111,642 research outputs found
Solvent coarse-graining and the string method applied to the hydrophobic collapse of a hydrated chain
Using computer simulations of over 100,000 atoms, the mechanism for the
hydrophobic collapse of an idealized hydrated chain is obtained. This is done
by coarse-graining the atomistic water molecule positions over 129,000
collective variables that represent the water density field and then using the
string method in these variables to compute the minimum free energy pathway
(MFEP) for the collapsing chain. The dynamical relevance of the MFEP (i.e. its
coincidence with the mechanism of collapse) is validated a posteriori using
conventional molecular dynamics trajectories. Analysis of the MFEP provides
atomistic confirmation for the mechanism of hydrophobic collapse proposed by
ten Wolde and Chandler. In particular, it is shown that lengthscale-dependent
hydrophobic dewetting is the rate-limiting step in the hydrophobic collapse of
the considered chain.Comment: 11 pages, 7 figures, including supporting informatio
Transition Temperature of a Uniform Imperfect Bose Gas
We calculate the transition temperature of a uniform dilute Bose gas with
repulsive interactions, using a known virial expansion of the equation of
state. We find that the transition temperature is higher than that of an ideal
gas, with a fractional increase K_0(na^3)^{1/6}, where n is the density and a
is the S-wave scattering length, and K_0 is a constant given in the paper. This
disagrees with all existing results, analytical or numerical. It agrees exactly
in magnitude with a result due to Toyoda, but has the opposite sign.Comment: Email correspondence to [email protected] ; 2 pages using REVTe
An Implication on the Pion Distribution Amplitude from the Pion-Photon Transition Form Factor with the New BABAR Data
The new BABAR data on the pion-photon transition form factor arouses people's
new interests on the determination of pion distribution amplitude. To explain
the data, we take both the leading valence quark state's and the non-valence
quark states' contributions into consideration, where the valence quark part up
to next-to-leading order is presented and the non-valence quark part is
estimated by a phenomenological model based on its limiting behavior at both
and . Our results show that to be consistent with the
new BABAR data at large region, a broader other than the asymptotic-like
pion distribution amplitude should be adopted. The broadness of the pion
distribution amplitude is controlled by a parameter . It has been found that
the new BABAR data at low and high energy regions can be explained
simultaneously by setting to be around 0.60, in which the pion distribution
amplitude is closed to the Chernyak-Zhitnitsky form.Comment: 19 pages, 6 figures, 2 tables. Slightly changed, references updated.
To be published in Phys.Rev.
Improved approach to the heavy-to-light form factors in the light-cone QCD sum
A systematic analysis shows that the main uncertainties in the form factors
are due to the twist-3 wave functions of the light mesons in the light-cone QCD
sum rules. We propose an improved approach, in which the twist-3 wave functions
doesn't make any contribution and therefore the possible pollution by them can
be avoided, to re-examine semileptonic form factors. Also, a
comparison between the previous and our results from the light-cone QCD sum
rules is made. Our method will be beneficial to the precise extracting of
from the experimental data on the processes .Comment: New version to appear in PR
Momentum Distribution for Bosons with Positive Scattering Length in a Trap
The coordinate-momentum double distribution function is calculated in the local density approximation for bosons with
positive scattering length in a trap. The calculation is valid to the first
order of . To clarify the meaning of the result, it is compared for a
special case with the double distribution function of
Wigner.Comment: Latex fil
Pion Form Factor in the Factorization Formalism
Based on the light-cone (LC) framework and the factorization formalism,
the transverse momentum effects and the different helicity components'
contributions to the pion form factor are recalculated. In
particular, the contribution to the pion form factor from the higher helicity
components (), which come from the spin-space Wigner
rotation, are analyzed in the soft and hard energy regions respectively. Our
results show that the right power behavior of the hard contribution from the
higher helicity components can only be obtained by fully keeping the
dependence in the hard amplitude, and that the dependence in LC wave
function affects the hard and soft contributions substantially. As an example,
we employ a model LC wave function to calculate the pion form factor and then
compare the numerical predictions with the experimental data. It is shown that
the soft contribution is less important at the intermediate energy region.Comment: 21 pages, 4 figure
Electricity infrastructure enhancement for the security of supply against coordinated malicious attacks
© 2016 IEEE. The impact of coordinated malicious attacks may be dramatically severe and may yield a wide area blackout. A preventive measure is enhancing the infrastructure through investment. Due to limited budget, a decision making is required to select the best possible options, considering cost/benefit ratio. We designed a time-step simulation framework representing the evolution of post-contingency failures and load/system restoration. System unserved energy is translated into economic losses. Different enhancement options can be compared in terms of benefit (reduction in the cost of unserved energy) and of cost (investments needed) to eventually rank them. The simulation framework also provides a way to derive an optimal lost load recovering strategy to accelerate system restoration. In this paper the simulation framework is applied to a real network (Austrian transmission grid) to evaluate the technical and economic impacts of a coordinated malicious attack
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