Rising of gas bubbles in an aqueous medium in presence of surfactants

Summary Experiments based on the direct comparison of the gas-bubble rising times in a surfactant aqueous solution, in respect to those in pure water, give support to the hypothesis that a rising path of many metres is needed to reach the saturation of the adsorption process on bubbles (0.2÷0.3) cm in diameter. A maximum is evidenced in thet/t ₀ ratiovs. surfactant concentration at the highest concentrations tested. An explanation, on a qualitative basis, of the appearance of the observed maximum is proposed. Work presented at the IV Congress of the CNR (National Research Council) National Group of the Atmosphere and Ocean Physics, Rome, June 22–24, 1987.     

Reading entanglement in terms of spin configurations in quantum magnets

We consider a quantum many-body system made of N interacting S=1/2 spins on a lattice, and develop a formalism which allows to extract, out of conventional magnetic observables, the quantum probabilities for any selected spin pair to be in maximally entangled or factorized two-spin states. This result is used in order to capture the meaning of entanglement properties in terms of magnetic behavior. In particular, we consider the concurrence between two spins and show how its expression extracts information on the presence of bipartite entanglement out of the probability distributions relative to specific sets of two-spin quantum states. We apply the above findings to the antiferromagnetic Heisenberg model in a uniform magnetic field, both on a chain and on a two-leg ladder. Using Quantum Monte Carlo simulations, we obtain the above probability distributions and the associated entanglement, discussing their evolution under application of the field.     

Role of electron confinement in the formation of Tamm surface levels in nanoparticles

We study the effect of electron confinement in a nanoparticle on the parameters of Tamm’s levels. It is shown using the combination of the Tamm model and the Kronig-Penney model that an increase in the gap width in the electron spectrum of the crystal leads to an increase in the energy of the Tamm state and a decrease in the degree of localization of the wavefunction of the Tamm state. Some applications of the results on the properties of the Tamm level (e.g., the effect on the surface tension of a nanocluster, the manifestation of modifications considered here in the multiple exciton generation effect in quantum dots, the possible role of the shape of a nanoparticle during its growth, and the role of varying Tamm states in catalysis by nanoparticles) are indicated.     

Singularities in determination of the diffusion coefficients of components in melts of AIIIBV systems

A critical analysis is performed of the mathematical expressions used to compute the diffusion coefficients of components on the basis of data on the growth rate or dissolution of crystals of A^IIIB^V compounds. It is shown that neglect of high-order terms of the series that are the solution of the mass transport differential equations will result in substantial errors during processing of the experimental results. To simplify the computations and eliminate mathematical inaccuracy, it is proposed to use the analytic solution of the diffusion mass transport equations in the approximation of a semi-infinite medium. The diffusion coefficient of arsenic in liquid indium in the 550–750C temperature range is computed on the basis of experimental results on the rate of InAs dissolution in an unsaturated In-As melt by using the method proposed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 19–25, April, 1987.     

离散坐标法在计算生物组织内光场空间角分布中的应用

从辐射传输理论出发,研究了准直光照下层状生物组织内漫射光场的角分布.在辐射传输方程的基础上,采用离散坐标法得到了描述层状生物组织内漫射光传输问题的微分方程组形式,并用特征值-特征矢量方法对其进行了求解,给出了通解形式.结合边界条件对两类典型生物组织内漫射光场角分布进行了数值计算-各向同性组织和前向散射组织,给出了组织内不同深度处漫射光场空间角分布曲线.通过对计算结果比较分析,得到了生物组织内漫射光场空间角分布随深度的变化规律,及边界效应和光学参量对组织内漫射光场空间角分布的影响.     

Simulation of secondary processes in breakdown in air

The simulation of the buildup of a breakdown in air is made in a gap with an applied uniform electric field. The computer program is based on the classic determinist model of Townsend with account to secondary effects on the cathode and space charge effects in the gap. Nevertheless, this model takes into account the different ionic and electronic creative processes in the discharge. To the direct ionization must be added attachment, detachment and charge exchange processes. The continuity equation gouverning the densities is written for each charge carriers kind. The resolution of this system represents accurately the spatio-temporel evolution of the discharge. The results are in good agreement with the experimental results found in literature.     

Modelling of flows in micromixers

A method is proposed for modelling fluid flows in microchannels. The method is tested on the known experimental data on studying the flows in microchannels with the aid of the micro-PIV. The flow regimes in micromixers of the Y- and T-types are studied. The passive and active mixers are considered. The dependence of the mixing efficiency on the Reynolds and Péclet numbers as well as the possibility of using the hydrophobic and ultra-hydrophobic coatings are analysed. A T-mixer is proposed as an active technique of mixing, in which the flow rate in one of the inlet channels varied according to the harmonic law. The dependence of the mixing efficiency on the frequency of the variation of the flow rate and its amplitude is established.     

Disclinations in nematics in the presence of flexoelectricity

The stability problems of wedge disclinations (with pure splay and bend distortions) in nematic liquid crystals (NLC) are considered in the presence of flexoelectricity. We write NLC director equations in the cylindrical coordinate system, taking into account flexoelectricity. These equations allow us to solve many interesting problems on the influence of flexoelectricity on the orientational structures of NLC. In particular, it is shown that the line of disclination with radial distribution of director can be stabilized in the presence of flexoelectricity even far from nematicsmectic phase transition point. For the disclination with azimuthal distribution of director for all physical sizes the line is not stable and escapes in the third dimension.     

Inhibition of corrosion of aluminium in presence of fluorescein in basic medium

The influence of Fluorescein in conjunction with calcium oxide on the corrosion of Aluminium in 1.0 N NaOH was studied by galvanostatic studies and weight loss studies. It has been found that the inhibition of corrosion of aluminium increased with the increasing concentration of the inhibitor. The maximum inhibition efficiency of fluorescein alone was found to be 30.80%. However, the addition of calcium oxide increased the maximum inhibition efficiency to 53.71%. The corrosion process was found to be under the anodic control, in the presence or in the absence of inhibitor. The inhibition was found to be mixed type. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, Inida, Nov. 28–30, 2003.     

Features in phase-contrast images of micropipes in SiC in white synchrotron radiation beam

An interesting feature in phase-contrast images of micropipes in silicon carbide in white synchrotron radiation beam was experimentally studied and theoretically explained. This feature consists in that a change in micropipe cross-section sizes does not lead to changes in its image sizes, but has an effect only on the contrast. The experiment was performed on the synchrotron radiation source in Pohang, South Korea. On the one hand, this effect is explained by a small phase progression caused by the micropipe, and, on the other hand, by satisfying the conditions for Fraunhofer diffraction, when the transverse micropipe size is smaller than the first Fresnel zone diameter. As a rule, the near-field conditions are satisfied in X-ray optics when only object edges are imaged. However, micropipes are so small that the standard edge theory is inapplicable. A universal intensity distribution profile was obtained for micropipes with very small cross sections.     

Ethylene terephthalate oligomers in the processes of modification of polyester fabrics in supercritical carbon dioxide

The influence of the conditions of processing of polyester fiber material in the supercritical carbon dioxide (SC-CO₂) medium on the localization of ethylene terephthalate cyclic oligomers on the surface of fibers is studied. It is shown that cyclic oligomers are deposited on the surface of polyester fiber materials in the form of large associates. The mechanism of migration of oligomers from the interior of polyester fibers plasticized in the SC-CO₂ medium is considered. Recommendations to minimize the amount of surface oligomers in the dyeing of polyester fiber materials in SC-CO₂ are given. It is shown that the deposition of oligomers on the surface of polyester fabric does not adversely affect the quality of their hydrophobization with ultrafine polytetrafluoroethylene in the SC-CO₂ medium.     

Ultrashort optical pulse in an order-disorder ferroelectric in the presence of a lattice of defects

The dynamics of an ultrashort optical pulse in an order-disorder ferroelectric in the presence of a lattice of defects is considered within the microscopic pseudospin formalism in the unidirectional propagation approximation, without limitations on the pulse power. The effective equations for the electric field amplitude and ferroelectric polarization are obtained and numerically solved. Quasi-soliton modes of ultrashort optical pulse propagation in a system with regular defects are revealed and the dependences on the microscopic Hamiltonian parameters are analyzed. The effect of the parameters of defects of different types on the pulse propagation is revealed.     

ANSYS在气体探测器电场分布计算中的应用

介绍了气体探测器电场分布的计算方法,以计算MSGC探测器单元电场分布为例说明了如何用ANSYS软件包来计算结构较复杂的气体探测器内部电场分布,同时讨论了电场分布对气体探测器性能的影响.     

Influence of topology in the evolution of coordination in complex networks under information diffusion constraints

In this paper, we study the influence of the topological structure of social systems on the evolution of coordination in them. We simulate a coordination game (“Stag-hunt”) on four well-known classes of complex networks commonly used to model social systems, namely scale-free, small-world, random and hierarchical-modular, as well as on the well-mixed model. Our particular focus is on understanding the impact of information diffusion on coordination, and how this impact varies according to the topology of the social system. We demonstrate that while time-lags and noise in the information about relative payoffs affect the emergence of coordination in all social systems, some topologies are markedly more resilient than others to these effects. We also show that, while non-coordination may be a better strategy in a society where people do not have information about the payoffs of others, coordination will quickly emerge as the better strategy when people get this information about others, even with noise and time lags. Societies with the so-called small-world structure are most conducive to the emergence of coordination, despite limitations in information propagation, while societies with scale-free topologies are most sensitive to noise and time-lags in information diffusion. Surprisingly, in all topologies, it is not the highest connected people (hubs), but the slightly less connected people (provincial hubs) who first adopt coordination. Our findings confirm that the evolution of coordination in social systems depends heavily on the underlying social network structure.     

Heat transfer in boiling of refrigerant R-21 in a downward flow in an assembly of minichannels

The paper presents the results of an experimental study of heat transfer in boiling of refrigerant R-21 in a downward flow in a vertical assembly of minichannels of a plate-fin heat exchanger. Characteristic regimes of vapor-liquid flow and heat transfer coefficients have been obtained for the case of plain fins in the ranges of low mass velocities and heat fluxes that are typical of the industry but poorly studied. The obtained data show no significant dependence of the heat transfer coefficient on the heat flux density and mass velocity, which may be explained by the decisive effect of the evaporation of thin liquid film on the heat transfer at low heat flux density.     

Towards a test of QED in investigations of the hyperfine splitting in heavy ions

A possibility for investigations of quantum electrodynamics (QED) in experiments on the hyperfine splitting in heavy ions is examined. It is found that QED effects can be probed on the level of a few percent in a specific difference of the hyperfine splitting values in hydrogenlike and lithiumlike bismuth. This could provide a test of QED in the strongest electric field available at present for experimental study.     

Formation of defects in gallium phosphide grown in the presence of oxygen

The influence of oxygen introduced in the gaseous phase on the formation of defects in GaP epitaxial layers is investigated by deep-level transient spectroscopy. The extremal dependences of the concentrations of charge carriers and electron traps with energy E _c−0.24 eV on the oxygen flux are discussed. Zh. Tekh. Fiz. 67, 52–55 (September 1997)     

Application of the BASNEF Model in Safety Training in Automobile Manufacturing Plants

After controls, including engineering and management, the final way to control noise is to use hearing protection devices. Due to the lack of a standardized questionnaire regarding investigating workers’ use of hearing protection devices on the basis of the BASNEF behavioral model, the present study was conducted to investigate the effect of health education based on the BASNEF model on the use of hearing protection devices in workers of an automobile manufacturing plant in Iran. This quasi-experimental and prospective intervention study was performed on 80 workers at an automobile manufacturing plant who are exposed to noise levels above 85 decibels and do not use hearing protection devices. In this study, 40 people working in a cast iron foundry were selected as the intervention group, and 40 working in aluminum casting were chosen as the control group. Questionnaires were analyzed at the beginning of the intervention and three months after the intervention in the intervention and control groups. There was no significant difference between the intervention and control groups before the intervention. There was a significant difference between the intervention and control groups after the intervention in the area of knowledge. A significant correlation was observed between the intervention and control groups after the intervention program in all areas of the BASNEF educational model except behavioral intention. In this study, the effect of educational intervention on the use of hearing protection devices was investigated, and with the educational intervention, it was tried to get help from influential people and enabling factors in education based on the BASNEF model. The results showed that the educational intervention based on the BASNEF model can improve the knowledge of individuals in both the intervention and control groups.     

Role of the second-order photorefractive effect in phase matching in second-harmonic generation in a ferroelectric

A phenomenological model of second-harmonic generation (SHG) in ferroelectrics in the absence of phase matching is considered. It is shown that conversion efficiency can be increased owing to a strong dependence of the second-order susceptibility on the second-harmonic intensity. The dependence of the conversion efficiency on the pump wave intensity is studied.     

High-voltage photovoltaic effect in layers of silicon evaporated in vacuum

Silicon layers which generate a photovoltaic voltage of up to 150 V/cm at room temperature are obtained by evaporation in a vacuum onto an insulating substrate. The spectral characteristics of the voltage, the effect of thermal processing on the value of the voltage and on the resistance of the layers, and the dependence of the voltage on the direction of the illumination and on the structure of the photosensitive layers are investigated. It is concluded that the photosensitive layers of silicon possess a microcrystalline structure with an ordered arrangement of the small crystals, separated by high-resistance oxide-type layers, and are sources of elementary photovoltaic voltages which are added along the layer. It is suggested that the reason for the formation of the elementary photovoltaic voltages is the separation of electron-hole pairs, produced by the light, by the field of the barriers which exist on the surfaces of the individual crystals of the layer and in the gaps between the crystals.The authors thank M. A. Rumsha for help with the electron diffraction investigations and for useful discussions, and also M. I. Rudenok for making the electron microscope investigations.