Thin film growth of boron nitride on α-Al2O3 (0 0 1) substrates by reactive sputtering

Boron nitride thin films were grown on α-Al₂O₃ (0 0 1) substrates by reactive magnetron sputtering. Infrared attenuated total reflection (ATR) spectra of the films gave an intense signal associated with in-plane B-N stretching TO mode of short range ordered structure of BN hexagonal sheets. X-ray diffraction for the film prepared at a low working pressure (ca. 1 × 10⁻³ Torr) gave a diffraction peak at slightly lower angle than that corresponding to crystal plane h-BN (0 0 2). It is notable that crystal thickness calculated from X-ray peak linewidth (45 nm) was close to film thickness (53 nm), revealing well developed sheet stacking along the direction perpendicular to the substrate surface. When the substrates of MgO (0 0 1) and Si (0 0 1) were used, the short-range ordered structure of h-BN sheet was formed but the films gave no X-ray diffraction. The film showed optical band gap of 5.9 eV, being close to that for bulk crystalline h-BN.     

Highly loaded silicone nanocomposite exhibiting quick thermoresponsive optical behavior

Bulk silicone nanocomposites with thermoresponsive optical behavior were fabricated using silica nanoparticle fillers within a cross-linked silicone matrix. Silica nanoparticles (25 nm diameter) were surface-modified, allowing for even distribution at 6-24 wt % within and covalent bonding to the silicone matrix. Utilizing the temperature-dependent match/mismatching of the refractive indices of the silica nanoparticle filler and the silicone matrix, bulk nanocomposites are highly transparent at room temperature and demonstrate significant increases in opacity with increasing temperature up to 100-150 °C. Such a response could be cycled quickly and repeatedly with no detrimental effect on the material.     

Shape-sensitive reflectance by nanostructured metal attached on an optical waveguide-mode sensor

The optical reflectance of He-Ne laser light on a waveguide-mode sensor was measured as a function of light incident angle, in the case of either a metal (Au, Cr or Pt) film or nanoparticles being attached to the waveguide surface of the sensor. A dip appears in the reflectance spectrum as a function of incident angle at the angle where waveguide-mode excitation is induced. It is found that the dip moves toward a lower angle in the case that the attached metal is of a film shape, while it shifts toward a higher angle when the metal is an ensemble of nanoparticles. This difference in the direction of shift can be explained well by theoretical calculations using average refractive indices of the metal-containing layers. The present result indicates that one can estimate whether a metal nanostructure is film-like or an ensemble of spherical nanoparticles by the sensor.     

Crystal growth and thermal neutron scintillation response of Ce doped KLiYF5

K⁶Li(Y_1−xCe_x)F₅ (x = 0.003, 0.02) single crystals were grown from the melt using the precise atmosphere control type Micro-Pulling-Down (μ-PD) method to examine their potential as a new thermal neutron scintillators. The grown crystals were single-phase materials as confirmed by XRD. The crystals demonstrated 40-60% transmittance above 320 nm and Ce³⁺ 5d-4f luminescence observed around 340 nm when exited by α-ray. The radio luminescence measurements under thermal neutron excitation (²⁵²Cf) demonstrated the light yield of 890 (Ph/neutron) and the decay time excited by α-ray exhibited 20 and 259 ns.     

Development of a 3He Refrigerator for Possible Experiments of Solid 4He on a Small Jet Plane

The gravity on the Earth (g _E) has not been taken seriously to mask the fundamental phenomena on quantum solids, though there are some important studies on the critical phenomena of superfluid ⁴He under microgravity. We are planning to investigate the effect of gravity on the equilibrium shape of solid ⁴He. Since we had a chance to do such an experiment on a small jet plane through the ground based program by JAXA, we got started to construct a cryostat which could cool down as low as 500?mK and meet severe restrictions of experiments on a jet plane. The main part of the refrigerator was a usual ³He-evaporator pumped by a scroll pump. A?small GM refrigerator was installed to provide 4?K stage. 1?K pot was also put in which was also pumped by another scroll pump to condense ³He gas and sample ⁴He. The cryostat was designed to have two optical windows to be able to observe solid ⁴He under microgravity. In the test flight for the refrigerator, the minimum temperature of 690?mK was kept during the entire flight of two hours in which 7 to 8 times parabolic flight was performed. Each parabolic flight includes about 20?seconds microgravity and 20?seconds 1.5 to 2.0?g _E period before and after the microgravity. We did some preliminary experiments with bcc solid ⁴He under microgravity. The crystal remained stuck to the bottom of the sample cell even in the 20 seconds microgravity condition.     

Thermal and dynamic mechanical properties of organic–inorganic hybrid composites of itaconate‐containing poly(butylene succinate) and methacrylate‐substituted polysilsesquioxane

Itaconate‐unit‐containing poly(butylene succinate) (PBSI) was synthesized by the reaction of 1,4‐butanediol, succinic acid, and itaconic acid in a molar ratio of 2.0 : 1.0 : 1.0, and the obtained PBSI was reacted with methacryl‐group‐substituted polysilsesquioxane (ME‐PSQ) in the presence of benzoyl peroxide (BPO) at 130°C to produce PBSI/ME‐PSQ hybrid composites. The thermal and dynamic mechanical properties of the PBSI/ME‐PSQ hybrid composites were investigated in comparison with those of PBSI cured at 130°C in the presence of BPO. As a result, the hybrid composites showed a much higher thermal degradation temperature and storage modulus in the rubbery state than the cured PBSI (C‐PBSI). The thermal degradation temperature and storage modulus of the hybrid composites increased with increasing ME‐PSQ content. The glass‐transition temperature, measured by dynamic mechanical analysis of the hybrid composites, somewhat increased with increasing ME‐PSQ content. However, the glass‐transition temperatures of all the hybrid composites were lower than that of C‐PBSI. Although the IR absorption peak related to C?C groups was not detected for C‐PBSI, some olefinic absorption peaks remained for all the hybrid composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Heat transfer characteristics of a reservoir embedded loop heat pipe (2nd report,Influence of noncondensable gas on heat transfer characteristics)

High‐powered satellites need larger heat rejection areas. A deployable radiator is one of the key technologies for a high‐powered satellite bus. A Reservoir Embedded Loop Heat Pipe (RELHP) is a two‐phase heat transfer device that constitutes the deployable radiator. RELHP has an evaporator core which is used as a liquid reservoir to enhance operational reliability. For use on satellites, RELHP is required to have a lifetime greater than 10 years. In the case of conventional heat pipes, it is generally known that noncondensable gas (NCG) has worse heat transport characteristics. On the other hand, the influence of NCG on a RELHP is not still obvious. This paper presents the heat transport characteristics of RELHP for the case of changing NCG volume by experiment and calculation. It was found that NCG increases temperature rise at the evaporator. NCG volume in a RELHP has a great influence on heat transport characteristics due to the reservoir pressure increase caused by NCG. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(8): 459–473, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20181     

New concept bioceramics composed of octacalcium phosphate (OCP) and dicarboxylic acid-intercalated OCP via hydrothermal hot-pressing

Octacalcium phosphate (OCP) and adipic acid-intercalated complexed OCP (Adi-OCP) were synthesized. Moreover, we made ceramic bodies out of them through a hydrothermal hot-pressing (HHP) method. Characteristic features of both the powder and ceramics were investigated by the X-ray diffraction method (XRD). Surface morphology of the ceramics was observed by scanning electron microscopy (SEM). Density, compressive strength and pore size distribution of the ceramics were measured. Crystalline structure of the newly developed OCP ceramics had no phase transformation from the starting materials. Moreover, the newly developed OCP ceramics had good mechanical properties only through the HHP treatment with a temperature as low as 110 °C. In order to evaluate bioactivity, the ceramics were immersed in simulating body fluid (SBF). It was predicted that OCP and Adi-OCP had better bioactivity than that of conventional HAp ceramics.     

Reaction–diffusion algorithm for stereo disparity detection

The present paper proposes a novel stereo algorithm utilizing multi-sets of reaction–diffusion equations. The problem of detecting a stereo disparity map becomes the segmentation problem, in which the uniqueness assumption and the continuity assumption on disparity distribution are taken into account. A set of reaction–diffusion equations realizes the continuity assumption, while a mutual-inhibition mechanism among the multi-sets realizes the uniqueness one. In addition, each set of equations has a self-inhibition mechanism, which is necessary for the reaction-diffusion equations applied to stereo disparity detection. Performance of the proposed algorithm is evaluated for well-known test stereo images.     

A comparative study on determination method of heat transfer coefficient using inverse heat transfer and iterative modification

The distortion control of heat-treated steel parts is a main consideration when dealing with hardening by quenching process. Before implementing this heat treating process, prediction of distortion is necessary to be done by experiment and computer simulation for determining a quenching technique which gives the smaller distortion. Temperature-dependent heat transfer coefficient (HTC) estimated from SUS304 cylinder can be determined by both iterative modification of lumped heat capacity method (LumpHC) and inverse heat transfer method (InvHT). Predicted HTC from silver probe is needed for the LumpHC, whereas initial set of assumption is needed for the InvHT. The zone-based HTC estimated from SUS304 cylinder then is employed on S45C cylinder. The prediction accuracy results from both methods are evaluated. As expected, stir quenching gives less distortion than that of still quenching. More accurate prediction of cooling curves, cooling rate curves, and distortion is achieved by employing the LumpHC than that by the InvHT. All analyses were performed by DEFORM-HT 2D.