arXiv subjects

Sushil Kumar

Publications and source records attributed to Sushil Kumar.

At least 37 records · Page 2Linked to original sources

arXiv2025

Review of magnetic- and antimagnetic-rotational structures in nuclei

This work is an update of the 2000 publication of magnetic-rotational bands by Amita et al. [1], followed by an unpublished update of 2006 [2], and reviews detailed experimental data extracted from original publications for 228 magnetic-rotational (MR or Shears) structures spread over 117 nuclides, and 40 antimagnetic-rotational (AMR) structures in 28 nuclei, with a brief commentary about each band. Many of these nuclei are located at or near the semi-magic nucleon numbers, mostly for protons. For example, 88 MR bands are currently known for the Pb (Z=82) nuclei, and 29 AMR band in Pd, Cd and In nuclei. It is interesting that the proton magic numbers appear to play a major role in the MR phenomenon, which seems less well understood. A brief discussion of the salient features of the MR and AMR bands and their theoretical interpretation has been presented in the present review. The tables contain gamma-ray energies, associated level energies with spins and parities, level lifetimes, B(M1), B(E2), and B(M1)/B(E2) ratios and probable spherical quasiparticle configurations. We find that many bands claimed in the literature as MR and AMR bands still have tentative assignments, as level lifetimes, thus B(M1) and B(E2) values, for a large number of MR and AMR bands, which can potentially provide critical criteria for firm identification of such structures, are lacking. Additionally, theoretical model calculations for many of these bands, which could provide insight for a better description of nuclear structure, are also lacking in literature. While this review is mainly based on original research articles, nuclear structure databases ENSDF [3], XUNDL [4], and NSR [5] have been consulted for completeness. The literature cut-off date March 31, 2025.

nucl-th↗

arXiv2024

RIS-Assisted MIMO CV-QKD at THz Frequencies: Channel Estimation and SKR Analysis

In this paper, a multiple-input multiple-output (MIMO) wireless system incorporating a reconfigurable intelligent surface (RIS) to efficiently operate at terahertz (THz) frequencies is considered. The transmitter, Alice, employs continuous-variable quantum key distribution (CV-QKD) to communicate secret keys to the receiver, Bob, which utilizes either homodyne or heterodyne detection. The latter node applies the least-squared approach to estimate the effective MIMO channel gain matrix prior to receiving the secret key, and this estimation is made available to Alice via an error-free feedback channel. An eavesdropper, Eve, is assumed to employ a collective Gaussian entanglement attack on the feedback channel to avail the estimated channel state information. We present a novel closed-form expression for the secret key rate (SKR) performance of the proposed RIS-assisted THz CV-QKD system. The effect of various system parameters, such as the number of RIS elements and their phase configurations, the channel estimation error, and the detector noise, on the SKR performance are studied via numerical evaluation of the derived formula. It is demonstrated that the RIS contributes to larger SKR for larger link distances, and that heterodyne detection is preferable over homodyne at lower pilot symbol powers.

cs.IT↗

arXiv2024

RIS-Assisted THz MIMO Wireless System in the Presence of Direct Link for CV-QKD with Limited Quantum Memory

A reconfigurable intelligent surface (RIS)-aided multiple-input multiple-output (MIMO) wireless communication system is considered in this paper wherein the transmitter, Alice modulates secret keys, by using a continuous variable quantum key distribution technique to be transmitted to the receiver, Bob, which employs homodyne detection for data decoding. The data is transmitted over two paths, namely a direct path between Alice and Bob and the wireless path between them via the RIS. Transmit and receive beamsplitters are employed in the system to transform the MIMO terahertz channels into parallel single-input single-output channels. Considering an eavesdropper, Eve, to attack all the three wireless channels in the system (i.e., the direct channel, the channel between Alice and RIS, and between the RIS and Bob) but having restricted quantum memory limiting it to store the ancilla modes from either of these three wireless channels, novel expressions for the secret key rate (SKR) of the system are derived. Numerical results are presented to demonstrate the dependency of the system's performance on various system parameters. It is observed that the RIS plays a key role in increasing the SKR of the system and the transmission distance, ensuring secure communications between Alice and Bob. The significance of employing RIS is observed specifically for the case when Eve measures the ancilla modes of the channel between the RIS and Bob. Furthermore, for all such measurement scenarios, optimal angles are obtained for the phase shifts of the RIS elements to maximize the SKR for various MIMO configurations and transmission distance between Alice and Bob.

cs.IT↗

arXiv2023

Sharp Estimates on Coefficient functionals of Ozaki close-to-convex functions

The goal of this manuscript to establish the best possible estimate on coefficient functionals like Hermitian-Toeplitz determinant of secoend order involving logarithmic coefficients, initial logarithmic inverse coefficients and initial order Schwarzian derivatives of the Ozaki close-to-convex functions.

math.CV↗

arXiv2023

Sharp bounds on Coefficient functionals of certain Sakaguchi functions

We determine sharp bounds on some Hankel determinants involving initial coefficients, inverse coefficients, and logarithmic inverse coefficients for two subclasses of Sakaguchi functions which are associated with the right half of the lemniscate of Bernoulli and the exponential function. Further, we compute sharp bounds on the second Hermitian-Toeplitz determinants involving logarithmic coefficients and logarithmic inverse coefficients. We also discuss invariant property for the obtained estimates with respect to various coefficients.

math.CV↗

arXiv2023

Starlikeness Using Special Functions and Subordination

The association of subordination and special functions is used to find sharp estimates on the parameter $β$ such that the analytic function $p(z)$ is subordinate to certain functions having positive real part whenever $p(z)+βz p'(z)$ is subordinate to the Janowski function. Further, when the traditional approach of solving higher order differential subordination implications failed, the concept of admissibility is employed to establish certain second and third order differential subordination relations between the analytic function $p$ and the functions associated with right half plane. As a sequel, we demonstrated the starlikeness of various well-known analytic functions as well.

math.CV↗

arXiv2023

Constrained Radius Estimates Of Certain Analytic Functions

Let $\mathcal{P}$ denote the Carathéodory class accommodating all the analytic functions $p$ having positive real part and satisfying $p(0)=1$. In this paper, the second coefficient of the normalized analytic function $f$ defined on the open unit disc is constrained to define new classes of analytic functions. The classes are characterised by the functions $f/g$ having positive real part or satisfying the inequality $|(f(z)/g(z))-1|<1$ such that $f(z)(1-z^2)/z$ and $g(z)(1-z^2)/z$ are Carathéodory functions for some analytic function $g$. This paper aims at determining radius of starlikeness for the introduced classes.

math.CV↗

arXiv2023

High-spin spectroscopy in $^{207}$At: Evidence of a 29/2$^{+}$ isomeric state

Yrast and near-yrast states above the known 25/2$^{+}$ isomer in $^{207}$At are established for the first time. The level scheme is extended up to 47/2$\hbar$ and 6.5 MeV with the addition of about 60 new $γ$-ray transitions. The half-life of the 25/2$^{+}$ isomer is revisited and a value of $T_{1/2}$ = 107.5(9) ns is deduced. Evidence of a hitherto unobserved 29/2$^{+}$ isomer in $^{207}$At is presented. A systematic study of $B(E3)$ values for the transitions de-exciting the 29/2$^{+}$ isomer in the neighboring odd-$A$ At isotopes suggests a half-life in the 2$-$4.5 $μ$s range for this state in $^{207}$At. The experimental results are compared with large-scale shell-model calculations performed using the KHM3Y effective interaction in the $Z$ = 50$-$126, $N$ = 82$-$184 model space and an overall good agreement is noted between the theory and the experiment. A qualitative comparison of the excited states and the isomers with analogous states in neighboring nuclei provides further insight into the structure of $^{207}$At.

nucl-ex↗

arXiv2022

Resolving Semantic Confusions for Improved Zero-Shot Detection

Zero-shot detection (ZSD) is a challenging task where we aim to recognize and localize objects simultaneously, even when our model has not been trained with visual samples of a few target ("unseen") classes. Recently, methods employing generative models like GANs have shown some of the best results, where unseen-class samples are generated based on their semantics by a GAN trained on seen-class data, enabling vanilla object detectors to recognize unseen objects. However, the problem of semantic confusion still remains, where the model is sometimes unable to distinguish between semantically-similar classes. In this work, we propose to train a generative model incorporating a triplet loss that acknowledges the degree of dissimilarity between classes and reflects them in the generated samples. Moreover, a cyclic-consistency loss is also enforced to ensure that generated visual samples of a class highly correspond to their own semantics. Extensive experiments on two benchmark ZSD datasets - MSCOCO and PASCAL-VOC - demonstrate significant gains over the current ZSD methods, reducing semantic confusion and improving detection for the unseen classes.

cs.CV↗

arXiv2022

Generalized radius problems for quotient functions having fixed second coefficient

In this manuscript, we deal with three classes of quotient functions having fixed second coefficient described on open unit disk. The radius of strongly starlikeness, lemniscate starlikeness, lune starlikeness, parabolic starlikeness, sine starlikeness, exponential starlikeness and several other radius estimates for such classes are examined. Relevant relations of obtained radius estimates with the existing estimates are also discussed.

math.CV↗

arXiv2022

Certain subclasses of Analytic Functions with Fixed Second Coefficient

This paper aims to pursue some classes of normalized analytic functions $f$ with fixed second coefficient defined on open unit disk, such that ${(1+z)^2f(z)}/{z}$ and ${(1+z)f(z)}/{z}$ are functions having positive real part. The radius of strongly starlikeness, the radius of lemniscate starlikeness, the radius of parabolic starlikeness and other starlikeness estimates are calculated for such functions. As well relevant connections of computed radii estimates with the existing one are also shown.

math.CV↗

arXiv2021

Anisotropy in interface stress at the BCC-iron solid-melt interface: molecular dynamics and phase field crystal modelling

The interface stresses at of the solid-melt interface are, in general, anisotropic. The anisotropy in the interfacial stress can be evaluated using molecular dynamics (MD) and phase field crystal (PFC) models. In this paper, we report our results on the evaluation of the anisotropy in interface stress in a BCC solid with its melt. Specifically, we study Fe using both MD and PFC models. We show that while both MD and PFC can be used for the evaluation, and the PFC and the amplitude equations based on PFC give quantitatively consistent results, the MD and PFC results are qualitatively the same but do not match quantitatively. We also find that even though the interfacial free energy is only weakly anisotropic in BCC interfacial stress anisotropy is strong. This strong anisotropy has implications for the equilibrium shapes, growth morphologies and other properties at nano-scale in these materials.

cond-mat.mtrl-sci↗

arXiv2021

Observations of the Quiet Sun During the Deepest Solar Minimum of the Past Century with Chandrayaan-2 XSM -- Sub-A Class Microflares Outside Active Regions

Solar flares, with energies ranging over several orders of magnitude, result from impulsive release of energy due to magnetic reconnection in the corona. Barring a handful, almost all microflares observed in X-rays are associated with the solar active regions. Here we present, for the first time, a comprehensive analysis of a large sample of quiet Sun microflares observed in soft X-rays by the Solar X-ray Monitor (XSM) on board the Chandrayaan-2 mission during the 2019-20 solar minimum. A total of 98 microflares having peak flux below GOES A-level were observed by the XSM during observations spanning 76 days. By using the derived plasma temperature and emission measure of these events obtained by fitting the XSM spectra along with volume estimates from concurrent imaging observations in EUV with the Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA), we estimated their thermal energies to be ranging from 3e26 to 6e27 erg. We present the frequency distribution of the quiet Sun microflares with energy and discuss the implications of these observations of small-scale magnetic reconnection events outside active regions on coronal heating.

astro-ph.SR↗

arXiv2021

Observations of the Quiet Sun During the Deepest Solar Minimum of the Past Century with Chandrayaan-2 XSM -- Elemental Abundances in the Quiescent Corona

Elements with low First Ionization Potential (FIP) are known to be three to four times more abundant in active region loops of the solar corona than in the photosphere. There have been observations suggesting that this observed "FIP bias" may be different in other parts of the solar corona and such observations are thus important in understanding the underlying mechanism. The Solar X-ray Monitor (XSM) on board the Chandrayaan-2 mission carried out spectroscopic observations of the Sun in soft X-rays during the 2019-20 solar minimum, considered to be the quietest solar minimum of the past century. These observations provided a unique opportunity to study soft X-ray spectra of the quiescent solar corona in the absence of any active regions. By modelling high resolution broadband X-ray spectra from XSM, we estimate the temperature and emission measure during periods of possibly the lowest solar X-ray intensity. We find that the derived parameters remain nearly constant over time with a temperature around 2 MK, suggesting the emission is dominated by X-ray Bright Points (XBPs). We also obtain the abundances of Mg, Al, and Si relative to H, and find that the FIP bias is ~2, lower than the values observed in active regions.

astro-ph.SR↗

arXiv2021

Differential Subordination implications for Certain Carathéodory functions

In this article, we wish to establish some first order differential subordination relations for certain Carathéodory functions with nice geometrical properties. Moreover, several implications are determined so that the normalized analytic function belongs to various subclasses of starlike functions.

math.CV↗

arXiv2020

Differential Subordinations For Functions With Positive Real Part Using Admissibility Conditions

Some sufficient conditions on certain constants which are involved in some first, second and third order differential subordinations associated with certain functions with positive real part like modified Sigmoid function, exponential function and Janowski function are obtained so that the analytic function p normalized by the condition p(0) = 1, is subordinate to Janowski function. The admissibility conditions for Janowski function are used as a tool in the proof of the results. As application, several sufficient conditions are also computed for Janowski starlikeness.

math.CV↗

arXiv2020

Solar X-ray Monitor On Board the Chandrayaan-2 Orbiter: In-flight Performance and Science Prospects

The Solar X-ray Monitor (abbreviated as XSM) on board India's Chandrayaan-2 mission is designed to carry out broadband spectroscopy of the Sun from lunar orbit. It observes the Sun as a star and measures the spectrum every second in the soft X-ray band of 1 - 15 keV with an energy resolution better than 180 eV at 5.9 keV. The primary objective of the XSM is to provide the incident solar spectrum for the X-ray fluorescence spectroscopy experiment on the Chandrayaan-2 orbiter, which aims to generate elemental abundance maps of the lunar surface. However, observations with the XSM can independently be used to study the Sun as well. The Chandrayaan-2 mission was launched on 22 July 2019, and the XSM began nominal operations, in lunar orbit, from September 2019. The in-flight observations, so far, have shown that its spectral performance has been identical to that on the ground. Measurements of the effective area from ground calibration were found to require some refinement, which has been carried out using solar observations at different incident angles. It also has been shown that the XSM is sensitive enough to detect solar activity well below A-class. This makes the investigations of microflares and the quiet solar corona feasible in addition to the study of the evolution of physical parameters during intense flares. This article presents the in-flight performance and calibration of the XSM instrument and discusses some specific science cases that can be addressed using observations with the XSM.

astro-ph.SR↗

arXiv2020

Sharp Bohr Radius Constants For Certain Analytic Functions

The Bohr radius for a class $\mathcal{G}$ consisting of analytic functions $f(z)=\sum_{n=0}^{\infty}a_nz^n$ in unit disc $\mathbb{D}=\{z\in\mathbb{C}:|z|<1\}$ is the largest $r^*$ such that every function $f$ in the class $\mathcal{G}$ satisfies the inequality \begin{equation*} d\left(\sum_{n=0}^{\infty}|a_nz^n|, |f(0)|\right) = \sum_{n=1}^{\infty}|a_nz^n|\leq d(f(0), \partial f(\mathbb{D})) \end{equation*} for all $|z|=r \leq r^*$, where $d$ is the Euclidean distance. In this paper, our aim is to determine the Bohr radius for the classes of analytic functions $f$ satisfying differential subordination relations $zf'(z)/f(z) \prec h(z)$ and $f(z)+βz f'(z)+γz^2 f''(z)\prec h(z)$, where $h$ is the Janowski function. Analogous results are obtained for the classes of $α$-convex functions and typically real functions, respectively. All obtained results are sharp.

math.CV↗