Minimal qubit tomography

We present, and analyze thoroughly, a highly symmetric and efficient scheme for the determination of a single-qubit state, such as the polarization properties of photons emitted by a single-photon source. In our scheme there are only four measured probabilities, just enough for the determination of the three parameters that specify the qubit state, whereas the standard procedure would measure six probabilities.Comment: 14 pages, 10 figures; final versio

Eigenvalue and Eigenvector Analysis of Stability for a Line of Traffic

Many authors have recognized that traffic under the traditional car-following model (CFM) is subject to flow instabilities. A recent model achieves stability using bilateral control (BCM)—by looking both forward and backward [1]. (Looking back may be difficult or distracting for human drivers, but is not a problem for sensors.) We analyze the underlying systems of differential equations by studying their eigenvalues and eigenvectors under various boundary conditions. Simulations further confirm that bilateral control can avoid instabilities and reduce the chance of collisions

Long-lived qubit from three spin-1/2 atoms

A system of three spin-1/2 atoms allows the construction of a reference-frame-free (RFF) qubit in the subspace with total angular momentum $j=1/2$. The RFF qubit stays coherent perfectly as long as the spins of the three atoms are affected homogeneously. The inhomogeneous evolution of the atoms causes decoherence, but this decoherence can be suppressed efficiently by applying a bias magnetic field of modest strength perpendicular to the plane of the atoms. The resulting lifetime of the RFF qubit can be many days, making RFF qubits of this kind promising candidates for quantum information storage units. Specifically, we examine the situation of three $^6\textrm{Li}$ atoms trapped in a $\textrm{CO}_2$-laser-generated optical lattice and find that, with conservatively estimated parameters, a stored qubit maintains a fidelity of 0.9999 for two hours.Comment: 15 pages, 9 figures; version 2 reports a much improved analysis; version 3 contains more details about the four-atom cas

Redes de bibliotecas en España: la cooperación bibliotecaria como instrumento de desarrollo cultural y científico

Se ofrece una panorámica de la evolución del sistema bibliotecario español en los 10/15 últimos años, comparándola con la situación en el mundo bibliotecario anglosajón. Se analizan los proyectos de cooperación bibliotecaria en España y se apuntan las líneas de interés en los proyectos europeos con participación española. Finalmente se presentan unas conclusiones sobre lo expuesto y una reflexión del papel que deben jugar las bibliotecas en un sistema organizado de Investigación

Relation of Gallbladder Motility to Viscosity and Composition of Gallbladder Bile in Patients with Cholesterol Gallstones

Background/Aims: Increased viscosity and supersaturation of cholesterol in gallbladder bile, as well as an impaired motility of the gallbladder, are considered to be important factors in the pathogenesis of cholesterol gallstones. However, the relation of these parameters has not yet been determined. Material and Methods: Bile viscosity (mPa.s) was measured by rotation viscosimetry and the composition of gallbladder bile was determined using standard methodology. Gallbladder motility was calculated as ejection fraction in percent of total volume 45 min after a test meal using ultrasonography in patients with gallstones prior to elective cholecystectomy. Results: The study included 35 patients with cholesterol gallstones. Viscosity of gallbladder bile ranged between 0.9 and 12.5 mPa.s (median 2.2 mPa.s) and an ejection fraction of the gallbladder of 55.4 +/- 18.3% (mean +/- SD) was determined. No significant correlation (r = 0.19, p < 0.2) between the 2 parameters could be calculated. Analysis of the composition of gallbladder bile revealed a positive correlation of all components to biliary viscosity but not to the motility of the gallbladder, with the exceptions of a negative correlation (r = 0.39, p < 0.02) between mucin concentration and the ejection fraction at 45 min after the test meal. Conclusions: The motility of the gallbladder appears to be unrelated to the viscosity of gallbladder bile or gallbladder bile composition. The negative correlation between the ejection fraction of the gallbladder and mucin concentration of gallbladder bile suggests that chronic inflammation of the gallbladder wall is associated with both an impaired motility of the gallbladder and increased mucin release into gallbladder bile. Copyright (C) 2009 S. Karger AG, Base

Bildungsfinanzierung neu gestalten

In Deutschland sind die privaten Bildungsausgaben anders zusammengesetzt als in vergleichbaren Industrieländern. Der private Finanzierungsanteil an den gesamten Bildungsausgaben ist hierzulande für die vorschulische Bildung deutlich höher als für die Schul-, Betriebs- und Hochschulbildung. Im internationalen Vergleich zeigt sich: Diese Aufteilung ist nicht geeignet, Chancengerechtigkeit herzustellen und bedarf daher einer gründlichen Überarbeitung. Der Kronberger Kreis fordert den Staat auf, sich an der Finanzierung der vorschulischen Bildung stärker zu beteiligen, so dass einkommensschwache Familien keine Kindergartengebühren zahlen müssen. Das letzte Kindergartenjahr vor der Einschulung könnte verpflichtend sein. Im Hochschulbereich plädiert der Kronberger Kreis hingegen für die Wiedereinführung von Studiengebühren. In dieser Studie finden sich darüber hinaus konkrete Vorschläge zur Stärkung des Wettbewerbs zwischen öffentlichen und privaten Schulen sowie zur Ausgestaltung der steuerlichen Förderung von Bildungsinvestitionen

On mechanisms that enforce complementarity

In a recent publication Luis and Sanchez-Soto arrive at the conclusion that complementarity is universally enforced by random classical phase kicks. We disagree. One could just as well argue that quantum entanglement is the universal mechanism. Both claims of universality are unjustified, however.Comment: 4 page

(Micro)evolutionary changes and the evolutionary potential of bird migration

Seasonal migration is the yearly long-distance movement of individuals between their breeding and wintering grounds. Individuals from nearly every animal group exhibit this behavior, but probably the most iconic migration is carried out by birds, from the classic V-shape formation of geese on migration to the amazing nonstop long-distance flights undertaken by Arctic Terns Sterna paradisaea. In this chapter, we discuss how seasonal migration has shaped the field of evolution. First, this behavior is known to turn on and off quite rapidly, but controversy remains concerning where this behavior first evolved geographically and whether the ancestral state was sedentary or migratory (Fig. 7.1d, e). We review recent work using new analytical techniques to provide insight into this topic. Second, it is widely accepted that there is a large genetic basis to this trait, especially in groups like songbirds that migrate alone and at night precluding any opportunity for learning. Key hypotheses on this topic include shared genetic variation used by different populations to migrate and only few genes being involved in its control. We summarize recent work using new techniques for both phenotype and genotype characterization to evaluate and challenge these hypotheses. Finally, one topic that has received less attention is the role these differences in migratory phenotype could play in the process of speciation. Specifically, many populations breed next to one another but take drastically different routes on migration (Fig. 7.2). This difference could play an important role in reducing gene flow between populations, but our inability to track most birds on migration has so far precluded evaluations of this hypothesis. The advent of new tracking techniques means we can track many more birds with increasing accuracy on migration, and this work has provided important insight into migration's role in speciation that we will review here