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961.
962.
963.
利用冲击力信号判断泥石流颗粒垂向分选的试验研究 总被引:1,自引:0,他引:1
分别提出根据冲击力数据的波动强度和峰值情况进行泥石流颗粒垂向分选研究的系统方法,并配置了三组不同容重(2 095 kg/m3、2 008 kg/m3和1 960 kg/m3)的粘性泥石流样品开展泥石流冲击试验。两种方法的分析结果基本一致,即容重为2 095 kg/m3的泥石流分选不明显,其他两组泥石流呈现出正粒序分布且容重越小分选越显著。量纲分析表明,开展的试验粘滞力在运动中起主导作用,颗粒之间作用力较小,不容易发生反粒序分选,这与通过冲击力分析颗粒垂向分选的结果一致,因此提出的利用冲击力信号判断泥石流颗粒垂向分选的系统方法具有适用性。 相似文献
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965.
Z. WangR.F. Grant M.A. ArainB.N. Chen N. CoopsR. Hember W.A. KurzD.T. Price G. StinsonJ.A. Trofymow J. Yeluripati Z. Chen 《Ecological modelling》2011,222(17):3236-3249
Forest productivity is strongly affected by seasonal weather patterns and by natural or anthropogenic disturbances. However weather effects on forest productivity are not currently represented in inventory-based models such as CBM-CFS3 used in national forest C accounting programs. To evaluate different approaches to modelling these effects, a model intercomparison was conducted among CBM-CFS3 and four process models (ecosys, CN-CLASS, Can-IBIS and 3PG) over a 2500 ha landscape in the Oyster River (OR) area of British Columbia, Canada. The process models used local weather data to simulate net primary productivity (NPP), net ecosystem productivity (NEP) and net biome productivity (NBP) from 1920 to 2005. Other inputs used by the process and inventory models were generated from soil, land cover and disturbance records. During a period of intense disturbance from 1928 to 1943, simulated NBP diverged considerably among the models. This divergence was attributed to differences among models in the sizes of detrital and humus C stocks in different soil layers to which a uniform set of soil C transformation coefficients was applied during disturbances. After the disturbance period, divergence in modelled NBP among models was much smaller, and attributed mainly to differences in simulated NPP caused by different approaches to modelling weather effects on productivity. In spite of these differences, age-detrended variation in annual NPP and NEP of closed canopy forest stands was negatively correlated with mean daily maximum air temperature during July-September (Tamax) in all process models (R2 = 0.4-0.6), indicating that these correlations were robust. The negative correlation between Tamax and NEP was attributed to different processes in different models, which were tested by comparing CO2 fluxes from these models with those measured by eddy covariance (EC) under contrasting air temperatures (Ta). The general agreement in sensitivity of annual NPP to Tamax among the process models led to the development of a generalized algorithm for weather effects on NPP of coastal temperate coniferous forests for use in inventory-based models such as CBM-CFS3: NPP′ = NPP − 57.1 (Tamax − 18.6), where NPP and NPP′ are the current and temperature-adjusted annual NPP estimates from the inventory-based model, 18.6 is the long-term mean daily maximum air temperature during July-September, and Tamax is the mean value for the current year. Our analysis indicated that the sensitivity of NPP to Tamax was nonlinear, so that this algorithm should not be extrapolated beyond the conditions of this study. However the process-based methodology to estimate weather effects on NPP and NEP developed in this study is widely applicable to other forest types and may be adopted for other inventory based forest carbon cycle models. 相似文献
966.
Research has shown a complex relationship between turnover and firm performance. Not only does it matter who leaves (e.g., high‐performing versus low‐performing employees), but the context also stands to influence this effect in complex ways. We apply human capital theory, social capital theory, and the cost–benefit perspective to propose two boundary conditions to the high‐performer turnover and firm performance relationship. Specifically, we predict that the negative impact of high‐performer turnover on firm performance will be the strongest for reputable firms and for firms who invest less in human capital (e.g., selection, training, and incentive‐based pay). We present data from 155 South Korean firms that support the hypothesized model. We discuss findings in terms of current and future theory, practical implications, and subsequent research needs. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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968.
Qingwu Zhang Juncheng Jiang Mingwei You Yuan Yu Yihu Cui 《Journal of Loss Prevention in the Process Industries》2013,26(6):1230-1237
A pilot scale interconnected vessels experiment system was established, and the closed and vented gas explosion characteristics in the system were studied, using 10% methane–air mixture. Regularity of pressure variation in vessels and flame propagation in linked pipes was analyzed. Furthermore, the effects of transmission style, ignition position, pipe length, and initial pressure on explosion severity were discussed. For the closed explosion: explosion in interconnected vessels presents strongly destructive power to secondary vessel, especially transmission from the big vessel to the small one; the worst ignition position is shifting from ignition in the interconnected pipe to the walls of the two vessels; as far as ignition in big vessel is concerned, the peak pressure in secondary vessel increases with the pipe length much faster than that for ignition in small vessel; the peak pressures in two vessels are approximate linear functions of initial pressure. For the vented explosion: the transmission style and interconnected pipe length have significant impacts on the effect of venting on the protection; in order to obtain the better venting effect, the use of a divergent interconnected pipe from the big vessel to the small one in industry is advised and it is necessary to reduce the interconnected pipe length as far as possible or install flame arrester in the interconnected pipe. 相似文献
969.
Simon P. Boilard Paul R. Amyotte Faisal I. Khan Ashok G. Dastidar Rolf K. Eckhoff 《Journal of Loss Prevention in the Process Industries》2013,26(6):1646-1654
Explosibility of micron- and nano-titanium was determined and compared according to explosion severity and likelihood using standard dust explosion equipment. ASTM methods were followed using a Siwek 20-L explosion chamber, MIKE 3 apparatus and BAM oven. The explosibility parameters investigated for both size ranges of titanium include explosion severity (maximum explosion pressure (Pmax) and size-normalized maximum rate of pressure rise (KSt)) and explosion likelihood (minimum explosible concentration (MEC), minimum ignition energy (MIE) and minimum ignition temperature (MIT)). Titanium particle sizes were ?100 mesh (<150 μm), ?325 mesh (<45 μm), ≤20 μm, 150 nm, 60–80 nm, and 40–60 nm. The results show a significant increase in explosion severity as the particle size decreases from ?100 mesh with an apparent plateau being reached at ?325 mesh and ≤20 μm. Micron-size explosion severity could not be compared with that for nano-titanium due to pre-ignition of the nano-powder in the 20-L chamber. The likelihood of an explosion increases significantly as the particle size decreases into the nano range. Nano-titanium is very sensitive and can self-ignite under the appropriate conditions. The explosive properties of the nano-titanium can be suppressed by adding nano-titanium dioxide to the dust mixture. Safety precautions and procedures for the nano-titanium are also discussed. 相似文献
970.
Developing prototypes of pressure sensitive mats and testing their practical application were the aims of this study. Two contact plate mats were designed and constructed: rubber-rubber (R) and metal-metal (M). A recipe for rubber mixes and the production technology were prepared. Two laboratory test stands for measuring the actuating force, response time, static pressure resistance, and the durability of the mats were constructed. Computer software was written to control the operation of those test stands. Methods of testing pressure sensitive mats were based on PrDIN 31 006 (Deutsches Institut fur Normung [DIN], 1990) and EN 1760–1 (Comite Europeen de Normalisation [CEN], 1997). Both prototypes of contact plate mats were tested under laboratory and industrial conditions.The test results proved that the design was correct, the setup requirements were fulfilled, and the mats were efficient and reliable in the industrial environment. 相似文献