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Munoz-Darias T.,National institute for astrophysics | Motta S.,National institute for astrophysics | Motta S.,University dettInsubria | Pawar D.,Ramniranjan Jhunjhunwala College | And 3 more authors.
Monthly Notices of the Royal Astronomical Society: Letters

We present a 2-day long Rossi X-ray Timing Explorer observation and simultaneous Swift data of the bright X-ray transient XTE J1752-223. Spectral and timing properties were stable during the observation. The energy spectrum is well described by a broken power law with a high-energy cut-off. A cold disc (~0.3 keV) is observed when Swift/X-Rsy Telescope data are considered. The fractional root mean square amplitude of the aperiodic variability (0.002-128 Hz) is 48.2 ± 0.1 per cent, and it is not energy dependent. The continuum of the power density spectrum can be fitted by using four broad-band Lorentzians. A high-frequency (~21 Hz) component and two weak quasi-periodic oscillation-like features are also present. Time lags between soft and hard X-rays roughly follow the relation Δt ∝ ν-0.7, with delays dropping from ~0.5 (0.003 Hz) to ~0.0015 (≥10 Hz) s. Our results are consistent with XTE J1752-223 being a black hole candidate, with all timing and spectral components very similar to those of Cyg X-l during its canonical hard state. © 2010 The Authors. Journal compilation © 2010 RAS. Source

Basu H.,Tata Institute of Fundamental Research | Kolwankar K.M.,Ramniranjan Jhunjhunwala College | Dharmadhikari A.K.,Tata Institute of Fundamental Research | Dharmadhikari J.A.,Tata Institute of Fundamental Research | And 3 more authors.
Journal of Physical Chemistry C

We report a scheme for very significantly accelerated growth of dendritic patterns in organic, inorganic, polymeric, and biological liquids, using laser power as low as a few hundred microwatts in the presence of an efficient absorber such as carbon nanotubes (CNTs). The CNTs act as a heat source that drives dendritic growth; their anisotropy ensures a rich diversity of branched patterns. We have studied the time evolution of the accelerated growth patterns; growth patterns are seen on millisecond time scales. We rationalize such unprecedented speed of dendritic growth using a diffusion equation for the temperature field with an additional source term. The predictions of the well-established microscopic solvability theory (MST) are seen to hold on time scales in excess of 100 ms even with the introduction of an additional source term to account for our laser beam. On the other hand, on time scales shorter than 100 ms, MST is seen to break down. Our method opens new vistas for studies on the dynamics of dendritic patterns and crystal growth. © 2012 American Chemical Society. Source

Prasade A.,Bombay Natural History Society | Apte D.,Bombay Natural History Society | Kale P.,Ramniranjan Jhunjhunwala College | Oliveira O.M.P.,Federal University of ABC
Check List

The benthic ctenophore Vallicula multiformis Rankin, 1956 is recorded for the first time in the Arabian Sea, from the Gulf of Kutch, west coast of India in March 2013. This occurrence represents a remarkable extension of its geographic distribution that until now included only known the Pacific and Atlantic oceans. © 2015 Check List and Authors. Source

Pawar D.D.,Ramniranjan Jhunjhunwala College | Kalamkar M.,University of Amsterdam | Altamirano D.,University of Amsterdam | Linares M.,Institute Astmfisica Of Canarias | And 4 more authors.
Monthly Notices of the Royal Astronomical Society

We report the discovery of kHz quasi-periodic oscillations (QPOs) in three Rossi X-ray Timing Explorer observations of the low-mass X-ray binary XTE J1701-407. In one of the observations we detect a kHz QPO with a characteristic frequency of 1153 ± 5 Hz, while in the other two observations we detect twin QPOs at characteristic frequencies of 740 ± 5, 1112 ± 17 Hz and 740 ± 11,1098 ± 5 Hz. All detections happen when XTE J1701-407 was in its high-intensity soft state, and their single-trial significance is in the 3.1-7.5σ range. The frequency difference in the centroid frequencies of the twin kHz QPOs (385 ± 13 Hz) is one of the largest seen till date. The 3-30 keV fractional rms amplitude of the upper kHz QPO varies between ∼18 and ∼30 per cent. XTE J1701-407, with a persistent luminosity close to 1 per cent of the Eddington limit, is among the small group of low-luminosity kHz QPO sources and has the highest rms for the upper kHz QPO detected in any source. The X-ray spectral and variability characteristics of this source indicate its atoll source nature. © 2013 The Authors. Source

Ren Q.,Peking University | Ren Q.,Max Planck Institute for Mathematics in the Sciences | Kolwankar K.M.,Max Planck Institute for Mathematics in the Sciences | Kolwankar K.M.,Ramniranjan Jhunjhunwala College | And 4 more authors.
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics

We study the interplay of topology and dynamics in a neural network connected with spike-timing-dependent plasticity (STDP) synapses. Stimulated with periodic spike trains, the STDP-driven network undergoes a synaptic pruning process and evolves to a residual network. We examine the variation of topological and dynamical properties of the residual network by varying two key parameters of STDP: synaptic delay and the ratio between potentiation and depression. Our extensive numerical simulations of the leaky integrate-and-fire model show that there exists two regions in the parameter space. The first corresponds to fixed-point configurations, where the distribution of peak synaptic conductances and the firing rate of neurons remain constant over time. The second corresponds to oscillating configurations, where both topological and dynamical properties vary periodically, which is a result of a fixed point becoming a limit cycle via a Hopf bifurcation. This leads to interesting questions regarding the implications of these rhythms in the topology and dynamics of the network for learning and cognitive processing. © 2012 American Physical Society. Source

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