Fluctuations around classical solutions for gauge theories in Lagrangian and Hamiltonian approach

We analyze the dynamics of gauge theories and constrained systems in general under small perturbations around a classical solution (background) in both Lagrangian and Hamiltonian formalisms. We prove that a fluctuations theory, described by a quadratic Lagrangian, has the same constraint structure and number of physical degrees of freedom as the original non-perturbed theory, assuming the non-degenerate solution has been chosen. We show that the number of Noether gauge symmetries is the same in both theories, but that the gauge algebra in the fluctuations theory becomes Abelianized. We also show that the fluctuations theory inherits all functionally independent rigid symmetries from the original theory, and that these symmetries are generated by linear or quadratic generators according to whether the original symmetry is preserved by the background, or is broken by it. We illustrate these results with the examples.Comment: 27 pages; non-essential but clarifying changes in Introduction, Sec. 3 and Conclusions; the version to appear in J.Phys.

Inhibition of Escherichia coli chemotaxis by omega-conotoxin, a calcium ion channel blocker

Escherichia coli chemotaxis was inhibited by omega-conotoxin, a calcium ion channel blocker. With Tris-EDTA-permeabilized cells, nanomolar levels of omega-conotoxin inhibited chemotaxis without loss of motility. Cells treated with omega-conotoxin swam with a smooth bias, i.e., tumbling was inhibited

Finite-temperature properties of frustrated classical spins coupled to the lattice

We present extensive Monte Carlo simulations for a classical antiferromagnetic Heisenberg model with both nearest ($J_1$) and next-nearest ($J_2$) exchange couplings on the square lattice coupled to the lattice degrees of freedom. The Ising-like phase transition, that appears for $J_2/J_1>1/2$ in the pure spin model, is strengthened by the spin-lattice coupling, and is accompanied by a lattice deformation from a tetragonal symmetry to an orthorhombic one. Evidences that the universality class of the transition does not change with the inclusion of the spin-lattice coupling are reported. Implications for ${\rm Li_2VOSiO_4}$, the prototype for a layered $J_1{-}J_2$ model in the collinear regime, are also discussed.Comment: 6 pages and 8 figure

Quantum Statistical Relation for black holes in nonlinear electrodynamics coupled to Einstein-Gauss-Bonnet AdS gravity

We consider curvature-squared corrections to Einstein-Hilbert gravity action in the form of Gauss-Bonnet term in D>4 dimensions. In this theory, we study the thermodynamics of charged static black holes with anti-de Sitter (AdS) asymptotics, and whose electric field is described by nonlinear electrodynamics (NED). These objects have received considerable attention in recent literature on gravity/gauge dualities. It is well-known that, within the framework of anti de-Sitter/Conformal Field Theory (AdS/CFT) correspondence, there exists a nonvanishing Casimir contribution to the internal energy of the system, manifested as the vacuum energy for global AdS spacetime in odd dimensions. Because of this reason, we derive a Quantum Statistical Relation directly from the Euclidean action and not from the integration of the First Law of thermodynamics. To this end, we employ a background-independent regularization scheme which consists in the addition to the bulk action of counterterms that depend on both extrinsic and intrinsic curvatures of the boundary (Kounterterm series). This procedure results in a consistent inclusion of the vacuum energy and chemical potential in the thermodynamic description for Einstein-Gauss-Bonnet AdS gravity regardless the explicit form of the NED Lagrangian.Comment: 22 pages, no figures; 3 references and a subsection on Thermodynamic Charges added; Final version for PR

Ising transition driven by frustration in a 2D classical model with SU(2) symmetry

We study the thermal properties of the classical antiferromagnetic Heisenberg model with both nearest ($J_1$) and next-nearest ($J_2$) exchange couplings on the square lattice by extensive Monte Carlo simulations. We show that, for $J_2/J_1 > 1/2$, thermal fluctuations give rise to an effective $Z_2$ symmetry leading to a {\it finite-temperature} phase transition. We provide strong numerical evidence that this transition is in the 2D Ising universality class, and that $T_c\to 0$ with an infinite slope when $J_2/J_1\to 1/2$.Comment: 4 pages with 4 figure

Topological regularization and self-duality in four-dimensional anti-de Sitter gravity

It is shown that the addition of a topological invariant (Gauss-Bonnet term) to the anti-de Sitter (AdS) gravity action in four dimensions recovers the standard regularization given by holographic renormalization procedure. This crucial step makes possible the inclusion of an odd parity invariant (Pontryagin term) whose coupling is fixed by demanding an asymptotic (anti) self-dual condition on the Weyl tensor. This argument allows to find the dual point of the theory where the holographic stress tensor is related to the boundary Cotton tensor as $T_{j}^{i}=\pm (\ell ^{2}/8\pi G)C_{j}^{i}$, which has been observed in recent literature in solitonic solutions and hydrodynamic models. A general procedure to generate the counterterm series for AdS gravity in any even dimension from the corresponding Euler term is also briefly discussed.Comment: 13 pages, no figures; enlarged discussion on self-duality condition for AAdS spacetimes, references added, final version for PR

Conus peptides: biodiversity-based discovery and exogenomics

Journal ArticleThe venoms of the ~700 species of predatory cone snails (genus Conus) are being systematically characterized. Each Conus species contains 100-200 small, highly structured venom peptides (colloquially known as conotoxins), which are synthesized and secreted in a venom duct (for overviews, see Refs. 1-3). The biomedical potential of these small venom peptides is now well established; recent developments are summarized below. Additionally, the genetic basis and biological rationale for Conus peptide diversity is addressed

Conus venom peptides, receptor and ion channel targets, and drug design: 50 million years of neuropharmacology

Journal ArticleThe predatory cone snails (Conus) are among the most successful living marine animals (~500 living species). Each Conus species is a specialist in neuropharmacology, and uses venom to capture prey, to escape from and defend against predators and possibly to deter competitors. An individual cone snail's venom contains a diverse mixture of pharmacological agents, mostly small, structurally constrained peptides (conotoxins). Individual peptides are selectively targeted to a specific isoform of receptor or ion channel

Subfamily Turrinae in the Philippines: the genus Turris (Roding, 1798)

Journal ArticleMarine gastropods of the family Turridae, commonly known as turrids, comprise the largest living group of venomous snails. The taxonomy of this group, however, has been generally neglected. In this work, the genus Tunis (Roding 1798) is discussed. Out of more than 200 different turrid genera, this genus comprises some of the largest and most distinctive living turrid species. The last comprehensive treatment of this particular genus (Powell 1964) identified seven species from the Philippines. In this paper, twelve distinct species of Turns found in the Philippine waters are recognized. Four new species are described: TurrJs dollyae, T. normandavidsoni, T. pagasa and T. totiphyllis. Insufficient material makes it premature to conclude whether three additional distinctive Turn's forms are separate species, or unusual varieties of other species. The taxonomic status of the genus Turns and its relationship to other Turrinae is further discussed. Alternative hypotheses regarding the evolutionary origins of this group are also considered. In addition, two species of Gemmula, with particular affinities for species clades in Turris are noted: one is a new species and one is a renamed homony