arXiv subjects

Abhishek Kumar Singh

Publications and source records attributed to Abhishek Kumar Singh.

At least 19 recordsLinked to original sources

arXiv2026

A fully parallel densely connected probabilistic Ising machine with inertia for real-time applications

Ising machines---special-purpose hardware for heuristically solving Ising optimization problems---based on probabilistic bits (p-bits) have been established as a promising alternative to heuristic optimization algorithms run on conventional computers. However, it has---until now---been thought that Ising spins that are connected in probabilistic Ising machines (PIMs) cannot be updated in parallel without ruining the machine's solving ability. This has presented a major challenge to realizing the potential for probabilistic Ising machines to act as fast solvers for densely connected Ising problems. In this paper, we show that it is possible to circumvent this conventional wisdom. We introduce a modified form of Ising spin dynamics for PIMs, adding an inertia term, and verify in algorithm simulations, field-programmable gate array (FPGA) emulation, and in FPGA experiments that the modified dynamics enables fully parallel, synchronous updates and at the same time improves the achieved success probability. Our evaluations were performed with various types of abstract (Max-Cut and Sherrington-Kirkpatrick model) and application-derived (multiple-input and multiple-output, MIMO detection) dense Ising benchmark instances. Performing fully parallel updates results in a speed advantage that grows superlinearly with the number of spins, giving rise to large time-to-solution reductions for practical problem sizes. For both MC and the SK model at a problem size of 200, our approach achieved an average speedup of ~34x, with the best single-instance speedup reaching 150x. As an example of the practical utility of our approach in an application where speed is critical, we co-design the algorithm dynamics and hardware implementation for MIMO detection, achieving improved detection accuracy relative to the standard linear detector and higher throughput than the conventional sequential-update PIM.

cs.ET↗

arXiv2026

Stochastic Galerkin Method for Fractional Boundary Value Problems: Convergence Analysis and Numerical Treatment

We study two-point fractional boundary value problems with uncertain input data, where randomness may enter through the coefficients and boundary conditions. To quantify the resulting uncertainty in the solution, we employ the generalized polynomial chaos (gPC) framework and develop a stochastic Galerkin formulation of the problem. A particular focus of this work is the convergence analysis of the resulting approximation. Rather than imposing assumptions directly on the stochastic coefficients appearing in the gPC representation, we introduce minimal regularity assumptions on the input data and use them to establish the properties required for the convergence analysis. Based on these results, we prove the convergence of the stochastic Galerkin approximation to the corresponding gPC solution. Numerical experiments are presented to illustrate the theoretical findings and to investigate the influence of random coefficients and boundary conditions on the statistical behavior of the solution.

math.NA↗

arXiv2026

Spectro-polarimetry of HAbitable Planet Earth (SHAPE) on Chandrayaan-3: Instrument characteristics, calibration and onboard performance

The orbiter of the Chandrayaan-3 mission of the Indian Space Research Organisation (ISRO) carries an experimental payload called SHAPE (Spectro-polarimetry of HAbitable Planet Earth). This payload makes disc-integrated observations of Earth as an exoplanet, from the Moon as well as from the high altitude Earth orbit. The instrument consists of an Acousto-Optic Tunable Filter (AOTF) based near-infrared spectro-polarimeter making the measurements in the two orthogonally polarized directions using a pair of Indium-Gallium-Arsenide (InGaAs) detectors. The laboratory characterization of the flight model of the instrument included a relative measurement of the response of the two channels of the instrument. The field measurements of the instrument revealed a non-uniformity in the field response. In the light of non-identical response of the two channels and the non-uniformity of the field response, a theoretical model of such a polarimeter is developed to gain insights into the performance of a polarimeter. Analysis of lunar observations obtained within the SHAPE field of view indicates that the transmission ratio between the two polarized channels lies in the range 0.8-1.2. Such deviations from unity can introduce offsets in the measured polarization of up to about 10%. The suitability of SHAPE for studying the band polarization, defined as the relative polarization within a spectral absorption band, is studied. Using the Moon observations and the theoretical instrumental model, the suitability of measuring the relative band polarization is demonstrated. A study of systematic biases in the band polarization demonstrates a maximum offset of less than 1% in the measured value of the band polarization. The initial results of Earth observations, spectra and flux measurements across phase angles, and the methodology for retrieving the band polarization from these observations are also discussed.

astro-ph.IM↗

arXiv2026

AgentAudit: An Open, Extensible Framework for Full-Lifecycle Trust Evaluation of AI Agents

Existing evaluation frameworks mostly assess only one part of AI agents, such as task completion (AgentBench) or security robustness (AgentDojo, ASB), rather than the complete pipeline of planning, tool selection, tool execution, memory and reasoning. Failures can occur at any stage, yet existing benchmarks rarely identify their precise source. AgentAudit evaluates the entire execution trace across ten capability, grounding, security and behavioural dimensions, namely instruction integrity, planner, memory, tool selection, tool invocation, tool correctness, alignment, tool faithfulness, security and execution integrity, combined with behavioural classification and failure attribution to pinpoint the exact stage responsible for an observed failure. AgentAudit can evaluate any LLM-based AI agent, since it attaches to the agent instead of replacing it. It reads only the recorded execution trace and does not interfere with how the agent runs, so it places no constraint on the agent's internal implementation. We evaluate five language models (OpenAI GPT-5, Claude Sonnet 5, Sarvam 105B, Llama 3.3 70B and Gemini 2.5 Flash) across nine capability and adversarial tasks. Claude Sonnet 5 and GPT-5 obtain the highest mean Composite Trust Scores (95.1 and 80.6 out of 100, respectively), while Sarvam 105B, Llama 3.3 70B and Gemini 2.5 Flash trail substantially (57.6, 45.7 and 22.6). All traces were scored by a single fixed judge model, which was itself one of the evaluated models, a limitation discussed in Section VII.E. More importantly, models with similar task-completion behaviour can diverge sharply in trustworthiness, as several non-frontier models are repeatedly classified Unsafe_Compliance on adversarial tasks rather than merely failing them, a distinction that pass/fail benchmarks cannot surface.

cs.AI↗

arXiv2026

Comparative Assessment of Thermal Transport Theories: Dual-Channel Mechanism Dictates Heat Transport in Ultralow-$κ$ Materials

Anomalous heat transport in strongly anharmonic crystalline solids poses both a fundamental challenge to the theoretical understanding and an opportunity for thermoelectric and thermal barrier coating applications. Although Green-Kubo theory reproduces experimental thermal conductivity ($κ$) at high temperatures, it lacks microscopic insight and neglects the Bose-Einstein statistics of lattice vibrations. On the other hand, the conventional Boltzmann transport equation (BTE) framework, based on a phonon-gas picture, fails due to strong anharmonicity-induced overdamped phonons. Herein, the thermal transport properties in TlAgSe, a metal chalcogenide, and Cs$_2$PbI$_2$C$_2$, an all-inorganic layered Ruddlesden-Popper perovskite, are investigated by explicitly accounting for temperature-dependent lattice dynamics through machine learning interatomic potentials and employing the Wigner transport equation (WTE) framework. Crucially, heat conduction is governed not only by higher-order phonon scattering-dominated populations' transport channel described within the BTE, but also by a coherences' channel in the WTE framework arising from wave-like interbranch coherence between eigenstates. Incorporating four-phonon scattering, WTE predicts average room-temperature $κ$ values of 0.31 Wm$^{-1}$K$^{-1}$ (TlAgSe) and 0.38 Wm$^{-1}$K$^{-1}$ (Cs$_2$PbI$_2$C$_2$), in excellent agreement with experiments. Phonon scattering-rate analysis reveals strong coherences' contributions and prevalent overdamped phonon modes, demonstrating the breakdown of the conventional BTE framework based on the phonon quasiparticle picture with only first-order anharmonic perturbation. This computational approach provides a unified description of heat transport in ultralow-$κ$ materials, offering a basis for the rational design of phononic and thermoelectric devices.

cond-mat.mtrl-sci↗

arXiv2026

Inspect India Evals: An Open Benchmarking Framework for Evaluating Large Language Models in the Indian Linguistic and Cultural Context

India is a vast nation of over 1.4 billion people, varied by hundreds of diverse and locally specific traditions and cultures and 22 officially recognized languages. Large language models (LLMs) are now being deployed on a massive scale throughout the mainland as well as in remote villages. However, the common benchmarks - MMLU, BIG-Bench, and TruthfulQA are almost exclusively English- and Western-centric. They do not identify those safety, fairness, and accuracy failures unique to the Indian context. That is the gap Inspect India Evals seeks to fill. It is an open-source framework built on top of UK AISI's Inspect AI platform. It has six benchmarks: Multilingual MMLU across sixteen Indian languages, BharatBBQ (our adaptation of BBQ for Indian social bias), a safety evaluation for Digital Public Infrastructure, a multilingual safety test using harmful prompts in Indian languages, a multi-turn jailbreak resistance test, and an Indian cultural knowledge benchmark scored using LLM-as-judge rubrics. In this study, we tested five open-weight models ranging from 8B to 32B parameters. Sarvam-M 24B and Gemma 2 27B came out on top, both scoring 80% on the composite India Fairness Index, with Sarvam-M even beating larger 32B models on Indian cultural knowledge and DPI safety compliance. All models scored 100% refusal on Multilingual Safety, whereas DPI safety varied from 20% to 100%. The framework is public. It's built to work with the UK AISI registry. Anyone can reproduce or extend this work.

cs.CL↗

arXiv2026

Anisotropic In-plane Thermal Conductivity of Freestanding Few-layer ReS2

Rhenium disulfide (ReS2) is a low-symmetry transition metal dichalcogenide (TMDC) exhibiting strong in-plane anisotropy, weak interlayer coupling, and stacking-dependent physical properties. While anisotropic thermal conductivity has been reported in bulk ReS2, experimental studies on stackingdependent thermal conductivity and its thickness evolution in the few-layer regime remain largely unexplored. Here, we have extracted the thermal conductivity of freestanding, few-layer ReS2 samples (thickness < 10 nm) using polarization-resolved optothermal Raman thermometry after correcting for polarization dependent absorbance. All measured ReS2 samples show pronounced in-plane anisotropic thermal conductivity. Notably, the ~3.5 nm AA-stacked flake shows higher thermal conductivity than the AB-stacked flake of the same thickness, highlighting the influence of stacking order on phonon transport. The in-plane thermal conductivity displays a non-monotonic dependence on thickness over the 2.5 to 8 nm range which is supported by density functional theory (DFT) calculations. These findings provide key insight into anisotropic phonon transport in low-symmetry 2D materials and highlight the potential of few-layer ReS2 for nanoscale thermal management and thermoelectric applications.

cond-mat.mes-hall↗

arXiv2026

A numerical study on the coefficient of restitution of wet collisions

Using smoothed particle hydrodynamics (SPH) simulations, we investigate the coefficient of restitution (COR) in wet collisions and identify a scaling law governing its behavior. The simulations employ an updated-Lagrangian, mesh-free framework that is validated against experimental measurements. We neglect surface tension effects since the impact conditions correspond to a moderate-to-high Weber number regime. The COR is found to depend on the Stokes number and a dimensionless film thickness defined as the ratio of the liquid film thickness to the diameter of the impacting solid bead. Two distinct regimes are observed, each characterized by different power-law exponents.

physics.flu-dyn↗

arXiv2026

Synergistic Interplay between Surface Polarons and Adsorbates for Photocatalytic Nitrogen Reduction on TiO$_2$(110)

Photocatalytic nitrogen reduction under ambient conditions represents a promising pathway toward sustainable ammonia production. However, the fundamental mechanisms, particularly the role of photogenerated charge carriers and their interactions with surface defects and adsorbates, remain elusive. Here, we employ density functional theory with Hubbard U corrections and hybrid functionals to demonstrate that the synergistic interactions between photogenerated electron polarons and point defects are essential for enabling nitrogen reduction on TiO$_2$(110). We reveal that water adsorption promotes polaron migration from subsurface to surface sites, while subsequent water dissociation stabilizes polarons near oxygen vacancies through proton coupled electron polaron transfer (PCEpT). This surface localization of polarons is critical for effective N$_2$ adsorption and activation. Our findings are consistent with previous experimental reports utilizing EPR that confirm the presence of reduced Ti species and STM, which shows the presence of water dimers on the surface. Moreover, the simultaneous interaction between polarons and reaction intermediates facilitates polaron transfer, thereby driving the completion of the nitrogen reduction reaction. Our findings elucidate the pivotal role of surface polarons in photocatalytic nitrogen fixation and provide mechanistic insights applicable to a broad range of oxide surfaces and interfaces capable of hosting small polarons, offering new design principles for efficient photocatalysts operating under ambient conditions.

cond-mat.mtrl-sci↗

arXiv2026

Persistence of Layer-Tolerant Defect Levels in ReS2

Defects in two-dimensional (2D) semiconductors play a decisive role in determining their electronic, optical, catalytic and quantum properties. Understanding how defect energy levels respond to variations in layer thickness is essential for achieving reproducible and scalable device performance. We report the persistence of layer-tolerant defect levels in rhenium disulfide (ReS2), where both donor- and acceptor-type charge transition levels remain nearly unchanged from monolayer to bulk in both AA and AB stacking. The associated two-level quantum system also retains its character across thicknesses, enabling ReS2 to serve as a platform for layer-tolerant single-photon emitters. The invariance arises from the interplay between electronic energy minimization and structural relaxation, which together counteract quantum confinement and reduced dielectric screening. Additionally, the intrinsically weak interlayer coupling in ReS2 plays a crucial role. Our findings uncover the microscopic origin of this unique behavior, distinguishing ReS2 from other transitionmetal dichalcogenides and highlighting its potential for thickness-independent optoelectronic and quantum photonic applications.

cond-mat.mtrl-sci↗

arXiv2026

Phonon Band Center: A Robust Descriptor to Capture Anharmonicity

Understanding anharmonicity is crucial for designing materials with desired lattice thermal conductivity. Designing a material descriptor that effectively captures anharmonicity while being cost-effective remains a significant challenge. This work proposes a simple metric that helps explain the diversity in lattice thermal conductivity (kl) among materials by quantifying their anharmonic effects. This descriptor "phonon band center" (PBC) encapsulates the critical factors associated with the physics of phonon scattering, revealing a simple inverse relationship with the Gruneisen parameter, the response of phonons with changing volume, and strong correlation with lattice thermal conductivity. This metric has been established using the chalcopyrite class of materials and subsequently validated across various classes of materials using experimental kl. Our approach effectively differentiates materials based on PBC, thereby streamlining the identification of candidates with desirable kl.

cond-mat.mtrl-sci↗

arXiv2026

Origin of Bright Quantum Emissions with High Debye-Waller factor in Silicon Nitride

Silicon nitride has emerged as a promising photonic platform for integrated single-photon sources, yet the microscopic origin of the recently observed bright quantum emissions remains unclear. Using hybrid density functional theory, we show that the negatively charged N$_\text{Si}$V$_\text{N}$ center (NV$^{-}$) in the C$_{1h}$ configuration exhibits a linearly polarized zero-phonon line (ZPL) at 2.46 eV, with a radiative lifetime of 9.01 ns and a high Debye-Waller (DW) factor of 33%. We further find that the C$_{1h}$ configuration is prone to a pseudo-Jahn-Teller distortion, yielding two symmetrically equivalent defect structures that emit bright, linearly polarized ZPL at 1.80 eV with a lifetime of 10.17 ns and an increased DW factor of 41%. These nitrogen-vacancy-related defects explain the origins of visible quantum emissions, paving the way for deterministic and monolithically integrated silicon-nitride quantum photonics.

cond-mat.mtrl-sci↗

arXiv2026

Plasma-Enhanced Germination in North Indian Wheat

The application of nonthermal plasma in agriculture has emerged as a sustainable and eco-friendly method to enhance seed vigor, germination, and crop productivity. This study investigates the effects of atmospheric pressure plasma treatment on five popular bread wheat varieties of North India, WH 1142, HI 1544, GW 366, GW 322, and GW 273. Direct dielectric barrier discharge (DBD) plasma exposure and plasma activated water irrigation were tested. Results indicated significant improvements in seed wettability, germination index, root and shoot growth, spike length, and grain yield compared to controls. Among treatments, 3 min DBD exposure and 15 min PAW irrigation consistently produced the best results, with variety specific differences in vigor and yield. These findings demonstrate the potential of plasma seed treatment as a chemical free technology to enhance productivity in wheat, contributing to sustainable agriculture in India.

physics.plasm-ph↗

arXiv2026

Plasma-Activated Zn, Fe, Mn Micronutrient Solutions for Crop Biofortification

Micronutrient deficiency in soils limits crop productivity and reduces the nutritional quality of cereals and pulses. Conventional fertilizer supplementation often suffers from low bioavailability and environmental losses. In this study, we investigate the use of Plasma Activated Water (PAW) enriched with divalent micronutrient ions as a sustainable alternative to enhance nutrient uptake, soil fertility, and seed vigor. The PAW was generated using a gliding arc plasma system in air, and ion-enriched solutions were prepared at controlled concentrations. The physicochemical parameters (pH, ORP, conductivity, RONS species) were analyzed to assess the plasma induced reactivity. Treatments were applied to micronutrient deficient soils for wheat (Triticum aestivum) and chickpea (Cicer arietinum) seeds under greenhouse conditions. Results demonstrated significant enhancement in germination index, chlorophyll content, and shoot root biomass compared to controls. PAW and ionic treatments notably increased the micronutrient content in grains, indicating effective biofortification. Soil microbial activity and enzyme assays showed no toxicity and a mild stimulatory effect due to reactive nitrogen species. This study establishes a green, scalable method of delivering micronutrients through plasma-activated irrigation water, linking plasma chemistry with sustainable agronomy and nutritional security.

q-bio.OT↗

arXiv2026

Synergistic Bioactivity of Neem and Tulsi Infusions Treated with Plasma-Activated Water

The integration of plasma activated water (PAW) with herbal infusions offers a sustainable approach to enhancing the functional bioactivity of plant derived compounds. In this study, neem (Azadirachta indica) and tulsi (Ocimum sanctum) infusions were treated with PAW generated using an atmospheric pressure gliding arc discharge system. The aim was to investigate plasma induced modifications in phytochemicals and their subsequent effects on antimicrobial and antioxidant properties. Spectroscopic (UV Vis, FTIR) and chromatographic (HPLC) analyses demonstrated structural alterations in key polyphenolic constituents, accompanied by mild acidification and changes in redox potential. Total phenolic content (TPC) and flavonoid levels increased significantly following 10 min PAW treatment, while prolonged exposure (15 min) led to partial degradation, suggesting an optimum treatment window. Antioxidant assays (DPPH, ABTS, FRAP) confirmed improved radical scavenging capacity, correlating with enhanced reducing power of modified phytochemicals. Antimicrobial evaluation against Escherichia coli and Staphylococcus aureus revealed synergistic inhibitory effects, with reduced minimum inhibitory concentrations (MIC) for PAW-treated infusions. Collectively, the results highlight the potential of PAW to modulate herbal bioactives, extending their efficacy in natural preservation systems and biomedical formulations. This green plasma-herbal synergy provides a promising pathway toward eco-friendly food safety and healthcare applications.

physics.plasm-ph↗

arXiv2025

Edge-Aware Graph Attention Model for Structural Optimization of High Entropy Carbides

Predicting relaxed atomic structures of chemically complex materials remains a major computational challenge, particularly for high-entropy systems where traditional first-principles methods become prohibitively expensive. We introduce the edge-aware graph attention model, a physics-informed graph neural network tailored for predicting relaxed atomic structures of high-entropy systems. the edge-aware graph attention model employs chemically and geometrically informed descriptors that capture both atomic properties and local structural environments. To effectively capture atomic interactions, our model integrates a multi-head self-attention mechanism that adaptively weighs neighbouring atoms using both node and edge features. This edge-aware attention framework learn complex chemical and structural relationships independent of global orientation or position. We trained and evaluated the edge-aware GAT model on a dataset of carbide systems, spanning binary to high-entropy carbide compositions, and demonstrated its accuracy, convergence efficiency, and transferability. The architecture is lightweight, with a very low computational footprint, making it highly suitable for large-scale materials screening. By providing invariance to rigid-body transformations and leveraging domain-informed attention mechanisms, our model delivers a fast, scalable, and cost-effective alternative to DFT, enabling accelerated discovery and screening of entropy-stabilised materials.

cond-mat.dis-nn↗

arXiv2025

Anisotropic in-plane lattice thermal conductivity in bilayer ReS2

The significantly weak interlayer coupling strength and puckered structure provide the novel layer-tolerant and anisotropic features in two-dimensional (2D) ReS2. These unique features offer an opportunity to modulate the optoelectronic, vibrational, and transport properties along different lattice directions in ReS2. Here, using first-principles density functional theory (DFT), we investigated the thermal transport properties of ReS2 in AA and AB stacking orders. The anisotopic ratios for lattice thermal conductivities (\k{appa}) are found to be 1.08 and 1.12 for AA and AB stacking, respectively. This anisotropic nature remains intact even at higher temperatures up to 1000K, demonstrating anisotropic robustness. Lower symmetry in AB stacking leads to higher phonon scattering, which results in lower group velocity, smaller phonon lifetime, and thereby lower \k{appa} along both directions as compared to AA stacking. The strong breathing and shear Raman modes in AB stacking indicate stronger layer coupling, further confirming the dominant contribution of acoustic modes towards thermal transport. The findings underscore that the stacking-order-driven preferential heat flow in ReS2 and opens up a new dimension for optimizing device performance.

cond-mat.mtrl-sci↗

arXiv2025

Fractional Quadrature rule and using its Exactness for the Müntz-Legendre Scaling Functions for Solving Fractional Differential Equations

Fractional operators (derivatives/integrals) are defined via the integration of the functions. When the function is produced by a spanning set of fractional power functions, traditional quadrature rules often need to be revised, failing to provide exact evaluations for fractional power functions and thus introducing approximation errors. In this paper, we have formulated a fractional quadrature rule that achieves exact integration for functions within this specific set to address this issue. Some properties of the fractional quadrature rule have been proved, and the absolute error bound in the proposed fractional quadrature rule has been derived. The behavior of roots of the orthogonal Müntz polynomial has also been observed for its application as nodes in the fractional quadrature rule. To illustrate the effectiveness of the newly proposed fractional quadrature rule, we focus on fractional differential equations that incorporate the left Caputo fractional derivative. In this context, Müntz-Legendre scaling functions are utilized to approximate the Caputo derivative of functions involved in these equations. Additionally, we have derived an operational matrix for Riemann-Liouville integration to approximate the respective functions with the help of the fractional quadrature rule. To demonstrate the practical utility of our method, we provide illustrative examples that compare the $L_2$-error estimates in the solutions of fractional differential equations using our approach against those obtained with the Block-pulse method. These comparisons underscore the superior accuracy of our proposed method.

math.NA↗