Philipp Brune

Cyclic Spin Exchange in Cuprate Spin Ladders

We investigate the influence of a cyclic spin exchange J_{cyc} on the one- and two-triplet excitations of an undoped two-leg S=1/2 ladder, using the density matrix renormalization group (DMRG). The dispersion of the S=0 two-triplet bound state is dramatically reduced by J_{cyc} due to a repulsion between triplets on neighboring rungs. In (La,Ca)_{14}Cu_{24}O_{41} a consistent description of both the spin gap and the S=0 bound state requires

Disorder-induced enhancement of the persistent current for strongly interacting electrons in one-dimensional rings

J_{cyc}/J_\perp \approx 0.20-0.27

Determining Software Product Release Readiness by the Change-Error Correlation Function: On the Importance of the Change-Error Time Lag

and

Online Support for the Elderly - Why Service and Social Network Platforms should be Integrated

J/J_{\perp} \approx 1.25-1.35

A Description and Retrieval Model for Web Services Including Extended Semantic and Commercial Attributes

. With these coupling ratios the recently developed dynamical DMRG yields an excellent description of the entire S=0 excitation spectrum observed in the optical conductivity, including the continuum contribution.

User Interfaces with a Touch of Grey? – Towards a Specific UI Design for People in the Transition Age

We show that disorder increases the persistent current of a half-filled one-dimensional Hubbard-Anderson ring at strong interaction. This unexpected effect results from a perturbative expansion starting from the strongly interacting Mott insulator ground state. The analytical result is confirmed and extended by numerical calculations.

Towards an empirical examination of IT security infrastructures in SME

In software development determining the release readiness plays an essential role. The number of errors is frequently used as an important measure to decide about the quality of a software implementation. Therefore, error prediction techniques have been intensively studied in the literature for many years. Despite this, their adoption in practice is still strongly limited to date. In this paper, an alternative model for error prediction in software projects based on linear response theory and the change-error cross correlation function is proposed. It is applied to data collected in projects of a major embedded systems vendor in the communication industry. Under similar conditions, a universal behavior of the change-error cross-correlation function is observed. Moreover, a time lag of 4-6 weeks between the change and the detection of related errors is discovered. This clearly demonstrates that for reliable release decisions not only the current number of errors but also of changes is essential.

Simulating User Interactions: A Model and Tool for Semi-realistic Load Testing of Social App Backend Web Services

Most developed countries currently face a demographic change towards an aging society. In this respect, the so-called transition age between 55 and 75 is crucial for individual health and wellbeing, since it usually is connected with the transition from work life to retirement. This leads to a fundamental change in daily routines and social life, often causing mental or physical health problems. Online Social Networks have been studied for some time already as a means for supporting social inclusion of elderly people. On the other hand, by healthcare providers and welfare organizations an increasing number of support services for elderly people are or will be provided also online in the future. However, the combination of both aspects in order to provide a more holistic online support for elderly people, in particular to those between 55-75, has not been discussed so far. Therefore, in this paper we argue in favor of the concept of an integrated online service and social network for elderly people and present an outline of its intended functionality.

May the Ontologies Be with You! Towards a User-Friendly Web-Based Editor for Semantic Web Service Description

Commercially available web services pose certain challenges to the customer. Whereas the technical service description is usually well defined and published, the semantic and especially the commercial description does often not reach the necessary depth. Therefore, identifying the most suitable web service from a technical, semantic and commercial perspective is often a difficult quest. This research develops a holistic web service description language integrating the semantic and commercial perspective and based on XML. The newly defined description rules for web services enable a requestor to identify the most suitable web services according to a given set of parameters. The model is tested with a prototype and the proof-of-concept shows that it is a fully functional description. Applying this model on a broad scale would lead to better decisions in web service selection, especially if non-technical staff is involved.

Impurities in a Hubbard-chain

Abstract While applications and user interfaces (UI) for elderly people have been discussed by various authors, the specific requirements of people in the transition age from work life to retirement (55-75 years) have not been analyzed in detail yet. Therefore, in this paper we present results from a qualitative empirical analysis within this age group, evaluate their specific usage behavior and system requirements and derive basic UI design guidelines from it. The results indicate that indeed this age group differs in its requirements from older people (75+) mainly considered in the existing literature.