Superconducting properties of the composite-processed Nb3Sn superconductor with the Cu-Sn-Zn matrix

Effects of the Zn addition to the Cu-Sn matrix of the Nb₃Sn composite tape have been investigated by measuring the matrix work-hardening behaviour, the rate of Nb₃Sn layer formation and the pertinent superconducting properties. The Zn addition drastically enhances the diffusion rate of Nb₃Sn formation at each Sn level in the matrix examined, leading to sufficient superconducting properties even at a low Sn level of 3.5 at. %; a sample containing 3.5 at. % Sn and 15 at. % Zn in the matrix exhibits a critical temperature and critical current density comparable with those of samples at a Sn level of 7 at. %. The upper critical field obtained for a sample with the 6 at. % Cu-6 at. % Sn-4 at. % Zn matrix beyond 200 kOe. The work-hardening of the composite matrix is found to be essentially a function of Sn level, and insensitive to the Zn addition.     

The operation of the ISR facility in relation to the UHV environment

At CERN Geneva, two kilometers of UHV at 10⁻¹⁰ torr is in daily use at the Intersecting Storage Ring (ISR) facility. An appreciable fraction of the stainless steel vacuum chamber, some 200 m in fact, is continuously at 10⁻¹¹ torr.     

Phase relationships in the yttria-rich part of the yttria-zirconia system

Phase equilibria in yttria-zirconia mixtures containing not less than 50 mol % YO_1.5 have been studied between 1200 and 2200° C. The solubility of zirconia in yttria is shown to decrease with increasing temperature: the miscibility gap between the zirconia (fluorite) and yttria (type C rare earth) solid solutions extends from 64 to 75 mol % YO_1.5 at 1400° C, from 66 to 79% at 1700° C and from 73 to 85% at 2000° C. An ordered fluorite-related phase with the ideal formula Zr₃Y₄O₁₂ and a narrow homogeneity range, which disorders at about 1370° C, is reported.     

Significance of the deviations of the crack front into the plane perpendicular to the crack propagation direction - II. Crack-front vibration

In this part II, the influence of thermal vibration on the shape of a crack front and on the conditions for crack motion are investigated. We have considered a static crack model in mode I loading in a linear isotropic elastic medium whose front vibrates in the form of a standing wave with displacement ξ perpendicular to both the average crack plane and the crack propagation direction; ξis assumed to be sum of standing sine waves and the crack to be represented by a continuous distribution of vibrating edge dislocations. The displacement and stress fields due to an infinitely long edge dislocation, oscillating in the form of a standing wave, are first given. Then it is shown that, in free vibration conditions, ξ would satisfy the d'Alembert wave equation with a constant phase velocity corresponding to the velocity of a travelling sine wave along an edge dislocation. It is also shown that the sites for the initiation of crack motion are located on the average crack plane at the nodes of the vibrating crack front. The crack opening force G per unit length of the crack front, at the sites of crack propagation initiation, is found to be different from that of the rigid planar crack, when averaged over time, but the magnitude of the difference is relatively small. G decreases with increasing temperature T and is found to be proportional to T ² at very low temperature and to T at higher temperatures. The relation for G leads to view the vibrating crack front as being non straight on average over time. In tungsten, a nearly isotropic material, the theory yields a mean crack front inclination angle of about 1° at absolute zero, 3.2° at room temperature and 10.6° at the melting point.     

On the change in the modulus of elasticity with a decrease in the size of a nanocrystal

A model of nanocrystal in the form of a rectangular parallelepiped with a variable surface shape is used to show that, at high temperatures, modulus of elasticity B decreases with a decrease in size of the nanocrystal N, which is due to the increase in the surface pressure. However, at low temperatures, dependence B(N) is less pronounced and can even rise with a decrease in the nanocrystal size. This is because, at low temperatures, the increase in the surface pressure (which is larger than at high temperatures) leads to an increase in the modulus of elasticity for the entire nanocrystal. The more the nanocrystal shape deviates from the most energetically stable shape, the more pronounced the change in the dependence B(N) is.     

Invariant three- and four-phase equilibria in the magnesium-rich corner of the Mg-Cu-Sn ternary system

Invariant three- and four-phase equilibria in the magnesium-rich corner of the Mg-Cu-Sn ternary system have been studied by differential thermal analysis, optical microscopy, electron probe microanalysis and X-ray diffraction. The L(Mg) + Mg₂ Cu + Mg₂Sn ternary eutectic reaction was found to be at 467 °C and at Mg–13.5 at % Cu–4.4 at% Sn. The LMg₂Cu + Mg₂Sn pseudo-binary eutectic reaction is tentatively located at 522°C and at Mg–26.0 at % Cu–7.7 at % Sn.     

The influence of the diffusion cooling on the noise band of the superconductor NbN hot-electron bolometer operating in the terahertz range

Results of an experimental study of the noise temperature (T _n ) and noise bandwidth (NBW) of the superconductor NbN hot-electron bolometer (HEB) mixer as a function of its temperature (T _b ) are presented. It was determined that the NBW of the mixer is significantly wider at temperatures close to the critical ones (T _c ) than are values measured at 4.2 K. The NBW of the mixer measured at the heterodyne frequency of 2.5 THz at temperature T _b close to T _c was ~13 GHz, as compared with 6 GHz at Tb = 4.2 K. This experiment clearly demonstrates the limitation of the thermal flow from the NbN bridge at T _b ? T _c for mixers manufactured by the in situ technique. This limitation is close in its nature to the Andreev reflection on the superconductor/ metal boundary. In this case, the noise temperature of the studied mixer increased from 1100 to 3800 K.     

Influence of temperature on the reduction mechanism of Ti(III) ions on iron in the LiF–NaF–KF eutectic melt and on the electrochemical behavior of the resultant titanium coatings

The electroreduction mechanism of Ti(III) ions on iron in the LiF–NaF–KF eutectic melt was studied at 700 and 900 °C using cyclic voltammetry. At both temperatures, the reduction occurs through a three-electron transfer, but at 700 °C only pure titanium is deposited, whereas the successive formation of Fe₂Ti and FeTi intermetallic compounds precedes pure titanium deposition at 900 °C. At 900 °C under open-circuit conditions, the different phases appear successively at the electrode/electrolyte interface by interphase movements due to intermetallic diffusion. At the same temperature but under anodic polarization, each phase appears at the electrode surface according to a layer-by-layer dissolution.     

Analysis of the relationship between the kink effect and the indium levels in MOS transistors

In this work, we investigate the effects of indium ion implantation on the channel of nMOSFETs. Deep level transient spectroscopy (DLTS) and admittance spectroscopy (AS) measurements have been made on a series of indium doped silicon N⁺P structures and MOS capacitors. To analyse the indium-related levels in nMOSFETs, we used a low frequency (LF) output conductance dispersion analysis, which is based on the Gain-Phase versus frequency at different temperatures. These experiences show that the indium level when operated at low temperatures at which the majority of carriers freeze-out exhibit a kink effect. The effects of indium doping on the kink were studied using the variation of channel conductance g_d and transconductance g_m versus temperature in the kink zone. The excess drain current versus drain and gate voltage show the maximums of both conductance g_d and transconductance g_m at around T = 124 K when the indium level is activated.     

Effect of the fluoride additives on the oxidation of AlN

The oxidation of AlN powder added by the fluorides at temperatures below 700°C in air was discovered in this study. The obvious onset of oxidation of AlN with cryolite and YF₃ additions is below 700°C with the product of α-Al₂O₃ phase, which usually occurs in single AlN powder above 1100°C. The changes on the weight and the FTIR spectra of the AlN powder fired at temperatures lower than 700°C show that cryolite and YF₃ greatly promote the oxidation of AlN powder at these temperatures. Different from the action of cryolite and YF₃ powder, CaF₂ has no obvious effect on the oxidation of AlN. A possible oxidation process, in part corroborated by FTIR and XRF, was proposed to explain the results in the experiments. The oxidation kinetics of AlN in the presence of cryolite were also discussed at the temperatures ranging from 550 to 700°C from the data of the weight gains in this region. The result shows that the oxidation follows a linear law, which implies a reaction rate-controlled process. The considerably low activation energy of 67 kJ mol⁻¹, which is associated with the quick oxidation and the formation of α-Al₂O₃ at temperatures below 700°C, was determined from the slope of the line fit.     

Estimation of the cavitation peak pressure using the Na D-line structure in the sonoluminescence spectra

The sonoluminescence (SL) spectra of an Ar-saturated NaCl solution in the region of the Na D line excited by ultrasound at a frequency of 22 and 44 kHz have been measured at a solution temperature within 5–20°C and the normal and elevated hydrostatic pressure. Based on an analysis of the obtained results in comparison to published data, it is established that variations in the intensity and structure of the Na D line in the SL spectra of NaCl solutions are related to changes in the intensity of the so-called red satellite. Using the measured red satellite intensity, the peak pressure in the cavitation bubbles was estimated at 800–1200 bar depending on the experimental conditions.     

An Adiabatic Calorimeter for the Realization of the ITS-90 in the Cryogenic Range at the LNE-CNAM

The LNE-CNAM, in cooperation with the IPN, has recently developed a new cryogen-free adiabatic calorimeter, to realize the International Temperature Scale of 1990 (ITS-90) in the temperature range between 6 K and 84 K. The new calorimeter, cooled by a closed-cycle Gifford-McMahon refrigerator, is equipped with three thermal shields and two separate vacuum chambers, to minimize the effect of parasitic heat fluxes. The inner adiabatic chamber can accommodate either a multi-compartment cell??containing the triple points of hydrogen, neon, oxygen, and argon, to realize the ITS-90 between 14 K and 84 K??or a comparison block for thermometers, the calibration of rhodium?Ciron (RhFe) thermometers between 6 K and 24 K. The use of a cryogen-free system and a fully computer-controlled measurement chain allow long lasting experiments and good thermal control, resulting in a substantial reduction of the measurement uncertainties. The new adiabatic calorimeter has been successfully tested at the LNE-CNAM. The overall standard uncertainties in the realization of the ITS-90 have been reduced from 2.08 mK to 0.37 mK at the hydrogen triple point, from 1.40 mK to 0.30 mK at the triple point of neon, and are maintained below 0.26 mK at the triple points of oxygen and argon. In the temperature range between 6 K and 24 K, calibrations of rhodium?Ciron resistance thermometers have been carried out with a standard uncertainty of the order of 0.80 mK.     

Graphene-GaAs-graphene stacked layers for the improvement of the transmission at the wavelength of 1.55 μm

Transmission filter operating at the wavelength of 1.55 μm and based on stacked graphene-GaAs-graphene layers separated by air gaps is presented. By using the transfer matrix method (TMM), we show that the addition of a graphene layer at each interface of a GaAs-based stratified structure, which initially exhibit only 30% transmission at 1.55 μm, allows the active control of the transmission by the adjustment of the graphene chemical potential. Transmission of almost 100% at the wavelength of 1.55 μm is achieved after addition of graphene layers. These results show the potential role of stacked graphene-GaAs-graphene layers in the development of new optical active communications devices.     

Summary of the Intercomparison of the Force Standard Machines of the National Institute of Standards and Technology,USA, and the Physikalisch-Technische Bundesanstalt,Germany

A comparison of force measurements performed at the National Institute of Standards and Technology, USA, and at the Physikalisch-Technische Bundesanstalt, Germany is reported. The focus of the study was the intercomparison of the forces realized by the two Institutes rather than the measurement process. The transfer standards used in the comparison consisted of force transducers and associated readout instrumentation. The results of the intercomparison reveal that over a range of 50 kN to 4.5 MN, the forces realized at NIST and at PTB compare favorably. For forces up to 900 kN the agreement is within ±40 ppm; above 900 kN the agreement is within ± 100 ppm.     

On the role of vacancies in the process of self-diffusion at low temperatures

Expressions for the calculation of the parameters of self-diffusion in a crystal of simple substance at temperatures close to absolute zero are derived. It is established that, in “loose” crystal structures (with the first coordination number below 12), the amount of atoms involved in diffusion motion exceeds the number of vacant sites in the crystal lattice at T=0 K. The results of calculations of the vacancy and diffusion parameters at T=0 K for ten cryocrystals show that the phenomenon of “nonvacancy self-diffusion at T=0 K” can take place only in bcc helium.     

Dislocation-based interpretation on the effect of the loading frequency on the fatigue properties of JIS S15C low carbon steel

Fatigue properties of low carbon steels are known to be particularly sensitive to the loading frequency. Indeed, literatures related to this field usually point out an increasing fatigue life with an increase of the loading frequency. The authors of the present paper have already reconfirmed such a general phenomenon in the case of JIS S15C (0.15%C) low carbon steel. In that paper, S–N properties under usual frequencies of 0.2–140 Hz can be successfully normalized by the lower yield stress at the individual frequency. Nevertheless, some irregularities have been detected on the fatigue property at 20 kHz. In order to clarify the physical meaning of such irregularities, we will compare fatigue properties at usual frequencies and ultrasonic frequency.In this work, the former experimental results were reintroduced and new discussions were developed by performing additional experiments and analyses paying an attention to microstructure and dislocation structure. Thus, it was found that the loading frequency effect at ultrasonic frequency is due to a particular behavior of B.C.C. ferrite under high strain rate. Such a behavior causes strain inhomogeneities at grain boundaries, and then facilitates the intergranular crack initiation mode rather than the usual intragranular one often reported at lower loading frequencies. Longer ultrasonic fatigue lives at ultrasonic frequency are directly related to this transition of the crack initiation mode. In addition, effects of the pearlitic volume fraction on the fatigue behavior have been also discussed in the present work.     

White-light interferometry with polarization phase-shifter at the input of the interferometer

Abstract

In white-light interferometry the surface profile is determined by measuring the fringe contrast function of the white-light interferogram. One of the techniques proposed for the measurement of the fringe contrast function is the use of the phase shifting technique with the help of an achromatic phaseshifter. The available phase-shifters employ a rotating polarization component at the output end of the interferometer. Using a rotating polarization component at the input end, rather than at the output end, has certain advantages. In this paper we investigate a rotating half-wave plate phase-shifter at the input end for its applications to a white-light interferometer.     

The nature of the change in the conditions for surmounting pinning centers by dislocation in lead at the superconducting transition

The effect of the presence of Sb on the amplitude dependence of ultrasonic attenuation α in the concentration range 1.7×10 ^?3 to 4.25×10 ^?1 at % has been studied systematically on Pb single crystals at 1.4 and 4.2 K (superconducting and normal states) and 77 K. The dependence curve shifts toward greater amplitudesU with increasing concentrationC and to smallerU whenT goes from 1.4 to 4.2 K. The shift toward greaterU at the transition to the normal state is observed for all concentrations. The amplitude-independent attenuation α _i varies with concentration nonmonotonically: IncreasingC causes α _i first to diminish (the minimum atC=0.034 at %) and then to grow. AtC≥0.034at %, α _i does not change at the n-s transition. The studies suggest that the damping factor for dislocations in impure crystals practically does not change at the superconducting transition. Here the damping is essentially due to the dynamic dislocation-impurity interaction. The change in the conditions for a dislocation surmounting the pinning centers at the superconducting transition is determined by the quasistatic mechanism of lowering barriers.     

Interferometrical measurement of the craze stiffness and structure of the craze fibrils in PMMA

The stiffness of a single craze produced in polymethylmethacrylate (PMMA) at several temperatures at the tip of a running crack has been measured at –25° C and 11 Hz. It has been shown that the craze stiffness increases by a factor of five when the craze is left unloaded during 400 sec at 20° C. A craze produced at 70° C is ten times stiffer than that produced at –25° C. The analogy between the craze structure and an open-cell foam or a crosslinked rubber suggests that the density of knots between craze fibrils is a relevant stiffness parameter, and it has been inferred that re-entanglement (welding) occurs between the craze fibrils during the relaxation process and in high-temperature crazes.     

Prediction and correction of the PVT-data of various substances along the saturation line

The occurrence of three similarity points (T _mel , T _m , T _cr ) in vapors at saturation has allowed one to develop, along with polynomial expansions, a method for predicting and correcting the PVT-data of the vapor phase.The curve of the vapor branch of saturation was described by the function y(x)=P_sV_s(2/3RT_cr)^-1.Theoretical values of y(x) were determined with the aid of Legendre polynomials.Notation P pressure - V volume - T temperature, K - P_s pressure at saturation - V_s volume at saturation - P_m pressure at the point of the maximum of P_s/V_s - V_m volume at the point of the maximum of the product P_s/V_s - T_m temperature at the point of the maximum of the product P_s/V_s - T_cr critical temperature - reduced temperature - A critical compressibility factor - R universal gas constant Murmansk Higher Engineering Naval College, Murmansk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 64, No. 4, pp. 433–439, April, 1993.