Element Fractionation in Suspended Matter in Landfill Leachate Using Single Extractions

This study presents the determination of the pseudo-total and available element contents in suspended matter in leachate using stripping voltammetry (DPASV) on a hanging mercury drop electrode and an inductively coupled plasma mass spectrometer (ICP-MS). The following elements were studied: Zn, Pb, As, Sb, Co, Cu, Ni, Cr, Sn, Mo and Cd. To determine the pseudo-total metal contents, we applied microwave digestion using a mixture of HNO₃ and HClO₄ with a small quantity of HF. To assess the metal availability from suspended matter in leachate, the single extraction procedure with 0.1mol·L^–1 acetic acid and 0.01mol·L^–1 ammonium acetate was applied. Metal bioavailability based on single extraction with 15% H₂O₂ was determined. We also estimated the association with particular phases of suspended matter in leachate.     

一类可修系统贮存可靠性的MML法推断

本文研究了两种可修贮存模型组成串联系统可靠性统计推断的MML法,并与Fiducial方法进行比较．模拟结果表明MML法对威布尔型设备为主的串联系统可用度进行推断时具有优越性．     

TAILORING POINT COUNTS FOR INFERENCE ABOUT AVIAN DENSITY: DEALING WITH NONDETECTION AND AVAILABILITY

Point counts are commonly used for bird surveys, but interpretation is ambiguous unless there is an accounting for the imperfect detection of individuals. We show how repeated point counts, supplemented by observation distances, can account for two aspects of the counting process: (1) detection of birds conditional on being available for observation and (2) the availability of birds for detection given presence. We propose a hierarchical model that permits the radius in which birds are available for detection to vary with forest stand age (or other relevant habitat features), so that the number of birds available at each location is described by a Poisson‐gamma mixture. Conditional on availability, the number of birds detected at each location is modeled by a beta‐binomial distribution. We fit this model to repeated point count data of Florida scrub‐jays and found evidence that the area in which birds were available for detection decreased with increasing stand age. Estimated density was 0.083 (95%CI: 0.060–0.113) scrub‐jays/ha. Point counts of birds have a number of appealing features. Based on our findings, however, an accounting for both components of the counting process may be necessary to ensure that abundance estimates are comparable across time and space. Our approach could easily be adapted to other species and habitats.     

基于FNP-ADC模型的弹药调度系统保障效能评估

正确评估诸如弹药调度系统此类复杂武器装备的系统效能,可为作战指挥决策提供重要支撑依据,从装备系统结构组成及复杂性出发,合理地表示工作状态及其转移过程,在流水网络计划(flow network planning,FNP)技术框架下应用ADC模型开展效能评估.以FNP时间参数为基础,确定了组成分系统故障一般概率分布下的可用性、可信性和保障能力表示方法,分别表示为影响因素的函数关系,最终建立了FNP-ADC模型.综合进行保障效能评估,可进一步分析因素对效能的影响程度,并给出了案例分析.     

Characterization of mercury species in soils by HPLC-ICP-MS and measurement of fraction removed by diffusive gradient in thin films

The properties and behaviour of Hg depend on both the oxidation state and the chemical form: the bioavailability, toxicity, persistence and accumulation of mercury in the food web are strongly influenced by chemical speciation. The present work aims to determine the chemical forms of mercury present in soil and to evaluate the fraction of mercury in soil solution available to plants. In order to do this, we analyzed eight samples of contaminated soils with Hg concentrations ranging from 1.31 to 21.7 mg kg⁻¹, collected from different depths (0–10 and 40–50 cm) close to an abandoned industrial site in Val Basento (southern Italy). Two innovative analytical techniques were used: HPLC–ICP-MS and diffusive gradient in thin films (DGT). The analytical procedure was validated using ERM 580-certified sediment and spiked samples in the case of HPLC–ICP-MS, and by a performance test in the case of DGT. In all samples, the only species found in soil and soil solution was MeHg⁺ and Hg²⁺. In soil, the MeHg⁺/Hg_tot ratio ranged from 0.05% to 0.82%; total mercury in soil solution was less than 0.01% of total mercury in soil. The percentage of MeHg⁺ in soil solution varied considerably (from 0% to 50%), with a maximum concentration of 0.02 mg L⁻¹. The root available concentration evaluated by DGT is comparable to the total mercury content of the soil solution measured by HPLC–ICP-MS. The DGT results suggest that all mercury in solution is available for uptake in DGT, and that mercury is supplied from soil to solution. However, for all samples the soluble and root available (DGT-labile) fractions of mercury are generally very low with respect to the total mercury concentration. This study confirmed that both HPLC–ICP-MS and DGT techniques are suitable tools for the estimation of Hg root availability and in assessing the risk from contaminated soils.     

金融可得性对绿色全要素生产率的影响

收集中国31个省市自治区(暂不包括港澳台数据,下同)2007-2017年的面板数据,采用面板向量自回归模型研究金融可得性对绿色全要素生产率的影响.研究结果显示,金融可得性与绿色全要素生产率之间存在单向因果关系,且金融可得性对绿色全要素生产率具有显著正向影响.     

具有不同失效率和修理率的n中连续取k的可修系统

研究了具有不同失效率和修理率的,2中连续取k的可修系统．在假设失效部件的修理规则为后到先修,且修复如新的条件下,得到了具有不同失效率和修理率的n中连续取k的可修系统各状态的概率,并进一步获得了这类可修系统的一些重要的可靠性指标或者其Laplace变换．     

Stationary availability of a semi‐Markov system with random maintenance

We consider a reparable system with a finite state space, evolving in time according to a semi‐Markov process. The system is stopped for it to be preventively maintained at random times for a random duration. Our aim is to find the preventive maintenance policy that optimizes the stationary availability, whenever it exists. The computation of the stationary availability is based on the fact that the above maintained system evolves according to a semi‐regenerative process. As for the optimization, we observe on numerical examples that it is possible to limit the study to the maintenance actions that begin at deterministic times. We demonstrate this result in a particular case and we study the deterministic maintenance policies in that case. In particular, we show that, if the initial system has an increasing failure rate, the maintenance actions improve the stationary availability if and only if they are not too long on the average, compared to the repairs ( a bound for the mean duration of the maintenance actions is provided). On the contrary, if the initial system has a decreasing failure rate, the maintenance policy lowers the stationary availability. A few other cases are studied. Copyright © 2000 John Wiley & Sons, Ltd.