Thermal stability and percolation threshold of Ge-Se-Fe glasses

The characteristic temperatures such as the glass transition temperature (T_g), the onset temperature of crystallization (T_c) and the melting temperatures, (T_m) have been determined for glasses belonging to the Ge_xSe_{100 − x − y}Fe_y (y = 2, 4 and 6 at.%). Differential scanning calorimetry and differential thermal analysis measurements have been used for their determination. These temperatures have been used to evaluate the thermal stability of the investigated glassy alloys using Dietzel (ΔT) and Hruby (H_r) criteria. The variations of ΔT and H_r with the average coordination number, n, have been specified. It is found that both ΔT and H_r exhibit a maximum at n = 2.4. This observation is a realization of Phillips'-Thorpe threshold where the maximum stability of the network is just obtained if the percolation threshold limit is reached. The overall mean bond energies of the studied compositions have also been calculated and their correlation with the glass transition temperature is discussed.     

Roles of minor additions in formation and properties of bulk metallic glasses

Bulk metallic glasses (BMGs) are of current interest worldwide in materials science and engineering because of their unique properties. Exploring BMGs materials becomes one of the hottest topics in the materials science field. To date, there is very active worldwide development of new BMGs, and extensive efforts have been carried out to understand and improve the glass-forming ability of metallic materials supported by large government and industry programs in North America, Asia, and Europe. Minor addition or microalloying technique, which has been widely used in other metallurgical fields, plays effective and important roles in formation, crystallization, thermal stability and property improvement of BMGs. This simple approach provides a powerful tool for the BMG-forming alloys development and design. In this paper, we present a comprehensive review of the history and the recent developments of this technique in the field of BMGs. The roles of the minor addition in the formation and the properties of the BMGs and the BMG-based composites will be discussed and summarized within the framework of thermodynamics, kinetics and microstructure. The empirical criteria, or the principles and guidelines for the applications of the technique in BMG field are outlined.     

Temperature and Pressure Dependence of the Speed of Sound in Seawater

The speed of sound in sea water has been measured for various salinities over the temperature range 0.1–30°C at excess pressures of 0–60 MPa. The results are presented in tables and an equation derived by least-squares fitting that gives the difference in the speed of sound between distilled water and seawater. The data are compared with calculations on the Chen-Millero algorithm, which was used in compiling the UNESCO international tables for the speed of sound. Suggestions are made for setting up GSSSD tables Seawater: Speed of sound.     

Observation of Shrinkage of Silica Aerogel during Capillary Condensation of 4He

Silica aerogels are highly porous and very compressible materials. They are transparent and suitable for observation of the liquefaction process in them. We reported that capillary condensation of ⁴He in a very light aerogel with a porosity of 99.5% proceeded with two steps under a nonequilibrium condition. The aerogel sucked outer liquid with two separated interfaces which were regarded as precursor films and avalanches (Nomura, R., et al. in Phys. Rev. E 73:032601, 2006). During the capillary condensation, shrinkage of the aerogel was large enough to be visually observable, shrinking about 1.5% in length by the capillary force. During the rapid evacuation at high temperatures, shrinkage was enhanced to as much as 7% and was easily seen. By repeated filling and evacuating of the liquid in the aerogel, the shrinkage became less. For denser aerogels with porosities of 95.8 and 90.4%, the shrinkage was not large enough to be observed by our method.     

Heat Capacity of Adsorbed Helium-3 at Ultra-Low Temperatures

We report on direct measurements of the heat capacity of monolayers of ³He adsorbed on the surface of a copper cell filled with superfluid ³He. We found that at ultra low temperatures the surface ³He heat capacity dominates over the heat capacity of the bulk liquid ³He. The replacement of adsorbed ³He by ⁴He changes the heat capacity of the sample by an order of magnitude. These investigations were made in the framework of the “ULTIMA” project, a dark matter detector based on superfluid ³He in the limit of ultra low temperatures.     

Measurements of Third Sound Attenuation at T=1.35 K

The results of measurements of ordinary third sound attenuation at T=1.35 K are reported. The attenuation is measured by using a continuous wave technique for frequencies up to 40 kHz. We find that for helium film thicknesses in the regime 5.09≤d≤9.90 layers the attenuation of third sound increases both with frequency and film thickness. We discuss our results in the context of previous work in this area.     

Temperature Predictions in Thick Composite Laminates at Low Cure Temperatures

Results from experiments and simulation of the cure behaviour of thick glass/epoxy laminates cured at low initial temperatures are presented. The objective is to study how sensitive the temperature development in a commercial epoxy is to initial cure temperature for a few different combinations of wall thickness and fiber content. The general accuracy of all the temperature predictions are good. For low initial cure temperatures (50–80°C), will however small inaccuracies in the reaction kinetics and material data have an effect on the predictions. Analysis of the results indicates that the main error source is likely to be the used reaction kinetics data/model at these temperatures. These inaccuracies will furthermore affect the temperature predictions during the remaining cure cycle.     

Pressure and Temperature Dependence of the Speed of Sound and Related Properties in Normal Octadecane and Nonadecane

The speed of sound was mesured in liquid n-octadecane and n-nonadecane using a pulse technique operating at 3 MHz. The measurements were carried out at pressures up to 150 MPa in the temperature range from 313 to 383 K. The experimental results combined with atmospheric density measurements were then used to evaluate volumetric properties such as the density and the isentropic and isothermal compressibilities up to 150 MPa in the same range of temperature. The density data were fitted with a six-parameter modified Tait equation within the experimental uncertainty.     

Infrared spectroscopy of Si-O bonding in low-dose low-energy separation by implanted oxygen materials

The effects of the processing conditions on the formation of buried oxide (BOX) layers in low-dose low-energy separation by implanted oxygen materials were investigated by using infrared spectroscopy and transmission electron microscopy. In as-implanted samples, the Si-O-Si stretching frequency increases either with increasing the oxygen dose or with decreasing implantation energy because the oxide composition becomes stoichiometric. However, the plateau frequencies were observed above a certain dose due to the compressive stress in the BOX layers. Upon ramping up to 1100 °C, the compressive stress decreases. Annealing beyond 1100 °C, the out diffusion of oxygen atoms was detected.     

Pulsed Third Sound in the Presence of a Superfluid Flow

We report measurements of pulsed third sound in the presence of a uniform superfluid flow at T=0.89 K. The superfluid flow is created using a heater technique. For increasingly large values of power dissipated in the heater used to create the flow, the shapes of the received third sound pulses evolve. The pulses propagating parallel to the flow grow while the pulses propagating against the flow decrease. When the heater power is increased further such that film thinning effects occur, the pulses propagating antiparallel to the flow qualitatively resemble the derivative of the drive pulse. Similar effects were also observed in thin films at T=1.35 K. A possible explanation for the growth and decrease of the pulses will be discussed. The cause of the pulse shapes that resemble the derivative of the drive pulse is not understood.     

Temperature Dependence of the Velocity of Sound in Liquid Metals of Group XIV

The temperature dependences of the velocity of sound in liquid Pb, Sn, Ge, and Si have been measured by means of the pulse transmission technique over temperature ranges of 610–1078 K, 608–1463 K, 1215–1443 K, and 1723–1888 K, respectively. In both liquid Pb and Sn, the velocities of sound decrease linearly with increasing temperature, which is the same temperature dependence as shown in many other liquid metals. On the other hand, the velocities of sound in liquid Ge and Si exhibit anomalous temperature dependences. In Ge, the velocity of sound has a distinct maximum around 1280 K and decreases linearly at higher temperatures. In Si, the velocity of sound increases monotonically with increasing temperature in the temperature range investigated. It is considered that these results predict that the coordination numbers of liquid Ge and Si increase with increasing temperature.     

Nonlinear resistance behavior of ultrathin epitaxial YBa2Cu3O7−x films in the vicinity of superconducting transition

The resistance-current dependencies R(I, T) of ultrathin YBa₂Cu₃O_7?x films were investigated in wide regions of resistance and temperatures in zero magnetic field. Ultrathin YBa₂Cu₃O_7?x (near 30Å of the thickness) films were prepared in the form of epitaxial heterostructure YBa₂Cu₃O_7?x /PrBa₂Cu₃O_7?x. The R(I,T) curves show ohmic behavior at low currents and nonlinear one at higher current. At Tc (resistive transition temperature) shapes of R(I) curves undergo remarkable changes. Ohmic behavior vanishes down to T_c≈36K and the curvature of logR(logI) plots changes sign from convex downward to upward showing “real” high critical current I_c,T?4.2K≥3·10⁶ A/cm².     

On the transfer function of a weak link ultra-low capacity RF-SQUID

In the investigation of the transfer function (field sensitivity) of a weak link ultra-low capacity RF-SQUID, there is a problem which concerns the response of the quantum nonlinear oscillator formed by the geometrical inductance of the superconducting ring, the Josephson inductance and the weak link capacity, to the external magnetic flux. In order to account for the influence of the small quantum charge fluctuation on the Josephson potential, a phenomenological approach is proposed, which leads to a phase shift consisting of two additives. The first additive is a constant depending on the weak link parameters, and the second is linear in the external magnetic flux. The influence of the quantum fluctuation is effectively reduced to increasing the period of the current-phase relation for the RF-SQUID in the external magnetic flux, which leads to a reduction of the response of such a quantum SQUID in comparison with the usual RF SQUID.     

高速高压低温温度传感器的试验研究

简要介绍了高速高压低温条件下温度传感器的试验研究方法。试验研究的着重点是尽量利用现有的设备、试验条件和有关的氢氧发动机研制过程中的试验，对传感器进行一些针对性试验，以取得可靠的试验数据。通过对试验数据的分析和研究，验证考核传感器的性能。主要给出了强度试验、动态特性试验和恢复系数试验的模拟试验方案和方法及搭载试验方法，给出了某传感器进行上述试验的试验结果，结果表明，这种试验研究方法是可行且可靠的。     

Temperature Modulation Measurements of the Thermal Properties of Nanosystems at Low Temperatures

We report on the dynamic measurements of thermal properties of nanosystems at very low temperatures. These techniques are based on the modulation of the temperature and hence leads to highly sensitive measurements. We will discuss the intrinsic limitations of these methods when the thermal properties of nano-objects are studied at very low temperatures, much below 1 K. Firstly, we will present thermal conductance measurements using the 3ω method. This technique is limited at low temperatures due to the significant increase of the mean free path. Secondly, heat capacity measurements using ac calorimetry are outlined, and again restrictions occur due to the continuous temperature gradient inherent to that technique. Propositions are made in order to overcome these limitations.     

Critical cooling rate for the glass formation of ferromagnetic Fe40Ni40P14B6 alloy

Bulk ferromagnetic amorphous Fe-Ni-P-B alloys in rod shape were formed by a rapid solidification technique. The largest amorphous specimen prepared had a diameter of ∼ 2.5 mm and the corresponding cooling rate for the glass formation of this alloy system in our experiment can be estimated to be around 492.4 K/s by the method of finite-difference numerical calculation. This value is on the same order of magnitude as the critical cooling rate R_c of Fe₄₀Ni₄₀P₁₄B₆ alloy estimated by the method of constructing the continuous-cooling-transformation (CCT) curve. It is indicated that the heterophase impurities have been eliminated well in our experiment.     

Temperature and Time Dependence on Recovery Stress Relaxation in Nickel Titanium Wire during Isothermal Holding at High Temperatures

In this study, the influence of kinematically constrained thermal cycling (heating, isothermal holding and cooling) on the recovery stress in annealed nickel titanium wire was investigated. A 4% pre‐strained nickel titanium wire was heated to temperatures (150, 200, 250 and 300 °C) much higher than the austenite finish temperature. It was observed that the maximum recovery stress obtained at different conditions decreases significantly after the first thermal cycle and reduces gradually with further increasing the number of thermal cycles. It was also seen that the recovery stress increases with time during isothermal holding at 150 °C. During isothermal holding at other temperatures, the recovery stress shows an exponential decrease, and the decrease rate of the recovery stress depends on the isothermal holding temperature. The higher isothermal holding temperature is the more the recovery stress decreases. The decrease rate reduces with increasing the number of thermal cycles.     

Speed of Sound of n-Hexane and n-Hexadecane at Temperatures Between 298 and 373 K and Pressures up to 100 MPa

Measurements of the speed of sound u for n-hexane and n-hexadecane at temperatures of 298.3, 323.15, 348.15, and 373.15 K and at pressures up to 100 MPa are reported. The speeds of sound, the temperatures, and the pressures are subject to an uncertainty of ±0.1%, ±0.01 K, and ±0.2 MPa, respectively. These measurements were undertaken using a new apparatus which has been constructed for measurement of the speed of sound in liquids and supercritical fluids at pressures up to 200 MPa and at temperatures between 248 and 473 K. The technique is based on a pulse-echo method with a single transducer placed between two plane parallel reflectors. The speed of sound is obtained from the difference between the round-trip transit times in the two paths. It is expected that both the precision and the accuracy of the method can be further improved.     

Logarithmic Singularity of Specific Heat in Liquid Helium II at the λ Point

The experimental width of the second sound peak in Brillouin scattering is less than the instrumental width. It is also less than the width of the first sound peak near the λ point. The theoretical width of the second sound peak becomes infinitely large at the λ point in the traditional viewpoint. This discrepancy suggests that the second sound peak detected in Brillouin scattering is an elementary excitation. We calculate the specific heat of liquid helium near the λ point by considering the second sound peak. The calculated temperature-dependence of the specific heat has a logarithmic divergence at the λ point. Furthermore, the calculated values of the specific heat agree well with data derived from experiments.