Cosmic-Ray Events as Background in Imaging Atmospheric Cherenkov Telescopes

The dominant background for observations of gamma-rays in the energy region above 50 GeV with Imaging Atmospheric Cherenkov telescopes are cosmic-ray events. The images of most of the cosmic ray showers look significantly different from those of gamma-rays and are therefore easily discriminated. However, a small fraction of events seems to be indistinguishable from gamma-rays. This constitutes an irreducible background to the observation of high-energy gamma-ray sources, and limits the sensitivity achievable with a given instrument. Here, a Monte Carlo study of gamma-like cosmic-ray events is presented. The nature of gamma-like cosmic-ray events, the shower particles that are responsible for the gamma-like appearance, and the dependence of these results on the choice of the hadronic interaction model are investigated. Most of the gamma-like cosmic ray events are characterised by the production of high-energy pi0's early in the shower development which dump most of the shower energy into electromagnetic sub-showers. Also Cherenkov light from single muons can mimic gamma-rays in close-by pairs of telescopes. Differences of up to 25% in the collection area for gamma-like proton showers between QGSJet/FLUKA and Sibyll/FLUKA simulations have been found.Comment: Accepted by Journal of Astroparticle Physic

The size and polydispersity of silica nanoparticles under simulated hot spring conditions

The nucleation and growth of silica nanoparticles in supersaturated geothermal waters was simulated using a flow-through geothermal simulator system. The effect of silica concentration ([SiO2]), ionic strength (IS), temperature (T) and organic additives on the size and polydispersity of the forming silica nanoparticles was quantified. A decrease in temperature (58 to 33°C) and the addition of glucose restricted particle growth to sizes <20 nm, while varying [SiO2] or ISdid not affect the size (30-35 nm) and polydispersity (±9 nm) observed at 58°C. Conversely, the addition of xanthan gum induced the development of thin films that enhanced silica aggregation

A Broad Search for Counterrotating Gas and Stars: Evidence for Mergers and Accretion

We measure the frequency of bulk gas-stellar counterrotation in a sample of 67 galaxies drawn from the Nearby Field Galaxy Survey, a broadly representative survey of the local galaxy population down to M_B-15. We detect 4 counterrotators among 17 E/S0's with extended gas emission (24% +8 -6). In contrast, we find no clear examples of bulk counterrotation among 38 Sa-Sbc spirals, although one Sa does show peculiar gas kinematics. This result implies that, at 95% confidence, no more than 8% of Sa-Sbc spirals are bulk counterrotators. Among types Sc and later, we identify only one possible counterrotator, a Magellanic irregular. We use these results together with the physical properties of the counterrotators to constrain possible origins for this phenomenon.Comment: 19 pages, 4 figures, AJ, accepte

Developing the evidence base for adult social care practice: The NIHR School for Social Care Research

In a foreword to 'Shaping the Future of Care Together', Prime Minister Gordon Brown says that a care and support system reflecting the needs of our times and meeting our rising aspirations is achievable, but 'only if we are prepared to rise to the challenge of radical reform'. A number of initiatives will be needed to meet the challenge of improving social care for the growing older population. Before the unveiling of the green paper, The National Institute for Health Research (NIHR) announced that it has provided 15m pounds over a five-year period to establish the NIHR School for Social Care Research. The School's primary aim is to conduct or commission research that will help to improve adult social care practice in England. The School is seeking ideas for research topics, outline proposals for new studies and expert advice in developing research methods

Violence Prevention In High Schools: Choices for Effectiveness

Every two days, guns kill the equivalent of a classroom of youngsters and injure 60 more

Parameters for Twisted Representations

The study of Hermitian forms on a real reductive group $G$ gives rise, in the unequal rank case, to a new class of Kazhdan-Lusztig-Vogan polynomials. These are associated with an outer automorphism $\delta$ of $G$, and are related to representations of the extended group $$. These polynomials were defined geometrically by Lusztig and Vogan in "Quasisplit Hecke Algebras and Symmetric Spaces", Duke Math. J. 163 (2014), 983--1034. In order to use their results to compute the polynomials, one needs to describe explicitly the extension of representations to the extended group. This paper analyzes these extensions, and thereby gives a complete algorithm for computing the polynomials. This algorithm is being implemented in the Atlas of Lie Groups and Representations software

Equivalence of domains for hyperbolic Hubbard-Stratonovich transformations

We settle a long standing issue concerning the traditional derivation of non-compact non-linear sigma models in the theory of disordered electron systems: the hyperbolic Hubbard-Stratonovich (HS) transformation of Pruisken-Schaefer type. Only recently the validity of such transformations was proved in the case of U(p,q) (non-compact unitary) and O(p,q) (non-compact orthogonal) symmetry. In this article we give a proof for general non-compact symmetry groups. Moreover we show that the Pruisken-Schaefer type transformations are related to other variants of the HS transformation by deformation of the domain of integration. In particular we clarify the origin of surprising sign factors which were recently discovered in the case of orthogonal symmetry.Comment: 30 pages, 3 figure

Decomposition of time-covariant operations on quantum systems with continuous and/or discrete energy spectrum

Every completely positive map G that commutes which the Hamiltonian time evolution is an integral or sum over (densely defined) CP-maps G_\sigma where \sigma is the energy that is transferred to or taken from the environment. If the spectrum is non-degenerated each G_\sigma is a dephasing channel followed by an energy shift. The dephasing is given by the Hadamard product of the density operator with a (formally defined) positive operator. The Kraus operator of the energy shift is a partial isometry which defines a translation on R with respect to a non-translation-invariant measure. As an example, I calculate this decomposition explicitly for the rotation invariant gaussian channel on a single mode. I address the question under what conditions a covariant channel destroys superpositions between mutually orthogonal states on the same orbit. For channels which allow mutually orthogonal output states on the same orbit, a lower bound on the quantum capacity is derived using the Fourier transform of the CP-map-valued measure (G_\sigma).Comment: latex, 33 pages, domains of unbounded operators are now explicitly specified. Presentation more detailed. Implementing the shift after the dephasing is sometimes more convenien