2017 |
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| 194. | Sharma, Amit; Shrimali, Manish Dev; Prasad, Awadhesh; Ramaswamy, Ram Time-delayed conjugate coupling in dynamical systems Journal Article European Physical Journal: Special Topics, 226 (9), pp. 1903–1910, 2017, ISSN: 19516401. Abstract | Links | BibTeX | Tags: Amplitude Death, Landau-Stuart, Oscillation Death, Time Delay @article{Sharma2017, title = {Time-delayed conjugate coupling in dynamical systems}, author = {Amit Sharma and Manish Dev Shrimali and Awadhesh Prasad and Ram Ramaswamy}, url = {https://ramramaswamy.org/papers/168.pdf}, doi = {10.1140/epjst/e2017-70026-4}, issn = {19516401}, year = {2017}, date = {2017-01-01}, journal = {European Physical Journal: Special Topics}, volume = {226}, number = {9}, pages = {1903–1910}, abstract = {textcopyright 2017, EDP Sciences and Springer-Verlag GmbH Germany. We study the effect of time-delay when the coupling between nonlinear systems is ‚Äúconjugate‚Äù, namely through dissimilar variables. This form of coupling can induce anomalous transitions such as the emergence of oscillatory dynamics between regimes of amplitude death and oscillation death. The specific cases of coupled Landau-Stuart oscillators as well as a predator-prey model system with cross-predation are discussed. The dynamical behaviour is analyzed numerically and the regions corresponding to different asymptotic states are identified in parameter space.}, keywords = {Amplitude Death, Landau-Stuart, Oscillation Death, Time Delay}, pubstate = {published}, tppubtype = {article} } textcopyright 2017, EDP Sciences and Springer-Verlag GmbH Germany. We study the effect of time-delay when the coupling between nonlinear systems is ‚Äúconjugate‚Äù, namely through dissimilar variables. This form of coupling can induce anomalous transitions such as the emergence of oscillatory dynamics between regimes of amplitude death and oscillation death. The specific cases of coupled Landau-Stuart oscillators as well as a predator-prey model system with cross-predation are discussed. The dynamical behaviour is analyzed numerically and the regions corresponding to different asymptotic states are identified in parameter space. |
| 193. | Ujjwal, Sangeeta R; Ramaswamy, Ram Symmetries and symmetry-breaking in oscillator ensembles Journal Article Physics News, 47 (2), pp. 11–16, 2017. Links | BibTeX | Tags: Chaos Theory, Symmetry Breaking @article{Ujjwal2017b, title = {Symmetries and symmetry-breaking in oscillator ensembles}, author = {Sangeeta R Ujjwal and Ram Ramaswamy}, url = {https://ramramaswamy.org/papers/.pdf}, year = {2017}, date = {2017-01-01}, journal = {Physics News}, volume = {47}, number = {2}, pages = {11–16}, keywords = {Chaos Theory, Symmetry Breaking}, pubstate = {published}, tppubtype = {article} } |
2016 |
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| 192. | Ramaswamy, Ram (Ed.) Adventures Into the Unknown: Essays Book First Edition, Three Essays Collective, Gurugram, India, 2016, ISBN: 978-93-83968-11-4. Abstract | Links | BibTeX | Tags: Book, Kosambi @book{KosambiEssays2016, title = {Adventures Into the Unknown: Essays}, editor = {Ram Ramaswamy}, url = {https://threeessays.com/books/adventures-into-the-unknown/}, isbn = {978-93-83968-11-4}, year = {2016}, date = {2016-06-01}, publisher = {Three Essays Collective}, address = {Gurugram, India}, edition = {First Edition}, abstract = {As the essays in this collection testify, even half a century after his death in 1966, D D Kosambi continues to be provocative, instructive, and contemporary. Many of the arguments that he makes in his two didactic and hitherto unpublished essays are insightful and incisive, and display, in a new setting, the range of his scholarship and the breadth of his interests. The other essays that are included here are his passionate advocacy of solar energy, and his posthumously published autobiographical essay that outlines his credo, and that lends its title to the book.}, keywords = {Book, Kosambi}, pubstate = {published}, tppubtype = {book} } As the essays in this collection testify, even half a century after his death in 1966, D D Kosambi continues to be provocative, instructive, and contemporary. Many of the arguments that he makes in his two didactic and hitherto unpublished essays are insightful and incisive, and display, in a new setting, the range of his scholarship and the breadth of his interests. The other essays that are included here are his passionate advocacy of solar energy, and his posthumously published autobiographical essay that outlines his credo, and that lends its title to the book. |
| 191. | Ramaswamy, Ramakrishna (Ed.) D.D. Kosambi: Selected Works in Mathematics and Statistics Book First Edition, Springer India, 2016, ISBN: 978-81-322-3676-4. Abstract | Links | BibTeX | Tags: Book, Kosambi @book{KosambiMaths2016, title = {D.D. Kosambi: Selected Works in Mathematics and Statistics}, editor = {Ramaswamy, Ramakrishna}, url = {https://www.springer.com/gp/book/9788132236740 }, doi = {10.1007/978-81-322-3676-4}, isbn = {978-81-322-3676-4}, year = {2016}, date = {2016-01-01}, publisher = {Springer India}, edition = {First Edition}, abstract = {This book fills an important gap in studies on D. D. Kosambi. For the first time, the mathematical work of Kosambi is described, collected and presented in a manner that is accessible to non-mathematicians as well. A number of his papers that are difficult to obtain in these areas are made available here. In addition, there are essays by Kosambi that have not been published earlier as well as some of his lesser known works. Each of the twenty four papers is prefaced by a commentary on the significance of the work, and where possible, extracts from technical reviews by other mathematicians.}, keywords = {Book, Kosambi}, pubstate = {published}, tppubtype = {book} } This book fills an important gap in studies on D. D. Kosambi. For the first time, the mathematical work of Kosambi is described, collected and presented in a manner that is accessible to non-mathematicians as well. A number of his papers that are difficult to obtain in these areas are made available here. In addition, there are essays by Kosambi that have not been published earlier as well as some of his lesser known works. Each of the twenty four papers is prefaced by a commentary on the significance of the work, and where possible, extracts from technical reviews by other mathematicians. |
| 190. | Ujjwal, Sangeeta Rani; Punetha, Nirmal; Ramaswamy, Ramakrishna Phase oscillators in modular networks: The effect of nonlocal coupling Journal Article Physical Review E, 93 (1), pp. 1–10, 2016, ISSN: 24700053. Abstract | Links | BibTeX | Tags: Modular Network, Nonlocal Coupling, Synchronization @article{Ujjwal2016, title = {Phase oscillators in modular networks: The effect of nonlocal coupling}, author = {Sangeeta Rani Ujjwal and Nirmal Punetha and Ramakrishna Ramaswamy}, url = {https://ramramaswamy.org/papers/161.pdf}, doi = {10.1103/PhysRevE.93.012207}, issn = {24700053}, year = {2016}, date = {2016-01-01}, journal = {Physical Review E}, volume = {93}, number = {1}, pages = {1–10}, abstract = {We study the dynamics of nonlocally coupled phase oscillators in a modular network. The interactions include a phase lag, $alpha$. Depending on the various parameters the system exhibits a number of different dynamical states. In addition to global synchrony there can also be modular synchrony when each module can synchronize separately to a different frequency. There can also be multicluster frequency chimeras, namely coherent domains consisting of modules that are separately synchronized to different frequencies, coexisting with modules within which the dynamics is desynchronized. We apply the Ott-Antonsen ansatz in order to reduce the effective dimensionality and thereby carry out a detailed analysis of the different dynamical states.}, keywords = {Modular Network, Nonlocal Coupling, Synchronization}, pubstate = {published}, tppubtype = {article} } We study the dynamics of nonlocally coupled phase oscillators in a modular network. The interactions include a phase lag, $alpha$. Depending on the various parameters the system exhibits a number of different dynamical states. In addition to global synchrony there can also be modular synchrony when each module can synchronize separately to a different frequency. There can also be multicluster frequency chimeras, namely coherent domains consisting of modules that are separately synchronized to different frequencies, coexisting with modules within which the dynamics is desynchronized. We apply the Ott-Antonsen ansatz in order to reduce the effective dimensionality and thereby carry out a detailed analysis of the different dynamical states. |
| 189. | Ujjwal, Sangeeta Rani; Punetha, Nirmal; Ramaswamy, Ram; Agrawal, Manish; Prasad, Awadhesh Driving-induced multistability in coupled chaotic oscillators: Symmetries and riddled basins Journal Article Chaos, 26 (6), 2016, ISSN: 10541500. Abstract | Links | BibTeX | Tags: Chaos, Multistability, Riddled Basins @article{Ujjwal2016a, title = {Driving-induced multistability in coupled chaotic oscillators: Symmetries and riddled basins}, author = {Sangeeta Rani Ujjwal and Nirmal Punetha and Ram Ramaswamy and Manish Agrawal and Awadhesh Prasad}, url = {http://dx.doi.org/10.1063/1.4954022}, doi = {10.1063/1.4954022}, issn = {10541500}, year = {2016}, date = {2016-01-01}, journal = {Chaos}, volume = {26}, number = {6}, abstract = {The human brain, power grids, arrays of coupled lasers and the Amazon rainforest are all characterized by multistability. The likelihood that these systems will remain in the most desirable of their many stable states depends on their stability against significant perturbations, particularly in a state space populated by undesirable states. Here we claim that the traditional linearization-based approach to stability is too local to adequately assess how stable a state is. Instead, we quantify it in terms of basin stability, a new measure related to the volume of the basin of attraction. Basin stability is non-local, nonlinear and easily applicable, even to high-dimensional systems. It provides a long-sought-after explanation for the surprisingly regular topologies of neural networks and power grids, which have eluded theoretical description based solely on linear stability. We anticipate that basin stability will provide a powerful tool for complex systems studies, including the assessment of multistable climatic tipping elements.}, keywords = {Chaos, Multistability, Riddled Basins}, pubstate = {published}, tppubtype = {article} } The human brain, power grids, arrays of coupled lasers and the Amazon rainforest are all characterized by multistability. The likelihood that these systems will remain in the most desirable of their many stable states depends on their stability against significant perturbations, particularly in a state space populated by undesirable states. Here we claim that the traditional linearization-based approach to stability is too local to adequately assess how stable a state is. Instead, we quantify it in terms of basin stability, a new measure related to the volume of the basin of attraction. Basin stability is non-local, nonlinear and easily applicable, even to high-dimensional systems. It provides a long-sought-after explanation for the surprisingly regular topologies of neural networks and power grids, which have eluded theoretical description based solely on linear stability. We anticipate that basin stability will provide a powerful tool for complex systems studies, including the assessment of multistable climatic tipping elements. |
| 188. | Kumar, Rupesh; Bilal, Shakir; Ramaswamy, Ram Synchronization properties of coupled chaotic neurons: The role of random shared input Journal Article Chaos, 26 (6), 2016, ISSN: 10541500. Abstract | Links | BibTeX | Tags: Neurons, Synchronization @article{Kumar2016, title = {Synchronization properties of coupled chaotic neurons: The role of random shared input}, author = {Rupesh Kumar and Shakir Bilal and Ram Ramaswamy}, url = {http://dx.doi.org/10.1063/1.4954377}, doi = {10.1063/1.4954377}, issn = {10541500}, year = {2016}, date = {2016-01-01}, journal = {Chaos}, volume = {26}, number = {6}, abstract = {textcopyright 2016 Author(s). Spike-time correlations of neighbouring neurons depend on their intrinsic firing properties as well as on the inputs they share. Studies have shown that periodically firing neurons, when subjected to random shared input, exhibit asynchronicity. Here, we study the effect of random shared input on the synchronization of weakly coupled chaotic neurons. The cases of so-called electrical and chemical coupling are both considered, and we observe a wide range of synchronization behaviour. When subjected to identical shared random input, there is a decrease in the threshold coupling strength needed for chaotic neurons to synchronize in-phase. The system also supports lag-synchronous states, and for these, we find that shared input can cause desynchronization. We carry out a master stability function analysis for a network of such neurons and show agreement with the numerical simulations. The contrasting role of shared random input for complete and lag synchronized neurons is useful in understanding spike-time correlations observed in many areas of the brain.}, keywords = {Neurons, Synchronization}, pubstate = {published}, tppubtype = {article} } textcopyright 2016 Author(s). Spike-time correlations of neighbouring neurons depend on their intrinsic firing properties as well as on the inputs they share. Studies have shown that periodically firing neurons, when subjected to random shared input, exhibit asynchronicity. Here, we study the effect of random shared input on the synchronization of weakly coupled chaotic neurons. The cases of so-called electrical and chemical coupling are both considered, and we observe a wide range of synchronization behaviour. When subjected to identical shared random input, there is a decrease in the threshold coupling strength needed for chaotic neurons to synchronize in-phase. The system also supports lag-synchronous states, and for these, we find that shared input can cause desynchronization. We carry out a master stability function analysis for a network of such neurons and show agreement with the numerical simulations. The contrasting role of shared random input for complete and lag synchronized neurons is useful in understanding spike-time correlations observed in many areas of the brain. |
| 187. | Jafri, Haider Hasan; Singh, K.Brojen R; Ramaswamy, Ramakrishna Generalized synchrony of coupled stochastic processes with multiplicative noise Journal Article Physical Review E, 94 (5), pp. 1–8, 2016, ISSN: 24700053. Abstract | Links | BibTeX | Tags: Generalized Synchronization, Stochasticity @article{Jafri2016, title = {Generalized synchrony of coupled stochastic processes with multiplicative noise}, author = {Haider Hasan Jafri and K.Brojen R Singh and Ramakrishna Ramaswamy}, url = {https://ramramaswamy.org/papers/164.pdf}, doi = {10.1103/PhysRevE.94.052216}, issn = {24700053}, year = {2016}, date = {2016-01-01}, journal = {Physical Review E}, volume = {94}, number = {5}, pages = {1–8}, abstract = {textcopyright 2016 American Physical Society. We study the effect of multiplicative noise in dynamical flows arising from the coupling of stochastic processes with intrinsic noise. Situations wherein such systems arise naturally are in chemical or biological oscillators that are coupled to each other in a drive-response configuration. Above a coupling threshold we find that there is a strong correlation between the drive and the response: This is a stochastic analog of the phenomenon of generalised synchronization. Since the dynamical fluctuations are large when there is intrinsic noise, it is necessary to employ measures that are sensitive to correlations between the variables of drive and the response, the permutation entropy, or the mutual information in order to detect the transition to generalized synchrony in such systems.}, keywords = {Generalized Synchronization, Stochasticity}, pubstate = {published}, tppubtype = {article} } textcopyright 2016 American Physical Society. We study the effect of multiplicative noise in dynamical flows arising from the coupling of stochastic processes with intrinsic noise. Situations wherein such systems arise naturally are in chemical or biological oscillators that are coupled to each other in a drive-response configuration. Above a coupling threshold we find that there is a strong correlation between the drive and the response: This is a stochastic analog of the phenomenon of generalised synchronization. Since the dynamical fluctuations are large when there is intrinsic noise, it is necessary to employ measures that are sensitive to correlations between the variables of drive and the response, the permutation entropy, or the mutual information in order to detect the transition to generalized synchrony in such systems. |
2015 |
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| 186. | Agrawal, Manish; Prasad, Awadhesh; Ramaswamy, Ram Erratum: Driving-induced bistability in coupled chaotic attractors [Phys. Rev. E 87 , 042909 (2013)] Journal Article Physical Review E – Statistical, Nonlinear, and Soft Matter Physics, 92 (4), pp. 49903, 2015, ISSN: 1539-3755. Abstract | Links | BibTeX | Tags: @article{Agrawal2015, title = { Erratum: Driving-induced bistability in coupled chaotic attractors [Phys. Rev. E 87 , 042909 (2013)] }, author = {Manish Agrawal and Awadhesh Prasad and Ram Ramaswamy}, url = {https://ramramaswamy.org/papers/148e.pdf}, doi = {10.1103/PhysRevE.87.042909}, issn = {1539-3755}, year = {2015}, date = {2015-01-01}, journal = {Physical Review E – Statistical, Nonlinear, and Soft Matter Physics}, volume = {92}, number = {4}, pages = {49903}, abstract = {We examine the effects of symmetry-preserving and -breaking interactions in a drive-response system where the response has an invariant symmetry in the absence of the drive. Subsequent to the onset of generalized synchronization, we find that there can be more than one stable attractor. Numerical as well as analytical results establish the presence of phase synchrony in such coexisting attractors. These results are robust to external noise.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We examine the effects of symmetry-preserving and -breaking interactions in a drive-response system where the response has an invariant symmetry in the absence of the drive. Subsequent to the onset of generalized synchronization, we find that there can be more than one stable attractor. Numerical as well as analytical results establish the presence of phase synchrony in such coexisting attractors. These results are robust to external noise. |
| 185. | Punetha, Nirmal; Ujjwal, Sangeeta Rani; Atay, Fatihcan M; Ramaswamy, Ramakrishna Delay-induced remote synchronization in bipartite networks of phase oscillators Journal Article Physical Review E – Statistical, Nonlinear, and Soft Matter Physics, 91 (2), pp. 1–7, 2015, ISSN: 15502376. Abstract | Links | BibTeX | Tags: Bipartite Network, Delay, Synchronization @article{Punetha2015, title = {Delay-induced remote synchronization in bipartite networks of phase oscillators}, author = {Nirmal Punetha and Sangeeta Rani Ujjwal and Fatihcan M Atay and Ramakrishna Ramaswamy}, url = {https://ramramaswamy.org/papers/159.pdf}, doi = {10.1103/PhysRevE.91.022922}, issn = {15502376}, year = {2015}, date = {2015-01-01}, journal = {Physical Review E – Statistical, Nonlinear, and Soft Matter Physics}, volume = {91}, number = {2}, pages = {1–7}, abstract = {We study a system of mismatched oscillators on a bipartite topology with time-delay coupling, and analyze the synchronized states. For a range of parameters, when all oscillators lock to a common frequency, we find solutions such that systems within a partition are in complete synchrony, while there is lag synchronization between the partitions. Outside this range, such a solution does not exist and instead one observes scenarios of remote synchronization—namely, chimeras and individual synchronization, where either one or both of the partitions are synchronized independently. In the absence of time delay such states are not observed in phase oscillators.}, keywords = {Bipartite Network, Delay, Synchronization}, pubstate = {published}, tppubtype = {article} } We study a system of mismatched oscillators on a bipartite topology with time-delay coupling, and analyze the synchronized states. For a range of parameters, when all oscillators lock to a common frequency, we find solutions such that systems within a partition are in complete synchrony, while there is lag synchronization between the partitions. Outside this range, such a solution does not exist and instead one observes scenarios of remote synchronization—namely, chimeras and individual synchronization, where either one or both of the partitions are synchronized independently. In the absence of time delay such states are not observed in phase oscillators. |
| 184. | Punetha, Nirmal; Ramaswamy, Ramakrishna; Atay, Fatihcan M Bipartite networks of oscillators with distributed delays: Synchronization branches and multistability Journal Article Physical Review E – Statistical, Nonlinear, and Soft Matter Physics, 91 (4), pp. 1–10, 2015, ISSN: 15502376. Abstract | Links | BibTeX | Tags: Bipartite Network, Multistability, Synchronization @article{Punetha2015a, title = {Bipartite networks of oscillators with distributed delays: Synchronization branches and multistability}, author = {Nirmal Punetha and Ramakrishna Ramaswamy and Fatihcan M Atay}, url = {https://ramramaswamy.org/papers/160.pdf}, doi = {10.1103/PhysRevE.91.042906}, issn = {15502376}, year = {2015}, date = {2015-01-01}, journal = {Physical Review E – Statistical, Nonlinear, and Soft Matter Physics}, volume = {91}, number = {4}, pages = {1–10}, abstract = {We study synchronization in bipartite networks of phase oscillators with general nonlinear coupling and distributed time delays. Phase-locked solutions are shown to arise, where the oscillators in each partition are perfectly synchronized among themselves but can have a phase difference with the other partition, with the phase difference necessarily being either zero or $pi$ radians. Analytical conditions for the stability of both types of solutions are obtained and solution branches are explicitly calculated, revealing that the network can have several coexisting stable solutions. With increasing value of the mean delay, the system exhibits hysteresis, phase flips, final state sensitivity, and an extreme form of multistability where the numbers of stable in-phase and antiphase synchronous solutions with distinct frequencies grow without bound. The theory is applied to networks of Landau-Stuart and Rossler oscillators and shown to accurately predict both in-phase and antiphase synchronous behavior in appropriate parameter ranges.}, keywords = {Bipartite Network, Multistability, Synchronization}, pubstate = {published}, tppubtype = {article} } We study synchronization in bipartite networks of phase oscillators with general nonlinear coupling and distributed time delays. Phase-locked solutions are shown to arise, where the oscillators in each partition are perfectly synchronized among themselves but can have a phase difference with the other partition, with the phase difference necessarily being either zero or $pi$ radians. Analytical conditions for the stability of both types of solutions are obtained and solution branches are explicitly calculated, revealing that the network can have several coexisting stable solutions. With increasing value of the mean delay, the system exhibits hysteresis, phase flips, final state sensitivity, and an extreme form of multistability where the numbers of stable in-phase and antiphase synchronous solutions with distinct frequencies grow without bound. The theory is applied to networks of Landau-Stuart and Rossler oscillators and shown to accurately predict both in-phase and antiphase synchronous behavior in appropriate parameter ranges. |
| 183. | Shastri, P; Kurup, A; Resmi, L; Ramaswamy, R; Ubale, S; Bagchi, S; Rao, S; Narasimhan, S Towards gender equity in physics in India: Initiatives, investigations, and questions Journal Article AIP Conference Proceedings, 1697 , pp. 53–56, 2015, ISSN: 15517616. Abstract | Links | BibTeX | Tags: Gender Equity @article{Shastri2015, title = {Towards gender equity in physics in India: Initiatives, investigations, and questions}, author = {P Shastri and A Kurup and L Resmi and R Ramaswamy and S Ubale and S Bagchi and S Rao and S Narasimhan}, url = {https://ramramaswamy.org/papers/OA24.pdf}, doi = {10.1063/1.4937669}, issn = {15517616}, year = {2015}, date = {2015-01-01}, journal = {AIP Conference Proceedings}, volume = {1697}, pages = {53–56}, abstract = {Initiatives towards gender parity in the sciences in India have occurred$backslash$nboth at national, governmental levels and at local, institutional$backslash$nlevels. A gender gap persists in physics, but data suggest that this gap$backslash$nis due neither to lack of interest in science nor to a lack of career$backslash$ngoals in science among girls. We outline investigations that are$backslash$nimportant to pursue and recommendations that build on the existing$backslash$nscience interest and the impact of initiatives so far.}, keywords = {Gender Equity}, pubstate = {published}, tppubtype = {article} } Initiatives towards gender parity in the sciences in India have occurred$backslash$nboth at national, governmental levels and at local, institutional$backslash$nlevels. A gender gap persists in physics, but data suggest that this gap$backslash$nis due neither to lack of interest in science nor to a lack of career$backslash$ngoals in science among girls. We outline investigations that are$backslash$nimportant to pursue and recommendations that build on the existing$backslash$nscience interest and the impact of initiatives so far. |
2014 |
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| 182. | Bilal, Shakir; Ramaswamy, Ramakrishna Synchronization and amplitude death in hypernetworks Journal Article Physical Review E – Statistical, Nonlinear, and Soft Matter Physics, 89 (6), pp. 1–6, 2014, ISSN: 15502376. Abstract | Links | BibTeX | Tags: @article{Bilal2014, title = {Synchronization and amplitude death in hypernetworks}, author = {Shakir Bilal and Ramakrishna Ramaswamy}, url = {https://ramramaswamy.org/papers/155.pdf}, doi = {10.1103/PhysRevE.89.062923}, issn = {15502376}, year = {2014}, date = {2014-01-01}, journal = {Physical Review E – Statistical, Nonlinear, and Soft Matter Physics}, volume = {89}, number = {6}, pages = {1–6}, abstract = {We study dynamical systems on a hypernetwork, namely by coupling them through several variables. For the case when the coupling(s) are all linear, a comprehensive analysis of the master stability function (MSF) for synchronized dynamics is presented and, through application to a number of paradigmatic examples, the typical forms of the MSF are discussed. The MSF formalism for hypernetworks also provides a framework to study synchronization in systems that are diffusively coupled through dissimilar variables – the so-called conjugate coupling that can lead to amplitude or oscillation death. textcopyright 2014 American Physical Society.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We study dynamical systems on a hypernetwork, namely by coupling them through several variables. For the case when the coupling(s) are all linear, a comprehensive analysis of the master stability function (MSF) for synchronized dynamics is presented and, through application to a number of paradigmatic examples, the typical forms of the MSF are discussed. The MSF formalism for hypernetworks also provides a framework to study synchronization in systems that are diffusively coupled through dissimilar variables – the so-called conjugate coupling that can lead to amplitude or oscillation death. textcopyright 2014 American Physical Society. |
| 181. | Srivastava, Alok; Kumar, Suraj; Ramaswamy, Ramakrishna Two-layer modular analysis of gene and protein networks in breast cancer Journal Article BMC Systems Biology, 8 (1), pp. 1–15, 2014, ISSN: 17520509. Abstract | Links | BibTeX | Tags: Gene expression, Gene ontology, Modules, Networks, Protein-protein interaction @article{Srivastava2014, title = {Two-layer modular analysis of gene and protein networks in breast cancer}, author = {Alok Srivastava and Suraj Kumar and Ramakrishna Ramaswamy}, url = {https://ramramaswamy.org/papers/156.pdf}, doi = {10.1186/1752-0509-8-81}, issn = {17520509}, year = {2014}, date = {2014-01-01}, journal = {BMC Systems Biology}, volume = {8}, number = {1}, pages = {1–15}, abstract = {Background: Genomic, proteomic and high-throughput gene expression data, when integrated, can be used to map the interaction networks between genes and proteins. Different approaches have been used to analyze these networks, especially in cancer, where mutations in biologically related genes that encode mutually interacting proteins are believed to be involved. This system of integrated networks as a whole exhibits emergent biological properties that are not obvious at the individual network level. We analyze the system in terms of modules, namely a set of densely interconnected nodes that can be further divided into submodules that are expected to participate in multiple biological activities in coordinated manner.Results: In the present work we construct two layers of the breast cancer network: the gene layer, where the correlation network of breast cancer genes is analyzed to identify gene modules, and the protein layer, where each gene module is extended to map out the network of expressed proteins and their interactions in order to identify submodules. Each module and its associated submodules are analyzed to test the robustness of their topological distribution. The constituent biological phenomena are explored through the use of the Gene Ontology. We thus construct a ” network of networks” , and demonstrate that both the gene and protein interaction networks are modular in nature. By focusing on the ontological classification, we are able to determine the entire GO profiles that are distributed at different levels of hierarchy. Within each submodule most of the proteins are biologically correlated, and participate in groups of distinct biological activities.Conclusions: The present approach is an effective method for discovering coherent gene modules and protein submodules. We show that this also provides a means of determining biological pathways (both novel and as well those that have been reported previously) that are related, in the present instance, to breast cancer. Similar strategies are likely to be useful in the analysis of other diseases as well. textcopyright 2014 Srivastava et al.; licensee BioMed Central Ltd.}, keywords = {Gene expression, Gene ontology, Modules, Networks, Protein-protein interaction}, pubstate = {published}, tppubtype = {article} } Background: Genomic, proteomic and high-throughput gene expression data, when integrated, can be used to map the interaction networks between genes and proteins. Different approaches have been used to analyze these networks, especially in cancer, where mutations in biologically related genes that encode mutually interacting proteins are believed to be involved. This system of integrated networks as a whole exhibits emergent biological properties that are not obvious at the individual network level. We analyze the system in terms of modules, namely a set of densely interconnected nodes that can be further divided into submodules that are expected to participate in multiple biological activities in coordinated manner.Results: In the present work we construct two layers of the breast cancer network: the gene layer, where the correlation network of breast cancer genes is analyzed to identify gene modules, and the protein layer, where each gene module is extended to map out the network of expressed proteins and their interactions in order to identify submodules. Each module and its associated submodules are analyzed to test the robustness of their topological distribution. The constituent biological phenomena are explored through the use of the Gene Ontology. We thus construct a ” network of networks” , and demonstrate that both the gene and protein interaction networks are modular in nature. By focusing on the ontological classification, we are able to determine the entire GO profiles that are distributed at different levels of hierarchy. Within each submodule most of the proteins are biologically correlated, and participate in groups of distinct biological activities.Conclusions: The present approach is an effective method for discovering coherent gene modules and protein submodules. We show that this also provides a means of determining biological pathways (both novel and as well those that have been reported previously) that are related, in the present instance, to breast cancer. Similar strategies are likely to be useful in the analysis of other diseases as well. textcopyright 2014 Srivastava et al.; licensee BioMed Central Ltd. |
| 180. | Karnatak, Rajat; Ramaswamy, Ram; Feudel, Ulrike Conjugate coupling in ecosystems: Cross-predation stabilizes food webs Journal Article Chaos, Solitons and Fractals, 68 , pp. 48–57, 2014, ISSN: 09600779. Abstract | Links | BibTeX | Tags: Conjugate Coupling, Population Dynamics, Predator-Prey @article{Karnatak2014, title = {Conjugate coupling in ecosystems: Cross-predation stabilizes food webs}, author = {Rajat Karnatak and Ram Ramaswamy and Ulrike Feudel}, url = {http://dx.doi.org/10.1016/j.chaos.2014.07.003}, doi = {10.1016/j.chaos.2014.07.003}, issn = {09600779}, year = {2014}, date = {2014-01-01}, journal = {Chaos, Solitons and Fractals}, volume = {68}, pages = {48–57}, publisher = {Elsevier Ltd}, abstract = {We study the dynamics of two predator-prey systems that are coupled via cross-predation, in which each predator consumes also the other prey. This setup constitutes a model system in which conjugate coupling emerges naturally and denotes the transition from two separate food chains to a food web. We show that cross-predation of a certain strength leads to amplitude death stabilizing the food web in a new equilibrium. }, keywords = {Conjugate Coupling, Population Dynamics, Predator-Prey}, pubstate = {published}, tppubtype = {article} } We study the dynamics of two predator-prey systems that are coupled via cross-predation, in which each predator consumes also the other prey. This setup constitutes a model system in which conjugate coupling emerges naturally and denotes the transition from two separate food chains to a food web. We show that cross-predation of a certain strength leads to amplitude death stabilizing the food web in a new equilibrium. |
| 179. | Punetha, Nirmal; Prasad, Awadhesh; Ramaswamy, Ramakrishna Phase-locked regimes in delay-coupled oscillator networks Journal Article Chaos, 24 (4), 2014, ISSN: 10541500. Abstract | Links | BibTeX | Tags: @article{Punetha2014, title = {Phase-locked regimes in delay-coupled oscillator networks}, author = {Nirmal Punetha and Awadhesh Prasad and Ramakrishna Ramaswamy}, url = {https://ramramaswamy.org/papers/158.pdf}, doi = {10.1063/1.4897360}, issn = {10541500}, year = {2014}, date = {2014-01-01}, journal = {Chaos}, volume = {24}, number = {4}, abstract = {textcopyright 2014 AIP Publishing LLC. For an ensemble of globally coupled oscillators with time-delayed interactions, an explicit relation for the frequency of synchronized dynamics corresponding to different phase behaviors is obtained. One class of solutions corresponds to globally synchronized in-phase oscillations. The other class of solutions have mixed phases, and these can be either randomly distributed or can be a splay state, namely with phases distributed uniformly on a circle. In the strong coupling limit and for larger networks, the in-phase synchronized configuration alone remains. Upon variation of the coupling strength or the size of the system, the frequency can change discontinuously, when there is a transition from one class of solutions to another. This can be from the in-phase state to a mixed-phase state, but can also occur between two in-phase configurations of different frequency. Analytical and numerical results are presented for coupled Landau-Stuart oscillators, while numerical results are shown for Rössler and FitzHugh-Nagumo systems.}, keywords = {}, pubstate = {published}, tppubtype = {article} } textcopyright 2014 AIP Publishing LLC. For an ensemble of globally coupled oscillators with time-delayed interactions, an explicit relation for the frequency of synchronized dynamics corresponding to different phase behaviors is obtained. One class of solutions corresponds to globally synchronized in-phase oscillations. The other class of solutions have mixed phases, and these can be either randomly distributed or can be a splay state, namely with phases distributed uniformly on a circle. In the strong coupling limit and for larger networks, the in-phase synchronized configuration alone remains. Upon variation of the coupling strength or the size of the system, the frequency can change discontinuously, when there is a transition from one class of solutions to another. This can be from the in-phase state to a mixed-phase state, but can also occur between two in-phase configurations of different frequency. Analytical and numerical results are presented for coupled Landau-Stuart oscillators, while numerical results are shown for Rössler and FitzHugh-Nagumo systems. |
| 178. | Saxena, Garima; Punetha, Nirmal; Prasad, Awadhesh; Ramaswamy, Ram Amplitude death: The cessation of oscillations in coupled nonlinear dynamical systems Journal Article AIP Conference Proceedings, 1582 , pp. 158–171, 2014, ISSN: 15517616. Abstract | Links | BibTeX | Tags: Amplitude quenching, Bifurcation, Control Network, Fixed-point solution, Interaction, Synchronization @article{Saxena2014, title = {Amplitude death: The cessation of oscillations in coupled nonlinear dynamical systems}, author = {Garima Saxena and Nirmal Punetha and Awadhesh Prasad and Ram Ramaswamy}, url = {https://ramramaswamy.org/papers/RC44.pdf}, doi = {10.1063/1.4865354}, issn = {15517616}, year = {2014}, date = {2014-01-01}, journal = {AIP Conference Proceedings}, volume = {1582}, pages = {158–171}, abstract = {Here we extend a recent review (Physics Reports $backslash$bf 521, 205 (2012)) of amplitude death, namely the suppression of oscillations due to the coupling interactions between nonlinear dynamical systems. This is an important emergent phenomenon that is operative under a variety of scenarios. We summarize results of recent studies that have significantly added to our understanding of the mechanisms that underlie the process, and also discuss the phase–flip transition, a characteristic and unusual effect that occurs in the transient dynamics as the oscillations die out.}, keywords = {Amplitude quenching, Bifurcation, Control Network, Fixed-point solution, Interaction, Synchronization}, pubstate = {published}, tppubtype = {article} } Here we extend a recent review (Physics Reports $backslash$bf 521, 205 (2012)) of amplitude death, namely the suppression of oscillations due to the coupling interactions between nonlinear dynamical systems. This is an important emergent phenomenon that is operative under a variety of scenarios. We summarize results of recent studies that have significantly added to our understanding of the mechanisms that underlie the process, and also discuss the phase–flip transition, a characteristic and unusual effect that occurs in the transient dynamics as the oscillations die out. |
2013 |
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| 177. | Manchanda, Kaustubh; Yadav, Avinash Chand; Ramaswamy, Ramakrishna Scaling behavior in probabilistic neuronal cellular automata Journal Article Physical Review E, 87 (1), pp. 1–6, 2013, ISSN: 15393755. Abstract | Links | BibTeX | Tags: @article{Manchanda2013, title = {Scaling behavior in probabilistic neuronal cellular automata}, author = {Kaustubh Manchanda and Avinash Chand Yadav and Ramakrishna Ramaswamy}, url = {https://ramramaswamy.org/papers/146.pdf}, doi = {10.1103/PhysRevE.87.012704}, issn = {15393755}, year = {2013}, date = {2013-01-01}, journal = {Physical Review E}, volume = {87}, number = {1}, pages = {1–6}, abstract = {We study a neural network model of interacting stochastic discrete two-state cellular automata on a regular lattice. The system is externally tuned to a critical point which varies with the degree of stochasticity (or the effective temperature). There are avalanches of neuronal activity, namely, spatially and temporally contiguous sites of activity; a detailed numerical study of these activity avalanches is presented, and single, joint, and marginal probability distributions are computed. At the critical point, we find that the scaling exponents for the variables are in good agreement with a mean-field theory. textcopyright 2013 American Physical Society.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We study a neural network model of interacting stochastic discrete two-state cellular automata on a regular lattice. The system is externally tuned to a critical point which varies with the degree of stochasticity (or the effective temperature). There are avalanches of neuronal activity, namely, spatially and temporally contiguous sites of activity; a detailed numerical study of these activity avalanches is presented, and single, joint, and marginal probability distributions are computed. At the critical point, we find that the scaling exponents for the variables are in good agreement with a mean-field theory. textcopyright 2013 American Physical Society. |
| 176. | Bilal, Shakir; Ramaswamy, Ramakrishna Quasiperiodically driven maps in the low-dissipation limit Journal Article Physical Review E, 87 (3), pp. 3–6, 2013, ISSN: 15393755. Abstract | Links | BibTeX | Tags: @article{Bilal2013, title = {Quasiperiodically driven maps in the low-dissipation limit}, author = {Shakir Bilal and Ramakrishna Ramaswamy}, url = {https://ramramaswamy.org/papers/147.pdf}, doi = {10.1103/PhysRevE.87.034901}, issn = {15393755}, year = {2013}, date = {2013-01-01}, journal = {Physical Review E}, volume = {87}, number = {3}, pages = {3–6}, abstract = {We study the quasiperiodically driven Hénon and Standard maps in the weak dissipative limit. In the absence of forcing, there are a large number of coexisting periodic attractors. Although chaotic attractors can also be found, these typically have vanishingly small basins of attraction. Quasiperiodic forcing reduces the multistability in the system, and as the bifurcation parameter is varied, strange nonchaotic attractors (SNAs) are created. The attractor basin for SNAs appears to be the largest among those of all coexisting attractors at such a transition. textcopyright 2013 American Physical Society.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We study the quasiperiodically driven Hénon and Standard maps in the weak dissipative limit. In the absence of forcing, there are a large number of coexisting periodic attractors. Although chaotic attractors can also be found, these typically have vanishingly small basins of attraction. Quasiperiodic forcing reduces the multistability in the system, and as the bifurcation parameter is varied, strange nonchaotic attractors (SNAs) are created. The attractor basin for SNAs appears to be the largest among those of all coexisting attractors at such a transition. textcopyright 2013 American Physical Society. |
| 175. | Agrawal, Manish; Prasad, Awadhesh; Ramaswamy, Ram Driving-induced bistability in coupled chaotic attractors Journal Article Physical Review E – Statistical, Nonlinear, and Soft Matter Physics, 87 (4), pp. 1–5, 2013, ISSN: 15393755. Abstract | Links | BibTeX | Tags: @article{Agrawal2013, title = {Driving-induced bistability in coupled chaotic attractors}, author = {Manish Agrawal and Awadhesh Prasad and Ram Ramaswamy}, url = {https://ramramaswamy.org/papers/148.pdf}, doi = {10.1103/PhysRevE.87.042909}, issn = {15393755}, year = {2013}, date = {2013-01-01}, journal = {Physical Review E – Statistical, Nonlinear, and Soft Matter Physics}, volume = {87}, number = {4}, pages = {1–5}, abstract = {We examine the effects of symmetry–preserving and breaking interactions in a drive–response system where the response has an invariant symmetry in the absence of the drive. Subsequent to the onset of generalized synchronization, we find that there can be more than one stable attractor. Numerical, as well as analytical results establish the presence of phase synchrony in such coexisting attractors. These results are robust to external noise.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We examine the effects of symmetry–preserving and breaking interactions in a drive–response system where the response has an invariant symmetry in the absence of the drive. Subsequent to the onset of generalized synchronization, we find that there can be more than one stable attractor. Numerical, as well as analytical results establish the presence of phase synchrony in such coexisting attractors. These results are robust to external noise. |