An exact analytical solution for convective heat transfer in rectangular ducts

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.     

Understanding Quantum Numbers in General Chemistry Textbooks

Quantum numbers and electron configurations form an important part of the general chemistry curriculum and textbooks. The objectives of this study are: (1) Elaboration of a framework based on the following aspects: (a) Origin of the quantum hypothesis, (b) Alternative interpretations of quantum mechanics, (c) Differentiation between an orbital and electron density, (d) Differentiation and comparison between classical and quantum mechanics, and (e) Introduction of quantum numbers based on electron density; (2) Formulation of five criteria based on the different aspects (a, b, c, d, and e), and (3) Evaluation of 55 freshman college‐level general chemistry textbooks. Results obtained show: Criterion 1, none of the textbooks described satisfactorily that Planck’s role in the origin of the quantum hypothesis was more at the level of an empirical adjustment, whereas Einstein provided the physical significance of the quantum hypothesis; Criterion 2, few textbooks (two satisfactory and four mentioned) included alternative interpretations of quantum mechanics (e.g., Bohm) and thus ignored that most theories are underdetermined by experimental evidence; Criterion 3, none of the textbooks described satisfactorily that orbitals are mathematical constructs and the shapes of the orbitals (s, p, d, f) are not derived from quantum mechanics but instead from electron density measurements; Criterion 4, although, quantum mechanics approaches classical mechanics as a limiting case, none of the textbooks presented a framework to facilitate transition in student understanding from classical to quantum mechanics (28 textbooks made a simple mention); and Criterion 5, few textbooks (one satisfactory, five mentioned) facilitated the introduction of quantum numbers based on experimental determination of electron density (photoelectron spectrum). It is concluded that the inclusion of these criteria in textbooks can facilitate students’ conceptual understanding of quantum numbers and electron configurations.     

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

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.     

Non-occupational lead exposure and hypertension in Pakistani adults

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…     

Whither constructivism?—A chemistry teachers’ perspective

Constructivism in science education has been the subject of considerable debate in the science education literature. The purpose of this study was to facilitate chemistry teachers’ understanding that the tentative nature of scientific knowledge leads to the coexistence and rivalries among different forms of constructivism in science education. The study is based on 17 in-service teachers who had registered for a 11-week course on ‘Epistemology of Science Teaching’ as part of their Master's degree program. The course is based on 17 readings drawing on nature of science and a critical evaluation of constructivism. Course activities included written reports, classroom discussions based on participants’ presentations and written exams. Based on the results obtained, it is plausible to suggest that participant teachers experienced the following transitions leading to greater understanding, as they acquired experience with respect to constructivism: (a) Active participation of students as a pre-requisite for change; (b) Different forms of constructivism represent competing and conflicting interpretations of progress in science; (c) Acceptance of the present state of constructivism as a Kuhnian paradigm; (d) Social constructivism as the preferred form of constructivism; (e) Critical appraisal of social constructivism; (f) Despite its popularity, social constructivism does not constitute a Kuhnian paradigm (due to controversies, there is no consensus in the science education community); (g) Contradictions faced by constructivism in science education provide the base for its advance and evolution towards more progressive forms, and hence the need to consider, whither constructivism?     

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

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.     

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

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.     

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

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.     

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

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.     

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

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.