The Telescope Array (TA) collaboration has measured the energy spectrum of ultra-high energy cosmic rays (UHECRs) with primary energies above 1.6 × 10 18 eV. This measurement is based upon four years of observation by the surface detector component of TA. The spectrum shows a dip at an energy of 4.6 × 10 18 eV and a steepening at 5.4 × 10 19 eV which is consistent with the expectation from the GZK cutoff. We present the results of a technique, new to the analysis of UHECR surface detector data, that involves generating a complete simulation of UHECRs striking the TA surface detector. The procedure starts with shower simulations using the CORSIKA Monte Carlo program where we have solved the problems caused by use of the "thinning" approximation. This simulation method allows us to make an accurate calculation of the acceptance of the detector for the energies concerned.
We have searched for intermediate-scale anisotropy in the arrival directions of ultrahigh-energy cosmic rays with energies above 57 EeV in the northern sky using data collected over a 5 yr period by the surface detector of the Telescope Array experiment. We report on a cluster of events that we call the hotspot, found by oversampling using 20 • radius circles. The hotspot has a Li-Ma statistical significance of 5.1σ , and is centered at R.A. = 146. • 7, decl. = 43. • 2. The position of the hotspot is about 19 • off of the supergalactic plane. The probability of a cluster of events of 5.1σ significance, appearing by chance in an isotropic cosmic-ray sky, is estimated to be 3.7 × 10 −4 (3.4σ).
The Telescope Array (TA) experiment, located in the western desert of
Utah,USA, is designed for observation of extensive air showers from extremely
high energy cosmic rays. The experiment has a surface detector array surrounded
by three fluorescence detectors to enable simultaneous detection of shower
particles at ground level and fluorescence photons along the shower track. The
TA surface detectors and fluorescence detectors started full hybrid observation
in March, 2008. In this article we describe the design and technical features
of the TA surface detector.Comment: 32 pages, 17 figure
We report the growth of exceptionally well aligned and vertically oriented GaN nanowires
on r-plane sapphire wafers via metal–organic chemical vapour deposition. The nanowires were
grown without the use of either a template or patterning. Transmission electron microscopy
indicates the nanowires are single crystalline, free of threading dislocations, and have
triangular cross-sections. The high degree of vertical alignment is explained by the
crystallographic match between the oriented nanowires and the r-plane sapphire surface. We find that the degree of alignment and size uniformity of the
nanowires are highly dependent on the nickel nitrate catalyst concentration used, with the
highest degree of uniformity and alignment occurring at concentrations much more dilute
than typically employed for vapour–liquid–solid-based nanowire growth. Additionally, we
report here a strong dependence of the optical and electrical properties of the nanowires on
the growth temperature, which we hypothesize is due to increased carbon incorporation at
lower growth temperatures.
In situ Raman spectroscopy and cyclic voltammetry have been used simultaneously to study anodic film growth and dissolution on Cu and Ag in strongly alkaline solution. On copper,
Cu2O
and another species, believed to be a hydroxide, were detected spectroscopically during anodic film formation. Raman spectra of electrochemically formed hydroxides on copper have not previously been reported. On silver,
normalAgO
was detected. Neither
normalCuO
nor
Ag2O
was observed by Raman spectroscopy, although for certain potentials,
normalAgO
was apparently produced by photochemical conversion of
Ag2O
. Experiments were performed using both the 488 nm line from an argon laser and the 647.1 nm line from a krypton laser. It was concluded that the detection of these thin film oxides was by spontaneous or resonant Raman scattering and did not involve surface enhanced Raman scattering (SERS).
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