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

Couplings between Chern-Simons gravities and 2p-branes

The interaction between Chern-Simons (CS) theories and localized external sources (2p-branes) is analyzed. This interaction generalizes the minimal coupling between a point charge (0-brane) and a gauge connection. The external currents that define the 2p-branes are covariantly constant (D-2p-1)-forms coupled to (2p-1) CS forms. The general expression for the sources --charged with respect to the corresponding gauge algebra-- is presented, focusing on two special cases: 0-branes and (D-3)-branes. In any dimension, 0-branes are constructed as topological defects produced by a surface deficit of (D-2)-sphere in AdS space, and they are not constant curvature spaces for D>3. They correspond to dimensionally continued black holes with negative mass. On the other hand, in the case of CS (super) gravities, the (D-3)-branes are naked conical singularities (topological defects) obtained by identification of points with a Killing vector. In 2+1 dimensions, extremal spinning branes of this type are BPS states. Stable (D-3)-branes are shown to exist also in higher dimensions, as well. Classical field equations are also discussed and in the presence of sources there is a large number of inequivalent and disconnected sectors in solution space.Comment: 29 pages, no figures; version accepted in PRD; extended introduction and several references added; some sections have been reorganized and several minor corrections mad

GPS Based Design of the Local Clock Control System based on the Optimally Unbiased Moving Average Filter

In this paper we made the simulation steering of the local clock t'ime errors with simple moving average (MA), optimally unbiased moving average (OMA), the two and three-state Kalman filters. The references signal (precise time) was suministred by GPS. In this task we have two important activities, estimating and the error control, so the,principal parameter in this study is the root mean square error (RMSE) of steering. When steering the GPS-based time error in the local clock with four filters, we found out that, of the filter with the same time constant, the optimally unbiased MA filter desmostred the steering error between the two and three state Kalman filter.Universidad de Guanajuat

Synthesis of hierarchically structured Y2O3:Eu3*@ Ag nanocomposites with plasmon enhanced luminesencence via ultrasonic spray pyrolysis

Y2O3:Eu3+@Ag nanocomposites have been successfully synthesized by ultrasonic spray pyrolysis (USP) and examined to reveal effects of surface plasmon resonance, associated to silver nanoparticles, to the luminescence efficiency of Y2O3: Eu3+ red-emitting phosphors. Various Ag concentrations (1, 2.5 and 5 wt. %) and heat-treatment regimes (as prepared, 2h, 12h) were applied to understand how size and distribution of the Ag nanoparticles affect the luminescence efficiency. Samples were characterized by TEM, XRPD and STEM to evaluate crystal structure and distribution of Eu3+ in Y2O3 matrix. In terms of Y, O and Eu ions, uniform distribution was observed in the particles interior, while the Ag is present at the particles surface showing that USP is feasible for synthesis of hierarchically organized Y2O3:Eu3+@Ag. In the case of higher Ag concentration, a deviation from uniform and finely distributed Ag nanoparticles on Y2O3:Eu3+ surface was detected having detrimental effect to the plasmon enhanced luminescence. Regardless from silver concentrations, all heat treated samples exhibited superior luminescence with respect to asprepared ones, while decrease of luminescence efficiency was detected with the increase of Ag concentration. The most intense red luminescence at 612 nm which is due Eu3+ 5D0→7F2 transition was observed in Y2O3:Eu3+@Ag system for sample with 1wt% Ag, annealed for 12 hours

Characterization of YAG:Ce powders thermal treated at different temperatures

Poster presented at the First International Meeting on Applied Physics - Applied Physics 2003, Badajoz, Spain

Study of the kinetics of antibodies titres against viral pathogens and detection of rotavirus and parainfluenza 3 infections in captive crias of guanacos (Lama guanicoe)

A longitudinal study was conducted to investigate the presence of antibodies (Ab) to Rotavirus (RV), Parainfluenza-3 virus (PI-3), Bovine Herpesvirus-1 (BoHV-1), Bovine Viral Diarrhoea virus (BVDV-1) and Bluetongue virus (BTV) in eleven guanaco's crias (chulengos) relocated from Rio Negro to Buenos Aires Province (Argentina) and reared in captivity for a year in an experimental field. Serum samples were collected periodically to detect the evidence of viral infections. Faecal samples were collected to investigate RV shedding. We detected the evidence of Ab to RV from the beginning of the experience, suggesting the presence of maternal Ab against the virus. RV infection was detected in seven of the eleven chulengos, by seroconversion (4), virus shedding in stools (1) or both (2). In all cases, the RV strain was typed as [P1]G8, the same G/P type combination detected in captive chulengos with acute diarrhoea sampled in Rio Negro, in 2001. In contrast, we could not detect antibodies against PI-3, BoHV-1, BVDV or BT in any of initial samples. No Abs against BoHV-1, BVDV or BTV were detected in the chulengos throughout the study. However, all the chulengos became asymptomatically seropositive to PI-3 by the 7 month after arrival. This study suggest that wild-born guanacos raised in captivity can be relatively susceptible to common livestock viral infections, such as RV and PI-3, which are easily spread among chulengos.Fil: Marcoppido, G.. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de Virología; ArgentinaFil: Olivera, Valeria. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de Patobiología; ArgentinaFil: Bok, Karin. Dirección Nacional de Instituto de Investigación.Administración Nacional de Laboratorios e Institutos de Salud "Dr. Carlos G. Malbrán"; ArgentinaFil: Parreño, Gladys Viviana. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de Virología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Influence of Fertilization System on Wheat Yields in Terms of Global Climate Change

Over the last few decades, wheat production, both in Serbia and worldwide, has been practiced under characteristic agrometeorological conditions. It has generally been affected by specific strongly marked agrometeorological and climate extremes, most notably extreme temperature and drought events during critical periods in the growing season, which mostly had a negative impact on the growth, development and yield of wheat in Central Serbia.This paper presents results and discussion on both the potential effect of climate change on winter wheat yield and the possibility to alleviate it through an appropriately adjusted fertilization system.The present study on the effect of different rates and ratios of NPK fertilizers on grain yield in seven winter wheat cultivars under different (dry and “normal“) conditions during the year was conducted in a long-term field experiment at the Small Grains Research Centre in Kragujevac over a period of seven years (2000/01-2006/07).Depending on the fertilization treatment, the average yield reduction in dry years showed 50% variation relative to “normal” years. The highest reduction in grain yield and other productive traits of wheat in dry years was observed in the treatment involving nitrogen nutrition, particularly lower application rates. As compared to the non-treated control, the use of complete NPK fertilization having an increased amount of phosphorus resulted in the lowest yield reduction during the dry years that were unfavorable for winter wheat production. The average grain yield reduction in dry years was lowest in wheat cultivar Matica and highest in Kg-100, respectively

The Low Temperature Aerosol Synthesis of YAG:Ce3+ Nanostructures: comparative Study of XRPD Microstructural Parameters

Poster presented at the 8th Conference of Yugoslav Materials Research Society – YUCOMAT 2006, Herceg Novi, Montenegro, September 4-8, 200

Ethylenediaminetetraacetic acid (EDTA) assisted hydro/solvothermal synthesis of up-converting rare earth fluorides

Over the last decade, a lot of effort was directed toward developing of the representative methodologies for the preparation of up-converting (UC) particles which exhibit a unique narrow visible emission when excited by lower-energy photon radiation. This work presents the impact of different processing parameters on structural, morphological and optical properties of up-converting (UC) rare earth fluorides obtained by hydro/solvothermal synthesis. Monodisperse NaYF4:Yb3+/Er3+ particles with different morphology, size and crystal phase were synthesized with a help of ethylenediaminetetraacetic acid (EDTA) through adjusting the precursor concentration, degree of doping, polarity of solvent and reaction time. They are characterized by X-ray powder diffraction, scanning and transmission electron microscopy, energy dispersive X-ray and Furrier transform infrared spectroscopy, as well as photoluminescence measurements. It was shown that particle size and phase composition are dependent on the precursor concentration, type of solvent and doping degree, while the cubic to hexagonal transformation of NaYF4:Yb3+/Er3+ phase is affected by the reaction time. The crystallization of the orthorhombic YF3:Yb3+/Er3+ phase is established either after decreasing concentration of dopants or increasing polarity of solvents. All of the synthesized particles exhibited efficient up-conversion emission which can be tuned from pure green to the yellowish-orange through control of particles size and phase composition

Synthesis of ZnO:Ag core-shell nanoparticles with enhanced photocatalytic properties by single - and two-steps USP

Synthesis of ZnO:Ag core-shell nanoparticles were performed by ultrasonic spray pyrolysis (USP) from the corresponding nitrate solutions. Varying relative concentrations of Ag and ZnO precursors and two different equipment installation, allowing either common (single-step) or separate precipitation (two-steps) of Ag and ZnO, were examined in terms of their effect on final microstructure and photocatalytic properties using X-ray powder diffraction (XRPD), scanning and transmission electron microscopy (SEM, TEM, HRTEM), UV-Vis spectroscopy and photocatalytic tests. Formation of phase-pure ZnO:Ag core- shell like particles where ZnO secondary submicron sized particles formed by primary crystals with the size of 5-20 nm were confirmed by TEM analyses. Structural analyses revealed variations in silver distribution and morphology within ZnO core depending on experimental conditions. Samples with fine and uniform silver distribution on ZnO surface display a strong silver-induced enhancement of photocatalytic performance and exhibits a significantly improved photocatalytic activity in the degradation of methyl blue (MB) than that of other noble metal free ZnO systems. Photocatalytic analyses (all samples reached > 45% MB degradation) confirm the all synthesized ZnO:Ag USP systems viability for environmental applications. The best result (93% of dye elimination) is obtained for sample exhibiting maximum available surface, which strongly depends on particle morphology, size and distribution. Moreover, all samples synthesized by single-step USP revealed higher dye elimination with respect to ones with two- steps USP due to favored distribution of silver in microstructure