A maximum power point tracking for a photovoltaic system based on optimum sinusoidal modulated control pulses

Photovoltaic systems have grown rapidly in the last few decades. This growth has enhanced research about this technology, focusing on reducing cost and improving efficiency. Maximum power point tracking (MPPT), which increases the overall efficiency of a PV system, is a main part of a PV system. In this paper, some MPPT methods have been critically reviewed. Fractional open-circuit voltage has been investigated. The approach of a separate PV array to obtain the open circuit voltage (Voc) is adopted. The proposed idea in this paper is based on optimising the control pulses for the DC-DC converter. The generation of control pulses is based on sinusoidal modulated pulse width modulation (SPWM). The output from the DC-DC converter is then fed into a low frequency square wave voltage-fed inverter circuit. The output is a fine sinusoidal waveform, although the inverter operates at a low frequency. The block diagrams and the results are presented

Voltage regulation considerations for the design of hybrid distribution transformers

The future substation depends on finding a way to mitigate the effects of the drawbacks of the conventional legacy by employing the efficiency of the solid state switches [1]. This paper discusses the considerations of designing a distribution transformer that provides additional functions in regulating the voltage and controlling the reactive power that is injected in the distribution network, using a fractional rated converter attached partially with the windings of the transformer. This approach aims mainly to enhance the unit with more flexibility in controlling the voltage at the last mile of the network, in order to decrease the losses and meet the future expectations for low voltage networks modifications, and that by using a power electronic (PE) approach has less losses and more functionality (depending on the reliability of transformer and intelligence of PE). The design of a hybrid distribution transformer is detailed and its functionality in regulating the voltage is discussed as a combination between the features of one of the most reliable network devices, the transformer, and the effect of PE existence with less losses in both switching and conduction losses. Reduced ratings PE are used in this approach, whereby the solid state switches are controlled according to the immediate need for voltage control in low voltage (LV) networks

Usefulness of Φ-order kinetics for the investigation, characterisation and quantification of photodegradation processes

Φ-order kinetics has been shown to be the best tool to study photokinetics [1 – 6]. Various species have been studied using this approach including photochromes [1, 2] and drugs [3 – 6]. The unimolecular photodegradation processes of the form AB (1Φ) and photoreversible systems AB (2Φ), where A, the initial species phototransforms into a product B (A→B) which itself can return to A (A→B) via two distinct photoprocesses, each characterized each by an individual efficiency (Φ), have been mathematically described by integrated rate-law equations which express the so called 'Φ-order' kinetics [1 – 6]. The application of this novel approach was found to be useful to determine a number of photoreaction attributes. The reaction's photochemical quantum yield(s), the effects of initial species concentration, or the impact of competitive absorbers on the rate-constant of the photoactive species were all made readily accessible by simple methods. More importantly, the Φ-order kinetics has proven to facilitate the development of a wide range of actinometers from AB (1Φ) and AB (2Φ) systems [2 – 6]. This novel Φ-order kinetic method clearly has the potential for application in various fields including the photodegradation of natural products. The details of Φ-order elucidation kinetic methods will be discussed here and examples of application presented

The impact of corporate governance on major shareholdings : the case of Saudi Arabia

PhD ThesisThe aim of this thesis is to examine whether the Corporate Governance (CG) structure in potential investee companies in Saudi Arabia has an impact on major shareholders choices of shares. Scholars argue that good CG practices provide investors with more confidence to invest their wealth in capital markets especially in developing countries (McKinsey, 2000). Saudi Arabia embraces unique cultural, economic, social, religious settings and is characterised with a prevalent presence of major shareholders in the capital market that is accompanied by allegedly weak legal settings, which was observed after the infamous collapse of the Saudi capital market in February 2006 (Ramady, 2010; Al-Nodel and Hussainey, 2010; Al-Matari, Al-Swidi and Fadzil, 2012). In order to investigate the impact of corporate governance on major shareholdings in the Saudi capital market, a full review of the CG evolution in Saudi Arabia is presented and two sets of questions are identified to achieve the objectives of this thesis. To address the research questions, this thesis employs triangulation (i.e., mixed methods, quantitative and qualitative) and embraces agency theory as main theoretical framework. The quantitative assessment is performed using a panel data analysis of 97 non-financial listed companies in the Saudi capital market over the period from 2013 to 2017 (485 observations). The qualitative assessment is performed by conducting semi-structured interviews with fifteen participants of different categories of major shareholders within the Saudi capital market. Overall, the regression analysis has shown that total major shareholdings have a significant negative relationship with CG score. Some interviewees expressed similar views toward such mechanisms as they are believed to be responsible for the limitation of their power over investee firms. The results of regression analysis to each category of major shareholders have revealed that the only categories that are significantly related to CG is wealthy families (negative) and wealthy individuals (positive), which is also supported by the findings of the qualitative assessment. The qualitative assessment of the rest of major shareholders categories have provided mixed results concerning CG preferences. Few interviewees believe that some parts of CG structure of investee firms play a role during the decision-making of their investments. On the other hand, most interviewees have revealed that CG in general is not taken into consideration when making investment decisions. This explains the insignificant relationship between CG and most categories of major shareholders revealed by the regression analysis.The government of Saudi Arabia and Imam Abdulrahman Bin Faisal Universit

An Investigation of Health and Safety issues at Highway Construction sites in developing countries

Construction activities on the highway projects are key source of the safety risks to workers and motorists. Workplace fatalities and injuries have significantly reduced since 1970 after implementation of the Occupational Safety and Health Administration (OSHA) regulations. However, ergonomic injuries caused by ergonomic risk factors such as awkward or sustained posture, forceful exertion or stain, contract pressure, exposure to vibration, extreme heat or cold environment have major impact on the productivity and safety on the highway construction sites. The paper focuses on identifying the existing safety practices that aid to prevent ergonomic injuries at the highway construction sites. A comprehensive review of literature reveals that majority of workplace injuries and fatality victims are from the private employment whereas a very few injuries coming from the state or local government employees. The primary data was collected using questionnaire survey, interview and observations. Spreadsheet was used to analyse the collected data about the causes of workplace injuries and possible measures. The survey results reveal that the most of the injuries such as musculoskeletal disorders, strain and accidents transpired due to the collision with equipment and vehicle’s related incidents. Dump truck, tippers, motor graders and cars cause the frequently reported workplace injuries. The paper concludes that the use of Personal Protective Equipment (PPE), compliance to safety regulations, improving traffic control system and changing the culture of employers and employees are potential safety measures need to be adopted to mitigate the ergonomic workplace injuries in the highway construction projects particularly in the developing and least developed countries

An Effective Knowledge-Based Modeling Approach towards a “Smart-School Care Coordination System” for Children and Young People with Special Educational Needs and Disabilities

There is a significant need for a computer-aided modeling, effective information analysis and ontology knowledge base models to support both special needs children and care providers. As this research work correlated to the symmetry scope, it proposes an innovative generic smart knowledge-based “School Care Coordination System” (SCCS), which is established on a novel holistic six-layered data management model. The development of the Smart-SCCS adopts a methodology of ontology engineering to transform the given theoretical unstructured special educational needs and disabilities (SEND) code of practice into a comprehensive knowledge representation and reasoning system. The intended purpose is to deliver a system that can coordinate and bring together education, health and social care services into a single application to meet the needs of children and young people (CYP) with SEND. Moreover, it enables coordination, integration and monitoring of education, health and social care activities between different actors (formal, informal and CYP in the education sector) involved in the school care process network to provide personalized care interventions based on a predefined care plan. The developed ontology knowledge-based model has been proven efficient and solved the enormous difficulties faced by schools and local authorities on a daily basis. It enabled the coordination of care and integration of information for CYP from different departments in health, social care and education. The developed model has received significant attention with great feedback from all the schools and the local authorities involved, showing its efficiency and robustness

Pleiotropic Effects of Tetracyclines in the Management of COVID-19: Emerging Perspectives

Coronavirus disease 2019 (COVID-19) is a global infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Approximately 15% of severe cases require an intensive care unit (ICU) admission and mechanical ventilation due to development of acute respiratory distress syndrome (ARDS). Tetracyclines (TCs) are a group of bacteriostatic antibiotics, like tetracycline, minocycline, and doxycycline, effective against aerobic and anaerobic bacteria as well as Gram-positive and Gram-negative bacteria. Based on available evidences, TCs may be effective against coronaviruses and thus useful to treat COVID-19. Thus, this review aims to provide a brief overview on the uses of TCs for COVID-19 management. SARS-CoV-2 and other coronaviruses depend mainly on the matrix metalloproteinases (MMPs) for their proliferation, cell adhesion, and infiltration. The anti-inflammatory mechanisms of TCs are linked to different pathways. Briefly, TCs inhibit mitochondrial cytochrome c and caspase pathway with improvement of lymphopenia in early COVID-19. Specifically, minocycline is effective in reducing COVID-19–related complications, through attenuation of cytokine storm as apparent by reduction of interleukin (IL)-6, IL-1, and tumor necrosis factor (TNF)-a. Different clinical trials recommend the replacement of azithromycin by minocycline in the management of COVID-19 patients at high risk due to two main reasons: 1) minocycline does not prolong the QT interval and even inhibits ischemia-induced arrhythmia; 2) minocycline displays synergistic effect with chloroquine against SARS-CoV-2. Taken together, the data presented here show that TCs, mainly doxycycline or minocycline, may be potential partners in COVID-19 management, derived pneumonia, and related complications, such as acute lung injury (ALI) and ARDS.The authors thank all members of the College of Medicine, Al-Mustansiyria University. NC-M acknowledges the Portuguese Foundation for Science and Technology under the Horizon 2020 Program (PTDC/PSI-GER/28076/2017)