Gaussian, exponential, and power-law decay of time-dependent correlation functions in quantum spin chains

Dynamic spin correlation functions $$ for the 1D $S=1/2$ $XX$ model $H = -J\Sigma_i \{S_i^x S_{i+1}^x + S_i^y S_{i+1}^y \}$ are calculated exactly for finite open chains with up to N=10000 spins. Over a certain time range the results are free of finite-size effects and thus represent correlation functions of an infinite chain (bulk regime) or a semi-infinite chain (boundary regime). In the bulk regime, the long-time asymptotic decay as inferred by extrapolation is Gaussian at $T=\infty$, exponential at $0 < T < \infty$, and power-law $(\sim t^{-1/2})$ at T=0, in agreement with exact results. In the boundary regime, a power-law decay obtains at all temperatures; the characteristic exponent is universal at T=0 $(\sim t^{-1})$ and at $0 < T < \infty$ $(\sim t^{-3/2})$, but is site-dependent at $T=\infty$. In the high-temperature regime $(T/J \gg 1)$ and in the low-temperature regime $(T/J \ll 1)$, crossovers between different decay laws can be observed in $<S_i^x (t)S_j^x>$. Additional crossovers are found between bulk-type and boundary-type decay for $i=j$ near the boundary, and between space-like and time-like behavior for $i \neq j$.Comment: 9 pages, 8 figures appended as uuencoded compressed postscript fil

Security measures abroad and extraterritorial human rights obligations

International human rights law (IHRL) was initiated after the Second World War as part of public international law, which in turn had been based on the Westphalian concept of exclusive territorial sovereignty. As a result, IHRL has been informed by this territorial paradigm: A state is, first and foremost, obligated to respect, protect and fulfil human rights of those located on its territory. In light of today’s globalization processes, the enormous social, political and economic transnational interdependence, and risks and opportunities entailed by new means of communication and technology, this approach creates a protection vacuum. Targeted killings by unmanned aerial vehicles (UAVs) or trans-border surveillance systems, as the paramount examples of security interventions of our time, reflect this: Today, states can violate human rights without having to set foot on the territory the victim resides on. Extraterritorial intelligence strategies that establish “legal black holes” are on the rise. Not only cyber-attacks and big data but also terrorism, climate change or global migration all intro-duce novel dimensions of security challenges and multiply the scope of individuals a state can and does affect – at home as well as abroad. The security-related measures states adopt in these domains often come into conflict with human rights. In which way does the foundational idea that state conduct is constrained by human rights also pertain to these transnational, diagonal relations between states and “outsiders”? This contribution intends to comment on the legitimacy of states’ extraterritorial human rights obligations from the perspective of legal philosophy

The inverse cascade of magnetic helicity in magnetohydrodynamic turbulence

The nonlinear dynamics of magnetic helicity, $H^M$, which is responsible for large-scale magnetic structure formation in electrically conducting turbulent media is investigated in forced and decaying three-dimensional magnetohydrodynamic turbulence. This is done with the help of high resolution direct numerical simulations and statistical closure theory. The numerically observed spectral scaling of $H^M$ is at variance with earlier work using a statistical closure model [Pouquet et al., J. Fluid Mech. \textbf{77} 321 (1976)]. By revisiting this theory a universal dynamical balance relation is found that includes effects of kinetic helicity, as well as kinetic and magnetic energy on the inverse cascade of $H^M$ and explains the above-mentioned discrepancy. Considering the result in the context of mean-field dynamo theory suggests a nonlinear modification of the $\alpha$-dynamo effect important in the context of magnetic field excitation in turbulent plasmas.Comment: Minor corrections and improvements mad

Methoden des Marketing-Accounting : Konzeptionen und Excel-Anwendungen

Das Marketing-Accounting ist intergraler Bestandteil des Marketing-Controllings. Es umfasst jene Bestandteile des Marketing-Controllings, die mit der Bereitstellung und Nutzung entscheidungsorientierter Rechnungsweseninformationen zusammenhängen (vgl. Reckenfelderbäumer 1995, S. 4). Das Marketing-Controlling und somit auch das Marketing-Accounting führt das eher intern orientierte Controlling mit dem am Markt und damit extern ausgerichteten Marketing zusammen und sorgt dafür, das sich beide Sichtweisen ergänzen (vgl. Horváth 1986, S. 13). Das Ziel der vorliegenden Untersuchung besteht darin, ein Informationsinstrumentarium auf Basis des Rechnungswesens zu entwickeln. Diese Rechnungsmodelle werden zunächst näher erläutert, dann nach Möglichkeit in Excel umgesetzt und zum Schluss auf ihre Vorund Nachteile untersucht

A Schema of Possible Negative Effects of Advanced Driver Assistant Systems

The purpose of Advanced Driver Assistance Systems (ADAS) is to enhance traffic safety and efficiency. ADAS can be considered as a (still incomplete) collection of systems and subsystems towards a fully automated highway system, such as autonomous cars. However, as many researchers argue, in assessing the benefits of ADAS it has to be taken into account that any gains in terms of security may be again reduced by the fact they affect the drivers\u27 behavior. In this paper, we introduce a schema of possible negative effects of advanced driver assistant systems according to which consequences of a system failure largely depend on the magnitude of over-reliance. Based on that schema, we itemize hypotheses on possible behavioral effects of a specific ADAS type, namely local danger alerts

ACon: A learning-based approach to deal with uncertainty in contextual requirements at runtime

Context: Runtime uncertainty such as unpredictable operational environment and failure of sensors that gather environmental data is a well-known challenge for adaptive systems. Objective: To execute requirements that depend on context correctly, the system needs up-to-date knowledge about the context relevant to such requirements. Techniques to cope with uncertainty in contextual requirements are currently underrepresented. In this paper we present ACon (Adaptation of Contextual requirements), a data-mining approach to deal with runtime uncertainty affecting contextual requirements. Method: ACon uses feedback loops to maintain up-to-date knowledge about contextual requirements based on current context information in which contextual requirements are valid at runtime. Upon detecting that contextual requirements are affected by runtime uncertainty, ACon analyses and mines contextual data, to (re-)operationalize context and therefore update the information about contextual requirements. Results: We evaluate ACon in an empirical study of an activity scheduling system used by a crew of 4 rowers in a wild and unpredictable environment using a complex monitoring infrastructure. Our study focused on evaluating the data mining part of ACon and analysed the sensor data collected onboard from 46 sensors and 90,748 measurements per sensor. Conclusion: ACon is an important step in dealing with uncertainty affecting contextual requirements at runtime while considering end-user interaction. ACon supports systems in analysing the environment to adapt contextual requirements and complements existing requirements monitoring approaches by keeping the requirements monitoring specification up-to-date. Consequently, it avoids manual analysis that is usually costly in today’s complex system environments.Peer ReviewedPostprint (author's final draft