50175 research outputs found
Sort by
Two negative regulators of biofilm development exhibit functional divergence in conferring virulence potential to Candida albicans
No full textCandida albicans, a human pathogen, carries an expanded family of Zn(II)2Cys6 transcription factors. A CTG Glade-specific protein Zcf32 and its closely related protein Upc2, a well-conserved transcription factor across the various fungal species, belong to this family of proteins. Unlike Upc2, Zcf32 is poorly studied in C. albicans. Here, we examined roles played by these two related transcription factors in biofilm development and virulence of C. albicans. Our data show that the null mutants of each of Zcf32 or Upc2 form better biofilms than the wild-type suggesting that both of them negatively regulate the biofilm development. While acting as negative regulators of biofilm formation, these two transcription factors target a different set of bio film genes. A mouse model of candidiasis reveals that zcf32/zcf32 was hypervirulent, while upc2/upc2 shows compromised virulence compared to the wild-type. Notably, the absence of Zcf32 enhances detrimental inflammation brought about by TNF alpha, IFN beta and IFN gamma. upc2/upc2 failed to generate a similar feedback, instead demonstrated an elevated anti-inflammatory (IL4 and IL10) host response. Taking together, we show how a recently evolved transcription factor Zcf32 retained functional resemblance with a more ubiquitous member Upc2 but also functionally diverged from the latter in the regulation of biofilm development and virulence of the pathogen
Distinct properties of a hypoxia specific paralog of single stranded DNA binding (SSB) protein in mycobacteria
No full textIn addition to the canonical Single Stranded DNA Binding (SSBa) protein, many bacterial species, including mycobacteria, have a paralogous SSBb. The SSBb proteins have not been well characterized. While in B. subtilis, SSBb has been shown to be involved in genetic recombination; in S. coelicolor it mediates chromosomal segregation during sporulation. Sequence analysis of SSBs from mycobacterial species suggests low conservation of SSBb proteins, as compared to the conservation of SSBa proteins. Like most bacterial SSB proteins, M. smegmatis SSBb (MsSSBb) forms a stable tetramer. However, solution studies indicate that MsSSBb is less stable to thermal and chemical denaturation than MsSSBa. Also, in contrast to the 5-20 fold differences in DNA binding affinity between paralogous SSBs in other organisms, MsSSBb is only about two-fold poorer in its DNA binding affinity than MsSSBa. The expression levels of ssbB gene increased during UV and hypoxic stresses, while the levels of ssbA expression declined. A direct physical interaction of MsSSBb and RecA, mediated by the C-terminal tail of MsSSBb, was also established. The results obtained in this study indicate a role of MsSSBb in recombination repair during stress
Reduced Rating Active Phase Converter for Three Phase Induction Generator based Single Phase Grid-Tied Systems
No full textThe distribution systems and microgrids in remote and rural areas are often of single-phase in nature due to economic viability. However, three-phase induction generators (IG) is a popular machine even in such applications due to the large utility and its competitive price features. This paper proposes a control approach for injecting power to a single-phase grid from an active phase converter (APC) assisted three-phase IG. The presented approach ensures balanced operation of the IG even with variable generation. A method is proposed that reduces the loading on the APC and improves operating power factor at the single-phase grid. Closed form expression of the grid current for a given operating point of the IG is derived. Simulation and experimental results are provided to validate the theoretical framework and APC control approach. The experimental results with a 3 kW IG substantiate the proposed APC control approach injecting 2.6 kW real power into the single-phase grid at near unity power factor
Dynamic Modeling and Analysis of Buck Converter based Solar PV Charge Controller for Improved MPPT Performance
No full textMaximum power point tracking (MPPT) control is a key functionality in solar photo-voltaic (PV) based power generation systems that enhances the efficacy of energy extraction. A pulse-width modulated (PWM) power converter connected to the PV is designed to perform this essential function. A variety of MPPT control schemes are available in literature, many of which are voltage based techniques wherein the PV bus voltage is controlled in closed loop to the required level that achieves MPP tracking. However, a suitable plant model of the PV fed converter system that facilitates the design of such a PV voltage control loop for MPPT purpose, is not fully covered in literature. In this paper, a small-signal model is developed for a buck converter based charger system fed by a PV source, which is a non-linear active source. Based on this model, the relevant transfer functions are analytically derived. The control to converter input voltage transfer-function (v) over tilde (in)/(d) over bar thus obtained, is useful in the systematic design of voltage controller bandwidth, that facilitates the selection of perturbation period of a typical perturb & observe (P&O) MPPT controller. Such an approach for control design is verified in this work on a PV system with energy storage, which is typically used in dual-mode or standalone PV applications. The P&O MPPT control is validated on a buck PV charge controller system employing a 36 V battery bank. Experiments conducted on a 1 kW hardware prototype verify the accuracy of the proposed analytical transfer-functions and the performance of the PV-charger system
Automatic Optic Disc Localization Using Particle Swarm Optimization Technique
No full textThere is a growing need for plenarily automated algorithms that expeditiously localize the optic disc region in retinal fundus images for the analysis of retinal pathologies such as glaucoma. In this paper, we propose a methodology based on particle swarm optimization for automatic localization of optic disc region from retinal fundus images, where minimization of the fitness function is utilized to resolve optimization quandaries. Here, kernels are modeled as particles and they test the region-of-interest based on the fitness function, in the respective databases, where it is likely that the optic disc exists. The proposed method is validated on a total of 1670 fundus images obtained from various publicly available fundus image datasets. The optic disc localization accuracy obtained by the proposed method are 100%, 98.01%, 96.15%, 98.87%, 100%, and 100% on DRIVE, DRISHTIGS, DIARETDB0, DIARETDB1, DRIONS-DB, and MESSIDOR fundus image databases, respectively. The precision of localization was improved with initialization of kernel particles within bright region-of-interest in fundus images
CESI: Canonicalizing Open Knowledge Bases using Embeddings and Side Information
No full textOpen Information Extraction (OpenIE) methods extract (noun phrase, relation phrase, noun phrase) triples from text, resulting in the construction of large Open Knowledge Bases (Open KBs). The noun phrases (NPs) and relation phrases in such Open KBs are not canonicalized, leading to the storage of redundant and ambiguous facts. Recent research has posed canonicalization of Open KBs as clustering over manually defined feature spaces. Manual feature engineering is expensive and often sub-optimal. In order to overcome this challenge, we propose Canonicalization using Embeddings and Side Information (CESI) a novel approach which performs canonicalization over learned embeddings of Open KBs. CESI extends recent advances in KB embedding by incorporating relevant NP and relation phrase side information in a principled manner. Through extensive experiments on multiple real-world datasets, we demonstrate CESI's effectiveness
Comprehensive Exploratory Analysis of Truck Route Choice Diversity in Florida
No full textThis study presents a comprehensive exploratory analysis of truck route choice diversity in the state of Florida, for both long-haul and short-haul truck travel segments. It employs six metrics to measure three different dimensions of diversity in truck route choice between any given origin-destination (OD) pair. These dimensions are: (a) number of distinct routes used to travel between the OD pair, (b) the extent of overlap (or lack thereof) among the routes, and (c) the evenness (or dominance) in the usage of different unique routes. The diversity metrics were applied to a large database of 73,000 truck routes derived from 200 million GPS records. Descriptive analysis and statistical modeling of the diversity metrics offered insights into the determinants of various dimensions of truck route choice diversity between any OD pair. The results are useful for improving choice set generation algorithms for truck route choice modeling and in truck route policies and investments
Supercapacitor based approach towards development of Graphene Sensors
No full textGraphene has been extensively studied and used in energy storage applications like Supercapacitors owing to its high Electric Double Layer Capacitance (EDLC). However, this property of Graphene has not been used in Sensor technology. We report a novel approach for the development of Graphene Capacitive sensors by adopting the Supercapacitor property of Graphene. Graphene was synthesized by Electro-exfoliation process followed by Hydrazine hydrate reduction. The obtained material was characterized using XRD and FE-SEM to ensure structural and morphological properties. An Interdigitized Electrode (IDE) pattern was prepared with reduced Exfoliated Graphene (rEG) as electrode and PVA-H2SO4 electrolytic gel was used to realize EDLC. The fabricated strain sensing device was found to have a gauge factor of 97.3. This low cost, flexible, highly sensitive and easy to fabricate device opens up a new area of capacitance based sensors with wide applications in the chemical & automotive industry, healthcare, robotics, aerospace, mining etc
PROPER HOLOMORPHIC MAPPINGS ONTO SYMMETRIC PRODUCTS OF A RIEMANN SURFACE
No full textWe show that the structure of proper holomorphic maps between the n-fold symmetric products, n >= 2, of a pair of non-compact Riemann surfaces X and Y, provided these are reasonably nice, is very rigid. Specifically, any such map is determined by a proper holomorphic map of X onto Y. This extends existing results concerning bounded planar domains, and is a non-compact analogue of a phenomenon observed in symmetric products of compact Riemann surfaces. Along the way, we also provide a condition for the complete hyperbolicity of all n-fold symmetric products of a non-compact Riemann surface
Safe Operating Area (SOA) Reliability of Polarization Super Junction (PSJ) GaN FETs
No full textFor the first time, this work reports Safe Operating Area (SOA) assessment and degradation physics in Polarization Super Junction (PSJ) based GaN FETs made on Silicon and sapphire substrates under high voltage and high current injection conditions. Impact of device design parameters on SOA, associated trap assisted device degradation, and thermal failure are studied. Correlation between polarization super junction length and failure threshold is discovered, beside power and field dependence of SOA boundary