372 research outputs found
Utilization of wetland ecosystem through fish-crop diversification for enhanced productivity and economic stability for fish-farm community of Indian sub-continent
This paper deals with a number of case studies that were undertaken during the last 8- 10 years in utilizing divergent æTalÆwetland ecosystems (deep, semi-deep, temporary in a range of agro-ecological zones like NAZ, OAZ and Coastal Zone of the region) for the development of integrated management programmes using a range of approaches. These included (i) system approach (excavation & renovation, methodological approach), (ii) management (fish-crop management, inter & post-harvest care & processing, marketing), (iii) integrated natural resource management utilizing organic as well inorganic sources, and (iv) low-cost fish-feeds, based on fish-crop diversification. This paper also deals with some endangered indigenous fish species. The unique approach of watershed plans (bherri system), which were formulated for upright production systems, was economically successful. Economic indicators reveal there were comparative advantages of mixed farming systems compared to monoculture, exhibiting less than 2.5 fold gains even for resource poor fish farming families.Fishery management, Resource management
Laser induced breakdown of the magnetic field reversal symmetry in the propagation of unpolarized light
We show how a medium, under the influece of a coherent control field which is
resonant or close to resonance to an appropriate atomic transition, can lead to
very strong asymmetries in the propagation of unpolarized light when the
direction of the magnetic field is reversed. We show how EIT can be used to
mimic effects occuring in natural systems and that EIT can produce very large
asymmetries as we use electric dipole allowed transitions. Using density matrix
calculations we present results for the breakdown of the magnetic field
reversal symmetry for two different atomic configurations.Comment: RevTex, 6 pages, 10 figures, Two Column format, submitted to Phys.
Rev.
Proteinlike behavior of a spin system near the transition between ferromagnet and spin glass
A simple spin system is studied as an analog for proteins. We investigate how
the introduction of randomness and frustration into the system effects the
designability and stability of ground state configurations. We observe that the
spin system exhibits protein-like behavior in the vicinity of the transition
between ferromagnet and spin glass.
Our results illuminate some guiding principles in protein evolution.Comment: 12 pages, 4 figure
The order of the metal to superconductor transition
We present results from large-scale Monte Carlo simulations on the full
Ginzburg-Landau (GL) model, including fluctuations in the amplitude and the
phase of the matter-field, as well as fluctuations of the non-compact
gauge-field of the theory. {}From this we obtain a precise critical value of
the GL parameter \kct separating a first order metal to superconductor
transition from a second order one, \kct = (0.76\pm 0.04)/\sqrt{2}. This
agrees surprisingly well with earlier analytical results based on a disorder
theory of the superconductor to metal transition, where the value
\kct=0.798/\sqrt{2} was obtained. To achieve this, we have done careful
infinite volume and continuum limit extrapolations. In addition we offer a
novel interpretation of \kct, namely that it is also the value separating
\typeI and \typeII behaviour.<Comment: Minor corrections, present version accepted for publication in PR
Diffusion with rearranging traps
A model for diffusion on a cubic lattice with a random distribution of traps
is developed. The traps are redistributed at certain time intervals. Such
models are useful for describing systems showing dynamic disorder, such as
ion-conducting polymers. In the present model the traps are infinite, unlike an
earlier version with finite traps, this model has a percolation threshold. For
the infinite trap version a simple analytical calculation is possible and the
results agree qualitatively with simulation.Comment: Latex, five figure
Superconducting Coherence and the Helicity Modulus in Vortex Line Models
We show how commonly used models for vortex lines in three dimensional
superconductors can be modified to include k=0 excitations. We construct a
formula for the k=0 helicity modulus in terms of fluctuations in the projected
area of vortex loops. This gives a convenient criterion for the presence of
superconducting coherence. We also present Monte Carlo simulations of a
continuum vortex line model for the melting of the Abrikosov vortex lattice in
pure YBCO.Comment: 4 pages RevTeX, 2 eps figures included using eps
Critical behavior of Ginzburg-Landau model coupled to massless Dirac fermions
We point out interesting effects of additional massless Dirac fermions with
N_F colors upon the critical behavior of the Ginzburg-Landau model. For
increasing N_F, the model is driven into the type II regime of
superconductivity. The critical exponents are given as a function of N_F.Comment: RevTex4, 4 pages, 1 figure; author information and latest update to
this paper at http://www.physik.fu-berlin.de/~kleinert/institution.html;
version 2: new references and comments on chiral symmetry breaking adde
Vortex-line liquid phases: Longitudinal superconductivity in the lattice London model
We study the vortex-line lattice and liquid phases of a clean type-II
superconductor by means of Monte Carlo simulations of the lattice London model.
Motivated by a recent controversy regarding the presence, within this model, of
a vortex-liquid regime with longitudinal superconducting coherence over long
length scales, we directly compare two different ways to calculate the
longitudinal coherence. For an isotropic superconductor, we interpret our
results in terms of a temperature regime within the liquid phase in which
longitudinal superconducting coherence extends over length scales larger than
the system thickness studied. We note that this regime disappears in the
moderately anisotropic case due to a proliferation, close to the flux-line
lattice melting temperature, of vortex loops between the layers.Comment: 8 pages, Revtex, with eps figures. To appear in Phys. Rev.
Vortex Interactions and Thermally Induced Crossover from Type-I to Type-II Superconductivity
We have computed the effective interaction between vortices in the
Ginzburg-Landau model from large-scale Monte-Carlo simulations, taking thermal
fluctuations of matter fields and gauge fields fully into account close to the
critical temperature. We find a change, in the form of a crossover, from
attractive to repulsive effective vortex interactions in an intermediate range
of Ginzburg-Landau parameters upon increasing
the temperature in the superconducting state. This corresponds to a thermally
induced crossover from \typeI to \typeII superconductivity around a temperature
, which we map out in the vicinity of the
metal-to-superconductor transition. In order to see this crossover, it is
essential to include amplitude fluctuations of the matter field, in addition to
phase-fluctuations and gauge-field fluctuations. We present a simple physical
picture of the crossover, and relate it to observations in \metal{Ta} and
\metal{Nb} elemental superconductors which have low-temperature values of
in the relevant range.Comment: 9 pages, 6 figures. Accepted for publication in Physical Review
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