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Search Results: 1 - 10 of 262022 matches for " B. K. Chakraverty "
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Quantum Phase Fluctuations in High Tc Superconductors
B. K. Chakraverty
Physics , 1999,
Abstract: If phase coherence determines the superconducting transition temperature Tc in the cuprate oxides, it is of great interest to understand the role that dynamics of the phase fluctuation plays in bringing about depletion of the superconducting condensate. We will show that a phase correlation function can be calculated that allows us to describe depletion of superconducting condensate as a result of the quantum fluctuation. In two dimension, dynamic phase fluctuation or pair fluctuation gives rise to a condensate depletion linear with temperature as T$\to O$ in superconductors with nodes at the fermi surface.
Effective action for Superconductors and BCS-Bose crossover
S. De Palo,C. Castellani,C. Di Castro,B. K. Chakraverty
Physics , 1999, DOI: 10.1103/PhysRevB.60.564
Abstract: A standard perturbative expansion around the mean-field solution is used to derive the low-energy effective action for superconductors at T=0. Taking into account the density fluctuations at the outset we get the effective action where the density $\rho$ is the conjugated momentum to the phase $\theta$ of the order parameter. In the hydrodynamic regime, the dynamics of the superconductor is described by a time dependent non-linear Schr\"odinger equation (TDNLS) for the field $\Psi(x)=\sqrt{\rho/2} e^{i\theta}$. The evolution of the density fluctuations in the crossover from weak-coupling (BCS) to strong-coupling (Bose condensation of localized pairs) superconductivity is discussed for the attractive Hubbard model. In the bosonic limit, the TDNLS equation reduces to the the Gross-Pitaevskii equation for the order parameter, as in the standard description of superfluidity. The conditions under which a phase-only action can be derived in the presence of a long-range interaction to describe the physics of the superconductivity of ``bad metals'' are discussed.
Andreev reflection off a fluctuating superconductor in the absence of equilibrium
P. Devillard,R. Guyon,T. Martin,I. Safi,B. K. Chakraverty
Physics , 2002, DOI: 10.1103/PhysRevB.66.165413
Abstract: Andreev reflection between a normal metal and a superconductor whose order parameter exhibits quantum phase fluctuations is examined. The approach chosen is non perturbative in the tunneling Hamiltonian and enables to probe the whole range of voltage biases up to the gap amplitude. Results are illustrated using the one-dimensional Josephson- Junction Array model previously introduced in the linear response regime. Phase fluctuations are shown to affect the differential conductance and are compared to the result of Blonder, Tinkham and Klapwijk for a rigid BCS superconductor. The noise spectrum of the Andreev current is also obtained and its second derivative with respect to frequency is proposed as a direct tool to analyze the phase fluctuations.
Low 25(OH) vitamin D concentrations in international UK track and field athletes
N Pollock, P Dijkstra, R Chakraverty, B Hamilton
South African Journal of Sports Medicine , 2012,
Abstract: Objective. While it is recognised that vitamin D deficiency is common in the general population, there have been no studies in elite athletes in the UK. This observational study aimed to assess the 25 hydroxy-vitamin D (25(OH)D) status of elite athletes on the Great Britain track and field team. Methods. A cross-sectional observational study was performed by analysing blood results from elite athletes on the British athletics team (N=63; mean ± standard deviation (SD) age 24.9±4.2 years). Athletes on the elite programme were offered blood tests through the winter and summer of 2009 and were eligible for inclusion in the study. Results. Nineteen per cent (n=12) of athletes in the current study can be classified as 25(OH)D deficient (<20 mcg/l), while a further 29% (n=18) can be classified as having insufficient serum 25(OH)D levels (20 - 30 mcg/l). Female sex (insufficent and deficient OH(D) prevalence 58%, n=18) and dark skin (prevalence 65%, n=20) were found to be independent predictors of serum 25(OH)D levels of <30 mcg/l. Conclusion. This study reveals a notable prevalence of low serum 25(OH)D levels in elite athletes and subsequent management of deficient athletes is likely to be of importance for athlete health. The impact of these results on athletic performance remains to be determined, and clinical trials to assess performance, particularly muscular performance, following correction of 25(OH)D status in deficient athletes are required.
Effective Theory Approach to SUSY Hadron Spectroscopy
D. Chakraverty,T. De,B. Dutta-Roy,A. Kundu
Physics , 1995, DOI: 10.1103/PhysRevD.53.5293
Abstract: Supersymmetric hadrons of the type $\tg\tg$, $\tg g$ and $\tg q\bar q$ could exist depending on the masses of the gluino and the squarks being in an appropriate range of values. We find the energy levels of $\tg g$ and $\tg q\bar q$ bound states (where $q$ denotes a light quark, $u$, $d$ or $s$), as well as the strong interaction transition rates among them, using a Heavy Gluino Effective Theory, much in the same spirit as the well-known Heavy Quark Effective Theory. The results are obtained with greater ease and elegance in comparison to other approaches.
The power of the electronic thesis
Anita Chakraverty
Genome Biology , 2001, DOI: 10.1186/gb-spotlight-20010402-01
Abstract: Electronic theses and dissertations (ETDs) consist of masters or doctoral research work that is submitted or archived electronically by an institution, either on an internal network or on the web. Although most ETDs are currently formatted as straight text documents, the electronic medium offers enormous flexibility and can support multimedia, animation and interactive features.Representatives from more than 15 nations attended the symposium. Many of those visiting from developing countries were sponsored by UNESCO, which is currently setting up international guidelines for ETDs via the Digital Media Institute. UNESCO is committed to the free flow of scientific information and promoting the internet as a tool for disseminating scientific knowledge. The UNESCO guide aims to standardize formats and archiving of ETDs internationally and to facilitate the setting up of ETD systems at individual institutions. "ETDs are crucial for creating an open and democratic information society," said Axel Plathe, UNESCO representative at the conference.Institutions in the US are pioneering the use of ETDs and several have been encouraging their students to submit electronically for a number of years. Virginia Tech was the first university to set up an ETD service and now has more than 3000 theses stored and searchable via the internet. In 1997, it made electronic submission of theses from masters and doctoral candidates mandatory. Many of the university representatives attending the conference were, however, still initiating schemes or in their first year of accepting voluntary ETD submissions. For these attendees, there were still issues of copyright, access and submission procedures to address.The NDLTD (Networked Digital Library of Theses and Dissertations) - the international consortium that organised the conference - is now hoping to develop a central website that will enable visitors to browse through ETDs from any university that makes its research available online. The NDLTD
PREPARATION AND EVALUATION OF SUSTAINED RELEASE MICROSPHERE OF NORFLOXACIN USING SODIUM ALGINATE
Raja Chakraverty
International Journal of Pharmaceutical Sciences and Research , 2012,
Abstract: Oral controlled drug delivery systems represent the most popular form of sustained drug delivery systems for the obvious advantages of oral route of drug administration. Such systems release the drug with constant or variable release rates. The oral controlled release systems shows a typical pattern of drug release in which the drug concentration is maintained in the therapeutic window for a prolonged period of time (sustained release), thereby ensuring sustained therapeutic action. They are used as single dosage form. Present work involves preparation and evaluation of sustained release of microspheres of Norfloxacin employing sodium alginate as natural polymer. The technique employed for microencapsulation of the drug is ionotropic gelation.
A phenomenological model of the Resonance peak in High Tc Superconductors
Benoy Chakraverty
Physics , 2005,
Abstract: A notable aspect of high-temperature superconductivity in the copper oxides is the unconventional nature of the underlying paired-electron states. The appearance of a resonance peak, observed in inelastic neutron spectroscopy in the superconducting state of the High Tc cuprates, its apparent linear correlation with the critical superconducting temperature of each of the compounds and its disappearance in the normal state are rather intriguing. It may well be that this peak is the signature of the singlet to triplet excitation, and is an unique characteristic of a d-wave superconductor. We develop a simple criterion for the resonance peak which is based on the concept of twist sti ness and its disappearance at T=Tc.
Is Brain in a Superfluid State? Physics of Consciousness
Benoy Chakraverty
Physics , 2010,
Abstract: The article "Physics of Consciousness" treats mind as an abstract Hilbert space with a set of orthogonal base vectors to describe information like particles, which are considered to be the elementary excitation of a quantum field. A non-Hermitian operator of Self is introduced to create these information like particles which in turn will constitute a coherent information field. The non - zero average of this self operator is shown to constitute our basic I. Awareness and consciousness is described very simply as a response function of these operators to external world. We show with a very simple neural model how a baby less than two years old develop self-awareness as the neural connectivity achieves a critical value. The all-important I is the basic cognitive order parameter of each human brain and is a result of thermodynamic phase transition from a chaotic disordered state to a symmetry broken coherent ordered state, very akin to physics of superfluidity.
A Compact Model of Silicon-Based Nanowire Field Effect Transistor for Circuit Simulation and Design
Mayank Chakraverty
Computer Science , 2014,
Abstract: As the conventional silicon metal-oxide-semiconductor field-effect transistor (MOSFET) approaches its scaling limits; many novel device structures are being extensively explored. Among them, the silicon nanowire transistor (SNWT) has attracted broad attention. To understand device physics in depth and to assess the performance limits of SNWTs, simulation is becoming increasingly important. The objectives of this work are: 1) to theoretically explore the essential physics of SNWTs (e.g., electrostatics, transport and band structure) by performing computer-based simulations, and 2) to assess the performance limits and scaling potentials of SNWTs and to address the SNWT design issues. The computer based simulations carried out are essentially based on DFT using NEGF formalism. A silicon nanowire has been modeled as PN diode (Zener Diode), PIN diode, PIP & NIN diode configurations by selectively doping the nanowire and simulated by biasing one end of the nanowire to ground and sweeping the other end of the nanowire from -1 V to 1 V to obtain the electrical characteristics of the respective diodes. In order to determine the effectiveness of the modeled diodes in silicon nanowire, the same diodes have been modeled using a germanium nanowire by selective doping and simulated in the same manner to obtain the electrical characteristics of the germanium nanowire based diodes which has been used as a reference to analyze the characteristics obtained using silicon nanowire. The modeled diodes are extremely small in dimension when compared to the conventional bulk silicon and germanium based diodes. This work is followed by modeling and simulation of a gate all around nanowire field effect transistor using two different gate dielectrics, followed by temperature dependence of the nanowire FET characteristics and the off state current and conductance variation using the two dielectrics.
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