Can a charged dust ball be sent through the Reissner--Nordstr\"{o}m wormhole?

In a previous paper we formulated a set of necessary conditions for the spherically symmetric weakly charged dust to avoid Big Bang/Big Crunch, shell crossing and permanent central singularities. However, we did not discuss the properties of the energy density, some of which are surprising and seem not to have been known up to now. A singularity of infinite energy density does exist -- it is a point singularity situated on the world line of the center of symmetry. The condition that no mass shell collapses to $R = 0$ if it had $R > 0$ initially thus turns out to be still insufficient for avoiding a singularity. Moreover, at the singularity the energy density $\epsilon$ is direction-dependent: $\epsilon \to - \infty$ when we approach the singular point along a $t =$ const hypersurface and $\epsilon \to + \infty$ when we approach that point along the center of symmetry. The appearance of negative-energy-density regions turns out to be inevitable. We discuss various aspects of this property of our configuration. We also show that a permanently pulsating configuration, with the period of pulsation independent of mass, is possible only if there exists a permanent central singularity.Comment: 30 pages, 21 figures; several corrections after referee's comments, 4 figures modifie

Self-Similar Evaporation of a Rigidly-Rotating Cosmic String Loop

The gravitational back-reaction on a certain type of rigidly-rotating cosmic string loop, first discovered by Allen, Casper and Ottewill, is studied at the level of the weak-field approximation. The near-field metric perturbations are calculated and used to construct the self-acceleration vector of the loop. Although the acceleration vector is divergent at the two kink points on the loop, its net effect on the trajectory over a single oscillation period turns out to be finite. The net back-reaction on the loop over a single period is calculated using a method due to Quashnock and Spergel, and is shown to induce a uniform shrinkage of the loop while preserving its original shape. The loop therefore evolves by self-similar evaporation.Comment: 41 pages, 5 figures. Accepted for publication in Classical and Quantum Gravit

Community rotorcraft air transportation benefits and opportunities

Information about rotorcraft that will assist community planners in assessing and planning for the use of rotorcraft transportation in their communities is provided. Information useful to helicopter researchers, manufacturers, and operators concerning helicopter opportunities and benefits is also given. Three primary topics are discussed: the current status and future projections of rotorcraft technology, and the comparison of that technology with other transportation vehicles; the community benefits of promising rotorcraft transportation opportunities; and the integration and interfacing considerations between rotorcraft and other transportation vehicles. Helicopter applications in a number of business and public service fields are examined in various geographical settings

A topos for algebraic quantum theory

The aim of this paper is to relate algebraic quantum mechanics to topos theory, so as to construct new foundations for quantum logic and quantum spaces. Motivated by Bohr's idea that the empirical content of quantum physics is accessible only through classical physics, we show how a C*-algebra of observables A induces a topos T(A) in which the amalgamation of all of its commutative subalgebras comprises a single commutative C*-algebra. According to the constructive Gelfand duality theorem of Banaschewski and Mulvey, the latter has an internal spectrum S(A) in T(A), which in our approach plays the role of a quantum phase space of the system. Thus we associate a locale (which is the topos-theoretical notion of a space and which intrinsically carries the intuitionistic logical structure of a Heyting algebra) to a C*-algebra (which is the noncommutative notion of a space). In this setting, states on A become probability measures (more precisely, valuations) on S(A), and self-adjoint elements of A define continuous functions (more precisely, locale maps) from S(A) to Scott's interval domain. Noting that open subsets of S(A) correspond to propositions about the system, the pairing map that assigns a (generalized) truth value to a state and a proposition assumes an extremely simple categorical form. Formulated in this way, the quantum theory defined by A is essentially turned into a classical theory, internal to the topos T(A).Comment: 52 pages, final version, to appear in Communications in Mathematical Physic

High-field Zeeman effect of shallow acceptors in germanium

Zeeman absorption spectra have been obtained for B and Ga in Ge for B∥〈100〉 in the Voigt configuration with plane-polarized radiation. All twelve allowed transitions were observed for both the G and D lines. The corresponding excited states of these two lines for both impurities behave identically; two recent theoretical results are in good agreement. The measurements are a sensitive probe of the ground states; there are differences between the behavior of these for the two acceptors

Cuando la vida anduvo errática: Un factor ambiental para la biomineralización de metazoos

The sudden appearance of biomineralized metazoans in limestone facies of the Pockenbank Member (Namibia) appears to reflect a rapid change of redox state, calcium concentration and alkalinity of the ocean. The coupling of a major biological innovation with the end of a profound carbon isotope excursion supports the view that the Shuram was a tectonic and oceanographic phenomenon, as opposed to a global diagenetic conspiracy. The temporal concordance of these profound events as preserved in strata from southern Namibia may thus be considered as exceptional geological markers for the base of the terminal Ediacaran.La repentina aparición de metazoos biomineralizados en las facies calcáreas del Miembro de Pockenbank (Namibia) parece reflejar un rápido cambio en el estado redox, la concentración de calcio y la alcalinidad del océano. La combinación de una importante innovación biológica con el final de una profunda excursión de isótopos de carbono respalda la idea de que la anomalía Shuram fue un fenómeno tectónico y oceanográfico, en contraposición a una “conspiración” diagenética mundial. La concordancia temporal de estos profundos acontecimientos, tal como se conservan en los estratos de Namibia meridional puede considerarse, por tanto, como marcadores geológicos excepcionales para la base del Ediacárico terminal

Systematic reviews of complementary therapies - an annotated bibliography. Part 1: Acupuncture

Background Complementary therapies are widespread but controversial. We aim to provide a comprehensive collection and a summary of systematic reviews of clinical trials in three major complementary therapies (acupuncture, herbal medicine, homeopathy). This article is dealing with acupuncture. Potentially relevant reviews were searched through the register of the Cochrane Complementary Medicine Field, the Cochrane Library, Medline, and bibliographies of articles and books. To be included articles had to review prospective clinical trials of acupuncture; had to describe review methods explicitly; had to be published; and had to focus on treatment effects. Information on conditions, interventions, methods, results and conclusions was extracted using a pretested form and summarized descriptively. Results From a total of 48 potentially relevant reviews preselected in a screeening process 39 met the inclusion criteria. 22 were on various pain syndromes or rheumatic diseases. Other topics addressed by more than one review were addiction, nausea, asthma and tinnitus. Almost unanimously the reviews state that acupuncture trials include too few patients. Often included trials are heterogeneous regarding patients, interventions and outcome measures, are considered to have insufficient quality and contradictory results. Convincing evidence is available only for postoperative nausea, for which acupuncture appears to be of benefit, and smoking cessation, where acupuncture is no more effective than sham acupuncture. Conclusions A large number of systematic reviews on acupuncture exists. What is most obvious from these reviews is the need for (the funding of) well-designed, larger clinical trials

Performing under pressure: Quiet eye training improves surgical knot-tying performance

Background: We examined the effectiveness of traditional technical training (TT) and quiet eye training (QET) on the performance of one-handed square knot tying in first-year surgery residents under normal and high anxiety conditions. Methods: Twenty surgery residents were assigned randomly to the two groups and completed pretest, training, and simple and complex retention tests under conditions of high and low anxiety. The TT group received traditional instruction on improving hand movements; the QET group received feedback on their gaze behaviors. Participants wore an eye tracker that recorded simultaneously their gaze and hand movements. Dependent variables were: knot tying performance (%), quiet eye duration (%), number of fixations, and total movement time (s). Results: Both groups improved their knot tying performance (p 0.05). The QET group also demonstrated more efficient gaze and hand movements post training. Conclusions: These data demonstrate the effectiveness of training gaze behaviors, not only to improve the effectiveness and efficiency of performance, but also to mediate any negative effects of anxiety on performance. These findings may have important implications for medical educators and practitioners, as well as surgeons who may be (re)training or learning new procedures

Quiet eye training improves surgical knot tying more than traditional technical training: A randomized controlled study

Background We examined the effectiveness of technical training (TT) and quiet eye training (QE) on the performance of one-handed square knot tying in surgical residents. Methods Twenty surgical residents were randomly assigned to the 2 groups and completed pretest, training, retention, and transfer tests. Participants wore a mobile eye tracker that simultaneously recorded their gaze and hand movements. Dependent variables were knot tying performance (%), QE duration (%), number of fixations, total movement time (s), and hand movement phase time (s). Results The QE training group had significantly higher performance scores, a longer QE duration, fewer fixations, faster total knot tying times, and faster movement phase times compared with the TT group. The QE group maintained performance in the transfer test, whereas the TT group significantly decreased performance from retention to transfer. Conclusions QE training significantly improved learning, retention, and transfer of surgical knot tying compared with a traditional technical approach. Both performance effectiveness (performance outcome) and movement efficiency (hand movement times) were improved using QE modeling, instruction, and feedback. © 2014 Elsevier Inc. All rights reserved

Naked Singularity and Thunderbolt

We consider quantum theoretical effects of the sudden change of the boundary conditions which mimics the occurrence of naked singularities. For a simple demonstration, we study a massless scalar field in $(1 + 1)$-dimensional Minkowski spacetime with finite spatial interval. We calculate the vacuum expectation value of the energy-momentum tensor and explicitly show that singular wave or {\em thunderbolt} appears along the Cauchy horizon. The thunderbolt possibly destroys the Cauchy horizon if its backreaction on the geometry is taken into account, leading to quantum restoration of the global hyperbolicity. The result of the present work may also apply to the situation that a closed string freely oscillating is traveling to a brane and changes itself to an open string pinned-down by the ends satisfying the Dirichlet boundary conditions on the brane.Comment: 12 pages, 1 figure, references added, to appear in Phys. Rev.