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Ana Proykova

Publications and source records attributed to Ana Proykova.

11 recordsLinked to original sources
arXiv2017

A model provides insight into electric field-induced rupture mechanism of water-in-toluene emulsion films

This paper presents the first MD simulations of a model, which we have designed for understanding the development of electro-induced instability of a thin toluene emulsion film in contact with saline aqueous phase. This study demonstrates the charge accumulation role in toluene film rupture when a DC electric field is applied. The critical value of the external field at which film ruptures, thin film charge distribution, capacitance, number densities and film structure have been obtained in simulating the system within NVT and NPT ensembles. A mechanism of thin film rupture driven by the electric discharge is suggested.We show that NPT ensemble with a constant surface tension is a better choice for further modeling of the systems that resemble more close the real films.

physics.chem-ph↗
arXiv2007

Monte Carlo Simulation of Age-Dependent Host-Parasite Relations

The death of a biological population is an extreme event which we investigate here for a host-parasitoid system. Our simulations using the Penna ageing model show how biological evolution can ``teach'' the parasitoids to avoid extinction by waiting for the right age of the host. We also show the dependence of extinction time on the population size.

q-bio.PE↗
arXiv2007

Monte Carlo Simulation of Medical Resource Allocation

Computer simulations prove that we should spend more money on red wine than on medication. We optimise the problem of how to distribute a fixed amount of money between medication and food spendings, using the Penna ageing model.

q-bio.PE↗
arXiv2004

Simulated Stress and Stretch of SWCNT

The mechanical stability of open single wall carbon nanotubes (SWCNT) under axial stress (compression and tension) and twist has been re-examined in a search of specific tube-length and load scaling. SWCNT with different chiralities and lengths have been simulated with a classical molecular dynamics method employing the many-body empirical Tersoff-Brenner potential. Stress has been achieved by enforcing constant linear velocity on the edge atoms from both sides of the SWCNT as suggested by Srivastava and Barnard. We have found opposite length scaling at fast (1/10 of vs the sound velocity in carbon tubes) and slow (1/20 vs) loading of (10, 0) tubes. Another finding is that at fast loading short zigzag (10, 0) tubes transform from elastic to plastic states before they break in the middle, while tubes, longer than 13 nm, break-up directly in the elastic state. Thus, short tubes behave like metals or ionic solids, while long tubes resemble ceramics or glasses under the conditions studied. All tubes form spiral-like structures when twisted. Standing waves, generated under specific conditions, determine the different behavior of tubes with various lengths and chiralities. Keywords: Molecular Dynamics simulations, elasticity and inelasticity, single-wall carbon nanotubes, nanoscale pattern formation, constant-composition solid-solid phase transformations, pressure treatment PACS: 02.70.Ns, 81.30.Hd, 81.40.Jj, 81.40.Vw

cond-mat.mtrl-sci↗
arXiv2003

Can Small Free Methane Clusters Exhibit Phase-like Transitions?

Low-temperature (below 60K) phase changes of free clusters containing 50, 137, and 229 methane molecules have been observed in isoenergetic Molecular Dynamics computations. Bulk solid methane exhibits structural phase transformation at 20.4 K. However, clusters of 50 molecules already melt at about 25 K, which makes the observation of solid-solid transformations rather challenging. Molecular Dynamics calculations of isoenergetic free methane clusters show that they exhibit transformations from an orientationally-ordered (~ 10K) and a disordered phase (above 20K). There is no hysteresis in the cooling-heating regime - a signal for continuous transition.

physics.atm-clus↗
arXiv2003

A Model for Randomly Correlated Deposition

A simple, discrete, parametric model is proposed to describe conditional (correlated) deposition of particles on a surface and formation of a connecting (percolating) cluster. The surface changes spontaneously its properties (phase transition) when a percolating cluster appears. The parameter k is included in the probability p(k) of particles to stick together and form a cluster on the surface. The case k=1 corresponds to the ordinary 2D percolation on a square lattice. Thus the percolation threshold is controlled by the k-value: the larger k the higher threshold for percolation. The growth model seen from the percolation point of view allows us to describe several interesting applications in addition to irreversible aggregation in the presence of a repulsive force, k>1. For example, the occupied lattice sites might represent regions of specific magnetization in an otherwise disordered medium. Then the whole system is ordered or not according to the concentration of the deposited particles. Object-oriented code is developed for the Monte Carlo part of the calculations.

cond-mat.stat-mech↗
arXiv2003

Simple Simulation of Magnetic Structure for Nanoclusters

A simple discrete model for magnetic structures of chromium nanoclusters, found with the help of local-spin DFT by Kohl and Bertsch, still confirms their conclusion that in most of the clusters the magnetic moments are not collinear; instead, in most of the cases they are oriented within one plane. We also simulate the destruction of the anti-ferromagnetic ordering by thermal fluctuations.

cond-mat.stat-mech↗
arXiv2003

Cellular Automata Simulation of Medication-Induced Autoimmune Diseases

We implement the cellular automata model proposed by Stauffer and Weisbuch in 1992 to describe the response of the immune system to antigens in the presence of medications. The model contains two thresholds, $θ_1$ and $θ_2$, suggested by de Boer, Segel, and Perelson to present the minimum field needed to stimulate the proliferation of the receptors and to suppress it, respectively. The influence of the drug is mimicked by increasing the second threshold, thus enhancing the immune response. If this increase is too strong, the immune response is triggered in the whole immune repertoire, causing it to attack the own body. This effect is seen in our simulations to depend both on the ratio of the thresholds and on their absolute values.

cond-mat.stat-mech↗
arXiv2001

Nucleation of Market Shocks in Sornette-Ide model

The Sornette-Ide differential equation of herding and rational trader behaviour together with very small random noise is shown to lead to crashes or bubbles where the price change goes to infinity after an unpredictable time. About 100 time steps before this singularity, a few predictable roughly log-periodic oscillations are seen.

cond-mat.stat-mech↗
arXiv1999

Symmetry in Order-Disorder Changes of Molecular Clusters

The dynamic orientational order-disorder transition of clusters consisting of octahedral molecules is formulated in terms of symmetry-adapted rotator functions. The transition from a higher-temperature body-centered-cubic, orientationally disordered phase to a lower-temperature, monoclinic, orientationally-ordered phase is a two-step process. The higher-temperature transition has two local minima in the free energy, like a finite-system counterpart of a first-order transition. Simulations show the lower-temperature transition is continuous. The analytic theory predicts a temperature of 27K for this transition, for a 59-molecule cluster of tellurium hexafluoride in a good agreement with the ~30K result of canonical Monte Carlo calculations.

physics.atm-clus↗