3,240 research outputs found
Weak interactions and quasi-stable particle energy loss
We discuss the interplay between electromagnetic energy loss and weak
interactions in the context of quasistable particle particle propagation
through materials. As specific examples, we consider staus, where weak
interactions may play a role, and taus, where they don't.Comment: 4 pages, 4 figures, to appear in the proceedings of the Second
Workshop on TeV Particle Astrophysics (August 2006, Madison, WI
Consequences of short range interactions between dark matter and protons in galaxy clusters
Protons gain energy in short range collisions with heavier dark matter
particles (DMPs) of comparable velocity dispersion. We examine the conditions
under which the heating of baryons by scattering off DMPs can offset radiative
cooling in the cores of galaxy clusters. Collisions with a constant cross
section independent of the relative velocity of the colliding particles, cannot
produce stable thermal balance. In this case, avoiding an unrealistic increase
of the central temperatures yields the upper bound on the cross-section,
\sigma_xp<10^-25 cm^2 (m_x/m_p), where m_x and m_p are the DMP and proton mass,
respectively. A stable balance, however, can be achieved for a power law
dependence on the relative velocity, V, of the form \sigma_xp \propto V^a with
a<-3. An advantage of this heating mechanism is that it preserves the metal
gradients observed in clusters.Comment: 7 pages, new calculations include
Evidence for a Mixed Mass Composition at the ‘ankle’ in the Cosmic-ray Spectrum
We report a first measurement for ultrahigh energy cosmic rays of the correlation between the depth of shower maximum and the signal in the water Cherenkov stations of air-showers registered simultaneously by the fluorescence and the surface detectors of the Pierre Auger Observatory. Such a correlation measurement is a unique feature of a hybrid air-shower observatory with sensitivity to both the electromagnetic and muonic components. It allows an accurate determination of the spread of primary masses in the cosmic-ray flux. Up till now, constraints on the spread of primary masses have been dominated by systematic uncertainties. The present correlation measurement is not affected by systematics in the measurement of the depth of shower maximum or the signal in the water Cherenkov stations. The analysis relies on general characteristics of air showers and is thus robust also with respect to uncertainties in hadronic event generators. The observed correlation in the energy range around the ‘ankle’ at lg(E/eV) = 18.5–19.0 differs significantly from expectations for pure primary cosmic-ray compositions. A light composition made up of proton and helium only is equally inconsistent with observations. The data are explained well by a mixed composition including nuclei with mass A \u3e 4. Scenarios such as the proton dip model, with almost pure compositions, are thus disfavoredas the sole explanation of the ultrahigh-energy cosmic-ray flux at Earth
Tribal Water Quality Standards: Are There Any Limits
Thermoelectric generators (TEG) directly convert heat energy into electrical energy. The impediments as to why this technology has not yet found extensive application are the low conversion efficiency and high costs per watt. On the one hand, the manufacturing process is a cost factor. On the other, the high-‐priced thermoelectric (TE) materials have an enormous impact on the costs per watt. In this thesis both factors will be examined: the production process and the selection of TE materials. Technical screen printing is a possible way of production, because this method is very versatile with respect to the usable materials, substrates as well as printing inks. The organic conductor PEDOT:PSS offers reasonable thermoelectric properties and can be processed very well in screen printing. It was demonstrated by prototypes of fully printed TEGs that so-‐called vertical printed TEGs are feasible using standard graphic arts industry processes. In addition, the problems that occur with print production of TEGs are identified. Finally, approaches to solve these problems are discussed
The fate of ultrahigh energy nuclei in the immediate environment of young fast-rotating pulsars
Young, fast-rotating neutron stars are promising candidate sources for the
production of ultrahigh energy cosmic rays (UHECRs). The interest in this model
has recently been boosted by the latest chemical composition measurements of
cosmic rays, that seem to show the presence of a heavy nuclear component at the
highest energies. Neutrons stars, with their metal-rich surfaces, are
potentially interesting sources of such nuclei, but some open issues remain: 1)
is it possible to extract these nuclei from the star's surface? 2) Do the
nuclei survive the severe conditions present in the magnetosphere of the
neutron star? 3) What happens to the surviving nuclei once they enter the wind
that is launched outside the light cylinder? In this paper we address these
issues in a quantitative way, proving that for the most reasonable range of
neutron star surface temperatures (K), a large fraction of heavy
nuclei survive photo-disintegration losses. These processes, together with
curvature losses and acceleration in the star's electric potential, lead to
injection of nuclei with a chemical composition that is mixed, even if only
iron is extracted from the surface. We show that under certain conditions the
chemical composition injected into the wind region is compatible with that
required in previous work based on purely phenomenological arguments (typically
protons, CNO and Fe), and provides a
reasonable explanation of the mass abundance inferred from ultra high energy
data.Comment: 15 pages, 3 figures, accepted in JCAP, minor modification
Ultrahigh Energy Cosmic Rays and Black Hole Mergers
The recent detection of the gravitational wave source GW150914 by the LIGO
collaboration motivates a speculative source for the origin of ultrahigh energy
cosmic rays as a possible byproduct of the immense energies achieved in black
hole mergers, provided that the black holes have spin as seems inevitable and
there are relic magnetic fields and disk debris remaining from the formation of
the black holes or from their accretion history. We argue that given the modest
efficiency required per event per unit of gravitational wave energy
release, merging black holes potentially provide an environment for
accelerating cosmic rays to ultrahigh energies.Comment: 4 pages, version to appear in ApJ Lett., minor changes, but one
significant new point: connection made with fast radio burst
Four Zuni-Mountain Miniatures
My wife and I bought and fenced 20 acres of Zuni-Mountain land, to allow it to recover from years of overgrazing. I reveled in the beauty and used the piece as a kind of journal. Back in Albuquerque, I could recall the feel of the place in different seasons and at different times of day
The DarkSide project
DarkSide is a graded experimental project based on radiopure argon, and is now, and will be, used in direct dark matter searches. The present DarkSide-50 detector, operating at the Gran Sasso National Laboratory, is a dual-phase, 50 kg, liquid argon time-projection-chamber surrounded by an active liquid scintillator veto. It is designed to be background free in 3 years of operation. DS-50 performances, when filled with atmospheric argon, are reporte
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