10,519 research outputs found
On the composition dependence of the microscopic structure, thermodynamic, dynamic and dielectric properties of water-dimethyl formamide model mixtures. Molecular dynamics simulation results
Isothermal-isobaric molecular dynamics simulations have been performed to
examine an ample set of properties of the model water-N,N-dimethylformamide
(DMF) mixture as a function of composition. The SPC-E and TIP4P-Ew water models
together with two united atom models for DMF [Chalaris M., Samios J., J. Chem.
Phys., 2000, 112, 8581; Cordeiro J., Int. J. Quantum Chem., 1997, 65, 709] were
used. Our principal analyses concern the behaviour of structural properties in
terms of radial distribution functions, and the number of hydrogen bonds
between molecules of different species as well as thermodynamic properties.
Namely, we explore the density, excess mixing molar volume and enthalpy, the
heat capacity and excess mixing heat capacity. Finally, the self-diffusion
coefficients of species and the dielectric constant of the system are
discussed. In addition, surface tension of water-DMF mixtures has been
calculated and analyzed.Comment: 15 pages, 11 figure
Benchmarking electron-cloud simulations and pressure measurements at the LHC
During the beam commissioning of the Large Hadron Collider (LHC) with 150,
75, 50 and 25-ns bunch spacing, important electron-cloud effects, like pressure
rise, cryogenic heat load, beam instabilities or emittance growth, were
observed. A method has been developed to infer different key beam-pipe surface
parameters by benchmarking simulations and pressure rise observed in the
machine. This method allows us to monitor the scrubbing process (i.e. the
reduction of the secondary emission yield as a function of time) in the regions
where the vacuum-pressure gauges are located, in order to decide on the most
appropriate strategies for machine operation. In this paper we present the
methodology and first results from applying this technique to the LHC.Comment: 5 pages, 7 figures, presented at ECLOUD 12: Joint
INFN-CERN-EuCARD-AccNet Workshop on Electron-Cloud Effects, La Biodola, Isola
d Elba, Italy, 5-9 June 201
Temperature dependence of the microscopic structure and density anomaly of the SPC/E and TIP4P-Ew water models. Molecular dynamics simulation results
We have investigated temperature trends of the microscopic structure of the
SPC/E and TIP4P-Ew water models in terms of the pair distribution functions,
coordination numbers, the average number of hydrogen bonds, the distribution of
bonding states of a single molecule as well as the angular distribution of
molecules by using the constant pressure molecular dynamics simulations. The
evolution of the structure is put in correspondence with the dependence of
water density on high temperatures down to the region of temperatures where the
system becomes supercooled. It is shown that the fraction of molecules with
three and four bonds determine the maximum density for both models. Moreover,
the temperature dependence of the dielectric constant is obtained and analyzed.Comment: 11 pages, 5 figure
Corrections to the Gell-Mann-Oakes-Renner relation and chiral couplings and
Next to leading order corrections to the
Gell-Mann-Oakes-Renner relation (GMOR) are obtained using weighted QCD Finite
Energy Sum Rules (FESR) involving the pseudoscalar current correlator. Two
types of integration kernels in the FESR are used to suppress the contribution
of the kaon radial excitations to the hadronic spectral function, one with
local and the other with global constraints. The result for the pseudoscalar
current correlator at zero momentum is , leading to the chiral corrections to GMOR: . The resulting uncertainties are mostly due to variations in the upper
limit of integration in the FESR, within the stability regions, and to a much
lesser extent due to the uncertainties in the strong coupling and the strange
quark mass. Higher order quark mass corrections, vacuum condensates, and the
hadronic resonance sector play a negligible role in this determination. These
results confirm an independent determination from chiral perturbation theory
giving also very large corrections, i.e. roughly an order of magnitude larger
than the corresponding corrections in chiral . Combining
these results with our previous determination of the corrections to GMOR in
chiral , , we are able to determine two low
energy constants of chiral perturbation theory, i.e. , and , both at the
scale of the -meson mass.Comment: Revised version with minor correction
An Easy Laboratory Method for Optimizing the Parameters for the Mechanical Densification Process: An Evaluation with an Extruder
Rosana G. Moreira, Editor-in-Chief; Texas A&M UniversityThis is a paper from International Commission of Agricultural Engineering (CIGR, Commission Internationale du Genie Rural) E-Journal Volume 8 (2006): An Easy Laboratory Method for Optimizing the Parameters for the Mechanical Densification Process: An Evaluation with an Extruder. Manuscript PM 06 015. Vol. VIII. July, 2006
Isobaric-isothermal molecular dynamics computer simulations of the properties of water-1,2-dimethoxyethane model mixtures
Isothermal-isobaric molecular dynamics simulations have been performed to
examine a broad set of properties of the model water-1,2-dimethoxyethane (DME)
mixture as a function of composition. The SPC-E and TIP4P-Ew water models and
the modified TraPPE model for DME were applied. Our principal focus was to
explore the trends of behaviour of the structural properties in terms of the
radial distribution functions, coordination numbers and number of hydrogen
bonds between molecules of different species, and of conformations of DME
molecules. Thermodynamic properties, such as density, molar volume, enthalpy of
mixing and heat capacity at constant pressure have been examined. Finally, the
self-diffusion coefficients of species and the dielectric constant of the
system were calculated and analyzed.Comment: 14 pages, 9 figure
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