Knowledge-based Model Building with KONWERK

Modeling a real world optimization problem in a form which can be processed by a machine (computer) is usually a very difficult and complex task. Therefore, building and verifying the model is often the most time consuming part of the whole process of solving a real world problem using methods of Operations Research. Software tools, which integrate representation methods developed in the field of Artificial Intelligence (AI) and methods of OR, can facilitate and speed up the process of model development. The paper introduces the idea of knowledge based modeling as a model development and representation technique facilitating the complex process of model building. We describe the KONWERK tool-box which combines hierarchical structured knowledge representation and object oriented methodology thus providing a framework for model building and application of different optimization methods. We want the reader to form an idea of the methodology of model development and knowledge representation with KONWERK and to understand the hierarchical structure of the knowledge base. The model of the Nitra River Case is used to describe and explain the modeling and knowledge representation with KONWERK. A given multicriteria model of the Nitra River Case was reimplemented using KONWERK within about three weeks and later enlarged by implementation of additional fairness criteria

Simple Lattice-Models of Ion Conduction: Counter Ion Model vs. Random Energy Model

The role of Coulomb interaction between the mobile particles in ionic conductors is still under debate. To clarify this aspect we perform Monte Carlo simulations on two simple lattice models (Counter Ion Model and Random Energy Model) which contain Coulomb interaction between the positively charged mobile particles, moving on a static disordered energy landscape. We find that the nature of static disorder plays an important role if one wishes to explore the impact of Coulomb interaction on the microscopic dynamics. This Coulomb type interaction impedes the dynamics in the Random Energy Model, but enhances dynamics in the Counter Ion Model in the relevant parameter range.Comment: To be published in Phys. Rev.

Lifetime and production rate of NOx in the upper stratosphere and lower mesosphere in the polar spring/summer after the solar proton event in October - November 2003

We present altitude-dependent lifetimes of NOx, determined with MIPAS/ENVISAT (the Michelson Interferometer for Passive Atmospheric Sounding/the European Environment Satellite), for the Southern polar region after the solar proton event in October–November 2003. Between 50° S and 90° S and decreasing in altitude they range from about two days at 64 km to about 20 days at 44 km. The lifetimes are controlled by transport, mixing and photochemistry. We infer estimates of dynamical lifetimes by comparison of the observed decay to photochemical lifetimes calculated with the SLIMCAT 3-D Model. Photochemical loss contributes to the observed NOx depletion by 0.1% at 44 km, increasing with altitude to 45% at 64 km. In addition, we show the correlation of modelled ionization rates and observed NOx densities under consideration of the determined lifetimes of NOx, and calculate altitudedependent effective production rates of NOx due to ionization. For that we compare ionization rates of the AIMOS data base with the MIPAS measurements from 15 October–31 December 2003. We derive effective NOx-production rates to be applied to the AIMOS ionization rates which range from about 0.2 NOx-molecules per ion pair at 44 km to 0.7 NOx-molecules per ion pair at 62 km. These effective production rates are considerably lower than predicted by box model simulations which could hint at an overestimation of the modelled ionization rates

Channel diffusion of sodium in a silicate glass

We use classical molecular dynamics simulations to study the dynamics of sodium atoms in amorphous Na$_2$O-4SiO$_2$. We find that the sodium trajectories form a well connected network of pockets and channels. Inside these channels the motion of the atoms is not cooperative but rather given by independent thermally activated hops of individual atoms between the pockets. By determining the probability that an atom returns to a given starting site, we show that such events are not important for the dynamics of this system.Comment: 10 pages of Latex, 5 figures, one figure added, text expande

Do vibrationally excited OH molecules affect middle and upper atmospheric chemistry?

Except for a few reactions involving electronically excited molecular or atomic oxygen or nitrogen, atmospheric chemistry modelling usually assumes that the temperature dependence of reaction rates is characterized by Arrhenius' law involving kinetic temperatures. It is known, however, that in the upper atmosphere the vibrational temperatures may exceed the kinetic temperatures by several hundreds of Kelvins. This excess energy has an impact on the reaction rates. We have used upper atmospheric OH populations and reaction rate coefficients for OH(<i>v</i>=0...9)+O<sub>3</sub> and OH(<i>v</i>=0...9)+O to estimate the effective (i.e. population weighted) reaction rates for various atmospheric conditions. We have found that the effective rate coefficient for OH(<i>v</i>=0...9)+O<sub>3</sub> can be larger by a factor of up to 1470 than that involving OH in its vibrational ground state only. At altitudes where vibrationally excited states of OH are highly populated, the OH reaction is a minor sink of O<sub>x</sub> and O<sub>3</sub> compared to other reactions involving, e.g., atomic oxygen. Thus the impact of vibrationally excited OH on the ozone or O<sub>x</sub> sink remains small. Among quiescent atmospheres under investigation, the largest while still small (less than 0.1%) effect was found for the polar winter upper stratosphere and mesosphere. The contribution of the reaction of vibrationally excited OH with ozone to the OH sink is largest in the upper polar winter stratosphere (up to 4%), while its effect on the HO<sub>2</sub> source is larger in the lower thermosphere (up to 1.5% for polar winter and 2.5% for midlatitude night conditions). For OH(<i>v</i>=0...9)+O the effective rate coefficients are lower by up to 11% than those involving OH in its vibrational ground state. The effects on the odd oxygen sink are negative and can reach −3% (midlatitudinal nighttime lowermost thermosphere), i.e. neglecting vibrational excitation overestimates the odd oxygen sink. The OH sink is overestimated by up to 10%. After a solar proton event, when upper atmospheric OH can be enhanced by an order of magnitude, the excess relative odd oxygen sink by consideration of vibrational excitation in the reaction of OH(<i>v</i>=0...9)+O<sub>3</sub> is estimated at up to 0.2%, and the OH sink by OH(<i>v</i>=0...9)+O can be reduced by 12% in the thermosphere by vibrational excitation

Do vibrationally excited OH molecules affect middle and upper atmospheric chemistry?

Except for a few reactions involving electronically excited molecular or atomic oxygen or nitrogen, atmospheric chemistry modelling usually assumes that the temperature dependence of reaction rates is characterized by Arrhenius’ law involving kinetic temperatures. It is known, however, that in the upper atmosphere the vibrational temperatures may exceed the kinetic temperatures by several hundreds of Kelvins. This excess energy has an impact on the reaction rates. We have used upper atmospheric OH populations and reaction rate coefficients for OH(υ = 0...9)+O3 and OH(υ = 0...9)+O to estimate the effective (i.e. population weighted) reaction rates for various atmospheric conditions. We have found that the effective rate coefficient for OH(υ =0...9)+O3 can be larger by a factor of up to 1470 than that involving OH in its vibrational ground state only. At altitudes where vibrationally excited states of OH are highly populated, the OH reaction is a minor sink of Ox and O3 compared to other reactions involving, e.g., atomic oxygen. Thus the impact of vibrationally excited OH on the ozone or Ox sink remains small. Among quiescent atmospheres under investigation, the largest while still small (less than 0.1%) effect was found for the polar winter upper stratosphere and mesosphere. The contribution of the reaction of vibrationally excited OH with ozone to the OH sink is largest in the upper polar winter stratosphere (up to 4%), while its effect on the HO2 source is larger in the lower thermosphere (up to 1.5% for polar winter and 2.5% for midlatitude night conditions). For OH(υ =0...9)+O the effective rate coefficients are lower by up to 11% than those involving OH in its vibrational ground state. The effects on the odd oxygen sink are negative and can reach −3% (midlatitudinal nighttime lowermost thermosphere), i.e. neglecting vibrational excitation overestimates the odd oxygen sink. The OH sink is overestimated by up to 10%. After a solar proton event, when upper atmospheric OH can be enhanced by an order of magnitude, the excess relative odd oxygen sink by consideration of vibrational excitation in the reaction of OH(υ =0...9)+O3 is estimated at up to 0.2%, and the OH sink by OH(υ =0...9)+O can be reduced by 12% in the thermosphere by vibrational excitation