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

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

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

Predictors of burnout among Belgrade veterinary students: A cross-sectional study

Background To the best of our knowledge, studies are lacking on burnout among veterinary students in Serbia, and this is the first study trying to address such a problem. Therefore, the aim of this cross-sectional study was to investigate the predictors of burnout among Belgrade veterinary students. Methods Maslach Burnout Inventory (MBI) and anonymous structured questionnaire addressed to personal data, health habits and stressful influence of educational process were applied among 496 respondents from a total of 1113 students from all grades in spring semester 2014 (response rate 44.6%). Results The prevalence of burnout was 43.3%. High scores on depersonalization and emotional exhaustion scales of MBI were found among 79.4% and 45.0% students, respectively; low personal accomplishment was reported by 50.5% students. Female students reported higher levels of emotional exhaustion compared to males (p = 0.012). A low score on personal achievement scale of MBI was least frequent among the freshmen and most frequent among sophomores (41.1% and 65.3%, respectively; p = 0.986). There were more students with burnout who considered their health as a worsened vs. pre-study period compared to students with no burnout, both concerning mental (61.4% vs. 38.6%) and physical health (61.1% vs. 38.9%; both p lt 0.001). There were more smokers among students who suffered from burnout compared to students who did not (52.0% vs. 48.0%; p = 0.013). A multiple regression revealed an independent dose-response effect of perceived stress at exams on the onset of burnout (moderate stress OR = 2.164 and high stress OR = 3.878). Also, students with the moderate and high stressful effect of communication with teaching staff, as well as, those with worse self-perceived physical and mental health had more than two times higher presence of burnout. Conclusions The prevalence of burnout among Belgrade veterinary students is relatively high. Primary prevention should be focused on the revealed predictors of burnout

Barriers and Enablers for Industry 4.0 in SMEs: A Combined Integration Framework

Although Industry 4.0 was introduced a decade ago, many small and medium-sized enterprises (SMEs) still have not adopted several technologies. Therefore, integrating SMEs along horizontal, vertical, and end-to-end engineering dimensions remains challenging. Due to the importance of SMEs for industrial value chains, understanding SMEs' barriers and respective enablers for Industry 4.0 integration is vital. Applying a multiple case study approach, this paper investigates their experience in Industry 4.0 through technological, organizational, and environmental factors. We aggregate the barriers and respective enablers to Industry 4.0 into an integration framework, which helps to understand Industry 4.0 in SMEs from a broader viewpoint inside these firms, upstream and downstream supply chains, and beyond manufacturing. The findings show that the success of Industry 4.0 integration is more oriented toward operational benefits than strategic advantages and depends upon how these technologies are integrated with various stakeholders across the supply chain, such as original equipment manufacturers, R&D agencies, or sub-suppliers