227 research outputs found
Microscopic black hole detection in UHECR: the double bang signature
According to recent conjectures on the existence of large extra dimensions in
our universe, black holes may be produced during the interaction of Ultra High
Energy Cosmic Rays with the atmosphere. However, and so far, the proposed
signatures are based on statistical effects, not allowing identification on an
event by event basis, and may lead to large uncertainties. In this note, events
with a double bang topology, where the production and instantaneous decay of a
microscopic black hole (first bang) is followed, at a measurable distance, by
the decay of an energetic tau lepton (second bang) are proposed as an almost
background free signature. The characteristics of these events and the
capability of large cosmic ray experiments to detect them are discussed.Comment: revised version, 5 figure
Has the GZK suppression been discovered?
The energy spectra of ultra high energy cosmic rays reported by the AGASA,
Fly's Eye, Haverah Park, HiRes, and Yakutsk experiments are all shown to be in
agreement with each other for energies below 10^{20} eV (after small
adjustments, within the known uncertainties, of the absolute energy scales).
The data from HiRes, Fly's Eye, and Yakutsk are consistent with the expected
flux suppression above 5\times 10^{19} eV due to interactions of cosmic rays
with the cosmic microwave background, the Greisen-Zatsepin-Kuzmin (GZK)
"supression," and are inconsistent with a smooth extrapolation of the observed
cosmic ray energy spectrum to energies > 5\times 10^{19}$ eV. AGASA data show
an excess of events above 10^{20} eV, compared to the predicted GZK suppression
and to the flux measured by the other experiments.Comment: Editorial changes, including replacing 'cutoff' by 'supression
A third cluster of red supergiants in the vicinity of the massive cluster RSGC3
Recent studies have shown that the area around the massive, obscured cluster
RSGC3 may harbour several clusters of red supergiants. In this paper, we
analyse a clump of photometrically selected red supergiant candidates 20' south
of RSGC3 in order to confirm the existence of another of these clusters. Using
medium-resolution infrared spectroscopy around 2.27 microns, we derived
spectral types and velocities along the line of sight for the selected
candidates, confirming their nature and possible association. We find a compact
clump of eight red supergiants and four other candidates at some distance, all
of them spectroscopically confirmed red supergiants. The majority of these
objects must form an open cluster, which we name Alicante 10. Because of the
high reddening and strong field contamination, the cluster sequence is not
clearly seen in 2MASS or GPS-UKIDSS. From the observed sources, we derive
E(J-Ks)=2.6 and d~6 kpc. Although the cluster is smaller than RSGC3, it has an
initial mass in excess of 10000 solar masses, and it seems to be part of the
RSGC3 complex. With the new members this association already has 35
spectroscopically confirmed red supergiants, confirming its place as one of the
most active sites of recent stellar formation in the Galaxy.Comment: Accepted for publication on A&
Visualising Conversation Structure across Time: Insights into Effective Doctor-Patient Consultations
Effective communication between healthcare professionals and patients is critical to patients’ health outcomes. The doctor/patient dialogue has been extensively researched from different perspectives, with findings emphasising a range of behaviours that lead to effective communication. Much research involves self-reports, however, so that behavioural engagement cannot be disentangled from patients’ ratings of effectiveness. In this study we used a highly efficient and time economic automated computer visualisation measurement technique called Discursis to analyse conversational behaviour in consultations. Discursis automatically builds an internal language model from a transcript, mines the transcript for its conceptual content, and generates an interactive visual account of the discourse. The resultant visual account of the whole consultation can be analysed for patterns of engagement between interactants. The findings from this study show that Discursis is effective at highlighting a range of consultation techniques, including communication accommodation, engagement and repetition
Wavenumber-explicit continuity and coercivity estimates in acoustic scattering by planar screens
We study the classical first-kind boundary integral equation reformulations
of time-harmonic acoustic scattering by planar sound-soft (Dirichlet) and
sound-hard (Neumann) screens. We prove continuity and coercivity of the
relevant boundary integral operators (the acoustic single-layer and
hypersingular operators respectively) in appropriate fractional Sobolev spaces,
with wavenumber-explicit bounds on the continuity and coercivity constants. Our
analysis is based on spectral representations for the boundary integral
operators, and builds on results of Ha-Duong (Jpn J Ind Appl Math 7:489--513
(1990) and Integr Equat Oper Th 15:427--453 (1992)).Comment: v2 has minor corrections compared to v1. arXiv admin note:
substantial text overlap with arXiv:1401.280
High Energy Neutrinos from Astrophysical Sources: An Upper Bound
We show that cosmic-ray observations set a model-independent upper bound to
the flux of high-energy, > 10^14 eV, neutrinos produced by photo-meson (or p-p)
interactions in sources of size not much larger than the proton photo-meson (or
pp) mean-free-path. The bound applies, in particular, to neutrino production by
either AGN jets or GRBs. This upper limit is two orders of magnitude below the
flux predicted in some popular AGN jet models, but is consistent with our
predictions from GRB models. We discuss the implications of these results for
future km^2 high-energy neutrino detectors.Comment: Added discussion showing bound cannot be evaded by invoking magnetic
fields. Accepted Phys Rev
Leptogenesis in Theories with Large Extra Dimensions
We study the scenario of baryogenesis through leptogenesis in
higher-dimensional theories, in which the scale of quantum gravity is many
orders of magnitude smaller than the usual Planck mass. The minimal realization
of these theories includes an isosinglet neutrino which feels the presence of
large compact dimensions, whereas all the SM particles are localized on a
-dimensional subspace. In the formulation of minimal leptogenesis
models, we pay particular attention to the existence of Majorana spinors in
higher dimensions. After compactification of the extra dimensions, we obtain a
tower of Majorana Kaluza-Klein excitations which act as an infinite series of
CP-violating resonators, and derive the necessary conditions for their
constructive interference. Based on this CP-violating mechanism, we find that
the decays of the heavy Majorana excitations can produce a leptonic asymmetry
which is reprocessed into the observed baryonic asymmetry of the Universe by
means of out-of-equilibrium sphaleron interactions, provided the reheat
temperature is above 5 GeV.Comment: 34 pages, minor rewordings, to appear in Physical Review
Activation of adherent vascular neutrophils in the lung during acute endotoxemia
BACKGROUND: Neutrophils constitute the first line of defense against invading microorganisms. Whereas these cells readily undergo apoptosis under homeostatic conditions, their survival is prolonged during inflammatory reactions and they become biochemically and functionally activated. In the present study, we analyzed the effects of acute endotoxemia on the response of a unique subpopulation of neutrophils tightly adhered to the lung vasculature. METHODS: Rats were treated with 5 mg/kg lipopolysaccharide (i.v.) to induce acute endotoxemia. Adherent neutrophils were isolated from the lung vasculature by collagenase digestion and sequential filtering. Agarose gel electrophoresis, RT-PCR, western blotting and electrophoretic mobility shift assays were used to evaluate neutrophil activity. RESULTS: Adherent vascular neutrophils isolated from endotoxemic animals exhibited decreased apoptosis when compared to cells from control animals. This was associated with a marked increase in expression of the anti-apoptotic protein, Mcl-1. Cells isolated 0.5–2 hours after endotoxin administration were more chemotactic than cells from control animals and expressed increased tumor necrosis factor-alpha and cyclooxygenase-2 mRNA and protein, demonstrating that they are functionally activated. Endotoxin treatment of the animals also induced p38 and p44/42 mitogen activated protein kinases in the adherent lung neutrophils, as well as nuclear binding activity of the transcription factors, NF-κB and cAMP response element binding protein. CONCLUSION: These data demonstrate that adherent vascular lung neutrophils are highly responsive to endotoxin and that pathways regulating apoptosis and cellular activation are upregulated in these cells
- …