Experimental Investigation of the Melting Behavior and the Transient Heat Transfer in a Phase Change Material (PCM)

Phase change materials (PCMs) used in thermal energy storage (TES) system as heat storage media can play crucial role in various engineering applications. PCMs have the inherent ability to store large amount of heat by exploiting their heat of fusions, predominantly during their solid-liquid phase-change period. The present study reports an experimental investigation on the melting process in a PCM and the associated heat transfer in a transient manner. The experiments were conducted in a rectangular chamber filled with paraffin wax used as the PCM and, a cylindrical copper tube with different geometries and orientations as the heat source. The simultaneously recorded temperatures and the images enabled to analyze the spatio-temporal behavior of the PCM during melting and provided a platform to characterize various important thermophysical parameters associated with the phase transition process. The results show a nonlinear melting rate of the PCM and a wavy and non-uniform profile of the solid-liquid interface. The results also show the development of convective motions within the liquid PCM which influenced the local heat transfer coefficient in a transient manner and is believed to have immensely influenced the nature of this distinctive and non-linear pattern of the solid-liquid interface. The convective heat transfer coefficient, h increased sharply at the early stage of melting, followed by a more gradual increment in h, which then became nearly steady when the melted fraction reached approximately two-third of the total PCM volume. The continuous change in the structures of the flow inside the convective cell is believed to have significantly influenced the heat transfer coefficient. The results enabled to characterize various important thermophysical correlations in non dimensionless form associated with the PCM during the melting process to comprehend the convective heat transfer behavior and to extend the understanding on the interface dynamics. These correlations were found to have similar trends compared to other empirical correlations found in the literature. On the other hand, most PCM suffer from the inherently common problem of low thermal conductivity which hampers in the heat transfer rates. This study also focused on the understanding of thermal conductive enhancement in PCM using nanoparticles with it. Results show a substantial improvements in various thermophysical parameters of the PCM with a small percentage of nanoparticles added

The performance of robust estimator on linear regression model having both continuous and categorical variables with heteroscedastic errors

The ordinary least squares (OLS) technique is often used in practice to estimate the parameters of a multiple linear regression model with both continuous and categorical variables. It has been the most popular technique due to its optimal properties and ease of computation. Nevertheless, in the presence of outliers, the OLS can result in very poor estimates. Outliers which arise from bad data points may have unduly effect on the OLS estimates. The problem is further complicated when both outliers and heteroscedasticity or non-constant error variances are present in the data. The influence of outliers and heteroscedasticity cannot be removed or reduced by simply transforming the data using known transformation such as logarithmic transformation. In this paper, we proposed a robust technique to deal with these two problems simultaneously. A robust estimate of scales for each level of categorical variables are first estimated by using robust distance S and M (RDSM) estimates. Then we determine the weighting scheme for each level of the categorical variables and transform the model. The reweighted least squares based on RDSM (RLSRDSM) is then applied to the transformed model. The empirical evidence shows that the proposed method has reduced the heteroscedastic effect to a greater extent

Wireless Networks (Attacks ‎‏–‏Security): A Review

يعد أمن الشبكات اللاسلكية جزءًا مهمًا ومؤثرًا وفعالًا في حماية الشبكات اللاسلكية من عمليات التطفل والثغرات الأمنية التي يسببها المتسللون والمهاجمون. أجرى هذا البحث مراجعة لمتطلبات أمان الشبكة اللاسلكية، بما في ذلك المصادقة والسرية والتوافر والنزاهة، بالإضافة إلى الهجمات ضد الشبكات اللاسلكية بناءً على هذه المتطلبات، وأبرزها هجوم الرجل في الوسط، والتنصت، وهجوم رفض الخدمة. بالإضافة إلى ذلك، تمت مراجعة بعض الخطوات التي من شأنها حماية وتأمين الشبكات اللاسلكية من هجمات المتطفلين.Wireless network security is an important, influential, and effective part of defending wireless networks from intrusions and security holes caused by hackers and attackers. This paper conducted a review of wireless network security requirements, including authentication, confidentiality, availability, and integrity, as well as attacks against wireless networks based on these requirements, most notably Man in the Middle Attack, Eavesdropping, and Denial of Service attack. In addition, some steps were reviewed that would protect and secure wireless networks from hacker attacks

Internet Characteristics and Online Alternative Dispute Resolution

Electronic commerce is important, and perhaps, inevitable. Thus, to consider the legal implications of the growth and development of electronic commerce is essential. However, the lack of suitable dispute resolution mechanisms in cyberspace will constitute a serious obstacle to the further development of electronic commerce. Bearing this in mind, this thesis argues that when Alternative Dispute Resolution (ADR) moves to cyberspace, particularly arbitration and mediation as the main types of ADR, the form of Online Alternative Dispute Resolution (OADR) can maximize the growth of e-commerce. This paper argues that the advent of the internet has created challenges and opportunities for dispute resolution mechanisms and particularly ADR. These challenges and opportunities are interconnected inexorably with each other and with internet characteristics. This paper concludes that a number of technical issues need to be addressed if there is to be a swift and successful deployment of OADR mechanisms in a cross-border environment. Some uncertainties remain due to technological limitations. Indeed, the growth of OADR is tied to the development of technology

Pearl Millet as an Alternative to Maize or Sorghum in the Diets of Broilers in Sokoto, Nigeria

The performance of broilers fed maize, sorghum or millet as sources of energy was studied for 8 weeks using two hundred and seventy six day-old chicks. The birds were randomly allocated to three treatment groups, each replicated four times such that each replicate had 23 chicks. The study was divided into two phases i.e. starter (0-4 weeks) and finisher (5-8 weeks). Three diets were formulated for each phase. Maize, sorghum or millet was used as the major source of energy in each of the three diets for each phase. Data on daily feed intake, weight gain and mortality were recorded. Feed conversion ratio was later calculated using feed intake and weight gain records. Results showed that at the starter phase, feed intake and weight gain of broilers fed pearl millet was significantly lower (P<0.05) than those fed maize or sorghum. Feed conversion ratio was also better (P<0.05) for broilers fed the two cereal grains compared to those fed pearl millet. At the finisher phase however, there was no significant difference (P>0.05) in all parameters monitored. This indicates that pearl millet may not particularly be as suitable as source of energy for broilers at the starter phase as maize or sorghum. It is however a good alternative to maize or sorghum for broilers in the finisher phase

The Case of Income Tax Evasion in Jordan: Symptoms and Solutions

The purpose of this paper is to examine income tax evasion in Jordan and set forth various cures for this problem.The paper investigates the phenomenon of income tax evasion. In doing so, the paper reviews reports from academics and statistics from the Income Tax Department. The paper begins with an overview of the Income Tax Law. The paper then distinguishes between tax evasion and tax avoidance and provides empirical data on the size of income tax evasion in Jordan. A study of article 42 of the Income Tax Law, the anti-tax evasion provision, is made. In the final analysis, the paper suggests several means that can be used to address income tax evasion

Effect of Three Medicinal Plants Extracts on the Growth of Some Yeasts

This study conducted to detect the effect of the ethanolic extracts for some medicinal plants on 16 yeast species isolated from the oral cavity of cancer patients, three plants which are  Lavandula angustifolia, Salvia officinalis and Syzygium aromaticum were used to study their inhibition  bioactivity and compare their effect with three antifungal drugs (Fluconazole, Ketoconazole and Nystatin), the results showed that Ethanolic extract of L. angustifolia exhibited antifungal bioactivity against all yeast species and revealed inhibition zones ranged from 16-36 mm. with highest effect on C. parapsilosis whereas the lowest effect was on species H. uvarum, while the ethanolic extract of S. officinalis and S. aromaticum showed inhibition zones 16-27 mm. and 17-31 mm. respectively, the results showed that the plants extracts having much more effect on the yeasts growth from the antifungal drugs. Keywords: yeasts, medicinal plants, Ethanolic extracts