arXiv subjects

Sakshi Gupta

Publications and source records attributed to Sakshi Gupta.

12 recordsLinked to original sources

arXiv2026

Stellar Wind Driven Alfv\'en Wing Dynamics in Planetary and Exoplanetary Magnetospheres

Magnetized obstacles embedded within a plasma flow generate magnetohydrodynamic structures known as Alfv\'en wings, which act as primary conduits for the transfer of momentum and energy between the body and the surrounding medium. This study employs three-dimensional resistive magnetohydrodynamic simulations to explore how these wings and the magnetosphere respond to diverse stellar wind conditions. Our results, gleaned from a large number of systematic simulations spanning a wide range of stellar wind speed and magnetic field -- and planetary dipole field -- show that the global magnetospheric configuration is highly sensitive to the upstream Alfv\'en Mach number. We find that increasing stellar wind speed leads to a systematic closure and narrowing of Alfv\'en wing structures, while stronger stellar magnetic fields facilitate their opening. Analysis of the Alfv\'en wing morphology demonstrates a distinct dependence of wing opening angle on stellar wind speed, with internal wing analysis showing a reduction in plasma velocity and significant magnetic-flux accumulation. Our results exhibit a clear interdependence between the day-side magnetopause stand-off distance and the night-side magnetotail current sheet length. We find a linear scaling between the magnetotail dynamics and upstream forcing parameters. This study bridges the gap between solar system observations and (exo)planetary systems by demonstrating how Earth-like magnetospheres might transform into wing-dominated configurations during extreme stellar events or within the sub-Alfv\'enic regimes of close-in (exo)planets. Our findings can aid the interpretation of Alfv\'en wing signatures in observational data and enhance our understanding of how (exo)planetary magnetospheres respond to dynamic stellar wind forcing.

astro-ph.EP↗

arXiv2026

Counting Rational Points on Danielewski and Double Danielewski Surfaces over Finite Fields

Let $\Fq$ be the finite field with $q$ elements. We study the number of $\Fq$-rational points on Danielewski and double Danielewski surfaces. For Danielewski surfaces, the point count is reduced to the number of roots of $P(Z)$ over $\Fq.$ For double Danielewski surfaces, one has to count the number of tuples $(\be,\g)\in\Fq^2$, such that $P(0,\g)=0$, $Q(0,\be,\g)=0$ hold simultaneously. We compute these numbers using gcd methods, resultants, character sums, Gauss sums, and the K\"onig--Rados theorem. We obtain explicit formulas in several structured cases, derive general bounds, and give a Macaulay2 algorithm for verification and show an intresting connection between the number of $\Fq$-rational points of these surfaces and polygonal numbers.

math.NT↗

arXiv2026

Ultra-broadband Mid to Long-wave Infrared Spintronic Poisson Bolometer

Infrared detectors have traditionally been divided into two fundamental classes, mid-wave (MWIR, 3-5 um) and long-wave (LWIR, 8-14 um). Integrating MWIR and LWIR within a single device is challenging due to distinct materials, cooling needs, and detection mechanisms, while such integration is critical for improved object recognition, temperature estimation, and environmental sensing. In this work, we demonstrate a Spintronic Poisson (SP) bolometer enabling room-temperature ultra-broadband sensing across 3-14 um. Unlike conventional bolometers that rely on continuous analog signals, the SP bolometer implements a Poisson-counting detection paradigm, encoding temperature in discrete stochastic events, which turns thermal noise from a limitation into the basis of the estimator itself. We fabricate the SP bolometer using a spintronic transduction layer integrated with a plasmonic nanoantenna array to enhance broadband infrared absorption. Using spintronic transduction, the device achieves the noise-equivalent temperature difference (NETD, thermal sensitivity metric) of 80-100 mK at 300 K, surpassing uncooled detectors and approaching cooled technologies. This work establishes a statistical detection paradigm for room-temperature infrared sensing with broad application potential.

physics.optics↗

arXiv2025

Optical Response in Spintronic Poisson Bolometers

Analog bolometers based on temperature-dependent phase-transition materials such as vanadium oxide (VOx) and barium titanate (BTO) represent the state of the art in uncooled infrared detectors. Recently, the first room-temperature spintronic Poisson bolometer based on magnetic tunnel junctions (MTJs) was proposed and demonstrated as a promising infrared detector. Unlike conventional bolometers, the spintronic Poisson bolometer operates in a probabilistic regime dominated by Poissonian noise, where the response is governed by resistance fluctuations arising from thermally activated magnetization transitions. Spontaneous transitions between two metastable magnetic states occur even in the absence of incident light, and the transition probability increases under illumination. In this work, we experimentally study the statistical properties of the optical response of the spintronic Poisson bolometer under illumination. We demonstrate that transitions in spintronic Poisson bolometers, both in the absence and presence of light, exhibit Poissonian behavior, with transition rates and interarrival times modulated by incident radiation. Under illumination, we observe a 153% increase in the count rate accompanied by a 70% reduction in interarrival time. These results establish spintronic Poisson bolometers as a promising platform for probabilistic, high-speed, and high-sensitivity infrared detection at room temperature.

physics.optics↗

arXiv2025

Enhanced Sensitivity to Blackbody Radiation in Spintronic Poisson Bolometers

High-sensitivity long-wave infrared (LWIR) detection is crucial for observing weak thermal radiation. Recently, the Poisson bolometer has been proposed as a fundamentally new platform for uncooled infrared detection. In contrast to traditional analog detectors, where signal and noise are determined by continuous currents or voltages, the Poisson bolometer's signal and noise are governed by Poissonian counting statistics regardless of the light source. In this work, we demonstrate advancements in uncooled infrared detection towards cryogenic-level sensitivity through the integration of spintronic and plasmonic materials. Specifically, a spintronic Poisson bolometer is experimentally integrated with a plasmonic nanoantenna array optimized for broadband LWIR absorption to enhance the temperature increase of the sensing layer. The plasmonic absorber exhibits an absorptance exceeding 60\% across the LWIR spectrum, matching the peak of room-temperature blackbody radiation. We demonstrate that these devices are capable of achieving a noise equivalent differential temperature (NEDT) of 35 mK at a 50 Hz frame rate, demonstrating room-temperature performance comparable to the most sensitive uncooled LWIR detectors reported to date. This work opens up a pathway to removing bulky and expensive cooling requirements from high-sensitivity LWIR detection and imaging applications, such as remote sensing, high-speed imaging, and industrial monitoring.

physics.optics↗

arXiv2025

Long wave infrared detection using probabilistic spintronic bolometer arrays

The use of probabilistic spintronic devices for infrared radiation detection has introduced a shift in approach to thermal imaging. The integration of probabilistic magnetic tunnel junctions with infrared plasmonic nano-antennas achieves high-sensitivity digital-mode infrared sensors at room temperature. Here, we present a scalable approach towards multipixel plasmonic-spintronic bolometer array fabrication and readout. We fabricate proof-of-concept 2x2 row-column multiplexed probabilistic plasmonic sprintronic arrays and show their response to long-wave infrared radiation (8-14um) with high readout speeds (10K-1M counts per second). These spintronic, ultrafast, nanoscale (SUN) bolometers can result in novel high-pixel density CMOS compatible infrared detection platforms. Our work provides a broadband (9kHz to 3GHz) readout platform for future digital probabilistic detector applications. Furthermore, our approach addresses a key challenge associated with scaling infrared pixel sizes that can drive progress towards high pixel density detector arrays for infrared sensing and microscopy applications.

physics.ins-det↗

arXiv2025

Stellar Magnetic Storm Induced Magnetospheric Polarity Reversals: Distinguishing between Unmagnetised and Magnetised Exoplanets

Exoplanetary and planetary environments are forced by stellar activity which manifest through variable radiation, particle and magnetic fluxes, stellar winds, flares and magnetic storms known as coronal mass ejections (CMEs). Recent studies have shown that (exo)planets with intrinsic magnetic fields and magnetospheres respond differently to this stellar forcing compared to planets which lack an intrinsic magnetism; this is borne out by observations in solar system planets. However, detailed investigations to uncover the subtle ways in which stellar magnetic storms impact exoplanets are still at a nascent stage. Here we utilize 3D magnetohydrodynamic simulations to investigate the impact of stellar CMEs on Earth-like planets with different magnetic fields. Our results show that planetary atmospheric mass loss rates are dependent on the relative orientation of stellar wind and planetary magnetic fields, with significantly higher losses when the CME and planetary magnetic fields are oppositely oriented -- favoring enhanced magnetic reconnections. In contrast, for unmagnetised planets, the mass loss rate do not strongly depend on stellar magnetic field orientation. More significantly, we find that stellar CME induced polarity reversals can distinguish between planets with and without intrinsic magnetism. In unmagnetised or weakly magnetised (exo)planets, the polarity of the externally imposed magnetosphere are prone to global polarity reversals forced by stellar magnetised storms. Our analysis of the magnetotail current density dynamics during polarity reversals aligns with observations of Venus. This distinction in magnetospheric response provides a new paradigm to differentiate between (exo)planets with or without significant (intrinsic) magnetic fields.

astro-ph.EP↗

arXiv2024

History and Habitability of the LP 890-9 Planetary System

We present numerous aspects of the evolution of the LP 890-9 (SPECULOOS-2/TOI-4306) planetary system, focusing on the likelihood that planet c can support life. We find that the host star reaches the main sequence in 1 Gyr and that planet c lies close to the inner boundary of the habitable zone. We find the magma ocean stage can last up to 50 Myr, remove 8 Earth-oceans of water, and leave up to 2000 bars of oxygen in the atmosphere. However, if the planet forms with a hydrogen envelope as small as 0.1 Earth-masses, no water will be lost during the star's pre-main sequence phase from thermal escape processes. We find that the planets are unlikely to be in a 3:1 mean motion resonance and that both planets tidally circularize within 0.5 Gyr when tidal dissipation is held constant. However, if tidal dissipation is a function of mantle temperature and rheology, then we find that planet c's orbit may require more than 7 Gyr to circularize, during which time tidal heating may reach hundreds of terawatts. We thus conclude that the habitability of planet c depends most strongly on the initial volatile content and internal properties, but no data yet preclude the viability of an active biosphere on the planet.

astro-ph.EP↗

arXiv2023

Impact of Changing Stellar and Planetary Magnetic Fields on (Exo)planetary Environments and Atmospheric Mass Loss

The magnetic activity of a star -- which modulates the stellar wind outflow -- shapes the immediate environments of orbiting planets and induces atmospheric loss thereby impacting their habitability. We perform a detailed parameter space study using three dimensional magnetohydrodynamic simulations to understand the effect of changing stellar wind magnetic field and planetary magnetic field strengths on planetary magnetospheric topology and atmospheric losses. It is observed that the relative strengths of stellar and planetary magnetic fields play a significant role in determining the steady state magnetospheric configuration and atmospheric erosion. When the stellar field is strengthened or the planetary field is weakened, stellar magnetic field accumulation occurs at the day-side of the planet which forces the magnetopause to shift closer to its surface. The magnetotail opens up leading to the formation of Alfvén wings in the night-side wake region. We demonstrate how reconnection processes and wind conditions lead to the bifurcation of the magnetotail current sheet. With increasing stellar wind magnetic field strength, the day-side reconnection point approaches the planet thereby enhancing mass loss. We establish an analytic equation which successfully captures the modeled mass-loss rate variations of planets with changing magnetic field strengths. Our results are relevant for understanding how the interplay of stellar and planetary magnetism influence (exo)planetary environments and their habitability in star-planet systems with differing relative magnetic field strengths, or in a single star-planet system over the course of their evolution with age.

astro-ph.EP↗

arXiv2022

On generalized cyclotomic derivations

In this article we study the field of rational constants and Darboux polynomials of a generalized cyclotomic $K$-derivation $d$ of $K[X]$. It is shown that $d$ is without Darboux polynomials if and only if $K(X)^d=K$. Result is also studied in the tensor product of polynomial algebras.

math.AC↗

arXiv2016

Shallow Parsing Pipeline for Hindi-English Code-Mixed Social Media Text

In this study, the problem of shallow parsing of Hindi-English code-mixed social media text (CSMT) has been addressed. We have annotated the data, developed a language identifier, a normalizer, a part-of-speech tagger and a shallow parser. To the best of our knowledge, we are the first to attempt shallow parsing on CSMT. The pipeline developed has been made available to the research community with the goal of enabling better text analysis of Hindi English CSMT. The pipeline is accessible at http://bit.ly/csmt-parser-api .

cs.CL↗

arXiv2014

Optimizing the For loop: Comparison of For loop and micro For loop

Looping is one of the fundamental logical instructions used for repeating a block of code. It is used in programs across all programming languages. Traditionally, in languages like C, the for loop is used extensively for repeated execution of a block of code, due to its ease for use and simplified representation. This paper proposes a new way of representing the for loop to improve its runtime efficiency and compares the experimental statistics with the traditional for loop representation. It is found that for small number of iterations, the difference in computational time may not be considerable. But given any large number of iterations, the difference is noticeable.

cs.PL↗