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 $10^{14}$ eV and $10^{17}$ eV, in which the position of the knee is clearly seen at around 4 PeV. The spectral index is -2.68 $\pm$ 0.02(stat.) below 1PeV, while it is -3.12 $\pm$ 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 $\sim 40 \sigma$ level. The center of the moon was detected in the direction away from the apparent center of the moon by 0.23$^\circ$ 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

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$^2$) in Tibet to obtain the energy spectra of primary protons and heliums. From three-year operation, these energy spectra are deduced between $10^{15}$ and $10^{16}$ 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 $-3.01 \pm 0.11$ and $-3.05 \pm 0.12$ based on the QGSJET+HD and SIBYLL+HD models, respectively, which are steeper than that extrapolated from the direct observations of $-2.74 \pm 0.01$ in the energy range below $10^{14}$ 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 $3 \times 10^{15}$ 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

Growth responses and phytoremediation characteristics of Mirabilis Jalapa L. in Benzo[a]pyrene and pyrene co-contaminated soils

Pot culture experiments were conducted to investigate the effect of Benzo[a]pyrene(B[a]P) and pyrene on seed germination and growth factors of Mirabilis Jalapa L. and their uptake, accumulation and dissipation. The results showed that B[a]P and pyrene at the lower concentrations could accelerate seed germination and photosynthesis rate. There weren't significant relationships between shoot height, root length, or biomass and the concentrations of B[a]P and pyrene in soil. The relative absorptivity of B[a]P and pyrene in roots of M. Jalapa was less than 11%. But the amount of B[a]P and pyrene in shoots was close to zero. The relative removal rate of B[a]P and pyrene was up to 83-99% and 5-98%, respectively. Therefore, Plant-promoted rhizomorph biodegradation is the dominant contribution to remove B[a]P and pyrene. M. Jalapa might be useful for phytoremediation of B[a]P and pyrene co-contaminated sites. © 2011 Springer-Verlag Berlin Heidelberg

Myocardial extracellular volume fraction quantification based on T1 mapping at 3 T: quality optimization by contour-based registration and segmental analysis

Background Myocardial extracellular volume fraction (ECV) assessment can be affected by various technical and subject-related factors. Purpose To evaluate the role of contour-based registration in quantification of ECV and investigate normal segment-based myocardial ECV values at 3T. Material and Methods Pre- and post-contrast T1 mapping images of the left ventricular basal, mid-cavity, and apical slices were obtained in 26 healthy volunteers. ECV maps were generated using motion correction with and without contour-based registration. The image quality of all ECV maps was evaluated by a 4-point scale. Slices were dichotomized according to the occurrence of misregistration in the source data. Contour-registered ECVs and standard ECVs were compared within each subgroup using analysis of variance for repeated measurements and generalized linear mixed models. Results In all three slices, higher quality of ECV maps were found using contour-registered method than using standard method. Standard ECVs were statistically different from contour-registered ECVs in global (26.8% +/- 2.8% vs. 25.8% +/- 2.4%; P = 0.001), mid-cavity (25.4% +/- 3.1% vs. 24.3% +/- 2.5%; P = 0.016), and apical slices (28.7% +/- 4.1% vs. 27.2% +/- 3.4%; P = 0.010). In the misregistration subgroups, contour-registered ECVs were lower with smaller SDs (basal: 25.2% +/- 1.8% vs. 26.7% +/- 2.6%; P = 0.038; mid-cavity: 24.4% +/- 2.3% vs. 26.8% +/- 3.1%; P = 0.012; apical: 27.5% +/- 3.6% vs. 29.7% +/- 4.5%; P = 0.016). Apical (27.2% +/- 3.4%) and basal-septal ECVs (25.6% +/- 2.6%) were statistically higher than mid-cavity ECV (24.3% +/- 2.5%; both P < 0.001). Conclusion Contour-based registration can optimize image quality and improve the precision of ECV quantification in cases demonstrating ventricular misregistration among source images.Cardiovascular Aspects of Radiolog

Angular dependence of magnetic reversal in two-phased nanolayers

10.1016/j.commatsci.2008.01.019Computational Materials Science441117-121CMMS