77 research outputs found
The energy spectrum of all-particle cosmic rays around the knee region observed with the Tibet-III air-shower array
We have already reported the first result on the all-particle spectrum around
the knee region based on data from 2000 November to 2001 October observed by
the Tibet-III air-shower array. In this paper, we present an updated result
using data set collected in the period from 2000 November through 2004 October
in a wide range over 3 decades between eV and eV, in which
the position of the knee is clearly seen at around 4 PeV. The spectral index is
-2.68 0.02(stat.) below 1PeV, while it is -3.12 0.01(stat.) above 4
PeV in the case of QGSJET+HD model, and various systematic errors are under
study now.Comment: 12 pages, 7 figures, accepted by Advances in space researc
Moon Shadow by Cosmic Rays under the Influence of Geomagnetic Field and Search for Antiprotons at Multi-TeV Energies
We have observed the shadowing of galactic cosmic ray flux in the direction
of the moon, the so-called moon shadow, using the Tibet-III air shower array
operating at Yangbajing (4300 m a.s.l.) in Tibet since 1999. Almost all cosmic
rays are positively charged; for that reason, they are bent by the geomagnetic
field, thereby shifting the moon shadow westward. The cosmic rays will also
produce an additional shadow in the eastward direction of the moon if cosmic
rays contain negatively charged particles, such as antiprotons, with some
fraction. We selected 1.5 x10^{10} air shower events with energy beyond about 3
TeV from the dataset observed by the Tibet-III air shower array and detected
the moon shadow at level. The center of the moon was detected
in the direction away from the apparent center of the moon by 0.23 to
the west. Based on these data and a full Monte Carlo simulation, we searched
for the existence of the shadow produced by antiprotons at the multi-TeV energy
region. No evidence of the existence of antiprotons was found in this energy
region. We obtained the 90% confidence level upper limit of the flux ratio of
antiprotons to protons as 7% at multi-TeV energies.Comment: 13pages,4figures; Accepted for publication in Astroparticle Physic
High Altitude test of RPCs for the ARGO-YBJ experiment
A 50 m**2 RPC carpet was operated at the YangBaJing Cosmic Ray Laboratory
(Tibet) located 4300 m a.s.l. The performance of RPCs in detecting Extensive
Air Showers was studied. Efficiency and time resolution measurements at the
pressure and temperature conditions typical of high mountain laboratories, are
reported.Comment: 16 pages, 10 figures, submitted to Nucl. Instr. Met
Determination of Superconducting Gap of SmFeAsFxO1-x Superconductors by Andreev Reflection Spectroscopy
The superconducting gap in FeAs-based superconductor SmFeAs(O1-xFx) (x = 0.15
and 0.30) and the temperature dependence of the sample with x = 0.15 have been
measured by Andreev reflection spectroscopy. The intrinsic superconducting gap
is independent of contacts while many other "gap-like" features vary
appreciably for different contacts. The determined gap value of 2D = 13.34
+/-0.47 meV for SmFeAs(O0.85F0.15) gives 2D/kBTC = 3.68, close to the BCS
prediction of 3.53. The superconducting gap decreases with temperature and
vanishes at TC, in a manner similar to the BCS behavior but dramatically
different from that of the nodal pseudogap behavior in cuprate superconductors.Comment: 13 pages, 9 figures, Special Issue of Physica C on Superconducting
Pnictide
Are protons still dominant at the knee of the cosmic-ray energy spectrum?
A hybrid experiment consisting of emulsion chambers, burst detectors and the
Tibet II air-shower array was carried out at Yangbajing (4,300 m a.s.l., 606
g/cm) in Tibet to obtain the energy spectra of primary protons and heliums.
From three-year operation, these energy spectra are deduced between
and eV by triggering the air showers associated with a high energy
core and using a neural network method in the primary mass separation. The
proton spectrum can be expressed by a single power-law function with a
differential index of and based on the
QGSJET+HD and SIBYLL+HD models, respectively, which are steeper than that
extrapolated from the direct observations of in the energy
range below eV. The absolute fluxes of protons and heliums are
derived within 30% systematic errors depending on the hadronic interaction
models used in Monte Carlo simulation. The result of our experiment suggests
that the main component responsible for the change of the power index of the
all-particle spectrum around eV, so-called ``knee'', is
composed of nuclei heavier than helium. This is the first measurement of the
differential energy spectra of primary protons and heliums by selecting them
event by event at the knee energy region.Comment: This paper has been accepted for publication Physics Letters B on
October 19th, 2005. This paper has been accepted for publication Physics
Letters B on October 19th, 200
Nano oxides reinforced high-entropy alloy coatings synthesized by atmospheric plasma spraying
The high-entropy alloy coatings reinforced with nano oxides were synthesized by the atmospheric plasma spraying (APS). The crystal structure, microstructure, surface morphology, hardness and wear resistance properties of the CoCrFeNiAl and CoCrFeNiMo high-entropy alloy coatings are investigated. For CoCrFeNiAl high entropy coating (HEC) not only has high hardness (573 ± 19 Hv0.1) but also has good wear resistance [The coefficients of friction (COF) is 0.49 ± 0.04]. The transition of the wear mechanism obviously appears between the two HECs. The influences of the structure, composition and hardness on the tribological behavior of high-entropy alloy coatings were discussed in details
Novel Trifluoromethylpyrazole Acyl Thiourea Derivatives: Synthesis, Antifungal Activity and Docking Study
Analysis on psychological disorder and related factors in 98 patients with cancer and intervention measures thereon
SAEP: Simulated Annealing Based Ensemble Projecting Method for Solving Conditional Nonlinear Optimal Perturbation
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