Order and disorder in the triangular-lattice t-J-V model at 2/3 electron density

Motivated by the recent discovery of superconductivity in Na$_x$CoO$_2\cdot y$H$_2$O, we use series expansion methods and cluster mean-field theory to study spontaneous charge order, Neel order, ferromagnetic order, dimer order and phase-separation in the triangular-lattice t-J-V model at 2/3 electron density. We find that for t<0, the charge ordered state, with electrons preferentially occupying a honeycomb lattice, is very robust. Quite surprisingly, hopping to the third sublattice can even enhance Neel order. At large negative t and small V, the Nagaoka ferromagnetic state is obtained. For large positive t, charge and Neel order vanish below a critical V, giving rise to an itinerant antiferromagnetically correlated state.Comment: 4 pages, 5 figure

The global burden of neonatal hypothermia: systematic review of a major challenge for newborn survival

BACKGROUND: To provide evidence on the global epidemiological situation of neonatal hypothermia and to provide recommendations for future policy and research directions. METHODS: Using PubMed as our principal electronic reference library, we searched studies for prevalence and risk factor data on neonatal hypothermia in resource-limited environments globally. Studies specifying study location, setting (hospital or community based), sample size, case definition of body temperature for hypothermia, temperature measurement method, and point estimates for hypothermia prevalence were eligible for inclusion. RESULTS: Hypothermia is common in infants born at hospitals (prevalence range, 32% to 85%) and homes (prevalence range, 11% to 92%), even in tropical environments. The lack of thermal protection is still an underappreciated major challenge for newborn survival in developing countries. Although hypothermia is rarely a direct cause of death, it contributes to a substantial proportion of neonatal mortality globally, mostly as a comorbidity of severe neonatal infections, preterm birth, and asphyxia. Thresholds for the definition of hypothermia vary, and data on its prevalence in neonates is scarce, particularly on a community level in Africa. CONCLUSIONS: A standardized approach to the collection and analysis of hypothermia data in existing newborn programs and studies is needed to inform policy and program planners on optimal thermal protection interventions. Thermoprotective behavior changes such as skin-to-skin care or the use of appropriate devices have not yet been scaled up globally. The introduction of simple hypothermia prevention messages and interventions into evidence-based, cost-effective packages for maternal and newborn care has promising potential to decrease the heavy global burden of newborn deaths attributable to severe infections, prematurity, and asphyxia. Because preventing and treating newborn hypothermia in health institutions and communities is relatively easy, addressing this widespread challenge might play a substantial role in reaching Millennium Development Goal 4, a reduction of child mortality

Density Matrix Renormalisation Group Approach to the Massive Schwinger Model

The massive Schwinger model is studied, using a density matrix renormalisation group approach to the staggered lattice Hamiltonian version of the model. Lattice sizes up to 256 sites are calculated, and the estimates in the continuum limit are almost two orders of magnitude more accurate than previous calculations. Coleman's picture of `half-asymptotic' particles at background field theta = pi is confirmed. The predicted phase transition at finite fermion mass (m/g) is accurately located, and demonstrated to belong in the 2D Ising universality class.Comment: 38 pages, 18 figures, submitted to PR

The relationship of childhood adversity with diurnal cortisol patterns and C-reactive protein at 60-64 years of age in the 1946 National Survey of Health and Development

Background: Early life adversity is increasingly prevalent and associated with greater morbidity and mortality. It is hypothesised that the link between psychosocial early life adversity and poor health in adulthood is due to abnormal hypothalamic-pituitary-adrenal (HPA) axis functioning (often measured as cortisol patterning) and inflammation (often measured via c-reactive protein (CRP)). This study aimed to investigate the relationship between early life psychosocial adversity and cortisol patterning and CRP at 60-64 years of age. / Methods: The MRC National Survey of Health and Development (NSHD) was used. The analytic “cortisol sample” included 843 individuals and the “CRP sample” included 1,150 individuals. Data on adversity experienced between ages 0-15 years were utilised to compose a cumulative childhood psychosocial early life adversity (ELA) score (0, 1, 2, 3+). CRP and salivary cortisol (waking, 30 min after waking, and evening) were collected at 60-64 years. Associations between the psychosocial ELA score and cortisol outcomes (cortisol awakening response (CAR), diurnal slope (DS), and evening and morning cortisol) were assessed using general linear regression. Tobit regression was used to assess the association between psychosocial ELA score and CRP. Adjustments were made for age at follow-up, sex, childhood maternal education, childhood paternal social class, childhood housing tenure, and birth weight. After testing for sex by ELA score interactions, analyses were repeated stratified by sex for the CRP sample. / Results: In fully adjusted models, individuals who experienced the highest level of childhood psychosocial adversity (3+) had a 24.63 (-41.49, -7.76) % lower waking cortisol and a 7.30 (1.49, 13.12) % lower decline in cortisol across the day compared to those with a psychosocial ELA score of zero. In females, the highest level of childhood psychosocial adversity, compared to the lowest, was associated with 32.61 (2.98, 62.25) % higher CRP at 60-64 years, which attenuated to 20.38% (-9.38, 50.14) upon adjustment for measures of early life socioeconomic position. Conversely, the association between childhood psychosocial adversity and CRP in males was null. / Conclusions: Our results suggest that high-levels of psychosocial adversity in childhood might result in a lower morning cortisol and flatter DS in mid-to-late-adulthood. The finding that adversity was related to higher CRP in females but not males requires replication and further investigation

The Relationship of Early-Life Adversity With Adulthood Weight and Cardiometabolic Health Status in the 1946 National Survey of Health and Development

OBJECTIVE: Evidence linking early-life adversity with an adverse cardiometabolic profile in adulthood is equivocal. This study investigates early-life adversity in relation to weight and cardiometabolic health status at ages 60 to 64 years. METHODS: We included 1059 individuals from the 1946 National Survey of Health and Development. Data on adversity between ages 0 to 15 years were used to create a cumulative childhood psychosocial adversity score and a socioeconomic adversity score. Cardiometabolic and weight/height data collected at ages 60 to 64 years were used to create four groups: metabolically healthy normal weight, metabolically unhealthy normal weight, metabolically healthy overweight/obese, and metabolically unhealthy overweight/obese. Associations between the two exposure scores and weight/health status were examined using multinomial logistic regression, with adjustment for sex and age at the outcome visit. RESULTS: Sixty-two percent of normal-weight individuals were metabolically healthy, whereas only 34% of overweight/obese individuals were metabolically healthy. In a mutually adjusted model including both exposure scores, a psychosocial score of ≥3 (compared with 0) was associated with increased risk of being metabolically unhealthy (compared with healthy) in both normal-weight adults (relative risk = 2.49; 95% confidence interval = 0.87–7.13) and overweight/obese adults (1.87; 0.96–3.61). However, the socioeconomic adversity score was more strongly related to metabolic health status in overweight/obese adults (1.60; 0.98–2.60) than in normal-weight adults (0.95; 0.46–1.96). CONCLUSIONS: Independently of socioeconomic adversity, psychosocial adversity in childhood may be associated with a poor cardiometabolic health profile, in both normal-weight and overweight/obese adults. Childhood adversity might cause obesity via the adoption of unhealthy behaviors. It might also cause poor cardiometabolic health, either via obesity or via another pathway (e.g., altered stress response). Robson et al. found that childhood adversity was associated with poor cardiometabolic health at ages 60 to 64 years, in both normal-weight and overweight/obese adults. Further research is needed to understand the mechanisms by which childhood adversity might affect cardiometabolic health without necessarily increasing body weight

Ground state parameters, finite-size scaling, and low-temperature properties of the two-dimensional S=1/2 XY model

We present high-precision quantum Monte Carlo results for the S=1/2 XY model on a two-dimensional square lattice, in the ground state as well as at finite temperature. The energy, the spin stiffness, the magnetization, and the susceptibility are calculated and extrapolated to the thermodynamic limit. For the ground state, we test a variety of finite-size scaling predictions of effective Lagrangian theory and find good agreement and consistency between the finite-size corrections for different quantities. The low-temperature behavior of the susceptibility and the internal energy is also in good agreement with theoretical predictions.Comment: 6 pages, 8 figure

Series Expansions for three-dimensional QED

Strong-coupling series expansions are calculated for the Hamiltonian version of compact lattice electrodynamics in (2+1) dimensions, with 4-component fermions. Series are calculated for the ground-state energy per site, the chiral condensate, and the masses of `glueball' and positronium states. Comparisons are made with results obtained by other techniques.Comment: 13 figure

Critical Behaviour of Mixed Heisenberg Chains

The critical behaviour of anisotropic Heisenberg models with two kinds of antiferromagnetically exchange-coupled centers are studied numerically by using finite-size calculations and conformal invariance. These models exhibit the interesting property of ferrimagnetism instead of antiferromagnetism. Most of our results are centered in the mixed Heisenberg chain where we have at even (odd) sites a spin-S (S') SU(2) operator interacting with a XXZ like interaction (anisotropy $\Delta$). Our results indicate universal properties for all these chains. The whole phase, $1>\Delta>-1$, where the models change from ferromagnetic $( \Delta=1 )$ to ferrimagnetic $(\Delta=-1)$ behaviour is critical. Along this phase the critical fluctuations are ruled by a c=1 conformal field theory of Gaussian type. The conformal dimensions and critical exponents, along this phase, are calculated by studying these models with several boundary conditions.Comment: 21 pages, standard LaTex, to appear in J.Phys.A:Math.Ge

Direct Calculation of the Spin Stiffness in the J1J_1--J2J_2 Heisenberg Antiferromagnet

We calculate the spin stiffness $\rho_s$ for the frustrated spin-$\frac{1}{2}$ Heisenberg antiferromagnet on a square lattice by exact diagonalizations on finite clusters of up to $36$ sites followed by extrapolations to the thermodynamic limit. For the non-frustrated case, we find that $\rho_s = (0.183\pm 0.003)J_1$, in excellent agreement with the best results obtained by other means. Turning on frustration, the extrapolated stiffness vanishes for $0.4 \lesssim J_2/J_1 \lesssim 0.6$. In this intermediate region, the finite-size scaling works poorly -- an additional sign that their is neither N\'eel nor collinear magnetic order. Using a hydrodynamic relation, and previous results for the transverse susceptibility, we also estimate the spin-wave velocity in the N\'eel-ordered region.Comment: 4 pages, uuencoded compressed ps-file (made with uufiles