Numerical solution to a nonlinear,one-dimensional problem of thermoelasticity with volume force and heat supply in a half-space

A numerical solution is presented for a nonlinear, one-dimensional boundary-value problem of thermoelasticity with variable volume force and heat supply in a half-space. The surface of the body is subjected to a given periodic displacement. The volume force and bulk heating simulate the effect of a beam of particles infiltrating the medium. No phase transition is considered and the domain of the solution excludes any shock wave formation. The basic equations are formulated in material coordinates, making them adequate for dealing with moving boundaries. The used numerical scheme reproduces correctly the process of coupled thermomechanical wave propagation. The presented figures display the process of propagation of the coupled nonlinear thermoelastic waves. They also show the effects of volume force and heat supply on the distributions of the mechanical displacements and temperature inside the medium. Moreover, the interplay between these two factors and the applied boundary disturbance is outlined. The presented solutions, however, is not meant to capture the expected process of shock formation at the breaking distance.     

Investigation of the optimum optical design for pulsed-laser crossed-beam thermal lens spectrometry in infinite and finite samples

Optimization of the optical design for pulsed-laser crossed-beam thermal lens (PLCBTL) spectrometry has been investigated. Experiments have been carried out with large samples as well as for very small samples in a microchannel and using different lens combinations to focus the probe and excitation beams. The results have been interpreted in terms of the influence of the excitation beam size as well as the degree of mode-mismatching of the excitation and probe beams on the optimum sample position and on the amplitude and decay of the photothermal signal. A semi-empirical formula that describes the influence of the sample position with respect to the probe beam waist has been established. We have shown that the optimum signal is inversely proportional to the waist of the excitation beam and is independent of the sample size as long as the size of the excitation beam is smaller than the microchannel. Time-resolved experiments have also shown that when the excitation beam is smaller than the sample, the signal decay depends not only on the size of the excitation beam but also on the mode-mismatching factor. Otherwise, the temporal characteristics are closely related to the size of the microchannel.     

Deformation of a Superconducting Cylindrical Tube in a Perpendicular Magnetic Field

Stresses and displacements are obtained for an elastic superconductor in the form of an infinitely long, circular cylindrical tube subjected to an initially uniform magnetic field perpendicular to the tube's axis. The effect of the magnetic field penetration on the stressed state is assessed by solving the problem, firstly taking into account this penetration and, secondly, neglecting it. The problem involves the solution of a non-homogeneous biharmonic equation in two dimensions for the stress function. The special case of a circular cylinder is also given. Numerical calculations estimate the variation between the two cases for some quantities of practical interest. It is shown, in particular, that neglecting the penetration of the magnetic field in the elastic superconductor may induce a non negligible error in the appreciation of the stressed state.     

Molecular dynamics studies of displacement cascades in the uranium dioxide matrix

In the context of studies on long-time storage of irradiated spent fuel, molecular dynamics simulations have been carried out in order to understand the physical phenomena, on the atomic scale, linked to modifications and damage that the uranium dioxide structure undergoes during α-decay irradiation in repository conditions. Simulations of atomic displacement cascades over an energy range from 1 to 20?keV for the initial primary knock-on atom (PKA) do not show any amorphization of the structure in agreement with what has been found experimentally, and there is very little correlation between the initial orientation of the PKA and the cascade morphology. The number of Frenkel pairs, as a function of the initial energy of the PKA, exhibits a power-law behaviour with an exponent of 0.9 which is contrary to the theoretical linear Norgett–Robinson–Torrens law. Finally, for both species the vacancies have a tendency to aggregate and cluster near the core of the cascade while interstitial atoms are preferentially located at the periphery of the branches corresponding to subcascades.     

Effect of Ni(II) substitution on phase stabilization electrical properties of BICo(III)VOX.20 oxide-ion conductor

The BICO_0.20–xNI_xVOX solid electrolyte was synthesized by the standard solid-state reaction. The effect of Ni(II) substitution for Co(III) on phase stabilization and oxide-ion performance has been investigated in the compositional range 0?≤?x?≤?0.20 using X-ray powder diffraction, differential thermal analysis and AC impedance spectroscopy. The highly conductive γ′-phase was effectively stabilized at room temperature for compositions with x?≥?0.13 whose thermal stability increases with Ni content. The complex plane plots of impedance were typically represented at temperatures below 380?°C, suggesting a major contribution of polycrystalline grains to the overall electrical conductivity. The dielectric permittivity measurements revealed the fact that suppression of the ferroelectric transition is compositionally dependent. Interestingly, the maximum ionic conductivity at lower temperatures (~2.56?×?10^?4?S^?cm^?1 at 300?°C) was observed for the composition with x?=?0.13. The variation of low-temperature conductivity with Ni content was accompanied with a general drop in the corresponding values of ΔE_LT. However, the local minimum high-temperature conductivity, σ₆₀₀?°C?~?2.26?×?10^?2?S^?cm^?1 for x?=?0.10, coupled with a local maximum value of ΔE_HT?~?0.48?eV was attributed to an increased defect trapping effect correlated with the V(V)?→?V(IV) reduction at elevated temperatures.     

Kinetics of ultrasonic release of doxorubicin from pluronic P105 micelles

The aim of this research was to measure and model the kinetics of acoustic release and subsequent re-encapsulation of Doxorubicin (DOX) from Pluronic P105 micelles. A fluorescence detection ultrasound exposure chamber was used. Experimental data showed that no significant release was observed when DOX loaded in Pluronic P105 micelles was exposed to ultrasound for less than 0.1 s at a power density of 58 mW/cm² and a frequency of 20 kHz. Above this threshold, the amount of release was shown to increase as the pulse length increased up to 0.6 s. The same experiments showed that it requires at least 0.1 s of no ultrasound for measurable re-encapsulation to occur. Release and re-encapsulation are completed within about 0.6 s of the beginning of the ON and OFF phases of pulsed ultrasound. Several physical models and their corresponding mathematical solutions were analyzed to see which most closely fit the data. The model of zero-order release with first-order re-encapsulation appears to represent data from this polymeric system better than other models. This technique has possible applications in site-specific chemotherapy.     

漫谈有效数字和计算器

介绍了有效数字的概念及其计算规则,介绍了计算器的一般特性及使用技巧,并给出计算实例.     

速度算符和电子的颤动

指出了国外某些量子力学教材中关于速度算符的概念错误和相对论自由电子进行颤动的错误,分析了错误的原因.     

Effect of Sm-, Gd-codoping on structural modifications in aluminoborosilicate glasses under β-irradiation

Two series of Sm-, Gd-codoped aluminoborosilicate glasses with different total rare earth content have been studied in order to examine the codoping effect on the structural modifications of β-irradiated glasses. The data obtained by electron paramagnetic resonance (EPR) spectroscopy indicated that the relative amount of Gd³⁺ ions located in network former positions reveals a non-linear dependence on the Sm/Gd ratio. Besides, codoping leads to the evolution of the EPR signal attributed to defects created by irradiation. The superhyperfine structure of boron oxygen hole centres EPR line becomes less noticeable and less resolved with the increase of Gd. This fact manifests that Gd³⁺ ions are mainly diluted in the vicinity of the boron network. By Raman spectroscopy, we showed that the structural changes induced by the irradiation also reveal non-linear behavior with the Sm/Gd ratio. In fact, the shift of the Si-O-Si bending vibration modes has a clear minimum for the samples containing equal amount of Sm and Gd (50:50) in both series of the investigated glasses. In contrast, for single-doped glass there is no influence of dopant’s content on Si-O-Si shift (in the case of Gd) or its diminution (in the case of Sm) occurs, which is explained by the reduction process influence. At the same time, no noticeable effect of codoping on Sm³⁺ intensity as well as on Sm²⁺ emission or on Sm reduction process was observed.