Some aspects of nonisothermal crystallization of polymers. III. Crystallization during melt spinning

Crystallization during melt spinning is studied as an example of the nonisothermal crystallization of polymers. The following equation is derived, taking the temperature distribution within a filament into consideration: where T = temperature, X = crystallinity, κ = thermal diffusivity, V = velocity, ΔH = heat of crystallization, and C_p = specific heat at constant pressure. The assumptions and the procedure for a numerical calculation of crystallinity and temperature within a running filament are described, and some results of calculation are illustrated. The results are compared with those obtained by a simpler calculation in which the radial temperature distribution is neglected. The simpler method proved useful in connection with x-ray measurements.     

Analysis of lateral-mode behavior in broad-area InGaN quantum-welllasers

A wave-optical model that is coupled to a microscopic gain theory is used to investigate lateral mode behavior in group-III nitride quantum-well lasers. Beam filamentation due to self-focusing in the gain medium is found to limit fundamental-mode output to narrow stripe lasers or to operation close to lasing threshold. Differences between nitride and conventional near-infrared semiconductor lasers arise because of band structure differences, in particular, the presence of a strong quantum-confined Stark effect in the former. Increasing mirror reflectivities in plane-plane resonators to reduce lasing threshold current tends to exacerbate the filamentation problem. On the other hand, a negative-branch unstable resonator is found to mitigate filament effects, enabling fundamental-mode operation far above threshold in broad-area lasers     

Optical interconnection using VCSELs and polymeric waveguidecircuits

We investigated the waveguide loss and transmission characteristics for optical interconnection using vertical-cavity surface-emitting lasers (VCSELs) and multimode polymeric waveguide circuits with crossings. The excess loss with 100 crossings is 2.2 dB when the image magnification from a VCSEL to a waveguide is 2.3. We obtained error-free (i.e., bit error rate <10^-11) optical interconnection at 1.0625 Gbps regardless of the number of crossings or the magnification. These results suggest the practicality of large-scale optical interconnection between VCSEL-based smart-pixel chips using multimode waveguides with more than 100 crossings     

Thermal pre-treatment of wet microalgae harvest for efficient hydrocarbon recovery

Botryococcus braunii, a green colonial microalga, is an unusually rich renewable source of hydrocarbons. In this study, wet microalgae harvest was thermally pretreated to enhance hydrocarbon recovery using a solvent extraction process. Samples containing a mixture of B. braunii and water were kept below 100 °C for 10 min. The observed hydrocarbon recovery was 97.8% at 90 °C. The extraction results suggest that the energy-intensive concentration and drying processes of the harvest could be eliminated. The proposed thermal pretreatment would revolutionize the conventional downstream processes.     

Microstructure of AlN with two-domain structure on (001) diamond substrate grown by metal-organic vapor phase epitaxy

We investigate the microstructures of domain boundaries in an AlN layer grown on a (001) diamond substrate by metal-organic vapor phase epitaxy. The AlN layer has a two-domain structure with crystal orientation along either <112?0> AlN [named by AlN^I domain] or <101?0> AlN [named by AlN^II domain] parallel to [110] direction of diamond. The AlN^I and AlN^II domains are not atomically bonded at two-domain boundary from initial to final step of growth, while an edge-type dislocation is generated at single-domain boundary (SDB). In addition, an inversion AlN^I domain [named by AlN^I?] is randomly-ordered at the initial stage of the coalescence between the AlN^I domains. The AlN^I? is easily terminated with increasing the thickness of AlN^I domain. The inversion domain boundary changes to the edge-type dislocation at the SDB with further growth, which reduces the defect density in the AlN^I domains.     

Highly Active Titania Photocatalyst Particles of Controlled Crystal Phase, Size, and Polyhedral Shapes

Mesoscopic crystalline anatase particles of titanium(IV) oxide (titania) with decahedral morphology and with octahedral morphology were synthesized by gas-phase reaction of titanium(IV) chloride with oxygen and hydrothermal reaction of titanate nanowires in an alkaline medium, respectively, and their photocatalytic activities in relation with their crystal morphology were investigated.     

Submillimetre-wave lines of H2D+ and D2H+ as probes into chemistry in cold dark clouds

We discuss past and recent progress of our continuing project of submillimetre-wave spectroscopic investigations of H2D+ and D2H+. Three new lines of H2D+ in the 2.5-3.5 THz range are measured with a tunable far-infrared laser system. Since these molecules are very light asymmetric molecules, analysis based on a conventional effective Hamiltonian is not very useful in predicting the transition frequencies to the accuracy of the order of several MHz or better. In this respect, any addition of new accurate measurements of transition frequencies is important. In this paper, some discussions will be made on H5+ and its deuterated species as probable interstellar species in cold dark clouds. In particular, D3+, which is predicted to be abundant in cold dark clouds, can be (indirectly) detected by observing D3+ x H2.     

Mechanical and electrical cold bonding based on metallic nanowire surface fasteners

Mass production of surface mount devices (SMDs) relies heavily on reflow soldering and has become the cornerstone of today's electronic industry. However, the traditional reflow soldering technique is characterized by high heating temperatures, toxic solder materials and low recycling rate of SMDs. Here, we propose a new patterned structure of Au nanowire arrays named a surface fastener through which cold bonding for surface mount technology can be realized. The mechanical bonding enables normal and shear bonding strengths of more than 5?N?cm(-2). Simultaneously, the parasitic resistance of a pair of surface fasteners is only approximately 2?Ω. The present technique can be performed at room temperature, thereby improving the process compatibility and reliability of SMDs. Surface fasteners based on high melting point metallic nanowires are temperature-resistant for many critical applications. In addition, bonding without solder material is positive for the recycling of rare metals in SMDs.