77 research outputs found
Bounds on the cosmogenic neutrino flux
Under the assumption that some part of the observed highest energy cosmic
rays consists of protons originating from cosmological distances, we derive
bounds on the associated flux of neutrinos generated by inelastic processes
with the cosmic microwave background photons. We exploit two methods. First, a
power-like injection spectrum is assumed. Then, a model-independent technique,
based on the inversion of the observed proton flux, is presented. The inferred
lower bound is quite robust. As expected, the upper bound depends on the
unknown composition of the highest energy cosmic rays. Our results represent
benchmarks for all ultrahigh energy neutrino telescopes.Comment: 12 pages, 6 figure
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A Uniform Residence Time Flow Cell for the Microreactor-Assisted Solution Deposition of CdS on an FTO-Glass Substrate
Photovoltaic cells have long been a desirable alternative to the consumption of fossil fuels, but current manufacturing practices suffer from poor energy efficiency, large carbon footprints, low material utilization, and high processing temperatures. A critical step in production of thin film CdTe and CuInSe₂ solar cells is the chemical bath deposition of a CdS thin film to serve as a “buffer layer” between the optically absorbent layer and the transparent conducting oxide. In prior work, functional CdS films were demonstrated at low temperature using a continuous flow, microreactor-assisted deposition process showing good selectivity of heterogeneous surface reactions over homogeneous bulk precipitation. In this paper, we develop a flow cell for implementing a uniform CdS film over a 152 mm substrate. Analytical models are coupled with computational fluid dynamic simulations to design a flow cell with more uniform flow fields. Experimental results demonstrate a 12% coefficient of variance for a 21.5 nm thick film
Super-GZK Photons from Photon-Axion Mixing
We show that photons with energies above the GZK cutoff can reach us from
very distant sources if they mix with light axions in extragalactic magnetic
fields. The effect which enables this is the conversion of photons into axions,
which are sufficiently weakly coupled to travel large distances unimpeded.
These axions then convert back into high energy photons close to the Earth. We
show that photon-axion mixing facilitates the survival of super-GZK photons
most efficiently with a photon-axion coupling scale of order 10^11 GeV, which
is in the same range as the scale for the photon-axion mixing explanation for
the dimming of supernovae without cosmic acceleration. We discuss possible
observational consequences of this effect.Comment: 17 pages, 5 figures. Published versio
Ultra-High Energy Cosmic Ray production in the polar cap regions of black hole magnetospheres
We develop a model of ultra-high energy cosmic ray (UHECR) production via
acceleration in a rotation-induced electric field in vacuum gaps in the
magnetospheres of supermassive black holes (BH). We show that if the poloidal
magnetic field near the BH horizon is misaligned with the BH rotation axis,
charged particles, which initially spiral into the BH hole along the equatorial
plane, penetrate into the regions above the BH "polar caps" and are ejected
with high energies to infinity. We show that in such a model acceleration of
protons near a BH of typical mass 3e8 solar masses is possible only if the
magnetic field is almost aligned with the BH rotation axis. We find that the
power of anisotropic electromagnetic emission from an UHECR source near a
supermassive BH should be at least 10-100 times larger then UHECR power of the
source. This implies that if the number of UHECR sources within the 100 Mpc
sphere is ~100, the power of electromagnetic emission which accompanies proton
acceleration in each source, erg/s, is comparable to the typical
luminosities of active galactic nuclei (AGN) in the local Universe. We also
explore the acceleration of heavy nuclei, for which the constraints on the
electromagnetic luminosity and on the alignment of magnetic field in the gap
are relaxed
PT-symmetric noncommutative spaces with minimal volume uncertainty relations
We provide a systematic procedure to relate a three dimensional q-deformed
oscillator algebra to the corresponding algebra satisfied by canonical
variables describing noncommutative spaces. The large number of possible free
parameters in these calculations is reduced to a manageable amount by imposing
various different versions of PT-symmetry on the underlying spaces, which are
dictated by the specific physical problem under consideration. The
representations for the corresponding operators are in general non-Hermitian
with regard to standard inner products and obey algebras whose uncertainty
relations lead to minimal length, areas or volumes in phase space. We analyze
in particular one three dimensional solution which may be decomposed to a two
dimensional noncommutative space plus one commuting space component and also
into a one dimensional noncommutative space plus two commuting space
components. We study some explicit models on these type of noncommutative
spaces.Comment: 18 page
Upper Bounds on the Neutrino-Nucleon Inelastic Cross Section
Extraterrestrial neutrinos can initiate deeply developing air showers, and
those that traverse the atmosphere unscathed may produce cascades in the ice or
water. Up to now, no such events have been observed. This can be translated
into upper limits on the diffuse neutrino flux. On the other hand, the
observation of cosmic rays with primary energies > 10^{10} GeV suggests that
there is a guaranteed flux of cosmogenic neutrinos, arising from the decay of
charged pions (and their muon daughters) produced in proton interactions with
the cosmic microwave background. In this work, armed with these cosmogenic
neutrinos and the increased exposure of neutrino telescopes we bring up-to-date
model-independent upper bounds on the neutrino-nucleon inelastic cross section.
Uncertainties in the cosmogenic neutrino flux are discussed and taken into
account in our analysis. The prospects for improving these bounds with the
Pierre Auger Observatory are also estimated. The unprecedented statistics to be
collected by this experiment in 6 yr of operation will probe the
neutrino-nucleon inelastic cross section at the level of Standard Model
predictions.Comment: To be published in JCA
Simulation of the cosmic ray tau neutrino telescope (CRTNT) experiment
A tau lepton can be produced in a charged current interaction by cosmic ray
tau neutrino with material inside a mountain. If it escapes from the mountain,
it will decay and initiate a shower in the air, which can be detected by an air
shower fluorescence/Cherenkov light detector. Designed according to such a
principle, the Cosmic Ray Tau Neutrino Telescope (CRTNT) experiment, located at
the foothill of Mt. Balikun in Xinjiang, China, will search for very
high-energy cosmic tau neutrinos from energetic astrophysical sources by
detecting those showers. This paper describes a Monte Carlo simulation for a
detection of tau neutrino events by the CRTNT experiment. Ultra-high-energy
cosmic ray events are also simulated to estimate the potential contamination.
With the CRTNT experiment composed of four detector stations, each covering 64
by 14 degrees field of view, the expected event rates are 28.6, 21.9 and 4.7
per year assuming AGN neutrino flux according to Semikoz et. al. 2004, MPR AGN
jet model and SDSS AGN core model, respectively. Null detection of such tau
event by the CRTNT experiment in one year could set 90% C.L. upper limit at
19.9 (eV^-1 cm^-2 s^-1 sr^-1) for E^-2 neutrino spectrum.Comment: 14 page
Determining the neurotransmitter concentration profile at active synapses
Establishing the temporal and concentration profiles of neurotransmitters during synaptic release is an essential step towards understanding the basic properties of inter-neuronal communication in the central nervous system. A variety of ingenious attempts has been made to gain insights into this process, but the general inaccessibility of central synapses, intrinsic limitations of the techniques used, and natural variety of different synaptic environments have hindered a comprehensive description of this fundamental phenomenon. Here, we describe a number of experimental and theoretical findings that has been instrumental for advancing our knowledge of various features of neurotransmitter release, as well as newly developed tools that could overcome some limits of traditional pharmacological approaches and bring new impetus to the description of the complex mechanisms of synaptic transmission
Observations of Ultra-High Energy Cosmic Rays
The status of measurements of the arrival directions, mass composition and
energy spectrum of cosmic rays above 3 x 10^18 eV (3 EeV) is reviewed using
reports presented at the 29th International Cosmic Ray Conference held in Pune,
India, in August 2005. The paper is based on a plenary talk given at the
TAUP2005 meeting in Zaragoza, 10 - 14 September 2005.Comment: 7 pages and two figure
Searching for a Correlation Between Cosmic-Ray Sources Above 10^{19} eV and Large-Scale Structure
We study the anisotropy signature which is expected if the sources of ultra
high energy, >10^{19} eV, cosmic-rays (UHECRs) are extragalactic and trace the
large scale distribution of luminous matter. Using the PSCz galaxy catalog as a
tracer of the large scale structure (LSS), we derive the expected all sky
angular distribution of the UHECR intensity. We define a statistic, that
measures the correlation between the predicted and observed UHECR arrival
direction distributions, and show that it is more sensitive to the expected
anisotropy signature than the power spectrum and the two point correlation
function. The distribution of the correlation statistic is not sensitive to the
unknown redshift evolution of UHECR source density and to the unknown strength
and structure of inter-galactic magnetic fields. We show, using this statistic,
that recently published >5.7x10^{19} eV Auger data are inconsistent with
isotropy at ~98% CL, and consistent with a source distribution that traces LSS,
with some preference to a source distribution that is biased with respect to
the galaxy distribution. The anisotropy signature should be detectable also at
lower energy, >4x10^{19} eV. A few fold increase of the Auger exposure is
likely to increase the significance to >99% CL, but not to >99.9% CL (unless
the UHECR source density is comparable or larger than that of galaxies). In
order to distinguish between different bias models, the systematic uncertainty
in the absolute energy calibration of the experiments should be reduced to well
below the current ~25%.Comment: 17 pages, 8 figures. v2: reference added, typos corrected, accepted
to JCA
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