蜗杆凸轮间歇机构的设计及参数选择

用优化设计的观点，论述了蜗杆凸轮间歇（分度）运动机构的工作原理、参数与运动规律的选择、设计方法。     

地下水动态监测周期的优化

地下水动态监测是获得地下水动态信息,掌握其变化规律的直接手段。目前,地下水动态长期监测多数采用5天一次的监测周期,也有选用10天的。根据数理统计分析的原理,可针对不同动态类型区地下水变化特征以及不同时期的地下水变化规律,观测精度要求,采用不同的监测周期。     

Non-food-chain transfer of sediment-associated persistent organic pollutants to a marine benthic fish

We investigated the transfer of persistent organic pollutants (POPs) from unspiked bottom sediment to a benthic marine fish, marbled sole (Pleuronectes yokohamae), via non-food-chain pathways, i.e., via sediment particles and water column. One-year-old sole were held for 28 days in an exposure tank with bottom sediment or in a control tank. o,p′-DDE and tri- to penta-chlorobiphenyls were transferred from the sediment to the fish via non-food-chain pathways, as demonstrated by concentrations in the exposed fish at 2.5-30 times the control levels. A model analysis based on first-order kinetic equations indicated that the overall rate constant of transfer of these compounds from sediment to fish was generally lower than that from food (median of ratio, 0.48). It also suggested that relatively high concentrations of the other POPs in the food and the longer times necessary for them to reach a steady state masked any transfer of them from the sediment.     

A coastal prediction system as an event response tool: Particle tracking simulation of an anhydrous ammonia spill in Tampa Bay

A coastal prediction system for Tampa Bay, comprised of a numerical circulation model and Lagrangian particle transport model, rapidly produces hindcast/forecast simulations that alert authorities to high impact areas following the introduction of hazardous material into the bay. The effectiveness of the prediction system as an event response tool is evaluated during an anhydrous ammonia spill. A week-long simulation predicts the trajectory of the material due to winds and currents. Physical transport of the model particles alternates from being tidally driven to being driven both by wind action and residual circulation. A forecast simulation showing particle distribution drove field sampling that resulted in the detection of a Pseudo-nitzschia bloom likely initiated from excess ammonium in the bay. An online component of the coastal prediction system is in development to better manage response and mitigation efforts for future hazardous material spills in Tampa Bay.     

Downstream trends in sediment size and composition of channel-bed, bar, and bank deposits related to hydrologic and lithologic controls in the Llano River watershed, central Texas, USA

The downstream fining of fluvial sediments is a fundamental tenet of drainage systems and, for decades, has been the subject of considerable research. Most of this research has focused on variability in channel-bed material. Other sedimentological components such as channel bars and banks, however, represent distinctively different processes occurring at various flow magnitudes and durations and thus provide an opportunity to examine a more comprehensive set of controls on the larger fluvial system. This study analyses downstream patterns of sediment size and composition for channel-bed material, bars, and banks in the Llano River watershed (11,568 km²) in central Texas, USA.Fluvial deposits in the study area were characterized through field, laboratory, and statistical analyses and standard sedimentary indices (d₁₆, d₅₀, d₈₄, sorting) were computed. Two hundred thirty-eight sediment samples were collected at 15 sites along the main-stem channel with sampling occurring at the low-flow channel (thalweg), lateral bars, banks, and overbank locations. Channel-bar deposits are characterized by a downstream reduction in particle size, but low-flow-channel deposits have a substantially weaker trend, a discrepancy possibly attributed to uniformity and continuity of hydraulic sorting mechanisms during moderate and high flows. Channel-bar deposits reveal an abrupt downstream reduction in gravel size in the upper watershed, which is attributed to an increase in drainage area. Further, an abrupt gravel-to-sand transition occurs immediately downstream of a distinct lithologic change from mostly carbonate rocks to igneous and metamorphic rocks. The downstream decrease in channel-bar particle size occurs despite an increasingly constricted alluvial valley, commonly associated with greater unit stream power and relatively coarse sediment. Contrasting with channel-bed material, particle size of channel banks increases downstream, which is attributed to the addition of sand-sized sediment from igneous and metamorphic rocks. The consideration of distinctive sedimentological components of a dynamic fluvial system represents a more comprehensive and nuanced study of the topic of downstream sediment trends than prior studies, which is important to a range of engineering, biological, and planning issues at the watershed scale.     

Particle finite element analysis of large deformation and granular flow problems

A version of the Particle Finite Element Method applicable to geomechanics applications is presented. A simple rigid-plastic material model is adopted and the governing equations are cast in terms of a variational principle which facilitates a straightforward solution via mathematical programming techniques. In addition, frictional contact between rigid and deformable solids is accounted for using an approach previously developed for discrete element simulations. The capabilities of the scheme is demonstrated on a range of quasi-static and dynamic problems involving very large deformations.     

A laboratory study of meteor smoke analogues: Composition, optical properties and growth kinetics

Meteoric smoke forms in the mesosphere from the recondensation of the metallic species and silica produced by meteoric ablation. A photochemical flow reactor was used to generate meteoric smoke mimics using appropriate photolytic precursors of Fe and Si atoms in an excess of oxidant. The following systems were studied: (i) Fe+O₃/O₂, (ii) Fe+O₃/O₂+H₂O, (iii) Fe+Si/SiO+O₃/O₂ and (iv) Si/SiO+O₃/O₂. The resulting nano-particles were captured for imaging by transmission electron microscopy, combined with elemental analysis using X-ray (EDX) and electron energy loss (EELS) techniques. These systems generated particle compositions consistent with: (i) Fe₂O₃ (hematite), (ii) FeOOH (goethite), (iii) Fe₂SiO₄ (fayalite) and (iv) SiO₂ (silica). Electron diffraction revealed that the Fe-containing particles were entirely amorphous, while the SiO₂ particles displayed some degree of crystallinity. The Fe-containing particles formed fractal aggregates with chain-like morphologies, whereas the SiO₂ particles were predominantly spherical and compact in appearance. The optical extinction spectra of the Fe-containing particles were measured from 300 nm<λ<650 nm. Excellent agreement was found with the extinction calculated from Mie theory using the refractive indices for the bulk compounds, and assuming that the fractal aggregates are composed of poly-disperse distributions of constituent particles with radii ranging from 5 to 100 nm. These sizes were confirmed from measurements of the particle size distributions and microscopic imaging. Finally, the particle growth kinetics of the Fe-containing systems exhibit unexpectedly rapid agglomerative coagulation. This was modelled by assuming an initial period of coalescent particle growth resulting from diffusional (Brownian) coagulation to form primary particles; further growth of these particles is then dominated by long-range magnetic dipole–dipole interactions, leading to the fractal aggregates observed. The atmospheric implications of this work are then discussed.     

地源热泵项目的经济分析及设计优化——以北京市昌平区某地源热泵改造工程为例

以北京地区浅层地温能资源开发利用现状调查为基础,选取有代表性的昌平区某地源热泵供暖改造工程为实例,对地源热泵项目进行了技术．经济分析,并对地源热泵的设计方案提出了合理化建议。     

Mineral ballast and particle settling rates in the coastal upwelling system off NW Africa and the South Atlantic

The ocean off NW Africa is the second most important coastal upwelling system with a total annual primary production of 0.33 Gt of carbon per year (Carr in Deep Sea Res II 49:59–80, 2002). Deep ocean organic carbon fluxes measured by sediment traps are also fairly high despite low biogenic opal fluxes. Due to a low supply of dissolved silicate from subsurface waters, the ocean off NW Africa is characterized by predominantly carbonate-secreting primary producers, i.e. coccolithophorids. These algae which are key primary producers since millions of years are found in organic- and chlorophyll-rich zooplankton fecal pellets, which sink rapidly through the water column within a few days. Particle flux studies in the Mauretanian upwelling area (Cape Blanc) confirm the hypothesis of Armstrong et al. (Deep Sea Res II 49:219–236, 2002) who proposed that ballast availability, e.g. of carbonate particles, is essential to predict deep ocean organic carbon fluxes. The role of dust as ballast mineral for organic carbon, however, must be also taken into consideration in the coastal settings off NW Africa. There, high settling rates of larger particles approach 400 m day⁻¹, which may be due to a particular composition of mineral ballast. An assessment of particle settling rates from opal-production systems in the Southern Ocean of the Atlantic Sector, in contrast, provides lower values, consistent with the assumptions of Francois et al. (Global Biogeochem Cycles 16(4):1087, 2002). Satellite chlorophyll distributions, particle distributions and fluxes in the water column off NW Africa as well as modelling studies suggest a significant lateral flux component and export of particles from coastal shelf waters into the open ocean. These transport processes have implications for paleo-reconstructions from sediment cores retrieved at continental margin settings.     

参考作物蒸散模型对比分析及评价

利用山东省6个气象台站45 a(1960-2004年)的逐日气象资料并选用7种参考作物蒸散模型,分别计算了上述各地的参考作物蒸散,对模型结果进行时空分布对比分析;进而以FAO推荐的Penman-Monteith模型为对照,利用最小一乘法对其余6种模型进行优化并对优化前后的模型进行时空比较.结果表明:Makkink模型在6个台站的时空分布模拟效果均最好,Mass-transfer模型在7-8月明显偏低,Net Radiation模型各站全年基本都偏高;根据不同月份的相对偏差情况,采用最小一乘法进行分月优化,优化后的模型预测月参考作物蒸散标准误差小于5 mm,平均相对误差小于8.5%,台站的年参考作物蒸散相对误差也基本小于10%,说明这些含参数较少的模型经优化后基本上可用,当资料缺损时不失为Penman-Monteith模型的替代模型.