41,699 research outputs found
Collapsible loop antenna for space vehicle Patent
Collapsible, space erectable loop antenna system for space vehicl
Trace Metals and Major Elements in Water-Soluble Rocks of Northwest Arkansas
Trace metals in limestone are potential water contaminants because they can enter the ground water when the limestone is dissolved by carbonic acid and other naturally occurring acids. Four local limestones, the St. Joe and Pitkin Formations (Mississippian) and the Brentwood and Kessler Members of the Bloyd Formation (Pennsylvanian) were sampled in a five county area in Northwest Arkansas. Atomic absorption analyses were made for Na, K, Mg, Ca, Zh, Cu, Ba, Fe, Co, Cr, Ni, Mn, Li and Sr on the acid soluble material of the samples. All the limestones are relatively pure CaCO3 with Pitkin the purest, 93.4%. Calcium and acid soluble material values varied only 3-5% from the average among the limestones whereas 71-108% variation occurred for Fe, Mn, K and Cr. Other elements showed intermediate variations. Only Fe and Mn are present on the average in the limestones at concentration levels which might lead to contamination of ground water to undesirably high levels. Analyses compare well with the reported average limestone except for acid insoluble elements which were not dissolved in our scheme and lithium (1.5 ppm average vs 20 in reference). Ratios of Sr/Ca and Mg/Ca were similar to reported values for limestones of comparable geologic age. Maxima in the areal variation of these ratios occurred at about the same latitude for three of the formations. The areal variation of Fe/Ca and Mn/Ca was also determined for the four limestone formations. Interelement correlations in the limestones showed: Na, Sr, Li, Fe and Zn contents increased with Mg content; Mn and Cr increased with Fe content. Indications were obtained that detrital and other materials not in the calcite structure can be determined by their relative insolubility in acetic acid compared to hydrochloric acid
Timelike vs spacelike DVCS from JLab, Compass to ultraperipheral collisions and AFTER@LHC
Timelike and spacelike virtual Compton scattering in the generalized Bjorken
scaling regime are complementary tools to access generalized parton
distributions. We stress that the gluonic contributions are by no means
negligible, even in the medium energy range which will be studied intensely at
JLab12 and in the COMPASS-II experiment at CERN. Ultraperipheral collisions
with proton or ion beams may also be used at RHIC and at collider or fixed
target experiments at LHC.Comment: 7 pages, Presented at the Low x workshop, May 30 - June 4 2013,
Rehovot and Eilat, Israe
NLO QCD corrections for DVCS and TCS
The inclusion of QCD corrections to the Born amplitude of deeply virtual
Compton scattering in both spacelike (DVCS) and timelike (TCS) regimes modifies
the extraction process of generalized parton distributions (GPDs) from
observables. In particular, gluon contributions are by no means negligible even
in the medium energy range accessible at JLab12. We emphasize the
complementarity of spacelike and timelike measurements and raise the question
of factorization scale dependence of the O(alpha_S) results.Comment: 6 pages, 6 figures, Proceedings of the conference Photon 2013, 20-24
May 2013 Paris, France, to be published in Proceedings of Scienc
On timelike and spacelike deeply virtual Compton scattering at next to leading order
We study timelike and spacelike virtual Compton scattering in the generalized
Bjorken scaling regime at next to leading order in the strong coupling
constant, in the medium energy range which will be studied intensely at JLab12
and in the COMPASS-II experiment at CERN. We show that the Born amplitudes get
sizeable O(\alpha_s) corrections and, even at moderate energies, the gluonic
contributions are by no means negligible. We stress that the timelike and
spacelike cases are complementary and that their difference deserves much
special attention
Interaction effects and charge quantization in single-particle quantum dot emitters
We discuss a theoretical model of an on-demand single-particle emitter that
employs a quantum dot, attached to an integer or fractional quantum Hall edge
state. Via an exact mapping of the model onto the spin-boson problem we show
that Coulomb interactions between the dot and the chiral quantum Hall edge
state, unavoidable in this setting, lead to a destruction of precise charge
quantization in the emitted wave-packet. Our findings cast doubts on the
viability of this set-up as a single-particle source of quantized charge
pulses. We further show how to use a spin-boson master equation approach to
explicitly calculate the current pulse shape in this set-up.Comment: 5+5 pages, 3 figures, fixed typos, update Supplement Material and
update figure
Reducing sample variance: halo biasing, non-linearity and stochasticity
Comparing clustering of differently biased tracers of the dark matter
distribution offers the opportunity to reduce the cosmic variance error in the
measurement of certain cosmological parameters. We develop a formalism that
includes bias non-linearities and stochasticity. Our formalism is general
enough that can be used to optimise survey design and tracers selection and
optimally split (or combine) tracers to minimise the error on the
cosmologically interesting quantities. Our approach generalises the one
presented by McDonald & Seljak (2009) of circumventing sample variance in the
measurement of . We analyse how the bias, the noise,
the non-linearity and stochasticity affect the measurements of and explore
in which signal-to-noise regime it is significantly advantageous to split a
galaxy sample in two differently-biased tracers. We use N-body simulations to
find realistic values for the parameters describing the bias properties of dark
matter haloes of different masses and their number density.
We find that, even if dark matter haloes could be used as tracers and
selected in an idealised way, for realistic haloes, the sample variance limit
can be reduced only by up to a factor .
This would still correspond to the gain from a three times larger survey volume
if the two tracers were not to be split. Before any practical application one
should bear in mind that these findings apply to dark matter haloes as tracers,
while realistic surveys would select galaxies: the galaxy-host halo relation is
likely to introduce extra stochasticity, which may reduce the gain further.Comment: 21 pages, 13 figures. Published version in MNRA
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