Spectroscopic observations of the planets

Spectroscopic observations of planets showing absorption variations in NH3 and CH4 band

Maternal haemodynamic function differs in pre‐eclampsia when it is associated with a small‐for‐gestational‐age newborn: a prospective cohort study

Objective To describe maternal haemodynamic differences in gestational hypertension with small‐for‐gestational‐age babies (HDP + SGA), gestational hypertension with appropriate‐for‐gestational‐age babies (HDP‐only) and control pregnancies. Design Prospective cohort study. Setting Tertiary Hospital, UK. Population Women with gestational hypertension and healthy pregnant women. Methods Maternal haemodynamic indices were measured using a non‐invasive Ultrasound Cardiac Output Monitor (USCOM‐1A®) and corrected for gestational age and maternal characteristics using device‐specific reference ranges. Main outcome measures Maternal cardiac output, stroke volume, systemic vascular resistance. Results We included 114 HDP + SGA, 202 HDP‐only and 401 control pregnancies at 26–41 weeks of gestation. There was no significant difference in the mean arterial blood pressure (110 versus 107 mmHg, P = 0.445) between the two HDP groups at presentation. Pregnancies complicated by HDP + SGA had significantly lower median heart rate (76 versus 85 bpm versus 83 bpm), lower cardiac output (0.85 versus 0.98 versus 0.97 MoM) and higher systemic vascular resistance (1.4 versus 1.0 versus 1.2 MoM) compared with control and HDP‐only pregnancies, respectively (all P < 0.05). Conclusion Women with HDP + SGA present with more severe haemodynamic dysfunction than HDP‐only. Even HDP‐only pregnancies exhibit impaired haemodynamic indices compared with normal pregnancies, supporting a role of the maternal cardiovascular system in gestational hypertension irrespective of fetal size. Central haemodynamic changes may play a role in the pathogenesis of pre‐eclampsia and should be considered alongside placental aetiology

Evidence for uteroplacental malperfusion in fetuses with major congenital heart defects.

AIMS: Fetuses affected by congenital heart defects (CHD) are considered to be at increased risk of fetal growth restriction and intrauterine demise. Whether these risks are a direct consequence of fetal CHD or a result of associated uteroplacental dysfunction is not evident from the data of recent studies. The aim of this study was to investigate the prevalence of uteroplacental dysfunction reflected by abnormal uterine artery Doppler indices and reduced fetal growth in CHD pregnancies. METHODS: This is a retrospective case-control study including singleton pregnancies referred for detailed fetal cardiac assessment subsequently diagnosed with or without CHD. Mid-trimester uterine artery Doppler assessment at 20-24 weeks as well as third trimester fetal biometry and arterial Doppler pulsatility indices (PI) were performed. All fetal biometry were converted into centiles and Doppler values to multiples of median (MoM) to adjust for physiological changes with gestation. RESULTS: The study included 811 pregnancies including 153 cases where the fetus was diagnosed with CHD. Mid-pregnancy uterine artery PI was significantly higher in women with fetal CHD compared to controls (0.90MoM vs 0.83MoM; p = 0.006). In the third trimester, median centiles for fetal head circumference (45.4 vs 57.07; p<0.001), abdominal circumference (51.17 vs 55.71; p = 0.014), estimated fetal weight (33.6 vs 56.7; p<0.001) and cerebroplacental ratio (CPR: 0.84MoM vs 0.95MoM; p<0.001) were significantly lower in fetuses with CHD compared to controls. The percentage of small for gestational age births <10th centile (24.0% vs 10.7%; <0.001) and low CPR <0.6MoM (11.7% vs 2.5%; p<0.001) were significantly higher in the fetal CHD cohort. CONCLUSIONS: Mid-pregnancy uterine artery resistance is increased and subsequent fetal biometry reduced in pregnancies with CHD fetuses. These findings suggest that fetal CHD are associated with uteroplacental dysfunction, secondary to impaired maternal uteroplacental perfusion resulting in relative fetal hypoxaemia and reduced fetal growth

Mean field and Monte Carlo studies of the magnetization-reversal transition in the Ising model

Detailed mean field and Monte Carlo studies of the dynamic magnetization-reversal transition in the Ising model in its ordered phase under a competing external magnetic field of finite duration have been presented here. Approximate analytical treatment of the mean field equations of motion shows the existence of diverging length and time scales across this dynamic transition phase boundary. These are also supported by numerical solutions of the complete mean field equations of motion and the Monte Carlo study of the system evolving under Glauber dynamics in both two and three dimensions. Classical nucleation theory predicts different mechanisms of domain growth in two regimes marked by the strength of the external field, and the nature of the Monte Carlo phase boundary can be comprehended satisfactorily using the theory. The order of the transition changes from a continuous to a discontinuous one as one crosses over from coalescence regime (stronger field) to nucleation regime (weaker field). Finite size scaling theory can be applied in the coalescence regime, where the best fit estimates of the critical exponents are obtained for two and three dimensions.Comment: 16 pages latex, 13 ps figures, typos corrected, references adde

Error estimation and reduction with cross correlations

Besides the well-known effect of autocorrelations in time series of Monte Carlo simulation data resulting from the underlying Markov process, using the same data pool for computing various estimates entails additional cross correlations. This effect, if not properly taken into account, leads to systematically wrong error estimates for combined quantities. Using a straightforward recipe of data analysis employing the jackknife or similar resampling techniques, such problems can be avoided. In addition, a covariance analysis allows for the formulation of optimal estimators with often significantly reduced variance as compared to more conventional averages.Comment: 16 pages, RevTEX4, 4 figures, 6 tables, published versio

On the Symmetry of Universal Finite-Size Scaling Functions in Anisotropic Systems

In this work a symmetry of universal finite-size scaling functions under a certain anisotropic scale transformation is postulated. This transformation connects the properties of a finite two-dimensional system at criticality with generalized aspect ratio $\rho > 1$ to a system with $\rho < 1$. The symmetry is formulated within a finite-size scaling theory, and expressions for several universal amplitude ratios are derived. The predictions are confirmed within the exactly solvable weakly anisotropic two-dimensional Ising model and are checked within the two-dimensional dipolar in-plane Ising model using Monte Carlo simulations. This model shows a strongly anisotropic phase transition with different correlation length exponents $\nu_{||} \neq \nu_\perp$ parallel and perpendicular to the spin axis.Comment: RevTeX4, 4 pages, 3 figure

Orbital moment of a single Co atom on a Pt(111) surface - a view from correlated band theory

The orbital magnetic moment of a Co adatom on a Pt(111) surface is calculated in good agreement with experimental data making use of the LSDA+U method. It is shown that both electron correlation induced orbital polarization and structural relaxation play essential roles in orbital moment formation. The microscopic origins of the orbital moment enhancement are discussed

Cross-correlations in scaling analyses of phase transitions

Thermal or finite-size scaling analyses of importance sampling Monte Carlo time series in the vicinity of phase transition points often combine different estimates for the same quantity, such as a critical exponent, with the intent to reduce statistical fluctuations. We point out that the origin of such estimates in the same time series results in often pronounced cross-correlations which are usually ignored even in high-precision studies, generically leading to significant underestimation of statistical fluctuations. We suggest to use a simple extension of the conventional analysis taking correlation effects into account, which leads to improved estimators with often substantially reduced statistical fluctuations at almost no extra cost in terms of computation time.Comment: 4 pages, RevTEX4, 3 tables, 1 figur