Science.gov

Sample records for pd transient collisional

  1. Improved energy coupling into the gain region of the Ni-like Pd transient collisional x-ray laser

    SciTech Connect

    Smith, R; Dunn, J; Filevich, J; Moon, S; Nilsen, J; Keenan, R; Shlyaptsev, V; Rocca, J; Hunter, J; Shepherd, R; Booth, R; Marconi, M

    2004-10-05

    We present within this paper a series of experiments, which yield new observations to further our understanding of the transient collisional x-ray laser medium. We use the recently developed technique of picosecond x-ray laser interferometry to probe the plasma conditions in which the x-ray laser is generated and propagates. This yields two dimensional electron density maps of the plasma taken at different times relative to the peak of the 600ps plasma-forming beam. In another experimental campaign, the output of the x-ray laser plasma column is imaged with a spherical multilayer mirror onto a CCD camera to give a two-dimensional intensity map of the x-ray laser output. Near-field imaging gives insights into refraction, output intensity and spatial mode structure. Combining these images with the density maps gives an indication of the electron density at which the x-ray laser is being emitted at (yielding insights into the effect of density gradients on beam propagation). Experimental observations coupled with simulations predict that most effective coupling of laser pump energy occurs when the duration of the main heating pulse is comparable to the gain lifetime ({approx}10ps for Ni-like schemes). This can increase the output intensity by more than an order of magnitude relative to the case were the same pumping energy is delivered within a shorter heating pulse duration (< 3ps). We have also conducted an experiment in which the output of the x-ray laser was imaged onto the entrance slit of a high temporal resolution streak camera. This effectively takes a one-dimensional slice of the x-ray laser spatial profile and sweeps it in time. Under some conditions we observe rapid movement of the x-ray laser ({approx} 3 {micro}m/ps) towards the target surface.

  2. Progress in table-top transient collisional excitation x-ray lasers at LLNL

    SciTech Connect

    Da Silva, L B; Dunn, J; Li, Y; Nilsen, J; Osterheld, A; Shepherd, R; Shlyaptsev, V N

    1999-02-07

    We present progress in experiments for high efficiency Ne-like and Ni-like ion x-ray lasers using the transient collisional excitation scheme. Experimental results have been obtained on the COMET 15 TW table-top laser system at the Lawrence Livermore National Laboratory (LLNL). The plasma formation, ionization and collisional excitation of the x-ray laser have been optimized using two sequential laser pulses of 600 ps and 1 ps duration with an optional pre-pulse. We have observed high gains up to 55 cm{sup {minus}1} in Ne-like and Ni-like ion schemes for various atomic numbers. We report strong output for the 4d - 4p line in lower Z Ni-like ion sequence for Mo to Y, lasing from {approximately}190 {angstrom} to 240 {angstrom}, by pumping with less than 5 J energy on target.

  3. Optimal main pulse angle for different preplasma conditions in transient collisionally pumped x-ray lasers.

    PubMed

    Ursescu, Daniel; Zielbauer, Bernhard; Kuehl, Thomas; Neumayer, Paul; Pert, Geoff

    2007-04-01

    The effects of the incidence angle of the main pump (MP) pulse in non-normal pumping geometry and the influence of the MP duration are investigated experimentally and theoretically for a transient collisionally pumped (TCE) x-ray laser in Ni-like Zr at 45 degrees and 72 degrees incidence angle on the target. The way they transfer to the x-ray laser output depends on the preplasma conditions, most notably on the average ionization distribution at the arrival of the MP. Moreover, contrary to previous grazing incidence pumping results, it is found that the shortest attainable MP maximizes the output. Modeling of the experimental results is performed with EHYBRID code. The results are important for scaling high repetition-rate non-normal incidence pumped lasers to sub- 10nm wavelengths. PMID:17500953

  4. Status of MBI activities: Will a transient collisional x-ray laser with high repetition rate come soon?

    NASA Astrophysics Data System (ADS)

    Nickles, Peter V.; Janulewicz, Karol A.; Priebe, Gerd; Lucianetti, Antonio; Kroemer, Robert K.; Gerlitzke, Anne-Kathrin; Sandner, Wolfgang

    2003-12-01

    Some prospects for development of collisional X-ray lasers with a high repetition rate based on the output characteristics of a transient Ni-like Ag soft X-ray laser pumped by a single picosecond laser pulse are analysed. Such problems as target technology, new driver development and the active medium parameters are discussed.

  5. Table-top transient collisional excitation x-ray laser research at LLNL: Status June 1997

    SciTech Connect

    Dunn, J., LLNL

    1997-07-01

    This is a status report of transient collisional excitation x-ray laser experiments at LLNL during June 1997 that have the advantage of being conducted on a table-top. Two laser drivers with modest energy {approximately}6 J are used in the scheme: a long {approximately}1 ns pulse to preform and ionize the plasma followed by a short {approximately}1 ps pulse to produce the excitation and population inversion. The beams are co-propagated and focused using a combination of a cylindrical lens and paraboloid to a line of {approximately}70 {micro}m x 12.5 mm dimensions. High repetition rates approaching 1 shot/3 min. allow typically in excess of 50 target shots in a day. Various slab targets have been irradiated and we report preliminary results for x-ray laser gain in 3p-3s J=0-1 Ne-like Ti and Fe transitions where gains as high as 24 cm{sup -1} and gL products of {approximately}15 have been observed.

  6. Collisional and Radiative Effects in Transient sub-Doppler Hole Burning: Double Resonance Measurements in CN

    SciTech Connect

    Hause,M.L.; Hall,G.; Sears, T.J.

    2009-07-05

    We report transient hole-burning and saturation recovery measurements in the CN radical with MHz frequency resolution and 20 ns time resolution. Narrow velocity groups of individual hyperfine levels of selected rotational states in CN (X{sup 2} {Sigma}{sup +}) are depleted and excited (A{sup 2}{pi}{sub i}) with a saturation laser and probed by a counterpropagating, frequency modulated probe beam. Recent work in our lab has used this method to measure and characterize the hyperfine splittings for a set of rotational, fine structure, and parity components of CN (A{sup 2}{pi}{sub i}, v=1). Extending this work, we report time and frequency dependence of the saturation signals following abrupt switching of the CW saturation beam on and off with an electro-optic amplitude modulator. Recovery of the unsaturated absorption following the turnoff of the saturation beam follows pressure-dependent kinetics, driven by collisions with the undissociated NCCN precursor with a rate coefficient of 2 x 10{sup -9} cm{sup 3} s{sup -1} molec{sup -1}. Similar recovery kinetics are observed for two-level saturation resonances, where the signal observed is a combination of X- and A-state kinetics, as well as for three-level crossover resonances, which can be chosen to probe selectively the holefilling in the X state or the decay of velocity-selected A state radicals. The observed recovery rates are 8-10 times faster than the estimated rotationally inelastic contribution. The observed recovery rates are likely dominated by velocity-changing collisions in both X and A states, occurring with similar rates, despite the large difference in the properties of these electronic states. Transient signal risetimes following the turning on of the saturation pulse are consistent with the expected Rabi frequency. At lower pressures ({approx}50 mTorr) and higher beam power ({approx}200 mW), we can observe multiple Rabi cycles before collisions disrupt the coherent excitation and the transient signal

  7. Mechanism of CO 2 Hydrogenation on Pd/Al 2 O 3 Catalysts: Kinetics and Transient DRIFTS-MS Studies

    SciTech Connect

    Wang, Xiang; Shi, Hui; Kwak, Ja Hun; Szanyi, János

    2015-09-17

    The hydrogenation of CO2 was investigated over a wide range of reaction conditions, using two Pd/γ-Al2O3 catalysts with different Pd loadings (5% and 0.5%) and dispersions (~11% and ~100%, respectively). Turnover rates for CO and CH4 formation were both higher over 5% Pd/Al2O3 with a larger average Pd particle size than those over 0.5% Pd/Al2O3 with a smaller average particle size. The selectivity to methane (22-40%) on 5% Pd/Al2O3 was higher by a factor of 2-3 than that on 0.5% Pd/Al2O3. The drastically different rate expressions and apparent energies of activation for CO and CH4 formation lead us to conclude that reverse water gas shift and CO2 methanation do not share the same rate-limiting step on Pd, and that the two pathways are probably catalyzed at different surface sites. Measured reaction orders in CO2 and H2 pressures were similar over the two catalysts, suggesting that the reaction mechanism for each pathway does not change with particle size. In accordance, the DRIFTS results reveal that the prevalent surface species and their evolution patterns are comparable on the two catalysts during transient and steady-state experiments, switching feed gases among CO2, H2 and CO2+H2. The DRIFTS and MS results also demonstrate that no direct dissociation of CO2 takes place over the two catalysts, and that CO2 has to first react with surface hydroxyls on the oxide support. The thus-formed bicarbonates react with dissociatively adsorbed hydrogen on Pd particles to produce adsorbed formate species (bifunctional catalyst: CO2 activation on the oxide support, and H2 dissociation on the metal particles). Formates near the Pd particles (most likely at the metal/oxide interface) can react rapidly with adsorbed H

  8. Energetically consistent collisional gyrokinetics

    SciTech Connect

    Burby, J. W.; Brizard, A. J.; Qin, H.

    2015-10-01

    We present a formulation of collisional gyrokinetic theory with exact conservation laws for energy and canonical toroidal momentum. Collisions are accounted for by a nonlinear gyrokinetic Landau operator. Gyroaveraging and linearization do not destroy the operator's conservation properties. Just as in ordinary kinetic theory, the conservation laws for collisional gyrokinetic theory are selected by the limiting collisionless gyrokinetic theory. (C) 2015 AIP Publishing LLC.

  9. Energetically consistent collisional gyrokinetics

    SciTech Connect

    Burby, J. W.; Brizard, A. J.; Qin, H.

    2015-10-15

    We present a formulation of collisional gyrokinetic theory with exact conservation laws for energy and canonical toroidal momentum. Collisions are accounted for by a nonlinear gyrokinetic Landau operator. Gyroaveraging and linearization do not destroy the operator's conservation properties. Just as in ordinary kinetic theory, the conservation laws for collisional gyrokinetic theory are selected by the limiting collisionless gyrokinetic theory.

  10. Energetically consistent collisional gyrokinetics

    DOE PAGESBeta

    Burby, J. W.; Brizard, A. J.; Qin, H.

    2015-10-30

    Here, we present a formulation of collisional gyrokinetic theory with exact conservation laws for energy and canonical toroidal momentum. Collisions are accounted for by a nonlinear gyrokinetic Landau operator. Gyroaveraging and linearization do not destroy the operator's conservation properties. Just as in ordinary kinetic theory, the conservation laws for collisional gyrokinetic theory are selected by the limiting collisionless gyrokinetic theory. (C) 2015 AIP Publishing LLC.

  11. Collisional Cascades Revisited

    NASA Astrophysics Data System (ADS)

    Schlichting, Hilke; Pan, M.

    2013-01-01

    Collisional cascades are believed to be the primary mechanism operating in circumstellar dusty debris disks, and are thought to be important in the Kuiper and Asteroid belt. Collisional cascades transfer mass via destructive collisions from larger bodies to smaller ones. Their widespread occurrence and potential importance in understanding planet formation and planet-disk interactions have motivated detailed studies of collisional cascades. The standard theoretical treatment of collisional cascades derives a steady-state size distribution assuming a single constant velocity dispersion for all bodies regardless of size. We relax this assumption and solve self-consistently for the bodies' steady-state size and size-dependent velocity distributions. Specifically, we account for viscous stirring, dynamical friction, and collisional damping of the bodies' random velocities in addition to the mass conservation requirement typically applied to find the size distribution in a steady-state cascade. The resulting size distributions are significantly steeper than those derived without velocity evolution. For example, accounting self-consistently for the velocities can change the standard q = 3.5 power-law index of the Dohnanyi differential size spectrum to an index as large as q = 4. Similarly, for bodies held together by their own gravity, the corresponding power-law index range 2.88 < q < 3.14 of Pan & Sari (2005) can steepen to values as large as q = 3.26. These differences in the size distribution power law index are very important when estimating the total disk mass, including larger bodies, by extrapolating from the observed dust masses. Our velocity results allow quantitative predictions of the bodies' scale heights as a function of size. Together with our predictions, observations of the scale heights for different-sized bodies in, for example, extrasolar debris disks may constrain the total mass in large bodies stirring the cascade as well as the colliding bodies

  12. Collisional lifetimes of meteoroids

    NASA Astrophysics Data System (ADS)

    Soja, R. H.; Schwarzkopf, G. J.; Sommer, M.; Vaubaillon, J.; Albin, T.; Rodmann, J.; Grün, E.; Srama, R.

    2016-01-01

    Collisions of meteoroids with interplanetary dust grain fragments particles, dispersing larger particles amongst lower mass intervals. Here we use the method of Grün et al. (1985) and the IMEM interplanetary dust model to calculate the collisional lifetimes for different orbits, and for particles in different meteor showers. The timescales are usually long - of order 10^4 years for 1mm grains on Jupiter-family and Hally-type comet orbits. However, near-sun orbits particles suffer more frequent collisions and therefore have much shorter lifetimes. We discuss factors that affect the accuracy of these calculations.

  13. FLYCHK Collisional-Radiative Code

    National Institute of Standards and Technology Data Gateway

    SRD 160 FLYCHK Collisional-Radiative Code (Web, free access)   FLYCHK provides a capability to generate atomic level populations and charge state distributions for low-Z to mid-Z elements under NLTE conditions.

  14. Laser cooling by collisional redistribution of radiation.

    PubMed

    Vogl, Ulrich; Weitz, Martin

    2009-09-01

    The general idea that optical radiation may cool matter was put forward 80 years ago. Doppler cooling of dilute atomic gases is an extremely successful application of this concept. More recently, anti-Stokes cooling in multilevel systems has been explored, culminating in the optical refrigeration of solids. Collisional redistribution of radiation has been proposed as a different cooling mechanism for atomic two-level systems, although experimental investigations using moderate-density gases have not reached the cooling regime. Here we experimentally demonstrate laser cooling of an atomic gas based on collisional redistribution of radiation, using rubidium atoms in argon buffer gas at a pressure of 230 bar. The frequent collisions in the ultradense gas transiently shift a highly red-detuned laser beam (that is, one detuned to a much lower frequency) into resonance, whereas spontaneous decay occurs close to the unperturbed atomic resonance frequency. During each excitation cycle, kinetic energy of order k(B)T-that is, the thermal energy (k(B), Boltzmann's constant; T, temperature)-is extracted from the dense atomic sample. In a proof-of-principle experiment with a thermally non-isolated sample, we demonstrate relative cooling by 66 K. The cooled gas has a density more than ten orders of magnitude greater than the typical values used in Doppler-cooling experiments, and the cooling power reaches 87 mW. Future applications of the technique may include supercooling beyond the homogeneous nucleation temperature and optical chillers. PMID:19727195

  15. Collisional Evolution of Terrestrial Planets

    NASA Astrophysics Data System (ADS)

    Agnor, C.; Asphaug, E.

    2004-12-01

    The terrestrial planets are generally thought to have formed via the collisional accumulation of rocky bodies. The characteristics of the planets produced by this process are, to a large degree, determined by their collisional evolution, and their associated differentiation and thermal evolution. Studies of planet formation and planetary collisional evolution have typically been conducted separately. Most works of late-stage planet formation use perfectly inelastic mergers to model collisions (e.g. Agnor, Canup & Levison 1999, Chambers 2001, Levison & Agnor 2003), with certain recognized inadequacies, notably prohibitively large spin angular momentum acquired as a planet grows. To date, studies of the collisional evolution of terrestrial planets has focused on determining the efficacy of single impacts to account for particular planetary characteristics and the formation of satellites (e.g. Benz et al. 1988, Canup & Asphaug 2001, Canup 2004). It has been recognized for some time (Wetherill 1985) that the final characteristics (e.g. spin state, bulk composition, isotopic age) of an accreting planet are determined not by the last or single largest collision but by all of the major collisional encounters in a planet's history (Agnor, Canup & Levison 1999). As demonstrated by our impact models, each major impact changes the silicate to metal ratio, the thermal state, and the spin state, and sets the stage for the subsequent collision. We are studying collisional dynamics and outcomes common to the late stage of terrestrial planet formation. We use smooth particle hydrodynamics model collisions in an effort to identify the range of impact dynamics that allow for accretion (i.e. mass growth instead of mass loss). In our initial study we found that for dynamical environments typical of most late stage accretion models, about half of all collisions between equal mass planetary embryos do not result in accumulation into a larger embryo (Agnor & Asphaug 2004). We will

  16. Registration of PD 05064, PD 05069, PD 05070, and PD 05071 germplasm lines of cotton

    Technology Transfer Automated Retrieval System (TEKTRAN)

    PD 05064, PD 05069, PD 05070, and PD 05071 are noncommercial breeding lines of cotton jointly released by the Agricultural Research Service, United States Department of Agriculture, the Clemson University Experiment Station, and Cotton Incorporated in 2014. PD 05064, PD 05069, PD 05070, and PD 05071...

  17. Collisional Evolution of Terrestrial Planets

    NASA Astrophysics Data System (ADS)

    Agnor, C. B.; Asphaug, E. I.

    2003-05-01

    The currently accepted model for the formation of terrestrial planets describes their growth as the collisional accumulation of rocky or sometimes molten planetesimals. The characteristics of the planets produced by this process are, to a large degree, determined by their collisional evolution, and their associated differentiation and thermal evolution. Studies of planet formation and planetary collisional evolution have typically been conducted separately. Most works of late-stage planet formation use perfectly inelastic mergers to model collisions (e.g. Agnor, Canup & Levison 1999, Chambers 2001, Levison & Agnor 2003), with certain recognized inadequacies, notably rotationally unstable spin rates acquired as a planet grows. Do planets really accrete in this manner? On the other hand, most of the work studying the collisional evolution of terrestrial planets has focused on determining the efficacy of single impacts to account for particular planetary characteristics and the formation of satellites (e.g. Benz et al. 1988, Canup & Asphaug 2001). It has been recognized for some time (Wetherill 1985) that the final characteristics (e.g. spin state, bulk composition, isotopic age) of an accreting planet are determined not by the last or single largest collision (Agnor, Canup & Levison 1999) but by all of the major collisional encounters in a planet's history. As demonstrated in our impact models, each major impact changes the silicate to metal ratio, the thermal state, and the spin state, and sets the stage for subsequent collisions. We have commenced a detailed study of collision dynamics and outcomes common to the late stage of terrestrial planet accretion. We are modeling collisions using smooth particle hydrodynamics to examine, primarily, the regimes of impact that truly allow for accretion (i.e. mass accumulation instead of mass loss). We are also studying the cumulative affect of giant impacts on major planetary characteristics (such as composition and spin) and

  18. Collisionally processed rocks on mars

    PubMed

    Horz; Cintala; Rochelle; Kirk

    1999-09-24

    The Pathfinder landing site on Mars has boulders that may be cratered (Stimpy), split (Chimp), fragmented (Book End and Flat Top), or otherwise partly destroyed (Yogi and Frog) by collisional processes. Atmospheric-entry calculations show that centimeter-sized projectiles survive passage through the martian atmosphere and encounter the surface of Mars at velocities of a few kilometers per second. Craters less than 1 meter in diameter may contribute to the evolution of the martian surface and its soils. PMID:10497123

  19. Collisional decoherence of polar molecules

    NASA Astrophysics Data System (ADS)

    Walter, Kai; Stickler, Benjamin A.; Hornberger, Klaus

    2016-06-01

    The quantum state of motion of a large and rotating polar molecule can lose coherence through the collisions with gas atoms. We show how the associated quantum master equation for the center of mass can be expressed in terms of the orientationally averaged differential and total scattering cross sections, for which we provide approximate analytic expressions. The master equation is then utilized to quantify collisional decoherence in a interference experiment with polar molecules.

  20. Using molecular alignment to track ultrafast collisional relaxation

    NASA Astrophysics Data System (ADS)

    Karras, G.; Hertz, E.; Billard, F.; Lavorel, B.; Hartmann, J.-M.; Faucher, O.

    2014-06-01

    Field-free molecular alignment has been used in order to track the collisional relaxation occurring in a molecular gas. CO2 molecules were initially irradiated by a short linearly polarized laser pulse resulting in the increase of their rotational energy. The evolution of the subsequent ultrafast relaxation process was optically probed after irradiating the sample with a second, weaker, short pulse leading to the alignment of the preheated molecules. Using classical molecular dynamic simulations, we were able to quantitatively reproduce the experimental shapes and amplitudes of the recorded revival transients for a time interval extending from 25 to 500 ps until thermalization of the gas sample is reached.

  1. Collisional plateaus. [in earth and Venus lithospheres

    NASA Technical Reports Server (NTRS)

    Morgan, P.; Burke, K.

    1985-01-01

    Aspects of the geology of collisional plateaus formed by the thickening of continental crust are briefly reviewed. The history of studies of collisional plateaus is summarized, and igneous activity in collisional plateaus is discussed. Isostatic considerations pertaining to these plateaus are addressed, developing models of isostatic support of topography which illustrate the importance of compressional tectonics in the creation of high altitude plateaus. Possible analogous environments on Venus are considered. Finally, the paradox of extension associated with compression in the plateaus is discussed.

  2. QCD Collisional Energy Loss Reexamined

    NASA Astrophysics Data System (ADS)

    Peshier, A.

    2006-11-01

    It is shown that at a large temperature and E→∞ the QCD collisional energy loss reads dE/dx˜α(mD2)T2. Compared to previous approaches, which led to dEB/dx˜α2T2ln⁡(ET/mD2) similar to the Bethe-Bloch formula in QED, we take into account the running of the strong coupling. As one significant consequence, due to asymptotic freedom, dE/dx becomes E independent for large parton energies. Some implications with regard to heavy ion collisions are pointed out.

  3. QCD collisional energy loss reexamined.

    PubMed

    Peshier, A

    2006-11-24

    It is shown that at a large temperature and E --> infinity the QCD collisional energy loss reads dE/dx approximately alpha(m(D)2)T2. Compared to previous approaches, which led to dE(B)/dx approximately alpha2 T2 ln(ET/m(D)2) similar to the Bethe-Bloch formula in QED, we take into account the running of the strong coupling. As one significant consequence, due to asymptotic freedom, dE/dx becomes E independent for large parton energies. Some implications with regard to heavy ion collisions are pointed out. PMID:17155739

  4. Collisional {delta}f method

    SciTech Connect

    Chen, Y.; White, R.B.

    1997-12-31

    A general method for including various collisional effects, such as the drag and diffusion of test particles due to background plasmas, the effect of particle source and sink, and the like-particle Coulomb collisions, is presented. The marker density g is generally unknown along the particle trajectory, and its evaluation depends on the way particles are initially loaded and new particles are injected into the simulation. The method is demonstrated for the problem of the nonlinear evolution of the Toroidicity Induced Alfven eigenmode, driven by energetic {alpha} particles. The saturation amplitude is found to scale with the collision rate in a way as predicted by theory.

  5. Problems of collisional stellar dynamics

    NASA Astrophysics Data System (ADS)

    Heggie, D. C.

    2011-03-01

    The discovery of dynamical friction was Chandrasekhar's best known contribution to the theory of stellar dynamics, but his work ranged from the few-body problem to the limit of large N (in effect, galaxies). Much of this work was summarised in the text "Principles of Stellar Dynamics" tep{C1942,C1960}, which ranges from a precise calculation of the time of relaxation, through a long analysis of galaxy models, to the behaviour of star clusters in tidal fields. The later edition also includes the work on dynamical friction and related issues. In this review we focus on progress in the collisional aspects of these problems, i.e. those where few-body interactions play a dominant role, and so we omit further discussion of galaxy dynamics. But we try to link Chandrasekhar's fundamental discoveries in collisional problems with the progress that has been made in the 50 years since the publication of the enlarged edition. There is one other such problem to which Chandrasekhar contributed, though the paper in question tep{C1944} was not reprinted in the book. See Section ref{sec:binaries}. For more on the collisionless problems studied by Chandrasekhar, see the paper by N. Wyn Evans (2011) in the present volume.

  6. Generalized parallel heat transport equations in collisional to weakly collisional plasmas

    NASA Astrophysics Data System (ADS)

    Zawaideh, Emad; Kim, N. S.; Najmabadi, Farrokh

    1988-11-01

    A new set of two-fluid heat-transport equations for heat conduction in collisional to weakly collisional plasmas was derived on the basis of gyrokinetic equations in flux coordinates. In these equations, no restrictions on the anisotropy of the ion distribution function or the collisionality are imposed. In the highly collisional limit, these equations reduce to the classical heat conduction equation of Spitzer and Haerm (1953), while in the weakly collisional limit, they describe a saturated heat flux. Numerical examples comparing these equations with conventional heat transport equations are presented.

  7. Neoclassical Transport Including Collisional Nonlinearity

    SciTech Connect

    Candy, J.; Belli, E. A.

    2011-06-10

    In the standard {delta}f theory of neoclassical transport, the zeroth-order (Maxwellian) solution is obtained analytically via the solution of a nonlinear equation. The first-order correction {delta}f is subsequently computed as the solution of a linear, inhomogeneous equation that includes the linearized Fokker-Planck collision operator. This equation admits analytic solutions only in extreme asymptotic limits (banana, plateau, Pfirsch-Schlueter), and so must be solved numerically for realistic plasma parameters. Recently, numerical codes have appeared which attempt to compute the total distribution f more accurately than in the standard ordering by retaining some nonlinear terms related to finite-orbit width, while simultaneously reusing some form of the linearized collision operator. In this work we show that higher-order corrections to the distribution function may be unphysical if collisional nonlinearities are ignored.

  8. Collisional Aggregation Due to Turbulence

    NASA Astrophysics Data System (ADS)

    Pumir, Alain; Wilkinson, Michael

    2016-03-01

    Collisions between particles suspended in a fluid play an important role in many physical processes. As an example, collisions of microscopic water droplets in clouds are a necessary step in the production of macroscopic raindrops. Collisions of dust grains are also conjectured to be important for planet formation in the gas surrounding young stars and to play a role in the dynamics of sand storms. In these processes, collisions are favored by fast turbulent motions. Here we review recent advances in the understanding of collisional aggregation due to turbulence. We discuss the role of fractal clustering of particles and caustic singularities of their velocities. We also discuss limitations of the Smoluchowski equation for modeling such processes. These advances lead to a semiquantitative understanding on the influence of turbulence on collision rates and point to deficiencies in the current understanding of rainfall and planet formation.

  9. Theory of runaway collisional transport

    SciTech Connect

    Tessarotto, M. ); White, R.B. )

    1993-11-01

    The purpose of this paper is to formulate the transport problem for a multispecies rotating toroidal magnetoplasma in the so-called runaway regime, which is defined by an appropriate ordering of relevant characteristic frequencies, in particular, the Larmor frequency, the characteristic acceleration frequency due to the applied electric field and the effective collision frequency, all evaluated at some characteristic speed [ital v][sub 0]. A suitable form of the gyrokinetic equation is obtained to describe the time-dependent, multispecies plasma response to an applied electric field, in toroidal geometry and for a strongly rotating, quiescent, and collisional plasma. Its moment equations are proven to imply the reduction of the energy equation to Joule's law, as well as consequences on the form of Ohm's law and of the Grad--Shafranov equation. To construct an approximate solution of the gyrokinetic equation and to evaluate all relevant fluxes, appearing in the moment equations, a general variational solution method is developed.

  10. Universal collisional activation ion trap mass spectrometry

    DOEpatents

    McLuckey, S.A.; Goeringer, D.E.; Glish, G.L.

    1993-04-27

    A universal collisional activation ion trap comprises an ion trapping means containing a bath gas and having connected thereto a noise signal generator. A method of operating a universal collisional activation ion trap comprises the steps of: providing an ion trapping means; introducing into the ion trapping means a bath gas; and, generating a noise signal within the ion trapping means; introducing into the ion trapping means a substance that, when acted upon by the noise signal, undergoes collisional activation to form product ions.

  11. Universal collisional activation ion trap mass spectrometry

    DOEpatents

    McLuckey, Scott A.; Goeringer, Douglas E.; Glish, Gary L.

    1993-01-01

    A universal collisional activation ion trap comprises an ion trapping means containing a bath gas and having connected thereto a noise signal generator. A method of operating a universal collisional activation ion trap comprises the steps of: providing an ion trapping means; introducing into the ion trapping means a bath gas; and, generating a noise signal within the ion trapping means; introducing into the ion trapping means a substance that, when acted upon by the noise signal, undergoes collisional activation to form product ions.

  12. Collisional pumping in polarized sodium vapor

    SciTech Connect

    Kaplan, S.N.; pyle, R.V.; Ruby, L.; Schlachter, A.S.; Stearns, J.W.; Anderson, L.W.

    1986-01-01

    Collisional pumping has been proposed as a mechanism for efficient transfer of spin from an electron-spin-polarized target to the nuclei of a fast atom or ion beam. Collisional pumping takes place in low magnetic fields, can give polarization transfer approaching 100%, and offers the potential for producing polarized beams orders of magnitude more intense than presently achieved. Recently reported calculations of electronic spin-exchange cross sections at useful ion-source energies suggest significantly greater rates of pumping than first estimated, and give cause for increased optimism about sucessful implementation. Collisional pumping is described, and beam characteristics are given for prototype polarized source parameters.

  13. Collisional Records in Iron Meteorites

    NASA Astrophysics Data System (ADS)

    Marti, K.; Lavielle, B.; Jeannot, J.-P.

    1995-09-01

    The asteroid belt is considered to be the ultimate source of iron meteorites and it would be of considerable interest to obtain a chronology of break-ups of asteroidal objects. However, as multiple fragmentation of such objects did likely occur, the exposure ages date the break-off of iron masses from shielded locations within the immediate parent object. Meteorites which were fragmented in more than one collisional event may have recorded integral effects of cosmic ray interactions in varying geometrical configuration and individual stages may be difficult to unravel; we term such exposure histories "complex". Exposure age histograms based on potassium ages have been discussed by Voshage [1] and he concluded that irons of groups IIIA and IIIB reveal similar histograms and probably were derived from the same parent body. He also noted a cluster for group IVA members ,but no clear evidence for other clusters. We present the collisional evidence based on published noble gas data, coupled to the new production rates which we calculate for central locations, adjusted for off-center locations whenever concentration profiles can be inferred. Unlike potassium ages which show large uncertainties for ages < 300 Ma, T38 ages can be obtained for all iron meteorites. We note, however,that T38 values of five "old" irons are systematically 15% lower than potassium ages. We confirm the evidence for stochastic events for IIIAB and IVA irons. The statistics are improved because of the larger data base. There are interesting clusters also among ages < 100 Ma, in the range which overlaps the histograms of chondrites. Recent reports [2,3] of H-chondritic inclusions in IIE irons, whose exposure ages are consistent with H-chondrite clusters, point to a genetic link. Group IIAB reveals two clusters with T38 < 100 Ma, and both events appear to involve also IIE irons. Clusterings of two thirds of group IIIE members and of group IID irons appear significant. The youngest IVB ages coincide

  14. Collisional versus Collisionless Dark Matter.

    PubMed

    Moore; Gelato; Jenkins; Pearce; Quilis

    2000-05-20

    We compare the structure and substructure of dark matter halos in model universes dominated by collisional, strongly self-interacting dark matter (SIDM) and collisionless, weakly interacting dark matter (CDM). While SIDM virialized halos are more nearly spherical than CDM halos, they can be rotationally flattened by as much as 20% in their inner regions. Substructure halos suffer ram-pressure truncation and drag, which are more rapid and severe than their gravitational counterparts tidal stripping and dynamical friction. Lensing constraints on the size of galactic halos in clusters are a factor of 2 smaller than predicted by gravitational stripping, and the recent detection of tidal streams of stars escaping from the satellite galaxy Carina suggests that its tidal radius is close to its optical radius of a few hundred parsecs-an order of magnitude smaller than predicted by CDM models but consistent with SIDM models. The orbits of SIDM satellites suffer significant velocity bias, sigmaSIDM&solm0;sigmaCDM=0.85, and are more circular than CDM satellites, betaSIDM approximately 0.5, in agreement with the inferred orbits of the Galaxy's satellites. In the limit of a short mean free path, SIDM halos have singular isothermal density profiles; thus, in its simplest incarnation SIDM, is inconsistent with galactic rotation curves. PMID:10828999

  15. PD-1/PD-L1 inhibitors.

    PubMed

    Sunshine, Joel; Taube, Janis M

    2015-08-01

    Tumors may adopt normal physiologic checkpoints for immunomodulation leading to an imbalance between tumor growth and host surveillance. Antibodies targeting the PD-1/PD-L1 checkpoint have shown dynamic and durable tumor regressions, suggesting a rebalancing of the host-tumor interaction. Nivolumab and pembrolizumab are the anti-PD-1 antibodies that are currently the furthest in clinical development, and anti-PD-L1 agents under investigation include MPDL3280A, MEDI4736, and BMS-936559. These agents have been used to treat advanced melanoma, non-small cell lung cancer, renal cell carcinoma, bladder cancer and Hodgkin lymphoma, amongst other tumor types. In this article, we review the updated response results for early clinical trials, note recent FDA actions regarding this class of agents, and summarize results across trials looking at PD-L1 status as a predictor of response to anti-PD-1/PD-L1. PMID:26047524

  16. IDENTIFYING COLLISIONAL FAMILIES IN THE KUIPER BELT

    SciTech Connect

    Marcus, Robert A.; Ragozzine, Darin; Murray-Clay, Ruth A.; Holman, Matthew J.

    2011-05-20

    The identification and characterization of numerous collisional families-clusters of bodies with a common collisional origin-in the asteroid belt has added greatly to the understanding of asteroid belt formation and evolution. More recent study has also led to an appreciation of physical processes that had previously been neglected (e.g., the Yarkovsky effect). Collisions have certainly played an important role in the evolution of the Kuiper Belt as well, though only one collisional family has been identified in that region to date, around the dwarf planet Haumea. In this paper, we combine insights into collisional families from numerical simulations with the current observational constraints on the dynamical structure of the Kuiper Belt to investigate the ideal sizes and locations for identifying collisional families. We find that larger progenitors (r {approx} 500 km) result in more easily identifiable families, given the difficulty in identifying fragments of smaller progenitors in magnitude-limited surveys, despite their larger spread and less frequent occurrence. However, even these families do not stand out well from the background. Identifying families as statistical overdensities is much easier than characterizing families by distinguishing individual members from interlopers. Such identification seems promising, provided the background population is well known. In either case, families will also be much easier to study where the background population is small, i.e., at high inclinations. Overall, our results indicate that entirely different techniques for identifying families will be needed for the Kuiper Belt, and we provide some suggestions.

  17. Collisional damping rates for plasma waves

    NASA Astrophysics Data System (ADS)

    Tigik, S. F.; Ziebell, L. F.; Yoon, P. H.

    2016-06-01

    The distinction between the plasma dynamics dominated by collisional transport versus collective processes has never been rigorously addressed until recently. A recent paper [P. H. Yoon et al., Phys. Rev. E 93, 033203 (2016)] formulates for the first time, a unified kinetic theory in which collective processes and collisional dynamics are systematically incorporated from first principles. One of the outcomes of such a formalism is the rigorous derivation of collisional damping rates for Langmuir and ion-acoustic waves, which can be contrasted to the heuristic customary approach. However, the results are given only in formal mathematical expressions. The present brief communication numerically evaluates the rigorous collisional damping rates by considering the case of plasma particles with Maxwellian velocity distribution function so as to assess the consequence of the rigorous formalism in a quantitative manner. Comparison with the heuristic ("Spitzer") formula shows that the accurate damping rates are much lower in magnitude than the conventional expression, which implies that the traditional approach over-estimates the importance of attenuation of plasma waves by collisional relaxation process. Such a finding may have a wide applicability ranging from laboratory to space and astrophysical plasmas.

  18. Recombination and collisionally excited Balmer lines

    NASA Astrophysics Data System (ADS)

    Raga, A. C.; Castellanos-Ramírez, A.; Esquivel, A.; Rodríguez-González, A.; Velázquez, P. F.

    2015-10-01

    We present a model for the statistical equilibrium of the levels of H, considering recombinations to excited levels, collisional excitations up from the ground state and spontaneous radiative transitions. This problem has a simple "cascade matrix" solution, describing a cascade of downwards spontaneous transitions fed by both recombinations and collisional excitations. The resulting predicted Balmer line ratios show a transition between a low temperature and a high temperature regime (dominated by recombinations and by collisional excitations, respectively), both with only a weak line ratio vs. temperature dependence. This clear characteristic allows a direct observational identification of regions in which the Balmer lines are either recombination or collisionally excited transitions. We find that for a gas in coronal ionization equilibrium the Halpha and Hbeta lines are collisionally excited for all temperatures. In order to have recombination Halpha and Hbeta it is necessary to have higher ionization fractions of H than the ones obtained from coronal equilibrium (e.g., such as the ones found in a photoionized gas).

  19. Collisional Orientation Transfer Faciliated Polarozation Spectroscopy

    NASA Astrophysics Data System (ADS)

    Bai, Jianmei; Ahmed, E. H.; Beser, B.; Guan, Y.; Lyyra, A. M.; Ashman, S.; Wolfe, C. M.; Huennekens, J.

    2011-06-01

    Collisional orientation transfer facilitated V-type double-resonance polarization spectroscopy technique was applied to study the A-b complex of Rb2 and Cs2. Since spectral congestion makes it difficult to find isolated pump transitions for heavy molecules such as Rb2 and Cs2, this technique significantly enlarges the range of rotational levels that can be observed per vibrational level. Collisional satellite lines with ΔJ up to 58 were observed in the Rb2 polarization experiment. In the Cs2 experiment, due to weaker Franck-Condon factors, collisional satellite lines with ΔJMax equals to 12 were observed. Collisional orientation transfer in polarization spectroscopy was first observed with buffer gas pressure of several hundred Torr. The high pressure led to loss of spectral resolution from collisional broadening. Only 1 to 3 Torr of argon buffer gas pressure was used in our experiments to obtain spectra with much higher resolution. Among the six types of possible probe signals, we assigned and analyzed the signals from the V type excitation scheme. The data was used in the global deperturbation analysis of the A-b complex of both Rb2 and Cs2. H. Salami et al. Phys. Rev. A 80, 022515 (2009) Jianmei Bai et al., Phys. Rev. A, to appear (2011) B. Teets et al. Phys. Rev. Lett. 37, 683 (1976) . Okada et al. J. Chem. Phys. 105, 3458 (1996)

  20. Jeans stability in collisional quantum dusty magnetoplasmas

    SciTech Connect

    Jamil, M.; Asif, M.; Mir, Zahid; Salimullah, M.

    2014-09-15

    Jeans instability is examined in detail in uniform dusty magnetoplasmas taking care of collisional and non-zero finite thermal effects in addition to the quantum characteristics arising through the Bohm potential and the Fermi degenerate pressure using the quantum hydrodynamic model of plasmas. It is found that the presence of the dust-lower-hybrid wave, collisional effects of plasma species, thermal effects of electrons, and the quantum mechanical effects of electrons have significance over the Jeans instability. Here, we have pointed out a new class of dissipative instability in quantum plasma regime.

  1. Investigation of collisional effects within the bending magnet region of a DIII-D neutral beamline

    SciTech Connect

    Kessler, D.N.; Hong, R.; Kellman, D.H.

    1993-10-01

    The region between the pole faces of the DIII-D neutral beamline residual ion bending magnets is an area of transient high gas pressure which may cause beam defocusing and increased heating of beamline internal components due to collisional effects. An investigation of these effects helps in understanding residual ion trajectories and in providing information for studying in the beamline capability for operation with increased pulse duration. Examination of collisional effects, and of the possible existence of space charge blow-up, was carried out by injecting deuterium gas into the region between the magnet pole faces with rates varying from 0 to 18 torr-{ell}/sec. Thermocouple and waterflow calorimetry data were taken to measure the beamline component heating and beam powder deposition on the magnet pole shields, magnet louvers, ion dump, beam collimators, and calorimeter. Data was also taken at gas flow rates varying from 0 to 25 torr-{ell}/sec into the neutralizer cell and is compared with the magnet region gas injection data obtained. Results show that both collisional effects and space charge blow-up play a role in magnet region component heating and that neutralizer gas flow sufficiently reduces component heating without incurring unacceptable power losses through collisional effects.

  2. Buoyancy instabilities in degenerate, collisional, magnetized plasmas

    NASA Astrophysics Data System (ADS)

    Chang, Philip; Quataert, Eliot

    2010-03-01

    In low-collisionality plasmas, anisotropic heat conduction due to a magnetic field leads to buoyancy instabilities for any non-zero temperature gradient. We study analogous instabilities in degenerate collisional plasmas, i.e. when the electron collision frequency is large compared to the electron cyclotron frequency. Although heat conduction is nearly isotropic in this limit, the small residual anisotropy ensures that collisional degenerate plasmas are also convectively unstable independent of the sign of the temperature gradient. We show that the range of wavelengths that are unstable is independent of the magnetic field strength, while the growth time increases with decreasing magnetic field strength. We discuss the application of these collisional buoyancy instabilities to white dwarfs and neutron stars. Magnetic tension and the low specific heat of a degenerate plasma significantly limit their effectiveness; the most promising venues for growth are in the liquid oceans of young, weakly magnetized neutron stars (B <~ 109 G) and in the cores of young, high magnetic field white dwarfs (B ~ 109 G).

  3. Ambient tremors in a collisional orogenic belt

    USGS Publications Warehouse

    Chuang, Lindsay Yuling; Chen, Kate Huihsuan; Wech, Aaron G.; Byrne, Timothy; Peng, Wei

    2014-01-01

    Deep-seated tectonic tremors have been regarded as an observation tied to interconnected fluids at depth, which have been well documented in worldwide subduction zones and transform faults but not in a collisional mountain belt. In this study we explore the general features of collisional tremors in Taiwan and discuss the possible generation mechanism. In the 4 year data, we find 231 ambient tremor episodes with durations ranging from 5 to 30 min. In addition to a coseismic slip-induced stress change from nearby major earthquake, increased tremor rate is also highly correlated with the active, normal faulting earthquake swarms at the shallower depth. Both the tremor and earthquake swarm activities are confined in a small, area where the high attenuation, high thermal anomaly, the boundary between high and low resistivity, and localized veins on the surfaces distributed, suggesting the involvement of fluids from metamorphic dehydration within the orogen.

  4. Fine velocity structures collisional dissipation in plasmas

    NASA Astrophysics Data System (ADS)

    Pezzi, Oreste; Valentini, Francesco; Veltri, Pierluigi

    2016-04-01

    In a weakly collisional plasma, such as the solar wind, collisions are usually considered far too weak to produce any significant effect on the plasma dynamics [1]. However, the estimation of collisionality is often based on the restrictive assumption that the particle velocity distribution function (VDF) shape is close to Maxwellian [2]. On the other hand, in situ spacecraft measurements in the solar wind [3], as well as kinetic numerical experiments [4], indicate that marked non-Maxwellian features develop in the three-dimensional VDFs, (temperature anisotropies, generation of particle beams, ring-like modulations etc.) as a result of the kinetic turbulent cascade of energy towards short spatial scales. Therefore, since collisional effects are proportional to the velocity gradients of the VDF, the collisionless hypothesis may fail locally in velocity space. Here, the existence of several characteristic times during the collisional relaxation of fine velocity structures is investigated by means of Eulerian numerical simulations of a spatially homogeneous force-free weakly collisional plasma. The effect of smoothing out velocity gradients on the evolution of global quantities, such as temperature and entropy, is discussed, suggesting that plasma collisionality can increase locally due to the velocity space deformation of the particle velocity distribution. In particular, by means of Eulerian simulations of collisional relaxation of a spatially homogeneous force-free plasma, in which collisions among particles of the same species are modeled through the complete Landau operator, we show that the system entropy growth occurs over several time scales, inversely proportional to the steepness of the velocity gradients in the VDF. We report clear evidences that fine velocity structures are dissipated by collisions in a time much shorter than global non-Maxwellian features, like, for example, temperature anisotropies. Moreover we indicate that, if small-scale structures

  5. Collisional thulium vapour gas-discharge laser

    SciTech Connect

    Gerasimov, V A; Pavlinskii, A V

    2004-01-31

    A collisional laser on a system of atomic levels based on the principle proposed by Gould is built for the first time. The population of the upper laser level and relaxation of the lower level occur upon inelastic collisions of excited thulium atoms with helium atoms. The lower-level relaxation occurs in a reaction with an energy defect of > 13000 cm{sup -1}. (active media. lasers)

  6. Collisional excitation of interstellar methyl cyanide

    NASA Technical Reports Server (NTRS)

    Green, Sheldon

    1986-01-01

    Theoretical calculations are used to determine the collisional excitation rates of methyl cyanide under interstellar molecular cloud conditions. The required Q(L,M) as a function of kinetic temperature were determined by averaging fixed energy IOS (infinite order sudden) results over appropriate Boltzmann distributions of collision energies. At a kinetic temperature of 40 K, rates within a K ladder were found to be accurate to generally better than about 30 percent.

  7. Collisionally induced atomic clock shifts and correlations

    SciTech Connect

    Band, Y. B.; Osherov, I.

    2011-07-15

    We develop a formalism to incorporate exchange symmetry considerations into the calculation of collisional frequency shifts for atomic clocks using a density-matrix formalism. The formalism is developed for both fermionic and bosonic atomic clocks. Numerical results for a finite-temperature {sup 87}Sr {sup 1}S{sub 0} (F=9/2) atomic clock in a magic wavelength optical lattice are presented.

  8. Collisional records in LL-chondrites

    NASA Technical Reports Server (NTRS)

    Graf, Thomas; Marti, Kurt

    1994-01-01

    One third of all the LL-chondrites have exposure ages of approx. 15 Ma and were exposed to cosmic rays following a collisional break-up. The probability that the 15-Ma peak represents a random signal is calculated to be less than 2%. Considerably lower probabilities are obtained if only LL5s or subgroups of high Ar-40 retention are used. Furthermore, we show that the peak shape agrees with statistical constraints obtained from multiple analyses of samples from the St. Severin LL6-chondrites. The frequency in and out of the 15-Ma peak varies significantly for different petrographic LL-types. The radiogenic Ar-40 retention systematics (most LL-chondrites retained Ar-40(sub rad) shows that no substantial heat pulse resulted in the 15-Ma collisional event. Interestingly, smaller exposure age clusters at approx. 28 Ma and approx. 40 Ma match up well with clusters in the histogram of L-chondrites. The distribution of LL-exposure ages is not consistent with that expected for a quasi-continuous injection of LL material into a resonance zone of the asteroid belt. The near absence of exposure ages shorter than 8 Ma either indicates a lack of recent collisional events or considerably longer transfer times than inferred from dynamical considerations.

  9. Superfluorescence polarization: Signature of collisional redistribution

    NASA Astrophysics Data System (ADS)

    Kumarakrishnan, A.; Chudasama, S.; Han, X. L.

    2003-09-01

    We have studied effects of magnetic sublevel degeneracy on the polarization of superfluorescent pulses generated on the Ca 4s4p 1P1 3d4s 1D2 transition at 5.5 μm. These pulses were generated from a cell of length 50 cm by optically pumping calcium vapor on the 4s2 1S0 4s4p 1P1 transition in the presence of Ar gas. The axis of ellipticity of superfluorescence (SF) polarization is oriented parallel to the axis of the pump-laser polarization at large detunings, and undergoes an abrupt rotation through 90° for detunings close to resonance. The distribution of populations in the magnetic sublevels of the 1P1 state can be estimated using a simple model based on previously calculated cross sections for collisionally aided absorption in the presence of an intense (pump) field. For large detunings, these estimates are consistent with the polarized SF intensity measured in the experiment. A direct measurement of the populations of the 1P1 magnetic sublevels also supports the collisional redistribution predicted by the calculated cross sections. We therefore suggest that SF polarization can be a useful signature of collisional redistribution. However, the change in ellipticity is unexpected, and probable causes for this effect are discussed.

  10. Transition from Collisionless to Collisional MRI

    SciTech Connect

    Prateek Sharma; Gregory W. Hammett; Eliot Quataert

    2003-07-24

    Recent calculations by Quataert et al. (2002) found that the growth rates of the magnetorotational instability (MRI) in a collisionless plasma can differ significantly from those calculated using MHD. This can be important in hot accretion flows around compact objects. In this paper, we study the transition from the collisionless kinetic regime to the collisional MHD regime, mapping out the dependence of the MRI growth rate on collisionality. A kinetic closure scheme for a magnetized plasma is used that includes the effect of collisions via a BGK operator. The transition to MHD occurs as the mean free path becomes short compared to the parallel wavelength 2*/k(sub)||. In the weak magnetic field regime where the Alfven and MRI frequencies w are small compared to the sound wave frequency k(sub)||c(sub)0, the dynamics are still effectively collisionless even if omega << v, so long as the collision frequency v << k(sub)||c(sub)0; for an accretion flow this requires n less than or approximately equal to *(square root of b). The low collisionality regime not only modifies the MRI growth rate, but also introduces collisionless Landau or Barnes damping of long wavelength modes, which may be important for the nonlinear saturation of the MRI.

  11. Collisional Behaviors of Astrophysical Collisionless Plasmas

    NASA Astrophysics Data System (ADS)

    Bret, A.

    2015-12-01

    In collisional fluids, a number of key processes rely on the frequency of binary collisions. Collisions seem necessary to generate a shock wave when two fluids collide fast enough, to fulfill the Rankine-Hugoniot (RH) relations, to establish an equation of state or a Maxwellian distribution. Yet, these seemingly collisional features are routinely either observed or assumed, in relation with collisionless astrophysical plasmas. This article will review our current answers to the following questions: How do colliding collisionless plasmas end-up generating a shock as if they were fluids? To which extent are the RH relations fulfilled in this case? Do collisionless shocks propagate like fluid ones? Can we use an equation of state to describe collisionless plasmas, like MHD codes for astrophysics do? Why are Maxwellian distributions ubiquitous in particle-in-cell simulations of collisionless shocks? Time and length scales defining the border between the collisional and the collisionless behavior will be given when relevant. In general, when the time and length scales involved in the collisionless processes responsible for the fluid-like behavior may be neglected, the system may be treated like a fluid.

  12. ACCRETION IN PROTOPLANETARY DISKS BY COLLISIONAL FUSION

    SciTech Connect

    Wettlaufer, J. S.

    2010-08-10

    The formation of a solar system such as ours is believed to have followed a multi-stage process around a protostar and its associated accretion disk. Whipple first noted that planetesimal growth by particle agglomeration is strongly influenced by gas drag, and Cuzzi and colleagues have shown that when midplane particle mass densities approach or exceed those of the gas, solid-solid interactions dominate the drag effect. The size dependence of the drag creates a 'bottleneck' at the meter scale with such bodies rapidly spiraling into the central star, whereas much smaller or larger particles do not. Independent of whether the origin of the drag is angular momentum exchange with gas or solids in the disk, successful planetary accretion requires rapid planetesimal growth to kilometer scales. A commonly accepted picture is that for collisional velocities V{sub c} above a certain threshold value, V {sub th{approx}} 0.1-10 cm s{sup -1}, particle agglomeration is not possible; elastic rebound overcomes attractive surface and intermolecular forces. However, if perfect sticking is assumed for all ranges of interparticle collision speeds the bottleneck can be overcome by rapid planetesimal growth. While previous work has dealt with the influences of collisional pressures and the possibility of particle fracture or penetration, the basic role of the phase behavior of matter-phase diagrams, amorphs, and polymorphs-has been neglected. Here, it is demonstrated for compact bodies that novel aspects of surface phase transitions provide a physical basis for efficient sticking through collisional melting/amorphization/polymorphization and subsequent fusion/annealing to extend the collisional velocity range of primary accretion to {Delta}V{sub c} {approx} 1-100 m s{sup -1} >> V {sub th}, which encompasses both typical turbulent rms speeds and the velocity differences between boulder-sized and small grains {approx}1-50 m s{sup -1}. Therefore, as inspiraling meter-sized bodies collide

  13. Accretion in Protoplanetary Disks by Collisional Fusion

    NASA Astrophysics Data System (ADS)

    Wettlaufer, J. S.

    2010-08-01

    The formation of a solar system such as ours is believed to have followed a multi-stage process around a protostar and its associated accretion disk. Whipple first noted that planetesimal growth by particle agglomeration is strongly influenced by gas drag, and Cuzzi and colleagues have shown that when midplane particle mass densities approach or exceed those of the gas, solid-solid interactions dominate the drag effect. The size dependence of the drag creates a "bottleneck" at the meter scale with such bodies rapidly spiraling into the central star, whereas much smaller or larger particles do not. Independent of whether the origin of the drag is angular momentum exchange with gas or solids in the disk, successful planetary accretion requires rapid planetesimal growth to kilometer scales. A commonly accepted picture is that for collisional velocities Vc above a certain threshold value, V th~ 0.1-10 cm s-1, particle agglomeration is not possible; elastic rebound overcomes attractive surface and intermolecular forces. However, if perfect sticking is assumed for all ranges of interparticle collision speeds the bottleneck can be overcome by rapid planetesimal growth. While previous work has dealt with the influences of collisional pressures and the possibility of particle fracture or penetration, the basic role of the phase behavior of matter-phase diagrams, amorphs, and polymorphs—has been neglected. Here, it is demonstrated for compact bodies that novel aspects of surface phase transitions provide a physical basis for efficient sticking through collisional melting/amorphization/polymorphization and subsequent fusion/annealing to extend the collisional velocity range of primary accretion to ΔVc ~ 1-100 m s-1 Gt V th, which encompasses both typical turbulent rms speeds and the velocity differences between boulder-sized and small grains ~1-50 m s-1. Therefore, as inspiraling meter-sized bodies collide with smaller particles in this high velocity collisional fusion

  14. Molecular characterization of immunoinhibitory factors PD-1/PD-L1 in chickens infected with Marek’s disease virus

    PubMed Central

    2012-01-01

    Background An immunoinhibitory receptor, programmed death-1 (PD-1), and its ligand, programmed death-ligand 1 (PD-L1), are involved in immune evasion mechanisms for several pathogens causing chronic infections and for neoplastic diseases. However, little has been reported for the functions of these molecules in chickens. Thus, in this study, their expressions and roles were analyzed in chickens infected with Marek’s disease virus (MDV), which induces immunosuppression in infected chickens. Results A chicken T cell line, Lee1, which constitutively produces IFN-γ was co-cultured with DF-1 cells, which is a spontaneously immortalized chicken fibroblast cell line, transiently expressing PD-L1, and the IFN-γ expression level was analyzed in the cell line by real-time RT-PCR. The IFN-γ expression was significantly decreased in Lee1 cells co-cultured with DF-1 cells expressing PD-L1. The expression level of PD-1 was increased in chickens at the early cytolytic phase of the MDV infection, while the PD-L1 expression level was increased at the latent phase. In addition, the expression levels of PD-1 and PD-L1 were increased at tumor lesions found in MDV-challenged chickens. The expressions levels of PD-1 and PD-L1 were also increased in the spleens and tumors derived from MDV-infected chickens in the field. Conclusions We demonstrated that the chicken PD-1/PD-L1 pathway has immunoinhibitory functions, and PD-1 may be involved in MD pathogenesis at the early cytolytic phase of the MDV infection, whereas PD-L1 could contribute to the establishment and maintenance of MDV latency. We also observed the increased expressions of PD-1 and PD-L1 in tumors from MDV-infected chickens, suggesting that tumor cells transformed by MDV highly express PD-1 and PD-L1 and thereby could evade from immune responses of the host. PMID:22612856

  15. State dependence of Rydberg interaction-induced collisional loss

    NASA Astrophysics Data System (ADS)

    Feng, Zhigang; Zhao, Kejia; Miao, Jingyuan; Li, Difei; Yang, Zhijun; Wu, Zhaochun; He, Zhao; Zhao, Jianming; Jia, Suotang

    2016-09-01

    We present a simple analytical formula from an existing theoretical model and theoretically investigate in detail the state dependence of interaction-induced collisional loss rate coefficients, and the various parameter effects on collisional loss rate. We also investigate the different mechanisms and corresponding effects on collisional loss by analyzing our previous experimental results using the present formula, and even investigate the time evolution of Rydberg atom number for different Rydberg states.

  16. COLLISIONALLY BORN FAMILY ABOUT 87 SYLVIA

    SciTech Connect

    Vokrouhlicky, David; Nesvorny, David; Bottke, William F.; Morbidelli, Alessandro E-mail: davidn@boulder.swri.ed E-mail: morby@obs-nice.f

    2010-06-15

    There are currently more than 1000 multi-opposition objects known in the Cybele population, adjacent and exterior to the asteroid main belt, allowing a more detailed analysis than was previously possible. Searching for collisionally born clusters in this population, we find only one statistically robust case: a family of objects about (87) Sylvia. We use a numerical model to simulate the Sylvia family long-term evolution due to gravitational attraction from planets and thermal (Yarkovsky) effects and to explain its perturbed structure in the orbital element space. This allows us to conclude that the Sylvia family must be at least several hundreds of million years old, in agreement with evolutionary timescales of Sylvia's satellite system. We find it interesting that other large Cybele-zone asteroids with known satellites-(107) Camilla and (121) Hermione-do not have detectable families of collisional fragments about them (this is because we assume that binaries with large primary and small secondary components are necessarily impact generated). Our numerical simulations of synthetic clusters about these asteroids show they would suffer a substantial dynamical depletion by a combined effect of diffusion in numerous weak mean-motion resonances and Yarkovsky forces provided their age is close to {approx}4 billion years. However, we also believe that a complete effacement of these two families requires an additional component, very likely due to resonance sweeping or other perturbing effects associated with the late Jupiter's inward migration. We thus propose that both Camilla and Hermione originally had their collisional families, as in the Sylvia case, but they lost them in an evolution that lasted a billion years. Their satellites are the only witnesses of these effaced families.

  17. Missing Mass in Collisional Debris from Galaxies

    NASA Astrophysics Data System (ADS)

    Bournaud, Frédéric; Duc, Pierre-Alain; Brinks, Elias; Boquien, Médéric; Amram, Philippe; Lisenfeld, Ute; Koribalski, Bärbel S.; Walter, Fabian; Charmandaris, Vassilis

    2007-05-01

    Recycled dwarf galaxies can form in the collisional debris of massive galaxies. Theoretical models predict that, contrary to classical galaxies, these recycled galaxies should be free of nonbaryonic dark matter. By analyzing the observed gas kinematics of such recycled galaxies with the help of a numerical model, we demonstrate that they do contain a massive dark component amounting to about twice the visible matter. Staying within the standard cosmological framework, this result most likely indicates the presence of large amounts of unseen, presumably cold, molecular gas. This additional mass should be present in the disks of their progenitor spiral galaxies, accounting for a substantial part of the so-called missing baryons.

  18. Collisional Drift Waves in Stellarator Plasmas

    SciTech Connect

    J.L.V. Lewandowski

    2003-10-07

    A computational study of resistive drift waves in the edge plasma of a stellarator with an helical magnetic axis is presented. Three coupled field equations, describing the collisional drift wave dynamics in the linear approximation, are solved as an initial-value problem along the magnetic field line. The magnetohydrodynamic equilibrium is obtained from a three-dimensional local equilibrium model. The use of a local magnetohydrodynamic equilibrium model allows for a computationally efficient systematic study of the impact of the magnetic field structure on drift wave stability.

  19. Simulation of collisional fragmentation with explosives

    NASA Technical Reports Server (NTRS)

    Housen, Kevin

    1993-01-01

    For practical reasons, experimental studies of collisional fragmentation must at times rely on explosives to fragment a target body. For example, Housen et al., described experiments in which spheres were fragmented in a pressurized atmosphere. Explosives were used because impacts could not be performed in the pressure chamber. Explosives can also be used to study targets much larger than those which can be disrupted by conventional light-gas guns, thereby allowing size- and rate-effects to be investigated. The purpose of this study is to determine the charge burial depth required to simulate various aspects of collisions.

  20. Ion closure theory for high collisionality revisited

    SciTech Connect

    Ji, Jeong-Young Held, Eric D.

    2015-06-15

    According to analytical calculations of the ion collision operator, the ion-electron collision terms could be larger than the ion-ion collision terms. In the previous work [J.-Y. Ji and E. D. Held, Phys. Plasmas 20, 042114 (2013)], the ion-electron collision effects are diminished by the ion temperature change terms introduced from unlikely assumptions. In this work, the high-collisionality closures for ions are calculated without the temperature change terms. The ion-electron collision terms significantly modify existing closure coefficients.

  1. Electron parallel closures for arbitrary collisionality

    SciTech Connect

    Ji, Jeong-Young Held, Eric D.

    2014-12-15

    Electron parallel closures for heat flow, viscosity, and friction force are expressed as kernel-weighted integrals of thermodynamic drives, the temperature gradient, relative electron-ion flow velocity, and flow-velocity gradient. Simple, fitted kernel functions are obtained for arbitrary collisionality from the 6400 moment solution and the asymptotic behavior in the collisionless limit. The fitted kernels circumvent having to solve higher order moment equations in order to close the electron fluid equations. For this reason, the electron parallel closures provide a useful and general tool for theoretical and computational models of astrophysical and laboratory plasmas.

  2. Wavepacket theory of collisional dissociation in molecules

    SciTech Connect

    Kulander, K.

    1980-01-01

    An explicit integration scheme is used to solve the time dependent Schroedinger equation for wavepackets which model collisions in the collinear H + H/sub 2/ system. A realistic LEPS-type potential energy surface is used. Collision energies considered are above the dissociation threshold and probabilities for collision induced dissociation are reported. Also quantum mechanical state-to-state transition probabilities are generated. These results are compared to extensive classical trajectory calculations performed on this same system. The time evolution of the wavepacket densities is studied to understand the dynamics of the collinear collisional dissociation process.

  3. Transient performance

    NASA Astrophysics Data System (ADS)

    Curnock, Barry

    Gas turbine engine transient behavior, that which is concerned with the changes in engine parameters during acceleration or decceleration of an engine from one steady state point to a different steady state point, is considered. An engine can also experience cyclic aerodynamic phenomena which occur at a nominally steady condition; examples are compressor rotator stall and intake or afterburner buzz. The following are discussed: certification requirements; mechanism of acceleration; compressor working lines and surge; and some important factors (pressure level, moment of inertia, heat soakage, clearances, measurement of transients, thrust reversal, and transient maneuvers which involve significant changes to the shaft speeds of the engine). A set of graphics illustrating transient performance is presented.

  4. G6PD Deficiency

    MedlinePlus

    Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a genetic disorder that is most common in males. About 1 in 10 African American males in the United States has it. G6PD deficiency mainly affects red blood cells, which carry oxygen ...

  5. Generalized parallel heat transport equations in collisional to weakly collisional plasmas

    SciTech Connect

    Zawaideh, E.; Kim, N.S.; Najmabadi, F.

    1988-11-01

    A new set of two-fluid heat transport equations that is valid from collisional to weakly collisional limits is derived. Starting from gyrokinetic equations in flux coordinates, a set of moment equations describing plasma energy transport along the field lines of a space- and time-dependent magnetic field is derived. No restrictions on the anisotropy of the ion distribution function or collisionality are imposed. In the highly collisional limit, these equations reduce to the classical heat conduction equation (e.g., Spitzer and Haerm or Braginskii), while in the weakly collisional limit, they describe a saturated heat flux (flux limited). Numerical examples comparing these equations with conventional heat transport equations show that in the limit where the ratio of the mean free path lambda to the scale length of the temperature gradient L/sub T/ approaches zero, there is no significant difference between the solutions of the new and conventional heat transport equations. As lambda/L/sub T/..-->..1, the conventional heat conduction equation contains a significantly larger error than (lambda/L/sub T/)/sup 2/. The error is found to be O(lambda/L)/sup 2/, where L is the smallest of the scale lengths of the gradient in the magnetic field, or the macroscopic plasma parameters (e.g., velocity scale length, temperature scale length, and density scale length). The accuracy of the flux-limited model depends significantly on the value of the flux limit parameter which, in general, is not known. The new set of equations shows that the flux-limited parameter is a function of the magnetic field and plasma parameter profiles.

  6. Coherence measurements of a transient 14.7-nm x-ray laser

    NASA Astrophysics Data System (ADS)

    Dunn, James; Smith, Raymond F.; Hubert, Sebastian; Fajardo, Marta; Zeitoun, Philippe; Hunter, James R.; Remond, Christian; Vanbostal, Laurent; Jacquemot, Sylvie; Nilsen, Joseph; Lewis, Ciaran L. S.; Marmoret, Remy; Shlyaptsev, Vyacheslav N.; Ravet, Marie-Francoise; Delmotte, Franck

    2003-12-01

    We present the longitudinal coherence measurement of the transient inversion collisional x-ray laser for the first time. The Ni-like Pd x-ray laser at 14.68 nm is generated by the LLNL COMET laser facility and is operating in the gain-saturated regime. Interference fringes are produced using a Michelson interferometer setup in which a thin multilayer-coated membrane is used as a beam splitter. The longitudinal coherence length for the picosecond duration 4d1S0 --> 4p1P1 lasing transition is determined to be ~400 µm (1/e HW) by adjusting the length of one interferometer arm and measuring the resultant variation in fringe visibility. This is four times improved coherence than previous measurements on quasi-steady state schemes largely as a result of the narrower line profile in the lower temperature plasma. The inferred gain-narrowed linewidth of ~0.29 pm is also substantially narrower than previous measurements on quasi-steady state x-ray laser schemes. This study shows that the coherence of the x-ray laser beam can be improved by changing the laser pumping conditions. The x-ray laser is operating at 4 5 times the transform-limited pulse.

  7. Archean collisional tectonics in SW Montana

    SciTech Connect

    Mogk, D.; Rickmond, D.; Salt, K.; Clark, M.; Mueller, P.; Lafrenze, D.; Wooden, J.; Henry, D.

    1985-01-01

    The Archean continental crust of SW Montana evolved through alternating cycles of stable platform sedimentation followed by crustal thickening through collisional tectonics. The ancient sialic crust in the Beartooth Mountains served as the nucleus for accretion of younger terranes to the west. The oldest orogenic cycle recognized in the Beartooth Mountains involves a 3.4 Ga old supracrustal sequence which was metamorphosed in the granulite facies (T=700-800/sup 0/C, P=6Kb, 35/sup 0/C/Km); deep burial is interpreted as the result of collisional tectonic thickening. The second orogenic cycle is subduction related and has produced 2.8 Ga old andesites, 2.75 Ga old calc-alkaline intrusives, upper amphibolite grade metamorphism, transcurrent faulting (in the North Snowy Block and Yankee Jim canyon at 2.8 Ga) and nappe emplacement. In the central Beartooths post-orogenic granites intrude pelitic schists (T=600/sup 0/C, P=8Kb, 25/sup 0/C/Km). West of the Beartooths the basement consists of 2.75-2.70 Ga old, tectonically telescoped coarse clastics (Gallatin, Madison Ranges) and stable platform sequences (Gravelly, Tobacco Root, Ruby Ranges). Nappe formation and granulite-migmatite (700-750/sup 0/C) associations are common, suggesting deep burial through tectonic thickening. A later-kinematic mesozonal (8Kb) qtz diorite-granodiorite batholithic complex is present in the northern Madison Range. Quartzofeldspathic paragneisses in the westernmost Archean basement are derived from either a continental or island arc source.

  8. A COLLISIONAL ORIGIN FOR THE LEO RING

    SciTech Connect

    Michel-Dansac, Leo; Emsellem, Eric; Duc, Pierre-Alain; Bournaud, Frederic; Oosterloo, Tom; Morganti, Raffaella; Serra, Paolo; Ibata, Rodrigo

    2010-07-10

    Extended H I structures around galaxies are of prime importance for probing galaxy formation scenarios. The giant H I ring in the Leo group is one of the largest and most intriguing H I structures in the nearby universe. Whether it consists of primordial gas, as suggested by the apparent absence of any optical counterpart and the absence of an obvious physical connection to nearby galaxies, or of gas expelled from a galaxy in a collision is actively debated. We present deep wide field-of-view optical images of the ring region obtained with MegaCam on the CFHT. They reveal optical counterparts to several H I and UV condensations along the ring, in the g', r', and i' bands, which likely correspond to stellar associations formed within the gaseous ring. Analyzing the spectral energy distribution of one of these star-forming regions, we found it to be typical for a star-forming region in pre-enriched tidal debris. We then use simulations to test the hypothesis that the Leo ring results from a head-on collision between Leo group members NGC 3384 and M96. According to our model which is able to explain, at least qualitatively, the main observational properties of the system, the Leo ring is consistent with being a collisional ring. It is thus likely another example of extended intergalactic gas made-up of pre-enriched collisional debris.

  9. Collisional-Radiative Kinetics in Monatomic Gases

    NASA Astrophysics Data System (ADS)

    Le, Hai; Karagozian, Ann

    2012-11-01

    A detailed model of electronic excited states is essential in capturing all the nonequilibrium processes of a partially ionized plasma by means of collisional and radiative interactions. This collisional-radiative (CR) model allows us to consider deviations from equilibrium distribution of the internal states, and is now more commonly used in the study of plasma discharges. Prior studies by Kapper and Cambier and Panesi et al. suggest that this level of detail is needed for an accurate prediction of the flow field, and it is particularly relevant to plasma-combustion interactions. The required number of excited states needed to be included in the CR model is often prohibitively large due to the nonequilibrium condition of the plasma. The consequence is a large system of ODE's which needs to be solved at each time step. A reduced mechanism for the CR model can be attained by grouping the upper states of the atomic state distribution (ASDF) into a pseudo-level in which the population is characterized either by a uniform distribution or a Boltzmann distribution. This talk presents both detailed and reduced models for an ionizing shock in Argon. Supported by the US Air Force/ERC, Inc. under subcontract RS111738.

  10. Heat flux viscosity in collisional magnetized plasmas

    SciTech Connect

    Liu, C.; Fox, W.; Bhattacharjee, A.

    2015-05-15

    Momentum transport in collisional magnetized plasmas due to gradients in the heat flux, a “heat flux viscosity,” is demonstrated. Even though no net particle flux is associated with a heat flux, in a plasma there can still be momentum transport owing to the velocity dependence of the Coulomb collision frequency, analogous to the thermal force. This heat-flux viscosity may play an important role in numerous plasma environments, in particular, in strongly driven high-energy-density plasma, where strong heat flux can dominate over ordinary plasma flows. The heat flux viscosity can influence the dynamics of the magnetic field in plasmas through the generalized Ohm's law and may therefore play an important role as a dissipation mechanism allowing magnetic field line reconnection. The heat flux viscosity is calculated directly using the finite-difference method of Epperlein and Haines [Phys. Fluids 29, 1029 (1986)], which is shown to be more accurate than Braginskii's method [S. I. Braginskii, Rev. Plasma Phys. 1, 205 (1965)], and confirmed with one-dimensional collisional particle-in-cell simulations. The resulting transport coefficients are tabulated for ease of application.

  11. Intense sediment transport: Collisional to turbulent suspension

    NASA Astrophysics Data System (ADS)

    Berzi, Diego; Fraccarollo, Luigi

    2016-02-01

    A recent simple analytical approach to the problem of steady, uniform transport of sediment by a turbulent shearing fluid dominated by interparticle collisions is extended to the case in which the mean turbulent lift may partially or totally support the weight of the sediment. We treat the granular-fluid mixture as a continuum and make use of constitutive relations of kinetic theory of granular gases to model the particle phase and a simple mixing-length approach for the fluid. We focus on pressure-driven flows over horizontal, erodible beds and divide the flow itself into layers, each dominated by different physical mechanisms. This permits a crude analytical integration of the governing equations and to obtain analytical expressions for the distribution of particle concentration and velocity. The predictions of the theory are compared with existing laboratory measurements on the flow of glass spheres and sand particles in water. We also show how to build a regime map to distinguish between collisional, turbulent-collisional, and fully turbulent suspensions.

  12. Collisional model for granular impact dynamics.

    PubMed

    Clark, Abram H; Petersen, Alec J; Behringer, Robert P

    2014-01-01

    When an intruder strikes a granular material from above, the grains exert a stopping force which decelerates and stops the intruder. Many previous studies have used a macroscopic force law, including a drag force which is quadratic in velocity, to characterize the decelerating force on the intruder. However, the microscopic origins of the force-law terms are still a subject of debate. Here, drawing from previous experiments with photoelastic particles, we present a model which describes the velocity-squared force in terms of repeated collisions with clusters of grains. From our high speed photoelastic data, we infer that "clusters" correspond to segments of the strong force network that are excited by the advancing intruder. The model predicts a scaling relation for the velocity-squared drag force that accounts for the intruder shape. Additionally, we show that the collisional model predicts an instability to rotations, which depends on the intruder shape. To test this model, we perform a comprehensive experimental study of the dynamics of two-dimensional granular impacts on beds of photoelastic disks, with different profiles for the leading edge of the intruder. We particularly focus on a simple and useful case for testing shape effects by using triangular-nosed intruders. We show that the collisional model effectively captures the dynamics of intruder deceleration and rotation; i.e., these two dynamical effects can be described as two different manifestations of the same grain-scale physical processes. PMID:24580216

  13. Heat flux viscosity in collisional magnetized plasmas

    NASA Astrophysics Data System (ADS)

    Liu, C.; Fox, W.; Bhattacharjee, A.

    2015-05-01

    Momentum transport in collisional magnetized plasmas due to gradients in the heat flux, a "heat flux viscosity," is demonstrated. Even though no net particle flux is associated with a heat flux, in a plasma there can still be momentum transport owing to the velocity dependence of the Coulomb collision frequency, analogous to the thermal force. This heat-flux viscosity may play an important role in numerous plasma environments, in particular, in strongly driven high-energy-density plasma, where strong heat flux can dominate over ordinary plasma flows. The heat flux viscosity can influence the dynamics of the magnetic field in plasmas through the generalized Ohm's law and may therefore play an important role as a dissipation mechanism allowing magnetic field line reconnection. The heat flux viscosity is calculated directly using the finite-difference method of Epperlein and Haines [Phys. Fluids 29, 1029 (1986)], which is shown to be more accurate than Braginskii's method [S. I. Braginskii, Rev. Plasma Phys. 1, 205 (1965)], and confirmed with one-dimensional collisional particle-in-cell simulations. The resulting transport coefficients are tabulated for ease of application.

  14. Collisional population transfer in yterbium ions

    SciTech Connect

    Schauer, Martin Michael; Torgerson, Justin R; Danielson, Jeremy R; Zhao, Xinxin; Nguyen, Ahn - Tuan; Wang, Li - Bang

    2009-01-01

    Long-lived metastable states of Yb+ ions are used for atomic frequency standards, precision measurements, and quantum information research. The effect of population trapping and transfer in these states must be well understood. We report here the transfer of Yb+ ions into the long-lived {sup 2}F{sub 7/2} state by means of collisions between He buffer gas and Yb+ ions held in a linear Paul trap. Transfer rates were measured as functions of buffer-gas pressure and repump-laser power, and the collisional population transfer rates were extracted. The measured transfer rate coefficients are 8.32(75)x10-11 and 8.65(33)x10-11 cm3/s for the collisional processes {sup 2}P{sub 1/2}{yields}{sup 2}D{sub 5/2} and {sup 2}D{sub 3/2}{yields}{sup 2}F{sub 7/2}, respectively.

  15. Polarization of fast particle beams by collisional pumping

    DOEpatents

    Stearns, J. Warren; Kaplan, Selig N.; Pyle, Robert V.; Anderson, L. Wilmer; Ruby, Lawrence; Schlachter, Alfred S.

    1988-01-01

    Method and apparatus for highly polarizing a fast beam of particles by collisional pumping, including generating a fast beam of particles, and also generating a thick electron-spin-polarized medium positioned as a target for the beam. The target is made sufficiently thick to allow the beam to interact with the medium to produce collisional pumping whereby the beam becomes highly polarized.

  16. Collisional effects in weakly collisional plasmas: nonlinear electrostatic waves and recurrence phenomena

    NASA Astrophysics Data System (ADS)

    Camporeale, E.; Pezzi, O.; Valentini, F.

    2015-12-01

    The longstanding problem of collisions in plasmas is a very fascinating and huge topic in plasma physics. The 'natural' operator that describes the Coulombian interactions between charged particles is the Landau (LAN) integral operator. The LAN operator is a nonlinear, integro-differential and Fokker-Planck type operator which satisfies the H theorem for the entropy growth. Due to its nonlinear nature and multi-dimensionality, any approach to the solution of the Landau integral is almost prohibitive. Therefore collisions are usually modeled by simplified collisional operators. Here collisional effects are modeled by i) the one-dimensional Lenard-Bernstein (LB) operator and ii) the three-dimensional Dougherty (DG) operator. In the first case i), by focusing on a 1D-1V phase space, we study recurrence effects in a weakly collisional plasma, being collisions modeled by the LB operator. By decomposing the linear Vlasov-Poisson system in the Fourier-Hermite space, the recurrence problem is investigated in the linear regime of the damping of a Langmuir wave and of the onset of the bump-on-tail instability. The analysis is then confirmed and extended to the nonlinear regime through a Eulerian collisional Vlasov-Poisson code. Despite being routinely used, an artificial collisionality is not in general a viable way of preventing recurrence in numerical simulations. Moreover, recursive phenomena affect both the linear exponential growth and the nonlinear saturation of a linear instability by producing a fake growth in the electric field, thus showing that, although the filamentation is usually associated with low amplitude fluctuations contexts, it can occur also in nonlinear phenomena. On the other hand ii), the effects of electron-electron collisions on the propagation of nonlinear electrostatic waves are shown by means of Eulerian simulations in a 1D-3V (one dimension in physical space, three dimensions in velocity space) phase space. The nonlinear regime of the symmetric

  17. Collisional effects on nonlinear ion drag force for small grains

    SciTech Connect

    Hutchinson, I. H.; Haakonsen, C. B.

    2013-08-15

    The ion drag force arising from plasma flow past an embedded spherical grain is calculated self-consistently and non-linearly using particle in cell codes, accounting for ion-neutral collisions. Using ion velocity distribution appropriate for ion drift driven by a force field gives wake potential and force greatly different from a shifted Maxwellian distribution, regardless of collisionality. The low-collisionality forces are shown to be consistent with estimates based upon cross-sections for scattering in a Yukawa (shielded) grain field, but only if non-linear shielding length is used. Finite collisionality initially enhances the drag force, but only by up to a factor of 2. Larger collisionality eventually reduces the drag force. In the collisional regime, the drift distribution gives larger drag than the shift distribution even at velocities where their collisionless drags are equal. Comprehensive practical analytic formulas for force that fit the calculations are provided.

  18. Aeolian Sand Transport with Collisional Suspension

    NASA Technical Reports Server (NTRS)

    Jenkins, James T.; Pasini, Jose Miguel; Valance, Alexandre

    2004-01-01

    Aeolian transport is an important mechanism for the transport of sand on Earth and on Mars. Dust and sand storms are common occurrences on Mars and windblown sand is responsible for many of the observed surface features, such as dune fields. A better understanding of Aeolian transport could also lead to improvements in pneumatic conveying of materials to be mined for life support on the surface of the Moon and Mars. The usual view of aeolian sand transport is that for mild winds, saltation is the dominant mechanism, with particles in the bed being dislodged by the impact of other saltating particles, but without in-flight collisions. As the wind becomes stronger, turbulent suspension keeps the particles in the air, allowing much longer trajectories, with the corresponding increase in transport rate. We show here that an important regime exists between these two extremes: for strong winds, but before turbulent suspension becomes dominant, there is a regime in which in-flight collisions dominate over turbulence as a suspension mechanism, yielding transport rates much higher than those for saltation. The theory presented is based on granular kinetic theory, and includes both turbulent suspension and particle-particle collisions. The wind strengths for which the calculated transport rates are relevant are beyond the published strengths of current wind tunnel experiments, so these theoretical results are an invitation to do experiments in the strong-wind regime. In order to make a connection between the regime of saltation and the regime of collisional suspension, it is necessary to better understand the interaction between the bed and the particles that collide with it. This interaction depends on the agitation of the particles of the bed. In mild winds, collisions with the bed are relatively infrequent and the local disturbance associated with a collision can relax before the next nearby collision. However, as the wind speed increases, collision become more frequent

  19. Collisional quenching of highly rotationally excited HF

    NASA Astrophysics Data System (ADS)

    Yang, B.; Walker, K. M.; Forrey, R. C.; Stancil, P. C.; Balakrishnan, N.

    2015-06-01

    Context. Collisional excitation rate coefficients play an important role in the dynamics of energy transfer in the interstellar medium. In particular, accurate rotational excitation rates are needed to interpret microwave and infrared observations of the interstellar gas for nonlocal thermodynamic equilibrium line formation. Aims: Theoretical cross sections and rate coefficients for collisional deexcitation of rotationally excited HF in the vibrational ground state are reported. Methods: The quantum-mechanical close-coupling approach implemented in the nonreactive scattering code MOLSCAT was applied in the cross section and rate coefficient calculations on an accurate 2D HF-He potential energy surface. Estimates of rate coefficients for H and H2 colliders were obtained from the HF-He collisional data with a reduced-potential scaling approach. Results: The calculation of state-to-state rotational quenching cross sections for HF due to He with initial rotational levels up to j = 20 were performed for kinetic energies from 10-5 to 15 000 cm-1. State-to-state rate coefficients for temperatures between 0.1 and 3000 K are also presented. The comparison of the present results with previous work for lowly-excited rotational levels reveals significant differences. In estimating HF-H2 rate coefficients, the reduced-potential method is found to be more reliable than the standard reduced-mass approach. Conclusions: The current state-to-state rate coefficient calculations are the most comprehensive to date for HF-He collisions. We attribute the differences between previously reported data and our results to differences in the adopted interaction potential energy surfaces. The new He rate coefficients can be used in a variety of applications. The estimated H2 and H collision rates can also augment the smaller datasets previously developed for H2 and electrons. Rate coefficient tables are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130

  20. Collisional electron spectroscopy method for gas analysis

    NASA Astrophysics Data System (ADS)

    Stefanova, M. S.; Pramatarov, P. M.; Kudryavtsev, A. A.; Peyeva, R. A.; Patrikov, T. B.

    2016-05-01

    Recently developed collisional electron spectroscopy (CES) method, based on identification of gas impurities by registration of groups of nonlocal fast electrons released by Penning ionization of the impurity particles by helium metastable atoms, is verified experimentally. Detection and identification of atoms and molecules of gas impurities in helium at pressures of 14 - 90 Torr with small admixtures of Ar, Kr, CO2, and N2 are carried out. The nonlocal negative glow plasma of short dc microdischarge is used as most suitable medium. Records of the energy spectra of penning electrons are performed by means of an additional electrode - sensor, located at the boundary of the discharge volume. Maxima appear in the electron energy spectra at the characteristic energies corresponding to Penning ionization of the impurity particles by helium metastable atoms.

  1. Wind enhanced planetary escape: Collisional modifications

    NASA Technical Reports Server (NTRS)

    Curtis, S. A.; Hartle, R. E.

    1976-01-01

    The problem of thermal escape is considered in which both the effects of thermospheric winds at the exobase and collisions below the exobase are included in a Monte Carlo calculation. The collisions are included by means of a collisional relaxation layer of a background gas which models the transition region between the exosphere and the thermosphere. The wind effects are considered in the limiting cases of vertical and horizontal flows. Two species are considered: terrestrial hydrogen and terrestrial helium. In the cases of terrestrial hydrogen the escape fluxes were found to be strongly filtered or throttled by collisions at high exospheric temperatures. The model is applied to molecular hydrogen diffusing through a methane relaxation layer under conditions possible on Titan. The results are similar to the case of terrestrial hydrogen with wind enhanced escape being strongly suppressed by collisions. It is concluded that wind enhanced escape is not an important process on Titan.

  2. Collisional and Dynamical Evolution of Planetary Systems

    NASA Technical Reports Server (NTRS)

    Weidenschilling, Stuart J.

    2004-01-01

    Senior Scientst S. J. Weidenschilling presents his final administrative report in the research program entitled "Collisional and Dynamical Evolution of Planetary Systems," on which he was the Principal Investigator. This research program produced the following publications: 1) "Jumping Jupiters" in binary star systems. F. Marzari, S. J. Weidenschilling, M. Barbieri and V. Granata. Astrophys. J., in press, 2005; 2) Formation of the cores of the outer planets. To appear in "The Outer Planets" (R. Kallenbach, ED), ISSI Conference Proceedings (Space Sci. Rev.), in press, 2005; 3) Accretion dynamics and timescales: Relation to chondrites. S. J. Weidenschilling and J. Cuzzi. In Meteorites and the Early Solar System LI (D. Lauretta et al., Eds.), Univ. of Arizona Press, 2005; 4) Asteroidal heating and thermal stratification of the asteroid belt. A. Ghosh, S. J.Weidenschilling, H. Y. McSween, Jr. and A. Rubin. In Meteorites and the Early Solar System I1 (D. Lauretta et al., Eds.), Univ. of Arizona Press, 2005.

  3. PD-1, PD-L1 and PD-L2 expression in mouse prostate cancer

    PubMed Central

    Yang, Shijie; Zhang, Qiuyang; Liu, Sen; Wang, Alun R; You, Zongbing

    2016-01-01

    Programmed cell death protein 1 (PD-1) and its ligands PD-L1 and PD-L2 play critical roles in maintaining an immunosuppressive tumor microenvironment. The purpose of the present study was to assess expression of PD-1, PD-L1, and PD-L2 in mouse prostate tumors. A total of 33 mouse prostate tumors derived from Pten-null mice were examined using immunohistochemical staining for PD-1, PD-L1, and PD-L2. The animals were either with interleukin-17 receptor c (Il-17rc) wild-type or knockout genotype, or fed with regular diet or high-fat diet to 30 weeks of age. We found that Il-17rc wild-type mouse prostate tumors had significantly higher levels of PD-1, PD-L1, and PD-L2 than Il-17rc knockout mouse prostate tumors. High-fat diet-induced obese mice had significantly higher levels of PD-1, PD-L1, and PD-L2 in their prostate tumors than lean mice fed with regular diet. Increased expression of PD-1, PD-L1, and PD-L2 was associated with increased number of invasive prostate tumors formed in the Il-17rc wild-type and obese mice compared to the Il-17rc knockout and lean mice, respectively. Our findings suggest that expression of PD-1, PD-L1, and PD-L2 may enhance development of mouse prostate cancer through creating an immunosuppressive tumor microenvironment. PMID:27069956

  4. The complex correspondence between families and collisional events

    NASA Astrophysics Data System (ADS)

    Milani Comparetti, Andrea

    2015-08-01

    Asteroid families are identified as statistically significant concentrations of asteroids in the space of proper elements. The purpose of family classifications is meant to be the identification of the largest collisional events occurred during the history of the asteroid main belt. However, are the families as found in 1-1 correspondence with ancient collisional events? A recent analysis of larger classifications, based on larger and more accurate datasets of proper elements, indicates that this is not the case. There are multiple cratering events on the same parent body. There are collisional families split into two by the YORP effect. There are subfamilies arising from secondary collisions after the one forming a larger family, and this is not limited to recent events. There are families overlapping in proper elements space but with composition incompatible with a common parent body. There are cases not yet understood, but pointing to a complex collisional history. In total at least 10 cases of complex correpondence between families and collisional events have been identified, more are suspected but not yet supported by enough evidence. The disentagling of these complex collisional histories is an essential step towards the understanding of the asteroid collisional evolution.

  5. Solar Wind Collisional Age from a Global Magnetohydrodynamics Simulation

    NASA Astrophysics Data System (ADS)

    Chhiber, R.; Usmanov, AV; Matthaeus, WH; Goldstein, ML

    2016-04-01

    Simple estimates of the number of Coulomb collisions experienced by the interplanetary plasma to the point of observation, i.e., the “collisional age”, can be usefully employed in the study of non-thermal features of the solar wind. Usually these estimates are based on local plasma properties at the point of observation. Here we improve the method of estimation of the collisional age by employing solutions obtained from global three-dimensional magnetohydrodynamics simulations. This enables evaluation of the complete analytical expression for the collisional age without using approximations. The improved estimation of the collisional timescale is compared with turbulence and expansion timescales to assess the relative importance of collisions. The collisional age computed using the approximate formula employed in previous work is compared with the improved simulation-based calculations to examine the validity of the simplified formula. We also develop an analytical expression for the evaluation of the collisional age and we find good agreement between the numerical and analytical results. Finally, we briefly discuss the implications for an improved estimation of collisionality along spacecraft trajectories, including Solar Probe Plus.

  6. Collisional Penrose process in a rotating wormhole spacetime

    NASA Astrophysics Data System (ADS)

    Tsukamoto, Naoki; Bambi, Cosimo

    2015-05-01

    In a collisional Penrose process, two particles coming from the asymptotically flat region collide in the ergosphere of a compact object. The collision produces two new particles, one with positive energy and one with negative energy. When the particle with positive energy escapes to infinity, the process extracts energy from the compact object. In this paper, we study the collisional Penrose process in a rotating wormhole spacetime. We consider the simple case of a head-on collision at the throat of a Teo wormhole. We find that the process of energy extraction from a Teo wormhole can be substantially more efficient than the collisional Penrose process in the Kerr black hole spacetime.

  7. Field-free molecular alignment for probing collisional relaxation dynamics

    NASA Astrophysics Data System (ADS)

    Vieillard, Th.; Chaussard, F.; Billard, F.; Sugny, D.; Faucher, O.; Ivanov, S.; Hartmann, J.-M.; Boulet, C.; Lavorel, B.

    2013-02-01

    We report the experimental study of field-free molecular alignment in CO2 gas mixtures induced by intense femtosecond laser pulses in the presence of collisional processes. We demonstrate that the alignment signals exhibit specific features due to nontrivial collisional propensity rules that tend to preserve the orientation of the rotational angular momentum of the molecules. The analysis is performed with a quantum approach based on the modeling of rotational J- and M-dependent state-to-state transfer rates. The present work paves the way for strong-field spectroscopy of collisional dynamics.

  8. Collisional coupling in counterstreaming laser-produced plasmas

    NASA Technical Reports Server (NTRS)

    Koopman, D. W.; Goforth, R. R.

    1974-01-01

    The collisional processes which transfer momentum between counterstreaming plasmas are reviewed and applied to the example of a laser-produced plasma expanding into a partially ionized background. Experimental measurements of the dependence of the ion flow field on collisional momentum transfer demonstrate the validity of the simplified treatment of collision processes which have been adopted. A numerical model which simulates the laser-plasma interaction with the background confirms the importance of collisions in previous experimental studies of momentum coupling, and provides some insight into the distinction between collisional and collisionless flow regimes.

  9. Impact of collisionality on fluctuation characteristics of micro-turbulence

    SciTech Connect

    Vermare, L.; Hennequin, P.; Guercan, Oe. D.; Bourdelle, C.; Clairet, F.; Garbet, X.; Sabot, R.

    2011-01-15

    The influence of changing collisionality on density fluctuation characteristics is studied during dedicated {nu}* scaling experiments, using Doppler backscattering system. First, the repartition of fluctuation energy over different spatial scales, as represented by the wavenumber spectrum, is investigated and a modification of the shape of the perpendicular wavenumber spectrum in the low wavenumber part of the spectrum is observed when changing collisionality. In addition, a new procedure to evaluate the dispersion relation of micro-turbulence is presented. From the behavior of the perpendicular mean velocity of density fluctuations with the perpendicular wavenumber, different dispersion relations are obtained between low and high collisionality cases.

  10. Transient Heat Transfer in TCAP Coils

    SciTech Connect

    Steimke, J.L.

    1999-03-09

    The Thermal Cycling Absorption Process (TCAP) is used to separate isotopes of hydrogen. TCAP involves passing a stream of mixed hydrogen isotopes through palladium deposited on kieselguhr (Pd/k) while cycling the temperature of the Pd/k. Kieselguhr is a silica mineral also called diatomite. To aid in the design of a full scale facility, the Thermal Fluids Laboratory was used by the Chemical and Hydrogen Technology Section to compare the heat transfer properties of three different configurations of stainless steel coils containing kieselguhr and helium. Testing of coils containing Pd/k and hydrogen isotopes would have been more prototypical but would have been too expensive. Three stainless steel coils filled with kieselguhr were tested; one made from 2.0 inch diameter tubing, one made from 2.0 inch diameter tubing with foam copper embedded in the kieselguhr and one made from 1.25 inch diameter tubing. It was known prior to testing that increasing the tubing diameter from 1.25 inch to 2.0 inch would slow the rate of temperature change. The primary purpose of the testing was to measure to what extent the presence of copper foam in a 2.0" tubing coil would compensate for the effect of larger diameter. Each coil was connected to a pressure gage and the coil was evacuated and backfilled with helium gas. Helium was used instead of a mixture of hydrogen isotopes for reasons of safety. Each coil was quickly immersed in a stirred bath of ethylene glycol at a temperature of approximately 100 degrees Celsius. The coil pressure increased, reflecting the increase in average temperature of its contents. The pressure transient was recored as a function of time after immersion. Because of the actual process will use Pd/k instead of kieselguhr, additional tests were run to determine the differences in thermal properties between the two materials. The method was to position a thermocouple at the center of a hollow sphere and pack the sphere with Pd/k. The sphere was sealed, quickly

  11. Transient Heat Transfer in TCAP Coils

    SciTech Connect

    Steimke, J.L.

    1999-03-09

    The Thermal Cycling Absorption Process (TCAP) is used to separate isotopes of hydrogen. TCAP involves passing a stream of mixed hydrogen isotopes through palladium deposited on kieselguhr (Pd/k) while cycling the temperature of the Pd/k. Kieselguhr is a silica mineral also called diatomite. To aid in the design of a full scale facility, the Thermal Fluids Laboratory was used by the Chemical and Hydrogen Technology Section to compare the heat transfer properties of three different configurations of stainless steel coils containing kieselguhr and helium. Testing of coils containing Pd/k and hydrogen isotopes would have been more prototypical but would have been too expensive. Three stainless steel coils filled with kieselguhr were tested; one made from 2.0 inch diameter tubing, one made from 2.0 inch diameter tubing with foam copper embedded in the kieselguhr and one made from 1.25 inch diameter tubing. It was known prior to testing that increasing the tubing diameter from 1.25 inch to 2.0 inch would slow the rate of temperature change. The primary purpose of the testing was to measure to what extent the presence of copper foam in a 2.0 tubing coil would compensate for the effect of larger diameter. Each coil was connected to a pressure gage and the coil was evacuated and backfilled with helium gas. Helium was used instead of a mixture of hydrogen isotopes for reasons of safety. Each coil was quickly immersed in a stirred bath of ethylene glycol at a temperature of approximately 100 degrees Celsius. The coil pressure increased, reflecting the increase in average temperature of its contents. The pressure transient was recored as a function of time after immersion. Because of the actual process will use Pd/k instead of kieselguhr, additional tests were run to determine the differences in thermal properties between the two materials. The method was to position a thermocouple at the center of a hollow sphere and pack the sphere with Pd/k. The sphere was sealed, quickly

  12. THE CREATION OF HAUMEA'S COLLISIONAL FAMILY

    SciTech Connect

    Schlichting, Hilke E.; Sari, Re'em E-mail: sari@tapir.caltech.edu

    2009-08-01

    Recently, the first collisional family was discovered in the Kuiper Belt. The parent body of this family, Haumea, is one of the largest objects in the Kuiper Belt and is orbited by two satellites. It has been proposed that the Haumea family was created from dispersed fragments that resulted from a giant impact. This proposed origin of the Haumea family is however in conflict with the observed velocity dispersion between the family members ({approx} 140 m s{sup -1}) which is significantly less than the escape velocity from Haumea's surface ({approx} 900 m s{sup -1}). In this paper we propose a different formation scenario for Haumea's collisional family. In our scenario the family members are ejected while in orbit around Haumea. This scenario, therefore, naturally gives rise to a lower velocity dispersion among the family members than expected from direct ejection from Haumea's surface. In our scenario Haumea's giant impact forms a single moon that tidally evolves outward until it suffers a destructive collision from which the family is created. We show that this formation scenario yields a velocity dispersion of {approx} 190 m s{sup -1} among the family members which is in good agreement with the observations. We discuss an alternative scenario that consists of the formation and tidal evolution of several satellites that are ejected by collisions with unbound Kuiper Belt objects. However, the formation of the Haumea family in this latter way is difficult to reconcile with the large abundance of Kuiper Belt binaries. We, therefore, favor forming the family by a destructive collision of a single moon of Haumea. The probability for Haumea's initial giant impact in today's Kuiper Belt is less than 10{sup -3}. In our scenario, however, Haumea's giant impact can occur before the excitation of the Kuiper Belt and the ejection of the family members afterward. This has the advantage that one can preserve the dynamical coherence of the family and explain Haumea's original

  13. THE COLLISIONAL EVOLUTION OF DEBRIS DISKS

    SciTech Connect

    Gaspar, Andras; Rieke, George H.; Balog, Zoltan E-mail: grieke@as.arizona.edu

    2013-05-01

    We explore the collisional decay of disk mass and infrared emission in debris disks. With models, we show that the rate of the decay varies throughout the evolution of the disks, increasing its rate up to a certain point, which is followed by a leveling off to a slower value. The total disk mass falls off {proportional_to}t {sup -0.35} at its fastest point (where t is time) for our reference model, while the dust mass and its proxy-the infrared excess emission-fades significantly faster ({proportional_to}t {sup -0.8}). These later level off to a decay rate of M{sub tot}(t){proportional_to}t {sup -0.08} and M{sub dust}(t) or L{sub ir}(t){proportional_to}t {sup -0.6}. This is slower than the {proportional_to}t {sup -1} decay given for all three system parameters by traditional analytic models. We also compile an extensive catalog of Spitzer and Herschel 24, 70, and 100 {mu}m observations. Assuming a log-normal distribution of initial disk masses, we generate model population decay curves for the fraction of stars harboring debris disks detected at 24 {mu}m. We also model the distribution of measured excesses at the far-IR wavelengths (70-100 {mu}m) at certain age regimes. We show general agreement at 24 {mu}m between the decay of our numerical collisional population synthesis model and observations up to a Gyr. We associate offsets above a Gyr to stochastic events in a few select systems. We cannot fit the decay in the far-infrared convincingly with grain strength properties appropriate for silicates, but those of water ice give fits more consistent with the observations (other relatively weak grain materials would presumably also be successful). The oldest disks have a higher incidence of large excesses than predicted by the model; again, a plausible explanation is very late phases of high dynamical activity around a small number of stars. Finally, we constrain the variables of our numerical model by comparing the evolutionary trends generated from the exploration

  14. Particle Segregation in Collisional Shearing Flows

    NASA Technical Reports Server (NTRS)

    Jenkins, J. T.; Louge, M. Y.

    1999-01-01

    The size segregation of flowing or shaken grains is a commonly observed phenomenon in industrial processes and in nature. In systems that do not involve much agitation of the grains, several mechanisms that involve gravity have been identified as leading to such segregation. In highly agitated flows, there is a mechanism independent of gravity that is available to drive separation of different grains. This is associated with spatial gradients in the energy of their velocity fluctuations. Because collisions between grains inevitably dissipate energy, collisional granular shear flows are usually of limited extent in the direction transverse to the flow. One consequence of this is that shear flows are strongly influenced by their boundaries. Because grains, on average, slip relative to boundaries, a bumpy or frictional boundary can convert slip energy into fluctuation energy. However, because each collision between a grain and the boundary dissipates fluctuation energy, there is a competition between production and dissipation. In principle, it is possible to design the geometry of the boundary - for example, the size and spacing of the bumps - so that the boundary either produces or dissipates fluctuation energy. This permits the control of the component of the spatial gradient of the fluctuation energy that is normal to the boundary. The gradients in fluctuation energy established by such boundaries may be exploited to drive the separation by size or other properties in a binary mixture of spherical grains. Microgravity makes the visual observations possible by permitting us to employ moderate rates of shear. On earth, the effects of gravity can be minimized by shearing so rapidly that the particle pressure overwhelms gravity. However, in this event, separation takes place too rapidly for visual observation, buoyancy and/or condensation associated with the centripetal acceleration must be accounted for, and the particles can be severely damaged. Because, in the

  15. Synthesis and characterization of Pd(0), PdS, and Pd@PdO core-shell nanoparticles by solventless thermolysis of a Pd-thiolate cluster

    NASA Astrophysics Data System (ADS)

    Jose, Deepa; Jagirdar, Balaji R.

    2010-09-01

    Colloids of palladium nanoparticles have been prepared by the solvated metal atom dispersion (SMAD) method. The as-prepared Pd colloid consists of particles with an average diameter of 2.8±0.1 nm. Digestive ripening of the as-prepared Pd colloid, a process involving refluxing the as-prepared colloid at or near the boiling point of the solvent in the presence of a passivating agent, dodecanethiol resulted in a previously reported Pd-thiolate cluster, [Pd(SC 12H 25) 2] 6 but did not render the expected narrowing down of the particle size distribution. Solventless thermolysis of the Pd-thiolate complex resulted in various Pd systems such as Pd(0), PdS, and Pd@PdO core-shell nanoparticles thus demonstrating its versatility. These Pd nanostructures have been characterized using high-resolution electron microscopy and powder X-ray diffraction methods.

  16. Collisional Relaxation of Fine Velocity Structures in Plasmas.

    PubMed

    Pezzi, Oreste; Valentini, Francesco; Veltri, Pierluigi

    2016-04-01

    The existence of several characteristic times during the collisional relaxation of fine velocity structures is investigated by means of Eulerian numerical simulations of a spatially homogeneous force-free weakly collisional plasma. The effect of smoothing out velocity gradients on the evolution of global quantities, such as temperature and entropy, is discussed, suggesting that plasma collisionality can locally increase due to velocity space deformations of the particle velocity distribution function. These results support the idea that high-resolution measurements of the particle velocity distribution function are crucial for an accurate description of weakly collisional systems, such as the solar wind, in order to answer relevant scientific questions, related, for example, to particle heating and energization. PMID:27104713

  17. Collisional Relaxation of Fine Velocity Structures in Plasmas

    NASA Astrophysics Data System (ADS)

    Pezzi, Oreste; Valentini, Francesco; Veltri, Pierluigi

    2016-04-01

    The existence of several characteristic times during the collisional relaxation of fine velocity structures is investigated by means of Eulerian numerical simulations of a spatially homogeneous force-free weakly collisional plasma. The effect of smoothing out velocity gradients on the evolution of global quantities, such as temperature and entropy, is discussed, suggesting that plasma collisionality can locally increase due to velocity space deformations of the particle velocity distribution function. These results support the idea that high-resolution measurements of the particle velocity distribution function are crucial for an accurate description of weakly collisional systems, such as the solar wind, in order to answer relevant scientific questions, related, for example, to particle heating and energization.

  18. Weak turbulence theory for collisional plasmas

    NASA Astrophysics Data System (ADS)

    Yoon, P. H.; Ziebell, L. F.; Kontar, E. P.; Schlickeiser, R.

    2016-03-01

    Plasma is an ionized gas in which the collective behavior dominates over the individual particle interactions. For this reason, plasma is often treated as collisionless or collision-free. However, the discrete nature of the particles can be important, and often, the description of plasmas is incomplete without properly taking the discrete particle effects into account. The weak turbulence theory is a perturbative nonlinear theory, whose essential formalism was developed in the late 1950s and 1960s and continued on through the early 1980s. However, the standard material found in the literature does not treat the discrete particle effects and the associated fluctuations emitted spontaneously by thermal particles completely. Plasma particles emit electromagnetic fluctuations in all frequencies and wave vectors, but in the standard literature, the fluctuations are approximately treated by considering only those frequency-wave number regimes corresponding to the eigenmodes (or normal modes) satisfying the dispersion relations, while ignoring contributions from noneigenmodes. The present paper shows that the noneigenmode fluctuations modify the particle kinetic equation so that the generalized equation includes the Balescu-Lénard-Landau collision integral and also modify the wave kinetic equation to include not only the collisional damping term but also a term that depicts the bremsstrahlung emission of plasma normal modes.

  19. Current driven instability in collisional dusty plasmas

    NASA Astrophysics Data System (ADS)

    Pandey, B. P.; Vladimirov, S. V.; Samarian, A.

    2009-11-01

    The current driven electromagnetic instability in a collisional, magnetized, dusty medium is considered in the present work. It is shown that in the presence of the magnetic field aligned current, the low-frequency waves in the medium can become unstable if the ratio of the current to the ambient field is larger than the light speed times the wave number. The growth rate of the instability depends upon the ratio of the Alfvén to the dust cyclotron frequency as well as on the ratio of the current density J to the dust charge density Zend, where Z is the number of electronic charge on the grain, e is the electron charge, and nd is the dust number density. The typical growth rate of this instability is on the order of Alfvén frequency which compares favorably with the electrostatic, cross-field current driven, Farley-Buneman instability and thus could play an important role in the Earth's ionosphere.

  20. Collisional Ionization Equilibrium for Optically Thin Plasmas

    NASA Technical Reports Server (NTRS)

    Bryans, P.; Mitthumsiri, W.; Savin, D. W.; Badnell, N. R.; Gorczyca, T. W.; Laming, J. M.

    2006-01-01

    Reliably interpreting spectra from electron-ionized cosmic plasmas requires accurate ionization balance calculations for the plasma in question. However, much of the atomic data needed for these calculations have not been generated using modern theoretical methods and their reliability are often highly suspect. We have utilized state-of-the-art calculations of dielectronic recombination (DR) rate coefficients for the hydrogenic through Na-like ions of all elements from He to Zn. We have also utilized state-of-the-art radiative recombination (RR) rate coefficient calculations for the bare through Na-like ions of all elements from H to Zn. Using our data and the recommended electron impact ionization data of Mazzotta et al. (1998), we have calculated improved collisional ionization equilibrium calculations. We compare our calculated fractional ionic abundances using these data with those presented by Mazzotta et al. (1998) for all elements from H to Ni, and with the fractional abundances derived from the modern DR and RR calculations of Gu (2003a,b, 2004) for Mg, Si, S, Ar, Ca, Fe, and Ni.

  1. Collisional Disruption of super-Earths

    NASA Astrophysics Data System (ADS)

    Marcus, Robert A.; Stewart, S. T.; Sasselov, D.; Hernquist, L. E.

    2009-05-01

    The late stages of planet formation are dominated by collisions between planetary embryos with masses on the order of one tenth the mass of the Earth in our solar system (e.g., Agnor et al. 1999). The dynamics of this stage determine the final configuration of planets in the system. In the solar system, there is evidence of possible late giant impacts in the histories of both Mercury (Benz et al. 1988, 2007) and the Earth (e.g., Canup 2004). Here we consider high energy collisions (near catastrophic disruption) between planets of initially terrestrial composition with a range of masses into the super-Earth regime. We derive the transition between collisional accretion and erosion for super-Earths, following the method of Stewart and Leinhardt (2009). We identify both a catastrophic disruption regime and grazing impact and bouncing regime, as found by Agnor and Asphaug (2004). In the disruption regime, we derive a scaling law for changing the bulk composition (iron to silicate ratio). We then discuss the observational implications for such missions as Kepler.

  2. IONIZATION EQUILIBRIUM TIMESCALES IN COLLISIONAL PLASMAS

    SciTech Connect

    Smith, Randall K.; Hughes, John P. E-mail: jph@physics.rutgers.ed

    2010-07-20

    Astrophysical shocks or bursts from a photoionizing source can disturb the typical collisional plasma found in galactic interstellar media or the intergalactic medium. The spectrum emitted by this plasma contains diagnostics that have been used to determine the time since the disturbing event, although this determination becomes uncertain as the elements in the plasma return to ionization equilibrium. A general solution for the equilibrium timescale for each element arises from the elegant eigenvector method of solution to the problem of a non-equilibrium plasma described by Masai and Hughes and Helfand. In general, the ionization evolution of an element Z in a constant electron temperature plasma is given by a coupled set of Z + 1 first-order differential equations. However, they can be recast as Z uncoupled first-order differential equations using an eigenvector basis for the system. The solution is then Z separate exponential functions, with the time constants given by the eigenvalues of the rate matrix. The smallest of these eigenvalues gives the scale of the slowest return to equilibrium independent of the initial conditions, while conversely the largest eigenvalue is the scale of the fastest change in the ion population. These results hold for an ionizing plasma, a recombining plasma, or even a plasma with random initial conditions, and will allow users of these diagnostics to determine directly if their best-fit result significantly limits the timescale since a disturbance or is so close to equilibrium as to include an arbitrarily long time.

  3. Cancellation of the Collisional Frequency Shift in Caesium Fountain Clocks

    SciTech Connect

    Szymaniec, K.; Chalupczak, W.; Tiesinga, E.; Williams, C. J.; Weyers, S.; Wynands, R.

    2007-04-13

    We have observed that the collisional frequency shift in primary caesium fountain clocks varies with the clock state population composition and, in particular, is zero for a given fraction of the |F=4,m{sub F}=0> atoms, depending on the initial cloud parameters. We present a theoretical model explaining our observations. The possibility of the collisional shift cancellation implies an improvement in the performance of caesium fountain standards and a simplification in their operation.

  4. Effect of collisionality and diamagnetism on the plasma dynamo

    SciTech Connect

    Ji, H.; Yagi, Y.; Hattori, K.; Almagri, A.F.; Prager, S.C.; Hirano, Y.; Sarff, J.S.; Shimada, T.; Maejima, Y.; Hayase, K. ||

    1995-08-07

    Fluctuation-induced dynamo electric fields are measured over a wide range of electron collisionality in the edge of TPE-1RM20 reversed-field pinch (RFP). In the collisionless region the magnetohydrodynamic dynamo alone can sustain the parallel current, while in the collisional region a new dynamo mechanism resulting from the fluctuations in the electron diamagnetic drift becomes dominant. A comprehensive picture of the RFP dynamo emerges by combining with earlier results from MST and REPUTE RFPs.

  5. The effect of collisionality and diamagnetism on the plasma dynamo

    SciTech Connect

    Ji, H.; Yagi, Y.; Hattori, K.; Hirano, Y.; Shimada, T.; Maejima, Y.; Hayase, K.; Almagri, A.F.; Prager, S.C.; Sarff, J.S.

    1995-04-28

    Fluctuation-induced dynamo forces are measured over a wide range of electron collisionality in the edge of TPE-1RM20 Reversed-Field Pinch (RFP). In the collisionless region the Magnetohydrodynamic (MHD) dynamo alone can sustain the parallel current, while in the collisional region a new dynamo mechanism resulting from the fluctuations in the electron diamagnetic drift becomes dominant. A comprehensive picture of the RFP dynamo emerges by combining with earlier results from MST and REPUTE RFPs.

  6. Polarization of fast particle beams by collisional pumping

    DOEpatents

    Stearns, J.W.; Kaplan, S.N.; Pyle, R.V.; Anderson, L.W.; Schlachter, A.S.; Ruby, L.

    1984-10-19

    The invention relates to method and apparatus for polarizing a fast beam of particles by collisional pumping, including generating a fast beam of particles, and generating a thick electron-spin-polarized medium positioned as a target for said beam, said medium being sufficiently thick to allow said beam to interact with said medium to produce collisional pumping whereby said particle beam becomes highly polarized.

  7. Collectivity of 98Pd

    NASA Astrophysics Data System (ADS)

    Fransen, C.; Blazhev, A.; Dewald, A.; Jolie, J.; Mü; cher, D.; Möller, O.; Pissulla, T.

    2009-01-01

    The N = 52 nucleus 98Pd was investigated at the Cologne TANDEM accelerator both with the Cologne plunger using the recoil distance Doppler-shift method (RDDS) and with the Cologne HORUS spectrometer for a γγ angular correlation experiment. For the first time lifetimes of yrast states and highly excited low-spin states were measured in 98Pd and the low-spin level scheme was extended. From our data we were able to interpret 98Pd as a nucleus that exhibits some collective features, but is obviously much less collective than the neighboring N = 52 isotones 94Mo and 96Ru due to its closeness to doubly-magic 100Sn.

  8. Dependence of pedestal structure on collisionality at fixed beta in JT-60U

    NASA Astrophysics Data System (ADS)

    Urano, H.; Aiba, N.; Kamiya, K.; Kamada, Y.; the JT-60 Team

    2016-01-01

    The dependence of pedestal structure on collisionality at fixed beta has been investigated in JT-60U. In the ITER-relevant low collisionality regime, the pedestal width does not change with edge collisionality. In the high collisionality regime, the pedestal width broadens with increased edge collisionality. The pedestal pressure gradient and width are not significantly changed when the pedestal is close to an intermediate n peeling-ballooning mode boundary at low collisionality. The experimental result indicates that conventional pedestal models where the pedestal width is independent of collisionality and is determined by {β\\text{p}} at the pedestal is not a bad assumption in the ITER-relevant low collisionality regime. On the other hand, the pressure gradient decreases and the pedestal width increases at high collisionality. The pedestal broadening becomes significant when the pedestal is marginal to be unstable at the high n ballooning mode in the high collisionality regime.

  9. Synthesis and characterization of Pd(0), PdS, and Pd-PdO core-shell nanoparticles by solventless thermolysis of a Pd-thiolate cluster

    SciTech Connect

    Jose, Deepa; Jagirdar, Balaji R.

    2010-09-15

    Colloids of palladium nanoparticles have been prepared by the solvated metal atom dispersion (SMAD) method. The as-prepared Pd colloid consists of particles with an average diameter of 2.8{+-}0.1 nm. Digestive ripening of the as-prepared Pd colloid, a process involving refluxing the as-prepared colloid at or near the boiling point of the solvent in the presence of a passivating agent, dodecanethiol resulted in a previously reported Pd-thiolate cluster, [Pd(SC{sub 12}H{sub 25}){sub 2}]{sub 6} but did not render the expected narrowing down of the particle size distribution. Solventless thermolysis of the Pd-thiolate complex resulted in various Pd systems such as Pd(0), PdS, and Pd-PdO core-shell nanoparticles thus demonstrating its versatility. These Pd nanostructures have been characterized using high-resolution electron microscopy and powder X-ray diffraction methods. - Graphical abstract: Solventless thermolysis of a single palladium-thiolate cluster affords various Pd systems such as Pd(0), Pd-PdO core-shell, and PdS nanoparticles demonstrating the versatility of the precursor and the methodology.

  10. Observation of New Dynamics in the State-Resolved Collisional Relaxation of Highly Excited Molecules

    NASA Astrophysics Data System (ADS)

    Echebiri, Geraldine O.; Smarte, Matthew; Walters, Wendell W.; Cleveland, Jill M.; McCarl, Christine; Kunin, Alice; Mullin, Amy S.

    2013-06-01

    The dynamics of collisional deactivation of highly energized molecules, pyrazine-h_{4} and pyrazine-d_{4}, by HCl molecules at 300 K show evidence of a new mechanism for collisional energy transfer. Highly vibrationally excited (E_{vib} = 37,900 wn) pyrazine-h_{4} and pyrazine-d_{4} molecules are produced in separate experiments by pulsed excitation with the fourth harmonic output of a Nd:YAG laser at λ = 266 nm. Collisions between the energized isotopes and HCl molecules are monitored by measuring the nascent transient IR absorption of scattered HCl in individual rotational states. The results indicate that HCl molecules are scattered with a gain in rotational and translational energy, but the largest recoil energies are observed for the lowest rotational energy states of HCl. This behavior is opposite to that seen for other bath molecules including DCl and CO_{2}. The results point to differences in intermolecular interactions between the energy donor and acceptor molecules as contributing factors to the observed differences in the mechanism of energy transfer.

  11. G6PD: The Test

    MedlinePlus

    ... is it used? Glucose-6-phosphate dehydrogenase (G6PD) enzyme testing is used to screen for and help ... and the District of Columbia. G6PD is an enzyme found in all cells, including red blood cells ( ...

  12. Collisional relaxation in a nonintegrable potential

    NASA Astrophysics Data System (ADS)

    Kandrup, H. E.; Willmes, D. E.

    1994-03-01

    In galactic dynamics, a test star is assumed typically to follow a smooth trajectory in some slowly varying mean field potential and, in addition, to be subjected to 'random' close encounters with neighboring field stars which are modeled essentially as a Brownian process. With the noteable exception of Pfenniger (1986), most analyses of the collisonal relaxation induced by these close encounters have assumed that the effects of the mean field may be ignored completely, and that it suffices to consider Brownian particles moving in the absence of any systematic potential. The idealization of zero potential is problematic, as is any integrable potential in which all the mean field orbits are stable. For this reason, the paradigm of Brownian motion is reexamined here, allowing for a time-dependent, non-integrable potential, in which some subset of the mean field trajectories correspond to exponentially unstable orbits with positive Liapounov exponent. A nontrivial deterministic equation of motion is convereted into a stochastic differential equation incorporating dynamical friction and delta-correlated white noise, related via a fluctuation-dissipation theorem, and the effects of the friction and noise are analyzed perturbatively. The principal conclusion is that a coupling to a nonintegrable background potential can decrease by orders of magnitude the time scale on which noise and friction modify positions and velocities along an unperturbed, deterministic trajectory. Specifically, one finds that, even in the weak noise limit, perturbations in position and velocity grow exponentially on a time scale tlambda determined by the Liapounov exponent, although, for a strictly time-dependent potential, perturbations in energy and other collisionless invariants will only grow on a much longer relaxation time tr. Some potential implications of this accelerated collisional relaxation are discussed.

  13. Collisional energy transfer in highly excited molecules.

    PubMed

    Houston, Paul L; Conte, Riccardo; Bowman, Joel M

    2014-09-11

    The excitation/de-excitation step in the Lindemann mechanism is investigated in detail using model development and classical trajectory studies based on a realistic potential energy surface. The model, based on a soft-sphere/line-of-centers approach and using elements of Landau-Teller theory and phase space theory, correctly predicts most aspects of the joint probability distribution P(ΔE,ΔJ) for the collisional excitation and de-excitation process in the argon-allyl system. The classical trajectories both confirm the validity of the model and provide insight into the energy transfer. The potential employed was based on a previously available ab initio intramolecular potential for the allyl fit to 97418 allyl electronic energies and an intermolecular potential fit to 286 Ar-allyl energies. Intramolecular energies were calculated at the CCSD(T)/AVTZ level of theory, while intermolecular energies were calculated at the MP2/AVTZ level of theory. Trajectories were calculated for each of four starting allyl isomers and for an initial rotational level of Ji = 0 as well as for Ji taken from a microcanonical distribution. Despite a dissimilarity in Ar-allyl potentials for fixed Ar-allyl geometries, energy transfer properties starting from four different isomers were found to be remarkably alike. A contributing factor appears to be that the orientation-averaged potentials are almost identical. The model we have developed suggests that most hydrocarbons should have similar energy transfer properties, scaled by differences in the potential offset of the atom-hydrogen interaction. Available data corroborate this suggestion. PMID:25116732

  14. Collisional dynamics of the Milky Way

    NASA Astrophysics Data System (ADS)

    Griv, Evgeny; Gedalin, Michael; Yuan, Chi

    1997-12-01

    The effect of gravitational (elastic) encounters between stars and giant molecular clouds on the stability of small-amplitude perturbations of the Milky Way's self-gravitating disk is considered, using the exact Landau (Fokker-Planck type) collision integral, and compared with the results obtained by Griv & Peter (1996), who used the simple phenomenological Bhatnagar-Gross-Krook (Bhatnagar et al. 1954) collisional model. The present analysis is carried out for the case of a spatially inhomogeneous, highly flattened system, i.e., an inhomogeneous system in which the thickness is very small in comparison with the disk's radial extension. According to observations (Grivnev & Fridman 1990), the dynamics of a system with rare, kappa (2) >> nu_c (2) (and weak, omega (2) >> nu_c (2) ), interparticle encounters is considered, where kappa is the epicyclic frequency, omega is the frequency of excited waves, and nu_c ~ 10(-9) yr(-1) is the effective frequency of star-cloud encounters. The evolution of the stellar distribution is determined primarily by interactions with collective modes of oscillations - gravitational Jeans-type and gradient-dissipative modes - rather than by ordinary (``close") star-cloud encounters. On the basis of a local kinetic theory, it is shown that the Landau integral and the Bhatnagar et al. model give practically identical results in the case of perturbations with the wavelength lambda that is comparable to the mean epicyclic radius of stars rho , that is, in the case of the most dangerous, in the sense of the loss of stability, gravitational Jeans-type perturbations. The models, however, have essentially different qualitative and quantitative behaviors in the extreme limits of long-wavelength perturbations, (pi rho /lambda )(2) << 1, and of short-wavelength perturbations, (pi rho /lambda )(2) >> 1. Certain observational implications of the present theory are discussed.

  15. Collisional Effects on Nonlinear Ion Drag Force for Small Grains

    NASA Astrophysics Data System (ADS)

    Hutchinson, I. H.; Haakonsen, C. B.

    2013-10-01

    Ion drag force arising from plasma flow past an embedded grain in a plasma is a vital part of dusty plasma dynamics. Ion-neutral collisions are often significant for experimental dusty plasmas. They are here included self-consistently in properly nonlinear comprehensive drag calculations, for the first time. The ion drag on a spherical grain is calculated using particle in cell codes SCEPTIC and COPTIC. Using ion velocity ``drift'' distribution appropriate for flow driven by a force field gives wake potential and force greatly different from a shifted Maxwellian distribution, regardless of collisionality level. The low-collisionality forces are shown to be consistent with estimates based upon cross-sections for scattering in a Yukawa (shielded) grain field, but only if nonlinear shielding length is used. Finite collisionality initially enhances the drag force, but only by up to a factor of 2. Larger collisionality eventually reduces the drag force. In the collisional regime, the drift distribution gives larger drag than the shift distribution even at velocities where their collisionless drags are equal. Comprehensive practical analytic formulas for force that fit the calculations are provided. Partially supported by NSF/DOE Grant DE-FG02-06ER54982 and Science Graduate Fellowship Program DE-AC05-06OR23100.

  16. Collisional activation with random noise in ion trap mass spectrometry

    SciTech Connect

    McLuckey, S.A.; Goeringer, D.E.; Glish, G.L.

    1992-07-01

    Random noise applied to the end caps of a quadrupole ion trap is shown to be an effective means for the collisional activation of trapped ions independent of mass/charge ratio and number of ions. This technique is compared and contrasted with conventional single-frequency collisional activation for the molecular ion of N,N-dimethylaniline, protonated cocaine, the molecular anion of 2,4,6-trinitrotoluene, and doubly protonated neuromedin U-8. Collisional activation with noise tends to produce more extensive fragmentation than the conventional approach due to the fact that product ions are also kinetically excited in the noise experiment. The efficiency of the noise experiment in producing detectable product ions relative to the conventional approach ranges from being equivalent to being a factor of 3 less efficient. Furthermore, discrimination against low mass/charge product ions is apparent in the data from multiply charged biomolecules. Nevertheless, collisional activation with random noise provides a very simple means for overcoming problems associated with the dependence of single-frequency collisional activation on mass/charge ratio and the number of ions in the ion trap. 45 refs., 7 figs.

  17. Eulerian simulations of collisional effects on electrostatic plasma waves

    NASA Astrophysics Data System (ADS)

    Pezzi, Oreste; Valentini, Francesco; Perrone, Denise; Veltri, Pierluigi

    2013-09-01

    The problem of collisions in a plasma is a wide subject with a huge historical literature. In fact, the description of realistic plasmas is a tough problem to attack, both from the theoretical and the numerical point of view. In this paper, a Eulerian time-splitting algorithm for the study of the propagation of electrostatic waves in collisional plasmas is presented. Collisions are modeled through one-dimensional operators of the Fokker-Planck type, both in linear and nonlinear forms. The accuracy of the numerical code is discussed by comparing the numerical results to the analytical predictions obtained in some limit cases when trying to evaluate the effects of collisions in the phenomenon of wave plasma echo and collisional dissipation of Bernstein-Greene-Kruskal waves. Particular attention is devoted to the study of the nonlinear Dougherty collisional operator, recently used to describe the collisional dissipation of electron plasma waves in a pure electron plasma column [M. W. Anderson and T. M. O'Neil, Phys. Plasmas 14, 112110 (2007)]. Finally, for the study of collisional plasmas, a recipe to set the simulation parameters in order to prevent the filamentation problem can be provided, by exploiting the property of velocity diffusion operators to smooth out small velocity scales.

  18. DBCC Software as Database for Collisional Cross-Sections

    NASA Astrophysics Data System (ADS)

    Moroz, Daniel; Moroz, Paul

    2014-10-01

    Interactions of species, such as atoms, radicals, molecules, electrons, and photons, in plasmas used for materials processing could be very complex, and many of them could be described in terms of collisional cross-sections. Researchers involved in plasma simulations must select reasonable cross-sections for collisional processes for implementing them into their simulation codes to be able to correctly simulate plasmas. However, collisional cross-section data are difficult to obtain, and, for some collisional processes, the cross-sections are still not known. Data on collisional cross-sections can be obtained from numerous sources including numerical calculations, experiments, journal articles, conference proceedings, scientific reports, various universities' websites, national labs and centers specifically devoted to collecting data on cross-sections. The cross-sections data received from different sources could be partial, corresponding to limited energy ranges, or could even not be in agreement. The DBCC software package was designed to help researchers in collecting, comparing, and selecting cross-sections, some of which could be constructed from others or chosen as defaults. This is important as different researchers may place trust in different cross-sections or in different sources. We will discuss the details of DBCC and demonstrate how it works and why it is beneficial to researchers working on plasma simulations.

  19. Eulerian simulations of collisional effects on electrostatic plasma waves

    SciTech Connect

    Pezzi, Oreste; Valentini, Francesco; Perrone, Denise; Veltri, Pierluigi

    2013-09-15

    The problem of collisions in a plasma is a wide subject with a huge historical literature. In fact, the description of realistic plasmas is a tough problem to attack, both from the theoretical and the numerical point of view. In this paper, a Eulerian time-splitting algorithm for the study of the propagation of electrostatic waves in collisional plasmas is presented. Collisions are modeled through one-dimensional operators of the Fokker-Planck type, both in linear and nonlinear forms. The accuracy of the numerical code is discussed by comparing the numerical results to the analytical predictions obtained in some limit cases when trying to evaluate the effects of collisions in the phenomenon of wave plasma echo and collisional dissipation of Bernstein-Greene-Kruskal waves. Particular attention is devoted to the study of the nonlinear Dougherty collisional operator, recently used to describe the collisional dissipation of electron plasma waves in a pure electron plasma column [M. W. Anderson and T. M. O'Neil, Phys. Plasmas 14, 112110 (2007)]. Finally, for the study of collisional plasmas, a recipe to set the simulation parameters in order to prevent the filamentation problem can be provided, by exploiting the property of velocity diffusion operators to smooth out small velocity scales.

  20. The Collisional Evolution of Debris Disks

    NASA Astrophysics Data System (ADS)

    Gáspár, A.; Rieke, G. H.; Psaltis, D.; Özel, F.; Balog, Z.

    2014-03-01

    With their discovery, debris disks gave the first proof of existence of extrasolar planetary systems (Aumann et al. 1984, Smith & Terrile 1984). Although extrasolar planets are now readily detected, the importance of debris disks in characterizing their host systems is not diminished. Debris disks are relatively easy to detect at infrared wavelengths, independent of their viewing angle; they enable the study of the dynamical evolution of their host systems; they are able to reveal the outer regions of the systems where planets are difficult to detect; and coronagraphic scattered light images show the active sites of major dust production within the systems. During their operational lifetime, the Spitzer Space Telescope and the Herschel Space Observatory have observed many hundreds of resolved and unresolved debris disks. These detections have helped us characterize the thermal emission and also location of the disks. The observations have also shown a general decay in the observed infrared luminosity of the debris disks as a function of system age and disk location. This evolution must be understood thoroughly before probing other parameters, such as their dependence on stellar metallicity or binarity. A second critical parameter is the shape of the particle size distribution, which can strongly influence conclusions from spectral energy distribution models. I will describe results obtained with our collisional cascade code, which has been optimized to study the time evolution of debris disk dust. I will show that the rate of the decay varies throughout the evolution of the disks, increasing its rate up to a certain point, which is followed by a leveling off to a value of Lir(t)~-0.6. This is slower than the ~-1 decay given by traditional analytic models. I will show how our numerical code can reproduce the fraction of detected debris disk sources within an extensive catalog of Spitzer and Herschel 24, 70, and 100 µm observations (Gaspar et al. 2013). I will also

  1. Collisional evolution of asteroids - Populations, rotations, and velocities

    NASA Technical Reports Server (NTRS)

    Davis, D. R.; Chapman, C. R.; Greenberg, R.; Weidenschilling, S. J.; Harris, A. W.

    1979-01-01

    The collisional evolution of various initial populations of asteroids is simulated numerically and compared with the present asteroid size-frequency distribution to find those populations which collisionally relax to the present belt. Both orbital and size distributions are treated, as well as the simultaneous evolution of two collisionally interacting populations with different physical properties. If the initial belt distribution was a power law, the initial belt population at the time when the present high-collision speed was established was probably only modestly larger than the present population. However, other distributions allow a more massive early belt. The rotational evolution due to collisions of asteroids with power-law distributions is also examined and compared with observations, leading to conclusions generally in agreement with those of size evolution. The high-collision speed in the present belt is likely due to Jupiter. Gravitational stirring by massive Jupiter-scattered planetesimals or secular resonances sweeping through the belt are the most probable mechanisms.

  2. Fundamentally distinct outcomes of asteroid collisional evolution: Itokawa and Eros

    NASA Astrophysics Data System (ADS)

    Cheng, A. F.; Barnouin-Jha, O.; Hirata, N.; Miyamoto, H.; Nakamura, R.; Yano, H.

    2007-05-01

    The outcomes of asteroid collisional evolution are presently unclear: are most asteroids larger than 1 km size gravitational aggregates reaccreted from fragments of a parent body that was collisionally disrupted, while much smaller asteroids are collisional shards that were never completely disrupted? The 16 km mean diameter S-type asteroid 433 Eros, visited by the NEAR mission, has surface geology consistent with being a fractured shard. The Hayabusa spacecraft visited an S-asteroid smaller than 1 km, namely 25143 Itokawa. Here we report the first comparative analyses of Itokawa and Eros geology. Itokawa lacks a global lineament fabric, and its blocks, craters, and regolith are inconsistent with formation and evolution as a fractured shard, unlike Eros. Itokawa is not a scaled-down Eros, but formed by a distinct process of catastrophic disruption and reaccumulation.

  3. Symplectic integration for the collisional gravitational N-body problem

    NASA Astrophysics Data System (ADS)

    Hernandez, David M.; Bertschinger, Edmund

    2015-09-01

    We present a new symplectic integrator designed for collisional gravitational N-body problems which makes use of Kepler solvers. The integrator is also reversible and conserves nine integrals of motion of the N-body problem to machine precision. The integrator is second order, but the order can easily be increased by the method of Yoshida. We use fixed time step in all tests studied in this paper to ensure preservation of symplecticity. We study small N collisional problems and perform comparisons with typically used integrators. In particular, we find comparable or better performance when compared to the fourth-order Hermite method and much better performance than adaptive time step symplectic integrators introduced previously. We find better performance compared to SAKURA, a non-symplectic, non-time-reversible integrator based on a different two-body decomposition of the N-body problem. The integrator is a promising tool in collisional gravitational dynamics.

  4. Collisional dynamics of perturbed particle disks in the solar system

    NASA Technical Reports Server (NTRS)

    Roberts, William W., Jr.

    1989-01-01

    Theoretical and computational studies were carried out on galactic and planetary disks. With the goal of addressing important open questions centered on galactic structure, the cloudy interstellar medium, giant molecular clouds, and star formation in galactic disks and the collisional dynamics of perturbed particulate matter in planetary disks, focus was largely on the self-gravitational effects, dissipative effects, and collisional dynamics of cloud-particle disks. N-body, 'cloud-particle' computational algorithms were developed for the purpose of isolating the role of gaseous self gravity from the roles of other dominant physical mechanisms and dynamical processes, e.g. the collisional dynamics and dissipative processes. The efforts focused largely on galactic disks show that observational constraints provide stringent tests of the numerical simulation techniques developed. Self gravitational effects of the galactic interstellar medium's gas clouds are included by means of Fourier Transform technique.

  5. Effects of Collisional Zonal Flow Damping on ITG turbulence

    NASA Astrophysics Data System (ADS)

    Lin, Zhihong

    1999-11-01

    In most previous transport studies, ion-ion collisions have been assumed to have little or no effect on the ion-temperature-gradient (ITG) turbulence, and tokamak core ion thermal transport have been considered ``collisionless''. However, recent transport scaling studies on DIII-D(C.C. Petty and T.C. Luce, Phys. Plasmas) 6, 909 (1999). core plasmas showed that effective thermal diffusivity strongly depends on collisionality in the H-mode, and is almost independent of collisionality in the L-mode. Here we report results of massively parallel gyrokinetic particle simulations which show that the ion thermal transport from electrostatic ITG turbulence depends on ion-ion collisions for representative tokamak core H-mode plasma parameters. The collisionality-dependence of the turbulent transport comes from the neoclassical damping of self-generated E × B zonal flows(Z. Lin, T.S. Hahm, W.W. Lee, W.M. Tang, and R.B. White, Science) 281, 1835 (1998). which regulate the turbulence. The results from our full torus gyrokinetic simulations with a momentum and energy conserving Fokker-Planck operator are consistent with the experimental observation that the collisional dependence of transport is much more pronounced in the enhanced confinement regime where turbulence is expected to be weaker than that of typical L-mode plasmas. Furthermore, the fluctuations and heat transport in these simulations exhibit bursting behavior with a period corresponding to the collisional damping time of poloidal flows. This is consistent with the observation in TFTR core plasmas(E. Mazzucato et al.), Phys. Rev. Lett. 77, 3145 (1996). of a density fluctuation bursting with a period ( ~ 3 ms) close to the collisional flow damping time calculated from experimental plasma parameters.

  6. Radiation-induced collisional pumping of molecules containing few atoms

    SciTech Connect

    Vasil'ev, G.K.; Chernyshev, Y.A.; Makarov, E.F.; Yakushev, V.G.

    1986-01-01

    The authors analyze the radiation-induced collisional pumping of few-atom molecules by laser emission taking into account both collisional and noncollisional processes of vibrational energy transfer in a molecule. For typical values of the parameters the vibrational energy of the molecules was found to depend on the laser emission intensity; regions of weak absorption, optimum absorption, and saturation appear as the pumping rate rises. Qualitative general conclusions are reached concerning the optimum conditions for the realization, in a medium absorbing laser emission, of either nonequilibrium dissociation or a chemical reaction involving vibrationally excited molecules.

  7. Radiative and collisional processes in CNA 2Π i

    NASA Astrophysics Data System (ADS)

    Halpern, Joshua B.; Huang, Yuhui; Titarchuk, Tatiana

    1996-02-01

    In the last four years we have carried out a number of studies on the radiative and collisional processes in theA 2Π i state of CN. Many of these of interest to those studying planetary atmospheres, comets and solar spectra are summarized in this paper. Data for CNA 2Π i fluorescence lifetimes and quenching rates, and collisional energy transfer between CNA 2Π i andX 2∑+ are reported. Detailed comparisons and a discussion of the results may be found in several already published papers.

  8. PD trivia: Making learning fun.

    PubMed

    Kennedy, Liana

    2006-01-01

    Nurses are educators. It is the aim of every educator that his or her teaching should translate into learning. Effective teaching is especially of importance in assuring that patients learn to perform their own peritoneal dialysis (PD). In facilitating an environment where learning can occur, making learning fun is the objective. It is with this mandate that PD Trivia was created. PD Trivia is an interactive game created to facilitate and reinforce learning. PD Trivia consists of 100 essential questions to making PD a success at home. Evaluations at the peritoneal dialysis clinic have revealed excellent quantitative and qualitative results of this simple but comprehensive teaching tool for effective learning of PD. PMID:17061697

  9. Plasma-wall transition in weakly collisional plasmas

    SciTech Connect

    Manfredi, G.; Devaux, S.

    2008-10-15

    This paper reviews some theoretical and computational aspects of plasma-wall interactions, in particular the formation of sheaths. Some fundamental results are derived analytically using a simple fluid model, and are subsequently tested with kinetic simulations. The various regions composing the plasma-wall transition (Debye sheath, collisional and magnetic presheaths) are discussed in details.

  10. Electron transport in a collisional plasma with multiple ion species

    SciTech Connect

    Simakov, Andrei N. Molvig, Kim

    2014-02-15

    A generalization of the Braginskii electron fluid description [S. I. Braginskii, Sov. Phys. JETP 6, 358 (1958)] to the case of an unmagnetized collisional plasma with multiple ion species is presented. A description of the plasma ions with disparate masses is also discussed.

  11. Collisional Evolution Of The Populations Of Trans-Neptunian Objects

    NASA Astrophysics Data System (ADS)

    Campo Bagatin, Adriano; Benavidez, P. G.

    2006-09-01

    The Trans-Neptunian region is yet another example of a collisional system of small bodies in the Solar System. In the last decade the number of TNOs with reliable orbital elements is steadily increasing and we can begin to try and compare collisional evolution models to observed populations. We are developing a model that takes into account the known physics of the fragmentation of icy/rocky bodies, and that considers the different orbital characteristics of the Trans-Neptunian regions ("plutinos" or resonant objects, classical belt and scattered disk) and their mutual interactions. In the last few years it has been proposed that the outer planets, and in particular Neptune, have undergone a migration to their present location and that the TNO region may have experienced a similiar process. With this purpose we also mimick this migration and compare the corresponding outcomes with other possible scenarios. What was the primordial distribution in this region? Is the collisional cascade efficient enough to justify the loss of mass occurred in this region? Is the Trans-Neptunian belt collisionally relaxed? How did Neptune's migration affect the distribution of TNOs? These are some of the key questions regarding TNOs and the evolution of the outer Solar System that we try to help answering with this work. With aknowledgements to the spanish Ministerio de Educacion y Ciencia for financial support.

  12. Comment on "Paleoclassical Transport in Low-Collisionality Toroidal Plasmas"

    SciTech Connect

    LoDestro, L L

    2006-10-13

    Paleoclassical transport [1] is a recently proposed fundamental process that is claimed to occur in resistive plasmas and to be missing in the collisional drift-kinetic equations (DKE) in standard use. In this Comment we raise three puzzles presented by paleoclassical transport as developed in [1], one to do with conservation and two concerning uniqueness.

  13. The limits of the Bohm criterion in collisional plasmas

    SciTech Connect

    Valentini, H.-B.; Kaiser, D.

    2015-05-15

    The sheath formation within a low-pressure collisional plasma is analysed by means of a two-fluid model. The Bohm criterion takes into account the effects of the electric field and the inertia of the ions. Numerical results yield that these effects contribute to the space charge formation, only, if the collisionality is lower than a relatively small threshold. It follows that a lower and an upper limit of the drift speed of the ions exist where the effects treated by Bohm can form a sheath. This interval becomes narrower as the collisionality increases and vanishes at the mentioned threshold. Above the threshold, the sheath is mainly created by collisions and the ionisation. Under these conditions, the sheath formation cannot be described by means of Bohm like criteria. In a few references, a so-called upper limit of the Bohm criterion is stated for collisional plasmas where the momentum equation of the ions is taken into account, only. However, the present paper shows that this limit results in an unrealistically steep increase of the space charge density towards the wall, and, therefore, it yields no useful limit of the Bohm velocity.

  14. Collisional diffusion in toroidal plasmas with elongation and triangularity

    SciTech Connect

    Martin, P.; Castro, E.; Haines, M. G.

    2007-05-15

    Collisional diffusion is analyzed for plasma tokamaks with different ellipticities and triangularities. Improved nonlinear equations for the families of magnetic surfaces are used here. Dimensionless average velocities are calculated as a function of the inductive electric field, elongation, triangularity, and Shafranov shift. Confinement has been found to depend significantly on triangularity.

  15. Comets as collisional fragments of a primordial planetesimal disk

    NASA Astrophysics Data System (ADS)

    Morbidelli, A.; Rickman, H.

    2015-11-01

    Context. The Rosetta mission and its exquisite measurements have revived the debate on whether comets are pristine planetesimals or collisionally evolved objects. Aims: We investigate the collisional evolution experienced by the precursors of current comet nuclei during the early stages of the solar system in the context of the so-called Nice model. Methods: We considered two environments for the collisional evolution: (1) the transplanetary planetesimal disk, from the time of gas removal until the disk was dispersed by the migration of the ice giants; and (2) the dispersing disk during the time that the scattered disk was formed. We performed simulations using different methods in the two cases to determine the number of destructive collisions typically experienced by a comet nucleus of 2 km radius. Results: In the widely accepted scenario, where the dispersal of the planetesimal disk occurred at the time of the Late Heavy Bombardment about 4 Gy ago, comet-sized planetesimals have a very low probability of surviving destructive collisions in the disk. On the extreme assumption that the disk was dispersed directly upon gas removal, a significant fraction of the planetesimals might have remained intact. However, these survivors would still bear the marks of many nondestructive impacts. Conclusions: The Nice model of solar system evolution predicts that typical km-sized comet nuclei are predominantly fragments resulting from collisions experienced by larger parent bodies. An important goal for future research is to investigate whether the observed properties of comet nuclei are compatible with such a collisional origin.

  16. Peculiarities of collisional excitation transfer with excited screened energy levels of atoms

    SciTech Connect

    Gerasimov, V. A.; Gerasimov, V. V.; Pavlinskiy, A. V.

    2007-09-15

    We report an experimental discovery of deviations from the known regularities in collisional excitation transfer processes for metal atoms. The collisional excitation transfer with excited screened energy levels of thulium and dysprosium atoms is studied. The selecting role of the screening 6s shell in collisional excitation transfer is shown.

  17. Petrologic evidence for collisional heating of chondritic asteroids

    NASA Technical Reports Server (NTRS)

    Rubin, Alan E.

    1995-01-01

    The identification of the mechanism(s) responsible for heating asteroids is among the major problems in planetary science. Because of difficulties with models of electromagnetic induction and the decay of short-lived radionuclides, it is worthwhile to evaluate the evidence for collisional heating. New evidence for localized impact heating comes from the high proportion of relict type-6 material among impact-melt-bearing ordinary chondrites (OC). This relict material was probably metamorphosed by residual heat within large craters. Olivine aggregates composed of faceted crystals with 120 deg triple junctions occur within the melted regions of the Chico and Rose City OC melt rocks; the olivine aggregates formed from shocked, mosaicized olivine grains that underwent contact metamorphism. Large-scale collisional heating is supoorted by the correlation in OC between petrologic type and shock stage; no other heating mechanism can readily account for this correlation. The occurrence of impact-melt-rock clasts in OC that have been metamorphosed along with their whole rocks indicates that some impact events preceded or accompanied thermal metamorphism. Such impacts events, occurring during or shortly after accretion, are probably responsible for substantially melting approximately 0.5% of OC. These events must have heated a larger percentage of OC to subsolidus temperatures sufficient to have caused significant metamorphism. If collisional heating is viable, then OC parent asteroids must have been large; large OC asteroids in the main belt may include those of the S(IV) spectral subtype. Collisional heating is inconsistent with layered ('onion-shell') structures in OC asteroids (wherein the degree of metamorphism increases with depth), but the evidence for such structures is weak. It seems likely that collisional heating played an important role in metamorphosing chondritic asteroids.

  18. Localization of collisionally inhomogeneous condensates in a bichromatic optical lattice

    NASA Astrophysics Data System (ADS)

    Cheng, Yongshan; Adhikari, S. K.

    2011-02-01

    By direct numerical simulation and variational solution of the Gross-Pitaevskii equation, we studied the stationary and dynamic characteristics of a cigar-shaped, localized, collisionally inhomogeneous Bose-Einstein condensate trapped in a one-dimensional bichromatic quasiperiodic optical-lattice potential, as used in a recent experiment on the localization of a Bose-Einstein condensate [Roati , Nature (London)NATUAS0028-083610.1038/nature07071 453, 895 (2008)]. The effective potential characterizing the spatially modulated nonlinearity is obtained. It is found that the collisional inhomogeneity has influence not only on the central region but also on the tail of the Bose-Einstein condensate. The influence depends on the sign and value of the spatially modulated nonlinearity coefficient. We also demonstrate the stability of the stationary localized state by performing a standard linear stability analysis. Where possible, the numerical results are shown to be in good agreement with the variational results.

  19. Collisional current drive in two interpenetrating plasma jets

    SciTech Connect

    Ryutov, D. D.; Kugland, N. L.; Park, H.-S.; Pollaine, S. M.; Remington, B. A.; Ross, J. S.

    2011-10-15

    The magnetic field generation in two interpenetrating, weakly collisional plasma streams produced by intense lasers is considered. The generation mechanism is very similar to the neutral beam injection current drive in toroidal fusion devices, with the differences related to the absence of the initial magnetic field, short interaction time, and different geometry. Spatial and temporal characteristics of the magnetic field produced in two counterstreaming jets are evaluated; it is shown that the magnetic field of order of 1 T can be generated for modest jet parameters. Conditions under which this mechanism dominates that of the ''Biermann battery'' are discussed. Other settings where the mechanism of the collisional current drive can be important for the generation of seed magnetic fields include astrophysics and interiors of hohlraums.

  20. Collisional dynamics of perturbed particle disks in the solar system

    NASA Technical Reports Server (NTRS)

    Roberts, W. W.; Stewart, G. R.

    1987-01-01

    Investigations of the collisional evolution of particulate disks subject to the gravitational perturbation of a more massive particle orbiting within the disk are underway. Both numerical N-body simulations using a novel collision algorithm and analytical kinetic theory are being employed to extend our understanding of perturbed disks in planetary rings and during the formation of the solar system. Particular problems proposed for investigation are: (1) The development and testing of general criteria for a small moonlet to clear a gap and produce observable morphological features in planetary rings; (2) The development of detailed models of collisional damping of the wavy edges observed on the Encke division of Saturn's A ring; and (3) The determination of the extent of runaway growth of the few largest planetesimals during the early stages of planetary accretion.

  1. Scaled Energy Spectroscopy of Collisionally Perturbed Potassium Rydberg States

    NASA Astrophysics Data System (ADS)

    Keeler, Matthew Len; Setzer, William

    2010-03-01

    We will present preliminary results on the recurrence spectroscopy (or scaled energy spectroscopy) of highly-excited potassium in the presence of collisional perturbations. Recurrence spectroscopy, with the aid of closed orbit theory, has produced useful insights into the semi-classical description of non-hydrogenic spectral features of excited atoms in external fields. We demonstrate how to apply recurrence spectroscopy to the Stark spectrum of potassium subject to collisional line-shift and line-broadening. When krypton gas is added to the system the absorption spectrum experiences line broadening, differential line shifts, and state mixing. With an appropriately modified energy scale, perturbations of the absorption spectrum become meaningful features within the scaled-energy spectrum. New features found within the recurrence spectra can then, with semi-classical closed orbit theory, be interpreted in terms of classical decoherence, elastic and inelastic collisions.

  2. Collisional energy loss above the critical temperature in QCD

    NASA Astrophysics Data System (ADS)

    Lin, Shu; Pisarski, Robert D.; Skokov, Vladimir V.

    2014-03-01

    We compute the collisional energy loss for a heavy quark above the critical temperature in Quantum ChromoDynamics (QCD). We work in the semi Quark-Gluon Plasma, which assumes that this region is dominated by the non-trivial holonomy of the thermal Wilson line. Relative to the result of leading order in perturbation theory, at a fixed value of the coupling constant we generically find that collisional energy loss is suppressed by powers of the Polyakov loop, l<1. For small values of the loop, this suppression is linear when the heavy quark scatters off of light quarks, and quadratic when the heavy quark scatters off of gluons, or for Compton scattering.

  3. Collisional effects on Rayleigh-Taylor-induced magnetic fields

    SciTech Connect

    Manuel, M. J.-E.; Flaig, M.; Plewa, T.; Li, C. K.; Séguin, F. H.; Frenje, J. A.; Casey, D. T.; Petrasso, R. D.; Hu, S. X.; Betti, R.; Hager, J.; Meyerhofer, D. D.; Smalyuk, V.

    2015-05-15

    Magnetic-field generation from the Rayleigh-Taylor (RT) instability was predicted more than 30 years ago, though experimental measurements of this phenomenon have only occurred in the past few years. These pioneering observations demonstrated that collisional effects are important to B-field evolution. To produce fields of a measurable strength, high-intensity lasers irradiate solid targets to generate the nonaligned temperature and density gradients required for B-field generation. The ablation process naturally generates an unstable system where RT-induced magnetic fields form. Field strengths inferred from monoenergetic-proton radiographs indicate that in the ablation region diffusive effects caused by finite plasma resistivity are not negligible. Results from the first proof-of-existence experiments are reviewed and the role of collisional effects on B-field evolution is discussed in detail.

  4. Sheath formation under collisional conditions in presence of dust

    SciTech Connect

    Moulick, R. Goswami, K. S.

    2014-08-15

    Sheath formation is studied for collisional plasma in presence of dust. In common laboratory plasma, the dust acquires negative charges because of high thermal velocity of the electrons. The usual dust charging theory dealing with the issue is that of the Orbit Motion Limited theory. However, the theory does not find its application when the ion neutral collisions are significantly present. An alternate theory exists in literature for collisional dust charging. Collision is modeled by constant mean free path model. The sheath is considered jointly with the bulk of the plasma and a smooth transition of the plasma profiles from the bulk to the sheath is obtained. The various plasma profiles such as the electrostatic force on the grain, the ion drag force along with the dust density, and velocity are shown to vary spatially with increasing ion neutral collision.

  5. Collisional shifts in optical-lattice atom clocks

    SciTech Connect

    Band, Y. B.; Vardi, A.

    2006-09-15

    We theoretically study the effects of elastic collisions on the determination of frequency standards via Ramsey-fringe spectroscopy in optical-lattice atom clocks. Interparticle interactions of bosonic atoms in multiply occupied lattice sites can cause a linear frequency shift, as well as generate asymmetric Ramsey-fringe patterns and reduce fringe visibility due to interparticle entanglement. We propose a method of reducing these collisional effects in an optical lattice by introducing a phase difference of {pi} between the Ramsey driving fields in adjacent sites. This configuration suppresses site-to-site hopping due to interference of two tunneling pathways, without degrading fringe visibility. Consequently, the probability of double occupancy is reduced, leading to cancellation of collisional shifts.

  6. Cosmological evolution in f (R ,T ) theory with collisional matter

    NASA Astrophysics Data System (ADS)

    Baffou, E. H.; Houndjo, M. J. S.; Rodrigues, M. E.; Kpadonou, A. V.; Tossa, J.

    2015-10-01

    We study the evolution of the cosmological parameters, namely, the deceleration parameter q (z ) and the parameter of effective equation of state in a Universe containing, besides ordinary matter and dark energy, a self-interacting (collisional) matter, in the generalized f (R ,T ) theory of gravity, where R and T are the curvature scalar and the trace of the energy-momentum tensor, respectively. We use the generalized Friedmann-Robertson-Walker equations and the equation of continuity and obtain a differential equation in H (z ) , and we solve it numerically for studying the evolution of the cosmological parameters. Two f (R ,T ) models are considered. The results with collisional matter are compared with the ones of the Λ cold dark matter model, and also with the model where only noncollisional matter exists. The curves show that the models are acceptable because the values found for weff are consistent with observed data.

  7. Gyrokinetic simulation of the collisional micro-tearing mode instability

    NASA Astrophysics Data System (ADS)

    Startsev, Edward; Lee, Wei-Li; Wang, Weixing

    2015-11-01

    An application of recently developed perturbative particle simulation scheme for finite- β plasmas in the presence of background inhomogeneities is presented. Originally, using similar scheme, we were able to simulate shear-Alfven waves, finite- β modified drift waves and ion temperature gradient modes using a simple gyrokinetic particle code based on realistic fusion plasma parameters. Recently, we have successfully used the scheme for simulation of linear tearing and drift-tearing modes, in both collisionless semi-collisional regimes in slab geometry with sheared magnetic field. Here, we present further development of this scheme for the simulation of linear semi-collisional micro-tearing mode driven by electron temperature gradient in high-aspect ratio cylindrical cross-section tokamak using the modified turbulence code GTS. Research supported by the U. S. Department of Energy.

  8. Radiative and rovibrational collisional relaxation of sodium dimer

    NASA Astrophysics Data System (ADS)

    Bayram, Burcin; Horton, Tim; McFarland, Jacob

    2016-05-01

    Radiative and rovibrational collisional relaxation of sodium dimer of the A1Σu+ (8,30) state have been measured by direct observation of the decay fluorescence. Sodium molecular vapor is created in a heatpipe oven at 600 K and excited using a 6-ns pulsed dye laser pumped by a Nd:YAG, operating at 532 nm. The preliminary lifetime measurement was done by directly acquiring lifetime data through boxcar averager from the stored oscilloscope trace of the fluorescence. Analysis of the exponential decay of the fluorescence allows us to obtain the radiative lifetime. By introducing the argon buffer gas and varying the pressure of the heatpipe, a collisional cross section between excited sodium dimer and ground state argon atom collision can be extracted using Stern-Volmer relation.

  9. Kinetic model for the collisionless sheath of a collisional plasma

    NASA Astrophysics Data System (ADS)

    Tang, Xian-Zhu; Guo, Zehua

    2016-08-01

    Collisional plasmas typically have mean-free-path still much greater than the Debye length, so the sheath is mostly collisionless. Once the plasma density, temperature, and flow are specified at the sheath entrance, the profile variation of electron and ion density, temperature, flow speed, and conductive heat fluxes inside the sheath is set by collisionless dynamics, and can be predicted by an analytical kinetic model distribution. These predictions are contrasted here with direct kinetic simulations, showing good agreement.

  10. Collisional Radiative Models for non-Maxwellian plasmas

    NASA Astrophysics Data System (ADS)

    Hartgers, Bart; van Dijk, Jan; van der Mullen, Joost

    1999-10-01

    Collisional Radiative models are a useful tool for studying plasmas. In their simplest form, they are used to calculate an atomic state distribution function (ASDF) from given electron and neutral densities and an electron temperature. Additionally, global ionization and recombination coefficients can be calculated as a function of electron density and temperature. In turn, these coefficients are used as input for the general plasma model

  11. Collisional Evolution of Edgeworth-Kuiper Belt Objects

    NASA Astrophysics Data System (ADS)

    Davis, D. R.; Farinella, P.

    1997-01-01

    The Edgeworth-Kuiper Belt contains a population of objects ≈10 3times that of the main asteroid belt, spread over a volume ≈10 3larger and with relative speeds ≈10 times lower. As for the asteroids, the size distribution of Edgeworth-Kuiper Belt objects has been modified by mutual impacts over Solar System history. We have modeled this collisional evolution process using a numerical code developed originally to study asteroid collisional evolution but modified to reflect collision rates in the Edgeworth-Kuiper Belt. Our numerical simulations show that collisional evolution is substantial in the inner part of the Edgeworth-Kuiper Belt, but its intensity decreases with increasing distance from the Sun. In the inner belt, objects with diameters D> 50-100 km are not depleted by disruptive collisions; hence they reflect the original (formative) population (many of them, however, may have been converted into "rubble piles"). On the other hand, smaller objects are mostly multigenerational fragments, although the original population must have contained a significant number of bodies down to at least a few tens of kilometers in size in order to initiate a collisional cascade. About 10 fragments, 1-10 km in size, are produced per year in the inner Edgeworth-Kuiper Belt, with a few percent of them inserted into chaotic resonant orbits. This is in rough agreement with the required influx rate of Jupiter-family comets. Both collisions and dynamical instabilities associated with resonances are processes that can inject comets into the "escape hatches," but our results indicate that most comets coming from the Edgeworth-Kuiper Belt would be fragments from larger parent bodies, rather than primitive planetesimals. However, this does not apply to Chiron-sized ( D> 100 km) objects, which must be primordial and delivered to the outer Solar System by either dynamical processes or nondisruptive collisions.

  12. System and method for collisional activation of charged particles

    DOEpatents

    Ibrahim, Yehia M; Belov, Mikhail E; Prior, David C

    2013-09-24

    A collision cell is disclosed that provides ion activation in various selective modes. Ion activation is performed inside selected segments of a segmented quadrupole that provides maximum optimum capture and collection of fragmentation products. The invention provides collisional cooling of precursor ions as well as product fragments and further allows effective transmission of ions through a high pressure interface into a coupled mass analysis instrument.

  13. Collisional and dynamical processes in moon and planet formation

    NASA Technical Reports Server (NTRS)

    1979-01-01

    The collisional and dynamical processes in moon and planet formation are discussed. A hydrodynamic code of collision calculations, the orbital element changes due to gravitational scattering, a validation of the mass shifting algorithm, a theory of rotations, and the origin of asteroids are studied. A numerical model of planet growth is discussed and a methodology to evaluate the rate at which megaregolith increases its depth as a function of total accumulate number of impacts on an initially smooth, coherent surface is described.

  14. Kinetic simulation of a collisional shock wave in a plasma

    SciTech Connect

    Casanova, M.; Larroche, O. ); Matte, J. )

    1991-10-14

    The ion kinetic structure of a planar collisional shock front in a fully ionized plasma is investigated using a new Vlasov-Fokker-Planck code. The effects of ionic viscosity and ionic thermal conduction are found to be much larger than assumed in usual hydrodynamic plasma simulations with classical transport coefficients. This might have consequences on the numerical modeling of inertial-confinement fusion targets.

  15. Constitution and thermodynamics of the Mo-Ru, Mo-Pd, Ru-Pd and Mo-Ru-Pd systems

    NASA Astrophysics Data System (ADS)

    Kleykamp, H.

    1989-09-01

    The constitution of the Mo-Ru, Mo-Pd and Ru-Pd systems was reinvestigated between 800 and 2000°C. The Mo-Ru system is of the eutectic type, a σ-phase Mo 5Ru 3 exists between 1915 and 1143°C. The Mo-Pd system is characterized by an hcp phase Mo 9Pd 11 and by two peritectic reactions, β- Mo( Pd) + L = Mo9Pd11andMo9Pd11 + L = α- Pd( Mo). Mo 9Pd 11 decomposes eutectoidally at 1370°C. The Ru-Pd system is simple peritectic. The continuous series of the hcp solid solutions between Mo 9Pd 11 and ɛ-Ru(Mo, Pd) in the ternary Mo-Ru-Pd system observed at 1700°C are suppressed below 1370°C near the Mo-Pd boundary system by the formation of a narrow α + β + ɛ three-phase field. Relative partial molar Gibbs energies of Mo, Mo and Ru in the respective binary systems and of Mo in the ternary system were measured by the EMF method with a Zr(Ca)O 2 electrolyte. xsΔ ḠMo∞ quantities were evaluated at 1200 K which give -43 kJ/mol Mo in Ru and -94 kJ/mol Mo in Pd at infinite dilution. Gibbs energies of formation of the Mo-Ru and Mo-Pd systems were calculated.

  16. An anomalous current drive mechanism in low collisionality plasmas

    NASA Astrophysics Data System (ADS)

    McDevitt, Chris; Tang, Xianzhu; Guo, Zehua

    2013-10-01

    Steady state tokamak operation requires non-inductive current drive, of which the neoclassical bootstrap current is the most economic option. Here we report a novel mechanism through which a bootstrap current may be driven even in a collisionless plasma. In analogy with the neoclassical mechanism, in which the collisional equilibrium established between trapped and passing electrons produces a steady state current, we show that resonant scattering of electrons by drift wave microturbulence provides an additional means of determining the equilibrium between trapped and passing electrons. The resulting collisionless equilibrium is shown to produce a mean current whose magnitude scales with the thermodynamic forces. Employing a linearized Fokker-Planck collision operator, the plasma current in the presence of both collisions and resonant electron scattering is computed as a function of collisionality. It is found that while the volume integrated electron current is only modestly affected by the turbulent fluctuations, the radial distribution of electron current is significantly modified in low collisionality plasmas. This work was supported by DOE OFES.

  17. COLLISIONAL EVOLUTION OF ULTRA-WIDE TRANS-NEPTUNIAN BINARIES

    SciTech Connect

    Parker, Alex H.; Kavelaars, J. J.

    2012-01-10

    The widely separated, near-equal mass binaries hosted by the cold classical Kuiper Belt are delicately bound and subject to disruption by many perturbing processes. We use analytical arguments and numerical simulations to determine their collisional lifetimes given various impactor size distributions and include the effects of mass loss and multiple impacts over the lifetime of each system. These collisional lifetimes constrain the population of small (R {approx}> 1 km) objects currently residing in the Kuiper Belt and confirm that the size distribution slope at small size cannot be excessively steep-likely q {approx}< 3.5. We track mutual semimajor axis, inclination, and eccentricity evolution through our simulations and show that it is unlikely that the wide binary population represents an evolved tail of the primordially tight binary population. We find that if the wide binaries are a collisionally eroded population, their primordial mutual orbit planes must have preferred to lie in the plane of the solar system. Finally, we find that current limits on the size distribution at small radii remain high enough that the prospect of detecting dust-producing collisions in real time in the Kuiper Belt with future optical surveys is feasible.

  18. Collisional ballooning mode dispersion relation in the banana regime

    SciTech Connect

    Zheng, L.; Tessarotto, M.

    1995-08-01

    Collisional ballooning mode theory in the banana regime is developed for tokamak configurations from the gyrokinetic formalism. A general dispersion relation is obtained, which in principle can deal with a collision operator of any type. However, investigation of an approximate Fokker--Planck collision operator developed in recent neoclassical transport theory is detailed. The most significant feature of the present theory as compared to the customary treatment lies in that the distinction between particle and fluid velocities is made in the ordering analyses. This reveals that the eigenfrequency of modes is determined by balancing the small-parallel-ion-velocity (SPIV) effect [L.-J. Zheng and M. Tessarotto, Phys. Plasmas {bold 1}, 3928 (1994)], instead of the fluid inertia one, with the instability drives. Since the parallel-electric-field effect is found to be negligible as compared to the SPIV effect, in contrast to the customary resistive ballooning mode picture, the leading collisional effect is demonstrated to be the modification of the SPIV effect instead of the relaxation of the frozen-in-law. The ion--ion collisions are the cause for this modification, while the electron collisional effect is shown to be negligible. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  19. Tearing instabilities in the banana-plateau collisionality regime

    SciTech Connect

    Qu, W.X.; Callen, J.D.

    1985-04-01

    Starting from a resistive MHD set of equations and adding neoclassical currents (bootstrap, enhanced polarization and pinch type), we derive the eigenmode equation and relevant dispersion relation for ''neoclassical MHD'' tearing modes in the banana-plateau collisionality regime. The ballooning mode representation and a multiple length scale approximation are utilized. Analysis of the dispersion relation shows that the neoclassical effects on tearing modes are quite strong for ..sqrt..epsilon ..beta../sub p/(1 + nu/sub *//sub e/)/sup -1/ > S/sup -2/5/ (epsilon is the inverse aspect ratio, ..beta../sub p/ is the poloidal beta value, nu/sub *//sub e/ is the electron collisionality factor and S is the neoclassical MHD Reynolds number). The growth rate ..gamma.. and singular layer width deltax are increased typically by more than one order of magnitude from the usual values for epsilon ..beta../sub p/ approx. = 1. For our model, the changes in the tearing modes from the banana-plateau collisionality regime to the usual Pfirsch-Schlueter regime are very clear and natural.

  20. Damping of Bernstein-Greene-Kruskal modes in collisional plasmas

    NASA Astrophysics Data System (ADS)

    Valentini, Francesco

    2008-02-01

    In this paper, the effect of Coulomb collisions on the stability of Bernstein-Greene-Kruskal (BGK) modes [I. B. Bernstein, J. M. Greene, and M. D. Krukal, Phys. Rev. 108, 546 (1957)] is analyzed by comparing the numerical results of collisional particle-in-cell (PIC) simulations with the theoretical predictions by Zakharov and Karpman [V. E. Zakharov and V. I. Karpman, Sov. Phys. JETP 16, 351 (1963)], for the collisional damping of nonlinear plasma waves. In the absence of collisions, BGK modes are undamped nonlinear electrostatic oscillations, solutions of the Vlasov-Poisson equations; in these structures nonlinearity manifests as the formation of a plateau in the resonant region of the particle distribution function, due to trapping of resonant particles, thus preventing linear Landau damping. When particle-particle Coulomb collisions are effective, this plateau is smoothed out since collisions drive the velocity distribution towards the Maxwellian shape, thus destroying the BGK structure. As shown by Zakharov and Karpman in 1963, under certain assumptions, an exponential time decay with constant damping rate is predicted for the electric field amplitude and a linear dependence of the damping rate on the collision frequency is found. In this paper, the theory by Zakharov and Karpman is revisited and the effects of collisions on the stability of BGK modes and on the long time evolution of nonlinear Landau damping are numerically investigated. The numerical results are obtained through a collisional PIC code that reproduces a physical phenomenology also observed in recent experiments with trapped pure electron plasmas.

  1. Constraining Collisional Models of Planetesimals in Debris Disks

    NASA Astrophysics Data System (ADS)

    MacGregor, Meredith A.; Wilner, David J.; Hughes, A. Meredith; Steele, Amy; Ricci, Luca; Andrews, Sean M.; Chandler, Claire J.; Tahli Maddison, Sarah

    2016-01-01

    Debris disks around main-sequence stars are produced by the ongoing collisional erosion of planetesimals, analogous to Kuiper Belt Objects (KBOs) or comets in our own Solar System. Observations of these dusty belts offer a window into the physical and dynamical properties of planetesimals in extrasolar systems through the size distribution of dust grains. In particular, the millimeter/radio spectral index of thermal dust emission encodes information on the grain size distribution that can be used to test proposed collisional models of planetesimals. We have made sensitive Jansky Very Large Array (JVLA) observations of a sample of 7 nearby debris disks at 9 mm and combine these with archival Australia Telescope Compact Array (ATCA) observations of 8 additional debris disks at 7 mm. Using measurements at (sub)millimeter wavelengths from the literature, we place tight constraints on the millimeter spectral indices and thus grain size distributions of this sample of debris disks. Our analysis gives a weighted mean for the slope of the power-law grain distribution that is close to the classical prediction for a steady-state collisional cascade (q=3.5), but not consistent with the steeper distributions predicted by recent models that include more complex fragmentation processes. To interpret this result, we explore the effects of material strengths, velocity distributions, and small-size cutoffs on the steady-state grain size distribution.

  2. Transient tachypnea - newborn

    MedlinePlus

    TTN; Wet lungs - newborns; Retained fetal lung fluid; Transient RDS; Prolonged transition; Neonatal - transient tachypnea ... As the baby grows in the womb, the lungs make a special fluid. This fluid fills the ...

  3. Transient dynamics in motor control of patients with Parkinson's disease

    NASA Astrophysics Data System (ADS)

    Beuter, Anne; Labrie, Christiane; Vasilakos, Konstantinon

    1991-10-01

    Experimental observations of movement disorders including tremor and voluntary microdisplacements recorded in patients with Parkinson's disease (PD) during a simple visuomotor tracking task are analyzed. The performance of patients with PD having a very large amplitude tremor is characterized either by the intermittent appearance of transient dynamics or by the presence of sudden transitions in the amplitude or frequency of the signal. The need to develop new tools to characterize changes in dynamics (i.e., transitions) and to redefine neurological degeneration, such as Parkinson's disease, in terms of qualitative changes in oscillatory behaviors is emphasized.

  4. The Dependence of H-mode Energy Confinement and Transport on Collisionality in NSTX

    SciTech Connect

    Kaye, S. M.; Gerhardt, S.; Guttenfelder, W.; Maingi, R.; Bell, R. E.; Diallo, A.; LeBlanc, B. P.; Podesta, M.

    2012-11-27

    Understanding the dependence of confi nement on collisionality in tokamaks is important for the design of next-step devices, which will operate at collisionalities at least one order of magnitude lower than in present generation. A wide range of collisionality has been obtained in the National Spherical Torus Experiment (NSTX) by employing two different wall conditioning techniques, one with boronization and between-shot helium glow discharge conditioning (HeGDC+B), and one using lithium evaporation (Li EVAP). Previous studies of HeGDC+B plasmas indicated a strong and favorable dependence of normalized con nement on collisionality. Discharges with lithium conditioning discussed in the present study gen- erally achieved lower collisionality, extending the accessible range of collisionality by almost an order of unity. While the confinement dependences on dimensional, engineering variables of the HeGDC+B and Li EVAP datasets differed, collisionality was found to unify the trends, with the lower collisionality lithium conditioned discharges extending the trend of increasing normalized confi nement time with decreasing collisionality when other dimension less variables were held as fi xed as possible. This increase of confi nement with decreasing collisionality was driven by a large reduction in electron transport in the outer region of the plasma. This result is consistent with gyrokinetic calculations that show microtearing and Electron Temperature Gradient modes to be more stable for the lower collisionality discharges. Ion transport, near neoclassical at high collisionality, became more anomalous at lower collisionality, possibly due to the growth of hybrid TEM/KBM modes in the outer regions of the plasma.

  5. The Dependence of H-mode Energy Confinement and Transport on Collisionality in NSTX

    SciTech Connect

    Kaye, S. M.; Gerhardt, S.; Guttenfelder, W.; Maingi, R.; Bell, R. E.; Diallo, A.; LeBlanc, B. P.; Podesta, M.

    2012-11-28

    Understanding the dependence of confi nement on collisionality in tokamaks is important for the design of next-step devices, which will operate at collisionalities at least one order of magnitude lower than in present generation. A wide range of collisionality has been obtained in the National Spherical Torus Experiment (NSTX) by employing two different wall conditioning techniques, one with boronization and between-shot helium glow discharge conditioning (HeGDC+B), and one using lithium evaporation (Li EVAP). Previous studies of HeGDC+B plasmas indicated a strong and favorable dependence of normalized con nement on collisionality. Discharges with lithium conditioning discussed in the present study gen- erally achieved lower collisionality, extending the accessible range of collisionality by almost an order of unity. While the confinement dependences on dimensional, engineering variables of the HeGDC+B and Li EVAP datasets differed, collisionality was found to unify the trends, with the lower collisionality lithium conditioned discharges extending the trend of increasing normalized confi nement time with decreasing collisionality when other dimension less variables were held as fi xed as possible. This increase of confi nement with decreasing collisionality was driven by a large reduction in electron transport in the outer region of the plasma. This result is consistent with gyrokinetic calculations that show microtearing and Electron Temperature Gradient modes to be more stable for the lower collisionality discharges. Ion transport, near neoclassical at high collisionality, became more anomalous at lower collisionality, possibly due to the growth of hybrid TEM/KBM modes in the outer regions of the plasma

  6. Transient drainage summary report

    SciTech Connect

    1996-09-01

    This report summarizes the history of transient drainage issues on the Uranium Mill Tailings Remedial Action (UMTRA) Project. It defines and describes the UMTRA Project disposal cell transient drainage process and chronicles UMTRA Project treatment of the transient drainage phenomenon. Section 4.0 includes a conceptual cross section of each UMTRA Project disposal site and summarizes design and construction information, the ground water protection strategy, and the potential for transient drainage.

  7. Detection prospects for GeV neutrinos from collisionally heated gamma-ray bursts with IceCube/DeepCore.

    PubMed

    Bartos, I; Beloborodov, A M; Hurley, K; Márka, S

    2013-06-14

    Jet reheating via nuclear collisions has recently been proposed as the main mechanism for gamma-ray burst (GRB) emission. In addition to producing the observed gamma rays, collisional heating must generate 10-100 GeV neutrinos, implying a close relation between the neutrino and gamma-ray luminosities. We exploit this theoretical relation to make predictions for possible GRB detections by IceCube + DeepCore. To estimate the expected neutrino signal, we use the largest sample of bursts observed by the Burst and Transient Source Experiment in 1991-2000. GRB neutrinos could have been detected if IceCube + DeepCore operated at that time. Detection of 10-100 GeV neutrinos would have significant implications, shedding light on the composition of GRB jets and their Lorentz factors. This could be an important target in designing future upgrades of the IceCube + DeepCore observatory. PMID:25165903

  8. Charging of a conducting sphere in a weakly ionized collisional plasma: Temporal dynamics and stationary state

    SciTech Connect

    Grach, V. S. Garasev, M. A.

    2015-07-15

    We consider the interaction of a isolated conducting sphere with a collisional weakly ionized plasma in an external field. We assume that the plasma consists of two species of ions neglecting of electrons. We take into account charging of the sphere due to sedimentation of plasma ions on it, the field of the sphere charge and the space charge, as well as recombination and molecular diffusion. The nonstationary problem of interaction of the sphere with the surrounding plasma is solved numerically. The temporal dynamics of the sphere charge and plasma perturbations is analyzed, as well as the properties of the stationary state. It is shown that the duration of transient period is determined by the recombination time and by the reverse conductivity of ions. The temporal dynamics of the sphere charge and plasma perturbations is determined by the intensity of recombination processes relative to the influence of the space charge field and diffusion. The stationary absolute value of the sphere charge increases linearly with the external electric field, decreases with the relative intensity of recombination processes and increases in the presence of substantial diffusion. The scales of the perturbed region in the plasma are determined by the radius of the sphere, the external field, the effect of diffusion, and the relative intensity of recombination processes. In the limiting case of the absence of molecular diffusion and a strong external field, the properties of the stationary state coincide with those obtained earlier as a result of approximate solution.

  9. Collisional quenching reaction rate coefficients of N2 (A3Σu+) by C2F6 and C3F8

    NASA Astrophysics Data System (ADS)

    Suzuki, Susumu; Kuboaki, Masaru; Itoh, Haruo

    2015-09-01

    The collisional quenching reaction rate coefficient of N2 (A3Σu+) by various air pollutant gases were determined from the measurement of the effective lifetime of N2 (A3Σu+) in pure N2 (5-nine) with a small amount of air pollutant gases as an admixture. Derivation of the rate coefficient was performed the waveform analysis of the transient ionization current after turning off the UV light in the Townsend discharge. In this paper, we report that the obtained collisional quenching reaction rate coefficients of N2 (A3Σu+) by C2F6 and C3F8 are (2.3 +/- 1.8) × 10-15 cm3/s and (1.6 +/- 0.8) × 10-14 cm3/s, respectively. Furthermore, we investigate the relationship between the rate coefficient and the mass number of their quenching molecular gases. Firstly, it is confirmed that the rate coefficient take large value with an increase in the mass number of the quenching gases. Secondly, if H atom is included in the gas molecules such as CH4, C2F6 and C3F8 the rate coefficient take large value, but if the molecules including F atom such as C2F6 and C3F8 instead of H atom in this study, more smaller values of the collisional quenching reaction rate coefficient are observed.

  10. Breakdown of the Brillouin limit and classical fluxes in rotating collisional plasmas

    SciTech Connect

    Rax, J. M.; Fruchtman, A.; Gueroult, R.; Fisch, N. J.

    2015-09-15

    The classical collisionless analysis displaying the occurrence of slow and fast rigid body rotation modes in magnetized plasmas is extended to collisional discharges. Collisions speed up the fast mode, slow down the slow one, and break down the classical Brillouin limit. Rigid body rotation has a strong impact on transport, and a collisional radial transport regime, different from the classical Braginskii collisional flux, is identified and analyzed.

  11. Clinical and prognostic significance of PD-1 and PD-L1 expression in sarcomas.

    PubMed

    Paydas, Semra; Bagir, Emine Kilic; Deveci, Mehmet Ali; Gonlusen, Gulfiliz

    2016-08-01

    Programmed death-1 (PD-1) and programmed death-ligand 1 (PD-L1) are new targets in cancer immunotherapy in recent years. The aim of this study is to evaluate the PD-1/PD-L1 expressions in sarcomas and to determine association between PD-1/PD-L1 expressions and clinical/pathological properties in some sarcoma subtypes. Formalin-fixed, paraffin-embedded tissue samples from 65 cases with sarcomas were analyzed. Immunohistochemical staining was performed to detect the PD-1 and PD-L1 expressions in tumor tissue and microenvironment, separately. PD-1 expression in tumor tissue and microenvironment was detected in 11 (17 %) and 8 (12 %) cases, respectively. PD-L1 expression in tumor tissue and microenvironment was detected in 19 (29 %) and 20 cases (30 %), respectively. None of the 5 Ewing sarcomas involving bone showed PD-1/PD-L1 expression, while 2 of 3 cases with Ewing sarcomas involving soft tissue showed PD-1 and PD-L1 expression. Among 5 cases with Kaposi sarcoma, four showed PD-1 and/or PD-L1 expression in tumor or microenvironment. PD-1/PD-L1 expressions were detected 3 of 6 cases with pleomorphic sarcoma, 2 of 4 cases with peripheral nerve sheath tumors and 1 of 4 cases with synovial sarcoma. Interestingly, strongest PD-1/PD-L1 expressions in our study group were detected in 2 sarcoma cases with the history of giant cell tumor. PD-1 and PD-L1 expressions are up to 30 % of the cases with sarcomas. It may be rational to target programmed death pathway in Kaposi sarcoma, pleomorphic sarcoma and peripheral nerve sheath tumors. Strong expression of PD-1/PD-L1 in cases with previous giant cell bone tumor has been found to be interesting and must be studied in giant cell tumor samples. PMID:27421997

  12. Fractionation of hydrogen and deuterium on Venus due to collisional ejection

    NASA Technical Reports Server (NTRS)

    Gurwell, Mark A.; Yung, Yuk L.

    1993-01-01

    The collisional ejection process for hydrogen on Venus is reanalyzed. Improved values for the efficiency of H and D escape as a function of the ionospheric temperature are reported. It is proposed that the reduction of the hydrogen flux for collisional ejection be reduced from 8 to 3.5 x 10 exp 6/sq cm/s, and a revised D/H fractional factor of 0.47 due to collisional ejection is suggested. The resulting deuterium flux is 3.1 x 10 exp 4/sq cm/s, roughly six times the flux due to charge exchange, making collisional ejection the dominant escape mechanism for deuterium on Venus.

  13. Collisional Shift and Broadening of Iodine Spectral Lines in Air Near 543 nm

    NASA Technical Reports Server (NTRS)

    Fletcher, D. G.; McDaniel, J. C.

    1995-01-01

    The collisional processes that influence the absorption of monochromatic light by iodine in air have been investigated. Measurements were made in both a static cell and an underexpanded jet flow over the range of properties encountered in typical compressible-flow aerodynamic applications. Experimentally measured values of the collisional shift and broadening coefficients were 0.058 +/- 0.004 and 0.53 +/- 0.010 GHz K(exp 0.7)/torr, respectively. The measured shift value showed reasonable agreement with theoretical calculations based on Lindholm-Foley collisional theory for a simple dispersive potential. The measured collisional broadening showed less favorable agreement with the calculated value.

  14. Fractionation of hydrogen and deuterium on Venus due to collisional ejection

    NASA Astrophysics Data System (ADS)

    Gurwell, M. A.; Yung, Y. L.

    1993-02-01

    The collisional ejection process for hydrogen on Venus is reanalyzed. Improved values for the efficiency of H and D escape as a function of the ionospheric temperature are reported. It is proposed that the reduction of the hydrogen flux for collisional ejection be reduced from 8 to 3.5 x 10 exp 6/sq cm/s, and a revised D/H fractional factor of 0.47 due to collisional ejection is suggested. The resulting deuterium flux is 3.1 x 10 exp 4/sq cm/s, roughly six times the flux due to charge exchange, making collisional ejection the dominant escape mechanism for deuterium on Venus.

  15. Free electron degeneracy effects on collisional excitation, ionization, de-excitation and three-body recombination

    NASA Astrophysics Data System (ADS)

    Tallents, G. J.

    2016-09-01

    Collisional-radiative models enable average ionization and ionization populations, plus the rates of absorption and emission of radiation to be calculated for plasmas not in thermal equilbrium. At high densities and low temperatures, electrons may have a high occupancy of the free electron quantum states and evaluations of rate coefficients need to take into account the free electron degeneracy. We demonstrate that electron degeneracy can reduce collisional rate coefficients by orders-of-magnitude from values calculated neglecting degeneracy. We show that assumptions regarding the collisional differential cross-section can alter collisional ionization and recombination rate coefficients by a further factor two under conditions relevant to inertial fusion.

  16. The collisional history of dwarf planet Ceres revealed by Dawn

    NASA Astrophysics Data System (ADS)

    Marchi, S.; Williams, D. A.; Mest, S. C.; Schenk, P.; O'Brien, D. P.; De Sanctis, M. C.; Ermakov, A.; Castillo, J. C.; Jaumann, R.; Neesemann, A.; Hiesinger, H.; Park, R. S.; Kneissl, T.; Schmedemann, N.; Raymond, C. A.; Russell, C. T.

    2015-12-01

    Impact craters are a ubiquitous feature of solid surfaces of celestial objects. Craters are oftentimes used to constrain the past evolution of their host objects, as well as to assess their crustal structures. The Dawn spacecraft, currently in orbit around the dwarf planet Ceres, has revealed a surface peppered with impact craters. Two important facts emerge from their global spatial distribution: i) significant longitudinal and latitudinal asymmetries in the crater areal density, ii) and the lack of well-preserved craters larger than 400 km in imaging data. Interestingly, most of the low crater density terrains are found in the vicinity of the three largest, well-preserved impact craters ranging from ~160 to ~290 km in diameter. These low crater areal density terrains expand over a greater distance than observed for large craters on rocky bodies and icy satellites, which typically are confined within one crater radius from the rim. To assess the collisional history of Ceres we developed a Monte Carlo model that tracks the timing, size and number of collisions throughout the history of the solar system. The model shows that Ceres' collisional evolution should have resulted typically in a factor of 10 more craters than observed, with some ~10 craters larger than 400 km expected to have formed over the last 4.5 Gyr ago. While small craters may have reached an equilibrium level, which does not allow then to further increase in number, the lack of evident large craters is a puzzle. A possibility is that the scars of large craters have been obliterated by topography relaxation due to an ice-rich crust. Here we will present an overview of the Ceres' crater spatial distribution and compare it to other siblings (such as the asteroid Vesta), and collisional evolution models. We will also discuss how these results pose important constraints on the internal structure of the dwarf planet in conjunction with surface composition and gravity data acquired by Dawn.

  17. A Collisional Algorithm for Modeling Circumstellar Debris Disks

    NASA Technical Reports Server (NTRS)

    Nesvold, Erika; Kuchner, Marc

    2011-01-01

    Many planetary systems harbor circumstellar disks of dust and planetesimals thought to be debris left over from planet formation. These debris disks exhibit a range of morphological features which can arise from the gravitational perturbations of planets. Accurate models of these features, accounting for the interactions of the particles in a disk with each other and with whatever planets they contain, can act as signposts for planets in debris disks that otherwise could not be detected. Such models can also constrain the planet's mass and orbital parameters. Current models for many disks consider the gravitational and radiative effects of the star and planets on the disk, but neglect the morphological consequences of collisional interactions between the planetesimals. Many observed disk features are not satisfactorily explained by the current generation of models. I am developing a new kind of debris disk model that considers both the gravitational shaping of the disk by planets and the inelastic collisions between particles. I will use a hybrid N-body integrator to numerically solve the equations of motion for the particles and planets in the disk. To include the collisional effects, I begin with an algorithm that tests for collisions at each step of the orbit integration and readjusts the velocities of colliding particles. I am adapting this algorithm to the problem at hand by allowing each particle to represent a "swarm" of planetesimals with a range of masses. When the algorithm detects an encounter between swarms, two or three swarms are produced to approximate the range of possible trajectories of the daughter planetesimals. Here I present preliminary results from my collisional algorithm.

  18. The Collisional Evolution of the Main Asteroid Belt

    NASA Astrophysics Data System (ADS)

    Bottke, W. F.; Brož, M.; O'Brien, D. P.; Campo Bagatin, A.; Morbidelli, A.; Marchi, S.

    Collisional and dynamical models of the main asteroid belt allow us to glean insights into planetesimal- and planet-formation scenarios as well as how the main belt reached its current state. Here we discuss many of the processes affecting asteroidal evolution and the constraints that can be used to test collisional model results. We argue the main belt's wavy size-frequency distribution for diameter D < 100-km asteroids is increasingly a byproduct of comminution as one goes to smaller sizes, with its shape a fossil-like remnant of a violent early epoch. Most D > 100-km asteroids, however, are primordial, with their physical properties set by planetesimal formation and accretion processes. The main-belt size distribution as a whole has evolved into a collisional steady state, and it has possibly been in that state for billions of years. Asteroid families provide a critical historical record of main-belt collisions. The heavily depleted and largely dispersed "ghost families," however, may hold the key to understanding what happened in the primordial days of the main belt. New asteroidal fragments are steadily created by both collisions and mass shedding events via YORP spinup processes. A fraction of this population, in the form of D < 30 km fragments, go on to escape the main belt via the Yarkovsky/YORP effects and gravitational resonances, thereby creating a quasi-steady-state population of planet-crossing and near-Earth asteroids. These populations go on to bombard all inner solar system worlds. By carefully interpreting the cratering records they produce, it is possible to constrain how portions of the main-belt population have evolved with time.

  19. s-Wave collisional frequency shift of a fermion clock.

    PubMed

    Hazlett, Eric L; Zhang, Yi; Stites, Ronald W; Gibble, Kurt; O'Hara, Kenneth M

    2013-04-19

    We report an s-wave collisional frequency shift of an atomic clock based on fermions. In contrast to bosons, the fermion clock shift is insensitive to the population difference of the clock states, set by the first pulse area in Ramsey spectroscopy, θ(1). The fermion shift instead depends strongly on the second pulse area θ(2). It allows the shift to be canceled, nominally at θ(2)=π/2, but correlations perturb the null to slightly larger θ(2). The frequency shift is relevant for optical lattice clocks and increases with the spatial inhomogeneity of the clock excitation field, naturally larger at optical frequencies. PMID:23679589

  20. A+M Collisional Databases in ALADDIN Format

    DOE Data Explorer

    ALADDIN (A Labelled Atomic Data Interface) is a database system developed in order to provide a standard and flexible format and interface for the exchange and management of atomic, molecular and plasma-material interaction data of interest to fusion research. As part of the Atomic and Molecular Data Information System (AMDIS), introduced by the IAEA Atomic and Molecular Data Unit, the ALADDIN interface is available on-line. Twelve databases from DOE and IAEA sources are available from the CFADC website under the heading A+M Collisional Databases.

  1. Collisional width of giant resonances and interplay with Landau damping

    SciTech Connect

    Bonasera, A.; Burgio, G. F.; Di Toro, M.; Wolter, H. H.

    1989-06-01

    We present a semiclassical method to calculate the widths of giant resonances. We solve a mean-field kinetic equation (Vlasov equation) with collision terms treated within the relaxation time approximation to construct a damped strength distribution for collective motions. The relaxation time is evaluated from the time evolution of distortions in the nucleon momentum distribution using a test-particle approach. The importance of an energy dependent nucleon-nucleon cross section is stressed. Results are shown for isoscalar giant quadrupole and octupole motions. A quite important interplay between self-consistent (Landau) and collisional damping is revealed.

  2. Zeeman degeneracy effects in collisional intense-field resonance fluorescence

    NASA Technical Reports Server (NTRS)

    Cooper, J.; Ballagh, R. J.; Burnett, K.

    1980-01-01

    Resonance fluorescence due to intense laser fields from a Zeeman degenerate atom being perturbed by collisional interactions is calculated in the impact regime by using the quantum-fluctuation-regression theorem. Various interesting effects are found. For example, the scattered intensity spectrum for a J = 0 to J = 1 transition for polarization parallel to the laser polarization is essentially an asymmetric triplet, whereas for a perpendicular polarization due to collisions the spectrum is essentially a doublet (whose frequencies do not correspond with any of those of the triplet). Further, the width of the fluorescent component (whose frequency is close to the unperturbed frequency) actually decreases with increasing laser power.

  3. Trapped-Particle-Mediated Collisional Damping of Nonaxisymmetric Plasma Waves

    SciTech Connect

    Kabantsev, A. A.; Driscoll, C. F.

    2006-09-01

    Weak axial variations in magnetic or electric confinement fields in pure electron plasmas cause slow electrons to be trapped locally, and collisional diffusion across the trapping separatrix then causes surprisingly large trapped-particle-mediated (TPM) damping and transport effects. Here we characterize TPM damping of m{sub {theta}}{ne}0, m{sub z}={+-}1 Trivelpiece-Gould plasma modes in large-amplitude long-lived Bernstein-Greene-Kruskal states. The TPM damping gives {gamma}{sub BGK}/{omega}{approx}10{sup -4} and seems to dominate in regimes of weak interparticle collisions.

  4. Comparison of Secondary Islands in Collisional Reconnection to Hall Reconnection

    SciTech Connect

    Shepherd, L. S.; Cassak, P. A.

    2010-07-02

    Large-scale resistive Hall-magnetohydrodynamic simulations of the transition from Sweet-Parker (collisional) to Hall (collisionless) magnetic reconnection are presented; the first to separate secondary islands from collisionless effects. Three main results are described. There exists a regime with secondary islands but without collisionless effects, and the reconnection rate is faster than Sweet-Parker, but significantly slower than Hall reconnection. This implies that secondary islands do not cause the fastest reconnection rates. The onset of Hall reconnection ejects secondary islands from the vicinity of the X line, implying that energy is released more rapidly during Hall reconnection. Coronal applications are discussed.

  5. Differential induction of PD-1/PD-L1 in Neuroimmune cells by drug of abuse.

    PubMed

    Mishra, Vikas; Schuetz, Heather; Haorah, James

    2015-01-01

    Interaction of programmed cell death protein 1 (PD-1) and programmed death-ligand 1 (PD-L1) plays a critical role in regulating the delicate balance between protective immunity and tolerance. Human neuroimmune cells express very low or undetectable levels of PD-1/PD-L1 in normal physiological condition.We seek to examine if exposure of these cells to drug of abuse such as methamphetamine (METH) alters the profile of PD-1/PD-L1 levels, thereby dampens the innate immune response of the host cells. Thus, we assessed the changes in the levels of PD-1/PD-L1 in primary human macrophages, brain endothelial cells (hBECs), astrocytes, microglia, and neurons after exposure to METH. We observed that stimulation of these neuroimmune cells by METH responded differentially to PD-1/PD-L1 expression. Stimulation of macrophage culture with 50 μM of METH exhibited immediate gradual upregulation of PD-L1, while increase in PD-1 took 2-4 hours later than PD-L1. The response of hBECs to PD-1/PD-L1 induction occurred at 24 hours, while increase of PD-1/PD-L1 levels in neurons and microglia was immediate following METH exposure. We found that astrocytes expressed moderate levels of endogenous PD-1/PD-L1, which was diminished by METH exposure. Our findings show a differential expression of PD-1/PD-L1 in neuroimmune cells in response to METH stimulation, suggesting that PD-1/PD-L1 interplay in these cell types could orchestrate the intercellular interactive communication for neuronal death or protection in the brain environment. PMID:26330898

  6. Differential induction of PD-1/PD-L1 in Neuroimmune cells by drug of abuse

    PubMed Central

    Mishra, Vikas; Schuetz, Heather; Haorah, James

    2015-01-01

    Interaction of programmed cell death protein 1 (PD-1) and programmed death-ligand 1 (PD-L1) plays a critical role in regulating the delicate balance between protective immunity and tolerance. Human neuroimmune cells express very low or undetectable levels of PD-1/PD-L1 in normal physiological condition.We seek to examine if exposure of these cells to drug of abuse such as methamphetamine (METH) alters the profile of PD-1/PD-L1 levels, thereby dampens the innate immune response of the host cells. Thus, we assessed the changes in the levels of PD-1/PD-L1 in primary human macrophages, brain endothelial cells (hBECs), astrocytes, microglia, and neurons after exposure to METH. We observed that stimulation of these neuroimmune cells by METH responded differentially to PD-1/PD-L1 expression. Stimulation of macrophage culture with 50 μM of METH exhibited immediate gradual upregulation of PD-L1, while increase in PD-1 took 2-4 hours later than PD-L1. The response of hBECs to PD-1/PD-L1 induction occurred at 24 hours, while increase of PD-1/PD-L1 levels in neurons and microglia was immediate following METH exposure. We found that astrocytes expressed moderate levels of endogenous PD-1/PD-L1, which was diminished by METH exposure. Our findings show a differential expression of PD-1/PD-L1 in neuroimmune cells in response to METH stimulation, suggesting that PD-1/PD-L1 interplay in these cell types could orchestrate the intercellular interactive communication for neuronal death or protection in the brain environment. PMID:26330898

  7. Collectivity of {sup 98}Pd

    SciTech Connect

    Fransen, C.; Blazhev, A.; Dewald, A.; Jolie, J.; Muecher, D.; Pissulla, T.; Moeller, O.

    2009-01-28

    The N = 52 nucleus {sup 98}Pd was investigated at the Cologne TANDEM accelerator both with the Cologne plunger using the recoil distance Doppler-shift method (RDDS) and with the Cologne HORUS spectrometer for a {gamma}{gamma} angular correlation experiment. For the first time lifetimes of yrast states and highly excited low-spin states were measured in {sup 98}Pd and the low-spin level scheme was extended. From our data we were able to interpret {sup 98}Pd as a nucleus that exhibits some collective features, but is obviously much less collective than the neighboring N = 52 isotones {sup 94}Mo and {sup 96}Ru due to its closeness to doubly-magic {sup 100}Sn.

  8. Optical & NIR Transient Surveys

    NASA Astrophysics Data System (ADS)

    Cross, Nicholas J. G.; Djorgovski, S. G.

    2012-04-01

    A workshop on Optical & Near Infrared Transients took place during the first afternoon of the Symposium. It ran for two sessions. The first was given over to talks about various current optical and near-infrared transient surveys, focussing on the Vista surveys, the Catalina Real-Time Transient Survey, Pan-STARRS, Gaia, TAOS and TAOS2. The second session was a panel-led discussion about coordinating multi-wavelength surveys and associated follow-ups.

  9. Phantom crossing with collisional matter in f(T) gravity

    NASA Astrophysics Data System (ADS)

    Zubair, M.

    2016-02-01

    We study the late-time cosmological evolution of f(T) (where T is the torsion scalar) theories with matter contents consisting of collisional self-interacting matter and radiations. The power law, exponential and logarithmic f(T) models are considered to explore the evolution of Hubble parameter H(z), dark energy (DE) equation of state (EoS) ωDE and effective EoS parameter ωeff. We show that crossing of phantom divide line can be realized in the presence of collisional matter as compared to the results obtained for the choice of noncollisional matter [K. Bamba, C.-Q. Geng, C.-C. Lee and L.-W. Luo, J. Cosmol. Astropart. Phys. 01 (2011) 021; K. Bamba, C.-Q. Geng and C.-C. Lee, arXiv:1008.4036]. The evolutionary behavior of ωDE is consistent with the one developed in [P. Wu and H. Yu, Eur. Phys. J. C 71 (2011) 1552] and recent observational data [U. Alam, V. Sahni and A. A. Starobinsky, J. Cosmol. Astropart. Phys. 0406 (2004) 008; S. Nesseris and L. Perivolaropoulos, J. Cosmol. Astropart. Phys. 0701 (2007) 018; P. Wu and H. Yu, Phys. Lett. B 643 (2006) 315; U. Alam, V. Sahni and A. A. Starobinsky, J. Cosmol. Astropart. Phys. 0702 (2007) 011; H. K. Jassal, J. S. Bagla and T. Padmanabhan, Mon. Not. R. Astron. Soc. 405 (2010) 2639].

  10. Ultrahigh-Energy Debris from the Collisional Penrose Process

    NASA Astrophysics Data System (ADS)

    Berti, Emanuele; Brito, Richard; Cardoso, Vitor

    2015-06-01

    Soon after the discovery of the Kerr metric, Penrose realized that superradiance can be exploited to extract energy from black holes. The original idea (involving the breakup of a single particle) yields only modest energy gains. A variant of the Penrose process consists of particle collisions in the ergoregion. The collisional Penrose process has been explored recently in the context of dark matter searches, with the conclusion that the ratio η between the energy of postcollision particles detected at infinity and the energy of the colliding particles should be modest (η ≲1.5 ). Schnittman [Phys. Rev. Lett. 113, 261102 (2014)] has shown that these studies underestimated the maximum efficiency by about 1 order of magnitude (i.e., η ≲15 ). In this work we show that particle collisions in the vicinity of rapidly rotating black holes can produce high-energy ejecta and result in high efficiencies under much more generic conditions. The astrophysical likelihood of these events deserves further scrutiny, but our study hints at the tantalizing possibility that the collisional Penrose process may power gamma rays and ultrahigh-energy cosmic rays.

  11. GAP CLEARING BY PLANETS IN A COLLISIONAL DEBRIS DISK

    SciTech Connect

    Nesvold, Erika R.; Kuchner, Marc J. E-mail: Marc.Kuchner@nasa.gov

    2015-01-10

    We apply our 3D debris disk model, SMACK, to simulate a planet on a circular orbit near a ring of planetesimals that are experiencing destructive collisions. Previous simulations of a planet opening a gap in a collisionless debris disk have found that the width of the gap scales as the planet mass to the 2/7th power (α = 2/7). We find that gap sizes in a collisional disk still obey a power law scaling with planet mass, but that the index α of the power law depends on the age of the system t relative to the collisional timescale t {sub coll} of the disk by α = 0.32(t/t {sub coll}){sup –0.04}, with inferred planet masses up to five times smaller than those predicted by the classical gap law. The increased gap sizes likely stem from the interaction between collisions and the mean motion resonances near the chaotic zone. We investigate the effects of the initial eccentricity distribution of the disk particles and find a negligible effect on the gap size at Jovian planet masses, since collisions tend to erase memory of the initial particle eccentricity distributions. Finally, we find that the presence of Trojan analogs is a potentially powerful diagnostic of planets in the mass range ∼1-10 M {sub Jup}. We apply our model to place new upper limits on planets around Fomalhaut, HR 4796 A, HD 202628, HD 181327, and β Pictoris.

  12. Early cosmochemical fractionation by collisional erosion during the Earth's accretion

    NASA Astrophysics Data System (ADS)

    Boujibar, A.; Andrault, D.; Bolfan-Casanova, N.; Bouhifd, M. A.

    2014-12-01

    Early in the Solar System history, planets grew through energetic collisions between planetesimals. Partial destruction of planetary embryos could have produce heterogeneous bodies, because of widespread internal chemical differentiation through core-segregation, partial melting of silicated mantles and fractional crystallization of magma oceans. On larger proto-planets, including the early Earth, meteoritic impacts have potentially induced erosion of part of the surface, which could have affected significantly the final chemical composition of terrestrial planets. Here we report that collisional erosion of 15-18% of the early Earth's surface reconciles the major apparent compositional differences between the known enstatite chondrites (EC) and the bulk Earth. We base our arguments on experimental measurements of the melting properties of an EC body at pressures between 1 bar and 25 GPa. At low degree of partial melting, the silicate melts are found highly enriched in SiO2, Al2O3 and Na2O and strongly depleted in MgO. Loss through collisional erosion of the surface of such differentiated planetesimal should ultimately raise its Mg/Si ratio and decrease its concentration in incompatible elements. We elaborate auto-coherent models of the Earth formation. Vaporization into space of the protocrusts could be a source of the Na-rich SiO gas that interacted with chondrules and explain the enrichments of enstatite chondrites in SiO2 and volatile lithophile elements.

  13. A collisional origin to Earth's non-chondritic composition?

    NASA Astrophysics Data System (ADS)

    Bonsor, Amy; Leinhardt, Zoë M.; Carter, Philip J.; Elliott, Tim; Walter, Michael J.; Stewart, Sarah T.

    2015-02-01

    Several lines of evidence indicate a non-chondritic composition for bulk Earth. If Earth formed from the accretion of chondritic material, its non-chondritic composition, in particular the super-chondritic 142Nd /144Nd and low Mg/Fe ratios, might be explained by the collisional erosion of differentiated planetesimals during its formation. In this work we use an N-body code, that includes a state-of-the-art collision model, to follow the formation of protoplanets, similar to proto-Earth, from differentiated planetesimals (>100 km) up to isolation mass (>0.16 M⊕). Collisions between differentiated bodies have the potential to change the core-mantle ratio of the accreted protoplanets. We show that sufficient mantle material can be stripped from the colliding bodies during runaway and oligarchic growth, such that the final protoplanets could have Mg/Fe and Si/Fe ratios similar to that of bulk Earth, but only if Earth is an extreme case and the core is assumed to contain 10% silicon by mass. This may indicate an important role for collisional differentiation during the giant impact phase if Earth formed from chondritic material.

  14. The Collisional Cascade Model For Saturn's Ring Spokes

    NASA Astrophysics Data System (ADS)

    Hamilton, D. P.; Jontof-Hutter, D.

    2014-12-01

    Dust particles are ubiquitous in the saturnian system, spewing forth from the geysers of Enceladus and lurking as mysterious wedge-shaped spokes in the planet's main rings. The smallest dust grains are strongly influenced by electromagnetic forces arising from the motions of charged dust particles relative to Saturn's rotating magnetic field while large dust grains follow Keplerian paths determined by the planet's gravity. The most interesting dynamics result when the two forces have similar strengths, typically for particles ~100 nanometer in size. Differences between the motions of dust grains and much larger ring particles provides a free energy source that powers spoke formation. Most observations of ongoing spoke formation can be understood in the context of a Collisional Cascade model in which a hail of rapidly-moving ~50nm dust grains rain down upon more massive ring particles. After leaving the ring plane en masse from the site of an initial disturbance, these mid-sized grains are accelerated by the magnetic field to high speeds relative to ring particles. When they return to the ring plane - nearly simultaneously over a large radial range - they strike dust-coated fluffy ring particles, freeing both visible 0.5 micron spoke particles and additional 50nm debris that goes on to continue the cascade. The Collisional Cascade model can account for the rapid onset of spokes, their hour-long active phases, and the propensity of spokes to prefer certain magnetic longitudes.

  15. Quasi-collisional Magneto-optic Effects in Collisionless Plasmas

    NASA Astrophysics Data System (ADS)

    Keenan, Brett; Ford, Alex; Medvedev, Mikhail

    2016-03-01

    High-amplitude, chaotic/turbulent electromagnetic fluctuations are ubiquitous in astrophysical plasmas, where they can be excited by various kinetic-streaming and/or anisotropy-driven instabilities, such as the Weibel instability. These fields typically exist on ``sub-Larmor scales'' -- scales smaller than the electron Larmor radius. Electrons moving through such magnetic fields undergo small-angle stochastic deflections of their pitch-angles, thus establishing diffusive transport on long time-scales. We show that this behavior, under certain conditions, is equivalent to Coulomb collisions in collisional plasmas. The magnetic pitch-angle diffusion coefficient, which acts as an effective ``collision'' frequency, may be substantial in these, otherwise, collisionless environments. We show that this effect, colloquially referred to as the plasma ``quasi-collisionality'', may radically alter the expected radiative transport properties of candidate plasmas. We argue that the modified magneto-optic effects in these plasmas provide an attractive, novel radiative diagnostic tool for the exploration and characterization of small-scale magnetic turbulence.

  16. Nonlinear transport processes in tokamak plasmas. I. The collisional regimes

    SciTech Connect

    Sonnino, Giorgio; Peeters, Philippe

    2008-06-15

    An application of the thermodynamic field theory (TFT) to transport processes in L-mode tokamak plasmas is presented. The nonlinear corrections to the linear ('Onsager') transport coefficients in the collisional regimes are derived. A quite encouraging result is the appearance of an asymmetry between the Pfirsch-Schlueter (P-S) ion and electron transport coefficients: the latter presents a nonlinear correction, which is absent for the ions, and makes the radial electron coefficients much larger than the former. Explicit calculations and comparisons between the neoclassical results and the TFT predictions for Joint European Torus (JET) plasmas are also reported. It is found that the nonlinear electron P-S transport coefficients exceed the values provided by neoclassical theory by a factor that may be of the order 10{sup 2}. The nonlinear classical coefficients exceed the neoclassical ones by a factor that may be of order 2. For JET, the discrepancy between experimental and theoretical results for the electron losses is therefore significantly reduced by a factor 10{sup 2} when the nonlinear contributions are duly taken into account but, there is still a factor of 10{sup 2} to be explained. This is most likely due to turbulence. The expressions of the ion transport coefficients, determined by the neoclassical theory in these two regimes, remain unaltered. The low-collisional regimes, i.e., the plateau and the banana regimes, are analyzed in the second part of this work.

  17. Experimental observations of low-velocity collisional systems

    NASA Astrophysics Data System (ADS)

    Jorges, Jeffery; Dove, Adrienne; Colwell, Joshua

    Low-velocity collisions in systems of centimeter-sized objects may result in particle growth by accretion, rebounding, or erosive processes that result in the production of additional smaller particles. Numerical simulations of these systems are limited by a need to understand the collisional parameters governing the outcomes of these collisions over a range of conditions. Here, we present the results from laboratory experiments designed to explore low-velocity collisions by conducting experiments in a vacuum chamber in our 0.8-sec drop tower apparatus. These experiments utilize a variety of impacting spheres, including glass, Teflon, aluminum, stainless steel, and brass. These spheres are either used in their natural state or are ``mantled'' - coated with a few-mm thick layer of a cohesive powder. A high-speed, high-resolution video camera is used to record the motion of the colliding bodies. These videos are then processed and we track the particles to determine impactor speeds before and after collision and the collisional outcome. We determine how the coefficient of restitution varies as a function of material type, morphology, and impact velocity. For impact velocities in the range from about 20-100 cm/s we observe that mantling of particles has the most significant effect, reducing the coefficients of restitution.

  18. Gap Clearing by Planets in a Collisional Debris Disk

    NASA Astrophysics Data System (ADS)

    Nesvold, Erika R.; Kuchner, Marc J.

    2015-01-01

    We apply our 3D debris disk model, SMACK, to simulate a planet on a circular orbit near a ring of planetesimals that are experiencing destructive collisions. Previous simulations of a planet opening a gap in a collisionless debris disk have found that the width of the gap scales as the planet mass to the 2/7th power (α = 2/7). We find that gap sizes in a collisional disk still obey a power law scaling with planet mass, but that the index α of the power law depends on the age of the system t relative to the collisional timescale t coll of the disk by α = 0.32(t/t coll)-0.04, with inferred planet masses up to five times smaller than those predicted by the classical gap law. The increased gap sizes likely stem from the interaction between collisions and the mean motion resonances near the chaotic zone. We investigate the effects of the initial eccentricity distribution of the disk particles and find a negligible effect on the gap size at Jovian planet masses, since collisions tend to erase memory of the initial particle eccentricity distributions. Finally, we find that the presence of Trojan analogs is a potentially powerful diagnostic of planets in the mass range ~1-10 M Jup. We apply our model to place new upper limits on planets around Fomalhaut, HR 4796 A, HD 202628, HD 181327, and β Pictoris.

  19. SELF-CONSISTENT SIZE AND VELOCITY DISTRIBUTIONS OF COLLISIONAL CASCADES

    SciTech Connect

    Pan, Margaret; Schlichting, Hilke E. E-mail: hilke@ucla.edu

    2012-03-10

    The standard theoretical treatment of collisional cascades derives a steady-state size distribution assuming a single constant velocity dispersion for all bodies regardless of size. Here we relax this assumption and solve self-consistently for the bodies' steady-state size and size-dependent velocity distributions. Specifically, we account for viscous stirring, dynamical friction, and collisional damping of the bodies' random velocities in addition to the mass conservation requirement typically applied to find the size distribution in a steady-state cascade. The resulting size distributions are significantly steeper than those derived without velocity evolution. For example, accounting self-consistently for the velocities can change the standard q = 3.5 power-law index of the Dohnanyi differential size spectrum to an index as large as q = 4. Similarly, for bodies held together by their own gravity, the corresponding power-law index range 2.88 < q < 3.14 of Pan and Sari can steepen to values as large as q = 3.26. Our velocity results allow quantitative predictions of the bodies' scale heights as a function of size. Together with our predictions, observations of the scale heights for different-sized bodies for the Kuiper belt, the asteroid belt, and extrasolar debris disks may constrain the mass and number of large bodies stirring the cascade as well as the colliding bodies' internal strengths.

  20. Recombination and collisional x-ray lasers at LULI

    NASA Astrophysics Data System (ADS)

    Jamelot, Gerard; Jaegle, Pierre; Carillon, Antoine; Gauthe, Bernard; Goedtkindt, P.; Guennou, M.; Klisnick, Annie; Moeller, Clary; Rus, Bedrich; Sureau, Alain; Zeitoun, Philippe

    1994-02-01

    We present our recent efforts to produce X-ray lasers in the 200 angstroms range by using the moderate power drive of the LULI facility in Palaiseau. The 4 - 5 transitions of Li-like sulfur exhibit large gain-length products in recombining plasmas, and appear to be less sensitive to plasma non-uniformity than the 3 - 4 and 3 - 5 transitions previously studied. From numerical simulations this is likely due to smaller radiative and collisional excitation from 4f than from 3d levels. In collisional scheme, neon-like zinc gives analogous results to similar works on other elements for the 3p - 3s, J equals 2 yields 1 transitions, but the J equals 0 yields 1 transition shows a surprisingly large gain coefficient of 4.9 cm-1. From a detailed comparison of time-dependent intensities of the J equals 0 yields 1 and the J equals 2 yields 1 lines, we conclude that transitions from J equals 0 and from J equals 2 are not emitted in the same region of the plasma.

  1. Multi-fluid plasma modeling with Braginskii collisional transport processes

    NASA Astrophysics Data System (ADS)

    Ho, A.; Shumlak, U.; Miller, S. T.

    2015-11-01

    Magnetohydrodynamics (MHD) works well where transport processes are primarily advective. Extensions of the MHD model are capable of capturing some collisional phenomena such as electrical resistivity, which are important in systems with mean free paths less than the characteristic length. However, MHD models have difficulties resolving systems where the Debye length cannot be assumed to approach zero. These systems arise in low density, hot plasmas. By modeling the ions and electrons as distinct fluids, the 5-moment multi-fluid plasma model is able to capture these short-range transport processes that are not accounted for in MHD. To model the transport processes the Braginskii transport terms are added to the 5-moment model, which introduces viscosity, heat conduction, and binary species interactions. These transport properties are affected by strong magnetic fields, resulting in anisotropic collisional effects. The multi-fluid equations are evolved explicitly and are coupled with Maxwell's equations. This research extends the University of Washington's WARPXM code to include the Braginskii terms with the 5-moment multi-fluid plasma model. The implementation is validated against theoretical results from a Hartmann flow benchmark problem. This work is supported by a grant from the United States Air Force Office of Scientific Research.

  2. Dynamical and collisional evolution of Kuiper belt binaries

    NASA Astrophysics Data System (ADS)

    Brunini, Adrián; Zanardi, Macarena

    2016-02-01

    We present numerical simulations of the evolution of synthetic transneptunian binaries (TNBs) under the influence of the solar perturbation, tidal friction, and collisions with the population of classical Kuiper belt objects (KBOs). We show that these effects, acting together, have strongly sculpted the primordial population of TNBs. If the population of classical KBOs have a power-law size distribution as the ones that are inferred from recent observational surveys, the fraction of surviving binaries at present would be ˜70 per cent of the primordial population. The orbits of the surviving synthetic systems match reasonably well the observed sample. The collisional process excites the mutual orbital eccentricity of the binaries, acting against the effect of tides. Therefore only ˜10 per cent of the objects reach total orbital circularization (e ≤ 10-4). In addition, our results predict that the population of contact binaries in the transneptunian region should be small. Ultrawide binaries are naturally obtained by the combined action of Kozai cycles and tidal friction and collisional evolution, being the number and orbital distribution of them very similar to the ones of the observed population.

  3. Collisional cooling investigation of THz rotational transitions of water

    SciTech Connect

    Dick, Michael J.; Drouin, Brian J.; Pearson, John C.

    2010-02-15

    An investigation of the pressure broadening by helium and hydrogen of six rotational transitions of water has been completed. The six transitions studied included two para water transitions (0{sub 00}-1{sub 11} and 1{sub 11}-2{sub 02}) and four ortho water transitions (1{sub 01}-1{sub 10}, 2{sub 21}-3{sub 12}, 3{sub 03}-3{sub 12} and 3{sub 12}-3{sub 21}) in the frequency region 0.55-1.17 THz. This survey was accomplished using the collisional cooling technique which allowed the broadening of each transition to be studied below the water condensation temperature. For each of the transitions studied, the temperature dependence of the pressure broadening by helium showed little dependence on temperature, while the broadening by hydrogen showed a sharp decrease at the lowest temperatures. This behavior was modeled, for each transition broadened by helium and hydrogen, with a power law, or a power law modified with a Boltzmann-like step function, and the results of these fits will be presented. In addition, an extensive investigation of the systematic error in the temperature of the water vapor in the collisional cooling experiment will be discussed. Finally, the impact of these new broadening measurements on models of star formation in the interstellar medium will be outlined.

  4. Observation of anomalous field penetration in collisional, cylindrical ICP discharges

    NASA Astrophysics Data System (ADS)

    Evans, John D.; Chen, Francis F.; Arnush, Donald

    2000-10-01

    Measurements of the radial penetration of RF-generated B-fields are performed in a large diameter cylindrical ICP. A loop antenna surrounds a dome-shaped Pyrex top that sits on top of a magnetic bucket. Rtop=15cm height of top, Rbucket 18cm, bucket height 30cm, N 1011cm-3, Te 3eV, Prf < 1.4kW, Frf = 2-27.12MHz, Po 1-100mT. Field penetration (``skin") depths Lsd are measured in the outer plasma region (r > R/2) that are consistent with collisional skin depth theory. However, in the interior region (r < R/2), non-monotonic radial profiles and interference phenomena that resemble standing wave behavior (e.g. nodes) are observed, where no propagating waves are predicted to occur. Similar phenomena have been observed by other groups [1], but for chambers sizes such that R Lsd. Such observations were explained as manifestations of the anomalous skin effect (ASE), the electromagnetic analog of Debye shielding. However, these phenomena are more apparent as Po (and collisionality) is increased, in apparent contradiction to the predictions of ASE theory. Results of a detailed experimental investigation of interference phenomena under conditions that fall outside of the ASE regime will be presented, as well as a simple physical picture that resolves this apparent paradox. [1]. B. Joye and H. Schneider, Helv. Phys. Acta 51, 804 (1978).

  5. Ultrahigh-Energy Debris from the Collisional Penrose Process.

    PubMed

    Berti, Emanuele; Brito, Richard; Cardoso, Vitor

    2015-06-26

    Soon after the discovery of the Kerr metric, Penrose realized that superradiance can be exploited to extract energy from black holes. The original idea (involving the breakup of a single particle) yields only modest energy gains. A variant of the Penrose process consists of particle collisions in the ergoregion. The collisional Penrose process has been explored recently in the context of dark matter searches, with the conclusion that the ratio η between the energy of postcollision particles detected at infinity and the energy of the colliding particles should be modest (η≲1.5). Schnittman [Phys. Rev. Lett. 113, 261102 (2014)] has shown that these studies underestimated the maximum efficiency by about 1 order of magnitude (i.e., η≲15). In this work we show that particle collisions in the vicinity of rapidly rotating black holes can produce high-energy ejecta and result in high efficiencies under much more generic conditions. The astrophysical likelihood of these events deserves further scrutiny, but our study hints at the tantalizing possibility that the collisional Penrose process may power gamma rays and ultrahigh-energy cosmic rays. PMID:26197116

  6. Thermal diffusivity of nanofluids containing Au/Pd bimetallic nanoparticles of different compositions.

    PubMed

    Sánchez-Ramírez, J F; Jiménez Pérez, J L; Cruz Orea, A; Gutierrez Fuentes, R; Bautista-Hernández, A; Pal, U

    2006-03-01

    Colloidal suspensions of bimetallic Au/Pd nanoparticles were prepared by simultaneous reduction of the metal ions from their corresponding chloride salts with polymer (PVP) stabilizer. Thermal properties of water containing bimetallic nanoparticles with different nominal compositions (Au/Pd = 12/1, 5/1, 1/1, 1/5) were measured using the mode mismatched dual-beam thermal lens technique to determine the effect of particle composition on the thermal diffusivity of the nanofluids. The characteristic time constant of the transient thermal lens was estimated by fitting the experimental data to the theoretical expression for transient thermal lens. The thermal diffusivity of the nanofluids (water, containing Au/Pd bimetallic nanoparticles) is seen to be strongly dependent on the composition of the particles. The maximum diffusivity was achieved for the nanoparticles with highest Au/Pd molar ratio. A possible mechanism for such high thermal diffusivity of the nanofluids with bimetallic particles is given. UV-Vis spectroscopy, TEM and high-resolution electron microscopy (HREM) techniques were used to characterize the Au/Pd bimetallic nanoparticles. PMID:16573121

  7. On negative ion-drag force for dust in collisional plasmas

    SciTech Connect

    Patacchini, Leonardo; Hutchinson, Ian H.

    2008-09-07

    The ion-drag force on a dust particle in collisional plasmas is self-consistently calculated using the Particle In Cell code SCEPTIC in the entire range of charge-exchange collisionlality. It is shown that the ion-drag only reverses in the strongly collisional regime, where other forces are of much stronger magnitude than the ion-drag itself.

  8. On negative ion-drag force for dust in collisional plasmas

    NASA Astrophysics Data System (ADS)

    Patacchini, Leonardo; Hutchinson, Ian H.

    2008-09-01

    The ion-drag force on a dust particle in collisional plasmas is self-consistently calculated using the Particle In Cell code SCEPTIC in the entire range of charge-exchange collisionlality. It is shown that the ion-drag only reverses in the strongly collisional regime, where other forces are of much stronger magnitude than the ion-drag itself.

  9. Collisional damping of the geodesic acoustic mode with toroidal rotation. I. Viscous damping

    NASA Astrophysics Data System (ADS)

    Gong, Xueyu; Xie, Baoyi; Guo, Wenfeng; Chen, You; Yu, Jiangmei; Yu, Jun

    2016-03-01

    With the dispersion relation derived for the geodesic acoustic mode in toroidally rotating tokamak plasmas using the fluid model, the effect of the toroidal rotation on the collisional viscous damping of the geodesic acoustic mode is investigated. It is found that the collisional viscous damping of the geodesic acoustic mode has weak increase with respect to the toroidal Mach number.

  10. Interstellar formaldehyde. I - The collisional pumping mechanism for anomalous 6-centimeter absorption.

    NASA Technical Reports Server (NTRS)

    Thaddeus, P.

    1972-01-01

    Investigation of the quantum mechanics of the collisional pumping process which Townes and Cheung (1969) propose as the cause of 'anomalous' formaldehyde absorption in diffuse dark nebulae discussed by Palmer et al. (1969). Quantum effects are taken into account in an attempt to determine whether such nebulae are likely to provide the physical conditions required for the collisional pumping process.

  11. Registration of PD 05035 and PD 05041 germplasm lines of cotton

    Technology Transfer Automated Retrieval System (TEKTRAN)

    PD 05035 and PD 05041 are noncommercial breeding lines of cotton jointly released by the Agricultural Research Service, United States Department of Agriculture, the Clemson University Experiment Station, and Cotton Incorporated in 2014. PD 05035 was selected from a cross of PD 93007 and ‘SG 747’, an...

  12. Registration of PD 06001 and PD 06078 germplasm lines of cotton

    Technology Transfer Automated Retrieval System (TEKTRAN)

    PD 06001 and PD 06078 are noncommercial breeding lines of cotton jointly released by the Agricultural Research Service, United States Department of Agriculture, the Clemson University Experiment Station, and Cotton Incorporated in 2014. PD 06001 is a breeding line selected from a cross of PD 93007 a...

  13. Perception of acoustic transients

    NASA Astrophysics Data System (ADS)

    Howard, J. H., Jr.

    1984-01-01

    The research investigates the role of knowledge based or top-down processing in the perception of nonlinguistic, transient signals. The experiments address issues in transient pattern classification, target observation, attentional focusing, auditory induction, and computer based performance aids. The theoretical significance and naval relevance of the research is considered.

  14. NO Adsorption on Pd(111)

    NASA Astrophysics Data System (ADS)

    Garda, Graciela R.; Ferullo, Ricardo M.; Castellani, Norberto J.

    The reactive behavior of NO on Pd(111) has been studied using a semiempirical theoretical method. The adsorption sites and the related electronic structure have been considered. In particular, the dissociation process has been studied and compared with CO. Different dissociation mechanisms have been proposed and the formation of NCO species has been considered. The results follow the trends reported in the experimental literature.

  15. First-principles study of ferromagnetism in Pd-doped and Pd- Cu-codoped BN

    NASA Astrophysics Data System (ADS)

    Wang, Q.; Wang, S.; Dai, J. F.; Li, W. X.

    2016-07-01

    In this paper, we aimed at probing the ferromagnetism properties of Pd and Pd-Cu- codoped supercell BN based on the first-principles methods. The formation energy, lattice constants, energy band structures, spin density of state, energy difference between ferromagnetism (FM) and autiferromagnetism (AFM) orderings were calculated. Formation energy calculations showed that Pd atom tended to replace B atom in the supercell. Pd-doped BN exhibited a half-metallic ferromagnetic. And the ferromagnetism arised form the strong hybridization between the Pd4d and N2p state. Pd-Cu-codoped BN also displayed a half-metallic ferromagnetic. The incorporation of Pd and Pd-Cu induced some impurity energy differences between FM and AFM orderings. It also showed that FM state was the ground state, and room temperature ferromagnetism may be expected. These results pointed out the possibility of fabricating BN based on dilute magnetic semiconductors (DMS) by doping with Pd and Pd-Cu.

  16. Human Cancer Immunotherapy with PD-1/PD-L1 Blockade

    PubMed Central

    Zheng, Peilin; Zhou, Zhiguang

    2015-01-01

    The ligation of programmed cell death-1 (PD-1) to its ligands PD-L1 and PD-L2 counteracts T-cell activation, which is critical in immune tolerance. The persistent high expression of PD-1 and PD-L1 are also observed on tumor-infiltrating lymphocytes and various tumor cells, maintaining the highly suppressive microenvironment in tumor sites and promoting tumor malignancies. The blockade of PD-1 axis with PD-L2 fusion protein or monoclonal antibodies against either PD-1 or PD-L1 has been clinically evaluated in various tumor types. This short review summarizes the progress of PD-1 axis blockade in clinical trials to evaluate its effectiveness in the antitumor immunotherapy. PMID:26448693

  17. Preparation of (103)Pd brachytherapy seeds by electroless plating of (103)Pd onto carbon bars.

    PubMed

    Li, Zhong-Yong; Gao, Hui-Bo; Deng, Xue-Song; Zhou, Leng; Zhang, Wen-Hui; Han, Lian-Ge; Jin, Xiao-Hai; Cui, Hai-Ping

    2015-09-01

    A method for preparing (103)Pd brachytherapy seeds is reported. The key of the method was to deposit (103)Pd onto carbon bars by electroless plating so as to prepare source cores. After each carbon bar with (103)Pd was sealed in a titanium capsule, the (103)Pd seeds were fabricated. This paper provides valuable experiences and data for the preparation of (103)Pd brachytherapy seeds. PMID:26092353

  18. Electromagnetic drift waves dispersion for arbitrarily collisional plasmas

    SciTech Connect

    Lee, Wonjae Krasheninnikov, Sergei I.; Angus, J. R.

    2015-07-15

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

  19. Cosmochemical fractionation by collisional erosion during the Earth's accretion

    NASA Astrophysics Data System (ADS)

    Boujibar, Asmaa; Andrault, Denis; Bolfan-Casanova, Nathalie; Bouhifd, Mohamed Ali; Monteux, Julien

    2015-09-01

    Early in the Solar System's history, energetic collisions of differentiated bodies affected the final composition of the terrestrial planets through partial destruction. Enstatite chondrites (EC) are the best candidates to represent the primordial terrestrial precursors as they present the most similar isotopic compositions to Earth. Here we report that collisional erosion of >15% of the early Earth's mass can reconcile the remaining compositional differences between EC and the Earth. We base our demonstration on experimental melting of an EC composition at pressures between 1 bar and 25 GPa. At low pressures, the first silicate melts are highly enriched in incompatible elements Si, Al and Na, and depleted in Mg. Loss of proto-crusts through impacts raises the Earth's Mg/Si ratio to its present value. To match all major element compositions, our model implies preferential loss of volatile lithophile elements and re-condensation of refractory lithophile elements after the impacts.

  20. Collisional dynamics in a gas of molecular super-rotors.

    PubMed

    Khodorkovsky, Yuri; Steinitz, Uri; Hartmann, Jean-Michel; Averbukh, Ilya Sh

    2015-01-01

    Recently, femtosecond laser techniques have been developed that are capable of bringing gas molecules to extremely fast rotation in a very short time, while keeping their translational motion relatively slow. Here we study collisional equilibration dynamics of this new state of molecular gases. We show that the route to equilibrium starts with a metastable 'gyroscopic stage' in the course of which the molecules maintain their fast rotation and orientation of the angular momentum through many collisions. The inhibited rotational-translational relaxation is characterized by a persistent anisotropy in the molecular angular distribution, and is manifested in the optical birefringence and anisotropic diffusion in the gas. After a certain induction time, the 'gyroscopic stage' is abruptly terminated by an explosive rotational-translational energy exchange, leading the gas towards the final equilibrium. We illustrate our conclusions by direct molecular dynamics simulation of several gases of linear molecules. PMID:26160223

  1. Collisional-radiative modelling of an Ar helicon plasma discharge

    NASA Astrophysics Data System (ADS)

    Loch, Stuart

    2005-10-01

    We report on recent modelling results of emission observed from a helicon plasma, comparing theoretical and observed line intensities and line ratios of Ar, Ar^+ and Ar^2+. Our Helicon plasma is from the ASTRAL device at Auburn University, with spectral measurements from 275 nm through to 1015 nm. We concentrate on the Ar^+ ion stage, and present the results of a collisional-radiative model using various qualities of atomic data. In particular, we compare the modelling results using Plane-Wave Born, Distorted-Wave and R-matrix electron impact excitation data with those observed from the plasma. As part of the modelling work, we investigate the potential use of various lines as plasma diagnostic tools.

  2. Cosmochemical fractionation by collisional erosion during the Earth's accretion

    PubMed Central

    Boujibar, Asmaa; Andrault, Denis; Bolfan-Casanova, Nathalie; Bouhifd, Mohamed Ali; Monteux, Julien

    2015-01-01

    Early in the Solar System's history, energetic collisions of differentiated bodies affected the final composition of the terrestrial planets through partial destruction. Enstatite chondrites (EC) are the best candidates to represent the primordial terrestrial precursors as they present the most similar isotopic compositions to Earth. Here we report that collisional erosion of >15% of the early Earth's mass can reconcile the remaining compositional differences between EC and the Earth. We base our demonstration on experimental melting of an EC composition at pressures between 1 bar and 25 GPa. At low pressures, the first silicate melts are highly enriched in incompatible elements Si, Al and Na, and depleted in Mg. Loss of proto-crusts through impacts raises the Earth's Mg/Si ratio to its present value. To match all major element compositions, our model implies preferential loss of volatile lithophile elements and re-condensation of refractory lithophile elements after the impacts. PMID:26395157

  3. Bohm's criterion in a collisional magnetized plasma with thermal ions

    SciTech Connect

    Hatami, M. M.; Shokri, B.

    2012-08-15

    Using the hydrodynamic model and considering a planar geometry, the modified Bohm's sheath criterion is investigated in a magnetized, collisional plasma consisting of electron and positive ions with finite temperature. It is assumed that the singly charged positive ions enter into the sheath region obliquely, i.e., their velocity at the sheath edge is not normal to the wall, and the electron densities obey Boltzmann relations. It is shown that there are both upper and lower limit for the Bohm entrance velocity of ions in this case and both of these limits depend on the magnitude and direction of the applied magnetic field. To determine the accuracy of our derived generalized Bohm's criterion, it reduced to some familiar physical condition. Also, using this generalized Bohm's criterion, the behavior of the electron and positive ion density distributions are studied in the sheath region.

  4. Flexural extension of the upper continental crust in collisional foredeeps

    USGS Publications Warehouse

    Bradley, D.C.; Kidd, W.S.F.

    1991-01-01

    Normal faults on the outer slopes of trenches and collisional foredeeps reveal that high-amplitude lithospheric flexure can result in inelastic extensional deformation of the convex side of a flexed plate. This process, which we call "flexural extension', differs fundamentally from rifting in that the lower lithosphere contracts while the upper lithosphere extends. Structural evidence does not support common illustrations of flexural normal faults as planar-irrotational structures which simply die out at shallow crustal depths. Instead, the surface geology shows that flexural normal faulting must be rotational with respect to the enveloping surface of the flexed plate. This toppled domino geometry implies the presence at depth of a detachment or zone of distributed ductile simple shear where fault displacement and block rotation are accommodated. -from Authors

  5. Collisional effects in the dynamics of a dipolar gas

    NASA Astrophysics Data System (ADS)

    Sykes, Andrew

    2016-05-01

    In this talk, we discuss the role of collisions in dipolar gases which are far from equilibrium. We compare and contrast collisional mechanisms with mean-field effects. We consider several cases of dynamical behaviour. We begin with cross-dimensional relaxation, where the time-scale of equilibration is studied following a quench in the trap parameters. We also discuss the damping of monopole and quadrupole excitations. Finally we discuss time-of-flight expansion dynamics. Our results demonstrate that collisions can play a significant role. We use these results to extract an estimate of the deca-heptuplet s-partial-wave scattering length of bosonic dysprosium, and to improve the accuracy of experimental time-of-flight expansion imaging. Financial support from the Marie Sklodowska-Curie H2020 framework program.

  6. Self-focusing of electromagnetic pulsed beams in collisional plasmas

    SciTech Connect

    Faisal, Mohammad; Verma, M. P.; Sodha, Mahendra Singh

    2008-10-15

    In this paper, the self-focusing of an electromagnetic pulsed beam in a collisional plasma has been investigated in the paraxial approximation, following the formalism developed by Akhmanov. The energy balance equation for electrons, the equation expressing the equality of pressure gradient (of electrons and ions) to the force due to space charge field, and the equation for the beam width parameter f (obtained by following Akhmanov's approach) have been simultaneously solved for given initial (z=0) time profile of the pulse to obtain f as a function of {xi} (cz/{omega}r{sub 0}{sup 2}) and t{sup '}=t-z/V{sub g}, where V{sub g} is the group velocity. Both Gaussian and sine time profiles of the pulse have been investigated.

  7. Collisional Processing of Comet Surfaces: Impact Experiments into Olivine

    NASA Technical Reports Server (NTRS)

    Lederer, S. M.; Jensen, E. A.; Cintala, M. J.; Smith, D. C.; Nakamura-Messenger, K.; Keller, L. P.; Wooden, D. H.; Fernandez, Y. R.; Zolensky, M. E.

    2011-01-01

    A new paradigm has emerged where 3.9 Ga ago, a violent reshuffling reshaped the placement of small bodies in the solar system (the Nice model). Surface properties of these objects may have been affected by collisions caused by this event, and by collisions with other small bodies since their emplacement. In addition, objects in the Kuiper Belt are believed to undergo extensive collisional processing while in the Kuiper Belt. Physical manifestations of shock effects (e.g., planar dislocations) in minerals typically found in comets will be correlated with spectral changes (e.g. reddening, loss and shift of peaks, new signatures) to allow astronomers to better understand geophysical impact processing that has occurred on small bodies. Targets will include solid and granular olivine (forsterite), impacted over a range of impact speeds with the Experimental Impact Laboratory at NASA JSC. Analyses include quantification of the dependence of the spectral changes with respect to impact speed, texture of the target, and temperature.

  8. Test ion transport in a collisional, field-reversed configuration

    NASA Astrophysics Data System (ADS)

    Roche, T.; McWilliams, R.; Heidbrink, W. W.; Bolte, N.; Garate, E. P.; Morehouse, M.; Slepchenkov, M.; Wessel, F.

    2014-08-01

    Diffusion of test-ions in a flux-coil generated, collisional, field-reversed configuration is measured via time-resolved tomographic reconstruction of Ar+ optical emission in the predominantly nitrogen plasma. Azimuthal test ion diffusion across magnetic field lines is found to be classical during the stable period of the discharge. Test ion radial confinement is enhanced by a radial electric field, reducing the observed outward radial transport rate below predictions based solely on classical cross-field diffusion rates. Test ion diffusion is ˜500 m2 s-1 during the stable period of the discharge. The electric field inferred from plasma potential measurements and from equilibrium calculations is consistent with the observed reduction in argon transport.

  9. Simulations of a molecular plasma in collisional-radiative nonequilibrium

    NASA Technical Reports Server (NTRS)

    Cambier, Jean-Luc; Moreau, Stephane

    1993-01-01

    A code for the simulation of nonequilibrium plasmas is being developed, with the capability to couple the plasma fluid-dynamics for a single fluid with a collisional-radiative model, where electronic states are treated as separate species. The model allows for non-Boltzmann distribution of the electronic states. Deviations from the Boltzmann distributions are expected to occur in the rapidly ionizing regime behind a strong shock or in the recombining regime during a fast expansion. This additional step in modeling complexity is expected to yield more accurate predictions of the nonequilibrium state and the radiation spectrum and intensity. An attempt at extending the code to molecular plasma flows is presented. The numerical techniques used, the thermochemical model, and the results of some numerical tests are described.

  10. Magnetosonic shock wave in collisional pair-ion plasma

    NASA Astrophysics Data System (ADS)

    Adak, Ashish; Sikdar, Arnab; Ghosh, Samiran; Khan, Manoranjan

    2016-06-01

    Nonlinear propagation of magnetosonic shock wave has been studied in collisional magnetized pair-ion plasma. The masses of both ions are same but the temperatures are slightly different. Two fluid model has been taken to describe the model. Two different modes of the magnetosonic wave have been obtained. The dynamics of the nonlinear magnetosonic wave is governed by the Korteweg-de Vries Burgers' equation. It has been shown that the ion-ion collision is the source of dissipation that causes the Burgers' term which is responsible for the shock structures in equal mass pair-ion plasma. The numerical investigations reveal that the magnetosonic wave exhibits both oscillatory and monotonic shock structures depending on the strength of the dissipation. The nonlinear wave exhibited the oscillatory shock wave for strong magnetic field (weak dissipation) and monotonic shock wave for weak magnetic field (strong dissipation). The results have been discussed in the context of the fullerene pair-ion plasma experiments.

  11. Collisional dynamics in a gas of molecular super-rotors

    NASA Astrophysics Data System (ADS)

    Khodorkovsky, Yuri; Steinitz, Uri; Hartmann, Jean-Michel; Averbukh, Ilya Sh.

    2015-07-01

    Recently, femtosecond laser techniques have been developed that are capable of bringing gas molecules to extremely fast rotation in a very short time, while keeping their translational motion relatively slow. Here we study collisional equilibration dynamics of this new state of molecular gases. We show that the route to equilibrium starts with a metastable `gyroscopic stage' in the course of which the molecules maintain their fast rotation and orientation of the angular momentum through many collisions. The inhibited rotational-translational relaxation is characterized by a persistent anisotropy in the molecular angular distribution, and is manifested in the optical birefringence and anisotropic diffusion in the gas. After a certain induction time, the `gyroscopic stage' is abruptly terminated by an explosive rotational-translational energy exchange, leading the gas towards the final equilibrium. We illustrate our conclusions by direct molecular dynamics simulation of several gases of linear molecules.

  12. The acoustic instabilities in magnetized collisional dusty plasmas

    SciTech Connect

    Pandey, B. P.; Vladimirov, S. V.; Dwivedi, C. B.

    2014-09-15

    The present work investigates the wave propagation in collisional dusty plasmas in the presence of electric and magnetic field. It is shown that the dust ion-acoustic waves may become unstable to the reactive instability whereas dust-acoustic waves may suffer from both reactive and dissipative instabilities. If the wave phase speed is smaller than the plasma drift speed, the instability is of reactive type whereas in the opposite case, the instability becomes dissipative in nature. Plasma in the vicinity of dust may also become unstable to reactive instability with the instability sensitive to the dust material: dielectric dust may considerably quench this instability. This has implications for the dust charging and the use of dust as a probe in the plasma sheath.

  13. Searching for Multiple Systems in Trojan Collisional Families and Centaurs

    NASA Astrophysics Data System (ADS)

    Marchis, Franck

    2006-08-01

    We propose to finalize our search for moonlet companions around Trojan asteroids using the Keck LGS AO capability at their opposition (Aug. for L5). We will focus on Trojans members of a collisional family to maximize the chance of detection, since recent study indicated than ~20% of the main-belt asteroid of the Koronis family are binary (Merline et al. 2005) and the discovery two moonlets orbiting around 87 Sylvia rubble-pile asteroid (Marchis et al. 2005) confirms that the collisions play a major role in the formation of binary systems. A search for binary Centaur asteroids, which may be connected to the Trojan family, will be initiated to complete the night.

  14. Searching for Multiple Systems in L5-Trojan Collisional Families

    NASA Astrophysics Data System (ADS)

    Marchis, Franck

    2007-02-01

    After our successfull search for binary moonlet in the L4 Trojan swarm, leading to the discovery of a moonlet around 624 Hektor (Marchis et al., 2006), we propose to conduct the same program in the L5 Trojan population at opposition in Apr. 2007. We will focus also on Trojans members of a collisional family to maximize the chance of detection, since recent study indicated than ~20% of the main-belt asteroid of the Koronis family are binary (Merline et al. 2005) and the discovery two moonlets orbiting around 87 Sylvia rubble-pile asteroid (Marchis et al. 2005) confirms that the collisions play a major role in the formation of binary systems.

  15. On collisional disruption - Experimental results and scaling laws

    NASA Technical Reports Server (NTRS)

    Davis, Donald R.; Ryan, Eileen V.

    1990-01-01

    Both homogeneous and inhomogeneous targets have been addressed by the present experimental consideration of the impact strengths, fragment sizes, and fragment velocities generated by cement mortar targets whose crushing strengths vary by an order of magnitude, upon impact of projectiles in the velocity range of 50-5700 m/sec. When combined with additional published data, dynamic impact strength is found to correlate with quasi-static material strengths for materials ranging in character from basalt to ice; two materials not following this trend, however, are weak mortar and clay targets. Values consistent with experimental results are obtainable with a simple scaling algorithm based on impact energy, material properties, and collisional strain rate.

  16. Collisionality dependence of the quasilinear particle flux due to microinstabilities

    SciTech Connect

    Fueloep, T.; Pusztai, I.; Helander, P.

    2008-07-15

    The collisionality dependence of the quasilinear particle flux due to the ion temperature gradient (ITG) and trapped electron mode (TEM) instabilities is studied by including electron collisions modeled by a pitch-angle scattering collision operator in the gyrokinetic equation. The inward transport due to ITG modes is caused mainly by magnetic curvature and thermodiffusion and can be reversed as electron collisions are introduced, if the plasma is far from marginal stability. However, if the plasma is close to marginal stability, collisions may even enhance the inward transport. The sign and the magnitude of the transport are sensitive to the form of the collision operator, to the magnetic drift normalized to the real frequency of the mode, and to the density and temperature scale lengths. These analytical results are in agreement with previously published gyrokinetic simulations. Unlike the ITG-driven flux, the TEM-driven flux is expected to be outwards for conditions far from marginal stability and inwards otherwise.

  17. MODELING COLLISIONAL CASCADES IN DEBRIS DISKS: THE NUMERICAL METHOD

    SciTech Connect

    Gaspar, Andras; Psaltis, Dimitrios; Oezel, Feryal; Rieke, George H.; Cooney, Alan E-mail: dpsaltis@as.arizona.edu E-mail: grieke@as.arizona.edu

    2012-04-10

    We develop a new numerical algorithm to model collisional cascades in debris disks. Because of the large dynamical range in particle masses, we solve the integro-differential equations describing erosive and catastrophic collisions in a particle-in-a-box approach, while treating the orbital dynamics of the particles in an approximate fashion. We employ a new scheme for describing erosive (cratering) collisions that yields a continuous set of outcomes as a function of colliding masses. We demonstrate the stability and convergence characteristics of our algorithm and compare it with other treatments. We show that incorporating the effects of erosive collisions results in a decay of the particle distribution that is significantly faster than with purely catastrophic collisions.

  18. Cosmochemical fractionation by collisional erosion during the Earth's accretion.

    PubMed

    Boujibar, Asmaa; Andrault, Denis; Bolfan-Casanova, Nathalie; Bouhifd, Mohamed Ali; Monteux, Julien

    2015-01-01

    Early in the Solar System's history, energetic collisions of differentiated bodies affected the final composition of the terrestrial planets through partial destruction. Enstatite chondrites (EC) are the best candidates to represent the primordial terrestrial precursors as they present the most similar isotopic compositions to Earth. Here we report that collisional erosion of >15% of the early Earth's mass can reconcile the remaining compositional differences between EC and the Earth. We base our demonstration on experimental melting of an EC composition at pressures between 1 bar and 25 GPa. At low pressures, the first silicate melts are highly enriched in incompatible elements Si, Al and Na, and depleted in Mg. Loss of proto-crusts through impacts raises the Earth's Mg/Si ratio to its present value. To match all major element compositions, our model implies preferential loss of volatile lithophile elements and re-condensation of refractory lithophile elements after the impacts. PMID:26395157

  19. Recombination and collisional X-UV lasers at ORSAY

    SciTech Connect

    Klisnick, A.; Carillon, A.; Dhez, P.; Goedtkindt, P.; Guennou, H.; Jamelot, G.; Jaegle, P.; Sureau, A.; Rus, B.; Zeitoun, P. ); Chenais-Popovics, C.; Renaudin, P.; Rancu, O.; Gauthier, J.C. ); Back, C.A. )

    1995-01-10

    In this paper we describe the progress achieved recently in our laboratory in the field of X-ray lasers. Both collisional excitation and recombination pumped systems are under investigation. We show that the 5g-4f transition in lithium-like ions could bring out a significant increase of the gain-length accessible with recombination X-ray lasers. We present preliminary results on an absorption spectroscopy experiment designed to probe the ionization state of recombination X-ray laser plasmas. Finally we report on the observation of a strong amplified signal at 212 A, the wavelength of a 3p-3s (J=0--1) in neon-like zinc. [copyright] 1995 [ital American] [ital Institute] [ital of] [ital Physics

  20. Spatial structure of a collisionally inhomogeneous Bose-Einstein condensate

    SciTech Connect

    Li, Fei; Zhang, Dongxia; Rong, Shiguang; Xu, Ying

    2013-11-15

    The spatial structure of a collisionally inhomogeneous Bose-Einstein condensate (BEC) in an optical lattice is studied. A spatially dependent current with an explicit analytic expression is found in the case with a spatially dependent BEC phase. The oscillating amplitude of the current can be adjusted by a Feshbach resonance, and the intensity of the current depends heavily on the initial and boundary conditions. Increasing the oscillating amplitude of the current can force the system to pass from a single-periodic spatial structure into a very complex state. But in the case with a constant phase, the spatially dependent current disappears and the Melnikov chaotic criterion is obtained via a perturbative analysis in the presence of a weak optical lattice potential. Numerical simulations show that a strong optical lattice potential can lead BEC atoms to a state with a chaotic spatial distribution via a quasiperiodic route.

  1. Short-Period Comets: Primordial Bodies or Collisional Fragments?

    PubMed

    Farinella; Davis

    1996-08-16

    Modeling results show that collisions among Edgeworth-Kuiper Belt Objects (EKOs), a vast swarm of small bodies orbiting beyond Neptune, have been a major process affecting this population and its progeny, the short-period comets. Most EKOs larger than about 100 kilometers in diameter survive over the age of the solar system, but at smaller sizes collisional breakup is frequent, producing a cascade of fragments having a power law size-frequency distribution. Collisions are also a plausible mechanism for injecting EKOs 1 to 10 kilometers in diameter into dynamical resonances, where they can be transported into the inner solar system to become short-period comets. The fragmental nature of these comets may explain their physical properties, such as shape, color, and strength. PMID:8688073

  2. Signal Propagation in Collisional Plasma with Negative Ions

    SciTech Connect

    I. Kaganovich; S.V. Berezhnoi; C.B. Shin

    2000-12-18

    The transport of charged species in collisional currentless plasmas is traditionally thought of as a diffusion-like process. In this paper, it is demonstrated that, in contrast to two-component plasma, containing electrons and positive ions, the transport of additional ions in multi-species plasmas is not governed by diffusion, rather described by nonlinear convection. As a particular example, plasmas with the presence of negative ions have been studied. The velocity of a small perturbation of negative ions was found analytically and validated by numerical simulation. As a result of nonlinear convection, initially smooth ion density profiles break and form strongly inhomogeneous shock-like fronts. These fronts are different from collisionless shocks and shocks in fully ionized plasma. The structure of the fronts has been found analytically and numerically.

  3. Collisional stabilization of van der Waals states of ozone

    NASA Astrophysics Data System (ADS)

    Ivanov, Mikhail V.; Babikov, Dmitri

    2011-05-01

    The mixed quantum-classical theory developed earlier [M. Ivanov and D. Babikov, J. Chem. Phys. 134, 144107 (2011)] is employed to treat the collisional energy transfer and the ro-vibrational energy flow in a recombination reaction that forms ozone. Assumption is that the van der Waals states of ozone are formed in the O + O2 collisions, and then stabilized into the states of covalent well by collisions with bath gas. Cross sections for collision induced dissociation of van der Waals states of ozone, for their stabilization into the covalent well, and for their survival in the van der Waals well are computed. The role these states may play in the kinetics of ozone formation is discussed.

  4. A collisional-radiative average atom model for hot plasmas

    SciTech Connect

    Rozsnyai, B.F.

    1996-10-17

    A collisional-radiative `average atom` (AA) model is presented for the calculation of opacities of hot plasmas not in the condition of local thermodynamic equilibrium (LTE). The electron impact and radiative rate constants are calculated using the dipole oscillator strengths of the average atom. A key element of the model is the photon escape probability which at present is calculated for a semi infinite slab. The Fermi statistics renders the rate equation for the AA level occupancies nonlinear, which requires iterations until the steady state. AA level occupancies are found. Detailed electronic configurations are built into the model after the self-consistent non-LTE AA state is found. The model shows a continuous transition from the non-LTE to the LTE state depending on the optical thickness of the plasma. 22 refs., 13 figs., 1 tab.

  5. The Violent Collisional History of Asteroid 4 Vesta

    NASA Astrophysics Data System (ADS)

    Marchi, S.; McSween, H. Y.; O'Brien, D. P.; Schenk, P.; De Sanctis, M. C.; Gaskell, R.; Jaumann, R.; Mottola, S.; Preusker, F.; Raymond, C. A.; Roatsch, T.; Russell, C. T.

    2012-05-01

    Vesta is a large differentiated rocky body in the main asteroid belt that accreted within the first few million years after the formation of the earliest solar system solids. The Dawn spacecraft extensively imaged Vesta’s surface, revealing a collision-dominated history. Results show that Vesta’s cratering record has a strong north-south dichotomy. Vesta’s northern heavily cratered terrains retain much of their earliest history. The southern hemisphere was reset, however, by two major collisions in more recent times. We estimate that the youngest of these impact structures, about 500 kilometers across, formed about 1 billion years ago, in agreement with estimates of Vesta asteroid family age based on dynamical and collisional constraints, supporting the notion that the Vesta asteroid family was formed during this event.

  6. Species separation and kinetic effects in collisional plasma shocks

    SciTech Connect

    Bellei, C. Wilks, S. C.; Amendt, P. A.; Rinderknecht, H.; Zylstra, A.; Rosenberg, M.; Sio, H.; Li, C. K.; Petrasso, R.

    2014-05-15

    The properties of collisional shock waves propagating in uniform plasmas are studied with ion-kinetic calculations, in both slab and spherical geometry and for the case of one and two ion species. Despite the presence of an electric field at the shock front—and in contrast to the case where an interface is initially present [C. Bellei et al., Phys. Plasmas 20, 044702 (2013)]—essentially no ion reflection at the shock front is observed due to collisions, with a probability of reflection ≲10{sup −4} for the cases presented. A kinetic two-ion-species spherical convergent shock is studied in detail and compared against an average-species calculation, confirming effects of species separation and differential heating of the ion species at the shock front. The effect of different ion temperatures on the DT and D{sup 3}He fusion reactivity is discussed in the fluid limit and is estimated to be moderately important.

  7. Collisional Time Scales in the Kuiper Disk and Their Implications

    NASA Technical Reports Server (NTRS)

    Stern, S. Alan

    1995-01-01

    We explore the rate of collisions among bodies in the present-day Kuiper Disk as a function of the total mass and population size structure of the disk. We find that collisional evolution is an important evolutionary process in the disk as a whole, and indeed, that it is likely the dominant evolutionary process beyond approx. 42 AU, where dynamical instability time scales exceed the age of the solar system. Two key findings we report from this modeling work are: that unless the disk's population structure is sharply truncated for radii smaller than approx. 1-2 km, collisions between comets and smaller debris are occurring so frequently in the disk, and with high enough velocities, that the small body (i.e., KM-class object) population in the disk has probably developed into a collisional cascade, thereby implying that the Kuiper Disk comets may not all be primordial, and that the rate of collisions of smaller bodies with larger 100 less R less 400 km objects (like 1992QB(sub 1) and its cohorts) is so low that there appears to be a dilemma in explaining how QB(sub 1)s could have grown by binary accretion in the disk as we know it. Given these findings, it appears that either the present-day paradigm for the formation of Kuiper Disk is failed in some fundamental respect, or that the present-day disk is no longer representative of the ancient structure from which it evolved. This in turn suggests the intriguing possibility that the present-day Kuiper Disk evolved through a more erosional stage reminiscent of the disks around the stars Beta Pictorus, alpha PsA, and alpha Lyr.

  8. THE COLLISIONAL DIVOT IN THE KUIPER BELT SIZE DISTRIBUTION

    SciTech Connect

    Fraser, Wesley C.

    2009-11-20

    This paper presents the results of collisional evolution calculations for the Kuiper Belt starting from an initial size distribution similar to that produced by accretion simulations of that region-a steep power-law large object size distribution that breaks to a shallower slope at r approx 1-2 km, with collisional equilibrium achieved for objects r approx< 0.5 km. We find that the break from the steep large object power law causes a divot, or depletion of objects at r approx 10-20 km, which, in turn, greatly reduces the disruption rate of objects with r approx> 25-50 km, preserving the steep power-law behavior for objects at this size. Our calculations demonstrate that the roll-over observed in the Kuiper Belt size distribution is naturally explained as an edge of a divot in the size distribution; the radius at which the size distribution transitions away from the power law, and the shape of the divot from our simulations are consistent with the size of the observed roll-over, and size distribution for smaller bodies. Both the kink radius and the radius of the divot center depend on the strength scaling law in the gravity regime for Kuiper Belt objects. These simulations suggest that the sky density of r approx 1 km objects is approx10{sup 6}-10{sup 7} objects per square degree. A detection of the divot in the size distribution would provide a measure of the strength of large Kuiper Belt objects, and constrain the shape of the size distribution at the end of accretion in the Kuiper Belt.

  9. Fluid-assisted melting in a collisional orogen

    NASA Astrophysics Data System (ADS)

    Berger, A.; Burri, T.; Engi, M.; Roselle, G. T.

    2003-04-01

    The Southern Steep Belt (SSB) of the Central Alps is the location of backthrusting during syn- to post-collisional deformation. From its metamorphic evolution and lithological contents the SSB has been interpreted as a tectonic accretion channel (TAC [1]). The central part of the SSB is additionally characterized by anatexites, leucogranitic aplites and pegmatites. Dehydration melting of muscovite is rare but did occurr locally. Moreover, no evidence of dehydration melting of biotite has been formed in that products of incongruent melting reactions (garnet, opx or cordierite) are missing. The melts are mainly produced by the infiltration of an external aqueous fluid. The fluids must have originated from the breakdown of hydrous minerals at temperatures below the water saturated solidus of the quartz-feldspar-system, such that the liberated fluids could not been trapped in the melt. Using the thermal modeling program MELONPIT [2] and assuming that solid fragments ascended in combination with tectonic accreated radioactive material, a complex thermal evolution inside the TAC has been derived. During subduction of the downgoing plate, isotherms were locally inverted, then subsequently relaxed, when subduction slowed down. At the collisional stage a small region develope, where the isotherms were still bent, and where temperatures increased during decompression. Assuming that dehydration reactions were followed by upward flow of fluids released from this region fluid present partial melting was triggered. The flow direction of the fluid was controlled by the pressure gradient and the steeply oriented foliations in the SSB. According to the model, the area of upward flowing fluids should be limited to the SSB. This is consistent with the observed regional distribution of leucosomes derived from in-situ melts. [1] Engi et al. (2001) Geology 29: 1143-1146 [2] Roselle et al. (2002) Am. J. Sci. 302: 381-409

  10. High-energy transients.

    PubMed

    Gehrels, Neil; Cannizzo, John K

    2013-06-13

    We present an overview of high-energy transients in astrophysics, highlighting important advances over the past 50 years. We begin with early discoveries of γ-ray transients, and then delve into physical details associated with a variety of phenomena. We discuss some of the unexpected transients found by Fermi and Swift, many of which are not easily classifiable or in some way challenge conventional wisdom. These objects are important insofar as they underscore the necessity of future, more detailed studies. PMID:23630376

  11. Transient nucleation in glasses

    NASA Technical Reports Server (NTRS)

    Kelton, K. F.

    1991-01-01

    Nucleation rates in condensed systems are frequently not at their steady state values. Such time dependent (or transient) nucleation is most clearly observed in devitrification studies of metallic and silicate glasses. The origin of transient nucleation and its role in the formation and stability of desired phases and microstructures are discussed. Numerical models of nucleation in isothermal and nonisothermal situations, based on the coupled differential equations describing cluster evolution within the classical theory, are presented. The importance of transient nucleation in glass formation and crystallization is discussed.

  12. Surface lysine residues modulate the collisional transfer of fatty acid from adipocyte fatty acid binding protein to membranes.

    PubMed

    Herr, F M; Matarese, V; Bernlohr, D A; Storch, J

    1995-09-19

    The transfer of unesterified fatty acids (FA) from adipocyte fatty acid binding protein (A-FABP) to phospholipid membranes is proposed to occur via a collisional mechanism involving transient ionic and hydrophobic interactions [Wootan & Storch (1994) J. Biol. Chem. 269, 10517-10523]. In particular, it was suggested that membrane acidic phospholipids might specifically interact with basic residues on the surface of A-FABP. Here we addressed whether lysine residues on the surface of the protein are involved in this collisional transfer mechanism. Recombinant A-FABP was acetylated to neutralize all positively charged surface lysine residues. Protein fluorescence, CD spectra, and chemical denaturant data indicate that acetylation did not substantially alter the conformational integrity of the protein, and nearly identical affinities were obtained for binding of the fluorescently labeled FA [12-(9-anthroyloxy)oleate] to native and acetylated protein. Transfer of 2-(9-anthroyloxy)palmitate (2AP) from acetylated A-FABP to small unilamellar vesicles (SUV) was 35-fold slower than from native protein. In addition, whereas the 2AP transfer rate from native A-FABP was directly dependent on SUV concentration, 2AP transfer from acetylated protein was independent on the concentration of acceptor membranes. Factors which alter aqueous-phase solubility of FA, such as ionic strength and acyl chain length and saturation, affected the AOFA transfer rate from acetylated but not native A-FABP. Finally, an increase in the negative charge density of the acceptor SUV resulted in a marked increase in the rate of transfer from native A-FABP but did not increase the rate from acetylated A-FABP.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:7547918

  13. Hydrogen electrosorption into Pd-Cd nanostructures.

    PubMed

    Adams, Brian D; Ostrom, Cassandra K; Chen, Aicheng

    2010-05-18

    Hydrogen-absorbing materials are crucial for both the purification and storage of hydrogen. Pd and Pd-based alloys have been studied extensively for their use as both hydrogen dissociation catalysts and hydrogen selective membrane materials. It is known that incorporating metal atoms of different sizes into the Pd lattice has a major impact on the hydrogen absorption process. In this paper, hydrogen electrosorption into nanostructured Pd-Cd alloys has been studied for different compositions of Cd that varied from 0 to 15 at. %. The low cost of Cd makes it an attractive material to combine with Pd for hydrogen sorption. A combination of chronoamperometry and cyclic voltammetric experiments was used to determine the ratio of the H/(Pd + Cd) and the kinetics of hydrogen sorption into these Pd-Cd alloys at different potentials. It was found that the maximum H/(Pd + Cd) value was 0.66 for pure Pd, and this decreased with increasing the amount of Cd. Also, the alpha (solid solution) to beta phase (metal hydride) hydrogen transition was determined to be the slowest step in the absorption process and was practically eliminated when an optimum amount of Cd atoms was doped (i.e., Pd-Cd(15%)). With increasing the amount of Cd, more hydrogen was absorbed into the Pd-Cd nanostructures at the higher potentials (the alpha phase region). The faster kinetics, along with the decrease in the phase transition of hydrogen sorption into the Pd-Cd nanostructures when compared to pure Pd, makes the Pd-Cd nanostructures attractive for use as a hydrogen dissociation catalytic capping layer for other metal hydrides or as a hydrogen selective membrane. PMID:20099788

  14. [Perioperative Management of PD Patients].

    PubMed

    Reichmann, H

    2016-07-01

    Both patients and caregivers but also treating physicians are concerned about complications along with surgical interventions. A major problem is abrupt cessation of anti-Parkinson medication, which leads to manifold disturbances, sometimes even to an akinetic crisis. There are several means to guarantee continuous dopaminergic stimulation even in patients that are not allowed to take medication orally before they undergo surgery. Amongst others rectally applied levodopa, amantadine infusions, and especially the use of a rotigotine patch are good means to overcome oral intake. Perioperative management is important due to the fact that in Germany alone each year more than 10 000 PD patients undergo surgery. Main reasons for this are fractures, but also elective interventions. Further emergency situations that cause treatment as an inpatient are psychosis, motoric disability, but also pneumonia and cardiovascular disturbances. In contrast PD patients suffer less often from cancer. PMID:27276074

  15. High energy transients

    NASA Technical Reports Server (NTRS)

    Woosley, S. E.

    1984-01-01

    A meeting was convened on the campus of the University of California at Santa Cruz during the two-week interval July 11 through July 22, 1983. Roughly 100 participants were chosen so as to give broad representation to all aspects of high energy transients. Ten morning review sessions were held in which invited speakers discussed the current status of observations and theory of the above subjects. Afternoon workshops were also held, usually more than one per day, to informally review various technical aspects of transients, confront shortcomings in theoretical models, and to propose productive courses for future research. Special attention was also given to the instrumentation used to study high energy transient and the characteristics and goals of a dedicated space mission to study transients in the next decade were determined. A listing of articles written by various members of the workshop is included.

  16. Strain effects on ensemble populations in AuPd/Pd(100) surface alloys

    NASA Astrophysics Data System (ADS)

    Stephens, J. Adam; Hwang, Gyeong S.

    2013-10-01

    The effects of applied strain on the arrangement of atoms in AuPd/Pd(100) surface alloys are studied using Monte Carlo simulations and cluster expansion Hamiltonians. The strain effects are found to be significant, with heteronuclear (Au-Pd) interactions more strongly enhanced by biaxial compression than homonuclear (Pd-Pd) ones. In particular, compressive strain causes an increase in the population of Pd monomers and second nearest-neighbor pairs of Pd monomers, both of which have been identified previously as important ensembles for various catalytic reactions. We also discuss the origin of these effects using density functional theory calculations of the surface electronic structure of strained AuPd/Pd(100).Our findings may suggest an additional means of employing strain to tune the catalytic properties of surface alloys.

  17. Gamma ray transients

    NASA Technical Reports Server (NTRS)

    Cline, Thomas L.

    1987-01-01

    The discovery of cosmic gamma ray bursts was made with systems designed at Los Alamos Laboratory for the detection of nuclear explosions beyond the atmosphere. HELIOS-2 was the first gamma ray burst instrument launched; its initial results in 1976, seemed to deepen the mystery around gamma ray transients. Interplanetary spacecraft data were reviewed in terms of explaining the behavior and source of the transients.

  18. Effects of Global Boundary and Local Collisionality on Magnetic Reconnection in a Laboratory Plasma

    SciTech Connect

    Kuritsyn, A.; Ji, H.; Gerhardt, S. P.; Ren, Y.; Yamada, M.

    2007-07-24

    The magnetic reconnection process is studied in a wide range of operating conditions in the well-controlled Magnetic Reconnection Experiment. The reconnection rate is observed to be a function of both global (i.e., system size) and local (collisionality) plasma parameters. When only local collisionality is lowered, the current sheet is shortened while effective resistivity is enhanced, both accelerating reconnection rates. At a fixed collisionality, the current sheet length increases with system size, resulting in the reduction of the reconnection rate. These results quantitatively agree with a generalized Sweet-Parker analysis.

  19. The Collisional and Radiative Processes of the Hydroxyl Radical

    NASA Astrophysics Data System (ADS)

    Steffens, Kristen Lisa

    1995-01-01

    The OH radical is an important species in the chemistry of atmospheric and combustion environments, where an understanding of OH concentration and chemistry is necessary to create and validate chemical models. Laser-induced fluorescence (LIF) is used with great success in OH detection, but OH LIF measurements require a vast knowledge of the collisional and spectroscopic properties of OH. Information is still lacking, especially concerning vibrational levels v^' > 0 of the rm A^2Sigma^+ electronic state. We investigate transition probabilities and collisional processes of these higher vibrational levels. Experimental vibrational band transition probabilities from v^' = 3 and 2 of OH rm A^2Sigma^+ are needed to determine the electronic transition moment for the rm A^2Sigma^+ -rm X^2Pi_{i } system to calculate a consistent set of rotational and vibrational dependent transition probabilities for uses including rm X^2Pi_ {i} temperature determinations and rm A^2Sigma^+ and rm X^2Pi_{i} nascent population determinations. Using LIF in a low -pressure CH_4/O_2 flame, we measured relative emission intensities for vibrational bands (3,0) through (3,5) and (2,0) through (2,6). Our emission intensities have been used in another study to determine the best rm A^2 Sigma^+-rm X^2 Pi_{i} electronic transition moment. For quantitative OH concentration measurements in high pressure flames exciting the predissociative v ^' = 3 level, one must account for vibrational energy transfer (VET). We measure the amounts of VET occurring from v^' = 3 in CH_4/O_2 , CH_4/air, and H _2/O_2 flames at pressures between 14 and 760 Torr. Significant amounts of VET occur in all flames and must be accounted for to get accurate OH concentrations. Stratospheric OH concentration measurement employs OH rm A^2Sigma^+v ^' = 1 excitation, which requires accurate VET and quenching cross sections for major colliders. We use LIF to measure the v^ ' = 1 VET and quenching cross sections for N_2, O_2 and CO_2

  20. Collisional transfer of population and orientation in NaK.

    PubMed

    Wolfe, C M; Ashman, S; Bai, J; Beser, B; Ahmed, E H; Lyyra, A M; Huennekens, J

    2011-05-01

    Collisional satellite lines with |ΔJ| ≤ 58 have been identified in recent polarization spectroscopy V-type optical-optical double resonance (OODR) excitation spectra of the Rb(2) molecule [H. Salami et al., Phys. Rev. A 80, 022515 (2009)]. Observation of these satellite lines clearly requires a transfer of population from the rotational level directly excited by the pump laser to a neighboring level in a collision of the molecule with an atomic perturber. However to be observed in polarization spectroscopy, the collision must also partially preserve the angular momentum orientation, which is at least somewhat surprising given the extremely large values of ΔJ that were observed. In the present work, we used the two-step OODR fluorescence and polarization spectroscopy techniques to obtain quantitative information on the transfer of population and orientation in rotationally inelastic collisions of the NaK molecules prepared in the 2(A)(1)Σ(+)(v' = 16, J' = 30) rovibrational level with argon and potassium perturbers. A rate equation model was used to study the intensities of these satellite lines as a function of argon pressure and heat pipe oven temperature, in order to separate the collisional effects of argon and potassium atoms. Using a fit of this rate equation model to the data, we found that collisions of NaK molecules with potassium atoms are more likely to transfer population and destroy orientation than collisions with argon atoms. Collisions with argon atoms show a strong propensity for population transfer with ΔJ = even. Conversely, collisions with potassium atoms do not show this ΔJ = even propensity, but do show a propensity for ΔJ = positive compared to ΔJ = negative, for this particular initial state. The density matrix equations of motion have also been solved numerically in order to test the approximations used in the rate equation model and to calculate fluorescence and polarization spectroscopy line shapes. In addition, we have measured

  1. Collisional model of quasilinear transport driven by toroidal electrostatic ion temperature gradient modes

    SciTech Connect

    Pusztai, I.; Fueloep, T.; Candy, J.; Hastie, R. J.

    2009-07-15

    The stability of ion temperature gradient (ITG) modes and the quasilinear fluxes driven by them are analyzed in weakly collisional tokamak plasmas using a semianalytical model based on an approximate solution of the gyrokinetic equation, where collisions are modeled by a Lorentz operator. Although the frequencies and growth rates of ITG modes far from threshold are only very weakly sensitive to the collisionality, the a/L{sub Ti} threshold for stability is affected significantly by electron-ion collisions. The decrease in collisionality destabilizes the ITG mode driving an inward particle flux, which leads to the steepening of the density profile. Closed analytical expressions for the electron and ion density and temperature responses have been derived without expansion in the smallness of the magnetic drift frequencies. The results have been compared with gyrokinetic simulations with GYRO and illustrated by showing the scalings of the eigenvalues and quasilinear fluxes with collisionality, temperature scale length, and magnetic shear.

  2. Reply to 'Comment on 'Collisional cooling investigation of THz rotational transitions of water''

    SciTech Connect

    Drouin, Brian J.; Pearson, John C.; Dick, Michael J.

    2010-09-15

    This response describes the authors' reaction to a critique of recent work on the ultracold physics of water. The possibility of spin-selective adsorption occurring in the context of the collisional cooling experiment is discussed.

  3. Accommodation of collisional shortening along the Alpine plate boundary : plate kinematics vs rheological controls

    NASA Astrophysics Data System (ADS)

    Rosenberg, Claudio; Bellahsen, Nicolas

    2016-04-01

    The style of collision in the Alps varies along strike, reflecting different amounts and different modes of accommodation of collisional shortening. These differences control the patterns of exhumation during collision. Whereas the western Alps largely consist of a metamorphic complex formed during subduction and largely exhumed before the initiation of collision, the subduction nappe-stack of the Central and the Eastern Alps is strongly overprinted by collisional shortening and by Barrovian metamorphism. Based on compiled and new data we estimate amounts of collisional shortening along the strike of the chain and set it in relationship to the geometry of the collisional prism. The western Alpine collisional structures form a very large (in map view), but moderately shortened wedge, terminating in front of a poorly developed Molasse basin. Shortening of this wedge was mainly localized along its external parts, resulting in accretion of basement and cover units thrusted towards the foreland. Back-folding and back-thrusting are barely developed and no shortening takes place in the upper, Adriatic plate. In the Central Alps, the amount of collisional shortening is larger and it is distributed both in the lower and in the upper plate. The collisional prism is bivergent and partitioning of the amount of shortening between the upper and lower plates varies along strike, being most probably controlled by rheological, heterogeneities. The thickened accreted lower plate is strongly affected by Barrovian metamorphism where shortening is largest and localized within a confined area. A deep Molasse basin developed in front of the prism. In the Eastern Alps collisional kinematics vary from east to west, with orogen-parallel displacements dominating in the east and orogen-perpendicular ones in the West, where they culminate in the structural and metamorphic dome of the Tauern Window. Nowhere else in the Alps collisional shortening is so strongly localized in one and the same

  4. The LOFAR Transients Pipeline

    NASA Astrophysics Data System (ADS)

    Swinbank, John D.; Staley, Tim D.; Molenaar, Gijs J.; Rol, Evert; Rowlinson, Antonia; Scheers, Bart; Spreeuw, Hanno; Bell, Martin E.; Broderick, Jess W.; Carbone, Dario; Garsden, Hugh; van der Horst, Alexander J.; Law, Casey J.; Wise, Michael; Breton, Rene P.; Cendes, Yvette; Corbel, Stéphane; Eislöffel, Jochen; Falcke, Heino; Fender, Rob; Grießmeier, Jean-Mathias; Hessels, Jason W. T.; Stappers, Benjamin W.; Stewart, Adam J.; Wijers, Ralph A. M. J.; Wijnands, Rudy; Zarka, Philippe

    2015-06-01

    Current and future astronomical survey facilities provide a remarkably rich opportunity for transient astronomy, combining unprecedented fields of view with high sensitivity and the ability to access previously unexplored wavelength regimes. This is particularly true of LOFAR, a recently-commissioned, low-frequency radio interferometer, based in the Netherlands and with stations across Europe. The identification of and response to transients is one of LOFAR's key science goals. However, the large data volumes which LOFAR produces, combined with the scientific requirement for rapid response, make automation essential. To support this, we have developed the LOFAR Transients Pipeline, or TraP. The TraP ingests multi-frequency image data from LOFAR or other instruments and searches it for transients and variables, providing automatic alerts of significant detections and populating a lightcurve database for further analysis by astronomers. Here, we discuss the scientific goals of the TraP and how it has been designed to meet them. We describe its implementation, including both the algorithms adopted to maximize performance as well as the development methodology used to ensure it is robust and reliable, particularly in the presence of artefacts typical of radio astronomy imaging. Finally, we report on a series of tests of the pipeline carried out using simulated LOFAR observations with a known population of transients.

  5. An Extended Magnetohydrodynamics Model for Relativistic Weakly Collisional Plasmas

    NASA Astrophysics Data System (ADS)

    Chandra, Mani; Gammie, Charles F.; Foucart, Francois; Quataert, Eliot

    2015-09-01

    Black holes that accrete far below the Eddington limit are believed to accrete through a geometrically thick, optically thin, rotationally supported plasma that we will refer to as a radiatively inefficient accretion flow (RIAF). RIAFs are typically collisionless in the sense that the Coulomb mean free path is large compared to {GM}/{c}2, and relativistically hot near the event horizon. In this paper we develop a phenomenological model for the plasma in RIAFs, motivated by the application to sources such as Sgr A* and M87. The model is derived using Israel–Stewart theory, which considers deviations up to second order from thermal equilibrium, but modified for a magnetized plasma. This leads to thermal conduction along magnetic field lines and a difference in pressure, parallel and perpendicular to the field lines (which is equivalent to anisotropic viscosity). In the non-relativistic limit, our model reduces to the widely used Braginskii theory of magnetized, weakly collisional plasmas. We compare our model to the existing literature on dissipative relativistic fluids, describe the linear theory of the plasma, and elucidate the physical meaning of the free parameters in the model. We also describe limits of the model when the conduction is saturated and when the viscosity implies a large pressure anisotropy. In future work, the formalism developed in this paper will be used in numerical models of RIAFs to assess the importance of non-ideal processes for the dynamics and radiative properties of slowly accreting black holes.

  6. Fragmentation efficiencies of peptide ions following low energy collisional activation

    NASA Astrophysics Data System (ADS)

    Summerfield, Scott G.; Gaskell, Simon J.

    1997-11-01

    Low energy fragmentations of protonated peptides in the gas phase are generally attributed to charge-directed processes. The extent and location of peptide backbone fragmentation is accordingly influenced by the extent to which charge is sequestered on amino acid side-chains. We describe systematic studies of the efficiencies of decomposition of peptide ions to assess in particular the influence of the presence of basic amino acid residues and of the protonation state. In a set of analogues containing two arginine, two histidine or two lysine residues, the extent of fragmentation of [M + 2H]2+ ions decreases with increased basicity, reflecting decreased backbone protonation. The collisionally activated dissociation of multiply protonated melittin ions shows an increase in fragmentation efficiency with higher charge state (using activation conditions which are similar for each charge state). For a single charge state, acetylation of primary amine groups increases fragmentation efficiency, consistent with the reduction in basicity of lysine side-chains. Conversion of arginine residues to the less basic dimethylpyrimidylornithine, however, decreases fragmentation efficiency, suggesting more effective sequestering of ionizing protons; the effect may be attributable to a disfavouring of proton-bridged structures but this hypothesis requires further study. Preliminary data for the decompositions of [M- 2H]2- ions derived from peptides containing two acidic residues suggest that the sequestration of charge away from the backbone is again detrimental to efficient fragmentation. Apparently diagnostic cleavages adjacent to aspartic acid residues are observed.

  7. Expansion of Collisional Radiative Model for Helium line ratio spectroscopy

    NASA Astrophysics Data System (ADS)

    Cinquegrani, David; Cooper, Chris; Forest, Cary; Milhone, Jason; Munoz-Borges, Jorge; Schmitz, Oliver; Unterberg, Ezekial

    2015-11-01

    Helium line ratio spectroscopy is a powerful technique of active plasma edge spectroscopy. It enables reconstruction of plasma edge parameters like electron density and temperature by use of suitable Collisional Radiative Models (CRM). An established approach is successful at moderate plasma densities (~1018m-3 range) and temperature (30-300eV), taking recombination and charge exchange to be negligible. The goal of this work is to experimentally explore limitations of this approach to CRM. For basic validation the Madison Plasma Dynamo eXperiment (MPDX) will be used. MPDX offers a very uniform plasma and spherical symmetry at low temperature (5-20 eV) and low density (1016 -1017m-3) . Initial data from MPDX shows a deviation in CRM results when compared to Langmuir probe data. This discrepancy points to the importance of recombination effects. The validated model is applied to first time measurement of electron density and temperature in front of an ICRH antenna at the TEXTOR tokamak. These measurements are important to understand RF coupling and PMI physics at the antenna limiters. Work supported in part by start up funds of the Department of Engineering Physics at the UW - Madison, USA and NSF CAREER award PHY-1455210.

  8. Nonextensive statistics and the sheath criterion in collisional plasmas

    SciTech Connect

    Hatami, M. M.

    2015-01-15

    The Bohm criterion in an electropositive plasma containing nonextensively distributed electrons and warm ions is investigated by using a steady state two-fluid model. Taking into account the ion-neutral collisions and finite temperature of ions, a modified Bohm criterion is derived which limits both maximum and minimum allowable velocity of ions at the sheath edge (u{sub 0i}). It is found that the degree of nonextensivity of electrons (q) and temperature of positive ions (T{sub i}) affect only the lower limit of the entrance velocity of ions into the sheath while the degree of ion collisionality (α) influences both lower and upper limits of the ion velocities at the sheath edge. In addition, depending on the value of q, it is shown that the minimum velocity of positive ions at the sheath edge can be greater or smaller than its Maxwellian counterpart. Moreover, it is shown that, depending on the values of α and T{sub i}, the positive ions with subsonic velocity may enter the sheath for either q > 1 or −1 < q < 1. Finally, as a practical application, the density distribution of charged particles in the sheath region is studied for different values of u{sub 0i}, and it is shown that monotonical reduction of the positive ion density distribution occurs only when the velocity of positive ions at the sheath edge lies between two above mentioned limits.

  9. On the inclusion of collisional correlations in quantum dynamics

    SciTech Connect

    Slama, N.; Reinhard, P.-G.; Suraud, E.

    2015-04-15

    We present a formalism to describe collisional correlations responsible for thermalization effects in finite quantum systems. The approach consists in a stochastic extension of time dependent mean field theory. Correlations are treated in time dependent perturbation theory and loss of coherence is assumed at some time intervals allowing a stochastic reduction of the correlated dynamics in terms of a stochastic ensemble of time dependent mean-fields. This theory was formulated long ago in terms of density matrices but never applied in practical cases because of its complexity. We propose here a reformulation of the theory in terms of wave functions and use a simplified 1D model of cluster and molecules allowing to test the theory in a schematic but realistic manner. We illustrate the performance in terms of several observables, in particular global moments of the density matrix and single particle entropy built on occupation numbers. The occupation numbers remain fixed in time dependent mean-field propagation and change when evaluating the correlations, then taking fractional values. They converge asymptotically towards Fermi distributions which is a clear indication of thermalization.

  10. Collisional excitation of electron Landau levels in strong magnetic fields

    NASA Technical Reports Server (NTRS)

    Langer, S. H.

    1981-01-01

    The cross sections for the excitation and deexcitation of the quantized transverse energy levels of an electron in a magnetic field are calculated for electron-proton and electron-electron collisions in light of the importance of the cross sections for studies of X-ray pulsar emission. First-order matrix elements are calculated using the Dirac theory of the electron, thus taking into account relativistic effects, which are believed to be important in accreting neutron stars. Results for the collisional excitation of ground state electrons by protons are presented which demonstrate the importance of proton recoil and relativistic effects, and it is shown that electron-electron excitations may contribute 10 to 20% of the excitation rate from electron-proton scattering in a Maxwellian plasma. Finally, calculations of the cross section for electron-proton small-angle scattering are presented which lead to relaxation rates for the electron velocity distribution which are modified by the magnetic field, and to a possible increase in the value of the Coulomb logarithm.

  11. Global, Collisional Model of High-Energy Photoelectrons

    NASA Technical Reports Server (NTRS)

    Khazanov, G. V.; Moore, T. E.; Liemohn, M. W.; Jordanova, V. K.; Fok, M.-C.

    1996-01-01

    A previously-developed colissional, interhemispheric flux tube model for photoelectrons (PE) has been extended to three dimensions by including transport due to vector E x vector B and magnetic gradient-curvature drifts. Using this model, initial calculations of the high-energy (greater then 50 eV) PE distribution as a function of time, energy, pitch angle, and spatial location in the equatorial plane, are reported for conditions of low geomagnetic activity. To explore both the dynamic and steady behaviors of the model, the simulation starts with the abrupt onset of photoelectron excitation, and is followed to steady state conditions. The results illustrate several features of the interaction of photoelectrons with typical magnetospheric plasmas and fields, including collisional diffusion of photoelectrons in pitch angle with flux tube filling, diurnal intensity and pitch angle asymmetries introduced by directional sunlight, and energization of the photoelectron distribution in the evening sector. Cross-field drift is shown to have a long time scale, taking 12 to 24 hours to reach a steady state distribution. Future applications of the model are briefly outlined.

  12. Collisional Grooming Models of the Kuiper Belt Dust Cloud

    NASA Technical Reports Server (NTRS)

    Kuchner, Marc J.; Stark, Christopher C.

    2010-01-01

    We modeled the three-dimensional structure of the Kuiper Belt (KB) dust cloud at four different dust production rates, incorporating both planet-dust interactions and grain-grain collisions using the collisional grooming algorithm. Simulated images of a model with a face-on optical depth of approximately 10 (exp -4) primarily show an azimuthally- symmetric ring at 40-47 AU in submillimeter and infrared wavelengths; this ring is associated with the cold classical KB. For models with lower optical depths (10 (exp -6) and 10 (exp-7)), synthetic infrared images show that the ring widens and a gap opens in the ring at the location of Neptune; this feature is caused by trapping of dust grains in Neptune's mean motion resonances. At low optical depths, a secondary ring also appears associated with the hole cleared in the center of the disk by Saturn. Our simulations, which incorporate 25 different grain sizes, illustrate that grain-grain collisions are important in sculpting today's KB dust, and probably other aspects of the solar system dust complex; collisions erase all signs of azimuthal asymmetry from the submillimeter image of the disk at every dust level we considered. The model images switch from being dominated by resonantly trapped small grains ("transport dominated") to being dominated by the birth ring ("collision dominated") when the optical depth reaches a critical value of r approximately v/c, where v is the local Keplerian speed.

  13. Effects of Collisional Dissipation on the "Colliding Beam Fusion Reactor "

    NASA Astrophysics Data System (ADS)

    Lampe, Martin; Manheimer, Wallace M.

    1998-11-01

    Rostoker, Binderbauer and Monkhorst have recently proposed a "colliding beam fusion reactor" (CBFR) for use with the p-B11 reaction. We have examined the various dissipative processes resulting from Coulomb collisions, and have concluded that the CBFR equilibrium cannot be sustained for long enough to permit net fusion gain. There are many collisional processes which occur considerably faster than fusion, and result in particle loss, energy loss, or detuning of the resonant energy for the p-B reaction. Pitch-angle scattering of protons off the boron beam, which occurs 100 times faster than fusion, isotropizes the proton beam and results in proton loss. Energy exchange between protons and boron, which is 20 times faster than fusion, detunes the resonance. Proton-proton scattering, which is faster than fusion for all CBFR scenarios, Maxwellianizes the protons and thus detunes the resonance. Ion-electron collisions lead indirectly to a friction between the two ion beams, which is typically fast compared to the fusion process. Results of Fokker-Planck analyses of each process will be shown.

  14. Isotope Effects in Collisional VT Relaxation of Molecular Hydrogen

    NASA Technical Reports Server (NTRS)

    Bieniek, R. J.

    2006-01-01

    A simple exponential-potential model of molecular collisions leads to a two-parameter analytic expression for rates of collisionally induced vibrational-translation (VT) energy exchange that has been shown to be accurate over variations of orders of magnitude as a function of temperature in a variety of systems. This includes excellent agreement with reported experimental and theoretical results for the fundamental self-relaxation rate of molecular hydrogen H2(v = 1) + H2 yields H2(v = 0) + H2. The analytic rate successfully follows the five-orders-of-magnitude change in experimental values for the temperature range 50-2000 K. This approach is now applied to isotope effects in the vibrational relaxation rates of excited HD and D2 in collision with H2: HD(v = 1)+H2 yields HD(v = 0)+H2 and D2(v = 1)+H2 yields D2(v = 0)+H2. The simplicity of the analytic expression for the thermal rate lends itself to convenient application in modeling the evolving vibrational populations of molecular hydrogen in shocked astrophysical environments.

  15. Triangularity effects on the collisional diffusion for elliptic tokamaks

    NASA Astrophysics Data System (ADS)

    Martín, Pablo; Castro, Enrique

    2015-09-01

    The effect of ellipticity and triangularity will be analyzed for axisymmetric tokamak in the collisional regime. Analytic forms for the magnetic field cross sections are taken from those derived recently by other authors. Analytic results can be obtained in elliptic plasmas with triangularity by using an special system of tokamak coordinates previously published. Our results show that triangularities smaller than 0.6 increase confinement for ellipticities in the range 1.2-2. This behavior happens for negative and positive triangularities, however this effect is stronger for negative than for positive triangularities. The maximum diffusion velocity is not obtained for zero triangularity, but for small negative triangularities. Ellipticity is also very important in confinement, but the effect of triangularity seems to be more important. High electric inductive fields increase confinement, though this field is difficult to modify once the tokamak has been built. The analytic form of the current produced by this field is like that of a weak Ware pinch with an additional factor, which weakens the effect by an order of magnitude. The dependence of the triangularity effect with the Shafranov shift is also analyzed.

  16. Evolution of a Gaussian laser beam in warm collisional magnetoplasma

    NASA Astrophysics Data System (ADS)

    Jafari, M. J.; Jafari Milani, M. R.; Niknam, A. R.

    2016-07-01

    In this paper, the spatial evolution of an intense circularly polarized Gaussian laser beam propagated through a warm plasma is investigated, taking into account the ponderomotive force, Ohmic heating, external magnetic field, and collisional effects. Using the momentum transfer and energy equations, both modified electron temperature and electron density in plasma are obtained. By introducing the complex dielectric permittivity of warm magnetized plasma and using the complex eikonal function, coupled differential equations for beam width parameter are established and solved numerically. The effects of polarization state of laser and magnetic field on the laser spot size evolution are studied. It is observed that in case of the right-handed polarization, an increase in the value of external magnetic field causes an increase in the strength of the self-focusing, especially in the higher values, and consequently, the self-focusing occurs in shorter distance of propagation. Moreover, the results demonstrate the existence of laser intensity and electron temperature ranges where self-focusing can occur, while the beam diverges outside of these regions; meanwhile, in these intervals, there exists a turning point for each of intensity and temperature in which the self-focusing process has its strongest strength. Finally, it is found that the self-focusing effect can be enhanced by increasing the plasma frequency (plasma density).

  17. Hiding in the Shadows. II. Collisional Dust as Exoplanet Markers

    NASA Astrophysics Data System (ADS)

    Dobinson, Jack; Leinhardt, Zoë M.; Lines, Stefan; Carter, Philip J.; Dodson-Robinson, Sarah E.; Teanby, Nick A.

    2016-03-01

    Observations of the youngest planets (˜1-10 Myr for a transitional disk) will increase the accuracy of our planet formation models. Unfortunately, observations of such planets are challenging and time-consuming to undertake, even in ideal circumstances. Therefore, we propose the determination of a set of markers that can preselect promising exoplanet-hosting candidate disks. To this end, N-body simulations were conducted to investigate the effect of an embedded Jupiter-mass planet on the dynamics of the surrounding planetesimal disk and the resulting creation of second-generation collisional dust. We use a new collision model that allows fragmentation and erosion of planetesimals, and dust-sized fragments are simulated in a post-process step including non-gravitational forces due to stellar radiation and a gaseous protoplanetary disk. Synthetic images from our numerical simulations show a bright double ring at 850 μm for a low-eccentricity planet, whereas a high-eccentricity planet would produce a characteristic inner ring with asymmetries in the disk. In the presence of first-generation primordial dust these markers would be difficult to detect far from the orbit of the embedded planet, but would be detectable inside a gap of planetary origin in a transitional disk.

  18. Constraining scalar fields with stellar kinematics and collisional dark matter

    SciTech Connect

    Amaro-Seoane, Pau; Barranco, Juan; Bernal, Argelia; Rezzolla, Luciano E-mail: jbarranc@aei.mpg.de E-mail: rezzolla@aei.mpg.de

    2010-11-01

    The existence and detection of scalar fields could provide solutions to long-standing puzzles about the nature of dark matter, the dark compact objects at the centre of most galaxies, and other phenomena. Yet, self-interacting scalar fields are very poorly constrained by astronomical observations, leading to great uncertainties in estimates of the mass m{sub φ} and the self-interacting coupling constant λ of these fields. To counter this, we have systematically employed available astronomical observations to develop new constraints, considerably restricting this parameter space. In particular, by exploiting precise observations of stellar dynamics at the centre of our Galaxy and assuming that these dynamics can be explained by a single boson star, we determine an upper limit for the boson star compactness and impose significant limits on the values of the properties of possible scalar fields. Requiring the scalar field particle to follow a collisional dark matter model further narrows these constraints. Most importantly, we find that if a scalar dark matter particle does exist, then it cannot account for both the dark-matter halos and the existence of dark compact objects in galactic nuclei.

  19. Consistent analytic approach to the efficiency of collisional Penrose process

    NASA Astrophysics Data System (ADS)

    Harada, Tomohiro; Ogasawara, Kota; Miyamoto, Umpei

    2016-07-01

    We propose a consistent analytic approach to the efficiency of collisional Penrose process in the vicinity of a maximally rotating Kerr black hole. We focus on a collision with arbitrarily high center-of-mass energy, which occurs if either of the colliding particles has its angular momentum fine-tuned to the critical value to enter the horizon. We show that if the fine-tuned particle is ingoing on the collision, the upper limit of the efficiency is (2 +√{3 })(2 -√{2 })≃2.186 , while if the fine-tuned particle is bounced back before the collision, the upper limit is (2 +√{3 })2≃13.93 . Despite earlier claims, the former can be attained for inverse Compton scattering if the fine-tuned particle is massive and starts at rest at infinity, while the latter can be attained for various particle reactions, such as inverse Compton scattering and pair annihilation, if the fine-tuned particle is either massless or highly relativistic at infinity. We discuss the difference between the present and earlier analyses.

  20. Potential around a dust grain in collisional plasma

    SciTech Connect

    Moulick, R. Goswami, K. S.

    2015-04-15

    The ion neutral collision can lead to interesting phenomena in dust charging, totally different from the expectations based on the traditional orbit motion limited theory. The potential around a dust grain is investigated for the collisional plasma considering the presence of ion neutral collisions. Fluid equations are solved for the one dimensional radial coordinate. It is observed that with the gradual increase in ion neutral collision, the potential structure around the dust grain changes its shape and is different from the usual Debye-Hückel potential. The shift however starts from a certain value of ion neutral collision and the electron-ion density varies accordingly. The potential variation is interesting and reconfirms the fact that there exists a region of attraction for negative charges. The collision modeling is done for the full range of plasma, i.e., considering the bulk and the sheath jointly. The potential variation with collision is also shown explicitly and the variation is found to cope up with the earlier observations.

  1. Direct and Collisional Excitation of Automotive Fuel Components)

    NASA Astrophysics Data System (ADS)

    White, Allen R.; Wilson, Kyle; Sakai, Stephen; Devasher, Rebecca B.

    2010-06-01

    Adding energy directly into the vibrational modes of automotive fuel may reduce the threshold energy required for combustion, without raising the combustion charge temperature. This energy can be supplied either directly via incident laser radiation or indirectly through collision with directly excited molecules. The most common chemical in commercial gasoline, isooctane, does not absorb infrared radiation sufficiently at any wavelength for which an infrared laser is readily available. However, CO2 lasers are relatively cheap, and are available at wavelengths which are absorbed by isopropanol as well as ethanol, which is also a component of commercial gasoline. In this study, the infrared absorption of isopropanol and ethanol in balance isooctane were measured at three wavelengths (10.6 m, 10.2 m, and 9.3 m) of incident CO2 laser radiation. Additional time-resolved emission measurements were performed for these mixtures. The data support the existence of the proposed collisional pathway for energy transfer from ethanol and isopropanol to isooctane.

  2. Collisional disruption of gravitational aggregates in the tidal environment

    SciTech Connect

    Hyodo, Ryuki; Ohtsuki, Keiji

    2014-05-20

    The degree of disruption in collisions in free space is determined by specific impact energy, and the mass fraction of the largest remnant is a monotonically decreasing function of impact energy. However, it has not been shown whether such a relationship is applicable to collisions under the influence of a planet's tidal force, which is important in ring dynamics and satellite accretion. Here we examine the collisional disruption of gravitational aggregates in the tidal environment by using local N-body simulations. We find that outcomes of such a collision largely depend on the impact velocity, the direction of impact, and the radial distance from the planet. In the case of a strong tidal field corresponding to Saturn's F ring, collisions in the azimuthal direction are much more destructive than those in the radial direction. Numerical results of collisions sensitively depend on the impact velocity, and a complete disruption of aggregates can occur even in impacts with velocity much lower than their escape velocity. In such low-velocity collisions, the deformation of colliding aggregates plays an essential role in determining collision outcomes, because the physical size of the aggregate is comparable to its Hill radius. On the other hand, the dependence of collision outcomes on impact velocity becomes similar to the case in free space when the distance from the planet is sufficiently large. Our results are consistent with Cassini observations of the F ring, which suggest ongoing creation and disruption of aggregates within the ring.

  3. COLLISIONAL GROOMING MODELS OF THE KUIPER BELT DUST CLOUD

    SciTech Connect

    Kuchner, Marc J.; Stark, Christopher C. E-mail: starkc@umd.ed

    2010-10-15

    We modeled the three-dimensional structure of the Kuiper Belt (KB) dust cloud at four different dust production rates, incorporating both planet-dust interactions and grain-grain collisions using the collisional grooming algorithm. Simulated images of a model with a face-on optical depth of {approx}10{sup -4} primarily show an azimuthally symmetric ring at 40-47 AU in submillimeter and infrared wavelengths; this ring is associated with the cold classical KB. For models with lower optical depths (10{sup -6} and 10{sup -7}), synthetic infrared images show that the ring widens and a gap opens in the ring at the location of Neptune; this feature is caused by trapping of dust grains in Neptune's mean motion resonances. At low optical depths, a secondary ring also appears associated with the hole cleared in the center of the disk by Saturn. Our simulations, which incorporate 25 different grain sizes, illustrate that grain-grain collisions are important in sculpting today's KB dust, and probably other aspects of the solar system dust complex; collisions erase all signs of azimuthal asymmetry from the submillimeter image of the disk at every dust level we considered. The model images switch from being dominated by resonantly trapped small grains ('transport dominated') to being dominated by the birth ring ('collision dominated') when the optical depth reaches a critical value of {tau} {approx} v/c, where v is the local Keplerian speed.

  4. A collisional family of icy objects in the Kuiper belt.

    PubMed

    Brown, Michael E; Barkume, Kristina M; Ragozzine, Darin; Schaller, Emily L

    2007-03-15

    The small bodies in the Solar System are thought to have been highly affected by collisions and erosion. In the asteroid belt, direct evidence of the effects of large collisions can be seen in the existence of separate families of asteroids--a family consists of many asteroids with similar orbits and, frequently, similar surface properties, with each family being the remnant of a single catastrophic impact. In the region beyond Neptune, in contrast, no collisionally created families have hitherto been found. The third largest known Kuiper belt object, 2003 EL61, however, is thought to have experienced a giant impact that created its multiple satellite system, stripped away much of an overlying ice mantle, and left it with a rapid rotation. Here we report the discovery of a family of Kuiper belt objects with surface properties and orbits that are nearly identical to those of 2003 EL61. This family appears to be fragments of the ejected ice mantle of 2003 EL61. PMID:17361177

  5. COLLISIONAL STRIPPING AND DISRUPTION OF SUPER-EARTHS

    SciTech Connect

    Marcus, Robert A.; Sasselov, Dimitar; Hernquist, Lars; Stewart, Sarah T.

    2009-08-01

    The final stage of planet formation is dominated by collisions between planetary embryos. The dynamics of this stage determine the orbital configuration and the mass and composition of planets in the system. In the solar system, late giant impacts have been proposed for Mercury, Earth, Mars, and Pluto. In the case of Mercury, this giant impact may have significantly altered the bulk composition of the planet. Here we present the results of smoothed particle hydrodynamics simulations of high-velocity (up to {approx}5v {sub esc}) collisions between 1 and 10 M {sub +} planets of initially terrestrial composition to investigate the end stages of formation of extrasolar super-Earths. As found in previous simulations of collisions between smaller bodies, when collision energies exceed simple merging, giant impacts are divided into two regimes: (1) disruption and (2) hit-and-run (a grazing inelastic collision and projectile escape). Disruption occurs when the impact parameter is near zero, when the projectile mass is small compared to the target, or at extremely high velocities. In the disruption regime, we derive the criteria for catastrophic disruption (when half the total colliding mass is lost), the transition energy between accretion and erosion, and a scaling law for the change in bulk composition (iron-to-silicate ratio) resulting from collisional stripping of a mantle.

  6. Langmuir probe measurements of weakly collisional electropositive RF discharge plasmas

    NASA Astrophysics Data System (ADS)

    Bryant, Paul; Dyson, Anthony; Allen, John E.

    2001-05-01

    We report on Langmuir probe measurements of low-pressure (0.1-20 Pa) electropositive plasmas in an RF discharge at 13.56 MHz. From the probe I-V characteristic it is found that the electron density inferred from the ion current in the ion saturation region using radial motion (Allen, Boyd and Reynolds, ABR) theory can be up to one-half that obtained directly from the electron current at the plasma potential. The reduction in the ion current is attributed to orbital motion (OM) of the ions and also to a small number of ion-neutral collisions in the presheath. We show that if a sufficiently large probe is chosen so as to minimize the OM effects then the collisional theory developed by Shih and Levi (1971) can be used to give an appropriate correction factor over a narrow pressure range. The corrected electron density is found to agree with the knee current value to typically 10% for Ar, N2 and Kr plasmas.

  7. Collisional Transfer of Population and Orientation in NaK

    NASA Astrophysics Data System (ADS)

    Wolfe, C. M.; Ashman, S.; Huennekens, J.; Beser, B.; Bai, J.; Lyyra, A. M.

    2010-03-01

    We report current work to study transfer of population and orientation in collisions of NaK molecules with argon and potassium atoms using polarization labeling (PL) and laser- induced fluorescence (LIF) spectroscopy. In the PL experiment, a circularly polarized pump laser excites a specific NaK A^1&+circ;(v'=16, J') <- X^1&+circ;(v''=0, J'±1) transition, creating an orientation (non-uniform MJ' level distribution) in both levels. The linearly polarized probe laser is scanned over various 3^1π(v, J'±1) <- A^1&+circ;(v'=16, J') transitions. The probe laser passes through a crossed linear polarizer before detection, and signal is recorded if the probe laser polarization has been modified by the vapor (which occurs when it comes into resonance with an oriented level). Using both spectroscopic methods, analysis of weak collisional satellite lines adjacent to these directly populated lines, as a function of argon buffer gas pressure and cell temperature, allows us to discern separately the effects collisions with argon atoms and potassium atoms have on the population and orientation of the molecule. In addition, code has been written which provides a theoretical analysis of the process, through a solution of the density matrix equations of motion for the system.

  8. Collisional energy transfer and quenching of electronic excitation

    PubMed Central

    Lin, S. H.; Eyring, H.

    1975-01-01

    The purpose of this paper has been to explore in a preliminary way the nature and mechanism of collisional energy transfer and quenching of electronic excitation. For this purpose, the Born approximation has been used, and the triplet-triplet and singlet-singlet transfer, and the triplet-triplet and singlet-singlet quenching have been studied. It has been shown theoretically that (i) the singlet-singlet transfer constants (or cross sections) are always larger than the triplet-triplet transfer constants (or cross sections) for the same system of donor and acceptor; (ii) for the singlet-singlet transfer, the observed cross section varies linearly with respect to the spectral overlap between the donor emission and the acceptor absorption; (iii) the reason that the quenching constants (or cross sections) are always smaller than the energy transfer constants (or cross sections) is due to the fact that for the quenching the vibration of the acceptor hardly participates in accepting the electronic excitation and for the energy transfer only part of the excited electron energy of the donor is converted into the energy of nuclear motion; and (iv) the polar acceptor molecules are better quenchers than nonpolar acceptor molecules. PMID:16592281

  9. Elimination of collisional dephasing by control laser fields

    NASA Astrophysics Data System (ADS)

    Sokolov, Alexei

    2003-05-01

    The perturbation of electronic states during a molecular collision results in an adiabatic shift of natural molecular frequencies. It is this frequency shift (integrated over the collision time) that produces an oscillation phase shift, and ultimately leads to dephasing of a molecular ensemble. However, the fact that during the collision all molecular levels shift in unison can be used to eliminate the shift of one selected transition, by applying a control laser field to an adjacent (control) transition. The amplitude and frequency of the control field can be adjusted such that the time-varying Stark shift produced by this field precisely compensates collisional frequency shift for the transition of interest, and as a result suppresses dephasing. This technique can possibly be extended to adiabatic atomic collisions, and to different types of inhomogeneous broadening. Earlier workers have demonstrated similar methods for Doppler width reduction, by utilizing velocity-dependent Stark shifts produced by control fields. There is also a relation of this proposal to electromagnetically induced transparency.

  10. The radial gradients and collisional properties of solar wind electrons

    NASA Technical Reports Server (NTRS)

    Gilvie, K. W.; Scudder, J. D.

    1977-01-01

    The plasma instrument on Mariner 10 carried out measurements of electron density and temperature in the interplanetary medium between heliocentric distances of 0.85 and 0.45 AU. Due to the stable coronal configuration and low solar activity during the period of observation, the radial variations of these quantities could be obtained. The power-law exponent of the core temperature was measured to be -0.3 + or - 0.04, and the halo temperature was found to be almost independent of heliocentric distance. The exponent of the power law for the density variation was 2.5 + or - 0.2 and the extrapolated value at 1 AU was consistent with measured values during the same period. Calculations of the core electron self-collision time, and the core-halo equipartition time were made as a function of radial distance. These measurements indicate a macroscale picture of a Coulomb-collisional core and a collisionless isothermal halo. Extrapolating back to the sun, core and halo temperatures become equal at a radial distance of approx. 2-15 radii.

  11. On collisional diffusion in a stochastic magnetic field

    SciTech Connect

    Abdullaev, S. S.

    2013-08-15

    The effect of particle collisions on the transport in a stochastic magnetic field in tokamaks is investigated. The model of resonant magnetic perturbations generated by external coils at the plasma edge is used for the stochastic magnetic field. The particle collisions are simulated by a random walk process along the magnetic field lines and the jumps across the field lines at the collision instants. The dependencies of the local diffusion coefficients on the mean free path λ{sub mfp}, the diffusion coefficients of field lines D{sub FL}, and the collisional diffusion coefficients, χ{sub ⊥} are studied. Based on these numerical data and the heuristic arguments, the empirical formula, D{sub r}=χ{sub ⊥}+v{sub ||}D{sub FL}/(1+L{sub c}/λ{sub mfp}), for the local diffusion coefficient is proposed, where L{sub c} is the characteristic length of order of the connection length l{sub c}=πqR{sub 0}, q is the safety factor, R{sub 0} is the major radius. The formula quite well describes the results of numerical simulations. In the limiting cases, the formula describes the Rechester-Rosenbluth and Laval scalings.

  12. On collisional diffusion in a stochastic magnetic field

    NASA Astrophysics Data System (ADS)

    Abdullaev, S. S.

    2013-08-01

    The effect of particle collisions on the transport in a stochastic magnetic field in tokamaks is investigated. The model of resonant magnetic perturbations generated by external coils at the plasma edge is used for the stochastic magnetic field. The particle collisions are simulated by a random walk process along the magnetic field lines and the jumps across the field lines at the collision instants. The dependencies of the local diffusion coefficients on the mean free path λmfp, the diffusion coefficients of field lines DFL, and the collisional diffusion coefficients, χ⊥ are studied. Based on these numerical data and the heuristic arguments, the empirical formula, Dr=χ⊥+v||DFL/(1+Lc/λmfp), for the local diffusion coefficient is proposed, where Lc is the characteristic length of order of the connection length lc=πqR0, q is the safety factor, R0 is the major radius. The formula quite well describes the results of numerical simulations. In the limiting cases, the formula describes the Rechester-Rosenbluth and Laval scalings.

  13. Collisional evolution - an analytical study for the non steady-state mass distribution.

    NASA Astrophysics Data System (ADS)

    Vieira Martins, R.

    1999-05-01

    To study the collisional evolution of asteroidal groups one can use an analytical solution for the self-similar collision cascades. This solution is suitable to study the steady-state mass distribution of the collisional fragmentation. However, out of the steady-state conditions, this solution is not satisfactory for some values of the collisional parameters. In fact, for some values for the exponent of the mass distribution power law of an asteroidal group and its relation to the exponent of the function which describes "how rocks break" the author arrives at singular points for the equation which describes the collisional evolution. These singularities appear since some approximations are usually made in the laborious evaluation of many integrals that appear in the analytical calculations. They concern the cutoff for the smallest and the largest bodies. These singularities set some restrictions to the study of the analytical solution for the collisional equation. To overcome these singularities the author performed an algebraic computation considering the smallest and the largest bodies and he obtained the analytical expressions for the integrals that describe the collisional evolution without restriction on the parameters. However, the new distribution is more sensitive to the values of the collisional parameters. In particular the steady-state solution for the differential mass distribution has exponents slightly different from 11/6 for the usual parameters in the asteroid belt. The sensitivity of this distribution with respect to the parameters is analyzed for the usual values in the asteroidal groups. With an expression for the mass distribution without singularities, one can evaluate also its time evolution. The author arrives at an analytical expression given by a power series of terms constituted by a small parameter multiplied by the mass to an exponent, which depends on the initial power law distribution. This expression is a formal solution for the

  14. Atomistic Modeling of Surface and Bulk Properties of Cu, Pd and the Cu-Pd System

    NASA Technical Reports Server (NTRS)

    Bozzolo, Guillermo; Garces, Jorge E.; Noebe, Ronald D.; Abel, Phillip; Mosca, Hugo O.; Gray, Hugh R. (Technical Monitor)

    2002-01-01

    The BFS (Bozzolo-Ferrante-Smith) method for alloys is applied to the study of the Cu-Pd system. A variety of issues are analyzed and discussed, including the properties of pure Cu or Pd crystals (surface energies, surface relaxations), Pd/Cu and Cu/Pd surface alloys, segregation of Pd (or Cu) in Cu (or Pd), concentration dependence of the lattice parameter of the high temperature fcc CuPd solid solution, the formation and properties of low temperature ordered phases, and order-disorder transition temperatures. Emphasis is made on the ability of the method to describe these properties on the basis of a minimum set of BFS universal parameters that uniquely characterize the Cu-Pd system.

  15. Association between PD-1/PD-L1 and T regulate cells in early recurrent miscarriage

    PubMed Central

    Li, Guiyu; Lu, Caixia; Gao, Jing; Wang, Xietong; Wu, Huanling; Lee, Chao; Xing, Baoxiang; Zhang, Qi

    2015-01-01

    In this study, we try to testify the relationship between the programmed cell death receptor-1 (PD-1)/programmed cell death ligand 1 (PD-L1) passway and Treg cells in maternal-fetal immune regulation through PD-1 blockade on lymphocytes of normal early pregnancy in vitro and investigation of the PD-1 and PD-L1 changes in early recurrent miscarriage patients. CD4+ CD25+ Treg cells and PD-1 (CD279) positive cell were detected in deciduas in early recurrent miscarriage patients by flow cytometry. And the normal early pregnant women were as controls. Meanwhile the mRNA level of PD-1 and molecular expression of PD-L1 in deciduas of early recurrent miscarriage patients were detected by real time RT-PCR test and Immunohistochemical staining respectively. Also through antibody blocking assay to block PD-1 on lymphocytes of normal early pregnancy in vitro further testify the relationship between PD-1/PD-L1 and Treg cells, the results were analyzed by flow cytometry. CD4+ CD25+ Treg cells decreased both in deciduas in RM (P < 0.05), and for all almost 100% Treg cells (CD4+ CD25+) expressed PD-1, but there was no difference between the PD-1 positive cells in decidual lymphocytes in RM and that in normal pregnancy women (P > 0.05). PD-L1 mRNA in deciduas decreased in RM (P < 0.001), but PD-1 mRNA no difference (P > 0.1). After PD-1 blockade there was no change in CD4+ CD25+ Treg cells percentage, while the CD4+ T cell percentage increased (P < 0.01), as well as the level of IFN-gamma in cells supernatant (P < 0.01). PD-1 blockade has a little influence on the number of Treg cells, and may lead to impaired Treg cells function, the decrease of PD-L1 may closely relates to the occurrence of early recurrent miscarriage and implies that Treg cells may through PD-1/PD-L1 pathway play a role of immunosuppression regulation, and the impairment of Treg cells function in recurrent early abortion cases may be due to PD-L1 decrease in deciduas or trophoblast cells rather than PD-1 change

  16. Degenerate four-wave mixing and phase conjugation in a collisional plasma

    SciTech Connect

    Federici, J.F.; Mansfield, D.K.

    1986-06-01

    Although degenerate four-wave mixing (DFWM) has many practical applications in the visible regime, no successful attempt has been made to study or demonstrate DFWM for wavelengths longer than 10..mu..m. Recently, Steel and Lam established plasma as a viable DFWM and phase conjugation (PC) medium for infrared, far-infrared, and microwaves. However, their analysis is incomplete since collisional effects were not included. Using a fluid description, our results demonstrate that when collisional absorption is small and the collisional mean-free path is shorter than the nonlinear density grating scale length, collisional heating generates a thermal force which substantially enhances the phase conjugate reflectivity. When the collisional attenuation length becomes comparable to the length of the plasma, the dominant effect is collisional absorption of the pump waves. Numerical estimates of the phase conjugate reflectivity indicate that for modest power levels, gains greater than or equal to1 are possible in the submillimeter to centimeter wavelength range. This suggests that a plasma is a viable PC medium at those long wavelengths. In addition, doubly DFWM is discussed.

  17. Dark energy and equation of state oscillations with collisional matter fluid in exponential modified gravity

    NASA Astrophysics Data System (ADS)

    Oikonomou, V. K.; Karagiannakis, N.; Park, Miok

    2015-03-01

    We study some aspects of cosmological evolution in a universe described by a viable curvature corrected exponential F (R ) gravity model, in the presence of matter fluids consisting of collisional matter and radiation. Particularly, we express the Friedmann-Robertson-Walker equations of motion in terms of parameters that are appropriate for describing the dark energy oscillations and compare the dark energy density and the dark energy equation of state parameter corresponding to collisional and noncollisional matter. In addition to these, and owing to the fact that the cosmological evolution of collisional and noncollisional matter universes, when quantified in terms of the Hubble parameter and the effective equation of states parameters, is very much alike, we further scrutinize the cosmological evolution study by extending the analysis to the study of matter perturbations in the matter domination era. We quantify this analysis in terms of the growth factor of matter perturbations, in which case the resulting picture of the cosmological evolution is clear, since collisional and noncollisional universes can be clearly distinguished. Interestingly enough, since it is known that the oscillations of the effective equation of state parameter around the phantom divide are undesirable and unwanted in F (R ) gravities, when these are considered for redshifts near the matter domination era and before, in the curvature corrected exponential model with collisional matter that we study here there exist oscillations that never cross the phantom divide. Therefore, this rather unwanted feature of the effective equation of state parameter is also absent in the collisional matter filled universe.

  18. A Pd/silica composite with highly uniform Pd nanoparticles on silica lamella via layered silicate

    NASA Astrophysics Data System (ADS)

    Hao, Jing; Cui, Zhi-Min; Cao, Chang-Yan; Song, Weiguo

    2016-08-01

    Pd nanoparticles was loaded on silica lamella via layered silicate through a simple ion-exchange and in situ reduction method. The obtained Pd/silica composite has Pd nanoparticles with highly uniform size dispersed well on the silica lamella. The Pd/silica composite is active and recoverable catalyst for the hydrogenation reaction and the reaction can be completed in a short time of 2 h at room temperature and 1 atm H2 pressure.

  19. The Transient Universe

    NASA Astrophysics Data System (ADS)

    Shappee, Benjamin John

    When one looks at the night sky, one usually gets the impression of a static and constant universe. Quite apart from appearances, the sky is teeming with violent, variable, and transient events that shape our universe. These capricious objects are not only penetrating probes into physical conditions too extreme for earthbound laboratories, but they are also useful tools to measure the universe. In this dissertation, I investigate the observational and theoretical properties of three classes of transient/variable objects: thermonuclear supernovae, Cepheid variable stars, and active galactic nuclei.

  20. Transient Uncoupling Induces Synchronization

    NASA Astrophysics Data System (ADS)

    Schröder, Malte; Mannattil, Manu; Dutta, Debabrata; Chakraborty, Sagar; Timme, Marc

    2015-07-01

    Finding conditions that support synchronization is a fertile and active area of research with applications across multiple disciplines. Here we present and analyze a scheme for synchronizing chaotic dynamical systems by transiently uncoupling them. Specifically, systems coupled only in a fraction of their state space may synchronize even if fully coupled they do not. While for many standard systems coupling strengths need to be bounded to ensure synchrony, transient uncoupling removes this bound and thus enables synchronization in an infinite range of effective coupling strengths. The presented coupling scheme therefore opens up the possibility to induce synchrony in (biological or technical) systems whose parameters are fixed and cannot be modified continuously.

  1. Transient Uncoupling Induces Synchronization.

    PubMed

    Schröder, Malte; Mannattil, Manu; Dutta, Debabrata; Chakraborty, Sagar; Timme, Marc

    2015-07-31

    Finding conditions that support synchronization is a fertile and active area of research with applications across multiple disciplines. Here we present and analyze a scheme for synchronizing chaotic dynamical systems by transiently uncoupling them. Specifically, systems coupled only in a fraction of their state space may synchronize even if fully coupled they do not. While for many standard systems coupling strengths need to be bounded to ensure synchrony, transient uncoupling removes this bound and thus enables synchronization in an infinite range of effective coupling strengths. The presented coupling scheme therefore opens up the possibility to induce synchrony in (biological or technical) systems whose parameters are fixed and cannot be modified continuously. PMID:26274420

  2. Laboratory Measurement of OH(υ = 2) Collisional Deactivation by Oxygen Atoms

    NASA Astrophysics Data System (ADS)

    Marschall, J.; Kalogerakis, K. S.; Copeland, R. A.

    2001-05-01

    Vibrationally excited hydroxyl radicals (υ = 6-9) are generated in the 80 to 100 km altitude range of the Earth's atmosphere by the reaction of atomic hydrogen with ozone. Low vibrational levels (υ < 5) are populated from the higher vibrational levels via collisions with molecular oxygen. For these low vibrational levels molecular oxygen relaxation is inefficient (1.3 - 17 x10-13 cm3-s-1 at room temperature [1]) and collisions with oxygen atoms may play an important role in the collisional lifetime in the atmosphere. Given the importance of O-atom collisions, we have developed an experimental approach and performed experiments on the collisional removal of OH(υ = 2) with O-atoms. In our experimental approach, we use the output of a pulsed excimer laser at 248 nm to photodissociate ozone in an O3/H2O/N2 mixture and the wavelength tunable output of a frequency-double Nd:YAG-pumped dye laser to probe the transient population of OH in the υ = 0, 1, and 2 vibrational levels using laser-induced fluorescence spectroscopy. Vibrationally excited OH molecules are produced, in vibrational levels up to and including υ = 2, through the exothermic reaction of O(1D) with water. By adjusting the composition of the O3/H2O/N2 mixture and by varying the 248 nm laser fluence to control the ozone dissociation fraction, the dominant relaxation partner can be varied systematically from ozone and water to atomic oxygen. We can dissociate > 90% of the ozone in the beam with easily obtainable laser fluences, generating copious amounts of O atoms. Using this method we obtained a preliminary rate constant of 4 \\pm 1 x10-11 cm3-s-1 for removal of OH(υ = 2) with O atoms. This rate constant is only slightly larger than the value of 3.3 \\pm 0.7 x10-11 cm3-s-1 for the reaction of OH(υ = 0) with O atoms to generate H atoms and oxygen molecules [2]. This weak dependence of OH loss rates on vibrational excitation is in contrast to previous measurements indicating a factor of 3 to 5 increase

  3. Selective reduction of a Pd pincer PCP complex to well-defined Pd(0) species.

    PubMed

    Melero, Cristóbal; Martínez-Prieto, Luis M; Palma, Pilar; del Rio, Diego; Alvarez, Eleuterio; Cámpora, Juan

    2010-12-14

    Well-defined dimeric or polymeric Pd(0) complexes [Pd(μ-(iPr)PCHP)](n) (n = 2 or ∞) containing the bridging ligand α,α'-bis(diisopropylphosphino)-m-xylene ((iPr)PCHP) are produced under mild conditions when the cyclometallated PCP pincer complex ((iPr)PCP)Pd-OH reacts with methanol or isopropanol. PMID:20967320

  4. PD-1/PD-L1 blockade in cancer treatment: perspectives and issues.

    PubMed

    Hamanishi, Junzo; Mandai, Masaki; Matsumura, Noriomi; Abiko, Kaoru; Baba, Tsukasa; Konishi, Ikuo

    2016-06-01

    Recent studies showed that tumor cells 'edit' host immunity in several ways to evade immune defenses in the tumor microenvironment. This phenomenon is called "cancer immune escape." One of the most important components in this system is an immunosuppressive co-signal (immune checkpoint) mediated by the PD-1 receptor and its ligand, PD-L1. PD-1 is mainly expressed on activated T cells, whereas PD-L1 is expressed on several types of tumor cells. Preclinical studies have shown that inhibition of the interaction between PD-1 and PD-L1 enhances the T-cell response and mediates antitumor activity. Several clinical trials of PD-1/PD-L1 signal-blockade agents have exhibited dramatic antitumor efficacy in patients with certain types of solid or hematological malignancies. In this review, we highlight recent clinical trials using anti-PD-1 or anti-PD-L1 antibodies against several types of malignancies, including a trial conducted in our department, and describe the clinical perspectives and issues regarding the PD-1/PD-L1 blockade in cancer treatment. PMID:26899259

  5. Methane Oxidation on Pd-Ceria. A DFT Study of the Combustion Mechanism over Pd, PdO and Pd-ceria Sites

    SciTech Connect

    Mayernick, Adam D.; Janik, Michael J.

    2010-12-24

    Palladium/ceria exhibits unique catalytic activity for hydrocarbon oxidation; however, the chemical and structural properties of active sites on the palladium–ceria surface are difficult to characterize. Strong interactions between palladium and the ceria support stabilize oxidized Pdδ+ species, which may contribute to the significant activity of Pd/ceria for methane oxidation. We present a density functional theory (DFT + U) investigation into methane oxidation over Pd/ceria and quantify the activity of the PdxCe1-xO2(1 1 1) mixed oxide surface in comparison with the PdO(1 0 0) and Pd(1 1 1) surfaces. The methane activation barrier is lowest over the PdxCe1-xO2(1 1 1) surface, even lower than over the Pd(1 1 1) surface or low coordinated stepped or kinked Pd sites. Subsequent reaction steps in complete oxidation, including product desorption and vacancy refilling, are considered to substantiate that methane activation remains the rate-limiting step despite the low barrier over PdxCe1-xO2(1 1 1). The low barrier over the PdxCe1-xO2(1 1 1) surface demonstrates that mixed ceria-noble metal oxides offer the potential for improved hydrocarbon oxidation performance with respect to dispersed noble metal particles on ceria.

  6. Element-selective investigation of domain structure in CoPd and FePd alloys using small-angle soft X-ray scattering

    NASA Astrophysics Data System (ADS)

    Weier, C.; Adam, R.; Frömter, R.; Bach, J.; Winkler, G.; Kobs, A.; Oepen, H. P.; Grychtol, P.; Kapteyn, H. C.; Murnane, M. M.; Schneider, C. M.

    2014-03-01

    Recent optical pump-probe experiments on magnetic multilayers and alloys identified perpendicular spin superdiffusion as one of possible mechanisms responsible for femtosecond magnetization dynamics. On the other hand, no strong evidence for the ultrafast lateral spin transport has been reported, so far. To address this question, we studied magnetic domain structure of CoPd and FePd thin films using small-angle scattering of soft X-rays. By tuning the synchrotron-generated X-rays to the absorption edges of Fe or Co we recorded Fourier images of the magnetic domain structure corresponding to a chosen element. Applying in - situ magnetic fields resulted in pronounced rearrangement of domain structure that was clearly observed in scattering images. Our analysis of both the stand-alone, as well as magnetically coupled CoPd/FePd layers provides insight into the formation of domains under small magnetic field perturbations and pave the way to better understanding of transient changes expected in magneto-dynamic measurements.

  7. Immune biomarkers PD-1/PD-L1 and TLR3 in malignant pleural mesotheliomas.

    PubMed

    Combaz-Lair, Christelle; Galateau-Sallé, Françoise; McLeer-Florin, Anne; Le Stang, Nolwenn; David-Boudet, Laurence; Duruisseaux, Mickael; Ferretti, Gilbert R; Brambilla, Elisabeth; Lebecque, Serge; Lantuejoul, Sylvie

    2016-06-01

    Malignant pleural mesothelioma (MPM) is an aggressive tumor with no effective therapy. However PD-L1/PD-1 immunity checkpoint therapies gave encouraging results; TLR3 is a programmed death factor, which triggering up-regulates PD-L1. As PD-1/PD-L1 blocking antibodies could restore antitumor immune responses alone or in combination with TLR3 agonists, we investigated PD-L1/PD-1 and TLR3 expressions in MPM to select patients for immunotherapy. Sixty-eight pleural surgical specimens, including 58 MPM (epithelioid, n = 34; biphasic, n = 11; sarcomatoid, n = 13) and 10 benign lesions, were studied. PD-L1 expression was assessed using E1L3N and SP142 clones in tumor cells (TCs) and in tumor-infiltrating lymphocytes (TILs) (positivity threshold of 1%), and compared with overall survival. PD-1, CD3 and CD8 expression by TILs, and TLR3 expression by TCs were analyzed concomitantly. PD-L1 was more expressed by sarcomatoid subtype than by other MPM (62% versus 23% and 9% for E1L3N; 38% versus 11% for SP142) (P = .01 and .04, respectively). Specificity and sensitivity of E1L3N and SP142 were of 53% and 98%, and 90% and 86%, respectively. PD-L1 expression by TILs and TCs correlated for SP142 (P = .023), and PD-L1 SP142 expression by TCs was associated with shorter overall survival (P = .016). TLR3 was expressed in most MPM, but weakly in sarcomatoid MPM. We confirm by comparing two commercially available antibodies that PD-L1 expression is higher in sarcomatoid MPM and correlates with a shorter survival. Whereas TLR3 agonists could be tested in MPM expressing TLR3, the sarcomatoid subtype could benefit from anti-PD-L1/PD-1 therapies alone or in combination. PMID:26980049

  8. Spectroscopy and electronic structure of jet-cooled NiPd and PdPt

    NASA Astrophysics Data System (ADS)

    Taylor, Scott; Spain, Eileen M.; Morse, Michael D.

    1990-03-01

    Resonant two-photon ionization spectroscopy of jet-cooled NiPd and PdPt has revealed a dense vibronic spectrum for NiPd and a much more sparse spectrum for PdPt. Four vibrational progressions have been identified for NiPd, and three have been located for PdPt. High resolution investigations of NiPd have established a ground state bond length of r″0 =2.242±0.005 Å with Ω″=2. The observed spectra have been used to bracket the ionization potentials, giving IP(NiPd)=7.18±0.76 eV and IP(PdPt)=8.27±0.38 eV. In contrast to previous work on Ni2, NiPt, and Pt2, no abrupt onset of rapid predissociation is observed for either NiPd or PdPt. A discussion of this result in terms of the expected potential energy curves for the palladium-containing diatomics is presented, which when combined with the frequencies of the highest energy vibronic bands observed yields estimates of D0(NiPd)≊1.46 eV and D0(PdPt)≊1.98 eV. The lack of observable vibronic transitions in Pd2 above 11 375 cm-1 places D0(Pd2) below 1.41 eV, in agreement with Knudsen effusion mass spectrometry. Finally a comparison of the platinum group dimers and the coinage metal dimers is given, demonstrating the increasing importance of d-orbital contributions to the bonding in the platinum group dimers as one moves down the periodic table. The anomalous behavior of the palladium-containing diatomics is also discussed in terms of the highly stable 4d105s0, 1S0 ground state of atomic palladium.

  9. Measuring Transient Memory Load

    ERIC Educational Resources Information Center

    Wanner, Eric; Shiner, Sandra

    1976-01-01

    Two experiments are reported in which subjects performed simple mental arithmetic problems which were presented visually in a sequential fashion. At some point in the presentation of each problem, the sequential display was interrupted and a memory task introduced. The purpose was to validate a measure of transient memory load. (Author/RM)

  10. Rotor transient analysis

    NASA Technical Reports Server (NTRS)

    Allaire, P. E.; Choy, K. C.; Gunter, E. J.

    1980-01-01

    Undamped modes approximate dynamic behavior of rotors and bearings. Application of modal analysis to uncouple equations of motion simplifies stability, steady-state unbalance response, and transient response analysis of system; nonlinear stability is predicted from calculated frequency spectra. Analysis provides designers with complete information without involving large-scale computational costs. Programs are written in FORTRAN IV for use on CDC 6600 computer.

  11. Measurements of ejection velocities in collisional disruption of ice spheres

    NASA Astrophysics Data System (ADS)

    Arakawa, Masahiko; Higa, Michiya

    1996-09-01

    Impact experiments are performed on ice spheres to measure the velocity field of ejected ice fragments and the conditions under which the fragments would reaccumulate during accretion in the outer solar system are considered. A single-stage light gas gun set in a cold room at -18°C and an image-converter camera running at 2 × 10 5-1 × 10 4 frames per second with a xenon flash lamp are used for observing the collisional phenomena. Spherical projectiles of ice ( mp = 1.5 g) collide head-on with spherical targets ( Mt = 1.5, 12, 172 g) at 150-690 m s -1. The ejection velocity is observed to vary with the initial position and ranges from 3 to 1/10 of the impact velocity ( Vi). The ejection velocity of fragments at the rear side of the target ( Ve) varies with distance from the impact point according to a power law relation, V e = V a( 1/D) -n, where Va is the antipodal velocity, l and D are the distance and the target diameter, and n = 1.5-2.0. Va depends on the specific energy ( Q) at a constant mass ratio ( m p/M t = 0.13 ) and the empirical dependence is written as Va = 0.35 × Q0.52. The ejection velocity of fine fragments formed by the jetting process near the impact point is determined to be 1.7-2.9 times as large as the impact velocity irrespective of the target size and the impact velocity.

  12. Evolving Magnetic Reconnection in Well Confined Plasmas with Low Collisionalities*

    NASA Astrophysics Data System (ADS)

    Coppi, B.

    2009-11-01

    There are two kinds of modes, producing large scale magnetic islands in well confined plasmas with low degrees of collisionality. These have phase velocities of opposite signs and are expected to emerge following the excitation of other modes as they cannot be found to be linearly unstable. One type is the ``drift-tearing'' [1] mode with a phase velocity in the direction of the electron diamagnetic velocity (vde) and the other is classified as an ``inductive'' mode [2] with a phase velocity in the direction of vdi. The ``drift-tearing'' can be excited after a mode that has the effect of decreasing the ratio of the longitudinal to the transverse electron thermal conductivity, like the ``micro-reconnecting'' mode discussed in Ref. [3]. The second type requires the previous excitation of a pressure gradient driven mode [4] that has a flow velocity in the vdi direction. Moreover, a mode-particle resonance with a high energy particle population [1] is involved in the growth of both the primary and the secondary (reconnecting) mode. Recent experimental observations [4] are consistent with these conclusions. Sawtooth oscillations that involve periodic reconnection events and modes that are related to those described earlier are discussed. *Sponsored in part by the U.S. DoE. [1] B. Coppi, Phys. Fluids 8, 2273 (1965) [2] B. Coppi, Bull. Am. Phys. Soc 45, 366 (2000) [3] B. Coppi, in ``Collective Phenomena etc.'' pg. 59, Eds. G. Bertin et. al., Publ. World Scientific (2007) [4] P. Buratti et al. Paper 02.007, 2009 E.P.S. Conference

  13. BUOYANCY INSTABILITIES IN A WEAKLY COLLISIONAL INTRACLUSTER MEDIUM

    SciTech Connect

    Kunz, Matthew W.; Stone, James M.; Bogdanovic, Tamara; Reynolds, Christopher S. E-mail: jstone@astro.princeton.edu E-mail: chris@astro.umd.edu

    2012-08-01

    The intracluster medium (ICM) of galaxy clusters is a weakly collisional plasma in which the transport of heat and momentum occurs primarily along magnetic-field lines. Anisotropic heat conduction allows convective instabilities to be driven by temperature gradients of either sign: the magnetothermal instability (MTI) in the outskirts of clusters and the heat-flux buoyancy-driven instability (HBI) in their cooling cores. We employ the Athena magnetohydrodynamic code to investigate the nonlinear evolution of these instabilities, self-consistently including the effects of anisotropic viscosity (i.e., Braginskii pressure anisotropy), anisotropic conduction, and radiative cooling. We find that, in all but the innermost regions of cool-core clusters, anisotropic viscosity significantly impairs the ability of the HBI to reorient magnetic-field lines orthogonal to the temperature gradient. Thus, while radio-mode feedback appears necessary in the central few Multiplication-Sign 10 kpc, heat conduction may be capable of offsetting radiative losses throughout most of a cool core over a significant fraction of the Hubble time. Magnetically aligned cold filaments are then able to form by local thermal instability. Viscous dissipation during cold filament formation produces accompanying hot filaments, which can be searched for in deep Chandra observations of cool-core clusters. In the case of MTI, anisotropic viscosity leads to a nonlinear state with a folded magnetic field structure in which field-line curvature and field strength are anti-correlated. These results demonstrate that, if the HBI and MTI are relevant for shaping the properties of the ICM, one must self-consistently include anisotropic viscosity in order to obtain even qualitatively correct results.

  14. Buoyancy Instabilities in a Weakly Collisional Intracluster Medium

    NASA Astrophysics Data System (ADS)

    Kunz, Matthew W.; Bogdanović, Tamara; Reynolds, Christopher S.; Stone, James M.

    2012-08-01

    The intracluster medium (ICM) of galaxy clusters is a weakly collisional plasma in which the transport of heat and momentum occurs primarily along magnetic-field lines. Anisotropic heat conduction allows convective instabilities to be driven by temperature gradients of either sign: the magnetothermal instability (MTI) in the outskirts of clusters and the heat-flux buoyancy-driven instability (HBI) in their cooling cores. We employ the Athena magnetohydrodynamic code to investigate the nonlinear evolution of these instabilities, self-consistently including the effects of anisotropic viscosity (i.e., Braginskii pressure anisotropy), anisotropic conduction, and radiative cooling. We find that, in all but the innermost regions of cool-core clusters, anisotropic viscosity significantly impairs the ability of the HBI to reorient magnetic-field lines orthogonal to the temperature gradient. Thus, while radio-mode feedback appears necessary in the central few× 10 kpc, heat conduction may be capable of offsetting radiative losses throughout most of a cool core over a significant fraction of the Hubble time. Magnetically aligned cold filaments are then able to form by local thermal instability. Viscous dissipation during cold filament formation produces accompanying hot filaments, which can be searched for in deep Chandra observations of cool-core clusters. In the case of MTI, anisotropic viscosity leads to a nonlinear state with a folded magnetic field structure in which field-line curvature and field strength are anti-correlated. These results demonstrate that, if the HBI and MTI are relevant for shaping the properties of the ICM, one must self-consistently include anisotropic viscosity in order to obtain even qualitatively correct results.

  15. Collisional processes and transfer of mass among the planetary satellites

    NASA Astrophysics Data System (ADS)

    Marchi, S.; Dell'Oro, A.; Paolicchi, P.; Barbieri, C.

    2001-08-01

    Several pairs of planetary satellites may have been involved, during the history of the Solar System, in mutual mass transfer processes. Such processes can be triggered by catastrophic collisions of a satellite (parent body) with a third object. As a consequence, the collision fragments are injected into independent orbits that can cross the trajectory of the another satellite (target). These swarms of secondary impacts may be of some importance influencing the properties of the target body. Even the formation of the atmosphere around some giant satellites may have been triggered by the gas released after the impacts of fragments onto the target's surface. Moreover, the different albedos and the different surface density of impact craters within the same satellite system may be connected to peculiar collisional phenomena, such as those we are dealing with. A quantitative modelling of the role of mass transfer processes obviously requires an estimate of how much material the parent bodies are able to supply, and under what circumstances the process may take place. A general analysis of the various pairs throughout the major satellite systems present in the Solar System has been performed in the present paper. Our analysis uses a statistical algorithm, computing, as a function of the initial properties of the fragments (masses and ejection velocities from their parent body), the mean intrinsic probability of impact, and then the mean lifetime of a fragment before impacting the target, as well as the distribution of the relative velocity. For an order-of-magnitude estimate of the available amount of mass, some simple analytical equations have been derived to evaluate the fraction of fragments from the parent body that can reach the target. These formulae allow a preliminary discrimination of the interesting cases. The pair Hyperion-Titan and the Uranus system have been analyzed in detail.

  16. Immune targeting of PD-1{sup hi} expressing cells during and after antiretroviral therapy in SIV-infected rhesus macaques

    SciTech Connect

    Vargas-Inchaustegui, Diego A.; Xiao, Peng; Hogg, Alison E.; Demberg, Thorsten; McKinnon, Katherine; Venzon, David; Brocca-Cofano, Egidio; DiPasquale, Janet; Lee, Eun M.; Hudacik, Lauren; Pal, Ranajit; Sui, Yongjun; Berzofsky, Jay A.; Liu, Linda; Langermann, Solomon; Robert-Guroff, Marjorie

    2013-12-15

    High-level T cell expression of PD-1 during SIV infection is correlated with impaired proliferation and function. We evaluated the phenotype and distribution of T cells and Tregs during antiretroviral therapy plus PD-1 modulation (using a B7-DC-Ig fusion protein) and post-ART. Chronically SIV-infected rhesus macaques received: 11 weeks of ART (Group A); 11 weeks of ART plus B7-DC-Ig (Group B); 11 weeks of ART plus B7-DC-Ig, then 12 weeks of B7-DC-Ig alone (Group C). Continuous B7-DC-Ig treatment (Group C) decreased rebound viremia post-ART compared to pre-ART levels, associated with decreased PD-1{sup hi} expressing T cells and Tregs in PBMCs, and PD-1{sup hi} Tregs in lymph nodes. It transiently decreased expression of Ki67 and α{sub 4}β{sub 7} in PBMC CD4{sup +} and CD8{sup +} Tregs for up to 8 weeks post-ART and maintained Ag-specific T-cell responses at low levels. Continued immune modulation targeting PD-1{sup hi} cells during and post-ART helps maintain lower viremia, keeps a favorable T cell/Treg repertoire and modulates antigen-specific responses. - Highlights: • B7-DC-Ig modulates PD-1{sup hi} cells in SIV-infected rhesus macaques during and post-ART. • Continued PD-1 modulation post-ART maintains PD-1{sup hi} cells at low levels. • Continued PD-1 modulation post-ART maintains a favorable T cell and Treg repertoire.

  17. On the Orbital and Collisional History of (433) Eros

    NASA Astrophysics Data System (ADS)

    Bottke, W. F.

    2001-12-01

    (433) Eros, a ~ 20 km S-type asteroid extensively explored by the NEAR spacecraft, has had a enigmatic collisional and dynamical history. Its orbital parameters (a = 1.46 AU, e = 0.22, and i = 10.8o) place it in the Near-Earth object (NEO) population, defined as those asteroid and comets having perihelia q < 1.3~AU and aphelia Q > 0.983 AU. NEOs, however, tend to be short-lived; typical residents have dynamical lifetimes of 10 Myr before they strike the Sun, a terrestrial planet, or are ejected out of the inner solar system via a close encounter with Jupiter. For this reason, we hypothesize that Eros has only recently evolved out of the main belt and that it has followed a complicated dynamical path to reach its current orbit. A plausible evolutionary scenario for Eros is the following: (1) A catastrophic disruption event liberates Eros from its parent body. Given Eros's relatively large size, it is likely that this event also produced an observable asteroid family (e.g., Maria family; Zappalà et al., 1997, Icarus 129, 1.). (2) The Yarkovsky effect, a radiation drag force, causes Eros to migrate towards a resonant "escape hatch" (e.g., 3:1 mean motion resonance with Jupiter). Typical drift rates for Eros-sized bodies are slow enough (da/dt ~ 5 x 10-6 AU Myr-1) that Eros could have taken billions of years to escape the main belt (Farinella and Vokrouhlický, 1999, Science 283, 1507). (3) Eros reaches its escape resonance and has its eccentricity pumped up high enough to enter the NEO region. (4) A combination of close encounters with the terrestrial planets and inner solar system resonances move Eros to its current orbital position. If this evolutionary history is correct, the cratering record of Eros is linked to its dynamical history, such that numerical modeling can begin to fill in the qualitative gaps discussed above. Integration results of test bodies evolving from the main belt (Bottke et al., 2001, Icarus, in press) suggest that Eros has a ~ 20% chance of

  18. Resolving the energy and temperature dependence of C6H6 (∗) collisional relaxation via time-dependent bath temperature measurements.

    PubMed

    West, Niclas A; Winner, Joshua D; Bowersox, Rodney D W; North, Simon W

    2016-07-01

    The relaxation of highly vibrationally excited benzene, generated by 193 nm laser excitation, was studied using the transient rotational-translational temperature rise of the N2 bath, which was measured by proxy using two-line laser induced fluorescence of seeded NO. The resulting experimentally measured time-dependent N2 temperature rises were modeled with MultiWell based simulations of Collisional Energy Transfer (CET) from benzene vibration to N2 rotation-translation. We find that the average energy transferred in benzene deactivating collisions depends linearly on the internal energy of the excited benzene molecules and depends approximately linearly on the N2 bath temperature between 300 K and 600 K. The results are consistent with experimental studies and classical trajectory calculations of CET in similar systems. PMID:27394109

  19. Resolving the energy and temperature dependence of C6H6∗ collisional relaxation via time-dependent bath temperature measurements

    NASA Astrophysics Data System (ADS)

    West, Niclas A.; Winner, Joshua D.; Bowersox, Rodney D. W.; North, Simon W.

    2016-07-01

    The relaxation of highly vibrationally excited benzene, generated by 193 nm laser excitation, was studied using the transient rotational-translational temperature rise of the N2 bath, which was measured by proxy using two-line laser induced fluorescence of seeded NO. The resulting experimentally measured time-dependent N2 temperature rises were modeled with MultiWell based simulations of Collisional Energy Transfer (CET) from benzene vibration to N2 rotation-translation. We find that the average energy transferred in benzene deactivating collisions depends linearly on the internal energy of the excited benzene molecules and depends approximately linearly on the N2 bath temperature between 300 K and 600 K. The results are consistent with experimental studies and classical trajectory calculations of CET in similar systems.

  20. TiOx thin films grown on Pd(100) and Pd(111) by chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Farstad, M. H.; Ragazzon, D.; Grönbeck, H.; Strømsheim, M. D.; Stavrakas, C.; Gustafson, J.; Sandell, A.; Borg, A.

    2016-07-01

    The growth of ultrathin TiOx (0≤x≤2) films on Pd(100) and Pd(111) surfaces by chemical vapor deposition (CVD), using Titanium(IV)isopropoxide (TTIP) as precursor, has been investigated by high resolution photoelectron spectroscopy, low energy electron diffraction and scanning tunneling microscopy. Three different TiOx phases and one Pd-Ti alloy phase have been identified for both surfaces. The Pd-Ti alloy phase is observed at the initial stages of film growth. Density functional theory (DFT) calculations for Pd(100) and Pd(111) suggest that Ti is alloyed into the second layer of the substrate. Increasing the TTIP dose yields a wetting layer comprising Ti2 + species (TiOx, x ∼0.75). On Pd(100), this phase exhibits a mixture of structures with (3 × 5) and (4 × 5) periodicity with respect to the Pd(100) substrate, while an incommensurate structure is formed on Pd(111). Most importantly, on both surfaces this phase consists of a zigzag pattern similar to observations on other reactive metal surfaces. Further increase in coverage results in growth of a fully oxidized (TiO2) phase on top of the partially oxidized layer. Preliminary investigations indicate that the fully oxidized phase on both Pd(100) and Pd(111) may be the TiO2(B) phase.

  1. Analysis of Collisional Cross Sections of Rydberg nS and nD States of Ultracold Caesium Atoms

    NASA Astrophysics Data System (ADS)

    Feng, Zhigang; Miao, Jingyuan; Zhao, Kejia; Li, Difei; Yang, Zhijun; Wu, Fan; Wu, Zhaochun; Zhao, Jianming; Jia, Suotang

    2016-05-01

    We present a simple analytical formula derived from an existing theoretical model and a detailed theoretical investigation of effects of the van der Waals interaction and dipole–dipole interaction on collisional cross sections as functions of various parameters. We analyze the main mechanism leading to large collisional cross sections on the basis of our previous experimental results using the present formula and also analyze the effects of some other factors on collisional cross sections.

  2. Transient neonatal zinc deficiency.

    PubMed

    Krieger, I; Alpern, B E; Cunnane, S C

    1986-06-01

    We report an infant who developed clinical manifestations of zinc deficiency during the first month of life although the diet was adequate for zinc and no other causes could be ascertained. The diagnosis was confirmed by low plasma-zinc concentrations and a positive response to zinc treatment. The fatty acid profile of plasma phospholipids was typical of zinc deficiency (ie, arachidonic acid was markedly decreased). The transient nature of this disorder was evident when no relapse occurred after cessation of zinc therapy and plasma-zinc and arachidonic acid concentrations remained normal. Several explanations for the development of transient neonatal zinc deficiency are offered. The observation demonstrates that occasional infants may have requirements for zinc that are beyond the intakes of the conventional RDA. PMID:3717070

  3. Transient infrared emission spectroscopy

    SciTech Connect

    Jones, R.W.; McClelland, J.F.

    1989-04-01

    Transient infrared emission spectroscopy (TIRES) is a new method that produces analytically useful emission spectra from optically thick, solid samples by greatly reducing self-absorption of emitted radiation. The method reduces self-absorption by creating a thin, short-lived, heated layer at the sample surface and collecting the transient emission from this layer. The technique requires no sample preparation and may be applied to both moving and stationary samples. The single-ended, noncontact TIRES measurement geometry is ideal for on-line and other remote-sensing applications. TIRES spectra acquired via a Fourier transform infrared spectrometer on moving samples of coal, plastic, and paint are presented and compared to photoacoustic absorption spectra of these materials. The TIRES and photoacoustic results are in close agreement as predicted by Kirchhoff's law.

  4. The VAO Transient Facility

    NASA Astrophysics Data System (ADS)

    Graham, Matthew J.; Djorgovski, S. G.; Drake, Andrew; Mahabal, Ashish; Williams, Roy; Seaman, Rob

    2012-04-01

    The time-domain community wants robust and reliable tools to enable the production of, and subscription to, community-endorsed event notification packets (VOEvent). The Virtual Astronomical Observatory (VAO) Transient Facility (VTF) is being designed to be the premier brokering service for the community, both collecting and disseminating observations about time-critical astronomical transients but also supporting annotations and the application of intelligent machine-learning to those observations. Two types of activity associated with the facility can therefore be distinguished: core infrastructure, and user services. We review the prior art in both areas, and describe the planned capabilities of the VTF. In particular, we focus on scalability and quality-of-service issues required by the next generation of sky surveys such as LSST and SKA.

  5. Late-time cosmological evolution in f (R ) theories with ordinary and collisional matter

    NASA Astrophysics Data System (ADS)

    Oikonomou, V. K.; Karagiannakis, N.

    2015-04-01

    We study the late-time cosmological evolution of f(R) theories of modified gravity, with the matter content of the Universe being that of collisional self-interacting matter. We assume that the Universe is described by a flat Friedmann-Lemaitre-Robertson-Walker metric and that it is matter and dark energy dominated. The results of our numerical analysis for a collisional matter f(R) theory are compared with those resulting from pressureless matter f(R) theory and from the Λ CDM model. As we shall demonstrate, the resulting picture can vary from model to model, indicating that the effect of collisional matter in f(R) theories is strongly model dependent. In all studied cases, the effective equation of state parameter does not cross the phantom divide, both in the collisional matter and pressureless matter f(R) theories. Finally, we thoroughly study the effects of collisional matter on one of the f(R) models that is known to provide a unified description of early time inflation and late-time acceleration. The overall picture of the evolution of the Universe is not drastically affected, apart from the matter era, which is further enhanced with an additional matter energy contribution. However, a fully consistent description of the Universe’s evolution requires the introduction of a dark energy compensate in the total energy density, a concept very well known from the literature.

  6. Ion drag force on a dust grain in a weakly ionized collisional plasma

    SciTech Connect

    Semenov, I. L.; Krivtsun, I. V.; Zagorodny, A. G.

    2013-01-15

    The problem of calculating the ion drag force acting on a dust grain immersed in a weakly ionized collisional plasma is studied using an approach based on the direct numerical solution of the Vlasov-Bhatnagar-Gross-Krook kinetic equations. A uniform subthermal flow of argon plasma past a spherical dust grain is considered. The numerical computations are performed for a wide range of plasma pressures. On the basis of the obtained results, the effect of ion-neutral collisions on the ion drag force is analyzed in a wide range of ion collisionality. In the collisionless limit, our results are shown to be in good agreement with the results obtained by the binary collision approach. As the ion collisionality increases, the ion drag force is found to decrease sharply and even become negative, i.e., directed oppositely to the plasma flow. A qualitative explanation of this effect is presented and a comparison of our results with those obtained using the drift diffusion approach is discussed. The velocity dependence of the ion drag force in the highly collisional regime is examined. The relationship between the ion and the neutral drag forces in the highly collisional limit is analyzed and the possibility of a superfluid-like behavior of dust grains is discussed.

  7. Collisional modelling of the AU Microscopii debris disc

    NASA Astrophysics Data System (ADS)

    Schüppler, Ch.; Löhne, T.; Krivov, A. V.; Ertel, S.; Marshall, J. P.; Wolf, S.; Wyatt, M. C.; Augereau, J.-C.; Metchev, S. A.

    2015-09-01

    AU Microscopii's debris disc is one of the most famous and best-studied debris discs and one of only two resolved debris discs around M stars. We perform in-depth collisional modelling of the AU Mic disc including stellar radiative and corpuscular forces (stellar winds), aiming at a comprehensive understanding of the dust production and the dust and planetesimal dynamics in the system. Our models are compared to a suite of observational data for thermal and scattered light emission, ranging from the ALMA radial surface brightness profile at 1.3 mm to spatially resolved polarisation measurements in the visible. Most of the data are shown to be reproduced with dust production in a belt of planetesimals with an outer edge at around 40 au and subsequent inward transport of dust by stellar winds. A low dynamical excitation of the planetesimals with eccentricities up to 0.03 is preferred. The radial width of the planetesimal belt cannot be constrained tightly. Belts that are 5 au and 17 au wide, as well as a broad 44 au-wide belt, are consistent with observations. All models show surface density profiles that increase with distance from the star up to ≈40 au, as inferred from observations. The best model is achieved by assuming a stellar mass loss rate that exceeds the solar one by a factor of 50. The models reproduce the spectral energy distribution and the shape of the ALMA radial profile well, but deviate from the scattered light observations more strongly. The observations show a bluer disc colour and a lower degree of polarisation for projected distances <40 au than predicted by the models. These deviations may be reduced by taking irregularly shaped dust grains which have scattering properties different from the Mie spheres used in this work. From tests with a handful of selected dust materials, we favour mixtures of silicate, carbon, and ice of moderate porosity. We also address the origin of the unresolved central excess emission detected by ALMA and show that

  8. Spoke Formation in Saturn's Ring: The Collisional Cascade Model

    NASA Astrophysics Data System (ADS)

    Hamilton, Douglas P.

    2014-11-01

    The mysterious wedge-shaped spokes in Saturn's main rings have defied explanation ever since their discovery during the Voyager flybys of the early 1980s. No earlier model can explain the three disparate timescales over which spokes evolve: i) the 10-minute formation time for a new spoke, ii) the hour-long period over which a spoke's radial edge remains active, and iii) the day-long timescale over which the magnetic longitude of earlier spoke activity is preferentially repopulated with subsequent spokes. This and other observations of ongoing spoke formation can be understood in the context of a Collisional Cascade model in which a hail of rapidly-moving submicron dust grains rain down upon more massive ring particles. Tiny ~0.1 micron grains leave the ring plane en masse from the site of an initial disturbance (likely a meteoroid impact) and are accelerated by the magnetic field to high speeds relative to more massive ring particles. When the dust returns to the ring plane -nearly simultaneously over a large radial range - they strike fluffy dust-coated ring particles at km/s speeds, freeing both visible 0.5 micron spoke particles and additional submicron debris. Differences between the motions of the 0.1 micron dust grains and the much larger ring particles provides a potent free energy source that powers spoke formation. The onset of this hail of tiny energetic impactors can account for the observed rapid formation of spokes and, as the hail continues to fall, for the hour-long active periods over which some spoke edges remains nearly radial. The hour-long timescale is controlled by differences in initial launch velocities and different grain charge-to-mass ratios which strongly affect vertical motions. Additional tiny grains liberated in the first hailstorm go on to continue the cascade, returning to strike the same magnetic longitude in the ring hours to days later and stirring up more micron-sized spoke particles. This continuing cascade nicely accounts for

  9. Collisional Disruption of Gravity Dominated Bodies: New Data and Scaling

    NASA Astrophysics Data System (ADS)

    Movshovitz, N.; Nimmo, F.; Korycansky, D. G.; Asphaug, E. I.; Owen, M.

    2015-12-01

    We present data from a suite of 169 hydrocode simulations of collisions between planetary bodies with radii from 100 to 1000 km. The data is used to derive a simple scaling law for the threshold for catastrophic disruption, defined as a collision that leads to half the total colliding mass escaping the system post impact. For a target radius 100≤R_T≤1000 km and a mass MTM_T and a projectile radius r_p≤R_T and mass mpm_p we find that a head-on impact with velocity magnitude vv is catastrophic if the kinetic energy of the system in the center of mass frame, K=0.5{M_T}{m_p}/(M_T+m_p)v^2, exceeds K∗R_D=(3.3±0.6)U_R U_R where U_R=(3/5)G{M_T}^2/R_T + (3/5)G{m_p}^2/{r_p}+G{M_T}{m_p}/(M_T+{m_p}) is the gravitational binding energy of the system at the moment of impact; GG is the gravitational constant. Oblique impacts are catastrophic when the fraction of kinetic energy contained in the volume of the projectile intersecting the target at impact exceeds ˜1.9K∗_RD for 30° impacts and ˜3.5K∗_RD for 45deg; impacts. We compare predictions made with this scaling to those made with existing scaling laws in the literature extrapolated from numerical studies on smaller targets. We find significant divergence between predictions where in general our data suggest a lower threshold for disruption except for highly oblique impacts with r_p≪R_T. This result has implications for the efficiency of collisional grinding in the asteroid belt (Morbidelli, A., Bottke, W. F., Nesvorny, D., & Levison, H. F., 2009, Icarus, 204, 558-573), Kuiper belt (Greenstreet, S., Gladman, B., & McKinnon, W. B., 2015, Icarus, 258, 267-288), and early solar system accretion (Chambers, J. E., 2013, Icarus, 224, 43-56).

  10. Reactor System Transient Code.

    1999-07-14

    RELAP3B describes the behavior of water-cooled nuclear reactors during postulated accidents or power transients, such as large reactivity excursions, coolant losses or pump failures. The program calculates flows, mass and energy inventories, pressures, temperatures, and steam qualities along with variables associated with reactor power, reactor heat transfer, or control systems. Its versatility allows one to describe simple hydraulic systems as well as complex reactor systems.

  11. Two Transients discovered by PSST

    NASA Astrophysics Data System (ADS)

    Smith, K. W.; Wright, D.; Smartt, S. J.; Young, D. R.; Huber, M.; Chambers, K. C.; Flewelling, H.; Willman, M.; Primak, N.; Schultz, A.; Gibson, B.; Magnier, E.; Waters, C.; Tonry, J.; Wainscoat, R. J.; Foley, R. J.; Jha, S. W.; Rest, A.; Scolnic, D.

    2016-08-01

    Two transients have been discovered as part of the Pan-STARRS Survey for Transients (PSST). Information on all objects discovered by the Pan-STARRS Survey for Transients is available at http://star.pst.qub.ac.uk/ps1threepi/ (see Huber et al. ATel #7153).

  12. Bright Transients discovered by PSST

    NASA Astrophysics Data System (ADS)

    Smith, K. W.; Wright, D.; Smartt, S. J.; Young, D. R.; Huber, M.; Chambers, K. C.; Flewelling, H.; Willman, M.; Primak, N.; Schultz, A.; Gibson, B.; Magnier, E.; Waters, C.; Tonry, J.; Wainscoat, R. J.; Foley, R. J.; Jha, S. W.; Rest, A.; Scolnic, D.

    2016-08-01

    Six bright transients have been discovered as part of the Pan-STARRS Survey for Transients (PSST). Information on all objects discovered by the Pan-STARRS Survey for Transients is available at http://star.pst.qub.ac.uk/ps1threepi/ (see Huber et al. ATel #7153).

  13. Bright Transients discovered by PSST

    NASA Astrophysics Data System (ADS)

    Smith, K. W.; Wright, D.; Smartt, S. J.; Huber, M.; Chambers, K. C.; Flewelling, H.; Willman, M.; Primak, N.; Schultz, A.; Gibson, B.; Magnier, E.; Waters, C.; Tonry, J.; Wainscoat, R. J.; Denneau, L.; Stalder, B.; Heinze, A.; Sherstyuk, A.; Foley, R. J.; Jha, S. W.; Rest, A.; Scolnic, D.

    2016-04-01

    Seven bright transients have been discovered as part of the Pan-STARRS Survey for Transients (PSST). Information on all objects discovered by the Pan-STARRS Survey for Transients is available at http://star.pst.qub.ac.uk/ps1threepi/ (see Huber et al. ATel #7153).

  14. ON DETECTING TRANSIENT PHENOMENA

    SciTech Connect

    Belanger, G.

    2013-08-10

    Transient phenomena are interesting and potentially highly revealing of details about the processes under observation and study that could otherwise go unnoticed. It is therefore important to maximize the sensitivity of the method used to identify such events. In this article, we present a general procedure based on the use of the likelihood function for identifying transients which is particularly suited for real-time applications because it requires no grouping or pre-processing of the data. The method makes use of all the information that is available in the data throughout the statistical decision-making process, and is suitable for a wide range of applications. Here we consider those most common in astrophysics, which involve searching for transient sources, events or features in images, time series, energy spectra, and power spectra, and demonstrate the use of the method in the case of a weak X-ray flare in a time series and a short-lived quasi-periodic oscillation in a power spectrum. We derive a fit statistic that is ideal for fitting arbitrarily shaped models to a power density distribution, which is of general interest in all applications involving periodogram analysis.

  15. Advanced PFBC transient analysis

    SciTech Connect

    White, J.S.; Bonk, D.L.

    1997-05-01

    Transient modeling and analysis of advanced Pressurized Fluidized Bed Combustion (PFBC) systems is a research area that is currently under investigation by the US Department of Energy`s Federal Energy Technology Center (FETC). The object of the effort is to identify key operating parameters that affect plant performance and then quantify the basic response of major sub-systems to changes in operating conditions. PC-TRAX{trademark}, a commercially available dynamic software program, was chosen and applied in this modeling and analysis effort. This paper describes the development of a series of TRAX-based transient models of advanced PFBC power plants. These power plants burn coal or other suitable fuel in a PFBC, and the high temperature flue gas supports low-Btu fuel gas or natural gas combustion in a gas turbine topping combustor. When it is utilized, the low-Btu fuel gas is produced in a bubbling bed carbonizer. High temperature, high pressure combustion products exiting the topping combustor are expanded in a modified gas turbine to generate electrical power. Waste heat from the system is used to raise and superheat steam for a reheat steam turbine bottoming cycle that generates additional electrical power. Basic control/instrumentation models were developed and modeled in PC-TRAX and used to investigate off-design plant performance. System performance for various transient conditions and control philosophies was studied.

  16. The Pyrite Structure of PdS2 and PdSe2 Monolayers

    NASA Astrophysics Data System (ADS)

    Singh, Arunima K.; Hennig, Richard G.; National Institute of Standards; Technology Collaboration; University of Florida Collaboration

    There has been a rising interest in two-dimensional (2D) materials due to a range of extraordinary electronic, optical and mechanical properties which are different from their bulk counterparts. The structure, stability and electronic properties of 2D PdS2 and PdSe2 have been investigated in the past in the well-known hexagonal 1T and 2H structures. However, bulk PdS2 and PdSe2 are layered compounds with individual rhombohedral pyrite-type monolayers vertically stacked with van-der Waals forces. Using density functional theory simulations, and five different functionals, we compare the energetic stability of 2D PdS2 and PdSe2 pyrite structure with the 1T and 2H structures. We find that the PdS2 is most stable in the pyrite structure, whereas the PdSe2 is most stable in the 1T structure with the pyrite structure closely competing in energy. The fundamental band gap of these compounds as a function of the structure, number of layers, the stacking arrangement and in-layer strain has been investigated. The pyrite structures of PdS2 and PdSe2 are found to be semi-conducting with indirect band gaps, and effective masses comparable to that of monolayer MoS2; thus are potential candidates for nano-electronic applications.

  17. Hydrogen solubility in inhomogeneous Pd alloys

    SciTech Connect

    Flanagan, T.B.; Wang, D.; Clewley, J.D.

    1998-12-31

    As-cast, arc-melted Pd-Ni alloys are inhomogeneous and the H{sub 2} isotherms for these differ from their homogeneous counterparts in the two phase, (dilute + hydride), regions but not in the dilute phase regions. Pd-Ni alloys, which become inhomogeneous via a ternary (Pd + Ni + H) equilibrium phase change, have H{sub 2} isotherms which differ from those of the homogeneous alloy in both the two-phase and the dilute phase regions. These results are discussed with respect to the expected type of inhomogeneities.

  18. Collisionality scaling of turbulence and transport in advanced inductive plasmas in DIII-D

    NASA Astrophysics Data System (ADS)

    Yan, Z.; McKee, G. R.; Petty, C.; Luce, T.; Chen, X.; Holland, C.; Rhodes, T.; Schmitz, L.; Wang, G.; Zeng, L.; Marinoni, A.; Solomon, W.; DIII-D Team

    2015-11-01

    The collisionality scaling of multiscale turbulence properties and thermal transport characteristics in high-beta, high confinement Advanced Inductive (AI) plasmas was determined via systematic dimensionless scaling experiments on DIII-D. Preliminary estimate indicates a weak collisionality dependence of energy confinement as v* varied by a factor of ~2. Electron density and scaled (~Bt2) temperature profiles are well matched in the scan. Interestingly, low-k density fluctuation amplitudes are observed to decrease at lower v* near ρ ~ 0 . 75 . Ion and electron thermal transport values, computed with ONETWO using experimentally measured profiles and sources, will be presented, along with multi-scale turbulence measurements obtained with various fluctuation diagnostics. Altering collisionality should change the relative contribution of different modes to transport.

  19. A multi-species 13-moment model for moderately collisional plasmas

    NASA Astrophysics Data System (ADS)

    Miller, S. T.; Shumlak, U.

    2016-08-01

    Fluid-based models of collisional transport in multi-species plasmas have typically been applied to parameter regimes where a local thermal equilibrium is assumed. While this parameter regime is valid for low temperature and/or high density applications, it begins to fail as plasmas enter the collisionless regime and kinetic effects dominate the physics. A plasma model is presented that lays the foundation for extending the validity of the collisional fluid regime using an anisotropic 13-moment fluid model derived from the Pearson type-IV probability distribution. The model explicitly evolves the pressure tensor and heat flux vector along with the density and flow velocity to capture dynamics usually restricted to kinetic models. Each particle species is modeled individually and collectively coupled through electromagnetic and collisional interactions.

  20. Collisional stochastic ripple diffusion of alpha particles and beam ions on TFTR

    SciTech Connect

    Redi, M.H.; Zarnstorff, M.C.; White, R.B.; Budny, R.V.; Janos, A.C.; Owens, D.K.; Schivell, J.F.; Scott, S.D.; Zweben, S.J.

    1995-07-01

    Predictions for ripple loss of fast ions from TFTR are investigated with a guiding center code including both collisional and ripple effects. A synergistic enhancement of fast ion diffusion is found for toroidal field ripple with collisions. The total loss is calculated to be roughly twice the sum of ripple and collisional losses calculated separately. Discrepancies between measurements and calculations of plasma beta at low current and large major radius are resolved when both effects are included for neutral beam ions. A 20--30% reduction in alpha particle heating is predicted for q{sub a} = 6--14, R = 2.6 m DT plasmas on TFTR due to first orbit and collisional stochastic ripple diffusion.

  1. Formation and evolution of vortices in a collisional strongly coupled dusty plasma

    NASA Astrophysics Data System (ADS)

    Jana, Sayanee; Banerjee, Debabrata; Chakrabarti, Nikhil

    2016-07-01

    Formation and evolution of vortices are studied in a collisional strongly coupled dusty plasma in the framework of a Generalized Hydrodynamic model (GH). Here we mainly present the nonlinear dynamical response of this strongly coupled system in presence of dust-neutral collisional drag. It is shown that the interplay between the nonlinear elastic stress and the dust-neutral collisional drag results in the generation of non-propagating monopole vortex for some duration before it starts to propagate like transverse shear wave. It is also found that the interaction between two unshielded monopole vortices having both same (co-rotating) and opposite (counter rotating) rotations result in the formation of two propagating dipole vortices of equal and unequal strength respectively. These results will provide some new understanding on the transport properties in such a strongly coupled system. The numerical simulation is carried out using a de-aliased doubly periodic pseudo-spectral code with Runge-Kutta-Gill time integrator.

  2. New Regime of Low Ion Collisionality in the Neoclassical Equilibrium of Tokamak Plasmas

    NASA Astrophysics Data System (ADS)

    Ramos, J. J.

    2015-11-01

    The neoclassical description of an axisymmetric toroidal plasma equilibrium is formulated for an unconventionally low ordering of the collisionality that suits realistic thermonuclear fusion conditions. This requires a drift-kinetic analysis to the second order of the ion Larmor radius, which yields a new contribution to the leading solution for the non-Maxwellian part of the ion distribution function if the equilibrium geometry is not up-down symmetric. An explicit geometrical factor weighs this second Larmor-radius order, low-collisionality effect that modifies the neoclassical ion parallel flow and the ion contribution to the bootstrap current. For this low-collisionality neoclassical equilibrium solution, the pressure anisotropy part of the Chew-Goldberger-Low stress tensor is comparable to the gyroviscosity and their contributions to the flux-surface-averaged parallel momentum equation balance exactly. Work supported by the U.S. D.O.E.

  3. Investigation of the Electron-Ion Hybrid Instability in a Collisional Environment

    NASA Astrophysics Data System (ADS)

    Tejero, E. M.; Enloe, L.; Sotnikov, V. I.; Amatucci, B.; Ganguli, G.

    2013-12-01

    The Electron-Ion Hybrid (EIH) instability, a transverse velocity shear-driven instability with frequency near the lower hybrid frequency, was previously predicted theoretically to explain the observation of lower hybrid waves in applications from the plasma sheet boundary layer to laser produced plasmas. The EIH instability has also been observed in the laboratory in scaled magnetospheric plasma conditions and in laser produced plasma expansion experiments across magnetic fields. In the work presented, we have expanded the theoretical framework to highly collisional plasmas for applications to the plasma region surrounding a hypersonic vehicle. In this collisional plasma layer, strongly sheared transverse flows can exist that can give rise to the EIH instability. We wish to study whether the resulting lower hybrid turbulence can impede communication to and from the hypersonic vehicle. Results from theory and a comparison from laboratory experiments on the generation of the EIH instability in a collisional plasma environment will be presented.

  4. Interrelated structures of the transport shock and collisional relaxation layer in a multitemperature, multilevel ionized gas

    NASA Technical Reports Server (NTRS)

    Vinolo, A. R.; Clarke, J. H.

    1972-01-01

    The gas dynamic structures of the transport shock and the downstream collisional relaxation layer are evaluated for partially ionized monatomic gases. Elastic and inelastic collisional nonequilibrium effects are taken into consideration. Three electronic levels are accounted for in the microscopic model of the atom. Nonequilibrium processes with respect to population of levels and species plus temperature are considered. By using an asymptotic technique the shock morphology is found on a continuum flow basis. The asymptotic procedure gives two distinct layers in which the nonequilibrium effects to be considered are different. A transport shock appears as the inner solution to an outer collisional relaxation layer in which the gas reaches local equilibrium. A family of numerical examples is displayed for different flow regimes. Argon and helium models are used in these examples.

  5. Leap frog integrator modifications in highly collisional particle-in-cell codes

    NASA Astrophysics Data System (ADS)

    Hanzlikova, N.; Turner, M. M.

    2014-07-01

    Leap frog integration method is a standard, simple, fast, and accurate way to implement velocity and position integration in particle-in-cell codes. Due to the direct solution of kinetics of particles in phase space central to the particle-in-cell procedure, important information can be obtained on particle velocity distributions, and consequently on transport and heating processes. This approach is commonly associated with physical situations where collisional effects are weak, but can also be profitably applied in some highly collisional cases, such as occur in semiconductor devices and gaseous discharges at atmospheric pressure. In this paper, we show that the implementation of the leap frog integration method in these circumstances can violate some of the assumptions central to the accuracy of this scheme. Indeed, without adaptation, the method gives incorrect results. We show here how the method must be modified to deal correctly with highly collisional cases.

  6. Modeling of tokamak divertor plasma for weakly collisional parallel electron transport

    NASA Astrophysics Data System (ADS)

    Umansky, M. V.; Dimits, A. M.; Joseph, I.; Omotani, J. T.; Rognlien, T. D.

    2015-08-01

    The parallel electron heat transport in a weakly collisional regime can be represented in the framework of the Landau-fluid model (Hammett et al., 1990). Practical implementation of Landau-fluid transport has become possible due to the recent invention of an efficient non-spectral method for the non-local closure operators (Dimits et al., 2014). Here the implementation of a Landau-fluid based model for the parallel plasma transport is described, and the model is tested for different collisionality regimes against Fokker-Planck simulations. The new method appears to represent the weakly collisional electron transport more accurately than the conventional flux-limiter based models, on the other hand it is computationally efficient enough to be incorporated in comprehensive edge plasma simulations.

  7. Collisional pumping of water masers by species of particles at different temperatures

    NASA Technical Reports Server (NTRS)

    Anderson, Nels; Watson, William D.

    1990-01-01

    It has been reported that the extreme power of astrophysical water masers can be obtained from purely collisional pumping in environments with two kinetic temepratures. It is found that this pumping vanishes when the latest rates are utilized for the collisional excitation of H2O molecules by neutrals. Energetic ions must also be present under the conditions that have been proposed for such 'two-temperature' pumping, but they have been ignored in the past due to lack of information about the relevant cross sections. Quantal, multichannel calculations in the impact parameter approximation are performed to provide a basis for estimating these rates for the collisional excitation of H2O molecules by ions. Including the effects of these ions does not restore the inversion, but rather reduces the pumping for H2O masers in the proposed 'two-temperature' environments.

  8. Collisional statistics and dynamics of two-dimensional hard-disk systems: From fluid to solid.

    PubMed

    Taloni, Alessandro; Meroz, Yasmine; Huerta, Adrián

    2015-08-01

    We perform extensive MD simulations of two-dimensional systems of hard disks, focusing on the collisional statistical properties. We analyze the distribution functions of velocity, free flight time, and free path length for packing fractions ranging from the fluid to the solid phase. The behaviors of the mean free flight time and path length between subsequent collisions are found to drastically change in the coexistence phase. We show that single-particle dynamical properties behave analogously in collisional and continuous-time representations, exhibiting apparent crossovers between the fluid and the solid phases. We find that, both in collisional and continuous-time representation, the mean-squared displacement, velocity autocorrelation functions, intermediate scattering functions, and self-part of the van Hove function (propagator) closely reproduce the same behavior exhibited by the corresponding quantities in granular media, colloids, and supercooled liquids close to the glass or jamming transition. PMID:26382368

  9. A new code to study structures in collisionally active, perturbed debris discs: application to binaries

    NASA Astrophysics Data System (ADS)

    Thébault, P.

    2012-01-01

    Context. Debris discs are traditionally studied using two distinct types of numerical models: statistical particle-in-a-box codes to study their collisional and size distribution evolution, and dynamical N-body models to study their spatial structure. The absence of collisions in N-body codes is in particular a major shortcoming, as collisional processes are expected to significantly alter the results obtained from pure N-body runs. Aims: We present a new numerical model, to study the spatial structure of perturbed debris discs in both a dynamical and collisional steady-state. We focus on the competing effects of gravitational perturbations by a massive body (planet or star), the collisional production of small grains, and the radiation pressure placing these grains in possibly dynamically unstable regions. Methods: We consider a disc of parent bodies in a dynamical steady-state, from which small radiation-pressure-affected grains are released in a series of runs, each corresponding to a different orbital position of the perturber, where particles are assigned a collisional destruction probability. These collisional runs produce successive position maps that are then recombined, following a complex procedure, to generate surface density profiles for each orbital position of the perturbing body. Results: We apply our code to the case of a circumprimary disc in a binary. We find pronounced structures inside and outside the dynamical stability regions. For low eB, the disc's structure is time varying, with spiral arms in the dynamically "forbidden" region precessing with the companion star. For high eB, the disc is strongly asymmetric but time invariant, with a pronounced density drop in the binary's periastron direction.

  10. Linear tearing mode stability equations for a low collisionality toroidal plasma

    NASA Astrophysics Data System (ADS)

    Connor, J. W.; Hastie, R. J.; Helander, P.

    2009-01-01

    Tearing mode stability is normally analysed using MHD or two-fluid Braginskii plasma models. However for present, or future, large hot tokamaks like JET or ITER the collisionality is such as to place them in the banana regime. Here we develop a linear stability theory for the resonant layer physics appropriate to such a regime. The outcome is a set of 'fluid' equations whose coefficients encapsulate all neoclassical physics: the neoclassical Ohm's law, enhanced ion inertia, cross-field transport of particles, heat and momentum all play a role. While earlier treatments have also addressed this type of neoclassical physics we differ in incorporating the more physically relevant 'semi-collisional fluid' regime previously considered in cylindrical geometry; semi-collisional effects tend to screen the resonant surface from the perturbed magnetic field, preventing reconnection. Furthermore we also include thermal physics, which may modify the results. While this electron description is of wide relevance and validity, the fluid treatment of the ions requires the ion banana orbit width to be less than the semi-collisional electron layer. This limits the application of the present theory to low magnetic shear—however, this is highly relevant to the sawtooth instability—or to colder ions. The outcome of the calculation is a set of one-dimensional radial differential equations of rather high order. However, various simplifications that reduce the computational task of solving these are discussed. In the collisional regime, when the set reduces to a single second-order differential equation, the theory extends previous work by Hahm et al (1988 Phys. Fluids 31 3709) to include diamagnetic-type effects arising from plasma gradients, both in Ohm's law and the ion inertia term of the vorticity equation. The more relevant semi-collisional regime pertaining to JET or ITER, is described by a pair of second-order differential equations, extending the cylindrical equations of Drake

  11. Asymmetric magnetic proximity effect in a Pd/Co/Pd trilayer system

    DOE PAGESBeta

    Kim, Dong -Ok; Song, Kyung Mee; Choi, Yongseong; Min, Byoung -Chul; Kim, Jae -Sung; Choi, Jun Woo; Lee, Dong Ryeol

    2016-05-06

    In spintronic devices consisting of ferromagnetic/nonmagnetic systems, the ferromagnet-induced magnetic moment in the adjacent nonmagnetic material significantly influences the spin transport properties. In this study, such magnetic proximity effect in a Pd/Co/Pd trilayer system is investigated by x-ray magnetic circular dichroism and x-ray resonant magnetic reflectivity, which enables magnetic characterizations with element and depth resolution. We observe that the total Pd magnetic moments induced at the top Co/Pd interface are significantly larger than the Pd moments at the bottom Pd/Co interface, whereas transmission electron microscopy and reflectivity analysis indicate the two interfaces are nearly identical structurally. Furthermore, such asymmetry inmore » magnetic proximity effects could be important for understanding spin transport characteristics in ferromagnetic/nonmagnetic systems and its potential application to spin devices.« less

  12. Asymmetric magnetic proximity effect in a Pd/Co/Pd trilayer system.

    PubMed

    Kim, Dong-Ok; Song, Kyung Mee; Choi, Yongseong; Min, Byoung-Chul; Kim, Jae-Sung; Choi, Jun Woo; Lee, Dong Ryeol

    2016-01-01

    In spintronic devices consisting of ferromagnetic/nonmagnetic systems, the ferromagnet-induced magnetic moment in the adjacent nonmagnetic material significantly influences the spin transport properties. In this study, such magnetic proximity effect in a Pd/Co/Pd trilayer system is investigated by x-ray magnetic circular dichroism and x-ray resonant magnetic reflectivity, which enables magnetic characterizations with element and depth resolution. We observe that the total Pd magnetic moments induced at the top Co/Pd interface are significantly larger than the Pd moments at the bottom Pd/Co interface, whereas transmission electron microscopy and reflectivity analysis indicate the two interfaces are nearly identical structurally. Such asymmetry in magnetic proximity effects could be important for understanding spin transport characteristics in ferromagnetic/nonmagnetic systems and its potential application to spin devices. PMID:27151368

  13. Asymmetric magnetic proximity effect in a Pd/Co/Pd trilayer system

    NASA Astrophysics Data System (ADS)

    Kim, Dong-Ok; Song, Kyung Mee; Choi, Yongseong; Min, Byoung-Chul; Kim, Jae-Sung; Choi, Jun Woo; Lee, Dong Ryeol

    2016-05-01

    In spintronic devices consisting of ferromagnetic/nonmagnetic systems, the ferromagnet-induced magnetic moment in the adjacent nonmagnetic material significantly influences the spin transport properties. In this study, such magnetic proximity effect in a Pd/Co/Pd trilayer system is investigated by x-ray magnetic circular dichroism and x-ray resonant magnetic reflectivity, which enables magnetic characterizations with element and depth resolution. We observe that the total Pd magnetic moments induced at the top Co/Pd interface are significantly larger than the Pd moments at the bottom Pd/Co interface, whereas transmission electron microscopy and reflectivity analysis indicate the two interfaces are nearly identical structurally. Such asymmetry in magnetic proximity effects could be important for understanding spin transport characteristics in ferromagnetic/nonmagnetic systems and its potential application to spin devices.

  14. Toxicities of the anti-PD-1 and anti-PD-L1 immune checkpoint antibodies.

    PubMed

    Naidoo, J; Page, D B; Li, B T; Connell, L C; Schindler, K; Lacouture, M E; Postow, M A; Wolchok, J D

    2015-12-01

    Immune checkpoint antibodies that augment the programmed cell death protein 1 (PD-1)/PD-L1 pathway have demonstrated antitumor activity across multiple malignancies, and gained recent regulatory approval as single-agent therapy for the treatment of metastatic malignant melanoma and nonsmall-cell lung cancer. Knowledge of toxicities associated with PD-1/PD-L1 blockade, as well as effective management algorithms for these toxicities, is pivotal in order to optimize clinical efficacy and safety. In this article, we review selected published and presented clinical studies investigating single-agent anti-PD-1/PD-L1 therapy and trials of combination approaches with other standard anticancer therapies, in multiple tumor types. We summarize the key adverse events reported in these studies and their management algorithms. PMID:26371282

  15. Asymmetric magnetic proximity effect in a Pd/Co/Pd trilayer system

    PubMed Central

    Kim, Dong-Ok; Song, Kyung Mee; Choi, Yongseong; Min, Byoung-Chul; Kim, Jae-Sung; Choi, Jun Woo; Lee, Dong Ryeol

    2016-01-01

    In spintronic devices consisting of ferromagnetic/nonmagnetic systems, the ferromagnet-induced magnetic moment in the adjacent nonmagnetic material significantly influences the spin transport properties. In this study, such magnetic proximity effect in a Pd/Co/Pd trilayer system is investigated by x-ray magnetic circular dichroism and x-ray resonant magnetic reflectivity, which enables magnetic characterizations with element and depth resolution. We observe that the total Pd magnetic moments induced at the top Co/Pd interface are significantly larger than the Pd moments at the bottom Pd/Co interface, whereas transmission electron microscopy and reflectivity analysis indicate the two interfaces are nearly identical structurally. Such asymmetry in magnetic proximity effects could be important for understanding spin transport characteristics in ferromagnetic/nonmagnetic systems and its potential application to spin devices. PMID:27151368

  16. Terahertz generation by beating two Langmuir waves in a warm and collisional plasma

    SciTech Connect

    Zhang, Xiao-Bo; Qiao, Xin; Cheng, Li-Hong; Tang, Rong-An; Zhang, Ai-Xia; Xue, Ju-Kui

    2015-09-15

    Terahertz (THz) radiation generated by beating of two Langmuir waves in a warm and collisional plasma is discussed theoretically. The critical angle between the two Langmuir waves and the critical wave-length (wave vector) of Langmuir waves for generating THz radiation are obtained analytically. Furthermore, the maximum radiation energy is obtained. We find that the critical angle, the critical wave-length, and the generated radiation energy strongly depend on plasma temperature and wave-length of the Langmuir waves. That is, the THz radiation generated by beating of two Langmuir waves in a warm and collisional plasma can be controlled by adjusting the plasma temperature and the Langmuir wave-length.

  17. New regime of low ion collisionality in the neoclassical equilibrium of tokamak plasmas

    NASA Astrophysics Data System (ADS)

    Ramos, J. J.

    2015-07-01

    The neoclassical description of an axisymmetric toroidal plasma equilibrium is formulated for an unconventionally low ordering of the collisionality that suits realistic thermonuclear fusion conditions. This requires a drift-kinetic analysis to the second order of the ion Larmor radius, which yields a new contribution to the leading solution for the non-Maxwellian part of the ion distribution function if the equilibrium geometry is not up-down symmetric. An explicit geometrical factor weighs this second Larmor-radius order, low-collisionality effect that modifies the neoclassical ion parallel flow, and the ion contribution to the bootstrap current.

  18. Collisional narrowing by polyatomic buffer gases in an optically pumped CH3F laser

    NASA Technical Reports Server (NTRS)

    Lawandy, N. M.; Koepf, G. A.

    1980-01-01

    The gain linewidth of an optically pumped CH3F molecular laser is observed with the addition of various polyatomic buffer gases. This is interpreted as collisional (Dicke) narrowing. The measurement is the first observation of collisional narrowing by polyatomic buffer gases. It is also the first observation of the effect in a laser oscillator. The effect was observed using a heterodyne mixing technique at the laser emission frequency of 604 GHz. Collision cross sections for SF6-CH3F and CS2-CH3F are obtained.

  19. New regime of low ion collisionality in the neoclassical equilibrium of tokamak plasmas

    SciTech Connect

    Ramos, J. J.

    2015-07-15

    The neoclassical description of an axisymmetric toroidal plasma equilibrium is formulated for an unconventionally low ordering of the collisionality that suits realistic thermonuclear fusion conditions. This requires a drift-kinetic analysis to the second order of the ion Larmor radius, which yields a new contribution to the leading solution for the non-Maxwellian part of the ion distribution function if the equilibrium geometry is not up-down symmetric. An explicit geometrical factor weighs this second Larmor-radius order, low-collisionality effect that modifies the neoclassical ion parallel flow, and the ion contribution to the bootstrap current.

  20. Thermodynamic and kinetic characterization of H-D exchange in Pd and Pd alloys.

    SciTech Connect

    Luo, Weifang

    2010-09-01

    A Sieverts apparatus coupled with an RGA is an effective method to detect composition variations during isotopic exchange. This experimental setup provides a powerful tool for the thermodynamic and kinetic characterization of H-D isotope exchange on metals and alloys. H-D exchange behavior during absorption and desorption in the plateau region in Pd have been investigated and reported here. It was found that in the plateau region of H-D-Pd system the equilibrium pressures are between those of H2-Pd and D2-Pd for both absorption and desorption and the equilibrium pressures are higher when the fractions of D in the Pd are higher. Adding a dose of gas H2 (or D2) to Pd-D (or Pd-H) system results in releasing of gas D2 and HD (or H2 and HD) in {beta}-phase of Pd-D (or {beta}-phase of Pd-H), but this does not happen in the plateau region. The equilibrium constants have been determined during exchange and it was found that they agree well with the calculated values reported in literature. The separation factor {alpha} values during exchange have been measured and compared with the literature values. The exchange rates have been determined from the exchange profiles and a first order kinetic model for the exchange of H-D-Pd systems has been employed for the analysis. The exchange activation energies for both directions, H2+PdD and D2+PdH, have been determined.

  1. Exploring the collisional evolution of the asteroid belt

    NASA Astrophysics Data System (ADS)

    Bottke, W.; Broz, M.; O'Brien, D.; Campo Bagatin, A.; Morbidelli, A.

    2014-07-01

    The asteroid belt is a remnant of planet-formation processes. By modeling its collisional and dynamical history, and linking the results to constraints, we can probe how the planets and small bodies formed and evolved. Some key model constraints are: (i) The wavy shape of the main-belt size distribution (SFD), with inflection points near 100-km, 10--20-km, 1 to a few km, and ˜0.1-km diameter; (ii) The number of asteroid families created by the catastrophic breakup of large asteroid bodies over the last ˜ 4 Gy, with the number of disrupted D > 100 km bodies as small as ˜20 or as large as 60; (iii) the flux of small asteroids derived from the main belt that have struck the Moon over the last 3.5 Ga --- crater SFDs on lunar terrains with known ages suggest the D < 0.1 km projectile population has not varied appreciably over this interval; (iv) Vesta has an intact basaltic crust with two very large basins, but only two, on its surface. Fits to these parameters allow us to predict the shape of the initial main-belt SFD after accretion and the approximate asteroid disruption scaling law, with the latter consistent with numerical hydrocode simulations. Overall, we find that the asteroid belt probably experienced the equivalent of ˜6--10 Gy of comminution over its history. This value may seem strange, considering the solar system is only 4.56 Gy old. One way to interpret it is that the main belt once had more mass that was eliminated by early dynamical processes between 4--4.56 Ga. This would allow for more early grinding, and it would suggest the main belt's wavy-shaped SFD is a ''fossil'' from a more violent early epoch. Simulations suggest that most D > 100 km bodies have been significantly battered, but only a fraction have been catastrophically disrupted. Conversely, most small asteroids today are byproducts of fragmentation events. These results are consistent with growing evidence that most of the prominent meteorite classes were produced by young asteroid

  2. Workshop on Radio Transients

    NASA Astrophysics Data System (ADS)

    Croft, Steve; Gaensler, Bryan

    2012-04-01

    abstract-type="normal">SummaryWe are entering a new era in the study of variable and transient radio sources. This workshop discussed the instruments and the strategies employed to study those sources, how they are identified and classified, how results from different surveys can be compared, and how radio observations tie in with those at other wavelengths. The emphasis was on learning what common ground there is between the plethora of on-going projects, how methods and code can be shared, and how best practices regarding survey strategy could be adopted. The workshop featured the four topics below. Each topic commenced with a fairly brief introductory talk, which then developed into discussion. By way of preparation, participants had been invited to upload and discuss one slide per topic to a wiki ahead of the workshop. 1. Telescopes, instrumentation and survey strategy. New radio facilities and on-going projects (including upgrades) are both studying the variability of the radio sky, and searching for transients. The discussion first centred on the status of those facilities, and on projects with a time-domain focus, both ongoing and planned, before turning to factors driving choices of instrumentation, such as phased array versus single pixel feeds, the field of view, spatial and time resolution, frequency and bandwidth, depth, area, and cadence of the surveys. 2. Detection, pipelines, and classification. The workshop debated (a) the factors that influence decisions to study variability in the (u,v) plane, in images, or in catalogues, (b) whether, and how much, pipeline code could potentially be shared between one project and another, and which software packages are best for different approaches, (c) how data are stored and later accessed, and (d) how transients and variables are defined and classified. 3. Statistics, interpretation, and synthesis. It then discussed how (i) the choice of facility and strategy and (ii) detection and classification schemes

  3. Thermal transient anemometer

    DOEpatents

    Bailey, J.L.; Vresk, J.

    1989-07-18

    A thermal transient anemometer is disclosed having a thermocouple probe which is utilized to measure the change in temperature over a period of time to provide a measure of fluid flow velocity. The thermocouple probe is located in the fluid flow path and pulsed to heat or cool the probe. The cooling of the heated probe or the heating of the cooled probe from the fluid flow over a period of time is measured to determine the fluid flow velocity. The probe is desired to be locally heated near the tip to increase the efficiency of devices incorporating the probe. 12 figs.

  4. Thermal transient anemometer

    DOEpatents

    Bailey, James L.; Vresk, Josip

    1989-01-01

    A thermal transient anemometer having a thermocouple probe which is utilized to measure the change in temperature over a period of time to provide a measure of fluid flow velocity. The thermocouple probe is located in the fluid flow path and pulsed to heat or cool the probe. The cooling of the heated probe or the heating of the cooled probe from the fluid flow over a period of time is measured to determine the fluid flow velocity. The probe is desired to be locally heated near the tip to increase the efficiency of devices incorporating the probe.

  5. The Rapid Transient Surveyor

    NASA Astrophysics Data System (ADS)

    Baranec, Christoph; Tonry, John; Wright, Shelley; Tully, R. Brent; Lu, Jessica R.; Takamiya, Marianne Y.; Hunter, Lisa

    2016-01-01

    The next decade of astronomy will be dominated by large area surveys (see the detailed discussion in the Astro-2010 Decadal survey and NRC's recent OIR System Report). Ground-based optical transient surveys, e.g., LSST, ZTF and ATLAS and space-based exoplanet, supernova, and lensing surveys such as TESS and WFIRST will join the Gaia all-sky astrometric survey in producing a flood of data that will enable leaps in our understanding of the universe. There is a critical need for further characterization of these discoveries through high angular resolution images, deeper images, spectra, or observations at different cadences or periods than the main surveys. Such follow-up characterization must be well matched to the particular surveys, and requires sufficient additional observing resources and time to cover the extensive number of targets.We describe plans for the Rapid Transient Surveyor (RTS), a permanently mounted, rapid-response, high-cadence facility for follow-up characterization of transient objects on the U. of Hawai'i 2.2-m telescope on Maunakea. RTS will comprise an improved robotic laser adaptive optics system, based on the prototype Robo-AO system (formerly at the Palomar 1.5-m and now at the Kitt Peak 2.2-m telescope), with simultaneous visible and near-infrared imagers as well as a near-infrared integral field spectrograph (R~100, λ = 850 - 1830 nm, 0.15″ spaxels, 8.7″×6.0″ FoV). RTS will achieve an acuity of ~0.07″ in visible wavelengths and < 0.16″ in the near infrared leading to an increase of the infrared point-source sensitivity against the sky background by a factor of ~9, crucial for efficient near-infrared spectroscopy.RTS will allow us to map the dark matter distribution in the z < 0.1 local universe with ten times better accuracy and precision than previous experiments. ATLAS will discover several thousand SNIae per year, measuring SNIa peak brightness, and decline rates, while RTS will measure reddening by dust, confirm SN type and

  6. Initial growth process of Co (Pd) layers on a Pd (Co) surface

    SciTech Connect

    Nishizawa, N. Porquez, J. G.; Munekata, H.; Kitamoto, Y.

    2015-05-07

    The deposition process of ultra-thin Co and Pd layers is studied using DC magnetron sputtering and ex situ atomic force microscopy (AFM). It is found that observation with AFM in the air atmosphere is reliable to discuss nucleation of Co and Pd crystallites. It is discussed that a Co ultra-thin layer is formed primarily through the process of two-dimensional island formation, whereas a Pd ultra-thin layer is formed through the process of mixed two- and three-dimensional island formation. On the basis of those results, Co/Pd multilayers having a flat top surface are prepared successfully.

  7. Transient quantum coherent response to a partially coherent radiation field

    SciTech Connect

    Sadeq, Zaheen S.; Brumer, Paul

    2014-02-21

    The response of an arbitrary closed quantum system to a partially coherent electric field is investigated, with a focus on the transient coherences in the system. As a model we examine, both perturbatively and numerically, the coherences induced in a three level V system. Both rapid turn-on and pulsed turn-on effects are investigated. The effect of a long and incoherent pulse is also considered, demonstrating that during the pulse the system shows a coherent response which reduces after the pulse is over. Both the pulsed scenario and the thermally broadened CW case approach a mixed state in the long time limit, with rates dictated by the adjacent level spacings and the coherence time of the light, and via a mechanism that is distinctly different from traditional decoherence. These two excitation scenarios are also explored for a minimal “toy” model of the electronic levels in pigment protein complex PC645 by both a collisionally broadened CW laser and by a noisy pulse, where unexpectedly long transient coherence times are observed and explained. The significance of environmentally induced decoherence is noted.

  8. Fabrication of Pd-Cr wire

    NASA Technical Reports Server (NTRS)

    Diamond, Sidney; Leach, Dennen M.

    1989-01-01

    Fabrication of Pd-13 percent Cr alloy wires is described. Melting, casting, swaging and annealing processes are discussed. Drawing to reach two diameters (0.003 inch and 0.00176 inch) of wire is described. Representative micrographs of the Pd-Cr alloy at selected stages during wire fabrication are included. The resistance of the wire was somewhat lower, by about 15 to 20 percent, than comparable wire of other alloys used for strain gages.

  9. Transients in the composition of material sputtered from alloy targets

    NASA Astrophysics Data System (ADS)

    Andersen, H. H.; Stenum, B.; Sørensen, T.; Whitlow, H. J.

    1984-03-01

    Material sputtered with 20-320 keV Ar + ions from the binary alloys CuPt, Ni 5Pd and NiPt has been collected sequentially on thin carbon foils. The composition of the collected material was analyzed by Rutherford backscattering to reveal transients in the composition of the sputtered flux. In the beginning Cu and Ni were preferentially ejected. These results, together with earlier data for AgAu and Cu 3Au, where Ag and Cu were preferentially ejected, show the lighter element to be preferentially emitted during the transient, but particularly the results for Cu 3Au and Ni 5Pd suggest that a native oxide layer may play a substantial role, althogh only for the case of Cu 3Au did such an oxide have a sufficient thickness to be revealed by Rutherford backscattering. Measurements have further been carried out for pure copper bombarded with 45 keV Bi + ions. Here, the bismuth re-emission reaches a steady-state a factor of 10 faster than the copper yield, a fact which again may be related to oxygen-driven surface segregation.

  10. YBCO coated conductors on highly textured Pd-buffered Ni-W tape

    NASA Astrophysics Data System (ADS)

    Celentano, G.; Galluzzi, V.; Mancini, A.; Rufoloni, A.; Vannozzi, A.; Augieri, A.; Petrisor, T.; Ciontea, L.; Gambardella, U.

    2006-06-01

    High critical current density YBa2Cu3O7-x (YBCO) coated conductors were obtained on cube textured Ni-W. The use of a Pd transient layer as a first buffer led to a sharp out-of-plane grains alignment of the CeO2/YSZ/CeO2 buffer layer. YBCO films grown on this template exhibit an out-of-plane orientation with a full width at half maximum of about 3°, less than 50% of the respective starting Ni-W value. Despite the complete interdiffusion between Ni-W and Pd after the YBCO film deposition, the coated conductors exhibit good film adherence as well as a crack free and smooth surface of the YBCO film. YBCO thin films show critical temperature values above than 88 K and a critical current density of 2.1 MA/cm2 at 77 K and self field.

  11. Measurand transient signal suppressor

    NASA Technical Reports Server (NTRS)

    Bozeman, Richard J., Jr. (Inventor)

    1994-01-01

    A transient signal suppressor for use in a controls system which is adapted to respond to a change in a physical parameter whenever it crosses a predetermined threshold value in a selected direction of increasing or decreasing values with respect to the threshold value and is sustained for a selected discrete time interval is presented. The suppressor includes a sensor transducer for sensing the physical parameter and generating an electrical input signal whenever the sensed physical parameter crosses the threshold level in the selected direction. A manually operated switch is provided for adapting the suppressor to produce an output drive signal whenever the physical parameter crosses the threshold value in the selected direction of increasing or decreasing values. A time delay circuit is selectively adjustable for suppressing the transducer input signal for a preselected one of a plurality of available discrete suppression time and producing an output signal only if the input signal is sustained for a time greater than the selected suppression time. An electronic gate is coupled to receive the transducer input signal and the timer output signal and produce an output drive signal for energizing a control relay whenever the transducer input is a non-transient signal which is sustained beyond the selected time interval.

  12. Characterizing Nanoscale Transient Communication.

    PubMed

    Chen, Yifan; Anwar, Putri Santi; Huang, Limin; Asvial, Muhamad

    2016-04-01

    We consider the novel paradigm of nanoscale transient communication (NTC), where certain components of the small-scale communication link are physically transient. As such, the transmitter and the receiver may change their properties over a prescribed lifespan due to their time-varying structures. The NTC systems may find important applications in the biomedical, environmental, and military fields, where system degradability allows for benign integration into life and environment. In this paper, we analyze the NTC systems from the channel-modeling and capacity-analysis perspectives and focus on the stochastically meaningful slow transience scenario, where the coherence time of degeneration Td is much longer than the coding delay Tc. We first develop novel and parsimonious models to characterize the NTC channels, where three types of physical layers are considered: electromagnetism-based terahertz (THz) communication, diffusion-based molecular communication (DMC), and nanobots-assisted touchable communication (TouchCom). We then revisit the classical performance measure of ϵ-outage channel capacity and take a fresh look at its formulations in the NTC context. Next, we present the notion of capacity degeneration profile (CDP), which describes the reduction of channel capacity with respect to the degeneration time. Finally, we provide numerical examples to demonstrate the features of CDP. To the best of our knowledge, the current work represents a first attempt to systematically evaluate the quality of nanoscale communication systems deteriorating with time. PMID:26955048

  13. Transient Observations with LSST

    NASA Astrophysics Data System (ADS)

    Walkowicz, Lucianne

    2010-12-01

    In the coming decade, LSST';s combination of all-sky coverage, consistent long-term monitoring, and flexible criteria for event identification will revolutionize studies of a wide variety of astrophysical phenomena. The umbrella of time domain science with LSST encompasses objects both familiar and exotic, from classical variables within our Galaxy to explosive cosmological events. LSST will make localization for gravity wave events possible, identify counterparts to GRBs and X-ray flashes, and discover new supernovae. Increased sample sizes of known-but-rare observational phenomena will quantify their distributions for the first time, thus challenging existing theory. Perhaps most excitingly, LSST will provide the opportunity to sample previously untouched regions of parameter space, where transient events are expected on theoretical grounds, but have not yet been observed. LSST will generate "alerts" within 60 seconds of detecting a new transient, permitting the community t o follow up unusual events in greater detail. Here, I highlight some of the scientific opportunities LSST will provide, as well as the challenges we face and opportunities for community involvement.

  14. The hydrogen permeability of Pd{sub 4}S

    SciTech Connect

    O'Brien, Casey; Miller, James; Gellman, Andrew; Morreale, Bryan

    2011-04-01

    Hydrogen permeates rapidly through pure Pd membranes, but H{sub 2}S, a common minor component in hydrogen-containing streams, produces a Pd{sub 4}S film on the Pd surface that severely retards hydrogen permeation. Hydrogen still permeates through the bi-layered Pd{sub 4}S/Pd structure, indicating that the Pd{sub 4}S surface is active for H{sub 2} dissociation; the low hydrogen permeability of the Pd4S film is responsible for the decreased rate of hydrogen transport. In this work, the hydrogen permeability of Pd{sub 4}S was determined experimentally in the 623-773 K temperature range. Bi-layered Pd{sub 4}S/Pd foils were produced by exposing pure Pd foils to H{sub 2}S. H{sub 2} fluxes through the bi-layered Pd{sub 4}S/Pd foils were measured during exposure to both pure H{sub 2} and a 1000 ppm H{sub 2}S in H{sub 2} gas mixture. Our results show that H{sub 2}S slows hydrogen permeation through Pd mainly by producing a Pd{sub 4}S film on the Pd surface that is roughly an order-of-magnitude less permeable to hydrogen (k{sub Pd{sub 4}S} = 10{sup −7.5} exp(−0.22 eV/k{sub B}T) molH{sub 2}/m/s/Pa{sup 1/2}) than pure Pd. The presence of H{sub 2}S in the gas stream results in greater inhibition of hydrogen transport than can be explained by the very low permeability of Pd{sub 4}S. H{sub 2}S may block H2 dissociation sites at the Pd{sub 4}S surface.

  15. Enhanced hydrogenation and reduced lattice distortion in size selected Pd-Ag and Pd-Cu alloy nanoparticles

    SciTech Connect

    Sengar, Saurabh K.; Mehta, B. R.; Kulriya, P. K.; Khan, S. A.

    2013-10-21

    Important correlation between valence band spectra and hydrogenation properties in Pd alloy nanoparticles is established by studying the properties of size selected and monocrystalline Pd, Ag, Cu, Pd-Ag, and Pd-Cu nanoparticles. The X-ray photoelectron spectroscopy and elastic recoil detection analysis show that size induced Pd4d centroid shift is related to enhanced hydrogenation with H/Pd ratio of 0.57 and 0.49 in Pd-Ag and Pd-Cu nanoparticles in comparison to reported bulk values of 0.2 and 0.1, respectively. Pd-alloy nanoparticles show lower hydrogen induced lattice distortion. The reduced distortion and higher hydrogen reactivity of Pd-alloy nanoparticles is important for numerous hydrogen related applications.

  16. The joy of transient chaos

    SciTech Connect

    Tél, Tamás

    2015-09-15

    We intend to show that transient chaos is a very appealing, but still not widely appreciated, subfield of nonlinear dynamics. Besides flashing its basic properties and giving a brief overview of the many applications, a few recent transient-chaos-related subjects are introduced in some detail. These include the dynamics of decision making, dispersion, and sedimentation of volcanic ash, doubly transient chaos of undriven autonomous mechanical systems, and a dynamical systems approach to energy absorption or explosion.

  17. The Discovery and Modeling of O-Type-Like Collisional Ring Galaxies

    NASA Astrophysics Data System (ADS)

    Wu, Y.-T.; Jiang, I.-G.

    2013-10-01

    A new type of ring galaxies is discovered from the catalog of collisional ring galaxies in Madore et al. (2009). They are galaxies with axis-symmetric rings but originally classified as P-type collisional ring galaxies due to the existence of nearby companions. We call them O-Type-Like Collisional Ring Galaxies and model their formation through simulations of head-on galactic mergers. After head-on collisions by dwarf galaxies moving along the symmetric axis of disk galaxies, it was found that the simulations with smaller initial relative velocities between two galaxies, or the cases with heavier dwarf galaxies, could produce rings with higher density contrasts. There are more than one generation of rings in one collision and the lifetime of any generation of rings is about one dynamical time. We found that head-on penetrations could explain O-Type-Like Collisional Ring Galaxies well and the simulated rings resembling the observational images of rings are those at the early stage of one of the ring-generations.

  18. COLLISIONAL ACTIVATION MASS SPECTRA OF M-. IONS OF AZO DYES CONTAINING 2-NAPHTHOL

    EPA Science Inventory

    Collisionally activated decomposition mass spectra of M- ions of azo dyes are presented. he compounds are of general structure Ar(l)-N=N-Ar(2), where Ar(l) is substituted phenyl and Ar(2) is 2-naphthol. Characteristic fragment ions observed include m/z 157, which corresponds to t...

  19. Dusty Plasma Modeling of the Fusion Reactor Sheath Including Collisional-Radiative Effects

    SciTech Connect

    Dezairi, Aouatif; Samir, Mhamed; Eddahby, Mohamed; Saifaoui, Dennoun; Katsonis, Konstantinos; Berenguer, Chloe

    2008-09-07

    The structure and the behavior of the sheath in Tokamak collisional plasmas has been studied. The sheath is modeled taking into account the presence of the dust{sup 2} and the effects of the charged particle collisions and radiative processes. The latter may allow for optical diagnostics of the plasma.

  20. Speed-dependent collisional effects on the 326.1-nm Cd line perturbed by Xe

    SciTech Connect

    Brym, S.; Ciuryl Trawinski, R.S.; Bielski, A.

    1997-12-01

    The experimental values of pressure broadening and shift parameters of the 326.1-nm Cd line perturbed by Xe are measured and compared with those calculated from the impact theory for different interaction potentials. The role of the correlations between collisional and Doppler broadening for the Cd-Xe system is discussed. {copyright} {ital 1997} {ital The American Physical Society}

  1. Comparison of continuous and discontinuous collisional bumpers: Dimensionally scaled impact experiments into single wire meshes

    NASA Technical Reports Server (NTRS)

    Hoerz, Friedrich; Cintala, Mark; See, Thomas; Bernhard, Ronald; Cardenas, Frank; Davidson, William; Haynes, Jerry

    1992-01-01

    An experimental inquiry into the utility of discontinuous bumpers was conducted to investigate the collisional outcomes of impacts into single grid-like targets and to compare the results with more traditional bumper designs that employ continuous sheet stock. We performed some 35 experiments using 6.3 and 3.2 mm diameter spherical soda-lime glass projectiles at low velocities (less than 2.5 km/s) and 13 at velocities between 5 and 6 km/s, using 3.2 mm spheres only. The thrust of the experiments related to the characterization of collisional fragments as a function of target thickness or areal shield mass of both bumper designs. The primary product of these experiments was witness plates that record the resulting population of collisional fragments. Substantial interpretive and predictive insights into bumper performance were obtained. All qualitative observations (on the witness plates) and detailed measurements of displaced masses seem simply and consistently related only to bumper mass available for interaction with the impactor. This renders the grid bumper into the superior shield design. These findings present evidence that discontinuous bumpers are a viable concept for collisional shields, possibly superior to continuous geometries.

  2. Collisional transport across the magnetic field in drift-fluid models

    NASA Astrophysics Data System (ADS)

    Madsen, J.; Naulin, V.; Nielsen, A. H.; Rasmussen, J. Juul

    2016-03-01

    Drift ordered fluid models are widely applied in studies of low-frequency turbulence in the edge and scrape-off layer regions of magnetically confined plasmas. Here, we show how collisional transport across the magnetic field is self-consistently incorporated into drift-fluid models without altering the drift-fluid energy integral. We demonstrate that the inclusion of collisional transport in drift-fluid models gives rise to diffusion of particle density, momentum, and pressures in drift-fluid turbulence models and, thereby, obviates the customary use of artificial diffusion in turbulence simulations. We further derive a computationally efficient, two-dimensional model, which can be time integrated for several turbulence de-correlation times using only limited computational resources. The model describes interchange turbulence in a two-dimensional plane perpendicular to the magnetic field located at the outboard midplane of a tokamak. The model domain has two regions modeling open and closed field lines. The model employs a computational expedient model for collisional transport. Numerical simulations show good agreement between the full and the simplified model for collisional transport.

  3. Interrelated structures of the transport shock and collisional relaxation layer in a multitemperature, multilevel ionized gas

    NASA Technical Reports Server (NTRS)

    Vinolo, A. R.; Clarke, J. H.

    1973-01-01

    The gas dynamic structures of the transport shock and the downstream collisional relaxation layer are evaluated for partially ionized monatomic gases. Elastic and inelastic collisional nonequilibrium effects are taken into consideration. In the microscopic model of the atom, three electronic levels are accounted for. By using an asymptotic technique, the shock morphology is found on a continuum flow basis. This procedure gives two distinct layers in which the nonequilibrium effects to be considered are different. A transport shock appears as the inner solution to an outer collisional relaxation layer. The results show four main interesting points: (1) on structuring the transport shock, ionization and excitation rates must be included in the formulation, since the flow is not frozen with respect to the population of the different electronic levels; (2) an electron temperature precursor appears at the beginning of the transport shock; (3) the collisional layer is rationally reduced to quadrature for special initial conditions, which (4) are obtained from new Rankine-Hugoniot relations for the inner shock.

  4. THERMOSPRAY IONIZATION WITH REPELLER-INDUCED COLLISIONALLY ACTIVATED DISSOCIATION OF DYES

    EPA Science Inventory

    Thermospray ionization with repeller-induced collisionally activated dissociation (repeller-CAD) has been used to acquire mass spectra of a series of dyes. hese were obtained by applying a voltage of 400 V on the wire repeller. he mass spectra contained arge number of fragment io...

  5. On collisionally enhanced laser pumping of supersonic jets of SF6

    NASA Astrophysics Data System (ADS)

    Bartell, L. S.; Goates, S. R.; Kacner, M. A.

    1980-12-01

    Electron-diffraction analyses of SF6 molecules in a microjet irradiated by a cw infrared laser are reported. Excitations of several photons per molecule are achieved in the collisional region extending for the order of a nozzle diameter before molecules become cold and dilute. A model accounting for results is proposed.

  6. Collisional Evolution of High-Inclination Asteroids: Implications for Asteroid Strength

    NASA Astrophysics Data System (ADS)

    O'Brien, David P.; Michel, P.; Jutzi, M.

    2009-09-01

    Asteroids with inclinations larger than 20 degrees collide with one another, and with lower-inclination asteroids, with a velocity roughly twice as large as the average collisional velocity in the asteroid belt ( 10 km/sec for high-inclination bodies vs. 5 km/sec main belt average). Thus, their size distribution can potentially evolve differently than the main belt as a whole, for two reasons: 1) the larger collision velocity means that a smaller impactor can lead to their catastrophic disruption; and 2) the energy needed for catastrophic disruption is likely a function of collision velocity [1]. Using a collisional evolution model [2,3] modified to treat two interacting populations, as well as new velocity-dependent scaling laws for asteroid collisional disruption, we study the possible differences in the size distribution of high-inclination asteroids that may result from their increased collision velocity. Recent observations suggest that the size distribution of asteroids around a kilometer in diameter may be shallower for high-inclination asteroids than for low-inclination asteroids [4]. We will discuss the implications that such observational constraints have for the collisional properties of asteroids, namely their strength against catastrophic disruption and how it varies with impact velocity. References: [1] Benz and Asphaug (1999), Icarus 142, 5-20. [2] Bottke et al. (2005), Icarus 175, 111-140. [3] O'Brien (2009), Icarus, in press. [4] Terai and Itoh (2008), ACM 2008, abstract #8215.

  7. Do the Pop II field blue stragglers have a collisional origin

    SciTech Connect

    Leonard, P.J.T.

    1993-01-01

    The hypothesis that the Pop II field blue stragglers have a collisional origin is considered. It appears unlikely that the majority of these stragglers were formed via collisions, but it is difficult to rule out the possibility that a small, but observable, fraction of them were.

  8. Do the Pop II field blue stragglers have a collisional origin?

    SciTech Connect

    Leonard, P.J.T.

    1993-03-01

    The hypothesis that the Pop II field blue stragglers have a collisional origin is considered. It appears unlikely that the majority of these stragglers were formed via collisions, but it is difficult to rule out the possibility that a small, but observable, fraction of them were.

  9. The Zwicky Transient Facility

    NASA Astrophysics Data System (ADS)

    Kulkarni, Shrinivas R.

    2016-01-01

    The Zwicky Transient Facility (ZTF) has been designed with a singular focus: a systematic exploration of the night sky at a magnitude level well suited for spectral classification and follow up with the existing class of 4-m to 10-m class telescopes. ZTF is the successor to the Palomar Transient Factory (PTF). The discovery engine for ZTF is a 47 square degree camera (realized through 16 e2V monolithic CCDs) that fills the entire focal plane of the 48-inch Oschin telescope of the Palomar Observatory. Single 30-s epoch sensitivity is about 20.5 in g and R bands. The Infarared Processing & Analysis Center (IPAC) is the data center for ZTF. ZTF is a public-private partnership with equal contributions from a consortium of world-wide partners and an NSF MSIP grant. Forty percent of ZTF time is set aside for two major community surveys: a 3-day cadence survey of high latitudes (to mimic LSST) and a time domain survey of the entire Northern Galactic plane. We expect first light in February 2017 and begin a 3-year survey starting summer of 2017. The first year will be spent on building up deep reference images of the sky (a must for transient surveys). During the second year IPAC will deliver near archival quality photometric products within 12 hours of observations. By comparison to reference images photometric alerts will be sent out. Year 3 will see the near real-time release of image differencing products. A Community Science Advisory Committee (CSAC), chaired by S. Ridgway (NOAO), has been set up to both advise the PI and to ensure that the US community's interests are well served. Astronomers interested in getting a head start on ZTF may wish to peruse the data releases from PTF. Young people (or young at heart) may wish to attend the annual summer school on PTF/ZTF (August, Caltech campus). The Principal Investigator (PI) for the project is S. Kulkarni and the Project Scientist is Eric Bellm.For further details please consult http://www.ptf.caltech.edu/ztf

  10. Independent assessment of TRAC-PD2 and RELAP5/MOD1 codes at BNL in FY 1981. [PWR

    SciTech Connect

    Saha, P; Jo, J H; Neymotin, L; Rohatgi, U S; Slovik, G

    1982-12-01

    This report documents the independent assessment calculations performed with the TRAC-PD2 and RELAP/MOD1 codes at Brookhaven National Laboratory (BNL) during Fiscal Year 1981. A large variety of separate-effects experiments dealing with (1) steady-state and transient critical flow, (2) level swell, (3) flooding and entrainment, (4) steady-state flow boiling, (5) integral economizer once-through steam generator (IEOTSG) performance, (6) bottom reflood, and (7) two-dimensional phase separation of two-phase mixtures were simulated with TRAC-PD2. In addition, the early part of an overcooling transient which occurred at the Rancho Seco nuclear power plant on March 20, 1978 was also computed with an updated version of TRAC-PD2. Three separate-effects tests dealing with (1) transient critical flow, (2) steady-state flow boiling, and (3) IEOTSG performance were also simulated with RELAP5/MOD1 code. Comparisons between the code predictions and the test data are presented.

  11. CO₂ electroreduction at bare and Cu-decorated Pd pseudomorphic layers: catalyst tuning by controlled and indirect supporting onto Au(111).

    PubMed

    Januszewska, Aneta; Jurczakowski, Rafal; Kulesza, Pawel J

    2014-12-01

    We report here the results of electrochemical studies on CO2 electroreduction at multilayered catalyst composed of the monatomic layer of copper covering palladium overlayers (0.8-10 monolayers) deposited on the well-defined Au(111) surface. These multilayered systems were obtained by successive underpotential deposition steps: Pd on Au(111) as well as Cu on Pd/Au(111). Low index orientation of Au substrate was chosen to compare Pd overlayers with bulk Pd(111), which is known to reduce CO2 to CO adsorbates in acidic solutions. The process of CO2 electroreduction was studied by using classical transient electrochemical methods. Catalytic activity of bare Pd layers was investigated in acidic and neutral solutions. In the latter case, much higher activity of Pd overlayers was observed. The results showed that the palladium layer thickness significantly changed the catalytic activities of both bare Pd overlayers and the one Cu monolayer covered electrodes toward CO2 electroreduction. Results show that catalytic activity can be finely tuned by using the multilayered near-surface-alloy approach. PMID:25350872

  12. Immune escape to PD-L1/PD-1 blockade: seven steps to success (or failure).

    PubMed

    Kim, J M; Chen, D S

    2016-08-01

    The emergence of programmed death-ligand 1 (PD-L1)/programmed death-1 (PD-1)-targeted therapy has demonstrated the importance of the PD-L1 : PD-1 interaction in inhibiting anticancer T-cell immunity in multiple human cancers, generating durable responses and extended overall survival. However, not all patients treated with PD-L1/PD-1-targeted therapy experience tumor shrinkage, durable responses, or prolonged survival. To extend such benefits to more cancer patients, it is necessary to understand why some patients experience primary or secondary immune escape, in which the immune response is incapable of eradicating all cancer cells. Understanding immune escape from PD-L1/PD-1-targeted therapy will be important to the development of rational immune-combination therapy and predictive diagnostics and to the identification of novel immune targets. Factors that likely relate to immune escape include the lack of strong cancer antigens or epitopes recognized by T cells, minimal activation of cancer-specific T cells, poor infiltration of T cells into tumors, downregulation of the major histocompatibility complex on cancer cells, and immunosuppressive factors and cells in the tumor microenvironment. Precisely identifying and understanding these mechanisms of immune escape in individual cancer patients will allow for personalized cancer immunotherapy, in which monotherapy and combination immunotherapy are chosen based on the presence of specific immune biology. This approach may enable treatment with immunotherapy without inducing immune escape, resulting in a larger proportion of patients obtaining clinical benefit. PMID:27207108

  13. Differential control of CD4+ T cell subsets by the PD-1/PD-L1 axis in allergic asthma

    PubMed Central

    McAlees, Jaclyn W.; Lajoie, Stephane; Dienger, Krista; Sproles, Alyssa A.; Richgels, Phoebe K.; Yang, Yanfen; Khodoun, Marat; Azuma, Miyuki; Yagita, Hideo; Fulkerson, Patricia C.; Wills-Karp, Marsha; Lewkowich, Ian P.

    2015-01-01

    Studies examining the role of PD-1 family members in allergic asthma have yielded conflicting results. Using a mouse model of allergic asthma, we find that blockade of PD-1/PD-L1 has distinct influences on different CD4+ T cell subsets. PD-1/PD-L1 blockade enhances AHR not by altering the magnitude of the underlying Th2 immune response, but by allowing the development of a concomitant Th17 immune response. Supporting differential CD4+ T cell responsiveness to PD-1-mediated inhibition, naïve PD-1−/− mice displayed elevated Th1 and Th17 levels, but diminished Th2 cytokine levels, ligation of PD-1 limited cytokine production by in vitro-polarized Th1 and Th17 cells, but slightly enhanced cytokine production by in vitro-polarized Th2 cells, and PD-1 ligation enhanced Th2 cytokine production by naïve T cells cultured under non-polarizing conditions. These data demonstrate that different CD4+ T cell subsets respond differentially to PD-1 ligation and may explain some of the variable results observed in control of allergic asthma by the PD-1 family members. As the PD-1/PD-L1 axis limits asthma severity by constraining Th17 cell activity, this suggests that severe allergic asthma may be associated with a defective PD-1/PD-L1 regulatory axis in some individuals. PMID:25630305

  14. Crystal Structure of the Complex Between Programmed Death-1 (PD-1) and its Ligand PD-L2

    SciTech Connect

    Lazar-Molnar,E.; Yan, Q.; Cao, E.; Ramagopal, U.; Nathenson, S.; Almo, S.

    2008-01-01

    Programmed death-1 (PD-1) is a member of the CD28/B7 superfamily that delivers negative signals upon interaction with its two ligands, PD-L1 or PD-L2. The high-resolution crystal structure of the complex formed by the complete ectodomains of murine PD-1 and PD-L2 revealed a 1:1 receptor:ligand stoichiometry and displayed a binding interface and overall molecular organization distinct from that observed in the CTLA-4/B7 inhibitory complexes. Furthermore, our structure also provides insights into the association between PD-1 and PD-L1 and highlights differences in the interfaces formed by the two PD-1 ligands (PD-Ls) Mutagenesis studies confirmed the details of the proposed PD-1/PD-L binding interfaces and allowed for the design of a mutant PD-1 receptor with enhanced affinity. These studies define spatial and organizational constraints that control the localization and signaling of PD-1/PD-L complexes within the immunological synapse and provide a basis for manipulating the PD-1 pathways for immunotherapy.

  15. Transient complex peroxisomal interactions

    PubMed Central

    Bonekamp, Nina A.; Schrader, Michael

    2012-01-01

    Mitochondria and peroxisomes are ubiquitous subcellular organelles that fulfill essential metabolic functions, rendering them indispensable for human development and health. Both are highly dynamic organelles that can undergo remarkable changes in morphology and number to accomplish cellular needs. While mitochondrial dynamics are also regulated by frequent fusion events, the fusion of mature peroxisomes in mammalian cells remained a matter of debate. In our recent study, we clarified systematically that there is no complete fusion of mature peroxisomes analogous to mitochondria. Moreover, in contrast to key division components such as DLP1, Fis1 or Mff, mitochondrial fusion proteins were not localized to peroxisomes. However, we discovered and characterized novel transient, complex interactions between individual peroxisomes which may contribute to the homogenization of the often heterogeneous peroxisomal compartment, e.g., by distribution of metabolites, signals or other “molecular information” via interperoxisomal contact sites. PMID:23336019

  16. Optical transient monitor

    NASA Astrophysics Data System (ADS)

    Bernas, Martin; Páta, Petr; Hudec, René; Soldán, Jan; Rezek, Tomáš; Castro-Tirado, Alberto J.

    1998-05-01

    Although there are several optical GRB follow-up systems in operation and/or in development, some of them with a very short response time, they will never be able to provide true simultaneous (no delay) and pre-burst optical data for GRBs. We report on the development and tests of a monitoring experiment expected to be put into test operation in 1998. The system should detect Optical Transients down to mag 6-7 (few seconds duration assumed) over a wide field of view. The system is based on the double CCD wide-field cameras ST8. For the real time evaluation of the signal from both cameras, two TMS 320C40 processors are used. Using two channels differing in spectral sensitivity and processing of temporal sequence of images allows us to eliminate man-made objects and defects of the CCD electronics. The system is controlled by a standard PC computer.

  17. Transient Dentritic Solidification Experiment

    NASA Technical Reports Server (NTRS)

    2000-01-01

    The Transient Dentritic Solidification Experiment (TDSE) is being developed as a candidate for flight aboard the International Space Station. TDSE will study the growth of dentrites (treelike crystalline structures) in a transparent material (succinonitrile or SCN) that mimics the behavior of widely used iron-based metals. Basic work by three Space Shuttle flights (STS-62, STS-75, and STS-87) of the Isothermal Dendritic Growth Experiment (IDGE) is yielding new insights into virtually all industrially relevant metal and alloy forming operations. The TDSE is similar to IDGE, but will maintain a constant temperature while varying pressure on the dentrites. Shown here is a cutaway of the isothermal bath containing its growth cell at the heart of the TDSE. The principal investigator is Matthew Koss of College of the Holy Cross in Worcester, MA. Note: an Acrobat PDF version is available from http://microgravity.nasa.gov/gallery

  18. Transient heliosheath modulation

    NASA Astrophysics Data System (ADS)

    Quenby, J. J.; Webber, W. R.

    2015-10-01

    Voyager 1 has explored the solar wind-interstellar medium interaction region between the terminal shock and heliopause, following the intensity distribution of Galactic cosmic ray protons above 200 MeV energy. Before this component reached the expected galactic flux level at 121.7 au from the Sun, four episodes of rapid intensity change occurred with a behaviour similar to that found in Forbush Decreases in the inner Solar system, rather than that expected from a mechanism related to models for the long-term modulation found closer to the Sun. Because the mean solar wind flow is both expected and observed to be perpendicular to the radial direction close to the heliopause, an explanation is suggested in terms of transient radial flows related to possible heliopause boundary flapping. It is necessary that the radial flows are of the order either of the sound speed found for conditions downstream of the terminal shock or of the fluctuations found near the boundary by the Voyager 1 Low Energy Charged Particle detector and that the relevant cosmic ray diffusion perpendicular to the mean field is controlled by `slab' fluctuations accounting for about 20 per cent of the total power in the field variance. However, additional radial drift motion related to possible north to south gradients in the magnetic field may allow the inclusion of some diffusion according to the predictions of a theory based upon the presence of 2D turbulence. The required field gradients may arise due to field variation in the field carried by solar plasma flow deflected away from the solar equatorial plane. Modulation amounting to a total 30 per cent drop in galactic intensity requires explanation by a combination of transient effects.

  19. Leucogranites of the Teton Range, Wyoming: A record of Archean collisional orogeny

    NASA Astrophysics Data System (ADS)

    Frost, Carol D.; Swapp, Susan M.; Frost, B. Ronald; Finley-Blasi, Lee; Fitz-Gerald, D. Braden

    2016-07-01

    Leucogranitic rocks formed by crustal melting are a prominent feature of collisional orogens of all ages. This study describes leucogranitic gneisses associated with an Archean collisional orogeny preserved in the Teton Range of northwestern Wyoming, USA. These leucogneisses formed at 2.68 Ga, and initial Nd isotopic compositions suggest they are derived from relatively juvenile sources. Two distinct groups of leucogneisses, both trondhjemitic, are identified on the basis of field relations, petrology, and geochemistry. The Webb Canyon gneiss forms large, sheet-like bodies of hornblende biotite trondhjemite and granodiorite. This gneiss is silica-rich (SiO2 = 70-80%), strongly ferroan, comparatively low in alumina, and is characterized by high Zr and Y, low Sr, and high REE contents that define "seagull"-shaped REE patterns. The Bitch Creek gneiss forms small sills, dikes, and plutons of biotite trondhjemite. Silica, Zr, Y, and REE are lower and alumina and Sr are higher than in the Webb Canyon gneiss. These differences reflect different melting conditions: the Webb Canyon gneiss formed by dehydration melting in which amphibole and quartz breaks down, accounting for the low alumina, high FeO, high silica content and observed trace element characteristics. The Bitch Creek gneiss formed by H2O-excess melting in which plagioclase breaks down leaving an amphibole-rich restite, producing magmas higher in alumina and Sr and lower in FeO and HREE. Both melt mechanisms are expected in collisional environments: dehydration melting accompanies gravitational collapse and tectonic extension of dramatically thickened crust, and water-excess melting may occur when collision places a relatively cool, hydrous lower plate beneath a hotter upper plate. The Archean leucogranitic gneisses of the Teton Range are calcic trondhjemites and granodiorites whereas younger collisional leucogranites typically are true granites. The difference in leucogranite composition reflects the

  20. From pebbles to dust: experiments to observe low-velocity collisional outcomes

    NASA Astrophysics Data System (ADS)

    Dove, A.; Jorges, J.; Colwell, J. E.

    2015-12-01

    Particle size evolution in planetary ring systems can be driven by collisions at relatively low velocities (<1 m/s) occurring between objects with a range of sizes from very fine dust to decimeter-sized objects. In these complex systems, collisions between centimeter-sized objects may result in particle growth by accretion, rebounding, or erosive processes that result in the production of additional smaller particles. The outcomes of these collisions are dependent on factors such as collisional energy, particle size, and particle morphology. Numerical simulations are limited by a need to understand these collisional parameters over a range of conditions. We present the results of a sequence of laboratory experiments designed to explore collisions over a range of these parameters. We are able to observe low-velocity collisions by conducting experiments in vacuum chambers in our 0.8-sec drop tower apparatus. Initial experiments utilize a variety of impacting spheres, including glass, Teflon, aluminum, stainless steel, and brass. These spheres are either used in their natural state or are "mantled" - coated with a few-mm thick layer of a cohesive powder. A high-speed, high-resolution video camera is used to record the motion of the colliding bodies. These videos are then processed and we track the particles to determine impactor speeds before and after collision and the collisional outcome; in the case of the mantled impactors, we can assess how much of the powder was released in the collision. We also determine how the coefficient of restitution varies as a function of material type, morphology, and impact velocity. Impact velocities range from about 20-60 cm/s, and we observe that mantling of particles significantly reduces their coefficients of restitution. These results will contribute to an empirical model of collisional outcomes that can help refine our understanding of dusty ring system collisional evolution.

  1. Domain structures and magnetization reversal in Co/Pd and CoFeB/Pd multilayers

    SciTech Connect

    Sbiaa, R.; Ranjbar, M.; Åkerman, J.

    2015-05-07

    Domain structures and magnetization reversal of (Co/Pd) and (CoFeB/Pd) multilayers with 7 and 14 repeats were investigated. The Co-based multilayers show much larger coercivities, a better squareness, and a sharper magnetization switching than CoFeB-based multilayers. From magnetic force microscopy observations, both structures show strong reduction in domains size as the number of repeats increases but the magnetic domains for Co-based multilayers are more than one order of magnitude larger than for CoFeB-based multilayers. By imaging domains at different times, breaks in the (CoFeB/Pd) multilayer stripes were observed within only few hours, while no change could be seen for (Co/Pd) multilayers. Although CoFeB single layers are suitable for magnetoresistive devices due to their large spin polarization and low damping constants, their lamination with Pd suffers mainly from thermal instability.

  2. Detection of a Pd-Ni interlayer at the Pd/Ni interface of an epitaxial Pd film on cube textured nickel ( 0 0 1 )

    NASA Astrophysics Data System (ADS)

    Je, J. H.; You, H.; Cullen, W. G.; Maroni, V. A.; Ma, B.; Koritala, R. E.; Thieme, C.

    2002-12-01

    We studied the microstructure of a Pd overlayer deposited on a cube textured Ni(0 0 1) substrate using synchrotron X-ray scattering. We find the existence of an epitaxial Pd-Ni interlayer between the epitaxial Pd layer and the Ni substrate. The Pd-Ni interlayer, which is compressively strained in a manner similar to the Pd overlayer, seemingly acts to relieve the strain at the Pd/Ni interface caused by the Pd-Ni lattice mismatch. The Ni mosaic distribution of our samples is multiply spiked with a rocking angle spread of ∼16°, which reconciles the previously reported observation of saw tooth peaks on top of a Gaussian distribution for a similarly prepared Pd on Ni specimen. The observed sharpening of the mosaic distributions for the Pd(0 0 2) grains (full-width at half-maximum (FWHM)=1.95°) and for the (0 0 2) grains of Pd-Ni interlayer (FWHM=3.0°) indicates that the Pd and Pd-Ni(0 0 2) layers conform to the surface morphology instead of to the (0 0 1) crystallographic planes of Ni-substrate grains.

  3. Nanocrystalline Pd alloy films coated by electroless deposition.

    PubMed

    Strukov, G V; Strukova, G K; Batov, I E; Sakharov, M K; Kudrenko, E A; Mazilkin, A A

    2011-10-01

    The structures of palladium and palladium alloys thin films deposited from organic electrolytes onto metallic substrates by electroless plating method have been investigated. The coatings are dense, pore-free 0.005-1 microm thick films with high adhesive strength to the substrate surface. EDX, XRD, SEM and TEM methods were used to determine the composition and structure of alloy coatings of the following binary systems: Pd-Au, Pd-Ag, Pd-Ni, Pd-Pb, and ternary system Pd-Au-Ni. The coatings of Pd-Au, Pd-Ag and Pd-Ni have a solid solution structure, whereas Pd-Pb is intermetallic compound. It has been found that the deposited films consist of nanocrystalline grains with sizes in the range of 11-35 nm. Scanning and transmission electron microscopy investigations reveal the existence of clusters formed by nanocrystalline grains. The origin for the formation of nanocrystalline structures of coating films is discussed. PMID:22400291

  4. CTLA-4 and PD-1 Pathways

    PubMed Central

    Desai, Anupam

    2016-01-01

    The cytotoxic T-lymphocyte–associated antigen 4 (CTLA-4) and programmed death 1 (PD-1) immune checkpoints are negative regulators of T-cell immune function. Inhibition of these targets, resulting in increased activation of the immune system, has led to new immunotherapies for melanoma, non–small cell lung cancer, and other cancers. Ipilimumab, an inhibitor of CTLA-4, is approved for the treatment of advanced or unresectable melanoma. Nivolumab and pembrolizumab, both PD-1 inhibitors, are approved to treat patients with advanced or metastatic melanoma and patients with metastatic, refractory non-small cell lung cancer. In addition the combination of ipilimumab and nivolumab has been approved in patients with BRAF WT metastatic or unresectable melanoma. The roles of CTLA-4 and PD-1 in inhibiting immune responses, including antitumor responses, are largely distinct. CTLA-4 is thought to regulate T-cell proliferation early in an immune response, primarily in lymph nodes, whereas PD-1 suppresses T cells later in an immune response, primarily in peripheral tissues. The clinical profiles of immuno-oncology agents inhibiting these 2 checkpoints may vary based on their mechanistic differences. This article provides an overview of the CTLA-4 and PD-1 pathways and implications of their inhibition in cancer therapy. PMID:26558876

  5. Deep Crustal Metamorphic Carbon Cycling in Collisional Orogens: What do we Really Know?

    NASA Astrophysics Data System (ADS)

    Ague, J.

    2012-12-01

    The classic study of Bowen (1940) showed that CO2 is lost during metamorphic heating of common carbonate-bearing rocks. Despite tremendous progress in our understanding of devolatilization since Bowen's time, the fact remains that the metamorphic CO2 flux from active mountain belts is one of the most poorly-understood components of the global C cycle. A basic question is: do large fluid fluxes accompany collisional orogenesis? It has been argued that metamorphic rocks are overpressured and, thus, permeability is low and fluid fluxes are limited. In contrast, field-based studies commonly estimate large time-integrated fluxes of the order of 103 m3 m-2 or more. These opposing viewpoints can be reconciled by recognizing that large fluxes can pass through rocks on geologic timescales even if permeability is low, and that transient events such as fracturing can greatly increase permeability and facilitate flow. Large regional fluxes make possible significant CO2 transfer from the deep roots of mountain belts to the shallow hydrosphere and atmosphere. Important prograde CO2 release processes include "internally-buffered" reactions, fluid infiltration, carbonate mineral dissolution, and oxidation of graphite (or diamond). The relative roles of these processes, particularly the latter two, are topics of active research. Regardless of process, however, field-based results commonly show prograde loss of 10 to 15 kg CO2 per 100 kg rock for a range of carbonate mineral-bearing lithologies from sub-greenschist to upper amphibolite facies metamorphism. Could this CO2 make a real difference to C cycling? A new assessment of the mean loss of CO2 from metamorphic sequences in New England, USA, for example, yields a minimum release rate of about 1018 mol Ma-1 during the Acadian orogeny (Devonian). This is comparable to Kerrick and Caldeira's (1993) threshold needed to affect global atmospheric temperatures. Flow around large, deep-seated intrusions could easily produce even larger

  6. Transients by substructuring with DMAP

    NASA Technical Reports Server (NTRS)

    Butler, T. G.

    1978-01-01

    Automated substructuring in level 16 of NASTRAN was employed as a preface to the solution of a direct transient analysis. The DMAP ALTER statements written to adapt the substructuring for transient purposes are explained. Data recovery was accomplished with transfer functions. Proof of the success of the method is presented with an application to a missile structure.

  7. Understanding Physical Developer (PD): Part II--Is PD targeting eccrine constituents?

    PubMed

    de la Hunty, Mackenzie; Moret, Sébastien; Chadwick, Scott; Lennard, Chris; Spindler, Xanthe; Roux, Claude

    2015-12-01

    Physical developer (PD) is a fingermark development technique that deposits silver onto fingermark ridges. It is the only technique currently in routine operational use that gives results on porous substrates that have been wet. There is a reasonable understanding of the working solution chemistry, but the chemical constituent(s) contained in fingermark residue that are specifically targeted by PD are largely unknown. A better understanding of the PD technique will permit a more informed selection of alternative or complementary detection methods, and greater usage in operational laboratories. Recent research by our group has shown that PD does not selectively target the lipids present in the residue. This research investigated the hypothesis that PD targets the eccrine constituents in fingermark residue. This was tested by comparison of PD and indanedione-zinc (Ind-Zn) treated natural fingermarks that had been deposited successively, and marks that had been deposited with a ten second interval in between depositions. Such an interval allows for the regeneration of secretions from the pores located on the ridges of the fingers. On fingermark depletions with no time interval between depositions, PD and Ind-Zn treated depletions successively (and comparatively) decreased in development intensity as the amount of residue diminished. Short time intervals in between successive depletions resulted in additional secretions from the pores intermittently occurring, the increased development of which was visualised by treatment with both PD and Ind-Zn. The changes in development intensity were seen with both techniques on the same split depletions in a series, comparably and proportionately. These results indicate that the components targeted by PD are contained in the material excreted by the friction ridge pores through its mirrored development with Ind-Zn. Repetition of the experiments on marks that only contained eccrine material showed good Ind-Zn development but poor

  8. Magnetic characteristics of CoPd and FePd antidot arrays on nanoperforated Al2O3 templates

    NASA Astrophysics Data System (ADS)

    Maximenko, A.; Fedotova, J.; Marszałek, M.; Zarzycki, A.; Zabila, Y.

    2016-02-01

    Hard magnetic antidot arrays show promising results in context of designing of percolated perpendicular media. In this work the technology of magnetic FePd and CoPd antidot arrays fabrication is presented and correlation between surface morphology, structure and magnetic properties is discussed. CoPd and FePd antidot arrays were fabricated by deposition of Co/Pd and Fe/Pd multilayers (MLs) on porous anodic aluminum oxide templates with bowl-shape cell structure with inclined intercellular regions. FePd ordered L10 structure was obtained by successive vacuum annealing at elevated temperatures (530 °C) and confirmed by XRD analysis. Systematic analysis of magnetization curves evidenced perpendicular magnetic anisotropy of CoPd antidot arrays, while FePd antidot arrays revealed isotropic magnetic anisotropy with increased out-of-plane magnetic contribution. MFM images of antidots showed more complicated contrast, with alternating magnetic dots oriented parallel and antiparallel to tip magnetization moment.

  9. High-Resolution PET Imaging with Therapeutic Antibody-based PD-1/PD-L1 Checkpoint Tracers

    PubMed Central

    Hettich, Michael; Braun, Friederike; Bartholomä, Mark D.; Schirmbeck, Reinhold; Niedermann, Gabriele

    2016-01-01

    Checkpoint-blocking antibodies like those targeting the PD-1/PD-L1 pathway have revolutionized oncology. We developed radiotracers based on therapeutic checkpoint-blocking antibodies permitting sensitive and high-resolution PET imaging of both PD-1 and PD-L1 in immunocompetent mice. ImmunoPET of naive mice revealed similar overall expression patterns for PD-1 and PD-L1 in secondary lymphoid organs (spleen and lymph nodes). Interestingly, PD-L1 was also detected in brown adipose tissue (BAT), confirming the notion that BAT is immunologically relevant. Under pathophysiological conditions, strong expression of the receptor/ligand pair was also found in non-lymphoid tissues. Both were specifically detected in malignant tumors. PD-1 was readily detected after combined immunoradiotherapy causing massive tumor infiltration by PD-1+ lymphocytes. PD-L1 tracer uptake was reduced in PD-L1 knockout tumors. Moreover, monitoring the expression changes of PD-L1 in response to its main inducer, the effector T cell cytokine IFN-γ, revealed robust upregulation in the lung. This suggests that T cell responses in the lung, a vital organ continuously exposed to a variety of antigens, are strongly restrained by the PD-1 checkpoint. In turn, this could explain the association of PD-1 checkpoint inhibition with potentially fatal immune-mediated pneumonitis and partially also its efficacy in lung cancer. PMID:27446497

  10. Decomposition of ethylene on small Pd particles

    NASA Technical Reports Server (NTRS)

    Durrer, W. G.; Poppa, H.; Dickinson, J. T.; Park, C.

    1985-01-01

    New results have been obtained which contribute to the understanding of hydrocarbon reactions on the surface of highly dispersed metal systems. Small particle of Pd were grown by electron beam evaporation on cleavage planes of high purity natural mica under ultrahigh vacuum conditions. Samples were subsequently characterized by transmission electron microscopy. Average particle sizes ranged from about 1 to 10 nm diameter. The chemisoption and decomposition of C2H4 on the Pd particles was studied using Auger electron spectroscopy and flash thermal desorption. It is shown that (a) C2H4 decomposes on Pd particles at room temperature, (b) specific surface sites are causing decomposition, and (c) the proportion of such active sites is significantly greater for the smaller metal particles. This enhanced reactivity may be due to an increase in the density of step, corner, and edge sites with a decrease in particle size.

  11. Plunger Lifetime Measurements in 102Pd

    SciTech Connect

    Kalyva, G.; Spyrou, A.; Axiotis, M.; Harissopulos, S.; Dewald, A.; Fitzler, A.; Saha, B.; Liennemann, A.; Vlastou, R.; Napoli, D. R.; Marginean, N.; Rusu, C.; De Angelis, G.; Ur, C.; Bazzacco, D.; Farnea, E.; Balabanski, D. L.; Julin, R.

    2006-04-26

    Recently, an intense experimental effort has been devoted to the search of empirical proofs of critical-point symmetries in nuclear structure. These symmetries describe shape-phase transitions and provide parameter-free predictions (up to over-all scale factors) for excitation spectra and B(E2) values. This contribution reports on recent plunger-lifetime measurements ON 102Pd carried out at LNL, Legnaro, with the Cologne plunger apparatus coupled to the GASP spectrometer and using the 92Zr(13C,3n)102Pd reaction at 48 MeV. According to the results of our measurements, 102Pd is so far the best known paradigm of the E(5) critical-point symmetry.

  12. Experimental evidence of resonant energy collisional transfers between argon 1s and 2p states and ground state H atoms by laser collisional induced fluorescence

    NASA Astrophysics Data System (ADS)

    Carbone, Emile; van Dijk, Jan; Kroesen, Gerrit

    2015-04-01

    In this paper, laser collisional induced fluorescence (LCIF) is used to probe resonant excitation transfers in an argon/hydrogen plasma resulting from heavy particle collisions. Different radiative transitions between the 1s and 2p states (in Paschen's notation) of argon are optically pumped by a nanosecond laser pulse. The spontaneous fluorescence and collisional responses of the argon and hydrogen systems are monitored by optical emission spectroscopy. A surfatron plasma source is used to generate an argon plasma with a few per cent hydrogen addition at pressures between 0.65 and 20 mbar. The electron density is measured independently by means of Thomson scattering. The overall response of the plasma due to optical pumping of argon is briefly discussed and an overview of the known heteronuclear excitation transfers in an argon/hydrogen plasma is given. The propagation of the shortcut in the Ar(1s) to H(n = 2) excitation transfer due to the optical pumping of the Ar(1s) states is seen in the atomic hydrogen LCIF responses. For the first time, we give direct experimental evidence of the existence of an efficient excitation transfer: Additionally, measurements are performed in order to estimate the resonant energy transfer between the resonant argon 1s states and hydrogen atoms: for which no previously measured cross sections could be found in the literature. These are extra quenching channels of argon 1s and 2p states that should be included in collisional-radiative modeling of argon-hydrogen discharges. The high repetition rate of the dye laser allows us to obtain a high sensitivity in the measurements. LCIF is shown to be a powerful tool for unraveling electron and also heavy particle excitation channels in situ in the plasma phase. The technique was previously developed for measuring electron or species densities locally in the plasma, but we show that it can be advantageously used to probe collisional transfers between very short-lived species which exist

  13. Nitrite reduction mechanism on a Pd surface.

    PubMed

    Shin, Hyeyoung; Jung, Sungyoon; Bae, Sungjun; Lee, Woojin; Kim, Hyungjun

    2014-11-01

    Nitrate (NO3-) is one of the most harmful contaminants in the groundwater, and it causes various health problems. Bimetallic catalysts, usually palladium (Pd) coupled with secondary metallic catalyst, are found to properly treat nitrate-containing wastewaters; however, the selectivity toward N2 production over ammonia (NH3) production still requires further improvement. Because the N2 selectivity is determined at the nitrite (NO2-) reduction step on the Pd surface, which occurs after NO3- is decomposed into NO2- on the secondary metallic catalyst, we here performed density functional theory (DFT) calculations and experiments to investigate the NO2- reduction pathway on the Pd surface activated by hydrogen. Based on extensive DFT calculations on the relative energetics among ∼100 possible intermediates, we found that NO2- is easily reduced to NO* on the Pd surface, followed by either sequential hydrogenation steps to yield NH3 or a decomposition step to N* and O* (an adsorbate on Pd is denoted using an asterisk). Based on the calculated high migration barrier of N*, we further discussed that the direct combination of two N* to yield N2 is kinetically less favorable than the combination of a highly mobile H* with N* to yield NH3. Instead, the reduction of NO2- in the vicinity of the N* can yield N2O* that can be preferentially transformed into N2 via diverse reaction pathways. Our DFT results suggest that enhancing the likelihood of N* encountering NO2- in the solution phase before combination with surface H* is important for maximizing the N2 selectivity. This is further supported by our experiments on NO2- reduction by Pd/TiO2, showing that both a decreased H2 flow rate and an increased NO2- concentration increased the N2 selectivity (78.6-93.6% and 57.8-90.9%, respectively). PMID:25280017

  14. Anti-PD-1/PD-L1 therapy of human cancer: past, present, and future.

    PubMed

    Chen, Lieping; Han, Xue

    2015-09-01

    Major progress has been made toward our understanding of the programmed death-1/programmed death ligand-1 (PD-1/PD-L1) pathway (referred to as the PD pathway). mAbs are already being used to block the PD pathway to treat human cancers (anti-PD therapy), especially advanced solid tumors. This therapy is based on principles that were discovered through basic research more than a decade ago, but the great potential of this pathway to treat a broad spectrum of advanced human cancers is just now becoming apparent. In this Review, we will briefly review the history and development of anti-PD therapy, from the original benchwork to the most up-to-date clinical results. We will then focus the discussion on three basic principles that define this unique therapeutic approach and highlight how anti-PD therapy is distinct from other immunotherapeutic approaches, namely tumor site immune modulation, targeting tumor-induced immune defects, and repairing ongoing (rather than generating de novo) tumor immunity. We believe that these fundamental principles set the standard for future immunotherapies and will guide our efforts to develop more efficacious and less toxic immune therapeutics to treat human cancers. PMID:26325035

  15. Magnetic properties of Mn2PdSn and Mn2PdIn

    NASA Astrophysics Data System (ADS)

    Xu, Xiao; Kanomata, Takeshi; Hayasaka, Masanobu; Umino, Ryosuke; Endo, Keita; Nishihara, Hironori; Adachi, Yoshiya; Kainuma, Ryosuke; Ziebeck, Kurt R. A.

    2016-03-01

    New Mn2PdZ (Z=In, Sn) alloys have been synthesized. Both alloys crystallize in a Heusler-type cubic structure. The lattice parameters of solution-treated Mn2PdSn and Mn2PdIn were found to be 6.351 Å and 6.399 Å, respectively. Magnetization measurements were carried out under magnetic fields up to 68 kOe. Both the solution-treated alloys have spontaneous magnetizations. The magnetic moment at 6 K and the Curie temperature of solution-treated Mn2PdSn were estimated to be 1.70 μB / f . u . and 411 K, respectively. The magnetic moment at 6 K of solution-treated Mn2PdIn was found to be 0.59 μB / f . u .. Ageing heat treatments at 673 K on these alloy, instead of an increase of degree of atomic order, resulted in phase decomposition. Thin-plate precipitates and a very fine Widmanstätten morphology were found for the aged Mn2PdSn and Mn2PdIn alloys, respectively.

  16. The Debris Disk of Vega: A Steady-state Collisional Cascade, Naturally

    NASA Astrophysics Data System (ADS)

    Müller, S.; Löhne, T.; Krivov, A. V.

    2010-01-01

    The archetypical debris disk around Vega has been observed intensively over the past 25 years. It has been argued that the resulting photometric data and images may be in contradiction with a standard, steady-state collisional scenario of the disk evolution. In particular, the emission in the mid-infrared (mid-IR) appears to be in excess of what is expected from a "Kuiper belt" at ~100 AU, which is evident in the submillimeter images and inferred from the majority of photometric points. Here we re-address the question of whether or not the Vega disk observations are compatible with a continuous dust production through a collisional cascade. Instead of seeking a size and spatial distribution of dust that provide the best fit to observations, our approach involves physical modeling of the debris disk "from the sources." We assume that dust is maintained by a belt of parent planetesimals, and employ our collisional and radiative transfer codes to consistently model the size and radial distribution of the disk material and then thermal emission of dust. In doing so, we vary a broad set of parameters, including the stellar properties, the exact location, extension, and dynamical excitation of the planetesimal belt, chemical composition of solids, and the collisional prescription. We are able to reproduce the spectral energy distribution in the entire wavelength range from the near-IR to millimeter, as well as the mid-IR and submillimeter radial brightness profiles of the Vega disk. Thus, our results suggest that the Vega disk observations are not in contradiction with a steady-state collisional dust production, and we put important constraints on the disk parameters and physical processes that sustain it. The total disk mass in lsim100 km-sized bodies is estimated to be ~10 Earth masses. Provided that collisional cascade has been operating over much of the Vega age of ~350 Myr, the disk must have lost a few Earth masses of solids during that time. We also demonstrate

  17. THE DEBRIS DISK OF VEGA: A STEADY-STATE COLLISIONAL CASCADE, NATURALLY

    SciTech Connect

    Mueller, S.; Loehne, T.; Krivov, A. V.

    2010-01-10

    The archetypical debris disk around Vega has been observed intensively over the past 25 years. It has been argued that the resulting photometric data and images may be in contradiction with a standard, steady-state collisional scenario of the disk evolution. In particular, the emission in the mid-infrared (mid-IR) appears to be in excess of what is expected from a 'Kuiper belt' at approx100 AU, which is evident in the submillimeter images and inferred from the majority of photometric points. Here we re-address the question of whether or not the Vega disk observations are compatible with a continuous dust production through a collisional cascade. Instead of seeking a size and spatial distribution of dust that provide the best fit to observations, our approach involves physical modeling of the debris disk 'from the sources'. We assume that dust is maintained by a belt of parent planetesimals, and employ our collisional and radiative transfer codes to consistently model the size and radial distribution of the disk material and then thermal emission of dust. In doing so, we vary a broad set of parameters, including the stellar properties, the exact location, extension, and dynamical excitation of the planetesimal belt, chemical composition of solids, and the collisional prescription. We are able to reproduce the spectral energy distribution in the entire wavelength range from the near-IR to millimeter, as well as the mid-IR and submillimeter radial brightness profiles of the Vega disk. Thus, our results suggest that the Vega disk observations are not in contradiction with a steady-state collisional dust production, and we put important constraints on the disk parameters and physical processes that sustain it. The total disk mass in approx<100 km-sized bodies is estimated to be approx10 Earth masses. Provided that collisional cascade has been operating over much of the Vega age of approx350 Myr, the disk must have lost a few Earth masses of solids during that time. We

  18. Analytic model of a magnetically insulated transmission line with collisional flow electrons

    NASA Astrophysics Data System (ADS)

    Stygar, W. A.; Wagoner, T. C.; Ives, H. C.; Corcoran, P. A.; Cuneo, M. E.; Douglas, J. W.; Gilliland, T. L.; Mazarakis, M. G.; Ramirez, J. J.; Seamen, J. F.; Seidel, D. B.; Spielman, R. B.

    2006-09-01

    We have developed a relativistic-fluid model of the flow-electron plasma in a steady-state one-dimensional magnetically insulated transmission line (MITL). The model assumes that the electrons are collisional and, as a result, drift toward the anode. The model predicts that in the limit of fully developed collisional flow, the relation between the voltage Va, anode current Ia, cathode current Ik, and geometric impedance Z0 of a 1D planar MITL can be expressed as Va=IaZ0h(χ), where h(χ)≡[(χ+1)/4(χ-1)]1/2-ln⁡⌊χ+(χ2-1)1/2⌋/2χ(χ-1) and χ≡Ia/Ik. The relation is valid when Va≳1MV. In the minimally insulated limit, the anode current Ia,min⁡=1.78Va/Z0, the electron-flow current If,min⁡=1.25Va/Z0, and the flow impedance Zf,min⁡=0.588Z0. {The electron-flow current If≡Ia-Ik. Following Mendel and Rosenthal [Phys. Plasmas 2, 1332 (1995)PHPAEN1070-664X10.1063/1.871345], we define the flow impedance Zf as Va/(Ia2-Ik2)1/2.} In the well-insulated limit (i.e., when Ia≫Ia,min⁡), the electron-flow current If=9Va2/8IaZ02 and the flow impedance Zf=2Z0/3. Similar results are obtained for a 1D collisional MITL with coaxial cylindrical electrodes, when the inner conductor is at a negative potential with respect to the outer, and Z0≲40Ω. We compare the predictions of the collisional model to those of several MITL models that assume the flow electrons are collisionless. We find that at given values of Va and Z0, collisions can significantly increase both Ia,min⁡ and If,min⁡ above the values predicted by the collisionless models, and decrease Zf,min⁡. When Ia≫Ia,min⁡, we find that, at given values of Va, Z0, and Ia, collisions can significantly increase If and decrease Zf. Since the steady-state collisional model is valid only when the drift of electrons toward the anode has had sufficient time to establish fully developed collisional flow, and collisionless models assume there is no net electron drift toward the anode, we expect these two types

  19. Collisional evolution - an analytical study for the nonsteady-state mass distribution

    NASA Astrophysics Data System (ADS)

    Martins, R. Vieira

    1999-05-01

    To study the collisional evolution of asteroidal groups we can use an analytical solutionfor the self-similar collision cascades. This solution is suitable to study the steady-state massdistribution of the collisional fragmentation. However, out of the steady-state conditions, thissolution is not satisfactory for some values of the collisional parameters. In fact, for some valuesfor the exponent of the mass distribution power law of an asteroidal group and its relation to theexponent of the function which describes how rocks break we arrive at singular points for theequation which describes the collisional evolution. These singularities appear since someapproximations are usually made in the laborious evaluation of many integrals that appear in theanalytical calculations. They concern the cutoff for the smallest and the largest bodies. Thesesingularities set some restrictions to the study of the analytical solution for the collisionalequation. To overcome these singularities we performed an algebraic computationconsidering the smallest and the largest bodies and we obtained the analytical expressions for theintegrals that describe the collisional evolution without restriction on the parameters. However,the new distribution is more sensitive to the values of the collisional parameters. In particular thesteady-state solution for the differential mass distribution has exponents slightly different from11⧸6 for the usual parameters in the Asteroid Belt. The sensitivity of this distribution with respectto the parameters is analyzed for the usual values in the asteroidal groups. With anexpression for the mass distribution without singularities, we can evaluate also its time evolution.We arrive at an analytical expression given by a power series of terms constituted by a smallparameter multiplied by the mass to an exponent, which depends on the initial power lawdistribution. This expression is a formal solution for the equation which describes the collisionalevolution

  20. PD-L1 Expression in Triple Negative Breast Cancer

    PubMed Central

    Mittendorf, Elizabeth A.; Philips, Anne V.; Meric-Bernstam, Funda; Qiao, Na; Wu, Yun; Harrington, Susan; Su, Xiaoping; Wang, Ying; Gonzalez-Angulo, Ana M.; Akcakanat, Argun; Chawla, Akhil; Curran, Michael; Hwu, Patrick; Sharma, Padmanee; Litton, Jennifer K.; Molldrem, Jeffrey J.; Alatrash, Gheath

    2014-01-01

    Early phase trials targeting the T-cell inhibitory molecule PD-L1 have shown clinical efficacy in cancer. This study was undertaken to determine whether PD-L1 is overexpressed in triple-negative breast cancer (TNBC) and to investigate the loss of the phosphatase and tensin homolog (PTEN) as a mechanism of PD-L1 regulation. The Cancer Genome Atlas (TCGA) RNA sequencing data showed significantly greater expression of the PD-L1 gene in TNBC (n=120) compared to non-TNBC (n=716) (P<0.001). Breast tumor tissue microarrays were evaluated for PD-L1 expression which was present in 19% (20 of 105) TNBC specimens. PD-L1+ tumors had greater CD8+ T-cell infiltrate than PD-L1− tumors (688 cells/mm versus 263 cells/mm; P<0.0001). To determine the effect of PTEN loss on PD-L1 expression, stable cell lines were generated using PTEN shRNA. PTEN knockdown led to significantly higher cell-surface PD-L1 expression and PD-L1 transcripts, suggesting transcriptional regulation. Moreover, PI3K pathway inhibition using the AKT inhibitor MK-2206 or rapamycin resulted in decreased PD-L1 expression, further linking PTEN and PI3K signaling to PD-L1 regulation. Co-culture experiments were performed to determine the functional effect of altered PD-L1 expression. Increased PD-L1 cell surface expression by tumor cells induced by PTEN loss led to decreased T cell proliferation and increased apoptosis. PD-L1 is expressed in 20% of TNBC, suggesting PD-L1 as a therapeutic target in TNBC. Since PTEN loss is one mechanism regulating PD-L1 expression, agents targeting the PI3K pathway may increase the antitumor adaptive immune responses. PMID:24764583

  1. The clinical utility of PD-L1 testing in selecting non-small cell lung cancer patients for PD1/PD-L1-directed therapy.

    PubMed

    Villaruz, L C; Socinski, M A

    2016-09-01

    Lung cancer is the leading cause of cancer mortality in the United States and worldwide. Long thought to be nonimmunogenic, immunotherapy in lung cancer has historically been met with disappointing results. Programmed death-1 (PD-1), and the PD-1 ligand, PD-L1, are immune checkpoint proteins that fine-tune the antigen-specific T-cell response after stimulation of the T-cell receptor and are crucial for self-tolerance. This pathway in particular is co-opted by tumors through expression of PD-L1 on the tumor cell surface and within the tumor microenvironment, allowing for direct suppression of antitumor cytolytic T-cell activity by the tumor. Indeed, induction of the PD1/PD-L1 pathway represents an adaptive immune resistance mechanism exerted by tumor cells in response to endogenous antitumor activity. In 2015, the US Food and Drug Administration (FDA) approved two immuno-oncology agents, the PD-1 inhibitors nivolumab and pembrolizumab, for the treatment of previously treated advanced non-small cell lung cancer (NSCLC). Coincident with the clinical trials that led to these regulatory approvals has been the development of several immunohistochemistry (IHC) tests of PD-L1 expression, which may serve to select patients who will derive the most benefit from PD1- or PD-L1-directed therapy. The PD-L1 IHC assays are distinct in their methods and interpretation, which poses a challenge to clinicians selecting patients for these therapies. PMID:27090296

  2. Transient catalytic combustor model

    NASA Technical Reports Server (NTRS)

    Tien, J. S.

    1981-01-01

    A quasi-steady gas phase and thermally thin substrate model is used to analyze the transient behavior of catalytic monolith combustors in fuel lean operation. The combustor response delay is due to the substrate thermal inertia. Fast response is favored by thin substrate, short catalytic bed length, high combustor inlet and final temperatures, and small gas channel diameters. The calculated gas and substrate temperature time history at different axial positions provides an understanding of how the catalytic combustor responds to an upstream condition change. The computed results also suggest that the gas residence times in the catalytic bed in the after bed space are correlatable with the nondimensional combustor response time. The model also performs steady state combustion calculations; and the computed steady state emission characteristics show agreement with available experimental data in the range of parameters covered. A catalytic combustor design for automotive gas turbine engine which has reasonably fast response ( 1 second) and can satisfy the emission goals in an acceptable total combustor length is possible.

  3. THE EFFECT OF CO ON HYDROGEN PERMEATION THROUGH PD AND INTERNALLY OXIDIZED AND UN-OXIDIZED PD ALLOY MEMBRANES

    SciTech Connect

    Shanahan, K.; Flanagan, T.; Wang, D.

    2010-10-20

    The H permeation of internally oxidized Pd alloy membranes such as Pd-Al and Pd-Fe, but not Pd-Y alloys, is shown to be more resistant to inhibition by CO(g) as compared to Pd or un-oxidized Pd alloy membranes. The increased resistance to CO is found to be greater at 423 K than at 473 K or 523 K. In these experiments CO was pre-adsorbed onto the membranes and then CO-free H{sub 2} was introduced to initiate the H permeation.

  4. Initiation of a coronal transient

    SciTech Connect

    Low, B.C.; Munro, R.H.; Fisher, R.R.

    1982-03-01

    This paper analyzes the coronal transient/eruptive prominence event of 1980 August 5 observed by the Mauna Loa experiment system. This event yielded data on the early development of the transient in the low corona between 1.2 R/sub sun/ and 2.2 R/sub sun/, information which was not available when earlier attempts were made to explain transient phenomena. The transient's initial appearance in the form of a rising density-depleted structure, prior to the eruption of the associated prominence, can be explained as an effect of magnetic buoyancy. The data indicate that this transient has a density depletion of 17% to 33% relative to an undisturbed corona which is approximately isothermal with a temperature of 1.5 x 10/sup 6/ K and a coronal density of 1.0 x 10/sup 9/ cm/sup -3/ at the base of the corona. The height versus base length relationship of the evolving transient resembles, remarkably well, the theoretical predictions obtained from a quasi-static model of a margnetically buoyant loop system. By matching this relationship with the theoretical model, we estimate the magnetic field at the base of the transient to be between 2 and 3 gauss. It is also shown that the initial, nearly constant speed of the top of the transient, 80 +- 20 km s/sup -1/, is consistent with a theoretical estimate calculated from the quasi-static model. These results suggest that some transients are not initiated impulsively, the initial stage of the development being driven by a quasi-static response to a slow change in magnetic field conditions at the base of the corona.

  5. G6PD Deficiency (Glucose-6-Phosphate Dehydrogenase) (For Parents)

    MedlinePlus

    ... are high-risk areas for the infectious disease malaria . Researchers have found evidence that the parasite that ... deficiency may have developed as a protection against malaria. continue G6PD Deficiency Symptom Triggers Kids with G6PD ...

  6. Structure of quenched alloys of the Ti-Pd system

    NASA Astrophysics Data System (ADS)

    Dobromyslov, A. V.; Taluts, N. I.

    2016-07-01

    The quenched alloys of the Ti-Pd system containing 2-15 at % Pd have been studied using X-ray diffraction analysis, optical metallography, transmission electron microscopy, and measurements of the microhardness. It has been found that, in the course of quenching, epy alloys containing 2, 3, and 5 at % Pd undergo a eutectoid decomposition into the α phase and Ti2Pd intermetallic compound, and the Ti-7 at % Pd and Ti-9 at % Pd alloys undergo a β → α' martensitic transformation. In the alloys with Pd contents of more than 9 at %, the β phase is fixed in the metastable state. The complete stabilization of the β phase takes place in the alloys containing 11 at % Pd and more. It has been found that the formation of the orthorhombic α" phase and metastable ω phase in the quenched alloys of this system does not occur.

  7. How Does Your Doctor Make a PD Diagnosis?

    MedlinePlus

    ... More > Español In Your Area NPF Shop How Does Your Doctor Make a PD Diagnosis Make Text ... and possible falls, also called postural instability How does your doctor make a PD diagnosis? The bedside ...

  8. Transient upsets in microprocessor controllers

    NASA Technical Reports Server (NTRS)

    Glaser, R. E.; Masson, G. M.

    1981-01-01

    The modeling and analysis of transient faults in microprocessor based controllers are discussed. Such controllers typically consist of a microprocessor, read only memory storing and application program, random access memory for data storage, and input/output devices for external communications. The effects of transient faults on the performance of the controller are reviewed. An instruction level perspective of performance is taken which is the basis of a useful high level program state description of the microprocessor controller. A transition matrix is defined which determines the controller's response to transient fault arrivals.

  9. Transient Photoconduction in Phthalocyanines

    NASA Astrophysics Data System (ADS)

    Petty, David Matthew

    1991-02-01

    Available from UMI in association with The British Library. Requires signed TDF. Photoconduction occurs when illumination interacts with a sample to cause a change in the flow of current through that sample. The work described in this thesis is centred on the investigation of the processes which effect photoconduction. These processes include the way in which charge carriers move the electrodes, the way in which charge carriers transit the bulk and the way in which charge carriers are excited and relax. The thesis is divided into three parts. Part I is essentially a literature survey of the theories which describe photoconduction. An overview of photoconduction at a microscopic level in all types of sample is given. By categorising the sample as neutral or supporting a single carrier space charge, the mathematical description of photoconduction behaviour can be simplified. In Part II existing theories which describe photoconduction in charged samples are reviewed. A new theory yields two important equations: (i) the Plasma equation which describes the conditions for a neutral sample and those for a single carrier space charge, (ii) the BUIC (Bulk Uniform Injected Charge) equation which describes the time and field dependence of a photoconductor which supports a single carrier space charge. The BUIC equation is compared with existing theories and its ability to describe photoconduction in sandwich cells of phthalocyanine compounds is discussed. Part III contains an investigation of photoconduction in phthalocyanines. Steady state and chopped light transient photoconduction experiments are carried out on nine different Phthalocyanine compounds under a variety of conditions. The results obtained are interpreted using the BUIC, Plasma equations and neutral photoconductor theories.

  10. Particle pinch and collisionality in gyrokinetic simulations of tokamak plasma turbulence

    SciTech Connect

    Angioni, C.; Candy, J.; Waltz, R. E.; Fable, E.; Maslov, M.; Weisen, H.; Peeters, A. G.

    2009-06-15

    The generic problem of how, in a turbulent plasma, the experimentally relevant conditions of a particle flux very close to the null are achieved, despite the presence of strong heat fluxes, is addressed. Nonlinear gyrokinetic simulations of plasma turbulence in tokamaks reveal a complex dependence of the particle flux as a function of the turbulent spatial scale and of the velocity space as collisionality is increased. At experimental values of collisionality, the particle flux is found close to the null, in agreement with the experiment, due to the balance between inward and outward contributions at small and large scales, respectively. These simulations provide full theoretical support to the prediction of a peaked density profile in a future nuclear fusion reactor.

  11. Inward particle transport at high collisionality in the Experimental Advanced Superconducting Tokamak

    NASA Astrophysics Data System (ADS)

    Wang, G. Q.; Ma, J.; Weiland, J.; Zang, Q.

    2013-10-01

    We have made the first drift wave study of particle transport in the Experimental Advanced Superconducting Tokamak (Wan et al., Nucl. Fusion 49, 104011 (2009)). The results reveal that collisions make the particle flux more inward in the high collisionality regime. This can be traced back to effects that are quadratic in the collision frequency. The particle pinch is due to electron trapping which is not very efficient in the high collisionality regime so the approach to equilibrium is slow. We have included also the electron temperature gradient (ETG) mode to give the right electron temperature gradient, since the Trapped Electron Mode (TE mode) is weak in this regime. However, at the ETG mode number ions are Boltzmann distributed so the ETG mode does not give particle transport.

  12. Collisional processes in the O2 B 3Σu- state

    NASA Astrophysics Data System (ADS)

    Sick, Volker; Decker, Michael; Heinze, Johannes; Stricker, Winfried

    1996-02-01

    Collisional processes, which influence quantitative laser-induced fluorescence (LIF) measurements involving the B3Σ u- state of molecular oxygen, were investigated. Since the B state is strongly predissociating, these processes are though to be important only at higher pressure. However, we found that in LIF experiments in methane/air flames in the pressure range between atmospheric pressure and 40 bar collisional quenching and rotational energy transfer (RET) are important even at moderate pressures. Total quenching cross sections of 30(± 10) Å2for ν' = 2 and 100(± 30) Å2for ν = 0 and total RET cross sections of 40(± 16) Å2 were found. An upper limit of 0.7 Å 2 for the cross section for vibrational energy transfer (VET) out of ν' = 2 could be determined.

  13. Improved modeling of relativistic collisions and collisional ionization in particle-in-cell codes

    SciTech Connect

    Perez, F.; Gremillet, L.; Decoster, A.; Drouin, M.; Lefebvre, E.

    2012-08-15

    An improved Monte Carlo collisional scheme modeling both elastic and inelastic interactions has been implemented into the particle-in-cell code CALDER[E. Lefebvre et al., Nucl. Fusion 43, 629 (2003)]. Based on the technique proposed by Nanbu and Yonemura [J. Comput. Phys. 145, 639 (1998)] allowing to handle arbitrarily weighted macro-particles, this binary collision scheme uses a more compact and accurate relativistic formulation than the algorithm recently worked out by Sentoku and Kemp [J. Comput. Phys. 227, 6846 (2008)]. Our scheme is validated through several test cases, demonstrating, in particular, its capability of modeling the electrical resistivity and stopping power of a solid-density plasma over a broad parameter range. A relativistic collisional ionization scheme is developed within the same framework, and tested in several physical scenarios. Finally, our scheme is applied in a set of integrated particle-in-cell simulations of laser-driven fast electron transport.

  14. Collisional relaxation of bi-Maxwellian plasma temperatures in magnetized plasmas

    NASA Astrophysics Data System (ADS)

    Yoon, Peter H.

    2016-07-01

    In the literature, collisional processes are customarily discussed within the context of the Boltzmann-Balescu-Lenard-Landau type of collision integral, but such an equation is strictly valid for unmagnetized plasmas. For plasmas immersed in the ambient magnetic field, the foundational equation that describes binary collisions must be generalized to include the effects of magnetic field. The present paper makes use of such an equation in order to describe the collisional relaxation of temperatures under the assumption of bi-Maxwellian velocity distribution function. The formalism derived in the present paper may be useful for studying the effects of binary collisions on the isotropization of temperatures in the solar wind plasma, among possible applications.

  15. Collisional excitation of HC3N by para- and ortho-H2

    NASA Astrophysics Data System (ADS)

    Faure, Alexandre; Lique, François; Wiesenfeld, Laurent

    2016-08-01

    New calculations for rotational excitation of cyanoacetylene by collisions with hydrogen molecules are performed to include the lowest 38 rotational levels of HC3N and kinetic temperatures to 300 K. Calculations are based on the interaction potential of Wernli et al. whose accuracy is checked against spectroscopic measurements of the HC3N-H2 complex. The quantum coupled-channel approach is employed and complemented by quasi-classical trajectory calculations. Rate coefficients for ortho-H2 are provided for the first time. Hyperfine resolved rate coefficients are also deduced. Collisional propensity rules are discussed and comparisons between quantum and classical rate coefficients are presented. This collisional data should prove useful in interpreting HC3N observations in the cold and warm ISM, as well as in protoplanetary discs.

  16. Accurate Collisional Cross-Sections: Important Non-Lte Input Data

    NASA Astrophysics Data System (ADS)

    Mashonkina, L.

    2010-11-01

    Non-LTE modelling for a particular atom requires accurate collisional excitation and ionization cross-sections for the entire system of transitions in the atom. This review concerns with inelastic collisions with electrons and neutral hydrogen atoms. For the selected atoms, H i and Ca ii, comparisons are made between electron impact excitation rates from ab initio calculations and various theoretical approximations. The effect of the use of modern data on non-LTE modelling is shown. For most transitions and most atoms, hydrogen collisional rates are calculated using a semi-empirical modification of the classical Thomson formula for ionization by electrons. Approaches used to estimate empirically the efficiency of hydrogenic collisions in the statistical equilibrium of atoms are reviewed. This research was supported by the Deutsche Forschungsgemeinschaft with grant 436 RUS 17/13/07.

  17. Collisional Transport in a Low Aspect Ratio Tokamak -- Beyond the Drift Kinetic Formalism

    SciTech Connect

    D.A. Gates; R.B. White

    2004-01-28

    Calculations of collisional thermal and particle diffusivities in toroidal magnetic plasma confinement devices order the toroidal gyroradius to be small relative to the poloidal gyroradius. This ordering is central to what is usually referred to as neoclassical transport theory. This ordering is incorrect at low aspect ratio, where it can often be the case that the toroidal gyroradius is larger than the poloidal gyroradius. We calculate the correction to the particle and thermal diffusivities at low aspect ratio by comparing the diffusivities as determined by a full orbit code (which we refer to as omni-classical diffusion) with those from a gyroaveraged orbit code (neoclassical diffusion). In typical low aspect ratio devices the omni-classical diffusion can be up to 2.5 times the calculated neoclassical value. We discuss the implications of this work on the analysis of collisional transport in low aspect ratio magnetic confinement experiments.

  18. Model for collisional fast ion diffusion into Tokamak Fusion Test Reactor loss cone

    SciTech Connect

    Chang, C.S. |; Zweben, S.J.; Schivell, J.; Budny, R.; Scott, S.

    1994-08-01

    An analytic model is developed to estimate the classical pitch angle scattering loss of energetic fusion product ions into prompt loss orbits in a tokamak geometry. The result is applied to alpha particles produced by deutrium-tritium fusion reactions in a plasma condition relevant to Tokamak Fusion Test Reactor (TFTR). A poloidal angular distribution of collisional fast ion loss at the first wall is obtained and the numerical result from the TRANSP code is discussed. The present model includes the effect that the prompt loss boundary moves away from the slowing-down path due to reduction in banana thickness, which enables us to understand, for the first time. the dependence of the collisional loss rate on Z{sub eff}.

  19. Collisional removal of HI from the inner disks of Virgo cluster galaxies

    NASA Technical Reports Server (NTRS)

    Valluri, Monica; Jog, Chanda J.

    1990-01-01

    There is sufficient observational evidence to show that many Virgo Cluster spirals are HI deficient in their inner disks (in addition to being HI deficient globally, as previously established). It is shown here that collisions between galaxies in a cluster can lead to the removal of HI gas from these galaxies while leaving the H2 gas, undisturbed. This follows directly from the application of the Spitzer-Baade collisional gas removal mechanism to galaxies consisting of stars and a two-component interstellar medium (ISM) consisting of HI and H2, with HI having the largest filling factor. This can account for both the observed HI deficiency in the inner regions and the normal H2 content of these galaxies. The frequency of galaxy collisions in the Virgo Cluster is shown to be large enough to make collisional gas removal a viable mechanism.

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

    NASA Technical Reports Server (NTRS)

    Liffman, Kurt

    1990-01-01

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

  1. Ion Collisional Transport Coefficients in the Solar Wind at 1 au

    NASA Astrophysics Data System (ADS)

    Hellinger, Petr

    2016-07-01

    Proton and alpha particle collisional transport coefficients (isotropization, relative deceleration frequencies, and heating rates) at 1 au are quantified using the Wind/Solar Wind Experiment data. In agreement with previous studies, the ion–ion Coulomb collisions are generally important for slow solar wind streams and tend to reduce the temperature anisotropies, the differential streaming, and the differences between the proton and alpha particle temperatures. In slow solar wind streams the Coulomb collisions between protons and alpha particles are important for the overall proton energetics, as well as the relative deceleration between the two species. It is also shown that ion temperature anisotropies and differential streaming need to be taken into account for evaluation of the collisional transport coefficients.

  2. Collisional electrostatic ion cyclotron waves as a possible source of energetic heavy ions in the magnetosphere

    NASA Technical Reports Server (NTRS)

    Providakes, Jason; Seyler, Charles E.

    1990-01-01

    A new mechanism is proposed for the source of energetic heavy ions (NO/+/, O2/+/, and O/+/) found in the magnetosphere. Simulations using a multispecies particle simulation code for resistive current-driven electrostatic ion cyclotron waves show transverse and parallel bulk heating of bottomside ionospheric heavy ion populations. The dominant mechanism for the transverse bulk heating is resonant ion heating by wave-particle ion trapping. Using a linear kinetic dispersion relation for a magnetized, collisional, homogenous, and multiion plasma, it is found that collisional electrostatic ion cyclotron waves near the NO(+), O2(+), and O(+) gyrofrequencies are unstable to field-aligned currents of 50 microA/sq m for a typical bottomside ionosphere.

  3. Asteroid collisional evolution - An integrated model for the evolution of asteroid rotation rates

    NASA Technical Reports Server (NTRS)

    Farinella, P.; Davis, D. R.; Paolicchi, P.; Cellino, A.; Zappala, V.

    1992-01-01

    A comprehensive model for the changes in asteroid spin rates due to large collisions was developed by combining the theoretical results of Cellino et al. (1990) with previously published work on spin rate changes for cratering impacts (Harris, 1979; Dobrovolskis and Burns, 1984). The spin change algorithm, when incorporated into an existing simulation of collisional effects on asteroid sizes, produced an integrated model for studying the simultaneous evolution of asteroid sizes and spin rates over the solar system history. As a result of an analysis of 32 collisional scenarios with regard to the change in the spin rate as a function of asteroid size, it is concluded that the spin rates of all asteroids, except possibly the largest ones, have been significantly altered by collisions over the solar system history and that, in general, shattering impacts are much more important than cratering events in changing the spin of asteroids.

  4. COLLISIONALLY EXCITED FILAMENTS IN HUBBLE SPACE TELESCOPE Hα AND Hβ IMAGES OF HH 1/2

    SciTech Connect

    Raga, A. C.; Castellanos-Ramírez, A.; Reipurth, B.; Chiang, Hsin-Fang; Bally, J.

    2015-01-01

    We present new Hα and Hβ images of the HH 1/2 system, and we find that the Hα/Hβ ratio has high values in ridges along the leading edges of the HH 1 bow shock and of the brighter condensations of HH 2. These ridges have Hα/Hβ = 4 → 6, which is consistent with collisional excitation from the n = 1 to the n = 3 and 4 levels of hydrogen in a gas of temperatures T = 1.5 → 10 × 10{sup 4} K. This is therefore the first direct evidence that the collisional excitation/ionization region of hydrogen just behind Herbig-Haro shock fronts is detected.

  5. Propagation of surface waves on a semi-bounded quantum magnetized collisional plasma

    SciTech Connect

    Niknam, A. R.; Taheri Boroujeni, S.; Khorashadizadeh, S. M.

    2013-12-15

    The propagation of surface waves on a semi-bounded quantum plasma in the presence of the external magnetic field and collisional effects is investigated by using quantum magnetohydrodynamics model. A general analytical expression for the dispersion relation of surface waves is obtained by considering the boundary conditions. It is shown that, in some special cases, the obtained dispersion relation reduces to the results reported in previous works. It is also indicated that the quantum, external magnetic field and collisional effects can facilitate the propagation of surface waves on a semi-bounded plasma. In addition, it is found that the growth rate of the surface wave instability is enhanced by increasing the collision frequency and plasmonic parameter.

  6. Study of electron acceleration through the ? mode in a collisional plasma-filled cylindrical waveguide

    NASA Astrophysics Data System (ADS)

    Abdoli-Arani, A.; Moghaddasi, M.

    2016-07-01

    Acceleration of an externally injected electron inside the collisional plasma-filled cylindrical waveguide during its motion in the fields of the ? mode excited by microwave radiation is studied. The effect of the electron collision frequency with background ions on the deflection angle and energy gain of electron, when it is injected along the direction of the mode propagation is investigated. The fields for the mode, the deflection angle of electron trajectory, due to these fields, and the electron energy gradient are obtained. The results for collisionless and collisional plasma are graphically presented. The numerical results illustrate that the presence of the electron collision term in the dielectric permittivity can reduce the electron's energy gain in the configuration.

  7. Collisional tearing in a field-reversed sheet pinch assuming nonparallel propagation

    NASA Technical Reports Server (NTRS)

    Quest, K. B.; Coroniti, F. V.

    1985-01-01

    Linear tearing in a collisional reversed-field sheet pinch is examined assuming that the wave vector k is not parallel to the equilibrium magnetic field. Equilibrium and magnetic geometry are defined, and a set of perturbed moment equations is derived assuming quasi-parallel propagation. It is shown that the usual expression for collisional growth is recovered, assuming that k sub y = 0. It is shown that the y component of momentum balance requires the generation of nonzero dJ sub x well away from the null, and an interial coupling when z not equal to 0. The effects of k sub y not equal to 0 on the growth rate are discussed.

  8. Nonextensive statistics and skin depth of transverse wave in collisional plasma

    NASA Astrophysics Data System (ADS)

    Hashemzadeh, M.

    2016-05-01

    Skin depth of transverse wave in a collisional plasma is studied taking into account the nonextensive electron distribution function. Considering the kinetic theory for charge particles and using the Bhatnagar-Gross-Krook collision model, a generalized transverse dielectric permittivity is obtained. The transverse dispersion relation in different frequency ranges is investigated. Obtaining the imaginary part of the wave vector from the dispersion relation, the skin depth for these frequency ranges is also achieved. Profiles of the skin depth show that by increasing the q parameter, the penetration depth decreases. In addition, the skin depth increases by increasing the electron temperature. Finally, it is found that in the high frequency range and high electron temperature, the penetration depth decreases by increasing the collision frequency. In contrast, by increasing the collision frequency in a highly collisional frequency range, the skin depth of transverse wave increases.

  9. State of Supported Pd during Catalysis in Water

    SciTech Connect

    Chase, Zizwe; Fulton, John L.; Camaioni, Donald M.; Mei, Donghai; Balasubramanian, Mahalingam; Pham, Van Thai; Zhao, Chen; Weber, Robert S.; Wang, Yong; Lercher, Johannes A.

    2013-08-29

    In operando X-ray absorption was used to measure the structure and chemical state of supported Pd nanoparticles with 3 -10 nm diameter in contact with H2 saturated water at 298-473 K. The Pd-Pd distances determined were consistent with the presence of subsurface hydrogen, i.e., longer than those measured by others for bare, reduced Pd particles, and within the range of distances for Pd hydrides. During the Pd-catalyzed hydrogenation of phenol, cyclohexanone, cyclohexanol or cyclohexene in the presence of water, the Pd nanoparticles exhibited a lengthening of the Pd-Pd bond that we attribute to a change in the concentration of sorbed H related to the steady state of H at the surface of the Pd particles. This steady state is established by all reactions involving H2, i.e., the sorption/desorption into the bulk, the sorption at the surface, and the reaction with adsorbed unsaturated reactants. Thus, first insight into the chemical state of Pd and the H/Pd ratio during catalysis in water is provided. The Pd particles did not change upon their exposure to water or reactants; nor did the spectra show any effect from the interaction of the Pd particles with various supports. The experimental results are consistent with ab initio molecular dynamic simulations, which indicate that Pd-water interactions are relatively weak for Pd metal and that these interactions become even weaker, when hydrogen is incorporated into the metal particles. This work was supported by the US Department of Energy (DOE), Office of Basic Energy Sciences (BES), Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory is a multi-program national laboratory operated for DOE by Battelle through Contract DE-AC05-76RL01830.

  10. Efficient evaluation of collisional energy transfer terms for plasma particle simulations

    NASA Astrophysics Data System (ADS)

    Turrell, A. E.; Sherlock, M.; Rose, S. J.

    2016-01-01

    Particle-based simulations, such as in particle-in-cell (PIC) codes, are widely used in plasma physics research. The analysis of particle energy transfers, as described by the second moment of the Boltzmann equation, is often necessary within these simulations. We present computationally efficient, analytically derived equations for evaluating collisional energy transfer terms from simulations using discrete particles. The equations are expressed as a sum over the properties of the discrete particles.

  11. Particle simulation model of transport in a bounded, Coulomb collisional plasma

    SciTech Connect

    Procassini, R.J.; Birdsall, C.K. )

    1991-08-01

    The transport of particles and energy in a fully ionized, collisional plasma is studied through the use of a kinetic transport model. A particle-in-cell (PIC) code has been coupled to a Monte Carlo, binary particle model of Coulomb collisions, to provide a fully kinetic, self-consistent description of transport and potential formation in a single spatial dimension and two velocity components (parallel and perpendicular to the spatial coordinate). The dependence of plasma transport on Coulomb collisionality is investigated by varying the normalized collision frequency within the range 10{sup {minus}2}{le}{nu}{sub *}{equivalent to}{nu}{sub {ital c}0}/{nu}{sub {ital be}0}{le}5, where {nu}{sub {ital c}0} is the average electron/ion collision frequency and {nu}{sub {ital be}0} is the frequency at which thermal electrons bounce between the collector sheath potential drops located adjacent to the absorbing plates at each end of the system. Collisions between charged-plasma and recycled-neutral particles are omitted in this study. For finite values of {nu}{sub *}, the heat conduction flux is found to be reduced from the value predicted by classical, hydrodynamic transport theory. The electron heat conduction flux is shown to lie between 12% and 21% of the free-streaming thermal flux {ital q}{sup {ital e}}{sub {ital fs}}{equivalent to}{ital n}{sub {ital e}v}{sub {parallel},{ital te}}{ital kT}{sub {ital e}}, where {ital n}{sub {ital e}}, {ital v}{sub {parallel},{ital te}}, and {ital kT}{sub {ital e}} are the steady-state values of the electron density, parallel thermal velocity, and temperature, respectively. The variation of several transport quantities with collisionality is presented, and the results are compared against those from other collisional plasma transport models.

  12. The electromagnetic interchange mode in a partially ionized collisional plasma. [spread F region

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

    A collisional electromagnetic dispersion relation is derived from two-fluid theory for the interchange mode coupled to the Alfven, acoustic, drift and entropy modes in a partially ionized plasma. The fundamental electromagnetic nature of the interchange model is noted; coupling to the intermediate Alfven mode is strongly stabilizing for finite k sub z. Both ion viscous and ion-neutral stabilization are included, and it was found that collisions destroy the ion finite Larmor radius cutoff at short perpendicular wavelengths.

  13. A study of the collisional dynamics for collisions of UF with atoms and molecules

    NASA Astrophysics Data System (ADS)

    Doverspike, L. D.; Champion, R. D.

    1980-08-01

    Absolute total cross sections for the collisional decomposition of the negative ion of uranium hexafluoride into its three lowest asymptotic channels in collisions with the rare gases were measured for collision energies ranging from below thresholds for decomposition up to a laboratory collision energy of 500 eV. The experimental results were found to be consistent with the predictions of a two step collision model where the unimolecular decomposition of the excited molecular negative ions is described with a statistical theory.

  14. Gain Calculations for Inner-Shell Lasing by Electron Collisional Ionisation

    NASA Astrophysics Data System (ADS)

    Upcraft, L. M.

    2002-11-01

    Current high power femtosecond lasers have been shown to produce electron pulses which may be appropriate for the pumping of X-Ray lasers through collisional ionisation. Non-radiative Coster-Kronig type decay processes may be fast enough to form an inverted state and allow X-ray lasing within the biologically interesting "water window". Calculations of the atomic processes in metallic Ti, Mn and Cu are presented that potentially useable gains on the M1 - L3 transition.

  15. Collisional Relaxation of a Strongly Magnetized, Two Isotope, Pure Ion Plasma

    NASA Astrophysics Data System (ADS)

    Chim, C. Y.; O'Neil, T. M.; Dubin, D. H. E.

    2011-10-01

    The collisional relaxation of a strongly magnetized pure ion plasmathat is composed of two species with slightly different mass is discussed. We have in mind two isotopes of the same singly ionized atom. Parameters are assumed to be ordered as Ωc 1, Ωc 2 >> |Ωc 1 -Ωc 2 | >> v / b , where Ωc 1 and Ωc 2 are the two cyclotron frequencies, v is the thermal velocity, and b is the classical distance of closest approach. For this ordering, the total cyclotron action for the two species, J1 =∑jɛ 1m1v⊥12 / 2Ωc 1 and J2 =∑jɛ 2m2v⊥j2 / 2Ωc 2 , are adiabatic invariants that constrain the collisional dynamics. On the time scale of a few collisions, entropy is maximized subject to the constancy of the total Hamiltonian H and the two actions J1 and J2, yielding a Gibbs distribution of the form exp [ - H / T -α1J1 -α2J2 ] . Collisional relaxation to the usual Gibbs distribution, exp [ - H / T ] , takes place on two time scales, each of which is exponentially longer than the usual collisional time scale. First, the two species share action so that α1 and α2 relax to a common value α. On an even longer time scale, the total action ceases to be a good constant of the motion and α relaxes to zero. Supported by NSF PHY-0903877 and DOE DE-SC0002451.

  16. Collisional pumping for the production of intense spin-polarized neutral beams: target considerations. Revision

    SciTech Connect

    Stearns, J.W.; Burrell, C.F.; Kaplan, S.N.; Pyle, R.V.; Ruby, L.; Schlachter, A.S.

    1985-04-01

    Polarized beams at intensity levels heretofore not considered feasible have recently been proposed for heating and fueling fusion plasmas. Polarized-beam fueling could increase fusion rates by 50% as well as allow control of the directionality of the fusion products. A process which we have recently described, and called collisional pumping, promises to produce beams of polarized ions vastly more intense than producible by current methods.

  17. OBSERVED BINARY FRACTION SETS LIMITS ON THE EXTENT OF COLLISIONAL GRINDING IN THE KUIPER BELT

    SciTech Connect

    Nesvorny, David; Vokrouhlicky, David; Bottke, William F.; Levison, Harold F.; Noll, Keith

    2011-05-15

    The size distribution in the cold classical Kuiper Belt (KB) can be approximated by two idealized power laws: one with steep slope for radii R > R* and one with shallow slope for R < R*, where R* {approx} 25-50 km. Previous works suggested that the size frequency distribution (SFD) rollover at R* can be the result of extensive collisional grinding in the KB that led to the catastrophic disruption of most bodies with R < R*. Here, we use a new code to test the effect of collisions in the KB. We find that the observed rollover could indeed be explained by collisional grinding provided that the initial mass in large bodies was much larger than the one in the present KB and was dynamically depleted. In addition to the size distribution changes, our code also tracks the effects of collisions on binary systems. We find that it is generally easier to dissolve wide binary systems, such as the ones existing in the cold KB today, than to catastrophically disrupt objects with R {approx} R*. Thus, the binary survival sets important limits on the extent of collisional grinding in the KB. We find that the extensive collisional grinding required to produce the SFD rollover at R* would imply a strong gradient of the binary fraction with R and separation, because it is generally easier to dissolve binaries with small components and/or those with wide orbits. The expected binary fraction for R {approx}< R* is {approx}<0.1. The present observational data do not show such a gradient. Instead, they suggest a large binary fraction of {approx}0.4 for R = 30-40 km. This may indicate that the rollover was not produced by disruptive collisions, but is instead a fossil remnant of the KB object formation process.

  18. Collisional Histories of Comets and Trojan Asteroids: Insights from Forsterite and Enstatite Impact Studies

    NASA Technical Reports Server (NTRS)

    Lederer. S. M.; Jensen, E. A.; Wooden, D. H.; Lindsay, S. S.; Smith, D. C.; Cintala, M. J.; Nakamura-Messenger, K.; Keller, L. P.

    2012-01-01

    Impacts into forsterite and orthoenstatite at speeds typically encountered by comets demonstrate that shock imparted by collisions is detectable in the infrared signatures of their dust. The spectral signatures can be traced to physical alterations in their crystalline structures, as observed in TEM imaging and modeled using a dipole approximation. These results yield tantalizing insights into the collisional history of our solar system, as well as the history of individual comets and Trojan asteroids.

  19. The Collisional Evolution of the Trans-Neptunian Object Size Distribution

    NASA Astrophysics Data System (ADS)

    O'Brien, D. P.; Greenberg, R.

    2004-11-01

    The HST survey of trans-Neptunian objects (TNOs) by Bernstein et al. [1] detected two distinct populations, `classical' and `excited', and found a deficit of smaller (≲100 km) TNOs relative to the power law found earlier for larger bodies. Using the analytical model of O'Brien and Greenberg [2] and a numerical collisional evolution model [3] with reasonable strength parameters for icy bodies [4], we find that the TNO populations likely started with shallow initial size distributions, and that bodies ≳ 10 km in diameter are likely not in a collisional steady state. If the initial size distributions were steeper than the current size distributions, collisional erosion could not remove enough bodies over the age of the solar system to match the observations. The size distribution of TNOs ≳ 10 km in diameter must therefore be primordial. We also use our numerical model to address the origin of Jupiter-family comets (JFCs). Comparing the `classical' and `excited' size distributions to the results of numerical simulations of the supply of JFCs, Bernstein et al. find that most JFCs are ˜1 km in diameter and come from the `excited' population. An upturn in the size distribution at sizes below their survey limit could increase the size of JFC precursors and possibly allow the `classical' population to contribute a significant number of JFCs. Our numerical simulations show that the collisional production of bodies below ˜10 km in diameter can create a small upturn in the `classical' and `excited' size distributions, but it is not able to substantially increase the contribution of JFCs from the `classical' population or increase the size of JFC precursors. [1] Bernstein et al., AJ, submitted (AstroPH/0308467 v.3). [2] O'Brien and Greenberg, Icarus 164, 2003. [3] O'Brien and Greenberg, in prep. [4] Benz and Asphaug, Icarus 142, 1999.

  20. Coupling of an average-atom model with a collisional-radiative equilibrium model

    SciTech Connect

    Faussurier, G. Blancard, C.; Cossé, P.

    2014-11-15

    We present a method to combine a collisional-radiative equilibrium model and an average-atom model to calculate bound and free electron wavefunctions in hot dense plasmas by taking into account screening. This approach allows us to calculate electrical resistivity and thermal conductivity as well as pressure in non local thermodynamic equilibrium plasmas. Illustrations of the method are presented for dilute titanium plasma.

  1. The Next Immune-Checkpoint Inhibitors: PD-1/PD-L1 Blockade in Melanoma

    PubMed Central

    Mahoney, Kathleen M.; Freeman, Gordon J.; McDermott, David F.

    2015-01-01

    Purpose Blocking the interaction between the programmed cell death (PD)-1 protein and one of its ligands, PD-L1, has been reported to have impressive antitumor responses. Therapeutics targeting this pathway are currently in clinical trials. Pembrolizumab and nivolumab are the first of this anti-PD-1 pathway family of checkpoint inhibitors to gain accelerated approval from the US Food and Drug Administration (FDA) for the treatment of ipilimumab-refractory melanoma. Nivolumab has been associated with improved overall survival compared with dacarbazine in patients with previously untreated wild-type serine/threonine-protein kinase B-raf proto-oncogene BRAF melanoma. Although the most mature data are in the treatment of melanoma, the FDA has granted approval of nivolumab for squamous cell lung cancer and the breakthrough therapy designation to immune-checkpoint inhibitors for use in other cancers: nivolumab, an anti-PD-1 monoclonal antibody, for Hodgkin lymphoma, and MPDL-3280A, an anti-PD-L1 monoclonal antibody, for bladder cancer and non–small cell lung cancer. Here we review the literature on PD-1 and PD-L1 blockade and focus on the reported clinical studies that have included patients with melanoma. Methods PubMed was searched to identify relevant clinical studies of PD-1/PD-L1–targeted therapies in melanoma. A review of data from the current trials on clinicaltrial.gov was incorporated, as well as data presented in abstracts at the 2014 annual meeting of the American Society of Clinical Oncology, given the limited number of published clinical trials on this topic. Findings The anti-PD-1 and anti-PD-L1 agents have been reported to have impressive antitumor effects in several malignancies, including melanoma. The greatest clinical activity in unselected patients has been seen in melanoma. Tumor expression of PD-L1 is a suggestive, but inadequate, biomarker predictive of response to immune-checkpoint blockade. However, tumors expressing little or no PD-L1 are

  2. Expression of PD-1, PD-L1 and PD-L2 is associated with differentiation status and histological type of endometrial cancer

    PubMed Central

    Mo, Zhongfu; Liu, Jing; Zhang, Qiuyang; Chen, Zhiquan; Mei, Jiandong; Liu, Lunxu; Yang, Shijie; Li, Huina; Zhou, Lifei; You, Zongbing

    2016-01-01

    Endometrial cancer (EC) is the most frequent gynecological malignancy and a major cause of morbidity and mortality for women worldwide. Programmed cell death protein 1 (PD-1) and its ligands programmed death ligand 1 (PD-L1) and programmed death ligand 2 (PD-L2) have been well studied in lung cancer, melanoma and renal-cell cancer. However, few studies have been performed in EC. The purpose of the present study was to assess the expression of PD-1, PD-L1 and PD-L2 in 35 human normal endometrial tissue samples and 75 human EC tissue samples using immunohistochemical staining. It was found that 61.3% of ECs were positive for PD-1 staining, which was almost exclusively found in the tumor-infiltrating immune cells. By contrast, PD-1 was not expressed in the tumor cells or normal endometrial tissues. It was also found that 14.3% of normal endometria and 17.3% of EC tissues were positive for PD-L1 expression, while 20.0% of normal endometrium and 37.3% of EC tissues were positive for PD-L2 expression; however, there was no statistically significant difference between the normal endometrium and EC tissues. PD-1 expression in the tumor-infiltrating immune cells was more frequently found in the moderately and poorly-differentiated ECs and non-endometrioid (type II) ECs than in the well-differentiated ECs and endometrioid (type I) ECs. Similarly, PD-L1 and PD-L2 expression in the tumor-infiltrating immune cells was more frequently found in the moderately and poorly-differentiated ECs and type II ECs than in the type I ECs. The present findings indicate a possible better outcome for future treatment with anti-PD-1 or anti-PD-L1 antibody-based therapies against these subgroups of endometrial cancers with frequent expression of the PD-1/PD-L1/PD-L2 axis. PMID:27446374

  3. The anticancer immune response of anti-PD-1/PD-L1 and the genetic determinants of response to anti-PD-1/PD-L1 antibodies in cancer patients

    PubMed Central

    Han, Weidong; Wang, Xian; Fang, Yong; Li, Da; Pan, Hongming; Zhang, Li

    2015-01-01

    The programmed death-1 (PD-1), a coinhibitory receptor expressed on activated T cells and B cells, is demonstrated to induce an immune-mediated response and play a critical role in tumor initiation and development. The cancer patients harboring PD-1 or PD ligand 1 (PD-L1) protein expression have often a poor prognosis and clinical outcome. Currently, targeting PD-1 pathway as a potential new anticancer strategy is attracting more and more attention in cancer treatment. Several monoclonal antibodies against PD-1 or PD-L1 have been reported to enhance anticancer immune responses and induce tumor cell death. Nonetheless, the precise molecular mechanisms by which PD-1 affects various cancers remain elusive. Moreover, this therapy is not effective for all the cancer patients and only a fraction of patients respond to the antibodies targeting PD-1 or PD-L1, indicating these antibodies may only works in a subset of certain cancers. Thus, understanding the novel function of PD-1 and genetic determinants of response to anti-PD-1 therapy will allow us to develop a more effective and individualized immunotherapeutic strategy for cancer. PMID:26305724

  4. Characterization and functionalities of Pd/hydrotalcite catalysts

    NASA Astrophysics Data System (ADS)

    Naresh, Dhachapally; Kumar, Vanama Pavan; Harisekhar, Mitta; Nagaraju, Nekkala; Putrakumar, Balla; Chary, Komandur V. R.

    2014-09-01

    A series of palladium supported on calcined hydrotalcite (CHT) catalysts with varying palladium (Pd) loadings (1.0-8.0 wt%) were prepared by impregnation method. Their catalytic performance was evaluated for the reductive amination of phenol to aniline that showed a tremendous interest in the chemical industry. The catalysts were characterized by BET surface area, XRD, TEM, XPS, TPR of H2, TPD of CO2 and CO chemisorption. BET surface area decreased continuously with increase in Pd content. XRD results confirmed the changes in the crystalline phases with altering Pd content. TEM results showed the formation of fine particles at lower loadings and agglomerates at higher loadings. TPR profiles revealed that the reducibility increases with increase of Pd loading. CO2 TPD results illustrate the catalysts basicity increases with increase of Pd loading up to 4.0 wt% and decreases at higher loadings. Pd dispersion, metal area and crystallite sizes were determined by CO chemisorption method. Pd dispersion and metal area decreases with increase of Pd content and crystallite sizes. The results demonstrated that the Pd dispersion and basic properties are depending on the Pd loading. The catalytic performance clearly showed that the increase Pd loading the conversion of phenol increased up to 2.0 wt% and level off beyond the loading. The catalytic properties are well correlated with the active Pd sites determined by CO chemisorption, dispersion and basicity.

  5. In situ encapsulation of Pd inside the MCM-41 channel.

    PubMed

    Lin, Xi-Jie; Zhong, Ai-Zhi; Sun, Yong-Bin; Zhang, Xing; Song, Wei-Guo; Lu, Rong-Wen; Cao, An-Min; Wan, Li-Jun

    2015-05-01

    Pd nanoparticles were successfully introduced into the channels of mesoporous silica MCM-41 with their dispersion well-tuned. We identified the dual role played by CTAB, which was critical for both the micelle template and Pd grafting, leading to the formation of a highly active Pd-MCM-41 nanocomposite for catalysing the Suzuki reaction. PMID:25827909

  6. Collisional-radiative modeling of tungsten at temperatures of 1200–2400 eV

    SciTech Connect

    Colgan, James; Fontes, Christopher; Zhang, Honglin; Abdallah, Jr., Joseph

    2015-04-30

    We discuss new collisional-radiative modeling calculations of tungsten at moderate temperatures of 1200 to 2400 eV. Such plasma conditions are relevant to ongoing experimental work at ASDEX Upgrade and are expected to be relevant for ITER. Our calculations are made using the Los Alamos National Laboratory (LANL) collisional-radiative modeling ATOMIC code. These calculations formed part of a submission to the recent NLTE-8 workshop that was held in November 2013. This series of workshops provides a forum for detailed comparison of plasma and spectral quantities from NLTE collisional-radiative modeling codes. We focus on the LANL ATOMIC calculations for tungsten that were submitted to the NLTE-8 workshop and discuss different models that were constructed to predict the tungsten emission. In particular, we discuss comparisons between semi-relativistic configuration-average and fully relativistic configuration-average calculations. We also present semi-relativistic calculations that include fine-structure detail, and discuss the difficult problem of ensuring completeness with respect to the number of configurations included in a CR calculation.

  7. Linear stability of low mode number tearing modes in the banana collisionality regime

    SciTech Connect

    Fitzpatrick, R. , Abingdon, OX14 3DB, England )

    1989-12-01

    The semicollisional layer equations governing the linear stability of small mode number tearing modes in a low beta, large aspect ratio, tokamak equilibrium are derived from an expansion of the gyrokinetic equation. In this analysis only the cases where the ion Larmor radius is either much less than, or much greater than, the layer width are considered. Both the electrons and the ions are assumed to lie in the banana collisionality regime. One interesting feature of the derived layer equations, in the limit of small ion Larmor radius, is a substantial reduction in the effective collisionality of the system due to neoclassical ion dynamics. Next, using a shooting code, a dispersion relation is obtained from the layer equations in the limits of small ion Larmor radius and a vanishingly small fraction of trapped particles. As expected, strong semicollisional stabilization of the mode is found, but, in addition, a somewhat weaker destabilizing effect is obtained in the transition region between the collisional and semicollisional regimes.

  8. Effect of collisional heat transfer in ICRF power modulation experiment on ASDEX Upgrade

    SciTech Connect

    Tsujii, N.; D'Inca, R.; Bilato, R.; Bobkov, Vl. V.; Brambilla, M.; Schneider, P.; Noterdaeme, J.-M.; Van Eester, D.; Lerche, E. A.; Jaeger, E. F.; Collaboration: ASDEX Upgrade Team

    2014-02-12

    ICRF (ion cyclotron range of frequencies) heating experiments were performed in D-H plasmas at various H concentrations on ASDEX Upgrade. The rf power was modulated to measure the electron power deposition profile from electron temperature modulation. To minimize the contribution from indirect collisional heating and the effect of radial transport, the rf power was modulated at 50 Hz. However, peaking of electron temperature modulation was still observed around the hydrogen cyclotron resonance indicating collisional heating contribution. Time dependent simulation of the hydrogen distribution function was performed for the discharges, using the full-wave code AORSA (E.F. Jaeger, et al., Phys. Plasmas, Vol. 8, page 1573 (2001)) coupled to the Fokker-Planck code CQL3D (R.W. Harvey, et al., Proc. IAEA (1992)). In the present experimental conditions, it was found that modulation of the collisional heating was comparable to that of direct wave damping. Impact of radial transport was also analyzed and found to appreciably smear out the modulation profile and reduce the phase delay.

  9. RATE COEFFICIENTS FOR THE COLLISIONAL EXCITATION OF MOLECULES: ESTIMATES FROM AN ARTIFICIAL NEURAL NETWORK

    SciTech Connect

    Neufeld, David A.

    2010-01-01

    An artificial neural network (ANN) is investigated as a tool for estimating rate coefficients for the collisional excitation of molecules. The performance of such a tool can be evaluated by testing it on a data set of collisionally induced transitions for which rate coefficients are already known: the network is trained on a subset of that data set and tested on the remainder. Results obtained by this method are typically accurate to within a factor of approx2.1 (median value) for transitions with low excitation rates and approx1.7 for those with medium or high excitation rates, although 4% of the ANN outputs are discrepant by a factor of 10 or more. The results suggest that ANNs will be valuable in extrapolating a data set of collisional rate coefficients to include high-lying transitions that have not yet been calculated. For the asymmetric top molecules considered in this paper, the favored architecture is a cascade-correlation network that creates 16 hidden neurons during the course of training, with three input neurons to characterize the nature of the transition and one output neuron to provide the logarithm of the rate coefficient.

  10. NanoRocks: Experimental Study of Collisional Damping and Aggregation at Low Velocities

    NASA Astrophysics Data System (ADS)

    Colwell, Joshua E.; Brisset, Julie; Dove, Adrienne R.; Metzger, Jessica; Rascon, Allison

    2015-11-01

    The NanoRocks experiment on the International Space Station consists of 8 separate sample trays of particles from ~0.1 mm - 2.0 mm in diameter that undergo collisional evolution. The microgravity environment of the ISS allows collision speeds of less than 1 mm/s to be studied. At these speeds the experiment reproduces the velocity dispersion found in unperturbed regions of Saturn’s rings. Observations of the rings from Cassini instruments hint at aggregation and fragmentation of clumps depending on the local surface mass density, particle size distribution and velocity dispersion.The eight NanoRocks samples include plastic beads, copper, glass, and JSC-1 lunar regolith simulant. The samples are shaken at 1 minute intervals to provide initial collision velocities of a few cm/s, and video is recorded of the collisional evolution of the particle samples. We derive mean coefficients of restitution for the different samples based on the damping of the mean velocity dispersion as well as tracking of individual particle trajectories. The evolution of the velocity distribution is consistent with a uniform random distribution of the coefficient of restitution, independent of collision velocity. This is consistent with results of Heißelmann et al. (Icarus Vol. 206, pp. 424-430, 2010) using larger icy particles. We also find the onset of cluster formation at speeds of a few mm/s. We will present our results and discuss applications to models of the collisional evolution of Saturn’s rings.

  11. Collisional-radiative modeling of tungsten at temperatures of 1200–2400 eV

    DOE PAGESBeta

    Colgan, James; Fontes, Christopher; Zhang, Honglin; Abdallah, Jr., Joseph

    2015-04-30

    We discuss new collisional-radiative modeling calculations of tungsten at moderate temperatures of 1200 to 2400 eV. Such plasma conditions are relevant to ongoing experimental work at ASDEX Upgrade and are expected to be relevant for ITER. Our calculations are made using the Los Alamos National Laboratory (LANL) collisional-radiative modeling ATOMIC code. These calculations formed part of a submission to the recent NLTE-8 workshop that was held in November 2013. This series of workshops provides a forum for detailed comparison of plasma and spectral quantities from NLTE collisional-radiative modeling codes. We focus on the LANL ATOMIC calculations for tungsten that weremore » submitted to the NLTE-8 workshop and discuss different models that were constructed to predict the tungsten emission. In particular, we discuss comparisons between semi-relativistic configuration-average and fully relativistic configuration-average calculations. We also present semi-relativistic calculations that include fine-structure detail, and discuss the difficult problem of ensuring completeness with respect to the number of configurations included in a CR calculation.« less

  12. Is the Bohm Criterion satisfied in magnetized plasmas, and how does ion-neutral collisionality matter?

    NASA Astrophysics Data System (ADS)

    Severn, Greg; Green, Jonathan; Winters, Victoria; Yip, Chi-Shung; Hershkowitz, Noah; Schmitz, Oliver

    2015-09-01

    It is taken for granted that the usual Bohm criterion must be satisfied for weakly collisional, magnetized plasmas at the plasma-wall boundary for the case in which the magnetic field is normally incident on the boundary, but there is a paucity of experimental works that confirm it. Beyond this, theorists view the Bohm criterion as approximately true, holding only for collisionless plasmas. The question is whether Bohm's criterion really is satisfied in weakly collisional magnetized plasmas in the simplest case (n ∧ ∥ B /B, where n ∧ is the boundary surface normal vector) and how that criterion (the ions reaching a sonic point at the end of the presheath) is modified as collisionality rises. Experiments are conducted in a linear magnetized helicon plasma source at the University of Wisconsin, Madison, an upgraded version of MARIA (MARIA-Magnetized Anisot Ropic Ion-distribution Apparatus), in order to address these questions. Experimental results are discussed in light of relevant theoretical works. Work supported by NSF Grant Nos. PHY-1206421, CBET-0903783, and CBET-0903832, and MSN178461, and DOE Grant Nos. DE-FG02-97ER54437, DE FG02-03ER54728, and MSN170010.

  13. Theoretical investigation of superconductivity in SrPd2Ge2 , SrPd2As2 , and CaPd2As2

    NASA Astrophysics Data System (ADS)

    Karaca, Ertuǧrul; Tütüncü, H. M.; Uzunok, H. Y.; Srivastava, G. P.; Uǧur, Ş.

    2016-02-01

    Ab initio pseudopotential calculations have been performed to investigate the structural, electronic, and vibrational properties of SrPd2Ge2 , SrPd2As2 , and CaPd2As2 crystallizing in the ThCr2Si2 -type body-centered tetragonal structure. Our electronic results show that the density of states at the Fermi level is mainly dominated by the strong hybridization of Pd d states and Ge (or As) p states. The linear response method and the Migdal-Eliashberg approach have been used to calculate the Eliashberg spectral function for all these compounds. By integrating the Eliashberg spectral function, the average electron-phonon coupling parameter (λ ) is found to be 0.74 for SrPd2Ge2 , 0.66 for SrPd2As2 , and 0.72 for CaPd2As2 . Using the calculated values of λ and the logarithmically averaged phonon frequency ωln the superconducting critical temperature (Tc) values for SrPd2Ge2 , SrPd2As2 , and CaPd2As2 are found to be 3.20, 2.05, and 2.48 K, respectively, which are in acceptable agreement with the corresponding experimental values. The relative differences in the Tc values between the Ge and As compounds have been explained in terms of some key physical parameters.

  14. The Pd2Si - /Pd/ - Ni - solder plated metallization system for silicon solar cells

    NASA Technical Reports Server (NTRS)

    Coleman, M. G.; Pryor, R. A.; Sparks, T. G.

    1978-01-01

    The rationale and application of a plated metal system, Pd2Si Pd - Ni - solder, is presented. This metallization system is particularly useful on shallow p-n junction solar cells. The advantages of such plated solar cell contacts are discussed. A process sequence for applying the metallization system is outlined. A specific example is presented, including chemical plating solution formulations and detailed process step descriptions. Electrical test data for solar cells metallized with the palladium-nickel-solder system are provided.

  15. Synthesis of Fe-Pd and Fe-Pd/Ta magnetic nanocomposites by severe plastic deformation

    SciTech Connect

    Saha, S.; Kulovits, A.; Soffa, W.A.; Barnard, J.A.

    2005-05-15

    Severe plastic deformation (SPD) and cyclic codeformation were used to prepare bulk magnetic nanocomposite of ordered L1{sub 0} Fe-Pd phase and soft {alpha}-Fe following an atomic ordering and precipitation reaction. Enhanced coercivity and remanence have been achieved with this method. Layering of Ta foils with the Fe-34 at. %Pd foils was explored in an effort to minimize nanocomposite grain size by confinement. Faster kinetics and improvement in the remanence resulted from Ta layering.

  16. Transient nucleation in condensed systems

    NASA Technical Reports Server (NTRS)

    Kelton, K. F.; Greer, A. L.; Thompson, C. V.

    1983-01-01

    Using classical nucleation theory we consider transient nucleation occurring in a one-component, condensed system under isothermal conditions. We obtain an exact closed-form expression for the time dependent cluster populations. In addition, a more versatile approach is developed: a numerical simulation technique which models directly the reactions by which clusters are produced. This simulation demonstrates the evolution of cluster populations and nucleation rate in the transient regime. Results from the simulation are verified by comparison with exact analytical solutions for the steady state. Experimental methods for measuring transient nucleation are assessed, and it is demonstrated that the observed behavior depends on the method used. The effect of preexisting cluster distributions is studied. Previous analytical and numerical treatments of transient nucleation are compared to the solutions obtained from the simulation. The simple expressions of Kashchiev are shown to give good descriptions of the nucleation behavior.

  17. Predictive Markers for the Efficacy of Anti-PD-1/PD-L1 Antibodies in Lung Cancer.

    PubMed

    Shukuya, Takehito; Carbone, David P

    2016-07-01

    Blockade of the programmed death protein 1 (PD-1)/programmed death ligand 1 (PD-L1) axis using antibodies against the associated receptors and ligands has yielded good clinical responses and improved overall survival in patients with non-small cell lung cancer (NSCLC). Once patients show a response to anti-PD-1/PD-L1 antibody, the median duration of response is often longer than that achieved using existing cytotoxic agents and even some molecular targeted agents. However, the response rates to these antibodies are only 15% to 20% in unselected patients with NSCLC and the cost of this therapy is high. Therefore, there is an urgent need for effective predictive biomarkers to identify patients likely to benefit. PD-L1 expression, which can be detected by immunohistochemical analysis, is a rational biomarker for selecting responders to anti-PD-1/PD-L1 antibody treatments, and this selection method has been introduced into clinical practice. However, the response rate to anti-PD-1/PD-L1 antibody in PD-L1-expressing patients with NSCLC is only 15% to 45%, response can occur in PD-L1-negative patients, and predictability based on PD-L1 expression may differ between nonsquamous NSCLC and squamous cell NSCLC. In addition, the methods of immunohistochemical analysis and evaluation of its results differ for different anti-PD-1/PD-L1 agents. This article reviews the existing data on predictive markers for the efficacy of anti-PD-1/PD-L1 antibodies in NSCLC. PMID:26944305

  18. PD-1 and PD-L1 expression in molecularly selected non-small-cell lung cancer patients

    PubMed Central

    D'Incecco, A; Andreozzi, M; Ludovini, V; Rossi, E; Capodanno, A; Landi, L; Tibaldi, C; Minuti, G; Salvini, J; Coppi, E; Chella, A; Fontanini, G; Filice, M E; Tornillo, L; Incensati, R M; Sani, S; Crinò, L; Terracciano, L; Cappuzzo, F

    2015-01-01

    Background: Agents targeting programmed death-1 receptor (PD-1) and its ligand (PD-L1) are showing promising results in non-small-cell lung cancer (NSCLC). It is unknown whether PD-1/PD-L1 are differently expressed in oncogene-addicted NSCLC. Methods: We analysed a cohort of 125 NSCLC patients, including 56 EGFR mutated, 29 KRAS mutated, 10 ALK translocated and 30 EGFR/KRAS/ALK wild type. PD-L1 and PD-1 expression were assessed by immunohistochemistry. All cases with moderate or strong staining (2+/3+) in >5% of tumour cells were considered as positive. Results: PD-1 positive (+) was significantly associated with current smoking status (P=0.02) and with the presence of KRAS mutations (P=0.006), whereas PD-L1+ was significantly associated to adenocarcinoma histology (P=0.005) and with presence of EGFR mutations (P=0.001). In patients treated with EGFR tyrosine kinase inhibitors (N=95), sensitivity to gefitinib or erlotinib was higher in PD-L1+ vs PD-L1 negative in terms of the response rate (RR: P=0.01) time to progression (TTP: P<0.0001) and survival (OS: P=0.09), with no difference in PD1+ vs PD-1 negative. In the subset of 54 EGFR mutated patients, TTP was significantly longer in PD-L1+ than in PD-L1 negative (P=0.01). Conclusions: PD-1 and PD-L1 are differentially expressed in oncogene-addicted NSCLC supporting further investigation of specific checkpoint inhibitors in combination with targeted therapies. PMID:25349974

  19. Catalina/Palomar Optical Transient

    NASA Astrophysics Data System (ADS)

    Ganeshalingam, M.; Griffith, C. V.; Filippenko, A. V.; Foley, R. J.

    2008-07-01

    Inspection of a CCD spectrum (range 330-1000 nm), obtained on July 7 UT with the 3-m Shane reflector (+ Kast spectrograph) at Lick Observatory, shows that the transient reported in ATel 1604 has a very blue, featureless continuum. This could be a very young Type II supernova (though at this time no clear hydrogen Balmer features are present), or some kind of Galactic transient. Further observations are encouraged.

  20. Development of membranes for hydrogen separation: Pd-coated V-10Pd

    SciTech Connect

    Paglieri, Stephen N; Wermer, Joseph R; Buxbaum, Robert E; Ciocco, Michael V; Howard, Bret H; Morreale, Bryan D

    2009-01-01

    Numerous Group IVB and VB alloys were prepared and tested as potential membrane materials but most of these materials were brittle or exhibited cracking during hydrogen exposure. One of the more ductile alloys, V-10Pd (at. %), was fabricated into a thin (107-{micro}m thick) composite membrane coated with 100 nm of Pd on each side. The material was tested for hydrogen permeability, resistance to hydrogen embrittlement, and long term hydrogen flux stability. The hydrogen permeability, {phi}, of the V-10Pd membrane was 3.86 x 10{sup -8} mol H{sub 2} m{sup -1} s{sup -1} Pa{sup -0.5} (avg. of three different samples) at 400 C, which is slightly higher than the permeability of Pd-23Ag at that temperature. A 1400 h hydrogen flux test at 400 C demonstrated that the rate of metallic interdiffusion was slow between the V-10Pd foil and the 100-nm-thick Pd coating on the surface. However, at the end of testing the membrane cracked at 118 C because of hydrogen embrittlement.

  1. Targeting PD-1/PD-L1 in the treatment of metastatic renal cell carcinoma

    PubMed Central

    Weinstock, Matthew; McDermott, David

    2015-01-01

    Immunostimulatory therapies have been a cornerstone of treatment for metastatic renal cell carcinoma (RCC) since the 1990s. However, the use of traditional immunotherapeutic approaches for RCC, such as high-dose interleukin-2 and interferon-α, has been limited by significant systemic toxicities and the need to deliver these therapies at centers of expertise. Furthermore, in spite of the success of these immunostimulatory therapies for some patients with RCC, it is clear that most patients fail to respond to cytokine therapy. More effective immune therapy for RCC has therefore been necessary. The interaction between programmed death-1 (PD-1, present on T cells), and one of its ligands (PD-L1, present on antigen-presenting cells and tumor cells) constitutes an immune checkpoint through which tumors can induce T-cell tolerance and avoid immune destruction. Monoclonal antibodies that disrupt the PD-1/PD-L1 interaction serve as inhibitors of this immune checkpoint, and have demonstrated favorable activity in RCC as monotherapy and in combination with other active agents. This review summarizes the current landscape of anti-PD-1/PD-L1 therapy for RCC, and highlights challenges for the future development of this promising approach. PMID:26622321

  2. Pd surface and Pt subsurface segregation in Pt1-c Pd c nanoalloys.

    PubMed

    De Clercq, A; Giorgio, S; Mottet, C

    2016-02-17

    The structure and chemical arrangement of Pt1-c Pd c nanoalloys with the icosahedral and face centered cubic symmetry are studied using Monte Carlo simulations with a tight binding interatomic potential fitted to density-functional theory calculations. Pd surface segregation from the lowest to the highest coordinated sites is predicted by the theory together with a Pt enrichment at the subsurface, whatever the structure and the size of the nanoparticles, and which subsists when increasing the temperature. The onion-shell chemical configuration is found for both symmetries and is initiated from the Pd surface segregation. It is amplified in the icosahedral symmetry and small sizes but when considering larger sizes, the oscillating segregation profile occurs near the surface on about three to four shells whatever the structure. Pd segregation results from the significant lower cohesive energy of Pd as compared to Pt and the weak ordering tendency leads to the Pt subsurface segregation. The very weak size mismatch does not prevent the bigger atoms (Pt) from occupying subsurface sites which are in compression whereas the smaller ones (Pd) occupy the central site of the icosahedra where the compression is an order of magnitude higher. PMID:26795206

  3. Pd surface and Pt subsurface segregation in Pt1-c Pd c nanoalloys

    NASA Astrophysics Data System (ADS)

    De Clercq, A.; Giorgio, S.; Mottet, C.

    2016-02-01

    The structure and chemical arrangement of Pt1-c Pd c nanoalloys with the icosahedral and face centered cubic symmetry are studied using Monte Carlo simulations with a tight binding interatomic potential fitted to density-functional theory calculations. Pd surface segregation from the lowest to the highest coordinated sites is predicted by the theory together with a Pt enrichment at the subsurface, whatever the structure and the size of the nanoparticles, and which subsists when increasing the temperature. The onion-shell chemical configuration is found for both symmetries and is initiated from the Pd surface segregation. It is amplified in the icosahedral symmetry and small sizes but when considering larger sizes, the oscillating segregation profile occurs near the surface on about three to four shells whatever the structure. Pd segregation results from the significant lower cohesive energy of Pd as compared to Pt and the weak ordering tendency leads to the Pt subsurface segregation. The very weak size mismatch does not prevent the bigger atoms (Pt) from occupying subsurface sites which are in compression whereas the smaller ones (Pd) occupy the central site of the icosahedra where the compression is an order of magnitude higher.

  4. Transient Tsunamis in Lakes

    NASA Astrophysics Data System (ADS)

    Couston, L.; Mei, C.; Alam, M.

    2013-12-01

    A large number of lakes are surrounded by steep and unstable mountains with slopes prone to failure. As a result, landslides are likely to occur and impact water sitting in closed reservoirs. These rare geological phenomena pose serious threats to dam reservoirs and nearshore facilities because they can generate unexpectedly large tsunami waves. In fact, the tallest wave experienced by contemporary humans occurred because of a landslide in the narrow bay of Lituya in 1958, and five years later, a deadly landslide tsunami overtopped Lake Vajont's dam, flooding and damaging villages along the lakefront and in the Piave valley. If unstable slopes and potential slides are detected ahead of time, inundation maps can be drawn to help people know the risks, and mitigate the destructive power of the ensuing waves. These maps give the maximum wave runup height along the lake's vertical and sloping boundaries, and can be obtained by numerical simulations. Keeping track of the moving shorelines along beaches is challenging in classical Eulerian formulations because the horizontal extent of the fluid domain can change over time. As a result, assuming a solid slide and nonbreaking waves, here we develop a nonlinear shallow-water model equation in the Lagrangian framework to address the problem of transient landslide-tsunamis. In this manner, the shorelines' three-dimensional motion is part of the solution. The model equation is hyperbolic and can be solved numerically by finite differences. Here, a 4th order Runge-Kutta method and a compact finite-difference scheme are implemented to integrate in time and spatially discretize the forced shallow-water equation in Lagrangian coordinates. The formulation is applied to different lake and slide geometries to better understand the effects of the lake's finite lengths and slide's forcing mechanism on the generated wavefield. Specifically, for a slide moving down a plane beach, we show that edge-waves trapped by the shoreline and free

  5. Transient Alerts in LSST

    NASA Astrophysics Data System (ADS)

    Kantor, J.

    During LSST observing, transient events will be detected and alerts generated at the LSST Archive Center at NCSA in Champaign-Illinois. As a very high rate of alerts is expected, approaching ˜ 10 million per night, we plan for VOEvent-compliant Distributor/Brokers (http://voevent.org) to be the primary end-points of the full LSST alert streams. End users will then use these Distributor/Brokers to classify and filter events on the stream for those fitting their science goals. These Distributor/Brokers are envisioned to be operated as a community service by third parties who will have signed MOUs with LSST. The exact identification of Distributor/Brokers to receive alerts will be determined as LSST approaches full operations and may change over time, but it is in our interest to identify and coordinate with them as early as possible. LSST will also operate a limited Distributor/Broker with a filtering capability at the Archive Center, to allow alerts to be sent directly to a limited number of entities that for some reason need to have a more direct connection to LSST. This might include, for example, observatories with significant follow-up capabilities whose observing may temporarily be more directly tied to LSST observing. It will let astronomers create simple filters that limit what alerts are ultimately forwarded to them. These user defined filters will be possible to specify using an SQL-like declarative language, or short snippets of (likely Python) code. We emphasize that this LSST-provided capability will be limited, and is not intended to satisfy the wide variety of use cases that a full-fledged public Event Distributor/Broker could. End users will not be able to subscribe to full, unfiltered, alert streams coming directly from LSST. In this session, we will discuss anticipated LSST data rates, and capabilities for alert processing and distribution/brokering. We will clarify what the LSST Observatory will provide versus what we anticipate will be a

  6. Collisional relaxation of a strongly magnetized two-species pure ion plasma

    NASA Astrophysics Data System (ADS)

    Chim, Chi Yung; O'Neil, Thomas M.; Dubin, Daniel H.

    2014-04-01

    The collisional relaxation of a strongly magnetized pure ion plasma that is composed of two species with slightly different masses is discussed. We have in mind two isotopes of the same singly ionized atom. Parameters are assumed to be ordered as Ω1,Ω2≫|Ω1-Ω2|≫v¯ij/b ¯ and v¯⊥j/Ωj≪b ¯, where Ω1 and Ω2 are two cyclotron frequencies, v¯ij=√T∥/μij is the relative parallel thermal velocity characterizing collisions between particles of species i and j, and b ¯=2 e2/T∥ is the classical distance of closest approach for such collisions, and v ¯⊥j/Ωj=√2T⊥j/mj /Ωj is the characteristic cyclotron radius for particles of species j. Here, μij is the reduced mass for the two particles, and T∥ and T⊥j are temperatures that characterize velocity components parallel and perpendicular to the magnetic field. For this ordering, the total cyclotron action for the two species, I1=∑i ∈1m1v⊥i2/(2Ω1) and I2=∑i∈2m2v⊥i2/(2Ω2) are adiabatic invariants that constrain the collisional dynamics. On the timescale of a few collisions, entropy is maximized subject to the constancy of the total Hamiltonian H and the two actions I1 and I2, yielding a modified Gibbs distribution of the form exp[-H /T∥-α1I1-α2I2]. Here, the αj's are related to T∥ and T⊥j through T⊥j=(1/T∥+αj/Ωj)-1. Collisional relaxation to the usual Gibbs distribution, exp[-H /T∥], takes place on two timescales. On a timescale longer than the collisional timescale by a factor of (b ¯2Ω12/v¯112)exp{5[3π(b¯|Ω1-Ω2|/v ¯12)]2/5/6}, the two species share action so that α1 and α2 relax to a common value α. On an even longer timescale, longer than the collisional timescale by a factor of the order exp {5[3π(v¯11)]2/5/6}, the total action ceases to be a good constant of the motion and α relaxes to zero.

  7. Astrophysical Gyrokinetics: Kinetic and Fluid Turbulent Cascades In Magentized Weakly Collisional Plasmas

    SciTech Connect

    Schekochihin, A. A.; Cowley, S. C.; Dorland, W.; Hammett, G. W.; Howes, G. G.; Quataert, E.; Tatsuno, T.

    2009-04-23

    This paper presents a theoretical framework for understanding plasma turbulence in astrophysical plasmas. It is motivated by observations of electromagnetic and density fluctuations in the solar wind, interstellar medium and galaxy clusters, as well as by models of particle heating in accretion disks. All of these plasmas and many others have turbulentmotions at weakly collisional and collisionless scales. The paper focuses on turbulence in a strong mean magnetic field. The key assumptions are that the turbulent fluctuations are small compared to the mean field, spatially anisotropic with respect to it and that their frequency is low compared to the ion cyclotron frequency. The turbulence is assumed to be forced at some system-specific outer scale. The energy injected at this scale has to be dissipated into heat, which ultimately cannot be accomplished without collisions. A kinetic cascade develops that brings the energy to collisional scales both in space and velocity. The nature of the kinetic cascade in various scale ranges depends on the physics of plasma fluctuations that exist there. There are four special scales that separate physically distinct regimes: the electron and ion gyroscales, the mean free path and the electron diffusion scale. In each of the scale ranges separated by these scales, the fully kinetic problem is systematically reduced to a more physically transparent and computationally tractable system of equations, which are derived in a rigorous way. In the "inertial range" above the ion gyroscale, the kinetic cascade separates into two parts: a cascade of Alfvenic fluctuations and a passive cascade of density and magnetic-fieldstrength fluctuations. The former are governed by the Reduced Magnetohydrodynamic (RMHD) equations at both the collisional and collisionless scales; the latter obey a linear kinetic equation along the (moving) field lines associated with the Alfvenic component (in the collisional limit, these compressive fluctuations

  8. Thermal and electrochemically assisted Pd-Cl bond cleavage in the d9-d9 Pd2dppm2Cl2 complex by Pd3 dppm3COn+ clusters (n = 2, 1, 0).

    PubMed

    Cugnet, Cyril; Mugnier, Yves; Dal Molin, Sophie; Brevet, David; Lucas, Dominique; Harvey, Pierre D

    2007-04-16

    A new aspect of reactivity of the cluster [Pd3(dppm)3(micro3-CO)]n+, ([Pd3]n+, n = 2, 1, 0) with the low-valent metal-metal-bonded Pd2(dppm)2Cl2 dimer (Pd2Cl2) was observed using electrochemical techniques. The direct reaction between [Pd3]2+ and Pd2Cl2 in THF at room temperature leads to the known [Pd3(dppm)3(micro3-CO)(Cl)]+ ([Pd3(Cl)]+) adduct and the monocationic species Pd2(dppm)2Cl+ (very likely as Pd2(dppm)2(Cl)(THF)+, [Pd2Cl]+) as unambiguously demonstrated by UV-vis and 31P NMR spectroscopy. In this case, [Pd3]2+ acts as a strong Lewis acid toward the labile Cl- ion, which weakly dissociates from Pd2Cl2 (i.e., dissociative mechanism). Host-guest interactions between [Pd3]2+ and Pd2Cl2 seem unlikely on the basis of computer modeling because of the strong screening of the Pd-Cl fragment by the Ph-dppm groups in Pd2Cl2. The electrogenerated clusters [Pd3]+ and [Pd3]0 also react with Pd2Cl2 to unexpectedly form the same oxidized adduct, [Pd3(Cl)]+, despite the known very low affinity of [Pd3]+ and [Pd3]0 toward Cl- ions. The reduced biproduct in this case is the highly reactive zerovalent species "Pd2(dppm)2" or "Pd(dppm)" as demonstrated by quenching with CDCl3 (forming the well-known complex Pd(dppm)Cl2) or in presence of dppm (forming the known Pd2(dppm)3 d10-d10 dimer). To bring these halide-electron exchange reactions to completion for [Pd3]+ and [Pd3]0, 0.5 and 1.0 equiv of Pd2Cl2 are necessary, respectively, accounting perfectly for the number of exchanged electrons. The presence of a partial dissociation of Pd2Cl2 into the Cl- ion and the monocation [Pd2Cl]+, which is easier to reduce than Pd2Cl2, is suggested to explain the overall electrochemical results. It is possible to regulate the nature of the species formed from Pd2Cl2 by changing the state of charge of the title cluster. PMID:17371010

  9. Anti-PD-1/PD-L1 antibody therapy for pretreated advanced nonsmall-cell lung cancer

    PubMed Central

    Zhou, Guo-Wu; Xiong, Ye; Chen, Si; Xia, Fan; Li, Qiang; Hu, Jia

    2016-01-01

    Abstract Background: Anti-PD-1/PD-L1 antibody therapy is a promising clinical treatment for nonsmall-cell lung cancer (NSCLC). However, whether anti-PD-1/PD-L1 antibody therapy can provide added benefits for heavily pretreated patients with advanced NSCLC and whether the efficacy of anti-PD-1/PD-L1 antibody therapy relates to the tumor PD-L1 expression level remain controversial. Thus, this meta-analysis evaluated the efficacy and safety of anti-PD-1/PD-L1 antibody therapy for pretreated patients with advanced NSCLC. Methods: Randomized clinical trials were retrieved by searching the PubMed, EMBASE, ASCO meeting abstract, clinicaltrial.gov, and Cochrane library databases. The pooled hazard ratios (HRs) for overall survival (OS) and progression-free survival (PFS), and odds ratios for the overall response rate and adverse events (AEs) were calculated by STATA software. Results: Three randomized clinical trials involving 1141 pretreated patients with advanced NSCLC were included. These trials all compared the efficacy and safety of anti-PD-1/PD-L1 antibodies (nivolumab and MPDL3280A) with docetaxel. The results suggested that, for all patients, anti-PD-1/PD-L1 therapy could acquire a greater overall response (odds ratio = 1.50, 95% CI: 1.08–2.07, P = 0.015, P for heterogeneity [Ph] = 0.620) and longer OS (HR = 0.71, 95% CI: 0.61–0.81, P < 0.001, Ph = 0.361) than docetaxel, but not PFS (HR = 0.83, 95% CI: 0.65–1.06, P = 0.134; Ph = 0.031). Subgroup analyses according to the tumor PD-L1 expression level showed that anti-PD-1/PD-L1 therapy could significantly improve both OS and PFS in patients with high expressions of PD-L1, but not in those with low expressions. Generally, the rates of grade 3 or 4 AEs of anti-PD-1/PD-L1 therapy were significantly lower than that of docetaxel. However, the risks of pneumonitis and hypothyroidism were significantly higher. Conclusion: Anti-PD-1/PD-L1 antibody therapy may significantly improve

  10. Fabrication of Pd/Pd-Alloy Films by Surfactant Induced Electroless Plating for Hydrogen Separation from Advanced Coal Gasification Processes

    SciTech Connect

    Ilias, Shamsuddin; Kumar, Dhananjay

    2012-07-31

    Dense Pd, Pd-Cu and Pd-Ag composite membranes on microporous stainless steel substrate (MPSS) were fabricated by a novel electroless plating (EP) process. In the conventional Pd-EP process, the oxidation-reduction reactions between Pd-complex and hydrazine result in an evolution of NH{sub 3} and N{sub 2} gas bubbles. When adhered to the substrate surface and in the pores, these gas bubbles hinder uniform Pd-film deposition which results in dendrite growth leading to poor film formation. This problem was addressed by introducing cationic surfactant in the electroless plating process known as surfactant induced electroless plating (SIEP). The unique features of this innovation provide control of Pd-deposition rate, and Pd-grain size distribution. The surfactant molecules play an important role in the EP process by tailoring grain size and the process of agglomeration by removing tiny gas bubbles through adsorption at the gas-liquid interface. As a result surfactant can tailor a nanocrystalline Pd, Cu and Ag deposition in the film resulting in reduced membrane film thickness. Also, it produces a uniform, agglomerated film structure. The Pd-Cu and Pd-Ag membranes on MPSS support were fabricated by sequential deposition using SIEP method. The pre- and post-annealing characterizations of these membranes (Pd, Pd-Cu and Pd-Ag on MPSS substrate) were carried out by SEM, EDX, XRD, and AFM studies. The SEM images show significant improvement of the membrane surface morphology, in terms of metal grain structures and grain agglomeration compared to the membranes fabricated by conventional EP process. The SEM images and helium gas-tightness studies indicate that dense and thinner films of Pd, Pd-Cu and Pd-Ag membranes can be produced with shorter deposition time using surfactant. H{sub 2} Flux through the membranes fabricated by SIEP shows large improvement compared to those by CEP with comparable permselectivity. Pd-MPSS composite membrane was subjected to test for long term

  11. Kinetics of monolayer graphene growth by segregation on Pd(111)

    SciTech Connect

    Mok, H. S.; Murata, Y.; Kodambaka, S.; Ebnonnasir, A.; Ciobanu, C. V.; Nie, S.; McCarty, K. F.

    2014-03-10

    Using in situ low-energy electron microscopy and density functional theory calculations, we follow the growth of monolayer graphene on Pd(111) via surface segregation of bulk-dissolved carbon. Upon lowering the substrate temperature, nucleation of graphene begins on graphene-free Pd surface and continues to occur during graphene growth. Measurements of graphene growth rates and Pd surface work functions establish that this continued nucleation is due to increasing C adatom concentration on the Pd surface with time. We attribute this anomalous phenomenon to a large barrier for attachment of C adatoms to graphene coupled with a strong binding of the non-graphitic C to the Pd surface.

  12. Magnetic properties of metastable Fe Pd alloys by mechanical alloying

    NASA Astrophysics Data System (ADS)

    Yabe, Hiromasa; O'Handley, Robert C.; Kuji, Toshiro

    2007-03-01

    Metastable Fe-Pd powder samples with various Pd content were synthesized by mechanical alloying. Their fundamental properties, i.e., structure, magnetization and coercive fore are discussed. The saturation magnetizations of the metastable Fe-Pd powders gradually decreases with increasing Pd content. The coercive forces observed in as-milled samples are all less than 40 Oe. However, some of the heat-treated samples, notably, Pd content around 55 at% with L1 0 structure, shows Hc up to 1589 Oe.

  13. Transient F Ring Dust Features in Cassini UVIS Solar Occultations

    NASA Astrophysics Data System (ADS)

    Becker, T. M.; Colwell, J. E.; Esposito, L. W.; Attree, N.; Murray, C.

    2015-12-01

    We present results from an investigation of the variable particle size distribution in Saturn's dynamic F ring. We analyze 13 solar occultations observed by the Cassini Ultraviolet Imaging Spectrograph (UVIS), of which 4 occultations show a clear signature of diffracted sunlight. The magnitude and scattering angle of the diffraction signal suggest the presence of a significant population of micron-sized dust particles; however, the lack of a detection of diffracted light in other solar occultations implies that such a population is transient or spatially variable. Initial comparisons with images from the Cassini Imaging Science Subsystem (ISS) suggest that a diffraction signal is detected in UVIS occultations that coincide with a recent collisional event in the F ring core, as seen in the ISS images. This implies that such events release a significant population of dust, which can then be measured by the diffraction signature in the UVIS data. We use a forward-modeling approach to place constraints on the particle size distribution of the F ring during each solar occultation. We present these measurements of the size distribution and our comparisons of the F ring dust population as measured by UVIS with the ISS images of the ring.

  14. Gaia transient detection efficiency: hunting for nuclear transients

    NASA Astrophysics Data System (ADS)

    Blagorodnova, N.; Van Velzen, S.; Harrison, D. L.; Koposov, S.; Mattila, S.; Campbell, H.; Walton, N. A.; Wyrzykowski, Ł.

    2016-01-01

    We present a study of the detectability of transient events associated with galaxies for the Gaia European Space Agency astrometric mission. We simulated the on-board detections, and on-ground processing for a mock galaxy catalogue to establish the properties required for the discovery of transient events by Gaia, specifically tidal disruption events (TDEs) and supernovae (SNe). Transients may either be discovered by the on-board detection of a new source or by the brightening of a previously known source. We show that Gaia transients can be identified as new detections on-board for offsets from the host galaxy nucleus of 0.1-0.5 arcsec, depending on magnitude and scanning angle. The Gaia detection system shows no significant loss of SNe at close radial distances to the nucleus. We used the detection efficiencies to predict the number of transients events discovered by Gaia. For a limiting magnitude of 19, we expect around 1300 SNe per year: 65 per cent SN Ia, 28 per cent SN II and 7 per cent SN Ibc, and ˜20 TDEs per year.

  15. PD-1 on Immature and PD-1 Ligands on Migratory Human Langerhans Cells Regulate Antigen-Presenting Cell Activity

    PubMed Central

    Peña-Cruz, Victor; McDonough, Sean M.; Diaz-Griffero, Felipe; Crum, Christopher P.; Carrasco, Ruben D.; Freeman, Gordon J.

    2010-01-01

    Langerhans cells (LCs) are known as “sentinels” of the immune system that function as professional antigen-presenting cells (APCs) after migration to draining lymph node. LCs are proposed to have a role in tolerance and the resolution of cutaneous immune responses. The Programmed Death-1 (PD-1) receptor and its ligands, PD-L1 and PD-L2, are a co-inhibitory pathway that contributes to the negative regulation of T-lymphocyte activation and peripheral tolerance. Surprisingly, we found PD-1 to be expressed on immature LCs (iLCs) in situ. PD-1 engagement on iLCs reduced IL-6 and macrophage inflammatory protein (MIP)-1α cytokine production in response to TLR2 signals but had no effect on LC maturation. PD-L1 and PD-L2 were expressed at very low levels on iLCs. Maturation of LCs upon migration from epidermis led to loss of PD-l expression and gain of high expression of PD-L1 and PD-L2 as well as co-stimulatory molecules. Blockade of PD-L1 and/or PD-L2 on migratory LCs (mLCs) and DDCs enhanced T-cell activation, as has been reported for other APCs. Thus the PD-1 pathway is active in iLCs and inhibits iLC activities, but expression of receptor and ligands reverses upon maturation and PD-L1 and PD-L2 on mLC function to inhibit T-cell responses. PMID:20445553

  16. Activation of the PD-1/PD-L1 immune checkpoint confers tumor cell chemoresistance associated with increased metastasis

    PubMed Central

    Black, Madison; Barsoum, Ivraym B.; Truesdell, Peter; Cotechini, Tiziana; Macdonald-Goodfellow, Shannyn K.; Petroff, Margaret; Siemens, D. Robert; Koti, Madhuri; Craig, Andrew W.B.; Graham, Charles H.

    2016-01-01

    The ability of tumor cells to avoid immune destruction (immune escape) as well as their acquired resistance to anti-cancer drugs constitute important barriers to the successful management of cancer. Interaction between the Programmed Death Ligand 1 (PD-L1) on the surface of tumor cells with the Programmed Death-1 (PD-1) receptor on cytotoxic T lymphocytes leads to inactivation of these immune effectors and, consequently, immune escape. Here we show that the PD-1/PD-L1 axis also leads to tumor cell resistance to conventional chemotherapeutic agents. Using a panel of PD-L1-expressing human and mouse breast and prostate cancer cell lines, we found that incubation of breast and prostate cancer cells in the presence of purified recombinant PD-1 resulted in resistance to doxorubicin and docetaxel as determined using clonogenic survival assays. Co-culture with PD-1-expressing Jurkat T cells also promoted chemoresistance and this was prevented by antibody blockade of either PD-L1 or PD-1 or by silencing of the PD-L1 gene. Moreover, inhibition of the PD-1/PD-L1 axis using anti-PD-1 antibody enhanced doxorubicin chemotherapy to inhibit metastasis in a syngeneic mammary orthotopic mouse model of metastatic breast cancer. To further investigate the mechanism of tumor cell survival advantage upon PD-L1 ligation, we show that exposure to rPD-1 promoted ERK and mTOR growth and survival pathways leading to increased cell proliferation. Overall, the findings of this study indicate that combinations of chemotherapy and immune checkpoint blockade may limit chemoresistance and progression to metastatic disease. PMID:26859684

  17. 102Pd(n, {gamma}) Cross Section Measurement Using DANCE

    SciTech Connect

    Hatarik, R.; Alpizar-Vicente, A. M.; Bredeweg, T. A.; Esch, E.-I.; Haight, R. C.; O'Donnell, J. M.; Reifarth, R.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Wouters, J. M.; Greife, U.

    2006-03-13

    The neutron capture cross section of the proton rich nucleus 102Pd was measured with the Detector for Advanced Neutron Capture Experiments (DANCE) at the Los Alamos Neutron Science Center. The target was a 2 mg Pd foil with 78% enriched 102Pd. It was held by a 0.9 {mu}m thick Mylar bag which was selected after comparing different thicknesses of Kapton and Mylar for their scattering background. To identify the contribution of the other Pd isotopes the data of a natural Pd sample was compared to the data of the 102Pd enriched sample. A 12C sample was used to determine the scattering background. The 102Pd(n, {gamma}) rate is of importance for the p-process nucleosynthesis.

  18. High-spin structure of 95Pd

    NASA Astrophysics Data System (ADS)

    Mărginean, R.; Rusu, C.; Mărginean, N.; Bucurescu, D.; Ur, C. A.; de Angelis, G.; Axiotis, M.; Bazzacco, D.; Farnea, E.; Gadea, A.; Ionescu-Bujor, M.; Iordăchescu, A.; Krolas, W.; Kröll, Th.; Lenzi, S. M.; Lunardi, S.; Napoli, D. R.; Alvarez, C. Rossi; Wrzesinski, J.

    2012-09-01

    The level scheme of the neutron-deficient nucleus 95Pd has been studied with the 58Ni + 40Ca fusion-evaporation reaction at 135 MeV with the GASP γ-ray array, the ISIS silicon ball, and the N-ring neutron detector. Excited levels with spins at least up to (45)/(2)ℏ are reported for both parities. The observed experimental data are compared to large-scale shell-model calculations.

  19. Primary charge carrier dynamics of water-solubilized CdZnS/ZnS core/shell and CdZnS/ZnS·Pd nanoparticle adducts

    NASA Astrophysics Data System (ADS)

    Busby, Erik; Thibert, Arthur; Page, Leah E.; Jawaid, Ali M.; Snee, Preston T.; Larsen, Delmar S.

    2013-06-01

    The primary photodynamics of 5-nm CdZnS core, CdZnS/ZnS core/shell, and CdZnS/ZnS·Pd nanoparticle adducts are characterized with broadband ultrafast transient absorption spectroscopy. Photogenerated excitons in the CdZnS and CdZnS/ZnS nanoparticles exhibit long-lived (>20 ns) lifetimes and further functionalizing of the type-I CdZnS/ZnS core/shells with Pd nanoparticles resulted in rapid exciton quenching (<250 ps) due to the transfer of electrons from the CdZnS core into the Pd nanocrystals via tunneling through the insulating ZnS shell. The shell-induced surface trap passivation and near-unity charge carrier injection efficiency into a platinum-group metal nanoparticle shows potential for enhanced colloidal photocatalytic applications, while enhancing photostability.

  20. Emotional manifestations of PD: Neurobiological basis.

    PubMed

    Castrioto, Anna; Thobois, Stéphane; Carnicella, Sebastien; Maillet, Audrey; Krack, Paul

    2016-08-01

    Neuropsychiatric symptoms are common and disabling in PD. Their neurobiological bases are complex, partly because of the disease itself and partly because of the dopaminergic treatment. The aim of this review is to focus on the emotional manifestations stemming from the neurodegenerative process itself. We focus on depression, anxiety, apathy, and fatigue, which can all be part of the clinical spectrum of premotor disease and may be improved or masked by medications targeting parkinsonian motor signs or psychiatric symptoms as the disease progresses. Findings from clinical, neuroimaging, and animal studies are reviewed, showing a major contribution of the dopaminergic system to the pathophysiology of these disabling symptoms. Degeneration of noradrenergic and serotonergic projection systems also has an impact on psychiatric symptoms of PD. The available literature is reviewed, but at present there is a lack of studies that would allow disentangling the separate contribution of each of the monoaminergic systems. The use of a pragmatic classification of all these symptoms under the umbrella of hypodopaminergic behavioral syndrome seems clinically useful, as it emphasizes the crucial, although not exclusive, nature of their dopaminergic neurobiological basis, which has important implications in the clinical management of PD. © 2016 International Parkinson and Movement Disorder Society. PMID:27041545