Effect of variable heat treatment modes on microstructures in Fe-Cr-B cast iron alloy

The effect of heat treatment mode on the microstructure of Fe-Cr-B cast iron alloys was investigated in this paper by comparing the difference of precipitation patterns of secondary particles after thermal cycling treatment (TCT) with those after normal heat treatment (NHT). No obvious differences were found in precipitation patterns of secondary particles between TCT and NHT when experimental temperature was below Ar. However, when temperature was over Ar, there were significant differences, with secondary particles prominently segregated at the grain boundaries under TCT, while the particles evenly distributed in the matrix under NHT. The reason for the microstructure differences could be associated with the development of non-equilibrium segregation of boron during TCT

Primary proton spectrum between 200 TeV and 1000 TeV observed with the Tibet burst detector and air shower array

Since 1996, a hybrid experiment consisting of the emulsion chamber and burst detector array and the Tibet-II air-shower array has been operated at Yangbajing (4300 m above sea level, 606 g/cm^2) in Tibet. This experiment can detect air-shower cores, called as burst events, accompanied by air showers in excess of about 100 TeV. We observed about 4300 burst events accompanied by air showers during 690 days of operation and selected 820 proton-induced events with its primary energy above 200 TeV using a neural network method. Using this data set, we obtained the energy spectrum of primary protons in the energy range from 200 to 1000 TeV. The differential energy spectrum obtained in this energy region can be fitted by a power law with the index of -2.97 $\pm$ 0.06, which is steeper than that obtained by direct measurements at lower energies. We also obtained the energy spectrum of helium nuclei at particle energies around 1000 TeV.Comment: 25 pages, 22 figures, Accepted for publication in Phys. Rev.

Measurement of air shower cores to study the cosmic ray composition in the knee energy region

Since 1996, a hybrid experiment consisting of an emulsion chamber and a burst detector array and the Tibet-II air shower array has been operated at Yangbajing (4300 m above sea level) in Tibet. This experiment can detect air-shower cores, called burst events, accompanied by air showers in excess of about 100 TeV. Using the burst event data observed by this experiment, we discuss the primary cosmic ray composition around the knee in comparison with the Monte Carlo simulations. In this paper, we show that all the features of burst events are wholly compatible with the heavy enriched composition in the knee energy region.Comment: 20 pages, 21 figures, to appear in Physical Review

A study of the shadowing of galactic cosmic rays by the sun in a quiet phase of solar activity with the Tibet air shower array

We have shown that the Sun's shadow by high energy cosmic rays moves year by year and its behavior is correlated with a time variation of the large-scale structure of the solar and interplanetary magnetic fields. The solar activity was near minimum in the period from 1996 through 1997. Using the data obtained with the Tibet air shower array, we examined the shadowing of cosmic rays by the Sun in this quiet phase of solar cycle, and found that the Sun's shadow was just in the apparent direction of the Sun, though it was observed at the position considerably away from the Sun to the south-west in the period between 1990 and 1993. It is known that the magnetic pole of equivalent solar dipole was reversed during the previous active phase, and near solar minimum the dipole was aligned with the rotating axis, preserving its N-pole on the north pole side of the Sun. This causes the solar magnetic field to shift the Sun's shadow to the east. Thus, the observed results suggest that the shift of the Sun's shadow due to the solar magnetic field was pushed back by the effect of the geomagnetic field, since the geomagnetic field always make the shadow shift to the west. We discuss the Sun's shadow observed during the period near solar minimum in 1996-1997 and compare it with the simulation results.Comment: 13 pages, 6 figures, to appear in Ap

Stress and load distribution analysis in bolt connection with modified thread profile under high temperature conditions

In this paper, the load distribution of a bolt connection structure with a variable thread profile at high temperature is investigated. The parameters of time-hardening creep model of aluminum alloy at high temperature were obtained by fitting the uniaxial creep tensile test data of aluminum alloy at 250◦C. Based on ABAQUS, a two-dimensional axisymmetric model of the bolt connection structure was established, and according to the thread load distribution considering linear elasticity, plasticity and creep characteristics, modification of standard metric thread profile was carried out. The load distribution law of the thread of the modified bolt connection structure were investigted. The results show that the load- -bearing ratio of the first thread can be significantly reduced and the load-bearing distribu- tion uniformity of all threads can be improved when the modified thread is applied to the bolt connection structure