arXiv subjects

Ashwani Kumar

Publications and source records attributed to Ashwani Kumar.

At least 19 recordsLinked to original sources

arXiv2025

Protonic Nickelate Device Networks for Spatiotemporal Neuromorphic Computing

Computation in biological neural circuits arises from the interplay of nonlinear temporal responses and spatially distributed dynamic network interactions. Replicating this richness in hardware has remained challenging, as most neuromorphic devices emulate only isolated neuron- or synapse-like functions. In this work, we introduce an integrated neuromorphic computing platform in which both nonlinear spatiotemporal processing and programmable memory are realized within a single perovskite nickelate material system. By engineering symmetric and asymmetric hydrogenated NdNiO3 junction devices on the same wafer, we combine ultrafast, proton-mediated transient dynamics with stable multilevel resistance states. Networks of symmetric NdNiO3 junctions exhibit emergent spatial interactions mediated by proton redistribution, while each node simultaneously provides short-term temporal memory, enabling nanoseconds scale operation with an energy cost of 0.2 nJ per input. When interfaced with asymmetric output units serving as reconfigurable long-term weights, these networks allow both feature transformation and linear classification in the same material system. Leveraging these emergent interactions, the platform enables real-time pattern recognition and achieves high accuracy in spoken-digit classification and early seizure detection, outperforming temporal-only or uncoupled architectures. These results position protonic nickelates as a compact, energy-efficient, CMOS-compatible platform that integrates processing and memory for scalable intelligent hardware.

cs.ET↗

arXiv2025

A Combined Theoretical and Experimental Study of Oxygen Vacancies in Co$_3$O$_4$ for Liquid-Phase Oxidation Catalysis

In the present work, we investigate oxygen vacancies (V$_\mathrm{O}$) in Co$_3$O$_4$, both in the bulk phase and under liquid-phase ethylene glycol oxidation, by combining theoretical and experimental techniques. Density functional theory calculations for bulk Co$_3$O$_4$ show that introducing an oxygen vacancy reduces two adjacent Co$^{3+}$ ions to Co$^{2+}$ and narrows the band gap. The newly formed Co$^{2+}$ ions adopt high-spin configurations in distorted octahedral sites and remain stable in this state in ab initio molecular dynamics simulations at $300$ K. Computed O and Co K-edge X-ray absorption spectra for ideal and vacancy-containing Co$_3$O$_4$ show excellent agreement with the experimental data and serve as references to analyze the liquid-phase ethylene glycol oxidation. The comparison with experimental O K-edge spectra of fresh and post-reaction catalysts shows that fresh samples resemble the vacancy-containing reference, whereas post-reaction spectra shift toward the ideal reference. These results suggest that under liquid-phase ethylene glycol oxidation conditions, Co$_3$O$_4$ becomes more oxidized rather than reduced, by refilling preexisting oxygen vacancies. This is further supported by the observation that higher O$_2$ pressures increase the conversion and that the catalyst remains stable and active over several cycles.

cond-mat.mtrl-sci↗

arXiv2025

Density Functional Theory Analysis of Na3AgO: Assessing its Viability as a Sustainable Material for Solar Energy Applications

This study mainly emphasis the fascinating features of inverse perovskites Na3AgO using density functional theory (DFT). Inverse perovskite (IP) Na3AgO structural features have been examined, and the space group and cubic structure of Pm-3m (221) have been confirmed. The experimental formulation and thermal stability of IP have been confirmed by the formation energy. Phonon dispersion curves were used to assess dynamic stability. The dynamic stability of the examined IP and the bonding strength against cubic structure deformation are confirmed by the lack of negative frequencies. The energy gap or the characteristics of semiconducting behaviour have been predicted by the electronic properties of Na3AgO with a band gap of 1.273 eV. In order to confirmthe viability of solar cells, the light-dependent properties have also been identified. Born stability criteria are also used to verify the mechanical stability, and additional elastic characteristics are identified in order to forecast the anisotropy, ductility, strength, and hardness. These anti-perovskites, which possess intriguing characteristics, have the potential to be effective materials for photovoltaic applications, as indicated by the analysed findings.

cond-mat.mtrl-sci↗

arXiv2025

Exploring PdCrAs Half-Heusler Alloy for Sustainable Energy Solutions: An Ab-initio Study

This work presents a comprehensive investigation of the HH alloy PdCrAs using first - principles methods, highlighting its potential applications in various fields, including spintronics, thermoelectrics, and optoelectronics. We employed density functional theory (DFT) within the full potential linearized augmented plane wave (FLAPW) framework. Structural optimizations indicate that the alloy stabilizes in the ferromagnetic phase. Both mechanical and dynamical stability have been confirmed through analyses of elastic constants and phonon dispersion. Our calculations of the electronic band structure and density of states (DOS) reveal that PdCrAs exhibits half-metallic behavior, with a spin-polarized band gap of 0.670 eV in the minority spin channel. The magnetic moment aligns with the Slater Pauling (SP) rule, indicating robust ferromagnetism. Mechanical analysis shows that the material is ductile in nature. Thermodynamic analysis highlights the alloy's resilience, supported by consistent trends in entropy, heat capacity, and Debye temperature.Its optical response demonstrates strong absorption in the visible and ultraviolet (UV) regions, along with pronounced dielectric and plasmonic features, suggesting potential applications in optoelectronics and refracective coatings. Furthermore, evaluations of the transport properties reveal high Seebeck coefficients and a significantly tunable figure of merit (ZT), with values approaching 0.9 across the temperature range of 300 - 1500 K, indicating excellent thermoelectric characteristics. Overall, these findings position PdCrAs as a promising multifunctional material suitable sustainable energy solutions.

cond-mat.mtrl-sci↗

arXiv2025

Thermoelectric Potential of NaVAs Half-Heusler Alloy: Insights from Ab-initio Calculations

This work presents a comprehensive investigation of the HH alloy NaVAs using first - principles methods, emphasizing its potential applications in various fields, including spintronics, thermoelectrics, and optoelectronics. We utilized density functional theory (DFT) within the full-potential linearized augmented plane wave (FLAPW) framework. Structural optimizations indicate that the alloy stabilizes in the ferromagnetic phase. Both mechanical and dynamical stability have been confirmed through analysis of elastic constants and phonon dispersion. Our calculations of the electronic band structure and density of states (DOS) reveal that NaVAs exhibits half-metallic behavior, with a spin-polarized band gap of 2.77 eV in the minority spin channel. The magnetic moment aligns with the Slater Pauling (SP) rule, demonstrating robust ferromagnetism. Mechanical analysis shows that the material is brittle in nature. The thermodynamic analysis highlights the alloy's resilience, supported by consistent trends in entropy, heat capacity, and Debye temperature. Its optical response indicates strong absorption in the visible and ultraviolet (UV) regions, along with pronounced dielectric and plasmonic features, suggesting potential for applications in optoelectronics and refective coatings. Furthermore, evaluations of the transport properties show high Seebeck coefficients and a significantly tunable figure of merit (ZT). ZT values approach 1.0 across the temperature range of 600 - 1500 K, demonstrating excellent thermoelectric characteristics. Overall, these findings position NaVAs as a promising multifunctional material suitable for advanced technological applications in green energy area.

cond-mat.mtrl-sci↗

arXiv2025

Computational insights into Cobalt-based novel half-Heusler alloy for sustainable energy applications

The quest for efficient and sustainable green energy solutions has led to a growing interest in half Heusler alloys, particularly for thermoelectric and spintronic applications. This study investigates the multifaceted nature of cobalt based half Heusler alloy, CoVAs, employing DFT with advanced computational techniques, such as the FLAPW method. The elastic, electronic, magnetic, thermodynamic, and optical properties of CoVAs are meticulously analyzed. Structural and mechanical evaluations reveal mechanical stability and brittleness under varying pressures. Electronic and magnetic properties are examined through band structure and DOS analysis, revealing a half metallic nature with a minority spin band gap. The total magnetic moment aligns with the Slater Pauling rule, further confirming ferromagnetism and half metallicity. Thermodynamic investigations, based on the quasi-harmonic Debye approximation, provide insights into temperature- and pressure dependent behavior, including thermal expansion, heat capacity, and Debye temperature, establishing CoVAs as a viable candidate for high temperature applications. Additionally, the optical properties underestimate its potential in optoelectronic applications due to high absorption in the UV region, showing a distinct absorption edge corresponding to the electronic band gap. Phonon dispersion relations reflect the stability of the alloy, and the figure of merit confirms the alloy's suitability for thermodynamics applications. The findings highlight the potential of CoVAs as a promising candidate for spintronic photovoltaic and optoelectronic applications, providing insights into its fundamental properties that could facilitate experimental synthesis and industrial implementation for green energy and advanced technological applications.

cond-mat.mtrl-sci↗

arXiv2025

Computational Studies of NaVTe Half Heusler Alloy for Green Energy Applications

To lessen the quick depletion of fossil fuels and the resulting environmental harm, it is necessary to investigate effective and eco-friendly materials that can convert lost energy into electricity. The structural, optical, electronic, thermo-electric, and thermodynamic properties of the novel half-Heusler (HH) material NaVTe were examined in the current work using density functional theory (DFT). The Birch-Murnaghan equations of states were used to confirm the structural stability of the NaVTe HH alloy under investigation. These equations show that the compound in question has structural stability because its ground-state energy levels are negative. For spin-down configurations, NaVTe possesses an energy band gap of 3.2 eV, according to band structure and total density of state analysis. NaVTe is a material that is desirable for optoelectronic applications due to its optical features, which include maximum conductivity and absorption of electromagnetic radiation. The figure of merit and other thermodynamic and thermoelectric parameters are calculated. According to these predicted outcomes, the NaVTe HH alloy would be the ideal option for thermo-electric and renewable energy applications.

cond-mat.mtrl-sci↗

arXiv2024

First Principle Analysis of Novel Half Heusler Alloys VPdZ (Z= Ge, Sn) for thermodynamic, spintronics and optoelectronic applications

This study explores the structural stability, elastic, mechanical, electronic, thermophysical, magnetic, optical and lattice dynamic properties of VPdZ (Z= Ge, Sn) half Heusler alloys using density functional theory. The alloys show stability in type-{\alpha} ferromagnetic phase and have half-metallic band topologies. The half-metallic feature is indicated by the spin-polarized behavior that is revealed by the detailed profiles of the electronic band structures. According to the electronic band profiles both alloys are half-metallic, with indirect energy gaps in the spin down channel of 1.10 eV and 1.02 eV for VPdGe and VPdSn half Heusler alloys respectively. The Quasi-Harmonic Debye model helps study thermodynamic parameters, and the magnetic moment values align with the Slater-Pauling rule. The alloys have potential applications in thermodynamic, spintronic, and optoelectronic fields.

cond-mat.mtrl-sci↗

arXiv2024

First-principles investigation of multifaceted properties; lattice dynamic, structural stability, mechanical, electronic, magnetic and thermodynamic response of Alkali metals-based semi Heusler alloys

Taking into considerations the wide compositional stretch of Heusler alloys, the first principles density functional theory based calculations are excellently suitable for estimating the multifaceted properties of alkali metal based LiVSb and NaVSb Heusler alloys. We calculated ground state stability by optimizing the energy in alpha, beta and gamma phase configurations. The materials are dynamically stable in spin polarised phase type alpha. To explore the electronic structure, we successfully employed the generalized gradient approximation potential. The electronic band structures indicate a half-metallic nature featuring a wide indirect band gap of 1.40eV and 1.45eV. We computed the second-order elastic parameters at different pressure levels. The Pugh ratio less than 0.25 assessed that both alloys are brittle in nature and mechanically stable. The obtained magnetic moment is consistent with the Slater-Pauling rule. By executing the Quasi-Harmonic Debye model and Boltzmann theory we assessed the various thermodynamic parameters and transport coefficients of both alloys at different temperatures and pressures. All positive frequencies in lattice dynamic study confirmed their stability. Our findings highlight the potential of these alloys in modern semiconductor technology, and thermoelectric applications.

cond-mat.mtrl-sci↗

arXiv2024

Spin-polarized DFT calculations for physical properties of novel KVSb half-Heusler compound for spintronic and thermodynamic applicability

In the reported study we have investigated the robust phase stability, elasto-mechanical, thermophysical and magnetic properties of KVSb half Heusler compound by implementing density functional theory models in Wien2k simulation package. The dynamic phase stability is computed in phase type I, II & III phase configurations by optimising their energy. It is observed that given compound is more stable in spin-polarised state of phase type I. To explore the electronic band structure, we apply the generalised gradient approximation. The electronic band profile of the Heusler alloy display a half-metallic nature. Moreover, the calculated second-order elastic parameters divulge the ductile nature. To understand the thermodynamical and thermoelectric stability of the alloy at various temperature and pressures ranges we have utilised the Quasi-Harmonic Debye model. The computed value of magnetic moment found in good agreement with Slater-Pauling rule. Our findings confirms that the predicted half Heusler alloy can be used in various spintronics and thermoelectric applications.

cond-mat.mtrl-sci↗

arXiv2024

First-principle screening of structural, electronic and hydrogen storage properties of Vanadium based hydride perovskites XVH$_3$ (X = Li, K)

V-based XVH$_3$ (X = Li,K) hydrides perovskites are investigated for their hydrogen storage capacity using the WIEN2K code. To verify the stability of these hydrides, first-principles investigations are employed to examine their structural, electronic and hydrogen storage properties. According to structural studies these compositions hydrides are stable and part of the cubic space group (221 Pm-3m). We have examined many aspects of these compositions throughout, using the PBE-GGA exchange correlation potential. We obtained the energy versus volume curve and found the stable phase and structural parameter of these hydrides using equation of state given by Birch-Murnaghan's. These hydrides thermodynamic stability is expressed in terms of their gravimetric hydrogen storage capacity.The goal of this study is to compute the standard enthalpy of formation and thermal desorption to ascertain the stability of these hydrides. Based on band structure and density of state plots it is found that these compositions are metallic in nature. The study presents a preliminary theoretical approach for hydrogen storage applications of thermoelectric compositions, revealing their strong thermoelectric responses and potential for green energy sources.

cond-mat.mtrl-sci↗

arXiv2023

Multi-level, Forming Free, Bulk Switching Trilayer RRAM for Neuromorphic Computing at the Edge

Resistive memory-based reconfigurable systems constructed by CMOS-RRAM integration hold great promise for low energy and high throughput neuromorphic computing. However, most RRAM technologies relying on filamentary switching suffer from variations and noise leading to computational accuracy loss, increased energy consumption, and overhead by expensive program and verify schemes. Low ON-state resistance of filamentary RRAM devices further increases the energy consumption due to high-current read and write operations, and limits the array size and parallel multiply & accumulate operations. High-forming voltages needed for filamentary RRAM are not compatible with advanced CMOS technology nodes. To address all these challenges, we developed a forming-free and bulk switching RRAM technology based on a trilayer metal-oxide stack. We systematically engineered a trilayer metal-oxide RRAM stack and investigated the switching characteristics of RRAM devices with varying thicknesses and oxygen vacancy distributions across the trilayer to achieve reliable bulk switching without any filament formation. We demonstrated bulk switching operation at megaohm regime with high current nonlinearity and programmed up to 100 levels without compliance current. We developed a neuromorphic compute-in-memory platform based on trilayer bulk RRAM crossbars by combining energy-efficient switched-capacitor voltage sensing circuits with differential encoding of weights to experimentally demonstrate high-accuracy matrix-vector multiplication. We showcased the computational capability of bulk RRAM crossbars by implementing a spiking neural network model for an autonomous navigation/racing task. Our work addresses challenges posed by existing RRAM technologies and paves the way for neuromorphic computing at the edge under strict size, weight, and power constraints.

cs.ET↗

arXiv2021

Ordinal Pooling

In the framework of convolutional neural networks, downsampling is often performed with an average-pooling, where all the activations are treated equally, or with a max-pooling operation that only retains an element with maximum activation while discarding the others. Both of these operations are restrictive and have previously been shown to be sub-optimal. To address this issue, a novel pooling scheme, named\emph{ ordinal pooling}, is introduced in this work. Ordinal pooling rearranges all the elements of a pooling region in a sequence and assigns a different weight to each element based upon its order in the sequence. These weights are used to compute the pooling operation as a weighted sum of the rearranged elements of the pooling region. They are learned via a standard gradient-based training, allowing to learn a behavior anywhere in the spectrum of average-pooling to max-pooling in a differentiable manner. Our experiments suggest that it is advantageous for the networks to perform different types of pooling operations within a pooling layer and that a hybrid behavior between average- and max-pooling is often beneficial. More importantly, they also demonstrate that ordinal pooling leads to consistent improvements in the accuracy over average- or max-pooling operations while speeding up the training and alleviating the issue of the choice of the pooling operations and activation functions to be used in the networks. In particular, ordinal pooling mainly helps on lightweight or quantized deep learning architectures, as typically considered e.g. for embedded applications.

cs.CV↗

arXiv2021

An Efficient Parallel Algorithm for finding Bridges in a Dense Graph

This paper presents a simple and efficient approach for finding the bridges and failure points in a densely connected network mapped as a graph. The algorithm presented here is a parallel algorithm which works in a distributed environment. The main idea of our algorithm is to generate a sparse certificate for a graph and finds bridges using a simple DFS (Depth First Search). We first decompose the graph into independent and minimal subgraphs using a minimum spanning forest algorithm. To identify the bridges in the graph network, we convert these subgraphs into a single compressed graph and use a DFS approach to find bridges. The approach presented here is optimized for the use cases of dense graphs and gives the time complexity of O(E/M + Vlog(M)), for a given graph G(V,E) running on M machines.

cs.DC↗

arXiv2021

Assertion Based Functional Verification of March Algorithm Based MBIST Controller

The thesis work presents assertion based functional verification of RTL representation of a digital design. The MBIST controller is designed based on a memory testing March algorithm. This March algorithm is a little modified March C algorithm which is modified by adding a paused element to test memory data retention faults. In assertion based functional verification, creation of verification plan, for MBIST controller RTL model and the implementation & simulation of the verification plan using System-Verilog and Synopsys-VCS are done. In ABV, verification plan includes the MBIST controller design and functional specification, functional coverage goals, code coverage goals, and assertions. Assertions are used to check the errors in RTL model of MBIST controller and to provide the functionality coverage. Functional coverage metrics are used to track the level or quality of verification. Most of the functional metrics score approximately reached the planned goal of 100 % which is planned in the verification plan. The designed MBIST controller is verified against the intended features. ABV approach helped to make the verification and design process efficient and less time-consuming by finding the bugs, exercising the corner cases in the design, and using the directed test cases in a small design. ABV helped to write directed and efficient test cases (25) which are approx 32 % less than the use of maximum possible random test cases (88) for designed MBIST controller with 100% assertion coverage and approximately equal total functional coverage, i.e., 97 % approx. In this way, ABV helped to fasten the design and verification process with better quality and assurance of correct functionality of MBIST controller after the integration in MBIST architecture.

cs.SE↗

arXiv2018

Ordinal Pooling Networks: For Preserving Information over Shrinking Feature Maps

In the framework of convolutional neural networks that lie at the heart of deep learning, downsampling is often performed with a max-pooling operation that only retains the element with maximum activation, while completely discarding the information contained in other elements in a pooling region. To address this issue, a novel pooling scheme, Ordinal Pooling Network (OPN), is introduced in this work. OPN rearranges all the elements of a pooling region in a sequence and assigns different weights to these elements based upon their orders in the sequence, where the weights are learned via the gradient-based optimisation. The results of our small-scale experiments on image classification task demonstrate that this scheme leads to a consistent improvement in the accuracy over max-pooling operation. This improvement is expected to increase in deeper networks, where several layers of pooling become necessary.

cs.CV↗

arXiv2017

Exploiting OxRAM Resistive Switching for Dynamic Range Improvement of CMOS Image Sensors

We present a unique application of OxRAM devices in CMOS Image Sensors (CIS) for dynamic range (DR) improvement. We propose a modified 3T-APS (Active Pixel Sensor) circuit that incorporates OxRAM in 1T-1R configuration. DR improvement is achieved by resistive compression of the pixel output signal through autonomous programming of OxRAM device resistance during exposure. We show that by carefully preconditioning the OxRAM resistance, pixel DR can be enhanced. Detailed impact of OxRAM SET-to-RESET and RESET-to-SET transitions on pixel DR is discussed. For experimental validation with specific OxRAM preprogrammed states, a 4 Kb 10 nm thick HfOx (1T-1R) matrix was fabricated and characterized. Best case, relative pixel DR improvement of ~ 50 dB was obtained for our design.

cs.ET↗

arXiv2014

Anomalous Gap Reversal of the $3+1/3$ and $3+1/5$ Fractional Quantum Hall States

In this work we report the opening of an energy gap at the filling factor $ν=3+1/3$, firmly establishing the ground state as a fractional quantum Hall state. This and other odd-denominator states unexpectedly break particle-hole symmetry. Specifically, we find that the relative magnitudes of the energy gaps of the $ν=3+1/3$ and $3+1/5$ states from the upper spin branch are reversed when compared to the $ν=2+1/3$ and $2+1/5$ counterpart states in the lower spin branch. Our findings raise the possibility that the former states have a non-conventional origin.

cond-mat.str-el↗