Photovoltaic Generators Interfacing a DC Micro-Grid: Design Considerations for a Double-Stage Boost Power Converter System

A photovoltaic generator (PVG) is usually connected to a DC micro-grid via a multi-stage-step-up power converter to improve system modularity, minimise shading effects and boost PVG voltage. Under varying operating conditions, the nonlinear characteristics of a PVG may affect performance of the entire PVG system. Further, if these issues are not properly taken into account at the design stage, significant changes in system dynamics may risk stability of the system. Therefore, it is important to understand interactions between a PVG and the rest of the system. A clear understanding of these interactions can help to set system design recommendations and guidelines. In particular, this paper explores the effects of a nonlinear PVG source interfacing a double-stage conventional boost converter connected to a DC bus. It addresses the impact of these effects on the design of both the power circuit and the control loops. Finally, this paper provides system design recommendations to ensure stability under varying operating conditions

Interest-Free Banking in Islamic Economics

This project investigates the possibility of the movement and proposals for establishing interest-free banking within the systems presently existing in the Muslim countries . which range from free enterprise in the western sense to socialist attempts. . This project takes as precepts the Islamic thought in economics; it does not occupy itself with their legal and ideological justification but rather it goes on to investigate their economic significance and implications . In other words , the Islamic economy is given by assumption in this project . Its purpose is to show how this economy works and how its major variables are determined, such variables as investment , savings , consumption . It focuses on the effects of such variables as are generated by the Islamic injunctions themselves. Before any economic analysis of the interest-free economy of Islam can be undertaken, the tremendous difference of thought among the radical and moderate thinkers is worth brief mention. The dispute is focused upon two points: whether there is any difference between consumption and production loans, and whether the rate of interest is to be considered or not. These two points are in reality merely the reflections of basic questions . Shall Muslims accept the status quo (i.e •• banking with interest) which exists in Muslim countries today with some few changes, or is this status quo as a whole , un-Islamic . requiring replacement by an Islamic system? Io the Islamic literature, one can hardly find any distinction between hoarding and saving . Both are considered as the same, and the literature does not make any distinction between whether the income saved is measured in money units and is concealed under the ground or in the bank\u27s vault as long as it is not put into the production process itself . The mere act of saving and depositing in a bank is an economically-negative action; therefore, it should be penalized rather than rewarded, and this is actually the case in Islam. The real productive act, from economic point of view, is the introduction of these savings into the production process in terms of capital, land or labor, and this act should have its reward, and so it is in Islam . This latter act is known as Mudarabah. The abolition of interest and the establishment of Mudaraan banks will not in any way decrease the propensity to save because savings are a function of income , and earnings making interest only a minor motive for saving. In the absence of interest, the possibility of making profits on the basis of participation with mudarabah banks or by buying government- owned industrial shares will serve the same purpose. Further more , the major portion of savings in modern industrial countries comes from institutional sources , irrespective of interest rate and not from individua ls . Above all, there will not be any very great need for liquid assets in an Islamic economy both because gambling houses , casinos and other luxurious unlawful things which create its demand will be prohibited and because of the general satisfaction and peace of mind people will experience as a result of the Islamic reforms. This discusses Chapter project consists of seven chapters. Chapter one Islam and economics. It deals with its methodology. two discusses Islam and other economic systems . It introduces the reader to the Islamic, capitalist, communist, and socialist economic systems. Chapter three discusses in detail the Islam economic development, and its policy implications . Chapter four introduces Riha and its transactions . It discusses Zakat Islam as an alternative . Chapter six Chapter five discusses Islamic discusses banking in banking in Muslim countries . And Chapter seven is a summary and conclusions

New Insights on Avoiding the Causes of Projects Delays: A Framework

In this paper, we study and analyze the reasons behind the delay of some projects. Our aim is shed light on how one reduces the effect of the different obstacles and improves achievement either in quality or time. Different challenges play the main reasons in the stalled project including planning, designing, construction, and weak leaders or poor administrative decisions. We focus on developing a framework that helps in improving the management of the projects and finishing the projects on time. This includes developing a contingency plan and coordination mechanism between internal and external stakeholders. Following the steps of the methodology will help project managers to avoid project delay and solve the problems of the staled ones. Finally, we represent some managerial insights and recommendations that related parties should follow with the projects

Variation in morphology and branching pattern of superior mesenteric artery

The anatomical variations of superior mesenteric artery branches are common. In this study we reported an extraordinary morphology and branching of superior mesenteric artery, during our routine dissection of a 38-year-old Sudanese male cadaver, where the superior mesenteric artery forms an arch over the confluence of inferior vena cava and left renal vein. Other variations observed were: 1) The superior mesenteric artery shares the same origin of coeliac trunk; 2) The unusual origin of right hepatic artery. We think that the knowledge of these variations plays an important role in conducting and planning of radiological and surgical procedures especially in hepatobiliary and pancreatic surgery. Morphology and branching patterns of this artery is anecdotic, which makes this case the most unique

Stress response and pathogenicity in Streptococcus pneumoniae

The pathogen Streptococcus pneumoniae encounters different levels of oxygen during the infection cycle including colonisation, pneumonia, bateraemia and meningitis. These different anatomical niches require high levels of genome changes to sense and respond to those external environmental stimuli. The bacterial gene expression is known to be affected by oxygen, and it must react properly for survival and for developing invasive pneumococcal desiseases (IPDs). Microarray techniques have allowed scanning the whole pneumococcal genome during growth in different tensions of oxygen mimicking in vivo conditions. It was found that oxygenated growth conditions have significantly elevated several key virulence genes. This was further confirmed with qRT-PCR for a selection of genes implicated in pathogenicity. Moreover, post-transcriptional stages have been also investigated such as protein production, biofilm formation, biological activities and adherence assays for several virulence factors performed under the effect of presence or absence of oxygen. The data illustrate that 420 out of 2,236 genes (17 % of the entire TIGR4 genome) were differentially expressed in the presence of oxygen compared to its absence. 262 genes (11 %) were over-expressed when pneumococci were grown in oxygenated conditions relative to transcriptional profile in anaerobic growth conditions, indicating the magnitude of roles played by oxygen on pneumococcal gene expression. Anaerobic growth of TIGR4 showed down-regulation of 158 genes (7 %). Oxygen modulates induction of ply, pspC and other seven genes involved in pili structuring subunits (rlrA, rrgA, rrgB and rrgC) and assembling enzymes (srtB, srtC and srtD). This may suggest that the pneumococcal population grown under atmospheric environment is equipped with greater capability to progress IPDs compared to anaerobically grown bacteria. In addition to this, pneumococcal adhesion in vitro for TIGR4 grown in oxygenated or anaerobic growth conditions revealed a significant increase in those grown in oxygenated growth conditions, indicating that oxygen may play a key role in bacterial-host attachment. Interestingly, ablation of pspC has resulted in similar adhesion percentages of TIGR4 grown under both conditions, oxygenated and anaerobic. Furthermore, several genes involved in metabolism were up-regulated in oxygenated environment, particularly transporters, which are considered highly important for a bacterium that lacks an electron transport chain, catalase and tricarboxylic acid. Additionally, the results showed phenotypic characterisation and changes in cells morphology from pneumococcal growth curves for several strainswith different genome backgrounds grown under different levels of oxygen concentrations. Further investigation of the pathogen biology revealed differences in pneumolysin production and activity. These findings highlight that virulence genes expression is induced once the micro-organism is exposed to oxygenated environment, and data analysis has demonstrated potential links between pneumococcal metabolism and their ability to cause diseases

Neutral point inverter controller using H infinity techniques

For applications in renewable energy and distributed generation, there is often a need to have a neutral line to provide a current path. This can be achieved by using a neutral-point circuit that consists of a conventional neutral leg and a split dc link. In this project, a H infinity (H∞ ) current controller is proposed to force the current flowing through the split dc link to be nearly zero so that the neutral-point current is stable, and then, a current control loop is added to eliminate the imbalance of the current so that the neutral-point current is balanced with respect to the dc terminals. This leads to very small deviations of the neutral point from the mid-point of the DC source, in spite of the possibly large neutral current. Simulation of inverter circuit, neutral-point and H infinity (H∞ ) has been performed using MATLAB/SIMULINK software. The simulation results confirm the validity of the proposed metho

PREPARATION OF CHITOSAN-TPP NANOPARTICLES: THE INFLUENCE OF CHITOSAN POLYMERIC PROPERTIES AND FORMULATION VARIABLES

Objective: The aim of this work was to prepare chitosan nanoparticles (CS NPs) using sodium tripolyphosphate (TPP) as crosslinker and to study the effect of chitosan polymeric properties and experimental conditions on the properties and stability of NPs.Methods: CS NPs were prepared by ionic gelation method, using TPP as a crosslinker. The particle size (PS), polydispersity index (PDI), zeta potential (ZP) and the morphologies of the NPs were studied. CS NPs prepared by varying the concentration of TPP, Chitosan molecular weight and its degree of deacetylation, the stirring speed, the rate of TPP addition and the freeze-drying method to study the effect of these variables on the NPs. The stability of the CS NPs was evaluated by storing aqueous suspensions of NPs and comparing the PS, PDI and ZP at the beginning and the end of the experiment.Results: This study shows that the PS, ZP and dispersity of the NPs depend on the chitosan polymeric properties and experimental conditions. The NPs sizes range between 145.73 and 724.23 nm. They all carried positive charges ranging between+4.32 and+43.67 mV. Most of the NPs have the same sizes after freeze-drying, but showed higher monodispersity and ZP, indicating higher stability. After twenty days of studying the stability, the NPs that had low ZP showed a large increment in size in comparison to the highly charged NPs.Conclusion: In conclusion, the polymeric properties and formulation variables in the ionic gelation method have a great influence on the CS NPs formed

Outdoor Assessment of Airborne Microorganisms During the COVID-19 Outbreak in Madinah City, KSA

The COVID-19 outbreak was a serious challenge for countries around the globe. With the objective of mitigating the spread of the virus, both national and international health organizations swiftly enacted quarantine measures across numerous cities around the globe. This presented a unique chance to evaluate the consequences of human actions on the quality of the air. This study aimed to investigate airborne microbial levels in different outdoor locations in Al-Madinah City, Kingdom of Saudi Arabia (KSA), during the COVID-19 pandemic by comparing lockdown against non-lockdown conditions. Twelve outdoor locations were investigated in terms of microbial total counts using the open plate method during and after the COVID-19 lockdown. Environmental factors that could affect the airborne microbial load, including humidity, temperature and wind speed, were recorded during the assessment. The means of the total colony-forming units (CFU) for each cubic meter (m3) of air were calculated. Lockdown restrictions caused significant decreases in the biological contaminants in all locations compared with the numbers after the pandemic. Gram-positive bacteria represented most of the samples, with fewer fungal strains detected. The outdoor average total bacterial counts ranged between 0.00±0.00-8337.50±248.98 CFU/m3, compared with 2903.75±407.60-19722.50±475.03 CFU/m3 after the pandemic. The mean concentrations of total fungi were lower than those of bacteria and ranged between 0.00±0.00-143.75±131.75 CFU/m3 during the COVID-19 lockdown and were elevated after the lockdown to reach 28.75±49.80-776.25±298.78 CFU/m3. Based on the available data, there are no studies comparing outdoor microbial counts during and after the COVID-19 pandemic. Therefore, this research offers additional perspectives on the air quality experienced amidst the COVID-19 pandemic and the subsequent implementation of lockdown measures and could serve as a valuable resource for monitoring and implementing measures to control air pollution

Nanocomposite-based dual enzyme system for broad-spectrum scavenging of reactive oxygen species

A broad-spectrum reactive oxygen species (ROS)-scavenging hybrid material (CASCADE) was developed by sequential adsorption of heparin (HEP) and poly(L-lysine) (PLL) polyelectrolytes together with superoxide dismutase (SOD) and horseradish peroxidase (HRP) antioxidant enzymes on layered double hydroxide (LDH) nanoclay support. The synthetic conditions were optimized so that CASCADE possessed remarkable structural (no enzyme leakage) and colloidal (excellent resistance against salt-induced aggregation) stability. The obtained composite was active in decomposition of both superoxide radical anions and hydrogen peroxide in biochemical assays revealing that the strong electrostatic interaction with the functionalized support led to high enzyme loadings, nevertheless, it did not interfere with the native enzyme conformation. In vitro tests demonstrated that ROS generated in human cervical adenocarcinoma cells were successfully consumed by the hybrid material. The cellular uptake was not accompanied with any toxicity effects, which makes the developed CASCADE a promising candidate for treatment of oxidative stress-related diseases