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Infrared observations of the interstellar medium have unveiled the existence of numerous solid-phase molecules. The recent detection of uracil within the (162173) Ryugu asteroid has opened new prospects for the discovery of additional compounds, including nitrogenous bases, in the near future. To facilitate the comprehension, identification, and observation of these substances within astrophysical environments, precise measurements of their infrared band strengths are crucial. In this study, we present the outcomes of laboratory experiments conducted to investigate the behavior of adenine at various temperatures. The measured band strength from 3600 to 1970 cm−1 was determined to be 3.21⋅10−16 cm molecule−1. Additionally, as the temperature decreased, its behavior exhibited a well-fitted second-degree polynomial function. Notably, the experiments indicated no permanent phase changes or hysteresis during the cool-down and warm-up processes, further elucidating the thermal properties of adenine. [ABSTRACT FROM AUTHOR]

For CuInP2S6 layered crystal the temperature anomalies of the heat capacity and entropy at the ferrielectric ordering are explained based on the theoretical studies which predict the appearance of a critical endpoint and a bicritical endpoint on the phase diagram. Thus, the splitting of the anomaly of the heat capacity in Ag0.1Cu0.9InP2S6 mixed crystal can be interpreted as a transformation of the ferrielectric first-order phase transition, that is observed for CuInP2S6, into the sequent paraelectric–ferrielectric second-order phase transition and the isostructural first-order transition with a sharp change of the polarization in the ferrielectric phase. [ABSTRACT FROM AUTHOR]

The field dependence of magnetization at T = 4.2 K and in magnetic fields of up to 70 kOe, temperature dependences of magnetization (2 K < T < 300 K), heat capacity (2 K < T < 30 K) and magnetic susceptibility (2 K < T < 1000 K) for Mn1.99Co0.96Al1.05 and Mn1.79Co1.25Al0.96 alloys, closed in composition to the Mn2CoAl spin gapless semiconductor, were studied. Alloys studied were demonstrated to be the band ferromagnets. Their high-field (H > 11 kOe) magnetization is described in the Stoner models with the Rhodes-Wohlfarth parameter pRW = 1.3 for Mn1.99Co0.96Al1.05 and pRW = 2.3 for Mn1.79Co1.25Al0.96. When the composition deviates from the stoichiometric Mn2CoAl, the spontaneous moment decreases slightly, the effective moment, on the contrary, increases. In this case, a negative sign of the temperature-independent component of the paramagnetic susceptibility is observed. The density of states n(EF) at Fermi level and the Debye temperature ΘD of studied alloys have the usual values for 3d-metal alloys. [ABSTRACT FROM AUTHOR]

The Mayer group expansion for solids proposed earlier is applied in prediction of the location of polymorphic phase transition line between the cubic and layered phases of polymeric nitrogen. The comparison with existing measurements revealed that theoretical calculations based on the proposed potential model calibrated on ab initio energy calculations are in agreement with existing experimental data. Predicted location of the polymorphic transition line and specific behavior of thermal properties of both phases in a wide temperature range is discussed. [ABSTRACT FROM AUTHOR]

The observation of the thermoelectric effect, which is the spontaneous electric polarization of a cell with liquid He II during the thermal excitation of standing second-sound waves, has been confirmed [Low Temperature Physics 30, 1321 (2004)]. The relationship of this effect with the thermal and hydrodynamic properties of He II is studied in detail in the temperature range of 1.4 K < T < 2 K. It is established that the dependence of the amplitude of electric potential oscillations on the excitation intensity changes significantly during the thermal vibrations' transition from the laminar to the turbulent regime. The threshold value of the excitation power w = w0 (T) is recorded: in the region w < w0, the potential oscillations are regular and their amplitude increases in proportion to the power; at w > w0, the electric response becomes random in nature as the fluctuations increase and the amplitude decreases to zero, with a peculiar electromagnetic "noise" being observed. The experimental results are compared with the conclusions drawn from the theory of flexoelectric polarization of liquid helium. The polarization of liquid helium upon excitation of the first-sound waves, as well as pressure and temperature shock waves, has also been discussed. [ABSTRACT FROM AUTHOR]

A model of a one-dimensional nonideal gas in an external transverse force field is used to interpret the experimentally observed thermodynamic properties of xenon deposited in grooves on the surface of carbon nanobundles. A nonideal gas model with pairwise interactions is not entirely adequate for describing dense adsorbates (at low temperatures), but makes it easy to account for the exchange of particles between the 1D adsorbate and the 3D atmosphere, which is an important factor at intermediate (on the order of 35K for xenon) and, especially, high (∼100 K) temperatures. In this paper, we examine a 1D real gas taking only the one-dimensional Lennard-Jones interaction into account, but under exact equilibrium with respect to the number of particles between the 1D adsorbate and the 3D atmosphere of the measurement cell. The low-temperature branch of the specific heat is fitted independently by an elastic chain model so as to obtain the best agreement between theory and experiment over the widest possible region, beginning at zero temperature. The gas approximation sets in after temperatures for which the phonon specific heat of the chain essentially transforms to a one-dimensional equipartition law. Here the basic parameters of both models can be chosen so that the heat capacity C(T) of the chain transforms essentially continuously into the corresponding curve for the gas approximation. Thus, it can be expected that an adequate interpretation of the real temperature dependences of the specific heat of low-dimensionality atomic adsorbates can be obtained through a reasonable combination of the phonon and gas approximations. The main parameters of the gas approximation (such as the desorption energy) obtained by fitting the theory to experiments on the specific heat of xenon correlate well with published data.VC [ABSTRACT FROM AUTHOR]

The thermal conductivity of three single crystal samples of n-type gallium nitride with electron densities of 4.0 × 1016, 2.6 × 1018, and 1.1 × 1020 cm-3 has been determined in the temperature range 4-320K. The measurements were carried out within the ab plane using the stationary method. The thermal conductivity depends strongly on the donor concentration. The analysis within the Callaway approach and the Debye model shows a significant influence of phonon-electron scattering on the thermal conductivity of the samples. In addition, some preliminary results obtained along the c axes of GaN layered samples are presented. The latter measurements have been carried out using the 3ω method. [ABSTRACT FROM AUTHOR]

Creep in solid 4He at temperatures of ~100-1000 mK is studied experimentally by detecting the flow of helium through a frozen porous membrane under a constant external force. Creep curves are measured for different temperatures and mechanical stresses. This method has made it possible to detect low creep rates in helium down to the lowest temperatures in these experiments. It is found that throughout this temperature range, creep is thermally activated and the activation energy decreases with falling temperature and increasing mechanical stress. An analysis shows that for temperatures above ≈500 mK, Nabarro-Herring diffusive creep takes place in solid helium with mass transfer by self diffusion of atoms and a counterflow of vacancies. The experimental data have been used to obtain the self-diffusion coefficient as a function of temperature for different stresses. At temperatures below ≈500 mK creep takes place at a very low flow rate (~10-13 cm/s) and a very low activation energy (~0.5-0.7 K), while the creep mechanism remains unclear. [ABSTRACT FROM AUTHOR]

A reduction in the transmission of terahertz radiation through a periodically modulated slab of layered superconductor owing to diffraction of the incident wave and resonance excitation of eigenmodes is predicted and studied theoretically. The slab thickness is assumed to be much less than the skin depth and when there is no modulation the slab transmission is close to unity. [ABSTRACT FROM AUTHOR]

The effect of combined deformation, including equal-channel multiangle pressing (ECMAP), lowtemperature (77 K) drawing, and thermal processing, on the critical current density of superconducting wires based on Nb-Ti alloys is investigated. Reasonable parameters are established for deformation-thermal processing of NT-50 alloy using ECMAP that will ensure improved functionality of superconductors based on this alloy. Vortex pinning on structural inhomogeneities of these alloys is analyzed qualitatively. [ABSTRACT FROM AUTHOR]

The effect of oxygen impurities on the radial thermal expansion αr of bundles of closed, single-walled carbon nanotubes has been investigated at temperatures of 2.2-48 K by a dilatometric method. Saturation of bundles of nanotubes with oxygen causes an increase in the positive αr-values over the entire range of temperatures studied here. Also, several peaks appeared in the αr(T) curve above 20 K. Low-temperature desorption of oxygen from powders consisting of bundles of single-walled nanotubes with open and closed ends has been investigated. [ABSTRACT FROM AUTHOR]

The dynamics of low-density trapped magnetic fluxes, including local fluxes, are investigated in single-crystal YBCO in the region of strong thermal fluctuations near the superconducting phase transition. A substantial difference of the isothermal magnetization-relaxation behavior from the quasi-logarithmic behavior observed earlier in strong magnetic fields is established for the first time. The effective pinning potential in the temperature interval close to the critical temperature is estimated in terms of the simplest model of thermally activated creep. [ABSTRACT FROM AUTHOR]

The structure and growth processes of clusters formed in adiabatically expanding supersonic jets of gaseous mixtures of rare gases are investigated for the first time. Ar–Kr mixtures containing 0.1, 0.5, 2.5, and 20% Kr atoms are studied at temperatures and pressures of the gaseous mixtures at the nozzle entrance T0=100 and 120 K and P0=0.15–2.5 atm. The experiments give a number of results that shed light on the picture of cluster formation in Ar–Kr gaseous mixtures. It is established that the mechanisms of cluster formation depend substantially on the krypton impurity concentration and the temperature of the gaseous mixture at the nozzle entrance. The evolution of the character of the cluster formation, from homogeneous to heterogeneous, is traced. The intensification of rare-gas cluster growth by an impurity is revealed for the first time, and the concentration dependence of the transition from a process of formation of solid solutions to the formation of clusters containing only impurity krypton is traced. [ABSTRACT FROM AUTHOR]

The temperature, field, and intensity (amplitude) dependences of the surface impedance of magnetron-sputtered YBa2Cu3O7-δ quasi-single-crystal films on a sapphire substrate with a CeO2 buffer layer were measured. The measurements were performed with a coplanar resonator at 5.25 GHz in a weak constant magnetic field 0

The temperature dependences of the lattice parameters are investigated on the perovskite-like structures Eu1+x(Ba1-yRy)2-xCu3O7-d with Ba substitution by light rare earth, using x-ray diffraction techniques. A negative thermal expansion effect is observed and explained in detail. © 2005 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The exchange coupling of magnetically ordered layers (MOLs) through a nonmagnetic metallic spacer is calculated. The induced magnetization in the spacer, taking into account the influence of an external magnetic field, is calculated, too. This calculation shows that the energy of coupling of the MOLs through the nonmagnetic metallic spacer is a long-periodic function of the spacer thickness and magnetic field, i.e., the exchange coupling between the layers varies from ferromagnetic to antiferromagnetic and vice versa depending on the spacer thickness and magnetic field. Also this calculation shows that in nonferromagnetic spacer the induced magnetization can undergo many complete rotations, depending on distance to the boundaries with the MOLs. Moreover, absolute value of the induced magnetization decays nonmonotonically with distance from the interfaces inside the spacer. It is shown that the character of the decay of the absolute value of the magnetization from the interfaces into the interior of the spacer is influenced by magnetic field. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The transformation of the magnetic absorption spectra of a narrow-band ferromagnetic conductor containing local f and quasilocal d magnetic moments under conditions of weak spin–lattice coupling and spatial randomization of the g factors of the quasilocal and local spin subsystems is investigated. It is shown that randomization of the g factors (e.g., as a result of the introduction of an impurity) leads mainly to the “opening” (i.e., to the appearance in the magnetic absorption spectrum) of acoustic and optical magnon bands formed in the system while not affecting the position and shape of the narrow magnetic resonance lines comprising the spectrum of the impurity-free crystal. The effects of spin–lattice coupling, besides the “opening” of the phonon and magnon bands, lead to a shift and a temperature smearing of the narrow resonance lines. The relative corrections to the effective magnon masses generated by the spin–lattice coupling in a 4f–5d metal amount to ∼2×10-4 for an acoustic mode and to ∼4×10-4 for an optical mode. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The equations for the nuclear magnetizations which describe the dynamics of nuclear spin-systems with strong Larmor and Rabi inhomogeneous broadenings of the NMR line under conditions of their nonequilibrium are obtained in the framework of the Mims transformation matrix method; these equations have been obtained previously by the statistical tensors method. As an example, the properties of the proton single-pulse echo and its secondary signals in a test material (silicone oil) coated on the surface of high-Tc superconducting-oxide powders and in metallic hydride are presented. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A model is proposed which describes the formation and reversible rearrangement of the equilibrium domain structure in bulk antiferromagnets with a rather strong magnetoelastic coupling. The model is based on the assumed existence of a microscopic ordering of a tensor nature—the microstress tensor that arises due to magnetoelastic coupling during the formation of the magnetic moment. It is necessary to take such a parameter into account for adequate description not only of the macroscopic internal stresses and the spontaneous strains corresponding to them but also of the microstructure of the crystal (e.g., the domain structure). The microstresses arising locally in each unit cell are equivalent, from a formal standpoint, to elastic dipoles, and they create long-range fields whose contribution to the free energy of the crystal is analogous to that of the magnetostatic energy in ferromagnets and favors a decrease in the macroscopic strain of the sample through the formation of an equilibrium domain structure. The corresponding contribution is given the name “destressing energy” by the authors. It is shown that taking this energy into account in antiferromagnetic crystals allows one not only to explain the cause of the formation of the domain structure but also to trace its dependence on the shape of the crystal and the external fields. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The vibrational spectrum of a one-dimensional disordered chain of atoms with light isotopic substitutional impurities is calculated numerically for frequencies near a local mode of an isolated impurity atom. It is shown that in the entire frequency region accessible to the calculation, the spectrum does indeed have the characteristic features of a fractal. Series of lines clustered around the lines of an isolated impurity atom or of two and three impurity atoms are examined. It is shown that in these cases a self-similar structure is preserved at arbitrary reductions of the scale both outside and inside the concentration broadening region. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The features of the variation in the superconducting transition temperature Tc of Re1-xMox alloys in the interval of Mo concentrations C up to 5 at. % (within the solid solution region) are investigated at pressures P of up to 10 kbar. A nonlinear increase of Tc to ≈5 K is observed when an impurity of C≈4.7 at. % Mo is added, and an inflection point is observed at C≈2.35 at. % Mo. The dependence (∂Tc/∂P)(C) has a minimum at the same Mo concentration. This attests to the presence of a critical energy Ec

Polycrystalline samples of fullerite C60 with different concentrations of molecular nitrogen impurity are studied by luminescence spectroscopy at temperatures of 20-230 K. The photoluminescence characteristics of the C60-N2 solutions vary significantly. At T = 20 K there is a significant contribution to the luminescence from emission centers ("deep X-traps") determined by the concentration of N2 molecules in octahedral voids of the fcc C60 lattice. The experimentally observed differences in the effect of nitrogen impurities on the structural and luminescence characteristics of C60-N2 solutions show that the filling of the lattice voids into the depth (from the surface) of the samples is substantially inhomogeneous. The temperature dependences of the integrated emission intensity from samples with different nitrogen concentrations are studied. N2 molecules are found to have little effect on the formation of fullerite orientational glass. A tendency for the vitrification temperature of these C60-N2 solutions to fall with increasing impurity concentration is observed experimentally. [ABSTRACT FROM AUTHOR]

Describes the effect of zero-temperature attenuation on various processes in helium and ferromagnetic systems. Spin dynamics of Fermi liquids; Theoretical and experimental data on zero-temperature attenuation in transverse spin dynamics of helium systems; Coupling between longitudinal and transverse processes.

This paper discusses the temperature and field dependences of the magnetization of the nanocomposite compound GdNiO3 in the temperature interval 0.5–150 K in magnetic fields up to 14 T. The temperature dependences of the heat capacity are also investigated in magnetic fields up to 9 T. Anomalies of the static susceptibility, heat capacity, and dynamic magnetization are detected at temperatures of 0.7, 1.6, and 13 K, respectively. The detected anomalies are associated with magnetic phase transitions. [ABSTRACT FROM AUTHOR]

The low-temperature stationary creep of solid normal hydrogen grown in a polycrystalline form is investigated. The experimental temperature range 1.4–4.2 K includes the temperature T[sub c] of the phase transformation of n-H[sub 2]. It is found that as the temperature of n-H[sub 2] decreases to T[sub c] the stationary creep rate of the samples abruptly decreases. This which could be due to stiffening of the n-H[sub 2] lattice as a result of orientational ordering of the orthomolecules.© 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The isochoric thermal conductivities of the solid solutions (CO2)0.905Kr0.095 and (CO2)1-xXex (x=0.052 and 0.097) of different densities are investigated in the temperature interval from 150 K to the onset of melting. An unusual effect of point defects on the thermal conductivity has been detected. In pure CO2 at T>150 K the isochoric thermal conductivity decreases smoothly with increasing temperature. In contrast, the thermal conductivity of CO2/Kr and CO2/Xe solid solutions first decreases, passing through a minimum at 200–210 K, and then starts to increase with temperature up to the onset of melting. This behavior of the isochoric thermal conductivity is attributed to the rotation of the CO2 molecules, which gain more freedom as the spherically symmetrical inert gas atoms are dissolved in the CO2. [ABSTRACT FROM AUTHOR]

The NMR method is used to study the temperature variations of local fields on 57Fe nuclei in the octahedral positions 12k, 4f2, and 2a of the iron ions in the ferrite BaFe12O19. The possibility of applying Bloch’s spin-wave theory to describe the temperature variations of the local fields on the iron nuclei is examined. Deviations from Bloch’s 3/2 power law are found in the temperature range 4.2–77 K. These deviations cannot be described on the basis of the behavioral characteristics due to the presence of an energy gap in the acoustic magnon spectrum. © 2005 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The ESR spectrum of a powder sample of the metal-organic complex Cu(C10H8N2)(H2O)2SO4 is investigated in the temperature interval 2–30 K. It is found that the orbital ground level of the Cu2+ ion in this compound is the Kramers doublet |x2-y2>. The temperature dependences of the effective g-factor components and of the resonance linewidth ΔH of individual powder particles are obtained. Low-temperature broadening of the resonance line connected with short-range magnetic order in the system is observed. An estimate of the value of the exchange coupling in the magnetic system is made. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

It is shown that a strong disorder in the distribution of exchange couplings between magnetic impurities and hosts in quantum spin chains and non-Fermi-liquid rare-earth and actinide compounds can be the cause of magnetic orderings in these systems at low temperatures. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Examines the theory for normal state critical Kapitza resistance of helium isotopes. Incorporation of critical order parameter fluctuations near the boundary in non-local thermal resistivity expression; Manifestation of Kapitza resistance by a temperature rise at boundary; Calculation-sensitivity to Dirichlel boundary condition application.

The isochoric thermal conductivity of the solid solutions Kr[sub 1-ξ]Xe[sub ξ] (ξ=0.14 and 0.37) is investigated in the temperature interval from 80 K to the onset of melting. Its value and temperature dependence are in good agreement with the lower limit of the thermal conductivity of the crystal lattice. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The features of the temperature behavior of the lattice constant and the coefficient of thermal expansion of silicon crystals are analyzed in the bond-charge model. The coefficient of thermal expansion and the Gru¨neisen factor for the natural isotopic composition are described to reasonable quantitative accuracy. The influence of the isotopic composition on the value of the lattice constant is discussed in detail. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The thermodynamic properties and distribution functions of highly compressed molecular hydrogen are investigated in a nonempirical atom-atom approximation. Quantum corrections are introduced on the basis of the Feynman variational approach. The pressure, energy, compressibility, thermal expansion, heat capacity, and sound velocity are calculated by the Monte Carlo method at temperatures of 200-500 K and pressures up to 5 GPa. The results are compared with the available experimental data. It is shown that effects due to incompressibility of the molecules and quantum effects must be taken into account in calculating the contributions to the thermodynamic functions from inter- and intramolecular forces. The behavior of the properties of fluid hydrogen near the line of crystallization outside the investigated region is predicted, and an estimate is made for the jump in volume upon crystallization of hydrogen at T=300 K. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]