104 research outputs found
Effect of microbial biofilm in the nursery phase of mrigal, Cirrhinus mrigala
The experiment was conducted for 35 days in nine cement tubs (1 x 1 x 1 m) having 15 cm sandy-loam soil base with three treatments in triplicate, viz., cow dung alone at the rate of 1 kg/tub (T sub(1)), cow dung at 1 kg/tub and feed at 10% body wt/d in two meals (T sub(2)), and cow dung at 1 kg and paddy straw at 200 g/tub (T sub(3)). Both manure and substrate were added on dry weight basis. All the tubs were stocked with 10 fry each mrigal (100,000/ha) of average weight of 0.09 g, seven days after the addition of manure and substrate. The total plate count of bacteria in water did not vary much between the treatments and the mean values were 5.13, 5.49 and 5.85 (CFU x 10 super(4)/ml) in T sub(1) T sub(2) and T sub(3) respectively. The number of phytoplankters and zooplankters in water differed significantly between the treatments. The average number of attached algae (no./cm³) and fish food organisms (no./cm³) recorded on the substrate were 145.28 and 70.67, respectively. The mean final weight of mrigal differed significantly (P < 0.05) between the treatments with T sub(3) registering the highest value of 6.93 g followed by T sub(2) (5.01 g) and T sub(1) (3.37 g). The specific growth rate and growth increment of fish also followed the same trend as that of weight recorded in the different treatments. Survival was higher in T sub(2) (83.33%), followed by T sub(3) (80.00%) and T sub(1) (76.67%). The study demonstrates that by the introduction of biodegradable substrates like paddy straw into the culture systems, significantly higher growth and survival can be obtained in the nursery rearing of mrigal
The Race Between Stars and Quasars in Reionizing Cosmic Hydrogen
The cosmological background of ionizing radiation has been dominated by
quasars once the Universe aged by ~2 billion years. At earlier times (redshifts
z>3), the observed abundance of bright quasars declined sharply, implying that
cosmic hydrogen was reionized by stars instead. Here, we explain the physical
origin of the transition between the dominance of stars and quasars as a
generic feature of structure formation in the concordance LCDM cosmology. At
early times, the fraction of baryons in galaxies grows faster than the maximum
(Eddington-limited) growth rate possible for quasars. As a result, quasars were
not able to catch up with the rapid early growth of stellar mass in their host
galaxies.Comment: 5 pages, 1 figure, Accepted for publication in JCA
The critical amplitude ratio of the susceptibility in the random-site two-dimensional Ising model
We present a new way of probing the universality class of the site-diluted
two-dimensional Ising model. We analyse Monte Carlo data for the magnetic
susceptibility, introducing a new fitting procedure in the critical region
applicable even for a single sample with quenched disorder. This gives us the
possibility to fit simultaneously the critical exponent, the critical amplitude
and the sample dependent pseudo-critical temperature. The critical amplitude
ratio of the magnetic susceptibility is seen to be independent of the
concentration of the empty sites for all investigated values of . At the same time the average effective exponent is found
to vary with the concentration , which may be argued to be due to
logarithmic corrections to the power law of the pure system. This corrections
are canceled in the susceptibility amplitude ratio as predicted by theory. The
central charge of the corresponding field theory was computed and compared well
with the theoretical predictions.Comment: 6 pages, 4 figure
Role of Umklapp Processes in Conductivity of Doped Two-Leg Ladders
Recent conductivity measurements performed on the hole-doped two-leg ladder
material reveal an approximately linear
power law regime in the c-axis DC resistivity as a function of temperature for
. In this work, we employ a bosonic model to argue that umklapp processes
are responsible for this feature and for the high spectral weight in the
optical conductivity which occurs beyond the finite frequency Drude-like peak.
Including quenched disorder in our model allows us to reproduce experimental
conductivity and resistivity curves over a wide range of energies. We also
point out the differences between the effect of umklapp processes in a single
chain and in the two-leg ladder.Comment: 10 pages, 2 figure
Crossover and self-averaging in the two-dimensional site-diluted Ising model
Using the newly proposed probability-changing cluster (PCC) Monte Carlo
algorithm, we simulate the two-dimensional (2D) site-diluted Ising model. Since
we can tune the critical point of each random sample automatically with the PCC
algorithm, we succeed in studying the sample-dependent and the sample
average of physical quantities at each systematically. Using the
finite-size scaling (FSS) analysis for , we discuss the importance of
corrections to FSS both in the strong-dilution and weak-dilution regions. The
critical phenomena of the 2D site-diluted Ising model are shown to be
controlled by the pure fixed point. The crossover from the percolation fixed
point to the pure Ising fixed point with the system size is explicitly
demonstrated by the study of the Binder parameter. We also study the
distribution of critical temperature . Its variance shows the power-law
dependence, , and the estimate of the exponent is consistent
with the prediction of Aharony and Harris [Phys. Rev. Lett. {\bf 77}, 3700
(1996)]. Calculating the relative variance of critical magnetization at the
sample-dependent , we show that the 2D site-diluted Ising model
exhibits weak self-averaging.Comment: 6 pages including 6 eps figures, RevTeX, to appear in Phys. Rev.
Dynamic Scaling in Diluted Systems Phase Transitions: Deactivation trough Thermal Dilution
Activated scaling is confirmed to hold in transverse field induced phase
transitions of randomly diluted Ising systems. Quantum Monte Carlo calculations
have been made not just at the percolation threshold but well bellow and above
it including the Griffiths-McCoy phase. A novel deactivation phenomena in the
Griffiths-McCoy phase is observed using a thermal (in contrast to random)
dilution of the system.Comment: 4 pages, 4 figures, RevTe
Influence of thermal fluctuations on quantum phase transitions in one-dimensional disordered systems: Charge density waves and Luttinger liquids
The low temperature phase diagram of 1D weakly disordered quantum systems
like charge or spin density waves and Luttinger liquids is studied by a
\emph{full finite temperature} renormalization group (RG) calculation. For
vanishing quantum fluctuations this approach is amended by an \emph{exact}
solution in the case of strong disorder and by a mapping onto the \emph{Burgers
equation with noise} in the case of weak disorder, respectively. At \emph{zero}
temperature we reproduce the quantum phase transition between a pinned
(localized) and an unpinned (delocalized) phase for weak and strong quantum
fluctuations, respectively, as found previously by Fukuyama or Giamarchi and
Schulz.
At \emph{finite} temperatures the localization transition is suppressed: the
random potential is wiped out by thermal fluctuations on length scales larger
than the thermal de Broglie wave length of the phason excitations. The
existence of a zero temperature transition is reflected in a rich cross-over
phase diagram of the correlation functions. In particular we find four
different scaling regions: a \emph{classical disordered}, a \emph{quantum
disordered}, a \emph{quantum critical} and a \emph{thermal} region. The results
can be transferred directly to the discussion of the influence of disorder in
superfluids. Finally we extend the RG calculation to the treatment of a
commensurate lattice potential. Applications to related systems are discussed
as well.Comment: 19 pages, 7 figure
Renormalization Group Approach to the Coulomb Pseudopotential for C_{60}
A numerical renormalization group technique recently developed by one of us
is used to analyse the Coulomb pseudopotential () in
for a variety of bare potentials. We find a large reduction in due to
intraball screening alone, leading to an interesting non-monotonic dependence
of on the bare interaction strength.
We find that is positive for physically reasonable bare parameters,
but small enough to make the electron-phonon coupling a viable mechanism for
superconductivity in alkali-doped fullerides. We end with some open problems.Comment: 12 pages, latex, 7 figures available from [email protected]
Competition between quantum-liquid and electron-solid phases in intermediate Landau levels
On the basis of energy calculations we investigate the competition between
quantum-liquid and electron-solid phases in the Landau levels n=1,2, and 3 as a
function of their partial filling factor. Whereas the quantum-liquid phases are
stable only in the vicinity of quantized values 1/(2s+1) of the partial filling
factor, an electron solid in the form of a triangular lattice of clusters with
a few number of electrons (bubble phase) is energetically favorable between
these fillings. This alternation of electron-solid phases, which are insulating
because they are pinned by the residual impurities in the sample, and quantum
liquids displaying the fractional quantum Hall effect explains a recently
observed reentrance of the integral quantum Hall effect in the Landau levels
n=1 and 2. Around half-filling of the last Landau level, a uni-directional
charge density wave (stripe phase) has a lower energy than the bubble phase.Comment: 12 pages, 9 figures; calculation of exact exchange potential for
n=1,2,3 included, energies of electron-solid phases now calculated with the
help of the exact potential, and discussion of approximation include
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