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.
Quasiparticle properties of Ge(111)-2 times 1 surface
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.
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.
Quark susceptibility in a generalized dynamical quasiparticle model
NASA Astrophysics Data System (ADS)
Berrehrah, H.; Cassing, W.; Bratkovskaya, E.; Steinert, Th.
2016-04-01
The quark susceptibility χq at zero and finite quark chemical potential provides a critical benchmark to determine the quark-gluon-plasma (QGP) degrees of freedom in relation to the results from lattice QCD (lQCD) in addition to the equation of state and transport coefficients. Here we extend the familiar dynamical quasiparticle model (DQPM) to partonic propagators that explicitly depend on the three-momentum with respect to the partonic medium at rest in order to match perturbative QCD (pQCD) at high momenta. Within the extended dynamical quasiparticle model (DQPM*) we reproduce simultaneously the lQCD results for the quark number density and susceptibility and the QGP pressure at zero and finite (but small) chemical potential μq. The shear viscosity η and the electric conductivity σe from the extended quasiparticle model (DQPM*) also turn out to be in close agreement with lattice results for μq=0 . The DQPM*, furthermore, allows one to evaluate the momentum p , temperature T , and chemical potential 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 5 <√{sN N}<10 GeV.
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.
Pump probe spectroscopy of quasiparticle dynamics in cuprate superconductors
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.
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.
Dilepton production by dynamical quasi-particles in the strongly interacting quark-gluon plasma
NASA Astrophysics Data System (ADS)
Linnyk, O.
2011-02-01
We address the dilepton production by the constituents of the strongly interacting quark-gluon plasma (sQGP). In order to make quantitative predictions for dilepton rates at experimentally relevant low dilepton mass (O(1GeV)) and strong coupling (αS ~ 0.5-1), we take into account non-perturbative spectral functions and self-energies of the quarks, antiquarks and gluons. For this purpose, we use parametrizations of the quark and gluon propagators provided by the dynamical quasi-particle model (DQPM) matched to reproduce lattice quantum chromodynamics (QCD) data. The DQPM describes QCD properties in terms of the single-particle Green's functions and leads to the notion of the constituents of the sQGP being effective quasi-particles, which are massive and have broad spectral functions (due to large interaction rates). By 'dressing' the quark and gluon lines with the effective propagators, we derive the off-shell cross sections for dilepton production in the reactions q+\\,\\bar{q}\\rightarrow l^+l^- (Born mechanism), q+ \\,\\bar{q}\\rightarrow g+\\,l^+l^- (quark annihilation with the gluon bremsstrahlung in the final state), q(\\bar{q})+g\\rightarrow q(\\bar{q})+ l^+l^- (gluon-Compton scattering), g\\rightarrow q+\\bar{q}+l^+l^- and q(\\bar{q})\\rightarrow q(\\bar{q})+g+l^+l^- (virtual gluon decay, virtual quark decay). In contrast to previous calculations of these cross sections, we account for virtualities of all the quarks and gluons. We find that finite masses of the effective quasi-particles not only screen the singularities typical of the perturbative cross sections with massless quarks, but also modify the shape of the dilepton production cross sections, especially at low dilepton mass Q and at the edges of the phase space. Finally, we use the calculated mass-dependent cross sections to identify the dependence of the dilepton rates on the spectral function widths of the initial and final quarks and gluons, which has not been estimated so far. The results
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.
NASA Astrophysics Data System (ADS)
Kumar, Nardeep
Layered materials in which atomic sheets are stacked together by weak van der Waals forces can be used to fabricate two-dimensional systems. They represent a diverse and rich, but largely unexplored, source of materials. Atomically-thin structures derived from these materials possess a number of interesting electrical, optical, and mechanical properties, and are attractive for new nanodevices. For their applications in semiconductor industry, it is necessary to understand the dynamics of photoexcited quasiparticles that occur on ultrafast time scales of less than one nanosecond. In this dissertation, I discuss ultrafast optical experimental techniques and results from various two-dimensional materials, which provide information about electronic dynamics. First, a second harmonic generation technique that can be used to find the crystalline orientation, thickness uniformity, layer stacking, and single-crystal domain size is discussed, with results presented on exfoliated and chemical vapor deposition MoS2 samples. Second, a third harmonic generation technique is discussed, which can be used to explore nonlinear optical properties of materials, and results are presented on graphene and few-layer graphite films. Third, a spatially resolved femtosecond pump-probe is described, which can be used to study hot carrier and photoexcited phonon dynamics and results are presented on Bi2 Se3 sample. Then, exciton dynamics in MoS2 and MoSe2 are explored by using transient absorption microscopy with a high spatiotemporal resolution. Finally, a polarization-resolved femtosecond transient absorption spectroscopy that can be used to study valley and spin dynamics is discussed, with results presented on monolayer, few-layer, and bulk MoSe2 samples.
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
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.
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.
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.
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.
Quasiparticle and optical properties of rutile and anatase TiO2
NASA Astrophysics Data System (ADS)
Kang, Wei; Hybertsen, Mark S.
2010-08-01
Quasiparticle excitation energies and optical properties of TiO2 in the rutile and anatase structures are calculated using many-body perturbation-theory methods. Calculations are performed for a frozen crystal lattice; electron-phonon coupling is not explicitly considered. In the GW method, several approximations are compared and it is found that inclusion of the full frequency dependence as well as explicit treatment of the Ti semicore states are essential for accurate calculation of the quasiparticle energy-band gap. The calculated quasiparticle energies are in good agreement with available photoemission and inverse photoemission experiments. The results of the GW calculations, together with the calculated static screened Coulomb interaction, are utilized in the Bethe-Salpeter equation to calculate the dielectric function γ2(ω) for both the rutile and anatase structures. The results are in good agreement with experimental observations, particularly the onset of the main absorption features around 4 eV. For comparison to low-temperature optical-absorption measurements that resolve individual excitonic transitions in rutile, the low-lying discrete excitonic energy levels are calculated with electronic screening only. The lowest energy exciton found in the energy gap of rutile has a binding energy of 0.13 eV. In agreement with experiment, it is not dipole allowed but the calculated exciton energy exceeds that measured in absorption experiments by about 0.22 eV and the scale of the exciton binding energy is also too large. The quasiparticle energy alignment of rutile is calculated for nonpolar (110) surfaces. In the GW approximation, the valence-band maximum is 7.8 eV below the vacuum level, showing a small shift from density-functional theory results.
Quasiparticle properties of the nonlinear Holstein model at finite doping and temperature
NASA Astrophysics Data System (ADS)
Li, Shaozhi; Nowadnick, Beth; Johnston, Steven
Models with linear electron-phonon (e-ph) interactions often predict the formation of small polarons with large lattice displacements. This directly violates the approximations made in deriving the linear model, which implies that one should consider higher order terms in the interaction. Previously we have shown that even small positive nonlinear e-ph interactions dramatically suppress charge-density-wave formation and s-wave superconductivity relative to the linear model [EPL. 109, 27007 (2015)]. In this talk, we present a determinant quantum Monte Carlo study of thesingle-particle properties of quasiparticles and phonons in a two-dimensional Holstein model that includes an additional nonlinear e-ph interaction. We show that a small positive nonlinear e-ph interaction reduces the effective coupling between electrons and phonons and hardens the effective phonon frequency. Conversely, a small negative nonlinear interaction can enhance e-ph coupling resulting in heavier quasiparticles. In addition, we find that an effective linear model fails to simultaneously capture the quantitative effects of the nonlinearity of both the electronic and phononic degrees of freedom, even though it can qualitatively reproduce properties.
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.
Quasiparticle properties of the nonlinear Holstein model at finite doping and temperature
NASA Astrophysics Data System (ADS)
Li, Shaozhi; Nowadnick, E. A.; Johnston, S.
2015-08-01
We use determinant quantum Monte Carlo to study the single-particle properties of quasiparticles and phonons in a variant of the two-dimensional Holstein model that includes an additional nonlinear electron-phonon (e-ph) interaction. We find that a small positive nonlinear interaction reduces the effective coupling between the electrons and the lattice, suppresses charge-density-wave (CDW) correlations, and hardens the effective phonon frequency. Conversely, a small negative nonlinear interaction can enhance the e-ph coupling resulting in heavier quasiparticles, an increased tendency towards a CDW phase at all fillings, and a softened phonon frequency. An effective linear model with a renormalized interaction strength and phonon frequency can qualitatively capture this physics; however, the quantitative effects of the nonlinearity on both the electronic and phononic degrees of freedom cannot be captured by such a model. These results are significant for typical nonlinear coupling strengths found in real materials, indicating that nonlinearity can have an important influence on the physics of many e-ph coupled systems.
Quasiparticle Properties of a Mobile Impurity in a Bose-Einstein Condensate
NASA Astrophysics Data System (ADS)
Christensen, Rasmus Søgaard; Levinsen, Jesper; Bruun, Georg M.
2015-10-01
We develop a systematic perturbation theory for the quasiparticle properties of a single impurity immersed in a Bose-Einstein condensate. Analytical results are derived for the impurity energy, effective mass, and residue to third order in the impurity-boson scattering length. The energy is shown to depend logarithmically on the scattering length to third order, whereas the residue and the effective mass are given by analytical power series. When the boson-boson scattering length equals the boson-impurity scattering length, the energy has the same structure as that of a weakly interacting Bose gas, including terms of the Lee-Huang-Yang and fourth order logarithmic form. Our results, which cannot be obtained within the canonical Fröhlich model of an impurity interacting with phonons, provide valuable benchmarks for many-body theories and for experiments.
Quasiparticle Properties of a Mobile Impurity in a Bose-Einstein Condensate.
Christensen, Rasmus Søgaard; Levinsen, Jesper; Bruun, Georg M
2015-10-16
We develop a systematic perturbation theory for the quasiparticle properties of a single impurity immersed in a Bose-Einstein condensate. Analytical results are derived for the impurity energy, effective mass, and residue to third order in the impurity-boson scattering length. The energy is shown to depend logarithmically on the scattering length to third order, whereas the residue and the effective mass are given by analytical power series. When the boson-boson scattering length equals the boson-impurity scattering length, the energy has the same structure as that of a weakly interacting Bose gas, including terms of the Lee-Huang-Yang and fourth order logarithmic form. Our results, which cannot be obtained within the canonical Fröhlich model of an impurity interacting with phonons, provide valuable benchmarks for many-body theories and for experiments. PMID:26550852
Quasiparticle dynamics and spin-orbital texture of the SrTiO3 two-dimensional electron gas.
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
2014-01-01
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. PMID:24572991
Quasiparticle dynamics and spin-orbital texture of the SrTiO3 two-dimensional electron gas
NASA Astrophysics Data System (ADS)
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.
2014-02-01
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.
NASA Astrophysics Data System (ADS)
Mertelj, T.; Stojchevska, L.; Zhigadlo, N. D.; Karpinski, J.; Mihailovic, D.
2013-05-01
We investigate temperature and fluence dependent dynamics of the photoexcited quasiparticle relaxation and low-energy electronic structure in electron-doped 1111-structure Sm(Fe0.93Co0.07)AsO single crystal. We find that the behavior is qualitatively identical to the 122-structure Ba(Fe,Co)2As2 including the presence of a normal state pseudogap and a marked twofold symmetry breaking in the tetragonal phase that we relate to the electronic nematicity. The twofold symmetry breaking appears to be a general feature of the electron-doped iron pnictides.
Non-analytic magnetic field dependence of quasi-particle properties of two-dimensional metals
NASA Astrophysics Data System (ADS)
Drukier, Casper; Lange, Philipp; Kopietz, Peter
2015-02-01
We show that in a weak external magnetic field H the quasi-particle residue and the renormalized electron Landé factor of two-dimensional Fermi liquids exhibit a non-analytic magnetic field dependence proportional to | H | which is due to electron-electron interactions and the Zeeman effect. We explicitly calculate the corresponding prefactors to second order in the interaction and show that they are determined by low-energy scattering processes involving only momenta close to the Fermi surface. These non-analytic terms appear in measurable quantities such as the density of states and the magnetoconductivity.
NASA Astrophysics Data System (ADS)
Lin, Kung-Hsuan; Wang, Kuan-Jen; Chang, Chung-Chieh; Wen, Yu-Chieh; Lv, Bing; Chu, Ching-Wu; Wu, Maw-Kuen
2016-05-01
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.
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
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
Quasiparticle band structures and thermoelectric transport properties of p-type SnSe
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.
Recombination and propagation of quasiparticles in cuprate superconductors
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
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.
NASA Astrophysics Data System (ADS)
van Roekeghem, Ambroise; Richard, Pierre; Ding, Hong; Biermann, Silke
2016-01-01
Electronic Coulomb correlations lead to characteristic signatures in the spectroscopy of transition metal pnictides and chalcogenides: quasi-particle renormalizations, lifetime effects or incoherent badly metallic behavior above relatively low coherence temperatures are measures of many-body effects due to local Hubbard and Hund's couplings. We review and compare the results of angle-resolved photoemission spectroscopy experiments (ARPES) and of combined density functional/dynamical mean-field theory (DFT+DMFT) calculations. We emphasize the doping-dependence of the quasi-particle mass renormalization and coherence properties.
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.
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.
Spectral Function and Quasiparticle Damping of Interacting Bosons in Two Dimensions
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.
Polyakov loop and gluon quasiparticles in Yang-Mills thermodynamics
NASA Astrophysics Data System (ADS)
Ruggieri, M.; Alba, P.; Castorina, P.; Plumari, S.; Ratti, C.; Greco, V.
2012-09-01
We study the interpretation of lattice data about the thermodynamics of the deconfinement phase of SU(3) Yang-Mills theory, in terms of gluon quasiparticles propagating in a background of a Polyakov loop. A potential for the Polyakov loop, inspired by the strong coupling expansion of the QCD action, is introduced; the Polyakov loop is coupled to transverse gluon quasiparticles by means of a gaslike effective potential. This study is useful to identify the effective degrees of freedom propagating in the gluon medium above the critical temperature. A main general finding is that a dominant part of the phase transition dynamics is accounted for by the Polyakov loop dynamics; hence, the thermodynamics can be described without the need for diverging or exponentially increasing quasiparticle masses as T→Tc, at variance respect to standard quasiparticle models.
Suppressing decoherence of superconducting qubits by trapping non-equilibrium quasiparticles
NASA Astrophysics Data System (ADS)
Gao, Yvonne; Wang, Chen; Pop, I. M.; Vool, U.; Axline, C.; Brecht, T.; Heeres, R. W.; Frunzio, L.; Devoret, M. H.; Catelani, G.; Glazman, L. I.; Schoelkopf, R. J.
2015-03-01
We report a counter-intuitive observation that vortices can improve the coherence of superconducting qubits by suppressing non-equilibrium quasiparticles. This effect is systematically studied by measuring the magnetic-field dependence of qubit coherence times and quasiparticle lifetimes in transmons with different geometries in a 3D cQED architecture. Varying quasiparticle dynamics by vortices allows separation of dissipation mechanisms and measurement of the stray generation rate of quasiparticles in our devices. More details are described in Ref. Our results indicate that quasiparticles contribute significantly to qubit decoherence. Hence suppression of quasiparticle density in the device is essential for further improvement of coherence times of superconducting qubits and we will present recent results aimed at alleviating decoherence due to quasiparticles.
Anisotropic System of Quasiparticles in Superfluid Helium
Adamenko, I.N.; Nemchenko, K.E.; Slipko, V.A.; Wyatt, A.F.G.
2006-02-17
The thermodynamic properties of anisotropic quasiparticle systems of He II are considered for all degrees of anisotropy. It is shown that the thermodynamic functions of a strongly anisotropic phonon-roton system are mainly determined by rotons at all temperatures. Analytical expressions for the roton thermodynamic functions are obtained for all degrees of anisotropy. The maximum anisotropy is limited by the criterion for thermodynamic stability, which is here derived for the whole temperature range.
NASA Astrophysics Data System (ADS)
Shen, Yi
Methods to produce MgB2 thin films and tunneling devices have been developed. Thin films have been optimized for high field applications by exploring a range of doping and growth conditions. Josephson junction devices have been produced using a novel technique to optimize the quality of the barrier and near-interface superconducting materials. The effects of impurities incorporation in MgB2 thin films in the physical properties were studied. First, rubidium and cesium were ex-situ introduced into thin films by annealing in quartz ampoules containing elemental alkali metals. No significant change in transition temperature (Tc) was observed by resistivity measurement, in contrast to an earlier report of enhanced Tcs (>50 K) from susceptibility measurements. A significant drop in Jc and an increase in Deltarho (rho 300-rho40) arise from a decrease in inter-granular connectivity during annealing. Second, oxygen was incorporated using in-situ post-growth anneals in an oxygen environment. Analysis of the electrical data indicates that oxygen is distributed both within and between the grains. High values of Jc (˜4x105 A/cm2 at 8 T and 4.2 K), extrapolated Hc2(0) > 45 T and |dHc2/dT| Tc| ≈ 1.4 T/K are observed. A novel deposition approach allows films of magnesium plus boron to be deposited on unheated c-plane sapphire substrates by co-evaporation, and then subsequently annealed in a reducing atmosphere at temperatures below 600°C. The use of a combination of a magnesium rich stoichiometry (Mg/B > 1/2) in the as-deposited film, and a two-step annealing process, was found to be critical in obtaining unusual high values of Hc2(0) > 43 T and |dH c2/dT|Tc| ≈ 2.5 T/K. Josephson junctions fabricated by pressing two oxidized MgB2 thin films together. This facilitates the production of Josephson Junctions with two MgB2 electrodes without exposure to the high second electrode deposition temperature. These junctions, with electrode Tcs of ˜32 K, have critical currents up to
Phonon Quasiparticles and Anharmonic Free Energy in Complex Systems
NASA Astrophysics Data System (ADS)
Zhang, Dong-Bo; Sun, Tao; Wentzcovitch, Renata M.
2014-02-01
We use a hybrid strategy to obtain anharmonic frequency shifts and lifetimes of phonon quasiparticles 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 quasiparticles are well defined. We validate this approach to obtain anharmonic effects with calculations in MgSiO3 perovskite, the major Earth forming mineral phase. First, we reproduce irregular thermal frequency shifts of well characterized Raman modes. Second, we combine the phonon gas model (PGM) with quasiparticle frequencies and reproduce free energies obtained using thermodynamic integration. Combining thoroughly sampled quasiparticle dispersions with the PGM we then obtain first-principles anharmonic free energy in the thermodynamic limit (N→∞).
Phonon quasiparticles and anharmonic free energy in complex systems.
Zhang, Dong-Bo; Sun, Tao; Wentzcovitch, Renata M
2014-02-01
We use a hybrid strategy to obtain anharmonic frequency shifts and lifetimes of phonon quasiparticles 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 quasiparticles are well defined. We validate this approach to obtain anharmonic effects with calculations in MgSiO3 perovskite, the major Earth forming mineral phase. First, we reproduce irregular thermal frequency shifts of well characterized Raman modes. Second, we combine the phonon gas model (PGM) with quasiparticle frequencies and reproduce free energies obtained using thermodynamic integration. Combining thoroughly sampled quasiparticle dispersions with the PGM we then obtain first-principles anharmonic free energy in the thermodynamic limit (N→∞). PMID:24580631
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.
Quantum Numbers of Textured Hall Effect Quasiparticles
Nayak, C.; Wilczek, F.
1996-11-01
We propose a class of variational wave functions with slow variation in spin and charge density and simple vortex structure at infinity, which properly generalize both the Laughlin quasiparticles and baby Skyrmions. We argue, on the basis of these wave functions and a spin-statistics relation in the relevant effective field theory, that the spin of the corresponding quasiparticle has a fractional part related in a universal fashion to the properties of the bulk state. We propose a direct experimental test of this claim. We show that certain spin-singlet quantum Hall states can be understood as arising from primary polarized states by Skyrmion condensation. {copyright} {ital 1996 The American Physical Society.}
NASA Astrophysics Data System (ADS)
Deslippe, Jack; Samsonidze, Georgy; Strubbe, David A.; Jain, Manish; Cohen, Marvin L.; Louie, Steven G.
2012-06-01
BerkeleyGW is a massively parallel computational package for electron excited-state properties that is based on the many-body perturbation theory employing the ab initio GW and GW plus Bethe-Salpeter equation methodology. It can be used in conjunction with many density-functional theory codes for ground-state properties, including PARATEC, PARSEC, Quantum ESPRESSO, SIESTA, and Octopus. The package can be used to compute the electronic and optical properties of a wide variety of material systems from bulk semiconductors and metals to nanostructured materials and molecules. The package scales to 10 000s of CPUs and can be used to study systems containing up to 100s of atoms. Program summaryProgram title: BerkeleyGW Catalogue identifier: AELG_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AELG_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Open source BSD License. See code for licensing details. No. of lines in distributed program, including test data, etc.: 576 540 No. of bytes in distributed program, including test data, etc.: 110 608 809 Distribution format: tar.gz Programming language: Fortran 90, C, C++, Python, Perl, BASH Computer: Linux/UNIX workstations or clusters Operating system: Tested on a variety of Linux distributions in parallel and serial as well as AIX and Mac OSX RAM: (50-2000) MB per CPU (Highly dependent on system size) Classification: 7.2, 7.3, 16.2, 18 External routines: BLAS, LAPACK, FFTW, ScaLAPACK (optional), MPI (optional). All available under open-source licenses. Nature of problem: The excited state properties of materials involve the addition or subtraction of electrons as well as the optical excitations of electron-hole pairs. The excited particles interact strongly with other electrons in a material system. This interaction affects the electronic energies, wavefunctions and lifetimes. It is well known that ground-state theories, such as standard methods
Quasiparticle energy studies of bulk semiconductors, surfaces and nanotubes
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.
Quasiparticle relaxation mechanisms in superconductor/ferromagnet bilayers.
Attanasio, Carmine; Cirillo, Carla
2012-02-29
In this paper we review some recent results obtained on superconducting/ferromagnetic (S/F) structures when measuring the dynamic instabilities of the vortex lattice at high driving currents. The role played on the non-equilibrium properties of the hybrids by both the ferromagnetic and the superconducting materials has been analyzed with a special focus on the values and the temperature dependence of the quasiparticle relaxation times, τ(E). Knowledge of the relaxation mechanisms in these systems is extremely important in view of possible applications since it can drive the optimal choice of both materials to realize, in particular, ultrafast superconducting single photon detectors based on S/F hybrid structures. PMID:22314798
Dynamic properties of ceramic materials
Grady, D.E.; Wise, J.L.
1993-09-01
Controlled impact methods have been employed to obtain dynamic response properties of armor materials. Experimental data have been obtained for high-strength ceramics. Continued analysis of time-resolved velocity interferometer measurements has produced systematic material-property data for Hugoniot and release response, initial and post-yield strength, pressure-induced phase transformation, and dynamic fracture strength. A new technique has been developed to measure hydrodynamic properties of ceramic through shock-wave experiments on metal-ceramic composites and data obtained for silicon carbide. Additional data on several titanium diboride ceramics and high-quality aluminum oxide ceramic have been acquired, and issues regarding the influence of microstructure on dynamic properties have emerged. Comparison of dynamic (Hugoniot elastic limit) strength and indentation hardness data has been performed and important correlations revealed. Innovative impact experiments on confined and unconfined alumina rods using axial and transverse VISAR diagnostics have been demonstrated which permit acquisition of multiaxial dynamic response data. Dynamic failure properties of a high-density aluminosilicate glass, similar in composition to the intergranular glassy phase of some aluminas, have been investigated with regard to yield, spall, and failure-wave propagation.
Condensing Non-Abelian Quasiparticles
Hermanns, M.
2010-02-05
A most interesting feature of certain fractional quantum Hall states is that their quasiparticles obey non-Abelian fractional statistics. So far, candidate non-Abelian wave functions have been constructed from conformal blocks in cleverly chosen conformal field theories. In this work we present a hierarchy scheme by which we can construct daughter states by condensing non-Abelian quasiparticles (as opposed to quasiholes) in a parent state, and show that the daughters have a non-Abelian statistics that differs from the parent. In particular, we discuss the daughter of the bosonic, spin-polarized Moore-Read state at nu=4/3 as an explicit example.
Mass properties measurement system dynamics
NASA Technical Reports Server (NTRS)
Doty, Keith L.
1993-01-01
The MPMS mechanism possess two revolute degrees-of-freedom and allows the user to measure the mass, center of gravity, and the inertia tensor of an unknown mass. The dynamics of the Mass Properties Measurement System (MPMS) from the Lagrangian approach to illustrate the dependency of the motion on the unknown parameters.
Controlling quasiparticle excitations in a trapped Bose-Einstein condensate
Woo, S.J.; Choi, S.; Bigelow, N.P.
2005-08-15
We describe an approach to quantum control of the quasiparticle excitations in a trapped Bose-Einstein condensate based on adiabatic and diabatic changes in the trap anisotropy. We describe our approach in the context of the Landau-Zener transition at the avoided crossings in the quasiparticle excitation spectrum. We find also that there can be population oscillation between different modes at the specific aspect ratios of the trapping potential at which the mode energies are almost degenerate. These effects may have implications in the expansion of an excited condensate as well as the dynamics of a moving condensate in an atomic waveguide with a varying width.
Topological and dynamical properties of a generalized cluster model in one dimension
NASA Astrophysics Data System (ADS)
Ohta, Takumi; Tanaka, Shu; Danshita, Ippei; Totsuka, Keisuke
2016-04-01
We study the ground-state phase diagram and dynamics of the one-dimensional cluster model with several competing interactions. Paying particular attention to the relation between the entanglement spectrum (ES) and the bulk topological (winding) number, we first map out the ground-state phases of the model and determine the universality classes of the transitions from the exact solution. We then investigate the dynamical properties during interaction sweeps through the critical points of topological phase transitions. When the sweep speed is slow, the correlation functions and the entanglement entropy exhibit spatially periodic structures. On top of this, the levels in the ES oscillate temporally during the dynamics. By explicitly calculating the above quantities for excited states, we attribute these behaviors to the Bogoliubov quasiparticles generated near the critical points. We also show that the ES reflects the strength of the Majorana correlation even for the excited states.
Lightwave-driven quasiparticle collisions on a subcycle timescale.
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
Dakovski, Georgi L.; Durakiewicz, Tomasz; Zhu, Jian-Xin; Riseborough, Peter S.; Gu, Genda; Gilbertson, Steve M.; Taylor, Antoinette; Rodriguez, George
2015-10-12
A hallmark in the cuprate family of high-temperature superconductors is the nodal-antinodal dichotomy. In this regard, angle-resolved photoemission spectroscopy (ARPES) has proven especially powerful, providing band structure information directly in energy-momentum space. Time-resolved ARPES (trARPES) holds great promise of adding ultrafast temporal information, in an attempt to identify different interaction channels in the time domain. Previous studies of the cuprates using trARPES were handicapped by the low probing energy which significantly limits the accessible momentum space. Using 20.15eV, 12 fs pulses we show for the first time the evolution of quasiparticles in the antinodal region of Bi2Sr2CaCu2O8+δ and demonstrate thatmore » nonmonotonic relaxation dynamics dominates above a certain fluence threshold. The dynamics is heavily influenced by transient modification of the electron-phonon interaction and phase space restrictions, in severe contrast to the monotonic relaxation in the nodal and off-nodal regions.« less
Dakovski, Georgi L.; Durakiewicz, Tomasz; Zhu, Jian-Xin; Riseborough, Peter S.; Gu, Genda; Gilbertson, Steve M.; Taylor, Antoinette; Rodriguez, George
2015-01-01
A hallmark in the cuprate family of high-temperature superconductors is the nodal-antinodal dichotomy. In this regard, angle-resolved photoemission spectroscopy (ARPES) has proven especially powerful, providing band structure information directly in energy-momentum space. Time-resolved ARPES (trARPES) holds great promise of adding ultrafast temporal information, in an attempt to identify different interaction channels in the time domain. Previous studies of the cuprates using trARPES were handicapped by the low probing energy, which significantly limits the accessible momentum space. Using 20.15 eV, 12 fs pulses, we show for the first time the evolution of quasiparticles in the antinodal region of Bi2Sr2CaCu2O8+δ and demonstrate that non-monotonic relaxation dynamics dominates above a certain fluence threshold. The dynamics is heavily influenced by transient modification of the electron-phonon interaction and phase space restrictions, in stark contrast to the monotonic relaxation in the nodal and off-nodal regions. PMID:26798826
Dynamic properties of ceramic materials
Grady, D.E.
1995-02-01
The present study offers new data and analysis on the transient shock strength and equation-of-state properties of ceramics. Various dynamic data on nine high strength ceramics are provided with wave profile measurements, through velocity interferometry techniques, the principal observable. Compressive failure in the shock wave front, with emphasis on brittle versus ductile mechanisms of deformation, is examined in some detail. Extensive spall strength data are provided and related to the theoretical spall strength, and to energy-based theories of the spall process. Failure waves, as a mechanism of deformation in the transient shock process, are examined. Strength and equation-of-state analysis of shock data on silicon carbide, boron carbide, tungsten carbide, silicon dioxide and aluminum nitride is presented with particular emphasis on phase transition properties for the latter two. Wave profile measurements on selected ceramics are investigated for evidence of rate sensitive elastic precursor decay in the shock front failure process.
Shear viscosity over entropy density ratio with extended quasiparticles
NASA Astrophysics Data System (ADS)
Horváth, M.; Jakovác, A.
2016-03-01
We consider an effective field theory description of beyond-quasiparticle excitations aiming to associate the transport properties of the system with the spectral density of states. Tuning various properties of the many-particle correlations, we investigate how the robust microscopic features are translated into the macroscopic observables like shear viscosity and entropy density. The liquid-gas crossover is analysed using several examples. A thermal constraint on the fluidity measure η /s is discussed.
Dynamical properties of piano soundboards.
Chaigne, Antoine; Cotté, Benjamin; Viggiano, Roberto
2013-04-01
In pianos, the transfer of energy from strings to soundboard and the radiation of sound are highly dependent on the dynamical properties of the soundboard. In this paper, a numerical study is conducted for various rib configurations, showing that even slight irregularities in rib spacing can induce a strong localization of the soundboard velocity pattern. The effective vibrating area can be further reduced due to the spatial filtering effect of the bridge. Numerical predictions of modal shapes and operating deflection shapes are confirmed by series of measurements made on upright piano soundboards. Simulations of radiated pressure based on measured and calculated soundboard velocity fields show that localization tends to broaden the cone of directivity and to reduce the number of lobes. PMID:23556610
Qubit dephasing due to quasiparticle tunneling
NASA Astrophysics Data System (ADS)
Zanker, Sebastian; Marthaler, Michael
2015-05-01
We study dephasing of a superconducting qubit due to quasiparticle tunneling through a Josephson junction. While qubit decay due to tunneling processes is well understood within a golden rule approximation, pure dephasing due to BCS quasiparticles gives rise to a divergent golden rule rate. We calculate qubit dephasing due to quasiparticle tunneling beyond lowest-order approximation in coupling between qubit and quasiparticles. Summing up a certain class of diagrams, we show that qubit dephasing due to purely longitudinal coupling to quasiparticles leads to dephasing ˜exp[-x (t )] where x (t ) ∝t3 /2 for short-time scales and x (t )∝t ln(t ) for long-time scales.
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.
Tunable quasiparticle trapping in Meissner and vortex states of mesoscopic superconductors
NASA Astrophysics Data System (ADS)
Taupin, M.; Khaymovich, I. M.; Meschke, M.; Mel'Nikov, A. S.; Pekola, J. P.
2016-03-01
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.
Tunable quasiparticle trapping in Meissner and vortex states of mesoscopic superconductors
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
A Quasiparticle Detector for Quantum Turbulence Imaging in Superfluid 3 He-B
NASA Astrophysics Data System (ADS)
Fisher, Shaun; Bradley, Ian; Clovevcko, Marcel; Ahlstrom, Sean; Guise, Ed; Haley, Rich; Holt, Steve; Pickett, George; Schanon, Roch; Tsepelin, Viktor; Woods, Andrew
2014-03-01
We describe the development of a two-dimensional quasiparticle detector to visualise quantum turbulence in superfluid 3He-B at ultra-low temperatures. The detector consists of 25 pixels each containing a miniature quartz tuning fork. The damping on each fork provides a measure of the local quasiparticle flux. The detector is illuminated by a beam of ballistic quasiparticles generated from a near-by black-body radiator. Vortices have a large cross-section for Andreev reflecting ballistic quasiparticles at low temperatures. We generate a tangle of vortices (quantum turbulence) in the path of the beam using a vibrating wire resonator. The vortices cast a shadow onto the face of the detector due to the Andreev reflection. This allows us to image the vortex tangle and to investigate the tangle dynamics. We describe the detector and present some preliminary results.
Tunable quasiparticle trapping in Meissner and vortex states of mesoscopic superconductors.
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
Quasiparticle interference from magnetic impurities
NASA Astrophysics Data System (ADS)
Derry, Philip G.; Mitchell, Andrew K.; Logan, David E.
2015-07-01
Fourier transform scanning tunneling spectroscopy (FT-STS) measures the scattering of conduction electrons from impurities and defects, giving information about the electronic structure of both the host material and adsorbed impurities. We interpret such FT-STS measurements in terms of the quasiparticle interference (QPI), here investigating in detail the QPI due to single magnetic impurities adsorbed on a range of representative nonmagnetic host surfaces, and contrasting with the case of a simple scalar impurity or point defect. We demonstrate how the electronic correlations present for magnetic impurities markedly affect the QPI, showing, e.g., a large intensity enhancement due to the Kondo effect, and universality at low temperatures/scanning energies. The commonly used joint density of states interpretation of FT-STS measurements is also considered, and shown to be insufficient in many cases, including that of magnetic impurities.
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.
Thermal Transport by Ballistic Quasiparticles in Superfluid 3He-B in the Low Temperature Limit
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.
Obtaining railpad properties via dynamic mechanical analysis
NASA Astrophysics Data System (ADS)
Oregui, M.; de Man, A.; Woldekidan, M. F.; Li, Z.; Dollevoet, R.
2016-02-01
In this paper, we propose combining dynamic mechanical analysis (DMA) and the time-temperature superposition principle to determine various railpad dynamic properties. Having accurate information regarding the dynamic properties of a railpad is a fundamental requirement for designing tracks and understanding track deterioration. By testing three different railpad types, we demonstrate that the dynamic behavior of railpads over a wide frequency range can be successfully obtained under different preloads and temperatures if time-temperature superposition can be applied. To investigate railpad aging, worn railpads taken from a mainline in the Netherlands are tested. In this case, worn railpads are softer and possess a lower damping capacity than new railpads. In addition to performing these measurements, a Prony series material model is proposed to reproduce the dynamic behavior of railpads. The Prony series model is in good agreement with the measurements. Measured railpad dynamic properties and the corresponding Prony series numerical model provide valuable information for track design and modeling.
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.
Quasiparticle electronic structure of bismuth telluride in the GW approximation
Kioupakis, Emmanouil; Tiago, Murilo L; Louie, Steven G.
2010-01-01
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 interpo- lation 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.
Challenges associated with sampling dynamic soil properties
Technology Transfer Automated Retrieval System (TEKTRAN)
The determination of dynamic soil properties (DSPs) for agricultural practices poses significant challenges, particularly in the context of values derived as part of the National Soil Survey. Although DSPs have been defined as those properties that change over human time scales, limits on the time ...
Exact-exchange-based quasiparticle calculations
Aulbur, Wilfried G.; Staedele, Martin; Goerling, Andreas
2000-09-15
One-particle wave functions and energies from Kohn-Sham calculations with the exact local Kohn-Sham exchange and the local density approximation (LDA) correlation potential [EXX(c)] are used as input for quasiparticle calculations in the GW approximation (GWA) for eight semiconductors. Quasiparticle corrections to EXX(c) band gaps are small when EXX(c) band gaps are close to experiment. In the case of diamond, quasiparticle calculations are essential to remedy a 0.7 eV underestimate of the experimental band gap within EXX(c). The accuracy of EXX(c)-based GWA calculations for the determination of band gaps is as good as the accuracy of LDA-based GWA calculations. For the lowest valence band width a qualitatively different behavior is observed for medium- and wide-gap materials. The valence band width of medium- (wide-) gap materials is reduced (increased) in EXX(c) compared to the LDA. Quasiparticle corrections lead to a further reduction (increase). As a consequence, EXX(c)-based quasiparticle calculations give valence band widths that are generally 1-2 eV smaller (larger) than experiment for medium- (wide-) gap materials. (c) 2000 The American Physical Society.
Pairing within the self-consistent quasiparticle random-phase approximation at finite temperature
Dang, N. Dinh; Hung, N. Quang
2008-06-15
An approach to pairing in finite nuclei at nonzero temperature is proposed, which incorporates the effects due to the quasiparticle-number fluctuation (QNF) around Bardeen-Cooper-Schrieffer (BCS) mean field and dynamic coupling to quasiparticle-pair vibrations within the self-consistent quasiparticle random-phase approximation (SCQRPA). The numerical calculations of pairing gap, total energy, and heat capacity were carried out within a doubly folded multilevel model as well as realistic nuclei {sup 56}Fe and {sup 120}Sn. The results obtained show that, under the effect of QNF, in the region of moderate and strong couplings, the sharp transition between the superconducting and normal phases is smoothed out, resulting in a thermal pairing gap, which does not collapse at the BCS critical temperature, but has a tail, which extends to high temperature. The dynamic coupling of quasiparticles to SCQRPA vibrations significantly improves the agreement with the results of exact calculations and those obtained within the finite-temperature quantal Monte Carlo method for the total energy and heat capacity. It also causes a deviation of the quasiparticle occupation numbers from the Fermi-Dirac distributions for free fermions.
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
Quasiparticles of strongly correlated Fermi liquids at high temperatures and in high magnetic fields
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.
Bogoliubov quasiparticles coupled to the antiferromagnetic spin mode in a vortex core
NASA Astrophysics Data System (ADS)
Berthod, C.
2015-12-01
In copper- and iron-based unconventional superconductors, the Bogoliubov quasiparticles interact with a spin resonance at momentum (π ,π ) . This interaction is revealed by specific signatures in the quasiparticle spectroscopies, like kinks in photoemission and dips in tunneling. We study these signatures, as they appear inside and around a vortex core in the local density of states (LDOS), a property accessible experimentally by scanning tunneling spectroscopy. Our model retains the whole nonlocal structure of the self-energy in space and time and is therefore not amenable to a Hamiltonian treatment using Bogoliubov-de Gennes equations. The interaction with the spin resonance does not suppress the zero-bias peak at the vortex center, although it reduces its spectral weight; neither does it smear out the vortex LDOS, but rather it adds structure to it. Some of the signatures we find may have been already measured in FeSe, but remained unnoticed. We compare the LDOS as a function of both energy and position with and without coupling to the spin resonance and observe, in particular, that the quasiparticle interference patterns around the vortex are strongly damped by the coupling. We study in detail the transfer of spectral weight induced both locally and globally by the interaction and also by the formation of the vortex. Finally, we introduce a new way of imaging the quasiparticles in real space, which combines locality and momentum-space sensitivity. This approach allows one to access quasiparticle properties that are not contained in the LDOS.
Quasiparticles near domain walls in hexagonal superconductors
NASA Astrophysics Data System (ADS)
Mukherjee, S. P.; Samokhin, K. V.
2016-02-01
We calculate the energy spectrum of quasiparticles trapped by a domain wall separating different time-reversal symmetry-breaking ground states in a hexagonal superconductor, such as UPt3. The bound-state energy is found to be strongly dependent on the gap symmetry, the domain-wall orientation, the quasiparticle's direction of semiclassical propagation, and the phase difference between the domains. We calculate the corresponding density of states and show how one can use its prominent features, in particular, the zero-energy singularity, to distinguish between different pairing symmetries.
Quasiparticles near domain walls in hexagonal superconductors
NASA Astrophysics Data System (ADS)
Mukherjee, Soumya; Samokhin, Kirill
We calculate the energy spectrum of quasiparticles trapped by a domain wall separating different time reversal symmetry-breaking ground states in a hexagonal superconductor, such as UPt3. The bound state energy is found to be strongly dependent on the gap symmetry, the domain wall orientation, the quasiparticle's direction of semiclassical propagation, and the phase difference between the domains. We calculate the corresponding density of states and show how one can use its prominent features, in particular, the zero-energy singularity, to distinguish between different pairing symmetries. Discovery Grant from the Natural Sciences and Engineering Research Council of Canada.
Physical properties and mantle dynamics
Shankland, T.J.; Johnson, P.A.; McCall, K.R.
1997-11-01
This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Because planetary interiors are remote, laboratory methods and associated theory are an essential step for interpreting geophysical measurements in terms of quantities that are needed for understanding Earth--temperature, composition, stress state, history, and hazards. One objective is the study of minerals and rocks as materials using experimental methods; another is to develop new methods, as in high pressure research, codes for computation in rock/soil physics, or nuclear-based analysis. Accomplishments include developing a single-crystal x-ray diffraction apparatus with application to materials at extremely high pressure and temperature; P-V-T equations of state and seismic velocity measurements for understanding the composition of Earth`s outer 1,000 km; creating computational tools to explain complex stress-strain histories of rocks; and measuring tungsten/thorium ratios W/Th that agree with the hypothesis that Earth accreted heterogeneously. Work performed in this project applies to geosciences, geothermal energy, mineral and rock properties, seismic detection, and isotope dating.
A Quasiparticle Detector for Imaging Quantum Turbulence in Superfluid He-B
NASA Astrophysics Data System (ADS)
Ahlstrom, S. L.; Bradley, D. I.; Fisher, S. N.; Guénault, A. M.; Guise, E. A.; Haley, R. P.; Holt, S.; Kolosov, O.; McClintock, P. V. E.; Pickett, G. R.; Poole, M.; Schanen, R.; Tsepelin, V.; Woods, A. J.
2014-06-01
We describe the development of a two-dimensional quasiparticle detector for use in visualising quantum turbulence in superfluid He-B at ultra-low temperatures. The detector consists of a matrix of pixels, each a 1 mm diameter hole in a copper block containing a miniature quartz tuning fork. The damping on each fork provides a measure of the local quasiparticle flux. The detector is illuminated by a beam of ballistic quasiparticles generated from a nearby black-body radiator. A comparison of the damping on the different forks provides a measure of the cross-sectional profile of the beam. Further, we generate a tangle of vortices (quantum turbulence) in the path of the beam using a vibrating wire resonator. The vortices cast a shadow onto the face of the detector due to the Andreev reflection of quasiparticles in the beam. This allows us to image the vortices and to investigate their dynamics. Here we give details of the design and construction of the detector and show some preliminary results for one row of pixels which demonstrates its successful application to measuring quasiparticle beams and quantum turbulence.
Dynamic property studies of Sterling engines
NASA Technical Reports Server (NTRS)
Tani, Y.; Seibara, M.; Takenai, K.; Yamaguchi, W.
1984-01-01
A description is given of the results of dynamic property tests that were carried out using a trial produced prototype of a 50 KW Sterling engine. The features of the engine are shown graphically. A high thermal efficiency is found in the low rotation region.
Chemical potential beyond the quasiparticle mean field
Dinh Dang, N.; Hung, N. Quang
2010-03-15
The effects of quantal and thermal fluctuations beyond the BCS quasiparticle mean field on the chemical potential are studied within a model, which consists of N particles distributed amongst {Omega} doubly folded equidistant levels interacting via a pairing force with parameter G. The results obtained at zero and finite temperatures T within several approaches, which include the fluctuations beyond the BCS theory, are compared with the exact results. The chemical potential, defined as the Lagrangian multiplier to preserve the average number of particles, is compared with the corresponding quantity, which includes the effect from fluctuations of particle and quasiparticle numbers beyond the BCS quasiparticle mean field. The analysis of the results shows that the latter differs significantly from the former as functions of G and T. The chemical potential loses its physical meaning in the system with a fixed number of particles or after eliminating quantal fluctuations of particle (quasiparticle) numbers by means of particle number projection. The validity of the criterion for the signature of the transition to Bose-Einstein condensation, which occurs in infinite systems when the chemical potential hits the bottom of the energy spectrum, is reexamined for the finite multilevel model.
Dynamical simulation of dipolar Janus colloids: Dynamical properties
NASA Astrophysics Data System (ADS)
Hagy, Matthew C.; Hernandez, Rigoberto
2013-05-01
The dynamical properties of dipolar Janus particles are studied through simulation using our previously-developed detailed pointwise (PW) model and an isotropically coarse-grained (CG) model [M. C. Hagy and R. Hernandez, J. Chem. Phys. 137, 044505 (2012), 10.1063/1.4737432]. The CG model is found to have accelerated dynamics relative to the PW model over a range of conditions for which both models have near identical static equilibrium properties. Physically, this suggests dipolar Janus particles have slower transport properties (such as diffusion) in comparison to isotropically attractive particles. Time rescaling and damping with Langevin friction are explored to map the dynamics of the CG model to that of the PW model. Both methods map the diffusion constant successfully and improve the velocity autocorrelation function and the mean squared displacement of the CG model. Neither method improves the distribution of reversible bond durations f(tb) observed in the CG model, which is found to lack the longer duration reversible bonds observed in the PW model. We attribute these differences in f(tb) to changes in the energetics of multiple rearrangement mechanisms. This suggests a need for new methods that map the coarse-grained dynamics of such systems to the true time scale.
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
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.
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.
Gap-engineered quasiparticle traps in the fluxonium artificial atom
NASA Astrophysics Data System (ADS)
Serniak, K.; de Lange, G.; Vool, U.; Hays, M.; Burkhart, L. D.; Gao, Y. Y.; Wang, C.; Sliwa, K. M.; Pop, I. M.; Frunzio, L.; Glazman, L. I.; Schoelkopf, R. J.; Devoret, M. H.
Recent experiments have shown that the density of quasiparticles in superconducting quantum circuits exceeds the expected thermal density. In Josephson junction based superconducting qubits, these non-equilibrium quasiparticles can tunnel through the junctions of the circuit, causing decoherence. Quasiparticle traps aim to reduce the density of quasiparticles near the junctions, and therefore the rate of energy loss and dephasing due to tunneling events. These traps must be designed to not introduce any additional losses in the qubit. In this talk we will discuss recent progress in the design and implementation of quasiparticle traps in the fluxonium artificial atom. Work supported by ARO, ONR, YINQE, and the European Union.
Superconducting resonators with trapped vortices under direct injection of quasiparticles
NASA Astrophysics Data System (ADS)
Nsanzineza, Ibrahim; Patel, Umesh; Dodge, K. R.; McDermott, R. F.; Plourde, B. L. T.
Nonequilibrium quasiparticles and trapped magnetic flux vortices can significantly impact the performance of superconducting microwave resonant circuits and qubits at millikelvin temperatures. Quasiparticles result in excess loss, reducing resonator quality factors and qubit lifetimes. Vortices trapped near regions of large microwave currents also contribute excess loss. However, vortices located in current-free areas in the resonator or in the ground plane of a device can actually trap quasiparticles and lead to a reduction in the quasiparticle loss. We will describe experiments involving the controlled trapping of vortices in superconducting resonators with direct injection of quasiparticles using Normal metal-Insulator-Superconductor (NIS)-tunnel junctions.
Field-induced dynamical properties of the XXZ model on a honeycomb lattice
NASA Astrophysics Data System (ADS)
Maksimov, P. A.; Chernyshev, A. L.
2016-01-01
We present a comprehensive 1 /S study of the field-induced dynamical properties of the nearest-neighbor XXZ antiferromagnet on a honeycomb lattice using the formalism of nonlinear spin-wave theory developed for this model. The external magnetic field controls spin frustration in the system and induces noncollinearity of the spin structure, which is essential for the two-magnon decay processes. Our results include an intriguing field-evolution of the regions of the Brillouin zone wherein decays of spin excitations are prominent, a detailed classification of the decay channels involving magnons from both excitation branches, and a thorough analysis of the singularities in the magnon spectra due to coupling to the two-magnon continuum, all of which are illustrated for several field and anisotropy values. We highlight a number of features related to either the non-Bravais nature of the lattice or the existence of the Dirac-like points in the spectrum. In addition, the asymptotic behavior of the decay rates near high-symmetry points is analyzed in detail. The inelastic neutron-scattering spin-spin structure factor is obtained in the leading 1 /S order and is shown to exhibit qualitatively distinct fingerprints of the decay-induced magnon dynamics such as quasiparticle peaks broadened by decays and strong spectral weight redistribution.
Normal Metal Quasiparticle Traps in 3D-Transmon Qubits
NASA Astrophysics Data System (ADS)
Burkhart, Luke D.; Gao, Yvonne Y.; Wang, Chen; Serniak, Kyle; de Lange, Gijs; Chu, Yiwen; Vool, Uri; Frunzio, Luigi; Devoret, Michel H.; Catelani, Gianluigi; Glazman, Leonid I.; Schoelkopf, Robert J.
Quasiparticles are a known source of decoherence in Josephson-junction based superconducting qubits. While equilibrium quasiparticles should not be present in devices operated at dilution refrigeration temperatures well below the superconducting energy gap, non-thermal quasiparticles have been observed in many different superconducting qubits, including 3D-transmons and fluxonium qubits. Vortices induced by applied magnetic fields have been shown to improve non-equilibrium quasiparticle decay rates and improve coherence times by creating regions of the superconductor with vanishing energy gap, which act as quasiparticle traps. We aim to further mitigate quasiparticle-induced limits on coherence by engineering strong trapping via the introduction of normal metal to the superconducting qubit. In this talk, we present recent results regarding normal metal quasiparticle traps in 3D-transmon qubits. Work supported by ARO, A*STAR.
Quasiparticle-continuum level repulsion in a quantum magnet
Plumb, K. W.; Hwang, Kyusung; Qiu, Y.; Harriger, Leland W.; Granroth, G. Â 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
Quasiparticle-continuum level repulsion in a quantum magnet
Plumb, K. W.; Hwang, Kyusung; Qiu, Y.; Harriger, Leland W.; Granroth, G. Â 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 BiCu_{2}PO_{6}.
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.
Multifractal properties of ball milling dynamics
Budroni, M. A. Pilosu, V.; Rustici, M.; Delogu, F.
2014-06-15
This work focuses on the dynamics of a ball inside the reactor of a ball mill. We show that the distribution of collisions at the reactor walls exhibits multifractal properties in a wide region of the parameter space defining the geometrical characteristics of the reactor and the collision elasticity. This feature points to the presence of restricted self-organized zones of the reactor walls where the ball preferentially collides and the mechanical energy is mainly dissipated.
Quasiparticles and Fermi liquid behaviour in an organic metal
Kiss, T.; Chainani, A.; Yamamoto, H.M.; Miyazaki, T.; Akimoto, T.; Shimojima, T.; Ishizaka, K.; Watanabe, S.; Chen, C.-T.; Fukaya, A.; Kato, R.; Shin, S.
2012-01-01
Many organic metals display exotic properties such as superconductivity, spin-charge separation and so on and have been described as quasi-one-dimensional Luttinger liquids. However, a genuine Fermi liquid behaviour with quasiparticles and Fermi surfaces have not been reported to date for any organic metal. Here, we report the experimental Fermi surface and band structure of an organic metal (BEDT-TTF)3Br(pBIB) obtained using angle-resolved photoelectron spectroscopy, and show its consistency with first-principles band structure calculations. Our results reveal a quasiparticle renormalization at low energy scales (effective mass m*=1.9 me) and ω2 dependence of the imaginary part of the self energy, limited by a kink at ~50 meV arising from coupling to molecular vibrations. The study unambiguously proves that (BEDT-TTF)3Br(pBIB) is a quasi-2D organic Fermi liquid with a Fermi surface consistent with Shubnikov-de Haas results. PMID:23011143
Polymer nanocomposites: permeability, chain dynamics, mechanical properties
NASA Astrophysics Data System (ADS)
Sahu, Laxmi
2005-03-01
Polymer nanocomposites based on dispersion of surfactant treated expandable smectite clays such as montmorillonite layered silicates (MLS) have shown promise as organic-inorganic hybrids with the potential to improve barrier properties. Separately, flexible displays based on plastic substrates have reduced lifetimes tied to the low barrier properties. While there has been a general attribution of improved barrier properties to the tortuous path, this does not consider the influence the introduction of a secondary filler has on the morphology of the host polymer. Here we examine the influence of MLS nanoplatelets on the barrier properties and chain dynamics of polymers. We investigate the potential for host polymer modification by comparing two crystallizable polymers nylon and PET and resulting well dispersed nanocomposites. We study mechanical, cyclic fatigue and permeability of films. Permeability of the biaxially stretched film and when the film undergoes fatigue of 50 and 10000 cycles are also measured. Chain dynamics were modeled based on the Burger model fit to creep-recovery data. A systematic approach to predict the permeability considering amorphous, crystalline and MLS content and comparison with experimental values were done. We also conducted water absorption measurements to highlight the water absorption differences in the two polymers. Dimensional stability of PET was studied by measuring coefficient of thermal expansion of thin film on Si substrate by ellipsometry method.
Dynamic properties of Drosophila olfactory electroantennograms.
Schuckel, Julia; Meisner, Shannon; Torkkeli, Päivi H; French, Andrew S
2008-05-01
Time-dependent properties of chemical signals are probably crucially important to many animals, but little is known about the dynamics of chemoreceptors. Behavioral evidence of dynamic sensitivity includes the control of moth flight by pheromone plume structure, and the ability of some blood-sucking insects to detect varying concentrations of carbon dioxide, possibly matched to host breathing rates. Measurement of chemoreceptor dynamics has been limited by the technical challenge of producing controlled, accurate modulation of olfactory and gustatory chemical concentrations over suitably wide ranges of amplitude and frequency. We used a new servo-controlled laminar flow system, combined with photoionization detection of surrogate tracer gas, to characterize electroantennograms (EAG) of Drosophila antennae during stimulation with fruit odorants or aggregation pheromone in air. Frequency response functions and coherence functions measured over a bandwidth of 0-100 Hz were well characterized by first-order low-pass linear filter functions. Filter time constant varied over almost a tenfold range, and was characteristic for each odorant, indicating that several dynamically different chemotransduction mechanisms are present. Pheromone response was delayed relative to fruit odors. Amplitude of response, and consequently signal-to-noise ratio, also varied consistently with different compounds. Accurate dynamic characterization promises to provide important new information about chemotransduction and odorant-stimulated behavior. PMID:18320197
Dynamic molecular crystals with switchable physical properties.
Sato, Osamu
2016-06-21
The development of molecular materials whose physical properties can be controlled by external stimuli - such as light, electric field, temperature, and pressure - has recently attracted much attention owing to their potential applications in molecular devices. There are a number of ways to alter the physical properties of crystalline materials. These include the modulation of the spin and redox states of the crystal's components, or the incorporation within the crystalline lattice of tunable molecules that exhibit stimuli-induced changes in their molecular structure. A switching behaviour can also be induced by changing the molecular orientation of the crystal's components, even in cases where the overall molecular structure is not affected. Controlling intermolecular interactions within a molecular material is also an effective tool to modulate its physical properties. This Review discusses recent advances in the development of such stimuli-responsive, switchable crystalline compounds - referred to here as dynamic molecular crystals - and suggests how different approaches can serve to prepare functional materials. PMID:27325090
Dynamic tensile properties of human placenta.
Manoogian, Sarah J; Bisplinghoff, Jill A; McNally, Craig; Kemper, Andrew R; Santago, Anthony C; Duma, Stefan M
2008-12-01
Automobile crashes are the largest cause of injury death for pregnant females and the leading cause of traumatic fetal injury mortality in the United States. Computational models, useful tools to evaluate the risk of fetal loss in motor vehicle crashes, are based on a limited number of quasi-static material tests of the placenta. This study presents a total of 20 dynamic uniaxial tensile tests on the maternal side of the placenta and 10 dynamic uniaxial tensile tests on the chorion layer of the placenta. These tests were completed from 6 human placentas to determine material properties at a strain rate of 7.0 strains/s. The results show that the average peak strain at failure for both the maternal portion and the chorion layer of the placenta are similar with a value of 0.56 and 0.61, respectively. However, the average failure stress for the chorion layer, 167.8 kPa, is much higher than the average failure stress for the placenta with the chorionic plate removed, 18.6 kPa. This is due to differences in the structure and function of these layers in the placenta. In summary, dynamic loading data for the placenta have been determined for use in computational modeling of pregnant occupant kinematics in motor vehicle crashes. Moreover the computational model should utilize the material properties for the placenta without the chorion layer. PMID:18996533
Structural and dynamical properties of complex networks
NASA Astrophysics Data System (ADS)
Ghoshal, Gourab
Recent years have witnessed a substantial amount of interest within the physics community in the properties of networks. Techniques from statistical physics coupled with the widespread availability of computing resources have facilitated studies ranging from large scale empirical analysis of the worldwide web, social networks, biological systems, to the development of theoretical models and tools to explore the various properties of these systems. Following these developments, in this dissertation, we present and solve for a diverse set of new problems, investigating the structural and dynamical properties of both model and real world networks. We start by defining a new metric to measure the stability of network structure to disruptions, and then using a combination of theory and simulation study its properties in detail on artificially generated networks; we then compare our results to a selection of networks from the real world and find good agreement in most cases. In the following chapter, we propose a mathematical model that mimics the structure of popular file-sharing websites such as Flickr and CiteULike and demonstrate that many of its properties can solved exactly in the limit of large network size. The remaining part of the dissertation primarily focuses on the dynamical properties of networks. We first formulate a model of a network that evolves under the addition and deletion of vertices and edges, and solve for the equilibrium degree distribution for a variety of cases of interest. We then consider networks whose structure can be manipulated by adjusting the rules by which vertices enter and leave the network. We focus in particular on degree distributions and show that, with some mild constraints, it is possible by a suitable choice of rules to arrange for the network to have any degree distribution we desire. In addition we define a simple local algorithm by which appropriate rules can be implemented in practice. Finally, we conclude our
Robustness of superconducting quantum modes against direct quasiparticle injection
NASA Astrophysics Data System (ADS)
Patel, U.; Nsanzineza, I.; Vavilov, M. G.; Plourde, B. L. T.; McDermott, R.
Classical Josephson digital logic based on Single Flux Quantum (SFQ) pulses offers a path to high-fidelity coherent control of large-scale superconducting quantum machines. However, an SFQ pulse driver generates nonequilibrium quasiparticles that contribute to qubit relaxation, and steps must be taken to protect the qubit from this decoherence channel. Here we describe experiments to characterize the robustness of high-Q superconducting linear resonators and qubits against direct quasiparticle injection. We use NIS junctions and SFQ elements to controllably inject quasiparticles into the groundplane of superconducting resonator and qubit chips, and we characterize the quasiparticle contribution to dissipation. We examine the effectiveness of groundplane cuts, normal metal quasiparticle traps, and spatially-varying superconducting gaps at protecting the quantum modes against quasiparticle loss. Finally, we discuss strategies for the integration of multiqubit circuits with on-chip SFQ control elements.
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.
Physical and Dynamical Properties of Asteroid Families
NASA Astrophysics Data System (ADS)
Zappalà, V.; Cellino, A.; dell'Oro, A.; Paolicchi, P.
2002-03-01
The availability of a number of statistically reliable asteroid families and the independent confirmation of their likely collisional origin from dedicated spectroscopic campaigns has been a major breakthrough, making it possible to develop detailed studies of the physical properties of these groupings. Having been produced in energetic collisional events, families are an invaluable source of information on the physics governing these phenomena. In particular, they provide information about the size distribution of the fragments, and on the overall properties of the original ejection velocity fields. Important results have been obtained during the last 10 years on these subjects, with important implications for the general understanding of the collisional history of the asteroid main belt, and the origin of near-Earth asteroids. Some important problems have been raised from these studies and are currently debated. In particular, it has been difficult so far to reconcile the inferred properties of family-forming events with current understanding of the physics of catastrophic collisional breakup. Moreover, the contribution of families to the overall asteroid inventory, mainly at small sizes, is currently controversial. Recent investigations are also aimed at understanding which kind of dynamical evolution might have affected family members since the time of their formation. In addition to potential consequences on the interpretation of current data, there is some speculative possibility of obtaining some estimate of the ages of these groupings. Physical characterization of families will likely represent a prerequisite for further advancement in understanding the properties and history of the asteroid population.
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.
Intact quasiparticles at an unconventional quantum critical point
NASA Astrophysics Data System (ADS)
Sutherland, M. L.; O'Farrell, E. C. T.; Toews, W. H.; Dunn, J.; Kuga, K.; Nakatsuji, S.; Machida, Y.; Izawa, K.; Hill, R. W.
2015-07-01
We report measurements of in-plane electrical and thermal transport properties in the limit T →0 near the unconventional quantum critical point in the heavy-fermion metal β -YbAlB4 . The high Kondo temperature TK≃200 K in this material allows us to probe transport extremely close to the critical point, at unusually small values of T /TK<5 ×10-4 . Here we find that the Wiedemann-Franz law is obeyed at the lowest temperatures, implying that the Landau quasiparticles remain intact in the critical region. At finite temperatures we observe a non-Fermi-liquid T -linear dependence of inelastic-scattering processes to energies lower than those previously accessed. These processes have a weaker temperature dependence than in comparable heavy fermion quantum critical systems, revealing a temperature scale of T ˜0.3 K which signals a sudden change in the character of the inelastic scattering.
Exact dynamic properties of molecular motors
NASA Astrophysics Data System (ADS)
Boon, N. J.; Hoyle, R. B.
2012-08-01
Molecular motors play important roles within a biological cell, performing functions such as intracellular transport and gene transcription. Recent experimental work suggests that there are many plausible biochemical mechanisms that molecules such as myosin-V could use to achieve motion. To account for the abundance of possible discrete-stochastic frameworks that can arise when modeling molecular motor walks, a generalized and straightforward graphical method for calculating their dynamic properties is presented. It allows the calculation of the velocity, dispersion, and randomness ratio for any proposed system through analysis of its structure. This article extends work of King and Altman ["A schematic method of deriving the rate laws of enzyme-catalyzed reactions," J. Phys. Chem. 60, 1375-1378 (1956)], 10.1021/j150544a010 on networks of enzymatic reactions by calculating additional dynamic properties for spatially hopping systems. Results for n-state systems are presented: single chain, parallel pathway, divided pathway, and divided pathway with a chain. A novel technique for combining multiple system architectures coupled at a reference state is also demonstrated. Four-state examples illustrate the effectiveness and simplicity of these methods.
Exact dynamic properties of molecular motors.
Boon, N J; Hoyle, R B
2012-08-28
Molecular motors play important roles within a biological cell, performing functions such as intracellular transport and gene transcription. Recent experimental work suggests that there are many plausible biochemical mechanisms that molecules such as myosin-V could use to achieve motion. To account for the abundance of possible discrete-stochastic frameworks that can arise when modeling molecular motor walks, a generalized and straightforward graphical method for calculating their dynamic properties is presented. It allows the calculation of the velocity, dispersion, and randomness ratio for any proposed system through analysis of its structure. This article extends work of King and Altman ["A schematic method of deriving the rate laws of enzyme-catalyzed reactions," J. Phys. Chem. 60, 1375-1378 (1956)] on networks of enzymatic reactions by calculating additional dynamic properties for spatially hopping systems. Results for n-state systems are presented: single chain, parallel pathway, divided pathway, and divided pathway with a chain. A novel technique for combining multiple system architectures coupled at a reference state is also demonstrated. Four-state examples illustrate the effectiveness and simplicity of these methods. PMID:22938213
Quasiparticle energies and lifetimes in a metallic chain model of a tunnel junction.
Szepieniec, Mark; Yeriskin, Irene; Greer, J C
2013-04-14
As electronics devices scale to sub-10 nm lengths, the distinction between "device" and "electrodes" becomes blurred. Here, we study a simple model of a molecular tunnel junction, consisting of an atomic gold chain partitioned into left and right electrodes, and a central "molecule." Using a complex absorbing potential, we are able to reproduce the single-particle energy levels of the device region including a description of the effects of the semi-infinite electrodes. We then use the method of configuration interaction to explore the effect of correlations on the system's quasiparticle peaks. We find that when excitations on the leads are excluded, the device's highest occupied molecular orbital and lowest unoccupied molecular orbital quasiparticle states when including correlation are bracketed by their respective values in the Hartree-Fock (Koopmans) and ΔSCF approximations. In contrast, when excitations on the leads are included, the bracketing property no longer holds, and both the positions and the lifetimes of the quasiparticle levels change considerably, indicating that the combined effect of coupling and correlation is to alter the quasiparticle spectrum significantly relative to an isolated molecule. PMID:24981526
Quasiparticle band structure of HgSe
Rohlfing, M.; Louie, S.G.
1998-04-01
Motivated by a recent discussion about the existence of a fundamental gap in HgSe [Phys. Rev. Lett. {bold 78}, 3165 (1997)], we calculate the quasiparticle band structure of HgSe within the GW approximation for the electron self-energy. The band-structure results show that HgSe is a semimetal, which is in agreement with most experimental data. We observe a strong wave-vector dependence of the self-energy of the lowest conduction band, leading to an increased dispersion and a small effective mass. This may help to interpret recent photoemission spectroscopy measurements. {copyright} {ital 1998} {ital The American Physical Society}
Charge of a quasiparticle in a superconductor
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
Charge of a quasiparticle in a superconductor.
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
NASA Astrophysics Data System (ADS)
Sharifzadeh, Sahar; Biller, Ariel; Kronik, Leeor; Neaton, Jeffrey B.
2012-03-01
The broad use of organic semiconductors for optoelectronic applications relies on quantitative understanding and control of their spectroscopic properties. Of paramount importance are the transport gap—the difference between ionization potential and electron affinity—and the exciton binding energy—inferred from the difference between the transport and optical absorption gaps. Transport gaps are commonly established via photoemission and inverse photoemission spectroscopy (PES/IPES). However, PES and IPES are surface-sensitive, average over a dynamic lattice, and are subject to extrinsic effects, leading to significant uncertainty in gaps. Here, we use density functional theory and many-body perturbation theory to calculate the spectroscopic properties of two prototypical organic semiconductors, pentacene, and 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA), quantitatively comparing with measured PES, IPES, and optical absorption spectra. For bulk pentacene and PTCDA, the computed transport gaps are 2.4 and 3.0 eV, and optical gaps are 1.7 and 2.1 eV, respectively. Computed bulk quasiparticle spectra are in excellent agreement with surface-sensitive photoemission measurements over several eV only if the measured gap is reduced by 0.6 eV for pentacene and 0.6-0.9 eV for PTCDA. We attribute this redshift to several physical effects, including incomplete charge screening at the surface, static and dynamical disorder, and experimental resolution. Optical gaps are in excellent agreement with experiment with solid-state exciton binding energies of ˜0.5 eV for both systems; for pentacene the exciton is delocalized over several molecules and exhibits significant charge transfer character. Our parameter-free calculations provide new interpretation of spectroscopic properties of organic semiconductors critical to optoelectronics.
Aspects of nodal quasiparticle transport in high-Tc superconductors
NASA Astrophysics Data System (ADS)
Smith, Michael F.
Various low-temperature thermodynamic and transport properties of high TC superconductors at temperatures well below TC are studied theoretically under the assumption that the low-energy excited states can be regarded as independent Bogolubov quasiparticles near the nodes of the superconducting order parameter. In the limiting case of temperatures well above that corresponding to the impurity scattering rate, a Boltzmann-equation description of the quasiparticle distribution is used to study thermal and electrical transport for several scattering mechanisms. In particular, the dominant scattering mechanism for the relaxation of microwave electrical currents well below TC is identified, and the observed temperature dependence of the microwave conductivity data in optimally-doped YBa2Cu3O7-delta thus explained. The Knight shift and nuclear spin relaxation rate at temperatures well above the impurity scattering rate are also calculated and compared with available data. In the opposite limiting case of temperatures well below that corresponding to the impurity scattering rate, the sound attenuation and electron-phonon heat transfer rate are calculated. A model for the electron-phonon interaction in square-lattice tight-binding materials is developed and used to explain the huge measured anisotropy of the normal-state sound attenuation in the unconventional superconductor Sr2RuO4 and to rule out certain candidates for the order parameter symmetry of this material. A calculation of the electron-phonon heat transfer rate for d-wave superconductors gives the dependence of this quantity on various material parameters. Finally, the result for the electron-phonon heat transfer rate is used to explain the origin of the anomalous downturns in the thermal conductivity that have been observed in both the normal and superconducting state of cuprate superconductors, most notably in Pr2-xCe xCuO7-delta.
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)
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
Dakovski, Georgi L.; Durakiewicz, Tomasz; Zhu, Jian-Xin; Riseborough, Peter S.; Gu, Genda; Gilbertson, Steve M.; Taylor, Antoinette; Rodriguez, George
2015-10-12
A hallmark in the cuprate family of high-temperature superconductors is the nodal-antinodal dichotomy. In this regard, angle-resolved photoemission spectroscopy (ARPES) has proven especially powerful, providing band structure information directly in energy-momentum space. Time-resolved ARPES (trARPES) holds great promise of adding ultrafast temporal information, in an attempt to identify different interaction channels in the time domain. Previous studies of the cuprates using trARPES were handicapped by the low probing energy which significantly limits the accessible momentum space. Using 20.15eV, 12 fs pulses we show for the first time the evolution of quasiparticles in the antinodal region of Bi_{2}Sr_{2}CaCu_{2}O_{8+δ} and demonstrate that nonmonotonic relaxation dynamics dominates above a certain fluence threshold. The dynamics is heavily influenced by transient modification of the electron-phonon interaction and phase space restrictions, in severe contrast to the monotonic relaxation in the nodal and off-nodal regions.
Xu, Wenhu; Haule, Kristjan; Kotliar, Gabriel
2013-07-19
We investigate the transport properties of a correlated metal within dynamical mean-field theory. Canonical Fermi liquid behavior emerges only below a very low temperature scale T(FL). Surprisingly the quasiparticle scattering rate follows a quadratic temperature dependence up to much higher temperatures and crosses over to saturated behavior around a temperature scale T(sat). We identify these quasiparticles as constituents of the hidden Fermi liquid. The non-Fermi-liquid transport above T(FL), in particular the linear-in-T resistivity, is shown to be a result of a strongly temperature dependent band dispersion. We derive simple expressions for the resistivity, Hall angle, thermoelectric power and Nernst coefficient in terms of a temperature dependent renormalized band structure and the quasiparticle scattering rate. We discuss possible tests of the dynamical mean-field theory picture of transport using ac measurements. PMID:23909344
Dynamical properties of the Watsonia asteroid family
NASA Astrophysics Data System (ADS)
Tsirvoulis, G.; Novakovic, B.; Knezevic, Z.; Cellino, A.
2014-07-01
Introduction: In recent years, a rare class of asteroids has been discovered [1], with its distinguishing characteristic being the anomalous polarimetric properties of its members. Named Barbarians, after (234) Barbara, the prototype of the class, these asteroids show negative polarization at unusually high phase-angles compared to normal asteroids. Motivated by the fact that some of the few discovered Barbarians seemed to be related to the Watsonia asteroid family, Cellino et al. [2] performed a search for more Barbarians among its members. A positive result of this search led to the conclusion that Watsonia is indeed an important repository of Barbarian asteroids. Based on these findings, we decided to analyze this family in detail. Basic information: According to available data, Watsonia is an L-type asteroid family, located in the middle of the main asteroid belt (2.68 < a_{p} < 2.82 au), with low to moderate orbital eccentricities (0.1 < e_{p} < 0.15) and relatively high inclinations (16.5^{o} < i_{p} < 18^{o}). Methodology: The first step in our study is to derive a reliable list of Watsonia family members. To that purpose, we first calculate the synthetic proper elements [3] of an extended catalogue including numbered, as well as multi and single opposition asteroids, in a wide region around the family. To this catalogue we apply the Hierarchical Clustering Method (HCM)[4] to determine the membership of the family, coinciding with the requirement that all confirmed neighboring Barbarians are included (see figure). To detect potential interlopers and refine the membership list, additional data such as the SDSS colors and WISE albedos are used. Moreover, we identify all relevant resonances and analyze the dynamical characteristics of the region occupied by the family. Then we estimate the age of the family, and finally, we perform numerical integrations of test particles to investigate possible dynamical links to other known Barbarians and to the near
Finite quasiparticle lifetime in disordered superconductors.
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.
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.
Efficient quasiparticle band-structure calculations for cubic and noncubic crystals
Wenzien, B.; Cappellini, G.; Bechstedt, F.
1995-05-15
An efficient method developed for the calculation of quasiparticle corrections to density-functional-theory--local-density-approximation (DFT-LDA) band structures of diamond and zinc-blende materials is generalized for crystals with other cubic, hexagonal, tetragonal, and orthorhombic Bravais lattices. Local-field effects are considered in the framework of a LDA-like approximation. The dynamical screening is treated by expanding the self-energy linearly in energy. The anisotropy of the inverse dielectric matrix is taken into account. The singularity of the Coulomb potential in the screened-exchange part of the electronic self-energy is treated using auxiliary functions of the appropriate symmetry. An application to the electronic quasiparticle band structure of wurtzite 2{ital H}-SiC is presented within the approach of norm-conserving, nonlocal, fully separable pseudopotentials and a plane-wave expansion of the wave functions for the underlying DFT-LDA.
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
2014-01-01
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 (La2CuO(4+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. PMID:25290587
Separable pairing force for relativistic quasiparticle random-phase approximation
Tian Yuan; Ma Zhongyu; Ring, Peter
2009-06-15
We have introduced a separable pairing force, which was adjusted to reproduce the pairing properties of the Gogny force in nuclear matter. This separable pairing force is able to describe in relativistic Hartree-Bogoliubov (RHB) calculations the pairing properties in the ground state of finite nuclei on almost the same footing as the original Gogny interaction. In this work we investigate excited states using the Relativistic Quasiparticle Random-Phase Approximation (RQRPA) with the same separable pairing force. For consistency the Goldstone modes and the convergence with various cutoff parameters in this version of RQRPA are studied. The first excited 2{sup +} states for the chain of Sn isotopes with Z=50 and the chain of isotones with N=82 isotones are calculated in RQRPA together with the 3{sup -} states of Sn isotopes. By comparing our results with experimental data and with the results of the original Gogny force we find that this simple separable pairing interaction is very successful in depicting the pairing properties of vibrational excitations.
Quasiparticles in the pseudogap Phase of Underdoped Cuprate
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.
Quasiparticle-mediated spin Hall effect in a superconductor.
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. PMID:25985459
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.
Localization of Bogoliubov quasiparticles in interacting Bose gases with correlated disorder
NASA Astrophysics Data System (ADS)
Lugan, P.; Sanchez-Palencia, L.
2011-07-01
We study the Anderson localization of Bogoliubov quasiparticles (elementary many-body excitations) in a weakly interacting Bose gas of chemical potential μ subjected to a disordered potential V. We introduce a general mapping (valid for weak inhomogeneous potentials in any dimension) of the Bogoliubov-de Gennes equations onto a single-particle Schrödinger-like equation with an effective potential. For disordered potentials, the Schrödinger-like equation accounts for the scattering and localization properties of the Bogoliubov quasiparticles. We derive analytically the localization lengths for correlated disordered potentials in the one-dimensional geometry. Our approach relies on a perturbative expansion in V/μ, which we develop up to third order, and we discuss the impact of the various perturbation orders. Our predictions are shown to be in very good agreement with direct numerical calculations. We identify different localization regimes: For low energy, the effective disordered potential exhibits a strong screening by the quasicondensate density background, and localization is suppressed. For high-energy excitations, the effective disordered potential reduces to the bare disordered potential, and the localization properties of quasiparticles are the same as for free particles. The maximum of localization is found at intermediate energy when the quasicondensate healing length is of the order of the disorder correlation length. Possible extensions of our work to higher dimensions are also discussed.
Rate of tunneling nonequilibrium quasiparticles in superconducting qubits
NASA Astrophysics Data System (ADS)
Ansari, Mohammad H.
2015-04-01
In superconducting qubits the lifetime of quantum states cannot be prolonged arbitrarily by decreasing temperature. At low temperature quasiparticles tunneling between the electromagnetic environment and superconducting islands takes the condensate state out of equilibrium due to charge imbalance. We obtain the tunneling rate from a phenomenological model of non-equilibrium, where nonequilibrium quasiparticle tunnelling stimulates a temperature-dependent chemical potential shift in the superconductor. As a result we obtain a non-monotonic behavior for relaxation rate as a function of temperature. Depending on the fabrication parameters for some qubits, the lowest tunneling rate of nonequilibrium quasiparticles can take place only near the onset temperature below which nonequilibrium quasiparticles dominate over equilibrium one. Our theory also indicates that such tunnelings can influence the probability of transitions in qubits through a coupling to the zero-point energy of phase fluctuations.
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.
One-quasiparticle states in odd-Z heavy nuclei
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.
Shooting quasiparticles from Andreev bound states in a superconducting constriction
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.
Shooting quasiparticles from Andreev bound states in a superconducting constriction
NASA Astrophysics Data System (ADS)
Riwar, R.-P.; Houzet, M.; Meyer, J. S.; Nazarov, Y. V.
2014-12-01
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.
Quasiparticle Level Alignment for Photocatalytic Interfaces.
Migani, Annapaoala; 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. PMID:26580537
Signatures of Weyl semimetals in quasiparticle interference
NASA Astrophysics Data System (ADS)
Mitchell, Andrew K.; Fritz, Lars
2016-01-01
Impurities act as in situ probes of nontrivial electronic structure, causing real-space modulations in the density of states detected by scanning tunneling spectroscopy on the sample surface. We show that distinctive topological features of Weyl semimetals can be revealed in the Fourier transform of this map, interpreted in terms of quasiparticle interference (QPI). We develop an exact Green's function formalism and apply it to generalized models of Weyl semimetals with an explicit surface. The type of perturbation lifting the Dirac node degeneracy to produce the three-dimensional bulk Weyl phase determines the specific QPI signatures appearing on the surface. QPI Fermi arcs may or may not appear, depending on the relative surface orientation and quantum interference effects. Line nodes give rise to tube projections of width controlled by the bias voltage. We consider the effect of crystal warping, distinguishing dispersive arclike features from true Fermi arcs. Finally, we demonstrate that the commonly used joint-density-of-states approach fails qualitatively, and cannot describe QPI extinction.
Nodal Quasiparticle in Pseudogapped Colossal Magnetoresistive Manganites
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.
QCD critical point in a quasiparticle model
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.
Quasiparticle Level Alignment for Photocatalytic Interfaces
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.
Quasiparticle bands and spectra of Ga2O3 polymorphs
NASA Astrophysics Data System (ADS)
Furthmüller, J.; Bechstedt, F.
2016-03-01
Within the framework of density functional theory and Hedin's G W approximation for single-particle excitations, we present quasiparticle band structures and densities of states for two gallium oxide polymorphs: rhombohedral α -Ga2O3 and monoclinic β -Ga2O3 . The gap problem is attacked. In addition, their electron effective mass tensors are given. Solving the Bethe-Salpeter equation we also calculate excitonic optical spectra of the two polymorphs. The treatment of excitonic effects allows for a trustable prediction of optical properties from the band gap to the ultraviolet region. In addition, for few other polymorphs we also discuss the frequency-dependent dielectric tensor within the independent-particle approximation (random phase approximation) and densities of states on density functional level. We demonstrate that apart from subtle details, the overall densities of states and optical spectra, in particular the isotropically averaged spectra, are rather similar for all polymorphs, while the electronic dielectric constants vary with the structure. For all polymorphs, complete sets of elastic constants are given.
NASA Astrophysics Data System (ADS)
Brennan, John K.; Lísal, Martin; Gubbins, Keith E.; Rice, Betsy M.
2004-12-01
A molecular simulation method to study the dynamics of chemically reacting mixtures is presented. The method uses a combination of stochastic and dynamic simulation steps, allowing for the simulation of both thermodynamic and transport properties. The method couples a molecular dynamics simulation cell (termed dynamic cell) to a reaction mixture simulation cell (termed control cell) that is formulated upon the reaction ensemble Monte Carlo (RxMC) method, hence the term reaction ensemble molecular dynamics. Thermodynamic and transport properties are calculated in the dynamic cell by using a constant-temperature molecular dynamics simulation method. RxMC forward and reverse reaction steps are performed in the control cell only, while molecular dynamics steps are performed in both the dynamic cell and the control cell. The control cell, which acts as a sink and source reservoir, is maintained at reaction equilibrium conditions via the RxMC algorithm. The reaction ensemble molecular dynamics method is analogous to the grand canonical ensemble molecular dynamics technique, while using some elements of the osmotic molecular dynamics method, and so simulates conditions that directly relate to real, open systems. The accuracy and stability of the method is assessed by considering the ammonia synthesis reaction N2+3H2⇔2NH3 . It is shown to be a viable method for predicting the effects of nonideal environments on the dynamic properties (particularly diffusion) as well as reaction equilibria for chemically reacting mixtures.
Properties of earthquakes generated by fault dynamics
NASA Technical Reports Server (NTRS)
Carlson, J. M.; Langer, J. S.
1989-01-01
A model for fault dynamics consisting of a uniform chain of blocks and springs pulled slowly across a rough surface is presented. The only nonlinear element of the model is a slip-stick friction force between the blocks and the surface. It is found that this model gives rise to events of all sizes. The numerical evaluation of the distribution of earthquake magnitudes results in a power-law spectrum similar to what is observed in nature. Like certain other dissipative dynamical systems, the observed large fluctuations in earthquake magnitude persist because the system is in a state of marginal stability.
STARCH FILLED TERNARY POLYMER COMPOSITES I: DYNAMIC MECHANICAL PROPERTIES
Technology Transfer Automated Retrieval System (TEKTRAN)
It has been shown that the dynamic mechanical properties of starch filled blends of polyethylene (PE) and poly (hydroxy ester ether) (PHEE) are strongly dependent on the properties and distribution of the minor component of the blend (PHEE). The effect of this minor component on the viscoelastic pr...
Quasiparticle band structure for the Hubbard systems: Application to. alpha. -CeAl sub 2
Costa-Quintana, J.; Lopez-Aguilar, F. ); Balle, S. ); Salvador, R. Supercomputer Computations Research Institute, Florida State University, Tallahassee, Florida 32306-4052 )
1990-04-01
A self-energy formalism for determining the quasiparticle band structure of the Hubbard systems is deduced. The self-energy is obtained from the dynamically screened Coulomb interaction whose bare value is the correlation energy {ital U}. A method for integrating the Schroedingerlike equation with the self-energy operator is given. The method is applied to the cubic Laves phase of {alpha}-CeAl{sub 2} because it is a clear Hubbard system with a very complex electronic structure and, moreover, this system provides us with sufficient experimental data for testing our method.
Impurity effects in quasiparticle spectrum of high-Tc superconductors (Review Article)
NASA Astrophysics Data System (ADS)
Pogorelov, Yu. G.; Santos, M. C.; Loktev, V. M.
2011-08-01
The revision is made of Green function methods that describe the dynamics of electronic quasiparticles in disordered superconducting systems with d-wave symmetry of order parameter. Various types of impurity perturbations are analyzed within the simplest T-matrix approximation. The extension of the common self-consistent T-matrix approximation (SCTMA) to the so-called group expansions in clusters of interacting impurity centers is discussed and hence the validity criteria for SCTMA are established. A special attention is paid to the formation of impurity resonance states and localized states near the characteristic points of energy spectrum, corresponding to nodal points on the Fermi surface.
In Vitro Tissue Differentiation using Dynamics of Tissue Mechanical Properties
NASA Astrophysics Data System (ADS)
Lin, Wei-Chiang; Phillips, Paul J.
2002-03-01
Dynamics of tissue mechanical properties of various human tissue types were studied at macroscopic as well as microscopic level in vitro. This study was conducted to enable the development of a feedback system based on dynamics of tissue mechanical properties for intraoperative guidance for tumor treatment (e.g., RF ablation of liver tumor) and noninvasive tumor localization. Human liver tissues, including normal, cancerous, and cirrhotic tissues, were obtained from patients receiving liver transplant or tumor resection at Vanderbilt University Medical Center with the approval of the Vanderbilt Institutional Review Board. Tissue samples, once resected from the patients, were snap-frozen using liquid nitrogen and stored at -70 oC. Measurements of the mechanical properties of these tissue samples were conducted at the University of Tennessee at Knoxville. Dynamics of tissue mechanical properties were measured from both native and thermally coagulated tissue samples at macroscopic and microscopic level. Preliminary results suggest the dynamics of mechanical properties of normal liver tissues are very different from those of cancerous liver tissues. The correlation between the dynamics of mechanical properties at macroscopic level and those at microscopic level is currently under investigation.
Evaluation of overlaps between arbitrary fermionic quasiparticle vacua
NASA Astrophysics Data System (ADS)
Avez, B.; Bender, M.
2012-03-01
We derive an expression that allows for the unambiguous evaluation of the overlap between two arbitrary quasiparticle vacua, including its sign. Our expression is based on the Pfaffian of a skew-symmetric matrix, extending the overlap formula recently proposed by Robledo [Phys. Rev. CPRVCAN0556-281310.1103/PhysRevC.79.021302 79, 021302(R) (2009)] to the most general case of quasiparticle vacua, including the one of the overlap between two different blocked n-quasiparticle states for either even or odd systems. The powerfulness of the method is illustrated for a few typical matrix elements that appear in realistic angular-momentum-restored generator coordinate method calculations when breaking time-reversal invariance and using the full model space of occupied single-particle states.
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.
Optical techniques for determining dynamic material properties
Paisley, D.L.; Stahl, D.B.
1996-12-31
Miniature plates are laser-launched with a 10-Joule Nd:YAG for one-dimensional (1-D) impacts on to target materials much like gas gun experiments and explosive plane wave plate launch. By making the experiments small, flyer plates (3 mm diameter x 50 micron thick) and targets (10 mm diameter x 200 micron thick), 1-D impact experiments can be performed in a standard laser-optical laboratory with minimum confinement and collateral damage. The laser-launched plates do not require the traditional sabot on gas guns nor the explosives needed for explosive planewave lenses, and as a result are much more amenable to a wide variety of materials and applications. Because of the small size very high pressure gradients can be generated with relative ease. The high pressure gradients result in very high strains and strain rates that are not easily generated by other experimental methods. The small size and short shock duration (1 - 20 ns) are ideal for dynamically measuring bond strengths of micron-thick coatings. Experimental techniques, equipment, and dynamic material results are reported.
Deformed nuclear state as a quasiparticle-pair condensate
Dobaczewski, J.; Skalski, J.
1988-07-01
The deformed nuclear states, obtained in terms of the Hartree-Fock plus Bardeen-Cooper-Schrieffer (BCS) method with the Skyrme SIII interaction, are approximated by condensates of the low-angular-momentum quasiparticle and particle pairs. It is shown that the quasiparticle pairs, which are essentially the particle-hole nuclear excitations, provide for a better approximation than the valence particle pairs. In both cases, the inclusion of J = 0, 2, and 4 components is necessary to reproduce the Hartree-Fock plus BCS equilibrium deformation and deformation energy.
Light quasiparticles dominate electronic transport in molecular crystal field-effect transistors
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.
Equation of state of a quasiparticle model at finite chemical potential and quark star
NASA Astrophysics Data System (ADS)
Tian, Ya-Lan; Yan, Yan; Li, Hua; Luo, Xin-Lian; Zong, Hong-Shi
2012-02-01
In this paper, we employ the equation of state (EOS) of the quasiparticle model proposed in A. M. Zhao , Mod. Phys. Lett. A 25, 47 (2010)MPLAEQ0217-732310.1142/S0217732310031361] which incorporates the effect of vacuum negative pressure to study the properties of quark stars. In our model the EOS has the correct behavior required by QCD in the small and large μ limit. We employ this EOS to calculate the mass-radii relation and mass-energy density relation of quark stars. Our results are found to be consistent with the most recent astronomical observations.
Band Mapping and Quasiparticle Suppression in the One-Dimensional Organic Conductor TTF-TCNQ
NASA Astrophysics Data System (ADS)
Zwick, F.; Jérome, D.; Margaritondo, G.; Onellion, M.; Voit, J.; Grioni, M.
1998-10-01
Dispersing 1D bands have been observed for the first time in an organic conductor by high resolution photoemission experiments on TTF-TCNQ (tetrathiafulvalene-tetracyanoquinodimethane). Their properties are extremely unusual: the bandwidth is much larger than traditional estimates, and the quasiparticle states are strongly renormalized, with no weight at the chemical potential. A deep pseudogap around the Fermi energy persists, and even increases, up to room temperature. We also report a direct determination of kF in this material, and the observation of the opening of a Peierls gap in the low-temperature charge density wave phase.
Multi-quasiparticle isomers in the vicinity of {sup 132}Sn
Watanabe, Hiroshi
2010-05-12
Nuclear isomers with multi-quasiparticle configurations near closed shells serve as valuable experimental probes which reveal the nature of residual nucleon-nucleon interactions. We have populated stable and neutron-rich odd-A antimony (Z = 51) and iodine (Z = 53) isotopes using multi-nucleon transfer and fusion-fission reactions with {sup 136}Xe beams and also using incomplete-fusion reactions with {sup 7}Li beams. The decay properties of high-spin isomers have been investigated by means of time-correlated gamma-ray and electron spectroscopy and the measurement of gamma-ray angular correlations.
Clustering properties of dynamical dark energy models
Avelino, P. P.; Beca, L. M. G.; Martins, C. J. A. P.
2008-05-15
We provide a generic but physically clear discussion of the clustering properties of dark energy models. We explicitly show that in quintessence-type models the dark energy fluctuations, on scales smaller than the Hubble radius, are of the order of the perturbations to the Newtonian gravitational potential, hence necessarily small on cosmological scales. Moreover, comparable fluctuations are associated with different gauge choices. We also demonstrate that the often used homogeneous approximation is unrealistic, and that the so-called dark energy mutation is a trivial artifact of an effective, single fluid description. Finally, we discuss the particular case where the dark energy fluid is nonminimally coupled to dark matter.
Dynamic and rheological properties of soft biological cell suspensions
Yazdani, Alireza; Li, Xuejin
2016-01-01
Quantifying dynamic and rheological properties of suspensions of soft biological particles such as vesicles, capsules, and red blood cells (RBCs) is fundamentally important in computational biology and biomedical engineering. In this review, recent studies on dynamic and rheological behavior of soft biological cell suspensions by computer simulations are presented, considering both unbounded and confined shear flow. Furthermore, the hemodynamic and hemorheological characteristics of RBCs in diseases such as malaria and sickle cell anemia are highlighted. PMID:27540271
Dynamical Properties of Collisionless Star Streams
NASA Astrophysics Data System (ADS)
Carlberg, R. G.
2015-02-01
A sufficiently extended satellite in the tidal field of a host galaxy loses mass to create nearly symmetric leading and trailing tidal streams. We study the case in which tidal heating drives mass loss from a low mass satellite. The stream effectively has two dynamical components, a common angular momentum core superposed with episodic pulses with a broader angular momentum distribution. The pulses appear as spurs on the stream, oscillating above and below the stream centerline, stretching and blurring in configuration space as they move away from the cluster. Low orbital eccentricity streams are smoother and have less differential motion than high eccentricity streams. The tail of a high eccentricity stream can develop a fan of particles that wraps around at apocenter in a shell feature. We show that scaling the essentially stationary action-angle variables with the cube root of the satellite mass allows a low mass satellite stream to accurately predict the features in the stream from a satellite a thousand times more massive. As a practical astrophysical application, we demonstrate that narrow gaps in a moderate eccentricity stream, such as GD-1, blur out to 50% contrast over approximately six radial periods. A high eccentricity stream, such as Pal 5, will blur small gaps in only two radial orbits as can be understood from the much larger dispersion of angular momentum in the stream.
OPTICAL AND DYNAMIC PROPERTIES OF UNDOPED AND DOPED SEMICONDUCTOR NANOSTRUCTURES
Grant, C D; Zhang, J Z
2007-09-28
This chapter provides an overview of some recent research activities on the study of optical and dynamic properties of semiconductor nanomaterials. The emphasis is on unique aspects of these properties in nanostructures as compared to bulk materials. Linear, including absorption and luminescence, and nonlinear optical as well as dynamic properties of semiconductor nanoparticles are discussed with focus on their dependence on particle size, shape, and surface characteristics. Both doped and undoped semiconductor nanomaterials are highlighted and contrasted to illustrate the use of doping to effectively alter and probe nanomaterial properties. Some emerging applications of optical nanomaterials are discussed towards the end of the chapter, including solar energy conversion, optical sensing of chemicals and biochemicals, solid state lighting, photocatalysis, and photoelectrochemistry.
Quasiparticle collapsing in an anisotropic t -J ladder
NASA Astrophysics Data System (ADS)
Zhu, Zheng; Weng, Zheng-Yu
2015-12-01
Quasiparticle collapsing is a central issue in the study of strongly correlated electron systems. In the one-dimensional case, the quasiparticle collapsing in a form of spin-charge separation has been well established, but the problem remains elusive in dimensions higher than one. By using the density matrix renormalization group (DMRG) algorithm, we show that in an anisotropic two-leg t -J ladder, an injected single hole behaves like a well-defined quasiparticle in the strong rung limit but undergoes a "phase transition" with the effective mass diverging at a quantum critical point (QCP) towards the isotropic limit. After the transition, the quasiparticle collapses into a loosely bound object of a charge (holon) and a spin-1/2 (spinon) accompanied by an unscreened phase string as well as a substantially enhanced binding energy between two doped holes. A phase diagram of multileg ladders is further obtained, which extrapolates the QCP towards the two-dimensional limit. The underlying mechanism generic for any dimensions is also discussed.
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.
Kondo physics from quasiparticle poisoning in Majorana devices
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
Mass properties measurement system: Dynamics and statics measurements
NASA Technical Reports Server (NTRS)
Doty, Keith L.
1993-01-01
This report presents and interprets experimental data obtained from the Mass Properties Measurement System (MPMS). Statics measurements yield the center-of-gravity of an unknown mass and dynamics measurements yield its inertia matrix. Observations of the MPMS performance has lead us to specific design criteria and an understanding of MPMS limitations.
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.
Static and dynamic properties of supercooled water in small nanotubes.
Khademi, Mahdi; Sahimi, Muhammad
2016-07-14
The static and dynamic properties of water in small silicon-carbide and carbon nanotubes have been studied over the temperature range 100 K-298 K, using extensive molecular dynamics simulations. The computed properties include the radial distribution function, the cage correlation function, the space-time autocorrelation function, the velocity autocorrelation function, and the self-diffusivity. They all indicate that, under the conditions that we study, water does not freeze in small nanotubes; the Stokes-Einstein relation breaks down, and the self-diffusivity exhibits a transition around 230 K, very close to 228 K, the temperature at which a fragile-to-strong dynamic crossover is supposed to happen. The cage correlation function C(t) decays according to a stretched-exponential function, C(t) ∼ exp[ - (t/τ)(β)], where τ is a relaxation time and β is a topological exponent. PMID:27421415
Static and dynamic properties of supercooled water in small nanotubes
NASA Astrophysics Data System (ADS)
Khademi, Mahdi; Sahimi, Muhammad
2016-07-01
The static and dynamic properties of water in small silicon-carbide and carbon nanotubes have been studied over the temperature range 100 K-298 K, using extensive molecular dynamics simulations. The computed properties include the radial distribution function, the cage correlation function, the space-time autocorrelation function, the velocity autocorrelation function, and the self-diffusivity. They all indicate that, under the conditions that we study, water does not freeze in small nanotubes; the Stokes-Einstein relation breaks down, and the self-diffusivity exhibits a transition around 230 K, very close to 228 K, the temperature at which a fragile-to-strong dynamic crossover is supposed to happen. The cage correlation function C(t) decays according to a stretched-exponential function, C(t) ˜ exp[ - (t/τ)β], where τ is a relaxation time and β is a topological exponent.
Dirac charge dynamics in graphene by infrared spectroscopy
Martin, Michael C; Li, Z.Q.; Henriksen, E.A.; Jiang, Z.; Hao, Z.; Martin, Michael C; Kim, P.; Stormer, H.L.; Basov, Dimitri N.
2008-04-29
A remarkable manifestation of the quantum character of electrons in matter is offered by graphene, a single atomic layer of graphite. Unlike conventional solids where electrons are described with the Schrödinger equation, electronic excitations in graphene are governed by the Dirac hamiltonian. Some of the intriguing electronic properties of graphene, such as massless Dirac quasiparticles with linear energy-momentum dispersion, have been confirmed by recent observations. Here, we report an infrared spectromicroscopy study of charge dynamics in graphene integrated in gated devices. Our measurements verify the expected characteristics of graphene and, owing to the previously unattainable accuracy of infrared experiments, also uncover significant departures of the quasiparticle dynamics from predictions made for Dirac fermions in idealized, free-standing graphene. Several observations reported here indicate the relevance of many-body interactions to the electromagnetic response of graphene.
Evaluation of biological cell properties using dynamic indentation measurement.
Cao, Guoxin; Chandra, Namas
2010-02-01
Viscoelastic mechanical properties of biological cells are commonly measured using atomic force microscope (AFM) dynamic indentation with spherical tips. A semiempirical analysis based on numerical simulation is built to determine the cell mechanical properties. It is shown that the existing analysis cannot reflect the accurate values of cell elastic/dynamic modulus due to the effects of substrate, indenter tip size, and cell size. Among these factors, substrate not only increases the true contact radius but also interferes the indentation stress field, which can cause the overestimation of cell moduli. Typically, the substrate effect is much stronger than the other two influences in cell indentation; and, thus, the cell modulii are usually overestimated. It is estimated that the moduli can be overestimated by as high as over 200% using the existing analysis. In order to obtain the accurate properties of cells, correction factors that account for these effects are required in the existing analysis. PMID:20365612
Shimizu, Yusei; Kittaka, Shunichiro; Sakakibara, Toshiro; Haga, Yoshinori; Yamamoto, Etsuji; Amitsuka, Hiroshi; Tsutsumi, Yasumasa; Machida, Kazushige
2015-04-10
Low-energy quasiparticle excitations in the superconducting (SC) state of UBe_{13} were studied by means of specific-heat (C) measurements in a rotating field. Quite unexpectedly, the magnetic-field dependence of C(H) is linear in H with no angular dependence at low fields in the SC state, implying that the gap is fully open over the Fermi surfaces, in stark contrast to previous expectations. In addition, a characteristic cubic anisotropy of C(H) was observed above 2 T with a maximum (minimum) for H∥[001] ([111]) within the (11[over ¯]0) plane, in the normal as well as in the SC states. This oscillation possibly originates from the anisotropic response of the heavy quasiparticle bands, and might be a key to understand the unusual properties of UBe_{13}. PMID:25910153
Dynamic properties of elastomer cartridge specimens under a rotating load
NASA Technical Reports Server (NTRS)
Darlow, M. S.; Smalley, A. J.; Cunningham, R. E.
1979-01-01
This paper presents the results of a program of analysis and test to determine the dynamic properties of elastomer cartridges operating under a rotating load. These measured properties were compared to predictions based on results of unidirectional tests with the same elastomer material. The test method for the dynamic stiffness and damping measurements was essentially the same as the Base Excitation Resonant Mass Method. The primary difference is that the exciting force used for these most recent tests was exerted by rotating unbalance in a rotational test rig rather than a shake table. The specimens tested were: two rectangular cross-section, continuous ring cartridges of different cross-section and three cylindrical button cartridges of different button thickness. Tests were performed for strains from about 0.0001 to about 0.01 (double amplitude). Material properties and prediction equations determined from reciprocating tests were used to make numerical predictions of stiffness, damping, and loss coefficient for the test elements, with encouraging results. Strain was shown to be an important parameter in determining these dynamic properties, particularly damping and loss coefficient.
Structural and dynamical properties of hot dense matter by a Thomas-Fermi-Dirac molecular dynamics
NASA Astrophysics Data System (ADS)
Lambert, F.; Clérouin, J.; Mazevet, S.
2006-09-01
We use a model combining, in a consistent way, orbital-free density functional theory (OF-DFT) and molecular dynamics (MD), to compute the thermodynamical, structural and dynamical properties of Fe and Au plasmas at conditions relevant to astrophysics and inertial confinement fusion (ICF). The newly developed parallel numerical scheme presented here allows to propagate hundreds of particles and to obtain accurate transport properties. This allows us to investigate the validity of the commonly used one-component plasma (OCP) model in predicting the pair correlation, the diffusion and viscosity coefficients for these two high-temperature high-density plasmas.
γ vibrational band and quasiparticle excitations in 80Sr
NASA Astrophysics Data System (ADS)
Sienko, T. A.; Lister, C. J.; Kaye, R. A.
2003-06-01
Non-yrast states in 80Sr were populated in the 24Mg(58Ni,2p)80Sr reaction at 200 MeV and their γ decays investigated using Gammasphere, in order to investigate shape softness and quasiparticle excitations. A large data set was collected which was A and Z gated, using the Argonne Fragment Mass Analyzer and a focal plane ion chamber. The excellent channel selection enhanced the sensitivity to energetically nonfavored configurations. Several new rotational bands were found, and many conflicts between previous experiments were resolved. In particular, the gamma vibrational band is now clearly delineated, and more than ten quasiparticle bandheads have been identified. At the highest spins, evidence for a long-predicted shape change was found.
Finite temperature quasiparticle self-consistent GW approximation
Vanschilfgaarde, Mark; Leonard, Francois; Desjarlais, Michael Paul; Kotani, Takao; Faleev, Sergey V
2005-10-01
We present a new ab initio method for electronic structure calculations of materials at finite temperature (FT) based on the all-electron quasiparticle self-consistent GW (QPscGW) approximation and Keldysh time-loop Green's function approach. We apply the method to Si, Ge, GaAs, InSb, and diamond and show that the band gaps of these materials universally decrease with temperature in contrast with the local density approximation (LDA) of density functional theory (DFT) where the band gaps universally increase. At temperatures of a few eV the difference between quasiparticle energies obtained in FT-QPscGW and FT-LDA approaches significantly reduces. This result suggests that existing simulations of very high temperature materials based on the FT-LDA are more justified then it might appear from well-known LDA band gap errors at zero-temperature.
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.
Quasi-Particle Self-Consistent GW for Molecules.
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
Quasiparticle spin resonance and coherence in superconducting aluminium
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
Quasiparticle and excitonic gaps of one-dimensional carbon chains.
Mostaani, E; Monserrat, B; Drummond, N D; Lambert, C J
2016-06-01
We report diffusion quantum Monte Carlo (DMC) calculations of the quasiparticle and excitonic gaps of hydrogen-terminated oligoynes and extended polyyne. The electronic gaps are found to be very sensitive to the atomic structure in these systems. We have therefore optimised the geometry of polyyne by directly minimising the DMC energy with respect to the lattice constant and the Peierls-induced carbon-carbon bond-length alternation. We find the bond-length alternation of polyyne to be 0.136(2) Å and the excitonic and quasiparticle gaps to be 3.30(7) and 3.4(1) eV, respectively. The DMC zone-centre longitudinal optical phonon frequency of polyyne is 2084(5) cm(-1), which is consistent with Raman spectroscopic measurements for large oligoynes. PMID:27104222
Quasiparticle spin resonance and coherence in superconducting aluminium
NASA Astrophysics Data System (ADS)
Quay, C. H. L.; Weideneder, M.; Chiffaudel, Y.; Strunk, C.; Aprili, M.
2015-10-01
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.
Relating Dynamic Properties to Atomic Structure in Metallic Glasses
Sheng, H.W.; Ma, E.; Kramer, Matthew J.
2012-07-18
Atomic packing in metallic glasses is not completely random but displays various degrees of structural ordering. While it is believed that local structures profoundly affect the properties of glasses, a fundamental understanding of the structure–property relationship has been lacking. In this article, we provide a microscopic picture to uncover the intricate interplay between structural defects and dynamic properties of metallic glasses, from the perspective of computational modeling. Computational methodologies for such realistic modeling are introduced. Exploiting the concept of quasi-equivalent cluster packing, we quantify the structural ordering of a prototype metallic glass during its formation process, with a new focus on geometric measures of subatomic “voids.” Atomic sites connected with the voids are found to be crucial in terms of understanding the dynamic, including vibrational and atomic transport, properties. Normal mode analysis is performed to reveal the structural origin of the anomalous boson peak (BP) in the vibration spectrum of the glass, and its correlation with atomic packing cavities. Through transition-state search on the energy landscape of the system, such structural disorder is found to be a facilitating factor for atomic diffusion, with diffusion energy barriers and diffusion pathways significantly varying with the degree of structural relaxation/ordering. The implications of structural defects for the mechanical properties of metallic glasses are also discussed.
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.
The rate of quasiparticle recombination probes the onset of coherence in cuprate superconductors
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
The rate of quasiparticle recombination probes the onset of coherence in cuprate superconductors
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
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.
The Quasiparticle Puzzle: Reconciling ARPES and FTSTS Studies of Bi2212
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.
The rate of quasiparticle recombination probes the onset of coherence in cuprate superconductors.
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
Photoluminescence properties and exciton dynamics in monolayer WSe2
NASA Astrophysics Data System (ADS)
Yan, Tengfei; Qiao, Xiaofen; Liu, Xiaona; Tan, Pingheng; Zhang, Xinhui
2014-09-01
In this work, comprehensive temperature and excitation power dependent photoluminescence and time-resolved photoluminescence studies are carried out on monolayer WSe2 to reveal its properties of exciton emissions and related excitonic dynamics. Competitions between the localized and delocalized exciton emissions, as well as the exciton and trion emissions are observed, respectively. These competitions are suggested to be responsible for the abnormal temperature and excitation intensity dependent photoluminescence properties. The radiative lifetimes of both excitons and trions exhibit linear dependence on temperature within the temperature regime below 260 K, providing further evidence for two-dimensional nature of monolayer material.
El-Batanouny, Maged
2015-08-03
We propose to investigate the surface structural, dynamics and magnetic properties of the novel class of topological insulator crystals, as well as crystals that exhibit multiferroicity, magnetoelectricity and thermoelectricity. Topological insulators (TIs) are a new class of insulators in which a bulk gap for electronic excitations is generated because of the strong spin-orbit coupling inherent to these systems. These materials are distinguished from ordinary insulators by the presence of gapless metallic surface states, resembling chiral edge modes in quantum Hall systems, but with unconventional spin textures. These exotic metallic states are formed by topological conditions that also render the electrons travelling on such surfaces insensitive to scattering by impurities. The electronic quasi-particles populating the topological surface state are Dirac fermions; they have a linear dispersion and thus are massless just like photons. We propose to investigate the interaction of these massless Dirac fermions with the massive lattice in the newly discovered crystals, Bi2Se3, Bi2Te3 and Sb2Te3. We shall use inelastic helium beam scattering from surfaces to search for related signatures in surface phonon dispersions mappings that cover the entire surface Brillouin zone of these materials. Our recent investigations of the (001) surface of the multiferroic crystals (Li/Na)Cu2O2 revealed an anomalous surface structural behavior where surface Cu$^{2+}$ row rise above the surface plane as the crystal was cooled. Subsequent worming revealed the onset of a thermally activated incommensurate surface phase, driven by the elevated rows. We are currently investigating the structure of the magnetic phases in these quasi-one-dimensional magnetic rows. Multiferroics are excellent candidates for large magnetoelectric response. We propose to extend this investigation to the class of delafossites which are also multiferroics and have been investigated as good candidates for
NASA Astrophysics Data System (ADS)
Vig, Sean; Kogar, Anshul; Mishra, Vivek; Norman, Mike; Gu, Genda; Abbamonte, Peter
2015-03-01
The kink features in the low energy quasiparticle dispersion in cuprate superconductors have been extensively studied using angle-resolved photoemission spectroscopy (ARPES). The existence of these kinks is a signature of a renormalization of the fermionic quasiparticles due to coupling to some bosonic collective mode at a scale related to the kink energy. In this talk, I will present angle-resolved inelastic electron scattering studies of the bosonic collective excitations in optimally doped Bi2Sr2CaCu2O8+δ. Performing a 2D momentum parameterization of these modes, we reconstruct the complete dynamical susceptibility, χ (q , ω) , which we use to perform a one-loop self energy correction to the quasiparticle dispersion. The result reproduces well the dispersion observed with ARPES, indicating that these excitations are the origin of the observed kinks. I will discuss the implications of our study for phonon vs. spin fluctuation interpretation of these effects. This work was supported as part of the Center for Emergent Superconductivity, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science.
Josephson effect and quasiparticle states in d-wave superconductors
Tanaka, Yukio; Kashiwaya, Satoshi
1996-12-31
A general formula for the Josephson current in a d-wave/insulator/d-wave-superconductor junction is presented by taking account of the zero-energy states formed around the interfaces. For a fixed phase difference between the two superconductors, the current component becomes either positive or negative depending on the injection angle of the quasiparticle. Anomalous temperature dependences are predicted in the maximum Josephson current and in the free energy minima.
On the fundamental properties of dynamically hot galaxies
NASA Astrophysics Data System (ADS)
Kritsuk, Alexei G.
1997-01-01
A two-component isothermal equilibrium model is applied to reproduce basic structural properties of dynamically hot stellar systems immersed in their massive dark haloes. The origin of the fundamental plane relation for giant ellipticals is naturally explained as a consequence of dynamical equilibrium in the context of the model. The existence of two galactic families displaying different behaviour in the luminosity-surface-brightness diagram is shown to be a result of a smooth transition from dwarfs, dominated by dark matter near the centre, to giants dominated by the luminous stellar component. The comparison of empirical scaling relations with model predictions suggests that probably a unique dissipative process was operating during the violent stage of development of stellar systems in the dark haloes, and the depth of the potential well controlled the observed luminosity of the resulting galaxies. The interpretation also provides some restrictions on the properties of dark haloes implied by the fundamental scaling laws.
Real Spin in Pseudospin Quasiparticles of Bilayer Quantum Hall systems
NASA Astrophysics Data System (ADS)
Roostaei, Bahman; Fertig, H. A.; Mullen, Kieran
2005-03-01
Recent experiments have observed enhanced nuclear spin relaxation in double layer quantum Hall systems near the phase boundary between compressible and incompressible states(1). We investigate the electronic spin structure of such systems by calculating the groundstate close to ν= 1 using the Hartree-Fock approximation. This state is a quasiparticle lattice, and we examine the possibility of optimizing its energy by allowing the real spin to tilt away from the majority direction in the quasiparticle cores, analogous to what has been suggested in field theoretic studies of single quasiparticles(2). A broken symmetry of these states introduces low energy spin modes which may couple to the nuclear spins. We calculate both the spin and pseudospin textures for the system near the transition and discuss whether they can account for the observed relaxation rates.1) I.B. Spielman et al., cond-mat/0410092; N. Kumada et al., cond-mat/04104952) S. Ghosh and R. Rajaraman, Phys. Rev. B63, 035304 (2001); Z.F. Izawa and G. Tsitsishvili, cond- mat/0311406.Grants: NSF MRSEC DMR-0080054, NSF EPS-9720651 and NSF DMR- 0454699
Information for Coarticulation: Static Signal Properties or Formant Dynamics?
Viswanathan, Navin; Magnuson, James S.; Fowler, Carol A.
2014-01-01
Perception of a speech segment changes depending on properties of surrounding segments in a phenomenon called compensation for coarticulation (Mann, 1980). The nature of information that drives these perceptual changes is a matter of debate. One account attributes perceptual shifts to low-level auditory system contrast effects based on static portions of the signal (e.g., third formant [F3] center or average frequency; Lotto & Kluender, 1998). An alternative account is that listeners' perceptual shifts result from listeners attuning to the acoustic effects of gestural overlap and that this information for coarticulation is necessarily dynamic (Fowler, 2006). In a pair of experiments, we used sinewave speech precursors to investigate the nature of information for compensation for coarticulation. In Experiment 1, as expected by both accounts, we found that sinewave speech precursors produce shifts in following segments. In Experiment 2, we investigated whether effects in Experiment 1 were driven by static F3 offsets of sinewave speech precursors, or by dynamic relationships among their formants. We temporally reversed F1 and F2 in sinewave precursors, preserving static F3 offset and average F1, F2, and F3 frequencies, but disrupting dynamic formant relationships. Despite having identical F3s, selectively-reversed precursors produced effects that were significantly smaller and restricted to only a small portion of the continuum. We conclude that dynamic formant relations rather than static properties of the precursor provide information for compensation for coarticulation. PMID:24730744
Information for coarticulation: Static signal properties or formant dynamics?
Viswanathan, Navin; Magnuson, James S; Fowler, Carol A
2014-06-01
Perception of a speech segment changes depending on properties of surrounding segments in a phenomenon called compensation for coarticulation (Mann, 1980). The nature of information that drives these perceptual changes is a matter of debate. One account attributes perceptual shifts to low-level auditory system contrast effects based on static portions of the signal (e.g., third formant [F3] center or average frequency; Lotto & Kluender, 1998). An alternative account is that listeners' perceptual shifts result from listeners attuning to the acoustic effects of gestural overlap and that this information for coarticulation is necessarily dynamic (Fowler, 2006). In a pair of experiments, we used sinewave speech precursors to investigate the nature of information for compensation for coarticulation. In Experiment 1, as expected by both accounts, we found that sinewave speech precursors produce shifts in following segments. In Experiment 2, we investigated whether effects in Experiment 1 were driven by static F3 offsets of sinewave speech precursors, or by dynamic relationships among their formants. We temporally reversed F1 and F2 in sinewave precursors, preserving static F3 offset and average F1, F2 and F3 frequencies, but disrupting dynamic formant relationships. Despite having identical F3s, selectively reversed precursors produced effects that were significantly smaller and restricted to only a small portion of the continuum. We conclude that dynamic formant relations rather than static properties of the precursor provide information for compensation for coarticulation. PMID:24730744
Dynamic and mechanical properties of supported lipid bilayers.
Wu, Hsing-Lun; Tsao, Heng-Kwong; Sheng, Yu-Jane
2016-04-21
Supported lipid bilayers (SLBs) offer an excellent model system for investigating the physico-chemical properties of the cell membrane. In this work, dynamic and mechanical properties of SLBs are explored by dissipative particle dynamics simulations for lipids with different architectures (chain length, kink, and asymmetry associated with lipid tails). It is found that the lateral diffusivity (Dx) and flip-flop rate (FF) grow with increasing temperature in both gel and liquid phases and can be described by an Arrhenius-like expression. Three regimes can be clearly identified for symmetric and asymmetric saturated lipids but only two regimes are observed for kinked lipids. Both Dx and FF grow with decreasing tail length and increasing number of kinks. The stretching (KA) and apparent bending (KB) moduli exhibit concave upward curves with temperature and the minima are attained at Tm. In general, the minima of KA and KB decrease with the chain length and increase with number of kinks. The typical relation among the bending modulus, area stretching modulus, and bilayer thickness is still followed, KB = βKAh(2) and β is much smaller in the gel phase. The dynamic and mechanical properties of lipids with asymmetric tails are found to situate between their symmetric counterparts. PMID:27389237
Dynamic and mechanical properties of supported lipid bilayers
NASA Astrophysics Data System (ADS)
Wu, Hsing-Lun; Tsao, Heng-Kwong; Sheng, Yu-Jane
2016-04-01
Supported lipid bilayers (SLBs) offer an excellent model system for investigating the physico-chemical properties of the cell membrane. In this work, dynamic and mechanical properties of SLBs are explored by dissipative particle dynamics simulations for lipids with different architectures (chain length, kink, and asymmetry associated with lipid tails). It is found that the lateral diffusivity (Dx) and flip-flop rate (FF) grow with increasing temperature in both gel and liquid phases and can be described by an Arrhenius-like expression. Three regimes can be clearly identified for symmetric and asymmetric saturated lipids but only two regimes are observed for kinked lipids. Both Dx and FF grow with decreasing tail length and increasing number of kinks. The stretching (KA) and apparent bending (KB) moduli exhibit concave upward curves with temperature and the minima are attained at Tm. In general, the minima of KA and KB decrease with the chain length and increase with number of kinks. The typical relation among the bending modulus, area stretching modulus, and bilayer thickness is still followed, KB = βKAh2 and β is much smaller in the gel phase. The dynamic and mechanical properties of lipids with asymmetric tails are found to situate between their symmetric counterparts.
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.
Graph Theoretic Foundations of Multibody Dynamics Part I: Structural Properties.
Jain, Abhinandan
2011-06-21
This is the first part of two papers that use concepts from graph theory to obtain a deeper understanding of the mathematical foundations of multibody dynamics. The key contribution is the development of a unifying framework that shows that key analytical results and computational algorithms in multibody dynamics are a direct consequence of structural properties and require minimal assumptions about the specific nature of the underlying multibody system. This first part focuses on identifying the abstract graph theoretic structural properties of spatial operator techniques in multibody dynamics. The second part paper exploits these structural properties to develop a broad spectrum of analytical results and computational algorithms.Towards this, we begin with the notion of graph adjacency matrices and generalize it to define block-weighted adjacency (BWA) matrices and their 1-resolvents. Previously developed spatial operators are shown to be special cases of such BWA matrices and their 1-resolvents. These properties are shown to hold broadly for serial and tree topology multibody systems. Specializations of the BWA and 1-resolvent matrices are referred to as spatial kernel operators (SKO) and spatial propagation operators (SPO). These operators and their special properties provide the foundation for the analytical and algorithmic techniques developed in the companion paper.We also use the graph theory concepts to study the topology induced sparsity structure of these operators and the system mass matrix. Similarity transformations of these operators are also studied. While the detailed development is done for the case of rigid-link multibody systems, the extension of these techniques to a broader class of systems (e.g. deformable links) are illustrated. PMID:22102790
Viscoelastic properties of a spinal posterior dynamic stabilisation device.
Lawless, Bernard M; Barnes, Spencer C; Espino, Daniel M; Shepherd, Duncan E T
2016-06-01
The purpose of this study was to quantify the frequency dependent viscoelastic properties of two types of spinal posterior dynamic stabilisation devices. In air at 37°C, the viscoelastic properties of six BDyn 1 level, six BDyn 2 level posterior dynamic stabilisation devices (S14 Implants, Pessac, France) and its elastomeric components (polycarbonate urethane and silicone) were measured using Dynamic Mechanical Analysis. The viscoelastic properties were measured over the frequency range 0.01-30Hz. The BDyn devices and its components were viscoelastic throughout the frequency range tested. The mean storage stiffness and mean loss stiffness of the BDyn 1 level device, BDyn 2 level device, silicone component and polycarbonate urethane component all presented a logarithmic relationship with respect to frequency. The storage stiffness of the BDyn 1 level device ranged from 95.56N/mm to 119.29N/mm, while the BDyn 2 level storage stiffness ranged from 39.41N/mm to 42.82N/mm. BDyn 1 level device and BDyn 2 level device loss stiffness ranged from 10.72N/mm to 23.42N/mm and 4.26N/mm to 9.57N/mm, respectively. No resonant frequencies were recorded for the devices or its components. The elastic property of BDyn 1 level device is influenced by the PCU and silicone components, in the physiological frequency range. The viscoelastic properties calculated in this study may be compared to spinal devices and spinal structures. PMID:27018832
NASA Astrophysics Data System (ADS)
Banuelos, E. U.; Amarillas, A. P.
2004-02-01
In this work we studied the temperature-induced changes in the structural and dynamical properties of liquid Ag using molecular dynamics (DM) computer simulation. The atomic interactions are modeled through a semiempirical potential function which incorporates n-body effects and is based on the second moments approximation of the density of states of a tight-binding Hamiltonian. The caloric curve was used to calculate the latent heat of fusion and the pair distribution function, g(r), was calculated from a set of atomic configurations collected at several time-steps. The dynamical properties are studied through the velocity autocorrelation function and the mean-square displacement. The self-diffusion coefficient and its behavior with the temperature, obtained from our simulations, shows the typical behavior of the simple liquids. Our results are compared to available experimental data.
Estimating the biophysical properties of neurons with intracellular calcium dynamics
NASA Astrophysics Data System (ADS)
Ye, Jingxin; Rozdeba, Paul J.; Morone, Uriel I.; Daou, Arij; Abarbanel, Henry D. I.
2014-06-01
We investigate the dynamics of a conductance-based neuron model coupled to a model of intracellular calcium uptake and release by the endoplasmic reticulum. The intracellular calcium dynamics occur on a time scale that is orders of magnitude slower than voltage spiking behavior. Coupling these mechanisms sets the stage for the appearance of chaotic dynamics, which we observe within certain ranges of model parameter values. We then explore the question of whether one can, using observed voltage data alone, estimate the states and parameters of the voltage plus calcium (V+Ca) dynamics model. We find the answer is negative. Indeed, we show that voltage plus another observed quantity must be known to allow the estimation to be accurate. We show that observing both the voltage time course V (t) and the intracellular Ca time course will permit accurate estimation, and from the estimated model state, accurate prediction after observations are completed. This sets the stage for how one will be able to use a more detailed model of V+Ca dynamics in neuron activity in the analysis of experimental data on individual neurons as well as functional networks in which the nodes (neurons) have these biophysical properties.
Dynamic properties influence the perception of facial expressions.
Kamachi, Miyuki; Bruce, Vicki; Mukaida, Shigeru; Gyoba, Jiro; Yoshikawa, Sakiko; Akamatsu, Shigeru
2013-01-01
Two experiments were conducted to investigate the role played by dynamic information in identifying facial expressions of emotion. Dynamic expression sequences were created by generating and displaying morph sequences which changed the face from neutral to a peak expression in different numbers of intervening intermediate stages, to create fast (6 frames), medium (26 frames), and slow (101 frames) sequences. In experiment 1, participants were asked to describe what the person shown in each sequence was feeling. Sadness was more accurately identified when slow sequences were shown. Happiness, and to some extent surprise, was better from faster sequences, while anger was most accurately detected from the sequences of medium pace. In experiment 2 we used an intensity-rating task and static images as well as dynamic ones to examine whether effects were due to total time of the displays or to the speed of sequence. Accuracies of expression judgments were derived from the rated intensities and the results were similar to those of experiment 1 for angry and sad expressions (surprised and happy were close to ceiling). Moreover, the effect of display time was found only for dynamic expressions and not for static ones, suggesting that it was speed, not time, which was responsible for these effects. These results suggest that representations of basic expressions of emotion encode information about dynamic as well as static properties. PMID:24601038
Reservoir Computing Properties of Neural Dynamics in Prefrontal Cortex
Procyk, Emmanuel; Dominey, Peter Ford
2016-01-01
Primates display a remarkable ability to adapt to novel situations. Determining what is most pertinent in these situations is not always possible based only on the current sensory inputs, and often also depends on recent inputs and behavioral outputs that contribute to internal states. Thus, one can ask how cortical dynamics generate representations of these complex situations. It has been observed that mixed selectivity in cortical neurons contributes to represent diverse situations defined by a combination of the current stimuli, and that mixed selectivity is readily obtained in randomly connected recurrent networks. In this context, these reservoir networks reproduce the highly recurrent nature of local cortical connectivity. Recombining present and past inputs, random recurrent networks from the reservoir computing framework generate mixed selectivity which provides pre-coded representations of an essentially universal set of contexts. These representations can then be selectively amplified through learning to solve the task at hand. We thus explored their representational power and dynamical properties after training a reservoir to perform a complex cognitive task initially developed for monkeys. The reservoir model inherently displayed a dynamic form of mixed selectivity, key to the representation of the behavioral context over time. The pre-coded representation of context was amplified by training a feedback neuron to explicitly represent this context, thereby reproducing the effect of learning and allowing the model to perform more robustly. This second version of the model demonstrates how a hybrid dynamical regime combining spatio-temporal processing of reservoirs, and input driven attracting dynamics generated by the feedback neuron, can be used to solve a complex cognitive task. We compared reservoir activity to neural activity of dorsal anterior cingulate cortex of monkeys which revealed similar network dynamics. We argue that reservoir computing is a
The Evolving Properties of Water in a Dynamic Protoplanetary Disk
NASA Astrophysics Data System (ADS)
Ciesla, Fred
2015-08-01
Protoplanetary disks are dynamic objects, through which mass and angular momentum are transported as part of the final stages of pre-main sequence evolution of their central stars. These disks are also rich chemical factories, in which materials inherited from the interstellar medium are transformed through a series of reactions (involving, gases, solids, ions, and photons) to the eventual building blocks of the planets.The chemical and physical evolution of a protoplanetary disk are intimately connected. Both solids and gases are subjected to large-scale motions associated with disk evolution and diffusion within the gas. Solids also settle toward the disk midplane and migrate inwards due to gravity and gas drag. This dynamical evolution exposes primitive materials to a range of physical conditions (pressure, temperature, radiation environment) within the disk. It is the integrated effects of these environments that define the physical and chemical properties of a solid grain prior to its incorporation into a planetesimal or planet.Water serves as an interesting tracer of this evolution, as it would be processed in a variety of ways within a protoplanetary disk. I will discuss new methods that allow us to trace the dynamical movement of water vapor and ice throughout the lifetime of a protoplanetary disk and to determine the physical environments to which the water would be exposed. In particular, I will show how the early evolution of a protoplanetary disk impacts the D/H ratio of the water inherited by planetary materials. I will also explore how photodesorption of water by UV photons can lead to the formation of amorphous ice and thus the trapping of noble gases and other volatiles at levels that are much greater than predicted by equilibrium chemistry models. These effects combine to lead to constantly evolving properties of water during the early stages of planet formation. I will also discuss how the observed properties of Solar System bodies constrain these
Inferring Network Dynamics and Neuron Properties from Population Recordings
Linaro, Daniele; Storace, Marco; Mattia, Maurizio
2011-01-01
Understanding the computational capabilities of the nervous system means to “identify” its emergent multiscale dynamics. For this purpose, we propose a novel model-driven identification procedure and apply it to sparsely connected populations of excitatory integrate-and-fire neurons with spike frequency adaptation (SFA). Our method does not characterize the system from its microscopic elements in a bottom-up fashion, and does not resort to any linearization. We investigate networks as a whole, inferring their properties from the response dynamics of the instantaneous discharge rate to brief and aspecific supra-threshold stimulations. While several available methods assume generic expressions for the system as a black box, we adopt a mean-field theory for the evolution of the network transparently parameterized by identified elements (such as dynamic timescales), which are in turn non-trivially related to single-neuron properties. In particular, from the elicited transient responses, the input–output gain function of the neurons in the network is extracted and direct links to the microscopic level are made available: indeed, we show how to extract the decay time constant of the SFA, the absolute refractory period and the average synaptic efficacy. In addition and contrary to previous attempts, our method captures the system dynamics across bifurcations separating qualitatively different dynamical regimes. The robustness and the generality of the methodology is tested on controlled simulations, reporting a good agreement between theoretically expected and identified values. The assumptions behind the underlying theoretical framework make the method readily applicable to biological preparations like cultured neuron networks and in vitro brain slices. PMID:22016731
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.
Quasiparticle Diffusion in CRESST Light Detectors
NASA Astrophysics Data System (ADS)
Angloher, G.; Bauer, P.; Ferreiro, N.; Hauff, D.; Tanzke, A.; Strauss, R.; Kiefer, M.; Petricia, F.; Reindl, F.; Seidel, W.; Pröbst, F.; Wüstrich, M.
2016-07-01
CRESST-II is a direct dark matter experiment that uses scintillating calorimeters to detect WIMP-induced nuclear scatter processes. Heat and light signals are read out with tungsten transition edge sensors (TESs) that are optimized toward their sensitivity to non-thermal phonons. The usage of superconducting thin film structures (e.g., aluminum) serving as phonon collectors to increase the collection area for this signal component is an approach to improve the sensitivity of the TES. The performance of the phonon collectors depends on the material properties and the quality achieved in the production process. We optimized the size of the phonon collectors for the given quality of CRESST-II light detectors. The diffusion lengths measured in this work are mathcal {O}(1 mm) and show a strong correlation to the Residual Resistivity Ratio of the respective films. First tests of CRESST-II light detectors with larger as well as thicker phonon collectors individually show improvements in the measured pulse height of 30 %.
Quasiparticle Diffusion in CRESST Light Detectors
NASA Astrophysics Data System (ADS)
Angloher, G.; Bauer, P.; Ferreiro, N.; Hauff, D.; Tanzke, A.; Strauss, R.; Kiefer, M.; Petricia, F.; Reindl, F.; Seidel, W.; Pröbst, F.; Wüstrich, M.
2016-02-01
CRESST-II is a direct dark matter experiment that uses scintillating calorimeters to detect WIMP-induced nuclear scatter processes. Heat and light signals are read out with tungsten transition edge sensors (TESs) that are optimized toward their sensitivity to non-thermal phonons. The usage of superconducting thin film structures (e.g., aluminum) serving as phonon collectors to increase the collection area for this signal component is an approach to improve the sensitivity of the TES. The performance of the phonon collectors depends on the material properties and the quality achieved in the production process. We optimized the size of the phonon collectors for the given quality of CRESST-II light detectors. The diffusion lengths measured in this work are {O} (1 mm) and show a strong correlation to the Residual Resistivity Ratio of the respective films. First tests of CRESST-II light detectors with larger as well as thicker phonon collectors individually show improvements in the measured pulse height of 30 %.
Quasiparticle Diffusion in CRESST Light Detectors
NASA Astrophysics Data System (ADS)
Angloher, G.; Bauer, P.; Ferreiro, N.; Hauff, D.; Tanzke, A.; Strauss, R.; Kiefer, M.; Petricia, F.; Reindl, F.; Seidel, W.; Pröbst, F.; Wüstrich, M.
2016-07-01
CRESST-II is a direct dark matter experiment that uses scintillating calorimeters to detect WIMP-induced nuclear scatter processes. Heat and light signals are read out with tungsten transition edge sensors (TESs) that are optimized toward their sensitivity to non-thermal phonons. The usage of superconducting thin film structures (e.g., aluminum) serving as phonon collectors to increase the collection area for this signal component is an approach to improve the sensitivity of the TES. The performance of the phonon collectors depends on the material properties and the quality achieved in the production process. We optimized the size of the phonon collectors for the given quality of CRESST-II light detectors. The diffusion lengths measured in this work are {O}(1 mm) and show a strong correlation to the Residual Resistivity Ratio of the respective films. First tests of CRESST-II light detectors with larger as well as thicker phonon collectors individually show improvements in the measured pulse height of 30 %.
The Stationary Dirac Equation as a Generalized Pauli Equation for Two Quasiparticles
NASA Astrophysics Data System (ADS)
Chuprikov, Nikolay L.
2015-06-01
By analyzing the Dirac equation with static electric and magnetic fields it is shown that Dirac's theory is nothing but a generalized one-particle quantum theory compatible with the special theory of relativity. This equation describes a quantum dynamics of a single relativistic fermion, and its solution is reduced to solution of the generalized Pauli equation for two quasiparticles which move in the Euclidean space with their effective masses holding information about the Lorentzian symmetry of the four-dimensional space-time. We reveal the correspondence between the Dirac bispinor and Pauli spinor (two-component wave function), and show that all four components of the Dirac bispinor correspond to a fermion (or all of them correspond to its antiparticle). Mixing the particle and antiparticle states is prohibited. On this basis we discuss the paradoxical phenomena of Zitterbewegung and the Klein tunneling.
Craven, Galen T; Popov, Alexander V; Hernandez, Rigoberto
2015-04-21
The dynamical properties of a system of soft rods governed by stochastic hard collisions (SHCs) have been determined over a varying range of softness using molecular dynamics simulations in one dimension and analytic theory. The SHC model allows for interpenetration of the system's constituent particles in the simulations, generating overlapping clustering behavior analogous to the spatial structures observed in systems governed by deterministic bounded potentials. Through variation of an assigned softness parameter δ, the limiting ranges of intermolecular softness are bridged, connecting the limiting ensemble behavior from hard to ideal (completely soft). Various dynamical and structural observables are measured from simulation and compared to developed theoretical values. The spatial properties are found to be well predicted by theories developed for the deterministic penetrable-sphere model with a transformation from energetic to probabilistic arguments. While the overlapping spatial structures are complex, the dynamical properties can be adequately approximated through a theory built on impulsive interactions with Enskog corrections. Our theory suggests that as the softness of interaction is varied toward the ideal limit, correlated collision processes are less important to the energy transfer mechanism, and Markovian processes dominate the evolution of the configuration space ensemble. For interaction softness close to hard limit, collision processes are highly correlated and overlapping spatial configurations give rise to entanglement of single-particle trajectories. PMID:25903909
Stochastic dynamics of penetrable rods in one dimension: Entangled dynamics and transport properties
Craven, Galen T.; Popov, Alexander V.; Hernandez, Rigoberto
2015-04-21
The dynamical properties of a system of soft rods governed by stochastic hard collisions (SHCs) have been determined over a varying range of softness using molecular dynamics simulations in one dimension and analytic theory. The SHC model allows for interpenetration of the system’s constituent particles in the simulations, generating overlapping clustering behavior analogous to the spatial structures observed in systems governed by deterministic bounded potentials. Through variation of an assigned softness parameter δ, the limiting ranges of intermolecular softness are bridged, connecting the limiting ensemble behavior from hard to ideal (completely soft). Various dynamical and structural observables are measured from simulation and compared to developed theoretical values. The spatial properties are found to be well predicted by theories developed for the deterministic penetrable-sphere model with a transformation from energetic to probabilistic arguments. While the overlapping spatial structures are complex, the dynamical properties can be adequately approximated through a theory built on impulsive interactions with Enskog corrections. Our theory suggests that as the softness of interaction is varied toward the ideal limit, correlated collision processes are less important to the energy transfer mechanism, and Markovian processes dominate the evolution of the configuration space ensemble. For interaction softness close to hard limit, collision processes are highly correlated and overlapping spatial configurations give rise to entanglement of single-particle trajectories.
The number comb for a soil physical properties dynamic measurement
NASA Astrophysics Data System (ADS)
Olechko, K.; Patiño, P.; Tarquis, A. M.
2012-04-01
We propose the prime numbers distribution extracted from the soil digital multiscale images and some physical properties time series as the precise indicator of the spatial and temporal dynamics under soil management changes. With this new indicator the soil dynamics can be studied as a critical phenomenon where each phase transition is estimated and modeled by the graph partitioning induced phase transition. The critical point of prime numbers distribution was correlated with the beginning of Andosols, Vertisols and saline soils physical degradation under the unsustainable soil management in Michoacan, Guanajuato and Veracruz States of Mexico. The data banks corresponding to the long time periods (between 10 and 28 years) were statistically compared by RISK 5.0 software and our own algorithms. Our approach makes us able to distill free-form natural laws of soils physical properties dynamics directly from the experimental data. The Richter (1987) and Schmidt and Lipson (2009) original approaches were very useful to design the algorithms to identify Hamiltonians, Lagrangians and other laws of geometric and momentum conservation especially for erosion case.
Optical properties of X-rays--dynamical diffraction.
Authier, André
2012-01-01
The first attempts at measuring the optical properties of X-rays such as refraction, reflection and diffraction are described. The main ideas forming the basis of Ewald's thesis in 1912 are then summarized. The first extension of Ewald's thesis to the X-ray case is the introduction of the reciprocal lattice. In the next step, the principles of the three versions of the dynamical theory of diffraction, by Darwin, Ewald and Laue, are given. It is shown how the comparison of the dynamical and geometrical theories of diffraction led Darwin to propose his extinction theory. The main optical properties of X-ray wavefields at the Bragg incidence are then reviewed: Pendellösung, shift of the Bragg peak, fine structure of Kossel lines, standing waves, anomalous absorption, paths of wavefields inside the crystal, Borrmann fan and double refraction. Lastly, some of the modern applications of the dynamical theory are briefly outlined: X-ray topography, location of adsorbed atoms at crystal surfaces, optical devices for synchrotron radiation and X-ray interferometry. PMID:22186282
Dynamics of hydraulic properties due to biological clogging
NASA Astrophysics Data System (ADS)
Rosenzweig, R.; Shavit, U.; Furman, A.
2012-04-01
Classic treatment of soil-water flow is described by the unsaturated version of Darcy's law and Richards' equation, assuming time invariant hydraulic properties, e.g. the saturated hydraulic conductivity, Ks, and van Genuchten-Mualem's α and n. However, when bacteria is present the soil is quite far from being time invariant and biological activity constantly alters the pore-scale structure, leading to macro-scale alteration of the hydraulic properties. This may be of high relevance to processes such as subsurface bioremediation, soil aquifer treatment, wastewater irrigation, and more. In this work we explore the dynamic alteration of soil hydraulic properties by a combination of column experiments and pore-network modeling. We experimentally demonstrate how biological activity clogs an unsaturated soil column and reduces its hydraulic conductivity, while a similar column where biological activity is limited does not clog. Further, we demonstrate that the clogging is preferential to the nutrient input. Next, we develop a pore-network model that uses triangular shape channels. This allows a dual occupancy (water-air) of each channel and high connectivity. The model solves the flow of water, nutrient transport, and biological dynamics. It includes biofilm growth and decay, attachment and detachment, and nutrient exchange between the water and biofilm phases. We perform a sensitivity analysis of the model and qualitatively show through the loss of connectivity how the clogging that was observed in our experiment can be explained.
Locomotion as an emergent property of muscle contractile dynamics.
Biewener, Andrew A
2016-01-01
Skeletal muscles share many common, highly conserved features of organization at the molecular and myofilament levels, giving skeletal muscle fibers generally similar and characteristic mechanical and energetic properties; properties well described by classical studies of muscle mechanics and energetics. However, skeletal muscles can differ considerably in architectural design (fiber length, pinnation, and connective tissue organization), as well as fiber type, and how they contract in relation to the timing of neuromotor activation and in vivo length change. The in vivo dynamics of muscle contraction is, therefore, crucial to assessing muscle design and the roles that muscles play in animal movement. Architectural differences in muscle-tendon organization combined with differences in the phase of activation and resulting fiber length changes greatly affect the time-varying force and work that muscles produce, as well as the energetic cost of force generation. Intrinsic force-length and force-velocity properties of muscles, together with their architecture, also play important roles in the control of movement, facilitating rapid adjustments to changing motor demands. Such adjustments complement slower, reflex-mediated neural feedback control of motor recruitment. Understanding how individual fiber forces are integrated to whole-muscle forces, which are transmitted to the skeleton for producing and controlling locomotor movement, is therefore essential for assessing muscle design in relation to the dynamics of movement. PMID:26792341
Dynamic properties of high structural integrity auxetic open cell foam
NASA Astrophysics Data System (ADS)
Scarpa, F.; Ciffo, L. G.; Yates, J. R.
2004-02-01
This paper illustrates various dynamic characteristics of open cell compliant polyurethane foam with auxetic (negative Poisson's ratio) behaviour. The foam is obtained from off-the-shelf open cell polyurethane grey foam with a manufacturing process based on mechanical deformation on a mould in a temperature-controlled oven. The Poisson's ratio is measured with an image processing technique based on edge detection with wavelet methods. Foam samples have been tested in a viscoelastic analyser tensile test machine to determine the Young's modulus and loss factor for small dynamic strains. The same samples have also been tested in an acoustic impedance tube to measure acoustic absorption and specific acoustic resistance and reactance with a transmissibility technique. Another set of tests has been set up on a cam plastometer machine for constant strain rate dynamic crushing analysis. All the tests have been carried out on auxetic and normal foam samples to provide a comparison between the two types of cellular solids. The results from the experimental tests are discussed and interpreted using microstructure models for cellular materials existing in the literature. The negative Poisson's ratio foam presented in this paper shows an overall superiority regarding damping and acoustic properties compared to the original conventional foam. Its dynamic crushing performance is also significantly superior to the normal foam, suggesting a possible use in structural integrity compliant elements.
Dynamic Properties of DNA-Programmable Nanoparticle Crystallization.
Yu, Qiuyan; Zhang, Xuena; Hu, Yi; Zhang, Zhihao; Wang, Rong
2016-08-23
The dynamics of DNA hybridization is very important in DNA-programmable nanoparticle crystallization. Here, coarse-grained molecular dynamics is utilized to explore the structural and dynamic properties of DNA hybridizations for a self-complementary DNA-directed nanoparticle self-assembly system. The hexagonal close-packed (HCP) and close-packed face-centered cubic (FCC) ordered structures are identified for the systems of different grafted DNA chains per nanoparticle, which are in good agreement with the experimental results. Most importantly, the dynamic crystallization processes of DNA hybridizations are elucidated by virtue of the mean square displacement, the percentage of hybridizations, and the lifetime of DNA bonds. The lifetime can be modeled by the DNA dehybridization, which has an exponential form. The lifetime of DNA bonds closely depends on the temperature. A suitable temperature for the DNA-nanoparticle crystallization is obtained in the work. Moreover, a too large volume fraction hinders the self-assembly process due to steric effects. This work provides some essential information for future design of nanomaterials. PMID:27409362
Dynamic relaxation of the elastic properties of hard carbon films
Hirvonen, J.; Koskinen, J.; Kaukonen, M.; Nieminen, R.; Scheibe, H.
1997-06-01
The effect of enhanced atomic mobility on the growth of hard carbon films was examined. Tetrahedrally bonded amorphous carbon films were deposited by condensing energetic carbon ions using an arc-discharge deposition method. The deposition temperature varied between 50 and 400{degree}C. The dependence of elastic properties on deposition temperature was examined by determining the frequency-dependent propagation velocity of ultrasonic surface acoustic waves induced by a laser. A remarkable decrease in elastic coefficient was revealed above the deposition temperature of 300{degree}C and complete relaxation was obtained at 400{degree}C. This observation was analyzed by using a simple model which was in turn supported by molecular dynamics simulations. The relaxation turns out to be a thermally activated, dynamic process with an activation energy of 0.57 eV. Possible relaxation mechanisms associated with the migration of atoms or defects on a growing surface are discussed. {copyright} {ital 1997 American Institute of Physics.}
Nickel-aluminum alloy clusters -- structural and dynamical properties
Jellinek, J.; Krissinel, E.B.
1997-08-01
Structural and dynamical properties of mixed Ni{sub n}Al{sub m} alloy clusters mimicked by a many-body potential are studied computationally for all the possible compositions n and m such that n + m = 13. It is shown that the manifold of the usually very large number of the different possible structural forms can be systematized by introducing classes of structures corresponding to the same concentration of the components, geometry and type of the central atom. General definitions of mixing energy and mixing coefficient are introduced, and it is shown that the energy ordering of the structural forms within each class is governed by the mixing coefficient. The peculiarities of the solid-to-liquid-like transition are described as a function of the concentration of the two types of atoms. These peculiarities are correlated with and explained in terms of the energy spectra of the structural forms. Class-dependent features of the dynamics are described and analyzed.
TRITIUM EFFECTS ON DYNAMIC MECHANICAL PROPERTIES OF POLYMERIC MATERIALS
Clark, E
2008-11-12
Dynamic mechanical analysis has been used to characterize the effects of tritium gas (initially 1 atm. pressure, ambient temperature) exposure over times up to 2.3 years on several thermoplastics-ultrahigh molecular weight polyethylene (UHMW-PE), polytetrafluoroethylene (PTFE), and Vespel{reg_sign} polyimide, and on several formulations of elastomers based on ethylene propylene diene monomer (EPDM). Tritium exposure stiffened the elastic modulus of UHMW-PE up to about 1 year and then softened it, and reduced the viscous response monotonically with time. PTFE initially stiffened, however the samples became too weak to handle after nine months exposure. The dynamic properties of Vespel{reg_sign} were not affected. The glass transition temperature of the EPDM formulations increased approximately 4 C. following three months tritium exposure.
Dynamic properties of interfaces in soft matter: Experiments and theory
NASA Astrophysics Data System (ADS)
Sagis, Leonard M. C.
2011-10-01
The dynamic properties of interfaces often play a crucial role in the macroscopic dynamics of multiphase soft condensed matter systems. These properties affect the dynamics of emulsions, of dispersions of vesicles, of biological fluids, of coatings, of free surface flows, of immiscible polymer blends, and of many other complex systems. The study of interfacial dynamic properties, surface rheology, is therefore a relevant discipline for many branches of physics, chemistry, engineering, and life sciences. In the past three to four decades a vast amount of literature has been produced dealing with the rheological properties of interfaces stabilized by low molecular weight surfactants, proteins, (bio)polymers, lipids, colloidal particles, and various mixtures of these surface active components. In this paper recent experiments are reviewed in the field of surface rheology, with particular emphasis on the models used to analyze surface rheological data. Most of the models currently used are straightforward generalizations of models developed for the analysis of rheological data of bulk phases. In general the limits on the validity of these generalizations are not discussed. Not much use is being made of recent advances in nonequilibrium thermodynamic formalisms for multiphase systems, to construct admissible models for the stress-deformation behavior of interfaces. These formalisms are ideally suited to construct thermodynamically admissible constitutive equations for rheological behavior that include the often relevant couplings to other fluxes in the interface (heat and mass), and couplings to the transfer of mass from the bulk phase to the interface. In this review recent advances in the application of classical irreversible thermodynamics, extended irreversible thermodynamics, rational thermodynamics, extended rational thermodynamics, and the general equation for the nonequilibrium reversible-irreversible coupling formalism to multiphase systems are also discussed
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.
Adaptation of the Landau-Migdal quasiparticle pattern to strongly correlated Fermi systems
Khodel, V. A.; Clark, J. W.; Zverev, M. V.
2011-09-15
A quasiparticle pattern advanced in Landau's first article on Fermi-liquid theory is adapted to elucidate the properties of a class of strongly correlated Fermi systems characterized by a Lifshitz phase diagram featuring a quantum critical point (QCP) where the density of states diverges. The necessary condition for stability of the Landau Fermi-Liquid state is shown to break down in such systems, triggering a cascade of topological phase transitions that lead, without symmetry violation, to states with multi-connected Fermi surfaces. The end point of this evolution is found to be an exceptional state whose spectrum of single-particle excitations exhibits a completely flat portion at zero temperature. Analysis of the evolution of the temperature dependence of the single-particle spectrum yields results that provide a natural explanation of classical behavior of this class of Fermi systems in the QCP region.
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.
Hung, N. Quang; Dang, N. Dinh
2010-05-15
We propose a description of pairing properties in finite systems within the canonical and microcanonical ensembles. The approach is derived by solving the BCS and self-consistent quasiparticle random-phase approximation with the Lipkin-Nogami particle-number projection at zero temperature. The obtained eigenvalues are embedded into the canonical and microcanonical ensembles. The results obtained are found in quite good agreement with the exact solutions of the doubly-folded equidistant multilevel pairing model as well as the experimental data for {sup 56}Fe nucleus. The merit of the present approach resides in its simplicity and its application to a wider range of particle number, where the exact solution is impracticable.
Massive Dirac quasiparticles in the optical absorbance of graphene, silicene, germanene, and tinene
NASA Astrophysics Data System (ADS)
Matthes, Lars; Pulci, Olivia; Bechstedt, Friedhelm
2013-10-01
We present first-principles studies of the optical absorbance of the group IV honeycomb crystals graphene, silicene, germanene, and tinene. We account for many-body effects on the optical properties by using the non-local hybrid functional HSE06. The optical absorption peaks are blueshifted due to quasiparticle corrections, while the influence on the low-frequency absorbance remains unchanged and reduces to a universal value related to the Sommerfeld fine structure constant. At the Dirac points spin-orbit interaction opens fundamental band gaps; parabolic bands with a very small effective mass emerge. Consequently, the low-frequency absorbance is modified with a spin-orbit-induced transparency region and an increase of the absorbance at the fundamental absorption edge.
World-trade web: Topological properties, dynamics, and evolution
NASA Astrophysics Data System (ADS)
Fagiolo, Giorgio; Reyes, Javier; Schiavo, Stefano
2009-03-01
This paper studies the statistical properties of the web of import-export relationships among world countries using a weighted-network approach. We analyze how the distributions of the most important network statistics measuring connectivity, assortativity, clustering, and centrality have coevolved over time. We show that all node-statistic distributions and their correlation structure have remained surprisingly stable in the last 20years —and are likely to do so in the future. Conversely, the distribution of (positive) link weights is slowly moving from a log-normal density towards a power law. We also characterize the autoregressive properties of network-statistics dynamics. We find that network-statistics growth rates are well-proxied by fat-tailed densities like the Laplace or the asymmetric exponential power. Finally, we find that all our results are reasonably robust to a few alternative, economically meaningful, weighting schemes.
Dynamic compressive properties of bovine knee layered tissue
NASA Astrophysics Data System (ADS)
Nishida, Masahiro; Hino, Yuki; Todo, Mitsugu
2015-09-01
In Japan, the most common articular disease is knee osteoarthritis. Among many treatment methodologies, tissue engineering and regenerative medicine have recently received a lot of attention. In this field, cells and scaffolds are important, both ex vivo and in vivo. From the viewpoint of effective treatment, in addition to histological features, the compatibility of mechanical properties is also important. In this study, the dynamic and static compressive properties of bovine articular cartilage-cancellous bone layered tissue were measured using a universal testing machine and a split Hopkinson pressure bar method. The compressive behaviors of bovine articular cartilage-cancellous bone layered tissue were examined. The effects of strain rate on the maximum stress and the slope of stress-strain curves of the bovine articular cartilage-cancellous bone layered tissue were discussed.
Static and Dynamical Properties of heavy actinide Monopnictides of Lutetium
Mir, Showkat H.; Jha, Prakash C.; Islam, M. S.; Banarjee, Amitava; Luo, Wei; Dabhi, Shweta D.; Jha, Prafulla K.; Ahuja, R.
2016-01-01
In this work, density functional theory within the framework of generalized gradient approximation has been used to investigate the structural, elastic, mechanical, and phonon properties of lutetium monopnictides in rock-salt crystal structure. The spin orbit coupling and Hubbard-U corrections are included to correctly predict the essential properties of these compounds. The elastic constants, Young’s modulus E, Poisson’s ratio v, shear modulus G, anisotropy factor A and Pugh’s ratio are computed. We found that all lutetium monopnictides are anisotropic and show brittle character. From the wave velocities along [100], [110] and [111] directions, melting temperature of lutetium monopnictides are predicted. Dynamical stability of these monopnictides has been studied by density functional perturbation theory. PMID:27384709
Tuning properties and dynamic range of type 1 vomeronasal receptors
Haga-Yamanaka, Sachiko; Ma, Limei; Yu, C. Ron
2015-01-01
The mouse vomeronasal organ (VNO) expresses chemosensory receptors that detect intra-species as well as inter-species cues. The vomeronasal neurons are thought to be highly selective in their responses. The tuning properties of individual receptors remain difficult to characterize due to the lack of a robust heterologous expression system. Here, we take a transgenic approach to ectopically express two type 1 vomeronasal receptors in the mouse VNO and characterize their responses to steroid compounds. We find that V1rj2 and V1rj3 are sensitive to two sulfated estrogens (SEs) and can be activated by a broad variety of sulfated and glucuronidated steroids at high concentrations. Individual neurons exhibit narrow range of concentration-dependent activation. Collectively, a neuronal population expressing the same receptor covers a wide dynamic range in their responses to SEs. These properties recapitulate the response profiles of endogenous neurons to SEs. PMID:26236183
Tuning properties and dynamic range of type 1 vomeronasal receptors.
Haga-Yamanaka, Sachiko; Ma, Limei; Yu, C Ron
2015-01-01
The mouse vomeronasal organ (VNO) expresses chemosensory receptors that detect intra-species as well as inter-species cues. The vomeronasal neurons are thought to be highly selective in their responses. The tuning properties of individual receptors remain difficult to characterize due to the lack of a robust heterologous expression system. Here, we take a transgenic approach to ectopically express two type 1 vomeronasal receptors in the mouse VNO and characterize their responses to steroid compounds. We find that V1rj2 and V1rj3 are sensitive to two sulfated estrogens (SEs) and can be activated by a broad variety of sulfated and glucuronidated steroids at high concentrations. Individual neurons exhibit narrow range of concentration-dependent activation. Collectively, a neuronal population expressing the same receptor covers a wide dynamic range in their responses to SEs. These properties recapitulate the response profiles of endogenous neurons to SEs. PMID:26236183
Static and Dynamical Properties of heavy actinide Monopnictides of Lutetium.
Mir, Showkat H; Jha, Prakash C; Islam, M S; Banarjee, Amitava; Luo, Wei; Dabhi, Shweta D; Jha, Prafulla K; Ahuja, R
2016-01-01
In this work, density functional theory within the framework of generalized gradient approximation has been used to investigate the structural, elastic, mechanical, and phonon properties of lutetium monopnictides in rock-salt crystal structure. The spin orbit coupling and Hubbard-U corrections are included to correctly predict the essential properties of these compounds. The elastic constants, Young's modulus E, Poisson's ratio v, shear modulus G, anisotropy factor A and Pugh's ratio are computed. We found that all lutetium monopnictides are anisotropic and show brittle character. From the wave velocities along [100], [110] and [111] directions, melting temperature of lutetium monopnictides are predicted. Dynamical stability of these monopnictides has been studied by density functional perturbation theory. PMID:27384709
Simultaneous quasiparticle and Josephson tunneling in BSCCO-2212 break junctions.
Ozyuzer, L.
1998-10-27
Tunneling measurements are reported for superconductor-insulator-superconductor (SIS) break junctions on underdoped, optimally-doped, and overdoped single crystals of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} (Bi-2212). The junction I-V characteristics exhibit well-defined quasiparticle current jumps at eV = 2A as well as hysteretic Josephson currents. The quasiparticle branch has been analyzed in the framework of d{sub x{sup 2}-y{sup 2}} (d-wave) superconductivity and indicates that there is preferential tunneling along the lobe directions of the d-wave gap. For overdoped Bi-2212 with T{sub c} = 62 K, the Josephson current is measured as a function of junction resistance, R{sub n}, which varied by two orders of magnitude (1 k{Omega} to 100 k{Omega}). I{sub c}R{sub n} product is proportional to the 0.47 power of I{sub c} and displays a maximum of 7.0 mV. When the hole doping is decreased from overdoped (T{sub c} = 62 K) to the underdoped regime (T{sub c} = 70 K), the average I{sub c}R{sub n} product increases as does the quasiparticle gap. The maximum I{sub c}R{sub n} is {approximately} 40% of the {Delta}/e at each doping level, with a value as high as 25 mV in underdoped Bi-2212.
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.
Dynamic linear viscoelastic properties and extensional failure of asphalt binders
NASA Astrophysics Data System (ADS)
Ruan, Yonghong
Billions of dollars are spent annually in USA to maintain old pavements that are badly cracked. In order to reduce this expenditure, it is desirable to have criteria for selecting asphalts with superior cracking resistance that will provide pavements with longer durability. Literature reports indicate that the ductility of binders recovered from asphalt pavements correlates with cracking failure. However, ductility measurement is a time and material consuming process, and subject to reproducibility difficulties, as are all failure tests. In addition, ductility measurement does not belong to the currently used Superpave(TM) specification. Correlations between ductility and dynamic viscoelastic properties (measured with the dynamic shear rheometer, DSR), which are much easier and faster to perform and may be included into the Superpave(TM) system, are studied for both straight and modified binders. Ductility correlates quite well with G'/(eta '/G') for conventional asphalt binders aged at different conditions, especially when ductility is below 10 cm. However, for modified asphalts, there is no universal correlation between ductility and G'/(eta'/G'), even in the low ductility region. As far as the asphalt binder in pavement is concerned, the loss due to oxidative aging of its ductility is an important reason for pavement cracking. Polymer modification modifies the rheological and oxidative hardening properties of asphalt binders. The effect of polymeric modifiers on various properties of asphalt binders was investigated. Modifiers studied were diblock poly (styrene-b-butadiene) rubber (SBR), triblock poly (styrene-b-butadiene-b-styrene) (SBS), and tire rubber. Polymer modified binders have a lower hardening and oxidation rate than their corresponding base asphalts. In addition, modified binders have lower hardening susceptibility compared with their base materials and in some cases the results can be dramatic. Polymer modification improves asphalt binders' shear
Disappearance of quasiparticles in a Bose lattice gas
NASA Astrophysics Data System (ADS)
Chen, David; Meldgin, Carolyn; Russ, Philip; DeMarco, Brian; Mueller, Erich
2016-08-01
We use a momentum-space hole-burning technique implemented via stimulated Raman transitions to measure the momentum relaxation time for a gas of bosonic atoms trapped in an optical lattice. By changing the lattice potential depth, we observe a smooth crossover between relaxation times larger and smaller than the bandwidth. The latter condition violates the Mott-Ioffe-Regel bound and indicates a breakdown of the quasiparticle picture. We produce a simple kinetic model that quantitatively predicts these relaxation times. Finally, we introduce a cooling technique based upon our hole-burning technique.
Finite amplitude method for the quasiparticle random-phase approximation
Avogadro, Paolo; Nakatsukasa, Takashi
2011-07-15
We present the finite amplitude method (FAM), originally proposed in Ref. [17], 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 {sup 174}Sn, modifying the hfbrad code, to demonstrate the accuracy, feasibility, and usefulness of the FAM.
Transport properties of the hot and dense sQGP
NASA Astrophysics Data System (ADS)
Berrehrah, H.; Bratkovskaya, E.; Cassing, W.; Marty, R.
2015-05-01
The transport properties of the quark gluon plasma (QGP) are studied in a QCD medium at finite temperature and chemical potential. We calculate the shear viscosity η(T,μq) and the electric conductivity σe(T, μq) for a system of interacting massive and broad quasi-particles as described by the dynamical quasi-particle model “DQPM” at finite temperature T and quark chemical potential μq within the relaxation time approximation. Our results are in a good agreement with lattice QCD at finite temperature and show clearly the increase of the transport coefficients with increasing T and μq. Our results provide the basic ingredients for the study of the hot and dense matter in the Beam Energy Scan (BES) at RHIC and CBM at FAIR.
NASA Astrophysics Data System (ADS)
Yuya, Philip A.; Patel, Nimitt G.
2014-08-01
In the last few decades, nanoindentation has gained widespread acceptance as a technique for materials properties characterization at micron and submicron length scales. Accurate and precise characterization of material properties with a nanoindenter is critically dependent on the ability to correctly model the response of the test equipment in contact with the material. In dynamic nanoindention analysis, a simple Kelvin-Voigt model is commonly used to capture the viscoelastic response. However, this model oversimplifies the response of real viscoelastic materials such as polymers. A model is developed that captures the dynamic nanoindentation response of a viscoelastic material. Indenter tip-sample contact forces are modelled using a generalized Maxwell model. The results on a silicon elastomer were analysed using conventional two element Kelvin-Voigt model and contrasted to analysis done using the Maxwell model. The results show that conventional Kelvin-Voigt model overestimates the storage modulus of the silicone elastomer by ~30%. Maxwell model represents a significant improvement in capturing the viscoelastic material behaviour over the Voigt model.
Thermally induced changes in dynamic mechanical properties of native silks.
Guan, Juan; Porter, David; Vollrath, Fritz
2013-03-11
Dynamic mechanical thermal analysis (DMTA) on individual native silk fibers demonstrates changes in the dynamic mechanical properties of storage modulus and loss tangent as a function of temperature and temperature history ranging from -100 to 250 °C. These property changes are linked quantitatively to two main types of change in the silk structure. First, the evaporation of water with increasing temperature up to 100 °C increases the storage modulus and removes two characteristic loss tangent peaks at -60 and +60 °C. Second, various discrete loss tangent peaks in the range 150-220 °C are associated with specific disordered silk structures that are removed or converted to a limiting high-temperature relaxed structure by the combination of increasing temperature and static load in the DMTA tests. The results identify important origins of silk filament quality based on the analysis of measurements that can be traced back to differences in production and processing history. PMID:23405856
Dynamic material properties of the pregnant human uterus.
Manoogian, Sarah J; Bisplinghoff, Jill A; Kemper, Andrew R; Duma, Stefan M
2012-06-01
Given that automobile crashes are the largest single cause of death for pregnant females, scientists are developing advanced computer models of pregnant occupants. The purpose of this study is to quantify the dynamic material properties of the human uterus in order to increase the biofidelity of these models. A total of 19 dynamic tension tests were performed on pregnant human uterus tissues taken from six separate donors. The tissues were collected during full term Cesarean style deliveries and tested within 36 h of surgery. The tissues were processed into uniform coupon sections and tested at 1.5 strains/s using linear motors. Local stress and strain were determined from load data and optical markers using high speed video. The experiments resulted in a non-linear stress versus strain curves with an overall average peak failure true strain of 0.32±0.112 and a corresponding peak failure true stress of 656.3±483.9 kPa. These are the first data available for the dynamic response of pregnant human uterus tissues, and it is anticipated they will increase the accuracy of future pregnant female computational models. PMID:22542221
Effect of dynamical interactions on integrated properties of globular clusters
NASA Astrophysics Data System (ADS)
Zhuang, Yulong; Zhang, Fenghui; Anders, Peter; Ruan, Zhifeng; Cheng, Liantao; Kang, Xiaoyu
2015-02-01
Globular clusters (GCs) are generally treated as natural validators of simple stellar population (SSP) models. However, there are still some differences between real GCs and SSPs. In this work, we use a direct N-body simulation code NBODY6 to study the influences of dynamical interactions, metallicity and primordial binaries on Milky Way GCs' integrated properties. Our models start with N = 100 000 stars, covering a metallicity range Z = 0.0001 ˜ 0.02, a subset of our models contain primordial binaries, resulting in a binary fraction as currently observed at a model age of GCs. Stellar evolution and external tidal field representative for an average Milky Way GC are taken into consideration. The integrated colours and Lick indices are calculated using BaSeL and Bluered stellar spectral libraries separately. By including dynamical interactions, our model clusters show integrated features (i.e. colours up to 0.01 mag bluer, Hβ up to 0.1 Å greater and [MgFe]' 0.05 Å smaller) making the clusters appear slightly younger than the model clusters without dynamical interactions. This effect is caused mainly by the preferential loss of low-mass stars which have a stronger contribution to redder passbands as well as different spectral features compared to higher mass stars. In addition, this effect is larger at lower metallicities. On the contrary, the incorporation of primordial binaries reduces this effect.
Lu, Bo; Lamnawar, Khalid; Maazouz, Abderrahim; Zhang, Huagui
2016-04-01
An effort was made to demonstrate the dynamic heterogeneity of poly(methyl methacrylate) (PMMA)/poly(vinylidene fluoride) (PVDF) blends, where its composition dependence and the role of interphase were probed. Firstly, the composition dependence of thermorheological complexity of PMMA/PVDF blends in the melt was revealed. The molecular entanglement state involving intra- and interchain entanglements was found to govern the scenario of thermorheological complexity. Intriguingly, local heterogeneity was further demonstrated to exist in the melt-state blends with intermediate compositions, and its origin was depicted to be the interphase. The interphase, coupled with unfavourable interchain entanglements in those blends, could explain the reduced viscosity and speed-up relaxations, contributing to the overall thermorheological complexity. Besides, two experimental glass transition temperatures of blends were resolved in view of segment motions in the miscible phase and the crystal-amorphous interphase, and further assessed via the "self-concentration" concept. The presence of a crystal-amorphous interphase, likely leading to three distinct dynamics of segments in blends, was supposed to contribute to the dynamic heterogeneity in segment relaxations for PMMA/PVDF blends in the solid state. Lastly, effects of dynamic heterogeneity on dynamic mechanical properties were also evaluated. PMID:26932245
Temporal dynamics of connectivity and epidemic properties of growing networks
NASA Astrophysics Data System (ADS)
Fotouhi, Babak; Shirkoohi, Mehrdad Khani
2016-01-01
Traditional mathematical models of epidemic disease had for decades conventionally considered static structure for contacts. Recently, an upsurge of theoretical inquiry has strived towards rendering the models more realistic by incorporating the temporal aspects of networks of contacts, societal and online, that are of interest in the study of epidemics (and other similar diffusion processes). However, temporal dynamics have predominantly focused on link fluctuations and nodal activities, and less attention has been paid to the growth of the underlying network. Many real networks grow: Online networks are evidently in constant growth, and societal networks can grow due to migration flux and reproduction. The effect of network growth on the epidemic properties of networks is hitherto unknown, mainly due to the predominant focus of the network growth literature on the so-called steady state. This paper takes a step towards alleviating this gap. We analytically study the degree dynamics of a given arbitrary network that is subject to growth. We use the theoretical findings to predict the epidemic properties of the network as a function of time. We observe that the introduction of new individuals into the network can enhance or diminish its resilience against endemic outbreaks and investigate how this regime shift depends upon the connectivity of newcomers and on how they establish connections to existing nodes. Throughout, theoretical findings are corroborated with Monte Carlo simulations over synthetic and real networks. The results shed light on the effects of network growth on the future epidemic properties of networks and offers insights for devising a priori immunization strategies.
Temporal dynamics of connectivity and epidemic properties of growing networks.
Fotouhi, Babak; Shirkoohi, Mehrdad Khani
2016-01-01
Traditional mathematical models of epidemic disease had for decades conventionally considered static structure for contacts. Recently, an upsurge of theoretical inquiry has strived towards rendering the models more realistic by incorporating the temporal aspects of networks of contacts, societal and online, that are of interest in the study of epidemics (and other similar diffusion processes). However, temporal dynamics have predominantly focused on link fluctuations and nodal activities, and less attention has been paid to the growth of the underlying network. Many real networks grow: Online networks are evidently in constant growth, and societal networks can grow due to migration flux and reproduction. The effect of network growth on the epidemic properties of networks is hitherto unknown, mainly due to the predominant focus of the network growth literature on the so-called steady state. This paper takes a step towards alleviating this gap. We analytically study the degree dynamics of a given arbitrary network that is subject to growth. We use the theoretical findings to predict the epidemic properties of the network as a function of time. We observe that the introduction of new individuals into the network can enhance or diminish its resilience against endemic outbreaks and investigate how this regime shift depends upon the connectivity of newcomers and on how they establish connections to existing nodes. Throughout, theoretical findings are corroborated with Monte Carlo simulations over synthetic and real networks. The results shed light on the effects of network growth on the future epidemic properties of networks and offers insights for devising a priori immunization strategies. PMID:26871086
Extinction of quasiparticle interference in underdoped cuprates with coexisting order
NASA Astrophysics Data System (ADS)
Andersen, Brian M.; Hirschfeld, P. J.
2009-04-01
Scanning tunneling spectroscopy (STS) measurements [Y. Kohsaka , Nature (London) 454, 1072 (2008)] have shown that dispersing quasiparticle interference (QPI) peaks in Fourier-transformed conductance maps disappear as the bias voltage exceeds a certain threshold corresponding to the coincidence of the contour of constant quasiparticle energy with the period-doubled (e.g., antiferromagnetic) zone boundary. Here we show that this may be caused by coexisting order present in the d -wave superconducting phase. We show explicitly how QPI peaks are extinguished in the situation with coexisting long-range spin-density wave order and discuss the connection with the more realistic case where short-range order is created by quenched disorder. Since it is the localized QPI peaks rather than the underlying antinodal states themselves which are destroyed at a critical bias, our proposal resolves a conflict between STS and photoemission spectroscopy regarding the nature of these states. We also study the momentum-summed density of states in the coexisting phase and show how the competing order produces a kink inside the “V”-shaped d -wave superconducting gap in agreement with recent STS measurements [J. W. Alldredge , Nat. Phys. 4, 319 (2008)].
Quasiparticle Trapping in Microwave Kinetic Inductance Strip Detectors
NASA Astrophysics Data System (ADS)
Moore, D. C.; Mazing, B. A.; Golwala, S.; Bumble, B.; Gao, J.; Young, B. A.; McHugth, S.; Day, P. K.; LeDuc, H. G.; Zmuidzinas, J.
2009-12-01
Microwave Kinetic Inductance Detectors (MKIDs) are thin-film, superconducting resonators, which are attractive for making large detector arrays due to their natural frequency domain multiplexing at GHz frequencies. For X-ray to IR wavelengths, MKIDs can provide high-resolution energy and timing information for each incoming photon. By fabricating strip detectors consisting of a rectangular absorber coupled to MKIDs at each end, high quantum efficiency and spatial resolution can be obtained. A similar geometry is being pursued for phonon sensing in a WIMP dark matter detector. Various materials have been tested including tantalum, tin, and aluminum for the absorbing strip, and aluminum, titanium, and aluminum manganese for the MKID. Initial Ta/Al X-ray devices have shown energy resolutions as good as 62 eV at 6 keV. A Ta/Al UV strip detector with an energy resolution of 0.8 eV at 4.9 eV has been demonstrated, but we find the coupling of the MKIDs to the absorbers is unreliable for these thinner devices. We report on progress probing the thicknesses at which the absorber/MKID coupling begins to degrade by using a resonator to inject quasiparticles directly into the absorber. In order to eliminate the absorber/MKID interface, a modified design for implanted AlMn/Al UV strip detectors was developed, and results showing good transmission of quasiparticles from the absorber to MKID in these devices are presented.
NASA Astrophysics Data System (ADS)
Suthar, K.; Angom, D.
2016-06-01
We explore the collective excitation of two-species Bose-Einstein condensates (TBECs) confined in quasi-two-dimensional optical lattices. For this we use a set of coupled discrete nonlinear Schrödinger equations to describe the system and we employ Hartree-Fock-Bogoliubov theory with the Popov approximation to analyze the quasiparticle spectra at zero temperature. The ground-state geometry, evolution of quasiparticle energies, structure of quasiparticle amplitudes, and dispersion relations are examined in detail. We observe that the TBEC acquires a side-by-side density profile when it is tuned from the miscible to the immiscible phase. In addition, the quasiparticle energies are softened as the system is tuned towards phase separation, but harden after phase separation and mode degeneracies are lifted. In terms of structure, in the miscible phase the quasiparticles have well-defined azimuthal quantum numbers, but that is not the case for the immiscible phase.
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.
Quasiparticle Self-Recombination in Double STJs Strip X-ray Detectors
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.
Dynamic properties of bacterial pili measured by optical tweezers
NASA Astrophysics Data System (ADS)
Fallman, Erik G.; Andersson, Magnus J.; Schedin, Staffan S.; Jass, Jana; Uhlin, Bernt Eric; Axner, Ove
2004-10-01
The ability of uropathogenic Escherichia coli (UPEC) to cause urinary tract infections is dependent on their ability to colonize the uroepithelium. Infecting bacteria ascend the urethra to the bladder and then kidneys by attaching to the uroepithelial cells via the differential expression of adhesins. P pili are associated with pyelonephritis, the more severe infection of the kidneys. In order to find means to treat pyelonephritis, it is therefore of interest to investigate the properties P pili. The mechanical behavior of individual P pili of uropathogenic Escherichia coli has recently been investigated using optical tweezers. P pili, whose main part constitutes the PapA rod, composed of ~1000 PapA subunits in a helical arrangement, are distributed over the bacterial surface and mediate adhesion to host cells. We have earlier studied P pili regarding its stretching/elongation properties where we have found and characterized three different elongation regions, of which one constitute an unfolding of the quaternary (helical) structure of the PapA rod. It was shown that this unfolding takes place at an elongation independent force of 27 +/- 2 pN. We have also recently performed studies on its folding properties and shown that the unfolding/folding of the PapA rod is completely reversible. Here we present a study of the dynamical properties of the PapA rod. We show, among other things, that the unfolding force increases and that the folding force decreases with the speed of unfolding and folding respectively. Moreover, the PapA rod can be folded-unfolded a significant number of times without loosing its characteristics, a phenomenon that is believed to be important for the bacterium to keep close contact to the host tissue and consequently helps the bacterium to colonize the host tissue.
Nodal Quasiparticle Meltdown in Ultra-High Resolution Pump-Probe Angle-Resolved Photoemission
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
Dynamic properties of integrated nanostructure on metallic surface
NASA Astrophysics Data System (ADS)
Zerirgui, D.; Tigrine, R.; Bourahla, B.
2012-02-01
We investigated the vibration properties of integrated nanostructure on crystalline surface. The embedded chain of molecules is parallel to y-axis and takes three different positions: top, hollow, and bridge. The vibrational dynamics of the structure is considered within the harmonic approximation framework. The evanescent and propagating vibrational field of the perfect lattice is determined and interpreted. The presence of the diatomic molecule chain breakdown the translation symmetry in one direction, and gives rise to localized states on its neighborhood. Our study is based on the matching method and the Green functions, the spectral and state densities associated to localized modes are determined and calculated numerically. Our results show that the presence of the inhomogeneity contribute to the creation of new branches of localized vibrational modes, and their number and feature depend strongly on structural parameters of the system and the position of the diatomic chain.
Lotung downhole array. 1: Evaluation of site dynamic properties
Elgamal, A.W.; Zeghal, M.; Tang, H.T.; Stepp, J.C.
1995-04-01
The Lotung large-scale seismic test (LSST) site in Taiwan was instrumented in 1985 with an array of downhole and surface accelerometers, by the Electric Power Research Institute (EPRI), Palo Alto, California, and the Taiwan Power Company (TPC), Taipei, Taiwan. A total of 18 earthquakes were recorded during the period 1985--86. Correlation and spectral analyses of the recorded downhole accelerations are performed to evaluate shear wave propagation characteristics, variation of shear wave velocity with depth, and site resonant frequencies and modal configurations. A shear-beam model, calibrated by the identified site properties, is found to represent the site dynamic response characteristics over a wide frequency range. In a companion paper, strong-motion earthquake records are utilized to investigate the Lotung site large-strain soil response characteristics.
Quantum molecular dynamics simulations of thermophysical properties of fluid ethane
NASA Astrophysics Data System (ADS)
Zhang, Yujuan; Wang, Cong; Zheng, Fawei; Zhang, Ping
2012-12-01
We have performed first-principles molecular-dynamics simulations based on density-functional theory to study the thermophysical properties of ethane under extreme conditions. We present results for the equation of state of fluid ethane in the warm dense region. The optical conductivity is calculated via the Kubo-Greenwood formula from which the dc conductivity and optical reflectivity are derived. The close correlation between the nonmetal-metal transition of ethane and its decomposition, that ethane dissociates significantly into molecular and/or atomic hydrogen and some long alkane chains, has been systematically studied by analyzing the optical conductivity spectra, pair correlation functions, electronic density of states, and charge density distribution of fluid ethane.
Anisotropic mechanical properties of graphene: a molecular dynamics study
NASA Astrophysics Data System (ADS)
Yu, Ming; Zeng, Anna; Zeng, Kevin
2014-03-01
The anisotropic mechanical properties of monolayer graphene with different shapes have been studied using an efficient quantum mechanics molecular dynamics scheme based on a semi-empirical Hamiltonian (refereed as SCED-LCAO) [PRB 74, 15540; PHYSE 42, 1]. We have found the anisotropic nature of the membrane stress. The stresses along the armchair direction are slightly stronger than that along the zigzag direction, showing strong direction selectivity. The graphene with the rectangular shape could sustain strong load (i . e ., 20%) in both armchair and zigzag directions. The graphene with the rhombus shape show large difference in the strain direction: it will quickly crack after 18 % of strain in armchair the direction, but slowly destroyed after 20% in the zigzag direction. The obtained 2D Young's modulus at infinitesimal strain and the third-order (effective nonlinear) elastic modulus are in good consistent with the experimental observation.
Xie, Jun Yu; Ding, Guang Hong; Karttunen, Mikko
2014-03-01
Membranes' response to lateral tension, and eventual rupture, remains poorly understood. In this study, pure dipalmitoylphosphatidylcholine (DPPC) lipid bilayers, under tension/pressure, were studied using molecular dynamics (MD) simulations. The irreversible membrane breakdown is demonstrated to depend on the amplitude of lateral tension, loading rate, and the size of the bilayer. In all of our simulations, -200bar lateral pressure was found to be enough to rupture lipid membrane regardless of the loading rate or the membrane size. Loading rate and membrane size had a significant impact on rupture. A variety of dynamic properties of lipid molecules, probability distribution of area per lipid particularly, have been determined, and found to be fundamental for describing membrane behavior in detail, thus providing the quantitative description for the requirement of membrane rupture. PMID:24374317
Molecular dynamics simulation studies of structural and dynamical properties of rapidly quenched Al
Shen, B.; Liu, C. Y.; Jia, Y.; Yue, G. Q.; Ke, F. S.; Zhao, H. B.; Chen, L. Y.; Wang, S. Y.; Wang, Cai-Zhuang; Ho, Kai-Ming
2013-06-11
The structural and dynamical properties of rapidly quenched Al are studied by molecular dynamics simulations. The pair-correlation function of high temperature liquid Al agrees well with the experimental results. Different cooling rates are applied with high cooling rates leading to glass formation, while low cooling rates leading to crystallization. The local structures are characterized by Honeycutt–Andersen indices and Voronoi tessellation analysis. The results show that for high cooling rates, the local structures of the liquid and glassy Al are predominated by icosahedral clusters, together with considerable amount of face-centered cubic and hexagonal close packed short-range orders. These short-range order results are further confirmed using the recently developed atomic cluster alignment method. Moreover, the atomic cluster alignment clearly shows the crystal nucleation process in supercooled liquid of Al. Finally, the mean square displacement for the liquid is also analyzed, and the corresponding diffusion coefficient as a function of temperature is calculated.
Structure and dynamic properties of colloidal asphaltene aggregates.
Eyssautier, Joëlle; Frot, Didier; Barré, Loïc
2012-08-21
The abundant literature involving asphaltene often contrasts dynamic measurements of asphaltene solutions, highlighting the presence of small particle sizes between 1 and 3 nm, with static scattering measurements, revealing larger aggregates with a radius of gyration around 7 nm. This work demonstrates the complementary use of the two techniques: a homemade dynamic light scattering setup adapted to dark and fluorescent solutions, and small-angle X-ray and neutron scattering. Asphaltene solutions in toluene are prepared by a centrifugation separation to investigate asphaltene polydispersity. These experiments demonstrate that asphaltene solutions are made of Brownian colloidal aggregates. The hydrodynamic radii of asphaltene aggregates are between 5 and 10 nm, while their radii of gyration are roughly comparable, between 3.7 and 7.7 nm. A small fraction of asphaltenes with hydrodynamic and gyration radii around 40 nm is found in the pellet of the centrifugation tube. The fractal character of the largest clusters is observed from small angle scattering nearly on a decade length scale. Previous results on aggregation mechanisms are confirmed ( Eyssautier, J., et al. J. Phys. Chem. B 2011 , 115 , 6827 ): nanoaggregates of 3 nm radius, and with hydrodynamic properties also frequently illustrated in the literature, aggregate to form fractal clusters with a dispersity of aggregation number. PMID:22827858
Structural and dynamical properties of liquid Al-Au alloys
NASA Astrophysics Data System (ADS)
Peng, H. L.; Voigtmann, Th.; Kolland, G.; Kobatake, H.; Brillo, J.
2015-11-01
We investigate temperature- and composition-dependent structural and dynamical properties of Al-Au melts. Experiments are performed to obtain accurate density and viscosity data. The system shows a strong negative excess volume, similar to other Al-based binary alloys. We develop a molecular-dynamics (MD) model of the melt based on the embedded-atom method (EAM), gauged against the available experimental liquid-state data. A rescaling of previous EAM potentials for solid-state Au and Al improves the quantitative agreement with experimental data in the melt. In the MD simulation, the admixture of Au to Al can be interpreted as causing a local compression of the less dense Al system, driven by less soft Au-Au interactions. This local compression provides a microscopic mechanism explaining the strong negative excess volume of the melt. We further discuss the concentration dependence of self- and interdiffusion and viscosity in the MD model. Al atoms are more mobile than Au, and their increased mobility is linked to a lower viscosity of the melt.
Influence of snow-cover properties on avalanche dynamics
NASA Astrophysics Data System (ADS)
Steinkogler, W.; Sovilla, B.; Lehning, M.
2012-04-01
Snow avalanches with the potential of reaching traffic routes and settlements are a permanent winter threat for many mountain communities. Snow safety officers have to take the decision whether to close a road, a railway line or a ski slope. Those decisions are often very difficult as they demand the ability to interpret weather forecasts, to establish their implication for the stability and the structure of the snow cover and to evaluate the influence of the snow cover on avalanche run-out distances. In the operational programme 'Italy-Switzerland, project STRADA' we focus on the effects of snow cover on avalanche dynamics, and thus run-out distance, with the aim to provide a better understanding of this influence and to ultimately develop tools to support snow safety officers in their decision process. We selected five avalanches, measured at the Vallée de la Sionne field site, with similar initial mass and topography but different flow dynamics and run-out distances. Significant differences amongst the individual avalanches could be observed for front and internal velocities, impact pressures, flow regimes, deposition volumes and run-out distances. For each of these avalanches, the prevailing snow conditions at release were reconstructed using field data from local snowpits or were modeled with SNOWPACK. Combining flow dynamical data with snow cover properties shows that erodible snow depth, snow density and snow temperature in the snow pack along the avalanche track are among the decisive variables that appear to explain the observed differences. It is further discussed, how these influencing factors can be quantified and used for improved predictions of site and time specific avalanche hazard.
The Dynamical Structure of Dark Matter Halos with Universal Properties
NASA Astrophysics Data System (ADS)
Van Hese, Emmanuel; Baes, Maarten; Dejonghe, Herwig
2009-01-01
N-body simulations have unveiled several apparently universal properties of dark matter halos, including a cusped density profile, a power-law pseudo-phase-space density ρ/σ3 r , and a linear β-γ relation between the density slope and the velocity anisotropy. We present a family of self-consistent phase-space distribution functions (DFs) F(E, L), based on the Dehnen-McLaughlin Jeans models, that incorporate these universal properties very accurately. These DFs, derived using a quadratic programming technique, are analytical, positive, and smooth over the entire phase space and are able to generate four-parameter velocity anisotropy profiles β(r) with arbitrary asymptotic values β0 and β∞. We discuss the orbital structure of six radially anisotropic systems in detail and argue that, apart from its use for generating initial conditions for N-body studies, our dynamical modeling provides a valuable complementary approach to understand the processes involved in the formation of dark matter halos.
Studying properties of RNA nanotubes via molecular dynamics
NASA Astrophysics Data System (ADS)
Badu, Shyam; Melnik, Roderick; Prabhakar, Sanjay
2015-04-01
RNA molecules are very flexible in nature. This feature allows us to build various motifs which are essential in bionanotechnological applications. Based on our earlier developed models of RNA nanoclusters, in this contribution we analyze the structure and properties of RNA nanotubes in physiological solutions at different concentrations. Our major tool here is the molecular dynamics (MD) method that was implemented by using the NAMD and VMD packages, with which we study the structural and thermal properties of the nanotubes in physiological solutions. In particular, we have analyzed such characteristics as the Root Mean Square Deviation (RMSD), the radius of gyration, the number of hydrogen bonds per base pairs, and the radial distribution function (RDF) of a RNA nanotube at different concentrations of the physiological solution. Furthermore, the number of 23Na+ and 35Cl-ions around the nanotubes within the distance of 5 Å at two different concentrations has also been analyzed in detail. It has been found that the number of ions accumulated around the nanotubes within the particular distance is growing by small amount while the concentrations of the 23Na+ and 35Cl-ions are substantially increased.
Dynamic mechanical and swelling properties of maleated hyaluronic acid hydrogels.
Lin, Hai; Liu, Jun; Zhang, Kai; Fan, Yujiang; Zhang, Xingdong
2015-06-01
A series of maleated hyaluronan (MaHA) are developed by modification with maleic anhydride. The degrees of substitution (DS) of MaHA vary between 7% and 75%. The DS of MaHA is both higher and wider than methacrylated HA derivatives (MeHA) reported in the literature. MaHA hydrogels are then prepared by photopolymerization and their dynamic mechanical and swelling properties of the hydrogels are investigated. The results showed that MaHA hydrogels with moderate DS (25%, 50% and 65%) have higher storage modulus and lower equilibrium swelling ratios than those with either low or high DS (7%, 15% and 75%). Theoretical analyses also suggest a similar pattern among hydrogels with different DS. The results confirm that the increased cross-linking density enhances the strength of hydrogels. Meanwhile, the hydrophilicity of introduced groups during modification and the degree of incomplete crosslinking reaction might have negative impact on the mechanical and swelling properties of MaHA hydrogels. PMID:25843871
Lattice dynamics and elastic properties of the 4f electron system: CeN
NASA Astrophysics Data System (ADS)
Kanchana, V.; Vaitheeswaran, G.; Zhang, Xinxin; Ma, Yanming; Svane, A.; Eriksson, O.
2011-11-01
The electronic structure, structural stability, and lattice dynamics of cerium mononitride are investigated using ab initio density-functional methods involving an effective potential derived from the generalized gradient approximation and without special treatment for the 4f states. The 4f states are hence allowed to hop from site to site, without an on-site Hubbard U, and contribute to the bonding, in a picture often referred to as itinerant. It is argued that this picture is appropriate for CeN at low temperatures, while the anomalous thermal expansion observed at elevated temperatures indicates entropy-driven localization of the Ce f electrons, similar to the behavior of elemental cerium. The elastic constants are predicted from the total energy variation of strained crystals and are found to be large, typical for nitrides. The phonon dispersions are calculated showing no soft modes, and the Grüneisen parameter behaves smoothly. The electronic structure is also calculated using the quasiparticle self-consistent GW approximation (where G denotes the Green's function and W denotes the screened interaction). The Fermi surface of CeN is dominated by large egg-shaped electron sheets centered on the X points, which stem from the p-f mixing around the X point. In contrast, assuming localized f electrons leads to a semimetallic picture with small band overlaps around X.
Quasiparticle Interference Imaging on SmB6
NASA Astrophysics Data System (ADS)
Pirie, Harris; He, Yang; Hamidian, Mohammad; Yee, Michael; Kim, Dae-Jeong; Fisk, Zachary; Hoffman, Jennifer
Theoretical interest in SmB6 as a possible topological Kondo insulator with spin-textured Dirac surface states spanning the bulk hybridization gap has been well supported by recent transport, quantum oscillation, and spin-resolved ARPES experiments. However, the influence of surface reconstruction and polarization on the observed dispersion remains unclear. Scanning tunneling microscopy (STM) and spectroscopy (STS) enable simultaneous measurement of local real- and momentum-space structure through quasiparticle interference (QPI) imaging. We use QPI imaging to detect and measure the dispersion of states near the hybridization gap on a non-polar, 2 × 1 reconstructed surface of SmB6. We compare these results with recent theoretical predictions to gain insight into the low energy excitations of SmB6. This work was supported by the US National Science Foundation under the Grant DMR-1410480.
Nuclear shell structure and response with quasiparticle-vibration coupling
NASA Astrophysics Data System (ADS)
Litvinova, Elena; Ring, Peter
Extensions of the covariant density functional theory by quasiparticle-vibration coupling (QVC) are discussed. The formalism for one-body and two-body propagators in the nuclear medium allows calculations of single-particle energies and spectroscopic factors as well as the response to various types of excitations. In both cases QVC leads to a fragmentation of states, in agreement with experimental observations. Peculiarities of various 2p2h coupling schemes in the nuclear response function are discussed. The theory of the spin-isospin response includes both QVC and pion exchange and provides a framework for calculations of beta-decay, electron capture and charge-exchange reaction characteristics. The presented approaches are illustrated by realistic calculations for medium-mass and heavy nuclei.
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.
Quasiparticle Interactions in Neutron Matter for Applications in Neutron Stars
NASA Technical Reports Server (NTRS)
Wambach, J; Ainsworth, T. L.; Pines, D.
1993-01-01
A microscopic model for the quasiparticle interaction in neutron matter is presented. Both-particle (pp) and particle-hole (ph) correlations are included. The pp correlations are treated in semi-empirical way, while ph correlations are incorporated by solving coupled two-body equations for particle-hole interaction and the scattering amplitude of the Fermi sphere. The resulting integral equations self-consistently sum the ph reducible diagrams. Antisymmetry is kept at all stages and hence the forward-scattering sum rules for the scattering amplitude are obeyed. Results for Landau parameters and transport coefficients in a density regime representing the crust of a neutron star are presented. We also estimate the (1)S(sub 0) gap parameter for neutron superfluidity and comment briefly on neutron-star implications.
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.
Quasiparticle scattering image in hidden order phases and chiral superconductors
NASA Astrophysics Data System (ADS)
Thalmeier, Peter; Akbari, Alireza
2016-02-01
The technique of Bogoliubov quasiparticle interference (QPI) has been successfully used to investigate the symmetry of unconventional superconducting gaps, also in heavy fermion compounds. It was demonstrated that QPI can distinguish between the d-wave singlet candidates in CeCoIn5. In URu2Si2 presumably a chiral d-wave singlet superconducting (SC) state exists inside a multipolar hidden order (HO) phase. We show that hidden order leaves an imprint on the symmetry of QPI pattern that may be used to determine the essential question whether HO in URu2Si2 breaks the in-plane rotational symmetry or not. We also demonstrate that the chiral d-wave SC gap leads to a crossover to a quasi-2D QPI spectrum below Tc which sharpens the HO features. Furthermore we investigate the QPI image of chiral p-wave multigap superconductor Sr2RuO4.
Thermal properties and dynamic mechanical properties of ceramic fillers filled epoxy composites
NASA Astrophysics Data System (ADS)
Saidina, D. S.; Mariatti, M.; Juliewatty, J.
2015-07-01
This present study is aimed to enhance the thermal and dynamic mechanical properties of ceramic fillers such as Calcium Copper Titanate, CaCu3Ti4O12 (CCTO) and Barium Titanate (BaTiO3) filled epoxy thin film composites. As can be seen from the results, 20 vol% BaTiO3/epoxy thin film composite showed the lowest coefficient of thermal expansion (CTE) value, the highest decomposition temperature (T5 and Tonset) and weight of residue among the composites as the filler has low CTE value, distributed homogeneously throughout the composite and less voids can be seen between epoxy resin and BaTiO3 filler.
NASA Astrophysics Data System (ADS)
Shekhar, Adarsh
nanoporous silica are different from that of bulk water, and insight into the properties of confined water is important for our understanding of many geological and biological processes. Nanoporous silica has a wide range of technological applications because it is easy to tune the size of pores and their morphologies and to functionalize pore surfaces with a variety of molecular moieties. Nanoporous silica is used in catalysis, chromatography, anticorrosion coatings, desalination membranes, and as drug delivery vehicles. We use reactive molecular dynamics to study the structure and dynamics of nanoconfined water between 100 and 300 K
Microscopic dynamics of synchronization in driven colloids
Juniper, Michael P.N.; Straube, Arthur V.; Besseling, Rut; Aarts, Dirk G.A.L.; Dullens, Roel P.A.
2015-01-01
Synchronization of coupled oscillators has been scrutinized for over three centuries, from Huygens' pendulum clocks to physiological rhythms. One such synchronization phenomenon, dynamic mode locking, occurs when naturally oscillating processes are driven by an externally imposed modulation. Typically only averaged or integrated properties are accessible, leaving underlying mechanisms unseen. Here, we visualize the microscopic dynamics underlying mode locking in a colloidal model system, by using particle trajectories to produce phase portraits. Furthermore, we use this approach to examine the enhancement of mode locking in a flexible chain of magnetically coupled particles, which we ascribe to breathing modes caused by mode-locked density waves. Finally, we demonstrate that an emergent density wave in a static colloidal chain mode locks as a quasi-particle, with microscopic dynamics analogous to those seen for a single particle. Our results indicate that understanding the intricate link between emergent behaviour and microscopic dynamics is key to controlling synchronization. PMID:25994921
Microscopic dynamics of synchronization in driven colloids.
Juniper, Michael P N; Straube, Arthur V; Besseling, Rut; Aarts, Dirk G A L; Dullens, Roel P A
2015-01-01
Synchronization of coupled oscillators has been scrutinized for over three centuries, from Huygens' pendulum clocks to physiological rhythms. One such synchronization phenomenon, dynamic mode locking, occurs when naturally oscillating processes are driven by an externally imposed modulation. Typically only averaged or integrated properties are accessible, leaving underlying mechanisms unseen. Here, we visualize the microscopic dynamics underlying mode locking in a colloidal model system, by using particle trajectories to produce phase portraits. Furthermore, we use this approach to examine the enhancement of mode locking in a flexible chain of magnetically coupled particles, which we ascribe to breathing modes caused by mode-locked density waves. Finally, we demonstrate that an emergent density wave in a static colloidal chain mode locks as a quasi-particle, with microscopic dynamics analogous to those seen for a single particle. Our results indicate that understanding the intricate link between emergent behaviour and microscopic dynamics is key to controlling synchronization. PMID:25994921
Structure, properties, and dynamic behavior of Earth's inner core
NASA Astrophysics Data System (ADS)
Reaman, Daniel Marcus
Long-standing debate has persisted regarding the nature of the Earth's inner core, from its age and composition to its structure and dynamic high-pressure, high-temperature behavior. The equation of state of the alloy which comprises the inner core, the material transport properties of inner-core materials and the mechanism responsible for its structure are all required to gain further insight into the current and past state of the Earth's deep interior. Experimental work in the diamond-anvil cell (DAC) coupled with theoretical calculations are reported here to constrain these aspects of the Earth's inner core. Use of the DAC has allowed us to determine an equation of state of a planetary-core representative Fe64Ni36 alloy to 95 GP and ˜ 3000 K. Increasing the Ni content in these experiments relative to the estimated abundance in the inner core (˜5--10%) provides a critical investigation on the effects of increasing Ni content on the equation of state of FeNi alloys, thereby providing insight in to the behavior of these alloys at high pressures and temperatures with applications to other planetary cores. The use of micro-fabricated samples in the DAC is a novel new way of measuring material transport properties under high-pressure and temperature conditions. Using micro-fabricated samples in these experiments, with a controlled geometry of Fe and Ni, has allowed the measurement of interdiffusion coefficients in FeNi alloys and extended the previous pressure range of these experiments by a factor of three. The resulting data has been extrapolated to inner-core conditions to place constraints on material transport properties at those conditions while providing insight into some of the other physical properties of inner-core material, such as the solid-state viscosity. The seismically-anisotropic structure of the inner core remains a point of contention amongst geophysicists. Though many viable hypotheses have been put forth regarding the nature of this structure
Relativistic quasiparticle time blocking approximation: Dipole response of open-shell nuclei
NASA Astrophysics Data System (ADS)
Litvinova, E.; Ring, P.; Tselyaev, V.
2008-07-01
The self-consistent relativistic quasiparticle random-phase approximation (RQRPA) is extended by the quasiparticle-phonon coupling (QPC) model using the quasiparticle time blocking approximation (QTBA). The method is formulated in terms of the Bethe-Salpeter equation (BSE) in the two-quasiparticle space with an energy-dependent two-quasiparticle residual interaction. This equation is solved either in the basis of Dirac states forming the self-consistent solution of the ground state or in the momentum representation. Pairing correlations are treated within the Bardeen-Cooper-Schrieffer (BCS) model with a monopole-monopole interaction. The same NL3 set of the coupling constants generates the Dirac-Hartree-BCS single-quasiparticle spectrum, the static part of the residual two-quasiparticle interaction and the quasiparticle-phonon coupling amplitudes. A quantitative description of electric dipole excitations in the chain of tin isotopes (Z=50) with the mass numbers A=100,106,114,116,120, and 130 and in the chain of isotones with (N=50) Sr88, Zr90, Mo92 is performed within this framework. The RQRPA extended by the coupling to collective vibrations generates spectra with a multitude of 2q⊗phonon (two quasiparticles plus phonon) states providing a noticeable fragmentation of the giant dipole resonance as well as of the soft dipole mode (pygmy resonance) in the nuclei under investigation. The results obtained for the photo absorption cross sections and for the integrated contributions of the low-lying strength to the calculated dipole spectra agree very well with the available experimental data.
Structural and Dynamic Properties of the Human Prion Protein
Chen, Wei; van der Kamp, Marc W.; Daggett, Valerie
2014-01-01
Prion diseases involve the conformational conversion of the cellular prion protein (PrPC) to its misfolded pathogenic form (PrPSc). To better understand the structural mechanism of this conversion, we performed extensive all-atom, explicit-solvent molecular-dynamics simulations for three structures of the wild-type human PrP (huPrP) at different pH values and temperatures. Residue 129 is polymorphic, being either Met or Val. Two of the three structures have Met in position 129 and the other has Val. Lowering the pH or raising the temperature induced large conformational changes of the C-terminal globular domain and increased exposure of its hydrophobic core. In some simulations, HA and its preceding S1-HA loop underwent large displacements. The C-terminus of HB was unstable and sometimes partially unfolded. Two hydrophobic residues, Phe-198 and Met-134, frequently became exposed to solvent. These conformational changes became more dramatic at lower pH or higher temperature. Furthermore, Tyr-169 and the S2-HB loop, or the X-loop, were different in the starting structures but converged to common conformations in the simulations for the Met-129, but not the Val-129, protein. α-Strands and β-strands formed in the initially unstructured N-terminus. α-Strand propensity in the N-terminus was different between the Met-129 and Val129 proteins, but β-strand propensity was similar. This study reveals detailed structural and dynamic properties of huPrP, providing insight into the mechanism of the conversion of PrPC to PrPSc. PMID:24606939
Decoherence and Decay of Two-level Systems due to Non-equilibrium Quasiparticles
NASA Astrophysics Data System (ADS)
Zanker, Sebastian; Marthaler, Michael; Schön, Gerd; Institut für Theoretische Festkörperphysik Team
It is frequently observed that even at very low temperatures the number of quasiparticles in superconducting materials is higher than predicted by standard BCS-theory. These quasiparticles can interact with two-level systems, such as superconducting qubits or two-level systems (TLS) in the amorphous oxide layer of a Josephson junction. This interaction leads to decay and decoherence of the TLS, with specific results, such as the time dependence, depending on the distribution of quasiparticles and the form of the interaction. We study the resulting decay laws for different experimentally relevant protocols. This work was supported by the German-Israeli Foundation for Scientific Research and Development (GIF).
NASA Astrophysics Data System (ADS)
Guerrero-Becerra, Karina A.; Tomadin, Andrea; Polini, Marco
2016-03-01
Tunneling of quasiparticles between two nearly aligned graphene sheets produces resonant current-voltage characteristics because of the quasiexact conservation of in-plane momentum. We claim that, in this regime, vertical transport in graphene/boron nitride/graphene heterostructures carries precious information on electron-electron interactions and the quasiparticle spectral function of the two-dimensional electron system in graphene. We present extensive microscopic calculations of the tunneling spectra with the inclusion of quasiparticle lifetime effects and elucidate the range of parameters (interlayer bias, temperature, twist angle, and gate voltage) under which electron-electron interaction physics emerges.
Dynamic tensile material properties of human pelvic cortical bone.
Kemper, Andrew R; McNally, Craig; Duma, Stefan M
2008-01-01
IIn order for finite element models of the human body to predict pelvic injuries accurately, the appropriate material properties must be applied. Therefore, the purpose of this study was to quantify the dynamic material properties of human pelvic cortical bone in tension. In order to accomplish this, a total of 20 tension coupon specimens were obtained from four regions of four human cadaver pelves: anterior ilium wing, posterior ilium wing, superior pubic ramus, and ischium body. For the anterior and posterior regions of the ilium wing, samples were taken in two orientations to investigate any direction dependence. A high-rate servo-hydraulic Material Testing System (MTS) with a custom slack adaptor was used to apply tension loads to failure at a constant loading rate of 0.5 strains/s. The horizontally oriented anterior ilium specimens were found to have a significantly larger ultimate stress (p=0.02), ultimate strain (p>0.01), and modulus (p=0.02) than the vertically oriented anterior ilium specimens. There were no significant differences in ultimate stress (p=0.27), ultimate strain (p=0.85), or modulus (p=0.87) found between horizontally oriented and vertically oriented posterior ilium specimens. However, additional testing should be conducted at specimen orientation 45 degree from the orientations used in the current study to further investigate the effect of specimen orientation on the posterior portion of the ilium wing. There were no significant differences in ultimate stress (p=0.79), ultimate strain (p=0.31), or modulus (p=0.15) found between the superior pubic ramus and ischium body specimens. However, the statistical comparison between superior pubic ramus and ischium body specimens was considered weak due to the limited samples and large variation between subjects. PMID:19141951
NASA Astrophysics Data System (ADS)
Li, Bing-Huan; Zhang, Zhen-Hua; Lei, Yi-An
2013-01-01
Two-quasiparticle bands and low-lying excited high-K four-, six-, and eight-quasiparticle bands in the doubly-odd174,176 Lu are analyzed by using the cranked shell model (CSM) with the pairing correlations treated by a particle-number conserving (PNC) method, in which the blocking effects are taken into account exactly. The proton and neutron Nilsson level schemes for174,176, Lu are taken from the adjacent odd-A Lu and Hf isotopes, which are adopted to reproduce the experimental bandhead energies of the one-quasiproton and one-quasineutron bands of these odd-A Lu and Hf nuclei, respectively. Once the quasiparticle configurations are determined, the experimental bandhead energies and the moments of inertia of these two- and multi-quasiparticle bands are well reproduced by PNC-CSM calculations. The Coriolis mixing of the low-K (K=|Ω1-Ω2|) two-quasiparticle band of the Gallagher-Moszkowski doublet with one nucleon in the Ω=1/2 orbital is analyzed.
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.
Exploring chromatin organization mechanisms through its dynamic properties.
Bronshtein, Irena; Kanter, Itamar; Kepten, Eldad; Lindner, Moshe; Berezin, Shirly; Shav-Tal, Yaron; Garini, Yuval
2016-03-01
The organization of the genome in the nucleus is believed to be crucial for different cellular functions. It is known that chromosomes fold into distinct territories, but little is known about the mechanisms that maintain these territories. To explore these mechanisms, we used various live-cell imaging methods, including single particle tracking to characterize the diffusion properties of different genomic regions in live cells. Chromatin diffusion is found to be slow and anomalous; in vast contrast, depletion of lamin A protein significantly increases chromatin motion, and the diffusion pattern of chromatin transforms from slow anomalous to fast normal. More than this, depletion of lamin A protein also affects the dynamics of nuclear bodies. Our findings indicate that chromatin motion is mediated by lamin A and we suggest that constrained chromatin mobility allows to maintain chromosome territories. Thus, the discovery of this function of nucleoplasmic lamin A proteins sheds light on the maintenance mechanism of chromosome territories in the interphase nucleus, which ensures the proper function of the genome. PMID:26854963
On the pressure evolution of dynamic properties of supercooled liquids
NASA Astrophysics Data System (ADS)
Drozd-Rzoska, Aleksandra; Rzoska, Sylwester J.; Roland, C. Michael; Imre, Attila R.
2008-06-01
A pressure counterpart of the Vogel-Fulcher-Tammann (VFT) equation for representing the evolution of dielectric relaxation times or related dynamic properties is discussed: τ(P) = τ0Pexp[DPΔP(P0-ΔP)], where ΔP = P-PSL, P0 is the ideal glass pressure estimation, DP is the pressure fragility strength coefficient, and the prefactor τ0P is related to the relaxation time at the stability limit (PSL) in the negative pressure domain. The discussion is extended to the Avramov model (AvM) relation τ(T,P) = τ0exp[ɛ(Tg(P)/T)D], supplemented with a modified Simon-Glatzel-type equation for the pressure dependence of the glass temperature (Tg(P)), enabling an insight into the negative pressure region. A recently postulated (Dyre 2006 Rev. Mod. Phys. 78 953) comparison between the VFT and the AvM-type descriptions is examined, for both the temperature and the pressure paths. Finally, we address the question 'Does fragility depend on pressure?' from the title of Paluch M et al (2001 J. Chem. Phys. 114 8048) and propose a pressure counterpart for the 'Angell plot'.
Mechanical properties of irradiated nanowires - A molecular dynamics study
NASA Astrophysics Data System (ADS)
Figueroa, Emilio; Tramontina, Diego; Gutiérrez, Gonzalo; Bringa, Eduardo
2015-12-01
In this work we study, by means of molecular dynamics simulation, the change in the mechanical properties of a gold nanowire with pre-existing radiation damage. The gold nanowire is used as a simple model for a nanofoam, made of connected nanowires. Radiation damage by keV ions leads to the formation of a stacking fault tetrahedron (SFT), and this defect leads to a reduced plastic threshold, as expected, when the nanowire is subjected to tension. We quantify dislocation and twin density during the deformation, and find that the early activation of the SFT as a dislocation source leads to reduced dislocation densities compared to the case without radiation damage. In addition, we observed a total destruction of the SFT, as opposed to a recent simulation study where it was postulated that SFTs might act as self-generating dislocation sources. The flow stress at large deformation is also found to be slightly larger for the irradiated case, in agreement with recent experiments.
Self-diagnosis of smart structures based on dynamical properties
NASA Astrophysics Data System (ADS)
Fritzen, C.-P.; Kraemer, P.
2009-08-01
When we talk about "smart structures" we can think about different properties and capabilities which make a structure "intelligent" in a certain sense. Originally, the expression "smart" was used in the context that a structure can react and adapt to certain environmental conditions, such as change of shape, compensation of deformations, active vibration damping, etc. Over the last year, the expression "smart" has been extended to the field of structural health monitoring (SHM), where sensor networks, actuators and computational capabilities are used to enable a structure to perform a self-diagnosis with the goal that this structure can release early warnings about a critical health state, locate and classify damage or even to forecast the remaining life-time. This paper intends to give an overview and point out recent developments of vibration-based methods for SHM. All these methods have in common that a structural change due to a damage results in a more or less significant change of the dynamic behavior. For the diagnosis an inverse problem has to be solved. We discuss the use of modal information as well as the direct use of forced and ambient vibrations in the time and frequency domain. Examples from civil and aerospace engineering as well as off-shore wind energy plants show the applicability of these methods.
Molecular Dynamics Simulation of Thermodynamic Properties in Uranium Dioxide
Wang, Xiangyu; Wu, Bin; Gao, Fei; Li, Xin; Sun, Xin; Khaleel, Mohammad A.; Akinlalu, Ademola V.; Liu, L.
2014-03-01
In the present study, we investigated the thermodynamic properties of uranium dioxide (UO2) by molecular dynamics (MD) simulations. As for solid UO2, the lattice parameter, density, and enthalpy obtained by MD simulations were in good agreement with existing experimental data and previous theoretical predictions. The calculated thermal conductivities matched the experiment results at the midtemperature range but were underestimated at very low and very high temperatures. The calculation results of mean square displacement represented the stability of uranium at all temperatures and the high mobility of oxygen toward 3000 K. By fitting the diffusivity constant of oxygen with the Vogel-Fulcher-Tamman law, we noticed a secondary phase transition near 2006.4 K, which can be identified as a ‘‘strong’’ to ‘‘fragile’’ supercooled liquid or glass phase transition in UO2. By fitting the oxygen diffusion constant with the Arrhenius equation, activation energies of 2.0 and 2.7 eV that we obtained were fairly close to the recommended values of 2.3 to 2.6 eV. Xiangyu Wang, Bin Wu, Fei Gao, Xin Li, Xin Sun, Mohammed A. Khaleel, Ademola V. Akinlalu and Li Liu
Static and dynamic properties of confined, cold ion plasmas: MD (molecular dynamics) simulations
Schiffer, J.P.
1989-01-01
Some four years ago it was suggested that in the new generation of heavy ion accelerator storage rings for multiply charged ions, being planned in Europe, one may well attain internal temperatures that would correspond to very cold plasmas. Since that time, the techniques of electron or laser cooling of such beams has evolved and it may well be possible to reach temperatures corresponding to a plasma coupling parameter {Gamma} >> 100. I was fortunate to have had an opportunity to collaborate during 1986-87 with my former colleague Aneesur Rahman, of Molecular Dynamics fame, and we adapted the MD method to the calculation of the properties of cold confined plasmas. After Rahman's premature death two years ago I have continued the exploration of these systems and would like to summarize the results here. 9 refs., 10 figs.
Development of a Spatially Resolved ^3He Quasi-Particle Detector
NASA Astrophysics Data System (ADS)
Barquist, C. S.; Zheng, P.; Jiang, W. G.; Lee, Y.; Yoon, Y. K.; Schumann, T.; Nogan, J.; Lilly, M.
2016-05-01
Andreev surface bound sates are known to exist on the boundaries of superfluid ^3He-B. However, the detailed nature of their interaction with bulk quasi-particles is not well known. In a manner similar to angle-resolved photo-emission spectroscopy, surface states can be probed by measuring the change in momentum of bulk quasi-particles scattered from the surface. In order to make such a measurement, we have designed a spatially resolved quasi-particle detector. The detector consists of an array of micro-machined resonators, which are sensitive to quasi-particle flux. The detector is based on previously developed micro-machined resonators, which have been successfully used to study superfluid ^3He-B and ^4He. Presented here is the design of the detector and the fabrication procedure.
Normal State Spectral Lineshapes of Nodal Quasiparticles in Single Layer Bi2201 Superconductor
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.
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.
Anomalous Quasiparticles on the Domain Wall Between Topological Insulators and Spin Ice Compounds
NASA Astrophysics Data System (ADS)
Kanazawa, I.; Sasaki, T.
We have discussed the behavior of anomalous quasiparticle with fractional electronic charge on the domain wall between topological insulators and spin ice compounds from the standpoint of the field-theoretical formula.
Quasiparticle and Optical Excitations in Solid Ne and Ar: GW and BSE Approximations
Patterson, Charles H.; Galamic-Mulaomerovic, S.
2007-12-26
The GW approximation and the Bethe-Salpeter equation (BSE) have been used to calculate quasiparticle and optical excitations in solid Ne and Ar. Absolute positions of quasiparticle and quasihole energies are found to be in very good agreement with experimental values. Binding energies of Frenkel excitons for these systems calculated using the BSE are also in good agreement with experiment. Splitting of excitons into longitudinal and transverse modes is calculated and found to be approximately twice the experimentally measured value.
One and two quasiparticle state densities in the ESM: Combinatorial approach vs. exact results
Noy, R.C.; Silvera, M.P.; Martinez, R.P.
1994-12-31
An exact method proposed by Zhang and Yang to calculate the effect of Pauli exclusion principle in particle-hole state densities is used to derive closed formulas for one and two quasiparticle state densities. Analytical results are tested against exact combinatorial calculation in the framework of BCS theory using equidistant shell model spectra. Relationship between particle-hole and quasiparticle state densities is discussed.
Quasiparticle Self-Recombination in Superconducting Tunnel Junction X-ray Detectors
NASA Astrophysics Data System (ADS)
Andrianov, V. A.; Gorkov, V. P.
2016-07-01
The mathematical modelling of the X-ray detectors based on superconducting tunnel junctions was performed taking into account diffusion of nonequilibrium quasiparticles, quasiparticle tunnelling and losses, self-recombination and exchange 2Δ -phonons. The effects of recombination were examined in detail. The dependence of the signal on the photon energy and the energy resolution of the detectors were considered. A new analytical expression for a contribution of self-recombination to the signal was obtained.
Connecting neutron star observations to the high density equation of state of a quasiparticle model
NASA Astrophysics Data System (ADS)
Yan, Yan; Cao, Jing; Luo, Xin-Lian; Sun, Wei-Min; Zong, Hongshi
2012-12-01
The observation of the 1.97±0.04 solar-mass neutronlike star gives constraint on the equation of state of cold, condensed matter. In this paper, the equation of state for both the pure quark star and the hybrid star with a quark core described by the quasiparticle model are considered. The parameters of the quasiparticle model that affect the mass of both the quark star and the hybrid star can be constrained by the observation.
Behavior of one-quasiparticle levels in odd isotonic chains of heavy nuclei
Adamian, G. G.; Antonenko, N. V.; Kuklin, S. N.; Malov, L. A.; Lu, B. N.; Zhou, S. G.
2011-08-15
The low-lying one-quasiparticle states are studied in the isotonic chains with N=147, 149, 151, 153, and 155 within the microscopic-macroscopic and self-consistent approaches. The energies of one-quasiparticle states change rather smoothly in the isotonic chains if there is no cross of the proton subshell. The {alpha}-decay schemes of several nuclei are suggested. The isomeric states in the odd isotopes of Fm and No are discussed.
Crystal dynamics and thermal properties of neptunium dioxide
NASA Astrophysics Data System (ADS)
Maldonado, P.; Paolasini, L.; Oppeneer, P. M.; Forrest, T. R.; Prodi, A.; Magnani, N.; Bosak, A.; Lander, G. H.; Caciuffo, R.
2016-04-01
We report an experimental and theoretical investigation of the lattice dynamics and thermal properties of the actinide dioxide NpO2. The energy-wave-vector dispersion relation for normal modes of vibration propagating along the [001 ] , [110 ] , and [111 ] high-symmetry lines in NpO2 at room temperature has been determined by measuring the coherent one-phonon scattering of x rays from an ˜1.2 -mg single-crystal specimen, the largest available single crystal for this compound. The results are compared against ab initio phonon dispersions computed within the first-principles density functional theory in the generalized gradient approximation plus Hubbard U correlation (GGA+U ) approach, taking into account third-order anharmonicity effects in the quasiharmonic approximation. Good agreement with the experiment is obtained for calculations with an on-site Coulomb parameter U =4 eV and Hund's exchange J =0.6 eV in line with previous electronic structure calculations. We further compute the thermal expansion, heat capacity, thermal conductivity, phonon linewidth, and thermal phonon softening, and compare with available experiments. The theoretical and measured heat capacities are in close agreement with another. About 27% of the calculated thermal conductivity is due to phonons with energy higher than 25 meV (˜6 THz ), suggesting an important role of high-energy optical phonons in the heat transport. The simulated thermal expansion reproduces well the experimental data up to about 1000 K, indicating a failure of the quasiharmonic approximation above this limit.
Dynamic properties of microemulsions in the single-phase channels.
Wolf, Lukas; Hoffmann, Heinz; Richter, Walter; Teshigawara, Takashi; Okamoto, Tohru
2011-09-29
We have studied the dynamic and rheological properties in the single-phase channels of a microemulsion system with a mixed anionic/nonionic surfactant system and decane from the aqueous to the oil phase. One isotropic channel, called the "upper" channel, begins at the L(3) phase (sponge-like phase) of the binary surfactant mixture on the water side and passes with a shallow minimum for the surfactant composition to the oil side. The other "lower" single-phase channel begins at the micellar L(1) phase and ends in the middle of the phase diagram. Both isotropic channels are separated by a huge anisotropic single phase L(α) channel that reaches from the water side to 90% of oil in the solvent mixture. The structural relaxation time of the viscous fluids could be measured with electric birefringence (EB) measurements, where a signal is caused by the deformation of the internal nanostructure of the fluids by an electric field. For the L(3) phase, the EB signal can be fitted with a single time constant. With increasing oil in the upper channel, the main structural relaxation time passes over a maximum and correlates with the viscosity. Obviously, this time constant controls the viscosity of the fluid (η(o) = G'·τ). It is remarkable that the longest structural relaxation time increases three decades, and the viscosity increases two decades when 10% of oil is solubilized into the L(3) phase. Conductivity data imply that the fluid in the upper channel has a bicontinuous structure from the L(3) phase to the microemulsion with only 10% oil. In this oil range, the conductivity decreases three decades, and the electric birefringence signals are complicated because of a superposition of up to three processes. For higher oil ratios, the structure obviously changes to a HIPE (high internal phase emulsion) structure with water droplets in the oil matrix. PMID:21842905
Tyrosine Aminotransferase: Biochemical and Structural Properties and Molecular Dynamics Simulations
P Mehere; Q Han; J Lemkul; C Vavricka; H Robinson; D Bevan; J Li
2011-12-31
Tyrosine aminotransferase (TAT) catalyzes the transamination of tyrosine and other aromatic amino acids. The enzyme is thought to play a role in tyrosinemia type II, hepatitis and hepatic carcinoma recovery. The objective of this study is to investigate its biochemical and structural characteristics and substrate specificity in order to provide insight regarding its involvement in these diseases. Mouse TAT (mTAT) was cloned from a mouse cDNA library, and its recombinant protein was produced using Escherichia coli cells and purified using various chromatographic techniques. The recombinant mTAT is able to catalyze the transamination of tyrosine using {alpha}-ketoglutaric acid as an amino group acceptor at neutral pH. The enzyme also can use glutamate and phenylalanine as amino group donors and p-hydroxy-phenylpyruvate, phenylpyruvate and alpha-ketocaproic acid as amino group acceptors. Through macromolecular crystallography we have determined the mTAT crystal structure at 2.9 {angstrom} resolution. The crystal structure revealed the interaction between the pyridoxal-5'-phosphate cofactor and the enzyme, as well as the formation of a disulphide bond. The detection of disulphide bond provides some rational explanation regarding previously observed TAT inactivation under oxidative conditions and reactivation of the inactive TAT in the presence of a reducing agent. Molecular dynamics simulations using the crystal structures of Trypanosoma cruzi TAT and human TAT provided further insight regarding the substrate-enzyme interactions and substrate specificity. The biochemical and structural properties of TAT and the binding of its cofactor and the substrate may help in elucidation of the mechanism of TAT inhibition and activation.
Tyrosine aminotransferase: biochemical and structural properties and molecular dynamics simulations
Mehere, P.; Robinson, H.; Han, Q.; Lemkul, J. A.; Vavricka, C. J.; Bevan, D. R.; Li, J.
2010-11-01
Tyrosine aminotransferase (TAT) catalyzes the transamination of tyrosine and other aromatic amino acids. The enzyme is thought to play a role in tyrosinemia type II, hepatitis and hepatic carcinoma recovery. The objective of this study is to investigate its biochemical and structural characteristics and substrate specificity in order to provide insight regarding its involvement in these diseases. Mouse TAT (mTAT) was cloned from a mouse cDNA library, and its recombinant protein was produced using Escherichia coli cells and purified using various chromatographic techniques. The recombinant mTAT is able to catalyze the transamination of tyrosine using {alpha}-ketoglutaric acid as an amino group acceptor at neutral pH. The enzyme also can use glutamate and phenylalanine as amino group donors and p-hydroxy-phenylpyruvate, phenylpyruvate and alpha-ketocaproic acid as amino group acceptors. Through macromolecular crystallography we have determined the mTAT crystal structure at 2.9 {angstrom} resolution. The crystal structure revealed the interaction between the pyridoxal-5'-phosphate cofactor and the enzyme, as well as the formation of a disulphide bond. The detection of disulphide bond provides some rational explanation regarding previously observed TAT inactivation under oxidative conditions and reactivation of the inactive TAT in the presence of a reducing agent. Molecular dynamics simulations using the crystal structures of Trypanosoma cruzi TAT and human TAT provided further insight regarding the substrate-enzyme interactions and substrate specificity. The biochemical and structural properties of TAT and the binding of its cofactor and the substrate may help in elucidation of the mechanism of TAT inhibition and activation.
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.
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.
Dynamic properties of one-component strongly coupled plasmas: The sum-rule approach
Arkhipov, Yu. V.; Askaruly, A.; Davletov, A. E.; Ballester, D.; Tkachenko, I. M.
2010-02-15
The dynamic characteristics of strongly coupled one-component plasmas are studied within the moment approach. Our results on the dynamic structure factor and the dynamic local-field correction satisfy the sum rules and other exact relations automatically. A quantitative agreement is obtained with numerous simulation data on the plasma dynamic properties, including the dispersion and decay of collective modes. Our approach allows us to correct and complement the results previously found with other treatments.
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.
Planar Quasiparticle Tunneling Spectroscopy of Bi2212 Single Crystals
NASA Astrophysics Data System (ADS)
Aubin, H.; Pugel, D. E.; Greene, L. H.; Jian, S.; Hinks, D.
2000-03-01
Using techniques of quasi-particle planar tunneling spectroscopy, the in-plane density of states of the high-Tc superconductor Bi2212 is investigated. The 0.3 mm thick single crystals used allow tunneling into crystal faces of various crystallographic orientations, and a newly-developed technique allows for exposing these crystal faces with little damage. The planar tunnel junction is fabricated with the insulating dielectric CaF2 as the tunnel barrier and a noble metal counter-electrode. The tunneling conductance measured with the current injected perpendicular to the copper-oxide planes differs substantially from that measured with the current injected parallel to the planes. The in-plane tunneling density of states exhibits a zero-bias conductance peak which is attributed to the formation of an Andreev bound state, as predicted to occur at the ab-plane oriented surface of a d-wave superconductor. Tunneling spectra as a function of temperature, magnetic field and crystallographic orientation will be presented. These results will be discussed and compared with those obtained previously on YBCO-based tunnel junctions. This research was supported by the NSF-STCS (NSF-DMR 91-20000). DGH acknowledges support by the US DOE (W-31-109-ENG-38).
Maximally-localized Wannier functions for GW quasiparticles
NASA Astrophysics Data System (ADS)
Hamann, D. R.; Vanderbilt, David
2009-03-01
Recent efforts carrying the GW many-body approximation to self-consistency have given improved electronic structure results.^1 Maximally-localized Wannier functions^2 formed from the quasiparticle wave functions^3 provide an efficient and highly accurate basis for interpolating the SCGW bands from a coarse Brillouin-zone mesh to symmetry lines. Since the MLWF's correspond to chemists' bond orbitals, they potentially also provide insight into the qualitative effects of the improved treatment of correlations in SCGW compared to LDA. We report results on SrTiO3, solid Ar, and molecular CO. Band interpolation is accurate and effective for both solids. Small shifts in the degree of hybridization can be visualized for some of the SrTiO3 and CO MLWF's. In Ar, individual conduction-band Bloch functions were found to have large differences between LDA and SCGW.^1 However, a manifold of 9 d and spd-hybrid MLWF's which proved to be the minimum necessary for the lower conduction bands showed minimal differences in the two cases. A fully-functional interface to the WANNIER90 library within the SCGW-capable ABINIT code has been implemented and will be publicly available in the near future. 1. F. Bruneval et al., Phys. Rev. B 74, 045102 (2006). 2. N. Marzari and D. Vanderbilt, Phys. Rev. B 56, 12 847 (1997). 3. M. van Schilfgaarde et al., Phys. Rev. Lett. 96, 226402 (2006).
Visualizing global properties of a molecular dynamics trajectory.
Zhou, Hao; Li, Shangyang; Makowski, Lee
2016-01-01
Molecular dynamics (MD) trajectories are very large data sets that contain substantial information about the dynamic behavior of a protein. Condensing these data into a form that can provide intuitively useful understanding of the molecular behavior during the trajectory is a substantial challenge that has received relatively little attention. Here, we introduce the sigma-r plot, a plot of the standard deviation of intermolecular distances as a function of that distance. This representation of global dynamics contains within a single, one-dimensional plot, the average range of motion between pairs of atoms within a macromolecule. Comparison of sigma-r plots calculated from 10 ns trajectories of proteins representing the four major SCOP fold classes indicates diversity of dynamic behaviors which are recognizably different among the four classes. Differences in domain structure and molecular weight also produce recognizable features in sigma-r plots, reflective of differences in global dynamics. Plots generated from trajectories with progressively increasing simulation time reflect the increased sampling of the structural ensemble as a function of time. Single amino acid replacements can give rise to changes in global dynamics detectable through comparison of sigma-r plots. Dynamic behavior of substructures can be monitored by careful choice of interatomic vectors included in the calculation. These examples provide demonstrations of the utility of the sigma-r plot to provide a simple measure of the global dynamics of a macromolecule. PMID:26522428
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).
Landau quantization and quasiparticle interference in the three-dimensional Dirac semimetal Cd3As2
NASA Astrophysics Data System (ADS)
Jeon, Sangjun; Zhou, Brian B.; Gyenis, Andras; Feldman, Benjamin E.; Kimchi, Itamar; Potter, Andrew C.; Gibson, Quinn D.; Cava, Robert J.; Vishwanath, Ashvin; Yazdani, Ali
2014-09-01
Condensed-matter systems provide a rich setting to realize Dirac and Majorana fermionic excitations as well as the possibility to manipulate them for potential applications. It has recently been proposed that chiral, massless particles known as Weyl fermions can emerge in certain bulk materials or in topological insulator multilayers and give rise to unusual transport properties, such as charge pumping driven by a chiral anomaly. A pair of Weyl fermions protected by crystalline symmetry effectively forming a massless Dirac fermion has been predicted to appear as low-energy excitations in a number of materials termed three-dimensional Dirac semimetals. Here we report scanning tunnelling microscopy measurements at sub-kelvin temperatures and high magnetic fields on the II-V semiconductor Cd3As2. We probe this system down to atomic length scales, and show that defects mostly influence the valence band, consistent with the observation of ultrahigh-mobility carriers in the conduction band. By combining Landau level spectroscopy and quasiparticle interference, we distinguish a large spin-splitting of the conduction band in a magnetic field and its extended Dirac-like dispersion above the expected regime. A model band structure consistent with our experimental findings suggests that for a magnetic field applied along the axis of the Dirac points, Weyl fermions are the low-energy excitations in Cd3As2.
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.
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.
Quasiparticle random-phase approximation with interactions from the Similarity Renormalization Group
Hergert, H.; Papakonstantinou, P.; Roth, R.
2011-06-15
We have developed a fully consistent framework for calculations in the quasiparticle random-phase approximation (QRPA) with NN interactions from the Similarity Renormalization Group (SRG) and other unitary transformations of realistic interactions. The consistency of our calculations, which use the same Hamiltonian to determine the Hartree-Fock-Bogoliubov ground states and the residual interaction for QRPA, guarantees an excellent decoupling of spurious strength, without the need for empirical corrections. While work is under way to include SRG-evolved 3N interactions, we presently account for some 3N effects by means of a linearly density-dependent interaction, whose strength is adjusted to reproduce the charge radii of closed-shell nuclei across the whole nuclear chart. As a first application, we perform a survey of the monopole, dipole, and quadrupole response of the calcium isotopic chain and of the underlying single-particle spectra, focusing on how their properties depend on the SRG parameter {lambda}. Unrealistic spin-orbit splittings suggest that spin-orbit terms from the 3N interaction are called for. Nevertheless, our general findings are comparable to results from phenomenological QRPA calculations using Skyrme or Gogny energy density functionals. Potentially interesting phenomena related to low-lying strength warrant more systematic investigations in the future.
Alemany, Manuel M. G.; Longo, Roberto; Gallego, Luis; Gonzales, D. J.; Gonzales, L. E.; Tiago, Murilo L; Chelikowsky, James
2007-01-01
We performed a comprehensive study of the static, dynamic and electronic properties of liquid Pb at T = 650 kelvins, density 0.0309 angstroms^{-3} by means of 216-particle ab initio molecular dynamics simulations based on a real-space implementation of pseudopotentials constructed within density-functional theory. The predicted results and available experimental data are very in good agreement, which confirms the adequacy of this technique to achieve a reliable description of the behavior of liquid metals, including their dynamic properties. Although some of the computed properties of liquid Pb are similar to those of simple liquid metals, others differ markedly. Our results show that an appropriate description of liquid Pb requires the inclusion of relativistic effects in the determination of the pseudopotentials of Pb.
Dynamic Properties of Langmuir Films by Laser Light Scattering
NASA Astrophysics Data System (ADS)
Sanders, John Newell
A technique and instrumentation for measuring visco-elastic properties of Langmuir film organic monolayers has been developed. This technique is used to characterize certain films used in the manufacture of Langmuir-Blodgett solid films. Furthermore a comparison of the dynamic viscous and elastic moduli determined by this technique is made with static values determined from the Pressure versus Area Isotherm. Briefly, a Langmuir film consists of amphiphilic organic molecules spread in a trough filled with pure water. The hydrophobic ends of the molecules trap them on the water surface. When spread at a dilute concentration the molecules exhibit two dimensional ideal gas behavior. By increasing the surface concentration one obtains two dimensional liquid and finally two dimensional solid behavior. The measurement is performed by electrodynamically driving the liquid surface with the electric field from a razor blade brought to within less than 1 mm of the surface. A sinusoidally varying electric field induces dipoles in the water subphase and generates waves at twice the driving frequency (Attractive dipoles are generated whether the field is positive or negative). The space propagation and damping of these waves is measured by laser light scattering. A focused laser beam incident on the surface is reflected at an angle due to the slope of the waves on the surface. By observing the movement of the beam the amplitude and phase of the oscillation with respect to the driving function may be determined (via a Lock-In amplifier) at various distances from the razor blade. One may directly profile the waves by translating the profiler, or one may observe the variation in amplitude and phase while scanning the frequency or surface pressure. In the latter cases one uses a known reference state to determine the wavelength and damping from the amplitude and phase change. This data is fit by a non-linear least squares curve fitting program to determine the wavelength and space
Static and dynamic properties of vortex pairs in asymmetric nanomagnets
NASA Astrophysics Data System (ADS)
Koop, B. C.; Gruschke, M.; Descamps, T.; Bondarenko, A.; Ivanov, B. A.; Korenivski, V.
2016-05-01
Stacked spin-vortex pairs in magnetic multilayered nanopillars, with vertical separation between the vortices small compared to the vortex core size and pure magnetostatic coupling, exhibit spin dynamics absent in individual vortices. This dynamics is nonlinear and is due to the strong direct core-core coupling in the system, dominating energetically for small-signal excitation. We observe and explain the appearance of spin resonance modes, forbidden within linear dynamics, and discuss how they depend on the magnetic and morphological asymmetries in the samples.
ELLIPSOMETRY IN THE STUDY OF DYNAMIC MATERIAL PROPERTIES
Obst, A. W.; Alrick, K.R.; Boboridis, K.; Buttler, William T.; Lamoreaux, Steve Keith; Montgomery, S. L.; Payton, J. R.; Wilke, M. D.
2001-01-01
Measurements of the time-dependent absolute temperature of surfaces shocked using high explosives (HE) provide valuable constraints on the equations-of-state (EOS) of materials and on the state of ejecta from those surfaces. In support of these dynamic surface temperature measurements, techniques for measuring the dynamic surface emissivity of shocked metals in the near infrared (IR) are being developed. These consist of time-dependent laser ellipsometric measurements, using several approaches. A discussion of these ellipsometric techniques is included here. Ellipsometry permits an accurate determination of the dynamic emissivity at a given wavelength, and may also provide a signature of melt in shocked metals.
Unusual dynamic properties of water near the ice-binding plane of hyperactive antifreeze protein
Kuffel, Anna; Czapiewski, Dariusz; Zielkiewicz, Jan
2015-10-07
The dynamical properties of solvation water of hyperactive antifreeze protein from Choristoneura fumiferana (CfAFP) are analyzed and discussed in context of its antifreeze activity. The protein comprises of three well-defined planes and one of them binds to the surface of ice. The dynamical properties of solvation water around each of these planes were analyzed separately; the results are compared with the dynamical properties of solvation water of ice around its two crystallographic planes: basal and prism. Three main conclusions are inferred from our investigations. The first one is that the solvation shell of CfAFP does not seem to be particularly far-ranged, at least not beyond what is usually observed for proteins that do not interact with ice. Therefore, it does not appear to us that the antifreeze activity is enhanced by a long-ranged retardation of water mobility. Also the correlation between the collective mobility of water and the collective mobility of protein atoms highly resembles the one measured for the protein that does not interact with ice. Our second conclusion is that the dynamical properties of solvation water of CfAFP are non-uniform. The dynamics of solvation water of ice-binding plane is, in some respects, different from the dynamics of solvation water of the two remaining planes. The feature that distinguishes the dynamics of solvation water of the three planes is the activation energy of diffusion process. The third conclusion is that—from the three analyzed solvation shells of CfAFP—the dynamical properties of solvation water of the ice-binding plane resemble the most the properties of solvation water of ice; note, however, that these properties still clearly differ from the dynamic properties of solvation water of ice.
Calderín, L; González, L E; González, D J
2009-05-21
We report a study on several static, dynamic, and electronic properties of liquid Hg at room temperature. We have performed ab initio molecular dynamics simulations using Kohn-Sham density functional theory combined with a nonlocal ultrasoft pseudopotential. The calculated static structure shows good agreement with the available experimental data. We present results for the single-particle dynamics, and recent experimental data are analyzed. The calculated dynamic structure factors S(q,omega) fairly agree with their experimental counterparts as measured by inelastic x-ray (and neutron) scattering experiments. The dispersion relation exhibits a positive dispersion, which however is not so marked as suggested by the experiment; moreover, its slope at the long-wavelength limit provides a good estimate of the experimental sound velocity. We have also analyzed the dynamical processes behind the S(q,omega) in terms of a model including a relaxation mechanism with both fast and slow characteristic time scales. PMID:19466841
The dynamic shear properties of structural honeycomb materials
NASA Astrophysics Data System (ADS)
Adams, R. D.; Maheri, M. R.
A technique is described for measuring the dynamic modulus and damping of honeycomb materials. Results of tests on both aluminium and Nomex honeycombs are presented and compared with those reported in the literature.
Ganesan, Narayan; Bauer, Brad A; Lucas, Timothy R; Patel, Sandeep; Taufer, Michela
2011-11-15
We present results of molecular dynamics simulations of fully hydrated DMPC bilayers performed on graphics processing units (GPUs) using current state-of-the-art non-polarizable force fields and a local GPU-enabled molecular dynamics code named FEN ZI. We treat the conditionally convergent electrostatic interaction energy exactly using the particle mesh Ewald method (PME) for solution of Poisson's Equation for the electrostatic potential under periodic boundary conditions. We discuss elements of our implementation of the PME algorithm on GPUs as well as pertinent performance issues. We proceed to show results of simulations of extended lipid bilayer systems using our program, FEN ZI. We performed simulations of DMPC bilayer systems consisting of 17,004, 68,484, and 273,936 atoms in explicit solvent. We present bilayer structural properties (atomic number densities, electron density profiles), deuterium order parameters (S(CD)), electrostatic properties (dipole potential, water dipole moments), and orientational properties of water. Predicted properties demonstrate excellent agreement with experiment and previous all-atom molecular dynamics simulations. We observe no statistically significant differences in calculated structural or electrostatic properties for different system sizes, suggesting the small bilayer simulations (less than 100 lipid molecules) provide equivalent representation of structural and electrostatic properties associated with significantly larger systems (over 1000 lipid molecules). We stress that the three system size representations will have differences in other properties such as surface capillary wave dynamics or surface tension related effects that are not probed in the current study. The latter properties are inherently dependent on system size. This contribution suggests the suitability of applying emerging GPU technologies to studies of an important class of biological environments, that of lipid bilayers and their associated integral
Observer properties for understanding dynamical displays: Capacities, limitations, and defaults
NASA Technical Reports Server (NTRS)
Proffitt, Dennis R.; Kaiser, Mary K.
1991-01-01
People's ability to extract relevant information while viewing ongoing events is discussed in terms of human capabilities, limitations, and defaults. A taxonomy of event complexity is developed which predicts which dynamical events people can and cannot construe. This taxonomy is related to the distinction drawn in classical mechanics between particle and extended body motions. People's commonsense understandings of simple mechanical systems are impacted little by formal training, but rather reflect heuristical simplifications that focus on a single dimension of perceived dynamical relevance.
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.
Dynamic properties of biologically active synthetic heparin-like hexasaccharides.
Angulo, Jesús; Hricovíni, Milos; Gairi, Margarida; Guerrini, Marco; de Paz, José Luis; Ojeda, Rafael; Martín-Lomas, Manuel; Nieto, Pedro M
2005-10-01
A complete study of the dynamics of two synthetic heparin-like hexasaccharides, D-GlcNHSO3-6-SO4-alpha-(1-->4)-L-IdoA-2-SO4-alpha-(1-->4)-D-GlcNHSO3-6-SO4-alpha-(1-->4)-L-IdoA-2-SO4-alpha-(1-->4)-D-GlcNHSO3-6-SO4-alpha-(1-->4)-L-IdoA-2-SO4-alpha-1-->iPr (1) and -->4)-L-IdoA-2-SO4-alpha-(1-->4)-D-GlcNHAc-6-SO4-alpha-(1-->4)-L-IdoA-alpha-(1-->4)-D-GlcNHSO3-alpha-(1-->4)-L-IdoA-2-SO4-alpha-1-->iPr (2), has been performed using 13C-nuclear magnetic resonance (NMR) relaxation parameters, T1, T2, and heteronuclear nuclear Overhauser effect (NOEs). Compound 1 is constituted from sequences corresponding to the major polysaccharide heparin region, while compound 2 contains a sequence never found in natural heparin. They differ from each other only in sulphation patterns, and are capable of stimulating fibroblast growth factors (FGFs)-1 induced mitogenesis. Both oligosaccharides exhibit a remarkable anisotropic overall motion in solution as revealed by their anisotropic ratios (tau /tau||), 4.0 and 3.0 respectively. This is a characteristic behaviour of natural glycosaminoglycans (GAG) which has also been observed for the antithrombin (AT) binding pentasaccharide D-GlcNHSO3-6-SO4-alpha-(1-->4)-D-GlcA-beta-(1-->4)-D-GlcNHSO3-(3,6-SO4)-alpha-(1-->4)-L-IdoA-2-SO4-alpha-(1-->4)-D-GlcNHSO3-6-SO4-alpha-1-->Me (3) (Hricovíni, M., Guerrini, M., Torri, G., Piani, S., and Ungarelli, F. (1995) Conformational analysis of heparin epoxide in aqueous solution. An NMR relaxation study. Carbohydr. Res., 277, 11-23). The motional properties observed for 1 and 2 provide additional support to the suitability of these compounds as heparin models in agreement with previous structural (de Paz, J.L., Angulo, J., Lassaletta, J.M., Nieto, P.M., Redondo-Horcajo, M., Lozano, R.M., Jiménez-Gallego, G., and Martín-Lomas, M. (2001) The activation of fibroblast growth factors by heparin: synthesis, structure and biological activity of heparin-like oligosaccharides. Chembiochem, 2, 673-685; Ojeda, R
On the dynamical properties of an elliptical-oval billiard with static boundary
NASA Astrophysics Data System (ADS)
Oliveira, Diego F. M.; Leonel, Edson D.
2010-04-01
Some dynamical properties for a classical particle confined inside a closed region with an elliptical-oval-like shape are studied. The dynamics of the model is made by using a two-dimensional nonlinear mapping. The phase space of the system is of mixed kind and we have found the condition that breaks the invariant spanning curves in the phase space. We have discussed also some statistical properties of the phase space and obtained the behaviour of the positive Lyapunov exponent.
Jang, Seung Woo; Kotani, Takao; Kino, Hiori; Kuroki, Kazuhiko; Han, Myung Joon
2015-01-01
Despite decades of progress, an understanding of unconventional superconductivity still remains elusive. An important open question is about the material dependence of the superconducting properties. Using the quasiparticle self-consistent GW method, we re-examine the electronic structure of copper oxide high-Tc materials. We show that QSGW captures several important features, distinctive from the conventional LDA results. The energy level splitting between and is significantly enlarged and the van Hove singularity point is lowered. The calculated results compare better than LDA with recent experimental results from resonant inelastic xray scattering and angle resolved photoemission experiments. This agreement with the experiments supports the previously suggested two-band theory for the material dependence of the superconducting transition temperature, Tc. PMID:26206417
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).
Effect of dynamically charged helium on tensile properties of V-4Cr-4Ti
Chung, H.M.; Loomis, B.A.; Nowicki, L.; Smith, D.L.
1995-04-01
The objective of this work is to determine the effect of displacement damage and dynamically charged helium on tensile properties of V-4Cr-4Ti alloy irradiated to 18-31 dpa at 425-600{degree}C in the Dynamic Helium Charging Experiment (DHCE).
Dynamic monitoring of cell mechanical properties using profile microindentation
Guillou, L.; Babataheri, A.; Puech, P.-H.; Barakat, A. I.; Husson, J.
2016-01-01
We have developed a simple and relatively inexpensive system to visualize adherent cells in profile while measuring their mechanical properties using microindentation. The setup allows simultaneous control of cell microenvironment by introducing a micropipette for the delivery of soluble factors or other cell types. We validate this technique against atomic force microscopy measurements and, as a proof of concept, measure the viscoelastic properties of vascular endothelial cells in terms of an apparent stiffness and a dimensionless parameter that describes stress relaxation. Furthermore, we use this technique to monitor the time evolution of these mechanical properties as the cells’ actin is depolymerized using cytochalasin-D. PMID:26857265
Dynamic monitoring of cell mechanical properties using profile microindentation.
Guillou, L; Babataheri, A; Puech, P-H; Barakat, A I; Husson, J
2016-01-01
We have developed a simple and relatively inexpensive system to visualize adherent cells in profile while measuring their mechanical properties using microindentation. The setup allows simultaneous control of cell microenvironment by introducing a micropipette for the delivery of soluble factors or other cell types. We validate this technique against atomic force microscopy measurements and, as a proof of concept, measure the viscoelastic properties of vascular endothelial cells in terms of an apparent stiffness and a dimensionless parameter that describes stress relaxation. Furthermore, we use this technique to monitor the time evolution of these mechanical properties as the cells' actin is depolymerized using cytochalasin-D. PMID:26857265
Dynamic monitoring of cell mechanical properties using profile microindentation
NASA Astrophysics Data System (ADS)
Guillou, L.; Babataheri, A.; Puech, P.-H.; Barakat, A. I.; Husson, J.
2016-02-01
We have developed a simple and relatively inexpensive system to visualize adherent cells in profile while measuring their mechanical properties using microindentation. The setup allows simultaneous control of cell microenvironment by introducing a micropipette for the delivery of soluble factors or other cell types. We validate this technique against atomic force microscopy measurements and, as a proof of concept, measure the viscoelastic properties of vascular endothelial cells in terms of an apparent stiffness and a dimensionless parameter that describes stress relaxation. Furthermore, we use this technique to monitor the time evolution of these mechanical properties as the cells’ actin is depolymerized using cytochalasin-D.
Droplets in microchannels: dynamical properties of the lubrication film
NASA Astrophysics Data System (ADS)
Huerre, Axel; Theodoly, Olivier; Leshansky, Alexander; Valignat, Marie-Pierre; Cantat, Isabelle; Jullien, Marie-Caroline
2015-11-01
The motion of droplets or bubbles in confined geometries has been extensively studied; showing an intrinsic relationship between the lubrication film thickness and the droplet velocity. When capillary forces dominate, the lubrication film thickness evolves non linearly with the capillary number due to viscous dissipation both in the droplet and between meniscus and wall. However, this film may become thin enough (tens of nanometers) that intermolecular forces come into play and affect classical scalings. Our experiments yield highly resolved topographies of the shape of the interface and allow us to bring new insights into droplet dynamics in microfluidics. We find and characterize two distinct dynamical regimes, dominated respectively by capillary and intermolecular forces. In the first regime, we also identified a model with interfacial boundary condition considering only viscous stress continuity that agrees well with film thickness dynamics and interface velocity measurement.
Acoustic and dynamic mechanical properties of a polyurethane rubber
NASA Astrophysics Data System (ADS)
Mott, Peter H.; Roland, C. Michael; Corsaro, Robert D.
2002-04-01
Acoustical and dynamic mechanical measurements were carried out on a commercial polyurethane rubber, DeSoto PR1547. The sound speed and attenuation were measured over the range from 12.5 to 75 kHz and 3.9 to 33.6 °C. Shear modulus was measured from 10-4 to 2 Hz and -36 to 34 °C. The peak heights of the shear loss tangent varied with temperature, demonstrating thermorheological complexity. At higher temperatures, time-temperature superpositioning could be applied, with the shift factors following the Williams-Landel-Ferry equation. From the combined acoustical and mechanical measurements, values for the dynamic bulk modulus were determined. Moreover, superposition of the bulk modulus data was achieved using the shift factors determined from the dynamic mechanical shear measurements. Finally, this work illustrates the capability and the working rules of acoustical measurements in a small tank.
Analytical properties of a three-compartmental dynamical demographic model
NASA Astrophysics Data System (ADS)
Postnikov, E. B.
2015-07-01
The three-compartmental demographic model by Korotaeyv-Malkov-Khaltourina, connecting population size, economic surplus, and education level, is considered from the point of view of dynamical systems theory. It is shown that there exist two integrals of motion, which enables the system to be reduced to one nonlinear ordinary differential equation. The study of its structure provides analytical criteria for the dominance ranges of the dynamics of Malthus and Kremer. Additionally, the particular ranges of parameters enable the derived general ordinary differential equations to be reduced to the models of Gompertz and Thoularis-Wallace.
An evaluation of the dynamic soil properties pilot project in Arches National Park, Utah
Technology Transfer Automated Retrieval System (TEKTRAN)
Dynamic soil properties are gaining increasing attention by producers and users of soil survey data. Near-surface property data, along with vegetation characteristics, provides soil survey users with important new tools, and is a valuable aid in the development and monitoring of state in transition ...
Ji, Pengfei; Zhang, Yuwen; Yang, Mo
2013-12-21
The structural, dynamic, and vibrational properties during heat transfer process in Si/Ge superlattices are studied by analyzing the trajectories generated by the ab initio Car-Parrinello molecular dynamics simulation. The radial distribution functions and mean square displacements are calculated and further discussions are made to explain and probe the structural changes relating to the heat transfer phenomenon. Furthermore, the vibrational density of states of the two layers (Si/Ge) are computed and plotted to analyze the contributions of phonons with different frequencies to the heat conduction. Coherent heat conduction of the low frequency phonons is found and their contributions to facilitate heat transfer are confirmed. The Car-Parrinello molecular dynamics simulation outputs in the work show reasonable thermophysical results of the thermal energy transport process and shed light on the potential applications of treating the heat transfer in the superlattices of semiconductor materials from a quantum mechanical molecular dynamics simulation perspective.
Transient dynamic mechanical properties of resilin-based elastomeric hydrogels
Li, Linqing; Kiick, Kristi L.
2014-01-01
The outstanding high-frequency properties of emerging resilin-like polypeptides (RLPs) have motivated their development for vocal fold tissue regeneration and other applications. Recombinant RLP hydrogels show efficient gelation, tunable mechanical properties, and display excellent extensibility, but little has been reported about their transient mechanical properties. In this manuscript, we describe the transient mechanical behavior of new RLP hydrogels investigated via both sinusoidal oscillatory shear deformation and uniaxial tensile testing. Oscillatory stress relaxation and creep experiments confirm that RLP-based hydrogels display significantly reduced stress relaxation and improved strain recovery compared to PEG-based control hydrogels. Uniaxial tensile testing confirms the negligible hysteresis, reversible elasticity and superior resilience (up to 98%) of hydrated RLP hydrogels, with Young's modulus values that compare favorably with those previously reported for resilin and that mimic the tensile properties of the vocal fold ligament at low strain (<15%). These studies expand our understanding of the properties of these RLP materials under a variety of conditions, and confirm the unique applicability, for mechanically demanding tissue engineering applications, of a range of RLP hydrogels. PMID:24809044
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.
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.
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.
Fendley, Paul; Fisher, Matthew P.A.; Nayak, Chetan
2009-07-15
We explain how (perturbed) boundary conformal field theory allows us to understand the tunneling of edge quasiparticles in non-Abelian topological states. The coupling between a bulk non-Abelian quasiparticle and the edge is due to resonant tunneling to a zero mode on the quasiparticle, which causes the zero mode to hybridize with the edge. This can be reformulated as the flow from one conformally invariant boundary condition to another in an associated critical statistical mechanical model. Tunneling from one edge to another at a point contact can split the system in two, either partially or completely. This can be reformulated in the critical statistical mechanical model as the flow from one type of defect line to another. We illustrate these two phenomena in detail in the context of the {nu}=5/2 quantum Hall state and the critical Ising model. We briefly discuss the case of Fibonacci anyons and conclude by explaining the general formulation and its physical interpretation.
NASA Astrophysics Data System (ADS)
Parameswaran, S. A.; Kivelson, S. A.; Shankar, R.; Sondhi, S. L.; Spivak, B. Z.
2012-12-01
We study the structure of Bogoliubov quasiparticles, bogolons, the fermionic excitations of paired superfluids that arise from fermion (BCS) pairing, including neutral superfluids, superconductors, and paired quantum Hall states. The naive construction of a stationary quasiparticle in which the deformation of the pair field is neglected leads to a contradiction: it carries a net electrical current even though it does not move. However, treating the pair field self-consistently resolves this problem: in a neutral superfluid, a dipolar current pattern is associated with the quasiparticle for which the total current vanishes. When Maxwell electrodynamics is included, as appropriate to a superconductor, this pattern is confined over a penetration depth. For paired quantum Hall states of composite fermions, the Maxwell term is replaced by a Chern-Simons term, which leads to a dipolar charge distribution and consequently to a dipolar current pattern.
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.
Dynamic relaxation properties of aromatic polyimides and polymer nanocomposites
NASA Astrophysics Data System (ADS)
Comer, Anthony C.
The dynamic relaxation characteristics of MatrimidRTM (BTDA-DAPI) polyimide and several functionalized aromatic polyimides have been investigated using dynamic mechanical and dielectric methods. The functionalized polyimides were thermally rearranged to generate polybenzoxazole membranes with controlled free volume characteristics. All polyimides have application in membrane separations and exhibit three motional processes with increasing temperature: two sub-glass relaxations (gamma and beta transitions), and the glass-rubber (alpha) transition. For Matrimid, the low-temperature gamma transition is purely non-cooperative, while the beta sub-glass transition shows a more cooperative character as assessed via the Starkweather method. For the thermally rearranged polyimides, the gamma transition is a function of the polymer synthesis method, thermal history, and ambient moisture. The beta relaxation shows a dual character with increasing thermal rearrangement, the emerging lower-temperature component reflecting motions encompassing a more compact backbone contour. For the glass-rubber (alpha) transition, dynamic mechanical studies reveal a strong shift in Talpha to higher temperatures and a progressive reduction in relaxation intensity with increasing degree of thermal rearrangement. The dynamic relaxation characteristics of poly(ether imide) and poly(methyl methacrylate) nanocomposites were investigated by dynamic mechanical analysis and dielectric spectroscopy. The nanoparticles used were native and surface-modified fumed silicas. The nanocomposites display a dual glass transition behavior encompassing a bulk polymer glass transition, and a second, higher-temperature transition reflecting relaxation of polymer chain segments constrained owing to their proximity to the particle surface. The position and intensity of the higher-temperature transition varies with particle loading and surface chemistry, and reflects the relative populations of segments constrained or
Molecular dynamics modelling of mechanical properties of polymers for adaptive aerospace structures
NASA Astrophysics Data System (ADS)
Papanikolaou, Michail; Drikakis, Dimitris; Asproulis, Nikolaos
2015-02-01
The features of adaptive structures depend on the properties of the supporting materials. For example, morphing wing structures require wing skin materials, such as rubbers that can withstand the forces imposed by the internal mechanism while maintaining the required aerodynamic properties of the aircraft. In this study, Molecular Dynamics and Minimization simulations are being used to establish well-equilibrated models of Ethylene-Propylene-Diene Monomer (EPDM) elastomer systems and investigate their mechanical properties.
Dynamical properties of non-Markovian stochastic differential equations
NASA Astrophysics Data System (ADS)
Hernández-Machado, A.; San Miguel, M.
1984-04-01
We study nonstationary non-Markovian processes defined by Langevin-type stochastic differential equations with an Ornstein-Uhlenbeck driving force. We concentrate on the long time limit of the dynamical evolution. We derive an approximate equation for the correlation function of a nonlinear nonstationary non-Markovian process, and we discuss its consequences. Non-Markovicity can introduce a dependence on noise parameters in the dynamics of the correlation function in cases in which it becomes independent of these parameters in the Markovian limit. Several examples are discussed in which the relaxation time increases with respect to the Markovian limit. For a Brownian harmonic oscillator with fluctuating frequency, the non-Markovicity of the process decreases the domain of stability of the system, and it can change an infradamped evolution into an overdamped one.
Dynamical properties of the soft-wall elliptical billiard.
Kroetz, Tiago; Oliveira, Hércules A; Portela, Jefferson S E; Viana, Ricardo L
2016-08-01
Physical systems such as optical traps and microwave cavities are realistically modeled by billiards with soft walls. In order to investigate the influence of the wall softness on the billiard dynamics, we study numerically a smooth two-dimensional potential well that has the elliptical (hard-wall) billiard as a limiting case. Considering two parameters, the eccentricity of the elliptical equipotential curves and the wall hardness, which defines the steepness of the well, we show that (1) whereas the hard-wall limit is integrable and thus completely regular, the soft wall elliptical billiard exhibits chaos, (2) the chaotic fraction of the phase space depends nonmonotonically on the hardness of the wall, and (3) the effect of the hardness on the dynamics depends strongly on the eccentricity of the billiard. We further show that the limaçon billiard can exhibit enhanced chaos induced by wall softness, which suggests that our findings generalize to quasi-integrable systems. PMID:27627309
NASA Astrophysics Data System (ADS)
Kruszka, Leopold; Vorobiov, Iurii S.; Ovcharova, Nataliia Iu.
2015-09-01
Protective structures such as process chambers, protective boxes, facing elements of vehicles, personal protection equipment, motors cases etc. widely used in modern technology has been tested in the following project. Under the influence of impact loads, the three-dimensional dynamic stress-strain state with finite dynamic displacements and deformations has arised. The deformations occur in the elastic- plastic stage. In the analysis of the high-rate deformations, the dynamic properties of the materials, which are determined based on experimental data should be taken into account. The dynamic stress state of structural elements depends essentially on the dynamic properties of the materials used. The problem is solved using the finite element method, which takes into account the specifics of the process. Boundary conditions in the element nodes must satisfy the equality movement as well as derivatives. The formed function allows to describe continuous and smooth stress changes. The numerical analysis of the dynamic stress-strain state of structural elements under impact loads, takes into account different dynamic properties of the materials. A series of numerical calculations allows to reveal the features of high-rate deformation elements of protective structures and makes recommendations to improve their dynamic strength under different loading conditions.
Dynamics and thermodynamic properties of CXCL7 chemokine.
Herring, Charles A; Singer, Christopher M; Ermakova, Elena A; Khairutdinov, Bulat I; Zuev, Yuriy F; Jacobs, Donald J; Nesmelova, Irina V
2015-11-01
Chemokines form a family of signaling proteins mainly responsible for directing the traffic of leukocytes, where their biological activity can be modulated by their oligomerization state. We characterize the dynamics and thermodynamic stability of monomer and homodimer structures of CXCL7, one of the most abundant platelet chemokines, using experimental methods that include circular dichroism (CD) and nuclear magnetic resonance (NMR) spectroscopy, and computational methods that include the anisotropic network model (ANM), molecular dynamics (MD) simulations and the distance constraint model (DCM). A consistent picture emerges for the effects of dimerization and Cys5-Cys31 and Cys7-Cys47 disulfide bonds formation. The presence of disulfide bonds is not critical for maintaining structural stability in the monomer or dimer, but the monomer is destabilized more than the dimer upon removal of disulfide bonds. Disulfide bonds play a key role in shaping the characteristics of native state dynamics. The combined analysis shows that upon dimerization flexibly correlated motions are induced between the 30s and 50s loop within each monomer and across the dimer interface. Interestingly, the greatest gain in flexibility upon dimerization occurs when both disulfide bonds are present, and the homodimer is least stable relative to its two monomers. These results suggest that the highly conserved disulfide bonds in chemokines facilitate a structural mechanism that is tuned to optimally distinguish functional characteristics between monomer and dimer. PMID:26297927
Static and dynamic properties of large polymer melts in equilibrium
NASA Astrophysics Data System (ADS)
Hsu, Hsiao-Ping; Kremer, Kurt
2016-04-01
We present a detailed study of the static and dynamic behaviors of long semiflexible polymer chains in a melt. Starting from previously obtained fully equilibrated high molecular weight polymer melts [G. Zhang et al., ACS Macro Lett. 3, 198 (2014)], we investigate their static and dynamic scaling behaviors as predicted by theory. We find that for semiflexible chains in a melt, results of the mean square internal distance, the probability distributions of the end-to-end distance, and the chain structure factor are well described by theoretical predictions for ideal chains. We examine the motion of monomers and chains by molecular dynamics simulations using the ESPResSo++ package. The scaling predictions of the mean squared displacement of inner monomers, center of mass, and relations between them based on the Rouse and the reptation theory are verified, and related characteristic relaxation times are determined. Finally, we give evidence that the entanglement length Ne,PPA as determined by a primitive path analysis (PPA) predicts a plateau modulus, GN 0 = /4 5 ( ρ k B T / N e ) , consistent with stresses obtained from the Green-Kubo relation. These comprehensively characterized equilibrium structures, which offer a good compromise between flexibility, small Ne, computational efficiency, and small deviations from ideality, provide ideal starting states for future non-equilibrium studies.
Anomalous lattice-dynamical properties of a quenched diffuse ω phase in Zr-Nb alloys
NASA Astrophysics Data System (ADS)
Yamada, Y.; Fuchizaki, K.
1990-11-01
Anomalous lattice-dynamical properties of Zr-Nb alloys observed by neutron inelastic scattering have been analyzed based on the viewpoint that the anomaly is due to the strong lattice anharmonicity in these alloys. The large-amplitude fluctuations of the atoms in the anharmonic lattice are divided into kinematical and dynamical parts. The former is characterized by the quasistatic heterophase fluctuations, while the latter has characteristics of ordinary phonons. The scattering function due to the dynamical fluctuations under excitation of heterophase fluctuations is computed with use of molecular dynamics. The results reproduce the anomalous characteristics of the observed spectra of neutron inelastic scattering.
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.
Measurement of quasiparticle transport in aluminum films using tungsten transition-edge sensors
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.
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.
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.
Tunneling spectroscopy of quasiparticle bound states in a spinful Josephson junction.
Chang, W; Manucharyan, V E; Jespersen, T S; Nygård, J; Marcus, C M
2013-05-24
The spectrum of a segment of InAs nanowire, confined between two superconducting leads, was measured as function of gate voltage and superconducting phase difference using a third normal-metal tunnel probe. Subgap resonances for odd electron occupancy-interpreted as bound states involving a confined electron and a quasiparticle from the superconducting leads, reminiscent of Yu-Shiba-Rusinov states-evolve into Kondo-related resonances at higher magnetic fields. An additional zero-bias peak of unknown origin is observed to coexist with the quasiparticle bound states. PMID:23745916
Trapping hot quasi-particles in a high-power superconducting electronic cooler
NASA Astrophysics Data System (ADS)
Nguyen, H. Q.; Aref, T.; Kauppila, V. J.; Meschke, M.; Winkelmann, C. B.; Courtois, H.; Pekola, J. P.
2013-08-01
The performance of hybrid superconducting electronic coolers is usually limited by the accumulation of hot quasi-particles in their superconducting leads. This issue is all the more stringent in large-scale and high-power devices, as required by the applications. Introducing a metallic drain connected to the superconducting electrodes via a fine-tuned tunnel barrier, we efficiently remove quasi-particles and obtain electronic cooling from 300 mK down to 130 mK with a 400 pW cooling power. A simple thermal model accounts for the experimental observations.
Bose polarons: Dynamical decay and RF signatures
NASA Astrophysics Data System (ADS)
Corson, John; Bohn, John
2016-05-01
Interactions of a single impurity with a quantum many-body environment are known to alter the character of the impurity, thereby forming a ``quasiparticle''. The condensed matter tradition often identifies quasiparticles as poles of a Green function in the complex plane, a notion whose sophistication sometimes obscures the underlying physics. The problem of a single quantum impurity in a Bose condensate, or Bose polaron, is an illustrative example where the meaning of the impurity Green function, and hence the quasiparticle itself, becomes especially transparent. Using direct diagonalization in a truncated Hilbert space, we examine the dynamical evolution and quasiparticle decay of the repulsive Bose polaron. This approach also allows us to simulate RF spectroscopy across a Feshbach resonance and outside the linear regime, as well as account for motional and thermal effects in a harmonic trap.
Molecular properties of aqueous solutions: a focus on the collective dynamics of hydration water.
Comez, L; Paolantoni, M; Sassi, P; Corezzi, S; Morresi, A; Fioretto, D
2016-07-01
When a solute is dissolved in water, their mutual interactions determine the molecular properties of the solute on one hand, and the structure and dynamics of the surrounding water particles (the so-called hydration water) on the other. The very existence of soft matter and its peculiar properties are largely due to the wide variety of possible water-solute interactions. In this context, water is not an inert medium but rather an active component, and hydration water plays a crucial role in determining the structure, stability, dynamics, and function of matter. This review focuses on the collective dynamics of hydration water in terms of retardation with respect to the bulk, and of the number of molecules whose dynamics is perturbed. Since water environments are in a dynamic equilibrium, with molecules continuously exchanging from around the solute towards the bulk and vice versa, we examine the ability of different techniques to measure the water dynamics on the basis of the explored time scales and exchange rates. Special emphasis is given to the collective dynamics probed by extended depolarized light scattering and we discuss whether and to what extent the results obtained in aqueous solutions of small molecules can be extrapolated to the case of large biomacromolecules. In fact, recent experiments performed on solutions of increasing complexity clearly indicate that a reductionist approach is not adequate to describe their collective dynamics. We conclude this review by presenting current ideas that are being developed to describe the dynamics of water interacting with macromolecules. PMID:27280176
Green-Kubo relations for dynamic interfacial excess properties
NASA Astrophysics Data System (ADS)
Sagis, Leonard M. C.
2012-08-01
In this paper we analyze the fluctuations of the in-plane interfacial excess fluxes in multiphase systems, in the context of the extended irreversible thermodynamics formalism. We derive expressions for the time correlation functions of the surface extra stress tensor, the surface mass flux vector, and the surface energy flux vector, and use these expressions to derive Green-Kubo relations for the surface shear viscosity, the surface dilatational viscosity, the surface diffusion coefficient, and the surface thermal conductivity. These Green-Kubo relations can be used to compute these excess transport coefficients using for example molecular dynamics simulations.
Properties of fiber reinforced plastics about static and dynamic loadings
NASA Astrophysics Data System (ADS)
Kudinov, Vladimir V.; Korneeva, Natalia V.
2016-05-01
A method for investigation of impact toughness of anisotropic polymer composite materials (reinforced plastics) with the help of CM model sample in the configuration of microplastic (micro plastic) and impact pendulum-type testing machine under static and dynamic loadings has been developed. The method is called "Break by Impact" (Impact Break IB). The estimation of impact resistance CFRP by this method showed that an increase in loading velocity ~104 times the largest changes occurs in impact toughness and deformation ability of a material.
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.
Technology Transfer Automated Retrieval System (TEKTRAN)
Dynamic and static shell properties of eggs provide important insight to egg quality. Understanding how processing and handling procedures affect both dynamic and static shell properties can enhance the safety and quality of egg reaching consumers. A study was conducted to determine if dynamic she...
Droplets in Microchannels: Dynamical Properties of the Lubrication Film.
Huerre, Axel; Theodoly, Olivier; Leshansky, Alexander M; Valignat, Marie-Pierre; Cantat, Isabelle; Jullien, Marie-Caroline
2015-08-01
We study the motion of droplets in a confined, micrometric geometry, by focusing on the lubrication film between a droplet and a wall. When capillary forces dominate, the lubrication film thickness evolves nonlinearly with the capillary number due to the viscous dissipation between the meniscus and the wall. However, this film may become thin enough (tens of nanometers) that intermolecular forces come into play and affect classical scalings. Our experiments yield highly resolved topographies of the shape of the interface and allow us to bring new insights into droplet dynamics in microfluidics. We report the novel characterization of two dynamical regimes as the capillary number increases: (i) at low capillary numbers, the film thickness is constant and set by the disjoining pressure, while (ii) above a critical capillary number, the interface behavior is well described by a viscous scenario. At a high surfactant concentration, structural effects lead to the formation of patterns on the interface, which can be used to trace the interface velocity, that yield direct confirmation of the boundary condition in the viscous regime. PMID:26296118
Droplets in Microchannels: Dynamical Properties of the Lubrication Film
NASA Astrophysics Data System (ADS)
Huerre, Axel; Theodoly, Olivier; Leshansky, Alexander M.; Valignat, Marie-Pierre; Cantat, Isabelle; Jullien, Marie-Caroline
2015-08-01
We study the motion of droplets in a confined, micrometric geometry, by focusing on the lubrication film between a droplet and a wall. When capillary forces dominate, the lubrication film thickness evolves nonlinearly with the capillary number due to the viscous dissipation between the meniscus and the wall. However, this film may become thin enough (tens of nanometers) that intermolecular forces come into play and affect classical scalings. Our experiments yield highly resolved topographies of the shape of the interface and allow us to bring new insights into droplet dynamics in microfluidics. We report the novel characterization of two dynamical regimes as the capillary number increases: (i) at low capillary numbers, the film thickness is constant and set by the disjoining pressure, while (ii) above a critical capillary number, the interface behavior is well described by a viscous scenario. At a high surfactant concentration, structural effects lead to the formation of patterns on the interface, which can be used to trace the interface velocity, that yield direct confirmation of the boundary condition in the viscous regime.
General Critical Properties of the Dynamics of Scientific Discovery
Bettencourt, L. M. A.; Kaiser, D. I.
2011-05-31
Scientific fields are difficult to define and compare, yet there is a general sense that they undergo similar stages of development. From this point of view it becomes important to determine if these superficial similarities can be translated into a general framework that would quantify the general advent and subsequent dynamics of scientific ideas. Such a framework would have important practical applications of allowing us to compare fields that superficially may appear different, in terms of their subject matter, research techniques, typical collaboration size, etc. Particularh' important in a field's history is the moment at which conceptual and technical unification allows widespread exchange of ideas and collaboration, at which point networks of collaboration show the analog of a percolation phenomenon, developing a giant connected component containing most authors. Here we investigate the generality of this topological transition in the collaboration structure of scientific fields as they grow and become denser. We develop a general theoretical framework in which each scientific field is an instantiation of the same large-scale topological critical phenomenon. We consider whether the evidence from a variety of specific fields is consistent with this picture, and estimate critical exponents associated with the transition. We then discuss the generality of the phenomenon and to what extent we may expect other scientific fields — including very large ones — to follow the same dynamics.
Effect of microstructure on static and dynamic mechanical properties of high strength steels
NASA Astrophysics Data System (ADS)
Qu, Jinbo
The high speed deformation behavior of a commercially available dual phase (DP) steel was studied by means of split Hopkinson bar apparatus in shear punch (25m/s) and tension (1000s-1) modes with an emphasis on the influence of microstructure. The cold rolled sheet material was subjected to a variety of heat treatment conditions to produce several different microstructures, namely ferrite plus pearlite, ferrite plus bainite and/or acicular ferrite, ferrite plus bainite and martensite, and ferrite plus different fractions of martensite. Static properties (0.01mm/s for shear punch and 0.001s -1 for tension) of all the microstructures were also measured by an MTS hydraulic machine and compared to the dynamic properties. The effects of low temperature tempering and bake hardening were investigated for some ferrite plus martensite microstructures. In addition, two other materials, composition designed as high strength low alloy (HSLA) steel and transformation induced plasticity (TRIP) steel, were heat treated and tested to study the effect of alloy chemistry on the microstructure and property relationship. A strong effect of microstructure on both static and dynamic properties and on the relationship between static and dynamic properties was observed. According to the variation of dynamic factor with static strength, three groups of microstructures with three distinct behaviors were identified, i.e. classic dual phase (ferrite plus less than 50% martensite), martensite-matrix dual phase (ferrite plus more than 50% martensite), and non-dual phase (ferrite plus non-martensite). Under the same static strength level, the dual phase microstructure was found to absorb more dynamic energy than other microstructures. It was also observed that the general dependence of microstructure on static and dynamic property relationship was not strongly influenced by chemical composition, except the ferrite plus martensite microstructures generated by the TRIP chemistry, which exhibited
Setterbo, Jacob J.; Chau, Anh; Fyhrie, Patricia B.; Hubbard, Mont; Upadhyaya, Shrini K.; Symons, Jennifer E.; Stover, Susan M.
2012-01-01
Background Racetrack surface is a risk factor for racehorse injuries and fatalities. Current research indicates that race surface mechanical properties may be influenced by material composition, moisture content, temperature, and maintenance. Race surface mechanical testing in a controlled laboratory setting would allow for objective evaluation of dynamic properties of surface and factors that affect surface behavior. Objective To develop a method for reconstruction of race surfaces in the laboratory and validate the method by comparison with racetrack measurements of dynamic surface properties. Methods Track-testing device (TTD) impact tests were conducted to simulate equine hoof impact on dirt and synthetic race surfaces; tests were performed both in situ (racetrack) and using laboratory reconstructions of harvested surface materials. Clegg Hammer in situ measurements were used to guide surface reconstruction in the laboratory. Dynamic surface properties were compared between in situ and laboratory settings. Relationships between racetrack TTD and Clegg Hammer measurements were analyzed using stepwise multiple linear regression. Results Most dynamic surface property setting differences (racetrack-laboratory) were small relative to surface material type differences (dirt-synthetic). Clegg Hammer measurements were more strongly correlated with TTD measurements on the synthetic surface than the dirt surface. On the dirt surface, Clegg Hammer decelerations were negatively correlated with TTD forces. Conclusions Laboratory reconstruction of racetrack surfaces guided by Clegg Hammer measurements yielded TTD impact measurements similar to in situ values. The negative correlation between TTD and Clegg Hammer measurements confirms the importance of instrument mass when drawing conclusions from testing results. Lighter impact devices may be less appropriate for assessing dynamic surface properties compared to testing equipment designed to simulate hoof impact (TTD
Dynamic properties of human tympanic membrane based on frequency-temperature superposition.
Zhang, Xiangming; Gan, Rong Z
2013-01-01
The human tympanic membrane (TM) transfers sound in the ear canal into the mechanical vibration of the ossicles in the middle ear. The dynamic properties of TM directly affect the middle ear transfer function. The static or quasi-static mechanical properties of TM were reported in the literature, but the dynamic properties of TM over the auditory frequency range are very limited. In this paper, a new method was developed to measure the dynamic properties of human TM using the Dynamic-Mechanical Analyzer (DMA). The test was conducted at the frequency range of 1-40 Hz at three different temperatures: 5, 25, and 37 °C. The frequency-temperature superposition was applied to extend the testing frequency range to a much higher level (at least 3800 Hz). The generalized linear solid model was employed to describe the constitutive relation of the TM. The storage modulus E' and the loss modulus E″ were obtained from 11 specimens. The mean storage modulus was 15.1 MPa at 1 Hz and 27.6 MPa at 3800 Hz. The mean loss modulus was 0.28 MPa at 1 Hz and 4.1 MPa at 3800 Hz. The results show that the frequency-temperature superposition is a feasible approach to study the dynamic properties of the ear soft tissues. The dynamic properties of human TM obtained in this study provide a better description of the damping behavior of ear tissues. The properties can be transferred into the finite element model of the human ear to replace the Rayleigh type damping. The data reported here contribute to the biomechanics of the middle ear and improve the accuracy of the FE model for the human ear. PMID:22820983
NASA Astrophysics Data System (ADS)
Weber, Cédric; Haule, Kristjan; Kotliar, Gabriel
2008-10-01
We use the local density approximation in combination with the dynamical mean-field theory to investigate intermediate energy properties of the copper oxides. We identify coherent and incoherent spectral features that result from doping a charge-transfer insulator, namely quasiparticles, Zhang-Rice singlet band, and the upper and lower Hubbard bands. Angle resolving these features, we identify a waterfall-like feature between the quasiparticle part and the incoherent part of the Zhang-Rice band. We investigate the asymmetry between particle and hole doping. On the hole-doped side, there is a very rapid transfer of spectral weight upon doping in the one particle spectra. The optical spectral weight increases superlinearly on the hole-doped side in agreement with experiments.
Measurement of interstage fluid-annulus dynamical properties
NASA Technical Reports Server (NTRS)
Adams, M. L.; Makay, E.; Diaz-Tous, I. A.
1982-01-01
The work described in this paper is part of an Electric Power Research Institute sponsored effort to improve rotor vibrational performance on power plant feed water pumps. A major objective of this effort is to reduce vibration levels by devising inter-stage sealing configurations with optimized damping capacity, realizing that the typical multi-stage centrifugal pump has several ore inter-stage fluid annuli than it has journal bearings. Also, the fluid annuli are distributed between the journal bearings where vibration levels are highest and can therefore be 'exercised' more as dampers than can the bearings. Described in this paper is a test apparatus which has been built to experimentally determine fluid-annulus dynamical coefficients for various configurations of inter-stage sealing geometry.
RAPID DYNAMICAL MASS SEGREGATION AND PROPERTIES OF FRACTAL STAR CLUSTERS
Yu Jincheng; Chen Li; De Grijs, Richard
2011-05-01
We investigate the evolution of young star clusters using N-body simulations. We confirm that subvirial and fractal-structured clusters will dynamically mass segregate on a short timescale (within 0.5 Myr). We adopt a modified minimum-spanning-tree method to measure the degree of mass segregation, demonstrating that the stars escaping from a cluster's potential are important for the temporal dependence of mass segregation in the cluster. The form of the initial velocity distribution will also affect the degree of mass segregation. If it depends on radius, the outer parts of the cluster would expand without undergoing collapse. In velocity space, we find 'inverse mass segregation', which indicates that massive stars have higher velocity dispersions than their lower-mass counterparts.
Dynamical properties of nucleus boundaries in photoinduced structural change
NASA Astrophysics Data System (ADS)
Ishida, Kunio; Nasu, Keiichiro
2014-01-01
Dynamics of the boundaries of photoinduced nuclei in electron-phonon systems is theoretically studied. By regarding the spatial distribution of the excited electronic state population as a geometric pattern, we applied the multifractal analysis to it and calculated the temporal behavior of the fractal dimension f(α) as a function of the Lipschitz-Hölder exponent α, which is an appropriate method for understanding the cooperative relaxation process of photoexcited states. We found that the incubation period observed in various types of photoinduced cooperative phenomena corresponds to the formation of embryonic nuclei which is driven by nonadiabatic/adiabatic transition between electronic states during the relaxation of the Franck-Condon state.
Dynamic properties of structural transition in iron under uniaxial compression.
Shao, J L; Duan, S Q; He, A M; Qin, C S; Wang, P
2009-06-17
By using molecular dynamics simulations, we have successfully simulated the bcc [Formula: see text] hcp structural transition in single-crystal iron under isothermal compression along the [001] direction. The results reveal a distinct softening of C(33) and a hardening of C(31) (or C(32)) prior to the transition and an over-relaxation of the stress after transition. Above the critical stress the morphology evolution of structural transition is analyzed, which can be divided into four stages: hcp homogeneously nucleated, columnar grains formed, nuclei competed and merged, and a laminar structure formed along {110} planes. Besides, our simulations demonstrate that in mixed phases the hcp phase has negative shear stress and the potential of the hcp phase is higher than the bcc phase, and the shear stress of the system keeps a linear decrease with hcp mass fraction. The effect of temperature on the structural transition is also discussed. PMID:21693955
Dynamical properties of ultracold bosons in an optical lattice
Huber, S. D.; Blatter, G.; Altman, E.; Buechler, H. P.
2007-02-15
We study the excitation spectrum of strongly correlated lattice bosons for the Mott-insulating phase and for the superfluid phase close to localization. Within a Schwinger-boson mean-field approach we find two gapped modes in the Mott insulator and the combination of a sound mode (Goldstone) and a gapped (Higgs) mode in the superfluid. To make our findings comparable with experimental results, we calculate the dynamic structure factor as well as the linear response to the optical lattice modulation introduced by Stoeferle et al. [Phys. Rev. Lett. 92, 130403 (2004)]. We find that the puzzling finite frequency absorption observed in the superfluid phase could be explained via the excitation of the gapped (Higgs) mode. We check the consistency of our results with an adapted f-sum rule and propose an extension of the experimental technique by Stoeferle et al. to further verify our findings.
Dynamical properties of nimodipine molecules confined in SBA-15 matrix
NASA Astrophysics Data System (ADS)
Kiwilsza, A.; Pajzderska, A.; Mielcarek, J.; Jenczyk, J.; Wąsicki, J.
2016-08-01
The paper reports results of 13C and 1H ssNMR for nimodipine confined in mesopores of SBA-15 for the samples (i) containing nimodipine molecules inside and on the external surface of silica, (ii) containing nimodipine only inside pores forming an incomplete monolayer on the surface (iii) for bulk nimodipine. The measurements permitted comparison of the dynamics of nimodipine bulk and confined in pores. The confined nimodipine is in an amorphous state and has additional degrees of rotational freedom with respect to the bulk one. The height of the energy barrier related to the rotation of methyl groups in confined nimodipine is lower than in bulk nimodipine. The higher mobility of nimodipine molecules confined in silica pores can explain the higher release rate of nimodipine from silica matrix than dissolution rate of bulk drug.
Coherent Exciton Dynamics in Atomically Thin Semiconductors
NASA Astrophysics Data System (ADS)
Li, Xiaoqin (Elaine)
The near band-edge optical response of an emerging class of semiconductors, known as the transitional metal dichalcogenides (TMDs), is dominated by tightly-bound excitons and charged excitons (i.e. trions). A fundamental property of these quasiparticles (excitons and trions) is quantum decoherence time, which reflects irreversible quantum dissipation arising from system (excitons and trions) and bath (vacuum and other quasiparticles) interactions and determines the timescale during which excitons can be coherently manipulated. Dephasing time is also equivalent to the intrinsic homogeneous linewidth of exciton resonance. In addition, excitons in TMDs are localized at the corners of the Brillouin zone and provide a convenient way to optical manipulate the valley degree of freedom, which may act as a useful information carrier analogous to electronic charge or spin. Direct measurement of valley coherence time is challenging because it corresponds to a non-radiative coherence between two degenerate states. Using ultrafast multi-dimensional optical spectroscopy, we investigate the intrinsic homogeneous linewidth of excitons, exciton valley coherence as well as coupling between excitons and trions. Our studies reveal coherent electronic dynamics on the order of ~100 fs in monolayer TMDs. We gratefully acknowledge financial support from NSF, AFOSR, and the Welch Foundation.
Schwanzer, Dieter F; Coslovich, Daniele; Kahl, Gerhard
2016-10-19
Systems with short-range attractive and long-range repulsive interactions are able to form mesophases at sufficiently low temperatures. In two dimensions, such mesophases emerge as clusters, stripes or bubbles. Using extensive Monte Carlo simulations we investigate the static and the dynamic properties of such a cluster-forming system over a broad temperature range and for different densities. Via the static properties we analyse how ordering into close packed configurations sets in both at the level of the particles as well as at the level of the clusters. The dynamic properties provide information on how, at low temperature, the motion of individual particles is influenced by the dynamic slowing down of the clusters. Finally, we discuss the different diffusion mechanisms at play at low and intermediate densities. PMID:27546155
Analysis of the renormalization of the quasiparticle dispersion in high-Tc superconductors
NASA Astrophysics Data System (ADS)
Li, Jian-Xin; Wang, Z. D.
2005-03-01
Based on the slave-boson approach to the bilayer t-t^'- J model, the renormalization of the quasiparticle dispersion in high-Tc cuprates is investigated by examining both interactions of fermions with spin fluctuations and phonons. It is shown that both interactions can give rise to a kink in the dispersion around the antinodes of the d-wave gap (near (,) and (0,π)). However, three remarkable differences caused by these interactions are found, namely the peak/dip/hump structure in the quasiparticle lineshape, the doping dependence of the quasiparticle weight, and the role played by the interlayer coupling on the formation of the antinodal kink. These differences are suggested to serve as a discriminance to single out the main residual interaction in the superconducting state. A comparison to the recent angle-resolved photoemission (ARPES) experiments shows that the coupling to the spin resonance dominates for quasiparticles around the antinodes. ^1National Laboratory of Solid State of Microstructure and Department of Physics, Nanjing University, Nanjing 210093, China^2Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, China^3The Interdisciplinary Center of Theoretical Studies, Chinese Academy of Science, Beijing 100080, China.
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.
NASA Technical Reports Server (NTRS)
Wei, J. Y. T.; Yeh, N. C.; Vasquez, R. P.
1998-01-01
Scanning tunneling spectroscopy was performed at 4.2K on epitaxial thin-film heterostructures comprising YBa2Cu3O7 and La0.7Ca0.3MnO3, to study the microscopic effects of spin-polarized quasiparticle injection from the half-metallic ferromagnetic manganite on the high-Tc cuprate superconductor.
Ab initio quasiparticle bandstructure of ABA and ABC-stacked graphene trilayers
NASA Astrophysics Data System (ADS)
Menezes, Marcos; Capaz, Rodrigo; Louie, Steven
2013-03-01
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 quasiparticle 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 quasiparticle corrections. Finally, other effects, such as trigonal warping, electron-hole assymetry and energy gaps are discussed in terms of the associated parameters. This work was supported by the Brazilian funding agencies: CAPES, CNPq, FAPERJ and INCT-Nanomateriais de Carbono. It was also supported by NSF grant No. DMR10-1006184 and U.S. DOE under Contract No. DE-AC02-05CH11231.
Static and Dynamic Properties of Ferroelectric Thin Film Memories.
NASA Astrophysics Data System (ADS)
Duiker, Hendrik Matthew
Several properties of ferroelectric thin-film memories have been modeled. First, it has been observed experimentally that the bulk phase KNO_3 has a first-order phase transition, and that the transition temperature of KNO_3 thin-films increases as the thickness of the film is decreased. A Landau theory of first-order phase transitions in bulk systems has been generalized by adding surface terms to the free energy expansion to account for these transition properties. The model successfully describes the observed transition properties and predicts the existence of films in which the surfaces are ordered at temperatures higher than the bulk transition temperature. Second, the Avrami model of polarization-reversal kinetics has been modified to describe the following cases: ferroelectrics composed of a large number of small grains; ferroelectric thin-films in which nucleation occurs at the surfaces, not in the bulk; ferroelectrics in which long-range dipolar interactions significantly affect the nucleation rate; and non-square wave switching pulses. The models were verified by applying them to the results of two-dimensional Ising model simulations. It was shown that the models allow the possibility of directly obtaining microscopic parameters, such as the nucleation rate and domain wall velocity, from bulk measurements. Finally, a model describing the fatigue of ferroelectric memories has been developed. As a ferroelectric memory fatigues the spontaneous polarization per unit volume decreases, the switching time decreases, and eventually the memory "shorts out" and becomes conducting. The model assumes the following: during each polarization reversal the film undergoes, every unit cell in the film has a chance of "degrading" and thus losing an ion. Degraded cells no longer contribute to the polarization. The ions are allowed to diffuse to the surfaces of the film and form, with other ions, conducting dendrites which grow into the bulk of the film. Computer simulations
Transport Properties of Metallic Ruthenates: A DFT +DMFT Investigation
NASA Astrophysics Data System (ADS)
Deng, Xiaoyu; Haule, Kristjan; Kotliar, Gabriel
2016-06-01
We present a systematical theoretical study on the transport properties of an archetypal family of Hund's metals, Sr2RuO4 , Sr3 Ru2 O7 , SrRuO3 , and CaRuO3 , within the combination of first principles density functional theory and dynamical mean field theory. The agreement between theory and experiments for optical conductivity and resistivity is good, which indicates that electron-electron scattering dominates the transport of ruthenates. We demonstrate that in the single-site dynamical mean field approach the transport properties of Hund's metals fall into the scenario of "resilient quasiparticles." We explain why the single layered compound Sr2 RuO4 has a relative weak correlation with respect to its siblings, which corroborates its good metallicity.
Transport Properties of Metallic Ruthenates: A DFT+DMFT Investigation.
Deng, Xiaoyu; Haule, Kristjan; Kotliar, Gabriel
2016-06-24
We present a systematical theoretical study on the transport properties of an archetypal family of Hund's metals, Sr_{2}RuO_{4}, Sr_{3}Ru_{2}O_{7}, SrRuO_{3}, and CaRuO_{3}, within the combination of first principles density functional theory and dynamical mean field theory. The agreement between theory and experiments for optical conductivity and resistivity is good, which indicates that electron-electron scattering dominates the transport of ruthenates. We demonstrate that in the single-site dynamical mean field approach the transport properties of Hund's metals fall into the scenario of "resilient quasiparticles." We explain why the single layered compound Sr_{2}RuO_{4} has a relative weak correlation with respect to its siblings, which corroborates its good metallicity. PMID:27391734
NASA Astrophysics Data System (ADS)
Dass, W.; Merkle, D. H.; Bratton, J. L.
1983-04-01
Constitutive modeling of cohesionless soil for both standard static test conditions and insitu impulsive dynamic load conditions is discussed in this annual report. Predicted laboratory response for several different types of models is evaluated using data from a coordinated testing program. The modeling of insitu soil response to explosive events (CIST and DISC Test) is considered, and the laboratory-derived models are tested for their convenience and accuracy in predicting ground motions. Several important laboratory and insitu phenomena which were not reflected by the model exercises are discussed. Based on the conclusions from this study, testing and modeling requirements for dynamic loading situations are proposed.
Wang, Yufei; Zhang, Xuehua; Li, Dan
2015-12-28
The dynamic configuration of reduced graphene oxide (rGO) in an aqueous dispersion is revealed by several characterization methods, showing a spontaneous and seemingly irreversible configuration transition from flat to highly corrugated sheets over time. Such dynamic behaviour of rGO leads to a tailored porous structure of graphene-based thin films. This affects their permeation and electrochemical properties, as well as future industry adoption of graphene. PMID:26498678
Transformation properties and third-order aberrations of thin dynamic χ(2) holograms
NASA Astrophysics Data System (ADS)
Miloglyadov, E. V.; Stasel'ko, D. I.
2016-07-01
The results of a theoretical study of the transformation properties of thin dynamic χ(2) holograms for all frequency mixing versions are generalized, and a general pattern of transformations of reconstructed images (recorded and read at different frequencies) is developed. The principles of ray geometric construction of reconstructed images are determined. The theory of thin dynamic χ(2) holograms is extended to the range of third-order aberrations.
Laboratory measurements of static and dynamic elastic properties in carbonate
NASA Astrophysics Data System (ADS)
Bakhorji, Aiman M.
S-wave velocities, Gassmann's model consistently over-predict the saturated at low pressure and closely fit the measured velocities at high pressure, whereas, Biot model over-predicts the saturated velocities in most of the studied samples. The strains measured from the vertical and horizontal strain gages are differing by around 27%. The strains over the horizontal axis are higher than the vertical axis suggesting that the majority of the compliant pores and crack-like pores are oriented almost in direction parallel to the length of the sample. The static bulk modulus is always lower than dynamic one for all measured samples. There is no correlation between porosity and static-dynamic ratio. The measured grain bulk modulus obtained from the unjacketed test is reasonably close to the bulk modulus of the constituent mineral phases.
Bio-inspired artificial cilia with magnetic dynamic properties
NASA Astrophysics Data System (ADS)
Sun, Leilei; Zheng, Yongmei
2015-04-01
Inspired by the structure and properties of natural cilia, we focused on a facile template-free approach to prepare magnetic artificial cilia grown on the substrate (glass, PDMS, or others). In an applied magnetic field, the cilia formed spontaneously and immediately from magnetic nanoparticles and elastomeric polymer in a liquid solvent by bottom-up self-assembly. The length of prepared cilia could be in the scale of millimeter and reach a high aspect ratio of even over 100. We studied the effect of the magnetic strength applied and the size of nanoparticles to get tunable scale of cilia. The cilia show reversibly bending in an external magnetic field and this bending actuation gave some important functions: to transport macroscopic nonmagnetic materials on the cilia and to mix liquids.
Dynamic elastic properties of magneto-rheological slurries
NASA Astrophysics Data System (ADS)
Donado, F. F.; Mendoza, M. E. M. E.; Carrillo, J. L.
2001-06-01
We study the propagation of elastic perturbations in magneto-rheological slurries of iron particles dispersed in glycerine. The complexity of these systems is revealed in the fibrillar structure acquired under the application of a magnetic field. Recently, it has been reported the observation of two different low frequency modes of propagation. One of these modes has been associated to the propagation of the perturbation through the fluid medium. The other one has been qualitatively explained as the propagation of the elastic perturbation through the suspended particles. This second mode appears when a magnetic field is applied to the slurry. The propagation speed for both modes depends on the field intensity and on the properties of the magnetic particles. Theoretically, we analyze these modes and calculate the sound velocity. We obtain a quantitative good agreement with the experimental results.
Feedback between node and network dynamics can produce real-world network properties
NASA Astrophysics Data System (ADS)
Brot, Hilla; Muchnik, Lev; Goldenberg, Jacob; Louzoun, Yoram
2012-12-01
Real-world networks are characterized by common features, including among others a scale-free degree distribution, a high clustering coefficient and a short typical distance between nodes. These properties are usually explained by the dynamics of edge and node addition and deletion. In a different context, the dynamics of node content within a network has been often explained via the interaction between nodes in static networks, ignoring the dynamic aspect of edge addition and deletion. We here propose to combine the dynamics of the node content and of edge addition and deletion, using a threshold automata framework. Within this framework, we show that the typical properties of real-world networks can be reproduced with a Hebbian approach, in which nodes with similar internal dynamics have a high probability of being connected. The proper network properties emerge only if an imbalance exists between excitatory and inhibitory connections, as is indeed observed in real networks. We further check the plausibility of the suggested mechanism by observing an evolving social network and measuring the probability of edge addition as a function of the similarity between the contents of the corresponding nodes. We indeed find that similarity between nodes increases the emergence probability of a new link between them. The current work bridges between multiple important domains in network analysis, including network formation processes, Kaufmann Boolean networks and Hebbian learning. It suggests that the properties of nodes and the network convolve and can be seen as complementary parts of the same process.
Nanocrystalline silicon: Lattice dynamics and enhanced thermoelectric properties
Claudio, Tania; Stein, Niklas; Stroppa, Daniel G.; Klobes, Benedikt; Koza, Michael Marek; Kudejova, Petra; Petermann, Nils; Wiggers, Hartmut; Schierning, Gabi; Hermann, Raphaël P.
2014-12-21
In this study, silicon has several advantages when compared to other thermoelectric materials, but until recently it was not used for thermoelectric applications due to its high thermal conductivity, 156 W K-1 m-1 at room temperature. Nanostructuration as means to decrease thermal transport through enhanced phonon scattering has been a subject of many studies. In this work we have evaluated the effects of nanostructuration on the lattice dynamics of bulk nanocrystalline doped silicon. The samples were prepared by gas phase synthesis, followed by current and pressure assisted sintering. The heat capacity, density of phonons states, and elastic constants were measured,more » which all reveal a significant, ≈25%, reduction in the speed of sound. The samples present a significantly decreased lattice thermal conductivity, ≈25 W K-1 m-1, which, combined with a very high carrier mobility, results in a dimensionless figure of merit with a competitive value that peaks at ZT ≈ 0.57 at 973 °C. Due to its easily scalable and extremely low-cost production process, nanocrystalline Si prepared by gas phase synthesis followed by sintering could become the material of choice for high temperature thermoelectric generators.« less
Nanocrystalline silicon: Lattice dynamics and enhanced thermoelectric properties
Claudio, Tania; Stein, Niklas; Stroppa, Daniel G.; Klobes, Benedikt; Koza, Michael Marek; Kudejova, Petra; Petermann, Nils; Wiggers, Hartmut; Schierning, Gabi; Hermann, Raphaël P.
2014-12-21
In this study, silicon has several advantages when compared to other thermoelectric materials, but until recently it was not used for thermoelectric applications due to its high thermal conductivity, 156 W K^{-1} m^{-1} at room temperature. Nanostructuration as means to decrease thermal transport through enhanced phonon scattering has been a subject of many studies. In this work we have evaluated the effects of nanostructuration on the lattice dynamics of bulk nanocrystalline doped silicon. The samples were prepared by gas phase synthesis, followed by current and pressure assisted sintering. The heat capacity, density of phonons states, and elastic constants were measured, which all reveal a significant, ≈25%, reduction in the speed of sound. The samples present a significantly decreased lattice thermal conductivity, ≈25 W K^{-1} m^{-1}, which, combined with a very high carrier mobility, results in a dimensionless figure of merit with a competitive value that peaks at ZT ≈ 0.57 at 973 °C. Due to its easily scalable and extremely low-cost production process, nanocrystalline Si prepared by gas phase synthesis followed by sintering could become the material of choice for high temperature thermoelectric generators.
Physical properties of components in multiple stars and their dynamics
NASA Astrophysics Data System (ADS)
Zhuchkov, R. Ya.; Kiyaeva, O. V.; Orlov, V. V.; Malogolovets, E. V.; Balega, Yu. Yu.; Bikmaev, I. F.
2013-05-01
We have considered a few multiple stars which have a weak hierarchy: HD 40887, HD 76644 (ι UMa), HD 136176, HD 150680, HD 217675 (o And), HD 222326, and HD 284419 (T Tau). We have calculated the masses of components and orbital elements of the subsystems, using data from the literature and original observations by the 1.5-m Russian-Turkey Telescope RTT 150 at Tubitak (spectroscopic observations) and 6-m telescope BTA in the Special Astrophysical Observatory (speckle interferometry). We have determined the structure and multiplicity of the systems more accurately. For system HD 222326, the new component was confirmed, so the system is quadruple. The spectroscopic observations were used to obtain new estimates of the component masses. The speckle-interferometric data were attracted to calculate the orbital parameters for close subsystems. The orbital parameters were found by classical Thiele-Innes method and apparent motion parameter method developed in Pulkovo Observatory. To determine the dynamical stability of the systems, we have applied the well-known stability criteria for triple systems, as well as the numerical simulations of the N-body problem. The stability and instability regions were outlined within the set of orbital parameters and masses. The unstable scenario is probable for the quadruple system HD~76644. Other systems are probably stable. We discuss possible reasons to violate the stability. Also we discuss possible future efforts in studies of multiple stars.
Molecular-dynamics calculations of thermodynamic properties of metastable alloys
Mazzone, G.; Rosato, V.; Pintore, M.; Delogu, F.; Demontis, P.; Suffritti, G.B.
1997-01-01
In order to improve our current understanding of the microscopic structure of metastable alloys of immiscible elements such as Ag-Cu and Co-Cu, the Helmholtz free energy of several microstructures based on an fcc unit cell has been calculated and compared with that of a reference state. The microstructures considered for the free energy calculations at fixed volume are (1) a structure formed by alternating layers of fixed thickness of metal 1 and metal 2 separated by coherent interfaces; (2) an atomically disordered solid solution; (3) a structure comprising a random distribution of elemental cubic grains separated by coherent interfaces. Numerical results show that the Helmholtz free energy of structure (3) decreases with increasing grain size and that its value calculated for a sufficiently large grain size approaches the free energy of structure (1). Further molecular-dynamics simulations for the Ag-Cu system have allowed the calculation of the enthalpy at the equilibrium volume of several microstructures including some of those listed above. A comparison of the calculated values of the enthalpy with the heat release observed experimentally allows the advancement of an hypothesis concerning the reaction path and the structure of the equiatomic Ag-Cu alloy obtained by ball milling.
Dynamical properties and chaos synchronization of improved Colpitts oscillators
NASA Astrophysics Data System (ADS)
Kengne, J.; Chedjou, J. C.; Kenne, G.; Kyamakya, K.
2012-07-01
In this paper, the dynamics and synchronization of improved Colpitts oscillators designed to operate in ultrahigh frequency range are considered. The model is described by a continuous time four-dimensional autonomous system with an exponential nonlinearity. The system is integrated numerically and various bifurcation diagrams and corresponding graphs of largest 1D Lyapunov exponent are plotted to summarize different scenarios leading to chaos. It is found that the oscillator moves from the state of fixed point motion to chaos via the usual paths of period-doubling, intermittency and interior crisis routes when monitoring the bias (i.e. power supply) in tiny ranges. In order to promote chaos-based synchronization designs of this type of oscillators, a synchronization strategy based upon the design of a nonlinear state observer is successfully adapted. The suggested approach enables synchronization to be achieved via a scalar transmitted signal which represents a suitable feature for communication applications. Numerical simulations are performed to demonstrate the effectiveness and feasibility of the proposed technique.
Characterization of Sensory Properties of Flavanols - A Molecular Dynamic Approach.
Ferrer-Gallego, Raúl; Quijada-Morín, Natalia; Brás, Natércia F; Gomes, Paula; de Freitas, Victor; Rivas-Gonzalo, Julián C; Escribano-Bailón, M Teresa
2015-07-01
In this work, sensations elicited by catechin and procyanidins in comparison with those elicited by gallocatechin and prodelphinidins were evaluated by means of a sensory panel. To obtain further insights into the mechanisms of action, molecular dynamics (MD) simulations and saturation transfer difference nuclear magnetic resonance (STD NMR) experiments have been performed. Results showed clear differences between the 2 types of flavanols. Dihydroxylated B-ring flavanols were more astringent, bitter, dry, rough, unripe, and persistent than trihydroxylated B-ring ones. Besides, these last compounds were smoother, more velvety, and viscous. MD simulations and STD NMR experiments support results obtained from tasting panel. MD results suggested that catechin binds to a human salivary proline-rich peptide IB714 faster than gallocatechin and this interaction is maintained longer. IB714 can interact with 2 catechin molecules concurrently while only interacts with 1 gallocatechin molecule. Accordingly, STD NMR experiments showed a greater affinity of catechin than gallocatechin for the peptide (K D = 2.7 and 25.7, respectively). Results indicate that the number of hydroxyl substituents present in B-ring of the flavanic nucleus is decisive for the interaction with salivary proteins and the development of astringency perception. PMID:25934978
Dynamic Properties of Shock Loaded Thin Uranium Foils
NASA Astrophysics Data System (ADS)
Robbins, David L.; Kelly, Ann M.; Alexander, David J.; Hanrahan, Robert J.; Snow, Ronny C.; Gehr, Russell J.; Rupp, Ted D.; Sheffield, Stephen A.; Stahl, David B.
2002-07-01
A series of spall experiments has been completed with thin depleted uranium targets, nominally 0.1 mm thick. The first set of uranium spall targets was cut and ground to final thickness from electro-refined, high-purity, cast uranium. The second set was rolled to final thickness from low purity uranium. The impactors for these experiments were laser-launched 0.05-mm thick copper flyers, 3 mm in diameter. Laser energies were varied to yield a range of flyer impact velocities. This resulted in varying degrees of damage to the uranium targets, from deformation to complete spall or separation at the higher velocities. Dynamic measurements of the uranium target free surface velocities were obtained with dual velocity interferometers. Uranium targets were recovered and sectioned after testing. Free surface velocity profiles were similar for the two types of uranium, but spall strengths (estimated from the magnitude of the pull-back signal) are higher for the high-purity cast uranium. Velocity profiles and microstructural evidence of spall from the sectioned uranium targets are presented.
Phonon properties of graphene derived from molecular dynamics simulations
Koukaras, Emmanuel N.; Kalosakas, George; Galiotis, Costas; Papagelis, Konstantinos
2015-01-01
A method that utilises atomic trajectories and velocities from molecular dynamics simulations has been suitably adapted and employed for the implicit calculation of the phonon dispersion curves of graphene. Classical potentials widely used in the literature were employed. Their performance was assessed for each individual phonon branch and the overall phonon dispersion, using available inelastic x-ray scattering data. The method is promising for systems with large scale periodicity, accounts for anharmonic effects and non-bonding interactions with a general environment, and it is applicable under finite temperatures. The temperature dependence of the phonon dispersion curves has been examined with emphasis on the doubly degenerate Raman active Γ-E2g phonon at the zone centre, where experimental results are available. The potentials used show diverse behaviour. The Tersoff-2010 potential exhibits the most systematic and physically sound behaviour in this regard, and gives a first-order temperature coefficient of χ = −0.05 cm−1/K for the Γ-E2g shift in agreement with reported experimental values. PMID:26316252
The Dynamical Properties of Virgo Cluster Disk Galaxies
NASA Astrophysics Data System (ADS)
Ouellette, N. N. Q.; Courteau, S.; Holtzman, J. A.; Dalcanton, J. J.; McDonald, M.; Zhu, Y.
2014-03-01
By virtue of its proximity, the Virgo Cluster is an ideal laboratory for testing our understanding of structure formation in the Universe. In this spirit, we present a dynamical study of Virgo galaxies as part of the Spectroscopic and H-band Imaging of Virgo (SHIVir) survey. Hα rotation curves (RC) for our gas-rich galaxies were modeled with a multi-parameter fit function from which various velocity measurements were inferred. Our study takes advantage of archival and our own new data as we aim to compile the largest Tully-Fisher relation (TFR) for a cluster to date. Extended velocity dispersion profiles (VDP) are integrated over varying aperture sizes to extract representative velocity dispersions (VDs) for gas-poor galaxies. Considering the lack of a common standard for the measurement of a fiducial galaxy VD in the literature, we rectify this situation by determining the radius at which the measured VD yields the tightest Fundamental Plane (FP). We found that radius to be at least 1 Re, which exceeds the extent of most dispersion profiles in other works.
Nanocrystalline silicon: lattice dynamics and enhanced thermoelectric properties.
Claudio, Tania; Stein, Niklas; Stroppa, Daniel G; Klobes, Benedikt; Koza, Michael Marek; Kudejova, Petra; Petermann, Nils; Wiggers, Hartmut; Schierning, Gabi; Hermann, Raphaël P
2014-12-21
Silicon has several advantages when compared to other thermoelectric materials, but until recently it was not used for thermoelectric applications due to its high thermal conductivity, 156 W K(-1) m(-1) at room temperature. Nanostructuration as means to decrease thermal transport through enhanced phonon scattering has been a subject of many studies. In this work we have evaluated the effects of nanostructuration on the lattice dynamics of bulk nanocrystalline doped silicon. The samples were prepared by gas phase synthesis, followed by current and pressure assisted sintering. The heat capacity, density of phonons states, and elastic constants were measured, which all reveal a significant, ≈25%, reduction in the speed of sound. The samples present a significantly decreased lattice thermal conductivity, ≈25 W K(-1) m(-1), which, combined with a very high carrier mobility, results in a dimensionless figure of merit with a competitive value that peaks at ZT≈ 0.57 at 973 °C. Due to its easily scalable and extremely low-cost production process, nanocrystalline Si prepared by gas phase synthesis followed by sintering could become the material of choice for high temperature thermoelectric generators. PMID:24848359
Wang, Yuliang; Wang, Huimin; Bi, Shusheng; Guo, Bin
2016-01-01
The dynamic wetting properties of atomic force microscopy (AFM) tips are of much concern in many AFM-related measurement, fabrication, and manipulation applications. In this study, the wetting properties of silicon and silicon nitride AFM tips are investigated through dynamic contact angle measurement using a nano-Wilhelmy balance based method. This is done by capillary force measurement during extension and retraction motion of AFM tips relative to interfacial nanobubbles. The working principle of the proposed method and mathematic models for dynamic contact angle measurement are presented. Geometric models of AFM tips were constructed using scanning electronic microscopy (SEM) images taken from different view directions. The detailed process of tip-nanobubble interaction was investigated using force-distance curves of AFM on nanobubbles. Several parameters including nanobubble height, adhesion and capillary force between tip and nanobubbles are extracted. The variation of these parameters was studied over nanobubble surfaces. The dynamic contact angles of the AFM tips were calculated from the capillary force measurements. The proposed method provides direct measurement of dynamic contact angles for AFM tips and can also be taken as a general approach for nanoscale dynamic wetting property investigation. PMID:27452115
NASA Astrophysics Data System (ADS)
Bekele, Selemon; Tsige, Mesfin
Surfaces of polymers such as atactic polystyrene (aPS) represent very good model systems for amorphous material surfaces. Such polymer surfaces are usually modified either chemically or physically for a wide range of applications that include friction, lubrication and adhesion. It is thus quite important to understand the structural and dynamical properties of liquids that come in contact with them to achieve the desired functional properties. Using molecular dynamics (MD) simulations, we investigate the structural and dynamical properties of water molecules in a slab of water in contact with atactic polystyrene surfaces of varying polarity. We find that the density of water molecules and the number distribution of hydrogen bonds as a function of distance relative to an instantaneous surface exhibit a structure indicative of a layering of water molecules near the water/PS interface. For the dynamics, we use time correlation functions of hydrogen bonds and the incoherent structure function for the water molecules. Our results indicate that the polarity of the surface dramatically affects the dynamics of the interfacial water molecules with the dynamics slowing down with increasing polarity. This work was supported by NSF Grant DMR1410290.
Wang, Yuliang; Wang, Huimin; Bi, Shusheng; Guo, Bin
2016-01-01
The dynamic wetting properties of atomic force microscopy (AFM) tips are of much concern in many AFM-related measurement, fabrication, and manipulation applications. In this study, the wetting properties of silicon and silicon nitride AFM tips are investigated through dynamic contact angle measurement using a nano-Wilhelmy balance based method. This is done by capillary force measurement during extension and retraction motion of AFM tips relative to interfacial nanobubbles. The working principle of the proposed method and mathematic models for dynamic contact angle measurement are presented. Geometric models of AFM tips were constructed using scanning electronic microscopy (SEM) images taken from different view directions. The detailed process of tip-nanobubble interaction was investigated using force-distance curves of AFM on nanobubbles. Several parameters including nanobubble height, adhesion and capillary force between tip and nanobubbles are extracted. The variation of these parameters was studied over nanobubble surfaces. The dynamic contact angles of the AFM tips were calculated from the capillary force measurements. The proposed method provides direct measurement of dynamic contact angles for AFM tips and can also be taken as a general approach for nanoscale dynamic wetting property investigation. PMID:27452115
NASA Astrophysics Data System (ADS)
Wang, Yuliang; Wang, Huimin; Bi, Shusheng; Guo, Bin
2016-07-01
The dynamic wetting properties of atomic force microscopy (AFM) tips are of much concern in many AFM-related measurement, fabrication, and manipulation applications. In this study, the wetting properties of silicon and silicon nitride AFM tips are investigated through dynamic contact angle measurement using a nano-Wilhelmy balance based method. This is done by capillary force measurement during extension and retraction motion of AFM tips relative to interfacial nanobubbles. The working principle of the proposed method and mathematic models for dynamic contact angle measurement are presented. Geometric models of AFM tips were constructed using scanning electronic microscopy (SEM) images taken from different view directions. The detailed process of tip-nanobubble interaction was investigated using force-distance curves of AFM on nanobubbles. Several parameters including nanobubble height, adhesion and capillary force between tip and nanobubbles are extracted. The variation of these parameters was studied over nanobubble surfaces. The dynamic contact angles of the AFM tips were calculated from the capillary force measurements. The proposed method provides direct measurement of dynamic contact angles for AFM tips and can also be taken as a general approach for nanoscale dynamic wetting property investigation.
Lattice dynamics and thermoelectric properties of nanocrystalline silicon-germanium alloys
Claudio, Tania; Stein, Niklas; Peterman, Nils; Stroppa, Daniel; Koza, Michael M.; Wiggers, Hartmut; Klobes, B.; Schierning, Gabi; Hermann, Raphael P.
2015-10-26
The lattice dynamics and thermoelectric properties of sintered phosphorus-doped nanostructured silicon- germanium alloys obtained by gas-phase synthesis were studied. Measurements of the density of phonon states by inelastic neutron scattering were combined with measurements of the elastic constants and the low- temperature heat capacity. A strong influence of nanostructuring and alloying on the lattice dynamics was observed. The thermoelectric transport properties of samples with different doping as well as samples sintered at different temperature were characterized between room temperature and 1000C. A peak figure of merit zT = 0:88 at 900C is observed and comparatively insensitive to the aforementioned param- eter variations.
Avalanche properties in a transport model based on critical-gradient fluctuation dynamics
Garcia, L.; Carreras, B.A.
2005-09-15
A simple one-dimensional transport model based on critical-gradient fluctuation dynamics is applied to describe some of the properties of plasma-turbulence-induced transport. This model combines avalanche-like transport with diffusion. The particle flux is self-regulated by the stability properties of the fluctuations. A high-gradient edge region emerges where transport dynamics is close to marginal stability. In steady state, the core remains at the subcritical gradient. The avalanches change from quasiperiodic events triggered mostly near the edge region to intermittent transport events depending on the noise level of the particle source.
NASA Technical Reports Server (NTRS)
Grauer, Jared A.; Morelli, Eugene A.
2013-01-01
A nonlinear simulation of the NASA Generic Transport Model was used to investigate the effects of errors in sensor measurements, mass properties, and aircraft geometry on the accuracy of dynamic models identified from flight data. Measurements from a typical system identification maneuver were systematically and progressively deteriorated and then used to estimate stability and control derivatives within a Monte Carlo analysis. Based on the results, recommendations were provided for maximum allowable errors in sensor measurements, mass properties, and aircraft geometry to achieve desired levels of dynamic modeling accuracy. Results using other flight conditions, parameter estimation methods, and a full-scale F-16 nonlinear aircraft simulation were compared with these recommendations.
Stiffness and energy dissipation characteristics of guyed tower with dynamic mooring properties
Morrison, D.G.
1984-03-01
A simple model for a complex system is presented that contains the essential properties of the guyed tower. The dynamic response to wave load of a guyed tower is represented by a single degree of freedom model. Tower response, with different wave heights and hydrodynamic coefficients, using statically and dynamically determined mooring properties were calculated for a specific tower in 1100 ft (335 m) of water. The importance of this study lies in a good modeling of the cable forces, including the hysteretic effects of line damping, and in identifying cases where the quasi-static model may fail.
Impact and dynamic mechanical thermal properties of textile silk reinforced epoxy resin composites
NASA Astrophysics Data System (ADS)
Yang, K.; Guan, J.
2016-07-01
Silk fabric reinforced epoxy resin composites (SFRPs) were prepared using simple techniques of hand lay-up, hot-press and vacuum treatment, and a series of volume fractions of silk reinforcements were achieved. The impact properties and dynamic mechanical properties of SFRPs were investigated using a pendulum impact testing method and dynamic mechanical thermal analysis (DMTA). The results suggest that silk reinforcement could greatly enhance the mechanical performances of SFRPs. The impact strength reached a maximum of 71 kJ/m2 for 60%-silk SFRP, which demonstrated a potential of silk composites for defence and impact- resistant materials.
NASA Astrophysics Data System (ADS)
Zhao, G.; Mu, H. F.
2014-11-01
Using ab initio molecular dynamics simulations, the pressure dependence of structural and dynamical properties in melt sulfur along 1085 K isotherm was studied with pressure range from 4.18 to 15.8 GPa. It was found that the atomic chains in melt sulfur abruptly break twice with increasing pressure. The electric density of state near EF and the diffusion coefficient both show abrupt increase along with these two times of breakages. These changes would strongly influence the physical properties such as conductivity and viscosity. However, the density discontinuity along the isotherm, indication of a first-order phase transition, was not found.
Dynamic Mechanical Properties of Intact Human Cervical Spine Ligaments
Ivancic, Paul C.; Coe, Marcus P.; Ndu, Anthony B.; Tominaga, Yasuhiro; Carlson, Erik J.; Rubin, Wolfgang; (FH), Dipl-Ing; Panjabi, Manohar M.
2009-01-01
BACKGROUND CONTEXT Most previous studies have investigated ligaments mechanical properties at slow elongation rates of less than 25 mm/s. PURPOSE To determine the tensile mechanical properties, at a fast elongation rate, of intact human cervical anterior and posterior longitudinal, capsular, and interspinous and supraspinous ligaments, middle-third disc, and ligamentum flavum. STUDY DESIGN/SETTING In vitro biomechanical study. METHODS A total of 97 intact bone-ligament-bone specimens (C2–C3 to C7-T1) were prepared from six cervical spines (average age: 80.6 years, range, 71 to 92 years) and were elongated to complete rupture at an average (SD) peak rate of 723 (106) mm/s using a custom-built apparatus. Non-linear force vs. elongation curves were plotted and peak force, peak elongation, peak energy, and stiffness were statistically compared (P<0.05) among ligament. A mathematical model was developed to determine the quasi-static physiological ligament elongation. RESULTS Highest average peak force, up to 244.4 and 220.0 N in the ligamentum flavum and capsular ligament, respectively, were significantly greater than in the anterior longitudinal ligament and middle-third disc. Highest peak elongation reached 5.9 mm in the intraspinous and supraspinous ligaments, significantly greater than in the middle-third disc. Highest peak energy of 0.57 J was attained in the capsular ligament, significantly greater than in the anterior longitudinal ligament and middle-third disc. Average stiffness was generally greatest in the ligamentum flavum and least in the intraspinous and supraspinous ligaments. For all ligaments, peak elongation was greater than average physiological elongation computed using the mathematical model. CONCLUSIONS Comparison of the present results with previously reported data indicated that high speed elongation may cause cervical ligaments to fail at a higher peak force and smaller peak elongation and may be stiffer and absorb less energy, as compared to a
Dynamical properties of the hydration shell of fully deuterated myoglobin
NASA Astrophysics Data System (ADS)
Achterhold, Klaus; Ostermann, Andreas; Moulin, Martine; Haertlein, Michael; Unruh, Tobias; Parak, Fritz G.
2011-10-01
Freeze-dried perdeuterated sperm whale myoglobin was kept in a water-saturated atmosphere in order to obtain a hydration degree of 335 1H2O molecules per one myoglobin molecule. Incoherent neutron scattering was performed at the neutron spectrometer TOFTOF at the FRM II in an angular range of q from 0.6 to 1.8 Å-1 and a temperature range from 4 to 297 K. We used neutrons with a wavelength of λ αE 6 Å and an energy resolution of about 65 μeV corresponding to motions faster than 10 ps. At temperatures above 225 K, broad lines appear in the spectra caused by quasielastic scattering. For an explanation of these lines, we assumed that there are only two types of protons, those that are part of the hydration water (72%) and those that belong to the protein (28%). The protons of the hydration water were analyzed with the diffusion model of Singwi and Sjölander [Phys. Rev.PHRVAO0031-899X10.1103/PhysRev.119.863 119, 863 (1960)]. In this model, a water molecule stays for a time τ0 in a bound state performing oscillatory motions. Thereafter, the molecule performs free diffusion for the time τ1 in a nonbound state followed again by the oscillatory motions for τ0 and so forth. We used the general formulation with no simplifications as τ0≫τ1 or τ1≫τ0. At room temperature, we obtained τ0 αE 104 ps and τ1 αE 37 ps. For the protein bound hydrogen, the dynamics is described by a Brownian oscillator where the protons perform overdamped motions in limited space.
Dynamical properties of the hydration shell of fully deuterated myoglobin
Achterhold, Klaus; Parak, Fritz G.; Ostermann, Andreas; Moulin, Martine; Haertlein, Michael; Unruh, Tobias
2011-10-15
Freeze-dried perdeuterated sperm whale myoglobin was kept in a water-saturated atmosphere in order to obtain a hydration degree of 335 {sup 1}H{sub 2}O molecules per one myoglobin molecule. Incoherent neutron scattering was performed at the neutron spectrometer TOFTOF at the FRM II in an angular range of q from 0.6 to 1.8 A{sup -1} and a temperature range from 4 to 297 K. We used neutrons with a wavelength of {lambda}{alpha}E 6 A and an energy resolution of about 65 {mu}eV corresponding to motions faster than 10 ps. At temperatures above 225 K, broad lines appear in the spectra caused by quasielastic scattering. For an explanation of these lines, we assumed that there are only two types of protons, those that are part of the hydration water (72%) and those that belong to the protein (28%). The protons of the hydration water were analyzed with the diffusion model of Singwi and Sjoelander [Phys. Rev. 119, 863 (1960)]. In this model, a water molecule stays for a time {tau}{sub 0} in a bound state performing oscillatory motions. Thereafter, the molecule performs free diffusion for the time {tau}{sub 1} in a nonbound state followed again by the oscillatory motions for {tau}{sub 0} and so forth. We used the general formulation with no simplifications as {tau}{sub 0}>>{tau}{sub 1} or {tau}{sub 1}>>{tau}{sub 0}. At room temperature, we obtained {tau}{sub 0} {alpha}E 104 ps and {tau}{sub 1} {alpha}E 37 ps. For the protein bound hydrogen, the dynamics is described by a Brownian oscillator where the protons perform overdamped motions in limited space.
The effects of dynamic stretching on plantar flexor muscle-tendon tissue properties.
Samukawa, Mina; Hattori, Masaki; Sugama, Naoko; Takeda, Naoki
2011-12-01
Dynamic stretching is commonly used in warm-up routines for athletic activities. Even though several positive effects of dynamic stretching on athletic performance have been reported, the effects on the muscle-tendon unit (MTU) itself are still unclear. The objective of this study is to determine the effects of dynamic stretching on the ankle plantar flexor muscle-tendon properties by use of ultrasonography. Twenty healthy male subjects participated in the present study. The subjects were asked to engage in dynamic stretching of plantar flexors for 30 s and to repeat for 5 sets. Ankle dorsiflexion ROM was measured before and after the dynamic stretching. Changes in the displacement of the myotendinous junction (MTJ), pennation angle, and fascicle length were also determined by using ultrasonography. Ankle dorsiflexion ROM increased significantly after the dynamic stretching (p < 0.0001). A significant distal displacement of the MTJ was observed until the second stretching set (p < 0.001) with no significant changes thereafter. Pennation angle, and fascicle length were unaffected by the dynamic stretching. Dynamic stretching was shown to be effective in increasing ankle joint flexibility. Outcomes that could have indicated changes in muscle tissue (such as the pennation angle and fascicle length) were unaltered. However, a significant displacement of the MTJ was found, indicating some change in the tendon tissues. Therefore, dynamic stretching of the plantar flexors was considered an effective means of lengthening the tendon tissues. PMID:21813313
Lattice Dynamical Properties of Ferroelectric Thin Films at the Nanoscale
Xi, Xiaoxing
2014-01-13
In this project, we have successfully demonstrated atomic layer-by-layer growth by laser MBE from separate targets by depositing SrTiO3 films from SrO and TiO2 targets. The RHEED intensity oscillation was used to monitor and control the growth of each SrO and TiO2 layer. We have shown that by using separate oxide targets, laser MBE can achieve the same level of stoichiometry control as the reactive MBE. We have also studied strain relaxation in LaAlO3 films and its effect on the 2D electron gas at LaAlO3/SrTiO3 interface. We found that there are two layers of different in-plane lattice constants in the LaAlO3 films, one next to the SrTiO3 substrate nearly coherently strained, while the top part relaxed as the film thickness increases above 20 unit cells. This strain relaxation significantly affect the transport properties of the LaAlO3/SrTiO3 interface.
Dynamical and structural properties of benzene in supercritical water.
Nieto-Draghi, Carlos; Bonet Avalos, Josep; Contreras, Oliver; Ungerer, Philippe; Ridard, Jacqueline
2004-12-01
We have employed an anisotropic united atom model of benzene (R. O. Contreras, Ph.D. thesis, Universitat Rovira i Virgili 2002) that reproduces the quadrupolar moment of this molecule through the inclusion of seven point charges. We show that this kind of interaction is required to reproduce the solvation of these molecules in supercritical water. We have computed self-diffusion coefficient and Maxwell-Stefan coefficients as well as the shear viscosity for the mixture water-benzene at supercritical conditions. A strong density and composition dependence of these properties is observed. In addition, our simulations are in qualitative agreement with the experimental evidence that, at medium densities (0.6 g/cm(3) and 673 K), almost half of the benzene molecules have one hydrogen bond with water molecules. We also observe that these bonds are longer lived than the corresponding hydrogen bonds between water molecules. Similarly, we obtain an important reduction of the dielectric constant of the mixture with the increment of the amount of benzene molecules at medium and high densities. PMID:15549940
Dynamic biaxial tissue properties of the human cadaver aorta.
Shah, Chirag S; Hardy, Warren N; Mason, Matthew J; Yang, King H; Van Ee, Chris A; Morgan, Richard; Digges, Kennerly
2006-11-01
This study focuses on the biaxial mechanical properties of planar aorta tissue at strain rates likely to be experienced during automotive crashes. It also examines the structural response of the whole aorta to longitudinal tension. Twenty-six tissue-level tests were conducted using twelve thoracic aortas harvested from human cadavers. Cruciate samples were excised from the ascending, peri-isthmic, and descending regions. The samples were subjected to equibiaxial stretch at two nominal speed levels using a new biaxial tissue-testing device. Inertia-compensated loads were measured to facilitate calculation of true stress. High-speed videography and regional correlation analysis were used to track ink dots marked on the center of each sample to obtain strain. In a series of component-level tests, the response of the intact thoracic aorta to longitudinal stretch was obtained using seven aorta specimens. The aorta fails within the peri-isthmic region. The aorta fails in the transverse direction, and the intima fails before the media or adventitia. The aorta tissue exhibits nonlinear behavior. The aorta as complete structure can transect completely from 92 N axial load and 0.221 axial strain. Complete transection can be accompanied by intimal tears. These results have application to finite element modeling and the better understanding of traumatic rupture of the aorta. PMID:17311166
Dynamic properties of small-scale solar wind plasma fluctuations
Riazantseva, M. O.; Budaev, V. P.; Zelenyi, L. M.; Zastenker, G. N.; Pavlos, G. P.; Safrankova, J.; Nemecek, Z.; Prech, L.; Nemec, F.
2015-01-01
The paper presents the latest results of the studies of small-scale fluctuations in a turbulent flow of solar wind (SW) using measurements with extremely high temporal resolution (up to 0.03 s) of the bright monitor of SW (BMSW) plasma spectrometer operating on astrophysical SPECTR-R spacecraft at distances up to 350 000 km from the Earth. The spectra of SW ion flux fluctuations in the range of scales between 0.03 and 100 s are systematically analysed. The difference of slopes in low- and high-frequency parts of spectra and the frequency of the break point between these two characteristic slopes was analysed for different conditions in the SW. The statistical properties of the SW ion flux fluctuations were thoroughly analysed on scales less than 10 s. A high level of intermittency is demonstrated. The extended self-similarity of SW ion flux turbulent flow is constantly observed. The approximation of non-Gaussian probability distribution function of ion flux fluctuations by the Tsallis statistics shows the non-extensive character of SW fluctuations. Statistical characteristics of ion flux fluctuations are compared with the predictions of a log-Poisson model. The log-Poisson parametrization of the structure function scaling has shown that well-defined filament-like plasma structures are, as a rule, observed in the turbulent SW flows. PMID:25848078
Dynamic properties of small-scale solar wind plasma fluctuations.
Riazantseva, M O; Budaev, V P; Zelenyi, L M; Zastenker, G N; Pavlos, G P; Safrankova, J; Nemecek, Z; Prech, L; Nemec, F
2015-05-13
The paper presents the latest results of the studies of small-scale fluctuations in a turbulent flow of solar wind (SW) using measurements with extremely high temporal resolution (up to 0.03 s) of the bright monitor of SW (BMSW) plasma spectrometer operating on astrophysical SPECTR-R spacecraft at distances up to 350,000 km from the Earth. The spectra of SW ion flux fluctuations in the range of scales between 0.03 and 100 s are systematically analysed. The difference of slopes in low- and high-frequency parts of spectra and the frequency of the break point between these two characteristic slopes was analysed for different conditions in the SW. The statistical properties of the SW ion flux fluctuations were thoroughly analysed on scales less than 10 s. A high level of intermittency is demonstrated. The extended self-similarity of SW ion flux turbulent flow is constantly observed. The approximation of non-Gaussian probability distribution function of ion flux fluctuations by the Tsallis statistics shows the non-extensive character of SW fluctuations. Statistical characteristics of ion flux fluctuations are compared with the predictions of a log-Poisson model. The log-Poisson parametrization of the structure function scaling has shown that well-defined filament-like plasma structures are, as a rule, observed in the turbulent SW flows. PMID:25848078
Dynamical thermoelectric properties of doped AA-stacked bilayer graphene
NASA Astrophysics Data System (ADS)
Rezania, Hamed; Yarmohammadi, Mohsen
2016-01-01
The frequency dependence of thermoelectric properties of doped biased bilayer graphene are investigated using the Green's function approach in the context of tight-binding model. We find that the thermoelectric figure of merit (ZT) can be remarkably enhanced by electronic chemical potential, temperature, bias voltage and frequency. The electronic contribution to thermal conductivity of doped materials is dominant and therefore we have considered this contribution. The improvement due to the combined increase in the Seebeck coefficient and the reduction in the thermal conductivity outweighing the decrease in the electrical conductance is studied. We have found a good ZT value for normal conditions in the lab, i.e, for room temperature (RT), high bias voltages and low frequencies. We have found the temperature dependence of ZT for different values of frequency, bias voltage and chemical potential. Also the dependence of ZT on the chemical potential and bias voltage has been investigated in details. The calculated ZT values qualify bilayer graphene as a very promising material for thermoelectric applications.
Dynamic Boundary Layer Properties in Turbulent Thermal Convection
NASA Astrophysics Data System (ADS)
Xia, Ke-Qing; Har Cheung, Yin; Sun, Chao
2004-11-01
We report an experimental study on the properties of the velocity and temperature boundary layers in turbulent thermal convection in a rectangular-shaped box over a range of Rayleigh numbers and at a constant Prandtl number. Velocity components both parallel and perpendicular to the conducting plate are measured simultaneously using the PIV technique. Our results show that, for the given geometry of the cell, the velocity boundary layer at the conduction plate is of a Blasius type, i.e. the boundary layer thickness δv scales with the Reynolds number Re as δv ˜ Re-1/2. The measurement further reveals that, at the velocity boundary layer, the turbulent (Reynolds) shear tress becomes larger than the viscous shear stress when Ra reaches 1-2×10^10, indicating that the boundary layer becomes turbulent for Ra >10^10. The viscous dissipation rate calculated based on the measured velocity field shows that it is dominated by contribution from the bulk over that from the boundary layer.
High-temperature properties of thorium dioxide: A first-principles molecular dynamics study
NASA Astrophysics Data System (ADS)
Nakamura, Hiroki; Machida, Masahiko
2016-09-01
Thorium has been considered a potential nuclear fuel for decades. To develop evaluation method for high-temperature properties of thorium dioxide as a candidate nuclear fuel, we perform first-principles molecular dynamics. The calculated enthalpy and thermal expansion agree well with the observed data. The Bredig transition temperature also coincides with experiments. Our results indicate that this method can provide reliable data of thermal properties of nuclear fuels.
Červinka, Ctirad; Pádua, Agilio A H; Fulem, Michal
2016-03-10
This work presents a molecular dynamics simulation study concerning the thermodynamic data of ionic liquids (ILs) including phase change enthalpies, liquid phase densities, radial and spatial distribution functions, and diffusive properties. Three homologous series of ILs were selected for this study, namely, 1-alkyl-3-methylimidazolium tetrafluoroborates, hexafluorophosphates, and 1,1,2,2-tetrafluoroethanesulfonates, so that properties of 36 ILs are calculated in total. The trends of calculated properties are compared to available experimental data and thoroughly discussed in context of the homologous series. The calculated trends of the vaporization enthalpies within the series are supported by analyzing the structural properties of the ILs. An excellent agreement of calculated structural properties (liquid phase density) with the experimental counterparts is reached. The calculated enthalpic properties are overestimated considerably; thus, further development of the force fields for ILs is required. PMID:26848831
NASA Astrophysics Data System (ADS)
da Jornada, Felipe H.; Ong, Chin Shen; Qiu, Diana Y.; Louie, Steven G.
There has been a considerable effort to experimentally characterize the electronic and optical properties of novel atomically thin 2D semiconductors, such as mono- and few-layer transition metal dichalcogenides (TMDs). However, the role that different substrates play in these experiments still remains unclear. From a theoretical perspective, it is hard to include the substrate in an ab initio framework, while in experiments, it is often difficult to suspend these samples. Here, we present a new method to compute the substrate effect on the quasiparticle and optical properties of quasi-2D materials based on state-of-the-art ab initio GW and GW plus Bethe-Salpeter equation (GW-BSE) methods. We compute the effects of different metallic and semiconducting substrates, and show that the quasiparticle gap and exciton binding energy can be dramatically reduced even with semiconducting substrates. This work was supported by the National Science Foundation under Grant No. DMR15-1508412 and the DOE under Contract No. DE-AC02-05CH11231.
Battiste, Richard L.
2007-12-25
Methods and apparatus are described for characterizing the temporal-spatial properties of a dynamic fluid front within a mold space while the mold space is being filled with fluid. A method includes providing a mold defining a mold space and having one or more openings into the mold space; heating a plurality of temperature sensors that extend into the mold space; injecting a fluid into the mold space through the openings, the fluid experiencing a dynamic fluid front while filling the mold space with the fluid; and characterizing temporal-spatial properties of the dynamic fluid front by monitoring a temperature of each of the plurality of heated temperature sensors while the mold space is being filled with the fluid. An apparatus includes a mold defining a mold space; one or more openings for introducing a fluid into the mold space and filling the mold space with the fluid, the fluid experiencing a dynamic fluid front while filling the mold space; a plurality of heated temperature sensors extending into the mold space; and a computer coupled to the plurality of heated temperature sensors for characterizing the temporal-spatial properties of the dynamic fluid front.
Battiste, Richard L
2013-12-31
Methods and apparatus are described for characterizing the temporal-spatial properties of a dynamic fluid front within a mold space while the mold space is being filled with fluid. A method includes providing a mold defining a mold space and having one or more openings into the mold space; heating a plurality of temperature sensors that extend into the mold space; injecting a fluid into th emold space through the openings, the fluid experiencing a dynamic fluid front while filling the mold space with a fluid; and characterizing temporal-spatial properties of the dynamic fluid front by monitoring a termperature of each of the plurality of heated temperature sensors while the mold space is being filled with the fluid. An apparatus includes a mold defining a mold space; one or more openings for introducing a fluid into th emold space and filling the mold space with the fluid, the fluid experiencing a dynamic fluid front while filling the mold space; a plurality of heated temperature sensors extending into the mold space; and a computer coupled to the plurality of heated temperature sensors for characterizing the temporal-spatial properties of the dynamic fluid front.
Sampling dynamic soil properties and vegetation for soil survey and ecological site descriptions
Technology Transfer Automated Retrieval System (TEKTRAN)
Dynamic soil property data can be collected during soil survey updates to add value to soil survey products and meet users needs for ecological site descriptions. Producers and land managers need information about soil and ecosystem change in order to plan for long-term productivity, conduct monito...
Technology Transfer Automated Retrieval System (TEKTRAN)
Quantification of soil-water patterns in space and time is essential for understanding soil hydrological processes and to aid land management decisions. In undulating terrain, dynamics of profile soil water can vary by landscape position in relation to terrain attributes, soil properties, and plant ...
Guidelines for sampling for dynamic soil properties for soil survey updates
Technology Transfer Automated Retrieval System (TEKTRAN)
Dynamic soil property data can be collected during soil survey updates to add value to soil survey products and meet users’ needs. Producers and land managers need information about soil and ecosystem change in order to plan for long-term productivity, conduct monitoring and assessments and predict ...
Morrison, Erin S; Badyaev, Alexander V
2016-08-01
The network of the interactions among genes, proteins, and metabolites delineates a range of potential phenotypic diversifications in a lineage, and realized phenotypic changes are the result of differences in the dynamics of the expression of the elements and interactions in this deterministic network. Regulatory mechanisms, such as hormones, mediate the relationship between the structural and dynamic properties of networks by determining how and when the elements are expressed and form a functional unit or state. Changes in regulatory mechanisms lead to variable expression of functional states of a network within and among generations. Functional properties of network elements, and the magnitude and direction of evolutionary change they determine, depend on their location within a network. Here, we examine the relationship between network structure and the dynamic mechanisms that regulate flux through a metabolic network. We review the mechanisms that control metabolic flux in enzymatic reactions and examine structural properties of the network locations that are targets of flux control. We aim to establish a predictive framework to test the contributions of structural and dynamic properties of deterministic networks to evolutionary diversifications. PMID:27252203
ERIC Educational Resources Information Center
Grable-Wallace, Lisa; And Others
1989-01-01
Evaluates seven courseware packages covering the topics of fluid dynamics, kinetic theory, and thermal properties. Discusses the price range, sub-topics, program type, interaction, time, calculus required, graphics, and comments of each courseware. Selects some packages based on the criteria. (YP)
NASA Technical Reports Server (NTRS)
Grauer, Jared A.; Morelli, Eugene A.
2013-01-01
The NASA Generic Transport Model (GTM) nonlinear simulation was used to investigate the effects of errors in sensor measurements, mass properties, and aircraft geometry on the accuracy of identified parameters in mathematical models describing the flight dynamics and determined from flight data. Measurements from a typical flight condition and system identification maneuver were systematically and progressively deteriorated by introducing noise, resolution errors, and bias errors. The data were then used to estimate nondimensional stability and control derivatives within a Monte Carlo simulation. Based on these results, recommendations are provided for maximum allowable errors in sensor measurements, mass properties, and aircraft geometry to achieve desired levels of dynamic modeling accuracy. Results using additional flight conditions and parameter estimation methods, as well as a nonlinear flight simulation of the General Dynamics F-16 aircraft, were compared with these recommendations
Size and Geometry Effects on the Mechanical Properties of Carrara Marble Under Dynamic Loadings
NASA Astrophysics Data System (ADS)
Zou, Chunjiang; Wong, Louis Ngai Yuen
2016-05-01
The effects of specimen size and geometry on the dynamic mechanical properties of Carrara marble including compressive strength, failure strain and elastic modulus are investigated in this research. Four different groups of specimens of different sizes and cross-sectional geometries are loaded under a wide range of strain rates by the split Hopkinson pressure bar setup. The experimental results indicate that all these mechanical properties are significantly influenced by the specimen size and geometry to different extent, hence highlighting the importance of taking into account of the specimen size and geometry in dynamic tests on rock materials. In addition, the transmission coefficient and the determination of strain rate under dynamic tests are discussed in detail.
De Mitri, N.; Monti, S.; Barone, V.
2015-01-01
The properties of a low molecular weight organic dye, namely 4-naphtoyloxy-1-methoxy-2,2,6,6-tetramethylpiperidine, covalently bound to an apolar polyolefin are investigated by means of a multi-level approach, combining classical molecular dynamics simulations, based on an purposely parameterized force fields, and quantum mechanical calculations, based on density functional theory (DFT) and its time-dependent extension (TD-DFT). The structure and dynamics of the dye in its embedding medium is analyzed and discussed in the light of the entangling effect of the surrounding polymer, also by comparing it to the results obtained for a different environment, i.e. toluene solution. The influence on photophysical properties of long lived cages, found in the polymeric embedding is eventually investigated in terms of slow and fast dye’s internal dynamics, by comparing computed IR and UV spectra with their experimental counterparts. PMID:24988373
NASA Astrophysics Data System (ADS)
Alfi, V.; Cristelli, M.; Pietronero, L.; Zaccaria, A.
2009-02-01
We present a detailed study of the statistical properties of the Agent Based Model introduced in paper I [Eur. Phys. J. B, DOI: 10.1140/epjb/e2009-00028-4] and of its generalization to the multiplicative dynamics. The aim of the model is to consider the minimal elements for the understanding of the origin of the stylized facts and their self-organization. The key elements are fundamentalist agents, chartist agents, herding dynamics and price behavior. The first two elements correspond to the competition between stability and instability tendencies in the market. The herding behavior governs the possibility of the agents to change strategy and it is a crucial element of this class of models. We consider a linear approximation for the price dynamics which permits a simple interpretation of the model dynamics and, for many properties, it is possible to derive analytical results. The generalized non linear dynamics results to be extremely more sensible to the parameter space and much more difficult to analyze and control. The main results for the nature and self-organization of the stylized facts are, however, very similar in the two cases. The main peculiarity of the non linear dynamics is an enhancement of the fluctuations and a more marked evidence of the stylized facts. We will also discuss some modifications of the model to introduce more realistic elements with respect to the real markets.
NASA Astrophysics Data System (ADS)
Liu, Jun; Cao, Dapeng; Zhang, Liqun
2009-07-01
The effects of the cross-linking density on the static and dynamic properties of polymer networks are examined by using a molecular dynamics simulation based on a simple elastomer model. Simulation results indicate that the introduced cross-linking junctions show almost no effect on the static structure factor. The glass transition temperature Tg increases slightly with the cross-linking density. By analyzing the mean square displacement of the monomers, the chain diffusion, and the incoherent intermediate dynamic structure factor ϕqs(t) at the chain and segmental length scales, it is found that the mobilities of the monomers and chains are retarded and the relaxation behavior is hindered by the cross linking of polymers. Furthermore, the spatial localization of the monomers is also observed at a long time period for a highly cross-linked system. For the cross-linked system, the time-temperature superposition principle is valid at the segmental length scale but breaks down at the chain length scale. The effect of the cross-linking density on the terminal relaxation is investigated by the end-to-end vector correlation, which is well fitted to the Kohlrauch-William-Watts (KWW) or modified KWW functions. The characteristic relaxation time shows an approximately linear relationship with the cross-linking density. It is demonstrated that the relaxation behavior tends to broaden, attributed to the stronger intermolecular coupling or cooperativity induced by the cross linking, suggesting that the system with a higher cross-linking degree becomes more fragile. For the dynamic properties, the bond orientation and the end-to-end distance along the deformed direction, which is an indicator of the entropic change, and the nonbonded energy are examined during the deformation and relaxation processes, respectively. The results explore the molecular mechanism accounting for the residual stress in the stress relaxation of cross-linked elastomer networks.
Liu, Jun; Cao, Dapeng; Zhang, Liqun
2009-07-21
The effects of the cross-linking density on the static and dynamic properties of polymer networks are examined by using a molecular dynamics simulation based on a simple elastomer model. Simulation results indicate that the introduced cross-linking junctions show almost no effect on the static structure factor. The glass transition temperature T(g) increases slightly with the cross-linking density. By analyzing the mean square displacement of the monomers, the chain diffusion, and the incoherent intermediate dynamic structure factor phi(q)(s)(t) at the chain and segmental length scales, it is found that the mobilities of the monomers and chains are retarded and the relaxation behavior is hindered by the cross linking of polymers. Furthermore, the spatial localization of the monomers is also observed at a long time period for a highly cross-linked system. For the cross-linked system, the time-temperature superposition principle is valid at the segmental length scale but breaks down at the chain length scale. The effect of the cross-linking density on the terminal relaxation is investigated by the end-to-end vector correlation, which is well fitted to the Kohlrauch-William-Watts (KWW) or modified KWW functions. The characteristic relaxation time shows an approximately linear relationship with the cross-linking density. It is demonstrated that the relaxation behavior tends to broaden, attributed to the stronger intermolecular coupling or cooperativity induced by the cross linking, suggesting that the system with a higher cross-linking degree becomes more fragile. For the dynamic properties, the bond orientation and the end-to-end distance along the deformed direction, which is an indicator of the entropic change, and the nonbonded energy are examined during the deformation and relaxation processes, respectively. The results explore the molecular mechanism accounting for the residual stress in the stress relaxation of cross-linked elastomer networks. PMID:19624229
Dynamic Material Properties of the Heat-Affected Zone (haz) in Resistance SPOT Welding
NASA Astrophysics Data System (ADS)
Ha, Ji-Woong; Song, Jung-Han; Huh, Hoon; Lim, Ji-Ho; Park, Sung-Ho
This paper is concerned with a methodology to identify the dynamic material properties of the heat-affected zone (HAZ) near the base metal in a resistance spot weld process at various strain rates. In order to obtain the dynamic material properties of the HAZ in the spot-welded steel sheet, specimens are prepared to have similar material properties, hardness and microstructure to the actual HAZ. Such thermally simulated specimens are fabricated with the material thermal cycle simulator (MTCS) and compared with the real one for the hardness and microstructure. Dynamic tensile tests are then conducted with a high speed material testing machine. Stress-strain curves of the thermally simulated HAZ are obtained at various strain rates ranged from 0.001/sec to 100/sec. Obtained material properties are applied to the finite element analysis of the spot-welded tensile-shear specimen in order to verify validity of the proposed testing methodology and obtained results. Analysis results demonstrate that the material properties obtained are appropriate for the FE analysis of spot-welded specimens.
Porto, Bruna Castro; Augusto, Pedro E D; Terekhov, Anton; Hamaker, Bruce R; Cristianini, Marcelo
2015-09-20
Dynamic high pressure (DHP) appears to be an alternative approach to physical modification of polysaccharides aimed improving their technological properties. Therefore, its effect on the functional properties of polysaccharides (i.e., oil absorption capacity, emulsifier, and rheology) needs to be investigated. Cashew tree gum (CG) is a biological macromolecule that has been proposed to be used as an emulsifier in beverage emulsions. To the best of our knowledge, none of the articles in the literature investigates the effect of DHP on the CG properties. This work presents a study on the evaluation of the effects of DHP on functional characteristics of CG, including rheological properties, molecular weight, glycosyl-linkage analysis, solubility, swelling and oil absorption capacity (OAC). The results suggest that DHP is able to modify the technological properties of cashew tree gum (increasing solubility and decreasing apparent viscosity). PMID:26050904
NASA Astrophysics Data System (ADS)
Kitiashvili, Irina N.; Mansour, Nagi N.; Kosovichev, Alexander; Wray, Alan A.
2015-08-01
Unique observational data from the Kepler mission open new perspectives for detail investigation of dynamical and internal properties of numerous stars. However, the new observational results require better understand links between the stellar turbulent convection and oscillations. We perform 3D numerical radiative hydrodynamics simulations of convective and oscillation properties of main-sequence stars from the solar-type stars to more massive F- and A-type stars. As the stellar mass increases the convection zone shrinks making it possible to include the whole convection zone in the computational domain. Also in more massive stars the scale and intensity of the turbulent motions dramatically increases, providing more energy for excitation of acoustic and gravity modes. In this talk I will discuss properties of the turbulent dynamics of the stars, interaction between the radiative and convection zones, and excitation of acoustic and gravity modes.
NASA Astrophysics Data System (ADS)
Russo, Pietro; Acierno, Domenico; Simeoli, Giorgio; Lopresto, Valentina
2014-05-01
Potentialities of polyolefin wastes in place of virgin polypropylene to produce composite laminates have been investigated. Plaques reinforced with a woven glass fabric were prepared by film-stacking technique and systematically analyzed in terms of thermal, mechanical and dynamic-mechanical properties. In case of PP matrices, the use of a typical compatibilizer to improve the adhesion at the interface has been considered. Thermal properties emphasized the chemical nature of plastic wastes. About mechanical properties, static tests showed an increase of flexural parameters for compatibilized systems due to the coupling effect between grafted maleic anhydride and silane groups on the surface of the glass fabric. These effects, maximized for composites based on car bumper wastes, is perfectly reflected in terms of storage modulus and damping ability of products as determined by single-cantilever bending dynamic tests.
Lavoratti, Alessandra; Scienza, Lisete Cristine; Zattera, Ademir José
2016-01-20
Composites of unsaturated polyester resin (UPR) and cellulose nanofibers (CNFs) obtained from dry cellulose waste of softwood (Pinus sp.) and hardwood (Eucalyptus sp.) were developed. The fiber properties and the influence of the CNFs in the dynamic-mechanical and thermomechanical properties of the composites were evaluated. CNFs with a diameter of 70-90 nm were obtained. Eucalyptus sp. has higher α-cellulose content than Pinus sp. fibers. The crystallinity of the cellulose pulps decreased after grinding. However, high values were still obtained. The chemical composition of the fibers was not significantly altered by the grinding process. Eucalyptus sp. CNF composites had water absorption close to the neat resin at 1 wt% filler. The dynamic-mechanical properties of Eucalyptus sp. CNFs were slightly increased and the thermal stability was improved. PMID:26572434
Mei, Liang; Somesfalean, Gabriel; Svanberg, Sune
2014-01-01
In the present work, fiber-based frequency-modulated light scattering interferometry (FMLSI) is developed and employed for studies of optical properties and dynamics in liquid phantoms made from Intralipid®. The fiber-based FMLSI system retrieves the optical properties by examining the intensity fluctuations through the turbid medium in a heterodyne detection scheme using a continuous-wave frequency-modulated coherent light source. A time resolution of 21 ps is obtained, and the experimental results for the diluted Intralipid phantoms show good agreement with the predicted results based on published data. The present system shows great potential for assessment of optical properties as well as dynamic studies in liquid phantoms, dairy products, and human tissues. PMID:25136504
Dynamically stabilized magnetic skyrmions
Zhou, Y.; Iacocca, E.; Awad, A. A.; Dumas, R. K.; Zhang, F. C.; Braun, H. B.; Åkerman, J.
2015-01-01
Magnetic skyrmions are topologically non-trivial spin textures that manifest themselves as quasiparticles in ferromagnetic thin films or noncentrosymmetric bulk materials. So far attention has focused on skyrmions stabilized either by the Dzyaloshinskii–Moriya interaction (DMI) or by dipolar interaction, where in the latter case the excitations are known as bubble skyrmions. Here we demonstrate the existence of a dynamically stabilized skyrmion, which exists even when dipolar interactions and DMI are absent. We establish how such dynamic skyrmions can be nucleated, sustained and manipulated in an effectively lossless medium under a nanocontact. As quasiparticles, they can be transported between two nanocontacts in a nanowire, even in complete absence of DMI. Conversely, in the presence of DMI, we observe that the dynamical skyrmion experiences strong breathing. All of this points towards a wide range of skyrmion manipulation, which can be studied in a much wider class of materials than considered so far. PMID:26351104
NASA Astrophysics Data System (ADS)
Jeon, Changwoo; Park, Jaeyeong; Kim, Choongnyun Paul; Kim, Hyoung Seop; Lee, Sunghak
2016-04-01
In this study, dynamic tensile properties of dendrite-containing Ti-based amorphous matrix composites were examined, and effects of dendrite size on dynamic deformation were investigated. The composites contained 73 to 76 vol pct of dendrites whose effective sizes were varied from 63 to 103 μm. The dynamic tensile test results indicated that the ultimate tensile strength increased up to 1.25 GPa, whereas the elongation decreased to 1 pct, although the overall strength and elongation trends followed those of the quasi-static tensile test. According to the observation of dynamic tensile deformation behavior, very few deformation bands were observed beneath the fracture surface in the composite containing large dendrites. In the composite containing small dendrites, deformation bands initiated inside small dendrites propagated into adjacent dendrites through the amorphous matrix, and were crossly intersect perpendicularly in widely deformed areas, which beneficially worked for elongation as well as strength.
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.
Naudé, Jérémie; Cessac, Bruno; Berry, Hugues; Delord, Bruno
2013-09-18
Homeostatic intrinsic plasticity (HIP) is a ubiquitous cellular mechanism regulating neuronal activity, cardinal for the proper functioning of nervous systems. In invertebrates, HIP is critical for orchestrating stereotyped activity patterns. The functional impact of HIP remains more obscure in vertebrate networks, where higher order cognitive processes rely on complex neural dynamics. The hypothesis has emerged that HIP might control the complexity of activity dynamics in recurrent networks, with important computational consequences. However, conflicting results about the causal relationships between cellular HIP, network dynamics, and computational performance have arisen from machine-learning studies. Here, we assess how cellular HIP effects translate into collective dynamics and computational properties in biological recurrent networks. We develop a realistic multiscale model including a generic HIP rule regulating the neuronal threshold with actual molecular signaling pathways kinetics, Dale's principle, sparse connectivity, synaptic balance, and Hebbian synaptic plasticity (SP). Dynamic mean-field analysis and simulations unravel that HIP sets a working point at which inputs are transduced by large derivative ranges of the transfer function. This cellular mechanism ensures increased network dynamics complexity, robust balance with SP at the edge of chaos, and improved input separability. Although critically dependent upon balanced excitatory and inhibitory drives, these effects display striking robustness to changes in network architecture, learning rates, and input features. Thus, the mechanism we unveil might represent a ubiquitous cellular basis for complex dynamics in neural networks. Understanding this robustness is an important challenge to unraveling principles underlying self-organization around criticality in biological recurrent neural networks. PMID:24048833
Characterization of dynamic change of Fan-delta reservoir properties in water-drive development
Wu Shenghe; Xiong Qihua; Liu Yuhong
1997-08-01
Fan-delta reservoir in Huzhuangji oil field of east China, is a typical highly heterogeneous reservoir. The oil field has been developed by water-drive for 10 years, but the oil recovery is less than 12%, and water cut is over 90%, resulting from high heterogeneity and serious dynamic change of reservoir properties. This paper aims at the study of dynamic change of reservoir properties in water-drive development. Through quantitative imaging analysis and mercury injection analysis of cores from inspection wells, the dynamic change of reservoir pore structure in water-drive development was studied. The results show that the {open_quotes}large pore channels{close_quotes} develop in distributary channel sandstone and become larger in water-drive development, resulting in more serious pore heterogeneity. Through reservoir sensitivity experiments, the rock-fluid reaction in water-drive development is studied. The results show the permeability of some distal bar sandstone and deserted channel sandstone becomes lower due to swelling of I/S clay minerals in pore throats. OD the other hand, the permeability of distributary channel and mouth bar sandstone become larger because the authigenic Koalinites in pore throats are flushed away with the increase of flow rate of injection water. Well-logging analysis of flooded reservoirs are used to study the dynamic change of reservoir properties in various flow units. The distribution of remaining oil is closely related to the types and distribution of flow units.
NASA Astrophysics Data System (ADS)
Satoh, Katsuhiko
2013-08-01
The thermodynamic scaling of molecular dynamic properties of rotation and thermodynamic parameters in a nematic phase was investigated by a molecular dynamic simulation using the Gay-Berne potential. A master curve for the relaxation time of flip-flop motion was obtained using thermodynamic scaling, and the dynamic property could be solely expressed as a function of TV^{γ _τ }, where T and V are the temperature and volume, respectively. The scaling parameter γτ was in excellent agreement with the thermodynamic parameter Γ, which is the logarithm of the slope of a line plotted for the temperature and volume at constant P2. This line was fairly linear, and as good as the line for p-azoxyanisole or using the highly ordered small cluster model. The equivalence relation between Γ and γτ was compared with results obtained from the highly ordered small cluster model. The possibility of adapting the molecular model for the thermodynamic scaling of other dynamic rotational properties was also explored. The rotational diffusion constant and rotational viscosity coefficients, which were calculated using established theoretical and experimental expressions, were rescaled onto master curves with the same scaling parameters. The simulation illustrates the universal nature of the equivalence relation for liquid crystals.
Effects of dynamical evolution on the internal kinematical properties of star clusters
NASA Astrophysics Data System (ADS)
Tiongco, Maria; Vesperini, Enrico; Varri, Anna Lisa
2016-05-01
The observational characterization of the internal kinematics of Galactic globular clusters will soon reach an unprecedented level of richness, thanks to the synergy between the astrometric data provided by Gaia and HST, and a number of ESO/VLT spectroscopic programs. Such a wealth of information on the three-dimensional velocity space of star clusters, offers the unique opportunity to address a number of open questions on the phase space evolution of collisional stellar systems.Driven by these motivations, I will present some highlighted results of a large survey of N-body simulations aimed at exploring the long-term dynamical evolution of the kinematical properties of tidally limited star clusters. First, I will discuss of the evolution of the anisotropy in velocity space, with particular attention to the dependence on the cluster initial structural properties and dynamical history. I will then focus on the implications of cluster dynamical evolution and loss of stars on its internal rotation. Such an enriched picture of the kinematical properties of star clusters offers a solid bedrock for addressing a range of exciting new questions related to the dynamics of multiple stellar populations in globular clusters. In this context, I will illustrate some results on the internal rotational velocity profiles and the evolution of the differences in the rotation of different stellar populations.
Satoh, Katsuhiko
2013-08-28
The thermodynamic scaling of molecular dynamic properties of rotation and thermodynamic parameters in a nematic phase was investigated by a molecular dynamic simulation using the Gay-Berne potential. A master curve for the relaxation time of flip-flop motion was obtained using thermodynamic scaling, and the dynamic property could be solely expressed as a function of TV(γτ) , where T and V are the temperature and volume, respectively. The scaling parameter γτ was in excellent agreement with the thermodynamic parameter Γ, which is the logarithm of the slope of a line plotted for the temperature and volume at constant P2. This line was fairly linear, and as good as the line for p-azoxyanisole or using the highly ordered small cluster model. The equivalence relation between Γ and γ(τ) was compared with results obtained from the highly ordered small cluster model. The possibility of adapting the molecular model for the thermodynamic scaling of other dynamic rotational properties was also explored. The rotational diffusion constant and rotational viscosity coefficients, which were calculated using established theoretical and experimental expressions, were rescaled onto master curves with the same scaling parameters. The simulation illustrates the universal nature of the equivalence relation for liquid crystals. PMID:24007031
Shape vibration and quasiparticle excitations in the lowest 0+ excited state in erbium isotopes
NASA Astrophysics Data System (ADS)
Chen, Fang-Qi; Egido, J. Luis
2016-06-01
The ground and first excited 0+ states of the -172Er156 isotopes are analyzed in the framework of the generator coordinate method. The shape parameter β is used to generate wave functions with different deformations which together with the two-quasiparticle states built on them provide a set of states. An angular momentum and particle number projection of the latter spawn the basis states of the generator coordinate method. With this ansatz and using the separable pairing plus quadrupole interaction we obtain a good agreement with the experimental spectra and E 2 transition rates up to moderate spin values. The structure of the wave functions suggests that the first excited 0+ states in the soft Er isotopes are dominated by shape fluctuations, while in the well deformed Er isotopes the two-quasiparticle states are more relevant. In between, both degrees of freedom are necessary.
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.
Non-exponential energy decay and quasi-particle fluctuations in a superconducting flux qubit
NASA Astrophysics Data System (ADS)
Gustavsson, Simon; Yan, Fei; Catelani, Gianluigi; Kamal, Archana; Bylander, Jonas; Yoshihara, Fumiki; Nakamura, Yasunobu; Orlando, Terry; Oliver, Wiliam
2015-03-01
We measure pronounced non-exponential energy relaxation in a superconducting flux qubit, observing a decay function that exhibits a fast initial decay followed by a much slower decay for long times. When applying a sequence of pi pulses to the qubit and measuring the decay after the last pi pulse, we observe strong modifications to the decay function, including a slow-down of the fast initial decay and a three-fold increase of the 1/e-time. If we attribute the non-exponential decay to quasiparticle number fluctuations, we speculate that the improvements in T1 are due to a qubit-mediated shuffling of quasiparticles between the metallic islands of the device, which will eventually pump them away from the Josephson junctions to a larger ground plane where their contribution to qubit energy relaxation become negligible.
Quasiparticle Scattering Rate and Antiferromagnetic Excitations in YBa_2Cu_3O_7.
NASA Astrophysics Data System (ADS)
Stojković, Branko P.; Blumberg, G.; Klein, M. V.
1996-03-01
In quasi-two-dimensional d-wave superconductors Van Hove singularities close to the Fermi surface lead to magnetic quasi-particle excitations.(G. Blumberg, B. P. Stojković and M. V. Klein, preprint.) Assuming a model electron-magnon interaction and realistic electronic band structure for YBa_2Cu_3O_7, we calculate the inelastic electronic scattering rate in both normal and superconducting states. In agreement with the momentum dependent spectral function broadening observed in YBCO in the superconducting state by photoemission spectroscopy, we find different quasiparticle scattering rates as a function of energy and temperature for different regions of the Brillouin zone. We calculate the magnetic excitation spectra in momentum space and use them to discuss the implications of our results for NMR, inelastic neutron scattering, and Raman spectroscopy.
Coherent quasiparticles with a small fermi surface in lightly doped Sr(3)Ir(2)O(7).
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
Structure of three-quasiparticle isomers in {sup 169}Ho and {sup 171}Tm
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.
Fast decay of a three-quasiparticle isomer in {sup 171}Tm
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.
Two-quasiparticle states in {sup 250}Bk studied by decay scheme and transfer reaction spectroscopy
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.
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.
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.
Coherent quasiparticles with a small Fermi Surface in lightly doped Sr3Ir2O7
NASA Astrophysics Data System (ADS)
de la Torre, Alberto; McKeown Walker, Siobhan; Tamai, Anna; Hunter, Emily; Subedi, Alaska; Kim, Timur; Hoesch, Moritz; Perry, Robin; Georges, Antoine; Baumberger, Felix
2015-03-01
We characterize the electron doping evolution of (Sr1-xLax)Ir2O7 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 3 x / 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 Sr3Ir2O7, in stark contrast with underdoped cuprates.
Coherent Quasiparticles with a Small Fermi Surface in Lightly Doped Sr3Ir2O7
NASA Astrophysics Data System (ADS)
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.
2014-12-01
We characterize the electron doping evolution of (Sr1 -xLax)3Ir2O7 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 3 x /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 Sr3Ir2O7 .
Parity switching and decoherence by quasiparticles in single-junction transmons
NASA Astrophysics Data System (ADS)
Catelani, Gianluigi
2014-03-01
Transmons are at present among the most coherent superconducting qubits, reaching quality factors of order 106 both in 3D and 2D architectures. These high quality factors enable detailed investigations of decoherence mechanisms. An intrinsic decoherence process originates from the coupling between the qubit degree of freedom and the quasiparticles that tunnel across Josephson junctions. In a transmon, tunneling of a single quasiparticle is associated with a change in parity. I will discuss the theory of the parity switching rate in single-junction transmons, compare it with recent measurements, and consider the role of parity switching in limiting the coherence time. Partial support by the EU under REA grant agreement CIG-618258 is acknowledged.
Structure of three-quasiparticle isomers in {sup 169}Ho and {sup 171}Tm.
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.
NASA Astrophysics Data System (ADS)
Ishii, T.; Makii, H.; Asai, M.; Tsukada, K.; Toyoshima, A.; Matsuda, M.; Makishima, A.; Shigematsu, S.; Kaneko, J.; Shizuma, T.; Toume, H.; Hossain, I.; Kohno, T.; Ogawa, M.
2008-11-01
We have measured de-excitation γ rays in Cm249 populated by one-neutron stripping reactions with a Cm248 target and 162-MeV O16, 162-MeV O18, and 120-MeV C13 beams. γ rays in Cm249 were identified by measuring kinetic energies of outgoing particles using Si ΔE-E detectors. It was demonstrated that high-j orbitals were selectively populated in the (O16, O15) reaction having a large negative Q value. We have observed eight quasiparticle states above the deformed shell gap of N=152. The 1/2+[620], 1/2-[750], and 7/2+[613] bands were extended up to 19/2+, 19/2-, and 13/2+ states, respectively. We have established the 9/29/2+[615] state at 526 keV, the 9/29/2+[604] state with a short life of T1/2≪2 ps at 1030 keV, and the 11/211/2-[725] state with T1/2=19(1) ns at 375 keV. Furthermore, the 17/21/2+[880] state, having a large component of the k17/2 spherical single-particle state, has been identified at 1505 keV. We discuss the properties of those quasiparticle states in the framework of a deformed shell model.
NASA Astrophysics Data System (ADS)
Osorio-Guillén, J. M.; Espinosa-García, W. F.; Moyses Araujo, C.
2015-09-01
First-principles quasi-particle theory has been employed to assess catalytic power of graphitic carbon nitride, g-C3N4, for solar fuel production. A comparative study between g-h-triazine and g-h-heptazine has been carried out taking also into account van der Waals dispersive forces. The band edge potentials have been calculated using a recently developed approach where quasi-particle effects are taken into account through the GW approximation. First, it was found that the description of ground state properties such as cohesive and surface formation energies requires the proper treatment of dispersive interaction. Furthermore, through the analysis of calculated band-edge potentials, it is shown that g-h-triazine has high reductive power reaching the potential to reduce CO2 to formic acid, coplanar g-h-heptazine displays the highest thermodynamics force toward H2O/O2 oxidation reaction, and corrugated g-h-heptazine exhibits a good capacity for both reactions. This rigorous theoretical study shows a route to further improve the catalytic performance of g-C3N4.
NASA Astrophysics Data System (ADS)
Ritwiset, Aksornnarong; Krongsuk, Sriprajak; Johns, Jeffrey Roy
2016-09-01
Niosomes are non-ionic surfactant vesicles having a bilayer structure formed by self-assembly of hydrated surfactants, usually with cholesterol incorporation. Stability and mechanical properties of niosomes strongly depend on type of non-ionic surfactants and compositions used. In this study we present the structural and dynamical properties of niosome bilayers composed of sorbitan monostearate (Span60) with 0% and 50% cholesterol compositions which are investigated by using molecular dynamics simulations. The simulations reveal that niosome bilayer without cholesterol prefer to form in the gel phase with a higher order structure, while in the presence of cholesterol the bilayer exhibits more fluidity having a less ordered structure. The niosome bilayer with 50% cholesterol inclusion shows an increase of area per lipid (∼11%) and thickness (∼39%) compared with the niosome bilayer without cholesterol. The Span60 tailgroup orientation of the niosome bilayers without cholesterol exhibits more tilt (34.5o ± 0.5) than that of the bilayer with 50% cholesterol (15.4o ± 0.8). Additionally, our results show that the addition of cholesterol to the bilayer causes the higher in lateral and transverse diffusion, as well as an increase in the hydrogen bond number between Span60 and water. Such characteristics not only enhance the niosome stability but also increase the fluidity, which are necessary for the niosomal drug delivery.
Zeng, Yongping; Wang, Chunfeng; Xu, Yueyang; Xu, WenLin; Ju, Shengui
2015-07-01
Structrual and dynamic properties of thiophene (C4H4S) in supercritical carbon dioxide were studied using Car-Parrinello molecular dynamics simulations. The geometries and energies optimized for the thiophene-CO2 complex show a stable C-H···O hydrogen bond interactions both in gas phase and in supercritical CO2. The radial distribution functions of CO2 around thiophene in the supercritical phase state show a correlation suggesting C-H···O hydrogen bond and S···C interaction. Local structural properties of the mixtures were investigated by angular-radial distributions and spatial distribution functions. The results show a mutually parallel arrangement between the thiophene plane and CO2 molecules at short distances and a high probability of the thiophene being located in the radial directions of the CO2 molecules. The decay of orientational correlations at 318.15 K shows slower relaxation compared to those of 298.15 K for first and second rank correlations. The vibrations of CO2 and thiophene molecules have been examined through an analysis of the velocity autocorrelation functions of the atoms. The C-H stretching modes of thiophene in the isolated configuration are less red-shifted and have a much narrower frequency range than that in the mixtures. PMID:26087291
Qian Chen
2008-08-18
The generation, motion, and interaction of dislocations play key roles during the plastic deformation process of crystalline solids. 3D Dislocation Dynamics has been employed as a mesoscale simulation algorithm to investigate the collective and cooperative behavior of dislocations. Most current research on 3D Dislocation Dynamics is based on the solutions available in the framework of classical isotropic elasticity. However, due to some degree of elastic anisotropy in almost all crystalline solids, it is very necessary to extend 3D Dislocation Dynamics into anisotropic elasticity. In this study, first, the details of efficient and accurate incorporation of the fully anisotropic elasticity into 3D discrete Dislocation Dynamics by numerically evaluating the derivatives of Green's functions are described. Then the intrinsic properties of perfect dislocations, including their stability, their core properties and disassociation characteristics, in newly discovered rare earth-based intermetallics and in conventional intermetallics are investigated, within the framework of fully anisotropic elasticity supplemented with the atomistic information obtained from the ab initio calculations. Moreover, the evolution and interaction of dislocations in these intermetallics as well as the role of solute segregation are presented by utilizing fully anisotropic 3D dislocation dynamics. The results from this work clearly indicate the role and the importance of elastic anisotropy on the evolution of dislocation microstructures, the overall ductility and the hardening behavior in these systems.
Volume dependent quasiparticle spectral weight in NiS2-xSex system
NASA Astrophysics Data System (ADS)
Marini, C.; Perucchi, A.; Dore, P.; Topwal, D.; Sarma, D. D.; Lupi, S.; Postorino, P.
2012-05-01
We discuss the evolution of Infrared reflectivity at room temperature under various pressures (P) and Se alloying concentration in the strongly correlated NiS2-xSex pyrite. Measurements gave a complete picture of the optical response of the system on approaching the P-induced and Se-induced metallic state. A peculiar non-monotonic (V-shaped) volume dependence was found for the quasiparticle spectral weight of both pure and Se-doped compounds.
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.
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.
A quasiparticle-trap-assisted transition-edge sensor for phonon-mediated particle detection
NASA Astrophysics Data System (ADS)
Irwin, K. D.; Nam, S. W.; Cabrera, B.; Chugg, B.; Young, B. A.
1995-11-01
We have demonstrated the operation of composite superconducting tungsten and aluminum transition-edge sensors which take advantage of quasiparticle trapping and electrothermal feedback. We call these devices W/Al QETs (quasiparticle-trap-assisted electrothermal feedback transition-edge sensors). The quasiparticle trapping mechanism makes it possible to instrument large surface areas without increasing sensor heat capacity, thus allowing larger absorbers and reducing phonon collection times. The sensor consists of a 30-nm-thick superconducting tungsten thin film with Tc˜80 mK deposited on a high-purity silicon substrate. The W film is patterned into 200 parallel lines segments, each 2 μm wide and 800 μm long. Eight superconducting aluminum thin film pads are electrically connected to each segment, and cover a much larger surface area than the W. When phonons from particle interactions in the silicon crystal impinge on an aluminum pad, Cooper pairs are broken, forming quasiparticles which diffuse to the tungsten lines where they are rapidly thermalized. The W film is voltage biased, and self-regulates in temperature within its superconducting transition region by electrothermal feedback. Heat deposited in the film causes a current pulse of ˜100 μs duration, which is measured with a series array of dc superconducting quantum interference devices. We have demonstrated an energy resolution of <350 eV full width at half-maximum for 6 keV x rays incident on the backside of a 1 cm×1 cm×1 mm (0.25 g) silicon absorber, the highest resolution that has been reported for a fast (<1 ms pulse duration) calorimetric detector with an absorber mass≳0.1 g. Applications of this technology include dark matter searches and neutrino detection.
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.
Evans, W J; Yoo, C; Lee, G W; Cynn, H; Lipp, M J; Visbeck, K
2007-02-23
We have developed a unique device, a dynamic diamond anvil cell (dDAC), which repetitively applies a time-dependent load/pressure profile to a sample. This capability allows studies of the kinetics of phase transitions and metastable phases at compression (strain) rates of up to 500 GPa/sec ({approx}0.16 s{sup -1} for a metal). Our approach adapts electromechanical piezoelectric actuators to a conventional diamond anvil cell design, which enables precise specification and control of a time-dependent applied load/pressure. Existing DAC instrumentation and experimental techniques are easily adapted to the dDAC to measure the properties of a sample under the varying load/pressure conditions. This capability addresses the sparsely studied regime of dynamic phenomena between static research (diamond anvil cells and large volume presses) and dynamic shock-driven experiments (gas guns, explosive and laser shock). We present an overview of a variety of experimental measurements that can be made with this device.
NASA Astrophysics Data System (ADS)
Souto, J.; Alemany, M. M. G.; Gallego, L. J.; Gonzalez, L. E.; Gonzalez, D. J.
2013-03-01
We perform an ab initio molecular dynamics study of the static, dynamic and electronic properties of the liquid Bi-Pb alloy at three concentrations, including the eutectic one. This alloy is of particular technological interest for its possible use as coolant in fast reactors. Our predictions are in good agreement with the available experimental data. In particular, the computed total static structure factors reproduce accurately the neutron diffraction results, and the predicted adiabatic sound velocity and shear viscosity compare well with the experimental values. The partial dynamic structure factors exhibit clear side peaks indicative of propagating density fluctuations, and the longitudinal and transverse dispersion relations show several branches.The electronic density of states show that the liquid Bi-Pb alloy is a good metal, but with strong deviations from the free-electron parabolic curve. Supported by FIS2008-02490/FIS, FIS2008-04894/FIS, VA068A06, GR120, INCITE09E2R206033ES and INCITE08PXIB206107PR
NASA Astrophysics Data System (ADS)
Pomata, Matías H. H.; Laria, Daniel; Skaf, Munir S.; Elola, M. Dolores
2008-12-01
We present results from molecular dynamics simulations performed on reverse micelles immersed in cyclohexane. Three different inner polar phases are considered: water (W), formamide (FM), and an equimolar mixture of the two solvents. In all cases, the surfactant was sodium bis(2-ethylhexyl) sulfosuccinate (usually known as AOT). The initial radii of the micelles were R~15 A˚, while the corresponding polar solvent-to-surfactant molar ratios were intermediate between w0=4.3 for FM and w0=7 for W. The resulting overall shapes of the micelles resemble distorted ellipsoids, with average eccentricities of the order of ~0.75. Moreover, the pattern of the surfactant layer separating the inner pool from the non-polar phase looks highly irregular, with a roughness characterized by length scales comparable to the micelle radii. Solvent dipole orientation polarization along radial directions exhibit steady growths as one moves from central positions toward head group locations. Local density correlations within the micelles indicate preferential solvation of sodium ionic species by water, in contrast to the behavior found in bulk equimolar mixtures. Still, a sizable fraction of ~90% of Na+ remains associated with the head groups. Compared to bulk results, the translational and rotational modes of the confined solvents exhibit important retardations, most notably those operated in rotational motions where the characteristic time scales may be up to 50 times larger. Modifications of the intramolecular connectivity expressed in terms of the average number of hydrogen bonds and their lifetimes are also discussed.
Static and dynamic elastic properties of rocks from the Canadian Shield
King, M.S.
1983-01-01
As part of a number of research studies in the Canadian Shield associated with the stability of underground mine openings, seismic reflection surveys, and the proposed use of a tunnel-boring machine (TBM) for developing mine headings, a long-term laboratory rock mechanics program has been conducted to determine the static and dynamic elastic properties of samples of igneous and metamorphic rocks from the Canadian Shield. This paper reports the results of 174 measurements of static elastic modulus and 152 measurements of uniaxial compressive strength for these rocks as a function of dynamic elastic modulus. 20 references, 5 figures.
Transformation properties of dynamic χ(2) holograms generating at the difference frequency
NASA Astrophysics Data System (ADS)
Miloglyadov, E. V.; Stasel'ko, D. I.
2016-07-01
The transformation properties of dynamic χ(2) holograms generating at the difference frequency are analyzed as applied to the position and scales of reconstructed images. Some regularities are established for the spatial localization and scales of images for different combinations of frequencies and positions of the reference and object point sources, involved in the formation of a holographic image. The formation of amplitude transparency images, reconstructed by dynamic χ(2) holograms with a decrease or conservation of the object beam frequency, and their transformations are experimentally demonstrated.
Test methods for the dynamic mechanical properties of polymeric materials. Final report
Baker, G.K.
1980-06-01
Various test geometries and procedures for the dynamic mechanical analysis of polymers employing a mechanical spectrometer have been evaluated. The methods and materials included in this work are forced torsional pendulum testing of Kevlar/epoxy laminates and rigid urethane foams, oscillatory parallel plate testing to determine the kinetics of the cure of VCE with Hylene MP, oscillatory compressive testing of B-3223 cellular silicone, and oscillatory tensile testing of Silastic E and single Kevlar filaments. Fundamental dynamic mechanical properties, including the storage and loss moduli and loss tangent of the materials tested, were determined as a function of temperature and sometimes of frequency.
NASA Astrophysics Data System (ADS)
Pagliai, Marco; Muniz-Miranda, Francesco; Cardini, Gianni; Righini, Roberto; Schettino, Vincenzo
2011-05-01
In order to extract spectroscopic information from trajectories obtained by classical or ab initio molecular dynamics simulations, usually Fourier transforms are employed. In recent years wavelet transforms have been shown to be a valid alternative tool to analyze time-series, due to their capability of localizing a signal both in time and frequency. In this article wavelet transforms are applied for the analysis of Car-Parrinello molecular dynamics simulations to the purpose of time-correlating structural and spectroscopic properties of methyl acetate dissolved in water and methanol. The results demonstrate the possibility of obtaining information that may be of valuable help in the interpretation of time-resolved spectroscopic data.
Chatelin, Simon; Oudry, Jennifer; Périchon, Nicolas; Sandrin, Laurent; Allemann, Pierre; Soler, Luc; Willinger, Rémy
2011-01-01
Understanding the mechanical properties of human liver is one of the most critical aspects of its numerical modeling for medical applications or impact biomechanics. Generally, model constitutive laws come from in vitro data. However, the elastic properties of liver may change significantly after death and with time. Furthermore, in vitro liver elastic properties reported in the literature have often not been compared quantitatively with in vivo liver mechanical properties on the same organ. In this study, both steps are investigated on porcine liver. The elastic property of the porcine liver, given by the shear modulus G, was measured by both Transient Elastography (TE) and Dynamic Mechanical Analysis (DMA). Shear modulus measurements were realized on in vivo and in vitro liver to compare the TE and DMA methods and to study the influence of testing conditions on the liver viscoelastic properties. In vitro results show that elastic properties obtained by TE and DMA are in agreement. Liver tissue in the frequency range from 0.1 to 4 Hz can be modeled by a two-mode relaxation model. Furthermore, results show that the liver is homogeneous, isotropic and more elastic than viscous. Finally, it is shown in this study that viscoelastic properties obtained by TE and DMA change significantly with post mortem time and with the boundary conditions. PMID:21811013
Tóth, László; Fekete, Attila; Balogh, Gábor; Bereczky, Zsuzsanna; Komáromi, István
2015-09-01
While antithrombin (AT) has small basal inhibitory activity, it reaches its full inhibitory potential against activated blood coagulation factors, FXa, FIXa, and FIIa (thrombin), via an allosteric and/or template (bridging) mechanism by the action of heparin, heparan sulfate, or heparin-mimetic pentasaccharides (PS). From the numerous X-ray structures available for different conformational states of AT, only indirect and incomplete conclusions can be drawn on the inherently dynamic properties of AT. As a typical example, the basal inhibitory activity of AT cannot be interpreted on the basis of "non-activated" free antithrombin X-ray structures since the Arg393 side chain, playing crucial role in antithrombin-proteinase interaction, is not exposed. In order to reveal the intrinsic dynamic properties and the reason of basal inhibitory activity of antithrombin, 2 μs molecular dynamics simulations were carried out on its native free-forms. It was shown from the simulation trajectories that the reactive center loop which is functioning as "bait" for proteases, even without any biasing potential can populate conformational state in which the Arg393 side chain is solvent exposed. It is revealed from the trajectory analysis that the peptide sequences correspond to the helix D extension, and new helix P formation can be featured with especially large root-mean-square fluctuations. Mutual information analyses of the trajectory showed remarkable (generalized) correlation between those regions of antithrombin which changed their conformations as the consequence of AT-PS complex formation. This suggests that allosteric information propagation pathways are present even in the non-activated native form of AT. PMID:25483839
Quasi-particles ultrafastly releasing kink bosons to form Fermi arcs in a cuprate superconductor
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
Quasiparticle degrees of freedom versus the perfect fluid as descriptors of the quark-gluon plasma
Levy, L. A. Linden; Nagle, J. L.; Rosen, C.; Steinberg, P.
2008-10-15
The hot nuclear matter created at the Relativistic Heavy Ion Collider has been characterized by near-perfect fluid behavior. We demonstrate that this stands in contradiction to the identification of quantum chromodynamics quasiparticles with the thermodynamic degrees of freedom in the early (fluid) stage of heavy-ion collisions. The empirical observation of constituent quark 'n{sub q}' scaling of elliptic flow [PHENIX, A. Adare et al., Phys. Rev. Lett. 98, 162301 (2007)] is juxtaposed with the lack of such scaling behavior in hydrodynamic fluid calculations followed by Cooper-Frye freeze-out to hadrons. As the hydrodynamic fluid expands, increasing viscous effects may allow for a short time period of 'quasiparticle transport' prior to hadronization. However, without a detailed understanding of the transitions between these time stages, the 'n{sub q}' scaling is not a necessary consequence of this prescription. Also, if the duration of this stage is too short, it may not support well-defined quasiparticles. By comparing and contrasting the coalescence of quarks into hadrons with the similar process of producing light nuclei from nucleons, it is shown that the observation of 'n{sub q}' scaling in the final state does not necessarily imply that the constituent degrees of freedom were the relevant ones in the initial state.
Decay and Fission Hindrance of Two- and Four-Quasiparticle K Isomers in 254Rf
NASA Astrophysics Data System (ADS)
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.
2015-09-01
Two isomers decaying by electromagnetic transitions with half-lives of 4.7(1.1) and 247 (73 ) μ s have been discovered in the heavy 254Rf 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 Kπ=8- , ν2(7 /2+[624 ],9 /2-[734 ]) two-quasineutron and the Kπ=1 6+, 8-ν2(7 /2+[624 ],9 /2-[734 ])⊗8-π2(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 254Rf ground state that decays exclusively by spontaneous fission with a half-life of 23.2 (1.1 ) μ s . The absence of sizable fission branches from either of the isomers implies unprecedented fission hindrance relative to the ground state.
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.
Probing the Unconventional Superconducting State of LiFeAs by Quasiparticle Interference
NASA Astrophysics Data System (ADS)
Hänke, Torben; Sykora, Steffen; Schlegel, Ronny; Baumann, Danny; Harnagea, Luminita; Wurmehl, Sabine; Daghofer, Maria; Büchner, Bernd; van den Brink, Jeroen; Hess, Christian
2012-03-01
A crucial step in revealing the nature of unconventional superconductivity is to investigate the symmetry of the superconducting order parameter. Scanning tunneling spectroscopy has proven a powerful technique to probe this symmetry by measuring the quasiparticle interference (QPI) which sensitively depends on the superconducting pairing mechanism. A particularly well-suited material to apply this technique is the stoichiometric superconductor LiFeAs as it features clean, charge neutral cleaved surfaces without surface states and a relatively high Tc˜18K. Our data reveal that in LiFeAs the quasiparticle scattering is governed by a van Hove singularity at the center of the Brillouin zone which is in stark contrast to other pnictide superconductors where nesting is crucial for both scattering and s± superconductivity. Indeed, within a minimal model and using the most elementary order parameters, calculations of the QPI suggest a dominating role of the holelike bands for the quasiparticle scattering. Our theoretical findings do not support the elementary singlet pairing symmetries s++, s±, and d wave. This brings to mind that the superconducting pairing mechanism in LiFeAs is based on an unusual pairing symmetry such as an elementary p wave (which provides optimal agreement between the experimental data and QPI simulations) or a more complex order parameter (e.g., s+id wave symmetry).
Modulation of the penetration depth of Nb and NbN films by quasiparticle injection
Track, E.K.; Radparvar, M.; Faris, S.M.
1989-03-01
A novel approach to modulating the inductance of a superconducting microstrip is described. This approach could be the basis for numerous practical applications, such as phase shifters and high frequency tuning elements. The physical mechanisms involved are quasiparticle injection, gap suppression, and penetration depth modulation. In this current, the authors have investigated the modulation of the penetration depth of niobium and niobium nitride films by excess quasiparticle injection. To this effect, all-niobium and all-niobium-nitride SQUID circuits are designed and fabricated. These circuits allow quasiparticle injection into the inductive element of the SQUID. This injection is achieved by 1. optical irradiation through an opening in a Nb reflective layer which partially masks the rest of the circuit, and 2. electronic current injection through a tunnel junction overlaid on the microstrip inductance. Penetration depth modulation is achieved with both methods. The magnitude of the effect varies from 10% to over 200% change in inductance. These results and their dependence on temperature and on the parameters of the control mechanism (light intensity, amount of current injection, etc.) are presented and discussed.
The birth of a quasiparticle in silicon observed in time-frequency space.
Hase, Muneaki; Kitajima, Masahiro; Constantinescu, Anca Monia; Petek, Hrvoje
2003-11-01
The concept of quasiparticles in solid-state physics is an extremely powerful tool for describing complex many-body phenomena in terms of single-particle excitations. Introducing a simple particle, such as an electron, hole or phonon, deforms a many-body system through its interactions with other particles. In this way, the added particle is 'dressed' or 'renormalized' by a self-energy cloud that describes the response of the many-body system, so forming a new entity--the quasiparticle. Using ultrafast laser techniques, it is possible to impulsively generate bare particles and observe their subsequent dressing by the many-body interactions (that is, quasiparticle formation) on the time and energy scales governed by the Heisenberg uncertainty principle. Here we describe the coherent response of silicon to excitation with a 10-femtosecond (10(-14) s) laser pulse. The optical pulse interacts with the sample by way of the complex second-order nonlinear susceptibility to generate a force on the lattice driving coherent phonon excitation. Transforming the transient reflectivity signal into frequency-time space reveals interference effects leading to the coherent phonon generation and subsequent dressing of the phonon by electron-hole pair excitations. PMID:14603313
Quantum confinement and quasiparticle corrections in α-HgS from first principles
NASA Astrophysics Data System (ADS)
Lanzillo, Nicholas A.; Roy, Sujit; Nayak, Saroj K.
2015-06-01
Using a combination of density functional theory and many-body GW corrections, we calculate the quasiparticle band gap of bulk α-HgS and investigate the effect of quantum confinement on the geometric, electronic and optical structures. The basic structural unit of α-HgS is a one-dimensional helical chain consisting of covalently bound Hg and S atoms. When isolated to just a single helix or to a few-helix configuration, we find that α-HgS becomes a wide-gap semiconductor with a quasiparticle band gap as large as 7.0 eV, in contrast to the bulk structure with a direct quasiparticle band gap of 2.8 eV and an indirect gap of 2.14 eV. This dramatic increase in the band gap is attributed to quantum confinement effects on the geometry and intra-helix bonding. Shifts in the band gaps are also reflected as shifts in the low-energy optical absorption spectra calculated via density functional theory. As more helical chains are added, the band gap decreases sharply while the geometry becomes more bulk-like. This work illustrates the strong effects of quantum confinement in low-dimensional α-HgS nanostructures.
Quasi-particles ultrafastly releasing kink bosons to form Fermi arcs in a cuprate superconductor.
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. PMID:26728626
Thermoelectric and Lattice Dynamical Properties of Ge2Sb2Te5
NASA Astrophysics Data System (ADS)
Mukhopadhyay, Saikat; Sun, Jifeng; Subedi, Alaska; Singh, David
2015-03-01
Ge2Sb2Te5 (GST) has been widely used as phase-change materials in optical data storage media and nonvolatile RAM devices. At elevated temperature, GST is known to undergo subsequent structural transitions from a non-conducting amorphous to (metastable) disordered cubic phase and then to a conducting hexagonal phase above 300°C. Given that hexagonal-GST has already been reported to have promising thermoelectric properties and transport properties critically depend on the bonding information, a direct correlation between its structural- and transport properties needs to be established. In this talk, we will present the evolution of thermoelectric and lattice dynamical properties of GST in different phases via first principles calculations based on density functional theory. A better understanding of the origin of low-thermal conductivity in hexagonal-GST may provide critical information for further improvement of its thermoelectric figure of merit (ZT).
Coupled light transport-heat diffusion model for laser dosimetry with dynamic optical properties
London, R.A.; Glinsky, M.E.; Zimmerman, G.B.; Eder, D.C.; Jacques, S.L.
1995-03-01
The effect of dynamic optical properties on the spatial distribution of light in laser therapy is studied via numerical simulations. A two-dimensional, time dependent computer program called LATIS is used. Laser light transport is simulated with a Monte Carlo technique including anisotropic scattering and absorption. Thermal heat transport is calculated with a finite difference algorithm. Material properties are specified on a 2-D mesh and can be arbitrary functions of space and time. Arrhenius rate equations are solved for tissue damage caused by elevated temperatures. Optical properties are functions of tissue damage, as determined by previous measurements. Results are presented for the time variation of the light distribution and damage within the tissue as the optical properties of the tissue are altered.
Decay of fermionic quasiparticles in one-dimensional quantum liquids.
Matveev, K A; Furusaki, A
2013-12-20
The low-energy properties of one-dimensional quantum liquids are commonly described in terms of the Tomonaga-Luttinger liquid theory, in which the elementary excitations are free bosons. To this approximation, the theory can be alternatively recast in terms of free fermions. In both approaches, small perturbations give rise to finite lifetimes of excitations. We evaluate the decay rate of fermionic excitations and show that it scales as the eighth power of energy, in contrast to the much faster decay of bosonic excitations. Our results can be tested experimentally by measuring the broadening of power-law features in the density structure factor or spectral functions. PMID:24483750
Multi-quasiparticle isomers near stability and reduced pairing
Dracoulis, G.D.
1996-12-31
The proximity of high-{Omega} orbitals near both proton and neutron Fermi surfaces in nuclei near Z = 74 and N = 104 results in high-K states competing with collective rotation of low-seniority configurations to generate the yrast line. In favorable situations it is possible to observe both the intrinsic states and associated rotational bands. The band properties allow characterization of the configurations and evaluation of orbital and seniority-dependent effects, including pairing reduction and consequent loss of nuclear superfluidity.
NASA Technical Reports Server (NTRS)
Tesar, Delbert; Tosunoglu, Sabri; Lin, Shyng-Her
1990-01-01
Research results on general serial robotic manipulators modeled with structural compliances are presented. Two compliant manipulator modeling approaches, distributed and lumped parameter models, are used in this study. System dynamic equations for both compliant models are derived by using the first and second order influence coefficients. Also, the properties of compliant manipulator system dynamics are investigated. One of the properties, which is defined as inaccessibility of vibratory modes, is shown to display a distinct character associated with compliant manipulators. This property indicates the impact of robot geometry on the control of structural oscillations. Example studies are provided to illustrate the physical interpretation of inaccessibility of vibratory modes. Two types of controllers are designed for compliant manipulators modeled by either lumped or distributed parameter techniques. In order to maintain the generality of the results, neither linearization is introduced. Example simulations are given to demonstrate the controller performance. The second type controller is also built for general serial robot arms and is adaptive in nature which can estimate uncertain payload parameters on-line and simultaneously maintain trajectory tracking properties. The relation between manipulator motion tracking capability and convergence of parameter estimation properties is discussed through example case studies. The effect of control input update delays on adaptive controller performance is also studied.
NASA Astrophysics Data System (ADS)
Shah, Kruti; Choi, Seung-Bok; Choi, Hyoung Jin
2015-05-01
In this work, the field-dependent rheological properties of a nano-sized magnetic particle-based ferrofluid (NMPFF) are experimentally investigated in dynamic mode at different temperatures. This NMPFF has several inherent rheological properties such as improved shear thinning, elevated dynamic moduli, and thermo-rheological complexity. These properties come from the presence of a long chain- like structure in the NMPFF under the influence of an applied magnetic field. The proposed NMPFF is a magnetic colloidal suspension of a mixture of two different nano-sized magnetic particles, which are dispersed in a carrier liquid in an appropriate weight fraction. The structural and morphological properties of the particles are firstly investigated using small-angle neutron scattering and a transmission electron microscope, respectively. Subsequently, the temperature-dependent rheological properties of the NMPFF are measured in an oscillatory mode using the magneto-rheometer. In the amplitude sweep test, it is observed that as the temperature increases due to the thermal expansion of the carrier liquid, the structure continuously expands up to critical temperature. In the frequency sweep test, it is found that the magnitude of the storage modulus is nearly constant with increasing temperature.
Static and dynamic mechanical properties of amorphous recycled poly-(ethylene terepthalate)
NASA Astrophysics Data System (ADS)
Rajakutty, Arjun
Scope and Method of Study: Polymers are among the largest used materials today in the world. PET has a significant market share among all the other polymers. More than 90% of plastic bottles made in the world are from PET. With this huge amount of material being used, the impact on the environment in the form of increasing landfills and carbon dioxide emissions has also been high. Hence the need to recycle PET and reuse it has been a topic of interest over the last few years. However, loss in properties of recycled PET (rPET) has been a concern and it is still considered secondary to virgin PET. This work was aimed at studying the mechanical properties of rPET and comparing these properties with those from virgin PET. The dynamic behavior of PET was part of this study. Apart from studying the mechanical properties of rPET, several other tests were performed to study thermal properties, crystallinity, color measurements (yellowing), friction behavior and also to determine structural performance of blow molded bottles. Material properties obtained from experimental results were used as input for Finite Element simulations. Findings and Conclusions: The findings and results from this research have provided a framework to understand the mechanical properties of rPET. The method of tensile testing using the custom fixture was an efficient means of determining bulk mechanical properties. rPET was found to have properties similar to virgin PET resins with dynamic measurements showing the greatest differences near 100 mm/min. The dynamic properties with increasing strain rates generally fit power law or exponential curves. DSC measurements along the preform helped to understand the crystallinity distribution and validate the new tensile sample injection method. Strain induced crystallization was also observed. Color measurements provided a good indication of the yellowness index values in rPET and changes in these values on addition of coloring agents. Top load and hoop
The use of molecular dynamics for the thermodynamic properties of simple and transition metals
Straub, G.K.
1987-04-01
The technique of computer simulation of the molecular dynamics in metallic systems to calculate thermodynamic properties is discussed. The nature of a metal as determined by its electronic structure is used to determine the total adiabatic potential. The effective screened ion-ion interaction can then be used in a molecular dynamics simulation. The method for the construction of a molecular dynamics ensemble, its relation to the canonical ensemble, and the definition of thermodynamic functions from the Helmholtz free energy is given. The method for the analysis of the molecular dynamics results from quasiharmonic lattice dynamics and the decomposition in terms of harmonic and anharmonic contributions is given for solids. For fluid phase metals, procedures for calculating the thermodynamics and determining the constant of entropy are presented. The solid-fluid phase boundary as a function of pressure and temperature is determined using the results of molecular dynamics. Throughout, examples and results for metallic sodium are used. The treatment of the transition metal electronic d-states in terms of an effective pair-wise interaction is also discussed and the phonon dispersion curves of Al, Ni, and Cu are calculated.