Papers by RAMESH NARAYANAN
Pramana, 2010
The behaviour of runaway electrons in the SINP tokamak, which can be operated in a normal edge sa... more The behaviour of runaway electrons in the SINP tokamak, which can be operated in a normal edge safety factor (qa) (NQ) discharge configuration as well as in a low q a (LQ) configuration, was experimentally investigated, during the initial plasma generation phase. An energy analysis of the runaway electron dynamics in the rise phase of the SINP tokamak discharges was also made. A comparison of the runaway electron diffusion coefficients in NQ and LQ is carried out in this paper.
Comparative study of nonlinear properties of EEG signals of normal persons and epileptic patients
Plasma Research Express, 2019
Investigations on argon and hydrogen plasmas produced by compact ECR plasma source To cite this a... more Investigations on argon and hydrogen plasmas produced by compact ECR plasma source To cite this article: Anshu Verma et al 2019 Plasma Res. Express 1 035012 View the article online for updates and enhancements.
arxiv.org
Stochasticity is one of the most extensively researched topics in laboratory and space plasmas si... more Stochasticity is one of the most extensively researched topics in laboratory and space plasmas since it has been successful in explaining the various anomalous processes like transport, particle heating, particle loss etc. Since there is a growing need for better understanding of this ...
Modelling Critical and Catastrophic Phenomena in Geoscience
Physica Scripta, 2003
The quantum physics of light is a most fascinating field. Here I present a very personal viewpoin... more The quantum physics of light is a most fascinating field. Here I present a very personal viewpoint, focusing on my own path to quantum entanglement and then on to applications. I have been fascinated by quantum physics ever since I heard about it for the first time in school. The theory struck me immediately for two reasons: (1) its immense mathematical beauty, and (2) the unparalleled precision to which its predictions have been verified again and again. Particularly fascinating for me were the predictions of quantum mechanics for individual particles, individual quantum systems. Surprisingly, the experimental realization of many of these fundamental phenomena has led to novel ideas for applications. Starting from my early experiments with neutrons, I later became interested in quantum entanglement, initially focusing on multi-particle entanglement like GHZ states. This work opened the experimental possibility to do quantum teleportation and quantum hyper-dense coding. The latter became the first entanglement-based quantum experiment breaking a classical limitation. One of the most fascinating phenomena is entanglement swapping, the teleportation of an entangled state. This phenomenon is fundamentally interesting because it can entangle two pairs of particles which do not share any common past. Surprisingly, it also became an important ingredient in a number of applications, including quantum repeaters which will connect future quantum computers with each other. Another application is entanglement-based quantum cryptography where I present some recent long-distance experiments. Entanglement swapping has also been applied in very recent so-called loophole-free tests of Bell's theorem. Within the physics community such loophole-free experiments are perceived as providing nearly definitive proof that local realism is untenable. While, out of principle, local realism can never be excluded entirely, the 2015 achievements narrow down the remaining possibilities for local realistic explanations of the quantum phenomenon of entanglement in a significant way. These experiments may go down in the history books of science. Future experiments will address particularly the freedom-of-choice loophole using cosmic sources of randomness. Such experiments confirm that unconditionally secure quantum cryptography is possible, since quantum cryptography based on Bell's theorem can provide unconditional security. The fact that the experiments were loophole-free proves that an eavesdropper cannot avoid detection in an experiment that correctly follows the protocol. I finally discuss some recent experiments with single-and entangled-photon states in higher dimensions. Such experiments realized quantum entanglement between two photons, each with quantum numbers beyond 10 000 and also simultaneous entanglement of two photons where each carries more than 100 dimensions. Thus they offer the possibility of quantum communication with more than one bit or qubit per photon. The paper concludes discussing Einstein's contributions and viewpoints of quantum mechanics. Even if some of his positions are not supported by recent experiments, he has to be given credit for the fact that his analysis of fundamental issues gave rise to developments which led to a new information technology. Finally, I reflect on some of the lessons learned by the fact that Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Physics of Plasmas, 2009
Continuous wavelet transform (CWT) based timescale and multi-fractal analyses have been carried o... more Continuous wavelet transform (CWT) based timescale and multi-fractal analyses have been carried out on the anode glow related nonlinear floating potential fluctuations in a hollow cathode glow discharge plasma. CWT has been used to obtain the contour and ridge plots. Scale shift (or inversely frequency shift) which is a typical nonlinear behaviour, has been detected from the undulating contours. From the ridge plots, we have identified the presence of nonlinearity and degree of chaoticity. Using the wavelet transform modulus maxima technique we have obtained the multi-fractal spectrum for the fluctuations at different discharge voltages and the spectrum was observed to become a monofractal for periodic signals. These multi-fractal spectra were also used to estimate different quantities like the correlation and fractal dimension, degree of multi-fractality and complexity parameters. These estimations have been found to be consistent with the nonlinear time series analysis.
Chaos: An Interdisciplinary Journal of Nonlinear Science, 2007
Glow discharge plasmas exhibit various types of self excited oscillations for different initial c... more Glow discharge plasmas exhibit various types of self excited oscillations for different initial conditions like discharge voltages and filling pressures. The behavior of such oscillations associated with the anode glow have been investigated using nonlinear techniques like correlation dimension, largest Lyapunov exponent etc. It is seen that these oscillations go to an ordered state from a chaotic state with increase in input energy i.e. with discharge voltages implying occurrence of inverse bifurcations. These results are different from the other observations wherein the fluctuations have been observed to go from ordered to chaotic state.
Nonlinear Biomedical Physics, 2009
Background: Investigation of the functioning of the brain in living systems has been a major effo... more Background: Investigation of the functioning of the brain in living systems has been a major effort amongst scientists and medical practitioners. Amongst the various disorder of the brain, epilepsy has drawn the most attention because this disorder can affect the quality of life of a person. In this paper we have reinvestigated the EEGs for normal and epileptic patients using surrogate analysis, probability distribution function and Hurst exponent. Results: Using random shuffled surrogate analysis, we have obtained some of the nonlinear features that was obtained by Andrzejak et al. [Phys Rev E 2001, 64:061907], for the epileptic patients during seizure. Probability distribution function shows that the activity of an epileptic brain is nongaussian in nature. Hurst exponent has been shown to be useful to characterize a normal and an epileptic brain and it shows that the epileptic brain is long term anticorrelated whereas, the normal brain is more or less stochastic. Among all the techniques, used here, Hurst exponent is found very useful for characterization different cases. Conclusion: In this article, differences in characteristics for normal subjects with eyes open and closed, epileptic subjects during seizure and seizure free intervals have been shown mainly using Hurst exponent. The H shows that the brain activity of a normal man is uncorrelated in nature whereas, epileptic brain activity shows long range anticorrelation.
Pramana, 2000
The experimental determination of the dependance of confinement time of runaways on various disch... more The experimental determination of the dependance of confinement time of runaways on various discharge parameters has been presented along with the angular distribution of hard X-rays (HXrays) emitted from the torus in presence and absence of Langmuir probes.
Pramana, 2011
A tokamak plasma discharge having an increase in duration accompanied with enhanced runaway elect... more A tokamak plasma discharge having an increase in duration accompanied with enhanced runaway electron flux has been experimentally studied in this paper. The discharges have been obtained by controlling the applied vertical magnetic field (B appl v) to below a critical value. Such discharges have been observed to have 'negative edge plasma currents', detected using an internal Rogowskii coil (IRC). We have tried to correlate the runaway behaviour with the negative edge plasma currents and have explained that these observations are a result of beam plasma instabilities.
Nuclear Fusion, 2012
Long-distance correlations (LDCs) of plasma potential fluctuations in the plasma edge have been i... more Long-distance correlations (LDCs) of plasma potential fluctuations in the plasma edge have been investigated in the TCABR tokamak in the regime of edge biasing H-mode using an array of multi-pin Langmuir probes. This activity was carried out as part of the scientific programme of the 4th IAEA Joint Experiment (2009). The experimental data confirm the effect of amplification of LDCs
math.tifrbng.res.in
Abstract Turbulence is a very common phenomenon in the edge re-gion of tokamaks. We have carried... more Abstract Turbulence is a very common phenomenon in the edge re-gion of tokamaks. We have carried out a detailed analysis of potential and density fluctuations of the plasma in SINP tokamak. Using the continuous wavelet transforms we have estimated the fractal ...
Review of Scientific Instruments, 2006
An internal Rogowskii coil (IRC) has been developed to measure current profiles within SINP tokam... more An internal Rogowskii coil (IRC) has been developed to measure current profiles within SINP tokamak discharges. The present article has highlighted measurements using the IRC in SINP tokamak discharges exhibiting extension in phase after the discharge decays to ...
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Papers by RAMESH NARAYANAN