arXiv subjects

Ewa Gudowska-Nowak

Publications and source records attributed to Ewa Gudowska-Nowak.

46 records · Page 3Linked to original sources

arXiv2004

Hopping Models of Charge Transfer in a Complex Environment: New Class of Coupled Memory Continous-Time Random Walks

Charge transport processes in disordered complex media are accompanied by anomalously slow relaxation for which usually a broad distribution of relaxation times is adopted. To account for those properties of the environment, a standard kinetic approach in description of the system is addressed either in the framework of continuous-time random walks (CTRW) or fractional diffusion. In this paper the power of the CTRW approach is illustrated by use of the probabilistic formalism and limit theorems that allow to predict the limiting distributions of the paths traversed by charges and to derive effective relaxation properties of the entire system of interest. Application of the method is discussed for non-exponential electron-transfer processes controlled by dynamics of the surrounding medium.

cond-mat.stat-mech↗

arXiv2004

Population growth and control in stochastic models of cancer development

We study the joint effect of thermal bath fluctuations and an external noise tuning activity of cytotoxic cells on the triggered immune response in a growing cancerous tissue. The immune response is assumed to be primarily mediated by effector cells that develop a cytotoxic activity against the abnormal tissue. The kinetics of such a reaction is represented by an enzymatic-like Michaelis-Menten two step process. Effective free-energy surface for the process is further parametrized by the fluctuating energy barrier between the states of high and low concentration of cancerous cells. By analyzing the far from equilibrium escape problem across the fluctuating potential barrier, we determine condtions of the most efficient decay kinetics of the cancer cell-population in the presence of dichotomously fluctuating concentration of cytotoxic cells.

q-bio.PE↗

arXiv2003

Infinite Products of Large Random Matrices and Matrix-valued Diffusion

We use an extension of the diagrammatic rules in random matrix theory to evaluate spectral properties of finite and infinite products of large complex matrices and large hermitian matrices. The infinite product case allows us to define a natural matrix-valued multiplicative diffusion process. In both cases of hermitian and complex matrices, we observe an emergence of "topological phase transition" in the spectrum, after some critical diffusion time $τ_{\rm crit}$ is reached. In the case of the particular product of two hermitian ensembles, we observe also an unusual localization-delocalization phase transition in the spectrum of the considered ensemble. We verify the analytical formulae obtained in this work by numerical simulation.

math-ph↗

arXiv2003

Resonant activation in the presence of non-equilibrated baths

We study the generic problem of the escape of a classical particle over a fluctuating barrier under the influence of non-Gaussian noise mimicking the effects of not-fully equilibrated bath. Our attention focuses on the effect of the stable noises on the mean escape time and on the phenomenon of resonant activation (RA). Possible physical interpretation of the occurrence of Lévy noises in the system of interest is discussed and the connection between the Tsallis statistics and the Fractional Fokker Planck Equation is addressed.

cond-mat.stat-mech↗

arXiv2003

Implication of Barrier Fluctuations on the Rate of Weakly Adiabatic Electron Transfer

The problem of escape of a Brownian particle in a cusp-shaped metastable potential is of special importance in nonadiabatic and weakly-adiabatic rate theory for electron transfer (ET) reactions. Especially, for the weakly-adiabatic reactions, the reaction follows an adiabaticity criterion in the presence of a sharp barrier. In contrast to the non-adiabatic case, the ET kinetics can be, however considerably influenced by the medium dynamics. In this paper, the problem of the escape time over a dichotomously fluctuating cusp barrier is discussed with its relevance to the high temperature ET reactions in condensed media.

cond-mat.stat-mech↗

arXiv2003

Electronic Properties of Random Polymers: Modelling Optical Spectra of Melanins

Melanins are a group of complex pigments of biological origin, widely spread in all species from fungi to man. Among diverse types of melanins, the human melanins, eumelanins,are brown or black nitrogen-containing pigments, mostly known for their photoprotective properties in human skin. We have undertaken theoretical studies aimed to understand absorption spectra of eumelanins and their chemical precursors. The structure of the biopigment is poorly defined, although it is believed to be composed of cross-linked heteropolymers based on indolequinones. As a basic model of the eumelanin structure, we have chosen pentamers containing hydroquinones (HQ) and/or 5,6-indolequinones (IQ) and/or semiquinones (SQ) often listed as structural melanin monomers. The eumelanin oligomers have been constructed as random compositions of basic monomers and opitimized for the energy of bonding. Absorption spectra of model assemblies have been calculated within the semiempirical intermediate neglect of differential overlap (INDO) approximation. Model spectrum of eumelanin has been further obtained by sum of independent spectra of singular polymers. By comparison with experimental data it is shown that the INDO/CI method manages to reproduce well characteristic properties of experimental spectrum of synthetic eumelanins.

physics.bio-ph↗

arXiv2003

Fundamental building blocks of eumelanins: electronic properties of indolequinone-dimers

We present results from the theoretical INDO calculations of the electronic structure for stacked eumelanins' monomers. As basic indolic components of the eumelanin structure 5,6-dihydroxyindole (DHI or HQ) and its oxidized forms (SQ and IQ) were chosen. The results reveal dependency of electronic properties of such aggregates on monomers' redox states. They point out also a tendency to localize an extra charge on one of dimer's subunits that could be suggestive of an electron hopping as a model mechanism forthe electron transfer in eumelanins.

physics.bio-ph↗

arXiv2002

Influence of the Barrier Shape on Resonant Activation

The escape of a Brownian particle over a dichotomously fluctuating barrier is investigated for various shapes of the barrier. The problem of resonant activation is revisited with the attention on the effect of the barrier shape on optimal value of the mean escape time in the system. The characteristic features of resonant behavior are analyzed for barriers switching either between different heights, or "on" and "off" positions. PACS number(s): 05.10-a, 02.50.-r, 82.20.-wj.

cond-mat.stat-mech↗

arXiv1997

Bridged-assisted electron transfer. Random matrix theory approach

We discuss the effective donor/acceptor coupling for a bridged electron transfer system with a site-diagonal disorder of bridge energies. The average spectral properties of the system are discussed by using the Wegner model (Anderson's type tight-binding Hamiltonian (TBH))for the electronic part of the problem. Spectral properties of the system are discussed using the concept of the functional inverse of the resolvent (``Blue's function'', introduced by Zee) for various limits of noise versus site-site coupling ratio.

cond-mat↗

arXiv1997

Two-level system with noise: Blue's function approach

By using the random matrix approach and generalized Blue's function representation we solve analytically the model of an effective two-level system coupled to a noise reservoir. We show that calculated spectral properties of the system are in agreement with the numerically simulated results. We outline possible applications of the model in the field of condensed phase reactions.

cond-mat↗