10,353 research outputs found
Spectroscopic observations of the planets
Spectroscopic observations of planets showing absorption variations in NH3 and CH4 band
A model for a non-minimally coupled scalar field interacting with dark matter
In this work we investigate the evolution of a Universe consisted of a scalar
field, a dark matter field and non-interacting baryonic matter and radiation.
The scalar field, which plays the role of dark energy, is non-minimally coupled
to space-time curvature, and drives the Universe to a present accelerated
expansion. The non-relativistic dark matter field interacts directly with the
dark energy and has a pressure which follows from a thermodynamic theory. We
show that this model can reproduce the expected behavior of the density
parameters, deceleration parameter and luminosity distance.Comment: 3 pages, 4 figures. To appear in Brazilian Journal of Physic
A Multicanonical Algorithm and the Surface Free Energy in SU(3) Pure Gauge Theory
We present a multicanonical algorithm for the SU(3) pure gauge theory at the
deconfinement phase transition. We measure the tunneling times for lattices of
size L^3x2 for L=8,10, and 12. In contrast to the canonical algorithm the
tunneling time increases only moderately with L. Finally, we determine the
interfacial free energy applying the multicanonical algorithm.Comment: 6 pages, HLRZ-92-3
Maternal haemodynamic function differs in preâeclampsia when it is associated with a smallâforâgestationalâage newborn: a prospective cohort study
Objective
To describe maternal haemodynamic differences in gestational hypertension with smallâforâgestationalâage babies (HDP + SGA), gestational hypertension with appropriateâforâgestationalâage babies (HDPâonly) 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 nonâinvasive Ultrasound Cardiac Output Monitor (USCOMâ1AÂź) and corrected for gestational age and maternal characteristics using deviceâspecific reference ranges.
Main outcome measures
Maternal cardiac output, stroke volume, systemic vascular resistance.
Results
We included 114 HDP + SGA, 202 HDPâonly and 401 control pregnancies at 26â41 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 HDPâonly pregnancies, respectively (all P < 0.05).
Conclusion
Women with HDP + SGA present with more severe haemodynamic dysfunction than HDPâonly. Even HDPâonly 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 preâeclampsia and should be considered alongside placental aetiology
Interfacial friction between semiflexible polymers and crystalline surfaces
The results obtained from molecular dynamics simulations of the friction at
an interface between polymer melts and weakly attractive crystalline surfaces
are reported. We consider a coarse-grained bead-spring model of linear chains
with adjustable intrinsic stiffness. The structure and relaxation dynamics of
polymer chains near interfaces are quantified by the radius of gyration and
decay of the time autocorrelation function of the first normal mode. We found
that the friction coefficient at small slip velocities exhibits a distinct
maximum which appears due to shear-induced alignment of semiflexible chain
segments in contact with solid walls. At large slip velocities the decay of the
friction coefficient is independent of the chain stiffness. The data for the
friction coefficient and shear viscosity are used to elucidate main trends in
the nonlinear shear rate dependence of the slip length. The influence of chain
stiffness on the relationship between the friction coefficient and the
structure factor in the first fluid layer is discussed.Comment: 31 pages, 12 figure
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
Monte Carlo investigations of phase transitions: status and perspectives
Using the concept of finite-size scaling, Monte Carlo calculations of various
models have become a very useful tool for the study of critical phenomena, with
the system linear dimension as a variable. As an example, several recent
studies of Ising models are discussed, as well as the extension to models of
polymer mixtures and solutions. It is shown that using appropriate cluster
algorithms, even the scaling functions describing the crossover from the Ising
universality class to the mean-field behavior with increasing interaction range
can be described. Additionally, the issue of finite-size scaling in Ising
models above the marginal dimension (d*=4) is discussed.Comment: 23 pages, including 14 PostScript figures. Presented at
StatPhys-Taiwan, August 9-16, 1999. Also available as PDF file at
http://www.cond-mat.physik.uni-mainz.de/~luijten/erikpubs.htm
Nitrite Photochemistry in 2-Propanol/Water Solution
Nitrite ion, a component of nitrogen oxide pollution, is an important source of free radicals in the environment. N02- absorbs ambient ultraviolet light to break into NO and 0-, and in environmental conditions, 0- is converted to hydroxyl radical, OH. Hydroxyl radical reacts with a wide variety of environmental pollutants, including hydrocarbons and nitrogen oxides, so its sources are of interest to environmental chemists. In order to investigate the processes of nitrite photochemistry, nitrite ion was photolyzed at 366 nm in 2-propanol/water solution. This mixed solvent system allows investigation of the effects of varying the solvent cage composition and scavenger concentration on the photolysis process and OH production in particular. A secondary goal was to follow nitrite ion and OH scavenging product concentrations simultaneously. OH radicals were scavenged by 2-propanol to form acetone, which was quantified by derivatization with 2,4-dinitrophenylhydrazine followed by HPLC detection. Acetone yields were compared to nitrite disappearance quantified by ultraviolet spectroscopy for nitrite ion photolyses in 96/4, 98/2, and 100/0 mass/mass 2-propanol/water solutions. Acetone was formed at a higher rate in the 100% 2-propanol solvent, suggesting a shift in mechanism at much lower water concentrations
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