Characteristic rainfall for warning of debris flows

A characteristic rainfall is introduced to overcome the difficulties encountered in determining a critical rainfall value for triggering debris flow. The characteristic value is defined as the rainfall at which debris-flow occurrence probability shows a rapid increase, and can be used as a warning rainfall threshold for debris flows. Investigation of recorded debris flows and 24-hour rainfall data at Jiangjia basin, Yunnan Province, in southwestern China, demonstrates the existence of such a characteristic rainfall. It was found that the characteristic rainfall corresponds to the daily rainfall of 90% cumulative probability by analyzing the basin's daily rainfall histogram. The result provides a simple and useful method for estimating a debris-flow warning rainfall threshold from the daily rainfall distribution. It was applied to estimate the debris-flow warning rainfall threshold for the Subaohe basin, a watershed in the 2008 Wenchuan earthquake zone with many physical characteristics similar to those of the Jiangjia basin.

Radiative electron capture and subsequent radiative decay in collisions of U89+ ions with N-2

To evaluate the radiative electron capture for the collisions of U89+ ion with N-2, radiative recombination cross sections and the corresponding emitted photon energies are calculated from the ground state 1s(2)2s to 1s(2)2snl(j) (2 <= n <= 9, 0 <= l <= 6) using the newly developed relativistic radiative recombination program RERR06 based on the multiconfiguration Dirac-Fock method. The x-ray spectra for radiative electron capture in the collision have been obtained by convolving the radiative recombination cross sections and the Compton profile of N2. Good agreement is found between the calculated and experimental spectra. In addition, the transition energy levels and probabilities among the 147 levels from the captured 1s(2)2snl(j) have been calculated. From the calculated results, radiative decay cascade processes followed by the radiative electron capture have also been studied with the help of multistep model and coupled rate equations, respectively. The present results not only make us understand the details of the radiative electron captures and the radiative decay cascade spectra in the experiment but also show a more efficient way to obtain the cascade spectra. Finally, the equivalence between the multistep model and coupled rate equations has been shown under a proper condition and the latter can hopefully be extended to investigate other cascade processes.

Photoionization of 1s electron and corresponding shake-up process in ground and excited lithium atoms

The cross sections of the 18 electron photoionization and corresponding shake-up processes for Li atoms in the ground state 1s(2)2s and excited states 1s(2)2p, 1s(2)3p, 1s(2)3p and 1s(2)3d are calculated using the multi-configuration Dirac-Fock method. The latest experimental photoelectron spectrum at hv = 100 eV [Cubaynes D et al. Phys. Rev. Lett. 99 (2007) 213004] has been reproduced by the present theoretical investigation excellently. The relative intensity of the shake-up satellites shows that the effects of correlation and relaxation become more important for the higher excited states of the lithium atom, which are explained very well by the spatial overlap of the initial and final state wavefunctions. In addition, strong dependence of the cross section on the atomic orbitals of the valence electrons are found, especially near the threshold.

Dependence of isoscaling parameters on nucleon-nucleon cross section and momentum-dependent interaction

Influences of the isospin dependence of the in-medium nucleon-nucleon cross section and the momentum-dependant interaction (MDI) on the isotope scaling are investigated by using the isospin-dependent quantum molecular dynamics model (IQMD). The results show that both the isospin dependence of the in-medium nucleon-nucleon cross section and the momentum-dependent interaction affect the isoscaling parameters appreciably and independently. The influence caused by the isospin dependence of two-body collision is relatively larger than that from the MDI in the mean field. Aiming at exploring the implication of isoscaling behaviour, which the statistical equilibrium in the reaction is reached, the statistical properties in the mass distribution and the kinetic energy distribution of the fragments simulated by IQMD are presented.

Theoretical study of the 4d photoabsorption of the Cs+ ion

Calculations of the 4d absolute photoabsorption cross sections of the Xe-like Cs+ ion covering the energy region from 80 to 190 eV have been performed by using the multi-configuration Dirac-Fock method. The calculated cross sections are compared with the absolute experimental photoabsorption cross-section spectrum (Kjeldsen et al 2002 J. Phys. B: At. Mol. Opt. Phys. 35 2845) and other available theoretical results. In the 80-90 eV region, the discrete structure resulting from photoexcitation of a 4d electron into nf and np orbits are successfully identified. Above the 4d threshold, i.e. in the 90-190 eV energy region, a reasonable agreement between experiment and computations is found for the intense 4d -> epsilon f shape resonance.

Light alkenes preparation by the gas phase oxidative cracking or catalytic oxidative cracking of high hydrocarbons

The preparation of light alkenes by the gas phase oxidative cracking (GOC) or catalytic oxidative cracking (COC) of model high hydrocarbons ( hexane, cyclohexane, isooctane and decane in the GOC process and hexane in the COC process) was investigated in this paper. The selection for the feed in the GOC process was flexible. Excellent conversion of hydrocarbons ( over 85%) and high yield of light alkenes ( about 50%) were obtained in the GOC of various hydrocarbons including cyclohexane at 750 degreesC. In the GOC process, the utilization ratio of the carbon resources was high; CO dominated the produced COX (the selectivity to CO2 was always below 1%); and the total selectivity to light alkenes and CO was near or over 70%. In the COC of hexane over three typical catalysts (HZSM-5, 10% La2O3/HZSM-5 and 0.25% Li/MgO), the selectivity to COX was hard to decrease and the conversion of hexane and yield of light alkenes could not compete with those in the GOC process. With the addition of H-2 in the feed, the selectivity to COX was reduced below 5% over 0.1% Pt/HZSM-5 or 0.1% Pt/MgAl2O4 catalyst. The latter catalyst was superior to the former catalyst due to its perfect performance at high temperature, and with the latter, excellent selectivity to light alkenes ( 70%) and the conversion of hexane (92%) were achieved at 850 degreesC ( a yield of light alkenes of 64%, correspondingly).

A comparative study of non-oxidative pyrolysis and oxidative cracking of cyclohexane to light alkenes

Naphthene is generally considered difficult to convert in traditional pyrolysis, but the ring rupture becomes fairly easy with the presence of oxygen in the gas phase oxidative cracking of the model compound, cyclohexane. About 86.8% conversion of cyclohexane, 43.7% yield of light alkenes, 6.6% yield of benzene and 14.3% yield of CO could be obtained at 750 degreesC, at which temperature the pyrolysis of cyclohexane was negligible, while at 850 degreesC, the total yield of alkenes, benzene and CO was as high as 80% (50%, 12% and 18%, respectively) with 98% conversion of cyclohexane. The gas phase oxidative cracking process could be run in an autothermal way (cyclohexane/O-2 mole ratio of 0.69-0.8 in theory), which would minimize energy consumption and capital costs of the whole process. CO prevailed in the produced CO, and the yield Of CO2 was always below 1%, which means about 90% Of CO2 emission by fuel burning in pyrolysis would be saved. The gas phase oxidative cracking process appears to be an environmentally benign and efficient route for light alkene production with naphthene rich feedstocks. (C) 2004 Published by Elsevier B.V.