Modeling texture development in a magnesium single crystal during equal channel angular pressing

Modeling of texture development is performed for the case of a magnesium single crystal processed by equal channel angular pressing. The viscoplastic self-consistent approach is used for modeling. It is shown that a the slight bending of the sample must be included in the model at the initial stage of deformation in order to improve agreement with the experimental data.     

Deformation of nuclei as a function of angular momentum in the U(6) ⊃ SU(3) model

In the framework of a hybrid rotational model, proposed recently by Moshinsky as a consequence of a comparison between the Gneuss and Greiner extension of the Bohr and Mottelson model and the interacting boson model, we study the shape of nuclei by calculating the average of the expectation value of the square of the deformation parameter β with respect to the rotational states with the same angular momentum belonging to a given irreducible representation of SU(3). This work generalises to three dimensions the corresponding analysis carried out in two dimensions by Chacón, Moshinsky, and Vanagas. We use the canonical chain for U(3), i.e., the chain U(6) ? U(3) ? U(2) ? U(1), to obtain an analytical formula for the quantity studied. We bring out the overall stretching effect of the angular momentum on the shape of nuclei. The influence of other parameters, such as the boson number and the irreducible representation of SU(3), is also studied.     

Combined implementing the hole-drilling method and reflection hologram interferometry for residual stresses determination in cylindrical shells and tubes

Main features inherent in simplified approach to residual stresses determination in cylindrical shells and tubes, external diameter of which is not less than 60 mm, by combing the hole-drilling method and reflection hologram interferometry are discussed in detail. Initial experimental information in a form of hole diameter increments in principal stress directions is derived from high-quality reflection holograms recorded near cylindrical objects of intermediate curvature value. Converting measured parameters into required stress values is based on the transition model that corresponds to plane stress conditions of pure membrane type. The technique developed is capable of determining residual stress component values within 5% accuracy in an absence of stress gradients over the probe hole diameter when a type of residual stress field corresponds to the transition model adopted. The accuracy analysis involved is based on matrix formulation of conventionally direct problem and an assumption on a pure membrane character of residual stress field under study for thin-walled shell. Required error estimations in a case of inspecting thick-walled cylindrical tube are obtained by combining the above-mentioned approach and an analogy of reconstructed fringe patterns with actual and artificial interferograms, which follow from drilling blind hole of the same geometrical parameters in thick-walled plates. Experimental verification of the developed approach is founded upon a determination of actual stresses in thin-walled cylindrical shell and obtaining residual stress distributions at the proximity of welded joint in thick-walled cylindrical tube.     

Non-destructive testing of tubes using a time reverse numerical simulation (TRNS) method

A method for the detection of defects in cylindrical structures and the determination of their positions and orientations is presented in this paper. The scattered field, which is generated by the interaction of excited guided waves with a defect, is evaluated with an approach named time reverse numerical simulation method (TRNS). Since the excited waves and the scattered field propagate along the sample, the time-consuming scanning of the whole tube can be eliminated. The scattered displacement field is measured in three dimensions over time with a laser vibrometer at different locations distributed equally around the circumference at a fixed axial coordinate far away from the defect. Instead of analyzing the complicated time signals directly, they are played back in time. If the recorded displacement histories of the scattered field are reversed in time and played back in an identical structure, the waves travel back the same path and interfere to a maximum at their origin. The result is an amplitude increase at the position of the defect where the scattered field was generated. Instead of playing back the recorded time signals in an experiment, this step is replaced by a numerical simulation. Only this enables the visualization and detection of the amplitude increase. As long as the simulation is of high accuracy, the position of the maximum interference corresponds exactly to the location of the defect in the experiment, although no defect is implemented in the simulation.     

SU(3) symmetry for orbital angular momentum and method of extremal projection operators

Basic elements of the formalism of the theory that is based on the representations of the SU(3) group for the case of its reduction to the SO(3) subgroup of orbital angular momentum and which is widely used in theoretical physics is presented in a systematic and consistent form. Irreducible SU(3) ? SO(3) bases, both a nonorthogonal one chosen among Elliott vectors and an orthogonal one obtained from a nonorthogonal one by diagonalizing the Bargmann-Moshinsky operator, are described in detail. In particular, it is shown that there is wide arbitrariness in choosing a basis among Elliott vectors. The SU(3) ? SO(3) Clebsch-Gordan coefficients are considered in detail, along with all of their classical symmetry properties. A brief survey (history of discovery) of the method of extremal projection operators for Lie symmetries (Lie algebras and superalgebras and their quantum analogs) is given.     

Alpha-gamma angular correlation measurements as a sensitive method determining the sign of the nuclear quadrupole deformation

In-plane ²⁴Mg(α, α₁γ) angular correlations habe been measured at E_α = 104 MeV. The correlation parameters and the reaction amplitudes extracted from the data have been studied by a coupled-channel analysis. Drastic effects of the sign of the intrinsic quadrupole deformation are found.     

Long-time behavior of the angular velocity autocorrelation function for a fluid of rough spheres

According to hydrodynamical and mode-coupling theories, the angular velocity autocorrelation function decays at long times as ₀(t/10^–14 sec)^–5/2. For rough spheres under the conditions reported here, the quantity ₀ is predicted to be 262. The molecular dynamics studies presented here yield a long-time tail of the form 230(t/10^–14 sec)^–2.38. The disagreement between theory and computer results probably arises from statistical error intrinsic to the computations.The authors are indebted to the National Science Foundation and the Computer Center of the University of Minnesota for financial support of the research reported here.     

SU(3) flux tubes in a model of the stochastic vacuum

We calculate the squared gluon field strengths of a heavyq- $\bar q$ -pair in the model of the stochastic vacuum. We observe that with increasing separation a chromoelectric flux tube is built. The properties of the emerging flux tube are investigated.     

Total electronic energy of a noble metal ordered alloy in the pseudopotential method

Application of the pseudopotential method to noble metal ordered alloys is considered in this paper. Expressions are obtained for the Fourier components of the crystal potential and for the total electronic energy of the alloy. The pseudopotential matrix elements are factorized, and the possibility of transforming to a pair interaction representation is shown. Expressions are obtained for the pair potential of indirect interionic interactions in a noble metal binary ordered alloy.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 21–28, August, 1973.     

Compensation temperature in a cylindrical Ising nanowire (or nanotube)

The critical temperature and the compensation temperature in a cylindrical Ising nanowire (or nanotube) with a negative interlayer coupling at the surface are investigated by the use of both the effective-field theory with correlations and the shell-core concept. Particular emphasis is given to the effects of the surface and its dilution on them. We have found that, for appropriate values of the system parameters, a compensation point may be obtained in the present systems.     

Numerical modeling of lithium ion battery for predicting thermal behavior in a cylindrical cell

The thermal behavior of lithium ion battery during charge and discharge is investigated by a numerical simulation. The commercially available cylindrical 18650 battery is modeled in this study. Two different models are used. The porous electrode model is simulated to obtain the Li content inside the particles. The transient thermo-electric model is used to predict the temperature distribution inside the cell. The results suggest that the increase in temperature during discharge is higher than that during charge. The temperature difference between charge and discharge is decreased with increasing C-rates. At a rate of 1C, the discharge temperature increases with a waving region at the beginning, whereas the charge temperature increases until certain point and then decreases. The thermal behavior is closely related to the change in entropy and applied current.     

Calculation of the drag and heat transfer from a sphere in the gas flow in a cylindrical channel

A numerical experiment on the simulation of heat transfer from a sphere to a gas flow in a cylindrical channel in the Stokes and transient flow regimes has been described. Radial and axial profiles of the gas temperature and the dependences of drag coefficient C_d of the body and Nusselt number Nu on Reynolds number Re have been calculated and analyzed. The problem of the influence of the early drag crisis for a sphere on its heat transfer to the gas flow has been considered. The estimation of this phenomenon has shown that the early drag crisis of the sphere in a strongly turbulent flow causes a reduction in heat transfer from the sphere to the gas by three to six times (in approximately the same proportion as for its drag coefficient).     

Optical conductivity as a probe of a hidden Fermi-liquid behavior in BaFe_(1.904) Ni_(0.096) As_2

We measured the infrared reflectivity of BaFe1.904Ni0.096As2 single crystal from room temperature down to 20 K.Two Drude terms and a Lorentz term well describe the real part of the optical conductivity σ1(ω). We fit the reciprocal of static optical conductivity 1/σ1(0) by the power law ρ(T)=ρ0+ATnwith n=1.6. The broad Drude component exhibits an incoherent background with a T-independent scattering rate 1/τb, while the other narrow one reveals a T-quadratic scattering rate 1/τn, indicating a hidden Fermi-liquid behavior in BaFe1.904Ni0.096As2 compound.     

Blast waves in a cylindrical channel generated by the nonideal detonation of aluminum-Teflon-RDX high-density formulations

The pressure at the front and the pressure impulse of blast waves generated in a cylindrical tube by the expanding products of the nonideal detonation of low-porosity charges prepared by pressing of fine-grained powders of aluminum, Teflon, and RDX were measured. The measured parameters are compared to the same parameters of blast waves produced by the detonation of TNT charges of identical mass. The relative quantities were used to evaluate the effectiveness of blast waves with respect to those generated by TNT. Mixed compositions differing in the shape (brand) of the aluminum powder particles and the ratio between the components at 30% RDX are studied. It is shown that, for the investigated compositions, the pressure at the leading front of the wave exceeds the pressure achieved during TNT explosion on average by 10–30%, almost independently of the distance traveled along the tube in the range from 0.8 to 3.8 m. The dependence of the wave amplitude on the particle shape and aluminum content was weak. In the same range of distances, the relative pulse pressure increases strongly, from 0.5 to 2.1 and higher, mainly due to an increase in the width of the wave. This result is of interest from the point of view of achieving a high pressure impulse of the blast wave in an area remote from the charge. The obtained data suggest that RDX mainly reacts in the detonation wave, with the chemical transformation of Teflon and aluminum in the detonation wave and near-to-charge zone occurring, if at all, to a small extent. On the contrary, as the blast wave front moves through the channel, the burning of aluminum in the fluoride formed during the decomposition of Teflon provides an appreciable support to the blast wave, causing a significant increase in the pressure impulse.     

The effects of non-Kolmogorov turbulence on the orbital angular momentum of a photon-beam propagation in a slant channel

We analyze the effects of non-Kolmogorov turbulence on the orbital angular momentum of a photon-beam propagation through atmosphere. The probability models of the orbital angular momentum crosstalk for single photons propagation in the channel with the non-Kolmogorov turbulence aberration have been established. It is found that the crosstalk among orbits increases as the orbital angular momentum quantum number of launch beam rises, the ground turbulence strength ${C_n^{2} \left( 0 \right)}$ enhances or the non-Kolmogorov parameter α of turbulence-channel increases. As non-Kolmogorov parameter α approaches 4, the crosstalk probabilities among neighbor orbits are approximately the same.