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Strongly enhanced electrocaloric effects in doped BaTiO3 with reduced grain size
No full textFerroelectrics are promising candidates in the field of green solid state refrigeration technology due to showing a thermal response with the application/removal of an electric field. However, thermal responses of ferroelectrics are too low; at present, this approach is not able to compete with the conventional refrigeration approach. Guzman-Verri et al (2016 APL Materials 4, 064106) theoretically predicted that the thermal response of ferroelectrics can be elevated up to a considerable amount via modulation of the correlation length of the fluctuation of polarization. In this letter, we report a giant electrocaloric response (-Delta S-E = 16.8 J/kg-K) in 1 wt%Bi2O3-BaTiO3, via manipulation of micro-structural configuration. Addition of Bi2O3 during the sintering process is responsible for the growth of grains of small size, which alters the fluctuation of polarization and reduction in the domain wall, thereby increasing the thermal response. The dielectric properties of Bi2O3 added BaTiO3 remain similar to the bare BaTiO3
Large-Scale Neuromorphic Spiking Array Processors: A Quest to Mimic the Brain
No full textNeuromorphic engineering (NE) encompasses a diverse range of approaches to information processing that are inspired by neurobiological systems, and this feature distinguishes neuromorphic systems from conventional computing systems. The brain has evolved over billions of years to solve difficult engineering problems by using efficient, parallel, low-power computation. The goal of NE is to design systems capable of brain-like computation. Numerous large-scale neuromorphic projects have emerged recently. This interdisciplinary field was listed among the top 10 technology breakthroughs of 2014 by the MIT Technology Review and among the top 10 emerging technologies of 2015 by the World Economic Forum. NE has two-way goals: one, a scientific goal to understand the computational properties of biological neural systems by using models implemented in integrated circuits (ICs); second, an engineering goal to exploit the known properties of biological systems to design and implement efficient devices for engineering applications. Building hardware neural emulators can be extremely useful for simulating large-scale neural models to explain how intelligent behavior arises in the brain. The principal advantages of neuromorphic emulators are that they are highly energy efficient, parallel and distributed, and require a small silicon area. Thus, compared to conventional CPUs, these neuromorphic emulators are beneficial in many engineering applications such as for the porting of deep learning algorithms for various recognitions tasks. In this review article, we describe some of the most significant neuromorphic spiking emulators, compare the different architectures and approaches used by them, illustrate their advantages and drawbacks, and highlight the capabilities that each can deliver to neural modelers. This article focuses on the discussion of large-scale emulators and is a continuation of a previous review of various neural and synapse circuits (Indiveri et al., 2011). We also explore applications where these emulators have been used and discuss some of their promising future applications
A modelling and simulation study of soluble lead redox flow battery: Effect of presence of free convection on the battery characteristics
No full textIn this paper, we develop a mathematical model for soluble lead redox flow battery. The model accounts for simultaneous effect of forced convection and induced free convection in electrolyte domain of the battery. It predicts existence of dominant free convection over the forced convection in vicinity of the electrodes. The predictions suggests that both, electrode kinetics and ion transfer assisted by free convection alone, controls charge-discharge characteristics of the battery. The free convection augments ion transfer rate to the electrodes. By virtue of this, limiting current density at the electrodes increases to twice the theoretical limit under forced convection. The predictions coherently explains Collins et al. 1]'s observations of high charge efficiencies when charging currents are higher than the theoretical limit. Also, the model consistently explains Pletcher et al. 2]'s observation of insensitivity of the battery characteristics to the electrolyte flow rate. The model predicts satisfactory battery performance even at microscopic (mu L s(-1)) flow rates which opens up the possibility for significant reduction in electrolyte pumping cost
Feedback in W49A diagnosed with radio recombination lines and models
No full textWe present images of radio recombination lines (RRLs) at wavelengths around 17 cm from the star-forming region W49A to determine the kinematics of ionized gas in the THOR survey (The H I/OH/Recombination line survey of the inner Milky Way) at an angular resolution of 16 `'.00 8 x 13 `'.00 8. The distribution of ionized gas appears to be affected by feedback processes from the star clusters in W49A. The velocity structure of the RRLs shows a complex behavior with respect to the molecular gas. We find a shell-like distribution of ionized gas as traced by RRL emission surrounding the central cluster of OB stars in W49A. We describe the evolution of the shell with the recent feedback model code WARPFIELD that includes the important physical processes and has previously been applied to the 30 Doradus region in the Large Magellanic Cloud. The cloud structure and dynamics of W49A are in agreement with a feedback-driven shell that is re-collapsing. The shell may have triggered star formation in other parts of W49A. We suggest that W49A is a potential candidate for star formation regulated by feedback-driven and re-collapsing shells
Machine Learning Constrained with Dimensional Analysis and Scaling Laws: Simple, Transferable, and Interpretable Models of Materials from Small Datasets
No full textMachine learning (ML) from materials data-bases can accelerate the design and discovery of new materials through the development of accurate, computationally inexpensive models to predict materials properties. These models in turn enable rapid screening of large materials search space. However, materials datasets describing functional properties are typically small, which creates challenges pertaining to interpretability and transferability when exploring them with conventional ML approaches. Further, correlations within the dataset can lead to instability (nonunique functional models relating inputs to outputs) and overfitting. In this work, we address these issues by developing a new approach, in which ML with the Bootstrapped projected gradient descent algorithm is constrained with Buckingham Pi theorem-based dimensional analysis and scaling laws of relationships between different input descriptors (properties). This constrained learning model enables us to learn from small data and develop predictive models that are accurate, computationally inexpensive, and physically interpretable. We demonstrate this approach by developing a simple model to predict the intrinsic dielectric breakdown field based on an available dataset of 82 compounds. Our approach is generic in nature and is expected to work effectively with other sparse materials datasets
Talker change detection: A comparison of human and machine performance
No full textThe automatic analysis of conversational audio remains difficult, in part, due to the presence of multiple talkers speaking in turns, often with significant intonation variations and overlapping speech. The majority of prior work on psychoacoustic speech analysis and system design has focused on single-talker speech or multi-talker speech with overlapping talkers (for example, the cocktail party effect). There has been much less focus on how listeners detect a change in talker or in probing the acoustic features significant in characterizing a talker's voice in conversational speech. This study examines human talker change detection (TCD) in multi-party speech utterances using a behavioral paradigm in which listeners indicate the moment of perceived talker change. Human reaction times in this task can be well-estimated by a model of the acoustic feature distance among speech segments before and after a change in talker, with estimation improving for models incorporating longer durations of speech prior to a talker change. Further, human performance is superior to several online and offline state-of-the-art machine TCD systems. (C) 2019 Acoustical Society of America
Measurement of differential cross sections for Z boson pair production in association with jets at root s=8 and 13 TeV
No full textThis Letter reports measurements of differential cross sections for the production of two Z bosons in association with jets in proton-proton collisions at root s = 8 and 13 TeV. The analysis is based on data samples collected at the LHC with the CMS detector, corresponding to integrated luminosities of 19.7 and 35.9 fb(-1) at 8 and 13 TeV, respectively. The measurements are performed in the leptonic decay modes ZZ -> l(+)l(-)l'(+)l'(-), where, l, l' = e, mu The differential cross sections as a function of the jet multiplicity, the transverse momentum p(T), and pseudorapidity of the P-T-leading and subleading jets are presented. In addition, the differential cross sections as a function of variables sensitive to the vector boson scattering, such as the invariant mass of the two P-T-leading jets and their pseudorapidity separation, are reported. The results are compared to theoretical predictions and found in good agreement within the theoretical and experimental uncertainties. (C) 2018 The Author(s). Published by Elsevier B.V
Impact of Multiple Primaries and Partial CSI on Transmit Antenna Selection for Interference-Outage Constrained Underlay CR
No full textTransmit antenna selection is a low-complexity multiple-antenna technique that exploits spatial diversity using only one radio frequency chain. We investigate it for an underlay cognitive radio system that operates in the presence of multiple primary receivers and is subject to a constraint on the interference outage it causes at any of the primary receivers. The selection is based on a practically motivated and general partial channel state information (CSI) model in which the secondary transmitter (STx) only knows the channel power gains to a subset of the primary receivers. We derive a novel and general antenna selection rule that provably minimizes the symbol error probability (SEP) of the secondary system. We also derive insightful analytical expressions for its average SEP and interference-outage probability. These apply to a general class of channel fading models and any number of transmit and receive antennas, and include the special cases in which the STx knows channel power gains of all or none of the primary receivers. Our numerical results bring out a new insensitivity of the average SEP of the optimal rule to the interference power threshold when the CSI available is partial
Kinetic and catalytic properties of M.HpyAXVII, a phase-variable DNA methyltransferase from Helicobacter pylori
No full textThe bacterium Helicobacter pylori is one of the most common infectious agents found in the human stomach. H. pylori has an unusually large number of DNA methyltransferases (MTases), prompting speculation that they may be involved in the cancerization of epithelial cells. The mod-4a/4b locus, consisting of the hp1369 and hp1370 ORFs, encodes for a truncated and inactive MTase in H. pylori strain 26695. However, slipped-strand synthesis within the phase-variable polyguanine tract in hp1369 results in expression of an active HP1369-1370 fusion N-6-adenine methyltransferase, designated M.HpyAXVII. Sequence analysis of the mod-4a/4b locus across 74 H. pylori strain genomes has provided insights into the regulation of M.HpyAXVII expression. To better understand the role of M.HpyAXVII in the H. pylori biology, here we cloned and overexpressed the hp1369-70 fusion construct in Escherichia coli BL21(DE3) cells. Results from size-exclusion chromatography and multi-angle light scattering (MALS) analyses suggested that M.HpyAXVII exists as a dimer in solution. Kinetic studies, including product and substrate inhibition analyses, initial velocity dependence between substrates, and isotope partitioning, suggested that M.HpyAXVII catalyzes DNA methylation in an ordered Bi Bi mechanism in which the AdoMet binding precedes DNA binding and AdoMet's methyl group is then transferred to an adenine within the DNA recognition sequence. Altering the highly conserved catalytic motif (DPP(Y/F)) as well as the AdoMet-binding motif (FXGXG) by site-directed mutagenesis abolished the catalytic activity of M.HpyAXVII. These results provide insights into the enzyme kinetic mechanism of M.HpyAXVII. We propose that AdoMet binding conformationally ``primes'' the enzyme for DNA binding
Electrodeposited carbon fiber and epoxy based sandwich architectures suppress electromagnetic radiation by absorption
No full textFunctional polymer composites are in huge demand in electronic industry in general and for electromagnetic interference shielding in particular, due to ease of processing, design flexibility and lightweight. Herein, efforts are made to enhance electromagnetic interference shielding effectiveness in epoxy/carbon fiber composite, by electrodepositing magnetic particles on the surface of carbon fiber. This approach results in 100% enhancement in shielding effectiveness with respect to epoxy/Carbon fiber composites. Electrodeposition, an industrially viable and a scalable technique, is adopted here to obtain nickel decorated carbon fiber. Various nickel deposited carbon fiber morphologies are obtained by varying the applied current. Various microstructures of nickel deposited carbon fiber are obtained and the final parameters are fixed. Further, X-ray diffraction confirms the presence of nickel on the carbon fiber surface. In addition magnetic, electrical, thermal behaviour of nickel deposited carbon fiber is evaluated systematically. Epoxy/carbon fiber composites are fabricated using vacuum assisted resin transfer moulding technique. 2-Layered sandwich structure is prepared with layer 1 as nickel deposited carbon fiber and layer 2 as only carbon fiber. EMI shielding effectiveness is measured in the frequency range of 12-18 GHz. Epoxy with nickel deposited carbon fiber and bare carbon fiber sandwich architecture showed excellent shielding effectiveness up to 50 dB and with maximum absorption of up to 40 dB at 15 GHz. Thermal studies are also carried out to understand the materials response at higher temperature and frequency. Such thin, light-weight, excellent EM absorbers can be used as EMI enclosures for battery casings of hybrid electric vehicles, communication systems etc