Plane constrained uniaxial extension of a single crystal strip

Within continuum dislocation theory the plane constrained uniaxial extension of a single crystal strip deforming in single or double slip is analyzed. For the single and symmetric double slip, the closed-form analytical solutions are found which exhibits the energetic and dissipative thresholds for dislocation nucleation, the Bauschinger translational work hardening, and the size effect. Numerical solutions for the non-symmetric double slip are obtained by finite element procedures. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photocount statistic and correlation for a single Lorentzian

The photocount statistic and the second order correlation function was measured for a simple diffusion process. The former was fitted to the exact Bédard formula, taking straylight and 4th order dead-time corrections into account. The coherence time determined from count statistic and correlation are compared.     

Growth of GaSb single crystal in space

The crystal growth under microgravity condition in space has attracted a lot of attention, for the quality of crystals can be improved under microgravity because it creates an environment where nature convection is suppressed and mass transportation is controlled by diffusion. This is a joint work between Institute of Physics, the Chinese Academy of Sciences and Department of Electronics Engineering, the University of Tokyo. A rod of GaSb single crystal doped with Te, whose diameter is 6 mm and length is 30 mm, was grown in space during the China returnable satellite mission No. 14 in 1992. The research results show that there was no striations in the space-grown crystal part, and furthermore the dislocation density was close to zero in the part where melt was not in contact with quartz wall during the crystal growing in the space, but it increased rapidly after the melt was in contact with the wall. This paper summarizes the growth and research results of the GaSb crystal in detail, and analyzes the influences of microgravity on crystal growth and its potential developments in the future.     

β-γ Perturbed angular correlation in the decay of124Sb

The β-γ perturbed angular correlation technique is applied to the determination ofg-factor of 603 keV (2⁺) state (τ = 8.5 psec) of¹²⁴Te populated in the decay of¹²⁴Sb. The activity was diffused into a thin iron foil. A small C type electromagnet was used for polarizing the sample. Internal field acting at the Tellurium nucleus in iron was used for perturbing the β-γ angular correlation. Theg-factor extracted isg = 0.28 ± 0.05. This is in good agreement with that obtained by γ-γ perturbed angular correlation method.     

ESR study of irradiated single crystal ofp-toluidinium chloride

Electron spin-resonance has been observed in irradiated single crystals ofp-toluidinium chloride. The spectra obtained for different orientations of the crystal are analysed on the basis of the formation of cyclohexadienyl type of radicals. Partially deuteratedp-toluidinium-ND₃ chloride sample was studied to confirm these results. A qualitative study of irradiatedo-toluidinium bromide and the related deuterium labelled compounds has supported the formation of such radicals.     

Beta-gamma-gamma angular correlation studies of the radiations from the decay of Sb124

Beta→ gamma→ gamma angular correlation studies are done for the following two cascades in Te¹²⁴ from the decay of Sb¹²⁴.

1. Beta-rays of E_max. 622 KeV → gamma-rays of 1691 KeV→ gamma-rays of 603 KeV;
2. Beta-rays of E_max. 222 KeV → gamma-rays of 2091 KeV → gamma-rays of 603 KeV;

The multipolarities of 1691 and 2091 KeV are determined and spins of the excited levels are confirmed by beta → gamma → gamma angular correlation technique.     

Parameter studies of modal vibrations associated with impurity pinned dislocations in a metal single crystal

Koehler's model [1–2] of motion for edge‐type dislocations in a metal single crystal that are pinned down by impurity atoms is studied. An exact solution can be found, which is composed of a rapidly decaying transient and a steady time‐oscillating, steady state vibration. This solution is used to improve Koehler's [1] approximation to the steady time‐oscillating steady state vibration. General parameter studies of the modes of oscillation are then performed. The present result is of some significance, because it allows insight into the behavior of crystalline solids over a wide parameter range, whereas Koehler's asymptotic approach is valid only for materials that exhibit order‐of‐magnitude variation in system parameters. © 2001 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 17: 427–439, 2001.     

Nonlocal damage-viscoplastic model for high temperature creep of single crystal superalloys

A new nonlocal damage-viscoplastic model for high temperature creep of single crystal superalloys is developed. It is based on the variational formulation consisting of free energy, plastic and damage dissipation potentials. Evolution equations for plastic strain and damage variables are derived from the minimum principle for dissipation potentials [1]. The model is capable of describing different stages of creep in a unified way. The evolution of dislocation densities of gamma and gamma prime phases in superalloys incorporates plastic deformation. It results in the time-dependence of the creep rate in primary and secondary creep. Tertiary creep is taken into account by introducing local and nonlocal damage variables. Herein the nonlocal one is considered as numerical treatment to remove mesh-dependence. Numerical results and comparisons with experimental data of the single crystal superalloy LEK94 are shown. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electron spin resonance of Mn2+ in NaCl single crystal and lattice defects

The electron spin resonance spectra of Mn²⁺ in NaCl single crystals are investigated in detail. Seven different spectra (I, II, III₁, III₂, IV, V and VI) are observed. The spectra I–IV are the same as those observed by earlier workers, while the spectra V and VI are observed here for the first time. The local symmetry at the paramagnetic ion is orthorhombic for the spectra IV and V and tetragonal for the spectrum VI about the crystallographic [001] direction. The properties of the spectrum IV are explained in terms of an associated pair Mn²⁺: O₂ ^2? with O₂ ^2? molecular ion at the nearest neighbour anion site in the [001] direction with its internuclear axis in the (001) plane. The spectrum V is assigned to the associated pair Mn²⁺: O₂ ^2? coupled with a nearby cation vacancy in the [001] direction and the spectrum VI to Mn²⁺ ion associated with OH^? ion at the anion site in the [001] direction with a probable second neighbour cation vacancy. All the observed spectra are analysed in terms of the parameters of the usual spin-Hamiltonian.     

Forbidden hyperfine transitions in electron spin resonance of Mn2+ in NaCl single crystal

Forbidden hyperfine transitions are observed in the electron spin resonance spectrum of divalent Mn⁵⁵ ion in NaCl single crystal for a particular associated pair. From the measurements of the M = + 1/2 → ?1/2, Δm = ± 1 transitions the parametersQ′ and Q″ of the nuclear electric quadrupole part of the spin-Hamiltonian H_o = Q′ [I_z ² ? 1/3 I (I + 1)] + Q″ (I_x ²?I_y ²) are found to be + 1.70 × 10^?4 cm.^?1 and +0.16 × 10^?4 cm.^?1 respectively.     

Paramagnetic resonance of Mn2+ in KNO3 single crystal: Motional effects

The electron paramagnetic resonance of Mn²⁺ in KNO₃ single crystal is investigated over a temperature cycle through transition temperatures. The hyperfine coupling constant, A, half width,Δ H, and the line intensity, I, are found to show sudden changes at the transition temperature, at whichα-KNO₃ changes intoβ-KNO₃. The lines are much sharper in the high temperatureβ-phase than inα-phase of the crystal. They are explained, qualitatively, in terms of structure change and rotation of NO ₃ ^? ions. The spectra in the two phases,α andβ, are analysed in terms of usual spin-Hamiltonian. A search of metastableγ-phase is also made and probable indications for the same are found.     

A generalized micromechanics constitutive theory of single crystal with thermoelastic martensitic transformation

Based on the crystallography theory of martensitic transformation and Hill-Rice’s internal variable constitutive theory, a generalized micromechanics constitutive model is established to describe the thermoelastic martensitic transformation and reorientation of single crystal. This model can describe the macroscopic constitutive behavior due to the microstructure changes of forward transformation, reverse transformation and reorientation in single crystal under complex thermodynamic loading condition. The theoretical predictions agree well with the available experiment. Project supported by the National Natural Science Foundation of China and the State Education Commission of China. Due to the limit of space, for detailed derivation, please refer to Yan Wenyi, Micromechanics constitutive researches for transformable materials and transformation localization analysis,Ph.D. Thesis (in Chinese), Beijing: Tsinghua University, 1995.     

Banach spaces in which a theorem of orlicz is not true

Let the Banach space X be such that for every numerical sequencet _n ↘0 there exists in X an unconditionally convergent series σx_n, the terms of which are subject to the condition ∥x_n∥=t_n (n=1,2,...). Then $$\mathop {sup}\limits_n \mathop {inf}\limits_{X_n } d(X_n ,l_\infty ^n )< \infty ,$$ where X_n ranges over all the n-dimensional subspaces of X.     

Uniaxial extension of polystyrene with a constant true stress

A apparatus designed for the extension (stretching) of yielding polymers at a constant true stress is described. The changes taking place in the general, rubber-elastic, and irreversible deformations aredetermined, together with the corresponding rates of deformation, as well as the viscosity and relaxation characteristics, during the extension (tensile strain) of block polystyrene at various constant true stresses and a temperatore of 130°C.All-Union Scientific-Research Institute of Synthetic Fiber, Kalinin. Translated from Mekhanika Polimerov, No. 6, pp. 1104–1109, November–December, 1972.     

Towards a methodology for measuring the true degree of efficiency in a speculative market

Betting markets have drawn much attention in the economics, finance and operational research literature because they provide a valuable window on the manner in which individuals use information in wider financial markets. One question that has received particular attention is to what extent individuals discount information in market prices. The predominant approach to explore this issue involves predictive modeling to forecast market outcomes and examining empirically whether abnormal returns can be made by employing these forecasts. It is argued here that present practices to assess such forecasting models, including the use of point estimates and information, which would not be available in practice (at the forecasting stage) and failing to update forecasting models with information from the recent past, may give rise to misleading conclusions regarding a market's informational efficiency. Hypotheses are developed to conceptualize these views and are tested by means of extensive empirical experimentation using real-world data from the Hong Kong horserace betting market. Our study identifies several sources of bias and confirms that current practices may not be relied upon. A more appropriate modeling procedure for assessing the true degree of market efficiency is then proposed.     

Electrodeposition of copper on copper single crystal (100) face in presence of chloride ions

Observations of copper electrodeposits on to the (100) plane of copper was made from highly purified solutions of copper sulphate containing known concentration of hydrochloric acid from 10^?10 to 10^?1 m/L. In pure solutions at current densities of 5 and 10 mA/cm.² layers and pyramids were noticed. In the presence of hydrochloric acid of concentration 10^?9 to 10^?5 m/L there is a gradual decrease of distance between successive steps. At 10^?4 m/L of HCl there was the breaking of layers giving rise to ridge type of growth. With the increase of concentration to 3·5×10^?3 m/L pyramids appear again. On increasing the concentration of HCl to 10^?2 m/L there was the formation of triangular pyramids of cuprous chloride and on still increasing the concentration, polycrystalline type of deposit was noticed. The transition from layer to ridge, ridge to pyramids and to polycrystalline deposit occurs at all c.d. studied but the critical concentration of HCl needed for the transition depends upon the current density.