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81.
研究了燃烧风洞内不同纵向风速、不同火源功率条件下,隧道近火源区顶部温度沿纵向分布情况。结果表明,纵向风对不同尺寸火源条件下的顶部温度的影响呈不同特征。对较小尺寸火源,隧道顶部温升随风速增加而减小至稳定值;而对较大尺寸火源,顶部温升随风速增加先增加后减小。对于矩形火源,当纵向风较小(0.5~1.5m/s)时,长边平行于纵向风时顶部最高温升大于长边垂直于纵向风的情况;而当纵向风较大(≥2 m/s)时,两种油盘放置方式的顶部最高温升一致。纵向风作用下,顶部最高温升位置向下游呈现"两次移动"特征,即随着纵向风速增加该位置先向下游移动,当风速达到某一值时,隧道拱顶的加热机制由对流和辐射共同主控转变为辐射单独主控,最高温升位置突变回到上游后再次逐渐向下游移动。 相似文献
82.
为了测定煤层硫化氢(H2S)含量,防治矿井H2S涌出,提出一种通过钻屑法测定煤层H2S含量的方法。在未受采动影响的新鲜煤壁,采用钻屑法取样,通过测定煤样H2S解吸量、取样过程损失量和H2S残存量确定煤层H2S含量。根据溶于水中H2S的p H值和色谱分析解吸气体中H2S体积分数,确定H2S解吸量;根据煤样解吸规律和气样H2S体积分数,确定H2S损失量;根据色谱分析残存气体中H2S体积分数,确定其残存量。用此方法,对山西某矿H2S涌出煤层进行现场和实验室测定。研究表明,该矿H2S含量为(4.465~6.701)×10-3m3/t。钻屑法测定煤层H2S含量是可行的,可以为矿井H2S治理提供基础数据。 相似文献
83.
84.
应急物资的高效快速配置是降低灾害损失和顺利实施应急救援的有力保障。应急逆向物流包括废旧物资的回收利用以及可重复利用物资的回收再利用,能起到缓解应急物资匮乏,减少环境污染的作用。本文根据随机Petri网理论,构建考虑逆向物流的应急物资配置模型,通过对同构于该模型的马尔可夫链进行仿真,求得各种状态的稳态概率,结合马尔可夫链性质对关键因素进行静态分析和动态分析;通过“雅安地震”的案例应用表明,当地震灾害发生时,此模型可以反映各因素对应急物资配置整体流程的影响,并通过数值变化趋势反映不同条件下应急物资配置的关键环节,可以为灾后救援和应急物资的利用提供理论支持。 相似文献
85.
The existing literature (i) examines bycatch and discard behavior in a static framework and (ii) treats bycatch as a deterministic process uniform across vessels. Using a dynamic representative agent model in a two-stock resource, this paper explores strategic interactions between a social planner and two groups of harvesters, one of which imposes a stochastic “technological externality” (bycatch) on the other. In addition to limitations on entry and the number of trips taken in each industry, three bycatch control instruments are compared to the unconstrained case: taxes, trip limits, and value-based quotas. Implementation and enforcement costs aside, taxes dominate both types of quota, and value limits outperform trip limits by eliminating one type of discarding. In simulations, relative performance depends upon variance in the bycatch process, differences in the ex vessel prices of stocks, relative efficiency of the harvester types, and fixed costs on the trip and industry margins. 相似文献
86.
87.
Recruitment data for 18 marine fish stocks are smoothed using 10 parametric families of probability distributions. Comparative fit of the 10 families is assessed by means of the maximized log-likelihood. Results indicate that the gamma distribution provides an overall good fit in the right-hand tail of the data, but that some adjustment to the gamma distribution is called for in the left-hand tail. Weight functions and weighted distributions are suggested as one means of achieving the needed adjustment. 相似文献
88.
Laboratory analyses in a variety of contexts may result in left- and interval-censored measurements. We develop and evaluate a maximum likelihood approach to linear regression analysis in this setting and compare this approach to commonly used simple substitution methods. We explore via simulation the impact on bias and power of censoring fraction and sample size in a range of settings. The maximum likelihood approach represents only a moderate increase in power, but we show that the bias in substitution estimates may be substantial. 相似文献
89.
The Value of Biodiversity in Reserve Selection: Representation, Species Weighting, and Benefit Functions 总被引:7,自引:0,他引:7
ANNI ARPONEN§ RISTO K. HEIKKINEN† CHRIS D. THOMAS‡ ATTE MOILANEN 《Conservation biology》2005,19(6):2009-2014
Abstract: The limited availability of resources for conservation has led to the development of many quantitative methods for selecting reserves that aim to maximize the biodiversity value of reserve networks. In published analyses, species are often considered equal, although some are in much greater need of protection than others. Furthermore, representation is usually treated as a threshold: a species is either represented or not, but varying levels of representation over or under a given target level are not valued differently. We propose that a higher representation level should also have higher value. We introduce a framework for reserve selection that includes species weights and benefit functions for under- and overrepresentation (number of locations for each species). We applied the method to conservation planning for herb-rich forests in southern Finland. Our use of benefit functions and weighting changed the identity of about 50% of the selected sites at different funding levels and improved the representation of rare and threatened species. We also identified a small area of additional land that would substantially enhance the existing reserve network. We suggest that benefit functions and species weighting should be considered as standard options in reserve-selection applications. 相似文献
90.
A general model is developed to examine the patterns of the regional movement of tagged and released fish from mark-recapture
experiments. It is a stochastic model that incorporates fishing mortality, natural mortality, fish movement, tag-shedding,
and different rates of reporting. A likelihood function is constructed for estimating its parameters. We used this model to
analyze data on the Pacific halibut from mark-recapture experiments conducted by the International Pacific Halibut Commission
(IPHC), with a total of 36,058 releases from 1982 to 1986 and 5,826 recoveries from 1982 to 2000. We estimated their rates
of movement among IPHC management areas, along with their instantaneous rates of natural and fishing mortalities. Our analysis
revealed that fish movement was not significant among areas, with a resident probability of > 0.92. This lends support to
the IPHC catch-at-age stock assessment model (which has no built-in movement components). The estimated instantaneous rate
of natural mortality (0.198 year−1) lies between that assumed in all IPHC stock assessments before 1998 (0.20 year−1) and that from 1999 onwards (0.15 year−1). The estimates of the instantaneous rates of fishing mortality were consistent with those from the IPHC stock assessment
model.
Received: April 2003 / Revised: May 2005 相似文献