6,564 research outputs found
Too close for comfort: spatial patterns in acorn barnacle populations
Spatial patterns in aggregations form as a result of the interplay between costs and benefits experienced by individuals. Such self-organisation of aggregations can be explained using a zonal model in which a short-range zone of repulsion and longer-range zone of attraction surrounding individuals leads to emergent pattern properties. The signal of these processes can be detected using spatial pattern analyses. Furthermore, in sessile organisms, post-settlement mortality reveals the relative costs and benefits of positions within the aggregation. Acorn barnacles are known to require contact with conspecifics for reproduction and are therefore believed to aggregate for this purpose; isolated individuals may also be more susceptible to abiotic stress and predation. At short distances, however, competition for space and resources is likely to occur. In this study spatial patterns of barnacles (Semibalanus balanoides L.) were analysed using pair-correlation functions. Individuals were dispersed at distances below 0.30 cm, but peak relative density occurred at a distance of 0.36 cm from conspecifics. This is much closer than required for reproductive access, implying a strong aggregative drive, up to the point of physical contact with neighbours. Nevertheless, analysis of dead barnacles illustrated that such proximity carries a cost as barnacles with many neighbours were more likely to have died. The inferences obtained from these patterns are that barnacles aggregate as closely as they can, and that local neighbourhood competition is a powerful determinant of mortality. These processes give rise to the observed pattern properties
Evidence Of Dark Matter Annihilations In The WMAP Haze
The WMAP experiment has revealed an excess of microwave emission from the
region around the center of our Galaxy. It has been suggested that this signal,
known as the ``WMAP Haze'', could be synchrotron emission from relativistic
electrons and positrons generated in dark matter annihilations. In this letter,
we revisit this possibility. We find that the angular distribution of the WMAP
Haze matches the prediction for dark matter annihilations with a cusped density
profile, in the inner kiloparsecs. Comparing the
intensity in different WMAP frequency bands, we find that a wide range of
possible WIMP annihilation modes are consistent with the spectrum of the haze
for a WIMP with a mass in the 100 GeV to multi-TeV range. Most interestingly,
we find that to generate the observed intensity of the haze, the dark matter
annihilation cross section is required to be approximately equal to the value
needed for a thermal relic, cm/s. No
boost factors are required. If dark matter annihilations are in fact
responsible for the WMAP Haze, and the slope of the halo profile continues into
the inner Galaxy, GLAST is expected to detect gamma rays from the dark matter
annihilations in the Galactic Center if the WIMP mass is less than several
hundred GeV.Comment: 4 pages, 3 figure
Probing Exotic Physics With Cosmic Neutrinos
Traditionally, collider experiments have been the primary tool used in
searching for particle physics beyond the Standard Model. In this talk, I will
discuss alternative approaches for exploring exotic physics scenarios using
high energy and ultra-high energy cosmic neutrinos. Such neutrinos can be used
to study interactions at energies higher, and over baselines longer, than those
accessible to colliders. In this way, neutrino astronomy can provide a window
into fundamental physics which is highly complementary to collider techniques.
I will discuss the role of neutrino astronomy in fundamental physics,
considering the use of such techniques in studying several specific scenarios
including low scale gravity models, Standard Model electroweak instanton
induced interactions, decaying neutrinos and quantum decoherence.Comment: 11 pages, 6 figures; For the proceedings of From Colliders To Cosmic
Rays, Prague, Czech Republic, September 7-13, 200
The implications of sustainable development for airport duty-free business models
© HENRY STEWART PUBLICATIONS. This paper considers how the challenges underpinning sustainable development are likely to impact on duty-and tax-free retailing in airports and, by implication, in the entire aviation industry. The paper defines the role of retail as a vital source of airport revenues, before considering the carbon consequences of the sector’s incumbent business models. It finds that products taken onto aircraft increase aircraft weight and fuel burn and are a primary source of carbon emissions for duty-free retailers. The implications for the sector are discussed, and the potential for implementing more sustainable business models is presented. Here it is identified that the specific logistical, economic, and political constraints of operating in the airport make alternative business models difficult, if not impossible to implement. The specialisations that have helped this sector to flourish are constraining their ability to adapt to the climate challenge
The Indirect Search for Dark Matter with IceCube
We revisit the prospects for IceCube and similar kilometer-scale telescopes
to detect neutrinos produced by the annihilation of weakly interacting massive
dark matter particles (WIMPs) in the Sun. We emphasize that the astrophysics of
the problem is understood; models can be observed or, alternatively, ruled out.
In searching for a WIMP with spin-independent interactions with ordinary
matter, IceCube is only competitive with direct detection experiments if the
WIMP mass is sufficiently large. For spin-dependent interactions IceCube
already has improved the best limits on spin-dependent WIMP cross sections by
two orders of magnitude. This is largely due to the fact that models with
significant spin-dependent couplings to protons are the least constrained and,
at the same time, the most promising because of the efficient capture of WIMPs
in the Sun. We identify models where dark matter particles are beyond the reach
of any planned direct detection experiments while being within reach of
neutrino telescopes. In summary, we find that, even when contemplating recent
direct detection results, neutrino telescopes have the opportunity to play an
important as well as complementary role in the search for particle dark matter.Comment: 17 pages, 10 figures, published in the New Journal of Physics 11
105019 http://www.iop.org/EJ/abstract/1367-2630/11/10/105019, new version
submitted to correct Abstract in origina
Creep strain measurement using a potential drop technique
AbstractThis paper will demonstrate the use of a potential drop sensor to monitor strain. In particular, the suitability of the technique to high temperature or harsh environment applications presents an opportunity for monitoring strain in components operating under creep conditions. Monitoring creep damage in power station components is a long standing technological challenge to the non-destructive evaluation community. It is well established in the literature that strain rate serves as an excellent indicator of the progress of creep damage and can be used for remnant life calculations. To facilitate the use of such strain rate based evaluation methods, a permanently installed, strain sensitive, potential drop technique has been developed. The technique has very simple and robust hardware lending itself to use at high temperatures or in harsh environments. Strain inversions are presented and demonstrated experimentally; a room temperature, plastic deformation experiment is used for validation and additionally an accelerated creep test demonstrates operation at high temperature (600°C+). Excellent agreement is shown between potential drop inverted strain and control measurements
Ergodic directions for billiards in a strip with periodically located obstacles
We study the size of the set of ergodic directions for the directional
billiard flows on the infinite band with periodically placed
linear barriers of length . We prove that the set of ergodic
directions is always uncountable. Moreover, if is rational
the Hausdorff dimension of the set of ergodic directions is greater than 1/2.
In both cases (rational and irrational) we construct explicitly some sets of
ergodic directions.Comment: The article is complementary to arXiv:1109.458
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