Proton irradiation of simple gas mixtures: Influence of irradiation parameters

In order to get information about the influence of irradiation parameters on radiolysis processes of astrophysical interest, methane gas targets were irradiated with 6.5 MeV protons at a pressure of 1 bar and room temperature. Yields of higher hydrocarbons like ethane or propane were found by analysis of irradiated gas samples using gas chromatography. The handling of the proton beam was of great experimental importance for determining the irradiation parameters. In a series of experiments current density of the proton beam and total absorbed energy were shown to have a large influence on the yields of produced hydrocarbons. Mechanistic interpretations of the results are given and conclusions are drawn with regard to the chemistry and the simulation of various astrophysical systems

Upper Error Bounds for Approximations of Stochastic Differential Equations with Markovian Switching

We consider stochastic differential equations with Markovian switching (SDEwMS). An SDEwMS is a stochastic differential equation with drift and diffusion coefficients depending not only on the current state of the solution but also on the current state of a right-continuous Markov chain taking values in a finite state space. Consequently, an SDEwMS can be viewed as the result of a finite number of different scenarios switching from one to the other according to the movement of the Markov chain. The generator of the Markov chain is given by transition probabilities involving a parameter which controls the intensity of switching from one state to another. We construct numerical schemes for the approximation of SDE\u27swMS and present upper error bounds for these schemes. Our numerical schemes are based on a time discretization with constant step-size and on the values of a discrete Markov chain at the discretization points. It turns out that for the Euler scheme a similar upper bound as in the case of stochastic ordinary differential equations can be obtained, while for the Milstein scheme there is a strong connection between the power of the step-size appearing in the upper bound and the intensity of the switching

Stability of numerical schemes for stochastic differential equations with multiplicative noise.

A notion of stability for a special type of test equations is proposed. These are stochastic differential equations with multiplicative noise for which there is a connection between the parameters in the drift and diffusion coefficient. By means of the Euler scheme and two different implicit Euler schemes a method to find the regions of stability is also examined

National Inventory of Swiss Bryophytes (NISM)

The NISM-database (GIVD ID EU-CH-004) contains bryophyte records from 1,237 relevés of 100 m². 408 of these relevés are located on a systematic grid which covers the whole of Switzerland and Liechtenstein (1 relevé). Further 430 plots have been placed randomly (429 in CH, 1 in LI) and 399 plots have been positioned arbitrarily into different habitat types (387 in CH, 12 in LI). On each plot all bryophyte species present were recorded. For each species on each plot the main substrate where the species was growing has been noted as well as their fertility. In total, the database contains 19,000 records from these relevés. At the moment we are just starting to analyse the data, but joint projects with other working groups are welcome

Stability of weak numerical schemes for stochastic differential equations.

The paper considers numerical stability and convergence of weak schemes solving stochastic differential equations. A relatively strong notion of stability for a special type of test equations is proposed. These are stochastic differential equations with multiplicative noise. For different explicit and implicit schemes the regions of stability are also examined

On quasi-Monte Carlo simulation of stochastic differential equations

In a number of problems of mathematical physics and other fields stochastic differential equations are used to model certain phenomena. Often the solution of those problems can be obtained as a functional of the solution of some specific stochastic differential equation. Then we may use the idea of weak approximation to carry out numerical simulation. We analyze some complexity issues for a class of linear stochastic differential equations (Langevin type), which can be given by dXt = -α:Xtdt + β(t)dWt, X0 ≔ 0, where α > 0 and β: [0, T] → ℝ. It turns out that for a class of input data which are not more than Lipschitz continuous the explicit Euler scheme gives rise to an optimal (by order) numerical method. Then we study numerical phenomena which occur when switching from (real) Monte Carlo simulation to quasi-Monte Carlo one, which is the case when we carry out the simulation on computers. It will easily be seen that completely uniformly distributed sequences yield good substitutes for random variates, while not all uniformly distributed (mod1) sequences are suited. In fact we provide necessary conditions on a sequence in order to serve for quasi-Monte Carlo purposes. This condition is expressed in terms of the measure of well distribution. Numerical examples complement the theoretical analysis

The role of subunit composition on prepulse facilitation of the cardiac L-type calcium channel

AbstractFacilitation of calcium current by depolarizing prepulses has been observed in many cells including cardiac muscle. The mechanism underlying prepulse facilitation is controversial with respect to the requirements of channel subunits and cAMP kinase. We found that coexpression of the cardiac α1C-a subunit with the cardiac β2a subunit significantly promotes the facilitation of IBa by strong depolarizing prepulses. The magnitude of IBa facilitation depended on the voltage potential of the prepulse and the interval duration between prepulse and test pulse. Prepulse facilitation was not affected by coexpression of AKAP79 and conditions favoring cAMP-dependent phosphorylation. Prepulse facilitation was also observed in cells expressing an α1C-a subunit which was truncated at residue 1733 removing the cAMP kinase site at Ser-1928. Facilitation was abolished by coexpression of the α2δ-1 or α2δ-3 subunit. We conclude that the expressed α1C-a β2a complex is sufficient to support prepulse facilitation. Facilitation is prevented by coexpression of the α2δ subunit