Regenerating Pt-3d-Pt model electrocatalysts through oxidation-reduction cycles monitored at atmospheric pressure

The interchange between the Pt-Ni-Pt and Ni-Pt-Pt bimetallic configurations in O₂ and H₂ is confirmed experimentally at atmospheric pressure using in situ X-ray absorption spectroscopy (XAS). The subsurface Pt-3d-Pt structure, a desirable configuration as cathode electrocatalysts for PEM fuel cells, is found to be preferred in the reducing environment of H₂ whereas the surface 3d-Pt-Pt configuration is preferred in O₂. This process has been found to be reversible, providing useful insights into the maintenance and regeneration of the desirable subsurface structure.     

Design charts for the general instability of ring-stiffened conical shells under external hydrostatic pressure

The paper describes experimental tests carried out on three ring-stiffened circular conical shells that suffered plastic general instability under uniform external hydrostatic pressure. In this mode of failure, the entire ring–shell combination buckles bodily in its flank. The cones were carefully machined from EN1A mild steel to a very high degree of precision.Using the results obtained from these three vessels, together with the results obtained from elsewhere, the paper also provides two-design charts, which are much easier to use than older design charts. The design charts allow the possibility of obtaining a plastic knockdown factor, so that the theoretical elastic buckling pressures for perfect vessels, can be divided by the plastic knockdown factor, to give the predicted buckling pressures. Although similar design charts have been produced in the past, the design charts presented here are based on using the simpler ring-stiffened circular cylinder, which has been made equivalent to the much more complex ring-stiffened circular conical shell. The advantage of using this method is that it is simpler and the design time is reduced by a factor of about 10 with little loss of precision. This method can also be used for the design of full-scale vessels.     

AM1 molecular screening of novel porphyrin analogues as dye-sensitized solar cells

AM1 calculations were used to study the charge-separated state of porphyrin analogues as sensitizers. Initial calculations were performed on the donor and acceptor moieties to determine the molecular orbital (MO) energy levels independently. The analogues were modeled by combining the donor and acceptor moieties. The charge-separated state of the porphyrin analogues was analyzed from the MO energy levels of the donor and acceptor moieties, and from the porphyrin analogues (donor–acceptor pairs). MO spatial orientations were also used to elucidate the charge-separated state of the analogues. Our results revealed that the relative positions of the lowest unoccupied molecular orbital (LUMO) levels of the donor and acceptor moieties could predict the MO spatial orientations of the porphyrin analogues, i.e., the donor–acceptor pairs. The LUMO is localized in the acceptor and the highest occupied molecular orbital (HOMO) in the donor region when the difference between LUMO_donor and LUMO_acceptor is positive, which indicates a charge-separated state. Of the molecular models, (Zn-5G) had the smallest HOMO–LUMO gap and had a relative difference of 0.16 eV compared to (Zn-1A), which has a known cell efficiency of 4.8%.     

Investigations on thermally forced hydrolysis and phase formation in aqueous iron(III) nitrate solutions

The hydrolysis of 0.06 mol dm^-3 Fe(NO₃)₃ solutions was followed at 65°C by means of pH and dynamic light scattering measurements. The hydrolysis products were characterized by transmission electron microscopy and nitrogen adsorption. Depending on the heating procedure different phases were observed, i.e. -FeOOH (goethite) was formed on heating a 0.06 mol dm^-3 solution to 65°C, and -Fe₂O₃ (hematite) if an appropriate amount of a concentrated stock solution was added to the preheated water at 65°C. An explanation of this behaviour is offered by taking into account the possible formation of quite different structural units of both solid phases in the course of the hydrolysis process.     

Hall-Effect in LuNi2B2C and YNi2B2C Borocarbides in Normal and Superconducting Mixed States

It was shown that the Hall resistivity _xy for LuNi ₂ B ₂ C and YNi ₂ B ₂ C is negative in the normal and mixed states and has no sign reversal below T _c . In the mixed state the scaling relation _{xy xx} (_xx is the longitudinal resistivity) was found for both compounds with 2.0. In the normal state a distinct nonlinearity in the _xy(H) dependence, accompanied by a large magnetoresistance, was found below 40 K only for LuNi ₂ B ₂ C. The difference in the behaviour of Lu- and Y-based borocarbides seems to be connected with the difference in the Fermi surfaces of these compounds.     

RoHS实施的总结工程师必须理解长期供应链问题

RoHS的截至日期和里程碑已经过去了。在唤起关注和促使业界转向RoHS的过程中,主要的元器件分销商发挥了重要作用,他们将符合规范的库存进行了流水线管理,其结果就是,整个业界为迎接这些变化所做的准备要比预期多。全球市场对符合RoHS指令的产品的需求达到空前的水平,预计大多数地区的OEM厂商都将提供相应的产品。在美国,对符合RoHS规范的产品的需求还远没有达到供应链的预期,这让一些OEM厂商保持现状,同时紧张地关注供应链究竟会发生什么变化。这使得设计工程师在选择器件时难下决心。如果错误理解RoHS风险所带来的长期供应链问题,…     

Low-altitude infrared propagation in a coastal zone: refraction and scattering

Midwave and long-wave infrared propagation were measured in the marine atmosphere close to the surface of the ocean. Data were collected near San Diego Bay for two weeks in November 1996 over a 15-km horizontal path. The data are interpreted in terms of effects expected from molecules, aerosol particles, and refraction. Aerosol particles are a dominant influence in this coastal zone. They induce a diurnal variation in transmission as their character changes with regular changes in wind direction. A refractive propagation factor calculation is introduced, and it is systematically applied to the model and to the data analysis. It is shown that this refractive propagation factor is a necessary component of a complete near-sea-surface infrared transmission model.     

Temporal correlations in stochastic networks of spiking neurons.

The determination of temporal and spatial correlations in neuronal activity is one of the most important neurophysiological tools to gain insight into the mechanisms of information processing in the brain. Its interpretation is complicated by the difficulty of disambiguating the effects of architecture, single-neuron properties, and network dynamics. We present a theory that describes the contribution of the network dynamics in a network of "spiking" neurons. For a simple neuron model including refractory properties, we calculate the temporal cross-correlations in a completely homogeneous, excitatory, fully connected network in a stable, stationary state, for stochastic dynamics in both discrete and continuous time. We show that even for this simple network architecture, the cross-correlations exhibit a large variety of qualitatively different properties, strongly dependent on the level of noise, the decay constant of the refractory function, and the network activity. At the critical point, the cross-correlations oscillate with a frequency that depends on the refractory properties or decay exponentially with a diverging damping constant (for "weak" refractory properties). We also investigate the effect of the synaptic time constants. It is shown that these time constants may, apart from their influence on the asymmetric peak arising from the direct synaptic connection, also affect the long-term properties of the cross-correlations.