The results of TEM investigation indicate that magnetite and maghemite are the major ferromagnetic minerals in loess-paleosol sequences. Primary magnetite has the similar morphology and surface characteristics as eoli...The results of TEM investigation indicate that magnetite and maghemite are the major ferromagnetic minerals in loess-paleosol sequences. Primary magnetite has the similar morphology and surface characteristics as eolian detrital particles. The magnetite can be classified into two categories, high-titanium and low-titanium, which may be the indicators of magmatic rocks and metamorphic rocks, respectively. TEM investigation at nanometer scale shows that primary detrital magnetite of micron scale had been partially weathered to maghemite of 5～20 nanometer during the pedogenic process, which maintain the pseudomorphism of the aeolian debris. Some chlorite particles were also weathered to nanometer scale magnetite or maghemite in the pedogenic process. So weathering of the two minerals leads to formation of superparamagnetism, which may be the important mechanism of magnetic-susceptibility increase in paleosols. The magnetite or maghemite resulting from the weathering of chlorite contains a small amount of P and S, which is the signal of microbe-mineral interaction, and indicates that microbes may play a certain role in chlorite weathering and formation of superparamagnetic particles.展开更多
In this paper, an unstructured, collocated finite volume method for solvingthe Navier-Stokes equations was developed by virtue of auxiliary points. The derivatives weredetermined by the Gauss theorem. The proposed met...In this paper, an unstructured, collocated finite volume method for solvingthe Navier-Stokes equations was developed by virtue of auxiliary points. The derivatives weredetermined by the Gauss theorem. The proposed method could provide control volumes with arbitrarygeometry and preserve the second-order accuracy even if highly distorted grids are used. Althougharbitrary number of cell faces can be used, the hybrid quadrilateral/triangular grids are moredesirable for the simplicity of implementation and applications to engineering problems. Thepressure-velocity coupling was treated using a SIMPLE-like algorithm. The Generalized MinimumResidual (GMRES) method with the Incomplete LU (ILU) preconditioner was used to solve linearequations. Four test cases were studied for validating the proposed method. In using this method,grid quality is not important. Thus, engineers can pay mostly attention to physical mechanism ofproblems. Turbulence models can be simply integrated and the method can be straightforwardlyextended to treat three-dimensional problems.展开更多
Pulsed laser photolysis/laser-induced fluores-cence 0LP-LIF) is utilized to measure rate constants for C2(a^3Пu) reactions with NO, N2O, O2, H2 and NH3. Multiphoton dissociation of C2C!4 at 266 nm is employed for the...Pulsed laser photolysis/laser-induced fluores-cence 0LP-LIF) is utilized to measure rate constants for C2(a^3Пu) reactions with NO, N2O, O2, H2 and NH3. Multiphoton dissociation of C2C!4 at 266 nm is employed for the generation of C2(a^3Пu) radicals. The C2(a^3Пu) concentration is monitored by the fluorescence of the (0, 0) band of the (d^3Пg←→a^3Пu) transition at 516.5 nm. C2(a^3Пu) removal rate constants for the reactions are determined as kNO = (5.46 × 0.10) × 10^-11- cm^3 molecule^-1 s^-1, kN2O = (1.63 × 0.20) × 10^-13 cm^3 molecule^-1 s^-1, kN2O = (1.58 × 0.16) × 10^-11 cm^3 molecule^-l s^-1, kO2 = (5.92 × 1.00) × 10^-14 cm^3 molecule^-1 s^-1, kH2 < 1.0× 10^-14 cm^3 molecule^-1 s^-1. Based on the data analysis and theoretical calculation, we suggest that the C2(a^3Пu) reactions with H2 and NH3 proceed via the hydrogen abstraction mechanism, barriers exist at the entrance channel of the reactions of C2(a^3Пu) with H2 and NH3.展开更多
The methods of X-ray diffraction (XRD) and ICP-AES are applied to analyzing the mineral composition of modern and fossil snail shells in Luochuan section and Xifeng section. The results show that the mineral phase of ...The methods of X-ray diffraction (XRD) and ICP-AES are applied to analyzing the mineral composition of modern and fossil snail shells in Luochuan section and Xifeng section. The results show that the mineral phase of calcium carbonate in modern snail shells is aragonite, but for some fossil snail shells in certain layers of loess sequences, a part of aragonite is transformed into calcite. In Luochuan and Xifeng sections, the stratigraphic borderline of arago- nite-calcite transformation appearing obviously is between L5 and L6. Under the earth surface condition, the arago- nite-calcite transformation is influenced by the factor of temperature only in a long time scale. It seems that the pres- sure is not the factor influencing the aragonite-calcite trans- formation. The results also show that existing age of snail shells is possibly the dominant and principal factor for the aragonite-calcite transformation. To a certain extent, the degree of aragonite-calcite transformation in snail shell is controlled by the content of trace element, such as Mg2+. The trace element can improve the stability of snail shell arago- nite and impede the process of aragonite transforming into calcite.展开更多
基金supported by the Outstanding Overseas Chinese Scholars Fund of the Chinese Academy of Sciences(Grant No.2003-1-7)the National Natural Science Foundation of China(Grant Nos.40072017,40273002 and 40173003)the National Basic Research Development Program(Grant No.G1999043401).
文摘The results of TEM investigation indicate that magnetite and maghemite are the major ferromagnetic minerals in loess-paleosol sequences. Primary magnetite has the similar morphology and surface characteristics as eolian detrital particles. The magnetite can be classified into two categories, high-titanium and low-titanium, which may be the indicators of magmatic rocks and metamorphic rocks, respectively. TEM investigation at nanometer scale shows that primary detrital magnetite of micron scale had been partially weathered to maghemite of 5～20 nanometer during the pedogenic process, which maintain the pseudomorphism of the aeolian debris. Some chlorite particles were also weathered to nanometer scale magnetite or maghemite in the pedogenic process. So weathering of the two minerals leads to formation of superparamagnetism, which may be the important mechanism of magnetic-susceptibility increase in paleosols. The magnetite or maghemite resulting from the weathering of chlorite contains a small amount of P and S, which is the signal of microbe-mineral interaction, and indicates that microbes may play a certain role in chlorite weathering and formation of superparamagnetic particles.
文摘In this paper, an unstructured, collocated finite volume method for solvingthe Navier-Stokes equations was developed by virtue of auxiliary points. The derivatives weredetermined by the Gauss theorem. The proposed method could provide control volumes with arbitrarygeometry and preserve the second-order accuracy even if highly distorted grids are used. Althougharbitrary number of cell faces can be used, the hybrid quadrilateral/triangular grids are moredesirable for the simplicity of implementation and applications to engineering problems. Thepressure-velocity coupling was treated using a SIMPLE-like algorithm. The Generalized MinimumResidual (GMRES) method with the Incomplete LU (ILU) preconditioner was used to solve linearequations. Four test cases were studied for validating the proposed method. In using this method,grid quality is not important. Thus, engineers can pay mostly attention to physical mechanism ofproblems. Turbulence models can be simply integrated and the method can be straightforwardlyextended to treat three-dimensional problems.
文摘Pulsed laser photolysis/laser-induced fluores-cence 0LP-LIF) is utilized to measure rate constants for C2(a^3Пu) reactions with NO, N2O, O2, H2 and NH3. Multiphoton dissociation of C2C!4 at 266 nm is employed for the generation of C2(a^3Пu) radicals. The C2(a^3Пu) concentration is monitored by the fluorescence of the (0, 0) band of the (d^3Пg←→a^3Пu) transition at 516.5 nm. C2(a^3Пu) removal rate constants for the reactions are determined as kNO = (5.46 × 0.10) × 10^-11- cm^3 molecule^-1 s^-1, kN2O = (1.63 × 0.20) × 10^-13 cm^3 molecule^-1 s^-1, kN2O = (1.58 × 0.16) × 10^-11 cm^3 molecule^-l s^-1, kO2 = (5.92 × 1.00) × 10^-14 cm^3 molecule^-1 s^-1, kH2 < 1.0× 10^-14 cm^3 molecule^-1 s^-1. Based on the data analysis and theoretical calculation, we suggest that the C2(a^3Пu) reactions with H2 and NH3 proceed via the hydrogen abstraction mechanism, barriers exist at the entrance channel of the reactions of C2(a^3Пu) with H2 and NH3.
基金This work was supported by the National Key Program for Basic Research(Grant No.2001 CCB00100)the Key Pro-gram of National Natural Science Foundation of China(Grant No:4033 1001)the National Basic Research Program of China(Grant No:2004CB720204).
文摘The methods of X-ray diffraction (XRD) and ICP-AES are applied to analyzing the mineral composition of modern and fossil snail shells in Luochuan section and Xifeng section. The results show that the mineral phase of calcium carbonate in modern snail shells is aragonite, but for some fossil snail shells in certain layers of loess sequences, a part of aragonite is transformed into calcite. In Luochuan and Xifeng sections, the stratigraphic borderline of arago- nite-calcite transformation appearing obviously is between L5 and L6. Under the earth surface condition, the arago- nite-calcite transformation is influenced by the factor of temperature only in a long time scale. It seems that the pres- sure is not the factor influencing the aragonite-calcite trans- formation. The results also show that existing age of snail shells is possibly the dominant and principal factor for the aragonite-calcite transformation. To a certain extent, the degree of aragonite-calcite transformation in snail shell is controlled by the content of trace element, such as Mg2+. The trace element can improve the stability of snail shell arago- nite and impede the process of aragonite transforming into calcite.
