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Papers by Sayantan Chowdhury

Research paper thumbnail of Perspective on attractive-repulsive interactions in dynamical networks: Progress and future

EPL (Europhysics Letters)

Research paper thumbnail of Antiphase synchronization in multiplex networks with attractive and repulsive interactions

Physical Review E

A series of recent publications, within the framework of network science, have focused on the coe... more A series of recent publications, within the framework of network science, have focused on the coexistence of mixed attractive and repulsive (excitatory and inhibitory) interactions among the units within the same system, motivated by the analogies with spin glasses as well as to neural networks, or ecological systems. However, most of these investigations have been restricted to single layer networks, requiring further analysis of the complex dynamics and particular equilibrium states that emerge in multilayer configurations. This article investigates the synchronization properties of dynamical systems connected through multiplex architectures in the presence of attractive intralayer and repulsive interlayer connections. This setting enables the emergence of antisynchronization, i.e., intralayer synchronization coexisting with antiphase dynamics between coupled systems of different layers. We demonstrate the existence of a transition from interlayer antisynchronization to antiphase synchrony in any connected bipartite multiplex architecture when the repulsive coupling is introduced through any spanning tree of a single layer. We identify, analytically, the required graph topologies for interlayer antisynchronization and its interplay with intralayer and antiphase synchronization. Next, we analytically derive the invariance of intralayer synchronization manifold and calculate the attractor size of each oscillator exhibiting interlayer antisynchronization together with intralayer synchronization. The necessary conditions for the existence of interlayer antisynchronization along with intralayer synchronization are given and numerically validated by considering Stuart-Landau oscillators. Finally, we also analytically derive the local stability condition of the interlayer antisynchronization state using the master stability function approach.

Research paper thumbnail of Facilitators and Barriers to Implementation of Childhood Tuberculosis Control Program in Bangladesh: a Mixed-methods Study From BRAC Urban DOTS Centres in Dhaka

BackgroundWorld Health Organisation (WHO) estimates childhood tuberculosis (tb) in high burden co... more BackgroundWorld Health Organisation (WHO) estimates childhood tuberculosis (tb) in high burden countries to be at least 10-15% of all cases. Despite intensive efforts on the childhood tb control program in Bangladesh, case detection rates stand below 5%. This study investigated the implementation pathway of childhood tb in Bangladesh. The study aims to identify the factors that enable and hinder the diagnosis and treatment of childhood tb in Bangladesh.MethodsAn exploratory-explanatory mixed-methods study was carried out in eight (top four and bottom four based on new case identification) urban DOTS (Directly Observed Treatment, Short-course) centres of the BRAC tb program in Dhaka Metropolitan City, Bangladesh. The study was conducted between September and December 2017. The knowledge, attitude, and practice (KAP) assessment on diagnosis and treatment of childhood tb were conducted among 111 Shasthya Shebika (SS), frontline health care workers engaged in the tb program. Field worke...

Research paper thumbnail of Effect of repulsive links on frustration in attractively coupled networks

Physical Review E

We investigate the impact of attractive-repulsive interaction in networks of limit cycle oscillat... more We investigate the impact of attractive-repulsive interaction in networks of limit cycle oscillators. Mainly we focus on the design principle for generating an anti-phase state between adjacent nodes in a complex network. We establish that a partial negative control throughout the branches of a spanning tree inside the positively coupled limit cycle oscillators works efficiently well in comparison with randomly chosen negative links to establish zero frustration (anti-phase synchronization) in bipartite graphs. Based on the emergence of zero frustration, we develop a universal 0 − π rule to understand the anti-phase synchronization in a bipartite graph. Further, this rule is used to construct a non-bipartite graph for a given non-zero frustrated value. We finally show the generality of 0−π rule by implementing it in arbitrary undirected non-bipartite graphs of attractive-repulsively coupled limit cycle oscillators and successfully calculate the non-zero frustration value which matches with numerical data. The validation of the rule is checked through the bifurcation analysis of small networks. Our work may unveil the underlying mechanism of several synchronization phenomena that exist in a network of oscillators having a mixed type of coupling.

Research paper thumbnail of Hidden attractors: A new chaotic system without equilibria

The European Physical Journal Special Topics

Research paper thumbnail of Utilisation and financial protection for hospital care under publicly funded health insurance in three states in Southern India

BMC Health Services Research

Background Many LMICs have implemented Publicly Funded Health Insurance (PFHI) programmes to impr... more Background Many LMICs have implemented Publicly Funded Health Insurance (PFHI) programmes to improve access and financial protection. The national PFHI scheme implemented in India for a decade has been recently modified and expanded to cover free hospital care for 500 million persons. Since increase in annual cover amount is one of the main design modifications in the new programme, the relevant policy question is whether such design change can improve financial protection for hospital care. An evaluation of state-specific PFHI programmes with vertical cover larger than RSBY can help answer this question. Three states in Southern India - Andhra Pradesh, Karnataka and Tamil Nadu have been pioneers in implementing PFHI with a large insurance cover. Methods The current study was meant to evaluate the PFHI in above three states in improving utilisation of hospital services and financial protection against expenses of hospitalization. Two cross-sections from National Sample Survey’s heal...

Research paper thumbnail of Convergence of chaotic attractors due to interaction based on closeness

Research paper thumbnail of Chimera states in a ring of map-based neurons

Physica A: Statistical Mechanics and its Applications

Research paper thumbnail of Synchronization to extreme events in moving agents

New Journal of Physics

Interactions amongst agents frequently exist only at particular moments in time, depending on the... more Interactions amongst agents frequently exist only at particular moments in time, depending on their closeness in space and movement parameters. Here we propose a minimal model of moving agents where the network of contacts changes over time due to their motion. In particular, agents interact based on their proximity in a two-dimensional space, but only if they belong to the same fixed interaction zones. Our research reveals the emergence of global synchronization if all the interaction zones are attractive. However, if some of the interaction zones are repulsive, they deflect synchrony and lead to short-lasting but recurrent deviations that constitute extreme events in the network. We use two paradigmatic oscillators for the description of the agent dynamics to demonstrate our findings numerically, and we also provide an analytical formulation to describe the emergence of complete synchrony and the thresholds that distinguish extreme events from other intermittent states based on the peak-over-threshold approach.

Research paper thumbnail of Matching theory for cognitive radio networks: An overview

Research paper thumbnail of Synchronization in dynamic network using threshold control approach

EPL (Europhysics Letters)

Research paper thumbnail of Trends of nutritional status among rural adults in six states of India: findings from national survey data

Clinical Epidemiology and Global Health

Introduction: There is lack of evidence available on understanding of exact trend and distributio... more Introduction: There is lack of evidence available on understanding of exact trend and distribution of dual burden of nutrition in India. Objective: The study aimed to find out 25 years trend of nutritional status among rural adults of six states in India, pooled estimate for India and predict the estimate for future 20 years. Design: The body mass index (BMI) data of both men and women of six states and India for the year 1992-2011 was collected from the publicly available reports of National Nutrition Monitoring Bureau (NNMB) and for 2014-15 was taken from National Family and Health Survey-IV (NFHS-IV). The data for monthly per capita expenditure was extracted from national sample survey (NSS) reports. The 25-year historical BMI prevalence data between 1991-92 and 2014 were tested for linear, quadratic and cubic trends. The analysis was done using STATA. Settings: Data for six states of India and pooled estimate of India was collected and analyzed. Main findings: All states show a decline trend in underweight and increase trend in overweight/obesity. The pooled estimates for India reports though the trend of underweight is declining in both men and women still it is above 20% and after 20 years the prevalence will be 10%. The trend test for overweight/ obesity was found to be significant at P value < 0.05 in all the six states and India in both the sex. Conclusion: The regional variances in prevalence of the nutrition among rural Indians and suggests state specific nutritional policy should be developed for double burden of nutrition.

Research paper thumbnail of Book Review: Paulo Coelho’s The Spy

Rupkatha Journal on Interdisciplinary Studies in Humanities

It deals with the encounter of the historical figure Margaretha Gertrude Zelle, famously known as... more It deals with the encounter of the historical figure Margaretha Gertrude Zelle, famously known as Mata Hari. The incident took place during the World War I. As the epilogue of the book contains the report published in the newspaper on October 15, 1917 about her encounter, it was clearly reported that she had been "court-martialled on the charge of espionage." In this story Coelho has used the history and presented it wrapped in the colourful cover of myth and fantasy. He has used imaginary and most probable conversations.

Research paper thumbnail of A throughput-efficient cooperative sensing and allocation model for cognitive radio networks

2015 IEEE International Conference on Advanced Networks and Telecommuncations Systems (ANTS), 2015

Research paper thumbnail of Analysis of Uranium Leaching Process and Effect of Cake Washing on Uranium Recovery

Sulphuric acid is the most preferred leachant for the recovery of uranium from ores because it is... more Sulphuric acid is the most preferred leachant for the recovery of uranium from ores because it is cheap, less corrosive, and produces anionic uranyl complex, which makes the separation of uranium from other cationic gangue mineral easy using an anionic exchanger subsequently. Sulphuric acid leaching of Narwapahar (INDIA) uranium ore assisted with acoustic cavitation and without cavitation has been studied. The primary uranium minerals of Narwapahar ore are uraninite and pitchblende with minor presence of brannerite, allanite, xenotime, and davidite. In this paper, we have discussed selective leaching of uranium using sulphuric acid from Narwapahar uranium ore relative to other leachable compounds and material balance has been carried out around each of the leaching experiments. Material balance of uranium ore and also that of uranium leaching for with and without cavitation could be established within ±10%.

Research paper thumbnail of Perspective on attractive-repulsive interactions in dynamical networks: Progress and future

EPL (Europhysics Letters)

Research paper thumbnail of Antiphase synchronization in multiplex networks with attractive and repulsive interactions

Physical Review E

A series of recent publications, within the framework of network science, have focused on the coe... more A series of recent publications, within the framework of network science, have focused on the coexistence of mixed attractive and repulsive (excitatory and inhibitory) interactions among the units within the same system, motivated by the analogies with spin glasses as well as to neural networks, or ecological systems. However, most of these investigations have been restricted to single layer networks, requiring further analysis of the complex dynamics and particular equilibrium states that emerge in multilayer configurations. This article investigates the synchronization properties of dynamical systems connected through multiplex architectures in the presence of attractive intralayer and repulsive interlayer connections. This setting enables the emergence of antisynchronization, i.e., intralayer synchronization coexisting with antiphase dynamics between coupled systems of different layers. We demonstrate the existence of a transition from interlayer antisynchronization to antiphase synchrony in any connected bipartite multiplex architecture when the repulsive coupling is introduced through any spanning tree of a single layer. We identify, analytically, the required graph topologies for interlayer antisynchronization and its interplay with intralayer and antiphase synchronization. Next, we analytically derive the invariance of intralayer synchronization manifold and calculate the attractor size of each oscillator exhibiting interlayer antisynchronization together with intralayer synchronization. The necessary conditions for the existence of interlayer antisynchronization along with intralayer synchronization are given and numerically validated by considering Stuart-Landau oscillators. Finally, we also analytically derive the local stability condition of the interlayer antisynchronization state using the master stability function approach.

Research paper thumbnail of Facilitators and Barriers to Implementation of Childhood Tuberculosis Control Program in Bangladesh: a Mixed-methods Study From BRAC Urban DOTS Centres in Dhaka

BackgroundWorld Health Organisation (WHO) estimates childhood tuberculosis (tb) in high burden co... more BackgroundWorld Health Organisation (WHO) estimates childhood tuberculosis (tb) in high burden countries to be at least 10-15% of all cases. Despite intensive efforts on the childhood tb control program in Bangladesh, case detection rates stand below 5%. This study investigated the implementation pathway of childhood tb in Bangladesh. The study aims to identify the factors that enable and hinder the diagnosis and treatment of childhood tb in Bangladesh.MethodsAn exploratory-explanatory mixed-methods study was carried out in eight (top four and bottom four based on new case identification) urban DOTS (Directly Observed Treatment, Short-course) centres of the BRAC tb program in Dhaka Metropolitan City, Bangladesh. The study was conducted between September and December 2017. The knowledge, attitude, and practice (KAP) assessment on diagnosis and treatment of childhood tb were conducted among 111 Shasthya Shebika (SS), frontline health care workers engaged in the tb program. Field worke...

Research paper thumbnail of Effect of repulsive links on frustration in attractively coupled networks

Physical Review E

We investigate the impact of attractive-repulsive interaction in networks of limit cycle oscillat... more We investigate the impact of attractive-repulsive interaction in networks of limit cycle oscillators. Mainly we focus on the design principle for generating an anti-phase state between adjacent nodes in a complex network. We establish that a partial negative control throughout the branches of a spanning tree inside the positively coupled limit cycle oscillators works efficiently well in comparison with randomly chosen negative links to establish zero frustration (anti-phase synchronization) in bipartite graphs. Based on the emergence of zero frustration, we develop a universal 0 − π rule to understand the anti-phase synchronization in a bipartite graph. Further, this rule is used to construct a non-bipartite graph for a given non-zero frustrated value. We finally show the generality of 0−π rule by implementing it in arbitrary undirected non-bipartite graphs of attractive-repulsively coupled limit cycle oscillators and successfully calculate the non-zero frustration value which matches with numerical data. The validation of the rule is checked through the bifurcation analysis of small networks. Our work may unveil the underlying mechanism of several synchronization phenomena that exist in a network of oscillators having a mixed type of coupling.

Research paper thumbnail of Hidden attractors: A new chaotic system without equilibria

The European Physical Journal Special Topics

Research paper thumbnail of Utilisation and financial protection for hospital care under publicly funded health insurance in three states in Southern India

BMC Health Services Research

Background Many LMICs have implemented Publicly Funded Health Insurance (PFHI) programmes to impr... more Background Many LMICs have implemented Publicly Funded Health Insurance (PFHI) programmes to improve access and financial protection. The national PFHI scheme implemented in India for a decade has been recently modified and expanded to cover free hospital care for 500 million persons. Since increase in annual cover amount is one of the main design modifications in the new programme, the relevant policy question is whether such design change can improve financial protection for hospital care. An evaluation of state-specific PFHI programmes with vertical cover larger than RSBY can help answer this question. Three states in Southern India - Andhra Pradesh, Karnataka and Tamil Nadu have been pioneers in implementing PFHI with a large insurance cover. Methods The current study was meant to evaluate the PFHI in above three states in improving utilisation of hospital services and financial protection against expenses of hospitalization. Two cross-sections from National Sample Survey’s heal...

Research paper thumbnail of Convergence of chaotic attractors due to interaction based on closeness

Research paper thumbnail of Chimera states in a ring of map-based neurons

Physica A: Statistical Mechanics and its Applications

Research paper thumbnail of Synchronization to extreme events in moving agents

New Journal of Physics

Interactions amongst agents frequently exist only at particular moments in time, depending on the... more Interactions amongst agents frequently exist only at particular moments in time, depending on their closeness in space and movement parameters. Here we propose a minimal model of moving agents where the network of contacts changes over time due to their motion. In particular, agents interact based on their proximity in a two-dimensional space, but only if they belong to the same fixed interaction zones. Our research reveals the emergence of global synchronization if all the interaction zones are attractive. However, if some of the interaction zones are repulsive, they deflect synchrony and lead to short-lasting but recurrent deviations that constitute extreme events in the network. We use two paradigmatic oscillators for the description of the agent dynamics to demonstrate our findings numerically, and we also provide an analytical formulation to describe the emergence of complete synchrony and the thresholds that distinguish extreme events from other intermittent states based on the peak-over-threshold approach.

Research paper thumbnail of Matching theory for cognitive radio networks: An overview

Research paper thumbnail of Synchronization in dynamic network using threshold control approach

EPL (Europhysics Letters)

Research paper thumbnail of Trends of nutritional status among rural adults in six states of India: findings from national survey data

Clinical Epidemiology and Global Health

Introduction: There is lack of evidence available on understanding of exact trend and distributio... more Introduction: There is lack of evidence available on understanding of exact trend and distribution of dual burden of nutrition in India. Objective: The study aimed to find out 25 years trend of nutritional status among rural adults of six states in India, pooled estimate for India and predict the estimate for future 20 years. Design: The body mass index (BMI) data of both men and women of six states and India for the year 1992-2011 was collected from the publicly available reports of National Nutrition Monitoring Bureau (NNMB) and for 2014-15 was taken from National Family and Health Survey-IV (NFHS-IV). The data for monthly per capita expenditure was extracted from national sample survey (NSS) reports. The 25-year historical BMI prevalence data between 1991-92 and 2014 were tested for linear, quadratic and cubic trends. The analysis was done using STATA. Settings: Data for six states of India and pooled estimate of India was collected and analyzed. Main findings: All states show a decline trend in underweight and increase trend in overweight/obesity. The pooled estimates for India reports though the trend of underweight is declining in both men and women still it is above 20% and after 20 years the prevalence will be 10%. The trend test for overweight/ obesity was found to be significant at P value < 0.05 in all the six states and India in both the sex. Conclusion: The regional variances in prevalence of the nutrition among rural Indians and suggests state specific nutritional policy should be developed for double burden of nutrition.

Research paper thumbnail of Book Review: Paulo Coelho’s The Spy

Rupkatha Journal on Interdisciplinary Studies in Humanities

It deals with the encounter of the historical figure Margaretha Gertrude Zelle, famously known as... more It deals with the encounter of the historical figure Margaretha Gertrude Zelle, famously known as Mata Hari. The incident took place during the World War I. As the epilogue of the book contains the report published in the newspaper on October 15, 1917 about her encounter, it was clearly reported that she had been "court-martialled on the charge of espionage." In this story Coelho has used the history and presented it wrapped in the colourful cover of myth and fantasy. He has used imaginary and most probable conversations.

Research paper thumbnail of A throughput-efficient cooperative sensing and allocation model for cognitive radio networks

2015 IEEE International Conference on Advanced Networks and Telecommuncations Systems (ANTS), 2015

Research paper thumbnail of Analysis of Uranium Leaching Process and Effect of Cake Washing on Uranium Recovery

Sulphuric acid is the most preferred leachant for the recovery of uranium from ores because it is... more Sulphuric acid is the most preferred leachant for the recovery of uranium from ores because it is cheap, less corrosive, and produces anionic uranyl complex, which makes the separation of uranium from other cationic gangue mineral easy using an anionic exchanger subsequently. Sulphuric acid leaching of Narwapahar (INDIA) uranium ore assisted with acoustic cavitation and without cavitation has been studied. The primary uranium minerals of Narwapahar ore are uraninite and pitchblende with minor presence of brannerite, allanite, xenotime, and davidite. In this paper, we have discussed selective leaching of uranium using sulphuric acid from Narwapahar uranium ore relative to other leachable compounds and material balance has been carried out around each of the leaching experiments. Material balance of uranium ore and also that of uranium leaching for with and without cavitation could be established within ±10%.