arXiv subjects

Abhishek Mishra

Publications and source records attributed to Abhishek Mishra.

43 records · Page 3Linked to original sources

arXiv2017

A K-fold Method for Baseline Estimation in Policy Gradient Algorithms

The high variance issue in unbiased policy-gradient methods such as VPG and REINFORCE is typically mitigated by adding a baseline. However, the baseline fitting itself suffers from the underfitting or the overfitting problem. In this paper, we develop a K-fold method for baseline estimation in policy gradient algorithms. The parameter K is the baseline estimation hyperparameter that can adjust the bias-variance trade-off in the baseline estimates. We demonstrate the usefulness of our approach via two state-of-the-art policy gradient algorithms on three MuJoCo locomotive control tasks.

cs.AI↗

arXiv2015

Structural and Spectral properties of Corona Graphs

Product graphs have been gainfully used in literature to generate mathematical models of complex networks which inherit properties of real networks. Realizing the duplication phenomena imbibed in the definition of corona product of two graphs, we define Corona graphs. Given a small simple connected graph which we call seed graph, Corona graphs are defined by taking corona product of a seed graph iteratively. We show that the cumulative degree distribution of Corona graphs decay exponentially when the seed graph is regular and cumulative betweenness distribution follows power law when seed graph is a clique. We determine explicit formulae of eigenvalues, Laplacian eigenvalues and signless Laplacian eigenvalues of Corona graphs when the seed graph is regular. Computable expressions of eigenvalues and signless Laplacian eigenvalues of Corona graphs are also obtained when the seed graph is a star graph.

math.SP↗

arXiv2014

From nuclear reactions to compact stars: a unified approach

An equation of state (EoS) for symmetric nuclear matter is constructed using the density dependent M3Y effective interaction and extended for isospin asymmetric nuclear matter. Theoretically obtained values of symmetric nuclear matter incompressibility, isobaric incompressibility, symmetry energy and its slope agree well with experimentally extracted values. Folded microscopic potentials using this effective interaction, whose density dependence is determined from nuclear matter calculations, provide excellent descriptions for proton, alpha and cluster radioactivities, elastic and inelastic scattering. The nuclear deformation parameters extracted from inelastic scattering of protons agree well with other available results. The high density behavior of symmetric and asymmetric nuclear matter satisfies the constraints from the observed flow data of heavy-ion collisions. The neutron star properties studied using $β$-equilibrated neutron star matter obtained from this effective interaction for pure hadronic model agree with the recent observations of the massive compact stars such as PSR J1614-2230, but if a phase transition to quark matter is considered such agreement is no longer possible.

nucl-th↗

arXiv2013

A Comparison of Six Methods for Stabilizing Population Dynamics

Over the last two decades, several methods have been proposed for stabilizing the dynamics of biological populations. However, these methods have typically been evaluated using different population dynamics models and in the context of very different concepts of stability, which makes it difficult to compare their relative efficiencies. Moreover, since the dynamics of populations are dependent on the life-history of the species and its environment, it is conceivable that the stabilizing effects of control methods would also be affected by such factors, a complication that has typically not been investigated. In this study we compare six different control methods with respect to their efficiency at inducing a common level of enhancement (50% increase) for two kinds of stability (constancy and persistence) under four different life history/ environment combinations. Since these methods have been analytically studied elsewhere, we focus on an intuitive understanding of realistic simulations incorporating noise, extinction probability and lattice effect. We show that for these six methods, even when the magnitude of stabilization attained is the same, other aspects of the dynamics like population size distribution can be very different. Consequently, correlated aspects of stability, like the amount of persistence for a given degree of constancy stability (and vice versa) or the corresponding effective population size (a measure of resistance to genetic drift) vary widely among the methods. Moreover, the number of organisms needed to be added or removed to attain similar levels of stabilization also varies for these methods, a fact that has economic implications. Finally, we compare the relative efficiency of these methods through a composite index of various stability related measures. We find that restocking to a constant lower threshold seems to be the optimal method under most conditions.

q-bio.PE↗

arXiv2012

Proton radioactivity half lives with Skyrme interactions

The potential barrier impeding the spontaneous emission of protons in the proton radioactive nuclei is calculated as the sum of nuclear, Coulomb and centrifugal contributions. The nuclear part of the proton-nucleus interaction potential is obtained in the energy density formalism using Skyrme effective interaction that results into a simple algebraic expression. The half-lives of the proton emitters are calculated for the different Skyrme sets within the improved WKB framework. The results are found to be in reasonable agreement with the earlier results obtained for more complicated calculations involving finite range interactions.

nucl-th↗

arXiv2012

Rapidly rotating axisymmetric neutron stars with quark cores

We present a systematic study of the properties of pure hadronic and hybrid compact stars. The nuclear equation of state (EoS) for beta-equilibrated neutron star matter was obtained using density dependent effective nucleon-nucleon interaction which satisfies the constraints from the observed flow data from heavy-ion collisions. The energy density of quark matter is lower than that of this nuclear EoS at higher densities implying the possibility of transition to quark matter inside the core. We solve the Einstein's equations for rotating stars using pure nuclear matter and quark core. The beta- equilibrated neutron star matter with a thin crust is able to describe highly massive compact stars but find that the nuclear to quark matter deconfinement transition inside neutron stars causes reduction in their masses. Recent observations of the binary millisecond pulsar J1614-2230 by P. B. Demorest et al. [1] suggest that the masses lie within 1.97\pm0.04 M\odot where M\odot is the solar mass. In conformity with recent observations, pure nucleonic EoS determines that the maximum mass of NS rotating with frequency below r-mode instability is ~1.95 M\odot with radius ~10 kilometers. Although compact stars with quark cores rotating with Kepler's frequency have masses up to ~2 M\odot, but if the maximum frequency is limited by the r-mode instability, the maximum mass ~1.7 M\odot turns out to be lower than the observed mass of 1.97\pm0.04 M\odot, by far the highest yet measured with such certainty, implying exclusion of quark cores for such massive pulsars.

nucl-th↗

arXiv2011

Nuclear reaction rates and the primordial nucleosynthesis

The theoretical predictions of the primordial abundances of elements in the big-bang nucleosynthesis (BBN) are dominated by uncertainties in the input nuclear reaction rates. We investigate the effect of modifying these reaction rates on light element abundance yields in BBN by replacing the thirty-five reaction rates out of the existing eighty-eight. We have studied these yields as functions of evolution time or temperature. We find that using these new reaction rates results in only a little increase in helium mass fraction over that obtained previously in BBN calculations. This allows insights into the role of the nuclear reaction rates in the setting of the neutron-to-proton ratio during the BBN epoch. We observe that even with considerable nuclear physics uncertainties, most of these nuclear reactions have minimal effect on the standard BBN abundance yields of $^6$Li and $^7$Li.

nucl-th↗