论岩体表征单元体积REV岩体力学参数取值的一个基本问题

本文论述了岩体力学性质的尺寸效应,提出了与岩体弹性参数相应的表征单元体REV的力学描述,根据中心极限定理推导了估算裂隙岩体REV 的数学表达式。研究表明,岩体表征单元体的大小是岩体力学性质尺寸效应的客观反映。本研究成果为合理选取岩体力学参数提供了一条新途径。     

Sediment and nutrient transport dynamics in two tributaries of Lake Erie: A numerical model

The objective of this research is to investigate spatial and temporal variation in the transport of phosphate by grain size fractions of suspended sediment in two Lake Erie tributaries. A sediment-phosphate transport model is proposed to evaluate and quantify the kinetic control of dissolved phosphate by fluvial sediment. A first-order assessment of the sediment-phosphate export from Big Otter Creek and Big Creek to Lake Erie is presented. Output from this model was calculated using historical discharge and sediment data collected by Environment Canada in combination with adsorption coefficients derived from laboratory experiments for a range of sediment grain size fractions. Results of these calculations provide a quantitative interpretation of the influence of suspended sediment on phosphate dynamics in tributaries and the potential impact on water quality of receiving waters.     

Vibration characteristics of rigid body placed on sand ground

This study aims to investigate experimentally the vibration properties of rigid body placed on sand ground surface. The rigid body models with circular or rectangular base with variable mass, inertial moment and base sizes, were prepared, and the vibration behavior was observed in some series of free vibration tests and forced vibration tests. The observed behavior was analyzed and the vibration mode, vibration period and damping ratio were examined. It was found that the natural vibration period depends not only on the mechanical properties of rigid body and ground, but also on the magnitude of vibration amplitude. This suggested the notable effect of nonlinear strain dependent stiffness of ground material. A physical model with distributed spring–dashpot element was used to model the interactive mechanical behavior between rigid body and ground. The stiffness of the spring–dashpot element was evaluated through the modal analysis of the observed vibration behaviors. The effects of base shape, base size and base pressure on the stiffness of spring–dashpot element are discussed. The spring–dashpot model was verified with the behavior observed in forced vibration tests.     

Traffic aerosols (18 nm particle size 18 μm) source apportionment during the winter period

In November 2004–January 2005, a micro orifice uniform deposit impactor (MOUDI) and a Nanometer (nanometer)-MOUDI were used in the center of Taiwan to measure particle size (18 nm particle size 18 μm) distributions of atmospheric aerosols at a traffic site during the winter period. The average Mass in Media Aerodynamic Diameter (MMAD) of suspended particles is 0.99 μm this study. As for the ultra fine and nanometer (nanometer) particle mode, the composition order for these major ions species was SO₄²⁻ NH₄⁺ NO₃⁻ Mg²⁺ Ca²⁺ Na⁺ K⁺ Cl⁻. An ion Chromatography (DIONEX-100) was used to analyze major anion species, Cl⁻, NO₃⁻, SO₄²⁻ and cation species, NH₄⁺Na⁺, K⁺, Ca²⁺Mg²⁺. Their concentrations were also extracted from various particles size modes (nanometer (nanometer), ultra fine, fine and coarse). The results obtained in this study also indicated that the average portions for the major ionic species (SO₄²⁻, NH₄⁺ and Mg²⁺) in the nanometer (nanometer), ultra fine, fine and coarse particulate modes are about 34%, 37%, 63% and 30%, respectively at this traffic sampling site during the winter period.     

FRACTIONAL TRANSPORT OF SEDIMENT MIXTURES

A new method based on the Transport Capacity Fraction (TCF) concept is proposed to compute the fractional transport rates for nonuniform sediment mixtures in sand-bed channels. The TCF concept is derived from the understanding that the measurements and predictions of bed-material load are more accurate and reliable than the measurements and predictions of fractional loads. First the bed-material load is computed using an appropriate equation, then the fractional transport rates are determined by distributing the bed-material load into size groups through a transport capacity distribution function. For the computation of bed-material loads, the Ackers and White, Engelund and Hansen, and Yang equations are used in this study. Two new transport capacity distribution functions are developed for flows in sand-bed channels. The new expressions presented in this paper account for the sheltering and exposure effects that exist in mixtures. Comparisons with measured data show that the proposed method can signifi     

Self-consistent binary cluster size distributions: nucleation of sulfuric acid–water vapors

The incorporation of additional information on free energies of small clusters in a cluster distribution based on the capillarity approximation is considered in relation with self-consistency (SC). The concept of fictitious average monomers is applied to expand the self-consistent form of a unary size distribution to cover also the distribution of a binary system. The experimental data on the free energies of monohydrates and dihydrates of sulfuric acid are used to obtain the partially self-consistent size distribution of clusters. Using these distributions, the concentrations of sulfuric acid and water, required for obtaining a unit nucleation rate, are calculated and compared among themselves and with experimental concentrations. Free energies of cluster formation are estimated by the thermodynamically consistent classical theory taking into account the difference between interior and surface compositions of a cluster. The partially self-consistent size distribution gives the best agreement with experimental data. The self-consistent distribution of the proposed form overestimates hydration and, therefore, largely underestimates nucleation rates compared to experimental rates.     

尺度相似变换中边坡工程行为变化的定性分析

本文应用相似理论和已有的岩土体边坡研究成果, 探讨了边坡在几何尺寸相似放大过程中所表现出的应力场、位移场及强度等工程特性的变化规律, 对运用已有边坡研究成果认识高边坡力学行为有重要的指导意义。     

The evolution of Pinatubo aerosols in the Arctic stratosphere during 1994–2000

Balloon-borne aerosol measurements were performed with an optical particle counter between 1994 and 2000 at Ny-Ålesund (79°N), Svarbard. Throughout the observation period, continuous decay was found in the concentrations of particles with 0.4–0.6 μm in radius in the Arctic stratosphere, suggesting that Pinatubo aerosols remained even at the end of the 1990s. The decay rate was clearly higher for larger particle sizes, and higher at higher altitude (e-folding time of 970–526 days), suggesting a gravitational sedimentation effect. For smaller particles with R<0.4 μm, slight increases in concentration with time were found, which agreed with the measurements at mid-latitude. The sulfate mass mixing ratio in the Arctic stratosphere before 1998 showed values higher than those at middle latitude, while values were almost the same in both regions after 1998. A possible explanation of the latitudinal difference is a time lag (of 0.5–1 year) in the arrival of Pinatubo aerosols in the Arctic.     

Diatom taxonomic and morphological changes as indicators of metal pollution and recovery in Lac Dufault (Québec, Canada)

We studied diatom taxonomic composition and the presence of morphological alterations (size and deformations) along a sediment core collected in Lac Dufault, Abitibi, whose watershed has a long history of mining pollution presently undergoing mitigation. According to sediment dating with ²¹⁰Pb and metal profiles along the core, we could identify four periods in the contamination history of the lake, which were characterized by different diatoms. Tabellaria flocculosa was dominant in the pre-mining period but was drastically reduced at the onset of pollution when Fragilaria cf. tenera became important. This diatom, together with other Fragilaria species and cysts of Chaetoceros muelleri, typified the transition period in which Cu reached its maximum value and other metals started to increase. During the period of maximum contamination with Zn, Cd, and Fe accompanied by acid mine drainage, Achnanthes minutissima and Brachysira vitrea were dominant. These taxa started to wane in the most recent sediments representing a partial chemical recovery. Asterionella formosa, which almost vanished at mining onset, reappeared with high abundance in these superficial sections. Beside these taxonomical shifts, we observed during the contamination period significant reduction in valve length together with increased percentages of valve deformations. Because available data on water chemistry and a diatom-based pH reconstruction suggest that Lac Dufault escaped severe acidification, diatom patterns observed in the core can be mostly ascribed to metal contamination. Individual diatom abundance and valve length had strong statistical relationships with the different metals identified in the core. Diatom changes both taxonomic and morphological can be excellent specific indicator of metal contamination and early recovery.