Spinons as Composite Fermions

We show that gauge invariant composites in the fermionic realization of $SU(N)_1$ conformal field theory explicitly exhibit the holomorphic factorization of the corresponding WZW primaries. In the $SU(2)_1$ case we show that the holomorphic sector realizes the spinon $Y(sl_2)$ algebra, thus allowing the classification of the chiral Fock space in terms of semionic quasi-particle excitations created by the composite fermions.Comment: SU(N)_1 case included. Final version to appear in Mod. Phys. Lett. A. Latex, 13 page

Toxicity of three comercial tannins to the nuisance invasive species Limnoperna fortunei (Dunker, 1857): implications for control

Adding biocides to water is one strategy to control macrofouling organisms. A natural biocide that helps to prevent/control macrofouling of Limnoperna fortunei (Dunker, 1857) on human installations is one way to minimize environmental impacts of different control strategies. Laboratory tests were carried out to evaluate effects of three commercial tannis preparations (ECOTEC®-UA, ECOTEC®-L and ECOTEC®-MC) on the survival of two life-history stages (larvae and adults) of L. fortunei. In addition tests were performed on two non-target species, a crustacean Daphnia magna and a plant Lactuca sativa, to evaluate effects of these tannins on the aquatic environment. The larvae of L. fortunei were more vulnerable to the concentrations of the three tannins than adults. The two nontarget species were not affected at concentrations that were effective for larvae. These results suggest that these products could be used as biocides to control macrofouling caused by L. fortunei.Fil: Pereyra, Patricio Javier. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Bulus Rossini, Gustavo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Química. Centro de Investigaciones del Medio Ambiente; ArgentinaFil: Darrigran, Gustavo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentin

Explicit connection between conformal field theory and 2+1 Chern-Simons theory

We give explicit field theoretical representations for the observables of 2+1 dimensional Chern-Simons theory in terms of gauge invariant composites of 2D WZW fields. To test our identification we compute some basic Wilson loop correlators reobtaining known results.Comment: 13 pages, Latex file. To appear in Mod.Phys.Lett.

Comparison between disordered quantum spin-1/2 chains

We study the magnetic properties of two types of one-dimensional XX spin-1/2 chains. The first type has only nearest-neighbor interactions which can be either antiferromagnetic or ferromagnetic, and the second type has both nearest-neighbor and next-nearest-neighbor interactions, but only antiferromagnetic in character. We study these systems in the presence of low magnetic fields both analytically and numerically. Comparison of results shows a close relation between the two systems, which is in agreement with results previously found in Heisenberg chains by means of a numerical real-space renormalization-group procedure.Facultad de Ciencias Exacta

Nonuniversal nonequilibrium critical dynamics with disorder

We investigate finite-size scaling aspects of disorder reaction-diffusion processes in one dimension utilizing both numerical and analytical approaches. The former averages the spectrum gap of the associated evolution operators by doubling their degrees of freedom, while the latter uses various techniques to map the equations of motion to a first-passage time process. Both approaches are consistent with nonuniversal dynamic exponents and with stretched exponential scaling forms for particular disorder realizations.Departamento de Físic

Toxicity of Neem’s oil, a potential biocide against the invasive Mussel Limnoperna fortunei (Dunker 1857)

The golden mussel Limnoperna fortunei (Dunker 1857) is one of the most distributed Nuisance Invasive Species (NIS) in South America, and a threat of great concern for the industry of the area. In this study, we carried out toxicity tests made with a Neem’s oil solution with L. fortunei larvae and benthonic adults (7, 13 and 19 ± 1 mm). Tests with non-target species (Daphnia magna, Lactuca sativa and Cnesterodon decemmculatus) were also made with the aim to evaluate the potential toxicity of the Neem’s solution in the environment. The LC100 of Neem’s solution obtained for larvae was 500 µl/L, a value much higher than the one obtained for D. magna and C. decemmaculatus. Thus, we recommend that it should not be used in open waters. However, since the adults were killed in 72 h and the larvae in 24 h, this product can be used in closed systems, in man-made facilities.O Mexilhão dourado Limnoperna fortunei (Dunker 1857) é uma das espécies invasoras melhor distribuídas na América do Sul, sendo motivo de grande preocupação para a indústria local. Neste estudo, nós realizamos ensaios de toxicidade de soluções de Óleo de Neem em larvas e adultos bentônicos de L. fortune (7, 13 e 19 ± 1 mm). Com o objetivo de avaliar o potencial tóxico do Óleo de Neem no ambiente também foram realizados testes com organismos não alvo (Daphnia magna, Lactuca sativa e Cnesterodon decemmculatus). A LC100 da solução de Neem para larvas foi 500 µl/L, um valor muito superior ao obtido para D. magna e C. decemmaculatus. Desta forma, nossa recomendação é que este óleo não deve ser utilizado em ambientes naturais abertos. No entanto, uma vez que os adultos morreram em 72h e as larvas em 24h, este produto pode ser utilizado em sistemas fechados construídos pelo homem.Fil: Pereyra, Patricio Javier. Universidad Nacional de la Plata. Facultad de Cs.naturales y Museo. Catedra de Zoologia de Invertebrados I; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Bulus Rossini, Gustavo Daniel. Universidad Nacional de la Plata. Facultad de Cs.naturales y Museo. Catedra de Zoologia de Invertebrados I; ArgentinaFil: Darrigran, Gustavo Alberto. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Quasiparticle operators with non-Abelian braiding statistics

We study the gauge invariant fermions in the fermion coset representation of $SU(N)_k$ Wess-Zumino-Witten models which create, by construction, the physical excitations (quasiparticles) of the theory. We show that they provide an explicit holomorphic factorization of $SU(N)_k$ Wess-Zumino-Witten primaries and satisfy non-Abelian braiding relations.Comment: 13 pages, no figures, final version to appear in Physics Letters

On the Path Integral Representation for Spin Systems

We propose a classical constrained Hamiltonian theory for the spin. After the Dirac treatment we show that due to the existence of second class constraints the Dirac brackets of the proposed theory represent the commutation relations for the spin. We show that the corresponding partition function, obtained via the Fadeev-Senjanovic procedure, coincides with the one obtained using coherent states. We also evaluate this partition function for the case of a single spin in a magnetic field.Comment: To be published in J.Phys. A: Math. and Gen. Latex file, 12 page

Screening of Sediment Pollution in Tributaries from the Southwestern Coast of the Río de la Plata Estuary

Sediment chemistry and textural properties of transported materials from different surface water basins of South America has recently started to be investigated in relation to provenance materials and pollution sources. The objective of the present study is to analyze and compare pollution burdens in bottom sediments from distal positions of three drainage basins running across urban and industrialized areas and to compare them with more preserved sectors (an upstream position and a water stream with low anthropic influence). The surface bodies of water cross wind and water-reworked substrate materials from the Pampean loess and discharge into the Río de la Plata. Sampling was done in distal positions of the Luján and Riachuelo rivers, Canal Oeste, and Juan Blanco creek, and in Las Flores creek, a tributary of the Luján River. Standardized methods for the determination of granulometric parameters, major matrix components, and organic and inorganic pollutants were employed. Assessment of similarities between rivers by Principal Component Analysis show that distal positions of the Luján and Juan Blanco rivers and the tributary group together, and that Riachuelo and Canal Oeste split from that group by the effect of the components 1 and 2. The last two bodies of water also split from each other mainly by effect of component 2. Variables contributing most to the separation of these two bodies of water between each other are mainly given by heavy metals and sulfide. A similar behavior is also shown by cluster analysis.Recientemente se han iniciado investigaciones sobre la química de sedimentos y las propiedades texturales de materiales transportados de diferentes cuencas hidrológicas de América del Sur, en relación con la proveniencia de los materiales y fuentes de contaminación. El objetivo del presente estudio es el de analizar y comparar cargas de contaminación de sedimentos de fondo extraídos en posiciones distales de tres cuencas que atraviesan zonas urbanizadas e industrializadas, y compararlos con sectores más preservados (un sector aguas arriba y un arroyo con baja influencia antrópica). Los cuerpos de agua superficial atraviesan sustratos compuestos por materiales retrabajados de origen eólico y fluvial pertenecientes al Loess Pampeano y descargan en el Río de la Plata. Los muestreos fueron realizados en posiciones distales del Río Luján, Riachuelo, Canal Oeste y Arroyo Juan Blanco, además del Arroyo Las Flores, tributario del Río Luján. Se emplearon métodos estandarizados para la determinación de parámetros granulométricos, componentes mayoritarios de la matriz, contaminantes orgánicos e inorgánicos. La evaluación de similitudes entre ríos por Análisis de Componentes Principales indica que las posiciones distales de los ríos Luján y Juan Blanco, además del tributario se agrupan entre sí, y que el Riachuelo y Canal Oeste se separan del grupo por efecto de las componentes 1 y 2. A su vez, estos dos últimos cuerpos de agua se separan entre si por efecto de la componente 2. Las variables que contribuyen en mayor medida a la separación de los mismos entre si, son principalmente los metales pesados y los sulfuros. El análisis de clusters muestra un comportamiento similar al mencionado

Long-range interactions in antiferromagnetic quantum spin chains

We study the role of long-range dipolar interactions on antiferromagnetic spin chains, from the classical S → ∞ limit to the deep quantum case S = 1/2 , including a transverse magnetic field. To this end, we combine different techniques such as classical energy minima, classical Monte Carlo, linear spin waves, bosonization, and density matrix renormalization group (DMRG). We find a phase transition from the already reported dipolar ferromagnetic region to an antiferromagnetic region for high enough antiferromagnetic exchange. Thermal and quantum fluctuations destabilize the classical order before reaching magnetic saturation in both phases, and also close to zero field in the antiferromagnetic phase. In the extreme quantum limit S = 1/2 , extensive DMRG computations show that the main phases remain present with transition lines to saturation significatively shifted to lower fields, in agreement with the bosonization analysis. The overall picture maintains a close analogy with the phase diagram of the anisotropic XXZ spin chain in a transverse field.Instituto de Física La Plat