Centering predictor variables in cross-sectional multilevel models: A new look at an old issue.

Appropriately centering Level 1 predictors is vital to the interpretation of intercept and slope parameters in multilevel models (MLMs). The issue of centering has been discussed in the literature, but it is still widely misunderstood. The purpose of this article is to provide a detailed overview of grand mean centering and group mean centering in the context of 2-level MLMs. The authors begin with a basic overview of centering and explore the differences between grand and group mean centering in the context of some prototypical research questions. Empirical analyses of artificial data sets are used to illustrate key points throughout. The article provides a number of practical recommendations designed to facilitate centering decisions in MLM applications. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Fatigue life estimation of MD36 and MD523 bogies based on damage accumulation and random fatigue theory

Bogies are one of the multifunctional parts of trains which are extremely subjected to random loads. This type of oscillating and random excitation arises from irregularities of the track including rail surface vertical roughness, rail joints, variance in super-elevation, and also wheel imperfections like wheel flats and unbalancy. Since most of the prementioned sources have random nature, a random based theory should be applied for fatigue life estimation of the bogie frame. Two methods of fatigue life estimation are investigated in this paper. The first approach which is being implemented in time domain is based on the damage accumulation (DA) approach. Using Monte-Carlo simulation algorithm, the rail surface roughness is generated. Finite element (FE) model of the bogie is subjected to the generated random excitation in the first approach and the stress time histories are obtained, and consequently the fatigue life is estimated by using the rain-flow algorithm. In the second approach, the fatigue life is estimated in frequency domain. Power spectral density (PSD) of the stress is obtained by using the FE model of the bogie frame and the fatigue life is estimated using Rayleigh technique in random fatigue theory. A comprehensive parametric study is carried out and effects of different parameters like the train speeds and level of the rail surface vertical roughness on the estimated fatigue life are investigated. This paper was recommended for publication in revised form by Associate Editor Hong Hee Yoo Davood Younesian received his MSc and PhD in Mechanical Engineering, both from Sharif University of Technology, Iran. He joined the Iran University of Science and Technology in 2005 as an Assistant Professor in the School of Railway Engineering. Dr Younesian’s research area is mainly focused on non-linear and random vibrations, optimal control of vibrations, dynamics and vibration of structures and railway vehicle systems. He has published more than 75 papers in international journals and conference proceedings in the areas of his research. Ali Solhmirzaei received his BSc in Railway Engineering (Rolling Stock) from Iran University of Science and Technology and his MSc in Mechanical Engineering from K.N.T University of Technology, Iran. His research is mainly focused on finite elements, railway vehicle dynamics and fatigue analysis of railway structures. Alireza Gachloo received his BSc in Railway Engineering (Rolling Stock) from Iran University of Science and Technology, Iran. His research is mainly focused on random vibration, railway vehicle dynamics and random fatigue.     

Electrooxidation of 4-methylcatechol in the presence of barbituric acid derivatives

Electrooxidation of 4-methylcatechol (1) in the presence of 1,3-dimethylbarbituric acid (2a) and 1,3-diethylthiobarbituric acid (2b) as nucleophiles has been studied in detail by cyclic voltammetry and controlled-potential coulometry. The results indicate that 1 can be oxidized to its related o-benzoquinone (1a) and without conversion to its quinone methide tautomeric form, via an ECEC mechanism pathway, is converted to barbiturate derivatives (5a-b). The electrochemical synthesis of 5a-b have been successfully performed in one-pot in an undivided cell.     

Thermal analysis of a moving fin using the radial basis function approximation

In this study, the heat transfer and temperature distribution in a moving fin have been analyzed. The fin velocity was considered constant, and the thermal conductivity coefficient was variable with temperature, and the fin was under the effect of convection, radiation, and conduction heat transfer. The main equation of the problem was solved by the radial basis function method and validated by the numerical 4th-order Runge–Kutta method. Several parameters such as thermal conductivity parameter from 0 to 1, sink temperature parameter from 0.2 to 0.8, and N_r, N_c, Pe number from 1 to 4, were examined. The outcomes illustrate that increasing the thermal conductivity by 51.5% raises the conduction heat transfers as well as the dimensionless temperature by 3.42%. Moreover, increasing the sink temperature leads to a slow rise in ambient temperature by 22.8% in the maximum state. By raising the N_c and N_r parameters, near 33.3%, the temperature distribution profile is declined by 4% and 10.5%, respectively. And increasing the Pe number by 100% results in a rise in the temperature distribution by about 7%.     

Theoretical investigation of aromatics production enhancement in thermal coupling of naphtha reforming and hydrodealkylation of toluene

In the current research, an exothermic reaction is proposed to be coupled with naphtha reforming reactions. Hydrodealkylation (HDA) of toluene, which is a well-known petrochemical reaction, is discussed and is suggested as a potential exothermic reaction to be coupled with the endothermic naphtha reforming reactions. The first, the second, and the third reactor of the conventional naphtha reforming process have been substituted in three different cases by thermally coupled reactors and optimized parameters of the final case have been investigated. Considering lower operational costs due to the elimination of inter stage heaters, investigation of thermally coupled reactors has been the first priority of this research. The investigation shows that substitution of the first two reactors and, in the final case, all conventional reactors by the new configuration can improve the production yield of the aromatics by 14% and 21%, respectively compared with conventional naphtha reforming process. The final case has been optimized as well, and 45% and 11% improvement in aromatics and hydrogen production has been observed.     

Optimized Reliable Data Combining Cooperative Spectrum Sensing Method in Cognitive Radio Networks

Spectrum sensing is one of the most important tasks of each cognitive radio network. Cooperation among secondary users, by increasing the sensing accuracy can improve the network throughput, but also increases the energy consumption of cognitive radio network. In this paper, we propose the reliable data combining method for cooperative spectrum sensing, according to which the fusion center by using two threshold values, makes the final decision only if it is confident enough in validity of received local data. Otherwise, an additional sensing will be performed. Throughput maximization problems under interference constraints are formulated for both soft and hard fusion schemes and the optimal sensing time and threshold values are obtained. Simulations show that for all SNRs, higher absolute throughput and also higher throughput per energy consumption are accessible, rather than conventional cooperative sensing. Moreover, for a large range of SNRs the less energy is consumed.     

Experimental and Numerical Study of Turbulent Fluid Flow and Heat Transfer of Al2O3/Water Nanofluid in a Spiral-Coil Tube

Enhancement of heat transfer by nanofluids is reported by a large number of researchers. In this study, numerical and experimental investigation of heat transfer and flow characteristics of Al₂O₃/water nanofluid flowing in a spiral-coil tube is performed for various flow conditions. The spiral-coil tube is immersed horizontally in a hot water bath maintained at 60°C. Experiments are conducted in a turbulent flow regime using distilled water and nanofluid with 0.5%, 1%, and 1.5% particle volume concentrations. Also, a computational fluid dynamics methodology is used to simulate heat transfer and flow characteristics corresponding to the experimental measurements and for further flow conditions. Simulation results are compared with the experimental measurements, and 85% agreement between the results is observed. The results showed that convective heat transfer coefficient of nanofluid is enhanced up to 61% compared with that of the base fluid. Based on the experimental measurements, a new correlation is developed to predict convection heat transfer from nanofluids in spiral-coil tubes.     

Audio-visual emotion recognition using FCBF feature selection method and particle swarm optimization for fuzzy ARTMAP neural networks

Multimedia Tools and Applications - Humans use many modalities such as face, speech and body gesture to express their feeling. So, to make emotional computers and make the human-computer...