Spin-stiffness of anisotropic Heisenberg model on square lattice and possible mechanism for pinning of the electronic liquid crystal direction in YBCO

Using series expansions and spin-wave theory we calculate the spin-stiffness anisotropy $\rho_{sx}/\rho_{sy}$ in Heisenberg models on the square lattice with anisotropic couplings $J_x,J_y$. We find that for the weakly anisotropic spin-half model ($J_x\approx J_y$), $\rho_{sx}/\rho_{sy}$ deviates substantially from the naive estimate $\rho_{sx}/\rho_{sy} \approx J_x/J_y$. We argue that this deviation can be responsible for pinning the electronic liquid crystal direction, a novel effect recently discovered in YBCO. For completeness, we also study the spin-stiffness for arbitrary anisotropy $J_x/J_y$ for spin-half and spin-one models. In the limit of $J_y/J_x\to 0$, when the model reduces to weakly coupled chains, the two show dramatically different behavior. In the spin-one model, the stiffness along the chains goes to zero, implying the onset of Haldane-gap phase, whereas for spin-half the stiffness along the chains increases monotonically from a value of $0.18 J_x$ for $J_y/J_x=1$ towards $0.25 J_x$ for $J_y/J_x\to 0$. Spin-wave theory is extremely accurate for spin-one but breaks down for spin-half presumably due to the onset of topological terms.Comment: 6 pages, 3 figure

The orbifold cohomology of moduli of genus 3 curves

In this work we study the additive orbifold cohomology of the moduli stack of smooth genus g curves. We show that this problem reduces to investigating the rational cohomology of moduli spaces of cyclic covers of curves where the genus of the covering curve is g. Then we work out the case of genus g=3. Furthermore, we determine the part of the orbifold cohomology of the Deligne-Mumford compactification of the moduli space of genus 3 curves that comes from the Zariski closure of the inertia stack of M_3.Comment: 29 pages, 2 figures. Minor changes, to appear in Manuscripta Mat

Magnetic excitations and electronic interactions in Sr2_2CuTeO6_6: a spin-1/2 square lattice Heisenberg antiferromagnet

Sr$_2$CuTeO$_6$ presents an opportunity for exploring low-dimensional magnetism on a square lattice of $S=1/2$ Cu$^{2+}$ ions. We employ ab initio multi-reference configuration interaction calculations to unravel the Cu$^{2+}$ electronic structure and to evaluate exchange interactions in Sr$_2$CuTeO$_6$. The latter results are validated by inelastic neutron scattering using linear spin-wave theory and series-expansion corrections for quantum effects to extract true coupling parameters. Using this methodology, which is quite general, we demonstrate that Sr$_2$CuTeO$_6$ is an almost realization of a nearest-neighbor Heisenberg antiferromagnet but with relatively weak coupling of 7.18(5) meV.Comment: 10 pages, 7 figure

Structural abnormalities of the coronary arterial wall - in addition to luminal narrowing - Affect myocardial blood flow reserve

Multislice CT provides information on coronary luminal narrowing and on the structural abnormalities of the coronary arterial wall using densitometric analysis. We sought to investigate the effects of coronary luminal narrowing, structural abnormalities of the coronary arterial wall, and cardiovascular risk factors on regional and global myocardial blood flow (MBF) reserve. Methods: We studied 68 patients (mean age ± SD, 61 ± 10 y; 41 men, 27 women) with an intermediate probability of coronary artery disease. We measured the severity of coronary stenoses and the fibroadipose, fibromuscular, and calcium components of the coronary arterial wall by 64-row multislice CT coronary angiography. We also measured regional and global MBF reserve by PET using 13N-ammonia as a flow tracer at rest and after dipyridamole. Results: One or more significant coronary stenoses (≥50% luminal narrowing) was present in 32 patients (47%), and nonsignificant stenoses were present in 15 patients (22%). Regional MBF reserve was significantly different in the territories perfused by normal coronary arteries, nonsignificant coronary stenoses, and significant coronary stenoses (P < 0.001). Calcium content was higher in the coronary arteries with significant or nonsignificant stenoses (0.95% ± 1.08% and 0.73% ± 0.93%, respectively) than in those without stenoses (0.11% ± 0.38%, P < 0.001). Significant coronary stenosis (P = 0.047) and calcium content (P = 0.017) were the only independent determinants of impaired regional MBF reserve using multivariate analysis. At multiple logistic regression analysis, the Framingham risk score, an index of global cardiovascular risk burden, was the only significant determinant of global MBF reserve (P = 0.028). Conclusion: Coronary stenoses and coronary calcium content independently affect regional MBF reserve. Framingham risk score is the only significant determinant of global MBF reserve. Copyright © 2011 by the Society of Nuclear Medicine, Inc

On the canonical map of surfaces with q>=6

We carry out an analysis of the canonical system of a minimal complex surface of general type with irregularity q>0. Using this analysis we are able to sharpen in the case q>0 the well known Castelnuovo inequality K^2>=3p_g+q-7. Then we turn to the study of surfaces with p_g=2q-3 and no fibration onto a curve of genus >1. We prove that for q>=6 the canonical map is birational. Combining this result with the analysis of the canonical system, we also prove the inequality: K^2>=7\chi+2. This improves an earlier result of the first and second author [M.Mendes Lopes and R.Pardini, On surfaces with p_g=2q-3, Adv. in Geom. 10 (3) (2010), 549-555].Comment: Dedicated to Fabrizio Catanese on the occasion of his 60th birthday. To appear in the special issue of Science of China Ser.A: Mathematics dedicated to him. V2:some typos have been correcte

Performance of the 2007 WHO Algorithm to diagnose Smear-negative Pulmonary Tuberculosis in a HIV prevalent setting

The 2007 WHO algorithm for diagnosis of smear-negative pulmonary tuberculosis (PTB) including Mycobacterium tuberculosis (MTB) culture was evaluated in a HIV prevalent area of Kenya

Factors associated with Toxoplasma gondii infection in confined farrow-to-finish pig herds in western France: an exploratory study in 60 herds

Background: Infection by Toxoplasma gondii postnatally can occur after ingestion of contaminated meat or water (tissue cysts/oocysts). In Europe, percentage of meat borne infections is estimated between 30 and 63 %, out of which pork makes the most important source. The aim of this study was to (i) investigate the seroprevalence of T. gondii in intensive pig farms from western France; and (ii) identify the risk factors associated with seropositivity. Methods: Data were collected between November 2006 and February 2008 in 60 intensive farrow-to-finish farms, where sera were taken from 3595 fattening pigs, weaned and suckling piglets. Information about three classes of potential seropositivity risk factors were obtained through a questionnaire concerning: (i) breeding characteristics; (ii) farm management; and (iii) husbandry and hygiene. The modified agglutination test (MAT) was used for detection of specific anti T. gondii antibodies in pig sera, starting from 1/6 dilution. Results: The overall proportion of seropositive animals was 6.9 %, but the proportion of herds with at least one positive pig was 100 %. Multivariate logistic mixed model showed an increased seropositivity risk in weaned compared to suckling piglets, and a decreasing risk for mid-sized and large farms. The presence of a Danish entry facility, that clearly separates clean and dirty areas, had a protective effect on T. gondii seropositivity as well. Conclusions: The observed proportion of herds with at least one T. gondii seropositive animal provides further evidence that even in confined conditions of pig breeding, infection occurs, and is common. The highest risk for acquiring T. gondii is at the end of weaning period. Smaller confined pig farms demonstrate higher T. gondii seropositivity levels. This study also showed that Danish entry on farm buildings provides effective protection against T. gondii

A social and ecological assessment of tropical land uses at multiple scales: the Sustainable amazon network

Science has a critical role to play in guiding more sustainable development trajectories. Here, we present the Sustainable Amazon Network (Rede Amazônia Sustentável, RAS): a multidisciplinary research initiative involving more than 30 partner organizations working to assess both social and ecological dimensions of land-use sustainability in eastern Brazilian Amazonia. The research approach adopted by RAS offers three advantages for addressing land-use sustainability problems: (i) the collection of synchronized and co-located ecological and socioeconomic data across broad gradients of past and present human use; (ii) a nested sampling design to aid comparison of ecological and socioeconomic conditions associated with different land uses across local, landscape and regional scales; and (iii) a strong engagement with a wide variety of actors and non-research institutions. Here, we elaborate on these key features, and identify the ways in which RAS can help in highlighting those problems in most urgent need of attention, and in guiding improvements in land-use sustainability in Amazonia and elsewhere in the tropics. We also discuss some of the practical lessons, limitations and realities faced during the development of the RAS initiative so far