Role of Self-Heating and Polarization in AlGaN/GaN Based Heterostructures

The interplay of self-heating and polarization affecting resistance is studied in AlGaN/GaN Transmission Line Model (TLM) heterostructures with a scaled source-to-drain distance. The study is based on meticulously calibrated TCAD simulations against I-V experimental data using an electrothermal model. The electro-thermal simulations show hot-spots (with peak temperature in a range of 566 K - 373 K) at the edge of the drain contact due to a large electric field. The electrical stress on Ohmic contacts reduces the total polarization, leading to the inverse/converse piezoelectric effect. This inverse effect decreases the polarization by 7 %, 10 %, and 17 % during a scaling of the source-to-drain distance in the 12 μ m, μ8 m and 4μ m TLM heterostructures, respectively, when compared to the largest 18μ m heterostructure

Roles of Cholesteryl--Glucoside Transferase and Cholesteryl Glucosides in Maintenance of Helicobacter pylori Morphology, Cell Wall Integrity, and Resistance to Antibiotics

ABSTRACT Infection of the human stomach caused by Helicobacter pylori is very common, as the pathogen colonizes more than half of the world’s population. It is associated with varied outcomes of infection, such as peptic ulcer disease, gastric ulcers, and mucosa-associated lymphoid tissue lymphoma, and is generally considered a risk factor for the development of gastric adenocarcinoma. Cholesteryl glucosides (CGs) constitute a vital component of the cell wall of H. pylori and contribute to its pathogenicity and virulence. The hp0421 gene, which encodes cholesteryl-α-glucoside transferase (CGT), appears critical for the enzymatic function of integrating unique CGs into the cell wall of H. pylori, and deletion of this gene leads to depletion of CGs and their variants. Herein, we report that the deletion of hp0421 and consequent deficiency of cholesterol alter the morphology, shape, and cell wall composition of H. pylori cells, as demonstrated by high-resolution confocal microscopy and flow cytometry analyses of two different type strains of H. pylori, their isogenic knockouts as well as a reconstituted strain. Moreover, measurement of ethidium bromide (EtBr) influx by flow cytometry showed that lack of CGs increased cell wall permeability. Antimicrobial susceptibility testing revealed that the hp0421 isogenic knockout strains (Hp26695Δ421 and Hp76Δ421) were sensitive to antibiotics, such as fosfomycin, polymyxin B, colistin, tetracycline, and ciprofloxacin, in contrast to the wild-type strains that were resistant to the above antibiotics and tended to form denser biofilms. Lipid profile analysis of both Hp76 and Hp76Δ421 strains showed an aberrant profile of lipopolysaccharides (LPS) in the Hp76Δ421 strain. Taken together, we herein provide a set of mechanistic evidences to demonstrate that CGs play critical roles in the maintenance of the typical spiral morphology of H. pylori and its cell wall integrity, and any alteration in CG content affects the characteristic morphological features and renders the H. pylori susceptible to various antibiotics. IMPORTANCE Helicobacter pylori is an important cause of chronic gastritis leading to peptic ulcer and is a major risk factor for gastric malignancies. Failure in the eradication of H. pylori infection and increasing antibiotic resistance are two major problems in preventing H. pylori colonization. Hence, a deeper understanding of the bacterial survival strategies is needed to tackle the increasing burden of H. pylori infection by an appropriate intervention. Our study demonstrated that the lack of cholesteryl glucosides (CGs) remarkably altered the morphology of H. pylori and increased permeability of the bacterial cell wall. Further, this study highlighted the substantial role of CGs in maintaining the typical H. pylori morphology that is essential for retaining its pathogenic potential. We also demonstrated that the loss of CGs in H. pylori renders the bacterium susceptible to different antibiotics

A Parametric Technique for Traps Characterization in AlGaN/GaN HEMTs

A new parametric and cost-effective tech- nique is developed to decouple the mechanisms behind current degradation in AlGaN/GaN HEMTs under a nor- mal device operation: self-heating and charge trapping. A unique approach that investigates charge trapping using both source (IS) and drain (ID) transient currents for the first time. Two types of charge trapping mechanisms are identified: (i) bulk charge trapping occurring on a time scale of less than 1 ms, followed by (ii) surface charge trapping with a time constant larger than a millisecond. Through monitoring the difference between IS and ID, a bulk charge trapping time constant is found to be independent of both drain (VDS ) and gate (VGS ) biases. Surface charge trapping is found to have a much greater impact on a slow degrada- tion when compared to bulk trapping and self-heating. At a short timescale ( 1 ms), the dynamic ON resistance degradation is predominantly limited by surface charge trapping

A Source and Drain Transient Currents Technique for Trap Characterisation in AlGaN/GaN HEMTs

The source/drain and gate induced charge trapping within an AlGaN/GaN high electron mobility transistor is studied, under normal device operation, by excluding self-heating effects, for the first time. Through direct measurement of current transients of both source and drain terminals, a characterisation technique has been developed to: (i) analyse the transient current degradations from μs to seconds, and (ii) evaluate the drain and gate induced charge trapping mechanisms. Two degradation mechanisms of current are observed: bulk trapping at a short time (1ms). The bulk charge trapping is found to occur during both ON and OFF states of the device when VDS>0V; where its trapping time constant is independent of bias conditions. In addition, the time constant of the slower current degradation is found to be mainly dependent on surface trapping and redistribution, not by the second heat transient

Farnesol attenuates cadmium-induced kidney injury by mitigating oxidative stress, inflammation and necroptosis and upregulating cytoglobin and PPARγ in rats

Heavy metals are environmental pollutants that can harm animals and humans even at low concentrations. Cadmium (Cd) is known for its serious health effects on different organs and its toxicity is associated with oxidative stress (OS) and inflammation. Farnesol (FAR), a sesquiterpene alcohol found in many vegetables and fruits, possesses promising anti-inflammatory and antioxidant activities. This study evaluated the effect of FAR on Cd-induced kidney injury, pinpointing its effect of the redox status, inflammation, fibrosis and necroptosis. Rats in this study received FAR for 14 days and Cd on day 7. Elevated serum creatinine, urea and uric acid, and several kidney histopathological alterations were observed in Cd-administered rats. Cd increased MDA, decreased antioxidants, downregulated PPARγ and upregulated NF-κB p65, IL-6, TNF-α, and IL-1β. Necroptosis mediators (RIP1, RIP3, MLKL, and caspase-8) and α-SMA were upregulated, and collagen deposition was increased in Cd-administered rats. FAR ameliorated kidney injury markers and tissue damage, attenuated OS, suppressed NF-κB and inflammatory mediators, and enhanced antioxidants. In addition, FAR suppressed RIP1, RIP3, MLKL, caspase-8, and α-SMA, and enhanced kidney cytoglobin and PPARγ. In conclusion, FAR protects against Cd nephrotoxicity by suppressing OS, inflammatory response and necroptosis, effects associated with enhanced antioxidants, cytoglobin, and PPARγ

A Parametric Technique for Traps Characterization in AlGaN/GaN HEMTs

A new parametric and cost-effective technique is developed to decouple the mechanisms behind current degradation in AlGaN=GaN HEMTs under a normal device operation: self-heating and charge trapping. Our unique approach investigates charge trapping using both source (IS) and drain (ID) transient currents for the first time. Two types of charge trapping mechanisms are identified: (i) bulk charge trapping occurring on a time scale of less than 1 ms, followed by (ii) surface charge trapping with a time constant larger than a millisecond. Through monitoring the difference between IS and ID, a bulk charge trapping time constant is found to be independent of both drain (VDS) and gate (VGS) biases. Surface charge trapping is found to have a much greater impact on a slow degradation when compared to bulk trapping and self-heating. At a short timescale ( 1 ms), the dynamic ON resistance degradation is predominantly limited by surface charge trapping

Hydrodynamic resistance analysis of new hull design for multipurpose amphibious vehicle applying with finite volume method

This paper numerically investigated the hydrodynamic resistance of Multipurpose Amphibious Vehicles (MAV) in three bow shapes to approach the better hull bow shape design. This type of vehicle and other blunt-shaped floating vehicles encounter the problem of a large bow wave forming at high speeds. This wave formation is accompanied by higher resistance and at a critical speed results in bow submergence or swamping. Three new shapes of hull bow design for the multipurpose amphibious vehicle were conducted at several speeds to investigate the hydrodynamic phenomena using Computational Fluid Dynamics (CFD, RANS code) which is applied by Ansys-CFX14.0 and Maxsurf. The vehicle’s hydrodynamic bow shapes were able to break up induced waves and avoid swamping. Comparative results with the vehicle fitted with U-shape, V-shape and Flat-shape of hull bow, showed that the U-shape of the hull bow has reduced the total resistance to 20.3% and 13.6% compared with the V-shape and flat shape respectively. Though, the U-shape of hull bow is capable to increase the amphibious operating life and speed of vehicle in calm water. Also it has ability to reduce the vehicle’s required power, fossil fuel consumption and wetted hull surfac

Umbelliferone inhibits spermatogenic defects and testicular injury in lead-intoxicated rats by suppressing oxidative stress and inflammation, and improving Nrf2/HO-1 signaling

© 2020 Alotaibi et al. Introduction: Lead (Pb) is an environmental toxic metal that threatens human health. Umbelliferone (UMB) is a coumarin with known medicinal and protective properties against cytotoxicity. This study explored the ameliorative effect of UMB against Pb-induced testicular toxicity in rats, focusing on steroidogenesis, oxidative stress and inflammation. Materials and Methods: Rats received lead acetate (50 mg/kg) and UMB (25, 50 or 100 mg/kg) via oral gavage for 4 weeks. Results: Pb-intoxicated rats exhibited testicular tissue injury and decreased serum levels of LH, FSH and testosterone. The count, viability, motility and normal morphology of the sperms were decreased accompanied with downregulated steroidogenesis markers in Pbinduced group. UMB prevented testicular injury, increased serum levels of LH, FSH and testosterone, upregulated steroidogenesis markers and improved the semen quality. In addition, UMB attenuated oxidative stress and oxidative DNA damage, downregulated the expression of pro-inflammatory mediators and Bax, boosted antioxidant defenses and Bcl2, and upregulated Nrf2/HO-1 signaling in Pb-intoxicated rats. Conclusion: UMB prevents Pb-induced testicular injury by suppressing oxidative damage, inflammation and cell death, and boosting antioxidant defenses, Nrf2/HO-1 signaling and pituitary-gonadal axis. Thus, UMB may represent a protective and cost-effective agent against Pb testicular toxicity, pending further investigations to elucidate other underlying mechanisms.Open Access funding provided by the Qatar National Library