低甲醇透过直接甲醇燃料电池(Low Methanol Crossover Direct Methanol Fuel Cell)

直接甲醇燃料电池与间接甲醇燃料电池相比，体积更小，重量更轻，因此在一些领域有诱人的应用前景。但是，在它们实际应用之前，必须解决一些具体的技术难题。目前，甲醇从阳极透过到阴极是影响电池性能的主要难题之一，另外，催化剂和电极的制备方法也对电池的性能有重要的影响。本论文的主要目的在于研制低甲醇透过直接甲醇燃料电池并有效地提高电池的性能。为了减小甲醇在Nafion117膜中的透过，提出并研制了铭纳米粒子修饰的Nafion复合膜，该方法包括与[Pd(NH_4)_4]~(2+)离子的离子交换过程和化学还原过程。研究了一种制备高分散性铂基催化剂的方法。另外我们还研究并分析了不同的电池运行参数，例如温度、甲醇浓度等，刘一电池性能和甲醇透过的影响。主要结果如下：1.采用离子交换还原法在Nafionll7膜内部沉积纳米把粒子，制备成高聚物电解质复合膜。研究了镀把前后Nafion膜表面形态、甲醇透过和膜的电导的变化和对直接甲醇燃料电池的性能的影响等。由于把纳米粒子阻碍了甲醇透过，同时，由于它对氢离子的强吸引力，不但不对氢离子的透过产生影响，而且还提高了膜佩狗电导。所以镀把后电解质膜的甲醇透过减少，膜电导增加，无论在低电流密度区还是在高电流密度区，电池性能都有效地提高。2.研究了一种制备高分散性铂基催化剂的新方法一预沉淀还原法。并采用TEM,XRD和电化学等技术来表征催化剂中铂的粒径、晶态结构和催化活性：与传统的化学还原法相比，因为该方法在化学还原过程中反应物与载体的作用力得到增强，所以采用该方法制备的催化剂铂分散性更好、晶态结构更低、粒径更小并且催化活性更好。该方法在直接甲醇燃料一电池中有应用价值。3.研究并分析了不同的电池运行参数，例如温度、甲醇浓度等，对电池性能和甲醇透过的影响。研究发现当电池运行温度增加时，电池性能提高，甲醇透过增加；甲醇浓度增加时，甲醇透过增加，但是，甲醇浓度对电池性能有不同的影响，在低甲醇浓度区，甲醇浓度增加，电池性能提高；在高甲醇浓度区，甲醇浓度增加，电池性能降低；存在一个最佳甲醇浓度，在该甲醇浓度的条件下，电池的性能最高。实验结果为：采用Nafion117膜时，电池的最佳甲醇浓度为2. 0 mol/L，采用镀把Nafion117膜时，电池的最佳甲醇浓度高于4.0 mol/Lo

THE MATRIX ANALYSIS FOR AN OPTICAL FREE-SPACE SWITCHING NETWORK AND AN OPTICAL CROSSOVER NETWORK WITH 4-FUNCTION INTERCHANGE NODES

A matrix analysis for free-space switching networks, such as perfect shuffle-exchange omega, crossover and Banyan is presented. On the basis of matrix analysis, the equivalence of these three switching networks and the route selection between input and output ports are simply explained. Furthermore, an optical crossover switching network, where MQW SEED arrays are used as electrically addressed four-function interchange nodes, is described and the optical crossover interconnection of 64 x 64, and high-speed four-function, interchange nodes is demonstrated in the experiment.

Superfluid nuclear matter in BCS theory and beyond

Medium polarization effects are studied for S-1(0) pairing in nuclear matter within BHF approach. The screening potential is calculated in the RPA limit, suitably renormalized to cure the low density mechanical instability of nuclear matter. The self-energy corrections are consistently included resulting in a strong depletion of the Fermi surface. The self-energy effects always lead to a quenching of the gap, whereas it is almost completely compensated by the anti-screening effect in nuclear matter.

Dimensional crossover of heat conduction in low dimensions

The dimensional crossover phenomena of heat conduction is studied by a two-dimensional (2D) Fermi-Pasta-Ulam lattice. The 2D divergence law of the thermal conductivity is confirmed by the simulations results. The divergence law of the thermal conductivity will change from the 2D class to 1D class as delta=N-y/N-x decreases, here N-y is the size in transverse direction and N-x in longitude direction. The simulation's results suggest that the dimensional crossover happens in delta(*)-> 0 as N-x ->infinity.

Improved BCS-type pairing for the relativistic mean-field theory

A density-dependent delta interaction (DDDI) is proposed in the formalism of BCS-type pairing correlations for exotic nuclei whose Fermi surfaces are close to the threshold of the unbound state. It provides the possibility to pick up those states whose wave functions are concentrated in the nuclear region by making the pairing matrix elements state dependent. On this basis, the energy level distributions, occupations, and ground-state properties are self-consistently studied in the RMF theory with deformation. Calculations are performed for the Sr isotopic chain. A good description of the total energy per nucleon, deformations, two-neutron separation energies and isotope shift from the proton drip line to the neutron drip line is found. Especially, by comparing the single-particle structure from the DDDI pairing interaction with that from the constant pairing interaction for a very neutron-rich nucleus it is demonstrated that the DDDI pairing method improves the treatment of the pairing in the continuum.

Crystallization Behaviors of n-Octadecane in Confined Space: Crossover of Rotator Phase from Transient to Metastable Induced by Surface Freezing

In this paper, the confined crystallization and phase transition behaviors of n-octadecane in microcapsules with a diameter of about 3 Pm were studied with the combination of differential scanning calorimetry (DSC), temperature dependent Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD).

Ethanol crossover phenomena and its influence on the performance of DEFC

In the present work, Nafion (R) membrane porosity changes were determined in aqueous ethanol solutions with different concentrations by weighing vacuum-dried and ethanol aqueous solution equilibrated membranes at room temperature. The ethanol crossover rate through Nafion (R)-115 membrane at different temperatures and different concentrations had been investigated in a fuel cell test apparatus by using membrane gets higher as ethanol solution gas chromatography analysis. The experimental results show that the swelling degree of Nafion (R) concentration increases. The ethanol crossover rate increases with ethanol concentration and temperature increment. The single direct ethanol fuel cell (DEFC) tests were carried out to investigate the effect of ethanol concentration on ethanol crossover and consequently, on the open circuit voltage and the cell performance of DEFC. It can be found that ethanol crossover presented a negative effect on the OCV and the cell performance of DEFC. It can also be found that an improved DEFC performance was obtained as temperature increased although the ethanol crossover rate increased with temperature increment. (c) 2005 Elsevier B.V. All rights reserved.

肉、奶牛B超活体取卵方法

本发明涉及一种肉、奶牛B超活体取卵方法，属生物技术领域。本方法的吸卵真空泵的压力为50-90mmHg，吸卵液为含0.5-1％,青-链霉素和5-10IU肝素的磷酸缓冲液，洗卵液为含5-12％,BCS的磷酸缓冲液和改良的基础培养液-Hepes液；采卵频率为1次/4天/头；穿刺对象为所有直径≥2mm的卵泡；取1-3级的卵母细胞分装、备用；对7-8岁的供体经产牛按程序注射等量的外源性FSH，总量为30-55μg；对≥14岁的老年牛按程序肌肉注射总量为150-200μg的外源性FSH，以提高卵母细胞发育潜能。本发明的优点在于，从活体可重复、无损伤获取卵母细胞；≥2mm直径卵泡作为穿刺对象和每4天1次的取卵频率保证了卵母细胞的质量和发育同步性；用外源性FSH诱导可提高卵母细胞的发育潜能；本方法的取卵效果佳。

克洛曲对癌痛的双盲双模拟自身交叉研究

为了观察克洛曲在慢性癌痛病人中的疗效,采用多中心、双盲双模拟、自身交叉对照研究的方法, 比较了克洛曲片、曲马多胶囊和安慰剂对108 例中、重度癌痛的镇痛效果。结果表明克洛曲片的总有效率为 88. 0 % ,明显高于曲马多胶囊的72. 2 %( P < 0. 01) 和安慰剂的35. 2 %( P < 0. 001) ; 克洛曲片的缓解时间明 显延长( P < 0. 01) ; 克洛曲片的药物不良反应的发生率与曲马多胶囊相似, 但便秘的发生率明显低于曲马 多胶囊( P < 0. 05) 。克洛曲片对中、重度癌痛的镇痛效果确切,安全性较大。文章还对镇痛药临床研究的策 略方法及安慰剂效应进行了详细的讨论。

Effect of electron-electron scattering on spin dephasing in a high-mobility low-density two-dimensional electron gas

By utilizing time-resolved Kerr rotation techniques, we have investigated the spin dynamics of a high-mobility low density two-dimensional electron gas in a GaAs/Al0.35Ga0.65As heterostructure in the dependence on temperature from 1.5 to 30 K. It is found that the spin relaxation/dephasing time under a magnetic field of 0.5 T exhibits a maximum of 3.12 ns around 14 K, which is superimposed on an increasing background with rising temperature. The appearance of the maximum is ascribed to that at the temperature where the crossover from the degenerate to the nondegenerate regime takes place, electron-electron Coulomb scattering becomes strongest, and thus inhomogeneous precession broadening due to the D'yakonov-Perel' mechanism becomes weakest. These results agree with the recent theoretical predictions [J. Zhou et al., Phys. Rev. B 15, 045305 (2007)], which verify the importance of electron-electron Coulomb scattering to electron spin relaxation/dephasing.

Spin relaxation and dephasing mechanism in (Ga,Mn)As studied by time-resolved Kerr rotation

Spin dynamics in (Ga,Mn)As films grown on GaAs(001) was investigated by Time-resolved magneto-optical Kerr effect. The Kerr signal decay time of (Ga,Mn)As without external magnetic field applied was found to be several hundreds picoseconds, which suggested that photogenerated polarized holes and magnetic ions are coupled as a ferromagnetic system. Nonmonotonic temperature dependence of relaxation and dephasing (R&D) time and Larmor frequency manifests that Bir-Aronov-Pikus mechanism dominates the spin R&D time at low temperature, while D'yakonov-Perel mechanism dominates the spin R&D time at high temperature, and the crossover between the two regimes is Curie temperature.

Photoluminescence from self-assembled long-wavelength InAs/GaAs quantum dots under pressure

The photoluminescence from self-assembled long-wavelength InAs/GaAs quantum dots was investigated at 15 K under hydrostatic pressure up to 9 GPa. Photoemission from both the ground and the first excited states in large InAs dots was observed. The pressure coefficients of the two emissions were 69 and 72 meV/GPa, respectively. A nonlinear elasticity theory was used to interpret the significantly small pressure coefficients of the large dots. The sequential quenching of the ground and the excited state emissions with increasing pressure suggests that the excited state emissions originate from the optical transitions between the first excited electron states and the first excited hole states. (C) 2004 American Institute of Physics.

AMPS modeling of light J-V characteristics of a-Si based solar cells

AMPS (Analysis of microelectronic and photonic structures) mode,which was developed by Pennsylvania State University, has been used to module the light J-V characteristics of a-Si solar cells with a structure of TCO/p-a-SiC:H/i-a-Si:H/n-a-Si:H/ metal. The effects of valence band offset and contact barriers at p/i and TOC/p, n/metal interfaces on the light J-V characteristics have been examined. The modeling has qualitatively categorized and explained the non-ideal J-V behaviors (rollover, crossover, Voc shift,and rollunder) observed in a-Si based solar cells.