arXiv subjects

Vivek Kumar Singh

Publications and source records attributed to Vivek Kumar Singh.

At least 55 records · Page 3Linked to original sources

arXiv2021

A long term multi-frequency study of solar rotation using solar radio flux and its relationship with solar cycles

This paper examines long-term temporal and spatial fluctuations in the solar rotation (more than four solar cycles) by investigating radio emission escapes from various layers of the solar atmosphere during the years 1967-2010. The flux modulation approach can also be used to investigate variations in solar rotation, which is a contentious topic in solar physics. The current study makes use of a time series of radio flux data at different frequencies (245-15400 MHz) obtained at Sagamore Hill Solar Radio Observatory in Massachusetts, USA, and other observatories from 1967 to 2010. The periodicity present in the temporal variation of time series is estimated through Lomb Scargle Periodogram (LSP). The rotation period estimated for five radio emissions (606, 1415, \& 2695 MHz; from corona, and 4995 \& 8800 MHz; from transition region) through statistical approach shows continuous temporal and spatial variation throughout the years. The smoothed rotation period shows the presence of $\sim$ 22-yrs periodic and $\sim$ 11-yrs components in it. The 22-year component could be linked to the reversal of the solar magnetic field (Hale's) cycle, while the 11-yrs component is most likely related to the sunspot (Schwabe's) cycle. Besides these two components, random components are also prominently present in the analyzed data. The cross-correlation between the sunspot number and the rotation period obtained shows a strong correlation with 11-yrs Schwabe's and 22-yr Hale cycle. The corona rotates faster or slower than transition region in different epoch. The swap of faster rotation speed between corona and transition region also follows the 22-yrs cycle.

astro-ph.SR↗

arXiv2021

SLSNet: Skin lesion segmentation using a lightweight generative adversarial network

The determination of precise skin lesion boundaries in dermoscopic images using automated methods faces many challenges, most importantly, the presence of hair, inconspicuous lesion edges and low contrast in dermoscopic images, and variability in the color, texture and shapes of skin lesions. Existing deep learning-based skin lesion segmentation algorithms are expensive in terms of computational time and memory. Consequently, running such segmentation algorithms requires a powerful GPU and high bandwidth memory, which are not available in dermoscopy devices. Thus, this article aims to achieve precise skin lesion segmentation with minimum resources: a lightweight, efficient generative adversarial network (GAN) model called SLSNet, which combines 1-D kernel factorized networks, position and channel attention, and multiscale aggregation mechanisms with a GAN model. The 1-D kernel factorized network reduces the computational cost of 2D filtering. The position and channel attention modules enhance the discriminative ability between the lesion and non-lesion feature representations in spatial and channel dimensions, respectively. A multiscale block is also used to aggregate the coarse-to-fine features of input skin images and reduce the effect of the artifacts. SLSNet is evaluated on two publicly available datasets: ISBI 2017 and the ISIC 2018. Although SLSNet has only 2.35 million parameters, the experimental results demonstrate that it achieves segmentation results on a par with the state-of-the-art skin lesion segmentation methods with an accuracy of 97.61%, and Dice and Jaccard similarity coefficients of 90.63% and 81.98%, respectively. SLSNet can run at more than 110 frames per second (FPS) in a single GTX1080Ti GPU, which is faster than well-known deep learning-based image segmentation models, such as FCN. Therefore, SLSNet can be used for practical dermoscopic applications.

eess.IV↗

arXiv2021

Radial Differential Rotation of Solar Corona using Radio Emissions

The present work is an effort to investigate possible radial variations in the solar coronal rotation by analyzing the solar radio emission data at 15 different frequencies (275-1755 MHz) for the period starting from July 1994 to May 1999. We used a time series of disk-integrated radio flux recorded daily at these frequencies through radio telescopes situated at Astronomical Observatory of the Jagellonian University in Cracow. The different frequency radiation originates from different heights in the solar corona. Existing models, indicate its origin at the height range from nearly $\sim12,000$ km (for emission at 275 MHz), below up to $\sim2,400$ km (for emission at 1755 MHz). There are some data gaps in the time series used for the study, so we used statistical analysis using the Lomb-Scargle Periodogram (LSP). This method has successfully estimated the periodicity present in time series even with such data gaps. The rotation period estimated through LSP shows variation in rotation period, which is compared with the earlier reported estimate using auto correlation technique. The present study indicates some similarity as well as contradiction with studies reported earlier. The radial and temporal variation in solar rotation period are presented and discussed for the whole period analyzed.

astro-ph.SR↗

arXiv2021

What do Indian Researchers download from Sci-Hub

Recently three foreign academic publishers filed a case of copyright infringement against Sci-Hub and LibGen before the Delhi High Court and prayed for complete blocking these websites in India. In this context, this paper attempted to assess the impact that blocking of Sci-Hub may have on Indian research community. The download requests originating from India on a daily-basis are counted, geotagged and analysed by discipline, publisher, country and publication year etc. Results indicate that blocking Sci-Hub in India may actually hurt Indian research community in a significant way.

cs.DL↗

arXiv2021

India's rank and global share in scientific research -- how publication counting method and subject selection can vary the outcomes

During the last two decades, India has emerged as a major knowledge producer in the world, however different reports put it at different ranks, varying from 3rd to 9th places. The recent commissioned study reports of Department of Science and Technology (DST) done by Elsevier and Clarivate Analytics, rank India at 5thand 9th places, respectively. On the other hand, an independent report by National Science Foundation (NSF) of United States (US), ranks India at 3rd place on research output in Science and Engineering area. Interestingly, both, the Elsevier and the NSF reports use Scopus data, and yet surprisingly their outcomes are different. This article, therefore, attempts to investigate as to how the use of same database can still produce different outcomes, due to differences in methodological approaches. The publication counting method used and the subject selection approach are the two main exogenous factors identified to cause these variations. The implications of the analytical outcomes are discussed with special focus on policy perspectives.

cs.DL↗

arXiv2021

A large-scale comparison of social media coverage and mentions captured by the two altmetric aggregators- Altmetric.com and PlumX

The increased social media attention to scholarly articles has resulted in efforts to create platforms & services to track and measure the social media transactions around scholarly articles in different social platforms (such as Twitter, Blog, Facebook) and academic social networks (such as Mendeley, Academia and ResearchGate). Altmetric.com and PlumX are two popular aggregators that track social media activity around scholarly articles from a variety of social platforms and provide the coverage and transaction data to researchers for various purposes. However, some previous studies have shown that the social media data captured by the two aggregators have differences in terms of coverage and magnitude of mentions. This paper aims to revisit the question by doing a large-scale analysis of social media mentions of a data sample of 1,785,149 publication records (drawn from multiple disciplines, demographies, publishers). Results obtained show that PlumX tracks more wide sources and more articles as compared to Altmetric.com. However, the coverage and average mentions of the two aggregators vary across different social media platforms, with Altmetric.com recording higher mentions in Twitter and Blog, and PlumX recording higher mentions in Facebook and Mendeley, for the same set of articles. The coverage and average mentions captured by the two aggregators across different document types, disciplines and publishers is also analyzed.

cs.DL↗

arXiv2021

The Journal Coverage of Web of Science, Scopus and Dimensions: A Comparative Analysis

Traditionally, Web of Science and Scopus have been the two most widely used databases for bibliometric analyses. However, during the last few years some new scholarly databases, such as Dimensions, have come up. Several previous studies have compared different databases, either through a direct comparison of article coverage or by comparing the citations across the databases. This article attempts to compare the journal coverage of the three databases: Web of Science, Scopus and Dimensions. The most recent master journal lists of the three databases have been used for the purpose of identifying the overlapping and unique journals covered in the databases. The results indicate that the databases have significantly different journal coverage, with the Web of Science being most selective and Dimensions being the most exhaustive. About 99.11% and 96.61% of the journals indexed in Web of Science are also indexed in Scopus and Dimensions, respectively. Scopus has 96.42% of its indexed journals also covered by Dimensions. Dimensions database has the most exhaustive coverage, with 82.22% more journals covered as compared to Web of Science and 48.17% more journals covered as compared to Scopus. We also analysed the research outputs for 20 highly productive countries for the 2010-2019 period, as indexed in the three databases, and identified database-induced variations in research output volume, rank and global share of different countries. In addition to variations in overall coverage of research output from different countries, the three databases appear to have differential coverage of different disciplines.

cs.DL↗

arXiv2021

Colored HOMFLY-PT for hybrid weaving knot $\hat{W}_{3}(m,n)$

Weaving knots $W(p, n)$ of type $(p, n)$ denote an infinite family of hyperbolic knots which have not been addressed by the knot theorists as yet. Unlike the well-known $(p,n)$ torus knots, we do not have a closed-form expression for HOMFLY-PT and the colored HOMFLY-PT for $W(p,n)$. In this paper, we confine to a hybrid generalization of $W(3,n)$ which we denote as $\hat{W}_3(m,n)$ and obtain a closed-form expression for HOMFLY-PT using the Reshitikhin and Turaev method involving $\mathcal R$-matrices. Further, we also compute $[r]$-colored HOMFLY-PT for $W(3,n)$. Surprisingly, we observe that trace of the product of two dimensional $\hat{\mathcal{R}}$-matrices can be written in terms of an infinite family of Laurent polynomials $\mathcal{V}_{n,t}[q]$ whose absolute coefficients has an interesting relation to the Fibonacci numbers $\mathcal{F}_{n}$. We also computed reformulated invariants and the BPS integers in the context of topological strings. From our analysis, we propose that certain refined BPS integers for weaving knot $W(3,n)$ can be explicitly derived from the coefficients of Chebyshev polynomials of the first kind.

hep-th↗

arXiv2021

Network-Agnostic Knowledge Transfer for Medical Image Segmentation

Conventional transfer learning leverages weights of pre-trained networks, but mandates the need for similar neural architectures. Alternatively, knowledge distillation can transfer knowledge between heterogeneous networks but often requires access to the original training data or additional generative networks. Knowledge transfer between networks can be improved by being agnostic to the choice of network architecture and reducing the dependence on original training data. We propose a knowledge transfer approach from a teacher to a student network wherein we train the student on an independent transferal dataset, whose annotations are generated by the teacher. Experiments were conducted on five state-of-the-art networks for semantic segmentation and seven datasets across three imaging modalities. We studied knowledge transfer from a single teacher, combination of knowledge transfer and fine-tuning, and knowledge transfer from multiple teachers. The student model with a single teacher achieved similar performance as the teacher; and the student model with multiple teachers achieved better performance than the teachers. The salient features of our algorithm include: 1)no need for original training data or generative networks, 2) knowledge transfer between different architectures, 3) ease of implementation for downstream tasks by using the downstream task dataset as the transferal dataset, 4) knowledge transfer of an ensemble of models, trained independently, into one student model. Extensive experiments demonstrate that the proposed algorithm is effective for knowledge transfer and easily tunable.

cs.CV↗

arXiv2020

Semiclassical limit of topological Rényi entropy in $3d$ Chern-Simons theory

We study the multi-boundary entanglement structure of the state associated with the torus link complement $S^3 \backslash T_{p,q}$ in the set-up of three-dimensional SU(2)$_k$ Chern-Simons theory. The focal point of this work is the asymptotic behavior of the Rényi entropies, including the entanglement entropy, in the semiclassical limit of $k \to \infty$. We present a detailed analysis for several torus links and observe that the entropies converge to a finite value in the semiclassical limit. We further propose that the large $k$ limiting value of the Rényi entropy of torus links of type $T_{p,pn}$ is the sum of two parts: (i) the universal part which is independent of $n$, and (ii) the non-universal or the linking part which explicitly depends on the linking number $n$. Using the analytic techniques, we show that the universal part comprises of Riemann zeta functions and can be written in terms of the partition functions of two-dimensional topological Yang-Mills theory. More precisely, it is equal to the Rényi entropy of certain states prepared in topological $2d$ Yang-Mills theory with SU(2) gauge group. Further, the universal parts appearing in the large $k$ limits of the entanglement entropy and the minimum Rényi entropy for torus links $T_{p,pn}$ can be interpreted in terms of the volume of the moduli space of flat connections on certain Riemann surfaces. We also analyze the Rényi entropies of $T_{p,pn}$ link in the double scaling limit of $k \to \infty$ and $n \to \infty$ and propose that the entropies converge in the double limit as well.

hep-th↗

arXiv2020

India's rank and global share in scientific research -- how data sourced from different databases can produce varying outcomes

India is emerging as a major knowledge producer of the world in terms of proportionate share of global research output and the overall research productivity rank. Many recent reports, both of commissioned studies from Government of India as well as independent international agencies, show India at different ranks of global research productivity (variations as large as from 3rd to 9th place). The paper examines this contradiction; tries to analyse as to why different reports places India at different ranks and what may be the reasons thereof. The research output data for India, along with the ten most productive countries in the world, is analysed from three major scholarly databases: Web of Science, Scopus and Dimensions for this purpose. Results show that both, the endogenous factors (such as database coverage variation and different subject classification schemes) and the exogenous factors (such as subject selection and publication counting methodology) cause the variations in different reports. This paper reports first part of the analysis, focusing mainly on variations due to use of data from different databases. The policy implications of the study are also discussed.

cs.DL↗

arXiv2020

Do 'altmetric mentions' follow Power Laws? Evidence from social media mention data in Altmetric.com

Power laws are a characteristic distribution that are ubiquitous, in that they are found almost everywhere, in both natural as well as in man-made systems. They tend to emerge in large, connected and self-organizing systems, for example, scholarly publications. Citations to scientific papers have been found to follow a power law, i.e., the number of papers having a certain level of citation x are proportional to x raised to some negative power. The distributional character of altmetrics has not been studied yet as altmetrics are among the newest indicators related to scholarly publications. Here we select a data sample from the altmetrics aggregator Altmetrics.com containing records from the platforms Facebook, Twitter, News, Blogs, etc., and the composite variable Alt-score for the period 2016. The individual and the composite data series of 'mentions' on the various platforms are fit to a power law distribution, and the parameters and goodness of fit determined using least squares regression. The log-log plot of the data, 'mentions' vs. number of papers, falls on an approximately linear line, suggesting the plausibility of a power law distribution. The fit is not very good in all cases due to large fluctuations in the tail. We show that fit to the power law can be improved by truncating the data series to eliminate large fluctuations in the tail. We conclude that altmetric distributions also follow power laws with a fairly good fit over a wide range of values. More rigorous methods of determination may not be necessary at present.

cs.DL↗

arXiv2020

Study of diffusion coefficients of identified particles at energies available at BNL Relativistic Heavy Ion Collider

Using event-by-event fluctuations, we study the diffusion parameters of net-charge, net-pion, net-kaon, and net-proton in the heavy-ion jet interaction generator (HIJING), and ultra-relativistic quantum molecular dynamics (UrQMD) models at different collision energies \sqsn available at BNL Relativistic Heavy Ion Collider (RHIC). The diffusion parameter ($σ$) of net-charge and identified particles are estimated in rapidity space at various \sqsn. It is observed that, the $σ$ values are independent of collision energies but emphasises the particle-species dependence of diffusion coefficient in the QGP medium. The present work on particle-species dependence of diffusion coefficient provides a baseline for comparison with the experimental data.

nucl-th↗

arXiv2020

Distinguishing Mutant Knots

Knot theory is actively studied both by physicists and mathematicians as it provides a connecting centerpiece for many physical and mathematical theories. One of the challenging problems in knot theory is distinguishing mutant knots. Mutant knots are not distinguished by colored HOMFLY-PT polynomials for knots colored by either symmetric and or antisymmetric representations of $SU(N)$. Some of the mutant knots can be distinguished by the simplest non-symmetric representation $[2,1]$. However there is a class of mutant knots which require more complex representations like $[4,2]$. In this paper we calculate polynomials and differences for the mutant knot polynomials in representations $[3,1]$ and $[4,2]$ and study their properties.

hep-th↗

arXiv2020

The Case of Significant Variations in Gold-Green and Black Open Access: Evidence from Indian Research Output

Open Access has emerged as an important movement worldwide during the last decade. There are several initiatives now that persuade researchers to publish in open access journals and to archive their pre- or post-print versions of papers in repositories. Institutions and funding agencies are also promoting ways to make research outputs available as open access. This paper looks at open access levels and patterns in research output from India by computationally analyzing research publication data obtained from Web of Science for India for the last five years (2014-2018). The corresponding data from other connected platforms -- Unpaywall and Sci-Hub -- are also obtained and analyzed. The results obtained show that about 24% of research output from India, during last five years, is available in legal forms of open access as compared to world average of about 30%. More articles are available in gold open access as compared to green and bronze. On the contrary, more than 90% of the research output from India is available for free download in Sci-Hub. We also found disciplinary differentiation in open access, but surprisingly these patterns are different for gold-green and black open access forms. Sci-Hub appears to be complementing the legal gold-green open access for less covered disciplines in them. The central institutional repositories in India are found to have low volume of research papers deposited.

cs.DL↗

arXiv2020

Does presence of social media plugins in a journal website result in higher social media attention of its research publications

Social media platforms have now emerged as an important medium for wider dissemination of research articles; with authors, readers and publishers creating different kinds of social media activity about the article. Some research studies have even shown that articles that get more social media attention may get higher visibility and citations. These factors are now persuading journal publishers to integrate social media plugins in their webpages to facilitate sharing and dissemination of articles in social media platforms. Many past studies have analyzed several factors (like journal impact factor, open access, collaboration etc.) that may impact social media attention of scholarly articles. However, there are no studies to analyze whether the presence of social media plugin in a journal could result in higher social media attention of articles published in the journal. This paper aims to bridge this gap in knowledge by analyzing a sufficiently large-sized sample of 99,749 articles from 100 different journals. Results obtained show that journals that have social media plugins integrated in their webpages get significantly higher social media mentions and shares for their articles as compared to journals that do not provide such plugins. Authors and readers visiting journal webpages appear to be a major contributor to social media activity around articles published in such journals. The results suggest that publishing houses should actively provide social media plugin integration in their journal webpages to increase social media visibility (altmetric impact) of their articles.

cs.DL↗

arXiv2020

Difference of mutant knot invariants and their differential expansion

We evaluate the differences of HOMFLY-PT invariants for pairs of mutant knots colored with representations of $SL(N)$, which are large enough to distinguish between them. These mutant pairs include the pretzel mutants, which require at least the representation, labeled by the Young diagram $[4,2]$. We discuss the differential expansion for the differences, it is non-trivial in the case of mutants, which have the non-zero defect. The most effective technical tool, in this case, turns out to be the standard Reshetikhin-Turaev approach.

hep-th↗

arXiv2020

Equivalence of Light-Front and Covariant Quantum Electrodynamics at One Loop Level and the form of the Gauge Boson Propagator

We discuss the equivalence of the standard covariant expressions and light-front expressions of the three fundamental one loop Feynman diagrams of Quantum Electrodynamics viz. vertex correction, fermion self-energy and vacuum polarization in the light-front gauge obtained using time-ordered Hamiltonian perturbation theory. Although this issue has been addressed by us and others previously, our emphasis in this article is to resolve any ambiguity regarding the correct form of the gauge boson propagator to be used in the light-front gauge. We show how integrating over the light-front energy consistently in the covariant expression of each of the three one loop corrections leads to the propagating as well as the instantaneous diagrams of the light-front theory. In doing so, we re-establish the necessity of using the doubly transverse gauge boson propagator.

hep-th↗