The radio counter-jet of the QSO 3C 48

We present multi- frequency radio observational results of the quasar 3C 48. The observations were carried out with the Very Large Array ( VLA) at five frequencies, 0.33, 1.5, 4.8, 8.4, and 22.5 GHz, and with the Multi- Element Radio Linked Interferometer Network ( MERLIN) at the two frequencies of 1.6 and 5 GHz. The source shows a one- sided jet to the north within 1", which then extends to the northeast and becomes diffuse. Two bright components ( N2 and N3), containing most of the flux density, are present in the northern jet. The spectral index of the two components is alpha(N2) similar to -0.99 +/- 0.12 and alpha(N3) similar to - 0.84 +/- 0.23 ( S proportional to nu(alpha)). Our images show the presence of an extended structure surrounding component N2, suggestive of strong interaction between the jet and the interstellar medium ( ISM) of the host galaxy. A steep- spectrum component, labelled S, located 0.25 " southwest to the flat- spectrum component which could be the core of 3C 48, is detected at a significance of > 15 sigma. Both the location and the steepness of the spectrum of component S suggest the presence of a counter- jet in 3C 48.

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

Experimental Investigation of Performance of a Miniature Direct Methanol Fuel Cell in Short-Term Microgravity

Experimental study of a liquid fed direct methanol fuel cell has been conducted in different gravity environments. A small single cell with 5 cm x 5 cm active area has single serpentine channel on the graphite cathode polar plate and 11 parallel straight channels on the graphite anode flow bed. Cell voltage and current have been measured and two-phase flow in anode channels has been in situ visually observed. The experimental results indicate that the effect of gravity on power performance of the direct methanol fuel cell is large when the concentration polarization governs fuel cells operation. Gravitational effect becomes larger at higher current density. Increasing methanol feeding molarity is conducive to weaken the influence of gravity on performance of liquid fed direct methanol fuel cells. Increasing feeding flow rate of methanol solution from 6 to 15 ml/min could reduce the size of carbon dioxide bubbles, while the influence of gravity still exist. Transport phenomena inside direct methanol fuel cells in microgravity is also analyzed and discussed.

Properties and applications of cold supersonic gas jet

By analyzing the formation mechanism of a supersonic gas jet, a set of equations which describe the atomic beam properties were established. The influence of initial temperature, initial pressure, background gas pressure and pumping speed was discussed in detail. A simulation program was developed based on the equations, and the results under different initial conditions were obtained. The results are in good agreement with the experimental data, and suggest that, in order to get much smaller transverse momentum in collision experiments, it is necessary to lower the initial temperature and the initial pressure of the supersonic gas jet, together with increasing the pumping speed. These results are very instructive for construction of a new generation of cold supersonic gas jets.

Performance comparison of low-temperature direct alcohol fuel cells with different anode catalysts

Low-temperature polymer electrolyte membrane fuel cells directly fed by methanol and ethanol were investigated employing carbon supported Pt, PtSn and PtRu as anode catalysts, respectively. Employing Pt/C as anode catalyst, both direct methanol fuel cell (DMFC) and direct ethanol fuel cell (DEFC) showed poor performances even in presence of high Pt loading on anode. It was found that the addition of Ru or Sn to the Pt dramatically enhances the electro-oxidation of both methanol and ethanol. It was also found that the single cell adopting PtRu/C as anode shows better DMFC performance, while PtSn/C catalyst shows better DEFC performance. The single fuel cell using PtSn/C as anode catalyst at 90degreesC shows similar power densities whenever fueled by methanol or ethanol. The cyclic voltammetry (CV) and single fuel cell tests indicated that PtRu is more suitable for DMFC while PtSn is more suitable for DEFC. (C) 2003 Elsevier B.V. All rights reserved.

CO selective oxidation in a microchannel reactor for PEM fuel cell

It is indispensable to remove CO at the level of less than 50ppm in H-2-rich feed gas for the proton exchange membrane (PEM) fuel cells. In this paper, catalyst with high activity and selectivity, and a microchannel reactor for CO preferential oxidation (PROX) have been developed. The results indicated that potassium on supported Rh metal catalysts had a promoting effect in the CO selective catalytic oxidation under H-2-rich stream, and microchannel reactor has an excellent ability to use in on-board hydrogen generation system. CO conversion keeps at high levels even at a very high GHSV as 500 000 h(-1), so, miniaturization of hydrogen generation system can be achieved by using the microchannel reactor. (C) 2004 Elsevier B.V. All rights reserved.