Arm current reversal-based modular multilevel DC-DC converter

Nowadays, most of the converters used in high-power high-voltage (HV) applications are the conventional modular multilevel converters (MMC). However, in the case of DC-DC conversion, an imbalance of the capacitor voltages occurs and the conventional MMC fails to operate correctly. This paper introduces an arm current reversal-based modular multilevel DC-DC converter, which successfully provides balance among the capacitor voltages while operating in DC-DC conversion. The proposed configuration is used in medium voltage DC grids to feed DC loads or to interconnect between two DC grids of different voltage levels. The proposed converter is a two-stage DC-DC modular converter, which consists of a single-phase half-bridge MMC with half-bridge submodules (HBMMC) followed by a single-phase H-bridge MMC with half-bridge submodules (SMs). The operational concept of the proposed converter is based on reversing the arm current direction and reversing the output terminals with the help of the H-bridge MMC stage, which ensures the same direction of the voltage at the load terminals. The proposed converter provides a high conversion ratio, bidirectional power flow, simple architecture, and a simple control scheme. Detailed illustrations, analysis, and design of the proposed converter are presented. Besides, MATLAB-based and Opal RT-based simulation results and experimental results are presented to validate the proposed configuration claims

A ring-connected dual active bridge based DC-DC multiport converter for EV fast-charging stations

This paper proposes a multiport DC-DC converter for EV fast-charging stations. The proposed converter is comprised of Ring-Connected Dual Active Bridge (RCDAB) DC-DC converters, where the connection point between every two adjacent DABs provides a DC port. Bypass switches are added to each DAB to eliminate unnecessary power processing stages in the event of idle ports (no EVs) (open circuit ports). The nature of the ring connection of the RCDAB theoretically allows infinite internal power flow solutions within the ring to satisfy a certain power flow scenario at the DC ports, hence, the optimal power flow solution can be selected to minimize total RMS current and losses. Single-phase shift control is applied to this optimization problem to make it simple. A novel closed-loop control scheme using Bisection optimization is developed to minimize the total RMS current. A control-hardware-in-the-loop (CHiL) validation is carried out for a 5-port network of the proposed topology to investigate the converter efficiency and fault tolerance/availability characteristics. Also, an experimental hardware validation is implemented for a 3-port network where different scenarios for power flow and faults are performed. Finally, a comparative discussion between the proposed topology and other multiport topologies in literature is presented revealing the superior performance of the RCDAB topology

Serum Vascular Endothelial Growth Factor in Egyptian Obese Women with Insulin Resistance

BACKGROUND: Obesity is a major factor in the development of several sub-clinical anomalies. Insulin resistance (IR) is associated with obesity. Vascular endothelial growth factor (VEGF) plays a significant role in inflammation and vascular neogenesis. However the precise relationships of its levels with clinical, lipid, and metabolic profiles are unknown. AIM: This study aimed to examine the association between serum VEGF concentrations with IR risk and metabolic and lipid parameters in obese women. METHODS: Serum VEGF, metabolic biomarkers and anthropometry were measured in 83 obese women with IR and 50 healthy women. Fat distributions in the abdominal, subcutaneous and visceral area were assessed. Homeostasis model assessment for insulin resistance index (HOMA-IR) was calculated. For analytical purposes, VEGF levels were categorised into three tertiles groups. RESULTS: Obese women with IR showed significantly higher levels of serum VEGF as compared with the control group. Moreover, obese women in the highest VEGF tertile had significantly higher values of obesity indices, visceral fat index, abnormal lipid levels and HOMA-IR compared to with those in the lower tertile. CONCLUSION: Elevated VEGF levels are associated with IR and high visceral fat index in obese women which in turn increased the risk for metabolic complications

Innovative solutions in last mile delivery: concepts, practices, challenges, and future directions

In the last decade, e-commerce has been growing consistently. Fostered by the covid pandemic, online retail has grown exponentially, particularly in industries including food, clothing, groceries and many others. This growth in online retailing activities has raised critical logistic challenges, especially in the last leg of the distribution, commonly referred to as the Last Mile. For instance, traditional truck-based home delivery has reached its limit within metropolitan areas and can no longer be an effective delivery method. Driven by technological progress, several other logistic solutions have been deployed as innovative alternatives to deliver parcels. This includes delivery by drones, smart parcel stations, robots, and crowdsourcing, among others. In this setting, this paper aims to provide a comprehensive review and analysis of the latest trends in last-mile delivery solutions from both industry and academic perspectives (see Figure 1 for overview). We use a content analysis literature review to analyse over 80 relevant publications, derive the necessary features of the latest innovation in the last mile delivery, and point out their different maturity levels and the related theoretical and operational challenges

Copeptin as a Biomarker of Atherosclerosis in Type 1 Diabetic Patients

AIM: To evaluate copeptin as an early marker of atherosclerosis in adolescent type 1 diabetics. METHODS: Sixty-two type 1 diabetic patients and 50 healthy volunteers were enrolled in the study. Serum copeptin, glycosylated haemoglobin (HbA1c), lipid profile, oxidised low-density lipoprotein (OxLDL), urinary albumin/creatinine ratio, carotid intimal medial thickness (cIMT), aortic intimal medial thickness (aIMT) and resistivity index were assessed for all participant in the study. RESULTS: HbA1, albumin/creatinine ratio, lipid profile, OxlDL, copeptin, cIMT and aIMT were significantly higher in diabetic patients. Copeptin was higher in patients with positive cIMT and aIMT. Copeptin correlated with cIMT and aIMT. Stepwise multiple regression analysis found that copeptin correlated with aIMT. ROC curve showed that copeptin had 100 % specificity with aIMT and cIMT and 95.2 and 60,7 sensitivity with aIMT and cIMT respectively. CONCLUSION: Copeptin can be used as a marker for early detection of atherosclerosis of type 1 diabetic patients

Irisin in Adolescent Type 1 Diabetic Patients and its Relation to Diabetes Control and Atherosclerosis

AIM: The objective of this was to determine the role of irisin in adolescent type 1 diabetes (T1D) patients. METHODS: This study was conducted on 65 patients with T1D and 50 healthy individuals as control group. Serum irisin, glycosylated hemoglobin (HbA1c), lipid profile, oxidized low-density lipoprotein (OxLDL), urinary albumin/creatinine ratio; carotid intimal medial thickness (cIMT), and aortic intimal medial thickness (aIMT) were evaluated for all participant. RESULTS: HbA1c, lipid profile, albumin/creatinine ratio, OxLDL, irisin, aIMT and cIMT were significantly higher in diabetic patients. Irisin had a positive correlation with age of diabetic patients, onset of diabetes, mid arm circumference, waist/height ratio, body mass index, HbA1c, and cIMT. CONCLUSION: Irisin is a marker for detection of diabetes control and early detection of subclinical atherosclerosis. Irisin had a relation with obesity

A new hybrid dual active bridge modular multilevel based DC-DC converter for HVDC networks

Multi-terminal high voltage DC transmission currently represents a leading technology in long-distance power transmission systems. Among the main technical challenges facing such technology, DC fault isolation, permitting different grounding schemes, providing interoperability, and high DC voltage stepping between different HVDC networks, and allowing high-speed power reversal without power interruption especially when connecting the pre-existing voltage source converters (VSC) and line commutated converters (LCC)-based HVDC networks. This paper introduces a new modular multilevel converter (MMC) based front-to-front DC-DC converter to interconnect two different types (LCC/VSC) of HVDC networks. The proposed topology comprises a voltage source MMC (VS-MMC) and a current source MMC (CS-MMC), while both are coupled via an AC link including the isolating transformer. The proposed topology can successfully provide an uninterruptible bi-directional power flow, high DC voltage stepping with a DC fault blocking capability, and low number of semiconductors due to the usage of only half-bridge SMs. The system design is provided with a detailed mathematical analysis. Furthermore, two active power control methodologies are proposed and compared. The first control technique is simpler and entails lower passive elements, while the second technique ensures a zero reactive power over the full range of active power flow. Furthermore, Losses analysis and comparison are provided between the two proposed control techniques. Finally, Control-Hardware-in-the-Loop (CHiL) test validation is employed to confirm the validity of the proposed system under healthy as well as different fault scenarios

Performance evaluation of PI controlled series stacked power delivery architectures for high-efficiency data centers

Series-stacked architectures have been successfully deployed for data center applications at substantially higher efficiencies than conventional power delivery architectures. In the series-stacked architectures, servers are series-connected electrically to reduce the high step-down conversion stage of voltage utilized in the conventional architectures. Differential power processing converters are, therefore, used to regulate the servers’ voltages and compensate for the unpredicted mismatch between servers’ currents. The main contribution of this paper comprises novel control approaches based on PI controllers purposeful for the two architectures that have reported the highest reliability and efficiency in differential power processing namely: server-to-bus and server-to-virtual bus. Both systems employ a dual active bridge (DAB) converter to accommodate the fluctuating loads of each server. Unlike hysteresis current/voltage control commonly employed in the available literature, the proposed control approaches offer less complexity, lower harmonics, and higher immunity towards the noise, thus no need for high-quality sensors to successfully achieve voltage balance and/or optimal string current flow. Moreover, a comparative study has been structured between the investigated series-stacked architectures under the proposed PI control approaches showing the merits and the demerits of each architecture. The proposed controllers have been validated based on simulations and experimentally

Histopathological study of the effect Of Eurycoma longifolia Jack (Tongkat Ali) extract on the prostate of rats

Objective: to study the effect of Eurycoma longifolia Jack extract on the prostate tissue of male rats and to find out if there are any pathological changes occurring in the prostate due to its use.Methodology:45 male rats where used in this study , they were divided into three groups ,group 1 contain 5 rats that represent the control group, group 2 has 20 rats and group 3 with 20 rats. The rats in group 1 received no treatment, group2 received 5mg/Kg body weight twice daily of 100:1 water extract of Eurycoma longifolia Jack roots,group3 received 10mg/kg body weight twice daily of the same extract .The duration of treatment for both groups was 4 weeks. At the end of the experiment the rats where terminated and prostatic tissue was obtained and processed into haematoxiline and eosin stained slides which were observed under light microscope. Results: histopathological examination of the specimens revealed that there were no significant observable changes in group 2 in comparison with the control group while group 3 showed a marked cell proliferation of the prostatic gland lining epithelium that appeared as infolding and multi-layering of the usual single layer columnar epithelium and also we observed areas of mild dysplastic changes in the lining epithelium characterized by nuclear enlargement and irregularities in the nuclear membrane . Conclusion: From the findings we can conclude that increasing the dose of extract may lead to abnormal proliferation in the prostatic epithelium and the presence of dysplastic changes may progress to more severe dysplasia and even malignant changes may occur with high doses or prolonged treatment

The effect of Eurycoma Longifolia Jack extract (Tongkat Ali) on serum leptin levels in male rats

Eurycoma Iongifolia Jack (E. L), which is known as Tongkat Ali is a plant which grows up to10 meters high and is found in primary and secondary evergreen and mixed deciduous forests in Burma, China, Thailand, Malaysia, Sumatra, Borneo and the Philippines.It has become famous as a sexual enhancer since it has been proved by various studies to increase the serum testosterone levels in male rats and humans. Recently it has also been shown to increase muscle mass in rats .That made us interested to find out if there is any change in the body fat content which is reflected through the serum leptin concentration. Leptin is a 16 kDa protein hormone that plays a key role in regulating energy intake and energy expenditure, including appetite and metabolism. It is one of the most important adipose derived hormones.The Ob (Lep) gene is located on chromosome 7 in humans. It is manufactured primarily in the adipocytes of white adipose tissue, and the level of circulating leptin is directly proportional to the total amount of fat in the body. Objectives: To study the effect of Eurycoma Longifolia jack (E. L.) extract on the serum leptin level of male rats. Methodology: Mature male Albino Wistar rats where used in this study, we measured the rats’ serum leptin and testosterone level before receiving treatment (control), the rats were divided into two groups ,group A received 5mg/kg body weight twice daily of pure 100:1 concentration E.L. extract, group B received 10mg/kg body weight twice daily of the same extract . The duration of treatment was 6 weeks for both groups. At the end of the experiment, we analyzed the serum leptin and testosterone levels in both groups. Results: The mean serum leptin and testosterone levels for the control group were 1.13ng/ml, 0.79ng/L, group A 1.08ng/ml, 0.98ng/L group B 0.89ng/ml,1.75ng/L respectively. Statistical analysis showed that serum leptin level of group B was significantly lower than that of control group (p<0.001) and group A(p<0.05). On the other hand, no significant difference in serum leptin levels were observed between the control group and group A. The serum testosterone level was significantly higher in group B than control and group A. Conclusion: According to our results we can see that E.L. extract can significantly decrease serum leptin levels however,the effect is dose dependant and maybe affected by the significant rise in serum testosterone level that occurs in group B only. This conclusion is based on previous studies that have reported the existence of a negative correlation between serum testosterone and leptin concentrations