82 research outputs found
Detecting a stochastic gravitational wave background with the Laser Interferometer Space Antenna
The random superposition of many weak sources will produce a stochastic
background of gravitational waves that may dominate the response of the LISA
(Laser Interferometer Space Antenna) gravitational wave observatory. Unless
something can be done to distinguish between a stochastic background and
detector noise, the two will combine to form an effective noise floor for the
detector. Two methods have been proposed to solve this problem. The first is to
cross-correlate the output of two independent interferometers. The second is an
ingenious scheme for monitoring the instrument noise by operating LISA as a
Sagnac interferometer. Here we derive the optimal orbital alignment for
cross-correlating a pair of LISA detectors, and provide the first analytic
derivation of the Sagnac sensitivity curve.Comment: 9 pages, 11 figures. Significant changes to the noise estimate
Limits on the high-energy gamma and neutrino fluxes from the SGR 1806-20 giant flare of December 27th, 2004 with the AMANDA-II detector
On December 27th 2004, a giant gamma flare from the Soft Gamma-ray Repeater
1806-20 saturated many satellite gamma-ray detectors. This event was by more
than two orders of magnitude the brightest cosmic transient ever observed. If
the gamma emission extends up to TeV energies with a hard power law energy
spectrum, photo-produced muons could be observed in surface and underground
arrays. Moreover, high-energy neutrinos could have been produced during the SGR
giant flare if there were substantial baryonic outflow from the magnetar. These
high-energy neutrinos would have also produced muons in an underground array.
AMANDA-II was used to search for downgoing muons indicative of high-energy
gammas and/or neutrinos. The data revealed no significant signal. The upper
limit on the gamma flux at 90% CL is dN/dE < 0.05 (0.5) TeV^-1 m^-2 s^-1 for
gamma=-1.47 (-2). Similarly, we set limits on the normalization constant of the
high-energy neutrino emission of 0.4 (6.1) TeV^-1 m^-2 s^-1 for gamma=-1.47
(-2).Comment: 14 pages, 3 figure
Exclusive measurement of two-pion production in the dd --> 4Hepipi reaction
The results from the first kinematically complete measurement of the dd -->
4Hepipi reaction are reported. The aim was to investigate a long standing
puzzle regarding the origin of the peculiar pipi-invariant mass distributions
appearing in double pion production in light ion collisions, the so-called ABC
effect. The measurements were performed at the incident deuteron energies of
712 MeV and 1029 MeV, with the WASA detector assembly at CELSIUS in Uppsala,
Sweden. We report the observation of a characteristic enhancement at low
pipi-invariant mass at 712 MeV, the lowest energy yet. At the higher energy, in
addition to confirming previous experimental observations, our results reveal a
strong angular dependence of the pions in the overall centre of mass system.
The results are qualitatively reproduced by a theoretical model, according to
which the ABC effect is described as resulting from a kinematical enhancement
in the production of the pion pairs from two parallel and independent NN--> dpi
sub-processes.Comment: 20 pages including 18 figure
First year performance of the IceCube neutrino telescope
The first sensors of the IceCube neutrino observatory were deployed at the South Pole during the austral summer of 2004-2005 and have been producing data since February 2005. One string of 60 sensors buried in the ice and a surface array of eight ice Cherenkov tanks took data until December 2005 when deployment of the next set of strings and tanks began. We have analyzed these data, demonstrating that the performance of the system meets or exceeds design requirements. Times are determined across the whole array to a relative precision of better than 3 ns, allowing reconstruction of muon tracks and light bursts in the ice, of air-showers in the surface array and of events seen in coincidence by surface and deep-ice detectors separated by up to 2.5 km
The ICECUBE prototype string in AMANDA
The Antarctic Muon And Neutrino Detector Array (Amanda) is a high-energy
neutrino telescope. It is a lattice of optical modules (OM) installed in the
clear ice below the South Pole Station. Each OM contains a photomultiplier tube
(PMT) that detects photons of Cherenkov light generated in the ice by muons and
electrons. IceCube is a cubic-kilometer-sized expansion of Amanda currently
being built at the South Pole. In IceCube the PMT signals are digitized already
in the optical modules and transmitted to the surface. A prototype string of 41
OMs equipped with this new all-digital technology was deployed in the Amanda
array in the year 2000. In this paper we describe the technology and
demonstrate that this string serves as a proof of concept for the IceCube
array. Our investigations show that the OM timing accuracy is 5 ns. Atmospheric
muons are detected in excellent agreement with expectations with respect to
both angular distribution and absolute rate
Limits to the muon flux from neutralino annihilations in the Sun with the AMANDA detector
A search for an excess of muon-neutrinos from neutralino annihilations in the
Sun has been performed with the AMANDA-II neutrino detector using data
collected in 143.7 days of live-time in 2001. No excess over the expected
atmospheric neutrino background has been observed. An upper limit at 90%
confidence level has been obtained on the annihilation rate of captured
neutralinos in the Sun, as well as the corresponding muon flux limit at the
Earth, both as functions of the neutralino mass in the range 100 GeV-5000 GeV.Comment: 13 pages, 3 figures. Submitted to Astropart. Phy
HIRO-NET: Self-organized robotic mesh networking for internet sharing in disaster scenarios
In this paper we present HIRO-NET, Heterogeneous Intelligent Robotic Network. HIRO-NET is an emergency infrastructure-less network tailored to address the problem of providing connectivity in the immediate aftermath of a natural disaster, where no cellular or wide area network is operational and no Internet access is available. HIRO-NET establishes a two-tier wireless mesh network where the Lower Tier connects nearby survivors in a self-organized mesh via Bluetooth Low Energy (BLE)and the Upper Tier creates long-range VHF links between autonomous robots exploring the disaster stricken area. HIRO-NET main goal is to enable users in the disaster to exchange text messages in order to share critical information and request help from first responders. The mesh network discovery problem is analyzed and a network protocol specifically designed to facilitate the exploration process is presented. We show how HIRO-NET robots successfully discover, bridge and interconnect local mesh networks. Results show that the Lower Tier always reaches network convergence and the Upper Tier can virtually extend HIRO-NET functionalities to the range of a small metropolitan area. In the event of an Internet connection still being available to some user, HIRO-NET is able to opportunistically share and provide access to low data-rate services (e.g. Twitter, Gmail)to the whole network. Results suggest that a temporary emergency network to cover a metropolitan area can be created in tens of minutes
An evaluation of the statistical convertibility of Function Points into COSMIC Function Points
The interactions of physical activity, exercise and genetics and their associations with bone mineral density: Implications for injury risk in elite athletes
Low bone mineral density (BMD) is established as a primary predictor of osteoporotic risk and can also have substantial implications for athlete health and injury risk in the elite sporting environment. BMD is a highly multi-factorial phenotype influenced by diet, hormonal characteristics and physical activity. The interrelationships between such factors, and a strong genetic component, suggested to be around 50-85% at various anatomical sites, determines skeletal health throughout life. Genome-wide association studies (GWAS) and case-control designs have revealed many loci associated with variation in BMD. However, a number of the candidate genes identified at these loci have no known associated biological function or have yet to be replicated in subsequent investigations. Furthermore, few investigations have considered gene-environment interactions - in particular, whether specific genes may be sensitive to mechanical loading from physical activity and the outcome of such an interaction for BMD and potential injury risk. Therefore, this review considers the importance of physical activity on BMD, genetic associations with BMD and how subsequent investigation requires consideration of the interaction between these strong determinants. Future research using well-defined independent cohorts such as elite athletes, who experience much greater mechanical stress than most, to study such phenotypes, can provide a greater understanding of these factors as well as the biological underpinnings of such a physiologically “extreme” population. Subsequently, modification of training, exercise or rehabilitation programmes based upon genetic characteristics could have substantial implications in both the sporting and public health domains once the fundamental research has been conducted successfully
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