84 research outputs found

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

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    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

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    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

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    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

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

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    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

    Enhanced performance modified discontinuous PWM technique for three phase Z-source inverter

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    Various industrial applications require a voltage conversion stage from DC to AC. Among them, commercial renewable energy systems (RES) need a voltage buck and/or boost stage for islanded/grid connected operation. Despite the excellent performance offered by conventional two-stage converter systems (DC-DC followed by dc-ac stages), the need for a single-stage conversion stage is attracting more interest for cost and size reduction reasons. Although voltage source inverters (VSIs) are voltage buck-only converters, single stage current source inverters (CSIs) can offer voltage boost features, although at the penalty of using a large DC-link inductor. Boost inverters are a good candidate with the demerit of complicated control strategies. The impedance source (Z-source) inverter is a high-performance competitor as it offers voltage buck/boost in addition to a reduced passive component size. Several pulse width modulation (PWM) techniques have been presented in the literature for three-phase Z-source inverters. Various common drawbacks are annotated, especially the non-linear behavior at low modulation indices and the famous trade-off between the operating range and the converter switches' voltage stress. In this paper, a modified discontinuous PWM technique is proposed for a three-phase z-source inverter offering: (i) smooth voltage gain variation, (ii) a wide operating range, (iii) reduced voltage stress, and (iv) improved total harmonic distortion (THD). Simulation, in addition to experimental results at various operating conditions, validated the proposed PWM technique's superior performance compared to the conventional PWM techniques

    Modified variable step-size incremental conductance MPPT technique for photovoltaic systems

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    A highly efficient photovoltaic (PV) system requires a maximum power point tracker to extract peak power from PV modules. The conventional variable step-size incremental conductance (INC) maximum power point tracking (MPPT) technique has two main drawbacks. First, it uses a pre-set scaling factor, which requires manual tuning under different irradiance levels. Second, it adapts the slope of the PV characteristics curve to vary the step-size, which means any small changes in PV module voltage will significantly increase the overall step-size. Subsequently, it deviates the operating point away from the actual reference. In this paper, a new modified variable step-size INC algorithm is proposed to address the aforementioned problems. The proposed algorithm consists of two parts, namely autonomous scaling factor and slope angle variation algorithm. The autonomous scaling factor continuously adjusts the step-size without using a pre-set constant to control the trade-off between convergence speed and tracking precision. The slope angle variation algorithm mitigates the impact of PV voltage change, especially during variable irradiance conditions to improve the MPPT efficiency. The theoretical investigations of the new technique are carried out while its practicability is confirmed by simulation and experimental results

    Qualitative traits of various Egyptian clover varieties under efficiency of bio-chemical phosphorus fertilization and lithovit regimes

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    Received: August 3rd, 2022 ; Accepted: October 19th, 2022 ; Published: November 1st, 2022 ; Correspondence: [email protected] investigation was performed at the Agriculture Research Station, Faculty of Agric. Zagazig Univ., Sharkia Governorate, Egypt, throughout the winter seasons of 2019/2020 and 2020/2021. The study aimed to evaluate the influence of ten bio-chemical fertilization and lithovit regimes on forage quality of 1st and 3rd cuts of various Egyptian clover varieties (Berseem, Trifolium alexandrinum L.) q.e. Helaly, Gemmeza 1, Sakha 4, Serw 1, Giza 6 and local variety. The ten fertilization regimes were F1, control; F2, chemical phosphorus 15.5 P2O5 kg fad-1 ; F3, bio-phosphorus fertilizer ‘phosphorein’; F4, 50% of F2 + phosphorein; F5, 25% of F2 + phosphorien; F6, F2 + lithovit; F7, F3 + lithovit; F8, F4 + lithovit; F9, F5 + lihtovit; F10, sole lithovit. Giza 6 Egyptian berseem variety ranked first in forage quality because of its high content of each CP (%), NFE (%), TDN (%), and DP (%) in the 3rd cut. The local berseem variety ranked the least over the six Egyptian clover varieties with the highest ash (%) in the 1st cut. Other varieties were in between. Allusion to the bio-chemical phosphorus fertilization and lithovit regimes, application of any phosphorus fertilization regimes surpassed the control treatment in most nutritive values. Application of F9 fertilization regime (25% chemical P + bio-fertilizer ‘phosphorien’ + nano-fertilizer ‘lithovit’) tended to produce high forage quality with high content of CP (%) in the 1st cut, TDN (%) in both 1st and 3rd cuts as well as DP (%) in the 1st cut

    Diffuse Large B-Cell Lymphoma Transformed from Mucosa-Associated Lymphoid Tissue Lymphoma Arising in a Female Urethra Treated with Rituximab for the First Time

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    A 30-year-old female patient presented to the gynecology clinic with a small (painless) swelling at the urethral orifice. She underwent surgical excision of the lesion. Pathological examination revealed non-Hodgkin's lymphoma of diffuse large B-cell type and mucosa-associated lymphoid tissue type, stage IE. The patient refused radiotherapy. Accordingly, we started CHOP-R chemotherapy. She received a total of 6 cycles of CHOP and 8 cycles of rituximab. Patient follow-up was done 3 months later through CT scan and cytoscopy confirming the complete remission. The patient has been disease-free for 4 years. We reviewed 26 cases of this rare entity reported previously

    Incidence and Outcome of the Radial Nerve Injury following Open Fracture of the Humerus

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    Background: Radial nerve injury is the most common peripheral nerve injury associated with humeral shaft fracture and can result in significant motor impairment of the arm and the wrist.Objectives: To evaluate the incidence, pattern and outcome of the radial nerve injury following open fracture of the humerus.Material and Methods: This is a multicentre cross-sectional descriptive study. It included all patients with radial nerve injuries following open fracture of the humerus presented to orthopaedic departments of the major hospitals in Khartoum State, Sudan during the period June 2009 - June 2013. Collected data were processed using SPSS computer package version 17.Result: A total of 48 patients were included, 34 males and 14 females (ratio 1.5: 1). Mean age ± standard error of mean of 30.71 ± 1.78 years (ranged 4 – 64 years). About 60.4% of injuries were due to gunshot and 24 (50.0%) patients were from conflict areas. Most of the injuries were in left side in about 68.8% of patients. The common patterns of the humeral fractures associated with radial nerve injury were open comminuted and transverse of middle or distal part. Neurapraxia was common type of radial nerve injury in about 89.6%. About 91.7% of the patients were treated conservatively and 81.3% of them recovered completely.Conclusions: Most of the radial nerve injuries following open fracture of the humerus were caused by gunshot injury in male soldiers mainly in the distal and middle parts. The fractures were mainly displaced comminuted and transverse types. The commonest type of radial nerve palsy was neurapraxia in 89.6% of cases. Most of the patients were treated conservatively and 81.3% of them recovered spontaneously after the first two months.Keywords: Neurapraxia, Repair, Recovery, Gun shot, Sudan
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