Mesoscopic non-equilibrium thermodynamics approach to the dynamics of polymers

We present a general formalism able to derive the kinetic equations of polymer dynamics. It is based on the application of nonequilibrium thermodynamics to analyze the irreversible processes taking place in the conformational space of the macromolecules. The Smoluchowski equation results from the analysis of the underlying diffusion process in that space within the scheme of nonequilibrium thermodynamics. We apply the method to different situations, concerning flexible, semiflexible and rod-like polymers and to the case of more concentrated solutions in which interactions become important.Comment: 13 pages (RevTex). To be published in Physica

Itä-Suomen ammattikorkeakoulut : Yhteistyössä hyvinvoinnin osaamista edistämässä

Pohjois-Karjalan ammattikorkeakoulu ja Savonia-ammattikorkeakoulu ovat osana ISAT-toimintaa tehneet yhteistyötä väljästi asutun alueen hyvinvointipalvelujen kehittämiseksi. Yhteistyö on toteutunut kaikilla korkeakoulujen tehtäväalueilla: koulutus, tutkimus-, kehittämis- ja innovaatiotoiminta sekä aluekehittäminen ja kansainvälinen yhteistyö. Tässä julkaisussa kuvataan edellä mainittua ISAT-yhteistyötä useista eri näkökulmista, useiden eri asiantuntijoiden kertomana. Tavoitteena on, että lukijalle syntyy mielikuva ISAT-yhteistyön monipuolisuudesta, koskien väljästi asutun alueen hyvinvointipalveluita

Evaluation of social competencies in chemical engineering: application and results of the pilot test (academic year 2012-2013)

The Escola Tècnica Superior d’Enginyeria Química has a long tradition in the deployment of social competencies in engineering curricula through Integrated Projects (IP) carried out in structured teams. Social competencies are taught and practiced during the development of the IPs. We conceptually introduce a methodology for a 360o assessment of the students’ social competencies, as a tool to foster the improvement of their competency levels. In this article we analyze the results of the pilot test where the aforementioned methodology has been implemented in the Bachelor studies of Chemical Engineering. The results indicate that it is possible to objectively obtain the student’s competency level discriminating among different social competencies, as well as among different students in the same team. The application of this tool fosters the development of specific educative actions to help the students with low competency profile, to reach acceptable levels for a successful insertion in the labor marketPeer Reviewe

Kinetics of Particles Adsorption Processes Driven by Diffusion

The kinetics of the deposition of colloidal particles onto a solid surface is analytically studied. We take into account both the diffusion of particles from the bulk as well as the geometrical aspects of the layer of adsorbed particles. We derive the first kinetic equation for the coverage of the surface (a generalized Langmuir equation) whose predictions are in agreement with recent simulation results where diffusion of particles from the bulk is explicitly considered.Comment: 4 page

Histogram Reweighting Method for Dynamic Properties

The histogram reweighting technique, widely used to analyze Monte Carlo data, is shown to be applicable to dynamic properties obtained from Molecular Dynamics simulations. The theory presented here is based on the fact that the correlation functions in systems in thermodynamic equilibrium are averages over initial conditions of functions of the trajectory of the system in phase-space, the latter depending on the volume, the total number of particles and the classical Hamiltonian. Thus, the well-known histogram reweighting method can almost straightforwardly be applied to reconstruct the probability distribution of initial states at different thermodynamic conditions, without extra computational effort. Correlation functions and transport coefficients are obtained with this method from few simulation data sets.Comment: 4 pages, 3 figure

Phenomenological approach to non-linear Langevin equations

In this paper we address the problem of consistently construct Langevin equations to describe fluctuations in non-linear systems. Detailed balance severely restricts the choice of the random force, but we prove that this property together with the macroscopic knowledge of the system is not enough to determine all the properties of the random force. If the cause of the fluctuations is weakly coupled to the fluctuating variable, then the statistical properties of the random force can be completely specified. For variables odd under time-reversal, microscopic reversibility and weak coupling impose symmetry relations on the variable-dependent Onsager coefficients. We then analyze the fluctuations in two cases: Brownian motion in position space and an asymmetric diode, for which the analysis based in the master equation approach is known. We find that, to the order of validity of the Langevin equation proposed here, the phenomenological theory is in agreement with the results predicted by more microscopic models.Comment: LaTex file, 2 figures available upon request, to appear in Phys.Rev.

Dissipative Particle Dynamics with Energy Conservation

The stochastic differential equations for a model of dissipative particle dynamics with both total energy and total momentum conservation in the particle-particle interactions are presented. The corresponding Fokker-Planck equation for the evolution of the probability distribution for the system is deduced together with the corresponding fluctuation-dissipation theorems ensuring that the ab initio chosen equilibrium probability distribution for the relevant variables is a stationary solution. When energy conservation is included, the system can sustain temperature gradients and heat flow can be modeled.Comment: 7 pages, submitted to Europhys. Let

Particle-Based Mesoscale Hydrodynamic Techniques

Dissipative particle dynamics (DPD) and multi-particle collision (MPC) dynamics are powerful tools to study mesoscale hydrodynamic phenomena accompanied by thermal fluctuations. To understand the advantages of these types of mesoscale simulation techniques in more detail, we propose new two methods, which are intermediate between DPD and MPC -- DPD with a multibody thermostat (DPD-MT), and MPC-Langevin dynamics (MPC-LD). The key features are applying a Langevin thermostat to the relative velocities of pairs of particles or multi-particle collisions, and whether or not to employ collision cells. The viscosity of MPC-LD is derived analytically, in very good agreement with the results of numerical simulations.Comment: 7 pages, 2 figures, 1 tabl