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A one-order parameter model of crystal-melt transition is used to study the thermodynamics of crystal-melt nucleation and the steady-state kinetics of melting and freezing, A simple Ginzburg-Landau free energy model is constructed using the density functional theory. A remarkable asymmetry between freezing and melting behaviors is found, which is shown to be related to the asymmetry of the free energy. This universal model successfully explains the observed universality of maximum undercooling and the asymmetry of planar freezing and the melting front.

The rate of the UV-stimulated HT oxidation was studied in H{sub 2}(HT)-O{sub 2}-O{sub 3} atmospheres with excess O{sub 3}. The concentration of HTO increased linearly with UV irradiation time. The formation rate of HTO was estimated to be 3.4 x 10{sup -2} Bq cm{sup -3} s{sup -1}, which was about 14000 times greater than that of the UV-stimulated HT oxidation in the H{sub 2}(HT)-O{sub 2} atmosphere. Namely the excess O{sub 3} greatly assisted the UV-stimulated HT oxidation. The HTO formation obeyed the half order kinetics to hydrogen pressure and 0.7 order with respect to photon flux. Computer simulation consisting of 33 elementary reactions was employed to make clear the mechanism of the HT oxidation. The computer simulation reproduced the same hydrogen pressure and photon flux dependences as the experimental results. It was revealed that the main path for HTO formation is as follows: (1) HT oxidation is initiated by photolysis of O{sub 3} to O({sup 1}D) radicals; (2) O({sup 1}D) radicals react with H{sub 2}(HT) to form OH(OT) radicals; and (3) OH(OT) radicals produce H{sub 2}O(HTO) by the reaction with H{sub 2}(HT). On the basis of computer analysis, it is concluded that the considerable increase in the rate of HTOmore » formation is due to the increase in O({sup 1}D) production in the presence of O{sub 3}. The present results suggest that the O{sub 3}-assisted UV-stimulated HT oxidation is expected to be applicable to non-catalytic oxidation of tritium in thermonuclear fusion reactors. 8 refs., 6 figs., 1 tab.« less

A superconducting power cable which has a structure similar to the conventional extruded polyethylene cable is proposed. The main features of the design are to exploit the excellent electrical properties of polymers at cryogenic temperatures and to separate the helium coolant from the electrical insulation. However, the most hazardous problem of this insulation system is cracking of the extruded polymer insulation during cooling. In order to examine the feasibility of the above proposal, a superconducting cable of rated voltage 20 kV and rated current 2 kA was manufactured, being suitable for the university laboratory tests. Extruded polyethylene or ethylene propylene rubber was adopted as electrical insulation. Current transmission tests up to 2.5 kA were performed with extruded polyethylene insulated superconducting cable though the insulation cracked during cooling. Voltage application tests were carried out with fair success at the liquid helium temperature with extruded ethylene propylene rubber insulated cable. This ia a breakthrough in terms of the electrical insulation design of cryogenic cables.

Mechanical and electrical properties of ethylene propylene rubber (EPR) pieces were studied in comparison with polyethylene (PE) in the cryogenic temperature region to examine the possibility of its use as solid electrical insulating material in superconducting cables. The mechanical properties of EPR are preferable to those of PE mainly because of its low shrinkage. The electric strength and dielectric loss tangent of EPR are comparable with those of PE at liquid helium temperature. Based on the encouraging results, an extruded EPR-insulated cable was fabricated and its 15-m length was cooled down to liquid helium temperature successfully. Partial discharge experiments at that temperature showed good electrical characteristics. This is a breakthrough in terms of the electrical insulation design of cryogenic cables. >

Single-crystal iron films with the [100], [110] and [111] planes were epitaxially grown on single-crystal GaAs plates with the respective crystallographic planes prepared by dual-ion-beam sputtering. Iron targets with different purity with 99.99%, 99.5% and 98% were used. Crystallinity of the films examined by X-ray diffraction was not so sensitive to the target purity, but magnetic properties and corrosion resistance were strongly influenced by the target purity; soft magnetic and high corrosion resistant films were obtained by high purity iron target. The most corrosion resistant films were obtained for [110] iron films using 99.99% iron target, which is comparable to high corrosion-resistant stainless steel.

The coupling phenomenon between the molecular translation and rotation is the fundamental process that governs the macroscopic behaviors of soft complex matters such as nematogens, polymers and micelles. Various techniques have been developed and applied for studying this effect. The flow birefringence gives information on the anisotropy induced by the steady shear stress of the fluid. The dynamic light scattering observes the spontaneous fluctuation in orientational order parameter that gives the coupling constant between the cooperative translation and rotation of the molecules. In this study we introduce a new technique named Quadrapole Flow Birefringence.

The authors present the experimental results obtained with multineedle discharge electrodes, for use in electrostatic separators, stressed with positive and negative DC voltage. The aim was to determine the effect of gap height and needle spacing on the current density pattern and its value on the plane electrode. Profiles of ion density on the plane electrode were measured precisely. Results of measurements are reported for different needle separations and gap height. The interaction between the needles and its effect on the corona current and onset voltage are discussed. >

The effect of light irradiation on S-N transition was investigated in a Bi-based oxide superconductor. The results suggest the possibility of a light triggered superconducting switching element. Critical current density and voltage—current characteristics were examined under visible light irradiation and in the dark for a Bi2Sr2CaCu2Oy sample immersed in liquid nitrogen. Light irradiation decreases Jc and increases the voltage drop across the sample above Jc. This phenomenon is observed even in pulsed light.

The purpose of this paper is to develop pre-casting permanent forms which are effective in improving the durability and appearance of concrete structures, conserving wood and modernizing cast-in-place concrete work. The influences of various materials used and accelerated curing methods on the properties of polymer cement mortar (PCM) applied to the forms were investigated. In these experiments, polymer dispersions composed of styrene-acryl (SA), polyacrylic ester (PAE), ethylene-vinyl acetate (EVA) and styrene-butadiene rubber (SBR) were used. Mixtures contained aggregate - crushed silica and ferro-nickel slag sand; cement - normal portland, high-early strength portland and white portland cement; and color pigment - red, green, yellow and black. Steam curing and oven-dry curing were carried out. The fluidity, compressive strength, flexural strength, resistance to abrasion, chloride ion penetration, carbonation and sulfate resistance, and surface color of PCM were examined. From these investigations, the following conclusions were obtained: The use of SA type polymer, ferro-nickel slag sand, high-early strength portland cement and color pigments were effective in getting PCM with high fluidity, mechanical strength, durability and tinting strength. Additionally, steam curing and oven-dry curing are practical for the early-age strength development of PCM.

Non-graphitizing carbon beads were heat-treated to 1300°∼1900° under 5 kbar. Whereas the original beads carbonized at 1000° graphitize abruptly at 1500° ∼ 1600°, the pre-heated ones demand higher temperature for their graphitization. The 1500°-pre-heated and 2100°-pre-heated graphitized above 1700°, and the 2670°-pre-heated above 1900°. In the HTT range where the graphitization occurs, the following changes in texture were observed: after the appearance of cactus-like projections, necks form between beads, needles and tiny flakes appear and optically anisotropic areas grow in size. A remarkable densification was found for the pre-heated beads in the same HTT range.

The transition from a glow discharge to an arc discharge at atmospheric pressure is suppressed, and homogeneous discharges are obtained, when the electrons produced by high-frequency corona discharge are scattered on the cathode surface continuously during the main discharge. This method is effective not only for mixed gases of CO2, N2 and He but also for mixed gases including oxygen.

We studied the far-infrared emission spectrum resulting from recombination of an electron with an ionized impurity of As and Sb in germanium under impact ionization at liquid, helium temperatures. The emission peaks at the position corresponding to the transition from the 2p± excited state to the ground state. This observation indicates that recombination occurs through the capture by the excited states of the donor impurity, which is consistent with the cascade trap model. The intensity of emission radiation is of the order of 10−7 watts for the excitation power of about one watt, which implies a dominant process of recombination to be accompanied by phonon emission.

Ac tree starting voltage of low density polyethylene has been found to be higher at liquid nitrogen temperature (42kV) than that at room temperature (7kV) and it is almost equal to the positive impulse tree starting voltage. This improvement may be due to either the partial-discharge free contact of the interface between the needle electrode and the polyethylene and for the moderation of the intense field at the needle tip by injected space charges. The space charge injection was examined by evaluating the dependence of impulse tree starting voltage on the rise time of the impulse voltage, and the dc prestress effect on impulse tree starting voltage. It was estimated from the peculiar shape of the impulse tree that the injection depth of space charge is about 10 ?m. The electroluminescence produced at the needle tip by ac voltage application was found to be completely different from the corona discharge in a void and it was explained by the radiative recombination process of space charges injected alternately.

A superconducting power cable which has a similar structure to the conventional extruded polyethylene cable is proposed. The rated voltage and current are 66 kV and 6 kA and ac three phase can carry 686 MVA. The special features of the design is to exploit the excellent properties of polyethylene in the cryogenic region and to separate helium coolant from the electrical insulation. The outer superconductor shielding is eliminated and the magnetic flux is allowed to leak out and eddy current loss is dissipated in the casing metal at room temperature. The simplicity of the design reduces the cost. The preliminary experiments of the cable contraction and tanδ are presented.

A transducer swing mechanism is introduced to accomplish a new scanning acoustic microscope system in the interference mode, which is applied to the quantitative measurement of acoustic velocities in thin materials. In this system, the distance between a pair of aligned focusing transducers along the beam axis is varied periodically, as the specimen is synchronously scanned in the X direction. Measurements of acoustic velocities are performed with this system for two kinds of polymer film, polyester and PVF2 films, and a dog's cardiac infarcted tissue at a frequency of 150 MHz.

In this paper a new configuration of CCD image sensor is proposed to improve smear. This new sensor introduces a storage region, with a selective gate and drain section, between the imaging region and a readout register. The configuration and operating principles of the new device are described. Preliminary experimental results with a 402(H) × 502(V) element image sensor are also reported. The introduction of the storage region is confirmed to be strikingly efficient in lowering the smear level.

Propagation characteristics of leaky SAWs at the boundary of water/silicon are investigated by the nonscanning reflection acoustic microscope using a line-focus beam. Experiments are performed for typical crystalline planes of silicon such as (111), (110), (001) and slightly inclined (111). These results obtained by the line-focus beam are compared to the experimental results obtained by the conventional point-focus beam.