Effect of random interactions in spin baths on decoherence

We study the decoherence of a central spin 1/2 induced by a spin bath with intrabath interactions. Since we are interested in the cumulative effect of interaction and disorder, we study baths comprising Ising spins with random ferro- and antiferromagnetic interactions between the spins. Using the resolvent operator method which goes beyond the standard Born-Markov master equation approach, we show that, in the weak coupling regime, the decoherence of the central spin at all times is entirely determined by the local-field distribution or equivalently, the dynamical structure factor of the Ising bath. We present analytic results for the Ising spin chain bath at arbitrary temperature for different distributions of the intrabath interaction strengths. We find clear evidence of non-Markovian behavior in the low temperature regime. We also consider baths described by Ising models on higher-dimensional lattices. We find that interactions lead to a significant reduction of the decoherence. An important feature of interacting spinbaths is the saturation of the asymptotic Markovian decay rate at high temperatures, as opposed to the conventional Ohmic boson bath.Comment: 13 page

Induction of reactive oxygen species in brain of Etroplus maculatus after exposure to bisphenol A

The present study was aimed to investigate that bisphenol A, an environmental estrogen, exposed at 648 ?g/ L concentration for 96 h could induce reactive oxygen species in brain of cichlid fish, Etroplus maculatus. Evaluation of antioxidant enzymes as superoxide dismutase, catalase and glutathione reductase showed a reductionin the activities at 5% level of significance with concomitant increase in the level of hydrogen peroxide generation (from 1.546 ± 0.426 (control), 1.506 ± 0.217 (DMSO) to 1.888 ± 0.368 (24 h), 5.332 ± 0.589 (72 h), 2.392 ± 0.341 (96 h)) and lipid peroxidation (from 2.805 ± 0.33 (control), 2.401 ± 0.309 (DMSO) to 3.596 ±0.373 (24 h), 5.65 ± 0.306 (72 h), 3.834 ± 0.236 (96 h)). The brain marker enzyme, acetylcholinesterase decreased at 24, 72 and 96 h in time-dependent manner than that of control groups. The present findings summarize that the increased production of oxygen free radicals due to the exposure of an environmental estrogen, bisphenol A at sub lethal concentration (648 ?g/ L) for 96 h inhibited the activities of antioxidant enzymes thereby induced oxidative stress in brain of fish. The decreased activity of brain marker enzyme, acetylcholinesterase reflect the neurotoxicity of bisphenol A in brain of fish, Etroplus maculatus and this could be one of the possible mechanisms of bisphenol A-induced neurodevelopmental disorders in fish

Short-term Exposure to Quinalphos Induced Biochemical and Haematological Changes in Freshwater Fish, Oreochromis Mossambicus

The toxic impact of quinalphos, an organothiophosphate, on the biochemical as well as haematological parameters was studied in the adult freshwater fish, Oreochromis mossambicus. In the present study, 0.5µl/ L quinalphos was chosen to represent sublethal concentration for 48 and 96 hours as short-term exposure and respective control animals were maintained. Quinalphos induced toxic stress to the exposed fishes, which is obvious by the reduction in the oxygen consumption of the fishes at the time of exposure and this could be due to shrinkage of the respiratory epithelium or possibly due to mucus accumulation on gills. Decrease in the haemoglobin content was observed and this may be due to either an increase in the rate at which the haemoglobin is destroyed or decreased rate of haemopoietic potential of the fish. In the present study, the significant increase in WBC count indicates hypersensitivity of leucocytes to quinalphos and these changes may be due to immunological reactions to produce antibodies to cope up with the stress. Decrease in the level of RBC count indicated decrease in erythropoietic activity or severe anemic state. Reduction in the plasma and tissue protein of quinalphos exposed fishes may be due to its utilization to mitigate the energy demand when the fishes are under stress. Increase of plasma glucose and the total glucose content in tissues like liver, muscle and gill might have resulted from gluconeogenesis to provide energy for the increased metabolic demands imposed by quinalphos stress. Thus the biochemical and hematological alterations due to acute short-term exposure to quinalphos were due to the toxic stress of the toxicant

A non-Hermitian critical point and the correlation length of strongly correlated quantum systems

We study a non-Hermitian generalization of quantum systems in which an imaginary vector potential is added to the momentum operator. In the tight-binding approximation, we make the hopping energy asymmetric in the Hermitian Hamiltonian. In a previous article, we conjectured that the non-Hermitian critical point where the energy gap vanishes is equal to the inverse correlation length of the Hermitian system and we confirmed the conjecture for two exactly solvable systems. In this article, we present more evidence for the conjecture. We also argue the basis of our conjecture by noting the dispersion relation of the elementary excitation.Comment: 25 pages, 18 figure

Numerical and approximate analytical results for the frustrated spin-1/2 quantum spin chain

We study the $T=0$ frustrated phase of the $1D$ quantum spin-$\frac 12$ system with nearest-neighbour and next-nearest-neighbour isotropic exchange known as the Majumdar-Ghosh Hamiltonian. We first apply the coupled-cluster method of quantum many-body theory based on a spiral model state to obtain the ground state energy and the pitch angle. These results are compared with accurate numerical results using the density matrix renormalisation group method, which also gives the correlation functions. We also investigate the periodicity of the phase using the Marshall sign criterion. We discuss particularly the behaviour close to the phase transitions at each end of the frustrated phase.Comment: 17 pages, Standard Latex File + 7 PostScript figures in separate file. Figures also can also be requested from [email protected]

Short-term exposure to quinalphos induced biochemical and haematological changes in freshwater fish, Oreochromis mossambicus

The toxic impact of quinalphos, an organothiophosphate, on the biochemical as well as haematological parameters was studied in the adult freshwater fish, Oreochromis mossambicus. In the present study, 0.5µl/ L quinalphos was chosen to represent sublethal concentration for 48 and 96 hours as short-term exposure and respective control animals were maintained. Quinalphos induced toxic stress to the exposed fishes, which is obvious by the reduction in the oxygen consumption of the fishes at the time of exposure and this could be due to shrinkage of the respiratory epithelium or possibly due to mucus accumulation on gills. Decrease in the haemoglobin content was observed and this may be due to either an increase in the rate at which the haemoglobin is destroyed or decreased rate of haemopoietic potential of the fish. In the present study, the significant increase in WBC count indicates hypersensitivity of leucocytes to quinalphos and these changes may be due to immunological reactions to produce antibodies to cope up with the stress. Decrease in the level of RBC count indicated decrease in erythropoietic activity or severe anemic state. Reduction in the plasma and tissue protein of quinalphos exposed fishes may be due to its utilization to mitigate the energy demand when the fishes are under stress. Increase of plasma glucose and the total glucose content in tissues like liver, muscle and gill might have resulted from gluconeogenesis to provide energy for the increased metabolic demands imposed by quinalphos stress. Thus the biochemical and hematological alterations due to acute short-term exposure to quinalphos were due to the toxic stress of the toxicant

Quinalphos Induced Antioxidant Status and Histopathological Changes in the Gill of the Freshwater Fish, Oreochromis mossambicus

To extend the knowledge about quinalphos induced antioxidant status and its related changes on the histopathology of gills, the freshwater fish Oreochromis mossambicus was chosen as a model system. Quinalphos treatment (0.5μl/ L for 30 and 60 days) decreased the activities of antioxidant enzymes with concomitant increase in the production of malondialdehyde. Increased reactive oxygen species generation coincides with the increase in the protein carbonyl in the gills of the treated fishes. Histological observation in the gill of quinalphos treated animal for 60 days showed several alterations as hypertrophy of gill arches, lifting of lamellar epithelium, degeneration of gill filament and lamellar epithelium and vasodilation in the lamellar axis when compared to the control group. These observations suggest that chronic exposure to pesticide affect the respiratory oxidative potential of the freshwater fish and this could be possibly due to quinalphos induced oxidative stress in the gill

Magnetization Properties of Some Quantum Spin Ladders

The experimental realization of various spin ladder systems has prompted their detailed theoretical investigations. Here we study the evolution of ground state magnetization with an external magnetic field for two different antiferromagnetic systems: a three-legged spin-1/2 ladder, and a two-legged spin-1/2 ladder with an additional diagonal interaction. The finite system density-matrix renormalization group method is employed for numerical studies of the three-chain system, and an effective low-energy Hamiltonian is used in the limit of strong interchain coupling to study the two- and three-chain systems. The three-chain system has a magnetization plateau at one-third of the saturation magnetization. The two-chain system has a plateau at zero magnetization due to a gap above the singlet ground state. It also has a plateau at half of the saturation magnetization for a certain range of values of the couplings. We study the regions of transitions between plateaus numerically and analytically, and find that they are described, at first order in a strong-coupling expansion, by an XXZ spin-1/2 chain in a magnetic field; the second order terms give corrections to the XXZ model. We also study numerically some low-temperature properties of the three-chain system, such as the magnetization, magnetic susceptibility and specific heat.Comment: Revtex, 26 pages including 17 epsf figures; a few minor changes; this is the final published versio

Magnetization Curves of Antiferromagnetic Heisenberg Spin-1/2 Ladders

Magnetization processes of spin-1/2 Heisenberg ladders are studied using strong-coupling expansions, numerical diagonalization of finite systems and a bosonization approach. We find that the magnetization exhibits plateaux as a function of the applied field at certain rational fractions of the saturation value. Our main focus are ladders with 3 legs where plateaux with magnetization one third of the saturation value are shown to exist.Comment: 5 pages REVTeX, 4 PostScript figures included using psfig.sty; this is the final version to appear in Phys. Rev. Let

Coulombian Disorder in Periodic Systems

We study the effect of unscreened charged impurities on periodic systems. We show that the long wavelength component of the disorder becomes long ranged and dominates static correlation functions. On the other hand, because of the statistical tilt symmetry, dynamical properties such as pinning remain unaffected. As a concrete example, we focus on the effect of Coulombian disorder generated by charged impurities, on 3D charge density waves with non local elasticity. We calculate the x-ray intensity and find that it is identical to the one produced by thermal fluctuations in a disorder-free smectic-A. We discuss the consequences of these results for experiments.Comment: 11 pages, 3 figures, revtex