arXiv subjects

Vikas Kumar

Publications and source records attributed to Vikas Kumar.

51 records · Page 3Linked to original sources

arXiv2020

Committee Selection with Attribute Level Preferences

We consider the problem of committee selection from a fixed set of candidates where each candidate has multiple quantifiable attributes. To select the best possible committee, instead of voting for a candidate, a voter is allowed to approve the preferred attributes of a given candidate. Though attribute based preference is addressed in several contexts, committee selection problem with attribute approval of voters has not been attempted earlier. A committee formed on attribute preferences is more likely to be a better representative of the qualities desired by the voters and is less likely to be susceptible to collusion or manipulation. In this work, we provide a formal study of the different aspects of this problem and define properties of weak unanimity, strong unanimity, simple justified representations and compound justified representation, that are required to be satisfied by the selected committee. We show that none of the existing vote/approval aggregation rules satisfy these new properties for attribute aggregation. We describe a greedy approach for attribute aggregation that satisfies the first three properties, but not the fourth, i.e., compound justified representation, which we prove to be NP-complete. Furthermore, we prove that finding a committee with justified representation and the highest approval voting score is NP-complete.

cs.GT↗

arXiv2020

Shell model study of high-spin states and band terminations in $^{67}$As

In the present work, recently available experimental data for different bands of $^{67}$As [Phys. Rev. C {\bf 98}, 024313 (2018)] have been interpreted within the framework of the shell model in full $f_{5/2}pg_{9/2}$ model space using JUN45 and jj44b effective interactions. The variation of $E$ - $E_{rot}$ energy versus spin for different bands is shown to obtain useful information about band termination. We have also reported the electromagnetic transition probabilities, quadrupole and magnetic moments of $^{67}$As. Except for some tentative high-spin states, the results are in good agreement with the available experimental data.The states $29/2^+$-$45/2^+$ are described by three particles in $g_{9/2}$, while $47/2^+$ and $51/2^+$ states are described by five particles in $g_{9/2}$. The shell model results corresponding to nine tentative states such as $41/2_1^+$ and $45/2_1^+$ in band-1b; $41/2_2^+$ and $45/2_2^+$ in band-1a; $43/2_2^+$, $47/2_2^+$ and $51/2_1^+$ in band-2a; $43/2_1^+$ and $47/2_1^+$ in band-2b are reported and discussed.

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arXiv2020

Gamow-Teller transition strengths for selected ${fp}$ shell nuclei

We have reported a systematic shell model description of the experimental Gamow-Teller transition strength for $^{44}$Sc $\rightarrow$ $^{44}$Ca, $^{45}$Ti $\rightarrow$ $^{45}$Sc, $^{48}$Ti $\rightarrow$ $^{48}$V, $^{66}$Co $\rightarrow$ $^{66}$Ni, and $^{66}$Fe $\rightarrow$ $^{66}$Co transitions using KB3G and GXPF1A interactions for $fp$ model space. In order to see the importance of higher orbital for $^{66}$Co $\rightarrow$ $^{66}$Ni and $^{66}$Fe $\rightarrow$ $^{66}$Co transitions, we have reported the shell model results with $fpg_{9/2}$ space using GXPF1Br+$V_{MU}$ interaction. We have obtained the qualitative agreement for the individual transitions, while the calculated summed transition strengths closely reproduce the observed ones.

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arXiv2019

Collaborative Filtering and Multi-Label Classification with Matrix Factorization

Machine learning techniques for Recommendation System (RS) and Classification has become a prime focus of research to tackle the problem of information overload. RS are software tools that aim at making informed decisions about the services that a user may like. On the other hand, classification technique deals with the categorization of a data object into one of the several predefined classes. In the multi-label classification problem, unlike the traditional multi-class classification setting, each instance can be simultaneously associated with a subset of labels. The focus of thesis is on the development of novel techniques for collaborative filtering and multi-label classification. We propose a novel method of constructing a hierarchical bi-level maximum margin matrix factorization to handle matrix completion of ordinal rating matrix. Taking the cue from the alternative formulation of support vector machines, a novel loss function is derived by considering proximity as an alternative criterion instead of margin maximization criterion for matrix factorization framework. We extended the concept of matrix factorization for yet another important problem of machine learning namely multi-label classification which deals with the classification of data with multiple labels. We propose a novel piecewise-linear embedding method with a low-rank constraint on parametrization to capture nonlinear intrinsic relationships that exist in the original feature and label space. We also study the embedding of labels together with the group information with an objective to build an efficient multi-label classifier. We assume the existence of a low-dimensional space onto which the feature vectors and label vectors can be embedded. We ensure that labels belonging to the same group share the same sparsity pattern in their low-rank representations.

cs.IR↗

arXiv2019

Block based Singular Value Decomposition approach to matrix factorization for recommender systems

With the abundance of data in recent years, interesting challenges are posed in the area of recommender systems. Producing high quality recommendations with scalability and performance is the need of the hour. Singular Value Decomposition(SVD) based recommendation algorithms have been leveraged to produce better results. In this paper, we extend the SVD technique further for scalability and performance in the context of 1) multi-threading 2) multiple computational units (with the use of Graphical Processing Units) and 3) distributed computation. We propose block based matrix factorization (BMF) paired with SVD. This enabled us to take advantage of SVD over basic matrix factorization(MF) while taking advantage of parallelism and scalability through BMF. We used Compute Unified Device Architecture (CUDA) platform and related hardware for leveraging Graphical Processing Unit (GPU) along with block based SVD to demonstrate the advantages in terms of performance and memory.

cs.LG↗

arXiv2018

Group Preserving Label Embedding for Multi-Label Classification

Multi-label learning is concerned with the classification of data with multiple class labels. This is in contrast to the traditional classification problem where every data instance has a single label. Due to the exponential size of output space, exploiting intrinsic information in feature and label spaces has been the major thrust of research in recent years and use of parametrization and embedding have been the prime focus. Researchers have studied several aspects of embedding which include label embedding, input embedding, dimensionality reduction and feature selection. These approaches differ from one another in their capability to capture other intrinsic properties such as label correlation, local invariance etc. We assume here that the input data form groups and as a result, the label matrix exhibits a sparsity pattern and hence the labels corresponding to objects in the same group have similar sparsity. In this paper, we study the embedding of labels together with the group information with an objective to build an efficient multi-label classification. We assume the existence of a low-dimensional space onto which the feature vectors and label vectors can be embedded. In order to achieve this, we address three sub-problems namely; (1) Identification of groups of labels; (2) Embedding of label vectors to a low rank-space so that the sparsity characteristic of individual groups remains invariant; and (3) Determining a linear mapping that embeds the feature vectors onto the same set of points, as in stage 2, in the low-dimensional space. We compare our method with seven well-known algorithms on twelve benchmark data sets. Our experimental analysis manifests the superiority of our proposed method over state-of-art algorithms for multi-label learning.

cs.LG↗

arXiv2017

Spectroscopic factor strengths using $ab ~ initio$ approaches

We have calculated the spectroscopic factor strengths for the one-proton and one-neutron pick-up reactions $^{27}$Al($d$,$^{3}$He)$^{26}$Mg and $^{27}$Al($d$,$t$)$^{26}$Al within the framework of the shell model. We employed two different $ab ~ initio$ approaches : an in-medium similarity renormalization targeted for a particular nucleus, and the coupled- cluster effective interaction. We also compared our results with recently determined experimental spectroscopic factors.

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arXiv2017

Multimodal Nonlinear Microscope based on a Compact Fiber-format Laser Source

We present a multimodal non-linear optical (NLO) laser-scanning microscope, based on a compact fiber-format excitation laser and integrating coherent anti-Stokes Raman scattering (CARS), stimulated Raman scattering (SRS) and two-photon-excitation fluorescence (TPEF) on a single platform. We demonstrate its capabilities in simultaneously acquiring CARS and SRS images of a blend of 6-μm poly(methyl methacrylate) beads and 3-μm polystyrene beads. We then apply it to visualize cell walls and chloroplast of an unprocessed fresh leaf of Elodea aquatic plant via SRS and TPEF modalities, respectively. The presented NLO microscope, developed in house using off-the-shelf components, offers full accessibility to the optical path and ensures its easy re-configurability and flexibility.

physics.optics↗

arXiv2016

High-spin structure of $^{87}$Sr and $^{87}$Zr nuclei : shell model interpretation

In the present work we report a comprehensive analysis of shell model results for high-spin states of $^{87}$Sr and $^{87}$Zr for recently available experimental data within the full $f_{5/2}pg_{9/2}$ model space using JUN45 and jj44b effective interactions developed for this model space. In this work we have compared the energy levels, electromagnetic transition probabilities, quadrupole and magnetic moments with available experimental data. We have confirmed structure of high-spin states of these two nuclei which were tentatively assigned in the recent experimental work. In the case of $^{87}$Sr, for positive parity states up to $\sim$ 7.5 MeV, both interactions predict very good agreement with experimental data, while negative parity states are slightly suppressed in jj44b calculation.For the $^{87}$Zr nucleus, the jj44b interaction predicts higher energies for the negative parity states beyond $J \geq 27/2^{-}$. The configuration, which have one hole in $νg_{9/2}$ orbital, is responsible for generating the states in $^{87}$Sr. In the case of $^{87}$Zr, low-lying positive parity states come with the configuration having three holes in the $νg_{9/2}$, while the odd-parity states have configuration $ν(f_{5/2}^{-1}g_{9/2}^{-2})$.

nucl-th↗

arXiv2016

Nuclear $β^-$-decay half-lives for $fp$ and $fpg$ shell nuclei

In the present work we calculate the allowed $β^-$-decay half-lives of nuclei with $Z = 20 -30$ and N $\leq$ 50 systematically under the framework of the nuclear shell model. A recent study shows that some nuclei in this region belong to the island of inversion. We perform calculation for $fp$ shell nuclei using KB3G effective interaction. In the case of Ni, Cu, and Zn, we used JUN45 effective interaction. Theoretical results of $Q$ values, half-lives, excitation energies, log$ft$ values, and branching fractions are discussed and compared with the experimental data. In the Ni region, we also compared our calculated results with recent experimental data [Z. Y. Xu {\it et al.}, \emph{Phys. Rev. Lett.} \textbf{113}, 032505, 2014]. Present results agree with the experimental data of half-lives in comparison to QRPA.

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arXiv2016

Shell model description of Gamow-Teller strengths in $pf$-shell nuclei

A systematic shell model description of the experimental Gamow-Teller transition strength distributions in $^{42}$Ti, $^{46}$Cr, $^{50}$Fe and $^{54}$Ni is presented. These transitions have been recently measured via $β$ decay of these $T_z$=-1 nuclei, produced in fragmentation reactions at GSI and also with ($^3${He},$t$) charge-exchange (CE) reactions corresponding to $T_z = + 1$ to $T_z = 0$ carried out at RCNP-Osaka.The calculations are performed in the $pf$ model space, using the GXPF1a and KB3G effective interactions. Qualitative agreement is obtained for the individual transitions, while the calculated summed transition strengths closely reproduce the observed ones.

nucl-th↗

arXiv2015

Analysis of proton and neutron pair breakings: High-spin structures of $^{124-127}$Te isotopes

In the present work recently available experimental data for high-spin states of four nuclei, $^{124}_{\ 52}$Te, $^{125}_{\ 52}$Te, $^{126}_{\ 52}$Te, and $^{127}_{\ 52}$Te have been interpreted using state-of-the-art shell model calculations. The calculations have been performed in the $50-82$ valence shell composed of $1g_{7/2}$, $2d_{5/2}$, $1h_{11/2}$, $3s_{1/2}$, and $2d_{3/2}$ orbitals. We have compared our results with the available experimental data for excitation energies and transition probabilities, including high-spin states. The results are in reasonable agreement with the available experimental data. The wave functions, particularly, the specific proton and neutron configurations which are involved to generate the angular momentum along the yrast lines are discussed. We have also estimated overall contribution of three-body forces in the energy level shifting. Finally, results with modified effective interaction are also reported.

nucl-th↗

arXiv2015

High-spin structures of $^{77,79,81,83}$As isotopes

In the present work we report comprehensive set of shell model calculations for arsenic isotopes. We performed shell model calculations with two recent effective interactions JUN45 and jj44b. The overall results for the energy levels and magnetic moments are in rather good agreement with the available experimental data. We have also reported competition of proton- and neutron-pair breakings analysis to identify which nucleon pairs are broken to obtain the total angular momentum of the calculated states. Further theoretical development is needed by enlarging model space by including $π0f_{7/2}$ and $ν1d_{5/2}$ orbitals.

nucl-th↗

arXiv2014

High-spin structures of $^{86,87,88,89}$Y: a shell model interpretation

In this work nuclear structure properties of $^{86,87,88,89}$Y isotopes have been investigated using large-scale shell-model calculations within the full $f_{5/2}pg_{9/2}$ model space. The calculations have been performed with JUN45 and jj44b effective interactions that have been proposed for use in the $f_{5/2}$, $p_{3/2}$, $p_{1/2}$, $g_{9/2}$ model space for both protons and neutrons. Reasonable agreement between experimental and calculated values are obtained. This work will add more information to previous study by projected shell model [Eur. Phys. J. A 48, 138 (2012)] where full-fledged shell model calculations proposed for these nuclei.

nucl-th↗

arXiv2013

Structure of odd $^{79,81,83}$Se isotopes with proton and neutron excitations across $Z=28$ AND $N= 40$

The recently measured experimental data of $^{79,81,83}$Se isotopes have been interpreted in terms of shell model calculations. The calculations have been performed in ${f_{5/2}pg_{9/2}}$ space with the recently derived interactions, namely with JUN45 and jj44b. To study the importance of the proton excitations across the $Z=28$ shell in this region. We have also performed calculation in ${fpg_{9/2}}$ valence space using an ${fpg}$ effective interaction with $^{48}$Ca core and imposing a truncation. Excitation energies, $B(2)$ values, quadrupole moments and magnetic moments are compared with experimental data when available. Present study reveals the importance of proton excitations across the $Z=28$ shell for predicting quadrupole and magnetic moments.

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