of runaways and the heat load deposition. Suppression techniques like massive gas injection and resonant magnetic perturbations are discussed.

  11. Sexual Health Information Seeking Online Among Runaway and Homeless Youth

    OpenAIRE

    Barman-Adhikari, Anamika; Rice, Eric

    2011-01-01

    Research shows runaway and homeless youth are reluctant to seek help from traditional health providers. The Internet can be useful in engaging this population and meeting their needs for sexual health information, including information about HIV and other sexually transmitted infections (STIs). Using a sample of homeless youth living in Los Angeles, California in June 2009, this study assesses the frequency with which runaway and homeless youth seek sexual health information via the Internet,...

  12. Stellar Metamorphosis:

    Science.gov (United States)

    2002-01-01

    [TOP LEFT AND RIGHT] The Hubble Space Telescope's Wide Field and Planetary Camera 2 has captured images of the birth of two planetary nebulae as they emerge from wrappings of gas and dust, like butterflies breaking out of their cocoons. These images highlight a fleeting phase in the stellar burnout process, occurring just before dying stars are transformed into planetary nebulae. The left-hand image is the Cotton Candy nebula, IRAS 17150-3224; the right-hand image, the Silkworm nebula, IRAS 17441-2411. Called proto-planetary nebulae, these dying stars have been caught in a transition phase between a red giant and a planetary nebula. This phase is only about 1,000 years long, very short in comparison to the 1 billion-year lifetime of a star. These images provide the earliest snapshots of the transition process. Studying images of proto-planetary nebulae is important to understanding the process of star death. A star begins to die when it has exhausted its thermonuclear fuel - hydrogen and helium. The star then becomes bright and cool (red giant phase) and swells to several tens of times its normal size. It begins puffing thin shells of gas off into space. These shells become the star's cocoon. In the Hubble images, the shells are the concentric rings seen around each nebula. But the images also reveal the nebulae breaking out from those shells. The butterfly-like wings of gas and dust are a common shape of planetary nebulae. Such butterfly shapes are created by the 'interacting winds' process, in which a more recent 'fast wind' - material propelled by radiation from the hot central star - punches a hole in the cocoon, allowing the nebula to emerge. (This 'interacting wind' theory was first proposed by Dr. Sun Kwok to explain the origin of planetary nebulae, and has been subsequently proven successful in explaining their shapes.) The nebulae are being illuminated by light from the invisible central star, which is then reflected toward us. We are viewing the nebulae

  13. Colliding Stellar Wind Models with Orbital Motion

    Science.gov (United States)

    Wilkin, Francis P.; O'Connor, Brendan

    2018-01-01

    We present thin-shell models for the collision between two ballistic stellar winds, including orbital motion.The stellar orbits are assumed circular, so that steady-state solutions exist in the rotating frame, where we include centrifugal and Coriolis forces. Exact solutions for the pre-shock winds are incorporated. Here we discuss 2-D model results for equal wind momentum-loss rates, although we allow for the winds to have distinct speeds and mass loss rates. For these unequal wind conditions, we obtain a clear violation of skew-symmetry, despite equal momentum loss rates, due to the Coriolis force.

  14. Numerical Simulations of a Jet-Cloud Collision and Starburst: Application to Minkowski’s Object

    Science.gov (United States)

    Fragile, P. Chris; Anninos, Peter; Croft, Steve; Lacy, Mark; Witry, Jason W. L.

    2017-12-01

    We present results of three-dimensional, multi-physics simulations of an AGN jet colliding with an intergalactic cloud. The purpose of these simulations is to assess the degree of “positive feedback,” i.e., jet-induced star formation, that results. We have specifically tailored our simulation parameters to facilitate a comparison with recent observations of Minkowski’s Object (MO), a stellar nursery located at the termination point of a radio jet coming from galaxy NGC 541. As shown in our simulations, such a collision triggers shocks, which propagate around and through the cloud. These shocks condense the gas and under the right circumstances may trigger cooling instabilities, creating runaway increases in density, to the point that individual clumps can become Jeans unstable. Our simulations provide information about the expected star formation rate, total mass converted to H I, H2, and stars, and the relative velocity of the stars and gas. Our results confirm the possibility of jet-induced star formation, and agree well with the observations of MO.

  15. Thermal Runaway Severity Reduction Assessment and Implementation: On Li-Ion Batteries

    Science.gov (United States)

    Darcy, Eric

    2015-01-01

    Preventing cell-cell thermal runaway propagation and flames/sparks from exiting battery enclosure is possible with proper thermal & electrical design and cell thermal runaway ejecta/effluent management and can be had with minimal mass/volume penalty.

  16. Plasma recombination in runaway discharges in tokamak TCABR

    Energy Technology Data Exchange (ETDEWEB)

    Soboleva, T.K. [Universidad Nacional Autonoma de Mexico, Mexico City (Mexico). Inst. de Ciencias Nucleares; Galvao, R.M.O.; Kuznetsov, Yu. K.; Nascimento, I.C. [Sao Paulo Univ., SP (Brazil). Inst. de Fisica; Krasheninnikov, S.I. [University of California, San Diego, CA (United States)

    2002-03-01

    A new regime of runaway discharges has been observed in the TCABR tokamak. One of the most distinctive features of this regime is the effect of plasma detachment from the limiter. This experimental fact can only be explained by the volume recombination, which requires a low-temperature plasma. The analysis of the energy and particle balance in the system plasma-relativistic runaway beam in TCABR, which takes into account only the collisional mechanism of the heat transfer from runaways to thermal electrons, predicts electron temperatures T{sub e} = 0.1 - 2 eV; the temperature decreases with the neutral density increase. The recombination process with the rate constant around 10{sup -16} m3/s is required for the explanation of plasma density behavior in the experiment. At present, it is difficult to conclude about the mechanism of recombination. More reliable and detailed experimental data, mainly about the plasma temperature, are necessary. (author)

  17. Generation of runaway electron beams in high-pressure nitrogen

    Science.gov (United States)

    Tarasenko, V. F.; Burachenko, A. G.; Baksht, E. Kh

    2017-07-01

    In this paper the results of experimental studies of the amplitude-temporal characteristics of a runaway electron beam, as well as breakdown voltage in nitrogen are presented. The voltage pulses with the amplitude in incident wave ≈120 kV and the rise time of ≈0.3 ns was used. The supershort avalanche electron beam (SAEB) was detected by a collector behind the flat anode. The amplitude-time characteristics of the voltage and SAEB current were studied with subnanosecond time resolution. The maximum pressure at which a SAEB is detectable by collector was ∼1 MPa. This pressure increases with decreasing the voltage rise time. The waveforms of the discharge and runaway electron beam currents was synchronized with the voltage pulses. The mechanism of the runaway electron generation in atmospheric-pressure gases is analyzed on the basis of the obtained experimental data.

  18. Effects of Spatial Gradients on Electron Runaway Acceleration

    Science.gov (United States)

    MacNeice, Peter; Ljepojevic, N. N.

    1996-01-01

    The runaway process is known to accelerate electrons in many laboratory plasmas and has been suggested as an acceleration mechanism in some astrophysical plasmas, including solar flares. Current calculations of the electron velocity distributions resulting from the runaway process are greatly restricted because they impose spatial homogeneity on the distribution. We have computed runaway distributions which include consistent development of spatial gradients in the energetic tail. Our solution for the electron velocity distribution is presented as a function of distance along a finite length acceleration region, and is compared with the equivalent distribution for the infinitely long homogenous system (i.e., no spatial gradients), as considered in the existing literature. All these results are for the weak field regime. We also discuss the severe restrictiveness of this weak field assumption.

  19. Relation of the runaway avalanche threshold to momentum space topology

    Science.gov (United States)

    McDevitt, Christopher J.; Guo, Zehua; Tang, Xian-Zhu

    2018-02-01

    The underlying physics responsible for the formation of an avalanche instability due to the generation of secondary electrons is studied. A careful examination of the momentum space topology of the runaway electron population is carried out with an eye toward identifying how qualitative changes in the momentum space of the runaway electrons is correlated with the avalanche threshold. It is found that the avalanche threshold is tied to the merger of an O and X point in the momentum space of the primary runaway electron population. Such a change of the momentum space topology is shown to be accurately described by a simple analytic model, thus providing a powerful means of determining the avalanche threshold for a range of model assumptions.

  20. Study of runaway electrons with Hard X-ray spectrometry of tokamak plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Shevelev, A.; Chugunov, I.; Khilkevitch, E.; Gin, D.; Doinikov, D.; Naidenov, V. [Ioffe Physical-Technical Institute of the Russian Academy of Sciences, Polytechnicheskaya 26, St. Petersburg, 194021 (Russian Federation); Kiptily, V. [EURATOM / CCFE Fusion Association, Abingdon, OX14 3DB (United Kingdom); Plyusnin, V. [Instituto de Plasmas e Fusão Nuclear, Associação EURATOM-IST, Instituto Superior Tecnico, Universidade Tecnica de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Collaboration: EFDA-JET Contributors

    2014-08-21

    Hard-X-ray spectrometry is a tool widely used for diagnostic of runaway electrons in existing tokamaks. In future machines, ITER and DEMO, HXR spectrometry will be useful providing information on runaway electron energy, runaway beam current and its profile during disruption.

  1. Formation of massive black holes in galactic nuclei: runaway tidal encounters

    Science.gov (United States)

    Stone, Nicholas C.; Küpper, Andreas H. W.; Ostriker, Jeremiah P.

    2017-06-01

    Nuclear star clusters (NSCs) and supermassive black holes (SMBHs) both inhabit galactic nuclei, coexisting in a range of bulge masses, but excluding each other in the largest or smallest galaxies. We propose that the transformation of NSCs into SMBHs occurs via runaway tidal captures, once NSCs exceed a certain critical central density and velocity dispersion. The bottleneck in this process is growing the first e-fold in black hole mass. The growth of a stellar mass black hole past this bottleneck occurs as tidally captured stars are consumed in repeated episodes of mass transfer at pericentre. Tidal captures may deactivate as a growth channel once the black hole mass ≳102-3 M⊙, but tidal disruption events will continue and can grow the seed SMBH to larger sizes. The runaway slows (becomes subexponential) once the seed SMBH consumes the core of its host NSC. While most of the cosmic mass density in SMBHs is ultimately produced by episodic gaseous accretion in very massive galaxies, the smallest SMBHs have probably grown from strong tidal encounters with NSC stars. SMBH seeds that grow for a time t entirely through this channel will follow simple power-law relations with the velocity dispersion, σ, of their host galaxy. In the simplest regime, it is M_\\bullet ˜ σ ^{3/2}√{M_\\star t / G} ˜ 106 M_{⊙} (σ / 50 {km s}^{-1})^{3/2}(t/10^{10} yr)^{1/2}, but the exponents and pre-factor can differ slightly depending on the details of loss cone refilling. Current tidal disruption event rates predicted from this mechanism are consistent with observations.

  2. On the origin of the hypervelocity runaway star HD271791

    OpenAIRE

    Gvaramadze, V.V.

    2009-01-01

    We discuss the origin of the runaway early B-type star HD271791 and show that its extremely high velocity (\\simeq 530-920 km/s) cannot be explained within the framework of the binary-supernova ejection scenario. Instead, we suggest that HD271791 attained its peculiar velocity in the course of a strong dynamical encounter between two hard massive binaries or via an exchange encounter between a hard massive binary and a very massive star, formed through runaway mergers of ordinary massive stars...

  3. Stellar Physics 2: Stellar Evolution and Stability

    CERN Document Server

    Bisnovatyi-Kogan, Gennady S

    2011-01-01

    "Stellar Physics" is a an outstanding book in the growing body of literature on star formation and evolution. Not only does the author, a leading expert in the field, very thoroughly present the current state of knowledge on stellar physics, but he handles with equal care the many problems that this field of research still faces. A bibliography with well over 1000 entries makes this book an unparalleled reference source. "Stellar Evolution and Stability" is the second of two volumes and can be read, as can the first volume "Fundamental Concepts and Stellar Equilibrium," as a largely independent work. It traces in great detail the evolution of protostars towards the main sequence and beyond this to the last stage of stellar evolution, with the corresponding vast range from white dwarfs to supernovae explosions, gamma-ray bursts and black hole formation. The book concludes with special chapters on the dynamical, thermal and pulsing stability of stars. This second edition is carefully updated in the areas of pre...

  4. Space dependent, full orbit effects on runaway electron dynamics in tokamak plasmas

    Science.gov (United States)

    Carbajal, L.; del-Castillo-Negrete, D.; Spong, D.; Seal, S.; Baylor, L.

    2017-04-01

    The dynamics of RE (runaway electrons) in fusion plasmas span a wide range of temporal scales, from the fast gyro-motion, ˜ 10 - 11 s, to the observational time scales, ˜ 10 - 2 → 1 s. To cope with this scale separation, RE are usually studied within the bounce-average or the guiding center approximations. Although these approximations have yielded valuable insights, a study with predictive capabilities of RE in fusion plasmas calls for the incorporation of full orbit effects in configuration space in the presence of three-dimensional magnetic fields. We present numerical results on this problem using the Kinetic Orbit Runaway electrons Code that follows relativistic electrons in general electric and magnetic fields under the full Lorentz force, collisions, and radiation losses. At relativistic energies, the main energy loss is due to radiation damping, which we incorporate using the Landau-Lifshitz formulation of the Abraham-Lorentz-Dirac force. The main focus is on full orbit effects on synchrotron radiation. It is shown that even in the absence of magnetic field stochasticty, neglecting orbit dynamics can introduce significant errors in the computation of the total radiated power and the synchrotron spectra. The statistics of collisionless (i.e., full orbit induced) pitch angle dispersion, and its key role played on synchrotron radiation, are studied in detail. Numerical results are also presented on the pitch angle dependence of the spatial confinement of RE and on full orbit effects on the competition of electric field acceleration and radiation damping. Finally, full orbit calculations are used to explore the limitations of gyro-averaging in the relativistic regime. To explore the practical impact of the results, DIII-D and ITER-like parameters are used in the simulations.

  5. Velocity Distributions of Runaway Stars Produced by Supernovae in ...

    Indian Academy of Sciences (India)

    J. Astrophys. Astr. (2016) 37: 22. DOI: 10.1007/s12036-016-9400-2. Velocity Distributions of Runaway Stars Produced by Supernovae in the Galaxy. Abudusaimaitijiang Yisikandeer. ∗. , Chunhua Zhu, Zhaojun Wang. & Guoliang Lü. School of Physical Science and Technology, Xinjiang University, Urumqi, 830046, China. ∗.

  6. Runaway beam studies during disruptions at JET-ILW

    Energy Technology Data Exchange (ETDEWEB)

    Reux, C., E-mail: cedric.reux@cea.fr [JET-EFDA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); CEA, IRFM, F-13108 Saint-Paul-lez-Durance (France); Plyusnin, V. [JET-EFDA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Instituto de Plasmas e Fuso Nuclear, Instituto Superior Tcnico, Universidade de Lisboa, Lisboa (Portugal); Alper, B. [JET-EFDA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); CCFE, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Alves, D. [JET-EFDA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Instituto de Plasmas e Fuso Nuclear, Instituto Superior Tcnico, Universidade de Lisboa, Lisboa (Portugal); Bazylev, B. [JET-EFDA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Institut für Hochleistungsimpuls und Mikrowellentechnik, Karlsruhe Institute of Technology, Campus Nord, 76021 Karlsruhe (Germany); Belonohy, E. [JET-EFDA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); EFDA-CSU, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Brezinsek, S. [JET-EFDA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Forschungszentrum Jülich GmbH, Institut für Energie-und Klimaforschung-Plasmaphysik, 52425 Jülich (Germany); Decker, J. [JET-EFDA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); CEA, IRFM, F-13108 Saint-Paul-lez-Durance (France); Devaux, S. [JET-EFDA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); CCFE, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); Vries, P. de [JET-EFDA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); ITER Organization, Route de Vinon sur Verdon, 13115 St Paul Lez Durance (France); Fil, A. [JET-EFDA, Culham Science Centre, Abingdon OX14 3DB (United Kingdom); CEA, IRFM, F-13108 Saint-Paul-lez-Durance (France); and others

    2015-08-15

    Highlights: • Runaway electrons (RE) have been obtained at JET-ILW using massive argon injection. • The runaway electron domain entry points are similar between JET-C and JET-ILW. • Inside the runaway electron domain, higher RE currents are observed with JET-ILW. • RE impact has been observed without material melting up to 100 kA RE current. • Heat deposition of 2 ± 1 mm is confirmed by measurements and simulations. - Abstract: Runaway electrons (RE) during disruptions are a concern for future tokamaks including ITER with its metallic wall. Although RE are rare in spontaneous disruptions with the JET ITER-like Wall (JET-ILW), RE beams up to 380 kA were obtained using massive injection (MGI) of argon in JET-ILW divertor discharges. Entry points into the RE domain defined by operational parameters (toroidal field, argon fraction in MGI) are unchanged but higher RE currents have been obtained inside the JET-ILW MGI-generated RE domain when compared to JET-C. This might be due to the influence of the metallic wall on the current quench plasma. Temperatures of 900 °C have been observed following RE impacts on beryllium tiles. Heat deposition depth of ∼2 mm has to be assumed to match the tile cooling time. 3D simulations of the RE energy deposition using the ENDEP/MEMOS codes show that material melting is unlikely with 100 kA RE beams.

  7. Structure and evolution of high-mass stellar mergers

    Science.gov (United States)

    Glebbeek, Evert; Gaburov, Evghenii; Portegies Zwart, Simon; Pols, Onno R.

    2013-10-01

    In young dense clusters repeated collisions between massive stars may lead to the formation of a very massive star (above 100 M⊙). In the past, the study of the long-term evolution of merger remnants has mostly focused on collisions between low-mass stars (up to about 2 M⊙) in the context of blue-straggler formation. The evolution of collision products of more massive stars has not been as thoroughly investigated. In this paper, we study the long-term evolution of a number of stellar mergers formed by the head-on collision of a primary star with a mass of 5-40 M⊙ with a lower mass star at three points in its evolution in order to better understand their evolution. We use smooth particle hydrodynamics calculations to model the collision between the stars. The outcome of this calculation is reduced to one dimension and imported into a stellar evolution code. We follow the subsequent evolution of the collision product through the main sequence at least until the onset of helium burning. We find that little hydrogen is mixed into the core of the collision products, in agreement with previous studies of collisions between low-mass stars. For collisions involving evolved stars, we find that during the merger the surface nitrogen abundance can be strongly enhanced. The evolution of most of the collision products proceeds analogously to that of normal stars with the same mass, but with a larger radius and luminosity. However, the evolution of collision products that form with a hydrogen-depleted core is markedly different from that of normal stars with the same mass. They undergo a long-lived period of hydrogen-shell burning close to the main-sequence band in the Hertzsprung-Russell diagram and spend the initial part of core-helium burning as compact blue supergiants.

  8. Runaway behavior among children in residential care in St. Petersburg: A qualitative study

    Directory of Open Access Journals (Sweden)

    Eritsyan K.Yu.

    2017-12-01

    Full Text Available Background. Runaway behavior among children in residential care is a serious social problem in all countries of the world. Existing scientific data on risk factors and motives of runaway from out-of-home care may not be absolutely relevant to the Russian cultural context. Objective. To describe risk factors and the motives that cause children to runaway from residential care. Design. A qualitative study that included 2 focus groups with staff and graduates of residential care supplemented by the analysis of 23 cases of child runaways from residential care in St. Petersburg. Results. The study revealed the following runaway risk factors and motives: 1 running to parents or relatives, 2 romantic and/or sexual relations, 3 interaction with peers, 4 psychiatric problems, 5 addictive behavior, 6 avoidance of conflicts, 7 physical or emotional violence, 8 unmotivated runaways for entertainment, 9 problems adapting to the care institution, 10 dissatisfaction with the conditions at the care institution. Moreover, in this study, two different types of runaways have been identified, including relatively “true” runaways and those who are not psychologically experienced as such, but are only disobeying the formal rules of the care institution. Conclusions. Runaways of children from residential care are extremely heterogeneous in nature. In further empirical studies, it should be taken into account that runaways may be true and formal. There can be multiple reasons for running away: the care institution itself, a child’s personality, or his or her social network outside of the care institution.

  9. Experimental and theoretical analysis of a method to predict thermal runaway in Li-ion cells

    Science.gov (United States)

    Shah, Krishna; Chalise, Divya; Jain, Ankur

    2016-10-01

    Thermal runaway is a well-known safety concern in Li-ion cells. Methods to predict and prevent thermal runaway are critically needed for enhanced safety and performance. While much work has been done on understanding the kinetics of various heat generation processes during thermal runaway, relatively lesser work exists on understanding how heat removal from the cell influences thermal runaway. Through a unified analysis of heat generation and heat removal, this paper derives and experimentally validates a non-dimensional parameter whose value governs whether or not thermal runaway will occur in a Li-ion cell. This parameter is named the Thermal Runaway Number (TRN), and comprises contributions from thermal transport within and outside the cell, as well as the temperature dependence of heat generation rate. Experimental data using a 26650 thermal test cell are in good agreement with the model, and demonstrate the dependence of thermal runaway on various thermal transport and heat generation parameters. This parameter is used to predict the thermal design space in which the cell will or will not experience thermal runaway. By combining all thermal processes contributing to thermal runaway in a single parameter, this work contributes towards a unified understanding of thermal runaway, and provides the fundamental basis for design tools for safe, high-performance Li-ion batteries.

  10. Space Weather: Linking Stellar Explosions to the Human Endeavor

    Science.gov (United States)

    Knipp, Delores

    2017-06-01

    Arguably humans have flourished as a result of stellar explosions; we are, after all, stardust. Nonetheless, rapid technology advances of the last 200 years sometimes put society and individuals on a collision course with the natural variability of stellar and solar atmospheres. Human space exploration, routine satellite navigation system applications, aviation safety, and electric power grids are examples of such vulnerable endeavors. In this presentation I will outline how global society relies on ‘normal’ solar and stellar emissions, yet becomes susceptible to extremes of these emissions. The imprints of these astronomical-terrestrial interactions abound. In particular, I will highlight ways in which stellar/solar bursts link with our space-atmosphere-interaction region, producing multi-year patterns in cosmic ray detection, gorgeous aurora, and deep concern for good order and function of global community.

  11. Observation of runaway electrons by infrared camera in J-TEXT.

    Science.gov (United States)

    Tong, R H; Chen, Z Y; Zhang, M; Huang, D W; Yan, W; Zhuang, G

    2016-11-01

    When the energy of confined runaway electrons approaches several tens of MeV, the runaway electrons can emit synchrotron radiation in the range of infrared wavelength. An infrared camera working in the wavelength of 3-5 μm has been developed to study the runaway electrons in the Joint Texas Experimental Tokamak (J-TEXT). The camera is located in the equatorial plane looking tangentially into the direction of electron approach. The runaway electron beam inside the plasma has been observed at the flattop phase. With a fast acquisition of the camera, the behavior of runaway electron beam has been observed directly during the runaway current plateau following the massive gas injection triggered disruptions.

  12. Stellar Chromospheric Activity

    Directory of Open Access Journals (Sweden)

    Hall Jeffrey C.

    2008-03-01

    Full Text Available The Sun, stars similar to it, and many rather dissimilar to it, have chromospheres, regions classically viewed as lying above the brilliant photosphere and characterized by a positive temperature gradient and a marked departure from radiative equilibrium. Stellar chromospheres exhibit a wide range of phenomena collectively called activity, stemming largely from the time evolution of their magnetic fields and the mass flux and transfer of radiation through the complex magnetic topology and the increasingly optically thin plasma of the outer stellar atmosphere. In this review, I will (1 outline the development of our understanding of chromospheric structure from 1960 to the present, (2 discuss the major observational programs and theoretical lines of inquiry, (3 review the origin and nature of both solar and stellar chromospheric activity and its relationship to, and effect on, stellar parameters including total energy output, and (4 summarize the outstanding problems today.

  13. Mechanistic elucidation of thermal runaway in potassium-ion batteries

    Science.gov (United States)

    Adams, Ryan A.; Varma, Arvind; Pol, Vilas G.

    2018-01-01

    For the first time, thermal runaway of charged graphite anodes for K-ion batteries is investigated, using differential scanning calorimetry (DSC) to probe the exothermic degradation reactions. Investigated parameters such as state of charge, cycle number, surface area, and binder demonstrate strong influences on the DSC profiles. Thermal runaway initiates at 100 °C owing to KxC8 - electrolyte reactions, but the K-ion graphite anode evolves significantly less heat as compared to the analogous Li-ion system (395 J g-1 vs. 1048 J g-1). The large volumetric expansion of graphite during potassiation cracks the SEI layer, enabling contact and reaction of KC8 - electrolyte, which diminishes with cycle number due to continuous SEI growth. High surface area graphite decreases the total heat generation, owing to thermal stability of the K-ion SEI layer. These findings illustrate the dynamic nature of K-ion thermal runaway and its many contrasts with the Li-ion graphite system, permitting possible engineering solutions for safer batteries.

  14. A search for pulsar companions to runaway OB stars

    Energy Technology Data Exchange (ETDEWEB)

    Philp, C. (Department of Physics and Astronomy, University of North Carolina at Chapel Hill, CB 3255 Chapel Hill, North Carolina 27599-3255 (United States)); Frail, D.A. (NRAO-VLA, P.O. Box O, Socorro, New Mexico 87801 (United States)); Evans, C.R. (Department of Physics and Astronomy, University of North Carolina at Chapel Hill, CB 3255 Chapel Hill, North Carolina 27599-3255 (United States)); Leonard, P.J.T. (T-6, MS B288 LANL, Los Alamos, New Mexico 87545 (United States))

    1994-07-05

    Runaway'' OB stars are distinguished from the normal population by large peculiar velocities ([gt]30 km s[sup [minus]1]) and/or large heights above the galactic plane (up to several kpc). There are two competing models to explain these properties: the supernova ejection mechanism and the dynamical ejection mechanism. The first predicts a high incidence of compact companions to the OB runaways ([gt]50%), while the second predicts a low percentage ([lt]10%). We have initiated a Very Large Array (VLA) search for radio pulsars at the positions of known OB runaways. We will use the High Time Resolution Processor (HTRP) to search for pulsed 20 cm emission, while also making continuum images at both 6 cm and 20 cm to distinguish thermal wind sources from nonthermal emitters. These two aspects of the search are complementary and can be performed simultaneously. As well as testing the two ejection hypotheses, this search might discover an object similar to PSR 1259[minus]63 (a pulsar--Be star binary system) which would shed further light on the link between neutron star formation in massive binaries and massive x-ray binaries. To improve the chances of detecting pulsars, we propose to observe stars later than O5. The winds from these stars, with their lower mass loss rates, are less likely to occult the pulsar's radio beam through free-free absorption or serve as a confusing point source.

  15. Relativistic runaway breakdown in low-frequency radio

    Science.gov (United States)

    Füllekrug, Martin; Roussel-Dupré, Robert; Symbalisty, Eugene M. D.; Chanrion, Olivier; Odzimek, Anna; van der Velde, Oscar; Neubert, Torsten

    2010-01-01

    The electromagnetic radiation emitted by an electron avalanche beam resulting from relativistic runaway breakdown within the Earth's atmosphere is investigated. It is found from theoretical modeling with a computer simulation that the electron beam emits electromagnetic radiation which is characterized by consecutive broadband pulses in the low-frequency radio range from ˜10 to 300 kHz at a distance of ˜800 km. Experimental evidence for the existence of consecutive broadband pulses is provided by low-frequency radio observations of sprite-producing lightning discharges at a distance of ˜550 km. The measured broadband pulses occur ˜4-9 ms after the sprite-producing lightning discharge, they exhibit electromagnetic radiation which mainly spans the frequency range from ˜50 to 350 kHz, and they exhibit complex waveforms without the typical ionospheric reflection of the first hop sky wave. Two consecutive pulses occur ˜4.5 ms and ˜3 ms after the causative lightning discharge and coincide with the sprite luminosity. It is concluded that relativistic runaway breakdown within the Earth's atmosphere can emit broadband electromagnetic pulses and possibly generates sprites. The source location of the broadband pulses can be determined with an interferometric network of wideband low-frequency radio receivers to lend further experimental support to the relativistic runaway breakdown theory.

  16. Advanced Stellar Compass

    DEFF Research Database (Denmark)

    Madsen, Peter Buch; Jørgensen, John Leif; Thuesen, Gøsta

    1997-01-01

    This document describes all interface properties for the Advanced Stellar Compass, developed for the German Research Satellite "CHAMP". Basic operations, modes, software protocol, calibration methods and closed loop test strategies are described.......This document describes all interface properties for the Advanced Stellar Compass, developed for the German Research Satellite "CHAMP". Basic operations, modes, software protocol, calibration methods and closed loop test strategies are described....

  17. Influence of the angular scattering of electrons on the runaway threshold in air

    DEFF Research Database (Denmark)

    Chanrion, O.; Bonaventura, Z.; Bourdon, A.

    2016-01-01

    The runaway electron mechanism is of great importance for the understanding of the generation of x- and gamma rays in atmospheric discharges. In 1991, terrestrial gamma-ray flashes (TGFs) were discovered by the Compton Gamma-Ray Observatory. Those emissions are bremsstrahlung from high energy ele...... scattering is not valid below 1 MeV where the runaway threshold usually is defined. These results are important for the thermal runaway and the runaway electron avalanche discharge mechanisms suggested to participate in the TGF generation....

  18. The Runaway Greenhouse Effect on Earth and other Planets

    Science.gov (United States)

    Rabbette, Maura; Pilewskie, Peter; McKay, Christopher; Young, Robert

    2001-01-01

    Water vapor is an efficient absorber of outgoing longwave infrared radiation on Earth and is the primary greenhouse gas. Since evaporation increases with increasing sea surface temperature, and the increase in water vapor further increases greenhouse warming, there is a positive feedback. The runaway greenhouse effect occurs if this feedback continues unchecked until all the water has left the surface and enters the atmosphere. For Mars and the Earth the runaway greenhouse was halted when water vapor became saturated with respect to ice or liquid water respectively. However, Venus is considered to be an example of a planet where the runaway greenhouse effect did occur, and it has been speculated that if the solar luminosity were to increase above a certain limit, it would also occur on the Earth. Satellite data acquired during the Earth Radiation Budget Experiment (ERBE) under clear sky conditions shows that as the sea surface temperature (SST) increases, the rate of outgoing infrared radiation at the top of the atmosphere also increases, as expected. Over the pacific warm pool where the SST exceeds 300 K the outgoing radiation emitted to space actually decreases with increasing SST, leading to a potentially unstable system. This behavior is a signature of the runaway greenhouse effect on Earth. However, the SST never exceeds 303K, thus the system has a natural cap which stops the runaway. According to Stefan-Boltzmann's law the amount of heat energy radiated by the Earth's surface is proportional to (T(sup 4)). However, if the planet has a substantial atmosphere, it can absorb all infrared radiation from the lower surface before the radiation penetrates into outer space. Thus, an instrument in space looking at the planet does not detect radiation from the surface. The radiation it sees comes from some level higher up. For the earth#s atmosphere the effective temperature (T(sub e)) has a value of 255 K corresponding to the middle troposphere, above most of the

  19. Suppression of the runaway electron generation by massive gas injection at TEXTOR

    Energy Technology Data Exchange (ETDEWEB)

    Lvovskiy, Andrey; Koslowski, Hans R. [Institute of Energy and Climate Research - Plasma Physics, Forschungszentrum Juelich GmbH, Juelich (Germany); Zeng, Long [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei (China)

    2014-07-01

    Runaway electrons (RE) are a serious threat for the first wall of the ITER tokamak. The mitigation of RE may be an insufficient action for the safety of such large tokamak. A safer approach is to completely suppress the generation of RE in ITER. Massive gas injection (MGI) may be one of the possible techniques for the suppression of RE generation. However, there is still no clear evidence that MGI effects so. TEXTOR tokamak is well-equipped for the MGI investigation. A small disruption mitigation valve (DMV) can inject an amount of particles up to 0.25 bar*liter in order to trigger the disruption and reliably generate RE. A larger DMV injects up to 9 bar*liter of Ar, Ne or He to suppress the RE due to collisions. The electron density is measured during disruption by a dispersion interferometer with time resolution of 2 mks for the reference to Connor-Hastie-Rosenbluth density. The aim of MGI experiments at TEXTOR was to determine the influence of species, amount of injected gas and the time delay between DMVs on suppression of RE generation. The suppression of RE generation in case of sufficient MGI before the current quench has been observed.

  20. PREFACE: A Stellar Journey A Stellar Journey

    Science.gov (United States)

    Asplund, M.

    2008-10-01

    The conference A Stellar Journey was held in Uppsala, Sweden, 23 27June 2008, in honour of Professor Bengt Gustafsson's 65th birthday. The choice of Uppsala as the location for this event was obvious given Bengt's long-standing association with the city stemming back to his school days. With the exception of a two-year postdoc stint in Copenhagen, five years as professor at Stockholm University and two years as director of the Sigtuna foundation, Bengt has forged his illustrious professional career at Uppsala University. The symposium venue was Museum Gustavianum, once the main building of the oldest university in Scandinavia. The title of the symposium is a paraphrasing of Bengt's popular astronomy book Kosmisk Resa (in English: Cosmic Journey) written in the early eighties. I think this aptly symbolizes his career that has been an astronomical voyage from near to far, from the distant past to the present. The original book title was modified slightly to reflect that most of his work to date has dealt with stars in one way or another. In addition it also gives credit to Bengt's important role as a guiding light for a very large number of students, colleagues and collaborators, indeed for several generations of astronomers. For me personally, the book Kosmisk Resa bears particular significance as it has shaped my life rather profoundly. Although I had already decided to become an astronomer, when I first read the book as a 14-year-old I made up my mind then and there that I would study under Bengt Gustafsson and work on stars. Indeed I have remained true to this somewhat audacious resolution. I suspect that a great number of us have similar stories how Bengt has had a major influence on our lives, whether on the professional or personal level. Perhaps Bengt's most outstanding characteristic is his enthralling enthusiasm. This is equally true whether he is pondering some scientific conundrum, supervising students or performing in front of an audience, be it an

  1. Interrupted Stellar Encounters in Star Clusters

    Science.gov (United States)

    Geller, Aaron M.; Leigh, Nathan W. C.

    2015-07-01

    Strong encounters between single stars and binaries play a pivotal role in the evolution of star clusters. Such encounters can also dramatically modify the orbital parameters of binaries, exchange partners in and out of binaries, and are a primary contributor to the rate of physical stellar collisions in star clusters. Often, these encounters are studied under the approximation that they happen quickly enough and within a small enough volume to be considered isolated from the rest of the cluster. In this paper, we study the validity of this assumption through the analysis of a large grid of single-binary and binary-binary scattering experiments. For each encounter we evaluate the encounter duration, and compare this with the expected time until another single or binary star will join the encounter. We find that for lower-mass clusters, similar to typical open clusters in our Galaxy, the percent of encounters that will be “interrupted” by an interloping star or binary may be 20%-40% (or higher) in the core, though for typical globular clusters we expect ≲1% of encounters to be interrupted. Thus, the assumption that strong encounters occur in relative isolation breaks down for certain clusters. Instead, many strong encounters develop into more complex “mini-clusters,” which must be accounted for in studying, for example, the internal dynamics of star clusters, and the physical stellar collision rate.

  2. INTERRUPTED STELLAR ENCOUNTERS IN STAR CLUSTERS

    Energy Technology Data Exchange (ETDEWEB)

    Geller, Aaron M. [Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (United States); Leigh, Nathan W. C., E-mail: a-geller@northwestern.edu, E-mail: nleigh@amnh.org [Department of Astrophysics, American Museum of Natural History, Central Park West and 79th Street, New York, NY 10024 (United States)

    2015-07-20

    Strong encounters between single stars and binaries play a pivotal role in the evolution of star clusters. Such encounters can also dramatically modify the orbital parameters of binaries, exchange partners in and out of binaries, and are a primary contributor to the rate of physical stellar collisions in star clusters. Often, these encounters are studied under the approximation that they happen quickly enough and within a small enough volume to be considered isolated from the rest of the cluster. In this paper, we study the validity of this assumption through the analysis of a large grid of single–binary and binary–binary scattering experiments. For each encounter we evaluate the encounter duration, and compare this with the expected time until another single or binary star will join the encounter. We find that for lower-mass clusters, similar to typical open clusters in our Galaxy, the percent of encounters that will be “interrupted” by an interloping star or binary may be 20%–40% (or higher) in the core, though for typical globular clusters we expect ≲1% of encounters to be interrupted. Thus, the assumption that strong encounters occur in relative isolation breaks down for certain clusters. Instead, many strong encounters develop into more complex “mini-clusters,” which must be accounted for in studying, for example, the internal dynamics of star clusters, and the physical stellar collision rate.

  3. Introduction to stellar structure

    CERN Document Server

    Maciel, Walter J

    2016-01-01

    In the first part of this book, the author presents the basic properties of the stellar interior and describes them thoroughly, along with deriving the main stellar structure equations of temperature, density, pressure and luminosity, among others. The process and application of solving these equations is explained, as well as linking these results with actual observations.  The second part of the text describes what happens to a star over time, and how to determine this by solving the same equations at different points during a star’s lifetime. The fate of various stars is quite different depending on their masses, and this is described in the final parts of the book. This text can be used for an upper level undergraduate course or an introductory graduate course on stellar physics.

  4. A Large-Scale Comparison of Perspectives on Parenting Between Teenage Runaways and Nonrunaways.

    Science.gov (United States)

    Loeb, Roger C.; And Others

    1986-01-01

    Compared teenage runaways to teenage nonrunaways concerning their views on parenting behaviors. Runaways emphasized typical teenage issues such as differences in values from parents and rebellion, while nonrunaways gave highest ratings to more dramatic issues such as parental abuse and drug use, as reasons for running away. (Author/ABB)

  5. Comparison of Family Therapy Outcome with Alcohol-Abusing, Runaway Adolescents

    Science.gov (United States)

    Slesnick, Natasha; Prestopnik, Jillian L

    2009-01-01

    Treatment evaluation for alcohol problem, runaway adolescents and their families is rare. This study recruited primary alcohol problem adolescents (N = 119) and their primary caretakers from two runaway shelters and assigned them to (a) home-based ecologically based family therapy (EBFT), (b) office-based functional family therapy (FFT), or (c)…

  6. Model Experiment of Thermal Runaway Reactions Using the Aluminum-Hydrochloric Acid Reaction

    Science.gov (United States)

    Kitabayashi, Suguru; Nakano, Masayoshi; Nishikawa, Kazuyuki; Koga, Nobuyoshi

    2016-01-01

    A laboratory exercise for the education of students about thermal runaway reactions based on the reaction between aluminum and hydrochloric acid as a model reaction is proposed. In the introductory part of the exercise, the induction period and subsequent thermal runaway behavior are evaluated via a simple observation of hydrogen gas evolution and…

  7. Life on the Streets: The Victimization of Runaway and Homeless Adolescents.

    Science.gov (United States)

    Whitbeck, Les B.; Simons, Ronald L.

    1990-01-01

    Examines the victimization of runaways using a sample of 84 adolescents in a midwestern city of about 250,000 people. Finds that these youth, like runaways in larger cities, are doubly victimized by abusive family situations and by life on the streets. Sex differences in the processes that influence victimization are discussed. (FMW)

  8. Propensity for Violence among Homeless and Runaway Adolescents: An Event History Analysis

    Science.gov (United States)

    Crawford, Devan M.; Whitbeck, Les B.; Hoyt, Dan R.

    2011-01-01

    Little is known about the prevalence of violent behaviors among homeless and runaway adolescents or the specific behavioral factors that influence violent behaviors across time. In this longitudinal study of 300 homeless and runaway adolescents aged 16 to 19 at baseline, the authors use event history analysis to assess the factors associated with…

  9. Calculations of neoclassical impurity transport in stellarators

    Science.gov (United States)

    Mollén, Albert; Smith, Håkan M.; Langenberg, Andreas; Turkin, Yuriy; Beidler, Craig D.; Helander, Per; Landreman, Matt; Newton, Sarah L.; García-Regaña, José M.; Nunami, Masanori

    2017-10-01

    The new stellarator Wendelstein 7-X has finished the first operational campaign and is restarting operation in the summer 2017. To demonstrate that the stellarator concept is a viable candidate for a fusion reactor and to allow for long pulse lengths of 30 min, i.e. ``quasi-stationary'' operation, it will be important to avoid central impurity accumulation typically governed by the radial neoclassical transport. The SFINCS code has been developed to calculate neoclassical quantities such as the radial collisional transport and the ambipolar radial electric field in 3D magnetic configurations. SFINCS is a cutting-edge numerical tool which combines several important features: the ability to model an arbitrary number of kinetic plasma species, the full linearized Fokker-Planck collision operator for all species, and the ability to calculate and account for the variation of the electrostatic potential on flux surfaces. In the present work we use SFINCS to study neoclassical impurity transport in stellarators. We explore how flux-surface potential variations affect the radial particle transport, and how the radial electric field is modified by non-trace impurities and flux-surface potential variations.

  10. Sexual Health Information Seeking Online Among Runaway and Homeless Youth.

    Science.gov (United States)

    Barman-Adhikari, Anamika; Rice, Eric

    2011-06-01

    Research shows runaway and homeless youth are reluctant to seek help from traditional health providers. The Internet can be useful in engaging this population and meeting their needs for sexual health information, including information about HIV and other sexually transmitted infections (STIs). Using a sample of homeless youth living in Los Angeles, California in June 2009, this study assesses the frequency with which runaway and homeless youth seek sexual health information via the Internet, and assesses which youth are more likely to engage in seeking health information from online sources. Drawing from Andersen's (1968) health behavior model and Pescosolido's (1992) network episode model, we develop and refine a model for seeking online sexual health information among homeless youth. Rather than testing the predicative strength of a given model, our aim is to identify and explore conceptually driven correlates that may shed light on the characteristics associated with these help seeking behaviors among homeless youth. Analyses using multivariate logistic regression models reveal that among the sample of youth, females and gay males most frequently seek sexual health information online. We demonstrate the structure of social network ties (e.g., connection with parents) and the content of interactions (e.g., e-mail forwards of health information) across ties are critical correlates of online sexual health information seeking. Results show a continued connection with parents via the Internet is significantly associated with youth seeking HIV or STI information. Similarly for content of interactions, more youth who were sent health information online also reported seeking HIV information and HIV-testing information. We discuss implications for intervention and practice, focusing on how the Internet may be used for dissemination of sexual health information and as a resource for social workers to link transient, runaway, and homeless youth to care.

  11. Relativistic runaway breakdown in low-frequency radio

    DEFF Research Database (Denmark)

    Fullekrug, M.; Roussel-Dupre, R.; Symbalisty, E.M.D.

    2011-01-01

    The electromagnetic radiation emitted by an electron avalanche beam resulting from relativistic runaway breakdown within the Earth's atmosphere is investigated. It is found from theoretical modeling with a computer simulation that the electron beam emits electromagnetic radiation which...... at a distance of similar to 550 km. The measured broadband pulses occur similar to 4-9 ms after the sprite-producing lightning discharge, they exhibit electromagnetic radiation which mainly spans the frequency range from similar to 50 to 350 kHz, and they exhibit complex waveforms without the typical...

  12. Observation of the Avalanche of Runaway Electrons in Air in a Strong Electric Field

    Science.gov (United States)

    Gurevich, A. V.; Mesyats, G. A.; Zybin, K. P.; Yalandin, M. I.; Reutova, A. G.; Shpak, V. G.; Shunailov, S. A.

    2012-08-01

    The generation of an avalanche of runaway electrons is demonstrated for the first time in a laboratory experiment. Two flows of runaway electrons are formed sequentially in an extended air discharge gap at the stage of delay of a pulsed breakdown. The first, picosecond, runaway electron flow is emitted in the cathode region where the field is enhanced. Being accelerated in the gap, this beam generates electrons due to impact ionization. These secondary electrons form a delayed avalanche of runaway electrons if the field is strong enough. The properties of the avalanche correspond to the existing notions about the runaway breakdown in air. The measured current of the avalanche exceeds up to an order the current of the initiating electron beam.

  13. Collision Mechanics

    DEFF Research Database (Denmark)

    Pedersen, Preben Terndrup; Servis, D.P.; Zhang, Shengming

    1999-01-01

    The first section of the present report describes the procedures that are being programmed at DTU for evaluation of the external collision dynamics. Then follows a detailed description of a comprehensive finite element analysis of one collision scenario for MS Dextra carried out at NTUA. The last...

  14. Stellar Structure and Evolution

    CERN Document Server

    Kippenhahn, Rudolf; Weiss, Achim

    2013-01-01

    This long-awaited second edition of the classical textbook on Stellar Structure and Evolution by Kippenhahn and Weigert is a thoroughly revised version of the original text. Taking into account modern observational constraints as well as additional physical effects such as mass loss and diffusion, Achim Weiss and Rudolf Kippenhahn have succeeded in bringing the book up to the state-of-the-art with respect to both the presentation of stellar physics and the presentation and interpretation of current sophisticated stellar models. The well-received and proven pedagogical approach of the first edition has been retained. The book provides a comprehensive treatment of the physics of the stellar interior and the underlying fundamental processes and parameters. The models developed to explain the stability, dynamics and evolution of the stars are presented and great care is taken to detail the various stages in a star’s life. Just as the first edition, which remained a standard work for more than 20 years after its...

  15. Relativistic stellar models

    Indian Academy of Sciences (India)

    Home; Journals; Pramana – Journal of Physics; Volume 77; Issue 3. Relativistic stellar models ... Upon specifying particular forms for one of the gravitational potentials and the electric field intensity, the condition for pressure isotropy is transformed into a hypergeometric equation with two free parameters. For particular ...

  16. Commission 35: Stellar Constitution

    Science.gov (United States)

    D'Antona, Francesca; Charbonnel, Corinne; Dziembowski, Wojciech; Fontaine, Gilles; Larson, Richard B.; Lattanzio, John; Liebert, Jim W.; Müller, Ewald; Weiss, Achim; Yungelson, Lev R.

    The Commission home page is maintained by Claus Leitherer and contains general information on the Commission structure and activities, including links to stellar structure resources that were made available by the owners. The resources contain evolutionary tracks and isochrones from various groups, nuclear reaction, EOS, and opacity data as well as links to main astronomical journals. As a routine activity, the Organizing Committee has commented on and ranked proposals for several IAU sponsored meetings. Our Commission acted as one of the coordinating bodies of a Symposium held at the IAU XXVI General Assembly in Prague, August 2006, (IAU Symposium No. 239 Convection in Astrophysics, and participated in the organization of the following Joint Discussions: JD05 Calibrating the Top of the Stellar Mass-Luminosity Relation, JD06 Neutron Stars and Black Holes in Star Clusters, JD08 Solar and Stellar Activity Cycles, JD11 Pre-Solar Grains as Astrophysical Tools; JD14 Modelling Dense Stellar Systems; and JD17 Highlights of Recent Progress in the Seismology of the Sun and Sun-like Stars.

  17. A Stellar Demonstrator

    Science.gov (United States)

    Ros, Rosa M.

    2009-01-01

    The main purpose of the stellar demonstrator is to help explain the movement of stars. In particular, students have difficulties understanding why, if they are living in the Northern Hemisphere, they may observe starts in the Southern Hemisphere, or why circumpolar stars are not the same in different parts of Europe. Using the demonstrator, these…

  18. Progress Toward Attractive Stellarators

    Energy Technology Data Exchange (ETDEWEB)

    Neilson, G H; Brown, T G; Gates, D A; Lu, K P; Zarnstorff, M C; Boozer, A H; Harris, J H; Meneghini, O; Mynick, H E; Pomphrey, N; Reiman, A H

    2011-01-05

    The quasi-axisymmetric stellarator (QAS) concept offers a promising path to a more compact stellarator reactor, closer in linear dimensions to tokamak reactors than previous stellarator designs. Concept improvements are needed, however, to make it more maintainable and more compatible with high plant availability. Using the ARIES-CS design as a starting point, compact stellarator designs with improved maintenance characteristics have been developed. While the ARIES-CS features a through-the-port maintenance scheme, we have investigated configuration changes to enable a sector-maintenance approach, as envisioned for example in ARIES AT. Three approaches are reported. The first is to make tradeoffs within the QAS design space, giving greater emphasis to maintainability criteria. The second approach is to improve the optimization tools to more accurately and efficiently target the physics properties of importance. The third is to employ a hybrid coil topology, so that the plasma shaping functions of the main coils are shared more optimally, either with passive conductors made of high-temperature superconductor or with local compensation coils, allowing the main coils to become simpler. Optimization tools are being improved to test these approaches.

  19. Advanced Stellar Compass FMECA

    DEFF Research Database (Denmark)

    Jørgensen, John Leif; Betto, Maurizio; Kilsgaard, Søren

    1998-01-01

    This documents describes the Advanced Stellar Compass (ASC) failure modes, effects and criticality analyses (FMECA).The objectives of the FMECA are:1)To identify the possible failure;2)To identify the effects of the possible failures including the identification of potential hazards to determine...

  20. THE ADVANCED STELLAR COMPASS

    DEFF Research Database (Denmark)

    Jørgensen, John Leif; Liebe, Carl Christian

    1997-01-01

    this demand the Advanced Stellar Compass (ASC), a fully autonomous miniature star tracker, was developed. This ASC is capable of both solving the "lost in space" problem and determine the attitude with arcseconds precision. The development, principles of operation and instrument autonomy of the ASC...

  1. Stellar ages from asteroseismology

    Science.gov (United States)

    Lebreton, Yveline; Montalbán, Josefina

    2009-06-01

    Asteroseismology has been recognized for a long time as a very powerful mean to probe stellar interiors. The oscillations frequencies are closely related to stellar internal structure properties via the density and the sound speed profiles. Since these properties are in turn tightly linked with the mass and evolutionary state, we can expect to determine the age and mass of a star from the comparison of its oscillation spectrum with the predictions of stellar models. Such a comparison will of course suffer both from the problems we face when modeling a particular star (for instance the uncertainties on its global parameters and chemical composition) and from our general misunderstanding of the physical processes at work in stellar interiors (for instance the various transport processes that may lead to core mixing and affect the ages predicted by models). However for stars where observations have provided very precise and numerous oscillation frequencies together with accurate global parameters and additional information (as the radius or the mass of the star if it is member of a binary system, the radius if it observable in interferometry or the mean density if the star is an exoplanet host), we can also expect to better constrain the physical description of the stellar structure and transport processes and to finally get a more reliable age estimation. After a brief survey of stellar pulsations, we present some general seismic diagnostics that can be used to infer the age of a pulsating star as well as their limitations. We then illustrate the ability of asteroseismology to scrutinize stellar interiors on the basis of a few examples. In the years to come, extended very precise asteroseismic observations are expected, either in photometry or in spectroscopy, from present and future ground-based (HARPS, CORALIE, ELODIE, UVES, UCLES, SIAMOIS, SONG) or spatial devices (MOST, CoRoT, WIRE, Kepler, PLATO). This will considerably enlarge the sample of stars eligible to

  2. Alice Munro's "Runaway" in the Mirror of Sigmund Freud

    Directory of Open Access Journals (Sweden)

    Raheleh Bahador

    2015-03-01

    Full Text Available Mirroring the complexities of the human psyche, literature has received new comprehension through a psychoanalytic lens.  Alice Munro's "Runaway" (2003 is character-based and has the psychological analysis potential but it had never received such kind of study. The objective of the present paper is to read Munro's "Runaway" in the mirror of Sigmund Freud to detect the psychological aspects of its fictional characters. The characters are driven by the Freudian mental agencies and undergo phases of psychic disorder.  In the present paper, Munro's short fiction has been discussed based on Sigmund Freud's theory of the Unconscious and its connection with the interpretation of dreams as well as the symbolization of three main characters based on tripartite agencies of the id, ego and superego. Clarifying the latent and manifest levels of characters and the world of dreams indicates the artistic creation of Alice Munro in handling complex characterization. The unconscious and its connection with the female character's dreams have been discussed. The unconscious of the female character is reflected in her dreams in result of repression and asocial drives and desires. Unconscious through dreams is the mirror of the repressed psyche of the female character. Scrutinizing the three main characters in terms of Freudian psychic trilogy, they prove to fit their psychological Freudian terms.

  3. Density dependence triggers runaway selection of reduced senescence.

    Directory of Open Access Journals (Sweden)

    Robert M Seymour

    2007-12-01

    Full Text Available In the presence of exogenous mortality risks, future reproduction by an individual is worth less than present reproduction to its fitness. Senescent aging thus results inevitably from transferring net fertility into younger ages. Some long-lived organisms appear to defy theory, however, presenting negligible senescence (e.g., hydra and extended lifespans (e.g., Bristlecone Pine. Here, we investigate the possibility that the onset of vitality loss can be delayed indefinitely, even accepting the abundant evidence that reproduction is intrinsically costly to survival. For an environment with constant hazard, we establish that natural selection itself contributes to increasing density-dependent recruitment losses. We then develop a generalized model of accelerating vitality loss for analyzing fitness optima as a tradeoff between compression and spread in the age profile of net fertility. Across a realistic spectrum of senescent age profiles, density regulation of recruitment can trigger runaway selection for ever-reducing senescence. This novel prediction applies without requirement for special life-history characteristics such as indeterminate somatic growth or increasing fecundity with age. The evolution of nonsenescence from senescence is robust to the presence of exogenous adult mortality, which tends instead to increase the age-independent component of vitality loss. We simulate examples of runaway selection leading to negligible senescence and even intrinsic immortality.

  4. Quantification of Lithium-ion Cell Thermal Runaway Energetics

    Energy Technology Data Exchange (ETDEWEB)

    Orendorff, Christopher; Lamb, Joshua; Steele, Leigh Anna Marie; Spangler, Scott Wilmer; Langendorf, Jill Louise

    2016-01-01

    Much of what is known about lithium-ion cell thermal runaway energetics has been measured and extrapolated from data acquired on relatively small cells (< 3 Ah). This work is aimed at understanding the effects of cell size on thermal runaway energetics on cells from 3 to 50 Ah of both LiFePO4 (LFP) and LiNi0.80Co0.15Al0.05O2 (NCA) chemistries. Results show that for both LFP and NCA cells, the normalized heating rate (W/Ah) increases roughly linearly for cells from 3-38 Ah while the normalized total heat released (kJ/Ah) is relatively constant over that cell size range. The magnitude of the normalized heating rate is on the order of 2x greater for NCA relative to LFP chemistries for 2-3 Ah cells, while that difference is on the order of 10x for 30-40 Ah cells. The total normalized heat release is ~ 15-20% greater for NCA relative to LFP cells across the entire size range studied 3-38 Ah.

  5. Radio Frequency Electromagnetic Radiation From Streamer Collisions.

    Science.gov (United States)

    Luque, Alejandro

    2017-10-16

    We present a full electromagnetic model of streamer propagation where the Maxwell equations are solved self-consistently together with electron transport and reactions including photoionization. We apply this model to the collision of counter-propagating streamers in gaps tens of centimeters wide and with large potential differences of hundreds of kilovolts. Our results show that streamer collisions emit electromagnetic pulses that, at atmospheric pressure, dominate the radio frequency spectrum of an extended corona in the range from about 100 MHz to a few gigahertz. We also investigate the fast penetration, after a collision, of electromagnetic fields into the streamer heads and show that these fields are capable of accelerating electrons up to about 100 keV. By substantiating the link between X-rays and high-frequency radio emissions and by describing a mechanism for the early acceleration of runaway electrons, our results support the hypothesis that streamer collisions are essential precursors of high-energy processes in electric discharges.

  6. Radio Frequency Electromagnetic Radiation From Streamer Collisions

    Science.gov (United States)

    Luque, Alejandro

    2017-10-01

    We present a full electromagnetic model of streamer propagation where the Maxwell equations are solved self-consistently together with electron transport and reactions including photoionization. We apply this model to the collision of counter-propagating streamers in gaps tens of centimeters wide and with large potential differences of hundreds of kilovolts. Our results show that streamer collisions emit electromagnetic pulses that, at atmospheric pressure, dominate the radio frequency spectrum of an extended corona in the range from about 100 MHz to a few gigahertz. We also investigate the fast penetration, after a collision, of electromagnetic fields into the streamer heads and show that these fields are capable of accelerating electrons up to about 100 keV. By substantiating the link between X-rays and high-frequency radio emissions and by describing a mechanism for the early acceleration of runaway electrons, our results support the hypothesis that streamer collisions are essential precursors of high-energy processes in electric discharges.

  7. Experimental Study of Thermal Runaway Process of 18650 Lithium-Ion Battery.

    Science.gov (United States)

    Liu, Jingjing; Wang, Zhirong; Gong, Junhui; Liu, Kai; Wang, Hao; Guo, Linsheng

    2017-02-25

    This study addresses the effects of the SOC (State of Charge) and the charging-discharging process on the thermal runaway of 18650 lithium-ion batteries. A series of experiments were conducted on an electric heating and testing apparatus. The experimental results indicate that 6 W is the critical heating power for 40% SOC. With a 20 W constant heating rate, the thermal runaway initial temperature of the lithium-ion battery decreases with the increasing SOC. The final thermal runaway temperature increases with the SOC when the SOC is lower than 80%. However, a contrary conclusion was obtained when the SOC was higher than 80%. Significant mass loss, accompanied by an intense exothermic reaction, took place under a higher SOC. The critical charging current, beyond which the thermal runaway occurs, was found to be 2.6 A. The thermal runaway initial temperature decreases with the increasing charging current, while the intensity of the exothermic reaction varies inversely. Mass ejection of gas and electrolytes exists during thermal runaway when the charging current is higher than 10.4 A, below which only a large amount of gas is released. The thermal runaway initial temperature of discharging is higher than that of non-discharging.

  8. Experimental Study of Thermal Runaway Process of 18650 Lithium-Ion Battery

    Directory of Open Access Journals (Sweden)

    Jingjing Liu

    2017-02-01

    Full Text Available This study addresses the effects of the SOC (State of Charge and the charging–discharging process on the thermal runaway of 18650 lithium-ion batteries. A series of experiments were conducted on an electric heating and testing apparatus. The experimental results indicate that 6 W is the critical heating power for 40% SOC. With a 20 W constant heating rate, the thermal runaway initial temperature of the lithium-ion battery decreases with the increasing SOC. The final thermal runaway temperature increases with the SOC when the SOC is lower than 80%. However, a contrary conclusion was obtained when the SOC was higher than 80%. Significant mass loss, accompanied by an intense exothermic reaction, took place under a higher SOC. The critical charging current, beyond which the thermal runaway occurs, was found to be 2.6 A. The thermal runaway initial temperature decreases with the increasing charging current, while the intensity of the exothermic reaction varies inversely. Mass ejection of gas and electrolytes exists during thermal runaway when the charging current is higher than 10.4 A, below which only a large amount of gas is released. The thermal runaway initial temperature of discharging is higher than that of non-discharging.

  9. Determination of the core temperature of a Li-ion cell during thermal runaway

    Science.gov (United States)

    Parhizi, M.; Ahmed, M. B.; Jain, A.

    2017-12-01

    Safety and performance of Li-ion cells is severely affected by thermal runaway where exothermic processes within the cell cause uncontrolled temperature rise, eventually leading to catastrophic failure. Most past experimental papers on thermal runaway only report surface temperature measurement, while the core temperature of the cell remains largely unknown. This paper presents an experimentally validated method based on thermal conduction analysis to determine the core temperature of a Li-ion cell during thermal runaway using surface temperature and chemical kinetics data. Experiments conducted on a thermal test cell show that core temperature computed using this method is in good agreement with independent thermocouple-based measurements in a wide range of experimental conditions. The validated method is used to predict core temperature as a function of time for several previously reported thermal runaway tests. In each case, the predicted peak core temperature is found to be several hundreds of degrees Celsius higher than the measured surface temperature. This shows that surface temperature alone is not sufficient for thermally characterizing the cell during thermal runaway. Besides providing key insights into the fundamental nature of thermal runaway, the ability to determine the core temperature shown here may lead to practical tools for characterizing and mitigating thermal runaway.

  10. Stellar Astrophysics with Arcus

    Science.gov (United States)

    Brickhouse, Nancy S.; Huenemoerder, David P.; Wolk, Scott; Schulz, Norbert; Foster, Adam; Brenneman, Laura; Poppenhaeger, Katja; Arcus Team

    2018-01-01

    The Arcus mission is now in Phase A of the NASA Medium-Class Explorer competition. We present here the Arcus science case for stellar astrophysics. With spectral resolving power of at least 2500 and effective area greater than 400 cm^2, Arcus will measure new diagnostic lines, e.g. for H- and He-like ions of oxygen and other elements. Weak dielectronic recombination lines will provide sensitive measurements of temperature to test stellar coronal heating models. Arcus will also resolve the coronal and accretion line components in young accreting stars, allowing detailed studies of accretion shocks and their post-shock behavior. Arcus can resolve line shapes and variability in hot star winds to study inhomogeneities and dynamics of wind structure. Such profiles will provide an independent measure of mass loss rates, for which theoretical and observational discrepancies can reach an order of magnitude. Arcus will also study exoplanet atmospheres through X-ray absorption, determing their extent and composition.

  11. Local Stellarator Equilibrium Model

    Science.gov (United States)

    Hudson, Stuart R.; Hegna, Chris C.; Lewandowski, Jerome W.

    2000-10-01

    Extensive calculations of ballooning and drift waves spectrums in asymmetric toroidal configurations (e.g. stellarators) to appreciate the role of magnetic geometry and profile variations are usually are usually prohibitive as the evaluation of the magneto-hydrodynamic (MHD) equilibrium is in itself a non-trivial problem. Although simple analytical MHD model equilibria do exist for tokamak configurations, their stellarator counterparts are usually crude or very approximate. In order to make more extensive stability calculations (of both ideal ballooning and drift-type modes), a technique for generating three-dimensional magneto-static equilibria, localized to a magnetic surface, has been developed. The technique allows one to easily manipulate various 3-D shaping and profile effects on a magnetic surface avoiding the need to recompute an entire three dimensional solution of the equilibrium. The model equilibrium has been implemented into existing ideal MHD ballooning and drift wave numerical codes. Marginal ballooning stability diagrams and drift wave calculations will be reported.

  12. Convection and stellar oscillations

    DEFF Research Database (Denmark)

    Aarslev, Magnus Johan

    2017-01-01

    of stars. For stars like the sun, energy transport in the outer layers occurs mainly through turbulent convection. Here, pressure mode oscillations are essentially propagating sound waves, whose properties can be altered by interaction with the turbulent motion of the gas. This has always been a problem...... for asteroseismology, because of the challenges inherent in modelling turbulent convection in 1D stellar models. As a result of oversimplifying the physics near the surface, theoretical calculations systematically overestimate the oscillation frequencies. This has become known as the asteroseismic surface effect. Due...... to lacking better options, this frequency difference is typically corrected for with ad-hoc formulae. The topic of this thesis is the improvement of 1D stellar convection models and the effects this has on asteroseismic properties. The source of improvements is 3D simulations of radiation...

  13. Li-ion battery thermal runaway suppression system using microchannel coolers and refrigerant injections

    Energy Technology Data Exchange (ETDEWEB)

    Bandhauer, Todd M.; Farmer, Joseph C.

    2016-11-08

    A battery management system with thermally integrated fire suppression includes a multiplicity of individual battery cells in a housing; a multiplicity of cooling passages in the housing within or between the multiplicity of individual battery cells; a multiplicity of sensors operably connected to the individual battery cells, the sensors adapted to detect a thermal runaway event related to one or more of the multiplicity of individual battery cells; and a management system adapted to inject coolant into at least one of the multiplicity of cooling passages upon the detection of the thermal runaway event by the any one of the multiplicity of sensors, so that the thermal runaway event is rapidly quenched.

  14. Suppression of runaway electron generation by massive helium injection after induced disruptions on TEXTOR

    Science.gov (United States)

    Lvovskiy, A.; Koslowski, H. R.; Zeng, L.

    2015-10-01

    > Disruptions with runaway electron generation have been deliberately induced by injection of argon using a disruption mitigation valve. A second disruption mitigation valve has been utilised to inject varying amounts of helium after a short time delay. No generation of runaway electrons has been observed when more than a critical amount of helium has been injected no later than 5 ms after the triggering of the first valve. The required amount of helium for suppression of runaway electron generation is up to one order of magnitude lower than the critical density according to Connor & Hastie (1975) and Rosenbluth & Putvinski (1997).

  15. A first approach to runaway electron control in FTU

    Energy Technology Data Exchange (ETDEWEB)

    Boncagni, L. [Associazione Euratom/ENEA sulla Fusione, Centro Ricerche Frascati, CP 65, 00044 Frascati, Roma (Italy); Carnevale, D., E-mail: carnevaledaniele@gmail.com [Dipartimento Ing. Civile ed Ing. Informatica Università di Roma, Tor Vergata, Via del Politecnico 1, 00133 Roma (Italy); Cianfarani, C.; Esposito, B. [Associazione Euratom/ENEA sulla Fusione, Centro Ricerche Frascati, CP 65, 00044 Frascati, Roma (Italy); Granucci, G. [Associazione Euratom-CNR sulla Fusione, IFP-CNR, Via R. Cozzi 53, 20125 Milano (Italy); Maddaluno, G.; Marocco, D. [Associazione Euratom/ENEA sulla Fusione, Centro Ricerche Frascati, CP 65, 00044 Frascati, Roma (Italy); Martin-Solis, J.R. [Universidad Carlos III de Madrid, Avda. de la Universidad 30, 28911 Leganes-Madrid (Spain); Pucella, G. [Associazione Euratom/ENEA sulla Fusione, Centro Ricerche Frascati, CP 65, 00044 Frascati, Roma (Italy); Sozzi, C. [Associazione Euratom-CNR sulla Fusione, IFP-CNR, Via R. Cozzi 53, 20125 Milano (Italy); Varano, G. [Dipartimento Ing. Civile ed Ing. Informatica Università di Roma, Tor Vergata, Via del Politecnico 1, 00133 Roma (Italy); Vitale, V. [Associazione Euratom/ENEA sulla Fusione, Centro Ricerche Frascati, CP 65, 00044 Frascati, Roma (Italy); Zaccarian, L. [CNRS, LAAS, 7 av. du colonel Roche, F-31400 Toulouse (France); Univ. de Toulouse, LAAS, F-31400 Toulouse (France)

    2013-10-15

    The Plasma Control System (PCS) of the Frascati Tokamak Upgrade (FTU) is not equipped with any runaway electron (RE) beam control or suppression tool. In this paper we propose an upgraded PCS including an architecture for the control of disruption-generated REs that, making use of filtering techniques to estimate the onsets of the current quench (CQ) and of the RE beam current plateau, provides a controlled plasma current shut-down and a simultaneous RE position control. The control strategy is based on a nonlinear technique, called Input Allocation, that allows to re-configure the current in the poloidal field (PF) coils and improve the PCS responsiveness needed for RE position control. Preliminary results on the implementation of the Input Allocation and an experimental proposal to test the control scheme architecture are discussed.

  16. Forgotten Youth: Homeless LGBT Youth of Color and the Runaway and Homeless Youth Act

    National Research Council Canada - National Science Library

    Michelle Page

    2017-01-01

    .... [...]this Comment focuses on how and why this problem occurs, the effects it has on homeless LGBT youth of color, and then proposes specific revisions to the Runaway and Homeless Youth Act that would...

  17. Situational runaway adolescents. A study on risk factors from a Turkish sample.

    Science.gov (United States)

    Ulusoy, Demet M; Demir, Nilüfer Ozcan

    2006-01-01

    Drawing on a sample of 726 non-clinical adolescents (aged 17-18 years) from high schools in Ankara, Turkey, this paper primarily aims to identify the risk factors related to situational run away behavior. This study was based on an ecological risk factors model and tried to discover the associations for runaways. Run away behavior is one of the problematic behaviors very commonly seen among Turkish adolescents. Regression analyses revealed that predictors for runaway behavior differed due to gender; while, delinquency, sexual intercourse, substance use, parental separation and suicidal ideation were the significant predictors for girl adolescent runaway behaviors, while lack of parental support and depression were the significant predictors for boy adolescent runaway behavior.

  18. Effects of Angular Fillers on Thermal Runaway of Lithium-Ion Battery

    National Research Council Canada - National Science Library

    Meng Wang Anh V.Le Yang Shi Daniel J.Noelle Hyojung Yoon Minghao Zhang Y.Shirley Meng Yu Qiao

    2016-01-01

    By adding 1 wt% damage homogenizer(DH), i.e. carbon black microparticles, into the electrodes of lithiumion batteries, thermal runaway can be mitigated as the battery cells are subjected to impact loadings...

  19. Effect of Resonant Helical Field (RHF) on Runaway Electrons in Tokamaks

    Science.gov (United States)

    Ghanbari, M. R.; Ghoranneviss, M.; Ghanbari, K.; Elahi, A. Salar; Salem, M. K.; Mohammadi, S.; Arvin, R.

    2013-10-01

    The high energy current of runaway electrons during a major disruption in tokamak reactors can cause serious damage to the first wall of the reactor and reduce its life time. Therefore, finding a method to minimize runaway electron is much needed. Resonant helical field (RHF) is one of the methods for controlling the magnetohydrodynamic (MHD) activity. This paper attempts to examine the effect of RHF on the generation of runaway electrons. Main parameters such as plasma current, loop voltage, emitted hard X-ray intensity, MHD oscillation, Hα radiation and MHD activity modes, in the presence and absence of RHF (L = 2 and L = 3), were measured. The results show that applying this system can change runaway electrons generation.

  20. New runaway O-type stars in the first Gaia Data Release

    Science.gov (United States)

    Maíz Apellániz, Jesús; Barbá, Rodolfo H.; Simón-Díaz, Sergio; Negueruela, Ignacio; Trigueros Páez, Emilio

    2017-11-01

    We have detected 13 new runaway-star candidates of spectral type O combining the TGAS (Tycho-Gaia Astrometric Solution) proper motions from Gaia Data Release 1 (DR1) and the sample from GOSSS (Galactic O-Star Spectroscopic Survey). We have also combined TGAS and Hipparcos proper motions to check that our technique recovers many of the previously known O-type runaways in the sample.

  1. Failure Analysis to Identify Thermal Runaway of Bypass Diodes in Fielded Modules

    Energy Technology Data Exchange (ETDEWEB)

    Xiao, Chuanxiao, Uchida, Yasunori; Johnston, Steve; Hacke, Peter; Wohlgemuth, John; Al-Jassim, Mowafak

    2017-03-14

    We studied a bypass diode recuperated from fielded modules in a rooftop installation to determine the failure mechanism. The field-failed diode showed similar characteristics to thermal runaway, specifically X-ray tomography evidence of migrated metal. We also observed burn marks on the silicon surface like those lab-stressed for thermal runaway. Reaction products are more soluble than silicon and the surface is oxygen rich.

  2. The Origin of B-type Runaway Stars: Non-LTE Abundances as a Diagnostic

    Energy Technology Data Exchange (ETDEWEB)

    McEvoy, Catherine M.; Dufton, Philip L.; Smoker, Jonathan V.; Keenan, Francis P. [Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast BT7 1NN (United Kingdom); Lambert, David L. [The University of Texas at Austin, Department of Astronomy, RLM 16.316, Austin, TX 78712 (United States); Schneider, Fabian R. N. [Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH (United Kingdom); De Wit, Willem-Jan [European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Vitacura, Santiago 19 (Chile)

    2017-06-10

    There are two accepted mechanisms to explain the origin of runaway OB-type stars: the binary supernova (SN) scenario and the cluster ejection scenario. In the former, an SN explosion within a close binary ejects the secondary star, while in the latter close multibody interactions in a dense cluster cause one or more of the stars to be ejected from the region at high velocity. Both mechanisms have the potential to affect the surface composition of the runaway star. tlusty non-LTE model atmosphere calculations have been used to determine the atmospheric parameters and the C, N, Mg, and Si abundances for a sample of B-type runaways. These same analytical tools were used by Hunter et al. for their analysis of 50 B-type open-cluster Galactic stars (i.e., nonrunaways). Effective temperatures were deduced using the Si-ionization balance technique, surface gravities from Balmer line profiles, and microturbulent velocities derived using the Si spectrum. The runaways show no obvious abundance anomalies when compared with stars in the open clusters. The runaways do show a spread in composition that almost certainly reflects the Galactic abundance gradient and a range in the birthplaces of the runaways in the Galactic disk. Since the observed Galactic abundance gradients of C, N, Mg, and Si are of a similar magnitude, the abundance ratios (e.g., N/Mg) are as obtained essentially uniform across the sample.

  3. Probing the heat sources during thermal runaway process by thermal analysis of different battery chemistries

    Science.gov (United States)

    Zheng, Siqi; Wang, Li; Feng, Xuning; He, Xiangming

    2018-02-01

    Safety issue is very important for the lithium ion battery used in electric vehicle or other applications. This paper probes the heat sources in the thermal runaway processes of lithium ion batteries composed of different chemistries using accelerating rate calorimetry (ARC) and differential scanning calorimetry (DSC). The adiabatic thermal runaway features for the 4 types of commercial lithium ion batteries are tested using ARC, whereas the reaction characteristics of the component materials, including the cathode, the anode and the separator, inside the 4 types of batteries are measured using DSC. The peaks and valleys of the critical component reactions measured by DSC can match the fluctuations in the temperature rise rate measured by ARC, therefore the relevance between the DSC curves and the ARC curves is utilized to probe the heat source in the thermal runaway process and reveal the thermal runaway mechanisms. The results and analysis indicate that internal short circuit is not the only way to thermal runaway, but can lead to extra electrical heat, which is comparable with the heat released by chemical reactions. The analytical approach of the thermal runaway mechanisms in this paper can guide the safety design of commercial lithium ion batteries.

  4. Formation of stellar clusters

    Science.gov (United States)

    Smilgys, Romas; Bonnell, Ian A.

    2017-12-01

    We investigate the triggering of star formation and the formation of stellar clusters in molecular clouds which form as the interstellar medium passes through spiral shocks. The spiral shock compresses gas into an ∼100 pc long main star formation ridge, where clusters form every 5-10 pc along the merger ridge. We use a gravitational potential-based cluster finding algorithm, which extracts individual clusters, calculates their physical properties and traces cluster evolution over multiple time-steps. Final cluster masses at the end of simulation range between 1000 and 30 000 M⊙ with their characteristic half-mass radii between 0.1 and 2 pc. These clusters form by gathering material from 10-20 pc size scales. Clusters also show a mass-specific angular momentum relation, where more massive clusters have larger specific angular momentum due to the larger size scales, and hence angular momentum from which they gather their mass. The evolution shows that more massive clusters experience hierarchical merging process, which increases stellar age spreads up to 2-3 Myr. Less massive clusters appear to grow by gathering nearby recently formed sinks, while more massive clusters with their large global gravitational potentials are increasing their mass growth from gas accretion.

  5. The DEMO Quasisymmetric Stellarator

    Directory of Open Access Journals (Sweden)

    Geoffrey B. McFadden

    2010-02-01

    Full Text Available The NSTAB nonlinear stability code solves differential equations in conservation form, and the TRAN Monte Carlo test particle code tracks guiding center orbits in a fixed background, to provide simulations of equilibrium, stability, and transport in tokamaks and stellarators. These codes are well correlated with experimental observations and have been validated by convergence studies. Bifurcated 3D solutions of the 2D tokamak problem have been calculated that model persistent disruptions, neoclassical tearing modes (NTMs and edge localized modes (ELMs occurring in the International Thermonuclear Experimental Reactor (ITER, which does not pass the NSTAB simulation test for nonlinear stability. So we have designed a quasiaxially symmetric (QAS stellarator with similar proportions as a candidate for the demonstration (DEMO fusion reactor that does pass the test [1]. The configuration has two field periods and an exceptionally accurate 2D symmetry that furnishes excellent thermal confinement and good control of the prompt loss of alpha particles. Robust coils are found from a filtered form of the Biot-Savart law based on a distribution of current over a control surface for the coils and the current in the plasma defined by the equilibrium calculation. Computational science has addressed the issues of equilibrium, stability, and transport, so it remains to develop an effective plan to construct the coils and build a diverter.

  6. Advective collisions

    OpenAIRE

    Andersson, B.; Gustavsson, K.; Mehlig, B.; Wilkinson, M.

    2007-01-01

    Small particles advected in a fluid can collide (and therefore aggregate) due to the stretching or shearing of fluid elements. This effect is usually discussed in terms of a theory due to Saffman and Turner [J. Fluid Mech., 1, 16-30, (1956)]. We show that in complex or random flows the Saffman-Turner theory for the collision rate describes only an initial transient (which we evaluate exactly). We obtain precise expressions for the steady-state collision rate for flows with small Kubo number, ...

  7. A catalog of stellar spectrophotometry

    Science.gov (United States)

    Adelman, S. J.; Pyper, D. M.; Shore, S. N.; White, R. E.; Warren, W. H., Jr.

    1989-01-01

    A machine-readable catalog of stellar spectrophotometric measurements made with rotating grating scanner is introduced. Consideration is given to the processes by which the stellar data were collected and calibrated with the fluxes of Vega (Hayes and Latham, 1975). A sample page from the spectrophotometric catalog is presented.

  8. Tidal effects on stellar activity

    Science.gov (United States)

    Poppenhaeger, K.

    2017-10-01

    The architecture of many exoplanetary systems is different from the solar system, with exoplanets being in close orbits around their host stars and having orbital periods of only a few days. We can expect interactions between the star and the exoplanet for such systems that are similar to the tidal interactions observed in close stellar binary systems. For the exoplanet, tidal interaction can lead to circularization of its orbit and the synchronization of its rotational and orbital period. For the host star, it has long been speculated if significant angular momentum transfer can take place between the planetary orbit and the stellar rotation. In the case of the Earth-Moon system, such tidal interaction has led to an increasing distance between Earth and Moon. For stars with Hot Jupiters, where the orbital period of the exoplanet is typically shorter than the stellar rotation period, one expects a decreasing semimajor axis for the planet and enhanced stellar rotation, leading to increased stellar activity. Also excess turbulence in the stellar convective zone due to rising and subsiding tidal bulges may change the magnetic activity we observe for the host star. I will review recent observational results on stellar activity and tidal interaction in the presence of close-in exoplanets, and discuss the effects of enhanced stellar activity on the exoplanets in such systems.

  9. Three-dimensional stellarator codes.

    Science.gov (United States)

    Garabedian, P R

    2002-08-06

    Three-dimensional computer codes have been used to develop quasisymmetric stellarators with modular coils that are promising candidates for a magnetic fusion reactor. The mathematics of plasma confinement raises serious questions about the numerical calculations. Convergence studies have been performed to assess the best configurations. Comparisons with recent data from large stellarator experiments serve to validate the theory.

  10. Three-dimensional stellarator codes

    Science.gov (United States)

    Garabedian, P. R.

    2002-01-01

    Three-dimensional computer codes have been used to develop quasisymmetric stellarators with modular coils that are promising candidates for a magnetic fusion reactor. The mathematics of plasma confinement raises serious questions about the numerical calculations. Convergence studies have been performed to assess the best configurations. Comparisons with recent data from large stellarator experiments serve to validate the theory. PMID:12140367

  11. Optimizing stellarators for turbulent transport.

    Science.gov (United States)

    Mynick, H E; Pomphrey, N; Xanthopoulos, P

    2010-08-27

    Up to now, the term "transport-optimized" stellarators has meant optimized to minimize neoclassical transport, while the task of also mitigating turbulent transport, usually the dominant transport channel in such designs, has not been addressed, due to the complexity of plasma turbulence in stellarators. Here, we demonstrate that stellarators can also be designed to mitigate their turbulent transport, by making use of two powerful numerical tools not available until recently, namely, gyrokinetic codes valid for 3D nonlinear simulations and stellarator optimization codes. Two initial proof-of-principle configurations are obtained, reducing the level of ion temperature gradient turbulent transport from the National Compact Stellarator Experiment baseline design by a factor of 2-2.5.

  12. Nucleosynthesis in stellar explosions

    Energy Technology Data Exchange (ETDEWEB)

    Woosley, S.E.; Axelrod, T.S.; Weaver, T.A.

    1983-01-01

    The final evolution and explosion of stars from 10 M/sub solar/ to 10/sup 6/ M/sub solar/ are reviewed with emphasis on factors affecting the expected nucleosynthesis. We order our paper in a sequence of decreasing mass. If, as many suspect, the stellar birth function was peaked towards larger masses at earlier times (see e.g., Silk 1977; but also see Palla, Salpeter, and Stahler 1983), this sequence of masses might also be regarded as a temporal sequence. At each stage of Galactic chemical evolution stars form from the ashes of preceding generations which typically had greater mass. A wide variety of Type I supernova models, most based upon accreting white dwarf stars, are also explored using the expected light curves, spectra, and nucleosynthesis as diagnostics. No clearly favored Type I model emerges that is capable of simultaneously satisfying all three constraints.

  13. Modelling of stellar convection

    Science.gov (United States)

    Kupka, Friedrich; Muthsam, Herbert J.

    2017-07-01

    The review considers the modelling process for stellar convection rather than specific astrophysical results. For achieving reasonable depth and length we deal with hydrodynamics only, omitting MHD. A historically oriented introduction offers first glimpses on the physics of stellar convection. Examination of its basic properties shows that two very different kinds of modelling keep being needed: low dimensional models (mixing length, Reynolds stress, etc.) and "full" 3D simulations. A list of affordable and not affordable tasks for the latter is given. Various low dimensional modelling approaches are put in a hierarchy and basic principles which they should respect are formulated. In 3D simulations of low Mach number convection the inclusion of then unimportant sound waves with their rapid time variation is numerically impossible. We describe a number of approaches where the Navier-Stokes equations are modified for their elimination (anelastic approximation, etc.). We then turn to working with the full Navier-Stokes equations and deal with numerical principles for faithful and efficient numerics. Spatial differentiation as well as time marching aspects are considered. A list of codes allows assessing the state of the art. An important recent development is the treatment of even the low Mach number problem without prior modification of the basic equation (obviating side effects) by specifically designed numerical methods. Finally, we review a number of important trends such as how to further develop low-dimensional models, how to use 3D models for that purpose, what effect recent hardware developments may have on 3D modelling, and others.

  14. Joule heating and runaway electron acceleration in a solar flare

    Science.gov (United States)

    Holman, Gordon D.; Kundu, Mukul R.; Kane, Sharad R.

    1989-01-01

    The hard and soft x ray and microwave emissions from a solar flare (May 14, 1980) were analyzed and interpreted in terms of Joule heating and runaway electron acceleration in one or more current sheets. It is found that all three emissions can be generated with sub-Dreicer electric fields. The soft x ray emitting plasma can only be heated by a single current sheet if the resistivity in the sheet is well above the classical, collisional resistivity of 10(exp 7) K, 10(exp 11)/cu cm plasma. If the hard x ray emission is from thermal electrons, anomalous resistivity or densities exceeding 3 x 10(exp 12)/cu cm are required. If the hard x ray emission is from nonthermal electrons, the emissions can be produced with classical resistivity in the current sheets if the heating rate is approximately 4 times greater than that deduced from the soft x ray data (with a density of 10(exp 10)/cu cm in the soft x ray emitting region), if there are at least 10(exp 4) current sheets, and if the plasma properties in the sheets are characteristic of the superhot plasma observed in some flares by Lin et al., and with Hinotori. Most of the released energy goes directly into bulk heating, rather than accelerated particles.

  15. Shape and Current Profile Effects on Runaway Electron Confinement

    Science.gov (United States)

    Izzo, V. A.; James, A. N.; Humphreys, D. A.; Granetz, R. S.; Whyte, D. G.; Olynyk, G. M.

    2011-10-01

    The potential for several MA of current carried by multi-MeV runaway electrons (REs) during ITER disruptions has motivated a variety of experiments in present-day tokamaks studying RE generation, confinement, and control. In both DIII-D and Alcator C Mod, different RE behavior is seen in limited vs. diverted plasmas, suggesting better RE confinement for limited shapes. NIMROD simulations of rapid shutdowns in both devices support this finding, and show reduced stochasticity in limited plasma shapes. Integration of RE drift-orbits also shows differences in RE strike-points that are consistent with experimental observations. In DIII-D a wide variation in RE confinement results for diverted discharges may also point to current density profile effects on RE confinement. Several DIII-D diverted discharges are modeled with NIMROD. Confined RE fractions found in NIMROD are mostly consistent with observed RE currents in DIII-D, although other effects, such as seed generation and avalanching may contribute to the experimental variation. Work supported by US DOE under DE-FC02-06ER54861, DE-FG02-05ER54809, DE-FG02-07ER54917, DE-FC02-04ER54698 and DE-FG02-04ER54762.

  16. Outskirts of Nearby Disk Galaxies: Star Formation and Stellar Populations

    Science.gov (United States)

    Elmegreen, Bruce G.; Hunter, Deidre A.

    The properties and star formation processes in the far-outer disks of nearby spiral and dwarf irregular galaxies are reviewed. The origin and structure of the generally exponential profiles in stellar disks is considered to result from cosmological infall combined with a non-linear star formation law and a history of stellar migration and scattering from spirals, bars and random collisions with interstellar clouds. In both spirals and dwarfs, the far-outer disks tend to be older, redder and thicker than the inner disks, with the overall radial profiles suggesting inside-out star formation plus stellar scattering in spirals and outside-in star formation with a possible contribution from scattering in dwarfs. Dwarf irregulars and the far-outer parts of spirals both tend to be gas dominated, and the gas radial profile is often non-exponential although still decreasing with radius. The ratio of Hα to far-UV flux tends to decrease with lower surface brightness in these regions, suggesting either a change in the initial stellar mass function or the sampling of that function or a possible loss of Hα photons.

  17. A backward Monte-Carlo method for time-dependent runaway electron simulations

    Science.gov (United States)

    Zhang, Guannan; del-Castillo-Negrete, Diego

    2017-09-01

    Kinetic descriptions of runaway electrons (REs) are usually based on Fokker-Planck models that determine the probability distribution function of REs in 2-dimensional momentum space. Despite the simplification involved, the Fokker-Planck equation can rarely be solved analytically and direct numerical approaches [e.g., continuum and particle-based Monte Carlo (MC)] can be time consuming, especially in the computation of asymptotic-type observables including the runaway probability, the slowing-down and runaway mean times, and the energy limit probability. Here, we present a novel backward MC approach to these problems based on backward stochastic differential equations that describe the dynamics of the runaway probability by means of the Feynman-Kac theory. The key ingredient of the backward MC algorithm is to place all the particles in a runaway state and simulate them backward from the terminal time to the initial time. As such, our approach can provide much faster convergence than direct MC methods (by significantly reducing the number of particles required to achieve a prescribed accuracy) while at the same time maintaining the advantages of particle-based methods (compared to continuum approaches). The proposed algorithm is unconditionally stable and can be parallelized as easy as the direct MC method, and its extension to dimensions higher than two is straightforward, thus paving the way for conducting large-scale RE simulation.

  18. Anti-Runaway Prevention System with Wireless Sensors for Intelligent Track Skates at Railway Stations.

    Science.gov (United States)

    Jiang, Chaozhe; Xu, Yibo; Wen, Chao; Chen, Dilin

    2017-12-19

    Anti-runaway prevention of rolling stocks at a railway station is essential in railway safety management. The traditional track skates for anti-runaway prevention of rolling stocks have some disadvantages since they are operated and monitored completely manually. This paper describes an anti-runaway prevention system (ARPS) based on intelligent track skates equipped with sensors and real-time monitoring and management system. This system, which has been updated from the traditional track skates, comprises four parts: intelligent track skates, a signal reader, a database station, and a monitoring system. This system can monitor the real-time situation of track skates without changing their workflow for anti-runaway prevention, and thus realize the integration of anti-runaway prevention information management. This system was successfully tested and practiced at Sunjia station in Harbin Railway Bureau in 2014, and the results confirmed that the system showed 100% accuracy in reflecting the usage status of the track skates. The system could meet practical demands, as it is highly reliable and supports long-distance communication.

  19. Investigation of a High Head Francis Turbine at Runaway Operating Conditions

    Directory of Open Access Journals (Sweden)

    Chirag Trivedi

    2016-03-01

    Full Text Available Hydraulic turbines exhibit total load rejection during operation because of high fluctuations in the grid parameters. The generator reaches no-load instantly. Consequently, the turbine runner accelerates to high speed, runaway speed, in seconds. Under common conditions, stable runaway is only reached if after a load rejection, the control and protection mechanisms both fail and the guide vanes cannot be closed. The runner life is affected by the high amplitude pressure loading at the runaway speed. A model Francis turbine was used to investigate the consequences at the runaway condition. Measurements and simulations were performed at three operating points. The numerical simulations were performed using standard k-ε, k-ω shear stress transport (SST and scale-adaptive simulation (SAS models. A total of 12.8 million hexahedral mesh elements were created in the complete turbine, from the spiral casing inlet to the draft tube outlet. The experimental and numerical analysis showed that the runner was subjected to an unsteady pressure loading up to three-times the pressure loading observed at the best efficiency point. Investigates of unsteady pressure pulsations at the vaneless space, runner and draft tube are discussed in the paper. Further, unsteady swirling flow in the blade passages was observed that was rotating at a frequency of 4.8-times the runaway runner angular speed. Apart from the unsteady pressure loading, the development pattern of the swirling flow in the runner is discussed in the paper.

  20. Anti-Runaway Prevention System with Wireless Sensors for Intelligent Track Skates at Railway Stations

    Directory of Open Access Journals (Sweden)

    Chaozhe Jiang

    2017-12-01

    Full Text Available Anti-runaway prevention of rolling stocks at a railway station is essential in railway safety management. The traditional track skates for anti-runaway prevention of rolling stocks have some disadvantages since they are operated and monitored completely manually. This paper describes an anti-runaway prevention system (ARPS based on intelligent track skates equipped with sensors and real-time monitoring and management system. This system, which has been updated from the traditional track skates, comprises four parts: intelligent track skates, a signal reader, a database station, and a monitoring system. This system can monitor the real-time situation of track skates without changing their workflow for anti-runaway prevention, and thus realize the integration of anti-runaway prevention information management. This system was successfully tested and practiced at Sunjia station in Harbin Railway Bureau in 2014, and the results confirmed that the system showed 100% accuracy in reflecting the usage status of the track skates. The system could meet practical demands, as it is highly reliable and supports long-distance communication.

  1. Stellar Presentations (Abstract)

    Science.gov (United States)

    Young, D.

    2015-12-01

    (Abstract only) The AAVSO is in the process of expanding its education, outreach and speakers bureau program. powerpoint presentations prepared for specific target audiences such as AAVSO members, educators, students, the general public, and Science Olympiad teams, coaches, event supervisors, and state directors will be available online for members to use. The presentations range from specific and general content relating to stellar evolution and variable stars to specific activities for a workshop environment. A presentation—even with a general topic—that works for high school students will not work for educators, Science Olympiad teams, or the general public. Each audience is unique and requires a different approach. The current environment necessitates presentations that are captivating for a younger generation that is embedded in a highly visual and sound-bite world of social media, twitter and U-Tube, and mobile devices. For educators, presentations and workshops for themselves and their students must support the Next Generation Science Standards (NGSS), the Common Core Content Standards, and the Science Technology, Engineering and Mathematics (STEM) initiative. Current best practices for developing relevant and engaging powerpoint presentations to deliver information to a variety of targeted audiences will be presented along with several examples.

  2. Optimizing Stellarators for Turbulent Transport

    Energy Technology Data Exchange (ETDEWEB)

    H.E. Mynick, N.Pomphrey, and P. Xanthopoulos

    2010-05-27

    Up to now, the term "transport-optimized" stellarators has meant optimized to minimize neoclassical transport, while the task of also mitigating turbulent transport, usually the dominant transport channel in such designs, has not been addressed, due to the complexity of plasma turbulence in stellarators. Here, we demonstrate that stellarators can also be designed to mitigate their turbulent transport, by making use of two powerful numerical tools not available until recently, namely gyrokinetic codes valid for 3D nonlinear simulations, and stellarator optimization codes. A first proof-of-principle configuration is obtained, reducing the level of ion temperature gradient turbulent transport from the NCSX baseline design by a factor of about 2.5.

  3. Stellar magnetic activity and exoplanets

    Directory of Open Access Journals (Sweden)

    Vidotto A.A.

    2017-01-01

    Full Text Available It has been proposed that magnetic activity could be enhanced due to interactions between close-in massive planets and their host stars. In this article, I present a brief overview of the connection between stellar magnetic activity and exoplanets. Stellar activity can be probed in chromospheric lines, coronal emission, surface spot coverage, etc. Since these are manifestations of stellar magnetism, these measurements are often used as proxies for the magnetic field of stars. Here, instead of focusing on the magnetic proxies, I overview some recent results of magnetic field measurements using spectropolarimetric observations. Firstly, I discuss the general trends found between large-scale magnetism, stellar rotation, and coronal emission and show that magnetism seems to be correlated to the internal structure of the star. Secondly, I overview some works that show evidence that exoplanets could (or not act as to enhance the activity of their host stars.

  4. Stellar magnetic activity and exoplanets

    Science.gov (United States)

    Vidotto, A. A.

    2017-10-01

    It has been proposed that magnetic activity could be enhanced due to interactions between close-in massive planets and their host stars. In this article, I present a brief overview of the connection between stellar magnetic activity and exoplanets. Stellar activity can be probed in chromospheric lines, coronal emission, surface spot coverage, etc. Since these are manifestations of stellar magnetism, these measurements are often used as proxies for the magnetic field of stars. Here, instead of focusing on the magnetic proxies, I overview some recent results of magnetic field measurements using spectropolarimetric observations. Firstly, I discuss the general trends found between large-scale magnetism, stellar rotation, and coronal emission and show that magnetism seems to be correlated to the internal structure of the star. Secondly, I overview some works that show evidence that exoplanets could (or not) act as to enhance the activity of their host stars.

  5. Stellar atmospheres behind transiting exoplanets

    Science.gov (United States)

    Dravins, D.; Ludwig, H.-G.; Dahlén, E.; Gustavsson, M.; Pazira, H.

    2017-09-01

    Stellar surfaces are covered with brighter and darker structures, just like on the Sun. While solar surface details can be easily studied with telescopes, stellar surfaces cannot thus be resolved. However, one can use planets that happen to pass in front of distant stars as "shades" that successively block out small portions of the stellar surface behind. By measuring how the light from the star changes during such a transit, one can deduce stellar surface properties. Knowing those is required not only to study the star as such, but also to deduce the chemical composition of the planet that is passing in front of it, where some of the detected starlight has been filtered through the planet's atmosphere.

  6. Origin of 1/f noise as a runaway phenomenon due to the zeropoint field (ZPF) of quantum electrodynamics (QED)

    Energy Technology Data Exchange (ETDEWEB)

    Cavalleri, Giancarlo [Dipartimento di Matematica e Fisica, Universita Cattolica del Sacro Cuore, Brescia (Italy); CNR/INFM, Brescia (Italy); Bosi, Leonardo [Dipartimento di Fisica, Politecnico di Milano (Polo Regionale di Lecco) (Italy); CNR/INFM, Milano (Italy)

    2007-03-15

    The origin of electron transport noise whose power spectral density is inversely proportional to the frequency f has been realized after 80 years of attempts. Here we give its conceptual explanation that has required a sequence of five ideas and corresponding results: 1) The reduction of the nonlinear Boltzmann equation with electron-electron (e-e) interaction to a Fokker-Planck (denoted as e-e FP) equation containing two electron collision frequencies {nu}{sub 1} and {nu}{sub 2}; 2) the application of the e-e FP to materials and its-steady state solution that depends on {nu}{sub 1}(v), {nu}{sub 2}(v), and the square a{sup 2} of the acceleration a=eE/m; 3) the steady-state solution of the e-e FP equation becomes similar to the Fermi-Dirac distribution function if a{sup 2} is considered as mainly due to the zero-point field (ZPF) of quantum electrodynamics (QED) or, realistically, of stochastic electrodynamics (SED); 4) in this {delta}v range the e-FP is similar to the usual FP solved by Stenflo when {nu}(v){proportional_to}1/v. It is just because of a{sup 2}{sub ZPF} that for any conduction current there is always a small interval {delta}v for the electron speed v where {nu}{sub 1} {proportional_to}{nu}{sub 2}{proportional_to} 1/v, condition that is at the threshold of runaways. The relevant time-dependent Green solution of the e-e FP equation decreases as {tau}{sup -{epsilon}} with {epsilon}<0.006. The consequent power spectral density S(f) turns out to be {proportional_to}1/f{sup 1-{epsilon}} in an indefinite medium. Our S(f) also depends on the electrons concentration N and excellently fits the experimental data; 5) In a finite sample the memory or a fluctuation is preserved beyond the electron transit time because the transmission of information is mainly due to e-e interactions and to the diffusion coefficient that diverges at the threshold of runaways. A pimple (due to fluctuation) in the distribution function on the electron speeds is almost crystallized

  7. A Thermal Runaway Simulation on a Lithium Titanate Battery and the Battery Module

    Directory of Open Access Journals (Sweden)

    Man Chen

    2015-01-01

    Full Text Available Based on the electrochemical and thermal model, a coupled electro-thermal runaway model was developed and implemented using finite element methods. The thermal decomposition reactions when the battery temperature exceeds the material decomposition temperature were embedded into the model. The temperature variations of a lithium titanate battery during a series of charge-discharge cycles under different current rates were simulated. The results of temperature and heat generation rate demonstrate that the greater the current, the faster the battery temperature is rising. Furthermore, the thermal influence of the overheated cell on surrounding batteries in the module was simulated, and the variation of temperature and heat generation during thermal runaway was obtained. It was found that the overheated cell can induce thermal runaway in other adjacent cells within 3 mm distance in the battery module if the accumulated heat is not dissipated rapidly.

  8. Big-Data-Based Thermal Runaway Prognosis of Battery Systems for Electric Vehicles

    Directory of Open Access Journals (Sweden)

    Jichao Hong

    2017-07-01

    Full Text Available A thermal runaway prognosis scheme for battery systems in electric vehicles is proposed based on the big data platform and entropy method. It realizes the diagnosis and prognosis of thermal runaway simultaneously, which is caused by the temperature fault through monitoring battery temperature during vehicular operations. A vast quantity of real-time voltage monitoring data is derived from the National Service and Management Center for Electric Vehicles (NSMC-EV in Beijing. Furthermore, a thermal security management strategy for thermal runaway is presented under the Z-score approach. The abnormity coefficient is introduced to present real-time precautions of temperature abnormity. The results illustrated that the proposed method can accurately forecast both the time and location of the temperature fault within battery packs. The presented method is flexible in all disorder systems and possesses widespread application potential in not only electric vehicles, but also other areas with complex abnormal fluctuating environments.

  9. Evaluation of runaway-electron effects on plasma-facing components for NET

    Science.gov (United States)

    Bolt, H.; Calén, H.

    1991-03-01

    Runaway electrons which are generated during disruptions can cause serious damage to plasma facing components in a next generation device like NET. A study was performed to quantify the response of NET plasma facing components to runaway-electron impact. For the determination of the energy deposition in the component materials Monte Carlo computations were performed. Since the subsurface metal structures can be strongly heated under runaway-electron impact from the computed results damage threshold values for the thermal excursions were derived. These damage thresholds are strongly dependent on the materials selection and the component design. For a carbonmolybdenum divertor with 10 and 20 mm carbon armour thickness and 1 degree electron incidence the damage thresholds are 100 MJ/m 2 and 220 MJ/m 2. The thresholds for a carbon-copper divertor under the same conditions are about 50% lower. On the first wall damage is anticipated for energy depositions above 180 MJ/m 2.

  10. High performance gamma-ray spectrometer for runaway electron studies on the FT-2 tokamak

    Science.gov (United States)

    Shevelev, A. E.; Khilkevitch, E. M.; Lashkul, S. I.; Rozhdestvensky, V. V.; Altukhov, A. B.; Chugunov, I. N.; Doinikov, D. N.; Esipov, L. A.; Gin, D. B.; Iliasova, M. V.; Naidenov, V. O.; Nersesyan, N. S.; Polunovsky, I. A.; Sidorov, A. V.; Kiptily, V. G.

    2016-09-01

    A gamma-ray spectrometer based on LaBr3(Ce) scintillator has been used for measurements of hard X-ray emission generated by runaway electrons in the FT-2 tokamak plasmas. Using of the fast LaBr3(Ce) has allowed extending count rate range of the spectrometer by a factor of 10. A developed digital processing algorithm of the detector signal recorded with a digitizer sampling rate of 250 MHz has provided a pulse height analysis at count rates up to 107 s-1. A spectrum deconvolution code DeGaSum has been applied for inferring the energy distribution of runaway electrons escaping from the plasma and interacting with materials of the FT-2 limiter in the vacuum chamber. The developed digital signal processing technique for LaBr3(Ce) spectrometer has allowed studying the evolution of runaways energy distribution in the FT-2 plasma discharges with time resolution of 1-5 ms.

  11. Modelling Venting and Pressure Build-up in a 18650 LCO Cell during Thermal Runaway (ABSTRACT)

    DEFF Research Database (Denmark)

    Coman, Paul Tiberiu; Veje, Christian; White, Ralph

    may lead to fires and explosions. To prevent this, it is therefore important to model thermal runaway considering different events such as venting and the pressure development inside the battery cell, which makes the main purpose of this paper. A model consisting of the different decomposition....... By fitting the activation energies, and measuring experimentally the mass of the ejecta during thermal runaway, the model is compared and validated against an extensive experiment performed by Golukbov et al. [1] during oven heating. When analysing the results, it is found that by including the venting......Li-ion batteries are a very popular type of electric storage devices that possess high energy density when compared to the other battery chemistries. Due to this property, when operating under abusive conditions such as high ambient temperature, the batteries can experience thermal runaway, which...

  12. Predicted space motions for hypervelocity and runaway stars: proper motions and radial velocities for the Gaia Era

    Energy Technology Data Exchange (ETDEWEB)

    Kenyon, Scott J.; Brown, Warren R.; Geller, Margaret J. [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Bromley, Benjamin C., E-mail: skenyon@cfa.harvard.edu, E-mail: wbrown@cfa.harvard.edu, E-mail: mgeller@cfa.harvard.edu, E-mail: bromley@physics.utah.edu [Department of Physics, University of Utah, 115 S 1400 E, Rm 201, Salt Lake City, UT 84112 (United States)

    2014-10-01

    We predict the distinctive three-dimensional space motions of hypervelocity stars (HVSs) and runaway stars moving in a realistic Galactic potential. For nearby stars with distances less than 10 kpc, unbound stars are rare; proper motions alone rarely isolate bound HVSs and runaways from indigenous halo stars. At large distances of 20-100 kpc, unbound HVSs are much more common than runaways; radial velocities easily distinguish both from indigenous halo stars. Comparisons of the predictions with existing observations are encouraging. Although the models fail to match observations of solar-type HVS candidates from SEGUE, they agree well with data for B-type HVS and runaways from other surveys. Complete samples of g ≲ 20 stars with Gaia should provide clear tests of formation models for HVSs and runaways and will enable accurate probes of the shape of the Galactic potential.

  13. Runaway gas accretion and gap opening versus type I migration

    Science.gov (United States)

    Crida, A.; Bitsch, B.

    2017-03-01

    Growing planets interact with their natal protoplanetary disc, which exerts a torque onto them allowing them to migrate in the disc. Small mass planets do not affect the gas profile and migrate in the fast type-I migration. Although type-I migration can be directed outwards for planets smaller than 20 - 30M⊕ in some regions of the disc, planets above this mass should be lost into the central star long before the disc disperses. Massive planets push away material from their orbit and open a gap. They subsequently migrate in the slower, type II migration, which could save them from migrating all the way to the star. Hence, growing giant planets can be saved if and only if they can reach the gap opening mass, because this extends their migration timescale, allowing them to eventually survive at large orbits until the disc itself disperses. However, most of the previous studies only measured the torques on planets with fixed masses and orbits to determine the migration rate. Additionally, the transition between type-I and type-II migration itself is not well studied, especially when taking the growth mechanism of rapid gas accretion from the surrounding disc into account. Here we use isothermal 2D disc simulations with FARGO-2D1D to study the migration behaviour of gas accreting protoplanets in discs. We find that migrating giant planets always open gaps in the disc. We further show analytically and numerically that in the runaway gas accretion regime, the growth time-scale is comparable to the type-I migration time-scale, indicating that growing planets will reach gap opening masses before migrating all the way to the central star in type-I migration if the disc is not extremely viscous and/or thick. An accretion rate limited to the radial gas flow in the disc, in contrast, is not fast enough. When gas accretion by the planet is taken into account, the gap opening process is accelerated because the planet accretes material originating from its horseshoe region. This

  14. Planets, stars and stellar systems

    CERN Document Server

    Bond, Howard; McLean, Ian; Barstow, Martin; Gilmore, Gerard; Keel, William; French, Linda

    2013-01-01

    This is volume 3 of Planets, Stars and Stellar Systems, a six-volume compendium of modern astronomical research covering subjects of key interest to the main fields of contemporary astronomy. This volume on “Solar and Stellar Planetary Systems” edited by Linda French and Paul Kalas presents accessible review chapters From Disks to Planets, Dynamical Evolution of Planetary Systems, The Terrestrial Planets, Gas and Ice Giant Interiors, Atmospheres of Jovian Planets, Planetary Magnetospheres, Planetary Rings, An Overview of the Asteroids and Meteorites, Dusty Planetary Systems and Exoplanet Detection Methods. All chapters of the handbook were written by practicing professionals. They include sufficient background material and references to the current literature to allow readers to learn enough about a specialty within astronomy, astrophysics and cosmology to get started on their own practical research projects. In the spirit of the series Stars and Stellar Systems published by Chicago University Press in...

  15. TEM turbulence optimisation in stellarators

    CERN Document Server

    Proll, J H E; Xanthopoulos, P; Lazerson, S A; Faber, B J

    2015-01-01

    With the advent of neoclassically optimised stellarators, optimising stellarators for turbulent transport is an important next step. The reduction of ion-temperature-gradient-driven turbulence has been achieved via shaping of the magnetic field, and the reduction of trapped-electron mode (TEM) turbulence is adressed in the present paper. Recent analytical and numerical findings suggest TEMs are stabilised when a large fraction of trapped particles experiences favourable bounce-averaged curvature. This is the case for example in Wendelstein 7-X [C.D. Beidler $\\textit{et al}$ Fusion Technology $\\bf{17}$, 148 (1990)] and other Helias-type stellarators. Using this knowledge, a proxy function was designed to estimate the TEM dynamics, allowing optimal configurations for TEM stability to be determined with the STELLOPT [D.A. Spong $\\textit{et al}$ Nucl. Fusion $\\bf{41}$, 711 (2001)] code without extensive turbulence simulations. A first proof-of-principle optimised equilibrium stemming from the TEM-dominated stella...

  16. New low temperature electrolytes with thermal runaway inhibition for lithium-ion rechargeable batteries

    Science.gov (United States)

    Mandal, Braja K.; Padhi, Akshaya K.; Shi, Zhong; Chakraborty, Sudipto; Filler, Robert

    This paper describes a low temperature electrolyte system for lithium-ion rechargeable batteries. The electrolyte exhibits high ionic conductivity, good electrochemical stability and no exothermic reaction in the presence of lithium metal. The system features a low lattice energy lithium salt in a specific mixture of carbonate solvents and a novel thermal runaway inhibitor.

  17. On the Absence of Non-thermal X-Ray Emission around Runaway O Stars

    Energy Technology Data Exchange (ETDEWEB)

    Toalá, J. A. [Institute of Astronomy and Astrophysics, Academia Sinica (ASIAA), Taipei 10617, Taiwan (China); Oskinova, L. M. [Institute for Physics and Astronomy, University of Potsdam, D-14476 Potsdam (Germany); Ignace, R. [Department of Physics and Astronomy, East Tennessee State University, Johnson City, TN 37614 (United States)

    2017-04-01

    Theoretical models predict that the compressed interstellar medium around runaway O stars can produce high-energy non-thermal diffuse emission, in particular, non-thermal X-ray and γ -ray emission. So far, detection of non-thermal X-ray emission was claimed for only one runaway star, AE Aur. We present a search for non-thermal diffuse X-ray emission from bow shocks using archived XMM-Newton observations for a clean sample of six well-determined runaway O stars. We find that none of these objects present diffuse X-ray emission associated with their bow shocks, similarly to previous X-ray studies toward ζ Oph and BD+43°3654. We carefully investigated multi-wavelength observations of AE Aur and could not confirm previous findings of non-thermal X-rays. We conclude that so far there is no clear evidence of non-thermal extended emission in bow shocks around runaway O stars.

  18. Runaway and thermally safe operation of a nitric acid oxidation in a semi-batch reactor

    NARCIS (Netherlands)

    van Woezik, B.A.A.

    2000-01-01

    A number of serious accidents has occurred due to a runaway reaction of a heterogeneous liquid-liquid reaction whereby a secondary side reaction was triggered. A basic lack of proper knowledge of all the phenomena, occurring in such a system, is one of the prime causes that may lead to overheating

  19. The Intergenerational Transmission of Running Away: Childhood Experiences of the Parents of Runaways.

    Science.gov (United States)

    Plass, Peggy S.; Hotaling, Gerald T.

    1995-01-01

    Data from the primary caretakers of 20,505 children in the National Incidence Study of Missing, Abducted, Runaway, and Throwaway Children illustrate the influence of parents' own childhood running-away experiences on their children's behavior. The importance of intergenerational transmission factors is illustrated. (SLD)

  20. On-line runaway detection in batch reactors using chaos theory techniques.

    NARCIS (Netherlands)

    Strozzi, F.; Strozzi, F.; Zaldivar, J.M.; Zaldivar, J.M.; Kronberg, Alexandre E.; Westerterp, K.R.

    1999-01-01

    In this work nonlinear time-series analysis using delay coordinate embedding was applied to simulated temperature data from isoperibolic batch reactors to develop an early-warning detection system of the runaway. In the first part of this study an early-warning detection criterion, that is, when the

  1. An electrochemical-thermal coupled overcharge-to-thermal-runaway model for lithium ion battery

    Science.gov (United States)

    Ren, Dongsheng; Feng, Xuning; Lu, Languang; Ouyang, Minggao; Zheng, Siqi; Li, Jianqiu; He, Xiangming

    2017-10-01

    This paper presents an electrochemical-thermal coupled overcharge-to-thermal-runaway (TR) model to predict the highly interactive electrochemical and thermal behaviors of lithium ion battery under the overcharge conditions. In this model, the battery voltage equals the difference between the cathode potential and the anode potential, whereas the temperature is predicted by modeling the combined heat generations, including joule heat, thermal runaway reactions and internal short circuit. The model can fit well with the adiabatic overcharge tests results at 0.33C, 0.5C and 1C, indicating a good capture of the overcharge-to-TR mechanism. The modeling analysis based on the validated model helps to quantify the heat generation rates of each heat sources during the overcharge-to-TR process. And the two thermal runaway reactions including the electrolyte oxidation reaction and the reaction between deposited lithium and electrolyte are found to contribute most to the heat generations during the overcharge process. Further modeling analysis on the critical parameters is performed to find possible solutions for the overcharge problem of lithium ion battery. The result shows that increasing the oxidation potential of the electrolyte, and increasing the onset temperature of thermal runaway are the two effective ways to improve the overcharge performance of lithium ion battery.

  2. Runaway reactions, their courses and the methods to establish safe process conditions

    Science.gov (United States)

    Gustin, J. L.

    1991-08-01

    Much of the literature on runaway reactions deals with the consequences such as mechanical damage toxic and flammable release. The DIERS literature provides effective methods for vent sizing where experimental information is requested. Thermal stability measurements provide information on the onset temperature and kinetic data for chemical reactions. There is less information on the way the runaway reactions occur whereas the runaway reactions may have different causes. The purpose of this paper is to describe the various process deviations which can cause a runaway reaction to occur and to discuss the experimental information necessary for risk assessment, the choice of a safe process and the mitigation of the consequences of the runaway reaction. Each possible hazardous process deviation is illustrated by examples from the process industry and/or relevant experimental information obtained from laboratory experiments. The typical hazardous situations to be considered are the following: 1) The homogeneous thermal runaway due to too high a temperature. 2) The homogeneous runaway reaction by unintended introduction of additional reactants or catalyst. 3) The heterogeneous runaway reaction due to too high a local temperature. 4) The heterogeneous runaway reaction caused by slow heat conduction to the outside. 5) The runaway reaction caused by excess residence time at the process temperature (autocatalytic reactions). 6) The runaway reaction caused by reactant accumulation. The controling reactant feed rate is higher than the consumption rate perhaps because the temperature is too low, or the catalyst is absent. 7) The runaway reaction due to the pressurization of the enclosure by gaseous oxidizing intermediates (typical of nitric oxidations). 8) The runaway reaction due to phase separation of unstable species (liquids, solids) by loss of mixing or on cooling. 9) The runaway reaction on mixing of fast reacting chemicals in separate phases. 10)The runaway reaction due

  3. Needs assessment of runaway females in Iran from an occupational therapy perspective.

    Science.gov (United States)

    Malekpour, Maryam

    2008-01-01

    The purpose of this descriptive study was to assess, from an occupational therapy perspective, the occupational performance needs of runaway females between 15 and 33 years old, residing in the state-run shelters in Mashhad, Iran. The inclusion criteria were: (1) participants who were 15 years old or above; (2) participants who resided in one of the state-run shelters in Mashhad; and (3) participants who could read, comprehend and write in Farsi. A written survey was completed by 44 runaway females (response rate: 36.6%). The findings revealed the occupational needs of this population to be as follows: vocational needs to find a meaningful job, emotional needs to manage depression and hopelessness, social participation needs to manage family and peer/friend relationships and peer interactions with the opposite sex to find an appropriate mate and educational needs to continue their education. Participants were from one area of Iran, so the results of the study cannot be generalized to runaway females residing in shelters in other areas of the country. Future research could include a qualitative design to explore more in-depth needs of this population. Also, a larger population of runaway females nationwide should be included in a study to increase generalizability. (c) 2008 John Wiley & Sons, Ltd.

  4. The effect of ITER-like wall on runaway electron generation in JET

    NARCIS (Netherlands)

    Papp, G.; Fülöp, T.; Fehér, T.; de Vries, P. C.; Riccardo, V.; Reux, C.; Lehnen, M.; Kiptily, V.; Plyusnin, V. V.; Alper, B.; JET-EFDA Contributors,

    2013-01-01

    This paper investigates the effect of the ITER-like wall (ILW) on runaway electron (RE) generation through a comparative study of similar slow argon injection JET disruptions, performed with different wall materials. In the carbon wall case, a RE plateau is observed, while in the ITER-like wall

  5. Thermal runaway and bistability in microwave heated slabs, cylinders, and spheres

    NARCIS (Netherlands)

    Vriezinga, C.A.

    2000-01-01

    This study analyzes the runaway of microwave (2450 MHz) heated slabs, cylinders, and spheres in free space. It is shown that the phenomenon can be described with an S-shaped response curve of steady-state temperature versus microwave power at any position within the sample. The analysis

  6. CFD Analysis of the Runaway Stability of a Model Pump-Turbine

    Science.gov (United States)

    Xia, L. S.; Cheng, Y. G.; You, J. F.; Jiang, Y. Q.

    2016-11-01

    The relations between the runaway stability characteristics and the flow patterns inside the runner of pump-turbine are supposed to be close and should be studied. The runaway processes of a model pump-turbine at four guide-vane openings (GVOs) were simulated by the three-dimensional computational fluid dynamics. The results show that the runaway stability characteristics for the pump-turbine are different at different GVOs. For the small GVOs, the turbine characteristic trajectory undergoes damped oscillations; however, for large GVOs, the turbine characteristic trajectory settles into an un-damping oscillation. The evolution features of the reverse flow vortex structures (RFVS) at the runner inlet during the runaway oscillations have distinct patterns between the small and large GVOs. For small GVOs, the RFVSs only locate at the mid-span; however, for the large GVOs, the location of the RFVSs switches back and forth between the mid-span section and the hub side when the turbine passes in and out the turbine braking mode. The changes of RFVS at the runner inlet dominate the energy transfer among the hydraulic, mechanical and dissipation energies during the transient processes, and therefore affect the stability of hydraulic system.

  7. High altitude atmospheric discharges according to the runaway air breakdown mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Symbalisty, E.; Roussel-Dupre, R.; Yukhimuk, V.; Taranenko, Y.

    1997-04-01

    High altitude optical transients - red sprites, blue jets, and elves - are modeled in the context of the relativistic electron runaway air breakdown mechanism. These emissions are usually associated with large mesoscale convective systems (hereafter MCS). In thunderstorms cloud electrification proceeds over a time scale long enough to permit the conducting atmosphere above the cloud to polarize and short out the thunderstorm electric field. When a lightning strike rapidly neutralizes a cloud charge layer runaway driving fields can develop in the stratosphere and mesosphere. According to present simulations of the full runaway process the variety of observed optical emissions are due to the nature of the normal lightning event in the MCS that kick starts the runaway avalanche. In this paper the authors describe some details of the model, present the results of the evolution of the primary electron population, and summarize the initial conditions necessary for different types of discharges. Two companion papers present (a) the predicted optical, gamma ray, and radio emissions caused by these electrical discharges, and (b) the time evolution of the secondary electron population and its implications in terms of observables.

  8. Street Life: Aggravated and Sexual Assaults among Homeless and Runaway Adolescents.

    Science.gov (United States)

    Terrell, Nathanial Eugene

    1997-01-01

    Examines aggravated and sexual assaults among 240 runaway and homeless adolescents (RHAs) in Des Moines (Iowa). Results suggest RHAs are at risk of life-threatening situations on the streets due to aggressive and abusive parents. Additionally, street life situations have significant impacts on the probability that RHAs will be victims of…

  9. Can Cell to Cell Thermal Runaway Propagation be Prevented in a Li-ion Battery Module?

    Science.gov (United States)

    Jeevarajan, Judith; Lopez, Carlos; Orieukwu, Josephat

    2014-01-01

    Increasing cell spacing decreased adjacent cell damage center dotElectrically connected adjacent cells drained more than physically adjacent cells center dotRadiant barrier prevents propagation when fully installed between BP cells center dotBP cells vent rapidly and expel contents at 100% SOC -Slower vent with flame/smoke at 50% -Thermal runaway event typically occurs at 160 degC center dotLG cells vent but do not expel contents -Thermal runaway event typically occurs at 200 degC center dotSKC LFP modules did not propagate; fuses on negative terminal of cell may provide a benefit in reducing cell to cell damage propagation. New requirement in NASA-Battery Safety Requirements document: JSC 20793 Rev C 5.1.5.1 Requirements - Thermal Runaway Propagation a. For battery designs greater than a 80-Wh energy employing high specific energy cells (greater than 80 watt-hours/kg, for example, lithium-ion chemistries) with catastrophic failure modes, the battery shall be evaluated to ascertain the severity of a worst-case single-cell thermal runaway event and the propensity of the design to demonstrate cell-to-cell propagation in the intended application and environment. NASA has traditionally addressed the threat of thermal runaway incidents in its battery deployments through comprehensive prevention protocols. This prevention-centered approach has included extensive screening for manufacturing defects, as well as robust battery management controls that prevent abuse-induced runaway even in the face of multiple system failures. This focused strategy has made the likelihood of occurrence of such an event highly improbable. b. The evaluation shall include all necessary analysis and test to quantify the severity (consequence) of the event in the intended application and environment as well as to identify design modifications to the battery or the system that could appreciably reduce that severity. In addition to prevention protocols, programs developing battery designs with

  10. Fundamental stellar properties from asteroseismology

    DEFF Research Database (Denmark)

    Silva Aguirre, V.; Casagrande, L.; Miglio, A.

    2013-01-01

    Accurate characterization of stellar populations is of prime importance to correctly understand the formation and evolution process of our Galaxy. The field of asteroseismology has been particularly successful in such an endeavor providing fundamental parameters for large samples of stars...... in different evolutionary phases. We present our results on determinations of masses, radii, and distances of stars in the CoRoT and Kepler fields, showing that we can map and date different regions of the galactic disk and distinguish gradients in the distribution of stellar properties at different heights...

  11. Identification of Stellar Sequences in Various Stellar Systems ...

    Indian Academy of Sciences (India)

    The spatial morphological study of stellar clusters has been carried out through their identified probable members. The field stars decontamination is performed by the statistical cleaning approach (depends on the magnitude and colour of stars within the field and cluster regions). The colour magnitude ratio diagram ...

  12. Simulation of runaway electron generation during plasma shutdown by impurity injection

    Energy Technology Data Exchange (ETDEWEB)

    Feher, Tamas

    2011-03-15

    Disruptions are dangerous instabilities in tokamaks that should be avoided or mitigated. One possible disruption mitigation method is to inject impurities into the plasma to shut it down in a controlled way. Runaway Electrons (REs) can be generated after the plasma is cooled down by the impurities and these electrons can damage the tokamak. In this work a simulation code is developed to investigate different disruption mitigation scenarios. The response of the bulk plasma, more precisely the temperature evolution of electrons, deuterium and impurity ions are described by energy balance equations in a 1D cylindrical plasma model. The induction and resistive diffusion of electric field is calculated. RE generation rates are used to calculate the runaway current. The Dreicer, hot-tail and avalanche effect is taken into account and a simple model for RE losses is also included. RE generation is studied in JET-like plasmas during pellet injection. Carbon pellets cause effective cooling but these scenarios are prone to runaway generation. A mixture of argon and deuterium gas could be used for safe shutdown without RE generation. In ITER the hot-tail RE generation process becomes important, and the simulation is therefore extended to take this into account. Shutdown scenarios with different concentration of neon and argon impurities were tested in ITER-like plasmas. To simplify the problem the impurity injection into the plasma is not modeled in these cases, only the response of the bulk plasma. The avalanche process cannot be suppressed in a simple way and would produce high runaway current. It can be avoided if some runaway loss phenomenon is included in the simulations, like diffusion due to magnetic perturbations

  13. Cas A and the Crab were not stellar binaries at death

    Science.gov (United States)

    Kochanek, C. S.

    2018-01-01

    The majority of massive stars are in binaries, which implies that many core collapse supernovae should be binaries at the time of the explosion. Here we show that the three most recent, local (visual) SNe (the Crab, Cas A and SN 1987A) were not stellar binaries at death, with limits on the initial mass ratios of q = M2/M1 ≲ 0.1. No quantitative limits have previously been set for Cas A and the Crab, while for SN 1987A we merely updated existing limits in view of new estimates of the dust content. The lack of stellar companions to these three ccSNe implies a 90 per cent confidence upper limit on the q ≳ 0.1 binary fraction at death of fb model (meaning no binary interactions), with a flat mass ratio distribution and a Salpeter IMF, the resulting 90 per cent confidence upper limit on the initial binary fraction of F < 63 per cent is in tension with observed massive binary statistics. Allowing a significant fraction fM ≃ 25 per cent of stellar binaries to merge reduces the tension, with F < 63({1-f}M)^{-1}{ per cent} ˜eq 81{ per cent}, but allowing for the significant fraction in higher order systems (triples, etc.) reintroduces the tension. That Cas A was not a stellar binary at death also shows that a surviving massive binary companion at the time of the explosion is not necessary for producing a Type IIb SNe. Much larger surveys for binary companions to Galactic SNe will become feasible with the release of the full Gaia proper motion and parallax catalogues providing a powerful probe of the statistics of such binaries and their role in massive star evolution, neutron star velocity distributions and runaway stars.

  14. Integrated Circuit Stellar Magnitude Simulator

    Science.gov (United States)

    Blackburn, James A.

    1978-01-01

    Describes an electronic circuit which can be used to demonstrate the stellar magnitude scale. Six rectangular light-emitting diodes with independently adjustable duty cycles represent stars of magnitudes 1 through 6. Experimentally verifies the logarithmic response of the eye. (Author/GA)

  15. Maximum stellar iron core mass

    Indian Academy of Sciences (India)

    Abstract. An analytical method of estimating the mass of a stellar iron core, just prior to core collapse, is .... approximately as an ideal gas, the mean kinetic energies of the free electrons and atomic nuclei will be equal. .... whose density varies from a maximum at the core's center to a minimum at its 'surface'. The dimensional ...

  16. Maximum stellar iron core mass

    Indian Academy of Sciences (India)

    An analytical method of estimating the mass of a stellar iron core, just prior to core collapse, is described in this paper. The method employed depends, in part, upon an estimate of the true relativistic mass increase experienced by electrons within a highly compressed iron core, just prior to core collapse, and is significantly ...

  17. Stellar model fits and inversions

    DEFF Research Database (Denmark)

    Christensen-Dalsgaard, J.

    2012-01-01

    The recent asteroseismic data from the CoRoT and Kepler missions have provided an entirely new basis for investigating stellar properties. This has led to a rapid development in techniques for analysing such data, although it is probably fair to say that we are still far from having the tools req...

  18. Stellar dynamics and black holes

    Indian Academy of Sciences (India)

    Chandrasekhar's most important contribution to stellar dynamics was the concept of dynamical friction. I briefly review that work, then discuss some implications of Chandrasekhar's theory of gravitational encounters for motion in galactic nuclei. Author Affiliations. David Merritt1. Department of Physics, Rochester Institute ...

  19. The Stellar-Solar Connection

    Science.gov (United States)

    Ayres, T. R.

    2004-05-01

    Many solar-stellar astronomers believe that the solar-stellar connection primarily is a one-way street: the exquisitely detailed studies of the solar surface, interior, and heliosphere strongly mold our views of the distant, unresolved stars. Perhaps many solar physicists have gone so far as to adopt the myopic view that stellar astronomy, by and large, is merely sponging up the fabulous insights from ever deeper examinations of our local star, but the ``dark side'' is not really capable of returning the favor. What could we possibly learn from the stars, that we don't already know from much better observations of the Sun? In my Introduction to this Topical Session, I will discuss two broad issues: (1) the present divergence between solar and stellar physics (driven by the different goals and tools of the two disciplines); and (2) the diversity of stars in the H-R diagram, to help inform our understanding of solar processes. Today, there are observations of stars that greatly exceed the quality of analogous solar measurements: e.g., HST/STIS UV echelle spectra of Alpha Cen A; Chandra transmission grating spectra of solar-type stars; and only recently have we obtained a definitive understanding of the Sun's soft X-ray luminosity in the key ROSAT/PSPC band. The lack of equivalent solar observations hinders practical applications of the solar-stellar connection. On the more informative side, the evolutionary paths of other stars can be quite different from the Sun's, with potentially dramatic influences on phenomena such as magnetic activity. Equally important, examples of Sun-like stars can be found at all stages of evolution, from proplyds to red giants, in the volume of nearby space out to 500 pc. In short, the solar-stellar connection need not be a one-way street, but rather a powerful tool to explore solar processes within the broader context of stars and stellar evolution. This work was supported by NASA grant NAG5-13058.

  20. Targeted Optimization of Quasi-Symmetric Stellarators

    Energy Technology Data Exchange (ETDEWEB)

    Hegna, Chris C. [Univ. of Wisconsin, Madison, WI (United States). Dept. of Engineering Physics; Anderson, D. T. [Univ. of Wisconsin, Madison, WI (United States); Talmadge, J. N. [Univ. of Wisconsin, Madison, WI (United States)

    2016-10-06

    The proposed research focuses on targeted areas of plasma physics dedicated to improving the stellarator concept. Research was pursued in the technical areas of edge/divertor physics in 3D configurations, magnetic island physics in stellarators, the role of 3D shaping on microinstabilities and turbulent transport and energetic ion confinement in stellarators.

  1. Runaway breakdown in strong electric field as a source of terrestrial gamma flashes and gamma bursts in lightning leader steps

    Energy Technology Data Exchange (ETDEWEB)

    Gurevich, A.V. [P.N. Lebedev Physical Institute, Russian Academy of Sciences, 119991 Moscow (Russian Federation)]. E-mail: alex@lpi.ru; Zybin, K.P. [P.N. Lebedev Physical Institute, Russian Academy of Sciences, 119991 Moscow (Russian Federation); Medvedev, Yu.V. [Joint Institute for High Temperature, Russian Academy of Sciences, 127412 Moscow (Russian Federation)

    2007-01-22

    The new model of lightning step leader is proposed. It includes three main processes developing simultaneously in a strong electric field: conventional breakdown, effect of runaway electrons and runaway breakdown (RB). The theory of RB in strong electric field is developed. Comparison with the existing observational data shows that the model can serve as a background for the explanation of gamma bursts in step leader and TGF.

  2. Demographic, Personality and Psychopathology Characteristics of the Runaway Girls in Social Emergency and Rehabilitation Centre of Shiraz, Iran

    OpenAIRE

    Toubaei, Shahin; Nateghi, GholamReza; Dehbozorgi, Gholam Reza; Sadr Esfahani, Hasan

    2012-01-01

    Objective: The problem of runaway girls is one of the social problems which has become more prevalent and is considered a serious challenge for families, welfare centers and governmental organizations in Iran. This study aimed at determining the demographic, personality and psychopathology characteristic of a sample of runaway girls in Shiraz, Iran. Methods: Fifty girls who had escaped from their home and were referred to the Women’s Social Emergency and Rehabilitant Centre of Shiraz were com...

  3. Infrared Photometric Properties of 709 Candidate Stellar Bowshock Nebulae

    Science.gov (United States)

    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.

  4. Microstructural Analysis of the Effects of Thermal Runaway on Li-Ion and Na-Ion Battery Electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Finegan, Donal [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Robinson, James B. [University College London; Heenan, Thomas M. M. [University College London; Smith, Katherine [Sharp Laboratories of Europe; Kendrick, Emma [Sharp Laboratories of Europe; University College London; Brett, Daniel J. L. [University College London; Shearing, Paul R. [University College London

    2017-12-06

    Thermal runaway is a phenomenon that occurs due to self-sustaining reactions within batteries at elevated temperatures resulting in catastrophic failure. Here, the thermal runaway process is studied for a Li-ion and Na-ion pouch cells of similar energy density (10.5 Wh, 12 Wh, respectively) using accelerating rate calorimetry (ARC). Both cells were constructed with a z-fold configuration, with a standard shutdown separator in the Li-ion and a low-cost polypropylene (PP) separator in the Na-ion. Even with the shutdown separator, it is shown that the self-heating rate and rate of thermal runaway in Na-ion cells is significantly slower than that observed in Li-ion systems. The thermal runaway event initiates at a higher temperature in Na-ion cells. The effect of thermal runaway on the architecture of the cells is examined using X-ray microcomputed tomography, and scanning electron microscopy (SEM) is used to examine the failed electrodes of both cells. Finally, from examination of the respective electrodes, likely due to the carbonate solvent containing electrolyte, it is suggested that thermal runaway in Na-ion batteries (NIBs) occurs via a similar mechanism to that reported for Li-ion cells.

  5. Collision Repair Campaign

    Science.gov (United States)

    The Collision Repair Campaign targets meaningful risk reduction in the Collision Repair source category to reduce air toxic emissions in their communities. The Campaign also helps shops to work towards early compliance with the Auto Body Rule.

  6. Characterizing stellar and exoplanetary environments

    CERN Document Server

    Khodachenko, Maxim

    2015-01-01

    In this book an international group of specialists discusses studies of exoplanets subjected to extreme stellar radiation and plasma conditions. It is shown that such studies will help us to understand how terrestrial planets and their atmospheres, including the early Venus, Earth and Mars, evolved during the host star’s active early phase. The book presents an analysis of findings from Hubble Space Telescope observations of transiting exoplanets, as well as applications of advanced numerical models for characterizing the upper atmosphere structure and stellar environments of exoplanets. The authors also address detections of atoms and molecules in the atmosphere of “hot Jupiters” by NASA’s Spitzer telescope. The observational and theoretical investigations and discoveries presented are both timely and important in the context of the next generation of space telescopes. 
 The book is divided into four main parts, grouping chapters on exoplanet host star radiation and plasma environments, exoplanet u...

  7. Quasi-axially symmetric stellarators

    Science.gov (United States)

    Garabedian, Paul R.

    1998-01-01

    Confinement of a plasma for controlled thermonuclear fusion is studied numerically. Toroidal equilibria are considered, with an emphasis on the Modular Helias-like Heliac 2 (MHH2), which is a stellarator of low aspect ratio with just two field periods surrounded by 16 modular coils. The geometry is fully three-dimensional, but there is an axial symmetry of the magnetic structure that is calculated to give confinement competitive with that in circular tokamaks. Additional vertical and toroidal field coils, together with a current drive, provide the flexibility and the control of rotational transform necessary for a successful experiment. An MHH3 device with three field periods and comparable quasi-axial symmetry is presented, too, and because of reversed shear, its physical properties may be better. Variational analysis of equilibrium and stability is shown to give a more reliable prediction of performance for these stellarators than linearized or local theories that suffer from a failure of differentiability and convergence. PMID:9707544

  8. Geometry Dependence of Stellarator Turbulence

    Energy Technology Data Exchange (ETDEWEB)

    H.E. Mynick, P. Xanthopoulos and A.H. Boozer

    2009-08-10

    Using the nonlinear gyrokinetic code package GENE/GIST, we study the turbulent transport in a broad family of stellarator designs, to understand the geometry-dependence of the microturbulence. By using a set of flux tubes on a given flux surface, we construct a picture of the 2D structure of the microturbulence over that surface, and relate this to relevant geometric quantities, such as the curvature, local shear, and effective potential in the Schrodinger-like equation governing linear drift modes.

  9. Stellar populations of shell galaxies

    Science.gov (United States)

    Carlsten, S. G.; Hau, G. K. T.; Zenteno, A.

    2017-12-01

    We present a study of the inner (out to ∼1 Reff) stellar populations of nine shell galaxies. We derive stellar population parameters from long-slit spectra by both analysing the Lick indices of the galaxies and by fitting single stellar population model spectra to the full galaxy spectra. The results from the two methods agree reasonably well. A few of the shell galaxies appear to have lower central Mg2 index values than the general population of galaxies of the same central velocity dispersion, which is possibly due to a past interaction event. Our sample shows a relation between central metallicity and velocity dispersion that is consistent with previous samples of non-shell galaxies. Analysing the metallicity gradients in our sample, we find an average gradient of -0.16 ± 0.10 dex decade-1 in radius. We compare this with formation models to constrain the merging history of shell galaxies. We argue that our galaxies likely have undergone major mergers but it is unclear whether the shells formed from these events or from separate minor mergers. Additionally, we find evidence for young stellar populations ranging in age from 500 Myr to 4-5 Gyr in four of the galaxies, allowing us to speculate on the age of the shells. For NGC 5670, we use a simple dynamical model to find the time required to produce the observed distribution of shells to be roughly consistent with the age of the young subpopulation, suggesting that the shells and subpopulation possibly formed from the same event.

  10. Ecton processes in the generation of pulsed runaway electron beams in a gas discharge

    Science.gov (United States)

    Mesyats, G. A.

    2017-09-01

    As was shown earlier for pulsed discharges that occur in electric fields rising with extremely high rates (1018 V/(cm s)) during the pulse rise time, the electron current in a vacuum discharge is lower than the current of runaway electrons in an atmospheric air discharge in a 1-cm-long gap. In this paper, this is explained by that the field emission current from cathode microprotrusions in a gas discharge is enhanced due to gas ionization. This hastens the initiation of explosive electron emission, which occurs within 10-11 s at a current density of up to 1010 A/cm2. Thereafter, a first-type cathode spot starts forming. The temperature of the cathode spot decreases due to heat conduction, and the explosive emission current ceases. Thus, the runaway electron current pulse is similar in nature to the ecton phenomenon in a vacuum discharge.

  11. On the Temporal Evolution of Red Sprites, Runaway Theory Versus Data

    Science.gov (United States)

    Yukhimuk, V.; Roussel-Dupre, R. A.; Symbalisty, E. M. D.

    1999-01-01

    The results of numerical simulations of red sprite discharges, namely the temporal evolutions of optical emissions, are presented and compared with observations. The simulations are done using the recently recalculated runaway avalanche rates. The temporal evolution of these simulations is in good agreement with ground-based photometer and CCD TV camera observations of red sprites. Our model naturally explains the "hairline" of red sprites as a boundary between the region where the intensity of optical emissions associated with runaway breakdown has a maximum and the region where the intensity of optical emissions caused by conventional breakdown and ambient electron heating has a maximum. We also present for the first time simulations of red sprites with a daytime conductivity profile.

  12. In-operando high-speed tomography of lithium-ion batteries during thermal runaway

    Science.gov (United States)

    Finegan, Donal P.; Scheel, Mario; Robinson, James B.; Tjaden, Bernhard; Hunt, Ian; Mason, Thomas J.; Millichamp, Jason; Di Michiel, Marco; Offer, Gregory J.; Hinds, Gareth; Brett, Dan J.L.; Shearing, Paul R.

    2015-01-01

    Prevention and mitigation of thermal runaway presents one of the greatest challenges for the safe operation of lithium-ion batteries. Here, we demonstrate for the first time the application of high-speed synchrotron X-ray computed tomography and radiography, in conjunction with thermal imaging, to track the evolution of internal structural damage and thermal behaviour during initiation and propagation of thermal runaway in lithium-ion batteries. This diagnostic approach is applied to commercial lithium-ion batteries (LG 18650 NMC cells), yielding insights into key degradation modes including gas-induced delamination, electrode layer collapse and propagation of structural degradation. It is envisaged that the use of these techniques will lead to major improvements in the design of Li-ion batteries and their safety features. PMID:25919582

  13. The runaway binary LP 400-22 is leaving the Galaxy

    Science.gov (United States)

    Kilic, Mukremin; Gianninas, A.; Brown, Warren R.; Harris, Hugh C.; Dahn, Conard C.; Agüeros, M. A.; Heinke, Craig O.; Kenyon, S. J.; Panei, J. A.; Camilo, Fernando

    2013-10-01

    We present optical spectroscopy, astrometry, radio and X-ray observations of the runaway binary LP 400-22. We refine the orbital parameters of the system based on our new radial velocity observations. Our parallax data indicate that LP 400-22 is significantly more distant (3σ lower limit of 840 pc) than initially predicted. LP 400-22 has a tangential velocity in excess of 830 km s-1; it is unbound to the Galaxy. Our radio and X-ray observations fail to detect a recycled millisecond pulsar companion, indicating that LP 400-22 is a double white dwarf system. This essentially rules out a supernova runaway ejection mechanism. Based on its orbit, a Galactic Centre origin is also unlikely. However, its orbit intersects the locations of several globular clusters; dynamical interactions between LP 400-22 and other binary stars or a central black hole in a dense cluster could explain the origin of this unusual binary.

  14. Stellar Echo Imaging of Exoplanets

    Science.gov (United States)

    Mann, Chris; Lerch, Kieran; Lucente, Mark; Meza-Galvan, Jesus; Mitchell, Dan; Ruedin, Josh; Williams, Spencer; Zollars, Byron

    2016-01-01

    All stars exhibit intensity fluctuations over several timescales, from nanoseconds to years. These intensity fluctuations echo off bodies and structures in the star system. We posit that it is possible to take advantage of these echoes to detect, and possibly image, Earth-scale exoplanets. Unlike direct imaging techniques, temporal measurements do not require fringe tracking, maintaining an optically-perfect baseline, or utilizing ultra-contrast coronagraphs. Unlike transit or radial velocity techniques, stellar echo detection is not constrained to any specific orbital inclination. Current results suggest that existing and emerging technology can already enable stellar echo techniques at flare stars, such as Proxima Centauri, including detection, spectroscopic interrogation, and possibly even continent-level imaging of exoplanets in a variety of orbits. Detection of Earth-like planets around Sun-like stars appears to be extremely challenging, but cannot be fully quantified without additional data on micro- and millisecond-scale intensity fluctuations of the Sun. We consider survey missions in the mold of Kepler and place preliminary constraints on the feasibility of producing 3D tomographic maps of other structures in star systems, such as accretion disks. In this report we discuss the theory, limitations, models, and future opportunities for stellar echo imaging.

  15. Debris disks in open stellar clusters

    Science.gov (United States)

    Gorlova, Nadiya Igorivna

    Indirect searches for planets (such as radial velocity studies) show that their formation may be quite common. The planets are however too small and faint to be seen against the glare of their host stars; therefore, their direct detection is limited to the nearest systems. Alternatively one can study planets by studying their "by-product"---dust. We see raw material available for planets around young stars, and debris dust around old stars betraying planet-induced activity. Dust has a larger surface area per unit mass compared with a large body; it can be spread over a larger solid angle, intercepting more starlight and emitting much more light via reprocessing. By studying dusty disks we can infer the presence of planets at larger distances. Here we present results of a survey conducted with the Spitzer Space Telescope of debris disks in three open clusters. With ages of 30--100 Myrs, these clusters are old enough that the primordial dust should have accreted into planetesimals, fallen onto the star, or been blown away due to a number of physical processes. The dust we observe must come from collisions or sublimation of larger bodies. The purpose of this study is to investigate the dust evolution in the terrestrial planet zone, analogous to the Zodiacal cloud in our Solar system. We are most sensitive to this zone because the peak of a 125 K black body radiation falls into the primary pass-band of our survey---24mm. We investigate the fraction and amount of the infra-red excesses around intermediate- to solar-mass stars in open stellar clusters with well defined ages. The results are analyzed in the context of disk studies at other wavelengths and ages, providing an understanding of the time-scale for disk dissipation and ultimately planet building and frequency.

  16. Development of thermal runaway preventing ZnO varistor for surge protective device.

    Science.gov (United States)

    Jeoung, Tae-Hoon; Kim, Young-Sung; Nam, Sung-Pill; Lee, Seung-Hwan; Kang, Jeong-Wook; Kim, Jea-Chul; Lee, Sung-Gap

    2014-12-01

    In this paper, the centre of electrode is suggested for heat conduction. Therefore, the specific reflow soldering process is needed. The comparison of temperature difference among the different areas of ZnO varistors is analyzed. With the nominal surge current, thermal behavior is analyzed. The operation point of temperature for disconnection is proposed. Accordingly, the thermal runaway-preventing ZnO varistors were covered with a fusible alloy, i.e., a thermal fuse, in the process of manufacture, which is expected to ensure there the liability of being resistant to lightning discharge and to ensure stability against thermal runaway in the failure mode. Additionally, it is expected to reduce much more limit voltage than the existing products to which the fuse was separately applied. The thermal runaway-preventing ZnO varistor of the surge protection devices can be widely used as part of the protection provisions of lightning discharge and surge protection demanded in connection with power IT about Green Growth which is nowadays becoming the buzzword in the electric power industry.

  17. High performance gamma-ray spectrometer for runaway electron studies on the FT-2 tokamak

    Energy Technology Data Exchange (ETDEWEB)

    Shevelev, A.E., E-mail: Shevelev@cycla.ioffe.ru [Ioffe Institute, Politekhnicheskaya 26, St. Petersburg 194021 (Russian Federation); Khilkevitch, E.M.; Lashkul, S.I.; Rozhdestvensky, V.V.; Altukhov, A.B.; Chugunov, I.N.; Doinikov, D.N.; Esipov, L.A.; Gin, D.B.; Iliasova, M.V.; Naidenov, V.O.; Nersesyan, N.S.; Polunovsky, I.A.; Sidorov, A.V. [Ioffe Institute, Politekhnicheskaya 26, St. Petersburg 194021 (Russian Federation); Kiptily, V.G. [CCFE, Culham Science Centre, Abingdon, Oxon X14 3DB (United Kingdom)

    2016-09-11

    A gamma-ray spectrometer based on LaBr{sub 3}(Ce) scintillator has been used for measurements of hard X-ray emission generated by runaway electrons in the FT-2 tokamak plasmas. Using of the fast LaBr{sub 3}(Ce) has allowed extending count rate range of the spectrometer by a factor of 10. A developed digital processing algorithm of the detector signal recorded with a digitizer sampling rate of 250 MHz has provided a pulse height analysis at count rates up to 10{sup 7} s{sup −1}. A spectrum deconvolution code DeGaSum has been applied for inferring the energy distribution of runaway electrons escaping from the plasma and interacting with materials of the FT-2 limiter in the vacuum chamber. The developed digital signal processing technique for LaBr{sub 3}(Ce) spectrometer has allowed studying the evolution of runaways energy distribution in the FT-2 plasma discharges with time resolution of 1–5 ms.

  18. Development of a Cherenkov-type diagnostic system to study runaway electrons within the COMPASS tokamak

    Science.gov (United States)

    Rabinski, M.; Jakubowski, L.; Malinowski, K.; Sadowski, M. J.; Zebrowski, J.; Jakubowski, M. J.; Mirowski, R.; Weinzettl, V.; Ficker, O.; Mlynar, J.; Panek, R.; Paprok, R.; Vlainic, M.

    2017-10-01

    Direct measurements of fast electrons, which are produced in high-temperature plasma and escape from tokamak-type facilities, are of particular interest for ITER and future fusion devices, where intense runaway electrons (RE) can significantly damage the first wall components. Therefore, the runaway control and mitigation based on credible measuring methods should be developed already in present devices. A team from the National Centre for Nuclear Research (NCBJ), Poland, developed special probes equipped with Cherenkov-type detectors for measurements of the fast electrons within edge plasmas of tokamaks. Studies of the fast runaway electrons were extensively carried out at the COMPASS tokamak at the Institute of Plasma Physics (IPP) in Prague during experimental campaigns in 2014–2016. In order to investigate an electron-beam energy distribution a three-channel probe equipped with the Cherenkov-type detectors sensitive to electrons of different energies has been constructed. The measurements performed by means of these detectors showed that the first fast electron peak appears usually in the current ramp-up phase, even before the hard X-rays (HXR) pulse. Some electron signals can also be observed during subsequent HXR emissions. However, the most distinct electron peaks in all energy channels appear mainly during the plasma disruption. A correlation of Cherenkov signals with the MHD activity was also studied.

  19. Thermal runaway detection of cylindrical 18650 lithium-ion battery under quasi-static loading conditions

    Science.gov (United States)

    Sheikh, Muhammad; Elmarakbi, Ahmed; Elkady, Mustafa

    2017-12-01

    This paper focuses on state of charge (SOC) dependent mechanical failure analysis of 18650 lithium-ion battery to detect signs of thermal runaway. Quasi-static loading conditions are used with four test protocols (Rod, Circular punch, three-point bend and flat plate) to analyse the propagation of mechanical failures and failure induced temperature changes. Finite element analysis (FEA) is used to model single battery cell with the concentric layered formation which represents a complete cell. The numerical simulation model is designed with solid element formation where stell casing and all layers followed the same formation, and fine mesh is used for all layers. Experimental work is also performed to analyse deformation of 18650 lithium-ion cell. The numerical simulation model is validated with experimental results. Deformation of cell mimics thermal runaway and various thermal runaway detection strategies are employed in this work including, force-displacement, voltage-temperature, stress-strain, SOC dependency and separator failure. Results show that cell can undergo severe conditions even with no fracture or rupture, these conditions may slow to develop but they can lead to catastrophic failures. The numerical simulation technique is proved to be useful in predicting initial battery failures, and results are in good correlation with the experimental results.

  20. Screening for abuse and mental health problems among illiterate runaway adolescents in an Indian metropolis.

    Science.gov (United States)

    Bhat, Deepti Pagare; Singh, Meghachandra; Meena, Gajendra Singh

    2012-11-01

    To evaluate the prevalence of physical and sexual abuse, and their relation to mental health problems among the illiterate/semiliterate runaway adolescents in New Delhi, India. Cross sectional. New Delhi, India. Runaway adolescent boys (n=119) aged 11 to 18 years at an observation home. Study subjects were screened for physical and sexual abuse using the Child Maltreatment History Self Report and Finkelhor's sexual abuse scale. Mental health problems were identified using the Achenbach's Youth Self-Report scale. As the participants were illiterate or semiliterate with Hindi being their primary language, the screening tools were appropriately translated, read out to them and their responses recorded. A total of 72 (62%) boys experienced domestic violence, 70 (59%) had engaged in substance abuse and 103 (87%) boys had been employed as child labourers. Physical abuse was reported by 86 (72%) and sexual abuse by 42 (35%). Mental health problems were recognised in 83 (70%) boys, which included internalising syndromes (59%) and externalising syndromes (34%). Multivariate analysis demonstrated that physical abuse was an independent predictor of internalising syndromes (OR: 3.3; 95% CI 1.2 to 9.1; pmental health disorders are widely prevalent among the runaway adolescents evaluated at an observation home in New Delhi. Appropriate modification of the standardised self-report screening tools may allow the identification of mental health disorders in this vulnerable illiterate/semiliterate population.

  1. Results of Compact Stellarator Eengineering Trade Studies

    Energy Technology Data Exchange (ETDEWEB)

    T. Brown, L. Bromberg, and M. Cole

    2009-09-25

    A number of technical requirements and performance criteria can drive stellarator costs, e.g., tight tolerances, accurate coil positioning, low aspect ratio (compactness), choice of assembly strategy, metrology, and complexity of the stellarator coil geometry. With the completion of a seven-year design and construction effort of the National Compact Stellarator Experiment (NCSX) it is useful to interject the NCSX experience along with the collective experiences of the NCSX stellarator community to improving the stellarator configuration. Can improvements in maintenance be achieved by altering the stellarator magnet configuration with changes in the coil shape or with the combination of trim coils? Can a mechanical configuration be identified that incorporates a partial set of shaped fixed stellarator coils along with some removable coil set to enhance the overall machine maintenance? Are there other approaches that will simplify the concepts, improve access for maintenance, reduce overall cost and improve the reliability of a stellarator based power plant? Using ARIES-CS and NCSX as reference cases, alternative approaches have been studied and developed to show how these modifications would favorably impact the stellarator power plant and experimental projects. The current status of the alternate stellarator configurations being developed will be described and a comparison made to the recently designed and partially built NCSX device and the ARIES-CS reactor design study.

  2. Results of Compact Stellarator Engineering Trade Studies

    Energy Technology Data Exchange (ETDEWEB)

    Tom Brown, L. Bromberg, M. Cole

    2009-05-27

    number of technical requirements and performance criteria can drive stellarator costs, e.g., tight tolerances, accurate coil positioning, low aspect ratio (compactness), choice of assembly strategy, metrology, and complexity of the stellarator coil geometry. With the completion of a seven-year design and construction effort of the National Compact Stellarator Experiment (NCSX) it is useful to interject the NCSX experience along with the collective experiences of the NCSX stellarator community to improving the stellarator configuration. Can improvements in maintenance be achieved by altering the stellarator magnet configuration with changes in the coil shape or with the combination of trim coils? Can a mechanical configuration be identified that incorporates a partial set of shaped fixed stellarator coils along with some removable coil set to enhance the overall machine maintenance? Are there other approaches that will simplify the concepts, improve access for maintenance, reduce overall cost and improve the reliability of a stellarator based power plant? Using ARIES-CS and NCSX as reference cases, alternative approaches have been studied and developed to show how these modifications would favorably impact the stellarator power plant and experimental projects. The current status of the alternate stellarator configurations being developed will be described and a comparison made to the recently designed and partially built NCSX device and the ARIES-CS reactor design study.

  3. Stellarator fusion neutronics research in Australia

    Energy Technology Data Exchange (ETDEWEB)

    Zimin, S.; Cross, R.C. [Sydney Univ., NSW (Australia). School of Physics; Dewar, R.L.; Gardner, H.J. [Australian National Univ., Canberra, ACT (Australia)

    1997-12-31

    The new status of the H-INF Heliac Stellaralor as a National Facility and the signed international Implementing Agreement on `Collaboration in the Development of the Stellarator Concept` represents a significant encouragement for further fusion research in Australia. In this report the future of fusion research in Australia is discussed with special attention being paid to the importance of Stellarator power plant studies and in particular stellarator fusion neutronics. The main differences between tokamak and stellarator neutronics analyses are identified, namely the neutron wall loading, geometrical modelling and total heating in in-vessel reactor components including toroidal field (TF) coils. Due to the more complicated nature of stellarator neutronics analyses, simplified approaches to fusion neutronics already developed for tokamaks are expected to be even more important and widely used for designing a Conceptual Stellarator Power Plant. 15 refs.

  4. Stellar Feedback from Galactic Bulges

    Science.gov (United States)

    Tang, Shikui; Wang, D. Q.

    2009-01-01

    We demonstrate that feedback from galactic bulges can play an essential role in the halo gas dynamics and the evolution of their host galaxies by conducting a series of 1-D and 3-D simulations. In our 1-D models we approximately divide the the bulge stellar feedback into two phases: 1) a starbusrt-induced blastwave from the formation of bulge built up through frequent major mergers at high redshift and 2) a gradual feedback in forms of stellar wind and Type Ia SNe from low mass stars. Our simulations show that the combination of the two-phase feedback can heat the surrounding gas beyond the virial radius and stop further gas accretion, which naturally produces a baryon deficit around MW-like galaxies and explains the lack of large-scale X-ray halos, consistent with observations. The hot gas dynamics depends sensitively on the environment and bulge formation history. This dependency may account for the large dispersion in the X-ray luminosities of the galaxies with similar L_B. In the 3-D simulations, we examine the spatial, thermal, and chemical substructures and their effects on X-ray measurements. The sporadic SN explosion creates wealth of filamentary and shell-like structures in the hot gas and produces a broad lognormal-like emission-measure distribution, which enhances the X-ray emission at a low and high temperatures. The luminosity at 0.3-2.0 keV band is nearly tripled due to the gas structures. We find that the SN Ia ejecta are not well-mixed with the ambient medium within the bulge scale, and the X-ray emission is primarily from shocked stellar wind materials which in general has low metallicity.

  5. Controlling turbulence in present and future stellarators.

    Science.gov (United States)

    Xanthopoulos, P; Mynick, H E; Helander, P; Turkin, Y; Plunk, G G; Jenko, F; Görler, T; Told, D; Bird, T; Proll, J H E

    2014-10-10

    Turbulence is widely expected to limit the confinement and, thus, the overall performance of modern neoclassically optimized stellarators. We employ novel petaflop-scale gyrokinetic simulations to predict the distribution of turbulence fluctuations and the related transport scaling on entire stellarator magnetic surfaces and reveal striking differences to tokamaks. Using a stochastic global-search optimization method, we derive the first turbulence-optimized stellarator configuration stemming from an existing quasiomnigenous design.

  6. Recent advances in stellarator optimization

    Science.gov (United States)

    Gates, D. A.; Boozer, A. H.; Brown, T.; Breslau, J.; Curreli, D.; Landreman, M.; Lazerson, S. A.; Lore, J.; Mynick, H.; Neilson, G. H.; Pomphrey, N.; Xanthopoulos, P.; Zolfaghari, A.

    2017-12-01

    Computational optimization has revolutionized the field of stellarator design. To date, optimizations have focused primarily on optimization of neoclassical confinement and ideal MHD stability, although limited optimization of other parameters has also been performed. The purpose of this paper is to outline a select set of new concepts for stellarator optimization that, when taken as a group, present a significant step forward in the stellarator concept. One of the criticisms that has been leveled at existing methods of design is the complexity of the resultant field coils. Recently, a new coil optimization code—COILOPT++, which uses a spline instead of a Fourier representation of the coils,—was written and included in the STELLOPT suite of codes. The advantage of this method is that it allows the addition of real space constraints on the locations of the coils. The code has been tested by generating coil designs for optimized quasi-axisymmetric stellarator plasma configurations of different aspect ratios. As an initial exercise, a constraint that the windings be vertical was placed on large major radius half of the non-planar coils. Further constraints were also imposed that guaranteed that sector blanket modules could be removed from between the coils, enabling a sector maintenance scheme. Results of this exercise will be presented. New ideas on methods for the optimization of turbulent transport have garnered much attention since these methods have led to design concepts that are calculated to have reduced turbulent heat loss. We have explored possibilities for generating an experimental database to test whether the reduction in transport that is predicted is consistent with experimental observations. To this end, a series of equilibria that can be made in the now latent QUASAR experiment have been identified that will test the predicted transport scalings. Fast particle confinement studies aimed at developing a generalized optimization algorithm are also

  7. Abundance measurements in stellar environments

    Science.gov (United States)

    Leone, F.

    2014-05-01

    Most of what we know about stars, and systems of stars, is derived from the analysis of their electromagnetic radiation. This lesson is an attempt to describe to Physicists, without any Astrophysical background, the framework to understand the present status of abundance determination in stellar environments and its limit. These notes are dedicated to the recently passed, November 21, 2013, Prof. Dimitri Mihalas who spent his life confuting the 19th century positivist philosopher Auguste Comte who stated that we shall not at all be able to determine the chemical composition of stars.

  8. Abundance measurements in stellar environments

    Energy Technology Data Exchange (ETDEWEB)

    Leone, F. [Università di Catania, Dipartimento di Fisica e Astronomia, Sezione Astrofisica, Via S. Sofia 78, 95123 Catania (Italy)

    2014-05-09

    Most of what we know about stars, and systems of stars, is derived from the analysis of their electromagnetic radiation. This lesson is an attempt to describe to Physicists, without any Astrophysical background, the framework to understand the present status of abundance determination in stellar environments and its limit. These notes are dedicated to the recently passed, November 21, 2013, Prof. Dimitri Mihalas who spent his life confuting the 19th century positivist philosopher Auguste Comte who stated that we shall not at all be able to determine the chemical composition of stars.

  9. Stellar Streams in the Dark Energy Survey

    Science.gov (United States)

    Shipp, Nora; Drlica-Wagner, Alex; Balbinot, Eduardo; DES Collaboration

    2018-01-01

    We present a search for Galactic stellar streams in the Dark Energy Survey (DES), using three years of optical data taken across 5000 sq. degrees of the southern sky. The wide-field, uniform DES photometry provides unprecedented sensitivity to the stellar density field in the southern hemisphere, allowing for the detection of faint stellar populations. We follow the “Field of Streams” procedure developed in the Sloan Digital Sky Survey (Belokurov et al., 2006) to identify stellar density features such as dwarf galaxies, globular clusters, and the stellar streams resulting from the tidal disruption of these objects. Improved analysis techniques applied to the DES data enable the discovery of new stellar streams, and provide added insight into the origin and stellar populations of previously identified objects. An increased sample size together with detailed characterization of individual stellar streams and their progenitors can inform our understanding of the formation of the Milky Way stellar halo, as well as the large and small scale distribution of dark matter in the Milky Way.

  10. Helical axis stellarator with noninterlocking planar coils

    Science.gov (United States)

    Reiman, Allan; Boozer, Allen H.

    1987-01-01

    A helical axis stellarator using only noninterlocking planar, non-circular coils, generates magnetic fields having a magnetic well and large rotational transform with resultant large equilibrium beta.

  11. Collision Risk and Damage after Collision

    DEFF Research Database (Denmark)

    Pedersen, Preben Terndrup; Hansen, Peter Friis; Nielsen, Lars Peter

    1996-01-01

    The paper presents a new and complete procedure for calculation of ship-ship collision rates on specific routes and the hull damage caused by such collisions.The procedure is applied to analysis of collision risks for Ro-Ro pasenger vessels. Given a collision the spatial probability distribution...... of the damage risk is calculated by a numerical procedure. These directly calculated distributions for hull damages are subsequently approximated by analytical expressions suited for probabilistic damage stability calculations similar to the procedure described in IMO regulation A.265.Numerical results...... are presented for threee different Ro-Ro passenger vessels of length 98 m 150 m and 180 m, respectively operating at three different routes. These routes are the Danish Great Belt route, a Finland-Sweden route and the Dover-Calais route....

  12. Flexible helical-axis stellarator

    Science.gov (United States)

    Harris, Jeffrey H.; Hender, Timothy C.; Carreras, Benjamin A.; Cantrell, Jack L.; Morris, Robert N.

    1988-01-01

    An 1=1 helical winding which spirals about a conventional planar, circular central conductor of a helical-axis stellarator adds a significant degree of flexibility by making it possible to control the rotational transform profile and shear of the magnetic fields confining the plasma in a helical-axis stellarator. The toroidal central conductor links a plurality of toroidal field coils which are separately disposed to follow a helical path around the central conductor in phase with the helical path of the 1=1 winding. This coil configuration produces bean-shaped magnetic flux surfaces which rotate around the central circular conductor in the same manner as the toroidal field generating coils. The additional 1=1 winding provides flexible control of the magnetic field generated by the central conductor to prevent the formation of low-order resonances in the rotational transform profile which can produce break-up of the equilibrium magnetic surfaces. Further, this additional winding can deepen the magnetic well which together with the flexible control provides increased stability.

  13. Compact stellarators with modular coils

    Science.gov (United States)

    Garabedian, P. R.

    2000-01-01

    Compact stellarator designs with modular coils and only two or three field periods are now available; these designs have both good stability and quasiaxial symmetry providing adequate transport for a magnetic fusion reactor. If the bootstrap current assumes theoretically predicted values a three field period configuration is optimal, but if that net current turns out to be lower, a device with two periods and just 12 modular coils might be better. There are also attractive designs with quasihelical symmetry and four or five periods whose properties depend less on the bootstrap current. Good performance requires that there be a satisfactory magnetic well in the vacuum field, which is a property lacking in a stellarator-tokamak hybrid that has been proposed for a proof of principle experiment. In this paper, we present an analysis of stability for these configurations that is based on a mountain pass theorem asserting that, if two solutions of the problem of magnetohydrodynamic equilibrium can be found, then there has to be an unstable solution. We compare results of our theory of equilibrium, stability, and transport with recently announced measurements from the large LHD experiment in Japan. PMID:10899993

  14. LEXUS heavy ion collisions

    CERN Document Server

    Sang Yong Jeon

    1997-01-01

    We use a Glauber-like approach to describe very energetic nucleus- nucleus collisions as a sequence of binary nucleon-nucleon collisions. No free parameters are needed: all the information comes from simple parametrizations of nucleon-nucleon collision data. Produced mesons are assumed not to interact with each other or with the original baryons. Comparisons are made to published experimental measurements of baryon rapidity and transverse momentum distributions, negative hadron rapidity and transverse momentum distributions, average multiplicities of pions, kaons, hyperons, and antihyperons, and zero degree energy distributions for sulfur-sulfur collisions at 200 GeV/c per nucleon and for lead-lead collisions at 158 GeV/c per nucleon. Good agreement is found except that the number of strange particles produced, especially antihyperons, is too small compared with experiment. We call this model LEXUS: Linear EXtrapolation of Ultrarelativistic nucleon-nucleon Scattering to heavy ion collisions. (11 refs).

  15. Midair Collisions: Aeromedical Considerations.

    Science.gov (United States)

    AVIATION ACCIDENTS , * COLLISION AVOIDANCE, FLIGHT CREWS, REACTION TIME, CASE STUDIES, INFLIGHT, HYPOXIA, VISION, VISUAL PERCEPTION, AVIATION SAFETY, VISUAL ACUITY, PSYCHOPHYSIOLOGY, AVIATION MEDICINE, GLARE.

  16. Asymmetric Drift and the Stellar Velocity Ellipsoid

    NARCIS (Netherlands)

    Westfall, Kyle B.; Bershady, Matthew A.; Verheijen, Marc A. W.; Andersen, David R.; Swaters, Rob A.

    2007-01-01

    We present the decomposition of the stellar velocity ellipsoid using stellar velocity dispersions within a 40° wedge about the major-axis (smaj), the epicycle approximation, and the asymmetric drift equation. Thus, we employ no fitted forms for smaj and escape interpolation errors resulting from

  17. The Kinematics of Galactic Stellar Disks

    NARCIS (Netherlands)

    Merrifield, M. R.; Kuijken, K.

    1998-01-01

    Abstract: The disks of galaxies are primarily stellar systems, and fundamentally dynamical entities. Thus, to fully understand galactic disks, we must study their stellar kinematics as well as their morphologies. Observational techniques have now advanced to a point where quite detailed

  18. Stellar Spectral Classification with Locality Preserving Projections ...

    Indian Academy of Sciences (India)

    With the help of computer tools and algorithms, automatic stellar spectral classification has become an area of current interest. The process of stellar spectral classification mainly includes two steps: dimension reduction and classification. As a popular dimensionality reduction technique, Principal Component Analysis (PCA) ...

  19. Stark broadening data for stellar plasma research.

    Science.gov (United States)

    Dimitrijević, M. S.

    Results of an effort to provide to astrophysicists and physicists an as much as possible complete set of Stark broadening parameters needed for stellar opacity calculations, stellar atmosphere modelling, abundance determinations and diagnostics of different plasmas in astrophysics, physics and plasma technology, are presented. Stark broadening has been considered within the semiclassical perturbation, and the modified semiempirical approaches.

  20. Increased insolation threshold for runaway greenhouse processes on Earth-like planets.

    Science.gov (United States)

    Leconte, Jérémy; Forget, Francois; Charnay, Benjamin; Wordsworth, Robin; Pottier, Alizée

    2013-12-12

    The increase in solar luminosity over geological timescales should warm the Earth's climate, increasing water evaporation, which will in turn enhance the atmospheric greenhouse effect. Above a certain critical insolation, this destabilizing greenhouse feedback can 'run away' until the oceans have completely evaporated. Through increases in stratospheric humidity, warming may also cause evaporative loss of the oceans to space before the runaway greenhouse state occurs. The critical insolation thresholds for these processes, however, remain uncertain because they have so far been evaluated using one-dimensional models that cannot account for the dynamical and cloud feedback effects that are key stabilizing features of the Earth's climate. Here we use a three-dimensional global climate model to show that the insolation threshold for the runaway greenhouse state to occur is about 375 W m(-2), which is significantly higher than previously thought. Our model is specifically developed to quantify the climate response of Earth-like planets to increased insolation in hot and extremely moist atmospheres. In contrast with previous studies, we find that clouds have a destabilizing feedback effect on the long-term warming. However, subsident, unsaturated regions created by the Hadley circulation have a stabilizing effect that is strong enough to shift the runaway greenhouse limit to higher values of insolation than are inferred from one-dimensional models. Furthermore, because of wavelength-dependent radiative effects, the stratosphere remains sufficiently cold and dry to hamper the escape of atmospheric water, even at large fluxes. This has strong implications for the possibility of liquid water existing on Venus early in its history, and extends the size of the habitable zone around other stars.

  1. On stellar X-ray emission

    Science.gov (United States)

    Rosner, R.; Golub, L.; Vaiana, G. S.

    1985-01-01

    Stellar X-ray astronomy represents an entirely new astronomical discipline which has emerged during the past five years. It lies at the crossroads of solar physics, stellar physics, and general astrophysics. The present review is concerned with the main physical problems which arise in connection with a study of the stellar X-ray data. A central issue is the extent to which the extrapolation from solar physics is justified and the definition (if possible) of the limits to such extrapolation. The observational properties of X-ray emission from stars are considered along with the solar analogy and the modeling of X-ray emission from late-type stars, the modeling of X-ray emission from early-type stars, the physics of stellar X-ray emission, stellar X-ray emission in the more general astrophysical context, and future prospects.

  2. Stellar Structure and Evolution: An Introduction

    Science.gov (United States)

    Jeffery, C. Simon

    The synthesis of new elements takes place inside stars. How do stars evolve and distribute this creation to the universe at large? This article starts with the observables that the theory of stellar evolution aims to reproduce, and gives a quick overview of what that theory predicts (Sects. 2-3). It presents the equations governing stellar structure and evolution (Sects. 4-6) and the physics of stellar interiors (Sects. 7-9). Approximate and numerical methods for their solution are outlined (Sects. 10-11) and the general results of stellar structure and evolution are discussed (Sects. 12-13). The structure and evolution of horizontal-branch stars, hydrogen-deficient stars and other stellar remnants are also considered (Sects. 14-15).

  3. Temperatures in a runaway greenhouse on the evolving Venus Implications for water loss

    Science.gov (United States)

    Watson, A. J.; Donahue, T. M.; Kuhn, W. R.

    1984-01-01

    Some aspects of the temperature structure of a runaway greenhouse on Venus are examined using one-dimensional radiative transfer techniques. It is found that there generally is a region high in the atmosphere where condensation and cloud formation can occur, while deep in the atmosphere the gas is strongly unsaturated with respect to water vapor. The necessity of including clouds introduces considerably uncertainty into the calculation of surface temperatures. Under reasonable assumptions concerning the clouds, temperatures deep in the atmosphere are high enough to produce a plastic or even molten surface, which may significantly ease the problem of explaining the loss of oxygen.

  4. Evolution of the fine-structure constant in runaway dilaton models

    Directory of Open Access Journals (Sweden)

    C.J.A.P. Martins

    2015-04-01

    Full Text Available We study the detailed evolution of the fine-structure constant α in the string-inspired runaway dilaton class of models of Damour, Piazza and Veneziano. We provide constraints on this scenario using the most recent α measurements and discuss ways to distinguish it from alternative models for varying α. For model parameters which saturate bounds from current observations, the redshift drift signal can differ considerably from that of the canonical ΛCDM paradigm at high redshifts. Measurements of this signal by the forthcoming European Extremely Large Telescope (E-ELT, together with more sensitive α measurements, will thus dramatically constrain these scenarios.

  5. Fluorescence excited in a thunderstorm atmosphere by relativistic runaway electron avalanches

    Science.gov (United States)

    Babich, L. P.; Bochkov, E. I.

    2017-05-01

    The spectrum and spatiotemporal evolution of the fluorescence of an atmospheric discharge developing in the regime of relativistic runaway electron avalanche (RREA) generation have been calculated without involving the relativistic feedback. The discharges generating narrow bipolar pulses, along with the discharges responsible for terrestrial gamma-ray flashes, are shown to be relatively dark. Nevertheless, the fluorescence excited by a discharge involving RREAs can be recorded with cameras used to record high-altitude optical phenomena. A possible connection between a certain class of optical phenomena observed at the tops of thunderclouds and RREA emission is pointed out.

  6. Impact of stellar activity on the determination of stellar parameters with interferometry

    Science.gov (United States)

    Ligi, R.; Mourard, D.; Lagrange, A.-M.; Perraut, K.; Chiavassa, A.

    2014-12-01

    With the new space missions dedicated to exoplanet detection and characterization, like PLATO, CHEOPS, TESS, the determination of stellar parameters with high accuracy becomes more and more essential. However, direct or indirect estimations of stellar parameters are affected by stellar activity (magnetic spots, bright plages, granulation) that introduces bias that lower those parameters accuracy. Improving the sensitivity and resolution of future interferometers will allow enlarging the number of common targets of space and ground instruments, and accessing the accuracy needed to distinguish between planetary signals and stellar activity signals. After presenting how visible interferometry contributes to the direct and accurate determination of stellar parameters and thus planetary ones, the impact of stellar activity on interferometric observables and stellar parameters will be presented. Finally, solutions to distinguish between exoplanet and spot signals will be discussed.

  7. Demographic, personality and psychopathology characteristics of the runaway girls in social emergency and rehabilitation centre of shiraz, iran.

    Science.gov (United States)

    Toubaei, Shahin; Nateghi, Gholamreza; Dehbozorgi, Gholam Reza; Sadr Esfahani, Hasan

    2012-01-01

    The problem of runaway girls is one of the social problems which has become more prevalent and is considered a serious challenge for families, welfare centers and governmental organizations in Iran. This study aimed at determining the demographic, personality and psychopathology characteristic of a sample of runaway girls in Shiraz, Iran. Fifty girls who had escaped from their home and were referred to the Women's Social Emergency and Rehabilitant Centre of Shiraz were compared with fifty girls who lived with their parents (control group). They were assessed by semi-structured interview based on the DSMIV-TR criteria, demographic questionnaire, the General Health Questionnaire-28 (GHQ-28) and the Eysenck Personality Questionnaire-R-106 (EPQ-R-106). Mean (±SD) age of the runaway girls was 19.9 (±3.81) years. Twenty (40%) were the first child of the family. Forty-three subjects (86%) were resident of cities. Physical abuse and neglect were more prevalent in the runaway girls (P GHQ-28, only in social function subscale, the runaway girls showed more disturbances in their social function compared to control group (P < 0.05). There were significant differences in extroversion, lying tendency, addiction tendency and crime seeking (P < 0.05) between the two groups and escaped girls showed more disturbances in comparison with the control group. The social burden of runaway girls in Shiraz is of significance and this subject warrants more attention from non-governmental and governmental organizations in order to provide more psychological and social support for these girls.

  8. Solar and stellar photospheric abundances

    Directory of Open Access Journals (Sweden)

    Carlos Allende Prieto

    2016-07-01

    Full Text Available Abstract The determination of photospheric abundances in late-type stars from spectroscopic observations is a well-established field, built on solid theoretical foundations. Improving those foundations to refine the accuracy of the inferred abundances has proven challenging, but progress has been made. In parallel, developments on instrumentation, chiefly regarding multi-object spectroscopy, have been spectacular, and a number of projects are collecting large numbers of observations for stars across the Milky Way and nearby galaxies, promising important advances in our understanding of galaxy formation and evolution. After providing a brief description of the basic physics and input data involved in the analysis of stellar spectra, a review is made of the analysis steps, and the available tools to cope with large observational efforts. The paper closes with a quick overview of relevant ongoing and planned spectroscopic surveys, and highlights of recent research on photospheric abundances.

  9. Parametrizing the stellar haloes of galaxies

    Science.gov (United States)

    D'Souza, Richard; Kauffman, Guinevere; Wang, Jing; Vegetti, Simona

    2014-09-01

    We study the stellar haloes of galaxies out to 70-100 kpc as a function of stellar mass and galaxy type by stacking aligned r- and g-band images from a sample of 45 508 galaxies from Sloan Digital Sky Survey Data Release 9 in the redshift range 0.06 ≤ z ≤ 0.1 and in the mass range 1010.0 M⊙ < M* < 1011.4 M⊙. We derive surface brightness profiles to a depth of almost μr ˜ 32 mag arcsec-2. We find that the ellipticity of the stellar halo is a function of galaxy stellar mass and that the haloes of high-concentration galaxies are more elliptical than those of low-concentration galaxies. Where the g - r colour of the stellar halo can be measured, we find that the stellar light is always bluer than in the main galaxy. The colour of the stellar halo is redder for more massive galaxies. We further demonstrate that the full two-dimensional surface intensity distribution of our galaxy stacks can only be fit through multicomponent Sérsic models. Using the fraction of light in the outer component of the models as a proxy for the fraction of accreted stellar light, we show that this fraction is a function of stellar mass and galaxy type. The fraction of accreted stellar light rises from 30 to 70 per cent and from 2 to 25 per cent for high- and low-concentration galaxies, respectively, over the mass range 1010.0-1011.4 M⊙.

  10. Comparison of thermal runaway limits under different test conditions based on a 4.5 kV IGBT

    DEFF Research Database (Denmark)

    Reigosa, Paula Diaz; Prindle, D.; Pâques, Gontran

    2016-01-01

    runaway takes place. In this paper guidelines are proposed based on the correlation among short circuit withstand capability and off-state leakage current for guarantying reliable operation and ensuring that they are thermally stable under parameter variations. This study is helpful to facilitate...... application engineers for defining the correct stability criteria and/or margins in respect of thermal runaway....... at high temperatures is given by comparing the different testing methods: Static performance (including and excluding self-heating effects), Short Circuit Safe Operating area and High-Temperature Reverse Bias. Additionally, a thermal model is used to predict the junction temperature at which thermal...

  11. Stellar coronae from Einstein - Observations and theory

    Science.gov (United States)

    Rosner, R.; Vaiana, G. S.

    1980-01-01

    Einstein Observatory observations of stellar X-ray emission are presented and their implications for the formation of stellar coronae and the problem of stellar angular momentum loss are discussed. Solar coronal X-ray observations and observations of stellar coronae made prior to Einstein are reviewed, and it is noted that they already suggest that the standard theory of acoustic coronal heating is inadequate. The principal results of the Einstein/CfA stellar survey are summarized, with attention given to variations of the level of X-ray flux detected along the main sequence, the decline of X-ray flux with increasing age of giants and supergiants, and indications of a large range of X-ray emission levels within a given type, which are clearly incompatible with models for acoustic flux generation. A new theory to explain stellar coronae and hence X-ray emission from them is then proposed in which stellar magnetic fields play the key role in determining the level of coronal emission, and the modulation of the surface magnetic flux level and the level of stressing of surface magnetic fields essentially determine the variation of mean coronal activity in the H-R diagram.

  12. Mitigating thermal runaway of lithium-ion battery through electrolyte displacement

    Science.gov (United States)

    Shi, Yang; Noelle, Daniel J.; Wang, Meng; Le, Anh V.; Yoon, Hyojung; Zhang, Minghao; Meng, Ying Shirley; Fan, Jiang; Wu, Dengguo; Qiao, Yu

    2017-02-01

    Alkanes are investigated as thermal-runaway retardants (TRR) for lithium-ion battery (LIB). TRR is a chemical that can rapidly terminate exothermic reactions in LIB. Under normal working conditions, TRR is sealed in separate packages in the LIB cell, and upon mechanical abuse, it is released to suppress heat generation. The alkanes under investigation include octane, pentadecane, and icosane, among which pentadecane has the highest thermal-runaway mitigation (TRM) efficiency. In nail penetration test on coin cells, ˜4 wt. % pentadecane reduced the maximum temperature by ˜60%; in impact test on pouch cells, ˜5 wt. % pentadecane reduced the maximum temperature by ˜90%. The high TRM efficiency of pentadecane is attributed to its high wettability to separator and its immiscibility with electrolyte. By forming a physical barrier between the cathode and anode, pentadecane interrupts lithium ion (Li+) transport and increases the charge transfer resistance by nearly two orders of magnitude. The diffusion rate of pentadecane in the electrode layer stack was measured to be ˜580 μm/s.

  13. Effective regimes of runaway electron beam generation in helium, hydrogen, and nitrogen

    Science.gov (United States)

    Tarasenko, V. F.; Baksht, E. Kh.; Burachenko, A. G.; Lomaev, M. I.; Sorokin, D. A.; Shut'ko, Yu. V.

    2010-04-01

    Runaway electron beam parameters and current-voltage characteristics of discharge in helium, hydrogen, and nitrogen at pressures in the range of several Torr to several hundred Torr have been studied. It is found that the maximum amplitudes of supershort avalanche electron beams (SAEBs) with a pulse full width at half maximum (FWHM) of ˜100 ps are achieved in helium, hydrogen, and nitrogen at a pressure of ˜60, ˜30, and ˜10 Torr, respectively. It is shown that, as the gas pressure is increased in the indicated range, the breakdown voltage of the gas-filled gap decreases, which leads to a decrease in the SAEB current amplitude. At pressures of helium within 20-60 Torr, hydrogen within 10-30 Torr, and nitrogen within 3-10 Torr, the regime of the runaway electron beam generation changes and, by varying the pressure in the gas-filled diode in the indicated intervals, it is possible to smoothly control the current pulse duration (FWHM) from ˜100 to ˜500 ps, while the beam current amplitude increases by a factor of 1.5-3.

  14. Runaway and moist greenhouse atmospheres and the evolution of Earth and Venus.

    Science.gov (United States)

    Kasting, J F

    1988-01-01

    A one-dimensional climate model is used to study the response of an Earth-like atmosphere to large increases in solar flux. For fully saturated, cloud-free conditions, the critical solar flux at which a runaway greenhouse occurs, that is, the oceans evaporate entirely, is found to be 1.4 times the present flux at Earth's orbit (S0). This value is close to the flux expected at Venus' orbit early in solar system history. Is is nearly independent of the amount of CO2 present in the atmosphere, but is sensitive to the H2O absorption coefficient in the 8- to 12-micrometers window region. Clouds should tend to depress the surface temperature on a warm, moist planet; thus, Venus may originally have had oceans if its initial water endowment was close to that of Earth. It lost them early in its history, however, because of rapid photodissociation of water vapor followed by escape of hydrogen to space. The critical solar flux above which water is rapidly lost could be as low as 1.1S0. The surface temperature of a runaway greenhouse atmosphere containing a full ocean's worth of water would have been in excess of 1500 degrees K--above the solidus for silicate rocks. The presence of such a steam atmosphere during accretion may have significantly influenced the early thermal evolution of both Earth and Venus.

  15. Cosmic Rays and Runaway Electrons: Evidence for Acceleration of Electrons during Thunderstorms

    Science.gov (United States)

    Lidvansky, A. S.; Khaerdinov, N. S.; Petkov, V. B.

    2003-12-01

    We present the data on correlations of the intensity of the soft component (10 -30 MeV) of cosmic rays with the local electric field of the near-earth atmosphere during thunderstorm periods at the Baksan Valley (North Caucasus, 1700 m a. s. l.). The large-area array for studying the extensive air showers of cosmic rays is used as a particle detector. An electric field meter of the `electric mill' type is mounted on the roof of the building in the center of this array. The data were obtained in the summer seasons of 2000--2002. We have observed strong enhancements of the soft component intensity before some lightning strokes [1]. The largest enhancement detected in the first season demonstrated an exponential growth of intensity before lightning and was interpreted as a confirmation of runaway electron breakdown mechanism [2]. However, this event is apparently very rare (a single event for three seasons of observation). The enhancements of a different pattern (slow events several minutes long) turned out to be much more numerous. Recently, a special experiment was made to estimate the minimum distance to lightning events [3], and the distances were found to be fairly large (2-5 km). At the same time, the analysis of the regression curve `intensity versus field' [4] discovers a bump at the field sign that is opposite to the field sign corresponding to acceleration of electrons (see Fig. 1). It is interpreted as a precipitation of runaway electrons from the region of the strong field (with the opposite sign) overhead. If this interpretation is true, one can conclude from these data that (i) Wilson's runaway electrons do exist, (ii) their energy can be pretty high (more than ten MeV), and (iii) they are not necessarily directly related to lightning events. Fig. 1. Deviation of the soft component intensity from its mean value versus the near-earth electric field during thunderstorms. The left-hand side of the plot corresponds to acceleration of electrons near the ground

  16. Hydrodynamics and stellar winds an introduction

    CERN Document Server

    Maciel, Walter J

    2014-01-01

    Stellar winds are a common phenomenon in the life of stars, from the dwarfs like the Sun to the red giants and hot supergiants, constituting one of the basic aspects of modern astrophysics. Stellar winds are a hydrodynamic phenomenon in which circumstellar gases expand towards the interstellar medium. This book presents an elementary introduction to the fundamentals of hydrodynamics with an application to the study of stellar winds. The principles of hydrodynamics have many other applications, so that the book can be used as an introduction to hydrodynamics for students of physics, astrophysics and other related areas.

  17. Stellarator Turbulence: Subdominant Eigenmodes and Quasilinear Modeling.

    Science.gov (United States)

    Pueschel, M J; Faber, B J; Citrin, J; Hegna, C C; Terry, P W; Hatch, D R

    2016-02-26

    Owing to complex geometry, gyrokinetic simulations in stellarator geometry produce large numbers of subdominant unstable and stable, near-orthogonal eigenmodes. Here, results based on the full eigenmode spectrum in stellarator geometry are presented for the first time. In the nonlinear state of a low-magnetic-shear ion-temperature-gradient-driven case, a multitude of these modes are active and imprint the system. Turbulent frequency spectra are broadband as a consequence, in addition to a nonlinear, narrow signature at electron frequencies. It is shown that successful quasilinear, mixing-length transport modeling is possible in stellarators, where it is essential to account for all subdominant unstable modes.

  18. Runaway electron studies with hard x-ray and microwave diagnostics in the FT-2 lower hybrid current drive discharges

    Science.gov (United States)

    Shevelev, A. E.; Khilkevitch, E. M.; Lashkul, S. I.; Rozhdestvensky, V. V.; Pandya, S. P.; Plyusnin, V. V.; Altukhov, A. B.; Kouprienko, D. V.; Chugunov, I. N.; Doinikov, D. N.; Esipov, L. A.; Gin, D. B.; Iliasova, M. V.; Naidenov, V. O.; Polunovsky, I. A.; Sidorov, A. V.; Kiptily, V. G.

    2018-01-01

    Studies of the super-thermal and runaway electron behavior in ohmic and lower hybrid current drive FT-2 tokamak plasmas have been carried out using information obtained from measurements of hard x-ray spectra and non-thermal microwave radiation intensity at the frequency of 10 GHz and in the range of (53 ÷ 78) GHz. A gamma-ray spectrometer based on a scintillation detector with a LaBr3(Ce) crystal was used, which provides measurements at counting rates up to 107 s‑1. Reconstruction of the energy distribution of RE interacting with the poloidal limiter of the tokamak chamber was made with application of the DeGaSum code. Super-thermal electrons accelerated up to 2 MeV by the LH waves at the high-frequency pumping of the plasma with low density ≤ft ~ 2  ×  1013 cm‑3 and then up to 7 MeV by vortex electric field have been found. Experimental analysis of the runaway electron beam generation and evolution of their energy distribution in the FT-2 plasmas is presented in the article and compared with the numerical calculation of the maximum energy gained by runaway electrons for given plasma parameters. In addition, possible mechanisms for limiting the maximum energy gained by the runaway electrons are also calculated and described for a FT-2 plasma discharge.

  19. 45 CFR 1351.19 - What additional information should an applicant or grantee have about a Runaway and Homeless...

    Science.gov (United States)

    2010-10-01

    ... 45 Public Welfare 4 2010-10-01 2010-10-01 false What additional information should an applicant or grantee have about a Runaway and Homeless Youth Program grant? 1351.19 Section 1351.19 Public Welfare Regulations Relating to Public Welfare (Continued) OFFICE OF HUMAN DEVELOPMENT SERVICES, DEPARTMENT OF HEALTH AND HUMAN SERVICES THE ADMINISTRATIO...

  20. A lumped model of venting during thermal runaway in a cylindrical lithium cobalt oxide lithium-ion cell

    DEFF Research Database (Denmark)

    Coman, Paul Tiberiu; Rayman, Sean; White, Ralph

    2016-01-01

    , Christoph Stangl, Gisela Fauler, Gernot Voitice Alexander Thaler and Viktor Hacker, RSC Advances, 4:3633–3642, 2014] for two cases - with flow and without flow. The results show that if the isentropic flow equations are not included in the model, the thermal runaway is triggered prematurely at the point...

  1. The Mediating Roles of Stress and Maladaptive Behaviors on Self-Harm and Suicide Attempts among Runaway and Homeless Youth

    Science.gov (United States)

    Moskowitz, Amanda; Stein, Judith A.; Lightfoot, Marguerita

    2013-01-01

    Runaway and homeless youth often have a constellation of background behavioral, emotional, and familial problems that contribute to stress and maladaptive behaviors, which, in turn, can lead to self-harming and suicidal behaviors. The current study examined the roles of stress and maladaptive behaviors as mediators between demographic and…

  2. Stellar matter with pseudoscalar condensates

    Energy Technology Data Exchange (ETDEWEB)

    Andrianov, A.A. [Saint-Petersburg State University, St. Petersburg (Russian Federation); Universitat de Barcelona, Departament d' Estructura i Constituents de la Materia and Institut de Ciencies del Cosmos (ICCUB), Barcelona, Catalonia (Spain); Andrianov, V.A.; Kolevatov, S.S. [Saint-Petersburg State University, St. Petersburg (Russian Federation); Espriu, D. [Universitat de Barcelona, Departament d' Estructura i Constituents de la Materia and Institut de Ciencies del Cosmos (ICCUB), Barcelona, Catalonia (Spain)

    2016-03-15

    In this work we consider how the appearance of gradients of pseudoscalar condensates in dense systems may possibly influence the transport properties of photons in such a medium as well as other thermodynamic characteristics. We adopt the hypothesis that in regions where the pseudoscalar density gradient is large the properties of photons and fermions are governed by the usual lagrangian extended with a Chern-Simons interaction for photons and a constant axial field for fermions. We find that these new pieces in the lagrangian produce non-trivial reflection coefficients both for photons and fermions when entering or leaving a region where the pseudoscalar has a non-zero gradient. A varying pseudoscalar density may also lead to instability of some fermion and boson modes and modify some properties of the Fermi sea. We speculate that some of these modifications could influence the cooling rate of stellar matter (for instance in compact stars) and have other observable consequences. While quantitative results may depend on the precise astrophysical details most of the consequences are quite universal and consideration should be given to this possibility. (orig.)

  3. Stellar X-Ray Polarimetry

    Science.gov (United States)

    Swank, J.

    2011-01-01

    Most of the stellar end-state black holes, pulsars, and white dwarfs that are X-ray sources should have polarized X-ray fluxes. The degree will depend on the relative contributions of the unresolved structures. Fluxes from accretion disks and accretion disk corona may be polarized by scattering. Beams and jets may have contributions of polarized emission in strong magnetic fields. The Gravity and Extreme Magnetism Small Explorer (GEMS) will study the effects on polarization of strong gravity of black holes and strong magnetism of neutron stars. Some part of the flux from compact stars accreting from companion stars has been reflected from the companion, its wind, or accretion streams. Polarization of this component is a potential tool for studying the structure of the gas in these binary systems. Polarization due to scattering can also be present in X-ray emission from white dwarf binaries and binary normal stars such as RS CVn stars and colliding wind sources like Eta Car. Normal late type stars may have polarized flux from coronal flares. But X-ray polarization sensitivity is not at the level needed for single early type stars.

  4. Stellar recipes for axion hunters

    Science.gov (United States)

    Giannotti, Maurizio; Irastorza, Igor G.; Redondo, Javier; Ringwald, Andreas; Saikawa, Ken'ichi

    2017-10-01

    There are a number of observational hints from astrophysics which point to the existence of stellar energy losses beyond the ones accounted for by neutrino emission. These excessive energy losses may be explained by the existence of a new sub-keV mass pseudoscalar Nambu-Goldstone boson with tiny couplings to photons, electrons, and nucleons. An attractive possibility is to identify this particle with the axion—the hypothetical pseudo Nambu-Goldstone boson predicted by the Peccei-Quinn solution to the strong CP problem. We explore this possibility in terms of a DFSZ-type axion and of a KSVZ-type axion/majoron, respectively. Both models allow a good global fit to the data, prefering an axion mass around 10 meV. We show that future axion experiments—the fifth force experiment ARIADNE and the helioscope IAXO—can attack the preferred mass range from the lower and higher end, respectively. An axion in this mass range can also be the main constituent of dark matter.

  5. Collisionless microinstabilities in stellarators II - numerical simulations

    CERN Document Server

    Proll, Josefine Henriette Elise; Helander, Per

    2013-01-01

    Microinstabilities exhibit a rich variety of behavior in stellarators due to the many degrees of freedom in the magnetic geometry. It has recently been found that certain stellarators (quasi-isodynamic ones with maximum-$J$ geometry) are partly resilient to trapped-particle instabilities, because fast-bouncing particles tend to extract energy from these modes near marginal stability. In reality, stellarators are never perfectly quasi-isodynamic, and the question thus arises whether they still benefit from enhanced stability. Here the stability properties of Wendelstein 7-X and a more quasi-isodynamic configuration, QIPC, are investigated numerically and compared with the National Compact Stellarator Experiment (NCSX) and the DIII-D tokamak. In gyrokinetic simulations, performed with the gyrokinetic code GENE in the electrostatic and collisionless approximation, ion-temperature-gradient modes, trapped-electron modes and mixed-type instabilities are studied. Wendelstein 7-X and QIPC exhibit significantly reduce...

  6. Starspots: A Key to the Stellar Dynamo

    Directory of Open Access Journals (Sweden)

    Berdyugina Svetlana V.

    2005-12-01

    Full Text Available Magnetic activity similar to that of the Sun is observed on a variety of cool stars with external convection envelopes. Stellar rotation coupled with convective motions generate strong magnetic fields in the stellar interior and produce a multitude of magnetic phenomena including starspots in the photosphere, chromospheric plages, coronal loops, UV, X-ray, and radio emission and flares. Here I review the phenomenon of starspots on different types of cool stars, observational tools and diagnostic techniques for studying starspots as well as starspot properties including their temperatures, areas, magnetic field strengths, lifetimes, active latitudes and longitudes, etc. Evolution of starspots on various time scales allows us to investigate stellar differential rotation, activity cycles, and global magnetic fields. Together these constitute the basis for our understanding of stellar and solar dynamos and provide valuable constraints for theoretical models.

  7. Physics of the interaction between runaway electrons and the background plasma of the current quench in tokamak disruptions

    Science.gov (United States)

    Reux, Cedric

    2017-10-01

    Runaway electrons are created during disruptions of tokamak plasmas. They can be accelerated in the form of a multi-MA beam at energies up to several 10's of MeV. Prevention or suppression of runaway electrons during disruptions will be essential to ensure a reliable operation of future tokamaks such as ITER. Recent experiments showed that the suppression of an already accelerated beam with massive gas injection was unsuccessful at JET, conversely to smaller tokamaks. This was attributed to a dense, cold background plasma (up to several 1020 m-3 accompanying the runaway beam. The present contribution reports on the latest experimental results obtained at JET showing that some mitigation efficiency can be restored by changing the features of the background plasma. The density, temperature, position of the plasma and the energy of runaways were characterized using a combined analysis of interferometry, soft X-rays, bolometry, magnetics and hard X-rays. It showed that lower density background plasmas were obtained using smaller amounts of gas to trigger the disruption, leading to an improved penetration of the mitigation gas. Based on the observations, a physical model of the creation of the background plasma and its subsequent evolution is proposed. The plasma characteristics during later stages of the disruption are indeed dependent on the way it was initially created. The sustainment of the plasma during the runaway beam phase is then addressed by making a power balance between ohmic heating, power transfer from runaway electrons, radiation and atomic processes. Finally, a model of the interaction of the plasma with the mitigation gas is proposed to explain why massive gas injection of runaway beams works only in specific situations. This aims at pointing out which parameters bear the most importance if this mitigation scheme is to be used on larger devices like ITER. Acknowledgement: This work has been carried out within the framework of the EUROfusion Consortium

  8. Mass outflows from young stellar objects

    Science.gov (United States)

    Strom, S. E.; Strom, K. M.

    1985-01-01

    The process of mass loss from young stellar objects is examined in a review of recent observational investigations and theoretical models. Consideration is given to the interaction of the stellar wind with surrounding molecular clouds, the high degree of collimation seen in some embedded objects, alignment of outflows from stars embedded in the same cloud complex, initially isotropic and intrinsically anisotropic models of mass outflow, and the kinds of observations needed to determine the actual mechanisms involved.

  9. Minimizing stellarator turbulent transport by geometric optimization

    Science.gov (United States)

    Mynick, H. E.

    2010-11-01

    Up to now, a transport optimized stellarator has meant one optimized to minimize neoclassical transport,ootnotetextH.E. Mynick, Phys. Plasmas 13, 058102 (2006). while the task of also mitigating turbulent transport, usually the dominant transport channel in such designs, has not been addressed, due to the complexity of plasma turbulence in stellarators. However, with the advent of gyrokinetic codes valid for 3D geometries such as GENE,ootnotetextF. Jenko, W. Dorland, M. Kotschenreuther, B.N. Rogers, Phys. Plasmas 7, 1904 (2000). and stellarator optimization codes such as STELLOPT,ootnotetextA. Reiman, G. Fu, S. Hirshman, L. Ku, et al, Plasma Phys. Control. Fusion 41 B273 (1999). designing stellarators to also reduce turbulent transport has become a realistic possibility. We have been using GENE to characterize the dependence of turbulent transport on stellarator geometry,ootnotetextH.E Mynick, P.A. Xanthopoulos, A.H. Boozer, Phys.Plasmas 16 110702 (2009). and to identify key geometric quantities which control the transport level. From the information obtained from these GENE studies, we are developing proxy functions which approximate the level of turbulent transport one may expect in a machine of a given geometry, and have extended STELLOPT to use these in its cost function, obtaining stellarator configurations with turbulent transport levels substantially lower than those in the original designs.

  10. Ubiquitous time variability of integrated stellar populations

    Science.gov (United States)

    Conroy, Charlie; van Dokkum, Pieter G.; Choi, Jieun

    2015-11-01

    Long-period variable stars arise in the final stages of the asymptotic giant branch phase of stellar evolution. They have periods of up to about 1,000 days and amplitudes that can exceed a factor of three in the I-band flux. These stars pulsate predominantly in their fundamental mode, which is a function of mass and radius, and so the pulsation periods are sensitive to the age of the underlying stellar population. The overall number of long-period variables in a population is directly related to their lifetimes, which is difficult to predict from first principles because of uncertainties associated with stellar mass-loss and convective mixing. The time variability of these stars has not previously been taken into account when modelling the spectral energy distributions of galaxies. Here we construct time-dependent stellar population models that include the effects of long-period variable stars, and report the ubiquitous detection of this expected ‘pixel shimmer’ in the massive metal-rich galaxy M87. The pixel light curves display a variety of behaviours. The observed variation of 0.1 to 1 per cent is very well matched to the predictions of our models. The data provide a strong constraint on the properties of variable stars in an old and metal-rich stellar population, and we infer that the lifetime of long-period variables in M87 is shorter by approximately 30 per cent compared to predictions from the latest stellar evolution models.

  11. Thermal Runaway

    National Research Council Canada - National Science Library

    Catherino, Henry A

    2005-01-01

    During battery discharge, the heat generated is the sum of the Joule (resistive) and enthalpic (chemical) heating effects. Conversely, during battery charging, the heat generated is the Joule minus the enthalpic heating...

  12. Habitability of waterworlds: runaway greenhouses, atmospheric expansion, and multiple climate states of pure water atmospheres.

    Science.gov (United States)

    Goldblatt, Colin

    2015-05-01

    There are four different stable climate states for pure water atmospheres, as might exist on so-called "waterworlds." I map these as a function of solar constant for planets ranging in size from Mars-sized to 10 Earth-mass. The states are as follows: globally ice covered (Ts ⪅ 245 K), cold and damp (270 ⪅ Ts ⪅ 290 K), hot and moist (350 ⪅ Ts ⪅ 550 K), and very hot and dry (Tsx2A86;900 K). No stable climate exists for 290 ⪅ T s ⪅ 350 K or 550 ⪅ Ts ⪅ 900 K. The union of hot moist and cold damp climates describes the liquid water habitable zone, the width and location of which depends on planet mass. At each solar constant, two or three different climate states are stable. This is a consequence of strong nonlinearities in both thermal emission and the net absorption of sunlight. Across the range of planet sizes, I account for the atmospheres expanding to high altitudes as they warm. The emitting and absorbing surfaces (optical depth of unity) move to high altitude, making their area larger than the planet surface, so more thermal radiation is emitted and more sunlight absorbed (the former dominates). The atmospheres of small planets expand more due to weaker gravity; the effective runaway greenhouse threshold is about 35 W m(-2) higher for Mars, 10 W m(-2) higher for Earth or Venus, but only a few W m(-2) higher for a 10 Earth-mass planet. There is an underlying (expansion-neglected) trend of increasing runaway greenhouse threshold with planetary size (40 W m(-2) higher for a 10 Earth-mass planet than for Mars). Summing these opposing trends means that Venus-sized (or slightly smaller) planets are most susceptible to a runaway greenhouse. The habitable zone for pure water atmospheres is very narrow, with an insolation range of 0.07 times the solar constant. A wider habitable zone requires background gas and greenhouse gas: N2 and CO2 on Earth, which are biologically controlled. Thus, habitability depends on inhabitance.

  13. Cosmic-ray source of runaway electrons in thundercloud electric field.

    Science.gov (United States)

    Babich, L. P.; Bochkov, E. I.; Kutsyk, I. M.

    2008-12-01

    To increase an accuracy of numerical simulations of the high-altitude and high-energy electric phenomena in thunderstorm atmosphere basing on the electric breakdown combining the cosmic-ray effects and relativistic runaway electron (RE) avalanches it is necessary to have accurate source of seed REs produced by cosmic rays. We calculated the source using the Monte-Carlo technique. Actually a number of secondary electrons was calculated with energies above the runaway threshold depending on the field overvoltage relative to the minimum of the drag force affecting electrons. The cosmic radiation propagation through the atmosphere was simulated based on simplified model of the nuclear cascade: a cosmic proton was assumed to completely lose its energy in the first interaction with air nuclei, producing 15 pions with equal energies. The flux of primary radiation was divided into 20 angular groups containing equal number of particles. In view of the lack of the experimental data on the RE source it is impossible to directly estimate the accuracy of the obtained source. Therefore the model reliability was verified by comparing results of secondary radiation calculations with known experimental altitude variations in the secondary cosmic rays and their spectra. The source was calculated as the specific generation rate of the secondary electrons by cosmic radiation dependent on electric field overvoltage and the altitude above the Earth's surface. It is recommended as a source of relativistic runaway electron avalanches in numerical simulations of electric discharges in atmosphere controlled by REs in thunderstorm fields and their emissions: optical, gamma and neutrons. The source already was used to simulate the high-altitude discharge and its emissions. In particular, the calculated gamma-ray pulses (photon numbers and spectra, pulse duration) agree with detected terrestrial gamma-ray flashes (TGFs). Conclusions of the published analyses (Cummer and Lyons, 2005; Cummer et

  14. Venus: The case for a wet origin and a runaway greenhouse

    Science.gov (United States)

    Kasting, J. F.

    1992-12-01

    To one interested in atmospheric evolution, the most intriguing aspect of our neighboring planet Venus is its lack of water. Measurements made by Pioneer Venus and by Several Venera spacecraft indicate that the present water abundance in Venus' lower atmosphere is of the order of 20 to 200 ppmv, or 3 x 10( exp -6) to 3 x 10 -5 of the amount of water in Earth's oceans. The exact depletion factor is uncertain, in part because of an unexplained vertical gradient in H2O concentration in the lowest 10 km of the venusian atmosphere, but the general scarcity of water is well established. The interesting question, then, is: Was venus deficient in water when it formed and, if not, where did its water go? The conclusion that Venus was originally wet is consistent with its large endowment of other volatiles and with the enhanced D/H ratio in the present atmosphere. The most likely mechanism by which Venus could have lost its water is by the development of a runaway or moist greenhouse atmosphere followed by photodissociation of water vapor and escape of hydrogen to space. Climate model calculations that neglect cloud albedo feedback predict the existence of two critical transitions in atmospheric behavior at high solar fluxes: (1) at a solar flux of approximately 1.1 times the value at Earth's orbit, S(o), the abundance of stratospheric water vapor increases dramatically, permitting rapid escape of hydrogen to space (termed a moist greenhouse) and (2) at a solar flux of approximately 1.4 S(o), the oceans vaporize entirely, creating a true runaway greenhouse. If cloudiness increases at high surface temperatures, as seems likely, and if the dominant effect of clouds is to cool the planet by reflecting incident solar radiation, the actual solar flux required to create moist or runaway conditions would be higher than the values quoted above. Early in solar system history, solar luminosity was about 25 percent to 30 percent less than today, putting the flux at Venus' orbit in the

  15. SMARTER Collision avoidance

    National Research Council Canada - National Science Library

    Keith Burton

    2017-01-01

    .... By 1981, researchers had developed the Traffic Collision Avoidance System, or TCAS, a box of electronics and software that transmits a radar signal that interrogates transponders on nearby planes...

  16. From collisions to clusters

    DEFF Research Database (Denmark)

    Loukonen, Ville; Bork, Nicolai; Vehkamaki, Hanna

    2014-01-01

    The clustering of sulphuric acid with base molecules is one of the main pathways of new-particle formation in the Earth's atmosphere. First step in the clustering process is likely the formation of a (sulphuric acid)1(base)1(water)n cluster. Here, we present results from direct first......-principles molecular dynamics collision simulations of (sulphuric acid)1(water)0, 1 + (dimethylamine) → (sulphuric acid)1(dimethylamine)1(water)0, 1 cluster formation processes. The simulations indicate that the sticking factor in the collisions is unity: the interaction between the molecules is strong enough...... to overcome the possible initial non-optimal collision orientations. No post-collisional cluster break up is observed. The reasons for the efficient clustering are (i) the proton transfer reaction which takes place in each of the collision simulations and (ii) the subsequent competition over the proton...

  17. Electron-molecule collisions

    CERN Document Server

    Takayanagi, Kazuo

    1984-01-01

    Scattering phenomena play an important role in modern physics. Many significant discoveries have been made through collision experiments. Amongst diverse kinds of collision systems, this book sheds light on the collision of an electron with a molecule. The electron-molecule collision provides a basic scattering problem. It is scattering by a nonspherical, multicentered composite particle with its centers having degrees of freedom of motion. The molecule can even disintegrate, Le., dissociate or ionize into fragments, some or all of which may also be molecules. Although it is a difficult problem, the recent theoretical, experimental, and computational progress has been so significant as to warrant publication of a book that specializes in this field. The progress owes partly to technical develop­ ments in measurements and computations. No less important has been the great and continuing stimulus from such fields of application as astrophysics, the physics of the earth's upper atmosphere, laser physics, radiat...

  18. Photon-photon collisions

    Energy Technology Data Exchange (ETDEWEB)

    Burke, D.L.

    1982-10-01

    Studies of photon-photon collisions are reviewed with particular emphasis on new results reported to this conference. These include results on light meson spectroscopy and deep inelastic e..gamma.. scattering. Considerable work has now been accumulated on resonance production by ..gamma gamma.. collisions. Preliminary high statistics studies of the photon structure function F/sub 2//sup ..gamma../(x,Q/sup 2/) are given and comments are made on the problems that remain to be solved.

  19. High elastic modulus polymer electrolytes suitable for preventing thermal runaway in lithium batteries

    Science.gov (United States)

    Mullin, Scott; Panday, Ashoutosh; Balsara, Nitash Pervez; Singh, Mohit; Eitouni, Hany Basam; Gomez, Enrique Daniel

    2014-04-22

    A polymer that combines high ionic conductivity with the structural properties required for Li electrode stability is useful as a solid phase electrolyte for high energy density, high cycle life batteries that do not suffer from failures due to side reactions and dendrite growth on the Li electrodes, and other potential applications. The polymer electrolyte includes a linear block copolymer having a conductive linear polymer block with a molecular weight of at least 5000 Daltons, a structural linear polymer block with an elastic modulus in excess of 1.times.10.sup.7 Pa and an ionic conductivity of at least 1.times.10.sup.-5 Scm.sup.-1. The electrolyte is made under dry conditions to achieve the noted characteristics. In another aspect, the electrolyte exhibits a conductivity drop when the temperature of electrolyte increases over a threshold temperature, thereby providing a shutoff mechanism for preventing thermal runaway in lithium battery cells.

  20. Growth and decay of runaway electrons above the critical electric field under quiescent conditions

    Energy Technology Data Exchange (ETDEWEB)

    Paz-Soldan, C., E-mail: paz-soldan@fusion.gat.com [Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee 37830-8050 (United States); Eidietis, N. W.; Wesley, J. C. [General Atomics, P.O. Box 85608, San Diego, California 92186-5608 (United States); Granetz, R. [Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, Massachusetts 02139 (United States); Hollmann, E. M.; Moyer, R. A. [University of California San Diego, 9500 Gilman Dr., La Jolla, California 92093-0417 (United States); Zhang, J.; Crocker, N. A. [University of California Los Angeles, P.O. Box 957099, Los Angeles, California 90095-7099 (United States); Austin, M. E. [University of Texas at Austin, 2100 San Jacinto Blvd, Austin, Texas 78712-1047 (United States); Wingen, A. [Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831 (United States); Zhu, Y. [University of California Irvine, University Dr., Irvine, California 92697 (United States)

    2014-02-15

    Extremely low density operation free of error field penetration supports the excitation of trace-level quiescent runaway electron (RE) populations during the flat-top of DIII-D Ohmic discharges. Operation in the quiescent regime allows accurate measurement of all key parameters important to RE excitation, including the internal broadband magnetic fluctuation level. RE onset is characterized and found to be consistent with primary (Dreicer) generation rates. Impurity-free collisional suppression of the RE population is investigated by stepping the late-time main-ion density, until RE decay is observed. The transition from growth to decay is found to occur 3–5 times above the theoretical critical electric field for avalanche growth and is thus indicative of anomalous RE loss. This suggests that suppression of tokamak RE avalanches can be achieved at lower density than previously expected, though extrapolation requires predictive understanding of the RE loss mechanism and magnitude.

  1. A Thermal Runaway Failure Model for Low-Voltage BME Ceramic Capacitors with Defects

    Science.gov (United States)

    Teverovsky, Alexander

    2017-01-01

    Reliability of base metal electrode (BME) multilayer ceramic capacitors (MLCCs) that until recently were used mostly in commercial applications, have been improved substantially by using new materials and processes. Currently, the inception of intrinsic wear-out failures in high quality capacitors became much greater than the mission duration in most high-reliability applications. However, in capacitors with defects degradation processes might accelerate substantially and cause infant mortality failures. In this work, a physical model that relates the presence of defects to reduction of breakdown voltages and decreasing times to failure has been suggested. The effect of the defect size has been analyzed using a thermal runaway model of failures. Adequacy of highly accelerated life testing (HALT) to predict reliability at normal operating conditions and limitations of voltage acceleration are considered. The applicability of the model to BME capacitors with cracks is discussed and validated experimentally.

  2. Runaway Electrons Modeling and Nanoparticle Plasma Jet Penetration into Tokamak Plasma

    Science.gov (United States)

    Galkin, S. A.; Bogatu, I. N.

    2017-10-01

    A novel idea to probe runaway electrons (REs) by superfast injection of high velocity nanoparticle plasma jet (NPPJ) from a plasma accelerator needs to be sustained by both RE dynamics modeling and simulation of NPPJ penetration through increasing tokamak magnetic field. We present our recent progress in both areas. RE simulation is based on the model, including Dreicer and ``avalanche'' mechanisms of RE generation, with emphasis on high Zeff effects. The high-density hyper-velocity C60 and BN NPPJ penetration through transversal B-field is conducted with the Hybrid Electro-Magnetic code (HEM-2D) in cylindrical coordinates, with 1/R B-field dependence for both DIII-D and ITER tokamaks. Work is supported in part by US DOE SBIR Grant.

  3. Social Support Networks and the Mental Health of Runaway and Homeless Youth

    Directory of Open Access Journals (Sweden)

    Eric R. Wright

    2017-09-01

    Full Text Available In response to growing concerns about the rising number of runaway and homeless youth (RHY in the U.S., researchers have sought to improve the scientific understanding of health and mental health needs, as well as the social resources available to these youths. In this paper, we examine the relationship between personal support network resources and the mental health status of a sample of RHY (N = 693 surveyed in metro-Atlanta, Georgia. The results suggest that having more supportive network ties reduces the risk of youth experiencing significant symptoms of a severe mental illness. We also find that older youth and youth who have been homeless for six months or longer have fewer personal support network resources. We conclude with a discussion of the implications of our findings for future research and services for this exceptionally vulnerable population.

  4. Role of Amines in Thermal-Runaway-Mitigating Lithium-Ion Battery.

    Science.gov (United States)

    Shi, Yang; Noelle, Daniel J; Wang, Meng; Le, Anh V; Yoon, Hyojung; Zhang, Minghao; Meng, Ying Shirley; Qiao, Yu

    2016-11-16

    Benzylamine (BA), dibenzylamine (DBA), and trihexylamine (THA) are investigated as thermal-runaway retardants (TRR) for lithium-ion batteries (LIBs). In a LIB, TRR is packaged separately and released when internal shorting happens, so as to suppress exothermic reactions and slow down temperature increase. THA is identified as the most efficient TRR. Upon nail penetration, 4 wt % THA can reduce the peak temperature by nearly 50%. The working mechanisms of the three amines are different: THA is highly wettable to the separator and immiscible with the electrolyte, and therefore, it blocks lithium-ion (Li+) transport. BA and DBA decrease the ionic conductivity of electrolyte and increase the charge transfer resistance. All three amines react with charged electrodes; the reactions of DBA and THA do not have much influence on the overall heat generation, while the reaction of BA cannot be ignored.

  5. Survival Outside Home: Sexual Behaviour of Homeless and Runaway Young Adults in Ghana

    Directory of Open Access Journals (Sweden)

    William Wilberforce Amoah

    2014-10-01

    Full Text Available Although homeless young adults are often seen on the streets of Ghana, little research had examined the nature of sexual behaviour among these homeless and runaway young adults. Due to the culturally sensitive nature of such studies in the Ghanaian setting, only fifty (50 respondents agreed to participate in the study. A thirty–five (35 item questionnaire, comprising of twenty-eight (28 closed-ended and seven (7 open-ended questions was used for data collection. The findings indicated poverty, inability of parents to cater for the young adult’s needs, peer pressure and lack of parental acceptance as the main causes of homelessness. Consequently, the findings also showed a trend of school dropout, teenage pregnancy and use of illicit drugs as effects of homelessness. These findings have implications for future studies, policy reform and care for homeless young adult.

  6. Assessment of lnternational Space Station (ISS) Lithium-ion Battery Thermal Runaway (TR)

    Science.gov (United States)

    Graika, Jason

    2017-01-01

    This task was developed in the wake of the Boeing 787 Dreamliner lithium-ion battery TR incidents of January 2013 and January 2014. The Electrical Power Technical Discipline Team supported the Dreamliner investigations and has followed up by applying lessons learned to conduct an introspective evaluation of NASA's risk of similar incidents in its own lithium-ion battery deployments. This activity has demonstrated that historically NASA, like Boeing and others in the aerospace industry, has emphasized the prevention of TR in a single cell within the battery (e.g., cell screening) but has not considered TR severity-reducing measures in the event of a single-cell TR event. center dotIn the recent update of the battery safety standard (JSC 20793) to address this paradigm shift, the NASA community included requirements for assessing TR severity and identifying simple, low-cost severity reduction measures. This task will serve as a pathfinder for meeting those requirements and will specifically look at a number of different lithium-ion batteries currently in the design pipeline within the ISS Program batteries that, should they fail in a Dreamliner-like incident, could result in catastrophic consequences. This test is an abuse test to understand the heat transfer properties of the cell and ORU in thermal runaway, with radiant barriers in place in a flight like test in on orbit conditions. This includes studying the heat flow and distribution in the ORU. This data will be used to validate the thermal runaway analysis. This test does not cover the ambient pressure case. center dotThere is no pass/ fail criteria for this test.

  7. Stellar Firework in a Whirlwind

    Science.gov (United States)

    2007-09-01

    VLT Image of Supernova in Beautiful Spiral Galaxy NGC 1288 Stars do not like to be alone. Indeed, most stars are members of a binary system, in which two stars circle around each other in an apparently never-ending cosmic ballet. But sometimes, things can go wrong. When the dancing stars are too close to each other, one of them can start devouring its partner. If the vampire star is a white dwarf - a burned-out star that was once like our Sun - this greed can lead to a cosmic catastrophe: the white dwarf explodes as a Type Ia supernova. In July 2006, ESO's Very Large Telescope took images of such a stellar firework in the galaxy NGC 1288. The supernova - designated SN 2006dr - was at its peak brightness, shining as bright as the entire galaxy itself, bearing witness to the amount of energy released. ESO PR Photo 39/07 ESO PR Photo 39/07 SN 2006dr in NGC 1288 NGC 1288 is a rather spectacular spiral galaxy, seen almost face-on and showing multiple spiral arms pirouetting around the centre. Bearing a strong resemblance to the beautiful spiral galaxy NGC 1232, it is located 200 million light-years away from our home Galaxy, the Milky Way. Two main arms emerge from the central regions and then progressively split into other arms when moving further away. A small bar of stars and gas runs across the centre of the galaxy. The first images of NGC 1288, obtained during the commissioning period of the FORS instrument on ESO's VLT in 1998, were of such high quality that they have allowed astronomers [1] to carry out a quantitative analysis of the morphology of the galaxy. They found that NGC 1288 is most probably surrounded by a large dark matter halo. The appearance and number of spiral arms are indeed directly related to the amount of dark matter in the galaxy's halo. The supernova was first spotted by amateur astronomer Berto Monard. On the night of 17 July 2006, Monard used his 30-cm telescope in the suburbs of Pretoria in South Africa and discovered the supernova as an

  8. Energy and fluxes of thermal runaway electrons produced by exponential growth of streamers during the stepping of lightning leaders and in transient luminous events

    National Research Council Canada - National Science Library

    Celestin, Sebastien; Pasko, Victor P

    2011-01-01

    ... to the exponential growth of electric potential differences in streamer heads. These electric potential differences are directly related to the energy that thermal runaway electrons can gain once created...

  9. Probabilistic stellar rotation periods with Gaussian processes

    Science.gov (United States)

    Angus, Ruth; Aigrain, Suzanne; Foreman-Mackey, Daniel

    2015-08-01

    Stellar rotation has many applications in the field of exoplanets. High-precision photometry from space-based missions like Kepler and K2 allows us to measure stellar rotation periods directly from light curves. Stellar variability produced by rotation is usually not sinusoidal or perfectly periodic, therefore sine-fitting periodograms are not well suited to rotation period measurement. Autocorrelation functions are often used to extract periodic information from light curves, however uncertainties on rotation periods measured by autocorrelation are difficult to define. A ‘by eye’ check, or a set of heuristic criteria are used to validate measurements and rotation periods are only reported for stars that pass this vetting process. A probabilistic rotation period measurement method, with a suitable generative model bypasses the need for a validation stage and can produce realistic uncertainties. The physics driving the production of variability in stellar light curves is still poorly understood and difficult to model. We therefore use an effective model for stellar variability: a Gaussian process with a quasi-periodic covariance function. By injecting fake signals into Kepler light curves we show that the GP model is well suited to quasi-periodic, non-sinusoidal signals, is capable of modelling noise and physical signals simultaneously and provides probabilistic rotation period measurements with realistic uncertainties.

  10. Stellarator Coil Design and Plasma Sensitivity

    Energy Technology Data Exchange (ETDEWEB)

    Long-Poe Ku and Allen H. Boozer

    2010-11-03

    The rich information contained in the plasma response to external magnetic perturbations can be used to help design stellarator coils more effectively. We demonstrate the feasibility by first devel- oping a simple, direct method to study perturbations in stellarators that do not break stellarator symmetry and periodicity. The method applies a small perturbation to the plasma boundary and evaluates the resulting perturbed free-boundary equilibrium to build up a sensitivity matrix for the important physics attributes of the underlying configuration. Using this sensitivity information, design methods for better stellarator coils are then developed. The procedure and a proof-of-principle application are given that (1) determine the spatial distributions of external normal magnetic field at the location of the unperturbed plasma boundary to which the plasma properties are most sen- sitive, (2) determine the distributions of external normal magnetic field that can be produced most efficiently by distant coils, (3) choose the ratios of the magnitudes of the the efficiently produced magnetic distributions so the sensitive plasma properties can be controlled. Using these methods, sets of modular coils are found for the National Compact Stellarator Experiment (NCSX) that are either smoother or can be located much farther from the plasma boundary than those of the present design.

  11. Weird Stellar Pair Puzzles Scientists

    Science.gov (United States)

    2008-05-01

    Astronomers have discovered a speedy spinning pulsar in an elongated orbit around an apparent Sun-like star, a combination never seen before, and one that has them puzzled about how the strange system developed. Orbital Comparison Comparing Orbits of Pulsar and Its Companion to our Solar System. CREDIT: Bill Saxton, NRAO/AUI/NSF Click on image for full caption information and available graphics. "Our ideas about how the fastest-spinning pulsars are produced do not predict either the kind of orbit or the type of companion star this one has," said David Champion of the Australia Telescope National Facility. "We have to come up with some new scenarios to explain this weird pair," he added. Astronomers first detected the pulsar, called J1903+0327, as part of a long-term survey using the National Science Foundation's Arecibo radio telescope in Puerto Rico. They made the discovery in 2006 doing data analysis at McGill University, where Champion worked at the time. They followed up the discovery with detailed studies using the Arecibo telescope, the NSF's Robert C. Byrd Green Bank Telescope (GBT) in West Virginia, the Westerbork radio telescope in the Netherlands, and the Gemini North optical telescope in Hawaii. The pulsar, a city-sized superdense stellar corpse left over after a massive star exploded as a supernova, is spinning on its axis 465 times every second. Nearly 21,000 light-years from Earth, it is in a highly-elongated orbit that takes it around its companion star once every 95 days. An infrared image made with the Gemini North telescope in Hawaii shows a Sun-like star at the pulsar's position. If this is an orbital companion to the pulsar, it is unlike any companions of other rapidly rotating pulsars. The pulsar, a neutron star, also is unusually massive for its type. "This combination of properties is unprecedented. Not only does it require us to figure out how this system was produced, but the large mass may help us understand how matter behaves at extremely

  12. Stellar explosions from accreting white dwarfs

    Science.gov (United States)

    Moore, Kevin L.

    Unstable thermonuclear burning on accreting white dwarfs (WDs) can lead to a wide variety of outcomes, and induce shock waves in several contexts. In classical and recurrent novae, a WD accreting hydrogen-rich material from a binary companion can experience thermonuclear runaways, ejecting mass into the interstellar/circumbinary environment at ~1000 km/s. This highly supersonic ejecta drives shock waves into the interstellar gas which may be relevant for sweeping out gas from globular clusters or forming circumstellar absorption regions in interacting supernovae. While runaway nuclear burning in novae releases enough energy for these objects to brighten by a factor of ~10 4 over roughly a weeklong outburst, it does not become dynamically unstable. In contrast, certain helium accretion scenarios may allow for dynamical burning modes, in part due to the higher temperature sensitivity of helium burning reactions and larger accreted envelopes. The majority of this thesis involves such dynamical burning modes, specifically detonations - shock waves sustained by nuclear energy release behind the shock front. We investigate when steady-state detonations are realizable in accreted helium layers on WDs, and model their strength and burning products using both semi-analytic and numerical models. We find the minimum helium layer thickness that will sustain a steady laterally propagating detonation and show that it depends on the density and composition of the helium layer, specifically 12 C and 16O. Though gravitationally unbound, the ashes still have unburned helium (~80% in the thinnest cases) and only reach up to heavy elements such as 40Ca, 44Ti, 48Cr, and 52Fe. It is rare for these thin shells to generate large amounts of radioactive isotopes necessary to power light curves, such as 56Ni. This has important implications on whether the unbound helium burning ashes may create faint and fast peculiar supernovae or events with virtually no radioactivity, as well as on off

  13. Gas explosions and thermal runaways during external heating abuse of commercial lithium-ion graphite-LiCoO2 cells at different levels of ageing

    Science.gov (United States)

    Larsson, Fredrik; Bertilsson, Simon; Furlani, Maurizio; Albinsson, Ingvar; Mellander, Bengt-Erik

    2018-01-01

    Commercial 6.8 Ah lithium-ion cells with different ageing/status have been abused by external heating in an oven. Prior to the abuse test, selected cells were aged either by C/2 cycling up to 300 cycles or stored at 60 °C. Gas emissions were measured by FTIR and three separate vents were identified, two well before the thermal runaway while the third occurred simultaneously with the thermal runaway releasing heavy smoke and gas. Emissions of toxic carbon monoxide (CO), hydrogen fluoride (HF) and phosphorous oxyfluoride (POF3) were detected in the third vent, regardless if there was a fire or not. All abused cells went into thermal runaway and emitted smoke and gas, the working cells also released flames as well as sparks. The dead cells were however less reactive but still underwent thermal runaway. For about half of the working cells, for all levels of cycle ageing, ignition of the accumulated battery released gases occurred about 15 s after the thermal runaway resulting in a gas explosion. The thermal runaway temperature, about 190 °C, varied somewhat for the different cell ageing/status where a weak local minimum was found for cells cycled between 100 and 200 times.

  14. Multi-scale full-orbit analysis on phase-space behavior of runaway electrons in tokamak fields with synchrotron radiation

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yulei; Liu, Jian, E-mail: jliuphy@ustc.edu.cn [School of Nuclear Science and Technology and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Key Laboratory of Geospace Environment, CAS, Hefei, Anhui 230026 (China); Qin, Hong [School of Nuclear Science and Technology and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States)

    2016-06-15

    In this paper, the secular full-orbit simulations of runaway electrons with synchrotron radiation in tokamak fields are carried out using a relativistic volume-preserving algorithm. Detailed phase-space behaviors of runaway electrons are investigated in different dynamical timescales spanning 11 orders. In the small timescale, i.e., the characteristic timescale imposed by Lorentz force, the severely deformed helical trajectory of energetic runaway electron is witnessed. A qualitative analysis of the neoclassical scattering, a kind of collisionless pitch-angle scattering phenomena, is provided when considering the coupling between the rotation of momentum vector and the background magnetic field. In large timescale up to 1 s, it is found that the initial condition of runaway electrons in phase space globally influences the pitch-angle scattering, the momentum evolution, and the loss-gain ratio of runaway energy evidently. However, the initial value has little impact on the synchrotron energy limit. It is also discovered that the parameters of tokamak device, such as the toroidal magnetic field, the loop voltage, the safety factor profile, and the major radius, can modify the synchrotron energy limit and the strength of neoclassical scattering. The maximum runaway energy is also proved to be lower than the synchrotron limit when the magnetic field ripple is considered.

  15. Recent advances in modeling stellar interiors (u)

    Energy Technology Data Exchange (ETDEWEB)

    Guzik, Joyce Ann [Los Alamos National Laboratory

    2010-01-01

    Advances in stellar interior modeling are being driven by new data from large-scale surveys and high-precision photometric and spectroscopic observations. Here we focus on single stars in normal evolutionary phases; we will not discuss the many advances in modeling star formation, interacting binaries, supernovae, or neutron stars. We review briefly: (1) updates to input physics of stellar models; (2) progress in two and three-dimensional evolution and hydrodynamic models; (3) insights from oscillation data used to infer stellar interior structure and validate model predictions (asteroseismology). We close by highlighting a few outstanding problems, e.g., the driving mechanisms for hybrid {gamma} Dor/{delta} Sct star pulsations, the cause of giant eruptions seen in luminous blue variables such as {eta} Car and P Cyg, and the solar abundance problem.

  16. Electron Capture Cross Sections for Stellar Nucleosynthesis

    Directory of Open Access Journals (Sweden)

    P. G. Giannaka

    2015-01-01

    Full Text Available In the first stage of this work, we perform detailed calculations for the cross sections of the electron capture on nuclei under laboratory conditions. Towards this aim we exploit the advantages of a refined version of the proton-neutron quasiparticle random-phase approximation (pn-QRPA and carry out state-by-state evaluations of the rates of exclusive processes that lead to any of the accessible transitions within the chosen model space. In the second stage of our present study, we translate the abovementioned e--capture cross sections to the stellar environment ones by inserting the temperature dependence through a Maxwell-Boltzmann distribution describing the stellar electron gas. As a concrete nuclear target we use the 66Zn isotope, which belongs to the iron group nuclei and plays prominent role in stellar nucleosynthesis at core collapse supernovae environment.

  17. Magnetospheric outflows in young stellar objects

    Science.gov (United States)

    Zanni, Claudio

    2014-01-01

    Different classes of outflows are associated with the magnetospheric activity of accreting T Tauri protostars. Stellar winds are accelerated along the open field lines anchored in the stellar surface; disk winds (extended or X-type) can be launched along the open magnetic surfaces threading the accretion disk; another type of ejection can arise from the region of interaction of the closed magnetosphere with the accretion disk (magnetospheric ejections, conical winds), where the magnetic surfaces undergo quasiperiodic episodes of inflation and reconnection. In this chapter I will present the main dynamical properties of these different types of outflow. Two main issues will be addressed. First, I will try to understand if these ejection phenomena can account for the origin of the jets often observed in young forming stellar systems. Second, I will evaluate the impact of these outflows on the angular momentum evolution of the central protostar.

  18. Magnetospheric outflows in young stellar objects

    Directory of Open Access Journals (Sweden)

    Zanni Claudio

    2014-01-01

    Full Text Available Different classes of outflows are associated with the magnetospheric activity of accreting T Tauri protostars. Stellar winds are accelerated along the open field lines anchored in the stellar surface; disk winds (extended or X-type can be launched along the open magnetic surfaces threading the accretion disk; another type of ejection can arise from the region of interaction of the closed magnetosphere with the accretion disk (magnetospheric ejections, conical winds, where the magnetic surfaces undergo quasiperiodic episodes of inflation and reconnection. In this chapter I will present the main dynamical properties of these different types of outflow. Two main issues will be addressed. First, I will try to understand if these ejection phenomena can account for the origin of the jets often observed in young forming stellar systems. Second, I will evaluate the impact of these outflows on the angular momentum evolution of the central protostar.

  19. Solar and stellar coronae and winds

    Science.gov (United States)

    Jardine, Moira

    2017-10-01

    Solar-like stars influence their environments through their coronal emis- sion and winds. These processes are linked through the physics of the stellar magnetic field, whose strength and geometry has now been explored for a large number of stars through spectropolarimetric observations. We have now detected trends with mass and rotation rate in the distribution of magnetic energies in different geometries and on also different length scales. This has implications both for the dynamo processes that generate the fields and also for the dynamics and evolution of the coronae and winds. Modelling of the surface driving processes on stars of various masses and rotation rates has revealed tantalising clues about the dynamics of stellar coronae and their ejecta. These new observations have also prompted a resurgence in the modelling of stellar winds, which is now uncovering the range of different interplanetary conditions that exoplanets might experience as they evolve.

  20. Students Excited by Stellar Discovery

    Science.gov (United States)

    2011-02-01

    In the constellation of Ophiuchus, above the disk of our Milky Way Galaxy, there lurks a stellar corpse spinning 30 times per second -- an exotic star known as a radio pulsar. This object was unknown until it was discovered last week by three high school students. These students are part of the Pulsar Search Collaboratory (PSC) project, run by the National Radio Astronomy Observatory (NRAO) in Green Bank, WV, and West Virginia University (WVU). The pulsar, which may be a rare kind of neutron star called a recycled pulsar, was discovered independently by Virginia students Alexander Snider and Casey Thompson, on January 20, and a day later by Kentucky student Hannah Mabry. "Every day, I told myself, 'I have to find a pulsar. I better find a pulsar before this class ends,'" said Mabry. When she actually made the discovery, she could barely contain her excitement. "I started screaming and jumping up and down." Thompson was similarly expressive. "After three years of searching, I hadn't found a single thing," he said, "but when I did, I threw my hands up in the air and said, 'Yes!'." Snider said, "It actually feels really neat to be the first person to ever see something like that. It's an uplifting feeling." As part of the PSC, the students analyze real data from NRAO's Robert C. Byrd Green Bank Telescope (GBT) to find pulsars. The students' teachers -- Debra Edwards of Sherando High School, Leah Lorton of James River High School, and Jennifer Carter of Rowan County Senior High School -- all introduced the PSC in their classes, and interested students formed teams to continue the work. Even before the discovery, Mabry simply enjoyed the search. "It just feels like you're actually doing something," she said. "It's a good feeling." Once the pulsar candidate was reported to NRAO, Project Director Rachel Rosen took a look and agreed with the young scientists. A followup observing session was scheduled on the GBT. Snider and Mabry traveled to West Virginia to assist in the

  1. Stellar Astrophysics for the Local Group

    Science.gov (United States)

    Aparicio, A.; Herrero, A.; Sánchez, F.

    2011-06-01

    1. Fundamentals of stellar evolution theory: understanding the HRD C. Chiosi; 2. Observations of the most luminous stars in local group galaxies P. Massey; 3. Quantitative spectroscopy of the brightest blue supergiant stars in galaxies R. P. Kudritzki; 4. Calibration of the extragalactic distance scale B. F. Madore and W. L. Freedman; 5. Dwarf galaxies G. S. Da Costa; 6. Resolved stellar populations of the luminous galaxies in the local group M. Mateo; 7. Chemical evolution of the ISM in nearby galaxies E. D. Skillman; 8. Populations of massive stars and the interstellar medium C. Leitherer.

  2. Stellar compass for the Clementine Mission

    Energy Technology Data Exchange (ETDEWEB)

    Wilson, B. [Lawrence Livermore National Lab., CA (United States)

    1994-11-15

    A CCD sensor with 42 x 28 degrees FOV and 576 x 384 pixels was built by the Advanced Technology Program (ATP) in the Physics Department at LLNL. That sensor, called the StarTracker camera, is used on the Clementine Lunar Mapping mission between January and May, 1994. Together with the Stellar Compass software, the StarTracker camera provided a way of identifying its orientation to within about 150 microradians in camera body pitch and yaw. This presentation will be an overview of basically how the Stellar Compass software works, along with showing some of its performance results.

  3. About the Collision Repair Campaign

    Science.gov (United States)

    EPA developed the Collision Repair Campaign to focus on meaningful risk reduction in the Collision Repair source sector to complement ongoing community air toxics work and attain reductions at a faster rate.

  4. Characteristics of four-channel Cherenkov-type detector for measurements of runaway electrons in the ISTTOK tokamak

    Energy Technology Data Exchange (ETDEWEB)

    Plyusnin, V. V.; Duarte, P.; Fernandes, H.; Silva, C. [Instituto de Plasmas e FuSao Nuclear - Laboratorio Associado, Association Euratom/IST, Instituto Superior Tecnico, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Jakubowski, L.; Zebrowski, J.; Malinowski, K.; Rabinski, M.; Sadowski, M. J. [The Andrzej Soltan Institute for Nuclear Studies (IPJ), 05-400 Otwock-Swierk (Poland)

    2010-10-15

    A diagnostics capable of characterizing the runaway and superthermal electrons has been developing on the ISTTOK tokamak. In previous paper, a use of single-channel Cherenkov-type detector with titanium filter for runaway electron studies in ISTTOK was reported. To measure fast electron populations with different energies, a prototype of a four-channel detector with molybdenum filters was designed. Test-stand studies of filters with different thicknesses (1, 3, 7, 10, 20, 50, and 100 {mu}m) have shown that they should allow the detection of electrons with energies higher than 69, 75, 87, 95, 120, 181, and 260 keV, respectively. First results of measurements with the four-channel detector revealed the possibility to measure reliably different fast electrons populations simultaneously.

  5. Ice particle collisions

    Science.gov (United States)

    Sampara, Naresh; Turnbull, Barbara; Hill, Richard; Swift, Michael

    2017-04-01

    Granular interactions of ice occur in a range of geophysical, astrophysical and industrial applications. For example, Saturn's Rings are composed of icy particles from micrometers to kilometres in size - inertial and yet too small to interact gravitationally. In clouds, ice crystals are smashed to pieces before they re-aggregate to for snow floccules in a process that is very much open to interpretation. In a granular flow of ice particles, the energy spent in collisions can lead to localized surface changes and wetting, which in turn can promote aggregation. To understand the induced wetting and its effects, we present two novel experimental methods which provide snippets of insight into the collisional behaviour of macroscopic ice particles. Experiment 1: Microgravity experiments provide minute details of the contact between the ice particles during the collision. A diamagnetic levitation technique, as alternative to the parabolic flight or falling tower experiments, was used to understand the collisional behaviour of individual macroscopic icy bodies. A refrigerated cylinder, that can control ambient conditions, was inserted into the bore of an 18 Tesla superconducting magnet and cooled to -10°C. Initial binary collisions were created, where one 4 mm ice particle was levitated in the magnet bore whilst another particle was dropped vertically from the top of the bore. The trajectories of both particles were captured by high speed video to provide the three-dimensional particle velocities and track the collision outcome. Introducing complexity, multiple particles were levitated in the bore and an azimuthal turbulent air flow introduced, allowing the particles to collide with other particles within a coherent fluid structure (mimicking Saturn's rings, or an eddy in a cloud). In these experiments, a sequence of collisions occur, each one different to the previous one due to the changes in surface characteristics created by the collisions themselves. Aggregation

  6. Spacecraft Collision Avoidance

    Science.gov (United States)

    Bussy-Virat, Charles

    The rapid increase of the number of objects in orbit around the Earth poses a serious threat to operational spacecraft and astronauts. In order to effectively avoid collisions, mission operators need to assess the risk of collision between the satellite and any other object whose orbit is likely to approach its trajectory. Several algorithms predict the probability of collision but have limitations that impair the accuracy of the prediction. An important limitation is that uncertainties in the atmospheric density are usually not taken into account in the propagation of the covariance matrix from current epoch to closest approach time. The Spacecraft Orbital Characterization Kit (SpOCK) was developed to accurately predict the positions and velocities of spacecraft. The central capability of SpOCK is a high accuracy numerical propagator of spacecraft orbits and computations of ancillary parameters. The numerical integration uses a comprehensive modeling of the dynamics of spacecraft in orbit that includes all the perturbing forces that a spacecraft is subject to in orbit. In particular, the atmospheric density is modeled by thermospheric models to allow for an accurate representation of the atmospheric drag. SpOCK predicts the probability of collision between two orbiting objects taking into account the uncertainties in the atmospheric density. Monte Carlo procedures are used to perturb the initial position and velocity of the primary and secondary spacecraft from their covariance matrices. Developed in C, SpOCK supports parallelism to quickly assess the risk of collision so it can be used operationally in real time. The upper atmosphere of the Earth is strongly driven by the solar activity. In particular, abrupt transitions from slow to fast solar wind cause important disturbances of the atmospheric density, hence of the drag acceleration that spacecraft are subject to. The Probability Distribution Function (PDF) model was developed to predict the solar wind speed

  7. Modeling and Simulation of the Thermal Runaway Behavior of Cylindrical Li-Ion Cells—Computing of Critical Parameters

    Directory of Open Access Journals (Sweden)

    Andreas Melcher

    2016-04-01

    Full Text Available The thermal behavior of Li-ion cells is an important safety issue and has to be known under varying thermal conditions. The main objective of this work is to gain a better understanding of the temperature increase within the cell considering different heat sources under specified working conditions. With respect to the governing physical parameters, the major aim is to find out under which thermal conditions a so called Thermal Runaway occurs. Therefore, a mathematical electrochemical-thermal model based on the Newman model has been extended with a simple combustion model from reaction kinetics including various types of heat sources assumed to be based on an Arrhenius law. This model was realized in COMSOL Multiphysics modeling software. First simulations were performed for a cylindrical 18650 cell with a L i C o O 2 -cathode to calculate the temperature increase under two simple electric load profiles and to compute critical system parameters. It has been found that the critical cell temperature T crit , above which a thermal runaway may occur is approximately 400 K , which is near the starting temperature of the decomposition of the Solid-Electrolyte-Interface in the anode at 393 . 15 K . Furthermore, it has been found that a thermal runaway can be described in three main stages.

  8. The Effect of the Mode of Gas Preionization on the Parameters of Runaway Electrons in High-Pressure Discharges

    Science.gov (United States)

    Kozhevnikov, V. Yu.; Kozyrev, A. V.; Semeniuk, N. S.

    2017-04-01

    The results of theoretical modeling of the process of formation of a nanosecond discharge in a coaxial discharge gap filled with a high-pressure gas are presented. Two cardinally different evolution scenarios of the nanosecond discharge are addressed: A) in a uniformly volume pre-ionized gas medium and B) in a strongly spatially-nonuniform initially-ionized region near the cathode with a small curvature radius. Relying on the minimal mathematical model of a high-voltage discharge and the description of the physical kinetics of runaway electrons, it is shown using the Boltzmann kinetic equation that the amplitude and duration of a current pulse of runaway electrons and their energy spectrum strongly depend on the mode of gas preionization in the gap. In particular, the other conditions being equal, near-cathode initiation gives rise to the generation of a large group of low-energy runaway electrons within the late current-switching stage. The volume-homogeneous gas preionization can reduce the number of fast electrons by nearly two orders of magnitude compared to the regime without preionization.

  9. Cathode material comparison of thermal runaway behavior of Li-ion cells at different state of charges including over charge

    Science.gov (United States)

    Mendoza-Hernandez, Omar Samuel; Ishikawa, Hiroaki; Nishikawa, Yuuki; Maruyama, Yuki; Umeda, Minoru

    2015-04-01

    The analysis of Li-ion secondary cells under outstanding conditions, as overcharge and high temperatures, is important to determine thermal abuse characteristics of electroactive materials and precise risk assessments on Li-ion cells. In this work, the thermal runaway behavior of LiCoO2 and LiMn2O4 cathode materials were compared at different state of charges (SOCs), including overcharge, by carrying out accelerating rate calorimetry (ARC) measurements using 18650 Li-ion cells. Onset temperatures of self-heating reactions and thermal runaway behavior were identified, and by using these onset points thermal mapping plots were made. We were able to identify non-self-heating, self-heating and thermal runaway regions as a function of state of charge and temperature. The cell using LiMn2O4 cathode material was found to be more thermally stable than the cell using LiCoO2. In parallel with the ARC measurements, the electrochemical behavior of the cells was monitored by measuring the OCV and internal resistance of the cells. The electrochemical behavior of the cells showed a slightly dependency on SOC.

  10. Ambitious Survey Spots Stellar Nurseries

    Science.gov (United States)

    2010-08-01

    -dimensional geometry of the Magellanic system. Chris Evans from the VMC team adds: "The VISTA images will allow us to extend our studies beyond the inner regions of the Tarantula into the multitude of smaller stellar nurseries nearby, which also harbour a rich population of young and massive stars. Armed with the new, exquisite infrared images, we will be able to probe the cocoons in which massive stars are still forming today, while also looking at their interaction with older stars in the wider region." The wide-field image shows a host of different objects. The bright area above the centre is the Tarantula Nebula itself, with the RMC 136 cluster of massive stars in its core. To the left is the NGC 2100 star cluster. To the right is the tiny remnant of the supernova SN1987A (eso1032). Below the centre are a series of star-forming regions including NGC 2080 - nicknamed the "Ghost Head Nebula" - and the NGC 2083 star cluster. The VISTA Magellanic Cloud Survey is one of six huge near-infrared surveys of the southern sky that will take up most of the first five years of operations of VISTA. Notes [1] VISTA ― the Visible and Infrared Survey Telescope for Astronomy ― is the newest telescope at ESO's Paranal Observatory in northern Chile. VISTA is a survey telescope working at near-infrared wavelengths and is the world's largest survey telescope. Its large mirror, wide field of view and very sensitive detectors will reveal a completely new view of the southern sky. The telescope is housed on the peak adjacent to the one hosting ESO's Very Large Telescope (VLT) and shares the same exceptional observing conditions. VISTA has a main mirror that is 4.1 m across. In photographic terms it can be thought of as a 67-megapixel digital camera with a 13 000 mm f/3.25 mirror lens. More information 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

  11. The “Building Blocks” of Stellar Halos

    Directory of Open Access Journals (Sweden)

    Kyle A. Oman

    2017-08-01

    Full Text Available The stellar halos of galaxies encode their accretion histories. In particular, the median metallicity of a halo is determined primarily by the mass of the most massive accreted object. We use hydrodynamical cosmological simulations from the apostle project to study the connection between the stellar mass, the metallicity distribution, and the stellar age distribution of a halo and the identity of its most massive progenitor. We find that the stellar populations in an accreted halo typically resemble the old stellar populations in a present-day dwarf galaxy with a stellar mass ∼0.2–0.5 dex greater than that of the stellar halo. This suggests that had they not been accreted, the primary progenitors of stellar halos would have evolved to resemble typical nearby dwarf irregulars.

  12. SCOPE - Stellar Classification Online Public Exploration

    Science.gov (United States)

    Harenberg, Steven

    2010-01-01

    The Astronomical Photographic Data Archive (APDA) has been established to be the primary North American archive for the collections of astronomical photographic plates. Located at the Pisgah Astronomical Research Institute (PARI) in Rosman, NC, the archive contains hundreds of thousands stellar spectra, many of which have never before been classified. To help classify the vast number of stars, the public is invited to participate in a distributed computing online environment called Stellar Classification Online - Public Exploration (SCOPE). Through a website, the participants will have a tutorial on stellar spectra and practice classifying. After practice, the participants classify spectra on photographic plates uploaded online from APDA. These classifications will be recorded in a database where the results from many users will be statistically analyzed. Stars with known spectral types will be included to test the reliability of classifications. The process of building the database of stars from APDA, which the citizen scientist will be able to classify, includes: scanning the photographic plates, orienting the plate to correct for the change in right ascension/declination using Aladin, stellar HD catalog identification using Simbad, marking the boundaries for each spectrum, and setting up the image for use on the website. We will describe the details of this process.

  13. Advanced Stellar Compass - Alenia Mars Express

    DEFF Research Database (Denmark)

    Kilsgaard, Søren; Betto, Maurizio; Jørgensen, John Leif

    1998-01-01

    This document, submitted in reply to an Alenia R.f.P., is a proposal to implement the Advanced Stellar Compass (ASC) in the Mars Express mission.The Mars Express is an ESA dedicated mission to Mars scientific investigation.The ASC is a very advanced instrument designed by the Space Instrumentation...

  14. Summary of the Advanced Stellar Compass

    DEFF Research Database (Denmark)

    Jørgensen, John Leif

    1997-01-01

    The current version of the Advanced Stellar Compass (ASC) is an improved implementation of the instrument developed for the Danish Geomagnetic Research Satellite Ørsted. The Ørsted version was successfully tested in space on the NASA sounding rocket "Thunderstorm III", that was launched September 2...

  15. Benchmarking the Multidimensional Stellar Implicit Code MUSIC

    Science.gov (United States)

    Goffrey, T.; Pratt, J.; Viallet, M.; Baraffe, I.; Popov, M. V.; Walder, R.; Folini, D.; Geroux, C.; Constantino, T.

    2017-04-01

    We present the results of a numerical benchmark study for the MUltidimensional Stellar Implicit Code (MUSIC) based on widely applicable two- and three-dimensional compressible hydrodynamics problems relevant to stellar interiors. MUSIC is an implicit large eddy simulation code that uses implicit time integration, implemented as a Jacobian-free Newton Krylov method. A physics based preconditioning technique which can be adjusted to target varying physics is used to improve the performance of the solver. The problems used for this benchmark study include the Rayleigh-Taylor and Kelvin-Helmholtz instabilities, and the decay of the Taylor-Green vortex. Additionally we show a test of hydrostatic equilibrium, in a stellar environment which is dominated by radiative effects. In this setting the flexibility of the preconditioning technique is demonstrated. This work aims to bridge the gap between the hydrodynamic test problems typically used during development of numerical methods and the complex flows of stellar interiors. A series of multidimensional tests were performed and analysed. Each of these test cases was analysed with a simple, scalar diagnostic, with the aim of enabling direct code comparisons. As the tests performed do not have analytic solutions, we verify MUSIC by comparing it to established codes including ATHENA and the PENCIL code. MUSIC is able to both reproduce behaviour from established and widely-used codes as well as results expected from theoretical predictions. This benchmarking study concludes a series of papers describing the development of the MUSIC code and provides confidence in future applications.

  16. Robust Modeling of Stellar Triples in PHOEBE

    Science.gov (United States)

    Conroy, Kyle E.; Prsa, Andrej; Horvat, Martin; Stassun, Keivan G.

    2017-01-01

    The number of known mutually-eclipsing stellar triple and multiple systems has increased greatly during the Kepler era. These systems provide significant opportunities to both determine fundamental stellar parameters of benchmark systems to unprecedented precision as well as to study the dynamical interaction and formation mechanisms of stellar and planetary systems. Modeling these systems to their full potential, however, has not been feasible until recently. Most existing available codes are restricted to the two-body binary case and those that do provide N-body support for more components make sacrifices in precision by assuming no stellar surface distortion. We have completely redesigned and rewritten the PHOEBE binary modeling code to incorporate support for triple and higher-order systems while also robustly modeling data with Kepler precision. Here we present our approach, demonstrate several test cases based on real data, and discuss the current status of PHOEBE's support for modeling these types of systems. PHOEBE is funded in part by NSF grant #1517474.

  17. The Ancient stellar population of Leo A.

    NARCIS (Netherlands)

    Saha, Abhijit; Fiorentino, Giuliana; Tolstoy, Eline; Cole, Andrew

    The primary goal of our proposal is the characterisation of the oldest stellar populations in Leo A using the properties of ancient RR Lyrae variable stars as tracers. Well known and long established correlations exist between the periods and luminosities of RR Lyrae variable stars and their ages

  18. The resolved stellar population of Leo A

    NARCIS (Netherlands)

    Tolstoy, E

    1996-01-01

    New observations of the resolved stellar population of the extremely metal-poor Magellanic dwarf irregular galaxy Leo A in Thuan-Gunn r, g, i, and narrowband Ha filters are presented. Using the recent Cepheid variable star distance determination to Leo A by Hoessel et al., we are able to create an

  19. Exploring the Morphology of RAVE Stellar Spectra

    NARCIS (Netherlands)

    Matijevic, G.; Zwitter, T.; Bienayme, O.; Bland-Hawthorn, J.; Boeche, C.; Freeman, K. C.; Gibson, B. K.; Gilmore, G.; Grebel, E. K.; Helmi, A.; Munari, U.; Navarro, J.; Parker, Q. A.; Reid, W.; Seabroke, G.; Siebert, A.; Siviero, A.; Steinmetz, M.; Watson, F. G.; Williams, M.; Wyse, R. F. G.

    The RAdial Velocity Experiment (RAVE) is a medium-resolution (R similar to 7500) spectroscopic survey of the Milky Way that has already obtained over half a million stellar spectra. They present a randomly selected magnitude-limited sample, so it is important to use a reliable and automated

  20. Galactic stellar haloes in the CDM model

    NARCIS (Netherlands)

    Cooper, A. P.; Cole, S.; Frenk, C. S.; White, S. D. M.; Helly, J.; Benson, A. J.; De Lucia, G.; Helmi, A.; Jenkins, A.; Navarro, J. F.; Springel, V.; Wang, J.

    2010-01-01

    We present six simulations of galactic stellar haloes formed by the tidal disruption of accreted dwarf galaxies in a fully cosmological setting. Our model is based on the Aquarius project, a suite of high-resolution N-body simulations of individual dark matter haloes. We tag subsets of particles in

  1. THE STELLAR KINEMATICS OF GALACTIC DISKS

    NARCIS (Netherlands)

    BOTTEMA, R

    Stellar velocity dispersion measurements of a sample of 12 galactic disks are summarized. The observed radial functionality is parameterized such that one dispersion value is assigned to each galaxy. Comparison of the galaxy dispersion with absolute magnitude and maximum rotation reveals that the

  2. Stellar Relics from the Early Galaxy

    Indian Academy of Sciences (India)

    2016-01-27

    Jan 27, 2016 ... Galactic halo; chemical evolution; metal poor stars; chemical abundances; inner halo; outer halo; globular clusters; ultra-faint dwarf galaxies. Abstract. We reviewed the recent progress in the field of stellar/galactic archeology, which is a study of the relics from the early galaxy. The oldest and most pristine ...

  3. Stellar chemical signatures and hierarchical galaxy formation

    NARCIS (Netherlands)

    Venn, KA; Irwin, M; Shetrone, MD; Tout, CA; Hill, [No Value; Tolstoy, E

    To compare the chemistries of stars in the Milky Way dwarf spheroidal (dSph) satellite galaxies with stars in the Galaxy, we have compiled a large sample of Galactic stellar abundances from the literature. When kinematic information is available, we have assigned the stars to standard Galactic

  4. Evolution and seismic tools for stellar astrophysics

    CERN Document Server

    Monteiro, Mario JPFG

    2008-01-01

    A collection of articles published by the journal "Astrophysics and Space Science, Volume 316, Number 1-4", August 2008. This work covers 10 evolution codes and 9 oscillation codes. It is suitable for researchers and research students working on the modeling of stars and on the implementation of seismic test of stellar models.

  5. Measuring Stellar Rotation Periods with Kepler

    DEFF Research Database (Denmark)

    Nielsen, M. B.; Gizon, L.; Schunker, H.

    2013-01-01

    We measure rotation periods for 12151 stars in the Kepler field, based on photometric variability caused by stellar activity. Our analysis returns stable rotation periods over at least six out of eight quarters of Kepler data. This large sample of stars enables us to study rotation periods...

  6. The Advanced Stellar Compass, Development and Operations

    DEFF Research Database (Denmark)

    Jørgensen, John Leif; Liebe, Carl Christian

    1996-01-01

    this demand the Advanced Stellar Compass (ASC), a fully autonomous miniature star tracker, was developed. This ASC is capable of both solving the "lost in space" problem and determine the attitude with arcseconds precision. The development, principles of operation and instrument autonomy of the ASC...

  7. Photon-photon collisions

    Energy Technology Data Exchange (ETDEWEB)

    Brodsky, S.J.

    1988-07-01

    Highlights of the VIIIth International Workshop on Photon-Photon Collisions are reviewed. New experimental and theoretical results were reported in virtually every area of ..gamma gamma.. physics, particularly in exotic resonance production and tests of quantum chromodynamics where asymptotic freedom and factorization theorems provide predictions for both inclusive and exclusive ..gamma gamma.. reactions at high momentum transfer. 73 refs., 12 figs.

  8. Droplet collisions in turbulence

    NARCIS (Netherlands)

    Oldenziel, G.

    2014-01-01

    Liquid droplets occur in many natural phenomena and play an important role in a large number of industrial applications. One of the distinct properties of droplets as opposed to solid particles is their ability to merge, or coalesce upon collision. Coalescence of liquid drops is of importance in for

  9. CMS SEES FIRST COLLISIONS

    CERN Multimedia

      A very special moment.  On 23rd November, 19:40 we recorded our first collisions with 450GeV beams well centred in CMS.   If you have any comments / suggestions please contact Karl Aaron GILL (Editor)

  10. Vocal Fold Collision Modeling

    DEFF Research Database (Denmark)

    Granados, Alba; Brunskog, Jonas; Misztal, M. K.

    2015-01-01

    When vocal folds vibrate at normal speaking frequencies, collisions occurs. The numerics and formulations behind a position-based continuum model of contact is an active field of research in the contact mechanics community. In this paper, a frictionless three-dimensional finite element model of t...

  11. Collisions in soccer kicking

    DEFF Research Database (Denmark)

    Andersen, Thomas Bull; Dörge, Henrik C.; Thomsen, Franz Ib

    1999-01-01

    An equation to describe the velocity of the soccer ball after the collision with a foot was derived. On the basis of experimental results it was possible to exclude certain factors and only describe the angular momentum of the system, consisting of the shank, the foot and the ball, leading...

  12. The impact of pollution on stellar evolution models

    OpenAIRE

    Dotter, Aaron; Chaboyer, Brian

    2003-01-01

    An approach is introduced for incorporating the concept of stellar pollution into stellar evolution models. The approach involves enhancing the metal content of the surface layers of stellar models. In addition, the surface layers of stars in the mass range of 0.5-2.0 Solar masses are mixed to an artificial depth motivated by observations of lithium abundance. The behavior of polluted stellar evolution models is explored assuming the pollution occurs after the star has left the fully convecti...

  13. Modules for Experiments in Stellar Astrophysics (MESA)

    Science.gov (United States)

    Paxton, Bill; Bildsten, Lars; Dotter, Aaron; Herwig, Falk; Lesaffre, Pierre; Timmes, Frank

    2011-01-01

    Stellar physics and evolution calculations enable a broad range of research in astrophysics. Modules for Experiments in Stellar Astrophysics (MESA) is a suite of open source, robust, efficient, thread-safe libraries for a wide range of applications in computational stellar astrophysics. A one-dimensional stellar evolution module, MESAstar, combines many of the numerical and physics modules for simulations of a wide range of stellar evolution scenarios ranging from very low mass to massive stars, including advanced evolutionary phases. MESAstar solves the fully coupled structure and composition equations simultaneously. It uses adaptive mesh refinement and sophisticated timestep controls, and supports shared memory parallelism based on OpenMP. State-of-the-art modules provide equation of state, opacity, nuclear reaction rates, element diffusion data, and atmosphere boundary conditions. Each module is constructed as a separate Fortran 95 library with its own explicitly defined public interface to facilitate independent development. Several detailed examples indicate the extensive verification and testing that is continuously performed and demonstrate the wide range of capabilities that MESA possesses. These examples include evolutionary tracks of very low mass stars, brown dwarfs, and gas giant planets to very old ages; the complete evolutionary track of a 1 M sun star from the pre-main sequence (PMS) to a cooling white dwarf; the solar sound speed profile; the evolution of intermediate-mass stars through the He-core burning phase and thermal pulses on the He-shell burning asymptotic giant branch phase; the interior structure of slowly pulsating B Stars and Beta Cepheids; the complete evolutionary tracks of massive stars from the PMS to the onset of core collapse; mass transfer from stars undergoing Roche lobe overflow; and the evolution of helium accretion onto a neutron star. MESA can be downloaded from the project Web site (http://mesa.sourceforge.net/).

  14. IMF shape constraints from stellar populations and dynamics from CALIFA

    NARCIS (Netherlands)

    Lyubenova, M.; Martín-Navarro, I.; van de Ven, G.; Falcón-Barroso, J.; Galbany, L.; Gallazzi, A.; García-Benito, R.; González Delgado, R.; Husemann, B.; La Barbera, F.; Marino, R. A.; Mast, D.; Mendez-Abreu, J.; Peletier, R. F. P.; Sánchez-Blázquez, P.; Sánchez, S. F.; Trager, S. C.; van den Bosch, R. C. E.; Vazdekis, A.; Walcher, C. J.; Zhu, L.; Zibetti, S.; Ziegler, B.; Bland-Hawthorn, J.; Collaboration, CALIFA

    2016-01-01

    In this Paper, we describe how we use stellar dynamics information to constrain the shape of the stellar initial mass function (IMF) in a sample of 27 early-type galaxies from the CALIFA survey. We obtain dynamical and stellar mass-to-light ratios, Υdyn and Υ*, over a homogenous aperture of 0.5 Re.

  15. Estimating inelastic heavy-particle - hydrogen collision data. II. Simplified model for ionic collisions and application to barium-hydrogen ionic collisions

    Science.gov (United States)

    Belyaev, Andrey K.; Yakovleva, Svetlana A.

    2017-12-01

    Aims: A simplified model is derived for estimating rate coefficients for inelastic processes in low-energy collisions of heavy particles with hydrogen, in particular, the rate coefficients with high and moderate values. Such processes are important for non-local thermodynamic equilibrium modeling of cool stellar atmospheres. Methods: The derived method is based on the asymptotic approach for electronic structure calculations and the Landau-Zener model for nonadiabatic transition probability determination. Results: It is found that the rate coefficients are expressed via statistical probabilities and reduced rate coefficients. It is shown that the reduced rate coefficients for neutralization and ion-pair formation processes depend on single electronic bound energies of an atomic particle, while the reduced rate coefficients for excitation and de-excitation processes depend on two electronic bound energies. The reduced rate coefficients are calculated and tabulated as functions of electronic bound energies. The derived model is applied to barium-hydrogen ionic collisions. For the first time, rate coefficients are evaluated for inelastic processes in Ba+ + H and Ba2+ + H- collisions for all transitions between the states from the ground and up to and including the ionic state. Tables with calculated data are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/608/A33

  16. Thermal Runaway of the 13 kA Busbar Joints in the LHC

    CERN Document Server

    Verweij, A P

    2010-01-01

    Triggered by the incident in the LHC in September 2008, the thermo-electrical stability of the 10,000 soldered busbar joints in the 13 kA circuits of the LHC has been re-assessed. For this purpose the computer model QP3 has been developed. In this paper the results of some calculations are presented, and it is shown how the results have been used to improve the quench detection system and ensure safe future operation. First the layout of the 13 kA circuits, the geometry of the soldered joints and the quench detection system will be described. Special focus is put on several types of defects in the joint that have been found in the LHC. The difference between slow and fast thermal run-away will be discussed, focusing on quench propagation and reduced thermal and electrical contacts between the various parts of the joint. It is shown that an enhancement of the LHC quench detection system with a much lower threshold will greatly reduce the risk of burn-out of the joint. Finally it is discussed that protection is...

  17. Runaway electron mitigation by 3D fields in the ASDEX-Upgrade experiment

    Science.gov (United States)

    Gobbin, M.; Li, L.; Liu, Y. Q.; Marrelli, L.; Nocente, M.; Papp, G.; Pautasso, G.; Piovesan, P.; Valisa, M.; Carnevale, D.; Esposito, B.; Giacomelli, L.; Gospodarczyk, M.; McCarthy, P. J.; Martin, P.; Suttrop, W.; Tardocchi, M.; Teschke, M.; the ASDEX Upgrade Team; the EUROfusion MST1 Team

    2018-01-01

    Disruption-generated runaway electron (RE) beams represent a severe threat for tokamak plasma-facing components in high current devices like ITER, thus motivating the search of mitigation techniques. The application of 3D fields might aid this purpose and recently was investigated also in the ASDEX Upgrade experiment by using the internal active saddle coils (termed B-coils). Resonant magnetic perturbations (RMPs) with dominant toroidal mode number n = 1 have been applied by the B-coils, in a RE specific scenario, before and during disruptions, which are deliberately created via massive gas injection. The application of RMPs affects the electron temperature profile and seemingly changes the dynamics of the disruption; this results in a significantly reduced current and lifetime of the generated RE beam. A similar effect is observed also in the hard-x-ray (HXR) spectrum, associated to RE emission, characterized by a partial decrease of the energy content below 1 MeV when RMPs are applied. The strength of the observed effects strongly depends on the upper-to-lower B-coil phasing, i.e. on the poloidal spectrum of the applied RMPs, which has been reconstructed including the plasma response by the code MARS-F. A crude vacuum approximation fails in the interpretation of the experimental findings: despite the relatively low β (< 0.5 % ) of these discharges, a modest amplification (factor of 2) of the edge kink response occurs, which has to be considered to explain the observed suppression effects.

  18. Synchrotron emission diagnostic of full-orbit kinetic simulations of runaway electrons in tokamaks plasmas

    Science.gov (United States)

    Carbajal Gomez, Leopoldo; Del-Castillo-Negrete, Diego

    2017-10-01

    Developing avoidance or mitigation strategies of runaway electrons (RE) for the safe operation of ITER is imperative. Synchrotron radiation (SR) of RE is routinely used in current tokamak experiments to diagnose RE. We present the results of a newly developed camera diagnostic of SR for full-orbit kinetic simulations of RE in DIII-D-like plasmas that simultaneously includes: full-orbit effects, information of the spectral and angular distribution of SR of each electron, and basic geometric optics of a camera. We observe a strong dependence of the SR measured by the camera on the pitch angle distribution of RE, namely we find that crescent shapes of the SR on the camera pictures relate to RE distributions with small pitch angles, while ellipse shapes relate to distributions of RE with larger pitch angles. A weak dependence of the SR measured by the camera with the RE energy, value of the q-profile at the edge, and the chosen range of wavelengths is found. Furthermore, we observe that oversimplifying the angular distribution of the SR changes the synchrotron spectra and overestimates its amplitude. Research sponsored by the LDRD Program of ORNL, managed by UT-Battelle, LLC, for the U. S. DoE.

  19. Violations of the equivalence principle in a dilaton-runaway scenario

    CERN Document Server

    Damour, Thibault Marie Alban Guillaume; Veneziano, Gabriele

    2002-01-01

    We explore a version of the cosmological dilaton-fixing and decoupling mechanism in which the dilaton-dependence of the low-energy effective action is extremized for infinitely large values of the bare string coupling $g_s^2 = e^{\\phi}$. We study the efficiency with which the dilaton $\\phi$ runs away towards its ``fixed point'' at infinity during a primordial inflationary stage, and thereby approximately decouples from matter. The residual dilaton couplings are found to be related to the amplitude of the density fluctuations generated during inflation. For the simplest inflationary potential, $V (\\chi) = {1/2} m_{\\chi}^2 (\\phi) \\chi^2$, the residual dilaton couplings are shown to predict violations of the universality of gravitational acceleration near the $\\Delta a / a \\sim 10^{-12}$ level. This suggests that a modest improvement in the precision of equivalence principle tests might be able to detect the effect of such a runaway dilaton. Under some assumptions about the coupling of the dilaton to dark matter...

  20. Dark Matter Substructure in Numerical Simulations: A Tale of Discreteness Noise, Runaway Instabilities, and Artificial Disruption

    Science.gov (United States)

    van den Bosch, Frank C.; Ogiya, Go

    2018-01-01

    To gain understanding of the complicated, non-linear and numerical processes associated with the tidal evolution of dark matter subhaloes in numerical simulation, we perform a large suite of idealized simulations that follow individual N-body subhaloes in a fixed, analytical host halo potential. By varying both physical and numerical parameters, we investigate under what conditions the subhaloes undergo disruption. We confirm the conclusions from our more analytical assessment in van den Bosch et al. that most disruption is numerical in origin; as long as a subhalo is resolved with sufficient mass and force resolution, a bound remnant survives. This implies that state-of-the-art cosmological simulations still suffer from significant overmerging. We demonstrate that this is mainly due to inadequate force-softening, which causes excessive mass loss and artificial tidal disruption. In addition, we show that subhaloes in N-body simulations are susceptible to a runaway instability triggered by the amplification of discreteness noise in the presence of a tidal field. These two processes conspire to put serious limitations on the reliability of dark matter substructure in state-of-the-art cosmological simulations. We present two criteria that can be used to assess whether individual subhaloes in cosmological simulations are reliable or not, and advocate that subhaloes that satisfy either of these two criteria be discarded from further analysis. We discuss the potential implications of this work for several areas in astrophysics.

  1. Runaway Electron Preionized Diffuse Discharge and Its Impact on Plane Anode

    Science.gov (United States)

    Tarasenko, Victor; Erofeev, Michael; Ripenko, Vasilii; Shulepov, Mikhail; Baksht, Evgenii; National Research Tomsk Polytechnic University Collaboration; Institute of High Current Electronics Collaboration

    2016-09-01

    The spatial structure of a runaway electrons preionized diffuse discharge (REP DD) in nonuniform electric field and the influence of its plasma on the surface of a plane anode have been studied. In our experiments, we used a NPG-18/3500N high-voltage generator. The incident voltage had negative polarity, amplitude of 20 kV, and FWHM of 6 ns; the discharge current was up to 200 A. The discharge plasma was formed in nitrogen by applying high voltage pulses to the interelectrode gap which was varied between 2 and 9 mm. Under such conditions, the specific input power reached up to 10 MW/cm3. It is established that diffuse channel is the initial stage of the discharge radiation; then anode spot, channel with high glow intensity based on the anode spot and spark channel are consecutively formed. Spark formation finished within 10-15 ns after the onset of the discharge. Microstructure of spark and diffuse channels with anode spot autograph have been detected. The traces of such discharge represents itself an aggregation of up to 100 microcraters with dimeters of 5-100 micrometers. It was also shown that diffuse discharge does not leave erosive action on an anode surface or on its carbon cover. This work was supported by the Russian Science Foundation under the Grant Number 14-29-00052.

  2. NASA Perspective and Modeling of Thermal Runaway Propagation Mitigation in Aerospace Batteries

    Science.gov (United States)

    Shack, P.; Iannello, C.; Rickman, S.; Button, R.

    2014-01-01

    NASA has traditionally sought to reduce the likelihood of a single cell thermal runaway (TR) in their aerospace batteries to an absolute minimum by employing rigorous screening program of the cells. There was generally a belief that TR propagation resulting in catastrophic failure of the battery was a forgone conclusion for densely packed aerospace lithium-ion batteries. As it turns out, this may not be the case. An increasing number of purportedly TR propagation-resistant batteries are appearing among NASA partners in the commercial sector and the Department of Defense. In the recent update of the battery safety standard (JSC 20793) to address this paradigm shift, the NASA community included requirements for assessing TR severity and identifying simple, low-cost severity reduction measures. Unfortunately, there are no best-practice guidelines for this work in the Agency, so the first project team attempting to meet these requirements would have an undue burden placed upon them. A NASA engineering Safety Center (NESC) team set out to perform pathfinding activities for meeting those requirements. This presentation will provide contextual background to this effort, as well as initial results in attempting to model and simulate TR heat transfer and propagation within battery designs.

  3. A comparison between spectra of runaway electron beams in SF6 and air

    Science.gov (United States)

    Zhang, Cheng; Tarasenko, Victor; Gu, Jianwei; Baksht, Evgenii; Wang, Ruexue; Yan, Ping; Shao, Tao

    2015-12-01

    Runaway electron (RAE) with extremely high-energy plays important role on the avalanche propagation, streamer formation, and ionization waves in nanosecond-pulse discharges. In this paper, the generation of a supershort avalanche electron beam (SAEB) in SF6 and air in an inhomogeneous electric field is investigated. A VPG-30-200 generator with a pulse rise time of ˜1.6 ns and a full width at half maximum of 3-5 ns is used to produce RAE beams. The SAEBs in SF6 and air are measured by using aluminum foils with different thicknesses. Furthermore, the SAEB spectra in SF6 and air at pressures of 7.5 Torr, 75 Torr, and 750 Torr are compared. The results showed that amplitude of RAE beam current generated at the breakdown in SF6 was approximately an order of magnitude less than that in air. The energy of SAEB in air was not smaller than that in SF6 in nanosecond-pulse discharges under otherwise equal conditions. Moreover, the difference between the maximum energy of the electron distributions in air and SF6 decreased when the rise time of the voltage pulse increased. It was because the difference between the breakdown voltages in air and SF6 decreased when the rise time of the voltage pulse increased.

  4. Nanoparticle Plasma Jet as Fast Probe for Runaway Electrons in Tokamak Disruptions

    Science.gov (United States)

    Bogatu, I. N.; Galkin, S. A.

    2017-10-01

    Successful probing of runaway electrons (REs) requires fast (1 - 2 ms) high-speed injection of enough mass able to penetrate through tokamak toroidal B-field (2 - 5 T) over 1 - 2 m distance with large assimilation fraction in core plasma. A nanoparticle plasma jet (NPPJ) from a plasma gun is a unique combination of millisecond trigger-to-delivery response and mass-velocity of 100 mg at several km/s for deep direct injection into current channel of rapidly ( 1 ms) cooling post-TQ core plasma. After C60 NPPJ test bed demonstration we started to work on ITER-compatible boron nitride (BN) NPPJ. Once injected into plasma, BN NP undergoes ablative sublimation, thermally decomposes into B and N, and releases abundant B and N high-charge ions along plasma-traversing path and into the core. We present basic characteristics of our BN NPPJ concept and first results from B and N ions on Zeff > 1 effect on REs dynamics by using a self-consistent model for RE current density. Simulation results of BNQ+ NPPJ penetration through tokamak B-field to RE beam location performed with Hybrid Electro-Magnetic code (HEM-2D) are also presented. Work supported by U.S. DOE SBIR Grant.

  5. Stellar population synthesis models between 2.5 and 5 mu m based on the empirical IRTF stellar library

    NARCIS (Netherlands)

    Roeck, B.; Vazdekis, A.; Peletier, R. F.; Knapen, J. H.; Falcon-Barroso, J.

    2015-01-01

    We present the first single-burst stellar population models in the infrared wavelength range between 2.5 and 5 mu m which are exclusively based on empirical stellar spectra. Our models take as input 180 spectra from the stellar IRTF (Infrared Telescope Facility) library. Our final single-burst

  6. The initial mass function and global rates of mass, momentum, and energy input to the interstellar medium via stellar winds

    Science.gov (United States)

    Van Buren, D.

    1985-01-01

    Published observational data are compiled and analyzed, using theoretical stellar-evolution models to determine the global rates of mass, momentum, and energy injected into the interstellar medium (ISM) by stellar winds. Expressions derived include psi = 0.00054 x (M to the -1.03) stars formed/sq kpc yr log M (where M is the initial mass function in solar mass units) and mass-loss = (2 x 10 to the -13th) x (L to the 1.25) solar mass/yr (with L in solar luminosity units). It is found that the wind/supernova injection of energy into the ISM and the mass loss from stars of 5 solar mass or more are approximately balanced by the dissipation of energy by cloud-cloud collisions and the formation of stars, respectively.

  7. Study of Stellar Clusters Containing Massive Stars

    Science.gov (United States)

    Costado, Teresa; Alfaro, E. J.; Delgado, A. J.; Djupvik, A. A.; Maíz Apellániz, J.

    2013-06-01

    Most stars form in clusters, but the percentage of stars born in dense stellar systems is currently matter of controversy and depends very much on the own definition of cluster. The cluster definition and hence the morphologies of individual clusters appear to vary significantly from region to region, as well as with age, which suggests that either, star formation in clusters is not universal and may depend on the local environment, or that all clusters form with the same morphology but early dynamical evolution quickly modifies the structure of the phase space distribution. In addition, young populated clusters containing massive stars are excellent labs for the study of the formation of the massive stellar component of the Galactic disk. Three main scenarios have been proposed for the formation of high-mass stars (M > 7-8 M_{⊙}): a) monolithic collapse of proto-stellar nuclei; b) competitive accretion inside the proto-cluster molecular cloud; and c) coalescence of proto-stellar nuclei and low-mass stars in very dense atmospheres. Both scientific questions: a) cluster formation and b) formation of high mass stars in clusters are intimately connected via the structural description of the phase space distribution of cluster stars and their Mass Function (MF). Models of static clusters with different initial spatial and kinematic distributions show how the spatial distribution dynamically evolves with time, allowing a characterization of their dynamical state from snapshots of their spatial distribution. Four are the main variables (and their distribution with mass and position) needed for a reliable characterization of the cluster dynamical state: a) Mass segregation parameter; b) Mapping of surface density for different ranges of masses; c) Q morphological parameter based on the minimum spanning tree graph and its variation with mass and cluster age, and d) MF of the cluster members. Two years ago, the Stellar System Group of IAA has begun an observational

  8. BONNSAI: correlated stellar observables in Bayesian methods

    Science.gov (United States)

    Schneider, F. R. N.; Castro, N.; Fossati, L.; Langer, N.; de Koter, A.

    2017-02-01

    In an era of large spectroscopic surveys of stars and big data, sophisticated statistical methods become more and more important in order to infer fundamental stellar parameters such as mass and age. Bayesian techniques are powerful methods because they can match all available observables simultaneously to stellar models while taking prior knowledge properly into account. However, in most cases it is assumed that observables are uncorrelated which is generally not the case. Here, we include correlations in the Bayesian code Bonnsai by incorporating the covariance matrix in the likelihood function. We derive a parametrisation of the covariance matrix that, in addition to classical uncertainties, only requires the specification of a correlation parameter that describes how observables co-vary. Our correlation parameter depends purely on the method with which observables have been determined and can be analytically derived in some cases. This approach therefore has the advantage that correlations can be accounted for even if information for them are not available in specific cases but are known in general. Because the new likelihood model is a better approximation of the data, the reliability and robustness of the inferred parameters are improved. We find that neglecting correlations biases the most likely values of inferred stellar parameters and affects the precision with which these parameters can be determined. The importance of these biases depends on the strength of the correlations and the uncertainties. For example, we apply our technique to massive OB stars, but emphasise that it is valid for any type of stars. For effective temperatures and surface gravities determined from atmosphere modelling, we find that masses can be underestimated on average by 0.5σ and mass uncertainties overestimated by a factor of about 2 when neglecting correlations. At the same time, the age precisions are underestimated over a wide range of stellar parameters. We conclude that

  9. The Search for Stellar Coronal Mass Ejections

    Science.gov (United States)

    Villadsen, Jacqueline Rose

    2017-05-01

    Coronal mass ejections (CMEs) may dramatically impact habitability and atmospheric composition of planets around magnetically active stars, including young solar analogs and many M dwarfs. Theoretical predictions of such effects are limited by the lack of observations of stellar CMEs. This thesis addresses this gap through a search for the spectral and spatial radio signatures of CMEs on active M dwarfs. Solar CMEs produce radio bursts with a distinctive spectral signature, narrow-band plasma emission that drifts to lower frequency as a CME expands outward. To search for analogous events on nearby stars, I worked on system design, software, and commissioning for the Starburst project, a wideband single-baseline radio interferometry backend dedicated to stellar observations. In addition, I led a survey of nearby active M dwarfs with the Karl G. Jansky Very Large Array (VLA), detecting coherent radio bursts in 13 out of 23 epochs, over a total of 58 hours. This survey's ultra-wide bandwidth (0.23-6.0 GHz) dynamic spectroscopy, unprecedented for stellar observations, revealed diverse behavior in the time-frequency plane. Flare star UV Ceti produced complex, luminous events reminiscent of brown dwarf aurorae; AD Leo sustained long-duration, intense, narrow-band "storms"; and YZ CMi emitted a burst with substructure with rapid frequency drift, resembling solar Type III bursts, which are attributed to electrons moving at speeds of order 10% of the speed of light. To search for the spatial signature of CMEs, I led 8.5-GHz observations with the Very Long Baseline Array simultaneous to 24 hours of the VLA survey. This program detected non-thermal continuum emission from the stars in all epochs, as well as continuum flares on AD Leo and coherent bursts on UV Ceti, enabling measurement of the spatial offset between flaring and quiescent emission. These observations demonstrate the diversity of stellar transients that can be expected in time-domain radio surveys, especially

  10. Synthetic clusters of massive stars to test stellar evolution models

    Science.gov (United States)

    Georgy, Cyril; Ekström, Sylvia

    2017-03-01

    During the last few years, the Geneva stellar evolution group has released new grids of stellar models, including the effect of rotation and with updated physical inputs (Ekström et al. 2012; Georgy et al. 2013a, b). To ease the comparison between the outputs of the stellar evolution computations and the observations, a dedicated tool was developed: the Syclist toolbox (Georgy et al. 2014). It allows to compute interpolated stellar models, isochrones, synthetic clusters, and to simulate the time-evolution of stellar populations.

  11. Constraining stellar physics from red-giant stars in binaries - stellar rotation, mixing processes and stellar activity

    Science.gov (United States)

    Beck, P. G.; Kallinger, T.; Pavlovski, K.; Palacios, A.; Tkachenko, A.; García, R. A.; Mathis, S.; Corsaro, E.; Johnston, C.; Mosser, B.; Ceillier, T.; do Nascimento, J.-D.; Raskin, G.

    2017-10-01

    The unparalleled photometric data obtained by NASA's Kepler Space Telescope has led to an improved understanding of stellar structure and evolution - in particular for solar-like oscillators in this context. Binary stars are fascinating objects. Because they were formed together, binary systems provide a set of two stars with very well constrained parameters. Those can be used to study properties and physical processes, such as the stellar rotation, dynamics and rotational mixing of elements and allows us to learn from the differences we find between the two components. In this work, we discussed a detailed study of the binary system KIC 9163796, discovered through Kepler photometry. The ground-based follow-up spectroscopy showed that this system is a double-lined spectroscopic binary, with a mass ratio close to unity. However, the fundamental parameters of the components of this system as well as their lithium abundances differ substantially. Kepler photometry of this system allows to perform a detailed seismic analysis as well as to derive the orbital period and the surface rotation rate of the primary component of the system. Indications of the seismic signature of the secondary are found. The differing parameters are best explained with both components located in the early and the late phase of the first dredge up at the bottom of the red-giant branch. Observed lithium abundances in both components are in good agreement with prediction of stellar models including rotational mixing. By combining observations and theory, a comprehensive picture of the system can be drawn.

  12. VizieR Online Data Catalog: Stellar parameters and assumed wind parameters (Cazorla+, 2017)

    Science.gov (United States)

    Cazorla, C.; Morel, T.; Naze, Y.; Rauw, G.; Semaan, T.; Daflon, S.; Oey, S.

    2017-03-01

    Stellar parameters derived for the stars in our sample and assumed wind parameters for our hotter stars. Because macroturbulent velocities cannot be determined reliably for fast rotators (Sect. 4.2), all values in column 6 are upper limits. Column 7 provides the multiplicity status (see Sect. 4.1 for the classification criterion and Appendix C for the RV studies of each individual object). The runaway status is based on literature studies (references are given on a star-to-star basis in Appendix C). Columns 15, 16, and 17 of the table presenting the results for the hotter stars list the assumed wind parameters. For stars with the lowest temperatures (typically B0.5 stars), the carbon abundance cannot be firmly determined due to the weakness of the CIII lines at these temperatures. Besides, NII lines may also be very weak for the hottest stars studied with DETAIL/SURFACE. In these cases, we provide upper limits for both carbon and nitrogen abundances. They correspond to predicted lines becoming detectable, i.e., having a depth significantly exceeding the local noise. Similarly, CMFGEN fits may converge towards very high or very low CNO abundances. In both cases, the upper or lower limits were determined from the chi2 curves and correspond to the limit of their flat minimum. Since the CNO abundances are measured relative to the hydrogen content (assumed to be constant in our study), a correction should in principle be applied to the CNO abundances of stars that exhibit a very high helium abundance (and therefore have a reduced hydrogen abundance). However, we found this correction to be negligible (<~0.1dex) even for the most He-rich stars. The 1σ errors on the parameters are given in dedicated columns. (2 data files).

  13. Correlating proper motion kinematics with stellar properties in a very young protocluster

    Science.gov (United States)

    Da Rio, Nicola

    2016-10-01

    We recently obtained the first epoch of a multi-cycle HST program (GO13742) aimed at the study of massive star cluster formation through proper motion-based analysis of kinematics. This program targeted the young, gas-dominated, still-forming protocluster G286 with WFC3/IR J, H and narrow band F167N, reaching down to the H-burning limit at A_V=20, and well into the substellar regime for the less-embedded parts of the system. With the second epoch (cycle 24) we will derive proper motions, kinematic subclustering, runaway objects and determine the overall expansion/contraction of the system. Here we propose to complement these observations with additional photometric bands, which will allow us to derive the stellar parameters of the low-mass members. We plan to use the H2O Teff band at 1.4micron, with a continuum at 1.3micron, to disentangle Teff and A_V for all low-mass young stars down to the H-burning limit at A_V=20, matching our previous data. This will enable us to construct the HRD, assign ages, look for spatial age gradients, and compare kinematic properties with age. Specifically, the identification of systematic variations in the proper motions with age will enable us to trace the initial morphology of the system at its formation, and determine the kinematic association of older stars with younger. Last, we plan to obtain accurate fluxes in Paschen beta, whose excess is indicative of accretion (allowing us to measure Mdot) and is an independent indicator of membership. Accretion properties, with ages, masses, and dynamics will enable a comprehensive picture of this young, massive protocluster in formation, testing theories of massive star cluster formation.

  14. Collision Probability Analysis

    DEFF Research Database (Denmark)

    Hansen, Peter Friis; Pedersen, Preben Terndrup

    1998-01-01

    It is the purpose of this report to apply a rational model for prediction of ship-ship collision probabilities as function of the ship and the crew characteristics and the navigational environment for MS Dextra sailing on a route between Cadiz and the Canary Islands.The most important ship and crew...... characteristics are: ship speed, ship manoeuvrability, the layout of the navigational bridge, the radar system, the number and the training of navigators, the presence of a look out etc. The main parameters affecting the navigational environment are ship traffic density, probability distributions of wind speeds...... probability, i.e. a study of the navigator's role in resolving critical situations, a causation factor is derived as a second step.The report documents the first step in a probabilistic collision damage analysis. Future work will inlcude calculation of energy released for crushing of structures giving...

  15. Stellar Streams Discovered in the Dark Energy Survey

    Energy Technology Data Exchange (ETDEWEB)

    Shipp, N.; et al.

    2018-01-09

    We perform a search for stellar streams around the Milky Way using the first three years of multi-band optical imaging data from the Dark Energy Survey (DES). We use DES data covering $\\sim 5000$ sq. deg. to a depth of $g > 23.5$ with a relative photometric calibration uncertainty of $< 1 \\%$. This data set yields unprecedented sensitivity to the stellar density field in the southern celestial hemisphere, enabling the detection of faint stellar streams to a heliocentric distance of $\\sim 50$ kpc. We search for stellar streams using a matched-filter in color-magnitude space derived from a synthetic isochrone of an old, metal-poor stellar population. Our detection technique recovers four previously known thin stellar streams: Phoenix, ATLAS, Tucana III, and a possible extension of Molonglo. In addition, we report the discovery of eleven new stellar streams. In general, the new streams detected by DES are fainter, more distant, and lower surface brightness than streams detected by similar techniques in previous photometric surveys. As a by-product of our stellar stream search, we find evidence for extra-tidal stellar structure associated with four globular clusters: NGC 288, NGC 1261, NGC 1851, and NGC 1904. The ever-growing sample of stellar streams will provide insight into the formation of the Galactic stellar halo, the Milky Way gravitational potential, as well as the large- and small-scale distribution of dark matter around the Milky Way.

  16. Observational consequences of unstable stellar interiors

    Science.gov (United States)

    Cantiello, M.

    2009-11-01

    Stars are responsible for the production of all the elements, aside from hydrogen, that constitute our body. To understand the life and death of such important astrophysical objects, their interiors need to be modeled. The evolution of stars, including the effects of rotation, internal magnetic fields, convection, thermohaline mixing and pair creation is the main topic of this study. Stars often come in pairs, and the consequences of binary interaction have been explored as well. A new channel for the formation of Long Gamma Ray-Bursts has been discovered thanks to the inclusion of the aforementioned effects. This scenario suggests that a possibly large fraction of long GRBs occurs in runaway stars. A novel study of convection in massive stars is also presented, showing that microturbulence in the photosphere of hot stars might be caused by the presence of sub-surface convection zones. Such study suggests that clumping in the winds of OB stars could be caused by the same mechanism, and that magnetic fields produced in such sub-surface convection zones could appear at the surface of OB stars.

  17. Onion-peeling inversion of stellarator images

    Science.gov (United States)

    Hammond, K. C.; Diaz-Pacheco, R. R.; Kornbluth, Y.; Volpe, F. A.; Wei, Y.

    2016-11-01

    An onion-peeling technique is developed for inferring the emissivity profile of a stellarator plasma from a two-dimensional image acquired through a CCD or CMOS camera. Each pixel in the image is treated as an integral of emission along a particular line-of-sight. Additionally, the flux surfaces in the plasma are partitioned into discrete layers, each of which is assumed to have uniform emissivity. If the topology of the flux surfaces is known, this construction permits the development of a system of linear equations that can be solved for the emissivity of each layer. We present initial results of this method applied to wide-angle visible images of the Columbia Neutral Torus (CNT) stellarator plasma.

  18. Mass outflows associated with young stellar objects

    Science.gov (United States)

    Strom, Stephen E.; Strom, Karen M.

    1987-01-01

    Properties of optical and molecular outflows associated with young stellar objects are discussed with emphasis placed on new results concerning outflow energetics, collimating structures, and the relationship between the outflow properties and the magnetic field geometry characterizing the host molecular clouds. Particular consideration is given to the IRAS observations of YSO mass outflows, which reveal extended far-IR emission associated with high-velocity molecular gas and in which a number of disk-like structures associated with YSO outflow sources were resolved. The disk axes appeared to lie along the direction of molecular outflows or stellar jets. The mass outflows showed a remarkable tendency to align along the direction of the magnetic fields which thread their host molecular clouds, suggesting that the cloud magnetic field must play an important role in determining the flattening (and perhaps the rotation) of protostellar structures.

  19. Simulating Stellar Cluster Formation and Early Evolution

    Science.gov (United States)

    Wall, Joshua; McMillan, Stephen L. W.; Mac Low, Mordecai-Mark; Ibañez-Mejia, Juan; Portegies Zwart, Simon; Pellegrino, Andrew

    2017-01-01

    We present our current development of a model of stellar cluster formation and evolution in the presence of stellar feedback. We have integrated the MHD code Flash into the Astrophysical Multi-Use Software Environment (AMUSE) and coupled the gas dynamics to an N-body code using a Fujii gravity bridge. Further we have integrated feedback from radiation using the FERVENT module for Flash, supernovae by thermal and kinetic energy injection, and winds by kinetic energy injection. Finally we have developed a method of implementing star formation using the Jeans criterion of the gas. We present initial results from our cluster formation model in a cloud using self-consistent boundary conditions drawn from a model of supernova-driven interstellar turbulence.

  20. Resolving Multiple Stellar Populations in G1

    Science.gov (United States)

    Gregg, Michael

    2017-08-01

    The most luminous and massive compact stellar system in the Local Group is G1, a satellite of M31. It has been speculated that G1 is the remnant nucleus of a tidally stripped dwarf elliptical galaxy. As such, G1 is key to understanding both the evolution of dwarf galaxies and the hierarchical assembly of bright spirals. Recently, new U-B-V-I broad band imaging techniques have revealed multiple stellar populations in Milky Way globular clusters. We propose to obtain new deep WFC3/UVIS F336W and F814W images, to be combined with archival WFC3 data, to probe the star formation and enrichment history of G1. This study will yield new and definitive insights into the origin and evolution of G1, the relationship of globular clusters to dwarf galaxies, and the formation of luminous spirals like M31 and the Milky Way.

  1. Energetic Particle Estimates for Stellar Flares

    Science.gov (United States)

    Youngblood, Allison; Chamberlin, Phil; Woods, Tom

    2018-01-01

    In the heliosphere, energetic particles are accelerated away from the Sun during solar flares and/or coronal mass ejections where they frequently impact the Earth and other solar system bodies. Solar (or stellar) energetic particles (SEPs) not only affect technological assets, but also influence mass loss and chemistry in planetary atmospheres (e.g., depletion of ozone). SEPs are increasingly recognized as an important factor in assessing exoplanet habitability, but we do not yet have constraints on SEP emission from any stars other than the Sun. Until indirect measurements are available, we must assume solar-like particle production and apply correlations between solar flares and SEPs detected near Earth to stellar flares. We present improved scaling relations between solar far-UV flare flux and >10 MeV proton flux near Earth. We apply these solar scaling relations to far-UV flares from exoplanet host stars and discuss the implications for modeling chemistry and mass loss in exoplanet atmospheres.

  2. Stellar evolution as seen by mixed modes

    Directory of Open Access Journals (Sweden)

    Mosser Benoît

    2015-01-01

    Full Text Available The detection of mixed modes in subgiants and red giants allows us to monitor stellar evolution from the main sequence to the asymptotic giant branch and draw seismic evolutionary tracks. Quantified asteroseismic definitions that characterize the change in the evolutionary stages have been defined. This seismic information can now be used for stellar modelling, especially for studying the energy transport in the helium burning core or for specifying the inner properties of stars all along their evolution. Modelling will also allow us to study stars identified in the helium subflash stage, high-mass stars either arriving or quitting the secondary clump, or stars that could be in the blue-loop stage.

  3. Onion-peeling inversion of stellarator images.

    Science.gov (United States)

    Hammond, K C; Diaz-Pacheco, R R; Kornbluth, Y; Volpe, F A; Wei, Y

    2016-11-01

    An onion-peeling technique is developed for inferring the emissivity profile of a stellarator plasma from a two-dimensional image acquired through a CCD or CMOS camera. Each pixel in the image is treated as an integral of emission along a particular line-of-sight. Additionally, the flux surfaces in the plasma are partitioned into discrete layers, each of which is assumed to have uniform emissivity. If the topology of the flux surfaces is known, this construction permits the development of a system of linear equations that can be solved for the emissivity of each layer. We present initial results of this method applied to wide-angle visible images of the Columbia Neutral Torus (CNT) stellarator plasma.

  4. SMASH: Survey of the MAgellanic Stellar History

    Science.gov (United States)

    Nidever, David L.; Olsen, Knut; Walker, Alistair R.; Vivas, A. Katherina; Blum, Robert D.; Kaleida, Catherine; Choi, Yumi; Conn, Blair C.; Gruendl, Robert A.; Bell, Eric F.; Besla, Gurtina; Muñoz, Ricardo R.; Gallart, Carme; Martin, Nicolas F.; Olszewski, Edward W.; Saha, Abhijit; Monachesi, Antonela; Monelli, Matteo; de Boer, Thomas J. L.; Johnson, L. Clifton; Zaritsky, Dennis; Stringfellow, Guy S.; van der Marel, Roeland P.; Cioni, Maria-Rosa L.; Jin, Shoko; Majewski, Steven R.; Martinez-Delgado, David; Monteagudo, Lara; Noël, Noelia E. D.; Bernard, Edouard J.; Kunder, Andrea; Chu, You-Hua; Bell, Cameron P. M.; Santana, Felipe; Frechem, Joshua; Medina, Gustavo E.; Parkash, Vaishali; Serón Navarrete, J. C.; Hayes, Christian

    2017-11-01

    The Large and Small Magellanic Clouds are unique local laboratories for studying the formation and evolution of small galaxies in exquisite detail. The Survey of the MAgellanic Stellar History (SMASH) is an NOAO community Dark Energy Camera (DECam) survey of the Clouds mapping 480 deg2 (distributed over ˜2400 square degrees at ˜20% filling factor) to ˜24th mag in ugriz. The primary goals of SMASH are to identify low surface brightness stellar populations associated with the stellar halos and tidal debris of the Clouds, and to derive spatially resolved star formation histories. Here, we present a summary of the survey, its data reduction, and a description of the first public Data Release (DR1). The SMASH DECam data have been reduced with a combination of the NOAO Community Pipeline, the PHOTRED automated point-spread-function photometry pipeline, and custom calibration software. The astrometric precision is ˜15 mas and the accuracy is ˜2 mas with respect to the Gaia reference frame. The photometric precision is ˜0.5%-0.7% in griz and ˜1% in u with a calibration accuracy of ˜1.3% in all bands. The median 5σ point source depths in ugriz are 23.9, 24.8, 24.5, 24.2, and 23.5 mag. The SMASH data have already been used to discover the Hydra II Milky Way satellite, the SMASH 1 old globular cluster likely associated with the LMC, and extended stellar populations around the LMC out to R ˜ 18.4 kpc. SMASH DR1 contains measurements of ˜100 million objects distributed in 61 fields. A prototype version of the NOAO Data Lab provides data access and exploration tools.

  5. A Golden Decade for Stellar Populations?

    Science.gov (United States)

    Abraham, Roberto G.

    2010-04-01

    People working on stellar populations can look forward to an exciting decade ahead. Investigations of stellar populations lie at the heart of the science cases being used to justify the development of upcoming telescopes and emerging instrumentation technologies. Examples abound, but I will focus on three case studies: (1) Wide field astronomy with upcoming ground-based and space-based survey facilities; (2) Adaptive optics, which has the potential to revolutionize our understanding of stellar populations in both nearby and distant galaxies; (3) The James Webb Space Telescope, which may well extend the reach of stellar population work to encompass the full range of the star-forming history of the Universe. However, most of these developments will require extensive advance preparation in order to be used effectively. The time to start that preparation is now (if not yesterday). Three areas which need urgent development are highlighted in these proceedings: (1) We need a wide-field high-resolution spectroscopic capability to augment wide-area imaging surveys; (2) We need a set of AO-friendly extragalactic deep fields in order to exploit upcoming AO-fed instrumentation; and (3) Existing tools for population synthesis modeling need to be extended in order to incorporate the effects of dust. Because the physics of dust creation and destruction is so complicated and uncertain, the latter capability sounds almost impossibly hard to develop, but in this talk I will argue that some simple approaches already exist that allow dust to be injected rather naturally into population synthesis models. I will show a concrete example where incorporation of dust into spectral synthesis models allows one to detect and characterize rate of formation of circumstellar disks at high redshifts.

  6. Stellarator optimization under several criteria using metaheuristics

    Science.gov (United States)

    Castejón, F.; Gómez-Iglesias, A.; Vega-Rodríguez, M. A.; Jiménez, J. A.; Velasco, J. L.; Romero, J. A.

    2013-01-01

    A new algorithm based on metaheuristics has been developed to perform stellarator optimization. This algorithm, which is inspired by the behaviour of bees and is called distributed asynchronous bees, has been used for the optimization under three criteria: minimization of B × grad(B) drift, Mercier and ballooning stability. This algorithm is tested by partially optimizing TJ-II and, afterwards, a three-period optimized configuration is found by performing a full optimization that starts from a three-period heliac.

  7. Clustering in the stellar abundance space

    Science.gov (United States)

    Boesso, R.; Rocha-Pinto, H. J.

    2018-03-01

    We have studied the chemical enrichment history of the interstellar medium through an analysis of the n-dimensional stellar abundance space. This work is a non-parametric analysis of the stellar chemical abundance space. The main goal is to study the stars from their organization within this abundance space. Within this space, we seek to find clusters (in a statistical sense), that is, stars likely to share similar chemo-evolutionary history, using two methods: the hierarchical clustering and the principal component analysis. We analysed some selected abundance surveys available in the literature. For each sample, we labelled the group of stars according to its average abundance curve. In all samples, we identify the existence of a main enrichment pattern of the stars, which we call chemical enrichment flow. This flow is set by the structured and well-defined mean rate at which the abundances of the interstellar medium increase, resulting from the mixture of the material ejected from the stars and stellar mass-loss and interstellar medium gas. One of the main results of our analysis is the identification of subgroups of stars with peculiar chemistry. These stars are situated in regions outside of the enrichment flow in the abundance space. These peculiar stars show a mismatch in the enrichment rate of a few elements, such as Mg, Si, Sc and V, when compared to the mean enrichment rate of the other elements of the same stars. We believe that the existence of these groups of stars with peculiar chemistry may be related to the accretion of planetary material on to stellar surfaces or may be due to production of the same chemical element by different nucleosynthetic sites.

  8. SMASH: Survey of the MAgellanic Stellar History

    Energy Technology Data Exchange (ETDEWEB)

    Nidever, David L.; Olsen, Knut; Blum, Robert D.; Saha, Abhijit [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Walker, Alistair R.; Vivas, A. Katherina [Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory, Casilla 603, La Serena (Chile); Kaleida, Catherine [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Choi, Yumi; Besla, Gurtina; Olszewski, Edward W. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson AZ, 85721 (United States); Conn, Blair C. [Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611 (Australia); Gruendl, Robert A. [National Center for Supercomputing Applications, 1205 West Clark Street, Urbana, IL 61801 (United States); Bell, Eric F. [Department of Astronomy, University of Michigan, 1085 S. University Avenue, Ann Arbor, MI 48109-1107 (United States); Muñoz, Ricardo R. [Departamento de Astronomía, Universidad de Chile, Camino del Observatorio 1515, Las Condes, Santiago (Chile); Gallart, Carme; Monelli, Matteo [Instituto de Astrofísica de Canarias, La Laguna, Tenerife (Spain); Martin, Nicolas F. [Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg, UMR 7550, F-67000 Strasbourg (France); Monachesi, Antonela [Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, D-85748 Garching (Germany); De Boer, Thomas J. L. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Johnson, L. Clifton, E-mail: dnidever@noao.edu [Center for Astrophysics and Space Sciences, UC San Diego, 9500 Gilman Drive, La Jolla, CA, 92093-0424 (United States); and others

    2017-11-01

    The Large and Small Magellanic Clouds are unique local laboratories for studying the formation and evolution of small galaxies in exquisite detail. The Survey of the MAgellanic Stellar History (SMASH) is an NOAO community Dark Energy Camera (DECam) survey of the Clouds mapping 480 deg{sup 2} (distributed over ∼2400 square degrees at ∼20% filling factor) to ∼24th mag in ugriz . The primary goals of SMASH are to identify low surface brightness stellar populations associated with the stellar halos and tidal debris of the Clouds, and to derive spatially resolved star formation histories. Here, we present a summary of the survey, its data reduction, and a description of the first public Data Release (DR1). The SMASH DECam data have been reduced with a combination of the NOAO Community Pipeline, the PHOTRED automated point-spread-function photometry pipeline, and custom calibration software. The astrometric precision is ∼15 mas and the accuracy is ∼2 mas with respect to the Gaia reference frame. The photometric precision is ∼0.5%–0.7% in griz and ∼1% in u with a calibration accuracy of ∼1.3% in all bands. The median 5 σ point source depths in ugriz are 23.9, 24.8, 24.5, 24.2, and 23.5 mag. The SMASH data have already been used to discover the Hydra II Milky Way satellite, the SMASH 1 old globular cluster likely associated with the LMC, and extended stellar populations around the LMC out to R  ∼ 18.4 kpc. SMASH DR1 contains measurements of ∼100 million objects distributed in 61 fields. A prototype version of the NOAO Data Lab provides data access and exploration tools.

  9. Solar and stellar flare observations using WATCH

    DEFF Research Database (Denmark)

    Brandt, Søren; Lund, Niels; Rao, A. R.

    1988-01-01

    The Danish experiment WATCH (Wide Angle Telescope for Cosmic Hard X-rays) is to be flown on board the Soviet satellite GRANAT in middle of 1989. The performance characteristics of the WATCH instrument is described. It is estimated that WATCH can detect about 100 solar hard X-ray bursts per day....... WATCH can also detect about 40 energetic stellar soft X-ray flares, similar to the fast transient X-ray emissions detected by the Ariel V satellite....

  10. Young stellar objects close to Sgr A*

    Science.gov (United States)

    Jalali, B.; Pelupessy, F. I.; Eckart, A.; Portegies Zwart, S.; Sabha, N.; Borkar, A.; Moultaka, J.; Mužić, K.; Moser, L.

    2014-05-01

    We aim at modeling small groups of young stars such as IRS 13N, 0.1 pc away from Sgr A*, which is suggested to contain a few embedded massive young stellar objects. We perform hydrodynamical simulations to follow the evolution of molecular clumps orbiting around a 4 × 106 M⊙ black hole, to constrain the formation and the physical conditions of such groups.

  11. The Stellar Imager (SI) Mission Concept

    Science.gov (United States)

    Carpenter, Kenneth S.; Schrijver, Carolus J.; Oegerle, William R. (Technical Monitor)

    2002-01-01

    The Stellar Imager (SI) is envisioned as a space-based, UV-optical interferometer composed of 10 or more one-meter class elements distributed with a maximum baseline of 0.5 approximately km. It will image stars and binaries with one hundred to one thousand resolution elements on their surface and enable long-term studies of stellar magnetic activity patterns and their evolution with time, for comparison with those on the sun. It will also sound their interiors through asteroseismology to image internal structure, differential rotation, and large-scale circulations. SI will enable us to understand the various effects of magnetic fields of stars, the dynamos that generate these fields, and the internal structure and dynamics of the stars in which these dynamos operate. The ultimate goal of the mission is to achieve the best possible forecasting of solar activity as a driver of climate and space weather on times scales ranging from months to decades, and an understanding of the impact of stellar magnetic activity on astrobiology and life in the Universe. The road to that goal will revolutionize our understanding of stars and stellar systems, the building blocks of the Universe. Fitting naturally within the NASA and ESA long-term time lines, SI complements defined missions, and with them will show us entire other solar systems, from the central star to their orbiting planets. In this paper we will describe the scientific goals of the mission, the performance requirements needed to address those goals, and the design concepts now under study.

  12. Numerical studies of new stellarator concepts

    Science.gov (United States)

    Bauer, F.; Betancourt, O.; Garabedian, P.

    1980-01-01

    A three-dimensional computer code has been developed to study the magnetohydrodynamic equilibrium and stability of a diffuse or sharp boundary plasma in toroidal geometry. It is shown how equilibria with net toroidal current identically zero can be determined and how growth rates of instabilities can be calculated. Applications are made to an l = 2, 3 stellarator configuration that offers the possibility of achieving a critical value as high as 10% for the plasma parameter

  13. The role of multiple parton collisions in hadron collisions

    CERN Document Server

    Walker, W D

    2000-01-01

    We have examined charged multiplicities arising from p-p and p-p collisions over the range of center of mass energies from 30 GeV to 1800 GeV. We find that a portion of each distribution does obey KNO scaling. Those parts of the distributions that do not scale are the result of multiparton collisions. Results from experiment E735 show not only double but also triple parton collisions. These multiparton collisions seem to account for a large part of the increase in the cross section in this energy domain. (4 refs).

  14. Stellar Cosmic Rays in a Habitable Zone

    Science.gov (United States)

    Struminsky, A.; Sadovski, A.

    2017-06-01

    According to recent observations, relative number of flare stars does not change very much from cool dwarfs to hot A stars. Flare energies are strongly correlated with stellar luminosity and radius. Whence it follows that the typical magnetic field associated with a flare is several tens of gauss and the typical flare loop length-scales are parts of the stellar radius. Flares on O-B stars were not observed, but they are possible, since strong magnetic fields are detected on O-B stars. Therefore, stars of O-M spectral classes are potential sources of cosmic rays. Energy estimates of a magnetic field strength in a tube in photospheres of O-M stars are performed. Basing on their values possible flare energies and numbers of accelerated protons are estimated. The values obtained for the Sun correspond to observations by order of magnitude that justify estimates for other stars. Values of magnetic field strength in a tube differ less than five times for O and M flares (700 and 3500 G), but corresponding flare energies and numbers of accelerated protons for O stars are greater by five orders. Contrary fluencies of stellar protons appear to be five orders less.

  15. STELLAR: fast and exact local alignments

    Directory of Open Access Journals (Sweden)

    Weese David

    2011-10-01

    Full Text Available Abstract Background Large-scale comparison of genomic sequences requires reliable tools for the search of local alignments. Practical local aligners are in general fast, but heuristic, and hence sometimes miss significant matches. Results We present here the local pairwise aligner STELLAR that has full sensitivity for ε-alignments, i.e. guarantees to report all local alignments of a given minimal length and maximal error rate. The aligner is composed of two steps, filtering and verification. We apply the SWIFT algorithm for lossless filtering, and have developed a new verification strategy that we prove to be exact. Our results on simulated and real genomic data confirm and quantify the conjecture that heuristic tools like BLAST or BLAT miss a large percentage of significant local alignments. Conclusions STELLAR is very practical and fast on very long sequences which makes it a suitable new tool for finding local alignments between genomic sequences under the edit distance model. Binaries are freely available for Linux, Windows, and Mac OS X at http://www.seqan.de/projects/stellar. The source code is freely distributed with the SeqAn C++ library version 1.3 and later at http://www.seqan.de.

  16. Intrinsic Turbulence Stabilization in a Stellarator

    Directory of Open Access Journals (Sweden)

    P. Xanthopoulos

    2016-06-01

    Full Text Available The magnetic surfaces of modern stellarators are characterized by complex, carefully optimized shaping and exhibit locally compressed regions of strong turbulence drive. Massively parallel computer simulations of plasma turbulence reveal, however, that stellarators also possess two intrinsic mechanisms to mitigate the effect of this drive. In the regime where the length scale of the turbulence is very small compared to the equilibrium scale set by the variation of the magnetic field, the strongest fluctuations form narrow bandlike structures on the magnetic surfaces. Thanks to this localization, the average transport through the surface is significantly smaller than that predicted at locations of peak turbulence. This feature results in a numerically observed upshift of the onset of turbulence on the surface towards higher ion temperature gradients as compared with the prediction from the most unstable regions. In a second regime lacking scale separation, the localization is lost and the fluctuations spread out on the magnetic surface. Nonetheless, stabilization persists through the suppression of the large eddies (relative to the equilibrium scale, leading to a reduced stiffness for the heat flux dependence on the ion temperature gradient. These fundamental differences with tokamak turbulence are exemplified for the QUASAR stellarator [G. H. Neilson et al., IEEE Trans. Plasma Sci. 42, 489 (2014].

  17. A method to deconvolve stellar rotational velocities

    Science.gov (United States)

    Curé, Michel; Rial, Diego F.; Christen, Alejandra; Cassetti, Julia

    2014-05-01

    Aims: Rotational speed is an important physical parameter of stars, and knowing the distribution of stellar rotational velocities is essential for understanding stellar evolution. However, rotational speed cannot be measured directly and is instead the convolution between the rotational speed and the sine of the inclination angle v sin i. Methods: We developed a method to deconvolve this inverse problem and obtain the cumulative distribution function for stellar rotational velocities extending the work of Chandrasekhar & Münch (1950, ApJ, 111, 142) Results: This method is applied: a) to theoretical synthetic data recovering the original velocity distribution with a very small error; and b) to a sample of about 12.000 field main-sequence stars, corroborating that the velocity distribution function is non-Maxwellian, but is better described by distributions based on the concept of maximum entropy, such as Tsallis or Kaniadakis distribution functions. Conclusions: This is a very robust and novel method that deconvolves the rotational velocity cumulative distribution function from a sample of v sin i data in a single step without needing any convergence criteria.

  18. Non-resonant divertors for stellarators

    Science.gov (United States)

    Boozer, Allen; Punjabi, Alkesh

    2017-10-01

    The outermost confining magnetic surface in optimized stellarators has sharp edges, which resemble tokamak X-points. The plasma cross section has an even number of edges at the beginning but an odd number half way through the period. Magnetic field lines cannot cross sharp edges, but stellarator edges have a finite length and do not determine the rotational transform on the outermost confining surface. Just outside the last confining surface, surfaces formed by magnetic field lines have splits containing two adjacent magnetic flux tubes: one with entering and the other with an equal existing flux to the walls. The splits become wider with distance outside the outermost confining surface. These flux tubes form natural non-resonant stellarator divertors, which we are studying using maps. This work is supported by the US DOE Grants DE-FG02-95ER54333 to Columbia University and DE-FG02-01ER54624 and DE-FG02-04ER54793 to Hampton University and used resources of the NERSC, supported by the Office of Science, US DOE, under Contract No. DE-AC02-.

  19. A 2017 stellar occultation by Orcus/Vanth

    Science.gov (United States)

    Sickafoose, Amanda A.; Bosh, Amanda S.; Levine, Stephen; Zuluaga, Carlos A.; Genade, Anja; Schindler, Karsten; Lister, Tim; Person, Michael J.

    2017-10-01

    (90482) Orcus is a large trans-Neptunian object (TNO) of diameter ~900 km, located in the 3:2 orbital resonance with Neptune. This plutino has a satellite, Vanth, approximately 280 km in diameter. Vanth orbits roughly 9000 km from Orcus in a ~9.5-day period. This system is particularly interesting, as Orcus falls between the small, spectrally-bland TNOs and the large TNOs having spectra rich in volatile features, while Vanth might have resulted from either collision or capture.A stellar occultation by Orcus was predicted to occur on 07 March 2017. Observations were made from five sites: the 0.6-m Astronomical Telescope of the University of Stuttgart (ATUS) at Sierra Remote Observatories (SRO), California; Las Cumbres Observatory’s 1-m telescope (ELP) at McDonald Observatory, Fort Davis, Texas; NASA’s 3-m InfraRed Telescope Facility (IRTF) on Mauna Kea, Hawaii; the 4.1-m Southern Astrophysical Research telescope (SOAR) on Cerro Pachón, Chile; and the 0.6-m Southeastern Association for Research in Astronomy telescope (SARA-CT) at Cerro Tololo, Chile. High-speed, visible-wavelength images were taken at all sites, in addition to simultaneous K-band images at the IRTF. A solid-body occultation was observed at both ELP and the IRTF. Offset midtimes and incompatible light ratios suggest that two different stars were occulted by two different bodies, likely Orcus and Vanth. See Bosh et al. this conference for details of the astrometry for the event. Here, we present results from the observations, including light curves, size and albedo estimates, and upper limits on a possible atmosphere.

  20. Origins of altruism diversity II: Runaway coevolution of altruistic strategies via "reciprocal niche construction".

    Science.gov (United States)

    Van Dyken, J David; Wade, Michael J

    2012-08-01

    Understanding the evolution of altruism requires knowledge of both its constraints and its drivers. Here we show that, paradoxically, ecological constraints on altruism may ultimately be its strongest driver. We construct a two-trait, coevolutionary adaptive dynamics model of social evolution in a genetically structured population with local resource competition. The intensity of local resource competition, which influences the direction and strength of social selection and which is typically treated as a static parameter, is here allowed to be an evolvable trait. Evolution of survival/fecundity altruism, which requires weak local competition, increases local competition as it evolves, creating negative environmental feedback that ultimately inhibits its further evolutionary advance. Alternatively, evolution of resource-based altruism, which requires strong local competition, weakens local competition as it evolves, also ultimately causing its own evolution to stall. When evolving independently, these altruistic strategies are intrinsically self-limiting. However, the coexistence of these two altruism types transforms the negative ecoevolutionary feedback generated by each strategy on itself into positive feedback on the other, allowing the presence of one trait to drive the evolution of the other. We call this feedback conversion "reciprocal niche construction." In the absence of constraints, this process leads to runaway coevolution of altruism types. We discuss applications to the origins and evolution of eusociality, division of labor, the inordinate ecological success of eusocial species, and the interaction between technology and demography in human evolution. Our theory suggests that the evolution of extreme sociality may often be an autocatalytic process. © 2012 The Author(s). Evolution© 2012 The Society for the Study of Evolution.

  1. A Semenov approach to the modelling of thermal runaway of damp combustible material

    Science.gov (United States)

    McIntosh, A. C.

    1993-01-01

    Semenov theory for the self-heating of a reactive slab is extended to take account of the presence of water vapour. In this paper, mass changes due to evaporation/condensation are neglected but heat exchange is retained in the energy equation. By doing this, a simple easily solvable set of equations can be set up to represent the thermal behaviour of the slab. No account is taken of possible wet exothermic reactions in this paper. The aim is simply to understand the effects of evaporation/condensation on the overall thermal history. Using a simple model which treats the mass changes within the material as negligible, the competitive effects of condensation and evaporation are shown to produce a two-time situation which depends crucially on the surface mass transfer/heat transfer ratio hm. Either self-heating occurs at a lower rate than that due to dry oxidation, or else a maximum temperature is reached before a lower equilibrium steady-state temperature is achieved. Thus, compared to the dry case, in general terms, evaporation certainly encourages stability. However, the final strictly subcritical steady state will not always be achieved due to the competitive process between recondensation and evaporation loss at the surface at medium timescales. A set of quasi-steady states is identified which yield plots of a more restrictive critical value of temperature against the Frank-Kamenetskii parameter (proportional to the thickness of the slab and its reactivity). If the value of hm is such that the maximum temperature reaches this critical value, then thermal runaway can still take place even though the starting value of temperature was strictly below the true (damp) final steady-state critical value.

  2. Early humans' egalitarian politics: runaway synergistic competition under an adapted veil of ignorance.

    Science.gov (United States)

    Harvey, Marc

    2014-09-01

    This paper proposes a model of human uniqueness based on an unusual distinction between two contrasted kinds of political competition and political status: (1) antagonistic competition, in quest of dominance (antagonistic status), a zero-sum, self-limiting game whose stake--who takes what, when, how--summarizes a classical definition of politics (Lasswell 1936), and (2) synergistic competition, in quest of merit (synergistic status), a positive-sum, self-reinforcing game whose stake becomes "who brings what to a team's common good." In this view, Rawls's (1971) famous virtual "veil of ignorance" mainly conceals politics' antagonistic stakes so as to devise the principles of a just, egalitarian society, yet without providing any means to enforce these ideals (Sen 2009). Instead, this paper proposes that human uniqueness flourished under a real "adapted veil of ignorance" concealing the steady inflation of synergistic politics which resulted from early humans' sturdy egalitarianism. This proposition divides into four parts: (1) early humans first stumbled on a purely cultural means to enforce a unique kind of within-team antagonistic equality--dyadic balanced deterrence thanks to handheld weapons (Chapais 2008); (2) this cultural innovation is thus closely tied to humans' darkest side, but it also launched the cumulative evolution of humans' brightest qualities--egalitarian team synergy and solidarity, together with the associated synergistic intelligence, culture, and communications; (3) runaway synergistic competition for differential merit among antagonistically equal obligate teammates is the single politically selective mechanism behind the cumulative evolution of all these brighter qualities, but numerous factors to be clarified here conceal this mighty evolutionary driver; (4) this veil of ignorance persists today, which explains why humans' unique prosocial capacities are still not clearly understood by science. The purpose of this paper is to start lifting

  3. First direct observation of runaway electron-driven whistler waves in tokamaks

    Science.gov (United States)

    Spong, Donald A.

    2017-10-01

    Whistlers are electromagnetic waves that can be driven unstable by energetic electrons and are observed in natural plasmas, such as the ionosphere and Van Allen belts. Recent DIII-D experiments at low density demonstrate the first direct observation of whistlers in tokamaks, with 100-200 MHz waves excited by runaway electrons (REs) in the multi-MeV range. Whistler activity is correlated with RE intensity and the frequencies scale with magnetic field strength and electron density consistent with a whistler dispersion relation. Fluctuations occur in discrete frequency bands, and not a continuum as would be expected from plane wave analysis, suggesting the important role of toroidicity. An MHD model including the bounded/periodic nature of the plasma identifies multiple eigenmode branches. For a toroidal mode number n = 10, the predicted frequencies and spacing are similar to observations. The instabilities are stabilized with increasing magnetic field, as expected from the anomalous Doppler resonance. The whistler amplitudes show intermittent time variations. Predator-prey cycles with electron cyclotron emission (ECE) signals are observed, which can be interpreted as wave-induced pitch angle scattering of moderate energy REs. Such nonlinear dynamics are supported by quasi-linear simulations indicating that REs are scattered both by whistlers and high frequency magnetized plasma waves. The whistler wave predominantly scatters the high energy REs, while the magnetized plasma wave scatters the low energy REs, abruptly enhancing the ECE signal. Amplitude variations are also associated with sawtooth activity, indicating that the REs sample the q = 1 surface. These features of the RE-driven whistler have connections to ionospheric plasmas and open up new directions for the modeling and active control of tokamak REs. Work supported by the US DOE under DE-FC02-04ER54698, DE-AC52-07NA27344, DE-FG02-07ER54917, DE-SC00-16268, and DE-AC05-00OR22725.

  4. Runaway Competition: A Correction and Extension of Results for a Model of Competitive Helping.

    Science.gov (United States)

    Wild, Erin; Cojocaru, Monica Gabriela

    2016-01-01

    We investigate and generalize an existing model of competitive helping within a biological market, first introduced for a population of competing individuals in which one individual provides help to all others; the rest compete for the help available from this individual by providing help themselves. Our generalized model comprises two strategies in which each individual of a specific type provides the same amount of help as all other individuals of that type. Each individual's fitness function is dependent on this level of help, the cost of providing the help, and the fact that help is proportionally reciprocated by other individuals. Competitive helping occurs when individuals actively try to help more than other individuals. To assess the emergence of equilibrium help strategies as adopted by proportions of the population, we examine the competition over available help within two settings: replicator dynamics and agent-based numerical simulations. To move one step further in our generalization, we use the agent-based model to study the N-person competitive helping game, where all individuals in the population are heterogeneous with respect to help provided. Our results show that helping does not increase indefinitely with the population size, as concluded previously, and while there are some instances of an increase in help provided as a result of competition, this competition can be detrimental to all individuals and in most cases, one type simply gives up (thus evolving to a "no help" strategy). The degree to which an individual's help is reciprocated by the others in the population has strong implications in the long-term behaviour of equilibrium help levels of types of individuals (and of individuals themselves); these equilibrium help levels diverge from existing conjectures in current literature. Lastly, small amounts of passively provided (costless) help results in runaway competition among all individuals.

  5. Road rage and collision involvement.

    Science.gov (United States)

    Mann, Robert E; Zhao, Jinhui; Stoduto, Gina; Adlaf, Edward M; Smart, Reginald G; Donovan, John E

    2007-01-01

    To assess the contribution of road rage victimization and perpetration to collision involvement. The relationship between self-reported collision involvement and road rage victimization and perpetration was examined, based on telephone interviews with a representative sample of 4897 Ontario adult drivers interviewed between 2002 and 2004. Perpetrators and victims of both any road rage and serious road rage had a significantly higher risk of collision involvement than did those without road rage experience. This study provides epidemiological evidence that both victims and perpetrators of road rage experience increased collision risk. More detailed studies of the contribution of road rage to traffic crashes are needed.

  6. Topics in atomic collision theory

    CERN Document Server

    Geltman, Sydney; Brueckner, Keith A

    1969-01-01

    Topics in Atomic Collision Theory originated in a course of graduate lectures given at the University of Colorado and at University College in London. It is recommended for students in physics and related fields who are interested in the application of quantum scattering theory to low-energy atomic collision phenomena. No attention is given to the electromagnetic, nuclear, or elementary particle domains. The book is organized into three parts: static field scattering, electron-atom collisions, and atom-atom collisions. These are in the order of increasing physical complexity and hence necessar

  7. Relations among stellar X-ray emission observed from Einstein, stellar rotation and bolometric luminosity

    Science.gov (United States)

    Pallavicini, R.; Golub, L.; Rosner, R.; Vaiana, G. S.; Ayres, T.; Linsky, J. L.

    1981-01-01

    The correlation between observed stellar X-ray luminosities, bolometric luminosities, and projected rotational velocities for stars of various spectral types and luminosity classes are determined. Early type stars (O3 to A5) have X-ray luminosities independent of rotational velocities, and correlating with bolometric luminosities. Late type stars of spectral type G to M have luminosities well correlated to equatorial rotational velocities, and are independent of luminosity class. The dependence of late type stars is found to be equivalent to a relation between the X-ray surface flux and the stellar angular velocity. F stars are intermediate with X-ray luminosities higher than would be predicted on the basis of the early type star relation, although lower than expected from the late type velocity dependence. The location of RS CVn stars as a class is also discussed, and it is found that the heating of late type stellar coronas does not result from direct conversion of ratational energy.

  8. A unified treatment of self-sputtering, process gas recycling, and runaway for high power impulse sputtering magnetrons

    Science.gov (United States)

    Brenning, N.; Gudmundsson, J. T.; Raadu, M. A.; Petty, T. J.; Minea, T.; Lundin, D.

    2017-12-01

    The combined processes of self-sputter (SS)-recycling and process gas recycling in high power impulse magnetron sputtering (HiPIMS) discharges are analyzed using the generalized recycling model (GRM). The study uses experimental data from discharges with current densities from the direct current magnetron sputtering range to the HiPIMS range, and using targets with self-sputter yields Y SS from ≈ 0.1 to 2.6. The GRM analysis reveals that, above a critical current density of the order of J crit ≈ 0.2 A cm‑2, a combination of self-sputter recycling and gas-recycling is generally the case. The relative contributions of these recycling mechanisms, in turn, influence both the electron energy distribution and the stability of the discharges. For high self-sputter yields, above Y SS ≈ 1, the discharges become dominated by SS-recycling, contain few hot secondary electrons from sheath energization, and have a relatively low electron temperature T e. Here, stable plateau values of the discharge current develop during long pulses, and these values increase monotonically with the applied voltage. For low self-sputter yields, below Y SS ≈ 0.2, the discharges above J crit are dominated by process gas recycling, have a significant sheath energization of secondary electrons and a higher T e, and the current evolution is generally less stable. For intermediate values of Y SS the discharge character gradually shifts between these two types. All of these discharges can, at sufficiently high discharge voltage, give currents that increase rapidly in time. For such cases we propose that a distinction should be made between ‘unlimited’ runaway and ‘limited’ runaway: in unlimited runaway the current can, in principle, increase without a limit for a fixed discharge voltage, while in limited runaway it can only grow towards finite, albeit very high, levels. For unlimited runway Y SS > 1 is found to be a necessary criterion, independent of the amount of gas-recycling in the

  9. Estimating inelastic heavy-particle-hydrogen collision data. I. Simplified model and application to potassium-hydrogen collisions

    Science.gov (United States)

    Belyaev, Andrey K.; Yakovleva, Svetlana A.

    2017-10-01

    Aims: We derive a simplified model for estimating atomic data on inelastic processes in low-energy collisions of heavy-particles with hydrogen, in particular for the inelastic processes with high and moderate rate coefficients. It is known that these processes are important for non-LTE modeling of cool stellar atmospheres. Methods: Rate coefficients are evaluated using a derived method, which is a simplified version of a recently proposed approach based on the asymptotic method for electronic structure calculations and the Landau-Zener model for nonadiabatic transition probability determination. Results: The rate coefficients are found to be expressed via statistical probabilities and reduced rate coefficients. It turns out that the reduced rate coefficients for mutual neutralization and ion-pair formation processes depend on single electronic bound energies of an atom, while the reduced rate coefficients for excitation and de-excitation processes depend on two electronic bound energies. The reduced rate coefficients are calculated and tabulated as functions of electronic bound energies. The derived model is applied to potassium-hydrogen collisions. For the first time, rate coefficients are evaluated for inelastic processes in K+H and K++H- collisions for all transitions from ground states up to and including ionic states. Tables with calculated data are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/606/A147

  10. Estimating precise metallicity and stellar mass evolution of galaxies

    Science.gov (United States)

    Mosby, Gregory

    2018-01-01

    The evolution of galaxies can be conveniently broken down into the evolution of their contents. The changing dust, gas, and stellar content in addition to the changing dark matter potential and periodic feedback from a super-massive blackhole are some of the key ingredients. We focus on the stellar content that can be observed, as the stars reflect information about the galaxy when they were formed. We approximate the stellar content and star formation histories of unresolved galaxies using stellar population modeling. Though simplistic, this approach allows us to reconstruct the star formation histories of galaxies that can be used to test models of galaxy formation and evolution. These models, however, suffer from degeneracies at large lookback times (t > 1 Gyr) as red, low luminosity stars begin to dominate a galaxy’s spectrum. Additionally, degeneracies between stellar populations at different ages and metallicities often make stellar population modeling less precise. The machine learning technique diffusion k-means has been shown to increase the precision in stellar population modeling using a mono-metallicity basis set. However, as galaxies evolve, we expect the metallicity of stellar populations to vary. We use diffusion k-means to generate a multi-metallicity basis set to estimate the stellar mass and chemical evolution of unresolved galaxies. Two basis sets are formed from the Bruzual & Charlot 2003 and MILES stellar population models. We then compare the accuracy and precision of these models in recovering complete (stellar mass and metallicity) histories of mock data. Similarities in the groupings of stellar population spectra in the diffusion maps for each metallicity hint at fundamental age transitions common to both basis sets that can be used to identify stellar populations in a given age range.

  11. Stellarator Research Opportunities: A report of the National Stellarator Coordinating Committee

    Energy Technology Data Exchange (ETDEWEB)

    Gates, David A. [Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); Anderson, David [University of Wisconsin-Madison

    2017-06-01

    This document is the product of a stellarator community workshop, organized by the National Stellarator Coordinating Committee and referred to as Stellcon, that was held in Cambridge, Massachusetts in February 2016, hosted by MIT. The workshop was widely advertised, and was attended by 40 scientists from 12 different institutions including national labs, universities and private industry, as well as a representative from the Department of Energy. The final section of this document describes areas of community wide consensus that were developed as a result of the discussions held at that workshop. Areas where further study would be helpful to generate a consensus path forward for the US stellarator program are also discussed. The program outlined in this document is directly responsive to many of the strategic priorities of FES as articulated in “Fusion Energy Sciences: A Ten-Year Perspective (2015-2025)” [2]. The natural disruption immunity of the stellarator directly addresses “Elimination of transient events that can be deleterious to toroidal fusion plasma confinement devices” an area of critical importance for the U.S. fusion energy sciences enterprise over the next decade. Another critical area of research “Strengthening our partnerships with international research facilities,” is being significantly advanced on the W7-X stellarator in Germany and serves as a test-bed for development of successful international collaboration on ITER. This report also outlines how materials science as it relates to plasma and fusion sciences, another critical research area, can be carried out effectively in a stellarator. Additionally, significant advances along two of the Research Directions outlined in the report; “Burning Plasma Science: Foundations - Next-generation research capabilities”, and “Burning Plasma Science: Long pulse - Sustainment of Long-Pulse Plasma Equilibria” are proposed.

  12. Massive stars reveal variations of the stellar initial mass function in the Milky Way stellar clusters

    Science.gov (United States)

    Dib, Sami; Schmeja, Stefan; Hony, Sacha

    2017-01-01

    We investigate whether the stellar initial mass function (IMF) is universal, or whether it varies significantly among young stellar clusters in the Milky Way. We propose a method to uncover the range of variation of the parameters that describe the shape of the IMF for the population of young Galactic clusters.These parameters are the slopes in the low and high stellar mass regimes, γ and Γ, respectively, and the characteristic mass, Mch. The method relies exclusively on the high-mass content of the clusters, but is able to yield information on the distributions of parameters that describe the IMF over the entire stellar mass range. This is achieved by comparing the fractions of single and lonely massive O stars in a recent catalogue of the Milky Way clusters with a library of simulated clusters built with various distribution functions of the IMF parameters. The synthetic clusters are corrected for the effects of the binary population, stellar evolution, sample incompleteness, and ejected O stars. Our findings indicate that broad distributions of the IMF parameters are required in order to reproduce the fractions of single and lonely O stars in Galactic clusters. They also do not lend support to the existence of a cluster mass-maximum stellar mass relation. We propose a probabilistic formulation of the IMF whereby the parameters of the IMF are described by Gaussian distribution functions centred around γ = 0.91, Γ = 1.37, and Mch = 0.41 M⊙, and with dispersions of σγ = 0.25, σΓ = 0.60, and σ _{M_{ch}}=0.27 M⊙ around these values.

  13. Habitability in different Milky Way stellar environments: a stellar interaction dynamical approach.

    Science.gov (United States)

    Jiménez-Torres, Juan J; Pichardo, Bárbara; Lake, George; Segura, Antígona

    2013-05-01

    Every Galactic environment is characterized by a stellar density and a velocity dispersion. With this information from literature, we simulated flyby encounters for several Galactic regions, numerically calculating stellar trajectories as well as orbits for particles in disks; our aim was to understand the effect of typical stellar flybys on planetary (debris) disks in the Milky Way Galaxy. For the solar neighborhood, we examined nearby stars with known distance, proper motions, and radial velocities. We found occurrence of a disturbing impact to the solar planetary disk within the next 8 Myr to be highly unlikely; perturbations to the Oort cloud seem unlikely as well. Current knowledge of the full phase space of stars in the solar neighborhood, however, is rather poor; thus we cannot rule out the existence of a star that is more likely to approach than those for which we have complete kinematic information. We studied the effect of stellar encounters on planetary orbits within the habitable zones of stars in more crowded stellar environments, such as stellar clusters. We found that in open clusters habitable zones are not readily disrupted; this is true if they evaporate in less than 10(8) yr. For older clusters the results may not be the same. We specifically studied the case of Messier 67, one of the oldest open clusters known, and show the effect of this environment on debris disks. We also considered the conditions in globular clusters, the Galactic nucleus, and the Galactic bulge-bar. We calculated the probability of whether Oort clouds exist in these Galactic environments.

  14. Constraining stellar physics from red-giant stars in binaries – stellar rotation, mixing processes and stellar activity

    Directory of Open Access Journals (Sweden)

    Beck P. G.

    2017-01-01

    Full Text Available The unparalleled photometric data obtained by NASA’s Kepler Space Telescope has led to an improved understanding of stellar structure and evolution - in particular for solar-like oscillators in this context. Binary stars are fascinating objects. Because they were formed together, binary systems provide a set of two stars with very well constrained parameters. Those can be used to study properties and physical processes, such as the stellar rotation, dynamics and rotational mixing of elements and allows us to learn from the differences we find between the two components. In this work, we discussed a detailed study of the binary system KIC 9163796, discovered through Kepler photometry. The ground-based follow-up spectroscopy showed that this system is a double-lined spectroscopic binary, with a mass ratio close to unity. However, the fundamental parameters of the components of this system as well as their lithium abundances differ substantially. Kepler photometry of this system allows to perform a detailed seismic analysis as well as to derive the orbital period and the surface rotation rate of the primary component of the system. Indications of the seismic signature of the secondary are found. The differing parameters are best explained with both components located in the early and the late phase of the first dredge up at the bottom of the red-giant branch. Observed lithium abundances in both components are in good agreement with prediction of stellar models including rotational mixing. By combining observations and theory, a comprehensive picture of the system can be drawn.

  15. The Effects of Stellar Dynamics on the Evolution of Young, Dense Stellar Systems

    Science.gov (United States)

    Belkus, H.; van Bever, J.; Vanbeveren, D.

    In this paper, we report on first results of a project in Brussels in which we study the effects of stellar dynamics on the evolution of young dense stellar systems using 3 decades of expertise in massive-star evolution and our population (number and spectral) synthesis code. We highlight an unconventionally formed object scenario (UFO-scenario) for Wolf Rayet binaries and study the effects of a luminous blue variable-type instability wind mass-loss formalism on the formation of intermediate-mass black holes.

  16. The runaway Greenhouse revisited: it's "theoretically possible for an Earth-like planet at 1 AU", plus implications for more diverse planets

    Science.gov (United States)

    Goldblatt, C.; Zahnle, K. J.; Crisp, D.; Robinson, T. D.

    2013-12-01

    For water-vapour rich atmospheres, there is an asymptotic limit on thermal emission to space. If more sunlight is absorbed than this limit, energy balance is no longer possible and runaway heating occurs, evaporating the ocean and sterilizing the planet en route. Here, we present recently published work (Goldblatt et al., 2013) which was the first full re-evaluation of the problem since classic 1980's era work (e.g. Watson et al., 1984; Abe & Matsui, 1988; Kasting, 1988). With modern molecular absorption databases and a line-by-line resolution model, we find that the thermal limit is lower than previous estimates (282Wm-2, down from 310Wm-2) and that much more sunlight is absorbed by a steam atmosphere (294Wm-2, up from 222Wm-2). The immediate implication is that a cloud-free moist atmosphere on Earth would cause a runaway greenhouse. Triggering it would simply be a matter of sufficient heating, with around 30,000ppmv being sufficient in our most Earth-like model. This is substantially different than previous calculations, where weak solar absorption meant that a higher solar flux was required. Our published calculations are for the limit of clear-skies; any clouds would reduce both the thermal radiation emitted and the solar radiation absorbed, so clouds could make the runaway greenhouse either more or less likely. It can be shown that and excess of cloud reflection over cloud greenhouse is required to maintain temperate climate on Earth today - but how clouds will change in a warming atmosphere is far from clear. Work in progress (and hopefully ready by December!) on cloudy runaway greenhouse models will hopefully constrain this better. Wider implications for planetary stability will also be discussed. For example, water-world planets, with minimal background gas in the atmosphere may be highly susceptible to runaway greenhouses (heating Europa might take it directly from a snowball to a runaway). High CO2 levels after previous Snowball Earth events did not

  17. Molecular collision theory

    CERN Document Server

    Child, M S

    2010-01-01

    This high-level monograph offers an excellent introduction to the theory required for interpretation of an increasingly sophisticated range of molecular scattering experiments. There are five helpful appendixes dealing with continuum wavefunctions, Green's functions, semi-classical connection formulae, curve-crossing in the momentum representation, and elements of classical mechanics.The contents of this volume have been chosen to emphasize the quantum mechanical and semi-classical nature of collision events, with little attention given to purely classical behavior. The treatment is essentiall

  18. An improved current potential method for fast computation of stellarator coil shapes

    CERN Document Server

    Landreman, Matt

    2016-01-01

    Several fast methods for computing stellarator coil shapes are compared, including the classical NESCOIL procedure [Merkel, Nucl. Fusion 27, 867 (1987)], its generalization using truncated singular value decomposition, and a Tikhonov regularization approach we call REGCOIL in which the squared current density is included in the objective function. Considering W7-X and NCSX geometries, and for any desired level of regularization, we find the REGCOIL approach simultaneously achieves lower surface-averaged and maximum values of both current density (on the coil winding surface) and normal magnetic field (on the desired plasma surface). This approach therefore can simultaneously improve the free-boundary reconstruction of the target plasma shape while substantially increasing the minimum distances between coils, preventing collisions between coils while improving access for ports and maintenance. The REGCOIL method also allows finer control over the level of regularization, and it eliminates two pathologies of NE...

  19. Recent Progress in Modeling Stellar Populations Near and Far

    Science.gov (United States)

    Bruzual, Gustavo

    2010-05-01

    I will present a summary of recent advances in the fields of stellar evolution, stellar model atmospheres, and stellar spectral libraries, which allow us to build more realistic stellar population synthesis models than those available up to now. Empirical and theoretical stellar libraries of increasing degree of completeness and accuracy covering from the EUV to the NIR and their usage in current models will be examined. In particular, the treatment of stars in the TP-AGB phase of stellar evolution will be discussed in detail. Understanding these stars is fundamental for the determination of the mass of distant galaxies using population synthesis models. Applications of these models to problems of current interest will be discussed. Problems that need to be understood and data sets that still need to be collected in order to solve issues present in these models will be indicated.

  20. Beyond Blue Stragglers: Products of Non-Standard Stellar Evolution Across the Color Magnitude Diagram

    Science.gov (United States)

    Leiner, Emily

    2018-01-01

    Optical color-magnitude diagrams (CMDs) of open clusters reveal large populations of stars that do not fall along standard isochrones, and thus are not evolving according to standard theory. The most numerous of these stars are the blue stragglers, stars brighter and bluer than the cluster turnoff that are likely formed from mass transfer in a binary, stellar mergers, or collisions during dynamical encounters. The origins of other non-standard stars are not well understood, including the “yellow stragglers” found between the blue straggler region and the red giant branch, and “sub-subgiants” found fainter and redder than the giant branch. Understanding the formation and evolution of these non-standard stars is critical to properly modeling galactic stellar populations and revealing the binary evolution channels that form exotic end products like X-ray binaries, double degenerates, and Type 1a supernovae. In this talk I will present results of the first asteroseismic study of a yellow straggler in the old open cluster M67. This study shows the yellow straggler to be a red clump giant with a mass of at least twice the turnoff mass of M67, suggesting it is an evolved blue straggler formed from a merger or collision. I will also discuss the observed properties of the growing population of sub-subgiants discovered in open and globular clusters, and present models describing three possible formation pathways for these stars: mass-transfer in a binary, rapid envelope mass loss, and inhibition of convection due to the presence of strong magnetic fields. These studies represent some of the first efforts to understand cluster CMD outliers beyond the blue stragglers, and are a critical step forward in understanding binary evolution pathways.

  1. The Yale-Potsdam Stellar Isochrones

    Science.gov (United States)

    Spada, F.; Demarque, P.; Kim, Y.-C.; Boyajian, T. S.; Brewer, J. M.

    2017-04-01

    We introduce the Yale-Potsdam Stellar Isochrones (YaPSI), a new grid of stellar evolution tracks and isochrones of solar-scaled composition. In an effort to improve the Yonsei-Yale database, special emphasis is placed on the construction of accurate low-mass models ({M}* < 0.6 {M}⊙ ), and in particular on their mass-luminosity and mass-radius relations, both crucial for characterizing exoplanet-host stars, and, in turn, their planetary systems. The YaPSI models cover the mass range 0.15-5.0 {M}⊙ densely enough to permit detailed interpolation in mass, and the metallicity and helium abundance ranges [Fe/H] = -1.5 to +0.3 and Y 0 = 0.25-0.37 are specified independently of each other (I.e., no fixed {{Δ }}Y/{{Δ }}Z relation is assumed). The evolutionary tracks are calculated from the pre-main sequence up to the tip of the red giant branch. The isochrones, with ages between 1 Myr and 20 Gyr, provide UBVRI colors in the Johnson-Cousins system, and JHK colors in the homogenized Bessell & Brett system, derived from two different semi-empirical {T}{eff}-color calibrations from the literature. We also provide utility codes, such as an isochrone interpolator, in age, metallicity, and helium content, and an interface of the tracks with an open-source Monte Carlo Markov-Chain tool for the analysis of individual stars. Finally, we present comparisons of the YaPSI models with the best empirical mass-luminosity and mass-radius relations available to date, as well as isochrone fitting of well-studied stellar clusters.

  2. Parameterizing Stellar Spectra Using Deep Neural Networks

    Science.gov (United States)

    Li, Xiang-Ru; Pan, Ru-Yang; Duan, Fu-Qing

    2017-03-01

    Large-scale sky surveys are observing massive amounts of stellar spectra. The large number of stellar spectra makes it necessary to automatically parameterize spectral data, which in turn helps in statistically exploring properties related to the atmospheric parameters. This work focuses on designing an automatic scheme to estimate effective temperature ({T}{eff}), surface gravity ({log}g) and metallicity [Fe/H] from stellar spectra. A scheme based on three deep neural networks (DNNs) is proposed. This scheme consists of the following three procedures: first, the configuration of a DNN is initialized using a series of autoencoder neural networks; second, the DNN is fine-tuned using a gradient descent scheme; third, three atmospheric parameters {T}{eff}, {log}g and [Fe/H] are estimated using the computed DNNs. The constructed DNN is a neural network with six layers (one input layer, one output layer and four hidden layers), for which the number of nodes in the six layers are 3821, 1000, 500, 100, 30 and 1, respectively. This proposed scheme was tested on both real spectra and theoretical spectra from Kurucz’s new opacity distribution function models. Test errors are measured with mean absolute errors (MAEs). The errors on real spectra from the Sloan Digital Sky Survey (SDSS) are 0.1477, 0.0048 and 0.1129 dex for {log}g, {log}{T}{eff} and [Fe/H] (64.85 K for {T}{eff}), respectively. Regarding theoretical spectra from Kurucz’s new opacity distribution function models, the MAE of the test errors are 0.0182, 0.0011 and 0.0112 dex for {log}g, {log}{T}{eff} and [Fe/H] (14.90 K for {T}{eff}), respectively.

  3. Outer Dynamics of Ship Collisions

    DEFF Research Database (Denmark)

    Pedersen, Preben Terndrup

    1996-01-01

    The purpose is to present analysis procedures for the motion of ships during ship-ship collisions and for ship collisions with offshore structures. The aim is to estimate that part of the lost kinetic energy which will have to be absorbed by rupture and plastic damage of the colliding structures....

  4. Advanced Stellar Compass, SAC-C, Interface Control Document

    DEFF Research Database (Denmark)

    Madsen, Peter Buch; Betto, Maurizio; Riis, Troels

    Interface Control Document for the Advanced Stellar Compass for the SAC-C satellite. The SAC-C is Argentine, Danish and NASA satellite. On the SAC-C satellite there are a simplified version of the Ørsted instrumentation platform. The Advanced Stellar Compass is a improved version of the Ørsted Star...... Imager. This document descibes the interface between the Advanced Stellar Compass and OBDH, the size of the DPU and the Camera etc....

  5. Imaging of Stellar Surfaces with the Navy Precision Optical Interferometer

    Science.gov (United States)

    2015-09-18

    Imaging of Stellar Surfaces with the Navy Precision Optical Interferometer Anders M. Jorgensena, H. R. Schmittb, G. T. van Bellec, D. J. Hutterd, J...phase observations on long baselines at shorter wavelengths in order to further increase the resolution. In this paper we describe the NPOI Stellar ...Imaging stellar surfaces requires aperture diameters of sometimes hundreds of meters. In general, the diffraction limited angular resolution of an aper

  6. IPS guidestar selection for stellar mode (ASTRO)

    Science.gov (United States)

    Mullins, Larry; Wooten, Lewis

    1988-01-01

    This report describes how guide stars are selected for the Optical Sensor Package (OSP) for the Instrument Pointing System (IPS) when it is operating in the stellar mode on the ASTRO missions. It also describes how the objective loads are written and how the various roll angles are related; i.e., the celestial roll or position angle, the objective load roll angles, and the IPS gimbal angles. There is a brief description of how the IPS operates and its various modes of operation; i.e., IDOP, IDIN, and OSPCAL.

  7. Generating physically realizable stellar structures via embedding

    Energy Technology Data Exchange (ETDEWEB)

    Maurya, S.K. [University of Nizwa, Department of Mathematical and Physical Sciences, College of Arts and Science, Nizwa (Oman); Govender, M. [Durban University of Technology, Department of Mathematics, Faculty of Applied Sciences, Durban (South Africa)

    2017-05-15

    In this work we present an exact solution of the Einstein-Maxwell field equations describing compact charged objects within the framework of classical general relativity. Our model is constructed by embedding a four-dimensional spherically symmetric static metric into a five-dimensional flat metric. The source term for the matter field is composed of a perfect fluid distribution with charge. We show that our model obeys all the physical requirements and stability conditions necessary for a realistic stellar model. Our theoretical model approximates observations of neutron stars and pulsars to a very good degree of accuracy. (orig.)

  8. Advanced Stellar Compass - ROCSAT 2 - Proposal

    DEFF Research Database (Denmark)

    Riis, Troels; Betto, Maurizio; Jørgensen, John Leif

    1998-01-01

    System Integration is supposed to take place at NSPO facilities.The ASC is a highly advanced and autonomous Stellar Reference Unit designed, developed and produced by the Space Instrumentation Group of the Department of Automation of the Technical University of Denmark.The document is structured...... and in section 7 the mechanical and electrical interfaces are given. In section 8 and 9 we address issues like manufacturing, transportation and storage and to conclude in section 10 the requirements imposed by the ASC on the system are given....

  9. MHD stability of the MHH2 stellarator

    Energy Technology Data Exchange (ETDEWEB)

    Garabedian, P.R. [New York Univ., NY (United States). Courant Inst. of Mathematical Sciences

    1998-12-31

    The NSTAB code provides a computer implementation of the variational principle of magnetohydrodynamics. Excellent resolution is obtained by combining a spectral representation in the toroidal and poloidal angles with a low order, but exceptionally accurate, finite difference scheme in the radial direction. Conservation form of the magnetostatics equations is used to capture islands and current sheets effectively on crude grids. This method enables one to discuss global stability by analyzing bifurcated solutions of the equilibrium problem. The author applies it to investigate the physics of the MHH2 stellarator, whose magnetic structure has a remarkable property of quasi-axial symmetry.

  10. The Stellar Observations Network Group - first results

    DEFF Research Database (Denmark)

    Antoci, Victoria; Grundahl, Frank; Christensen-Dalsgaard, Joergen

    SONG - the Stellar Observations Network Group is a Danish-led project set to design and build a global network of 1-m telescopes to carry out detailed studies of solar-like stars using asteroseismology and to discover and characterise exo-planets and their star system. Here we present more than 100...... nights of high-precision radial velocity measurements from 2014 of the subgiant mu Herculis. Preliminary analyses of the largest ground-based data set ever obtained for such as star clearly show the detection of stochastically excited pressure modes. The high quality of our data allows unique extraction...

  11. A Changing Wind Collision

    Science.gov (United States)

    Nazé, Yaël; Koenigsberger, Gloria; Pittard, Julian M.; Parkin, Elliot Ross; Rauw, Gregor; Corcoran, Michael F.; Hillier, D. John

    2018-02-01

    We report on the first detection of a global change in the X-ray emitting properties of a wind–wind collision, thanks to XMM-Newton observations of the massive Small Magellenic Cloud (SMC) system HD 5980. While its light curve had remained unchanged between 2000 and 2005, the X-ray flux has now increased by a factor of ∼2.5, and slightly hardened. The new observations also extend the observational coverage over the entire orbit, pinpointing the light-curve shape. It has not varied much despite the large overall brightening, and a tight correlation of fluxes with orbital separation is found without any hysteresis effect. Moreover, the absence of eclipses and of absorption effects related to orientation suggests a large size for the X-ray emitting region. Simple analytical models of the wind–wind collision, considering the varying wind properties of the eruptive component in HD 5980, are able to reproduce the recent hardening and the flux-separation relationship, at least qualitatively, but they predict a hardening at apastron and little change in mean flux, contrary to observations. The brightness change could then possibly be related to a recently theorized phenomenon linked to the varying strength of thin-shell instabilities in shocked wind regions. Based on XMM-Newton and Chandra data.

  12. Collision in space

    Science.gov (United States)

    Ellis, S. R.

    2000-01-01

    On June 25, 1997, the Russian supply spacecraft Progress 234 collided with the Mir space station, rupturing Mir's pressure hull, throwing it into an uncontrolled attitude drift, and nearly forcing evacuation of the station. Like many high-profile accidents, this collision was the consequence of a chain of events leading to the final piloting errors that were its immediate cause. The discussion in this article does not resolve the relative contributions of the actions and decisions in this chain. Neither does it suggest corrective measures, many of which are straightforward and have already been implemented by the National Aeronautics and Space Administration (NASA) and the Russian Space Agency. Rather, its purpose is to identify the human factors that played a pervasive role in the incident. Workplace stress, fatigue, and sleep deprivation were identified by NASA as contributory factors in the Mir-Progress collision (Culbertson, 1997; NASA, forthcoming), but other contributing factors, such as requiring crew to perform difficult tasks for which their training is not current, could potentially become important factors in future situations.

  13. Ship Collision and Grounding Analysis

    DEFF Research Database (Denmark)

    Pedersen, Preben Terndrup

    2010-01-01

    It is the purpose of the paper to present a review of prediction and analysis tools for collision and grounding analyses and to outline a probabilistic procedure whereby these tools can be used by the maritime industry to develop performance based rules to reduce the risk associated with human, e......, environmental and economic costs of collision and grounding events. The main goal of collision and grounding research should be to identify the most economic risk control options associated with prevention and mitigation of collision and grounding events......It is the purpose of the paper to present a review of prediction and analysis tools for collision and grounding analyses and to outline a probabilistic procedure whereby these tools can be used by the maritime industry to develop performance based rules to reduce the risk associated with human...

  14. Runaway sexual selection without genetic correlations: social environments and flexible mate choice initiate and enhance the Fisher process.

    Science.gov (United States)

    Bailey, Nathan W; Moore, Allen J

    2012-09-01

    Female mating preferences are often flexible, reflecting the social environment in which they are expressed. Associated indirect genetic effects (IGEs) can affect the rate and direction of evolutionary change, but sexual selection models do not capture these dynamics. We incorporate IGEs into quantitative genetic models to explore how variation in social environments and mate choice flexibility influence Fisherian sexual selection. The importance of IGEs is that runaway sexual selection can occur in the absence of a genetic correlation between male traits and female preferences. Social influences can facilitate the initiation of the runaway process and increase the rate of trait elaboration. Incorporating costs to choice do not alter the main findings. Our model provides testable predictions: (1) genetic covariances between male traits and female preferences may not exist, (2) social flexibility in female choice will be common in populations experiencing strong sexual selection, (3) variation in social environments should be associated with rapid sexual trait divergence, and (4) secondary sexual traits will be more elaborate than previously predicted. Allowing feedback from the social environment resolves discrepancies between theoretical predictions and empirical data, such as why indirect selection on female preferences, theoretically weak, might be sufficient for preferences to become elaborated. © 2012 The Author(s). Evolution© 2012 The Society for the Study of Evolution.

  15. Bent paths of a positive streamer and a cathode-directed spark leader in diffuse discharges preionized by runaway electrons

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Cheng; Shao, Tao, E-mail: st@mail.iee.ac.cn; Wang, Ruixue; Yan, Ping [Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190 (China); Key Laboratory of Power Electronics and Electric Drive, Chinese Academy of Sciences, Beijing 100190 (China); Tarasenko, Viktor F.; Beloplotov, Dmitry V.; Lomaev, Mikhail I.; Sorokin, Dmitry A. [Institute of High Current Electronics, Russian Academy of Science, Tomsk 634055 (Russian Federation); National Research Tomsk State University, 36 Lenin Ave., Tomsk 634050 (Russian Federation)

    2015-03-15

    Diffuse discharges preionized by runaway electrons can produce large-area homogeneous discharges at elevated pressures, which is an intriguing phenomenon in the physics of pulsed discharges. In this paper, runaway-electron-preionized diffuse discharge (REP DD) was obtained in a wide pressure range (0.05–0.25 MPa), and under certain conditions a positive streamer and a cathode-directed spark leader could be observed to propagate at some angles to the applied (background) electric field lines. For a 16-mm gap at an air pressure of 0.08–0.1 MPa, the percentage of pulses in which such propagation is observed is about 5%–50% of their total number, and in the other pulses such bent paths could not be observed because there is even no streamer or cathode-directed spark leader in diffuse discharges. In our opinion, such propagation of the positive streamer and the cathode-directed spark leader at some angle to the background electric field lines owes to different increase rates of the electron density in different regions of the discharge volume under REP DD conditions. Therefore, during the formation of a REP DD, the increase of the electron density is inhomogeneous and nonsimultaneous, resulting in an electron density gradient at the ionization wave front.

  16. Preventing thermal runaway propagation in lithium ion battery packs using a phase change composite material: An experimental study

    Science.gov (United States)

    Wilke, Stephen; Schweitzer, Ben; Khateeb, Siddique; Al-Hallaj, Said

    2017-02-01

    The safety issues of lithium ion batteries pose ongoing challenges as the market for Li-ion technology continues to grow in personal electronics, electric mobility, and stationary energy storage. The severe risks posed by battery thermal runaway necessitate safeguards at every design level - from materials, to cell construction, to module and pack assembly. One promising approach to pack thermal management is the use of phase change composite materials (PCC™), which offer passive protection at low weight and cost while minimizing system complexity. We present experimental nail penetration studies on a Li-ion pack for small electric vehicles, designed with and without PCC, to investigate the effectiveness of PCC thermal management for preventing propagation when a single cell enters thermal runaway. The results show that when parallel cells short-circuit through the penetrated cell, the packs without PCC propagate fully while those equipped with PCC show no propagation. In cases where no external short circuits occur, packs without PCC sometimes propagate, but not consistently. In all test conditions, the use of PCC lowers the maximum temperature experienced by neighboring cells by 60 °C or more. We also elucidate the propagation sequence and aspects of pack failure based on cell temperature, voltage, and post-mortem data.

  17. Bent paths of a positive streamer and a cathode-directed spark leader in diffuse discharges preionized by runaway electrons

    Science.gov (United States)

    Zhang, Cheng; Tarasenko, Viktor F.; Shao, Tao; Beloplotov, Dmitry V.; Lomaev, Mikhail I.; Wang, Ruixue; Sorokin, Dmitry A.; Yan, Ping

    2015-03-01

    Diffuse discharges preionized by runaway electrons can produce large-area homogeneous discharges at elevated pressures, which is an intriguing phenomenon in the physics of pulsed discharges. In this paper, runaway-electron-preionized diffuse discharge (REP DD) was obtained in a wide pressure range (0.05-0.25 MPa), and under certain conditions a positive streamer and a cathode-directed spark leader could be observed to propagate at some angles to the applied (background) electric field lines. For a 16-mm gap at an air pressure of 0.08-0.1 MPa, the percentage of pulses in which such propagation is observed is about 5%-50% of their total number, and in the other pulses such bent paths could not be observed because there is even no streamer or cathode-directed spark leader in diffuse discharges. In our opinion, such propagation of the positive streamer and the cathode-directed spark leader at some angle to the background electric field lines owes to different increase rates of the electron density in different regions of the discharge volume under REP DD conditions. Therefore, during the formation of a REP DD, the increase of the electron density is inhomogeneous and nonsimultaneous, resulting in an electron density gradient at the ionization wave front.

  18. An updated MILES stellar library and stellar population models (Research Note)

    NARCIS (Netherlands)

    Falcon-Barroso, J.; Sanchez-Blazquez, P.; Vazdekis, A.; Ricciardelli, E.; Cardiel, N.; Cenarro, A. J.; Gorgas, J.; Peletier, R. F.

    Aims: We present a number of improvements to the MILES library and stellar population models. We correct some small errors in the radial velocities of the stars, measure the spectral resolution of the library and models more accurately, and give a better absolute flux calibration of the models.

  19. The Stellar Imager (SI) - A Mission to Resolve Stellar Surfaces, Interiors, and Magnetic Activity

    Energy Technology Data Exchange (ETDEWEB)

    Christensen-Dalsgaard, Joergen [Department of Physics and Astronomy, Aarhus University (Denmark); Carpenter, Kenneth G [Code 667 NASA-GSFC, Greenbelt, MD 20771 (United States); Schrijver, Carolus J [LMATC 3251 Hanover St., Bldg. 252, Palo Alto, CA 94304 (United States); Karovska, Margarita, E-mail: jcd@phys.au.d, E-mail: Kenneth.G.Carpenter@nasa.gov, E-mail: schryver@lmsal.com, E-mail: karovska@head.cfa.harvard.edu [60 Garden St., Cambridge, MA 02138 (United States)

    2011-01-01

    The Stellar Imager (SI) is a space-based, UV/Optical Interferometer (UVOI) designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and of the Universe in general. It will also probe via asteroseismology flows and structures in stellar interiors. SI will enable the development and testing of a predictive dynamo model for the Sun, by observing patterns of surface activity and imaging of the structure and differential rotation of stellar interiors in a population study of Sun-like stars to determine the dependence of dynamo action on mass, internal structure and flows, and time. SI's science focuses on the role of magnetism in the Universe and will revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. SI is a 'Landmark/Discovery Mission' in the 2005 Heliophysics Roadmap, an implementation of the UVOI in the 2006 Astrophysics Strategic Plan, and a NASA Vision Mission ('NASA Space Science Vision Missions' (2008), ed. M. Allen). We present here the science goals of the SI Mission, a mission architecture that could meet those goals, and the technology development needed to enable this mission. Additional information on SI can be found at: http://hires.gsfc.nasa.gov/si/.

  20. Identification of Stellar Sequences in Various Stellar Systems: ESO65-SC03, Teutsch 106, Turner 6

    Science.gov (United States)

    Joshi, Gireesh C.

    2017-12-01

    The spatial morphological study of stellar clusters has been carried out through their identified probable members. The field stars decontamination is performed by the statistical cleaning approach (depends on the magnitude and colour of stars within the field and cluster regions). The colour magnitude ratio diagram (CMRD) approach is used to separate the stellar sequences of cluster systems. The age, distance and reddening of each cluster is estimated through the visual inspection of best fitted isochrone in colour magnitude diagrams (CMDs). The mean proper motion values of stellar clusters are obtained through the extracted data from PPMXL and UCAC4 catalogs. Moreover, these values vary according to the extracted data-set from these catalogues. This variation has occurred due to different estimation efficiency of proper motions. The two colour ratio (TCR) and two colour magnitude ratio (TCMR) values of each cluster is determined by utilizing the WISE and PPMXL catalogues, these values are found abnormal for Teutsch 106. In addition, the TCMR values are similar to TCR values at longer wavelength, whereas both values are far away from each other at shorter wavelength. The fraction of young stellar objects (YSOs) is also computed for each cluster.

  1. Stellar halos: a rosetta stone for galaxy formation and cosmology

    Science.gov (United States)

    Inglis Read, Justin

    2015-08-01

    Stellar halos make up about a percent of the total stellar mass in galaxies. Yet their old age and long phase mixing times make them living fossil records of galactic history. In this talk, I review the latest simulations of structure formation in our standard Lambda Cold Dark Matter cosmology. I discuss the latest predictions for stellar halos and the relationship between the stellar halo light and the underlying dark matter. Finally, I discuss how these simulations compare to observations of the Milky Way and Andromeda and, ultimately, what this means for our cosmological model and the formation history of the Galaxy.

  2. The effect of tangential drifts on neoclassical transport in stellarators close to omnigeneity

    Science.gov (United States)

    Calvo, Iván; Parra, Felix I.; Velasco, José Luis; Alonso, J. Arturo

    2017-05-01

    In general, the orbit-averaged radial magnetic drift of trapped particles in stellarators is non-zero due to the three-dimensional nature of the magnetic field. Stellarators in which the orbit-averaged radial magnetic drift vanishes are called omnigeneous, and they exhibit neoclassical transport levels comparable to those of axisymmetric tokamaks. However, the effect of deviations from omnigeneity cannot be neglected in practice, and it is more deleterious at small collisionalities. For sufficiently low collision frequencies (below the values that define the 1/ν regime), the components of the drifts tangential to the flux surface become relevant. This article focuses on the study of such collisionality regimes in stellarators close to omnigeneity when the gradient of the non-omnigeneous perturbation is small. First, it is proven that closeness to omnigeneity is required to actually preserve radial locality in the drift-kinetic equation for collisionalities below the 1/ν regime. Then, using the derived radially local equation, it is shown that neoclassical transport is determined by two layers located at different regions of phase space. One of the layers corresponds to the so-called \\sqrt{ν } regime and the other to the so-called superbanana-plateau regime. The importance of the superbanana-plateau layer for the calculation of the tangential electric field is emphasized, as well as the relevance of the latter for neoclassical transport in the collisionality regimes considered in this paper. In particular, the role of the tangential electric field is essential for the emergence of a new subregime of superbanana-plateau transport when the radial electric field is small. A formula for the ion energy flux that includes the \\sqrt{ν } regime and the superbanana-plateau regime is given. The energy flux scales with the square of the size of the deviation from omnigeneity. Finally, it is explained why below a certain collisionality value the formulation presented in

  3. Reversible simulations of elastic collisions

    Energy Technology Data Exchange (ETDEWEB)

    Perumalla, Kalyan S.; Protopopescu, Vladimir A.

    2013-05-01

    Consider a system of N identical hard spherical particles moving in a d-dimensional box and undergoing elastic, possibly multi-particle, collisions. We develop a new algorithm that recovers the pre-collision state from the post-collision state of the system, across a series of consecutive collisions, \\textit{with essentially no memory overhead}. The challenge in achieving reversibility for an n-particle collision (where, in general, n<< N) arises from the presence of nd-d-1 degrees of freedom (arbitrary angles) during each collision, as well as from the complex geometrical constraints placed on the colliding particles. To reverse the collisions in a traditional simulation setting, all of the particular realizations of these degrees of freedom (angles) during the forward simulation must be tracked. This requires memory proportional to the number of collisions, which grows very fast with N and d, thereby severely limiting the \\textit{de facto} applicability of the scheme. This limitation is addressed here by first performing a pseudo-randomization of angles, which ensures determinism in the reverse path for any values of n and d. To address the more difficult problem of geometrical and dynamic constraints, a new approach is developed which correctly samples the constrained phase space. Upon combining the pseudo-randomization with correct phase space sampling, perfect reversibility of collisions is achieved, as illustrated for n<=3, d=2, and n=2, d=3. This result enables, for the first time, reversible simulations of elastic collisions with essentially zero memory accumulation. In principle, the approach presented here could be generalized to larger values of n, which would be of definite interest for molecular dynamics simulations at high densities.

  4. The Origin of Stellar Species: constraining stellar evolution scenarios with Local Group galaxy surveys

    Science.gov (United States)

    Sarbadhicary, Sumit; Badenes, Carles; Chomiuk, Laura; Maldonado, Jessica; Caprioli, Damiano; Heger, Mairead; Huizenga, Daniel

    2018-01-01

    Our understanding of the progenitors of many stellar species, such as supernovae, massive and low-mass He-burning stars, is limited because of many poorly constrained aspects of stellar evolution theory. For my dissertation, I have focused on using Local Group galaxy surveys to constrain stellar evolution scenarios by measuring delay-time distributions (DTD). The DTD is the hypothetical occurrence rate of a stellar object per elapsed time after a brief burst of star formation. It is the measured distribution of timescales on which stars evolve, and therefore serves as a powerful observational constraint on theoretical progenitor models. The DTD can be measured from a survey of stellar objects and a set of star-formation histories of the host galaxy, and is particularly effective in the Local Group, where high-quality star-formation histories are available from resolved stellar populations. I am currently calculating a SN DTD with supernova remnants (SNRs) in order to provide the strongest constraints on the progenitors of thermonuclear and core-collapse supernovae. However, most SNRs do not have reliable age measurements and their evolution depends on the ambient environment. For this reason, I wrote a radio light curve model of an SNR population to extract the visibility times and rates of supernovae - crucial ingredients for the DTD - from an SNR survey. The model uses observational constraints on the local environments from multi-wavelength surveys, accounts for missing SNRs and employs the latest models of shock-driven particle acceleration. The final calculation of the SN DTD in the Local Group is awaiting completion of a systematic SNR catalog from deep radio-continuum images, now in preparation by a group led by Dr. Laura Chomiuk. I have also calculated DTDs for the LMC population of RR Lyrae and Cepheid variables, which serve as important distance calibrators and stellar population tracers. We find that Cepheids can have delay-times between 10 Myrs - 1 Gyr

  5. Sixteenth International Conference on the physics of electronic and atomic collisions

    Energy Technology Data Exchange (ETDEWEB)

    Dalgarno, A.; Freund, R.S.; Lubell, M.S.; Lucatorto, T.B. (eds.)

    1989-01-01

    This report contains abstracts of papers on the following topics: photons, electron-atom collisions; electron-molecule collisions; electron-ion collisions; collisions involving exotic species; ion- atom collisions, ion-molecule or atom-molecule collisions; atom-atom collisions; ion-ion collisions; collisions involving rydberg atoms; field assisted collisions; collisions involving clusters and collisions involving condensed matter.

  6. SUB-STELLAR COMPANIONS AND STELLAR MULTIPLICITY IN THE TAURUS STAR-FORMING REGION

    Energy Technology Data Exchange (ETDEWEB)

    Daemgen, Sebastian [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5H 3H4 (Canada); Bonavita, Mariangela [The University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Jayawardhana, Ray [Physics and Astronomy, York University, Toronto, Ontario L3T 3R1 (Canada); Lafrenière, David [Department of Physics, University of Montréal, Montréal, QC (Canada); Janson, Markus, E-mail: daemgen@astro.utoronto.ca [Department of Astronomy, Stockholm University, Stockholm (Sweden)

    2015-02-01

    We present results from a large, high-spatial-resolution near-infrared imaging search for stellar and sub-stellar companions in the Taurus-Auriga star-forming region. The sample covers 64 stars with masses between those of the most massive Taurus members at ∼3 M {sub ☉} and low-mass stars at ∼0.2 M {sub ☉}. We detected 74 companion candidates, 34 of these reported for the first time. Twenty-five companions are likely physically bound, partly confirmed by follow-up observations. Four candidate companions are likely unrelated field stars. Assuming physical association with their host star, estimated companion masses are as low as ∼2 M {sub Jup}. The inferred multiplicity frequency within our sensitivity limits between ∼10-1500 AU is 26.3{sub −4.9}{sup +6.6}%. Applying a completeness correction, 62% ± 14% of all Taurus stars between 0.7 and 1.4 M {sub ☉} appear to be multiple. Higher order multiples were found in 1.8{sub −1.5}{sup +4.2}% of the cases, in agreement with previous observations of the field. We estimate a sub-stellar companion frequency of ∼3.5%-8.8% within our sensitivity limits from the discovery of two likely bound and three other tentative very low-mass companions. This frequency appears to be in agreement with what is expected from the tail of the stellar companion mass ratio distribution, suggesting that stellar and brown dwarf companions share the same dominant formation mechanism. Further, we find evidence for possible evolution of binary parameters between two identified sub-populations in Taurus with ages of ∼2 Myr and ∼20 Myr, respectively.

  7. Stellarator News, Issue 38, March 1995

    CERN Document Server

    Rome, J A

    1995-01-01

    Stellarator News, an international journal of the stellarator community, is Published by Fusion Energy Division, Oak Ridge National Laboratory, James A. Rome, Editor In the March 1995 issue . . . **** Exerpts from the U.S. Congress Office of Technology Assment report on TPX and Alternate Concepts. **** Edge transport and turbulence studies on U-3M The turbulent-driven particle flow is shown to be comparable with the equilibrium flow at the boundary of the configuration under Alfven-heating conditions in the U-3M torsatron. **** Topological aspects of island divertor studies on W7-AS The structure of the edge plasma in W7-AS, observed with probes, television camera, and H-alpha light agrees at low beta with vacuum field calculations: the low-valued resonances at iotabar=5/m are resolved for m = 8 to 11; external perturbations are not significant at the edge, even for iotabar = 5/10. **** 140-GHz second harmonic O-mode electron cyclotron heating at W7-AS First experimental results are presented of 140-GHz secon...

  8. Color superconductivity in compact stellar hybrid configurations

    Science.gov (United States)

    Ranea-Sandoval, Ignacio F.; Orsaria, Milva G.; Han, Sophia; Weber, Fridolin; Spinella, William M.

    2017-12-01

    The discovery of pulsars PSR J1614-2230 and PSR J0348+0432 with masses of around 2 M⊙ imposes strong constraints on the equations of state of cold, ultradense matter. If a phase transition from hadronic matter to quark matter were to occur in the inner cores of such massive neutron stars, the energetically favorable state of quark matter would be a color superconductor. In this study, we analyze the stability and maximum mass of such neutron stars. The hadronic phase is described by nonlinear relativistic mean-field models, and the local Nambu-Jona Lasinio model is used to describe quark matter in the 2SC+s quark phase. The phase transition is treated as a Maxwell transition, assuming a sharp hadron-quark interface, and the "constant-sound-speed" (CSS) parametrization is employed to discuss the existence of stellar twin configurations. We find that massive neutron stars such as J1614-2230 and J0348+0432 can only exist on the connected stellar branch but not on the disconnected twin-star branch. The latter can only support stars with masses that are strictly below 2 M⊙ .

  9. A multi-institutional Stellarator Configuration Study

    Science.gov (United States)

    Gates, David

    2017-10-01

    A multi-institutional study aimed at mapping the space of quasi-axisymmetric stellarators has begun. The goal is to gain improved understanding of the dependence of important physics and engineering parameters (e.g. bootstrap current, stability, coil complexity, etc.) on plasma shape (average elongation, aspect ratio, number of periods). In addition, the stellarator optimization code STELLOPT will be upgraded with new capabilities such as improved coil design algorithms such as COILOPT + + and REGCOIL, divertor optimization options, equilibria with islands using the SPEC code, and improved bootstrap current calculations with the SFINCS code. An effort is underway to develop metrics for divertor optimization. STELLOPT has also had numerous improvements to numerical algorithms and parallelization capabilities. Simultaneously, we also are pursuing the optimization of turbulent transport according to the method of proxy functions. Progress made to date includes an elongation scan on quasi-axisymmetric equilibria and an initial comparison between the SFINCS code and the BOOTSJ calculation of bootstrap current currently available in STELLOPT. Further progress on shape scans and subsequent physics analysis will be reported. The status of the STELLOPT upgrades will be described. The eventual goal of this exercise is to identify attractive configurations for future US experimental facilities.. This work is supported by US DoE Contract Number DE-AC02-09CH11466.

  10. Il desiderio stellare del Principe di Salina

    Directory of Open Access Journals (Sweden)

    Rosalba Galvagno

    2013-05-01

    Full Text Available If desire originates from the stars –de sideribus- and, if we agree with this etymology, the Subject’s desire coincides with the Other’s desire, Tomasi di Lampedusa’s Il Gattopardo shows one of the most fascinating and enigmatic literary figures of stellar desire, as it can be read, furthermore, in the explicit of the seventh part of the novel: «Giunta faccia a faccia con lui sollevò il velo e così, pudica ma pronto ad esser posseduta, gli apparve più bella di come mai l’avesse intravista negli spazi stellari».            Why does this female figure descending from the stellar spaces in order to yield to Don Fabrizio who has reached the final stage of his journey, embody the object of a possessive desire which, paradoxically, corresponds to death? Indeed, death marks the entire novel since its memorable incipit: «”Nunc et in hora mortis nostrae. Amen”». What kind of desire is it precisely about? What is our unexpectedly Hamlet-like hero troubled by? The cues which the novel shows for the interpretation of this desire are few but meaningful. However we could appeal to Ricordi d’Infanzia which lead to the writer’s laboratory at the time of the Gattopardo, and, perhaps, let us know the “cause” of the prince of Salina’s desire.

  11. Diverse stellar haloes in nearby Milky Way mass disc galaxies

    Science.gov (United States)

    Harmsen, Benjamin; Monachesi, Antonela; Bell, Eric F.; de Jong, Roelof S.; Bailin, Jeremy; Radburn-Smith, David J.; Holwerda, Benne W.

    2017-04-01

    We have examined the resolved stellar populations at large galactocentric distances along the minor axis (from 10 kpc up to between 40 and 75 kpc), with limited major axis coverage, of six nearby highly inclined Milky Way (MW) mass disc galaxies using Hubble Space Telescope data from the Galaxy haloes, Outer discs, Substructure, Thick discs, and Star clusters (GHOSTS) survey. We select red giant branch stars to derive stellar halo density profiles. The projected minor axis density profiles can be approximated by power laws with projected slopes of -2 to -3.7 and a diversity of stellar halo masses of 1-6 × 109 M⊙, or 2-14 per cent of the total galaxy stellar masses. The typical intrinsic scatter around a smooth power-law fit is 0.05-0.1 dex owing to substructure. By comparing the minor and major axis profiles, we infer projected axis ratios c/a at ˜25 kpc between 0.4and0.75. The GHOSTS stellar haloes are diverse, lying between the extremes charted out by the (rather atypical) haloes of the MW and M31. We find a strong correlation between the stellar halo metallicities and the stellar halo masses. We compare our results with cosmological models, finding good agreement between our observations and accretion-only models where the stellar haloes are formed by the disruption of dwarf satellites. In particular, the strong observed correlation between stellar halo metallicity and mass is naturally reproduced. Low-resolution hydrodynamical models have unrealistically high stellar halo masses. Current high-resolution hydrodynamical models appear to predict stellar halo masses somewhat higher than observed but with reasonable metallicities, metallicity gradients, and density profiles.

  12. Runaway behavior and thermally safe operation of multiple liquid-liquid reactions in the semi-batch reactor. The nitric acid oxidation of 2-octanol.

    NARCIS (Netherlands)

    van Woezik, B.A.A.; Westerterp, K.R.

    2001-01-01

    The thermal runaway behavior of an exothermic, heterogeneous, multiple reaction system has been studied in a cooled semi-batch reactor. The nitric acid oxidation of 2-octanol has been used to this end. During this reaction, 2-octanone is formed, which can be further oxidized to unwanted carboxylic

  13. The Role of Child Gender, Problem Behaviors, and the Family Environment on Maternal Depressive Symptoms: Findings from Mothers of Substance Abusing Runaway Adolescents

    Science.gov (United States)

    Guo, Xiamei; Slesnick, Natasha

    2011-01-01

    This study examined the relation between maternal depressive symptoms and adolescents' problem behaviors, moderated by adolescent gender, as well as the association between maternal depressive symptoms and the family environment characteristics above and beyond child variables. Data were collected from 137 mothers of runaway adolescents with…

  14. Cooperative Retransmissions Through Collisions

    CERN Document Server

    Qureshi, Jalaluddin; Foh, Chuan Heng

    2011-01-01

    Interference in wireless networks is one of the key capacity-limiting factors. Recently developed interference-embracing techniques show promising performance on turning collisions into useful transmissions. However, the interference-embracing techniques are hard to apply in practical applications due to their strict requirements. In this paper, we consider utilising the interference-embracing techniques in a common scenario of two interfering sender-receiver pairs. By employing opportunistic listening and analog network coding (ANC), we show that compared to traditional ARQ retransmission, a higher retransmission throughput can be achieved by allowing two interfering senders to cooperatively retransmit selected lost packets at the same time. This simultaneous retransmission is facilitated by a simple handshaking procedure without introducing additional overhead. Simulation results demonstrate the superior performance of the proposed cooperative retransmission.

  15. Consumers’ Collision Insurance Decisions

    DEFF Research Database (Denmark)

    Austin, Laurel; Fischhoff, Baruch

    Using interviews with 74 drivers, we elicit and analyse how people think about collision coverage and, more generally, about insurance decisions. We compare the judgments and behaviours of these decision makers to the predictions of a range of theoretical models: (a) A model developed by Lee (2007......), which refines EU theory to incorporate income and predicts that property insurance is a normal good; (b) a mental accounting model based on the idea that consumers budget their income across consumption categories (Thaler, 1985); and (c) the baseline, classic EU theory, which predicts that insurance...... is an inferior good (Mossin, 1968). The behaviour reported by subjects in our study suggests that insurance is a normal good, while their verbal reports reveal desires to balance two conflicting goals in deductible decisions, keeping premiums “affordable” and keeping deductibles “affordable,” which suggests...

  16. Stellar survivor from explosion in 1572 AD

    Science.gov (United States)

    2004-10-01

    hi-res Size hi-res: 1051 kb Credits: NASA/ESA, CXO and P. Ruiz-Lapuente (University of Barcelona) Tycho's Supernova, SN 1572A These images show the location of a suspected runaway companion star to a titanic supernova explosion witnessed in the year 1572 by the Danish astronomer Tycho Brahe and other astronomers of that era. This discovery provides the first direct evidence supporting the long-held belief that Type Ia supernovae come from binary star systems containing a normal star and a burned-out white dwarf star. When the dwarf ultimately explodes by being overfueled by the companion star, the companion is slung away from the demised star. The Hubble Space Telescope played a key role by precisely measuring the surviving star's motion against the sky background. Right: A Hubble Space Telescope Wide Field Planetary Camera 2 image of a small section of sky containing the candidate star. The star is like our Sun except several thousand million years older. It is moving through space at three times the speed of the other stars in its neighbourhood. Hubble's sharp view allowed for a measurement of the star's motion, based on images taken in 1999 and 2003. The image consists of a single greyscale Hubble exposure colourised with the help of data from Digitized Sky Survey 2. Left: The Hubble view is superimposed on this wide-field view of the region enveloped by the expanding bubble of the supernova explosion; the bubble and candidate star are at approximately the same distance, 10 000 light-years. The star is noticeably offset from the geometric centre of the bubble. The colours in the Chandra X-Ray image of the hot bubble show different X-ray energies, with red, green and blue representing low, medium and high energies, respectively. (The image is cut off at the bottom because the southernmost region of the remnant fell outside the field of view of the Chandra camera.) hi-res Size hi-res: 1059 kb Credits: NASA/ESA and P. Ruiz-Lapuente (University of Barcelona) The

  17. On Impact Mechanics in Ship Collisions

    DEFF Research Database (Denmark)

    Pedersen, Preben Terndrup; Zhang, Shengming

    1998-01-01

    The purpose of this paper is to present analytical, closed-form expressions for the energy released for crushing and the impact impulse during ship collisions. Ship-ship collisions, ship collisions with rigid walls and ship collisions with flexible offshore structures are considered. The derived ...

  18. Gyrokinetic linearized Landau collision operator

    DEFF Research Database (Denmark)

    Madsen, Jens

    2013-01-01

    The full gyrokinetic electrostatic linearized Landau collision operator is calculated including the equilibrium operator, which represents the effect of collisions between gyrokinetic Maxwellian particles. First, the equilibrium operator describes energy exchange between different plasma species......, which is important in multiple ion-species plasmas. Second, the equilibrium operator describes drag and diffusion of the magnetic field aligned component of the vorticity associated with the E×B drift. Therefore, a correct description of collisional effects in turbulent plasmas requires the equilibrium...... operator, even for like-particle collisions....

  19. Proton Testing of Advanced Stellar Compass Digital Processing Unit

    DEFF Research Database (Denmark)

    Thuesen, Gøsta; Denver, Troelz; Jørgensen, Finn E

    1999-01-01

    The Advanced Stellar Compass Digital Processing Unit was radiation tested with 300 MeV protons at Proton Irradiation Facility (PIF), Paul Scherrer Institute, Switzerland.......The Advanced Stellar Compass Digital Processing Unit was radiation tested with 300 MeV protons at Proton Irradiation Facility (PIF), Paul Scherrer Institute, Switzerland....

  20. Recent advances in non-LTE stellar atmosphere models

    Science.gov (United States)

    Sander, Andreas A. C.

    2017-11-01

    In the last decades, stellar atmosphere models have become a key tool in understanding massive stars. Applied for spectroscopic analysis, these models provide quantitative information on stellar wind properties as well as fundamental stellar parameters. The intricate non-LTE conditions in stellar winds dictate the development of adequate sophisticated model atmosphere codes. The increase in both, the computational power and our understanding of physical processes in stellar atmospheres, led to an increasing complexity in the models. As a result, codes emerged that can tackle a wide range of stellar and wind parameters. After a brief address of the fundamentals of stellar atmosphere modeling, the current stage of clumped and line-blanketed model atmospheres will be discussed. Finally, the path for the next generation of stellar atmosphere models will be outlined. Apart from discussing multi-dimensional approaches, I will emphasize on the coupling of hydrodynamics with a sophisticated treatment of the radiative transfer. This next generation of models will be able to predict wind parameters from first principles, which could open new doors for our understanding of the various facets of massive star physics, evolution, and death.

  1. Operations of a non-stellar object tracker in space

    DEFF Research Database (Denmark)

    Riis, Troels; Jørgensen, John Leif; Betto, Maurizio

    1999-01-01

    The ability to detect and track non-stellar objects by utilizing a star tracker may seem rather straight forward, as any bright object, not recognized as a star by the system is a non stellar object. However, several pitfalls and errors exist, if a reliable and robust detection is required. To te...

  2. Substructure in the Stellar Halos of the Aquarius Simulations

    NARCIS (Netherlands)

    Helmi, Amina; Cooper, A. P.; White, S. D. M.; Cole, S.; Frenk, C. S.; Navarro, J. F.

    2011-01-01

    We characterize the substructure in the simulated stellar halos of Cooper et al. which were formed by the disruption of satellite galaxies within the cosmological N-body simulations of galactic halos of the Aquarius project. These stellar halos exhibit a wealth of tidal features: broad overdensities

  3. A Stellar Reference Unit Design Study for SIRTF

    DEFF Research Database (Denmark)

    Jørgensen, John Leif; Liebe, Carl Christian

    1996-01-01

    A design study for a stellar reference unit, or star tracker, for SIRTF was conducted in FY96 in conjunction with the Tracking Sensors Group of the Avionic Equipment Section of JPL. The resulting design was derived from the Oersted, autonomous, Advanced Stellar Compass, star tracker. The projecte...

  4. Variation of galactic cold gas reservoirs with stellar mass

    NARCIS (Netherlands)

    Maddox, Natasha; Hess, Kelley M.; Obreschkow, Danail; Blyth, S.-L.; Jarvis, Matt J.

    The stellar and neutral hydrogen (H I) mass functions at z ˜ 0 are fundamental benchmarks for current models of galaxy evolution. A natural extension of these benchmarks is the two-dimensional distribution of galaxies in the plane spanned by stellar and H I mass, which provides a more stringent test

  5. Spectroscopic evidence of distinct stellar populations in the counter-rotating stellar disks of NGC 3593 and NGC 4550

    Science.gov (United States)

    Coccato, L.; Morelli, L.; Pizzella, A.; Corsini, E. M.; Buson, L. M.; Dalla Bontà, E.

    2013-01-01

    Aims: We present the results of integral-field spectroscopic observations of the two disk galaxies NGC 3593 and NGC 4550 obtained with the Visible Multi Object Spectrograph at the Very Large Telescope. Both galaxies are known to host two counter-rotating stellar disks, with the ionized gas corotating with one of them. We measured in each galaxy the surface brightness, kinematics, mass surface density, and the stellar populations of the two stellar components, as well as the distribution, kinematics, and metallicity of the ionized-gas component to constrain the formation scenario of these peculiar galaxies. Methods: We applied a novel spectroscopic decomposition technique to both galaxies, to disentangle at each position in the field of view the relative contribution of the two counter-rotating stellar and one ionized-gas components to the observed spectrum. We measured the kinematics and the line strengths of the Lick indices of the two counter-rotating stellar components. We modeled the data of each stellar component with single stellar population models that account for the α/Fe overabundance. Results: In both galaxies we successfully separated the main from the secondary stellar component that is less massive and rotates in the same direction as the ionized-gas component. The two stellar components have exponential surface-brightness profiles. In NGC 3593 they have different scale lengths, with the secondary one dominating the innermost 500 pc. In NGC 4550 they have the same scale lengths, but slightly different scale heights. In both galaxies, the two counter-rotating stellar components have different stellar populations. The secondary stellar disk is younger, more metal poor, and more α-enhanced than the main galaxy stellar disk. Such a difference is stronger in NGC 3593 than in NGC 4550. Conclusions: Our findings rule out an internal origin of the secondary stellar component and favor a scenario where it formed from gas accreted on retrograde orbits from

  6. Improving 1D Stellar Models with 3D Atmospheres

    Science.gov (United States)

    Rørsted Mosumgaard, Jakob; Silva Aguirre, Víctor; Weiss, Achim; Christensen-Dalsgaard, Jørgen; Trampedach, Regner

    2017-10-01

    Stellar evolution codes play a major role in present-day astrophysics, yet they share common issues. In this work we seek to remedy some of those by the use of results from realistic and highly detailed 3D hydrodynamical simulations of stellar atmospheres. We have implemented a new temperature stratification extracted directly from the 3D simulations into the Garching Stellar Evolution Code to replace the simplified atmosphere normally used. Secondly, we have implemented the use of a variable mixing-length parameter, which changes as a function of the stellar surface gravity and temperature - also derived from the 3D simulations. Furthermore, to make our models consistent, we have calculated new opacity tables to match the atmospheric simulations. Here, we present the modified code and initial results on stellar evolution using it.

  7. Thermonuclear inverse magnetic pumping power cycle for stellarator reactor

    Science.gov (United States)

    Ho, Darwin D.; Kulsrud, Russell M.

    1991-01-01

    The plasma column in a stellarator is compressed and expanded alternatively in minor radius. First a plasma in thermal balance is compressed adiabatically. The volume of the compressed plasma is maintained until the plasma reaches a new thermal equilibrium. The plasma is then expanded to its original volume. As a result of the way a stellarator works, the plasma pressure during compression is less than the corresponding pressure during expansion. Therefore, negative work is done on the plasma over a complete cycle. This work manifests itself as a back-voltage in the toroidal field coils. Direct electrical energy is obtained from this voltage. Alternatively, after the compression step, the plasma can be expanded at constant pressure. The cycle can be made self-sustaining by operating a system of two stellarator reactors in tandem. Part of the energy derived from the expansion phase of a first stellarator reactor is used to compress the plasma in a second stellarator reactor.

  8. On impact mechanics in ship collisions

    DEFF Research Database (Denmark)

    Pedersen, Preben Terndrup; Zhang, Shengming

    1998-01-01

    The purpose of this paper is to present analytical, closed-form expressions for the energy released for crushing and the impact impulse during ship collisions. Ship–ship collisions, ship collisions with rigid walls and ship collisions with flexible offshore structures are considered. The derived...... of illustrative examples are presented. The procedure presented in the paper is well suited for inclusion in a probabilistic calculation model for damage of ship structures due to collisions....

  9. Collision attack against Tav-128 hash function

    Science.gov (United States)

    Hariyanto, Fajar; Hayat Susanti, Bety

    2017-10-01

    Tav-128 is a hash function which is designed for Radio Frequency Identification (RFID) authentication protocol. Tav-128 is expected to be a cryptographically secure hash function which meets collision resistance properties. In this research, a collision attack is done to prove whether Tav-128 is a collision resistant hash function. The results show that collisions can be obtained in Tav-128 hash function which means in other word, Tav-128 is not a collision resistant hash function.

  10. Dark matter constraints from stellar evolution

    Science.gov (United States)

    Ayala, A.; Domínguez, I.; Straniero, O.

    2016-01-01

    The study of dark matter constraints from its effect on star evolution has been discussed in recent years. We propose a star evolution simulation approach to determine those costraints from properties related to star evolutionary stages and propose globular cluster observables in order to check those constraints. My work in progress (my PhD project research) employs FRANEC code to simulate complete star evolution from pre-main sequence to AGB phase, and regards several DM candidates like axions or WIMPs, motivated by different unsolved physical problems. Detailed energy production or energy loss due to DM particles are included, taking into account the expected interaction between dark matter particles and stellar plasma within different models.

  11. Stellar pulsations in beyond Horndeski gravity theories

    Science.gov (United States)

    Sakstein, Jeremy; Kenna-Allison, Michael; Koyama, Kazuya

    2017-03-01

    Theories of gravity in the beyond Horndeski class recover the predictions of general relativity in the solar system whilst admitting novel cosmologies, including late-time de Sitter solutions in the absence of a cosmological constant. Deviations from Newton's law are predicted inside astrophysical bodies, which allow for falsifiable, smoking-gun tests of the theory. In this work we study the pulsations of stars by deriving and solving the wave equation governing linear adiabatic oscillations to find the modified period of pulsation. Using both semi-analytic and numerical models, we perform a preliminary survey of the stellar zoo in an attempt to identify the best candidate objects for testing the theory. Brown dwarfs and Cepheid stars are found to be particularly sensitive objects and we discuss the possibility of using both to test the theory.

  12. Stellar Pulsations in Beyond Horndeski Gravity Theories

    CERN Document Server

    Sakstein, Jeremy; Koyama, Kazuya

    2016-01-01

    Theories of gravity in the beyond Horndeski class recover the predictions of general relativity in the solar system whilst admitting novel cosmologies, including late-time de Sitter solutions in the absence of a cosmological constant. Deviations from Newton's law are predicted inside astrophysical bodies, which allow for falsifiable, smoking-gun tests of the theory. In this work we study the pulsations of stars by deriving and solving the wave equation governing linear adiabatic oscillations to find the modified period of pulsation. Using both semi-analytic and numerical models, we perform a preliminary survey of the stellar zoo in an attempt to identify the best candidate objects for testing the theory. Brown dwarfs and Cepheid stars are found to be particularly sensitive objects and we discuss the possibility of using both to test the theory.

  13. On the stellar rotation-activity connection

    Science.gov (United States)

    Rosner, R.

    1983-01-01

    The relationship between rotation rates and surface activity in late-type dwarf stars is explored in a survey of recent theoretical and observational studies. Current theoretical models of stellar-magnetic-field production and coronal activity are examined, including linear kinematic dynamo theory, nonlinear dynamos using approximations, and full numerical simulations of the MHD equations; and some typical results are presented graphically. The limitations of the modeling procedures and the constraints imposed by the physics are indicated. The statistical techniques used in establishing correlations between various observational parameters are analyzed critically, and the methods developed for quasar luminosity functions by Avni et al. (1980) are used to evaluate the effects of upper detection bounds, incomplete samples, and missing data for the case of rotation and X-ray flux data.

  14. Molecules in Outflows from Young Stellar Objects

    Science.gov (United States)

    Tafalla, M.

    2013-10-01

    Bipolar outflows from young stellar objects are excellent laboratories to study shock chemistry in the interstellar medium. Observations show that a number of molecular species suffer order-of-magnitude abundance enhancements in the outflow gas, likely due to a combination of dust-mantle disruption and high-temperature gas chemistry. The study of these enhanced species is of great interest to characterize shock chemistry. It also offers a highly selective tool to trace the interaction between the outflow and the cloud, which is necessary to elucidate the still mysterious nature of the outflow driving wind. This contribution reviews some of the recent progress in the study of the molecular composition of bipolar outflows with emphasis on the tracers most relevant for shock chemistry and on the new data from the Herschel Space Observatory.

  15. Modeling Neutral Hydrogen in the HSX Stellarator

    Science.gov (United States)

    Stephey, L.; Bader, A.; Anderson, D. T.; Talmadge, J. N.; Hegna, C.; Anderson, F. S. B.

    2012-10-01

    Efforts to improve the understanding of neutral hydrogen in the HSX stellarator are ongoing. The DEGAS code [1], a fully 3D Monte-Carlo neutral particle code, is used to simulate neutral particle density and synthetic H-alpha emission in HSX. DEGAS simulations are compared to EMC3-EIRENE [2] simulations in an effort to understand the similarities and differences in how each code predicts neutral physics in the unique HSX geometry and relatively low operating density. Additionally, experimentally motivated DEGAS simulations are presented of a supersonic gas injection system that will be installed on HSX. Finally, simulations of many different wall recycling scenarios are presented in an effort to develop a plasma wall interaction model that more closely matches experimental H-alpha measurements.[4pt] [1] D. B. Heifetz et al, J. Comp. Phys. Vol. 46 (1982) p. 309.[0pt] [2] Y. Feng et al, Contribution Plasma Physics, 44 1-3 (2004) p. 57-69.

  16. STRESS - STEREO TRansiting Exoplanet and Stellar Survey

    Science.gov (United States)

    Sangaralingam, Vinothini; Stevens, Ian R.; Spreckley, Steve; Debosscher, Jonas

    2010-02-01

    The Heliospheric Imager (HI) instruments on board the two STEREO (Solar TErrestrial RElations Observatory) spacecraft provides an excellent opportunity for space based stellar photometry. The HI instruments provide a wide area coverage (20° × 20° for the two HI-1 instruments and 70° × 70° for the two HI-2 instruments) and long continuous periods of observations (20 days and 70 days respectively). Using HI-1A which has a pass band of 6500Å to 7500Å and a cadence of 40 minutes, we have gathered photometric information for more than a million stars brighter than 12th magnitude for a period of two years. Here we present some early results from this study on a range of variable stars and the future prospects for the data.

  17. Carbon impurity measurements in the HSX stellarator

    Science.gov (United States)

    Mohoney, J. M.; Kumar, S. T. A.; Likin, K. M.; Anderson, D. T.

    2017-10-01

    Impurity behavior in stellarators is not fully understood despite important implications on device performance, in particular, an accumulation of core impurities can lead to degradation of plasma energy due to radiative losses. Experiments are being conducted at HSX to measure the radial profiles and the time history of carbon impurity density using the charge exchange recombination spectroscopy (CXRS) diagnostic. Measurements of fully ionized carbon have been performed on various magnetic configurations, showing a peaked profile at the core in the standard configuration. An inversion technique was also developed to calculate localized C +5 profiles. Comparisons of impurity behavior between the standard and broken-symmetry configurations are presented. Work supported by the US DOE under Grant DE-FG02-93ER54222 and the Hilldale Research Fellowship.

  18. Habitable zone dependence on stellar parameter uncertainties

    Energy Technology Data Exchange (ETDEWEB)

    Kane, Stephen R., E-mail: skane@sfsu.edu [Department of Physics and Astronomy, San Francisco State University, 1600 Holloway Avenue, San Francisco, CA 94132 (United States)

    2014-02-20

    An important property of exoplanetary systems is the extent of the Habitable Zone (HZ), defined as that region where water can exist in a liquid state on the surface of a planet with sufficient atmospheric pressure. Both ground- and space-based observations have revealed a plethora of confirmed exoplanets and exoplanetary candidates, most notably from the Kepler mission using the transit detection technique. Many of these detected planets lie within the predicted HZ of their host star. However, as is the case with the derived properties of the planets themselves, the HZ boundaries depend on how well we understand the host star. Here we quantify the uncertainties of HZ boundaries on the parameter uncertainties of the host star. We examine the distribution of stellar parameter uncertainties from confirmed exoplanet hosts and Kepler candidate hosts and translate these into HZ boundary uncertainties. We apply this to several known systems with an HZ planet to determine the uncertainty in their HZ status.

  19. Exoplanet Transits of Stellar Active Regions

    Science.gov (United States)

    Giampapa, Mark S.; Andretta, Vincenzo; Covino, Elvira; Reiners, Ansgar; Esposito, Massimiliano

    2018-01-01

    We report preliminary results of a program to obtain high spectral- and temporal-resolution observations of the neutral helium triplet line at 1083.0 nm in transiting exoplanet systems. The principal objective of our program is to gain insight on the properties of active regions, analogous to solar plages, on late-type dwarfs by essentially using exoplanet transits as high spatial resolution probes of the stellar surface within the transit chord. The 1083 nm helium line is a particularly appropriate diagnostic of magnetized areas since it is weak in the quiet photosphere of solar-type stars but appears strongly in absorption in active regions. Therefore, during an exoplanet transit over the stellar surface, variations in its absorption equivalent width can arise that are functions of the intrinsic strength of the feature in the active region and the known relative size of the exoplanet. We utilized the Galileo Telescope and the GIANO-B near-IR echelle spectrograph to obtain 1083 nm spectra during transits in bright, well-known systems that include HD 189733, HD 209458, and HD 147506 (HAT-P-2). We also obtained simultaneous auxiliary data on the same telescope with the HARPS-N UV-Visible echelle spectrograph. We will present preliminary results from our analysis of the observed variability of the strength of the He I 1083 nm line during transits.Acknowledgements: Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. The NSO is operated by AURA under a cooperative agreement with the NSF.

  20. Rapid mass segregation in small stellar clusters

    Science.gov (United States)

    Spera, Mario; Capuzzo-Dolcetta, Roberto

    2017-12-01

    In this paper we focus our attention on small-to-intermediate N-body systems that are, initially, distributed uniformly in space and dynamically `cool' (virial ratios Q=2T/|Ω| below ˜0.3). In this work, we study the mass segregation that emerges after the initial violent dynamical evolution. At this scope, we ran a set of high precision N-body simulations of isolated clusters by means of HiGPUs, our direct summation N-body code. After the collapse, the system shows a clear mass segregation. This (quick) mass segregation occurs in two phases: the first shows up in clumps originated by sub-fragmentation before the deep overall collapse; this segregation is partly erased during the deep collapse to re-emerge, abruptly, during the second phase, that follows the first bounce of the system. In this second stage, the proper clock to measure the rate of segregation is the dynamical time after virialization, which (for cold and cool systems) may be significantly different from the crossing time evaluated from initial conditions. This result is obtained for isolated clusters composed of stars of two different masses (in the ratio mh/ml=2), at varying their number ratio, and is confirmed also in presence of a massive central object (simulating a black hole of stellar size). Actually, in stellar systems starting their dynamical evolution from cool conditions, the fast mass segregation adds to the following, slow, secular segregation which is collisionally induced. The violent mass segregation is an effect persistent over the whole range of N (128 ≤ N ≤1,024) investigated, and is an interesting feature on the astronomical-observational side, too. The semi-steady state reached after virialization corresponds to a mass segregated distribution function rather than that of equipartition of kinetic energy per unit mass as it should result from violent relaxation.

  1. collision zone of an ISR

    CERN Multimedia

    This is a collision region from the world’s first proton collider, the Intersecting Storage Rings. The ISR was used at CERN from 1971-84 to study proton-proton collisions at the highest energy then available (60GeV). When operational, ISR collision regions were surrounded by detectors as shown in the photo. In 1972, the surprising discovery of fragments flying out sideways from head-on proton-proton collisions was the first evidence of quark-quark scattering inside the colliding protons . This was similar to Rutherford’s observation in 1911 of alpha particles scattering off the tiny nucleus inside atoms of gold. The ISR beamtubes had to be as empty as outer space, a vacuum 100 000 times better than other CERN machines at the time.

  2. Collision region of the ISR

    CERN Multimedia

    1970-01-01

    This is a collision region from the world’s first proton collider, the Intersecting Storage Rings. The ISR was used at CERN from 1971-84 to study proton-proton collisions at the highest energy then available (60GeV). When operational, ISR collision regions were surrounded by detectors as shown in the photo. In 1972, the surprising discovery of fragments flying out sideways from head-on proton-proton collisions was the first evidence of quark-quark scattering inside the colliding protons . This was similar to Rutherford’s observation in 1911 of alpha particles scattering off the tiny nucleus inside atoms of gold. The ISR beamtubes had to be as empty as outer space, a vacuum 100 000 times better than other CERN machines at the time.

  3. Neuromorphic UAS Collision Avoidance Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Using biologically-inspired neuromorphic optic flow algorithms is a novel approach in collision avoidance for UAS. Traditional computer vision algorithms rely on...

  4. Limits on evolution of the fine-structure constant in runaway dilaton models from Sunyaev–Zeldovich observations

    Directory of Open Access Journals (Sweden)

    R.F.L. Holanda

    2017-04-01

    Full Text Available In this paper, new bounds on possible variations of the fine structure constant, α, for a class of runaway dilaton models are performed. By considering a possible evolution with redshift, z, such as Δαα=−γln⁡(1+z, where in γ are the physical properties of the model, we constrain this parameter by using a deformed cosmic distance duality relation jointly with gas mass fraction (GMF measurements of galaxy clusters and luminosity distances of type Ia supernovae. The GMF's used in our analyses are from cluster mass data from 82 galaxy clusters in the redshift range 0.12

  5. Conceptual design of the Radial Gamma Ray Spectrometers system for α particle and runaway electron measurements at ITER

    DEFF Research Database (Denmark)

    Nocente, Massimo; Tardocchi, Marco; Barnsley, Robin

    2017-01-01

    We here present the principles and main physics capabilities behind the design of the radial gamma ray spectrometers (RGRS) system for alpha particle and runaway electron measurements at ITER. The diagnostic benefits from recent advances in gamma-ray spectrometry for tokamak plasmas and combines...... space and high energy resolution in a single device. The RGRS system as designed can provide information on α particles on a time scale of 1/10 of the slowing down time for the ITER 500 MW full power DT scenario. Spectral observations of the 3.21 and 4.44 MeV peaks from the 9Be (α, nϒ) 12C reaction make...

  6. Inferring probabilistic stellar rotation periods using Gaussian processes

    Science.gov (United States)

    Angus, Ruth; Morton, Timothy; Aigrain, Suzanne; Foreman-Mackey, Daniel; Rajpaul, Vinesh

    2018-02-01

    Variability in the light curves of spotted, rotating stars is often non-sinusoidal and quasi-periodic - spots move on the stellar surface and have finite lifetimes, causing stellar flux variations to slowly shift in phase. A strictly periodic sinusoid therefore cannot accurately model a rotationally modulated stellar light curve. Physical models of stellar surfaces have many drawbacks preventing effective inference, such as highly degenerate or high-dimensional parameter spaces. In this work, we test an appropriate effective model: a Gaussian Process with a quasi-periodic covariance kernel function. This highly flexible model allows sampling of the posterior probability density function of the periodic parameter, marginalizing over the other kernel hyperparameters using a Markov Chain Monte Carlo approach. To test the effectiveness of this method, we infer rotation periods from 333 simulated stellar light curves, demonstrating that the Gaussian process method produces periods that are more accurate than both a sine-fitting periodogram and an autocorrelation function method. We also demonstrate that it works well on real data, by inferring rotation periods for 275 Kepler stars with previously measured periods. We provide a table of rotation periods for these and many more, altogether 1102 Kepler objects of interest, and their posterior probability density function samples. Because this method delivers posterior probability density functions, it will enable hierarchical studies involving stellar rotation, particularly those involving population modelling, such as inferring stellar ages, obliquities in exoplanet systems, or characterizing star-planet interactions. The code used to implement this method is available online.

  7. Stellar contributions to the diffuse soft X-ray background

    Science.gov (United States)

    Bookbinder, J.; Avni, Y.; Golub, L.; Rosner, R.; Vaiana, G.

    1981-01-01

    One of the results of the EINSTEIN/C.f.A. X-ray stellar survey was a determination of the contribution of the disk stellar population to the galactic component of the diffuse soft (0.28 - 1.0 keV) X-ray background. This analysis employed both binned and unbinned nonparametric statistical methods that have been developed by Avni, et al. (1980). These methods permitted the use of the information contained in both the 22 detections and 4 upper bounds on the luminosities of 26 dM stars in order to derive their luminosity function. Luminosity functions for earlier stellar types are not yet developed. For these earlier stellar types, the median luminosities as determined by Vaiana, et al., are used (1981), which underestimates their contribution to the background. We find that it is the M dwarfs that dominate the disk population stellar contribution to this background. To calculate the contribution of the stellar sources to the background, simple models both for the spatial distribution of the stars and for the properties of the intervening interstellar medium are used. A model is chosen in which all stellar classes have the same functional form for their spatial distribution: an exponentially decreasing distribution above the galactic equatorial plane, and a uniform distribution within the galactic plane for a region of several kiloparsecs centered on the Sun.

  8. Radial velocity planet detection biases at the stellar rotational period

    Science.gov (United States)

    Vanderburg, Andrew; Plavchan, Peter; Johnson, John Asher; Ciardi, David R.; Swift, Jonathan; Kane, Stephen R.

    2016-07-01

    Future generations of precise radial velocity (RV) surveys aim to achieve sensitivity sufficient to detect Earth mass planets orbiting in their stars' habitable zones. A major obstacle to this goal is astrophysical RV noise caused by active areas moving across the stellar limb as a star rotates. In this paper, we quantify how stellar activity impacts exoplanet detection with radial velocities as a function of orbital and stellar rotational periods. We perform data-driven simulations of how stellar rotation affects planet detectability and compile and present relations for the typical time-scale and amplitude of stellar RV noise as a function of stellar mass. We show that the characteristic time-scales of quasi-periodic RV jitter from stellar rotational modulations coincides with the orbital period of habitable-zone exoplanets around early M-dwarfs. These coincident periods underscore the importance of monitoring the targets of RV habitable-zone planet surveys through simultaneous photometric measurements for determining rotation periods and activity signals, and mitigating activity signals using spectroscopic indicators and/or RV measurements at different wavelengths.

  9. Massive Black Hole Implicated in Stellar Destruction

    Science.gov (United States)

    2010-01-01

    New results from NASA's Chandra X-ray Observatory and the Magellan telescopes suggest that a dense stellar remnant has been ripped apart by a black hole a thousand times as massive as the Sun. If confirmed, this discovery would be a cosmic double play: it would be strong evidence for an intermediate mass black hole, which has been a hotly debated topic, and would mark the first time such a black hole has been caught tearing a star apart. This scenario is based on Chandra observations, which revealed an unusually luminous source of X-rays in a dense cluster of old stars, and optical observations that showed a peculiar mix of elements associated with the X-ray emission. Taken together, a case can be made that the X-ray emission is produced by debris from a disrupted white dwarf star that is heated as it falls towards a massive black hole. The optical emission comes from debris further out that is illuminated by these X-rays. The intensity of the X-ray emission places the source in the "ultraluminous X-ray source" or ULX category, meaning that it is more luminous than any known stellar X-ray source, but less luminous than the bright X-ray sources (active galactic nuclei) associated with supermassive black holes in the nuclei of galaxies. The nature of ULXs is a mystery, but one suggestion is that some ULXs are black holes with masses between about a hundred and several thousand times that of the Sun, a range intermediate between stellar-mass black holes and supermassive black holes located in the nuclei of galaxies. This ULX is in a globular cluster, a very old and crowded conglomeration of stars. Astronomers have suspected that globular clusters could contain intermediate-mass black holes, but conclusive evidence for this has been elusive. "Astronomers have made cases for stars being torn apart by supermassive black holes in the centers of galaxies before, but this is the first good evidence for such an event in a globular cluster," said Jimmy Irwin of the University

  10. The Dark Energy Survey: Prospects for resolved stellar populations

    Energy Technology Data Exchange (ETDEWEB)

    Rossetto, Bruno M. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Santiago, Basílio X. [Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Instituto de Fisica, Porto Alegre (Brazil); Girardi, Léo [Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Osservatorio Astronomica di Padova-INAF, Padova (Italy); Camargo, Julio I. B. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Balbinot, Eduardo [Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Instituto de Fisica, Porto Alegre (Brazil); da Costa, Luiz N. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Yanny, Brian [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Maia, Marcio A. G. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Makler, Martin [Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro (Brazil); Ogando, Ricardo L. C. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Pellegrini, Paulo S. [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Ramos, Beatriz [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); de Simoni, Fernando [Observatorio Nacional, Rio de Janeiro (Brazil); Lab. Interinstitucional de e-Astronomia-LIneA, Rio de Janeiro (Brazil); Armstrong, R. [Univ. of Illinois, Urbana, IL (United States); Bertin, E. [Univ. Pierre et Marie Curie, Paris (France); Desai, S. [Univ. of Illinois, Urbana, IL (United States); Kuropatkin, N. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Lin, H. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Mohr, J. J. [Max-Planck-Institut fur extraterrestrische Physik, Garching (Germany); Tucker, D. L. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)

    2011-05-06

    Wide angle and deep surveys, regardless of their primary purpose, always sample a large number of stars in the Galaxy and in its satellite system. We here make a forecast of the expected stellar sample resulting from the Dark Energy Survey and the perspectives that it will open for studies of Galactic structure and resolved stellar populations in general. An estimated 1.2 x 108 stars will be sampled in DES grizY filters in the southern equatorial hemisphere. This roughly corresponds to 20% of all DES sources. Most of these stars belong to the stellar thick disk and halo of the Galaxy.

  11. Studying stellar rotation and convection theoretical background and seismic diagnostics

    CERN Document Server

    Belkacem, Kévin; Neiner, Coralie; Lignières, Francois; Green, John

    2013-01-01

    This volume synthesizes the results of work carried out by several international teams of the SIROCO (Seismology for Rotation and Convection) collaboration. It provides the theoretical background required to interpret the huge quantity of high-quality observational data recently provided by space experiments such as CoRoT and Kepler. Asteroseismology allows astrophysicists to test, to model and to understand stellar structure and evolution as never before. The chapters in this book address the two groups of topics summarized as "Stellar Rotation and Associated Seismology" as well as "Stellar Convection and Associated Seismology". The book offers the reader solid theoretical background knowledge and adapted seismic diagnostic techniques.

  12. Dynamics of stellar filaments in f(G) gravity

    Science.gov (United States)

    Sharif, M.; Fatima, H. Ismat

    2017-03-01

    We discuss the dynamics of stellar filaments with cylindrical symmetry in the context of f( G) gravity. For this purpose, we consider the modified gravity coupled with a dissipative anisotropic fluid and construct scalar functions through orthogonal splitting of the Riemann tensor. We formulate the set of equations governing the evolution and structure of stellar filaments in terms of these scalars. Finally, we discuss all static solutions for cylindrical filaments with anisotropy as well as isotropy and conclude that stellar filaments are necessarily inhomogeneous in this gravity.

  13. CCFpams: Atmospheric stellar parameters from cross-correlation functions

    Science.gov (United States)

    Malavolta, Luca; Lovis, Christophe; Pepe, Francesco; Sneden, Christopher; Udry, Stephane

    2017-07-01

    CCFpams allows the measurement of stellar temperature, metallicity and gravity within a few seconds and in a completely automated fashion. Rather than performing comparisons with spectral libraries, the technique is based on the determination of several cross-correlation functions (CCFs) obtained by including spectral features with different sensitivity to the photospheric parameters. Literature stellar parameters of high signal-to-noise (SNR) and high-resolution HARPS spectra of FGK Main Sequence stars are used to calibrate the stellar parameters as a function of CCF areas.

  14. Galaxy collisions: A preliminary study

    Energy Technology Data Exchange (ETDEWEB)

    Miller, R.H.; Smith, B.F.

    1980-01-15

    Collisions of spherical galaxies were studied in a series of numerical experiments to see what happens when galaxies collide. Each experiment starts with two model galaxies, each consisting of 50,000 stars, moving toward each other along a specified orbit. Th series of experiments provides a systematic sampling of the parameter space spanned by the initial orbital energy and the initial angular momentum. Deeply penetrating collisions are emphasized. The collisions reported here scale to relative velocities as great as 500 km s/sup -1/, well into the range for collisions within clusters of galaxies. We find: (1) The galaxies contract momentarily to about half their original sizes shortly after close passage. This means that (a) the galaxies have ample time to respond dynamically during close passage; (b) energy first transfers into coherent mass flows within each galaxy; (c) in turn, (a) means that the impulsive and restricted three-body approximations, in which the response is ignored, are not valid for collisions of 1000 km s/sup -1/ or less. (2) The initial galaxies blend into a single dynamical system while they are near each other. This means that concepts such as energy transfer from orbital motion to internal degrees of freedom are not well defined until long after close approach, when two density maxima are well separated and each has settled down to a reasonably steady state.

  15. Automatic Collision Avoidance Technology (ACAT)

    Science.gov (United States)

    Swihart, Donald E.; Skoog, Mark A.

    2007-01-01

    This document represents two views of the Automatic Collision Avoidance Technology (ACAT). One viewgraph presentation reviews the development and system design of Automatic Collision Avoidance Technology (ACAT). Two types of ACAT exist: Automatic Ground Collision Avoidance (AGCAS) and Automatic Air Collision Avoidance (AACAS). The AGCAS Uses Digital Terrain Elevation Data (DTED) for mapping functions, and uses Navigation data to place aircraft on map. It then scans DTED in front of and around aircraft and uses future aircraft trajectory (5g) to provide automatic flyup maneuver when required. The AACAS uses data link to determine position and closing rate. It contains several canned maneuvers to avoid collision. Automatic maneuvers can occur at last instant and both aircraft maneuver when using data link. The system can use sensor in place of data link. The second viewgraph presentation reviews the development of a flight test and an evaluation of the test. A review of the operation and comparison of the AGCAS and a pilot's performance are given. The same review is given for the AACAS is given.

  16. Hunting for Stellar Coronal Mass Ejections

    Science.gov (United States)

    Korhonen, Heidi; Vida, Krisztián; Leitzinger, Martin; Odert, Petra; Kovács, Orsolya Eszter

    2017-10-01

    Coronal mass ejections (CMEs) are explosive events that occur basically daily on the Sun. It is thought that these events play a crucial role in the angular momentum and mass loss of late-type stars, and also shape the environment in which planets form and live. Stellar CMEs can be detected in optical spectra in the Balmer lines, especially in Hα, as blue-shifted extra emission/absorption. To increase the detection probability one can monitor young open clusters, in which the stars are due to their youth still rapid rotators, and thus magnetically active and likely to exhibit a large number of CMEs. Using ESO facilities and the Nordic Optical Telescope we have obtained time series of multi-object spectroscopic observations of late-type stars in six open clusters with ages ranging from 15 Myrs to 300 Myrs. Additionally, we have studied archival data of numerous active stars. These observations will allow us to obtain information on the occurrence rate of CMEs in late-type stars with different ages and spectral types. Here we report on the preliminary outcome of our studies.

  17. Exploration of turbulent optimization in stellarators & tokamaks

    Science.gov (United States)

    Mynick, H.; Pomphrey, N.; Xanthopoulos, P.; Lucia, M.

    2012-03-01

    A methodfootnotetextH.E. Mynick, N. Pomphrey, P. Xanthopoulos, Phys. Rev. Letters, 105, 095004 (2010).^,footnotetextH.E. Mynick, N. Pomphrey, P. Xanthopoulos, Phys. Plasmas, 18, 056101 (2011). recently developed for evolving toroidal configurations to ones with reduced turbulent transport, using the STELLOPT optimization codes and the GENE gyrokinetic code, is being applied and extended. The growing body of results has found that the effectiveness of the current proxy measure Qprox used by STELLOPT to estimate transport levels depends on the class of toroidal device considered. The present proxy works well for quasi-axisymmetric stellarators and tokamaks, modestly for quasi-helically symmetric designs, but not for the W7X quasi-omnigenous/quasi-isodynamic design. We are exploring the origin of this variation, and improving the dependence of the proxy on key geometric factors, extending the proxy to apply to transport channels other than the ITG turbulence it was originally developed for, and are also examining the relative effectiveness of different search algorithms. To help in these efforts, we have adapted STELLOPT to provide a new capability for mapping the topography of the cost function in the search space.

  18. First Stellar Occultation Observation with SOFIA

    Science.gov (United States)

    Dunham, Edward W.; Bida, T.; Bosh, A.; Collins, P.; Levine, S.; Person, M.; Pfueller, E.; Roeser, H.; Taylor, B.; Wiedemann, M.; Wolf, J.; Zuluaga, C.

    2012-01-01

    We successfully observed the 2011 June 23 UT stellar occultation by Pluto with the High-speed Imaging Photometer for Occultations (HIPO) instrument from Lowell Observatory and the Fast Diagnostic Camera (FDC) from the Deutches SOFIA Institut (DSI) mounted on the SOFIA telescope. A major prediction astrometry effort focused at MIT combined with the willingness of the SOFIA project to entertain the idea of an in-flight change to the flight plan allowed us to target the center of the occultation shadow. This was accomplished by means of an in-flight prediction update by satellite telephone and a real-time onboard flight plan modification to accommodate the prediction update. We obtained excellent results with both channels of HIPO and the FDC with each light curve showing a small, extended brightening while the star was occulted. We will discuss analysis results as well as SOFIA's considerable potential for future occultation work. We thank the SOFIA program for its willingness to attempt this challenging observation at such an early stage of SOFIA science operations. Lowell's SOFIA work was supported by a grant from USRA, MIT's prediction work was supported by the NASA Planetary Astronomy Program and the National Science Foundation, and the FDC work was supported by the DSI. We thank the US Naval Observatory Flagstaff Station for allowing us to use their facilities to obtain our prediction astrometry observations.

  19. Stellar Atmospheric Parameterization Based on Deep Learning

    Science.gov (United States)

    Pan, Ru-yang; Li, Xiang-ru

    2017-07-01

    Deep learning is a typical learning method widely studied in the fields of machine learning, pattern recognition, and artificial intelligence. This work investigates the problem of stellar atmospheric parameterization by constructing a deep neural network with five layers, and the node number in each layer of the network is respectively 3821-500-100-50-1. The proposed scheme is verified on both the real spectra measured by the Sloan Digital Sky Survey (SDSS) and the theoretic spectra computed with the Kurucz's New Opacity Distribution Function (NEWODF) model, to make an automatic estimation for three physical parameters: the effective temperature (Teff), surface gravitational acceleration (lg g), and metallic abundance (Fe/H). The results show that the stacked autoencoder deep neural network has a better accuracy for the estimation. On the SDSS spectra, the mean absolute errors (MAEs) are 79.95 for Teff/K, 0.0058 for (lg Teff/K), 0.1706 for lg (g/(cm·s-2)), and 0.1294 dex for the [Fe/H], respectively; On the theoretic spectra, the MAEs are 15.34 for Teff/K, 0.0011 for lg (Teff/K), 0.0214 for lg(g/(cm · s-2)), and 0.0121 dex for [Fe/H], respectively.

  20. An Unusual Stellar Death on Christmas Day

    Science.gov (United States)

    Thone, C. C.; de Ugarte Postigo, A.; Fryer, C. L.; Page, K. L.; Gorosabel, J.; Aloy, M. A.; Perley, D. A.; Kouveliotou, C.; Janka, H. T.; Mimica, P.; hide

    2011-01-01

    Long Gamma-Ray Bursts (GRBs) are the most dramatic examples of massive stellar deaths, usually associated with supernovae. They release ultra-relativistic jets producing non-thermal emission through synchrotron radiation as they interact with the surrounding medium. Here we report observations of the peculiar GRB 101225A (the "Christmas burst"). Its gamma-ray emission was exceptionally long and followed by a bright X-ray transient with a hot thermal component and an unusual optical couuterpart. During the first 10 days, the optical emission evolved as an expanding, cooling blackbody after which an additional component, consistent with a faint supernova, emerged. We determine its distance to 1.6 Gpc by fitting the spectral-energy distribution and light curve of the optical emission with a GRB-supernova template. Deep optical observations may have revealed a faint, unresolved host galaxy. Our proposed progenitor is a helium star-neutron star merger that underwent a common envelope phase expelling its hydrogen envelope. The resulting explosion created a GRB-like jet which gets thermalized by interacting with the dense, previously ejected material and thus creating the observed black-body, until finally the emission from the supernova dominated. An alternative explanation is a minor body falling onto a neutron star io the Galaxy

  1. Survival of planets around shrinking stellar binaries.

    Science.gov (United States)

    Muñoz, Diego J; Lai, Dong

    2015-07-28

    The discovery of transiting circumbinary planets by the Kepler mission suggests that planets can form efficiently around binary stars. None of the stellar binaries currently known to host planets has a period shorter than 7 d, despite the large number of eclipsing binaries found in the Kepler target list with periods shorter than a few days. These compact binaries are believed to have evolved from wider orbits into their current configurations via the so-called Lidov-Kozai migration mechanism, in which gravitational perturbations from a distant tertiary companion induce large-amplitude eccentricity oscillations in the binary, followed by orbital decay and circularization due to tidal dissipation in the stars. Here we explore the orbital evolution of planets around binaries undergoing orbital decay by this mechanism. We show that planets may survive and become misaligned from their host binary, or may develop erratic behavior in eccentricity, resulting in their consumption by the stars or ejection from the system as the binary decays. Our results suggest that circumbinary planets around compact binaries could still exist, and we offer predictions as to what their orbital configurations should be like.

  2. Cool WISPs for stellar cooling excesses

    Science.gov (United States)

    Giannotti, Maurizio; Irastorza, Igor; Redondo, Javier; Ringwald, Andreas

    2016-05-01

    Several stellar systems (white dwarfs, red giants, horizontal branch stars and possibly the neutron star in the supernova remnant Cassiopeia A) show a mild preference for a non-standard cooling mechanism when compared with theoretical models. This exotic cooling could be provided by Weakly Interacting Slim Particles (WISPs), produced in the hot cores and abandoning the star unimpeded, contributing directly to the energy loss. Taken individually, these excesses do not show a strong statistical weight. However, if one mechanism could consistently explain several of them, the hint could be significant. We analyze the hints in terms of neutrino anomalous magnetic moments, minicharged particles, hidden photons and axion-like particles (ALPs). Among them, the ALP or a massless HP represent the best solution. Interestingly, the hinted ALP parameter space is accessible to the next generation proposed ALP searches, such as ALPS II and IAXO and the massless HP requires a multi TeV energy scale of new physics that might be accessible at the LHC.

  3. New views of the distant stellar halo

    Science.gov (United States)

    Sanderson, Robyn E.; Secunda, Amy; Johnston, Kathryn V.; Bochanski, John J.

    2017-10-01

    Currently, only a small number of Milky Way (MW) stars are known to exist beyond 100 kpc from the Galactic Centre. Though the distribution of these stars in the outer halo is believed to be sparse, they can provide evidence of more recent accretion events than in the inner halo and help map out the MW's dark matter halo to its virial radius. We have re-examined the outermost regions of 11 existing stellar halo models with two synthetic surveys: one mimicking present-day searches for distant M giants and another mimicking RR Lyra (RRL) projections for the Large Synoptic Survey Telescope (LSST). Our models suggest that colour and proper motion cuts currently used to select M giant candidates for follow-up successfully remove nearly all self-contamination from foreground halo dwarf stars and are useful for focusing observations on distant M giants, of which there are thousands to tens of thousands beyond 100 kpc in our models. We likewise expect that LSST will identify comparable numbers of RRLe at these distances. We demonstrate that several observable properties of both tracers, such as proximity of neighbouring stars, proper motions and distances (for RRLe), could help us separate different accreted dwarf galaxies from one another in the distant MW halo. We also discuss prospects for using ratios of M giants to RRLe as a proxy for accretion time, which in the future could provide new constraints on the recent accretion history of our Galaxy.

  4. The Ancient stellar population of Leo A.

    Science.gov (United States)

    Saha, Abhijit; Fiorentino, Giuliana; Tolstoy, Eline; Cole, Andrew

    2010-02-01

    The primary goal of our proposal is the characterisation of the oldest stellar populations in Leo A using the properties of ancient RR Lyrae variable stars as tracers. Well known and long established correlations exist between the periods and luminosities of RR Lyrae variable stars and their ages and metallicities. Combining our Gemini study of the properties of RR Lyrae variable stars with deep HST/ACS imaging of the oldest main sequence turnoffs in Leo A will allow us to make a uniquely detailed study of the star formation history of Leo A at the earliest times. This will enable us to study how the formation and evolution of Leo A was affected (if at all) by events in the early universe, such as the formation of the first stars and the Epoch of Reionisation. This is a re-submission because our previous observations, in February-March 2009, suffered from bad weather conditions and did not allow us to complete more than 15% of our programme.

  5. Hydrogen-poor superluminous stellar explosions.

    Science.gov (United States)

    Quimby, R M; Kulkarni, S R; Kasliwal, M M; Gal-Yam, A; Arcavi, I; Sullivan, M; Nugent, P; Thomas, R; Howell, D A; Nakar, E; Bildsten, L; Theissen, C; Law, N M; Dekany, R; Rahmer, G; Hale, D; Smith, R; Ofek, E O; Zolkower, J; Velur, V; Walters, R; Henning, J; Bui, K; McKenna, D; Poznanski, D; Cenko, S B; Levitan, D

    2011-06-08

    Supernovae are stellar explosions driven by gravitational or thermonuclear energy that is observed as electromagnetic radiation emitted over weeks or more. In all known supernovae, this radiation comes from internal energy deposited in the outflowing ejecta by one or more of the following processes: radioactive decay of freshly synthesized elements (typically (56)Ni), the explosion shock in the envelope of a supergiant star, and interaction between the debris and slowly moving, hydrogen-rich circumstellar material. Here we report observations of a class of luminous supernovae whose properties cannot be explained by any of these processes. The class includes four new supernovae that we have discovered and two previously unexplained events (SN 2005ap and SCP 06F6) that we can now identify as members of the same class. These supernovae are all about ten times brighter than most type Ia supernova, do not show any trace of hydrogen, emit significant ultraviolet flux for extended periods of time and have late-time decay rates that are inconsistent with radioactivity. Our data require that the observed radiation be emitted by hydrogen-free material distributed over a large radius (∼10(15) centimetres) and expanding at high speeds (>10(4) kilometres per second). These long-lived, ultraviolet-luminous events can be observed out to redshifts z > 4.

  6. Report on the Workshop "Stellar Populations in Stellar Clusters and Dwarf Galaxies — New Astronomical and Astrophysical Challenges"

    Science.gov (United States)

    Dias, B.; Saviane, I.

    2017-06-01

    Chile hosts many world-leading expert groups working on stellar populations and stellar clusters. This field has undergone something of a revolution during the last decade with the advent of large photometric and spectroscopic surveys, and preparations for relevant new facilities are underway. A Chilean meeting on stellar populations and star clusters was therefore timely. The goal was to bring together experts in the field for discussion and to encourage collaboration. The workshop was open to all astronomers and advanced students, especially those in Chilean institutes, limited to a maximum of 50 participants in order to foster discussion.

  7. GrayStarServer: Stellar atmospheric modeling and spectrum synthesis

    Science.gov (United States)

    Short, C. Ian

    2017-01-01

    GrayStarServer is a stellar atmospheric modeling and spectrum synthesis code of pedagogical accuracy that is accessible in any web browser on commonplace computational devices and that runs on a timescale of a few seconds.

  8. Absolute stellar photometry on moderate-resolution FPA images

    Science.gov (United States)

    Stone, T.C.

    2009-01-01

    An extensive database of star (and Moon) images has been collected by the ground-based RObotic Lunar Observatory (ROLO) as part of the US Geological Survey program for lunar calibration. The stellar data are used to derive nightly atmospheric corrections for the observations from extinction measurements, and absolute calibration of the ROLO sensors is based on observations of Vega and published reference flux and spectrum data. The ROLO telescopes were designed for imaging the Moon at moderate resolution, thus imposing some limitations for the stellar photometry. Attaining accurate stellar photometry with the ROLO image data has required development of specialized processing techniques. A key consideration is consistency in discriminating the star core signal from the off-axis point spread function. The analysis and processing methods applied to the ROLO stellar image database are described. ?? 2009 BIPM and IOP Publishing Ltd.

  9. Exclusion of Stellar Companions to Exoplanet Host Stars

    Science.gov (United States)

    Wittrock, Justin M.; Kane, Stephen R.; Horch, Elliott P.; Howell, Steve B.; Ciardi, David R.; Everett, Mark E.

    2017-11-01

    Given the frequency of stellar multiplicity in the solar neighborhood, it is important to study the impacts this can have on exoplanet properties and orbital dynamics. There have been numerous imaging survey projects established to detect possible low-mass stellar companions to exoplanet host stars. Here, we provide the results from a systematic speckle imaging survey of known exoplanet host stars. In total, 71 stars were observed at 692 and 880 nm bands using the Differential Speckle Survey Instrument at the Gemini-north Observatory. Our results show that all but two of the stars included in this sample have no evidence of stellar companions with luminosities down to the detection and projected separation limits of our instrumentation. The mass-luminosity relationship is used to estimate the maximum mass a stellar companion can have without being detected. These results are used to discuss the potential for further radial velocity follow-up and interpretation of companion signals.

  10. Diagnostics Plan for the National Compact Stellarator Experiment

    Energy Technology Data Exchange (ETDEWEB)

    D. Johnson; T. Brown; H. Neilson; G. Schilling; H. Takahashi; M. Zarnstorff; M. Cole; E. Lazarus; and M. Fenstermacher

    2002-07-12

    The National Compact Stellarator Experiment (NCSX) is a stellarator-tokamak hybrid seeking to combine the good confinement, high beta and moderate aspect ratio of the tokamak with the quasi-steady-state operation and good stability properties of the stellarator. A preliminary list of measurement requirements, intended to satisfy the needs of the phased research plan, provides the basis for a full complement of plasma diagnostics. It is important to consider this full set, even at this early stage, to assess the adequacy of the stellarator design for diagnostic port access. The 3-D nature of the plasma is a measurement challenge, as is the necessity for high spatial resolution to assess the quality of magnetic surfaces. Other diagnostic requirements include the need for re-entrant views that penetrate the cryostat, for a convenient e-beam probe for field line mapping, and for a diagnostic neutral beam for active spectroscopy.

  11. Stellar winds, dead zones, and coronal mass ejections

    NARCIS (Netherlands)

    Keppens, R.; Goedbloed, J. P.

    2000-01-01

    Axisymmetric stellar wind solutions are presented that were obtained by numerically solving the ideal magnetohydrodynamic (MHD) equations. Stationary solutions are critically analyzed using the knowledge of the flux functions. These flux functions enter in the general variational principle governing

  12. Seyfert galaxies: A study of brightness variation and stellar concentration

    Science.gov (United States)

    Dawson, D. W.

    1976-01-01

    Ultraviolet photometry of Seyfert galaxies is analyzed for variations in nuclear magnitude. Using multiple apertures permits the estimation of stellar concentration; four Seyfert and two normal spiral galaxies are compared.

  13. Starchive: The Open Access, Open Source Stellar Database

    Science.gov (United States)

    Tanner, A. M.; Muna, D.; Addison, B.; Zohrabi, F.; Geneser, C.; Niffenegger, R.

    2017-11-01

    It has become clear that we must understand the host stars as well as their exoplanets. The Starchive is an open source, open access stellar database and intuitive front-end to help astronomers find planets and determine habitability.

  14. Young Stellar Objects in the Orion B Cloud

    Science.gov (United States)

    Petr-Gotzens, M. G.; Alcalá, J. M.; Spezzi, L.; Jørgensen, J. K.; Stanke, Th.; Lombardi, M.; Alves, J. F.

    2015-12-01

    Wide-field near-infrared imaging surveys offer an excellent opportunity to obtain spatially complete samples of young stars in nearby star-forming regions. By studying their spatial distribution and individual properties, the global star formation characteristics of a region can be established. Near-infrared wide-field imaging observations of a significantly large area in the Orion Molecular Cloud B, obtained with the VISTA telescope on Cerro Paranal are presented. On the basis of photometric selection criteria, we have identified 186 candidate young stellar objects that are associated with the stellar clusters NGC 2068 and NGC 2071, and with the stellar group around HH24-26. Overall, Orion B shows a lot of similarities in its star formation characteristics with other Galactic star-forming regions: a star formation efficiency of a few percent, a stellar mass distribution very similar to that of the Orion Trapezium cluster, and a high observed fraction of circumstellar discs.

  15. Stellar population gradients in isolated, local group dwarf galaxies

    Directory of Open Access Journals (Sweden)

    Hidalgo S.L.

    2012-02-01

    Full Text Available We discuss the detailed star formation as a function of radius that we have derived for the LCID galaxies, with particular emphasis on the stellar populations gradient and the effect of the UV-background.

  16. KINEMATICS OF CLASSICAL CEPHEIDS IN THE NUCLEAR STELLAR DISK

    Energy Technology Data Exchange (ETDEWEB)

    Matsunaga, Noriyuki; Fukue, Kei [Department of Astronomy, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Yamamoto, Ryo; Kobayashi, Naoto; Hamano, Satoshi [Institute of Astronomy, School of Science, The University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015 (Japan); Inno, Laura [European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching bei München (Germany); Genovali, Katia; Bono, Giuseppe [Dipartimento di Fisica, Universitá di Roma Tor Vergata, Via della Ricerca Scientifica 1, I-00133 Rome (Italy); Baba, Junichi [Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551 (Japan); Fujii, Michiko S.; Aoki, Wako; Tsujimoto, Takuji [National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Kondo, Sohei; Ikeda, Yuji [Koyama Astronomical Observatory, Kyoto Sangyo University, Motoyama, Kamigamo, Kita-ku, Kyoto 603-8555 (Japan); Nishiyama, Shogo [Miyagi University of Education, 149 Aramaki-aza-Aoba, Aoba-ku, Sendai, Miyagi 980-0845 (Japan); Nagata, Tetsuya, E-mail: matsunaga@astron.s.u-tokyo.ac.jp [Department of Astronomy, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502 (Japan)

    2015-01-20

    Classical Cepheids are useful tracers of the Galactic young stellar population because their distances and ages can be determined from their period-luminosity and period-age relations. In addition, the radial velocities and chemical abundance of the Cepheids can be derived from spectroscopic observations, providing further insights into the structure and evolution of the Galaxy. Here, we report the radial velocities of classical Cepheids near the Galactic center, three of which were reported in 2011 and a fourth being reported for the first time. The velocities of these Cepheids suggest that the stars orbit within the nuclear stellar disk, a group of stars and interstellar matter occupying a region of ∼200 pc around the center, although the three-dimensional velocities cannot be determined until the proper motions are known. According to our simulation, these four Cepheids formed within the nuclear stellar disk like younger stars and stellar clusters therein.

  17. ASTEROID ALBEDOS FROM STELLAR OCCULTATIONS V1.0

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set contains albedos for 57 asteroids determined from diameters obtained from stellar occultations. These albedos are from Shevchenko and Tedesco (2006).

  18. Three-Dimensional Analysis of Tokamaks and Stellarators

    National Research Council Canada - National Science Library

    Paul R. Garabedian

    2008-01-01

    The NSTAB equilibrium and stability code and the TRAN Monte Carlo transport code furnish a simple but effective numerical simulation of essential features of present tokamak and stellarator experiments...

  19. Novel mechanism of anomalous electron heat conductivity and thermal crashes during Alfvénic activity in the Wendelstein 7-AS stellarator.

    Science.gov (United States)

    Kolesnichenko, Ya I; Yakovenko, Yu V; Weller, A; Werner, A; Geiger, J; Lutsenko, V V; Zegenhagen, S

    2005-04-29

    Enhanced plasma heat conductivity in the presence of kinetic Alfvén waves (KAW) is predicted theoretically. The enhancement is shown to be strongest when the electron collision frequency exceeds the particle transit frequency in the wave field. Alfvén waves (both KAW and ideal MHD Alfvén eigenmodes generating the KAW) are studied in a shot of the Wendelstein 7-AS stellarator. On the basis of these results, strong thermal crashes observed during bursting Alfvénic activity in the mentioned shot are explained.

  20. Andromeda Optical & Infrared Disk Survey: Stellar Populations and Mass Decomposition

    Science.gov (United States)

    Sick, Jonathan; Courteau, Stephane; Cuillandre, Jean-Charles; Dalcanton, Julianne; de Jong, Roelof S.; McDonald, Michael; Tully, R. Brent

    2015-01-01

    M31 is ideal for understanding the structure and stellar populations of spiral galaxies thanks to its proximity and our external vantage point. The Andromeda Optical & Infrared Disk Survey (ANDROIDS) has used MegaCam and WIRCam on the Canada-France Hawaii Telescope to map the M31 bulge and disk out to R=40 kpc in ugriJKs bands. Through careful sky monitoring and modelling, ANDROIDS is uniquely able to observe both the resolved stars and integrated spectral energy distributions (SEDs) over M31's entire disk (complimenting HST's PHAT program). By simultaneously fitting stellar populations with isochrones and SED models for M31, we can assess the systematic uncertainties of SED fits to more distant unresolved systems, and constrain the stellar populations that contribute to each bandpass. We pay close attention to the near-IR light of asymptotic giant branch (AGB) stars in stellar population models. ANDROIDS has also surveyed M31 in narrowband TiO and CN bands, enabling a clean classification of Carbon AGB stars, and a mapping the ratio of Carbon and M-type AGB stars (C/M) across the entire disk. The correlation between C/M and stellar metallicity is useful for constraining the NIR colors of more distant galaxies. We also present a hierarchical Bayesian model of pixel-by-pixel stellar populations, yielding the most detailed map of M31's stellar mass and star formation history to date. We find that a full six-band optical-NIR fit provides the best constraints to stellar mass, a triumph for modern NIR stellar population synthesis models, though the results are consistent with an optical-only fits. Fits based on the popular g-i color combination find M/L* ratios biased by 0.1 dex, while color-mass-to-light prescriptions in the literature may differ by 0.3 dex. This result affirms that panchromatic SED modelling is crucial even for stellar mass estimation, let alone age and metallicity. Overall, we estimate the stellar mass of M31, within R=30 kpc, to be 10.3 (+2.3, -1