Numerical simulation of transient response of heat transfer from a hot-wire anemometer transducer

Both the steady state and transient response of the Nusselt number to variations in Reynolds number over the range 1 to 40 are given by the analysis of a time dependent numerical simulation of a hot-wire anemometer transducer described here. Transducer response can be modelled suitably by considering the system to consist of a phase independent non-linearity followed by a non-linear differential equation whose coefficient (approximate time constant) is Nusselt number dependent. Errors associated with slip flow and free convection constrain the minimum size of a hot-wire which may be used in calibration anemometry while the wire thermal inertia and, to a lesser extent, the response of the Nusselt number to Reynolds number limits the use of large diameter wires. Thus, although the tendency has been to use finer and finer wires, the basic fluid mechanics suggests that a compromise in the choice of the wire diameter is appropriate. Thus development of even more sophisticated hot-wire anemometer control systems as well as accurate calibration techniques for measurement in flows containing large amplitude high frequency turbulence is required     

First-passage-time and busy-period distributions of discrete-time Markovian queues:Geom(n)/Geom(n)/1/N

This paper gives simple explicit solutions of various first-passage-time distributions for a general class of discrete-time queueing models under arbitrary initial conditions, state-dependent transition probabilities and the finite waiting room. Explicit closed form expressions are obtained in terms of roots. These expressions are then used to get numerical as well as graphical results. Explicit closed-form expressions are also deduced for the continuous-time models including the busy-period distributions. The analysis is then extended to cover the case of two absorbing states.     

Thermal conductivity ofn-Tetracosan around the liquid-liquid transition temperatureT u

Forn-Tetracosan the temperature dependence of the thermal conductivity has been determined between 52 °C and 150 °C by the transient hot strip method. A decreasing thermal conductivity is followed by a constant one forT100 °C.The change in slope can be well estimated by using data of Brillouin scattering and specific volume measurements thus confirming the existence of theT _u -phenomenon.     

Markov Control Processes with the Expected Total Cost Criterion: Optimality, Stability, and Transient Models

This paper studies the expected total cost (ETC) criterion for discrete-time Markov control processes on Borel spaces, and possibly unbounded cost-per-stage functions. It presents optimality results which include conditions for a control policy to be ETC-optimal and for the ETC-value function to be a solution of the dynamic programming equation. Conditions are also given for the ETC-value function to be the limit of the -discounted cost value function as 1, and for the Markov control process to be `stable" in the sense of Lagrange and almost surely. In addition, transient control models are fully analized. The paper thus provides a fairly complete, up-dated, survey-like presentation of the ETC criterion for Markov control processes on Borel spaces.     

Intrinsic randomness and spontaneous symmetry-breaking in explosive systems

The effect of fluctuations of either thermodynamic or environmental origin on ignition in explosive systems is analyzed, with special emphasis on thermal explosion. A simple model due to Semenov is first analyzed in the zero-dimensional approximation. It is shown that the ignition times exhibit a wide dispersion, which at the level of the probability distribution of temperature shows up as a transient bimodality. Next, an extension to a spatially distributed system is developed. It is shown that fluctuations induce unexpected symmetry-breaking phenomena, reflected by a considerable dispersion of the position of the first hot spot initiated in the system.     

Threshold phenomena in the transient behaviour of Markovian models of communication networks and databases

This paper accompanies a talk given at the Workshop on Mathematical Methods in Queueing Networks held at the Mathematical Sciences Institute at Cornell University in August 1988. In earlier work we had exhibited a threshold phenomenon in the transient behaviour of a closed network of ./M/1 nodes: When there areN customers circulating, and the initial state isx, letd _x ^N (t) denote the total variation distance between the distribution at timet and the stationary distribution. Let d^N(t) = max _x d _x ^N (t). We explicitly founda _N proportional toN such thatd ^N(ta_N)1 forevery t<1, andd ^N(ta_N)0 forevery t>1. Thus it appears that the network has not yet converged to stationarity uptoa _N , but has converged to stationarity aftera _N , soa _N can be naturally interpreted as the settling time of the network. Here we briefly deal with some other similar models — closed networks of ./M/m nodes, a well studied model for circuit switched networks, and a model of Mitra for studying concurrency control in databases. Similar threshold phenomena are established in the transient behaviour of these models.Research supported by the National Science Foundation, Grant No. NCR 8710840.     

100Gb/s归零码信号的2R再生

本文提出了基于半导体光放大器(SOA)中的瞬态交叉相位调制(T-XPM)效应与交叉增益压缩(XGC)效应的全光2R再生方法, 同时研究了SOA中的T-XPM效应获得反逻辑码信号以及XGC 效应光开关门的特性, 实现了100 Gb/s归零码(RZ)信号的2R再生, 接收机灵敏度提高了1.7-2 dB; 对该方案中的反逻辑码对于再生效果的影响进行了量化研究, 并在C波段范围内研究了该再生方案的再生效果, 实现了覆盖1535-1555 nm的全光2R再生.     

Acid Treatment Enables Suppression of Electron–Hole Recombination in Hematite for Photoelectrochemical Water Splitting

We report a strategy for efficient suppression of electron–hole recombination in hematite photoanodes. Acid‐treated hematite showed a substantially enhanced photocurrent density compared to untreated samples. Electrochemical impedance spectroscopy studies revealed that the enhanced photocurrent is partly due to improved efficiency of charge separation. Transient absorption spectroscopic studies coupled to electrochemical measurements indicate that, in addition to improved bulk electrochemical properties, acid‐treated hematite has significantly decreased surface electron–hole recombination losses owing to a greater yield of the trapped photoelectrons being extracted to the external circuit.     

冲击高压下硝基甲烷的拉曼光谱及其结构稳定性

在单次冲击压缩实验中,借助新建的瞬态拉曼光谱技术实现了对液态硝基甲烷冲击拉曼光谱的原位观测,来探究该样品分子在冲击波作用下的结构稳定性.实验发现,在10.6 GPa的冲击加载下硝基甲烷的拉曼特征峰仅发生了蓝移和展宽,而在观测波段未发现化学变化产生的迹象.这一结果否定了文献所报道的硝基甲烷在6 GPa~8.5 GPa的单次冲击压力区间内发生了化学反应的推论,同时也证实了在10.6GPa的冲击压力下硝基甲烷分子在约为516 ns的压缩时间内能够保持其结构的稳定.     

Comparison of batch and in‐line PECVD of a‐Si:H passivation layers for silicon heterojunction solar cells

We present PECVD deposition of i‐a‐Si:H in an in‐line configuration for the fabrication of silicon heterojunction solar cells. For industry, in‐line processing has the potential to increase production throughput and yield. We compared batch and in‐line fabrication of i‐a‐Si:H passivation samples with identical plasma conditions and observed that the a‐Si:H material properties do not significantly differ. In batch‐type production the substrate is in the plasma zone at the moment of ignition, whereas for in‐line deposition the substrate is introduced into the plasma zone when steady plasma conditions have been reached. Our preliminary results show that there are depositions conditions that result both for in‐line and batch‐type deposition in good i‐a‐Si:H passivation layers. Therefore both methods can equally well be considered for the production of silicon heterojunction solar cells. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)