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.     

New Insights on the Intrinsic Anisotropy of YBCO Films

Careful investigation of the angular dependence of resistivity ρ(θ) (θ is the angle between the magnetic field and the ab-planes) and the temperature dependence of resistivity ρ(T) within the superconducting transition in an applied magnetic field B up to 1 T for a series of YBa₂Cu₃O_7−δ (YBCO) thin films revealed a large variation of intrinsic anisotropy factor γ. The series of films studied included both optimally doped and underdoped samples of different T _c , critical current density J _c , film thickness, and preparation techniques. The variation in the shape and depth of the minimum measured for ρ(θ) near θ=0° could be directly correlated to the intrinsic anisotropy of the YBCO films. The results of fitting of ρ(θ) using Bardeen–Stephen theory allowed a quantitative determination of the value of γ which varies between 7 and 230, and is independent of T _c , film thickness, or J _c . The sharper the minimum in ρ(θ) around θ=0° the larger is the anisotropy. For highly anisotropic film, ρ(θ) showed an identical behavior for B ∥ J and B ⊥ J (i.e., ρ(θ) is independent of the angle θ between B and J for this film). The large variation in γ could be attributed to the “buckling” of the CuO₂ planes.     

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.     

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.     

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.     

A decomposition of the class of semiconvex games

Summary The paper studies the classSC ^N of cooperative games with player setN which have the semiconvexity property.SC ^N is decomposed into an algebraic sum of convex cones of games for which generating sets are available. The union of these sets thus forms a generating set forSC ^N . Special attention is paid to one of the considered cones, in the decomposition ofSC ^N . In particular, the so called airport savings gamesW _y, ℝ ^N , defined byw _y (S)=Σ _jεS Y _i −max _jεS Y _j for 0 ≠S⋞N, are emphasized. This work is part of the Ph.D. thesis of the first author (Derks 1991).     

Optical properties of lead-bismuth cuprous glasses

The optical transmission and absorption spectra in UV- VIS were recorded in the wavelength range 350–800 nm for different glass compositions in the system (CuO) _x (PbO) ₅₀−x(Bi₂O₃)₅₀ (x = 2.5, 5.0, 7.5, 10.0, 12.5, 15.0, 20.0). Absorption coefficient (α), optical energy gap (E_opt), refractive index (n_D), optical dielectric constant (ε′_∞), measure of extent of band tailing (ΔE), constant (β) and ratio of carrier concentration to the effective mass (N/m*) have been reported. The effects of compositions of glasses on these parameters have been discussed. It has been indicated that a small compositional modification of the glasses lead to an important change in all the optical properties including non-linear behaviour. The optical parameters were found to be almost the same for different glasses in the same family.     

Uncatalyzed synthesis of polypyrrole with viologen side groups and its chemical properties

A substituted polypyrrole (PPr) with viologen side groups (polymer-1) was obtained from the reaction of N-aminopyrrole with 1-hexyl-1′-(2,4-dinitrophenyl)-4,4′-bipyridinium dihalide (salt-1). A model compound (model-1) was synthesized by the reaction of N-aminopyrrole with N-(2,4-dinitrophenyl)-4-(4-pyridyl)pyridinium chloride (salt-2). UV–vis spectra revealed that polymer-1 had an expanded π-conjugation system along the polymer chain: the polymer showed an onset position of absorption at a wavelength approximately 200 nm longer than the corresponding wavelength of model-1. Polymer-1 received an electrochemical oxidation of the pyrrole ring and reduction of the viologen group within the polymer.     

Polarization Effect in ESR of Co Doped CuGeO<Subscript>3</Subscript>

Electron spin resonance of a single crystal of CuGeO₃ doped with 2% of Co has been studied at f = 99 GHz in temperature range 1.8–50 K. Contributions to ESR absorption from Cu²⁺ chains and from Co²⁺ ions were derived. It is found that functions obtained for ESR integrated intensities: Curie-Weiss for Cu²⁺ (χCu ∼ C _Cu/(T + Θ), with Θ = 92 K) and Curie for Co²⁺ (χCo ∼ C _Co/T) are well consistent with temperature dependence of static magnetic susceptibility. Strong dependence of ESR absorption on polarization of oscillating magnetic field was discovered for Co²⁺ contribution. Polarization effect was studied for magnetic field applied along a, b and c directions. Values of g-factors of resonance lines are presented.     

Dynamic Remanent Vortices in Superfluid 3He-B

We investigate the decay of vortices in a rotating cylindrical sample of ³He-B, after rotation has been stopped. With decreasing temperature vortex annihilation slows down as the damping in vortex motion, the mutual friction dissipation α(T), decreases almost exponentially. Remanent vortices then survive for increasingly long periods, while they move towards annihilation in zero applied flow. After a waiting period Δt at zero flow, rotation is reapplied and the remnants evolve to rectilinear vortices. By counting these lines, we measure at temperatures above the transition to turbulence ∼0.6 T _c the number of remnants as a function of α(T) and Δt. At temperatures below the transition to turbulence T≲0.55 T _c, remnants expanding in applied flow become unstable and generate in a turbulent burst the equilibrium number of vortices. Here we measure the onset temperature T _on of turbulence as a function of Δt, applied flow velocity v=v _n−v _s, and length of sample L.     

Synthesis and nonlinear optical properties of novel Y-type polyurethanes with high thermal stability of dipole alignment

2,3-Di-(2′-hydroxyethoxy)benzylidenemalononitrile (3) was prepared and condensed with 2,4-toluenediisocyanate and 3,3′-dimethoxy-4,4′-biphenylenediisocyanate to yield novel Y-type polyurethanes 4–5 containing 2,3-dioxy benzylidenemalononitrile group as a nonlinear optical (NLO)-chromophore, which constituted parts of the polymer backbones. Polyurethanes 4–5 were soluble in common organic solvents such as acetone and N,N-dimethylformamide. They showed a thermal stability up to 270 °C in thermogravimetric analysis thermograms and the glass-transition temperatures (T _g) obtained from differential scanning calorimetry thermograms were around 116–135 °C. The second harmonic generation (SHG) coefficients (d ₃₃) of poled polymer films at 106.4 mm⁻¹ fundamental wavelength were around 9.07 × 10⁻¹⁹ C (2.72 × 10⁻⁹ esu). The dipole alignment exhibited high thermal stability up to 10 °C higher than T _g, and there was no SHG decay below 145 °C due to the partial main-chain character of the polymer structure, which was acceptable for nonlinear optical device applications.     

Possible ionization of mercury atoms by elastic reflection in hyperthermal surface ionization experiments

An elastic collision model baed on data given by Danon et al. [Phys. Rev. Lett. 65, 2038 (1990)] was used to calculate the ionization potential of mercury atoms (V′) at the critical charge transfer distance as a function of the kinetic energy of the atoms (E). The linear dependence V′(E) obtained supports the model of surface ionization of mercury atoms by elastic reflection from a surface. Pis’ma Zh. Tekh. Fiz. 25, 42–45 (July 26, 1999)     

Suhl Instability as a Mechanism of the Catastrophic Relaxation in the Superfluid 3He–B

In order to explain catastrophic relaxation, bulk mechanism based on Suhl instability (J. Phys. Chem. Solids 1, 209, 1957) is studied. It is shown, that at sufficiently low temperatures homogeneous precession of spin becomes unstable in the whole region of tipping angles of spin 0≤β≤π. In comparison with the previous publication of Surovtsev and Fomin (J. Exp. Theor. Phys. Lett. 83, 410, 2006) the leading zero temperature increments for the angles θ ₀≃104°≤β≤π are found. Estimation of the temperature of transition to the unstable state for the angle of 105°, that corresponds to the region of tipping angles in homogeneously precessing domain (HPD), is made.     

Estimate of the potential relief (rippling) of a surface associated with adsorption of d-metal atoms on d-substrates

A cohesion approach developed previously by Davydov and Tikhonov to describe adsorption properties [Surf. Sci. 371, 157 (1997)] is used to calculate the ripple parameter Ω=E _dif/E _des (where E _dif and E _des are the activation energy of surface diffusion and the adsorption energy) for atoms of d-metals adsorbed on a W(110) surface. The results of the calculations show good agreement with the experimental data. Pis’ma Zh. Tekh. Fiz. 24, 70–74 (December 12, 1998)     

Electrical and photoelectric properties of GeS layered crystals grown by different techniques

Thermally stimulated currents and anisotropic electrical conductivity are studied in GeS layered crystals prepared by the Bridgman-Stockbarger, Pizzarello, and sublimation techniques. All the crystals arep-type, regardless of the growth technique, owing to the presence of Ge vacancies. The conductivity anisotropy in the melt-grown crystals is high compared to the vapor-grown GeS. The anisotropy rises exponentially with temperature. The concentrations and ionization energies of traps in GeS crystals are determined from thermally stimulated current curves. The spectral response of the photocurrent through the crystals prepared by sublimation, whose structural perfection is higher than that of the melt-grown crystals, is governed by the spectral dependence of the absorption coefficient forad ≪ 1 (near-edge region) and by the spectral dependence of reflectivity for αd > 1 (high-α region). Regardless of the growth technique, the 293-K photocurrent spectra of GeS crystals show strongly polarized peaks at 1.65 (E ∥a) and 1.78 eV (E ∥b), which are due to the Λ ₁ ^v → Λ ₁ ^c and Δ ₂ ^v → Δ ₂ ^c optical transitions. The low-temperature photoresponse athv < 1.7 eV is due to absorption by Si impurity.     

Discharge estimation in compound channels with fixed and mobile bed

Two-dimensional (2-D) formulae for estimating discharge capacity of straight compound channels are reviewed and applied to overbank flows in straight fixed and mobile bed compound channels. The predictive capabilities of these formulae were evaluated using experimental data obtained from the small-scale University of Birmingham channel. Full details of these data and key references may be found at the following www.flowdata.bham.ac.uk (university website). 2-D formulae generally account for bed shear, lateral shear, and secondary flow effects via 3 coefficients f, λ and Γ In this paper, the secondary flow term (Γ) used within the 2-D methods analysed here is ignored in all applications. Two different 2-D formulae almost give practically the same results for the same data when the secondary flow term is ignored. For overall test cases, the value of dimensionless eddy viscosity λ used in 2-D formulae was kept at 0·13 as recommended for open channels. 2-D formulae gave good predictions for most of the data sets studied in comparison with the traditional 1-D methods, namely the Single Channel Method (SCM) and the Divided Channel Method (DCM). The accuracy of predictions of 2-D formulae was increased by calibrating of λ value where the calibration was needed. For overall data, the average errors for each method were Lateral Division Methods (LDMs), with λ value of 0·13, 2·8%, DCM 14·3% and SCM −26·8%. The average error was 0·5% for LDMs with the calibrated values of λ     

The Two Energy Scales of Tunneling Spectra of Cuprate Superconductors

The atomically resolved energy gap Δ(r) measured by Scanning Tunneling Microscopy has become a major challenge connecting to the nature of electronic states in cuprates superconductors. More recently, a two-energy-gap structure has been observed by many different experiments. We show that it is possible that the charge inhomogeneity gives rise to a potential barrier between the microscopic regions or grains that are the origin of these gaps. A larger Δ(r) is due to the single-particle bound states and the same potential gives rise to a smaller superconducting gap Δ _d (r). These results support the two-gap scenario and give a clear interpretation to the pseudogap phase.     

Synthesis and photovoltaic properties of conjugated copolymers bearing planar acenaphtho[1,2-b]quinoxaline moiety with deep HOMO level

A series of alternating copolymers (PC-AQx, PT-DTAQx, PC-DTAQx, PF-DTAQx, and PBDT-DTAQx) bearing novel planar acenaphtho[1,2-b]quinoxaline (AQx) or 8,11-di(thiophen- 2-yl)acenaphtho[1,2-b]quinoxaline (DTAQx)-acceptor cores have been synthesized via Suzuki or Stille coupling reactions. UV–vis absorption and GIXRD characterization results indicated that the presence of planar DTAQx unit is favorable for the promotion of well-ordered interchain packing in the solid state, and the incorporation of planar electron-donating benzo[1,2-b: 4,5-b′]-dithiophene (BDT) moiety would be propitious to the molecular self-organization. Electrochemical measurement results suggested that four copolymers possess deep HOMO energy level of −5.5 ~ −5.6 eV. The polymer solar cell with structure of ITO/PEDOT:PSS(30 nm)/polymer:PCBM (60 nm)/Bphen(10 nm)/Ag(100 nm) exhibited the highest V _oc of 0.84 V with PF-DTAQx as p-type polymer, while the best power conversion efficiency (PCE) of 0.9 % was obtained using a blend of PBDT-DTAQx and PCBM (1:4) as active layer.     

Influence of acoustic treatment on the photoconductivity of zinc selenide crystals

It is shown that acoustic treatment of piezoelectric zinc selenide crystals by exciting strong natural elastic vibrations can specifically alter their photoelectric and other properties. Irreversible changes in the stressed-strained state of the crystals under this treatment are responsible for characteristic features in the spectral dependences of the permittivity ε′(λ) and the dielectric loss coefficient ε′’(λ). These dependences plotted in the form of ε*(λ) diagrams on the complex plane and also the spectrum of natural elastic vibrations can be used to monitor the treatment process. Pis’ma Zh. Tekh. Fiz. 25, 24–29 (December 26, 1999)