Tractable Combinations of Global Constraints

We study the complexity of constraint satisfaction problems involving global constraints, i.e., special-purpose constraints provided by a solver and represented implicitly by a parametrised algorithm. Such constraints are widely used; indeed, they are one of the key reasons for the success of constraint programming in solving real-world problems. Previous work has focused on the development of efficient propagators for individual constraints. In this paper, we identify a new tractable class of constraint problems involving global constraints of unbounded arity. To do so, we combine structural restrictions with the observation that some important types of global constraint do not distinguish between large classes of equivalent solutions.Comment: To appear in proceedings of CP'13, LNCS 8124. arXiv admin note: text overlap with arXiv:1307.179

Introducing LoCo, a Logic for Configuration Problems

In this paper we present the core of LoCo, a logic-based high-level representation language for expressing configuration problems. LoCo shall allow to model these problems in an intuitive and declarative way, the dynamic aspects of configuration notwithstanding. Our logic enforces that configurations contain only finitely many components and reasoning can be reduced to the task of model construction.Comment: In Proceedings LoCoCo 2011, arXiv:1108.609

Ocular Blood Flow Measurements in Healthy White Subjects Using Laser Speckle Flowgraphy

Purpose. To assess the feasibility and reliability of Laser Speckle Flowgraphy (LSFG) to measure ocular perfusion in a sample of healthy white subjects and to elucidate the age-dependence of the parameters obtained. Methods: This cross-sectional study included 80 eyes of 80 healthy, non-smoking white subjects of Western European descent between 19 and 79 years of age. A commercial LSFG instrument was applied to measure ocular blood flow at the optic nerve head (ONH) three successive times before and after pharmacological pupil dilation. The mean blur rate (MBR), a measure of relative blood flow velocity, was obtained for different regions of the ONH. Eight parameters of ocular perfusion derived from the pulse-waveform analysis of MBR including blowout time (BOT) and falling rate (FR) were also recorded. Results Artifact-free LSFG images meeting the quality criteria for automated image analysis were obtainable in 93.8% without pupil dilation and in 98.8% with pharmacological pupil dilation. Measurements of MBR showed excellent repeatability with intraclass correlation coefficients >= 0.937 and were barely affected by pupil dilation. The majority of pulse-waveform derived variables exhibited equally high repeatability. MBR-related blood flow indices exhibited significant age dependence (p<0.001). FR (r = 0.747, p<0.001) and BOT (r = -0.714, p<0.001) most strongly correlated with age. Conclusions: LSFG represents a reliable method for the quantitative assessment of ocular blood flow in white subjects. Our data affirms that the LSFG-derived variables FR and BOT may be useful biomarkers for age-related changes in ocular perfusion

Optimization Methods for the Partner Units Problem

Abstract. In this work we present the Partner Units Problem as a novel challenge for optimization methods. It captures a certain type of configuration problem that frequently occurs in industry. Unfortunately, it can be shown that in the most general case an optimization version of the problem is intractable. We present and evaluate encodings of the problem in the frameworks of answer set programming, propositional satisfiability testing, constraint solving, and integer programming. We also show how to adapt these encodings to a class of problem instances that we have recently shown to be tractable.

Effect of Diffuse Luminance Flicker Light Stimulation on Total Retinal Blood Flow Assessed With Dual-Beam Bidirectional Doppler OCT

Purpose: We assess the increase in total retinal blood flow (TRBF) induced by flicker stimulation of the human retina in vivo and investigate the flicker induced hyperemia by means of a vascular flow model of the retinal circulation to study neurovascular coupling (NC). Methods: In six healthy subjects, TRBF was measured before and during stimulation with diffuse luminance flicker. Blood flow velocities in retinal vessels were measured via dual-beam bidirectional Doppler Fourier-domain optical coherence tomography (FD-OCT), retinal vessel diameters were assessed based on FD-OCT phase data. This allowed for the calculation of TRBF before and during visual stimulation. Additionally, a mathematical flow model for the retinal vasculature was adapted to study the implications of diameter variations on retinal perfusion. Measured and simulated perfusion was compared to draw conclusions on the diameter variations in different layers of the vascular tree. Results: The measured mean baseline flow was 36.4 6.5 l/min while the mean flow during flicker stimulation was 53.4% 8.3 l/min. The individual increase in TRBF during flicker stimulation ranged between 34% and 66%. The average increase in TRBF over all measured subjects was 47.6% 12.6%. Conclusions: Dual-beam bidirectional Doppler FD-OCT allowed quantifying NC in the human retina in vivo and may be a promising method for monitoring alterations in NC caused by various pathologies. The comparison of the measured data with the results obtained in the simulated vasculature indicates that the vasodilation induced by NC is more pronounced in smaller vessels.(VLID)484318

Wettbewerb und Regulierung jetzt auch in der Wasserwirtschaft

Die Verfügungen der Landeskartellbehörde Hessen gegen Wasserversorger wegen zu hoher Wasserpreise, die auf eine Vergleichsmarktanalyse gestützt wurden, und deren Bestätigung durch den BGH am 2.2.2010 waren erste Vorboten einer sich verschärfenden kartellrechtlichen Entgeltkontrolle der Wasserwirtschaft. Die folgende Entscheidung der Landeskartellbehörde Baden-Württemberg auf der Basis einer Kostenanalyse ein Jahr später ist dagegen unlängst vom OLG Stuttgart gestoppt worden. Vor dem Hintergrund der dadurch ausgelösten Unsicherheiten stellt sich die Frage, ob die Wasserwirtschaft nicht wie die anderen Netzwirtschaften (Telekommunikation, Energie, Post, Eisenbahntransport) auch einer Regulierung durch die in den übrigen Wirtschaftszweigen erfolgreich tätige Bundesnetzagentur unterworfen werden sollte. Der Beitrag gelangt zu dem Ergebnis, dass der kartellrechtliche Ansatz gegenwärtig sinnvoll ist und die Option auf eine abgabenrechtliche Kontrolle beseitigt werden muss. Sollte sich die kartellrechtliche Kontrolle jedoch nicht als wirksam herausstellen, so wäre eine bundeseinheitliche, sektorspezifische Lösung zu prüfen. Summary In the past, the Hessian Cartel Authority issued orders against water suppliers because they were charging excessively high prices and abused their dominant position. Those decisions were based on an analysis of comparable markets. These orders were upheld by the Federal Surpreme Court (BGH) on February 2, 2010. In this development one can see somewhat of a forerunner of a pricing regulation through antitrust law within the water industry. However, the following decision by the Cartel Authority of Baden-Wuerttemberg one year later, which was based on an analysis of the actual costs was only recently quashed by the Higher Regional Court (OLG) of Stuttgart. Considering the resulting insecurities regarding the application of the legal framework, the question arises, whether the water suppliers should be subjected to regulation by the Federal Network Authority – just like other network based industries, such as telecommunications, energy, post and railways. This paper comes to the conclusion that the current approach using the antitrust law is generally reasonable as a first step. What seems even more important than the choice between a sector specific regulation and antitrust law is to abolish the option of an administrative price control of public water suppliers which proved to be ineffective. Should the full application of cartel law, however, turn out to be ineffective in the future, a national sector specific solution should be considered. JEL Classification: K

Factors Determining Flicker-Induced Retinal Vasodilation in Healthy Subjects

PURPOSE. The purpose of this study was to analyze factors determining retinal arterial and venous responses to stimulation with diffuse luminance flicker in healthy subjects. METHODS. We retrospectively analyzed results obtained in 374 healthy subjects who had previously participated in clinical studies in our department. A total of 153 subjects underwent a protocol in which flicker stimulation was delivered through the fundus camera at 8 Hz (protocol 1), separating measurement and stimulation light depending on the wavelength, and 221 subjects underwent a protocol in which diffuse luminance flicker was delivered at 12.5 Hz with high modulation depth (protocol 2). We investigated whether sex, systemic blood pressure, baseline vessel size, blood plasma concentration of fasting glucose and hematocrit, and serum concentration of cholesterol, triglycerides, creatinine and Creactive protein influenced the retinal vascular response to flicker stimulation RESULTS. Flicker responses in arteries and veins were more pronounced in protocol 2 than in protocol 1 (P < 0.001, each). In both of the protocols the vascular response to stimulation with diffuse luminance flicker was larger in smaller vessels (P between 0.001 and 0.016). In protocol 2 the retinal arterial flicker response was negatively associated with cholesterol serum levels (P = 0.033); in protocol 1, only a tendency toward this effect was observed (P 0.056). CONCLUSIONS. The present analysis indicates that retinal arterial and venous responses to stimulation with diffuse luminance flicker depend on the way the stimulation is delivered through the ftndus camera. In addition, the flicker response varied with vessel size, that is, the smaller the vessel width, the larger the flicker response. Finally, our data indicate that, even within the normal range, higher cholesterol serum levels are associated with lower hyperemic flicker responses.KLI 250(VLID)311758

Scientific Reports / Retinal oxygen extraction in humans

Adequate function of the retina is dependent on proper oxygen supply. In humans, the inner retina is oxygenated via the retinal circulation. We present a method to calculate total retinal oxygen extraction based on measurement of total retinal blood flow using dual-beam bidirectional Doppler optical coherence tomography and measurement of oxygen saturation by spectrophotometry. These measurements were done on 8 healthy subjects while breathing ambient room air and 100% oxygen. Total retinal blood flow was 44.39.0l/min during baseline and decreased to 18.74.2l/min during 100% oxygen breathing (P<0.001) resulting in a pronounced decrease in retinal oxygen extraction from 2.330.51l(O2)/min to 0.880.14l(O2)/min during breathing of 100% oxygen. The method presented in this paper may have significant potential to study oxygen metabolism in hypoxic retinal diseases such as diabetic retinopathy.(VLID)491093