Environmental effects and relaxation in natural rubber

The change in attenuation of longitudinal ultrasonic waves has been measured as a function of frequency and temperature for natural rubber samples loaded with intermediate super abrasion furnace (ISAF) in increasing quantities and vulcanized with N-oxidiethylene benzotriazol sulfunamid (OBTS) after being subjected to natural aging for 5 years. Three relaxation processes, namely α, β, and γ, were noticed. The activation energy for each process was calculated and the results are discussed. Also, the dielectric constant ε′ and dielectric loss ε″ have been investigated for those samples after being immersed in various water media. The measurements were carried out in the frequency range from 100 Hz up to 100 kHz and at room temperature (～ 28°C). The results are compared with each other and the differences are interpreted.     

The effects of deposition variables on spray-deposited ZnO thin film prepared from Zn(C2H3O2)2

Undoped Zn0 thin films have been prepared by a modified spray technique under various deposition conditions and the effects of the different deposition variables on the electrical and optical properties of the prepared films have been studied in detail. Substrate temperature has been found to be the most important parameter for the deposition process. To obtain a low resistive highly transparent Zn0 film with appreciable Hall mobility and carrier concentration, a post-deposition heat treatment in vacuum is always necessary and is a precondition for undoped films. From the study of the optical transmission spectra in the visible and near-UV regions it was observed that the films are highly transparent (98%) in the visible range. The fundamental absorption edge of the films lies in the UV region. Values of refractive indices of these films were also determined.     

Degradation of benzene,toluene ethylbenzene and p‐xylene (BTEX) in aqueous solutions using UV/H2O2 system

The homogeneous degradation of benzene (B), toluene (T), ethylbenzene (E) and p‐xylene (X) (BTEX) was studied in aqueous solutions, at pH 3.0, of hydrogen peroxide (5.8 mM ) under UV irradiation in a photoreactor equipped with a 300 nm lamp of light intensity 3.5 × 10^?5 Ein L^?1 min^?1. BTEX was substantially degraded by the H₂O₂/UV system, with >90% disappearing in 10 min of irradiation. The decomposition of BTEX was studied either as single or as multi‐component systems. The effects of irradiation time, amounts of H₂O₂ in molar ratios, rate of degradation and competition between components were thoroughly examined. It can be stated that the rate of BTEX degradation in mixture was higher than those for the individual components due to external effects of the absorption of UV light by the mixture, and their effects on enhancing the formation of OH^? radicals. The appropriate figure of merit, the electrical energy per mass (EE/M), was estimated at various molar ratios and it was confirmed that the best value was the one depicted for p‐xylene (0.065 kWh kg^?1). A theoretical model for the degradation pathway was proposed. Copyright © 2004 Society of Chemical Industry     

Development of a supporting tool for optimal fuel management in research reactors using artificial neural networks

The present work investigates an appropriate way to solve the problem of optimizing fuel management in research reactors. A computer program has been developed, to automate this procedure. The program suggests an optimal core configuration, which satisfies to established safety constraints. The suggested solution was based upon the use of coupled methods in which a stochastic technique, simulated annealing, and an adaptive back-propagation neural network are connected to each other.An objective function was developed based on two performance parameters: cycle length, which can be determined through the evaluation of the effective multiplication factor K_eff and power peaking factor P_max. The system uses optimization of these two parameters to finds configurations in which K_eff is maximized, whether a penalty function is applied to limit the value of P_max which should be lower than the one given in the initial configuration.A series of tests have been performed using a modified core configuration of the benchmark 10 MW IAEA LEU (low enriched uranium) research reactor and the result achieved is the optimum configuration of the studied core.     

Cholecystogastrocolonic fistula with intrahepatic abscess: a rare complication of biliary stone disease

A 49-year-old female presented with a rare meningioma in the petrous bone. High resolution computed tomography and magnetic resonance imaging demonstrated that the tumor had developed in the jugular foramen and extended into the infralabyrinthine area of the petrous bone and intracranially into the cerebellopontine angle. The operative findings confirmed these observations. Meningiomas of the petrous bone may originate from the jugular foramen.     

An investigation of velocity distribution in rotating magnetohydrodynamic bearings

An analysis based on the Navier-Stokes equations is made for the flow of a liquid in magnetohydrodynamic circular bearings under rotating conditions. The analysis presents expressions for both radial and tangential velocities with and without inertia effects. The results show that the application of a magnetic field reduces both radial and tangential velocities. The rotational inertia effect has a greater effect on the radial velocity at small film thicknesses.     

Automatic solver for non‐linear partial differential equations with implicit local laws: Application to unilateral contact

In general, non‐linear continuum mechanics combine global balance equations and local constitutive laws. In this work, frictionless contact between a rigid tool and a thin elastic shell is considered. This class of boundary value problems involves two non‐linear algebraic laws: the first one gives explicitly the stress field as a function of the strain throughout the continuum part, whereas the second one is a non‐linear equation relating the contact forces and the displacement at the boundary.Given the fact that classical computational approaches sometimes require significant effort in implementation of complex non‐linear problems, a computation technique based on automatic differentiation of constitutive laws is presented in this paper. The procedure enables to compute automatically the higher‐order derivatives of these constitutive laws and thereafter to define the Taylor series that are the basis of the continuation technique called asymptotic numerical method. The algorithm is about the same with an explicit or implicit constitutive relation. In the modelling of forming processes, many tool shapes can be encountered. The presented computational technique permits an easy implementation of these complex surfaces, for instance in a finite element code: the user is only required to define the tool geometry and the computer is able to obtain the higher‐order derivatives. Copyright © 2013 John Wiley & Sons, Ltd.     

On modelling and characterization of single electron transistor

As the nanotechnology rose to the surface, single electron transistor (SET) was invented. In contrast to the well-known response of MOS current, SET current has peaks at certain gate voltages, which disappears at other gate voltages. The SET has promised to be valuable in many applications for its high speed and low power consumption. First, a comparison was drawn between different models of SET based on the orthodox theory. Such theory explains electron transport from source to drain, employing free energies, tunnel rates and coulomb blockade phenomenon, in addition to quantizing electron tunnelling. Afterwards, a simplified model was proposed to account for unnecessary lengthy calculation processes, resulting from the large number of states assumed for simulation. The proposed PSPICE simplified model was confirmed by comparing its results to the results of the available models, and it was found to agree well with them. Taking much less runtime than the available models, the proposed model can easily be used to simulate SET-based integrated circuits on PSPICE.     

Analysis and design of hydroformed thin-walled tubes using enhanced one-step method

This paper deals with the analysis and design of tube hydroforming parameters in order to reduce defects which may occur at the end of the forming process, such as necking and wrinkling. We propose a specific methodology based on the coupling between an enhanced one-step method for the rapid simulation of tube hydroforming process and a surrogate model based on a metamodeling technique. The basic formulation of the one-step method has been modified and adapted for the modeling of 3D tube hydroforming problems in which the initial geometry is a circular tube expanded by internal pressure and submitted to axial feeding. In the surrogate model, approximate responses are built using moving least squares method and constructed within a moving region of interest which moves across a predefined discrete grid of authorized experimental designs. Two applications of tube hydroforming of aluminum alloy 6061-T6 have been utilized to validate our methodology. The final design is validated using experiments together with the classical explicit dynamic incremental approach using ABAQUS? commercial code.     

多场景的MPTCP协议性能分析研究

利用多宿主设备的多个接口实现多路径传输、获取更多的网络吞吐量是因特网协议研究的热点。IETF所关注的MPTCP协议是当前比较成熟、关键的多路径传输协议。为了测试MPTCP在当前已部署的网络环境中的性能,分别在本地测试床、Internet环境测试场景和大规模多宿主系统NorNet测试床中对MPTCP多路径传输实际吞吐量性能进行了测试和分析,测试结果表明MPTCP相对TCP虽能获得吞吐量的提高,但在非相似带宽链路的场景中其性能仍然不完善,其路径管理和传输调度策略仍需要进一步改进。