Nonlinear macrolocalization of strain in hexagonal close-packed zirconium alloys

Using laser speckle interferometry and surface profiling methods, the evolution of plastic strain localization under uniaxial tension of hcp zirconium alloys is studied. It is found that oscillatory instability observed at the parabolic stage of plastic flow in zirconium alloys arises when the specimen locally and nonuniformly changes shape. It is shown that the cross-sectional area of the deforming specimen decreases nonlinearly and is determined by the oscillatory variation of contraction and extension strains at the site of macrolocalization in the hardening-softening mode.     

An expert system for identification of lines in vibrational-rotational spectra

An expert system for automatic identification of the complex vibrational-rotational spectra of molecules has been developed. An iteration approach is implemented in this system, in which employment of the exact combination rule is combined with determination of the spectroscopic constants by solving of the inverse problems and comparison of the calculated parameters of spectral lines with the corresponding measured values. In order to calculate the energy levels and the frequencies and intensities of lines, the Watson Hamiltonian, the Padé-Borel approximants, and generating functions are used. The system is based on the application of pattern-recognition algorithms. Recognition training makes it possible to obtain the required flexibility of the system and to use different methods of identification based on the application of combination rules both for the analysis of strong bands and for the assignment of weak single lines. The system developed can be used to analyze the spectra of the C _s and C _2V molecules, as well as employ the calculated spectrum of a molecule of any type prepared in advance. This system was successfully used to identify the H ₂ ¹⁶ O, H ₂ ¹⁷ O, H ₂ ¹⁸ O, D₂O, HDO, H ₂ ³² S, H ₂ ³⁴ S, and H ₂ ³³ S and molecules.     

Two new eudesmane derivatives from Verbesina virginica

<正>Two new eudesmane derivatives were isolated from the leaves and flowers of Verbesina virginica,along with the known 6-O-β-E -p-coumaroyl-4α-hydroxyeudesmane(1).Their structures were determined as 6-O-β-Z-p-coumaroyl-4α-hydroxyeudesmane(2) and 6-O-α-E-p-coumaroyl-1β-4α-dihydroxyeudesmane(3) by spectroscopic methods.     

Femtosecond midinfrared study of aggregation behavior in aqueous solutions of amphiphilic molecules

We study the spectral and orientational dynamics of HDO molecules in aqueous solutions of different concentrations of tertiary butyl alcohol (TBA) and trimethylamine-N-oxide (TMAO). The spectral dynamics is investigated with femtosecond two-dimensional infrared spectroscopy of the O-H stretch vibration of HDO:D(2)O, and the orientational dynamics is studied with femtosecond polarization-resolved pump-probe spectroscopy of the O-D stretch vibration of HDO:H(2)O. Both the spectral and orientational dynamics are observed to show bimodal behavior: part of the water molecules shows spectral and orientational dynamics similar to bulk liquid water and part of the water molecules displays a much slower dynamics. For low solute concentrations, the latter fraction of slow water increases linearly as a function of solute molality, indicating that the slow water is contained in the solvation shells of TBA and TMAO. At higher concentrations, the fraction of slow water saturates. The saturation behavior is much stronger for TBA solutions than for TMAO solutions, indicating the aggregation of the TBA molecules.     

Cyclicity of the dislocation restructuring in necking in an hcp Zr-Nb alloy

Cyclic dislocation transformations are detected in the deformation macrolocalization zone during tension of a Zr-1% Nb alloy, and this cyclicity is accompanied by periodic relaxation of internal stresses as a result of the decomposition of sub-boundaries and dislocation redistribution. The oscillatory instability of deformation localization in the hardening-softening mode at the parabolic stage of plastic flow in zirconium alloys is found to be related to the cyclicity of dislocation transformations in the macrolocalization zone during its transformation into a neck.     

The magneto-optical properties of an ensemble of ellipsoidal dielectric particles in a magnetic fluid

The paper deals with an analytical investigation of magnetic birefringence in a dilute suspension of ellipsoidal dielectric particles in a magnetic fluid. The major axes of particles tend to line up along the field because of the difference in the “demagnetizing” coefficients along and across the ellipsoid axis, which brings about a multiple increase in the optical anisotropy of the system. Formulas are derived which describe the field dependence of magnetization of the system and of the difference between the refractive indices for ordinary and extraordinary rays. It is demonstrated that, given the bulk concentration of impurity particles of several percent, the magnetization of the system varies insignificantly, while the birefringence signal may increase by two orders of magnitude.     

Magnetovibrational flows in a magnetic fluid

A new type of flow in a magnetic fluid has been experimentally detected and investigated. The interaction between an alternating nonuniform magnetic field and a magnetic fluid leads to the parametric excitation of traveling capillary-gravitational waves which are the direct cause of the average flow. A necessary condition of formation of hydrodynamic flows in an alternating field is also the presence of time-dependent harmonics with multiple frequencies synchronized with the first harmonic, so that the time dependence of the ponderomotive force is generally pulsed. It is shown that for plane vibrational flows the classical theory cannot explain the high intensity of the average flows observed. It is suggested that the high intensity of magnetovibrational flows is related to the violation of the cylindrical symmetry of the traveling capillary-gravitational waves and the transition to a three-dimensional motion. Perm’. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 124–133, January–February, 1998.     

Controlled supercontinuum generation for optimal pulse compression: a time-warp analysis of nonlinear propagation of ultra-broad-band pulses

We describe the virtues of the pump–probe approach for controlled supercontinuum generation in nonlinear media, using the example of pulse compression by cross-phase modulation in dielectrics. Optimization of a strong (pump) pulse and a weak (probe) pulse at the input into the medium opens the route to effective control of the supercontinuum phases at the output. We present an approximate semi-analytical approach which describes nonlinear transformation of the input pulse into the output pulse. It shows how the input and the output chirps are connected via a time-warp transformation which is almost independent of the shape of the probe pulse. We then show how this transformation can be used to optimize the supercontinuum generation to produce nearly single-cycle pulses tunable from mid-infrared to ultraviolet. PACS 42.65.Re; 42.65.Ky