arXiv subjects

Nitin Yadav

Publications and source records attributed to Nitin Yadav.

18 recordsLinked to original sources

arXiv2026

Solar Vortices: Catalysts of Magnetoacoustic Wave Dissipation and Atmospheric Heating

The propagation and dissipation of magnetohydrodynamic waves play a key role in transporting energy from the solar photosphere to the chromosphere. Using high-resolution three-dimensional radiative MHD simulations, we investigate the evolution of slow magnetoacoustic waves along magnetic field lines and examine the influence of photospheric vortex flows on wave dynamics and heating. Field-line tracking reveals upward-propagating slow-mode waves that amplify in the stratified atmosphere and steepen into shocks in the chromosphere, producing recurrent plasma surges with characteristic chromospheric shock signatures. Vortex regions are identified using the swirling strength diagnostic with height-dependent Gaussian smoothing to capture expanding vortex structures. A comparison between vortex and non-vortex field lines shows systematically enhanced temperature in vortex regions.Furthermore, a comparison of shock formation height between vortex and non-vortex regions reveals no systematic difference, indicating that rotational flows do not significantly alter the height at which shocks form. However, supersonic upflows at vortex locations exhibit somewhat higher parallel velocities compared to non-vortex regions, suggesting that vortex-driven motions may amplify the velocity of propagating shocks. These results indicate that vortex-driven motions contribute to increased shock dissipation and modify the thermal structure of the lower solar atmosphere, highlighting the coupled role of slow-mode shocks and vortex flows in chromospheric energy transport.

astro-ph.SR↗

arXiv2026

OMIND: Framework for Knowledge Grounded Finetuning and Multi-Turn Dialogue Benchmark for Mental Health LLMs

Large Language Models (LLMs) have shown remarkable capabilities for complex tasks, yet adaptation in medical domain, specifically mental health, poses specific challenges. Mental health is a rising concern globally with LLMs having large potential to help address the same. We highlight three primary challenges for LLMs in mental health - lack of high quality interpretable and knowledge grounded training data; training paradigms restricted to core capabilities, and evaluation of multi turn dialogue settings. Addressing it, we present oMind framework which includes training and aligning LLM agents for diverse capabilities including conversations; high quality ~164k multi-task SFT dataset, as a result of our generation pipeline based on Structured Knowledge retrieval, LLM based pruning, and review actions. We also introduce oMind-Chat - a novel multi turn benchmark dataset with expert annotated turn level and conversation level rubrics. Our diverse experiments on both core capabilities and conversations shows oMind LLMs consistently outperform baselines. oMind-LLM also shows significantly better reasoning with up to 80% win rate.

cs.CL↗

arXiv2026

A comparison of G-band brightness as a proxy-magnetometer in various magnetic configurations

We investigate the diagnostic potential of the G-band at 430.4 nm for probing small-scale magnetic fields in the solar photosphere. Combining three-dimensional MHD simulations from the MURaM code and spectral synthesis via the RH 1.5D code, we evaluate the intensity contrast in the G-band filtergrams by comparing the filter centered at 430.4 nm in comparison to the conventional 430.5 nm. Our results show that filtergrams centered at 430.4 nm provide higher contrast across varying magnetic environments, particularly at narrow filter widths. This enhancement arises from its slightly higher formation height and greater sensitivity to temperature variations in magnetized regions. These findings indicate that G-band filtergrams centered at 430.4 nm show enhanced diagnostic potential under the assumptions of the present modeling. The obtained results are also relevant and suggest potential applications in stellar contexts, where molecular bands are often used as proxies for magnetic activity.

astro-ph.SR↗

arXiv2026

Observing solar vortices with existing and future instrumentation. Solar Physics International Network for Swirls (SPINS) white paper (Helio)

Solar vortices are fundamental components of solar atmospheric dynamics, serving as natural laboratories for magnetic field twisting, energy concentration and transport, wave guidance, and plasma coupling across atmospheric layers. Numerical and observational studies show that solar vortices are intimately connected to key physical processes including magnetic reconnection, atmospheric heating, turbulence, and wave generation. This white paper, prepared for the UK Space Frontiers 2035 call, outline five high-priority scientific questions addressing vortex generation mechanisms, cross-layer coupling, magnetic restructuring, collective wave-guidance structures, and their role in triggering explosive events and modulating the solar wind. Key observations and capabilities required to make significant advancements over the coming decade are identified. The UK solar physics community has established world-leading expertise in vortex dynamics, combining strengths in high-resolution observations, MHD turbulence theory, numerical modelling, and space instrumentation. UK researchers have made foundational contributions to Solar Orbiter, delivered critical systems for DKIST, and maintain active involvement in MUSE and SOLAR-C EUVST missions. Our technical approach centres on developing next-generation instrumentation: a multi-band, space-qualified system employing four tunable Fabry-P\'erot Interferometers providing diffraction-limited, high-cadence spectropolarimetric coverage from the deep photosphere to the low corona. This capability will be validated through a staged mission architecture beginning with balloon-borne demonstrators. Continuing this effort over the coming decade is vital to maintain UK leadership in this field and achieve the goals of roadmap for solar system research.

astro-ph.IM↗

arXiv2025

Generating Query-Relevant Document Summaries via Reinforcement Learning

E-commerce search engines often rely solely on product titles as input for ranking models with latency constraints. However, this approach can result in suboptimal relevance predictions, as product titles often lack sufficient detail to capture query intent. While product descriptions provide richer information, their verbosity and length make them unsuitable for real-time ranking, particularly for computationally expensive architectures like cross-encoder ranking models. To address this challenge, we propose ReLSum, a novel reinforcement learning framework designed to generate concise, query-relevant summaries of product descriptions optimized for search relevance. ReLSum leverages relevance scores as rewards to align the objectives of summarization and ranking, effectively overcoming limitations of prior methods, such as misaligned learning targets. The framework employs a trainable large language model (LLM) to produce summaries, which are then used as input for a cross-encoder ranking model. Experimental results demonstrate significant improvements in offline metrics, including recall and NDCG, as well as online user engagement metrics. ReLSum provides a scalable and efficient solution for enhancing search relevance in large-scale e-commerce systems.

cs.IR↗

arXiv2025

Identifying Exceptional Points in Two-Dimensional Excitons Coupled to an Open Optical Cavity

Strong coupling in the conventional sense requires that the Rabi cycling process between two interacting states is faster than other dissipation rates. Some recent experimental findings show intriguing properties that were attributed to polaritonic states (e.g., plexcitons) even though the above criterion is not satisfied. Here, we theoretically predict and provide experimental evidence of polariton-like behavior in a system that does not show Rabi splitting. The photoluminescence of an exciton-cavity system consisting of a two-dimensional exciton monolayer (tungsten disulfide, WS2) coupled to a planar, open, one-mirror optical cavity configuration is studied. We experimentally observed a transition from the weak coupling regime crossing an exceptional point to form polariton-like states by varying the coupling strength and the cavity loss. Our observations are fully in agreement with a theoretical quasi-normal mode analysis, which predicts this transition and confirms the presence of exceptional points in the system. These results provide evidence that polaritonic effects can be experimentally observed even when the conventional strong coupling condition is not satisfied.

cond-mat.mtrl-sci↗

arXiv2025

Knowledge Distillation for Enhancing Walmart E-commerce Search Relevance Using Large Language Models

Ensuring the products displayed in e-commerce search results are relevant to users queries is crucial for improving the user experience. With their advanced semantic understanding, deep learning models have been widely used for relevance matching in search tasks. While large language models (LLMs) offer superior ranking capabilities, it is challenging to deploy LLMs in real-time systems due to the high-latency requirements. To leverage the ranking power of LLMs while meeting the low-latency demands of production systems, we propose a novel framework that distills a high performing LLM into a more efficient, low-latency student model. To help the student model learn more effectively from the teacher model, we first train the teacher LLM as a classification model with soft targets. Then, we train the student model to capture the relevance margin between pairs of products for a given query using mean squared error loss. Instead of using the same training data as the teacher model, we significantly expand the student model dataset by generating unlabeled data and labeling it with the teacher model predictions. Experimental results show that the student model performance continues to improve as the size of the augmented training data increases. In fact, with enough augmented data, the student model can outperform the teacher model. The student model has been successfully deployed in production at Walmart.com with significantly positive metrics.

cs.IR↗

arXiv2024

Vortex Dynamics in Various Solar Magnetic Field Configurations

We investigate vortex dynamics in three magnetic regions, viz., Quiet Sun, Weak Plage, and Strong Plage, using realistic three-dimensional simulations from a comprehensive radiation-MHD code, MURaM. We find that the spatial extents and spatial distribution of vortices vary for different setups even though the photospheric turbulence responsible for generating vortices has similar profiles for all three regions. We investigate kinetic and magnetic swirling strength and find them consistent with the Alfvén wave propagation. Using a flux tube expansion model and linear magnetohydrodynamics (MHD) wave theory, we find that the deviation in kinetic swirling strength from the theoretically expected value is the highest for the Strong Plage, least for the Weak Plage, and intermediate for the Quiet Sun at chromospheric heights. It suggests that Weak Plage is the most favoured region for chromospheric swirls, though they are of smaller spatial extents than in Quiet Sun. We also conjecture that vortex interactions within a single flux tube in Strong Plage lead to an energy cascade from larger to smaller vortices that further result in much lower values of kinetic swirling strength than other regions. Fourier spectra of horizontal magnetic fields at 1 Mm height also show the steep cascade from large to smaller scales for Strong Plage. These findings indicate the potential of vortex-induced torsional Alfvén waves to travel higher in the atmosphere without damping for weaker magnetic regions such as the Quiet Sun, whereas vortices would result in dissipation and heating due to the vortex interactions in narrow flux tubes for the strongly magnetized regions such as Strong Plage.

astro-ph.SR↗

arXiv2023

Wave transformations near a coronal magnetic null-point

We investigate the viability of MHD waves, in particular acoustic p-modes, in causing strong current accumulation at the null points. We begin with a three-dimensional numerical setup incorporating a gravitationally stratifed solar atmosphere and an axially symmetric magnetic feld including a coronal magnetic null point. To excite waves, we employ wave drivers mimicking global p-modes. We found that most of the vertical velocity transmits through the Alfvén acoustic equipartition layer maintaining acoustic nature while a small fraction generates fast waves via the mode conversion process. The fast waves undergo almost total refection at the transition region due to sharp gradients in density and Alfvén speed. There are only weak signatures of Alfvén wave generation near the transition region due to fast-to-Alfvén mode conversion. Since the slow waves propagate with the local sound speed, they are not much afected by the density gradients at the transition region and undergo secondary mode conversion and transmission at the Alfvén-acoustic equipartition layer surrounding the null point, leading to fast wave focusing at the null point. These fast waves have associated perturbations in current density, showing oscillatory signatures compatible with the second harmonic of the driving frequency which could result in resistive heating and enhanced intensity in the presence of fnite resistivity. We conclude that MHD waves could be a potential source for oscillatory current dissipation around the magnetic null point. We conjecture that besides oscillatory magnetic reconnection, global p-modes could lead to the formation of various quasiperiodic energetic events.

astro-ph.SR↗

arXiv2022

Price Formation in Field Prediction Markets: the Wisdom in the Crowd

Prediction markets are a popular, prominent, and successful structure for a collective intelligence platform. However the exact mechanism by which information known to the participating traders is incorporated into the market price is unknown. Kyle (1985) detailed a model for price formation in continuous auctions with information distributed heterogeneously amongst market participants. This paper demonstrates a novel method derived from the Kyle model applied to data from a field experiment prediction market. The method is able to identify traders whose trades have price impact that adds a significant amount of information to the market price. Traders who are not identified as informed in aggregate have price impact consistent with noise trading. Results are reproduced on other prediction market datasets. Ultimately the results provide strong evidence in favor of the Kyle model in a field market setting, and highlight an under-discussed advantage of prediction markets over alternative group forecasting mechanisms: that the operator of the market does not need to have information on the distribution of information amongst participating traders.

q-fin.PR↗

arXiv2022

Multiple damage detection in piezoelectric ceramic sensor using point contact excitation and detection method

Lead Zirconate Titanate [(ZrxTi1-x)O3 ]is used to make ultrasound transducers, sensors, and actuators due to its large piezoelectric coefficient. Several surfaces and subsurface micro defects develop within the Lead Zirconate Titanate (PZT) sensor due to delamination, corrosion, huge temperature fluctuation, etc., causing a decline in its performance. It is thus necessary to identify, locate, and quantify the defects. Non-Destructive Structural Health Monitoring (SHM) is the most optimal and economical method of evaluation. Traditional ultrasound SHM techniques have a huge impedance mismatch between air and any solid material. And most of the popular signal processing methods define time-series signals in only one domain which gives sub-optimal results. Thus to improve the accuracy of detection point contact excitation and detection methods have been implemented to determine the interaction of ultrasonic waves with microscale defects in the PZT. And Haar Discrete Wavelet Transformation (DWT) is applied to the time series data obtained from the Coulomb coupling setup. Using the above process, defect up to 100 um in diameter could be successfully distinguished and localized.

physics.app-ph↗

arXiv2021

Slow magneto-acoustic waves in simulations of a solar plage region carry enough energy to heat the chromosphere

We study the properties of slow magneto-acoustic waves that are naturally excited due to turbulent convection and investigate their role in the energy balance of a plage region using three dimensional (3D) radiation-MHD simulations. We calculate the horizontally averaged (over the whole domain) frequency power spectra for both longitudinal and vertical (i.e. the component perpendicular to the surface) components of velocity. To compare our results with the observations we degrade the simulation data with Gaussian kernels having FWHM of 100 km and 200 km, and calculate horizontally averaged power spectra for the vertical component of velocity. The power spectra of the longitudinal component of velocity, averaged over field lines in the core of a kG magnetic flux concentration, reveal that the dominant period of oscillations shifts from around 6.5 minutes in the photosphere to around 4 minutes in the chromosphere. At the same time, the velocity power spectra, averaged horizontally over the whole domain, show that low frequency waves (approximately 6.5 minute period) may reach well into the chromosphere. Importantly, waves with frequencies above 5 mHz propagating along different field lines are found to be out of phase with each other even within a single magnetic concentration. The horizontally averaged power spectra of the vertical component of velocity at various effective resolutions show that the observed acoustic wave energy fluxes are underestimated, by a factor of three even if determined from observations carried out at a high spatial resolution of 200 km. Our results show that longitudinal waves carry (just) sufficient energy to heat the chromosphere in solar plage. We conjecture that current observations (with spatial resolution around 200 km) underestimate the energy flux by roughly a factor of three, or more if the observations have lower spatial resolution.

astro-ph.SR↗

arXiv2020

Vortex Flow Properties in Simulations of Solar Plage Region: Evidence for their role in chromospheric heating

Vortex-flows exist across a broad range of spatial and temporal scales in the solar atmosphere. Small-scale vortices have been proposed to play an important role in energy transport in the solar atmosphere. However, their physical properties remain poorly understood due to the limited spatial resolution of the observations. We aim to explore and analyze the physical properties of small-scale vortices inside magnetic flux tubes using numerical simulations, and to investigate whether they contribute to heating the chromosphere in a plage region. Using the three-dimensional (3D) radiative magnetohydrodynamic (MHD) simulation code 'MURaM', we perform numerical simulations of a unipolar solar plage region. To detect and isolate vortices, we use the Swirling Strength criterion and select the locations where the fluid is rotating with an angular velocity greater than a certain threshold. We concentrate on small-scale as they are the strongest and carry most of the energy. We explore the spatial profiles of physical quantities viz. density, horizontal velocity, etc. inside these vortices. Moreover, to apprehend their general characteristics, a statistical investigation is performed. Magnetic flux tubes have a complex filamentary substructure harbouring an abundance of small-scale vortices. At the interfaces between vortices strong current sheets are formed that may dissipate and heat the solar chromosphere. Statistically, vortices have higher densities and higher temperatures than the average values at the same geometrical height in the chromosphere. We conclude that small-scale vortices are ubiquitous in solar plage regions, and they are denser and hotter structures that contribute to chromospheric heating, possibly by dissipation of the current sheets formed at their interfaces.

astro-ph.SR↗

arXiv2020

Simulations Show that Vortex Flows could Heat the Chromosphere in Solar Plage

The relationship between vortex flows at different spatial scales and their contribution to the energy balance in the chromosphere is not yet fully understood. We perform three-dimensional (3D) radiation-magnetohydrodynamic (MHD) simulations of a unipolar solar plage region at a spatial resolution of 10 km using the MURaM code. We use the swirling-strength criterion that mainly detects the smallest vortices present in the simulation data. We additionally degrade our simulation data to smooth-out the smaller vortices, so that also the vortices at larger spatial scales can be detected. Vortex flows at various spatial scales are found in our simulation data for different effective spatial resolutions. We conclude that the observed large vortices are likely clusters of much smaller ones that are not yet resolved by observations. We show that the vertical Poynting flux decreases rapidly with reduced effective spatial resolutions and is predominantly carried by the horizontal plasma motions rather than vertical flows. Since the small-scale horizontal motions or the smaller vortices carry most of the energy, the energy transported by vortices deduced from low resolution data is grossly underestimated. In full resolution simulation data, the Poynting flux contribution due to vortices is more than adequate to compensate for the radiative losses in plage, indicating their importance for chromospheric heating.

astro-ph.SR↗

arXiv2018

Phase transition in the knapsack problem

We examine the phase transition phenomenon for the Knapsack problem from both a computational and a human perspective. We first provide, via an empirical and a theoretical analysis, a characterization of the phenomenon in terms of two instance properties; normalised capacity and normalised profit. Then, we show evidence that average time spent by human decision makers in solving an instance peaks near the phase transition. Given the ubiquity of the Knapsack problem in every-day life, a better understanding of its structure can improve our understanding not only of computational techniques but also of human behavior, including the use and development of heuristics and occurrence of biases.

cs.AI↗

arXiv2016

Supervisory Control for Behavior Composition

We relate behavior composition, a synthesis task studied in AI, to supervisory control theory from the discrete event systems field. In particular, we show that realizing (i.e., implementing) a target behavior module (e.g., a house surveillance system) by suitably coordinating a collection of available behaviors (e.g., automatic blinds, doors, lights, cameras, etc.) amounts to imposing a supervisor onto a special discrete event system. Such a link allows us to leverage on the solid foundations and extensive work on discrete event systems, including borrowing tools and ideas from that field. As evidence of that we show how simple it is to introduce preferences in the mapped framework.

cs.AI↗

arXiv2012

Qualitative Approximate Behavior Composition

The behavior composition problem involves automatically building a controller that is able to realize a desired, but unavailable, target system (e.g., a house surveillance) by suitably coordinating a set of available components (e.g., video cameras, blinds, lamps, a vacuum cleaner, phones, etc.) Previous work has almost exclusively aimed at bringing about the desired component in its totality, which is highly unsatisfactory for unsolvable problems. In this work, we develop an approach for approximate behavior composition without departing from the classical setting, thus making the problem applicable to a much wider range of cases. Based on the notion of simulation, we characterize what a maximal controller and the "closest" implementable target module (optimal approximation) are, and show how these can be computed using ATL model checking technology for a special case. We show the uniqueness of optimal approximations, and prove their soundness and completeness with respect to their imported controllers.

cs.AI↗

arXiv2012

Reasoning about Agent Programs using ATL-like Logics

We propose a variant of Alternating-time Temporal Logic (ATL) grounded in the agents' operational know-how, as defined by their libraries of abstract plans. Inspired by ATLES, a variant itself of ATL, it is possible in our logic to explicitly refer to "rational" strategies for agents developed under the Belief-Desire-Intention agent programming paradigm. This allows us to express and verify properties of BDI systems using ATL-type logical frameworks.

cs.AI↗