High-current nanosecond electron beams for probing the parameters of solids

Special features and prospects of using high-current nanosecond electron beams for probing the parameters of solids are examined. Of all the variety of signals carrying information on the characteristics of the test object under electron-beam excitation, the potentialities and features of pulsed cathodoluminescence of dielectric and semiconducting materials and of optical absorption (emission) of atoms evaporated by electron beams from metal surfaces or those of conducting rocks are discussed in detail. Tomsk Polytechnical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 22–30, March, 2000.     

On the sensitivity analysis of porous material models

Porous materials are used in many vibroacoustic applications. Different available models describe their behaviors according to materials' intrinsic characteristics. For instance, in the case of porous material with rigid frame, and according to the Champoux–Allard model, five parameters are employed. In this paper, an investigation about this model sensitivity to parameters according to frequency is conducted. Sobol and FAST algorithms are used for sensitivity analysis. A strong parametric frequency dependent hierarchy is shown. Sensitivity investigations confirm that resistivity is the most influent parameter when acoustic absorption and surface impedance of porous materials with rigid frame are considered. The analysis is first performed on a wide category of porous materials, and then restricted to a polyurethane foam analysis in order to illustrate the impact of the reduction of the design space. In a second part, a sensitivity analysis is performed using the Biot–Allard model with nine parameters including mechanical effects of the frame and conclusions are drawn through numerical simulations.     

Thermoelastic modeling of microbump and nanojet formation on nanosize gold films under femtosecond laser irradiation

A model of elasto-plastic flow combined with the two-temperature model in a two-dimensional approximation has been developed to describe microbump and nanojet formation observed recently on nanosize gold films irradiated by femtosecond laser pulses. It has been shown that the effect of microbump and nanojet formation is conditioned by the elastic characteristics, yield stress, and other properties that are unique for gold. The numerical results are in excellent agreement with the experimental data with respect to a number of parameters, particularly the threshold fluence for nanojet formation at the tops of microbumps, which occurs nearby and above the melting threshold. The analysis of properties for a number of materials is performed and some other materials are discussed as possible candidates for nanotexturing of thin films by femtosecond laser pulses. PACS 79.20.Ds; 42.62.-b     

A three-dimensional model for T-shaped acoustic resonators with sound absorption materials

Recent development in noise control using T-shaped acoustic resonators calls for the development of more reliable and accurate models to predict their acoustic characteristics, which is unfortunately lacking in the literature. This paper attempts to establish such a model based on three-dimensional theory for T-shaped acoustic resonators containing sound absorption materials. The model is validated by experiments using various configurations. Predictions on fundamental and high-order resonance frequencies are compared with those obtained from the one-dimensional model and finite element analyses, and the effects of the physical and geometric parameters of the absorption materials on the resonance frequencies and Q-factor are also investigated numerically and experimentally. Limitations and applicability of existing one-dimensional models are assessed. The proposed general three-dimensional model proved to be able to provide an accurate and reliable prediction on the resonance frequencies for T-shaped acoustic resonators with or without absorption materials. This can eventually meet the requirement for resonator array design in terms of accuracy.     

Effect of surface fields on luminescence of ZnS and ZnO crystals

It is shown that changes in luminescence characteristics of zinc sulfide and oxide in the presence of external effects that alter the surface charge are associated with a change in the parameters of surface barriers and can be explained within the framework of a model that takes into account separation of recombining partners in the Schottky barriers. We suggest a barrier mechanism for the effect of the surface region of a crystal on experimentally measured luminescence parameters and show that errors occuring in the measurement of these parameters can reach 10% and greater, depending on the depth of penetration of light. Moscow State University of Railways, 15 Obraztsov Str., Moscow, 103055, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 6, pp. 804–808, November–December, 1999.     

Impact reduction of the uncertain geometrical parameters on magnetic material identification of an EI electromagnetic inductor using an adaptive inverse algorithm

The magnetic characteristics of the electromagnetic devices' core materials can be recovered by solving an inverse problem, where sets of measurements need to be properly interpreted using a forward numerical model of the device. However, the uncertainties of the geometrical parameter values in the forward model lead to appreciable recovery errors in the recovered values of the material parameters. In this paper, we propose an effective inverse approach technique, in which the influences of the uncertainties in the geometrical model parameters are minimized. In this proposed approach, the cost function that needs to be minimized is adapted with respect to the uncertain geometrical model parameters. The proposed methodology is applied onto the identification of the magnetizing B-H curve of the magnetic material of an EI core inductor. The numerical results show a significant reduction of the recovery errors in the identified magnetic material parameter values. Moreover, the proposed methodology is validated by solving an inverse problem starting from real magnetic measurements.     

Establishment and experimental verification of infrared BRDF model in rough surface

Because of the thermal radiation from materials, the influence of spontaneous radiation on infrared-material—BRDF could not be neglected. In this paper, the spatial distribution characteristics of the material spontaneous radiation energy are analyzed. Then a full infrared BRDF semi-physical model in rough surface is developed by incorporating the characteristic parameters of the material spontaneous radiation into the five-parameter BRDF model. Finally, the model is verified using experimental data. Experimental results demonstrate that the proposed model error is less than 1%. The semi-physical model is more suitable for describing real physical process, and can be applied to analyze stray radiation of infrared optical system and target infrared characteristics.     

A mixed method for measuring low-frequency acoustic properties of macromolecular materials

A mixed method for measuring low-frequency acoustic properties of macromolecular materials is presented. The dynamic mechanical parameters of materials are first measured by using Dynamic Mechanical Thermal Apparatus(DMTA) at low frequencies, usually less than 100 Hz; then based on the Principles of Time-Temperature Superposition (TTS), these parameters are extended to the frequency range that acousticians are concerned about, usually from hundreds to thousands of hertz; finally the extended dynamic mechanical parameters are transformed into acoustic parameters with the help of acoustic measurement and inverse analysis. To test the feasibility and accuracy, we measure a kind of rubber sample in DMTA and acquire the basic acoustic parameters of the sample by using this method. While applying the basic parameters to calculating characteristics of the sample in acoustic pipe, a reasonable agreement of sound absorption coefficients is obtained between the calculations and measurements in the acoustic pipe.     

New computational and experimental methods for determining the elastic and strength characteristics of materials and for predicting the behavior of structures

Experimental methods for determining the physicomechanical characteristics of powder, polymer, and composite materials under thermal-force static and dynamic loads are presented. The results of the experimental investigations are used in numerical methods for calculating the stress — strain state and the stability and for describing the supercritical behavior as well as in methods for efficient design of strong machine-building structures made from new constructional materials.Scientific-Research Institute of Applied Mathematics and Mechanics at Tomsk State University. Translated from Izyestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 137–147, April, 1993.     

A Study of the Swelling of Copolymers of NIPAM and DMA with Water by NMR Imaging

A range of copolymers of N-isopropylacrylamide and N,N-dimethylacrylamide (DMA) have been prepared and the properties of these materials in aqueous solution examined by nuclear magnetic resonance (NMR) imaging. All of the polymers apart from PDMA exhibit a lower critical solution temperature, with the temperature and width of the transition increasing with increasing DMA content. On exposure to water the polymers swell rapidly; the kinetics of mass uptake are seen to closely resemble those expected for Fickian kinetics, although the Frisch exponents are slightly larger than expected. NMR imaging however reveals that the diffusion of water into these polymers is highly anomalous, with concentration profiles more typical of Case II diffusion. The deformation model of Thomas and Windle was used to analyze the water content profiles, and the resultant parameters used in the fits related to the structure of the two constituent monomer units. Authors' address: Andrew K. Whittaker, Center for Magnetic Resonance, University of Queensland, Brisbane, QLD 4072, Australia     

Mechanism of current hysteresis in reduced rutile TiO2 crystals for resistive memory

Memory devices based on the reversible resistance switching of various materials are attractive for today’s semiconductor technology. The reproducible current hysteresis (resistance switching) characteristics of reduced TiO₂ single crystal are demonstrated. Basic models concerning the filamentary and Schottky barrier models are discussed. Good retention characteristics are exhibited by the accurate controlling of the annealing parameters.     

A system for the remote spectroscopy in the visible and infrared regions

Results of the design and development of a system for remote sensing of the state and evaluation of the parameters of the natural environment and objects are presented. The devices developed are based on a generalized structural model of measuring system for acquisition of data on spectral, energy, polarization, angular, and spatial characteristics of the optical radiation field of the object under investigation. A. N. Sevchenko Scientific Research Institute for Applied Physical Problems at the Belarusian State University, 7, Kurchatov St., Minsk, 220064, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 6, pp. 827–833, November–December, 1997.     

Identification of trends of time series for a random number of measurements

An algorithm for identifying the trend of a time series is suggested, when the number of measurements at each sampling time is random. Statistical characteristics of estimates of trend parameters are investigated. Tomsk Pedagogical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 14–18, April, 1999.     

Trapped Coupled Dielectric Overlay Guide Configuration at Millimeter Wave Frequencies

Trapped coupled dielectric overlay guide has several interesting characteristics useful for millimeter wave applications. Dispersion characteristics and wave impedance for even and odd modes are computed by using Effective Dielectric Constant (EDC) method. Dispersion curves realized for Trapped coupled overlay guide for various dielectric materials and dimensional parameters as a function of frequency. Conductor and dielectric loss in the above configuration have also been studied. Polystyrene (µ_r = 2.56) and Stycast (µ_r = 3.4) have been used as dielectric materials.     

Structural and electrophysical characteristics of YBCO films on sapphire

We present experimental results for the structural and electrophysical characteristics of YBCO films deposited on sapphire substrates without an interface layer. The films were deposited by laser sputtering of a target. We establish certain relationships between the structural and electrophysical characteristics of the films. We show the films’ electrophysical parameters are determined by the number of "defective" blocks whose [010] axes are at random angles relative to the [100] axis of the substrate. V. D. Kuznetsov Siberian Physicotechnical Institute, Tomsk University. Translated from Izvestiya Vysshikh Uchebnykh Zaved, Fizika, No. 5, pp. 75–78, May, 1998.     

Energy characteristics of a XeCl-laser with excitation by anLC-inverter

We present results of research on the effect of the parameters of an XeCl-laser excitation system patterned after an LC-inverter on the energy characteristics of the laser. The effect of each of the parameters and their collection is established. We obtained conditions for matching the parameters of the excitation circuit of an XeCl-laser on satisfaction of which the lasing energy acquires a maximum value. It is shown that the energy characteristics of the laser are determined by the processes occurring in the inversion circuit and by the dynamics of the voltage across the interelectrode spacing. To whom correspondence should be addressed. Reported at the Second International Scientific and Technical Conference on Quantum Electronics, Minsk, November 23–25, 1998. Ya. Kupala Grodno State University, 22, Ozheshko Str., Grodno, 230023, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 5, pp. 702–707, September–October, 1999.     

Structure and magnetic properties of mechanically alloyed ferrite nanopowders

The morphology, structure parameters, and magnetic characteristics of mechanically alloyed magnetite and cobalt and magnesium spinel-ferrite nanopowders are investigated. The effect of the nanopowder particle size on the saturation magnetization of the spinel ferrites and the roles of the surface anisotropy and magnetoelastic energy in the formation of the magnetic anisotropy of the materials under study are discussed within the framework of a core-shell model. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 40–44, September 2006.     

Simulated Effects of Physical Parameters on Heat Transfer of Intumescent Fire-Retardant Polypropylene during Burning

Physical properties of intumescent materials are important parameters as input data in modeling the combustion behavior of intumescent materials in a fire. In this paper, effects of important physical properties on heat transfer of intumescent materials during burning are simulated based on a combustion model of intumescent fire-retardant polypropylene (IFR-PP) materials. Physical properties selected are thermal conductivity of virgin material and char layer, specific heat capacity of virgin material, density of virgin material, surface emissivity of virgin material and char layer, and intumescent temperature. Predicted temperature curves at a location 9 mm from the bottom of the IFR-PP material at an incident heat flux of 50 kW/m² are shown for the varied physical parameters values. The results show that these varied parameter values can affect the heat transfer of materials remarkably.     

Supernovae and the Arrow of Time

Supernovae are explosions of stars and are a central problem in astrophysics. Rayleigh–Taylor (RT) and Richtmyer–Meshkov (RM) instabilities develop during the star’s explosion and lead to intense interfacial RT/RM mixing of the star materials. We handle the mathematical challenges of the RT/RM problem based on the group theory approach. We directly link the conservation laws governing RT/RM dynamics to the symmetry-based momentum model, derive the model parameters, and find the analytical solutions and characteristics of RT/RM dynamics with variable accelerations in the linear, nonlinear and mixing regimes. The theory outcomes explain the astrophysical observations and yield the design of laboratory experiments. They suggest that supernova evolution is a non-equilibrium process directed by the arrow of time.