Enhancement of nucleate pool boiling heat transfer in ammonia/water mixtures (Effect of surface‐active agent)

Nucleate boiling heat transfer coefficients of ammonia/water mixtures have been measured when a surface‐active agent was added into the mixtures. The experiment has been carried out on a horizontal heated wire at a pressure of 0.4 MPa. The effect of concentration of the ammonia and the surface‐active agent on the coefficients was investigated experimentally for the ammonia fractions C = 0.3 and 0.7 and the surfactant concentration C_S = 0 to 3500 ppm. The result shows that just after onset of boiling the nucleate boiling heat transfer coefficient enhances at the lower ammonia fraction i.e., C = 0.3. It was found that the enhancement effect by the surface‐active agent disappeared when the surfactant concentration is more than 1000 ppm at an ammonia fraction C = 0.3. It is also shown that the generated heat of mixing near the vaporBliquid interface can be removed easily and the pressure and temperature in the system can be controlled easily by placing a cooling pipe on the vaporBliquid interface, resulting in improvement of accuracy in measuring the heat transfer coefficients. We correlated the effect of the surfactant on the heat transfer coefficient using the improved measurement data in the current paper. 8 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/htj.20328     

Study of efficient homogenization algorithms for nonlinear problems

A framework for the homogenization of nonlinear problems is discussed with respect to block LU factorization of the micro–macro coupled equation, and based on the relation between the characteristic deformation and the Schur-Complement as the homogenized tangent stiffness. In addition, a couple of approximation methods are introduced to reduce the computational cost, i.e., a simple scheme to reuse the old characteristic deformation and a sophisticated method based on the mode-superposition method developed by our group. Note that these approximation methods satisfy the equilibrium conditions in both scales. Then, using a simplified FE model, the conventional algorithm, a relative algorithm originating from the block LU factorization, and the above-mentioned algorithms with the approximated Schur-Complement are compared and discussed. Finally, a large-scale heart simulation using parallel computation is presented, based on the proposed method.     

Chemical modification of flexible and rigid poly(vinyl chloride) by nucleophilic substitution with thiocyanate using a phase-transfer catalyst

The purpose of this study was to examine the effect of a phase-transfer catalyst on the chemical modification of flexible and rigid poly(vinyl chloride) (PVC) by substituting chloride with thiocyanate (SCN) in order to develop a new process for recycling PVC. The effects of temperature and time on the reaction of a SCN/ethylene glycol (EG) solution on PVC were investigated in the presence and absence of tetrabutylammonium bromide (TBAB) as a phase-transfer catalyst. TBAB was found to accelerate the dehydrochlorination of both flexible and rigid PVC, thus allowing the reaction to take place over shorter reaction times. The substitution yield and substitution/dehydrochlorination ratio were higher in the presence of TBAB than in its absence. By reducing the reaction temperature, the substitution/dehydrochlorination ratio increased, and substitution occurred more rapidly when TBAB was present. The differences between flexible and rigid PVC were negligible. Together, these results indicate that the phase-transfer catalyst TBAB is effective in accelerating the substitution of chloride by SCN. This two-phase reaction allows for the easy separation of the polymer from the solvent without using other chemicals or thermal processes.     

Control of magnetic anisotropy in Fe–Co–B soft magnetic underlayer for perpendicular magnetic recording media

Anisotropic residual stress induced in the Fe–Co–B/Ni–Fe layers causes high anisotropy field H _k in the films induced by magnetoelastic effect. The origin of residual stress in Fe–Co–B/Ni–Fe layers was investigated. The direction of magnetic anisotropy of Fe–Co–B/Ni–Fe layers was formed in the direction corresponding to the incident direction of sputtered particles reached substrate. The magnitude of the H _k depended strongly on the condition of argon gas pressure. An incident direction of sputtered particles, which has an important effect on the direction of H _k, seemed to be dispersed under high Ar gas pressure condition because of the increase of collision number between sputtered particles and Ar particles. However, a low gas pressure condition of 1 mTorr in which sputtered particles have a long mean free path led to restrain the dispersion of H _k direction. As a soft magnetic underlayer of high H _k, the noise level of the media with Fe–Co–B/Ni–Fe decreased about 4 dB compared to that with the layer of low H _k in low frequency.     

Self-Alignment of Optical Devices With Fiber for Low-Cost Optical Interconnect Modules

We propose a novel self-alignment process of optical devices with optical fiber. A vertical-cavity surface-emitting laser (VCSEL) was automatically coupled with a multimode fiber (MMF) through the surface tension of a liquid adhesive within 1.5 s. Misalignment between the center of the VCSEL and the fiber was measured to be 15 mum, which is acceptable for coupling the VCSEL with the MMF. High-speed pulse modulation of the self-aligned VCSEL up to 5 Gb/s, as well as at 1 Gb/s, was demonstrated. The average optical output power was as high as -5.9 dBm at 1 Gb/s.     

High optical coupling efficiency using 45 °-ended fibre for low-height and low-cost optical interconnect modules

High optical coupling efficiency of more than 80% between an optical fibre and a vertical-cavity surface-emitting laser (VCSEL) has been achieved without use of a lens. A 45deg-ended fine-drawn optical fibre can be positioned closer to a VCSEL than a conventional multimode fibre. 12.5 Gbit/s/ch optical signal transmissions using a low-height optical coupling structure have been demonstrated with optical output power as high as +2.0 dBm without use of a lens.     

Electrical characteristics of MOSFETs with La2O3/Y2O3 gate stack

A metal oxide semiconductor field effect transistor (MOSFET) with ultra-thin La₂O₃/Y₂O₃ high-k gate dielectric was fabricated. The effects of thermal treatment process on both physical and electrical characteristics of the La₂O₃/Y₂O₃ stack were studied using XPS and electrical measurements. It was observed that the effective mobility of the fabricated MOSFETs with La₂O₃/Y₂O₃ gate stack was not degraded with increasing the annealing temperatures up to 600 °C. X-ray photoelectron spectroscopy (XPS) analysis also revealed that the formation of SiO₂ and silicate layer at the interface was suppressed in La₂O₃/Y₂O₃ stack compare to that of in La₂O₃ single layer. Obtained results suggesting that La₂O₃/Y₂O₃ gate stack is one of the promising candidates for high-k gate insulator to be used in the future metal oxide field effect transistors.     

Lithium based ceramic materials and membranes for high temperature CO2 separation

The selective removal of CO₂ at high temperature is a topic of great significance owing to its use in managing CO₂ emissions to the atmosphere as well as in enhancing the efficiency of several catalytic processes where CO₂ is a product. CO₂ absorbent materials and CO₂ separating membranes made of lithium based ceramics have been applied to the selective separation of CO₂ from gas mixtures. In this review, a summary of the recent progress made in the processing and application of these materials and membranes will be given. The characteristics of the materials and the factors influencing their properties will be examined in detail. Critical issues will be discussed with a view to provide clues for future developments.     

A direct digital synthesizer with interpolation circuits

This paper presents a direct digital synthesizer (DDS) with no ROM that still produces square waves with low spurious signals. The main features are the interpolation of the analog-converted accumulator contents and the extraction of timing at the points where the interpolated signal is identical to a continuous sawtooth waveform. Experimental results confirm successful frequency synthesizer operation. The output frequency is determined by the frequency control word, and spurious signals present in the accumulator contents are greatly reduced