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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. Plasma conditions for improved energy coupling into the gain region of the Ni-like Pd transient collisional x-ray laser

    SciTech Connect

    Smith, R F; Dunn, J; Filevich, J; Moon, S; Nilsen, J; Keenan, R; Shlyaptsev, V N; Rocca, J J; Hunter, J R; Marconi, M C

    2004-10-04

    We have directly probed the plasma conditions in which the Ni-like Pd transient collisional x-ray laser is generated and propagates by measuring the near-field image and by utilizing picosecond resolution soft x-ray laser interferometry of the preformed Pd plasma gain medium. The electron density and gain region of the plasma have been determined experimentally and are found to be in good agreement with simulations. We observe a strong dependence of the laser pump-gain medium coupling on the laser pump parameters. The most efficient coupling of laser pump energy into the gain region occurs with the formation of lower density gradients in the pre-formed plasma and when the duration of the main heating pulse is comparable to the gain lifetime ({approx}10ps for mid-Z Ni-like schemes). This increases the output intensity by more than an order of magnitude relative to the commonly utilized case where the same pumping energy is delivered within a shorter heating pulse duration (< 3ps). In contrast, the higher intensity heating pulses are observed to be absorbed at higher electron densities and in regions where steep density gradients limit the effective length of the gain medium.

  3. Tabletop Transient Collisional Excitation X-Ray Lasers

    SciTech Connect

    Dunn, J; Li, Y; Osterheld, A L; Nilsen, J; Moon, S J; Fournier, K B; Hunter, J R; Faenov, A; Pikuz, T A; Shlyaptsev, V N

    1999-09-03

    Recent transient collisional excitation x-ray laser experiments are reported using the COMET tabletop laser driver at the Lawrence Livermore National Laboratory (LLNL). Ne-like and Ni-like ion x-ray laser schemes have been investigated with a combination of long 600 ps and short {approximately}1 ps high power laser pulses with 5-10 J total energy. We show small signal gain saturation for x-ray lasers when a reflection echelon traveling wave geometry is utilized. A gain length product of 18 has been achieved for the Ni-like Pd 4d{r_arrow}4p J=0-1 line at 147 {angstrom}, with an estimated output of {approximately}10{micro}J. Strong lasing on the 119 {angstrom} Ni-like Sn line has also been observed. To our knowledge this is the first time gain saturation has been achieved on a tabletop laser driven scheme and is the shortest wavelength tabletop x-ray laser demonstrated to date. In addition, we present preliminary results of the characterization of the line focus uniformity for a Ne-like ion scheme using L-shell spectroscopy.

  4. Transient and Capillary Collisional X-ray Laser

    SciTech Connect

    Shlyaptsev, V N; Dunn, J; Fournier, K B; Moon, S; Osterheld, A L; Rocca, J J; Detering, F; Rozmus, W; Matte, J P; Fiedorowicz, H; Bartnik, A; Kanouff, M

    2001-12-17

    In this work we report our numerical modeling results of laser-generated transient inversion and capillary discharge X-ray lasers. In the search for more efficient X-ray lasers we look closely at other approaches in conjunction with experiments at LLNL. In the search for improved X-ray lasers we perform modeling and experimental investigations of low density targets including gas puff targets. We have found the importance of plasma kinetics in transient X-ray lasers by expanding the physical model beyond hydrodynamics approach with Particle In Cell (PIC) and Fokker-Planck codes. The evidence of the Langdon effect was inferred from the recent experimental data obtained with the Ni-like Pd X-ray laser. We continue modeling different kinds of capillary discharge plasma configurations directed toward shorter wavelength X-ray lasers, plasma diagnostics and other applications.

  5. Femtosecond pulses in a dense two-level medium: Spectral transformations, transient processes, and collisional dynamics

    SciTech Connect

    Novitsky, Denis V.

    2011-07-15

    Propagation of ultrashort optical pulses in a dense resonant medium is considered in the semiclassical limit. In our analysis, we place emphasis on several main points. First, we study transformations of spectra in the process of pulse propagation and interactions with another pulse. The second point involves the transient processes (including pulse compression) connected with self-induced transparency soliton formation inside the medium. Finally, the third aspect is the study of collisions of co- and counterpropagating pulses in the medium. In the last case, the investigation of symmetric and asymmetric collisions shows the possibility of effectively controlling the parameters of transmitted radiation.

  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. Transient immunological and clinical effectiveness of treating mice bearing premalignant oral lesions with PD-1 antibodies.

    PubMed

    Levingston, Corinne A; Young, M Rita I

    2017-04-01

    A carcinogen-induced premalignant oral lesion model that progresses to oral cancer was used to examine the impact of blocking PD-1 on cytokine expression and on progression of lesions to cancer. The results of this study show increased production of IL-2 and the inflammatory cytokines IL-6, IL-17 and TNF-α by spleen cells of lesion-bearing mice that were treated with PD-1 antibody for 1 week compared to cytokine production by spleen cells of lesion-bearing mice treated with control antibody. Production of IFN-γ increased at 3 weeks of PD-1 antibody treatment, although production of the other Th1 and inflammatory mediators declined. By 5 weeks, levels of these cytokines declined for both control and PD-1 antibody-treated mice. Flow cytometric analysis for IFN-γ-expressing cells showed shifts in CD4(+) cells expressing IFN-γ consistent with the changes in cytokine secretion. Whether or not treatment generated reactivity to lesions or HNSCC was determined. Spleen cells from PD-1 antibody-treated mice were stimulated by lysates of premalignant lesion and HNSCC tongue tissues to produce increased levels of Th1 and select inflammatory cytokines early in the course of PD-1 antibody treatment. However, with continued treatment, reactivity to lesion and HNSCC lysates declined. Analysis of clinical response to treatment suggested an early delay in lesion progression but, with continued treatment, lesions in PD-1 antibody-treated mice progressed to the same degree as in control antibody-treated mice. Overall, these results show an early beneficial response to PD-1 antibody treatment, which then fails with continued treatment and lesion progression.

  8. Evaluation of Neuroprotection and Behavioral Recovery by the Kappa- Opioid, PD 117302 Following Transient Forebrain Ischemia

    DTIC Science & Technology

    1994-01-01

    recover at least 50% of baseline most rats, performance degradation was characterized by a com- values was caiculated. Quarter-life measures were...histological changes induced by transient global ce- 34:190-194; 1991. rebral ischemia in rats: Effects of cinnarizine and flunarizine. J. 17. Hall, E. D

  9. Transient and steady state CO oxidation kinetics on nanolithographically prepared supported Pd model catalysts: Experiments and simulations

    SciTech Connect

    Laurin, M.; Johanek, V.; Grant, A.W.; Kasemo, B.; Libuda, J.; Freund, H.-J.

    2005-08-01

    Applying molecular-beam methods to a nanolithographically prepared planar Pd/SiO{sub 2} model catalyst, we have performed a detailed study of the kinetics of CO oxidation. The model catalyst was prepared by electron-beam lithography, allowing individual control of particle size and position. The sample was structurally characterized by atomic force microscopy and scanning electron microscopy before and after reaction. In the kinetic experiments, the O-rich and CO-rich regimes were investigated systematically with respect to their transient and steady-state behaviors, both under bistable and monostable reaction conditions. Separate molecular beams were used in order to supply the reactants, allowing individual control over the reactant fluxes. The desorbing CO{sub 2} was detected by both angle-resolved and angle-integrated mass spectrometries. The experimental results were analyzed using different types of microkinetic models, including a detailed reaction-diffusion model, which takes into account the structural parameters of the catalyst as well as scattering of the reactants from the support. The model quantitatively reproduces the results as a function of the reactant fluxes and the surface temperature. Various kinetic effects observed are discussed in detail on the basis of the model. Specifically, it is shown that under conditions of limited oxygen mobility, the switching behavior between the kinetic regimes is largely driven by the surface mobility of CO.

  10. 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

  11. 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.

  12. Energetically consistent collisional gyrokinetics

    SciTech Connect

    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.

  13. Collisional Evolution of Planetesimals

    NASA Astrophysics Data System (ADS)

    Leinhardt, Zoë Malka

    2010-05-01

    Over 400 extrasolar planets have been discovered. These planetary systems are very different from our solar system and surprisingly diverse. The large number of planets detected suggests that planet formation is common around main sequence stars. The major problem facing the scientific community with regards to these discoveries is that observations cannot trace the history of planet formation. Observations provide snapshots of the early stages of a protoplanetary gas disk orbiting a young star and the late stages after planetary systems have formed. But the evolution from a young star to a planetary system has not been observed. Thus, the challenge is to connect the early and late stages of planet formation. Planets form from the collisional growth of planetary building blocks, planetesimals. In recent numerical work we found that the resistance of planetesimals to collisional erosion changes dramatically during planet formation. Young planetesimals are weak aggregates that are easily disrupted due to efficient momentum coupling during low-velocity collisions in early phases of collisional evolution. However, as impact speeds increase the same weak planetesimals become dramatically stronger because the shock from a supersonic impact loses energy to deformation and phase changes. Our work identifies a paradox for the early stages of planet formation. Objects in the km-size range are weak and susceptible to collisional disruption. However, this disruption may actually produce large amounts of debris that can be accreted by remaining undisrupted planetesimals allowing growth. As we work to disentangle these sorts of conundrums we can expect to put forward hypotheses for collisional remnants in our solar system - for example, the dwarf planet Haumea and its collisional family. In this talk I will review the current understanding of planetesimal evolution and discuss how future numerical simulations may connect observational snapshots to provide a complete history of

  14. 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.

  15. Collisional atomic mixing

    NASA Astrophysics Data System (ADS)

    Biersack, Jochen P.

    The collisional mixing of thin metal markers in silicon is investigated with the computer program TRIM-DYNAMIC (T-DYN). This code assumes that at high dose irradiation, the substrate Si or Ge, will get fully amorphized, and the recoil atom can stop in any position after slowing down below a certain final energy Ef (taken here as 3 eV). In order to avoid chemical effects, the system Au marker in a silicon matrix was chosen for the TRIM simulation. The results are in good agreement with the experimental findings, as compiled in the review article by Paine and Averback. Similar collisional mixing effects occur in the process of SIMS or Auger electron depth profiling, and cannot be avoided. An example is given here for a thin layer of arsenic vapor deposited on Si and covered by amorphous silicon. The analysing ion beam in this case was 14.5 keV Cs+ incident at 37° towards the surface normal. In comparison with the SIMS measurements by modern depth profiling equipment, again good agreement was found between the T-DYN results and the experiment.

  16. 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.

  17. Inclined, collisional sediment transport

    NASA Astrophysics Data System (ADS)

    Berzi, Diego; Fraccarollo, Luigi

    2013-10-01

    We apply the constitutive relations of kinetic theory of granular gases to the transport of cohesionless sediments driven by a gravitational liquid turbulent stream in steady uniform conditions. The sediment-laden flow forms self-equilibrated mechanisms of resistance at the bed surface, below which the sediments are at rest. This geo-physical process takes place quite often in streams at moderate slope and may be interpreted through tools common to fluid mechanics and particle physics. Taking into account the viscous dissipation of the fluctuation energy of the particles, and using approximate methods of integration of the governing differential equations, permit to obtain a set of simple formulas for predicting how depths and flow rates adjust to the angle of inclination of the bed, without requiring additional tuning parameters besides the particle and fluid properties. The agreement with laboratory experiments performed with either plastic cylinders or gravel in water is remarkable. We also provide quantitative criteria to determine the range of validity of the theory, i.e., the values of the Shields number and the angle of inclination of the bed for which the particle stresses can be mostly ascribed to collisional exchange of momentum.

  18. Laser cooling by collisional redistribution of radiation.

    PubMed

    Vogl, Ulrich; Weitz, Martin

    2009-09-03

    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.

  19. Transient Palladadiphosphanylcarbenes: Singlet Carbenes with an “Inverse” Electronic Configuration (pπ2 instead of σ2) and Unusual Transannular Metal–Carbene Interactions (πC→pd Donation and σPd→C Back-donation)

    PubMed Central

    Vignolle, Joan; Gornitzka, Heinz; Maron, Laurent; Schoeller, Wolfgang W.; Bourissou, Didier; Bertrand, Guy

    2008-01-01

    Upon treatment with [PdCl(allyl)]2, asymmetrically substituted α, α′-diphosphanyl diazo compounds eliminate dinitrogen to afford C-chlorodiphosphanylmethanide complexes in high yields. In the presence of a chloride-abstracting agent, such as sodium tetraphenylborate, the C-chlorodiphosphanylmethanide complexes react with pyridine and trimethylphosphine, readily affording the corresponding nitrogen and phosphorus ylides. The postulated intermediate in this process, namely palladadiphosphanylcarbenes, could not be spectroscopically characterized, but their transient formation was chemically supported further by a Lewis base exchange reaction between pyridine and 4-dimethylaminopyridine. This hypothesis has also been substantiated by computing the corresponding dissociation energy using two model systems featuring methyl groups at the phosphorus. Of particular interest, density functional theory calculations reveal that these palladadiphosphanylcarbenes have a singlet ground state with an “inverse” pπ2 electronic configuration and a distorted geometry associated with unusual transannular metal–carbene interactions (πC→Pd donation and σPd→C back-donation). PMID:17243835

  20. Collisional processes in cometary plasmas

    NASA Technical Reports Server (NTRS)

    Cravens, T. E.

    1991-01-01

    The interaction of the solar wind with comets is initiated at large distances from the nucleus by the ionization of cometary neutrals. The resulting contamination of the solar wind with cometary ions mass-loads the solar wind flow, causing it to slow down. The plasma-comet interaction is largely collisionless at large cometocentric distances. However, collisional processes become important in the inner coma (within the cometopause). Collisional processes include charge-transfer between solar wind protons and neutrals, ion-neutral friction, electron and ion thermal cooling, and ion-neutral chemistry. For example, the magnetometer on the Giotto spacecraft observed a diamagnetic cavity near closest approach. This cavity is a consequence of the balance between an inward-directed magnetic pressure gradient force and an outward ion-netural frictional force. Thermalization of the cometary ion distribution function by Coulomb collisions is another important process in the inner coma of an active comet.

  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. 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...

  3. Revisiting the interplay between ablation, collisional, and radiative processes during ns-laser ablation

    NASA Astrophysics Data System (ADS)

    Autrique, D.; Gornushkin, I.; Alexiades, V.; Chen, Z.; Bogaerts, A.; Rethfeld, B.

    2013-10-01

    A study of ns-laser ablation is presented, which focuses on the transient behavior of the physical processes that act in and above a copper sample. A dimensionless multiphase collisional radiative model describes the interplay between the ablation, collisional, and radiative mechanisms. Calculations are done for a 6 ns-Nd:YAG laser pulse operating at 532 nm and fluences up to 15 J/cm2. Temporal intensity profiles as well as transmissivities are in good agreement with experimental results. It is found that volumetric ablation mechanisms and photo-processes both play an essential role in the onset of ns-laser induced breakdown.

  4. 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.

  5. 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.

  6. 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.

  7. Collisional Effects On Laser-Induced Fluorescence Flame Measurements

    NASA Astrophysics Data System (ADS)

    Crosley, David R.

    1981-08-01

    Abstract. Laser-induced fluorescence (LIF) is a method of considerable utility for the measurement of the transient free radicals which are the keys to the chemistry of flames. Collisions experienced by the electronically excited state can alter the magnitude and the spectral form of the fluorescence signals. Recent studies on both quenching and energy transfer collisions, and their influence on LIF measurements, are treated in this review; special emphasis is given to the important and popular OH molecule. Different solutions to the problem of accounting for quenching are considered, and both effects and exploitation of energy transfer within the excited state are discussed. Although further research is needed to better quantify these collisional effects, LIF can currently provide data significant for the understanding of combustion chemistry.

  8. 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.

  9. 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.

  10. 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.

  11. Two-photon collisional redistribution of radiation

    NASA Technical Reports Server (NTRS)

    Alber, G.; Cooper, J.

    1985-01-01

    Collisional redistribution in the presence of two weakly exciting laser fields is studied, including the effects due to degeneracy of the radiator states. A general expression for the total redistributed intensity is derived valid for arbitrary detunings and polarizations of the exciting laser fields. In particular, this expression contains all single-collision and sequential-collision contributions, which are equally important under certain circumstances. The similarities and differences between the redistributed intensity as calculated in this paper and the collisionally aided radiative excitation cross sections studied by Yeh and Berman (1979) and Light and Szoke (1978) are pointed out.

  12. Understanding Pd-Pd bond length variation in (PNP)Pd-Pd(PNP) dimers.

    PubMed

    Walensky, Justin R; Fafard, Claudia M; Guo, Chengyun; Brammell, Christina M; Foxman, Bruce M; Hall, Michael B; Ozerov, Oleg V

    2013-03-04

    Analysis of the structures of three (PNP)Pd-Pd(PNP) dimers [where PNP stands for anionic diarylamido/bis(phosphine) pincer ligands] has been carried out with the help of single-crystal X-ray diffractometry and density functional theory (DFT) calculations on isolated molecules. The three dimers under study possess analogous ancillary ligands; two of them differ only by an F versus Me substituent in a remote (five bonds away from Pd) position of the pincer ligand. Despite these close similarities, X-ray structural determinations revealed two distinct structural motifs: a highly symmetric molecule with a long Pd-Pd bond or a highly distorted molecule with Pd-Pd bonds ca. 0.14 Å shorter. DFT calculations on a series of (PNP)Pd-Pd(PNP) dimers (as molecules in the gas phase) confirmed the existence of these distinct minima for dimers carrying large isopropyl substituents on the P-donor atoms (as in the experimental structure). These minima are nearly isoergic conformers. Evidently, the electronically preferred symmetric structure for the dimer (with a square-planar environment about Pd and a linear N-Pd-Pd-N vector) is not sterically possible with the preferred Pd-Pd distance. Thus, the minima correspond to either a symmetric structure with a long Pd-Pd bond distance or a structure with a short Pd-Pd distance but with substantial distortions in the Pd coordination environment to alleviate steric conflict. This notion is supported by finding only a single minimum (symmetric and with short Pd-Pd bonds) for each of the dimers carrying smaller substituents (H or Me) on the P atoms, regardless of the remote substitution.

  13. Collisional Transitions in Interstellar Asymmetric Top Molecules

    NASA Astrophysics Data System (ADS)

    Chandra, Suresh

    2012-07-01

    For the study of a molecule in interstellar space or in circumstellar envelopes of an evolved star, one has to deal with a multi-level system in the molecule. These levels are connected through radiative as well as collisional transitions. The NLTE effects in a molecule come in the picture only when collisional transitions are present. Computation of collisional rates is quite cumbersome task. Besides emission and absorption, two anomalous phenomena: (i) MASER action and (ii) Anomalous absorption (Absorption against the CMB) are shown by some molecules in interstellar space. Both of these phenomena are good examples of NLTE prevailing in the interstellar space and circumstellar envelopes of evolved stars. In the present talk, we shall discuss about the collisional transitions between rotational levels in a molecule. The collisional rate coefficients for the rotational transition J τ → J' τ' at the kinetic temperature T, averaged over the Maxwellian distribution are C(J τ → J' τ'|T) = \\Big(\\frac{8 k T}{π μ}\\Big)^{1/2} \\Big(\\frac{1}{k T}\\Big)^2 \\int_0^\\infty σ (J τ → J' τ'|E) E {e}^{-E/kT} {d} E where μ is the reduced mass of the system and the cross section σ(J τ → J' τ'|E) for the transition is \\begin{eqnarray} σ (J τ → J' τ'|E) = \\sum_{L M M'} S(J, τ, J', τ'|L, M, M') q(L, M, M'|E) The q(L, M, M'|E) are the parameters which can be obtained from the software MOLSCAT. The spectroscopic coefficients, S ( J, τ, J', τ'|L, M, M'), depend on the wave-functions of the molecules and on the angular momentum coupling factors: S(J, τ, J', τ'|L, M, M') = \\sum_{p, p', q, q'} g^p_{J τ} g^q_{J τ} g^{p'}_{J' τ'} g^{q'}_{J' τ'} \\big \\big Here, \\big represents the Clebsch-Gorden coefficient. The g-coefficients can be obtained from laboratory analysis of the molecule and the parameters q(L, M, M'|E) can be obtained with the help of the software MOLSCAT for a

  14. 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

  15. Collisional and collisionless expansion of Yukawa balls.

    PubMed

    Piel, Alexander; Goree, John A

    2013-12-01

    The expansion of Yukawa balls is studied by means of molecular dynamics simulations of collisionless and collisional situations. High computation speed was achieved by using the parallel computing power of graphics processing units. When the radius of the Yukawa ball is large compared to the shielding length, the expansion process starts with the blow-off of the outermost layer. A rarefactive wave subsequently propagates radially inward at the speed of longitudinal phonons. This mechanism is fundamentally different from Coulomb explosions, which employ a self-similar expansion of the entire system. In the collisionless limit, the outer layers carry away most of the available energy. The simulations are compared with analytical estimates. In the collisional case, the expansion process can be described by a nonlinear diffusion equation that is a special case of the porous medium equation.

  16. 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.

  17. 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.

  18. 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.

  19. 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)

  20. 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.

  1. Mantle conveyor beneath the Tethyan collisional belt

    NASA Astrophysics Data System (ADS)

    Faccenna, C.; Becker, T. W.

    2012-04-01

    Collisional belts are generated by the arrival of continental lithosphere into a subduction zone. The Tethyan suture from the Bitlis to the Himalayas is a prime example where the Arabian and Indian plates collided with Eurasia during the Cenozoic. While the kinematics of this process are well established, its dynamics are more uncertain. India and Arabia intriguingly keep advancing, in spite of large collisional resisting forces, and in the absence of a substantial, upper mantle slab driving force at present-day. We perform global mantle circulation computations to test the role of deep mantle flow as a driving force for the kinematics of the Tethyan collisional belt, evaluating different boundary conditions and mantle density distributions as inferred from seismic tomography or slab models. Our results show that mantle drag exerted on the base of the lithosphere by a large-scale, convective "conveyor belt" with an active upwelling component is likely the main cause for the ongoing indentation of the Indian and Arabian plates into Eurasia

  2. Mantle conveyor beneath the Tethyan collisional belt

    NASA Astrophysics Data System (ADS)

    Becker, Thorsten W.; Faccenna, Claudio

    2011-10-01

    Collisional belts are generated by the arrival of continental lithosphere into a subduction zone. The Tethyan suture from the Bitlis to the Himalayas is a prime example where the Arabian and Indian plates collided with Eurasia during the Cenozoic. While the kinematics of this process are well established, its dynamics are more uncertain. India and Arabia intriguingly keep advancing, in spite of large collisional resisting forces, and in the absence of a substantial, upper mantle slab driving force at present-day. We perform global mantle circulation computations to test the role of deep mantle flow as a driving force for the kinematics of the Tethyan collisional belt, evaluating different boundary conditions and mantle density distributions as inferred from seismic tomography or slab models. Our results show that mantle drag exerted on the base of the lithosphere by a large-scale, convective "conveyor belt" with an active upwelling component is likely the main cause for the ongoing indentation of the Indian and Arabian plates into Eurasia.

  3. Electron and Phonon Dynamics in Hexagonal Pd Nanosheets and Ag/Pd/Ag Sandwich Nanoplates.

    PubMed

    Wang, Li; Sagaguchi, Takuya; Okuhata, Tomoki; Tsuboi, Motohiro; Tamai, Naoto

    2017-02-28

    Pd and its hybrid nanostructures have attracted considerable attention over the past decade, with both catalytic and plasmonic properties. The electron and phonon properties directly govern conversion efficiencies in applications such as energy collectors and photocatalysts. We report the dynamic processes of electron-phonon coupling and coherent acoustic phonon vibration in hexagonal Pd nanosheets and Ag/Pd/Ag sandwich nanoplates using transient absorption spectroscopy. The electron-phonon coupling constant of Pd nanosheets, GPd-nanosheet (8.7 × 10(17) W/(m(3)·K)) is larger than that of the bulk GPd (5.0 × 10(17) W/(m(3)·K)). The effective coupling constant Geff of Ag/Pd/Ag nanoplates decreases with increasing Ag shell thickness, finally approaching the bulk GAg. The variation of Geff is explained in terms of reduced density of states near Fermi level of Pd nanosheets with 1.8 nm ultrathin thickness. Coherent acoustic phonon vibration in Pd nanosheets is assigned to a fundamental breathing mode, similar to the vibration of benzene. The period increases with increasing Ag shell thickness. For Ag/Pd/Ag nanoplates with 20 nm thick Ag shells, the vibrational mode is ascribed to a quasi-extensional mode. The results show that the modes of the coherent acoustic phonon vibration transform with the geometric variation of Pd nanosheets and Ag/Pd/Ag nanoplates. Our results represent an understanding of quantum-confinement related electron dynamics and bulk-like phonon kinetics in the ultrathin Pd nanosheets and their hybrid nanostructures.

  4. 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.

  5. 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.

  6. 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.

  7. Missing mass in collisional debris from galaxies.

    PubMed

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

    2007-05-25

    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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Collisional Features in Saturn's F Ring

    NASA Astrophysics Data System (ADS)

    Attree, Nicholas; Murray, Carl D; Cooper, Nicholas; Williams, Gareth

    2014-05-01

    Saturn’s F ring is a highly dynamic environment; changeable over timescales from hours to years and displaying a variety of features caused by both gravitational and collisional interactions with local objects. These objects range from the ‘shepherding’ moons Prometheus and Pandora down to small (radius < 1 km) moonlets, embedded in the ring or on nearby orbits. Previously (Attree et al. 2014) we catalogued nearly 900 small-scale collisional features (“mini-jets”) from Cassini images, placing constraints on the size and orbital distribution of the local colliding population. Here we will present the latest work on F ring collisions; updating the catalogue with new Cassini images to further refine our statistics of the population as well as discussing specific, interesting features which shed light on the collision process. We will also present the results of N-body simulations of the collisions and discuss ongoing work to survey the larger “jet” features. These are caused by higher velocity collisions 30m/s) with more distant objects like S/2004 S 6 which may represent the upper end of the moonlet population in size and in orbit.

  13. Hybrid simulations of weakly collisional plasmas

    NASA Astrophysics Data System (ADS)

    Xia, Qian; Reville, Brian; Tzoufras, Michail

    2016-10-01

    Laser produced plasma experiments can be exploited to investigate phenomena of astrophysical relevance. The high densities and velocities that can be generated in the laboratory provide ideal conditions to investigate weakly collisional or collisionless plasma shock physics. In addition, the high temperatures permit magnetic and kinetic Reynolds numbers that are difficult to achieve in other plasma experiments, opening the possibility to study plasma dynamo. Many of these experiments are based on a classic plasma physics problem, namely the interpenetration of two plasma flows. To investigate this phenomenon, we are constructing a novel multi-dimensional hybrid numerical scheme, that solves the ion distribution kinetically via a Vlasov-Fokker-Planck equation, with electrons providing a charge neutralizing fluid. This allows us to follow the evolution on hydrodynamic timescales, while permitting inclusion ofcollisionlesseffects on small scales. It also could be used to study the increasing collisional effects due to the stiff gradient and weakly anisotropic velocity distribution. We present some preliminary validation tests for the code, demonstrating its ability to accurately model key processes that are relevant to laboratory and astrophysical plasmas.

  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. Collisional Features in Saturn's F Ring

    NASA Astrophysics Data System (ADS)

    Attree, Nicholas Oliver; Murray, Carl; Cooper, Nicholas; Williams, Gareth

    2016-10-01

    Saturn's highly dynamic F ring contains a population of small (radius ~ 1 km) moonlets embedded within its core or on nearby orbits. These objects interact, both gravitationally and collisionally, with the ring producing a range of features, some of which are unique to it. Here we present a brief overview of F ring collisional processes, investigated using a combination of Cassini imaging, simulations and orbital dynamics. Collisions produce linear debris clouds, known as 'jets' and 'mini-jets', which evolve, due to differential orbital motion, over periods ranging from hours to months. Mini-jet-forming collisions occur daily in the F ring whilst larger, more dramatic, events are rarer but produce jets that persist for many months, 'wrapping around' the ring to form almost parallel strands. Measuring jet properties, such as formation rates and relative orbits, allows us to infer a local population of order hundreds of objects colliding at relative velocities of a few metres per second. N-body modelling of the collisions shows good agreement with observations when two aggregates are allowed to impact and partially fragment (as opposed to a solid moonlet encountering dust), implying massive objects both in the core and nearby. Multiple, repeated collisions by the same, or fragments of the same, object are also important in explaining some jet morphology, showing that many objects survive the collisions. The F ring represents a natural laboratory for observing low-velocity collisions between icy objects as well as the ongoing aggregation and accretion that most-likely forms them.

  16. Collisional deactivation of highly vibrationally excited pyrazine

    NASA Astrophysics Data System (ADS)

    Miller, Laurie A.; Barker, John R.

    1996-07-01

    The collisional deactivation of vibrationally excited pyrazine (C4N2H4) in the electronic ground state by 19 collider gases was studied using the time-resolved infrared fluorescence (IRF) technique. The pyrazine was photoexcited with a 308 nm laser and its vibrational deactivation was monitored following rapid radiationless transitions to produce vibrationally excited molecules in the electronic ground state. The IRF data were analyzed by a simple approximate inversion method, as well as with full collisional master equation simulations. The average energies transferred in deactivating collisions (<ΔE>d) exhibit a near-linear dependence on vibrational energy at lower energies and less dependence at higher energies. The deactivation of ground state pyrazine was found to be similar to that of ground state benzene [J. R. Barker and B. M. Toselli, Int. Rev. Phys. Chem. 12, 305 (1990)], but it is strikingly different from the deactivation of triplet state pyrazine [T. J. Bevilacqua and R. B. Weisman, J. Chem. Phys. 98, 6316 (1993)].

  17. 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.

  18. 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.

  19. Complexity Reduction of Collisional-Radiative Kinetics for Atomic Plasma

    DTIC Science & Technology

    2013-12-23

    or disclose the work. 14. ABSTRACT Thermal non- equilibrium processes in partially ionized plasmas can be most accurately modeled by collisional...prohibitively large, making multidimensional and unsteady simulations of non- equilibrium radiating plasma particularly challenging. In this paper, we...published online 23 December 2013) Thermal non- equilibrium processes in partially ionized plasmas can be most accurately modeled by collisional

  20. 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

  1. 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.

  2. Collisional Effects in Simulations of High Altitude Nuclear Explosions

    NASA Astrophysics Data System (ADS)

    Islam, Tanim

    2013-10-01

    The simulation of the later-time (> 1 second) debris dynamics of a high altitude nuclear explosion (HANE) require, at a minimum, an understanding of the interaction of the ionized blast material with the relatively collisional upper ionosphere and lower exosphere (<= 200 km). At these altitudes, the collisional mean free path of ionized atmospheric particles may become smaller than the length scale of the diamagnetic bubble. Here we report on the local dynamics about the debris/air interface for Starfish Prime like, and lower energy, HANEs at altitudes in which collisionality becomes important. We model the debris dynamics with the hybrid plasma simulation code KIM3D, and use a standard Miller-Combi particle pairing algorithm to model particle collisions. We demonstrate new dynamics associated with finite collisionality in mildly collisional HANEs.

  3. 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

  4. 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.

  5. Energy balance of the collisional tearing mode

    SciTech Connect

    Bondeson, A.; Sobel, J.R.

    1984-08-01

    The energy balance of the collisional tearing mode is examined within linear theory. It is found that in an asymmetric case the quadratic form given by Furth for the net release of magnetic energy must be completed with a term connected with the current gradient in the resistive layer. The growth-rate and the inner-layer solution are calculated in the limit where viscosity dominates over inertia. The amounts of energy going into Joule heating and either kinetic energy or viscous dissipation are calculated analytically. In the inertial regime 1/4 of the net decrease in magnetic energy goes into kinetic energy and (3)/(4) into Joule heating, while, in viscous regime, (1)/(6) goes into viscous dissipation and (5)/(6) into Joule heating. The analytical results, based on the constant-psi approximation, are in good agreement with numerical simulations when the resistive layer is sufficiently narrow.

  6. Size-dependent subnanometer Pd cluster (Pd4, Pd6, and Pd17) water oxidation electrocatalysis.

    PubMed

    Kwon, Gihan; Ferguson, Glen A; Heard, Christopher J; Tyo, Eric C; Yin, Chunrong; DeBartolo, Janae; Seifert, Sönke; Winans, Randall E; Kropf, A Jeremy; Greeley, Jeffrey; Johnston, Roy L; Curtiss, Larry A; Pellin, Michael J; Vajda, Stefan

    2013-07-23

    Water oxidation is a key catalytic step for electrical fuel generation. Recently, significant progress has been made in synthesizing electrocatalytic materials with reduced overpotentials and increased turnover rates, both key parameters enabling commercial use in electrolysis or solar to fuels applications. The complexity of both the catalytic materials and the water oxidation reaction makes understanding the catalytic site critical to improving the process. Here we study water oxidation in alkaline conditions using size-selected clusters of Pd to probe the relationship between cluster size and the water oxidation reaction. We find that Pd4 shows no reaction, while Pd6 and Pd17 deposited clusters are among the most active (in terms of turnover rate per Pd atom) catalysts known. Theoretical calculations suggest that this striking difference may be a demonstration that bridging Pd-Pd sites (which are only present in three-dimensional clusters) are active for the oxygen evolution reaction in Pd6O6. The ability to experimentally synthesize size-specific clusters allows direct comparison to this theory. The support electrode for these investigations is ultrananocrystalline diamond (UNCD). This material is thin enough to be electrically conducting and is chemically/electrochemically very stable. Even under the harsh experimental conditions (basic, high potential) typically employed for water oxidation catalysts, UNCD demonstrates a very wide potential electrochemical working window and shows only minor evidence of reaction. The system (soft-landed Pd4, Pd6, or Pd17 clusters on a UNCD Si-coated electrode) shows stable electrochemical potentials over several cycles, and synchrotron studies of the electrodes show no evidence for evolution or dissolution of either the electrode material or the clusters.

  7. SOLAR WIND COLLISIONAL AGE FROM A GLOBAL MAGNETOHYDRODYNAMICS SIMULATION

    SciTech Connect

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

    2016-04-10

    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.

  8. The aerobic oxidation of a Pd(II) dimethyl complex leads to selective ethane elimination from a Pd(III) intermediate.

    PubMed

    Khusnutdinova, Julia R; Rath, Nigam P; Mirica, Liviu M

    2012-02-01

    Oxidation of the Pd(II) complex (N4)Pd(II)Me(2) (N4 = N,N'-di-tert-butyl-2,11-diaza[3.3](2,6)pyridinophane) with O(2) or ROOH (R = H, tert-butyl, cumyl) produces the Pd(III) species [(N4)Pd(III)Me(2)](+), followed by selective formation of ethane and the monomethyl complex (N4)Pd(II)Me(OH). Cyclic voltammetry studies and use of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap suggest an inner-sphere mechanism for (N4)Pd(II)Me(2) oxidation by O(2) to generate a Pd(III)-superoxide intermediate. In addition, reaction of (N4)Pd(II)Me(2) with cumene hydroperoxide involves a heterolytic O-O bond cleavage, implying a two-electron oxidation of the Pd(II) precursor and formation of a transient Pd(IV) intermediate. Mechanistic studies of the C-C bond formation steps and crossover experiments are consistent with a nonradical mechanism that involves methyl group transfer and transient formation of a Pd(IV) species. Moreover, the (N4)Pd(II)Me(OH) complex formed upon ethane elimination reacts with weakly acidic C-H bonds of acetone and terminal alkynes, leading to formation of a new Pd(II)-C bond. Overall, this study represents the first example of C-C bond formation upon aerobic oxidation of a Pd(II) dimethyl complex, with implications in the development of Pd catalysts for aerobic oxidative coupling of C-H bonds.

  9. 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.

  10. 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

  11. 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

  12. 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

  13. The PD-1/PD-Ls pathway and autoimmune diseases.

    PubMed

    Dai, Suya; Jia, Ru; Zhang, Xiao; Fang, Qiwen; Huang, Lijuan

    2014-07-01

    The programmed death (PD)-1/PD-1 ligands (PD-Ls) pathway, is a new member of the B7/CD28 family, and consists of the PD-1 receptor and its ligands PD-L1 (B7-H1, CD274) and PD-L2 (B7-DC, CD273). Recently, it is reported that PD-1, PD-L1 and PD-L2 also have soluble forms aside from their membrane bound forms. The soluble forms increase the diversity and complexity of PD-1/PD-Ls pathway in both composition and function. The PD-1/PD-Ls pathway is broadly expressed and exerts a wider range of immunoregulatory roles in T-cell activation and tolerance compared with other B7/CD28 family members. Studies show that the PD-1/PD-Ls pathway regulates the induction and maintenance of peripheral tolerance and protects tissues from autoimmune attack in physiological conditions. In addition, it is also involved in various diseases mediated by T cells, such as autoimmunity, tumor immunity, chronic viral infections, and transplantation immunity. In this review, we will summarize the relevance of the soluble forms and the latest researches on the role of PD-1/PD-Ls pathway in autoimmune diseases.

  14. Deterministic single-file dynamics in collisional representation.

    PubMed

    Marchesoni, F; Taloni, A

    2007-12-01

    We re-examine numerically the diffusion of a deterministic, or ballistic single file with preassigned velocity distribution (Jepsen's gas) from a collisional viewpoint. For a two-modal velocity distribution, where half the particles have velocity +/-c, the collisional statistics is analytically proven to reproduce the continuous time representation. For a three-modal velocity distribution with equal fractions, where less than 12 of the particles have velocity +/-c, with the remaining particles at rest, the collisional process is shown to be inhomogeneous; its stationary properties are discussed here by combining exact and phenomenological arguments. Collisional memory effects are then related to the negative power-law tails in the velocity autocorrelation functions, predicted earlier in the continuous time formalism. Numerical and analytical results for Gaussian and four-modal Jepsen's gases are also reported for the sake of a comparison.

  15. The Collisional Ring Galaxy NGC 922

    NASA Astrophysics Data System (ADS)

    Pellerin, A.; Meurer, G. R.; Bekki, K.; Elmegreen, D. M.; Wong, O. I.; Knezek, P. M.

    2010-06-01

    We present a detailed study of the star cluster population detected in the galaxy NGC 922, one of the closest collisional ring galaxies, using HST/WFPC2 UBVI photometry, population synthesis models, and N-body/SPH simulations. We find that most clusters are younger than 7 Myr, and that most of them are located in the ring or along the bar, consistent with the strong Hα emission. The observed age distribution displays a slope not consistent with the simulated star formation history of NGC 922. However our simulations match the cluster age distribution best when cluster disruption is considered. We also find clusters with ages (>50 Myr) and masses (>105 Msun) that are excellent progenitors for faint fuzzy clusters. The images also show a tidal plume pointing toward the companion. Its stellar age suggests that it consists of stars significantly older than the epoch of collision and that they were stripped off during the passage of the companion. Finally, a comparison of the star-forming complexes observed in NGC 922 with those of a distant ring galaxy from the GOODS field indicates very similar masses and sizes, suggesting similar origins.

  16. 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.

  17. 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.

  18. Weak turbulence theory for collisional plasmas.

    PubMed

    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. 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.

  20. 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.

  1. A study of the collisional fragmentation problem using the Gamma distribution approximation.

    PubMed

    Kostoglou, M; Karabelas, A J

    2006-11-15

    The nonlinear fragmentation population balance formulation has been elevated in recent years from a prototype for studying nonlinear integro-differential equations to a vehicle for analyzing and understanding several physicochemical processes of technological interest. The so-called pure collisional fragmentation, which is the particular mode of nonlinear fragmentation induced by collisions between particles, is studied here. It is shown that the corresponding population balance equation admits large time asymptotic (self-similarity) solutions for homogeneous fragmentation and collision functions (kernels). The self-similar solutions are given in closed form for some simple kernels. Based on the shape of the self-similar solutions the method of moments with Gamma distribution approximation is employed for transient solution (from initial state to establishment of the asymptotic shape) of the collisional fragmentation equation. These solutions are presented for several sets of parameters and their behavior is discussed rather extensively. The present study is similar to the one has already been performed for the case of the much simpler linear fragmentation equation [G. Madras, B.J. McCoy, AIChE J. 44 (1998) 647].

  2. Diagnosing transient ionization in dynamic events

    NASA Astrophysics Data System (ADS)

    Doyle, J. G.; Giunta, A.; Madjarska, M. S.; Summers, H.; O'Mullane, M.; Singh, A.

    2013-09-01

    Aims: The present study aims to provide a diagnostic line ratio that will enable the observer to determine whether a plasma is in a state of transient ionization. Methods: We use the Atomic Data and Analysis Structure (ADAS) to calculate line contribution functions for two lines, Si iv 1394 Å and O iv 1401 Å, formed in the solar transition region. The generalized collisional-radiative theory is used. It includes all radiative and electron collisional processes, except for photon-induced processes. State-resolved direct ionization and recombination to and from the next ionization stage are also taken into account. Results: For dynamic bursts with a decay time of a few seconds, the Si iv 1394 Å line can be enhanced by a factor of 2-4 in the first fraction of a second with the peak in the line contribution function occurring initially at a higher electron temperature due to transient ionization compared to ionization equilibrium conditions. On the other hand, the O iv 1401 Å does not show such any enhancement. Thus the ratio of these two lines, which can be observed with the Interface Region Imaging Spectrograph, can be used as a diagnostic of transient ionization. Conclusions: We show that simultaneous high-cadence observations of two lines formed in the solar transition region may be used as a direct diagnostic of whether the observed plasma is in transient ionization. The ratio of these two lines can change by a factor of four in a few seconds owing to transient ionization alone.

  3. Overview of TRAC-PD2 assessment calculations

    SciTech Connect

    Waterman, M E

    1985-11-01

    A summary of Transient Reactor Analysis Code Version PD2 (TRAC-PD2) calculations performed at the Idaho National Engineering Laboratory (INEL) is presented in this report as part of the US Nuclear Regulatory Commission's (NRCs) overall assessment program of TRAC-PD2. The calculated and measured parameters summarized in this report are break mass flow rate, primary coolant system pressure, reactor core flow rates, and fuel rod cladding temperatures. The data were obtained from seven tests that were performed at two test facilities. The tests were conducted to study the various aspects of cold leg break transients, including the effects of large and small beaks, and core reflood phenomena. User experience gained from the various calculations is also summarized. 42 figs., 10 tabs.

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

    PubMed

    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.

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

    PubMed

    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 pronated 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.

  6. 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.

  7. 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.

  8. A mantle conveyor belt beneath the Tethyan collisional belt

    NASA Astrophysics Data System (ADS)

    Becker, T. W.; Faccenna, C.

    2011-12-01

    Collisional belts are generated by the arrival of continental lithosphere into a subduction zone, leading to stacking of crustal slices during indentation. The Tethyan suture from the Bitlis to the Himalayas is a prime example where the Arabian and Indian plates collided with Eurasia during the Cenozoic, generating the highest mountain belts on Earth (Argand, 1924). While the kinematics of this process are well established, its dynamics are more uncertain. India and Arabia intriguingly keep advancing in spite of large collisional resisting forces. We perform global mantle circulation computations to test the role of deep mantle flow as a driving force for the kinematics of the Tethyan collisional belt, evaluating different boundary conditions and mantle density distributions as inferred from seismic tomography or slab models. Our results show that mantle drag exerted on the base of the lithosphere by a large-scale upwelling is likely the main cause for the ongoing indentation of the Indian and Arabian plates into Eurasia.

  9. 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.

  10. Collisional redistribution effects on x-ray laser saturation behavior

    SciTech Connect

    Koch, J.A.; MacGowan, B.J.; Da Silva, L.B.; Matthews, D.J.; Lee, R.W.; London, R.A.; Mrowka, S.; Underwood, J.H.; Batson, P.J.

    1994-06-01

    We recently published a detailed summary of our experimental and theoretical research on Ne-like Se x-ray laser line widths, and one of our conclusions was that collisional redistribution rates are likely to have an effect on the saturation behavior of the 206.4 {angstrom} Se x-ray laser. In this paper we focus on the effects of collisional redistribution on x-ray laser gain coefficients, and discuss ways of including these effects in existing laser line- transfer models.

  11. PD-1 Blockers.

    PubMed

    Wolchok, Jedd D

    2015-08-27

    Nivolumab and pembrolizumab are monoclonal antibodies that block the programmed death-1 receptor (PD-1, CD279), resulting in dis-inhibition of tumor-specific immune responses. Both are recently approved for use in the treatment of metastatic melanoma, and nivolumab as well for non-small cell lung cancer.

  12. Collisional Relaxation of Vibrational Energy Transients in the Methylcyclopropane System. A Variable Encounter Method Study.

    DTIC Science & Technology

    1980-08-01

    L. H. Caveny Defense Technical Information 12 Anal-Syn Lab Inc. Center P.O. Box 547 OTIC-ODA-2 Paoli, PA 19301 Cameron Station Attn: Dr. V. J. Keenan ...Center Attn: Mr. L. Roslund Code 5042 Crane , Indiana 47522 Naval Surface Weapons Center 1 Attn: Dr. B. Douda Code R121 White Oak, Silver Spring, MD Rohm

  13. 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.

  14. Laser-induced collisional autoionization in europium and strontium atoms.

    PubMed

    Buffa, R

    1995-01-15

    An experiment that involves laser-induced collisional autoionization in europium and strontium atoms is proposed and the spectral line shape of the cross section is calculated on the basis of data available in the literature. The feasibility of the experiment both in oven cells and in a crossed-atomic-beam geometry is discussed.

  15. Does the Bohm Criterion have meaning for collisional plasmas?

    NASA Astrophysics Data System (ADS)

    Severn, Greg; Yip, Chi-Shung; Nourgostar, Sirous; Hershkowitz, Noah

    2014-10-01

    Theorists view the Bohm criterion as approximately true, holding only for collisionless plasmas. The question of whether there exists a collisionally modified Bohm Criterion (CMBC) is often answered in the negative, and it is only a question of how the Bohm Criterion fails for the case of finite collisionality. The question is of importance considering that nearly all practical plasma processing applications involve plasmas of finite collisionality. There is, however, very little experimental work to help choose between competing models of how Bohm's Criterion fails. The question of critical importance is this: in plasmas of finite collisionality, do ions reach the Bohm speed at the location where the quasineutral plasma ends and where space charge appears? We have begun to examine the question experimentally in single ion species plasmas, and our goal is to vary the ion-neutral mean free path λ within the interval 1 < λ /λD <103 , where λD is the Debye length, and to present both plasma potential data and ion velocity distribution function profiles, measured by emissive probes and by LIF, respectively, to help us understand and assess the validity of theoretical claims. Work supported by NSF Grant No. PHY-1206421, CBET-0903783, and CBET-0903832, and U.S. Department of Energy (DOE) Grant Nos. DE-FG02- 97ER54437 and DE FG02- 03ER54728.

  16. Formation and Collisional Evolution of Kuiper Belt Objects

    NASA Astrophysics Data System (ADS)

    Kenyon, S. J.; Bromley, B. C.; O'Brien, D. P.; Davis, D. R.

    This chapter summarizes analytic theory and numerical calculations for the formation and collisional evolution of Kuiper belt objects (KBOs) at 20-150 AU. We describe the main predictions of a baseline self-stirring model and show how dynamical perturbations from a stellar flyby or stirring by a giant planet modify the evolution. Although robust comparisons between observations and theory require better KBO statistics and more comprehensive calculations, the data are broadly consistent with KBO formation in a massive disk followed by substantial collisional grinding and dynamical ejection. However, there are important problems reconciling the results of coagulation and dynamical calculations. Contrasting our current understanding of the evolution of KBOs and asteroids suggests that additional observational constraints, such as the identification of more dynamical families of KBOs (like the 2003 EL61 family), would provide additional information on the relative roles of collisional grinding and dynamical ejection in the Kuiper belt. The uncertainties also motivate calculations that combine collisional and dynamical evolution, a "unified" calculation that should give us a better picture of KBO formation and evolution.

  17. Collisional and dynamic evolution of dust from the asteroid belt

    NASA Astrophysics Data System (ADS)

    Gustafson, Bo A. S.; Gruen, Eberhard; Dermott, Stanley F.; Durda, Daniel D.

    1992-12-01

    The size and spatial distribution of collisional debris from main belt asteroids is modeled over a 10 million year period. The model dust and meteoroid particles spiral toward the Sun under the action of Poynting-Robertson drag and grind down as they collide with a static background of field particles.

  18. Collisional and dynamic evolution of dust from the asteroid belt

    NASA Technical Reports Server (NTRS)

    Gustafson, Bo A. S.; Gruen, Eberhard; Dermott, Stanley F.; Durda, Daniel D.

    1992-01-01

    The size and spatial distribution of collisional debris from main belt asteroids is modeled over a 10 million year period. The model dust and meteoroid particles spiral toward the Sun under the action of Poynting-Robertson drag and grind down as they collide with a static background of field particles.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. Fabrication of vertically aligned Pd nanowire array in AAO template by electrodeposition using neutral electrolyte

    PubMed Central

    2010-01-01

    A vertically aligned Pd nanowire array was successfully fabricated on an Au/Ti substrate using an anodic aluminum oxide (AAO) template by a direct voltage electrodeposition method at room temperature using diluted neutral electrolyte. The fabrication of Pd nanowires was controlled by analyzing the current–time transient during electrodeposition using potentiostat. The AAO template and the Pd nanowires were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) methods and X-Ray diffraction (XRD). It was observed that the Pd nanowire array was standing freely on an Au-coated Ti substrate after removing the AAO template in a relatively large area of about 5 cm2, approximately 50 nm in diameter and 2.5 μm in length with a high aspect ratio. The nucleation rate and the number of atoms in the critical nucleus were determined from the analysis of current transients. Pd nuclei density was calculated as 3.55 × 108 cm−2. Usage of diluted neutral electrolyte enables slower growing of Pd nanowires owing to increase in the electrodeposition potential and thus obtained Pd nanowires have higher crystallinity with lower dislocations. In fact, this high crystallinity of Pd nanowires provides them positive effect for sensor performances especially. PMID:20596417

  4. Turbulence-driven bootstrap current in low-collisionality tokamaks.

    PubMed

    McDevitt, C J; Tang, Xian-Zhu; Guo, Zehua

    2013-11-15

    Neoclassical bootstrap current is expected to provide a significant fraction of the equilibrium plasma current in tokamak reactors. 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 and thus driving a bootstrap current. Employing a linearized Fokker-Planck collision operator, the plasma current in the presence of both collisions and resonant electron scattering is computed, allowing for the relative strength of these two mechanisms to be quantified as a function of collisionality and fluctuation amplitude.

  5. Optimal electric potential profile in a collisional magnetized thruster

    NASA Astrophysics Data System (ADS)

    Fruchtman, Amnon; Makrinich, Gennady

    2016-10-01

    A major figure of merit in propulsion in general and in electric propulsion in particular is the thrust per unit of deposited power, the ratio of thrust over power. We have recently demonstrated experimentally and theoretically that for a fixed deposited power in the ions, the momentum delivered by the electric force is larger if the accelerated ions collide with neutrals during the acceleration. As expected, the higher thrust for given power is achieved for a collisional plasma at the expense of a lower thrust per unit mass flow rate. Operation in the collisional regime can be advantageous for certain space missions. We analyze a Hall thruster configuration in which the flow is only weakly ionized but there are frequent ion-neutral collisions. With a variational method we seek an electric potential profile that maximizes thrust over power. We then examine what radial magnetic field profile should determine such a potential profile. Supported by the Israel Science Foundation Grant 765/11.

  6. 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.

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

    SciTech Connect

    Cheng Yongshan; Adhikari, S. K.

    2011-02-15

    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 et al., Nature (London) 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.

  8. ADAS tools for collisional-radiative modelling of molecules

    NASA Astrophysics Data System (ADS)

    Guzmán, F.; O'Mullane, M.; Summers, H. P.

    2013-07-01

    New theoretical and computational tools for molecular collisional-radiative models are presented. An application to the hydrogen molecule system has been made. At the same time, a structured database has been created where fundamental cross sections and rates for individual processes as well as derived data (effective coefficients) are stored. Relative populations for the vibrational states of the ground electronic state of H2 are presented and this vibronic resolution model is compared electronic resolution where vibronic transitions are summed over vibrational sub-states. Some new reaction rates are calculated by means of the impact parameter approximation. Computational tools have been developed to automate process and simplify the data assembly. Effective (collisional-radiative) rate coefficients versus temperature and density are presented.

  9. Collisional cooling of large ions in electrospray mass spectrometry.

    PubMed

    Chernushevich, Igor V; Thomson, Bruce A

    2004-03-15

    Collisional cooling of ions in the rf-only multipole guides has become a method of choice for coupling electrospray sources to various mass analyzers. Normally parameters of such ion guides (length, pressure) provide enough thermalization and focusing for ions in a wide mass range. Noncovalent complexes, however, have more compact conformations than denatured biomolecules of similar mass and, therefore may not be transmitted efficiently through standard ion guides, as demonstrated by theoretical analysis, simulations, and experiments. Several methods of improving collisional cooling for large compact ions have been developed on a quadrupole time-of-flight instrument, which include operating the ion guides at higher pressure and trapping ions to increase the cooling time. Improved transmission of heavy ions obtained with those methods is studied in experiments with proteasome 20S, an oligomeric protein noncovalent complex with molecular weight around 692,000, and a few other compounds.

  10. 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.

  11. 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.

  12. Uniform derivation of Coulomb collisional transport thanks to Debye shielding

    NASA Astrophysics Data System (ADS)

    Escande, Dominique; Elskens, Yves; Doveil, Fabrice

    2016-10-01

    The effective potential acting on particles in plasmas being essentially the Debye-shielded Coulomb potential, the particles collisional transport in thermal equilibrium is calculated for all impact parameters b, with a convergent expression reducing to Rutherford scattering for small b, in agreement with both usual expressions holding for large b and small b. No cutoff at the Debye length scale is needed, and the Coulomb logarithm is only slightly modified.

  13. 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

  14. Collisional and dissociative processes involving molecular free radicals

    NASA Astrophysics Data System (ADS)

    Dagdigian, Paul J.; Alexander, Millard H.

    1995-04-01

    A collaborative experimental and theoretical study of a number of elementary collisional processes involving small molecular free radicals of importance in combustion and in the decomposition of propellants has been carried out. These have involved chemical reactions and photodissociation, as well as nonreactive collision-induced rotational and electronic transitions. Information on non-bonding interactions involving free radicals was also obtained from analysis of the electronic spectrum of van der Waals complexes of these species.

  15. 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.

  16. 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.

  17. 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.

  18. Intersystem collisional transfer of excitation in low altitude aurora

    NASA Astrophysics Data System (ADS)

    Benesch, W.

    1983-03-01

    The characteristics of auroral optical emission as a function of altitude are exploited as a source of data for the investigation of the intersystem collisional transfer (ICT) of excitation in the nitrogen molecule. The procedure is based on a recently proposed model for the generation of the red lower border of type B auroras as resulting from the effect of the increased collision frequency at lower altitudes on the distribution of population within the excited molecules. In particular, the 85 km turn-on altitude for the red lower border of auroral arcs provides an indicator for the determination of the density and pressure required for the onset of the ICT process at mesopause temperatures. Values are obtained for collision cross sections and rate constants for the coupling of neighboring vibrational levels in adjacent electronic states in nitrogen. The results are compared with the findings of several laboratory studies on similar collisional transfers among nested electronic states. A two-part process is suggested to account for the observed features of intersystem collisional transfer phenomena.

  19. Ion loss in weakly collisional three ion species plasmas

    NASA Astrophysics Data System (ADS)

    Hershkowitz, Noah; Yip, Chi-Shung; Severn, Greg

    2016-10-01

    Ion velocity distribution functions (ivdfs) at sheath-presheath boundaries are studied with laser-induced fluorescence in weakly collisional Xe-Kr-Ar and Xe-Ar-Ne plasmas using tunable diode lasers for Ar + and Xe + ions. The argon and xenon ivdfs are measured at the sheath-presheath boundary near a negatively biased boundary plate. The plasma potential profiles are measured by an emissive probe throughout the sheath and presheath. Relative ion concentrations resulting from the neutral gas mixtures are calculated using G-H. Kim's loss-production balance method. Ne + and Kr + ions are added to plasmas with approximately equal amounts of Ar + and Xr + ions, where Ar + and Xe + ions are previously observed to reach the sheath edge at nearly the system sound speed. In two ion species plasmas, instability enhanced collisional friction was demonstrated to dictate the escape velocities of the ions. When three ion species are present, it is demonstrated that as the concentration of the third ion species increases, Xe + and Ar + ion velocities at the sheath edge deviates from the common sound speed and approach their individual Bohm velocities. These observations are consistent with the predictions of the instability enhanced collisional friction theory This work was supported by NSF under Grant No. 1464741 and U.S. DOE under Grant No. DE-SC00114226.

  20. New insights into main belt asteroid collisional lifetimes

    NASA Astrophysics Data System (ADS)

    Henych, Tomas; Holsapple, Keith

    2016-10-01

    We are developing a new Monte Carlo code to study the collisional and spin evolution of main belt asteroids. A byproduct is information on asteroid lifetimes. We find new interpretations and values of those lifetimes.In the conventional approach, the "collisional lifetime" is measured by the time when an asteroid is struck by an impactor large enough to remove one-half of the target's mass. That event is called a catastrophic disruption (CD). From an assumed population of impactors and Poisson statistics, one can estimate the largest expected impactor to impact in a given time interval to get its expected collisional lifetime. However, our Monte Carlo simulations give lifetimes that are distinctly shorter. That raises questions about the basic definition of catastrophic disruption.During its presence in the main belt, many other asteroids of all sizes continually strike a target asteroid. Before the CD one happens, there are many small impacts, and a few less than but not equal to the CD one. Each impact erodes the target asteroid. Very commonly, it is eroded to a much smaller mass before some CD event. We will present examples.So what shall we define as its collisional lifetime? Should it be the time for which its mass is reduced to one-half of its original mass, irrespective of how that happened, perhaps from many impacts? Or when any single impact reduces its mass to one-half of its original mass? Or when a single impact reduces it to one-half of its current mass?We propose that collisional lifetime is defined as the time at which it reaches 50% of its original mass, from any combination of small and/or large events. We use cratering and ejecta scaling formulas (e.g. Holsapple, 1993, Housen and Holsapple, 2011) to calculate the eroded mass history of the target for a history of impactors and calculate the outcome of any impact using the current size. In the gravity regime, the eroded body is easier to disrupt. We will present our lifetime estimates and those of

  1. 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

  2. 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.

  3. PD-1/PD-L and autoimmunity: A growing relationship.

    PubMed

    Zamani, Mohammad Reza; Aslani, Saeed; Salmaninejad, Arash; Javan, Mohammad Reza; Rezaei, Nima

    2016-12-01

    Programmed death 1 (PD-1) and its ligands, namely PD-L1 and PD-L2, are one of the key factors responsible for inhibitory T cell signaling, mediating the mechanisms of tolerance and providing immune homeostasis. Mounting evidence demonstrates that impaired PD-1:PD-L function plays an important role in a variety of autoimmune diseases such as Type 1 diabetes (T1D), encephalomyelitis, inflammatory bowel diseases (IBD), Rheumatoid Arthritis (RA), autoimmune hepatitis (AIH), Behcet's disease (BD), myasthenia gravis (MG), autoimmune uveitis (AU), Sjögren's syndrome (SjS), systemic lupus erythematosus (SLE), systemic sclerosis (SSc), myocarditis, and ankylosing spondylitis (AS). By investigating the candidate genes, genome-wide association studies, and identification of single nucleotide polymorphisms (SNPs) in PD-1 gene in humans, it has been shown that there is a higher risk in relevant genetic associations with developing autoimmune diseases in certain ethnic groups. In this review we have tried to present a comprehensive role of PD-1:PD-L in all recently studied autoimmune diseases.

  4. PD-1 and PD-L1 antibodies for melanoma

    PubMed Central

    Tsai, Katy K; Zarzoso, Inés; Daud, Adil I

    2015-01-01

    Melanoma is the most serious form of skin cancer. Metastatic melanoma historically carries a poor prognosis and until recently there have been few effective agents available to treat widely disseminated disease. Recognition of the immunogenic nature of melanoma has resulted in the development of various immunotherapeutic approaches, especially with regards to the programmed cell death 1 (PD-1) receptor and its ligand (PD-L1). Antibodies targeting the PD-1 axis have shown enormous potential in the treatment of metastatic melanoma. Here, we will review the immune basis for the disease and discuss approved immunotherapeutic options for advanced melanoma, as well as the current state of development of PD-1 and PD-L1 antibodies and their importance in shaping the future of melanoma treatment. PMID:25625924

  5. Detection Prospects for GeV Neutrinos from Collisionally Heated Gamma-ray Bursts with IceCube/DeepCore

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

    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.

  6. 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.

  7. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

    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 Processing of Olivine and Pyroxene in Cometary Dust

    NASA Technical Reports Server (NTRS)

    Lederer, S. M.; Cintala, M. J.; Olney, R. D.; Keller, L. P.; Nakamura-Messenger, K.; Zolensky, M.

    2008-01-01

    According to the nebular theory of solar-system formation, collisions between bodies occurred frequently early in the solar system s history and continue at a lower rate even today. Collisions have reworked the surface compositions and structures of cometary nuclei, though to an unknown degree. The majority of the collisional history of a typical Jupiter-family comet takes place while it resides in the Kuiper Belt. Impacts occur on the surfaces of small bodies over a large range of velocities by impactors of all sizes, but typical encounter speeds within the Kuiper Belt are 1.5 to 2.0 km/s[1]. Durda and Stern suggest that the interiors of most cometary nuclei with diameters <5 km have been heavily damaged by collisions [2]. They estimate that over a period of 3.5 Gy, a nucleus with a diameter of 2 km and an orbit between 35-45 AU will experience 90-300 collisions with objects greater than 8 m in diameter. In this same time interval, collisions between a typical Trans-Neptunian Object (TNO) 200 km in diameter and objects with d > 8 m would rework up to one-third of that TNO s surface. In fact, it has been proposed that most short-period comets from the Kuiper Belt (90%) are collisional fragments from larger TNOs - not primordial objects themselves [3] - and that most short-period comets from the Kuiper Belt will be collisionally processed both on their surfaces as well as in their interiors.

  10. 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.

  11. 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.

  12. 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.

  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. 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.

  15. Collisional Excitation of Automotive Fuel Components (ethanol and Isooctane)

    NASA Astrophysics Data System (ADS)

    Cobb, Rachelle H.; White, Allen R.; Devasher, Rebecca B.

    2009-06-01

    It is possible to excite fuel components indirectly via a 10.6 um CO2 laser. A 9% solution of isopropanol in ethanol was used, as it has a strong absorption cross section at 10.6 um. CO2 laser excitation of pure ethanol caused little or no change in absorption in the C-H stretch region. However, the ethanol/isopropanol mixture did show a response proportional to laser excitation. Further studies indicate that excitation of isooctane/isopropanol mixture is also possible via collisional energy transfer between the laser excited isopropanol and isooctane.

  16. Magnetosonic wave in pair-ion electron collisional plasmas

    NASA Astrophysics Data System (ADS)

    Hussain, S.; Hasnain, H.

    2017-03-01

    Low frequency magnetosonic waves in positive and negative ions of equal mass and opposite charges in the presence of electrons in collisional plasmas are studied. The collisions of ions and electrons with neutrals are taken into account. The nonlinearities in the plasma system arise due to ion and electrons flux, Lorentz forces, and plasma current densities. The reductive perturbation method is applied to derive the Damped Korteweg de Vries (DKdV) equation. The time dependent solution of DKdV is presented. The effects of variations of different plasma parameters on propagation characteristics of magnetosonic waves in pair-ion electron plasma in the context of laboratory plasmas are discussed.

  17. 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.

  18. 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.

  19. 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 ...

  20. 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.

  1. Modeling collisional processes in plasmas using discontinuous numerical methods

    NASA Astrophysics Data System (ADS)

    Miller, Sean

    Fluid-based plasma models are typically applied to parameter regimes where a local thermal equilibrium is assumed. The applicability of this regime is valid for many plasmas, however, it is limited to plasma dynamics dominated by collisional effects. This study attempts to extend 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 heat flux hyperbolically alongside the density, momentum, and energy in order to capture dynamics usually restricted to costly kinetic models. Each particle species is modeled individually and collectively coupled through electromagnetic and collision operators. To remove electromagnetic divergence errors inherent to numerical representations of Maxwell's equations, both hyperbolic and parabolic cleaning methods are presented. The plasma models are implemented using high-order finite volume and discontinuous Galerkin numerical methods designed for unstructured meshes. The unstructured code framework, numerical methods, and plasma models were developed in the University of Washington's WARPXM code for use on heterogeneous accelerated clusters.

  2. Shear Alfven waves with Landau and collisional effects

    SciTech Connect

    Hedrick, C.L.; Leboeuf, J.; Spong, D.A.

    1995-06-01

    Shear Alfven waves can be driven unstable by hot particles such as alpha particles in an ignited fusion device or hot ions in existing devices. Motivated by rather collisional Wendelstein 7 Advanced Stellarator (W7-AS) [Phys. Rev. Lett. {bold 72}, 1220 (1994)] beam-driven global Alfven instability experiments, the effect of electron and ion collisions on these modes has been examined. Collisions broaden and suppress the peak associated with Landau effects. This broadening makes ion damping more important, while the electron damping is suppressed. Additional resistive effects provide increased damping for the main part of the spectrum, which can have a rather high phase velocity. Of more general interest is the fact that collisional and collisionless resistivity has a numerically stabilizing effect that is known to be important for nonlinear resistive magnetohydrodynamics (MHD). This can preclude the need for introducing and testing the sensitivity to similar ad hoc effects. Numerical and analytic results for both a particle-conserving Krook collision operator and a Lorentz (pitch angle) collision operator are compared and contrasted.

  3. 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.

  4. 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.

  5. GAMMA-RAY BURSTS FROM MAGNETIZED COLLISIONALLY HEATED JETS

    SciTech Connect

    Vurm, Indrek; Beloborodov, Andrei M.; Poutanen, Juri E-mail: juri.poutanen@oulu.fi

    2011-09-01

    Jets producing gamma-ray bursts (GRBs) are likely to carry a neutron component that drifts with respect to the proton component. The neutron-proton collisions strongly heat the jet and generate electron-positron pairs. We investigate radiation produced by this heating using a new numerical code. Our results confirm the recent claim that collisional heating generates the observed Band-type spectrum of GRBs. We extend the model to study the effects of magnetic fields on the emitted spectrum. We find that the spectrum peak remains near 1 MeV for the entire range of the magnetization parameter 0 < {epsilon}{sub B} < 2 that is explored in our simulations. The low-energy part of the spectrum softens with increasing {epsilon}{sub B}, and a visible soft excess appears in the keV band. The high-energy part of the spectrum extends well above the GeV range and can contribute to the prompt emission observed by Fermi/LAT. Overall, the radiation spectrum created by the collisional mechanism appears to agree with observations, with no fine tuning of parameters.

  6. 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.

  7. Fast Collisional Lipid Transfer Among Polymer-Bounded Nanodiscs

    PubMed Central

    Cuevas Arenas, Rodrigo; Danielczak, Bartholomäus; Martel, Anne; Porcar, Lionel; Breyton, Cécile; Ebel, Christine; Keller, Sandro

    2017-01-01

    Some styrene/maleic acid (SMA) copolymers solubilise membrane lipids and proteins to form polymer-bounded nanodiscs termed SMA/lipid particles (SMALPs). Although SMALPs preserve a lipid-bilayer core, they appear to be more dynamic than other membrane mimics. We used time-resolved Förster resonance energy transfer and small-angle neutron scattering to determine the kinetics and the mechanisms of phospholipid transfer among SMALPs. In contrast with vesicles or protein-bounded nanodiscs, SMALPs exchange lipids not only by monomer diffusion but also by fast collisional transfer. Under typical experimental conditions, lipid exchange occurs within seconds in the case of SMALPs but takes minutes to days in the other bilayer particles. The diffusional and second-order collisional exchange rate constants for SMALPs at 30 °C are kdif = 0.287 s−1 and kcol = 222 M−1s−1, respectively. Together with the fast kinetics, the observed invariability of the rate constants with probe hydrophobicity and the moderate activation enthalpy of ~70 kJ mol−1 imply that lipids exchange through a “hydrocarbon continuum” enabled by the flexible nature of the SMA belt surrounding the lipid-bilayer core. Owing to their fast lipid-exchange kinetics, SMALPs represent highly dynamic equilibrium rather than kinetically trapped membrane mimics, which has important implications for studying protein/lipid interactions in polymer-bounded nanodiscs. PMID:28378790

  8. 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.

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

    NASA Astrophysics Data System (ADS)

    Sonnino, Giorgio; Peeters, Philippe

    2008-06-01

    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-Schlüter (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 102. 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 102 when the nonlinear contributions are duly taken into account but, there is still a factor of 102 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.

  10. 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.

  11. G6PD: The Test

    MedlinePlus

    ... initial findings. Screening tests typically involve a simple qualitative test that only tells if the person has ... this testing is used almost exclusively in the research setting. G6PD testing should not be done soon ...

  12. CO-induced Pd segregation and the effect of subsurface Pd on CO adsorption on CuPd surfaces

    NASA Astrophysics Data System (ADS)

    Padama, A. A. B.; Villaos, R. A. B.; Albia, J. R.; Diño, W. A.; Nakanishi, H.; Kasai, H.

    2017-01-01

    We report results of our study on the adsorption of CO on CuPd surfaces with bulk stoichiometric and nonstoichiometric layers using density functional theory (DFT). We found that the presence of Pd atoms in the subsurface layer promotes the adsorption of CO. We also observed CO-induced Pd segregation on the CuPd surface and we attribute this to the strong CO-Pd interaction. Lastly, we showed that the adsorption of CO promotes Pd-Pd interaction as compared to the pristine surface which promotes strong Cu-Pd interaction. These results indicate that CO adsorption on CuPd surfaces can be tuned by taking advantage of the CO-induced segregation and by considering the role of subsurface Pd atoms.

  13. Ag-Pd-Si (009)

    NASA Astrophysics Data System (ADS)

    Carow-Watamura, U.; Louzguine, D. V.; Takeuchi, A.

    This document is part of Part 1 http://dx.doi.org/10.1007/97.etType="URL"/> 'Systems from Ag-Al-Ca to Au-Pd-Si' of Subvolume B 'Physical Properties of Ternary Amorphous Alloys' of Volume 37 'Phase Diagrams and Physical Properties of Nonequilibrium Alloys' of Landolt-Börnstein - Group III 'Condensed Matter'. It contains the Chapter 'Ag-Pd-Si (009)' with the content:

  14. 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.

  15. 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.

  16. 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.

  17. G-6-PD Jalisco and G-6-PD Morelia: two new Mexican variants.

    PubMed

    Vaca, G; Ibarra, B; García Cruz, D; Medina, C; Romero, F; Cantú, J M; Beutler, E

    1985-01-01

    Two new G-6-PD variants designated G-6-PD Jalisco and G-6-PD Morelia were identified in two unrelated Mexican families. An additional G-6-PD variant was found in each family: G-6-PD Trinacria and G-6-PD A-. In both families compound heterozygotes were identified. G-6-PD Jalisco and G-6-PD Morelia belong to Classes 3 and 4, respectively. G-6-PD Morelia is the first variant from its class with a high Km for NADP and a low Ki for NADPH.

  18. Transition in Electron Physics of Magnetic Reconnection in Weakly Collisional Plasma

    NASA Astrophysics Data System (ADS)

    Le, A.; Roytershteyn, V.; Karimabadi, H.; Daughton, W. S.; Egedal, J.; Forest, C.

    2013-12-01

    Using self-consistent fully kinetic simulations with a Monte-Carlo treatment of the Coulomb collision operator, we explore the transition between collisional and kinetic regimes of magnetic reconnection in high-Lundquist-number current sheets. Recent research in collisionless reconnection has shown that electron kinetic physics plays a key role in the evolution. Large-scale electron current sheets may form, leading to secondary island formation and turbulent flux rope interactions in 3D. The new collisional simulations demonstrate how increasing collisionality modifies or eliminates these electron structures in the kinetic regimes. Additional basic questions that are addressed include how the reconnection rate and the release of magnetic energy into electrons and ions vary with collisionality. The numerical study provides insight into reconnection in dense regions of the solar corona, the solar wind, and upcoming laboratory experiments at MRX (Princeton) and MPDX (UW-Madison). The implications of these results for studies of turbulence dissipation in weakly collisional plasmas are discussed.

  19. 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.

  20. 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.

  1. Synchrotron and collisional damping effects on runaway electron distributions

    NASA Astrophysics Data System (ADS)

    Paz-Soldan, C.; Eidietis, N.; Pace, D.; Cooper, C.; Shiraki, D.; Commaux, N.; Hollmann, E.; Moyer, R.; Granetz, R.; Embreus, O.; Fulop, T.; Stahl, A.; Wilkie, G.; Aleynikov, P.; Brennan, D. P.; Liu, C.

    2016-10-01

    Validated models of runaway electron (RE) dissipation are required to confidently approve safe ITER Q = 10 operation. DIII-D experiments using quiescent REs are exploring the importance of synchrotron and collisional damping terms to RE dissipation. New time and energy-resolved measurements of RE bremsstrahlung hard X-ray (HXR) emission reveal stark differences between high and low energy REs as damping terms are varied. Previously reported anomalously high RE dissipation only applies to low energy REs. At high energy (where synchrotron effects are strongest) low synchrotron damping cases reach higher peak RE energy despite weaker particle confinement. Low-energy RE decay is observed concurrently with high-energy RE growth. RE dissipation models predict bump-on-tail distributions whose properties depend on the damping terms. Measured HXR spectra are very broad, as expected for bump-on-tail distributions. Work supported by the U.S. DOE under DE-FC02-04ER54698.

  2. Modeling Collisional Cascades in Debris Disks: The Numerical Method

    NASA Astrophysics Data System (ADS)

    Gáspár, András; Psaltis, Dimitrios; Özel, Feryal; Rieke, George H.; Cooney, Alan

    2012-04-01

    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.

  3. 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.

  4. The violent collisional history of asteroid 4 Vesta.

    PubMed

    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

    2012-05-11

    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.

  5. Equilibrium models of mass distribution and collisional lifetimes of asteroids

    NASA Technical Reports Server (NTRS)

    Williams, David R.; Wetherill, George

    1993-01-01

    An understanding of the steady state distribution expected in the present day asteroid belt is important to our understanding of the collisional evolution of the asteroids and their physical properties. We have extended earlier work to show that, in the absence of gravity, a simple power law distribution as a function of mass with constant exponent will give an equilibrium distribution of asteroids for all bodies much smaller than the largest asteroids. This result holds for realistic fragmentation mechanisms and is independent of the physical properties of the asteroids. Inclusion of the effects of gravity on disruption and fragmentation of asteroids precludes an analytic solution to this problem, and rules out a simple power law distribution. We are currently calculating numerical solutions in order to determine the expected steady state mass distribution in the asteroid belt.

  6. 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.

  7. 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.

  8. 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.

  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. 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.

  11. 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

  12. 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

  13. Turbulence Locality and Granularlike Fluid Shear Viscosity in Collisional Suspensions

    NASA Astrophysics Data System (ADS)

    Berzi, Diego; Fraccarollo, Luigi

    2015-11-01

    We reanalyze previous experimental measurements of solid volume fraction, mean velocity, and velocity fluctuations in collisional suspensions of plastic cylinders and water flowing over inclined, erodible beds. We show that the particle pressure scales with the granular temperature, as predicted by kinetic theory of granular gases. The assumption that the particle shear stress is also well predicted by kinetic theory permits us to determine the fluid shear stress and the effective fluid viscosity from the experiments. The fluid viscosity can be decomposed into turbulent and granularlike components: the turbulent viscosity can be modeled using a mixing length, which is a decreasing function of the local volume fraction and does not depend upon the distance from the bed; the granularlike viscosity, associated with the transfer of momentum due to the conjugate motion of the fluid mass added to the particles, can be modeled by replacing the particle density with the density of the added fluid mass in the viscosity of kinetic theory.

  14. Young Stellar Populations in the Collisional Ring Galaxy NGC 922

    NASA Astrophysics Data System (ADS)

    Pellerin, A.; Meurer, G. R.; Bekki, K.; Elmegreen, D. M.; Wong, O. I.; Knezek, P.

    2010-04-01

    We studied the star cluster population properties in the nearby collisional ring galaxy NGC 922 using HST/WFPC2 photometry and population synthesis modeling. We found that 69% of the detected clusters are younger than 7 Myr, and that most of them are located in the ring or along the bar, consistent with the strong Hα emission. The images also show a tidal plume pointing toward the companion. Its stellar age is consistent with pre-existing stars that were probably stripped off during the passage of the companion. We compared the star-forming complexes observed in NGC 922 with those of a distant ring galaxy from the GOODS eld. It indicates very similar masses and sizes, suggesting similar origins. Finally, we found clusters that are excellent progenitor candidates for faint fuzzy clusters.

  15. 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.

  16. Kinetic Theory of Instability-Enhanced Collisional Effects

    NASA Astrophysics Data System (ADS)

    Baalrud, Scott

    2009-10-01

    A generalization of the Lenard-Balescu collision operator is derived which accounts for the scattering of particles by instability amplified fluctuations that originate from the thermal motion of discrete particles (in contrast to evoking a fluctuation level externally, as is done in quasilinear kinetic theory) [1]. Emphasis is placed on plasmas with convective instabilities. It is shown that an instability-enhanced collective response results which can be the primary mechanism for scattering particles, being orders of magnitude more frequent than conventional Coulomb collisions, even though the fluctuations are in a linear growth phase. The resulting collision operator is shown to obey conservation laws (energy, momentum, and density), Galilean invariance, and the Boltzmann H-theorem. It has the property that Maxwellian is the unique equilibrium distribution function; again in contrast to weak turbulence or quasilinear theories. Instability-enhanced collisional effects can dominate the physics of low-temperature plasmas. For example, this theory has been applied to two outstanding problems: Langmuir's paradox [2] and determining Bohm's criterion for plasmas with multiple ion species. Langmuir's paradox is a measurement of anomalous electron scattering rapidly establishing a Maxwellian distribution in gas discharges with low temperature and pressure. This may be explained by instability-enhanced scattering in the plasma-boundary transition region (presheath) where convective ion-acoustic instabilities are excited. Bohm's criterion for multiple ion species is a single condition that the ion fluid speeds must obey at the sheath edge; but it is insufficient to determine the speed of individual species. It is shown that an instability-enhanced collisional friction, due to streaming instabilities in the presheath, determines this criterion.[4pt] [1] S.D. Baalrud, J.D. Callen, and C.C. Hegna, Phys. Plasmas 15, 092111 (2008).[0pt] [2] S.D. Baalrud, J.D. Callen, and C

  17. Collisional modelling of the debris disc around HIP 17439

    NASA Astrophysics Data System (ADS)

    Schüppler, Ch.; Löhne, T.; Krivov, A. V.; Ertel, S.; Marshall, J. P.; Eiroa, C.

    2014-07-01

    We present an analysis of the debris disc around the nearby K2 V star HIP 17439. In the context of the Herschel DUNES key programme, the disc was observed and spatially resolved in the far-IR with the Herschel PACS and SPIRE instruments. In a previous study, we assumed that the size and radial distribution of the circumstellar dust are independent power laws. There, several scenarios capable of explaining the observations were suggested after exploring a very broad range of possible model parameters. In this paper, we perform a follow-up in-depth collisional modelling of these scenarios to further distinguish between them. In our models we consider collisions, direct radiation pressure, and drag forces, which are the actual physical processes operating in debris discs. We find that all scenarios discussed in the first paper are physically reasonable and can reproduce the observed spectral energy distribution along with the PACS surface brightness profiles reasonably well. In one model, the dust is produced beyond 120 au in a narrow planetesimal belt and is transported inwards by Poynting-Robertson and stellar wind drag. Good agreement with the observed radial profiles would require stellar winds by about an order of magnitude stronger than the solar value, which is not confirmed - although not ruled out - by observations. Another model consists of two spatially separated planetesimal belts, a warm inner and a cold outer one. This scenario would probably imply the presence of planets clearing the gap between the two components. Finally, we show qualitatively that the observations can be explained by assuming the dust is produced in a single, but broad planetesimal disc with a surface density of solids rising outwards, as expected for an extended disc that experiences a natural inside-out collisional depletion. Prospects of distinguishing between the competing scenarios by future observations are discussed.

  18. Shoshonitic and ultrapotassic post-collisional dykes from northern Karakorum (Sinkiang, China)

    NASA Astrophysics Data System (ADS)

    Pognante, Ugo

    1991-01-01

    High-K calc-alkaline, shoshonitic and ultrapotassic post-collisional dykes of Neogene age have been found in the remote and little known region of northern Karakorum located around the Shaksgam valley, north of the K2-Gasherbrum range (China). The dykes derive from more or less comparable basic magma(s) and display rather unusual petrographic and geochemical characters with respect to the other K-rich rocks. The geochemical data are consistent with derivation of the basic magma(s) from small degrees of partial melting of garnet-lherzolites previously enriched in incompatible elements of crustal origin possibly during the subduction of the Indian plate beneath Karakorum. The spectrum of compositions reflects fractional crystallization governed by an early removal of clinopyroxene, phlogopite, plagioclase, garnet±amphibole followed by the precipitation of abundant alkali feldspar, amphibole±apatite±quartz. Additionally, assimilation of crustal rocks during magma ascent contributed to the unusual compositional characteristics and is suggested by the abundance of corroded quartz ( ± plagioclase) xenocrysts and by the occasional presence of granitic xenoliths. An apparent connection exists between magmatism and tectonism in the complex Karakorum Fault Zone (KFZ). It is suggested that, during the Neogene, the strike-slip KFZ and some adjacent post-metamorphic faults transiently behaved as extensional fault systems down to deep levels, triggering ascent and emplacement of the K-rich magma. The subsequent (re)activation of a compressive and transcurrent regime determined the rapid and recent uplift of the more primitive lamprophyres occurring in the plutonites and metamorphites of the upper Baltoro Glacier and K2-Gasherbrum range, relative to the more fractionated and contaminated lamprophyres injecting the shallower rocks of the Shaksgam valley area.

  19. 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.

  20. Pd segregation to the surface of Au on Pd(111) and on Pd/TiO2(110)

    NASA Astrophysics Data System (ADS)

    Sharpe, Ryan; Counsell, Jon; Bowker, Michael

    2017-02-01

    The interaction of Au and Pd in bimetallic systems is important in a number of areas of technology, especially catalysis. In order to investigate the segregation behaviour in such systems, the interaction of Pd and Au was investigated by surface science methods. In two separate sets of experiments, Au was deposited onto a Pd(111) single crystal, and Pd and Au were sequentially deposited onto TiO2(110), all in ultra-high vacuum using metal vapour deposition. Heating Au on Pd/TiO2(110) to 773 K resulted in the loss of the Au signal in the LEIS, whilst still remaining present in the XPS, due to segregation of Pd to the surface and the formation of a Au-Pd core-shell structure. It is likely that this is due to alloying of Au with the Pd and surface dominance of that alloy by Pd. The Au:Pd XPS peak area ratio is found to substantially decrease on annealing Au/Pd(111) above 773 K, corresponding with a large increase in the CO sticking probability to that for clean Pd(111). This further indicates that Au diffuses into the bulk of Pd on annealing to temperatures above 773 K. It therefore appears that Au prefers to be in the bulk in these systems, reflecting the exothermicity of alloy formation.

  1. Transient Plasma Ignition for Small Internal Combustion Engines

    DTIC Science & Technology

    2013-02-01

    Engines Gundersen, M . and Romney , P. University of Southern California FEBRUARY 2013 Final Report DISTRIBUTION A: Approved for public...so that heat release and combustion efficiency can be measured. References 1. Cathey, C., T. Tang, T. Shiraishi, T. Urushihara, A. Kuthi, and M . A...1, 1664-1668. 2. J.B. Liu, F. Wang, G. Li, A. Kuthi, E . J. Gutmark, P.D. Ronney, and M.A. Gundersen, “Transient Plasma Ignition,” IEEE

  2. 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

  3. Kinetic Theory of Instability-Enhanced Collisional Effects

    NASA Astrophysics Data System (ADS)

    Baalrud, Scott D.

    2009-11-01

    A generalization of the Lenard-Balescu collision operator is derived which accounts for the scattering of particles by instability amplified fluctuations that originate from the thermal motion of discrete particles (in contrast to evoking a fluctuation level externally, as is done in quasilinear kinetic theory) [1]. Emphasis is placed on plasmas with convective instabilities. It is shown that an instability-enhanced collective response results which can be the primary mechanism for scattering particles, being orders of magnitude more frequent than conventional Coulomb collisions, even though the fluctuations are in a linear growth phase. The resulting collision operator is shown to obey conservation laws (energy, momentum, and density), Galilean invariance, and the Boltzmann H-theorem. It has the property that Maxwellian is the unique equilibrium distribution function; again in contrast to weak turbulence or quasilinear theories. Instability-enhanced collisional effects can dominate particle scattering and cause strong frictional forces. For example, this theory has been applied to two outstanding problems: Langmuir's paradox [2] and determining Bohm's criterion for plasmas with multiple ion species [3]. Langmuir's paradox is a measurement of anomalous electron scattering rapidly establishing a Maxwellian distribution in gas discharges with low temperature and pressure. This may be explained by instability-enhanced scattering in the plasma-boundary transition region (presheath) where convective ion-acoustic instabilities are excited. Bohm's criterion for multiple ion species is a single condition that the ion fluid speeds must obey at the sheath edge; but it is insufficient to determine the speed of individual species. It is shown that an instability-enhanced collisional friction, due to streaming instabilities in the presheath, determines this criterion.[4pt] [1] S.D. Baalrud, J.D. Callen, and C.C. Hegna, Phys. Plasmas 15, 092111 (2008).[0pt] [2] S.D. Baalrud, J

  4. Vibrational states on Pd surfaces

    NASA Astrophysics Data System (ADS)

    Sklyadneva, I. Yu.; Rusina, G. G.; Chulkov, E. V.

    1997-04-01

    We present the calculation of vibrational modes and lattice relaxation for the Pd(100), (110) and (111) surfaces. The surface phonon frequencies and polarizations are obtained using embedded-atom potentials. Comparison of the calculated frequency values with available experimental data gives agreement within 0.2 THz.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Study of Mixed Collisionality Gas Flow in the VASIMR Thruster

    NASA Astrophysics Data System (ADS)

    Batishchev, Oleg; Molvig, Kim

    2000-11-01

    The degree of gas ionization in the VASIMR plasma thruster [1] is about one percent. This allows separating of the gas propellant flow from the plasma dynamics. The Knudsen number of the hydrogen (deuterium) or helium gas flow in a system of pipes of varying diameter falls into the .2-5 range. This indicates that the kinetic approach is required. First we present results from 1D hybrid Poiseuille-Knudsen model for viscous - free molecular pipe flow [2]. We compare simulation results to the experimental measurements. Next we study effects of (i) internal baffles to assist the retaining of the propellant, and (ii) gas pre-heating. Finally, we describe an extension of our 1D2V fully kinetic finite volume method [3] to a semi-collisional gas flow simulation. [1] F. Chang-Díaz et al., Bulletin of APS, 44 (1999) 99. [2] O. Batishchev and K. Molvig, AIAA 2000-3754 paper (2000). [3] Batishchev O. et al., J. Plasma Phys. 61 (1999) 347.

  13. HIDING IN THE SHADOWS. II. COLLISIONAL DUST AS EXOPLANET MARKERS

    SciTech Connect

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

    2016-03-20

    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.

  14. 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.

  15. Collisional and radiative processes in high-pressure discharge plasmas

    NASA Astrophysics Data System (ADS)

    Becker, Kurt H.; Kurunczi, Peter F.; Schoenbach, Karl H.

    2002-05-01

    Discharge plasmas at high pressures (up to and exceeding atmospheric pressure), where single collision conditions no longer prevail, provide a fertile environment for the experimental study of collisions and radiative processes dominated by (i) step-wise processes, i.e., the excitation of an already excited atomic/molecular state and by (ii) three-body collisions leading, for instance, to the formation of excimers. The dominance of collisional and radiative processes beyond binary collisions involving ground-state atoms and molecules in such environments allows for many interesting applications of high-pressure plasmas such as high power lasers, opening switches, novel plasma processing applications and sputtering, absorbers and reflectors for electromagnetic waves, remediation of pollutants and waste streams, and excimer lamps and other noncoherent vacuum-ultraviolet light sources. Here recent progress is summarized in the use of hollow cathode discharge devices with hole dimensions in the range 0.1-0.5 mm for the generation of vacuum-ultraviolet light.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Variational Algorithms for Drift and Collisional Guiding Center Dynamics

    NASA Astrophysics Data System (ADS)

    Ellison, C. Leland; Finn, John M.; Qin, Hong; Tang, William M.

    2014-10-01

    The simulation of guiding center test particle dynamics in the upcoming generation of magnetic confinement devices requires novel numerical methods to obtain the necessary long-term numerical fidelity. Geometric algorithms, which retain conserved quantities in the numerical time advances, are well-known to exhibit excellent long simulation time behavior. Due to the non-canonical Hamiltonian structure of the guiding center equations of motion, it is only recently that geometric algorithms have been developed for guiding center dynamics. This poster will discuss and compare several families of variational algorithms for application to 3-D guiding center test particle studies, while benchmarking the methods against standard Runge-Kutta techniques. Time-to-solution improvements using GPGPU hardware will be presented. Additionally, collisional dynamics will be incorporated into the structure-preserving guiding center algorithms for the first time. Non-Hamiltonian effects, such as polarization drag and simplified stochastic operators, can be incorporated using a Lagrange-d'Alembert variational principle. The long-time behavior of variational algorithms which include dissipative dynamics will be compared against standard techniques. This work was supported by DOE Contract DE-AC02-09CH11466.

  1. Predictions for collisional frequency shifts of ultracold rubidium atomic clocks

    NASA Astrophysics Data System (ADS)

    Kokkelmans, S. J. J. M. F.; Verhaar, B. J.; Heinzen, D. J.; Gibble, K.

    1997-04-01

    A few years ago atomic fountains using cold ^133Cs atoms led to a breakthrough in the field of atomic frequency standards(A. Clairon, C. Salomon, S. Guellati, and W. D. Phillips, Europhys. Lett. 16), 165 (1991); K. Gibble and S. Chu, Phys. Rev. Lett. 70, 1771 (1993).. It was soon found that the frequency shifts induced by collisions between atoms during their fountain orbit stand in the way to drawing the full benefits from this development. A possible way out is to switch to another atomic species(K. Gibble and B.J. Verhaar, Phys. Rev. A 52), 3370 (1995).. Recent experiments have made it possible to determine cold collision parameters for pairs of rubidium atoms with unprecedented accuracy(J.M. Vogels, C.C. Tsai, R.S. Freeland, S.J.J.M.F. Kokkelmans, B.J. Verhaar, and D.J. Heinzen (submitted).). Making use of these parameters we predict the collisional frequency shifts for a ^87Rb and a ^85Rb laser-cooled clock. Our results show the prospects for new atomic clocks based on ultracold rubidium to be promising.

  2. 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.

  3. 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.

  4. 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).

  5. 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.

  6. Multiscale mantle convection along the Tethyan collisional margin

    NASA Astrophysics Data System (ADS)

    Faccenna, Claudio; Becker, Thorsten

    2013-04-01

    We perform global mantle circulation to reconstruct the style and geometry of mantle convection beneath the Tethyan region, from the Mediterranean to the Hiamalayan belt. To quantify the contribution of mantle heterogeneity and subduction zones to mantle circulation and plate motions, we compute the instantaneous mantle flow that can be inferred from seismic tomography when velocity anomalies are converted into temperature. Model results are compared with geodesy, residual topography, and shear wave splitting observations. We evaluate different boundary conditions to test the role of slab pull and mantle convection as driving forces for the kinematics of the Tethyan system. Our results show that mantle drag exerted on the base of the lithosphere by a large-scale, convective "conveyor belt" with an active upwelling component is likely the main cause for the ongoing indentation of the Indian and Arabian plates into Eurasia. This large scale convection cell superimposed to small scale convection that could be resolved in region such as the Mediterranean, where high resolution seismic tomography is available. More in general, our model emphasizes that large scale mantle convection dragging continental block against Eurasia produce the necessary kinematic conditions to sustaine thick collisional orogen, whereas small scale convection confined in the upper mantle produces ephemeral, slab-pull dominated, orogenic belt.

  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. Collisional PIC Simulations of Particles in Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Peter, William

    2003-10-01

    Because of the long range of Coloumb forces, collisions with distant particles in plasmas are more important than collisions with near neighbors. In addition, many problems in space physics and magnetic confinement include regions of weak magnetic field where the MHD approximation breaks down. A particle-in-cell code based on the quiet direct simulation Monte-Carlo method(B. J. Albright, W. Daughton, D. Lemons, D. Winske, and M. E. Jones, Physics of Plasmas) 9, 1898 (2002). is being developed to study collisional (e.g., ν ˜ Ω) particle motion in magnetic fields. Primary application is to energetic particle loss in the radiation belts(K. Papadopoulos, COSPAR Meeting, Houston, TX, Oct., 2002.) at a given energy and L-shell. Other applications include trapping in rotating field-reversed configurations(N. Rostoker and A. Qerushi, Physics of Plasmas) 9, 3057 (2002)., and electron behavior in magnetic traps(V. Gorgadze, T. Pasquini, J. S. Wurtele, and J. Fajans, Bull. Am. Phys. Soc.) 47, 127 (2002).. The use of the random time-step method(W. Peter, Bull. Am. Phys. Soc.) 47, 52 (2002). to decrease simulation times by 1-2 orders of magnitude is also being studied.

  9. Prognostic value of PD-L1 and PD-1 expression in pulmonary neuroendocrine tumors

    PubMed Central

    Fan, Yangwei; Ma, Ke; Wang, Chuying; Ning, Jing; Hu, Yuan; Dong, Danfeng; Dong, Xuyuan; Geng, Qianqian; Li, Enxiao; Wu, Yinying

    2016-01-01

    Purpose Programmed death 1 (PD-1) receptor and its ligand, programmed death ligand-1 (PD-L1), play critical roles in the immune invasion of various tumors. This study aimed to explore the clinical significance of PD-L1/PD-1 expression in the progression of pulmonary neuroendocrine tumors (PNETs). Methods The expression of PD-L1 and PD-1 in 80 patients diagnosed with PNETs were investigated. Immunohistochemical analysis was performed on 80 formalin-fixed paraffin-embedded tissue specimens from PNETs and 20 corresponding cancer-adjacent tissue specimens. Results Tissues from PNETs had higher levels of PD-L1 (58.8%) and PD-1 (51.3%) compared to the cancer-adjacent tissues (25% and 20%, respectively). Meanwhile, PD-L1 expression was associated with PD-1 expression (P=0.007). PD-L1 expression was significantly associated with histological type (P=0.014) and tumor stage (P=0.014). Univariate analyses showed that the overall survival time of PNETs patients was significantly associated with PD-L1 expression in cancer cells (P=0.003), PD-1 expression in tumor-infiltrating lymphocytes (P=0.001), tumor node metastasis stage (P<0.05), and distant metastasis (P<0.001). Additionally, multivariate analysis revealed that PD-L1 expression, PD1 expression, and distant metastasis of PNETs were independently associated with survival time. Moreover, Kaplan–Meier survival curves analysis revealed that patients with negative PD-L1 and PD-1 expression had better prognoses. Conclusion Data suggested that PD-L1 and PD-1 can be useful prognostic biomarkers for survival and can pave the way toward new immunotherapy regimens against PNETs through targeting the PD-L1/PD-1 pathway. PMID:27785054

  10. 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

  11. Collisional modification to the exospheric theory of solar wind halo electron pitch angle distributions

    SciTech Connect

    Lemons, D.S.; Feldman, W.C.

    1983-09-01

    A theoretical model of suprathermal halo or strahl solar wind electrons, including both binary collisions and conservative force fields, is proposed. From this model we derive the collisionally modified electron pitch angle distribution and compare it with relevant measurements made in the solar wind at 1 AU by using the Los Alamos IMP 8 plasma analyzer. Although the collisionally modified distribution is more isotropic than that predicted by simple exospheric theory, it is not isotropic enough to describe the measurements.

  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. 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...

  14. [Transient epileptic amnesia].

    PubMed

    Muramatsu, Kazuhiro; Yoshizaki, Takahito

    2016-03-01

    Transient amnesia is one of common clinical phenomenon of epilepsy that are encountered by physicians. The amnestic attacks are often associated with persistent memory disturbances. Epilepsy is common among the elderly, with amnesia as a common symptom and convulsions relatively uncommon. Therefore, amnesia due to epilepsy can easily be misdiagnosed as dementia. The term 'transient epileptic amnesia (TEA)' was introduced in the early 1990s by Kapur, who highlighted that amnestic attacks caused by epilepsy can be similar to those occurring in 'transient global amnesia', but are distinguished by features brevity and recurrence. In 1998, Zeman et al. proposed diagnostic criteria for TEA.

  15. Luminous Extragalactic Transients

    NASA Astrophysics Data System (ADS)

    O'Brien, Paul; Jonker, Peter; Athena Explosive Transients Working Group

    2015-09-01

    The ESA Athena X-ray observatory mission will combine exceptionally high throughout with high spectral-energy resolution and will revolutionise many aspects of high-energy astrophysics. Many of the most powerful transient sources, including gamma-ray bursts and tidal disruptions events, are bright X-ray sources. Athena will be designed to have a fast-response capability permitting efficient observations of many transients. We will summarise the proposed capability of the mission and illustrate science programs to study transients ranging from the most distant GRBs to nuclear activity in nearby galaxies.

  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. PD-1/PD-L1 expression in extra-medullary lesions of multiple myeloma.

    PubMed

    Crescenzi, Anna; Annibali, Ombretta; Bianchi, Antonella; Pagano, Anastasia; Donati, Michele; Grifoni, Alba; Avvisati, Giuseppe

    2016-10-01

    Multiple myeloma patients may develop extraosseous involvement in the course of the disease making prognosis very poor and new drugs clearly needed. The PD-1/PD-L1 axis has emerged as a master immune checkpoint in antitumor responses and recent studies investigated the role of PD-L1 in multiple myeloma cells; no data however are still available about PD-L1 expression in extramedullary localizations. We demonstrate PD-L1 expression in 4/12 cases of extraosseous myeloma suggesting that these lesions represent a specialized microenvironment. We found presence of PD-1+ infiltrating lymphocytes in all observed cases supporting the relevance of PD-1/PD-L1 checkpoint in extramedullary myeloma. We also investigated the correlation in PD1/PD-L1 staining between marrow staining and EMP lesions.

  18. 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.

  19. PD-1/PD-L1 expression in chromophobe renal cell carcinoma: An immunological exception?

    PubMed

    Erlmeier, Franziska; Hartmann, Arndt; Autenrieth, Michael; Wiedemann, Max; Ivanyi, Philipp; Steffens, Sandra; Weichert, Wilko

    2016-11-01

    Immune checkpoint inhibitors targeting the inhibitory cross talk between tumor and immune cells have been approved for therapy in renal cell carcinoma (RCC). In contrast to clear cell RCC, little is known on PD-1/PD-L1 expression patterns in rarer RCC subtypes. The aim of this study was to evaluate the prevalence, distribution and prognostic impact of PD-1 and PD-L1 expression in chromophobe (ch)RCC. Patients who underwent renal surgery due to chRCC were retrospectively evaluated. Tumor specimen was analyzed for PD-1 and PD-L1 expression by immunohistochemistry. Expression data were correlated with clinic-pathological parameters including patient survival. Eighty-one chRCC patients were eligible for analysis, thereof 25 (30.9 %) and 11 (13.6 %) patients were positive for PD-1(+) tumor-infiltrating mononuclear cells (TIMCs) and tumoral PD-L1(+) expression, respectively. No significant associations were found for PD-1(+) TIMC or tumoral PD-L1(+) expression and clinical attributes. In addition, no differences in 5- and 10-year overall survival for PD-1(-) TIMC compared to PD-1(+) TIMC (90.5 and 72.2 vs. 100 and 75 %; p = 0.41) and for PD-L1(-) tumors compared to PD-L1(+) tumors (91.9 and 76.4 vs. 100 and 50 %; p = 0.48) were observed. In conclusion, to our knowledge this is the first study to evaluate the prognostic impact of PD-1 and PD-L1 in chRCC. PD-L1 does seem to be expressed in a minority of all chRCC, likewise only a minority of chRCC was infiltrated by PD-1-positive inflammatory cells. Neither PD-1(+) TIMC nor tumoral PD-L1(+) expression was associated with parameters of aggressiveness or survival.

  20. Transient topographical amnesia.

    PubMed Central

    Stracciari, A; Lorusso, S; Pazzaglia, P

    1994-01-01

    Ten healthy middle aged or elderly women experienced isolated episodes of topographical amnesia without an obvious aetiology. It is likely a benign cognitive disorder, similar to transient global amnesia. PMID:7964826

  1. Transient Global Amnesia

    MedlinePlus

    ... global amnesia is a sudden, temporary episode of memory loss that can't be attributed to a ... know well. But that doesn't make your memory loss less disturbing. Fortunately, transient global amnesia is ...

  2. Transient Astrophysics Observatory (TAO)

    NASA Astrophysics Data System (ADS)

    Racusin, J. L.; TAO Team

    2016-10-01

    The Transient Astrophysics Observatory (TAO) is a NASA MidEx mission concept (formerly known as Lobster) designed to provide simultaneous wide-field gamma-ray, X-ray, and near-infrared observations of the sky.

  3. 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.

  4. Transient multivariable sensor evaluation

    DOEpatents

    Vilim, Richard B.; Heifetz, Alexander

    2017-02-21

    A method and system for performing transient multivariable sensor evaluation. The method and system includes a computer system for identifying a model form, providing training measurement data, generating a basis vector, monitoring system data from sensor, loading the system data in a non-transient memory, performing an estimation to provide desired data and comparing the system data to the desired data and outputting an alarm for a defective sensor.

  5. 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.

  6. Primary and acquired resistance to PD-1/PD-L1 blockade in cancer treatment.

    PubMed

    Wang, Qiaohong; Wu, Xia

    2017-05-01

    PD-1/PD-L1 blockade appears to be a very promising immunotherapy with significant clinical benefits and durable responses in multiple tumor types. However, the effectual clinical benefits of PD-1/PD-L1 blockade are hampered by a high rate of primary resistance, where patients do not respond to PD-1/PD-L1 blockade initially. And more distressingly, most patients eventually develop acquired resistance after an initial response to PD-1/PD-L1 blockade. The mechanisms underlying primary and acquired resistance to PD-1/PD-L1 blockade have remained ambiguous. This review documents in detail the current understanding of the mechanisms through which resistance to anti-PD1/PD-L1 therapy occurs. The mechanisms underlying primary resistance to PD-1/PD-L1 blockade contain several immunoregulatory factors affecting tumor-specific immune responses within the immune microenvironment, co-enrichment of a group of 26 transcriptomic signatures (named innate anti-PD-1 resistance (IPRES) signatures) and cancer-cell-autonomous cues. The mechanism attributable to acquired resistance harbors evolution of neoantigen landscape, mutations of JAK and β-2-microglobulin, and epigenetic stability of exhausted T cells. At last, the promising therapeutic strategies to sensitize the resistant patients are also briefly discussed.

  7. Coupling Dynamical And Collisional Evolution Of Dust In Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Charnoz, Sebastien

    2010-10-01

    Gaseous circumstellar disks are rich in dust and are thought to be both accretionaly and dynamically active. Unfortunately large bodies that could be embedded in these disks are still difficult to observe and their putative properties are indirectly inferred from the observable small dust content. It is why constraining the size distribution coupled with dust-dynamics is so critical. Unfortunately, coupling effects such as a realistic time-dependant dynamics, fragmentation and coagulation, has been recognized as numerically challenging and almost no attempt really succeeded with a generic approach. In these disks, the dust dynamics is driven by a variety of processes (gravity, gas drag, radiation pressure..) inducing a size-dependant dynamics, and, at the same time collisional evolution changes the local size distributions. These two effects are intimately coupled because the local dynamics and size-distribution determines the local collision rates, that, in-turn, determines the size-distribution and modifies the particle's dynamics. Here we report on a new algorithm that overcomes these difficulties by using a hybrid approach extending the work of Charnoz & Morbidelli (Icarus, 2004, 2007). We will briefly present the method and focus on gaseous protoplanetary disks either laminar or turbulent (the time dependant transport and dust evolution will be shown) . We will show how the taking into account of a 3D dynamics helps to determine disantengle the dust size-distribution in the disk's photosphere and in the midplane and thus may provide observational signatures of accretion. We will show how the coupling of turbulence with fragmentation may significantly affect the dust/ratio for the smallest bodies. Finally, we will show that an accurate description of the time dependant dynamics of larger dusts (those with Stokes numbers >= 1) may provide a possible path to the formation of bodies larger than the accretion barrier, through accretion in a transitory regime.

  8. 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.

  9. Collision Strengths for Electron Collisional Excitation of S II

    NASA Technical Reports Server (NTRS)

    Tayal, S. S.

    1997-01-01

    Electron collisional excitation strengths for inelastic transitions in S II are calculated using the R-matrix method in a 19-state (3s(sup 2)3p(sup 3)(sup 4)S(sup o), (sup 2)D(sup o), (sup 2)p(sup o), 3s3p(sup 4)(sup 4)P, (sup 2)D, (sup 2)S, 3S(sup 2)3p(sup 2)3d(sup 2)P, (sup 4)F, (sup 4)D, (sup 2)F, (sup 4)P, 3s(sup 2)3p(sup 2)4s(sup 4)P, (sup 2)P, 3s(sup 2)3p(sup 2)4p(sup 2)S(s o), (sup 4)D(sup o), (sup 4)P(sup o), (sup 2)D(sup o), (sup 4)S(sup o), (sup 2)P(sup o)) close-coupling approximation. These target states are represented by extensive configuration-interaction wave functions that give excitation energies and oscillator strengths that are usually in good agreement with the experimental values and the available accurate calculations. The present results for collision strengths are in very good agreement with the recent merged beams energy loss measurement of Liao et al. and agree reasonably well with the 18-state R-matrix calculation of Ramsbottom, Bell, & Stafford, but show significant differences from the 12-state R-matrix calculation of Cai & Pradhan.

  10. Collisional and Radiative Processes in High-Pressure Discharge Plasmas

    NASA Astrophysics Data System (ADS)

    Becker, Kurt

    2001-10-01

    High-pressure discharge plasmas (HPDPs) with operating pressures up to and exceeding atmospheric pressure have gained prominence in many areas of application such as EM absorbers and reflectors, remediation of waste streams, deposition and surface modification, surface cleaning and sterilization, and light source development. In particular, HPDPs are widely used as sources for the generation of non-coherent UV and VUV light such as excimer emissions in the spectral range from 50 nm to 300 nm using rare gases or rare gas admixed with other gases as the operating medium. In this talk we will discuss several common types of HPDPs (e.g. microhollow cathode discharge plasmas, dielectric barrier discharge plasmas, capillary dielectrode discharge plasmas) that are commonly used for the generation of non-coherent excimer emissions. The main focus of this talk will be on the elucidation of the underlying microscopic collisional and radiative processes in these plasmas that lead to the photon emission and that determine the efficiency and spectral characteristics of various sources. Processes of particular interest are the generation of intense, monochromatic atomic line emissions in the 90 - 130 nm range, in particular the H Lyman-alpha emission at 121.6 nm, from HPDPs in gas mixtures containing high-pressure He, Ne, or Ar with trace amounts (1which may have great potential in photolithography and related applications. The mechanism for the emission of these intense atomic VUV lines are near-resonant energy transfer processes from the excimer molecule to the diatomic gas (H2, O2, N2). This work was supported by the NSF and by DARPA/ARO and carried out in collaboration with P. Kurunczi, K.H. Schoenbach, M. Laroussi, M. Gupta, and N. Masoud. Helpful discussions with U. Kogelschatz and E. Kunhardt are gratefully acknowledged.

  11. Acoustic Analysis of PD Speech

    PubMed Central

    Chenausky, Karen; MacAuslan, Joel; Goldhor, Richard

    2011-01-01

    According to the U.S. National Institutes of Health, approximately 500,000 Americans have Parkinson's disease (PD), with roughly another 50,000 receiving new diagnoses each year. 70%–90% of these people also have the hypokinetic dysarthria associated with PD. Deep brain stimulation (DBS) substantially relieves motor symptoms in advanced-stage patients for whom medication produces disabling dyskinesias. This study investigated speech changes as a result of DBS settings chosen to maximize motor performance. The speech of 10 PD patients and 12 normal controls was analyzed for syllable rate and variability, syllable length patterning, vowel fraction, voice-onset time variability, and spirantization. These were normalized by the controls' standard deviation to represent distance from normal and combined into a composite measure. Results show that DBS settings relieving motor symptoms can improve speech, making it up to three standard deviations closer to normal. However, the clinically motivated settings evaluated here show greater capacity to impair, rather than improve, speech. A feedback device developed from these findings could be useful to clinicians adjusting DBS parameters, as a means for ensuring they do not unwittingly choose DBS settings which impair patients' communication. PMID:21977333

  12. 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.

  13. Human cancer immunotherapy with antibodies to the PD-1 and PD-L1 pathway

    PubMed Central

    Ohaegbulam, Kim C; Assal, Amer; Lazar-Molnar, Eszter; Yao, Yu; Zang, Xingxing

    2014-01-01

    The PD-1 receptor and ligands PD-L1 and PD-L2, members of the CD28 and B7 families, play critical roles in T cell coinhibition and exhaustion. Overexpression of PD-L1 and PD-1 on tumor cells and tumor-infiltrating lymphocytes, respectively, correlates with poor disease outcome in some human cancers. Monoclonal antibodies (mAbs) blockading the PD-1/PD-L1 pathway have been developed for cancer immunotherapy via enhancing T cell functions. Clinical trials with mAbs to PD-1 and PD-L1 have shown impressive response rates in patients, particularly for melanoma, non-small-cell lung cancer, renal cell carcinoma, and bladder cancer. Further studies are needed to dissect mechanisms of variable response rate, to identify biomarkers for clinical response, to develop small molecule inhibitors, and to combine with other therapies. PMID:25440090

  14. Origin of perpendicular magnetic anisotropy in epitaxial Pd /Co /Pd (111 ) trilayers

    NASA Astrophysics Data System (ADS)

    Davydenko, A. V.; Kozlov, A. G.; Ognev, A. V.; Stebliy, M. E.; Samardak, A. S.; Ermakov, K. S.; Kolesnikov, A. G.; Chebotkevich, L. A.

    2017-02-01

    Perpendicular magnetic anisotropy in epitaxial Pd /Co /Pd (111 ) trilayered films grown on Si(111) substrate was investigated. Contributions to perpendicular magnetic anisotropy from the bottom and top Co/Pd interfaces were deduced by replacement of Pd layers by Cu layers and comparative analysis of the magnetic anisotropy in the samples. Perpendicular magnetic anisotropy in Pd/Co/Pd films was induced both by interface electronic effects and by stress caused by lattice mismatch between Pd and Co. Due to asymmetry of the stress in the Co film, the contribution to magnetic anisotropy induced by the bottom Co/Pd interface was stronger than that induced by the top Pd/Co interface. The energy of the perpendicular magnetic anisotropy and asymmetrical contributions from the bottom Co/Pd and top Pd/Co interfaces to anisotropy in Pd/Co/Pd trilayers strongly depend on the thickness of the bottom and top Pd layers and may be precisely controlled. The roughness of the interfaces does not have a large influence on the energy of perpendicular magnetic anisotropy in this system.

  15. Acute Malaria Induces PD1+CTLA4+ Effector T Cells with Cell-Extrinsic Suppressor Function

    PubMed Central

    Mackroth, Maria Sophia; Abel, Annemieke; Steeg, Christiane; Schulze zur Wiesch, Julian; Jacobs, Thomas

    2016-01-01

    In acute Plasmodium falciparum (P. falciparum) malaria, the pro- and anti-inflammatory immune pathways must be delicately balanced so that the parasitemia is controlled without inducing immunopathology. An important mechanism to fine-tune T cell responses in the periphery is the induction of coinhibitory receptors such as CTLA4 and PD1. However, their role in acute infections such as P. falciparum malaria remains poorly understood. To test whether coinhibitory receptors modulate CD4+ T cell functions in malaria, blood samples were obtained from patients with acute P. falciparum malaria treated in Germany. Flow cytometric analysis showed a more frequent expression of CTLA4 and PD1 on CD4+ T cells of malaria patients than of healthy control subjects. In vitro stimulation with P. falciparum-infected red blood cells revealed a distinct population of PD1+CTLA4+CD4+ T cells that simultaneously produced IFNγ and IL10. This antigen-specific cytokine production was enhanced by blocking PD1/PDL1 and CTLA4. PD1+CTLA4+CD4+ T cells were further isolated based on surface expression of PD1 and their inhibitory function investigated in-vitro. Isolated PD1+CTLA4+CD4+ T cells suppressed the proliferation of the total CD4+ population in response to anti-CD3/28 and plasmodial antigens in a cell-extrinsic manner. The response to other specific antigens was not suppressed. Thus, acute P. falciparum malaria induces P. falciparum-specific PD1+CTLA4+CD4+ Teffector cells that coproduce IFNγ and IL10, and inhibit other CD4+ T cells. Transient induction of regulatory Teffector cells may be an important mechanism that controls T cell responses and might prevent severe inflammation in patients with malaria and potentially other acute infections. PMID:27802341

  16. 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.

  17. Scalar and vector collisional interference in the vibration-rotation absorption spectra of H2 and HD

    NASA Technical Reports Server (NTRS)

    Herman, R. M.

    1987-01-01

    The only atomic or molecular spectra known to exhibit 'collisional interference' effects are those of H2 and its isotopes. Attention is presently given to the sharp absorption spectra of HD, which demonstrate collisional interference effects is a fashion that while surprising has been experimentally verified and theoretically characterized in detail. Collisional interference can dramatically alter the line shapes usually encountered in dipole absorption spectra, while nevertheless remaining narrow.

  18. 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.

  19. Comparative study of electroless copper deposition based on the seed layers of Pd, PtPd and AuPd

    NASA Astrophysics Data System (ADS)

    Ma, Chuanli; Ye, Weichun; Shi, Xuezhao; Chang, Yanlong; Chen, Yang; Wang, Chunming

    2009-01-01

    The article reports on electroless deposition of copper films onto p-silicon (1 0 0) using different seed (co-seed) layers of Pd, PtPd and AuPd. The dependence of the compositions and morphologies of different seed layers on resultant Cu films were comparatively studied in detail by atomic force microscopy (AFM), field emission scanning electron microscope (FE-SEM) and X-ray photoelectron spectroscopy (XPS). The activities of electroless copper deposition on the p-silicon (1 0 0) with different seed (co-seed) layers were evaluated by polarization curve. It is concluded that the bimetallic AuPd seed displayed the highest catalytic activity for electroless copper deposition, and followed by the order of PtPd > Pd.

  20. 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).

  1. Collisional Disruption of Ice by High-Velocity Impact

    NASA Astrophysics Data System (ADS)

    Arakawa, Masahiko

    1999-11-01

    High-velocity impact among icy planetesimals is a physical phenomenon important to the planetary evolution process in the outer Solar System. In order to study this phenomenon, impact experiments on water ice were made by using a two-stage light gas gun installed in a cold room (-10°C) to clarify the elementary processes of collisional disruption and to study the reaccumulation and the escape conditions of the impact fragments. Cubic ice targets ranging in size from 15 to 100 mm were impacted by a nylon projectile of 7 mg with an impact velocity ( vi) from 2.3 to 4.7 km/s. The corresponding mass ratio of the projectile to the target ( mp/ Mt) ranged from 10 -3 to 10 -6, which is two orders of magnitude lower than that used in previous studies (Arakawa et al. 1995, Icarus118, 341-354). As a result, we obtained data on elementary processes such as attenuation of the shock wave and fragmentation dynamics. We found that the shock pressure attenuates in the ice target according to the relation of P∝( Lp/ r2, irrespective of the mass ratio between 10 -3 and 10 -5, where Lp is the projectile size and r is a propagation distance. The largest fragment mass ( ml) normalized by the original target mass has a good relationship to a nondimensional impact stress ( PI, NDIS) defined as the ratio of the antipodal pressure to the material strength. This relationship is described as ml/ Mt ∝ PI-1.7 for a wide range of impact conditions (50 m/s< vi<4 km/s and 10 -1< ml/ Mt<10 -6), and shows the utility of NDIS. Using a measured shock wave decay constant of 2, the reaccumulation and the escape conditions of icy bodies in high-velocity collisions were estimated. As a result, it was clarified that a rubble pile could be formed when large icy bodies (radius>20 km) reaccumulated. On the other hand, when smaller icy bodies (radius<2 km) disrupted catastrophically, all fragments escaped and a rubble pile was never formed.

  2. The role of collisional compaction in primitive asteroids and comets

    NASA Astrophysics Data System (ADS)

    Trigo-Rodríguez, J. M.; Blum, J.

    2008-09-01

    During the early stages of solar system formation the consolidation of asteroids and comets took place. We have just learnt from recent space missions that some of these minor bodies have been preserved in a pristine way in several regions of our Solar System. From our experience on primitive meteorites we know that these bodies should contain valuable clues on the origin of the Solar System. Studies of the physical, chemical, and isotopic properties of the components of these minor bodies will provide important clues on their origin. We expect very different collisional histories undergone by these bodies depending on their particular formation, migration, and storage regions [1]. In Fig. 1 appears a schematic representation of the protoplanetary disk in the region of consolidation of the terrestrial planets about 4565 million years ago. Bodies located in the outer part of the main belt would have incorporated significant amounts of ice in their volume, but their migration to and residence times in other regions would have defined their physico-chemical properties. Recent laboratory studies and observational data compiled from comets, meteorites and meteoroids [2] suggest that the porosity of these bodies should have decreased with time depending on the degree of collisions, aqueous alteration and heating. For typical stony targets, the tensile strength and gravity are the main properties that are defining the formation of impact craters and subsequently the degree of impact metamorphism and mineralogy of the shocked materials. However, little is known about the influence of porosity on the impact process although the crushing of pore space is an efficient mechanism for absorbing shock waves, also increasing the postshock temperatures [2]. In this context, a Near-Earth Object (NEO) sample return mission called Marco Polo is being studied within the Cosmic Vision programme. Such kind of mission would be returning to the Earth unaltered material from a NEO, just

  3. Influence of collisional rate coefficients on water vapour excitation

    NASA Astrophysics Data System (ADS)

    Daniel, F.; Goicoechea, J. R.; Cernicharo, J.; Dubernet, M.-L.; Faure, A.

    2012-11-01

    Context. Water is a key molecule in many astrophysical studies that deal with star or planet forming regions, evolved stars, and galaxies. Its high dipole moment makes this molecule subthermally populated under the typical conditions of most astrophysical objects. This motivated calculation of various sets of collisional rate coefficients (CRC) for H2O (with He or H2), which are needed to model its rotational excitation and line emission. Aims: The most accurate set of CRC are the quantum rates that involve H2. However, they have been published only recently, and less accurate CRC (quantum with He or quantum classical trajectory (QCT) with H2) were used in many studies before that. This work aims to underline the impact that the new available set of CRC have on interpretations of water vapour observations. Methods: We performed accurate non-local, non-LTE radiative transfer calculations using different sets of CRC to predict the line intensities from transitions that involve the lowest energy levels of H2O (E < 900 K). The results obtained from the different CRC sets were then compared using line intensity ratio statistics. Results: For the whole range of physical conditions considered in this work, we find that the intensities based on the quantum and QCT CRC are in good agreement. However, at relatively low H2 volume density (n(H2) < 107 cm-3) and low water abundance (χ(H2O) < 10-6), which corresponds to physical conditions relevant when describing most molecular clouds, we find differences in the predicted line intensities of up to a factor of ~3 for the bulk of the lines. Most of the recent studies interpreting early Herschel Space Observatory spectra have used the QCT CRC. Our results show that, although the global conclusions from those studies will not be drastically changed, each case has to be considered individually, since depending on the physical conditions, the use of the QCT CRC may lead to a mis-estimate of the water vapour abundance of up to a

  4. Palomar Transient Factory

    NASA Astrophysics Data System (ADS)

    Kulkarni, S.; Quimby, R.

    2010-12-01

    The Palomar Transient Factory (PTF) was designed to explicitly to chart the transient sky with a particular focus on events which lie in the nova-supernova gap. With its innovative two-telescope architecture it achieves both high cadence and large areal rate of coverage. PTF was commissioned during the summer of 2009. PTF is now finding an extragalactic transient every 20 minutes and a Galactic (strong) variable every 10 minutes. Spectroscopy undertaken at Keck and Palomar has allowed us: identify an emerging class of ultra-luminous supernovae, discover luminous red novae, undertake UV spectroscopy of Ia supernovae, discover supernovae powered by something other than Nickel-56, clarification of sub-classes of core collapse and thermo-nuclear explosions, map the systematics of core collapse supernovae, a trove of eclipsing binaries and many others.

  5. Theoretical studies of chemisorption and dimer model systems: Moller-Plesset and configuration interaction calculations on PdH, PdC, PdO, PdF, Pd sub 2 , and PdCO

    SciTech Connect

    Schwerdtfeger, P.; McFeaters, J.S.; Moore, J.J.; McPherson, D.M.; Cooney, R.P.; Bowmaker, G.A. ); Dolg, M.; Andrae, D. )

    1991-01-01

    Ab initio SCF studies have been performed to study the molecular properties of several single-bonded palladium compounds, PdH, PdC, PdO, PdF, Pd{sub 2}, and PdCO, which are important in surface and materials science. Electron correlation effects were evaluated by a second- and third-order Moller-Plesset (MP) perturbation theory and a size-consistency-corrected configuration interaction with single and double substitutions (CISC). Relativistic effects were investigated for PdH and PdF. The ground state of PdC has been calculated at the CISC level to be a {sup 3}{Pi} state which is only 0.26 eV below the {sup 3}{Sigma}{sup {minus}} state (previously assigned ground state) and 0.51 eV below the {sup 1}{Sigma}{sup +} state. PdC is predicted to be stable in the gas phase, and the possibility of preparing this compound is investigated. The bonding in CO chemisorbed on palladium is studied by using the model Pd-CO system. The effect of d{sub {pi}}-{pi}{sup *} back-bonding, discussed at the Hartree-Fock and CI level, is compared with results from multiple-scattering {Chi}{alpha} calculations. The C-O stretching frequency shift for CO on palladium was analyzed at various levels of theory, and the results indicated that the decrease in the CO force constant associated with chemisorption is not solely the result of d{sub {pi}}-{pi}{sup *} back-bonding.

  6. The PD-1/PD-L1 axis may be aberrantly activated in occupational cholangiocarcinoma.

    PubMed

    Sato, Yasunori; Kinoshita, Masahiko; Takemura, Shigekazu; Tanaka, Shogo; Hamano, Genya; Nakamori, Shoji; Fujikawa, Masahiro; Sugawara, Yasuhiko; Yamamoto, Takatsugu; Arimoto, Akira; Yamamura, Minako; Sasaki, Motoko; Harada, Kenichi; Nakanuma, Yasuni; Kubo, Shoji

    2017-03-01

    An outbreak of cholangiocarcinoma in a printing company was reported in Japan, and these cases were regarded as an occupational disease (occupational cholangiocarcinoma). This study examined the expression status of programmed death-1 (PD-1) and programmed death-ligand 1 (PD-L1) in occupational cholangiocarcinoma. Immunostaining of PD-1, PD-L1, CD3, CD8, and CD163 was performed using tissue sections of occupational cholangiocarcinoma (n = 10), and the results were compared with those of control cases consisting of intrahepatic (n = 23) and extrahepatic (n = 45) cholangiocarcinoma. Carcinoma cells expressed PD-L1 in all cases of occupational cholangiocarcinoma, whereas the detection of PD-L1 expression in cholangiocarcinoma cells was limited to a low number of cases (less than 10%) in the control subjects. In cases of occupational cholangiocarcinoma, occasional PD-L1 expression was also noted in precancerous/preinvasive lesions such as biliary intraepithelial neoplasia and intraductal papillary neoplasm of the bile duct. Additionally, tumor-associated macrophages and tumor-infiltrating T cells expressed PD-L1 and PD-1, respectively. The number of PD-L1-positive mononuclear cells, PD-1-positive lymphocytes, and CD8-positive lymphocytes infiltrating within the tumor was significantly higher in occupational cholangiocarcinoma compared with that in control cases. These results indicate that immune escape via the PD-1/PD-L1 axis may be occurring in occupational cholangiocarcinoma.

  7. Transient elevation of adult hippocampal neurogenesis after dopamine depletion

    PubMed Central

    Park, June-Hee; Enikolopov, Grigori

    2010-01-01

    Degeneration of the midbrain dopaminergic neurons during Parkinson's disease (PD) may affect remote regions of the brain that are innervated by the projections of these neurons. The dentate gyrus (DG), a site of continuous production of new neurons in the adult hippocampus, receives dopaminergic inputs from the neurons of the substantia nigra (SN). Thus, depletion of the SN neurons during disease or in experimental settings may directly affect adult hippocampal neurogenesis. We show that experimental ablation of dopaminergic neurons in the 1-methyl-4-phenyl-1,2,3,6-tetrahydopyridine (MPTP) mouse model of PD results in a transient increase in cell division in the subgranular zone (SGZ) of the DG. This increase is evident for the amplifying neural progenitors and for their postmitotic progeny; our results also indicate that MPTP treatment affects division of the normally quiescent stem cells in the SGZ. We also show that L-DOPA, used in the clinical treatment of PD, while attenuating the MPTP-induced death of dopaminergic neurons, does not alter the effect of MPTP on cell division in the DG. Our results suggest that a decrease in dopaminergic signaling in the hippocampus leads to a transient activation of stem and progenitor cells in the DG. PMID:20079351

  8. Pd/GaN(0001) interface properties

    NASA Astrophysics Data System (ADS)

    Grodzicki, M.; Mazur, P.; Zuber, S.; Pers, J.; Ciszewski, A.

    2014-06-01

    This report concerns the properties of an interface formed between Pd films deposited onto the surface of (0001)-oriented n-type GaN at room temperature (RT) under ultrahigh vacuum. The surface of clean substrate and the stages of Pd-film growth were characterized in situ by X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), ultraviolet photoelectron spectroscopy (UPS), and low energy electron diffraction (LEED). As-deposited Pd films are grainy, cover the substrate surface uniformly and reproduce its topography. Electron affinity of the clean n-GaN surface amounts to 3.1 eV. The work function of the Pd-film is equal to 5.3 eV. No chemical interaction has been found at the Pd/GaN interface formed at RT. The Schottky barrier height of the Pd/GaN contact is equal to 1.60 eV.

  9. Antimagnetic rotation in 104Pd

    NASA Astrophysics Data System (ADS)

    Rather, N.; Roy, S.; Datta, P.; Chattopadhyay, S.; Goswami, A.; Nag, S.; Palit, R.; Pal, S.; Saha, S.; Sethi, J.; Trivedi, T.; Jain, H. C.

    2014-06-01

    The electric quadrupole transition rates for the high-spin yrast states of 104Pd have been measured by using the Doppler-shift attenuation method. These values decrease with the increase of angular momentum, which can be associated with the phenomenon of antimagnetic rotation. In the present work, a numerical calculation based on the semiclassical particle plus rotor model for antimagnetic rotation has been employed, giving a good description of the experimental Routhian and the transition rates and providing conclusive evidence of antimagnetic rotation in a nucleus other than cadmium.

  10. Induction of a transient dysexecutive syndrome in Parkinson's disease using a~subclinical dose of scopolamine.

    PubMed

    Bédard, M.A.; Lemay, S.; Gagnon, J.F.; Masson, H.; Paquet, F.

    1998-01-01

    Parkinson's Disease (PD) is often associated with a subcortico-frontal syndrome (SCFS) that is mainly characterized by executive dysfunctions. The complete biochemistry of these dysfunctions remain misunderstood although many studies have suggested a role of the dopaminergic lesions. However, cholinergic lesions in this disease may also account for the SCFS occurrence. The present study has assessed the effects of an acute subclinical dose of scopolamine in normal controls and in PD patients who were devoid of cognitive deficit. Results indicates that PD patients but not normal controls developed a transient SCFS for the duration of the drug action. In contrast to other populations with cholinergic depletions - such as Alzheimer's disease - cholinergic blockage in PD exacerbates specifically the dysexecutive syndrome without inducing amnesia or sedation. Such a discrepancy between these two neuropsychological profiles are discussed in terms of the specificity of the underlying cholinergic lesions.

  11. 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.

  12. Unique activity of Pd monomers: hydrogen evolution at AuPd(111) surface alloys.

    PubMed

    Pluntke, Y; Kibler, L A; Kolb, D M

    2008-07-07

    Well-defined Au/Pd(111) alloy films have been prepared on a Ru(0001) substrate by electrochemical metal deposition and subsequent heating up to 700 degrees C. The electrochemical behaviour of the 20 monolayers thick epitaxially-grown films is in excellent agreement with both equilibrium surface composition and distribution for Au/Pd alloys on Mo(110) as previously reported (D. W. Goodman et al., J. Phys. Chem., 2005, B109, 18535). The electrocatalytic activity of the AuPd(111) surface alloys was studied for the hydrogen evolution in 0.1 M H(2)SO(4) as a function of surface composition. Maximum activities were found for Pd fractions of 0.2 +/- 0.1, where the population of Pd atoms surrounded by Au has its maximum. These Pd monomers are found to be about 20 times more active than Pd atoms in the Pd overlayer.

  13. Role of Small Pd Ensembles in Boosting CO Oxidation in AuPd Alloys.

    PubMed

    Ham, Hyung Chul; Stephens, J Adam; Hwang, Gyeong S; Han, Jonghee; Nam, Suk Woo; Lim, Tae Hoon

    2012-03-01

    We present a theoretical explanation on how PdAu alloy catalysts can enhance the oxidation of CO molecules based on density functional theory calculations of CO adsorption and oxidation on AuPd/Pd(111) surfaces. Our study suggests that the enhanced activity is largely attributed to the possible existence of "partially-poisoned" Pd ensembles that accommodate fewer CO molecules than Pd atoms. Whereas the oxidation of preadsorbed CO is likely governed by O2 trapping, our study shows that small Pd ensembles such as dimers and compact trimers tend to provide more active sites than larger ensembles; CO adsorbed on a Pd monomer is found to react hardly with O2 to form CO2. In addition, we find the tendency of CO-induced Pd agglomeration, which may in turn facilitate CO oxidation by creating more dimers and compact trimers as compared with the adsorbate-free surface where monomers are likely prevailing.

  14. Antagonists of PD-1 and PD-L1 in Cancer Treatment

    PubMed Central

    Lipson, Evan J.; Forde, Patrick M.; Hammers, Hans-Joerg; Emens, Leisha A.; Taube, Janis M.; Topalian, Suzanne L.

    2015-01-01

    The PD-1 pathway, comprising the immune cell co-receptor Programmed Death 1 (PD-1) and its ligands, PD-L1 (B7-H1) and PD-L2 (B7-DC), mediates local immunosuppression in the tumor microenvironment. Drugs designed to block PD-1 or PD-L1 “release the brakes” on anti-tumor immunity and have demonstrated clinical activity in several types of advanced cancers, validating this pathway as a target for cancer therapy. Two such drugs have recently been approved to treat refractory advanced melanoma, and regulatory approvals in first- and second-line settings for additional cancer types are anticipated. The manageable safety profile of PD-1/PD-L1 blocking drugs identifies them as suitable for outpatient administration and the development of combinatorial therapies. Ongoing studies aim to identify biomarkers to guide patient selection, which would further improve the risk:benefit ratio for these drugs. PMID:26320063

  15. 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.

  16. Collisional Scaling of the Energy Transfer in Drift-Wave Zonal Flow Turbulence

    NASA Astrophysics Data System (ADS)

    Schmid, B.; Manz, P.; Ramisch, M.; Stroth, U.

    2017-02-01

    The collisionality scaling of density and potential coupling together with zonal flow energy transfer and spectral power is investigated at the stellarator experiment TJ-K. With a poloidal probe array, consisting of 128 Langmuir probes, density and potential fluctuations are measured on four neighboring flux surfaces simultaneously over the complete poloidal circumference. By analyzing Reynolds stress and pseudo-Reynolds stress, it is found that, for increasing collisionality, the coupling between density and potential decreases which hinders the zonal flow drive. Also, as a consequence, the nonlinear energy transfer, as well as the zonal flow contribution to the complete turbulent spectrum, decreases the same way. This is in line with theoretical expectations and is a first experimental verification of the importance of collisionality for large-scale structure formation in magnetically confined toroidal plasmas.

  17. 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.

  18. Collisionality Dependence of Multi-species Density Peaking in Turbulence Simulations of C-Mod Plasmas

    NASA Astrophysics Data System (ADS)

    Mikkelsen, D. R.; Bitter, M.; Delgado-Aparicio, L.; Hill, K. W.; Greenwald, M.; Howard, N.; Podpaly, Y.; Reinke, M.; Rice, J. E.; Hughes, J. W.; Ma, Y.; Candy, J.; Waltz, R. E.

    2012-10-01

    In nonlinear GYRO simulations of C-Mod plasmas, a turbulently driven pinch produces modest density peaking of all species. The ratio of density at r/a=0.44 and 0.74 is 1.2 for the majority and minority D & H (and electrons), and increases with impurity Z: 1.1 for helium, 1.15 for boron, 1.29 for neon, 1.36 for argon, 1.47 for molybdenum. Density peaking is only weakly affected when the ion temperature profile is varied to align the predicted heat flux to the experimental transport analysis. New simulations will extend the collisionality to the lower part of the experimentally accessible range in C-Mod to study the collisionality dependence of density peaking, and to establish whether much stronger peaking is predicted for lower collisionalities. Simulations based on measured I-mode ion and electron temperature profiles will also be presented.

  19. Nonlinear evolution of an ion acoustic wave in two-species, moderately collisional plasma.

    NASA Astrophysics Data System (ADS)

    Valeo, E. J.; Berger, R. L.

    2004-11-01

    The dispersion properties of ion acoustic waves (IAW) in two-species plasma with disparate ion charges and masses has shown a sensitivity to inter-species collisions in the moderate-collisionality regime where the heavy, highly-charged ions are strongly collisional (fluid-like), but where light-ion Landau damping is competitive with light-heavy collisions.(R. Berger, E. Valeo and S. Brunner, Bull. Am. Phys. Soc., 47), QP1.98 (2002). The nonlinear evolution of a driven IAW is simulated using a low-noise hybrid simulation technique in which the electrons are a massless fluid, the heavy ions are a cold fluid, and the light ions are evolved using the δ f method with an evolving background distribution. The relative importance of several nonlinear effects in determining the mode amplitude, including (collisionally interrupted) trapping and nonlinear frequency shifts, is assessed.

  20. 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.

  1. Collisional Scaling of the Energy Transfer in Drift-Wave Zonal Flow Turbulence.

    PubMed

    Schmid, B; Manz, P; Ramisch, M; Stroth, U

    2017-02-03

    The collisionality scaling of density and potential coupling together with zonal flow energy transfer and spectral power is investigated at the stellarator experiment TJ-K. With a poloidal probe array, consisting of 128 Langmuir probes, density and potential fluctuations are measured on four neighboring flux surfaces simultaneously over the complete poloidal circumference. By analyzing Reynolds stress and pseudo-Reynolds stress, it is found that, for increasing collisionality, the coupling between density and potential decreases which hinders the zonal flow drive. Also, as a consequence, the nonlinear energy transfer, as well as the zonal flow contribution to the complete turbulent spectrum, decreases the same way. This is in line with theoretical expectations and is a first experimental verification of the importance of collisionality for large-scale structure formation in magnetically confined toroidal plasmas.

  2. Electron-exchange and quantum screening effects on the collisional entanglement fidelity in degenerate quantum plasmas

    NASA Astrophysics Data System (ADS)

    Hong, Woo-Pyo; Jung, Young-Dae

    2014-06-01

    The influence of electron-exchange and quantum screening on the collisional entanglement fidelity for the elastic electron-ion collision is investigated in degenerate quantum plasmas. The effective Shukla-Eliasson potential and the partial wave method are used to obtain the collisional entanglement fidelity in quantum plasmas as a function of the electron-exchange parameter, Fermi energy, plasmon energy and collision energy. The results show that the quantum screening effect enhances the entanglement fidelity in quantum plasmas. However, it is found that the electron-exchange effect strongly suppresses the collisional entanglement fidelity. Hence, we have found that the influence of the electron-exchange reduces the transmission of quantum information in quantum plasmas. In addition, it is found that, although the entanglement fidelity decreases with an increase of the Fermi energy, it increases with increasing plasmon energy in degenerate quantum plasmas.

  3. Collisional Delta-f Scheme with Evolving Background for Transport Time Scale Simulations

    SciTech Connect

    E. Valeo; J. Krommes; S. Brunner

    1999-07-01

    The delta-f approach is extended for simulating the transport time-scale evolution of near-Maxwellian distributions in collisional plasmas. This involves simultaneously advancing weighted marker particles for representing the intrinsically kinetic component delta-f, and fluid equations for the parameters of the shifted Maxwellian background f(subSM). The issue of increasing numerical noise in a collisional delta-f algorithm, due to marker particle weight spreading, is addressed in detail, and a solution to this problem is proposed. To obtain higher resolution in critical regions of phase space, a practical procedure for implementing sources and sinks of marker particles is developed. As a proof of principal, this set of methods are applied for computing electrical Spitzer conductivity as well as collisional absorption in a homogeneous plasma.

  4. 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.

  5. 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.

  6. Eigenmodes and growth rates of relativistic current filamentation instability in a collisional plasma.

    PubMed

    Honda, M

    2004-01-01

    I theoretically found eigenmodes and growth rates of relativistic current filamentation instability in collisional regimes, deriving a generalized dispersion relation from self-consistent beam-Maxwell equations. For symmetrically counterstreaming, fully relativistic electron currents, the collisional coupling between electrons and ions creates the unstable modes of growing oscillation and wave, which stand out for long-wavelength perturbations. In the stronger collisional regime, the growing oscillatory mode tends to be dominant for all wavelengths. In the collisionless limit, those modes vanish, while maintaining another purely growing mode that exactly coincides with a standard relativistic Weibel mode. It is also shown that the effects of electron-electron collisions and thermal spread lower the growth rate of the relativistic Weibel instability. The present mechanisms of filamentation dynamics are essential for transport of homogeneous electron beam produced by the interaction of high power laser pulses with plasma.

  7. Neutron capture cross section of 102Pd

    NASA Astrophysics Data System (ADS)

    Duncan, C. L.; Krane, K. S.

    2005-05-01

    The cross sections for radiative neutron capture by 102Pd have been deduced from a measurement of the γ rays emitted by 17.0-d 103Pd. The thermal cross section has been determined to be σ=1.82±0.20 b, and the effective resonance integral is I=23±4 b. We also report thermal and resonance capture cross sections for 108Pd and note possible inconsistencies with the presently accepted values of the 110Pd cross sections.

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

    PubMed

    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.

  9. Transient lingual papillitis.

    PubMed

    Kornerup, Ida M; Senye, Mireya; Peters, Edmund

    2016-01-01

    A case of recurrent, clinically innocuous, but painful papules involving the tongue dorsum of a 25-year-old man is presented. The lesions were interpreted to represent a transient lingual papillitis. This a poorly understood, but benign and self-limited condition involving the tongue fungiform papillae, which does not appear to be widely recognized.

  10. Transient familial hyperbilirubinemia

    MedlinePlus

    ... please enable JavaScript. Transient familial hyperbilirubinemia is a metabolic disorder that is passed down through families. Babies with ... M. Editorial team. Related MedlinePlus Health Topics Jaundice Metabolic Disorders Browse the Encyclopedia A.D.A.M., Inc. ...

  11. Lightning-Transient Recorder

    NASA Technical Reports Server (NTRS)

    Grumm, R. L.

    1984-01-01

    Battery-powered system operates for more than one year. Recorder digitizes and records up to 146 current samples at selected intervals during lightning stroke. System continues to store time tags of lightning strokes even if transient current memory is full.

  12. Quiet Monte Carlo Method for the Simulation of Semi-Collisional Plasmas

    NASA Astrophysics Data System (ADS)

    Albright, Brian J.

    2001-10-01

    The modeling of collisions among particles in a plasma poses a challenge for computer simulation. Traditional simulation methods are able to model well the extremes of highly collisional plasmas (MHD and Hall-MHD simulations) and collisionless plasmas (particle-in-cell simulations). However, the intermediate, semi-collisional regime is more problematic. In semi-collisional plasmas, the collision times are comparable to the dynamical time scales of interest in the system and the collisionality often varies as a function of time or position. Some examples include interpenetrating laser-produced plasmas, tokamak plasmas near edges and divertors, plasmas in the Earth's ionosphere, cometary exospheres, and the interstellar medium. Some PIC plasma simulations have been developed that can, in a limited way, model collisions. These include the early work of Shanny et al. [Phys. Fluids 10, 1281 (1967)], the binary collision model of Takizuka and Abe [J. Comput. Phys. 25 205 (1977)], and the collision field method of Jones et al. [J. Comput. Phys. 117, 194 (1996)]. In this talk, a new approach to particle simulation, called ``quiet direct simulation Monte Carlo'' (QDSMC), will be described that can, in principle, treat plasmas with arbitrary and arbitrarily varying collisionality. The essence of the QDSMC approach is the use of carefully chosen weights for the particles (e.g., Gauss-Hermite, for Maxwellian distributions), which are destroyed each time step after the particle information is deposited onto the grid and then reconstructed at the beginning of the next time step. The method overcomes the usual limitations of particle methods: limited dynamical range and excessive statistical noise. The QDSMC method will be discussed, as will its application as ``proof of principle'' to diffusion, hydrodynamics, and radiation transport. A QDSMC formulation of collisional, kinetic plasma simulation will be outlined, and preliminary results will be presented.

  13. Determination of collisional quenching rate coefficients of metastable nitrogen molecules by air pollutants

    NASA Astrophysics Data System (ADS)

    Suzuki, Susumu; Itoh, Haruo

    2009-10-01

    It has already been investigated on the determination of the collisional quenching rate coefficients of the metastable nitrogen molecules N2(A^3σu^+ ) by some air pollutants [1] in our laboratory. In this report, we present the result on the collisional quenching rate coefficient of N2(A^3σu^+ ) by formaldehyde (CH2O) using a theoretical procedure that takes into account the reflection of metastables at the boundary. As far as we know, this report is the first result of the collisional quenching rate coefficients of N2(A^3σu^+ ) by CH2O. Formaldehyde is a colorless gas with the foul odor, and elements of the adhesive, paints, and preservative, etc. It is widely used for construction materials such as houses, because it is low cost. It is released from paint of construction materials in air, and, in that case, it is known as one of the causative agents of so-called ``Sick building syndrome'' to influence the human body harmfully even if it is a low concentration. The obtained collisional quenching rate coefficient of N2(A^3σu^+ ) by CH2O is (4.7±0.4) x 10-12 cm^3/s. Because the collisional quenching rate coefficient by CH2O is large, it is understood that CH2O receives energy easily from N2(A^3σu^+ ). In addition, we reports on the obtained collisional quenching rate coefficient of N2(A^3σu^+ ) by some air pollutants. [1] S. Suzuki, T.Suzuki and H.Itoh: Proc. of XXVIII ICPIG (Prague, Czech Republic), (2007) 1P01-40.

  14. 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.

  15. Is collisional breakup an important process within mixed-phase deep convective clouds?

    NASA Astrophysics Data System (ADS)

    Seifert, A.; Khain, A.; Mayer, F.

    2003-04-01

    The microphysics of deep convective clouds determines their precipitation efficiency as well as the dynamical evolution of cloud systems and is therefore of great importance for numerical weather prediction, flood forecasting and regional climate modeling. Of all cloud systems mixed-phase deep convection is maybe the most complex and least understood. One reason is that the numerous microphysical processes taking place are highly nonlinear and strongly coupled with each other as well as with the hydrodynamics of the cloud. Collisional breakup of raindrops is one of these cloud microphysical processes, but is often neglected or not well represented in state-of-the-art cloud resolving models. The importance of collisional breakup is well known for tropical cloud systems, which are dominated by warm phase processes. In addition various studies using so-called rainshaft models showed that collisional breakup can alter the raindrop size distribution below cloud base. But what happens within the clouds and especially within strong convective updrafts? Can collisional breakup lead to a different cloud evolution by changing the drop size distribution? Using the Hebrew University Cloud Model (HUCM), which includes the most detailed spectral microphysics model available today, we performed a sensitivity study to answer these questions. Collisional breakup was therefore recently included in HUCM using Bleck's numerical method, which is standard for simulation of the breakup process. Our breakup scheme itself is mainly based on the parameterization of Low and List (1982, JAS), but includes also additional data for small raindrops by Beard and Ochs (1995, JAS). As a test case a deep convective mixed-phase cloud is simulated with initial conditions based on a sounding from 13 August 1999, Midland/Texas. We present a detailed analysis of the simulated cloud evolution with and without collisional breakup taken into account. The conclusion from our sensitivity study is that

  16. Conservation laws for collisional and turbulent transport processes in toroidal plasmas with large mean flows

    NASA Astrophysics Data System (ADS)

    Sugama, H.; Nunami, M.; Nakata, M.; Watanabe, T.-H.

    2017-02-01

    A novel gyrokinetic formulation is presented by including collisional effects into the Lagrangian variational principle to yield the governing equations for background and turbulent electromagnetic fields and gyrocenter distribution functions, which can simultaneously describe classical, neoclassical, and turbulent transport processes in toroidal plasmas with large toroidal flows on the order of the ion thermal velocity. Noether's theorem modified for collisional systems and the collision operator given in terms of Poisson brackets are applied to derivation of the particle, energy, and toroidal momentum balance equations in the conservative forms, which are desirable properties for long-time global transport simulation.

  17. Collisional energy losses in relativistic nuclear collisions within an effective quasiparticle model

    SciTech Connect

    Tarasov, Yu. A.

    2009-10-15

    We investigate the collisional energy losses of the fast gluons and light quarks in quark-gluon plasma produced in central (Au+Au) collisions at at energies currently available at the BNL Relativistic Heavy Ion Collider (RHIC) ({radical}(s{sub NN})=200 GeV). We use the effective quasiparticle model for investigation of physical characteristic of expanding plasma. We take into account the possibility of hot glue production at the first stage. We calculate these energy losses and compare them with radiative energy losses of gluons and quarks in an analogous model. We show that radiative energy losses exceed considerably the collisional energy losses.

  18. 3D Fokker-Planck modeling of axisymmetric collisional losses of fusion products in TFTR

    SciTech Connect

    Goloborod`ko, V.Ya.; Reznik, S.N.; Yavorskij, V.A.; Zweben, S.J.

    1995-10-01

    Results of a 3D (in constants of motion space) Fokker-Planck simulation of collisional losses of fusion products in axisymmetric DT and DD discharges on TFTR are presented. The distributions of escaped ions over poloidal angle, pitch angle, and their energy spectra are obtained. Axisymmetric collisional losses of fusion products are found to be less than (2--5)%. The distribution of confined fusion products is shown to be strongly anisotropic and nonuniform in the radial coordinate mainly for slowed-down fusion products with small longitudinal energy. Comparison of these results of modeling and experimental data is done.

  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. 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.

  1. Salmonella impairs CD8 T cell response through PD-1: PD-L axis.

    PubMed

    López-Medina, Marcela; Carrillo-Martín, Ismael; Leyva-Rangel, Jessica; Alpuche-Aranda, Celia; Ortiz-Navarrete, Vianney

    2015-12-01

    We have shown that Salmonella remains for a long period of time within B cells, plasma cells, and bone marrow B cell precursors, which might allow persistence and dissemination of infection. Nonetheless, how infected cells evade CD8 T cell response has not been characterized. Evidence indicates that some pathogens exploit the PD-1: PD-L (PD-L1 and PD-L2) interaction to inhibit CD8 T cells response to contribute the chronicity of the infection. To determine whether the PD-1: PD-L axis plays a role during Salmonella infection; we evaluated PD-1 expression in antigen-specific CD8 T cells and PD-1 ligands in Salmonella-infected cells. Our results show that infected B cells and macrophages express continuously co-stimulatory (CD40, CD80, and CD86) and inhibitory molecules (PD-L1 and PD-L2) in early and late stages of chronic Salmonella infection, while antigen-specific CD8 T cells express in a sustained manner PD-1 in the late stages of infection. Blocking this axis restores the ability of the CD8 T cells to proliferate and eliminate primary infected APCs. Therefore, a continuous PD-1: PDL interaction might be a mechanism employed by Salmonella to negatively regulate Salmonella-specific CD8 T cell cytotoxic response in order to remain within the host for a long period of time.

  2. 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

  3. Collisional dust fragmentation near nuclear surface within cometary jets

    NASA Astrophysics Data System (ADS)

    Steckloff, J.; Melosh, J.

    2014-07-01

    model and find that Δ R_{(R)} ∝ R is additionally able to create power-law radiance profiles. For a thermal fragmentation mechanism, thermal skin depth considerations suggest that the splitting time in binary fission should have the dependence of τ_{s (R)} ∝ R^{2}, whereas the thickness of the shed layer Δ R in grain shedding should remain constant or grow with time, rather than decrease with time as the grain loses mass. Therefore, these functional dependencies of the fundamental splitting parameters are inconsistent with the thermal fragmentation mechanisms suspected to act on dust grains further away from the nucleus such as volatile sublimation [2] and sintering [4]. Our best fit to the most prominent Tempel 1 scarp jet [5,6] is a binary splitting mechanism where τ_{s (R)} R^{2} = const. (see Figure). This dependence of dust fragmentation upon the surface area of the dust grain suggests that dust fragmentation near the origin of Tempel 1's scarp jets is dominated by collisions, consistent with observed radiances. The low collisional speeds in this region are consistent with weak, fractal-like dust-grain structures.

  4. 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.

  5. Dependence of perpendicular magnetic anisotropy and hall resistivity on Pd-layer thickness in CoSiB/Pd multilayer

    NASA Astrophysics Data System (ADS)

    Jung, Sol; Yim, Haein; Kim, Sung Yong

    2015-08-01

    We investigated the perpendicular magnetic anisotropy and the Hall resistivity of CoSiB/Pd multilayers. The CoSiB/Pd multilayers consisted of CoSiB (7-Å thickness) and Pd (Pd thickness t Pd = 10, 12, 14, 16, 18, and 20 Å), and a CoSiB/Pd bilayer was stacked five times. The coercivity shows oscillating values between tPd = 12 Å and t Pd = 20 Å. The value of the saturation magnetization increased between t Pd = 10 Å and t Pd = 12 Å and then decreased after t Pd = 12 Å. The perpendicular magnetic anisotropy constant depended on the thickness of Pd-layer and the values repeatedly increased and decreased. All CoSiB/Pd multilayers exhibited a positive Hall effect, and the Hall resistivity was not proportional to the magnetic moment.

  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. Photoacoustic transient imagery

    NASA Astrophysics Data System (ADS)

    Franceschi, J. L.; Marty-Dessus, D.; Severac, H.; Boucher, Jean-Marc; Bastie, A.

    1993-01-01

    A collimated laser diode associated with a small, short focal length objective lens produces a focused laser beam on the top of a sample glued onto a piezoelectric transducer. This laser beam is horizontally scanned on the surface and its intensity is modulated by a square wave using a TTL signal generator. This system induces acoustic waves in the sample. With a specially designed control circuitry, by combining this acoustic signal and the scanned laser beam, imaging of the subsurface is possible. The transient analysis developed is described and we show how to select cut-away views of the subsurface specimen with some applications in failure analysis of integrated circuits. We present the apparatus, the transient photoacoustic signal theory, and make a comparison between scanning photoacoustic (SPAM) and scanning electron acoustic microscopy (SEAM).

  8. Unusual CRTS Transient

    NASA Astrophysics Data System (ADS)

    Drake, A. J.; Mahabal, A.; Djorgovski, S. G.; Williams, R.; Graham, M. J.; Beshore, E. C.; Larson, S. M.; Christensen, E.; Christensen, E.; Beshore, E. C.; Larson, S. M.

    2008-10-01

    We have detected an optical transient of unknown nature in Catalina 0.7m Schmidt telescope images from 28 Sep 2008 UT. The object has the following parameters:

    CSS080928:160837+041626 2008-09-28 UT 02:50:49 RA 16:08:37.23 Dec 04:16:26.7 Mag 17.7 Type ?
    A possible uncataloged match to the transient is present in SDSS images with magnitude r~22.5.

  9. Synthesized light transients.

    PubMed

    Wirth, A; Hassan, M Th; Grguras, I; Gagnon, J; Moulet, A; Luu, T T; Pabst, S; Santra, R; Alahmed, Z A; Azzeer, A M; Yakovlev, V S; Pervak, V; Krausz, F; Goulielmakis, E

    2011-10-14

    Manipulation of electron dynamics calls for electromagnetic forces that can be confined to and controlled over sub-femtosecond time intervals. Tailored transients of light fields can provide these forces. We report on the generation of subcycle field transients spanning the infrared, visible, and ultraviolet frequency regimes with a 1.5-octave three-channel optical field synthesizer and their attosecond sampling. To demonstrate applicability, we field-ionized krypton atoms within a single wave crest and launched a valence-shell electron wavepacket with a well-defined initial phase. Half-cycle field excitation and attosecond probing revealed fine details of atomic-scale electron motion, such as the instantaneous rate of tunneling, the initial charge distribution of a valence-shell wavepacket, the attosecond dynamic shift (instantaneous ac Stark shift) of its energy levels, and its few-femtosecond coherent oscillations.

  10. Transient Pulse Monitor

    DTIC Science & Technology

    1988-05-20

    connection to the test solar array pannels . One radiated electromagnetic signal sensor will be placed on one of the solar array panels (Figures 6 and 7). The...22 02 Spacecraft, Charging , Discharge, Transient, Environment 19. ABSTRACT (Cmntnue on mromN ifesor AWMI endwtfr by blok numfber) SRI International is...6 2.1.2 Particle Interactions with Satellite Materials: Charging ........................ 6 2.1.3 Discharges and Their Effects on Systems

  11. Coherent Transient Systems Evaluation

    DTIC Science & Technology

    1993-06-17

    europium doped yttrium silicate in collaboration with IBM Almaden Research Center. Research into divalent ion doped crystals as photon gated materials...demonstration of the coherent transient continuous optical processor was performed in europium doped yttrium silicate. Though hyperfine split ground...materials. Research into divalent samarium doped into other hosts is incomplete and may produce better results. Preliminary measurements on Tm:KCl revealed

  12. Transient Detection Using Wavelets.

    DTIC Science & Technology

    1995-03-01

    signaL and transients are nonstationary. A new technique for the analysis of this type of signal, called the Wavelet Transform , was applied to artificial...and real signals. A brief theoretical comparison between the Short Time Fourier Transform and the Wavelet Transform is introduced A multisolution...analysis approach for implementing the transform was used. Computer code for the Discrete Wavelet Transform was implemented. Different types of wavelets to use as basis functions were evaluated. (KAR) P. 2

  13. Lunar transient phenomena

    NASA Astrophysics Data System (ADS)

    Cameron, W. S.

    1991-03-01

    Lunar transient phenomena (LTP) sightings are classified into five categories: brightenings, darkenings, reddish colorations, bluish colorations, and obscurations. There is evidence that the remaining LTP's are of lunar origin. A substantial number of sightings are independently confirmed. They have been recorded on film and spectrograms, as well as with photoelectric photometers and polarization equipment. It suggested that the LTP's may be gentle outgassings of less-than-volcanic proportions.

  14. 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.

  15. G6PD Deficiency (Glucose-6-Phosphate Dehydrogenase) (For Parents)

    MedlinePlus

    ... trigger, is removed. In rare cases, G6PD deficiency leads to chronic anemia . With the right precautions, a child with G6PD deficiency can lead a healthy and active life. About G6PD Deficiency ...

  16. Inhibition of Hydrogen Absorption in Pd by the Formation of a Pd-Ru Surface Alloy

    NASA Astrophysics Data System (ADS)

    Cabrera, A. L.; Ferrari, P.; Rojas, S.; Diaz-Droguett, Donovan; Ramos-Moore, E.; Laboratorio Ciencia de Materiales Team

    2013-03-01

    Hydrogen absorption by palladium has been studied for decades due to the significant importance in a number of applications like production and storage of hydrogen and hydrogen sensors. Alloying Pd with just a 4% of Ru drastically reduces the absorption properties of the Pd. The fcc crystal structure is preserved but the lattice constant is reduced slightly. In order to understand this phenomenon, we used three samples: a Pd foil, a Pd-Ru(4%) alloy foil, and a Pd foil with a Pd-Ru surface alloy. The surface alloy was made evaporating 8 nm of Ru using an e-beam evaporation technique on top of Pd, followed with a heating the sample up to 700 °C in a high vacuum system. We studied the changes in absorption properties of these samples using Thermal Program Desorption (TPD), resistance changes and grazing incidence X-ray Diffraction (GID). Funds from VRI-Puente 10/2012

  17. 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.

  18. PD-L1, PD-L2 and PD-1 expression in metastatic melanoma: Correlation with tumor-infiltrating immune cells and clinical outcome.

    PubMed

    Obeid, Joseph M; Erdag, Gulsun; Smolkin, Mark E; Deacon, Donna H; Patterson, James W; Chen, Leiping; Bullock, Timothy N; Slingluff, Craig L

    2016-01-01

    Therapeutic blockade of PD-1/PD-L1 can have dramatic therapeutic benefit in some patients; however, the prognostic associations of PD-1 and its ligands, in the absence of therapeutic blockade have not been definitively addressed. In particular, associations of PD-L2 with immune infiltrates and with outcome have yet to be explored. We hypothesized that surface expression of both PD-L1 and PD-L2 by melanoma cells would be associated with immune cell infiltration and with overall patient survival, independent of checkpoint blockade therapy. We also characterized the heterogeneity of their distribution within a tumor and within tumors of the same patient. Tissue microarrays of metastatic melanoma samples from 147 patients were quantified for CD8(+), CD45, CD4(+), CD3, CD163, CD20, CD138, FoxP3, PD-1, PD-L1 and PD-L2 markers by immunohistochemistry. Relationships between the proportions of PD-L1 and PD-L2 expressing tumor cells with the immune cell count, distribution (immunotype) and patient survival were studied. Expressions of both PD-L1 and PD-L2 correlated significantly with increasing densities of immune cells in the tumor specimens and with immunotype. Positive PD-L2 expression was associated with improved overall survival and the simultaneous positive expression of both PD-1 ligands showed a higher association with survival. Significant heterogeneity of PD-L1 and PD-L2 expressions within tumors were observed, however, they were less pronounced with PD-L2. In conclusion, both are markers of immune infiltration and PD-L2, alone or in combination with PD-L1, is a marker for prognosis in metastatic melanoma patients. Larger tumor samples yield more reliable assessments of PD-L1/L2 expression.

  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. 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.

  1. Optimization of CFETR baseline performance by controlling rotation shear and pedestal collisionality through integrated modeling

    NASA Astrophysics Data System (ADS)

    Jian, Xiang; Chen, Jiale; Chan, Vincent S.; Zhuang, Ge; Li, Guoqiang; Deng, Zhao; Shi, Nan; Xu, Guoliang; Staebler, Gary M.; Guo, Wenfeng

    2017-04-01

    The optimization of a CFETR baseline scenario (Chan et al 2015 Nucl. Fusion 55 023017) with an electron cyclotron (EC) wave and neutral beam (NB) is performed using a multi-dimensional code suite. TGLF and NEO are used to calculate turbulent and neoclassical transport. The evaluation of sources and sinks, as well as the current evolution, are performed using ONETWO, and the equilibrium is updated using EFIT. The pedestal is consistent with the EPED model. Rotation shear is controlled using NB. It has been found that both fusion gain Q and NB power deposited in the edge increase with decreasing NB energy, with NB providing current drive, torque, energy and particle source simultaneously. By using an optimized combination of two NBs, Q can be kept at a high level while the NB edge power is reduced. Pedestal collisionality is controlled to find an optimization path for Q by trading off between the pedestal density and temperature with the pedestal pressure fixed. It has been found that Q increases with pedestal collisionality, while the density peaking factor (DPF) remains almost unchanged. The invariance of DPF can be explained by the change of the dominant type of turbulence from the core to the edge (i.e. trapped electron mode in the core and ion temperature gradient mode at the edge), and collisionality has the opposite effect on particle transport for these two modes. A weaker dependence of DPF on collisionality makes a higher density operation more favorable for fusion gain.

  2. Multi-Zone Simulations of the Collisional Evolution of Main Belt Asteroids

    NASA Astrophysics Data System (ADS)

    Granata, V.; Marzari, F.; Davis, D. R.; Paolicchi, P.; Vanzani, V.

    2011-03-01

    We have adapted the planet building code, a multizone code, to study the collisional evolution of asteroids in the main belt. In this way the effects of resonances and Yarkowski's drift are statistically included and we can estimate the flux of bodies into NEO orbits.

  3. The quest to find the plasma edge and discover a collisionally modified Bohm criterion

    NASA Astrophysics Data System (ADS)

    Franklin, R. N.; Franklin

    2013-10-01

    The concepts of `plasma edge' and `collisionally modified Bohm criterion' have occupied attention for many years since the publication of work by Bohm that gave rise to the Bohm criterion. He acknowledged that his description of the plasma-sheath transition was incomplete. We summarize work that shows that neither concept has precision, at the same time giving a critique.

  4. Comments on "a study of the collisional fragmentation problem using the gamma distribution approximation".

    PubMed

    Nadarajah, Saralees

    2007-04-15

    M. Kostoglou and A.J. Karabelas [J. Colloid Interface Sci. 303 (2006) 419-429] proposed using a gamma distribution approximation to study a collisional fragmentation problem. This approximation involved two types of integrals and the use of continued fraction expansions for their computation. In this Comment, explicit expressions are derived for computing the integrals.

  5. 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.

  6. Collisional Ion and Electron Scale Gyrokinetic Simulations in the Tokamak Pedestal

    NASA Astrophysics Data System (ADS)

    Belli, E. A.; Candy, J.; Snyder, P. B.

    2016-10-01

    A new gyrokinetic solver, CGYRO, has been developed for precise studies of high collisionality regimes, such as the H-mode pedestal and L-mode edge. Building on GYRO and NEO, CGYRO uses the same velocity-space coordinates as NEO to optimize the accuracy of the collision dynamics and allow for advanced operators beyond the standard Lorentz pitch-angle scattering model. These advanced operators include energy diffusion and finite-FLR collisional effects. The code is optimized for multiscale (coupled electron and ion turbulence scales) simulations, employing a new spatial discretization and array distribution scheme that targets scalability on next-generation (exascale) HPC systems. In this work, CGYRO is used to study the complex spectrum of modes in the pedestal region. The onset of the linear KBM with full collisional effects is assessed to develop an improved KBM/RBM model for EPED. The analysis is extended to high k to explore the role of electron-scale (ETG-range) physics. Comparisons with new analytic collisional theories are made. Inclusion of sonic toroidal rotation (including full centrifugal effects) for studies including heavy wall impurities is also reported. Work supported in part by the US DOE under DE-FC02-06ER54873 and DE-FC02-08ER54963.

  7. 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.

  8. 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.

  9. 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

  10. PD-L1 Expression and Combined Status of PD-L1/PD-1–Positive Tumor Infiltrating Mononuclear Cell Density Predict Prognosis in Glioblastoma Patients

    PubMed Central

    Han, Jiheun; Hong, Yongkil; Lee, Youn Soo

    2017-01-01

    Background Programmed death ligand 1 (PD-L1) in tumor cells is known to promote immune escape of cancer by interacting with programmed cell death 1 (PD-1) in tumor infiltrating immune cells. Immunotherapy targeting these molecules is emerging as a new strategy for the treatment of glioblastoma (GBM). Understanding the relationship between the PD-L1/PD-1 axis and prognosis in GBM patients may be helpful to predict the effects of immunotherapy. Methods PD-L1 expression and PD-1–positive tumor infiltrating mononuclear cell (PD-1+tumor infiltrating mononuclear cell [TIMC]) density were evaluated using tissue microarray containing 54 GBM cases by immunohistochemical analysis; the associations with patient clinical outcomes were evaluated. Results PD-L1 expression and high PD-1+TIMC density were observed in 31.5% and 50% of GBM cases, respectively. High expression of PD-L1 in tumor cells was an independent and significant predictive factor for worse overall survival (OS; hazard ratio, 4.958; p = .007) but was not a significant factor in disease-free survival (DFS). PD-1+TIMC density was not correlated with OS or DFS. When patients were classified based on PD-1 expression and PD-1+TIMC density, patients with PD-L1+/PD-1+TIMC low status had the shortest OS (13 months, p = .009) and DFS (7 months, p = .053). Conclusions PD-L1 expression in GBM was an independent prognostic factor for poor OS. In addition, combined status of PD-L1 expression and PD-1+TIMC density also predicted patient outcomes, suggesting that the therapeutic role of the PD-1/PD-L1 axis should be considered in the context of GBM immunity. PMID:27989100

  11. Characterizing the Disk of a Recent Massive Collisional Event

    NASA Astrophysics Data System (ADS)

    Song, Inseok

    2015-10-01

    Debris disks play a key role in the formation and evolution of planetary systems. On rare occasions, circumstellar material appears as strictly warm infrared excess in regions of expected terrestrial planet formation and so present an interesting opportunity for the study of terrestrial planetary regions. There are only a few known cases of extreme, warm, dusty disks which lack any colder outer component including BD+20 307, HD 172555, EF Cha, and HD 23514. We have recently found a new system TYC 8830-410-1 belonging to this rare group. Warm dust grains are extremely short-lived, and the extraordinary amount of warm dust near these stars can only be plausibly explainable by a recent (or on-going) massive transient event such as the Late Heavy Bombardment (LHB) or plantary collisions. LHB-like events are seen generally in a system with a dominant cold disk, however, warm dust only systems show no hint of a massive cold disk. Planetary collisions leave a telltale sign of strange mid-IR spectral feature such as silica and we want to fully characterize the spectral shape of the newly found system with SOFIA/FORCAST. With SOFIA/FORCAST, we propose to obtain two narrow band photometric measurements between 6 and 9 microns. These FORCAST photometric measurements will constrain the amount and temperature of the warm disk in the system. There are less than a handful systems with a strong hint of recent planetary collisions. With the firmly constrained warm disk around TYC 8830-410-1, we will publish the discovery in a leading astronomical journal accompanied with a potential press release through SOFIA.

  12. Surface Chemistry of PdO(101)

    NASA Astrophysics Data System (ADS)

    Weaver, Jason

    2014-03-01

    The formation of palladium oxide (PdO) is thought to be responsible for the exceptional activity of supported Pd catalysts toward the complete oxidation of alkanes under oxygen-rich conditions. In this talk, I will discuss our investigations of the surface chemical properties of a PdO(101) thin film, focusing particularly on the adsorption and selective activation of alkanes. We find that n-alkanes adsorb relatively strongly on the PdO(101) surface by forming σ-complexes along rows of coordinatively-unsaturated Pd atoms, and that this adsorbed state acts as the precursor for initial C-H bond cleavage. I will discuss characteristics of the binding and activation of alkane σ-complexes on PdO(101) as determined from both experiment and density functional theory calculations. I will also discuss elementary processes involved in adsorbate oxidation on PdO(101) and make comparisons with the chemical reactivity of other late transition metal oxides.

  13. PdCu@Pd Nanocube with Pt-like Activity for Hydrogen Evolution Reaction.

    PubMed

    Li, Jing; Li, Feng; Guo, Si-Xuan; Zhang, Jie; Ma, Jiantai

    2017-02-27

    The electronic properties of metal surfaces can be modulated to weaken the binding energy of adsorbed H-intermediates on the catalyst surface, thus enhancing catalytic activity for the hydrogen evolution reaction (HER). Here we first prepare PdCu alloy nanocubes (NCs) by coreduction of Cu(acac)2 (acac = acetylacetonate) and Na2PdCl4 in the presence of oleylamine (OAm) and trioctylphosphine (TOP). The PdCu NC coated glassy carbon electrode is then anodized at a constant potential of 0.51 V vs Ag/AgCl at room temperature in 0.5 M H2SO4 solution for 10 s, which converts PdCu NCs into core@shell PdCu@Pd NCs that show much enhanced Pt-like activity for the HER and much more robust durability. The improvements in surface property and HER activity are rationalized based on strain and ligand effects that enhance the activity of the edge-exposed Pd atoms on core@shell PdCu@Pd structure. This work opens up a new perspective for simultaneously reducing metal Pd cost and achieving excellent performance toward the HER.

  14. Formation of Pd/Au Nanostructures from Pd Nanowires via Galvanic Replacement Reaction

    SciTech Connect

    Teng,X.; Wang, Q.; Liu, P.; Han, W.; Frenkel, A.; Wen, W.; Marinkovic, N.; Hanson, J.; Rodriguez, J.

    2008-01-01

    Bimetallic nanostructures with non-random metal atoms distribution are very important for various applications. To synthesize such structures via benign wet chemistry approach remains challenging. This paper reports a synthesis of a Au/Pd alloy nanostructure through the galvanic replacement reaction between Pd ultrathin nanowires (2.4 {+-} 0.2 nm in width, over 30 nm in length) and AuCl3 in toluene. Both morphological and structural changes were monitored during the reaction up to 10 h. Continuous changes of chemical composition and crystalline structure from Pd nanowires to Pd68Au32 and Pd45Au55 alloys, and to Au nanoparticles were observed. More interestingly, by using combined techniques such as high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), energy dispersive X-ray spectrometry (EDS), UV-vis absorption, and extended X-ray absorption fine structure (EXAFS) spectroscopy, we found the formation of Pd68Au32 non-random alloy with Au-rich core and Pd-rich shell, and random Pd45Au55 alloy with uniformly mixed Pd and Au atom inside the nanoparticles, respectively. Density functional theory (DFT) calculations indicated that alkylamine will strongly stabilize Pd to the surface, resulting in diffusion of Au atoms into the core region to form a non-random alloy. We believe such benign synthetic techniques can also enable the large scale preparation of various types of non-random alloys for several technically important catalysis applications.

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

    PubMed

    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.

  16. 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.

  17. Transient gain-versus-absorption laser probing of spin-orbit states, kinetics and dynamics

    NASA Technical Reports Server (NTRS)

    Smedley, John E.; Hess, Wayne P.; Haugen, Harold K.; Leone, Stephen R.

    1986-01-01

    The spin-orbit populations of excited (2P1/2) and ground (2P3/2) state Br atoms at 2714 nm and I atoms at 1315 nm are examined using a tunable F-center laser and a diode laser. The transient laser gain-versus-absorption measurements are utilized to estimate quantum yields of the spin-orbit states in the photodissociation of Br- and I-containing compounds; the continuum yields for Br2 are investigated in terms of temperature. The collisional release, Doppler velocity effects, and differing reactivity of the spin-orbit excited and ground state atoms are studied. It is noted that the transient gain versus absorption technique is applicable to the analysis of kinetic phenomena due to its high sensitivity and excellent time resolution.

  18. 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

  19. Transient transformation of plants.

    PubMed

    Jones, Huw D; Doherty, Angela; Sparks, Caroline A

    2009-01-01

    Transient expression in plants is a valuable tool for many aspects of functional genomics and promoter testing. It can be used both to over-express and to silence candidate genes. It is also scaleable and provides a viable alternative to microbial fermentation and animal cell culture for the production of recombinant proteins. It does not depend on chromosomal integration of heterologous DNA so is a relatively facile procedure and can lead to high levels of transgene expression. Recombinant DNA can be introduced into plant cells via physical methods, via Agrobacterium or via viral vectors.

  20. 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.

  1. 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.

  2. 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

  3. 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

  4. 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

  5. PD-1/PD-L1 inhibitors in multiple myeloma: The present and the future.

    PubMed

    Jelinek, T; Hajek, R

    2016-01-01

    The introduction of PD-1/PD-L1 pathway inhibitors has marked a significant milestone in the treatment of various types of solid tumors. The current situation in multiple myeloma (MM) is rather unclear, as distinct research groups have reported discordant results. This discrepancy dominantly concerns the expression of PD-1/PD-L1 molecules as well as the identification of the responsible immune effector cell population. The results of monotherapy with PD-1/PD-L1 inhibitors have been unsatisfactory in MM, suggesting that a combination approach is needed. The most logical partners are immunomodulatory agents as they possess many synergistic effects. We are also proposing other rational and promising combinations (e.g., daratumumab, ibrutinib, anti-CD137) that warrant further investigation.

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

    DOE PAGES

    Kim, Dong -Ok; Song, Kyung Mee; Choi, Yongseong; ...

    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

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

    SciTech Connect

    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 in magnetic proximity effects could be important for understanding spin transport characteristics in ferromagnetic/nonmagnetic systems and its potential application to spin devices.

  8. Beyond melanoma: inhibiting the PD-1/PD-L1 pathway in solid tumors.

    PubMed

    Gentzler, Ryan; Hall, Richard; Kunk, Paul R; Gaughan, Elizabeth; Dillon, Patrick; Slingluff, Craig L; Rahma, Osama E

    2016-05-01

    Immune checkpoint inhibitors have been identified as breakthrough treatment in melanoma given its dramatic response to PD-1/PD-L1 blockade. This is likely to extend to many other cancers as hundreds of clinical trials are being conducted or proposed using this exciting modality of therapy in a variety of malignancies. While immune checkpoint inhibitors have been extensively studied in melanoma and more recently in lung cancer, little is known regarding immune checkpoint blockade in other cancers. This review will focus on the tumor immune microenvironment, the expression of PD-1/PD-L1 and the effect of immune modulation using PD-1 or PD-L1 inhibitors in patients with head and neck, prostate, urothelial, renal, breast, gastrointestinal and lung cancers.

  9. 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

  10. 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

  11. New immunotherapies targeting the PD-1 pathway

    PubMed Central

    Chinai, Jordan M.; Janakiram, Murali; Chen, Fuxiang; Chen, Wantao; Kaplan, Mark; Zang, Xingxing

    2015-01-01

    Ligands from the B7 family bind to receptors of the CD28 family, which regulate early T cell activation in lymphoid organs and control inflammation and autoimmunity in peripheral tissues. PD-1, a member of the CD28 family, is an inhibitory receptor on T cells and is responsible for their dysfunction in infectious diseases and cancers. The complex mechanisms controlling expression and signaling of PD-1 and PD-L1 are emerging. Recently completed and ongoing clinical trials that target these molecules have shown remarkable success by generating durable clinical responses in some cancer patients. In chronic viral infections, preclinical data reveal that targeting PD-1 and its ligands can improve T cell responses and viral clearance. There is also promise in stimulating this pathway for the treatment of autoimmune and inflammatory disorders. PMID:26162965

  12. Preparation of 103Pd seed-molecular plating of 103Pd onto silver rod.

    PubMed

    Zhang, Chunfu; Wang, Yongxian; Tian, Haibin; Yin, Duanzhi

    2002-09-01

    A method for 103Pd "molecular plating" onto the surface of a silver rod is reported. The optimal composition of the plating bath is as follows: palladium chloride 0.1 mol/l, formaldehyde 2 mol/l, nitric acid 1 mol/l, and formic acid 0.4 mol/l. The 103Pd molecular plating procedure will last 25 min at 30 degrees C. This article provides a valuable experience for the preparation of 103Pd brachytherapy seed.

  13. Observation of a Strongly Enhanced Magnetic Susceptibility of Pd in Au-Pd-Au Sandwiches

    NASA Astrophysics Data System (ADS)

    Brodsky, M. B.; Freeman, A. J.

    1980-07-01

    Exceptionally large increases in the magnetic susceptibility (indicating nearly magnetic ordering) of thin films of Pd sandwiched between thicker Au films have been observed at low temperatures-presumably due to the expansion of the Pd average lattice constant by the Au. The large resultant Stoner factors and the modified paramagnon model of Levin and Valls indicate the possibility of observing p-wave superconductivity in Pd structures with reduced proximity effects.

  14. PD-1 and PD-L1 antibodies in cancer: current status and future directions.

    PubMed

    Balar, Arjun Vasant; Weber, Jeffrey S

    2017-02-17

    Immunotherapy has moved to the center stage of cancer treatment with the recent success of trials in solid tumors with PD-1/PD-L1 axis blockade. Programmed death-1 or PD-1 is a checkpoint molecule on T cells that plays a vital role in limiting adaptive immune responses and preventing autoimmune and auto-inflammatory reactivity in the normal host. In cancer patients, PD-1 expression is very high on T cells in the tumor microenvironment, and PD-L1, its primary ligand, is variably expressed on tumor cells and antigen-presenting cells within tumors, providing a potent inhibitory influence within the tumor microenvironment. While PD-L1 expression on tumors is often regarded as a negative prognostic factor, it is clearly associated with a positive outcome for treatment with PD-1/PD-L1 blocking antibodies, and has been used to select patients for this therapy. Responses of long duration, a minority of patients with atypical responses in which progression may precede tumor shrinkage, and a pattern of autoimmune side effects often seen with this class of drugs characterize therapy with PD-1/PD-L1 blocking drugs. While excellent efficacy has been seen with a limited number of tumor types, most epithelial cancers do not show responses of long duration with these agents. In the current review, we will briefly summarize the scientific background data supporting the development of PD-1/PD-L1 blockade, and then describe the track record of these antibodies in multiple different histologies ranging from melanoma and lung cancer to less common tumor types as well as discuss biomarkers that may assist in patient selection.

  15. 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.

  16. Facile synthesis of Pt-Pd alloy nanocages and Pt nanorings by templating with Pd nanoplates

    DOE PAGES

    Wang, Xue; Luo, Ming; Huang, Hongwen; ...

    2016-09-06

    We report a facile method for the synthesis of Pt-Pd nanocages and Pt nanorings by conformally coating Pd nanoplates with Pt-based shells using polyol- and water-based protocols, respectively, followed by selective removal of the Pd cores. For the polyol-based system, Pd nanoplates were conformally coated with Pt-Pd alloy shells due to the use of a high reaction temperature of 200 °C and a slow injection rate for the Pt precursor. In comparison, Pt shells were formed on Pd nanoplates (with a larger thickness on the side face than on the top/bottom face) in the water-based system due to the usemore » of a low reaction temperature of 80 °C and the presence of twin boundaries on the side face. As such, the Pd@Pt nanoplates prepared using the polyol- and water-based protocols evolved into Pt-Pd nanocages and Pt nanorings, respectively, when the Pd templates in the cores were selectively removed by wet etching. As a result, the wall thickness of the nanocages and the ridge thickness of the nanorings could be reduced down to 1.1 nm and 1.8 nm, respectively, without breaking the hollow structures.« less

  17. ELS and XPS study of Pd/PdO methane oxidation catalysts

    NASA Astrophysics Data System (ADS)

    Hoflund, Gar B.; Hagelin, Helena A. E.; Weaver, Jason F.; Salaita, Ghaleb N.

    2003-01-01

    Electron energy loss spectra (ELS) and X-ray photoelectron spectroscopy (XPS) data obtained from palladium powder catalysts used for complete methane oxidation have been obtained in this study in order to gain information about the Pd chemical state. Metallic Pd and PdO yield significantly different ELS spectra making ELS useful for chemical-state determination. Palladium(II) oxide is readily detected by the presence of an energy loss feature at 3.7 eV. Species distribution in the direction normal to the surface can be determined using ELS by varying the primary beam energy. Both XPS and ELS data indicate that PdO forms during reaction, and the ELS data demonstrate that PdO forms as a film over the Pd metal. If any Pd metal is present in the PdO film, it is there at levels below the detection limit of ELS. These observations have important consequences with regard to the mechanism of methane oxidation over Pd-containing catalysts. Hydrous and anhydrous palladium(II) oxides have significantly different energy loss features in the low loss-energy region of the ELS spectra. ELS features attributed to water are observed at 5.5-6.5 and 8 eV for hydrous palladium(II) oxide.

  18. PD-1 and PD-L1 Immune Checkpoint Blockade to Treat Breast Cancer.

    PubMed

    Hartkopf, Andreas D; Taran, Florin-Andrei; Wallwiener, Markus; Walter, Christina B; Krämer, Bernhard; Grischke, Eva-Maria; Brucker, Sara Y

    2016-12-01

    Immune checkpoint inhibition represents a major recent breakthrough in the treatment of malignant diseases including breast cancer. Blocking the programmed death receptor-1 (PD-1) and its ligand, PD-L1, has shown impressive antitumor activity and may lead to durable long-term disease control, especially in the triple-negative subtypes of breast cancer (TNBC). Although immune checkpoint blockade is generally well tolerated, specific immune-related adverse events (irAEs) may occur. This review summarizes the clinical efficacy, perspectives, and future challenges of using PD-1/PD-L1-directed antibodies in the treatment of breast cancer.

  19. Facile synthesis of Pt-Pd alloy nanocages and Pt nanorings by templating with Pd nanoplates

    SciTech Connect

    Wang, Xue; Luo, Ming; Huang, Hongwen; Chi, Miaofang; Howe, Jane; Xie, Zhaoxiong; Xia, Younan

    2016-09-06

    We report a facile method for the synthesis of Pt-Pd nanocages and Pt nanorings by conformally coating Pd nanoplates with Pt-based shells using polyol- and water-based protocols, respectively, followed by selective removal of the Pd cores. For the polyol-based system, Pd nanoplates were conformally coated with Pt-Pd alloy shells due to the use of a high reaction temperature of 200 °C and a slow injection rate for the Pt precursor. In comparison, Pt shells were formed on Pd nanoplates (with a larger thickness on the side face than on the top/bottom face) in the water-based system due to the use of a low reaction temperature of 80 °C and the presence of twin boundaries on the side face. As such, the Pd@Pt nanoplates prepared using the polyol- and water-based protocols evolved into Pt-Pd nanocages and Pt nanorings, respectively, when the Pd templates in the cores were selectively removed by wet etching. As a result, the wall thickness of the nanocages and the ridge thickness of the nanorings could be reduced down to 1.1 nm and 1.8 nm, respectively, without breaking the hollow structures.

  20. Calculating transient rates from surveys

    NASA Astrophysics Data System (ADS)

    Carbone, D.; van der Horst, A. J.; Wijers, R. A. M. J.; Rowlinson, A.

    2017-03-01

    We have developed a method to determine the transient surface density and transient rate for any given survey, using Monte Carlo simulations. This method allows us to determine the transient rate as a function of both the flux and the duration of the transients in the whole flux-duration plane rather than one or a few points as currently available methods do. It is applicable to every survey strategy that is monitoring the same part of the sky, regardless the instrument or wavelength of the survey, or the target sources. We have simulated both top-hat and Fast Rise Exponential Decay light curves, highlighting how the shape of the light curve might affect the detectability of transients. Another application for this method is to estimate the number of transients of a given kind that are expected to be detected by a survey, provided that their rate is known.

  1. G6PD Deficiency (Glucose-6-Phosphate Dehydrogenase) (For Parents)

    MedlinePlus

    ... Old Feeding Your 1- to 2-Year-Old G6PD Deficiency KidsHealth > For Parents > G6PD Deficiency Print A A ... can lead a healthy and active life. About G6PD Deficiency G6PD is one of many enzymes that help ...

  2. 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.

  3. 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

  4. Transient arrest of psychogenic tremor induced by contralateral ballistic movements.

    PubMed

    Kumru, Hatice; Valls-Solé, Josep; Valldeoriola, Francesc; Marti, Maria José; Sanegre, Maria Teresa; Tolosa, Eduardo

    2004-11-11

    One of the clinical characteristics of psychogenic tremors (PT) is the disruption or transient cessation of tremor with distractive manoeuvres, including those involving the performance of voluntary movements with the contralateral hand. Seven patients with PT, 11 patients with Parkinson's disease (PD), 10 patients with essential tremor (ET) and 10 normal volunteers mimicking tremor (NV) were requested to perform a fast unilateral wrist movement to close a switch, at the perception of a visual cue, either at rest or during maintenance of a posture. We measured the time-locked changes in frequency and amplitude occurring in tremor oscillations of the contralateral hand. The reaction time task induced a significant reduction in amplitude or cessation of contralateral tremor oscillations in PT and NV, but not in PD and ET. The effect occurred with a delay with respect to the onset of the contralateral movement without significant differences in PT versus NV (p > 0.05). The physiological mechanisms accounting for the effect seen on tremor of NV and PT may involve the interhemispheric inhibition that accompanies the execution of a unilateral motor task. Tremor circuits in patients with PD and ET may be impervious to these inhibitory commands. The documentation and quantitation of the effects of a ballistic movement on contralateral rhythmic activity are of clinical relevance for the identification of patients with PT.

  5. Role of PD-1 in regulating T-cell immunity.

    PubMed

    Jin, Hyun-Tak; Ahmed, Rafi; Okazaki, Taku

    2011-01-01

    Programmed cell death-1 (PD-1) is a member of the CD28 superfamily that delivers negative signals upon interaction with its two ligands, PD-L1 or PD-L2. PD-1 and its ligands are broadly expressed and exert a wider range of immunoregulatory roles in T cells activation and tolerance compared with other CD28 members. Subsequent studies show that PD-1-PD-L interaction regulates the induction and maintenance of peripheral tolerance and protect tissues from autoimmune attack. PD-1 and its ligands are also involved in attenuating infectious immunity and tumor immunity, and facilitating chronic infection and tumor progression. The biological significance of PD-1 and its ligand suggests the therapeutic potential of manipulation of PD-1 pathway against various human diseases. In this review, we summarize our current understanding of PD-1 and its ligands ranging from discovery to clinical significance.

  6. Perturbations for transient acceleration

    SciTech Connect

    Vargas, Cristofher Zuñiga; Zimdahl, Winfried; Hipólito-Ricaldi, Wiliam S. E-mail: hipolito@ceunes.ufes.br

    2012-04-01

    According to the standard ΛCDM model, the accelerated expansion of the Universe will go on forever. Motivated by recent observational results, we explore the possibility of a finite phase of acceleration which asymptotically approaches another period of decelerated expansion. Extending an earlier study on a corresponding homogeneous and isotropic dynamics, in which interactions between dark matter and dark energy are crucial, the present paper also investigates the dynamics of the matter perturbations both on the Newtonian and General Relativistic (GR) levels and quantifies the potential relevance of perturbations of the dark-energy component. In the background, the model is tested against the Supernova type Ia (SNIa) data of the Constitution set and on the perturbative level against growth rate data, among them those of the WiggleZ survey, and the data of the 2dFGRS project. Our results indicate that a transient phase of accelerated expansion is not excluded by current observations.

  7. DSN Transient Observatory

    NASA Astrophysics Data System (ADS)

    Kuiper, T. B. H.; Monroe, R. M.; White, L. A.; Miro, C. Garcia; Levin, S. M.; Majid, W. A.; Soriano, M.

    The Deep Space Network (DSN) Transient Observatory (DTO) is a signal processing facility that can monitor up to four DSN downlink bands for astronomically interesting signals. The monitoring is done commensally with reception of deep space mission telemetry. The initial signal processing is done with two CASPERa ROACH1 boards, each handling one or two baseband signals. Each ROACH1 has a 10 GBe interface with a GPU-equipped Debian Linux workstation for additional processing. The initial science programs include monitoring Mars for electrostatic discharges, radio spectral lines, searches for fast radio bursts and pulsars and SETI. The facility will be available to the scientific community through a peer review process.

  8. Unexpected transient effect.

    PubMed

    Chame, A; Villain, J

    2001-02-01

    When a grooved periodic profile cut in a crystalline surface relaxes through surface diffusion, flatter parts appear at the top and bottom in the transient state which precedes complete smoothing. This has been attributed to a tendency of successive steps of identical sign to draw closer to one another. This kind of kinetic interaction is a consequence of the finite value of the interatomic distance, and is present even if no interaction between steps is taken into account. We investigate this effect in a very simplified model, namely, a one-dimensional profile with alternating pairs of up and down steps, where no annihilation of steps is allowed. The quantitative effect is partly treated analytically.

  9. Collisional model of energy dissipation in three-dimensional granular impact

    NASA Astrophysics Data System (ADS)

    Bester, Cacey Stevens; Behringer, Robert P.

    2017-03-01

    We study the dynamic process occurring when a granular assembly is displaced by a solid impactor. The momentum transfer from the impactor to the target is shown to occur through sporadic, normal collisions of high force carrying grains at the intruder surface. We therefore describe the stopping force of the impact through a collisional-based model. To verify the model in impact experiments, we determine the forces acting on an intruder decelerating through a dense granular medium by using high-speed imaging of its trajectory. By varying the intruder shape and granular target, intruder-grain interactions are inferred from the consequent path. As a result, we connect the drag to the effect of intruder shape and grain density based on a proposed collisional model.

  10. 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.

  11. Inward particle transport at high collisionality in the Experimental Advanced Superconducting Tokamak

    SciTech Connect

    Wang, G. Q.; Ma, J.; Weiland, J.; Zang, Q.

    2013-10-15

    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. 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.

  13. Morphology of collisional nonlinear spectra in H2-Kr and H2-Xe mixtures.

    PubMed

    Głaz, Waldemar; Bancewicz, Tadeusz; Godet, Jean-Luc; Maroulis, George; Haskopoulos, Anastasios

    2013-03-28

    This article reports new results of theoretical and numerical studies of spectral features of the collision-induced hyper-Rayleigh light scattered in dihydrogen-noble gas (H2-Rg) mixtures. The most massive and polarizable scattering supermolecules with Rg = Kr and Xe have been added to the previously considered systems in order to gain a more complete insight into the evolution of the spectral properties. The symmetry adapted components of the first collisional hyperpolarizabilities are obtained by means of the quantum chemistry numerical routines supplemented with appropriate theoretical methods. Roto-translational spectral lines are calculated on the grounds of the quantum-mechanical as well as semi-classical approach. The role of particular hyperpolarizability components in forming the line shapes is discussed. The intensities of the lines are compared with those obtained for less massive scatterers. Advantages of prospective application of the new scattering systems for experimental detection of the nonlinear collisional effects are indicated.

  14. Collisional-Radiative Recombination of Ar^+ Ions with Electrons in a Flowing Afterglow Plasma.

    NASA Astrophysics Data System (ADS)

    Skrzypkowski, Miroslaw P.; Golde, Michael F.; Johnsen, Rainer

    1998-10-01

    Langmuir probe measurements of electron densities, n_e, in an Ar^+/e^- plasma are quantitatively consistent with the semi-empirical rate coefficient for collisional-radiative recombination given by Stevefelt et al.(J. Stevefelt et al., Phys. Rev A 12, 1246 (1975)) : α_cr=1.55×10-10T-0.63 + 6.0×10-9T-2.18n_e^0.37+3.8×10- 9T-4.5ne over the initial electron density range 5×10^9-5×10^10cm-3 at T=300K. Optical emission spectroscopy data reveal transitions from highly-excited states of Ar to Ar(^3P). We believe that the collisional-radiative recombination of Ar^+ ions is responsible for the presence of Ar metastable atoms in flowing afterglow plasmas.

  15. 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.

  16. Collisional relaxation in the inhomogeneous Hamiltonian mean-field model: Diffusion coefficients

    NASA Astrophysics Data System (ADS)

    Benetti, F. P. C.; Marcos, B.

    2017-02-01

    Systems of particles with long-range interactions present two important processes: first, the formation of out-of-equilibrium quasistationary states (QSS) and, second, the collisional relaxation towards Maxwell-Boltzmann equilibrium in a much longer time scale. In this paper, we study the collisional relaxation in the Hamiltonian mean-field model using the appropriate kinetic equations for a system of N particles at order 1 /N : the Landau equation when collective effects are neglected and the Lenard-Balescu equation when they are taken into account. We derive explicit expressions for the diffusion coefficients using both equations for any magnetization, and we obtain analytic expressions for highly clustered configurations. An important conclusion is that in this system collective effects are crucial in order to describe the relaxation dynamics. We compare the diffusion calculated with the kinetic equations with simulations set up to simulate the system with or without collective effects, obtaining a very good agreement between theory and simulations.

  17. 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.

  18. Generalized collisional radiative model for light elements: C: Data for the B isonuclear sequence

    NASA Astrophysics Data System (ADS)

    Loch, S. D.; Ballance, C. P.; Pindzola, M. S.; Griffin, D. C.; Colgan, J. P.; Badnell, N. R.; O'Mullane, M. G.

    2015-01-01

    A first stage collision database is assembled which contains electron-impact excitation, ionization, and recombination rate coefficients for B, B+, B2+, B3+, and B4+. The first stage database is constructed using the R-matrix with pseudostates, time-dependent close-coupling, and perturbative distorted-wave methods. A second stage collision database is then assembled which contains generalized collisional-radiative ionization, recombination, and power loss rate coefficients as a function of both temperature and density. The second stage database is constructed by solution of the collisional-radiative equations in the quasi-static equilibrium approximation using the first stage database. Both collision database stages reside in electronic form at the IAEA Labeled Atomic Data Interface (ALADDIN) database and the Atomic Data Analysis Structure (ADAS) open database.

  19. Reduction of collisional-radiative models for laser-produced argon plasmas

    NASA Astrophysics Data System (ADS)

    Abrantes, Richard June; Karagozian, Ann; Le, Hai

    2016-10-01

    The formation of a laser-induced plasma involves a variety of physical phenomena stemming from the laser-plasma interaction. A thorough understanding of these processes encourages improvement and innovation for many applications. In this work, we aim to computationally reduce a previously-developed collisional-radiative (CR) model constructed from the LANL database, which includes all of the relevant collisional and radiative processes for all the ionic stages of argon. The laser is coupled to the plasma via multiphoton ionization and inverse Bremsstrahlung, processes important for electron production and heating. The use of the CR model allows us to identify dominant mechanisms responsible for initial breakdown of the gas and thermal equilibriation processes. The results are compared with experimental data from laser-induced breakdown experiments. Research supported by the AFOSR.

  20. 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}.

  1. 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.

  2. Collisional dependence of Alfvén mode saturation in tokamaks

    NASA Astrophysics Data System (ADS)

    Zhou, Muni; White, Roscoe

    2016-12-01

    Saturation of Alfvén modes driven unstable by a distribution of high energy particles as a function of collisionality is investigated with a guiding center code, using numerical eigenfunctions produced by linear theory and numerical high energy particle distributions. The most important resonance is found and it is shown that when the resonance domain is bounded, not allowing particles to collisionlessly escape, the saturation amplitude is given by the balance of the resonance mixing time with the time for nearby particles to collisionally diffuse across the resonance width. Saturation amplitudes are in agreement with theoretical predictions as long as the mode amplitude is not so large that it produces stochastic loss from the resonance domain.

  3. Comparison of Ti/Pd/Ag, Pd/Ti/Pd/Ag and Pd/Ge/Ti/Pd/Ag contacts to n-type GaAs for electronic devices handling high current densities

    NASA Astrophysics Data System (ADS)

    Huo, Pengyun; Galiana, Beatriz; Rey-Stolle, Ignacio

    2017-04-01

    In the quest for metal contacts for electronic devices handling high current densities, we report the results of Pd/Ti/Pd/Ag and Pd/Ge/Ti/Pd/Ag contacts to n-GaAs and compare them to Ti/Pd/Ag and AuGe/Ni/Au. These metal systems have been designed with the goal of producing an electrical contact with (a) low metal–semiconductor specific contact resistance, (b) very high sheet conductance, (c) good bondability, (d) long-term durability and (e) cost-effectiveness. The structure of the contacts consists of an interfacial layer (either Pd or Pd/Ge) intended to produce a low metal–semiconductor specific contact resistance; a diffusion barrier (Ti/Pd) and a thick top layer of Ag to provide the desired high sheet conductance, limited cost and good bondability. The results show that both systems can achieve very low metal resistivity (ρ M ∼ 2 × 10‑6 Ω cm), reaching values close to that of pure bulk silver. This fact is attributed to the Ti/Pd bilayer acting as an efficient diffusion barrier, and thus the metal sheet resistance can be controlled by the thickness of the deposited silver layer. Moreover, the use of Pd as interfacial layer produces contacts with moderate specific contact resistance (ρ C ∼ 10‑4 Ω cm2) whilst the use of Pd/Ge decreases the specific contact resistance to ρ C ∼ 1.5 × 10‑7 Ω cm2, as a result of the formation of a Pd4(GaAs, Ge2) compound at the GaAs interface.

  4. 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.

  5. Possible Effects of Collisional Breakup on Mixed-Phase Deep Convection Simulated by a Spectral (Bin) Cloud Model.

    NASA Astrophysics Data System (ADS)

    Seifert, Axel; Khain, Alexander; Blahak, Ulrich; Beheng, Klaus D.

    2005-06-01

    The effects of the collisional breakup of raindrops are investigated using the Hebrew University Cloud Model (HUCM). The parameterizations, which are combined in the new breakup scheme, are those of Low and List, Beard and Ochs, as well as Brown. A sensitivity study reveals strong effects of collisional breakup on the precipitation formation in mixed-phase deep convective clouds for strong as well as for weak precipitation events. Collisional breakup reduces the number of large raindrops, increases the number of small raindrops, and, as a consequence, decreases surface rain rates and considerably reduces the speed of rain formation. In addition, it was found that including breakup can lead to a more intense triggering of secondary convective cells. But a statistical comparison with observed raindrop size distributions shows that the parameterizations might systematically overestimate collisional breakup.

  6. PD-L1 predicts poor prognosis for nasopharyngeal carcinoma irrespective of PD-1 and EBV-DNA load

    PubMed Central

    Zhou, Yajuan; Shi, Dingbo; Miao, Jingjing; Wu, Haijun; Chen, Jiewei; Zhou, Xiaoyi; Hu, Desheng; Zhao, Chong; Deng, Wuguo; Xie, Conghua

    2017-01-01

    Programmed death-1 (PD-1) is an immunosuppressive receptor functionally bound with programmed death-ligand 1 (PD-L1), which has been reported in various malignancies. However, only a few studies are available for the clinical significance of PD-1/PD-L1 in nasopharyngeal carcinoma (NPC). In this study, we aim to investigate alterations in PD-1/PD-L1 by using immunohistochemistry analysis in a cohort of consecutively enrolled NPC patients (n = 99). To further analyse the correlation between PD-1/PD-L1 and factors involved in clinico-pathology, haematologic biomarkers, EBV-DNA load and outcomes, we collected clinical data for statistical analysis. We observed that lower haemoglobin (HB) and Body Mass Index (BMI) levels were associated with high levels of PD-L1 staining in NPC patients. Importantly, our results suggested that PD-L1 might be a negative indicator for NPC patients. In contrast, a correlation between the PD-1/PD-L1 level and EBV load was not identified. Moreover, PD-1 positivity was suggested to not be significantly correlated with clinical outcomes. Taken together, our results revealed that PD-L1 might be a potential prognostic biomarker for NPC patients. However, further studies are needed to clarify the underlying mechanism of EBV status in the immunosuppression process induced by the PD-1/PD-L1 axis. PMID:28256540

  7. 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.

  8. Finite Larmor Radius and Collisional Effects on the Electron-Ion Hybrid Instability

    DTIC Science & Technology

    2013-11-18

    Particle Physics Branch Plasma Physics Division V. SoTnikoV Air Force Research Laboratory Dayton, Ohio C.l. EnloE Air Force Academy Colorado Springs...applying this theory to the plasma region surrounding hypersonic vehicles. In this plasma layer, these sorts of transverse sheared flows can exist in...a collisional plasma . While this dense layer of plasma can itself impede communications, the density structures created by the lower hybrid

  9. 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.

  10. Observation of dynamic correlations in collisional redistribution and depolarization of light

    NASA Technical Reports Server (NTRS)

    Thomann, P.; Burnett, K.; Cooper, J.

    1980-01-01

    Theory shows that to explain the polarization of light collisionally redistributed from the far line wings of an atomic transition, one must consider correlated events in which absorption during a collision, and propagation to the final Zeeman-state superposition at the end of the collision is important. Polarizations of up to about 40% have been measured in the far line wings, substantially confirming this prediction, and showing that scattering experiments cannot just be characterized by simple absorption or emission profiles.

  11. Energy Deposition into a Collisional Gas from Optical Lattices Formed in an Optical Cavity (PREPRINT)

    DTIC Science & Technology

    2008-07-02

    pp. 1344-1347 2 Kuga et al., “Novel Optical Trap of Atoms with a Doughnut Beam,” Physical Review Letters 78, (1997), pp. 4713-4716 3 Dotsenko et...other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a ...Technical Paper 3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER Energy Deposition into a Collisional Gas from

  12. Can the electron heat flux at 1 AU be collisional ? Results from kinetic simulations.

    NASA Astrophysics Data System (ADS)

    Landi, Simone; Pantellini, Filippo; Matteini, Lorenzo

    2014-05-01

    Recent results using statistically significant data of the solar wind at 1AU (see Bale et al. ApJL 769:L22, 2013) have shown that when the thermal Knudsen number, the ratio between the electron mean free path and the temperature scale height, falls below ~0.3, the electron heat flux Q does rapidly approach the classical collisional Spitzer-Harm limit Q_SH ~ T5/2 dT/dr, where T is the temperature and r the heliocentric distance. This experimental finding seems to contradict a number of theoretical works which suggest that the collisional expression for the heat flux is only guaranteed for Knudsen numbers smaller than ~0.001 (e.g. Shoub ApJ, 266, 339-369, 1983; Scudder & Karimabadi, ApJ, 770:26, 2013) . Indeed, using a fully kinetic model including the effect of Coulomb collisions and the expansion of the solar wind with heliocentric distance, we do observe that the heat flux strength approaches the collisional value for Knudsen numbers below ~0.3, in rather good agreement with the experimental data of Bale et al (2013). However, closer inspection of the variation of the plasma parameters with heliocentric distance shows that for Knudsen numbers between 0.01-0.3 the heat flux Q does NOT vary with temperature as predicted by Q_SH. We conclude that even though observations at 1 AU seem to indicate that the electron heat flux intensity Q approaches the collisional limit Q_SH for Knudsen below ~0.3, the latter is not a generally valid closure in the solar wind for Knudsen large that 0.01.

  13. 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.

  14. 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.

  15. Pd-Ag chronometry of iron meteorites: Correction of neutron capture-effects and application to the cooling history of differentiated protoplanets

    NASA Astrophysics Data System (ADS)

    Matthes, Maximilian; Fischer-Gödde, Mario; Kruijer, Thomas S.; Leya, Ingo; Kleine, Thorsten

    2015-11-01

    The short-lived 107Pd-107Ag system is a versatile tool for dating iron meteorites, but neutron capture reactions during cosmic ray-exposure might have modified Ag isotope compositions. These cosmic ray-induced effects would vary depending on the exposure time of a sample and its location within the parent meteoroid and, therefore, could bias the age information inferred from Pd-Ag isotope systematics. Our new combined Pd-Ag and Pt isotope data for iron meteorites in conjunction with model calculations reveal large cosmic ray-induced downward shifts of 107Ag/109Ag, which preclude the determination of Pd-Ag isochrons based on measured Ag isotope compositions. For the strongly irradiated iron meteorites Ainsworth (IIAB) and Carbo (IID) these shifts are similar to or even larger than the effects from radiogenic ingrowth resulting from 107Pd-decay. For the less strongly irradiated IIIAB iron meteorites Boxhole, Grant and Henbury, the cosmic ray-induced shifts are smaller than the radiogenic 107Ag excesses, but are nevertheless significant. We have developed a method to quantify the cosmic ray-induced Ag isotope shifts using a neutron capture model and Pt isotope compositions as the neutron dose monitor. After correction, Pd-Ag isochrons are obtained for all investigated iron meteorites, even for the most strongly irradiated samples. The Pd-Ag ages inferred from the isochrons are in good agreement with other chronological data for iron meteorites, indicating that our neutron capture model provides a reliable correction method for quantifying cosmic ray-induced shifts on measured Ag isotope compositions. The Pd-Ag ages for iron meteorites obtained in this and previous studies indicate rapid crystallization and cooling of the parental metal cores within a few Ma after core formation and solar system formation. Such rapid cooling can be attributed to either small parent body sizes or collisional erosion of the insulating silicate mantle from larger bodies. The collisions

  16. 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.

  17. [Efficacy of PD-1/PD-L1 immune checkpoint inhibitors and PD-L1 testing in thoracic cancers].

    PubMed

    Duruisseaux, Michaël; Rouquette, Isabelle; Adam, Julien; Cortot, Alexis; Cazes, Aurélie; Gibault, Laure; Damotte, Diane; Lantuejoul, Sylvie

    2017-02-01

    Tumoral immune environment is a major component of cancer. Its composition and its organization represent a reproducible characteristic of tumors and a validated prognostic factor. In non-small cell lung cancer (NSCLC), cytotoxic T CD8+ lymphocyte density, associated with a Th1 environment and tertiary lymphoid structures impacts survival. Tumor cell-immune cell interaction is targeted by PD1/PD-L1 inhibitors. In advanced NSCLC, PD1/PD-L1 inhibitors are more effective than second-line chemotherapy. Pembrolizumab outperforms first-line chemotherapy in NSCLC strongly positive for PD-L1. PD1/PD-L1 inhibitors are currently tested in mesothelioma and thymic tumors. PD-L1 expression evaluated with immunochemistry is the most studied predictive biomarker of PD1/PD-L1 inhibitor efficacy. Tumor and immune cell expression of PD-L1 is still difficult to evaluate because of intra-tumoral heterogeneity and expression modulation by the microenvironment. Four commercial diagnostic antibodies are in development, with differences concerning recognized epitopes, methodology of evaluation of PD-L1 expression, positivity threshold, kit and platforms used. Clinical trials in NSCLC have shown that patients with tumors strongly positive for PD-L1 derived the best clinical benefit with PD1/PD-L1 inhibitors whereas clinical benefit is less common in tumors negative for PD-L1. PD-L1 expression is not a perfect biomarker since some PD-L1 negative NSCLC respond to PD1/PD-L1 inhibitors and some PD-L1 positive NSCLC do not. PD-L1 testing is likely to be implemented in daily practice for selection of advanced NSCLC that will be treated with pembrolizumab, underscoring the relevance of ongoing harmonization studies of the use of the different antibodies available for PD-L1 testing.

  18. Modeling of Weakly Collisional Parallel Electron Transport for Edge Plasma Simulations

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    The parallel electron heat transport in a weakly collisional regime can be represented in the framework of the Landau-fluid (LF) model. Practical implementation of LF-based transport models has become possible due to the recent invention of an efficient non- spectral method for the non-local closure operators. Here the implementation of a LF based model for the parallel plasma transport is described, and the model is tested for different collisionality regimes against a Fokker-Plank code. The new method appears to represent weakly collisional parallel electron transport more accurately than the conventional flux-limiter based models; on the other hand it is computationally efficient enough to be used in tokamak edge plasma simulations. Implementation of an LF-based model for the parallel plasma transport in the UEDGE code is described, and applications to realistic divertor simulations are discussed. Work performed for U.S. DoE by LLNL under Contract DE-AC52-07NA27344.

  19. Particle transport and density peaking at low collisionality on Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Greenwald, M.; Hughes, J. W.; Mikkelsen, D.; Terry, J.

    2007-11-01

    While H-modes tend to have very flat density profiles, modest density peaking is advantageous for fusion performance. Thus robust pinch mechanisms that could allow operation with peaked profiles, in the absence of any internal particle source, are of considerable interest. Recent experiments on C-Mod^1, at low collisionality, show just such peaking and are quantitatively consistent with earlier results from ASDEX-U^2 and JET^3. By extending the range in machine size, these data break the covariance between collisionality and n/nG, the density normalized to the density limit and strongly support the primary role of collisionality in determining the profile. The implication is that ITER will have density profiles with ne( 0 )/˜1.4-1.6. The C-Mod data also show a small but statistically significant dependence of the peaking factor on the edge safety factor, q. The effect is to increase the peaking by no more than 10% when q is raised from 3.5 to 5.Initial studies of gyrokinetic simulations for these discharges will be shown. ^1M. Greenwald, submitted to Nucl. Fusion, 2007 ^2C. Angioni, et al., PRL 90, 205003, 2003 ^3H.Weisen, Nucl. Fusion 45, L1, 2005

  20. Influence of non-collisional laser heating on the electron dynamics in dielectric materials

    NASA Astrophysics Data System (ADS)

    Barilleau, L.; Duchateau, G.; Chimier, B.; Geoffroy, G.; Tikhonchuk, V.

    2016-12-01

    The electron dynamics in dielectric materials induced by intense femtosecond laser pulses is theoretically addressed. The laser driven temporal evolution of the energy distribution of electrons in the conduction band is described by a kinetic Boltzmann equation. In addition to the collisional processes for energy transfer such as electron-phonon-photon and electron-electron interactions, a non-collisional process for photon absorption in the conduction band is included. It relies on direct transitions between sub-bands of the conduction band through multiphoton absorption. This mechanism is shown to significantly contribute to the laser heating of conduction electrons for large enough laser intensities. It also increases the time required for the electron distribution to reach the equilibrium state as described by the Fermi-Dirac statistics. Quantitative results are provided for quartz irradiated by a femtosecond laser pulse with a wavelength of 800 nm and for intensities in the range of tens of TW cm-2, lower than the ablation threshold. The change in the energy deposition induced by this non-collisional heating process is expected to have a significant influence on the laser processing of dielectric materials.

  1. Collisional-radiative modeling of tungsten at temperatures of 1200–2400 eV

    DOE PAGES

    Colgan, James; Fontes, Christopher; Zhang, Honglin; ...

    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

  2. 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.

  3. 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.

  4. Effect of collisional heat transfer in ICRF power modulation experiment on ASDEX Upgrade

    NASA Astrophysics Data System (ADS)

    Tsujii, N.; D'Inca, R.; Noterdaeme, J.-M.; Bilato, R.; Bobkov, Vl. V.; Brambilla, M.; van Eester, D.; Harvey, R. W.; Jaeger, E. F.; Lerche, E. A.; Schneider, P.; ASDEX Upgrade Team

    2014-02-01

    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.

  5. Full orbit simulation of collisional transport of impurity ions in the MAST spherical tokamak

    NASA Astrophysics Data System (ADS)

    Romanelli, M.; McClements, K. G.; Cross, J.; Knight, P. J.; Thyagaraja, A.; Callaghan, J.

    2011-05-01

    Transport analysis of MAST discharges indicates that collisions are an important loss mechanism in the core of a tight aspect ratio tokamak. In the strongly varying equilibrium fields of MAST many of the assumptions of drift kinetic and neoclassical theory (e.g. small plasma inverse aspect ratio and low ratio of toroidal Larmor radius to poloidal Larmor radius) are not met by all particle species and it becomes appropriate to use full orbit analysis to evaluate heat and particle fluxes. Collisional transport of impurity ions (C6+ and W20+) has been studied using a full orbit solver, CUEBIT, to integrate the test-particle dynamics. Electromagnetic fields in MAST plasma have been modelled using the cylindrical and toroidal two-fluid codes CUTIE and CENTORI. A detailed study of the scaling of the test-particle diffusivity with collisionality in the equilibrium field reveals deviations from the standard neoclassical theory, in both the Pfirsch-Schlüter and banana regimes, and difficulties in defining a local diffusivity at low collisionalities. The effect of electric and magnetic fluctuations is also briefly addressed. It is found that field fluctuations enhance the non-diffusive nature of transport. The full orbit analysis presented here predicts levels of transport and confinement times for the examined species broadly consistent with the experimental observations.

  6. Collisional activation of ions by off-resonance irradiation in ion cyclotron resonance spectrometry

    NASA Astrophysics Data System (ADS)

    Shin, Seung Koo; Han, Seung-Jin; Seo, Jongcheol

    2009-06-01

    Collisional activation of ions in the ion cyclotron resonance (ICR) cell by short off-resonance burst irradiation (ORBI) was studied by time-resolved photodissociation of the meta-bromotoluene radical cation. Off-resonance chirp or single-frequency burst was applied for 2 ms to the probe ion in the presence of Ar buffer gas. The amount of internal energy imparted to the probe ion by collision under ORBI was precisely determined by time-resolved photodissociation spectroscopy. The rate of unimolecular dissociation of the probe ion following the photolysis at 532 nm was measured by monitoring the real-time appearance of the C7H7+ product ion. The internal energy of the probe ion was extracted from the known rate-energy curve. To help understand the collisional activation of an ion under ORBI, we simulated the radial trajectory of the ion using Green's method. The calculated radial kinetic energy was converted to the collision energy in the center-of-mass frame, and the collision frequency was estimated by using a reactive hard-sphere collision model with an ion-induced dipole potential. Both experiments and trajectory simulations suggest that chirp irradiation leads to less collisional activation of ions than other waveforms.

  7. DNA demethylation in PD-1 gene promoter induced by 5-azacytidine activates PD-1 expression on Molt-4 cells.

    PubMed

    Zhang, Min; Xiao, Xin Q; Jiang, Yong F; Liang, Yun S; Peng, Min Y; Xu, Yun; Gong, Guo Z

    2011-01-01

    The expression of the programmed death 1 (PD-1) gene is an indicator of exhausted T-cells with decreased activation and function. It remains unknown, however, whether the methylation status of the PD-1 gene promoter is associated with PD-1 expression level. This study shows the changes of PD-1 expression levels and the demethylation status of the PD-1 promoter region in Molt-4 cells under different concentrations of 5-azacytidine (5-Zac). The result demonstrated that DNA demethylation at PD-1 promoter may contribute to PD-1 overexpression.

  8. 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.

  9. Reaction-Driven Restructuring of Rh-Pd and Pt-Pd Core-Shell Nanoparticles

    SciTech Connect

    Tao, Feng; Grass, Michael E.; Zhang, Yawen; Butcher, Derek R.; Renzas, James R.; Liu, Zhi; Chung, Jen Y.; Mun, Bongjin S.; Salmeron, Miquel; Somorjai, Gabor A.

    2009-06-17

    The structure and composition of core-shell Rh{sub 0.5}Pd{sub 0.5} and Pt{sub 0.5}Pd{sub 0.5} nanoparticle catalysts were studied in situ, during oxidizing, reducing, and catalytic reactions involving NO, O{sub 2}, CO, and H{sub 2} using X-ray photoelectron spectroscopy in the Torr pressure range. The Rh{sub 0.5}Pd{sub 0.5} nanoparticles undergo dramatic and reversible changes in composition and chemical state in response to oxidizing or reducing conditions. Under oxidizing conditions the Rh atoms segregate to the shell region while in reducing atmospheres the Pd atoms diffuse to the shell region. In contrast no significant segregation of Pd or Pt atoms was found in Pt{sub 0.5}Pd{sub 0.5} nanoparticles. The distinct behavior in restructuring and chemical response of Rh{sub 0.5}Pd{sub 0.5} and Pt{sub 0.5}Pd{sub 0.5} nanoparticle catalysts under the same reaction conditions illustrates the flexibility and tunability of the structure of bimetallic nanoparticle catalysts during catalytic reactions.

  10. 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.

  11. Scaling of crystal field parameters between Pd 2REIn and Pd 2RESn

    NASA Astrophysics Data System (ADS)

    Babateen, M.; Neumann, K.-U.; Ziebeck, K. R. A.

    1995-02-01

    Experimentally it is found that crystal field (CF) parameters between the same rare earth compounds in the alloy series Pd 2REIn and Pd 2RESn (RE = rare earth element) exhibit scaling properties. A phenomenological model is put forward to explain this observation.

  12. The MWA Transients Survey (MWATS).

    NASA Astrophysics Data System (ADS)

    Bell, M.; Murphy, T.; Kaplan, D. L.; Croft, S. D.; Hancock, P.; Rowlinson, A.; Wayth, R.; Gaensler, B.; Hurley-Walker, N.; Offringa, A.; Loi, C.; Bannister, K.; Trott, C.; Marquart, J.

    2017-01-01

    We propose the continuation of the MWA transients survey to search for and monitor low frequency transient and variable radio sources in the southern sky. This proposal is aimed at commensally utilising data from the GLEAM-X (G0008) project in semester 2017-A. The aim of this commensal data acquisition is to commission long baseline observations for transient science. In particular this will involve studying the impact of the ionosphere on calibration and imaging, and developing the techniques needed to produce science quality data products. The proposed drift scans with LST locking (see G0008 proposal) are particularly exciting as we can test image subtraction for transient and variable identification. This survey is targeted at studying objects such as AGN (intrinsic and extrinsic variability), long duration synchrotron emitters, pulsars and transients of unknown origin. The maps generated from this survey will be analysed with the Variables and Slow Transients (VAST) detection pipeline. The motivation for this survey is as follows: (i) To obtain temporal data on an extremely large and robust sample of low frequency sources to explore and quantify both intrinsic and extrinsic variability; (ii) To search and find new classes of low frequency radio transients that previously remained undetected and obscured from multi-wavelength discovery; (iii) To place rigorous statistics on the occurrence of both transients and variables prior to the Australian SKA era.

  13. Summer 1993 Transient Student Report.

    ERIC Educational Resources Information Center

    Kent State Univ., Warren, OH. Office of Institutional Research.

    A study was conducted by the Trumbull Campus (TC) of Kent State University, in Ohio, to determine the motivations, objectives, and level of satisfaction of transient students, or students pursuing a degree at another institution but enrolled in courses at TC. Surveys were mailed to 50 transient students enrolled in summer 1993, with completed…

  14. Domain structures and magnetization reversal in Co/Pd and CoFeB/Pd multilayers

    NASA Astrophysics Data System (ADS)

    Sbiaa, R.; Ranjbar, M.; Åkerman, J.

    2015-05-01

    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.

  15. 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.

  16. 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.

  17. 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

  18. Search for supernarrow dibaryons via the pd{yields}ppX and pd{yields}pdX reactions

    SciTech Connect

    Kuboki, H.; Hatano, M.; Saito, T.; Sakai, H.; Sasano, M.; Yako, K.; Tamii, A.; Fujita, K.; Hatanaka, K.; Sakemi, Y.; Shimizu, Y.; Tameshige, Y.; Kamiya, J.; Kudoh, T.; Sagara, K.; Shimomoto, S.; Shiota, M.; Wakasa, T.; Maeda, Y.; Uesaka, T.

    2006-09-15

    Supernarrow dibaryons (SNDs) have been searched for by the pd{yields}ppX and pd{yields}pdX reactions at E{sub p}=295 MeV over a mass range of 1898 to 1953 MeV, where three candidates of SNDs were found at the Moscow Meson Factory. The experiment was carried out at the Research Center for Nuclear Physics using a two-arm magnetic spectrometer system and a liquid deuterium target. A good mass resolution of 1 MeV and a low background condition were achieved. No resonance structure was observed in the missing mass spectra. Upper limits of the SND production cross section were determined.

  19. 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.

  20. 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.

  1. MULTIMOMENT RADIO TRANSIENT DETECTION

    SciTech Connect

    Spitler, L. G.; Cordes, J. M.; Chatterjee, S.; Stone, J.

    2012-04-01

    We present a multimoment technique for signal classification and apply it to the detection of fast radio transients in incoherently dedispersed data. Specifically, we define a spectral modulation index in terms of the fractional variation in intensity across a spectrum. A signal whose intensity is distributed evenly across the entire band has a lower modulation index than a spectrum whose intensity is localized in a single channel. We are interested in broadband pulses and use the modulation index to excise narrowband radio frequency interference by applying a modulation index threshold above which candidate events are removed. The technique is tested both with simulations and using data from known sources of radio pulses (RRAT J1928+15 and giant pulses from the Crab pulsar). The method is generalized to coherent dedispersion, image cubes, and astrophysical narrowband signals that are steady in time. We suggest that the modulation index, along with other statistics using higher order moments, should be incorporated into signal detection pipelines to characterize and classify signals.

  2. Transient internal probe

    NASA Astrophysics Data System (ADS)

    Jarboe, Thomas R.; Mattick, Arthur T.

    1993-12-01

    The Transient Internal Probe (TIP) diagnostic is a novel method for probing the interior of hot magnetic fusion plasmas that are inaccessible with ordinary stationary probes. A small probe of magneto-optic (Verdet) material is fired through a plasma at speeds of several km/sec, illuminated by a laser beam. The beam's polarization is rotated in the probe by the local magnetic field and retroreflection back to a polarimetry detector allows determination of the B-field profile across the diameter of a plasma at a spatial resolution of better than 1-cm and an absolute B-field resolution of a few tens of Gauss. The principal components of a TIP diagnostic system were developed and tested. A two-stage light gas gun was constructed that accelerates 30-caliber projectiles to 3 km/sec, and methods were examined for stripping a lexan sabot from a probe prior to entry into a plasma. Probes of CdMnTe and FR-5 Verdet glass were fabricated, and a polarimetry system was constructed for resolving polarization to within 0.25 deg. The diagnostic was validated by measuring a static B-field with a moving (dropped) TIP probe, and finding agreement with Hall-probe measurements to within experimental accuracy (40 Gauss).

  3. Transient catalytic combustor model

    NASA Astrophysics Data System (ADS)

    Tien, J. S.

    1981-05-01

    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.

  4. PD-L1 Expression in Lung Cancer

    PubMed Central

    Yu, Hui; Boyle, Theresa A.; Zhou, Caicun; Rimm, David L.; Hirsch, Fred R.

    2017-01-01

    Immunotherapies targeted against programmed death ligand 1 (PD-L1) and its receptor (PD-1) have improved survival in a subset of patients with advanced lung cancer. PD-L1 protein expression has emerged as a biomarker that predicts which patients are more likely to respond to immunotherapy. The understanding of PD-L1 as a biomarker is complicated by the history of use of different immunohistochemistry platforms with different PD-L1 antibodies, scoring systems, and positivity cut-offs for immunotherapy clinical trials with different anti-PD-L1 and anti-PD-1 drugs. Herein, we summarize the brief history of PD-L1 as a biomarker and describe the challenges remaining to harmonize PD-L1 detection and interpretation for best patient care. PMID:27117833

  5. 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

    2014-12-02

    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.

  6. PD-1 blockage delays murine squamous cell carcinoma development.

    PubMed

    Belai, Eduardo Bertoli; de Oliveira, Carine Ervolino; Gasparoto, Thaís Helena; Ramos, Rodrigo Nalio; Torres, Sergio Aparecido; Garlet, Gustavo Pompermaier; Cavassani, Karen Angélica; Silva, João Santana; Campanelli, Ana Paula

    2014-02-01

    Engagement of programmed death-1 (PD-1) with its two ligands [programmed death ligand-1 (PD-L1) and PD-L2] has been associated with the suppression of tumor-reactive T cells; however, the underlying mechanism for this T-cell dysfunction is not clear. We hypothesized that PD-1 and PD-L1 signals are, in part, responsible for squamous cell carcinoma (SCC) escape from immune antitumor regulation by modulation of the tumor environment. In the present study, we used a multistage model of SCC to examine the role of PD-1/PD-L1 activation during tumor development. Tumor sites presented an increased percentage of CD4(+) and CD8(+) T cells expressing PD-1 when compared with non-tumorigenic control mice, whereas the expression of PD-L1 was particularly increased in F4/80(+) macrophages in tumor sites. Further, the systemic immune neutralization of PD-1 resulted in a decreased number and delayed incidence rate of papillomas followed by a differential expression of cytokeratins, suggesting that the PD-1-PD-L1 interaction contributes to the progression of SCC by downregulation of antitumor responses. In fact, blocking PD-1 increased the percentage of CD8(+) and CD4(+) T cells, and the levels of interferon-γ in the tumor sites. Our results indicated involvement of PD-1(+) T cells in SCC development and in the modulation of the inflammatory immune response.

  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. PK/PD models in antibacterial development

    PubMed Central

    Velkov, Tony; Bergen, Phillip; Lora-Tamayo, Jaime; Landersdorfer, Cornelia B.; Li, Jian

    2013-01-01

    There is an urgent need for novel antibiotics to treat life-threatening infections caused by bacterial ‘superbugs’. Validated in vitro pharmacokinetic/pharmacodynamic (PK/PD) and animal infection models have been employed to identify the most predictive PK/PD indices and serve as key tools in the antibiotic development process. The results obtained can be utilized for optimizing study designs in order to minimize the cost and duration of clinical trials. This review outlines the key in vitro PK/PD and animal infection models which have been extensively used in antibiotic discovery and development. These models have shown great potential in accelerating drug development programs and will continue to make significant contributions to antibiotic development. PMID:23871724

  9. Nitrite reduction mechanism on a Pd surface.

    PubMed

    Shin, Hyeyoung; Jung, Sungyoon; Bae, Sungjun; Lee, Woojin; Kim, Hyungjun

    2014-11-04

    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).

  10. 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.

  11. 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.

  12. 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

  13. The rapid transient surveyor

    NASA Astrophysics Data System (ADS)

    Baranec, C.; Lu, J. R.; Wright, S. A.; Tonry, J.; Tully, R. B.; Szapudi, I.; Takamiya, M.; Hunter, L.; Riddle, R.; Chen, S.; Chun, M.

    2016-07-01

    The Rapid Transient Surveyor (RTS) is a proposed rapid-response, high-cadence adaptive optics (AO) facility for the UH 2.2-m telescope on Maunakea. RTS will uniquely address the need for high-acuity and sensitive near-infrared spectral follow-up observations of tens of thousands of objects in mere months by combining an excellent observing site, unmatched robotic observational efficiency, and an AO system that significantly increases both sensitivity and spatial resolving power. We will initially use RTS to obtain the infrared spectra of 4,000 Type Ia supernovae identified by the Asteroid Terrestrial-Impact Last Alert System over a two year period that will be crucial to precisely measuring distances and mapping the distribution of dark matter in the z < 0.1 universe. RTS will comprise an upgraded version of the Robo-AO laser AO system and will respond quickly to target-of-opportunity events, minimizing the time between discovery and characterization. RTS will acquire simultaneous-multicolor images with an acuity of 0.07-0.10" across the entire visible spectrum (20% i'-band Strehl in median conditions) and <0.16" in the near infrared, and will detect companions at 0.5" at contrast ratio of 500. The system will include a high-efficiency prism integral field unit spectrograph: R = 70-140 over a total bandpass of 840-1830nm with an 8.7" by 6.0" field of view (0.15" spaxels). The AO correction boosts the infrared point-source sensitivity of the spectrograph against the sky background by a factor of seven for faint targets, giving the UH 2.2-m the H-band sensitivity of a 5.7-m telescope without AO.

  14. Transient Effects in Turbulence Modelling.

    DTIC Science & Technology

    1979-12-01

    field data are reported for recirculat- !I " " Ing water flows under steady-state and transient flow conditions in en 0I, Improved 1/15 scale FFTF ...15 scale FFTF outlet plenum test-cell. A dual-channel Laser Doppler Anemometer is used, and a unique method for performing transient measurements is...Description of Loop 26 3.1.2 Repeatable Flow Transient Generator (RFTG) 27 3.1.3 FFTF Test Cell 28 3.2 Laser Doppler Anemometer (LOA) 31 5 3.2.1 General

  15. Targeting the PD-1/PD-L1 axis in non-small cell lung cancer.

    PubMed

    Kumar, Rajiv; Collins, Dearbhaile; Dolly, Saoirse; McDonald, Fiona; O'Brien, Mary E R; Yap, Timothy A

    2016-12-23

    The last decade has witnessed rapid advances in the discovery and development of immune checkpoint inhibitors in cancer medicine, particularly drugs targeting programmed cell death 1 (PD-1) and programmed cell death ligand 1 (PD-L1) in non-small cell lung cancer (NSCLC). The proven antitumor efficacy coupled with low rates of drug-related toxicities observed, albeit idiosyncratic, with these novel immunotherapeutics have led to the registration of multiple PD-1 and PD-L1 inhibitors, such as nivolumab, pembrolizumab, and atezolizumab, in second-line advanced NSCLC, whereas durvalumab and avelumab are in late-phase clinical testing. Moreover, pembrolizumab has shown a survival advantage in the first-line setting; however, nivolumab failed to show a survival benefit possibly relating to patient selection based on PD-L1 expression. Current patient selection is based on PD-L1 expression, using the relevant companion diagnostic test, where patients with strong PD-L1 expression being more likely to respond to these novel agents. Ongoing clinical research focuses on the development of PD-1 and PD-L1 inhibitor monotherapy in neoadjuvant and adjuvant NSCLC. There is also much interest in using these drugs as a therapeutic backbone for rational combinations with other treatment modalities including cytotoxic chemotherapies in the first-line NSCLC, other immunotherapies such as cytotoxic T-lymphocyte-associated protein 4 antagonists, molecularly targeted agents including EGFR and ALK inhibitors, and radiotherapy. Concurrent treatment with radiotherapy is of particular interest owing to the potential for the abscopal effect, using radiotherapy to facilitate systemic treatment.

  16. Understanding physical developer (PD): Part I--Is PD targeting lipids?

    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 involves the selective reduction of silver onto fingermark residue. PD can develop marks on porous substrates even if they have been wet, leading to the logical, long held belief that the reagent targets the water insoluble constituents in the fingermark residue. The present research has tested this hypothesis as part of a broader study that aims to identify the targets of physical developer. Spot tests of some fatty acids, cholesterol and squalene, treated with PD, showed that only cholesterol produced significant silver deposition. PD is known to be particularly effective on aged marks, however cholesterol degrades over time. These observations indicate that PD reactivity with fingermarks cannot solely be due to the presence of cholesterol. Fingermarks were deposited on paper and washed with various organic solvents before being treated with PD. PD effectiveness was intermittent on both solvent washed and unwashed sides of both natural and groomed marks; however, it was seen to effectively develop groomed samples that had been exposed to common lipid extraction solvents, shown to have removed the lipids by visualisation using the lipid stain Nile red. PD effectiveness was most affected by exposure of samples to solvents that could dissolve water soluble components, showing that the removal of these constituents (by either water, or other solvents) decreases the amount of silver deposited on the fingermark residue by the working solution. Close observation of PD developed samples showed variation in silver deposition uniformity when comparing a developed ridge to a pore site located on that ridge. Some samples showed an absence of silver, and other showed an increase of silver at pore locations. This indicates that the material excreted by the pores on the finger has an effect on silver deposition, suggesting that PD may be specifically targeting eccrine constituents that are present along the

  17. Hydrogen storage and phase transformations in Mg-Pd nanoparticles

    NASA Astrophysics Data System (ADS)

    Callini, E.; Pasquini, L.; Rude, L. H.; Nielsen, T. K.; Jensen, T. R.; Bonetti, E.

    2010-10-01

    Microstructure refinement and synergic coupling among different phases are currently explored strategies to improve the hydrogen storage properties of traditional materials. In this work, we apply a combination of these methods and synthesize Mg-Pd composite nanoparticles by inert gas condensation of Mg vapors followed by vacuum evaporation of Pd clusters. Irreversible formation of the Mg6Pd intermetallic phase takes place upon vacuum annealing, resulting in Mg/Mg6Pd composite nanoparticles. Their hydrogen storage properties are investigated and connected to the undergoing phase transformations by gas-volumetric techniques and in situ synchrotron radiation powder x-ray diffraction. Mg6Pd transforms reversibly into different Mg-Pd intermetallic compounds upon hydrogen absorption, depending on temperature and pressure. In particular, at 573 K and 1 MPa hydrogen pressure, the metal-hydride transition leads to the formation of Mg3Pd and Mg5Pd2 phases. By increasing the pressure to 5 MPa, the Pd-richer MgPd intermetallic is obtained. Upon hydrogen desorption, the Mg6Pd phase is reversibly recovered. These phase transformations result in a specific hydrogen storage capacity associated with Mg-Pd intermetallics, which attain the maximum value of 3.96 wt % for MgPd and influence both the thermodynamics and kinetics of hydrogen sorption in the composite nanoparticles.

  18. Sulfur modification of Au via treatment with Piranha solution provides low-Pd releasing and recyclable Pd material, SAPd.

    PubMed

    Hoshiya, Naoyuki; Shimoda, Masahiko; Yoshikawa, Hideki; Yamashita, Yoshiyuki; Shuto, Satoshi; Arisawa, Mitsuhiro

    2010-06-02

    We have found in the SR-HXPS measurement of Piranha-treated Au(111)/mica that the gold surface underwent sulfur modification during this treatment, which was believed to have only removed impurities from the gold surface. We also successfully developed a practical Pd material, SAPd, whose Pd was immobilized on sulfur-modified Au. With the lowest Pd-releasing levels and high recyclability, this is one of the best Pd materials thus far developed. Because it leaches extremely low levels of Pd into reaction mixtures, removal of the residual Pd is unnecessary using SAPd, even in syntheses involving pharmaceutical ingredients.

  19. 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.

  20. State-resolved collisional quenching of highly vibrationally excited pyridine by water: The role of strong electrostatic attraction in V-->RT energy transfer

    NASA Astrophysics Data System (ADS)

    Elioff, Michael S.; Fraelich, Margaret; Sansom, Rebecca L.; Mullin, Amy S.

    1999-08-01

    We report experiments that investigate the influence of long-range attractive forces on collisional energy loss from highly vibrationally excited molecules. State-resolved studies of energy transfer from highly vibrationally excited pyridine (μ=2.2 D) to water (μ=1.8 D) in a low-pressure environment at 298 K have been performed using high-resolution transient absorption spectroscopy of water at λ≈2.7 μm. Pyridine in its ground electronic state with 37 900 cm-1 of vibrational energy was prepared by absorption of pulsed ultraviolet light (λ=266 nm) to the S1 state, followed by rapid internal conversion to the S0 state. Collisions between vibrationally excited pyridine and water that result in rotational and translational excitation of the ground vibrationless state of H2O (000) were investigated by monitoring the populations of individual rotational states of H2O (000) at short times following pyridine excitation. The infrared probe of water was the highly allowed asymmetric stretching (000→001) transition. The nascent distribution of rotationally excited H2O (000) states is well described by a thermal distribution with a rotational temperature of Trot=770±80 K. Doppler-broadened transient linewidth measurements yield the velocity distributions of the recoiling H2O (000) molecules that correspond to center-of-mass translational temperatures of Ttrans˜515 K for all water rotational states investigated. Additionally, rate constants for energy gain in individual water states were determined, yielding an integrated rate constant of k2int=1.1×10-11 cm3 mol-1 s-1 for the appearance of H2O (000) with Erot=1000-2000 cm-1. These results are compared with previous relaxation studies of excited pyrazine (μ=0 D) with water and of excited pyridine with CO2 (μ=0 D), and the influence of electrostatic attraction on the relaxation dynamics is discussed.

  1. CHARACTERIZATION OF TRANSIENT PUFF EMISSIONS ...

    EPA Pesticide Factsheets

    Symposium Paper Transient puff emissions were characterized from burning carpet charges that were fed to a pilotscale rotary kiln combustor to assess the potential impact on emissions of using post-consumer carpet as an alternative fuel in cement kilns.

  2. Fully kinetic simulations of magnetic reconnction in semi-collisional plasmas

    SciTech Connect

    Daughton, William S; Roytershteyn, Vadim S; Albright, Brian J; Yin, Lin; Bowers, Kevin J; Karimabadi, Homa

    2009-01-01

    The influence of Coulomb collisions on the dynamics of magnetic reconnection is examined using fully kinetic simulations with a Monte-Carlo treatment of the Fokker-Planck collision operator. This powerful first-principles approach offers a bridge between kinetic and fluid regimes, which may prove useful for understanding the applicability of various fluid models. In order to lay the necessary groundwork, the collision algorithm is first carefully bench marked for a homogeneous plasma against theoretical predictions for beam-plasma interactions and electrical resistivity. Next, the collisional decay of a current layer is examined as a function of guide field, allowing direct comparisons with transport theory for the parallel and perpendicular resistivity as well as the thermoelectric force. Finally, the transition between collisional and collision less reconnection is examined in neutral sheet geometry. For modest Lundquist numbers S {approx}< 1000, a distinct transition is observed when the thickness of the Sweet-Parker layers falls below the ion inertia length {delta}{sub sp} {approx}< d,. At higher Lundquist number, deviations from the Sweet-Parker scaling are observed due to the growth of plasmoids (secondary-islands) within the elongated resistive layer. In certain cases, this instability leads to the onset of fast reconnection sooner than expected from {delta}{sub sp} {approx} d, condition. After the transition to fast reconnection, elongated electron current layers are formed which are unstable to the formation of new plasmoids. The structure and time-dependence of the electron diffusion region in these semi-collisional regimes is profoundly different than reported in two-fluid simulations.

  3. Multispecies density peaking in gyrokinetic turbulence simulations of low collisionality Alcator C-Mod plasmas

    SciTech Connect

    Mikkelsen, D. R. Bitter, M.; Delgado-Aparicio, L.; Hill, K. W.; Greenwald, M.; Howard, N. T.; Hughes, J. W.; Rice, J. E.; Reinke, M. L.; Podpaly, Y.; Ma, Y.; Candy, J.; Waltz, R. E.

    2015-06-15

    Peaked density profiles in low-collisionality AUG and JET H-mode plasmas are probably caused by a turbulently driven particle pinch, and Alcator C-Mod experiments confirmed that collisionality is a critical parameter. Density peaking in reactors could produce a number of important effects, some beneficial, such as enhanced fusion power and transport of fuel ions from the edge to the core, while others are undesirable, such as lower beta limits, reduced radiation from the plasma edge, and consequently higher divertor heat loads. Fundamental understanding of the pinch will enable planning to optimize these impacts. We show that density peaking is predicted by nonlinear gyrokinetic turbulence simulations based on measured profile data from low collisionality H-mode plasma in Alcator C-Mod. Multiple ion species are included to determine whether hydrogenic density peaking has an isotope dependence or is influenced by typical levels of low-Z impurities, and whether impurity density peaking depends on the species. We find that the deuterium density profile is slightly more peaked than that of hydrogen, and that experimentally relevant levels of boron have no appreciable effect on hydrogenic density peaking. The ratio of density at r/a = 0.44 to that at r/a = 0.74 is 1.2 for the majority D and minority H ions (and for electrons), and increases with impurity Z: 1.1 for helium, 1.15 for boron, 1.3 for neon, 1.4 for argon, and 1.5 for molybdenum. The ion temperature profile is varied to match better the predicted heat flux with the experimental transport analysis, but the resulting factor of two change in heat transport has only a weak effect on the predicted density peaking.

  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. 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.

  7. Seven Principles of Highly Collaborative PD

    ERIC Educational Resources Information Center

    Lee, Michele H.

    2010-01-01

    Convening professionals--physically or virtually--is necessary but certainly not sufficient for meaningful collaboration and networking to occur. Professional development (PD) must be designed and carried out in ways that encourage a culture of sustained collegiality (Loucks-Horsley et al. 2003). This article presents seven principles for creating…

  8. On the twinning in ZnPd.

    PubMed

    Ivarsson, Dennis C A; Burkhardt, Ulrich; Heggen, Marc; Ormeci, Alim; Armbrüster, Marc

    2017-02-22

    The intermetallic compound ZnPd has demonstrated excellent catalytic properties in methanol steam reforming. While it is known that defects and microstructures influence the catalytic properties, little is known about the defects occurring in ZnPd. Due to recent advances in synthetic methods, coarse-grained ZnPd samples are accessible. This enables the detection and investigation of twinning in ZnPd by studying the twinned regions from the macroscopic scale by polarised light and electron backscattering diffraction (EBSD) down to the atomic scale by high-resolution transmission electron microscopy (HR-TEM). Twinning occurs in {101} and is coupled with a change in the c/a ratio in the vicinity of the twin boundary. Quantum chemical calculations result in only very small energy differences between the ideal and the twinned structure, explaining the experimentally observed thermal stability of the latter. The chemical bonding was investigated by the electron localizability indicator (ELI) and compared to the one in the ideal structure. The results confirm twinning along the {101} plane and demonstrate the high stability of the twin boundaries after formation.

  9. Surface Composition of NiPd Alloys

    NASA Technical Reports Server (NTRS)

    Noebe, Ronald D.; Khalil, Joe; Bozzolo, Guillermo; Gray, Hugh R. (Technical Monitor)

    2002-01-01

    Surface segregation in Ni-Pd alloys has been studied using the BFS method for alloys. Not only does the method predict an oscillatory segregation profile but it also indicates that the number of Pd-enriched surface planes can vary as a function of orientation. The segregation profiles were computed as a function of temperature, crystal face, and composition. Pd enrichment of the first layer is observed in (111) and (100) surfaces, and enrichment of the top two layers occurs for (110) surfaces. In all cases, the segregation profile shows oscillations that are actually related to weak ordering tendencies in the bulk. An atom-by-atom analysis was performed to identify the competing mechanisms leading to the observed surface behaviors. Large-scale atomistic simulations were also performed to investigate the temperature dependence of the segregation profiles as well as for analysis of the bulk structures. Finally, the observed surface behaviors are discussed in relation to the bulk phase structure of Ni-Pd alloys, which exhibit a tendency to weakly order.

  10. Terahertz generation by two cross focused laser beams in collisional plasmas

    SciTech Connect

    Sharma, R. P. Singh, Ram Kishor

    2014-07-15

    The role of two cross-focused spatial-Gaussian laser beams has been studied for the high power and efficient terahertz (THz) radiation generation in the collisional plasma. The nonlinear current at THz frequency arises on account of temperature dependent collision frequency of electrons with ions in the plasma and the presence of a static electric field (applied externally in the plasma) and density ripple. Optimisation of laser-plasma parameters gives the radiated THz power of the order of 0.23  MW.

  11. On dust ion acoustic solitary waves in collisional dusty plasmas with ionization effect

    NASA Astrophysics Data System (ADS)

    Shalaby, M.; El-Labany, S. K.; El-Shamy, E. F.; Khaled, M. A.

    2010-04-01

    The propagation of solitary waves in an unmagnetized collisional dusty plasma consisting of a negatively charged dust fluid, positively charged ions, isothermal electrons, and background neutral particles is studied. The ionization, ion loss, ion-neutral, ion-dust, and dust-neutral collisions are considered. Applying a reductive perturbation theory, a damped Korteweg-de Vries (DKdV) equation is derived. On the other hand, at a critical phase velocity, the dynamics of solitary waves is governed by a damped modified Korteweg-de Vries (DMKdV) equation. The nonlinear properties of solitary waves in the two cases are discussed.

  12. Collisional Losses, Decoherence, and Frequency Shifts in Optical Lattice Clocks with Bosons

    SciTech Connect

    Lisdat, Ch.; Winfred, J. S. R. Vellore; Middelmann, T.; Riehle, F.; Sterr, U.

    2009-08-28

    We have quantified collisional losses, decoherence and the collision shift in a one-dimensional optical lattice clock on the highly forbidden transition {sup 1}S{sub 0}-{sup 3}P{sub 0} at 698 nm with bosonic {sup 88}Sr. We were able to distinguish two loss channels: inelastic collisions between atoms in the upper and lower clock state and atoms in the upper clock state only. Based on the measured coefficients, we determine the operation parameters at which a 1D-lattice clock with {sup 88}Sr shows no degradation due to collisions on the fractional uncertainty level of 10{sup -16}.

  13. Velocity-changing collisional effects in nonlinear atomic spectroscopy and photon echo decay in gases

    NASA Technical Reports Server (NTRS)

    Herman, R. M.

    1983-01-01

    A general theory of atomic dipole coherence under the influence of collisional phase changes, inelastic effects and optically active atom velocity changes, including those due to anisotropic interactions is presented. Velocity change effects are obtained in closed form. Line shapes appear as convolutions of standard pressure broadening contours with velocity-change contours. Width and shift parameters for the He-broadened Na D lines at 2 m bar pressure, 380 K are calculated, as are He-induced photon echo decay rates for these lines. Overall agreement with xperiment is reasonably good.

  14. Dust ion acoustic solitary waves in a collisional dusty plasma with dust grains having Gaussian distribution

    SciTech Connect

    Maitra, Sarit; Banerjee, Gadadhar

    2014-11-15

    The influence of dust size distribution on the dust ion acoustic solitary waves in a collisional dusty plasma is investigated. It is found that dust size distribution changes the amplitude and width of a solitary wave. A critical wave number is derived for the existence of purely damping mode. A deformed Korteweg-de Vries (dKdV) equation is obtained for the propagation of weakly nonlinear dust ion acoustic solitary waves and the effect of different plasma parameters on the solution of this equation is also presented.

  15. Experimental evidence for collisional shock formation via two obliquely merging supersonic plasma jets

    SciTech Connect

    Merritt, Elizabeth C. Adams, Colin S.; Moser, Auna L.; Hsu, Scott C. Dunn, John P.; Miguel Holgado, A.; Gilmore, Mark A.

    2014-05-15

    We report spatially resolved measurements of the oblique merging of two supersonic laboratory plasma jets. The jets are formed and launched by pulsed-power-driven railguns using injected argon, and have electron density ∼10{sup 14} cm{sup −3}, electron temperature ≈1.4 eV, ionization fraction near unity, and velocity ≈40 km/s just prior to merging. The jet merging produces a few-cm-thick stagnation layer, as observed in both fast-framing camera images and multi-chord interferometer data, consistent with collisional shock formation [E. C. Merritt et al., Phys. Rev. Lett. 111, 085003 (2013)].

  16. Self-focusing of intense high frequency electromagnetic waves in a collisional magnetoactive plasma

    SciTech Connect

    Niknam, A. R.; Hashemzadeh, M.; Aliakbari, A.; Majedi, S.; Haji Mirzaei, F.

    2011-11-15

    The self-focusing of an intense electromagnetic beam in a collisional magnetoactive plasma has been investigated by the perturbation method. Considering the relativistic and ponderomotive nonlinearities and the first three terms of perturbation expansion for the electron density and velocity, the nonlinear wave equation is obtained. This wave equation is solved by applying the source dependent expansion method and the evolution of electromagnetic beam spot-size is discussed. It is shown that the laser spot-size decreases with increasing the collision frequency and external magnetic field strength.

  17. A Study of the Collisional Dynamics for Collisions of UF(6)(-) with Atoms and Molecules.

    DTIC Science & Technology

    1981-08-01

    DiSTRIBUTION ST ATEMENT rotfill&s Repot) fn7 -viblc ralnzA 17. 0ISrISUION ST ATEMENT (a’of a bstract entered in Stock 20, if different trom Report) IS. SUPP...molecular targets. The collisional energy range which was emphasized ranged from a few electron volts up to a (laboratory) energy in the vicinity of 1...followed by a discussion of the surface electron attachment process in which the UF ion is6 created. The former aspect of the research effort has been

  18. Revealing an intermediate region between the collisional radiofrequency plasma bulk and its sheath

    NASA Astrophysics Data System (ADS)

    Beckers, J.; Trienekens, D. J. M.; Kroesen, G. M. W.

    2015-03-01

    Experimental evidence of the existence of an intermediate region between a capacitively coupled plasma and the collisional space-charge region at its borders is presented. This proof is generated by monitoring—in an airplane carrying out parabolic flights—the trajectory of plasma-confined microparticles. Based on only primary data and without the need for a sophisticated model, our analysis concludes a sharply marked transition from the sheath region into another region with a significantly lower—yet nonzero—space-charge density, i.e., a region which is often called the presheath.

  19. Collisional-radiative recombination Ar{sup +} + e + e: Experimental study at 77-180 K

    SciTech Connect

    Kotrik, Tomas; Dohnal, Petr; Roucka, Stepan; Jusko, Pavol; Plasil, Radek; Glosik, Juraj; Johnsen, Rainer

    2011-03-15

    Rate coefficients for collisional-radiative recombination (CRR) of Ar{sup +} ions with electrons have been measured at temperatures from 77 to 180 K in a helium-buffered flowing-afterglow (Cryo-FALP) experiment at electron densities n{sub e} from 10{sup 8} to 10{sup 10} cm{sup -3}. The measured ternary rate coefficient K{sub CRR} at 77 K is (1.1{+-}0.4)x10{sup -17} cm{sup 6}s{sup -1} and the observed variation with temperature agrees well with the theoretical T{sup -4.5} dependence.

  20. Gyrokinetic simulations in general geometry and applications to collisional damping of zonal flows

    SciTech Connect

    Lin, Z.; Hahm, T.S.; Lee, W.W.; Tang, W.M.; White, R.B.

    2000-02-15

    A fully three-dimensional gyrokinetic particle code using magnetic coordinates for general geometry has been developed and applied to the investigation of zonal flows dynamics in toroidal ion-temperature-gradient turbulence. Full torus simulation results support the important conclusion that turbulence-driven zonal flows significantly reduce the turbulent transport. Linear collisionless simulations for damping of an initial poloidal flow perturbation exhibit an asymptotic residual flow. The collisional damping of this residual causes the dependence of ion thermal transport on the ion-ion collision frequency even in regimes where the instabilities are collisionless.

  1. Asteroid 4 Vesta: Dynamical and collisional evolution during the Late Heavy Bombardment

    NASA Astrophysics Data System (ADS)

    Pirani, S.; Turrini, D.

    2016-06-01

    Asteroid 4 Vesta is the only currently identified asteroid for which we possess samples in the form of meteorites. These meteorites revealed us that Vesta is a differentiated body and that its differentiation produced a relatively thin basaltic crust that survived intact over its entire collisional history. The survival of the vestan basaltic crust has long been identified as a pivotal constraint in the study of the evolution of the asteroid belt and the Solar System but, while we possess a reasonably good picture of the effects of the last 4 Ga on such a crust, little is known about the effects of earlier events like the Late Heavy Bombardment. In this work we address this gap in our knowledge by simulating the Late Heavy Bombardment on Vesta in the different dynamical scenarios proposed for the migration of the giant planets in the broad framework of the Nice Model. The results of the simulations allowed us to assess the collisional history of the asteroid during the Late Heavy Bombardment in terms of produced crater population, surface saturation, mass loss and mass gain of Vesta and number of energetic or catastrophic impacts. Our results reveal that planet-planet scattering is a dynamically favorable migration mechanism for the survival of Vesta and its crust. The number of impacts of asteroids larger than about 1 km in diameter estimated as due to the LHB is 31 ± 5, i.e. about 5 times larger than the number of impacts that would have occurred in an unperturbed main belt in the same time interval. The contribution of a possible extended belt to the collisional evolution of Vesta during the LHB is quite limited and can be quantified in 2 ± 1 impacts of asteroids with diameter greater than or equal to 1 km. The chance of energetic and catastrophic impacts is less than 10% and is compatible with the absence of giant craters dated back to 4 Ga ago and with the survival of the asteroid during the Late Heavy Bombardment. The mass loss caused by the bombardment

  2. PD-L1, PD-1, CD4, and CD8 expression in neoplastic and nonneoplastic thymus.

    PubMed

    Marchevsky, Alberto M; Walts, Ann E

    2017-02-01

    The checkpoint protein programmed cell death ligand-1 protein (PD-L1) binds to its receptor (PD-1) activating the PD-L1/PD-1 pathway, an important therapeutic target. There is limited information regarding PD-L1 and PD-1 expression in thymic lesions. Sections from nonneoplastic thymi (n = 20), thymomas World Health Organization types A, AB, B1, B2, and B3 (n = 38) and thymic squamous cell carcinoma (n = 8) were stained for PD-L1 (clone SP142; Spring BioScience), PD-1 (MRQ22; Cell Marque), CD4 (clone SPO32; Cell Marque), and CD8 (JCB117; Ventana). Immunoreactivity for each antibody was classified as focal or diffuse and scored as follows: 0, negative; 1%-5%, 1+; 6%-20%, 2+; and >20%, 3+. The proportions of cases expressing PD-L1, PD-1, CD4, and C8 at score ≥1+ were compared by diagnosis, using χ(2) statistics. PD-L1 was expressed in 90% of nonneoplastic thymi, 92% of thymomas, and 50% of carcinomas, with significantly higher scores (P < .01) in B2 and B3 thymomas and carcinomas than in AB and B1 thymomas; PD-L1 was diffuse in most B2 and B3 thymomas and focal in carcinomas. PD-1 was focally expressed, and mostly with scores 1+, in 55% of nonneoplastic thymi, 63% of thymomas, and 37.5% of carcinomas. CD4+ and CD8+ cells were diffusely distributed with scores 3+ in all lesions other than B3 thymomas and carcinomas. The latter showed CD4+ cells mostly at the interface between neoplastic cells and stroma. PD-L1 and PD-1 are not expressed in similar locations and cellular proportions in thymic lesions, raising a question as to whether the PD-L1/PD-1 pathway is an actionable therapeutic target in these lesions.

  3. Ion mobility studies of carbohydrates as group I adducts: isomer specific collisional cross section dependence on metal ion radius.

    PubMed

    Huang, Yuting; Dodds, Eric D

    2013-10-15

    Carbohydrates play numerous critical roles in biological systems. Characterization of oligosaccharide structures is essential to a complete understanding of their functions in biological processes; nevertheless, their structural determination remains challenging in part due to isomerism. Ion mobility spectrometry provides the means to resolve gas phase ions on the basis of their shape-to-charge ratios, thus providing significant potential for separation and differentiation of carbohydrate isomers. Here, we report on the determination of collisional cross sections for four groups of isomeric carbohydrates (including five isomeric disaccharides, four isomeric trisaccharides, two isomeric pentasaccharides, and two isomeric hexasaccharides) as their group I metal ion adducts (i.e., [M + Li](+), [M + Na](+), [M + K](+), [M + Rb](+), and [M + Cs](+)). In all, 65 collisional cross sections were measured, the great majority of which have not been previously reported. As anticipated, the collisional cross sections of the carbohydrate metal ion adducts generally increase with increasing metal ion radius; however, the collisional cross sections were found to scale with the group I cation size in isomer specific manners. Such measurements are of substantial analytical value, as they illustrate how the selection of charge carrier influences carbohydrate ion mobility determinations. For example, certain pairs of isomeric carbohydrates assume unique collisional cross sections upon binding one metal ion, but not another. On the whole, these data suggest a role for the charge carrier as a probe of carbohydrate structure and thus have significant implications for the continued development and application of ion mobility spectrometry for the distinction and resolution of isomeric carbohydrates.

  4. Determination of (107)Pd in Pd Recovered by Laser-Induced Photoreduction with Inductively Coupled Plasma Mass Spectrometry.

    PubMed

    Asai, Shiho; Yomogida, Takumi; Saeki, Morihisa; Ohba, Hironori; Hanzawa, Yukiko; Horita, Takuma; Kitatsuji, Yoshihiro

    2016-12-20

    Safety evaluation of a radioactive waste repository requires credible activity estimates confirmed by actual measurements. A long-lived radionuclide, (107)Pd, which can be found in radioactive wastes, is one of the difficult-to-measure nuclides and results in a deficit in experimentally determined contents. In this study, a precipitation-based separation method has been developed for the determination of (107)Pd with inductively coupled plasma mass spectrometry. The photoreduction induced by pulsed laser irradiation at 355 nm provides short-time and one-step recovery of Pd. The proposed method was verified by applying it to a spent nuclear fuel sample. To recover Pd efficiently, a natural Pd standard was employed as the Pd carrier. Taking advantage of the absence of (102)Pd in spent nuclear fuel, (102)Pd in the Pd carrier was utilized as the internal standard. The chemical yield of Pd was about 90% with virtually no impurities, allowing accurate quantification of (107)Pd. The amount of (107)Pd in the Pd precipitate was 17.3 ± 0.7 ng, equivalent to 239 ± 9 ng per mg of (238)U in the sample.

  5. The PD-1/PD-L costimulatory pathway critically affects host resistance to the pathogenic fungus Histoplasma capsulatum.

    PubMed

    Lázár-Molnár, Eszter; Gácser, Attila; Freeman, Gordon J; Almo, Steven C; Nathenson, Stanley G; Nosanchuk, Joshua D

    2008-02-19

    The PD-1 costimulatory receptor inhibits T cell receptor signaling upon interacting with its ligands PD-L1 and PD-L2. The PD-1/PD-L pathway is critical in maintaining self-tolerance. In this study, we examined the role of PD-1 in a mouse model of acute infection with Histoplasma capsulatum, a major human pathogenic fungus. In a lethal model of histoplasmosis, all PD-1-deficient mice survived infection, whereas the wild-type mice died with disseminated disease. PD-L expression on macrophages and splenocytes was up-regulated during infection, and macrophages from infected mice inhibited in vitro T cell activation. Of interest, antibody blocking of PD-1 significantly increased survival of lethally infected wild-type mice. Thus, our studies extend the role of the PD-1/PD-L pathway in regulating antimicrobial immunity to fungal pathogens. The results show that the PD-1/PD-L pathway has a key role in the regulation of antifungal immunity, and suggest that manipulation of this pathway represents a strategy of immunotherapy for histoplasmosis.

  6. Pd size effect on the gas sensing properties of Pd-loaded SnO2 in humid atmosphere.

    PubMed

    Ma, Nan; Suematsu, Koichi; Yuasa, Masayoshi; Shimanoe, Kengo

    2015-07-22

    Pd particles of different nanosizes were loaded on the SnO2 surface by using different Pd precursors for the purpose of investigating the Pd size effect on gas sensing properties in humid atmosphere. One kind of Pd-loaded SnO2 nanoparticle was characterized by smaller Pd particles (2.6 nm) with high dispersion, while another kind was characterized by larger Pd particles (5-10 nm) with low dispersion. It was found that both kinds of Pd on the SnO2 surface let the mainly adsorbed oxygen species change from O(-) to O(2-) in humid atmosphere at 350 °C. In addition, the water vapor poisoning effect on electric resistance and sensor response was greatly reduced by loading Pd. Interestingly, for the CO response at 350 °C, Pd-SnO2 with small Pd size showed almost constant sensor response with varying humidity (0.5-4 vol % H2O). While the CO response of Pd-SnO2 with large Pd size even increased with increasing amount of water vapor. Moreover, the former CO response was increased from 300 to 350 °C, but the later response decreased with increase in operating temperature. These behaviors were analyzed by temperature programed reduction (TPR) in H2 and CO atmospheres, and they were supported by the different catalytic activities of different nanosized Pd particles.

  7. Accumulation of CD5(+)CD19(+) B lymphocytes expressing PD-1 and PD-1L in hypertrophied pharyngeal tonsils.

    PubMed

    Wlasiuk, Paulina; Niedzielski, Artur; Skorka, Katarzyna; Karczmarczyk, Agnieszka; Zaleska, Joanna; Zajac, Malgorzata; Putowski, Maciej; Pac-Kozuchowska, Elzbieta; Giannopoulos, Krzysztof

    2016-11-01

    Programmed death-1 (PD-1) is one of the most important inhibitory co-receptors expressed predominantly on activated T and B lymphocytes whose expression could be sustained by permanent antigenic stimulation accompanying chronic or recurrent tonsillitis. The expression of PD-1 and PD-1L was analyzed using flow cytometry on hypertrophied tonsils collected from 57 children. We observed high expression of PD-1 and PD-1L on certain lymphocytes subpopulations of hypertrophied tonsils; among T cells, the expression of PD-1 on protein level was higher on CD4(+) cells (70.3 %) than on CD8(+) cells (35 %). Interestingly, a limited expression of PD-1 was observed on CD19(+) B lymphocytes (6.5 %), while CD5(+)CD19(+) B cells overexpressed PD-1 (52.5 %). Moreover, the expression of PD-1L was also higher on CD5(+)CD19(+) B cells (16.5 %) than on CD19(+) B cells (3.5 %) and on CD4(+) T cells (20 %) than on CD8(+) T cells (10 %). PD-1 and PD-1L expressions correlated only on CD5(+)CD19(+) cells. In conclusion, high expression of PD-1 and PD-1L on T and B cells could represent hallmark of immune system adaptation to chronic antigenic exposition in patients with tonsillitis.

  8. Double beta decays into excited states in 110Pd and 102Pd

    NASA Astrophysics Data System (ADS)

    Lehnert, B.; Andreotti, E.; Degering, D.; Hult, M.; Laubenstein, M.; Wester, T.; Zuber, K.

    2016-11-01

    A search for double beta decays of {}110{Pd} and {}102{Pd} into excited states of the daughter nuclides has been performed using three ultra-low background gamma-spectrometry measurements in the Felsenkeller laboratory, Germany, the HADES laboratory, Belgium and at the LNGS, Italy. The combined Bayesian analysis of the three measurements sets improved half-life limits for the 2νββ and 0νββ decay modes of the {2}1+, {0}1+ and {2}2+ transitions in {}110{Pd} to 2.9\\cdot {10}20 yr, 4.0\\cdot {10}20 yr and 3.0\\cdot {10}20 yr, respectively, and in {}102{Pd} to 7.6\\cdot {10}18 yr, 8.8\\cdot {10}18 yr and 1.4\\cdot {10}19 yr, respectively, with 90% credibility.

  9. 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

  10. 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.

  11. PD-L1 expression and prognostic impact in glioblastoma

    PubMed Central

    Nduom, Edjah K.; Wei, Jun; Yaghi, Nasser K.; Huang, Neal; Kong, Ling-Yuan; Gabrusiewicz, Konrad; Ling, Xiaoyang; Zhou, Shouhao; Ivan, Cristina; Chen, Jie Qing; Burks, Jared K.; Fuller, Greg N.; Calin, George A.; Conrad, Charles A.; Creasy, Caitlin; Ritthipichai, Krit; Radvanyi, Laszlo; Heimberger, Amy B.

    2016-01-01

    Background Therapeutic targeting of the immune checkpoints cytotoxic T-lymphocyte-associated molecule-4 (CTLA-4) and PD-1/PD-L1 has demonstrated tumor regression in clinical trials, and phase 2 trials are ongoing in glioblastoma (GBM). Previous reports have suggested that responses are more frequent in patients with tumors that express PD-L1; however, this has been disputed. At issue is the validation of PD-L1 biomarker assays and prognostic impact. Methods Using immunohistochemical analysis, we measured the incidence of PD-L1 expression in 94 patients with GBM. We categorized our results according to the total number of PD-L1-expressing cells within the GBMs and then validated this finding in ex vivo GBM flow cytometry with further analysis of the T cell populations. We then evaluated the association between PD-L1 expression and median survival time using the protein expression datasets and mRNA from The Cancer Genome Atlas. Results The median percentage of PD-L1-expressing cells in GBM by cell surface staining is 2.77% (range: 0%–86.6%; n = 92), which is similar to the percentage found by ex vivo flow cytometry. The majority of GBM patients (61%) had tumors with at least 1% or more PD-L1-positive cells, and 38% had at least 5% or greater PD-L1 expression. PD-L1 is commonly expressed on the GBM-infiltrating T cells. Expression of both PD-L1 and PD-1 are negative prognosticators for GBM outcome. Conclusions The incidence of PD-L1 expression in GBM patients is frequent but is confined to a minority subpopulation, similar to other malignancies that have been profiled for PD-L1 expression. Higher expression of PD-L1 is correlated with worse outcome. PMID:26323609

  12. Poplar PdC3H17 and PdC3H18 are direct targets of PdMYB3 and PdMYB21, and positively regulate secondary wall formation in Arabidopsis and poplar.

    PubMed

    Chai, Guohua; Qi, Guang; Cao, Yingping; Wang, Zengguang; Yu, Li; Tang, Xianfeng; Yu, Yanchong; Wang, Dian; Kong, Yingzhen; Zhou, Gongke

    2014-07-01

    Wood biomass is mainly made of secondary cell walls, whose formation is controlled by a multilevel network. The tandem CCCH zinc finger (TZF) proteins involved in plant secondary wall formation are poorly understood. Two TZF genes, PdC3H17 and PdC3H18, were isolated from Populus deltoides and functionally characterized in Escherichia coli, tobacco, Arabidopsis and poplar. PdC3H17 and PdC3H18 are predominantly expressed in cells of developing wood, and the proteins they encode are targeted to cytoplasmic foci. Transcriptional activation assays showed that PdMYB2/3/20/21 individually activated the PdC3H17 and PdC3H18 promoters, but PdMYB3/21 were most significant. Electrophoretic mobility shift assays revealed that PdMYB3/21 bound directly to the PdC3H17/18 promoters. Overexpression of PdC3H17/18 in poplar increased secondary xylem width and secondary wall thickening in stems, whereas dominant repressors of them had the opposite effects on these traits. Similar alteration in secondary wall thickening was observed in their transgenic Arabidopsis plants. qRT-PCR results showed that PdC3H17/18 regulated the expression of cellulose, xylan and lignin biosynthetic genes, and several wood-associated MYB genes. These results demonstrate that PdC3H17 and PdC3H18 are the targets of PdMYB3 and PdMYB21 and are an additional two components in the regulatory network of secondary xylem formation in poplar.

  13. 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.

  14. 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.

  15. Targeting PD-1/PD-L1 in lung cancer: current perspectives

    PubMed Central

    González-Cao, María; Karachaliou, Niki; Viteri, Santiago; Morales-Espinosa, Daniela; Teixidó, Cristina; Sánchez Ruiz, Jesús; Molina-Vila, Miquel Ángel; Santarpia, Mariacarmela; Rosell, Rafael

    2015-01-01

    Increased understanding of tumor immunology has led to the development of effective immunotherapy treatments. One of the most important advances in this field has been due to pharmacological design of antibodies against immune checkpoint inhibitors. Anti-PD-1/PD-L1 antibodies are currently in advanced phases of clinical development for several tumors, including lung cancer. Results from Phase I–III trials with anti-PD-1/PD-L1 antibodies in non-small-cell lung cancer have demonstrated response rates of around 20% (range, 16%–50%). More importantly, responses are long-lasting (median duration of response, 18 months) and fast (50% of responses are detected at time of first tumor evaluation) with very low grade 3–4 toxicity (less than 5%). Recently, the anti-PD-1 antibody pembrolizumab received US Food and Drug Administration (FDA) breakthrough therapy designation for treatment of non-small-cell lung cancer, supported by data from a Phase Ib trial. Another anti-PD-1 antibody, nivolumab, has also been approved for lung cancer based on survival advantage demonstrated in recently released data from a Phase III trial in squamous cell lung cancer. PMID:28210151

  16. Forward pd elastic scattering and total spin-dependent pd cross sections at intermediate energies

    SciTech Connect

    Uzikov, Yu. N.; Haidenbauer, J.

    2009-02-15

    Spin-dependent total pd cross sections are considered using the optical theorem. For this aim the full spin dependence of the forward pd elastic scattering amplitude is considered in a model independent way. The single-scattering approximation is used to relate this amplitude to the elementary amplitudes of pp and pn scattering and the deuteron form factor. A formalism allowing to take into account Coulomb-nuclear interference effects in polarized pd cross sections is developed. Numerical calculations for the polarized total pd cross sections are performed at beam energies 20-300 MeV using the NN interaction models developed by the Juelich group. Double-scattering effects are estimated within the Glauber approach and found to be in the order of 10-20%. Existing experimental data on differential pd cross sections are in good agreement with the performed Glauber calculations. It is found that for the used NN models the total longitudinal and transversal pd cross sections are comparable in absolute value to those for pp scattering.

  17. 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.

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

    SciTech Connect

    Moser, Auna L. Hsu, Scott C.

    2015-05-15

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

  19. Effect of PD-1: PD-L1 in Invariant Natural Killer T-Cell Emigration and Chemotaxis Following Sepsis.

    PubMed

    Young, John S; Heffernan, Daithi S; Chung, Chun-Shiang; Kettenmann, Maude L; Young, Whitney A; Guillen, Valeria Sanabria; Cioffi, William G; Ayala, Alfred

    2016-05-01

    Invariant natural killer T-cells (iNKT) are a subset of T-cells that play a regulatory role in sepsis. Following cecal ligation and puncture (CLP), iNKT cells emigrate from the liver and into the circulation and peritoneum in a manner dependent upon coinhibitory molecule Programmed Cell Death Receptor 1 (PD-1). We hypothesized that the effect of PD-1 on iNKT-cell emigration was dependent upon the direct PD-1:PD-L1 interaction, and that PD-1 and PD-L1 would play a role in chemotaxis and chemokine receptor expression. Adoptive transfer of Vybrant-labeled wild-type (WT) cells showed the donor iNKT cells migrated from the liver to the peritoneum following CLP, but PD-L1 deficient donor iNKT cells did not. In a chemotaxis assay, WT-iNKT cells chemotaxed to CXCL12, but PD-1 and PD-L1 deficient iNKT cells did not. Using flow cytometry to evaluate chemokine receptor expression, peritoneal iNKT expression of CXCR4 increased following CLP in the WT, PD-1, and PD-L1 deficient animals, and CXCR6 increased in the WT and PD-1 deficient animals. In conclusion here we document that the hepatic emigration of iNKT cells following CLP to the peritoneum appears dependent upon the direct PD-1:PD-L1 interaction; however, although PD-1 and PD-L1 appear to play a role in chemotaxis, this is unlikely a reflection of iNKT-cell chemokine receptor expression changes.

  20. A highly Lewis-acidic Pd(IV) surface on Pd@SiO2 nanocatalysts for hydroalkoxylation reactions.

    PubMed

    Kim, Mijong; Lee, Suyeon; Kim, Kiseong; Shin, Dongwoo; Kim, Hyunwoo; Song, Hyunjoon

    2014-12-11

    The Pd(iv) species, known to be critical intermediates in homogeneous catalysis, were successfully generated on the surface of Pd nanocatalysts via oxidation with iodobenzene dichloride (PhICl2) or N-chlorosuccinimide (NCS). In particular, the Pd@SiO2 yolk-shell nanocatalyst activated by PhICl2 showed high reactivity and superior stability to the other Pd-based catalysts for hydroalkoxylation reactions even at 25 °C.

  1. Computational model of collisional-radiative nonequilibrium plasma in an air-driven type laser propulsion

    SciTech Connect

    Ogino, Yousuke; Ohnishi, Naofumi

    2010-05-06

    A thrust power of a gas-driven laser-propulsion system is obtained through interaction with a propellant gas heated by a laser energy. Therefore, understanding the nonequilibrium nature of laser-produced plasma is essential for increasing available thrust force and for improving energy conversion efficiency from a laser to a propellant gas. In this work, a time-dependent collisional-radiative model for air plasma has been developed to study the effects of nonequilibrium atomic and molecular processes on population densities for an air-driven type laser propulsion. Many elementary processes are considered in the number density range of 10{sup 12}/cm{sup 3}<=N<=10{sup 19}/cm{sup 3} and the temperature range of 300 K<=T<=40,000 K. We then compute the unsteady nature of pulsively heated air plasma. When the ionization relaxation time is the same order as the time scale of a heating pulse, the effects of unsteady ionization are important for estimating air plasma states. From parametric computations, we determine the appropriate conditions for the collisional-radiative steady state, local thermodynamic equilibrium, and corona equilibrium models in that density and temperature range.

  2. Two-Dimensional Fluid Simulation of Collisional Plasma Sheath over rf Powered Electrode with Cylindrical Hole

    NASA Astrophysics Data System (ADS)

    Hou, Lujing; Wang, Younian; Z, L. Miskvic

    2004-08-01

    The characteristics of collisional radio-frequency (rf) sheath dynamics over an electrode with a cylindrical hole is simulated by means of a self-consistent model which consists of two-dimensional time-dependent fluid equations coupled with Poisson equation. In addition, an equivalent-circuit model is coupled to the fluid equations in order to self-consistently determine relationship between the instantaneous potential at the rf-biased electrode and the sheath thickness. Two-dimensional profiles of the potential, the ion fluid velocity, and the distributions of the ion and electron densities within the sheath are computed under various discharge conditions, such as the discharge powers and the gas pressures. The results show that the existence of the cylindrical hole on the electrode significantly affects the sheath structure and generates a potential trap in the horizontal direction, which is particularly strong when the sheath thickness is comparable to the depth of the hole. Moreover, it is found that the collisional effects have a significant influence on the sheath characteristics.

  3. Collisional-radiative model in air for earth re-entry problems

    SciTech Connect

    Bultel, Arnaud; Cheron, Bruno G.; Bourdon, Anne; Motapon, Ousmanou; Schneider, Ioan F.

    2006-04-15

    A nonlinear time-dependent two-temperature collisional-radiative model for air plasma has been developed for pressures between 1 kPa and atmospheric pressure to be applied to the flow conditions of space vehicle re-entry into the Earth's atmosphere. The model consists of 13 species: N{sub 2}, O{sub 2}, N, O, NO, N{sub 2}{sup +}, O{sub 2}{sup +}, N{sup +}, O{sup +}, NO{sup +}, O{sub 2}{sup -}, O{sup -} in their ground state and major electronic excited states and of electrons. Many elementary processes are considered given the temperatures involved (up to 10 000 K). Time scales to reach the final nonequilibrium or equilibrium steady states are derived. Then we apply our model to two typical re-entry situations and show that O{sub 2}{sup -} and O{sup -} play an important role during the ionization phase. Finally, a comparison with existing reduced kinetic mechanisms puts forward significant discrepancies for high velocity flows when the flow is in chemical nonequilibrium and smaller discrepancies when the flow is close to chemical equilibrium. This comparison illustrates the interest of using a time-dependent collisional-radiative model to validate reduced kinetic schemes for the relevant time scales of the flows studied.

  4. Collisional heating of a plasma column slowly forced across a squeeze potential

    NASA Astrophysics Data System (ADS)

    Dubin, D. H. E.

    2016-10-01

    When equilibrium plasmas have two or more locally-trapped particle populations, perturbations to the equilibrium can produce phase-space discontinuities in the distribution function that strongly enhance transport, plasma loss, and wave damping. This poster presents a simple version of this process, wherein a plasma is heated as it is slowly forced back and forth across a squeeze potential (at a frequency ω that is small compared to the particle bounce frequency) that traps particles on either side of the squeeze. Adiabatic theory is developed for the distribution function, showing that trapped and passing particles have different responses to the forcing that produces a collisional boundary layer at the separatrix. Expressions for both the adiabatic and non-adiabatic distribution functions are presented, and the heating rate caused by the collisional boundary layer at the separatrix is derived. The heating is proportional to √ (ν ω) , where ν is the collision rate. Supported by NSF Grant PHY-1414570, and DOE Grants DE-SC0002451 and DE-SC0008693.

  5. Alpine Post-Collisional Orogeny: topics of debate and possible targets for AlpArray research

    NASA Astrophysics Data System (ADS)

    Kissling, Edi

    2016-04-01

    In all aspects, the Alps are by far the best documented orogen. Within their only 1000km lengths from Nice to Vienna, the Alps exhibit an extraordinary variation in structure along strike and from surface to great depth. The modern well-accepted mountain building concept calls for a material flux carefully balanced by mantle flow, plate convergence, subduction, crustal delamination, surface topography, uplift and erosion. The Alpine data set provides a basis to relate subduction processes with Penninic nappes evolution and overthrusting of Austroalpine lid, collision and oceanic slab break-off with build-up of topography, and post-collisional slab rollback and isostatic rebound due to erosional unloading to exhumation of deep European basement structures such as Tauern and Aar massiv. Temporal and spatial variations and relative importance of these processes and their relation to the overall convergence between the Adriatic/Africa and European continental plates, however, are still poorly understood and remain matters of debate. While the AlpArray Seismic Experiment will provide new geophysical information of unprecedented resolution and reliability, discussions and interdisciplinary earth science research among AlpArray community targeted at key questions will lead to a better understanding of collisional orogeny in general and Alpine evolution in particular.

  6. Paleogene Pseudoleucite Phonolites in South Tibet: Constrains on the Pre-collisional Mantle Characteristics

    NASA Astrophysics Data System (ADS)

    Qi, Yue; Gou, GuoNing; Wang, Qiang; Jiang, ZiQi

    2016-04-01

    Post-collisional (25-8Ma) ultra-potassic rocks occur along the NS-trending grabens or rifts in southern Tibet, which have been linked to the onset of east-west extensional stresses as the surface uplift of the Tibetan Plateau reached a near-maximum elevation. However, the petrogenesis of these rocks, especially source of enriched Sr-Nd isotopic compositions, remains controversial. Here we report on the Paleogene silicate-unsaturated pseudoleucite phonolite dike, in the Rongniduo area of central Lhasa terrane. Samples from this 62.7 ± 5.3Ma (in-suit SIMS Apatite U-Pb age) dike have distinctly more depleted whole rock Sr-Nd ((87Sr/86Sr)i = 0.7064 to 0.7062, ɛNd(t) = -1.5 to 0.4) isotopic composition, than those ((87Sr/86Sr)i = 0.7128 to 0.7406, ɛNd(t) = -18.0 to -12.4) of Miocene (25-8 Ma) ultrapotassic rocks in the central Lhasa subterrane, respectively. We suggest that these ~62 Ma pseudoleucite phonolites could be derived from the enriched mantle metasomatized by subducted Tethyan oceanic materials, which provides important constraints on pre-collisional mantle characteristics beneath the Lhasa Block. Therefore, our new data indicate that the Miocene ultrapotassic rocks with the enriched Sr-Nd isotopic composition were most probably derived from a mantle source metasomatized by subducted Indian continental materials.

  7. Collisional damping of helicon waves in a high density hydrogen linear plasma device

    NASA Astrophysics Data System (ADS)

    Caneses, Juan F.; Blackwell, Boyd D.

    2016-10-01

    In this paper, we investigate the propagation and damping of helicon waves along the length (50 cm) of a helicon-produced 20 kW hydrogen plasma ({{n}\\text{e}}˜ 1-2 × 1019 m-3, {{T}\\text{e}}˜ 1-6 eV, H2 8 mTorr) operated in a magnetic mirror configuration (antenna region: 50-200 G and mirror region: 800 G). Experimental results show the presence of traveling helicon waves (4-8 G and {λz}˜ 10-15 cm) propagating away from the antenna region which become collisionally absorbed within 40-50 cm. We describe the use of the WKB method to calculate wave damping and provide an expression to assess its validity based on experimental measurements. Theoretical calculations are consistent with experiment and indicate that for conditions where Coulomb collisions are dominant classical collisionality is sufficient to explain the observed wave damping along the length of the plasma column. Based on these results, we provide an expression for the scaling of helicon wave damping relevant to high density discharges and discuss the location of surfaces for plasma-material interaction studies in helicon based linear plasma devices.

  8. PLANETARY CORE FORMATION WITH COLLISIONAL FRAGMENTATION AND ATMOSPHERE TO FORM GAS GIANT PLANETS

    SciTech Connect

    Kobayashi, Hiroshi; Krivov, Alexander V.; Tanaka, Hidekazu

    2011-09-01

    Massive planetary cores ({approx}10 Earth masses) trigger rapid gas accretion to form gas giant planets such as Jupiter and Saturn. We investigate the core growth and the possibilities for cores to reach such a critical core mass. At the late stage, planetary cores grow through collisions with small planetesimals. Collisional fragmentation of planetesimals, which is induced by gravitational interaction with planetary cores, reduces the amount of planetesimals surrounding them, and thus the final core masses. Starting from small planetesimals that the fragmentation rapidly removes, less massive cores are formed. However, planetary cores acquire atmospheres that enlarge their collisional cross section before rapid gas accretion. Once planetary cores exceed about Mars mass, atmospheres significantly accelerate the growth of cores. We show that, taking into account the effects of fragmentation and atmosphere, initially large planetesimals enable formation of sufficiently massive cores. On the other hand, because the growth of cores is slow for large planetesimals, a massive disk is necessary for cores to grow enough within a disk lifetime. If the disk with 100 km sized initial planetesimals is 10 times as massive as the minimum mass solar nebula, planetary cores can exceed 10 Earth masses in the Jovian planet region (>5 AU).

  9. Boltzmann rovibrational collisional coarse-grained model for internal energy excitation and dissociation in hypersonic flows.

    PubMed

    Munafò, A; Panesi, M; Magin, T E

    2014-02-01

    A Boltzmann rovibrational collisional coarse-grained model is proposed to reduce a detailed kinetic mechanism database developed at NASA Ames Research Center for internal energy transfer and dissociation in N(2)-N interactions. The coarse-grained model is constructed by lumping the rovibrational energy levels of the N(2) molecule into energy bins. The population of the levels within each bin is assumed to follow a Boltzmann distribution at the local translational temperature. Excitation and dissociation rate coefficients for the energy bins are obtained by averaging the elementary rate coefficients. The energy bins are treated as separate species, thus allowing for non-Boltzmann distributions of their populations. The proposed coarse-grained model is applied to the study of nonequilibrium flows behind normal shock waves and within converging-diverging nozzles. In both cases, the flow is assumed inviscid and steady. Computational results are compared with those obtained by direct solution of the master equation for the rovibrational collisional model and a more conventional multitemperature model. It is found that the proposed coarse-grained model is able to accurately resolve the nonequilibrium dynamics of internal energy excitation and dissociation-recombination processes with only 20 energy bins. Furthermore, the proposed coarse-grained model provides a superior description of the nonequilibrium phenomena occurring in shock heated and nozzle flows when compared with the conventional multitemperature models.

  10. Band-structure-based collisional model for electronic excitations in ion-surface collisions

    SciTech Connect

    Faraggi, M.N.; Gravielle, M.S.; Alducin, M.; Silkin, V.M.; Juaristi, J.I.

    2005-07-15

    Energy loss per unit path in grazing collisions with metal surfaces is studied by using the collisional and dielectric formalisms. Within both theories we make use of the band-structure-based (BSB) model to represent the surface interaction. The BSB approach is based on a model potential and provides a precise description of the one-electron states and the surface-induced potential. The method is applied to evaluate the energy lost by 100 keV protons impinging on aluminum surfaces at glancing angles. We found that when the realistic BSB description of the surface is used, the energy loss obtained from the collisional formalism agrees with the dielectric one, which includes not only binary but also plasmon excitations. The distance-dependent stopping power derived from the BSB model is in good agreement with available experimental data. We have also investigated the influence of the surface band structure in collisions with the Al(100) surface. Surface-state contributions to the energy loss and electron emission probability are analyzed.

  11. Finite orbit width effect in ion collisional transport in TJ-II

    SciTech Connect

    Velasco, J. L.; Tarancon, A.; Castejon, F.

    2009-05-15

    The validity of the traditional local diffusive approach and of the use of monoenergetic calculations has been studied for the stellarator TJ-II [Alejaldre et al., Fusion Technol. 17, 131 (1990)]: it is shown to be doubtful, under some circumstances, even in a purely collisional description of transport. The diffusion in physical space starting from Dirac-delta-like initial conditions has been studied using the code Integrator of Stochastic Differential Equations for Plasmas by Castejon et al. [Plasma Phys. Controlled Fusion 49, 753 (2007)]. Particles may experience large radial excursions from their original magnetic surfaces in a single collisional time. The contribution of these particles to the flux may make it nondiffusive; non-Gaussian density distributions, characterized by long tails, are observed. In the velocity space, there are important variations in the average particle kinetic energy after one collision time. We discuss the effect of this fact over the calculation of monoenergetic transport coefficients and their convolution. A simple analysis based on Hurst exponents has shown nevertheless that the description of transport by means of a pinch term and an effective transport coefficient is more correct than expected.

  12. Low Collisionality Neoclassical Toroidal Viscosity in Tokamaks and Quasi-symmetric Stellarators

    NASA Astrophysics Data System (ADS)

    Cole, A. J.; Hegna, C. C.; Callen, J. D.

    2008-11-01

    Non-resonant magnetic perturbations can affect plasma rotation in toroidally confined plasmas through their modification to |B|. Variations along a field line induce nonambipolar radial transport and produce a global neoclassical toroidal viscous force [NTV]. In this work, previously calculated radial particle fluxes for the low-collisionality ``ν'' and ``1/ν'' regimes [1] are unified into a single particle flux (or toroidal viscous force). Provided pitch-angle scattering dominates over collisional energy exchange, the energy component of phase space can be decoupled into independent regions (E >Ec. for ν regime, E < Ec for 1/ν regime, with Ec determined by .νi(Ec) =ɛ,E) within which the perturbed distribution function can be calculated similar to [1]. Using a technique first employed in axisymmetric neoclassical theory [2], the smoothed particle flux is constructed by summing the partial contributions from ν and 1/ν banana drift effects respectively. The complete NTV force is expressed in terms of the equilibrium flows and a temperature-gradient-determined ``intrinsic'' flow. [1] K.C. Shaing, Phys. Plasmas, 10, 1443 (2003). [2] K.T. Tsang, and J.D. Callen, Phys. Fluids 19, 667 (1976).

  13. Fokker-Planck model for collisional loss of fast ions in tokamaks

    NASA Astrophysics Data System (ADS)

    Yavorskij, V.; Goloborod'ko, V.; Schoepf, K.

    2016-11-01

    Modelling of the collisional loss of fast ions from tokamak plasmas is important from the point of view of the impact of fusion alphas and neutral beam injection ions on plasma facing components as well as for the development of diagnostics of fast ion losses [1-3]. This paper develops a Fokker-Planck (FP) method for the assessment of distributions of collisional loss of fast ions as depending on the coordinates of the first wall surface and on the velocities of lost ions. It is shown that the complete 4D drift FP approach for description of fast ions in axisymmetric tokamak plasmas can be reduced to a 2D FP problem for lost ions with a boundary condition delivered by the solution of a 3D boundary value problem for confined ions. Based on this newly developed FP approach the poloidal distribution of neoclassical loss, depending on pitch-angle and energy, of fast ions from tokamak plasma may be examined as well as the contribution of this loss to the signal detected by the scintillator probe may be evaluated. It is pointed out that the loss distributions obtained with the novel FP treatment may serve as an alternative approach with respect to Monte-Carlo models [4, 5] commonly used for simulating fast ion loss from toroidal plasmas.

  14. Collisional dust production in extrasolar discs: a new dynamical and photometric model

    NASA Astrophysics Data System (ADS)

    Thebault, P.; Augereau, J.-C.

    2003-05-01

    In most extrasolar discs, the observed dust is believed to be produced by collisional cascades starting at (at least) kilometre-sized planetesimals. The numerical studies of Thebault et al. (A&A 2003) have shown on a peculiar example, the inner Beta-Pictoris disc, that the collisional size distribution from micron-sized grains to planetesimals might significantly depart from the classical dN α r-3.5dr power law. The main reason for this departure is the specific behaviour of the smallest grains, i.e. stellar radiation blow-out size limit and highly eccentric orbits, which indirectly affects the whole size distribution. We extend our approach to the more general case of any collisionaly produced dust disc. We consider mutualy interacting concentric annuli with a collisionaly evolving size distribution ranging from the blow-out size to 50 km objects. Realistic grain optical properties are taken into account in order to derive scattered light and thermal images. Complete S.E.D. profiles are also derived and compared to observational data. Preliminary results are presented for the β -Pic system and for other well known discs.

  15. Collisional effects on the numerical recurrence in Vlasov-Poisson simulations

    SciTech Connect

    Pezzi, Oreste; Valentini, Francesco; Camporeale, Enrico

    2016-02-15

    The initial state recurrence in numerical simulations of the Vlasov-Poisson system is a well-known phenomenon. Here, we study the effect on recurrence of artificial collisions modeled through the Lenard-Bernstein operator [A. Lenard and I. B. Bernstein, Phys. Rev. 112, 1456–1459 (1958)]. 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 an Eulerian collisional Vlasov-Poisson code. It is found that, despite being routinely used, an artificial collisionality is not a viable way of preventing recurrence in numerical simulations without compromising the kinetic nature of the solution. Moreover, it is shown how numerical effects associated to the generation of fine velocity scales can modify the physical features of the system evolution even in nonlinear regime. This means that filamentation-like phenomena, usually associated with low amplitude fluctuations contexts, can play a role even in nonlinear regime.

  16. Measurement of electron impact collisional excitation cross sections of Ni to Ge-like gold

    NASA Astrophysics Data System (ADS)

    May, M. J.; Beiersdorfer, P.; Jordan, N.; Scofield, J. H.; Reed, K. J.; Brown, G. V.; Hansen, S. B.; Porter, F. S.; Kelley, R.; Kilbourne, C. A.; Boyce, K. R.

    2017-03-01

    We have measured the collisional excitation cross sections for the 3d→4f and 3d→5f excitations in Au ions near the Ni-like charge state by using beam plasmas created in the Livermore electron beam ion trap EBIT-I. The cross sections have been experimentally determined at approximately 1, 2 and 3 keV above the threshold energy, ET, for the 3d→4f excitations (ET ˜ 2.5 keV) and at approximately 0.1, 1 and 2 keV above the threshold energy for the 3d→5f excitations (ET ˜ 3.3 keV). The cross section measurements were made possible by using the GSFC x-ray microcalorimeter at the Livermore EBIT facility. The absolute cross sections are determined from the ratio of the intensity of the collisionally excited bound-bound transitions to the intensity of the radiative recombination lines produced in EBIT-I plasmas. The effects of polarization and Auger decay channels are accounted for in the cross section determination. Measured cross sections are compared with those from HULLAC, DWS and FAC calculations. The measurements demonstrate that some errors exist in the calculated excitation cross sections.

  17. Secondary island formation in collisional and collisionless kinetic simulations of magnetic reconnection

    SciTech Connect

    Dayton, William S; Roytershteyn, Vadim; Gary, Peter; Yin, L; Albright, B J; Bowers, K J; Karimabadi, H

    2009-01-01

    The evolution of magnetic reconnection in large-scale systems often gives rise to extended current layers that are unstable to the formation of secondary magnetic islands. The role of these islands in the reconnection process and the conditions under which they form remains a subject of debate. In this work, we benchmark two different kinetic particle-in-cell codes to address the formation of secondary islands for several types of global boundary conditions. The influence on reconnection is examined for a range of conditions and collisionality limits. Although secondary islands are observed in all cases, their influence on reconnection may be different depending on the regime. In the collisional limit, the secondary islands playa key role in breaking away from the Sweet-Parker scaling and enabling faster reconnection. In the collisionless limit, their formation is one mechanism for controlling the length of the diffusion region. In both limits, the onset of secondary islands leads to a time dependent behavior in the reconnection rate. In all cases considered, the number of secondary islands increases for larger systems.

  18. MHD Analysis of the Tokamak Edge Pedestal in the Low Collisionality Regime

    NASA Astrophysics Data System (ADS)

    Snyder, P. B.; Wilson, H. R.; Konz, C.

    2005-10-01

    The peeling-ballooning model proposes that intermediate wavelength MHD instabilities are responsible for edge localized modes (ELMs) and impose constraints on the pedestal height. In typical discharges with ELMs, the pedestal goes unstable to coupled peeling-ballooning or pure ballooning modes shortly before an ELM is observed. However, at very low collisionality, the bootstrap current in the pedestal region can be large, even very near the separatrix, and the discharge can be most unstable to current-driven kink/peeling modes, typically at relatively low mode number (n˜,1-10). Recently, interesting ELM-free regimes, including both Quiescent (QH) and Resonant Magnetic Perturbation (RMP) H-mode, have been observed to occur in this low collisionality regime. Here we systematically explore MHD stability in this regime, including the effects of a conducting wall and sheared toroidal flow. We consider the implications for both RMP and QH discharges, including possible connections between the EHO observed in QH mode and low-n kink/peeling modes.

  19. Nonlinear coherent structures of Alfvén wave in a collisional plasma

    NASA Astrophysics Data System (ADS)

    Jana, Sayanee; Ghosh, Samiran; Chakrabarti, Nikhil

    2016-07-01

    The Alfvén wave dynamics is investigated in the framework of two-fluid approach in a compressible collisional magnetized plasma. In the finite amplitude limit, the dynamics of the nonlinear Alfvén wave is found to be governed by a modified Korteweg-de Vries Burgers equation (mKdVB). In this mKdVB equation, the electron inertia is found to act as a source of dispersion, and the electron-ion collision serves as a dissipation. The collisional dissipation is eventually responsible for the Burgers term in mKdVB equation. In the long wavelength limit, this weakly nonlinear Alfvén wave is shown to be governed by a damped nonlinear Schrödinger equation. Furthermore, these nonlinear equations are analyzed by means of analytical calculation and numerical simulation to elucidate the various aspects of the phase-space dynamics of the nonlinear wave. Results reveal that nonlinear Alfvén wave exhibits the dissipation mediated shock, envelope, and breather like structures. Numerical simulations also predict the formation of dissipative Alfvénic rogue wave, giant breathers, and rogue wave holes. These results are discussed in the context of the space plasma.

  20. Post-collisional magmatism in the central East African Orogen: The Maevarano Suite of north Madagascar

    USGS Publications Warehouse

    Goodenough, K.M.; Thomas, Ronald J.; De Waele, B.; Key, R.M.; Schofield, D.I.; Bauer, W.; Tucker, R.D.; Rafahatelo, J.-M.; Rabarimanana, M.; Ralison, A.V.; Randriamananjara, T.

    2010-01-01

    Late tectonic, post-collisional granite suites are a feature of many parts of the Late Neoproterozoic to Cambrian East African Orogen (EAO), where they are generally attributed to late extensional collapse of the orogen, accompanied by high heat flow and asthenospheric uprise. The Maevarano Suite comprises voluminous plutons which were emplaced in some of the tectonostratigraphic terranes of northern Madagascar, in the central part of the EAO, following collision and assembly during a major orogeny at ca. 550 Ma. The suite comprises three main magmatic phases: a minor early phase of foliated gabbros, quartz diorites, and granodiorites; a main phase of large batholiths of porphyritic granitoids and charnockites; and a late phase of small-scale plutons and sheets of monzonite, syenite, leucogranite and microgranite. The main phase intrusions tend to be massive, but with variably foliated margins. New U-Pb SHRIMP zircon data show that the whole suite was emplaced between ca. 537 and 522 Ma. Geochemically, all the rocks of the suite are enriched in the LILE, especially K, and the LREE, but are relatively depleted in Nb, Ta and the HREE. These characteristics are typical of post-collisional granitoids in the EAO and many other orogenic belts. It is proposed that the Maevarano Suite magmas were derived by melting of sub-continental lithospheric mantle that had been enriched in the LILE during earlier subduction events. The melting occurred during lithospheric delamination, which was associated with extensional collapse of the East African Orogen. ?? 2009 Natural Environment Research Council.

  1. Use of nonlocal helium microplasma for gas impurities detection by the collisional electron spectroscopy method

    SciTech Connect

    Kudryavtsev, Anatoly A.; Stefanova, Margarita S.; Pramatarov, Petko M.

    2015-10-15

    The collisional electron spectroscopy (CES) method, which lays the ground for a new field for analytical detection of gas impurities at high pressures, has been verified. The CES method enables the identification of gas impurities in the collisional mode of electron movement, where the advantages of nonlocal formation of the electron energy distribution function (EEDF) are fulfilled. Important features of dc negative glow microplasma and probe method for plasma diagnostics are applied. A new microplasma gas analyzer design is proposed. Admixtures of 0.2% Ar, 0.6% Kr, 0.1% N{sub 2}, and 0.05% CO{sub 2} are used as examples of atomic and molecular impurities to prove the possibility for detecting and identifying their presence in high pressure He plasma (50–250 Torr). The identification of the particles under analysis is made from the measurements of the high energy part of the EEDF, where maxima appear, resulting from the characteristic electrons released in Penning reactions of He metastable atoms with impurity particles. Considerable progress in the development of a novel miniature gas analyzer for chemical sensing in gas phase environments has been made.

  2. Model for cw laser collisionally induced fluorescence in low-temperature discharges

    PubMed

    Stewart; Smith; Borthwick; Paterson

    2000-08-01

    A perturbed steady-state rate-equation model has been developed for the cw laser collisionally induced fluorescence (LCIF) produced by excitation on one of the 1s-2p noble gas transitions. This work is one part of a wider complementary modeling program which includes cw optogalvanic spectroscopy, optical emission spectroscopy, and optical absorption spectroscopy, with the overall aim of testing all of these models with the same stringently assembled atomic and discharge data set. Our aim here is to demonstrate the principal features of our cw LCIF model by using it to describe our experimental observations produced by pumping transitions originating on the 1s(5) metastable and 1s(4) resonance states of neon atoms in the positive column of a normal glow discharge at 2.0 Torr and a discharge current of 5 mA. The model shows that these cw LCIF spectra are dominated by 1s-2p excitation and electron collisional coupling among the 2p states. We show that the model allows us to quantify explicitly the various individual contributions to each line in the cw LCIF spectra. The theory and analyses presented here apply equally well to other noble gases and we believe can be modified appropriately for trace noble gases in atomic-molecular mixtures.

  3. Rapid collisional evolution of comets during the formation of the Oort cloud.

    PubMed

    Stern, S A; Weissman, P R

    2001-02-01

    The Oort cloud of comets was formed by the ejection of icy planetesimals from the region of giant planets--Jupiter, Saturn, Uranus and Neptune--during their formation. Dynamical simulations have previously shown that comets reach the Oort cloud only after being perturbed into eccentric orbits that result in close encounters with the giant planets, which then eject them to distant orbits about 10(4) to 10(5) AU from the Sun (1 AU is the average Earth-Sun distance). All of the Oort cloud models constructed until now simulate its formation using only gravitational effects; these include the influence of the Sun, the planets and external perturbers such as passing stars and Galactic tides. Here we show that physical collisions between comets and small debris play a fundamental and hitherto unexplored role throughout most of the ejection process. For standard models of the protosolar nebula (starting with a minimum-mass nebula) we find that collisional evolution of comets is so severe that their erosional lifetimes are much shorter than the timescale for dynamical ejection. It therefore appears that collisions will prevent most comets escaping from most locations in the region of the giant planets until the disk mass there declines sufficiently that the dynamical ejection timescale is shorter than the collisional lifetime. One consequence is that the total mass of comets in the Oort cloud may be less than currently believed.

  4. Enhanced stabilisation of trapped electron modes by collisional energy scattering in tokamaks

    SciTech Connect

    Manas, P.; Camenen, Y.; Benkadda, S.; Hornsby, W. A.; Peeters, A. G.

    2015-06-15

    The collisional stabilisation via energy scattering and pitch-angle scattering of micro-instabilities in tokamak plasmas is investigated by means of gyrokinetic simulations with a special emphasis on the often neglected energy scattering operator. It is shown that in the linear regime energy scattering has a negligible effect on Ion Temperature Gradient (ITG) modes but enhances the stabilisation of Trapped Electron Modes (TEM) in presence of nonzero ion temperature and density gradients. This stabilisation is sensitive to the model used for the energy restoring term in the collision operator. The contributions of parallel and drift motion to the total growth rate in velocity space are used to characterize the complex stabilisation mechanisms behind pitch-angle and energy scattering for a range of relevant parameters such as the magnetic shear, the collisionality, the logarithmic density gradient, and the logarithmic ion temperature gradient. It is shown that depending on these parameters, energy scattering stabilisation of TEM can be either due to a decrease of the contribution from drifting trapped electrons or to an increase of the contribution from the parallel motion of passing electrons. Finally, for a standard ITG/TEM case, the effect of energy scattering on the nonlinear heat and particle fluxes is investigated.

  5. Collisional effects on the numerical recurrence in Vlasov-Poisson simulations

    NASA Astrophysics Data System (ADS)

    Pezzi, Oreste; Camporeale, Enrico; Valentini, Francesco

    2016-02-01

    The initial state recurrence in numerical simulations of the Vlasov-Poisson system is a well-known phenomenon. Here, we study the effect on recurrence of artificial collisions modeled through the Lenard-Bernstein operator [A. Lenard and I. B. Bernstein, Phys. Rev. 112, 1456-1459 (1958)]. 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 an Eulerian collisional Vlasov-Poisson code. It is found that, despite being routinely used, an artificial collisionality is not a viable way of preventing recurrence in numerical simulations without compromising the kinetic nature of the solution. Moreover, it is shown how numerical effects associated to the generation of fine velocity scales can modify the physical features of the system evolution even in nonlinear regime. This means that filamentation-like phenomena, usually associated with low amplitude fluctuations contexts, can play a role even in nonlinear regime.

  6. Nonlinear Coherent Structures of Alfvén Wave in a Collisional Plasma

    NASA Astrophysics Data System (ADS)

    Jana, Sayanee; Ghosh, Samiran; Chakrabarti, Nikhil

    2016-10-01

    The Alfvén wave dynamics is investigated in the framework of Lagrangian two-fluid model in a cold magnetized collisional plasma in presence of finite electron inertia. In the quasi-linear limit, the dynamics of the nonlinear Alfvén wave is shown to be governed by a modified Korteweg-de Vries Burgers (mKdVB) equation. In this mKdVB equation, the electron inertia is found to act as a source of dispersion and the electro-ion collision serves as a dissipation. In the long wavelength limit, we have also investigated wave modulation characteristics of the nonlinear Alfvén wave. The dynamics of this modulated wave is shown to be governed by a damped nonlinear Schrödinger equation (NLSE). These nonlinear equations are analysed by means of analytical and numerical simulation to elucidate the various aspects of the phase-space dynamics of the nonlinear wave. Results reveal that nonlinear Alfvén wave exhibits shock, envelope and breather like structures. Numerical simulations also predict the formation of Alfvénic rogue waves, rogue wave holes and giant breathers. These results could be useful for understanding the salient features of the Alfvénic magnetic field structures from observational data in very low- βmagnetized collisional plasmas in space and laboratory.

  7. Improved electron collisional line broadening for low-temperature ions and neutrals in plasma modeling

    DOE PAGES

    Johns, H. M.; Kilcrease, D. P.; Colgan, J.; ...

    2015-09-29

    In this study, electron collisional broadening of observed spectral lines depends on plasma electron temperature and density. Including this effect in models of measured spectra is necessary to determine plasma conditions; however, computational limits make accurate line broadening treatments difficult to implement in large-scale plasma modeling efforts. In this paper, we report on improvements to the treatment of electron collisional line broadening and illustrate this with calculations using the Los Alamos ATOMIC code. We implement the Dimitrijevic and Konjevic modified semi-empirical model Dimitrijevic and Konjevic (1986 Astron. and Astrophy. 163 297 and 1987 Astron. Astrophys. 172 345), which we amendmore » by employing oscillator strengths from Hartree–Fock calculations. This line broadening model applies to near-neutral plasmas with electron temperatures of Te ~ 1 eV and electron densities of Ne ~1017 cm-3. We evaluate the D.K.-inspired model against the previous hydrogenic approach in ATOMIC through comparison to NIST-rated measurements for selected neutral and singly-ionized Ca, O, Fe, and Sn lines using both fine-structure and configuration-averaged oscillator strengths. The new D.K.-inspired model is significantly more accurate than the previous hydrogenic model and we find the use of configuration-averaged oscillator strengths a good approximation for applications such as LIBS (laser induced breakdown spectroscopy), for which we demonstrate the use of the D.K.-inspired model.« less

  8. Improved electron collisional line broadening for low-temperature ions and neutrals in plasma modeling

    SciTech Connect

    Johns, H. M.; Kilcrease, D. P.; Colgan, J.; Judge, E. J.; Barefield II, J. E.; Wiens, R. C.; Clegg, S. M.

    2015-09-29

    In this study, electron collisional broadening of observed spectral lines depends on plasma electron temperature and density. Including this effect in models of measured spectra is necessary to determine plasma conditions; however, computational limits make accurate line broadening treatments difficult to implement in large-scale plasma modeling efforts. In this paper, we report on improvements to the treatment of electron collisional line broadening and illustrate this with calculations using the Los Alamos ATOMIC code. We implement the Dimitrijevic and Konjevic modified semi-empirical model Dimitrijevic and Konjevic (1986 Astron. and Astrophy. 163 297 and 1987 Astron. Astrophys. 172 345), which we amend by employing oscillator strengths from Hartree–Fock calculations. This line broadening model applies to near-neutral plasmas with electron temperatures of Te ~ 1 eV and electron densities of Ne ~1017 cm-3. We evaluate the D.K.-inspired model against the previous hydrogenic approach in ATOMIC through comparison to NIST-rated measurements for selected neutral and singly-ionized Ca, O, Fe, and Sn lines using both fine-structure and configuration-averaged oscillator strengths. The new D.K.-inspired model is significantly more accurate than the previous hydrogenic model and we find the use of configuration-averaged oscillator strengths a good approximation for applications such as LIBS (laser induced breakdown spectroscopy), for which we demonstrate the use of the D.K.-inspired model.

  9. Collisional relaxation of a strongly magnetized two-species pure ion plasma

    SciTech Connect

    Chim, Chi Yung; O’Neil, Thomas M.; Dubin, Daniel H.

    2014-04-15

    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 Ω{sub 1},Ω{sub 2}≫|Ω{sub 1}−Ω{sub 2}|≫v{sup ¯}{sub ij}/b{sup ¯} and v{sup ¯}{sub ⊥j}/Ω{sub j}≪b{sup ¯}, where Ω{sub 1} and Ω{sub 2} are two cyclotron frequencies, v{sup ¯}{sub ij}=√(T{sub ∥}/μ{sub ij}) is the relative parallel thermal velocity characterizing collisions between particles of species i and j, and b{sup ¯}=2e{sup 2}/T{sub ∥} is the classical distance of closest approach for such collisions, and v{sup ¯}{sub ⊥j}/Ω{sub j}=√(2T{sub ⊥j}/m{sub j})/Ω{sub j} is the characteristic cyclotron radius for particles of species j. Here, μ{sub ij} is the reduced mass for the two particles, and T{sub ∥} and T{sub ⊥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, I{sub 1}=∑{sub i∈1}m{sub 1}v{sub ⊥i}{sup 2}/(2Ω{sub 1}) and I{sub 2}=∑{sub i∈2}m{sub 2}v{sub ⊥i}{sup 2}/(2Ω{sub 2}) 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 I{sub 1} and I{sub 2}, yielding a modified Gibbs distribution of the form exp[−H/T{sub ∥}−α{sub 1}I{sub 1}−α{sub 2}I{sub 2}]. Here, the α{sub j}’s are related to T{sub ∥} and T{sub ⊥j} through T{sub ⊥j}=(1/T{sub ∥}+α{sub j}/Ω{sub j}){sup −1}. Collisional relaxation to the usual Gibbs distribution, exp[−H/T{sub ∥}], takes place on two timescales. On a timescale longer than the collisional timescale by a factor of (b{sup ¯2}Ω{sub 1}{sup 2}/v{sup ¯}{sub 11}{sup 2})exp(5[3π(b{sup ¯}|Ω{sub 1}−Ω{sub 2}|/v{sup ¯}{sub 12})]{sup 2/5}/6), the two

  10. Pd nanoparticle concentration dependent self-assembly of Pd@SiO₂ nanoparticles into leaching resistant microcubes.

    PubMed

    Datta, Abheek; Sadhu, Anustup; Santra, Subhankar; Shivaprasad, S M; Mandal, Swadhin K; Bhattacharyya, Sayan

    2014-09-18

    Pd NP concentration guided the self-assembly of core-shell Pd@SiO2 nanoparticles (NPs) into microcubes. The Pd NPs were stacked by molten dodecyltrimethylammonium bromide (DTAB) to create the SiO2 envelope. The microcubes demonstrated improved leaching resistance in heterogeneous catalysis over a conventional porous support.

  11. 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

  12. 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

  13. Hercynian post-collisional magmatism in the context of Paleozoic magmatic evolution of the Tien Shan orogenic belt

    NASA Astrophysics Data System (ADS)

    Seltmann, Reimar; Konopelko, Dmitry; Biske, Georgy; Divaev, Farid; Sergeev, Sergei

    2011-10-01

    The Hercynian Tien Shan (Tianshan) orogen formed during Late Palaeozoic collision between the Karakum-Tarim and the Kazakhstan paleo-continents. In order to constrain timing of Hercynian post-collisional magmatism, 27 intrusions were sampled for U-Pb zircon dating along a ca. 2000 km - long profile in Uzbekistan and Kyrgyzstan. The samples were dated utilizing sensitive high resolution ion microprobe (SHRIMP-II). The obtained ages, together with previously published age data, allowed the timing of Hercynian post-collisional magmatism to be constrained and interpreted in the context of the Paleozoic magmatic evolution of the region. Apart from Hercynian post-collisional magmatism, two older magmatic episodes have been recognized, and the following sequence of events has been established: (1) approximately 10 Ma after cessation of continuous Caledonian magmatism a number of Late Silurian-Early Devonian intrusions were emplaced in the Middle and Northern Tien Shan terranes between 420 and 390 Ma. The intrusions probably formed in an extensional back arc setting during coeval subduction under the margins of Caledonian Paleo-Kazakhstan continent; (2) the next relatively short Late Carboniferous episode of subduction under Paleo-Kazakhstan was registered in the Kurama range of the Middle Tien Shan. Calc-alkaline volcanics and granitoids with ages 315-300 Ma have distinct metallogenic affinities typical for subduction-related rocks and are not found anywhere outside the Middle Tien Shan terrane west of the Talas-Farghona fault; (3) the Early Permian Hercynian post-collisional magmatism culminated after the closure of the Paleo-Turkestan ocean and affected the whole region across terrane boundaries. The post-collisional intrusions formed within a relatively short time span between 295 and 280 Ma. The model for Hercynian post-collisional evolution suggests that after collision the Tien Shan was affected by trans-crustal strike-slip motions which provided suitable conduits

  14. GeV neutrinos from collisional heating in GRBs: Detection prospects with IceCube-DeepCore

    SciTech Connect

    Bartos, Imre

    2014-11-18

    The observed gamma-ray burst (GRB) emission may be due to jet reheating via nuclear collisions. The role of this collisional heating can be probed through the observation of 10–100 GeV neutrinos, which are generated in nuclear collisions along with gamma rays. Neutrino and gamma-ray luminosities are closely related, which further aids observations. If the main mechanism behind the production of GRBs is collisional heating then IceCube-DeepCore could detect the GeV-neutrino emission of GRBs with a few years of observation.

  15. 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.

  16. 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.

  17. The PD1:PD-L1/2 Pathway from Discovery to Clinical Implementation

    PubMed Central

    Bardhan, Kankana; Anagnostou, Theodora; Boussiotis, Vassiliki A.

    2016-01-01

    The immune system maintains a critically organized network to defend against foreign particles, while evading self-reactivity simultaneously. T lymphocytes function as effectors and play an important regulatory role to orchestrate the immune signals. Although central tolerance mechanism results in the removal of the most of the autoreactive T cells during thymic selection, a fraction of self-reactive lymphocytes escapes to the periphery and pose a threat to cause autoimmunity. The immune system evolved various mechanisms to constrain such autoreactive T cells and maintain peripheral tolerance, including T cell anergy, deletion, and suppression by regulatory T cells (TRegs). These effects are regulated by a complex network of stimulatory and inhibitory receptors expressed on T cells and their ligands, which deliver cell-to-cell signals that dictate the outcome of T cell encountering with cognate antigens. Among the inhibitory immune mediators, the pathway consisting of the programed cell death 1 (PD-1) receptor (CD279) and its ligands PD-L1 (B7-H1, CD274) and PD-L2 (B7-DC, CD273) plays an important role in the induction and maintenance of peripheral tolerance and for the maintenance of the stability and the integrity of T cells. However, the PD-1:PD-L1/L2 pathway also mediates potent inhibitory signals to hinder the proliferation and function of T effector cells and have inimical effects on antiviral and antitumor immunity. Therapeutic targeting of this pathway has resulted in successful enhancement of T cell immunity against viral pathogens and tumors. Here, we will provide a brief overview on the properties of the components of the PD-1 pathway, the signaling events regulated by PD-1 engagement, and their consequences on the function of T effector cells. PMID:28018338

  18. The PD1:PD-L1/2 Pathway from Discovery to Clinical Implementation.

    PubMed

    Bardhan, Kankana; Anagnostou, Theodora; Boussiotis, Vassiliki A

    2016-01-01

    The immune system maintains a critically organized network to defend against foreign particles, while evading self-reactivity simultaneously. T lymphocytes function as effectors and play an important regulatory role to orchestrate the immune signals. Although central tolerance mechanism results in the removal of the most of the autoreactive T cells during thymic selection, a fraction of self-reactive lymphocytes escapes to the periphery and pose a threat to cause autoimmunity. The immune system evolved various mechanisms to constrain such autoreactive T cells and maintain peripheral tolerance, including T cell anergy, deletion, and suppression by regulatory T cells (TRegs). These effects are regulated by a complex network of stimulatory and inhibitory receptors expressed on T cells and their ligands, which deliver cell-to-cell signals that dictate the outcome of T cell encountering with cognate antigens. Among the inhibitory immune mediators, the pathway consisting of the programed cell death 1 (PD-1) receptor (CD279) and its ligands PD-L1 (B7-H1, CD274) and PD-L2 (B7-DC, CD273) plays an important role in the induction and maintenance of peripheral tolerance and for the maintenance of the stability and the integrity of T cells. However, the PD-1:PD-L1/L2 pathway also mediates potent inhibitory signals to hinder the proliferation and function of T effector cells and have inimical effects on antiviral and antitumor immunity. Therapeutic targeting of this pathway has resulted in successful enhancement of T cell immunity against viral pathogens and tumors. Here, we will provide a brief overview on the properties of the components of the PD-1 pathway, the signaling events regulated by PD-1 engagement, and their consequences on the function of T effector cells.

  19. Therapeutic uses of anti-PD-1 and anti-PD-L1 antibodies.

    PubMed

    Philips, George K; Atkins, Michael

    2015-01-01

    Despite extensive investigation over the past three decades, cancer immunotherapy has produced limited success, with few agents achieving approval by the Food and Drug Administration and even the most effective helping only a minority of patients, primarily with melanoma or renal cancer. In recent years, immune checkpoints that maintain physiologic self-tolerance have been implicated in the down-regulation of anti-tumor immunity. Efforts to restore latent anti-tumor immunity have focused on antibody-based interventions targeting CTL antigen 4 (CTLA-4) and programmed cell death protein 1 (PD-1) on T lymphocytes and its principal ligand (PD-L1) on tumor cells. Ipilimumab, an antibody targeting CTLA-4, appears to restore tumor immunity at the priming phase, whereas anti-PD-1/PD-L1 antibodies restore immune function in the tumor microenvironment. Although ipilimumab can produce durable long-term responses in patients with advanced melanoma, it is associated with significant immune-related toxicities. By contrast, antibodies targeting either PD-1 or PD-L1 have produced significant anti-tumor activity with considerably less toxicity. Activity was seen in patients with melanoma and renal cancer, as well as those with non-small-cell lung, bladder and head and neck cancers, tumors not previously felt to be sensitive to immunotherapy. The tolerability of PD-1-pathway blockers and their unique mechanism of action have made them ideal backbones for combination regimen development. Combination approaches involving cytotoxic chemotherapy, anti-angiogenic agents, alternative immune-checkpoint inhibitors, immunostimulatory cytokines and cancer vaccines are currently under clinical investigation. Current efforts focus on registration trials of single agents and combinations in various diseases and disease settings and identifying predictive biomarkers of response.

  20. HDAC Inhibition Upregulates PD-1 Ligands in Melanoma and Augments Immunotherapy with PD-1 Blockade.

    PubMed

    Woods, David M; Sodré, Andressa L; Villagra, Alejandro; Sarnaik, Amod; Sotomayor, Eduardo M; Weber, Jeffrey

    2015-12-01

    Expression of PD-1 ligands by tumors and interaction with PD-1-expressing T cells in the tumor microenvironment can result in tolerance. Therapies targeting this coinhibitory axis have proven clinically successful in the treatment of metastatic melanoma, non-small cell lung cancer, and other malignancies. Therapeutic agents targeting the epigenetic regulatory family of histone deacetylases (HDAC) have shown clinical success in the treatment of some hematologic malignancies. Beyond direct tumor cell cytotoxicity, HDAC inhibitors have also been shown to alter the immunogenicity and enhance antitumor immune responses. Here, we show that class I HDAC inhibitors upregulated the expression of PD-L1 and, to a lesser degree, PD-L2 in melanomas. Evaluation of human and murine cell lines and patient tumors treated with a variety of HDAC inhibitors in vitro displayed upregulation of these ligands. This upregulation was robust and durable, with enhanced expression lasting past 96 hours. These results were validated in vivo in a B16F10 syngeneic murine model. Mechanistically, HDAC inhibitor treatment resulted in rapid upregulation of histone acetylation of the PD-L1 gene leading to enhanced and durable gene expression. The efficacy of combining HDAC inhibition with PD-1 blockade for treatment of melanoma was also explored in a murine B16F10 model. Mice receiving combination therapy had a slower tumor progression and increased survival compared with control and single-agent treatments. These results highlight the ability of epigenetic modifiers to augment immunotherapies, providing a rationale for combining HDAC inhibitors with PD-1 blockade.