Search results for "Diffusion"
showing 10 items of 1615 documents
Statics and dynamics of colloid-polymer mixtures near their critical point of phase separation: A computer simulation study of a continuous Asakura–O…
2008
We propose a new coarse-grained model for the description of liquid-vapor phase separation of colloid-polymer mixtures. The hard-sphere repulsion between colloids and between colloids and polymers, which is used in the well-known Asakura-Oosawa (AO) model, is replaced by Weeks-Chandler-Anderson potentials. Similarly, a soft potential of height comparable to thermal energy is used for the polymer-polymer interaction, rather than treating polymers as ideal gas particles. It is shown by grand-canonical Monte Carlo simulations that this model leads to a coexistence curve that almost coincides with that of the AO model and the Ising critical behavior of static quantities is reproduced. Then the …
Silica-coated calcium pectinate beads for colonic drug delivery
2013
The aim of this work is to develop novel organic-inorganic hybrid beads for colonic drug delivery. For this purpose, calcium pectinate beads with theophylline are prepared by a cross-linking reaction between amidated low-methoxyl pectin and calcium ions. The beads are then covered with silica, starting from tetraethyoxysilane (TEOS), by a sol-gel process. The influence of TEOS concentration (0.25, 0.50, 0.75 and 1.00 M) during the process is studied in order to modulate the thickness of the silica layer around the pectinate beads and thus to control the drug release. The interactions between the silica coating and the organic beads are weak according to the physicochemical characterizations…
Physical characterization of alginate-Pluronic F127 gel for endoluminal NABDs delivery
2014
Here we focus the attention on the physical characteristics of a highly biocompatible hydrogel made up of crosslinked alginate and Pluronic F127 (PF127). This is a composite polymeric blend we propose for artery endoluminal delivery of an emerging class of molecules named nucleic acid based drugs (NABDs). The physical characterization of our composite gel, i.e. mesh size distribution and PF127-alginate mutual organization after crosslinking, can significantly determine the NABDs release kinetics. Thus, to explore these aspects, different technical approaches, i.e. rheology, low/high field NMR and TEM, were used. While rheology provided information at the macroscopic and nano-level, the othe…
The lower rather than higher density charge carrier determines the NH 3 -sensing nature and sensitivity of ambipolar organic semiconductors
2018
International audience; Despite the extensive studies and great application potentials, the sensing nature of ambipolar organic semiconductor gas sensors still remains unclarified, unlike their inorganic counterparts. Herein, different numbers of thiophenoxy groups are introduced into the phthalocyanine periphery of bis(phthalocyaninato) rare earth semiconductors to continuously tune their HOMO and LUMO energies, resulting in the ambipolar M[Pc(SPh)(8)](2) [M = Eu (1), Ho (2)] and p-type M(Pc)[Pc(SPh)(8)] [M = Eu (3), Ho (4)]. An OFET in combination with direct I-V measurements over the devices from the self-assembled nanostructures of 1-4 revealed the original electron and hole densities (…
Ultrastructure of the Perineurium
2014
The perineurium is composed of multiple concentric single-cell layers enclosing individual nerve fascicles. Each layer has a thickness equivalent to the width of a perineurial cell. Groups of these cells join by means of tight junctions and desmosomes to form layers that function as a barrier against diffusion of particles across them. Perineurial internal layers have more of these specialized unions among perineurial cells, which are proximal to nerve fascicles.
Hyperpolarized helium-3 gas magnetic resonance imaging of the lung.
2003
3He magnetic resonance imaging (MRI) is capable of producing new and regional information on normal and abnormal lung ventilation. The basis of 3He MRI involves "optical pumping" to hyperpolarize the 3He nuclei by photon angular momentum transfer. The hyperpolarized gas is administered via inhalation. 3He is an inert, nontoxic noble gas and absorbed in less than 0.1%. Imaging consists of a four-step protocol. 1) Gas density 3He MRI with high spatial resolution displays the distribution of a 3He bolus in a 10-second breath-hold. An almost homogeneous distribution is regarded as normal. Patients with lung diseases show multiple ventilation defects. 3He MRI has been shown to be more sensitive …
Chemical self-organization in self-assembling biomimetic systems
2009
Abstract Far-from-equillibrium oscillating chemical reactions are among the simplest systems showing complex behaviors and emergent properties. This class of reactions is often employed to mimic and understand the mechanisms of a great variety of biological processes. In this context, pattern formation due to the coupling between reaction and transport phenomena represent an active and promising research area. In this paper, we present results coming from experiments where we tried to blend the structural properties of self-assembled matrixes (sodium dodecyl sulphate micelles and phospholipid bilayers) together with the evolutive peculiarities of the Belousov–Zhabotinsky reaction. A series …
A non-local model of fractional heat conduction in rigid bodies
2011
In recent years several applications of fractional differential calculus have been proposed in physics, chemistry as well as in engineering fields. Fractional order integrals and derivatives extend the well-known definitions of integer-order primitives and derivatives of the ordinary differential calculus to real-order operators. Engineering applications of fractional operators spread from viscoelastic models, stochastic dynamics as well as with thermoelasticity. In this latter field one of the main actractives of fractional operators is their capability to interpolate between the heat flux and its time-rate of change, that is related to the well-known second sound effect. In other recent s…
On Mathematical Modelling of Metals Distribution in Peat Layers
2014
In this paper we consider averaging and finite difference methods for solving the 3-D boundary-value problem in multilayered domain. We consider the metals Fe and Ca concentration in the layered peat blocks. Using experimental data the mathematical model for calculation of concentration of metals in different points in peat layers is developed. A specific feature of these problems is that it is necessary to solve the 3-D boundary-value problems for elliptic type partial differential equations (PDEs) of second order with piece-wise diffusion coefficients in the layered domain. We develop here a finite-difference method for solving of a problem of one, two and three peat blocks with periodica…
Numerical Simulation of a Contractivity Based Multiscale Cancer Invasion Model
2017
We present a problem-suited numerical method for a particularly challenging cancer invasion model. This model is a multiscale haptotaxis advection-reaction-diffusion system that describes the macroscopic dynamics of two types of cancer cells coupled with microscopic dynamics of the cells adhesion on the extracellular matrix. The difficulties to overcome arise from the non-constant advection and diffusion coefficients, a time delay term, as well as stiff reaction terms.