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Biological Pacemakers
Rajesh G,Johnson Francis
Indian Pacing and Electrophysiology Journal , 2006,
Abstract: Genetically engineered pacemakers could be a possible alternative to implantable electronic devices for the treatment of bradyarrhythmias. The strategies include upregulation of beta adrenergic receptors, conversion of myocytes into pacemaker cells and stem cell therapy. Pacemaker activity in adult ventricular myocytes is normally repressed by the inward rectifier potassium current (IK1). The IK1 current is encoded by the Kir2 gene family. Use of a negative construct that suppresses current when expressed with wild-type Kir2.1 is an experimental approach for genesis of genetic pacemaker. hyperpolarisation activated cyclic nucleotide gated (HCN) channels which generate If current, the pacemaker current of heart can be delivered to heart by using stem cell therapy approach and viral vectors. The unresolved issues include longevity and stability of pacemaker genes, limitations involved in adenoviral and stem cell therapy and creation of genetic pacemakers which can compete with the electronic units.
Relaxation oscillations and negative strain rate sensitivity in the Portevin - Le Chatelier effect
S. Rajesh,G. Ananthakrishna
Physics , 2000, DOI: 10.1103/PhysRevE.61.3664
Abstract: A characteristic feature of the Portevin - Le Chatelier effect or the jerky flow is the stick-slip nature of stress-strain curves which is believed to result from the negative strain rate dependence of the flow stress. The latter is assumed to result from the competition of a few relevant time scales controlling the dynamics of jerky flow. We address the issue of time scales and its connection to the negative strain rate sensitivity of the flow stress within the framework of a model for the jerky flow which is known to reproduce several experimentally observed features including the negative strain rate sensitivity of the flow stress. We attempt to understand the above issues by analyzing the geometry of the slow manifold underlying the relaxational oscillations in the model. We show that the nature of the relaxational oscillations is a result of the atypical bent geometry of the slow manifold. The analysis of the slow manifold structure helps us to understand the time scales operating in different regions of the slow manifold. Using this information we are able to establish connection with the strain rate sensitivity of the flow stress. The analysis also helps us to provide a proper dynamical interpretation for the negative branch of the strain rate sensitivity.
Incomplete approach to homoclinicity in a model with bent-slow manifold geometry
S. Rajesh,G. Ananthakrishna
Physics , 2000, DOI: 10.1016/S0167-2789(99)00241-9
Abstract: The dynamics of a model, originally proposed for a type of instability in plastic flow, has been investigated in detail. The bifurcation portrait of the system in two physically relevant parameters exhibits a rich variety of dynamical behaviour, including period bubbling and period adding or Farey sequences. The complex bifurcation sequences, characterized by Mixed Mode Oscillations, exhibit partial features of Shilnikov and Gavrilov-Shilnikov scenario. Utilizing the fact that the model has disparate time scales of dynamics, we explain the origin of the relaxation oscillations using the geometrical structure of the bent-slow manifold. Based on a local analysis, we calculate the maximum number of small amplitude oscillations, $s$, in the periodic orbit of $L^s$ type, for a given value of the control parameter. This further leads to a scaling relation for the small amplitude oscillations. The incomplete approach to homoclinicity is shown to be a result of the finite rate of `softening' of the eigen values of the saddle focus fixed point. The latter is a consequence of the physically relevant constraint of the system which translates into the occurrence of back-to-back Hopf bifurcation.
Delay Induced Oscillations in a Fundamental Power System Model
Rajesh G. Kavasseri
Physics , 2006,
Abstract: In this paper, we study the dynamics and stability of a fundamental power system model when a time delay is imposed on the excitation of the generator. It is observed that sustained oscillations can arise in an otherwise stable power system through a delay induced Andronov-Hopf bifurcation. Numerical simulations are conducted to explore the dynamics of the time delayed system after the bifurcation which indicate period doublings culminating in a strange attractor.
Long Tailed Maps as a Representation of Mixed Mode Oscillatory Systems
Rajesh Raghavan,G. Ananthakrishna
Physics , 2004, DOI: 10.1016/j.physd.2005.08.004
Abstract: Mixed mode oscillatory (MMO) systems are known to exhibit some generic features such as the reversal of period doubling sequences and crossover to period adding sequences as bifurcation parameters are varied. In addition, they exhibit a nearly one dimensional unimodal Poincare map with a longtail. We recover these common features from a general class of two parameter family of one dimensional maps with a unique critical point that satisfy a few general constraints that determine the nature of the map. We derive scaling laws that determine the parameter widths of the dominant windows of periodic orbits sandwiched between two successive states of RL^k sequence. An example of a two parameter map with a unique critical point is introduced to verify the analytical results.
Synthesis and Biological Evaluation of Cyclic Imides with Coumarins and Azacoumarins  [PDF]
R. Marulasiddaiah, Rajesh G. Kalkhambkar, Manohar V. Kulkarni
Open Journal of Medicinal Chemistry (OJMC) , 2012, DOI: 10.4236/ojmc.2012.23011
Abstract: A series of new N-substituted cyclic imides of coumarins and azacoumarins have been synthesized. All the compounds were screened for their antibacterial and antifungal activities. α-Amylase enzyme inhibition activities of some N-substituted phthalimide derivatives have been explored. All the compounds were characterized by IR, 1H-NMR, and GC-MS.
Synthesis and optical properties of monodispersed Ni2+-doped ZnS nanoparticles
G. Murugadoss,M. Rajesh Kumar
Applied Nanoscience , 2013, DOI: 10.1007/s13204-012-0167-8
Abstract: Nickel-doped zinc sulfide nanoparticles were successfully synthesized in air atmosphere through chemical precipitation method using surfactants in aqueous medium. The product was characterized by different techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), fourier transform infrared spectrometer (FT-IR), UV–visible absorption and photoluminescence (PL). Crystal structure, size and morphology of the ZnS:Ni2+ nanoparticles were investigated by XRD and TEM. In the PL emission, a couple of new peaks were observed instead of a single peak by changing the precursor solution. In addition, an enhanced PL emission was observed using surfactants. Phase changes were also observed at different temperatures.
A Multifractal Description of Wind Speed Records
Rajesh G. Kavasseri,Radhakrishnan Nagarajan
Physics , 2004, DOI: 10.1016/j.chaos.2004.09.004
Abstract: In this paper, a systematic analysis of hourly wind speed data obtained from four potential wind generation sites in North Dakota is conducted. The power spectra of the data exhibited a power law decay characteristic of $1/f^{\alpha}$ processes with possible long range correlations. The temporal scaling properties of the records were studied using multifractal detrended fluctuation analysis {\em MFDFA}. It is seen that the records at all four locations exhibit similar scaling behavior which is also reflected in the multifractal spectrum determined under the assumption of a binomial multiplicative cascade model.
Minimizing the effect of sinusoidal trends in detrended fluctuation analysis
Radhakrishnan Nagarajan,Rajesh G. Kavasseri
Physics , 2004, DOI: 10.1142/S021812740501279X
Abstract: The detrended fluctuation analysis (DFA) [Peng et al., 1994] and its extensions (MF-DFA) [Kantelhardt et al., 2002] have been used extensively to determine possible long-range correlations in self-affine signals. While the DFA has been claimed to be a superior technique, recent reports have indicated its susceptibility to trends in the data. In this report, a smoothing filter is proposed to minimize the effect of sinusoidal trends and distortion in the log-log plots obtained by DFA and MF-DFA techniques.
Evidence of crossover phenomena in wind speed data
Rajesh G. Kavasseri,Radhakrishnan Nagarajan
Physics , 2004,
Abstract: In this report, a systematic analysis of hourly wind speed data obtained from three potential wind generation sites (in North Dakota) is analyzed. The power spectra of the data exhibited a power-law decay characteristic of $1/f^{\alpha}$ processes with possible long-range correlations. Conventional analysis using Hurst exponent estimators proved to be inconclusive. Subsequent analysis using detrended fluctuation analysis (DFA) revealed a crossover in the scaling exponent ($\alpha$). At short time scales, a scaling exponent of $\alpha \sim 1.4$ indicated that the data resembled Brownian noise, whereas for larger time scales the data exhibited long range correlations ($\alpha \sim 0.7$). The scaling exponents obtained were similar across the three locations. Our findings suggest the possibility of multiple scaling exponents characteristic of multifractal signals.
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