arXiv subjects

S. Tarafdar

Publications and source records attributed to S. Tarafdar.

8 recordsLinked to original sources

arXiv2014

Studies of protein adsorption on implant materials in relation to biofilm formation I. Activity of Pseudomonas aeruginosa on Polypropylene and High density Polyethylene in presence of serum albumin

The surface of biomaterials used as implants are highly susceptible to bacterial colonization and subsequent infection. The amount of protein adsorption on biomaterials, among other factors, can affect the nature and quality of biofilms formed on them. The variation in the adsorption time of the protein on the biomaterial surface produces a phenotypic change in the bacteria by alteration of the production of EPS (exoplysaccharide) matrix. Knowledge of the effects of protein adsorption on implant infection will be very useful in understanding the chemistry of the biomaterial surfaces, which can deter the formation of biofilms. It is observed that the adsorption of BSA on the biomaterial surfaces increases with time and concentration, irrespective of their type and the nature of the EPS matrix of the bacterial biofilm is dependent on the amount of protein adsorbed on the biomaterial surface. The adsorption of protein (BSA) on the biomaterials, polypropylene (PP) and high density polyethylene (HDPE) has been studied and the formation of the biofilms of Pseudomonas aeruginosa on them has been examined.

physics.bio-ph↗

arXiv2003

Percolation in deposits for competitive models in (1+1)-dimensions

The percolation behaviour during the deposit formation, when the spanning cluster was formed in the substrate plane, was studied. Two competitive or mixed models of surface layer formation were considered in (1+1)-dimensional geometry. These models are based on the combination of ballistic deposition (BD) and random deposition (RD) models or BD and Family deposition (FD) models. Numerically we find, that for pure RD, FD or BD models the mean height of the percolation deposit $\bar h$ grows with the substrate length $L$ according to the generalized logarithmic law $\bar h\propto (\ln (L))^γ$, where $γ=1.0$ (RD), $γ=0.88\pm 0.020$ (FD) and $γ=1.52\pm 0.020$ (BD). For BD model, the scaling law between deposit density $p$ and its mean height $\bar h$ at the point of percolation of type $p-p_\infty \propto \bar h^{-1/ν_h}$ are observed, where $ν_h =1.74\pm0.02$ is a scaling coefficient. For competitive models the crossover, %in $h$ versus $L$ corresponding to the RD or FD -like behaviour at small $L$ and the BD-like behaviour at large $L$ are observed.

cond-mat.stat-mech↗

arXiv2002

Percolation in Models of Thin Film Depositions

We have studied the percolation behaviour of deposits for different (2+1)-dimensional models of surface layer formation. The mixed model of deposition was used, where particles were deposited selectively according to the random (RD) and ballistic (BD) deposition rules. In the mixed one-component models with deposition of only conducting particles, the mean height of the percolation layer (measured in monolayers) grows continuously from 0.89832 for the pure RD model to 2.605 for the pure RD model, but the percolation transition belong to the same universality class, as in the 2- dimensional random percolation problem. In two- component models with deposition of conducting and isolating particles, the percolation layer height approaches infinity as concentration of the isolating particles becomes higher than some critical value. The crossover from 2d to 3d percolation was observed with increase of the percolation layer height.

cond-mat.soft↗

arXiv2002

Condensation and evaporation on a randomly occupied square lattice

We study the evolution of an initially random distribution of particles on a square lattice, under certain rules for `growing' and `culling' of particles. In one version we allow the particles to move laterally along the surface (mobile layer) and in the other version this motion is not allowed (immobile case). In the former case both analytical and computer simulation results are presented, while in the latter only simulation is possible. We introduce growth and culling probabilities appropriate for condensation and evaporation on a two-dimensional surface, and compare results with existing models for this problem. Our results show very interesting behaviour, under certain conditions quite different from earlier models. We find a possibility of hysteresis not reported earlier for such models. ~

cond-mat.soft↗

arXiv2001

A Percolation Model of Diagenesis

The restructuring process of diagenesis in the sedimentary rocks is studied using a percolation type model. The cementation and dissolution processes are modeled by the culling of occupied sites in rarefied and growth of vacant sites in dense environments. Starting from sub-critical states of ordinary percolation the system evolves under the diagenetic rules to critical percolation configurations. Our numerical simulation results in two dimensions indicate that the stable configuration has the same critical behaviour as the ordinary percolation.

cond-mat.soft↗

arXiv1999

Ion-Conducting Polymers - Quenched to Dynamic Disorder

Ion conducting polymers have a biphasic character with crystalline as well as amorphous phases. There is moreover, a dynamic disorder due to motion of polymer chain segments. The PEO-NH$_4$ClO$_4$ system undergoes a crossover from a DLA-type morphology for low salt fraction (X) to a structure with polygonal spherulites. In the present communication we show that the low X regime exhibits a variation of diffusivity with crystallinity typical of a quenched system, whereas the high X regime has dynamic disorder with rapid rearrangement.

cond-mat↗

arXiv1998

Diffusion on a Rearranging Lattice

In this paper we present a computer simulation of a random walk (RW) for diffusion on a rearranging lattice. The lattice consists of two types of sites -- one good conducting (type 1) and the other poor conducting (type 2), distributed at random. The two types of sites are assigned different waiting times ($τ_{1}$ for type 1 and $τ_{2}$ for type 2) . We assume that at intervals of time $τ_{r}$, the site distribution changes. The effect of this rearrangement on the diffusion coefficient is studied with varying $τ_{r}$. We study this effect for different ratios of dwell times of the two types of sites (R) and also for different fractions (X) of the less conducting sites. An empirical relation for D($τ_{1}$ ,$τ_{2}$,$τ_{r}$,X) is suggested. We have employed the well model and considered diffusion controlled by sites, rather than bonds. So our approach is different from the dynamic bond percolation model, which studies these aspects. Our results show that the diffusion coefficient D may change by a factor of upto 3 (approximately) for rapid rearrangement, and there is a considerable effect of varying X and R on the range of variation of D, where X is the fraction of low conducting sites, and R is the ratio of the dwell times for the two types of sites. Further for $τ_{r}$ > 250$τ$ ($τ$ is the time unit for the random walk) the effect of rearrangement becomes negligible. The results may be useful for studying diffusion and conduction of ion conducting polymers.

cond-mat↗

arXiv1997

A computer simulation study of ionic conductivity in polymer electrolytes

In this paper we present a computer simulation study of ionic conductivity in solid polymeric electrolytes. The multiphase nature of the material is taken into account. The polymer is represented by a regular lattice whose sites represent either crystalline or amorphous regions with the charge carrier performing a random walk. Different waiting times are assigned to sites corresponding to the different phases. A random walk (RW) is used to calculate the conductivity through the Nernst-Einstein relation. Our walk algorithm takes into account the reorganisation of the different phases over time scales comparable to time scales for the conduction process. This is a characteristic feature of the polymer network. The qualitative nature of the variation of conductivity with salt concentration agrees with the experimental values for PEO-NH$_{4}$I and PEO-NH$_{4}$SCN. The average jump distance estimated from our work is consistent with the reported bond lengths for such polymers.

cond-mat↗