Screening in Strongly Coupled Plasmas: Universal Properties from Strings in Curved Space

We use the gauge/gravity correspondence to study the screening of a heavy quark-antiquark pair in various strongly coupled plasmas. Besides N=4 super Yang-Mills theory and the corresponding AdS_5 space we also study theories obtained as deformations of AdS_5, among them in particular a class of deformations solving supergravity equations of motion. We consider the dependence of the screening distance on the velocity and the orientation of the pair in the plasma. The value of the screening distance in N=4 SYM is found to be a minimum in the class of theories under consideration for all kinematic parameters.Comment: 10 pages, Talk presented by C.E. at Gribov-80 Memorial Workshop, ICTP Trieste, Italy, May 201

Applications of Holography to Strongly Coupled Plasmas

We study several observables related to heavy quarks in strongly coupled plasmas using the gauge/gravity correspondence. Besides the AdS_5 space dual to N=4 supersymmetric Yang-Mills theory we consider large classes of theories obtained from various deformations of the AdS_5 space. Among them are theories that solve equations of motion of a 5-dimensional Einstein-Hilbert-scalar action. Specifically, we calculate the screening distance of a heavy quark-antiquark pair moving at constant velocity through the plasma, the running coupling defined via the free energy of such a static pair, and the energy radiation from a heavy quark forced into a circular motion in the plasma. We find that these observables show universal behaviour in large classes of theories. The screening distance in these classes of theories, that is the maximal distance for which a heavy quark-antiquark pair is bound, is found to be bounded from below by its value in N=4 super Yang-Mills theory.Comment: 8 pages, Talk presented by K. S. at Xth Quark Confinement and the Hadron Spectrum, October 8-12, 2012, Munic

Beyond information extraction: The role of ontology in military report processing

Information extraction tools like SMES transform natural language into formal representation, e.g. into feature structures. Doing so, these tools exploit and apply linguistic knowledge about the syntactic and morphological regularities of the language used. However, these tools apply semantic as well as pragmatic knowledge only partially at best. Automatic processing of military reports has to result in a visualization of the reports content by map as well as in an actualization of the underlying database in order to allow for the actualization of the common operational picture. Normally, however, the information provided by the result of the information extraction is not explicit enough for visualization processes and database insertions. This originates from the reports themselves that are elliptical, ambiguous, and vague. In order to overcome this obstacle, the situational context and thus semantic and pragmatic aspects have to be taken into account. In the paper at hand, we present a system that uses an ontological module to integrate semantic and pragmatic knowledge. The result of the completion contains all the specifications to allow for a visualization of the report’s content on a map as well as for a database actualization

Analyzing E-Learning Adoption via Recursive Partitioning

The paper analyzes factors that influence the adoption of e-learning and gives an example of how to forecast technology adoption based on a post-hoc predictive segmentation using a classification and regression tree (CART). We find strong evidence for the existence of technological interdependencies and organizational learning effects. Furthermore, we find different paths to elearning adoption. The results of the analysis suggest a growing "digital divide" among firms. We use cross-sectional data from a European survey about e-business in June 2002, covering almost 6,000 enterprises in 15 industry sectors and 4 countries. Comparing the predictive quality of CART, we find that CART outperforms a traditional logistic regression. The results are more parsimonious, i. e. CARTs use less explanatory variables, better interpretable since different paths of adoption are detected, and from a statistical standpoint, because interactions between the covariates are taken into account.Technology Adoption, Path Dependence, Interaction between Different Technologies, Regression Trees, Predictive Segmentation, Logistic Regression, E-Learning, E-Business

Endogenous Acceleration of Technological Change

Our study shows that the technological development of a firm can be subject to an endogenous acceleration mechanism. The more advanced a firm is in using a particular set of technologies, the more likely will it adopt additional, related technologies. This acceleration mechanism implies that marginal differences in early adoption decisions lead to substantial differences in technology endowment later. This hypothesis is tested in a dataset that records the adoption times of various e-business technologies in a sample of 7,302 firms from 10 different industry sectors and 25 European countries. Estimation is carried out with a semi-parametric hazard rate model that controls for unobserved heterogeneity. The results show that the probability to adopt strictly increases with the number of previously adopted e-business technologies. Evidence for a growing digital divide among the companies in the sample is demonstrated for the period from 1994-2002. The endogenous acceleration mechanism is a possible source of early mover advantages, if technological uncertainty and technological improvements over time are not very large and if the price of the new technologies remains roughly constant.Technology adoption, Technological competition, Complementarity, Hazard rate models, IT

Transport functions of nitrogen up to 26,000 K

The current field strength characteristic, E(1), and a large number of radial temperature distributions, T(r,I), measured in a 5 mm N2 cascade arc at normal pressure are used to evaluate the transport properties of nitrogen up to 26,000 K. The electrical conductivity sigma (T) and the Coulomb cross section are determined directly from the E(I) and several T(r,I) curves. Between 10,000 and 15,000 K the radiative energy flux for different arc current, the thermal conductivity, and from this the charge exchange cross section are determined in a good approximation utilizing the large number of measured temperature distributions. It turns out, that at the highest measured arc current, i.e., 570 A, in the axial region of the arc about 95% of the supplied energy is carried off by radiation