Initial permeability studies on A13+ and Cr3+ substituted Ni–Zn ferrites

The chemical formula of the samples investigated is Ni0.7Zn0.3Alx/CrxFe2-xO4, where x=0.00, 0.05, 0.10, 0.15, 0.20 and 0.25. The samples were obtained by the usual ceramic technology from high-purity oxides. The initial permeability was calculated from the inductance measurements with a torroidal core of 100 turns, using the formula L=0.0046 iN2h log d2/d1. The initial permeability i decreases in Ni0.7Zn0.3Alx/CrxFe2-xO4 with increase in Al3+/Cr3+. The decrease in i is attributed to a decrease of grain size D from 4.9 m to 4.4 m with Al3+ and to 1.9 m with Cr3+ and to variations in the anisotropy constant K1. The main contribution to the variation of permeability with content of Al3+/Cr3+ in the system is the effect each of them has on domain wall motion. The trivalent substituents (Al3+/Cr3+) cause impedance to the domain wall motion, which increases as the content of these ions increases. Al3+ has a stronger effect than Cr3+. The initial permeability components and do not exhibit much variation with temperature, except near Tc, where they fall sharply. The maximum of near Tc has been attributed to a damping effect of domain wall motion. © 1998 Chapman & Hall     

Application of coherent-optical methods in physical studies of evaporation

The application of the methods of laser and holographic interferometry to the problems of measuring evaporation rates is examined. Mass transfer accompanying evaporation in the region of extradiffusion monitoring is studied.Notation j_v specific mass flux of the vapor, kg/(m²·sec) - _c coefficient of condensation - _v coefficient of evaporation - D coefficient of diffusion - m²/sec, wetting angle - R radius of the vessel, m - time, sec - h height of the segment, m - wavelength of the laser radiation, m - N order of the interference fringe or the number of fringes passing through a given point - density of the matter, kg/m³ - length of the cell with the liquid of interest, m - T temperature, K - n refractive index of the medium - m mass - kg, V volume of the spheroidal segment, m³ - _liq and _g molar mass, kg/mole - C₀ and C_p concentration of vapor in the gas, kg/m³ - a and b semiaxes of the spheroid, m - _e ellipsoidal coordinate of a point on the surface, m² - c/n derivative along the normal - r coordinate of a point on the surface of evaporation, m - n change in the refractive index of the medium Indices st standard liquid - liq liquid - g gas - 0 starting state - p equilibrium pressure Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 55, No. 4, pp. 605–611, October, 1988.     

Effect of phase transitions in copper-germanium thin film alloys on their electrical resistivity

An investigation was carried out to study the phase transitions in Cu-Ge thin films (80–200 nm in thickness) containing 0, 5, 15, 20, 25, 30, 35, 40, 45 and 50 at% Ge, and the corresponding effects on electrical resistivity. For these films, the phase transitions were found to follow the sequence: -phase (disordered face centred cubic, fcc, solid solution); 5 at% Ge -phase (disordered hexagonal close packed, hcp); 15 at% Ge -phase + ₁-phase (ordered orthorhombic, Cu₃Ge); 20 at% Ge ₁-phase; 25 at% Ge (₁-phase + progressively increasing proportions of a disordered Ge-rich solid solution); 30–50 at% Ge. Germanium was found to have no marked effect on grain size of all films studied excluding grain boundaries as electron scattering centres. Transition of the -phase into the -phase was found to occur in a highly coherent manner, which could be related to the reduced stacking fault energy of Cu by the addition of Ge. Most evidence pointed out that the initial increase in resistivity within the -phase range was related to hcp scattering centres, which could be associated with a localized high concentration of Ge. At 15 at% Ge, the resistivity reached a maximum value of about 50 cm associated with the complete transformation of -phase into the -phase. With continued increase in Ge concentration, the resistivity was found to gradually decrease reaching a minimum value of about 10 at 25 at% Ge, which was correlated with complete transition of the -phase into the ordered ₁-phase (Cu₃Ge). It was shown that the superlattice of Cu₃Ge could directly be derived from the disordered -phase by minor atom rearrangement on the [0 0 0 1]_hcp plane. Even though, minor proportions of a Ge-rich solid solution containing a small concentration of Cu were formed at Ge concentrations above 25 at%, the minimum resistivity of 10 cm was maintained as the Ge concentration was increased to 35 at%. Subsequently, the resistivity was increased reaching about 46 cm at 50 at% Ge.     

A note on the similarity solutions for free convection on a vertical plate

Summary The similarity solutions for free convection on a vertical plate when the (non-dimensional) plate temperature is x and when the (non-dimensional) surface heat flux is –x are considered. Solutions valid for 1 and 1 are obtained. Further, for the first problem it is shown that there is a value ₀, dependent on the Prandtl number, such that solutions of the similarity equations are possible only for >₀, and for the second problem that solutions are possible only for >–1 (for all Prandtl numbers). In both cases the solutions becomes singular as ₀ and as –1, and the natures of these singularities are discussed.     

Two-dimensional laminar boundary layer in flow of thermodynamically equilibrated water vapor

This paper examines the boundary problem of a laminar boundary layer in flow of thermodynamically equilibrated water vapor. An approximate method of solution is proposed, based on an approximation for the density and the coefficient of dynamic viscosity across the layer.Notation u and v longitudinal and transverse velocity components - x and y longitudinal and transverse coordinates - density - p pressure - T temperature - h enthalpy - V specific volume - Pr Prandtl number - z dryness level - adiabatic exponent of the heated vapor - , ,gu coefficients of thermal conductivity, dynamic and kinematic viscosity Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 35, No. 5, pp. 789–795, November, 1978.     

The analysis of scientometric matrices for policy implications

A method is explained for analysing matrices of statistics where each element should be approximately proportional to some column coefficient and also to some row coefficient. Using U. S. patent data as an example it is shown that entries are usually proportional to country size and patent category size. Deviations from proportionality expectations when tabulated often suggest policy implications.     

Spontaneous nuclear ferromagnetic ordering of in nuclei in AuIn2 Part I. Nuclear specific heat and nuclear susceptibility

We have measured the nuclear specific heat C_n and nuclear susceptibility _n of In nuclei (I=9/2, =5.5 _n) in the cubic intermetallic compound AuIn₂ (Korringa constant =0.11 Ksec) in the normal conducting state at 30K10mK and 2mTB115 mT. Our data show a positive nuclear Weiss temperature =+ 43 K and that the In nuclei undergo a nuclear ferromagnetic transition at T_c=35 K. The In nuclei experience an internal field of about 10 mT (obtained from C_n at T>T_c ). The nuclear ordering temperature T_c and the internal field increase with applied magnetic field. From the data we deduce exchange constants for the investigated system. The critical entropy reduction S(T_c)/S_max=8.6% and critical enthalpy E=0.28 RT_c are in reasonable agreement with the measured ordering temperature T_c,applying the Heisenberg model for a simple cubic I=9/2 spin system. The nuclear spin relaxation time calculated from the real and imaginary parts of _n is 10 msec at T>50 K, but drops to <1msec at T_c.This is the first observation of a spontaneous nuclear magnetic ordering transition in a not-hyperfine-enhanced metal at thermal equilibrium, i.e. at T _nuclear =T _electron .     

Measurement of the Thermal Diffusivity of Metallic Foils and Films by the Photoacoustic Method1

The thermal diffusivities of four kinds of metallic foils from 20 to 200m in thickness were measured by a photoacoustic method on the basis of the Rosencwaig and Gersho theory. The measured data for continuous foils of uniform microscopic structure almost agreed with the literature values. Measurements were also carried out on two kinds of metallic thin films with of 10m thickness produced by sputtering. The difference in thermal diffusivity between the foils and the sputtered films depended on the uniformity of the microscopic structure.     

Condensation rate and coefficients of refraction and reflection of vacuum cryocondensates of water vapors on a metallic mirror

Specific features of heat transfer are investigated at the gas—solid interface at low temperatures for the case of water vapor condensation.Notation wavelength, nm - n_red reduced refractive index - angle of incidence, deg - r thickness, m - p pressure, mm Hg - T temperature, K - R_red reduced reflection coefficient - U_red reduced condensation rate Kazakh State University, Alma-Ata. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 63, No. 4, pp. 457–461, October, 1992.     

Study of Broadband Long-Focus Optics for Synchrotron Infrared Diagnosis of Low-Energy Electron Beams

A special optical device for measuring the geometry and current parameters in electron rings by synchrotron infrared radiation is designed, fabricated, and studied. The optical elements of the device are made of an optical ceramic and operate at 1–8 m. The study results are presented.     

Coaxial variable-length resonator for determining the electromagnetic parameters of materials at normal and higher temperatures

Conclusions It is possible by means of the above resonator, according to our analysis and in the absence of air gaps between the sample and the line, to evaluate the real components and of permeability and permittivity respectively in the range of 2 to 100 with an error between ±3% and ±10% in the temperature range from room temperature to +400°C, and the imaginary components and (for tan and tan in the range of 0.001 to 2) with an error of 7 to 20% over the same temperature range.     

Chebyshev approximation for the roots of the equation BiWГ(μ)=μVГ(μ)

A minimax approximation, uniform for Bi [0, ), is developed for the roots of the equation BiW()=V(), by means of Chebyshev polynomials.Translated from Inzhenero-Fizicheskii Zhurnal, Vol. 28, No. 4, pp. 710–715, April, 1975.     

Study of the lattice strain relaxation in the Ga1-X Al X Sb/GaSb system by x-ray topography and high resolution diffraction

High resolution x-ray diffraction and topographic methods have been used to study lattice strain relaxation in the Ga_1-X Al _X Sb/GaSb system. Samples with layer thickness ranging between 0.1 and 6 m and with Al concentration x=0.402±0.005 have been grown by molecular beam epitaxy at 550 °C on (0 0 1) oriented undoped GaSb LEC substrates. A first critical thickness (t _C1), related to the misfit dislocation generation, has been found to be between 0.16 < t _C1 < 0.20 m. Due to the weak sensitivity of the rocking curve to the onset of relaxation, this result has been obtained by means of a double crystal topographic technique. A plateau region in the curve of the residual strain versus thickness has been observed for t ranging between 0.2 and 0.5 m. The residual strain _res shows a dependence close to t^–0.5 above a second critical thickness value t _C2 slightly larger than 0.5 m. Finally, in the last region above a layer thickness of 3 m, strong dislocation interaction effects seem to affect the relaxation. A comparison with theoretical models has been made.     

High-frequency magnetic properties of Co-Ti substituted barium ferrites prepared by modified chemical coprecipitation method

Co-Ti substituted barium ferrites were prepared by a modified chemical coprecipitation method. Microstructures and high-frequency magnetic properties were investigated by X-ray diffraction (XRD) transmission electron microscopy (TEM) scanning electron microscopy (SEM) and measurements of complex permeability spectra. Barium ferrites with Co-Ti substitution x=1.0 have the highest permeability and the lowest magnetic resonant frequency f_ros and f_ros can be changed continuously with changing Co-Ti substitution in the hyper-frequency region while keeps its high value at the same time. A higher sintering temperature corresponds to higher and lower f_ros due to the grain growth. The d.c. electrical resistivity for all samples was above 10⁸ cm.     

Effect of Intense Self-Irradiation on the Phase Composition of Metallic Plutonium

The crystal structure of film samples of "high-level" (based on ²³⁸Pu) and low-level (based on ²³⁹Pu) metallic plutonium during their prolonged (up to 343 days) storage (self-irradiation) at room temperature was studied by X-ray diffraction. In the samples of high-level plutonium, the -Pu and -Pu lattices coexist. In the period of 40-60 days, the other known crystal modifications of plutonium (-Pu, -Pu, -Pu, and -Pu) are also present. Low-level plutonium had only the -Pu lattice. A possible origin of this phenomenon is discussed.     

Submicron diameter nickel filaments and their polymer-matrix composites

Discontinuous nickel filaments of diameter 0.4 m and having a carbon core of diameter 0.1 m were fabricated by electroplating nickel on discontinuous carbon filaments. They exhibited a grain size of 0.016 m and electrical resistivity of about 5 × 10^–6 ·cm. In an amount as low as 7 vol.% in a polymer (polyether sulfone) matrix, they resulted in a composite exhibiting electromagnetic interference shielding effectiveness of 87 dB and reflection coefficient 0.95 at 1–2 GHz, tensile strength 52 MPa, tensile ductility 1.0%, and density 1.87 g/cm³.     

Electron-phonon coupling as a mechanism for high-temperature superconductivity

We have solved the Eliashberg gap equations which are valid for arbitrary phonon frequency, (_ph), electron-phonon coupling constant, (), and screened Coulomb interaction, ( ^*). We have used values of (_ph),, and ( ^*) appropriate to the cuprate superconductors, and calculated the density of states, the pair potential., and the value of the gap at T=0 K. Using the linearized Eliashberg equations in the matrix representation, we have calculatedT _c and 2/k T _c . We have found that we can account for the highT _c 's in the cuprates with reasonable values for, ^*, and _ph.     

The influence of ageing on the stability of β-γ/γ′ derived microstructures in Ni-Al-Cr-(Co) alloys

Multiphase Ni-Al-(Fe)-(Cr)-(Co)-based intermetallics with (B2)- (A1)/(L1₂), - or - microstructures can exhibit significant room-temperature tensile ductility. In the case of Ni-Al-Cr-based alloys, microstructural development is complicated by the precipitation of -Cr, which can supplant the -phase during ageing of three-phase -/ microstructures. An investigation of the stability, during ageing, of cast Ni-Al-Cr-(Co) alloys with microstructures derived from -/ is reported. In the as-cast condition, the materials investigated consisted of a dendritic matrix containing L1₀ type martensite and interdendritic /. Extensive intra- and interdendritic -Cr precipitation was also observed. The stability during ageing of the interdendritic / microstructure is also considered and transformation of the L1₀ martensite is examined.     

The Interplay of Electronic and Nuclear Magnetism in PtFe x at Milli-, Micro-, and Nanokelvin Temperatures

We have measured ac susceptibility, nuclear magnetic resonance, and nuclear heat capacity of two PtFe _x samples with concentrations of magnetic impurities x = 11 ppm and 41 ppm at magnetic fields (0 ± 0.05) mTB248 mT. The susceptibility data have been measured at temperatures of 0.3 KT100 mK, no hint for nuclear magnetic ordering could be detected to a temperature of 0.3 K. The nuclear heat capacity data taken at 1.4 KT10 mK show enhanced values which scale with x at low polarization. This effect is described by a model assuming an internal magnetic field caused by the impurities. No indication for nuclear magnetic ordering could be detected to 1.4 K. The nuclear magnetic resonance experiments have been performed on these samples at 0.8 KT0.5 mK and 2.5 mTB22.8 mT as well as on three other samples with x = 5, 10, 31 ppm in a different setup at 40 KT0.5 mK and at 5.4 mTB200 mT. Spin-lattice and effective spin-spin relaxation times ₁and ₂ ^* of ¹⁹⁵ Pt strongly depend on x and on the external magnetic field. No temperature dependence of ₁and ₂ ^* could be detected and the NMR data, too, give no hint for nuclear magnetic ordering to 0.8 K.     

The role of starting powder size on the compressive response of stand-alone plasma-sprayed alumina coatings

Cylindrical stand-alone tubes of plasma-sprayed alumina were tested in uniaxial compression at room temperature, using strain gages to monitor axial strains. The effect of lamella size on the mechanical response was investigated by employing different starting powders to fabricate samples. The average powder sizes investigated included 9 m, 19 m and 32 m alumina; the resulting effective lamella diameters were 10 m, 28 m, and 55 m, respectively. Similar stress-strain hysteresis was observed on unloading in all tubes, independent of lamella size. A strong correlation between the failure stress and the cumulative strain at failure was also observed for tubes fabricated from the three powders. For samples with approximately constant densities, tubes plasma sprayed with the 9 m powder exhibited greater moduli than tubes sprayed from either 19 or 32 m powders. This difference was attributed to the greater percentage of unmelted -Al₂O₃ in the coating.