1,629 research outputs found
Strong-randomness infinite-coupling phase in a random quantum spin chain
We study the ground-state phase diagram of the Ashkin-Teller random quantum
spin chain by means of a generalization of the strong-disorder renormalization
group. In addition to the conventional paramagnetic and ferromagnetic (Baxter)
phases, we find a partially ordered phase characterized by strong randomness
and infinite coupling between the colors. This unusual phase acts, at the same
time, as a Griffiths phase for two distinct quantum phase transitions both of
which are of infinite-randomness type. We also investigate the quantum
multi-critical point that separates the two-phase and three-phase regions; and
we discuss generalizations of our results to higher dimensions and other
systems.Comment: 9 pages, 6 eps figures, final version as publishe
Infinite randomness and quantum Griffiths effects in a classical system: the randomly layered Heisenberg magnet
We investigate the phase transition in a three-dimensional classical
Heisenberg magnet with planar defects, i.e., disorder perfectly correlated in
two dimensions. By applying a strong-disorder renormalization group, we show
that the critical point has exotic infinite-randomness character. It is
accompanied by strong power-law Griffiths singularities. We compute various
thermodynamic observables paying particular attention to finite-size effects
relevant for an experimental verification of our theory. We also study the
critical dynamics within a Langevin equation approach and find it extremely
slow. At the critical point, the autocorrelation function decays only
logarithmically with time while it follows a nonuniversal power-law in the
Griffiths phase.Comment: 10 pages, 2 eps figures included, final version as published
Emerging criticality in the disordered three-color Ashkin-Teller model
We study the effects of quenched disorder on the first-order phase transition
in the two-dimensional three-color Ashkin-Teller model by means of large-scale
Monte Carlo simulations. We demonstrate that the first-order phase transition
is rounded by the disorder and turns into a continuous one. Using a careful
finite-size-scaling analysis, we provide strong evidence for the emerging
critical behavior of the disordered Ashkin-Teller model to be in the clean
two-dimensional Ising universality class, accompanied by universal logarithmic
corrections. This agrees with perturbative renormalization-group predictions by
Cardy. As a byproduct, we also provide support for the strong-universality
scenario for the critical behavior of the two-dimensional disordered Ising
model. We discuss consequences of our results for the classification of
disordered phase transitions as well as generalizations to other systems.Comment: 18 pages, 18 eps figures included, final version as publishe
Distinct Roles for F-BAR Proteins Cdc15p and Bzz1p in Actin Polymerization at Sites of Endocytosis in Fission Yeast
SummaryBackgroundGenetic analyses of budding and fission yeast identified >50 proteins that assemble at sites of clathrin-mediated endocytosis in structures called actin patches. These proteins include clathrin, clathrin-interacting proteins, actin binding proteins, and peripheral membrane proteins such as F-BAR proteins. Many questions remain regarding the interactions of these proteins, particularly the participation of F-BAR proteins in the assembly of actin filaments.ResultsOur microscopic and genetic interaction experiments on fission yeast show that F-BAR proteins Cdc15p and Bzz1p accumulate in two distinct zones on invaginating membrane tubules and interact with Myo1p and Wsp1p, nucleation-promoting factors for Arp2/3 complex. The two F-BAR proteins peak prior to movement of the actin patch and their accumulation in actin patches depends on the nucleation-promoting factors. At their peak local concentrations, we estimated the stoichiometries of the proteins in actin patches to be one Bzz1p per two Wsp1p and one Cdc15p per Myo1p. Purified Bzz1p has two SH3 domains that interact with Wsp1p and stimulate actin polymerization by Arp2/3 complex. Cells lacking either Cdc15p or Bzz1p assemble 3- to 5-fold less actin in patches (in spite of normal levels of Wsp1p, Myo1p, and Arp2/3 complex), and patches move shorter distances from the plasma membrane.ConclusionWe propose that during clathrin-mediated endocytosis, F-BAR proteins interact with nucleation-promoting factors to stimulate Arp2/3 complex in two different zones along the invaginating tubule. We further propose that polymerization of actin filaments in these two zones contributes to membrane scission
Tuning a random field mechanism in a frustrated magnet
We study the influence of spinless impurities on a frustrated magnet
featuring a spin-density wave (stripe) phase by means of Monte Carlo
simulations. We demonstrate that the interplay between the impurities and an
order parameter that breaks a real-space symmetry triggers the emergence of a
random-field mechanism which destroys the stripe-ordered phase. Importantly,
the strength of the emerging random fields can be tuned by the repulsion
between the impurity atoms; they vanish for perfect anticorrelations between
neighboring impurities. This provides a novel way of controlling the phase
diagram of a many-particle system. In addition, we also investigate the effects
of the impurities on the character of the phase transitions between the
stripe-ordered, ferromagnetic, and paramagnetic phases.Comment: 5 + epsilon pages + 5 pages supplemental materia
Tuning a Random-Field Mechanism in a Frustrated Magnet
We study the influence of spinless impurities on a frustrated magnet featuring a spin-density wave (stripe) phase by means of Monte Carlo simulations. We demonstrate that the interplay between the impurities and an order parameter that breaks a real-space symmetry triggers the emergence of a random-field mechanism which destroys the stripe-ordered phase. Importantly, the strength of the emerging random fields can be tuned by the repulsion between the impurity atoms; they vanish for perfect anticorrelations between neighboring impurities. This provides a way of controlling the phase diagram of a many-particle system. In addition, we also investigate the effects of the impurities on the character of the phase transitions between the stripe-ordered, ferromagnetic, and paramagnetic phases
Cutting remains from Fish Cutting Centres - A feed source for fish farming in estuaries of Karnataka
Demonstration of small scale cage culture of
finfishes in coastal waters initiated by Mangalore
Research Centre of ICAR- CMFRI during 2008- 2009
period has resulted in large scale adoption of the
technology (Fig.1). The fish production through
finfish culture in small cages in Uppunda village of
Udupi district in Karnataka increased from an
estimated 1.2 tonnes (t) during the 2009-10 period
to 14 t in 2013-14. The success of cage farming in
estuarine areas which was launched as a pilot
project in Uppunda village of Udupi district has
extended to other estuaries
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