445 research outputs found
Maternal obesity is associated with the formation of small dense LDL and hypoadiponectinemia in the third trimester
Context: Maternal obesity is associated with high plasma triglyceride, poor vascular function, and an increased risk for pregnancy complications. In normal-weight pregnant women, higher triglyceride is associated with increased small, dense low-density lipoprotein (LDL).
Hypothesis: In obese pregnancy, increased plasma triglyceride concentrations result in triglyceride enrichment of very low-density lipoprotein-1 particles and formation of small dense LDL via lipoprotein lipase.
Design: Women (n = 55) of body mass index of 18–46 kg/m2 were sampled longitudinally at 12, 26, and 35 weeks' gestation and 4 months postnatally.
Setting: Women were recruited at hospital antenatal appointments, and study visits were in a clinical research suite.
Outcome Measures: Plasma concentrations of lipids, triglyceride-rich lipoproteins, lipoprotein lipase mass, estradiol, steroid hormone binding globulin, insulin, glucose, leptin, and adiponectin were determined.
Results: Obese women commenced pregnancy with higher plasma triglyceride, reached the same maximum, and then returned to higher postnatal levels than normal-weight women. Estradiol response to pregnancy (trimester 1–3 incremental area under the curve) was positively associated with plasma triglyceride response (r2 adjusted 25%, P < .001). In the third trimester, the proportion of small, dense LDL was 2-fold higher in obese women than normal-weight women [mean (SD) 40.7 (18.8) vs 21.9 (10.9)%, P = .014], and 35% of obese, 14% of overweight, and none of the normal-weight women displayed an atherogenic LDL subfraction phenotype. The small, dense LDL mass response to pregnancy was inversely associated with adiponectin response (17%, P = .013).
Conclusions: Maternal obesity is associated with an atherogenic LDL subfraction phenotype and may provide a mechanistic link to poor vascular function and adverse pregnancy outcome
Loneliness, social relations and health and wellbeing in deprived communities
There is growing policy concern about the extent of loneliness in advanced societies, and its
prevalence among various social groups. This study looks at loneliness among people living in
deprived communities, where there may be additional barriers to social engagement including low
incomes, fear of crime, poor services and transient populations. The aim was to examine the
prevalence of loneliness, and also its associations with different types of social contacts and forms of
social support, and its links to self-reported health and wellbeing in the population group. The
method involved a cross-sectional survey of 4,302 adults across 15 communities, with the data
analysed using multinomial logistic regression controlling for sociodemographics, then for all other
predictors within each domain of interest. Frequent feelings of loneliness were more common
among those who: had contact with family monthly or less; had contact with neighbours weekly or
less; rarely talked to people in the neighbourhood; and who had no available sources of practical or
emotional support. Feelings of loneliness were most strongly associated with poor mental health,
but were also associated with long-term problems of stress, anxiety and depression, and with low
mental wellbeing, though to a lesser degree. The findings are consistent with a view that situational
loneliness may be the product of residential structures and resources in deprived areas. The findings
also show that neighbourly behaviours of different kinds are important for protecting against
loneliness in deprived communities. Familiarity within the neighbourhood, as active acquaintance
rather than merely recognition, is also important. The findings are indicative of several mechanisms
that may link loneliness to health and wellbeing in our study group: loneliness itself as a stressor;
lonely people not responding well to the many other stressors in deprived areas; and loneliness as
the product of weak social buffering to protect against stressors
Scaling Flows and Dissipation in the Dilute Fermi Gas at Unitarity
We describe recent attempts to extract the shear viscosity of the dilute
Fermi gas at unitarity from experiments involving scaling flows. A scaling flow
is a solution of the hydrodynamic equations that preserves the shape of the
density distribution. The scaling flows that have been explored in the
laboratory are the transverse expansion from a deformed trap ("elliptic flow"),
the expansion from a rotating trap, and collective oscillations. We discuss
advantages and disadvantages of the different experiments, and point to
improvements of the theoretical analysis that are needed in order to achieve
definitive results. A conservative bound based on the current data is that the
minimum of the shear viscosity to entropy density ration is that eta/s is less
or equal to 0.5 hbar/k_B.Comment: 32 pages, prepared for "BCS-BEC crossoverand the Unitary Fermi Gas",
Lecture Notes in Physics, W. Zwerger (editor), Fig. 5 corrected, note added;
final version, corrected typo in equ. 9
Frequency and damping of hydrodynamic modes in a trapped Bose-condensed gas
Recently it was shown that the Landau-Khalatnikov two-fluid hydrodynamics
describes the collision-dominated region of a trapped Bose condensate
interacting with a thermal cloud. We use these equations to discuss the low
frequency hydrodynamic collective modes in a trapped Bose gas at finite
temperatures. We derive a variational expressions based on these equations for
both the frequency and damping of collective modes. A new feature is our use of
frequency-dependent transport coefficients, which produce a natural cutoff by
eliminating the collisionless low-density tail of the thermal cloud. Above the
superfluid transition, our expression for the damping in trapped inhomogeneous
gases is analogous to the result first obtained by Landau and Lifshitz for
uniform classical fluids. We also use the moment method to discuss the
crossover from the collisionless to the hydrodynamic region. Recent data for
the monopole-quadrupole mode in the hydrodynamic region of a trapped gas of
metastable He is discussed. We also present calculations for the damping of
the analogous monopole-quadrupole condensate mode in the superfluid
phase.Comment: 22 pages, 10 figures, submitted to Physical Review
Landau-Khalatnikov two-fluid hydrodynamics of a trapped Bose gas
Starting from the quantum kinetic equation for the non-condensate atoms and
the generalized Gross-Pitaevskii equation for the condensate, we derive the
two-fluid hydrodynamic equations of a trapped Bose gas at finite temperatures.
We follow the standard Chapman-Enskog procedure, starting from a solution of
the kinetic equation corresponding to the complete local equilibrium between
the condensate and the non-condensate components. Our hydrodynamic equations
are shown to reduce to a form identical to the well-known Landau-Khalatnikov
two-fluid equations, with hydrodynamic damping due to the deviation from local
equilibrium. The deviation from local equilibrium within the thermal cloud
gives rise to dissipation associated with shear viscosity and thermal
conduction. In addition, we show that effects due to the deviation from the
diffusive local equilibrium between the condensate and the non-condensate
(recently considered by Zaremba, Nikuni and Griffin) can be described by four
frequency-dependent second viscosity transport coefficients. We also derive
explicit formulas for all the transport coefficients. These results are used to
introduce two new characteristic relaxation times associated with hydrodynamic
damping. These relaxation times give the rate at which local equilibrium is
reached and hence determine whether one is in the two-fluid hydrodynamic
region.Comment: 26 pages, 3 postscript figures, submitted to PR
Damped Bogoliubov excitations of a condensate interacting with a static thermal cloud
We calculate the damping of condensate collective excitations at finite
temperatures arising from the lack of equilibrium between the condensate and
thermal atoms. We neglect the non-condensate dynamics by fixing the thermal
cloud in static equilibrium. We derive a set of generalized Bogoliubov
equations for finite temperatures that contain an explicit damping term due to
collisional exchange of atoms between the two components. We have numerically
solved these Bogoliubov equations to obtain the temperature dependence of the
damping of the condensate modes in a harmonic trap. We compare these results
with our recent work based on the Thomas-Fermi approximation.Comment: 9 pages, 3 figures included. Submitted to PR
Monte Carlo Simulations with Indefinite and Complex-Valued Measures
A method is presented to tackle the sign problem in the simulations of
systems having indefinite or complex-valued measures. In general, this new
approach is shown to yield statistical errors smaller than the crude Monte
Carlo using absolute values of the original measures. Exactly solvable,
one-dimensional Ising models with complex temperature and complex activity
illustrate the considerable improvements and the workability of the new method
even when the crude one fails.Comment: 10 A4 pages, postscript (140K), UM-P-93-7
Spin dynamics of a trapped spin-1 Bose Gas above the Bose-Einstein transition temperature
We study collective spin oscillations in a spin-1 Bose gas above the
Bose-Einstein transition temperature. Starting from the Heisenberg equation of
motion, we derive a kinetic equation describing the dynamics of a thermal gas
with the spin-1 degree of freedom. Applying the moment method to the kinetic
equation, we study spin-wave collective modes with dipole symmetry. The dipole
modes in the spin-1 system are found to be classified into the three type of
modes. The frequency and damping rate are obtained as functions of the peak
density. The damping rate is characterized by three relaxation times associated
with collisions.Comment: 19 pages, 5 figur
Financial correlations at ultra-high frequency: theoretical models and empirical estimation
A detailed analysis of correlation between stock returns at high frequency is
compared with simple models of random walks. We focus in particular on the
dependence of correlations on time scales - the so-called Epps effect. This
provides a characterization of stochastic models of stock price returns which
is appropriate at very high frequency.Comment: 22 pages, 8 figures, 1 table, version to appear in EPJ
The use of an e-learning constructivist solution in workplace learning
We wished to investigate whether an e-learning approach which uses constructivist principles can be successfully applied to train employees in a highly specialised skill thought to require expert individuals and extensive prolonged training. The approach involved the development of an e-learning package which included simulations and interactivity, then experimental testing in a case study workplace environment with the collection of both quantitative and qualitative data to assess the effectiveness of the package. Our study shows that this e-learning strategy improved the skills of the inexperienced
operator significantly. We therefore propose that such programmes could be used as a work based training aid and used as a model system for the training of employees in complex skilled tasks in the workplace. This research demonstrates that the e-learning can be applied outside the traditional learning environment to train unskilled employees to undertake complex practical tasks which traditionally would involve prohibitively expensive instruction. This work also illustrates that simulations and interactivity are powerful tools in the design of successful e-learning packages in preparing learners for real world practical situations. Finally this study shows that workplace learners can be better served by elearning environments rather than conventional training as they allow asynchronous learning and private study which are valued by employees who have other demands on their time and are more comfortable receiving tuition privately Relevance to industry: E-learning using constructivist principles, and incorporating simulations and interactivity can be used successfully in the training of highly specialised and skilled tasks required in the
modern workplace
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