124 research outputs found
Duality in Non-Trivially Compactified Heterotic Strings
We study the implications of duality symmetry on the analyticity properties
of the partition function as it depends upon the compactification length. In
order to obtain non-trivial compactifications, we give a physical prescription
to get the Helmholtz free energy for any heterotic string supersymmetric or
not. After proving that the free energy is always invariant under the duality
transformation and getting the zero temperature
theory whose partition function corresponds to the Helmholtz potential, we show
that the self-dual point is a generic singularity
as the Hagedorn one. The main difference between these two critical
compactification radii is that the term producing the singularity at the
self-dual point is finite for any . We see that this behavior at
actually implies a loss of degrees of freedom below that point.Comment: (Preprint No. FTUAM-92/12) 17 page
Finite Temperature Bosonic Closed Strings: Thermal Duality and the Kosterlitz Thouless Transition
We elucidate the properties of a gas of free closed bosonic strings in
thermal equilibrium. Our starting point is the intensive generating functional
of connected one-loop closed vacuum string graphs given by the Polyakov path
integral. Invariance of the path integral under modular transformations gives a
thermal duality invariant expression for the free energy of free closed strings
at finite temperature. The free bosonic string gas exhibits a self-dual
Kosterlitz-Thouless phase transition. The thermodynamic potentials of the gas
of free bosonic closed strings are shown to exhibit an infinite hierarchy of
thermal self-duality relations. Note Added (Sep 2005).Comment: 22pgs. Note Added (Sep 2005), clarifying conclusion
Neural network modelling of RC deep beam shear strength
YesA 9 x 18 x 1 feed-forward neural network (NN) model
trained using a resilient back-propagation algorithm and
early stopping technique is constructed to predict the
shear strength of deep reinforced concrete beams. The
input layer covering geometrical and material properties
of deep beams has nine neurons, and the corresponding output is the shear strength. Training, validation and testing of the developed neural network have been
achieved using a comprehensive database compiled from
362 simple and 71 continuous deep beam specimens.
The shear strength predictions of deep beams obtained
from the developed NN are in better agreement with
test results than those determined from strut-and-tie
models. The mean and standard deviation of the ratio between predicted capacities using the NN and measured shear capacities are 1.028 and 0.154, respectively, for simple deep beams, and 1.0 and 0.122, respectively, for continuous deep beams. In addition, the
trends ascertained from parametric study using the developed NN have a consistent agreement with those observed in other experimental and analytical investigations
The effect of mirabegron on energy expenditure and brown adipose tissue in healthy lean South Asian and Europid men
Aim: To compare the effects of cold exposure and the β3-adrenergic receptor agonist
mirabegron on plasma lipids, energy expenditure and brown adipose tissue (BAT)
activity in South Asians versus Europids.
Materials and Methods: Ten lean Dutch South Asian (aged 18-30 years; body mass
index [BMI] 18-25 kg/m2
) and 10 age- and BMI-matched Europid men participated in
a randomized, double-blinded, cross-over study consisting of three interventions:
short-term (~ 2 hours) cold exposure, mirabegron (200 mg one dose p.o.) and placebo. Before and after each intervention, we performed lipidomic analysis in serum,
assessed resting energy expenditure (REE) and skin temperature, and measured BAT
fat fraction by magnetic resonance imaging.
Results: In both ethnicities, cold exposure increased the levels of several serum lipid
species, whereas mirabegron only increased free fatty acids. Cold exposure increased
lipid oxidation in both ethnicities, while mirabegron increased lipid oxidation in
Europids only. Cold exposure and mirabegron enhanced supraclavicular skin temperature in both ethnicities. Cold exposure decreased BAT fat fraction in both
ethnicities. After the combination of data from both ethnicities, mirabegron
decreased BAT fat fraction compared with placebo.
Conclusions: In South Asians and Europids, cold exposure and mirabegron induced
beneficial metabolic effects. When combining both ethnicities, cold exposure and
mirabegron increased REE and lipid oxidation, coinciding with a higher supraclavicular
skin temperature and lower BAT fat fraction.Diabetes Research Foundation Fellowship
2015.81.1808Netherlands CardioVascular Research Initiative: 'the Dutch Heart Foundation, Dutch Federation of University Medical Centers, the Netherlands Organisation for Health Research and Development and the Royal Netherlands Academy of Sciences'
CVON2014-02 ENERGISE
CVON2017-20 GENIUS-IIEuropean Union (EU)
602485European Research Council (NOMA-MRI) PCNR is an Established Investigator of the Netherlands Heart Foundation
2009T03
Calorimetric study of geopolymer binders based on natural pozzolan
This paper investigates the kinetics of geopolymerisation in an inorganic polymeric binder based on a natural pozzolan. The heat released by the exothermic geopolymerisation reaction process is monitored under isothermal temperature conditions, maintained in a differential scanning calorimeter using a water circulation cell. Calorimetric data are obtained isothermally at 65, 75, and 85 °C with various Na2O/Al2O3 and SiO2/Na2O molar ratios and in the presence and absence of small amounts of calcium aluminate cement (used as an efflorescence control admixture in these binder systems). The first stage of reaction, which is rapid and strongly exothermic, is shortened as the temperature increases. The total heat of reaction increases in the mixes containing calcium aluminate cement, but the apparent activation energy calculated using a pseudo-first-order reaction model is lower than without added calcium aluminate cement. At a constant overall SiO2/Na2O molar ratio, the apparent activation energy is decreased as the Na2O/Al2O3 molar ratio increases. Calcium aluminate cement, therefore, reduces the minimum energy required to initiate geopolymerisation reactions of this natural pozzolan and facilitates the progress of the reactions which lead to formation of a cementitious product
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