水蓄冷运行控制分析

随着空调蓄冷技术的不断发展,它已逐渐在节能效果、经济效益和社会效益等方面展现出强大的生命力和广阔的市场。主要探讨了自然分层蓄冷形式,该方式利用温度和密度不同的原理,通过斜温层分隔高、低温水。必须严格进行水蓄冷系统的运行控制,否则极易打破其自然分层的规律。     

乳液聚合中单体醋酸乙烯酯与保护胶体聚乙烯醇的接枝反应研究

研究了以聚乙烯醇为保护胶体的醋酸乙烯乳液聚合中,聚乙烯醇与单体的接枝反应。探讨了引发剂用量、聚合反应温度、保护胶体聚合度等因素对接枝反应的影响。     

The onset of Taylor-Görtler vortices in impulsively decelerating swirl flow

The onset of hydrodynamical instability induced by impulsive spin-down to rest in a cylinder containing a Newtonian fluid is analyzed by using propagation theory. It is well-known that the primary transient swirl flow is laminar, but with initial high velocities secondary motion sets in at a certain time. The dimensionless critical time Τ_c to mark the onset of instability is presented here as a function of the Reynolds number Re. Available experimental data indicate that for large Re deviation of the velocity profiles from their momentum diffusion occurs starting from a certain time Τ≈4Τ_c. This means that secondary motion is detected at this characteristic time. It seems evident that during Τ_c⪯Τ⪯4Τ_c, secondary motion is relatively very weak and the primary diffusive momentum transfer is dominant.     

抗日战争时期的青年心理探析

抗日战争是中华民族历史上的一次大浩劫,中国人民为此承受了太多的痛苦与磨难,特别是对于肩负着国家与民族振兴使命的青年更是如此.分析战时青年的心理变化及原因,指出政府和社会对青年人的心理没有采取恰当的方法进行有效的疏导,提出要总结和吸取历史的经验教训,为我们今天应对大灾难提供借鉴.     

Effects of Copper Coating on the Crystalline Structure of Fine Barium Titanate Particles

We have investigated the effect of a metal coating—copper—on the tetragonal structure of fine barium titanate (BaTiO₃) particles. The BaTiO₃ particles were synthesized by a sol-gel method and heat treated at temperatures >900°C for various amounts of time before coating. The copper coating was achieved by an electroless coating technique. The transmission electron microscopy micrographs revealed that the coated powder contained fine BaTiO₃ particles that were embedded in copper patches. The X-ray diffractometry patterns showed that the copper coating increased the c/a ratio of the fine BaTiO₃ particles. For powders that were heat treated at 900°C for 10 h and were initially cubic, the copper coating changed the c/a ratio, from 1 to 1.0034. For powders that were calcined at 900°C for 20 h and were initially tetragonal, the copper coating further enhanced the c/a ratio, from 1.0028 to 1.0043. When the copper-coated BaTiO₃ particles were oxidized, the c/a ratio was reduced to a value that was approximately equal to or below that of the uncoated powders. A conductive coating can eliminate the depolarization energy of an insulating polar particle. The fact that the copper coating promoted the polar tetragonal phase but the nonconductive copper-oxide coating did not was consistent with the interpretation that the presence of the cubic phase (nonpolar) in small BaTiO₃ particles was caused by the depolarization effect.     

Highly ion-conductive solid polymer electrolytes based on polyethylene non-woven matrix

Highly ion-conductive solid polymer electrolyte (SPE) based on polyethylene (PE) non-woven matrix is prepared by filling poly(ethylene glycol) (PEG)-based crosslinked electrolyte inside the pores of the non-woven matrix. The PE non-woven matrix not only shows good mechanical strength for SPE to be a free-standing film, but also has very porous structure for high ion conductivity. The ion conductivity of SPE based on PE non-woven matrix can be enhanced by adding sufficient non-volatile plasticizer such as poly(ethylene glycol) dimethyl ether (PEGDME) into ion conduction phase without sacrificing mechanical strength. SPE with 20 wt.% crosslinking agent and 80 wt.% non-volatile plasticizer shows 3.1 × 10⁻⁴ S cm⁻¹ at room temperature (20 °C), to our knowledge, which is the highest level for SPEs. It is also electrochemically stable up to 5.2 V and has high transference number about 0.52 due to the introduction of anion receptor as an additive. The interfacial resistance between Li electrode and SPE is low enough to perform charge/discharge test of unit cell consisting of LiCoO₂/SPE/Li at room temperature. The discharge capacity of the unit cell shows 87% of theoretical value with 86% Coulombic efficiency.