Ndiaye D.,9201 University City Blvd
Applied Thermal Engineering | Year: 2017
A transient model of a refrigerant-to-water helically coiled double tube with corrugations in the inner tube is developed. The refrigerant flows in the annulus, and a secondary fluid (water, glycol/water solution, etc.) flows in the inner tube. The model addresses both the single-phase and the two-phase flows of the refrigerant and the single-phase flow of the secondary fluid. Both the ON/OFF operation of the compressor and of the secondary fluid pump (at compressor shut-down, the pump may be ON or OFF) are considered. To deal with the lack of suitable friction factor and heat transfer correlations, a superposition principle that allows to combine the effects of the curvature of the heat exchanger and of the flutes in the inner tube is adopted. The finite volume method is used to numerically solve the governing equations. The developed model is experimentally validated and achieves reasonable agreement with the experimental data in both steady-state and transient conditions, in both the heating and the cooling modes. © 2016 Elsevier Ltd.
Ndiaye D.,9201 University City Blvd
Renewable and Sustainable Energy Reviews | Year: 2016
The literature on Direct-expansion ground-coupled heat pumps (DX-GCHP) is reviewed. Despite being potentially the most efficient vapor compression-based air conditioning system, DX-GCHPs are not very popular due to the numerous operational and design issues they are faced with: shortage of field studies, oil return to the compressor, expansion valve hunting, refrigerant flow mal-distribution in parallel loops, high pressure drops and gains in the ground heat exchanger, variable speed operation of the compressor, lack of reliable numerical models of the ground heat exchanger and of the whole system, and lack of generalized design guidelines. This paper addresses these issues and discusses possible solutions to them. © 2016 Elsevier Ltd
Ndiaye D.,9201 University City Blvd
Procedia Engineering | Year: 2015
A better design of solar systems by preliminary dynamic simulation enhances their viability. Available simulation tools like TRNSYS are often complex and require much experience. This study proposes a simplified simulation model of solar systems using evacuated tube collectors with a storage tank that may be stratified or not. Models were developed for the three main components of the solar loop: global irradiation, the collector, and the storage tank. The differential equations generated were solved using a prediction-correction algorithm. A computer program, JANT-BI, was developed to allow for the monitoring of the different levels of temperature in the whole system. JANT-BI can be used to evaluate the solar coverage rate for a given load and as a function of different design parameters, and so is suitable for both numerical simulation and optimal design. A case study of process steam generation with a non-stratified system revealed that the tank volume is inversely proportional to the overall performance of the system. It was also found that for a given collector area, a collector arrangement that favors parallels against series provides a better solar coverage rate. © 2015 The Authors. Published by Elsevier Ltd.
Wang Y.,9201 University City Blvd
International Journal of Communication Networks and Distributed Systems | Year: 2011
Distributed control systems (DCS) and supervisory control and data acquisition (SCADA) systems were developed to reduce labour costs, and to allow system-wide monitoring and remote control from a central location. Control systems are widely used in critical infrastructures such as electric grid, natural gas, water and wastewater industries. While control systems can be vulnerable to a variety of types of cyber attacks that could have devastating consequences, little research has been done to secure the control systems. American Gas Association (AGA), IEC TC57 WG15, IEEE, NIST and National SCADA Test Bed Program have been actively designing cryptographic standard to protect SCADA systems. American Gas Association (AGA) had originally been designing cryptographic standard to protect SCADA communication links and finished the report AGA 12 part 1. The AGA 12 part 2 has been transferred to IEEE P1711. This paper presents an attack on the protocols in the first draft of AGA standard (Wright et al., 2004). This attack shows that the security mechanisms in the first version of the AGA standard protocol could be easily defeated. We then propose a suite of security protocols optimised for SCADA/DCS systems which include: point-to-point secure channels, authenticated broadcast channels, authenticated emergency channels, and revised authenticated emergency channels. These protocols are designed to address the specific challenges that SCADA systems have. Copyright © 2011 Inderscience Enterprises Ltd.
Barcus H.R.,Macalester College |
Simmons L.,9201 University City Blvd
Professional Geographer | Year: 2013
Scholars have long documented widespread aging and depopulation of rural communities in the Great Plains. Paralleling these trends is the emergence, growth, and spatial dispersion of new and longtime non-white populations across the region. The dual processes of population loss in many counties combined with the growth of new, non-white population groups suggest that the ethnic structure of the population is changing. In this article we utilize choropleth maps, Hoover and Simpson indexes, and cluster analysis to assess whether the emergence and growth of ethnic minority groups in the Great Plains between 1970 and 2008 is a localized phenomenon or region-wide shift in the ethnic composition of the population. Results suggest that as depopulation is occurring in many counties of this region, the growth of non-white populations, both immigrant and native born, is changing or restructuring the ethnic composition of the Great Plains. © 2013 Copyright Taylor and Francis Group, LLC.
Stokes A.Q.,9201 University City Blvd
Journal of Public Relations Research | Year: 2013
This article employs a constitutive, or meaning-generating, approach to investigate how the Slow Food USA social movement employs public relations to counter commercial food industry messages. It argues that Slow Food successfully employs the rhetorical public relations techniques of definition, identification through narrative building, and enactment to build relationships and attract broader support of the sustainable food movement, to translate its somewhat lofty messages to mainstream audiences, and to encourage supporters to live the Slow Food lifestyle. Examining Slow Food's public relations through a rhetorical approach expands theory and practice by answering the call to explore how noncorporate entities successfully use public relations techniques. © 2013 Copyright Taylor and Francis Group, LLC.
Arrigo B.A.,9201 University City Blvd
British Journal of Criminology | Year: 2010
This paper conceptually examines one specific case of international terrorism, including the emergence and maintenance of membership-allegiance in its militant extremist group. This is the case of the Islamic Resistance Movement (or Hamas) and the manifestation of its corresponding Palestinian identity. Although the social person is constituted by symbols and objects, acts and social acts, meanings, and role-taking and role-making, questions persist about how best to promote peaceful coexistence, advance the interests of non-violence and ensure the protection of basic human rights. These practices constitute an ethic grounded in Aristotelian virtue. The delineation of key principles emanating from critical restorative justice helps to specify this brand of moral reasoning. The integration of these principles with the proposed symbolic interactionist framework demonstrates how extremist violence can be mediated. Suggestive examples of the same involving Hamas and those with whom it struggles (Palestine, Israel and the United States) are used to guide the analysis. The proposed conceptual framework is then briefly assessed for its overall explanatory capabilities, especially in relation to furthering terrorism studies. © The Author 2009.
Abdel-Aal H.A.,Arts et Metiers ParisTech |
Abdel-Aal H.A.,9201 University City Blvd
Journal of the Mechanical Behavior of Biomedical Materials | Year: 2013
One way of controlling friction and associated energy losses is to engineer a deterministic structural pattern on the surface of the rubbing parts (i.e., texture engineering). Custom texturing enhances the quality of lubrication, reduces friction, and allows the use of lubricants of lower viscosity. To date, a standardized procedure to generate deterministic texture constructs is virtually non-existent. Many engineers, therefore, study natural species to explore surface construction and to probe the role that surface topography assumes in friction control. Snakes offer rich examples of surfaces where topological features allow the optimization and control of frictional behavior. In this paper, we investigate the frictional behavior of a constrictor type reptile, Python regius. The study employed a specially designed tribo-acoustic probe capable of measuring the coefficient of friction and detecting the acoustical behavior of the skin in vivo. The results confirm the anisotropy of the frictional response of snakeskin. The coefficient of friction depends on the direction of sliding: the value in forward motion is lower than that in the converse direction. Detailed analysis of the surface metrological feature reveals that tuning frictional response in snakes originates from the hierarchical nature of surface topology combined to the profile asymmetry of the surface micro-features, and the variation of the curvature of the contacting scales at different body regions. Such a combination affords the reptile the ability to optimize the frictional response. © 2012 Elsevier Ltd.
He L.,9201 University City Blvd |
Evans C.J.,9201 University City Blvd |
Davies A.,9201 University City Blvd
Optics Express | Year: 2012
This paper describes the use of the area structure function (SF) for the specification and characterization of optical surfaces. A twoquadrant area SF is introduced because the one-quadrant area SF does not completely describe surfaces with certain asymmetries. Area SF calculations of simulation data and of a diamond turned surface are shown and compared to area power spectral density (PSD) and area autocorrelation function (ACF) representations. The direct relationship between SF, PSD, and ACF for a stationary surface does not apply to non-stationary surfaces typical of optics with figure errors. © 2012 Optical Society of America.
Webb J.B.,9201 University City Blvd |
Hardin A.S.,9201 University City Blvd
Eating Behaviors | Year: 2012
The present pilot investigation explored whether BMI status at college entry moderated changes in body composition and eating behavior in a sample of 134 first-time, first-year undergraduate females (40% Black/African American). Participants had their body measurements [i.e. weight, BMI, hip and waist circumference (WC), percent body fat (PBF)] assessed and completed self-report measures of binge eating, night eating, and intuitive eating at both the beginning of the fall and the beginning of the spring semesters of their first year. Results for the 83 completers revealed that overweight/obese students (N = 28) experienced greater gains in weight (p < 0.05), BMI (p < 0.05), and a trend towards increased WCs (p < 0.06) across the first college semester relative to their underweight/normal weight peers (N = 55). Night eating increased (p < 0.05) and intuitive eating declined (p < 0.05) over time in the full sample. Overweight/obese participants indexed greater binge eating scores (p < 0.001) and lower intuitive eating scores (p < 0.01) irrespective of time. Most anthropometric findings were diminished while all eating behavior estimates were retained in subsequent models adjusted for parental income. Preliminary results call attention to the need for continued elucidation of the roles of socioeconomic and regional diversity in affecting both the prevalence of overweight/obesity and the relationship between higher weight and body composition changes among first-year college women. Findings also provide tentative behavioral targets for college wellness programming that may prove useful in promoting healthy weight management while acclimating to the college environment. © 2012 Elsevier Ltd.