A rational method for determining intermittency in the transitional boundary layer

A new rational procedure is proposed for determining the intermittency in the streamwise direction. One of the key parameters for the intermittency determination is the selection of a threshold value, which often involves a certain level of subjectivity. Here, a reliable way of choosing the threshold value in a more objective manner is proposed. The proposed approach involves a single threshold value, equal to the magnitude of the maximum laminar perturbation in the transitional flow. The results obtained are validated with the widely used dual-slope method. In this paper, the measurements are carried out on an experimental arrangement, involving the interaction of an upstream aerofoil wake with a downstream flat plate boundary layer. As a by-product of the study, a scaling parameter has been identified which captures the length of the transition zone as the proximity of the aerofoil in the wall-normal direction is varied

The Influence of Social Networking on Lifestyle: A Higher Education Perspective

Social networks have become a way of life for many people who use them to connect and communicate with the world at large. Social media is defined as any tool or service that uses the Internet to facilitate conversations. Facebook is one of the most popular social networking sites (SNSs) and has a total of 55 million active users worldwide with an average of 250000 new registrations per day. After Yahoo, MySpace and Google, Facebook is also the fourth most popular SNS in South Africa. The purpose of the paper was to determine whether social networks have an influence on higher education students’ lifestyles and behaviour. This research was descriptive and quantitative in nature. The sample comprised 386 students studying at the Durban University of Technology (DUT). The results indicated that the majority of the respondents preferred Facebook as their social network of choice. More than half of the respondents indicated that they access their preferred social network five times or more per day. The majority of the respondents agreed that social networks allow for global interaction and that maintaining relationships has become easier with social networking

The Influence of Social Networking on Lifestyle: A Higher Education Perspective

Abstract: Social networks have become a way of life for many people who use them to connect and communicate with the world at large. Social media is defined as any tool or service that uses the Internet to facilitate conversations. Facebook is one of the most popular social networking sites (SNSs) and has a total of 55 million active users worldwide with an average of 250000 new registrations per day. After Yahoo, MySpace and Google, Facebook is also the fourth most popular SNS in South Africa. The purpose of the paper was to determine whether social networks have an influence on higher education students' lifestyles and behaviour. This research was descriptive and quantitative in nature. The sample comprised 386 students studying at the Durban University of Technology (DUT). The results indicated that the majority of the respondents preferred Facebook as their social network of choice. More than half of the respondents indicated that they access their preferred social network five times or more per day. The majority of the respondents agreed that social networks allow for global interaction and that maintaining relationships has become easier with social networking

Overview of the use of hydrocarbon refrigerants in air conditioning systems

efrigerant used in air conditioning and refrigeration (ACR) industries has come to a full circle since the beginning of the industrial revolution. With concerns on issues relating to the environment, such as the global warming and climate change, caused by the use of harmful gases as refrigerants. Therefore, it is of outmost importance to mankind, to find suitable alternative gases as refrigerants, which are not detrimental to the ozone layer and does not adversely affect the climate. In view of this, hydrocarbons (HC) which were previously used as refrigerants are being reintroduced gradually because its lower GWP and which does not inhibit ozone layer, as replacement refrigerants. ACR industry players have blended in by introducing some new equipment and components that specifically designed for HC use. Malaysia too has targeted a 10 % reduction in hydrochlorofluorocarbons (HCFC) consumption, commencing in 2016; with the banning of ACR equipment of 7.03 kW and below from using HCFC 22 [chlorodifluoromethane, (CHClF2)]. Instead, hydrofluorocarbon (HFC) 410a [50 % difluoromethane (CH2F2) and 50 % pentafluoroethane (CHF2CF3)] is being introduced as replacement for HCFC 22. In fact, in other countries, the use of HFC, has already been phased down. HC has good potential to replace HCFC completely as refrigerant in the future; its performance, matches that of HCFC and the flammability issue can be overcome, with the use of effective and safety enhanced design. Their use can be facilitated further with the adaptation of a specific standard and by proper enacted legislation

Hydrocarbons as refrigerants-a review

Refrigerants used in air conditioning and refrigeration (AC&R) industries have come full circle since the beginning of the industrial revolution. With concern on issues relating to the environment such as the global warming and climate change issues, we should find a better alternative than to continue using these refrigerants that cause global warming and ozone depletion. AC&R industry players have blended in by introducing some new equipment and components that are specifically designed for hydrocarbon (HC) use. Most new refrigerators sold in Malaysia are already equipped with isobutane [a hydrocarbon designated as R-600a by the American Society of Heating, Refrigerating and Air- Conditioning Engineers (ASHRAE) standards] as refrigerants. Malaysia has ratified the Montreal Protocol and targetted a 10% reduction in hydrochlorofluorocarbon (HCFC) consumption, beginning 2016 with the banning of 2.5 horsepower (hp) and below in air-conditioning (AC) equipment to be used. Instead, hydrofluorocarbon (HFC) R-410a was introduced as a replacement for HCFC- 22, whereas in other countries this HFC has been phased down. This article was initiated because of the difficulty in finding a replacement for HCFC. Also, the possibilities of using HC as an alternative to replace HCFC instead of using HFC as a transitional refrigerant in place of HCFC is reviewed in this article. The performance of HC is very similar to HCFC and flammability issues could be easily overcome with the use of an effective design. Their use could be facilitated with the adaptation of specific standards and properly enacted legislation

Aerofoil wake-induced transition characteristics on a flat-plate boundary layer

This paper presents an experimental investigation of the characteristics of laminar– turbulent transition occurring on a flat-plate boundary layer due to the interaction with a non-impinging aerofoil wake. Previous studies have tended to focus on transition induced by free-stream turbulence or by the wake of a circular cylinder, both of which exhibit different forcing characteristics to the present experimental arrangement. A tripped NACA 0014 aerofoil was used to generate a fully turbulent wake, upstream of and at various heights above a laminar, flat-plate boundary layer, in the UK National Low-turbulence Wind Tunnel at City, University of London. Hot-wire measurements conducted in the pre-transitional region reveal the wall-normal and spanwise structure of the disturbances induced within the boundary layer and the rate of growth of disturbance energy. Disturbance profiles generally (but not uniquely) follow the non-modal distribution obtained from transient growth theory, but energy growth rates are mainly exponential rather than algebraic. Energy spectra demonstrate the existence of mixed transitional features (both natural and bypass) in the boundary layer. Two-point spatial correlations reveal the presence of a streaky structure, but with spanwise scale much larger than the boundary layer thickness, in contrast to the trends seen in free-stream turbulence-induced bypass transition and cylinder wake-induced transition. The gap between aerofoil and flat plate affects both the evolution of non-modal disturbance profile and the appearance of the streaky structure; the spacing of the streaks was also found to scale with the vertical gap between aerofoil and flat plate. Overall, the combination of observed characteristics is quite different from the forced transition mechanisms previously reported in the literature

Nucleon-Nucleon Interaction: A Typical/Concise Review

Nearly a recent century of work is divided to Nucleon-Nucleon (NN) interaction issue. We review some overall perspectives of NN interaction with a brief discussion about deuteron, general structure and symmetries of NN Lagrangian as well as equations of motion and solutions. Meanwhile, the main NN interaction models, as frameworks to build NN potentials, are reviewed concisely. We try to include and study almost all well-known potentials in a similar way, discuss more on various commonly used plain forms for two-nucleon interaction with an emphasis on the phenomenological and meson-exchange potentials as well as the constituent-quark potentials and new ones based on chiral effective field theory and working in coordinate-space mostly. The potentials are constructed in a way that fit NN scattering data, phase shifts, and are also compared in this way usually. An extra goal of this study is to start comparing various potentials forms in a unified manner. So, we also comment on the advantages and disadvantages of the models and potentials partly with reference to some relevant works and probable future studies.Comment: 85 pages, 5 figures, than the previous v3 edition, minor changes, and typos fixe

Absence of carious lesions at margins of glass-ionomer cement and amalgam restorations: An update of systematic review evidence

<p>Abstract</p> <p>Background</p> <p>This article aims to update the existing systematic review evidence elicited by Mickenautsch et al. up to 18 January 2008 (published in the European Journal of Paediatric Dentistry in 2009) and addressing the review question of whether, in the same dentition and same cavity class, glass-ionomer cement (GIC) restored cavities show less recurrent carious lesions on cavity margins than cavities restored with amalgam.</p> <p>Methods</p> <p>The systematic literature search was extended beyond the original search date and a further hand-search and reference check was done. The quality of accepted trials was assessed, using updated quality criteria, and the risk of bias was investigated in more depth than previously reported. In addition, the focus of quantitative synthesis was shifted to single datasets extracted from the accepted trials.</p> <p>Results</p> <p>The database search (up to 10 August 2010) identified 1 new trial, in addition to the 9 included in the original systematic review, and 11 further trials were included after a hand-search and reference check. Of these 21 trials, 11 were excluded and 10 were accepted for data extraction and quality assessment. Thirteen dichotomous datasets of primary outcomes and 4 datasets with secondary outcomes were extracted. Meta-analysis and cumulative meta-analysis were used in combining clinically homogenous datasets. The overall results of the computed datasets suggest that GIC has a higher caries-preventive effect than amalgam for restorations in permanent teeth. No difference was found for restorations in the primary dentition.</p> <p>Conclusion</p> <p>This outcome is in agreement with the conclusions of the original systematic review. Although the findings of the trials identified in this update may be considered to be less affected by attrition- and publication bias, their risk of selection- and detection/performance bias is high. Thus, verification of the currently available results requires further high-quality randomised control trials.</p

Neutron-diffraction studies of amorphous CNx materials

The results of neutron-diffraction experiments performed on two samples of amorphous CNx, with nitrogen concentrations of 5 and 30 at. %, prepared by a combination of filtered cathodic are and Kaufman-type ion source, are presented. Increasing the N content of the samples is seen to cause a decrease of the average bond length and the first coordination number. An increase in the average bond angle from 113 degrees to 121 degrees is also observed. The pair-distribution functions indicate that N incorporation results in some transformation of sp(3) C sites to sp(2) sites, but there is no evidence for N inducing the formation of crystalline graphitic clusters, and the overall structure remains amorphous. A direct subtraction of the two data sets emphasizes the loss of sp(3) bonds and the increasing sp(2) character of the higher-N-content sample, and shows the occurrence of a variety of bonding environments for N. More limited information on second neighbor correlations involving N is also revealed

Bone Morphogenetic Protein (BMP)-7 expression is decreased in human hypertensive nephrosclerosis

Background: Bone Morphogenetic Protein (BMP)-7 is protective in different animal models of acute and chronic kidney disease. Its role in human kidneys, and in particular hypertensive nephrosclerosis, has thus far not been described. Methods: BMP-7 mRNA was quantified using real-time PCR and localised by immunostaining in tissue samples from normal and nephrosclerotic human kidneys. The impact of angiotensin (AT)-II and the AT-II receptor antagonist telmisartan on BMP-7 mRNA levels and phosphorylated Smad 1/5/8 (pSmad 1/5/8) expression was quantified in proximal tubular cells (HK-2). Functional characteristics of BMP-7 were evaluated by testing its influence on TGF-b induced epithelial-to-mesenchymal transition (EMT), expression of TGF-b receptor type I (TGF-bRI) and phosphorylated Smad 2 (pSmad 2) as well as on TNF-a induced apoptosis of proximal tubular cells. Results: BMP-7 was predominantly found in the epithelia of the distal tubule and the collecting duct and was less abundant in proximal tubular cells. In sclerotic kidneys, BMP-7 was significantly decreased as demonstrated by real-time PCR and immunostaining. AT-II stimulation in HK-2 cells led to a significant decrease of BMP-7 and pSmad 1/5/8, which was partially ameliorated upon co-incubation with telmisartan. Only high concentrations of BMP-7 (100 ng/ml) were able to reverse TNF-a-induced apoptosis and TGF-b-induced EMT in human proximal tubule cells possibly due to a decreased expression of TGF-bRI. In addition, BMP-7 was able to reverse TGF-b-induced phosphorylation of Smad 2. Conclusions: The findings suggest a protective role for BMP-7 by counteracting the TGF-b and TNF-a-induced negative effects. The reduced expression of BMP-7 in patients with hypertensive nephrosclerosis may imply loss of protection and regenerative potential necessary to counter the disease