Showing papers by "Abhishek K. Singh published in 2021"

Electrooxidation of Hydrazine Utilizing High-Entropy Alloys: Assisting the Oxygen Evolution Reaction at the Thermodynamic Voltage

Abstract: Hydrazine electrooxidation is an important reaction as it assists in decreasing the OER overvoltage. Herein, we report the utilization of high entropy nano-catalyst alloy for the electrooxidation of hydrazine. High entropy nano-catalyst comprising five elements (Ag, Au, Pt, Pd, Cu) shows profound activity towards this molecule at low overvoltage. An intriguingly high entropy nano-catalyst prepared by the casting-cum-cryomilling method is endowed with unique catalytic activity for HzOR. Detailed analysis of gaseous product points to the formation of nitrogen as well as oxygen as the oxidation product, a sign of accompanying oxygen evolution reaction (OER). Interestingly, significant oxygen is detected at 1.13 V (RHE) in a neutral buffered medium, confirming that OER is functional at a voltage near to the thermodynamic voltage of 1.23V (RHE). The quantitative contribution of each hydrazine and OER reaction is ascertained which explains a vital insight into this reaction. Density functional theory calculations showed that both HzOR and OER assist each other where the electron-donating effect of H2O to the surface can reduce the endothermicity of the HzOR. Whereas, the electron acceptance of *NHNH2 helps in the favorable overlap of the HEA Fermi level and vacant states with the HOMO of H2O.

Ultralow Thermal Conductivity in Earth-Abundant Cu1.6Bi4.8S8: Anharmonic Rattling of Interstitial Cu

Abstract: Earth-abundant, nontoxic crystalline compounds with intrinsically low lattice thermal conductivity (Iolat) are centric to the development of thermoelectrics and thermal barrier coatings. Investigation of the fundamental origins of such low Iolat and understanding its relationship with the chemical bonding and structure in solids thus stands paramount in order to furnish such low thermally conductive compounds. Herein, we synthesized earth-abundant, cost-effective, and nontoxic n-type ternary sulfide Cu1.6Bi4.8S8, which exhibits an intrinsically ultralow Iolat of �0.71-0.44 W/m·K in the temperature range of 296-736 K. Structural analysis via atomic refinement unveiled large atomic displacement parameters (ADPs) for interstitial Cu clusters, demonstrating intrinsic rattling-like behavior. Electron localization function (ELF) analysis further shows that these rattling Cu atoms are weakly bonded and thus can generate low-energy Einstein vibrational modes. Low-temperature heat capacity (Cp) and temperature-dependent Raman spectra concord the presence of such low-energy optical modes. Density functional theory (DFT)-based phonon dispersions reveal that these low-lying optical phonons arise primarily due to the presence of chemical bonding hierarchy and simultaneous rattling of weakly bonded interstitial Cu atoms. These low-energy optical modes strongly scatter the heat-carrying acoustic phonons, thereby reducing the phonon lifetime to an ultrashort value (2-4.5 ps) and Iolat to a very low value, which is lower than that of the many state-of-the-art metal sulfides. © 2021 American Chemical Society. All rights reserved.

Nonlinear Optical Absorption of ReS2 Driven by Stacking Order

Abstract: The stacking order of 2D materials can result in fascinating physical properties. Two different stacking orders (AA and AB) were recently identified in ReS2, a rising star in the transition metal d...

Mechanistic study on nitrogen-doped graphitic carbon-reinforced chromium nitride as a durable electrocatalyst for oxygen reduction

Abstract: Designing efficient catalysts for major energy conversion devices like fuel cells and metal–air batteries is of prime importance as the commercially used Pt/C catalyst impedes scalable use due to high cost, low stability, and methanol-intolerant behavior. Herein, we report a one-step method to synthesize phase-pure CrN nanoparticles (CrN NPs, ∼4 nm) anchored on N-doped graphitic carbon (CrN@NG) as an excellent Pt-free electrocatalyst to boost the oxygen reduction reaction (ORR) in alkaline and acidic media. The as-synthesized CrN@NG-900 competes with 20 wt% Pt/C with an E1/2 that is only 30 and 60 mV negative of Pt/C in alkaline and acidic media, respectively. Furthermore, the low-cost CrN@NG shows better long-term stability (no NP leaching or agglomeration) and methanol immunity that is desirable to replace Pt for applications in a real system. Density functional theory (DFT) calculations reveal a synergistic interaction between CrN and the NG support, which optimizes the free energy of the reaction intermediates and favors the ORR. The robust stability of the catalyst due to the NG support, better electron transfer, and greater electrochemically active sites augment the ORR activity in alkaline and acidic media.

Formation of a Small Electron Polaron in Tantalum Oxynitride: Origin of Low Mobility

Abstract: Tantalum oxynitride (I²-TaON) is a potential photoanode because of its suitable band gap and band-edge positions for water-splitting. However, low carrier mobility restricts the solar-to-hydrogen conversion efficiency from the theoretical limit. Here, using the DFT + U formalism, we find that the excess electron tends to form a localized small polaron at the Ta-site (Ta+4 species) over delocalized electrons. The polarization potential created by lattice distortion around Ta+5(d0) generates a driving force to construct Ta+4(d1) by electron capture. The donated electron from n-type single donor defects becomes self-trapped and forms a weakly bound state with the defect. The thermally activated polaronic charge transfer via nearest-neighbor hopping is non-adiabatic using the DFT + U method. However, O substitution at bridging the N site increases the Ta-Ta hopping distance and changes the polaron hopping toward an adiabatic regime. The calculated polaron mobility because of the high migration barrier for both in pristine (0.31 eV) and in the presence of the ON defect (0.36 eV) supports the experimentally observed low mobility and high carrier lifetime in a I²-TaON photoanode. This study provides a mechanistic understanding of the factors controlling the formation and transport of electron polarons, which can guide in designing a I²-TaON photoanode with better efficiency. © copy; 2021 American Chemical Society.

Atypical behavior of intrinsic defects and promising dopants in two-dimensional WS 2

Abstract: The $2\mathrm{D}\text{\ensuremath{-}}\mathrm{W}{\mathrm{S}}_{2}$ is an emerging material for next-generation electronic and optoelectronic devices. These applications are very sensitive and can be adversely affected by defects incorporated during the sample growth. Using hybrid density functional approach, we carried out a comprehensive study on intrinsic and extrinsic defects in $2\mathrm{D}\text{\ensuremath{-}}\mathrm{W}{\mathrm{S}}_{2}$. All the intrinsic defects and their complexes are found to be deep and self-compensating. S vacancy $({\mathrm{V}}_{\text{S}})$, which has been previously attributed as the source of $n$-type conductivity, turns out to be an electron trap center. We found that ${\mathrm{V}}_{\text{S}}$ gives rise to a suboptical gap, which can be the source of single-photon emitters. Interestingly, hydrogen interstitial $({\mathrm{H}}_{i})$ makes multicenter bond and acts as a shallow donor. In addition, H as adatom (H-ad) also provides shallow donor levels and is the cause of unintentional $n$-type doping. Among the extrinsic defects, halogens and transition metals are found to be promising dopants. While halogens at the S site act as shallow donors, Nb at the W site provides a reasonable shallow acceptor level with low formation energy.

Safety and efficacy of incisional goniotomy as an adjunct with phacoemulsification in primary angle-closure glaucoma

Abstract: PURPOSE To evaluate the intraocular pressure (IOP)-lowering efficacy and safety of incisional goniotomy as an adjunct to phacoemulsification in primary angle-closure glaucoma (PACG) patients. METHODS Consecutive patients with PACG (high or borderline IOP) deemed fit for phacoemulsification were enrolled. After phacoemulsification, incisional goniotomy was performed with or without goniosynechialysis. Patient demographic profile, clinical data, and adverse events, if any, were analyzed during at least a 6-month follow-up period. Success was defined as IOP of 18 mm Hg or lesser with or without medications. SETTING Tertiary care Ophthalmic hospital. DESIGN Prospective interventional case series. RESULTS Of 46 eyes (38 patients) included, 69.6% eyes were classified as having advanced glaucoma. The mean treated IOP decreased by 7.3 ± 1.0 (SE) mm Hg (95% CI, 5.2-9.3) from 21.4 ± 6.6 to 14.2 ± 3.7 mm Hg at a mean duration of 11.7 ± 5.5 months (6-22 months) postoperatively (P < .001, paired t test). There was 66.6% reduction in median number of hypotensive medications (P < .001, Wilcoxon signed-rank test). Observed complications included hyphema (13 eyes [28%]), IOP spike (3 eyes [6.5%]), and cyclodialysis (1 eye [2.17%]). High treated IOP and number of medications were significantly associated with failure in univariate analysis (P < .05, Fisher exact test). The cumulative survival probability for qualified success at 22 months was 87.8% ± 0.07 (95% CI, 0.65-0.96). CONCLUSIONS Incisional goniotomy as an adjunct with phacoemulsification resulted in a significant and sustained reduction in IOP along with decrease in number of glaucoma medications in chronic PACG eyes, irrespective of the disease stage.

On the characteristics of reflected waves in Rotating Functionally graded Initially stressed piezoelectric-orthotropic half-space

Abstract: As a result of technological escalation in sensing applications, piezopolymers like Polyvinylidene fluoride (PVDF), very flexible in nature, are preferred over most of the piezoceramics which are s...

Anisotropic Interlayer Exciton in GeSe/SnS van der Waals Heterostructure.

Abstract: Stacking two or more two-dimensional materials to form a heterostructure is becoming the most effective way to generate new functionalities for specific applications. Herein, using GW and Bethe-Salpeter equation simulations, we demonstrate the generation of linearly polarized, anisotropic intra- and interlayer excitonic bound states in the transition metal monochalcogenide (TMC) GeSe/SnS van der Waals heterostructure. The puckered structure of TMC results in the directional anisotropy in band structure and in the excitonic bound state. Upon the application of compressive/tensile biaxial strain dramatic variation (∓3%) in excitonic energies, the indirect-to-direct semiconductor transition and the red/blue shift of the optical absorption spectrum are observed. The variations in excitonic energies and optical band gap have been attributed to the change in effective dielectric constant and band dispersion upon the application of biaxial strain. The generation and control over the interlayer excitonic energies can find applications in optoelectronics and optical quantum computers and as a gain medium in lasers.

Interlayer excitonic states in Mo Se 2 / Mo S 2 van der Waals heterostructures

Abstract: In the present work, we report different interlayer excitonic states of an aligned $\mathrm{Mo}{\mathrm{Se}}_{2}/\mathrm{Mo}{\mathrm{S}}_{2}$ incommensurate van der Waals (vdW) heterostructure (HS). The HS was fabricated by stacking chemical vapor deposited monolayers, and it was studied using photoluminescence (PL) measurements. We observed the emergence of two low-energy peaks in the PL spectrum of the HS measured at 100 K, which were absent in the constituent monolayers. The orbital resolved electronic band structure and the optical absorption considering the electron-hole interaction for these HSs were calculated using first-principles density functional theory simulations, which showed energy band hybridization and the presence of interlayer excitons (ILEs). Based on these observations, the peak at $\ensuremath{\sim}1.57$ eV was assigned to a momentum direct ILE, while the other peak at $\ensuremath{\sim}1.35$ eV showed feeble emission intensity and was assigned to a momentum indirect ILE. The emergence of both of these excitonic peaks in the HS PL spectrum can be attributed to the formation of a spatially periodic moir\'e potential at a nanometer length scale resulting in hybridization. Our results can help to understand the physics of ILEs and to engineer vdW HSs for efficient optoelectronic devices.

On propagation behavior of SH-wave and Rayleigh-type wave in an initially stressed exponentially graded fiber-reinforced viscoelastic layered structure

Abstract: The present article undertakes the study of propagation of SH-wave and Rayleigh-type wave in a layered structure with a layer overlying a semi-infinite medium composed of distinct initially stresse...

Accelerated Discovery of Thermoelectric Materials Using Machine Learning

Abstract: Optimized electronic and thermal transport properties are the key requirements for the discovery of efficient thermoelectric materials Owing to the complex interdependence, simultaneous optimization of these properties is a non-trivial and challenging task, especially if one wants to explore the large available search space of materials With the advent of statistical high-throughput and machine learning based approaches, several of these challenges for thermoelectrics have been addressed The goal of this chapter is to highlight these data-assisted efforts towards accelerated development of high-performance thermoelectric materials We will discuss the contribution of curated databases for high-throughput screening of desired electronic and thermal transport properties The utilization of these databases will also be described for development of prediction models of transport properties, which has accelerated the discovery of highly efficient thermoelectric materials Details of commonly used strategies and methods to select a relevant descriptor set for developing the prediction models will be covered A new approach for selecting descriptors by analyzing the high-throughput property map will be explained The potential of machine learning methods in relating the unrelated properties will be illustrated by establishing a connection between otherwise independent electronic and thermal transport properties Further, for designing the highly transferable models for a single target property of interest, we will also cover localized regression based algorithmic development

COVID-19 Tests Gone Rogue: Privacy, Efficacy,Mismanagement and Misunderstandings

Abstract: COVID-19 testing, the cornerstone for effective screening and identification of COVID-19 cases, remains paramount as an intervention tool to curb the spread of COVID-19 both at local and national levels. However, the speed at which the pandemic struck and the response was rolled out, the widespread impact on healthcare infrastructure, the lack of sufficient preparation within the public health system, and the complexity of the crisis led to utter confusion among test-takers. Invasion of privacy remains a crucial concern. The user experience of test takers remains low. User friction affects user behavior and discourages participation in testing programs. Test efficacy has been overstated. Test results are poorly understood resulting in inappropriate follow-up recommendations. Herein, we review the current landscape of COVID-19 testing, identify four key challenges, and discuss the consequences of the failure to address these challenges. The current infrastructure around testing and information propagation is highly privacy-invasive and does not leverage scalable digital components. In this work, we discuss challenges complicating the existing covid-19 testing ecosystem and highlight the need to improve the testing experience for the user and reduce privacy invasions. Digital tools will play a critical role in resolving these challenges.

Dynamic Alteration in the Vaginal Secretory Proteome across the Early and Mid-Trimesters of Pregnancy.

Abstract: Pregnancy is characterized by intense physiological and structural alterations in the vagina, cervix, and overlying fetal membranes. High vaginal fluid (HVF) is a proximal fluid that covers the lower part of the female reproductive system and the severity of vaginal pathology often adversely affects pregnancy outcomes. To identify the correlation of vaginal fluid proteome dynamics and physiological changes during the progression of pregnancy, a longitudinal study was performed on 20 pregnant women who delivered a baby in >37 weeks without any complications. SWATH-MS-based label-free quantitative proteomics was performed to profile the HVF proteome at three time points defined as V1 (7-12 weeks), V2 (18-20 weeks), and V3 (26-28 weeks). Linear mixed-effect models were used to estimate protein abundance as a function of the period of gestational age. In this study, we identified 1015 HVF proteins and 61 of them were significantly altered until late second trimester. Our result demonstrates that the HVF proteins reveal gestational age-specific expression patterns and the function of these proteins is associated with tissue remodeling, organ development, and microbial defense. Our study provides an opportunity to monitor the underlying physiology of pregnancy that may be further probed for the biomarker identification in pregnancy-related adverse outcomes. Data are available via ProteomeXchange with identifiers PXD014846 and PXD021811.

The GMRES solver for the interpolating meshless local Petrov–Galerkin method applied to heat conduction

Abstract: PurposeThe work presents a novel implementation of the generalized minimum residual (GMRES) solver in conjunction with the interpolating meshless local Petrov–Galerkin (MLPG) method to solve steady-state heat conduction in 2-D as well as in 3-D domains.Design/methodology/approachThe restarted version of the GMRES solver (with and without preconditioner) is applied to solve an asymmetric system of equations, arising due to the interpolating MLPG formulation. Its performance is compared with the biconjugate gradient stabilized (BiCGSTAB) solver on the basis of computation time and convergence behaviour. Jacobi and successive over-relaxation (SOR) methods are used as the preconditioners in both the solvers.FindingsThe results show that the GMRES solver outperforms the BiCGSTAB solver in terms of smoothness of convergence behaviour, while performs slightly better than the BiCGSTAB method in terms of Central processing Unit (CPU) time.Originality/valueMLPG formulation leads to a non-symmetric system of algebraic equations. Iterative methods such as GMRES and BiCGSTAB methods are required for its solution for large-scale problems. This work presents the use of GMRES solver with the MLPG method for the very first time.

Impact of curved boundary on the propagation characteristics of Rayleigh-type wave and SH-wave in a prestressed monoclinic media

Abstract: The present article delves the effect of curved boundary on the propagation characteristics of Rayleigh-type wave and SH wave in an initially stressed monoclinic media. The present communication fo...

Paley–Wiener–Schwartz Type Theorem for Ultradistributional Wavelet Transform

Abstract: In this paper, we discuss the wavelet transform on the space of ultradistributions of compact support. The Paley–Wiener–Schwartz type theorem for the wavelet transform of both test function and ultradistribution are obtained.

IoT Based Energy Efficient Agriculture Field Monitoring and Smart Irrigation System using NodeMCU

Abstract: Agriculture is the most important sector of the Indian economy and employs 50% of the country’s forces But, in recent times the economic contribution of agriculture to India’s GDP is steadily declining A major problem is the absence of an energy-efficient and reliable system for real-time monitoring of soil’s condition The paper proposes a smart alert and irrigation system with real-time monitoring of soil’s condition The proposed system detects the soil’s moisture content and temperature Using NodeMCU development kit, the data are sent to the cloud-based IoT platform for round the clock real-time monitoring of the soil’s condition A Message Queue Telemetry Transport communication protocol is used for data transmission The cloud-based IoT platform analyses the collected data and sends alert messages and controls the irrigation system according to the pre-set threshold conditions The proposed system is secure, economically feasible, reliable and energy-efficient which brings automation and IoT technology to the agriculture sector

Modified submental platysmal adipomyofascial flap: is it a reliable alternate reconstructive option for small- to mid-sized defects especially in male patients with oral/oropharyngeal cancer?

Abstract: To introduce modified submental platysmal adipomyofascial flap as a new and viable hairless locoregional option for reconstruction of small- to mid-sized defects after ablative surgery in oral/oropharyngeal cancer patients keeping in mind the present pandemic situation. An observational retrospective study was conducted using modified submental platysmal adipomyofascial flap as a locoregional reconstructive option for both intraoral and oropharyngeal defects in early-stage oral/oropharyngeal cancer patients, from Jan 2016 to May 2020 in a tertiary care hospital. All patients in this study were male and the overall flap outcome was evaluated with post-operative follow-up. Out of 18 patients, in 4 patients modified submental platysmal adipomyofascial flap was used as a combination of flaps for reconstruction. Six patients (33.33%) underwent adjuvant radiation therapy/radiation chemotherapy. The long-term functions (speech and swallowing) and cosmetic outcomes were good in the majority of the patients. One patient (5.55%) had pinhole oroantral fistula. No patient had any major flap failure. Modified submental platysmal adipomyofascial flap can be considered as a good alternative in male patients for reconstruction of small- to mid-sized oral cavity/oropharyngeal defects post-resection, especially during the prevailing pandemic crisis. It is an oncologically safe procedure with the major advantage of providing a hairless flap for oral cavity, tonsillar and BOT resection defects with lesser donor site morbidity.

Dispersion and attenuation of shear wave in couple stress stratum due to point source

Abstract: This study discusses the propagation of a horizontally polarised shear wave in a layered composite structure consisting of couple stress stratum over a functionally graded orthotropic viscoelastic ...

Study on propagation characteristics of SH-wave in an imperfectly bonded functionally graded structure with viscoelastic stratum and fibre-reinforced substrate

Abstract: Propagation behavior of SH-wave in a layered structure comprises of a functionally (exponentially) graded fibre-reinforced substrate imperfectly bonded to a functionally (exponentially) graded Voigt-type viscoelastic stratum is studied. The complex form of frequency equation is achieved in closed-form whose real part represents dispersion relation and imaginary part represents damping equation. In isotropic case, dispersion relation coincides with classical Love- wave equation whereas damping equation vanishes identically for the classical case. The effects of imperfect bonding, wave number, functional gradient parameters of stratum and substrate, viscoelasticity in stratum and reinforcement in the substrate are analyzed on the phase as well as damped velocities of SH-wave. Furthermore, the impact of imperfect common interface on the propagation of SH-wave is examined meticulously by analyzing the effect of flexibility and viscoelastic component associated to the imperfect bonding of stratum and substrate. Numerical calculations and graphical demonstrations are carried out for the present study which unravels some important peculiarities.