Shock compression and thermodynamics of highly nonideal metallic plasma

Using experimental data on compression and heating of dense metallic plasma by powerful shock waves, we have analyzed the effect of strong Coulomb interaction on both discrete and continuum bands of energy spectrum, the role of short-range repulsion, and the effect of degeneracy on the equation of state for a dense, nonideal metallic plasma. Explosive devices have been used to produce plasma for which the degree of ionization, nonideal parameter, and degeneracy varied over wide ranges. In order to increase effects of irreversible energy dissipation, metal targets of low densities have been used. Thermodynamic measurements have been compared to theoretical models taking into account Coulomb interaction, short-range repulsion, and degeneracy of electrons. The plasma models have been shown to be applicable to the equilibrium properties of multiply ionized plasma in a wide region of the phase diagram characterized by extremely high parameters [T⩾10⁴ K, P⩾10 GPa, and ρ=(0.1–1)ρ ₀], which is beyond the traditional domain of plasma physics. Zh. éksp. Teor. Fiz. 114, 1242–1265 (October 1998)     

Incoherent structure factor of hydrogen in NbH0.11

We show that the measurement of the quasielastic energy spectrumS(Q,) of incoherently scattered neutrons provides a direct andprecise method to determine the location of the H atom diffusing on interstitial sites in a metal lattice. At the reciprocal lattice points the spectrum contains a sharp elastic line with a relative intensity which is equal to the structure factor of the occupied sites. In a neutron scattering experiment performed on a NbH_0.11 single crystal, we have measured the structure factor at the (110), (200) and (222) reflection at elevated temperatures (148°C and 280°C). Our results give clear evidence of tetrahedral site occupancy and exclude an appreciable partial occupation of octahedral (3%) and triangular sites (7%) at 280°C. These findings support the basic assumption of the Chudley Elliott theory in the study of jump diffusion models of H assuming a negligible flight time in the jump process between neighbouring sites.     

Compton line profile component of atomic hydrogen in the profile of NbH1.2

The Compton profile of polycrystalline NbH_1.2 has been measured at room temperature using a -ray Compton spectrometer with a 1.85×10¹⁰ Bq(0.5 Ci)²⁴¹ Am annular source and an intrinsic Germanium detector. This is compared to the spherical average profile of NbH_0.3 single crystals oriented along [100], [110] and [111]. The difference between these profiles bears a striking similarity to the Compton profile of atomic hydrogen. This can be understood assuming that a large part of the dilute hydrogen forms atomic clusters at the grain boundaries.     

Magnetism and transport studies in off-stoichiometric metallic perovskite compounds GdPd3Bx (x=0.25, 0.50 and 0.75)

We report the magnetic and transport properties of the off-stoichiometric metallic perovskite like compounds GdPd₃B_x (x=0.25, 0.50 and 0.75). Our results show that doping with boron in the lattice of parent binary-compound GdPd₃ leads to lattice expansion. Which in turn manifests in contrasting magnetic and transport behaviors of the doped compounds in comparison with the undoped GdPd₃. An attempt has been made to compare and correlate the results of magnetic and transport measurements of GdPd₃B_x with that of stoichiometric compositions GdPd₃B_xC_1−x. The comparative study of GdPd₃B_x and GdPd₃B_xC_1−x confirms that there is a strong correlations between the structural, magnetic and transport properties of these compounds.     

Deuterium-deuterium nuclear cross-sections in insulator and metallic environments

The three-dimensional Thomas-Fermi (TF) model is used to simulate the variation of the d + d → t + p cross-section at low impact energies, when the target deuterium nucleus is embedded in metallic or insulator environments. The comparison of the computational results to recent experiments demonstrates that even though the TF model can explain some increase in the low-energy cross-section for metallic host, a full explanation of the experimental results is still lacking. Possible reasons for the disagreement are discussed.     

Reconstruction of bands in metallic hydrogen

The generalized theory of normal properties of a metal for the case of the properties of the electronic band of electron–phonon systems with a variable electron density of states is used to study the normal phase of metallic hydrogen at a pressure of 500 GPa and a temperature of 200 K. We calculated the frequency dependence of the real ReΣ(ω) and imaginary ImΣ(ω) parts of the self-energy part of the electron Green’s function Σ(ω), as well as the electron density of states N(ε) of the stable phase of metallic hydrogen with the I41/amd symmetry at a pressure of 500 GPa, renormalized by the strong electron–phonon coupling. It is found that the electron conduction band of the I41/amd phase of metallic hydrogen undergoes insignificant reconstruction near the Fermi level because of the renormalization by the electron–phonon coupling.     

Universal features of polymer shapes in crowded environments

We study the universal characteristics of the shape of a polymer chain in an environment with correlated structural obstacles, applying the field-theoretical renormalization group approach. Our results qualitatively indicate an increase of the asymmetry of the polymer shape in crowded environment comparing with the pure solution case.     

Spin glass behavior probed by various methods with different time- and space-scale of observation: Ising spin glass Fe0.50Mn0.50TiO3

Under the expectation that the behavior of a spin glass (SG) system shows various aspects depending on the time- and space-scale of observations, we have studied the typical Ising spin glass Fe_0.50Mn_0.50TiO₃ by measuring dc-magnetization, ac-susceptibility, Mössbauer spectrum, neutron scattering intensity and μ⁺SR time spectrum. We have demonstrated that the application of various methods with different time- and space-scale of observations to the same system is useful to clarify the property of the spin glass freezing, the Ising character and the de Almeida and Thouless-line.     

Shock compression of simple liquids: Implications for deuterium

Abstract

This report summarizes research on shock-compressed liquids: argon, xenon, nitrogen, and hydrogen. The purpose is to illustrate the common thread that connects all of these studies with the recent work on deuterium.     

金属玻璃温度依赖的拉压屈服不对称研究

通过引入静水应力对自由体积演化的影响, 研究了金属玻璃在不同温度下的拉压屈服行为. 结果表明, 在拉伸和压缩载荷下, 屈服强度均满足(T/T_g)^1/2的温度依赖关系; 同时, 在不同温度下, 材料的压力敏感系数保持为常值0.1. 随着温度的升高, 压力对自由体积的影响逐渐降低, 从而导致材料的拉压屈服不对称性逐渐趋于不显著. 在高温下, 显著的结构弛豫减缓了自由体积增长速率从而抑制材料迅速屈服. 这些结果将有助于更深入的认识金属玻璃屈服及其拉压不对称性的内在机理.     

Universal conductance fluctuations in three dimensional metallic single crystals of Si

In this paper we report the measurement of conductance fluctuations in 3D crystals of Si made metallic by heavy doping. ( L/L(straight phi) approximately 10(3), where L(straight phi) is the phase coherence length.) Temperature and magnetic field dependence of noise strongly indicate the universal conductance fluctuations as a predominant source of the observed magnitude of noise. Conductance fluctuations within a single phase coherent region of L(3)(straight phi) were found to be saturated at <(deltaG(straight phi))(2)> approximately (e(2)/h)(2). An accurate knowledge of the level of disorder enables us to calculate the change in conductance deltaG1 due to movement of a single scatterer as <(deltaG1)(2)> approximately (e(2)/h)(2), which is approximately 2 orders of magnitude higher than its theoretically expected value in 3D systems.     

Onset of metallic behavior in magnesium clusters

We have measured the photoelectron spectra of mass-selected magnesium cluster anions, Mg- n, over the size range, n=3-35. Their s-p band gaps were observed to close at n=18, signaling the onset of metallic behavior. Electronic shell structure was implicated by gap "reopenings" and mass spectral magic numbers. Complementary calculations are presented in the companion paper [P. H. Acioli and J. Jellinek, Phys. Rev. Lett. 89, 213402 (2002)]].     

Nonlinear response and avalanche behavior in metallic glasses

The response to different stress amplitudes at temperatures below the glass transition temperature is analyzed by mechanical oscillatory excitation of Pd₄₀Ni₄₀P₂₀ metallic glass samples in single cantilever bending geometry. While low amplitude oscillatory excitations are commonly used in mechanical spectroscopy to probe the relaxation spectrum, in this work the response to comparably high amplitudes is investigated. The strain response of the material is well below the critical yield stress even for highest stress amplitudes, implying the expectation of a linear relation between stress and strain according to Hooke’s Law. However, a deviation from the linear behavior is evident, which is analyzed in terms of temperature dependence and influence of the applied stress amplitude by two different approaches of evaluation. The nonlinear approach is based on a nonlinear expansion of the stress-strain-relation, assuming an intrinsic nonlinear character of the shear or elastic modulus. The degree of nonlinearity is extracted by a period-by-period Fourier-analysis and connected to nonlinear coefficients, describing the intensity of nonlinearity at the fundamental and higher harmonic frequencies. The characteristic timescale to adapt to a significant change in stress amplitude in terms of a recovery timescale to a steady state value is connected to the structural relaxation time of the material, suggesting a connection between the observed nonlinearity and primary relaxation processes. The second approach of evaluation is termed the incremental analysis and relates the observed response behavior to avalanches, which occur due to the activation and correlation of local microstructural rearrangements. These rearrangements are connected with shear transformation zones and correspond to localized plastic events, which are superimposed on the linear response behavior of the material.     

Anisotropy in the Compton profiles of Nb and NbH0.76

The Compton profiles of Nb and NbH_0.76 single crystals have been measured along [100] and [110] using 412 keV gamma-radiation from a¹⁹⁸Au source. The changes in the band electron profile of the metal following the introduction of hydrogen are interpreted in terms of the protonic model of the hydride. Qualitative changes in the directional profiles can be understood within the rigid band approximation.     

Reconstruction of the conduction band in metallic hydrogen sulfide

The theory of the normal properties of a metal generalized to the case of particular properties of an electron band with a finite width for electron–phonon systems with a varying electron density of states has been used to study the normal state of the SH₃ phase of hydrogen sulfide at a pressure of 225 GPa and a temperature of 200 K. The frequency dependences of the real, ReΣ(ω), and imaginary, ImΣ(ω), parts of the selfenergy part of the Green’s function of the electron Σ(ω), as well as the electron density of states N(ε) of the Im–3m stable orthorhombic structure of SH₃ hydrogen sulfide at a pressure of P = 225 GPa, which is renormalized by the strong electron–phonon coupling, have been calculated. It has been established that a part of the electron conduction band of the SH₃ phase of hydrogen sulfide adjacent to the Fermi level undergoes renormalization-induced reconstruction in the form of a number of energy pockets with the widths equal to fractions of the characteristic phonon energies of the system.     

Change of the 7Be electron capture half-life in metallic environments

For the electron capture of ⁷Be in the metallic environments Pd and In the ⁷Be half-life was observed to increase by 0.9±0.2 and 0.7±0.2%, respectively, while in the insulator Li₂O it was unchanged within experimental error (all samples cooled to T = 12K). The observations are consistent with the predictions of the Debye plasma model applied to the quasi-free electrons in the metals.     

Universal behavior in a generalized model of contagion

Models of contagion arise broadly in both the biological and the social sciences, with applications ranging from the transmission of infectious diseases to the spread of cultural fads. In this Letter, we introduce a general model of contagion which, by explicitly incorporating memory of past exposures to, for example, an infectious agent, rumor, or new product, includes the main features of existing contagion models and interpolates between them. We obtain exact solutions for a simple version of the model, finding that under general conditions only three classes of collective dynamics exist. Furthermore, we find that, for a given length of memory, the class into which a particular system falls is determined by only two parameters. Our model suggests novel measures for assessing the susceptibility of a population to large contagion events, and also a possible strategy for inhibiting or facilitating them.