Simultaneous Measurements of an Ultrasound and a Torsional Oscillator for Pressurized 4He in a Nanoporous Glass

Recently, torsional oscillator (Yamamoto et al. in Phys. Rev. Lett. 93:075302, 2004) and ultrasound (Kobayashi et al. in AIP Conf. Proc. 128:797, 2007) measurements were carried out for pressurized ⁴He filled in a nanoporous glass (Gelsil), and the superfluid transition temperature T _C shows a different pressure dependence. Thus motivated, we have performed simultaneous measurements with a torsional oscillator and with ultrasound for pressurized ⁴He in Gelsil. T _C is in agreement between the two techniques at all pressures, and the superfluid component above 0.5 K shows most of the same temperature dependence. Furthermore, it was found that the χ-factor (the fraction of superfluid which remains locked to the substrate ) is independent of measuring frequency between the torsional oscillator (kHz-order) and the ultrasound (MHz-order) ranges.     

Studies of the critical velocity of superfluid4he in a 2 μm by 2 μm aperture in a thin foil at various frequencies

Measurements of the critical velocity behavior of oscillatory superfluid⁴He flow through a 2 m by 2 m square aperture in a 0.1 m thick titanium foil are being made at temperatures between 0.36 K and 2.1 K and at pressures of less than 0.4 bar at various frequencies between 50 Hz and 1000 Hz. The purpose of this work is to study a micron-size aperture for possible frequency-dependent deviations from the critical velocity behavior seen in submicron-size apertures. Preliminary results show a nearly linear decrease of critical velocity with increasing temperature that is similar to the temperature dependences seen in smaller apertures and that is approximately independent of frequency. However, at frequencies above 500 Hz, a region appears at the lowest temperatures in which supercritical behavior is dominated by large energy-loss events requiring a number of half-cycles for completion, a region that extends up to 1.1 K at 970 Hz.     

Gas Pressure Dependence of the Heat Transport in Porous Solids with Pores Smaller than 10 μm

To elucidate the gaseous heat transfer in open porous materials with pore sizes below 10 μm, an experimental setup for hot-wire measurements at high gas pressures was designed and tested. The samples investigated were organic, resorcinol–formaldehyde-based aerogels with average pore sizes of about 600 nm and 7μm. The range in gas pressure covered was 10 Pa to 10 MPa. To avoid effects due to mass transport along the inner surface of the porous backbone of the samples, He and Ar, i.e., gases with very low interaction with the sample surface at ambient temperature, were chosen. The study reveals a significant contribution of coupling effects to the thermal transport in nanoporous media. A model has been developed that qualitatively describes the observed gas pressure dependence of the heat transport.     

Measurements of 10·6 μm Radiation Scattered by a Pseudo-random Surface of Rectangular Grooves

Measurements are presented of scattering of CO₂ laser radiation by a phase screen of rectangular grooves whose widths have a predetermined statistical distribution. The scattering statistics are interpreted using Huygens-Fresnel optics. The measurements provide a valuable model of scattering by naturally occurring phenomena.     

Specific Heat Near the Superfluid Transition of a 0.9869 μm 4He Film

We report measurements of the specific heat of ⁴He near the superfluid transition while confined between silicon wafers at 0.9869 m separation. These data are analyzed to check on the behavior expected from correlation-length scaling. Comparison is also made with other data for planar confinement, as well as data for cylindrical confinement. These represent different lower-dimensional crossovers. We find that the present data scale very well above the bulk transition temperature, and in the region immediately below it. Near the specific heat maximum however, the data for planar confinement do not collapse on a universal curve. We compare these results with specific theoretical scaling functions. In particular we find that on the normal side, and for large enough values of the scaling variable, one can describe the data well using the concept of the surface specific heat. The locus of the data in this region agrees well with the most recent theoretical calculations.     

Simultaneous Measurement of Torsional Oscillator and?NMR in Solid 4He with 10?ppm of 3He

We have performed the simultaneous measurement of torsional oscillator and NMR in solid ⁴He with 10 ppm of ³He at 3.6 MPa. In this solid, NCRI response appears below about 400 mK. NMR measurement shows that there is the same kind of phase-separated ³He cluster which is found in our previous measurement in solid ⁴He with over a hundred ppm of ³He. When we warm the solid above the phase separation temperature, the cluster disappears gradually. Below and above the phase separation temperature, the distribution of ³He atoms changes significantly with long time constant, which is as long as a day. However, even in such a long time span, we do not observe any systematic changes in the torsional oscillator response. This result suggests that the phase separation and related changes of the distribution of ³He is not directly related to the impurity effect of the NCRI response.     

Heterostructures of Quantum-Cascade Laser for the Spectral Range of 4.6 μm for Obtaining a Continuous-Wave Lasing Mode

Technical Physics Letters - The method of molecular-beam epitaxy was used to fabricate an elastically balanced heterostructure of a quantum-cascade laser for the spectral range of 4.6 μm based...     

The Interpretation of Phase-Slip and Critical-Velocity Data from the Flow of Superfluid 4He through a 2 μm by 2 μm Aperture

An analysis has been made of phase-slip and critical-velocity data for both the ac and dc flow of superfluid ⁴ He through a 2 m by 2 m aperture in a 0.1-m-thick titanium foil between 0.36 and 2.10 K. Single-2 phase slips were resolvable over the entire range of temperature in the ac flow measurements, carried out between 10 and 20 Hz, making it possible to determine the width of the critical-velocity distribution throughout the temperature range from these measurements. These data have been interpreted in terms of the thermal nucleation of vortex half-rings at the walls of the aperture, involving a velocity- and temperature-dependent energy barrier. The barrier can be modeled with moderate success using an approach close to that of Avenel and Varoquaux and coworkers.     

Optical and Electron Spin Resonance Studies of Destruction of Porous Structures Formed by Nitrogen–Rare Gas Nanoclusters in Bulk Superfluid Helium

We studied optical and electron spin resonance spectra during destruction of porous structures formed by nitrogen–rare gas (RG) nanoclusters in bulk superfluid helium containing high concentrations of stabilized nitrogen atoms. Samples were created by injecting products of a radio frequency discharge of nitrogen–rare gas–helium gas mixtures into bulk superfluid helium. These samples have a high energy density allowing the study of energy release in chemical processes inside of nanocluster aggregates. The rare gases used in the studies were neon, argon, and krypton. We also studied the effects of changing the relative concentrations between nitrogen and rare gas on thermoluminescence spectra during destruction of the samples. At the beginning of the destructions, \(\alpha \)-group of nitrogen atoms, Vegard–Kaplan bands of \(\hbox {N}_2\) molecules, and \(\beta \)-group of O atoms were observed. The final destruction of the samples were characterized by a series bright flashes. Spectra obtained during these flashes contain M- and \(\beta \)-bands of NO molecules, the intensities of which depend on the concentration of molecular nitrogen in the gas mixture as well as the type of rare gas present in the gas mixture.     

Interferometric Measurement of Refractive Index Variations in Infra-red Transmitting Materials at 10·6 μm

A procedure has been developed for determining the gross refractive index variations in infra-red transmitting materials. The technique uses an infra-red interferometer operating at 10·6 μm, with a pyroelectric vidicon (or any other suitable T.V. compatible) fringe visualization device, interfaced to a digital T.V. frame store. Representative examples of the results obtained are shown.     

Fatigue striation in a wide range of crack propagation rates up to 70 μm/cycle in a ductile structural steel

The relationship between striation spacing and fatigue crack propagation rate up to 70 m/cycle was investigated for a ductile structural steel, qualified as JIS SM58Q. A modified compact-type specimen 400 mm wide and a centre-cracked specimen 200 mm wide were tested at a stress ratio, R, of 0 and 0.8. The fracture surface of the specimen was examined in detail under a scanning electron microscope. The crack propagation rate was expressed by a power function of the range of stress intensity factor from 0.1 to 70 m/cycle for R=0 and to 0.5 m/cycle for R=0.8. The striation spacing coincided with the fatigue crack propagation rate over the range 0.1 to 70 m/cycle. The profile of striation was found to be a ridge and valley type, and the ridges on one fracture surface coincided with those on the matching surface. It is suggested that the striation is formed by a plastic blunting mechanism.     

Multilayer structures with quantum dots in the InAs/GaAs system emitting at a wavelength of 1.3 μm

The optical properties of multilayer structures with quantum dots in the heteroepitaxial InAs/GaAs system have been studied. The structures were obtained by the method of submonolayer migration-stimulated epitaxy. It is shown that the optimized growth conditions provide room-temperature luminescence at a wavelength of 1.3 μm.     

Study on I-V Behavior of YBCO Film on 5 mm × 10 mm LAO Under DC Pulse by Electric Transport Method

Journal of Superconductivity and Novel Magnetism - A set of DC pulse devices was built to measure the 5 mm?×?10 mm YBCO sheet in order to evaluate the impact of...     

Direct Observation of Vortex Structure in a High Tc YBa2Cu3O7−y Thin Film by Bitter Decoration Method

The Bitter decoration technique is one of the most powerful techniques to study the vortex structure of superconductor. We report the observation of vortex structure in a high T _c YBa ₂ Cu ₃ O _7–y (YBCO) thin film by Bitter decoration method. The image of vortex structure was monitored by SEM, AFM and high resolution optical microscope. For magnetic field about 4-6mT,a vortex structure is seen. The vortex image varied with changing magnetic field. As compared with the vortex image of a Bi ₂ Sr ₂ CaCu ₂ O _8+y single crystal, the observed image appeared to be more randomly distributed.     

Measurement by laser Doppler interferometry of intraocular distances in humans and chicks with a precision of better than ±20 µm

A laser Doppler interferometer was built for the precise measurement of intraocular optical distances in humans and chicks. A technique using Purkinje images was developed to position the chick's eye reproducibly. A computer algorithm for the objective analysis of the interference signal and determination of the optical distances is presented. The precision of this noncontact interferometric method for measuring the cornea-retina distance is better than ±20 μm.     

Experimental Study of Inducing Compressive Stress by Anti—welding Heating Treatment in a Thin Plate Weldment with Variant Temperatures

Significant compressive stress may be induced in thin plate weldment by anti-welding heating treatment(AWHT) with a temperature difference above 350 ℃ ，and an interesting phenomenon of ovbious residual stress reduction on non-treated surface was discovered.The method of AWHT has no great effect on the mechanical properties including hardness,strength and toughness of the metal material.The results in the paper prompt a possibility application in shipbuilding industry.     

Increasing output power of LEDs (λ = 1.7–2.4 μm) by changing directions of reflected light fluxes in GaSb/GaInAsSb/GaAlAsSb heterostructures

It is demonstrated, using the example of light-emitting diodes (LEDs) based n-GaSb/n-GaIn-AsSb/p-GaAlAsSb heterostructures, that the formation of a curvilinear reflecting surface consisting of hemispherical etch pits on the rear side of an LED chip leads to an increase in the output radiation power by a factor of 1.9–2 in the entire wavelength interval studied (λ = 1.7–2.4 μm) as compared to the LED chip design with a continuous absorbing ohmic contact. This increase in the LED efficiency is related to a change in the directions of reflected light fluxes upon reflection from the hemispherical etch pits.     

Study of the structure–property relationships in a high impact and shape memory polyester by the stereoisomer selection of the cyclobutane diol monomer

The diol and dicarboxylic acid in polyester synthesis are significant independent variables that relate directly to the structure–property-dependent variables of polyesters. The choice of the stereoisomers of the diol in the polyester synthesis can significantly alter the mechanical and thermal performance. Terephthalate polyesters prepared from the proper ratio of 2,2,4,4-tetramethyl-1,3-cyclobutanediol (CBDO) and 1,3-propanediol have superior impact resistance when compared to ballistics grade polycarbonate. In addition these polymers exhibit very strong self-healing behavior that is activated by heat. These copolymers were all produced with a mixture of cis and trans isomers with a ratio of 43/57, respectively. This study reports research conducted to determine the structure–property relationships that can be attributed to the stereoisomers of the CBDO monomer. The polyester prepared with 99 % cis (CBDO) monomer has significantly improved mechanical and thermal performance when compared with the polyester prepared with a 43:57 mixture of cis and trans isomers or 100 % trans isomer. Thermal gravimetric analysis and differential scanning calorimetry demonstrated that the cis CBDO polymer exhibit a much higher T _g (99 °C for cis and 69 °C for the trans 84.5 °C for the mixed polymer) and better thermal stability than the trans form of the polymer (onset of decomposition of trans at 345 and 360 °C for cis). Dynamic mechanical analysis and the Notched Izod demonstrated that the cis form of the polymer was much tougher than the trans form. Wide angle X-ray diffraction showed that the trans form was semicrystalline and the cis form was amorphous. The Notched Izod impact was 1070 J/m for the cis CBDO-based copolymer with the trans form having an impact factor of 841 J/m with the mixed polymer exhibiting an intermediate value of 944 J/M. Molecular modeling supports the experimental evidence that the choice of stereoisomers for the diol significantly influences the molecular architecture of the polyesters. The molecular architecture of polyesters in addition to polar attraction and molecular weight variables provides a dramatic increase in mechanical and thermal performance.     

Study of {332}<113> twinning in a multilayered Ti-10Mo-xFe (x = 1–3) alloy by ECCI and EBSD

We have investigated the propagation of {332}<113> twins in a multilayered Ti-10Mo-xFe (x = 1–3) alloy fabricated by multi-pass hot rolling. The material contains a macroscopic Fe-graded structure (about 130 μm width) between 1 and 3 wt% Fe in the direction perpendicular to rolling. We observe strong influence of the Fe-graded structure in the twin propagation behavior. The propagation of {332}<113> twins that are nucleated in Fe-lean regions (~1 wt% Fe) is interrupted in the grain interiors at a specific Fe content, namely, about 2 wt% Fe. We ascribe this effect to the role of Fe content in solid solution on the stress for twin propagation. The interruption of twins in the grain interiors results in the development of characteristic dislocation configurations such as highly dense dislocation walls (HDDWs) associated to strain localization phenomena. The nucleation and propagation of these dislocation configurations is ascribed to the underlying plastic accommodation mechanisms of the stress field at the twin tips. We find that the crystallographic alignment of HDDWs is determined by the stress field at the twin tips and the deformation texture. The excellent plastic accommodation at the interrupted twin tips allows attaining the good ductility of the present material (total elongation of 28%).     

Monochromatic Radiation Source Based on a Supercontinuum Laser for Measurement of Spectral Sensitivity of Radiation Detectors in the Range 0.9–1.6 μm with the Use of an Absolute Cryogenic Radiometer

Measurement Techniques - An improved monochromatic radiation source with spectral width 4 nm based on a supercontinuum laser and double monochromator is introduced into a unit based on an absolute...