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