Thermal expansion behavior of various aromatic polyimides

The thermal expansion behavior for various aromatic polymides was investigated. Usally polymers, including polyimides, have high thermal expansion coefficients (3–6 × 10^?5 K^?1), compared with metals and ceramics. However, there are some polyimides which have very low thermal expansion coefficients below 1 × 10^?5 K^?1. This property was observed for the polymides obtained from pyromellitic dianhydride or 3,3′ 4,4′-biphenyltetracarboxylic dianhydride and aromatic diamines which were constituted of only benzene rings fused at para positions. It was proposed that their low thermal expansion coefficient related to the linearity in their polymer molecular skeltons.     

Effect of alumina addition on hydroxyapatite biocomposites fabricated by underwater-shock compaction

Hydroxyapatite [HAp; Ca₁₀(PO₄)₆(OH)₂] biocomposites are ceramic materials that exhibit excellent bioactivity, but their inherent low fracture strength and toughness render them unusable for practical applications. Alumina (Al₂O₃) is added to improve in mechanical properties without diminution of biocompatibility. Powder mixtures of HAp and Al₂O₃ in various volume ratios (90:10, 80:20, and 70:30) were compacted by underwater shock waves generated by explosives. High explosives of 6900 m s⁻¹ detonation velocity served as the energy generators. The compacts were sintered at 1473, 1573, and 1673 K in order to investigate the influence of sintering temperature. All compacts were found to be free of defects and to have undergone continuous compositional changes to tricalcium phosphate and tetracalcium phosphate. K_1c showed maximum value with HAp–30vol.% Al₂O₃ that have been sintered at 1673 K for 7.2 ks, and the value of 3.0 MPa m^−1/2 is 2.5 times that of HAp monolithic material. The results of optical microscopy, scanning electron microscopy, X-ray diffraction, and other analyses are reported.     

Pre-emptive analgesia from intravenous administration of opioid: no effect with pentazocine

The influence of timing of administration of preoperative pentazocine on pain and analgesic requirements after surgery was studied in 46 patients undergoing total abdominal hysterectomy. Twenty-three patients received thiamylal 5 mg.kg-1 on induction of anesthesia, followed by pentazocine 30 mg or 60 mg before surgical incision (group A). Twenty-three control patients received pentazocine 30 mg or 60 mg, 5 min after abdominal incision (group B). The visual analogue scales for pain 24 h after operation were 6.0 cm at 30 mg dose in group A or 5.3 cm at 60 mg dose in group A and 5.7 cm at 30 mg dose in group B or 4.7 cm at 60 mg dose in group B. There were no differences in the visual analogues scales. Pentazocine consumption in the first 24 h after surgery was 67.5 mg at 30 mg dose in group A or 52.5 mg at 60 mg dose in group A and 70.9 mg at 30 mg dose in group B or 51.8 mg at 60 mg dose in group B. We conclude that postoperative pentazocine consumption and pain scores are no different when pentazocine is given before or after skin incision for abdominal hysterectomy and that there is no clinically useful pre-emptive analgesic effect with these doses of pentazocine.     

基于轴压调节的电压控制型逆变器的并网运行模式

目前应用中的逆变器存在难于控制输出电压频率、并离网模式切换困难及逆变器输出功率耦合等问题。通过电压控制型逆变器完善并网控制策略,可以较好地解决这些问题。为此提出了两种基于轴压概念的电压控制型并网逆变器功率控制模式:同步发电机运行模式与最大功率运行模式。数字仿真和实验结果吻合,验证了理论分析的正确性,有效提高了分布式发电系统的并网功率控制能力。     

Function of aluminum in crystal structure of rare earth–Mg–Ni hydrogen-absorbing alloy and deterioration mechanism of Nd0.9Mg0.1Ni3.5 and Nd0.9Mg0.1Ni3.3Al0.2 alloys

We investigated in detail the effect of incorporating Al in the crystal structure of rare earth–Mg–Ni hydrogen-absorbing alloys, which were developed as candidate materials for the metal hydride (MH) negative electrode in commercial Ni–MH batteries, using synchrotron powder X-ray diffraction. Partially substituting the Ni part with Al changes the lattice parameter of the major A₂B₇ phase, eliminating a mismatch between the AB₂ units and the AB₅ units. The change of the lattice parameter in the alloy leads to good hydrogen reversibility and good durability. Furthermore, we observed the alloy after 30 hydrogen absorption–desorption cycles using a scanning transmission electron microscope image. Consequently, we found that the surface layer of the Nd_0.9Mg_0.1Ni_3.5 alloy had an amorphous state, while the surface layer of the Nd_0.9Mg_0.1Ni_3.3Al_0.2 alloy did not. We confirmed that the deterioration mechanism of the Nd_0.9Mg_0.1Ni_3.3Al_0.2 alloy was due to partial expansion of the AB₂ unit along the c-axis; the local area of deterioration expanded during the cycling period.     

Relation between the peak effect and the magnetization step in Bi2Sr2CaCu2Oyyy

Local magnetization (B_l-H_a) as a function of magnetic field (H_a) was measured by using micro Hall probes in high quality Bi₂Sr₂CaCu₂O_8+y .     

Determination of optimum retrograde cerebral perfusion conditions

Retrograde cerebral perfusion through a superior vena caval cannula is a new technique used to protect the brain during operations on the aortic arch. We measured cerebral tissue blood flow, oxygen consumption, and cerebrospinal fluid pressure under various perfusion conditions in hypothermic (20 degrees C) mongrel dogs (n = 18, 12.8 +/- 0.6 kg) to determine the optimum conditions for retrograde cerebral perfusion. Retrograde cerebral perfusion was performed by infusion via the superior vena caval cannula and drainage via the ascending aortic cannula while the inferior vena cava and azygos vein were clamped. Retrograde cerebral perfusion was performed as the external jugular venous pressure was changed from 15 to 35 mm Hg in increments of 5 mm Hg. Cerebral tissue blood flow was measured by the hydrogen clearance method. Hypothermic retrograde cerebral perfusion with an external jugular venous pressure of 25 mm Hg provided about half the cerebral tissue blood flow of hypothermic (20 degrees C) cardiopulmonary bypass with a flow rate of 1000 ml/min (13.7 +/- 7.9 versus 32.7 +/- 8.5 ml/min per 100 gm). It decreased significantly as the external jugular venous pressure was decreased from 25 to 15 mm Hg but did not increase significantly as the external jugular venous pressure was increased from 25 to 35 mm Hg. Whole-body oxygen consumption during hypothermic retrograde cerebral perfusion with an external jugular venous pressure of 25 mm Hg was one quarter of that during hypothermic cardiopulmonary bypass (3.4 +/- 0.7 versus 12.7 +/- 5.6 ml/min) and varied in proportion to external jugular venous pressure. The cerebrospinal fluid pressure was a little lower than the external jugular venous pressure (19.2 +/- 4.5 mm Hg versus 24.8 +/- 2.4 mm Hg) but also varied with the external jugular venous pressure. The cerebrospinal fluid pressure remained lower than 25 mm Hg so long as the external jugular venous pressure remained lower than 25 mm Hg. High external jugular venous pressure was associated with high intracranial pressure, which restricts cerebral tissue blood flow and may cause brain edema. We believe that a venous pressure of 25 mm Hg is the optimum condition for retrograde cerebral perfusion.     

An ultrafast photonic ATM switch based on bit-interleavemultiplexing

An optical ATM switch is proposed in which cells from individual input channels are time-division multiplexed in a bit-interleave manner. This switch can easily handle multicast switching because it is based on a broadcast-and-select network. Compared to an alternative switch that uses a cell-interleave time-division multiplexing scheme, the proposed optical switch has a much simpler structure. It does not need a cell compressor at each input and a cell expander at each output, which greatly reduces hardware complexity. Feasibility analyzes showed that a 64×64 photonic ATM switch with 2.5 Gb/s input/output is possible using the proposed technology. In an experimental demonstration, 4 b cells were selected from a 55 Gb/s bit-interleave multiplexed cell stream by using a new nonlinear optical fiber switch. With its high switch throughput, our switch is a strong candidate for future large-capacity optical switching nodes     

Plasma-assisted catalytic ionization using porous nickel plate

Hydrogen atomic pair ions, i.e., H(+) and H(-) ions, are produced by plasma-assisted catalytic ionization using a porous nickel plate. Positive ions in a hydrogen plasma generated by dc arc discharge are irradiated to the porous plate, and pair ions are produced from the back of the irradiation plane. It becomes clear that the production quantity of pair ions mainly depends on the irradiation current of positive ions and the irradiation energy affects the production efficiency of H(-) ions.     

Effect of oxygen absorber on accumulation of free fatty acids in brown rice and whole grain wheat during storage

Because rapid rancidities of lipids in unpolished grains, such as brown rice and whole grain wheat, are often problematic, Suppressions of their lipid degradations during postharvest therefore important for their further utilization. In this study, effect of oxygen absorber on lipid deterioration in unpolished grain during storage was investigated. Kernels and flours of brown rice, rice with germ and whole grain wheat were stored for eight weeks at 4 °C and 26 °C, with and without oxygen absorber. Free fatty acids (FFAs) accumulation in the unpolished grains during storage was accelerated by polishing, milling and storage at high temperature (26 °C), because these storage conditions stimulated activities of their lipid hydrolyses. When oxygen absorber was added and the storage system was sealed, additional FFAs accumulations in these unpolished grains. Decreases both in absolute amounts of linoleic acids of the lipids and in total tocochromanols contained in these unpolished grains were depressed by addition of oxygen absorber to the storage system, which was confirmed by an anti-oxidative effect of oxygen absorber. These results suggested that introduction of oxygen absorber into the storage system of unpolished grains would be effective under the condition where their hydrolytic activities of lipids are suppressed.