Search

In this paper, an AlGaN/GaN heterojunction transistor on a wide band gap material substrate is designed and simulated with Silvaco TCAD software. The substrate material used in this work is β gallium oxide(β-Ga2O3). The cutoff frequency and maximum oscillation frequency of the device extracted are 82 and 360 GHz, respectively, which are better compared to those of recently reported works. These values of fT and fmax prove that the proposed high electron mobility transistor is suitable for radio frequency applications. [ABSTRACT FROM AUTHOR]

Variable speed drives incorporating multiphase motors have started gaining attention in recent years due to their benefits over three-phase counter parts. In this article, we propose a digital control scheme based on space vector pulse density modulation for two-level five phase induction motor drive. The scheme combines principles of digital signal processing techniques, such as sigma delta modulation and vector quantization, along with space vector modulation to form computationally efficient motor drives. In this article, vector space is divided into ten nonoverlapping regions, with each region partitioned into three voronoi regions. The reference vector is vector quantized to the nearest switching vector. Absence of dwell time calculations, less memory requirements, and reduced computational complexity of the scheme along with reduced acoustic noise and electromagnetic interference in the drive are the core advantages of the scheme. The work has been experimentally implemented with 2 HP five-phase induction motor drive and the results are compared with space vector pulsewidth modulation scheme for validation purpose. [ABSTRACT FROM AUTHOR]

A simplified space vector pulse density modulation (SVPDM) scheme for any odd-level inverter-based induction motor drive is proposed in this article. The control strategy uses three sigma delta modulators, wherein the reference space vector is vector quantized to generate the output switching vectors. The switching vectors for the inverters are derived without coordinate transformation and sector identification in this scheme, making the algorithm computationally simpler. The proposed SVPDM scheme retains the advantages over SVPWM scheme such as freedom from minimum pulsewidth problem, improved spectral features, convenience of digital implementation, avoidance of complex timing calculations, and less annoying acoustic noise pattern of motor. The scheme is experimentally verified for an open-end winding-based five-level induction motor drive. The performance of the proposed scheme is compared with the deterministic and nondeterministic schemes and the results obtained substantiate the efficiency of proposed scheme. [ABSTRACT FROM AUTHOR]

Power converters using deterministic switching frequency schemes have switching noise concentrated at harmonic frequencies, resulting in enhanced electromagnetic emission. To suppress the harmonic spikes in three-phase multilevel voltage source converters, a digital control scheme based on dithered sigma–delta modulation (SDM) is proposed in this paper. Introducing a dithered sequence in an SDM varies the switching frequency randomly, resulting in the suppression of the spurious harmonic spikes in the output spectrum even with a regular control input. Although the switching frequency varies randomly, the minimum pulsewidth of the proposed scheme is the sampling time period, avoiding the minimum pulsewidth problem. Instead of a conventional scalar quantizer, the quantizer in the proposed dithered sigma–delta converter uses the principle of space vector quantization. The proposed scheme is experimentally verified on a constant $v/f$ open-loop induction motor drive for a three-level inverter realized by cascading two two-level inverters. The performance of the proposed scheme is compared with different pulsewidth modulation schemes in the entire modulation index, including the overmodulation region. [ABSTRACT FROM PUBLISHER]

A new space-vector-based sigma delta modulation scheme for any general $N$-level voltage source inverter is proposed in this paper, which directly quantizes the reference space vector. The proposed scheme uses the sigma delta modulation with the quantizer implemented by the proposed space vector quantizer. A new scheme is proposed for directly quantizing the reference space vector to the multilevel inverter switching vectors without mapping it into two-level inverter vector space. Voronoi regions of the multilevel inverter vector space in the proposed space vector quantizer are defined as a parallelogram with the inverter switching vectors as its vertices. The property of the integer values of the inverter switching vectors in 60 ^{\circ} coordinates is utilized for the direct vector quantization of the instantaneous reference voltage space vector. The proposed scheme is implemented for five-level inverters realized by an open-end-winding induction motor fed with two three-level inverters from either side having symmetrical dc-link voltages, and results are presented. [ABSTRACT FROM PUBLISHER]

A generalized space-vector-based spread spectrum modulation scheme for multilevel inverters is proposed in this paper. The proposed scheme uses the principle of sigma–delta modulation as applied to analog-to-digital converters (ADCs), based on the view that a multilevel converter could be interpreted as an oversampling ADC. The principle of vector quantization is utilized for quantizing the instantaneous reference voltage space vector in the proposed space-vector-based sigma–delta converter. The switching vectors of the inverter are naturally selected without sector identification, ensuring optimum switching sequence under all conditions including the overmodulation region. As the sigma–delta converter results in a randomly varying switching frequency, the proposed scheme has spread spectrum characteristics. To avoid fractional arithmetic, a 60 ^\circ coordinate system is used to represent the space vector in this paper. The proposed scheme can be used for any general n-level inverter, and experimental results are presented for four-, five-, and six-level inverters, driving a 2-hp three-phase induction motor in an open-end winding configuration. The experimental results of the proposed scheme are compared with the space-vector pulsewidth modulation (PWM) scheme and random PWM scheme. [ABSTRACT FROM PUBLISHER]

A novel series of pyrrolidine-containing GPR40 agonists is described as a potential treatment for type 2 diabetes. The initial pyrrolidine hit was modified by moving the position of the carboxylic acid, a key pharmacophore for GPR40. Addition of a 4-cis-CF3 to the pyrrolidine improves the human GPR40 binding Ki and agonist efficacy. After further optimization, the discovery of a minor enantiomeric impurity with agonist activity led to the finding that enantiomers (R,R)-68 and (S,S)-68 have differential effects on the radioligand used for the binding assay, with (R,R)-68 potentiating the radioligand and (S,S)-68 displacing the radioligand. Compound (R,R)-68 activates both Gq-coupled intracellular Ca2+ flux and Gs-coupled cAMP accumulation. This signaling bias results in a dual mechanism of action for compound (R,R)-68, demonstrating glucose-dependent insulin and GLP-1 secretion in vitro. In vivo, compound (R,R)-68 significantly lowers plasma glucose levels in mice during an oral glucose challenge, encouraging further development of the series. [ABSTRACT FROM AUTHOR]

Abstract: The discovery, synthesis and preliminary SAR of a novel class of non-peptidic antagonists of the αv-integrins αvβ3 and αvβ5 is described. High-throughput screening of an extensive series of ECLiPS™ compound libraries led to the identification of compound 1 as a dual inhibitor of the αv-integrins αvβ3 and αvβ5. Optimization of compound 1 involving, in part, introduction of two novel constraints led to the discovery of compounds 15a and 15b with reduced PSA and much improved potency for both the αvβ3 and αvβ5 integrins. Compounds 15a and 15b were shown to have promising activity in functional cellular assays and compound 15a also exhibited a promising Caco-2 permeability profile. [Copyright &y& Elsevier]

Abstract: Angiopoietins and Tie2 receptor were recently identified as an endothelial cell-specific ligand-receptor system that is critical for vascular development and postnatal pathologic angiogenesis by mediating vascular integrity. In this study, we identified a series of small-molecule Tie2 inhibitors, which blocked Ang1-induced Tie2 autophosphorylation and downstream signaling with an IC50 value at 0.3μM. Further optimization yields improved selectivity, aqueous solubility, microsomal stability and cytochrome P450 profile for one of the compounds (compound 7). Both compound 1 and compound 7 inhibit endothelial cell tube formation. Furthermore, in a rat model of Matrigel-induced choroidal neovascularization, compound 7 significantly diminished aberrant vessel growth. Our findings demonstrate a potential clinical benefit by specifically targeting Tie2-mediated angiogenic disorders. [Copyright &y& Elsevier]

Abstract: γ-Secretase is a key enzyme involved in the production of β-amyloid peptides which are believed to play a critical role in the onset and progression of Alzheimer’s disease (AD). As such, inhibition of γ-secretase has been an attractive approach to AD therapy. In this paper, the design, synthesis, and evaluation of tetrahydroquinoline and pyrrolidine sulfonamide carbamates as γ -secretase inhibitors are described. [Copyright &y& Elsevier]

Abstract: A novel series of pyrrolidine heterocycles was prepared and found to show potent inhibitory activity of CCR1 binding and CCL3 mediated chemotaxis of a CCR1-expressing cell line. A potent, optimized triazole lead from this series was found to have acceptable pharmacokinetics and microsomal stability in rat and is suitable for further optimization and development. [ABSTRACT FROM AUTHOR]