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The anisotropy of the properties of a ceramic cutting insert (for three faces) obtained by the lithography-based technology from the Al2O3 + ZrO2 composite has been studied. The study was carried out using the indentation method and Mayer’s law. This method, in contrast to the bending test, excludes the sample destruction. All the studies were carried out on three faces of a ceramic cutting insert made of a composite Al2O3 + ZrO2. The behavior of the Mayer index was studied in the range of loads from 2 to 20 kg and from 0.2 to 1 kg. The results of studying the density, phase composition and microstructure of each face of the sample are presented. The study of the adhesion of the printed layers were also carried out using a Knoop indenter. No anisotropy of the hardness was observed in the load range up to 10 kg. It is shown that a layered structure present in the sample, contributes to the hardness anisotropy under the load of 20 kg and more. No anisotropy of the fracture toughness is observed in the load range of 2 – 20 kg. The results of using a Knoop indenter revealed a high adhesion between 3D printed layers. Studies using a Knoop indenter have indicated high adhesion between the layers of 3D printing.

The results of studying the efficiency of the laser-acoustic method of ultrasonic testing in determination of the degree of polymerization of the matrix of polymer composite material (PCM) are presented. We have studied the PCM samples used for manufacturing integrated structures. It is shown that excessive degree of polymerization of the preformed blanks leads to a decrease in the strength of connection of the structural elements and precludes obtaining the desired shape and geometric dimensions of the product. We developed fundamentally new diagnostic parameters, which are characterized by high reliability and accuracy of determination. To forecast sample curing regimes with given values of the degree of transformation, the reaction kinetics was analyzed using differential scanning calorimetry Experimental results used for calculation of the kinetic parameters were obtained on a thermoanalytical complex DSC 1 (Switzerland). The kinetic parameters of polymerization and degree of binder curing in plastics were determined by the thermal effect of the reaction. It is shown that when determining the degree of polymerization of a PCM matrix by an ultrasonic method (laser-acoustic method of exciting ultrasonic vibrations), the product of attenuation of the bottom signal of longitudinal ultrasonic vibrations by the signal round-trip time and energy of the structural noise (thus taking into account the porosity of the material), can be used as reliable parameters of diagnostics. The proposed method provides higher accuracy compared to other methods used for control of the degree of polymerization.

Applicability of Spark Plasma Sintering has been studied for production of high-density (98.6–99.5%) composite ceramics Y2.5Nd0.5Al5O12 (YAG:Nd) – x MgO (x = 5, 10, 20 vol %). Powder YAG:Nd-MgO compositions have been obtained by precipitation of the MgO phase from Mg(NO3)2 water solution of magnesium nitrate onto the surface of garnet nanoparticles YAG:Nd. It has been demonstrated that the intensity of sintering fine-grained YAG:Nd-MgO composites is governed by volume diffusion at low temperatures and by grain boundary diffusion at high temperatures. Faster sintering at low temperatures is caused by formation of MgAl2O4 spinel particles and internal stress fields that are manifested as broadening and shifting of garnet peaks in the sintered composites.

Density functional theory (DFT) calculations have been used to study the band structure and density of states of a Ga1 – xMnxAs diluted magnetic semiconductor. It has been shown that some of the Mn 3d states are hybridized with the valence band at the Fermi level. Magnetic properties have been calculated by a multiscale method using DFT densities of states and exchange integrals calculated for a Mn atom by the Hartree–Fock method. The theoretical ferromagnetic transition temperature TC of Ga0.9375Mn0.0625As agrees with experimental data. spintronic materials, diluted magnetic semiconductor, GaAs, Mn, density functional method, density of states, band structure

Admittance spectroscopy is used to study hole states in Si0.7–yGe0.3Sny/Si quantum wells in the tin content range y = 0.04–0.1. It is found that the hole binding energy increases with tin content. The hole size-quantization energies in structures containing a pseudomorphic Si0.7–yGe0.3Sny layer in the Si matrix are determined using the 6-band kp method. The valence-band offset at the Si0.7–yGe0.3Sny heterointerface is determined by combining the numerical calculation results and experimental data. It is found that the dependence of the experimental values of the valence-band offsets between pseudomorphic Si0.7–yGe0.3Sny layers and Si on the tin content is described by the expression ΔEV exp = (0.21 ± 0.01) + (3.35 ± 7.8 × 10–4)y eV.

It is shown experimentally that in silver- and copper-containing barium-phosphate glasses metal subnanosized luminescent molecular clusters are formed during the glass synthesis. X-ray irradiation and the subsequent thermal treatment of these glasses result in the considerable change of their luminescence spectra in visible spectral region. This effect is caused by the transformation of the charge state of molecular clusters. In the luminescence spectra of the glass doped with silver and copper simultaneously new luminescence bands appear in comparison with the spectra of glasses doped only with one metal. The reason of this can be the formation of hybrid Ag n Cu m molecular clusters. The computer simulation of the structure and optical properties of such stable clusters by TDDFT method is presented.

Density functional theory calculations have been used to study the electronic structure of Mn-doped, Ni-doped, and Mn/Ni-codoped InSb and GaAs semiconductors. The ferromagnetic transition energy has been calculated using a multiscale method in which exchange interaction is calculated by the Hartree–Fock exact atomic method and is then included as a Hubbard parameter in calculation of the electronic structure of the material. The present calculation results demonstrate that, in all cases, there is hybridization of the impurity d states with the valence band of the host semiconductor. The contributions of the Ni and Mn dopants are approximately additive.

Nowadays multi-chamber arresters are widely distributed as devices of lightning protection of overhead power lines. A mathematical modelling of processes in the discharge chamber of multichamber arrester is necessary to carry out in order to improve its breaking capacity. A three-dimensional mathematical transient model of thermal, gas-dynamic and electromagnetic processes taking place in the discharge chamber of multi-chamber arrester is presented in the article. Basic assumptions, model equations, a computational domain and the boundary conditions are described. Plasma turbulence is taken into account. The results of the calculation i.e. distributions of plasma temperature and overpressure in the discharge chamber at different time points are shown. The analysis of the results was carried out. It is shown that the presence of cavities in the electrodes design promotes electric arc extinction in the discharge chamber of multi-chamber arrester.

Description of electromagnetic processes inside an arc interrupting system of high-current circuit breaker is presented in article. Non-stationary mathematical model of the circuit-breaker operation (short-circuit currents mode) is developed. The main regularities of the displacement of the electric arc inside an arc chute are established. The influence of the movable contact position on the conditions for the displacement of the electric arc is presented. Also, the influence of the arc chute material on the motion and interrupting of an electric arc (alternating and direct currents) is established.

Results of ultrasonic testing of parts that are fabricated by selective laser melting are assessed using radiography and X-ray computed tomography. Peculiarities of revealing incompletefusion flaws with the above methods are considered.

Possibilities and peculiarities of ultrasonic testing of parts manufactured by selective laser melting are considered. Special features of revealing solidity violation flaws with ultrasonic echo-pulse method are demonstrated.

Possibilities, application domains, advantages, and limitations are considered for currently used physical methods of nondestructive testing of additive manufactured parts. The methods are classified according to the physical principle of operation.

Peculiarities of additive technologies are considered, and the most typical flaws are listed. The possibility of layer-by-layer nondestructive testing of parts immediately in the course of additive manufacturing is demonstrated. Based on the review of domestic and international publications, possibilities that are offered by various physical methods of nondestructive evaluation are analyzed and potential of their usage is reviewed.

Physical foundations for a technique of revealing cracks in laminated metal and nonmetal constructions by a low-frequency acoustic method are considered. In this technique, elastic vibrations in a product with one-sided access are excited and recorded by a double-crystal transducer when the product surface is scanned with simultaneous rotation of the transducer about its longitudinal axis. The technique allows one to improve the reliability and productivity of testing of multilayered constructions.

We have calculated the electronic structure of Ga1–x Mn x As and In1–x Mn x Sb diluted magnetic semiconductors and shown that, in agreement with recent photoelectron spectroscopy data, the Mn 4s and Mn 3d orbitals are hybridized with the valence band of the host semiconductor. A new approach has been developed for calculating exchange interaction in diluted magnetic semiconductors, which is based on the spin polarization of s-electrons at a magnetic center due to single-center exchange s–d matrix elements. The magnitude of exchange interaction calculated using Hartree–Fock atomic wave functions and the electrondensity-functional approach agrees well with previous data.

The results of theoretical and experimental studies of the features and excitation effectiveness of torsional waves in pipes depending on the parameters of excitation, the properties of the pipe material, and the dimensions of an object are given. The results can be used for the evaluation of the possibility of waveguide quality control of pipelines during the development of inspection procedures using torsional waves.

Flaws in metal parts that are typical for the selective laser melting technique are considered. The flaws are divided into four groups by the degree of their danger. The quantitative and qualitative indices of the flaws are given and the causes of their formation are described.

A new approach to the calculation of the exchange interaction in diluted magnetic semiconductors based on spin-polarization of electrons of the unfilled band at the magnetic center is developed. The magnitude of the exchange interaction calculated using the Hartree-Fock atomic wave functions and DFT method is in good agreement with the results of other authors. The theoretical position of the hybridized impurity band of the Ga0.875Mn0.125As semiconductor somewhat below the Fermi level is in good agreement with the experimental data found by photoelectron spectroscopy.

A numerical model of heat conduction in vacuum through contact between two rough bodies made of commercial-purity AD1 aluminium is developed. To this end, the elastic–plastic contact deformation problem is solved accounting strain hardening. A method for consideration of surface initial cold work hardening and indentation size effect (ISE) is provided. Plastic characteristics of surface micro-volumes of material were taken from indentation results. Numerical realisation of the model in ANSYS finite element software is considered. Fractal surface models of two levels of roughness were used. Introduction of the second level roughness (microroughness) to the model was found to have considerable effect on the real contact area only when ISE is taken into account. An attempt to compare simulation results with data obtained with Shlykov’s semi-empirical model was made.

By measuring temperatures Tw for the transition from the incomplete to complete wetting of grain boundaries in polyand bicrystals, the width of the spectrum of tilt grain boundaries and their contribution to the total energy spectrum of grain boundaries in polycrystals have been experimentally estimated. It has been shown that the tilt grain boundaries correspond to a rather narrow (only 5-10%) portion in the total energy spec� trum of grain boundaries in polycrystals. In metals with a low stacking fault energy (copper, tin, zinc), the tilt grain boundaries belong to 10-20% of the grain boundaries with the highest transition temperatures Tw (hence, with low energies). In a metal with a high stacking fault energy (aluminum), the values of Tw for the tilt grain boundaries lie nearly in the middle between the minimum (Tw,min) and maximum (Tw,max) transition temperatures from the incomplete to complete wetting of grain boundaries. This means that grain boundaries with the structure corresponding to a lower energy than that of the symmetric twin boundaries (or stacking faults) can exist in aluminum.

Engineered nanomaterials significantly entered commerce at the beginning of the 21st century. Concerns about serious potential health effects of nanomaterials were widespread. Now, approximately 15 years later, it is worthwhile to take stock of research and efforts to protect nanomaterial workers from potential risks of adverse health effects. This article provides and examines timelines for major functional areas (toxicology, metrology, exposure assessment, engineering controls and personal protective equipment, risk assessment, risk management, medical surveillance, and epidemiology) to identify significant contributions to worker safety and health. The occupational safety and health field has responded effectively to identify gaps in knowledge and practice, but further research is warranted and is described. There is now a greater, if imperfect, understanding of the mechanisms underlying nanoparticle toxicology, hazards to workers, and appropriate controls for nanomaterials, but unified analytical standards and exposure characterization methods are still lacking. The development of control-banding and similar strategies has compensated for incomplete data on exposure and risk, but it is unknown how widely such approaches are being adopted. Although the importance of epidemiologic studies and medical surveillance is recognized, implementation has been slowed by logistical issues. Responsible development of nanotechnology requires protection of workers at all stages of the technological life cycle. In each of the functional areas assessed, progress has been made, but more is required.

Assessing the need for and effectiveness of controlling airborne exposures to engineered nanomaterials in the workplace is difficult in the absence of occupational exposure limits (OELs). At present, there are practically no OELs specific to nanomaterials that have been adopted or promulgated by authoritative standards and guidance organizations. The vast heterogeneity of nanomaterials limits the number of specific OELs that are likely to be developed in the near future, but OELs could be developed more expeditiously for nanomaterials by applying dose–response data generated from animal studies for specific nanoparticles across categories of nanomaterials with similar properties and modes of action. This article reviews the history, context, and approaches for developing OELs for particles in general and nanoparticles in particular. Examples of approaches for developing OELs for titanium dioxide and carbon nanotubes are presented and interim OELs from various organizations for some nanomaterials are discussed. When adequate dose–response data are available in animals or humans, quantitative risk assessment methods can provide estimates of adverse health risk of nanomaterials in workers and, in conjunction with workplace exposure and control data, provide a basis for determining appropriate exposure limits. In the absence of adequate quantitative data, qualitative approaches to hazard assessment, exposure control, and safe work practices are prudent measures to reduce hazards in workers.

We propose a proactive approach to the management of occupational health risks in emerging technologies based on six features: qualitative risk assessment; the ability to adapt strategies and refine requirements; an appropriate level of precaution; global applicability; the ability to elicit voluntary cooperation by companies; and stakeholder involvement.

Nanotechnology is predicted to improve many aspects of human life. By 2015, it is estimated to represent $3.1 trillion in manufactured goods. Data is emerging that exposure to nanomaterials may pose a health risk to workers. If the economic promise of nanotechnology is to be achieved, ways need to be found to protect nanotechnology workers now. The Occupational Safety and Health Act of 1970 (OSHAct) gave the responsibility to protect workers to the Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH) through research, standards adoption, and standards enforcement. Since 1980, adopting new occupational health standards has grown more complex. The increased complexity has greatly slowed efforts to adopt protective standards for toxic agents that are well-known to pose significant risks. The likelihood of rapidly adopting standards to protect workers from nanomaterials, whose risks are just emerging, seems even more unlikely. Use of the OSHAct’s general duty clause to protect workers also seems uncertain at this time. In the interim, a national partnership led by NIOSH involving nanotech manufacturers and downstream users, workers, academic researchers, safety, and health practitioners is proposed. A National Nanotechnology Partnership would generate knowledge about the nature and the extent of worker risk, utilize that knowledge to develop risk control strategies to protect nanotechnology workers now, and provide an evidence base for NIOSH recommendations to OSHA for a nanotechnology program standard at a future date.

The Organization for Economic Cooperation and Development (OECD), an intergovernmental organization, is playing a critical global role in ensuring that emerging technologies, such as nanotechnology, are developed responsibly. This article describes OECD activities around occupational safety and health of nanotechnology and provides state-of-the-science overview resulting from an OECD workshop on exposure assessment and mitigation for nanotechnology workplace.

The band structures of pure semiconductors CdGeAs2 and CuGaTe2, as well as magnetic semiconductors Cd1 − x Mn x GeAs2 and Cu1 − x Mn x GaTe2 (x = 0.0625), have been calculated by the density functional theory method. In both compounds, the Mn3d orbitals form a narrow band near the Fermi level. In the case of Cd1 − x Mn x GeAs2, the Mn3d orbitals are slightly involved in chemical bonding. In the case of Cu1 − x Mn x GaTe2, the same orbitals are considerably involved in chemical bonding. The relationship of these results with the properties of the compounds and ferromagnetism models is discussed.

In the present article, the characteristics of the polyaniline (PANI)-fullerene-nematic liquid crystal (NLC) have been studied. It has been noticed that dealing with nanostructured medium based on fullerene-doped PANI sufficiently accelerates transitional processes in a dispersed LC structure, causing the mesophase reorientation in shorter times. A quasi-transition from the nematic phase to the smectic one has been observed. The registered switching times of the fullerene-containing NLC-systems are in the range of tens of microseconds, which is not peculiar to the substance in the nematic phase, and have been observed earlier in the smectic phase only. In addition, the nonlinear absorption of laser radiation has been established at a wavelength of 805 nm in the systems studied. These structures could be applied in human eye and optical device protecting systems.

The electron-density-functional approach is used to calculate the band structure of the CdGeAs2 semiconductor and the diluted magnetic semiconductor MnxCd1−xGeAs2, which has a ferromagnetic structure at x = 0.06. The results indicate that the incorporation of Mn increases the band gap at its center and leads to the formation of a band derived from Mn levels, whose energy is a weak function of wave vector. The calculation results agree with experimental data.

A testing method, theoretical and experimental studies of velocity, damping, and reflection of a torsion wave in a tube with a modeled longitudinal crack are discussed. The considered results can be regarded as a basis for the development of effective methods and means that use torsion waves to test acoustic tubes.

The kinetics and morphology of the grain boundary grooving of Zn bicrystals with 16° tilt GB by Sn(Zn) melt has been studied at 325°C in equilibrium conditions in vacuum. It is shown that grooving process is interface controlled at least on the first stage. Groove walls mobility is evaluated. Changing of GB grove shape from “faceted walls” corner for annealing time < 78 h to concave “Mullins type” groove for annealing time > 78 h at the same experimental temperature was observed for the first time.

Surface properties of respirable silica, which represents a major occupational safety concern, were investigated computationally, and a model for quantitative characterization of crystalline silica surface sites was developed. It was found that the surface energy of crystalline solids, such as silica and silicates, can be calculated as a product of the surface site density and site energy. The energies of sites formed by faceting tetrahedral silica polymorphs and aluminosilicate were determined by parametric fitting ab initio surface energies to site densities. Boltzmann’s statistics was used to describe the distribution of faces as an exponential function of unrelaxed surface energy in the comminuted crystalline solids. Using these findings, crystallographic face distributions on fractured quartz, coesite, tridymite, and cristobalite were derived and average silanol hydroxyl densities in fractured particulate of these materials were estimated as 0.070, 0.059, 0.058, and 0.055 A−2, respectively. The proposed method of quantitative characterization of the surface bridges the gap between microscopic simulations and measurable observables, such as cytotoxicity of respirable silica.

Fullerene-doped liquid crystal compounds have been considered as new nanostructured materials with promising photosensitivity and speed parameters. Self-organization in liquid crystal mesophase based on charge-transfer complexes between an organic donor and fullerene has been investigated. The switch-on time of 50 μs has been obtained. The results are discussed from the viewpoint of increasing the system polarizability and a possible transition from the nematic phase to the smectic one, which is caused by a complex formation.

The Cu(4 1 0)–O surface, involving a 0.5 monolayer (ML) coverage of oxygen, is known to be extremely stable and a range of Cu(1 0 0) vicinal surfaces facet to (4 1 0) in the presence of adsorbed oxygen. A new surface X-ray diffraction investigation of this surface has been conducted to determine its structure, and the detailed structural parameter values obtained are compared with the results of a density functional theory (DFT) calculation. The results show that the metal structure is unreconstructed, with the oxygen forming an overlayer with 0.25 ML O atoms at near-colinear step-edge sites and 0.25 ML O atoms at mid-terrace hollow sites, approximately 0.6 A above the terraces. The large number of independent structural parameters potentially relevant to this vicinal surface presents a significant challenge for unique structural optimisation, but various missing row reconstruction models can be clearly excluded. Two detailed structural solutions are identified which give equally acceptable fits to the X-ray diffraction data after imposition of a Lennard-Jones penalty factor. These models differ especially in the O positions, but one is found to be more favoured by comparison with the results of the DFT calculations, and by considerations based on bond lengths and valence. Substantial relaxations from the bulk metal positions occur for the outermost Cu atoms; the ability of the vicinal surface to relax in this way may help to account for its stability compared with the missing row reconstruction induced by oxygen chemisorption on the Cu(1 0 0) surface.

Organizations around the world have called for the responsible development of nanotechnology. The goals of this approach are to emphasize the importance of considering and controlling the potential adverse impacts of nanotechnology in order to develop its capabilities and benefits. A primary area of concern is the potential adverse impact on workers, since they are the first people in society who are exposed to the potential hazards of nanotechnology. Occupational safety and health criteria for defining what constitutes responsible development of nanotechnology are needed. This article presents five criterion actions that should be practiced by decision-makers at the business and societal levels-if nanotechnology is to be developed responsibly. These include (1) anticipate, identify, and track potentially hazardous nanomaterials in the workplace; (2) assess workers' exposures to nanomaterials; (3) assess and communicate hazards and risks to workers; (4) manage occupational safety and health risks; and (5) foster the safe development of nanotechnology and realization of its societal and commercial benefits. All these criteria are necessary for responsible development to occur. Since it is early in the commercialization of nanotechnology, there are still many unknowns and concerns about nanomaterials. Therefore, it is prudent to treat them as potentially hazardous until sufficient toxicology, and exposure data are gathered for nanomaterial-specific hazard and risk assessments. In this emergent period, it is necessary to be clear about the extent of uncertainty and the need for prudent actions.

The heat capacity of zeolite 4A (also known as LTA, Linde Type A and sodium zeolite A), in the temperature range from 37 to 311 K, is reported. The heat capacity shows no anomalies in this temperature range. Thermodynamic parameters, H, S and G, relative to their values at T=0 K were derived. From these data, we find that zeolite 4A is stabilized by strong enthalpic interactions. Furthermore, its thermodynamic stability results from the strong SiO and AlO bonds in the primary building units, with bond strengths very close to those in other similar materials.

Hydrogen-bond complexes of dihydrogen phosphate and dimethyl phosphate anions with orthosilicic acid, water, and ionic complexes with sodium cations are investigated with the density functional (B3LYP/6-31G(d,p) and B3LYP/6-31+G(d,p)) theory and the second-order perturbation (MP2/6-31+G(d,p)) theory. The geometries and IR spectra of the complexes obtained with the B3LYP/6-31+G(d,p) and MP2/6-31+G(d,p) level calculations are found to be very similar. Inclusion of diffuse functions in the basis set significantly improves the reproducibility of the experimental data. The BSSE corrections significantly reduce the differences in stabilization energies obtained at different levels of theory, and as expected are the largest with the least flexible basis set calculations.

The thermal conductivity of model zeolites was investigated using non-equilibrium molecular dynamics calculations. This type of calculation was found to overestimate the thermal conductivity of low-density silica polymorphs. A better reproduction of the experimental results was found for zeolites, and this was related to the lower phonon mean free path. The thermal conductivity of framework silicates was shown to be determined primarily by the vibrations of the continuous oxygen sublattice. Thus, the most drastic suppression of the heat transfer was related to alterations of the O-O distances; for example, a sixfold reduction in thermal conductivity compared to that of siliceous LTA zeolite was found for LTA-A1PO4. Framework cations were shown to affect the heat transfer by changing the vibrational modes of the structural building units of the framework and non-framework counter-cations, by disturbing the oxygen sublattice locally and acting as Rayleigh and resonant scatterers. A model assuming the heat transfer to be due only to non-dispersive acoustic phonons failed to reproduce the dependence of the thermal conductivity on the mass of the cations and the unit-cell dimension, thus suggesting a more sophisticated mechanism of heat transfer to be operative in framework materials. The effect of non-framework non-ionic species on the thermal conductivity was shown to be determined by their effect on the characteristics of the oxygen framework vibrations. Thus, repulsive interactions between the oxygen sublattice and Xe8 clusters, reducing the anisotropy and anharmonicity of the oxygen vibrations, give rise to enhanced heat transfer in LTA-SiO2 at ambient conditions.

An ultrasonic method for evaluation of composite structures by laser-excited wide-band acoustic pulses is proposed. Two types of laser optoacoustic transducers, in transmission and reflection modes, are used in the spectral range of 0.1–10 MHz. In the first case, the frequency dependence of the attenuation factor of ultrasound is measured. In the reflection mode, the optoacoustic transducer allows us to obtain the time-dependent shape and spectrum of the backscattered acoustic signal with one-sided access to a specimen or product. Specimens of a layered graphite-epoxy composite of different porosity (up to 1.2%) are studied. In the frequency range of 1–5 MHz, the attenuation factor of ultrasound measured in the transmission mode is the greater the higher the porosity of the specimen. The “noise” part of the backscattered acoustic pulse is found to increase with increasing porosity of the specimens. A 1% growth in porosity causes a threefold increase in the noise power. The results obtained confirm the advantages of the laser optoacoustic method for evaluation of composite materials and products during their manufacturing and operation.

Since carbon molecules with geodesic structures have been detected, the question for potential silicon-based analogues of these species has been raised. The existence of these hypothetical `silicon balls', however, has not been ascertained so far in spite of several theoretical as well as experimental attempts to do so. Several theoretical approaches have been put forward in the past to explain the experimentally observed features of Si N clusters and thus to account for the obvious dissimilarity between finite systems based on the isovalent elements silicon and carbon, but no comprehensive growth sequence model has been generally accepted for Si N so far. The present work is aimed at an exploration of closed-shell Si N systems, derived from highly symmetric cage-like geometries, in the size range N ≤26 by means of Hartree–Fock and post-Hartree–Fock procedures. Particular emphasis is placed on the question of the stabilities of these isomers as compared to the corresponding ground states, wherever available. Cohesive energy calculations suggest a tendency towards an increase of cluster stability with the number of constituents for cage-like Si N isomers up to N =10, while a trend towards destabilization with growing size is found for larger clusters.

Large Y-123 single domain textured sample was produced by slowly cooling Y-123+15% Y-211 precursor seeded with Sm-123 through the peritectic point. The sample was annealed in flowing O 2 at 380°C for 72 h. An O 2 distribution gradient in the range of 6.64–6.84 was determined in the volume of the sample by measuring ` c ' parameter of unit cell for the small cleaved sections. The J c of those sections was derived from hysteresis loops and T c from a.c. susceptibility. T c is practically constant in the range=6.84> x O >6.71 and drops sharply for smaller x O . A maximum J c of 76,000 A/cm 2 (77 K, self field) and an irreversibility field H irr =7.2 T were obtained for x O =6.77, which is in the range of structural transformation of orthorhombic I→orthorhombic II phase of oxygen superlattice, where the clustering in the oxygen superlattice is maximal. This results in a strong flux pinning, giving large J c and H irr . Any-minute deviation from x O =6.77 lowers J c and H irr substantially.

The chemical and energy structures of highly fluoridated fullerene films have been investigated. Analysis of the complex structure of carbon 1s spectra showed the presence of C-F and C-F2 fragments as well as nonfluoridated carbon atoms with an overwhelming quantity of C-F bonds. The band gap in fluoridated-fullerene and its films was estimated to be 8.0 eV and energy loss on an interband transition at 11 eV was also observed. Comparison of the valence-band spectra of the experimental samples showed that the valence band of fluoridated fullerenes is divided into anionic and cationic parts (similarly to alkali-halide crystals) and suggests that fluoridated fullerenes possess the corresponding properties, making it possible to find new materials with wide practical applications.

The mechanism for the unexpectedly strong interactions between the guest and lattice vibrations in clathrate hydrates is revealed from molecular dynamics and lattice dynamics calculations on model systems. It is shown that the vibrational couplings are the result of avoided crossings of the enclathrated guest localized rattling modes with the host lattice acoustic phonon branches of the same symmetry. Through these couplings, energy can be exchanged between the host lattice and the guest vibrations and lead to the anomalous glasslike behavior in the thermal conductivity of gas hydrates.

Magnetization cycles and relaxation measurements as a function of temperature and field are reported for a very thin single crystal (thickness ). The fishtail effect was observed between 15 and 26 K at about 400 Oe, at which the relaxation rate was also found to increase rapidly. The observed behaviour is attributed to the field-induced two-dimensional to three-dimensional crossover in the vortex lattice in the presence of bulk pinning and surface barriers which dominate in different regions of the B - T phase diagram.

With the improvement in both materials and processing techniques, very large-grained YBa 2 Cu 3 O 7 samples with overall dimension of 4×12×12 mm 3 were produced. Each sample was capable of levitating over a kilogram in weight. A high temperature superconducting magnetic-suspension (levitation) train prototype was constructed using the YBa 2 Cu 3 O 7 samples, to validate the concept of using an HTS Meissner effect magnetic suspension system. Measurements on important magnetic suspension parameters, such as relative suspension stability and suspension force, as well as magnetic field intensity and distribution are reported and discussed.

The MP2(fc)/6-31G∗ structures, energies and frequencies of the trisilaallyl cation (1) and a number of its Si3H5+ isomers reveal considerable differences from the C3H5+ potential energy surface. Unlike the allyl cation, 1 is not a minimum. A “quasi-cyclic” form (7), with a much shorter Si(1)Si(3) separation and aromatic character, is the global Si3H5+ minimum at MP2 and at B3LYP/6-311+G∗∗. However, Raghavachari's (J. Chem. Phys., 95 (1991) 7373) double-bridged isomer (5) is 1.4 kcal mol−1 lower in energy than 7 at the CCSD(T)/6-311+G ∗ //MP2/6-316 ∗ level. Conjugation in the planar C2v 1 and hyperconjugation in the rotated 9 form are decreased relative to the carbon analogs. The remarkable stability of 5 and 7 can be attributed to their effective charge delocalization.

Different precursor mixtures of 123 and 211 have been used to study the particle size distribution of the 211 phase. Melt texturing of these samples was performed by using a Sm-123 seed for preferential growth of single grain material and 211 substrates to soak the outflowing melt. The size distribution of the 211 inclusions was determined and their influence on the propagation of cracks in the textured material was studied. A precursor mixture of 15 wt% small grained 211 particles (1–5 μm) leads to the highest content of small sized 211 inclusions ( μ m). This material shows trapped magnetic fluxes up to 210 mT without any additional admixing.