2,434 research outputs found
Direct numerical simulations of statistically steady, homogeneous, isotropic fluid turbulence with polymer additives
We carry out a direct numerical simulation (DNS) study that reveals the
effects of polymers on statistically steady, forced, homogeneous, isotropic
fluid turbulence. We find clear manifestations of dissipation-reduction
phenomena: On the addition of polymers to the turbulent fluid, we obtain a
reduction in the energy dissipation rate, a significant modification of the
fluid energy spectrum, especially in the deep-dissipation range, a suppression
of small-scale intermittency, and a decrease in small-scale vorticity
filaments. We also compare our results with recent experiments and earlier DNS
studies of decaying fluid turbulence with polymer additives.Comment: consistent with the published versio
Two-dimensional, homogeneous, isotropic fluid turbulence with polymer additives
We present the most extensive direct numerical simulations, attempted so far,
of statistically steady, homogeneous, isotropic turbulence in two-dimensional
fluid films with air-drag-induced friction and with polymer additives. Our
study reveals that the polymers (a) reduce the total fluid energy, enstrophy,
and palinstrophy, (b) modify the fluid energy spectrum both in inverse- and
forward-cascade regimes, (c) reduce small-scale intermittency, (d) suppress
regions of large vorticity and strain rate, and (e) stretch in strain-dominated
regions. We compare our results with earlier experimental studies; and we
propose new experiments.Comment: 8 pages, 8 figure
Condensation of Silica Nanoparticles on a Phospholipid Membrane
The structure of the transient layer at the interface between air and the
aqueous solution of silica nanoparticles with the size distribution of
particles that has been determined from small-angle scattering has been studied
by the X-ray reflectometry method. The reconstructed depth profile of the
polarizability of the substance indicates the presence of a structure
consisting of several layers of nanoparticles with the thickness that is more
than twice as large as the thickness of the previously described structure. The
adsorption of 1,2-distearoyl-sn-glycero-3-phosphocholine molecules at the
hydrosol/air interface is accompanied by the condensation of anion silica
nanoparticles at the interface. This phenomenon can be qualitatively explained
by the formation of the positive surface potential due to the penetration and
accumulation of Na+ cations in the phospholipid membrane.Comment: 7 pages, 5 figure
Resource Allocation for Multiple Concurrent In-Network Stream-Processing Applications
This paper investigates the operator mapping problem for in-network stream-processing applications. In-network stream-processing amounts to applying one or more trees of operators in steady-state, to multiple data objects that are continuously updated at different locations in the network. The goal is to compute some final data at some desired rate. Different operator trees may share common subtrees. Therefore, it may be possible to reuse some intermediate results in different application trees. The first contribution of this work is to provide complexity results for different instances of the basic problem, as well as integer linear program formulations of various problem instances. The second second contribution is the design of several polynomial-time heuristics. One of the primary objectives of these heuristics is to reuse intermediate results shared by multiple applications. Our quantitative comparisons of these heuristics in simulation demonstrates the importance of choosing appropriate processors for operator mapping. It also allow us to identify a heuristic that achieves good results in practice
Analyzing the effects of surface distribution of pores in cell electroporation for a cell membrane containing cholesterol
This paper presents a model and numerical analysis (simulations) of
transmembrane potential induced in biological cell membrane under the influence
of externally applied electric field (i.e., electroporation). This model
differs from the established models of electroporation in two distinct ways.
Firstly, it incorporates the presence of cholesterol (~20% mole-fraction) in
biological membrane. Secondly, it considers the distribution of pores as a
function of the variation of transmembrane potential from one region of the
cell to another. Formulation is based on the role of membrane tension and
electrical forces in the formation of pores in a cell membrane, which is
considered as an infinitesimally thin insulator. The model has been used to
explore the process of creation and evolution of pores and to determine the
number and size of pores as a function of applied electric field (magnitude and
duration). Results show that the presence of cholesterol enhances poration by
changing the membrane tension. Analyses indicate that the number of pores and
average pore radii differ significantly from one part of the cell to the other.
While some regions of the cell membrane undergo rapid and dense poration,
others remain unaffected. The method can be a useful tool for a more realistic
prediction of pore formation in cells subjected to electroporation.Comment: 11 pages, 3 figures. v2: added new references, grammatical changes,
corrected typo
Role of trimetazidine in carbon tetrachloride induced liver damage in rats
Background: Hepatotoxicity by chemicals and drugs is a common clinical problem. Presently very few drugs are showing effectiveness in prevention and treatment of hepatic damage. So in this study, we evaluated the role of trimetazidine in carbon tetrachloride (CCl4) induced liver damage in rats. Objective of current study is to evaluate effects of prophylactic trimetazidine against carbon tetrachloride induced liver damage in rats.Methods: Liver damage was induced in 30 albino rats by CCl4 (0.5 ml/kg, i.p.) once daily for 7 days. Extent of damage was studied by assessing biochemical parameters (SGOT, SGPT, ALP, proteins and bilirubin). These biochemical observations were supplemented by pentobarbitone Sleeping Time and Histological Examination of liver. The effect of co-administration of trimetazidine (doses 5 and 10 mg/kg p. o.) on the above parameters was investigated. Liv.52® was used as Positive Control. Data was analyzed by one way ANOVA, followed by Dunnett's test.Results: Trimetazidine significantly prevented CCl4 induced elevation of serum SGOT, SGPT, ALP and bilirubin (total and direct), and reduction in protein level. Pentobarbitone sleeping time and histological examination of the liver showed consistent results. The results were comparable to that of Liv.52®.Conclusions: Trimetazidine, when administered prophylactically, shows hepatoprotective effect against CCl4 induced liver damage
Evidence for Excimer Photoexcitations in an Ordered {\pi}-Conjugated Polymer Film
We report pressure-dependent transient picosecond and continuous-wave
photomodulation studies of disordered and ordered films of
2-methoxy-5-(2-ethylhexyloxy) poly(para-phenylenevinylene). Photoinduced
absorption (PA) bands in the disordered film exhibit very weak pressure
dependence and are assigned to intrachain excitons and polarons. In contrast,
the ordered film exhibits two additional transient PA bands in the midinfrared
that blueshift dramatically with pressure. Based on high-order configuration
interaction calculations we ascribe the PA bands in the ordered film to
excimers. Our work brings insight to the exciton binding energy in ordered
films versus disordered films and solutions. The reduced exciton binding energy
in ordered films is due to new energy states appearing below the continuum band
threshold of the single strand.Comment: 5.5 pages, 5 figure
Turbulence-induced melting of a nonequilibrium vortex crystal in a forced thin fluid film
To develop an understanding of recent experiments on the turbulence-induced
melting of a periodic array of vortices in a thin fluid film, we perform a
direct numerical simulation of the two-dimensional Navier-Stokes equations
forced such that, at low Reynolds numbers, the steady state of the film is a
square lattice of vortices. We find that, as we increase the Reynolds number,
this lattice undergoes a series of nonequilibrium phase transitions, first to a
crystal with a different reciprocal lattice and then to a sequence of crystals
that oscillate in time. Initially the temporal oscillations are periodic; this
periodic behaviour becomes more and more complicated, with increasing Reynolds
number, until the film enters a spatially disordered nonequilibrium statistical
steady that is turbulent. We study this sequence of transitions by using
fluid-dynamics measures, such as the Okubo-Weiss parameter that distinguishes
between vortical and extensional regions in the flow, ideas from nonlinear
dynamics, e.g., \Poincare maps, and theoretical methods that have been
developed to study the melting of an equilibrium crystal or the freezing of a
liquid and which lead to a natural set of order parameters for the crystalline
phases and spatial autocorrelation functions that characterise short- and
long-range order in the turbulent and crystalline phases, respectively.Comment: 31 pages, 56 figures, movie files not include
Exact results and scaling properties of small-world networks
We study the distribution function for minimal paths in small-world networks.
Using properties of this distribution function, we derive analytic results
which greatly simplify the numerical calculation of the average minimal
distance, , and its variance, . We also discuss the
scaling properties of the distribution function. Finally, we study the limit of
large system sizes and obtain some analytic results.Comment: RevTeX, 4 pages, 5 figures included. Minor corrections and addition
Gravitational oscillations of a liquid column
We report gravity oscillations of a liquid column partially immersed in a
bath of liquid. We stress in particular some peculiarities of this system,
namely (i) the fact that the mass of this oscillator constantly changes with
time; (ii) the singular character of the beginning of the rise, for which the
mass of the oscillator is zero; (iii) the sources of dissipation in this
system, which is found to be dominated at low viscosity by the entrance (or
exit) effects, leading to a long-range damping of the oscillations. We conclude
with some qualitative description of a second-order phenomenon, namely the
eruption of a jet at the beginning of the rise.Comment: 22 pages, pdf. Submitted to Physics of Fluid
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