Structure and mobility of cyclohexane as a solvent for Trans-Polyisoprene

Solutions of {\it trans}$-$polyisoprene in cyclohexane are investigated in atomistic detail at different compositions at two different temperatures. We investigate the influence of polymer concentration on the dynamics of the solvent molecules and the structure of the solvation shell. The double bonds along the polymer backbone are preferentially approached by the solvent molecules. The mobility of cyclohexane molecules decreases with increasing polymer concentration at ambient conditions. The reorientation of molecules becomes more anisotropic with concentration as the polymer hinders the reorientation of the molecular plane. At elevated temperatures the influence of the polymer is weaker and the reorientation of the solvent is more isotropic. Additionally, a fast and efficient way to set up atomistic simulations is shown in detail in which the initial simulations increase in length and in the simulation time-step. The excess energy from initial overlaps is removed by resetting the velocities at regular intervals.Comment: 6 pages, 3 figure

Thinking Outside the Box: Using Computer Science Skills to Make Sense of the Biology of Life

While I liked coding and the logical aspects of computer programming, my gut was telling me I hadn\u27t quite found my niche yet. In what field could my computer science skills make a difference while also providing me with challenging problems to solve? As these questions percolated through my subconscious, I came across a brief article about a field called “bioinformatics.

Properties of Poly (isoprene) - Model Building in the Melt and in Solution

Properties of 1,4-\textit{trans} poly (isoprene) at ambient conditions are determined by simulations on two length scales based on two different models: a full-atomistic and a mesoscopic one. The models are linked via a mapping scheme such that one mesoscopic bead represents one chemical repeat unit. Melts as well as solutions of several chain lengths were investigated and mapped individually to the meso-scale. The resulting models are compared to each other. The meso-scale models could be simulated over a large variety of chain lengths and time-scales relevant for experimental comparison. Concerning static properties, we determined the persistence length of our systems and the scaling behavior of the radius of gyration. The latter was compared to experiments and the agreement is satisfactory. Furthermore, we find deviations from Rouse dynamics at all chain lengths at ambient conditions.Comment: 11 pictures 7 figure

Light-Quark Decays in Heavy Hadrons

We consider weak decays of heavy hadrons (bottom and charmed) where the heavy quark acts as a spectator. Theses decays are heavily phase-space suppressed but may become experimentally accessible in the near future. These decays are interesting as a QCD laboratory to study the behaviour of the light quarks in the colour-background field of the heavy spectator.Comment: 11 pages, 6 table

On approximative solutions of multistopping problems

In this paper, we consider multistopping problems for finite discrete time sequences $X_1,...,X_n$. $m$-stops are allowed and the aim is to maximize the expected value of the best of these $m$ stops. The random variables are neither assumed to be independent not to be identically distributed. The basic assumption is convergence of a related imbedded point process to a continuous time Poisson process in the plane, which serves as a limiting model for the stopping problem. The optimal $m$-stopping curves for this limiting model are determined by differential equations of first order. A general approximation result is established which ensures convergence of the finite discrete time $m$-stopping problem to that in the limit model. This allows the construction of approximative solutions of the discrete time $m$-stopping problem. In detail, the case of i.i.d. sequences with discount and observation costs is discussed and explicit results are obtained.Comment: Published in at http://dx.doi.org/10.1214/10-AAP747 the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org

Automatic Coarse Graining of Polymers

Several recently proposed semi--automatic and fully--automatic coarse--graining schemes for polymer simulations are discussed. All these techniques derive effective potentials for multi--atom units or super--atoms from atomistic simulations. These include techniques relying on single chain simulations in vacuum and self--consistent optimizations from the melt like the simplex method and the inverted Boltzmann method. The focus is on matching the polymer structure on different scales. Several ways to obtain a time-scale for dynamic mapping are discussed additionally. Finally, similarities to other simulation areas where automatic optimization are applied as well are pointed out.Comment: 17 pages, 5 figure