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A 5-Level Inverter Scheme Using Single DC Link With Reduced Number of Floating Capacitors and Switches for Open-End IM Drives
No full textThis paper presents a 5-level inverter topology for open-end induction motor drives by using a single dc source. The open stator windings of the drive are supplied with a 3-level flying capacitor inverter from one end and capacitor-fed 2-level inverter from another end. The voltage ratio of the dc link to the capacitor in 2-level inverter is maintained at 4:1 ratio to generate five-level voltage output. The capacitor in 2-level inverter is balanced by the switching redundant vector combinations from both the inverters while the floating capacitors in the 3-level inverter are balanced by using redundant switching states. The proposed topology gives 5-level operation with less number of floating capacitors and power semiconductor switches compared to other existing topologies. Also, the balancing of the capacitors is independent of load power factor and modulation index. Further, the generalization of the proposed dual inverter scheme for any n-level inverter is also included in this paper. The experimental results and required analysis are also presented to validate the inverter scheme
Enhancing the catalytic activity of recyclable nanocrystalline NiFe2O4 by replacing Ni by Cu
No full textHerein, we report an efficient, magnetically recoverable and recyclable nanocatalyst to drive a reduction reaction under mild reaction conditions. Nickel ferrite (NiFe2O4) and 20% copper substituted nickel ferrite (Ni0.8Cu0.2Fe2O4) nanocatalysts were synthesized using a facile glycine-nitrate autocombustion route and employed as catalysts to assess the reduction of 4-nitrophenol in aqueous medium. Phase purity, structural aspects, morphological features and magnetic characteristrics of as-synthesized ferrite powders were carried out using Xray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). Elemental compositions of the prepared materials were investigated using EDX analysis. Reduction of 4-nitrophenol to 4-aminophenol using NaBH4 as the reducing agent with the nanocatalyst was monitered using a UV Visible spectrophotometry. The results indicate that the Ni0.8Cu0.2Fe2O4 demonstrated a better catalytic activity with nearly 99% conversion against NiFe2O4, which showed almost negligible activity over a long period of time. For the first catalytic reduction cycle, time taken by the Ni0.8Cu0.2Fe2O4 was less than 2 min. However, the reduction time increased progressively as number of cycles increased. Ni0.8Cu0.2Fe2O4 also displayed a superior catalytic performance over 10 cycles, without a significant drop in its activity. The superior catalytic performance of Ni0.8Cu0.2Fe2O4 is likely to be due the surface contribution of smaller particles and the presence of Cu2+ at the octahedral site of the spinel ferrite
Temperature measurements in a laboratory scale furnace for manufacturing of silicon carbide through Acheson process
No full textA hot model for SiC production has been developed on the laboratory-scale to measure temperatures in harsh conditions at various locations of the furnace. A unique method has been adopted to measure the core temperature in reactive and high temperature environment. The temperatures of the core and at various radial and angular locations within the furnace were measured using a ratio pyrometer and by B and C-type thermocouples respectively; this type of controlled measurement is missing in this field. In this study, the power supply was maintained such that a constant core temperature was sustained. The temperature decrease along the radial direction is an indicative of the SiC production. Further, at the same radial distances, variations in the local temperature depended on the angular positions; upper regions showed higher temperatures due to escaping hot gases. The results obtained in this study are expected to be beneficial to the industries
Supervised I-vector modeling for language and accent recognition
No full textThe conventional i-vector approach to speaker and language recognition constitutes an unsupervised learning paradigm where a variable length speech utterance is converted into a fixed dimensional feature vector (termed as i-vector). The i-vector approach belongs to the broader family of factor analysis models where the utterance level adapted means of a Gaussian Mixture Model - Universal Background Model (GMM-UBM) are assumed to lie in a low rank subspace. The latent variables in the low rank model are assumed to have a standard Gaussian prior distribution. In this paper, we rework the theory of i-vector modeling in a supervised framework where the class labels (like language or accent) of the speech recordings are introduced directly into the i-vector model using a mixture Gaussian prior where each mixture component is associated with a class label. We provide the mathematical formulation for minimum mean squared error estimate (MMSE) of the supervised i-vector (s-vector) model. A detailed analysis of the s-vector model is given and this is contrasted with the traditional i-vector framework. The proposed model is used for language recognition tasks using the NIST Language Recognition Evaluation (LRE) 2017 dataset as well as an accent recognition task using the Mozilla common voices dataset. In these experiments, the s-vector model provides significant improvements over the conventional i-vector model (relative improvements of up to 24% for LRE task in terms of primary detection cost metric)
Revisiting the layered Na3Fe3(PO4)(4) phosphate sodium insertion compound: structure, magnetic and electrochemical study
No full textLayered sodium iron phosphate phase Na3Fe3(PO4)(4)] was synthesized by solution combustion synthesis method, marking the first attempt of solvothermal synthesis of this phase. Its crystal structure was verified by synchrotron and neutron powder diffraction. Rietveld analyses proved the phase purity and formation of monoclinic framework with C2/c symmetry. It undergoes an antiferromagnetic ordering ?27 K. This combustion prepared nanoscale Na3Fe3(PO4)(4) compound was found to be electrochemically active with a stepwise voltage profile involving an Fe3+/Fe2+ redox activity centred at 2.43 V vs. Na/Na+. Despite various cathode optimization, only 1.8 Na+ per formula unit could be reversibly inserted into the Na3Fe3(PO4)(4) framework leading to capacity close to 50 mAh g(?1). This limited electrochemical activity can be rooted to (i) relatively large diffusion barrier (ca. 0.28 eV) as per Bond valence site energy (BVSE) calculations and (ii) possible structural instability during (de)sodiation reaction
The digital twin of discrete dynamic systems: Initial approaches and future challenges
No full textThis paper employs a discrete damped dynamic system to investigate the emerging concept of a digital twin. Dynamic systems are well understood across engineering and science domains, and represent a familiar and convenient platform for exploring the various aspects of a digital twin design. The aim is to create a framework accessible to engineering sciences related to the aerospace, electrical, mechanical and computational area. The virtual model of the physical system is expressed as a differential equation in two-time scales, with the concept of a slow time being used to separate the evolution of the system properties from the instantaneous time. Cases involving stiffness variation and mass variation are considered, individually and together. It is assumed that the damped natural frequency and the time response are measured through sensors placed on the physical system. Issues of errors and reduced sampling rate in sensor measurements on the digital twin are investigated. The digital twin is expressed as an analytical solution through closed-form expressions and the effect of sensor errors is brought out through the simulations. Several key concepts introduced in this paper are summarized and ideas for urgent future research needs are proposed. The current work breaks free from the qualitative description of digital twins pervading the literature and can be used as benchmark solutions to validate digital twin of experimental dynamic systems and their implementation using sensors, the internet of things and deployment on the cloud computing systems
Nucleoside Diphosphate Kinase Escalates A-to-C Mutations in MutT-Deficient Strains of Escherichia coli
No full textThe chemical integrity of the nucleotide pool and its homeostasis are crucial for genome stability. Nucleoside diphosphate kinase (NDK) is a crucial enzyme that carries out reversible conversions from nucleoside diphosphate (NDP) to nucleoside triphosphate (NTP) and deoxynucleoside diphosphate (dNDP) to deoxynucleoside triphosphate (dNTP). Guanosine nucleotides (GDP, GTP, dGDP, and dGTP) are highly susceptible to oxidative damage to 8-oxo-GDP (8-O-GDP), 8-O-dGTP, 8-OGTP, and 8-O-dGTP. MutT proteins in cells hydrolyze 8-O-GTP to 8-O-GMP or 8-OdGTP to 8-O-dGMP to avoid its incorporation in nucleic acids. In Escherichia coli, 8-O-dGTP is also known to be hydrolyzed by RibA (GTP cyclohydrolase II). In this study, we show that E. coli NDK catalyzes the conversion of 8-O-dGDP to 8-O-dGTP or vice versa. However, the rate of NDK-mediated phosphorylation of 8-O-dGDP to 8-O-dGTP is about thrice as efficient as the rate of dephosphorylation of 8-O-dGTP to 8-O-dGDP, suggesting an additive role of NDK in net production of 8-O-dGTP in cells. Consistent with this observation, the depletion of NDK (Delta ndk) in E. coli Delta mutT or Delta mutT Delta ribA strains results in a decrease of A-to-C mutations. These observations suggest that NDK contributes to the physiological load of MutT in E. coli. IMPORTANCE Nucleoside diphosphate kinase (NDK), a ubiquitous enzyme, is known for its critical role in homeostasis of cellular nucleotide pools. However, NDK has now emerged as a molecule with pleiotropic effects in DNA repair, protein phosphorylation, gene expression, tumor metastasis, development, and pathogen virulence and persistence inside the host. In this study, we reveal an unexpected role of NDK in genome instability because of its activity in converting 8-O-dGDP to 8-O-dGTP. This observation has important consequences in escalating A-to-C mutations in Escherichia coll. The severity of NDK in enhancing these mutations may be higher in the organisms challenged with high oxidative stress, which promotes 8-O-dGDP/8-O-dGTP production
Evolution of cratons through the ages: A time-dependent study
No full textThe viscosity of cratons is key to understanding their long term survival. In this study, we present a time-dependent, full spherical, three dimensional mantle convection model to investigate the evolution of cratons of different viscosities. The models are initiated from 409 Ma and run forward in time till the present-day. We impose a surface velocity boundary condition, derived from plate tectonic reconstruction, to drive mantle convection in our models. Cratons of different viscosities evolve accordingly with the changing velocity field from their original locations. Along with the viscosity of cratons, the viscosity of the asthenosphere also plays an important role in cratons' long term survival. Our results predict that for the long-term survival of cratons they need to be at least 100 times more viscous than their surroundings and the asthenosphere needs to have a viscosity of the order of 1020 Pa-s or more
Transcriptome profiling reveals PDZ binding kinase as a novel biomarker in peritumoral brain zone of glioblastoma
No full textPurposePeritumoural brain zone (PT) of glioblastoma (GBM) is the area where tumour recurrence is often observed. We aimed to identify differentially regulated genes between tumour core (TC) and PT to understand the underlying molecular characteristics of infiltrating tumour cells in PT.Methods17 each histologically characterised TC and PT tissues of GBM along with eight control tissues were subjected to cDNA Microarray. PT tissues contained 25-30% infiltrating tumour cells. Data was analysed using R Bioconductor software. Shortlisted genes were validated using qRT-PCR. Expression of one selected candidate gene, PDZ Binding Kinase (PBK) was correlated with patient survival, tumour recurrence and functionally characterized in vitro using gene knock-down approach.ResultsUnsupervised hierarchical clustering showed that TC and PT have distinct gene expression profiles compared to controls. Further, comparing TC with PT, we observed a significant overlap in gene expression profile in both, despite PT having fewer infiltrating tumour cells. qRT-PCR for 13 selected genes validated the microarray data. Expression of PBK was higher in PT as compared to TC and recurrent when compared to newly diagnosed GBM tumours. PBK knock-down showed a significant reduction in cell proliferation, migration and invasion with increase in sensitivity to radiation and Temozolomide treatment.ConclusionsWe show that several genes of TC are expressed even in PT contributing to the vulnerability of PT for tumour recurrence. PBK is identified as a novel gene up-regulated in PT of GBM with a strong role in conferring aggressiveness, including radio-chemoresistance, thus contributing to recurrence in GBM tumours
Molecular Design Strategies for Efficient Intramolecular Singlet Exciton Fission
No full textThe process of carrier multiplication via singlet fission can potentially exceed the Shockley-Queisser limit on the efficiency of single-junction photovoltaics. In the recent past, theoretical analysis provided the principal guidelines on molecular design strategies for singlet fission. In this Perspective, we focus instead on correlating experimental results for different classes of reported singlet fission materials to identify principles to aid in the design of new molecules for efficient intramolecular singlet fission. Building on an evaluation of several series of multichromophoric and polymeric singlet fission materials, we extract new suggested strategies for molecular design