17,457 research outputs found
Managing Service-Heterogeneity using Osmotic Computing
Computational resource provisioning that is closer to a user is becoming
increasingly important, with a rise in the number of devices making continuous
service requests and with the significant recent take up of latency-sensitive
applications, such as streaming and real-time data processing. Fog computing
provides a solution to such types of applications by bridging the gap between
the user and public/private cloud infrastructure via the inclusion of a "fog"
layer. Such approach is capable of reducing the overall processing latency, but
the issues of redundancy, cost-effectiveness in utilizing such computing
infrastructure and handling services on the basis of a difference in their
characteristics remain. This difference in characteristics of services because
of variations in the requirement of computational resources and processes is
termed as service heterogeneity. A potential solution to these issues is the
use of Osmotic Computing -- a recently introduced paradigm that allows division
of services on the basis of their resource usage, based on parameters such as
energy, load, processing time on a data center vs. a network edge resource.
Service provisioning can then be divided across different layers of a
computational infrastructure, from edge devices, in-transit nodes, and a data
center, and supported through an Osmotic software layer. In this paper, a
fitness-based Osmosis algorithm is proposed to provide support for osmotic
computing by making more effective use of existing Fog server resources. The
proposed approach is capable of efficiently distributing and allocating
services by following the principle of osmosis. The results are presented using
numerical simulations demonstrating gains in terms of lower allocation time and
a higher probability of services being handled with high resource utilization.Comment: 7 pages, 4 Figures, International Conference on Communication,
Management and Information Technology (ICCMIT 2017), At Warsaw, Poland, 3-5
April 2017, http://www.iccmit.net/ (Best Paper Award
Hamiltonian Transformation to Compute Thermo-osmotic Forces.
If a thermal gradient is applied along a fluid-solid interface, the fluid experiences a thermo-osmotic force. In the steady state, this force is balanced by the gradient of the shear stress. Surprisingly, there appears to be no unique microscopic expression that can be used for computing the magnitude of the thermo-osmotic force. Here we report how, by treating the mass M of the fluid particles as a tensor in the Hamiltonian, we can eliminate the balancing shear force in a nonequilibrium simulation and therefore compute the thermo-osmotic force at simple solid-fluid interfaces. We compare the nonequilibrium force measurement with estimates of the thermo-osmotic force based on computing gradients of the stress tensor. We find that the thermo-osmotic force as measured in our simulations cannot be derived from the most common microscopic definitions of the stress tensor
Computing the local pressure in molecular dynamics simulations
Computer simulations of inhomogeneous soft matter systems often require
accurate methods for computing the local pressure. We present a simple
derivation, based on the virial relation, of two equivalent expressions for the
local (atomistic) pressure in a molecular dynamics simulation. One of these
expressions, previously derived by other authors via a different route,
involves summation over interactions between particles within the region of
interest; the other involves summation over interactions across the boundary of
the region of interest. We illustrate our derivation using simulations of a
simple osmotic system; both expressions produce accurate results even when the
region of interest over which the pressure is measured is very small.Comment: 11 pages, 4 figure
From a thin film model for passive suspensions towards the description of osmotic biofilm spreading
Biofilms are ubiquitous macro-colonies of bacteria that develop at various
interfaces (solid-liquid, solid-gas or liquid-gas). The formation of biofilms
starts with the attachment of individual bacteria to an interface, where they
proliferate and produce a slimy polymeric matrix - two processes that result in
colony growth and spreading. Recent experiments on the growth of biofilms on
agar substrates under air have shown that for certain bacterial strains, the
production of the extracellular matrix and the resulting osmotic influx of
nutrient-rich water from the agar into the biofilm are more crucial for the
spreading behaviour of a biofilm than the motility of individual bacteria. We
present a model which describes the biofilm evolution and the advancing biofilm
edge for this spreading mechanism. The model is based on a gradient dynamics
formulation for thin films of biologically passive liquid mixtures and
suspensions, supplemented by bioactive processes which play a decisive role in
the osmotic spreading of biofilms. It explicitly includes the wetting
properties of the biofilm on the agar substrate via a disjoining pressure and
can therefore give insight into the interplay between passive surface forces
and bioactive growth processes
Water activity in lamellar stacks of lipid bilayers: "Hydration forces" revisited
Water activity and its relationship with interactions stabilising lamellar
stacks of mixed lipid bilayers in their fluid state are investigated by means
of osmotic pressure measurements coupled with small-angle x-ray scattering. The
(electrically-neutral) bilayers are composed of a mixture in various
proportions of lecithin, a zwitterionic phospholipid, and Simulsol, a non-ionic
cosurfactant with an ethoxylated polar head. For highly dehydrated samples the
osmotic pressure profile always exhibits the "classical" exponential decay as
hydration increases but, depending on Simulsol to lecithin ratio, it becomes
either of the "bound" or "unbound" types for more water-swollen systems. A
simple thermodynamic model is used for interpreting the results without
resorting to the celebrated but elusive "hydration forces"Comment: 24 pages, 12 figures. Accepted for publication in The European
Physical Journal
Theory and simulations of rigid polyelectrolytes
We present theoretical and numerical studies on stiff, linear
polyelectrolytes within the framework of the cell model. We first review
analytical results obtained on a mean-field Poisson-Boltzmann level, and then
use molecular dynamics simulations to show, under which circumstances these
fail quantitatively and qualitatively. For the hexagonally packed nematic phase
of the polyelectrolytes we compute the osmotic coefficient as a function of
density. In the presence of multivalent counterions it can become negative,
leading to effective attractions. We show that this results from a reduced
contribution of the virial part to the pressure. We compute the osmotic
coefficient and ionic distribution functions from Poisson-Boltzmann theory with
and without a recently proposed correlation correction, and also simulation
results for the case of poly(para-phenylene) and compare it to recently
obtained experimental data on this stiff polyelectrolyte. We also investigate
ion-ion correlations in the strong coupling regime, and compare them to
predictions of the recently advocated Wigner crystal theories.Comment: 32 pages, 15 figures, proceedings of the ASTATPHYS-MEX-2001, to be
published in Mol. Phy
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