An exact analytical solution for convective heat transfer in rectangular ducts     

Mohammad Mohsen Shahmardan  Mahmood Norouzi  Mohammad Hassan Kayhani  Amin Amiri Delouei 《浙江大学学报(A卷英文版)》2012,13(10):768-781

An exact analytical solution is obtained for convective heat transfer in straight ducts with rectangular cross-sections for the first time. This solution is valid for both H1 and H2 boundary conditions, which are related to fully developed convective heat transfer under constant heat flux at the duct walls. The separation of variables method and various other mathematical techniques are used to find the closed form of the temperature distribution. The local and mean Nusselt numbers are also obtained as functions of the aspect ratio. A new physical constraint is presented to solve the Neumann problem in non-dimensional analysis for the H2 boundary conditions. This is one of the major innovations of the current study. The analytical results indicate a singularity occurs at a critical aspect ratio of 2.4912 when calculating the local and mean Nusselt numbers.  相似文献   

Numerical study of the melting of nano-enhanced phase change material in a square cavity     

Seyed Sahand SEBTI  Mohammad MASTIANI  Hooshyar MIRZAEI  Abdolrahman DADVAND  Sina KASHANI  Seyed Amir HOSSEINI 《浙江大学学报(A卷英文版)》2013,14(5):307-316

A comprehensive numerical study was conducted to investigate heat transfer enhancement during the melting process in a 2D square cavity through dispersion of nanoparticles. A paraffin-based nanofluid containing various volume fractions of Cu was applied. The governing equations were solved on a non-uniform mesh using a pressure-based finite volume method with an enthalpy porosity technique to trace the solid-liquid interface. The effects of nanoparticle dispersion in a pure fluid and of some significant parameters, namely nanoparticle volume fraction, cavity size and hot wall temperature, on the fluid flow, heat transfer features and melting time were studied. The results are presented in terms of temperature and velocity profiles, streamlines, isotherms, moving interface position, solid fraction and dimensionless heat flux. The suspended nanoparticles caused an increase in thermal conductivity of nano-enhanced phase change material (NEPCM) compared to conventional PCM, resulting in heat transfer enhancement and a higher melting rate. In addition, the nanofluid heat transfer rate increased and the melting time decreased as the volume fraction of nanoparticles increased. The higher temperature difference between the melting temperature and the hot wall temperature expedited the melting process of NEPCM.  相似文献   

Non-occupational lead exposure and hypertension in Pakistani adults     

Rahman S  Khalid N  Zaidi JH  Ahmad S  Iqbal MZ 《Journal of Zhejiang University. Science. B》2006,7(9):732-737

INTRODUCTION Blood-Pb levels are taken as representative of dose/exposure, as all clinical symptoms resulting from the toxic effects of Pb are manifested mainly in blood. Lead exposure of children correlates with de- creased IQ, symptoms of hyper kinesis or minima brain dysfunction, poor learning, or defects in specific neuromotor tasks (Landgrin et al., 1980). Large number of observations over the years has associated lead exposure with human diseases (McMichael and Johnson, 1982). Ca…  相似文献   

Identification of voltera kernels of a class of nonlinear systems by walsh function techniques     

Mohammad Maqusi 《Journal of The Franklin Institute》1980,310(1):65-75

This paper discusses the identification problem for a class of nonlinear systems. A member of this class may be represented by a single-valued power-law type nonlinearity preceded and succeeded by linear dyadic invariant systems. Such an arrangement allows for a Voltera functional series representation. The identification problem is then concerned with the specification of the associated Voltera kernels.Two approaches are presented for dealing with this problem. Both approaches are, however, based on Walsh function techniques. The first approach relies on direct output measurements when the input is a Walsh function. This approach is suitable for a deterministic case. The second approach assumes ergodic processes for the input. Based on measurements drawn from an input-output dyadic correlation function, determination of the Voltera kernels is made.  相似文献   

Implicit higher-order moment matching technique for model reduction of quadratic-bilinear systems     

Mian Mohammad Arsalan Asif  Mian Ilyas Ahmad  Peter Benner  Lihong Feng  Tatjana Stykel 《Journal of The Franklin Institute》2021,358(3):2015-2038

We propose a projection based multi-moment matching method for model order reduction of quadratic-bilinear systems. The goal is to construct a reduced system that ensures higher-order moment matching for the multivariate transfer functions appearing in the input-output representation of the non-linear system. An existing technique achieves this for the first two multivariate transfer functions, in what is called the symmetric form of the multivariate transfer functions. We extend this framework to an equivalent and simplified form, the regular form, which allows us to show moment matching for the first three multivariate transfer functions. Numerical results for three benchmark examples of quadratic-bilinear systems show that the proposed framework exhibits better performance with reduced computational cost in comparison to existing techniques.  相似文献   

The ethical attitudes of information technology professionals: a comparative study between the USA and the Middle East     

Luay Tahat  Mohammad I. Elian  Nabeel N. Sawalha  Fuad N. Al-Shaikh 《Ethics and Information Technology》2014,16(3):241-249

This paper aims at investigating comparatively the ethical orientation of information technology (IT) professionals in the Middle East and the United States. It tests for attitudes toward and awareness of ethically-related issues, namely intellectual property, privacy and other general ethical IT aspects. In addition, through a comparison between the two regions, this paper intends to examine whether differences in IT professional demographics and characteristics, including gender and academic level, have any impact on attitudes to business ethics. A t test is used to establish significant differences between the targeted samples, while an ANOVA F-test is conducted to determine significant differences among the sample countries on a group basis. The results show a general awareness of ethical issues concerning information technology, and no significant differences are found between the two samples. However, different ethical attitudes are reported among respondents in terms of their reactions to the targeted IT ethical aspects. On an individual sample basis, the results about gender support the claim that male and female respondents are different, while mixed results are revealed for the influence of academic level on attitudes towards IT ethics. For intellectual property, the results are significant regarding ethical attitude differences between Middle-Eastern professionals and their counterparts in the US, while no significance differences are reported in terms of privacy.  相似文献   

Adaptive pseudospectral methods for solving constrained linear and nonlinear time-delay optimal control problems     

Mohammad Maleki  Ishak Hashim 《Journal of The Franklin Institute》2014

In this paper, we first develop an adaptive shifted Legendre–Gauss (ShLG) pseudospectral method for solving constrained linear time-delay optimal control problems. The delays in the problems are on the state and/or on the control input. By dividing the domain of the problem into a uniform mesh based on the delay terms, the constrained linear time-delay optimal control problem is reduced to a quadratic programming problem. Next, we extend the application of the adaptive ShLG pseudospectral method to nonlinear problems through quasilinearization. Using this scheme, the constrained nonlinear time-delay optimal control problem is replaced with a sequence of constrained linear-quadratic sub-problems whose solutions converge to the solution of the original nonlinear problem. The method is called the iterative-adaptive ShLG pseudospectral method. One of the most important advantages of the proposed method lies in the case with which nonsmooth optimal controls can be computed when inequality constraints and terminal constraints on the state vector are imposed. Moreover, a comparison is made with optimal solutions obtained analytically and/or other numerical methods in the literature to demonstrate the applicability and accuracy of the proposed methods.  相似文献   

Bi-view semi-supervised active learning for cross-lingual sentiment classification     

Mohammad Sadegh Hajmohammadi  Roliana IbrahimAli Selamat 《Information processing & management》2014

Recently, sentiment classification has received considerable attention within the natural language processing research community. However, since most recent works regarding sentiment classification have been done in the English language, there are accordingly not enough sentiment resources in other languages. Manual construction of reliable sentiment resources is a very difficult and time-consuming task. Cross-lingual sentiment classification aims to utilize annotated sentiment resources in one language (typically English) for sentiment classification of text documents in another language. Most existing research works rely on automatic machine translation services to directly project information from one language to another. However, different term distribution between original and translated text documents and translation errors are two main problems faced in the case of using only machine translation. To overcome these problems, we propose a novel learning model based on active learning and semi-supervised co-training to incorporate unlabelled data from the target language into the learning process in a bi-view framework. This model attempts to enrich training data by adding the most confident automatically-labelled examples, as well as a few of the most informative manually-labelled examples from unlabelled data in an iterative process. Further, in this model, we consider the density of unlabelled data so as to select more representative unlabelled examples in order to avoid outlier selection in active learning. The proposed model was applied to book review datasets in three different languages. Experiments showed that our model can effectively improve the cross-lingual sentiment classification performance and reduce labelling efforts in comparison with some baseline methods.  相似文献   

What improves citizens’ privacy perceptions toward RFID technology? A cross-country investigation using mixed method approach     

Mohammad Alamgir Hossain  Yogesh K. Dwivedi 《International Journal of Information Management》2014

Privacy is a serious concern to radio frequency identification (RFID) technology. Worldwide, several companies scrapped RFID projects because of high resistance from consumers and their advocacy groups – which actually demand RFID-specific privacy policies. This concern is even more acute when RFID is used in public applications; because, in general case, citizens cannot refuse to provide data, and the data collected by a government agency would offer serious threats if are shared among third parties. Limited research has been performed in this specific issue; they all agree that perceived privacy increased RFID acceptance. But, what drives privacy perceptions are yet to be researched – this study closes this research gap. In order to conduct the current research, mixed method of research approach has been adopted. In the qualitative research stage, the authors conducted two focused-group discussion sessions and eight in-depth interviews in two different countries: Australia and Bangladesh; arguing that the status, and the perceptions and tolerance of the citizens on privacy are different in these two regions. The explored factors have been examined with empirical data obtained from these two countries. It is found that, there are distinct differences in perceptions in developed and developing countries. The detail findings offer practical suggestions to the agency managers so that they can ensure better privacy of the citizens. As a significant theoretical contribution, this study enhances existing literature identifying the antecedents of privacy, which play even different roles in different cultural backgrounds.  相似文献   

A micropillar array for sample concentration via in-plane evaporation     

Jae-Woo Choi  Seyyed Mohammad Hosseini Hashemi  David Erickson  Demetri Psaltis 《Biomicrofluidics》2014,8(4)

We present a method to perform sample concentration within a lab-on-a-chip using a microfluidic structure which controls the liquid-gas interface through a micropillar array fabricated in polydimethylsiloxane between microfluidic channels. The microstructure confines the liquid flow and a thermal gradient is used to drive evaporation at the liquid-gas-interface. The evaporation occurs in-plane to the microfluidic device, allowing for precise control of the ambient environment. This method is demonstrated with a sample containing 1 μm, 100 nm fluorescent beads and SYTO-9 labelled Escherichia coli bacteria. Over 100 s, the fluorescent beads and bacteria are concentrated by a factor of 10.  相似文献