arXiv subjects

Ajay Kumar

Publications and source records attributed to Ajay Kumar.

At least 37 records · Page 2Linked to original sources

arXiv2026

Nonlinear Aerodynamic Response and an Equivalent Static Wind-resistant Design for Anticlastic Conical Tensile Membranes

Conical Tensile Membrane Structure (TMS) is commonly used for aesthetics, economic design, high rain and snow loading. Such TMS shows complex aerodynamic behavior in presence of geometric nonlinearity, not adequately studied in the past. The aerodynamic responses of anticlastic conical TMS under random wind loading is presented herein along with an equivalent static wind resistant design approach. The stochastic wind loading on the TMS in the atmospheric boundary layer (ABL) is simulated via the Large Eddy simulation (LES); which is detailed in a previous study by the authors and hence not repeated here. The aerodynamic loading is then employed as input in conducting the nonlinear time history analyses considering open (i.e. without facade) and closed (with facade) TMS, supported by peripheral/radial cables. The influence of the key parameters (aerodynamic roughness height, the rise-span ratio of the TMS and the membrane prestress, notably) are demonstrated. Although increasing prestress and rise-to-span ratio enhances the stiffness of TMS, the former shows dominance. Increasing roughness height also lead to increased peak loading/responses by enhanced turbulence. An equivalent static wind-resistant design is presented via the Gust Response Factors (GRFs) and an additional Nonlinear Adjustment Factors (NAFs). These factors are presented systematically, encompassing alternative scenarios. Multi-linear regression models are presented for predictive modeling of these factors, along with a probabilistic analysis for their design values that can be employed in practice bypassing an involved nonlinear dynamic analysis.

physics.flu-dyn↗

arXiv2026

Evidence of energy conversion in weakly collisional plasma during an interplanetary coronal mass ejection

Intervals of enhanced turbulent fluctuations are typically less frequent within the magnetic cloud region of an interplanetary coronal mass ejection (ICME). We investigate two such intervals inside an ICME observed by the \textit{Wind} spacecraft on 8--9 June 2000 and characterize their associated wave populations. We focus on spectral analysis and plasma instability analysis, using ion-scale normalized magnetic helicity and polarization properties with respect to the background magnetic field $B_0$. In the first interval, the ion-scale normalized magnetic helicity shows a left-handed circularly polarized signature. In the second interval, the left-handed signature persists and an additional high-frequency right-handed population appears. The propagation is approximately parallel to $B_0$. The left-handed fluctuations are compatible with Alfvén ion-cyclotron (AIC) waves, while the right-handed fluctuations are consistent with fast magnetosonic/whistler (FM/W) waves. The ICME plasma accesses resonance conditions that support multiple ion-scale wave modes. Evolving anisotropies in the plasma and the approach to marginal stability allow the coexistence of AIC-like and fast-magnetosonic/whistler-like fluctuations, with enhanced electron heating favoring the growth of the FM/W contribution and strengthening the density--magnetic-field magnitude correlation.

astro-ph.SR↗

arXiv2026

Effect of hole pitch reduction on electron transport and diffusion: A comparative simulation study of Triple GEM detectors

Advances in fabrication techniques and high-performance electronics have facilitated the development of fine-pitch Gas Electron Multipliers (GEMs). Earlier experimental and simulation findings suggest that these reduced-pitch GEMs can outperform the standard configuration in terms of effective gain, collection efficiency, and position resolution. However, a noticeable fraction of avalanche electrons is lost within the GEM systems, resulting in a degradation of charge collection efficiency. Therefore, a comprehensive simulation-based study is essential to provide deeper insights into the extent of degradation and its contributing factors. In this context, we employ ANSYS and Garfield++ to model the Triple GEM detectors with reduced pitch sizes of 90 and 60 $μ$m, and perform a comparative performance analysis with the standard configuration (pitch size: 140 $μ$m). At first, the simulation framework is validated by comparing the results of the standard configuration with available experimental data and previously reported simulation outcomes. Despite the characteristic gain offset, the framework remains physically consistent and reliable in capturing microscopic avalanche dynamics, reproducing the experimental trend. Following validation, we investigate electron losses at the metal electrodes and within the Kapton holes, electron transmission through the transfer and induction regions, electron diffusion on the induction electrode, and the overall collection efficiency. These parameters are analyzed as functions of GEM potential, outer hole diameter, inner hole diameter, Kapton thickness, metal thickness, and gas composition, thereby offering insights for designing efficient GEM detectors.

physics.ins-det↗

arXiv2026

The Second CHIME/FRB Catalog of Fast Radio Bursts

We present a catalog of 4539 fast radio bursts (FRBs) observed with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope between 25 July 2018 and 15 September 2023. These bursts originate from 3641 unique sources, including 981 bursts from 83 known repeating sources. For each FRB, the catalog provides a $O(10')$ estimate of sky location along with corresponding measurements of cumulative exposure time and survey sensitivity over the observing period. It includes a total-intensity dynamic spectrum between 400 and 800 MHz at 0.983 ms resolution. From this spectrum, we constrain a model of the burst morphology and measure key parameters such as arrival time, intrinsic temporal width, dispersion measure, scattering time, and flux density. This second catalog includes all FRBs from the first catalog, with every event reprocessed using a uniform and improved analysis framework. We show that previously published inferences remain valid under the updated measurements. We assess consistency of the detection rate across observational parameters, present initial distributions of burst properties, and outline ongoing and future studies that will use this catalog to investigate the nature of FRBs and their utility as astrophysical and cosmological probes.

astro-ph.HE↗

arXiv2025

Waldschmidt constant of monomial ideals and Simis ideals

In 2017, Cooper et al. proposed a conjecture providing a lower bound for the Waldschmidt constant of monomial ideals. We confirm this conjecture for some classes of monomial ideals. Recently, Méndez, Pinto, and Villarreal formulated a conjecture stating that if $I$ is a monomial ideal without embedded associated primes, whose irreducible decomposition is minimal and which is a Simis ideal, then there exist a Simis squarefree monomial ideal $J$ and a standard linear weighting $w$ such that $I = J_{w}.$ In this work, we verify this conjecture for some classes of monomial ideals.

math.AC↗

arXiv2025

Optimization of airgap in a monocentric lens assembly and metasurface based anti-reflecting coating in the long-wave IR regime

Owing to minimal aberration, larger field-of-view, and high resolution, monocentric lenses are preferred over other imagers in hemispherical image surface scenarios, particularly in the long-wave infrared (LWIR) region. Herein, we study a monocentric lens assembly consisting of a ball lens and two hemispherical shell lenses of given radii of curvature and lens materials to enhance the transmission of LWIR ranging from 8μm to 12μm wavelength. We optimize the air gaps between the lenses of the assembly for a wider range of incidence angles, assuming antireflecting coating (ARC) on all surfaces of the lenses. Additionally, the effect of temperature variation on the transmittance is also studied to attain an optimum air gap between the lenses. With the variation in incidence angle and temperature, modulations in focal length and spot size are reported for different wavelengths. Further, we propose a metasurface design to replace conventional multilayer ARCs to enhance the transmittance through the lens assembly over the given wavelength range for a wide field-of-view.

physics.optics↗

arXiv2025

From Complex Magnetic Ground States to Magnetocaloric Effects: A Review of Rare Earth R$_2$In Intermetallic Compounds

R2In (R = rare earth) intermetallics exhibit unusual magnetic and magnetocaloric properties, driven by subtle electronic effects, lattice distortions, and spin-lattice coupling. Most of these binary compounds adopt the hexagonal Ni2In-type structure at room temperature, with Eu2In and Yb2In stabilizing in the orthorhombic Co2Si-type lattice. Lighter lanthanide compounds Eu2In, Nd2In, and Pr2In undergo first-order magnetic transitions with negligible hysteresis and minimal lattice volume change and exhibit giant cryogenic magnetocaloric effects, while heavy lanthanide R2In compounds including Gd2In show second-order transitions with moderate magnetocaloric effect. No lanthanide-based R2In compound exhibits symmetry-breaking structural transition, while Y2In transforms from hexagonal to orthorhombic structure near 250 K. Secondary low-temperature transitions, including spin reorientation or antiferromagnetic ordering, further enrich the magnetic phase landscape in these compounds. Integrating theoretical descriptors such as charge-induced strain and electronic structure provides predictive insight into phase stability and magnetocaloric performance, guiding the design of rare-earth intermetallics with tunable magnetic properties for cryogenic applications

cond-mat.mtrl-sci↗

arXiv2025

Optimizing the Variant Calling Pipeline Execution on Human Genomes Using GPU-Enabled Machines

Variant calling is the first step in analyzing a human genome and aims to detect variants in an individual's genome compared to a reference genome. Due to the computationally-intensive nature of variant calling, genomic data are increasingly processed in cloud environments as large amounts of compute and storage resources can be acquired with the pay-as-you-go pricing model. In this paper, we address the problem of efficiently executing a variant calling pipeline for a workload of human genomes on graphics processing unit (GPU)-enabled machines. We propose a novel machine learning (ML)-based approach for optimizing the workload execution to minimize the total execution time. Our approach encompasses two key techniques: The first technique employs ML to predict the execution times of different stages in a variant calling pipeline based on the characteristics of a genome sequence. Using the predicted times, the second technique generates optimal execution plans for the machines by drawing inspiration from the flexible job shop scheduling problem. The plans are executed via careful synchronization across different machines. We evaluated our approach on a workload of publicly available genome sequences using a testbed with different types of GPU hardware. We observed that our approach was effective in predicting the execution times of variant calling pipeline stages using ML on features such as sequence size, read quality, percentage of duplicate reads, and average read length. In addition, our approach achieved 2X speedup (on an average) over a greedy approach that also used ML for predicting the execution times on the tested workload of sequences. Finally, our approach achieved 1.6X speedup (on an average) over a dynamic approach that executed the workload based on availability of resources without using any ML-based time predictions.

cs.DC↗

arXiv2025

Low-frequency Probes of the Persistent Radio Sources associated with Repeating FRBs

The discovery of Persistent Radio Sources (PRSs) associated with three repeating fast radio bursts (FRBs) has provided insight into the local environments of these FRBs. Here, we present deep radio observations of the fields surrounding three highly active repeating FRBs namely, FRB 20220912A, FRB 20240114A, and FRB 20240619D using the upgraded Giant Metrewave Radio Telescope (uGMRT) at low radio frequencies. Towards FRB~20240114A, we report the detection of compact source at 650\,MHz with a flux density of 65.6$\pm$8.1\,$μ$Jy/beam. Our measurements of the spectral index, star formation rate of the host galaxy and recently reported constraints on the physical size strongly argue for our detected source to be a persistent radio source (PRS) associated with the FRB 20240114A. For FRB~20220912A, we detect radio emission that is most likely due to star formation in the host galaxy. For FRB 20240619D, we provide upper limits on the radio emission from an associated PRS or the host galaxy. The detection of the PRS associated with FRB~20240114A is a useful addition to the PRSs known to be associated with only three other FRBs so far, and further supports the origin of the PRS in the form of magnetoionic medium surrounding the FRB sources.

astro-ph.HE↗

arXiv2025

Pinching of ICME Flux Rope: Unprecedented Multipoint Observations of Internal Magnetic Reconnection during Gannon's Superstorm

The extreme solar storm of May 10, 2024, during the 25th solar cycle, which recorded a symmetric H component index (Sym-H) reaching -500 nT, was the strongest since the 2003 Halloween storm. This event offered a unique opportunity for unprecedented multipoint observation of the complex interaction of Interplanetary Coronal Mass Ejections (ICME) from different vantage points. Utilizing NASA's Wind, ACE, DSCOVR, THEMIS-C, STEREO-A, MMS, and ISRO's recently launched Aditya-L1 spacecraft, we comprehensively investigated the spatio-temporal variations in interplanetary plasma and magnetic field parameters. Our study reveals large-scale quasi-steady magnetic reconnection within the interior of the ICME flux rope, possibly triggered by interactions between multiple ICMEs. A current sheet (CS) forms within the flux rope, enabling internal magnetic reconnection between concentric magnetic surfaces, which leads to a sharp reversal of the IMF By component, as observed at the L1 point. Concurrently, reconnection exhaust and enhanced electron and ion fluxes were detected with the CS, extending over 200 RE (1.3 million km) along the GSE-y direction. This finding sheds new light on the role of internal reconnection in ICME evolution, highlighting its pivotal role in modifying the morphology of the ICME magnetic structure and exerting severe space weather effects on Earth.

astro-ph.SR↗

arXiv2025

Computational study of Adhesion and Friction Behavior of Crosslinked Polymer Network

In this study, we have utilized a molecular dynamics simulation approach to understand adhesion and friction behaviour of crosslinked polymer networks. We have used breakable quartic bond to model crosslinked polymers. We explored the structural characteristics and evaluated the coefficient of friction (CoF) as a function of crosslinked monomer fraction (cross-linking bond density) in four-fold cross-linked polymer networks. To estimate CoF, a rigid indenter was inserted to different depths of indentation. Subsequently a constant sliding speed was applied while keeping the depths of indentation fixed. Normal and friction forces were calculated at each depth to estimate CoF through a linear curve-fitting. For adhesion studies, using the force vs. displacement curve we quantified adhesion through the forces during the separation of rigid indenter from surface of crosslinked polymeric materials while unloading after indentation into the sample. The results indicate that as the fraction of crosslinked monomers increases, the stiffness of the crosslinked network increases, while the force of adhesion and CoF decrease. Additionally, increasing the depth of indentation during friction leads to higher frictional forces.

cond-mat.soft↗

arXiv2025

Cross talk between experimental data and simple validation of shell closure in pre-actinides

Two back-to-back experiments, 28Si + 178Hf and 28Si + 186W, were intentionally conducted to validate the role of shell closure in pre-actinides by studying neutron multiplicity in compound nucleus (CN) 206Rn and 214Ra. In the first experiment, Dubey et al. [Phys. Rev. C 112, L011602 (2025)], we established the influence of the neutron shell closure. In the present work, the CN 214Ra was deliberately selected to investigate the dependence of the total neutron multiplicity (Mtotal) on the proton number (Z), while keeping the neutron number constant at N = 126 in the pre-actinide region. The objective of the study is two-fold : (i) to examine the effect of proton shell closure when moving away from Z = 82, and (ii) to correlate the present results on proton shell closure with our previous finding on neutron shell closure. We have also used the previous reported data for N = 126 isotones 210Po, 212Rn, and 213Fr to establish the validation of shell closure. A systematic increase in Mtotal with increasing Z was observed from Z = 82 to Z = 88. Furthermore, comparison of the present results on proton shell closure with our earlier neutron shell closure observation, reveals that the cross-correlation between neutron and proton shell closure shows a systematic increase in Mtotal as one moves away from 208Pb, whether along isotonic or isotopic chains.

nucl-ex↗

arXiv2025

Non-trivial critical behavior at the magnetic transitions: A case study of Sm$_7$Pd$_3$

We present a comprehensive analysis of the critical behavior of Sm$_7$Pd$_3$ in the vicinity of its second-order magnetoelastic transition at $T_ {\rm c} = 173$ K. The critical exponents (CEs) $β$ and $γ$, determined using both the standard convergence procedure and the average normalized slope (ANS) method, diverge at $T_{\rm c}$: a characteristic typically associated with first-order transitions. Notably, none of the established universality classes satisfactorily describe the critical behavior of Sm$_7$Pd$_3$, and we discuss the possible origins of this deviation in the context of the strong spin-lattice coupling intrinsic to the sample. We emphasize the importance of accurately selecting the critical temperature and magnetic field ranges to ensure robust critical behavior analysis and propose a quantitative approach to assess the reliability of the extracted CEs. Additionally, we demonstrate that in the ANS method, the critical exponents $β$ and $γ$ should be calculated separately using data for $T \leqslant T_{\rm c}$ and $T \geqslant T_{\rm c}$, respectively. Our findings underscore the need for a revised theoretical framework to accurately describe second-order magnetoelastic transitions.

physics.app-ph↗

arXiv2025

CHIME/FRB/Pulsar discovery of a nearby long period radio transient with a timing glitch

We present the discovery of a 421 s long period radio transient (LPT) using the CHIME telescope, CHIME J0630+25. The source is localized to RA=06:30:38.4$\pm1'$ Dec=25:26:24$\pm1'$ using voltage data acquired with the CHIME baseband system. A timing analysis shows that a model including a glitch is preferred over a non-glitch model with $dF/F=1.3\times10^{-6}$, consistent with other glitching neutron stars. The timing model suggests a surface magnetic field of $\sim1.5\times10^{15}$ G and a characteristic age of $\sim1.28\times10^{6}$ yrs. A separate line of evidence to support a strong local magnetic field is an abnormally high rotation measure of $RM=-347.8(6) \mathrm{rad\, m^{-2}}$ relative to CHIME J0630+25's modest dispersion measure of 22(1) pc cm$^{-2}$, implying a dense local magneto-ionic structure. As a result, we believe that CHIME J0630+25 is a magnetized, slowly spinning, isolated neutron star. This marks CHIME J0630+25 as the longest period neutron star and the second long period neutron star with an inferred magnetar-like field. Based on dispersion measure models and comparison with pulsars with distance measurements, CHIME J0630+25 is located at a nearby distance of 170$^{+310}_{-100}$ pc (95.4\%), making it an ideal candidate for follow-up studies.

astro-ph.HE↗

arXiv2025

A Mixed-Primitive-based Gaussian Splatting Method for Surface Reconstruction

Recently, Gaussian Splatting (GS) has received a lot of attention in surface reconstruction. However, while 3D objects can be of complex and diverse shapes in the real world, existing GS-based methods only limitedly use a single type of splatting primitive (Gaussian ellipse or Gaussian ellipsoid) to represent object surfaces during their reconstruction. In this paper, we highlight that this can be insufficient for object surfaces to be represented in high quality. Thus, we propose a novel framework that, for the first time, enables Gaussian Splatting to incorporate multiple types of (geometrical) primitives during its surface reconstruction process. Specifically, in our framework, we first propose a compositional splatting strategy, enabling the splatting and rendering of different types of primitives in the Gaussian Splatting pipeline. In addition, we also design our framework with a mixed-primitive-based initialization strategy and a vertex pruning mechanism to further promote its surface representation learning process to be well executed leveraging different types of primitives. Extensive experiments show the efficacy of our framework and its accurate surface reconstruction performance.

cs.CV↗

arXiv2025

Investigating the effects of acceptor removal mechanism and impact ionization on proton irradiated 300 $μ$m thick LGAD

Low-Gain Avalanche Detectors (LGADs) are the leading 4D sensing technology selected for use in the High Luminosity Large Hadron Collider (HL-LHC). However, their proximity to the interaction point makes them highly susceptible to radiation-induced damage. Such degradation effects can be effectively studied through TCAD simulations. In this work, we extend the validation of a previously developed proton damage model for transitional sensors. The enhanced model for LGAD also incorporates an acceptor removal mechanism and modifications in impact ionization behavior, resulting in a more comprehensive and reliable tool for fabrication and performance analysis.

physics.ins-det↗

arXiv2025

Study of anisotropic flow of heavy hadrons in Au + Au collisions at $\sqrt{s_{NN}} =$ 200 GeV using HYDJET++ framework

A comprehensive study of the anisotropic flow of heavy hadrons ($D^{0}$, $D^{\pm}$, and $Λ_{c}$) in Au + Au collisions at $\sqrt{s_{NN}} = 200$ GeV using the HYDJET++ model is presented. This study aims to explore the collective behavior and thermalization of charm hadrons at RHIC energy. The modeling of anisotropic flow is performed using a centrality-dependent parameterization of anisotropic parameters. Our model results are consistent with STAR experimental results up to $p_{T} = 4$ GeV/c. It captures the centrality-dependent shifts of the flow peak towards lower $p_{T}$ as collisions become more peripheral. This shift is attributed to the weaker radial flow in peripheral collisions. The model also reproduces important features such as the number-of-constituent-quark scaling, mass ordering, and baryon-meson grouping, all consistent with experimental observations. Furthermore, we present comparisons with other models, like DUKE, SUBATECH, TAMU, and AMPT. Overall, our results highlight the efficacy of HYDJET++ in describing the collective dynamics of heavy-flavor hadrons in the quark-gluon plasma medium.

hep-ph↗

arXiv2025

Study of Heavy Hadron Production in Au + Au Collisions at a Center-of-Mass Energy of $\sqrt{s_{NN}}=200$ GeV

Using the Monte Carlo HYDJET++ model, the transverse momentum ($p_{T}$) spectra of heavy hadrons ($D^{0}$, $\overline{D}^{0}$, $D^{+}$, $D^{-}$ and $Λ_{c}$), as well as the nuclear modification factors of $D^{0}$ and $D^{\pm}$, produced in Au + Au collisions at $\sqrt{s_{NN}} = 200$ GeV RHIC energy across various centrality bins, are presented. This study is motivated by the need to understand the centrality dependence of the charm enhancement factor ($γ_{c}$) and the roles of different hadronization mechanisms such as coalescence and fragmentation, in charm hadron production. To achieve the best description of heavy hadron production, several input parameters in both the soft and hard components of the model are tuned. The study finds a decreasing trend of $γ_{c}$ from central to peripheral collisions and a mass dependence across charm hadrons. Moreover, the model effectively reproduces experimental data of $p_{T}$ spectra at low and intermediate $p_{T}$, capturing key features of charm hadron production in the quark-gluon plasma medium. However, it overpredicts the data at high $p_{T}$, indicating the need for improvements in modeling heavy quark energy loss mechanisms. Further, the nuclear modification factors ($R_{AA}$ and $R_{CP}$) for $D^{0}$ mesons exhibit significant suppression in central collisions, which matches with experimental observations. This highlights the roles of collisional and radiative energy loss due to collective effects, such as coalescence and radial flow. The antiparticle-to-particle and mixed particle ratios are also presented, showing good agreement with experimental data and revealing limitations in baryon production due to the absence of heavy quark coalescence in HYDJET++.

hep-ph↗