Inhomogeneous deformation of crystalline skeleton of syndiotactic polypropylene under uniaxial stretching

Structure changes of syndiotactic polypropylene (sPP) under uniaxial stretching are studied with the combination of micro-tensile tester and in situ wide angle X-ray diffraction (WAXD) measurement. Lamellae stacked “vertically” and “parallel” to the stretching direction (defined as “V” and “P” part) are separated on the basis of two-dimensional WAXD patterns. For all samples with different lamellar thickness, two critical points named as b ₁ and b ₂ were found in the stress–strain curves, while b ₁ and b ₂ points are the onsets of the rotation for the lamellae of “V” part and “P” part, respectively. The corresponding true stress and true strain for b ₂ point are bigger than that of b ₁ , demonstrating that for samples with initial isotropic lamellar orientation, inhomogeneous deformation of crystalline skeleton induced by uniaxial stretching is universal. And after b ₁ point, “stress-induced melting” always occurs simultaneously with lamellar slips. Furthermore, the relationship between lamellar thickness and the true stress for b ₁ and b ₂ point was also studied, illustrating a linear correlation between ln σ and 1/l (σ is the corresponding true stress, l is the lamellar thickness), consistent with Young’s model. However, the critical true strains for these two points did not change with the varying thickness.     

Bilateral bounds for the shear and torsion factors: comments on elementary derivations

This paper proposes a new simple derivation of bilateral bounds for the strain energy–based shear and torsion factors, χ _i , of an elastic beam together with some comments about the coherence of the current formulations. A rearrangement of the definition as a mean over the cross-section and an original decomposition of the shear stress in two parts—τ _eqv that is equivalent to the external force and a residual Δτ—allow (i) to interpret (χ − 1) as the mean quadratic deviation of the shear field with respect to the distribution τ _eqv and (ii) to easily evaluate an upper bound, using minimal information about the stress field. In this formulation, the lower bound becomes trivial. Several numerical examples illustrate the accuracy and suitability of the results obtained.     

Eigenvalues of damped structures: Vectoriteration in the original space of DOF

The equations of motion in structural dynamics as well as the corresponding eigenvalue problem are governed by 3 matrices for mass, damping and stiffness of order n which equals the number of degrees of freedom. High-performance eigenvalue-solvers are developed for only pairs A, B of matrices. Nevertheless, to benefit from these solvers, the original eigenvalue problem (λ² M+λD+K)x=0 is transformed into a linear eigenvalue representation with only two hypermatrices of double order 2n. Consequently the total numerical effort depends on this order 2n. This paper presents a vectoriteration process which actually works in the original space of order n and which needs no special actions like simultaneous iteration if complex conjugate eigenvalues λ, λˉ with identical norm have to be calculated. The theoretical foundation of this process still goes back to the pair of hypermatrices.     

Behavior of total internal reflection in optical crystals

It is shown that a crystal can be cut so that one incident beam undergoing reflected from an inclined face inside the crystal excites four beams, two ordinary and two extraordinary, propagating in different directions. Pis’ma Zh. Tekh. Fiz. 25, 46–51 (January 12, 1999)     

Oscillatory instability of the interface between conducting liquids in a normal electric field

It is shown that a new type of oscillatory instability, unlike the Tonks-Frenkel instability, may occur at a charged interface between two electrically conducting liquids in a perpendicular electrostatic field. Pis’ma Zh. Tekh. Fiz. 23, 41–44 (August 26, 1997)     

Systematic hardness measurements on mixed and doped crystals of rubidium halides

Efforts are made to improve the hardness of rubidium halide crystals by (i) solid solution hardening and (ii) impurity hardening. Systematic microhardness measurements have been made on rubidium halide mixed crystals (RbBr-RbI and KI-RbI) and rubidium halide crystals doped with Sr²⁺ ions. The composition dependence of the hardness of mixed crystals follows the law ΔH _v =K x (1− x),where ΔH _v is the enhancement in hardness,K a constant andx and (1 −x) the concentrations of the first and second component of the mixed crystals, respectively. The hardness of doped crystals increases with the concentrationC of the dopant according to the law, ΔH _v+6 =k C ^m ,wherek andm are constants. The relative efficacy of the two methods of hardening is discussed.     

Analysis of scenarios of the transition to chaos in a discrete two-mode model of a free-electron laser

A discrete two-parameter two-dimensional mapping, which describes the dynamics of two modes in a free-electron laser (FEL), is investigated by nonlinear dynamics methods. Pis’ma Zh. Tekh. Fiz. 25, 17–21 (June 26, 1999)     

Dielectric relaxation behaviour of Sr<Subscript><Emphasis Type="Bold">2</Emphasis></Subscript>SbMnO<Subscript><Emphasis Type="Bold">6</Emphasis></Subscript> ceramics fabricated from nanocrystalline powders prepared by molten salt synthesis

Double perovskite polycrystalline single phase and dense Sr ₂ SbMnO ₆ (SSM) ceramics, fabricated using the nanocrystalline powders synthesized by molten salt method, exhibited high dielectric constant with low dielectric loss as compared to that of SSM ceramics obtained from the powders prepared by solid-state synthesis method. The dielectric data obtained over a wide frequency (100 Hz–1 MHz) and temperature (190 K–300 K) ranges exhibited distinct relaxations owing to both the grain and grain boundary. The dielectric dispersion was modeled using the Cole–Cole equation consisting of two separate relaxation terms corresponding to the grain and grain boundary. The grain and grain boundary relaxations observed in the Nyquist plots (Z ^′ and Z ^″) were modeled by an equivalent circuit consisting of two parallel RC circuits connected in series with each other. A careful analysis of both the impedance (Z ^″ vs ω) and modulus (M ^″ vs ω) behaviour corroborated the conclusions drawn from the dielectric data.     

Beam model of waveguide regimes in a multilayer graded-index waveguide

Beam and wave approaches were used to obtain mode dispersion equations and to perform an analysis for a planar structure consisting of two waveguiding layers of which one is a graded-index layer. Pis’ma Zh. Tekh. Fiz. 25, 18–23 (December 26, 1999)     

Optical method of determining the components of the relative displacement vector

The theory of a laser interference method of determining in real time the relative displacement of two scattering objects in space is put forward and an experimental verification is described. Pis’ma Zh. Tekh. Fiz. 25, 88–94 (December 26, 1999)     

Photorefractive slit waves

It is shown that photorefractive slit waves may exist, localized near a narrow gap between two similar photorefractive crystals with a diffusion mechanism of nonlinearity and oppositly directed polar axes. Pis’ma Zh. Tekh. Fiz. 23, 30–35 (August 12, 1997)     

Coupled vertical microcavities

A design is proposed for a device consisting of two optically coupled vertical microcavities. It is shown that interaction between two localized optical modes in the coupled microcavities induces mode splitting. The feasibility of using this design to develop optoelectronic devices is analyzed. Pis’ma Zh. Tekh. Fiz. 23, 74–78 (February 12, 1997)     

Dislocation structures of low-angle boundaries in Nb-doped SrTiO3 bicrystals

Dislocation core structures in low-angle boundaries of Nb-doped SrTiO₃ bicrystals were investigated by high-resolution electron microscopy. Bicrystals with tilt angles of 2°, 4°, 6° and 8° with respect to the [001] zone axis were prepared by joining two single crystals at 1873 K. All of the boundaries consisted of a regular array of dislocations whose spacing gradually decreased with an increase in tilt angle. Except for the 2° tilt-angle boundary, the dislocation cores exhibited a dissociation from a[010] into two partials of a/2[010] on (100). Furthermore, two kinds of dislocation core structures were observed; Sr–Sr atomic columns and Ti–O atomic columns inside the cores. In addition, it was found that the positioning of adjacent cores along the boundary tended to change from a linear form to a zig-zagg shape as the tilt angle was increased from 4° to 8°. In the case of the linear array, dislocation core structures including Sr–Sr columns or Ti–O columns alternately appear. In contrast, only one core structure was observed in the zig-zagged array. On the other hand, the dislocation cores in the 2°-tilt-angle boundary had another type of dissociation with a/2[110] or a/2[111] partials, which included the twist component at a tilt axis of [001].     

Anomalously high conductivity in a thin polyphthalidylidene biphenylene film

An anomalously high conductivity was observed for the first time in a thin film of polyphthalidylidene biphenylene inserted between two metal electrodes with no electric field applied but exposed to the action of a small uniaxial mechanical pressure. Pis’ma Zh. Tekh. Fiz. 24, 89–94 (July 12, 1998)     

Identification of singular interfaces with Δ<Emphasis Type="Bold">g</Emphasis>s and its basis of the O-lattice

This article identifies singular interfaces according to singularity in terms of structural defects, including dislocations and ledges. Defect singularities are defined by the elimination of one or more classes of defects, which must be present in the vicinal interfaces. In addition to the three commonly classified structural interfaces, a new type of interface—the CS-coherent interface—is introduced. Singularities in dislocation and ledge structures have been integrated in the study of orientation relationships (OR). The dislocation structures are determined through the O-lattice theory, originally proposed by Bollmann. The basic concepts of the O-lattice and related formulas from the original theory and extended studies are briefly reviewed. According to the theory, singular interfaces exhibiting singularity in the dislocation structures have been identified. An interface that is singular with respect to the interface orientation must be normal to at least one Δg, a vector connecting two reciprocal points from different lattices. An interface that is singular also with respect to the OR must obey one or more Δg parallelism rules. The selection of proper Δgs for different preferred states of interfaces are explained. Identification of singular interfaces with measurable Δgs provides a convenient and effective approach to the interpretation of the observed facets and ORs. The ambiguity about the selection of the deformation matrix (A) for the O-lattice calculation and the advantage of the O-lattice approach over the approach using the Frank–Bilby equation for the calculation of the interfacial dislocations are clarified. Limitations of the present approach and further study are discussed.     

Mixing of granular materials in a half-filled rotating drum

The process of avalanche mixing of two fractions of granular material in a half-filled rotating drum is described accurately and it is shown that under these conditions, the fractions do not generally undergo complete mixing. Pis’ma Zh. Tekh. Fiz. 23, 43–48 (February 12, 1997)     

Direct confirmation of the Coulomb mechanism for atomic displacement in heavy-ion tracks in a dielectric

It is shown that the results of two independent experiments confirm the Coulomb mechanism for atomic displacement in heavy-ion tracks in dielectrics. Pis’ma Zh. Tekh. Fiz. 23, 51–54 (August 26, 1997)     

Transmission function of a directional coupler with a saturable nonlinearity

It is shown that when saturation is taken into account, the transmission function of a directional coupler is more complicated than the Kerr function. Specifically, transmission characteristics with two critical points of self-switching exist. Pis’ma Zh. Tekh. Fiz. 25, 7–12 (September 12, 1999)     

Power and gas pressure effects on properties of amorphous In–Ga–ZnO films by magnetron sputtering

Amorphous In–Ga–ZnO thin films were deposited on quartz glass substrate at room temperature utilizing radio frequency magnetron sputtering technique. Sputtering power and oxygen flow rate effects on the physical properties of the In–Ga–ZnO films were systematically investigated. It is shown the film deposition rate and the conductivity of the In–Ga–ZnO films increased with the sputtering power. The as-grown In–Ga–ZnO films deposited at 500 W exhibited the Hall mobility of 17.7 cm²/Vs. Average optical transmittance of the In–Ga–ZnO films is greater than 80% in the visible wavelength. The extracted optical band gap of the In–Ga–ZnO films increased from 3.06 to 3.46 eV with increasing the sputtering power. The electrical properties of the In–Ga–ZnO films are greatly dependent on the O₂/Ar gas flow ratio and post-growth annealing process. Increasing oxygen flow rate converted the In–Ga–ZnO films from semiconducting to semi-insulating, but the resistivity of the films was significantly reduced after being annealed in vacuum. Both the as-grown and annealed In–Ga–ZnO films show n-type electrical conductivity.     

Dependence of electron and hole lifetimes on the majority recombination impurity concentration in the presence of auxiliary carrier trapping centers

It has been shown that a substantial increase in carrier lifetimes in a certain range of increasing concentration of recombination impurities may also take place in the presence of auxiliary (background) deep impurities, and two maxima may even be observed. Pis’ma Zh. Tekh. Fiz. 23, 58–63 (December 26, 1997)