14,402 research outputs found
Quasichemical theory and the description of associating fluids relative to a reference: Multiple bonding of a single site solute
We derive an expression for the chemical potential of an associating solute
in a solvent relative to the value in a reference fluid using the quasichemical
organization of the potential distribution theorem. The fraction of times the
solute is not associated with the solvent, the monomer fraction, is expressed
in terms of (a) the statistics of occupancy of the solvent around the solute in
the reference fluid and (b) the Widom factors that arise because of turning on
solute-solvent association. Assuming pair-additivity, we expand the Widom
factor into a product of Mayer f-functions and the resulting expression is
rearranged to reveal a form of the monomer fraction that is analogous to that
used within the statistical associating fluid theory (SAFT). The present
formulation avoids all graph-theoretic arguments and provides a fresh, more
intuitive, perspective on Wertheim's theory and SAFT. Importantly, multi-body
effects are transparently incorporated into the very foundations of the theory.
We illustrate the generality of the present approach by considering examples of
multiple solvent association to a colloid solute with bonding domains that
range from a small patch on the sphere, a Janus particle, and a solute whose
entire surface is available for association
Mini-grand canonical ensemble: chemical potential in the solvation shell
Quantifying the statistics of occupancy of solvent molecules in the vicinity
of solutes is central to our understanding of solvation phenomena. Number
fluctuations in small `solvation shells' around solutes cannot be described
within the macroscopic grand canonical framework using a single chemical
potential that represents the solvent `bath'. In this communication, we
hypothesize that molecular-sized observation volumes such as solvation shells
are best described by coupling the solvation shell with a mixture of particle
baths each with its own chemical potential. We confirm our hypotheses by
studying the enhanced fluctuations in the occupancy statistics of hard sphere
solvent particles around a distinguished hard sphere solute particle.
Connections with established theories of solvation are also discussed
On the number of matroids
We consider the problem of determining , the number of matroids on
elements. The best known lower bound on is due to Knuth (1974) who showed
that is at least . On the other hand, Piff
(1973) showed that , and it has
been conjectured since that the right answer is perhaps closer to Knuth's
bound.
We show that this is indeed the case, and prove an upper bound on that is within an additive term of Knuth's lower bound. Our proof
is based on using some structural properties of non-bases in a matroid together
with some properties of independent sets in the Johnson graph to give a
compressed representation of matroids.Comment: Final version, 17 page
Pion-less effective field theory for atomic nuclei and lattice nuclei
We compute the medium-mass nuclei O and Ca using pionless
effective field theory (EFT) at next-to-leading order (NLO). The low-energy
coefficients of the EFT Hamiltonian are adjusted to experimantal data for
nuclei with mass numbers and , or alternatively to results from
lattice quantum chromodynamics (QCD) at an unphysical pion mass of 806 MeV. The
EFT is implemented through a discrete variable representation in the harmonic
oscillator basis. This approach ensures rapid convergence with respect to the
size of the model space and facilitates the computation of medium-mass nuclei.
At NLO the nuclei O and Ca are bound with respect to decay into
alpha particles. Binding energies per nucleon are 9-10 MeV and 30-40 MeV at
pion masses of 140 MeV and 806 MeV, respectively.Comment: 26 page
An entropy argument for counting matroids
We show how a direct application of Shearers' Lemma gives an almost optimum
bound on the number of matroids on elements.Comment: Short note, 4 page
On the Mixtures of Weibull and Pareto (IV) Distribution: An Alternative to Pareto Distribution
Finite mixture models have provided a reasonable tool to model various types of observed phenomena, specially those which are random in nature. In this article, a finite mixture of Weibull and Pareto (IV) distribution is considered and studied. Some structural properties of the resulting model are discussed including estimation of the model parameters via expectation maximization (EM) algorithm. A real-life data application exhibits the fact that in certain situations, this mixture model might be a better alternative than the rival popular models
System Support for Bandwidth Management and Content Adaptation in Internet Applications
This paper describes the implementation and evaluation of an operating system
module, the Congestion Manager (CM), which provides integrated network flow
management and exports a convenient programming interface that allows
applications to be notified of, and adapt to, changing network conditions. We
describe the API by which applications interface with the CM, and the
architectural considerations that factored into the design. To evaluate the
architecture and API, we describe our implementations of TCP; a streaming
layered audio/video application; and an interactive audio application using the
CM, and show that they achieve adaptive behavior without incurring much
end-system overhead. All flows including TCP benefit from the sharing of
congestion information, and applications are able to incorporate new
functionality such as congestion control and adaptive behavior.Comment: 14 pages, appeared in OSDI 200
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