194 research outputs found
AntimicrobialâResistant Enterococcus spp. in Wild Avifauna from Central Italy
Bacteria of the genus Enterococcus are opportunistic pathogens, part of the normal intestinal microflora of animals, able to acquire and transfer antimicrobial resistance genes. The aim of this study was to evaluate the possible role of wild avifauna as a source of antimicrobialâresistant enterococci. To assess this purpose, 103 Enterococcus spp. strains were isolated from the feces of wild birds of different species; they were tested for antimicrobial resistance against 21 molecules, vancomycin resistance, and highâlevel aminoglycosides resistance (HLAR). Furthermore, genes responsible for vancomycin, tetracycline, and HLAR were searched. E. faecium was the most frequently detected species (60.20% of isolates), followed by E. faecalis (34.95% of isolates). Overall, 99.02% of the isolated enterococci were classified as multidrugâresistant, with 19.41% extensively drugâresistant, and 2.91% possible pan drug-resistant strains. Most of the isolates were susceptible to amoxicillin/clavulanic acid (77.67%) and ampicillin (75.73%), with only 5.83% of isolates showing an ampicillin MIC â„ 64 mg/L. HLAR was detected in 35.92% of isolates, mainly associated with the genes ant(6)âIa and aac(6âČ)âIeâaph(2âČâ)âIa. Few strains (4.85%) were resistant to vancomycin, and the genes vanA and vanB were not detected. A percentage of 54.37% of isolates showed resistance to tetracycline; tet(M) was the most frequently detected gene in these strains. Wild birds may contribute to the spreading of antimicrobialâresistant enterococci, which can affect other animals and humans. Constant monitoring is essential to face up to the evolving antimicrobial resistance issue, and monitoring programs should include wild avifauna, to
High-Field Specific-Heat and Susceptibility Measurements: Relevance to the Spin-Peierls Phase Diagram and the Validity of a Soliton Picture
We discuss recent high-field specific-heat measurements on the spin-Peierls compound tetrathiafulvalinium bis-cis-(1,2-perfluoromethylethylene-1-2-dithiolato)âgold [TTF-BDT(Au)]. An ordering anomaly can clearly be detected which defines a high-field phase boundary, despite some extraneous structure in the data apparently reflecting experimental limitations. The high-field phase boundary is in good quantitative agreement with the theory of Cross and Fisher. Further, the specific-heat data are in good agreement with earlier ac susceptibility data, the reliability of which as indicators of a phase transition has been somewhat open to doubt because pronounced relaxation effects in the high-field regime result in striking differences between Ïac and Ïdc. Some observations are made concerning the extent of hysteresis associated with the phase boundary between dimerized and high-field phases. Finally, the extensive experimental data are employed in several tests to determine the applicability of recent soliton theories
Field-Dependent Differential Susceptibility Studies on Tetrathiafulvalene-AuS\u3csub\u3e4\u3c/sub\u3eC\u3csub\u3e4\u3c/sub\u3e(CF\u3csub\u3e3\u3c/sub\u3e)\u3csub\u3e4\u3c/sub\u3e: Universal Aspects of the Spin-Peierls Phase Diagram
An applied magnetic field is known to produce novel effects in the phase behavior of magnetoelastic spin-Peierls systems. Hence we report measurements of the differential susceptibility (Ï) and magnetization (M) in fields up to 40 kOe (4 T) on the spin-Peierls compound tetrathiafulvalene (TTF)-AuS4C4(CF3)4 in the temperature region (1.1K \u3c- T \u3c- 4.2K). This range of field and temperature encompasses an interesting phase region, including the zero-field spin-Peierls transition temperature Tc(0)=2.03 K. The measurements of the differential (ac) susceptibility provide a more sensitive probe of the transition behavior than magnetization measurements. The first definitive evidence for significant deviations from mean-field critical behavior appear in these measurements, and the appropriate criteria for determining the precise location of the transitions are thus provided by the thermodynamic theory of λ transitions. Using the new criteria, qualitative and even quantitative agreement is obtained with current theories of the field dependence of spin-Peierls transitions. A novel contour plot of Ïac in the H â T plane is shown to be useful for the delineation of the global phase-transition behavior. An investigation of the role of relaxation effects in Ïac relative to the nature of the phase boundaries is conducted. A major feature is the observation of a striking degree of universality in the phase behavior of three spin-Peierls systems TTF-AuS4C4(CF3)4, TTF-AuS4C4(CF3)4, and methylethylmorpholinium di-tetracyanoquinodimethane [MEM-(TCNQ)2]. hese universal features are preserved through considerable differences in lattice structure and a variation in Tc(0) of a factor of 10
Spin-Peierls transitions in magnetic donor-acceptor compounds of tetrathiafulvalene (TTF) with bisdithiolene metal complexes
The spin-Peierls transition is considered as a progressive spin-lattice dimerization occurring below a transition temperature in a system of one-dimensional antiferromagnetic Heisenberg chains. In the simplest theories, the transition is second order and the ground state is a singlet with a magnetic gap. The historical origins and theoretical development of the concept are examined. Magnetic susceptibility and EPR measurements on the Ï-donor-acceptor compounds TTF·MS4C4(CF3)4 (M=Cu, Au; TTF is tetrathiafulvalene) are reported. These compounds exhibit clearly the characteristics of the spin-Peierls transition in reasonably good agreement with a mean-field theory. The susceptibility of each compound has a broad maximum near 50 K, while the transitions occur at 12 and 2.1 K for M=Cu and Au, respectively. EPR linewidth observations over a broad temperature range are examined. Areas for further experimental and theoretical work are indicated, and a critical comparison is made of related observations on other materials
Observation of a Spin-Peierls Transition in a Heisenberg Antiferromagnetic Linear-Chain System
Magnetic-susceptibility and EPR measurements are reported which provide the first unambiguous evidence for a spin-Peierls transition in a system of linear one-dimensional antiferromagnetic Heisenberg chains. The material studied is TTFCuS4C4(CF3)4 (TFF stands for tetrathiafulvalinium). At 12 K, the spin-lattice system undergoes a second-order phase transition to a singlet ground state
Thermal and magnetic study of exchange in the quasi-1-D molecular compound, TTFâ PtS\u3csub\u3e4\u3c/sub\u3eC\u3csub\u3e4\u3c/sub\u3e(CF\u3csub\u3e3\u3c/sub\u3e)\u3csub\u3e4\u3c/sub\u3e
Single crystalmagnetic susceptibility results from 2.5 K to 270 K and specific heat results from 3 K to 16 K are reported for TTFâ
PtS4C4(CF3)4, (TTF=tetrathiafulvalene). The combined results are analyzed using a simple model which ignores differences between the two types of S=1/2 spin carriers and involves a system of ferromagnetic chains treated ââexactlyââ, with interchain antiferromagnetic interaction evaluated in a mean field approximation. Above an apparent ordering transition at 8 K, the susceptibility is well described by the model irrespective of whether the ferromagnetic exchange is Heisenberg, Ising or intermediate to these. The magnetic contribution to the specific heat is obtained using earlier results for the isostructural Au compound. Comparison with specific heat calculations for the Heisenberg, Ising and intermediate cases successfully narrows the ambiguity to an intermediate anisotropic exchange close to the Heisenberg limit
CAVE Size Matters: Effects of Screen Distance and Parallax on Distance Estimation in Large Immersive Display Setups
International audienceWhen walking within a CAVE-like system, accommodation distance, parallax and angular resolution vary according to the distance between the user and the projection walls which can alter spatial perception. As these systems get bigger, there is a need to assess the main factors influencing spatial perception in order to better design immersive projection systems and virtual reality applications. Such analysis is key for application domains which require the user to explore virtual environments by moving through the physical interaction space. In this article we present two experiments which analyze distance perception when considering the distance towards the projection screens and parallax as main factors. Both experiments were conducted in a large immersive projection system with up to ten meter interaction space. The first experiment showed that both the screen distance and parallax have a strong asymmetric effect on distance judgments. We observed increased underestimation for positive parallax conditions and slight distance overestimation for negative and zero parallax conditions. The second experiment further analyzed the factors contributing to these effects and confirmed the observed effects of the first experiment with a high-resolution projection setup providing twice the angular resolution and improved accommodative stimuli. In conclusion, our results suggest that space is the most important characteristic for distance perception, optimally requiring about 6 to 7-meter distance around the user, and virtual objects with high demands on accurate spatial perception should be displayed at zero or negative parallax
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