GAS-SOLIDS FLOW BEHAVIOR WITH A GAS VELOCITY CLOSE TO ZERO

In a 9.3 m high and 0.10 m i.d. gas-solids downflow fluidized bed (downer), the radial and axial distributions of the local solids holdups and particle velocities along the downer column were measured with the superficial gas velocity set to zero. A unique gas-solids flow structure was found in the downer system with zero gas velocity, which is completely different from that under conditions with higher gas velocities, in terms of its radial and axial flow structures as well as its micro flow structure. The gas-solids flow pattern under zero gas velocity conditions, together with that under low gas velocity conditions, can be considered as a special regime which differs from that under higher gas velocity conditions. According to the hydrodynamic properties of the two regimes, they can be named the “dense annulus“ regime for the flow pattern under zero or low gas velocity conditions and the “dense core“ regime for that under higher gas velocity conditions.     

Nonlinear optical phenomena at the interface with photorefractive crystals

Characteristics of nonlinear optical phenomena in reflection of light at the interface with photorfractive crystals having photovoltaic nonlinearity are studied. it is shown that under total reflection, hysteretic behavior of the reflection coefficient is possible as a function of the incident radiation intensity or the angle of incidence. It is important that previously required threshold intensities are rather low (≤1 W/cm²) in comparison with the known case of reflection from media with Kerr nonlinearity. The present results are of doubtless interest in view of the development of possible devices for controlling laser radiation. Interdepartmental Institute of Advanced Training of Personnel in New Trends in Engineering and Technology at the State Polytechnical Academy of Belarus, 77, Partizanskii Ave., Minsk-107, 220600 Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 915–920, November–December, 1998.     

Convexity considerations and spatial behavior for the harmonic vibrations in thermoelastic plates

In this paper we study the spatial behavior of the steady-state solutions for the approach of thin thermoelastic plates developed by Lagnese and Lions [J.E. Lagnese, J.-L. Lions, Modelling, Analysis and Control of Thin Plates, Collection RMA, vol. 6, Masson, Paris, 1988]. The model leads to a coupled complex system of partial differential equations, one of fourth order in terms of the amplitude of the vertical deflection and the other of second-order in terms of the amplitude of temperature field. Coupling in an appropriate way the two equations in an integral identity we are able to identify some cross-sectional line integral measures associated with the amplitudes of the vertical deflection and temperature vibrations, provided that the exciting frequency is less than a certain critical frequency. Furthermore, we are able to establish a second-order differential inequality whose integration furnishes a Saint-Venant type decay estimate for a bounded strip and an alternative of Phragmén-Lindelöf type for a semi-infinite strip. The critical frequency is individuated by means of the use of some Wirtinger and Knowles inequalities.     

New thermoelastic technique for detection of residual stress distribution in solids

I.IntroductionNondestructiveeva1uationofstressdistributioninmaterialandmovingor1oadedcompo-nentsisveryimportantinmaterialscienccandengineering.Theultrasonictechnique['l,Ramanspectroscope['l,X-ray['landneutrondiffrac1iontcchnique[4]areusua1lyusedtodetectthestressdistributioninanopaquesample.RecentlytheScanningE1ectronAcousticMicroscopy(SEAM)[s]andphotoacoustictcchniquc[6]havebccnrcportedasncwtechniquetodeterminetheresidualstressdistribution.Itisshownthatthethermalwavealsocanbeusedtomcasure…     

Flow regime development analysis in adiabatic upward two-phase flow in a vertical annulus

In this work radial and axial flow regime development in adiabatic upward air-water two-phase flow in a vertical annulus has been investigated. Local flow regimes have been identified using conductivity probes and neural networks techniques. The inner and outer diameters of the annulus are 19.1 mm and 38.1 mm, respectively. The equivalent hydraulic diameter of the flow channel, D_H, is 19.0 mm and the total length is 4.37 m. The flow regime map includes 1080 local flow regimes identifications in 72 flow conditions within a range of 0.01 m/s < 〈j_g〉 < 30 m/s and 0.2 m/s < 〈j_f〉 < 3.5 m/s where 〈j_g〉 and 〈j_f〉 are, respectively, superficial gas and liquid velocities. The local flow regime has been classified into four categories: bubbly, cap-slug, churn-turbulent and annular flows. In order to study the radial and axial development of flow regime the measurements have been performed at five radial locations. The three axial positions correspond to z/D_H = 52, 149 and 230, where z represents the axial position. The flow regime indicator has been chosen as some statistical parameters of local bubble chord length distributions and self-organized neural networks have been used as mapping system. This information has been also used to compare the results given by the existing flow regime transition models. The local flow regime is characterized basically by the void fraction and bubble chord length. The radial development of flow regime shows partial and complete local flow regime combinations. The radial development is controlled by axial location and superficial liquid velocity. The radial flow regime transition is always initiated in the center of the flow channel and it is propagated towards the channel boundaries. The axial development of flow regime is observed in all the flow maps and it is governed by superficial liquid velocity and radial location. The prediction results of the models are compared for each flow regime transition.     

An examination of HMM‐based investment strategies for asset allocation

We develop and analyse investment strategies relying on hidden Markov model approaches. In particular, we use filtering techniques to aid an investor in his decision to allocate all of his investment fund to either growth or value stocks at a given time. As this allows the investor to switch between growth and value stocks, we call this first strategy a switching investment strategy. This switching strategy is compared with the strategies of purely investing in growth or value stocks by tracking the quarterly terminal wealth of a hypothetical portfolio for each strategy. Using the data sets on Russell 3000 growth index and Russell 3000 value index compiled by Russell Investment Services for the period 1995–2008, we find that the overall risk‐adjusted performance of the switching strategy is better than that of solely investing in either one of the indices. We also consider a second strategy referred to as a mixed investment strategy which enables the investor to allocate an optimal proportion of his investment between growth and value stocks given a level of risk aversion. Numerical demonstrations are provided using the same data sets on Russell 3000 growth and value indices. The switching investment strategy yields the best or second best Sharpe ratio as compared with those obtained from the pure index strategies and mixed strategy in 14 intervals. The performance of the mixed investment strategy under the HMM setting is also compared with that of the classical mean–variance approach. To make the comparison valid, we choose the same level of risk aversion for each set‐up. Our findings show that the mixed investment strategy within the HMM framework gives higher Sharpe ratios in 5 intervals of the time series than that given by the standard mean–variance approach. The calculated weights through time from the strategy incorporating the HMM set‐up are more stable. A simulation analysis further shows a higher performance stability of the HMM strategies compared with the pure strategies and the mean–variance strategy. Copyright © 2009 John Wiley & Sons, Ltd.     

Generalized Malkmus line intensity distribution for CO2 infrared radiation in Doppler broadening regime

A new line intensity distribution function is introduced in order to improve the accuracy of statistical narrow-band (SNB) models in the Doppler line broadening regime and in a wide temperature range. This distribution function generalizes the Malkmus distribution through a parameter enabling to adjust the contribution of small line intensities. This new model is shown to enhance significantly SNB accuracy for CO₂ uniform column radiation, especially at low temperatures. For non-uniform columns, Lindquist-Simmons type approximations are derived for this new intensity distribution. Their results are in much closer agreement with line by line results than Curtis-Godson approximation ones when steep temperature gradients are considered.     

投资者心态对股票价格走势的作用机理研究

假设股价变化遵循马尔科夫转移过程,考察具有不同心态的投资者的市场行为,给出投资者心态与股价变化之间相互作用的模型,得到了股价走势的两个基本模式,并用此模型解释股价走势中的动量效应和反转效应.     

高聚焦高斯光束对左手性材料球轴向力的光线模型计算

采用几何光线模型, 将基模高聚焦高斯光束对微米量级介电球和左手性材料球的轴向作用力进行了理论推导和数值模拟, 并对介电球和左手性小球的受力进行了比较. 对于介电球, 可以实现单光束陷阱捕陷介电球; 在右手性材料环境中的左手性材料小球, 受到的轴向作用力总是沿光传播的方向, 激光和左手性材料球的参数共同决定轴向力的最大值出现在光轴上的位置. 而在相对折射率较小时, 左手性材料小球的受力是介电球的百倍. 关键词： 基模高斯光束 几何光线模型 轴向作用力 左手性材料