Does Vortex Lattice of YBa2Cu3O6.94 in H⊥c Melt Below Intrinsic-Pinning Irreversibility Line?

Vortex lattice melting in the Hc configuration of an YBa ₂ Cu ₃ O _6.94 single crystal has been investigated by means of the ac susceptibility – i and the magnetic torque . The melting transition of vortex lattice occurs in Hc, too. Since the torque curve shows a sharp peak in the irreversible torque at _c 90° due to intrinsic pinning at lower temperatures, we can determine the irreversibility line for the intrinsic pinning. The melting transition in the Hc configuration appears at temperatures where the intrinsic-pinning peak is absent. We consider that the intrinsic pinning does not affect the nature of the vortex melting transition in the Hc configuration.     

Reactivity of oxygen-deficient Mn(II)-bearing ferrites (Mn x Fe3-x O4-δ, O⩽x⩽1, δ>0) toward CO2 decomposition to carbon

The reduction of CO₂ to carbon was studied in oxygen-deficient Mn(II)-bearing ferrites (Mn _x Fe_3-x O_4-, Ox1, >0) at 300 °C. They were prepared by reducing Mn(II)-bearing ferrites with H₂ gas at 300°C. The oxygen-deficient Mn(II)-bearing ferrites showed a single phase with a spinel structure having an oxygen deficiency. The decomposition reaction of CO₂ to carbon was accompanied by oxidation of the oxygen-deficient Mn(II)-bearing ferrites. The decomposition rate slowed when the Mn(II) content in the Mn(II)-bearing ferrites increased. A Mössbauer study of the phase changes of the solid samples during the H₂ reduction and CO₂ decomposition indicated the following. Increases in the Mn(II) content lowered the electron conductivity of the Mn(II)-bearing ferrites. Increases in the oxygen deficiency, , contributed to an increase in electron conductivity and suggested that electron conduction due to the electron hopping determines the reductivity of CO₂ to carbon by the donation of an electron at adsorption sites.     

Mixed state odd Hall effect in YBa2Cu3O7−δ with unidirectional twins

We have studied the mixed state Hall effect in YBa₂Cu₃O_7– single crystals with unidirectional twins: _xy=f(H). An analysis of the Hall conductivity _xy in free flux flow regime reveals that _xy can be successfully described by two terms which are related to the quasiparticle excitations and the motion of free vortices respectively. We have discovered the strong twin dependence of the Hall conductivity _xy in the pinning (TAFF) regime and detected the sign reverse of the Hall conductivity _xy at changing angle (+45 °–45 °) between current and twin plane that indicated the presence of backflow of vortices. We have observed that _xy tends to - while approaching the melting line. These results provide the evidence of strong planar pinning influence on the Hall conductivity.     

Viscoelastic properties of the nucleus pulposus of the intervertebral disk in compression

The viscoelastic properties of the nucleus pulposus were measured in compression for 35 specimens dissected from 9 sheep. Measurements on 19 specimens were made on the day of slaughter; the remaining 16 specimens were stored frozen and thawed before testing. A preload of 0.2 N was applied to each specimen and a cyclic compression of 10 m applied at eight frequencies in the range 0.1–10 Hz at a temperature of 37 °C. Freezing appeared to increase the storage modulus, E , but not the loss modulus, E , or tan =E /E . These parameters, E , E and tan , had values of 64±28 kPa, 24±11 and 0.33 kPa±0.07, respectively. The value of tan passed through a minimum at a loading frequency of 0.9±0.2 Hz. The water content of the specimens was 80±2%. © 2001 Kluwer Academic Publishers     

Thermal conductivity of argon and argon-neon mixtures at high temperature

The thermal conductivity of neon and argon-neon mixtures is studied in the temperature range 400–1500°K. This is the first recording of such data above 793°K.Notation T_g true temperature drop in gas layer °K - ¯T temperature, °K, Q, effective thermal flux, W - Q_t, Qr thermal flux transmitted by thermal conductivity and radiation, respectively, W - T_sh correction for temperature shift, % - thermal conductivity of gas mixture, W/m·°K - x_i a molar concentration of neon - _i, _i, _ij, _ij potential function parameters for inter molecular interaction of homogeneous and inhomogeneous molecules - slope of exponential repulsion term Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 33, No. 5, pp. 848–856, November, 1977.     

The occurrence of stress-induced α′ martensite in an (α+γ) Fe-Cr-Ni alloy

The interaction of an applied stress with the displacive shear during the martensitic transformation determined theK-S variants which formed in three types of tensile specimens, with tensile directions of 0°, 45° and 90° to a rolling direction respectively. The 3–6, 4–5 and 1–3 variants in a 0°-specimen, 1–5 and 4–5 variants in a 45°-specimen and 4-4 and 3–6 variants in a 90°-specimen are chosen asK-S variants which have the maximum value ofU/ in respective tensile directions. These variants are related to the occurrence of martensite with particular orientations as (100), (110) and (211).     

Magnetization curves of (La1−x Sr x )2CuO4−δ single crystals as functions ofx and δ

The second peak effect in magnetization curves for overdoped (La_1–xSr_x)CuO_4– single crystals was examined by means of systematic variations of Sr content x and oxygen deficiency . Oxygen defect concentration was found to sensitively affect the critical temperature T_c and the macroscopic pinning force F_p, resulting in significant changes in magnetization hysteresis loops. Observations of dependence of M and F_p at the same reduced temperature T/T_c yielded an insight into the role of oxygen defects: increasing results in increasing the pinning center density N. The second peak field B_2pk seemed to be determined by the development of a percolating network of magnetically reversible regions from the observation that the temperature dependence of B_2pk showed similar behavior to the irreversibility field B_irr.     

Effect of crack shape,inclination angle,and friction coefficient in crack surface contact problems

In rolling/sliding contact fatigue, it is known that the crack propagates at a characteristic angle =15–30 deg to the surface. To analyze the mechanism, however, the body force method has been widely used assuming 3D crack models for =45–90. In this study, therefore, the unknown body force densities are newly approximated by using fundamental density functions and polynomials. Then, a semi-elliptical crack model is analyzed for =15–90 under compressive residual stresses and Hertzian contact loads. The stress intensity factors K _II, K _III are calculated with varying the crack shape b/a, inclination crack angle , and crack face friction coefficient . The calculations show that the present method is useful for the analysis for =15–30 deg with high accuracy. It is seen that the K _II-values when b/a0 are larger than the ones when b/a=1 by 0–24% for both under compressive residual stress and Hertzian contact load. Regarding the maximum K _II values under Hertzian contact load, the results of =15 deg are smaller than the ones of =45 deg by 23–34%. Regarding the amplitude of (K _{II max}–K _{II min}), the results of =15 deg are smaller than the ones of =45 deg by 4–24%. With increasing the value of friction coefficient for crack faces the value of K _II decreases significantly. When the crack is short and the inclination angle is small, the value of friction coefficient f for Hertzian contact load largely affect the K _II value.     

Dielectric properties of chemically vapour-deposited Si3N4

The dielectric properties of chemically vapour-deposited (CVD) amorphous and crystalline Si₃N₄ were measured in the temperature range from room temperature to 800° C. The a.c. conductivity ( _a.c.) of the amorphous CVD-Si₃N₄ was found to be less than that of the crystalline CVD-Si₃N₄ below 500° C, but became greater than that of the crystalline CVD-Si₃N₄ over 500° C due to the contribution of d.c. conductivity ( _d.c.). The measured loss factor () and dielectric constant () of the amorphous CVD-Si₃N₄ are smaller than those of the crystalline CVD-Si₃N₄ in all of the temperature and frequency ranges examined. The relationships of ^n-1, (- ) ^n-1 and/(- ) = cot (n/2) (were observed for the amorphous and crystalline specimens, where is angular frequency andn is a constant. The values ofn of amorphous and crystalline CVD-Si₃N₄ were 0.8 to 0.9 and 0.6 to 0.8, respectively. These results may indicate that the a.c. conduction observed for both of the above specimens is caused by hopping carriers. The values of loss tangent (tan) increased with increasing temperature. The relationship of log (tan) T was observed. The value of tan for the amorphous CVD-Si₃N₄ was smaller than that of the crystalline CVD-Si₃N₄.     

Upper critical and irreversibility fields in selectively doped YBa2Cu3O7

The electrical resistivity of (Y_1–xPr_x)Ba₂Cu₃O_7–gd and YBa₂(Cu_1–xZn_x)₃O_7– thin films and (Y_1–x. Tb_x)Ba₂Cu₃O_7– thin films and single crystals has been measured as a function of 0xx_crit, 2KT300K and OTH20T. The samples were oriented withc-axis parallel to applied fields. Upper critical field H_c2 and irreversibility field H_irr values have been determined from these measurements. Increased Tb doping appears to shift H_irr to higher temperatures. This coupled with observed twin peaks in magnetization measurements reflects an enhancement of flux pinning. Unlike Tb which does not appear to alterT _c , Pr and Zn doping of this system tends to depress bothT _c and the slope of the mean field normal phase-mixed phase boundary line (dH _c2/dT).     

Preparation of superconducting Bi-Sr-Ca-Cu-O ceramics by the sol-gel method

Superconducting Bi-(Pb)-Sr-Ca-Cu-O ceramics were prepared through the sol-gel method using an aqueous solution of metal acetates containing acetic acid and tartaric acid. The conditions of gelation and conversion of gel to Bi₂Sr₂CaCu₂O_x phase were studied by thermal analysis, infrared absorption spectroscopy and X-ray diffraction technique. It was found that transparent gels were obtained from the solutions containing tartaric acid, with a molar ratio of C₄H₆O₆/Cu of about 0.4. The gel matrix was assumed to be composed of carboxylate anions and metal cations. A gel of molar composition BiSrCaCu = 2223 was decomposed to CaCO₃, CaO, CuO and Bi_1-x Sr_xO_y (x = 0.2 to 0.3) at low temperatures of 270 to 600 ° C and produced Bi₂Sr₂CaCu₂O_x phase at 800 ° C via complex intermediate states. A rapid cooling of the heated product increasedT _c (end) in the gel of molar composition BiSrCaCu = 2223, while a slow cooling increasedT _c (end) in the lead-containing gel of molar composition BiPbSrCaCu = 1.850.351.92.03.1. The latter showedT _c (onset) at 115 K andT _c (end) at 105K.     

An apparatus for measuring the thermal conductivity and diffusivity of solid materials

An apparatus is described for measuring the thermal conductivity and diffusivity on small specimens of solid materials; also the results are shown which have been obtained for refractive high-alumina concrete by such measurements.Notation thermal conductivity at the mean temperature of specimens, W/m· °C - Q power of the central heater, W - F cross section area of a specimen, m² - t_1,2 temperature drop across the specimens, °C - ₁, ₂ difference in heights between the thermocouple beads, center-to-center, in the first and in the second specimen respectively, m - t temperature, °C - time coordinate, min - d₁= (d_1u+d_1l )/2 mean distance between specimen contact plane and nearest thermocouple beads, for the upper and lower specimen, m - d₂= (d_2u+d_2l )/2 mean distance between specimen contact plane and farthest thermocouple beads, for the upper and lower specimen, m - dt(d₁,)/d rate of temperature rise at section d₁ of the specimen at time, °C/h - t=t₁+t₂ sum of temperature drops in the specimens at time, °C - m heating rate, h^–1 - a thermal diffusivity of specimens, referred to their mean temperature, m²/h - =m/a, m^–1 b=¦(t_u–t_l)/t_u¦ heating nonuniformity factor Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 6, pp. 1049–1054, June, 1972.     

Anisotropic grain growth of R-α-sialon (R = Nd and Er)

Two R--sialon (R_0.6Si_9.3Al_2.7O_0.9N_15.1, R=Nd and Er) compositions were first fired at 1750°C/25 min and 1650°C/2 h respectively for completion of the phase transformation. Elongated -sialon grain morphology was developed in both samples after being re-fired at 1800°C for different periods of time. The growth in width of R--sialon grains is controlled by diffusion in the liquid, while the length growth tends to be interfacial reaction controlled. The anisotropic growth of R--sialon is attributed to the large difference in the growth rate constant between the length and the width directions of the grain.     

X-ray diffraction and magnetic analysis of deformation induced martensites in a Fe-17Mn-1.9Al-0.1C steel

The deformation induced martensitic transformations in a Fe-17Mn-1.9Al-0.1C steel are investigated by X-ray diffraction and magnetic measurements. Martensites and are formed at the same time during cold deformation of the steel. The starting (A _s) and final (A _f) temperatures of the reversion of martensite during continuous heating are 390°C and 540°C. The martensite seems to be reverted in the 300°C–450°C range. These results are discussed and compared with those previously obtained in conventional stainless steels.     

Numerical calculation of a generalized thermal model of radio-electronic apparatus

A method is proposed for numerical calculation of the temperature field of a generalized model of electronic equipment with high component density.Notation x,y,z,x,y spatial coordinates, m - time, sec - L_x, L_v, L_z dimensions of heated zone, m - _x, _y, _z effective thermal-conductivity coefficients of heated zone, W/m·deg - ₂ thermal conductivity of chassis, W/m·deg - a _z thermal diffusivity of heated zone along z axis, m²/sec - c₁ effective specific heat of heated zone, J/kg·deg - ₁ effective density of heated zone, kg/m³ - c₃, ₃, c₂, ₂ thermophysical characteristics of cooling agent and chassis, J/kg·deg·kg/m³ - q_v(x, ), q(x, y) volume heat-source distribution, W/m³ - q_s (x) surface heat-source distribution, W/m² - p number of cooling agent channels - Fo Fourier number - Bi Biot number - Uⁱ coolant velocity in i-th channel, m/sec - T₁(x, ), T₂(x, ), T₃(x, ) temperature distribution of heated zone, chassis, and coolant, °K - T₃₀, T₁₀(x), T₂₀(x) initial temperatures, °K - T_3in coolant temperature at input to channel, °K - T_T(x) effective temperature distribution of heat loss elements, °K - T_C temperature of external medium, °K - dimensionless heated zone temperature - _v(x) local volume heat exchange coefficient, W/m³·deg - ₁₂(x), _1C(x), _1T(x) heat liberation coefficients - W/m²·sec; ₂₁(x, y), _2c(x, y), _2T(x, y) volume heat-exchange coefficients of chassis with heated zone, medium, and cooling elements, W/m³·deg Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 40, No. 5, pp. 876–882, May, 1981.     

Structure and decomposition behaviour of rapidly solidified AI-Cu-Li-Mg-Zr alloys

The microstructural characteristics of AI-Cu-Li-Mg-Zr alloys have been studied after rapid solidification by melt spinning and after subsequent annealing at temperatures in the range 160 to 500°C, by using a combination of optical microscopy, scanning and transmission electron microscopy, X-ray diffraction, differential scanning calorimetry and microhardness measurements. The as-melt-spun alloys consist of a cellular microstructure with fine scale precipitates and icosahedral particles distributed within the cells and at cell boundaries. The icosahedral structure is equivalent to the T₂ phase reported by Hardy and Silcock. Annealing the melt-spun alloys leads to a complex precipitation sequence: + I + + I + S + + I + + T₁ + T₂ (bcc) + two other phases. The icosahedral particles coarsen progressively during annealing, especially at higher annealing temperatures. Fine-scale precipitates grow during annealing at low temperature, dissolve at higher annealing temperatures below 500°C, and then reprecipitate during cooling after annealing at 500°C. During annealing at low temperature, plates of and S precipitate and then dissolve, providing solute atoms for icosahedral particle growth. Stable T₁, T₂ (bcc) and two other phases precipitate after decomposition of the icosahedral particles during annealing at 500°C.     

Dynamic characteristics of thermoanemometers with glass-covered transducers

This study deals with the frequency characteristics of a glass-covered thermistor serving as transducer in a thermoanemometer and of a constant-resistance thermoanemometer with such probes.Notation A average-in-time coefficient of heat transfer at the glass-fluid boundary, W/m²· °C - A_tot coefficient of steady-state heat transfer at a bare probe (a fictitious quantity introduced for gauging the heat transfer between a glass-covered probe with the moving fluid), W/m²· °C - a thermal diffusivity of glass which insulated the heat sensitive element from the fluid, m²/sec - C_T total thermal capacity of transducer, W· sec/m²· °C - H₁ ratio of moduli in the expressions for current and resistance fluctuations in the transducer, dB - H₂ ratio of moduli in the expressions for heat transfer and resistance fluctuations in the transducer, dB - I quiescent current through thermistor, A - i transform of fluctuation current through thermistor, A - K_v voltage gain of feedback amplifier - k frequency parameter, 1/m - l thickness of glass layer, m - N intrinsic time constant of thermistor, sec - N time constant of constant-resistance thermoanemometer, sec - M intrinsic time constant of thermistor, sec - M time constant of constant-resistance thermoanemometer, sec - p complex variable in the Laplace transformation - Q average-in-time thermal flux from the transducer, W/m² - q transform of thermal flux fluctuations in the transducer, W/m² - R average-in-time operating resistance of thermistor, - R₁ constant resistance in series with the thermistor in the thermoanemometer circuit, - r transform of resistance fluctuations in the thermistor, - S effective surface area of heat transfer from the transducer, m² - T_D steady-state temperature of hot film, °K - T steady-state temperature of insulating glass layer, °K - T_L temperature of fluid, °K - u velocity of oncoming fluid, m/sec - W_T relation between resistance fluctuations and current in the thermistor, in operator form - y space coordinate in the mathematical model of the transducer, m - fluctuation component of heat transfer coefficient, W/m²· °C - temperature coefficient of resistance, 1/°C - thermal conductivity of insulating material, W/m· °C - _d transform of temperature fluctuations in the hot film, °K - transform of temperature fluctuations in the insulating glass layer, °K - coefficient in the transfer function of a thermistor at high frequencies Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 6, pp. 1042–1048, June, 1972.     

Subsolidus phase relations in the ZnS-In2S3 system: 600 to 1080° C

Eleven ternary compounds were synthesised, of which nine are new. The seven most ZnS-rich compounds form a series. Each has a primitive hexagonal lattice witha=3.85±0.01 Å. Thec-dimension varies from 37.47 Å (39 ZnS8 In₂S₃) to 18.63 Å (18 ZnS8 In₂S₃) with a periodicity of 3.14 Å which can be related to a decrease in the ZnS content. One of the four remaining compounds (12 ZnS8 In₂S₃) is triclinic, but at least two polytypes are present. The more common variety has the parameters:a=3.86 Å,b=15.48 Å,c=3.54 Å,=90° 16,=120° 02 and=89° 47. The structure of the other polytype and of compounds 17 ZnS:8 In₂S₃ and 10 ZnS8 In₂S₃ have not been determined. Stoichiometric ZnIn₂S₄ has a rhombic hexagonal lattice (a=3.86 Å,c=36.95 Å). This ternary compound which has been synthesised previously is the only one to show appreciable solid solution. Approximately 2 mole % ZnS is soluble in ZnIn₂S₄ at 600° C; this increases to 8 mole % at 1080° C.     

A superconducting vibrating reed applied to flux-line pinning. I. Theory

A theoretical treatment is given of a superconducting reed clamped at one end and performing flexural vibrations in a homogeneous longitudinal magnetic fieldB _a. When the flux lines are rigidly pinned the reed behaves like an ideal diamagnet whose bending distorts the external field. This generates a magnetic restoring force (line tension) B _a ² which is independent of the reed thicknessd, whereas the mechanical restoring force (stiffness) is d ³. Therefore, the resonance frequency /2 of a thin superconducting reed increases drastically when a fieldB _a is applied, or for a givenB _a, when the reed is cooled below its critical temperatureT _c. With decreasing pinning strength (characterized by Labusch's parameter ) the resonance frequency decreases, ²²– _pin ² where _pin ^{2 –1}, and an attenuation _v ^–2 occurs due to the viscous motion of flux lines. For larger vibration amplitudes an additional, amplitude-dependent damping _h ^–3 occurs due to the hysteretic losses caused by elastic instabilities during flux motion.On leave from Centro Atómico, Bariloche, Argentina.