A multiple factor model for European stocks

We present an empirical study focusing on the estimation of a fundamental multi-factor model for a universe of European stocks. Following the approach of the BARRA model, we have adopted a cross-sectional methodology. The proportion of explained variance ranges from 7.3% to 66.3% in the weekly regressions with a mean of 32.9%. For the individual factors we give the percentage of the weeks when they yielded statistically significant influence on stock returns. The best explanatory power – apart from the dominant country factors – was found among the statistical constructs „success“ and „variability in markets“.Vorgestellt wird eine empirische Studie, welche die Schätzung eines fundamentalen Multi-Faktor-Modells für ein Universum europäischer Aktien beinhaltet. Als Methode wurde in Anlehnung an die Vorgehensweise im BARRA-Modell der Querschnittsanalyse der Vorzug gegeben. Der Anteil der erklärten Varianz beläuft sich in den wöchentlichen Regressionen auf 7,3% bis 66,3% bei einem Durchschnitt von 32,9%. Für die einzelnen Faktoren wird die Häufigkeit angegeben, mit der sie sich in den Regressionen signifikant erwiesen haben. Den höchsten Erklärungsgehalt im Untersuchungszeitraum hatten Länderfaktoren, aber auch Konstrukte wie „Success“ oder „Variability in Markets“

Naive Realism about Operators

A source of much difficulty and confusion in the interpretation of quantum mechanics is a ``naive realism about operators.'' By this we refer to various ways of taking too seriously the notion of operator-as-observable, and in particular to the all too casual talk about ``measuring operators'' that occurs when the subject is quantum mechanics. Without a specification of what should be meant by ``measuring'' a quantum observable, such an expression can have no clear meaning. A definite specification is provided by Bohmian mechanics, a theory that emerges from Sch\"rodinger's equation for a system of particles when we merely insist that ``particles'' means particles. Bohmian mechanics clarifies the status and the role of operators as observables in quantum mechanics by providing the operational details absent from standard quantum mechanics. It thereby allows us to readily dismiss all the radical claims traditionally enveloping the transition from the classical to the quantum realm---for example, that we must abandon classical logic or classical probability. The moral is rather simple: Beware naive realism, especially about operators!Comment: 18 pages, LaTex2e with AMS-LaTeX, to appear in Erkenntnis, 1996 (the proceedings of the international conference ``Probability, Dynamics and Causality,'' Luino, Italy, 15-17 June 1995, a special issue edited by D. Costantini and M.C. Gallavotti and dedicated to Prof. R. Jeffrey

Electron Induced Break-up of Helium: Benchmark Experiments on a Dynamical Four-Body Coulomb System

Diese Arbeit stellt eine experimentelle Studie zu Fragmentationsprozessen von Helium durch Elektronenstoß vor. Dabei wurden absolute, vollständig differentielle Wirkungsquerschnitte zur einfachen Ionisation, zur gleichzeitigen Ionisation und Anregung sowie zur Doppelionisation gemessen. Durch Anwendung eines Abbildungsverfahrens für die geladenen Fragmente, einem sogenannten 'Reaktionsmikroskop', wird ein großer Teil des Impuls-Endzustandsraumes abgedeckt und die grundlegenden Einschränkungen der konventionellen Methoden überwunden. Das bisherige Reaktionsmikroskop konnte entscheidend verbessert werden, indem nun der Projektilstrahl parallel zu den Spektrometerfeldern geführt wird. In der Einfachionisation von Helium tritt bei beiden untersuchten Projektilenergien (102 eV und 1 keV) eine erhöhte Emission außerhalb der Streuebene auf, die auch bei Stößen mit Ionen beobachtet wurde (M. Schulz et al., Nature (London) 422, 48 (2003)). Die winkelaufgelösten Querschnitte für die Doppelionisation von Helium bei 105 eV Einschussenergie zeigen, dass der Prozess durch die gegenseitige Abstoßung der Elektronen dominiert wird, wobei jedoch Signaturen einer komplexeren Dynamik erkennbar werden. Die gewonnenen Daten dienen als Test für neu entwickelte theoretische Beschreibungen des dynamischen Drei- und Vier-Körper Coulomb Problems

Owner Valuation of Rabies Vaccination of Dogs, Chad

We estimated the association between amount charged and probability that dog owners in N’Djaména, Chad, would have their dogs vaccinated against rabies. Owners would pay ≈400–700 CFA francs (US $0.78–$1.36)/animal. To vaccinate >70% of dogs, and thus interrupt rabies transmission, health officials should substantially subsidize these vaccinations

Online Algorithms for Multi-Level Aggregation

In the Multi-Level Aggregation Problem (MLAP), requests arrive at the nodes of an edge-weighted tree T, and have to be served eventually. A service is defined as a subtree X of T that contains its root. This subtree X serves all requests that are pending in the nodes of X, and the cost of this service is equal to the total weight of X. Each request also incurs waiting cost between its arrival and service times. The objective is to minimize the total waiting cost of all requests plus the total cost of all service subtrees. MLAP is a generalization of some well-studied optimization problems; for example, for trees of depth 1, MLAP is equivalent to the TCP Acknowledgment Problem, while for trees of depth 2, it is equivalent to the Joint Replenishment Problem. Aggregation problem for trees of arbitrary depth arise in multicasting, sensor networks, communication in organization hierarchies, and in supply-chain management. The instances of MLAP associated with these applications are naturally online, in the sense that aggregation decisions need to be made without information about future requests. Constant-competitive online algorithms are known for MLAP with one or two levels. However, it has been open whether there exist constant competitive online algorithms for trees of depth more than 2. Addressing this open problem, we give the first constant competitive online algorithm for networks of arbitrary (fixed) number of levels. The competitive ratio is O(D^4 2^D), where D is the depth of T. The algorithm works for arbitrary waiting cost functions, including the variant with deadlines. We also show several additional lower and upper bound results for some special cases of MLAP, including the Single-Phase variant and the case when the tree is a path

Influence of static electric fields on an optical ion trap

We recently reported on a proof-of-principle experiment demonstrating optical trapping of an ion in a single-beam dipole trap superimposed by a static electric potential [Nat. Photonics 4, 772--775 (2010)]. Here, we first discuss the experimental procedures focussing on the influence and consequences of the static electric potential. These potentials can easily prevent successful optical trapping, if their configuration is not chosen carefully. Afterwards, we analyse the dipole trap experiments with different analytic models, in which different approximations are applied. According to these models the experimental results agree with recoil heating as the relevant heating effect. In addition, a Monte-Carlo simulation has been developed to refine the analysis. It reveals a large impact of the static electric potential on the dipole trap experiments in general. While it supports the results of the analytic models for the parameters used in the experiments, the analytic models cease their validity for significantly different parameters. Finally, we propose technical improvements for future realizations of experiments with optically trapped ions.Comment: 16 pages, 16 figure

Der Einfluss der L-Carnitin-Dosis auf die Magenentleerung und die orozökale Transitzeit bei gesunden Erwachsenen

Es wurde der Einfluss von L-Carnitin auf Magenentleerung und Dünndarmtransit untersucht. Hierbei wurde bei 12 Probanden unter Verwendung eines 13CO2-Atemtests die HWZ_ME und die OZTZ bestimmt. Die Tracer Natrium-[13C]azetat und 13C-LU ermöglichten die gleichzeitige Bestimmung dieser Transitzeiten. Es wurde ein Placebo , 1,5 g und 3 g L-Carnitin pro Tag über jeweils zehn Tage gegeben. Im Bezug auf die HWZME ergeben sich unter L-Carnitin keine Veränderungen. Bei der OZTZ ergeben sich die Zeiten 5,75 h, 4,73 h und 4,02 h. Die Transitzeitverkürzung ist signifikant. Eine Erklärung könnte der osmotische Effekt des L-Carnitin sein. Der zweite Ansatz wäre eine parasympathische Wirkung auf den Darms

On the Time-Dependent Analysis of Gamow Decay

Gamow's explanation of the exponential decay law uses complex "eigenvalues" and exponentially growing "eigenfunctions". This raises the question, how Gamow's description fits into the quantum mechanical description of nature, which is based on real eigenvalues and square integrable wave functions. Observing that the time evolution of any wave function is given by its expansion in generalized eigenfunctions, we shall answer this question in the most straightforward manner, which at the same time is accessible to graduate students and specialists. Moreover the presentation can well be used in physics lectures to students.Comment: 10 pages, 4 figures; heuristic argument simplified, different example discussed, calculation of decay rate adde

Hot electron driven enhancement of spin-lattice coupling in 4f ferromagnets observed by femtosecond x-ray magnetic circular dichroism

Femtosecond x-ray magnetic circular dichroism was used to study the time-dependent magnetic moment of 4 fs electrons in the ferromagnets Gd and Tb, which are known for their different spin-lattice coupling. We observe a two-step demagnetization with an ultrafast demagnetization time of 750 fs identical for both systems and slower times which differ sizeably with 40 ps for Gd and 8 ps for Tb. We conclude that spin-lattice coupling in the electronically excited state is enhanced up to orders of magnitude compared to equilibrium.Comment: added reference 24, clarified the meaning of photo-induced, emphasized that XMCD probes the magnetic moment localized at 4f electron