Generic closed loop controller for power regulation in dual active bridge DC-DC converter with current stress minimization

This paper presents a comprehensive and generalized analysis of the bidirectional dual active bridge (DAB) DC/DC converter using triple phase shift (TPS) control to enable closed loop power regulation while minimizing current stress. The key new achievements are: a generic analysis in terms of possible conversion ratios/converter voltage gains (i.e. Buck/Boost/Unity), per unit based equations regardless of DAB ratings, and a new simple closed loop controller implementable in real time to meet desired power transfer regulation at minimum current stress. Per unit based analytical expressions are derived for converter AC RMS current as well as power transferred. An offline particle swarm optimization (PSO) method is used to obtain an extensive set of TPS ratios for minimizing the RMS current in the entire bidirectional power range of - 1 to 1 per unit. The extensive set of results achieved from PSO presents a generic data pool which is carefully analyzed to derive simple useful relations. Such relations enabled a generic closed loop controller design that can be implemented in real time avoiding the extensive computational capacity that iterative optimization techniques require. A detailed Simulink DAB switching model is used to validate precision of the proposed closed loop controller under various operating conditions. An experimental prototype also substantiates the results achieved

Modular multilevel converter with modified half-bridge submodule and arm filter for dc transmission systems with DC fault blocking capability

Although a modular multilevel converter (MMC) is universally accepted as a suitable converter topology for the high voltage dc transmission systems, its dc fault ride performance requires substantial improvement in order to be used in critical infrastructures such as transnational multi-terminal dc (MTDC) networks. Therefore, this paper proposes a modified submodule circuit for modular multilevel converter that offers an improved dc fault ride through performance with reduced semiconductor losses and enhanced control flexibility compared to that achievable with full-bridge submodules. The use of the proposed submodules allows MMC to retain its modularity; with semiconductor loss similar to that of the mixed submodules MMC, but higher than that of the half-bridge submodules. Besides dc fault blocking, the proposed submodule offers the possibility of controlling ac current in-feed during pole-to-pole dc short circuit fault, and this makes such submodule increasingly attractive and useful for continued operation of MTDC networks during dc faults. The aforesaid attributes are validated using simulations performed in MATLAB/SIMULINK, and substantiated experimentally using the proposed submodule topology on a 4-level small-scale MMC prototype

Characterization of regulatory sequences in alternative promoters of hypermethylated genes associated with tumor resistance to cisplatin

The development of cisplatin resistance in human cancers is controlled by multiple genes and leads to therapeutic failure. Hypermethylation of specific gene promoters is a key event in clinical resistance to cisplatin. Although the usage of multiple promoters is frequent in the transcription of human genes, the role of alternative promoters and their regulatory sequences have not yet been investigated in cisplatin resistance genes. In a new approach, we hypothesized that human cancers exploit the specific transcription factor-binding sites (TFBS) and CpG islands (CGIs) located in the alternative promoters of certain genes to acquire platinum drug resistance. To provide a useful resource of regulatory elements associated with cisplatin resistance, we investigated the TFBS and CGIs in 48 alternative promoters of 14 hypermethylated cisplatin resistance genes previously reported. CGIs prone to methylation were identified in 28 alternative promoters of 11 hypermethylated genes. The majority of alternative promoters harboring CGIs (93%) were clustered in one phylogenetic subclass, whereas the ones lacking CGIs were distributed in two unrelated subclasses. Regulatory sequences, initiator and TATA-532 prevailed over TATA-8 and were found in all the promoters. B recognition element (BRE) sequences were present only in alternative promoters harboring CGIs, but CCAAT and TAACC were found in both types of alternative promoters, whereas downstream promoter element sequences were significantly less frequent. Therefore, it was hypothesized that BRE and CGI sequences co-localized in alternative promoters of cisplatin resistance genes may be used to design molecular markers for drug resistance. A more extensive knowledge of alternative promoters and their regulatory elements in clinical resistance to cisplatin is likely to usher novel avenues for sensitizing human cancers to treatment.Cancer Prevention and Research Institute of Texas (CPRIT; no. RP130266

Relationship between ethical corporate social responsibility and customer loyalty: the mediating role of customers’ gratitude

The purpose of this study was to examine whether customer gratitude mediates the association between ethical corporate social responsibility and customer loyalty. A cross-sectional survey was adopted. A total of 430 individual customers of retail banks located in some selected towns in north-east region of Nigeria were selected using convenience sampling. Structured questionnaires were used to collect. Descriptive statistics and partial least square structural equation modeling were used in data analysis. Finding showed that ethical corporate social responsibility positively and significantly affected customer loyalty. Also, a positive and significant effect of ethical corporate social responsibility on customer gratitude was observed. Furthermore, it was observed that customer gratitude and customer loyalty are positively associated. Also, customer gratitude mediated between ethical corporate social responsibility and customer loyalty. This study concluded that customer gratitude mediated the influence of ethical corporate social responsibility on customer loyalty. The finding of this study will help managers of Nigerian retail banks to develop ethical corporate social practices which strongly create feelings of gratitude among their banks’ customers in order to take advantage of customers’ gratitude, and eventually cultivate customers’ loyalty

A study on Prevalence of Drug Resistance in Drug Default Pulmonary Tuberculosis

Background: The emergence of resistance to drugs used to treat tuberculosis (TB), and particularly multidrug-resistant TB (MDR-TB), has become a significant public health problem in a number of countries and an obstacle to effective global TB control.Method: This is a prospective randomized cross sectional study to estimate the magnitude of MDR tuberculosis in two hospitals in Khartoum, Sudan. 111 patients who had defaulted their tuberculosis treatment on previous occasions and had presented to the hospital with several symptoms were studied. All patients provided sputum, which was examined for the presence of acid fast bacilli (AFB) by Ziehl- Neelsen stain. Sputa were also sent to the reference laboratory for mycobacterial culture and drug susceptibility testing. All culture positive sputa had drug sensitivity tested to the first line anti-TB drugs used in Sudan namely Streptomycin, Isoniazid, Rifampicin and Ethambutol.Results: Out of the 111 patients, 29.7% (n=33) were AFB sputum smear positive and 40.5% (n=45) were sputum culture positive for  mycobacterium. Sensitivity testing revealed that 48.9% (n=22) were resistant to Streptomycin, 62.2% (n=28) were resistant to Isoniazid, 55.6% (n=25) were resistant to Rifampicin and 37.8% (n=17) were resistantto Ethambutol. 42% ( n=19) of the patients were resistant to Rifampicin and Isoniazid only, while 26.6% (n=12) were resistant to all the first line drugs (Streptomycin, Isoniazid, Rifampicin and Ethambutol).Conclusion: This study showed that the prevalence of MDR tuberculosis among the defaulters in Khartoum is much higher than what was reported previously. This study highlights the extent of the problem of drug resistance in Khartoum and emphasises the need for proper treatment andstrengthening of the short course direct observed therapy strategy

An Enhanced Adaptive Learning System based on Microservice Architecture

This study aims to enhance Adaptive Learning Systems (ALS) in Petroleum Sector in Egypt by using the Microservice Architecture and measure the impact of enhancing ALS by participating ALS users through a statistical study and questionnaire directed to them if they accept to apply the Cloud Computing Service “Microservices” to enhance the ALS performance, quality and cost value or not. The study also aims to confirm that there is a statistically significant relationship between ALS and Cloud Computing Service “Microservices” and prove the impact of enhancing the ALS by using Microservices in the cloud in Adaptive Learning in the Egyptian Petroleum Sector. After developing and strengthening the ALS using the cloud computing with the benefits of using Function as a Services “FaaS”, the functions are start rapidly in order to allow handling of individual requests by using the Microservice Architecture. This study includes a description of the statistic field study approach (The study’s community and its sample. As well as used tools, methodologies, and their validity and reliability. It also includes used procedures for tools codification and their application. Finally, statistical processes that were relied upon in study analysis)

Modified dual active bridge DC/DC converter with improved efficiency and interoperability in hybrid LCC/VSC HVDC transmission grids

DC transmission grids are the promising electrical networks in the near future especially with the high penetration of large scale renewables. This paper proposes a modified version of the dual active bridge (DAB) DC/DC converter with AC link capacitors generating reactive power to compensate for non-active power consumption; hence mitigating current stresses and losses to improve efficiency. The proposed topology also enables the connectivity of current source line-commutated HVDC and voltage source HVDC technologies particularly during power reversal; a feature which conventional DAB is incapable of doing. Analysis and detailed design of the proposed converter are addressed and a comparative performance analysis is carried out with conventional DAB. Converter principle of operation is explained and Matlab/Simulink simulations are carried out to verify converter operation particularly under adverse conditions such as rated power reversal and DC fault conditions. A low scale prototype substantiates the theoretical analysis and simulation results

Zeolite/polyaniline based self-healing and silicon oxide coatings for microbially induced corrosion inhibition

Microbially induced corrosion (MIC) occurs due to the presence of microorganisms such as bacteria, which form biofilms on the metal surface that can cause corrosion. Among the different methods that have been used to protect against MIC, coating has gained more attention because of its ease of application, low-cost and high effectiveness. Recent research has shown that self-healing coatings concept based on releasing healing agent when micro-cracks are initiated in the coating surface and hydrophobic silicon oxide based organic and inorganic coatings have great potential for use as antifouling coating. The aim of this research is to investigate the effects of self-healing and silicon oxide (SiO) coatings on inhibiting MIC in saline environment. The self-healing coating was prepared via interfacial polymerization of zeolite, polyaniline, and zeolite/polyaniline composite and then encapsulated with urea fomaldehyde as a shell material to form the microcapsules and embedded in epoxy to form coating material which was applied on mild steel substrate. The SiO coating, on the other hand, was deposited on mild steel substrate using radio frequency (RF) magnetron sputtering physical vapor deposition (PVD) method with different parameters of RF power, temperature, pressure and deposition time in order to achieve optimum parameters based on minimum surface roughness and good adhesion. The surface topography and roughness were examined by atomic force microscope (AFM), while the thickness and morphology of the coatings were observed using field emission scanning electron microscope (FESEM) equipped with energy dispersive spectrometer (EDS). The adhesion test was performed using nano scratch test for SiO coating and Pull off test for self-healing coating and supported by Rockwell C test. The corrosion behavior was investigated through salt spray test for 28 days and immersion tests in nutrient rich simulated seawater (NRSS) medium with pseudomonas aeruginosa bacteria for 70 days. The Tafel electrochemical test and electrochemical impedance spectroscopy (EIS) was performed on both bare and coated steel samples. AFM results clearly revealed that by varying the sputtering parameters has a strong influence on the surface roughness of the deposited SiO coating in which its thickness varied between 30 nm to 50 nm. The thickness for self-healing coating was between 50 μm to 175 μm. From the adhesion results, both coating methods produced superior adhesion on steel substrates. Fourier transform infrared spectroscopy (FTIR) results show the successful encapsulation of the three synthesized materials. The total self-healing occurred after the release of the core material when the capsule was ruptured after 21 days left at room temperature. The specimen exposed in salt spray chamber exhibited excellent corrosion resistance for all investigated coating materials, while, the specimens immersed in NRSS medium with pseudomonas aeruginosa bacteria showed varying anti-corrosion properties. Tafel results show that the lowest corrosion rate was observed for SiO coating with a value of 0.219 mm/yr, followed by encapsulated zeolite/polyaniline composite self-healing embedded in epoxy of 0.334 mm/yr. EIS results show that among all the coatings, encapsulated zeolite/polyaniline composite self-healing embedded in epoxy coating has the highest impedance modulus (Z) at a frequency of 0.01 of 7800 ohms. In conclusion, zeolite/polyaniline composite self-healing coating is the best among all the coating materials which shows superior anticorrosive and MIC inhibition property

Single-stage ac–dc buck–boost converter for medium-voltage high-power applications

This study proposes three topologies based on single-stage three-phase ac-dc buck-boost converters suitable for medium-voltage high-power applications. The first two topologies are based on a dual three-phase buck-boost converter, with a three-winding phase-shifted transformer to achieve sinusoidal input currents, with relatively small ac filters. The limitation of these two topologies is the switching devices are exposed either to a high voltage beyond that tolerable by a single device. The third topology is based on three single-phase buck-boost converters; with their dc output terminals connected in series to generate high voltage. By using this approach, voltage stresses on the switching devices are greatly reduced, and sinusoidal input currents with nearly unity power factor is achieved over the entire operating range when using small ac filters. Analysis, PSCAD/EMTDC simulations and experimentation are used to assess the feasibility of the proposed topologies during normal operation. Major findings of this study are discussed and summarised as a comparison between the three topologies