Limit curve theorems in Lorentzian geometry

The subject of limit curve theorems in Lorentzian geometry is reviewed. A general limit curve theorem is formulated which includes the case of converging curves with endpoints and the case in which the limit points assigned since the beginning are one, two or at most denumerable. Some applications are considered. It is proved that in chronological spacetimes, strong causality is either everywhere verified or everywhere violated on maximizing lightlike segments with open domain. As a consequence, if in a chronological spacetime two distinct lightlike lines intersect each other then strong causality holds at their points. Finally, it is proved that two distinct components of the chronology violating set have disjoint closures or there is a lightlike line passing through each point of the intersection of the corresponding boundaries.Comment: 25 pages, 1 figure. v2: Misprints fixed, matches published versio

Microwave oven fabricated hybrid memristor devices for non-volatile memory storage

© 2014 IOP Publishing Ltd. Novel hybrid non-volatile memories made using an ultra-fast microwave heating method are reported for the first time. The devices, consisting of aligned ZnO nanorods embedded in poly (methyl methacrylate), require no forming step and exhibit reliable and reproducible bipolar resistive switching at low voltages and with low power usage. We attribute these properties to a combination of the high aspect ratio of the nanorods and the polymeric hybrid structure of the device. The extremely easy, fast and low-cost solution based method of fabrication makes possible the simple and quick production of cheap memory cells

Experimental Polarization State Tomography using Optimal Polarimeters

We report on the experimental implementation of a polarimeter based on a scheme known to be optimal for obtaining the polarization vector of ensembles of spin-1/2 quantum systems, and the alignment procedure for this polarimeter is discussed. We also show how to use this polarimeter to estimate the polarization state for identically prepared ensembles of single photons and photon pairs and extend the method to obtain the density matrix for generic multi-photon states. State reconstruction and performance of the polarimeter is illustrated by actual measurements on identically prepared ensembles of single photons and polarization entangled photon pairs

Integration of the Friedmann equation for universes of arbitrary complexity

An explicit and complete set of constants of the motion are constructed algorithmically for Friedmann-Lema\^{i}tre-Robertson-Walker (FLRW) models consisting of an arbitrary number of non-interacting species. The inheritance of constants of the motion from simpler models as more species are added is stressed. It is then argued that all FLRW models admit what amounts to a unique candidate for a gravitational epoch function (a dimensionless scalar invariant derivable from the Riemann tensor without differentiation which is monotone throughout the evolution of the universe). The same relations that lead to the construction of constants of the motion allow an explicit evaluation of this function. In the simplest of all models, the $\Lambda$CDM model, it is shown that the epoch function exists for all models with $\Lambda > 0$, but for almost no models with $\Lambda \leq 0$.Comment: Final form to appear in Physical Review D1

Interactive public digital displays: investigating its use in a high school context

This paper presents a longitudinal user study that investigated the adoption of some Bluetooth based functionalities for a public digital display in a high school. More specifically, the utilization of Bluetooth device naming extended beyond social identity representation and introduced the use of a simple interaction mechanism. The interaction mechanism involves recognizing parts of the Bluetooth device name as explicit instructions to trigger the generation of content on an interactive public display. Together with representatives of the teachers' community, the design team defined some social rules concerning usage in order to account for the specificities of the place. In the user study, three fully functional prototypes were deployed at the school hall of the high school. The functionalities introduced with the different prototypes were: the visualization on the display of the Bluetooth device names, the possibility to contribute to tag clouds and the possibility to choose icons from a given set for self-expression. The results suggest that people appropriated some but not all of the functionalities employed. Implications of our findings to the design of interactive digital displays are pointed out.(undefined

Spacelike surfaces with free boundary in the Lorentz-Minkowski space

We investigate a variational problem in the Lorentz-Minkowski space \l^3 whose critical points are spacelike surfaces with constant mean curvature and making constant contact angle with a given support surface along its common boundary. We show that if the support surface is a pseudosphere, then the surface is a planar disc or a hyperbolic cap. We also study the problem of spacelike hypersurfaces with free boundary in the higher dimensional Lorentz-Minkowski space \l^{n+1}.Comment: 16 pages. Accepted in Classical and Quantum Gravit

Labrador retrievers under primary veterinary care in the UK: demography, mortality and disorders

Abstract Background Labrador retrievers are reportedly predisposed to many disorders but accurate prevalence information relating to the general population are lacking. This study aimed to describe demography, mortality and commonly recorded diseases in Labrador retrievers under UK veterinary care. Methods The VetCompass™ programme collects electronic patient record data on dogs attending UK primary-care veterinary practices. Demographic analysis covered all33,320 Labrador retrievers in the VetCompass™ database under veterinary care during 2013 while disorder and mortality data were extracted from a random sample of 2074 (6.2%) of these dogs. Results Of the Labrador retrievers with information available, 15,427 (46.4%) were female and 15,252 (53.6%) were male. Females were more likely to be neutered than males (59.7% versus 54.8%, P <  0.001). The overall mean adult bodyweight was 33.0 kg (SD 6.1). Adult males were heavier (35.2 kg, SD 5.9 kg) than adult females (30.4 kg, SD 5.2 kg) (P <  0.001). The median longevity of Labrador retrievers overall was 12.0 years (IQR 9.9–13.8, range 0.0–16.0). The most common recorded colours were black (44.6%), yellow (27.8%) and liver/chocolate (reported from hereon as chocolate) (23.8%). The median longevity of non-chocolate coloured dogs (n = 139, 12.1 years, IQR 10.2–13.9, range 0.0–16.0) was longer than for chocolate coloured animals (n = 34, 10.7 years, IQR 9.0–12.4, range 3.8–15.5) (P = 0.028). Of a random sample of 2074 (6.2%) Labrador retrievers under care in 2013 that had full disorder data extracted, 1277 (61.6%) had at least one disorder recorded. The total number of dogs who died at any date during the study was 176. The most prevalent disorders recorded were otitis externa (n = 215, prevalence 10.4%, 95% CI: 9.1–11.8), overweight/obesity (183, 8.8%, 95% CI: 7.6–10.1) and degenerative joint disease (115, 5.5%, 95% CI: 4.6–6.6). Overweight/obesity was not statistically significantly associated with neutering in females (8.3% of entire versus 12.5% of neutered, P = 0.065) but was associated with neutering in males (4.1% of entire versus 11.4% of neutered, P < 0.001). The prevalence of otitis externa in black dogs was 12.8%, in yellow dogs it was 17.0% but, in chocolate dogs, it rose to 23.4% (P < 0.001). Similarly, the prevalence of pyo-traumatic dermatitis in black dogs was 1.1%, in yellow dogs it was 1.6% but in chocolate dogs it rose to 4.0% (P = 0.011). Conclusions The current study assists prioritisation of health issues within Labrador retrievers. The most common disorders were overweight/obesity, otitis externa and degenerative joint disease. Males were significantly heavier females. These results can alert prospective owners to potential health issues and inform breed-specific wellness checks

3D Simulations of MHD Jet Propagation Through Uniform and Stratified External Environments

We present a set of high-resolution 3D MHD simulations of steady light, supersonic jets, exploring the influence of jet Mach number and the ambient medium on jet propagation and energy deposition over long distances. The results are compared to simple self-similar scaling relations for the morphological evolution of jet-driven structures and to previously published 2D simulations. For this study we simulated the propagation of light jets with internal Mach numbers 3 and 12 to lengths exceeding 100 initial jet radii in both uniform and stratified atmospheres. The propagating jets asymptotically deposit approximately half of their energy flux as thermal energy in the ambient atmosphere, almost independent of jet Mach number or the external density gradient. Nearly one-quarter of the jet total energy flux goes directly into dissipative heating of the ICM, supporting arguments for effective feedback from AGNs to cluster media. The remaining energy resides primarily in the jet and cocoon structures. Despite having different shock distributions and magnetic field features, global trends in energy flow are similar among the different models. As expected the jets advance more rapidly through stratified atmospheres than uniform environments. The asymptotic head velocity in King-type atmospheres shows little or no deceleration. This contrasts with jets in uniform media with heads that are slowed as they propagate. This suggests that the energy deposited by jets of a given length and power depends strongly on the structure of the ambient medium. While our low-Mach jets are more easily disrupted, their cocoons obey evolutionary scaling relations similar to the high-Mach jets.Comment: Accepted in ApJ, 32 pages, 18 figures, animations available from: http://www.msi.umn.edu/Projects/twj/newsite/projects/radiojets/movies

Crossover from 2-dimensional to 1-dimensional collective pinning in NbSe3

We have fabricated NbSe$_3$ structures with widths comparable to the Fukuyama-Lee-Rice phase-coherence length. For samples already in the 2-dimensional pinning limit, we observe a crossover from 2-dimensional to 1-dimensional collective pinning when the crystal width is less than 1.6 $\mu$m, corresponding to the phase-coherence length in this direction. Our results show that surface pinning is negligible in our samples, and provide a means to probe the dynamics of single domains giving access to a new regime in charge-density wave physics.Comment: 4 pages, 2 figures, and 1 table. Accepted for publication in Physical Review

Precision Measurement of the Radiative B\Beta Decay of the Free Neutron

The standard model predicts that, in addition to a proton, an electron, and an antineutrino, a continuous spectrum of photons is emitted in the $\beta$ decay of the free neutron. We report on the RDK II experiment which measured the photon spectrum using two different detector arrays. An annular array of bismuth germanium oxide scintillators detected photons from 14 to 782~keV. The spectral shape was consistent with theory, and we determined a branching ratio of 0.00335 $\pm$ 0.00005 [stat] $\pm$ 0.00015 [syst]. A second detector array of large area avalanche photodiodes directly detected photons from 0.4 to 14~keV. For this array, the spectral shape was consistent with theory, and the branching ratio was determined to be 0.00582 $\pm$ 0.00023 [stat] $\pm$ 0.00062 [syst]. We report the first precision test of the shape of the photon energy spectrum from neutron radiative decay and a substantially improved determination of the branching ratio over a broad range of photon energies