Stable and Metastable vortex states and the first order transition across the peak effect region in weakly pinned 2H-NbSe_2

The peak effect in weakly pinned superconductors is accompanied by metastable vortex states. Each metastable vortex configuration is characterized by a different critical current density J_c, which mainly depends on the past thermomagnetic history of the superconductor. A recent model [G. Ravikumar, et al, Phys. Rev. B 61, R6479 (2000)] proposed to explain the history dependent J_c postulates a stable state of vortex lattice with a critical current density J_c^{st}, determined uniquely by the field and temperature. In this paper, we present evidence for the existence of the stable state of the vortex lattice in the peak effect region of 2H-NbSe_2. It is shown that this stable state can be reached from any metastable vortex state by cycling the applied field by a small amplitude. The minor magnetization loops obtained by repeated field cycling allow us to determine the pinning and "equilibrium" properties of the stable state of the vortex lattice at a given field and temperature unambiguously. The data imply the occurence of a first order phase transition from an ordered phase to a disordered vortex phase across the peak effect.Comment: 20 pages, 10 figures. Corresponding author: S. Ramakrishna

Real-Time Vector Automata

We study the computational power of real-time finite automata that have been augmented with a vector of dimension k, and programmed to multiply this vector at each step by an appropriately selected $k \times k$ matrix. Only one entry of the vector can be tested for equality to 1 at any time. Classes of languages recognized by deterministic, nondeterministic, and "blind" versions of these machines are studied and compared with each other, and the associated classes for multicounter automata, automata with multiplication, and generalized finite automata.Comment: 14 page

Calculation of minor hysteresis loops under metastable to stable transformations in vortex matter

We present a model in which metastable supercooled phase and stable equilibrium phase of vortex matter coexist in different regions of a sample. Minor hysteresis loops are calculated with the simple assumption of the two phases of vortex matter having field-independent critical current densities. We use our earlier published ideas that the free energy barrier separating the metastable and stable phases reduces as the magnetic induction moves farther from the first order phase transition line, and that metastable to stable transformations occur in local regions of the sample when the local energy dissipation exceeds a critical value. Previously reported anomalous features in minor hysteresis loops are reproduced, and calculated field profiles are presented.Comment: 9pages, 7 figure

Green facile synthesis of Ag-doped ZnO nanoparticles from Gymnema sylvestre leaf extract and investigation of their Antibacterial activity

The unique characteristics of the green synthesis pathway have opened the way for a new field of scientific investigation. The current study used green chemistry methodologies to produce pure zinc oxide (ZnO) (G1) and silver doped zinc oxide (Ag doped ZnO) (G2) nanoparticles (NPs) using Gymnema sylvestre (G. sylvestre) leaf extract as a reducing as well as capping agent. XRD, FESEM, EDAX, and FT-IR investigations were used to investigate the structural characterization of G1 and G2 NPs. The UV–Vis and PL analyses were used to examine the optical characteristics. The results clearly reveal that the leaf extract is the best possible stabilizing agent for the manufacture of G1 and G2 NPs, and that the generated nanoparticles operate as potent microbial agents, inhibiting the growth of a variety of dangerous microbes. Due to their eco–friendly and non–toxic compatibility, the prepared G1 and G2 NPs can be employed for therapeutic and other purposes

Gastrotomy for Retrieval of Thoracic Oesophageal Foriegn Body Using Long Forceps Technique in Three Dogs

Three dogs age between 3- 6 years old was presented to the Department of Veterinary Surgery and Radiology with the history of anorexia, attempt for vomiting, regurgitation, dysphagia, gagging, mild salivation after taking a piece of bone. Clinical examination revealed heart rate and respiratory were within physiological limits. Lateral plain radiograph of thorax revealed radio opaque foreign body was lodged between heart and diaphragm. Surgical invention was planned to retrieve thoracic oesophageal foreign body through gastrotomy incision. This clinical paper reports the successful surgical management of thoracic oesophageal foreign body through gastrotomy incision using long forceps without complication

Error-Correcting Tournaments

We present a family of pairwise tournaments reducing $k$-class classification to binary classification. These reductions are provably robust against a constant fraction of binary errors. The results improve on the PECOC construction \cite{SECOC} with an exponential improvement in computation, from $O(k)$ to $O(\log_2 k)$, and the removal of a square root in the regret dependence, matching the best possible computation and regret up to a constant.Comment: Minor wording improvement

Critical points in the Bragg glass phase of a weakly pinned crystal of Ca3_3Rh4_4Sn13_{13}

New experimental data are presented on the scan rate dependence of the magnetization hysteresis width $\Delta M(H)$ ($\propto$ critical current density $J_c(H)$) in isothermal $M-H$ scans in a weakly pinned single crystal of Ca$_3$Rh$_4$Sn$_{13}$, which displays second magnetization peak (SMP) anomaly as distinct from the peak effect (PE). We observe an interesting modulation in the field dependence of a parameter which purports to measure the dynamical annealing of the disordered bundles of vortices injected through the sample edges towards the destined equilibrium vortex state at a given $H$. These data, in conjunction with the earlier observations made while studying the thermomagnetic history dependence in $J_c(H)$ in the tracing of the minor hysteresis loops, imply that the partially disordered state heals towards the more ordered state between the peak field of the SMP anomaly and the onset field of the PE. The vortex phase diagram in the given crystal of Ca$_3$Rh$_4$Sn$_{13}$ has been updated in the context of the notion of the phase coexistence of the ordered and disordered regions between the onset field of the SMP anomaly and the spinodal line located just prior to the irreversibility line. A multi-critical point and a critical point in the ($H,T$) region of the Bragg glass phase have been marked in this phase diagram and the observed behaviour is discussed in the light of recent data on multi-critical point in the vortex phase diagram in a single crystal of Nb.Comment: To appear in Current trends in Vortex State Studies - Pramana J. Physic

Exact Solution of Return Hysteresis Loops in One Dimensional Random Field Ising Model at Zero Temperature

Minor hysteresis loops within the main loop are obtained analytically and exactly in the one-dimensional ferromagnetic random field Ising-model at zero temperature. Numerical simulations of the model show excellent agreement with the analytical results