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Sample records for pd quasiparticle random

  1. β -decay properties of neutron-rich Ge, Se, Kr, Sr, Ru, and Pd isotopes from deformed quasiparticle random-phase approximation

    NASA Astrophysics Data System (ADS)

    Sarriguren, P.

    2015-04-01

    β -decay properties of even- and odd-A neutron-rich Ge, Se, Kr, Sr, Ru, and Pd isotopes involved in the astrophysical rapid neutron capture process are studied within a deformed proton-neutron quasiparticle random-phase approximation. The underlying mean field is described self-consistently from deformed Skyrme-Hartree-Fock calculations with pairing correlations. Residual interactions in the particle-hole and particle-particle channels are also included in the formalism. The isotopic evolution of the various nuclear equilibrium shapes and the corresponding charge radii are investigated in all the isotopic chains. The energy distributions of the Gamow-Teller strength as well as the β -decay half-lives are discussed and compared with the available experimental information. It is shown that nuclear deformation plays a significant role in the description of the decay properties in this mass region. Reliable predictions of the strength distributions are essential to evaluate decay rates in astrophysical scenarios.

  2. Finite amplitude method for the quasiparticle random-phase approximation

    NASA Astrophysics Data System (ADS)

    Avogadro, Paolo; Nakatsukasa, Takashi

    2011-07-01

    We present the finite amplitude method (FAM), originally proposed in Ref. , for superfluid systems. A Hartree-Fock-Bogoliubov code may be transformed into a code of the quasiparticle-random-phase approximation (QRPA) with simple modifications. This technique has advantages over the conventional QRPA calculations, such as coding feasibility and computational cost. We perform the fully self-consistent linear-response calculation for the spherical neutron-rich nucleus 174Sn, modifying the hfbrad code, to demonstrate the accuracy, feasibility, and usefulness of the FAM.

  3. Efficient calculation for the quasiparticle random-phase approximation matrix

    NASA Astrophysics Data System (ADS)

    Avogadro, Paolo; Nakatsukasa, Takashi

    2013-01-01

    We present an efficient numerical technique to evaluate the matrix of the (quasiparticle-) random-phase approximation, using the finite-amplitude method (FAM). The method is tested in calculation of monopole excitations in 120Sn, compared with result obtained with the former iterative FAM. The neutron-pair-transfer modes are calculated with the present method and their character change in neutron-rich Pb isotopes is discussed. Computational aspects of different FAM approaches are also discussed for future applications to a large-scale computation.

  4. Neutrino reactions on {sup 12}C by the quasiparticle random-phase approximation (QRPA)

    SciTech Connect

    Cheoun, Myung-Ki; Ha, Eunja; Lee, Su Youn; Kim, K. S.; So, W. Y.; Kajino, Toshitaka

    2010-02-15

    We applied the quasiparticle random-phase approximation to neutrino reactions on {sup 12}C target. The quasiparticle random-phase approximation (QRPA) has been found to successfully explain the nuclear {beta} and {beta}{beta} decays. To describe neutrino-nucleus reactions, various multipole transitions by weak interactions with finite momentum transfers are added to the Gamow Teller transition in the {beta} decays. Our results are shown to well reproduce most of experimental data for neutrino reactions on {sup 12}C target. In particular, energy dependence of cross sections for the exclusive reaction, {sup 12}C(nu{sub e},e{sup -}){sup 12}N{sub g.s.(1+)}, is discussed in detail by comparing the QRPA calculations to related experimental data.

  5. Thermodynamic properties of hot nuclei within the self-consistent quasiparticle random-phase approximation

    SciTech Connect

    Hung, N. Quang; Dang, N. Dinh

    2010-10-15

    The thermodynamic properties of hot nuclei are described within the canonical and microcanonical ensemble approaches. These approaches are derived based on the solutions of the BCS and self-consistent quasiparticle random-phase approximation at zero temperature embedded into the canonical and microcanonical ensembles. The results obtained agree well with the recent data extracted from experimental level densities by the Oslo group for {sup 94}Mo, {sup 98}Mo, {sup 162}Dy, and {sup 172}Yb nuclei.

  6. Implementation of the finite amplitude method for the relativistic quasiparticle random-phase approximation

    NASA Astrophysics Data System (ADS)

    Nikšić, T.; Kralj, N.; Tutiš, T.; Vretenar, D.; Ring, P.

    2013-10-01

    A new implementation of the finite amplitude method (FAM) for the solution of the relativistic quasiparticle random-phase approximation (RQRPA) is presented, based on the relativistic Hartree-Bogoliubov (RHB) model for deformed nuclei. The numerical accuracy and stability of the FAM-RQRPA is tested in a calculation of the monopole response of 22O. As an illustrative example, the model is applied to a study of the evolution of monopole strength in the chain of Sm isotopes, including the splitting of the giant monopole resonance in axially deformed systems.

  7. Quasiparticle-random-phase approximation treatment of the transverse wobbling mode reconsidered

    NASA Astrophysics Data System (ADS)

    Frauendorf, S.; Dönau, F.

    2015-12-01

    The quasiparticle-random-phase approximation is used to study the properties of the wobbling bands in 163Lu. Assuming that the wobbling mode represents pure isoscalar orientation oscillations results in too low wobbling frequencies and transition probabilities between the one- and zero-phonon wobbling bands that are strongly collective but yet too weak for B (E2 ) out and too strong for B (M1 ) out . The inclusion of an LL interaction, which couples the wobbling mode to the scissors mode, generates the right upshift of the wobbling frequencies and the right suppression of the B (M1 ) out values toward the experimental values, but does not change the B (E2 ) out values. In analogy to the quenching of low-energy E 1 transition by coupling to the isovector giant dipole resonance, a general reduction of the M 1 transitions between quasiparticle configurations caused by coupling to the scissors mode is suggested. The small B (E2 ) out values are related to small triaxiality of the density distribution, which is found by all mean field calculations for the triaxial strongly deformed nuclei in the mass 160 region.

  8. Self-consistent quasiparticle random-phase approximation for a multilevel pairing model

    SciTech Connect

    Hung, N. Quang; Dang, N. Dinh

    2007-11-15

    Particle-number projection within the Lipkin-Nogami (LN) method is applied to the self-consistent quasiparticle random-phase approximation (SCQRPA), which is tested in an exactly solvable multilevel pairing model. The SCQRPA equations are numerically solved to find the energies of the ground and excited states at various numbers {omega} of doubly degenerate equidistant levels. The use of the LN method allows one to avoid the collapse of the BCS (QRPA) to obtain the energies of the ground and excited states as smooth functions of the interaction parameter G. The comparison between results given by different approximations such as the SCRPA, QRPA, LNQRPA, SCQRPA, and LNSCQRPA is carried out. Although the use of the LN method significantly improves the agreement with the exact results in the intermediate coupling region, we found that in the strong coupling region the SCQRPA results are closest to the exact ones.

  9. Linear response of light deformed nuclei investigated by self-consistent quasiparticle random-phase approximation

    SciTech Connect

    Losa, C.; Doessing, T.; Pastore, A.; Vigezzi, E.; Broglia, R. A.

    2010-06-15

    We present a calculation of the properties of vibrational states in deformed, axially-symmetric even-even nuclei, within the framework of a fully self-consistent quasiparticle random phase approximation (QRPA). The same Skyrme energy density and density-dependent pairing functionals are used to calculate the mean field and the residual interaction in the particle-hole and particle-particle channels. We have tested our software in the case of spherical nuclei against fully self-consistent calculations published in the literature, finding excellent agreement. We investigate the consequences of neglecting the spin-orbit and Coulomb residual interactions in QRPA. Furthermore we discuss the improvement obtained in the QRPA result associated with the removal of spurious modes. Isoscalar and isovector responses in the deformed {sup 24-26}Mg, {sup 34}Mg isotopes are presented and compared to experimental findings.

  10. Particle-particle and quasiparticle random phase approximations: Connections to coupled cluster theory

    NASA Astrophysics Data System (ADS)

    Scuseria, Gustavo E.; Henderson, Thomas M.; Bulik, Ireneusz W.

    2013-09-01

    We establish a formal connection between the particle-particle (pp) random phase approximation (RPA) and the ladder channel of the coupled cluster doubles (CCD) equations. The relationship between RPA and CCD is best understood within a Bogoliubov quasiparticle (qp) RPA formalism. This work is a follow-up to our previous formal proof on the connection between particle-hole (ph) RPA and ring-CCD. Whereas RPA is a quasibosonic approximation, CC theory is a "correct bosonization" in the sense that the wavefunction and Hilbert space are exactly fermionic, yet the amplitude equations can be interpreted as adding different quasibosonic RPA channels together. Coupled cluster theory achieves this goal by interacting the ph (ring) and pp (ladder) diagrams via a third channel that we here call "crossed-ring" whose presence allows for full fermionic antisymmetry. Additionally, coupled cluster incorporates what we call "mosaic" terms which can be absorbed into defining a new effective one-body Hamiltonian. The inclusion of these mosaic terms seems to be quite important. The pp-RPA and qp-RPA equations are textbook material in nuclear structure physics but are largely unknown in quantum chemistry, where particle number fluctuations and Bogoliubov determinants are rarely used. We believe that the ideas and connections discussed in this paper may help design improved ways of incorporating RPA correlation into density functionals based on a CC perspective.

  11. Giant resonances in {sup 238}U within the quasiparticle random-phase approximation with the Gogny force

    SciTech Connect

    Peru, S.; Gosselin, G.; Martini, M.; Dupuis, M.; Hilaire, S.

    2011-01-15

    Fully consistent axially-symmetric deformed quasiparticle random-phase approximation (QRPA) calculations have been performed, using the same Gogny D1S effective force for both the Hartree-Fock-Bogolyubov mean field and QRPA matrix. New implementation of this approach leads to the applicability of QRPA to heavy deformed nuclei. Giant resonances and low-energy collective states for monopole, dipole, quadrupole, and octupole modes are predicted for the heavy deformed nucleus {sup 238}U and compared with experimental data.

  12. Thermal quasiparticle random-phase approximation with Skyrme interactions and supernova neutral-current neutrino-nucleus reactions

    NASA Astrophysics Data System (ADS)

    Dzhioev, Alan A.; Vdovin, A. I.; Martínez-Pinedo, G.; Wambach, J.; Stoyanov, Ch.

    2016-07-01

    The thermal quasiparticle random-phase approximation is combined with the Skyrme energy density functional method (Skyrme-TQRPA) to study the response of a hot nucleus to an external perturbation. For the sample nuclei 56Fe and 82Ge, the Skyrme-TQRPA is applied to analyze thermal effects on the strength function of charge-neutral Gamow-Teller transitions, which dominate neutrino-nucleus reactions at Eν≲20 MeV. For the relevant supernova temperatures we calculate the cross sections for inelastic neutrino scattering. We also apply the method to examine the rate of neutrino-antineutrino pair emission by hot nuclei. The cross sections and rates are compared with those obtained earlier from the TQRPA calculations based on the phenomenological quasiparticle-phonon model Hamiltonian. For inelastic neutrino scattering on 56Fe we also compare the Skyrme-TQRPA results to those obtained earlier from a hybrid approach that combines shell-model and RPA calculations.

  13. Role of deformation on giant resonances within the quasiparticle random-phase approximation and the Gogny force

    SciTech Connect

    Peru, S.; Goutte, H.

    2008-04-15

    Fully consistent axially-symmetric-deformed quasiparticle random phase approximation (QRPA) calculations have been performed, in which the same Gogny D1S effective force has been used for both the Hartree-Fock-Bogolyubov mean field and the QRPA approaches. Giant resonances calculated in deformed {sup 26-28}Si and {sup 22-24}Mg nuclei as well as in the spherical {sup 30}Si and {sup 28}Mg isotopes are presented. Theoretical results for isovector-dipole and isoscalar monopole, quadrupole, and octupole responses are presented and the impact of the intrinsic nuclear deformation is discussed.

  14. Introduction of a valence space in quasiparticle random-phase approximation: Impact on vibrational mass parameters and spectroscopic properties

    NASA Astrophysics Data System (ADS)

    Lechaftois, F.; Deloncle, I.; Péru, S.

    2015-09-01

    For the first time, using a unique finite-range interaction (D1M Gogny force), a fully coherent and time-feasible calculation of the Bohr Hamiltonian vibrational mass is envisioned in a Hartree-Fock-Bogoliubov + quasiparticle random-phase approximation (QRPA) framework. In order to reach a reasonable computation time, we evaluate the feasibility of this method by considering two restrictions for the QRPA: the Tamm-Dancoff approximation and the insertion of a valence space. We validate our approach in the even-even tin isotopes by comparing the convergence scheme of the mass parameter with those of built-in QRPA outputs: excited-state energy and reduced transition probability. The seeming convergence of these intrinsic quantities is shown to be misleading and the difference with the theoretical expected value is quantified. This work is a primary step towards the systematic calculation of mass parameters.

  15. Continuum quasiparticle random-phase approximation for astrophysical direct neutron capture reactions on neutron-rich nuclei

    NASA Astrophysics Data System (ADS)

    Matsuo, Masayuki

    2015-03-01

    I formulate a many-body theory to calculate the cross section of direct radiative neutron capture reaction by means of the Hartree-Fock-Bogoliubov mean-field model and the continuum quasiparticle random-phase approximation (QRPA). A focus is put on very-neutron-rich nuclei and low-energy neutron kinetic energy in the range from 1 keV to several MeV, which is relevant to the rapid neutron capture process of nucleosynthesis. I begin with the photoabsorption cross section and the E 1 strength function. Next, in order to apply the reciprocity theorem, I decompose the cross section into partial cross sections corresponding to different channels of one- and two-neutron emission decays of photo-excited states. A numerical example is shown for the photo-absorption of 142Sn and the neutron capture of 141Sn .

  16. Systematics of the first 2{sup +} excitation in spherical nuclei with the Skyrme quasiparticle random-phase approximation

    SciTech Connect

    Terasaki, J.; Engel, J.; Bertsch, G. F.

    2008-10-15

    We use the quasiparticle random-phase approximation (QRPA) and the Skyrme interactions SLy4 and SkM* to systematically calculate energies and transition strengths for the lowest 2{sup +} state in spherical even-even nuclei. The SkM* functional, applied to 178 spherical nuclei between Z=10 and 90, produces excitation energies that are on average 11% higher than experimental values, with residuals that fluctuate about the average by -35% to +55%. The predictions of SkM* and SLy4 have significant differences, in part because of differences in the calculated ground state deformations; SkM* performs better in both the average and dispersion of energies. Comparing the QRPA results with those of generator-coordinate-method (GCM) calculations, we find that the QRPA reproduces trends near closed shells better than the GCM, and that it overpredicts the energies less severely in general.

  17. Large-scale deformed quasiparticle random-phase approximation calculations of the γ -ray strength function using the Gogny force

    NASA Astrophysics Data System (ADS)

    Martini, M.; Péru, S.; Hilaire, S.; Goriely, S.; Lechaftois, F.

    2016-07-01

    Valuable theoretical predictions of nuclear dipole excitations in the whole chart are of great interest for different nuclear applications, including in particular nuclear astrophysics. Here we present large-scale calculations of the E 1 γ -ray strength function obtained in the framework of the axially symmetric deformed quasiparticle random-phase approximation based on the finite-range Gogny force. This approach is applied to even-even nuclei, the strength function for odd nuclei being derived by interpolation. The convergence with respect to the adopted number of harmonic oscillator shells and the cutoff energy introduced in the 2-quasiparticle (2 -q p ) excitation space is analyzed. The calculations performed with two different Gogny interactions, namely D1S and D1M, are compared. A systematic energy shift of the E 1 strength is found for D1M relative to D1S, leading to a lower energy centroid and a smaller energy-weighted sum rule for D1M. When comparing with experimental photoabsorption data, the Gogny-QRPA predictions are found to overestimate the giant dipole energy by typically ˜2 MeV. Despite the microscopic nature of our self-consistent Hartree-Fock-Bogoliubov plus QRPA calculation, some phenomenological corrections need to be included to take into account the effects beyond the standard 2 -q p QRPA excitations and the coupling between the single-particle and low-lying collective phonon degrees of freedom. For this purpose, three prescriptions of folding procedure are considered and adjusted to reproduce experimental photoabsorption data at best. All of them are shown to lead to somewhat similar predictions of the E 1 strength, both at low energies and for exotic neutron-rich nuclei. Predictions of γ -ray strength functions and Maxwellian-averaged neutron capture rates for the whole Sn isotopic chain are also discussed and compared with previous theoretical calculations.

  18. Gogny-Hartree-Fock-Bogolyubov plus quasiparticle random-phase approximation predictions of the M 1 strength function and its impact on radiative neutron capture cross section

    NASA Astrophysics Data System (ADS)

    Goriely, S.; Hilaire, S.; Péru, S.; Martini, M.; Deloncle, I.; Lechaftois, F.

    2016-10-01

    Valuable theoretical predictions of nuclear dipole excitations in the whole chart are of great interest for different nuclear applications, including in particular nuclear astrophysics. Here we extend our large-scale calculations of the E 1 γ -ray strength function, obtained in the framework of the axially- symmetric-deformed quasiparticle random phase approximation (QRPA) based on the finite-range D1M Gogny force, to the calculation of the M 1 strength function. We compare our QRPA prediction of the M 1 strength with available experimental data and show that a relatively good agreement is obtained provided the strength is shifted globally by about 2 MeV and increased by an empirical factor of 2. Predictions of the M 1 strength function for spherical and deformed nuclei within the valley of β stability as well as in the neutron-rich region are discussed. Its impact on the radiative neutron capture cross section is also analyzed.

  19. Description of the 2ννββ decay within a fully renormalized proton-neutron quasiparticle random-phase approximation approach with a restored gauge symmetry

    NASA Astrophysics Data System (ADS)

    Raduta, C. M.; Raduta, A. A.

    2010-12-01

    A many-body Hamiltonian involving the mean field for a projected spherical single-particle basis, the pairing interactions for alike nucleons, and the dipole-dipole proton-neutron interactions in the particle-hole (ph) channel and the ph dipole pairing potential is treated by the projected gauge fully renormalized proton-neutron quasiparticle random phase approximation approach. The resulting wave functions and energies for the mother and daughter nuclei are used to calculate the 2νββ decay rate and the process half-life. For illustration, the formalism is applied for the decay 100Mo→100Ru. The calculated half-life is in agreement with the corresponding experimental data. The Ikeda sum rule is obeyed.

  20. Low-energy dipole excitations in neon isotopes and N=16 isotones within the quasiparticle random-phase approximation and the Gogny force

    SciTech Connect

    Martini, M.; Peru, S.; Dupuis, M.

    2011-03-15

    Low-energy dipole excitations in neon isotopes and N=16 isotones are calculated with a fully consistent axially-symmetric-deformed quasiparticle random phase approximation (QRPA) approach based on Hartree-Fock-Bogolyubov (HFB) states. The same Gogny D1S effective force has been used both in HFB and QRPA calculations. The microscopical structure of these low-lying resonances, as well as the behavior of proton and neutron transition densities, are investigated in order to determine the isoscalar or isovector nature of the excitations. It is found that the N=16 isotones {sup 24}O, {sup 26}Ne, {sup 28}Mg, and {sup 30}Si are characterized by a similar behavior. The occupation of the 2s{sub 1/2} neutron orbit turns out to be crucial, leading to nontrivial transition densities and to small but finite collectivity. Some low-lying dipole excitations of {sup 28}Ne and {sup 30}Ne, characterized by transitions involving the {nu}1d{sub 3/2} state, present a more collective behavior and isoscalar transition densities. A collective proton low-lying excitation is identified in the {sup 18}Ne nucleus.

  1. A Fully Automated Diabetes Prevention Program, Alive-PD: Program Design and Randomized Controlled Trial Protocol

    PubMed Central

    Azar, Kristen MJ; Block, Torin J; Romanelli, Robert J; Carpenter, Heather; Hopkins, Donald; Palaniappan, Latha; Block, Clifford H

    2015-01-01

    Background In the United States, 86 million adults have pre-diabetes. Evidence-based interventions that are both cost effective and widely scalable are needed to prevent diabetes. Objective Our goal was to develop a fully automated diabetes prevention program and determine its effectiveness in a randomized controlled trial. Methods Subjects with verified pre-diabetes were recruited to participate in a trial of the effectiveness of Alive-PD, a newly developed, 1-year, fully automated behavior change program delivered by email and Web. The program involves weekly tailored goal-setting, team-based and individual challenges, gamification, and other opportunities for interaction. An accompanying mobile phone app supports goal-setting and activity planning. For the trial, participants were randomized by computer algorithm to start the program immediately or after a 6-month delay. The primary outcome measures are change in HbA1c and fasting glucose from baseline to 6 months. The secondary outcome measures are change in HbA1c, glucose, lipids, body mass index (BMI), weight, waist circumference, and blood pressure at 3, 6, 9, and 12 months. Randomization and delivery of the intervention are independent of clinic staff, who are blinded to treatment assignment. Outcomes will be evaluated for the intention-to-treat and per-protocol populations. Results A total of 340 subjects with pre-diabetes were randomized to the intervention (n=164) or delayed-entry control group (n=176). Baseline characteristics were as follows: mean age 55 (SD 8.9); mean BMI 31.1 (SD 4.3); male 68.5%; mean fasting glucose 109.9 (SD 8.4) mg/dL; and mean HbA1c 5.6 (SD 0.3)%. Data collection and analysis are in progress. We hypothesize that participants in the intervention group will achieve statistically significant reductions in fasting glucose and HbA1c as compared to the control group at 6 months post baseline. Conclusions The randomized trial will provide rigorous evidence regarding the efficacy of

  2. Clinical Impact and Cost-Effectiveness of an Education Program for PD Patients: A Randomized Controlled Trial

    PubMed Central

    Ory-Magne, Fabienne; Arcari, Céline; Mohara, Christine; Pourcel, Laure; Derumeaux, Hélène; Bérard, Emilie; Bourrel, Robert; Molinier, Laurent; Brefel-Courbon, Christine

    2016-01-01

    Background Parkinson’s disease (PD) is characterized by its impact on quality of life, constituting a substantial economic burden on society. Education programs implicating patients more in the management of their illness and complementing medical treatment may be a beneficial adjunct in PD. This study assessed the impact of an education program on quality of life and its cost-effectiveness in PD patients. Methods This single-center, prospective, randomized study assessed an education program consisting of individual and group sessions over a 12-month period. A total of 120 PD patients were assigned to either the Treated by Behavioral Intervention group (TTBI) or the no TTBI group. The primary outcome criterion was quality of life assessed using PDQ39. The Unified Parkinson’s Disease Rating Scale (UPDRS) and psychological status were collected. An economic evaluation was performed, including calculations of incremental cost-effectiveness ratios (ICERs). Results After 12 months of follow-up, changes recorded in the PDQ39 between the groups were not significantly different but better changes were observed in each dimension in the TTBI group compared to the no TTBI group. UPDRS I, II and total score were significantly improved in TTBI group compared to the no TTBI group. Mean annual costs did not differ significantly between the two groups. Conclusion This study suggested that the education program positively impacts the perceived health of PD patients without increasing medical costs. PMID:27685455

  3. Effect of spin fluctuations on quasiparticles in simple metals

    NASA Astrophysics Data System (ADS)

    Lischner, Johannes; Bazhirov, Timur; MacDonald, Allan; Cohen, Marvin; Louie, Steven

    2014-03-01

    We present a first-principles theory for quasiparticle excitations in condensed matter systems that includes their interaction with spin fluctuations. We apply this theory to sodium and lithium. Despite several previous studies, the importance of spin fluctuations in these materials and, in particular, their effect on the occupied band width remains unclear. We show that the coupling to spin fluctuations does not significantly change the occupied band width, but gives an important contribution to the quasiparticle lifetime. To obtain quantitative agreement with experiment for the occupied band width, we find that it is necessary to include vertex corrections beyond the random-phase approximation in the screening by charge fluctuations. S. G. L. acknowledges support by a Simons Foundation Fellowship in Theoretical Physics. This work was supported by NSF Grant No. DMR10-1006184 and by DOE Grant No. DE-AC02-05CH11231.

  4. Quasiparticle breakdown in a quantum spin liquid.

    PubMed

    Stone, Matthew B; Zaliznyak, Igor A; Hong, Tao; Broholm, Collin L; Reich, Daniel H

    2006-03-01

    Much of modern condensed matter physics is understood in terms of elementary excitations, or quasiparticles--fundamental quanta of energy and momentum. Various strongly interacting atomic systems are successfully treated as a collection of quasiparticles with weak or no interactions. However, there are interesting limitations to this description: in some systems the very existence of quasiparticles cannot be taken for granted. Like unstable elementary particles, quasiparticles cannot survive beyond a threshold where certain decay channels become allowed by conservation laws; their spectrum terminates at this threshold. Such quasiparticle breakdown was first predicted for an exotic state of matter--super-fluid 4He at temperatures close to absolute zero, a quantum Bose liquid where zero-point atomic motion precludes crystallization. Here we show, using neutron scattering, that quasiparticle breakdown can also occur in a quantum magnet and, by implication, in other systems with Bose quasiparticles. We have measured spin excitations in a two-dimensional quantum magnet, piperazinium hexachlorodicuprate (PHCC), in which spin-1/2 copper ions form a non-magnetic quantum spin liquid, and find remarkable similarities with excitations in superfluid 4He. We observe a threshold momentum beyond which the quasiparticle peak merges with the two-quasiparticle continuum. It then acquires a finite energy width and becomes indistinguishable from a leading-edge singularity, so that excited states are no longer quasiparticles but occupy a wide band of energy. Our findings have important ramifications for understanding excitations with gapped spectra in many condensed matter systems, ranging from band insulators to high-transition-temperature superconductors.

  5. Quasiparticle breakdown in a quantum spin liquid.

    PubMed

    Stone, Matthew B; Zaliznyak, Igor A; Hong, Tao; Broholm, Collin L; Reich, Daniel H

    2006-03-01

    Much of modern condensed matter physics is understood in terms of elementary excitations, or quasiparticles--fundamental quanta of energy and momentum. Various strongly interacting atomic systems are successfully treated as a collection of quasiparticles with weak or no interactions. However, there are interesting limitations to this description: in some systems the very existence of quasiparticles cannot be taken for granted. Like unstable elementary particles, quasiparticles cannot survive beyond a threshold where certain decay channels become allowed by conservation laws; their spectrum terminates at this threshold. Such quasiparticle breakdown was first predicted for an exotic state of matter--super-fluid 4He at temperatures close to absolute zero, a quantum Bose liquid where zero-point atomic motion precludes crystallization. Here we show, using neutron scattering, that quasiparticle breakdown can also occur in a quantum magnet and, by implication, in other systems with Bose quasiparticles. We have measured spin excitations in a two-dimensional quantum magnet, piperazinium hexachlorodicuprate (PHCC), in which spin-1/2 copper ions form a non-magnetic quantum spin liquid, and find remarkable similarities with excitations in superfluid 4He. We observe a threshold momentum beyond which the quasiparticle peak merges with the two-quasiparticle continuum. It then acquires a finite energy width and becomes indistinguishable from a leading-edge singularity, so that excited states are no longer quasiparticles but occupy a wide band of energy. Our findings have important ramifications for understanding excitations with gapped spectra in many condensed matter systems, ranging from band insulators to high-transition-temperature superconductors. PMID:16525467

  6. Model Wavefunctions For Non-Abelian Quasiparticles

    NASA Astrophysics Data System (ADS)

    Bernevig, B. Andrei; Haldane, F. D. M.

    2008-03-01

    We present model wavefunctions for quasiparticle (as opposed to quasihole)excitations of the Zk parafermion sequence (Laughlin/Moore-Read/Read-Rezayi) of Fractional Quantum Hall states. These states satisfy two generalized clustering conditions: they vanish when either a cluster of k+2 electrons is put together, or when two clusters of k+1 electrons are formed at different positions. For Abelian Fractional Quantum Hall states (k=1), our construction reproduces the Jain quasielectron wavefunction, and elucidates the difference between the Jain and Laughlin quasiparticle constructions. For two (or more) quasiparticles, our states differ from those constructed using Jain's method. By adding our quasiparticles to the Laughlin state, we obtain a hierarchy scheme which gives rise to a non-abelian ν=2 5 FQH state.

  7. Comparing quasiparticle GW+DMFT and LDA+DMFT for the test bed material SrVO3

    NASA Astrophysics Data System (ADS)

    Taranto, C.; Kaltak, M.; Parragh, N.; Sangiovanni, G.; Kresse, G.; Toschi, A.; Held, K.

    2013-10-01

    We have implemented the quasiparticle GW+dynamical mean field theory (DMFT) approach in the Vienna ab initio simulation package. To this end, a quasiparticle Hermitization of the G0W0 self-energy a lá Kotani-Schilfgaarde is employed, and the interaction values are obtained from the locally unscreened random phase approximation (RPA) using a projection onto Wannier orbitals. We compare quasiparticle GW+DMFT and local density approximation (LDA)+DMFT against each other and against experiment for SrVO3. We observe a partial compensation of stronger electronic correlations due to the reduced GW bandwidth and weaker correlations due to a larger screening of the RPA interaction, so that the obtained spectra are quite similar and agree well with experiment. Noteworthy, the quasiparticle GW+DMFT better reproduces the position of the lower Hubbard side band.

  8. Quasiparticle excitations of adsorbates on doped graphene

    NASA Astrophysics Data System (ADS)

    Lischner, Johannes; Wickenburg, Sebastian; Wong, Dillon; Karrasch, Christoph; Wang, Yang; Lu, Jiong; Omrani, Arash A.; Brar, Victor; Tsai, Hsin-Zon; Wu, Qiong; Corsetti, Fabiano; Mostofi, Arash; Kawakami, Roland K.; Moore, Joel; Zettl, Alex; Louie, Steven G.; Crommie, Mike

    Adsorbed atoms and molecules can modify the electronic structure of graphene, but in turn it is also possible to control the properties of adsorbates via the graphene substrate. In my talk, I will discuss the electronic structure of F4-TCNQ molecules on doped graphene and present a first-principles based theory of quasiparticle excitations that captures the interplay of doping-dependent image charge interactions between substrate and adsorbate and electron-electron interaction effects on the molecule. The resulting doping-dependent quasiparticle energies will be compared to experimental scanning tunnelling spectra. Finally, I will also discuss the effects of charged adsorbates on the electronic structure of doped graphene.

  9. Quasiparticle calculations for solids and molecules

    NASA Astrophysics Data System (ADS)

    Kioupakis, Emmanouil Stylianos

    Advances in modern materials research have a direct impact in technological innovation. Devices such as transistors, light emitting diodes, photovoltaic cells and thermoelectric modules are only possible due to the nature of the underlying materials. One challenge for theorists is the understanding and prediction of the properties of these materials. With the advent of density functional theory, highly accurate ab initio electronic structure calculations for the electronic ground state became a routine and valuable research tool[1, 2, 3, 4]. Fundamental properties such as the atomic structure, chemical bonding, total energy and vibrational frequencies can be determined, and issues like the surface reconstruction, interface geometry, atomic diffusion and the energetics of reactions can be addressed. However, not all relevant material properties are determined by the ground state. For those that involve excited states, such as the band structure and electronic band gap, the optical absorption spectrum and optical gap, the electron transport properties, the effective mass tensor and the alignment of the bands at the interface of two materials, we need an understanding of the excited quasiparticles of the system. While density functional theory gives accurate values for the ground state properties, the Kohn-Sham eigenvalues do not have a direct physical meaning and cannot be identified with quasiparticle energies. For these, we need to use methods that correctly provide excited state properties. One method that can provide accurate quasiparticle energies and wave functions is the GW method, where G is the one-particle Green's function and W the screened Coulomb interaction. Today, GW quasiparticle calculations can routinely be performed for a wide array of solids, molecules and nanosystems with a quasiparticle energy accuracy of ˜0.1 eV. Moreover, one can employ the Bethe-Salpeter equation formalism to take into account the electron-hole interaction and determine the

  10. Topological quantum computing with only one mobile quasiparticle.

    PubMed

    Simon, S H; Bonesteel, N E; Freedman, M H; Petrovic, N; Hormozi, L

    2006-02-24

    In a topological quantum computer, universal quantum computation is performed by dragging quasiparticle excitations of certain two dimensional systems around each other to form braids of their world lines in 2 + 1 dimensional space-time. In this Letter we show that any such quantum computation that can be done by braiding n identical quasiparticles can also be done by moving a single quasiparticle around n - 1 other identical quasiparticles whose positions remain fixed.

  11. Using Quasiparticle Poisoning To Detect Photons

    NASA Technical Reports Server (NTRS)

    Echternach, Pierre; Day, Peter

    2006-01-01

    According to a proposal, a phenomenon associated with excitation of quasiparticles in certain superconducting quantum devices would be exploited as a means of detecting photons with exquisite sensitivity. The phenomenon could also be exploited to perform medium-resolution spectroscopy. The proposal was inspired by the observation that Coulomb blockade devices upon which some quantum logic gates are based are extremely sensitive to quasiparticles excited above the superconducting gaps in their leads. The presence of quasiparticles in the leads can be easily detected via the charge states. If quasiparticles could be generated in the leads by absorption of photons, then the devices could be used as very sensitive detectors of electromagnetic radiation over the spectral range from x-rays to submillimeter waves. The devices in question are single-Cooper-pair boxes (SCBs), which are mesoscopic superconducting devices developed for quantum computing. An SCB consists of a small superconducting island connected to a reservoir via a small tunnel junction and connected to a voltage source through a gate capacitor. An SCB is an artificial two-level quantum system, the Hamiltonian of which can be controlled by the gate voltage. One measures the expected value of the charge of the eigenvectors of this quantum system by use of a radio-frequency single-electron transistor. A plot of this expected value of charge as a function of gate voltage resembles a staircase that, in the ideal case, consists of steps of height 2 e (where e is the charge of one electron). Experiments have shown that depending on the parameters of the device, quasiparticles in the form of "broken" Cooper pairs present in the reservoir can tunnel to the island, giving rise to steps of 1 e. This effect is sometimes called "poisoning." Simulations have shown that an extremely small average number of quasiparticles can generate a 1-e periodic signal. In a device according to the proposal, this poisoning would be

  12. Quasiparticle-continuum level repulsion in a quantum magnet

    DOE PAGES

    Plumb, K. W.; Hwang, Kyusung; Qiu, Y.; Harriger, Leland W.; Granroth, G.  E.; Kolesnikov, Alexander I.; Shu, G. J.; Chou, F. C.; Rüegg, Ch.; Kim, Yong Baek; et al

    2015-11-30

    When the energy eigenvalues of two coupled quantum states approach each other in a certain parameter space, their energy levels repel each other and level crossing is avoided. Such level repulsion, or avoided level crossing, is commonly used to describe the dispersion relation of quasiparticles in solids. But, little is known about the level repulsion when more than two quasiparticles are present; for example, in a strongly interacting quantum system where a quasiparticle can spontaneously decay into a many-particle continuum. Here we show that even in this case level repulsion exists between a long-lived quasiparticle state and a continuum. Here,more » we observe a renormalization of the quasiparticle dispersion relation due to the presence of the continuum of multi-quasiparticle states, in our fine-resolution neutron spectroscopy study of magnetic quasiparticles in the frustrated quantum magnet BiCu2PO6.« less

  13. Quasiparticle-continuum level repulsion in a quantum magnet

    SciTech Connect

    Plumb, K. W.; Hwang, Kyusung; Qiu, Y.; Harriger, Leland W.; Granroth, G.  E.; Kolesnikov, Alexander I.; Shu, G. J.; Chou, F. C.; Rüegg, Ch.; Kim, Yong Baek; Kim, Young-June

    2015-11-30

    When the energy eigenvalues of two coupled quantum states approach each other in a certain parameter space, their energy levels repel each other and level crossing is avoided. Such level repulsion, or avoided level crossing, is commonly used to describe the dispersion relation of quasiparticles in solids. But, little is known about the level repulsion when more than two quasiparticles are present; for example, in a strongly interacting quantum system where a quasiparticle can spontaneously decay into a many-particle continuum. Here we show that even in this case level repulsion exists between a long-lived quasiparticle state and a continuum. Here, we observe a renormalization of the quasiparticle dispersion relation due to the presence of the continuum of multi-quasiparticle states, in our fine-resolution neutron spectroscopy study of magnetic quasiparticles in the frustrated quantum magnet BiCu2PO6.

  14. Quasiparticle-continuum level repulsion in a quantum magnet

    NASA Astrophysics Data System (ADS)

    Plumb, K. W.; Hwang, Kyusung; Qiu, Y.; Harriger, Leland W.; Granroth, G. E.; Kolesnikov, Alexander I.; Shu, G. J.; Chou, F. C.; Rüegg, Ch.; Kim, Yong Baek; Kim, Young-June

    2016-03-01

    When the energy eigenvalues of two coupled quantum states approach each other in a certain parameter space, their energy levels repel each other and level crossing is avoided. Such level repulsion, or avoided level crossing, is commonly used to describe the dispersion relation of quasiparticles in solids. However, little is known about the level repulsion when more than two quasiparticles are present; for example, in a strongly interacting quantum system where a quasiparticle can spontaneously decay into a many-particle continuum. Here we show that even in this case level repulsion exists between a long-lived quasiparticle state and a continuum. In our fine-resolution neutron spectroscopy study of magnetic quasiparticles in the frustrated quantum magnet BiCu2PO6, we observe a renormalization of the quasiparticle dispersion relation due to the presence of the continuum of multi-quasiparticle states.

  15. Superfluid 4He dynamics beyond quasiparticle excitations

    NASA Astrophysics Data System (ADS)

    Beauvois, K.; Campbell, C. E.; Dawidowski, J.; Fâk, B.; Godfrin, H.; Krotscheck, E.; Lauter, H.-J.; Lichtenegger, T.; Ollivier, J.; Sultan, A.

    2016-07-01

    The dynamics of superfluid 4He at and above the Landau quasiparticle regime is investigated by high-precision inelastic neutron scattering measurements of the dynamic structure factor. A highly structured response is observed above the familiar phonon-maxon-roton spectrum, characterized by sharp thresholds for phonon-phonon, maxon-roton, and roton-roton coupling processes. The experimental dynamic structure factor is compared to the calculation of the same physical quantity by a dynamic many-body theory including three-phonon processes self-consistently. The theory is found to provide a quantitative description of the dynamics of the correlated bosons for energies up to about three times that of the Landau quasiparticles.

  16. Quasiparticle interactions in frustrated Heisenberg chains

    NASA Astrophysics Data System (ADS)

    Vanderstraeten, Laurens; Haegeman, Jutho; Verstraete, Frank; Poilblanc, Didier

    2016-06-01

    Interactions between elementary excitations in quasi-one-dimensional antiferromagnets are of experimental relevance and their quantitative theoretical treatment has been a theoretical challenge for many years. Using matrix product states, one can explicitly determine the wave functions of the one- and two-particle excitations, and, consequently, the contributions to dynamical correlations. We apply this framework to the (nonintegrable) frustrated dimerized spin-1/2 chain, a model for generic spin-Peierls systems, where low-energy quasiparticle excitations are bound states of topological solitons. The spin structure factor involving two quasiparticle scattering states is obtained in the thermodynamic limit with full momentum and frequency resolution. This allows very subtle features in the two-particle spectral function to be revealed which, we argue, could be seen, e.g., in inelastic neutron scattering of spin-Peierls compounds under a change of the external pressure.

  17. Theoretical Model to Explain Excess of Quasiparticles in Superconductors.

    PubMed

    Bespalov, Anton; Houzet, Manuel; Meyer, Julia S; Nazarov, Yuli V

    2016-09-01

    Experimentally, the concentration of quasiparticles in gapped superconductors always largely exceeds the equilibrium one at low temperatures. Since these quasiparticles are detrimental for many applications, it is important to understand theoretically the origin of the excess. We demonstrate in detail that the dynamics of quasiparticles localized at spatial fluctuations of the gap edge becomes exponentially slow. This gives rise to the observed excess in the presence of a vanishingly weak nonequilibrium agent. PMID:27661716

  18. Quasiparticle properties of Ge(111)-2 times 1 surface

    SciTech Connect

    Zhu, X.; Louie, S.G.

    1992-08-01

    We have studied from first principles the quasiparticle properties of the 2 {times} 1 reconstructed (111) surface of Ge. Quasiparticle energies are calculated using the GW expansion of the electron self energy operator. The calculations explain a spectrum of experimental results obtained from photoemission, inverse photoemission, optical absorption, scanning tunneling microscopy, etc., for this surface. We also present a quasiparticle theory for the photoelectric threshold and examine the effects of many body corrections for this quantity.

  19. 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...

  20. Effect of spin fluctuations on quasiparticle excitations: First-principles theory and application to sodium and lithium

    NASA Astrophysics Data System (ADS)

    Lischner, Johannes; Bazhirov, Timur; MacDonald, Allan H.; Cohen, Marvin L.; Louie, Steven G.

    2014-02-01

    We present first-principles calculations for quasiparticle excitations in sodium and lithium, including the effects of charge and spin fluctuations. We employ the Overhauser-Kukkonen form for the electron self-energy arising from spin fluctuations and demonstrate that the coupling of electrons to spin fluctuations gives an important contribution to the quasiparticle lifetime but does not significantly reduce the occupied bandwidth. Including correlation effects beyond the random-phase approximation in the screening from charge fluctuations yields good agreement with experiment.

  1. Internal structure of hole quasiparticles in antiferromagnets

    NASA Astrophysics Data System (ADS)

    Simons, B. D.; Gunn, J. M. F.

    1990-04-01

    Holes in an Ising antiferromagnet give rise to quasiparticles with an internal structure associated with the distortion of the spin ordering. We show that the spectrum of excited states (of this internal structure) commences at a lower energy than previously thought, at an energy of the order of the exchange constant. The character of the corresponding states differ from those previously discussed in that the phases associated with the various spin configurations with the same number of spin flips differ. Moreover, these excited states dominate the optical absorption and may explain the experimental results of Thomas et al. [Phys. Rev. Lett. 61, 1313 (1988)].

  2. Finite quasiparticle lifetime in disordered superconductors

    NASA Astrophysics Data System (ADS)

    Žemlička, M.; Neilinger, P.; Trgala, M.; Rehák, M.; Manca, D.; Grajcar, M.; Szabó, P.; Samuely, P.; Gaži, Š.; Hübner, U.; Vinokur, V. M.; Il'ichev, E.

    2015-12-01

    We investigate the complex conductivity of a highly disordered MoC superconducting film with kFl ≈1 , where kF is the Fermi wave number and l is the mean free path, derived from experimental transmission characteristics of coplanar waveguide resonators in a wide temperature range below the superconducting transition temperature Tc. We find that the original Mattis-Bardeen model with a finite quasiparticle lifetime, τ , offers a perfect description of the experimentally observed complex conductivity. We show that τ is appreciably reduced by scattering effects. Characteristics of the scattering centers are independently found by scanning tunneling spectroscopy and agree with those determined from the complex conductivity.

  3. Quasiparticle virtual orbitals in electron propagator calculations.

    PubMed

    Flores-Moreno, R; Ortiz, J V

    2008-04-28

    The computational limits of accurate electron propagator methods for the calculation of electron binding energies of large molecules are usually determined by the rank of the virtual orbital space. Electron density difference matrices that correspond to these transition energies in the second-order quasiparticle approximation may be used to obtain a virtual orbital space of reduced rank that introduces only minor deviations with respect to the results produced with the full, original set of virtual orbitals. Numerical tests show the superior accuracy and efficiency of this approach compared to the usual practice of omission of virtual orbitals with the highest energies.

  4. Charge of a quasiparticle in a superconductor.

    PubMed

    Ronen, Yuval; Cohen, Yonatan; Kang, Jung-Hyun; Haim, Arbel; Rieder, Maria-Theresa; Heiblum, Moty; Mahalu, Diana; Shtrikman, Hadas

    2016-02-16

    Nonlinear charge transport in superconductor-insulator-superconductor (SIS) Josephson junctions has a unique signature in the shuttled charge quantum between the two superconductors. In the zero-bias limit Cooper pairs, each with twice the electron charge, carry the Josephson current. An applied bias VSD leads to multiple Andreev reflections (MAR), which in the limit of weak tunneling probability should lead to integer multiples of the electron charge ne traversing the junction, with n integer larger than 2Δ/eVSD and Δ the superconducting order parameter. Exceptionally, just above the gap eVSD ≥ 2Δ, with Andreev reflections suppressed, one would expect the current to be carried by partitioned quasiparticles, each with energy-dependent charge, being a superposition of an electron and a hole. Using shot-noise measurements in an SIS junction induced in an InAs nanowire (with noise proportional to the partitioned charge), we first observed quantization of the partitioned charge q = e*/e = n, with n = 1-4, thus reaffirming the validity of our charge interpretation. Concentrating next on the bias region eVSD ~ 2Δ, we found a reproducible and clear dip in the extracted charge to q ~ 0.6, which, after excluding other possibilities, we attribute to the partitioned quasiparticle charge. Such dip is supported by numerical simulations of our SIS structure. PMID:26831071

  5. Nodal quasiparticle in pseudogapped colossal magnetoresistive manganites

    NASA Astrophysics Data System (ADS)

    Mannella, N.; Yang, W. L.; Zhou, X. J.; Tanaka, K.; Zheng, H.; Mitchell, J. F.; Zaanen, J.; Devereaux, T. P.; Nagaosa, N.; Hussain, Z.; Shen, Z. X.

    2006-03-01

    In this talk, the result of a recent angle-resolved photoemission spectroscopy (ARPES) investigation which allowed elucidating the controversial nature of the ferromagnetic metallic groundstate in the prototypical colossal magnetoresistive manganite bilayer compound La1.2Sr1.8Mn2O7 will be discussed [1]. The distribution of spectral weight in momentum space exhibits a nodal--antinodal dichotomous character. Quasiparticle excitations have been detected for the first time along the nodal direction (i.e. diagonal), and they are found to determine the metallic transport properties of this compound. The weight of the quasiparticle peak diminishes rapidly while crossing over to the antinodal (i.e. parallel to the Mn--O bonds) parallel sections of the Fermi surface, with the spectra strongly resembling those found in heavily underdoped cuprates high temperature superconductors (HTSC) such as Ca2-xNaxCuO2Cl2 [2]. This dichotomy between the electronic excitations along the nodal and antinodal directions in momentum space was so far considered a characteristic unique feature of the copper oxide HTSC. These findings therefore cast doubt on the assumption that the pseudogap state in the cuprate HTSC and the nodal-antinodal dichotomy are hallmarks of the superconductivity state. [1] N. Mannella et al., Nature 438, 474 (2005) [2] K. M Shen et al., Science 307, 901 (2005).

  6. Charge of a quasiparticle in a superconductor

    PubMed Central

    Ronen, Yuval; Cohen, Yonatan; Kang, Jung-Hyun; Haim, Arbel; Rieder, Maria-Theresa; Heiblum, Moty; Mahalu, Diana; Shtrikman, Hadas

    2016-01-01

    Nonlinear charge transport in superconductor–insulator–superconductor (SIS) Josephson junctions has a unique signature in the shuttled charge quantum between the two superconductors. In the zero-bias limit Cooper pairs, each with twice the electron charge, carry the Josephson current. An applied bias VSD leads to multiple Andreev reflections (MAR), which in the limit of weak tunneling probability should lead to integer multiples of the electron charge ne traversing the junction, with n integer larger than 2Δ/eVSD and Δ the superconducting order parameter. Exceptionally, just above the gap eVSD ≥ 2Δ, with Andreev reflections suppressed, one would expect the current to be carried by partitioned quasiparticles, each with energy-dependent charge, being a superposition of an electron and a hole. Using shot-noise measurements in an SIS junction induced in an InAs nanowire (with noise proportional to the partitioned charge), we first observed quantization of the partitioned charge q = e*/e=n, with n = 1–4, thus reaffirming the validity of our charge interpretation. Concentrating next on the bias region eVSD∼2Δ, we found a reproducible and clear dip in the extracted charge to q ∼0.6, which, after excluding other possibilities, we attribute to the partitioned quasiparticle charge. Such dip is supported by numerical simulations of our SIS structure. PMID:26831071

  7. Charge of a quasiparticle in a superconductor.

    PubMed

    Ronen, Yuval; Cohen, Yonatan; Kang, Jung-Hyun; Haim, Arbel; Rieder, Maria-Theresa; Heiblum, Moty; Mahalu, Diana; Shtrikman, Hadas

    2016-02-16

    Nonlinear charge transport in superconductor-insulator-superconductor (SIS) Josephson junctions has a unique signature in the shuttled charge quantum between the two superconductors. In the zero-bias limit Cooper pairs, each with twice the electron charge, carry the Josephson current. An applied bias VSD leads to multiple Andreev reflections (MAR), which in the limit of weak tunneling probability should lead to integer multiples of the electron charge ne traversing the junction, with n integer larger than 2Δ/eVSD and Δ the superconducting order parameter. Exceptionally, just above the gap eVSD ≥ 2Δ, with Andreev reflections suppressed, one would expect the current to be carried by partitioned quasiparticles, each with energy-dependent charge, being a superposition of an electron and a hole. Using shot-noise measurements in an SIS junction induced in an InAs nanowire (with noise proportional to the partitioned charge), we first observed quantization of the partitioned charge q = e*/e = n, with n = 1-4, thus reaffirming the validity of our charge interpretation. Concentrating next on the bias region eVSD ~ 2Δ, we found a reproducible and clear dip in the extracted charge to q ~ 0.6, which, after excluding other possibilities, we attribute to the partitioned quasiparticle charge. Such dip is supported by numerical simulations of our SIS structure.

  8. Normal-metal quasiparticle traps for superconducting qubits

    NASA Astrophysics Data System (ADS)

    Riwar, R.-P.; Hosseinkhani, A.; Burkhart, L. D.; Gao, Y. Y.; Schoelkopf, R. J.; Glazman, L. I.; Catelani, G.

    2016-09-01

    The presence of quasiparticles in superconducting qubits emerges as an intrinsic constraint on their coherence. While it is difficult to prevent the generation of quasiparticles, keeping them away from active elements of the qubit provides a viable way of improving the device performance. Here we develop theoretically and validate experimentally a model for the effect of a single small trap on the dynamics of the excess quasiparticles injected in a transmon-type qubit. The model allows one to evaluate the time it takes to evacuate the injected quasiparticles from the transmon as a function of trap parameters. With the increase of the trap size, this time decreases monotonically, saturating at the level determined by the quasiparticles diffusion constant and the qubit geometry. We determine the characteristic trap size needed for the relaxation time to approach that saturation value.

  9. Quasiparticle Aggregation in the Fractional Quantum Hall Effect

    DOE R&D Accomplishments Database

    Laughlin, R. B.

    1984-10-10

    Quasiparticles in the Fractional Quantum Hall Effect behave qualitatively like electrons confined to the lowest landau level, and can do everything electrons can do, including condense into second generation Fractional Quantum Hall ground states. I review in this paper the reasoning leading to variational wavefunctions for ground state and quasiparticles in the 1/3 effect. I then show how two-quasiparticle eigenstates are uniquely determined from symmetry, and how this leads in a natural way to variational wavefunctions for composite states which have the correct densities (2/5, 2/7, ...). I show in the process that the boson, anyon and fermion representations for the quasiparticles used by Haldane, Halperin, and me are all equivalent. I demonstrate a simple way to derive Halperin`s multiple-valued quasiparticle wavefunction from the correct single-valued electron wavefunction. (auth)

  10. Coherent Suppression of Quasiparticle Dissipation in Superconducting Artificial Atom

    NASA Astrophysics Data System (ADS)

    Pop, Ioan M.

    2015-03-01

    We demonstrate immunity to quasiparticle dissipation in a Josephson junction. At the foundation of this protection rests a prediction by Brian Josephson from fifty years ago: the particle-hole interference of superconducting quasiparticles when tunneling across a Josephson junction. The junction under study is the central element of a fluxonium artificial atom, which we place in an extremely low loss environment and measure using radio-frequency dispersive techniques. Furthermore, by using a quantum limited amplifier (a Josephson Parametric Converter) we can observe quantum jumps between the 0 and 1 states of the qubit in thermal equilibrium with the environment. The distribution of the times in-between the quantum jumps reveals quantitative information about the population and dynamics of quasiparticles. The data is entirely consistent with the hypothesis that our system is sensitive to single quasiparticle excitations, which opens new perspectives for quasiparticle monitoring in low temperature devices. Work supported by: IARPA, ARO, and ONR.

  11. Quasiparticle interference, quasiparticle interactions, and the origin of the charge density wave in 2H-NbSe2.

    PubMed

    Arguello, C J; Rosenthal, E P; Andrade, E F; Jin, W; Yeh, P C; Zaki, N; Jia, S; Cava, R J; Fernandes, R M; Millis, A J; Valla, T; Osgood, R M; Pasupathy, A N

    2015-01-23

    We show that a small number of intentionally introduced defects can be used as a spectroscopic tool to amplify quasiparticle interference in 2H-NbSe2 that we measure by scanning tunneling spectroscopic imaging. We show, from the momentum and energy dependence of the quasiparticle interference, that Fermi surface nesting is inconsequential to charge density wave formation in 2H-NbSe2. We demonstrate that, by combining quasiparticle interference data with additional knowledge of the quasiparticle band structure from angle resolved photoemission measurements, one can extract the wave vector and energy dependence of the important electronic scattering processes thereby obtaining direct information both about the fermiology and the interactions. In 2H-NbSe2, we use this combination to confirm that the important near-Fermi-surface electronic physics is dominated by the coupling of the quasiparticles to soft mode phonons at a wave vector different from the charge density wave ordering wave vector.

  12. Quasiparticle interference, quasiparticle interactions, and the origin of the charge density wave in 2H–NbSe2

    DOE PAGES

    Arguello, C. J.; Rosenthal, E. P.; Andrade, E. F.; Jin, W.; Yeh, P. C.; Zaki, N.; Jia, S.; Cava, R. J.; Fernandes, R. M.; Millis, A. J.; et al

    2015-01-21

    We show that a small number of intentionally introduced defects can be used as a spectroscopic tool to amplify quasiparticle interference in 2H-NbSe₂, that we measure by scanning tunneling spectroscopic imaging. We show from the momentum and energy dependence of the quasiparticle interference that Fermi surface nesting is inconsequential to charge density wave formation in 2H-NbSe₂. Thus, we demonstrate that by combining quasiparticle interference data with additional knowledge of the quasiparticle band structure from angle resolved photoemission measurements, one can extract the wavevector and energy dependence of the important electronic scattering processes thereby obtaining direct information both about the fermiologymore » and the interactions. In 2H-NbSe₂, we use this combination to show that the important near-Fermi-surface electronic physics is dominated by the coupling of the quasiparticles to soft mode phonons at a wave vector different from the CDW ordering wave vector.« less

  13. Finite quasiparticle lifetime in disordered superconductors.

    SciTech Connect

    Zemlicka, M.; Neilinger, P.; Trgala, M; Rehak, M; Manca, D.; Grajcar, M.; Szabo, P.; Samuely, P.; Gazi, S.; Hubner, U.; Vinokur, V. M.; Il'ichev, E.

    2015-12-08

    We investigate the complex conductivity of a highly disordered MoC superconducting film with k(F)l approximate to 1, where k(F) is the Fermi wave number and l is the mean free path, derived from experimental transmission characteristics of coplanar waveguide resonators in a wide temperature range below the superconducting transition temperature T-c. We find that the original Mattis-Bardeen model with a finite quasiparticle lifetime, tau, offers a perfect description of the experimentally observed complex conductivity. We show that iota is appreciably reduced by scattering effects. Characteristics of the scattering centers are independently found by scanning tunneling spectroscopy and agree with those determined from the complex conductivity.

  14. Quasiparticle band structure of vanadium dioxide.

    PubMed

    Sakuma, R; Miyake, T; Aryasetiawan, F

    2009-02-11

    Vanadium dioxide is insulating below 340 K in experiments, whereas the band structure calculated in the local density approximation (LDA) is gapless. We study the self-energy effects using the ab initio GW method. We found that the self-energy depends strongly on the energy, and proper treatment of the dynamical effect is essential for getting precise quasiparticle energies. Off-diagonal matrix elements in the Kohn-Sham basis are also important for disentangling bands. Inclusion of the two effects opens up a direct gap. Our results also suggest that one-shot GW on top of LDA is not enough, and the impact of self-consistency is significant.

  15. Nonlinear nonequilibrium quasiparticle relaxation in Josephson junctions.

    PubMed

    Krasnov, V M

    2009-11-27

    I solve numerically a full set of nonlinear kinetic balance equations for stacked Josephson junctions, which allows analysis of strongly nonequilibrium phenomena. It is shown that nonlinearity becomes significant already at very small disequilibrium. The following new, nonlinear effects are obtained: (i) At even-gap voltages V = 2nDelta/e (n = 2, 3, ...) nonequilibrium bosonic bands overlap. This leads to enhanced emission of Omega = 2Delta bosons and to the appearance of dips in tunnel conductance. (ii) A new type of radiative solution is found at strong disequilibrium. It is characterized by the fast stimulated relaxation of quasiparticles. A stack in this state behaves as a light emitting diode and directly converts electric power to boson emission, without utilization of the ac-Josephson effect. The phenomenon can be used for realization of a new type of superconducting cascade laser in the THz frequency range.

  16. Nuclear response theory for spin-isospin excitations in a relativistic quasiparticle-phonon coupling framework

    NASA Astrophysics Data System (ADS)

    Robin, Caroline; Litvinova, Elena

    2016-07-01

    A new theoretical approach to spin-isospin excitations in open-shell nuclei is presented. The developed method is based on the relativistic meson-exchange nuclear Lagrangian of Quantum Hadrodynamics and extends the response theory for superfluid nuclear systems beyond relativistic quasiparticle random phase approximation in the proton-neutron channel (pn-RQRPA). The coupling between quasiparticle degrees of freedom and collective vibrations (phonons) introduces a time-dependent effective interaction, in addition to the exchange of pion and ρ -meson taken into account without retardation. The time-dependent contributions are treated in the resonant time-blocking approximation, in analogy to the previously developed relativistic quasiparticle time-blocking approximation (RQTBA) in the neutral (non-isospin-flip) channel. The new method is called proton-neutron RQTBA (pn-RQTBA) and is applied to the Gamow-Teller resonance in a chain of neutron-rich nickel isotopes 68-78Ni . A strong fragmentation of the resonance along with quenching of the strength, as compared to pn-RQRPA, is obtained. Based on the calculated strength distribution, beta-decay half-lives of the considered isotopes are computed and compared to pn-RQRPA half-lives and to experimental data. It is shown that a considerable improvement of the half-life description is obtained in pn-RQTBA because of the spreading effects, which bring the lifetimes to a very good quantitative agreement with data.

  17. Electric dipole response of neutron-rich calcium isotopes in relativistic quasiparticle time blocking approximation

    NASA Astrophysics Data System (ADS)

    Egorova, Irina A.; Litvinova, Elena

    2016-09-01

    New results for electric dipole strength in the chain of even-even calcium isotopes with the mass numbers A =40 -54 are presented. Starting from the covariant Lagrangian of quantum hadrodynamics, spectra of collective vibrations (phonons) and phonon-nucleon coupling vertices for J ≤6 and natural parity were computed in a self-consistent relativistic quasiparticle random-phase approximation (RQRPA). These vibrations coupled to Bogoliubov two-quasiparticle configurations (2 q ⊗phonon ) formed the model space for the calculations of the dipole response function in the relativistic quasiparticle time blocking approximation. The calculations in the latter approach were performed for the giant dipole resonance (GDR) and compared to those obtained with the RQRPA and to available data. The evolution of the dipole strength with the neutron number is investigated for both high-frequency GDRs and low-lying strengths. The development of a pygmy resonant structure on the low-energy shoulder of the GDR is traced and analyzed in terms of transition densities. A dependence of the pygmy dipole strength on the isospin asymmetry parameter is extracted.

  18. Quasiparticles in the pseudogap Phase of Underdoped Cuprate

    SciTech Connect

    Yang, K.; Yang, H; Johnson, P; Rice, T; Zhang, F

    2009-01-01

    Recent angle-resolved photoemission (Yang H.-B. et al., Nature, 456 (2008) 77) and scanning tunneling microscopy (Kohsaka Y. et al., Nature, 454 (2008) 1072) measurements on underdoped cuprates have yielded new spectroscopic information on quasiparticles in the pseudogap phase. New features of the normal state such as particle-hole asymmetry, maxima in the energy dispersion, and accompanying drops in the spectral weight of quasiparticles agree with the ansatz of Yang et al. for the single-particle propagator in the pseudogap phase. The coherent quasiparticle dispersion and reduced asymmetry in the tunneling density of states in the superconducting state can also be described by this propagator.

  19. 'Cosmological' quasiparticle production in harmonically trapped superfluid gases

    SciTech Connect

    Fedichev, Petr O.; Fischer, Uwe R.

    2004-03-01

    We show that a variety of cosmologically motivated effective quasiparticle space-times can be produced in harmonically trapped superfluid Bose and Fermi gases. We study the analog of cosmological particle production in these effective space-times, induced by trapping potentials and coupling constants possessing an arbitrary time dependence. The WKB probabilities for phonon creation from the superfluid vacuum are calculated, and an experimental procedure to detect quasiparticle production by measuring density-density correlation functions is proposed.

  20. One-quasiparticle states in odd-Z heavy nuclei

    SciTech Connect

    Adamian, G. G.; Antonenko, N. V.; Kuklin, S. N.; Scheid, W.

    2010-11-15

    The isotopic dependencies of one-quasiparticle states in Es and Md are treated. In {sup 253,255}Lr, the energies of the lowest one-quasiproton states are calculated. The one-quasiparticle isomer states are revealed in the nuclei of an {alpha}-decay chain starting from {sup 269}Rg. The {alpha} decays from some isomer states are predicted. The population of isomer states in the complete fusion reactions is discussed.

  1. Shooting quasiparticles from Andreev bound states in a superconducting constriction

    SciTech Connect

    Riwar, R.-P.; Houzet, M.; Meyer, J. S.; Nazarov, Y. V.

    2014-12-15

    A few-channel superconducting constriction provides a set of discrete Andreev bound states that may be populated with quasiparticles. Motivated by recent experimental research, we study the processes in an a.c. driven constriction whereby a quasiparticle is promoted to the delocalized states outside the superconducting gap and flies away. We distinguish two processes of this kind. In the process of ionization, a quasiparticle present in the Andreev bound state is transferred to the delocalized states leaving the constriction. The refill process involves two quasiparticles: one flies away while another one appears in the Andreev bound state. We notice an interesting asymmetry of these processes. The electron-like quasiparticles are predominantly emitted to one side of the constriction while the hole-like ones are emitted to the other side. This produces a charge imbalance of accumulated quasiparticles, that is opposite on opposite sides of the junction. The imbalance may be detected with a tunnel contact to a normal metal lead.

  2. Quasiparticle energy studies of bulk semiconductors, surfaces and nanotubes

    SciTech Connect

    Blase, X.F.

    1994-12-01

    Effects of many-body effects on electronic excitation energies (quasiparticle band structure) of these materials are explored. GW approximation, including local field effects, for self-energy operator is used to calculate quasi-particle energies. The newly discovered carbon nanotubes are studied; structural stability and band structures are calculated. BN nanotubes are also studied, and their stability is predicted. Unexpected electronic features are predicted for both systems. Filling of carbon nanotubes with metal atoms and the doping of BN nanotubes by carbon and other impurites is also studied. The occupied surface states at H/Si(111)-(1{times}1) surface are studied; it is shown that the electronic structure requires a full quasiparticle calculation even for this simple chemisorption system. The core level shift of the Si 2p levels for atoms near the H/Si(111)-(1{times}1) surface is calculated; a simple first order perturbation theory using pseudopotential and the local density approximation gives good results for the photoemission spectra of the core electrons. The quasiparticle energies of bulk hexagonal BN and those of an isolated BN sheet are studied; this provides an understanding of the quasiparticle band structure of BN nanotubes. A nearly free electron state with a wavefunction in the interlayer or vacuum region composes the bottom of the conduction bands. A mixed-space formalism is presented for calculating the dynamical screening effects and electron self-energy operator in solids; this provides an efficient algorithm to calculate quasiparticle energies for large systems.

  3. Nodal Quasiparticle in Pseudogapped Colossal Magnetoresistive Manganites

    SciTech Connect

    Mannella, N.

    2010-06-02

    A characteristic feature of the copper oxide high-temperature superconductors is the dichotomy between the electronic excitations along the nodal (diagonal) and antinodal (parallel to the Cu-O bonds) directions in momentum space, generally assumed to be linked to the d-wave symmetry of the superconducting state. Angle-resolved photoemission measurements in the superconducting state have revealed a quasiparticle spectrum with a d-wave gap structure that exhibits a maximum along the antinodal direction and vanishes along the nodal direction. Subsequent measurements have shown that, at low doping levels, this gap structure persists even in the high-temperature metallic state, although the nodal points of the superconducting state spread out in finite Fermi arcs. This is the so-called pseudogap phase, and it has been assumed that it is closely linked to the superconducting state, either by assigning it to fluctuating superconductivity or by invoking orders which are natural competitors of d-wave superconductors. Here we report experimental evidence that a very similar pseudogap state with a nodal-antinodal dichotomous character exists in a system that is markedly different from a superconductor: the ferromagnetic metallic groundstate of the colossal magnetoresistive bilayer manganite La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7}. Our findings therefore cast doubt on the assumption that the pseudogap state in the copper oxides and the nodal-antinodal dichotomy are hallmarks of the superconductivity state.

  4. QCD critical point in a quasiparticle model

    SciTech Connect

    Srivastava, P. K.; Tiwari, S. K.; Singh, C. P.

    2010-07-01

    Recent theoretical investigations have unveiled a rich structure in the quantum chromodynamics phase diagram, which consists of quark-gluon plasma and the hadronic phases but also supports the existence of a crossover transition ending at a critical end point (CEP). We find a too large variation in the determination of the coordinates of the CEP in the temperature (T) baryon chemical potential ({mu}{sub B}) plane; and, therefore, its identification in the current heavy-ion experiments becomes debatable. Here we use an equation of state for a deconfined quark-gluon plasma using a thermodynamically-consistent quasiparticle model involving noninteracting quarks and gluons having thermal masses. We further use a thermodynamically-consistent excluded-volume model for the hadron gas, which was recently proposed by us. Using these equations of state, a first-order deconfining phase transition is constructed using Gibbs's criteria. This leads to an interesting finding that the phase transition line ends at a critical end point (CEP) beyond which a crossover region exists. Using our thermal hadron gas model, we obtain a chemical freeze out curve, and we find that the CEP lies in close proximity to this curve as proposed by some authors. The coordinates of CEP are found to lie within the reach of Relativistic heavy-ion collider experiment.

  5. Quasiparticle Level Alignment for Photocatalytic Interfaces

    SciTech Connect

    Migani, Annapaola; Mowbray, Duncan J.; Zhao, Jin; Petek, Hrvoje; Rubio, Angel

    2014-05-13

    Electronic level alignment at the interface between an adsorbed molecular layer and a semiconducting substrate determines the activity and efficiency of many photocatalytic materials. Standard density functional theory (DFT)-based methods have proven unable to provide a quantitative description of this level alignment. This requires a proper treatment of the anisotropic screening, necessitating the use of quasiparticle (QP) techniques. However, the computational complexity of QP algorithms has meant a quantitative description of interfacial levels has remained elusive. We provide a systematic study of a prototypical interface, bare and methanol-covered rutile TiO2(110) surfaces, to determine the type of many-body theory required to obtain an accurate description of the level alignment. This is accomplished via a direct comparison with metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS), and two-photon photoemission (2PP) spectroscopy. We consider GGA DFT, hybrid DFT, and G0W0, scQPGW1, scQPGW0, and scQPGW QP calculations. Our results demonstrate that G0W0, or our recently introduced scQPGW1 approach, are required to obtain the correct alignment of both the highest occupied and lowest unoccupied interfacial molecular levels (HOMO/LUMO). These calculations set a new standard in the interpretation of electronic structure probe experiments of complex organic molecule/semiconductor interfaces.

  6. Quantum logic gates from Dirac quasiparticles

    NASA Astrophysics Data System (ADS)

    Marino, E. C.; Brozeguini, J. C.

    2015-03-01

    We show that one of the fundamental operations of topological quantum computation, namely the non-Abelian braiding of identical particles, can be physically realized in a general system of Dirac quasiparticles in 1 + 1D. Our method is based on the study of the analytic structure of the different Euclidean correlation functions of Dirac fields, which are conveniently expressed as functions of a complex variable. When the Dirac field is an (Abelian) anyon with statistics parameter s (2s not an integer), we show that the associated Majorana states of such a field present non-Abelian statistics. The explicit form of the unitary, non-commuting (monodromy) matrices generated upon braiding is derived as a function of s and is shown to satisfy the Yang-Baxter algebra. For the special case of s = 1/4, we show that the braiding matrices become the logic gates NOT, CNOT,… required in the algorithms of universal quantum computation. We suggest that maybe polyacetylene, alternately doped with alkali and halogen atoms, is a potential candidate for a physical material realization of the system studied here.

  7. Recombination and propagation of quasiparticles in cuprate superconductors

    SciTech Connect

    Gedik, Nuh

    2004-05-20

    Rapid developments in time-resolved optical spectroscopy have led to renewed interest in the nonequilibrium state of superconductors and other highly correlated electron materials. In these experiments, the nonequilibrium state is prepared by the absorption of short (less than 100 fs) laser pulses, typically in the near-infrared, that perturb the density and energy distribution of quasiparticles. The evolution of the nonequilibrium state is probed by time resolving the changes in the optical response functions of the medium that take place after photoexcitation. Ultimately, the goal of such experiments is to understand not only the nonequilibrium state, but to shed light on the still poorly understood equilibrium properties of these materials. We report nonequilibrium experiments that have revealed aspects of the cup rates that have been inaccessible by other techniques. Namely, the diffusion and recombination coefficients of quasiparticles have been measured in both YBa{sub 2}Cu{sub 3}O{sub 6.5} and Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x} using time-resolved optical spectroscopy. Dependence of these measurements on doping, temperature and laser intensity is also obtained. To study the recombination of quasiparticles, we measure the change in reflectivity {Delta}R which is directly proportional to the nonequilibrium quasiparticle density created by the laser. From the intensity dependence, we estimate {beta}, the inelastic scattering coefficient and {gamma}{sub th} thermal equilibrium quasiparticle decay rate. We also present the dependence of recombination measurements on doping in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+x}. Going from underdoped to overdoped regime, the sign of {Delta}R changes from positive to negative right at the optimal doping. This is accompanied by a change in dynamics. The decay of {Delta}R stops being intensity dependent exactly at the optimal doping. We provide possible interpretations of these two observations. To study the propagation of

  8. A Randomized, Double-Blind, Placebo-Controlled Assessment of BMS-936558, a Fully Human Monoclonal Antibody to Programmed Death-1 (PD-1), in Patients with Chronic Hepatitis C Virus Infection

    PubMed Central

    Gardiner, David; Lalezari, Jay; Lawitz, Eric; DiMicco, Michael; Ghalib, Rheem; Reddy, K. Rajender; Chang, Kyong-Mi; Sulkowski, Mark; Marro, Steven O’; Anderson, Jeffrey; He, Bing; Kansra, Vikram; McPhee, Fiona; Wind-Rotolo, Megan; Grasela, Dennis; Selby, Mark; Korman, Alan J.; Lowy, Israel

    2013-01-01

    Expression of the programmed death 1 (PD-1) receptor and its ligands are implicated in the T cell exhaustion phenotype which contributes to the persistence of several chronic viral infections, including human hepatitis C virus (HCV). The antiviral potential of BMS-936558 (MDX-1106) – a fully human anti-PD-1 monoclonal immunoglobulin-G4 that blocks ligand binding – was explored in a proof-of-concept, placebo-controlled single-ascending-dose study in patients (N = 54) with chronic HCV infection. Interferon-alfa treatment-experienced patients (n = 42) were randomized 5∶1 to receive a single infusion of BMS-936558 (0.03, 0.1, 0.3, 1.0, 3.0 mg/kg [n = 5 each] or 10 mg/kg [n = 10]) or of placebo (n = 7). An additional 12 HCV treatment-naïve patients were randomized to receive 10 mg/kg BMS-936558 (n = 10) or placebo (n = 2). Patients were followed for 85 days post-dose. Five patients who received BMS-936558 (0.1 [n = 1] or 10 mg/kg) and one placebo patient achieved the primary study endpoint of a reduction in HCV RNA ≥0.5 log10 IU/mL on at least 2 consecutive visits; 3 (10 mg/kg) achieved a >4 log10 reduction. Two patients (10 mg/kg) achieved HCV RNA below the lower limit of quantitation (25 IU/mL), one of whom (a prior null-responder) remained RNA-undetectable 1 year post-study. Transient reductions in CD4+, CD8+ and CD19+ cells, including both naïve and memory CD4+ and CD8+ subsets, were observed at Day 2 without evidence of immune deficit. No clinically relevant changes in immunoglobulin subsets or treatment-related trends in circulating cytokines were noted. BMS-936558 exhibited dose-related exposure increases, with a half-life of 20–24 days. BMS-936558 was mostly well tolerated. One patient (10 mg/kg) experienced an asymptomatic grade 4 ALT elevation coincident with the onset of a 4-log viral load reduction. Six patients exhibited immune-related adverse events of mild-to-moderate intensity, including two cases of

  9. Model for nodal quasiparticle scattering in a disordered vortex lattice

    NASA Astrophysics Data System (ADS)

    Maltseva, Marianna; Coleman, P.

    2009-10-01

    Recent scanning-tunneling experiments on Ca2-xNaxCuO2Cl2 by Hanaguri [Science 323, 923 (2009)] observe field-dependent quasiparticle interference effects which are sensitive to the sign of the d -wave order parameter. Their analysis of spatial fluctuations in the local density of states shows that there is a selective enhancement of quasiparticle scattering events that preserve the gap sign and a selective depression of the quasiparticle scattering events that reverse the gap sign. We introduce a model which accounts for this phenomenon as a consequence of vortex pinning to impurities. Each pinned vortex embeds several impurities in its core. The observations of recent experiments can be accounted for by assuming that the scattering potentials of the impurities inside the vortex cores acquire an additional resonant or Andreev scattering component, both of which induce gap sign preserving scattering events.

  10. Deformations and Quasiparticle Spectra of Nuclei in the Nobelium Region

    NASA Astrophysics Data System (ADS)

    Shi, Yue; Dobaczewski, J.; Greenlees, P. T.; Toivanen, J.; Toivanen, P.

    2014-09-01

    We have performed self-consistent Skyrme Hartree-Fock-Bogolyubov calculations for nuclei close to 254No. Self-consistent deformations, including β2,4,6,8 as functions of the rotational frequency, were determined for even-even nuclei 246,248,250Fm, 252,254No, and 256Rf. The quasiparticle spectra for N = 151 isotones and Z = 99 isotopes were calculated and compared with experimental data and the results of Woods-Saxon calculations. We found that our calculations give high-order deformations similar to those obtained for the Woods-Saxon potential, and that the experimental quasiparticle energies are reasonably well reproduced.

  11. Landau's quasiparticle mapping: Fermi liquid approach and Luttinger liquid behavior.

    PubMed

    Heidbrink, Caspar P; Uhrig, Götz S

    2002-04-01

    A continuous unitary transformation is introduced which realizes Landau's mapping of the elementary excitations (quasiparticles) of an interacting Fermi liquid system to those of the system without interaction. The conservation of the number of quasiparticles is important. The transformation is performed numerically for a one-dimensional system, i.e., the worst case for a Fermi liquid approach. Yet evidence for Luttinger liquid behavior is found. Such an approach may open a route to a unified description of Fermi and Luttinger liquids on all energy scales.

  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

    2013-03-01

    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. Lightwave-driven quasiparticle collisions on a subcycle timescale.

    PubMed

    Langer, F; Hohenleutner, M; Schmid, C P; Poellmann, C; Nagler, P; Korn, T; Schüller, C; Sherwin, M S; Huttner, U; Steiner, J T; Koch, S W; Kira, M; Huber, R

    2016-05-12

    Ever since Ernest Rutherford scattered α-particles from gold foils, collision experiments have revealed insights into atoms, nuclei and elementary particles. In solids, many-body correlations lead to characteristic resonances--called quasiparticles--such as excitons, dropletons, polarons and Cooper pairs. The structure and dynamics of quasiparticles are important because they define macroscopic phenomena such as Mott insulating states, spontaneous spin- and charge-order, and high-temperature superconductivity. However, the extremely short lifetimes of these entities make practical implementations of a suitable collider challenging. Here we exploit lightwave-driven charge transport, the foundation of attosecond science, to explore ultrafast quasiparticle collisions directly in the time domain: a femtosecond optical pulse creates excitonic electron-hole pairs in the layered dichalcogenide tungsten diselenide while a strong terahertz field accelerates and collides the electrons with the holes. The underlying dynamics of the wave packets, including collision, pair annihilation, quantum interference and dephasing, are detected as light emission in high-order spectral sidebands of the optical excitation. A full quantum theory explains our observations microscopically. This approach enables collision experiments with various complex quasiparticles and suggests a promising new way of generating sub-femtosecond pulses. PMID:27172045

  14. Kondo physics from quasiparticle poisoning in Majorana devices

    NASA Astrophysics Data System (ADS)

    Plugge, S.; Zazunov, A.; Eriksson, E.; Tsvelik, A. M.; Egger, R.

    2016-03-01

    We present a theoretical analysis of quasiparticle poisoning in Coulomb-blockaded Majorana fermion systems tunnel-coupled to normal-conducting leads. Taking into account finite-energy quasiparticles, we derive the effective low-energy theory and present a renormalization group analysis. We find qualitatively new effects when a quasiparticle state with very low energy is localized near a tunnel contact. For M =2 attached leads, such "dangerous" quasiparticle poisoning processes cause a spin S =1 /2 single-channel Kondo effect, which can be detected through a characteristic zero-bias anomaly conductance peak in all Coulomb blockade valleys. For more than two attached leads, the topological Kondo effect of the unpoisoned system becomes unstable. A strong-coupling bosonization analysis indicates that at low energy the poisoned lead is effectively decoupled and hence, for M >3 , the topological Kondo fixed point re-emerges, though now it involves only M -1 leads. As a consequence, for M =3 , the low-energy fixed point becomes trivial corresponding to decoupled leads.

  15. Kondo physics from quasiparticle poisoning in Majorana devices

    DOE PAGES

    Plugge, S.; Tsvelik, A. M.; Zazunov, A.; Eriksson, E.; Egger, R.

    2016-03-24

    Here, we present a theoretical analysis of quasiparticle poisoning in Coulomb-blockaded Majorana fermion systems tunnel-coupled to normal-conducting leads. Taking into account finite-energy quasiparticles, we derive the effective low-energy theory and present a renormalization group analysis. We find qualitatively new effects when a quasiparticle state with very low energy is localized near a tunnel contact. For M = 2 attached leads, such “dangerous” quasiparticle poisoning processes cause a spin S = 1/2 single-channel Kondo effect, which can be detected through a characteristic zero-bias anomaly conductance peak in all Coulomb blockade valleys. For more than two attached leads, the topological Kondo effectmore » of the unpoisoned system becomes unstable. A strong-coupling bosonization analysis indicates that at low energy the poisoned lead is effectively decoupled and hence, for M > 3, the topological Kondo fixed point re-emerges, though now it involves only M–1 leads. As a consequence, for M = 3, the low-energy fixed point becomes trivial corresponding to decoupled leads.« less

  16. Critical relaxation with overdamped quasiparticles in open quantum systems

    NASA Astrophysics Data System (ADS)

    Lang, Johannes; Piazza, Francesco

    2016-09-01

    We study the late-time relaxation following a quench in an open quantum many-body system. We consider the open Dicke model, describing the infinite-range interactions between N atoms and a single, lossy electromagnetic mode. We show that the dynamical phase transition at a critical atom-light coupling is characterized by the interplay between reservoir-driven and intrinsic relaxation processes in the absence of number conservation. Above the critical coupling, small fluctuations in the occupation of the dominant quasiparticle mode start to grow in time, while the quasiparticle lifetime remains finite due to losses. Near the critical interaction strength, we observe a crossover between exponential and power-law 1 /τ relaxation, the latter driven by collisions between quasiparticles. For a quench exactly to the critical coupling, the power-law relaxation extends to infinite times, but the finite lifetime of quasiparticles prevents aging from appearing in two-times response and correlation functions. We predict our results to be accessible to quench experiments with ultracold bosons in optical resonators.

  17. Nonequilibrium electron dynamics: Formation of the quasiparticle peak

    NASA Astrophysics Data System (ADS)

    Sayyad, Sharareh; Eckstein, Martin

    We characterize how the narrow quasiparticle band of the one-band Hubbard model forms out of a bad metallic state in a time-dependent metal-insulator transition, using nonequilibrium slave-rotor dynamical mean field theory. Our results exhibit a nontrivial electronic timescale which is much longer than the width of the quasiparticle peak itself. To study this timescale, we perform a fast ramp from the insulating phase into the metallic region of the phase diagram, resulting in a highly excited state, and study the equilibration of the system with a weakly coupled phononic bath. The slow relaxation behavior is explained by surveilling the interplay between spinon and rotor degrees of freedom. Since the system is initially prepared in an insulating phase, the quasi-particle peak emerges when spinons catch up the metal-insulator crossover region, which is reached earlier by the rotor. At this point, spinon and rotor become weakly coupled, and the resulting very slow equilibration of the spinon is a bottleneck for the dynamics. After the birth of the quasiparticle peak, its height enhances by the construction of the low-energy spectrum of the rotor, which then lacks behind the relaxation of the spinon.

  18. Non-Poissonian quantum jumps of a fluxonium qubit due to quasiparticle excitations.

    PubMed

    Vool, U; Pop, I M; Sliwa, K; Abdo, B; Wang, C; Brecht, T; Gao, Y Y; Shankar, S; Hatridge, M; Catelani, G; Mirrahimi, M; Frunzio, L; Schoelkopf, R J; Glazman, L I; Devoret, M H

    2014-12-12

    As the energy relaxation time of superconducting qubits steadily improves, nonequilibrium quasiparticle excitations above the superconducting gap emerge as an increasingly relevant limit for qubit coherence. We measure fluctuations in the number of quasiparticle excitations by continuously monitoring the spontaneous quantum jumps between the states of a fluxonium qubit, in conditions where relaxation is dominated by quasiparticle loss. Resolution on the scale of a single quasiparticle is obtained by performing quantum nondemolition projective measurements within a time interval much shorter than T₁, using a quantum-limited amplifier (Josephson parametric converter). The quantum jump statistics switches between the expected Poisson distribution and a non-Poissonian one, indicating large relative fluctuations in the quasiparticle population, on time scales varying from seconds to hours. This dynamics can be modified controllably by injecting quasiparticles or by seeding quasiparticle-trapping vortices by cooling down in a magnetic field. PMID:25541795

  19. A DOUBLE-BLIND RANDOMIZED CONTROLLED TRIAL OF OLANZAPINE PLUS SERTRALINE VERSUS OLANZAPINE PLUS PLACEBO FOR PSYCHOTIC DEPRESSION -- THE STOP-PD STUDY

    PubMed Central

    Meyers, Barnett S.; Flint, Alastair J.; Rothschild, Anthony J.; Mulsant, Benoit H.; Whyte, Ellen M.; Peasley-Miklus, Catherine; Papademetriou, Eros; Leon, Andrew C.; Heo, Moonseong

    2010-01-01

    Context: Expert guidelines recommend that the pharmacological treatment of major depression with psychotic features (MDpsy) combines antidepressant with antipsychotic medications. However, evidence for the efficacy of combination pharmacotherapy has been limited and without positive trials in geriatric patients. Objective: (1) Compare remission rates in MDpsy associated with combination atypical antipsychotic medication plus a serotonin-reuptake-inhibitor antidepressant (SSRI) to remission associated with antipsychotic monotherapy; (2) Compare the efficacy and tolerability of treatment in younger versus older adults. Design and Context: Twelve-week double-blind randomized controlled comparison of olanzapine plus sertraline to olanzapine plus placebo conducted on clinical services of four academic sites. Patients and Interventions: 259 subjects with MDpsy randomized by age ≥60 on a 1:1 basis; mean age of 117 younger adults = 41.3(10.8) versus 71.7(7.8) in 142 geriatric participants; target doses of olanzapine 15-20 mg/day plus masked sertraline or placebo at 150-200 mg/day. Results: Olanzapine/sertraline was associated with a higher remission rates over the trial than olanzapine/placebo (OR=1.28, 95% CI =1.12-1.47, p<.001). 41.9% of combination subjects were in remission at their last assessment compared to 23.9% of olanzapine monotherapy subjects (χ21= 9.53, p=.002). Combination therapy was comparably superior in younger adult (OR=1.25, 95% CI =1.05-1.50, p=.02) and older subjects (OR=1.34, 95% CI =1.09-1.66, p=0.01). Secondary efficacy measures also supported combination treatment. Overall tolerability was comparable across age groups, with age-related differences in specific side effects. Both age groups had significant increases in cholesterol and triglyceride levels, but statistically significant increases in glucose occurred only in younger adults (t=2.76, df=205, p=.01). Although both age groups experienced significant weight gain, younger adults gained

  20. Real-time measurement of quasiparticle tunneling in a single-junction transmon qubit using feedback

    NASA Astrophysics Data System (ADS)

    Ristè, Diego; Bultink, Niels; Tiggelman, Marijn; Schouten, Raymond; Lehnert, Konrad; Dicarlo, Leonardo

    2013-03-01

    With coherence times of superconducting qubits now exceeding 100 μs , the contribution of quasiparticle (QP) tunneling to qubit relaxation and dephasing becomes potentially relevant. We report the real-time measurement of QP tunneling across the single junction of a 3D transmon qubit. We integrate recent developments in projective qubit readout with 99 % fidelity and feedback-based reset to transform the qubit into a charge-parity detector with 6 μs resolution. We detect a symmetric random telegraph signal matching a QP tunneling time of 0 . 8 ms . By measuring the correlation function of charge parity conditioned on specific initial and final qubit states, we determine that most QP tunneling does not induce qubit transitions, in contradiction with recent theory. We extract a QP-induced qubit relaxation time T1qp ~ 3 ms , decidedly not limiting the measured T1 = 0 . 14 ms . Research supported by NWO, FOM, and EU Project SOLID.

  1. Quasiparticle scattering interference in the renormalized Hubbard model

    NASA Astrophysics Data System (ADS)

    Wang, Shu-Hua; Zhao, Huai-Song; Yuan, Feng

    2015-02-01

    In this paper, we study the quasiparticle scattering interference phenomenon in the presence of a single impurity within the renormalized Hubbard model. By calculating the energy and momentum dependence of the Fourier-transformed local density of states in the full Brillouin zone, we can qualitatively describe the main features of the quasiparticle scattering interference phenomenon in cuprate superconductors using a single point-like impurity. In particular, we show that with increasing energy, the position of the peak along the nodal ([0, 0] → [ π, π]) direction moves steadily to a large momentum region, while the position of the peak along the antinodal ([0, 0] → [ π, 0]) direction moves toward the center of the Brillouin zone.

  2. Quasiparticle spin resonance and coherence in superconducting aluminium

    PubMed Central

    Quay, C. H. L.; Weideneder, M.; Chiffaudel, Y.; Strunk, C.; Aprili, M.

    2015-01-01

    Conventional superconductors were long thought to be spin inert; however, there is now increasing interest in both (the manipulation of) the internal spin structure of the ground-state condensate, as well as recently observed long-lived, spin-polarized excitations (quasiparticles). We demonstrate spin resonance in the quasiparticle population of a mesoscopic superconductor (aluminium) using novel on-chip microwave detection techniques. The spin decoherence time obtained (∼100 ps), and its dependence on the sample thickness are consistent with Elliott–Yafet spin–orbit scattering as the main decoherence mechanism. The striking divergence between the spin coherence time and the previously measured spin imbalance relaxation time (∼10 ns) suggests that the latter is limited instead by inelastic processes. This work stakes out new ground for the nascent field of spin-based electronics with superconductors or superconducting spintronics. PMID:26497744

  3. Quasi-Particle Self-Consistent GW for Molecules.

    PubMed

    Kaplan, F; Harding, M E; Seiler, C; Weigend, F; Evers, F; van Setten, M J

    2016-06-14

    We present the formalism and implementation of quasi-particle self-consistent GW (qsGW) and eigenvalue only quasi-particle self-consistent GW (evGW) adapted to standard quantum chemistry packages. Our implementation is benchmarked against high-level quantum chemistry computations (coupled-cluster theory) and experimental results using a representative set of molecules. Furthermore, we compare the qsGW approach for five molecules relevant for organic photovoltaics to self-consistent GW results (scGW) and analyze the effects of the self-consistency on the ground state density by comparing calculated dipole moments to their experimental values. We show that qsGW makes a significant improvement over conventional G0W0 and that partially self-consistent flavors (in particular evGW) can be excellent alternatives. PMID:27168352

  4. Quasiparticle electronic structure of bismuth telluride in the GW approximation

    NASA Astrophysics Data System (ADS)

    Kioupakis, Emmanouil; Tiago, Murilo L.; Louie, Steven G.

    2010-12-01

    The quasiparticle band structure of bismuth telluride (Bi2Te3) , an important thermoelectric material that exhibits topologically insulating surface states, is calculated from first principles in the GW approximation. The quasiparticle energies are evaluated in fine detail in the first Brillouin zone using a Wannier-function interpolation method, allowing the accurate determination of the location of the band extrema (which is in the mirror plane) as well as the values of the quasiparticle band gap (0.17 eV) and effective-mass tensors. Spin-orbit interaction effects were included. The valence band exhibits two distinct maxima in the mirror plane that differ by just 1 meV, giving rise to one direct and one indirect band gap of very similar magnitude. The effective-mass tensors are in reasonable agreement with experiment. The Wannier interpolation coefficients can be used for the tight-binding parametrization of the band structure. Our work elucidates the electronic structure of Bi2Te3 and sheds light on its exceptional thermoelectric and topologically insulating properties.

  5. Lightwave-driven quasiparticle collisions on a subcycle timescale

    NASA Astrophysics Data System (ADS)

    Langer, F.; Hohenleutner, M.; Schmid, C. P.; Poellmann, C.; Nagler, P.; Korn, T.; Schüller, C.; Sherwin, M. S.; Huttner, U.; Steiner, J. T.; Koch, S. W.; Kira, M.; Huber, R.

    2016-05-01

    Ever since Ernest Rutherford scattered α-particles from gold foils, collision experiments have revealed insights into atoms, nuclei and elementary particles. In solids, many-body correlations lead to characteristic resonances—called quasiparticles—such as excitons, dropletons, polarons and Cooper pairs. The structure and dynamics of quasiparticles are important because they define macroscopic phenomena such as Mott insulating states, spontaneous spin- and charge-order, and high-temperature superconductivity. However, the extremely short lifetimes of these entities make practical implementations of a suitable collider challenging. Here we exploit lightwave-driven charge transport, the foundation of attosecond science, to explore ultrafast quasiparticle collisions directly in the time domain: a femtosecond optical pulse creates excitonic electron-hole pairs in the layered dichalcogenide tungsten diselenide while a strong terahertz field accelerates and collides the electrons with the holes. The underlying dynamics of the wave packets, including collision, pair annihilation, quantum interference and dephasing, are detected as light emission in high-order spectral sidebands of the optical excitation. A full quantum theory explains our observations microscopically. This approach enables collision experiments with various complex quasiparticles and suggests a promising new way of generating sub-femtosecond pulses.

  6. 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

  7. Experiments on Interaction of Quasiparticles with Two-Level-Systems in a Superconducting Phase Qubit

    NASA Astrophysics Data System (ADS)

    Bilmes, Alexander; Lisenfeld, Jürgen; Heimes, Andreas; Zanker, Sebastian; Schön, Gerd; Ustinov, Alexey

    2015-03-01

    Two-Level-Systems (TLS) are one of the main sources of decoherence in superconducting qubits. Some individual and coherent TLS, present in the tunnel barrier of the qubit's Josephson junction, can be coherently operated via the qubit. In the past, experiments on superconducting glasses indicated that quasiparticles may give rise to TLS energy loss similar to Korringa relaxation. We will present experiments in which we use a phase qubit to explore the interaction of single TLS with non-equilibrium quasiparticles. We have implemented in-situ quasiparticle injection by using an on-chip dc-SQUID that is pulse-biased beyond its critical current. The quasiparticle density is calibrated by measuring associated characteristic changes to the qubit resonance frequency and energy relaxation rate. The coherence times of individual TLS is measured in dependence of the non-equilibrium quasiparticle density and compared to thermally generated quasiparticles. PI, KIT, Wolfgang-Gaede-Strasse 1, 76131 Karlsruhe, Germany.

  8. Structure of quasiparticles and their fusion algebra in fractional quantum Hall states

    NASA Astrophysics Data System (ADS)

    Barkeshli, Maissam; Wen, Xiao-Gang

    2009-05-01

    It was recently discovered that fractional quantum Hall (FQH) states can be characterized quantitatively by the pattern of zeros that describe how the ground-state wave function goes to zero when electrons are brought close together. Quasiparticles in the FQH states can be described in a similar quantitative way by the pattern of zeros that result when electrons are brought close to the quasiparticles. In this paper, we combine the pattern of zeros approach and the conformal field theory (CFT) approach to calculate the topological properties of quasiparticles. We discuss how the quasiparticles in FQH states naturally form representations of a magnetic translation algebra, with members of a representation differing from each other by Abelian quasiparticles. We find that this structure dramatically simplifies topological properties of the quasiparticles, such as their fusion rules, charges, and scaling dimensions, and has consequences for the ground state degeneracy of FQH states on higher genus surfaces. We find constraints on the pattern of zeros of quasiparticles that can fuse together, which allow us to derive the fusion rules of quasiparticles from their pattern of zeros, at least in the case of the (generalized and composite) parafermion states. We also calculate from CFT the number of quasiparticle types in the generalized and composite parafermion states, which confirm the result obtained previously through a completely different approach.

  9. Electronic structure from relativistic quasiparticle self-consistent GW calculations

    NASA Astrophysics Data System (ADS)

    Blügel, Stefan

    Most theoretical studies of topological insulators (TIs) are based on tight-binding descriptions and density functional theory (DFT). But recently, many-body calculations within the GW approximation attract much attention in the study of these materials. We present an implementation of the quasiparticle self-consistent (QS) GW method where the spin-orbit coupling (SOC) is fully taken into account in each iteration rather than added a posteriori. Within the all-electron FLAPW formalism, we show DFT, one-shot GW , and QS GW calculations for several, well-known TIs. We present a comparison of the calculations to photoemission spectroscopy and show that the GW corrected bands agree much better with experiment. For example, we show that Bi2Se3 is a direct gap semiconductor, in contrast to what was believed for many years by interpreting experimental results on the basis of DFT and that small strains in Bi can lead to a semimetal-to-semiconductor or trivial-to-topological transitions. Quasiparticle calculations for low-dimensional systems are still very demanding. In order to study the topological surface states with an approach based on GW , we use Wannier functions to construct a Hamiltonian that reproduces the many-body band structure of the bulk, and that is used to construct a slab Hamiltonian. With this approach, we discuss the effect of quasiparticle corrections on the surface states of TIs and on the interaction between bulk and surface states Work was funded by the Virtual Institute for Topological Insulators of the Helmholtz Association and carried out in collaboration with Irene Aguilera, Gustav Bihlmayer, and Christoph Friedrich.

  10. Excited quasiparticles and entropy in 161,162Dy

    NASA Astrophysics Data System (ADS)

    Razavi, R.; Mohassel, A. Rashed; Mohammadi, S.

    2015-11-01

    In this paper, the nuclear level densities of 161,162Dy is studied by the use of a microscopic theory which includes nuclear pairing interaction. It is based on the modified harmonic oscillator model according to the Nilsson potential. The entropy of even-odd and even-even nuclei as a function of nuclear temperature is obtained. The entropy excess of 161Dy is compared with that of 162Dy. It is concluded that the difference is related to the entropy carried by the neutron hole coupled to the even-even core. The numbers of excited quasiparticles are calculated. Good agreement was observed between calculated results and the experimental data.

  11. Quasiparticle transformation during a metal-insulator transition in graphene.

    PubMed

    Bostwick, Aaron; McChesney, Jessica L; Emtsev, Konstantin V; Seyller, Thomas; Horn, Karsten; Kevan, Stephen D; Rotenberg, Eli

    2009-07-31

    Here we show, with simultaneous transport and photoemission measurements, that the graphene-terminated SiC(0001) surface undergoes a metal-insulator transition upon dosing with small amounts of atomic hydrogen. We find the room temperature resistance increases by about 4 orders of magnitude, a transition accompanied by anomalies in the momentum-resolved spectral function including a non-Fermi-liquid behavior and a breakdown of the quasiparticle picture. These effects are discussed in terms of a possible transition to a strongly (Anderson) localized ground state. PMID:19792520

  12. Quasiparticle tunneling in a periodically driven bosonic Josephson junction

    NASA Astrophysics Data System (ADS)

    Gertjerenken, Bettina; Holthaus, Martin

    2014-11-01

    A resonantly driven bosonic Josephson junction supports stable collective excitations, or quasiparticles, which constitute analogs of the Trojan wave packets previously explored with Rydberg atoms in strong microwave fields. We predict a quantum beating effect between such symmetry-related many-body Trojan states taking place on time scales which are long in comparison with the driving period. Within a mean-field approximation, this quantum beating can be regarded as a manifestation of dynamical tunneling. On the full N -particle level, the beating phenomenon leads to an experimentally feasible, robust strategy for probing highly entangled mesoscopic states.

  13. Dynamics of Weyl quasiparticles in an optical lattice

    NASA Astrophysics Data System (ADS)

    Li, Zhi; Wang, Huai-Qiang; Zhang, Dan-Wei; Zhu, Shi-Liang; Xing, Ding-Yu

    2016-10-01

    We investigate the dynamics of the Weyl quasiparticles emerged in an optical lattice where the topological Weyl semimetal and trivial band insulator phases can be adjusted with the on-site energy. The evolution of the density distribution is demonstrated to have an anomalous velocity in the Weyl semimetal but a steady Zitterbewegung effect in the band insulator. Our analysis demonstrates that the chirality of the system can be directly determined from the positions of the atomic center of mass. Furthermore, the amplitude and the period of the relativistic Zitterbewegung oscillations are shown to be observable with the time-of-flight experiments.

  14. ARPES Studies of Cuprate Fermiology: Superconductivity, Pseudogap and Quasiparticle Dynamics

    SciTech Connect

    Vishik, Inna

    2011-06-23

    We present angle-resolved photoemission spectroscopy (ARPES) studies of the cuprate high-temperature superconductors which elucidate the relation between superconductivity and the pseudogap and highlight low-energy quasiparticle dynamics in the superconducting state. Our experiments suggest that the pseudogap and superconducting gap represent distinct states, which coexist below T{sub c}. Studies on Bi-2212 demonstrate that the near-nodal and near-antinodal regions behave differently as a function of temperature and doping, implying that different orders dominate in different momentum-space regions. However, the ubiquity of sharp quasiparticles all around the Fermi surface in Bi-2212 indicates that superconductivity extends into the momentum-space region dominated by the pseudogap, revealing subtlety in this dichotomy. In Bi-2201, the temperature dependence of antinodal spectra reveals particle-hole asymmetry and anomalous spectral broadening, which may constrain the explanation for the pseudogap. Recognizing that electron-boson coupling is an important aspect of cuprate physics, we close with a discussion of the multiple 'kinks' in the nodal dispersion. Understanding these may be important to establishing which excitations are important to superconductivity.

  15. Pump probe spectroscopy of quasiparticle dynamics in cuprate superconductors

    SciTech Connect

    Segre, Gino P.

    2001-05-01

    Pump probe spectroscopy is used to examine the picosecond response of a BSCCO thin film, and two YBCO crystals in the near infrared. The role of pump fluence and temperature have been closely examined in an effort to clarify the mechanism by which the quasiparticles rejoin the condensate. BSCCO results suggest that the recombination behavior is consistent with the d-wave density of states in that quasiparticles appear to relax to the nodes immediately before they rejoin the condensate. The first substantial investigation of polarized pump probe response in detwinned YBCO crystals is also reported. Dramatic doping dependent anisotropies along the a and b axes are observed in time and temperature resolved studies. Among many results, we highlight the discovery of an anomalous temperature and time dependence of a- axis response in optimally doped YBCO. We also report on the first observation of the photoinduced response in a magnetic field. We find the amplitude of the response, and in some cases, the dynamics considerably changed with the application of a 6T field. Finally, we speculate on two of the many theoretical directions stimulated by our results. We find that the two-fluid model suggests a mechanism to explain how changes at very low energies are visible to a high-energy probe. Also discussed are basic recombination processes which may play a role in the observed decay.

  16. Dynamics of Hubbard-Band Quasiparticles in Disordered Optical Lattices

    NASA Astrophysics Data System (ADS)

    Scarola, Vito; Demarco, Brian

    Recent experiments use transport of degenerate Fermi gases in optical lattices (Kondov et al. Phys. Rev. Lett. 114, 083002 (2015) to probe the interplay of disorder and strong interactions. These experiments find evidence for an intriguing insulating phase where quantum diffusion is completely suppressed by strong disorder. Quantitative interpretation of these experiments remains an open problem that requires inclusion of non-zero entropy, strong interaction, and trapping in an Anderson-Hubbard model. We construct a theory of dynamics of Hubbard-band quasiparticles tailored to trapped optical lattice experiments. We compare the theory directly with center-of-mass transport experiments of Kondov et al. with no fitting parameters. The close agreement between theory and experiments shows that the suppression of transport is only partly due to finite entropy effects. We argue that the complete suppression of transport is consistent with short-time, finite size precursors of Anderson localization of Hubbard-band quasiparticles. The combination of our theoretical framework and optical lattice experiments offers an important platform for studying localization in isolated many-body quantum systems. V.W.S. acknowledges support from AFOSR under Grant FA9550-11-1-0313.

  17. Cubic scaling G W : Towards fast quasiparticle calculations

    NASA Astrophysics Data System (ADS)

    Liu, Peitao; Kaltak, Merzuk; Klimeš, Jiří; Kresse, Georg

    2016-10-01

    Within the framework of the full potential projector-augmented wave methodology, we present a promising low-scaling G W implementation. It allows for quasiparticle calculations with a scaling that is cubic in the system size and linear in the number of k points used to sample the Brillouin zone. This is achieved by calculating the polarizability and self-energy in the real-space and imaginary-time domains. The transformation from the imaginary time to the frequency domain is done by an efficient discrete Fourier transformation with only a few nonuniform grid points. Fast Fourier transformations are used to go from real space to reciprocal space and vice versa. The analytic continuation from the imaginary to the real frequency axis is performed by exploiting Thiele's reciprocal difference approach. Finally, the method is applied successfully to predict the quasiparticle energies and spectral functions of typical semiconductors (Si, GaAs, SiC, and ZnO), insulators (C, BN, MgO, and LiF), and metals (Cu and SrVO3). The results are compared with conventional G W calculations. Good agreement is achieved, highlighting the strength of the present method.

  18. Charge separation at nanoscale interfaces: Energy-level alignment including two-quasiparticle interactions

    SciTech Connect

    Li, Huashan; Lin, Zhibin; Lusk, Mark T. Wu, Zhigang

    2014-10-21

    The universal and fundamental criteria for charge separation at interfaces involving nanoscale materials are investigated. In addition to the single-quasiparticle excitation, all the two-quasiparticle effects including exciton binding, Coulomb stabilization, and exciton transfer are considered, which play critical roles on nanoscale interfaces for optoelectronic applications. We propose a scheme allowing adding these two-quasiparticle interactions on top of the single-quasiparticle energy level alignment for determining and illuminating charge separation at nanoscale interfaces. Employing the many-body perturbation theory based on Green's functions, we quantitatively demonstrate that neglecting or simplifying these crucial two-quasiparticle interactions using less accurate methods is likely to predict qualitatively incorrect charge separation behaviors at nanoscale interfaces where quantum confinement dominates.

  19. Quasiparticle Self-Recombination in Double STJs Strip X-ray Detectors

    SciTech Connect

    Andrianov, V. A.; Gorkov, V. P.

    2009-12-16

    The quasiparticle self-recombination was considered in the frame of 2D diffusion model of the strip X-ray detectors. The detector consists of a long superconducting strip, which is ended by the trapping layers and superconducting tunnel junctions at each end. The model takes into account the 2D-diffusion of the excess quasiparticles, quasiparticle trapping at the tunnel junctions and quasiparticle losses in the volume of the strip and at the strip boundaries. Self-recombination was described by a quadratic term. As the analytical solution is absent, the numeric calculations were carried out. It has been shown that the self-recombination as well as quasiparticle losses at the strip boundaries caused the dependence of the signals on the photon absorption site in transverse direction. The latter worsens the energy resolution and transforms the spectral line of the detector to nongaussian shape.

  20. Scaling and non-Abelian signature in fractional quantum Hall quasiparticle tunneling amplitude

    NASA Astrophysics Data System (ADS)

    Hu, Zi-Xiang; Lee, Ki H.; Rezayi, Edward H.; Wan, Xin; Yang, Kun

    2011-03-01

    We study the scaling behavior in the tunneling amplitude when quasiparticles tunnel along a straight path between the two edges of a fractional quantum Hall annulus. Such scaling behavior originates from the propagation and tunneling of charged quasielectrons and quasiholes in an effective field analysis. In the limit when the annulus deforms continuously into a quasi-one-dimensional (1D) ring, we conjecture the exact functional form of the tunneling amplitude for several cases, which reproduces the numerical results in finite systems exactly. The results for Abelian quasiparticle tunneling is consistent with the scaling analysis; this allows for the extraction of the conformal dimensions of the quasiparticles. We analyze the scaling behavior of both Abelian and non-Abelian quasiparticles in the Read-Rezayi { Z}_k -parafermion states. Interestingly, the non-Abelian quasiparticle tunneling amplitudes exhibit non-trivial k-dependent corrections to the scaling exponent.

  1. 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.

  2. Quasiparticle and optical properties of polythiophene-derived polymers

    NASA Astrophysics Data System (ADS)

    Samsonidze, Georgy; Ribeiro, Filipe J.; Cohen, Marvin L.; Louie, Steven G.

    2014-07-01

    Electron donor conjugated polymers blended with electron acceptor fullerene derivatives is one of the promising technologies for organic photovoltaics. However, with the energy conversion efficiency of only 9% in a single bulk heterojunction device structure, these solar cells are not yet competitive with conventional inorganic semiconductor technology. Some of the limitations are large optical band gaps and small electron affinities of polymers preventing the absorption of infrared radiation and leading to energy losses during charge separation at the donor-acceptor interface, respectively. In this work, we compute from first principles the quasiparticle and optical spectra of several different thiophene-, ethyne-, and vinylene-based copolymers using the GW method and the GW plus Bethe-Salpeter equation approach. One of the polymers is identified which has a preferential alignment of the energy levels at the interface with fullerene molecule compared to the reference case of polythiophene.

  3. Source conductance scaling for high frequency superconducting quasiparticle receivers

    NASA Technical Reports Server (NTRS)

    Ke, Qing; Feldman, M. J.

    1992-01-01

    It has been suggested that the optimum source conductance G(sub s) for the superconductor-insulator-superconductor (SIS) quasiparticle mixer should have a l/f dependence. This would imply that the critical current density of SIS junctions used for mixing should increase as frequency squared, a stringent constraint on the design of submillimeter SIS mixers, rather than in simple proportion to frequency as previously believed. We have used Tucker's quantum theory of mixing for extensive numerical calculations to determine G(sub s) for an optimized SIS receiver. We find that G(sub s) is very roughly independent of frequency (except for the best junctions at low frequency), and discuss the implications of our results for the design of submillimeter SIS mixers.

  4. Friedel oscillations as a probe of fermionic quasiparticles

    NASA Astrophysics Data System (ADS)

    Dalla Torre, Emanuele G.; Benjamin, David; He, Yang; Dentelski, David; Demler, Eugene

    2016-05-01

    When immersed in a sea of electrons, local impurities give rise to density modulations known as Friedel oscillations. In spite of the generality of this phenomenon, the exact shape of these modulations is usually computed only for noninteracting electrons with a quadratic dispersion relation. In actual materials, Friedel oscillations are a viable way to access the properties of electronic quasiparticles, including their dispersion relation, lifetime, and pairing. In this work we analyze the signatures of Friedel oscillations in STM and x-ray scattering experiments, focusing on the concrete example of cuprate superconductors. We identify signatures of Friedel oscillations seeded by impurities and vortices, and explain experimental observations that have been previously attributed to a competing charge order.

  5. Multiple magnetic impurities on surfaces: Scattering and quasiparticle interference

    NASA Astrophysics Data System (ADS)

    Mitchell, Andrew K.; Derry, Philip G.; Logan, David E.

    2015-06-01

    We study systems of multiple interacting quantum impurities deposited on a metallic surface in a three-dimensional host. For the real-space two-impurity problem, using numerical renormalization group calculations, a rich range of behavior is shown to arise due to the interplay between Kondo physics and effective Ruderman-Kittel-Kasuya-Yosida interactions—provided the impurity separation is small. Such calculations allow identification of the minimum impurity separation required for a description in terms of independent impurities, and thereby the onset of the "dilute-impurity limit" in many-impurity systems. A "dilute-cluster" limit is also identified in systems with higher impurity density, where interimpurity interactions are important only within independent clusters. We calculate the quasiparticle interference due to two and many impurities, and explore the consequences of the independent impurity and cluster paradigms. Our results provide a framework to investigate the effects of disorder due to interacting impurities at experimentally relevant surface coverages.

  6. Search for electron liquids with non-Abelian quasiparticles

    NASA Astrophysics Data System (ADS)

    Wójs, Arkadiusz

    2010-03-01

    We use exact numerical diagonalization in the search of fractional quantum Hall states with non-Abelian quasiparticle statistics. For the (most promising) states in a partially filled second Landau level, the search is narrowed to the range of filling factors 7/3 < ve < 8/3. In this range, the analysis of energy spectra and correlation functions, calculated including finite width and Landau level mixing, supports the prominent non-Abelian candidates at ve = 5/2 (paired Moore-Read "pfafian" state) and 12/5 (clustered Read-Rezayi "parafermion" state). Outside of this range, the noninteracting composite fermion model with four attached flux quanta is validated, yielding the family of quantum liquids with fractional, but Abelian statistics. The borderline ve = 7/3 state is shown to be adiabatically connected to the Laughlin liquid, but its short-range correlations are significantly different.

  7. Quasiparticle current and phase locking of intrinsic Josephson junctions

    NASA Astrophysics Data System (ADS)

    Seidel, P.; Grib, A. N.; Shukrinov, Yu. M.; Scherbel, J.; Hübner, U.; Schmidl, F.

    2001-09-01

    On the base of our experiments on thin film Josephson junctions in mesa geometry we discuss the quasiparticle branches of the intrinsic arrays within a tunnelling model using d-wave superconductor density of states. We find temperature dependent current contributions and a zero bias anomaly. The coherent behaviour is studied for intrinsic arrays with an additional side-wall shunt. The existence of thresholds of phase locking at small as well as at large inductances is demonstrated. We discuss the problems with experimental realisation of the shunts as well as with an alternative concept to enhance phase locking in such arrays towards application as oscillators in the frequency range up to some THz.

  8. 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.

  9. Hybrid quasiparticles within the orthorhombic or hexagonal topology of RMO3 (R =Nd,Pr,Tm,Er; M =Mn,Cr) under strong magnetic fields

    NASA Astrophysics Data System (ADS)

    Sopracase, R.; Holldack, K.; Del Campo, L.; Massa, N. E.; Martínez-Lope, M. J.; Alonso, J. A.

    2014-03-01

    We report on magnetoelectric quasiparticles that originate from electronic Coulomb and exchange correlations using a Bruker IFS125-HR interferometer at 0.5 cm-1 resolution in the THz beamline of the electron storage ring BESSYII in Berlin. Orthorhombic NdMnO3 and hexagonal TmMnO3 have quasiparticles at energies of zone center magnons. In both cases, increasing the applied field, the ~ 20 cm-1 line matching the lowest energy magnon, has its intensity reduced sharply while bands associated in TmMnO3 to magnon-acoustical phonon dispersion crossing and gap opening behave differently. The line at ~ 48 cm-1, the higher branch of the phonon gap, shows a Zeeman splitting-like behavior, while the lower branch at ~ 31 cm-1 has weak field dependences. The asymmetric envelope peaking at ~ 35 cm-1 in NdMnO3 weakens, softens, and evolves at 8 T into two unresolved bands suggesting field induced TA +magnon coupling materializing a condition for a multiferroic state. Metastable orthorhombic ErMnO3 has two bands at 5 K which resembles those of NdMnO3. A remarkable 35 cm-1 Zeeman splitting at 5 K in PrCrO3 is tentatively associated to Cr3+ electrons in a distorted polarizable p-d bond. ErCrO3 shows such a feature at 50 cm-1 as well additional zero field splitting at 8 and 9 cm-1 in the spin reorientation phase.

  10. Thermal Transport by Ballistic Quasiparticles in Superfluid 3He-B in the Low Temperature Limit

    SciTech Connect

    Bradley, D. I.; Fisher, S. N.; Guenault, A. M.; Haley, R. P.; Martin, H.; Pickett, G. R.; Roberts, J. E.; Tsepelin, V.

    2006-09-07

    In the temperature range below 0.2Tc, the gas of thermal excitations from the superfluid 3He-B ground state is in the ultra-dilute ballistic regime. Here we discuss preliminary measurements of the transport properties of this quasiparticle gas in a cell of cylindrical geometry with dimensions much smaller than any mean free path. The vertical cylinder, constructed from epoxy-coated paper, has vibrating wire resonator (VWR) heaters and thermometers at the top and bottom, and a small aperture at the top which provides the only exit for quasiparticles. Using the thermometer VWRs, we measure the difference in quasiparticle density between the top and bottom of the tube when we excite the top or bottom VWR heater. This gives information about the transport of energy along the cylindrical 3He sample and hence about the scattering behaviour involved when a quasiparticle impinges on the cylinder wall.

  11. Differences between the insulating limit quasiparticles of one-band and three-band cuprate models

    NASA Astrophysics Data System (ADS)

    Ebrahimnejad, H.; Sawatzky, G. A.; Berciu, M.

    2016-03-01

    We study the charge dynamics of the quasiparticle that forms when a single hole is doped in a two-dimensional antiferromagnet as described by the one-band t-{{t}\\prime} -{{t}\\prime \\prime} -J model, using a variational approximation that includes spin fluctuations in the vicinity of the hole. We explain why the spin fluctuations and the longer range hopping have complementary contributions to the quasiparticle dynamics, and thus why both are essential to obtain a dispersion in agreement with that measured experimentally. This is very different from the three-band Emery model in the strongly-correlated limit, where the same variational approximation shows that spin fluctuations have a minor effect on the quasiparticle dynamics. This difference proves that these one-band and three-band models describe qualitatively different quasiparticles in the insulating limit, and therefore that they cannot both be suitable to describe the physics of very underdoped cuprates.

  12. Tunable quasiparticle trapping in Meissner and vortex states of mesoscopic superconductors

    PubMed Central

    Taupin, M.; Khaymovich, I. M.; Meschke, M.; Mel'nikov, A. S.; Pekola, J. P.

    2016-01-01

    Nowadays, superconductors serve in numerous applications, from high-field magnets to ultrasensitive detectors of radiation. Mesoscopic superconducting devices, referring to those with nanoscale dimensions, are in a special position as they are easily driven out of equilibrium under typical operating conditions. The out-of-equilibrium superconductors are characterized by non-equilibrium quasiparticles. These extra excitations can compromise the performance of mesoscopic devices by introducing, for example, leakage currents or decreased coherence time in quantum devices. By applying an external magnetic field, one can conveniently suppress or redistribute the population of excess quasiparticles. In this article, we present an experimental demonstration and a theoretical analysis of such effective control of quasiparticles, resulting in electron cooling both in the Meissner and vortex states of a mesoscopic superconductor. We introduce a theoretical model of quasiparticle dynamics, which is in quantitative agreement with the experimental data. PMID:26980225

  13. Phonon Quasi-Particles and Anharmonic Free Energy in Complex Systems

    NASA Astrophysics Data System (ADS)

    Zhang, Dong-Bo; Sun, Tao; Wentzcovitch, Renata

    2014-03-01

    We use a hybrid strategy to obtain anharmonic frequency shifts and lifetimes of phonon quasi-particles from first principles molecular dynamics simulations in modest size supercells. This approach is effective irrespective of crystal structure complexity and facilitates calculation of full anharmonic phonon dispersions, as long as phonon quasi-particles are well defined. We validate this approach to obtaining anharmonic effects with calculations in MgSiO3-perovskite, the major Earth forming mineral phase. First, we reproduce irregular temperature induced frequency shifts of well characterized Raman modes. Second, we combine the phonon gas model (PGM) with quasi-particle frequencies and reproduce free energies obtained using a direct approach such as thermodynamic integration. Using thoroughly sampled quasi-particle dispersions with the PGM we then obtain first-principles anharmonic free energy in the thermodynamic limit (N --> ∞) . Research supported by Abu Dhabi-Minnesota Institute for Research Excellence (ADMIRE) and NSF grant EAR-1047629.

  14. Tunable quasiparticle trapping in Meissner and vortex states of mesoscopic superconductors.

    PubMed

    Taupin, M; Khaymovich, I M; Meschke, M; Mel'nikov, A S; Pekola, J P

    2016-01-01

    Nowadays, superconductors serve in numerous applications, from high-field magnets to ultrasensitive detectors of radiation. Mesoscopic superconducting devices, referring to those with nanoscale dimensions, are in a special position as they are easily driven out of equilibrium under typical operating conditions. The out-of-equilibrium superconductors are characterized by non-equilibrium quasiparticles. These extra excitations can compromise the performance of mesoscopic devices by introducing, for example, leakage currents or decreased coherence time in quantum devices. By applying an external magnetic field, one can conveniently suppress or redistribute the population of excess quasiparticles. In this article, we present an experimental demonstration and a theoretical analysis of such effective control of quasiparticles, resulting in electron cooling both in the Meissner and vortex states of a mesoscopic superconductor. We introduce a theoretical model of quasiparticle dynamics, which is in quantitative agreement with the experimental data. PMID:26980225

  15. Normal State Spectral Lineshapes of Nodal Quasiparticles in Single Layer Bi2201 Superconductor

    SciTech Connect

    Lanzara, A.

    2010-04-30

    A detailed study of the normal state photoemission lineshapes and quasiparticle dispersion for the single layer Bi{sub 2}Sr{sub 2-x}La{sub x}CuO{sub 6+{delta}}(Bi2201) superconductor is presented. We report the first experimental evidence of a double peak structure and a dip of spectral intensity in the energy distribution curves (EDCs) along the nodal direction. The double peak structure is well identified in the normal state, up to ten times the critical temperature. As a result of the same self-energy effect, a strong mass renormalization of the quasiparticle dispersion, i.e. kink, and an increase of the quasiparticle lifetime in the normal state are also observed. Our results provide unambiguous evidence on the existence of bosonic excitation in the normal state, and support a picture where nodal quasiparticles are strongly coupled to the lattice.

  16. Quasiparticle theory of transport coefficients for hadronic matter at finite temperature and baryon density

    NASA Astrophysics Data System (ADS)

    Albright, M.; Kapusta, J. I.

    2016-01-01

    We develop a flexible quasiparticle theory of transport coefficients of hot hadronic matter at finite baryon density. We begin with a hadronic quasiparticle model which includes a scalar and a vector mean field. Quasiparticle energies and the mean fields depend on temperature and baryon chemical potential. Starting with the quasiparticle dispersion relation, we derive the Boltzmann equation and use the Chapman-Enskog expansion to derive formulas for the shear and bulk viscosities and thermal conductivity. We obtain both relaxation-time approximation formulas and more general integral equations. Throughout the work, we explicitly enforce the Landau-Lifshitz conditions of fit and ensure the theory is thermodynamically self-consistent. The derived formulas should be useful for predicting the transport coefficients of the hadronic phase of matter produced in heavy-ion collisions at the Relativistic Heavy Ion Collider and at other accelerators.

  17. PD trivia: Making learning fun.

    PubMed

    Kennedy, Liana

    2006-01-01

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

  18. Harmonic and reactive behavior of the quasiparticle tunnel current in SIS junctions

    NASA Astrophysics Data System (ADS)

    Rashid, H.; Desmaris, V.; Pavolotsky, A.; Belitsky, V.

    2016-04-01

    In this paper, we show theoretically and experimentally that the reactive quasiparticle tunnel current of the superconductor tunnel junction could be directly measured at specific bias voltages for the higher harmonics of the quasiparticle tunnel current. We used the theory of quasiparticle tunneling to study the higher harmonics of the quasiparticle tunnel current in superconducting tunnel junction in the presence of rf irradiation. The impact of the reactive current on the harmonic behavior of the quasiparticle tunnel current was carefully studied by implementing a practical model with four parameters to model the dc I-V characteristics of the superconducting tunnel junction. The measured reactive current at the specific bias voltage is in good agreement with our theoretically calculated reactive current through the Kramers-Kronig transform. This study also shows that there is an excellent correspondence between the behavior of the predicted higher harmonics using the previously established theory of quasiparticle tunnel current in superconducting tunnel junctions by J.R. Tucker and M.J. Feldman and the measurements presented in this paper.

  19. Quasiparticle scattering off phase boundaries in epitaxial graphene.

    PubMed

    Mahmood, A; Mallet, P; Veuillen, J-Y

    2012-02-10

    We investigate the electronic structure of terraces of single layer graphene (SLG) by scanning tunnelling microscopy (STM) on samples grown by thermal decomposition of 6H-SiC(0001) crystals in ultra-high vacuum. We focus on the perturbations of the local density of states (LDOS) in the vicinity of edges of SLG terraces. Armchair edges are found to favour intervalley quasiparticle scattering, leading to the (√3 x √3)R30° LDOS superstructure already reported for graphite edges and more recently for SLG on SiC(0001). Using the Fourier transform of LDOS images, we demonstrate that the intrinsic doping of SLG is responsible for a LDOS pattern at the Fermi energy which is more complex than for neutral graphene or graphite, since it combines local (√3 x √3)R30° superstructure and long range beating modulation. Although these features have already been reported by Yang et al (2010 Nano Lett. 10 943-7) we propose here an alternative interpretation based on simple arguments classically used to describe standing wave patterns in standard two-dimensional systems. Finally, we discuss the absence of intervalley scattering off other typical boundaries: zig-zag edges and SLG/bilayer graphene junctions.

  20. Quasiparticle density of states by inversion with maximum entropy method

    NASA Astrophysics Data System (ADS)

    Sui, Xiao-Hong; Wang, Han-Ting; Tang, Hui; Su, Zhao-Bin

    2016-10-01

    We propose to extract the quasiparticle density of states (DOS) of the superconductor directly from the experimentally measured superconductor-insulator-superconductor junction tunneling data by applying the maximum entropy method to the nonlinear systems. It merits the advantage of model independence with minimum a priori assumptions. Various components of the proposed method have been carefully investigated, including the meaning of the targeting function, the mock function, as well as the role and the designation of the input parameters. The validity of the developed scheme is shown by two kinds of tests for systems with known DOS. As a preliminary application to a Bi2Sr2CaCu2O8 +δ sample with its critical temperature Tc=89 K , we extract the DOS from the measured intrinsic Josephson junction current data at temperatures of T =4.2 K , 45 K , 55 K , 95 K , and 130 K . The energy gap decreases with increasing temperature below Tc, while above Tc, a kind of energy gap survives, which provides an angle to investigate the pseudogap phenomenon in high-Tc superconductors. The developed method itself might be a useful tool for future applications in various fields.

  1. High-K multi-quasiparticle states in 254No

    NASA Astrophysics Data System (ADS)

    Clark, R. M.; Gregorich, K. E.; Berryman, J. S.; Ali, M. N.; Allmond, J. M.; Beausang, C. W.; Cromaz, M.; Deleplanque, M. A.; Dragojević, I.; Dvorak, J.; Ellison, P. A.; Fallon, P.; Garcia, M. A.; Gates, J. M.; Gros, S.; Jeppesen, H. B.; Kaji, D.; Lee, I. Y.; Macchiavelli, A. O.; Morimoto, K.; Nitsche, H.; Paschalis, S.; Petri, M.; Stavsetra, L.; Stephens, F. S.; Watanabe, H.; Wiedeking, M.

    2010-06-01

    We report results from an experiment on the decay of the high-K isomers in 254No. We have been able to establish the decay from the known high-lying four-quasiparticle isomer, which we assign as a K=16 state at an excitation energy of Ex=2.928(3) MeV. The decay of this state passes through a rotational band based on a previously unobserved state at Ex=2.012(2) MeV, which we suggest is based on a two-quasineutron configuration with K=10. This state in turn decays to a rotational band based on the known K=8 isomer, which we infer must also have a two quasineutron configuration. We are able to assign many new gamma-rays associated with the decay of the K=8 isomer, including the identification of a highly K-forbidden ΔK=8 E1 transition to the ground-state band. These results provide valuable new information on the orbitals close to the Fermi surface, pairing correlations, deformation and rotational response, and K-conservation in nuclei of the deformed trans-fermium region.

  2. Quasiparticle Representation of Coherent Nonlinear Optical Signals of Multiexcitons

    NASA Astrophysics Data System (ADS)

    Fingerhut, Benjamin; Bennet, Kochise; Roslyak, Oleksiy; Mukamel, Shaul

    2013-03-01

    Elementary excitations of many-Fermion systems can be described within the quasiparticle approach which is widely used in the calculation of transport and optical properties of metals, semiconductors, molecular aggregates and strongly correlated quantum materials. The excitations are then viewed as independent harmonic oscillators where the many-body interactions between the oscillators are mapped into anharmonicities. We present a Green's function approach based on coboson algebra for calculating nonlinear optical signals and apply it onwards the study of two and three exciton states. The method only requires the diagonalization of the single exciton manifold and avoids equations of motion of multi-exciton manifolds. Using coboson algebra many body effects are recast in terms of tetradic exciton-exciton interactions: Coulomb scattering and Pauli exchange. The physical space of Fermions is recovered by singular-value decomposition of the over-complete coboson basis set. The approach is used to calculate third and fifth order quantum coherence optical signals that directly probe correlations in two- and three exciton states and their projections on the two and single exciton manifold.

  3. Quasiparticle band structures and optical properties of magnesium fluoride

    NASA Astrophysics Data System (ADS)

    Yi, Zhijun; Jia, Ran

    2012-02-01

    The quasiparticle and optical properties of magnesium fluoride (MgF2) are computed within the GW approximation based on many-body perturbation theory (MBPT). The many-body effects appearing in self-energy and electron-hole interactions have an important influence on the electronic and optical properties. The DFT-LDA calculation shows a 6.78 eV band gap. Two methods are employed to evaluate the self-energy within the GW approximation in the present work. The generalized plasmon pole model (GPP) provides a band gap of 12.17 eV, which agrees well with the experimental value of 12.4 eV (Thomas et al 1973 Phys. Status Solidi b 56 163). Another band gap value of 11.30 eV is obtained by using a full frequency-dependent self-energy, which is also not far from the experimental value and is much better than the result from the LDA calculation. The calculated optical spectrum within DFT is significantly different from the experiment. Although the calculated optical absorption threshold within the GW method is close to the experiment, the overall shape of the spectrum is still similar to the case of DFT. However, the overall shape of the spectrum via the Bethe-Salpeter equation (BSE) method agrees well with the experiment.

  4. Quasiparticle band structures and optical properties of magnesium fluoride.

    PubMed

    Yi, Zhijun; Jia, Ran

    2012-02-29

    The quasiparticle and optical properties of magnesium fluoride (MgF(2)) are computed within the GW approximation based on many-body perturbation theory (MBPT). The many-body effects appearing in self-energy and electron-hole interactions have an important influence on the electronic and optical properties. The DFT-LDA calculation shows a 6.78 eV band gap. Two methods are employed to evaluate the self-energy within the GW approximation in the present work. The generalized plasmon pole model (GPP) provides a band gap of 12.17 eV, which agrees well with the experimental value of 12.4 eV (Thomas et al 1973 Phys. Status Solidi b 56 163). Another band gap value of 11.30 eV is obtained by using a full frequency-dependent self-energy, which is also not far from the experimental value and is much better than the result from the LDA calculation. The calculated optical spectrum within DFT is significantly different from the experiment. Although the calculated optical absorption threshold within the GW method is close to the experiment, the overall shape of the spectrum is still similar to the case of DFT. However, the overall shape of the spectrum via the Bethe-Salpeter equation (BSE) method agrees well with the experiment.

  5. ARPES view of orbitally resolved quasiparticle lifetimes in iron pnictides

    NASA Astrophysics Data System (ADS)

    Brouet, Véronique; LeBoeuf, David; Lin, Ping-Hui; Mansart, Joseph; Taleb-Ibrahimi, Amina; Le Fèvre, Patrick; Bertran, François; Forget, Anne; Colson, Dorothée

    2016-02-01

    We study with angle-resolved photoemission spectroscopy (ARPES) the renormalization and quasiparticle lifetimes of the dx y and dx z/dy z orbitals in two iron pnictides, LiFeAs and Ba (Fe0.92Co0.08 )2As2 (Co8). We find that both quantities depend on orbital character rather than on the position on the Fermi surface (for example, hole or electron pocket). In LiFeAs, the renormalizations are larger for dx y, while they are similar for both types of orbitals in Co8. The most salient feature, which proved robust against all the ARPES caveats we could think of, is that the lifetimes for dx y exhibit a markedly different behavior than those for dx z/dy z. They have smaller values near EF and exhibit larger ω and temperature dependences. While the behavior of dx y is compatible with a Fermi-liquid description, that is not the case for dx z/dy z. This situation should have important consequences for the physics of iron pnictides, which have not been considered up to now. More generally, it raises interesting questions about how a Fermi-liquid regime can be established in a multiband system with small effective bandwidths.

  6. The quasiparticle band dispersion in epitaxial multilayer silicene.

    PubMed

    De Padova, Paola; Avila, Jose; Resta, Andrea; Razado-Colambo, Ivy; Quaresima, Claudio; Ottaviani, Carlo; Olivieri, Bruno; Bruhn, Thomas; Vogt, Patrick; Asensio, Maria Carmen; Le Lay, Guy

    2013-09-25

    The growth of multilayer silicene is an exciting challenge for the future of silicon nano-electronics. Here, we use angle-resolved photoemission spectroscopy to map the entire Brillouin zone (BZ) of (√3 × √3)R30° reconstructed epitaxial multilayer silicene islands, growing on top of the first (3 × 3) reconstructed silicene wetting layer, on Ag(111) substrates. We found Λ- and V-shape linear dispersions, which we relate to the π and π* bands of massless quasiparticles in multilayer silicene, at the BZ centre [Formula: see text] and at all the [Formula: see text] centres of the (√3 × √3)R30° Brillouin zones in the extended scheme, due to folding of the Dirac cones at the [Formula: see text] and [Formula: see text] points of the (1 × 1) silicene BZ. The Fermi velocity of ∼0.3 × 10(6) m s(-1) obtained is highly promising for potential silicene-based devices.

  7. Two-dimensional model of interactions between thermal quasiparticles and turbulent structures in 3He-B

    NASA Astrophysics Data System (ADS)

    Sergeev, Y. A.; Barenghi, C. F.; Suramlishvili, N.; van Dijk, P. J.

    2010-06-01

    Using the two-dimensional model, we compute the ensemble average Andreev reflection coefficient of a flux of thermal quasiparticles in 3He-B incident upon the system of point vortices, each moving in the flow field generated by all other vortex points. In the case where the initial positions of all point vortices are random, such a vortex gas can be regarded as a (somewhat crude) two-dimensional model of a real, three-dimensional vortex tangle. On the other hand, in the case where vortices and antivortices are arranged in pairs, a random system of such pairs models, in two dimensions, a gas of three-dimensional vortex rings. Of particular interest is the change of the average Andreev reflection coefficient with the transition from a gas of vortex-antivortex pairs to a random system of point vortices. Our study is particularly motivated by the experimental observation at Lancaster University of the transition from a gas of vortex rings to a dense tangle. The question which we ask is whether a gas of vortex rings and a dense tangle have a different Andreev signature. We found that, due to the partial screening, a transition from the gas of vortex-antivortex pairs to the random point vortex gas is associated with the several-fold increase of the reflection coefficient. We note that these results, although consistent with observations at Lancaster, should be regarded as qualitative rather than quantitative.

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

    SciTech Connect

    Jose, Deepa; Jagirdar, Balaji R.

    2010-09-15

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

  9. G6PD: The Test

    MedlinePlus

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

  10. Emergence of massless Dirac quasiparticles in correlated hydrogenated graphene with broken sublattice symmetry

    NASA Astrophysics Data System (ADS)

    Seki, Kazuhiro; Shirakawa, Tomonori; Zhang, Qinfang; Li, Tao; Yunoki, Seiji

    2016-04-01

    Using the variational cluster approximation (VCA) and the cluster perturbation theory, we study the finite-temperature phase diagram of a half-depleted periodic Anderson model on the honeycomb lattice at half-filling for a model of graphone, i.e., single-side hydrogenated graphene. The ground state of this model is found to be ferromagnetic (FM) semimetal. The origin of this FM state is attributed to the instability of a flat band located at the Fermi energy in the noninteracting limit and is smoothly connected to the Lieb-Mattis-type ferromagnetism. The spin-wave dispersion in the FM state is linear in momentum at zero temperature but becomes quadratic at finite temperatures, implying that the FM state is fragile against thermal fluctuations. Indeed, our VCA calculations find that the paramagnetic (PM) state dominates the finite-temperature phase diagram. More surprisingly, we find that massless Dirac quasiparticles with the linear energy dispersion emerge at the Fermi energy upon introducing the electron correlation U at the impurity sites in the PM phase. The Dirac Fermi velocity is found to be highly correlated to the quasiparticle weight of the emergent massless Dirac quasiparticles at the Fermi energy and monotonically increases with U . These unexpected massless Dirac quasiparticles are also examined with the Hubbard-I approximation and the origin is discussed in terms of the spectral weight redistribution involving a large energy scale of U . Considering an effective quasiparticle Hamiltonian which reproduces the single-particle excitations obtained by the Hubbard-I approximation, we argue that the massless Dirac quasiparticles are protected by the electron correlation. Our finding therefore provides a unique example of the emergence of massless Dirac quasiparticles due to dynamical electron correlations without breaking any spatial symmetry. The experimental implications of our results for graphone as well as a graphene sheet on transition-metal substrates

  11. The application of the fractional exclusion statistics to the BCS theory-A redefinition of the quasiparticle energies

    NASA Astrophysics Data System (ADS)

    Anghel, Dragoş-Victor; Nemnes, George Alexandru

    2016-09-01

    The effective energy of a superconductor Eeff(T) at temperature T is defined as the difference between the total energy at temperature T and the total energy at 0 K. We call the energy of the condensate, Ec, the difference between Eeff and the sum of the quasiparticle energies Eqp. Ec, Eqp, as well as the BCS quasiparticle energy ɛ are positive and depend on the gap energy Δ, which, in turn, depends on the populations of the quasiparticle states (equivalently, they depend on T). So, from the energetic point of view, the superconductor is a Fermi liquid of interacting quasiparticles. We show that the choice of quasiparticles is not unique, but there is an infinite range of possibilities. Some of these possibilities have been explored in the context of the fractional exclusion statistics (FES), which is a general method of describing interacting particle systems as ideal gases. We apply FES here and transform the Fermi liquid of BCS excitations into an ideal gas by redefining the quasiparticle energies. The new FES quasiparticles exhibit the same energy gap as the BCS quasiparticles, but a different DOS, which is finite at any quasiparticle energy. We also discuss the effect of the remnant electron-electron interaction (electron-electron interaction beyond the BCS pairing model) and show that this can stabilize the BCS condensate, increasing the critical temperature.

  12. General properties of CePd1-xRhx at quantum critical point

    NASA Astrophysics Data System (ADS)

    Shaginyan, V. R.; Popov, K. G.

    2009-10-01

    The heavy-fermion metal CePd1-xRhx evolves from ferromagnetism at x=0 to a non-magnetic state at some critical concentration xc. Utilizing the quasiparticle picture and the concept of fermion condensation quantum phase transition (FCQPT), we address the non-Fermi liquid (NFL) behavior of ferromagnet CePd1-xRhx and show that it coincides with that of antiferromagnets YbRh2(Si0.95Ge0.05)2 and CeCoIn 5, paramagnets CeRu 2Si 2 and CeNi 2Ge 2 and 2D 3He. We show that the NFL behavior is independent of the peculiarities of specific alloy and universal. Our study of the NFL behavior allows us to calculate the magnetoresistance of CeCoIn 5. Obtained results are in good agreement with facts and reveal a new scaling behavior of magnetoresistance.

  13. PD-1, gender, and autoimmunity

    PubMed Central

    Dinesh, Ravi K.; Hahn, Bevra H.; Singh, Ram Pyare

    2010-01-01

    Programmed death 1 (PD-1) and its ligands (PD-L1 and PD-L2) are responsible for inhibitory T cell signaling that helps mediate the mechanisms of tolerance and immune homeostasis. The PD-1:PD-L signaling pathway has been shown to play an important role in a variety of diseases, including autoimmune conditions, chronic infection, and cancer. Recently, investigators have explored the role of sex hormones in modulating the pathway in autoimmune conditions. Exploring the effects of sex hormones on the PD-1:PD-L pathway could shed light on the gender biased nature of many autoimmune conditions as well as aide in the development of therapeutics targeting the immune system. PMID:20433954

  14. Quasiparticles of strongly correlated Fermi liquids at high temperatures and in high magnetic fields

    SciTech Connect

    Shaginyan, V. R.

    2011-08-15

    Strongly correlated Fermi systems are among the most intriguing, best experimentally studied and fundamental systems in physics. There is, however, lack of theoretical understanding in this field of physics. The ideas based on the concepts like Kondo lattice and involving quantum and thermal fluctuations at a quantum critical point have been used to explain the unusual physics. Alas, being suggested to describe one property, these approaches fail to explain the others. This means a real crisis in theory suggesting that there is a hidden fundamental law of nature. It turns out that the hidden fundamental law is well forgotten old one directly related to the Landau-Migdal quasiparticles, while the basic properties and the scaling behavior of the strongly correlated systems can be described within the framework of the fermion condensation quantum phase transition (FCQPT). The phase transition comprises the extended quasiparticle paradigm that allows us to explain the non-Fermi liquid (NFL) behavior observed in these systems. In contrast to the Landau paradigm stating that the quasiparticle effective mass is a constant, the effective mass of new quasiparticles strongly depends on temperature, magnetic field, pressure, and other parameters. Our observations are in good agreement with experimental facts and show that FCQPT is responsible for the observed NFL behavior and quasiparticles survive both high temperatures and high magnetic fields.

  15. Quasiparticles of strongly correlated Fermi liquids at high temperatures and in high magnetic fields

    NASA Astrophysics Data System (ADS)

    Shaginyan, V. R.

    2011-08-01

    Strongly correlated Fermi systems are among the most intriguing, best experimentally studied and fundamental systems in physics. There is, however, lack of theoretical understanding in this field of physics. The ideas based on the concepts like Kondo lattice and involving quantum and thermal fluctuations at a quantum critical point have been used to explain the unusual physics. Alas, being suggested to describe one property, these approaches fail to explain the others. This means a real crisis in theory suggesting that there is a hidden fundamental law of nature. It turns out that the hidden fundamental law is well forgotten old one directly related to the Landau-Migdal quasiparticles, while the basic properties and the scaling behavior of the strongly correlated systems can be described within the framework of the fermion condensation quantum phase transition (FCQPT). The phase transition comprises the extended quasiparticle paradigm that allows us to explain the non-Fermi liquid (NFL) behavior observed in these systems. In contrast to the Landau paradigm stating that the quasiparticle effective mass is a constant, the effective mass of new quasiparticles strongly depends on temperature, magnetic field, pressure, and other parameters. Our observations are in good agreement with experimental facts and show that FCQPT is responsible for the observed NFL behavior and quasiparticles survive both high temperatures and high magnetic fields.

  16. Electron-phonon induced complex quasiparticles in the 1x1 H/W(110) surface.

    NASA Astrophysics Data System (ADS)

    Eiguren, Asier; Ambrosch-Draxl, Claudia

    2008-03-01

    We show that the solution of the complex Dyson equation for the electron-phonon problem induces several quasiparticle states for a given wave vector. The Dyson equation is considered in the full complex plane and it is solved without considering the imaginary part of the self-energy as an small parameter. By a first principle application of the formalism to the 1x1 H covered W(110) surface, we show that some aspects of the surface band splitting [Rotenberg et. al., Phys. Rev. Lett. 84, 2925 (2000)] can be traced back to electron-phonon coupling, where we present the energy and lifetimes of each quasiparticle. Despite this breakdown of the single quasi-particle picture, it is remarkable that the spectral functions are very well Represented by the predicted multiple quasi-particles. From these results, we can deduce that some of the features that previously where prescribed in ARPES spectra as incoherent structure could eventually be re-interpreted as contributions from additional quasi-particle states. Our method could also help to understand similar phenomena observed in high Tc cuprates and various other surfaces.

  17. Phase Stability for the Pd-Si System: First-Principles, Experiments, and Solution-Based Modeling

    NASA Astrophysics Data System (ADS)

    Zhou, S. H.; Huo, Y.; Napolitano, Ralph E.

    2016-01-01

    The relative stabilities of the compounds in the binary Pd-Si system were assessed using first-principles calculations and experimental methods. Calculations of lattice parameters and enthalpy of formation indicate that Pd5Si-{μ }, Pd9Si_2-{α }, Pd_3Si-{β }, Pd_2Si-{γ }, and PdSi-{δ } are the stable phases at 0 K (-273 °C). X-ray diffraction analyses (XRD) and electron probe microanalysis (EPMA) of the as-solidified and heat-treated samples support the computational findings, except that the PdSi-{δ } phase was not observed at low temperature. Considering both experimental data and first-principles results, the compounds Pd5Si-{μ }, Pd9Si2-{α }, Pd3Si-{β }, and Pd_2Si-{γ } are treated as stable phases down to 0 K (-273 °C), while the PdSi-{δ } is treated as being stable over a limited range, exhibiting a lower bound. Using these findings, a comprehensive solution-based thermodynamic model is formulated for the Pd-Si system, permitting phase diagram calculation. The liquid phase is described using a three-species association model and other phases are treated as solid solutions, where a random substitutional model is adopted for Pd-fcc and Si-dia, and a two-sublattice model is employed for Pd5Si-{μ }, Pd9Si_2-{α }, Pd_3Si-{β }, Pd_2Si-{γ }, and PdSi-{δ }. Model parameters are fitted using available experimental data and first-principles data, and the resulting phase diagram is reported over the full range of compositions.

  18. Phase Stability for the Pd-Si System. First-Principles, Experiments, and Solution-Based Modeling

    DOE PAGES

    Zhou, S. H.; Huo, Y.; Napolitano, Ralph E.

    2015-11-05

    Relative stabilities of the compounds in the binary Pd-Si system were assessed using first-principles calculations and experimental methods. Calculations of lattice parameters and enthalpy of formation indicate that Pd5Si-μ, Pd9Si2-α, Pd3 Si-β, Pd2 Si-γ, and PdSi-δ are the stable phases at 0 K (-273 °C). X-ray diffraction analyses (XRD) and electron probe microanalysis (EPMA) of the as-solidified and heat-treated samples support the computational findings, except that the PdSi-δ phase was not observed at low temperature. Considering both experimental data and first-principles results, the compounds Pd 5 Si-μ, Pd9 Si2-α, Pd3Si-β, and Pd2Si-γ are treated as stable phases down to 0more » K (-273 °C), while the PdSi-δ is treated as being stable over a limited range, exhibiting a lower bound. Using these findings, a comprehensive solution-based thermodynamic model is formulated for the Pd-Si system, permitting phase diagram calculation. Moreover, the liquid phase is described using a three-species association model and other phases are treated as solid solutions, where a random substitutional model is adopted for Pd-fcc and Si-dia, and a two-sublattice model is employed for Pd5Si-μ, Pd9Si2-α, Pd3Si-β, Pd2Si-γ, and PdSi-δ. Model parameters are fitted using available experimental data and first-principles data, and the resulting phase diagram is reported over the full range of compositions.« less

  19. Biased impurity tunneling current emission spectrum in the presence of quasi-particle interaction

    NASA Astrophysics Data System (ADS)

    Maslova, N. S.; Arseyev, P. I.; Mantsevich, V. N.

    2016-09-01

    We performed theoretical investigations of the tunneling current noise spectra through single-level impurity in the presence of quasi-particle (electron-phonon) interaction by means of the non-equilibrium Green function formalism. We demonstrated a fundamental link between quantum noise in tunneling contact and light emission processes. We calculated tunneling current noise spectra through a single level impurity atom both in the presence and in the absence of quasi-particle interaction for a finite bias voltage and identified it as a source of experimentally observed light emission from bias STM contacts. The results turn out to be sensitive to the tunneling contact parameters. Our findings provide important insight into the nature of non-equilibrium electronic transport in tunneling junctions with quasi-particle interaction.

  20. Effect of magnetic field on quasiparticle branches of intrinsic Josephson junctions with ferromagnetic layer.

    SciTech Connect

    Ozyuzer, L.; Ozdemir, M.; Kurter, C.; Hinks, D. G.; Gray, K. E.

    2007-01-01

    The interlayer tunneling spectroscopy has been performed on micron-sized mesa arrays of HgBr{sub 2} intercalated superconducting Bi2212 single crystals. A ferromagnetic multilayer (Au/Co/Au) is deposited on top of the mesas. The spin-polarized current is driven along the c-axis of the mesas through a ferromagnetic Co layer and the hysteretic quasiparticle branches are observed at 4.2 K. Magnetic field evolution of hysteretic quasiparticle branches is obtained to examine the effect of injected spin-polarized current on intrinsic Josephson junction characteristics. It is observed that there is a gradual distribution in quasiparticle branches with the application of magnetic field and increasing field reduces the switching current progressively.

  1. Multi-quasiparticle high-K isomeric states in deformed nuclei

    NASA Astrophysics Data System (ADS)

    Xu, F. R.; Shi, Y.; Liu, H. L.; Liang, W. Y.; Walker, P. M.; Dracoulis, G. D.

    2016-09-01

    In the past years, we have made many theoretical investigations on multi-quasiparticle high-K isomeric states. A deformation-pairing-configuration self-consistent calculation has been developed by calculating a configuration-constrained multi-quasiparticle potential energy surface (PES). The specific single-particle orbits that define the high-K configuration are identified and tracked (adiabatically blocked) by calculating the average Nilsson numbers. The deformed Woods-Saxon potential was taken to give single-particle orbits. The configuration-constrained PES takes into account the shape polarization effect. Such calculations give good results on excitation energies, deformations and other structure information about multi-quasiparticle high-K isomeric states. Many different mass regions have been investigated.

  2. Quasi-particle spectrum in trilayer graphene: Role of onsite coulomb interaction and interlayer coupling

    NASA Astrophysics Data System (ADS)

    Kumar, Sanjay; Ajay

    2015-01-01

    Stacking dependent quasi-particle spectrum and density of states (DOS) in trilayer (ABC-, ABA- and AAA-stacked) graphene are analyzed using mean-field Green's function equations of motion method. Interlayer coupling (t1) is found to be responsible for the splitting of quasi-particle peaks in each stacking order. Coulomb interaction suppresses the trilayer splitting and generates a finite gap at Fermi level in ABC- while a tiny gap in ABA-stacked trilayer graphene. Influence of t⊥ is prominent for AAA-stacking as compared to ABC- and ABA-stacking orders. The theoretically obtained quasi-particle energies and DOS has been viewed in terms of recent angle resolved photoemission spectroscopic (ARPES) and scanning tunneling microscopic (STM) data available on these systems.

  3. Quasiparticle electronic structure of bulk and slab Bi2Se3 and Bi2Te3

    NASA Astrophysics Data System (ADS)

    Barker, Bradford; Deslippe, Jack; Yazyev, Oleg; Louie, Steven G.

    2014-03-01

    We present ab initio calculations of the quasiparticle electronic band structure of three-dimensional topological insulator materials Bi2Se3 and Bi2Te3. The mean-field DFT calculation is performed with fully relativistic pseudopotentials, generating spinor wavefunctions in a plane-wave basis. Quasiparticle properties are computed with a one-shot ab initio GW calculation. We use both bulk and slab forms of the materials to better understand the quasiparticle band gaps and Fermi velocities of the topological surface states of these materials. This work was supported by NSF grant No. DMR10-1006184 and U.S. DOE under Contract No. DE-AC02-05CH11231. Computational resources have been provided by DOE at LBNL's NERSC facility and the NSF through XSEDE resources at NICS.

  4. Quasiparticle and Josephson Current in the Intrinsic Josephson Junctions in Htsc

    NASA Astrophysics Data System (ADS)

    Shukrinov, Yu. M.; Namiranian, A.; Najafi, A.

    2000-09-01

    The tunneling properties of the model structure consisting of HTSC and normal metal are studied. The influence of the impurity concentration in CuO2 layers on the high energy features is investigated, taking into account tight binding band structure, d-wave gap symmetry, group velocity and tunneling directionality. The increasing of the impurity lifetime broadening factor changes the degree of tunneling conductance peaks asymmetry, leads to nonequal shifting of the quasiparticle peaks and their width. We consider that the underlying asymmetry of the conductance peaks is primarily due to the features of quasiparticle energy spectrum and the d-wave symmetry enhances the degree of the peaks asymmetry. The analysis of c-axis transport of quasiparticles and Cooper pairs of stacked intrinsic junctions in HTSC is done.

  5. Quasiparticle parity lifetime of bound states in a hybrid superconductor-semiconductor quantum dot

    NASA Astrophysics Data System (ADS)

    Higginbotham, Andrew; Albrecht, Sven; Kirsanskas, Gediminas; Chang, Willy; Kuemmeth, Ferdinand; Krogstrup, Peter; Jespersen, Thomas; Nygård, Jesper; Flensberg, Karsten; Marcus, Charles

    2015-03-01

    We measure quasiparticle transport in an InAs nanowire that is half-covered with epitaxial superconducting aluminum, then locally gated to form a quantum dot. We observe negative differential conductance at finite source-drain bias, and temperature dependent even-odd alternations in the Coulomb blockade peak spacings at zero bias. These observations can be understood in terms of a mid-gap semiconductor discrete state and a continuum of BCS quasiparticle states. Comparing with simple models, we bound the discrete state's parity lifetime and the quasiparticle temperature. These results indicate that parity fluctuations are slow, and imply Majorana qubit poisoning times on the order of a millisecond. Additional results indicate that the bound states move to zero energy in a magnetic field, qualitatively consistent with expectations for Majorana fermions in a finite system. Research supported by Microsoft Station Q, Danish National Research Foundation, Villum Foundation, Lundbeck Foundation, and the European Commission.

  6. Quasiparticle interaction function in a two-dimensional Fermi liquid near an antiferromagnetic critical point

    NASA Astrophysics Data System (ADS)

    Chubukov, Andrey V.; Wölfle, Peter

    2014-01-01

    We present the expression for the quasiparticle vertex function Γω(KF,PF) (proportional to the Landau interaction function) in a 2D Fermi liquid (FL) near an instability towards antiferromagnetism. This function is relevant in many ways in the context of metallic quantum criticality. Previous studies have found that near a quantum critical point, the system enters into a regime in which the fermionic self-energy is large near hot spots on the Fermi surface [points on the Fermi surface connected by the antiferromagnetic ordering vector qπ=(π,π)] and has much stronger dependence on frequency than on momentum. We show that in this regime, which we termed a critical FL, the conventional random-phase-approximation- (RPA) type approach breaks down, and to properly calculate the vertex function one has to sum up an infinite series of terms which were explicitly excluded in the conventional treatment. Besides, we show that, to properly describe the spin component of Γω(KF,PF) even in an ordinary FL, one has to add Aslamazov-Larkin (AL) terms to the RPA vertex. We show that the total Γω(KF,PF) is larger in a critical FL than in an ordinary FL, roughly by an extra power of magnetic correlation length ξ, which diverges at the quantum critical point. However, the enhancement of Γω(KF,PF) is highly nonuniform: It holds only when, for one of the two momentum variables, the distance from a hot spot along the Fermi surface is much larger than for the other one. This fact renders our case different from quantum criticality at small momentum, where the enhancement of Γω(KF,PF) was found to be homogeneous. We show that the charge and spin components of the total vertex function satisfy the universal relations following from the Ward identities related to the conservation of the particle number and the total spin. We show that in a critical FL, the Ward identity involves Γω(KF,PF) taken between particles on the FS. We find that the charge and spin components of

  7. Tunneling into thin superconducting films: Interface-induced quasiparticle lifetime reduction

    NASA Astrophysics Data System (ADS)

    Löptien, P.; Zhou, L.; Khajetoorians, A. A.; Wiebe, J.; Wiesendanger, R.

    2016-01-01

    Scanning tunneling spectroscopy measurements of superconducting thin lanthanum films grown on a normal metal tungsten substrate reveal an extraordinarily large broadening of the coherence peaks. The observed broadening corresponds to very short electron-like quasiparticle lifetimes in the tunneling process. A thorough analysis considering the different relaxation processes reveals that the dominant mechanism is an efficient quasiparticle relaxation at the interface between the superconducting film and the underlying substrate. This process is of general relevance to scanning tunneling spectroscopy studies on thin superconducting films and enables measurements of film thicknesses via a spectroscopic method.

  8. Proposal to measure the quasiparticle poisoning time of Majorana bound states

    NASA Astrophysics Data System (ADS)

    Colbert, Jacob R.; Lee, Patrick A.

    2014-04-01

    We propose a method of measuring the fermion parity lifetime of Majorana fermion modes due to quasiparticle poisoning. We model quasiparticle poisoning by coupling the Majorana modes to electron reservoirs, explicitly breaking parity conservation in the system. This poisoning broadens and shortens the resonance peak associated with Majorana modes. In a two-lead geometry, the poisoning decreases the correlation in current noise between the two leads from the maximal value characteristic of crossed Andreev reflection. The latter measurement allows for calculation of the poisoning rate even if the temperature is much higher than the resonance width.

  9. Measurement of quasiparticle transport in aluminum films using tungsten transition-edge sensors

    SciTech Connect

    Yen, J. J. Shank, B.; Cabrera, B.; Moffatt, R.; Redl, P.; Young, B. A.; Tortorici, E. C.; Brink, P. L.; Cherry, M.; Tomada, A.; Kreikebaum, J. M.

    2014-10-20

    We report on experimental studies of phonon sensors which utilize quasiparticle diffusion in thin aluminum films connected to tungsten transition-edge-sensors (TESs) operated at 35 mK. We show that basic TES physics and a simple physical model of the overlap region between the W and Al films in our devices enables us to accurately reproduce the experimentally observed pulse shapes from x-rays absorbed in the Al films. We further estimate quasiparticle loss in Al films using a simple diffusion equation approach. These studies allow the design of phonon sensors with improved performance.

  10. Emergent exclusion statistics of quasiparticles in two-dimensional topological phases

    NASA Astrophysics Data System (ADS)

    Hu, Yuting; Stirling, Spencer D.; Wu, Yong-Shi

    2014-03-01

    We demonstrate how the generalized Pauli exclusion principle emerges for quasiparticle excitations in 2D topological phases. As an example, we examine the Levin-Wen model with the Fibonacci data (specified in the text), and construct the number operator for fluxons living on plaquettes. By numerically counting the many-body states with fluxon number fixed, the matrix of exclusion statistics parameters is identified and is shown to depend on the spatial topology (sphere or torus) of the system. Our work reveals the structure of the (many-body) Hilbert space and some general features of thermodynamics for quasiparticle excitations in topological matter.

  11. PD-L1 and PD-L2 differ in their molecular mechanisms of interaction with PD-1

    PubMed Central

    Ghiotto, Marguerite; Gauthier, Laurent; Serriari, Nacer; Pastor, Sonia; Truneh, Alemseged; Nunès, Jacques; Olive, Daniel

    2010-01-01

    SUMMARY The programmed death-1 (PD-1) molecule is involved in peripheral tolerance and in the immune escape mechanisms during chronic viral infections and cancer. PD-1 interacts with two ligands, PD-L1 and PD-L2. We have investigated, the molecular mechanisms of PD-1 interactions with its ligands by surface plasmon resonance and cell surface binding as well as the ability of the two ligands to compete for PD-1 binding. PD-L1 and PD-L2 bound PD-1 with comparable affinities, but striking differences were observed at the level of the association and dissociation characteristics. PD-L1, but not PD-L2 had a delayed interaction reminiscent of a phenomenom of conformational transition. These mechanisms were confirmed by using PD-L1 mAbs that delayed the dissociation of PD-L1 from PD-1. This mechanism was not restricted to PD-1 binding since PD-L1 behaved in a similar manner with its second ligand, CD80. Finally, we could demonstrate that PD-L1 and PD-L2 competed for PD-1 binding and conversely, an antagonist PD-1 mAb blocked both PD-L1 and PD-L2 binding to PD-1 and strongly enhanced T cell proliferation. These data further emphasize the differential molecular mechanisms of interaction of PD-L1 and PD-L2 with PD-1, and suggest possible new approach for the therapy of chronic infection, cancer and transplantation. PMID:20587542

  12. PD-1, PD-L1, PD-L2 expression in the chordoma microenvironment

    PubMed Central

    Mathios, Dimitrios; Ruzevick, Jacob; Jackson, Christopher M.; Xu, Haiying; Shah, Sagar; Taube, Janis M.; Burger, Peter C.; McCarthy, Edward F.; Quinones-Hinojosa, Alfredo; Pardoll, Drew M.

    2015-01-01

    Chordomas are rare malignant tumors that are postulated to arise from remnants of the notochord. Currently, the interaction between chordomas and the host immune system is poorly understood. The checkpoint protein, PD-1 is expressed by circulating lymphocytes and is a marker of activation and exhaustion. Its ligands, PD-L1 (B7-H1, CD274) and PD-L2 (B7-DC, CD273), are expressed on a variety of human cancers; however this pathway has not been previously reported in chordomas. We used flow cytometric and RT-PCR analysis in three established primary and recurrent chordoma cell lines (U-CH1, U-CH2, and JHC7) as well as immunohistochemical analysis of chordoma tissues from 10 patients to identify and localize expression of PD-1 pathway proteins. PD-1 ligands are not constitutively expressed by chordoma cells, but their expression is induced in the setting of pro-inflammatory cytokines in all cell lines examined. In paraffin embedded tissues, we found that tumor infiltrating lymphocytes expressed PD-1 in 3/6 cases. We also found that, although chordoma cells did not express significant levels of PD-L1, PD-L1 expression was observed on tumor-infiltrating macrophages and tumor infiltrating lymphocytes. Our study suggests that PD-1, PD-L1, and PD-L2 are present in the microenvironment of a subset of chordomas analyzed. Future studies are needed to evaluate the contribution of the PD-1 pathway to the immunosuppressive microenvironment of chordomas. PMID:25349132

  13. Quasiparticle engineering and entanglement propagation in a quantum many-body system.

    PubMed

    Jurcevic, P; Lanyon, B P; Hauke, P; Hempel, C; Zoller, P; Blatt, R; Roos, C F

    2014-07-10

    The key to explaining and controlling a range of quantum phenomena is to study how information propagates around many-body systems. Quantum dynamics can be described by particle-like carriers of information that emerge in the collective behaviour of the underlying system, the so-called quasiparticles. These elementary excitations are predicted to distribute quantum information in a fashion determined by the system's interactions. Here we report quasiparticle dynamics observed in a quantum many-body system of trapped atomic ions. First, we observe the entanglement distributed by quasiparticles as they trace out light-cone-like wavefronts. Second, using the ability to tune the interaction range in our system, we observe information propagation in an experimental regime where the effective-light-cone picture does not apply. Our results will enable experimental studies of a range of quantum phenomena, including transport, thermalization, localization and entanglement growth, and represent a first step towards a new quantum-optic regime of engineered quasiparticles with tunable nonlinear interactions.

  14. Quasi-particle interference of heavy fermions in resonant x-ray scattering

    PubMed Central

    Gyenis, András; da Silva Neto, Eduardo H.; Sutarto, Ronny; Schierle, Enrico; He, Feizhou; Weschke, Eugen; Kavai, Mariam; Baumbach, Ryan E.; Thompson, Joe D.; Bauer, Eric D.; Fisk, Zachary; Damascelli, Andrea; Yazdani, Ali; Aynajian, Pegor

    2016-01-01

    Resonant x-ray scattering (RXS) has recently become an increasingly important tool for the study of ordering phenomena in correlated electron systems. Yet, the interpretation of RXS experiments remains theoretically challenging because of the complexity of the RXS cross section. Central to this debate is the recent proposal that impurity-induced Friedel oscillations, akin to quasi-particle interference signals observed with a scanning tunneling microscope (STM), can lead to scattering peaks in RXS experiments. The possibility that quasi-particle properties can be probed in RXS measurements opens up a new avenue to study the bulk band structure of materials with the orbital and element selectivity provided by RXS. We test these ideas by combining RXS and STM measurements of the heavy fermion compound CeMIn5 (M = Co, Rh). Temperature- and doping-dependent RXS measurements at the Ce-M4 edge show a broad scattering enhancement that correlates with the appearance of heavy f-electron bands in these compounds. The scattering enhancement is consistent with the measured quasi-particle interference signal in the STM measurements, indicating that the quasi-particle interference can be probed through the momentum distribution of RXS signals. Overall, our experiments demonstrate new opportunities for studies of correlated electronic systems using the RXS technique. PMID:27757422

  15. Decay spectroscopy of 160Sm: The lightest four-quasiparticle K isomer

    NASA Astrophysics Data System (ADS)

    Patel, Z.; Podolyák, Zs.; Walker, P. M.; Regan, P. H.; Söderström, P.-A.; Watanabe, H.; Ideguchi, E.; Simpson, G. S.; Nishimura, S.; Browne, F.; Doornenbal, P.; Lorusso, G.; Rice, S.; Sinclair, L.; Sumikama, T.; Wu, J.; Xu, Z. Y.; Aoi, N.; Baba, H.; Bello Garrote, F. L.; Benzoni, G.; Daido, R.; Dombrádi, Zs.; Fang, Y.; Fukuda, N.; Gey, G.; Go, S.; Gottardo, A.; Inabe, N.; Isobe, T.; Kameda, D.; Kobayashi, K.; Kobayashi, M.; Komatsubara, T.; Kojouharov, I.; Kubo, T.; Kurz, N.; Kuti, I.; Li, Z.; Liu, H. L.; Matsushita, M.; Michimasa, S.; Moon, C.-B.; Nishibata, H.; Nishizuka, I.; Odahara, A.; Şahin, E.; Sakurai, H.; Schaffner, H.; Suzuki, H.; Takeda, H.; Tanaka, M.; Taprogge, J.; Vajta, Zs.; Xu, F. R.; Yagi, A.; Yokoyama, R.

    2016-02-01

    The decay of a new four-quasiparticle isomeric state in 160Sm has been observed using γ-ray spectroscopy at the RIBF, RIKEN. The four-quasiparticle state is assigned a 2 π ⊗ 2 ν π5/2- [ 532 ], π5/2+ [ 413 ], ν5/2- [ 523 ], ν7/2+ [ 633 ] configuration. The half-life of this (11+) state is measured to be 1.8(4) μs. The (11+) isomer decays into a rotational band structure, based on a (6-) ν5/2- [ 523 ] ⊗ ν7/2+ [ 633 ] bandhead, consistent with the gK -gR values. This decays to a (5-) two-proton quasiparticle state, which in turn decays to the ground state band. Potential energy surface and blocked-BCS calculations were performed in the deformed midshell region around 160Sm. They reveal a significant influence from β6 deformation and that 160Sm is the best candidate for the lightest four-quasiparticle K isomer to exist in this region. The relationship between reduced hindrance and isomer excitation energy for E1 transitions from multiquasiparticle states is considered with the new data from 160Sm. The E1 data are found to agree with the existing relationship for E2 transitions.

  16. Ultrafast momentum-dependent quasiparticle dynamics in high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Bovensiepen, Uwe

    2013-03-01

    Femtosecond time- and angle-resolved photoelectron spectroscopy trARPES facilitates insight into electronic relaxation and electronic structure of non-equilibrium states of matter. Hot electrons and holes relax in metals on ultrafast time scales due to the screened Coulomb interaction. In superconductors the relaxation rates of quasiparticles at energies close to the superconducting gap edge are reduced because of the loss of quasiparticle states near EF. Since in the superconducting state the relaxation of optically excited carriers proceeds partly by Cooper pair reformation, the study of the quasiparticle dynamics bears the potential to analyze the interaction responsible for Cooper pair formation. Results of trARPES will be discussed for optimally doped Bi2Sr2CaCu2O8+δ in the superconducting state and on EuFe2As2 in the antiferromagnetic state. In the cuprate system we find a predominant excitation of quasiparticles at momenta near the antinode. We show furthermore, that at excitation densities of several 10 μJ/cm2 quasiparticle relaxation is dominated by Cooper pair reformation, which again proceeds near the antinode. In the Fe-pnictide material we monitor a difference in the relaxation rate for electrons and holes near the Fermi momentum, which disappears above the Neel temperature. We conclude that this anisotropic relaxation of electrons and holes is a consequence of the optical modification of the antiferromagnetic order. Analysis of energy transfer from electrons to phonons allows to determine the momentum averaged electron-phonon coupling constant λ. We find values below 0.25 for Bi2Sr2CaCu2O8+δ and below 0.15 for EuFe2As2. We acknowledge funding through the Deutsche Forschungsgemeinschaft through BO 1823/2, SPP 1458 and the Alexander von Humboldt foundation.

  17. Quasiparticle Tunneling in the Fractional Quantum Hall effect at filling fraction ν=5/2

    NASA Astrophysics Data System (ADS)

    Radu, Iuliana P.

    2009-03-01

    In a two-dimensional electron gas (2DEG), in the fractional quantum Hall regime, the quasiparticles are predicted to have fractional charge and statistics, as well as modified Coulomb interactions. The state at filling fraction ν=5/2 is predicted by some theories to have non-abelian statistics, a property that might be exploited for topological quantum computing. However, alternative models with abelian properties have been proposed as well. Weak quasiparticle tunneling between counter-propagating edges is one of the methods that can be used to learn about the properties of the state and potentially distinguish between models describing it. We employ an electrostatically defined quantum point contact (QPC) fabricated on a high mobility GaAs/AlGaAs 2DEG to create a constriction where quasiparticles can tunnel between counter-propagating edges. We study the temperature and dc bias dependence of the tunneling conductance, while preserving the same filling fraction in the constriction and the bulk of the sample. The data show scaling of the bias-dependent tunneling over a range of temperatures, in agreement with the theory of weak quasiparticle tunneling, and we extract values for the effective charge and interaction parameter of the quasiparticles. The ranges of values obtained are consistent with those predicted by certain models describing the 5/2 state, indicating as more probable a non-abelian state. This work was done in collaboration with J. B. Miller, C. M. Marcus, M. A. Kastner, L. N. Pfeiffer and K. W. West. This work was supported in part by the Army Research Office (W911NF-05-1-0062), the Nanoscale Science and Engineering Center program of NSF (PHY-0117795), NSF (DMR-0701386), the Center for Materials Science and Engineering program of NSF (DMR-0213282) at MIT, the Microsoft Corporation Project Q, and the Center for Nanoscale Systems at Harvard University.

  18. 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.

  19. Probing Bogoliubov Quasiparticles in Superfluid ^3He with a `Vibrating-Wire Like' MEMS Device

    NASA Astrophysics Data System (ADS)

    Defoort, M.; Dufresnes, S.; Ahlstrom, S. L.; Bradley, D. I.; Haley, R. P.; Guénault, A. M.; Guise, E. A.; Pickett, G. R.; Poole, M.; Woods, A. J.; Tsepelin, V.; Fisher, S. N.; Godfrin, H.; Collin, E.

    2016-05-01

    We have measured the interaction between superfluid ^3He-B and a micro-machined goalpost-shaped device at temperatures below 0.2 T_c. The measured damping follows well the theory developed for vibrating wires, in which the Andreev reflection of quasiparticles in the flow field around the moving structure leads to a nonlinear frictional force. At low velocities, the damping force is proportional to velocity, while it tends to saturate for larger excitations. Above a velocity of 2.6 mm s^{-1}, the damping abruptly increases, which is interpreted in terms of Cooper-pair breaking. Interestingly, this critical velocity is significantly lower than that reported with other mechanical probes immersed in superfluid ^3He. Furthermore, we report on a nonlinear resonance shape for large motion amplitudes that we interpret as an inertial effect due to quasiparticle friction, but other mechanisms could possibly be invoked as well.

  20. Inflationary Quasiparticle Creation and Thermalization Dynamics in Coupled Bose-Einstein Condensates.

    PubMed

    Posazhennikova, Anna; Trujillo-Martinez, Mauricio; Kroha, Johann

    2016-06-01

    A Bose gas in a double-well potential, exhibiting a true Bose-Einstein condensate (BEC) amplitude and initially performing Josephson oscillations, is a prototype of an isolated, nonequilibrium many-body system. We investigate the quasiparticle (QP) creation and thermalization dynamics of this system by solving the time-dependent Keldysh-Bogoliubov equations. We find avalanchelike QP creation due to a parametric resonance between BEC and QP oscillations, followed by slow, exponential relaxation to a thermal state at an elevated temperature, controlled by the initial excitation energy of the oscillating BEC above its ground state. The crossover between the two regimes occurs because of an effective decoupling of the QP and BEC oscillations. This dynamics is analogous to elementary particle creation in models of the early universe. The thermalization in our setup occurs because the BEC acts as a grand canonical reservoir for the quasiparticle system. PMID:27314725

  1. Fast decay of a three-quasiparticle isomer in {sup 171}Tm

    SciTech Connect

    Walker, P. M.; Wood, R. J.; El-Masri, H. M.; Wheldon, C.; Dracoulis, G. D.; Kibedi, T.; Bark, R. A.; Davidson, P. M.; Lane, G. J.; Moon, C.; Bruce, A. M.; Orce, J. N.; Estevez, F. M. Prados; Byrne, A. P.; Wilson, A. N.

    2009-04-15

    Incomplete-fusion reactions have been used to study high-spin states in {sup 171}Tm. Gamma rays and conversion electrons were measured using pulsed-beam conditions for enhanced isomer sensitivity. A K{sup {pi}}=19/2{sup +}, three-quasiparticle isomer was identified, with a half-life of 1.7(2){mu}s. The faster than expected transition rates from the isomer can be understood as being due to a chance near-degeneracy, with mixing between the isomeric state and the I{sup {pi}}=19/2{sup +} member of the one-quasiparticle rotational band to which it decays. The implied mixing matrix element is 12(2) eV.

  2. Interband quasiparticle scattering in superconducting LiFeAs reconciles photoemission and tunneling measurements.

    PubMed

    Hess, Christian; Sykora, Steffen; Hänke, Torben; Schlegel, Ronny; Baumann, Danny; Zabolotnyy, Volodymyr B; Harnagea, Luminita; Wurmehl, Sabine; van den Brink, Jeroen; Büchner, Bernd

    2013-01-01

    Several angle-resolved photoemission spectroscopy (ARPES) studies reveal a poorly nested Fermi surface of LiFeAs, far away from a spin density wave instability, and clear-cut superconducting gap anisotropies. On the other hand a very different, more nested Fermi surface and dissimilar gap anisotropies have been obtained from quasiparticle interference (QPI) data, which were interpreted as arising from intraband scattering within holelike bands. Here we show that this ARPES-QPI paradox is completely resolved by interband scattering between the holelike bands. The resolution follows from an excellent agreement between experimental quasiparticle scattering data and T-matrix QPI calculations (based on experimental band structure data), which allows disentangling interband and intraband scattering processes.

  3. Two-quasiparticle states in {sup 250}Bk studied by decay scheme and transfer reaction spectroscopy

    SciTech Connect

    Ahmad, I.; Kondev, F. G.; Koenig, Z. M.; McHarris, Wm. C.; Yates, S. W.

    2008-05-15

    Two-quasiparticle states in {sup 250}Bk were investigated with decay scheme studies and the single-neutron transfer reaction {sup 249}Bk(d,p){sup 250}Bk. Mass-separated sources of {sup 254}Es were used for {alpha} singles and {alpha}-{gamma} coincidence measurements. These studies, plus previous studies of {sup 254}Es{sup m} {alpha} decay and the {sup 249}Bk(n,{gamma}) reaction, provide spins and parities of the observed levels. The transfer reaction {sup 249}Bk(d,p){sup 250}Bk was used to deduce neutron single-particle components of the observed bands. Six pairs of singlet and triplet states, formed by the coupling of proton and neutron one-quasiparticle states, were identified. The splitting energies between the triplet and singlet states were found to be in agreement with previous calculations.

  4. Structure of three-quasiparticle isomers in {sup 169}Ho and {sup 171}Tm.

    SciTech Connect

    Dracoulis, G. D.; Lane, G. J.; Hughes, R. O.; Kondev, F. G.; Watanabe, H.; Seweryniak, D.; Zhu, S.; Carpenter, M. P.; Chiara, C. J.; Janssens, R. V. F.; Lauritsen, T.; Lister, C. J.; McCutchan, E. A.; Stefanescu, I.; Chowdhury, P.

    2010-09-17

    A three-quasiparticle isomer with {tau}=170(8) {micro}s and K{sup {pi}} = (19/2{sup +}) has been identified in the neutron-rich isotope {sup 169}Ho. The isomer decays with K-forbidden transitions to members of a band associated with the 7/2-[523] proton configuration, whose structure is characterized through analysis of the in-band {gamma}-ray branching ratios. In the isotone {sup 171}Tm, the rotational band based on the known 19/2{sup +}, three-quasiparticle isomer has also been observed. Alternative one-proton two-neutron configurations for the isomer in {sup 169}Ho are discussed in terms of multiquasiparticle calculations and through a comparison with the structures observed in {sup 171}Tm.

  5. Structure of three-quasiparticle isomers in {sup 169}Ho and {sup 171}Tm

    SciTech Connect

    Dracoulis, G. D.; Lane, G. J.; Hughes, R. O.; Kondev, F. G.; Chiara, C. J.; Watanabe, H.; Seweryniak, D.; Zhu, S.; Carpenter, M. P.; Janssens, R. V. F.; Lauritsen, T.; Lister, C. J.; McCutchan, E. A.; Stefanescu, I.; Chowdhury, P.

    2010-09-15

    A three-quasiparticle isomer with {tau}=170(8) {mu}s and K{sup {pi}=} (19/2{sup +}) has been identified in the neutron-rich isotope {sup 169}Ho. The isomer decays with K-forbidden transitions to members of a band associated with the 7/2{sup -}[523] proton configuration, whose structure is characterized through analysis of the in-band {gamma}-ray branching ratios. In the isotone {sup 171}Tm, the rotational band based on the known 19/2{sup +}, three-quasiparticle isomer has also been observed. Alternative one-proton two-neutron configurations for the isomer in {sup 169}Ho are discussed in terms of multiquasiparticle calculations and through a comparison with the structures observed in {sup 171}Tm.

  6. Inflationary Quasiparticle Creation and Thermalization Dynamics in Coupled Bose-Einstein Condensates.

    PubMed

    Posazhennikova, Anna; Trujillo-Martinez, Mauricio; Kroha, Johann

    2016-06-01

    A Bose gas in a double-well potential, exhibiting a true Bose-Einstein condensate (BEC) amplitude and initially performing Josephson oscillations, is a prototype of an isolated, nonequilibrium many-body system. We investigate the quasiparticle (QP) creation and thermalization dynamics of this system by solving the time-dependent Keldysh-Bogoliubov equations. We find avalanchelike QP creation due to a parametric resonance between BEC and QP oscillations, followed by slow, exponential relaxation to a thermal state at an elevated temperature, controlled by the initial excitation energy of the oscillating BEC above its ground state. The crossover between the two regimes occurs because of an effective decoupling of the QP and BEC oscillations. This dynamics is analogous to elementary particle creation in models of the early universe. The thermalization in our setup occurs because the BEC acts as a grand canonical reservoir for the quasiparticle system.

  7. Coherent quasiparticles with a small fermi surface in lightly doped Sr(3)Ir(2)O(7).

    PubMed

    de la Torre, A; Hunter, E C; Subedi, A; McKeown Walker, S; Tamai, A; Kim, T K; Hoesch, M; Perry, R S; Georges, A; Baumberger, F

    2014-12-19

    We characterize the electron doping evolution of (Sr_{1-x}La_{x})_{3}Ir_{2}O_{7} by means of angle-resolved photoemission. Concomitant with the metal insulator transition around x≈0.05 we find the emergence of coherent quasiparticle states forming a closed small Fermi surface of volume 3x/2, where x is the independently measured La concentration. The quasiparticle weight Z remains large along the entire Fermi surface, consistent with the moderate renormalization of the low-energy dispersion, and no pseudogap is observed. This indicates a conventional, weakly correlated Fermi liquid state with a momentum independent residue Z≈0.5 in lightly doped Sr_{3}Ir_{2}O_{7}. PMID:25554897

  8. Witnessing the formation and relaxation of dressed quasi-particles in a strongly correlated electron system

    NASA Astrophysics Data System (ADS)

    Novelli, Fabio; de Filippis, Giulio; Cataudella, Vittorio; Esposito, Martina; Vergara, Ignacio; Cilento, Federico; Sindici, Enrico; Amaricci, Adriano; Giannetti, Claudio; Prabhakaran, Dharmalingam; Wall, Simon; Perucchi, Andrea; Dal Conte, Stefano; Cerullo, Giulio; Capone, Massimo; Mishchenko, Andrey; Grüninger, Markus; Nagaosa, Naoto; Parmigiani, Fulvio; Fausti, Daniele

    2014-10-01

    The non-equilibrium approach to correlated electron systems is often based on the paradigm that different degrees of freedom interact on different timescales. In this context, photo-excitation is treated as an impulsive injection of electronic energy that is transferred to other degrees of freedom only at later times. Here, by studying the ultrafast dynamics of quasi-particles in an archetypal strongly correlated charge-transfer insulator (La2CuO4+δ), we show that the interaction between electrons and bosons manifests itself directly in the photo-excitation processes of a correlated material. With the aid of a general theoretical framework (Hubbard-Holstein Hamiltonian), we reveal that sub-gap excitation pilots the formation of itinerant quasi-particles, which are suddenly dressed by an ultrafast reaction of the bosonic field.

  9. Quasiparticle electronic structure of Bi2Se3 via the sc-COHSEX+GW approach

    NASA Astrophysics Data System (ADS)

    Barker, Bradford A.; Deslippe, Jack; Yazyev, Oleg; Louie, Steven G.

    We present ab initio calculations of the quasiparticle electronic band structure of three-dimensional topological insulator material Bi2Se3 using the full spinor GW approach. The mean-field is initially computed at the DFT level in the local density approximation (LDA) using fully-relativistic pseudopotentials. We then improve the mean-field electronic structure by solving Dyson's equation in the static COHSEX approximation, self-consistently updating the eigenvalues, eigenvectors, and dielectric screening. After a few iterations, we then perform a GW calculation to determine the quasiparticle energies. We compare our calculated results to experimental values of the band gaps and effective masses. This work was supported by NSF Grant No. DMR15-1508412 and U.S. DOE under Contract No. DE-AC02-05CH11231. Computational resources have been provided by DOE at LBNL's NERSC facility and the NSF through XSEDE resources at NICS.

  10. Properties of quark matter in a new quasiparticle model with QCD running coupling

    NASA Astrophysics Data System (ADS)

    Lu, ZhenYan; Peng, GuangXiong; Xu, JianFeng; Zhang, ShiPeng

    2016-06-01

    The running of the QCD coupling in the effective mass causes thermodynamic inconsistency problem in the conventional quasiparticle model. We provide a novel treatment which removes the inconsistency by an effective bag constant. The chemical potential dependence of the renormalization subtraction point is constrained by the Cauchy condition in the chemical potential space. The stability and microscopic properties of strange quark matter are then studied within the completely self-consistent quasiparticle model, and the obtained equation of state of quark matter is applied to the investigation of strange stars. It is found that our improved model can describe well compact stars with mass about two times the solar mass, which indicates that such massive compact stars could be strange stars.

  11. Long-Range Spin-Polarized Quasiparticle Transport in Mesoscopic Al Superconductors with a Zeeman Splitting

    NASA Astrophysics Data System (ADS)

    Hübler, F.; Wolf, M. J.; Beckmann, D.; v. Löhneysen, H.

    2012-11-01

    We report on nonlocal transport in multiterminal superconductor-ferromagnet structures, which were fabricated by means of e-beam lithography and shadow evaporation techniques. In the presence of a significant Zeeman splitting of the quasiparticle states, we find signatures of spin transport over distances of several μm, exceeding other length scales such as the coherence length, the normal-state spin-diffusion length, and the charge-imbalance length. The relaxation length of the spin signal shows a nearly linear increase with magnetic field, hinting at a freeze-out of relaxation by the Zeeman splitting. We propose that the relaxation length is given by the recombination length of the quasiparticles rather than a renormalized spin-diffusion length.

  12. Coherent quasiparticles with a small fermi surface in lightly doped Sr(3)Ir(2)O(7).

    PubMed

    de la Torre, A; Hunter, E C; Subedi, A; McKeown Walker, S; Tamai, A; Kim, T K; Hoesch, M; Perry, R S; Georges, A; Baumberger, F

    2014-12-19

    We characterize the electron doping evolution of (Sr_{1-x}La_{x})_{3}Ir_{2}O_{7} by means of angle-resolved photoemission. Concomitant with the metal insulator transition around x≈0.05 we find the emergence of coherent quasiparticle states forming a closed small Fermi surface of volume 3x/2, where x is the independently measured La concentration. The quasiparticle weight Z remains large along the entire Fermi surface, consistent with the moderate renormalization of the low-energy dispersion, and no pseudogap is observed. This indicates a conventional, weakly correlated Fermi liquid state with a momentum independent residue Z≈0.5 in lightly doped Sr_{3}Ir_{2}O_{7}.

  13. Quasiparticle-mediated spin Hall effect in a superconductor.

    PubMed

    Wakamura, T; Akaike, H; Omori, Y; Niimi, Y; Takahashi, S; Fujimaki, A; Maekawa, S; Otani, Y

    2015-07-01

    In some materials the competition between superconductivity and magnetism brings about a variety of unique phenomena such as the coexistence of superconductivity and magnetism in heavy-fermion superconductors or spin-triplet supercurrent in ferromagnetic Josephson junctions. Recent observations of spin-charge separation in a lateral spin valve with a superconductor evidence that these remarkable properties are applicable to spintronics, although there are still few works exploring this possibility. Here, we report the experimental observation of the quasiparticle-mediated spin Hall effect in a superconductor, NbN. This compound exhibits the inverse spin Hall (ISH) effect even below the superconducting transition temperature. Surprisingly, the ISH signal increases by more than 2,000 times compared with that in the normal state with a decrease of the injected spin current. The effect disappears when the distance between the voltage probes becomes larger than the charge imbalance length, corroborating that the huge ISH signals measured are mediated by quasiparticles.

  14. Inflationary Quasiparticle Creation and Thermalization Dynamics in Coupled Bose-Einstein Condensates

    NASA Astrophysics Data System (ADS)

    Posazhennikova, Anna; Trujillo-Martinez, Mauricio; Kroha, Johann

    2016-06-01

    A Bose gas in a double-well potential, exhibiting a true Bose-Einstein condensate (BEC) amplitude and initially performing Josephson oscillations, is a prototype of an isolated, nonequilibrium many-body system. We investigate the quasiparticle (QP) creation and thermalization dynamics of this system by solving the time-dependent Keldysh-Bogoliubov equations. We find avalanchelike QP creation due to a parametric resonance between BEC and QP oscillations, followed by slow, exponential relaxation to a thermal state at an elevated temperature, controlled by the initial excitation energy of the oscillating BEC above its ground state. The crossover between the two regimes occurs because of an effective decoupling of the QP and BEC oscillations. This dynamics is analogous to elementary particle creation in models of the early universe. The thermalization in our setup occurs because the BEC acts as a grand canonical reservoir for the quasiparticle system.

  15. 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.

  16. Four-Quasiparticle High-K States in Neutron-Deficient Lead and Polonium Nuclei

    NASA Astrophysics Data System (ADS)

    Shi, Yue; Xu, Furong

    2012-06-01

    Configuration-constrained potential energy surface calculations have been performed to investigate four-quasiparticle high-K configurations in neutron-deficient lead and polonium isotopes. A good agreement between the calculations and the experimental data has been found for the excitation energy of the observed Kπ = 19- state in 188Pb. Several lowly excited high-K states are predicted, and the large oblate deformation and low energy indicate high-K isomerism in these nuclei.

  17. Spectral Function and Quasiparticle Damping of Interacting Bosons in Two Dimensions

    SciTech Connect

    Sinner, Andreas; Kopietz, Peter; Hasselmann, Nils

    2009-03-27

    We employ the functional renormalization group to study dynamical properties of the two-dimensional Bose gas. Our approach is free of infrared divergences, which plague the usual diagrammatic approaches, and is consistent with the exact Nepomnyashchy identity, which states that the anomalous self-energy vanishes at zero frequency and momentum. We recover the correct infrared behavior of the propagators and present explicit results for the spectral line shape, from which we extract the quasiparticle dispersion and dampi0008.

  18. Analytical results for quasiparticle excitations in the Fractional Quantum Hall Effect regime

    NASA Astrophysics Data System (ADS)

    Bentalha, Z.

    2016-07-01

    In this work, quasiparticle energies for systems with N = 3 , 4 , 5 , 6 and 7 electrons are calculated analytically in both Laughlin and composite fermions (CF) theories by considering the electron-electron interaction potential. The exact results we have obtained for the first and the second excited states agree with previous numerical results. This study shows that at this level the CF-wave function has lower energy in comparison with Laughlin wave function energy.

  19. Determination of the Superfluid Gap in Atomic Fermi Gases by Quasiparticle Spectroscopy

    SciTech Connect

    Schirotzek, Andre; Shin, Yong-il; Schunck, Christian H.; Ketterle, Wolfgang

    2008-10-03

    We present majority and minority radio frequency spectra of strongly interacting imbalanced Fermi gases of {sup 6}Li. We observed a smooth evolution in the nature of pairing correlations from pairing in the superfluid region to polaron binding in the highly polarized normal region. The imbalance induces quasiparticles in the superfluid region even at very low temperature. This leads to a local bimodal spectral response, which allowed us to determine the superfluid gap {delta} and the Hartree energy U.

  20. Anomalous Quasiparticle Symmetries and Non-Abelian Defects on Symmetrically Gapped Surfaces of Weak Topological Insulators

    NASA Astrophysics Data System (ADS)

    Mross, David F.; Essin, Andrew; Alicea, Jason; Stern, Ady

    2016-01-01

    We show that boundaries of 3D weak topological insulators can become gapped by strong interactions while preserving all symmetries, leading to Abelian surface topological order. The anomalous nature of weak topological insulator surfaces manifests itself in a nontrivial action of symmetries on the quasiparticles; most strikingly, translations change the anyon types in a manner impossible in strictly 2D systems with the same symmetry. As a further consequence, screw dislocations form non-Abelian defects that trap Z4 parafermion zero modes.

  1. Anomalous Quasiparticle Symmetries and Non-Abelian Defects on Symmetrically Gapped Surfaces of Weak Topological Insulators.

    PubMed

    Mross, David F; Essin, Andrew; Alicea, Jason; Stern, Ady

    2016-01-22

    We show that boundaries of 3D weak topological insulators can become gapped by strong interactions while preserving all symmetries, leading to Abelian surface topological order. The anomalous nature of weak topological insulator surfaces manifests itself in a nontrivial action of symmetries on the quasiparticles; most strikingly, translations change the anyon types in a manner impossible in strictly 2D systems with the same symmetry. As a further consequence, screw dislocations form non-Abelian defects that trap Z_{4} parafermion zero modes.

  2. Enhanced interlayer exchange coupling in antiferromagnetically coupled ultrathin (Co70Fe30/Pd) multilayers

    NASA Astrophysics Data System (ADS)

    Meng, Zhaoliang; Qiu, Jinjun; Han, Guchang; Teo, Kie Leong

    2015-12-01

    We report the studies of magnetization reversal and magnetic interlayer coupling in synthetic antiferromagnetic (SAF) [Pd/Co70Fe30]9/Ru(tRu)/Pd(tPd)/[Co70Fe30/Pd]9 structure as functions of inserted Pd layer (tPd) and Ru layer (tRu) thicknesses. We found the exchange coupling field (Hex) and perpendicular magnetic anisotropy (PMA) can be controlled by both the tPd and tRu, The Hex shows a Ruderman-Kittel-Kasuya-Yosida-type oscillatory decay dependence on tRu and a maximum interlayer coupling strength Jex = 0.522 erg/cm2 is achieved at tPd + tRu ≈ 0.8 nm in the as-deposited sample. As it is known that a high post-annealing stability of SAF structure is required for magnetic random access memory applications, the dependence of Hex and PMA on the post-annealing temperature (Ta) is also investigated. We found that both high PMA of the top Co70Fe30/Pd multilayer is maintained and Hex is enhanced with increasing Ta up to 350 °C for tRu > 0.7 nm in our SAF structure.

  3. Effects of quasiparticle tunnelling in a circuit-QED realization of a strongly driven two-level system

    NASA Astrophysics Data System (ADS)

    Leppäkangas, J.; de Graaf, S. E.; Adamyan, A.; Fogelström, M.; Danilov, A. V.; Lindström, T.; Kubatkin, S. E.; Johansson, G.

    2013-11-01

    We experimentally and theoretically study the frequency shift of a driven cavity coupled to a superconducting charge qubit. In addition to previous studies, here we also consider drive strengths large enough to energetically allow for quasiparticle creation. Quasiparticle tunnelling leads to the inclusion of more than two charge states in the dynamics. To explain the observed effects, we develop a master equation for the microwave dressed charge states, including quasiparticle tunnelling. A bimodal behaviour of the frequency shift as a function of gate voltage can be used for sensitive charge detection. However, at weak drives, the charge sensitivity is significantly reduced by nonequilibrium quasiparticles, which induce transitions to a non-sensitive state. Unexpectedly, at high-enough drives, the quasiparticle tunnelling enables a very fast relaxation channel to the sensitive state. In this regime, the charge sensitivity is thus robust against externally injected quasiparticles and the desired dynamics prevail over a broad range of temperatures. We find very good agreement between the theory and experiment over a wide range of drive strengths and temperatures.

  4. GW correlation effects on plutonium quasiparticle energies: changes in crystal-field splitting

    SciTech Connect

    Albers, Robert C; Chantis, Athanasios N; Svane, Axel; Christensen, Niels E

    2009-01-01

    We present results for the electronic structure of plutonium by using a recently developed quasiparticle self-consistent GW method (QSGW). We consider a paramagnetic solution without spin-orbit interaction as a function of volume for the face-centered cubic (fcc) unit cell. We span unit-cell volumes ranging from 10% greater than the equilibrium volume of the 8 phase to 90 % of the equivalent for the a phase of Pu. The self-consistent GW quasiparticle energies are compared to those obtained within the Local Density Approximation (LDA). The goal of the calculations is to understand systematic trends in the effects of electronic correlations on the quasiparticle energy bands of Pu as a function of the localization of the J orbitals. We show that correlation effects narrow the f bands in two significantly different ways. Besides the expected narrowing of individual f bands (flatter dispersion), we find that an even more significant effect on the f bands is a decrease in the crystal-field splitting of the different bands

  5. Decay and Fission Hindrance of Two- and Four-Quasiparticle K Isomers in ^{254}Rf.

    PubMed

    David, H M; Chen, J; Seweryniak, D; Kondev, F G; Gates, J M; Gregorich, K E; Ahmad, I; Albers, M; Alcorta, M; Back, B B; Baartman, B; Bertone, P F; Bernstein, L A; Campbell, C M; Carpenter, M P; Chiara, C J; Clark, R M; Cromaz, M; Doherty, D T; Dracoulis, G D; Esker, N E; Fallon, P; Gothe, O R; Greene, J P; Greenlees, P T; Hartley, D J; Hauschild, K; Hoffman, C R; Hota, S S; Janssens, R V F; Khoo, T L; Konki, J; Kwarsick, J T; Lauritsen, T; Macchiavelli, A O; Mudder, P R; Nair, C; Qiu, Y; Rissanen, J; Rogers, A M; Ruotsalainen, P; Savard, G; Stolze, S; Wiens, A; Zhu, S

    2015-09-25

    Two isomers decaying by electromagnetic transitions with half-lives of 4.7(1.1) and 247(73) μs have been discovered in the heavy ^{254}Rf nucleus. The observation of the shorter-lived isomer was made possible by a novel application of a digital data acquisition system. The isomers were interpreted as the K^{π}=8^{-}, ν^{2}(7/2^{+}[624],9/2^{-}[734]) two-quasineutron and the K^{π}=16^{+}, 8^{-}ν^{2}(7/2^{+}[624],9/2^{-}[734])⊗8^{-}π^{2}(7/2^{-}[514],9/2^{+}[624]) four-quasiparticle configurations, respectively. Surprisingly, the lifetime of the two-quasiparticle isomer is more than 4 orders of magnitude shorter than what has been observed for analogous isomers in the lighter N=150 isotones. The four-quasiparticle isomer is longer lived than the ^{254}Rf ground state that decays exclusively by spontaneous fission with a half-life of 23.2(1.1) μs. The absence of sizable fission branches from either of the isomers implies unprecedented fission hindrance relative to the ground state.

  6. Quasi-particles ultrafastly releasing kink bosons to form Fermi arcs in a cuprate superconductor

    PubMed Central

    Ishida, Y.; Saitoh, T.; Mochiku, T.; Nakane, T.; Hirata, K.; Shin, S.

    2016-01-01

    In a conventional framework, superconductivity is lost at a critical temperature (Tc) because, at higher temperatures, gluing bosons can no longer bind two electrons into a Cooper pair. In high-Tc cuprates, it is still unknown how superconductivity vanishes at Tc. We provide evidence that the so-called ≲70-meV kink bosons that dress the quasi-particle excitations are playing a key role in the loss of superconductivity in a cuprate. We irradiated a 170-fs laser pulse on Bi2Sr2CaCu2O8+δ and monitored the responses of the superconducting gap and dressed quasi-particles by time- and angle-resolved photoemission spectroscopy. We observe an ultrafast loss of superconducting gap near the d-wave node, or light-induced Fermi arcs, which is accompanied by spectral broadenings and weight redistributions occurring within the kink binding energy. We discuss that the underlying mechanism of the spectral broadening that induce the Fermi arc is the undressing of quasi-particles from the kink bosons. The loss mechanism is beyond the conventional framework, and can accept the unconventional phenomena such as the signatures of Cooper pairs remaining at temperatures above Tc. PMID:26728626

  7. Fermionic q-deformation and its connection to thermal effective mass of a quasiparticle

    NASA Astrophysics Data System (ADS)

    Algin, Abdullah; Senay, Mustafa

    2016-04-01

    A fermionic deformation scheme is applied to a study on the low-temperature quantum statistical behavior of a quasifermion gas model with intermediate statistics. Such a model does not satisfy the Pauli exclusion principle, and its quantum statistical properties are based on a formalism of the fermionic q-calculus. For low temperatures, several thermostatistical functions of the model such as the chemical potential, the heat capacity, and the entropy are derived by means of a function of the model deformation parameter q. The effect of fermionic q-deformation on the low-temperature thermostatistical properties of the model are discussed in detail. Our results show that the present deformed (quasi)fermion model provides remarkable connections of the model deformation parameter q, first, with the thermal effective mass of a quasiparticle, and second, with the temperature parameter. Hence, it turns out that the model deformation parameter q has also a role controlling the strength of effective quasiparticle interactions in the model. Finally, we conclude that this work can be useful for understanding the details of interaction mechanism of fermions such as quasiparticle states emergent in the fractional quantum Hall effect.

  8. Quasi-particles ultrafastly releasing kink bosons to form Fermi arcs in a cuprate superconductor.

    PubMed

    Ishida, Y; Saitoh, T; Mochiku, T; Nakane, T; Hirata, K; Shin, S

    2016-01-01

    In a conventional framework, superconductivity is lost at a critical temperature (Tc) because, at higher temperatures, gluing bosons can no longer bind two electrons into a Cooper pair. In high-Tc cuprates, it is still unknown how superconductivity vanishes at Tc. We provide evidence that the so-called ≲ 70-meV kink bosons that dress the quasi-particle excitations are playing a key role in the loss of superconductivity in a cuprate. We irradiated a 170-fs laser pulse on Bi2Sr2CaCu2O(8+δ) and monitored the responses of the superconducting gap and dressed quasi-particles by time- and angle-resolved photoemission spectroscopy. We observe an ultrafast loss of superconducting gap near the d-wave node, or light-induced Fermi arcs, which is accompanied by spectral broadenings and weight redistributions occurring within the kink binding energy. We discuss that the underlying mechanism of the spectral broadening that induce the Fermi arc is the undressing of quasi-particles from the kink bosons. The loss mechanism is beyond the conventional framework, and can accept the unconventional phenomena such as the signatures of Cooper pairs remaining at temperatures above Tc.

  9. 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.

  10. PD-L1 and Survival in Solid Tumors: A Meta-Analysis

    PubMed Central

    Li, Lijun; Chai, Ying; Huang, Jian

    2015-01-01

    Background Numerous agents targeting PD-L1/PD-1 check-point are in clinical development. However, the correlation between PD-L1expression and prognosis of solid tumor is still in controversial. Here, we elicit a systematic review and meta-analysis to investigate the potential value of PD-L1 in the prognostic prediction in human solid tumors. Methods Electronic databases were searched for studies evaluating the expression of PD-L1 and overall survival (OS) of patients with solid tumors. Odds ratios (ORs) from individual studies were calculated and pooled by using a random-effect model, and heterogeneity and publication bias analyses were also performed. Results A total of 3107 patients with solid tumor from 28 published studies were included in the meta-analysis. The median percentage of solid tumors with PD-L1 overexpression was 52.5%. PD-L1 overexpression was associated with worse OS at both 3 years (OR = 2.43, 95% confidence interval (CI) = 1.60 to 3.70, P < 0.0001) and 5 years (OR = 2.23, 95% CI = 1.40 to 3.55, P = 0.0008) of solid tumors. Among the tumor types, PD-L1 was associated with worse 3 year-OS of esophageal cancer, gastric cancer, hepatocellular carcinoma, and urothelial cancer, and 5 year-OS of esophageal cancer, gastric cancer and colorectal cancer. Conclusions These results suggest that expression of PD-L1 is associated with worse survival in solid tumors. However, the correlations between PD-L1 and prognosis are variant among different tumor types. More studies are needed to investigate the clinical value of PD-L1 expression in prognostic prediction and treatment option. PMID:26114883

  11. Quasiparticle energies, excitonic effects, and dielectric screening in transparent conducting oxides

    NASA Astrophysics Data System (ADS)

    Schleife, André

    Using the power of high-performance super computers, computational materials scientists nowadays employ highly accurate quantum-mechanical approaches to reliably predict materials properties. In particular, many-body perturbation theory is an excellent framework for performing theoretical spectroscopy on novel materials including transparent conducting oxides, since this framework accurately describes quasiparticle and excitonic effects.We recently used hybrid exchange-correlation functionals and an efficient implementation of the Bethe-Salpeter approach to investigate several important transparent conducting oxides. Despite their exceptional potential for applications in photovoltaics and optoelectronics their optical properties oftentimes remain poorly understood: Our calculations explain the optical spectrum of bixbyite indium oxide over a very large photon energy range, which allows us to discuss the importance of quasiparticle and excitonic effects at low photon energies around the absorption onset, but also for excitations up to 40 eV. We show that in this regime the energy dependence of the electronic self energy cannot be neglected. Furthermore, we investigated the influence of excitonic effects on optical absorption for lanthanum-aluminum oxide and hafnium oxide. Their complicated conduction band structures require an accurate description of quasiparticle energies and we find that for these strongly polar materials, a contribution of the lattice polarizability to dielectric screening needs to be taken into account. We discuss how this affects the electron-hole interaction and find a strong influence on excitonic effects.The deep understanding of electronic excitations that can be obtained using these modern first-principles techniques, eventually will allow for computational materials design, e.g. of band gaps, densities of states, and optical properties of transparent conducting oxides and other materials with societally important applications.

  12. Multi-quasiparticle excitation: Extending shape coexistence in A~190 neutron-deficient nuclei

    NASA Astrophysics Data System (ADS)

    Shi, Yue; Xu, F. R.; Liu, H. L.; Walker, P. M.

    2010-10-01

    Multi-quasiparticle high-K states in neutron-deficient mercury, lead, and polonium isotopes have been investigated systematically by means of configuration-constrained potential-energy-surface calculations. An abundance of high-K states is predicted with both prolate and oblate shapes, which extends the shape coexistence of the mass region. Well-deformed shapes provide good conditions for the formation of isomers, as exemplified in Pb188. Of particular interest is the prediction of low-lying 10- states in polonium isotopes, which indicate long-lived isomers.

  13. Multi-quasiparticle excitation: Extending shape coexistence in A{approx}190 neutron-deficient nuclei

    SciTech Connect

    Shi Yue; Liu, H. L.; Xu, F. R.; Walker, P. M.

    2010-10-15

    Multi-quasiparticle high-K states in neutron-deficient mercury, lead, and polonium isotopes have been investigated systematically by means of configuration-constrained potential-energy-surface calculations. An abundance of high-K states is predicted with both prolate and oblate shapes, which extends the shape coexistence of the mass region. Well-deformed shapes provide good conditions for the formation of isomers, as exemplified in {sup 188}Pb. Of particular interest is the prediction of low-lying 10{sup -} states in polonium isotopes, which indicate long-lived isomers.

  14. Light quasiparticles dominate electronic transport in molecular crystal field-effect transistors

    SciTech Connect

    Li, Z. Q.; Podzorov, V.; Sai, N.; Martin, Michael C.; Gershenson, M. E.; Di Ventra, M.; Basov, D. N.

    2007-03-01

    We report on an infrared spectroscopy study of mobile holes in the accumulation layer of organic field-effect transistors based on rubrene single crystals. Our data indicate that both transport and infrared properties of these transistors at room temperature are governed by light quasiparticles in molecular orbital bands with the effective masses m[small star, filled]comparable to free electron mass. Furthermore, the m[small star, filled]values inferred from our experiments are in agreement with those determined from band structure calculations. These findings reveal no evidence for prominent polaronic effects, which is at variance with the common beliefs of polaron formation in molecular solids.

  15. Lowest four-quasiparticle magnetic dipole band in {sup 128}Ba

    SciTech Connect

    Vogel, O.; Dewald, A.; von Brentano, P.; Gableske, J.; Kruecken, R.; Nicolay, N.; Gelberg, A.; Petkov, P.; Gizon, A.; Gizon, J.; Bazzacco, D.; Rossi Alvarez, C.; Pavan, P.; Lunardi, S.; Napoli, D.R.; Frauendorf, S.; Doenau, F.

    1997-09-01

    The four-quasiparticle magnetic dipole band in {sup 128}Ba has been investigated with the {sup 96}Zr({sup 36}S,4n){sup 128}Ba reaction at the GASP spectrometer of the Laboratori Nazionali di Legnaro. Linking transitions to the previously known positive parity states have been observed for the first time in this mass region and new transitions on top of the band have been found. The experimental results are compared to previously made tilted axis cranking calculations. {copyright} {ital 1997} {ital The American Physical Society}

  16. Superconducting Gap Anisotropy and Quasiparticle Interactions: A Doping Dependent Photoemission Study

    SciTech Connect

    Mesot, J.; Norman, M.R.; Campuzano, J.C.; Mesot, J.; Campuzano, J.C.; Fretwell, H.M.; Kaminski, A.; Ding, H.; Randeria, M.; Paramekanti, A.; Takeuchi, T.; Yokoya, T.; Sato, T.; Takahashi, T.; Mochiku, T.; Kadowaki, K.

    1999-07-01

    Comparing photoemission measurements on Bi2212 with penetration depth data, we show that a description of the nodal excitations of the d -wave superconducting state in terms of noninteracting quasiparticles is inadequate, and we estimate the magnitude and doping dependence of the Landau interaction parameter which renormalizes the linear T contribution to the superfluid density. Furthermore, although consistent with d -wave symmetry, the gap with underdoping cannot be fit by the simple cos k{sub x}{minus}cos k{sub y} form, which suggests an increasing importance of long range interactions as the insulator is approached. {copyright} {ital 1999} {ital The American Physical Society }

  17. Resilient quasiparticles in Ruthenates: transport properties within LDA+DMFT method

    NASA Astrophysics Data System (ADS)

    Deng, Xiaoyu; Haule, Kristjan; Kotliar, Gabriel

    2015-03-01

    Many Rutheniums are strongly correlated metals with Fermi Liquid behavior found only a small temperature scale. Non-Fermi signatures appear in both their resistivity and optical conductivity. We study the transport properties of a set of Ruthenates within first principle methods in combination with dynamical mean field theory and find reasonable agreement with experimental findings. The non-Fermi-liquid features are attributed to the temperature dependence of resilient quasiparticles, which survives above the Fermi liquid temperature scale and exhibits a strong temperature dependence in their effective mass enhancement and scattering rate.

  18. Calculation of quasiparticle energy spectrum of silicon using the correlated Hartree-Fock method

    NASA Astrophysics Data System (ADS)

    Ishihara, Takamitsu; Yamagami, Hiroshi; Matsuzawa, Kazuya; Yasuhara, Hiroshi

    1999-06-01

    We present quasiparticle energy spectrum calculations of silicon using the correlated Hartree-Fock method proposed by Yasuhara and Takada [Phys. Rev. B 43, 7200 (1991)], in which the information on the effective mass of an electron liquid is included in the form of a nonlocal spin-parallel potential in addition to a local potential. The calculated band gaps of silicon are much improved, compared with the local density approximation values. The minimum indirect band gap is evaluated to be 1.37 eV.

  19. Spectroscopy in the second well of the {sup 148}Gd nucleus: Two quasiparticle and collective excitations

    SciTech Connect

    de Angelis, G.; Wyss, R.; Bazzacco, D.; De Poli, M.; Gadea, A.; Lunardi, S.; Napoli, D.R.; Petrache, C.M.; Rossi Alvarez, C.; Sferrazza, M.; Rubio, B. |||

    1996-02-01

    Six superdeformed (SD) bands have been observed in the nucleus {sup 148}Gd using the {gamma}-spectrometer GASP. The structure of the observed SD bands is discussed within the concept of cranked-Strutinsky-type calculations including pairing interaction. For the configuration assignments two different parametrizations of the Woods-Saxon potential are compared. Five of the observed SD bands are described in terms of quasiparticle configurations, whereas one is suggested to have vibrational-like structure. From this data a {Delta}{ital I}=2 staggering in the rotational spectrum of the yrast SD band also has been observed. {copyright} {ital 1996 The American Physical Society.}

  20. Projected quasiparticle calculations for the N =82 odd-proton isotones

    SciTech Connect

    Losano, L. ); Dias, H. )

    1991-12-01

    The structure of low-lying states in odd-mass {ital N}=82 isotones (135{le}{ital A}{le}145) is investigated in terms of a number-projected one- and three-quasiparticles Tamm-Dancoff approximation. A surface-delta interaction is taken as the residual nucleon-nucleon interaction. Excitation energies, dipole and quadrupole moments, and {ital B}({ital M}1) and {ital B}({ital E}2) values are calculated and compared with the experimental data.

  1. Anomalous Quasiparticle Symmetries and Non-Abelian Defects on Symmetrically Gapped Surfaces of Weak Topological Insulators.

    PubMed

    Mross, David F; Essin, Andrew; Alicea, Jason; Stern, Ady

    2016-01-22

    We show that boundaries of 3D weak topological insulators can become gapped by strong interactions while preserving all symmetries, leading to Abelian surface topological order. The anomalous nature of weak topological insulator surfaces manifests itself in a nontrivial action of symmetries on the quasiparticles; most strikingly, translations change the anyon types in a manner impossible in strictly 2D systems with the same symmetry. As a further consequence, screw dislocations form non-Abelian defects that trap Z_{4} parafermion zero modes. PMID:26849608

  2. Light quasiparticles dominate electronic transport in molecularcrystal field-effect transistors

    SciTech Connect

    Li, Z.Q.; Podzorov, V.; Sai, N.; Martin, M.C.; Gershenson, M.E.; Di Ventra, M.; Basov, D.N.

    2007-04-30

    We report on an infrared spectroscopy study of mobile holesin the accumulation layer of organic field effect transistors based onrubrene single crystals. Our data indicate that both transport andinfrared properties of these transistors at room temperature are governedby light quasiparticles in molecular orbital bands with the effectivemasses m* comparable to free electron mass. Furthermore, the m* valuesinferred from our experiments are in agreement with those determined fromband structure calculations. These findings reveal no evidence forprominent polaronic effects, which is at variance with the common beliefsof polaron formation in molecular solids.

  3. 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

  4. 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...

  5. Phase Stability for the Pd-Si System. First-Principles, Experiments, and Solution-Based Modeling

    SciTech Connect

    Zhou, S. H.; Huo, Y.; Napolitano, Ralph E.

    2015-11-05

    Relative stabilities of the compounds in the binary Pd-Si system were assessed using first-principles calculations and experimental methods. Calculations of lattice parameters and enthalpy of formation indicate that Pd5Si-μ, Pd9Si2-α, Pd3 Si-β, Pd2 Si-γ, and PdSi-δ are the stable phases at 0 K (-273 °C). X-ray diffraction analyses (XRD) and electron probe microanalysis (EPMA) of the as-solidified and heat-treated samples support the computational findings, except that the PdSi-δ phase was not observed at low temperature. Considering both experimental data and first-principles results, the compounds Pd 5 Si-μ, Pd9 Si2-α, Pd3Si-β, and Pd2Si-γ are treated as stable phases down to 0 K (-273 °C), while the PdSi-δ is treated as being stable over a limited range, exhibiting a lower bound. Using these findings, a comprehensive solution-based thermodynamic model is formulated for the Pd-Si system, permitting phase diagram calculation. Moreover, the liquid phase is described using a three-species association model and other phases are treated as solid solutions, where a random substitutional model is adopted for Pd-fcc and Si-dia, and a two-sublattice model is employed for Pd5Si-μ, Pd9Si2-α, Pd3Si-β, Pd2Si-γ, and PdSi-δ. Model parameters are fitted using available experimental data and first-principles data, and the resulting phase diagram is reported over the full range of compositions.

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  7. 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. PMID:27619200

  8. Ab Initio Study of Quasiparticle and Excitonic Properties of MoS2

    NASA Astrophysics Data System (ADS)

    Qiu, Diana; Jornada, Felipe; Louie, Steven

    2013-03-01

    MoS2 is a layered, transition-metal dichalcogenide that can be cleaved into single-layer sheets, in a manner similar to graphene. Monolayer MoS2 has a direct band gap, strong spin-orbit coupling and strongly enhanced photoluminescence, compared with the bulk. MoS2's interesting electronic and optical properties mean that it could have many applications in single-layer electronic devices, but on the theoretical level, when many-electron interaction effects are included, there is still some uncertainty about the quasiparticle and excitonic properties of MoS2. We use first-principles calculations to study the quasiparticle band structure and optical absorption spectrum of MoS2 at the GW +BSE level. We include spin-orbit coupling as a perturbation either before or after the GW calculation of the band structure, and we demonstrate that our calculations are fully converged with respect to the dielectric cutoff and summation over empty bands. This work was supported by NSF grant No. DMR10-1006184 and U.S. DOE under Contract No. DE-AC02-05CH11231. Computational resources have been provided by NERSC.

  9. Quasi-particle corrections to the LSDA+U electronic structure of solid bcc hydrogen

    NASA Astrophysics Data System (ADS)

    Kioupakis, Emmanouil

    2005-03-01

    Quasi-particle calculations within the GW approximation usually start with the LDA electronic structure as mean field solution, which works well for moderately correlated materials. For strongly correlated systems, such as the transition metal oxides, LSDA can give qualitatively wrong ground states, making any further improvement difficult. By starting with the LSDA+U mean field results in the GW approximation calculation of the electron self-energy, we expect to have a better understanding of the quasi-particle properties in these systems. We employ this approach in the study of solid hydrogen, a model system for which previous results exist in the literature. This will test the applicability of the technique to more realistic systems. This work was supported by National Science Foundation Grant No. DMR04-39768 and by the Director, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, U.S. Department of Energy under Contract No. DE-AC03-76SF00098. Computational resources have been provided by NSF at the National Partnership for Advanced Computational Infrastructure (NPACI) and DOE at the National Energy Research Scientific Computing Center (NERSC)

  10. The rate of quasiparticle recombination probes the onset of coherence in cuprate superconductors.

    PubMed

    Hinton, J P; Thewalt, E; Alpichshev, Z; Mahmood, F; Koralek, J D; Chan, M K; Veit, M J; Dorow, C J; Barišić, N; Kemper, A F; Bonn, D A; Hardy, W N; Liang, Ruixing; Gedik, N; Greven, M; Lanzara, A; Orenstein, J

    2016-01-01

    In the underdoped copper-oxides, high-temperature superconductivity condenses from a nonconventional metallic "pseudogap" phase that exhibits a variety of non-Fermi liquid properties. Recently, it has become clear that a charge density wave (CDW) phase exists within the pseudogap regime. This CDW coexists and competes with superconductivity (SC) below the transition temperature Tc, suggesting that these two orders are intimately related. Here we show that the condensation of the superfluid from this unconventional precursor is reflected in deviations from the predictions of BSC theory regarding the recombination rate of quasiparticles. We report a detailed investigation of the quasiparticle (QP) recombination lifetime, τqp, as a function of temperature and magnetic field in underdoped HgBa2CuO(4+δ) (Hg-1201) and YBa2Cu3O(6+x) (YBCO) single crystals by ultrafast time-resolved reflectivity. We find that τqp(T) exhibits a local maximum in a small temperature window near Tc that is prominent in underdoped samples with coexisting charge order and vanishes with application of a small magnetic field. We explain this unusual, non-BCS behavior by positing that Tc marks a transition from phase-fluctuating SC/CDW composite order above to a SC/CDW condensate below. Our results suggest that the superfluid in underdoped cuprates is a condensate of coherently-mixed particle-particle and particle-hole pairs. PMID:27071712

  11. The rate of quasiparticle recombination probes the onset of coherence in cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Hinton, J. P.; Thewalt, E.; Alpichshev, Z.; Mahmood, F.; Koralek, J. D.; Chan, M. K.; Veit, M. J.; Dorow, C. J.; Barišić, N.; Kemper, A. F.; Bonn, D. A.; Hardy, W. N.; Liang, Ruixing; Gedik, N.; Greven, M.; Lanzara, A.; Orenstein, J.

    2016-04-01

    In the underdoped copper-oxides, high-temperature superconductivity condenses from a nonconventional metallic ”pseudogap” phase that exhibits a variety of non-Fermi liquid properties. Recently, it has become clear that a charge density wave (CDW) phase exists within the pseudogap regime. This CDW coexists and competes with superconductivity (SC) below the transition temperature Tc, suggesting that these two orders are intimately related. Here we show that the condensation of the superfluid from this unconventional precursor is reflected in deviations from the predictions of BSC theory regarding the recombination rate of quasiparticles. We report a detailed investigation of the quasiparticle (QP) recombination lifetime, τqp, as a function of temperature and magnetic field in underdoped HgBa2CuO4+δ (Hg-1201) and YBa2Cu3O6+x (YBCO) single crystals by ultrafast time-resolved reflectivity. We find that τqp(T ) exhibits a local maximum in a small temperature window near Tc that is prominent in underdoped samples with coexisting charge order and vanishes with application of a small magnetic field. We explain this unusual, non-BCS behavior by positing that Tc marks a transition from phase-fluctuating SC/CDW composite order above to a SC/CDW condensate below. Our results suggest that the superfluid in underdoped cuprates is a condensate of coherently-mixed particle-particle and particle-hole pairs.

  12. Ab initio quasiparticle band structure of ABA and ABC-stacked graphene trilayers

    NASA Astrophysics Data System (ADS)

    Menezes, Marcos G.; Capaz, Rodrigo B.; Louie, Steven G.

    2014-01-01

    We obtain the quasiparticle band structure of ABA and ABC-stacked graphene trilayers through ab initio density-functional theory (DFT) and many-body quasiparticle calculations within the GW approximation. To interpret our results, we fit the DFT and GW π bands to a low-energy tight-binding model, which is found to reproduce very well the observed features near the K point. The values of the extracted hopping parameters are reported and compared with available theoretical and experimental data. For both stackings, the self-energy corrections lead to a renormalization of the Fermi velocity, an effect also observed in previous calculations on monolayer graphene. They also increase the separation between the higher-energy bands, which is proportional to the nearest-neighbor interlayer hopping parameter γ1. Both features are brought to closer agreement with experiment through the self-energy corrections. Finally, other effects, such as trigonal warping, electron-hole asymmetry, and energy gaps, are discussed in terms of the associated parameters.

  13. Theory of neutron scattering from thermally excited quasiparticles in superfluid 4He

    NASA Astrophysics Data System (ADS)

    Griffin, A.; Talbot, E.

    1981-11-01

    We present the first detailed theoretical study of the inelastic neutron scattering contribution Sth(Q-->,ω) from thermally excited quasiparticles in superfluid 4He, with emphasis on the low-Q collisionless limit. In the temperature region where rotons are the dominant excitation, our results for Sth(Q-->,ω) scale with Landau's normal fluid density. We argue that Sth(Q-->,ω) is the origin of the broad temperature-dependent continuum which Woods and Svensson (1978) have observed at temperatures above about 1.7 K. Our specific model calculations of Sth(Q-->,ω) are based on evaluating the regular part of the longitudinal momentum current-current correlation function within the Bogoliubov approximation, but the experimental quasiparticle (roton) spectrum is used in our numerical calculations. Our expression satisfies the normal fluid f-sum rule in the long-wavelength collisionless limit and is in essential agreement with the general picture suggested by Pines and Nozières in 1964. Our present theory involves several approximations which probably limit its validity to Q<~0.5 Å-1. Some generalizations to deal with the larger values of Q studied by Woods and Svensson are briefly discussed.

  14. Quasiparticle weight and renormalized Fermi velocity of graphene with long-range Coulomb interactions

    NASA Astrophysics Data System (ADS)

    Tang, Ho-Kin; Leaw, Jia Ning; Rodrigues, J. N. B.; Sengupta, P.; Assaad, F. F.; Adam, S.

    In this work, we study the effects of realistic Coulomb interactions in graphene using a projective quantum Monte Carlo simulation of electrons at half-filing on a honeycomb lattice. We compute the quasiparticle residue, the renormalized Fermi velocity and the antiferromagnetic order parameter as a function of both the long-range and short-range components of the Coulomb potential. We find that the Mott insulator transition is determined mostly by the short-range interaction and is consistent with the Gross-Neveu-Yukawa critical theory. Far from the critical point and in the semi-metallic regime, we find that the Fermi-velocity and quasiparticle residue are influenced by the long-range tail of the Coulomb potential, and for very small interaction strength are consistent with predictions of first order perturbation theory. For experimentally relevant and stronger values of the long-range interaction, our numerical data contradicts prediction from both perturbation theory and the renormalization group approaches. This work was supported by Singapore National Research Foundation (NRF-NRFF2012-01 and CA2DM mid-size Centre), Singapore Ministry of Education(Yale-NUS College R-607-265-01312 and MOE2014-T2-2-112), and DFG Grant No. AS120/9-1.

  15. The rate of quasiparticle recombination probes the onset of coherence in cuprate superconductors

    DOE PAGES

    Hinton, J. P.; Thewalt, E.; Alpichshev, Z.; Mahmood, F.; Koralek, J. D.; Chan, M. K.; Veit, M. J.; Dorow, C. J.; Barisic, N.; Kemper, A. F.; et al

    2016-04-13

    In the underdoped copper-oxides, high-temperature superconductivity condenses from a nonconventional metallic ”pseudogap” phase that exhibits a variety of non-Fermi liquid properties. Recently, it has become clear that a charge density wave (CDW) phase exists within the pseudogap regime. This CDW coexists and competes with superconductivity (SC) below the transition temperature Tc, suggesting that these two orders are intimately related. Here we show that the condensation of the superfluid from this unconventional precursor is reflected in deviations from the predictions of BSC theory regarding the recombination rate of quasiparticles. We report a detailed investigation of the quasiparticle (QP) recombination lifetime, τqp,more » as a function of temperature and magnetic field in underdoped HgBa2CuO4+δ (Hg-1201) and YBa2Cu3O6+x (YBCO) single crystals by ultrafast time-resolved reflectivity. We find that τqp(T) exhibits a local maximum in a small temperature window near Tc that is prominent in underdoped samples with coexisting charge order and vanishes with application of a small magnetic field. We explain this unusual, non-BCS behavior by positing that Tc marks a transition from phase-fluctuating SC/CDW composite order above to a SC/CDW condensate below. Lastly, our results suggest that the superfluid in underdoped cuprates is a condensate of coherently-mixed particle-particle and particle-hole pairs.« less

  16. A Plane-Wave Implementation of Quasiparticle Self-Consistent GW (QSGW)

    NASA Astrophysics Data System (ADS)

    Vigil Currey, Derek; Deslippe, Jack; Louie, Steven G.

    2011-03-01

    The use of GW techniques in calculating the quasiparticle properties of certain classes of materials, e.g. complex oxides, is sometimes hindered by the poor mean-field starting point that density functional theory (DFT) within standard Kohn-Sham implementations provides. There has been considerable effort in the community to improve upon the mean-field starting point for a broad range of materials. A recently proposed method, the quasiparticle self-consistent GW (QSGW) method, employs a process in which a mean-field exchange-correlation potential is approximated from and updated self-consistently using the self-energy operator from previous iteration GW calculations. We present an implementation of this method in a plane-wave basis, and discuss its accuracy, computational cost, and physical implications for a variety of semiconducting materials. This work was supported by NSF Grant No. DMR10-1006184 and U.S. DOE Contract No. DE-AC02-05CH11231. Computational resources were provided by NERSC. Derek Vigil Currey acknowledges funding from UC-Berkeley through the Chancellor's Fellowship.

  17. Loss of nodal quasiparticle integrity in underdoped YBa2Cu3O6+x

    NASA Astrophysics Data System (ADS)

    Fournier, D.; Levy, G.; Pennec, Y.; McChesney, J. L.; Bostwick, A.; Rotenberg, E.; Liang, R.; Hardy, W. N.; Bonn, D. A.; Elfimov, I. S.; Damascelli, A.

    2010-11-01

    A central question in the study of high-temperature superconductivity is whether this phenomenon is linked to the doped antiferromagnetic Mott insulator or whether it emerges from a Fermi-liquid state across the whole cuprate phase diagram. Discriminating between these orthogonal cases hinges on the quantitative determination of the elusive quasiparticle strength Z as a function of hole-doping p, from the heavily overdoped to the deeply underdoped regime. Here we show, by means of angle-resolved photoemission spectroscopy and an in situ doping technique, that the electronic structure of the overdoped metal (0.24<=p<=0.37) is in remarkable agreement with density functional theory and Fermi-liquid-like descriptions. However, below p~0.10-0.15, we observe the loss of nodal quasiparticle integrity. This marks a clear departure from Fermi-liquid behaviour and a more rapid than expected crossover to Mott physics, indicating that the physical properties of underdoped cuprates are dominated by incoherent excitations.

  18. The rate of quasiparticle recombination probes the onset of coherence in cuprate superconductors

    PubMed Central

    Hinton, J. P.; Thewalt, E.; Alpichshev, Z.; Mahmood, F.; Koralek, J. D.; Chan, M. K.; Veit, M. J.; Dorow, C. J.; Barišić, N.; Kemper, A. F.; Bonn, D. A.; Hardy, W. N.; Liang, Ruixing; Gedik, N.; Greven, M.; Lanzara, A.; Orenstein, J.

    2016-01-01

    In the underdoped copper-oxides, high-temperature superconductivity condenses from a nonconventional metallic ”pseudogap” phase that exhibits a variety of non-Fermi liquid properties. Recently, it has become clear that a charge density wave (CDW) phase exists within the pseudogap regime. This CDW coexists and competes with superconductivity (SC) below the transition temperature Tc, suggesting that these two orders are intimately related. Here we show that the condensation of the superfluid from this unconventional precursor is reflected in deviations from the predictions of BSC theory regarding the recombination rate of quasiparticles. We report a detailed investigation of the quasiparticle (QP) recombination lifetime, τqp, as a function of temperature and magnetic field in underdoped HgBa2CuO4+δ (Hg-1201) and YBa2Cu3O6+x (YBCO) single crystals by ultrafast time-resolved reflectivity. We find that τqp(T ) exhibits a local maximum in a small temperature window near Tc that is prominent in underdoped samples with coexisting charge order and vanishes with application of a small magnetic field. We explain this unusual, non-BCS behavior by positing that Tc marks a transition from phase-fluctuating SC/CDW composite order above to a SC/CDW condensate below. Our results suggest that the superfluid in underdoped cuprates is a condensate of coherently-mixed particle-particle and particle-hole pairs. PMID:27071712

  19. Quasiparticle cascade amplifier based on strong electron cooling of normal metal traps

    NASA Astrophysics Data System (ADS)

    Kuzmin, L.

    2002-08-01

    A novel concept of the quasiparticle amplifier based on the trapping of nonequilibrium quasiparticles, strong direct electron cooling, and the cascade principle of amplification has been suggested. The amplifier can be useful for the normal metal hot-electron bolometers (NHEB) with SIN tunnel junctions and similar devices. In the suggested concept, the second stage is working in a regime of strong direct electron cooling whereby all released energy is removed from the trap by the second tunnel junction. In this case, one can maintain the temperature of the trap near a base level while keeping a high coefficient of amplification. Another important feature of the proposed amplifier is adding the stimulated current I2 to the main measurement current I1 to increase amplification. In this regime, the coefficient of amplification will be greater than unity in any case. The junctions T1 and T2 (of a different area) work in opposite directions with the same voltage near Δ that can be realized only in voltage-biased mode. The principle of cascade amplification can be extended further for a third stage (and so on) with the same adding amplified currents from junctions of increased area. The cascade principle with the same voltage bias for all junctions gives an opportunity to realize an amplifier without an additional power supply and additional wires. This feature can be extremely important for the realization of the multi-pixel arrays of the sensors.

  20. New resonance-polariton Bose-quasiparticles enhances optical transmission into nanoholes in metal films

    NASA Astrophysics Data System (ADS)

    Minasyan, V. N.; Samoilov, V. N.

    2011-01-01

    We argue the existence of fundamental particles in nature, neutral Light-Particles with spin 1, and rest mass m=1.8ṡ10me, in addition to electrons, neutrons and protons. We call these particles Light Bosons because they create the electromagnetic field which represents Planck's gas of massless photons together with a gas of Light-Particles in the condensate. In this respect, the condensed Light-Particles, having no magnetic field, represent the constant electric field. In this context, we predict an existence of polariton-plasmon Bose-quasiparticles with effective masses ml≈10me and mr=0.5me, which are induced by interaction of the plasmon field and the resonance Frölich-Schafroth charged bosons with electromagnetic wave in metal. Also, we prove that the enhancement optical transmission into nanoholes in metal films and Surface Enhanced Raman Spectroscopy are provided by a new resonance-polariton Bose-quasiparticles but not model of surface plasmon-polariton. In this Letter, the quantization Fresnel's equations is presented which confirms that Light-Particles in the condensate are concentrated near on the wall of grooves in metallic grating and, in turn, represent as the constant electric field which provides the launching of the surface Frölich-Schafroth bosons on the surface metal holes.

  1. Quasiparticle band structure of infinite hydrogen fluoride and hydrogen chloride chains

    NASA Astrophysics Data System (ADS)

    Buth, Christian

    2006-10-01

    We study the quasiparticle band structure of isolated, infinite (HF)∞ and (HCl)∞ bent (zigzag) chains and examine the effect of the crystal field on the energy levels of the constituent monomers. The chains are one of the simplest but realistic models of the corresponding three-dimensional crystalline solids. To describe the isolated monomers and the chains, we set out from the Hartree-Fock approximation, harnessing the advanced Green's function methods local molecular orbital algebraic diagrammatic construction (ADC) scheme and local crystal orbital ADC (CO-ADC) in a strict second order approximation, ADC(2,2) and CO-ADC(2,2), respectively, to account for electron correlations. The configuration space of the periodic correlation calculations is found to converge rapidly only requiring nearest-neighbor contributions to be regarded. Although electron correlations cause a pronounced shift of the quasiparticle band structure of the chains with respect to the Hartree-Fock result, the bandwidth essentially remains unaltered in contrast to, e.g., covalently bound compounds.

  2. The Quasiparticle Puzzle: Reconciling ARPES and FTSTS Studies of Bi2212

    SciTech Connect

    Vishik, I.M.; Nowadnick, E.A.; Lee, W.S.; Shen, Z.X.; Moritz, B.; Devereaux, T.P.; Tanaka, K.; Sasagawa, T.; Fujii, T.; /Tokyo U.

    2009-12-17

    Angle Resolved Photoemission Spectroscopy (ARPES) probes the momentum-space electronic structure of materials, and provides invaluable information about the high-temperature superconducting cuprates. Likewise, cuprates real-space, inhomogeneous electronic structure is elucidated by Scanning Tunneling Spectroscopy (STS). Recently, STS has exploited quasiparticle interference (QPI) - wave-like electrons scattering off impurities to produce periodic interference patterns - to infer properties of the QP in momentum-space. Surprisingly, some interference peaks in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} (Bi-2212) are absent beyond the antiferromagnetic (AF) zone boundary, implying the dominance of particular scattering process. Here, we show that ARPES sees no evidence of quasiparticle (QP) extinction: QP-like peaks are measured everywhere on the Fermi surface, evolving smoothly across the AF zone boundary. This apparent contradiction stems from different natures of single-particle (ARPES) and two-particle (STS) processes underlying these probes. Using a simple model, we demonstrate extinction of QPI without implying the loss of QP beyond the AF zone boundary.

  3. Measuring, interpreting, and translating electron quasiparticle - Phonon interactions on the surfaces of the topological insulators bismuth selenide and bismuth telluride

    NASA Astrophysics Data System (ADS)

    Howard, Colin

    The following dissertation presents a comprehensive study of the interaction between Dirac fermion quasiparticles (DFQs) and surface phonons on the surfaces of the topological insulators Bi2Se3 and Bi2Te 3. Inelastic helium atom surface scattering (HASS) spectroscopy and time of flight (TOF) techniques were used to measure the surface phonon dispersion of these materials along the two high-symmetry directions of the surface Brillouin zone (SBZ). Two anomalies common to both materials are exhibited in the experimental data. First, there is an absence of Rayleigh acoustic waves on the surface of these materials, pointing to weak coupling between the surface charge density and the surface acoustic phonon modes and potential applications for soundproofing technologies. Secondly, both materials exhibit an out-of-plane polarized optical phonon mode beginning at the SBZ center and dispersing to lower energy with increasing wave vector along both high-symmetry directions of the SBZ. This trend terminates in a V-shaped minimum at a wave vector corresponding to 2 kF for each material, after which the dispersion resumes its upward trend. This phenomenon constitutes a strong Kohn anomaly and can be attributed to the interaction between the surface phonons and DFQs. To quantify the coupling between the optical phonons experiencing strong renormalization and the DFQs at the surface, a phenomenological model was constructed based within the random phase approximation. Fitting the theoretical model to the experimental data allowed for the extraction of the matrix elements of the coupling Hamiltonian and the modifications to the surface phonon propagator encoded in the phonon self energy. This allowed, for the first time, calculation of phonon mode-specific quasiparticle-phonon coupling lambdanu( q) from experimental data. Additionally, an averaged coupling parameter was determined for both materials yielding bar lambdaTe ≈ 2 and bar lambdaSe ≈ 0.7. These values are

  4. PD-1 as an Immune Modulatory Receptor

    PubMed Central

    Yao, Sheng; Chen, Lieping

    2015-01-01

    Programmed cell death 1 (PD-1) is an inducible immune modulatory receptor. Upon interaction with its ligands B7 homolog 1 (PD-L1) and B7-DC (PD-L2), PD-1 plays important roles in negative regulation of T cell responses to antigen stimulation and maintaining peripheral tolerance. In addition to the inducible expression pattern on conventional T cells, PD-1 is also found on regulatory T cells, follicular T and B cells, and antigen-presenting cells including activated dendritic cells and monocytes. Therefore, PD-1 may have a much broader functionality than expected in negative regulation of multiple arms of immune responses. In addition to cancer therapy, the manipulation of PD-1 and its ligands may hold great promise for therapeutic applications also in autoimmune and infectious diseases. PMID:25098286

  5. Coexistence of Antiferromagnetism and Superconductivity in Heavy Fermion Cerium Compound Ce3PdIn11

    PubMed Central

    Kratochvílová, M.; Prokleška, J.; Uhlířová, K.; Tkáč, V.; Dušek, M.; Sechovský, V.; Custers, J.

    2015-01-01

    Many current research efforts in strongly correlated systems focus on the interplay between magnetism and superconductivity. Here we report on coexistence of both cooperative ordered states in recently discovered stoichiometric and fully inversion symmetric heavy fermion compound Ce3PdIn11 at ambient pressure. Thermodynamic and transport measurements reveal two successive magnetic transitions at T1 = 1.67 K and TN = 1.53 K into antiferromagnetic type of ordered states. Below Tc = 0.42 K the compound enters a superconducting state. The large initial slope of dBc2/dT ≈ – 8.6 T/K indicates that heavy quasiparticles form the Cooper pairs. The origin of the two magnetic transitions and the coexistence of magnetism and superconductivity is briefly discussed in the context of the coexistence of the two inequivalent Ce-sublattices in the unit cell of Ce3PdIn11 with different Kondo couplings to the conduction electrons. PMID:26514364

  6. [Perioperative Management of PD Patients].

    PubMed

    Reichmann, H

    2016-07-01

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

  7. Design innovations and baseline findings in a long-term Parkinson’s trial: NET-PD LS-1

    PubMed Central

    2012-01-01

    Background Based on the pre-clinical and the results of a phase 2 futility study, creatine was selected for an efficacy trial in Parkinson’s disease (PD). We present the design rationale and a description of the study cohort at baseline. Methods A randomized, multicenter, double-blind, parallel group, placebo controlled Phase 3 study of creatine (10 gm daily) in participants with early, treated PD, the Long-term Study – 1 (LS-1) is being conducted by the NINDS Exploratory Trials in Parkinson’s Disease (NET-PD) network. The study utilizes a global statistical test (GST) encompassing multiple clinical rating scales to provide a multidimensional assessment of disease progression. Results A total of 1,741 PD participants from 45 sites in the U.S. and Canada were randomized 1:1 to either 10-gm creatine/day or matching placebo. Participants are being evaluated for a minimum of 5 years. The LS-1 baseline cohort includes participants treated with dopaminergic therapy and generally mild PD. Conclusions LS-1 represents the largest cohort of patients with early treated PD ever enrolled in a clinical trial. The GST approach should provide high power to test the hypothesis that daily administration of creatine (10gm/day) is more effective than placebo in slowing clinical decline in PD between baseline and the 5 year follow-up visit against the background of dopaminergic therapy and best PD care. PMID:23079770

  8. Hydrogen-induced atomic rearrangement in MgPd{sub 3}

    SciTech Connect

    Kohlmann, H. . E-mail: h.kohlmann@mx.uni-saarland.de; Renaudin, G.; Yvon, K.; Wannek, C.; Harbrecht, B.

    2005-04-15

    The hydrogenation behavior of MgPd{sub 3} has been studied by in situ X-ray powder diffraction and by neutron powder diffraction. At room temperature and p {approx}500kPa hydrogen pressure its structure is capable of incorporating up to one hydrogen atom per formula unit ({alpha}-MgPd{sub 3}H{sub {approx}}{sub 1}), thereby retaining a tetragonal ZrAl{sub 3}-type metal atom arrangement. Upon heating to 750K in a hydrogen atmosphere of 610kPa it transforms into a cubic modification with AuCu{sub 3}-type metal atom arrangement ({beta}-MgPd{sub 3}H{sub {approx}}{sub 0.7}). Neutron diffraction on the deuteride reveals an anion deficient anti-perovskite-type structure ({beta}-MgPd{sub 3}D{sub 0.67}, a=398.200(7)pm) in which octahedral sites surrounded exclusively by palladium atoms are occupied by deuterium. Complete removal of hydrogen (480K, 1Pa) stabilizes a new binary modification ({beta}-MgPd{sub 3}, a=391.78(2)pm) crystallizing with a primitive cubic AuCu{sub 3}-type structure. Mechanical treatment (grinding) transforms both {alpha} and {beta} modifications of MgPd{sub 3} into a cubic face-centered solid solution Mg{sub 0.25}Pd{sub 0.75} showing a random distribution of magnesium and palladium atoms.

  9. PD-1/PD-Ls pathways between CD4(+) T cells and pleural mesothelial cells in human tuberculous pleurisy.

    PubMed

    Yin, Wen; Tong, Zhao-Hui; Cui, Ai; Zhang, Jian-Chu; Ye, Zhi-Jian; Yuan, Ming-Li; Zhou, Qiong; Shi, Huan-Zhong

    2014-03-01

    Programmed death 1 (PD-1), PD-ligand 1 (PD-L1), and PD-L2 have been demonstrated to be involved in tuberculosis immunity, however, the expression and regulation of PD-1/PD-Ls pathways in pleural mesothelial cells (PMCs) and CD4(+) T cells in tuberculous pleural effusion (TPE) have not been investigated. Expression of PD-1 on CD4(+) T cells and expressions of PD-L1 and PD-L2 on PMCs in TPE were determined. The impacts of PD-1/PD-Ls pathways on proliferation, apoptosis, adhesion, and migration of CD4(+) T cells were explored. Concentrations of soluble PD-l, but not of soluble PD-Ls, were much higher in TPE than in serum. Expressions of PD-1 on CD4(+) T cells in TPE were significantly higher than those in blood. Expressions of PD-Ls were much higher on PMCs from TPE when compared with those from transudative effusion. Interferon-γ not only upregulated the expression of PD-1 on CD4(+) T cells, but also upregulated the expressions of PD-Ls on PMCs. Blockage PD-1/PD-Ls pathways abolished the inhibitory effects on proliferation and adhesion activity of CD4(+) T cells induced by PMCs. PD-1/PD-Ls pathways on PMCs inhibited proliferation and adhesion activity of CD4(+) T cells, suggesting that Mycobacterium tuberculosis might exploit PD-1/PD-Ls pathways to evade host cell immune response in human.

  10. Spin-flip scattering of critical quasiparticles and the phase diagram of YbRh2Si2

    NASA Astrophysics Data System (ADS)

    Wölfle, Peter; Abrahams, Elihu

    2015-10-01

    Several observed transport and thermodynamic properties of the heavy-fermion compound YbRh2Si2 in the quantum critical regime are unusual and suggest that the fermionic quasiparticles are critical, characterized by a scale-dependent diverging effective mass. A theory based on the concept of critical quasiparticles scattering off antiferromagnetic spin fluctuations in a strong-coupling regime has been shown to successfully explain the unusual existing data and to predict a number of so far unobserved properties. In this paper, we point out a new feature of a magnetic field-tuned quantum critical point of a heavy-fermion metal: anomalies in the transport and thermodynamic properties caused by the freezing out of spin-flip scattering of critical quasiparticles and the scattering off collective spin excitations. We show a steplike behavior as a function of magnetic field of, e.g., the Hall coefficient and magnetoresistivity results, which accounts quantitatively for the observed behavior of these quantities. That behavior has been described as a crossover line T*(H ) in the T -H phase diagram of YbRh2Si2 . Whereas some authors have interpreted this observation as signaling the breakdown of Kondo screening and an associated abrupt change of the Fermi surface, our results suggest that the T* line may be quantitatively understood within the picture of robust critical quasiparticles.

  11. Quasiparticle band gap of organic-inorganic hybrid perovskites: Crystal structure, spin-orbit coupling, and self-energy effects

    NASA Astrophysics Data System (ADS)

    Gao, Weiwei; Gao, Xiang; Abtew, Tesfaye; Sun, Yiyang; Zhang, Shengbai; Zhang, Peihong

    The quasiparticle band gaps of organic-inorganic hybrid perovskites are often determined (and can be controlled) by various factors, complicating predictive materials optimization. Here we report a comprehensive investigation on the band gap formation mechanism in CH3NH3PbI3 by decoupling various contributing factors which ultimately determine their electronic structure and quasiparticle band gap. Four major factors, namely, quasiparticle self-energy, spin-orbit coupling, volume (lattice constant) effects, and structural distortions due to the presence of organic molecules, and their influences on the quasiparticle band structure of organometal hybrid perovskites are illustrated. We find that although methylammonium cations do not contribute directly to the electronic states near band edges, they play an important role in defining the band gap through a lattice distortion mechanism and by controlling the overall lattice constants (thus the chemical bonding of the optically active PbI3-). The spin-orbit coupling effects drastically reduce the electron and hole effective masses in these systems, which is beneficial for high carrier mobilities and small exciton binding energies. This work is supported by the National Natural Science Foundation of China (Grant No. 11328401), NSF (Grant No. DMR-0946404 and DMR-1506669), and the SUNY Networks of Excellence.

  12. Quasiparticle-phonon model and quadrupole mixed-symmetry states of 96Ru

    NASA Astrophysics Data System (ADS)

    Stoyanov, Ch.; Pietralla, N.

    2016-01-01

    The structure of low-lying quadrupole states of 96Ru was calculated within the Quasiparticle-Phonon Model. It is shown that symmetric and mixed-symmetry properties manifest themselves via the structure of the excited states. The first 2+ state is collective and neutron and proton transition matrix elements Mn and Mp are in-phase, while the neutron and proton transition matrix elements Mn and Mp have opposite signs for the third 2+ state. This property of the third 2+ state leads to a large M1 transition between the first and third 2+ states. It is an unambigous demonstration of the mixed-symmetry nature of the third 2+ state. The structure of the first 1+ state is calculated. The state is a member of the two-phonon multiplet generated by the coupling of the [21+]QRPA and the [22+]QRPA states.

  13. Environment-Dependent Quasiparticle Bandgap of Monolayer MoS2

    NASA Astrophysics Data System (ADS)

    Kim, Yong-Sung; Noh, Ji-Young; Kim, Hanchul; Park, Minkyu; Santosh, K. C.; Cho, K. J.

    2015-03-01

    2D semiconductors are manifested by strong Coulomb interaction inside. The strong Coulomb interaction gives remarkable effects on various properties of the 2D semiconductors, including (i) large exciton binding energy (electron-hole), (ii) large quasi-particle self-energy (electron-electron), (iii) large scattering cross section in carrier transports by charged defects (electron-charged defects), (iv) deep defect transition level (bound electron-charged defects), and (v) strong interaction between charged defects (charged defects-charged defects). The ground state, optical, and transport properties are then largely affected by the dielectric environments surrounding the 2D semiconductors, because the Coulomb interaction is effectively screened by the dielectrics. We investigate the electronic band structures of a single-layer MoS2, as a prototype 2D semiconductor, with a variety of dielectric environments by using density-functional-theory (DFT) and GW calculations.

  14. Interpretation of scanning tunneling quasiparticle interference and impurity states in cuprates.

    PubMed

    Kreisel, A; Choubey, Peayush; Berlijn, T; Ku, W; Andersen, B M; Hirschfeld, P J

    2015-05-29

    We apply a recently developed method combining first principles based Wannier functions with solutions to the Bogoliubov-de Gennes equations to the problem of interpreting STM data in cuprate superconductors. We show that the observed images of Zn on the surface of Bi_{2}Sr_{2}CaCu_{2}O_{8} can only be understood by accounting for the tails of the Cu Wannier functions, which include significant weight on apical O sites in neighboring unit cells. This calculation thus puts earlier crude "filter" theories on a microscopic foundation and solves a long-standing puzzle. We then study quasiparticle interference phenomena induced by out-of-plane weak potential scatterers, and show how patterns long observed in cuprates can be understood in terms of the interference of Wannier functions above the surface. Our results show excellent agreement with experiment and enable a better understanding of novel phenomena in the cuprates via STM imaging. PMID:26066452

  15. Quasiparticle band structure of the almost-gapless transition-metal-based Heusler semiconductors

    NASA Astrophysics Data System (ADS)

    Tas, M.; Şaşıoǧlu, E.; Galanakis, I.; Friedrich, C.; Blügel, S.

    2016-05-01

    Transition-metal-based Heusler semiconductors are promising materials for a variety of applications ranging from spintronics to thermoelectricity. Employing the G W approximation within the framework of the FLAPW method, we study the quasiparticle band structure of a number of such compounds being almost gapless semiconductors. We find that in contrast to the s p -electron based semiconductors such as Si and GaAs, in these systems, the many-body corrections have a minimal effect on the electronic band structure and the energy band gap increases by less than 0.2 eV, which makes the starting point density functional theory (DFT) a good approximation for the description of electronic and optical properties of these materials. Furthermore, the band gap can be tuned either by the variation of the lattice parameter or by the substitution of the s p -chemical element.

  16. Quasiparticle interference of the Fermi arcs and surface-bulk connectivity of a Weyl semimetal.

    PubMed

    Inoue, Hiroyuki; Gyenis, András; Wang, Zhijun; Li, Jian; Oh, Seong Woo; Jiang, Shan; Ni, Ni; Bernevig, B Andrei; Yazdani, Ali

    2016-03-11

    Weyl semimetals host topologically protected surface states, with arced Fermi surface contours that are predicted to propagate through the bulk when their momentum matches that of the surface projections of the bulk's Weyl nodes. We used spectroscopic mapping with a scanning tunneling microscope to visualize quasiparticle scattering and interference at the surface of the Weyl semimetal TaAs. Our measurements reveal 10 different scattering wave vectors, which can be understood and precisely reproduced with a theory that takes into account the shape, spin texture, and momentum-dependent propagation of the Fermi arc surface states into the bulk. Our findings provide evidence that Weyl nodes act as sinks for electron transport on the surface of these materials. PMID:26965625

  17. Breaking the Theoretical Scaling Limit for Predicting Quasiparticle Energies: The Stochastic GW Approach

    NASA Astrophysics Data System (ADS)

    Neuhauser, Daniel; Gao, Yi; Arntsen, Christopher; Karshenas, Cyrus; Rabani, Eran; Baer, Roi

    2014-08-01

    We develop a formalism to calculate the quasiparticle energy within the GW many-body perturbation correction to the density functional theory. The occupied and virtual orbitals of the Kohn-Sham Hamiltonian are replaced by stochastic orbitals used to evaluate the Green function G, the polarization potential W, and, thereby, the GW self-energy. The stochastic GW (sGW) formalism relies on novel theoretical concepts such as stochastic time-dependent Hartree propagation, stochastic matrix compression, and spatial or temporal stochastic decoupling techniques. Beyond the theoretical interest, the formalism enables linear scaling GW calculations breaking the theoretical scaling limit for GW as well as circumventing the need for energy cutoff approximations. We illustrate the method for silicon nanocrystals of varying sizes with Ne>3000 electrons.

  18. Investigation of magnetic phases in parent compounds of iron-chalcogenides via quasiparticle scattering interference

    NASA Astrophysics Data System (ADS)

    Kamble, Bhaskar; Akbari, Alireza; Eremin, Ilya

    2016-04-01

    We employ a five-orbital tight-binding model to develop the mean-field solution for various possible spin density wave states in the iron-chalcogenides. The quasiparticle interference (QPI) technique is applied to detect signatures of these states due to scatterings arising from non-magnetic impurities. Apart from the experimentally observed double-striped structure with ordering vector (π/2,π/2) , the QPI method is investigated for the extended-stripe as well as the orthogonal double-stripe phase. We discuss QPI as a possible tool to detect and classify various magnetic structures with different electronic structure reconstruction within the framework of the \\text{Fe}1+y\\text{Te} compound.

  19. Tunneling of quasiparticles in the normal-insulator-superconductor-insulator-normal geometry

    NASA Astrophysics Data System (ADS)

    Hidaka, Mutsuo; Ishizaka, Satoshi; Sone, Jun'ichi

    1993-12-01

    The probability of quasiparticle transmission going through a normal-insulator- superconductor-insulator-normal (NISIN) geometry is theoretically calculated using Bogoliubov-de Gennes equations to investigate the feasibility of electron devices utilizing this geometry. This new calculation is able to include a current carried by Cooper pairs by employing hole injections from the outlet which destroy Cooper pairs at the outlet super- conductor-insulator boundary. Resonant tunneling phenomena occur even if the electron kinetic energy is less than the superconducting energy gap and electron tunneling probabilities are greatly modified by the resonance. When the unevenness of the superconductor (S) width thickness is large compared with the electron wavelength in the S layer, the resonance is smeared out in averaged tunneling probabilities. Then the tunneling probabilities can be controlled by the electron kinetic energy. Applications of the NISIN geometry for superconducting transistors are also discussed.

  20. Mixed quantum-classical versus full quantum dynamics: Coupled quasiparticle-oscillator system

    NASA Astrophysics Data System (ADS)

    Schanz, Holger; Esser, Bernd

    1997-05-01

    The relation between the dynamical properties of a coupled quasiparticle-oscillator system in the mixed quantum-classical and fully quantized descriptions is investigated. The system is considered as a model for applying a stepwise quantization. Features of the nonlinear dynamics in the mixed description such as the presence of a separatrix structure or regular and chaotic motion are shown to be reflected in the evolu- tion of the quantum state vector of the fully quantized system. In particular, it is demonstrated how wave packets propagate along the separatrix structure of the mixed description, and that chaotic dynamics leads to a strongly entangled quantum state vector. Special emphasis is given to viewing the system from a dyn- amical Born-Oppenheimer approximation defining integrable reference oscillators, and elucidating the role of the nonadiabatic couplings which complement this approximation into a rigorous quantization scheme.

  1. Quasiparticle mass enhancement approaching optimal doping in a high-Tc superconductor

    DOE PAGES

    Ramshaw, B. J.; Sebastian, S. E.; McDonald, R. D.; Day, J.; Tan, B. S.; Zhu, Z.; Betts, J. B.; Liang, Ruixing; Bonn, D. A.; Hardy, W. N.; et al

    2015-03-26

    In the quest for superconductors with higher transition temperatures (Tc), one emerging motif is that electronic interactions favorable for superconductivity can be enhanced by fluctuations of a broken-symmetry phase. In recent experiments it is suggested that the existence of the requisite broken-symmetry phase in the high-Tc cuprates, but the impact of such a phase on the ground-state electronic interactions has remained unclear. Here, we used magnetic fields exceeding 90 tesla to access the underlying metallic state of the cuprate YBa2Cu3O6+δ over a wide range of doping, and observed magnetic quantum oscillations that reveal a strong enhancement of the quasiparticle effectivemore » mass toward optimal doping. Finally, this mass enhancement results from increasing electronic interactions approaching optimal doping, and suggests a quantum critical point at a hole doping of pcrit ≈ 0.18.« less

  2. Quasiparticle energies, excitons, and optical spectra of few-layer black phosphorus

    NASA Astrophysics Data System (ADS)

    Tran, Vy; Fei, Ruixiang; Yang, Li

    2015-12-01

    We report first-principles GW-Bethe-Salpeter-equation (BSE) studies of excited-state properties of few-layer black phosphorus (BP) (phosphorene). With improved GW computational methods, we obtained converged quasiparticle band gaps and optical absorption spectra by the single-shot (G0W0) procedure. Moreover, we reveal fine structures of anisotropic excitons, including the series of one-dimensional like wave functions, spin singlet-triplet splitting, and electron-hole binding energy spectra by solving BSE. An effective-mass model is employed to describe these electron-hole pairs, shedding light on estimating the exciton binding energy of anisotropic two-dimensional semiconductors without expensive ab initio simulations. Finally, the anisotropic optical response of BP is explained by using optical selection rules based on the projected single-particle density of states at band edges.

  3. Quasiparticle interference of the Fermi arcs and surface-bulk connectivity of a Weyl semimetal.

    PubMed

    Inoue, Hiroyuki; Gyenis, András; Wang, Zhijun; Li, Jian; Oh, Seong Woo; Jiang, Shan; Ni, Ni; Bernevig, B Andrei; Yazdani, Ali

    2016-03-11

    Weyl semimetals host topologically protected surface states, with arced Fermi surface contours that are predicted to propagate through the bulk when their momentum matches that of the surface projections of the bulk's Weyl nodes. We used spectroscopic mapping with a scanning tunneling microscope to visualize quasiparticle scattering and interference at the surface of the Weyl semimetal TaAs. Our measurements reveal 10 different scattering wave vectors, which can be understood and precisely reproduced with a theory that takes into account the shape, spin texture, and momentum-dependent propagation of the Fermi arc surface states into the bulk. Our findings provide evidence that Weyl nodes act as sinks for electron transport on the surface of these materials.

  4. Nodal Quasiparticle Meltdown in Ultra-High Resolution Pump-Probe Angle-Resolved Photoemission

    SciTech Connect

    Graf, Jeff; Jozwiak, Chris; Smallwood, Chris L.; Eisaki, H.; Kaindl, Robert A.; Lee, Dung-Hai; Lanzara, Alessandra

    2011-06-03

    High-T{sub c} cuprate superconductors are characterized by a strong momentum-dependent anisotropy between the low energy excitations along the Brillouin zone diagonal (nodal direction) and those along the Brillouin zone face (antinodal direction). Most obvious is the d-wave superconducting gap, with the largest magnitude found in the antinodal direction and no gap in the nodal direction. Additionally, while antin- odal quasiparticle excitations appear only below T{sub c}, superconductivity is thought to be indifferent to nodal excitations as they are regarded robust and insensitive to T{sub c}. Here we reveal an unexpected tie between nodal quasiparticles and superconductivity using high resolution time- and angle-resolved photoemission on optimally doped Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} . We observe a suppression of the nodal quasiparticle spectral weight following pump laser excitation and measure its recovery dynamics. This suppression is dramatically enhanced in the superconducting state. These results reduce the nodal-antinodal dichotomy and challenge the conventional view of nodal excitation neutrality in superconductivity. The electronic structures of high-Tc cuprates are strongly momentum-dependent. This is one reason why the momentum-resolved technique of angle-resolved photoemission spectroscopy (ARPES) has been a central tool in the field of high-temperature superconductivity. For example, coherent low energy excitations with momenta near the Brillouin zone face, or antinodal quasiparticles (QPs), are only observed below T{sub c} and have been linked to superfluid density. They have therefore been the primary focus of ARPES studies. In contrast, nodal QPs, with momenta along the Brillouin zone diagonal, have received less attention and are usually regarded as largely immune to the superconducting transition because they seem insensitive to perturbations such as disorder, doping, isotope exchange, charge ordering, and temperature. Clearly

  5. Electronic quasiparticles in the quantum dimer model: Density matrix renormalization group results

    NASA Astrophysics Data System (ADS)

    Lee, Junhyun; Sachdev, Subir; White, Steven R.

    2016-09-01

    We study a recently proposed quantum dimer model for the pseudogap metal state of the cuprates. The model contains bosonic dimers, representing a spin-singlet valence bond between a pair of electrons, and fermionic dimers, representing a quasiparticle with spin-1/2 and charge +e . By density matrix renormalization group calculations on a long but finite cylinder, we obtain the ground-state density distribution of the fermionic dimers for a number of different total densities. From the Friedel oscillations at open boundaries, we deduce that the Fermi surface consists of small hole pockets near (π /2 ,π /2 ) , and this feature persists up to a doping density of 1/16. We also compute the entanglement entropy and find that it closely matches the sum of the entanglement entropies of a critical boson and a low density of free fermions. Our results support the existence of a fractionalized Fermi liquid in this model.

  6. Medium effects on the surface tension of strangelets in the extended quasiparticle model

    SciTech Connect

    Wen, X. J.; Li, J. Y.; Liang, J. Q.; Peng, G. X.

    2010-08-15

    We propose a modification of the finite size effects due to the effective bag function in the extended quark quasiparticle model with a running coupling constant. The bag function is associated with the quark chemical potential and the radius of strangelets. Considering the medium effects, the surface tension should be redefined with an additional term described by the surface term of the bag function. With the increasing baryon number of stable strangelets, it is found that the coupling strength becomes stronger while the surface tension decreases in the vicinity of 35 MeV fm{sup -2} for strangelets of the baryon number greater than 10{sup 3}. The comparison with the bag model is shown and the distinction for smaller strangelets is very clear.

  7. From dressed electrons to quasiparticles: The emergence of emergent entities in quantum field theory

    NASA Astrophysics Data System (ADS)

    Blum, Alexander S.; Joas, Christian

    2016-02-01

    In the 1970s, the reinterpretation of renormalization group techniques in terms of effective field theories and their subsequent rapid development led to a major reinterpretation of the entire renormalization program, originally formulated in the late 1940s within quantum electrodynamics (QED). A more gradual shift in its interpretation, however, occurred already in the early-to-mid-1950s when renormalization techniques were transferred to solid-state and nuclear physics and helped establish the notion of effective or quasi-particles, emergent entities that are not to be found in the original, microscopic description of the theory. We study how the methods of QED, when applied in different contexts, gave rise to this ontological reinterpretation.

  8. Compressed Sensing in Scanning Tunneling Microscopy/Spectroscopy for Observation of Quasi-Particle Interference

    NASA Astrophysics Data System (ADS)

    Nakanishi-Ohno, Yoshinori; Haze, Masahiro; Yoshida, Yasuo; Hukushima, Koji; Hasegawa, Yukio; Okada, Masato

    2016-09-01

    We applied a method of compressed sensing to the observation of quasi-particle interference (QPI) by scanning tunneling microscopy/spectroscopy to improve efficiency and save measurement time. To solve an ill-posed problem owing to the scarcity of data, the compressed sensing utilizes the sparseness of QPI patterns in momentum space. We examined the performance of a sparsity-inducing algorithm called least absolute shrinkage and selection operator (LASSO), and demonstrated that LASSO enables us to recover a double-circle QPI pattern of the Ag(111) surface from a dataset whose size is less than that necessary for the conventional Fourier transformation method. In addition, the smallest number of data required for the recovery is discussed on the basis of cross validation.

  9. Microwave determination of the quasiparticle scattering time in YBa2Cu3O6.95

    NASA Astrophysics Data System (ADS)

    Bonn, D. A.; Liang, Ruixing; Riseman, T. M.; Baar, D. J.; Morgan, D. C.; Zhang, Kuan; Dosanjh, P.; Duty, T. L.; Macfarlane, A.; Morris, G. D.; Brewer, J. H.; Hardy, W. N.; Kallin, C.; Berlinsky, A. J.

    1993-05-01

    We report microwave surface resistance (Rs) measurements on two very-high-quality YBa2Cu3O6.95 crystals which exhibit extremely low residual loss at 1.2 K (2-6 μΩ at 2 GHz), a broad, reproducible peak at around 38 K, and a rapid increase in loss, by 4 orders of magnitude, between 80 and 93 K. These data provide one ingredient in the determination of the temperature dependence of the real part of the microwave conductivity, σ1(T), and of the quasiparticle scattering time. The other necessary ingredient is an accurate knowledge of the magnitude and temperature dependence of the London penetration depth, λ(T). This is derived from published data, from microwave data of Anlage, Langley, and co-workers and from, high-quality μSR data. We infer, from a careful analysis of all available data, that λ2(0)/λ2(T) is well approximated by the simple function 1-t2, where t=T/Tc, and that the low-temperature data are incompatible with the existence of an s-wave, BCS-like gap. Combining the Rs and λ(T) data, we find that σ1(T), has a broad peak around 32 K with a value about 20 times that at Tc. Using a generalized two-fluid model, we extract the temperature dependence of the quasiparticle scattering rate which follows an exponential law, exp(T/T0), where T0~=12 K, for T between 15 and 84 K. Such a temperature dependence has previously been observed in measurements of the nuclear spin-lattice relaxation rate. Both the uncertainties in our analysis and the implications for the mechanism of high-temperature superconductivity are discussed.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

  12. Middle School Mathematics PD Study: Study Design and Methodology. Paper #1

    ERIC Educational Resources Information Center

    Stancavage, Fran; Garet, Michael; Wayne, Andrew

    2010-01-01

    The PD program evaluated in this study is designed to address the problem of low student achievement in topics in rational numbers. The study focuses on seventh grade, the culminating year for teaching those topics. The study randomly assigned 77 mid- and high-poverty schools from 12 districts to treatment and control conditions and collected…

  13. 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.

  14. Hot Adatom Diffusion Following Oxygen Dissociation on Pd(100) and Pd(111): A First-Principles Study of the Equilibration Dynamics of Exothermic Surface Reactions

    NASA Astrophysics Data System (ADS)

    Bukas, Vanessa J.; Reuter, Karsten

    2016-09-01

    We augment ab initio molecular dynamics simulations with a quantitative account of phononic dissipation to study the hyperthermal adsorbate dynamics resulting from a noninstantaneous energy dissipation during exothermic surface chemical reactions. Comparing the hot adatom diffusion ensuing O2 dissociation over Pd(100) and Pd(111) we find experimentally accessible product end distances to form a rather misleading measure for the lifetime of this hyperthermal state. The lifetime is particularly long at Pd(111) where a random-walk-type diffusion leads only to small net displacements. A detailed phonon analysis rationalizes the slow equilibration through long-lived Rayleigh mode excitations that spatially confine the released energy within a nanoscopic "hot spot" around the impingement region.

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

    NASA Astrophysics Data System (ADS)

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

    1990-03-01

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

  16. Quasiparticle interference, quasiparticle interactions, and the origin of the charge density wave in 2HNbSe2

    SciTech Connect

    Arguello, C. J.; Rosenthal, E. P.; Andrade, E. F.; Jin, W.; Yeh, P. C.; Zaki, N.; Jia, S.; Cava, R. J.; Fernandes, R. M.; Millis, A. J.; Valla, T.; Osgood, Jr., R. M.; Pasupathy, A. N.

    2015-01-21

    We show that a small number of intentionally introduced defects can be used as a spectroscopic tool to amplify quasiparticle interference in 2H-NbSe₂, that we measure by scanning tunneling spectroscopic imaging. We show from the momentum and energy dependence of the quasiparticle interference that Fermi surface nesting is inconsequential to charge density wave formation in 2H-NbSe₂. Thus, we demonstrate that by combining quasiparticle interference data with additional knowledge of the quasiparticle band structure from angle resolved photoemission measurements, one can extract the wavevector and energy dependence of the important electronic scattering processes thereby obtaining direct information both about the fermiology and the interactions. In 2H-NbSe₂, we use this combination to show that the important near-Fermi-surface electronic physics is dominated by the coupling of the quasiparticles to soft mode phonons at a wave vector different from the CDW ordering wave vector.

  17. PD98059 Protects Brain against Cells Death Resulting from ROS/ERK Activation in a Cardiac Arrest Rat Model

    PubMed Central

    Nguyen Thi, Phuong Anh; Chen, Meng-Hua; Li, Nuo; Zhuo, Xiao-Jun; Xie, Lu

    2016-01-01

    The clinical and experimental postcardiac arrest treatment has not reached therapeutic success. The present study investigated the effect of PD98059 (PD) in rats subjected to cardiac arrest (CA)/cardiopulmonary resuscitation (CPR). Experimental rats were divided randomly into 3 groups: sham, CA, and PD. The rats except for sham group were subjected to CA for 5 min followed by CPR operation. Once spontaneous circulation was restored, saline and PD were injected in CA and PD groups, respectively. The survival rates and neurologic deficit scores (NDS) were observed, and the following indices of brain tissue were evaluated: ROS, MDA, SOD, p-ERK1/2/ERK1/2, caspase-3, Bax, Bcl-2, TUNEL positive cells, and double fluorescent staining of p-ERK/TUNEL. Our results indicated that PD treatment significantly reduced apoptotic neurons and improved the survival rates and NDS. Moreover, PD markedly downregulated the ROS, MDA, p-ERK, and caspase-3, Bax and upregulated SOD and Bcl-2 levels. Double staining p-ERK/TUNEL in choroid plexus and cortex showed that cell death is dependent on ERK activation. The findings in present study demonstrated that PD provides neuroprotection via antioxidant activity and antiapoptosis in rats subjected to CA/CPR. PMID:27069530

  18. A VISTA on PD-1H.

    PubMed

    Liu, Yang

    2014-05-01

    Three years ago, two research groups independently identified a previously undescribed T cell cosignaling molecule; one referred to it as V-domain Ig suppressor of T cell activation (VISTA), and the other used the term programmed death-1 homolog (PD-1H). Recombinant and ectopically expressed PD-1H functions as a coinhibitory ligand for T cell responses. However, the function of endogenous PD-1H is not clear. In this issue of the JCI, Flies and colleagues demonstrate that endogenous PD-1H on both T cells and APCs serves as a coinhibitory molecule for T cell activation and provide further support for targeting PD-1H as a therapeutic strategy for transplantation and cancers.

  19. Strain relief in Cu-Pd heteroepitaxy.

    PubMed

    Lu, Yafeng; Przybylski, M; Trushin, O; Wang, W H; Barthel, J; Granato, E; Ying, S C; Ala-Nissila, T

    2005-04-15

    We present experimental and theoretical studies of Pd/Cu(100) and Cu/Pd(100) heterostructures in order to explore their structure and misfit strain relaxation. Ultrathin Pd and Cu films are grown by pulsed laser deposition at room temperature. For Pd/Cu, compressive strain is released by networks of misfit dislocations running in the [100] and [010] directions, which appear after a few monolayers (ML) already. In striking contrast, for Cu/Pd the tensile overlayer remains coherent up to about 9 ML, after which multilayer growth occurs. The strong asymmetry between tensile and compressive cases is in contradiction with continuum elasticity theory and is also evident in the structural parameters of the strained films. Molecular dynamics calculations based on classical many-body potentials confirm the pronounced tensile-compressive asymmetry and are in good agreement with the experimental data.

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

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

  1. Structural and electronic properties of Sn overlayers and {Pd}/{Sn} surface alloys on Pd(111)

    NASA Astrophysics Data System (ADS)

    Lee, Adam F.; Baddeley, Christopher J.; Tikhov, Mintcho S.; Lambert, Richard M.

    1997-03-01

    The first two layers of Sn deposited on Pd(111) at 300 K grow in layer-by-layer fashion after which crystallite formation commences. The electronic properties of these overlayers are dependent on the size of the 3D Sn islands. The occurrence of Sn→Pd valence charge-transfer is inferred, due allowance being made for initial and final state effects in the photoemission data. Evidence is presented for a significant Pd surface core-level shift enhancement by Sn of ≈0.7 eV. Depending on the initial Sn loading, heating generates stable monolayer (Pd 2Sn) or multilayer (Pd 3Sn) surface alloys exhibiting √3 and (2 × 2) periodicities, respectively. The very different CO adsorption capacity of these two phases indicates that on {Pd}/{Sn} alloy surfaces, only pure Pd threefold hollow-sites are capable of strongly chemisorbing CO.

  2. Strong lattice correlation of non-equilibrium quasiparticles in a pseudospin-1/2 Mott insulator Sr2IrO4

    DOE PAGES

    Li, Yuelin; Schaller, Richard D.; Zhu, Mengze; Walko, Donald A.; Kim, Jungho; Ke, Xianglin; Miao, Ludi; Mao, Z. Q.

    2016-01-20

    In correlated oxides the coupling of quasiparticles to other degrees of freedom such as spin and lattice plays critical roles in the emergence of symmetry-breaking quantum ordered states such as high temperature superconductivity. We report a strong lattice coupling of photon-induced quasiparticles in spin-orbital coupling Mott insulator Sr2IrO4 probed via optical excitation. Combining time-resolved x-ray diffraction and optical spectroscopy techniques, we reconstruct a spatiotemporal map of the diffusion of these quasiparticles. Lastly, due to the unique electronic configuration of the quasiparticles, the strong lattice correlation is unexpected but extends the similarity between Sr2IrO4 and cuprates to a new dimension ofmore » electron-phonon coupling which persists under highly non-equilibrium conditions.« less

  3. Strong lattice correlation of non-equilibrium quasiparticles in a pseudospin-1/2 Mott insulator Sr2IrO4

    PubMed Central

    Li, Yuelin; Schaller, Richard D.; Zhu, Mengze; Walko, Donald A.; Kim, Jungho; Ke, Xianglin; Miao, Ludi; Mao, Z. Q.

    2016-01-01

    In correlated oxides the coupling of quasiparticles to other degrees of freedom such as spin and lattice plays critical roles in the emergence of symmetry-breaking quantum ordered states such as high temperature superconductivity. We report a strong lattice coupling of photon-induced quasiparticles in spin-orbital coupling Mott insulator Sr2IrO4 probed via optical excitation. Combining time-resolved x-ray diffraction and optical spectroscopy techniques, we reconstruct a spatiotemporal map of the diffusion of these quasiparticles. Due to the unique electronic configuration of the quasiparticles, the strong lattice correlation is unexpected but extends the similarity between Sr2IrO4 and cuprates to a new dimension of electron-phonon coupling which persists under highly non-equilibrium conditions. PMID:26787094

  4. On the absence of higher generations of incompressible daughter states of composite Fermion quasiparticles

    NASA Astrophysics Data System (ADS)

    Quinn, John J.

    2016-03-01

    Jain [1] introduced a simple mean-field (MF) composite Fermion (CF) picture by attaching to each electron in a quantum Hall system a flux tube producing a Chern- Simons magnetic field b(r) = 2pϕ0 Σi δ(r - r i)ẑ. Here ϕ0 = hc/e is the quantum of flux, and the sum is over all electron coordinates r i. He then averaged the total flux and the total charge (electronic plus positive background) over the entire sample. This MF picture gave a system of noninteracting CFs in an effective magnetic field B * 0 = νB 0. It predicted incompressible quantum liquid (IQL) states at filling factors ν = n(1 + 2pn)-1 for integral values of n. Chen and Quinn [2] demonstrated that Jain’s MF CF picture predicted the total angular momentum values of the lowest energy band of states for any value of the applied magnetic field B0. Justification of when the MFCF picture was valid was given by Wojs and Quinn [3], who extended the CF hierarchy scheme of Sitko et al. [4]. The CF hierarchy gave the Jain states for integrally filled CF Landau levels (CF LLs), and the Haldane hierarchy of all odd denominator fractions when quasiparticles in the highest (partially filled) CF angular momentum shell had interactions sufficiently similar to the Coulomb interactions of electrons in the lowest Landau level. Sitko et al. showed that the predictions of the CF hierarchy scheme were not always correct. By using a simple pair angular momentum identity and the concept of fractional grandparentage, Wojs and Quinn showed that higher generations of CFs could result from the interactions of the original CF quasiparticles only if their interaction energy V QP(L 2) as a function of their pair angular momentum L 2 increased with increasing L 2 faster than L2(L2 + 1). For Laughlin quasielectrons of the ν = 1/3 IQL state this condition was not satisfied. Therefore, no second generation of CFs could occur. The observed IQL at electron filling factor ν = 4/11 can not be attributed to a daughter IQL state at

  5. Fermi Surface and Quasiparticle Excitations of Sr2RhO4

    SciTech Connect

    Baumberger, F.; Ingle, N. J. C.; Meevasana, W.; Lu, D. H.; Perry, R. S.; Mackenzie, A. P.; Hussain, Z; Singh, David J; Shen, Z. X.

    2006-01-01

    The electronic structure of the layered 4d transition metal oxide Sr2RhO4 is investigated by angle resolved photoemission. We find well-defined quasiparticle excitations with a highly anisotropic dispersion, suggesting a quasi-two-dimensional Fermi-liquid-like ground state. Markedly different from the isostructural Sr2RuO4, only two bands with dominant Rh 4dxz;zy character contribute to the Fermi surface. A quantitative analysis of the photoemission quasiparticle band structure is in excellent agreement with bulk data. In contrast, it is found that state-of-the-art density functional calculations in the local density approximation differ significantly from the experimental findings.

  6. Mechanism of PdO thin film formation during the oxidation of Pd(1 1 1)

    NASA Astrophysics Data System (ADS)

    Kan, Heywood H.; Weaver, Jason F.

    2009-09-01

    We investigated the mechanism by which a surface oxide layer on Pd(1 1 1) transforms to a PdO(1 0 1) thin film during oxidation with gaseous oxygen atoms in ultrahigh vacuum. Our results provide evidence that the precursor to bulk PdO formation is a distinct oxide phase that forms as small particles, referred to as PdO seeds, after the surface oxide saturates. With increasing oxygen coverage, the PdO seeds grow in size and eventually transform to more stable particles that agglomerate to yield a PdO film. Oxidation effectively ceases when the surface oxide layer is completely replaced by the bulk PdO film, demonstrating that the surface oxide is needed for PdO formation at the conditions studied. Both the kinetics of PdO formation and the final thickness of the PdO thin film depend strongly on the thermal stability of the PdO seeds. Below the decomposition temperature of the seeds (˜600 K), oxidation follows kinetics similar to Langmuirian adsorption and appears to be limited only by the rate of oxygen adsorption onto the surface oxide. In contrast, PdO formation above 600 K initially exhibits acceleratory kinetics, with the rates starting low but increasing steadily during the initial growth of PdO. We also observe a significant decrease in PdO(1 0 1) film thickness and improved crystallinity when oxidation is conducted below 600 K. We show that the trends observed in the oxidation kinetics and film thickness can be qualitatively explained within the context of a model in which the thermodynamic stability of PdO particles increases with increasing particle size and PdO seeds/particles coexist with a two-dimensional (2D) gas of oxygen atoms adsorbed on the surface oxide layer. This model suggests that the PdO particle-2D gas coexistence relation gives rise to three distinct growth regimes, namely, stable seed nucleation, metastable seed nucleation and oxygen dissolution into the subsurface where the latter is established at 2D gas coverages below the stability

  7. Hanbury-Brown Twiss noise correlation with time controlled quasi-particles in ballistic quantum conductors

    NASA Astrophysics Data System (ADS)

    Glattli, D. C.; Roulleau, P.

    2016-02-01

    We study the Hanbury Brown and Twiss correlation of electronic quasi-particles injected in a quantum conductor using current noise correlations and we experimentally address the effect of finite temperature. By controlling the relative time of injection of two streams of electrons it is possible to probe the fermionic antibunching, performing the electron analog of the optical Hong Ou Mandel (HOM) experiment. The electrons are injected using voltage pulses with either sine-wave or Lorentzian shape. In the latter case, we propose a set of orthogonal wavefunctions, describing periodic trains of multiply charged electron pulses, which give a simple interpretation to the HOM shot noise. The effect of temperature is then discussed and experimentally investigated. We observe a perfect electron anti-bunching for a large range of temperature, showing that, as recently predicted, thermal mixing of the states does not affect anti-bunching properties, a feature qualitatively different from dephasing. For single charge Lorentzian pulses, we provide experimental evidence of the prediction that the HOM shot noise variation versus the emission time delay is remarkably independent of the temperature.

  8. Quasiparticle band structures and thermoelectric transport properties of p-type SnSe

    SciTech Connect

    Shi, Guangsha; Kioupakis, Emmanouil

    2015-02-14

    We used density functional and many-body perturbation theory to calculate the quasiparticle band structures and electronic transport parameters of p-type SnSe both for the low-temperature Pnma and high-temperature Cmcm phases. The Pnma phase has an indirect band gap of 0.829 eV, while the Cmcm has a direct band gap of 0.464 eV. Both phases exhibit multiple local band extrema within an energy range comparable to the thermal energy of carriers from the global extrema. We calculated the electronic transport coefficients as a function of doping concentration and temperature for single-crystal and polycrystalline materials to understand the previous experimental measurements. The electronic transport coefficients are highly anisotropic and are strongly affected by bipolar transport effects at high temperature. Our results indicate that SnSe exhibits optimal thermoelectric performance at high temperature when doped in the 10{sup 19}–10{sup 20 }cm{sup −3} range.

  9. Direct Observation of a Majorana Quasiparticle Heat Capacity in 3He

    NASA Astrophysics Data System (ADS)

    Bunkov, Y. M.

    2014-04-01

    The Majorana fermion, which acts as its own antiparticle, was suggested by Majorana in 1937 (Nuovo Cimento 14:171). While no stable particle with Majorana properties has yet been observed, Majorana quasiparticles (QP) may exist at the boundaries of topological insulators. Here we report the preliminary results of direct observation of Majorana QPs by a precise measurements of superfluid 3He heat capacity. The bulk superfluid 3He heat capacity falls exponentially with cooling at the temperatures significantly below the energy gap. Owing to the zero energy gap mode the Majorana heat capacity falls in a power law. The Majorana heat capacity can be larger than bulk one at some temperature, which depends on surface to volume ratio of the experimental cell. Some times ago we developed the Dark matter particles detector (DMD) on a basis of superfluid 3He which is working at the frontier of extremely low temperatures (Winkelmann et al., Nucl. Instrum. Meth. A 559:384-386, 2006). Here we report the observation of zero gap mode of Majorana, follows from the new analyses of DMD heat capacity, published early. We have found a 10 % deviation from the bulk superfluid 3He heat capacity at the temperature of 135 μK. This deviation corresponds well to the theoretical value for Majorana heat capacity at such low temperature. (Note, there were no fitting parameters).

  10. Search for a 2-quasiparticle high-K isomer in {sup 256}Rf

    SciTech Connect

    Robinson, A. P.; Jenkins, D. G.; Marley, P.; Khoo, T. L.; Seweryniak, D.; Ahmad, I.; Back, B. B.; Carpenter, M. P.; Davids, C. N.; Greene, J.; Janssens, R. V. F.; Kondev, F. G.; Lauritsen, T.; Lister, C. J.; McCutchan, E.; Peterson, D.; Stefanescu, I.; Zhu, S.; Asai, M.; Chowdhury, P.

    2011-06-15

    The energies of 2-quasiparticle (2-qp) states in heavy shell-stabilized nuclei provide information on the single-particle states that are responsible for the stability of superheavy nuclei. We have calculated the energies of 2-qp states in {sup 256}Rf, which suggest that a long-lived, low-energy 8{sup -} isomer should exist. A search was conducted for this isomer through a calorimetric conversion electron signal, sandwiched in time between implantation of a {sup 256}Rf nucleus and its fission decay, all within the same pixel of a double-sided Si strip detector. A 17(5)-{mu}s isomer was identified. However, its low population, {approx}5(2)% that of the ground state instead of the expected {approx}30%, suggests that it is more likely a 4-qp isomer. Possible reasons for the absence of an electromagnetic signature of a 2-qp isomer decay are discussed. These include the favored possibility that the isomer decays by fission, with a half-life indistinguishably close to that of the ground state. Another possibility, that there is no 2-qp isomer at all, would imply an abrupt termination of axially symmetric deformed shapes at Z=104, which describes nuclei with Z=92-103 very well.

  11. Search for a 2-quasiparticle high-K isomer in {sup 256}Rf.

    SciTech Connect

    Robinson, A. P.; Khoo, T. L.; Seweryniak, D.; Ahmad, I.; Asai, M.; Back, B. B.; Carpenter, M. P.; Davids, C. N.; Greene, J.; Janssens, R. V. F.; Kondev, F. G.; Lauritsen, T.; Lister, C. J.; McCutchan, E.; Peterson, D.; Zhu, S.

    2011-06-13

    The energies of 2-quasiparticle (2-qp) states in heavy shell-stabilized nuclei provide information on the single-particle states that are responsible for the stability of superheavy nuclei. We have calculated the energies of 2-qp states in {sup 256}Rf, which suggest that a long-lived, low-energy 8{sup -} isomer should exist. A search was conducted for this isomer through a calorimetric conversion electron signal, sandwiched in time between implantation of a {sup 256}Rf nucleus and its fission decay, all within the same pixel of a double-sided Si strip detector. A 17(5)-{micro}s isomer was identified. However, its low population, {approx}5(2)% that of the ground state instead of the expected {approx}30%, suggests that it is more likely a 4-qp isomer. Possible reasons for the absence of an electromagnetic signature of a 2-qp isomer decay are discussed. These include the favored possibility that the isomer decays by fission, with a half-life indistinguishably close to that of the ground state. Another possibility, that there is no 2-qp isomer at all, would imply an abrupt termination of axially symmetric deformed shapes at Z = 104, which describes nuclei with Z = 92-103 very well.

  12. Particle-number conservation in quasiparticle representation in the isovector neutron-proton pairing case

    NASA Astrophysics Data System (ADS)

    Fellah, M.; Allal, N. H.; Hammache, Faiza; Oudih, M. R.

    2015-12-01

    Until now, the Sharp-Bardeen-Cooper-Schrieffer (SBCS) particle-number projection method, in the isovector neutron-proton pairing case, has been developed in the particle representation. However, this formalism is sometimes complicated and cumbersome. In this work, the formalism is developed in the quasiparticle representation. An expression of the projected ground state wave function is proposed. Expressions of the energy as well as the expectation values of the total particle-number operator and its square are deduced. It is shown that these expressions are formally similar to their homologues in the pairing between like-particles case. They are easier to handle than the ones obtained using the particle representation and are more adapted to numerical calculations. The method is then numerically tested within the schematic one-level model, which allows comparisons with exact results, as well as in the case of even-even nuclei within the Woods-Saxon model. In each case, it is shown that the particle-number fluctuations that are inherent to the BCS method are completely eliminated by the projection. In the framework of the one-level model, the values of the projected energy are clearly closer to the exact values than the BCS ones. In realistic cases, the relative discrepancies between projected and unprojected values of the energy are small. However, the absolute deviations may reach several MeV.

  13. Ab initio Sternheimer-GW method for quasiparticle calculations using plane waves

    NASA Astrophysics Data System (ADS)

    Lambert, Henry; Giustino, Feliciano

    2013-08-01

    We report on the extension and implementation of the Sternheimer-GW method introduced by Giustino [Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.81.115105 81, 115105 (2010)] to the case of first-principles pseudopotential calculations based on a plane-waves basis. The Sternheimer-GW method consists of calculating the GW self-energy operator without resorting to the standard expansion over unoccupied Kohn-Sham electronic states. The Green's function is calculated by solving linear systems for frequencies along the real axis. The screened Coulomb interaction is calculated for frequencies along the imaginary axis by using the Sternheimer equation. Analytic continuation to the real axis is performed using Padé approximants. The generalized plasmon-pole approximation is avoided by performing explicit calculations at multiple frequencies using Frommer's multishift solver. We demonstrate our methodology by reporting tests on common insulators and semiconductors, including Si, diamond, LiCl, and SiC. Our calculated quasiparticle energies are in agreement with the results of fully converged calculations based on the sum-over-states approach. As the Sternheimer-GW method yields the complete self-energy Σ(r,r',ω) and not only its expectation values on Kohn-Sham states, this work opens the way to nonperturbative GW calculations and to direct calculations of spectral functions for angle-resolved photoemission spectroscopy. As an example of the capabilities of the method we calculate the G0W0 spectral functions of silicon and diamond.

  14. Quasiparticle lifetime broadening in resonant x-ray scattering of NH4NO3

    NASA Astrophysics Data System (ADS)

    Vinson, John; Jach, Terrence; Müller, Matthias; Unterumsberger, Rainer; Beckhoff, Burkhard

    2016-07-01

    It has been previously shown that two effects cause dramatic changes in the x-ray absorption and emission spectra from the N K edge of the insulating crystal ammonium nitrate. First, vibrational disorder causes major changes in the absorption spectrum, originating not only from the thermal population of phonons, but, significantly, from zero-point motion as well. Second, the anomalously large broadening (˜4 eV) of the emission originating from nitrate σ states is due to the unusually short lifetimes of quasiparticles in an otherwise extremely narrow band. In this work, we investigate the coupling of these effects to core and valence excitons that are created as the initial x-ray excitation energy is progressively reduced toward the N edge. Using a G W /Bethe-Salpeter approach, we show the extent to which this anomalous broadening is captured by the G W approximation. The data and calculations demonstrate the importance that the complex self-energies (finite lifetimes) of the valence bands have on the interpretation of emission spectra. We produce a scheme to explain why extreme lifetimes should appear in σ states of other similar compounds.

  15. Interpretation of scanning tunneling quasiparticle interference and impurity states in cuprates

    DOE PAGES

    Kreisel, Andreas; Choubey, Peayush; Berlijn, Tom; Ku, W.; Andersen, Brian M.; Hirschfeld, Peter J.

    2015-05-27

    We apply a recently developed method combining first principles based Wannier functions with solutions to the Bogoliubov–de Gennes equations to the problem of interpreting STM data in cuprate superconductors. We show that the observed images of Zn on the surface of Bi2Sr2CaCu2O8 can only be understood by accounting for the tails of the Cu Wannier functions, which include significant weight on apical O sites in neighboring unit cells. This calculation thus puts earlier crude “filter” theories on a microscopic foundation and solves a long-standing puzzle. We then study quasiparticle interference phenomena induced by out-of-plane weak potential scatterers, and show howmore » patterns long observed in cuprates can be understood in terms of the interference of Wannier functions above the surface. Furthermore, our results show excellent agreement with experiment and enable a better understanding of novel phenomena in the cuprates via STM imaging.« less

  16. Spin-Orbit Effects in the Quasiparticle Bandstructure of Noble Metals

    NASA Astrophysics Data System (ADS)

    Mustafa, Jamal; Louie, Steven

    2014-03-01

    Applications of the GW approximation to the electron self-energy have proven quite successful for calculating the quasiparticle properties of materials. We find that for the noble metals, in line with previous work in such calculations, the semicore states need to be taken into account. We show that, with these semicore states, a large cutoff must be used to describe the screening and, in turn, a large number of empty states must be included. Taking all of this into account, and carefully checking convergence, shows G0W0 can describe experimental results from angle-resolved photoemission spectroscopy quite well when the effects of spin-orbit coupling is also included. We compare our results to recent self-consistent GW calculations on gold. This work was supported by NSF grant No. DMR10-1006184 and U.S. DOE under Contract No. DE-AC02-05CH11231. Computational resources have been provided by DOE at LBNL's NERSC facility.

  17. Inverse correlation between quasiparticle mass and T c in a cuprate high-T c superconductor.

    PubMed

    Putzke, Carsten; Malone, Liam; Badoux, Sven; Vignolle, Baptiste; Vignolles, David; Tabis, Wojciech; Walmsley, Philip; Bird, Matthew; Hussey, Nigel E; Proust, Cyril; Carrington, Antony

    2016-03-01

    Close to a zero-temperature transition between ordered and disordered electronic phases, quantum fluctuations can lead to a strong enhancement of electron mass and to the emergence of competing phases such as superconductivity. A correlation between the existence of such a quantum phase transition and superconductivity is quite well established in some heavy fermion and iron-based superconductors, and there have been suggestions that high-temperature superconductivity in copper-oxide materials (cuprates) may also be driven by the same mechanism. Close to optimal doping, where the superconducting transition temperature T c is maximal in cuprates, two different phases are known to compete with superconductivity: a poorly understood pseudogap phase and a charge-ordered phase. Recent experiments have shown a strong increase in quasiparticle mass m* in the cuprate YBa2Cu3O7-δ as optimal doping is approached, suggesting that quantum fluctuations of the charge-ordered phase may be responsible for the high-T c superconductivity. We have tested the robustness of this correlation between m* and T c by performing quantum oscillation studies on the stoichiometric compound YBa2Cu4O8 under hydrostatic pressure. In contrast to the results for YBa2Cu3O7-δ, we find that in YBa2Cu4O8, the mass decreases as T c increases under pressure. This inverse correlation between m* and T c suggests that quantum fluctuations of the charge order enhance m* but do not enhance T c. PMID:27034989

  18. Quasiparticle mass enhancement approaching optimal doping in a high-Tc superconductor

    SciTech Connect

    Ramshaw, B. J.; Sebastian, S. E.; McDonald, R. D.; Day, J.; Tan, B. S.; Zhu, Z.; Betts, J. B.; Liang, Ruixing; Bonn, D. A.; Hardy, W. N.; Harrison, N.

    2015-03-26

    In the quest for superconductors with higher transition temperatures (Tc), one emerging motif is that electronic interactions favorable for superconductivity can be enhanced by fluctuations of a broken-symmetry phase. In recent experiments it is suggested that the existence of the requisite broken-symmetry phase in the high-Tc cuprates, but the impact of such a phase on the ground-state electronic interactions has remained unclear. Here, we used magnetic fields exceeding 90 tesla to access the underlying metallic state of the cuprate YBa2Cu3O6+δ over a wide range of doping, and observed magnetic quantum oscillations that reveal a strong enhancement of the quasiparticle effective mass toward optimal doping. Finally, this mass enhancement results from increasing electronic interactions approaching optimal doping, and suggests a quantum critical point at a hole doping of pcrit ≈ 0.18.

  19. Characterizing Featureless Mott Insulating State by Quasiparticle Interferences - A DMFT Prospect

    NASA Astrophysics Data System (ADS)

    Mukherjee, Shantanu; Lee, Wei-Cheng

    In this talk we discuss the quasiparticle interferences (QPIs) of a Mott insulator using a T-matrix formalism implemented with the dynamical mean-field theory (T-DMFT). In the Mott insulating state, the DMFT predicts a singularity in the real part of electron self energy s (w) at low frequencies, which completely washes out the QPI at small bias voltage. However, the QPI patterns produced by the non-interacting Fermi surfaces can appear at a critical bias voltage in Mott insulating state. The existence of this non-zero critical bias voltage is a direct consequence of the singular behavior of Re[s (w)] /sim n/w with n behaving as the 'order parameter' of Mott insulating state. We propose that this reentry of non-interacting QPI patterns could serve as an experimental signature of Mott insulating state, and the 'order parameter' can be experimentally measured W.C.L acknowledges financial support from start up fund from Binghamton University.

  20. Interpretation of Scanning Tunneling Quasiparticle Interference and Impurity States in Cuprates

    SciTech Connect

    Kreisel, A.; Choubey, P.; Berlijn, T.; Ku, W.; Andersen, B. M.; Hirschfeld, P. J.

    2015-05-27

    We apply a recently developed method combining first principles based Wannier functions with solutions to the Bogoliubov-de Gennes equations to the problem of interpreting STM data in cuprate superconductors. We show that the observed images of Zn on the surface of Bi2Sr2CaCu2O8 can only be understood by accounting for the tails of the Cu Wannier functions, which include significant weight on apical O sites in neighboring unit cells. This calculation thus puts earlier crude “filter” theories on a microscopic foundation and solves a long standing puzzle. We then study quasiparticle interference (QPI) phenomena induced by out-of-plane weak potential scatterers, and show how patterns long observed in cuprates can be understood in terms of the interference of Wannier functions above the surface. Our results show excellent agreement with experiment and enable a better understanding of novel phenomena in the cuprates via STM imaging.

  1. Interpretation of Scanning Tunneling Quasiparticle Interference and Impurity States in Cuprates

    DOE PAGES

    Kreisel, A.; Choubey, P.; Berlijn, T.; Ku, W.; Andersen, B. M.; Hirschfeld, P. J.

    2015-05-27

    We apply a recently developed method combining first principles based Wannier functions with solutions to the Bogoliubov-de Gennes equations to the problem of interpreting STM data in cuprate superconductors. We show that the observed images of Zn on the surface of Bi2Sr2CaCu2O8 can only be understood by accounting for the tails of the Cu Wannier functions, which include significant weight on apical O sites in neighboring unit cells. This calculation thus puts earlier crude “filter” theories on a microscopic foundation and solves a long standing puzzle. We then study quasiparticle interference (QPI) phenomena induced by out-of-plane weak potential scatterers, andmore » show how patterns long observed in cuprates can be understood in terms of the interference of Wannier functions above the surface. Our results show excellent agreement with experiment and enable a better understanding of novel phenomena in the cuprates via STM imaging.« less

  2. Calculation of the spectrum of quasiparticle electron excitations in organic molecular semiconductors

    SciTech Connect

    Tikhonov, E. V.; Uspenskii, Yu. A.; Khokhlov, D. R.

    2015-06-15

    A quasiparticle electronic spectrum belongs to the characteristics of nanoobjects that are most important for applications. The following methods of calculating the electronic spectrum are analyzed: the Kohn-Sham equations of the density functional theory (DFT), the hybrid functional method, the GW approximation, and the Lehmann approximation used in the spectral representation of one-electron Green’s function. The results of these approaches are compared with the data of photoemission measurements of benzene, PTCDA, and phthalocyanine (CuPc, H{sub 2}Pc, FePc, PtPc) molecules, which are typical representatives of organic molecular semiconductors (OMS). This comparison demonstrates that the Kohn-Sham equations of DFT incorrectly reproduce the electronic spectrum of OMS. The hybrid functional method correctly describes the spectrum of the valence and conduction bands; however, the HOMO-LUMO gap width is significantly underestimated. The correct gap width is obtained in both the GW approximation and the Lehmann approach, and the total energy in this approach can be calculated in the local density approximation of DFT.

  3. Interpretation of scanning tunneling quasiparticle interference and impurity states in cuprates

    SciTech Connect

    Kreisel, Andreas; Choubey, Peayush; Berlijn, Tom; Ku, W.; Andersen, Brian M.; Hirschfeld, Peter J.

    2015-05-27

    We apply a recently developed method combining first principles based Wannier functions with solutions to the Bogoliubov–de Gennes equations to the problem of interpreting STM data in cuprate superconductors. We show that the observed images of Zn on the surface of Bi2Sr2CaCu2O8 can only be understood by accounting for the tails of the Cu Wannier functions, which include significant weight on apical O sites in neighboring unit cells. This calculation thus puts earlier crude “filter” theories on a microscopic foundation and solves a long-standing puzzle. We then study quasiparticle interference phenomena induced by out-of-plane weak potential scatterers, and show how patterns long observed in cuprates can be understood in terms of the interference of Wannier functions above the surface. Furthermore, our results show excellent agreement with experiment and enable a better understanding of novel phenomena in the cuprates via STM imaging.

  4. Fano resonance and the hidden order in URu2 Si 2 probed by quasiparticle scattering spectroscopy*

    NASA Astrophysics Data System (ADS)

    Park, W. K.; Greene, L. H.; Bauer, E. D.; Tobash, P. H.; Ronning, F.; Lu, X.; Sarrao, J. L.; Thompson, J. D.

    2011-03-01

    The nature of the hidden order transition occurring at 17.5 K in URu 2 Si 2 remains puzzling despite intensive investigations over the past two and half decades. Recent experimental and theoretical developments render it a timely subject to probe the hidden order state using quasiparticle tunneling and scattering techniques. We report on the Fano resonance in pure and Rh-doped URu 2 Si 2 single crystals using point-contact spectroscopy. The conductance spectra reproducibly reveal asymmetric double peak structures slightly off-centered around zero bias with the two peaks merging well above the hidden order transition temperature. An analysis using the Fano resonance model in a Kondo lattice [1] shows that the conductance peaks arise from the hybridization gap opening. Our estimated gap size agrees well with those reported from other measurements. We will present experimental results over a wide parameter space including temperature and doping dependences and discuss their underlying physics. M. Maltseva, M. Dzero, and P. Coleman, Phys. Rev. Lett. 103, 206402 (2009). * The work at UIUC is supported by the U.S. DOE under Award Nos. DE-FG02-07ER46453 and DE-AC02-98CH10886, and the work at LANL is carried out under the auspices of the U.S. DOE, Office of Science.

  5. Bose glass and Mott glass of quasiparticles in a doped quantum magnet.

    PubMed

    Yu, Rong; Yin, Liang; Sullivan, Neil S; Xia, J S; Huan, Chao; Paduan-Filho, Armando; Oliveira, Nei F; Haas, Stephan; Steppke, Alexander; Miclea, Corneliu F; Weickert, Franziska; Movshovich, Roman; Mun, Eun-Deok; Scott, Brian L; Zapf, Vivien S; Roscilde, Tommaso

    2012-09-20

    The low-temperature states of bosonic fluids exhibit fundamental quantum effects at the macroscopic scale: the best-known examples are Bose-Einstein condensation and superfluidity, which have been tested experimentally in a variety of different systems. When bosons interact, disorder can destroy condensation, leading to a 'Bose glass'. This phase has been very elusive in experiments owing to the absence of any broken symmetry and to the simultaneous absence of a finite energy gap in the spectrum. Here we report the observation of a Bose glass of field-induced magnetic quasiparticles in a doped quantum magnet (bromine-doped dichloro-tetrakis-thiourea-nickel, DTN). The physics of DTN in a magnetic field is equivalent to that of a lattice gas of bosons in the grand canonical ensemble; bromine doping introduces disorder into the hopping and interaction strength of the bosons, leading to their localization into a Bose glass down to zero field, where it becomes an incompressible Mott glass. The transition from the Bose glass (corresponding to a gapless spin liquid) to the Bose-Einstein condensate (corresponding to a magnetically ordered phase) is marked by a universal exponent that governs the scaling of the critical temperature with the applied field, in excellent agreement with theoretical predictions. Our study represents a quantitative experimental account of the universal features of disordered bosons in the grand canonical ensemble.

  6. Quasiparticle scattering interference in iron pnictides: A probe of the origin of nematicity

    NASA Astrophysics Data System (ADS)

    Zhang, Hai-Yang; Li, Jian-Xin

    2016-08-01

    In this paper, we investigate the quasiparticle scattering interference (QPI) in the nematic phase of iron pnictides, based on the magnetic and orbital scenarios of nematicity, respectively. In the spin density wave (SDW) state, the QPI pattern exhibits a dimer structure in the energy region of the SDW gap, with its orientation along the ferromagnetic direction of the SDW order. When the energy is increased to be near the Fermi level, it exhibits two sets of dimers along the same direction. The dimer structure of the QPI patterns persists in the magnetically driven nematic phase, although the two dimers tend to merge together with energies closing to the Fermi level. While in the orbital scenario, the QPI patterns exhibit a dimer structure in a wide energy region. It undergoes a π /2 rotation with the increasing of energy, which is associated with the inequivalent energies of the two Dirac nodes induced by the orbital order. These distinct features may be used to probe or distinguish two kinds of scenarios of the nematicity.

  7. Many-body quasiparticle spectrum of Co-doped ZnO: A GW perspective

    NASA Astrophysics Data System (ADS)

    Sarsari, I. Abdolhosseini; Pemmaraju, C. D.; Salamati, Hadi; Sanvito, S.

    2013-06-01

    In transition-metal-doped ZnO the energy position of the dopant 3d states relative to the host conduction and valence bands determines the possibility of long-range ferromagnetism. Density functional theory (DFT) can estimate the energy position of the Co-3d states in ZnO:Co but this depends substantially upon the choice of exchange-correlation functional. In this paper we investigate many-body GW corrections built on top of DFT+U and hybrid-DFT ground states to provide a theoretical benchmark for the quasiparticle energies in wurtzite ZnO:Co. Both single shot G0W0 as well as partially self-consistent GW0, wherein the wave functions are held fixed at the DFT level but the eigenvalues in G are iterated, are considered. The predicted energy position of the minority spin Co-t2 states is 3.0-3.6 eV above the ZnO conduction band minimum, which is closer to hybrid-DFT-based estimates. Such an electronic structure does not support carrier-mediated long-range ferromagnetism at achievable n-doping conditions.

  8. Inverse correlation between quasiparticle mass and T c in a cuprate high-T c superconductor.

    PubMed

    Putzke, Carsten; Malone, Liam; Badoux, Sven; Vignolle, Baptiste; Vignolles, David; Tabis, Wojciech; Walmsley, Philip; Bird, Matthew; Hussey, Nigel E; Proust, Cyril; Carrington, Antony

    2016-03-01

    Close to a zero-temperature transition between ordered and disordered electronic phases, quantum fluctuations can lead to a strong enhancement of electron mass and to the emergence of competing phases such as superconductivity. A correlation between the existence of such a quantum phase transition and superconductivity is quite well established in some heavy fermion and iron-based superconductors, and there have been suggestions that high-temperature superconductivity in copper-oxide materials (cuprates) may also be driven by the same mechanism. Close to optimal doping, where the superconducting transition temperature T c is maximal in cuprates, two different phases are known to compete with superconductivity: a poorly understood pseudogap phase and a charge-ordered phase. Recent experiments have shown a strong increase in quasiparticle mass m* in the cuprate YBa2Cu3O7-δ as optimal doping is approached, suggesting that quantum fluctuations of the charge-ordered phase may be responsible for the high-T c superconductivity. We have tested the robustness of this correlation between m* and T c by performing quantum oscillation studies on the stoichiometric compound YBa2Cu4O8 under hydrostatic pressure. In contrast to the results for YBa2Cu3O7-δ, we find that in YBa2Cu4O8, the mass decreases as T c increases under pressure. This inverse correlation between m* and T c suggests that quantum fluctuations of the charge order enhance m* but do not enhance T c.

  9. Association of PD-1, PD-1 ligands, and other features of the tumor immune microenvironment with response to anti-PD-1 therapy

    PubMed Central

    Taube, Janis M.; Klein, Alison; Brahmer, Julie R.; Xu, Haiying; Pan, Xiaoyu; Kim, Jung H.; Chen, Lieping; Pardoll, Drew M.; Topalian, Suzanne L.; Anders, Robert A.

    2014-01-01

    Purpose Immunomodulatory drugs differ in mechanism-of-action from directly cytotoxic cancer therapies. Identifying factors predicting clinical response could guide patient selection and therapeutic optimization. Experimental Design Patients (N=41) with melanoma, non-small cell lung carcinoma (NSCLC), renal cell carcinoma (RCC), colorectal carcinoma or castration-resistant prostate cancer were treated on an early phase trial of anti-PD-1 (nivolumab) at one institution and had evaluable pre-treatment tumor specimens. Immunoarchitectural features including PD-1, PD-L1, and PD-L2 expression, patterns of immune cell infiltration, and lymphocyte subpopulations, were assessed for interrelationships and potential correlations with clinical outcomes. Results Membranous (cell surface) PD-L1 expression by tumor cells and immune infiltrates varied significantly by tumor type and was most abundant in melanoma, NSCLC, and RCC. In the overall cohort, PD-L1 expression was geographically associated with infiltrating immune cells (p<0.001), although lymphocyte-rich regions were not always associated with PD-L1 expression. Expression of PD-L1 by tumor cells and immune infiltrates was significantly associated with expression of PD-1 on lymphocytes. PD-L2, the second ligand for PD-1, was associated with PD-L1 expression. Tumor cell PD-L1 expression correlated with objective response to anti-PD-1 therapy, when analyzing either the specimen obtained closest to therapy or the highest scoring sample among multiple biopsies from individual patients. These correlations were stronger than borderline associations of PD-1 expression or the presence of intratumoral immune cell infiltrates with response. Conclusions Tumor PD-L1 expression reflects an immune-active microenvironment and, while associated other immunosuppressive molecules including PD-1 and PD-L2, is the single factor most closely correlated with response to anti-PD-1 blockade. PMID:24714771

  10. Professional Development Effects on Teacher Efficacy: Results of Randomized Field Trial

    ERIC Educational Resources Information Center

    Ross, John; Bruce, Catherine

    2007-01-01

    We designed a professional development (PD) program to increase the teacher efficacy of mathematics teachers. We randomly assigned 106 Grade 6 teachers in 1 school district to treatment and control conditions in a delayed-treatment design. The PD explicitly addressed 4 sources of teacher-efficacy information identified in social-cognition theory…

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

    PubMed

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

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

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

    PubMed

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

    2015-12-01

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

  14. 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

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

    DOE PAGES

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

    2016-05-06

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

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

    SciTech Connect

    Luo, Weifang

    2010-09-01

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

  17. Incidence and risk of hepatic toxicities with PD-1 inhibitors in cancer patients: a meta-analysis

    PubMed Central

    Zhang, Xi; Ran, Yuge; Wang, Kunjie; Zhu, Yuanxue; Li, Jinghua

    2016-01-01

    Purpose Anti-programmed cell death receptor-1 (PD-1) antibodies have demonstrated antitumor activity in many cancer entities. Hepatic adverse events (AEs) are one of its major side effects, but the overall risks have not been systematically evaluated. Thus, we conducted this meta-analysis to investigate the overall incidence and risk of developing hepatic AEs in cancer patients treated with PD-1 inhibitors. Methods PubMed, Embase, and oncology conference proceedings were searched for relevant studies. Eligible studies were randomized controlled trials of cancer patients treated with PD-1 inhibitors with adequate data on hepatic AEs. Results A total of nine randomized controlled trials with a variety of solid tumors were eligible for the meta-analysis. The use of PD-1 inhibitors significantly increased the risk of developing all-grade hepatic AEs but not for high-grade hepatic AEs in comparison with chemotherapy or everolimus control. Additionally, the risk of all-grade and high-grade hepatic AEs with a nivolumab/ipilimumab combination was substantially higher than ipilimumab. No significant differences in the risk of all-grade and high-grade hepatic AEs were found between PD-1 inhibitors monotherapy and ipilimumab. Conclusion While the use of PD-1 inhibitors is associated with an increased risk of developing hepatic AEs in cancer patients, this is primarily for lower grade events. PMID:27729774

  18. Recovery of high-purity metallic Pd from Pd(II)-sorbed biosorbents by incineration.

    PubMed

    Won, Sung Wook; Lim, Areum; Yun, Yeoung-Sang

    2013-06-01

    This work reports a direct way to recover metallic palladium with high purity from Pd(II)-sorbed polyethylenimine-modified Corynebacterium glutamicum biosorbent using a combined method of biosorption and incineration. This study is focused on the incineration part which affects the purity of recovered Pd. The incineration temperature and the amount of Pd loaded on the biosorbent were considered as major factors in the incineration process, and their effects were examined. The results showed that both factors significantly affected the enhancement of the recovery efficiency and purity of the recovered Pd. SEM-EDX and XRD analyses were used to confirm that Pd phase existed in the ash. As a result, the recovered Pd was changed from PdO to zero-valent Pd as the incineration temperature was increased from 600 to 900°C. Almost 100% pure metallic Pd was recovered with recovery efficiency above 99.0% under the conditions of 900°C and 136.9 mg/g.

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

    SciTech Connect

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

    2015-05-07

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

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

    DOE PAGES

    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 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

  1. 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.

  2. Parental education and the WHO neonatal G-6-PD screening program: a quarter century later.

    PubMed

    Kaplan, M; Hammerman, C; Bhutani, V K

    2015-10-01

    Neonatal screening for glucose-6-phosphate dehydrogenase (G-6-PD) deficiency in any population with a male frequency >3-5%, combined with parental education regarding the dietary, environmental and sepsis-related triggers for hemolysis was recommended by the WHO (World Health Organization) Working Group in 1989. As the aim of identifying G-6-PD deficiency in the newborn period is to avert or detect extreme hyperbilirubinemia developing at home, before the development of kernicterus, the parental role in identifying evolving icterus was considered integral to any screening program. Now, a quarter century after publication of this report, severe bilirubin neurotoxicity associated with G-6-PD deficiency continues to be encountered worldwide. Screening programs have not been universally introduced but several national or regional maternal child health programs have implemented neonatal G-6-PD screening. Some reports detail the role of parental education, based on the above mentioned principles, through a variety of audio-visual materials. The paucity of randomized controlled trials or validated evidence to demonstrate the effectiveness of the contribution of parental education fails to meet the ideal testable evidence-based approach. However, our review of the cumulative experience and evidence currently available does supply certain information reflecting a positive impact of screening programs combined with parental input. We propose that the current information is sufficient to continue to support and apply the Working Group's recommendations. In order not to waste unnecessary time available, data may be used in lieu of randomized trials to continue to recommend screening programs, as suggested, in high-risk regions. If the incidence of kernicterus associated with G-6-PD deficiency is to be diminished, G-6-PD screening in combination with parental explanation may be one instance in which the consensus approach suggested by the WHO Working Group, rather than reliance

  3. A DFT study on structural, vibrational properties, and quasiparticle band structure of solid nitromethane.

    PubMed

    Appalakondaiah, S; Vaitheeswaran, G; Lebègue, S

    2013-05-14

    We report a detailed theoretical study of the structural and vibrational properties of solid nitromethane using first principles density functional calculations. The ground state properties were calculated using a plane wave pseudopotential code with either the local density approximation, the generalized gradient approximation, or with a correction to include van der Waals interactions. Our calculated equilibrium lattice parameters and volume using a dispersion correction are found to be in reasonable agreement with the experimental results. Also, our calculations reproduce the experimental trends in the structural properties at high pressure. We found a discontinuity in the bond length, bond angles, and also a weakening of hydrogen bond strength in the pressure range from 10 to 12 GPa, picturing the structural transition from phase I to phase II. Moreover, we predict the elastic constants of solid nitromethane and find that the corresponding bulk modulus is in good agreement with experiments. The calculated elastic constants show an order of C11> C22 > C33, indicating that the material is more compressible along the c-axis. We also calculated the zone center vibrational frequencies and discuss the internal and external modes of this material under pressure. From this, we found the softening of lattice modes around 8-11 GPa. We have also attempted the quasiparticle band structure of solid nitromethane with the G0W0 approximation and found that nitromethane is an indirect band gap insulator with a value of the band gap of about 7.8 eV with G0W0 approximation. Finally, the optical properties of this material, namely the absorptive and dispersive part of the dielectric function, and the refractive index and absorption spectra are calculated and the contribution of different transition peaks of the absorption spectra are analyzed. The static dielectric constant and refractive indices along the three inequivalent crystallographic directions indicate that this material

  4. A dynamical quasiparticle approach for the QGP bulk and transport properties

    NASA Astrophysics Data System (ADS)

    Berrehrah, Hamza; Bratkovskaya, Elena; Steinert, Thorsten; Cassing, Wolfgang

    2016-05-01

    The properties of quantum chromodynamics (QCD) nowadays are accessible by lattice QCD calculations at vanishing quark chemical potential μq = 0, but often lack a transparent physical interpretation. In this review, we report about results from an extended dynamical quasiparticle model (DQPM∗) in which the effective parton propagators have a complex self-energy that depends on the temperature T of the medium as well as on the chemical potential μq and the parton three-momentum p with respect to the medium at rest. It is demonstrated that this approach allows for a good description of QCD thermodynamics with respect to the entropy density, pressure, etc. above the critical temperature Tc ≈ 158 MeV. Furthermore, the quark susceptibility χq and the quark number density nq are found to be reproduced simultaneously at zero and finite quark chemical potential. The shear and bulk viscosities η,ζ, and the electric conductivity σe from the DQPM∗ also turn out in close agreement with lattice results for μq =0. The DQPM∗, furthermore, allows to evaluate the momentum p, T and μq dependencies of the partonic degrees of freedom also for larger μq which are mandatory for transport studies of heavy-ion collisions in the regime 5GeV < sNN < 10GeV. We finally calculate the charm quark diffusion coefficient Ds - evaluated from the differential cross-sections of partons in the medium for light and heavy quarks by employing the propagators and couplings from the DQPM - and compare it to the available lattice data. It is argued that the complete set of observables allows for a transparent interpretation of the properties of hot QCD.

  5. Validation of G6PD Point-of-Care Tests among Healthy Volunteers in Yangon, Myanmar

    PubMed Central

    Maw, Lwin Zar; Chowwiwat, Nongnud; Bansil, Pooja; Domingo, Gonzalo J.; Htun, Moh Moh; Thant, Kyaw Zin; Htut, Ye; Nosten, Francois

    2016-01-01

    Primaquine and other 8-amnoquinoline based anti-malarials can cause haemolysis in subjects with glucose-6-phosphate dehydrogenase (G6PD) deficiency. Correct diagnosis of G6PD status in patients is crucial for safe treatment of both relapsing stages of Plasmodium vivax and transmitting forms of Plasmodium falciparum. Lack of suitable point-of-care tests has hampered a much needed wide use of primaquine for malaria elimination. In this study we have assessed the performances of two qualitative tests, the fluorescent spot test (FST) and the G6PD CareStart test (CST), against the gold standard quantitative spectrophotometric assay in a population of 1000 random adult healthy volunteers living in Yangon, Myanmar. The prevalence of G6PD deficiency in the Bamar, Karen and in the whole sample set was 6.6% (10.1% in males), 9.2% (21.0% in males) and 6.8% (11.1% in males) respectively. The FST and CST showed comparable performances with sensitivity over 95% and specificity over 90%, however for cases with severe G6PD activity the FTS had improved performance. If used with a conservative interpretation of the signal, the CareStart test has the potential to be used in the field and, by allowing a wider use of primaquine, to help malaria elimination. PMID:27035821

  6. Diffusion Kinetics in the Pd/Cu(001) Surface Alloy

    SciTech Connect

    GRANT,M.L.; SWARTZENTRUBER,BRIAN S.; BARTELT,NORMAN C.; HANNON,J.B.

    2000-12-08

    We use atom-tracking scanning tunneling microscopy to study the diffusion of Pd in the Pd/Cu(001) surface alloy. By following the motion of individual Pd atoms incorporated in the surface, we show that Pd diffuses by a vacancy-exchange, mechanism. We measure an effective activation energy for the diffusion of incorporated Pd atoms of 0.88 eV, which is consistent with an ab initio calculated barrier of 0.94 eV.

  7. [Comparative analysis of PD25-V50 and PD20-FEV1 as a judgement of bronchial provocation test].

    PubMed

    Yao, W Z; Zhoa, M W; Han, R X

    1994-08-01

    PD25-V50 as a judgement of bronchial provocation test was compared with PD20-FEV1. Both PD25-V50 and PD20-FEV1 showed linear correlation, but PD25-V50 was more sensitive than PD20-FEV1 for the diagnosis of bronchial asthma, and had higher specificity and sensitivity, and lower false-negative and false-positiverate. Moreover PD25-V50 provided the advantages of shorter period of histamine provocation and lower dose of inhaled histamine, so that avoided the side effects of higher dose of histamine.

  8. Cooperative nucleation modes in polycrystalline CoxPd1-x nanowires

    NASA Astrophysics Data System (ADS)

    Viqueira, M. S.; Pozo-López, G.; Urreta, S. E.; Condó, A. M.; Cornejo, D. R.; Fabietti, L. M.

    2015-05-01

    Polycrystalline CoxPd1-x (x = 1, 0.60, 0.45, 0.23, and 0.11) cylindrical nanowires (ø = 18-35 nm, about 1 μm length) are produced by AC electrodeposition into hexagonally ordered alumina pores. Single-phase nanowires of an fcc Co-Pd solid solution, with randomly oriented equiaxed grains (7-12 nm) are obtained; in all the cases, the grain size is smaller than the wire diameter. The coercive field and the reduced remanence of Co-rich nanowire arrays are hardly sensitive to temperature within the range varying from 4 K to 300 K. On the other hand, in Pd-rich nanowires both magnitudes are smaller and they largely increase when cooling below 100 K. This behavior also depends on the mean grain size. These facts are systematized considering two main aspects: the non-trivial temperature and composition dependence of the crystalline anisotropy and the saturation magnetostriction in Co-Pd alloys; and a random anisotropy effect, which defines a nucleation localization length that may involve more than a single grain, and thus promotes more cooperative nucleation modes.

  9. 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.

  10. Potential of Diffusion Tensor Imaging and Relaxometry for the Detection of Specific Pathological Alterations in Parkinson's Disease (PD)

    PubMed Central

    Esterhammer, Regina; Seppi, Klaus; Reiter, Eva; Pinter, Bernadette; Mueller, Christoph; Kremser, Christian; Zitzelsberger, Tanja; Nocker, Michael; Scherfler, Christoph; Poewe, Werner; Schocke, Michael

    2015-01-01

    The purpose of the present study was to evaluate the potential of multimodal MR imaging including mean diffusivity (MD), fractional anisotropy (FA), relaxation rates R2 and R2* to detect disease specific alterations in Parkinson's Disease (PD). We enrolled 82 PD patients (PD-all) with varying disease durations (≤5 years: PD≤5, n = 43; >5 years: PD>5, n = 39) and 38 matched healthy controls (HC), receiving diffusion tensor imaging as well as R2 and R2* relaxometry calculated from multi-echo T2*-weighted and dual-echo TSE imaging, respectively. ROIs were drawn to delineate caudate nucleus (CN), putamen (PU), globus pallidus (GP) and substantia nigra (SN) on the co-registered maps. The SN was divided in 3 descending levels (SL 1–3). The most significant parameters were used for a flexible discrimination analysis (FDA) in a training collective consisting of 25 randomized subjects from each group in order to predict the classification of remaining subjects. PD-all showed significant increases in MD, R2 and R2* within SN and its subregions as well as in MD and R2* within different basal ganglia regions. Compared to the HC group, the PD≤5 and the PD>5 group showed significant MD increases within the SN and its lower two subregions, while the PD≤5 group exhibited significant increases in R2 and R2* within SN and its subregions, and tended to elevation within the basal ganglia. The PD>5 group had significantly increased MD in PU and GP, whereas the PD≤5 group presented normal MD within the basal ganglia. FDA achieved right classification in 84% of study participants. Micro-structural damage affects primarily the SN of PD patients and in later disease stages the basal ganglia. Iron contents of PU, GP and SN are increased at early disease stages of PD. PMID:26713760

  11. 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.

  12. 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.

  13. Pd/Cu site interchange in UCu{sub 5-x}Pd{sub x}

    SciTech Connect

    Booth, C.H.; Bauer, E.D.; Maple, M.B.; Chau, R.; Kwei, G.H.

    2001-07-11

    Although Pd/Cu site interchange in the non-Fermi liquid (NFL) material UCu{sub 4}Pd has been observed, the relationship between this disorder and the NFL behavior remains unclear. In order to better compare to the UCu{sub 5-x}Pd{sub x} phase diagram, they report results from Pd K edge x-ray absorption fine structure (XAFS) experiments on this series (x = 0.3-1.5) that determine the fraction of Pd atoms on the nominally Cu (16e) sites, s. They find that for these unannealed samples, s is at least 17% for all the samples measured, even for x < 1.0, although it does climb monotonically beyond its minimum at x = 0.7. These data are compared to changes in the lattice parameter as a function of x.

  14. 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.

  15. Single-band model of resonant inelastic x-ray scattering by quasiparticles in high-T(c) cuprate superconductors.

    PubMed

    Benjamin, David; Klich, Israel; Demler, Eugene

    2014-06-20

    We show that a simple model of noninteracting quasiparticles accurately describes resonant inelastic x-ray scattering (RIXS) experiments in the hole-doped cuprate superconductors. Band structure alone yields signatures previously attributed to collective magnetic modes, such as the dispersing peaks and nontrivial polarization dependence found in several experiments. We conclude that RIXS data can be explained without positing the existence of magnetic excitations that persist with increasing doping. In so doing we develop a formalism for RIXS in itinerant electron systems that accounts for the positively charged core hole exactly and discover a mechanism by which the core hole produces polarization dependence mimicking that of a magnetic system. PMID:24996103

  16. Studies of multi-quasiparticle k-isomers in rare-earth and trans-fermium nuclei.

    SciTech Connect

    Kondev, F. G.; Dracoulis, G. D.; Khoo, T. L.; Lane, G. J.; Byrne, A. P.; Kibedi, T.; Ahmad, I.; Carpenter, M. P.; Janssens, R. V. F.; Lauritzen, T.; Lister, C. J.; Seweryniak, D.; Zhu, S.; Chowdhury, P.; Tandel, S. K.; Australian National Univ.; Univ. of Massachusetts Lowell

    2007-01-01

    Nuclear K-isomers play an important role in understanding the structure of deformed axially symmetric nuclei. Examples are presented of recent studies in the rare-earth region (A {approx} 180) using deep-inelastic and multi-nucleon transfer reactions, and in the trans-fermium region (A {approx} 250) using fusion-evaporation reactions. A specific two-level mixing scenario is invoked to explain the unusual decay of the K{sup {pi}} = 13{sup +} isomer in {sup 174}Lu. The identification of 2- and 4-quasiparticle isomers in {sup 254}No is discussed and predictions of similar isomers in neighboring No and Rf nuclei are presented.

  17. 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.

  18. Brain photodiagnosis (PD), fluorescence guided resection (FGR) and photodynamic therapy (PDT): past, present and future.

    PubMed

    Eljamel, M Sam

    2008-03-01

    Intracranial tumours are an excellent target for photodiagnosis (PD), fluorescence guided resection (FGR) and photodynamic therapy (PDT), because the tumour to brain ratio of photosensitizers' concentration is very high. However, several attempts of proving the value of PDT in the most malignant type of brain tumours, gliobastoma multeforme (GBM) failed to demonstrate any significant worthwhile survival advantage in the past because of the very nature of this cancer and several compounding factors that led to this apparent disappointing outcome; variations in the photosensitizer and light dosages, variations in the photosensitizer administration to treatment time-intervals, and variations in photosensitizers used are just few to mention in this article. However, after a very long gestation period of brain PD, FGR and PDT, three randomized controlled trials (RCT) in brain PD, FGR and PDT were concluded by 2007. The first trial demonstrated that time to tumour progression (TTP) was significantly longer in patients who had PD and FGR compared to standard surgical resection but this difference did not translate into survival advantage in GBM due to the variability in the management of recurrent tumours and significant residual tumour cells left after FGR in about a third of patients leading to GBM relapse. The second trial compared single shot PDT in GBM and standard therapy. Neither the treatment nor the control group received PD or FGR. Again this RCT did not provide any survival advantage in patients who had had PDT due to the fact that standard surgical resection had left significant residual tumour in a large number of patients canceling any potential benefit from PDT. The last trial compared combined PD, FGR and repetitive PDT and standard therapy and confirmed that TTP was significantly longer in the treatment group and demonstrated that the treatment group had significant survival advantage in GBM. In conclusion, PD, FGR and PDT need to be combined to be

  19. Modification of local order in FePd films by low energy He{sup +} irradiation

    SciTech Connect

    Merkel, D. G.; Tancziko, F.; Sajti, Sz.; Major, M.; Nemeth, A.; Bottyan, L.; Horvath, Z. E.; Waizinger, J.; Stankov, S.; Kovacs, A.

    2008-07-01

    Owing to their strong perpendicular magnetic anisotropy, FePd, CoPd, and their Co(Fe)Pt counterparts are candidate materials for ultrahigh density magnetic recording. The stability and magnetic properties of such films are largely dependent on the orientation and local distribution of the L1{sub 0} FePd phase fraction. Therefore, the formation and transformation of the L1{sub 0} phase in such thin films have been the subject of continued interest. Highly ordered epitaxial FePd(001) thin films (with an L1{sub 0} phase fraction of 0.81) were prepared by molecular-beam epitaxy on a MgO(001) substrate. The effect of postgrown room temperature, 130 keV He{sup +} irradiation was investigated at fluences up to 14.9x10{sup 15} ions/cm{sup 2}. X-ray diffraction and conversion electron Moessbauer spectroscopy revealed that with increasing fluence, the L1{sub 0} FePd phase decomposes into the face centered cubic phase with random Fe and Pd occupation of the sites. A partially ordered local environment exhibiting a large hyperfine magnetic field also develops. Upon He{sup +} irradiation, the lattice parameter c of the FePd L1{sub 0} structure increases and the long range order parameter S steeply decreases. The Fe-Fe nearest-neighbor coordination in the Fe-containing environments increases on average from Fe{sub 47}Pd{sub 53} to Fe{sub 54}Pd{sub 46}, indicating a tendency of formation iron-rich clusters. The equilibrium parameters corresponding to the equiatomic L1{sub 0} phase were found at different fluences by conversion electron Moessbauer spectroscopy and by x-ray diffraction a difference, from which a plane-perpendicular compressive stress and a corresponding in-plane tensile stress are conjectured. The steep increase in the interface roughness above 7.4x10{sup 15} ions/cm{sup 2} is interpreted as a percolation-type behavior related to the high diffusion anisotropy in the L1{sub 0} phase.

  20. Investigation of the two-quasiparticle bands in the doubly-odd nucleus 166Ta using a particle-number conserving cranked shell model

    NASA Astrophysics Data System (ADS)

    Zhang, ZhenHua

    2016-07-01

    The high-spin rotational properties of two-quasiparticle bands in the doubly-odd 166Ta are analyzed using the cranked shell model with pairing correlations treated by a particle-number conserving method, in which the blocking effects are taken into account exactly. The experimental moments of inertia and alignments and their variations with the rotational frequency hω are reproduced very well by the particle-number conserving calculations, which provides a reliable support to the configuration assignments in previous works for these bands. The backbendings in these two-quasiparticle bands are analyzed by the calculated occupation probabilities and the contributions of each orbital to the total angular momentum alignments. The moments of inertia and alignments for the Gallagher-Moszkowski partners of these observed two-quasiparticle rotational bands are also predicted.

  1. The BCS-Bogoliubov and the su(2)-Algebraic Approach to the Pairing Model in Many-Fermion System --- The Quasiparticle in the Conservation of the Fermion Number ---

    NASA Astrophysics Data System (ADS)

    Tsue, Y.; Providência, C.; Providência, J. d.; Yamamura, M.

    2012-10-01

    The relation between two approaches to the su(2)-algebraic many-fermion model is discussed: (1) the BCS-Bogoliubov approach in terms of the use of the quasiparticles representing all the degrees of freedom except those related to the Cooper-pairs and (2) the conventional algebraic approach in terms of the use of the minimum weight states, from which the Cooper-pairs are excluded. In order to arrive at the goal, the idea of the quasiparticles is brought up in the conservation of the fermion number. Under the c-number replacement for the three su(2)-generators, the quasiparticles suggested in this paper are reduced to those in the BCS-Bogoliubov approach. It is also shown that the two approaches are equivalent through the c-number replacement. Further, a certain modification of the BCS-Bogoliubov approach is discussed.

  2. Charge Qubit Coupled to an Intense Microwave Electromagnetic Field in a Superconducting Nb Device: Evidence for Photon-Assisted Quasiparticle Tunneling

    NASA Astrophysics Data System (ADS)

    de Graaf, S. E.; Leppäkangas, J.; Adamyan, A.; Danilov, A. V.; Lindström, T.; Fogelström, M.; Bauch, T.; Johansson, G.; Kubatkin, S. E.

    2013-09-01

    We study a superconducting charge qubit coupled to an intensive electromagnetic field and probe changes in the resonance frequency of the formed dressed states. At large driving strengths, exceeding the qubit energy-level splitting, this reveals the well known Landau-Zener-Stückelberg interference structure of a longitudinally driven two-level system. For even stronger drives, we observe a significant change in the Landau-Zener-Stückelberg pattern and contrast. We attribute this to photon-assisted quasiparticle tunneling in the qubit. This results in the recovery of the qubit parity, eliminating effects of quasiparticle poisoning, and leads to an enhanced interferometric response. The interference pattern becomes robust to quasiparticle poisoning and has a good potential for accurate charge sensing.

  3. 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

  4. Decomposition of ethylene on small Pd particles

    NASA Technical Reports Server (NTRS)

    Durrer, W. G.; Poppa, H.; Dickinson, J. T.; Park, C.

    1985-01-01

    New results have been obtained which contribute to the understanding of hydrocarbon reactions on the surface of highly dispersed metal systems. Small particle of Pd were grown by electron beam evaporation on cleavage planes of high purity natural mica under ultrahigh vacuum conditions. Samples were subsequently characterized by transmission electron microscopy. Average particle sizes ranged from about 1 to 10 nm diameter. The chemisoption and decomposition of C2H4 on the Pd particles was studied using Auger electron spectroscopy and flash thermal desorption. It is shown that (a) C2H4 decomposes on Pd particles at room temperature, (b) specific surface sites are causing decomposition, and (c) the proportion of such active sites is significantly greater for the smaller metal particles. This enhanced reactivity may be due to an increase in the density of step, corner, and edge sites with a decrease in particle size.

  5. 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

  6. Plunger Lifetime Measurements in 102Pd

    SciTech Connect

    Kalyva, G.; Spyrou, A.; Axiotis, M.; Harissopulos, S.; Dewald, A.; Fitzler, A.; Saha, B.; Liennemann, A.; Vlastou, R.; Napoli, D. R.; Marginean, N.; Rusu, C.; De Angelis, G.; Ur, C.; Bazzacco, D.; Farnea, E.; Balabanski, D. L.; Julin, R.

    2006-04-26

    Recently, an intense experimental effort has been devoted to the search of empirical proofs of critical-point symmetries in nuclear structure. These symmetries describe shape-phase transitions and provide parameter-free predictions (up to over-all scale factors) for excitation spectra and B(E2) values. This contribution reports on recent plunger-lifetime measurements ON 102Pd carried out at LNL, Legnaro, with the Cologne plunger apparatus coupled to the GASP spectrometer and using the 92Zr(13C,3n)102Pd reaction at 48 MeV. According to the results of our measurements, 102Pd is so far the best known paradigm of the E(5) critical-point symmetry.

  7. 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

  8. Anti–PD-1/PD-L1 therapy of human cancer: past, present, and future

    PubMed Central

    Chen, Lieping; Han, Xue

    2015-01-01

    Major progress has been made toward our understanding of the programmed death-1/programmed death ligand-1 (PD-1/PD-L1) pathway (referred to as the PD pathway). mAbs are already being used to block the PD pathway to treat human cancers (anti-PD therapy), especially advanced solid tumors. This therapy is based on principles that were discovered through basic research more than a decade ago, but the great potential of this pathway to treat a broad spectrum of advanced human cancers is just now becoming apparent. In this Review, we will briefly review the history and development of anti-PD therapy, from the original benchwork to the most up-to-date clinical results. We will then focus the discussion on three basic principles that define this unique therapeutic approach and highlight how anti-PD therapy is distinct from other immunotherapeutic approaches, namely tumor site immune modulation, targeting tumor-induced immune defects, and repairing ongoing (rather than generating de novo) tumor immunity. We believe that these fundamental principles set the standard for future immunotherapies and will guide our efforts to develop more efficacious and less toxic immune therapeutics to treat human cancers. PMID:26325035

  9. Evolution of quasiparticle excitations with enhanced electron correlations in superconducting A Fe2As2 (A =K , Rb, and Cs)

    NASA Astrophysics Data System (ADS)

    Mizukami, Y.; Kawamoto, Y.; Shimoyama, Y.; Kurata, S.; Ikeda, H.; Wolf, T.; Zocco, D. A.; Grube, K.; Löhneysen, H. v.; Matsuda, Y.; Shibauchi, T.

    2016-07-01

    In the heavily hole-doped iron-based superconductors A Fe2As2 (A =K , Rb, and Cs), the electron effective mass increases rapidly with alkali-ion radius. To study the superconducting gap structure in this series, we measure the in-plane London penetration depth λa b(T ) in clean crystals of A Fe2As2 down to low temperature T ˜0.1 K. In KFe2As2 , the superfluid stiffness ρsa b(T ) =λab 2(0 ) /λab 2(T ) at low temperatures can be accounted for by the strongly band-dependent multiple gaps reported recently. Although the λa b(T ) in all systems exhibits similar nonexponential temperature dependence indicating nodes or small minima in the gap, we find that the quasiparticle excitations at low temperatures show a systematic suppression with increasing alkali-ion radius. A possible origin of such evolution of low-energy excitations is discussed in terms of the momentum-dependent effect of enhanced quasiparticle mass near a quantum critical point.

  10. Q-balls of quasi-particles in a (2, 0)-theory model of the fractional quantum Hall effect

    NASA Astrophysics Data System (ADS)

    Ganor, Ori J.; Hong, Yoon Pyo; Moore, Nathan; Sun, Hao-Yu; Tan, Hai Siong; Torres-Chicon, Nesty R.

    2015-09-01

    A toy model of the fractional quantum Hall effect appears as part of the low-energy description of the Coulomb branch of the A 1 (2 , 0)-theory formulated on ({S}^1× {{R}}^2)/{{Z}}_k , where the generator of {{Z}}_k acts as a combination of translation on S 1 and rotation by 2 π/k on {{R}}^2 . At low energy the configuration is described in terms of a 4+1D Super-Yang-Mills theory on a cone ({{R}}^2/{{Z}}_k) with additional 2+1D degrees of freedom at the tip of the cone that include fractionally charged particles. These fractionally charged "quasi-particles" are BPS strings of the (2 , 0)-theory wrapped on short cycles. We analyze the large k limit, where a smooth cigar-geometry provides an alternative description. In this framework a W-boson can be modeled as a bound state of k quasi-particles. The W-boson becomes a Q-ball, and it can be described as a soliton solution of Bogomolnyi monopole equations on a certain auxiliary curved space. We show that axisymmetric solutions of these equations correspond to singular maps from AdS 3 to AdS 2, and we present some numerical results and an asymptotic expansion.

  11. Ab initio calculations of quasiparticle energies of solids, liquids and molecules using a spectral decomposition of the dielectric matrix

    NASA Astrophysics Data System (ADS)

    Pham, Tuan Anh; Nguyen, Huy-Viet; Rocca, Dario; Galli, Giulia

    2013-03-01

    We recently developed a method for the calculation of quasiparticle energies within many body perturbation theory, at the GW level, which avoids costly summations over empty electronic states and does not require the use of plasmon-pole models. We present a comprehensive validation of this method, encompassing calculations of i) the vertical ionization energies of a set of over 80 molecules (containing from 14 to 424 valence electrons); ii) the relative position of energy levels of anions and water in hydrated sulfate and chloride clusters; iii) the band structure of a variety of semiconductors and (iv) the electronic properties of amorphous and liquid systems. The efficiency of our approach allowed us to compute quasiparticle energies of multiple configurations of liquid water, using samples with 64 molecules, selected over trajectories generated by ab initio molecular dynamics simulations. Work supported by DOE-BES Grant DE-FG02-06ER46262. Work at LLNL was performed under Contract DE-AC52-07NA27344.

  12. Pseudogap formation and unusual quasiparticle tunneling in cuprate superconductors: Polaronic and multiple-gap effects on the tunneling spectra

    NASA Astrophysics Data System (ADS)

    Dzhumanov, S.; Ganiev, O. K.; Djumanov, Sh. S.

    2013-10-01

    We propose new simple and generalized multiple-gap models of quasiparticle tunneling across the high-Tc cuprate superconductor (HTSC)/insulator/normal metal (SIN) junction based on the two different mechanisms for tunneling at positive and negative bias voltages, and the gap inhomogeneity (i.e., multiple-gap) picture. The tunneling of electrons from the normal metal into the quasiparticle states in HTSC with the BCS-type density of states (DOSs) takes place at V>0, while the tunneling of Cooper pairs and large polarons from the HTSC with the BCS DOS and quasi-free state DOS (which appears only in the dissociation of polarons) into the normal metal occurs at V<0. We show that most of the unusual features of tunneling spectra such as nearly U- and V-shaped subgap features, peak-dip-hump structure (appearing systematically at V<0) and asymmetry of the conductance peaks and their temperature and doping dependences, and shoulder-like features inside the main conductance peaks arise naturally in our specific models of SIN tunneling. The experimental tunneling spectra of Bi2Sr2CaCu2O8+δ are adequately reproduced by using the specific multiple-gap models and taking into account the distribution of BCS and polaronic gap values.

  13. Superperiods in Interference of eÕ3 Laughlin Quasiparticles Encircling Filling 2/5 FractionalQuantum Hall Island

    SciTech Connect

    Lin, P.V.; Camino, F.; Goldman, V.J.

    2009-12-01

    We report experiments in a large, 2.5 {mu}m diameter Fabry-Perot quantum Hall interferometer with two tunneling constrictions. Interference fringes are observed as conductance oscillations as a function of applied magnetic field (the Aharonov-Bohm flux through the electron island) or a global backgate voltage (electronic charge in the island). Depletion is such that in the fractional quantum Hall regime, filling 1/3 current-carrying chiral edge channels pass through constrictions when the island filling is 2/5. The interferometer device is calibrated with fermionic electrons in the integer quantum Hall regime. In the fractional regime, we observe magnetic flux and charge periods 5h/e and 2e, respectively, corresponding to creation of ten e/5 Laughlin quasiparticles in the island. These results agree with our prior report of the superperiods in a much smaller interferometer device. The observed experimental periods are interpreted as imposed by anyonic statistical interaction of fractionally charged quasiparticles.

  14. Dynamics of quasiparticles and antiferromagnetic correlations in electron-doped cuprate La2-xCexCuO4+/-δ (LCCO)

    NASA Astrophysics Data System (ADS)

    Vishik, I. M.; Mahmood, F.; Alpichshev, Z.; Higgins, J. S.; Greene, R. L.; Gedik, N.

    We studied quasiparticle dynamics in thin films of the electron-doped cuprate La2-xCexCuO4 (LCCO) via optical pump-probe spectroscopy. In underdoped LCCO, the quasiparticle recombination dynamics imply a nodeless superconducting gap, which can be realized with dx2-y2 symmetry if a nodal hole-pocket is absent. Meanwhile, optimally doped LCCO shows recombination dynamics consistent with line nodes. Above Tc, fluence-dependent dynamics indicate a fully-formed gap in the density of states, which is associated with antiferromagnetic correlations, and limits can be placed on the correlation length and time.

  15. Behavior of quasi-particles on hybrid spaces. Relations to the geometry of geodesics and to the problems of analytic number theory

    NASA Astrophysics Data System (ADS)

    Chernyshev, Vsevolod L.; Tolchennikov, Anton A.; Shafarevich, Andrei I.

    2016-09-01

    We review our recent results concerning the propagation of "quasi-particles" in hybrid spaces — topological spaces obtained from graphs via replacing their vertices by Riemannian manifolds. Although the problem is purely classical, it is initiated by the quantum one, namely, by the Cauchy problem for the time-dependent Schrödinger equation with localized initial data.We describe connections between the behavior of quasi-particles with the properties of the corresponding geodesic flows. We also describe connections of our problem with various problems in analytic number theory.

  16. The role of engineered materials in superconducting tunnel junction X-ray detectors - Suppression of quasiparticle recombination losses via a phononic band gap

    NASA Technical Reports Server (NTRS)

    Rippert, Edward D.; Ketterson, John B.; Chen, Jun; Song, Shenian; Lomatch, Susanne; Maglic, Stevan R.; Thomas, Christopher; Cheida, M. A.; Ulmer, Melville P.

    1992-01-01

    An engineered structure is proposed that can alleviate quasi-particle recombination losses via the existence of a phononic band gap that overlaps the 2-Delta energy of phonons produced during recombination of quasi-particles. Attention is given to a 1D Kronig-Penny model for phonons normally incident to the layers of a multilayered superconducting tunnel junction as an idealized example. A device with a high density of Bragg resonances is identified as desirable; both Nb/Si and NbN/SiN superlattices have been produced, with the latter having generally superior performance.

  17. The clinical utility of PD-L1 testing in selecting non-small cell lung cancer patients for PD1/PD-L1-directed therapy.

    PubMed

    Villaruz, L C; Socinski, M A

    2016-09-01

    Lung cancer is the leading cause of cancer mortality in the United States and worldwide. Long thought to be nonimmunogenic, immunotherapy in lung cancer has historically been met with disappointing results. Programmed death-1 (PD-1), and the PD-1 ligand, PD-L1, are immune checkpoint proteins that fine-tune the antigen-specific T-cell response after stimulation of the T-cell receptor and are crucial for self-tolerance. This pathway in particular is co-opted by tumors through expression of PD-L1 on the tumor cell surface and within the tumor microenvironment, allowing for direct suppression of antitumor cytolytic T-cell activity by the tumor. Indeed, induction of the PD1/PD-L1 pathway represents an adaptive immune resistance mechanism exerted by tumor cells in response to endogenous antitumor activity. In 2015, the US Food and Drug Administration (FDA) approved two immuno-oncology agents, the PD-1 inhibitors nivolumab and pembrolizumab, for the treatment of previously treated advanced non-small cell lung cancer (NSCLC). Coincident with the clinical trials that led to these regulatory approvals has been the development of several immunohistochemistry (IHC) tests of PD-L1 expression, which may serve to select patients who will derive the most benefit from PD1- or PD-L1-directed therapy. The PD-L1 IHC assays are distinct in their methods and interpretation, which poses a challenge to clinicians selecting patients for these therapies.

  18. A Randomized Controlled Trial of Professional Development for Interdisciplinary Civic Education: Impacts on Humanities Teachers and Their Students

    ERIC Educational Resources Information Center

    Barr, Dennis J.; Boulay, Beth; Selman, Robert L.; McCormick, Rachel; Lowenstein, Ethan; Gamse, Beth; Fine, Melinda; Leonard, M. Brielle

    2015-01-01

    Background/Context: Billions of dollars are spent annually on professional development (PD) for educators, yet few randomized controlled trials (RCT) have demonstrated the ultimate impact PD has on student learning. Further, while policymakers and others speak to the role schools should play in developing students' civic awareness, RCTs of PD…

  19. 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

  20. 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

  1. 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.

  2. Random Vibrations

    NASA Technical Reports Server (NTRS)

    Messaro. Semma; Harrison, Phillip

    2010-01-01

    Ares I Zonal Random vibration environments due to acoustic impingement and combustion processes are develop for liftoff, ascent and reentry. Random Vibration test criteria for Ares I Upper Stage pyrotechnic components are developed by enveloping the applicable zonal environments where each component is located. Random vibration tests will be conducted to assure that these components will survive and function appropriately after exposure to the expected vibration environments. Methodology: Random Vibration test criteria for Ares I Upper Stage pyrotechnic components were desired that would envelope all the applicable environments where each component was located. Applicable Ares I Vehicle drawings and design information needed to be assessed to determine the location(s) for each component on the Ares I Upper Stage. Design and test criteria needed to be developed by plotting and enveloping the applicable environments using Microsoft Excel Spreadsheet Software and documenting them in a report Using Microsoft Word Processing Software. Conclusion: Random vibration liftoff, ascent, and green run design & test criteria for the Upper Stage Pyrotechnic Components were developed by using Microsoft Excel to envelope zonal environments applicable to each component. Results were transferred from Excel into a report using Microsoft Word. After the report is reviewed and edited by my mentor it will be submitted for publication as an attachment to a memorandum. Pyrotechnic component designers will extract criteria from my report for incorporation into the design and test specifications for components. Eventually the hardware will be tested to the environments I developed to assure that the components will survive and function appropriately after exposure to the expected vibration environments.

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

    MedlinePlus

    ... are high-risk areas for the infectious disease malaria . Researchers have found evidence that the parasite that ... deficiency may have developed as a protection against malaria. continue G6PD Deficiency Symptom Triggers Kids with G6PD ...

  4. Structure of quenched alloys of the Ti-Pd system

    NASA Astrophysics Data System (ADS)

    Dobromyslov, A. V.; Taluts, N. I.

    2016-07-01

    The quenched alloys of the Ti-Pd system containing 2-15 at % Pd have been studied using X-ray diffraction analysis, optical metallography, transmission electron microscopy, and measurements of the microhardness. It has been found that, in the course of quenching, epy alloys containing 2, 3, and 5 at % Pd undergo a eutectoid decomposition into the α phase and Ti2Pd intermetallic compound, and the Ti-7 at % Pd and Ti-9 at % Pd alloys undergo a β → α' martensitic transformation. In the alloys with Pd contents of more than 9 at %, the β phase is fixed in the metastable state. The complete stabilization of the β phase takes place in the alloys containing 11 at % Pd and more. It has been found that the formation of the orthorhombic α" phase and metastable ω phase in the quenched alloys of this system does not occur.

  5. How Does Your Doctor Make a PD Diagnosis?

    MedlinePlus

    ... More > Español In Your Area NPF Shop How Does Your Doctor Make a PD Diagnosis Make Text ... and possible falls, also called postural instability How does your doctor make a PD diagnosis? The bedside ...

  6. Elevated Cellular PD1/PD-L1 Expression Confers Acquired Resistance to Cisplatin in Small Cell Lung Cancer Cells.

    PubMed

    Yan, Fei; Pang, Jiuxia; Peng, Yong; Molina, Julian R; Yang, Ping; Liu, Shujun

    2016-01-01

    Although small cell lung cancer (SCLC) is highly responsive to chemotherapies (e.g., cisplatin-etoposide doublet), virtually almost all responsive SCLC patients experience disease recurrence characterized by drug resistance. The mechanisms underlying cisplatin resistance remain elusive. Here we report that cell-intrinsic expression of PD1 and PD-L1, two immune checkpoints, is required for sustained expansion of SCLC cells under cisplatin selection. Indeed, PD1 and PD-L1 were expressed at a higher level in lung cancer cell lines, tumor tissues, and importantly, in SCLC cells resistant to cisplatin (H69R, H82R), when compared to respective controls. Genetic abrogation of PD1 and PD-L1 in H69R and H82R cells decreased their proliferation rate, and restored their sensitivity to cisplatin. Mechanistically, PD-L1 upregulation in H69R and H82R cells was attributed to the overexpression of DNA methyltransferase 1 (DNMT1) or receptor tyrosine kinase KIT, as knockdown of DNMT1 or KIT in H69R and H82R cells led to PD-L1 downregulation. Consequently, combined knockdown of PD-L1 with KIT or DNMT1 resulted in more pronounced inhibition of H69R and H82R cell growth. Thus, cell intrinsic PD1/PD-L1 signaling may be a predictor for poor efficacy of cisplatin treatment, and targeting the cellular PD1/PD-L1 axis may improve chemosensitization of aggressive SCLC.

  7. Pd-Co dental casting ferromagnetic alloys.

    PubMed

    Kinouchi, Y; Ushita, T; Tsutsui, H; Yoshida, Y; Sasaki, H; Miyazaki, T

    1981-01-01

    Three kinds of Pd-Co alloys have been newly developed. Their magnetic and physical properties and corrosion resistances have been examined. As a result, it was found that they are available as the dental casting ferromagnetic alloy which can be used in combination with Sm-Co magnets, overcoming such problems as non-castability and brittleness.

  8. High Magnetization FeCo/Pd multilayers

    NASA Astrophysics Data System (ADS)

    Walock, Michael; Klose, Frank; Chshiev, Mairbek; Mankey, Gary; Butler, William

    2007-03-01

    A high saturation magnetization is advantageous in magnetic recording. Currently, the peak of the Slater-Pauling curve is the BCC FeCo system with a saturation magnetization of 2.45 T. Recently, a magnetization of 2.57 T in the FeCo layers of a [40 nm Fe30Co70 /1.7 nm Pd]x25 superlattice has been reported [1, 2]. This behavior may be attributed to an enhanced Fe moment in the expanded FCC matrix, and an accompanying induced moment in the Pd. Our theoretical calculations show an atomic moment enhancement, but this is not great enough to overcome the overall magnetization density reduction caused by the incorporation of Pd in the matrix. The overall effect is a reduced magnetization. Through variation of the FeCo composition and Pd layer thickness, and the combinatorial methods of structural and magnetic characterization, we will gain insight into the magnetic structure of this tertiary thin film system. [1] K. Noma, M. Matsuoka, H. Kanai, Y. Uehara, K. Nomura, and N. Awaji. IEEE Trans. Magn. 42, 140 (2006). [2] ibid. 41, 2920 (2005).

  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. 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. Expression of PD-1, PD-L1 and PD-L2 is associated with differentiation status and histological type of endometrial cancer

    PubMed Central

    Mo, Zhongfu; Liu, Jing; Zhang, Qiuyang; Chen, Zhiquan; Mei, Jiandong; Liu, Lunxu; Yang, Shijie; Li, Huina; Zhou, Lifei; You, Zongbing

    2016-01-01

    Endometrial cancer (EC) is the most frequent gynecological malignancy and a major cause of morbidity and mortality for women worldwide. Programmed cell death protein 1 (PD-1) and its ligands programmed death ligand 1 (PD-L1) and programmed death ligand 2 (PD-L2) have been well studied in lung cancer, melanoma and renal-cell cancer. However, few studies have been performed in EC. The purpose of the present study was to assess the expression of PD-1, PD-L1 and PD-L2 in 35 human normal endometrial tissue samples and 75 human EC tissue samples using immunohistochemical staining. It was found that 61.3% of ECs were positive for PD-1 staining, which was almost exclusively found in the tumor-infiltrating immune cells. By contrast, PD-1 was not expressed in the tumor cells or normal endometrial tissues. It was also found that 14.3% of normal endometria and 17.3% of EC tissues were positive for PD-L1 expression, while 20.0% of normal endometrium and 37.3% of EC tissues were positive for PD-L2 expression; however, there was no statistically significant difference between the normal endometrium and EC tissues. PD-1 expression in the tumor-infiltrating immune cells was more frequently found in the moderately and poorly-differentiated ECs and non-endometrioid (type II) ECs than in the well-differentiated ECs and endometrioid (type I) ECs. Similarly, PD-L1 and PD-L2 expression in the tumor-infiltrating immune cells was more frequently found in the moderately and poorly-differentiated ECs and type II ECs than in the type I ECs. The present findings indicate a possible better outcome for future treatment with anti-PD-1 or anti-PD-L1 antibody-based therapies against these subgroups of endometrial cancers with frequent expression of the PD-1/PD-L1/PD-L2 axis. PMID:27446374

  12. The Pd2Si - /Pd/ - Ni - solder plated metallization system for silicon solar cells

    NASA Technical Reports Server (NTRS)

    Coleman, M. G.; Pryor, R. A.; Sparks, T. G.

    1978-01-01

    The rationale and application of a plated metal system, Pd2Si Pd - Ni - solder, is presented. This metallization system is particularly useful on shallow p-n junction solar cells. The advantages of such plated solar cell contacts are discussed. A process sequence for applying the metallization system is outlined. A specific example is presented, including chemical plating solution formulations and detailed process step descriptions. Electrical test data for solar cells metallized with the palladium-nickel-solder system are provided.

  13. Perpendicular magnetic tunnel junction with thin CoFeB/Ta/Co/Pd/Co reference layer

    SciTech Connect

    Gan, Huadong Malmhall, Roger; Wang, Zihui; Yen, Bing K; Zhang, Jing; Wang, Xiaobin; Zhou, Yuchen; Hao, Xiaojie; Jung, Dongha; Satoh, Kimihiro; Huai, Yiming

    2014-11-10

    Integration of high density spin transfer torque magnetoresistance random access memory requires a thin stack (less than 15 nm) of perpendicular magnetic tunnel junction (p-MTJ). We propose an innovative approach to solve this challenging problem by reducing the thickness and/or moment of the reference layer. A thin reference layer structure of CoFeB/Ta/Co/Pd/Co has 60% magnetic moment of the conventional thick structure including [Co/Pd] multilayers. We demonstrate that the perpendicular magnetization of the CoFeB/Ta/Co/Pd/Co structure can be realized by anti-ferromagnetically coupling to a pinned layer with strong perpendicular anisotropy via Ruderman-Kittel-Kasuya-Yosida exchange interaction. The pMTJ with thin CoFeB/Ta/Co/Pd/Co reference layer has a comparable TMR ratio (near 80%) as that with thick reference layer after annealing at 280 °C. The pMTJ with thin reference layer has a total thickness less than 15 nm, thereby significantly increasing the etching margin required for integration of high density pMTJ array on wafers with form factor of 300 mm and beyond.

  14. 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.

  15. The anticancer immune response of anti-PD-1/PD-L1 and the genetic determinants of response to anti-PD-1/PD-L1 antibodies in cancer patients.

    PubMed

    Sui, Xinbing; Ma, Junhong; Han, Weidong; Wang, Xian; Fang, Yong; Li, Da; Pan, Hongming; Zhang, Li

    2015-08-14

    The programmed death-1 (PD-1), a coinhibitory receptor expressed on activated T cells and B cells, is demonstrated to induce an immune-mediated response and play a critical role in tumor initiation and development. The cancer patients harboring PD-1 or PD ligand 1 (PD-L1) protein expression have often a poor prognosis and clinical outcome. Currently, targeting PD-1 pathway as a potential new anticancer strategy is attracting more and more attention in cancer treatment. Several monoclonal antibodies against PD-1 or PD-L1 have been reported to enhance anticancer immune responses and induce tumor cell death. Nonetheless, the precise molecular mechanisms by which PD-1 affects various cancers remain elusive. Moreover, this therapy is not effective for all the cancer patients and only a fraction of patients respond to the antibodies targeting PD-1 or PD-L1, indicating these antibodies may only works in a subset of certain cancers. Thus, understanding the novel function of PD-1 and genetic determinants of response to anti-PD-1 therapy will allow us to develop a more effective and individualized immunotherapeutic strategy for cancer.

  16. Development of Pd and Pd-Co catalysts supported on multi-walled carbon nanotubes for formic acid oxidation

    NASA Astrophysics Data System (ADS)

    Morales-Acosta, D.; Ledesma-Garcia, J.; Godinez, Luis A.; Rodríguez, H. G.; Álvarez-Contreras, L.; Arriaga, L. G.

    Pd-Co and Pd catalysts were prepared by the impregnation synthesis method at low temperature on multi-walled carbon nanotubes (MWCNTs). The nanotubes were synthesized by spray pyrolysis technique. Both catalysts were obtained with high homogeneous distribution and particle size around 4 nm. The morphology, composition and electrocatalytic properties were investigated by transmission electron microscopy, scanning electron microscopy-energy dispersive X-ray analysis, X-ray diffraction and electrochemical measurements, respectively. The electrocatalytic activity of Pd and PdCo/MWCNTs catalysts was investigated in terms of formic acid electrooxidation at low concentration in H 2SO 4 aqueous solution. The results obtained from voltamperometric studies showed that the current density achieved with the PdCo/MWCNTs catalyst is 3 times higher than that reached with the Pd/MWCNTs catalyst. The onset potential for formic acid electrooxidation on PdCo/MWCNTs electrocatalyst showed a negative shift ca. 50 mV compared with Pd/MWCNTs.

  17. 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.

  18. 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.

  19. Pd surface and Pt subsurface segregation in Pt1-c Pd c nanoalloys.

    PubMed

    De Clercq, A; Giorgio, S; Mottet, C

    2016-02-17

    The structure and chemical arrangement of Pt1-c Pd c nanoalloys with the icosahedral and face centered cubic symmetry are studied using Monte Carlo simulations with a tight binding interatomic potential fitted to density-functional theory calculations. Pd surface segregation from the lowest to the highest coordinated sites is predicted by the theory together with a Pt enrichment at the subsurface, whatever the structure and the size of the nanoparticles, and which subsists when increasing the temperature. The onion-shell chemical configuration is found for both symmetries and is initiated from the Pd surface segregation. It is amplified in the icosahedral symmetry and small sizes but when considering larger sizes, the oscillating segregation profile occurs near the surface on about three to four shells whatever the structure. Pd segregation results from the significant lower cohesive energy of Pd as compared to Pt and the weak ordering tendency leads to the Pt subsurface segregation. The very weak size mismatch does not prevent the bigger atoms (Pt) from occupying subsurface sites which are in compression whereas the smaller ones (Pd) occupy the central site of the icosahedra where the compression is an order of magnitude higher. PMID:26795206

  20. Fractional randomness

    NASA Astrophysics Data System (ADS)

    Tapiero, Charles S.; Vallois, Pierre

    2016-11-01

    The premise of this paper is that a fractional probability distribution is based on fractional operators and the fractional (Hurst) index used that alters the classical setting of random variables. For example, a random variable defined by its density function might not have a fractional density function defined in its conventional sense. Practically, it implies that a distribution's granularity defined by a fractional kernel may have properties that differ due to the fractional index used and the fractional calculus applied to define it. The purpose of this paper is to consider an application of fractional calculus to define the fractional density function of a random variable. In addition, we provide and prove a number of results, defining the functional forms of these distributions as well as their existence. In particular, we define fractional probability distributions for increasing and decreasing functions that are right continuous. Examples are used to motivate the usefulness of a statistical approach to fractional calculus and its application to economic and financial problems. In conclusion, this paper is a preliminary attempt to construct statistical fractional models. Due to the breadth and the extent of such problems, this paper may be considered as an initial attempt to do so.

  1. Neutron one-quasiparticle states in {sup 251}Fm{sub 151} populated via the {alpha} decay of {sup 255}No

    SciTech Connect

    Asai, M.; Tsukada, K.; Ishii, Y.; Toyoshima, A.; Ishii, T.; Nagame, Y.; Nishinaka, I.; Haba, H.; Ichikawa, T.; Kojima, Y.; Sueki, K.

    2011-01-15

    Excited states in {sup 251}Fm populated via the {alpha} decay of {sup 255}No are studied in detail through {alpha}-{gamma} coincidence and {alpha} fine-structure measurements. Five excited states reported previously in {sup 251}Fm are firmly established through the {alpha}-{gamma} coincidence measurement, and rotational bands built on one-quasiparticle states are newly established through the {alpha} fine-structure measurement. Spin-parities and neutron configurations of the excited states in {sup 251}Fm as well as the ground state of {sup 255}No are definitely identified on the basis of deduced internal conversion coefficients, lifetimes of {gamma} transitions, rotational-band energies built on one-quasiparticle states, and hindrance factors of {alpha} transitions. It is found that the excitation energy of the 1/2{sup +}[620] state in N=151 isotones increases with the atomic number, especially at Z{>=}100, while that of the 1/2{sup +}[631] state decreases at Z=100. Ground-state deformations and energies of neutron one-quasiparticle states in the N=151 isotones are calculated using a macroscopic-microscopic model, and the energy systematics of the one-quasiparticle states in the isotones are discussed in terms of the evolution of nuclear deformation involving the hexadecapole ({beta}{sub 4}) and hexacontatetrapole ({beta}{sub 6}) deformations.

  2. Characterization of the active site structure of Pd and Pd-promoted Mo sulfide catalysts by means of XAFS.

    PubMed

    Kubota, T; Okamoto, Y

    2001-03-01

    Recently, noble metal catalysts are noted as promising candidates for new super-deep-hydrodesulfurization (HDS) catalysts. In this study, we investigated the structure of Pd particles supported on zeolite and Al2O3 under a sulfidation or reduction condition. From EXAFS analysis, it was found for sulfided Pd catalysts that small Pd sulfide clusters are formed without sintering. It was also revealed that no extensive growth of metal Pd particles occurs in Pd/NaY sulfide catalysts even after a treatment with H2 at 673 K. The dispersion of Pd metal particles is improved by H2/H2S treatment. These results indicate that in the presence of H2S, Pd shows high resistance against particle growth. A comparison of the Mo and Pd K-edge EXAFS spectra for MoS(x)/Pd-NaY and Pd-NaY catalysts revealed the existence of Mo-Pd bondings by the addition of Mo sulfide, indicating a direct interaction between Mo and Pd sulfides.

  3. Enhanced Rates of Hydrogen Absorption Resulting from Oxidation of Pd and Internal Oxidation of Pd-Al Alloys

    SciTech Connect

    Shanahan, K.L.

    1999-08-20

    The goal of this research was the determination of the relative rates before and after internal oxidation of Pd--Al alloys and oxidation (Pd) and this is independent of whether heat transfer is the rate-limiting step for the internally oxidized Pd--Al alloys rather than a more fundamental step.

  4. Differential Activity of Nivolumab, Pembrolizumab and MPDL3280A according to the Tumor Expression of Programmed Death-Ligand-1 (PD-L1): Sensitivity Analysis of Trials in Melanoma, Lung and Genitourinary Cancers

    PubMed Central

    Carbognin, Luisa; Pilotto, Sara; Milella, Michele; Vaccaro, Vanja; Brunelli, Matteo; Caliò, Anna; Cuppone, Federica; Sperduti, Isabella; Giannarelli, Diana; Chilosi, Marco; Bronte, Vincenzo; Scarpa, Aldo

    2015-01-01

    Background The potential predictive role of programmed death-ligand-1 (PD-L1) expression on tumor cells in the context of solid tumor treated with checkpoint inhibitors targeting the PD-1 pathway represents an issue for clinical research. Methods Overall response rate (ORR) was extracted from phase I-III trials investigating nivolumab, pembrolizumab and MPDL3280A for advanced melanoma, non-small cell lung cancer (NSCLC) and genitourinary cancer, and cumulated by adopting a fixed and random-effect model with 95% confidence interval (CI). Interaction test according to tumor PD-L1 was accomplished. A sensitivity analysis according to adopted drug, tumor type, PD-L1 cut-off and treatment line was performed. Results Twenty trials (1,475 patients) were identified. A significant interaction (p<0.0001) according to tumor PD-L1 expression was found in the overall sample with an ORR of 34.1% (95% CI 27.6-41.3%) in the PD-L1 positive and 19.9% (95% CI 15.4-25.3%) in the PD-L1 negative population. ORR was significantly higher in PD-L1 positive in comparison to PD-L1 negative patients for nivolumab and pembrolizumab, with an absolute difference of 16.4% and 19.5%, respectively. A significant difference in activity of 22.8% and 8.7% according to PD-L1 was found for melanoma and NSCLC, respectively, with no significant difference for genitourinary cancer. Conclusion Overall, the three antibodies provide a significant differential effect in terms of activity according to PD-L1 expression on tumor cells. The predictive value of PD-L1 on tumor cells seems to be more robust for anti-PD-1 antibody (nivolumab and pembrolizumab), and in the context of advanced melanoma and NSCLC. PMID:26086854

  5. 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

  6. Tridentate assembling ligands based on oxazoline and phosphorus donors in dinuclear Pd(I)-Pd(I) complexes.

    PubMed

    Zhang, Jing; Pattacini, Roberto; Braunstein, Pierre

    2009-12-21

    To examine the bonding preferences of potentially tridentate phosphorus, nitrogen donor ligands on a dinuclear metal core, we have studied the coordination of the oxazoline-based ligands bis(4,5-dihydro-2-oxazolylmethyl)phenylphosphine (NPN) and bis(4,4-dimethyl-2-oxazolyl dimethylmethoxy)phenylphosphine (NOPON(Me2)) toward the dinuclear d(9)-d(9) Pd(I) complex [Pd(2)(NCMe)(6)][BF(4)](2). In the dinuclear product [Pd(2)(NPN-N,P,N)(2)](BF(4))(2) (1), in which the Pd-Pd bond length of 2.5489(7) A is rather short, the two interacting metal centers are P,N bridged by two molecules of the NPN ligand, forming two six-membered rings. The other oxazoline ring of each ligand further chelates a Pd center through its nitrogen atom, forming five-membered chelates, as in the mononuclear complex [PdCl(2)(NPN-N,P)] (5). In contrast, the reaction between [Pd(2)(NCMe)(6)](BF(4))(2) and NOPON(Me2) in the presence of LiCl afforded the mononuclear cationic complex [Pd(NOPON(Me2)-N,P,N)Cl](BF(4)) (3), which is also obtained by halide abstraction from [Pd(NOPON(Me2)-N,P)Cl(2)] with NaBF(4). When this reaction was performed in the presence of 1 equiv of t-BuNC, the new dinuclear Pd(I)-Pd(I) complex [Pd(2)Cl(2)(CNt-Bu)(NOPON(Me2)-N,P,N)] (4) was isolated, which can also be obtained from a comproportionation reaction between Pd(II) and Pd(0) complexes. The oxazoline in the P,N bridge is involved in a seven-membered ring moiety, a situation rarely encountered in Pd(I)-Pd(I) chemistry. Its nitrogen atom is coordinated trans to the isonitrile ligand whereas that of the P,N chelate at Pd(1) is trans to Pd(2). The fluxional processes involving the oxazoline moieties of the NPN and NOPON(Me2) ligands in 1 and 4, respectively, were examined by variable-temperature NMR spectroscopy. The crystal structures of 1, 3.0.5CH(3)CN, and 4 have been determined by X-ray diffraction. Prior to this work, relatively few complexes have been reported in the literature in which a potentially tridentate functional

  7. 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.

  8. Unadulterated spectral function of low-energy quasiparticles in Bi2Sr2CaCu2O8+δ

    NASA Astrophysics Data System (ADS)

    Evtushinsky, D. V.; Kordyuk, A. A.; Borisenko, S. V.; Zabolotnyy, V. B.; Knupfer, M.; Fink, J.; Büchner, B.; Pan, A. V.; Erb, A.; Lin, C. T.; Berger, H.

    2006-11-01

    Fitting the momentum distribution photoemission spectra to the Voigt profile appears to be a robust procedure to purify the interaction effects from the experimental resolution. In application to Bi2Sr2CaCu2O8+δ high- Tc cuprates, the procedure reveals the true scattering rate at low binding energies and temperatures, and consequently, the true value of the elastic scattering. Reaching the minimal value ˜16meV , the elastic scattering does not reveal a systematic dependence on doping level, but is rather sensitive to impurity concentration and can be explained by the forward scattering on out-of-plane impurities. The inelastic scattering is found to form well-defined quasiparticles with the scattering rate ˜ω2 and ˜ω3 , above and below Tc , respectively.

  9. Description of quasiparticle and satellite properties via cumulant expansions of the retarded one-particle Green's function

    NASA Astrophysics Data System (ADS)

    Mayers, Matthew Z.; Hybertsen, Mark S.; Reichman, David R.

    2016-08-01

    A cumulant-based G W approximation for the retarded one-particle Green's function is proposed, motivated by an exact relation between the improper Dyson self-energy and the cumulant generating function. Qualitative aspects of this method are explored within a simple one-electron independent phonon model, where it is seen that the method preserves the energy moment of the spectral weight while also reproducing the exact Green's function in the weak-coupling limit. For the three-dimensional electron gas, this method predicts multiple satellites at the bottom of the band, albeit with inaccurate peak spacing. However, its quasiparticle properties and correlation energies are more accurate than both previous cumulant methods and standard G0W0 . Our results point to features that may be exploited within the framework of cumulant-based methods and suggest promising directions for future exploration and improvements of cumulant-based G W approaches.

  10. Quasi-particle band structure of potassium-doped few-layer black phosphorus with GW approximation

    NASA Astrophysics Data System (ADS)

    Kim, Han-Gyu; Baik, Seung Su; Choi, Hyoung Joon

    We calculate the quasi-particle band structure of pristine and potassium-doped black phosphorus (BP) by using the GW approximation. We obtain band gaps of pristine bulk and few-layer BP and compare them with the result of the density functional calculations and experimental measurements. For potassium-doped cases, we calculate the electronic band structure of potassium-doped few-layer BPs with various doping densities. We obtain the critical doping density for the band-gap closing, and the energy-band dispersions when the band gap is inverted. We discuss Dirac semimetal properties of doped few-layer BPs obtained by the GW approximation. This work was supported by NRF of Korea (Grant No. 2011-0018306) and KISTI supercomputing center (Project No. KSC-2015-C3-039).

  11. Ultrafast dynamics of quasiparticles and coherent acoustic phonons in slightly underdoped (BaK)Fe2As2

    PubMed Central

    Lin, Kung-Hsuan; Wang, Kuan-Jen; Chang, Chung-Chieh; Wen, Yu-Chieh; Lv, Bing; Chu, Ching-Wu; Wu, Maw-Kuen

    2016-01-01

    We have utilized ultrafast optical spectroscopy to study carrier dynamics in slightly underdoped (BaK)Fe2As2 crystals without magnetic transition. The photoelastic signals due to coherent acoustic phonons have been quantitatively investigated. According to our temperature-dependent results, we found that the relaxation component of superconducting quasiparticles persisted from the superconducting state up to at least 70 K in the normal state. Our findings suggest that the pseudogaplike feature in the normal state is possibly the precursor of superconductivity. We also highlight that the pseudogap feature of K-doped BaFe2As2 is different from that of other iron-based superconductors, including Co-doped or P-doped BaFe2As2. PMID:27180873

  12. Improved quasiparticle wave functions and mean field for G0W0 calculations: Initialization with the COHSEX operator

    NASA Astrophysics Data System (ADS)

    Jain, Manish; Deslippe, Jack; Samsonidze, Georgy; Cohen, Marvin L.; Chelikowsky, James R.; Louie, Steven G.

    2014-09-01

    The GW approximation to the electron self-energy has become a standard method for ab initio calculation of excited-state properties of condensed-matter systems. In many calculations, the GW self-energy operator, Σ, is taken to be diagonal in the density functional theory (DFT) Kohn-Sham basis within the G0W0 scheme. However, there are known situations in which this diagonal G0W0 approximation starting from DFT is inadequate. We present two schemes to resolve such problems. The first, which we called sc -COHSEX+GW, involves construction of an improved mean field using the static limit of GW, known as COHSEX (Coulomb hole and screened exchange), which is significantly simpler to treat than GW. In this scheme, frequency-dependent self energy Σ (ω), is constructed and taken to be diagonal in the COHSEX orbitals after the system is solved self-consistently within this formalism. The second method is called off diagonal-COHSEX GW (od -COHSEX+GW). In this method, one does not self-consistently change the mean-field starting point but diagonalizes the COHSEX Hamiltonian within the Kohn-Sham basis to obtain quasiparticle wave functions and uses the resulting orbitals to construct the GW Σ in the diagonal form. We apply both methods to a molecular system, silane, and to two bulk systems, Si and Ge under pressure. For silane, both methods give good quasiparticle wave functions and energies. Both methods give good band gaps for bulk silicon and maintain good agreement with experiment. Further, the sc -COHSEX+GW method solves the qualitatively incorrect DFT mean-field starting point (having a band overlap) in bulk Ge under pressure.

  13. A direct approach to the calculation of many-body Green' s functions: quasi-particles and more

    NASA Astrophysics Data System (ADS)

    Reining, Lucia

    Many-body perturbation theory is a powerful approach to describe many properties of materials. Most often one uses Dyson equations with self-energy kernels that are approximated to low order in the interaction. In Hedin's GW approximation, for example, the self-energy is a product of the one-body Green's function and the screened Coulomb interaction. This is the state-of-the art method for bandstructure calculations in a wide range of materials. However, sometimes the GW approximation and related approaches are not sufficient, for example when one is interested in satellite structure beyond the quasi-particle peaks in the spectral function, or in the case of strong coupling, where the quasi-particle picture is no longer adequate. We explore an alternative route to the calculation of interacting electron Green's functions. It is based on a set of functional differential equations relating the one-body Green's function to its functional derivative with respect to an external perturbing potential. This set of equations can be used to generate the perturbation series. Here we will show that working directly with the differential equations yields precious insight concerning some fundamental questions, guidelines for practical calculations, and methods that lead to an improved description of spectra, in particular advanced versions of the cumulant expansion. Results will be illustrated on various levels of approximation starting from simple models, but with a focus on full ab inito calculations and comparison with, and interpretation of, experiment. In particular, we will discuss various kinds of photoemission satellites, and also address questions linked to strong correlation. This work has been carried out in collaboration with colleagues in the European Theoretical Spectroscopy Facility.

  14. PD-1 on Immature and PD-1 Ligands on Migratory Human Langerhans Cells Regulate Antigen-Presenting Cell Activity

    PubMed Central

    Peña-Cruz, Victor; McDonough, Sean M.; Diaz-Griffero, Felipe; Crum, Christopher P.; Carrasco, Ruben D.; Freeman, Gordon J.

    2010-01-01

    Langerhans cells (LCs) are known as “sentinels” of the immune system that function as professional antigen-presenting cells (APCs) after migration to draining lymph node. LCs are proposed to have a role in tolerance and the resolution of cutaneous immune responses. The Programmed Death-1 (PD-1) receptor and its ligands, PD-L1 and PD-L2, are a co-inhibitory pathway that contributes to the negative regulation of T-lymphocyte activation and peripheral tolerance. Surprisingly, we found PD-1 to be expressed on immature LCs (iLCs) in situ. PD-1 engagement on iLCs reduced IL-6 and macrophage inflammatory protein (MIP)-1α cytokine production in response to TLR2 signals but had no effect on LC maturation. PD-L1 and PD-L2 were expressed at very low levels on iLCs. Maturation of LCs upon migration from epidermis led to loss of PD-l expression and gain of high expression of PD-L1 and PD-L2 as well as co-stimulatory molecules. Blockade of PD-L1 and/or PD-L2 on migratory LCs (mLCs) and DDCs enhanced T-cell activation, as has been reported for other APCs. Thus the PD-1 pathway is active in iLCs and inhibits iLC activities, but expression of receptor and ligands reverses upon maturation and PD-L1 and PD-L2 on mLC function to inhibit T-cell responses. PMID:20445553

  15. 102Pd(n, {gamma}) Cross Section Measurement Using DANCE

    SciTech Connect

    Hatarik, R.; Alpizar-Vicente, A. M.; Bredeweg, T. A.; Esch, E.-I.; Haight, R. C.; O'Donnell, J. M.; Reifarth, R.; Rundberg, R. S.; Ullmann, J. L.; Vieira, D. J.; Wouters, J. M.; Greife, U.

    2006-03-13

    The neutron capture cross section of the proton rich nucleus 102Pd was measured with the Detector for Advanced Neutron Capture Experiments (DANCE) at the Los Alamos Neutron Science Center. The target was a 2 mg Pd foil with 78% enriched 102Pd. It was held by a 0.9 {mu}m thick Mylar bag which was selected after comparing different thicknesses of Kapton and Mylar for their scattering background. To identify the contribution of the other Pd isotopes the data of a natural Pd sample was compared to the data of the 102Pd enriched sample. A 12C sample was used to determine the scattering background. The 102Pd(n, {gamma}) rate is of importance for the p-process nucleosynthesis.

  16. Surface oxides on Pd(111): STM and density functional calculations

    NASA Astrophysics Data System (ADS)

    Klikovits, J.; Napetschnig, E.; Schmid, M.; Seriani, N.; Dubay, O.; Kresse, G.; Varga, P.

    2007-07-01

    The formation of one-layer surface oxides on Pd(111) has been studied by scanning tunneling microscopy (STM) and density functional theory (DFT). Besides the Pd5O4 structure determined previously, structural details of six different surface oxides on Pd(111) will be presented. These oxides are observed for preparation in oxygen-rich conditions, approaching the thermodynamic stability limit of the PdO bulk oxide at an oxygen chemical potential of -0.95to-1.02eV ( 570-605K , 5×10-4mbar O2 ). Sorted by increasing oxygen fraction in the primitive unit cell, the stoichiometry of the surface oxides is Pd5O4 , Pd9O8 , Pd20O18 , Pd23O21 , Pd19O18 , Pd8O8 , and Pd32O32 . All structures are one-layer oxides, in which oxygen atoms form a rectangular lattice, and all structures follow the same rules of favorable alignment of the oxide layer on the Pd(111) substrate. DFT calculations were used to simulate STM images as well as to determine the stability of the surface oxide structures. Simulated and measured STM images are in excellent agreement, indicating that the structural models are correct. Since the newly found surface oxides are clearly less stable than Pd5O4 , we conclude that Pd5O4 is the only thermodynamically stable phase, whereas all newly found structures are only kinetically stabilized. We also discuss possible mechanisms for the formation of these oxide structures.

  17. High-spin structure of 95Pd

    NASA Astrophysics Data System (ADS)

    Mărginean, R.; Rusu, C.; Mărginean, N.; Bucurescu, D.; Ur, C. A.; de Angelis, G.; Axiotis, M.; Bazzacco, D.; Farnea, E.; Gadea, A.; Ionescu-Bujor, M.; Iordăchescu, A.; Krolas, W.; Kröll, Th.; Lenzi, S. M.; Lunardi, S.; Napoli, D. R.; Alvarez, C. Rossi; Wrzesinski, J.

    2012-09-01

    The level scheme of the neutron-deficient nucleus 95Pd has been studied with the 58Ni + 40Ca fusion-evaporation reaction at 135 MeV with the GASP γ-ray array, the ISIS silicon ball, and the N-ring neutron detector. Excited levels with spins at least up to (45)/(2)ℏ are reported for both parities. The observed experimental data are compared to large-scale shell-model calculations.

  18. Emotional manifestations of PD: Neurobiological basis.

    PubMed

    Castrioto, Anna; Thobois, Stéphane; Carnicella, Sebastien; Maillet, Audrey; Krack, Paul

    2016-08-01

    Neuropsychiatric symptoms are common and disabling in PD. Their neurobiological bases are complex, partly because of the disease itself and partly because of the dopaminergic treatment. The aim of this review is to focus on the emotional manifestations stemming from the neurodegenerative process itself. We focus on depression, anxiety, apathy, and fatigue, which can all be part of the clinical spectrum of premotor disease and may be improved or masked by medications targeting parkinsonian motor signs or psychiatric symptoms as the disease progresses. Findings from clinical, neuroimaging, and animal studies are reviewed, showing a major contribution of the dopaminergic system to the pathophysiology of these disabling symptoms. Degeneration of noradrenergic and serotonergic projection systems also has an impact on psychiatric symptoms of PD. The available literature is reviewed, but at present there is a lack of studies that would allow disentangling the separate contribution of each of the monoaminergic systems. The use of a pragmatic classification of all these symptoms under the umbrella of hypodopaminergic behavioral syndrome seems clinically useful, as it emphasizes the crucial, although not exclusive, nature of their dopaminergic neurobiological basis, which has important implications in the clinical management of PD. © 2016 International Parkinson and Movement Disorder Society.

  19. Emotional manifestations of PD: Neurobiological basis.

    PubMed

    Castrioto, Anna; Thobois, Stéphane; Carnicella, Sebastien; Maillet, Audrey; Krack, Paul

    2016-08-01

    Neuropsychiatric symptoms are common and disabling in PD. Their neurobiological bases are complex, partly because of the disease itself and partly because of the dopaminergic treatment. The aim of this review is to focus on the emotional manifestations stemming from the neurodegenerative process itself. We focus on depression, anxiety, apathy, and fatigue, which can all be part of the clinical spectrum of premotor disease and may be improved or masked by medications targeting parkinsonian motor signs or psychiatric symptoms as the disease progresses. Findings from clinical, neuroimaging, and animal studies are reviewed, showing a major contribution of the dopaminergic system to the pathophysiology of these disabling symptoms. Degeneration of noradrenergic and serotonergic projection systems also has an impact on psychiatric symptoms of PD. The available literature is reviewed, but at present there is a lack of studies that would allow disentangling the separate contribution of each of the monoaminergic systems. The use of a pragmatic classification of all these symptoms under the umbrella of hypodopaminergic behavioral syndrome seems clinically useful, as it emphasizes the crucial, although not exclusive, nature of their dopaminergic neurobiological basis, which has important implications in the clinical management of PD. © 2016 International Parkinson and Movement Disorder Society. PMID:27041545

  20. [Targeting the PD-1/PD-L1 immune checkpoint signal - a new treatment strategy for cancer].

    PubMed

    Hamanishi, Junzo; Konishi, Ikuo

    2014-09-01

    Recent studies have revealed that tumor cells can acquire several mechanisms to evade host immunity in the tumor microenvironment, called cancer immune escape. One of the most important mechanisms in this system is an immunosuppressive co- signal, called immune checkpoint, in the programmed cell death-1(PD-1)/programmed death-ligand 1(PD-L1)pathway. PD-1 is mainly expressed on activated T cells, while PD-L1 is frequently expressed on tumor cells. Inhibition of the interaction between PD-1 and PD-L1 enhances T-cell response and mediates antitumor activity. Several clinical trials by several institutions and pharmaceutical companies in the world have shown the antitumor efficacy of PD-1/PD-L1 signal blockade in patients with some solid and hematological malignancies. Production of some drugs for use in anti-PD-1 therapies are on the verge of completion. Herein, we provide a background about the PD-1/PD-L1 signal and describe some previously performed foreign clinical trials, including a trial in our department.

  1. Blocking of the PD-1/PD-L1 Interaction by a D-Peptide Antagonist for Cancer Immunotherapy.

    PubMed

    Chang, Hao-Nan; Liu, Bei-Yuan; Qi, Yun-Kun; Zhou, Yang; Chen, Yan-Ping; Pan, Kai-Mai; Li, Wen-Wen; Zhou, Xiu-Man; Ma, Wei-Wei; Fu, Cai-Yun; Qi, Yuan-Ming; Liu, Lei; Gao, Yan-Feng

    2015-09-28

    Blockade of the protein-protein interaction between the transmembrane protein programmed cell death protein 1 (PD-1) and its ligand PD-L1 has emerged as a promising immunotherapy for treating cancers. Using the technology of mirror-image phage display, we developed the first hydrolysis-resistant D-peptide antagonists to target the PD-1/PD-L1 pathway. The optimized compound (D) PPA-1 could bind PD-L1 at an affinity of 0.51 μM in vitro. A blockade assay at the cellular level and tumor-bearing mice experiments indicated that (D) PPA-1 could also effectively disrupt the PD-1/PD-L1 interaction in vivo. Thus D-peptide antagonists may provide novel low-molecular-weight drug candidates for cancer immunotherapy.

  2. Is random access memory random?

    NASA Technical Reports Server (NTRS)

    Denning, P. J.

    1986-01-01

    Most software is contructed on the assumption that the programs and data are stored in random access memory (RAM). Physical limitations on the relative speeds of processor and memory elements lead to a variety of memory organizations that match processor addressing rate with memory service rate. These include interleaved and cached memory. A very high fraction of a processor's address requests can be satified from the cache without reference to the main memory. The cache requests information from main memory in blocks that can be transferred at the full memory speed. Programmers who organize algorithms for locality can realize the highest performance from these computers.

  3. DFT Study of Pd(0)-Promoted Intermolecular C-H Amination with O-Benzoyl Hydroxylamines.

    PubMed

    Zhou, Yunfei; Bao, Xiaoguang

    2016-09-16

    Computational studies were carried out to explore the mechanism of Pd-catalyzed intermolecular C-H amination with O-benzoyl hydroxylamines in which both Pd(0) and Pd(II) catalysts are effective. For the Pd(0)-catalyzed reaction, the generally assumed Pd(0)/Pd(II) catalytic cycle might not be feasible. Instead, Pd(0), being essentially a catalyst precursor, could be oxidized to Pd(II), and the C-H amination proceeds through the Pd(II)/Pd(IV) catalytic cycle. PMID:27573977

  4. Two Year Exercise Program Improves Physical Function in Parkinson’s Disease: the PRET-PD Study

    PubMed Central

    Prodoehl, Janey; Rafferty, Miriam; David, Fabian J.; Poon, Cynthia; Vaillancourt, David E.; Comella, Cynthia L.; Leurgans, Sue; Kohrt, Wendy M.; Corcos, Daniel M.; Robichaud, Julie A.

    2014-01-01

    Background The progressive resistance exercise (PRE) in Parkinson’s disease trial (PRET-PD) showed that PRE improved the motor signs of PD compared to a modified Fitness Counts (mFC) program. It is unclear how long-term exercise affects physical function in these individuals. Objective To examine the effects of long-term PRE and mFC on physical function outcome measures in individuals with PD. Methods A preplanned secondary analysis was conducted using data from the 38 patients with idiopathic PD who completed the PRET-PD trial. Participants were randomized into PRE or mFC groups and exercised 2 days/week up to 24 months. Blinded assessors obtained functional outcomes on and off medication at baseline, 6 and 24 months with the Modified Physical Performance Test (mPPT), five times sit to stand test (STS), Functional Reach Test (FRT), Timed Up and Go (TUG), Berg Balance Scale (BBS), 6 minute walk test (6MWT), and 50ft walking speed (walk speed). Results The groups did not differ on any physical function measure at 6 or 24 months (p’s > 0.1). Across time, all physical function measures improved from baseline to 24 months when tested on medication (p’s < .0001), except for 6MWT(p = .068). Off medication results were similar except that the 6MWT was now significant. Conclusions 24 months of supervised and structured exercise (either PRE or mFC) is effective at improving functional performance outcomes in individuals with moderate PD. Clinicians should strive to include structured and supervised exercise in the long-term plan of care for individuals with PD. PMID:24961994

  5. Cancer Treatment with Anti-PD-1/PD-L1 Agents: Is PD-L1 Expression a Biomarker for Patient Selection?

    PubMed

    Festino, Lucia; Botti, Gerardo; Lorigan, Paul; Masucci, Giuseppe V; Hipp, Jason D; Horak, Christine E; Melero, Ignacio; Ascierto, Paolo A

    2016-06-01

    Strategies to help improve the efficacy of the immune system against cancer represent an important innovation, with recent attention having focused on anti-programmed death (PD)-1/PD-ligand 1 (L1) monoclonal antibodies. Clinical trials have shown objective clinical activity of these agents (e.g., nivolumab, pembrolizumab) in several malignancies, including melanoma, non-small-cell lung cancer, bladder cancer, squamous head and neck cancer, renal cell cancer, ovarian cancer, microsatellite-unstable colorectal cancer, and Hodgkin's lymphoma. Expression of PD-L1 in the tumor microenvironment appears to be crucial for therapeutic activity, and initial trials suggested positive PD-L1 tumor expression was associated with higher response rates. However, subsequent observations have questioned the prospect of using PD-L1 expression as a biomarker for selecting patients for therapy, especially since many patients considered PD-L1-negative experience a benefit from treatment. Importantly, there is not yet a definitive test for determination of PD-L1 and a cut-off reference for PD-L1-positive status has not been established. Immunohistochemistry with different antibodies and different thresholds has been used to define PD-L1 positivity (1-50 %), with no clear superiority of one threshold over another for identifying which patients respond. Moreover, the type of cells on which PD-L1 expression is most relevant is not yet clear, with immune infiltrate cells and tumor cells both being used. In conclusion, while PD-L1 expression is often a predictive factor for treatment response, it must be complemented by other biomarkers or histopathologic features, such as the composition and amount of inflammatory cells in the tumor microenvironment and their functional status. Multi-parameter quantitative or semi-quantitative algorithms may become useful and reliable tools to guide patient selection. PMID:27229745

  6. Expression of PD-L1, PD-L2, PD-1 and CTLA4 in myelodysplastic syndromes is enhanced by treatment with hypomethylating agents.

    PubMed

    Yang, H; Bueso-Ramos, C; DiNardo, C; Estecio, M R; Davanlou, M; Geng, Q-R; Fang, Z; Nguyen, M; Pierce, S; Wei, Y; Parmar, S; Cortes, J; Kantarjian, H; Garcia-Manero, G

    2014-06-01

    Blockade of immune checkpoints is emerging as a new form of anticancer therapy. We studied the expression of programmed death ligand 1 (PD-L1), PD-L2, programmed death 1 (PD-1) and cytotoxic T lymphocyte-associated antigen 4 (CTLA4) mRNA in CD34+ cells from myelodysplastic syndrome (MDS), chronic myelomonocytic leukemia (CMML) and acute myeloid leukemia (AML) patients (N=124). Aberrant upregulation (⩾2-fold) was observed in 34, 14, 15 and 8% of the patients. Increased expression of these four genes was also observed in peripheral blood mononuclear cells (PBMNCs) (N=61). The relative expression of PD-L1 from PBMNC was significantly higher in MDS (P=0.018) and CMML (P=0.0128) compared with AML. By immunohistochemical analysis, PD-L1 protein expression was observed in MDS CD34+ cells, whereas stroma/non-blast cellular compartment was positive for PD-1. In a cohort of patients treated with epigenetic therapy, PD-L1, PD-L2, PD-1 and CTLA4 expression was upregulated. Patients resistant to therapy had relative higher increments in gene expression compared with patients who achieved response. Treatment of leukemia cells with decitabine resulted in a dose-dependent upregulation of above genes. Exposure to decitabine resulted in partial demethylation of PD-1 in leukemia cell lines and human samples. This study suggests that PD-1 signaling may be involved in MDS pathogenesis and resistance mechanisms to hypomethylating agents. Blockade of this pathway can be a potential therapy in MDS and AML.

  7. A Mini-Review for Cancer Immunotherapy: Molecular Understanding of PD-1/PD-L1 Pathway & Translational Blockade of Immune Checkpoints

    PubMed Central

    Li, Yongshu; Li, Fangfei; Jiang, Feng; Lv, Xiaoqing; Zhang, Rongjiang; Lu, Aiping; Zhang, Ge

    2016-01-01

    Interference of the binding of programmed cell death protein 1 (PD-1) and programmed death-ligand 1 (PD-L1) has become a new inspiring immunotherapy for resisting cancers. To date, the FDA has approved two PD-1 monoclonal antibody drugs against cancer as well as a monoclonal antibody for PD-L1. More PD-1 and PD-L1 monoclonal antibody drugs are on their way in clinical trials. In this review, we focused on the mechanism of the PD-1/PD-L1 signaling pathway and the monoclonal antibodies (mAbs) against PD-1 and PD-L1, which were approved by the FDA or are still in clinical trials. And also presented is the prospect of the PD-1/PD-L1 immune checkpoint blockade in the next generation of immunotherapy. PMID:27438833

  8. Immunotherapy: Beyond Anti-PD-1 and Anti-PD-L1 Therapies.

    PubMed

    Antonia, Scott J; Vansteenkiste, Johan F; Moon, Edmund

    2016-01-01

    Advanced-stage non-small cell lung cancer (NSCLC) and small cell lung cancer are cancers in which chemotherapy produces a survival benefit, although it is small. We now know that anti-PD-1/PD-L1 has substantial clinical activity in both of these diseases, with an overall response rate (ORR) of 15%-20%. These responses are frequently rapid and durable, increase median overall survival (OS) compared with chemotherapy, and produce long-term survivors. Despite these very significant results, many patients do not benefit from anti-PD-1/PD-L1. This is because of the potential for malignancies to co-opt myriad immunosuppressive mechanisms other than aberrant expression of PD-L1. Conceptually, these can be divided into three categories. First, for some patients there is likely a failure to generate sufficient functional tumor antigen-specific T cells. Second, for others, tumor antigen-specific T cells may be generated but fail to enter into the tumor parenchyma. Finally, there are a large number of immunosuppressive mechanisms that have the potential to be operational within the tumor microenvironment: surface membrane immune checkpoint proteins PD-1, CTLA-4, LAG3, TIM3, BTLA, and adenosine A2AR; soluble factors and metabolic alterations interleukin (IL)-10, transforming growth factor (TGF)-β, adenosine, IDO, and arginase; and inhibitory cells, cancer-associated fibroblasts (CAFs), regulatory T cells, myeloid-derived suppressor cells (MDSCs), and tumor-associated macrophages. In this article, we discuss three strategies to generate more tumor-reactive T cells for patients: anti-CTLA-4, therapeutic tumor vaccination, and adoptive cellular therapy, with T cells redirected to tumor antigens using T-cell receptor (TCR) or chimeric antigen receptor (CAR) gene modification. We also review some of the various strategies in development to thwart tumor microenvironment immunosuppressive mechanisms. Strategies to drive more T cells into tumors remain a significant challenge.

  9. Immunotherapy: Beyond Anti-PD-1 and Anti-PD-L1 Therapies.

    PubMed

    Antonia, Scott J; Vansteenkiste, Johan F; Moon, Edmund

    2016-01-01

    Advanced-stage non-small cell lung cancer (NSCLC) and small cell lung cancer are cancers in which chemotherapy produces a survival benefit, although it is small. We now know that anti-PD-1/PD-L1 has substantial clinical activity in both of these diseases, with an overall response rate (ORR) of 15%-20%. These responses are frequently rapid and durable, increase median overall survival (OS) compared with chemotherapy, and produce long-term survivors. Despite these very significant results, many patients do not benefit from anti-PD-1/PD-L1. This is because of the potential for malignancies to co-opt myriad immunosuppressive mechanisms other than aberrant expression of PD-L1. Conceptually, these can be divided into three categories. First, for some patients there is likely a failure to generate sufficient functional tumor antigen-specific T cells. Second, for others, tumor antigen-specific T cells may be generated but fail to enter into the tumor parenchyma. Finally, there are a large number of immunosuppressive mechanisms that have the potential to be operational within the tumor microenvironment: surface membrane immune checkpoint proteins PD-1, CTLA-4, LAG3, TIM3, BTLA, and adenosine A2AR; soluble factors and metabolic alterations interleukin (IL)-10, transforming growth factor (TGF)-β, adenosine, IDO, and arginase; and inhibitory cells, cancer-associated fibroblasts (CAFs), regulatory T cells, myeloid-derived suppressor cells (MDSCs), and tumor-associated macrophages. In this article, we discuss three strategies to generate more tumor-reactive T cells for patients: anti-CTLA-4, therapeutic tumor vaccination, and adoptive cellular therapy, with T cells redirected to tumor antigens using T-cell receptor (TCR) or chimeric antigen receptor (CAR) gene modification. We also review some of the various strategies in development to thwart tumor microenvironment immunosuppressive mechanisms. Strategies to drive more T cells into tumors remain a significant challenge. PMID

  10. Steering epitaxial alignment of Au, Pd, and AuPd nanowire arrays by atom flux change.

    PubMed

    Yoo, Youngdong; Seo, Kwanyong; Han, Sol; Varadwaj, Kumar S K; Kim, Hyun You; Ryu, Ji Hoon; Lee, Hyuck Mo; Ahn, Jae Pyoung; Ihee, Hyotcherl; Kim, Bongsoo

    2010-02-10

    We have synthesized epitaxial Au, Pd, and AuPd nanowire arrays in vertical or horizontal alignment on a c-cut sapphire substrate. We show that the vertical and horizontal nanowire arrays grow from half-octahedral seeds by the correlations of the geometry and orientation of seed crystals with those of as-grown nanowires. The alignment of nanowires can be steered by changing the atom flux. At low atom deposition flux vertical nanowires grow, while at high atom flux horizontal nanowires grow. Similar vertical/horizontal epitaxial growth is also demonstrated on SrTiO(3) substrates. This orientation-steering mechanism is visualized by molecular dynamics simulations.

  11. Enhanced T-cell immunity to osteosarcoma through antibody blockade of PD-1/PD-L1 interactions.

    PubMed

    Lussier, Danielle M; O'Neill, Lauren; Nieves, Lizbeth M; McAfee, Megan S; Holechek, Susan A; Collins, Andrea W; Dickman, Paul; Jacobsen, Jeffrey; Hingorani, Pooja; Blattman, Joseph N

    2015-04-01

    Osteosarcoma is the most common bone cancer in children and adolescents. Although 70% of patients with localized disease are cured with chemotherapy and surgical resection, patients with metastatic osteosarcoma are typically refractory to treatment. Numerous lines of evidence suggest that cytotoxic T lymphocytes (CTLs) limit the development of metastatic osteosarcoma. We have investigated the role of PD-1, an inhibitory TNFR family protein expressed on CTLs, in limiting the efficacy of immune-mediated control of metastatic osteosarcoma. We show that human metastatic, but not primary, osteosarcoma tumors express a ligand for PD-1 (PD-L1) and that tumor-infiltrating CTLs express PD-1, suggesting this pathway may limit CTLs control of metastatic osteosarcoma in patients. PD-L1 is also expressed on the K7M2 osteosarcoma tumor cell line that establishes metastases in mice, and PD-1 is expressed on tumor-infiltrating CTLs during disease progression. Blockade of PD-1/PD-L1 interactions dramatically improves the function of osteosarcoma-reactive CTLs in vitro and in vivo, and results in decreased tumor burden and increased survival in the K7M2 mouse model of metastatic osteosarcoma. Our results suggest that blockade of PD-1/PD-L1 interactions in patients with metastatic osteosarcoma should be pursued as a therapeutic strategy. PMID:25751499

  12. Synthesis of bimetallic Pt-Pd core-shell nanocrystals and their high electrocatalytic activity modulated by Pd shell thickness.

    PubMed

    Li, Yujing; Wang, Zhi Wei; Chiu, Chin-Yi; Ruan, Lingyan; Yang, Wenbing; Yang, Yang; Palmer, Richard E; Huang, Yu

    2012-02-01

    Bimetallic Pt-Pd core-shell nanocrystals (NCs) are synthesized through a two-step process with controlled Pd thickness from sub-monolayer to multiple atomic layers. The oxygen reduction reaction (ORR) catalytic activity and methanol oxidation reactivity of the core-shell NCs for fuel cell applications in alkaline solution are systematically studied and compared based on different Pd thickness. It is found that the Pd shell helps to reduce the over-potential of ORR by up to 50 mV when compared to commercial Pd black, while generating up to 3-fold higher kinetic current density. The carbon monoxide poisoning test shows that the bimetallic NCs are more resistant to the CO poisoning than Pt NCs and Pt black. It is also demonstrated that the bimetallic Pt-Pd core-shell NCs can enhance the current density of the methanol oxidation reaction, lowering the over-potential by 35 mV with respect to the Pt core NCs. Further investigation reveals that the Pd/Pt ratio of 1/3, which corresponds to nearly monolayer Pd deposition on Pt core NCs, gives the highest oxidation current density and lowest over-potential. This study shows for the first time the systematic investigation of effects of Pd atomic shells on Pt-Pd bimetallic nanocatalysts, providing valuable guidelines for designing high-performance catalysts for fuel cell applications. PMID:22159178

  13. Herbal Medicines for Parkinson's Disease: A Systematic Review of Randomized Controlled Trials

    PubMed Central

    Kim, Tae-Hun; Cho, Ki-Ho; Jung, Woo-Sang; Lee, Myeong Soo

    2012-01-01

    Objective We conducted systematic review to evaluate current evidence of herbal medicines (HMs) for Parkinson's disease (PD). Methods Along with hand searches, relevant literatures were located from the electronic databases including CENTRAL, MEDLINE, EMBASE, CINAHL, AMED, PsycInfo, CNKI, 7 Korean Medical Databases and J-East until August, 2010 without language and publication status. Randomized controlled trials (RCTs), quasi-randomized controlled trials and randomized crossover trials, which evaluate HMs for idiopathic PD were selected for this review. Two independent authors extracted data from the relevant literatures and any disagreement was solved by discussion. Results From the 3432 of relevant literatures, 64 were included. We failed to suggest overall estimates of treatment effects on PD because of the wide heterogeneity of used herbal recipes and study designs in the included studies. When compared with placebo, specific effects were not observed in favor of HMs definitely. Direct comparison with conventional drugs suggested that there was no evidence of better effect for HMs. Many studies compared combination therapy with single active drugs and combination therapy showed significant improvement in PD related outcomes and decrease in the dose of anti-Parkinson's drugs with low adverse events rate. Conclusion Currently, there is no conclusive evidence about the effectiveness and efficacy of HMs on PD. For establishing clinical evidence of HMs on PD, rigorous RCTs with sufficient statistical power should be promoted in future. PMID:22615738

  14. Elevated Cellular PD1/PD-L1 Expression Confers Acquired Resistance to Cisplatin in Small Cell Lung Cancer Cells

    PubMed Central

    Yan, Fei; Pang, Jiuxia; Peng, Yong; Molina, Julian R.; Yang, Ping; Liu, Shujun

    2016-01-01

    Although small cell lung cancer (SCLC) is highly responsive to chemotherapies (e.g., cisplatin-etoposide doublet), virtually almost all responsive SCLC patients experience disease recurrence characterized by drug resistance. The mechanisms underlying cisplatin resistance remain elusive. Here we report that cell-intrinsic expression of PD1 and PD-L1, two immune checkpoints, is required for sustained expansion of SCLC cells under cisplatin selection. Indeed, PD1 and PD-L1 were expressed at a higher level in lung cancer cell lines, tumor tissues, and importantly, in SCLC cells resistant to cisplatin (H69R, H82R), when compared to respective controls. Genetic abrogation of PD1 and PD-L1 in H69R and H82R cells decreased their proliferation rate, and restored their sensitivity to cisplatin. Mechanistically, PD-L1 upregulation in H69R and H82R cells was attributed to the overexpression of DNA methyltransferase 1 (DNMT1) or receptor tyrosine kinase KIT, as knockdown of DNMT1 or KIT in H69R and H82R cells led to PD-L1 downregulation. Consequently, combined knockdown of PD-L1 with KIT or DNMT1 resulted in more pronounced inhibition of H69R and H82R cell growth. Thus, cell intrinsic PD1/PD-L1 signaling may be a predictor for poor efficacy of cisplatin treatment, and targeting the cellular PD1/PD-L1 axis may improve chemosensitization of aggressive SCLC. PMID:27610620

  15. Elevated Cellular PD1/PD-L1 Expression Confers Acquired Resistance to Cisplatin in Small Cell Lung Cancer Cells.

    PubMed

    Yan, Fei; Pang, Jiuxia; Peng, Yong; Molina, Julian R; Yang, Ping; Liu, Shujun

    2016-01-01

    Although small cell lung cancer (SCLC) is highly responsive to chemotherapies (e.g., cisplatin-etoposide doublet), virtually almost all responsive SCLC patients experience disease recurrence characterized by drug resistance. The mechanisms underlying cisplatin resistance remain elusive. Here we report that cell-intrinsic expression of PD1 and PD-L1, two immune checkpoints, is required for sustained expansion of SCLC cells under cisplatin selection. Indeed, PD1 and PD-L1 were expressed at a higher level in lung cancer cell lines, tumor tissues, and importantly, in SCLC cells resistant to cisplatin (H69R, H82R), when compared to respective controls. Genetic abrogation of PD1 and PD-L1 in H69R and H82R cells decreased their proliferation rate, and restored their sensitivity to cisplatin. Mechanistically, PD-L1 upregulation in H69R and H82R cells was attributed to the overexpression of DNA methyltransferase 1 (DNMT1) or receptor tyrosine kinase KIT, as knockdown of DNMT1 or KIT in H69R and H82R cells led to PD-L1 downregulation. Consequently, combined knockdown of PD-L1 with KIT or DNMT1 resulted in more pronounced inhibition of H69R and H82R cell growth. Thus, cell intrinsic PD1/PD-L1 signaling may be a predictor for poor efficacy of cisplatin treatment, and targeting the cellular PD1/PD-L1 axis may improve chemosensitization of aggressive SCLC. PMID:27610620

  16. Role of the PD-1 Pathway in the Immune Response

    PubMed Central

    Riella, Leonardo V.; Paterson, Alison M.; Sharpe, Arlene H.; Chandraker, Anil

    2013-01-01

    Understanding immunoregulatory mechanisms is essential for the development of novel interventions to improve long-term allograft survival. Programmed death 1 (PD-1) and its ligands, PD-L1 and PD-L2, have emerged as critical inhibitory signaling pathways that regulate T cell response and maintain peripheral tolerance. PD-1 signaling inhibits alloreactive T cell activation, and can promote induced regulatory T cell development. Furthermore, the upregulation of PD-L1 on nonhematopoietic cells of the allograft may actively participate in the inhibition of immune responses and provide tissue-specific protection. In murine transplant models, this pathway has been shown to be critical for the induction and maintenance of graft tolerance. In this review, we discuss the current knowledge of the immunoregulatory functions of PD-1 and its ligands and their therapeutic potential in transplantation. PMID:22900886

  17. Atomistic Modeling of Pd Site Preference in NiTi

    NASA Technical Reports Server (NTRS)

    Bozzolo, Guillermo; Noebe, Ronald D.; Mosca, Hugo O.

    2004-01-01

    An analysis of the site subsitution behavior of Pd in NiTi was performed using the BFS method for alloys. Through a combination of Monte Carlo simulations and detailed atom-by-atom energetic analyses of various computational cells, representing compositions of NiTi with up to 10 at% Pd, a detailed understanding of site occupancy of Pd in NiTi was revealed. Pd subsituted at the expense of Ni in a NiTi alloy will prefer the Ni-sites. Pd subsituted at the expense of Ti shows a very weak preference for Ti-sites that diminishes as the amount of Pd in the alloy increases and as the temperature increases.

  18. Pd doped reduced graphene oxide for hydrogen storage

    SciTech Connect

    Das, Tapas; Banerjee, Seemita; Sudarsan, V.

    2015-06-24

    Pd nanoparticles dispersed reduced graphene oxide sample has been prepared by a simple chemical method using hydrazine as the reducing agent. Based on XRD and {sup 13}C MAS NMR studies it is confirmed that, Pd nanoparticles are effectively mixed with the reduced graphene oxide sample. Maximum hydrogen storage capacity has been estimated to be ∼1.36 wt % at 123K. Improved hydrogen storage capacity of Pd incorporated sample can be explained based on the phenomenon of spillover of atomic hydrogen.

  19. Superconductivity in Pd, Ir, and Pt chalcogenide

    NASA Astrophysics Data System (ADS)

    Oh, Yoon Seok; Yang, Junjie; Choi, Y. J.; Hogan, A.; Horibe, Y.; Cheong, S.-W.

    2012-02-01

    Large spin-orbit coupling in materials with heavy chalcogens can result in unique quantum states or functional properties such as topological insulator, giant thermoelectric power, and superconductivity. When materials contain heavy cations in addition to heavy chalcogens, spin-orbit coupling can be further enhanced. For these reasons, we have studied the superconductivity of Pd, Ir, and Pt tellurides and selenides. In the exploration of these chalcogenides, we have focused on the competition between superconductivity and charge density wave that is associated with superlattice reflections.

  20. Breaking of Cooper pairs in 108Pd

    NASA Astrophysics Data System (ADS)

    Rahmatinejad, A.; Kakavand, T.; Razavi, R.

    2016-04-01

    In this paper, breaking of Cooper pairs in 108Pd is investigated within the canonical ensemble framework and the BCS model. Our results show an evidence of two phase transitions, which are related to neutron and proton systems. Also, with consideration of pairing interaction, the role of neutron and proton systems in entropy, spin cutoff parameter and as a result in the moment of inertia are investigated. The results show minor role for the proton system at low temperatures and approximately equal roles for both neutron and proton systems after the critical temperature. Good agreement was observed between obtained results and the experimental data.

  1. Superfluid density and microwave conductivity of FeSe superconductor: ultra-long-lived quasiparticles and extended s-wave energy gap

    NASA Astrophysics Data System (ADS)

    Li, Meng; Lee-Hone, N. R.; Chi, Shun; Liang, Ruixing; Hardy, W. N.; Bonn, D. A.; Girt, E.; Broun, D. M.

    2016-08-01

    FeSe is an iron-based superconductor of immense current interest due to the large enhancements of T c that occur when it is pressurised or grown as a single layer on an insulating substrate. Here we report precision measurements of its superconducting electrodynamics, at frequencies of 202 and 658 MHz and at temperatures down to 0.1 K. The quasiparticle conductivity reveals a rapid collapse in scattering on entering the superconducting state that is strongly reminiscent of unconventional superconductors such as cuprates, organics and the heavy fermion material CeCoIn5. At the lowest temperatures the quasiparticle mean free path exceeds 50 μm, a record for a compound superconductor. From the superfluid response we confirm the importance of multiband superconductivity and reveal strong evidence for a non-zero energy-gap minimum.

  2. Quasiparticle and Optical Properties of Mono- and Bi-layer SnS2: A First-Principles GW and GW +BSE Study

    NASA Astrophysics Data System (ADS)

    Wu, Meng; Qiu, Diana; Louie, Steven G.

    2015-03-01

    Unlike most semiconducting transition metal dichalcogenides, SnS2, another layered metal dichalcogenide, is calculated within density functional theory to be an indirect bandgap semiconductor in both its bulk and monolayer forms. Experimental characterization of mono- and bi-layer SnS2 has been performed, but the details of its quasiparticle and excitonic properties remain unclear. Thus, we employ ab initio GW and GW +BSE calculations to study the quasiparticle band structure and optical absorption spectrum, respectively, of mono- and bi-layer SnS2 with spin-orbit coupling included throughout the calculations. We further investigate the character of excitonic states contributing to the optical spectrum. This work was supported by NSF Grant No. DMR10-1006184 and the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Computational resources have been provided by DOE at Lawrence Berkeley National Laboratory's NERSC facility.

  3. On the combined use of GW approximation and cumulant expansion in the calculations of quasiparticle spectra: The paradigm of Si valence bands

    NASA Astrophysics Data System (ADS)

    Gumhalter, Branko; Kovač, Vjekoslav; Caruso, Fabio; Lambert, Henry; Giustino, Feliciano

    2016-07-01

    Since the earliest implementations of the various GW approximations and cumulant expansion in the calculations of quasiparticle propagators and spectra, several attempts have been made to combine the advantageous properties and results of these two theoretical approaches. While the GW-plus-cumulant approach has proven successful in interpreting photoemission spectroscopy data in solids, the formal connection between the two methods has not been investigated in detail. By introducing a general bijective integral representation of the cumulants, we can rigorously identify at which point these two approximations can be connected for the paradigmatic model of quasiparticle interaction with the dielectric response of the system that has been extensively exploited in recent interpretations of the satellite structures in photoelectron spectra. We establish a protocol for consistent practical implementation of the thus established GW +cumulant scheme and illustrate it by comprehensive state-of-the-art first-principles calculations of intrinsic angle-resolved photoemission spectra from Si valence bands.

  4. Middle School Mathematics PD Study: Description of the PD Intervention. Paper #2

    ERIC Educational Resources Information Center

    Walters, Kirk; Garet, Michael; Leinwand, Steve

    2010-01-01

    This paper describes the PD program that was delivered during the first year of the study. The main goal of the intervention was to increase teachers' capability to teach positive rational number topics effectively. The program included a 3-day summer institute (18 hours per teacher), five 1-day seminars held during the school year (30 hours per…

  5. Low-energy electron diffraction investigation of epitaxial growth: Pt and Pd on Pd(100)

    SciTech Connect

    Flynn-Sanders, D.

    1990-09-21

    We investigate the epitaxial growth of Pt and Pd and Pd(100) via spot profile analysis using conventional low-energy electron diffraction (LEED). We resolve a central-spike and diffuse component in the spot profiles, reflecting the layer-occupations and pair-correlations, respectively. Kinetic limitations inhibit layer-by-layer growth at low temperatures. Our data suggest diffusion switches on at ca. 150 K for Pt and ca. 170 K for Pd indicating activation barriers to surface diffusion of ca. 10 and ca. 13 kcal/mol, respectively. To clarify the role of diffusion in determining the resulting film morphology, we develop a growth model that incorporates the adsorption-site requirement and predicts intensity oscillations. We present a new procedure to experimentally determine out-of-phase scattering conditions. At these energies, ring-structure is evident in the profiles during Pd growth between ca. 200 and 400 K. We report ring intensity oscillations as a function of coverage, which demonstrate the filling of individual layers.

  6. Low-energy dielectric screening in Pd and PdHx systems.

    PubMed

    Silkin, V M; Nazarov, V U; Chernov, I P; Sklyadneva, I Yu; Chulkov, E V

    2015-02-11

    Modifications in dielectric properties of palladium upon absorption of hydrogen are investigated theoretically in the low-energy (0-2 eV) region. The calculations were performed with full inclusion of the electronic band structure obtained within a self-consistent pseudopotential approach. In particular, we trace the evolution of the acoustic-like plasmon (AP) found previously in clean Pd with increasing hydrogen concentration. It exists in PdHx up to the hydrogen content x corresponding to the complete filling of the 4d Pd-derived energy bands because of the presence of two kinds of carriers at the Fermi surface. At higher H concentration the AP disappears since only one kind of carrier within the sp-like energy band exists at the Fermi level. Additionally, we investigate the spatial distribution inside the crystal of a potential caused by a time-dependent external perturbation and observe drastic modifications in the screening properties in the PdHx systems with energy and with hydrogen concentration.

  7. Synthesis of Au-Pd Nanoflowers Through Nanocluster Assembly

    SciTech Connect

    Xu, Jianguang; Howe, Jane Y; Chi, Miaofang; Wilson, Adria; Rathmall, Aaron; Wiley, Benjamin J

    2011-01-01

    Reduction of Pd ions by hydroquinone in the presence of gold nanoparticles and polyvinylpyrrolidone resulted in the formation of nanoflowers with a Au core and Pd petals. Addition of HCl to the synthesis halted the reduction by hydroquinone and enabled the acquisition of snapshots of the nanoflowers at different stages of growth. TEM images of the reaction after 10 s show that the nanoflower morphology resulted from the homogeneous nucleation of Pd clusters in solution and their subsequent attachment to gold seeds coated with a thin (0.8 {+-} 0.1 nm) shell of Pd. UV-visible spectra also indicate Pd clusters formed in the early stages of the reaction and disappeared as the nanoflowers grew. The speed at which this reaction can be halted is useful not only for producing a variety of bimetallic nanostructures with precisely controlled dimensions and morphologies but also for understanding the growth mechanism of these structures. The ability of the AuPd core-shell structure to catalyze the Suzuki coupling reaction of iodobenzene to phenylboronic acid was probed and compared against the activity of Pd nanocubes and thin-shelled AuPd core-shell nanoparticles. The results of this study suggest that Suzuki coupling was not affected by the surface structure or subsurface composition of the nanoparticles, but instead was primarily catalyzed by molecular Pd species that leached from the nanostructures.

  8. Synthesis and Catalytic Properties of Au Pd Nanoflowers

    SciTech Connect

    Xu, Jianguang; Wilson, Adria; Howe, Jane Y; Chi, Miaofang; Wiley, Benjamin J

    2011-01-01

    Reduction of Pd ions by hydroquinone in the presence of gold nanoparticles and polyvinylpyrrolidone resulted in the formation of nanoflowers with a Au core and Pd petals. Addition of HCl to the synthesis halted the reduction by hydroquinone and enabled the acquisition of snapshots of the nanoflowers at different stages of growth. TEM images of the reaction after 10 s show that the nanoflower morphology resulted from the homogeneous nucleation of Pd clusters in solution and their subsequent attachment to gold seeds coated with a thin (0.8 0.1 nm) shell of Pd. UV visible spectra also indicate Pd clusters formed in the early stages of the reaction and disappeared as the nanoflowers grew. The speed at which this reaction can be halted is useful not only for producing a variety of bimetallic nanostructures with precisely controlled dimensions and morphologies but also for understanding the growth mechanism of these structures. The ability of the AuPd core shell structure to catalyze the Suzuki coupling reaction of iodobenzene to phenylboronic acid was probed and compared against the activity of Pd nanocubes and thin-shelled AuPd core shell nanoparticles. The results of this study suggest that Suzuki coupling was not affected by the surface structure or subsurface composition of the nanoparticles, but instead was primarily catalyzed by molecular Pd species that leached from the nanostructures.

  9. New structures in Pd-rich ordered alloys

    NASA Astrophysics Data System (ADS)

    Corbitt, Jacqueline; Gilmartin, Erin; Hart, Gus

    2009-10-01

    An intriguing intermetallic structure with 8:1 stoichiometry was discovered in the 1950s in the Pt-Ti system. Since then a handful of other Pt/Pd/Ni-X binary systems have been observed to exhibit this curious structure (Pt8Zr, Pd8Mo,Ni8Nb, etc). Precipitates of this ordered structure can significantly increase the hardness of an alloy. For jewelry applications involving Pt and Pd, international hallmarking standards require that the alloys be at least 95% pure by weight. However, Pt- and Pd-rich alloys are often soft when purity is high if the minority atoms are disordered. Because the 8:1 structure maintains a high weight percentage of Pt/Pd, it can satisfy purity standards while increasing performance. Recent calculations and experiments suggest that the 8:1 structure may form in about 20 previously unsuspected Pt/Pd binary systems. Using first-principles calculations and cluster expansion modeling, we have performed a ground state search to find the stable structures in Pd-Nb, Pd-Cu, and Pd-Mg, and predict the temperatures at which the new structures may form.

  10. A photoemission study of Pd ultrathin films on Pt(111)

    SciTech Connect

    Mun, Bongjin Simon; Lee, Choongman; Stamenkovic, Vojislav; Markovic, Nenad M.; Ross Jr., Philip N.

    2005-05-11

    The origin of surface core-level shift (SCLS) of Pd thin films on Pt(111) substrate is investigated. At sub-monolayer coverage of Pd thin films, the splitting of Pd 3d core level peaks indicate the contribution of both initial and final-state of photo-ionization processes while there is almost no change on valence band (VB) spectra. When the coverage of Pd reaches to single monolayer, the final-state relaxation effect on the Pd 3d vanishes and only the initial-state effect, a negative SCLS, is present. Also, the VB spectrum at Pd monolayer films shows a clear band narrowing, that is the origin of the negative SCLS at monolayer coverage. As the Pd coverage is increased to more than monolayer thickness, the Pd 3d peaks start to show the surface layer contribution from second and third layers, positive SCLS, and the VB spectrum shows even narrower band width, possibly due to the formation of surface states and strained effect of Pd adlayers on top of the first pseudomorphic layer.

  11. Structural characterization of bimetallic Pd-Cu vapor derived catalysts

    NASA Astrophysics Data System (ADS)

    Balerna, Antonella; Evangelisti, Claudio; Psaro, Rinaldo; Fusini, Graziano; Carpita, Adriano

    2016-05-01

    Pd-Cu bimetallic Solvated Metal Atoms (SMA) were synthesized by metal vapor synthesis technique and supported on PVPy resin. Since the catalytic activity, of the Pd-Cu system turned out to be quite high also compared to the corresponding monometallic system, a structural characterization, using electron microscopy techniques and X-ray Absorption Fine Structure spectroscopy, was performed. HRTEM analysis showed the presence of Pd particles distributed in a narrow range with a mean diameter of about 2.5 nm while the XAFS analysis, confirmed the presence of the Pd nanoparticles but revealed also some alloying with Cu atoms.

  12. Superconductivity in Ta3Pd3Te14 with quasi-one-dimensional PdTe2 chains.

    PubMed

    Jiao, Wen-He; He, Lan-Po; Liu, Yi; Xu, Xiao-Feng; Li, Yu-Ke; Zhang, Chu-Hang; Zhou, Nan; Xu, Zhu-An; Li, Shi-Yan; Cao, Guang-Han

    2016-02-15

    We report bulk superconductivity at 1.0 K in a low-dimensional ternary telluride Ta3Pd3Te14 containing edge-sharing PdTe2 chains along crystallographic b axis, similar to the recently discovered superconductor Ta4Pd3Te16. The electronic heat capacity data show an obvious anomaly at the transition temperature, which indicates bulk superconductivity. The specific-heat jump is ΔC/(γ(n)T(c)) ≈ 1.35, suggesting a weak coupling scenario. By measuring the low-temperature thermal conductivity, we conclude that Ta3Pd3Te14 is very likely a dirty s-wave superconductor. The emergence of superconductivity in Ta3Pd3Te14 with a lower T(c), compared to that of Ta4Pd3Te16, may be attributed to the lower density of states.

  13. Heterostructured Au/Pd-M (M = Au, Pd, Pt) nanoparticles with compartmentalized composition, morphology, and electrocatalytic activity.

    PubMed

    Lutz, Patrick S; Bae, In-Tae; Maye, Mathew M

    2015-10-14

    The synthesis, processing, and galvanic exchange of three heterostructured nanoparticle systems is described. The surface accessibility and redox potential of a Au/Pd-Ag dumbbell nanoparticle, where a Au/Pd core/shell region, and a silver region make up the domains, was used to prepare the new nanostructures with controlled composition, morphology, and microstructure. Results indicate that the silver domain was particularly susceptible to galvanic displacement, and was exchanged to Au/Pd-M (M = Au, Pd, Pt). Interestingly, the dumbbell morphology remained after exchange, and the silver region was transformed to hollow, parachute, or concentric domains respectively. The morphology and microstructure change was visualized via TEM and HRTEM, and the composition changes were probed via STEM-EDS imaging and XPS. The electrocatalytic activity of the Au/Pd-M towards methanol oxidation was studied, with results indicating that the Au/Pd-Pt nanoparticles had high activity attributed to the porous nature of the platinum domains. PMID:26351824

  14. Superconductivity in Ta3Pd3Te14 with quasi-one-dimensional PdTe2 chains

    PubMed Central

    Jiao, Wen-He; He, Lan-Po; Liu, Yi; Xu, Xiao-Feng; Li, Yu-Ke; Zhang, Chu-Hang; Zhou, Nan; Xu, Zhu-An; Li, Shi-Yan; Cao, Guang-Han

    2016-01-01

    We report bulk superconductivity at 1.0 K in a low-dimensional ternary telluride Ta3Pd3Te14 containing edge-sharing PdTe2 chains along crystallographic b axis, similar to the recently discovered superconductor Ta4Pd3Te16. The electronic heat capacity data show an obvious anomaly at the transition temperature, which indicates bulk superconductivity. The specific-heat jump is ΔC/(γnTc) ≈ 1.35, suggesting a weak coupling scenario. By measuring the low-temperature thermal conductivity, we conclude that Ta3Pd3Te14 is very likely a dirty s-wave superconductor. The emergence of superconductivity in Ta3Pd3Te14 with a lower Tc, compared to that of Ta4Pd3Te16, may be attributed to the lower density of states. PMID:26876362

  15. Size and alloying induced shift in core and valence bands of Pd-Ag and Pd-Cu nanoparticles

    SciTech Connect

    Sengar, Saurabh K.; Mehta, B. R.; Govind

    2014-03-28

    In this report, X-ray photoelectron spectroscopy studies have been carried out on Pd, Ag, Cu, Pd-Ag, and Pd-Cu nanoparticles having identical sizes corresponding to mobility equivalent diameters of 60, 40, and 20 nm. The nanoparticles were prepared by the gas phase synthesis method. The effect of size on valence and core levels in metal and alloy nanoparticles has been studied by comparing the values to those with the 60 nm nanoparticles. The effect of alloying has been investigated by comparing the valence and core level binding energies of Pd-Cu and Pd-Ag alloy nanoparticles with the corresponding values for Pd, Ag, and Cu nanoparticles of identical sizes. These effects have been explained in terms of size induced lattice contractions, alloying induced charge transfer, and hybridization effects. The observation of alloying and size induced binding energy shifts in bimetallic nanoparticles is important from the point of view of hydrogen reactivity.

  16. Self-consistent quasiparticle formulation of a multiphonon method and its application to the neutron-rich O20 nucleus

    NASA Astrophysics Data System (ADS)

    De Gregorio, G.; Knapp, F.; Lo Iudice, N.; Vesely, P.

    2016-04-01

    A Bogoliubov quasiparticle formulation of an equation-of-motion phonon method, suited for open-shell nuclei, is derived. Like its particle-hole version, it consists of deriving a set of equations of motions whose iterative solution generates an orthonormal basis of n -phonon states (n =0 ,1 ,2 ,... ), built of quasiparticle Tamm-Dancoff phonons, which simplifies the solution of the eigenvalue problem. The method is applied to the open-shell neutron-rich O20 for illustrative purposes. A Hartree-Fock-Bogoliubov canonical basis, derived from an intrinsic two-body optimized chiral Hamiltonian, is used to derive and solve the eigenvalue equations in a space encompassing a truncated two-phonon basis. The spurious admixtures induced by the violation of the particle number and the center-of-mass motion are eliminated to a large extent by a Gram-Schmidt orthogonalization procedure. The calculation takes into account the Pauli principle, is self-consistent, and is parameter free except for the energy cutoff used to truncate the two-phonon basis, which induces an increasing depression of the ground state through its strong coupling to the quasiparticle vacuum. Such a cutoff is fixed so as to reproduce the first 1- level. The two-phonon states are shown to enhance the level density of the low-energy spectrum, consistently with the data, and to induce a fragmentation of the E 1 strength which, while accounting for the very low E 1 transitions, is not sufficient to reproduce the experimental cross section in the intermediate energy region. This and other discrepancies suggest the need of including the three-phonon states. These are also expected to offset the action of the two phonons on the quasiparticle vacuum and, therefore, free the calculation from any parameter.

  17. Hartree-Fock-Bogoliubov description of quasiparticle excitations in the superdeformed wells of 191,192Hg and 192,193Tl

    NASA Astrophysics Data System (ADS)

    Heenen, P.-H.; Janssens, R. V. F.

    1998-01-01

    The properties of superdeformed bands in 191,192Hg and 192,193Tl have been studied using the cranked Hartree-Fock-Bogoliubov method with the Lipkin-Nogami prescription, the Skm* interaction, and a surface-delta, density-dependent pairing force. In particular, quasiparticle excitations involving intruder orbitals are analyzed in detail. Comparisons between data and calculations are performed for J (2) moments, quadrupole moments, spins, transition energies, and alignments.

  18. Fine structure on flat surfaces of quasicrystalline Al-Pd-Mn

    NASA Astrophysics Data System (ADS)

    Shen, Z.; Stoldt, C. R.; Jenks, C. J.; Lograsso, T. A.; Thiel, P. A.

    1999-12-01

    We have analyzed the fine structure revealed by scanning tunneling microscopy for a flat (within 0.8 Å) fivefold surface of i-Al-Pd-Mn. Even though features in the image appear to be arranged randomly, self-similar features are separated by distinct distances. The distribution of such distances is compatible with the separations between pseudo-Mackay icosahedra tangent to the topmost layer, and with separations between other cluster-based units. We propose that the fine structure is due to electronic structure imposed by the clusters.

  19. G6PD Deficiency and Hemoglobinopathies: Molecular Epidemiological Characteristics and Healthy Effects on Malaria Endemic Bioko Island, Equatorial Guinea

    PubMed Central

    Lin, Min; Yang, Li Ye; Xie, Dong De; Chen, Jiang Tao; Nguba, Santiago-m Monte; Ehapo, Carlos Sala; Zhan, Xiao Fen; Eyi, Juan Urbano Monsuy; Matesa, Rocio Apicante; Obono, Maximo Miko Ondo; Yang, Hui; Yang, Hui Tian; Cheng, Ji Dong

    2015-01-01

    Background Glucose-6-phosphate dehydrogenase (G6PD) deficiency and hemoglobinopathies were the inherited conditions found mostly in African. However, few epidemiological data of these disorders was reported in Equatorial Guinea (EQG). This study aimed to assess the prevalence and healthy effects of G6PD deficiency and hemoglobinopathies among the people on malaria endemic Bioko Island, EQG. Materials and Methods Blood samples from 4,144 unrelated subjects were analyzed for G6PD deficieny by fluorescence spot test (FST), high-resolution melting assay and PCR-DNA sequencing. In addition, 1,186 samples were randomly selected from the 4,144 subjects for detection of hemoglobin S (HbS), HbC, and α-thalassemia deletion by complete blood count, PCR-DNA sequencing and reverse dot blot (RDB). Results The prevalence of malaria and anemia was 12.6% (522/4,144) and 32.8% (389/1,186), respectively. Overall, 8.7% subjects (359/4,144) were G6PD-deficient by FST, including 9.0% (249/2,758) males and 7.9% (110/1,386) females. Among the 359 G6PD-deficient individuals molecularly studied, the G6PD A- (G202A/A376G) were detected in 356 cases (99.2%), G6PD Betica (T968C/A376G) in 3 cases. Among the 1,186 subjects, 201 cases were HbS heterozygotes, 35 cases were HbC heterozygotes, and 2 cases were HbCS double heterozygotes; 452 cases showed heterozygous α-thalassemia 3.7 kb deletion (-α3.7 kb deletion) and 85 homozygous - α3.7 kb deletion. The overall allele frequencies were HbS 17.1% (203/1186); HbC, 3.1% (37/1186); and –α3.7 kb deletion 52.4% (622/1186), respectively. Conclusions High G6PD deficiency in this population indicate that diagnosis and management of G6PD deficiency is necessary on Bioko Island. Obligatory newborn screening, prenatal screening and counseling for these genetic disorders, especially HbS, are needed on the island. PMID:25915902

  20. An efficient photochemical route to Pd nanoparticles; application to the one-step synthesis of Pd@polymer nanocomposite films

    NASA Astrophysics Data System (ADS)

    Wolak, Séverine; Vidal, Loïc; Becht, Jean-Michel; Michelin, Laure; Balan, Lavinia

    2016-08-01

    We have developed a facile, efficient, low cost and ‘green’ photochemical approach to preparing surfactant-free Pd nanoparticles and Pd-immobilized@acrylate photo-polymer films at room temperature, under air and without any additional treatment. The reaction system only includes a photo-initiator used as a generator of free radicals and a Pd(II) salt. In ethanol solution, the photochemical reduction of Pd(II) to Pd(0) generates very small metal particles with a narrow size distribution (2-4 nm). Furthermore, we have shown that the formation of Pd nanoparticles from a Pd(II) salt can be reversible thus allowing easy handling and safe storage with the possibility of generating the nanoparticles just before use. In the presence of an acrylate bifunctional monomer, Pd@polymer film was obtained through a ‘one-pot, one-step’ process resulting from a simultaneous photo-reduction of Pd(II) and photo-polymerization of acrylate units. The simultaneous generation of a 3D polymer network and of metal particles leads to a homogeneous distribution of Pd nanoparticles in the photo-polymer matrix with an average diameter of approximately 3.7 ± 1.1 nm. Such as-prepared Pd@polymer films were found to efficiently catalyze the Mizoroki-Heck reaction in the presence of only 0.9 mequiv. of supported palladium. The major interest of this arrangement is its recoverability and reusability, which makes it very attractive both from a practical and economical viewpoint. Finally, it is worth noting that this innovation offers a great advantage over concurrent methods in that it is simply generated within minutes, it is highly stable, and there is sharp monodispersity in the size of the Pd nanoparticles that can be stored for months without alteration of their physico-chemical properties and catalytic activity.

  1. An efficient photochemical route to Pd nanoparticles; application to the one-step synthesis of Pd@polymer nanocomposite films

    NASA Astrophysics Data System (ADS)

    Wolak, Séverine; Vidal, Loïc; Becht, Jean-Michel; Michelin, Laure; Balan, Lavinia

    2016-08-01

    We have developed a facile, efficient, low cost and ‘green’ photochemical approach to preparing surfactant-free Pd nanoparticles and Pd-immobilized@acrylate photo-polymer films at room temperature, under air and without any additional treatment. The reaction system only includes a photo-initiator used as a generator of free radicals and a Pd(II) salt. In ethanol solution, the photochemical reduction of Pd(II) to Pd(0) generates very small metal particles with a narrow size distribution (2–4 nm). Furthermore, we have shown that the formation of Pd nanoparticles from a Pd(II) salt can be reversible thus allowing easy handling and safe storage with the possibility of generating the nanoparticles just before use. In the presence of an acrylate bifunctional monomer, Pd@polymer film was obtained through a ‘one-pot, one-step’ process resulting from a simultaneous photo-reduction of Pd(II) and photo-polymerization of acrylate units. The simultaneous generation of a 3D polymer network and of metal particles leads to a homogeneous distribution of Pd nanoparticles in the photo-polymer matrix with an average diameter of approximately 3.7 ± 1.1 nm. Such as-prepared Pd@polymer films were found to efficiently catalyze the Mizoroki–Heck reaction in the presence of only 0.9 mequiv. of supported palladium. The major interest of this arrangement is its recoverability and reusability, which makes it very attractive both from a practical and economical viewpoint. Finally, it is worth noting that this innovation offers a great advantage over concurrent methods in that it is simply generated within minutes, it is highly stable, and there is sharp monodispersity in the size of the Pd nanoparticles that can be stored for months without alteration of their physico-chemical properties and catalytic activity.

  2. Orientations to Professional Development Design and Implementation: Understanding Their Relationship to PD Outcomes across Multiple Projects

    ERIC Educational Resources Information Center

    Marra, Rose M.; Arbaugh, Fran; Lannin, John; Abell, Sandra; Ehlert, Mark; Smith, Rena; Merle-Johnson, Dominike; Rogers, Meredith Park

    2011-01-01

    Given the large investment in teacher professional development (PD), further understanding of the factors that impact PD success is needed. In a previous study, the authors established a framework for categorizing PD projects using the notion of orientations. A PD orientation is comprised of project characteristics that drive the PD design and…

  3. Surface and subsurface oxygen on Pd(111)

    NASA Astrophysics Data System (ADS)

    Leisenberger, F. P.; Koller, G.; Sock, M.; Surnev, S.; Ramsey, M. G.; Netzer, F. P.; Klötzer, B.; Hayek, K.

    2000-01-01

    The interaction of O2 with Pd(111) in the temperature range from 300 K to 1000 K was studied by molecular beam adsorption, thermal desorption (TDS), low energy electron diffraction (LEED), high-resolution X-ray photoelectron spectroscopy (XPS) and high-resolution electron energy loss spectroscopy (HREELS). Using a capillary array doser and high effective oxygen pressures, evidence was found for the formation of a densely packed chemisorbed oxygen adlayer saturating at ΘO close to 1 and separately for subsurface migration of oxygen at elevated temperatures, but not at room temperature and below. Up to completion of a p(2×2) oxygen adlayer at 0.25 ML surface coverage, the dissociative sticking probability of oxygen into the chemisorbed state is high and masks the much slower diffusion into the bulk. Beyond 0.25 ML surface coverage, the adsorption rate into the chemisorbed state becomes small and the influence of bulk migration detectable. Exposure of the sample to high oxygen dosages at 1000 K fills up the subsurface reservoir and subsequent sticking measurements are no longer influenced by oxygen loss to the bulk. The subsurface oxygen could be distinguished in both XPS and off-specular HREELS. These latter techniques revealed that considerable concentrations of oxygen in the near-surface region can build up, even at lower temperatures (523 K) and oxygen exposures (40 L). In contrast to chemisorbed oxygen atoms on Pd(111), the subsurface species cannot be removed by reaction with CO.

  4. Magnetic hysteresis in small-grained CoxPd1-x nanowire arrays

    NASA Astrophysics Data System (ADS)

    Viqueira, M. S.; Pozo-López, G.; Urreta, S. E.; Condó, A. M.; Cornejo, D. R.; Fabietti, L. M.

    2015-11-01

    Co-Pd nanowires with small grain size are fabricated by AC electrodeposition into hexagonally ordered alumina pores, 20-35 nm in diameter and about 1 μm long. The effects of the alloy composition, the nanowire diameter and the grain size on the hysteresis properties are considered. X-ray diffraction indicates that the nanowires are single phase, a fcc Co-Pd solid solution; electron microscopy results show that they are polycrystalline, with randomly oriented grains (7-12 nm), smaller than the wire diameter. Nanowire arrays are ferromagnetic, with an easy magnetization axis parallel to the nanowire long axis. Both, the coercive field and the loop squareness monotonously increase with the Co content and with the grain size, but no clear correlation with the wire diameter is found. The Co and Co-rich nanowire arrays exhibit coercive fields and reduced remanence values quite insensitive to temperature in the range 4 K-300 K; on the contrary, in Pd-rich nanowires both magnitudes are smaller and they largely increase during cooling below 100 K. These behaviors are systematized by considering the strong dependences displayed by the magneto-crystalline anisotropy and the saturation magnetostriction on composition and temperature. At low temperatures the effective anisotropy value and the domain-wall width to grain size ratio drastically change, promoting less cooperative and harder nucleation modes.

  5. Characterization of Pd/c-Al2O3 Catalysts Prepared Using [Pd(hfac)2] in Liquid CO2

    SciTech Connect

    Kelly, M.; Kim, J; Roberts, G; Lamb, H

    2008-01-01

    A series of Pd/{gamma}-Al{sub 2}O{sub 3} catalysts was prepared from (Pd(hfac){sub 2}) (hfac = hexafluoroacetylacetonate) in liquid carbon dioxide using the method reported by Kim et al. (Chem Mater 18:4710 (2006)). The catalysts were characterized using CO pulse chemisorption, diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS), X-ray absorption fine structure (XAFS) spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron microscopy. The catalysts were reduced initially in the high-pressure CO{sub 2} reaction cell using H{sub 2} at 75 C. Samples were removed, stored in a desiccator, and re-reduced in situ at 250 C prior to pulse chemisorption, DRIFTS and XAFS. CO pulse chemisorption evidenced that the Pd dispersion decreased from 55% to 5% as the Pd loading increased from 0.58 to 3.94 wt.%. The as-prepared 0.58 and 1.77 wt.% Pd/{gamma}-Al{sub 2}O{sub 3} catalysts (after air exposure) contained oxidized Pd species that were converted after in situ reduction to supported Pd particles. The average Pd particle sizes of these two catalysts (16 and 23 {angstrom}, respectively) estimated from the first-shell Pd-Pd coordination numbers are in good agreement with the CO chemisorption results. DRIFTS evidenced a prevalence of weakly bound linear CO (CO = 2083 cm{sup -1}) adsorbed on the 0.58 wt.% Pd catalyst. A 2.95 wt% Pd catalyst (49 {angstrom} average particle size) also exhibited a strong linear CO band (CO = 2093 cm{sup -1}). In contrast, CO chemisorption on a commercial 1 wt.% Pd/Al{sub 2}O{sub 3} catalyst (37 {angstrom} average particle size) gave predominantly 2-fold bridging CO species. We infer that the supported Pd particles prepared from (Pd(hfac){sub 2}) are rougher on the atomic scale (with a higher percentage of edge and corner atoms) than equivalently sized particles in conventionally prepared Pd/{gamma}-Al{sub 2}O{sub 3} catalysts.

  6. Characterization of Na+- beta-Zeolite Supported Pd and Pd Ag Bimetallic Catalysts using EXAFS, TEM and Flow Reactor

    SciTech Connect

    Huang,W.; Lobo, R.; Chen, J.

    2008-01-01

    Flow reactor studies of the selective hydrogenation of acetylene in the presence of ethylene have been performed on Na+ exchanged {beta}-zeolite supported Pd, Ag and PdAg catalysts, as an extension of our previous batch reactor studies [W. Huang, J.R. McCormick, R.F. Lobo, J.G. Chen, J. Catal. 246 (2007) 40-51]. Results from flow reactor studies show that the PdAg/Na+-{beta}-zeolite bimetallic catalyst has lower activity than Pd/Na+-{beta}-zeolite monometallic catalyst, while Ag/Na+-{beta}-zeolite does not show any activity for acetylene hydrogenation. However, the selectivity for the PdAg bimetallic catalyst is much higher than that for either the Pd catalyst or Ag catalyst. The selectivity to byproduct (ethane) is greatly inhibited on the PdAg bimetallic catalyst as well. The results from the current flow reactor studies confirmed the pervious results from batch reactor studies [W. Huang, J.R. McCormick, R.F. Lobo, J.G. Chen, J. Catal. 246 (2007) 40-51]. In addition, we used transmission electron microscope (TEM), extended X-ray absorption fine structure (EXAFS), and FTIR of CO adsorption to confirm the formation of Pd-Ag bimetallic alloy in the PdAg/Na+-{beta}-zeolite catalyst.

  7. Structural, vibrational, and quasiparticle band structure of 1,1-diamino-2,2-dinitroethelene from ab initio calculations

    SciTech Connect

    Appalakondaiah, S.; Vaitheeswaran, G.; Lebègue, S.

    2014-01-07

    The effects of pressure on the structural and vibrational properties of the layered molecular crystal 1,1-diamino-2,2-dinitroethelene (FOX-7) are explored by first principles calculations. We observe significant changes in the calculated structural properties with different corrections for treating van der Waals interactions to Density Functional Theory (DFT), as compared with standard DFT functionals. In particular, the calculated ground state lattice parameters, volume and bulk modulus obtained with Grimme's scheme, are found to agree well with experiments. The calculated vibrational frequencies demonstrate the dependence of the intra and inter-molecular interactions on FOX-7 under pressure. In addition, we also found a significant increment in the N–H...O hydrogen bond strength under compression. This is explained by the change in bond lengths between nitrogen, hydrogen, and oxygen atoms, as well as calculated IR spectra under pressure. Finally, the computed band gap is about 2.3 eV with generalized gradient approximation, and is enhanced to 5.1 eV with the GW approximation, which reveals the importance of performing quasiparticle calculations in high energy density materials.

  8. Quasiparticle self-consistent GW calculation of Sr2RuO4 and SrRuO3

    NASA Astrophysics Data System (ADS)

    Ryee, Siheon; Jang, Seung Woo; Kino, Hiori; Kotani, Takao; Han, Myung Joon

    2016-02-01

    By using quasiparticle self-consistent GW calculations, we reexamined the electronic structure of Sr2RuO4 and SrRuO3. Our calculations show that the correlation effects beyond the conventional local density approximation and generalized gradient approximation are reasonably well captured by the QSGW self-energy without any ad hoc parameter or any ambiguity related to the double-counting and the downfolding issues. While spectral weight transfer to the lower and upper Hubbard band is not observed, the noticeable bandwidth reduction and effective-mass enhancement are obtained. Important features in the electronic structures that have been debated over the last decades such as the photoemission spectra at around -3 eV in Sr2RuO4 and the half-metallicity for SrRuO3 are discussed in the light of our QSGW results and in comparison with the previous studies. The promising aspects of QSGW are highlighted as a first-principles calculation method to describe the moderately correlated 4 d transition-metal oxides along with the limitations of QSGW.

  9. Signatures of Fermi Arcs in the Quasiparticle Interferences of the Weyl Semimetals TaAs and NbP.

    PubMed

    Chang, Guoqing; Xu, Su-Yang; Zheng, Hao; Lee, Chi-Cheng; Huang, Shin-Ming; Belopolski, Ilya; Sanchez, Daniel S; Bian, Guang; Alidoust, Nasser; Chang, Tay-Rong; Hsu, Chuang-Han; Jeng, Horng-Tay; Bansil, Arun; Lin, Hsin; Hasan, M Zahid

    2016-02-12

    The recent discovery of the first Weyl semimetal in TaAs provides the first observation of a Weyl fermion in nature. Such a topological semimetal features a novel type of anomalous surface state, the Fermi arc, which connects a pair of Weyl nodes through the boundary of the crystal. Here, we present theoretical calculations of the quasiparticle interference (QPI) patterns that arise from the surface states including the topological Fermi arcs in the Weyl semimetals TaAs and NbP. Most importantly, we discover that the QPI exhibits termination points that are fingerprints of the Weyl nodes in the interference pattern. Our results, for the first time, propose a universal interference signature of the topological Fermi arcs in TaAs, which is fundamental for scanning tunneling microscope (STM) measurements on this prototypical Weyl semimetal compound. More generally, our work provides critical guideline and methodology for STM studies on new Weyl semimetals. Further, the scattering channels revealed by our QPIs are broadly relevant to surface transport and device applications based on Weyl semimetals. PMID:26919003

  10. Accurate all-electron G0W0 quasiparticle energies employing the full-potential augmented plane-wave method

    NASA Astrophysics Data System (ADS)

    Nabok, Dmitrii; Gulans, Andris; Draxl, Claudia

    2016-07-01

    The G W approach of many-body perturbation theory has become a common tool for calculating the electronic structure of materials. However, with increasing number of published results, discrepancies between the values obtained by different methods and codes become more and more apparent. For a test set of small- and wide-gap semiconductors, we demonstrate how to reach the numerically best electronic structure within the framework of the full-potential linearized augmented plane-wave (FLAPW) method. We first evaluate the impact of local orbitals in the Kohn-Sham eigenvalue spectrum of the underlying starting point. The role of the basis-set quality is then further analyzed when calculating the G0W0 quasiparticle energies. Our results, computed with the exciting code, are compared to those obtained using the projector-augmented plane-wave formalism, finding overall good agreement between both methods. We also provide data produced with a typical FLAPW basis set as a benchmark for other G0W0 implementations.

  11. Quasiparticle dynamics and spin-orbital texture of the SrTiO3 two-dimensional electron gas.

    PubMed

    King, P D C; McKeown Walker, S; Tamai, A; de la Torre, A; Eknapakul, T; Buaphet, P; Mo, S-K; Meevasana, W; Bahramy, M S; Baumberger, F

    2014-02-27

    Two-dimensional electron gases (2DEGs) in SrTiO3 have become model systems for engineering emergent behaviour in complex transition metal oxides. Understanding the collective interactions that enable this, however, has thus far proved elusive. Here we demonstrate that angle-resolved photoemission can directly image the quasiparticle dynamics of the d-electron subband ladder of this complex-oxide 2DEG. Combined with realistic tight-binding supercell calculations, we uncover how quantum confinement and inversion symmetry breaking collectively tune the delicate interplay of charge, spin, orbital and lattice degrees of freedom in this system. We reveal how they lead to pronounced orbital ordering, mediate an orbitally enhanced Rashba splitting with complex subband-dependent spin-orbital textures and markedly change the character of electron-phonon coupling, co-operatively shaping the low-energy electronic structure of the 2DEG. Our results allow for a unified understanding of spectroscopic and transport measurements across different classes of SrTiO3-based 2DEGs, and yield new microscopic insights on their functional properties.

  12. Anharmonic phonon quasiparticle theory of zero-point and thermal shifts in insulators: Heat capacity, bulk modulus, and thermal expansion

    NASA Astrophysics Data System (ADS)

    Allen, Philip B.

    2015-08-01

    The quasiharmonic (QH) approximation uses harmonic vibrational frequencies ωQ ,H(V ) computed at volumes V near V0 where the Born-Oppenheimer (BO) energy Eel(V ) is minimum. When this is used in the harmonic free energy, QH approximation gives a good zeroth order theory of thermal expansion and first-order theory of bulk modulus, where nth-order means smaller than the leading term by ɛn, where ɛ =ℏ ωvib/Eel or kBT /Eel , and Eel is an electronic energy scale, typically 2 to 10 eV. Experiment often shows evidence for next-order corrections. When such corrections are needed, anharmonic interactions must be included. The most accessible measure of anharmonicity is the quasiparticle (QP) energy ωQ(V ,T ) seen experimentally by vibrational spectroscopy. However, this cannot just be inserted into the harmonic free energy FH. In this paper, a free energy is found that corrects the double-counting of anharmonic interactions that is made when F is approximated by FH( ωQ(V ,T ) ) . The term "QP thermodynamics" is used for this way of treating anharmonicity. It enables (n +1 ) -order corrections if QH theory is accurate to order n . This procedure is used to give corrections to the specific heat and volume thermal expansion. The QH formulas for isothermal (BT) and adiabatic (BS) bulk moduli are clarified, and the route to higher-order corrections is indicated.

  13. Exciton analysis of many-body wave functions: Bridging the gap between the quasiparticle and molecular orbital pictures

    NASA Astrophysics Data System (ADS)

    Bäppler, Stefanie A.; Plasser, Felix; Wormit, Michael; Dreuw, Andreas

    2014-11-01

    Exciton sizes and electron-hole binding energies, which are central properties of excited states in extended systems and crucial to the design of modern electronic devices, are readily defined within a quasiparticle framework but are quite challenging to understand in the molecular-orbital picture. The intent of this work is to bridge this gap by providing a general way of extracting the exciton wave function out of a many-body wave function obtained by a quantum chemical excited-state computation. This methodology, which is based on the one-particle transition density matrix, is implemented within the ab initio algebraic diagrammatic construction scheme for the polarization propagator and specifically the evaluation of exciton sizes, i.e., dynamic charge separation distances, is considered. A number of examples are presented. For stacked dimers it is shown that the exciton size for charge separated states corresponds to the intermolecular separation, while it only depends on the monomer size for locally excited states or Frenkel excitons. In the case of conjugated organic polymers, the tool is applied to analyze exciton structure and dynamic charge separation. Furthermore, it is discussed how the methodology may be used for the construction of a charge-transfer diagnostic for time-dependent density-functional theory.

  14. Full self-consistency versus quasiparticle self-consistency in diagrammatic approaches: Exactly solvable two-site Hubbard model

    DOE PAGES

    Kutepov, A. L.

    2015-07-22

    Self-consistent solutions of Hedin's equations (HE) for the two-site Hubbard model (HM) have been studied. They have been found for three-point vertices of increasing complexity (Γ = 1 (GW approximation), Γ₁ from the first-order perturbation theory, and the exact vertex ΓE). Comparison is made between the cases when an additional quasiparticle (QP) approximation for Green's functions is applied during the self-consistent iterative solving of HE and when QP approximation is not applied. Results obtained with the exact vertex are directly related to the present open question—which approximation is more advantageous for future implementations, GW + DMFT or QPGW + DMFT.more » It is shown that in a regime of strong correlations only the originally proposed GW + DMFT scheme is able to provide reliable results. Vertex corrections based on Perturbation Theory systematically improve the GW results when full self-consistency is applied. The application of QP self-consistency combined with PT vertex corrections shows similar problems to the case when the exact vertex is applied combined with QP sc. An analysis of Ward Identity violation is performed for all studied in this work's approximations and its relation to the general accuracy of the schemes used is provided.« less

  15. Full self-consistency versus quasiparticle self-consistency in diagrammatic approaches: Exactly solvable two-site Hubbard model

    SciTech Connect

    Kutepov, A. L.

    2015-07-22

    Self-consistent solutions of Hedin's equations (HE) for the two-site Hubbard model (HM) have been studied. They have been found for three-point vertices of increasing complexity (Γ = 1 (GW approximation), Γ₁ from the first-order perturbation theory, and the exact vertex ΓE). Comparison is made between the cases when an additional quasiparticle (QP) approximation for Green's functions is applied during the self-consistent iterative solving of HE and when QP approximation is not applied. Results obtained with the exact vertex are directly related to the present open question—which approximation is more advantageous for future implementations, GW + DMFT or QPGW + DMFT. It is shown that in a regime of strong correlations only the originally proposed GW + DMFT scheme is able to provide reliable results. Vertex corrections based on Perturbation Theory systematically improve the GW results when full self-consistency is applied. The application of QP self-consistency combined with PT vertex corrections shows similar problems to the case when the exact vertex is applied combined with QP sc. An analysis of Ward Identity violation is performed for all studied in this work's approximations and its relation to the general accuracy of the schemes used is provided.

  16. Accurate energy bands calculated by the hybrid quasiparticle self-consistent GW method implemented in the ecalj package

    NASA Astrophysics Data System (ADS)

    Deguchi, Daiki; Sato, Kazunori; Kino, Hiori; Kotani, Takao

    2016-05-01

    We have recently implemented a new version of the quasiparticle self-consistent GW (QSGW) method in the ecalj package released at http://github.com/tkotani/ecalj. Since the new version of the ecalj package is numerically stable and more accurate than the previous versions, we can perform calculations easily without being bothered with tuning input parameters. Here we examine its ability to describe energy band properties, e.g., band-gap energy, eigenvalues at special points, and effective mass, for a variety of semiconductors and insulators. We treat C, Si, Ge, Sn, SiC (in 2H, 3C, and 4H structures), (Al, Ga, In) × (N, P, As, Sb), (Zn, Cd, Mg) × (O, S, Se, Te), SiO2, HfO2, ZrO2, SrTiO3, PbS, PbTe, MnO, NiO, and HgO. We propose that a hybrid QSGW method, where we mix 80% of QSGW and 20% of LDA, gives universally good agreement with experiments for these materials.

  17. Reprint of : Hanbury-Brown Twiss noise correlation with time controlled quasi-particles in ballistic quantum conductors

    NASA Astrophysics Data System (ADS)

    Glattli, D. C.; Roulleau, P.

    2016-08-01

    We study the Hanbury Brown and Twiss correlation of electronic quasi-particles injected in a quantum conductor using current noise correlations and we experimentally address the effect of finite temperature. By controlling the relative time of injection of two streams of electrons it is possible to probe the fermionic antibunching, performing the electron analog of the optical Hong Ou Mandel (HOM) experiment. The electrons are injected using voltage pulses with either sine-wave or Lorentzian shape. In the latter case, we propose a set of orthogonal wavefunctions, describing periodic trains of multiply charged electron pulses, which give a simple interpretation to the HOM shot noise. The effect of temperature is then discussed and experimentally investigated. We observe a perfect electron anti-bunching for a large range of temperature, showing that, as recently predicted, thermal mixing of the states does not affect anti-bunching properties, a feature qualitatively different from dephasing. For single charge Lorentzian pulses, we provide experimental evidence of the prediction that the HOM shot noise variation versus the emission time delay is remarkably independent of the temperature.

  18. Serum Iron Levels and the Risk of Parkinson Disease: A Mendelian Randomization Study

    PubMed Central

    Gögele, Martin; Lill, Christina M.; Bertram, Lars; Do, Chuong B.; Eriksson, Nicholas; Foroud, Tatiana; Myers, Richard H.; Nalls, Michael; Keller, Margaux F.; Benyamin, Beben; Whitfield, John B.; Pramstaller, Peter P.; Hicks, Andrew A.; Thompson, John R.; Minelli, Cosetta

    2013-01-01

    Background Although levels of iron are known to be increased in the brains of patients with Parkinson disease (PD), epidemiological evidence on a possible effect of iron blood levels on PD risk is inconclusive, with effects reported in opposite directions. Epidemiological studies suffer from problems of confounding and reverse causation, and mendelian randomization (MR) represents an alternative approach to provide unconfounded estimates of the effects of biomarkers on disease. We performed a MR study where genes known to modify iron levels were used as instruments to estimate the effect of iron on PD risk, based on estimates of the genetic effects on both iron and PD obtained from the largest sample meta-analyzed to date. Methods and Findings We used as instrumental variables three genetic variants influencing iron levels, HFE rs1800562, HFE rs1799945, and TMPRSS6 rs855791. Estimates of their effect on serum iron were based on a recent genome-wide meta-analysis of 21,567 individuals, while estimates of their effect on PD risk were obtained through meta-analysis of genome-wide and candidate gene studies with 20,809 PD cases and 88,892 controls. Separate MR estimates of the effect of iron on PD were obtained for each variant and pooled by meta-analysis. We investigated heterogeneity across the three estimates as an indication of possible pleiotropy and found no evidence of it. The combined MR estimate showed a statistically significant protective effect of iron, with a relative risk reduction for PD of 3% (95% CI 1%–6%; p = 0.001) per 10 µg/dl increase in serum iron. Conclusions Our study suggests that increased iron levels are causally associated with a decreased risk of developing PD. Further studies are needed to understand the pathophysiological mechanism of action of serum iron on PD risk before recommendations can be made. Please see later in the article for the Editors' Summary PMID:23750121

  19. Programmed Death Ligand 1 (PD-L1)-targeted TRAIL combines PD-L1-mediated checkpoint inhibition with TRAIL-mediated apoptosis induction.

    PubMed

    Hendriks, Djoke; He, Yuan; Koopmans, Iris; Wiersma, Valerie R; van Ginkel, Robert J; Samplonius, Douwe F; Helfrich, Wijnand; Bremer, Edwin

    2016-08-01

    Antibodies that block PD-L1/PD-1 immune checkpoints restore the activity of functionally-impaired antitumor T cells. These antibodies show unprecedented clinical benefit in various advanced cancers, particularly in melanoma. However, only a subset of cancer patients responds to current PD-L1/PD-1-blocking strategies, highlighting the need for further advancements in PD-L1/PD-1-based immunotherapy. Here, we report on a novel approach designed to combine PD-L1 checkpoint inhibition with the tumor-selective induction of apoptosis by TNF-related Apoptosis Inducing Ligand (TRAIL). In brief, a new bi-functional fusion protein, designated anti-PD-L1:TRAIL, was constructed comprising a PD-L1-blocking antibody fragment genetically fused to the extracellular domain of the pro-apoptotic tumoricidal protein TRAIL. Treatment of PD-L1-expressing cancer cells with anti-PD-L1:TRAIL induced PD-L1-directed TRAIL-mediated cancer cell death. Treatment of T cells with anti-PD-L1:TRAIL augmented T cell activation, as evidenced by increased proliferation, secretion of IFNγ and enhanced killing of cancer cell lines and primary patient-derived cancer cells in mixed T cell/cancer cell culture experiments. Of note, elevated levels of IFNγ further upregulated PD-L1 on cancer cells and simultaneously sensitized cancer cells to TRAIL-mediated apoptosis by anti-PD-L1:TRAIL. Additionally, anti-PD-L1:TRAIL converted immunosuppressive PD-L1-expressing myeloid cells into pro-apoptotic effector cells that triggered TRAIL-mediated cancer cell death. In conclusion, combining PD-L1 checkpoint inhibition with TRAIL-mediated induction of apoptosis using anti-PD-L1:TRAIL yields promising multi-fold and mutually reinforcing anticancer activity that may be exploited to enhance the efficacy of therapeutic PD-L1/PD-1 checkpoint inhibition. PMID:27622071

  20. Crystal structure and hydrogenation properties of pseudo-binary Mg 6Pd 0.5Ni 0.5 complex metallic alloy

    NASA Astrophysics Data System (ADS)

    Cuevas, F.; Fernández, J. F.; Ares, J. R.; Leardini, F.; Latroche, M.

    2009-10-01

    The crystal structure of the Ni-substituted Mg 6.10(2)Pd 0.52(2)Ni 0.41(2) complex metallic alloy has been determined by X-ray and neutron powder diffraction. The reaction of this compound at 573 K towards deuterium absorption for pressures up to 23 bar has also been studied. The crystal structure of Mg 6.10(2)Pd 0.52(2)Ni 0.41(2) compound was determined in the light of Samson's [Acta Crystallogr. B 28 (1972) 936) and Makongo's (Philos. Mag. 86 (2006) 427] models for the binary Mg 6Pd compound. It crystallizes in F4¯3m space group with lattice parameter 20.13331(7) Å. The refined unit-cell composition is Mg 342(1)Pd 29(1)Ni 23(1) with Z=56. Nickel by palladium substitution is not fully random. Nickel atoms preferentially locate on Pd sites with low coordination number due to steric effects. Deuterium uptake is 9.6 D/f.u. under the given conditions of pressure and temperature. Upon absorption, the intermetallic compound disproportionates into MgD 2, Mg 5Pd 2 and Mg 2NiD 4 phases. The Mg 2NiD 4 phase is observed to crystallize in the orthorhombic LT2 modification for which an averaged crystal structure in the Pcc2 space group is proposed.

  1. Preparation of PdAg and PdAu nanoparticle-loaded carbon black catalysts and their electrocatalytic activity for the glycerol oxidation reaction in alkaline medium

    NASA Astrophysics Data System (ADS)

    Lam, Binh Thi Xuan; Chiku, Masanobu; Higuchi, Eiji; Inoue, Hiroshi

    2015-11-01

    PdAg and PdAu alloy nanoparticle catalysts for the glycerol oxidation reaction (GOR) were prepared at room temperature by a wet method. The molar ratio of the precursors controlled the bulk composition of the PdAg and PdAu alloys, and their surface composition was Ag-enriched and Pd-enriched, respectively. On PdAg-loaded carbon black (PdAg/CB) electrodes, the onset potential of GOR was 0.10-0.15 V more negative than on the Pd/CB electrode due to the electronic effect. The ratio of GOR peak current densities in the backward and forward sweeps of CVs (ib/if) was smaller because of the improved tolerance to the poisoning species. The ratio of the GOR current density at 60 and 5 min (i60/i5) for the PdAg/CB electrodes was higher for more negative potentials than the Pd/CB electrode. In contrast, the PdAu-loaded CB (PdAu/CB) electrodes had an onset potential of GOR similar to the Pd/CB electrode and a higher GOR peak current density owing to the bi-functional effect. However, the ib/if ratio was higher for PdAu/CB because of the increase in ib as the Pd surface was recovered, and the i60/i5 ratio was higher for more positive potentials, similar to the Pd/CB electrode.

  2. Expression of PD-L1 on Canine Tumor Cells and Enhancement of IFN-γ Production from Tumor-Infiltrating Cells by PD-L1 Blockade

    PubMed Central

    Maekawa, Naoya; Konnai, Satoru; Ikebuchi, Ryoyo; Okagawa, Tomohiro; Adachi, Mami; Takagi, Satoshi; Kagawa, Yumiko; Nakajima, Chie; Suzuki, Yasuhiko; Murata, Shiro; Ohashi, Kazuhiko

    2014-01-01

    Programmed death 1 (PD-1), an immunoinhibitory receptor, and programmed death ligand 1 (PD-L1), its ligand, together induce the “exhausted” status in antigen-specific lymphocytes and are thus involved in the immune evasion of tumor cells. In this study, canine PD-1 and PD-L1 were molecularly characterized, and their potential as therapeutic targets for canine tumors was discussed. The canine PD-1 and PD-L1 genes were conserved among canine breeds. Based on the sequence information obtained, the recombinant canine PD-1 and PD-L1 proteins were constructed; they were confirmed to bind each other. Antibovine PD-L1 monoclonal antibody effectively blocked the binding of recombinant PD-1 with PD-L1–expressing cells in a dose-dependent manner. Canine melanoma, mastocytoma, renal cell carcinoma, and other types of tumors examined expressed PD-L1, whereas some did not. Interestingly, anti-PD-L1 antibody treatment enhanced IFN-γ production from tumor-infiltrating cells. These results showed that the canine PD-1/PD-L1 pathway is also associated with T-cell exhaustion in canine tumors and that its blockade with antibody could be a new therapeutic strategy for canine tumors. Further investigations are needed to confirm the ability of anti-PD-L1 antibody to reactivate canine antitumor immunity in vivo, and its therapeutic potential has to be further discussed. PMID:24915569

  3. Ultradiscretization of the theta function solution of pd Toda

    NASA Astrophysics Data System (ADS)

    Iwao, Shinsuke; Tokihiro, Tetsuji

    2007-10-01

    A periodic box-ball system (pBBS) is obtained by ultradiscretizing the periodic discrete Toda equation (pd Toda equation). We show the relation between a Young diagram of the pBBS and a spectral curve of the pd Toda equation. The formula for the fundamental cycle of the pBBS is obtained as a corollary.

  4. Muon spin relaxation in spin glass PdMn

    SciTech Connect

    Heffner, R.H.; Leon, M.; Schillaci, M.E.; Dodds, S.A.; Gist, G.A.; MacLaughlin, D.E.; Mydosh, J.A.; Nieuwenhuys, G.J.

    1983-01-01

    Muon spin relaxation (..mu..SR) rates have been measured in transverse, longitudinal, and zero applied field for the spin glass PdMn (7 at. %), and are compared with a previous study of the disordered ferromagnet PdMn (2 at. %). The calculated paramagnetic state transverse field relaxation rate for noninteracting spins is much larger than the observed rate in spin glass PdMn, but is in good agreement with ferromagnetic PdMn. The zero field relaxation rate shows a sharp cusp at T/sub g/=5K. An applied longitudinal field of 5 kG is insufficient to suppress this cusp in spin glss PdMn, but will suppress a similar cusp in ferromagnetic PdMn. Below T/sub g/=5K. An applied longitudinal field of 5 kG is insufficient to suppress this cusp in spin glass PdMn, but will suppress a similar cusp in ferromagnetic PdMn. Below T/sub g/, a distribution of quasistatic local fields is observed in zero field, which has the same temperature dependence for both samples. Comparisons with model calculations are discussed.

  5. Adsorption of molecular hydrogen on Pd(Pt) decorated graphene

    NASA Astrophysics Data System (ADS)

    Adhikari, Narayan; Khaniya, Asim; Lamichhane, Saran; Pantha, Nurapati

    2015-03-01

    We have performed the first-principles based Density Functional Theory (DFT) calculations to study the stability, geometrical structures, and electronic properties of a Pd(Pt) atom adsorbed graphene to investigate the possibility of using Pd(Pt) decorated graphene as energy storage materials with reference to pristine graphene. The London dispersion forces have been incorporated by the DFT-D2 levels of calculations implemented in Quantum Espresso packages. Our findings show that Pd and Pt both adsorb on graphene at Bridge site. The electronic structures of Pd(Pt) adsorbed graphene possesses band gap opening due to breaking of the symmetry of graphene. Further we have studied the adsorption of moelcular hydrogen ((H 2) n , n = 1-7) on the Pd(Pt)-graphene system. The adatom Pd(Pt) enhances the binding energy per hydrogen molecule in Pd(Pt)-graphene system in comparison to that in the pristine graphene. The binding energy per hydrogen molecule of the adatom-graphene system decreases as the number of H 2 molecules increases and finally it saturates to 0.15 eV (0.16 eV) per hydrogen molecule for Pd-graphene (Pt-graphene) systems respectively. ICTP-NET 56/TWAS.

  6. Electroanalysis of As(III) at nanodendritic Pd on PEDOT.

    PubMed

    Dash, Sthitaprajna; Munichandraiah, N

    2014-04-01

    Nanodendritic Pd electrodeposited on poly(3,4-ethylenedioxythiophene) (PEDOT) modified Pd nanodendrite electrodes has been studied for electroanalysis of As(III) in 1 M HCl solution. The Pd nanodendrites are grown on a porous thin film of PEDOT by electrodeposition process. Pd-PEDOT/C electrodes are characterized by physicochemical and electrochemical studies. Cyclic voltammetry studies show that Pd-PEDOT/C electrodes exhibit greater electrocatalytic activity towards As(iii)/As(0) redox reaction than the Pd/C electrodes. Differential pulse anodic stripping voltammetry (DPASV) is performed for analysis of As(iii) ion at pH 1.0. The Pd-PEDOT/C electrode is highly sensitive towards As(III) detection with sensitivity of 1482 μA cm(-2) μM(-1). A wide detection range up to 10 μM and low detection limit of 7 nM (0.52 ppb) are obtained with a pre-deposition time of 120 s under optimum conditions. High sensitivity and low detection limit obtained on Pd-PEDOT/C, for the first time in the literature, are attractive from a practical view point. Interference studies of Cu(II) ions are investigated and it is observed that Cu(II) ions do not interfere.

  7. New structures in Pd-rich ordered alloys

    NASA Astrophysics Data System (ADS)

    Corbitt, Jacqueline; Gilmartin, Erin; Hart, Gus

    2010-10-01

    An intriguing intermetallic structure with 8:1 stoichiometry was discovered in the 1950s in the Pt-Ti system. Since then a handful of other Pt/Pd/Ni binary systems have been observed to exhibit this curious structure (Pt8Zr, Pd8Mo, Ni8Nb, etc). This ordered structure can significantly increase the hardness of an alloy. For jewelry applications involving Pt and Pd, international hallmarking standards require that the alloys be at least 95% pure by weight. However, Pt- and Pd-rich alloys are often soft when purity is high if the minority atoms are disordered. Because the 8:1 structure maintains a high weight percentage of Pt/Pd, it can satisfy purity standards while increasing performance. Recent calculations and experiments suggest that the 8:1 structure may form in about 20 previously unsuspected Pt/Pd binary systems. Using first-principles calculations and cluster expansion modeling, we have performed a ground state search to find the stable structures in Pd-Nb and Pd-Cu. In collaboration with Candace Lang's group at University of Capetown South Africa, we are working to experimentally validate the predicted ground states.

  8. New structures in Pd-rich ordered alloys

    NASA Astrophysics Data System (ADS)

    Corbitt, Jacqueline; Gilmartin, Erin; Hart, Gus

    2009-03-01

    An intriguing intermetallic structure with 8:1 stoichiometry was discovered in the 1950s in the Pt-Ti system. Since then a handful of other Pt/Pd/Ni binary systems have been observed to exhibit this curious structure (Pt8Zr, Pd8Mo, Ni8Nb, etc). This ordered structure can significantly increase the hardness of an alloy. For jewelry applications involving Pt and Pd, international hallmarking standards require that the alloys be at least 95% pure by weight. However, Pt- and Pd-rich alloys are often soft when purity is high if the minority atoms are disordered. Because the 8:1 structure maintains a high weight percentage of Pt/Pd, it can satisfy purity standards while increasing performance. Recent calculations and experiments suggest that the 8:1 structure may form in about 20 previously unsuspected Pt/Pd binary systems. Using first-principles calculations and cluster expansion modeling, we have performed a ground state search to find the stable structures in Pd-Nb and Pd-Cu. In collaboration with Candace Lang's group at University of Capetown South Africa, we are working to experimentally validate the predicted ground states.

  9. New structures in Pd-rich ordered alloys

    NASA Astrophysics Data System (ADS)

    Corbitt, Jacqueline; Gilmartin, Erin; Hart, Gus

    2010-03-01

    An intriguing intermetallic structure with 8:1 stoichiometry was discovered in 1959 in the Pt-Ti system. Since then a handful of other Pt/Pd/Ni binary systems have been observed to exhibit this structure (Pt8Zr, Pd8Mo, Ni8Nb, etc). Precipitates of this ordered structure can significantly increase the hardness of an alloy. For jewelry applications involving Pt and Pd, international hallmarking standards require that the alloys be at least 95% pure by weight. However, Pt- and Pd-rich alloys are often too soft for jewelry applications when purity is high and the minority atoms are disordered. Because the 8:1 structure maintains a high weight percentage of Pt/Pd, it can satisfy hallmarking while increasing performance. Recent calculations and experiments suggest that the 8:1 structure may form in about 20 previously unsuspected Pt/Pd binary systems. Using first-principles calculations and cluster expansion modeling, we have performed a ground state search to find the stable structures in Pd-Nb and Pd-Cu. In collaboration with Candace Lang's group at University of Capetown South Africa, we are working to experimentally validate the predicted ground states.

  10. PD-1 marks dysfunctional regulatory T cells in malignant gliomas

    PubMed Central

    Lowther, Daniel E.; Goods, Brittany A.; Lucca, Liliana E.; Lerner, Benjamin A.; Raddassi, Khadir; van Dijk, David; Hernandez, Amanda L.; Duan, Xiangguo; Gunel, Murat; Coric, Vlad; Krishnaswamy, Smita; Hafler, David A.

    2016-01-01

    Immunotherapies targeting the immune checkpoint receptor programmed cell death protein 1 (PD-1) have shown remarkable efficacy in treating cancer. CD4+CD25hiFoxP3+ Tregs are critical regulators of immune responses in autoimmunity and malignancies, but the functional status of human Tregs expressing PD-1 remains unclear. We examined functional and molecular features of PD-1hi Tregs in healthy subjects and patients with glioblastoma multiforme (GBM), combining functional assays, RNA sequencing, and cytometry by time of flight (CyTOF). In both patients with GBM and healthy subjects, circulating PD-1hi Tregs displayed reduced suppression of CD4+ effector T cells, production of IFN-γ, and molecular signatures of exhaustion. Transcriptional profiling of tumor-resident Tregs revealed that several genes coexpressed with PD-1 and associated with IFN-γ production and exhaustion as well as enrichment in exhaustion signatures compared with circulating PD-1hi Tregs. CyTOF analysis of circulating and tumor-infiltrating Tregs from patients with GBM treated with PD-1-blocking antibodies revealed that treatment shifts the profile of circulating Tregs toward a more exhausted phenotype reminiscent of that of tumor-infiltrating Tregs, further increasing IFN-γ production. Thus, high PD-1 expression on human Tregs identifies dysfunctional, exhausted Tregs secreting IFN-γ that exist in healthy individuals and are enriched in tumor infiltrates, possibly losing function as they attempt to modulate the antitumoral immune responses. PMID:27182555

  11. Endo-Selective Pd-Catalyzed Silyl Methyl Heck Reaction

    PubMed Central

    2015-01-01

    A palladium (Pd)-catalyzed endo-selective Heck reaction of iodomethylsilyl ethers of phenols and aliphatic alkenols has been developed. Mechanistic studies reveal that this silyl methyl Heck reaction operates via a hybrid Pd-radical process and that the silicon atom is crucial for the observed endo selectivity. The obtained allylic silyloxycycles were further oxidized into (Z)-alkenyldiols. PMID:25494921

  12. Pembrolizumab: PD-1 inhibition as a therapeutic strategy in cancer.

    PubMed

    McDermott, J; Jimeno, A

    2015-01-01

    Programmed cell death protein 1 (PD-1) and its ligands, programmed cell death 1 ligand 1 (PD-L1) and 2 (PD-L2) play an important role in regulating immune response through various mechanisms. This inhibitory action is thought to assist in immune evasion by cancer cells as PD-1, PD-L1 and PD-L2 have been found to be abnormally expressed by tumor cells and lymphocytes in the tumor microenvironment. Preclinical studies described PD-1 blockade resulting in tumor growth suppression and even decreased metastasis. This has led to the development of pembrolizumab (MK-3475), a highly selective, humanized monoclonal IgG4-kappa isotype antibody against PD-1. Early clinical trials have shown high tumor response rates and long duration of effect in previously treated advanced melanoma resulting in accelerated FDA approval for the drug in this situation. Pembrolizumab has also had success in non-small cell lung cancer and is being tested in multiple other tumor types. This review will discuss the development, preclinical data, pharmacokinetics and clinical efficacy to date of pembrolizumab.

  13. Study of novel nanostructured Pd-Mn oxides

    NASA Astrophysics Data System (ADS)

    Zhang, Heng; Gromek, Jack; Augustine, Matthew; Fernando, Gayanath; Samuel Boorse, R.; Marcus, Harris L.

    2004-02-01

    Novel Pd-Mn oxides have been synthesized using chemical processing. The study indicated that the Pd-Mn oxide powders have nanometer structure. The alloying of Mn improves the thermal stability and modifies re-oxidation characteristic of the palladium oxide during the thermal cycling.

  14. Antitumor vaccination of prostate cancer patients elicits PD-1/PD-L1 regulated antigen-specific immune responses.

    PubMed

    Rekoske, Brian T; Olson, Brian M; McNeel, Douglas G

    2016-06-01

    We have previously reported that tumor antigen-specific DNA vaccination in mice led to an increase in IFNγ-secreting T cells and an increase in tumor expression of PD-L1. Further, we demonstrated that increasing the encoded antigen's MHC-binding affinity led to increased PD-1 expression on antigen-specific CD8(+) T cells. Together these phenomena provided resistance to antitumor immunization that was abrogated with PD-1/PD-L1 blockade. We consequently sought to determine whether similar regulation occurred in human patients following antitumor immunization. Using clinical samples from prostate cancer patients who were previously immunized with a DNA vaccine, we analyzed changes in checkpoint receptor expression on antigen-specific CD8(+) T cells, the effect of PD-1 blockade on elicited immune responses, and for changes in checkpoint ligand expression on patients' circulating tumor cells (CTCs). We observed no significant changes in T-cell expression of PD-1 or other checkpoint receptors, but antigen-specific immune responses were detected and/or augmented with PD-1 blockade as detected by IFNγ and granzyme B secretion or trans vivo DTH testing. Moreover, PD-L1 expression was increased on CTCs following vaccination, and this PD-L1 upregulation was associated with the development of sustained T-cell immunity and longer progression-free survival. Finally, similar results were observed with patients treated with sipuleucel-T, another vaccine targeting the same prostate antigen. These findings provide in-human rationale for combining anticancer vaccines with PD-1 blocking antibodies, particularly for the treatment of prostate cancer, a disease for which vaccines have demonstrated benefit and yet PD-1 inhibitors have shown little clinical benefit to date as monotherapies. PMID:27471641

  15. Ion beam induced effects on the ferromagnetism in Pd nanoparticles

    SciTech Connect

    Kulriya, P. K.; Mehta, B. R.; Agarwal, D. C.; Agarwal, Kanika; Kumar, Praveen; Shivaprasad, S. M.; Avasthi, D. K.

    2012-06-05

    Present study demonstrates the role of metal-insulator interface and ion irradiation induced defects on the ferromagnetic properties of the non-magnetic materials. Magnetic properties of the Pd nanoparticles(NPs) embedded in the a-silica matrix synthesized using atom beam sputtering technique, were determined using SQUID magnetometry measurements which showed that ferromagnetic response of Pd increased by 3.5 times on swift heavy ion(SHI) irradiation. The ferromagnetic behavior of the as-deposited Pd NPs is due to strain induced by the surrounding matrix and modification in the electronic structure at the Pd-silica interface as revealed by insitu XRD and XPS investigations, respectively. The defects created by the SHI bombardment are responsible for enhancement of the magnetization in the Pd NPs.

  16. Ion beam mixing in Ag-Pd alloys

    NASA Astrophysics Data System (ADS)

    Klatt, J. L.; Averback, R. S.; Peak, David

    1989-09-01

    Ion beam mixing during 750 keV Kr+ irradiation at 80 K was measured on a series of Ag-Pd alloys using Au marker atoms. The mixing in pure Ag was the greatest and it decreased monotonically with increasing Pd content, being a factor of 10 higher in pure Ag than in pure Pd. This large difference in mixing cannot be explained by the difference in cohesion energy between Ag and Pd in the thermodynamic model of ion beam mixing proposed by Johnson et al. [W. L. Johnson, Y. T. Cheng, M. Van Rossum, and M-A. Nicolet, Nucl. Instrum. Methods B 7/8, 657 (1985)]. An alternative model based on local melting in the cascade is shown to account for the ion beam mixing results in Ag and Pd.

  17. [PK/PD modeling of aminoglycoside nephrotoxicity].

    PubMed

    Rougier, F; Corvaisier, S; Ducher, M; Claude, D; Jelliffe, R W; Maire, P

    2003-06-01

    Aminoglycosides are bactericidial antibiotics with a serum concentration-dependent activity. They are mainly eliminated by the kidneys and the main difficulty arising in clinical use is their uptake by the renal cortex which leads to nephrotoxicity. An ototoxicity is also reported. We propose a PK/PD modelling of aminoglycoside nephrotoxicity which unifies more fourty years of physiological knowledge. This deterministic model successively describes the pharmacokinetics of aminoglycosides, their storage into renal cortex, their effect on renal cells, their consequences on the renal function through tubuloglomerular feedback and the changes in the serum concentrations of creatinine that is considered as a toxicity marker. The simulation of the model displays the leading effect of the shape and daily-time of administration schedule on the search for minimizing toxicity.

  18. Buffer layer annealing effects on the magnetization reversal process in Pd/Co/Pd systems

    NASA Astrophysics Data System (ADS)

    Fassatoui, A.; Belhi, R.; Vogel, J.; Abdelmoula, K.

    2016-12-01

    We have investigated the effect of annealing the buffer layer on the magnetization reversal behavior in Pd/Co/Pd thin films using magneto-optical Kerr microscopy. It was found that annealing the buffer layer at 150 °C for 1 h decreases the coercivity and increases the saturation magnetization and the effective magnetic anisotropy constant. This study also shows that the annealing induces a change of the magnetization reversal from a mixed nucleation and domain wall propagation process to one dominated by domain wall propagation. This result demonstrates that the main effect of annealing the buffer layer is to decrease the domain wall pinning in the Co layer, favoring the domain wall propagation mode.

  19. Chemical ordering in magnetic FePd/Pd(001) epitaxial thin films induced by annealing

    SciTech Connect

    Halley, D.; Bayle-Guillemaud, P.; Arenal, R.; Marty, A.; Samson, Y.; Gilles, B.

    2004-11-01

    Chemically disordered FePd epitaxial layers are grown at room temperature by molecular beam epitaxy on a Pd(001) buffer layer and then annealed in order to induce the chemically ordered L1{sub 0} (AuCu I) structure. Contrary to what is observed in the case of ordering during growth above room temperature, the ordered structure appears here with the three possible variants of the L1{sub 0} phase. The ratio of the three different variant volumes is set by the residual epitaxial strain in the layer before annealing. It thus explains that for long annealing times, the long-range order parameter associated with the L1{sub 0} variant with c along the (100) growth direction saturates at a value close to 0.65, and never reaches unity. Magnetic consequences of the ordering are studied.

  20. Steering epitaxial alignment of Au, Pd, and AuPd nanowire arrays by atom flux change.

    PubMed

    Yoo, Youngdong; Seo, Kwanyong; Han, Sol; Varadwaj, Kumar S K; Kim, Hyun You; Ryu, Ji Hoon; Lee, Hyuck Mo; Ahn, Jae Pyoung; Ihee, Hyotcherl; Kim, Bongsoo

    2010-02-10

    We have synthesized epitaxial Au, Pd, and AuPd nanowire arrays in vertical or horizontal alignment on a c-cut sapphire substrate. We show that the vertical and horizontal nanowire arrays grow from half-octahedral seeds by the correlations of the geometry and orientation of seed crystals with those of as-grown nanowires. The alignment of nanowires can be steered by changing the atom flux. At low atom deposition flux vertical nanowires grow, while at high atom flux horizontal nanowires grow. Similar vertical/horizontal epitaxial growth is also demonstrated on SrTiO(3) substrates. This orientation-steering mechanism is visualized by molecular dynamics simulations. PMID:20050692

  1. The influence of comorbid personality disorder on the effects of behavioural activation vs. antidepressant medication for major depressive disorder: results from a randomized trial in Iran.

    PubMed

    Moradveisi, Latif; Huibers, Marcus J H; Renner, Fritz; Arasteh, Modabber; Arntz, Arnoud

    2013-08-01

    There is a disagreement about the impact of personality disorder (PD) on treatment outcome for patients with major depressive disorder (MDD). 100 out-patients with MDD were randomized to 16 sessions of behavioural activation (BA) (n = 50) or antidepressant medication (ADM) (n = 50) in Iran. Main outcome was depression severity, measured with the Beck Depression Inventory (BDI-II) and the Hamilton Rating Scale for Depression (HRSD), and assessed at 0, 4, 13 and 49 weeks. Participants with comorbid PDs had higher scores on BDI and HRSD at baseline and throughout the study than participants without comorbid PD. Patients with and without comorbid personality pathology responded equally to treatment on the short-and the long-term. Overall, BA was better in reducing symptoms in patients but this effect was not influenced by comorbid PD. Similar effects were found for a dimensional PD-measure. Only cluster-C PD-traits turned out to be associated with overall depression severity. Cluster-A PD-traits predicted poorer long-term treatment response to ADM and BA, but only on the BDI, not on the HRSD. No effects of cluster-B PD-traits were found. However, PD was associated with higher dropout. The general conclusion is that comorbid PD pathology, especially from cluster-C, is associated with higher depression severity, but not with less response to treatment. Comorbid PD did predict increased chance of dropout.

  2. How to Do Random Allocation (Randomization)

    PubMed Central

    Shin, Wonshik

    2014-01-01

    Purpose To explain the concept and procedure of random allocation as used in a randomized controlled study. Methods We explain the general concept of random allocation and demonstrate how to perform the procedure easily and how to report it in a paper. PMID:24605197

  3. Adsorbate-Induced Segregation in a PdAg Membrane Model System: Pd3Ag(1 1 1)

    SciTech Connect

    Svenum, I. H.; Herron, Jeffrey A.; Mavrikakis, Manos; Venvik, H. J.

    2012-10-15

    Thin PdAg alloy membranes with 20–25% Ag are being developed for hydrogen separation technology. Despite many investigations on such membranes as well as representative experimental and theoretical model systems, unresolved issues remain concerning the effect of the alloy surface structure and composition on adsorption and vice versa. Therefore, the interaction between hydrogen, carbon monoxide or oxygen with the surface of a PdAg model alloy was studied using periodic self-consistent density functional theory (DFT-GGA) calculations. In particular, the adsorption structure, coverage dependence and possible adsorption-induced segregation phenomena were addressed using Pd3Ag(1 1 1) model surfaces with varying degrees of surface segregation. In agreement with previous experimental and theoretical investigations, we predict Ag surface termination to be energetically favorable in vacuum. The segregation of Ag is then reversed upon adsorption of H, CO or O. For these adsorbates, the binding is strongest on Pd three-fold hollow sites, and hence complete Pd termination is favored at high coverage of H or CO, while 25% Ag may remain under oxygen because of the lower O-saturation coverage. CO adsorption provides a somewhat stronger driving force for Pd segregation when compared to H, and this may have implications with respect to permeation properties of PdAg alloy surfaces. Our predictions for high coverage are particularly relevant in underlining the importance of segregation phenomena to the hydrogen transport properties of thin PdAg alloy membranes.

  4. Versatile and efficient catalysts for energy and environmental processes: Mesoporous silica containing Au, Pd and Au-Pd

    NASA Astrophysics Data System (ADS)

    da Silva, Anderson G. M.; Fajardo, Humberto V.; Balzer, Rosana; Probst, Luiz F. D.; Lovón, Adriana S. P.; Lovón-Quintana, Juan J.; Valença, Gustavo P.; Schreine, Wido H.; Robles-Dutenhefner, Patrícia A.

    2015-07-01

    We described a versatile approach for the synthesis of Au/MCM-41, Pd/MCM-41 and Au-Pd/MCM-41 by the direct incorporation of the noble metals into the MCM-41 framework. The structural, textural and chemical properties were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), N2-adsorption (BET and BJH methods), H2-chemisorption, small angle X-ray scattering (SAXS), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). The nanomaterials, being comprised of Au, Pd and Au-Pd nanoparticles and possessing high surface areas were applied as versatile and efficient catalysts in benzene, toluene and o-xylene (BTX) oxidation and in the steam reforming of ethanol for hydrogen production. The results revealed that the catalytic behavior in both processes was influenced by the experimental conditions and the nature of the catalyst employed. The Au-Pd/MCM-41 catalyst was the most active in the BTX total oxidation. On the basis of characterization data, it was proposed that the close contact between Pd and Au and the higher dispersion of Pd may be responsible for the enhanced activity of the bimetallic catalyst. However, the strong interaction between the noble metals did not improve the performance of the bimetallic catalyst in ethanol steam reforming, the Pd/MCM-41 catalyst being the most active and selective for hydrogen production.

  5. PD-L2 Elbows out PD-L1 to Rescue T Cell Immunity to Malaria.

    PubMed

    Crompton, Peter D; Pierce, Susan K

    2016-08-16

    How early interactions between innate and adaptive immune cells influence outcomes of acute infections is incompletely understood. In this issue of Immunity, Karunarathne et al. (2016) show that dendritic cells help CD4(+) T helper 1 cell immunity against malaria through PD-L2's competition with PD-L1.

  6. The advantages of PD1 activating chimeric receptor (PD1-ACR) engineered lymphocytes for PDL1(+) cancer therapy.

    PubMed

    Tang, Xiaolong; Li, Qingguo; Zhu, Yongqiang; Zheng, Donghui; Dai, Jingjing; Ni, Wenxuan; Wei, Jia; Xue, Yubao; Chen, Ke; Hou, Wei; Zhang, Chao; Feng, Xiaojun; Liang, Yong

    2015-01-01

    Tumors exploit immunoregulatory checkpoints to attenuate T cell responses as a means of circumventing immunologic rejection. By activating the inhibitory costimulatory pathway of Programmed Death 1 (PD1)/PDL1 which provides tumor cells an escape mechanism from immune surveillance, Programmed Death Ligand1 (PDL1)(+) tumors hamper activated tumor-specific T cell functions and render them functionally exhausted. To overcome the inhibitory costimulatory effects of PDL1 on the adoptively transferred T cells, we sought to convert PD1 to a T cell costimulatory receptor by exchanging its transmembrane and cytoplasmic tail with CD28 and 4-1BB signaling domains (PD1-CD28-4-1BB, PD1-ACR), anticipating the genetically modified effector T lymphocytes expressing PD1-ACR would exhibit enhanced functional attributes. And the results showed that PD1-ACR expressed T cells retained the ability to bind PDL1, resulting in T cell activation as evidenced by the elevated activity of phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt), the augmentation of cytokine secretion and the increased proliferative capacity. Moreover, when systemically administered in the mouse model of glioblastoma metastases, PD1-ACR T cells localized at the area of U87 invasive tumor, which results in suppressed tumor growth and enhanced survival of mice with established U87 glioblastoma. Together, these data demonstrated that PD1-ACR has a high potential to serve as a novel strategy to overcome PDL1 mediated immunosuppression of T cells for cancer therapy. PMID:26045887

  7. Treadmill training improves overground walking economy in Parkinson's disease: a randomized, controlled pilot study.

    PubMed

    Fernández-Del-Olmo, Miguel Angel; Sanchez, Jose Andres; Bello, Olalla; Lopez-Alonso, Virginia; Márquez, Gonzalo; Morenilla, Luis; Castro, Xabier; Giraldez, Manolo; Santos-García, Diego

    2014-01-01

    Gait disturbances are one of the principal and most incapacitating symptoms of Parkinson's disease (PD). In addition, walking economy is impaired in PD patients and could contribute to excess fatigue in this population. An important number of studies have shown that treadmill training can improve kinematic parameters in PD patients. However, the effects of treadmill and overground walking on the walking economy remain unknown. The goal of this study was to explore the walking economy changes in response to a treadmill and an overground training program, as well as the differences in the walking economy during treadmill and overground walking. Twenty-two mild PD patients were randomly assigned to a treadmill or overground training group. The training program consisted of 5 weeks (3 sessions/week). We evaluated the energy expenditure of overground walking, before and after each of the training programs. The energy expenditure of treadmill walking (before the program) was also evaluated. The treadmill, but not the overground training program, lead to an improvement in the walking economy (the rate of oxygen consumed per distance during overground walking at a preferred speed) in PD patients. In addition, walking on a treadmill required more energy expenditure compared with overground walking at the same speed. This study provides evidence that in mild PD patients, treadmill training is more beneficial compared with that of walking overground, leading to a greater improvement in the walking economy. This finding is of clinical importance for the therapeutic administration of exercise in PD.

  8. The role of antagonists of the PD-1:PD-L1/PD-L2 axis in head and neck cancer treatment.

    PubMed

    Pai, Sara I; Zandberg, Dan P; Strome, Scott E

    2016-10-01

    We review the current clinical knowledge surrounding one of the most promising immune checkpoint pathways currently investigated in head and neck squamous cell carcinoma patients, programmed cell death-1 (PD-1) and its ligands (PD-L1 and PD-L2). We review ongoing clinical trials and associated clinical responses observed with targeting the receptor, PD-1, and its ligand, PD-L1. A recent phase III clinical trial (Checkmate 141) demonstrated an improved overall survival in head and neck cancer patients treated with anti-PD-1 monotherapy as compared to standard of care for recurrent and/or metastatic disease, which raises questions on how best to incorporate immunotherapy in the context of standard of care. We discuss biomarkers of response to this class of novel drugs, which is an area of active investigation. Lastly, we project future directions in the field wherein understanding how the Fc portions of the various monoclonal antibodies may impact their clinical efficacy as well as discuss areas where our next advances may take place, such as combination strategies.

  9. Stereoselective alkoxycarbonylation of unactivated C(sp3)-H bonds with alkyl chloroformates via Pd(II)/Pd(IV) catalysis

    NASA Astrophysics Data System (ADS)

    Liao, Gang; Yin, Xue-Song; Chen, Kai; Zhang, Qi; Zhang, Shuo-Qing; Shi, Bing-Feng

    2016-09-01

    Several examples on Pd-catalysed carbonylation of methyl C(sp3)-H bonds with gaseous CO via Pd(II)/Pd(0) catalysis have been reported. However, methylene C(sp3)-H carbonylation remains a great challenge, largely due to the lack of reactivity of C-H bonds and the difficulty in CO migratory insertion. Herein, we report the stereoselective alkoxycarbonylation of both methyl and methylene C(sp3)-H bonds with alkyl chloroformates through a Pd(II)/Pd(IV) catalytic cycle. A broad range of aliphatic carboxamides and alkyl chloroformates are compatible with this protocol. In addition, this process is scalable and the directing group could be easily removed under mild conditions with complete retention of configuration.

  10. Synthesis of bimetallic Pt-Pd core-shell nanocrystals and their high electrocatalytic activity modulated by Pd shell thickness

    NASA Astrophysics Data System (ADS)

    Li, Yujing; Wang, Zhi Wei; Chiu, Chin-Yi; Ruan, Lingyan; Yang, Wenbing; Yang, Yang; Palmer, Richard E.; Huang, Yu

    2012-01-01

    Bimetallic Pt-Pd core-shell nanocrystals (NCs) are synthesized through a two-step process with controlled Pd thickness from sub-monolayer to multiple atomic layers. The oxygen reduction reaction (ORR) catalytic activity and methanol oxidation reactivity of the core-shell NCs for fuel cell applications in alkaline solution are systematically studied and compared based on different Pd thickness. It is found that the Pd shell helps to reduce the over-potential of ORR by up to 50mV when compared to commercial Pd black, while generating up to 3-fold higher kinetic current density. The carbon monoxide poisoning test shows that the bimetallic NCs are more resistant to the CO poisoning than Pt NCs and Pt black. It is also demonstrated that the bimetallic Pt-Pd core-shell NCs can enhance the current density of the methanol oxidation reaction, lowering the over-potential by 35 mV with respect to the Pt core NCs. Further investigation reveals that the Pd/Pt ratio of 1/3, which corresponds to nearly monolayer Pd deposition on Pt core NCs, gives the highest oxidation current density and lowest over-potential. This study shows for the first time the systematic investigation of effects of Pd atomic shells on Pt-Pd bimetallic nanocatalysts, providing valuable guidelines for designing high-performance catalysts for fuel cell applications.Bimetallic Pt-Pd core-shell nanocrystals (NCs) are synthesized through a two-step process with controlled Pd thickness from sub-monolayer to multiple atomic layers. The oxygen reduction reaction (ORR) catalytic activity and methanol oxidation reactivity of the core-shell NCs for fuel cell applications in alkaline solution are systematically studied and compared based on different Pd thickness. It is found that the Pd shell helps to reduce the over-potential of ORR by up to 50mV when compared to commercial Pd black, while generating up to 3-fold higher kinetic current density. The carbon monoxide poisoning test shows that the bimetallic NCs are more

  11. Non-Abelian quantum Hall states and their quasiparticles: From the pattern of zeros to vertex algebra

    SciTech Connect

    Lu Yuanming; Wang Ziqiang; Wen Xiaogang; Wang Zhenghan

    2010-03-15

    In the pattern-of-zeros approach to quantum Hall states, a set of data (n;m;S{sub a}|a=1,...,n;n,m,S{sub a} is n element of N) (called the pattern of zeros) is introduced to characterize a quantum Hall wave function. In this paper we find sufficient conditions on the pattern of zeros so that the data correspond to a valid wave function. Some times, a set of data (n;m;S{sub a}) corresponds to a unique quantum Hall state, while other times, a set of data corresponds to several different quantum Hall states. So in the latter cases, the pattern of zeros alone does not completely characterize the quantum Hall states. In this paper, we find that the following expanded set of data (n;m;S{sub a};c|a=1,...,n;n,m,S{sub a} is an element of N;c is an element of R) provides a more complete characterization of quantum Hall states. Each expanded set of data completely characterizes a unique quantum Hall state, at least for the examples discussed in this paper. The result is obtained by combining the pattern of zeros and Z{sub n} simple-current vertex algebra which describes a large class of Abelian and non-Abelian quantum Hall states PHI{sub Z{sub n}{sup sc}}. The more complete characterization in terms of (n;m;S{sub a};c) allows us to obtain more topological properties of those states, which include the central charge c of edge states, the scaling dimensions and the statistics of quasiparticle excitations.

  12. Targeting the PD1/PD-L1 axis in melanoma: biological rationale, clinical challenges and opportunities.

    PubMed

    Merelli, Barbara; Massi, Daniela; Cattaneo, Laura; Mandalà, Mario

    2014-01-01

    A dynamic interplay exists between host and tumor, and the ability of the tumor to evade immune recognition often determines the clinical course of the disease. Significant enthusiasm currently exists for a new immunotherapeutic strategy: the use of immunomodulatory monoclonal antibodies that directly enhance the function of components of the anti-tumor immune response such as T cells, or block immunologic checkpoints that would otherwise restrain effective anti-tumor immunity. This strategy is based on the evidence that development of cancer is facilitated by the dis-regulation and exploitation of otherwise physiological pathways that, under normal circumstances, down-regulate immune activation and maintain tolerance to self. Among these pathways an important role is covered by the Programmed death-1 (PD-1)/PD-Ligand (L) 1 axis. An emerging concept in cancer immunology is that inhibitory ligands such as PD-L1 are induced in response to immune attack, a mechanism termed "adaptive resistance". This potential mechanism of immune resistance by tumors suggests that therapy directed at blocking the interaction between PD-1 and PD-L1 might synergize with other treatments that enhance endogenous antitumor immunity. The anti-PD-1 strategy can be effective in several solid tumors such as renal cell carcinoma (RCC) or non-small cell lung cancer (NSCLC), however in this review we summarize the biological role of PD-1/PD-L1 on cancer by focusing our attention in the biological rationale, clinical challenges and opportunities to target the PD-1/PD-L1 axis in melanoma.

  13. Liquid phase catalytic hydrodebromination of tetrabromobisphenol A on supported Pd catalysts

    NASA Astrophysics Data System (ADS)

    Wu, Ke; Zheng, Mengjia; Han, Yuxiang; Xu, Zhaoyi; Zheng, Shourong

    2016-07-01

    Tetrabromobisphenol A (TBBPA) is a widely used brominated flame retardant and reductive debromination is an effective method for the abatement of TBBPA pollution. In this study, Pd catalysts supported on TiO2, CeO2, Al2O3 and SiO2 were prepared by the impregnation (the resulting catalyst denoted as im-Pd/support), deposition-precipitation (the resulting catalyst denoted as dp-Pd/support), and photo-deposition (the resulting catalyst denoted as pd-Pd/support) methods. The catalysts were characterized by N2 adsorption-desorption isotherm, X-ray diffraction, transmission electron microscopy, measurement of zeta potential, CO chemisorption, and X-ray photoelectron spectroscopy. The results showed that at an identical Pd loading amount (2.0 wt.%) Pd particle size in dp-Pd/TiO2 was much smaller than those in im-Pd/TiO2 and pd-Pd/TiO2. Pd particle size of the dp-Pd/TiO2 catalyst increased with Pd loading amount. Additionally, Pd particles in the dp-Pd/TiO2 catalysts were positively charged due to the strong metal-support interaction, whereas the cationization effect was gradually attenuated with the increase of Pd loading amount. For the liquid phase catalytic hydrodebromination (HDB) of TBBPA, tri-bromobisphenol A (tri-BBPA), di-bromobisphenol A (di-BBPA), and mono-bromobisphenol A (mono-BBPA) were identified as the intermediate products, indicative of a stepwise debromination process. The catalytic HDB of TBBPA followed the Langmuir-Hinshelwood model, reflecting an adsorption enhanced catalysis mechanism. At an identical Pd loading amount, the Pd catalyst supported on TiO2 exhibited a much higher catalytic activity than those on other supports. Furthermore, dp-Pd/TiO2 was found to be more active than im-Pd/TiO2 and pd-Pd/TiO2.

  14. Locating Pd in Transformers through Detailed Model and Neural Networks

    NASA Astrophysics Data System (ADS)

    Nafisi, Hamed; Abedi, Mehrdad; Gharehpetian, Gevorg B.

    2014-03-01

    In a power transformer as one of the major component in electric power networks, partial discharge (PD) is a major source of insulation failure. Therefore the accurate and high speed techniques for locating of PD sources are required regarding to repair and maintenance. In this paper an attempt has been made to introduce the novel methods based on two different artificial neural networks (ANN) for identifying PD location in the power transformers. In present report Fuzzy ARTmap and Bayesian neural networks are employed for PD locating while using detailed model (DM) for a power transformer for simulation purposes. In present paper PD phenomenon is implemented in different points of transformer winding using threecapacitor model. Then impulse test is applied to transformer terminals in order to use produced current in neutral point for training and test of employed ANNs. In practice obtained current signals include noise components. Thus the performance of Fuzzy ARTmap and Bayesian networks for correct identification of PD location in a noisy condition for detected currents is also investigated. In this paper RBF learning procedure is used for Bayesian network, while Markov chain Monte Carlo (MCMC) method is employed for training of Fuzzy ARTmap network for locating PD in a power transformer winding and results are compared.

  15. The promise of PD-1 inhibitors in gastro-esophageal cancers: microsatellite instability vs. PD-L1

    PubMed Central

    Jin, Zhaohui

    2016-01-01

    Preliminary clinical studies of anti-programmed cell death-1 (anti-PD-1) therapy in gastro-esophageal cancers have suggested promising single-agent activity. In patients who received prior treatment for advanced disease, pembrolizumab has been associated with a response rate of 20% in programmed cell death-1 ligand 1 (PD-L1)-positive tumors, and nivolumab with a response rate of 12% in unselected tumors. Both agents yielded a median duration of response lasting ~6–7 months. PD-L1 expression and microsatellite instability (MSI) have emerged as potential predictive markers for PD-1/PD-L1 blockade. PD-L1 expression in tumor cells and in immune cells within the tumor microenvironment has been detected in 14–24% and ~35% of patients with gastro-esophageal cancer, respectively. PD-L1 tumor cell expression appears to be more common in Epstein-Barr virus (EBV)-positive gastric cancers (GCs) and has been associated with an increased density of tumor-infiltrating lymphocytes (TIL). To date, data are too sparse to determine whether PD-L1 expression predicts efficacy of anti-PD-1 therapy in gastro-esophageal cancer, but data from other tumor types have not been consistent regarding its predictive value. MSI occurs in 10–20% of gastro-esophageal cancers and arises from deficient mismatch repair (MMR). MSI is highly correlated with non-synonymous mutation burden, as well as a dense accumulation of TILs. MSI has been associated with improved response to anti-PD-1 therapy in gastrointestinal cancers. Multiple studies are ongoing which examine therapeutic blockade of the PD-1/PD-L1 axis in unselected patients with gastro-esophageal cancer, as well as patients whose tumors express PD-L1 or exhibit MSI. These studies will clarify their activity in this disease and potentially can determine whether identify a strong predictive biomarker can be identified. Checkpoint inhibition is also being studied in combination with curative-intent chemo (radio) therapy and surgery. PMID

  16. Enhanced formic acid oxidation on Cu-Pd nanoparticles

    NASA Astrophysics Data System (ADS)

    Dai, Lin; Zou, Shouzhong

    Developing catalysts with high activity and high resistance to surface poisoning remains a challenge in direct formic acid fuel cell research. In this work, copper-palladium nanoparticles were formed through a galvanic replacement process. After electrochemically selective dissolution of surface Cu, Pd-enriched Cu-Pd nanoparticles were formed. These particles exhibit much higher formic acid oxidation activities than that on pure Pd nanoparticles, and they are much more resistant to the surface poisoning. Possible mechanisms of catalytic activity enhancement are briefly discussed.

  17. Fe induced hydride formation in ZrPd2

    SciTech Connect

    Gupta, Michele; Gupta, Raju; Singh, David J

    2008-01-01

    We show via first-principles calculations that the electronic structure of ZrPd{sub 2}, which does not form a hydride, can be modified by partial substitution of Fe for Pd, leading to a material that forms a hydride. We also show that PdZr{sub 2}, which forms a very stable hydride, can also be modified by Fe addition to lower the enthalpy of hydride formation. These results are explained in terms of electronic structure, specifically electronegativity, charge transfer, and s-d bonding, and clearly have implications in the search of new materials for hydrogen storage.

  18. Hydrogen catalysis and scavenging action of Pd-POSS nanoparticles

    SciTech Connect

    Maiti, A; Gee, R H; Maxwell, R; Saab, A

    2007-02-01

    Prompted by the need for a self-supported, chemically stable, and functionally flexible catalytic nanoparticle system, we explore a system involving Pd clusters coated with a monolayer of polyhedral oligomeric silsesquioxane (POSS) cages. With an initial theoretical focus on hydrogen catalysis and sequestration in the Pd-POSS system, we report Density Functional Theory (DFT) results on POSS binding energies to the Pd(110) surface, hydrogen storing ability of POSS, and possible pathways of hydrogen radicals from the catalyst surface to unsaturated bonds away from the surface.

  19. Clinical significance of PD-L1 and PD-L2 copy number gains in non-small-cell lung cancer

    PubMed Central

    Inoue, Yusuke; Yoshimura, Katsuhiro; Mori, Kazutaka; Kurabe, Nobuya; Kahyo, Tomoaki; Mori, Hiroki; Kawase, Akikazu; Tanahashi, Masayuki; Ogawa, Hiroshi; Inui, Naoki; Funai, Kazuhito; Shinmura, Kazuya; Niwa, Hiroshi; Suda, Takafumi; Sugimura, Haruhiko

    2016-01-01

    New reliable biomarkers are needed to predict the response to immune checkpoint inhibitors against programmed death-1 (PD-1) and its ligand (PD-L1), because PD-L1 expression on tumor cells has limited power for selecting patients who may benefit from such therapy. Here we investigated the significance of PD-L1 and PD-L2 gene copy number gains using fluorescence in situ hybridization as well as PD-L1 and PD-L2 expression in 654 patients with resected non-small-cell lung cancer. The prevalence of PD-L1 amplification and polysomy was 3.1% and 13.2%, respectively. The PD-L1 gene copy number status was in agreement with both the PD-L2 and Janus kinase 2 gene copy number statuses. PD-L1 and PD-L2 expression was observed in 30.7% and 13.1%, respectively. Both PD-L1 copy number gains and expression were associated with smoking-related tumors. Tumor cells with PD-L1 genomic gains exhibited significantly higher levels of PD-L1 expression than those without, but PD-L2 copy number gains were not related to PD-L2 augmentation. PD-L1 gene amplification and polysomy were independently associated with PD-L1 expression, with high immune infiltrates and EGFR expression in a multivariate logistic regression model. Comparative analysis between primary tumors and synchronous regional lymph node metastases revealed that the PD-L1 gene copy number alterations were highly consistent and reproducible compared with the PD-L1 expression. Both PD-L1 amplification and level of protein expression were predictors of poor survival using Cox univariate analyses. Therefore, we conclude that an increase in PD-L1 gene copy number can be a feasible alternative biomarker for predicting response to anti-PD-1/PD-L1 therapy. PMID:27050074

  20. Clinical significance of PD-L1 and PD-L2 copy number gains in non-small-cell lung cancer.

    PubMed

    Inoue, Yusuke; Yoshimura, Katsuhiro; Mori, Kazutaka; Kurabe, Nobuya; Kahyo, Tomoaki; Mori, Hiroki; Kawase, Akikazu; Tanahashi, Masayuki; Ogawa, Hiroshi; Inui, Naoki; Funai, Kazuhito; Shinmura, Kazuya; Niwa, Hiroshi; Suda, Takafumi; Sugimura, Haruhiko

    2016-05-31

    New reliable biomarkers are needed to predict the response to immune checkpoint inhibitors against programmed death-1 (PD-1) and its ligand (PD-L1), because PD-L1 expression on tumor cells has limited power for selecting patients who may benefit from such therapy. Here we investigated the significance of PD-L1 and PD-L2 gene copy number gains using fluorescence in situ hybridization as well as PD-L1 and PD-L2 expression in 654 patients with resected non-small-cell lung cancer. The prevalence of PD-L1 amplification and polysomy was 3.1% and 13.2%, respectively. The PD-L1 gene copy number status was in agreement with both the PD-L2 and Janus kinase 2 gene copy number statuses. PD-L1 and PD-L2 expression was observed in 30.7% and 13.1%, respectively. Both PD-L1 copy number gains and expression were associated with smoking-related tumors. Tumor cells with PD-L1 genomic gains exhibited significantly higher levels of PD-L1 expression than those without, but PD-L2 copy number gains were not related to PD-L2 augmentation. PD-L1 gene amplification and polysomy were independently associated with PD-L1 expression, with high immune infiltrates and EGFR expression in a multivariate logistic regression model. Comparative analysis between primary tumors and synchronous regional lymph node metastases revealed that the PD-L1 gene copy number alterations were highly consistent and reproducible compared with the PD-L1 expression. Both PD-L1 amplification and level of protein expression were predictors of poor survival using Cox univariate analyses. Therefore, we conclude that an increase in PD-L1 gene copy number can be a feasible alternative biomarker for predicting response to anti-PD-1/PD-L1 therapy. PMID:27050074

  1. Pt-Decorated PdCo@Pd/C Core-Shell Nanoparticles with Enhanced Stability and Electrocatalytic Activity for the Oxygen Reduction Reaction

    SciTech Connect

    Wang, Deli; Xin, Huolin L.; Yu, Yingchao; Wang, Hongsen; Rus, Eric; Muller, David A.; Abruña, Héctor D.

    2010-11-24

    A simple method for the preparation of PdCo@Pd core-shell nanoparticles supported on carbon based on an adsorbate-induced surface segregation effect has been developed. The stability of these PdCo@Pd nanoparticles and their electrocatalytic activity for the oxygen reduction reaction (ORR) were enhanced by decoration with a small amount of Pt deposited via a spontaneous displacement reaction. The facile method described herein is suitable for large-scale, lower-cost production and significantly lowers the Pt loading and thus the cost. The as-prepared PdCo@Pd and Pd-decorated PdCo@Pd nanocatalysts have a higher methanol tolerance than Pt/C in the ORR and are promising cathode catalysts for fuel cell applications.

  2. Targeting the PD-1/PD-L1 Immune Evasion Axis With DNA Aptamers as a Novel Therapeutic Strategy for the Treatment of Disseminated Cancers.

    PubMed

    Prodeus, Aaron; Abdul-Wahid, Aws; Fischer, Nicholas W; Huang, Eric H-B; Cydzik, Marzena; Gariépy, Jean

    2015-04-28

    Blocking the immunoinhibitory PD-1:PD-L1 pathway using monoclonal antibodies has led to dramatic clinical responses by reversing tumor immune evasion and provoking robust and durable antitumor responses. Anti-PD-1 antibodies have now been approved for the treatment of melanoma, and are being clinically tested in a number of other tumor types as both a monotherapy and as part of combination regimens. Here, we report the development of DNA aptamers as synthetic, nonimmunogenic antibody mimics, which bind specifically to the murine extracellular domain of PD-1 and block the PD-1:PD-L1 interaction. One such aptamer, MP7, functionally inhibits the PD-L1-mediated suppression of IL-2 secretion in primary T-cells. A PEGylated form of MP7 retains the ability to block the PD-1:PD-L1 interaction, and significantly suppresses the growth of PD-L1+ colon carcinoma cells in vivo with a potency equivalent to an antagonistic anti-PD-1 antibody. Importantly, the anti-PD-1 DNA aptamer treatment was not associated with off-target TLR-9-related immune responses. Due to the inherent advantages of aptamers including their lack of immunogenicity, low cost, long shelf life, and ease of synthesis, PD-1 antagonistic aptamers may represent an attractive alternative over antibody-based anti PD-1 therapeutics.

  3. Targeting the PD-1/PD-L1 Immune Evasion Axis With DNA Aptamers as a Novel Therapeutic Strategy for the Treatment of Disseminated Cancers

    PubMed Central

    Prodeus, Aaron; Abdul-Wahid, Aws; Fischer, Nicholas W.; Huang, Eric H-B; Cydzik, Marzena; Gariépy, Jean

    2015-01-01

    Blocking the immunoinhibitory PD-1:PD-L1 pathway using monoclonal antibodies has led to dramatic clinical responses by reversing tumor immune evasion and provoking robust and durable antitumor responses. Anti-PD-1 antibodies have now been approved for the treatment of melanoma, and are being clinically tested in a number of other tumor types as both a monotherapy and as part of combination regimens. Here, we report the development of DNA aptamers as synthetic, nonimmunogenic antibody mimics, which bind specifically to the murine extracellular domain of PD-1 and block the PD-1:PD-L1 interaction. One such aptamer, MP7, functionally inhibits the PD-L1-mediated suppression of IL-2 secretion in primary T-cells. A PEGylated form of MP7 retains the ability to block the PD-1:PD-L1 interaction, and significantly suppresses the growth of PD-L1+ colon carcinoma cells in vivo with a potency equivalent to an antagonistic anti-PD-1 antibody. Importantly, the anti-PD-1 DNA aptamer treatment was not associated with off-target TLR-9-related immune responses. Due to the inherent advantages of aptamers including their lack of immunogenicity, low cost, long shelf life, and ease of synthesis, PD-1 antagonistic aptamers may represent an attractive alternative over antibody-based anti PD-1 therapeutics. PMID:25919090

  4. An Overview of Experimental Studies on H/Pd Over-Loading with Thin pd Wires and Different Electrolytic Solutions

    NASA Astrophysics Data System (ADS)

    Spallone, A.; Celani, F.; Marini, P.; di Stefano, V.

    2006-02-01

    Hundreds of electrolytic loading tests of thin Pd wires in different experimental conditions have been performed in order to find out the best procedures for stable, high hydrogen overloading into the palladium lattice. In a very dilute acid solution thin Pd cathodes (50 or 100 μm in diameter) and thick Pt anodes (0.5 mm in diameter) were used in a parallel or coaxial geometry. Normalised resistance (R/R0) of the Pd cathode was on-line and continuously measured in order to determine the actual H/Pd values. Different electrolytic solutions have been tested by adding to the acid solution very low amounts of Ca, Sr, Li, and Hg ions; high loading H/Pd ratios have been achieved with a satisfactory grade of reproducibility. Several loading procedures have been performed in a wide range of electrolysis current (from a few mA up to 100 mA) and at different Hg ion concentrations. The obtained results allowed for the definition of a loading protocol that ensures very high H/Pd over-loading. Stable R/R0 ≤ 1.2 values (corresponding to H/Pd ratios ≥ 1) can be currently achieved with an extremely low power electrolytic supply (10 V, 5 mA).

  5. Random broadcast on random geometric graphs

    SciTech Connect

    Bradonjic, Milan; Elsasser, Robert; Friedrich, Tobias

    2009-01-01

    In this work, we consider the random broadcast time on random geometric graphs (RGGs). The classic random broadcast model, also known as push algorithm, is defined as: starting with one informed node, in each succeeding round every informed node chooses one of its neighbors uniformly at random and informs it. We consider the random broadcast time on RGGs, when with high probability: (i) RGG is connected, (ii) when there exists the giant component in RGG. We show that the random broadcast time is bounded by {Omicron}({radical} n + diam(component)), where diam(component) is a diameter of the entire graph, or the giant component, for the regimes (i), or (ii), respectively. In other words, for both regimes, we derive the broadcast time to be {Theta}(diam(G)), which is asymptotically optimal.

  6. A comparative first-principles study of martensitic phase transformations in TiPd2 and TiPd

    SciTech Connect

    Krcmar, Maja; Morris, James R

    2014-01-01

    Martensitic phase transformations in TiPd2 and TiPd alloys are studied employing density-functional, first-principles calculations. We examine the transformation of tetragonal C11b TiPd2 to the low-temperature orthorhombic phase (C11b oI6), and the transformation of cubic B2 TiPd under orthorhombic (B2 B19) and subsequent monoclinic transformations (B19 B19 ) as the system is cooled. To evaluate the transition temperature for TiPd2 we employ a theoretical approach based on a phenomenological Landau theory of the structural phase transition and a mean-field approximation for the free energy, utilizing first-principles calculations to obtain the deformation energy as a function of strains and to deduce parameters for constructing the free energy. The predicted transition temperature for the TiPd2 C11b oI6 transition temperature is in good agreement with reported experimental results. To investigate the TiPd B2 B19 transformation, we employ both the Cauchy-Born rule and a soft-mode- based approach, and elucidate on the importance of coupling of lattice distortion and atomic displacements (i.e., shuffling) in the formation of the final structure. The estimated B2 B19 transition temperature for TiPd system agrees well with the experimental results. We also find that there exists a very small but finite (0.0005 eV/atom) energy barrier of B19 TiPd under monoclinic deformation for B19 B19 structural phase transformation.

  7. G6PD testing in support of treatment and elimination of malaria: recommendations for evaluation of G6PD tests

    PubMed Central

    2013-01-01

    Malaria elimination will be possible only with serious attempts to address asymptomatic infection and chronic infection by both Plasmodium falciparum and Plasmodium vivax. Currently available drugs that can completely clear a human of P. vivax (known as “radical cure”), and that can reduce transmission of malaria parasites, are those in the 8-aminoquinoline drug family, such as primaquine. Unfortunately, people with glucose-6-phosphate dehydrogenase (G6PD) deficiency risk having severe adverse reactions if exposed to these drugs at certain doses. G6PD deficiency is the most common human enzyme defect, affecting approximately 400 million people worldwide. Scaling up radical cure regimens will require testing for G6PD deficiency, at two levels: 1) the individual level to ensure safe case management, and 2) the population level to understand the risk in the local population to guide Plasmodium vivax treatment policy. Several technical and operational knowledge gaps must be addressed to expand access to G6PD deficiency testing and to ensure that a patient’s G6PD status is known before deciding to administer an 8-aminoquinoline-based drug. In this report from a stakeholder meeting held in Thailand on October 4 and 5, 2012, G6PD testing in support of radical cure is discussed in detail. The focus is on challenges to the development and evaluation of G6PD diagnostic tests, and on challenges related to the operational aspects of implementing G6PD testing in support of radical cure. The report also describes recommendations for evaluation of diagnostic tests for G6PD deficiency in support of radical cure. PMID:24188096

  8. An Evaluation of the Impact of PD-1 Pathway Blockade on Reproductive Safety of Therapeutic PD-1 Inhibitors.

    PubMed

    Poulet, Frederique M; Wolf, Jayanthi J; Herzyk, Danuta J; DeGeorge, Joseph J

    2016-04-01

    This report discusses the principles of reproductive toxicity risk assessment for biopharmaceuticals blocking the PD-1/programmed cell death ligand 1 (PD-L1) pathway, which have been developed for the treatment of patients with advanced malignancies. The PD-1/PD-L1 pathway is a T-cell co-inhibitory pathway that normally maintains immune tolerance to self. Its role in pregnancy is to maintain immune tolerance to the fetal allograft. In cancer patients, this signaling pathway is hijacked by some neoplasms to avoid immune destruction. PD-1/PD-L1-blocking agents enhance functional activity of the target lymphocytes to eventually cause immune rejection of the tumor. A therapeutic blockade of PD-1/PD-L1 pathway that occurs at full target engagement provides a unique challenge to address the risk to pregnancy because disruption of the same pathway may also reduce or abrogate maternal immune tolerance to the fetal alloantigens inherited through the father. Typically, nonclinical reproductive and developmental toxicity (DART) studies in animals (rats and rabbits) with clinical drug candidates are conducted to identify potential risk in humans and to determine exposure margin for the effects on reproduction as part of the risk assessment. However, for biopharmaceuticals for which the desired mechanism of action cannot be separated from potential deleterious effects to the fetus and when the only relevant toxicology species is nonhuman primate (NHP), the risk to reproduction can be predicted by a mechanism-based assessment using data generated from murine surrogate models as supportive information without conducting DART in NHPs. Such an approach has been used in the evaluation of pregnancy risk of anti-PD-1 agent, pembrolizumab, and has been demonstrated as an important alternative to performing DART studies in NHPs. PMID:27062127

  9. Quasiparticles in the Superconducting State of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}}

    SciTech Connect

    Kaminski, A.; Mesot, J.; Fretwell, H.; Campuzano, J. C.; Randeria, M.; Ding, H.; Sato, T.; Takahashi, T.; Mochiku, T.

    2000-02-21

    Recent improvements in momentum resolution lead to qualitatively new angle-resolved photoemission spectroscopy results on the spectra of Bi{sub 2}Sr {sub 2}CaCu{sub 2}O{sub 8+{delta}} (Bi2212) along the ({pi}, {pi}) direction, where there is a node in the superconducting gap. We now see the intrinsic line shape, which indicates the presence of true quasiparticles at all Fermi momenta in the superconducting state, and lack thereof in the normal state. The region of momentum space probed here is relevant for charge transport, motivating a comparison of our results to conductivity measurements by infrared reflectivity. (c) 2000 The American Physical Society.

  10. Hartree-Fock-Bogoliubov description of quasiparticle excitations in the superdeformed wells of {sup 191,192}Hg and {sup 192,193}Tl

    SciTech Connect

    Heenen, P.; Janssens, R.V.

    1998-01-01

    The properties of superdeformed bands in {sup 191,192}Hg and {sup 192,193}Tl have been studied using the cranked Hartree-Fock-Bogoliubov method with the Lipkin-Nogami prescription, the Skm{sup {asterisk}} interaction, and a surface-delta, density-dependent pairing force. In particular, quasiparticle excitations involving intruder orbitals are analyzed in detail. Comparisons between data and calculations are performed for J{sup (2)} moments, quadrupole moments, spins, transition energies, and alignments. {copyright} {ital 1998} {ital The American Physical Society}

  11. Quantumness, Randomness and Computability

    NASA Astrophysics Data System (ADS)

    Solis, Aldo; Hirsch, Jorge G.

    2015-06-01

    Randomness plays a central role in the quantum mechanical description of our interactions. We review the relationship between the violation of Bell inequalities, non signaling and randomness. We discuss the challenge in defining a random string, and show that algorithmic information theory provides a necessary condition for randomness using Borel normality. We close with a view on incomputablity and its implications in physics.

  12. Decomposition of Furan on Pd(111)

    SciTech Connect

    Xu, Ye

    2012-01-01

    Periodic density functional theory calculations (GGA-PBE) have been performed to investigate the mechanism for the decomposition of furan up to CO formation on the Pd(111) surface. At 1/9 ML coverage, furan adsorbs with its molecular plane parallel to the surface in several states with nearly identical adsorption energies of -1.0 eV. The decomposition of furan begins with the opening of the ring at the C-O position with an activation barrier of E{sub a} = 0.82 eV, which yields a C{sub 4}H{sub 4}O aldehyde species that rapidly loses the {alpha} H to form C{sub 4}H{sub 3}O (E{sub a} = 0.40 eV). C{sub 4}H{sub 3}O further dehydrogenates at the {delta} position to form C{sub 4}H{sub 2}O (E{sub a} = 0.83 eV), before the {alpha}-{beta} C-C bond dissociates (E{sub a} = 1.08 eV) to form CO. Each step is the lowest-barrier dissociation step in the respective species. A simple kinetic analysis suggests that furan decomposition begins at 240-270 K and is mostly complete by 320 K, in close agreement with previous experiments. It is suggested that the C{sub 4}H{sub 2}O intermediate delays the decarbonylation step up to 350 K.

  13. Cu--Pd--M hydrogen separation membranes

    DOEpatents

    Do{hacek over }an, Omer N; Gao, Michael C; Young, Rongxiang Hu; Tafen, De Nyago

    2013-12-17

    The disclosure provides an H2 separation membrane comprised of an allow having the composition Cu.Sub.(100-x-y)Pd.sub.xM.sub.y, where x is from about 35 to about 50 atomic percent and where y is from greater than 0 to about 20 atomic percent, and where M consists of magnesium, yttrium, aluminum, titanium, lanthanum, or combinations thereof. The M elements act as strong stabilizers for the B2 phase of the allow, and extend the critical temperature of the alloy for a given hydrogen concentration and pressure. Due to the phase stabilization and the greater temperature range over which a B2 phase can be maintained, the allow is well suited for service as a H2 separation membrane, particularly when applicable conditions are established or cycled above about 600.degree. C. over the course of expected operations. In certain embodiments, the B2 phase comprises at least 60 estimated volume percent of the allow at a steady-state temperature of 400.degree. C. The B2 phase stability is experimentally validated through HT-XRD.

  14. PD-1 and PD-L1 inhibitors in melanoma treatment: past success, present application and future challenges.

    PubMed

    Lee, Jenny; Kefford, Richard; Carlino, Matteo

    2016-06-01

    Anti-programmed death (PD)-1 antibodies have now become the standard of care for advanced melanoma, with two drugs gaining US FDA approval in recent years: nivolumab and pembrolizumab. Both have demonstrated significant activity and durable response with a manageable toxicity profile. Despite initial success, ongoing challenges include patient selection and predictors of response, innate resistance and optimizing combination strategies. In this overview, we take a closer look at the history and development of therapeutic targets to the PD-1/PD-ligand (L)1 pathway, clinical evidence, availability of biomarkers and their limitations in clinical practice and future strategies to improve treatment outcomes. PMID:27197541

  15. Heterostructured Au/Pd-M (M = Au, Pd, Pt) nanoparticles with compartmentalized composition, morphology, and electrocatalytic activity

    NASA Astrophysics Data System (ADS)

    Lutz, Patrick S.; Bae, In-Tae; Maye, Mathew M.

    2015-09-01

    The synthesis, processing, and galvanic exchange of three heterostructured nanoparticle systems is described. The surface accessibility and redox potential of a Au/Pd-Ag dumbbell nanoparticle, where a Au/Pd core/shell region, and a silver region make up the domains, was used to prepare the new nanostructures with controlled composition, morphology, and microstructure. Results indicate that the silver domain was particularly susceptible to galvanic displacement, and was exchanged to Au/Pd-M (M = Au, Pd, Pt). Interestingly, the dumbbell morphology remained after exchange, and the silver region was transformed to hollow, parachute, or concentric domains respectively. The morphology and microstructure change was visualized via TEM and HRTEM, and the composition changes were probed via STEM-EDS imaging and XPS. The electrocatalytic activity of the Au/Pd-M towards methanol oxidation was studied, with results indicating that the Au/Pd-Pt nanoparticles had high activity attributed to the porous nature of the platinum domains.The synthesis, processing, and galvanic exchange of three heterostructured nanoparticle systems is described. The surface accessibility and redox potential of a Au/Pd-Ag dumbbell nanoparticle, where a Au/Pd core/shell region, and a silver region make up the domains, was used to prepare the new nanostructures with controlled composition, morphology, and microstructure. Results indicate that the silver domain was particularly susceptible to galvanic displacement, and was exchanged to Au/Pd-M (M = Au, Pd, Pt). Interestingly, the dumbbell morphology remained after exchange, and the silver region was transformed to hollow, parachute, or concentric domains respectively. The morphology and microstructure change was visualized via TEM and HRTEM, and the composition changes were probed via STEM-EDS imaging and XPS. The electrocatalytic activity of the Au/Pd-M towards methanol oxidation was studied, with results indicating that the Au/Pd-Pt nanoparticles had

  16. Composite Pd and Pd Alloy Porous Stainless Steel Membranes for Hydrogen Production and Process Intensification

    SciTech Connect

    Yi Hua Ma; Nikolaos Kazantzis; Ivan Mardilovich; Federico Guazzone; Alexander Augustine; Reyyan Koc

    2011-11-06

    The synthesis of composite Pd membranes has been modified by the addition of a Al(OH){sub 3} graded layer and sequential annealing at high temperatures to obtain membranes with high permeance and outstanding selectivity stability for over 4000 hours at 450°C. Most of the membranes achieved in this work showed H{sub 2} flux well above 2010 DOE targets and in some case, also above 2015 DOE targets. Similar composite membranes were tested in water gas shift reaction atmospheres and showed to be stable with high CO conversion and high hydrogen recovery for over 1000 hours. The H{sub 2} permeance of composite Pd-Au membranes was studied as well as its resistance in H{sub 2}S containing atmospheres. H{sub 2}S poisoning of Pd-based membranes was reduced by the addition of Au and the loss undergone by membranes was found to be almost totally recoverable with 10-30 wt%Au. PSA technique was studied to test the possibility of H{sub 2}S and COS removal from feed stream with limited success since the removal of H{sub 2}S also led to the removal of a large fraction of the CO{sub 2}. The economics of a WGS bundle reactor, using the information of the membranes fabricated under this project and integrated into an IGCC plant were studied based on a 2D reactor modeling. The calculations showed that without a government incentive to impose a CO{sub 2} tax, application of WGS membrane reactors in IGCC would be not as economically attractive as regular pulverized coal plants.

  17. Modeling of Co overlayers on Pd (111) from first principles

    NASA Astrophysics Data System (ADS)

    Uba, S.; Uba, L.; Antonov, V. N.

    2007-04-01

    The electronic, magnetic and magneto-optical properties of Co overlayers on Pd (1 1 1) substrate have been investigated by ab initio band structure calculations within the spin-polarized relativistic linear muffin-thin orbitals (LMTO) method and supercell approach. The role of the Co-Pd interface structure, the number of the Co atomic layers ( n Co ), as well as the spin-orbit interaction and induced Pd spin polarization, in formation of magneto-optical response of the structures for [ n CoCo/Pd (1 1 1)] system is shown. The sign reversal of the polar Kerr rotation obtained theoretically with decreasing thickness of Co overlayers agrees well with experiment. We will demonstrate the effectiveness of the extended numeric modeling of magneto-optical properties from first principles.

  18. P-d capture reactions in muonic molecules

    SciTech Connect

    Friar, J.L.

    1991-01-01

    Capture reactions for very low-energy n-d and p-d systems are calculated and compared with experiment, as are low-energy n-d and p-d scattering. We find excellent agreement for the n-d scattering lengths, but poor agreement for the p-d case, which we believe is a problem with the experimental extrapolation. The n-d radiative capture is sensitive to details of the meson-exchange currents, but reasonable models agree with the data. The latter models are in good agreement with experiment when extended to the p-d case. Our large quartet capture rate resolves a long-standing anomaly. The EO capture matrix element recently obtained from a reanalysis of internal conversion in muonic molecules is in excellent agreement with our predictions. This matrix element is very clean theoretically and provides the best test of the calculations. 33 refs., 3 figs., 1 tab.

  19. Manipulating the optical properties of symmetrically branched Au/Pd nanocrystals through interior design.

    PubMed

    DeSantis, Christopher J; Skrabalak, Sara E

    2014-05-25

    Au/Pd octopods with hollow, cubic interiors and Oh symmetry were synthesized for the first time by etching core@shell Pd@Au/Pd octopods to selectively remove their Pd interiors. Integration of multiple architectural features - in this case branching symmetry, composition, and interior design - into one nanostructure provides design strategies to new plasmonic colloids.

  20. Cluster expansion of fcc Pd-V intermetallics

    SciTech Connect

    de Fontaine, D.; Wolverton, C.; Ceder, G. ); Dreysse, H. . Lab. de Physique du Solide)

    1991-06-01

    A cluster expansion is used to compute fcc ground states from first principles for the Pd-V system. Intermetallic structures are not assumed but derived rigorously by minimizing the configurational energy subject to linear constraints. A large number of concentration-independent interactions are calculated by the method of direct configurational averaging. Agreement with the fcc-based portion of the experimentally-determined Pd-V phase diagram is quite satisfactory. 25 refs., 2 figs.