arXiv subjects

Suparna Roychowdhury

Publications and source records attributed to Suparna Roychowdhury.

At least 19 recordsLinked to original sources

arXiv2026

Spinning compact object and chaos in galactic centers

Galactic centres are highly dynamic regions dominated by a supermassive black hole (BH) surrounded by nuclear star clusters (NSC), molecular gas, and asymmetric matter distributions such as disks or halos. The combined gravitational effects of these components, along with relativistic corrections from the BH's spin, generate strongly nonlinear dynamics and frequent chaotic orbital behaviour. To model this environment, we employ a multipolar expansion potential in which the central compact object is represented by the Artemova-Bjornsson-Novikov pseudo-Newtonian potential, effectively capturing spin-dependent features of a Kerr-like BH. The surrounding halo is treated as an axisymmetric, shell-like mass distribution expanded up to third order in multipolar terms to account for realistic asymmetry. Previous studies have mainly explored the influence of multipolar moments and BH spin using Poincare sections, SALI, and related chaos indicators. In this work, we extend these analyses by incorporating stability analysis and basins of convergence to achieve a more complete understanding of the system's dynamics. Stability analysis around equilibrium points provides insight into local behavior, while basins of convergence highlight sensitivity to initial conditions and expose fractal basin boundaries. Our results show that the BH spin significantly reshapes phase space: depending on its magnitude and orientation, it can either amplify chaotic scattering caused by halo asymmetry or stabilize specific orbital families. These findings enhance our understanding of how relativistic spin effects and multipolar mass distributions jointly govern the dynamical architecture of galactic centers.

astro-ph.GA↗

arXiv2026

Exploring Chaotic Motion of a Particle in the Centre of a Galaxy with a Prolate Halo

The majority of galaxies are known to have supermassive black holes (SMBHs) at their core, which have a tremendous gravitational pull on the objects around them. When embedded within extended matter distributions such as prolate, shell-like halos, they give rise to complex gravitational fields that often drive nearby particles into chaotic orbits. The inherently nonlinear nature of such motion, shaped by general relativity, makes direct analysis highly challenging. To overcome this, pseudo-Newtonian potentials are used to approximate relativistic effects within a Newtonian framework. In this study, we model the central SMBH using the Artemova-Bjornsson-Novikov (1996) potential to mimic the rotational effects of a Kerr-like black hole. The surrounding prolate halo is treated as an axisymmetric, shell-like mass distribution, represented through a multipole expansion including dipole and quadrupole components. Poincare sections and the Maximum Lyapunov Exponent (MLE) reveal how the SMBH-halo system drives both order and chaos, with the SMBH spin modulating the dynamics by enhancing or suppressing chaos depending on its direction and magnitude.

nlin.CD↗

arXiv2025

Universal features of epidemic and vaccine models

In this paper, we study a stochastic susceptible-infected-susceptible (SIS) epidemic model that includes an additional immigration process. In the presence of multiplicative noise, generated by environmental perturbations, the model exhibits noise-induced transitions. The bifurcation diagram has two distinct regions of unimodality and bimodality in which the steady-state probability distribution has one and two peaks, respectively. Apart from first-order transitions between the two regimes, a critical-point transition occurs at a cusp point with the transition belonging to the mean-field Ising universality class. The epidemic model shares these features with the well-known Horsthemke-Lefever model of population genetics. The effect of vaccination on the spread/containment of the epidemic in a stochastic setting is also studied. We further propose a general vaccine-hesitancy model, along the lines of Kirman's ant model, with the steady-state distribution of the fraction of the vaccine-willing population given by the Beta distribution. The distribution is shown to give a good fit to the COVID-19 data on vaccine hesitancy and vaccination. We derive the steady-state probability distribution of the basic reproduction number, a key parameter in epidemiology, based on a beta-distributed fraction of the vaccinated population. Our study highlights the universal features that epidemic and vaccine models share with other dynamical models.

q-bio.PE↗

arXiv2024

Chaotic Dynamics in a Galactic Multipolar Halo with a Compact Primary

Observational evidence strongly supports the existence of a Super Massive Black Hole (SMBH) at the Galactic center, surrounded by dense stellar clusters. Modeling galactic centers with intricate structures like shells and rings pose challenges, prompting the use of simplified models such as a spherical monopole potential with a multipolar halo mass distribution. This approach, employing a multipolar expansion model, provides versatility for numerical analyses, revealing the complex dynamics of stars in this region. Pseudo-Potentials like Paczynsky-Wiita and Artemova-Bjornsson-Novikov are utilized to simulate the impacts of strong gravity from non-rotating and rotating compact objects respectively, elucidating their influence on stellar dynamics. Chaos naturally arises due to non-central forces, visualized using the Poincaré section technique. Of particular importance is the utilization of the Smaller Alignment Index (SALI), a powerful nonlinear dynamical tool, which categorizes particle orbits as escaping, regular, sticky, or chaotic. We exhaustively examine all combinations of multipolar moments up to the octupolar term along with spin using this tool, which had not been studied earlier. SALI provides a straightforward yet efficient method for assessing the interplay between the system's different multipolar moments, their combinations, and spin. Thus, our findings offer insights into the dynamics of compact objects enshrouded in a halo mass distribution and lay the groundwork for understanding complex astrophysical systems in galactic centers.

astro-ph.GA↗

arXiv2023

Chaotic dynamics of off-equatorial orbits around pseudo-Newtonian compact objects with dipolar halos

In this paper, we implement a generalised pseudo-Newtonian potential to study the off-equatorial orbits inclined at a certain angle with the equatorial plane around Schwarzschild and Kerr-like compact object primaries surrounded by a dipolar halo of matter. The chaotic dynamics of the orbits are detailed for both non-relativistic and special-relativistic test particles. The dependence of the degree of chaos on the Kerr parameter $a$ and the inclination angle $i$ is established individually using widely used indicators, such as the Poincaré Maps and the Maximum Lyapunov Exponents. Although the orbits' chaoticity has a positive correlation with $i$, the growth in the chaotic behaviour is not systematic. There is a threshold value of the inclination angle $i_{\text{c}}$, after which the degree of chaos sharply increases. On the other hand, the chaoticity of the inclined orbits anti-correlates with $a$ throughout its entire range. However, the negative correlation is systematic at lower values of the inclination angle. At higher values of $i$, the degree of chaos increases rapidly below a threshold value of the Kerr parameter, $a_{\text{c}}$. Above this threshold value, the correlation becomes weak. Furthermore, we establish a qualitative correlation between the threshold values and the overall chaoticity of the system. The studies performed with different orbital parameters and several initial conditions reveal the intricate nature of the system.

gr-qc↗

arXiv2023

Gender-Based Comparative Study of Type 2 Diabetes Risk Factors in Kolkata, India: A Machine Learning Approach

Type 2 diabetes mellitus represents a prevalent and widespread global health concern, necessitating a comprehensive assessment of its risk factors. This study aimed towards learning whether there is any differential impact of age, Lifestyle, BMI and Waist to height ratio on the risk of Type 2 diabetes mellitus in males and females in Kolkata, West Bengal, India based on a sample observed from the out-patient consultation department of Belle Vue Clinic in Kolkata. Various machine learning models like Logistic Regression, Random Forest, and Support Vector Classifier, were used to predict the risk of diabetes, and performance was compared based on different predictors. Our findings indicate a significant age-related increase in risk of diabetes for both males and females. Although exercising and BMI was found to have significant impact on the risk of Type 2 diabetes in males, in females both turned out to be statistically insignificant. For both males and females, predictive models based on WhtR demonstrated superior performance in risk assessment compared to those based on BMI. This study sheds light on the gender-specific differences in the risk factors for Type 2 diabetes, offering valuable insights that can be used towards more targeted healthcare interventions and public health strategies.

cs.LG↗

arXiv2023

Effect of air pollution on the growth of diabetic population

Diabetes mellitus is a disease which is currently a huge health hazard globally. The cases of diabetes had increased by a significant amount in past decades. Also it has been predicted that it will further increase in future. Diabetes depends on various factors like obesity, physical inactivity. Also diabetes can depend on various environmental issues. In this article, our main focus is to study the dependence of the diabetic cases on the air pollution. We have used the data for diabetic population and PM2.5 concentration in the air for five countries from 2010 to 2021. Here we have studied the correlation between the diabetic cases data and PM2.5 concentration data. Also, we have done the linear regression analysis to find whether this correlation is statistically significant.

physics.bio-ph↗

arXiv2023

Cellular automata in the light of COVID-19

Currently, the world has been facing the brunt of a pandemic due to a disease called COVID-19 for the last 2 years. To study the spread of such infectious diseases it is important to not only understand their temporal evolution but also the spatial evolution. In this work, the spread of this disease has been studied with a cellular automata (CA) model to find the temporal and the spatial behavior of it. Here, we have proposed a neighborhood criteria which will help us to measure the social confinement at the time of the disease spread. The two main parameters of our model are (i) disease transmission probability (q) which helps us to measure the infectivity of a disease and (ii) exponent (n) which helps us to measure the degree of the social confinement. Here, we have studied various spatial growths of the disease by simulating this CA model. Finally we have tried to fit our model with the COVID-19 data of India for various waves and have attempted to match our model predictions with regards to each wave to see how the different parameters vary with respect to infectivity and restrictions in social interaction.

physics.bio-ph↗

arXiv2023

Simulating the spread of COVID-19 with cellular automata: A new approach

Between the years 2020 to 2022, the world was hit by the pandemic of COVID-19 giving rise to an extremely grave situation. The global economy was badly hurt due to the consequences of various intervention strategies (like social distancing, lockdown) which were applied by different countries to control this pandemic. There are multiple speculations that humanity will again face such pandemics in the future. Thus it is very important to learn and gain knowledge about the spread of such infectious diseases and the various factors which are responsible for it. In this study, we have extended our previous work (Chowdhury et.al., 2022) on the probabilistic cellular automata (CA) model to reproduce the spread of COVID-19 in several countries by modifying its earlier used neighbourhood criteria. This modification gives us the liberty to adopt the effect of different restrictions like lockdown and social distancing in our model. We have done some theoretical analysis for initial infection and simulations to gain insights into our model. We have also studied the data from eight countries for COVID-19 in a window of 876 days and compared it with our model. We have developed a proper framework to fit our model on the data for confirmed cases of COVID-19 and have also re-checked the goodness of the fit with the data of the deceased cases for this pandemic. This model fits well with different peaks of COVID-19 data for all the eight countries and can be possibly generalized for a global prediction.

physics.soc-ph↗

arXiv2022

Heating of the intracluster medium by buoyant bubbles and sound waves

Active galactic nuclei (AGN) powered by the central Super-Massive Black Holes (SMBHs) play a major role in modifying the thermal properties of the intracluster medium (ICM). In this work, we implement two AGN heating models: (i) by buoyant cavities rising through stratified ICM (effervescent model) and, (ii) by viscous and conductive dissipation of sound waves (acoustic model). Our aim is to determine whether these heating models are consistent with ICM observables and if one is preferred over the other. We assume an initial entropy profile of ICM that is expected from the purely gravitational infall of the gas in the potential of the dark matter halo. We then incorporate heating, radiative cooling, and thermal conduction to study the evolution of ICM over the age of the clusters. Our results are: (i) Both the heating processes can produce comparable thermal profiles of the ICM with some tuning of relevant parameters. (ii) Thermal conduction is crucially important, even at the level of 10\% of the Spitzer values, in transferring the injected energy beyond the central regions, and without which the temperature/entropy profiles are unrealistically high. (iii) The required injected AGN power scales with cluster mass as $M_{\rm vir}^{1.5}$ for both models. (iv) The required AGN luminosity is comparable with the observed radio jet power, reinforcing the idea that AGNs are the dominant heating source in clusters. (v) Finally, we estimate that the fraction of the total AGN luminosity available as the AGN mechanical luminosity at $0.02r_{500}$ is less than 0.05\%.

astro-ph.CO↗

arXiv2021

A robust prediction from a minimal model of COVID-19 -- Can we avoid the third wave?

COVID-19 pandemic is one of the major disasters that humanity has ever faced. In this paper, we try to model the effect of vaccination in controlling the pandemic, particularly in context to the third wave which is predicted to hit globally. Here we have modified the SEIRD model by introducing a vaccination term. One of our main assumptions is that the infection rate (\b{eta}(t)) is oscillatory. This oscillatory nature has been discussed earlier in literature with reference to the seasonality of epidemics. However, in our case we invoke this nature of the infection rate (\b{eta}(t)) to model the cyclical behavior of the COVID-19 pandemic within a short period. This study focuses on a minimalistic approach where we have logically deduced that the infection rate (\b{eta}(t)) and the vaccination rate (λ) are the most important parameters while the other parameters can be assumed to be constants throughout the simulation. Finally, we have studied the rich interplay between the infection rate (\b{eta}(t)) and the vaccination rate (λ) on the infectious cases of COVID-19 and made some robust conclusions regarding the global behavior of this pandemic in near future.

q-bio.PE↗

arXiv2021

Universality and herd immunity threshold : Revisiting the SIR model for COVID-19

COVID-19 pandemic has been raging all around the world for almost a year now, as of November 1, 2020. In this paper, we try to analyze the variation of the COVID-19 pandemic in different countries in the light of some modifications to the susceptible-infected-recovered (SIR) model. The SIR model was modified by taking time-dependent rate parameters. From this modified SIR model, the basic reproduction number, effective reproduction number, herd immunity, and herd immunity threshold are redefined. The re-outbreak of the COVID-19 is a real threat to various countries. We have used the above-mentioned quantities to find the reasons behind the re-outbreak of this disease. Also, the effectiveness of herd immunity to prevent an epidemic has been analyzed with respect to this model. We have also tried to show that there are certain universal aspects in the spread and containment of the disease in various countries for a short period of time. Finally, we have also analyzed the current pandemic situation in India and have attempted to discuss the possibilities in order to predict its future behaviour using our model.

q-bio.PE↗

arXiv2020

Beyond-Newtonian dynamics of a planar circular restricted three-body problem with Kerr-like primaries

The dynamics of the planar circular restricted three-body problem with Kerr-like primaries in the context of a beyond-Newtonian approximation is studied. The beyond-Newtonian potential is developed by using the Fodor-Hoenselaers-Perjés procedure. An expansion in the Kerr potential is performed and terms up-to the first non-Newtonian contribution of both the mass and spin effects are included. With this potential, a model for a test particle of infinitesimal mass orbiting in the equatorial plane of the two primaries is examined. The introduction of a parameter, $ε$, allows examination of the system as it transitions from the Newtonian to the beyond-Newtonian regime. The evolution and stability of the fixed points of the system as a function of the parameter $ε$ is also studied. The dynamics of the particle is studied using the Poincaré map of section and the Maximal Lyapunov Exponent as indicators of chaos. Intermediate values of $ε$ seem to be the most chaotic for the two cases of primary mass-ratios ($=0.001,0.5$) examined. The amount of chaos in the system remains higher than the Newtonian system as well as for the planar circular restricted three-body problem with Schwarzschild-like primaries for all non-zero values of $ε$.

gr-qc↗

arXiv2020

Mathematical Model of ingested glucose in Glucose-Insulin Regulation

Here, we develop a mathematical model for glucose-insulin regulatory system. The model includes a new parameter which is the amount of ingested glucose. Ingested glucose is an external glucose source coming from digested food. We assume that the external glucose or ingested glucose decays exponentially with time. We establish a system of three linear ordinary differential equations with this new parameter, derive stability analysis and the solution of this model.

q-bio.TO↗

arXiv2015

Model dependence of the multi-transonic behavior, stability properties and corresponding acoustic geometry for accretion onto a spinning black hole

Multi-transonic accretion for a spinning black hole has been compared among different disc geometries within post Newtonian pseudo potential framework. The variation of stationary shock characteristics with black hole spin has been studied in details for all the disc models and compared for adiabatic as well as for isothermal scenario. The variations of surface gravity with spin for all these cases have also been investigated.

astro-ph.HE↗

arXiv2012

Solving relativistic hydrodynamic equation in presence of magnetic field for phase transition in a neutron star

Hadronic to quark matter phase transition may occur inside neutron stars (NS) having central densities of the order of 3-10 times normal nuclear matter saturation density ($n_0$). The transition is expected to be a two-step process; transition from hadronic to 2-flavour matter and two-flavour to $β$ equilibrated charge neutral three-flavour matter. In this paper we concentrate on the first step process and solve the relativistic hydrodynamic equations for the conversion front in presence of high magnetic field. Lorentz force due to magnetic field is included in the energy momentum tensor by averaging over the polar angles. We find that for an initial dipole configuration of the magnetic field with a sufficiently high value at the surface, velocity of the front increases considerably.

astro-ph.HE↗

arXiv2010

Magnetic fields and Sunyaev-Zel'dovich effect in galaxy clusters

In this work we study the contribution of magnetic fields to the Sunyaev Zeldovich (SZ) effect in the intracluster medium. In particular we calculate the SZ angular power spectrum and the central temperature decrement. The effect of magnetic fields is included in the hydrostatic equilibrium equation by splitting the Lorentz force into two terms one being the force due to magnetic pressure which acts outwards and the other being magnetic tension which acts inwards. A perturbative approach is adopted to solve for the gas density profile for weak magnetic fields (< 4 micro G}). This leads to an enhancement of the gas density in the central regions for nearly radial magnetic field configurations. Previous works had considered the force due to magnetic pressure alone which is the case only for a special set of field configurations. However, we see that there exists possible sets of configurations of ICM magnetic fields where the force due to magnetic tension will dominate. Subsequently, this effect is extrapolated for typical field strengths (~ 10 micro G) and scaling arguments are used to estimate the angular power due to secondary anisotropies at cluster scales. In particular we find that it is possible to explain the excess power reported by CMB experiments like CBI, BIMA, ACBAR at l > 2000 with sigma_8 ~ 0.8 (WMAP 5 year data) for typical cluster magnetic fields. In addition we also see that the magnetic field effect on the SZ temperature decrement is more pronounced for low mass clusters ( ~ 2 keV). Future SZ detections of low mass clusters at few arc second resolution will be able to probe this effect more precisely. Thus, it will be instructive to explore the implications of this model in greater detail in future works.

astro-ph.CO↗

arXiv2003

Implications of the Universal Temperature Profile for Galaxy Clusters

We study the X-ray cluster gas density distribution in hydrostatic equilibrium using the universal temperature profile obtained from recent simulations involving only gravitational processes. If this temperature profile is an indicator of the influence of gravitational processes alone on the intracluster medium, then the comparison of various X-ray parameters expected from this profile and the observed data would point towards any additional physics that may be required. We compare the entropy at 0.1 R_{200} and R_{500}, the scaled entropy profile, the gas fraction at 0.3 R_{200} and the gas fraction profile with recent observations and discuss the implications of this temperature profile in light of these data. We find that the entropy imparted to the gas from gravitational processes alone is larger than previously thought. The entropy at R_{500} for rich clusters is consistent with data, whereas the entropy at 0.1R_{200} is still less than the observed values. We also find that the gas fraction in the inner region of clusters, expected from gravitational processes alone, is smaller than previously thought but larger than the observed data. It does show a trend with the emission-weighted temperature ( ) as shown by data. We therefore find that the role of any additional non-gravitational process influencing the physical state of ICM would have to be revised in light of these findings.

astro-ph↗