Papers by Dr. Karan Singh Vinayak
Bulletin of Pure & Applied Sciences- Physics, 2021
In the present study, we aim to investigate the effect of density dependence of symmetry energy o... more In the present study, we aim to investigate the effect of density dependence of symmetry energy on multifragmentation, fragment’s flow (i.e. elliptical flow) as well as on nuclear stopping. The present work is performed within the framework of microscopic dynamical isospin-dependent quantum molecular dynamics (IQMD) model. We shall here attempt a descriptive analysis of the fragment production, elliptical flow associated with nucleons and fragments, nuclear dynamics (density & temperature) and nuclear stopping (or thermalization) reached in heavy-ion collisions subjected to different forms of density dependence of symmetry energy. Present study includes a detailed discussion of the consequences of different forms of symmetry energy in heavy-ion collisions at intermediate energies (i.e. between 10 MeV/nucleon and 1 GeV/nucleon). The present thesis is divided into seven chapters. Chapter 1 includes the general introduction regarding the isospin-dependence of the nuclear equation of st...
The Astrophysical Journal, 2019
We study the influence of density-dependent symmetry energy at high densities in simulations of c... more We study the influence of density-dependent symmetry energy at high densities in simulations of corecollapse supernovae, black hole formation and proto-neutron star cooling by extending the relativistic mean field (RMF) theory used for the Shen EOS table. We adopt the extended RMF theory to examine the density dependence of the symmetry energy with a small value of the slope parameter L, while the original properties of the symmetric nuclear matter are unchanged. In order to assess matter effects at high densities, we perform numerical simulations of gravitational collapse of massive stars adopting the EOS table at high densities beyond 10 14 g/cm 3 with the small L value, which is in accord with the experimental and observational constraints, and compare them with the results obtained by using the Shen EOS. Numerical results for 11.2M and 15M stars exhibit minor effects around the core bounce and in the following evolution for 200 ms. Numerical results for 40M and 50M stars reveal a shorter duration toward the black hole formation with a smaller maximum mass for the small L case. Numerical simulations of proto-neutron star cooling over 10 s through neutrino emissions demonstrate increasing effects of the symmetry energy at high densities. Neutrino cooling drastically proceeds in a relatively long timescale with high luminosities and average energies with the small symmetry energy. Evolution toward the cold neutron star is affected because of the different behavior of neutron-rich matter while supernova dynamics around core bounce remains similar in less neutron-rich environments.
Arxiv preprint arXiv:1107.5378, 2011
Arxiv preprint arXiv:1110.2290, 2011
Abstract: The effect of density dependent symmetry energy on nuclear-stopping is studied using is... more Abstract: The effect of density dependent symmetry energy on nuclear-stopping is studied using isospin-dependent quantum molecular dynamics model (IQMD). We have used the reduced isospin-dependent cross-section with soft (S) equation of state for the systems ...
Materials Today: Proceedings, 2021
Using isospin-dependent quantum molecular dynamics (IQMD) approach, we here check the role of iso... more Using isospin-dependent quantum molecular dynamics (IQMD) approach, we here check the role of isospin interactions on various fragments formed in the collisions of lighter to super heavy nuclei at intermediate energies. We demonstrated the direct impact of symmetry energy stiffness factor and Coulomb interactions on the final yield of fragments, simultaneously. The effects of Coulomb and different forms of density dependence of symmetry energy show an enhanced sensitivity for superheavy involved reactions compared to the earlier stable systems Index Terms-Isospin quantum molecular dynamical (IQMD) model, symmetry energy, super-heavy nuclei.
One of the fundamental questions in the nuclear physics is to understand the highly complex nucle... more One of the fundamental questions in the nuclear physics is to understand the highly complex nucleonic interactions, reaction dynamics related to stable and neutron rich nuclei and the equation of state as well as its isospin dependence. The nuclear equation of state, which is most commonly discussed in reference to its density dependence is often expanded in terms of the asymmetry dependence as [1, 2]:
The heavy-ion collisions (at intermediateenergies) are best suited to extract the infor-mation re... more The heavy-ion collisions (at intermediateenergies) are best suited to extract the infor-mation regarding the nuclear equation of stateas well as its isospin dependence. A full andproper accounting of the isospin is required tounderstand the complex dynamics involved inthe reaction. The multifragmentation is oneof the crucial parameters used to explore therole of symmetry energy as well as its densitydependence in heavy-ion collisions.Theoretical investigations provide evidencethat the symmetry energy or isospin depen-dent part of the nuclear equation of state canbe extracted from the isotopic distributionof primary fragments [1]. At the same time,the momentum dependence of equation ofstate has a signi cant impact on the fragmentproduction, especially at the peripheralcollisions [2]. By now, it is evident, that inintermediate energy heavy-ion collisions, theneutron-neutron, neutron-proton and proton-neutron interactions are entirely di erent.That is why, it is interesting to include ...
Bulletin of Pure & Applied Sciences- Physics, 2017
The purpose of this essay is to analyze two theories. One is a relatively new approach called Ins... more The purpose of this essay is to analyze two theories. One is a relatively new approach called Instrument Constituencies. The other is an established approach called the Advocacy Coalition Framework (ACF). This essay begins by comparing the two theories by an explicit set of criteria. It then lays out opportunities for refinement and advancement of Instrument Constituencies towards its better placement, usefulness, and longevity as a policy process theory. Research prospects at the intersection of Instrument Constituencies and the ACF are then presented with a set of research questions and hypotheses. This essay concludes with a summary of insights about the field of policy processes gained from this theoretical exploration. While there are opportunities for improvements and important caveats for consideration, this essay makes an optimistic argument for the potential of Instrument Constituencies to offer generalizable and context-specific knowledge in helping to advance policy process research.
IOP Conference Series: Earth and Environmental Science, 2021
Extended efficiency of solar cells to ensemble more solar energy as well as its optimum conversio... more Extended efficiency of solar cells to ensemble more solar energy as well as its optimum conversion and utilization is believed to be a major challenge in current times. The spectral mismatch between the distribution of energy in the solar spectrum incidence and the semiconducting material band gap is a major restriction in the performance of solar cells. The conversion of wavelength of the sun is a necessary requisite to reduce spectral disruption. Of late, the solar cell converters are presumed as up-converted components and products derived from down conversion. Materials like NaCsWO3, NaYF4, and NaYF4: Yb, Er are synthesized and used to overcome the problem like deficiency of up-conversion luminescence (UCL) materials and device structures. The intensity of UCL can be enhanced by a significant time when the amount of NaCsWO3 is 2.8 m mol per cent. UCL material is considered as one of the best approaches to obtain high-efficiency perovskite solar cells (PSCs). In order to overcome...
Physics of Atomic Nuclei, 2016
We performed a theoretical investigation of different mass-asymmetric reactions to access the dir... more We performed a theoretical investigation of different mass-asymmetric reactions to access the direct impact of the density-dependent part of symmetry energy on multifragmentation. The simulations are performed for a specific set of reactions having same system mass and N/Z content, using isospin-dependent quantum molecular dynamics model to estimate the quantitative dependence of fragment production on themass-asymmetry factor (τ) for various symmetry energy forms. The dynamics associated with different mass-asymmetric reactions is explored and the direct role of symmetry energy is checked. Also a comparison with the experimental data (asymmetric reaction) is presented for a different equation of states (symmetry energy forms).
AIP Conference Proceedings, 2016
Using isospin-dependent quantum molecular dynamics (IQMD) approach, we performed a theoretical in... more Using isospin-dependent quantum molecular dynamics (IQMD) approach, we performed a theoretical investigation of the evolution of various kinds of fragments in heavy and superheavy-ion reactions in the intermediate/medium energy domain. We demonstrated direct impact of symmetry energy and Coulomb interactions on the evolution of fragments. Final fragment spectra (yields) obtained from the analysis of various heavy/super-heavy ion reactions at different reaction conditions show high sensitivity towards Coulomb interactions and less significant sensitivity to symmetry energy forms. No inconsistent pattern of fragment structure is obtained in case of super-heavy ion involved reactions for all the parameterizations of density dependence of symmetry energy.
Reaction dynamics have been studied for maximum/average density and maximum/average temperature a... more Reaction dynamics have been studied for maximum/average density and maximum/average temperature as a function of stiffness factor of density dependent symmetry energy. Analysis has been carried out for the reactions 612C+79197 Au, 1724Al+79197 Au, 2858Ni+79197 Au, 40100Zr+79197 Au, 54131Xe+79197 Au and 79197Au+79197 Au, incident energy of E = 50 MeV/nucleon using Isospin dependent Quantum Molecular Dynamics (IQMD) model. Our study reveals a considerable change in average temperature and average density for the different reactions. For highly asymmetric reaction, the value of maximum/average density and maximum/average temperature is lesser than that for symmetric reaction for all the values of stiffness factor because of the minimum participant zone involved in the reaction dynamics. The ratio of maximum/average temperature for highly asymmetric to symmetric reaction decreases with increase in stiffness factor of density dependent symmetry energy. Similar is the case for maximum/average density.
The fragmentation of projectile and spectator matter is studied at different incident energies us... more The fragmentation of projectile and spectator matter is studied at different incident energies using an isospin-dependent QMD model with reduced isospin dependent cross-section. The sensitivity of the production of fragments is analyzed using different parametrizations of density dependence of symmetry energy. We shall also highlight the collective response of the momentum dependent interactions(MDI) and symmetry energy towards the fragmentation of
Journal of Physics G: Nuclear and Particle Physics, 2015
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Papers by Dr. Karan Singh Vinayak