NMR line shape in anisotropic superconductors in a tilted magnetic field

NMR line shape has been constructed for anisotropic type-II superconductors in tilted magnetic fields, with inclusion of vortex-lattice magnetic-field nonuniformities and of the skin effect near the superconductor surface. The NMR line shape parameters are shown to change considerably when the external magnetic field changes direction. This makes it possible to obtain more detailed information about the characteristics of a superconductor, in particular, its anisotropy parameter. Fiz. Tverd. Tela (St. Petersburg) 40, 993–997 (June 1998)     

Interactive process in the mechanism of thermostimulated luminescence in anion-defect α-Al2O3 crystals

A study of the role of deep traps in the specific features of the thermoluminescence (TL) of anion-defect α-Al₂O₃ single crystals is reported. The existence of deep traps is proven by direct observation of the associated TL peaks. Experimental support for the effect of deep-trap filling on the main characteristics of the main TL peak at 450 K is presented. A model involving trap interaction is proposed, which differs radically from the others described in the literature by taking into account the temperature dependence of the carrier capture probability by deep traps. This model was used to calculate the dependences on heating rate and deep-trap filling of the main parameters of the main TL peak for the crystals under study (TL yield, glow-curve shape, and sensitivity to the stored light sum), which were found to be close to those observed experimentally. Fiz. Tverd. Tela (St. Petersburg) 40, 229–234 (February 1998)     

Kinetics of brittle fracture of elastic materials

A phenomenological model is proposed for the evolution of microcavities in materials under load based on a study of the kinetics of brittle fracture in a linearly elastic deformable medium containing a microcavity. The basic principle of the model is that, during deformation of a material containing a micropore, fluctuations of its shape occur. The surface tension at the micropore-medium interface stabilizes these fluctuations but if the load exceeds a critical value, these fluctuations may begin to evolve. In so doing, they distort the shape of the microcavity. These fluctuations are none other than cracks. This concept of crack growth and their nature has a close analogy with the evolution of dendrites formed in supercooled melts as a result of the loss of stable crystal shape. An analysis is made of the laws governing the evolution of a microcavity and local loss of shape stability under steady-state pressure for the case of a sphere containing a quasispherical cavity. Fiz. Tverd. Tela (St. Petersburg) 40, 1259–1263 (July 1998)     

Inverse problems in the theory of electrostatic energy analyzers. I

General formulas are derived for reconstructing two-dimensional Laplace fields from specified focusing and dispersion characteristics in the plane of symmetry. The electrode configuration is determined for an energy analyzer with ideal focusing of a fan beam. The parameters of the plane trajectories, their shape, and their energy dispersion are determined. Zh. Tekh. Fiz. 69, 128–131 (September 1999)     

Conformational analysis of 2,3-dihydro-3-O-(1,4-naphthoquinon-2-yl)-2-oxo-1,4-naphthoquinone derivatives by the density functional method and IR spectroscopy

We have used the PBE/3z, B3LYP/6-31G, B3LYP/6-31G(d), and B3LYP/6-311G(d) methods to study the conformational mobility of 2,3-dihydro-3-O-(1,4-naphthoquinon-2-yl)-2-oxo-1,4-naphthoquinones (1–4). We have shown that more than 99% of these compounds exist as the major tautomeric form, while differences in the structure of the Q_2H (2,3-dihydro-2-oxo-1,4-naphthoquinones) and Q_1,4 (1,4-naphthoquinon-2-yl) moieties lead to qualitative differences in the internal rotation potentials of the ethyl substituents V(θ_Et−1) and V(θ_Et−2), and consequently each of compounds 1−4 exists as six different rotameric forms. For diquinone 3, we have calculated the dependences of the frequencies (ν) and intensities (A) of the normal vibrations on the torsional angles θ_Et−1 and θ_Et−2, and also on the changes in the geometry of the ether bond. We have found that the values of ν and A for the bands in the carbonyl region of the IR spectrum change little on going from one rotameric form to another, and also for the in-plane bends of the ether bond, and change considerably for the out-of-plane bends of the ether bond. However, for T ≤ 300 K, there is no qualitative change in the overall contour, and it can be interpreted based on a simple additive model. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 5, pp. 573–581, September–October, 2006.     

Stationary soliton on a charged surface of liquid helium and hydrogen films

A change in the shape of a charged surface of liquid hydrogen and helium — the formation of a solitary wave (a positively charged hump for hydrogen and a negatively charged dimple for helium)-is observed in an electric field exceeding a critical value under conditions of total compensation of the applied field by the surface charge. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 7, 547–552 (10 April 1997)     

Shape memory characteristics in the L1 0 -fcc order-disorder transformation of FePd

Shape recovery through L1 0 -fcc order-disorder transformation of FePd is examined. Under a uniaxial compressive stress, a reversible shape change associated with the order-disorder transformation is observed. Shape memory characteristics (transformation strain, time required for the transformation and temperature hysteresis) for single-crystal and polycrystal specimens are determined by a compression test under a constant stress. The transformation strain (4% for a single crystal) and time required for disordering (about 10 s for a single crystal) are comparable with those of conventional martensitic shape memory alloys. The alloys can be used as shape memory materials with relatively high transformation temperature.     

Stiffness of reinforced and unreinforced Bi2Te3 single crystals

We investigate the thermodynamics of Ω- and V-shaped bending of Bi₂Te₃ single crystals. To change the shape of the bending from Ω to V, the sample is reinforced with thin steel rods, arranged perpendicular to the cleavage planes. We find that reinforcement increases the ultimate strength of the samples by more than twofold. We show that the transition Ω→V leads to a substantial change in the spectrum of energy dissipation in the straining of the sample. Some aspects of the practical application of the observed effects are considered. Zh. Tekh. Fiz. 67, 50–54 (February 1997)     

On the Formation of Nanostructures from Stilbazolium-like Dyes

Nanostructures with well-defined shape and highly monodisperse size were fabricated from model stilbazolium-like dyes with specific molecular structural and conformational characteristics. With the help of absorption and fluorescence optical spectroscopy, the correlated spectroscopy (COSY) and two- dimensional nuclear Overhauser effect spectroscopy (2D NOESY) techniques, along with X-ray diffraction (XRD) measurement, distinctively different aggregation processes of the model molecules are demonstrated. For model dye molecule with linear donor–π system–acceptor (D–π–A) structure, strong D–A pair, and planar conformation, specific intermolecular interaction was identified and special crystal structures as well as spectral properties were observed. For model dye molecules bearing nonlinear D–π–A–π–D structure, weak D–A pair but actual amphiphilic characteristics, a special aggregation process was confirmed and a focused size distribution of the produced nanostructures was obtained.     

Singlet-triplet model of cuprate magnetism

A model for describing the spin subsystem of cuprates within a model of polar singlet-triplet Jahn-Teller centers is proposed. In this model spin ordering is described by two vector order parameters S (the total spin of a CuO₄ cluster) and V (the operator of the change in spin multiplicity per cluster). It is shown within a modified mean-field approximation that the formation of a noncollinear magnetic structure characterized by an antiferromagnetic wave vector, which, however, has a nontrivial temperature dependence of the order parameters, is possible along with the formation of ordinary collinear structures of the (anti)ferromagnetic type. The temperature dependences of the order parameters and the principal equilibrium thermodynamic characteristics, viz., the static susceptibility and the specific heat, are obtained. Fiz. Tverd. Tela (St. Petersburg) 40, 1785–1792 (October 1998)     

Formation mechanism for nanodefects on surfaces of loaded metals

Tunneling profilometry is used to investigate the shape and orientation of defects that form at the surfaces of Cu, Au, Mo and Pd under loading. The defects have the shape of an indented prism. The value of the angles at the tip of the defects coincide with the angles between glide planes, while the orientation of the walls coincide with the orientation of these planes. At the edges of the defects there exist “swellings” caused by expulsion of material at the surface. Based on these results, the creation of these defects is explained by the exit of dislocations as they burst through barriers formed at intersecting glide planes. Fiz. Tverd. Tela (St. Petersburg) 40, 668–671 (April 1998)     

Possibility of the appearance of spin autowaves in a model of a ferromagnet with nonuniform dissipation

A model of a ferromagnet with nonuniform dissipation is introduced for the Landau-Lifshitz equations. It is shown that in this model a ferromagnet can be regarded as an oscillating active medium where the formation of autowave structures — spin autowaves, pacemakers, and spiral waves — is possible. Their wave characteristics, expressed in terms of the parameters of the medium, are found for a special case. Fiz. Tverd. Tela (St. Petersburg) 39, 513–515 (March 1997)     

Microscopic theory of the electro-acoustic echo in order-disorder antiferroelectrics

A microscopic theory of the electro-acoustic echo (EAE) is proposed for the case in which two pulses of a variable electric field act on an antiferroelectric. This theory augments the phenomenological theory proposed for the purpose of interpreting experiments on the main regularities of the electro-acoustic echo in order-disorder antiferroelectrics. The deuterization effect and “pre-polarization” effect are explained. The shape of the echo signal is derived analytically and it is shown that this shape depends on the time interval between pump pulses. Fiz. Tverd. Tela (St. Petersburg) 40, 118–121 (January 1998)     

Regularity criteria for linear chains

The structural analysis of linear chains of arbitrary fixed shape is discussed in the context of a spectral approach. The shape of the chain is characterized by a set of scalar and pseudoscalar invariants, which remain constant under translations and rotations. The statistical properties of the set of invariants are compared with the analogous characteristics for a freely linked chain. The proposed criteria have the self-averaging property for relatively short (∼100–300 links) chains and can be used to discern possible latent periodicities and symmetries in a system. As examples, two applications of the theory are considered: the structural analysis of chains generated by random walks on a cubic lattice and protein C_α backbones. Zh. éksp. Teor. Fiz. 116, 620–635 (August 1999)     

Electromagnetic pulse amplification in a Cherenkov laser

An investigation is made of the amplification of a Gaussian electromagnetic pulse in a Cherenkov waveguide laser for the cases of long and short waveguides. It is shown that in the first case, the concept of a characteristic pulse duration τ ₀ can be introduced. It is established that when the pulse duration is short (τ<τ ₀) the gain is determined only by its spectral width, and the amplification process leads to a change in the pulse envelope. It is shown that in a short waveguide pulse amplification can be achieved without any change in shape. Zh. Tekh. Fiz. 69, 79–83 (April 1999)     

Polarization-interference effects in the bremsstrahlung of quasiclassical electrons on ions with a core

The polarization dependence of the stimulated bremsstrahlung and inverse bremsstrahlung (SBIB) of quasiclassical electrons on highly charged ions with a core is calculated in the approximation of a specified Coulomb current. Emission frequencies close to an eigenfrequency of the ion core are considered. The contributions of the static and polarization channels are taken into account in the amplitude of the process. When the nondipole nature of the interaction between the incident particle and a resonant transition in the ion core is taken into account, interference between these channels causes the spectral-amplitude characteristics of the process to assume a specific dependence on the angle α between the electric field intensity vector of the electromagnetic wave and the initial velocity vector of the incident particle. This dependence, which persists after integration of the cross section over the scattering angle of the incident particle, causes interference effects, viz., asymmetry of the line shape and dips in the dependence of the SBIB cross section on electric field intensity, to appear for α=π/2 and significantly reduces them for α=0. Zh. éksp. Teor. Fiz. 115, 1619–1629 (May 1999)     

Voltage rectification by hard superconductors

The Bean critical state model is used to calculate voltages and voltage waveforms in hard superconductors carrying ac and dc transport currents. A comparison with the experiment shows that these characteristics are accurately described by this model. The voltage rectification effect by current-carrying superconductors is explained. Zh. Tekh. Fiz. 69, 125–127 (July 1999)     

Mathematical simulation of the technology and properties of gradient spherical lenses

The possibilities of improving the optical characteristics of spherical lenses with an axial refractive index gradient are analyzed. The refractive index profile obtained as a result of the Fickian-diffusion exchange of molecules through a flat boundary of the medium is considered. It is shown for the specific polymer system polydiallyl isophthalate plus polymethyl methacrylate (PMMA) that the spherical aberrations can be reduced by almost an order of magnitude in comparison to the aberrations of a homogeneous lens of the same geometric shape made from PMMA. Zh. Tekh. Fiz. 68, 70–73 (October 1998)